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β-Aminopropionitrile-induced aortic aneurysm and dissection in mice

  • Hisashi Sawada
    Affiliations
    Saha Cardiovascular Research Center, University of Kentucky, Lexington, Ky

    Saha Aortic Center, University of Kentucky, Lexington, Ky

    Department of Physiology, University of Kentucky, Lexington, Ky
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  • Zachary A. Beckner
    Affiliations
    Saha Cardiovascular Research Center, University of Kentucky, Lexington, Ky

    Saha Aortic Center, University of Kentucky, Lexington, Ky
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  • Sohei Ito
    Affiliations
    Saha Cardiovascular Research Center, University of Kentucky, Lexington, Ky

    Saha Aortic Center, University of Kentucky, Lexington, Ky
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  • Alan Daugherty
    Correspondence
    Correspondence: Hong S. Lu, MD, PhD,; Alan Daugherty, Saha Cardiovascular Research Center, University of Kentucky, Biomedical/Biological Sciences Research Building, Rm 249, 741 S Limestone, Lexington, KY 40536-0509
    Affiliations
    Saha Cardiovascular Research Center, University of Kentucky, Lexington, Ky

    Saha Aortic Center, University of Kentucky, Lexington, Ky

    Department of Physiology, University of Kentucky, Lexington, Ky
    Search for articles by this author
  • Hong S. Lu
    Correspondence
    Correspondence: Hong S. Lu, MD, PhD,; Alan Daugherty, Saha Cardiovascular Research Center, University of Kentucky, Biomedical/Biological Sciences Research Building, Rm 249, 741 S Limestone, Lexington, KY 40536-0509
    Affiliations
    Saha Cardiovascular Research Center, University of Kentucky, Lexington, Ky

    Saha Aortic Center, University of Kentucky, Lexington, Ky

    Department of Physiology, University of Kentucky, Lexington, Ky
    Search for articles by this author
Open AccessPublished:January 03, 2022DOI:https://doi.org/10.1016/j.jvssci.2021.12.002

      Abstract

      The mechanistic basis for the formation of aortic aneurysms and dissection needs to be elucidated to facilitate the development of effective medications. β-Aminopropionitrile administration in mice has been used frequently to study the pathologic features and mechanisms of aortic aneurysm and dissection. This mouse model mimics several facets of the pathology of human aortic aneurysms and dissection, although many variables exist in the experimental design and protocols that must be resolved to determine its application to the human disease. In the present brief review, we have introduced the development of this mouse model and provided insights into understanding its pathologic features.

      Keywords

      Aortic aneurysm and dissection (AAD) are devastating diseases. Aortic aneurysms are defined as pathologic luminal dilatations with a high risk of uncontrolled bleeding due to aortic rupture and death.
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      Therapies for thoracic aortic aneurysms and acute aortic dissections.
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      Management of acute aortic syndrome.
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      Management of acute aortic dissection.
      Aortic aneurysms are most common in the infrarenal abdominal aortic region,
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      Infrarenal abdominal aortic aneurysms.
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      Thoracic and abdominal aortic aneurysms.
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      Aortic dissection leads to bleeding into the medial layers in the thoracic aorta and can extend into the abdominal aorta, causing organ malperfusion with critical consequences.
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      Therapies for thoracic aortic aneurysms and acute aortic dissections.
      • Clough R.E.
      • Nienaber C.A.
      Management of acute aortic syndrome.
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      Management of acute aortic dissection.
      Surgical procedures have been the primary therapy because no medications have been proved effective. Therefore, research using animal models that mimic facets of the human disease will hopefully provide mechanistic insights that will lead to a path for the development of effective medical therapies.
      Although many animal models of AAD have been developed, an increasingly common model is based on the administration of β-aminopropionitrile (BAPN) in mice. One premise for developing this model was the observation that turkeys died of aortic rupture after eating sweet peas, with the subsequent identification of BAPN as the active constituent.
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      The mechanistic basis for BAPN-induced aortopathy was proposed to be the inhibition of lysyl oxidase (LOX) activity, which catalyzed crosslinking of lysine residue in elastin and collagens to form desmosine. These extracellular matrix proteins are crucial components for maintaining aortic integrity.
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      Several studies have demonstrated that chronic BAPN administration results in AAD formation in mice, providing a model to investigate the pathophysiology and mechanisms of AAD.
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      BAPN administration has been used frequently with angiotensin II (AngII) infusion to promote AAD formation in mice. However, BAPN administration alone can also induce heterogeneous aortic pathologies that mimic facets of the human disease. In the present review, we have highlighted studies that used BAPN as the only chemical intervention to induce AAD in mice, summarized the BAPN-induced AAD pathologies and their detection using imaging modalities, and provided suggestions for optimal experimental designs.

      Development of BAPN-induced AAD in mice

      Effects of BAPN on LOX and LOX-like proteins

      LOX and LOX-like protein (LOXL) family members, LOXL1 to LOXL4, are essential enzymes for the crosslinking of elastin and collagens.
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      However, no studies have investigated AAD in mice deficient in any of the LOXL proteins. A missense mutation in LOX has been identified in patients with AAD that was replicated in a mouse model with this LOX mutation.
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      Loss of function mutation in LOX causes thoracic aortic aneurysm and dissection in humans.
      These findings support the notion that disruption of LOX contributes to the formation of AAD.
      BAPN was reported initially as an irreversible pharmacologic inhibitor of LOX and LOXL proteins.
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      • Siegel R.C.
      • Martin G.R.
      On the inhibition of lysyl oxidase by β-aminopropionitrile.
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      Purification of enzymatically active human lysyl oxidase and lysyl oxidase-like protein from Escherichia coli inclusion bodies.
      BAPN decreased LOX activity, as demonstrated using purified LOX from bovine aortas or chick cartilages.
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      • Siegel R.C.
      • Martin G.R.
      On the inhibition of lysyl oxidase by β-aminopropionitrile.
      ,
      • Tang S.S.
      • Simpson D.E.
      • Kagan H.M.
      Beta-substituted ethylamine derivatives as suicide inhibitors of lysyl oxidase.
      An in vitro study using Escherichia coli showed that LOXL1 and LOXL2 were also inhibited by BAPN.
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      • Kim H.C.
      • Kim Y.
      Purification of enzymatically active human lysyl oxidase and lysyl oxidase-like protein from Escherichia coli inclusion bodies.
      However, a recent report demonstrated that BAPN inhibited LOXL2 effectively in vitro but not LOX.
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      Inhibition of the LOX enzyme family members with old and new ligands: selectivity analysis revisited.
      No studies have reported the contribution of LOXL2 to AAD using in vivo models. Further study is needed to provide a consensus of which enzymes in the LOX/LOXL family are inhibited by BAPN. In addition, more insight is required regarding the roles of LOXL enzymes in AAD pathophysiology.

      BAPN administration

      Many of the initial studies had induced aortopathies by a combination of BAPN administration with another mode of provoking AAD. This was initially demonstrated by coadministration of BAPN and AngII, which induced AAD in adult male C57BL/6J mice.
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      Neutrophil-derived matrix metalloproteinase 9 triggers acute aortic dissection.
      Adult mice had not shown overt aortic pathologies when BAPN was administered alone.
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      • et al.
      Pharmacologically induced thoracic and abdominal aortic aneurysms in mice.
      Subsequent studies have demonstrated that BAPN administration combined with other manipulations will induce AAD in adult mice, including application of elastase to the adventitia of the infrarenal aorta or administration of DOCA (deoxycorticosterone acetate)-salt.
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      • et al.
      Pharmacologically induced thoracic and abdominal aortic aneurysms in mice.
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      • et al.
      A novel chronic advanced stage abdominal aortic aneurysm murine model.
      ,
      • Romary D.J.
      • Berman A.G.
      • Goergen C.J.
      High-frequency murine ultrasound provides enhanced metrics of BAPN-induced AAA growth.
      Among these manipulations, AngII infusion has been used most often in conjunction with BAPN to enhance AAD formation. In young (3-week-old) mice, AAD formation was observed with a 100% incidence when BAPN was administered for 4 weeks with an AngII (1 μg/kg/min) infusion for 24 hours before termination.
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      • Jia L.
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      • Lan F.
      • et al.
      β-Aminopropionitrile monofumarate induces thoracic aortic dissection in C57BL/6 mice.
      In 3- to 4-week-old mice after 3 to 4 weeks of BAPN administration, AngII infusion for 12, 24, and 48 hours led to death due to rupture at an incidence of 14% (7 of 50), 39% (18 of 46), and 67% (29 of 43), respectively.
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      • et al.
      Adventitial CXCL1/G-CSF expression in response to acute aortic dissection triggers local neutrophil recruitment and activation leading to aortic rupture.
      Therefore, studies have demonstrated consistently that transient AngII infusion augments BAPN-induced AAD.
      Accumulating evidence has shown that BAPN administration alone will induce AAD formation in young mice. In one study, 3-week-old male C57BL/6 mice had >80% AAD formation during BAPN administration without other manipulations.
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      • Jia L.
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      • Lan F.
      • et al.
      β-Aminopropionitrile monofumarate induces thoracic aortic dissection in C57BL/6 mice.
      BAPN administration started at 3 to 4 weeks of age suppressed elastogenesis but did not induce elastolysis.
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      A combined quantitative chemical, light, and electron microscope study of aortic development in normal and nitrile-treated mice: possible implications for elucidating nitrile-induced aortic lesions and regarding the genesis of spontaneous arterial lesions.
      BAPN irreversibly inhibits crosslinking of elastin and collagen. However, crosslinking of elastin and collagen is presumed to be minimal after the postnatal phase. Thus, inhibition of LOX/LOXL activity might not disrupt already formed elastic fibers. Patients with connective tissue disease, such as Marfan syndrome, Ehlers-Danlos syndrome, or Turner syndrome, often develop the complication of aortic dissection. The incidence of aortic complications peaks at 30 to 40 years of age in patients with these syndromes.
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      Because BAPN administration in young mice (age, 3-4 weeks) leads to AAD formation through the inhibition of elastin and collagen crosslinking during extracellular matrix maturation, this mouse model might mimic certain molecular mechanisms of aortic diseases complicated by the connective tissue diseases mentioned above.

      Route and dose of BAPN administration

      BAPN has been administered in several modes in mouse studies. Mini-osmotic pumps can be used to deliver BAPN to adult mice (age, 7-15 weeks).
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      • Nuki Y.
      • Liang E.I.
      • et al.
      Pharmacologically induced thoracic and abdominal aortic aneurysms in mice.
      ,
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      Protective effects of selective mineralocorticoid receptor antagonist against aortic aneurysm progression in a novel murine model.
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      • et al.
      High salt intake worsens aortic dissection in mice: involvement of IL (interleukin)-17A-dependent ECM (extracellular matrix) metabolism.
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      • Nagai R.
      • et al.
      Indomethacin reduces rates of aortic dissection and rupture of the abdominal aorta by inhibiting monocyte/macrophage accumulation in a murine model.
      However, it has been more common to administer BAPN in the drinking water for young mice (age, 3-4 weeks). A few studies have used BAPN administration via a gastric tube,
      • Anzai A.
      • Shimoda M.
      • Endo J.
      • Kohno T.
      • Katsumata Y.
      • Matsuhashi T.
      • et al.
      Adventitial CXCL1/G-CSF expression in response to acute aortic dissection triggers local neutrophil recruitment and activation leading to aortic rupture.
      diet,
      • Ren W.
      • Liu Y.
      • Wang X.
      • Jia L.
      • Piao C.
      • Lan F.
      • et al.
      β-Aminopropionitrile monofumarate induces thoracic aortic dissection in C57BL/6 mice.
      ,
      • Li X.
      • Liu D.
      • Zhao L.
      • Wang L.
      • Li Y.
      • Cho K.
      • et al.
      Targeted depletion of monocyte/macrophage suppresses aortic dissection with the spatial regulation of MMP-9 in the aorta.
      or intraperitoneal injection.
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      Increased aortic stiffness and attenuated lysyl oxidase activity in obesity.
      Mini-osmotic pumps provide a constant and continuous delivery of compounds. This approach has been used extensively for delivery of AngII to induce aortic aneurysms in mice.
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      • Moorleghen J.J.
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      • Cassis L.A.
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      Subcutaneous angiotensin II infusion using osmotic pumps induces aortic aneurysms in mice.
      ,
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      • Manning M.W.
      • Cassis L.A.
      Angiotensin II promotes atherosclerotic lesions and aneurysms in apolipoprotein E-deficient mice.
      Given a previous study demonstrating that the half-life (beta phase) of BAPN was 79 ± 5 minutes in rabbits,
      • Sevil M.B.
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      • Frejo M.T.
      • Llama E.
      • Capo M.A.
      Pharmacokinetic analysis of beta-aminopropionitrile in rabbits.
      subcutaneous infusion using osmotic pumps can be considered an optimal mode for BAPN administration. However, two considerations are important for the use of this mode: the solubility of the compound and the size of the pump. A commonly used infusion rate of BAPN has been 150 mg/kg/d for osmotic pump delivery. This dose requires a highly concentrated BAPN solution (>500 mg/mL) to enable the use of osmotic pumps (pump rate, ∼0.25 μL/h; model 2004; ALZET Osmotic Pumps; Durect Corp, Cupertino, Calif). Since the maximal solubility of BAPN in water is ∼50 mg/mL, it is challenging to dissolve BAPN (150 mg/kg/d) completely. In addition, the most commonly used osmotic pump, ALZET model 2004, is not recommended for use with mice weighing <20 g, which is incompatible with its use in young mice. Therefore, it is often not feasible to deliver BAPN via an osmotic pump, especially to young mice with a low body weight. Many recent studies have administered BAPN in the drinking water, with AngII delivered through mini-osmotic pumps.
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      Epidermal growth factor receptor inhibitor protects against abdominal aortic aneurysm in a mouse model.
      ,
      • Qi X.
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      A validated mouse model capable of recapitulating the protective effects of female sex hormones on ascending aortic aneurysms and dissections (AADs).
      This method appears to be an optimal mode for the administration of BAPN to young mice.
      Multiple studies in which BAPN was administered in drinking water have reported that the dose was 1 g/kg/d (Table I). However, it is unclear how this dose was calculated. This dosage might be appropriate for a mouse weighing ∼25 g that drink ∼ 5 mL of water daily.
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      However, body weight and water consumption may vary. In addition, mice aged 3 to 4 weeks will weigh 10 to 15 g, and their water consumption can be <5 mL/d. Consequently, an estimated dose of 1 g/kg/d of BAPN is likely to be inaccurate. Therefore, it would be preferable to provide a more direct description of the BAPN dose, such as 1 to 3 mg/mL
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      or 0.2% to 0.6% [% wt/vol (2-6 mg/mL)] as reported in selected studies.
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      • Davis J.P.
      • Schaheen B.
      • Downs E.
      • Roy R.J.
      • et al.
      A novel chronic advanced stage abdominal aortic aneurysm murine model.
      ,
      • Romary D.J.
      • Berman A.G.
      • Goergen C.J.
      High-frequency murine ultrasound provides enhanced metrics of BAPN-induced AAA growth.
      ,
      • Qi X.
      • Wang F.
      • Chun C.
      • Saldarriaga L.
      • Jiang Z.
      • Pruitt E.Y.
      • et al.
      A validated mouse model capable of recapitulating the protective effects of female sex hormones on ascending aortic aneurysms and dissections (AADs).
      ,
      • Xia L.
      • Sun C.
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      Table IAdministration of BAPN to study AAD in mice
      Mouse strainSexAge, weeksBAPN administrationReferences
      RouteDoseDuration, weeks
      C57BL/10Male3Drinking water0.5 g/kg/d4
      • Bachmanov A.A.
      • Reed D.R.
      • Beauchamp G.K.
      • Tordoff M.G.
      Food intake, water intake, and drinking spout side preference of 28 mouse strains.
      C57BL/6
      Substrain of C57BL/6 unknown.
      Male3Drinking water1 g/kg/d2-4
      • Ren W.
      • Liu Y.
      • Wang X.
      • Jia L.
      • Piao C.
      • Lan F.
      • et al.
      β-Aminopropionitrile monofumarate induces thoracic aortic dissection in C57BL/6 mice.
      ,
      • Aicher B.O.
      • Zhang J.
      • Muratoglu S.
      • Galisteo R.
      • Arai A.L.
      • Gray V.L.
      • et al.
      Moderate aerobic exercise prevents matrix degradation and death in a mouse model of aortic dissection and aneurysm.
      ,
      • Aicher B.O.
      • Mukhopadhyay S.
      • Lu X.
      • Muratoglu S.C.
      • Strickland D.K.
      • Ucuzian A.A.
      Quantitative micro-CT analysis of aortopathy in a mouse model of β-aminopropionitrile-induced aortic aneurysm and dissection.
      ,
      • Ohno-Urabe S.
      • Kukida M.
      • Franklin M.K.
      • Katsumata Y.
      • Su W.
      • Gong M.C.
      • et al.
      Authentication of in situ measurements for thoracic aortic aneurysms in mice.
      ,
      • Sawada H.
      • Franklin M.K.
      • Moorleghen J.J.
      • Howatt D.A.
      • Kukida M.
      • Lu H.S.
      • et al.
      Ultrasound monitoring of descending aortic aneurysms and dissections in mice.
      ,
      • Chen Y.
      • Wei X.
      • Zhang Z.
      • He Y.
      • Huo B.
      • Guo X.
      • et al.
      Downregulation of filamin A expression in the aorta is correlated with aortic dissection.
      ,
      • Liu C.
      • Zhang C.
      • Jia L.
      • Chen B.
      • Liu L.
      • Sun J.
      • et al.
      Interleukin-3 stimulates matrix metalloproteinase 12 production from macrophages promoting thoracic aortic aneurysm/dissection.
      ,
      • Zhang W.M.
      • Liu Y.
      • Li T.T.
      • Piao C.M.
      • Liu O.
      • Liu J.L.
      • et al.
      Sustained activation of ADP/P2ry12 signaling induces SMC senescence contributing to thoracic aortic aneurysm/dissection.
      C57BL/6JMale3Drinking water1 g/kg/d1, 2, or 4
      • Yang Y.Y.
      • Li L.Y.
      • Jiao X.L.
      • Jia L.X.
      • Zhang X.P.
      • Wang Y.L.
      • et al.
      Intermittent hypoxia alleviates β-aminopropionitrile monofumarate induced thoracic aortic dissection in C57BL/6 mice.
      ,
      • Ren W.
      • Liu Y.
      • Wang X.
      • Piao C.
      • Ma Y.
      • Qiu S.
      • et al.
      The complement C3a-C3aR axis promotes development of thoracic aortic dissection via regulation of MMP2 expression.
      ,
      • Jia L.X.
      • Zhang W.M.
      • Zhang H.J.
      • Li T.T.
      • Wang Y.L.
      • Qin Y.W.
      • et al.
      Mechanical stretch-induced endoplasmic reticulum stress, apoptosis and inflammation contribute to thoracic aortic aneurysm and dissection.
      ,
      • Jia L.X.
      • Zhang W.M.
      • Li T.T.
      • Liu Y.
      • Piao C.M.
      • Ma Y.C.
      • et al.
      ER stress dependent microparticles derived from smooth muscle cells promote endothelial dysfunction during thoracic aortic aneurysm and dissection.
      ,
      • Han L.
      • Dai L.
      • Zhao Y.F.
      • Li H.Y.
      • Liu O.
      • Lan F.
      • et al.
      CD40L promotes development of acute aortic dissection via induction of inflammation and impairment of endothelial cell function.
      ,
      • Shao Y.
      • Li G.
      • Huang S.
      • Li Z.
      • Qiao B.
      • Chen D.
      • et al.
      Effects of extracellular matrix softening on vascular smooth muscle cell dysfunction.
      ,
      • Xu K.
      • Xu C.
      • Zhang Y.
      • Qi F.
      • Yu B.
      • Li P.
      • et al.
      Identification of type IV collagen exposure as a molecular imaging target for early detection of thoracic aortic dissection.
      FVBMale3Drinking water1 g/kg/d4
      • Ren W.
      • Liu Y.
      • Wang X.
      • Jia L.
      • Piao C.
      • Lan F.
      • et al.
      β-Aminopropionitrile monofumarate induces thoracic aortic dissection in C57BL/6 mice.
      Mixed (C57BL/6
      Substrain of C57BL/6 unknown.
      and SJL)
      Male3-4Drinking water0.3% wt/vol8-30
      • Wang S.
      • Liu Y.
      • Zhao G.
      • He L.
      • Fu Y.
      • Yu C.
      • et al.
      Postnatal deficiency of ADAMTS1 ameliorates thoracic aortic aneurysm and dissection in mice.
      ,
      • Zhou B.
      • Li W.
      • Zhao G.
      • Yu B.
      • Ma B.
      • Liu Z.
      • et al.
      Rapamycin prevents thoracic aortic aneurysm and dissection in mice.
      C57BL/6JMale3-4Drinking water0.5% wt/vol12
      • Xia L.
      • Sun C.
      • Zhu H.
      • Zhai M.
      • Zhang L.
      • Jiang L.
      • et al.
      Melatonin protects against thoracic aortic aneurysm and dissection through SIRT1-dependent regulation of oxidative stress and vascular smooth muscle cell loss.
      ,
      • Wang X.
      • Zhang X.
      • Qiu T.
      • Yang Y.
      • Li Q.
      • Zhang X.
      Dexamethasone reduces the formation of thoracic aortic aneurysm and dissection in a murine model.
      C57BL/6
      Substrain of C57BL/6 unknown.
      Male3Drinking water0.6% wt/vol4
      • Gao Y.
      • Wang Z.
      • Zhao J.
      • Sun W.
      • Guo J.
      • Yang Z.
      • et al.
      Involvement of B cells in the pathophysiology of β-aminopropionitrile-induced thoracic aortic dissection in mice.
      C57BL/6
      Substrain of C57BL/6 unknown.
      Male3Diet0.4%, 1%, or 1.5%4
      • Ren W.
      • Liu Y.
      • Wang X.
      • Jia L.
      • Piao C.
      • Lan F.
      • et al.
      β-Aminopropionitrile monofumarate induces thoracic aortic dissection in C57BL/6 mice.
      AAD, Aortic aneurysm and dissection; BAPN, β-aminopropionitrile.
      a Substrain of C57BL/6 unknown.
      Although the common routes of BAPN administration have been subcutaneous infusion using an osmotic pump or drinking water, other routes have also been reported, including administration via the diet,
      • Ren W.
      • Liu Y.
      • Wang X.
      • Jia L.
      • Piao C.
      • Lan F.
      • et al.
      β-Aminopropionitrile monofumarate induces thoracic aortic dissection in C57BL/6 mice.
      ,
      • Li X.
      • Liu D.
      • Zhao L.
      • Wang L.
      • Li Y.
      • Cho K.
      • et al.
      Targeted depletion of monocyte/macrophage suppresses aortic dissection with the spatial regulation of MMP-9 in the aorta.
      gastric tube,
      • Anzai A.
      • Shimoda M.
      • Endo J.
      • Kohno T.
      • Katsumata Y.
      • Matsuhashi T.
      • et al.
      Adventitial CXCL1/G-CSF expression in response to acute aortic dissection triggers local neutrophil recruitment and activation leading to aortic rupture.
      or intraperitoneal injection.
      • Chen J.Y.
      • Tsai P.J.
      • Tai H.C.
      • Tsai R.L.
      • Chang Y.T.
      • Wang M.C.
      • et al.
      Increased aortic stiffness and attenuated lysyl oxidase activity in obesity.
      Adding BAPN to the mouse diet had effects similar to that of administering the compound via the drinking water. In the study by Ren et al,
      • Ren W.
      • Liu Y.
      • Wang X.
      • Jia L.
      • Piao C.
      • Lan F.
      • et al.
      β-Aminopropionitrile monofumarate induces thoracic aortic dissection in C57BL/6 mice.
      mice were fed BAPN at doses of 0.4, 1, or 1.5 g/100 g in their food. All the mice fed 0.4 g/100 g BAPN developed AAD (five died of aortic rupture). In the mice fed 1 g/100 g BAPN, two of six mice had developed thoracic aortic dissection. However, aortic dissection was not observed in the mice fed the highest dose. All BAPN-administered mice had lost body weight in a dose-dependent manner. Although the basis for this body weight loss was not determined, effects of BAPN on the lipid and glucose metabolisms might have contributed to its mechanism.
      • Miana M.
      • Galan M.
      • Martinez-Martinez E.
      • Varona S.
      • Jurado-Lopez R.
      • Bausa-Miranda B.
      • et al.
      The lysyl oxidase inhibitor beta-aminopropionitrile reduces body weight gain and improves the metabolic profile in diet-induced obesity in rats.
      ,
      • Xing C.
      • Jiang D.
      • Liu Y.
      • Tang Q.
      • Huang H.
      Lysyl oxidase inhibition enhances browning of white adipose tissue and adaptive thermogenesis.
      Because mixing BAPN in the food is logistically more difficult than dissolving the compound in the drinking water, the latter is an easier approach. Compared with food consumption ad libitum, gastric tube administration and intraperitoneal injection will provide more accurate and consistent administration of BAPN. However, the insertion of a gastric tube is technically demanding and time-consuming. It can also stress the mice, augmenting the formation of AAD and adding a confounding factor. Only one study administered BAPN by intraperitoneal injection, which had focused on aortic stiffness.
      • Chen J.Y.
      • Tsai P.J.
      • Tai H.C.
      • Tsai R.L.
      • Chang Y.T.
      • Wang M.C.
      • et al.
      Increased aortic stiffness and attenuated lysyl oxidase activity in obesity.
      Thus, the effect of intraperitoneal injection of BAPN on AAD formation has not yet been studied.
      Overall, the administration of BAPN (0.5% wt/vol) in the drinking water will induce a high incidence of AAD in young mice (age, 3-4 weeks). Because of the high incidence of AAD formation, this mouse model has facilitated investigations of whether an experimental intervention will attenuate AAD. Since different doses of BAPN can lead to differing severity of AAD, it is important to optimize the BAPN dose before performing experiments.

      Mouse strains and sex

      The most frequently studied mouse strain has been C57BL/6, with many studies reporting the use of the C57BL/6J substrain. It is important to distinguish between the C57BL/6 substrains. The C57BL/6J and C57BL/6N substrains have well-defined differences, including the recently demonstrated diversity in the development of aortopathies.
      • Simon M.M.
      • Greenaway S.
      • White J.K.
      • Fuchs H.
      • Gailus-Durner V.
      • Wells S.
      • et al.
      A comparative phenotypic and genomic analysis of C57BL/6J and C57BL/6N mouse strains.
      ,
      • Wortmann M.
      • Arshad M.
      • Peters A.S.
      • Hakimi M.
      • Bockler D.
      • Dihlmann S.
      The C57Bl/6J mouse strain is more susceptible to angiotensin II-induced aortic aneurysm formation than C57Bl/6N.
      It is also important to consider different mouse strains when designing an experiment because the strains have different susceptibilities to BAPN-induced AAD. Male FVB mice had a lower incidence of AAD compared with age-matched male C57BL/6 mice (substrain not reported): a 25% incidence of AAD and no aortic rupture in FVB mice vs an 87% incidence of AAD and a 37% incidence of aortic rupture in C57BL/6 mice.
      • Ren W.
      • Liu Y.
      • Wang X.
      • Jia L.
      • Piao C.
      • Lan F.
      • et al.
      β-Aminopropionitrile monofumarate induces thoracic aortic dissection in C57BL/6 mice.
      The high incidence of AAD in C57BL/6 mice has illustrated that the BAPN-induced AAD mouse model does not need a hypercholesterolemic background. However, no studies have determined whether hypercholesterolemia will augment the development of BAPN-induced AAD.
      Sexual dimorphism has also been reported in AAD formation in humans and mice.
      • Lemaire S.A.
      • McDonald M.L.
      • Guo D.C.
      • Russell L.
      • Miller III, C.C.
      • Johnson R.J.
      • et al.
      Genome-wide association study identifies a susceptibility locus for thoracic aortic aneurysms and aortic dissections spanning FBN1 at 15q21.1.
      • Hagan P.G.
      • Nienaber C.A.
      • Isselbacher E.M.
      • Bruckman D.
      • Karavite D.J.
      • Russman P.L.
      • et al.
      The International Registry of Acute Aortic Dissection (IRAD): new insights into an old disease.
      • Nienaber C.A.
      • Fattori R.
      • Mehta R.H.
      • Richartz B.M.
      • Evangelista A.
      • Petzsch M.
      • et al.
      Gender-related differences in acute aortic dissection.
      • Liang N.L.
      • Genovese E.A.
      • Al-Khoury G.E.
      • Hager E.S.
      • Makaroun M.S.
      • Singh M.J.
      Effects of gender differences on short-term outcomes in patients with type B aortic dissection.
      • Deery S.E.
      • Shean K.E.
      • Wang G.J.
      • Black J.H.
      • Upchurch Jr., G.R.
      • Giles K.A.
      • et al.
      Female sex independently predicts mortality after thoracic endovascular aortic repair for intact descending thoracic aortic aneurysms.
      • Zhang X.
      • Thatcher S.E.
      • Rateri D.L.
      • Bruemmer D.
      • Charnigo R.
      • Daugherty A.
      • et al.
      Transient exposure of neonatal female mice to testosterone abrogates the sexual dimorphism of abdominal aortic aneurysms.
      • Henriques T.
      • Zhang X.
      • Yiannikouris F.B.
      • Daugherty A.
      • Cassis L.A.
      Androgen increases AT1a receptor expression in abdominal aortas to promote angiotensin II-induced AAAs in apolipoprotein E-deficient mice.
      • Tashima Y.
      • He H.
      • Cui J.Z.
      • Pedroza A.J.
      • Nakamura K.
      • Yokoyama N.
      • et al.
      Androgens accentuate TGF-beta dependent Erk/Smad activation during thoracic aortic aneurysm formation in Marfan syndrome male mice.
      • Zhang X.
      • Thatcher S.
      • Wu C.
      • Daugherty A.
      • Cassis L.A.
      Castration of male mice prevents the progression of established angiotensin II-induced abdominal aortic aneurysms.
      In humans, AAD has been more prevalent in men than in women,
      • Lemaire S.A.
      • McDonald M.L.
      • Guo D.C.
      • Russell L.
      • Miller III, C.C.
      • Johnson R.J.
      • et al.
      Genome-wide association study identifies a susceptibility locus for thoracic aortic aneurysms and aortic dissections spanning FBN1 at 15q21.1.
      and the outcomes have frequently been worse for women.
      • Hagan P.G.
      • Nienaber C.A.
      • Isselbacher E.M.
      • Bruckman D.
      • Karavite D.J.
      • Russman P.L.
      • et al.
      The International Registry of Acute Aortic Dissection (IRAD): new insights into an old disease.
      ,
      • Nienaber C.A.
      • Fattori R.
      • Mehta R.H.
      • Richartz B.M.
      • Evangelista A.
      • Petzsch M.
      • et al.
      Gender-related differences in acute aortic dissection.
      Women have been shown to be more likely to experience mortality from aortic dissection, lower long-term survival after surgery, and a greater frequency of cardiac complications such as cardiac tamponade.
      • Hagan P.G.
      • Nienaber C.A.
      • Isselbacher E.M.
      • Bruckman D.
      • Karavite D.J.
      • Russman P.L.
      • et al.
      The International Registry of Acute Aortic Dissection (IRAD): new insights into an old disease.
      • Nienaber C.A.
      • Fattori R.
      • Mehta R.H.
      • Richartz B.M.
      • Evangelista A.
      • Petzsch M.
      • et al.
      Gender-related differences in acute aortic dissection.
      • Liang N.L.
      • Genovese E.A.
      • Al-Khoury G.E.
      • Hager E.S.
      • Makaroun M.S.
      • Singh M.J.
      Effects of gender differences on short-term outcomes in patients with type B aortic dissection.
      • Deery S.E.
      • Shean K.E.
      • Wang G.J.
      • Black J.H.
      • Upchurch Jr., G.R.
      • Giles K.A.
      • et al.
      Female sex independently predicts mortality after thoracic endovascular aortic repair for intact descending thoracic aortic aneurysms.
      In several mouse models, the incidence and severity of abdominal aortic aneurysms are sexually dimorphic, with greater severity in male mice.
      • Zhang X.
      • Thatcher S.E.
      • Rateri D.L.
      • Bruemmer D.
      • Charnigo R.
      • Daugherty A.
      • et al.
      Transient exposure of neonatal female mice to testosterone abrogates the sexual dimorphism of abdominal aortic aneurysms.
      • Henriques T.
      • Zhang X.
      • Yiannikouris F.B.
      • Daugherty A.
      • Cassis L.A.
      Androgen increases AT1a receptor expression in abdominal aortas to promote angiotensin II-induced AAAs in apolipoprotein E-deficient mice.
      • Tashima Y.
      • He H.
      • Cui J.Z.
      • Pedroza A.J.
      • Nakamura K.
      • Yokoyama N.
      • et al.
      Androgens accentuate TGF-beta dependent Erk/Smad activation during thoracic aortic aneurysm formation in Marfan syndrome male mice.
      • Zhang X.
      • Thatcher S.
      • Wu C.
      • Daugherty A.
      • Cassis L.A.
      Castration of male mice prevents the progression of established angiotensin II-induced abdominal aortic aneurysms.
      Consistent with this premise, a few studies have reported a lower incidence of AAD in female mice coadministered BAPN and AngII.
      • Qi X.
      • Wang F.
      • Chun C.
      • Saldarriaga L.
      • Jiang Z.
      • Pruitt E.Y.
      • et al.
      A validated mouse model capable of recapitulating the protective effects of female sex hormones on ascending aortic aneurysms and dissections (AADs).
      ,
      • Fashandi A.Z.
      • Spinosa M.
      • Salmon M.
      • Su G.
      • Montgomery W.
      • Mast A.
      • et al.
      Female mice exhibit abdominal aortic aneurysm protection in an established rupture model.
      However, no studies have reported on sexual dimorphism when BAPN was administered alone.

      Pathologic features of BAPN-induced AAD

      Progression of BAPN-induced AAD

      Most studies reported AAD formation within 4 weeks of BAPN administration (Table I). No apparent pathologies were noted within 7 days of BAPN administration. However, impairment of the endothelial layer was detected as early as 7 days after BAPN administration, which was demonstrated with an Evans blue injection into the angular vein 20 minutes before termination.
      • Yang Y.Y.
      • Li L.Y.
      • Jiao X.L.
      • Jia L.X.
      • Zhang X.P.
      • Wang Y.L.
      • et al.
      Intermittent hypoxia alleviates β-aminopropionitrile monofumarate induced thoracic aortic dissection in C57BL/6 mice.
      After 7 days of BAPN administration, 00CD45+ cells were detected, mainly in the tunica adventitia, and had increased after 14 days. Neutrophils (Ly6G+ cells) were also detected in the adventitia after 7 days but were not apparent after 14 days of BAPN administration.
      • Ren W.
      • Liu Y.
      • Wang X.
      • Piao C.
      • Ma Y.
      • Qiu S.
      • et al.
      The complement C3a-C3aR axis promotes development of thoracic aortic dissection via regulation of MMP2 expression.
      In addition to the pronounced accumulation of red blood cells, disruption of the elastic fibers was observed after 2 weeks of BAPN administration. Severe fragmentation of the elastic fibers and medial dissection became apparent after 3 weeks of BAPN administration. After 28 days of BAPN administration, the accumulation of leukocytes at the site of medial rupture and the surrounding adventitia was evident.
      • Aicher B.O.
      • Zhang J.
      • Muratoglu S.
      • Galisteo R.
      • Arai A.L.
      • Gray V.L.
      • et al.
      Moderate aerobic exercise prevents matrix degradation and death in a mouse model of aortic dissection and aneurysm.
      • Aicher B.O.
      • Mukhopadhyay S.
      • Lu X.
      • Muratoglu S.C.
      • Strickland D.K.
      • Ucuzian A.A.
      Quantitative micro-CT analysis of aortopathy in a mouse model of β-aminopropionitrile-induced aortic aneurysm and dissection.
      • Ohno-Urabe S.
      • Kukida M.
      • Franklin M.K.
      • Katsumata Y.
      • Su W.
      • Gong M.C.
      • et al.
      Authentication of in situ measurements for thoracic aortic aneurysms in mice.
      • Sawada H.
      • Franklin M.K.
      • Moorleghen J.J.
      • Howatt D.A.
      • Kukida M.
      • Lu H.S.
      • et al.
      Ultrasound monitoring of descending aortic aneurysms and dissections in mice.
      • Chen Y.
      • Wei X.
      • Zhang Z.
      • He Y.
      • Huo B.
      • Guo X.
      • et al.
      Downregulation of filamin A expression in the aorta is correlated with aortic dissection.
      ,
      • Ren W.
      • Liu Y.
      • Wang X.
      • Piao C.
      • Ma Y.
      • Qiu S.
      • et al.
      The complement C3a-C3aR axis promotes development of thoracic aortic dissection via regulation of MMP2 expression.
      • Jia L.X.
      • Zhang W.M.
      • Zhang H.J.
      • Li T.T.
      • Wang Y.L.
      • Qin Y.W.
      • et al.
      Mechanical stretch-induced endoplasmic reticulum stress, apoptosis and inflammation contribute to thoracic aortic aneurysm and dissection.
      • Jia L.X.
      • Zhang W.M.
      • Li T.T.
      • Liu Y.
      • Piao C.M.
      • Ma Y.C.
      • et al.
      ER stress dependent microparticles derived from smooth muscle cells promote endothelial dysfunction during thoracic aortic aneurysm and dissection.
      • Han L.
      • Dai L.
      • Zhao Y.F.
      • Li H.Y.
      • Liu O.
      • Lan F.
      • et al.
      CD40L promotes development of acute aortic dissection via induction of inflammation and impairment of endothelial cell function.
      ,
      • Le S.
      • Zhang H.
      • Huang X.
      • Chen S.
      • Wu J.
      • Chen S.
      • et al.
      PKM2 activator TEPP-46 attenuates thoracic aortic aneurysm and dissection by inhibiting NLRP3 inflammasome-mediated IL-1β secretion.
      For mice surviving 4 weeks of BAPN administration, thrombi had resolved; however, continuous leukocyte infiltration and disorganized collagen deposition were still prominent. After prolonged administration of BAPN for ≤12 weeks,
      • Xia L.
      • Sun C.
      • Zhu H.
      • Zhai M.
      • Zhang L.
      • Jiang L.
      • et al.
      Melatonin protects against thoracic aortic aneurysm and dissection through SIRT1-dependent regulation of oxidative stress and vascular smooth muscle cell loss.
      ,
      • Wang X.
      • Zhang X.
      • Qiu T.
      • Yang Y.
      • Li Q.
      • Zhang X.
      Dexamethasone reduces the formation of thoracic aortic aneurysm and dissection in a murine model.
      pronounced thinning of the aortic wall in the ascending and descending thoracic aortic regions was observed. The prolonged administration of BAPN can cause kyphosis and osteolathyrism in mice.
      • Barrow M.V.
      • Simpson C.F.
      • Miller E.J.
      Lathyrism: a review.
      No studies have reported detailed histologic features after protracted intervals of administration.
      Tearing of the aortic wall leads to bleeding. If bleeding is constrained by the media or adventitia, thrombi will form, surrounding the ruptured media or adventitia. Aortic rupture occurs if transmural bleeding ensues or the thrombi fail to constrain the blood within the medial and adventitial layers. In BAPN-administered mice, intra- or transmedial dissection was observed, in addition to luminal dilatation, predominantly in the thoracic aorta.
      • Ren W.
      • Liu Y.
      • Wang X.
      • Jia L.
      • Piao C.
      • Lan F.
      • et al.
      β-Aminopropionitrile monofumarate induces thoracic aortic dissection in C57BL/6 mice.
      The presence of medial dissection and the location of aortic dilatations are distinct pathologic features of this model compared with the AngII-induced abdominal aortic aneurysm model, which demonstrates luminal dilatation with adventitial dissection in the suprarenal abdominal aorta.
      • Daugherty A.
      • Manning M.W.
      • Cassis L.A.
      Angiotensin II promotes atherosclerotic lesions and aneurysms in apolipoprotein E-deficient mice.
      BAPN-induced AAD has high death rate from aortic rupture. For mice that died of aortic rupture, death has been noted as early as 10 days after the initiation of BAPN and became more frequent after 14 days of BAPN administration. The rate of death from aortic rupture has been reported to be ~ 50% to 80%.
      • Ren W.
      • Liu Y.
      • Wang X.
      • Jia L.
      • Piao C.
      • Lan F.
      • et al.
      β-Aminopropionitrile monofumarate induces thoracic aortic dissection in C57BL/6 mice.
      ,
      • Aicher B.O.
      • Mukhopadhyay S.
      • Lu X.
      • Muratoglu S.C.
      • Strickland D.K.
      • Ucuzian A.A.
      Quantitative micro-CT analysis of aortopathy in a mouse model of β-aminopropionitrile-induced aortic aneurysm and dissection.
      • Ohno-Urabe S.
      • Kukida M.
      • Franklin M.K.
      • Katsumata Y.
      • Su W.
      • Gong M.C.
      • et al.
      Authentication of in situ measurements for thoracic aortic aneurysms in mice.
      • Sawada H.
      • Franklin M.K.
      • Moorleghen J.J.
      • Howatt D.A.
      • Kukida M.
      • Lu H.S.
      • et al.
      Ultrasound monitoring of descending aortic aneurysms and dissections in mice.
      • Chen Y.
      • Wei X.
      • Zhang Z.
      • He Y.
      • Huo B.
      • Guo X.
      • et al.
      Downregulation of filamin A expression in the aorta is correlated with aortic dissection.
      • Liu C.
      • Zhang C.
      • Jia L.
      • Chen B.
      • Liu L.
      • Sun J.
      • et al.
      Interleukin-3 stimulates matrix metalloproteinase 12 production from macrophages promoting thoracic aortic aneurysm/dissection.
      • Zhang W.M.
      • Liu Y.
      • Li T.T.
      • Piao C.M.
      • Liu O.
      • Liu J.L.
      • et al.
      Sustained activation of ADP/P2ry12 signaling induces SMC senescence contributing to thoracic aortic aneurysm/dissection.
      • Yang Y.Y.
      • Li L.Y.
      • Jiao X.L.
      • Jia L.X.
      • Zhang X.P.
      • Wang Y.L.
      • et al.
      Intermittent hypoxia alleviates β-aminopropionitrile monofumarate induced thoracic aortic dissection in C57BL/6 mice.
      • Ren W.
      • Liu Y.
      • Wang X.
      • Piao C.
      • Ma Y.
      • Qiu S.
      • et al.
      The complement C3a-C3aR axis promotes development of thoracic aortic dissection via regulation of MMP2 expression.
      • Jia L.X.
      • Zhang W.M.
      • Zhang H.J.
      • Li T.T.
      • Wang Y.L.
      • Qin Y.W.
      • et al.
      Mechanical stretch-induced endoplasmic reticulum stress, apoptosis and inflammation contribute to thoracic aortic aneurysm and dissection.
      • Jia L.X.
      • Zhang W.M.
      • Li T.T.
      • Liu Y.
      • Piao C.M.
      • Ma Y.C.
      • et al.
      ER stress dependent microparticles derived from smooth muscle cells promote endothelial dysfunction during thoracic aortic aneurysm and dissection.
      ,
      • Shao Y.
      • Li G.
      • Huang S.
      • Li Z.
      • Qiao B.
      • Chen D.
      • et al.
      Effects of extracellular matrix softening on vascular smooth muscle cell dysfunction.
      ,
      • Xu K.
      • Xu C.
      • Zhang Y.
      • Qi F.
      • Yu B.
      • Li P.
      • et al.
      Identification of type IV collagen exposure as a molecular imaging target for early detection of thoracic aortic dissection.
      ,
      • Le S.
      • Zhang H.
      • Huang X.
      • Chen S.
      • Wu J.
      • Chen S.
      • et al.
      PKM2 activator TEPP-46 attenuates thoracic aortic aneurysm and dissection by inhibiting NLRP3 inflammasome-mediated IL-1β secretion.
      Although several studies have shown BAPN-induced aortic pathologies at different time points, the systematic determination of the sequential events during BAPN administration from the initiation to the progression of AAD is lacking. The data from previous studies, which usually provided pathology information after a single time point for 3- to 4-week-old mice administered BAPN, have shown that the aortic rupture rate is high. Also, recently formed or resolving hemorrhage in the medial layers has been noted frequently, accompanied by inflammatory cell accumulation, luminal dilation, and profound elastin breaks and extracellular matrix degradation.
      Overall, the BAPN-induced AAD mimics several aspects of the heterogeneity of human AAD (Table II). It might be an optimal model to allow us to understand the molecular mechanisms and explore potential therapeutic strategies for AAD. To perform a detailed characterization of the pathologic features over time throughout the diseased regions, it would be helpful to extend the observation period beyond 4 weeks, in addition to the short intervals.
      Table IIComparison of AAD between humans and BAPN-administered mice
      FeatureHumansBAPN-administered mice
      Location
       AneurysmAbdominal > thoracic aortaThoracic > abdominal aorta
       DissectionThoracic aortaThoracic aorta
      False lumen formationMediaMedia
      Elastin fragmentationYesYes
      Collagen depositionYesYes
      Inflammatory cell accumulationYesYes
      AAD, Aortic aneurysm and dissection; BAPN, β-aminopropionitrile.

      AAD location

      Aortic dissection in humans can be categorized into two types: Stanford types A and B. Stanford type A involves the ascending aorta with pathology in the ascending aorta alone or extending to the descending aorta, and type B includes pathologies initiated from the descending aorta. The use of this classification can help to decide the therapeutic strategy. A type A dissection requires urgent surgical repair. In contrast, treatment of type B dissections has not been consistent.
      • Clough R.E.
      • Nienaber C.A.
      Management of acute aortic syndrome.
      ,
      • Nienaber C.A.
      • Clough R.E.
      Management of acute aortic dissection.
      Therefore, it is important to elucidate the region-specific mechanisms of AAD.
      For BAPN-induced AAD, most studies have either focused on thoracic AAD or did not specify the AAD location. One study reported that, in male C57BL/6 mice in which BAPN administration had started at 3 weeks of age, 87% had developed thoracic aortic dissection and 13% had developed abdominal aortic dissection.
      • Ren W.
      • Liu Y.
      • Wang X.
      • Jia L.
      • Piao C.
      • Lan F.
      • et al.
      β-Aminopropionitrile monofumarate induces thoracic aortic dissection in C57BL/6 mice.
      However, it was unclear whether the mice with abdominal aortic dissection had also developed thoracic aortic dissection. Thus, it is important to describe the region of aortic dissection because concomitant thoracic and abdominal aortic dissection would suggest that the initiation of aortic dissection had started from the thoracic aortic region. In addition, the studies that had reported thoracic aortic dissection, most had not specified whether the aortic dissection had started in the ascending aortic region, aortic arch, or descending thoracic aortic region. The usefulness of this model would be enhanced by investigators including region-specific data, such as the aortic region of AAD initiation, the extension of the involved aortic regions, and the rupture location.

      Molecular mechanisms of BAPN-induced AAD

      Inflammation

      BAPN administration provoked increased plasma concentrations of multiple inflammatory molecules, such as interleukin (IL)-1β, IL-2, IL-3, IL-6, CD40 ligand, and tumor necrosis factor-α.
      • Bachmanov A.A.
      • Reed D.R.
      • Beauchamp G.K.
      • Tordoff M.G.
      Food intake, water intake, and drinking spout side preference of 28 mouse strains.
      ,
      • Liu C.
      • Zhang C.
      • Jia L.
      • Chen B.
      • Liu L.
      • Sun J.
      • et al.
      Interleukin-3 stimulates matrix metalloproteinase 12 production from macrophages promoting thoracic aortic aneurysm/dissection.
      A direct link of these increases to the development of aortopathies has been demonstrated by whole body deletion of either IL-3 or CD40 ligand that attenuated BAPN-induced AAD formation.
      • Bachmanov A.A.
      • Reed D.R.
      • Beauchamp G.K.
      • Tordoff M.G.
      Food intake, water intake, and drinking spout side preference of 28 mouse strains.
      ,
      • Liu C.
      • Zhang C.
      • Jia L.
      • Chen B.
      • Liu L.
      • Sun J.
      • et al.
      Interleukin-3 stimulates matrix metalloproteinase 12 production from macrophages promoting thoracic aortic aneurysm/dissection.
      Also, deletion of complement C3a receptor inhibited the development of BAPN-induced AAD.
      • Ohno-Urabe S.
      • Kukida M.
      • Franklin M.K.
      • Katsumata Y.
      • Su W.
      • Gong M.C.
      • et al.
      Authentication of in situ measurements for thoracic aortic aneurysms in mice.
      In addition, the anti-inflammatory compound, dexamethasone, attenuated BAPN-induced AAD, accompanied by diminished inflammation.
      • Han L.
      • Dai L.
      • Zhao Y.F.
      • Li H.Y.
      • Liu O.
      • Lan F.
      • et al.
      CD40L promotes development of acute aortic dissection via induction of inflammation and impairment of endothelial cell function.
      These findings support the idea that inflammation plays a critical role in the development of BAPN-induced AAD (Fig 1).
      Figure thumbnail gr1
      Fig 1Molecular mechanisms studied in β-aminopropionitrile (BAPN)-induced aortic aneurysm and dissection (AAD) mouse model. IL, Interleukin; MMP, metalloproteinase; SMC, smooth muscle cell.

      Metalloproteinase

      Several studies have demonstrated changes in metalloproteinases (MMPs) in mouse aortas during BAPN administration, in particular, the gelatinases, MMP2 and MMP9. Some studies have uniformly demonstrated increased MMP2 protein and mRNA,
      • Ren W.
      • Liu Y.
      • Wang X.
      • Jia L.
      • Piao C.
      • Lan F.
      • et al.
      β-Aminopropionitrile monofumarate induces thoracic aortic dissection in C57BL/6 mice.
      ,
      • Bachmanov A.A.
      • Reed D.R.
      • Beauchamp G.K.
      • Tordoff M.G.
      Food intake, water intake, and drinking spout side preference of 28 mouse strains.
      ,
      • Ohno-Urabe S.
      • Kukida M.
      • Franklin M.K.
      • Katsumata Y.
      • Su W.
      • Gong M.C.
      • et al.
      Authentication of in situ measurements for thoracic aortic aneurysms in mice.
      ,
      • Jia L.X.
      • Zhang W.M.
      • Li T.T.
      • Liu Y.
      • Piao C.M.
      • Ma Y.C.
      • et al.
      ER stress dependent microparticles derived from smooth muscle cells promote endothelial dysfunction during thoracic aortic aneurysm and dissection.
      ,
      • Xu K.
      • Xu C.
      • Zhang Y.
      • Qi F.
      • Yu B.
      • Li P.
      • et al.
      Identification of type IV collagen exposure as a molecular imaging target for early detection of thoracic aortic dissection.
      and aortic MMP9 protein was shown to increase in all
      • Aicher B.O.
      • Mukhopadhyay S.
      • Lu X.
      • Muratoglu S.C.
      • Strickland D.K.
      • Ucuzian A.A.
      Quantitative micro-CT analysis of aortopathy in a mouse model of β-aminopropionitrile-induced aortic aneurysm and dissection.
      ,
      • Ohno-Urabe S.
      • Kukida M.
      • Franklin M.K.
      • Katsumata Y.
      • Su W.
      • Gong M.C.
      • et al.
      Authentication of in situ measurements for thoracic aortic aneurysms in mice.
      ,
      • Jia L.X.
      • Zhang W.M.
      • Zhang H.J.
      • Li T.T.
      • Wang Y.L.
      • Qin Y.W.
      • et al.
      Mechanical stretch-induced endoplasmic reticulum stress, apoptosis and inflammation contribute to thoracic aortic aneurysm and dissection.
      ,
      • Han L.
      • Dai L.
      • Zhao Y.F.
      • Li H.Y.
      • Liu O.
      • Lan F.
      • et al.
      CD40L promotes development of acute aortic dissection via induction of inflammation and impairment of endothelial cell function.
      ,
      • Xu K.
      • Xu C.
      • Zhang Y.
      • Qi F.
      • Yu B.
      • Li P.
      • et al.
      Identification of type IV collagen exposure as a molecular imaging target for early detection of thoracic aortic dissection.
      but two studies
      • Ren W.
      • Liu Y.
      • Wang X.
      • Jia L.
      • Piao C.
      • Lan F.
      • et al.
      β-Aminopropionitrile monofumarate induces thoracic aortic dissection in C57BL/6 mice.
      ,
      • Bachmanov A.A.
      • Reed D.R.
      • Beauchamp G.K.
      • Tordoff M.G.
      Food intake, water intake, and drinking spout side preference of 28 mouse strains.
      (Fig 1). In addition to the gelatinases, several studies have reported an increase in aortic MMP3.
      • Bachmanov A.A.
      • Reed D.R.
      • Beauchamp G.K.
      • Tordoff M.G.
      Food intake, water intake, and drinking spout side preference of 28 mouse strains.
      ,
      • Zhang W.M.
      • Liu Y.
      • Li T.T.
      • Piao C.M.
      • Liu O.
      • Liu J.L.
      • et al.
      Sustained activation of ADP/P2ry12 signaling induces SMC senescence contributing to thoracic aortic aneurysm/dissection.
      ,
      • Wang S.
      • Liu Y.
      • Zhao G.
      • He L.
      • Fu Y.
      • Yu C.
      • et al.
      Postnatal deficiency of ADAMTS1 ameliorates thoracic aortic aneurysm and dissection in mice.
      A causal role in the changes of MMP abundance can be inferred from the single study in which suppression of MMP2 using short hairpin RNA attenuated BAPN-induced AAD formation.
      • Ohno-Urabe S.
      • Kukida M.
      • Franklin M.K.
      • Katsumata Y.
      • Su W.
      • Gong M.C.
      • et al.
      Authentication of in situ measurements for thoracic aortic aneurysms in mice.
      Although multiple studies have shown the contribution of MMPs to the pathophysiology of BAPN-induced AAD, it remains unknown how BAPN alters aortic MMPs. In addition, BAPN has been assumed to cause AAD through the inhibition of elastin and collagen crosslinking. Overall, the precise role of MMPs in BAPN-induced AAD formation remains to be clarified.

      Smooth muscle cells

      The loss of smooth muscle cells (SMCs) in BAPN-induced AAD has been attributed to apoptosis (Fig 1).
      • Aicher B.O.
      • Mukhopadhyay S.
      • Lu X.
      • Muratoglu S.C.
      • Strickland D.K.
      • Ucuzian A.A.
      Quantitative micro-CT analysis of aortopathy in a mouse model of β-aminopropionitrile-induced aortic aneurysm and dissection.
      ,
      • Sawada H.
      • Franklin M.K.
      • Moorleghen J.J.
      • Howatt D.A.
      • Kukida M.
      • Lu H.S.
      • et al.
      Ultrasound monitoring of descending aortic aneurysms and dissections in mice.
      ,
      • Chen Y.
      • Wei X.
      • Zhang Z.
      • He Y.
      • Huo B.
      • Guo X.
      • et al.
      Downregulation of filamin A expression in the aorta is correlated with aortic dissection.
      ,
      • Jia L.X.
      • Zhang W.M.
      • Zhang H.J.
      • Li T.T.
      • Wang Y.L.
      • Qin Y.W.
      • et al.
      Mechanical stretch-induced endoplasmic reticulum stress, apoptosis and inflammation contribute to thoracic aortic aneurysm and dissection.
      • Jia L.X.
      • Zhang W.M.
      • Li T.T.
      • Liu Y.
      • Piao C.M.
      • Ma Y.C.
      • et al.
      ER stress dependent microparticles derived from smooth muscle cells promote endothelial dysfunction during thoracic aortic aneurysm and dissection.
      • Han L.
      • Dai L.
      • Zhao Y.F.
      • Li H.Y.
      • Liu O.
      • Lan F.
      • et al.
      CD40L promotes development of acute aortic dissection via induction of inflammation and impairment of endothelial cell function.
      Consistent with the promotion of SMC apoptosis, AKT phosphorylation was downregulated in mice after BAPN administration.
      • Aicher B.O.
      • Mukhopadhyay S.
      • Lu X.
      • Muratoglu S.C.
      • Strickland D.K.
      • Ucuzian A.A.
      Quantitative micro-CT analysis of aortopathy in a mouse model of β-aminopropionitrile-induced aortic aneurysm and dissection.
      ,
      • Jia L.X.
      • Zhang W.M.
      • Zhang H.J.
      • Li T.T.
      • Wang Y.L.
      • Qin Y.W.
      • et al.
      Mechanical stretch-induced endoplasmic reticulum stress, apoptosis and inflammation contribute to thoracic aortic aneurysm and dissection.
      ,
      • Le S.
      • Zhang H.
      • Huang X.
      • Chen S.
      • Wu J.
      • Chen S.
      • et al.
      PKM2 activator TEPP-46 attenuates thoracic aortic aneurysm and dissection by inhibiting NLRP3 inflammasome-mediated IL-1β secretion.
      However, phosphorylation of ERK is controversial in the BAPN-induced AAD mouse model.
      • Han L.
      • Dai L.
      • Zhao Y.F.
      • Li H.Y.
      • Liu O.
      • Lan F.
      • et al.
      CD40L promotes development of acute aortic dissection via induction of inflammation and impairment of endothelial cell function.
      ,
      • Le S.
      • Zhang H.
      • Huang X.
      • Chen S.
      • Wu J.
      • Chen S.
      • et al.
      PKM2 activator TEPP-46 attenuates thoracic aortic aneurysm and dissection by inhibiting NLRP3 inflammasome-mediated IL-1β secretion.
      A direct role of SMC apoptosis has been inferred by the effects of rapamycin that prevented BAPN-induced AAD formation. It is of note that intermittent hypoxia alleviated BAPN-induced AAD with inhibition of SMC apoptosis.
      • Aicher B.O.
      • Mukhopadhyay S.
      • Lu X.
      • Muratoglu S.C.
      • Strickland D.K.
      • Ucuzian A.A.
      Quantitative micro-CT analysis of aortopathy in a mouse model of β-aminopropionitrile-induced aortic aneurysm and dissection.
      The effects of SMCs was also demonstrated by SMC-specific sirtuin-1 overexpression, which decreased the BAPN-induced AAD rupture rate.
      • Xu K.
      • Xu C.
      • Zhang Y.
      • Qi F.
      • Yu B.
      • Li P.
      • et al.
      Identification of type IV collagen exposure as a molecular imaging target for early detection of thoracic aortic dissection.
      Sirtuin-1 was reported to have antioxidative effects in the aorta.
      • Budbazar E.
      • Rodriguez F.
      • Sanchez J.M.
      • Seta F.
      The role of sirtuin-1 in the vasculature: focus on aortic aneurysm.
      Despite these studies, the mechanism by which BAPN induces SMC phenotypic changes has not yet been defined.
      During the past decade, many molecular mechanisms by which BAPN causes AAD formation have been explored. However, many studies had used aortas harvested after 4 weeks of BAPN administration, which could have had overt pathology, such as aneurysms and dissections. Thus, it is difficult to discern whether the observed changes were a cause or a consequence of the aortic pathology. For greater insight, it is important to determine which changes are present at early intervals of BAPN administration before the appearance of overt pathology.

      Imaging tools for detecting BAPN-induced AAD

      High-frequency ultrasound

      With the advent of high-frequency ultrasound instruments, noninvasive ultrasound has been commonly used to monitor aortic dilation in mice.
      • Sawada H.
      • Chen J.Z.
      • Wright B.C.
      • Moorleghen J.J.
      • Lu H.S.
      • Daugherty A.
      Ultrasound imaging of the thoracic and abdominal aorta in mice to determine aneurysm dimensions.
      Multiple studies have used ultrasound to assess BAPN-induced AAD.
      • Yang Y.Y.
      • Li L.Y.
      • Jiao X.L.
      • Jia L.X.
      • Zhang X.P.
      • Wang Y.L.
      • et al.
      Intermittent hypoxia alleviates β-aminopropionitrile monofumarate induced thoracic aortic dissection in C57BL/6 mice.
      • Ren W.
      • Liu Y.
      • Wang X.
      • Piao C.
      • Ma Y.
      • Qiu S.
      • et al.
      The complement C3a-C3aR axis promotes development of thoracic aortic dissection via regulation of MMP2 expression.
      • Jia L.X.
      • Zhang W.M.
      • Zhang H.J.
      • Li T.T.
      • Wang Y.L.
      • Qin Y.W.
      • et al.
      Mechanical stretch-induced endoplasmic reticulum stress, apoptosis and inflammation contribute to thoracic aortic aneurysm and dissection.
      ,
      • Han L.
      • Dai L.
      • Zhao Y.F.
      • Li H.Y.
      • Liu O.
      • Lan F.
      • et al.
      CD40L promotes development of acute aortic dissection via induction of inflammation and impairment of endothelial cell function.
      • Shao Y.
      • Li G.
      • Huang S.
      • Li Z.
      • Qiao B.
      • Chen D.
      • et al.
      Effects of extracellular matrix softening on vascular smooth muscle cell dysfunction.
      • Xu K.
      • Xu C.
      • Zhang Y.
      • Qi F.
      • Yu B.
      • Li P.
      • et al.
      Identification of type IV collagen exposure as a molecular imaging target for early detection of thoracic aortic dissection.
      ,
      • Zhou B.
      • Li W.
      • Zhao G.
      • Yu B.
      • Ma B.
      • Liu Z.
      • et al.
      Rapamycin prevents thoracic aortic aneurysm and dissection in mice.
      ,
      • Xia L.
      • Sun C.
      • Zhu H.
      • Zhai M.
      • Zhang L.
      • Jiang L.
      • et al.
      Melatonin protects against thoracic aortic aneurysm and dissection through SIRT1-dependent regulation of oxidative stress and vascular smooth muscle cell loss.
      ,
      • Ohno-Urabe S.
      • Kukida M.
      • Franklin M.K.
      • Katsumata Y.
      • Su W.
      • Gong M.C.
      • et al.
      Authentication of in situ measurements for thoracic aortic aneurysms in mice.
      • Sawada H.
      • Franklin M.K.
      • Moorleghen J.J.
      • Howatt D.A.
      • Kukida M.
      • Lu H.S.
      • et al.
      Ultrasound monitoring of descending aortic aneurysms and dissections in mice.
      ,
      • Le S.
      • Zhang H.
      • Huang X.
      • Chen S.
      • Wu J.
      • Chen S.
      • et al.
      PKM2 activator TEPP-46 attenuates thoracic aortic aneurysm and dissection by inhibiting NLRP3 inflammasome-mediated IL-1β secretion.
      Most studies had measured the luminal diameters in the proximal thoracic aorta as a parameter of AAD severity. Right and left parasternal approaches are the standard ultrasound modes for mice. However, these modes are not optimal for descending aortic imaging owing to interference from the lungs and ribs. A recent study reported a paraspinal dorsal approach for ultrasound imaging in the descending aortic region of mice (Fig 2, A).
      • Sawada H.
      • Franklin M.K.
      • Moorleghen J.J.
      • Howatt D.A.
      • Kukida M.
      • Lu H.S.
      • et al.
      Ultrasound monitoring of descending aortic aneurysms and dissections in mice.
      This approach can visualize aortic dilatations and false lumen formation through the descending thoracic aorta of BAPN-administered mice (Fig 2, A).
      Figure thumbnail gr2
      Fig 2Imaging tools for detecting β-aminopropionitrile (BAPN-induced aortic aneurysm and dissection (AAD) in mice. Representative aortic images of ultrasound
      • Wang X.
      • Zhang X.
      • Qiu T.
      • Yang Y.
      • Li Q.
      • Zhang X.
      Dexamethasone reduces the formation of thoracic aortic aneurysm and dissection in a murine model.
      (A), micro-computed tomography (CT),
      • Zhou B.
      • Li W.
      • Zhao G.
      • Yu B.
      • Ma B.
      • Liu Z.
      • et al.
      Rapamycin prevents thoracic aortic aneurysm and dissection in mice.
      ex vivo (authors’ unpublished data; C), and in situ
      • Xia L.
      • Sun C.
      • Zhu H.
      • Zhai M.
      • Zhang L.
      • Jiang L.
      • et al.
      Melatonin protects against thoracic aortic aneurysm and dissection through SIRT1-dependent regulation of oxidative stress and vascular smooth muscle cell loss.
      (D) approaches. OCT, Tissue-Tek optimal cutting temperature (compound; Sakura Finetek, Torrance, Calif). Scale bar = 1 mm.

      Micro-computed tomography

      Micro-computed tomography (CT) is a modality used for the acquisition of high-resolution aortic images of mice. Unlike ultrasound, micro-CT has less dependency on user skill for acquiring aortic images that can be used for quantitation of dimensions. In addition, micro-CT readily enables evaluation of the aortic size in three dimensions, which might provide more detailed structural information. Several studies have used micro-CT to detect BAPN-induced aneurysms at study termination (Fig 2, B).
      • Xia L.
      • Sun C.
      • Zhu H.
      • Zhai M.
      • Zhang L.
      • Jiang L.
      • et al.
      Melatonin protects against thoracic aortic aneurysm and dissection through SIRT1-dependent regulation of oxidative stress and vascular smooth muscle cell loss.
      ,
      • Aicher B.O.
      • Mukhopadhyay S.
      • Lu X.
      • Muratoglu S.C.
      • Strickland D.K.
      • Ucuzian A.A.
      Quantitative micro-CT analysis of aortopathy in a mouse model of β-aminopropionitrile-induced aortic aneurysm and dissection.
      Despite detailed information with high reliability, the necessity of an intravenous injection of contrast agent has impeded the use of serial micro-CT imaging studies. Sequential micro-CT monitoring has not been reported for BAPN-administered mice. Because BAPN leads to heterogeneous aortic pathologies, it would be interesting to monitor BAPN-induced AAD formation sequentially using micro-CT in live animals.

      Magnetic resonance imaging

      The mouse aorta can also be visualized using magnetic resonance imaging (MRI).
      • Weinreb D.B.
      • Aguinaldo J.G.
      • Feig J.E.
      • Fisher E.A.
      • Fayad Z.A.
      Non-invasive MRI of mouse models of atherosclerosis.
      MRI does not result in radiation exposure and might not require contrast agents for basic imaging of mouse aortas. One study using MRI showed overt dilatation of the proximal thoracic aorta in BAPN-administered mice that was consistent with the ultrasound and ex vivo findings.
      • Ren W.
      • Liu Y.
      • Wang X.
      • Piao C.
      • Ma Y.
      • Qiu S.
      • et al.
      The complement C3a-C3aR axis promotes development of thoracic aortic dissection via regulation of MMP2 expression.
      However, the spatial resolution of MRI is not sufficient to assess small structural alterations in mouse aortas. Its expense is also a barrier to the use of MRI. Thus, at present, MRI cannot be routinely applied for evaluating aortic morphology in mice.

      Ex vivo and in situ imaging

      Ex vivo approaches have been used most frequently to evaluate BAPN-induced AAD in mice (Fig 2, C).
      • Ren W.
      • Liu Y.
      • Wang X.
      • Jia L.
      • Piao C.
      • Lan F.
      • et al.
      β-Aminopropionitrile monofumarate induces thoracic aortic dissection in C57BL/6 mice.
      ,
      • Ohno-Urabe S.
      • Kukida M.
      • Franklin M.K.
      • Katsumata Y.
      • Su W.
      • Gong M.C.
      • et al.
      Authentication of in situ measurements for thoracic aortic aneurysms in mice.
      • Sawada H.
      • Franklin M.K.
      • Moorleghen J.J.
      • Howatt D.A.
      • Kukida M.
      • Lu H.S.
      • et al.
      Ultrasound monitoring of descending aortic aneurysms and dissections in mice.
      ,
      • Yang Y.Y.
      • Li L.Y.
      • Jiao X.L.
      • Jia L.X.
      • Zhang X.P.
      • Wang Y.L.
      • et al.
      Intermittent hypoxia alleviates β-aminopropionitrile monofumarate induced thoracic aortic dissection in C57BL/6 mice.
      • Ren W.
      • Liu Y.
      • Wang X.
      • Piao C.
      • Ma Y.
      • Qiu S.
      • et al.
      The complement C3a-C3aR axis promotes development of thoracic aortic dissection via regulation of MMP2 expression.
      • Jia L.X.
      • Zhang W.M.
      • Zhang H.J.
      • Li T.T.
      • Wang Y.L.
      • Qin Y.W.
      • et al.
      Mechanical stretch-induced endoplasmic reticulum stress, apoptosis and inflammation contribute to thoracic aortic aneurysm and dissection.
      • Jia L.X.
      • Zhang W.M.
      • Li T.T.
      • Liu Y.
      • Piao C.M.
      • Ma Y.C.
      • et al.
      ER stress dependent microparticles derived from smooth muscle cells promote endothelial dysfunction during thoracic aortic aneurysm and dissection.
      • Han L.
      • Dai L.
      • Zhao Y.F.
      • Li H.Y.
      • Liu O.
      • Lan F.
      • et al.
      CD40L promotes development of acute aortic dissection via induction of inflammation and impairment of endothelial cell function.
      • Shao Y.
      • Li G.
      • Huang S.
      • Li Z.
      • Qiao B.
      • Chen D.
      • et al.
      Effects of extracellular matrix softening on vascular smooth muscle cell dysfunction.
      • Xu K.
      • Xu C.
      • Zhang Y.
      • Qi F.
      • Yu B.
      • Li P.
      • et al.
      Identification of type IV collagen exposure as a molecular imaging target for early detection of thoracic aortic dissection.
      • Wang S.
      • Liu Y.
      • Zhao G.
      • He L.
      • Fu Y.
      • Yu C.
      • et al.
      Postnatal deficiency of ADAMTS1 ameliorates thoracic aortic aneurysm and dissection in mice.
      • Zhou B.
      • Li W.
      • Zhao G.
      • Yu B.
      • Ma B.
      • Liu Z.
      • et al.
      Rapamycin prevents thoracic aortic aneurysm and dissection in mice.
      • Xia L.
      • Sun C.
      • Zhu H.
      • Zhai M.
      • Zhang L.
      • Jiang L.
      • et al.
      Melatonin protects against thoracic aortic aneurysm and dissection through SIRT1-dependent regulation of oxidative stress and vascular smooth muscle cell loss.
      ,
      • Gao Y.
      • Wang Z.
      • Zhao J.
      • Sun W.
      • Guo J.
      • Yang Z.
      • et al.
      Involvement of B cells in the pathophysiology of β-aminopropionitrile-induced thoracic aortic dissection in mice.
      ,
      • Wang F.
      • Tu Y.
      • Gao Y.
      • Chen H.
      • Liu J.
      • Zheng J.
      Smooth muscle sirtuin 1 blocks thoracic aortic aneurysm/dissection development in mice.
      ,
      • Le S.
      • Zhang H.
      • Huang X.
      • Chen S.
      • Wu J.
      • Chen S.
      • et al.
      PKM2 activator TEPP-46 attenuates thoracic aortic aneurysm and dissection by inhibiting NLRP3 inflammasome-mediated IL-1β secretion.
      BAPN induces heterogeneous aortic pathologies in the entire thoracic aorta. Because ex vivo approaches can detect AAD directly in any region, it has advantages for the evaluation of aortic pathologies in BAPN-administered mice. However, owing to the absence of blood pressure, it is difficult to maintain the aortic dimensions after euthanasia, especially when severe pathologies are present. Therefore, formalin or latex perfusion has been used frequently to maintain aortic patency during ex vivo imaging.
      • Gallo E.M.
      • Loch D.C.
      • Habashi J.P.
      • Calderon J.F.
      • Chen Y.
      • Bedja D.
      • et al.
      Angiotensin II-dependent TGF-beta signaling contributes to Loeys-Dietz syndrome vascular pathogenesis.
      • Habashi J.P.
      • Judge D.P.
      • Holm T.M.
      • Cohn R.D.
      • Loeys B.L.
      • Cooper T.K.
      • et al.
      Losartan, an AT1 antagonist, prevents aortic aneurysm in a mouse model of Marfan syndrome.
      • Lin C.J.
      • Staiculescu M.C.
      • Hawes J.Z.
      • Cocciolone A.J.
      • Hunkins B.M.
      • Roth R.A.
      • et al.
      Heterogeneous cellular contributions to elastic laminae formation in arterial wall development.
      In situ imaging has also been a common approach for aortic evaluations in mice.
      • Ohno-Urabe S.
      • Kukida M.
      • Franklin M.K.
      • Katsumata Y.
      • Su W.
      • Gong M.C.
      • et al.
      Authentication of in situ measurements for thoracic aortic aneurysms in mice.
      ,
      • Sawada H.
      • Franklin M.K.
      • Moorleghen J.J.
      • Howatt D.A.
      • Kukida M.
      • Lu H.S.
      • et al.
      Ultrasound monitoring of descending aortic aneurysms and dissections in mice.
      ,
      • Li W.
      • Li Q.
      • Jiao Y.
      • Qin L.
      • Ali R.
      • Zhou J.
      • et al.
      TGFBR2 disruption in postnatal smooth muscle impairs aortic wall homeostasis.
      This approach can assess aortic morphology while the tissue resides in the anatomic position. A recent study demonstrated the reliability of aortic measurements using in situ images with optimal cutting temperature compound infused into BAPN-induced AAD.
      • Ohno-Urabe S.
      • Kukida M.
      • Franklin M.K.
      • Katsumata Y.
      • Su W.
      • Gong M.C.
      • et al.
      Authentication of in situ measurements for thoracic aortic aneurysms in mice.
      Optimal cutting temperature compound injection expanded the aortic lumen, and the aortic diameters were comparable to the ultrasound measurements (Fig 2, D). It is worth noting that the aortic diameters using ex vivo or in situ images are external, not luminal, diameters. Because external diameters will not correspond to luminal diameters in aortic dissections, other modalities, including ultrasound and micro-CT, could be considered to assess the luminal diameters in addition to external diameters.
      Several modalities and methods are available to evaluate aortic morphology in mice. Because each approach has different advantages and shortcomings, the imaging approaches should be chosen to optimize the endpoints of each study. In addition, the heterogeneity of BAPN-induced aortic pathologies has resulted in challenges to aortic imaging for the acquisition of authentic measurements. Therefore, for robust evaluations, we would recommend the use of multiple modes to validate BAPN-induced aortic pathologies in mice.

      Summary and perspectives

      BAPN-induced AAD replicates a spectrum of the features of human AAD (Table II). Thus, this mouse model provides opportunities to study the complex mechanisms of AAD from the early to advanced stages for exploring potential therapies. Although much research is required to translate animal findings into human uses, advances in research tools, including state-of-the-art imaging systems and well-controlled pharmacologic studies, will provide insights into defining therapies for AAD. Prospectively, collaborations between basic science investigators and physician scientists will enhance our knowledge of AAD mechanisms and pathophysiology in humans and provide ultimate insights into translating the findings from animal studies into human uses.

      Author Contributions

      Conception and design: AD, HL
      Analysis and interpretation: HS, AD, HL
      Data collection: HS, ZB, SI, HL
      Writing the article: HS, AD, HL
      Critical revision of the article: HS, ZB, SI, AD, HL
      Final approval of the article: HS, ZB, SI, AD, HL
      Statistical analysis: Not applicable
      Obtained funding: AD
      Overall responsibility: HL

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