Allylamine and beta-aminopropionitrile induced aortic medial necrosis: mechanisms of synergism

Methamphetamine induces thoracic aortic aneurysm/dissection through C/EBPβ

AIMS

Thoracic aortic aneurysm/dissection (TAAD) is a life-threatening disease with diverse clinical manifestations. Although the association between methamphetamine (METH) and TAAD is frequently observed, the causal relationship between METH abuse and aortic aneurysm/dissection has not been established. This study was designed to determine if METH causes aortic aneurysm/dissection and delineate the underlying mechanism.

METHODS AND RESULTS

A new TAAD model was developed by exposing METH to SD rats pre-treated with lysyl oxidase inhibitor β-aminopropionitrile (BAPN). Combination of METH and BAPN caused thoracic aortic aneurysm/dissection in 60% of rats. BAPN+METH significantly increased the expression and activities of both matrix metalloproteinase MMP2 and MMP9, consistent with the severe elastin breakage and dissection. Mechanistically, METH increased CCAAT-enhancer binding protein β (C/EBPβ) expression by enhancing mothers against decapentaplegic homolog 3 (Smad3) and extracellular regulated protein kinase (ERK1/2) signaling. METH also promoted C/EBPβ binding to MMP2 and MMP9 promoters. Blocking C/EBPβ significantly attenuated METH+BAPN-induced TAAD and MMP2/MMP9 expression. Moreover, BAPN+METH promoted aortic medial smooth muscle cell (SMC) apoptosis through C/EBPβ-mediated IGFBP5/p53/PUMA signaling pathways. More importantly, the expression of C/EBPβ, MMP2/MMP9, and apoptosis-promoting proteins was increased in the aorta of human patients with thoracic aortic dissection, suggesting that the mechanisms identified in animal study could be relevant to human disease.

CONCLUSIONS

Our study demonstrated that METH exposure has a casual effect on TAAD. C/EBPβ mediates METH-introduced TAAD formation by causing elastin breakage, medial cell loss and degeneration. Therefore, C/EBPβ may be a potential factor for TAAD clinical diagnosis or treatment.

Moderate aerobic exercise prevents matrix degradation and death in a mouse model of aortic dissection and aneurysm

Thoracic aortic aneurysm and dissection (TAAD) is a deadly disease characterized by intimal disruption induced by hemodynamic forces of the circulation. The effect of exercise in patients with TAAD is largely unknown. β-Aminopropionitrile (BAPN) is an irreversible inhibitor of lysyl oxidase that induces TAAD in mice. The objective of this study was to investigate the effect of aerobic exercise on BAPN-induced TAAD. Upon weaning, mice were given either BAPN-containing water or standard drinking water and subjected to either conventional cage activity (BAPN-CONV) or forced treadmill exercise (BAPN-EX) for up to 26 wk. Mortality was 23.5% (20/85) for BAPN-CONV mice versus 0% (0/22) for BAPN-EX mice (hazard ratio 3.8; P = 0.01). BAPN induced significant elastic lamina fragmentation and intimal-medial thickening compared with BAPN-untreated controls, and aneurysms were identified in 50% (5/10) of mice that underwent contrast-enhanced CT scanning. Exercise significantly decreased BAPN-induced wall thickening, calculated circumferential wall tension, and lumen diameter, with 0% (0/5) of BAPN-EX demonstrating chronic aortic aneurysm formation on CT scan. Expression of selected genes relevant to vascular diseases was analyzed by qRT-PCR. Notably, exercise normalized BAPN-induced increases in TGF-β pathway-related genes Cd109, Smad4, and Tgfβr1; inflammation-related genes Vcam1, Bcl2a1, Ccr2, Pparg, Il1r1, Il1r1, Itgb2, and Itgax; and vascular injury- and response-related genes Mmp3, Fn1, and Vwf. Additionally, exercise significantly increased elastin expression in BAPN-treated animals compared with controls. This study suggests that moderate aerobic exercise may be safe and effective in preventing the most devastating outcomes in TAAD.NEW & NOTEWORTHY Moderate aerobic exercise was shown to significantly reduce mortality, extracellular matrix degradation, and thoracic aortic aneurysm and dissection formation associated with lysyl oxidase inhibition in a mouse model. Gene expression suggested a reversal of TGF-β, inflammation, and extracellular matrix remodeling pathway dysregulation, along with augmented elastogenesis with exercise.

SPECT/CT imaging of apoptosis in aortic aneurysm with radiolabeled duramycin

The objective of this research was to estimate whether a ^[99mTc]duramycin probe can be used for apoptosis imaging in patients with aortic aneurysm (AA). Vascular smooth muscle cell (SMC) apoptosis has an important influence on AA development. Thus, non-invasive imaging of SMC apoptosis may be able to evaluate AA progress and risk stratification. SMCs were treated with hydrogen peroxide (H₂O₂; 200 μΜ) or culture medium as a control. Apoptosis was measured using flow cytometry and ^[99mTc]duramycin to detect the binding efficiency to apoptotic SMCs. C57/BL6 mice were administered angiotensin-II and beta-aminopropionitrile (BAPN) subcutaneously to establish an AA model, or saline for controls. Aortic specimens underwent pathological evaluation and their aortic diameters were measured after 6 weeks. Micro-SPECT/CT scanning of ^[99mTc]duramycin and ¹⁸F-FDG PET detection were performed. SMCs treated with H₂O₂ showed more apoptosis compared with the control group (67.2 ± 3.8% vs. 16.1 ± 0.6%, P < 0.01). The experimental group showed a high rate of AA formation (70%) compared with no AA formation in the control group. The average aorta diameter was higher and ^[99mTc]duramycin uptake at the AA site was higher in the experimental group compared with the control group. Compared with the normal aorta in the control group, AA in experiment group had more severe medial degeneration, elastic fiber reduction and fracture, and collagen degeneration. TUNEL staining verified the higher apoptosis rate at the AA site in experiment group compared with the control group (63.9 ± 3.7% in ascending AA, 66.4 ± 4.0% in thoracic AA, vs. 3.5 ± 0.3% in normal aorta, P < 0.01). ^[99mTc]Duramycin may be an effective probe to evaluate apoptosis in AA.

CD40L promotes development of acute aortic dissection via induction of inflammation and impairment of endothelial cell function

Acute aortic dissection is one of the most lethal cardiovascular disease. The major histopathological feature of AAD is medial degradation, especially breakdown of elastin and collagen. However, the underlying mechanism remains a mystery. Platelets expressed CD40 Ligand (CD40L) is recently recognised as a key effector of cardiovascular disease development through its pro-inflammatory effect. To clarify the role of CD40L in AAD, we examined level of CD40L in human blood serum samples and found that it is significantly higher in AAD patients compared with healthy subjects (26.8±5.52 ng/mL versus 13.4±4.00 ng/mL). To further investigate if CD40L is involve in the development of AAD, we applied β-aminopropionitrile (BAPN) induced mouse model of AAD. Consistent with the human data, circulating CD40L in AAD mice much higher than normal mice (148.40±75.96 pg/mL versus 44.09±19.65 pg/mL). Meanwhile, multiple pro-inflammatory chemokines significantly increased in AAD mice. Importantly, the CD40L-/- mice treated with BAPN did not develop these phenotypes. Lastly, we confirmed that endothelial cells migration was significantly inhibited by CD40L, suggesting impaired recovery from intimal injury. In summary, we found that CD40L promoted AAD development through its pro-inflammatory effects and inhibition of endothelial cell function.

Quantitative Micro-CT Analysis of Aortopathy in a Mouse Model of β-aminopropionitrile-induced Aortic Aneurysm and Dissection

Aortic aneurysm and dissection is associated with significant morbidity and mortality in the population and can be highly lethal. While animal models of aortic disease exist, in vivo imaging of the vasculature has been limited. In recent years, micro-computerized tomography (micro-CT) has emerged as a preferred modality for imaging both large and small vessels both in vivo and ex vivo. In conjunction with a method of vascular casting, we have successfully used micro-CT to characterize the frequency and distribution of aortic pathology in β-aminopropionitrile-treated C57/Bl6 mice. Technical limitations of this method include variations in the quality of the perfusion introduced by poor animal preparation, the application of proper methodologies for vessel size quantification, and the non-survivability of this procedure. This article details a methodology for the intravascular perfusion of a lead-based radiopaque silicone rubber for the quantitative characterization of aortopathy in a mouse model of aneurysm and dissection. In addition to visualizing aortic pathology, this method may be used for examining other vascular beds in vivo or vascular beds removed post-mortem.

A novel reproducible model of aortic aneurysm rupture

INTRODUCTION

Given the unknown biologic antecedents before aortic aneurysm rupture, the purpose of this study was to establish a reproducible model of aortic aneurysm rupture.

METHODS

We fed 7-week-old apolipoprotein E deficient mice a high-fat diet for 4 weeks and osmotic infusion pumps containing Angiotensin II were implanted. Angiotensin II was delivered continuously for 4 weeks at either 1,000 ng/kg/min (n = 25) or 2,000 ng/kg/min (n = 29). A third group (n = 14) were given Angiotensin II at 2,000 ng/kg/min and 0.2% β-aminopropionitrile dissolved in drinking water. Surviving mice were killed 28 days after pump placement, aortic diameters were measured, and molecular analyses were performed.

RESULTS

Survival at 28 days was significantly different among groups with 80% survival in the 1,000 ng/kg/min group, 52% in the 2,000 ng/kg/min group, and only 14% in the Angiotensin II/β-aminopropionitrile group (P = .0001). Concordantly, rupture rates were statistically different among groups (8% versus 38% versus 79%, P < .0001). Rates of abdominal aortic aneurysm were 48%, 55%, and 93%, respectively, with statistically higher rates in the Angiotensin II/β-aminopropionitrile group compared with both the 1,000 ng and 2,000 ng Angiotensin II groups (P = .006 and P = .0165, respectively). Rates of thoracic aortic aneurysm formation were 12%, 52%, and 79% in the 3 groups with a statistically higher rate in the Angiotensin II/β-aminopropionitrile group compared with 1,000 ng group (P < .0001).

CONCLUSIONS

A reproducible model of aortic aneurysm rupture was developed with a high incidence of abdominal and thoracic aortic aneurysm. This model should enable further studies investigating the pathogenesis of aortic rupture, as well as allow for targeted strategies to prevent human aortic aneurysm rupture.

Bilateral superior cervical ganglionectomy attenuates the progression of β-aminopropionitrile-induced aortic dissection in rats

AIMS

Aortic dissection (AD) represents one of the most common aortic emergencies with high incidence of morbidity and mortality. Clinical studies have shown that the increased excitability of the sympathetic nerve may be associated with the formation of AD. In this study, we examined the effects of bilateral superior cervical sympathectomy (SCGx) on the progression of β-aminopropionitrile (BAPN)-induced AD in rats.

MAIN METHODS

Sprague-Dawley rats were randomly divided into three groups, including BAPN, BAPN+SCGx and control groups. For terminal measurements, the mean arterial pressure (MAP) and heart rate (HR) were monitored and the basal sympathetic nerve activity (SNA) was assessed through recording the variation in arterial pressure in response to hexamethonium application. Pathological changes in the aortic wall were observed by histological staining. Matrix metalloproteinase-2 (MMP-2) and MMP-9 concentrations within the aortic wall were analyzed by western blot.

KEY FINDINGS

The results show that BAPN administration could elevate SNA and cause the formation of AD in rats with a high incidence (67.7%), while SCGx treatment inhibited the elevation of SNA and significantly reduced the incidence (20%). SCGx may suppress the formation of BAPN-induced AD via restraining the rise of HR and reducing the MMP-9 concentration in aortic wall.

SIGNIFICANCE

These results indicate that surgical techniques such as sympathetic nerve block may be a potentially useful therapy for the prevention of AD.

Comparison of β-aminopropionitrile-induced aortic dissection model in rats by different administration and dosage

This study compared three β-aminopropionitrile (BAPN) treatment rats to find the optimal BAPN model for thoracic aortic dissection and aneurysm in one study. Sixty rats were divided into five groups: control, injected control, 0.25% and 0.4% BAPN treatment (orally), and 667 mg/kg/day BAPN injection subcutaneously. Incidence of aortic dissection and aneurysm, aortic weight and diameter were measured directly. Thickness of media and area of aorta were measured by hematoxylin and eosin and Victoria blue staining. The mortality, incidence of aortic dissection and the rupture rate of dissected aneurysm in 0.25% group was much higher than in the other two BAPN treatment groups. The diameter of thoracic aorta in 0.25% and the whole aorta in 0.4% group significantly increased. Media thickness and area of thoracic aorta were increased by 91% and 54% in 0.25% group, and by 17% and 12% in the BAPN injection group. Thickness and area were increased by 49% and 35% on thoracic aorta, and 29% and 46% on abdominal aorta in 0.4% group. In conclusion, 0.25%, 0.4% and BAPN injection groups might be appropriate for aortic dissection and pharmaceutical study, thoracic-abdominal aortic aneurysm or dilation and biomechanical research, respectively.

Neutrophil-Derived Matrix Metalloproteinase 9 Triggers Acute Aortic Dissection

Background—

Acute aortic dissection (AAD) is a life-threatening vascular disease without effective pharmaceutical therapy. Matrix metalloproteinases (MMPs) are implicated in the development of chronic vascular diseases including aneurysm, but the key effectors and mechanism of action remain unknown. To define further the role of MMPs in AAD, we screened circulating MMPs in AAD patients, and then generated a novel mouse model for AAD to characterize the mechanism of action.

Methods and Results—

MMP9 and angiotensin II were elevated significantly in blood samples from AAD patients than in those from the patients with nonruptured chronic aortic aneurysm or healthy volunteers. Based on the findings, we established a novel AAD model by infusing angiotensin II to immature mice that had been received a lysyl oxidase inhibitor, β-aminopropionitrile monofumarate. AAD was developed successfully in the thoracic aorta by angiotensin II administration to β-aminopropionitrile monofumarate-treated wild-type mice, with an incidence of 20%, 80%, and 100% after 6, 12, and 24 hours, respectively. Neutrophil infiltrations were observed in the intima of the thoracic aorta, and the overexpression of MMP9 in the aorta was demonstrated by reverse transcription polymerase chain reaction, gelatin zymography, and immunohistochemistry. The incidence of AAD was reduced significantly by 40% following the administration of an MMP inhibitor and was almost blocked completely in MMP −/− mice without any influence on neutrophil infiltration. Neutrophil depletion by injection of anti-granulocyte-differentiation antigen-1 (anti-Gr-1) antibody also significantly decreased the incidence of AAD.

Conclusions—

These data suggest that AAD is initiated by neutrophils that have infiltrated the aortic intima and released MMP9 in response to angiotensin II.

Environmental risk factors for heart disease

In this review, we discuss current evidence linking environmental pollutants to cardiovascular disease (CVD). Extensive evidence indicates that environmental factors contribute to CVD risk, incidence, and severity. Migrant studies show that changes in the environment could substantially alter CVD risk in a genetically stable population. Additionally, CVD risk is affected by changes in nutritional and lifestyle choices. Recent studies in the field of environmental cardiology suggest that environmental toxins also influence CVD. Exposure to tobacco smoke is paradigmatic of such environmental risk and is strongly and positively associated with increased cardiovascular morbidity and mortality. In animal models of exposure, tobacco smoke induces endothelial dysfunction and prothrombotic responses and exacerbates atherogenesis and myocardial ischemic injury. Similar mechanism may be engaged by other pollutants or food constituents. Several large population-based studies indicate that exposure to fine or ultrafine particulate air pollution increases CVD morbidity and mortality, and the plausibility of this association is supported by data from animal studies. Exposure to other chemicals such as polyaromatic hydrocarbons, aldehydes, and metals has also been reported to elevate CVD risk by affecting atherogenesis, thrombosis, or blood pressure regulation. Maternal exposure to drugs, toxins, and infection has been linked with cardiac birth defects and premature CVD in later life. Collectively, the data support the notion that chronic environmental stress is an important determinant of CVD risk. Further work is required to assess the magnitude of this risk fully and to delineate specific mechanisms by which environmental toxins affect CVD.