17 Beta-estradiol attenuates development of angiotensin II-induced aortic abdominal aneurysm in apolipoprotein E-deficient mice

Arterial aneurysm and dissection: toward the evolving phenotype of Tatton-Brown-Rahman syndrome

BACKGROUND

Tatton-Brown-Rahman syndrome (TBRS) is a rare disorder, caused by DNMT3A heterozygous pathogenic variants, and first described in 2014. TBRS is characterised by overgrowth, intellectual disability, facial dysmorphism, hypotonia and musculoskeletal features, as well as neurological and psychiatric features. Cardiac manifestations have also been reported, mainly congenital malformations such as atrial septal defect, ventricular septal defect and cardiac valvular disease. Aortic dilatation has rarely been described.

METHODS

Here we have undertaken a detailed clinical and molecular description of eight previously unreported individuals, who had TBRS and arterial dilatation and/or dissection, mainly thoracic aortic aneurysm (TAA). We have also reviewed the seven previously published cases of TAA in individuals with TBRS to try to better delineate the vascular phenotype and to determine specific follow-up for this condition.

RESULTS

We include eight new patients with TBRS who presented with arterial aneurysms mainly involving aorta. Three of these patients presented with dissection that required critical surgery.

CONCLUSIONS

Arterial aneurysms and dissections are a potentially lethal, age-dependent manifestation. The prevalence of aortic disease in individuals with TBRS is far in excess of that expected in the general population. This cohort, together with individuals previously published, illustrates the importance to consider dilatation/dissection, mainly in aorta but also in other arteries. Arterial vascular weakness may therefore also be a cardinal feature of TBRS and vascular surveillance is recommended.

Aortic Size Index Versus Aortic Diameter in the Prediction of Rupture in Women With Abdominal Aortic Aneurysm

Abdominal aortic aneurysms (AAAs) pose significant challenges in clinical management, particularly in female patients, whose unique anatomical and physiological characteristics influence rupture risk. While aortic diameter (AD) has traditionally been the primary metric for predicting rupture, its limitations, especially in women, have spurred exploration into alternative measures such as the aortic size index (ASI). This review examines the anatomy and physiology of AAAs in women, gender-specific challenges in diagnosis and management, and the comparative effectiveness of ASI versus AD in predicting rupture risk. ASI, calculated as AD divided by body surface area (BSA), offers a more nuanced assessment by adjusting for individual body size differences, potentially mitigating gender disparities in rupture rates. Comparative analyses indicate ASI's superiority in predicting adverse aortic events, particularly in women, thereby advocating for its integration into clinical practice to improve patient outcomes. Additionally, emerging techniques such as 3D volumetric measurements and biomechanical assessments show promise in enhancing rupture risk prediction, heralding a shift toward more personalized and effective management strategies for AAA patients.

17 β-Estradiol Impedes Aortic Root Dilation and Rupture in Male Marfan Mice

Marfan syndrome causes a hereditary form of thoracic aortic aneurysms with worse outcomes in male compared to female patients. In this study, we examine the effects of 17 β-estradiol on aortic dilation and rupture in a Marfan mouse model. Marfan male mice were administered 17 β-estradiol, and the growth in the aortic root, along with the risk of aortic rupture, was measured. Transcriptomic profiling was used to identify enriched pathways from 17 β-estradiol treatments. Aortic smooth muscle cells were then treated with cytokines to validate functional mechanisms. We show that 17 β-estradiol decreased the size and rate of aortic root dilation and improved survival from rupture. The Marfan transcriptome was enriched in inflammatory genes, and the addition of 17 β-estradiol modulated a set of genes that function through TNFα mediated NF-κB signaling. In addition, 17 β-estradiol suppressed the induction of these TNFα induced genes in aortic smooth muscle cells in vitro in an NF-κB dependent manner, and 17 β-estradiol decreased the formation of adventitial inflammatory foci in aortic roots in vivo. In conclusion, 17 β-estradiol protects against the dilation and rupture of aortic roots in Marfan male mice through the inhibition of TNFα-NF-κB signaling.

17 β-estradiol impedes aortic root dilation and rupture in male Marfan mice

Marfan syndrome causes a hereditary form of thoracic aortic aneurysms with dilation of the aortic root. Human and animal models suggest a worse phenotype for males compared to females with respect to aneurysm size and risk of dissection. In this study we examine the effects of 17 β-estradiol on aortic dilation and rupture in a Marfan mouse model. Marfan male mice were administered 17 β-estradiol and the growth in aortic root size along with the risk of aortic rupture or dissection with the addition of angiotensin II was measured. Transcriptomic profiling was used to identify enriched pathways from 17 β-estradiol treatment. Aortic smooth muscle cells were then treated with cytokines in order to validate the mechanism of 17 β-estradiol protection. We show that 17 β-estradiol decreased the size and rate of aortic root dilation and improved survival from rupture and dissection after treatment with angiotensin II. The Marfan transcriptome was enriched in inflammatory genes and the addition of 17 β-estradiol modulated a set of genes that function through TNFα mediated NF-κB signaling. These included many proteins known to play a role in the phenotypic shift of aortic smooth muscle cells from a contractile to a more inflammatory-like state such as Vcam-1, Mcp-1, Lgals3, Il-6, Il-1b, and C3. In addition, 17 β-estradiol suppressed the induction of these TNFα induced genes in aortic smooth muscle cells in vitro and this effect appears to be NF-κB dependent. In conclusion, 17 β-estradiol protects against the dilation and rupture of aortic roots in Marfan male mice through the inhibition of TNFα -NF-κB signaling and thus prevents the phenotypic switch of aortic smooth muscle cells from a contractile to an inflammatory state.

MicroRNA-19b-3p dysfunction of mesenchymal stem cell-derived exosomes from patients with abdominal aortic aneurysm impairs therapeutic efficacy

Senescence of vascular smooth muscle cells (VSMCs) contributes to the formation of abdominal aortic aneurysm (AAA). Although mesenchymal stem cell exosomes (MSC-EXO) have been confirmed to restrict the development of AAA, their biological activity depends largely on the physiological state of the MSCs. This study aimed to compare the effects of adipose-derived MSC-EXO from healthy donors (HMEXO) and AAA patients (AMEXO) on senescence of VSMCs in AAA and explore the underlying mechanisms. An ApoE-/- mouse model of AAA was used to investigate the therapeutic effects of HMEXO, AMEXO or miR-19b-3p-AMEXO on AAA development. This in vitro model of AAA was established by treating VSMCs with Ang II (Angiotensin II). The senescence of VSMCs was determined by senescence-associated β-galactosidase (SA-β-gal) staining. The morphology of mitochondria in VSMCs was examined by MitoTracker staining. HMEXO exhibited superior capacity compared with AMEXO to inhibit VSMC senescence and attenuate AAA formation in Ang II-treated ApoE-/- mice. In vitro, both AMEXO and HMEXO inhibited Ang II-induced VSMC senescence via downregulation of mitochondrial fission. Notably, compared with HMEXO, the ability of AMEXO to inhibit VSMC senescence was significantly decreased. miRNA sequencing and the expression of miR-19b-3p was significantly decreased in AMEXO compared with HMEXO. Luciferase assay suggested that MST4 (Mammalian sterile-20-like kinase 4) is a potential target of miR-19b-3p. Mechanistically, miR-19b-3p in HMEXO ameliorated VSMC senescence by inhibiting mitochondrial fission via regulation of the MST4/ERK/Drp1 signaling pathway. Overexpression of miR-19b-3p in AMEXO improved their beneficial effect on AAA formation. Our study reveals that MSC-exosomal miR-19b-3p exerts protective effects against Ang II-induced AAA and VSMC senescence via regulation of the MST4/ERK/Drp1 pathway. The pathological state of AAA patients alters the miRNA components of AMEXO and impairs their therapeutic benefits.

Low Progesterone and Low Estradiol Levels Associate With Abdominal Aortic Aneurysms in Men

CONTEXT

Male sex is a major risk factor for abdominal aortic aneurysms (AAA) but few studies have addressed associations between sex hormone levels and AAA.

OBJECTIVE

We aimed to describe the associations between serum sex steroids and early, screening-detected AAA in men.

METHODS

We validated a high-sensitivity liquid chromatography-tandem mass spectrometry assay for comprehensive serum sex hormone profiling. This assay was then employed in a case-control study including 147 men with AAA (infrarenal aorta ≥ 30 mm) and 251 AAA-free controls recruited at the general population-based ultrasound screening for AAA in 65-year-old Swedish men.

OUTCOMES INCLUDED

associations between dehydroepiandrosterone, progesterone, 17α-hydroxyprogesterone, androstenedione, estrone, testosterone, dihydrotestosterone, and estradiol and AAA presence.

RESULTS

Dehydroepiandrosterone, progesterone, 17α-hydroxyprogesterone, testosterone, and estradiol, but not the other hormones, were lower in men with AAA. In models with adjustments for known AAA risk factors and comorbidity, only progesterone (odds ratio per SD decrease 1.62 [95% CI, 1.18-2.22]) and estradiol (1.40 [95% CI, 1.04-1.87]) remained inversely associated with the presence of AAA. Progesterone and estradiol contributed with independent additive information for prediction of AAA presence; compared with men with high (above median) levels, men with low (below median) levels of both hormones had a 4-fold increased odds ratio for AAA (4.06 [95% CI, 2.25-7.31]).

CONCLUSION

Measured by a high-performance sex steroid assay, progesterone and estradiol are inversely associated with AAA in men, independent of known risk factors. Future studies should explore whether progesterone and estradiol, which are important reproductive hormones in women, are protective in human AAA.

Sex Differences in Inflammation During Venous Remodeling of Arteriovenous Fistulae

Vascular disorders frequently have differing clinical presentations among women and men. Sex differences exist in vascular access for hemodialysis; women have reduced rates of arteriovenous fistula (AVF) maturation as well as fistula utilization compared with men. Inflammation is increasingly implicated in both clinical studies and animal models as a potent mechanism driving AVF maturation, especially in vessel dilation and wall thickening, that allows venous remodeling to the fistula environment to support hemodialysis. Sex differences have long been recognized in arterial remodeling and diseases, with men having increased cardiovascular events compared with pre-menopausal women. Many of these arterial diseases are driven by inflammation that is similar to the inflammation during AVF maturation. Improved understanding of sex differences in inflammation during vascular remodeling may suggest sex-specific vascular therapies to improve AVF success.

Resveratrol Attenuates Aortic Dissection by Increasing Endothelial Barrier Function Through the SIRT1 Pathway

Aortic dissection (AD) is a serious condition and a health issue on a global scale. β-Aminopropionitrile–induced AD in mice is similar to the pathogenesis of AD in humans. Resveratrol (RSV) is a natural polyphenolic substance that provides anti-inflammatory and cardiovascular effects, but the role of RSV in AD is unclear. In this study, we investigated the effects and mechanisms of RSV on β-aminopropionitrile–induced AD in mice. Our results indicate that RSV can prevent the occurrence of AD. More meaningfully, we found that the protective effect comprises an increase in sirtuin 1 (SIRT1) expression in endothelial cells for the reconstruction of their structure, reducing the recruitment of inflammatory cells by endothelial cells and inhibiting the inflammation response, thereby suppressing the occurrence of AD.

Photobiomodulation and estrogen stabilize mitochondrial membrane potential in angiotensin-II challenged porcine aortic smooth muscle cells

Rupture of Abdominal aortic aneurysm (AAA) is among the 15 leading causes of death after age 65. Using high frequency ultrasound, we showed that photobiomodulation (PBM) prevents formation and progression of AAA in the angiotensin-II (Ang-II)-infused, apolipoprotein-e-deficient mouse model. In the current study we report that while challenge of porcine aortic Smooth Muscle Cells (SMCs) with Ang-II (1 μM) resulted in a marked decay in mitochondrial membrane potential (MitMP) vs non-challenged cells, treatment with PBM (continuous diode laser, 780 nm, 6.7 mW/cm² , 5 minutes, 2 J/cm² ) or pre-incubation with estrogen (50 nM, 1 hour) significantly attenuated this deterioration in MitMP. We also report that PBM and estrogen markedly affected porcine aortic SMC contraction and modified mitochondrial dispersion reflecting important influence on SMC function. These studies provide strong evidence of the important underlying role of mitochondria in the preventive effect of PBM on formation and progression of AAA and its reduced incidence and delayed onset in women.

Monosomy X in Female Mice Influences the Regional Formation and Augments the Severity of Angiotensin II-Induced Aortopathies

OBJECTIVE

Turner syndrome women (monosomy X) have high risk of aortopathies consistent with a role for sex chromosomes in disease development. We demonstrated that sex chromosomes influence regional development of Ang II (angiotensin II)-induced aortopathies in mice. In this study, we determined if the number of X chromosomes regulates regional development of Ang II-induced aortopathies. Approach and Results: We used females with varying numbers of X chromosomes (XX female mice [XXF] or XO female mice [XOF]) on an C57BL/6J (ascending aortopathies) or low-density lipoprotein receptor deficient (Ldlr-/-) background (descending and abdominal aortopathies) compared with XY males (XYM). To induce aortopathies, mice were infused with Ang II. XOF (C57BL/6J) exhibited larger percent increases in ascending aortic lumen diameters than Ang II-infused XXF or XYM. Ang II-infused XOF (Ldlr-/-) exhibited similar incidences of thoracic (XOF, 50%; XYM, 71%) and abdominal aortopathies (XOF, 83%; XYM, 71%) as XYM, which were greater than XXF (XXF, 0%). Abdominal aortic lumen diameters and maximal external diameters were similar between XOF and XYM but greater than XXF, and these effects persisted with extended Ang II infusions. Larger aortic lumen diameters, abdominal aortopathy incidence (XXF, 20%; XOF, 75%), and maximal aneurysm diameters (XXF, 1.02±0.17; XOF, 1.96±0.32 mm; P=0.027) persisted in ovariectomized Ang II-infused XOF mice. Data from RNA-seq demonstrated that X chromosome genes that escape X-inactivation (histone lysine demethylases Kdm5c and Kdm6a) exhibited lower mRNA abundance in aortas of XOF than XXF (P=0.033 and 0.024, respectively). Conversely, DNA methylation was higher in aortas of XOF than XXF (P=0.038).

CONCLUSIONS

The absence of a second X chromosome promotes diffuse Ang II-induced aortopathies in females.

A Novel Hypothesis: A Role for Follicle Stimulating Hormone in Abdominal Aortic Aneurysm Development in Postmenopausal Women

An abdominal aortic aneurysm (AAA) is a dilatation of the abdominal aorta, which can potentially be fatal due to exsanguination following rupture. Although AAA is less prevalent in women, women with AAA have a more severe AAA progression compared to men as reflected by enhanced aneurysm growth rates and a higher rupture risk. Women are diagnosed with AAA at an older age than men, and in line with increased osteoporosis and cardiovascular events, the delayed AAA onset has been attributed to the reduction of the protective effect of oestrogens during the menopausal transition. However, new insights have shown that a high follicle stimulating hormone (FSH) level during menopause may also play a key role in those diseases. In this report we hypothesize that FSH may aggravate AAA development and progression in postmenopausal women via a direct and/or indirect role, promoting aorta pathology. Since FSH receptors (FSHR) are reported on many other cell types than granulosa cells in the ovaries, it is feasible that FSH stimulation of FSHR-bearing cells such as aortic endothelial cells or inflammatory cells, could promote AAA formation directly. Indirectly, AAA progression may be influenced by an FSH-mediated increase in osteoporosis, which is associated with aortic calcification. Also, an FSH-mediated decrease in cholesterol uptake by the liver and an increase in cholesterol biosynthesis will increase the cholesterol level in the circulation, and subsequently promote aortic atherosclerosis and inflammation. Lastly, FSH-induced adipogenesis may lead to obesity-mediated dysfunction of the microvasculature of the aorta and/or modulation of the periaortic adipose tissue. Thus the long term increased plasma FSH levels during the menopausal transition may contribute to enhanced AAA disease in menopausal women and could be a potential novel target for treatment to lower AAA-related events in women.

A validated mouse model capable of recapitulating the protective effects of female sex hormones on ascending aortic aneurysms and dissections (AADs)

Fewer females develop AADs (ascending aortic aneurysms and dissections) and the reasons for this protection remain poorly understood. The present study seeks to develop a mouse model that may be utilized to address this sexual dimorphism. Adult normolipidemic mice were challenged with BAPN (β-aminopropionitrile), AngII (angiotensin II), or BAPN + AngII. An initial protocol optimization found that 0.2% BAPN in drinking water plus AngII-infusion at 1,000 ng kg-1  min-1 produced favorable rates of AAD rupture (~50%) and dilation (~40%) in 28 days. Using these dosages, further experiments revealed that BAPN is toxic to naïve mature aortas and it acted synergistically with AngII to promote aortic tears and dissections. BAPN + AngII provoked early infiltration of myeloid cells and subsequent recruitment of lymphoid cells to the aortic wall. AADs established with BAPN + AngII, but not AngII alone, continued to expand after the cessation of AngII-infusion. This indefinite growth precipitated a 61% increase in the AAD diameter in 56 days. More importantly, with the optimized protocol, significant differences in AAD dilation (p = .012) and medial degeneration (p = .036) were detected between male and female mice. Treatment of ovariectomized mice with estradiol protected AAD formation (p = .014). In summary, this study developed a powerful mouse AAD model that can be used to study the sexual dimorphism in AAD formation.

Androgens Accentuate TGF-β Dependent Erk/Smad Activation During Thoracic Aortic Aneurysm Formation in Marfan Syndrome Male Mice

Background Male patients with Marfan syndrome have a higher risk of aortic events and root dilatation compared with females. The role androgens play during Marfan syndrome aneurysm development in males remains unknown. We hypothesized that androgens potentiate transforming growth factor beta induced Erk (extracellular-signal-regulated kinase)/Smad activation, contributing to aneurysm progression in males. Methods and Results Aortic diameters in Fbn1C1039G/+ and littermate wild-type controls were measured at ages 6, 8, 12, and 16 weeks. Fbn1C1039G/+ males were treated with (1) flutamide (androgen receptor blocker) or (2) vehicle control from age 6 to 16 weeks and then euthanized. p-Erk1/2, p-Smad2, and matrix metalloproteinase (MMP) activity were measured in ascending/aortic root and descending aorta specimens. Fbn1C1039G/+ male and female ascending/aortic root-derived smooth muscle cells were utilized in vitro to measure Erk/Smad activation and MMP-2 activity following dihydrotestosterone, flutamide or transforming growth factor beta 1 treatment. Fbn1C1039G/+ males have increased aneurysm growth. p-Erk1/2 and p-Smad2 were elevated in ascending/aortic root specimens at age 16 weeks. Corresponding with enhanced Erk/Smad signaling, MMP-2 activity was higher in Fbn1C1039G/+ males. In vitro smooth muscle cell studies revealed that dihydrotestosterone potentiates transforming growth factor beta-induced Erk/Smad activation and MMP-2 activity, which is reversed by flutamide treatment. Finally, in vivo flutamide treatment reduced aneurysm growth via p-Erk1/2 and p-Smad2 reduction in Fbn1C1039G/+ males. Conclusions Fbn1C1039G/+ males have enhanced aneurysm growth compared with females associated with enhanced p-Erk1/2 and p-Smad2 activation. Mechanistically, in vitro smooth muscle cell studies suggested that dihydrotestosterone potentiates transforming growth factor beta induced Erk/Smad activation. As biological proof of concept, flutamide treatment attenuated aneurysm growth and p-Erk1/2 and p-Smad2 signaling in Fbn1C1039G/+ males.

Role of PAR1-Egr1 in the Initiation of Thoracic Aortic Aneurysm in Fbln4-Deficient Mice

Objective:

Remodeling of the extracellular matrix plays a vital role in cardiovascular diseases. Using a mouse model of postnatal ascending aortic aneurysms (termed Fbln4 SMKO ), we have reported that abnormal mechanosensing led to aneurysm formation in Fbln4 SMKO with an upregulation of the mechanosensitive transcription factor, Egr1 (Early growth response 1). However, the role of Egr1 and its upstream regulator(s) in the initiation of aneurysm development and their relationship to an aneurysmal microenvironment are unknown.

Approach and Results:

To investigate the contribution of Egr1 in the aneurysm development, we deleted Egr1 in Fbln4 SMKO mice and generated double knockout mice ( DKO , Fbln4 SMKO ; Egr1 −/− ). Aneurysms were prevented in DKO mice (42.8%) and Fbln4 SMKO ; Egr1 +/− mice (26%). Ingenuity Pathway Analysis identified PAR1 (protease-activated receptor 1) as a potential Egr1 upstream gene. Protein and transcript levels of PAR1 were highly increased in Fbln4 SMKO aortas at postnatal day 1 before aneurysm formed, together with active thrombin and MMP (matrix metalloproteinase)-9, both of which serve as a PAR1 activator. Concordantly, protein levels of PAR1, Egr1, and thrombin were significantly increased in human thoracic aortic aneurysms. In vitro cyclic stretch assays (1.0 Hz, 20% strain, 8 hours) using mouse primary vascular smooth muscle cells induced marked expression of PAR1 and secretion of prothrombin in response to mechanical stretch. Thrombin was sufficient to induce Egr1 expression in a PAR1-dependent manner.

Conclusions:

We propose that thrombin, MMP-9, and mechanical stimuli in the Fbln4 SMKO aorta activate PAR1, leading to the upregulation of Egr1 and initiation of ascending aortic aneurysms.

Nuclear receptors in abdominal aortic aneurysms

Abdominal aortic aneurysms (AAA) pose a considerable health burden and at present are only managed surgically since there is no proven pharmacotherapy that will retard their expansion or reduce the incidence of fatal rupture. This pathology shares several pathophysiological mechanisms with atherosclerosis, such as macrophage infiltration, inflammation, and degradation of extracellular matrix. Therefore, therapeutic targets proven effective in the treatment of atherosclerosis could also be considered for treatment of AAA. Different members of the nuclear receptor (NR) superfamily have been extensively studied as potential targets in the treatment of cardiovascular disease (CVD) and therefore might also be suited for AAA treatment. In this context, this review summarizes the role of different NRs in CVD, mostly atherosclerosis, and discusses in detail the current knowledge of their implications in AAA. From this overview it becomes apparent that NRs that were attributed a beneficial or adverse role in CVD have similar roles in AAA. Together, this overview provides compelling evidence to consider several NRs as attractive targets for future treatment of AAA.

AVE0991, a nonpeptide angiotensin-(1-7) mimic, inhibits angiotensin II-induced abdominal aortic aneurysm formation in apolipoprotein E knockout mice

AVE0991, a nonpeptide angiotensin-(1-7) mimic, has similar protective effects for cardiovascular system to Ang-(1-7). In this article, we aimed to explore the effects of AVE0991 and Ang-(1-7) on abdominal aortic aneurysm (AAA) induced by Ang II in apolipoprotein E knockout mice. The mice AAA model was established by Ang II infusion, and then mice received different treatment with saline, Ang II (1.44 mg/kg/day), different dose AVE0991 (0.58 or 1.16 μmol/kg/day), or Ang-(1-7) (400 ng/kg/min). The incidence of AAA was 76%, 48%, 28%, and 24% in the vehicle, the low-dose AVE0991, high-dose AVE0991, and the Ang-(1-7) group, respectively. In comparison with control group, AVE0991 and Ang-(1-7) treatment significantly increased smooth muscle cells and decreased macrophage accumulation, the expression levels of monocyte chemoattractant protein-1 (MCP-1) and tumor necrosis factor α (TNF-α), and the expression and activity of metalloproteinases 2 and 9 in mice AAA model or in human smooth muscle cells (hVSMCs). The therapeutic effects may be contributed to reduction of oxidative stress and downregulation of P38 and ERK1/2 signal pathways via Mas receptor activation, whereas the positive impacts were reversed by co-administration with the Mas antagonist A779 (400 ng/kg/min) and AVE0991 in Ang II-infused mice or in hVSMCs. Therefore, AVE0991 and Ang-(1-7) might be novel and promising interventions in the prevention and treatment of AAA. KEY MESSAGES: • AVE0991 dose-dependently inhibited Ang II-induced AAA formation in Apoe^-/- mice. • Ang-(1-7) played the same protective role as high-dose AVE0991. • Inhibition of Mas receptor with A779 could reverse the protective effect of AVE0991. • The therapeutic effects may be contributed to reduction of oxidative stress and downregulation of P38 and ERK1/2 signal pathways via Mas receptor activation.

Expansive Vascular Remodeling and Increased Vascular Calcification Response to Cholecalciferol in a Murine Model of Obesity and Insulin Resistance

Objective- We hypothesized that ob/ob mice develop expansive vascular remodeling associated with calcification. Approach and Results- We quantified and investigated mechanisms of vascular remodeling and vascular calcification in ob/ob mice after vitamin D₃(VD) stimulation or PBS (control), compared with C57BL/6 mice. Both ob/ob (OBVD [VD-treated ob/ob mice]) and C57BL/6 (C57VD [VD-treated C57BL/6 mice]) received 8×10³ IU/day of intraperitoneal VD for 14 days. Control ob/ob (OBCT [PBS-treated ob/ob mice]) and C57BL/6 (C57CT [PBS-treated C57BL/6 mice]) received intraperitoneal PBS for 14 days. Hypervitaminosis D increased the external and internal elastic length in aortae from OBVD, resulting in increased total vascular area and lumen vascular area, respectively, which characterizes expansive vascular remodeling. OBVD decreased the aortic wall thickness, resulting in hypotrophic vascular remodeling. We demonstrated increased collagen deposition, elastolysis, and calcification in aortae from OBVD. Our results showed a positive correlation between expansive vascular remodeling and vascular calcification in OBVD. We demonstrated increased serum calcium levels, augmented Bmp (bone morphogenetic protein)-2 and osteochondrogenic proteins expression in OBVD aortae. Furthermore, aortae from OBVD increased oxidative stress, coincidently with augmented in situ MMP (matrix metalloproteinase) activity and exhibited no VDR (VD receptor) inhibition after VD. Conclusions- Our data provide evidence that obese and insulin-resistant mice (ob/ob) developed expansive hypotrophic vascular remodeling correlated directly with increased vascular calcification after chronic VD stimulation. Positive hypotrophic vascular remodeling and vascular calcification in this mouse model is possibly mediated by the convergence of absence VDR downregulation after VD stimulation, increased reactive oxygen species generation, and MMP activation.

Pharmacologic Management of Aneurysms

Current management of aortic aneurysms relies exclusively on prophylactic operative repair of larger aneurysms. Great potential exists for successful medical therapy that halts or reduces aneurysm progression and hence alleviates or postpones the need for surgical repair. Preclinical studies in the context of abdominal aortic aneurysm identified hundreds of candidate strategies for stabilization, and data from preoperative clinical intervention studies show that interventions in the pathways of the activated inflammatory and proteolytic cascades in enlarging abdominal aortic aneurysm are feasible. Similarly, the concept of pharmaceutical aorta stabilization in Marfan syndrome is supported by a wealth of promising studies in the murine models of Marfan syndrome-related aortapathy. Although some clinical studies report successful medical stabilization of growing aortic aneurysms and aortic root stabilization in Marfan syndrome, these claims are not consistently confirmed in larger and controlled studies. Consequently, no medical therapy can be recommended for the stabilization of aortic aneurysms. The discrepancy between preclinical successes and clinical trial failures implies shortcomings in the available models of aneurysm disease and perhaps incomplete understanding of the pathological processes involved in later stages of aortic aneurysm progression. Preclinical models more reflective of human pathophysiology, identification of biomarkers to predict severity of disease progression, and improved design of clinical trials may more rapidly advance the opportunities in this important field.

Sex differences in abdominal aortic aneurysms

Abdominal aortic aneurysm (AAA) is a vascular disorder with a high case fatality rate in the instance of rupture. AAA is a multifactorial disease, and the etiology is still not fully understood. AAA is more likely to occur in men, but women have a greater risk of rupture and worse prognosis. Women are reportedly protected against AAA possibly by premenopausal levels of estrogen and are, on average, diagnosed at older ages than men. Here, we review the present body of research on AAA pathophysiology in humans, animal models, and cultured cells, with an emphasis on sex differences and sex steroid hormone signaling.

Sex, pregnancy and aortic disease in Marfan syndrome

Background

Sex-related differences as well as the adverse effect of pregnancy on aortic disease outcome are well-established phenomena in humans with Marfan syndrome (MFS). The underlying mechanisms of these observations are largely unknown.

Objectives

In an initial (pilot) step we aimed to confirm the differences between male and female MFS patients as well as between females with and without previous pregnancy. We then sought to evaluate whether these findings are recapitulated in a pre-clinical model and performed in-depth cardiovascular phenotyping of mutant male and both nulliparous and multiparous female Marfan mice. The effect of 17β-estradiol on fibrillin-1 protein synthesis was compared in vitro using human aortic smooth muscle cells and fibroblasts.

Results

Our small retrospective study of aortic dimensions in a cohort of 10 men and 20 women with MFS (10 pregnant and 10 non-pregnant) confirmed that aortic root growth was significantly increased in the pregnant group compared to the non-pregnant group (0.64mm/year vs. 0.12mm/year, p = 0.018). Male MFS patients had significantly larger aortic root diameters compared to the non-pregnant and pregnant females at baseline and follow-up (p = 0.002 and p = 0.007, respectively), but no significant increase in aortic root growth was observed compared to the females after follow-up (p = 0.559 and p = 0.352). In the GT-8/+ MFS mouse model, multiparous female Marfan mice showed increased aortic diameters when compared to nulliparous females. Aortic dilatation in multiparous females was comparable to Marfan male mice. Moreover, increased aortic diameters were associated with more severe fragmentation of the elastic lamellae. In addition, 17β-estradiol was found to promote fibrillin-1 production by human aortic smooth muscle cells.

Conclusions

Pregnancy-related changes influence aortic disease severity in otherwise protected female MFS mice and patients. There may be a role for estrogen in the female sex protective effect.

Associations of estradiol levels and genetic polymorphisms of inflammatory genes with the risk of ischemic stroke

Background

Estrogen plays an important role as an anti-inflammatory and neuroprotective agent in ischemic stroke. In this study, we analyzed the effect of a polygenic risk score (PRS) constructed using inflammatory genes and estradiol levels on the risk of ischemic stroke.

Methods

This case-control study was conducted with 624 ischemic stroke patients and 624 age- and gender-matched controls. The PRS estimated the polygenic contribution of inflammatory genes from ischemic stroke susceptibility loci. Estradiol levels were measured using a radioimmunoassay. High and low estradiol levels were defined according to the log-transformed median estradiol levels in female and male controls.

Results

Subjects in the fourth quartile of the PRS had a significant 1.57-fold risk of ischemic stroke (95% confidence interval [CI], 1.12 ~ 2.19), after adjusting for covariates compared to individuals in the lowest quartile. Compared to individuals with high estradiol levels and a low PRS as the reference group, those exposed to low estradiol levels and a high PRS had an increased risk of ischemic stroke (odds ratio, 3.35; 95% CI, 1.79 ~ 6.28). Similar results were also observed in males when the analysis was stratified by gender.

Conclusions

Our data suggest that the PRS can be useful in evaluating a high risk of ischemic stroke among patients, especially those exposed to low estradiol levels.

Sex Hormones and Sex Chromosomes Cause Sex Differences in the Development of Cardiovascular Diseases

This review summarizes recent evidence concerning hormonal and sex chromosome effects in obesity, atherosclerosis, aneurysms, ischemia/reperfusion injury, and hypertension. Cardiovascular diseases occur and progress differently in the 2 sexes, because biological factors differing between the sexes have sex-specific protective and harmful effects. By comparing the 2 sexes directly, and breaking down sex into its component parts, one can discover sex-biasing protective mechanisms that might be targeted in the clinic. Gonadal hormones, especially estrogens and androgens, have long been found to account for some sex differences in cardiovascular diseases, and molecular mechanisms mediating these effects have recently been elucidated. More recently, the inherent sexual inequalities in effects of sex chromosome genes have also been implicated as contributors in animal models of cardiovascular diseases, especially a deleterious effect of the second X chromosome found in females but not in males. Hormonal and sex chromosome mechanisms interact in the sex-specific control of certain diseases, sometimes by opposing the action of the other.

Differential expression of sex hormone receptors in abdominal aortic aneurysms

OBJECTIVE

Male sex is a significant risk factor for abdominal aortic aneurysm (AAA). Female sex hormones have been reported to prevent aneurysm formation in animal models. The study aims to describe the expression profile of sex hormone receptors in the aneurysm wall of men and women with AAA and compare with unaffected controls.

METHODS

Aneurysm wall biopsies were obtained during elective open repair of AAA in men and women (n=16+16). Aortic vessel wall from controls were obtained at organ donation (n=6). Western blot-, mRNA expression- and immunohistochemical analyses were performed to assess the expression profile of the sex hormone receptors - androgen receptor (AR), progesterone receptor (PR), estrogen receptor α (ERα) and β (ERβ).

RESULTS

The mRNA- and protein expression levels of AR were higher in AAA compared with control aorta (7.26 vs. 5.14, P=0.001). mRNA- and protein expression levels of ERβ were lower in AAA compared with control aorta (9.15 vs. 12.29, P<0.001). mRNA expression levels of PR were higher in AAA compared with control aorta (8.73 vs. 6.21, P=0.003), but could not be confirmed on protein level. The expression profile of sex hormone receptors in men and women with AAA was similar.

CONCLUSION

Expression of sex hormone receptors differs in the aneurysmal aorta compared with unaffected aorta in men and women. A higher expression of AR and a lower expression of ERβ suggest that sex hormone activity could be associated with aneurysm development.

Abdominal aortic aneurysms and diabetes mellitus

There is accumulating evidence that risk profiles differ between coronary artery disease and abdominal aortic aneurysms (AAAs). However, diabetes mellitus (DM) appears to be negatively associated with AAA formation. The underlying mechanisms for this negative relationship are far from defined, but may include: increased arterial wall matrix formation via advanced glycation end products; suppression of plasmin and reduction of levels and activity of matrix metalloproteinases (MMP)-2 and 9; diminished aortic wall macrophage infiltration, elastolysis and neovascularization. In addition, the effect of pharmacological agents used for the treatment of patients with DM on AAA formation has been studied with rather controversial results. Statins, angiotensin converting enzyme inhibitors, angiotensin receptor blockers, fenofibrate, antibiotics and some hypoglycemic agents are beginning to be appreciated for a potential modest protection from AAAs, but further studies are needed.

Platelet Inhibitors Reduce Rupture in a Mouse Model of Established Abdominal Aortic Aneurysm

OBJECTIVE

Rupture of abdominal aortic aneurysms causes a high morbidity and mortality in the elderly population. Platelet-rich thrombi form on the surface of aneurysms and may contribute to disease progression. In this study, we used a pharmacological approach to examine a role of platelets in established aneurysms induced by angiotensin II infusion into hypercholesterolemic mice.

APPROACH AND RESULTS

Administration of the platelet inhibitors aspirin or clopidogrel bisulfate to established abdominal aortic aneurysms dramatically reduced rupture. These platelet inhibitors reduced abdominal aortic platelet and macrophage recruitment resulting in decreased active matrix metalloproteinase-2 and matrix metalloproteinase-9. Platelet inhibitors also resulted in reduced plasma concentrations of platelet factor 4, cytokines, and components of the plasminogen activation system in mice. To determine the validity of these findings in human subjects, a cohort of aneurysm patients were retrospectively analyzed using developed and validated algorithms in the electronic medical record database at Vanderbilt University. Similar to mice, administration of aspirin or P2Y12 inhibitors was associated with reduced death among patients with abdominal aortic aneurysm.

CONCLUSIONS

These results suggest that platelets contribute to abdominal aortic aneurysm progression and rupture.

Exogenous 17-β estradiol administration blunts progression of established angiotensin II-induced abdominal aortic aneurysms in female ovariectomized mice

Background

Abdominal aortic aneurysms (AAAs) occur predominately in males. However, AAAs in females have rapid growth rates and rupture at smaller sizes. Mechanisms contributing to AAA progression in females are undefined. We defined effects of ovariectomy, with and without 17-β estradiol (E2), on progression of established angiotensin II (AngII)-induced AAAs in female mice.

Methods

We used neonatal testosterone exposures at 1 day of age to promote susceptibility to AngII-induced AAAs in adult female Ldlr^−/− mice. Females were infused with AngII for 28 days to induce AAAs, and then stratified into groups that were sham, ovariectomized (Ovx, vehicle), or Ovx with E2 administration for 2 months of continued AngII infusions. Aortic lumen diameters were quantified by ultrasound and analyzed by linear mixed model, and maximal AAA diameters were analyzed by one-way ANOVA. Atherosclerosis was quantified en face in the aortic arch. AAA tissue sections were analyzed for cellular composition. We quantified effects of E2 on abdominal aortic smooth muscle cell (SMC) growth, α-actin and transforming growth factor-beta (TGF-β) production, and wound healing.

Results

Serum E2 concentrations were increased significantly by E2. Aortic lumen diameters increased over time in sham-operated and Ovx (vehicle) females, but not in Ovx females administered E2. At day 70, E2 administration decreased significantly aortic lumen diameters compared to Ovx vehicle and sham-operated females. Compared to Ovx females (vehicle), maximal AAA diameters were reduced significantly by E2. AAA tissue sections from Ovx females administered E2 exhibited significant increases in α-actin and decreases in neutrophils compared to Ovx females administered vehicle. In abdominal aortic SMCs, E2 resulted in a concentration-dependent increase in α-actin, elevated TGF-β, and more rapid wound healing. E2 administration to Ovx females also significantly reduced atherosclerotic lesions compared to sham-operated females. This effect was accompanied by significant reductions in serum cholesterol concentrations.

Conclusions

E2 administration to Ovx females abolished progressive growth and decreased severity of AngII-induced AAAs. These effects were accompanied by increased SMC α-actin, elevated TGF-β, and reduced neutrophils. Similarly, E2 administration reduced AngII-induced atherosclerosis. These results suggest that loss of E2 in post-menopausal females may contribute to progressive growth of AAAs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-015-0030-1) contains supplementary material, which is available to authorized users.

Hypertension overrides the protective effect of female hormones on the development of aortic aneurysm secondary to Alk5 deficiency via ERK activation

The prevalence of aortic aneurysm is five times higher in men than women among the general population. Similar sexual dimorphism also exists in syndromic aortic aneurysms triggered by TGF-β signaling disorders. To understand the responsible mechanisms, we developed an animal model where inducible deletion of the type I TGF-β receptor, Alk5, specifically in smooth muscle cells (Alk5iko) causes spontaneous aortic aneurysm formation. This model recapitulated an extreme scenario of the dimorphism in aortic aneurysm development between genders. In a comparative experiment, all Alk5iko males (n=42) developed aortic aneurysms and 26% of them died prematurely from aortic rupture. In contrast, the Alk5iko females (n=14) presented only a subclinical phenotype characteristic of scarcely scattered elastin breaks. Removal of male hormones via orchiectomy (n=7) resulted in only minimal influence on aortic pathology. However, reduction of female hormones via ovariectomy (n=15) increased the phenotypic penetrance from zero to 53%. Finally, an elevation of systolic blood pressure by 30 points unmasked the subclinical phenotype of Alk5iko females (n=17) to 59%. This exaggerated phenotypic penetrance was coupled with an early intensification of ERK signaling, a molecular signature that correlated to 100% phenotypic penetrance in normotensive Alk5iko males. In conclusion, aortic aneurysm induced by Alk5iko exhibits dimorphic incidence between genders with females less susceptible to aortic disease. This sexual dimorphism is partially the result from the protective effects of female hormones. Hypertension, a known risk factor for aortic aneurysm, is able to break the female sex protective effects through mechanisms associated with enhanced ERK activity.

Regulatory T cells prevent angiotensin II-induced abdominal aortic aneurysm in apolipoprotein E knockout mice

To test the hypothesis that adoptive transfer of regulatory T cells (Tregs) may dose-dependently inhibit the formation of angiotensin II-induced abdominal aortic aneurysm in apolipoprotein E knockout mice, we established an animal model of abdominal aortic aneurysm by angiotensin II infusion in apolipoprotein E knockout mice. Then mice received different treatment with PBS, low-dose Tregs, high-dose Tregs, or CD25-depleting PC61 antibody. Histopathologic analysis showed that the incidence of abdominal aortic aneurysm was 80%, 76%, 27%, and 71% in the PBS, low-dose Tregs, high-dose Tregs, and PC61 groups, respectively. Tregs treatment markedly decreased macrophage and CD4+ T-cell infiltration and preserved the medial smooth muscle cells. Furthermore, Tregs decreased the levels of proinflammatory cytokines, matrix metalloproteinase-2 (MMP-2) and MMP-9, increased the expression of anti-inflammatory interleukin-10 and transforming growth factor-β, and suppressed apoptosis and oxidative stress. In vitro, Tregs inhibited the response of human aortic smooth muscle cells to angiotensin II and reduced the expression of proinflammatory cytokines, MMP-2 and MMP-9, possibly by inhibiting the activation of nuclear factor-κB and extracellular signal-regulate kinase 1/2. In addition, Tregs downregulated macrophage type 1-related genes and upregulated macrophage type 2-related genes. However, Tregs-mediated effects were largely reversed by disrupting cell-cell contact or using neutralizing antibodies against interleukin-10 and transforming growth factor-β. Adoptive transfer of Tregs dose-dependently prevents angiotensin II-induced abdominal aortic aneurysm in apolipoprotein E knockout mice. The mechanisms may involve declined proinflammatory cytokine expression and MMP-2 and MMP-9 levels and enhanced anti-inflammatory cytokine expression, which is mediated by direct cell-cell contact and soluble mediators.

Aromatase is required for female abdominal aortic aneurysm protection

OBJECTIVE

The protective effects of female gender on the development of abdominal aortic aneurysms (AAAs) have been attributed to anti-inflammatory effects of estrogen. Estrogen synthesis is dependent on the enzyme aromatase, which is located both centrally in the ovaries and peripherally in adipose tissue, bone, and vascular smooth muscle cells. It is hypothesized that deletion of aromatase in both ovarian and peripheral tissues would diminish the protective effect of female gender and would be associated with increased aortic diameter in female mice.

METHODS

Male and female 8- to 10-week-old mice with aromatase (wild type: WT) and without aromatase (ArKO) underwent elastase aortic perfusion with aortic harvest 14 days following. For the contribution of central and peripheral estrogen conversion to be evaluated, female WT mice were compared with female WT and ArKO mice that had undergone ovariectomy (ovx) at 6 weeks followed by elastase perfusion at 8 to 10 weeks. At aortic harvest, maximal aortic dilation was measured and samples were collected for immunohistochemistry and protein analysis. Serum was collected for serum estradiol concentrations. Groups were compared with analysis of variance. Human and mouse AAA cross sections were analyzed with confocal immunohistochemistry for aromatase, smooth muscle markers, and macrophage markers.

RESULTS

Female WT mice had significant reduction in aortic dilation compared with male WT mice (F WT, 51.5% ± 15.1% vs M WT, 78.7% ± 14.9%; P < .005). The protective effects of female gender were completely eliminated with deletion of aromatase (F ArKO, 82.6% ± 13.8%; P < .05 vs F WT). Ovariectomy increased aortic dilation in WT mice (F WT ovx, 70.6% ± 11.7%; P < .05 vs F WT). Aromatase deletion with ovariectomy further increased aortic dilation compared with WT ovx mice (F ArKO ovx, 87.3% ± 14.7%, P < .001 vs F WT and P < .05 vs F WT ovx). Accordingly, female ArKO ovx mice had significantly higher levels of the proinflammatory cytokines monocyte chemoattractant protein 1 and interleukin-1β and were associated with increased macrophage staining and decreased elastin staining. Regarding serum hormone levels, decreasing estradiol levels correlated with increasing aortic diameter (R = -0.565; P < .01). By confocal immunohistochemistry, both human and mouse AAA smooth muscle cells (smooth muscle α-actin positive) and macrophages (CD68 positive or Mac-2 positive) expressed aromatase.

CONCLUSIONS

The protective effect of female gender on AAAs is due to estrogen synthesis and requires the presence of both ovarian and extragonadal/peripheral aromatase. Peripheral estrogen synthesis accounts for roughly half of the protective effect of female gender. If peripheral aromatase could be targeted, high levels of local estrogen could be produced and may avoid the side effects of systemic estrogen.

Neurofibromin-deficient myeloid cells are critical mediators of aneurysm formation in vivo

BACKGROUND

Neurofibromatosis type 1 (NF1) is a genetic disorder resulting from mutations in the NF1 tumor suppressor gene. Neurofibromin, the protein product of NF1, functions as a negative regulator of Ras activity in circulating hematopoietic and vascular wall cells, which are critical for maintaining vessel wall homeostasis. NF1 patients have evidence of chronic inflammation resulting in the development of premature cardiovascular disease, including arterial aneurysms, which may manifest as sudden death. However, the molecular pathogenesis of NF1 aneurysm formation is unknown.

METHOD AND RESULTS

With the use of an angiotensin II-induced aneurysm model, we demonstrate that heterozygous inactivation of Nf1 (Nf1(+/-)) enhanced aneurysm formation with myeloid cell infiltration and increased oxidative stress in the vessel wall. Using lineage-restricted transgenic mice, we show that loss of a single Nf1 allele in myeloid cells is sufficient to recapitulate the Nf1(+/-) aneurysm phenotype in vivo. Finally, oral administration of simvastatin or the antioxidant apocynin reduced aneurysm formation in Nf1(+/-) mice.

CONCLUSION

These data provide genetic and pharmacological evidence that Nf1(+/-) myeloid cells are the cellular triggers for aneurysm formation in a novel model of NF1 vasculopathy and provide a potential therapeutic target.

Dietary phytoestrogens inhibit experimental aneurysm formation in male mice

BACKGROUND

The purpose of these experiments was to test the hypothesis that dietary phytoestrogens would diminish experimental aortic aneurysm formation.

MATERIALS AND METHODS

Six-wk-old C57BL/6 mice were divided into groups, fed either a diet with minimal phytoestrogen content or a regular commercial rodent diet with high phytoestrogen content for 2 wk. At the age of 8 wk, aortic aneurysms were induced by infusing the isolated infrarenal abdominal aorta with 0.4% elastase for 5 min. Mice were recovered and the diameter of the infused aorta was measured at postoperative days 3, 7, and 14. Abdominal aorta samples were collected for histology, cytokine array, and gelatin zymography after aortic diameter measurement. Blood samples were also collected to determine serum phytoestrogens and estradiol levels. Multiple-group comparisons were done using an analysis of variance with post hoc Tukey tests.

RESULTS

Compared with mice on a minimal phytoestrogen diet, mice on a regular rodent diet had higher levels of serum phytoestrogens (male, 1138 ± 846 ng/dL; female, 310 ± 295 ng/dL). These serum phytoestrogen levels were also much higher than their own endogenous estradiol levels (109-fold higher for males and 35.5-fold higher for females). Although aortic diameters of female mice were unaffected by the phytoestrogen concentration in the diets, male mice on the regular rodent diet (M+ group) developed smaller aortic aneurysms than male mice on the minimal phytoestrogen diet (M- group) on postoperative day 14 (M+ 54.8 ± 8.8% versus M- 109.3 ± 37.6%; P < 0.001). During aneurysm development (postoperative days 3 and 7), there were fewer neutrophils, macrophages, and lymphocytes in the aorta from the M+ group than from the M- group. Concentrations of multiple proinflammatory cytokines (matrix metalloproteinases [MMPs]; interleukin 1β [IL-1β]; IL-6; IL-17; IL-23; monocyte chemoattractant protein-1; regulated on activation, normal T cell expressed and secreted; interferon γ; and tumor necrosis factor α) from aortas of the M+ group were also lower than those from the aortas of the M- group. Zymography also demonstrated that the M+ group had lower levels of aortic MMP-9s than the M- group on postoperative day 14 (P < 0.001 for pro-MMP-9, P < 0.001 for active MMP-9).

CONCLUSIONS

These results suggest that dietary phytoestrogens inhibit experimental aortic aneurysm formation in male mice via a reduction of the inflammatory response in the aorta wall. The protective effect of dietary phytoestrogens on aneurysm formation warrants further investigation.

Novel mechanisms of abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) are a common but asymptomatic disease that has high susceptibility to rupture. Current therapeutic options are limited to surgical procedures because no pharmacological approaches have been proven to decrease either expansion or rupture of human AAAs. The current dearth of effective medical treatment is attributed to insufficient understanding of the mechanisms underlying the initiation, propagation and rupture of AAAs. This review will emphasize recent advances in mechanistic studies that may provide insights into potential pharmacological treatments for this disease. While we primarily focus on recent salient findings, we also discuss mechanisms that continue to be controversial depending on models under study. Despite the progress on exploring mechanisms of experimental AAAs, ultimate validation of mechanisms will require completion of prospective double-blinded clinical trials. In addition, we advocate increased emphasis of collaborative studies using animal models and human tissues for determination of mechanisms that explore expansion and rupture of existing AAAs.

Can pharmacologic agents slow abdominal aortic aneurysm growth?

Multiple medical therapies have been proposed to prevent abdominal aortic aneurysm expansion. Use of these medications, hormones, vitamins, and dietary products is based on their ability to alter the pathophysiology of continued aortic wall growth. In this review, the explanation of how these medications can achieve suppression of abdominal aortic aneurysm is explained in relation to their effect on the various aspects of aortic wall inflammation. Despite the large number of animal and observational studies, there remain very few randomized clinical trials to support use of any of these agents. However, there may be sufficient evidence to suggest that statins, doxycycline, vitamin E, cyclooxygenase-2 inhibitors, angiotensin-converting enzyme inhibitors, and angiotensin II receptor blockers can prove beneficial in some individuals.

Recent advances in pharmacotherapy development for abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a common disease causing segmental expansion and rupture of the aorta with a high mortality rate. The lack of nonsurgical treatment represents a large and unmet need in terms of pharmacotherapy. Advances in AAA research revealed that activation of inflammatory signaling pathways through proinflammatory mediators shifts the balance of extracellular matrix (ECM) metabolism toward tissue degradation. This idea is supported by experimental evidence in animal models that pharmacologic intervention at each pathological step can prevent AAA development. Previously, we identified c-Jun N-terminal kinase (JNK), a pro-inflammatory signaling molecule, as a therapeutic target for AAA. Abnormal activation of JNK in AAA tissue regulates multiple pathological processes in a coordinated manner. Pharmacologic inhibition of JNK tips the ECM balance back towards repair rather than degradation. Interventions targeting signaling molecules such as JNK in order to manipulate multiple pathological processes may be an ideal therapeutic strategy for AAA. Furthermore, the development of biomarkers as well as appropriate drug delivery systems is essential to produce clinically practical pharmacotherapy for AAA.

Fenofibrate increases high-density lipoprotein and sphingosine 1 phosphate concentrations limiting abdominal aortic aneurysm progression in a mouse model

There are currently no acceptable treatments to limit progression of abdominal aortic aneurysm (AAA). Increased serum concentrations of high-density lipoprotein (HDL) are associated with reduced risk of developing an AAA. The present study aimed to assess the effects of fenofibrate on aortic dilatation in a mouse model of AAA. Male low-density lipoprotein receptor-deficient (Ldlr(-/-)) mice were maintained on a high-fat diet for 3 weeks followed by 6 weeks of oral administration of vehicle or fenofibrate. From 14 to 18 weeks of age, all mice were infused with angiotensin II (AngII). At 18 weeks of age, blood and aortas were collected for assessment of serum lipoproteins, aortic pathology, aortic Akt1 and endothelial nitric oxide synthase (eNOS) activities, immune cell infiltration, eNOS and inducible NOS (iNOS) expression, sphingosine 1 phosphate (S1P) receptor status, and apoptosis. Mice receiving fenofibrate had reduced suprarenal aortic diameter, reduced aortic arch Sudan IV staining, higher serum HDL levels, increased serum S1P concentrations, and increased aortic Akt1 and eNOS activities compared with control mice. Macrophages, T lymphocytes, and apoptotic cells were less evident and eNOS, iNOS, and S1P receptors 1 and 3 were up-regulated in aortas from mice receiving fenofibrate. The present findings suggest that fenofibrate antagonizes AngII-induced AAA and atherosclerosis by up-regulating serum HDL and S1P levels, with associated activation of NO-producing enzymes and reduction of aortic inflammation.

Estrogens and atherosclerosis: insights from animal models and cell systems

Estrogens not only play a pivotal role in sexual development but are also involved in several physiological processes in various tissues including vasculature. While several epidemiological studies documented an inverse relationship between plasma estrogen levels and the incidence of cardiovascular disease and related it to the inhibition of atherosclerosis, an interventional trial showed an increase in cardiovascular events among postmenopausal women on estrogen treatment. The development of atherosclerotic lesions involves complex interplay between various pro- or anti-atherogenic processes that can be effectively studied only in vivo in appropriate animal models. With the advent of genetic engineering, transgenic mouse models of atherosclerosis have supplemented classical dietary cholesterol-induced disease models such as the cholesterol-fed rabbit. In the last two decades, these models were widely applied along with in vitro cell systems to specifically investigate the influence of estrogens on the development of early and advanced atherosclerotic lesions. The present review summarizes the results of these studies and assesses their contribution toward better understanding of molecular mechanisms underlying anti- and/or pro-atherogenic effects of estrogens in humans.

Chinese red yeast rice attenuates the development of angiotensin II-induced abdominal aortic aneurysm and atherosclerosis

OBJECTIVE

Abdominal aortic aneurysm (AAA) is a chronic vascular disease characterized by medial degradation and inflammation. No medical approaches have been validated for treating AAA, and therapeutic options are limited to regular surveillance leading to surgical intervention. This study aimed to investigate whether administration of Chinese red yeast rice (Monascus purpureus; RYR) suppressed angiotensin II (AngII)-induced AAA and atherosclerosis.

METHODS AND RESULTS

Apolipoprotein E-deficient male mice fed a normal diet were administered either RYR extract (200 mg/kg/day) or vehicle by gavage for 1 week before initiating AngII infusion (1000 ng/kg/min) via subcutaneous osmotic pumps for 28 days. Red yeast rice extract administration significantly suppressed AngII-induced expansion of suprarenal diameter and area (P<.05). Furthermore, RYR extract significantly reduced atherosclerotic lesion areas in both the intima of aortic arches and cross sections of aortic roots (P<.05). These effects were associated with reductions of serum total cholesterol, intercellular adhesion molecule 1, vascular cell adhesion molecule 1, matrix metalloproteinase (MMP) 2 and increases of serum macrophage migration inhibitory factor, but no changes in serum interleukin (IL) 1α, IL-6, monocyte chemoattractant protein 1, MMP-9 and expression of MMP-2 and MMP-9 in aortic walls.

CONCLUSIONS

This study demonstrated that RYR extract administration suppressed AngII-induced AAA and atherosclerosis associated with regulating inflammation responses independent of lipid-lowering effects. Red yeast rice may have preventive potential for patients with AAA.

Efficacy of simvastatin in reducing aortic dilatation in mouse models of abdominal aortic aneurysm

PURPOSE

Currently there is no effective drug therapy for abdominal aortic aneurysm (AAA). The aim of this study was to assess the ability of simvastatin to inhibit aortic dilatation in two mouse models.

METHODS

AAAs were induced in two mice strains predisposed to atherosclerosis. Firstly, 11 weeks old male apolipoprotein E deficient (ApoE(-/-)) mice were given vehicle control (n = 27) or simvastatin (50 mg/kg/d, n = 27) prior to being infused with angiotensin II (1 μg/kg/min) subcutaneously for 4 weeks. Secondly, 9 weeks old male low-density lipoprotein receptor deficient (LDLR(-/-)) mice were fed a high fat diet, then given vehicle control (n = 17) or simvastatin (50 mg/kg/d, n = 18) and from 14 to 18 weeks of age infused with angiotensin II. Subsequently aortas were harvested, maximum suprarenal aortic diameter measured, aortic arch atheroma assessed by sudan IV staining and blood extracted to measure serum lipids. In the LDLR(-/-) mice the suprarenal aortic diameter was also measured by ultrasound prior to aortic harvesting.

RESULTS

In ApoE(-/-) mice suprarenal aortic diameters were modestly smaller in animals receiving simvastatin without significant change despite reduction in macrophage infiltration. Aortic arch atheroma was substantially reduced in LDLR(-/-) mice receiving simvastatin with borderline significant reduction in suprarenal aortic diameters. Simvastatin did not favourably modify serum lipids in either mouse model.

CONCLUSIONS

In this study involving two mouse models of AAA, simvastatin had limited efficacy in restricting aortic dilatation but substantial ability to reduce atheroma progression.

Experimental models of abdominal aortic aneurysms

Despite being a leading cause of death in the West, the pathophysiology of abdominal aortic aneurysms (AAA) is still incompletely understood. Pharmacotherapy to reduce the growth of small AAAs is limited and techniques for repairing aneurysms continue to evolve. Experimental models play a key role in AAA research, as they allow a detailed evaluation of the pathogenesis of disease progression. This review focuses on in vivo experimental models, which have improved our understanding of the potential mechanisms of AAA development and contributed to the advancement of new treatments.

Soluble epoxide hydrolase in atherosclerosis

Like many eicosanoids, epoxyeicosatrienoic acids (EETs) have multiple biological functions, including reduction of blood pressure, inflammation, and atherosclerosis in multiple species. Hydration of EETs by the soluble epoxide hydrolase (sEH) is the major route of their degradation to the less bioactive diols. Inhibition of the sEH stabilizes EETs, thus, enhancing the beneficial effects of EETs. Human data show an association of sEH (Ephx2) gene polymorphisms with increased risk of atherosclerosis and cardiovascular diseases. These data suggest a potential therapeutic effect of sEH inhibitors (sEHI) in the treatment of atherosclerosis. Indeed, two laboratories reported independently that using different sEHIs in apolipoprotein E-deficient mice significantly attenuated atherosclerosis development and aneurysm formation. The antiatherosclerotic effects of sEHI are correlated with elevation in EET levels and associated with reduction of low-density lipoprotein and elevation of high-density lipoprotein cholesterols, as well as attenuation of expression of proinflammatory genes and proteins. In addition, the antihypertensive effects and improvement of endothelial function also contribute to the mechanism of the antiatherosclerotic effects of sEHI. The broad spectrum of biological action of EETs and sEHIs with multiple biological beneficial actions provides a promising new class of therapeutics for atherosclerosis and other cardiovascular diseases.

Loss of STAT1 is associated with increased aortic rupture in an experimental model of aortic dissection and aneurysm formation

BACKGROUND

Transcription factor signal transducer and activator of transcription (STAT) 1 has been linked to a variety of pathologic states involved with matrix remodeling, but its role in aortic pathology has not been previously described. The current study hypothesized that STAT1 regulates aneurysmal degeneration and its role was evaluated in human abdominal aortic aneurysm (AAA) and in a mouse model of aortic dissection.

METHODS

Apolipoprotein E knockout mice (ApoE-/-) or ApoE/STAT1 double knockout mice (ApoE/STAT1-/-) were infused with 1000 ng/kg/min of angiotensin II. Systolic blood pressure (SBP) was measured in the rodent tail. At sacrifice, aortic diameters and extent of aneurysm formation were measured by digital microscopy. STAT1 and phosphorylated-STAT1 protein levels were assessed in ApoE-/- mice at 0, 7, 14, and 28 days (n = 8/time point) by enzyme-linked immunosorbent assay. Histology was performed using hematoxylin and eosin (H&E) and Movat stains. Statistical analyses included chi(2) test, t test, and analysis of variance.

RESULTS

STAT1 messenger RNA and total protein were greater in human AAA vs non-AAA controls. In addition, aneurysms occurred in 8%, 50%, and 80% of ApoE-/- mice at 7, 14, and 28 days, respectively. Total STAT1 levels were not altered during the course of angiotensin II infusion. Phosphorylated STAT1 levels peaked at 7 days with a 1.4-fold increase over baseline (P < .05). Aneurysms occurred in 0%, 100%, and 100% of ApoE/STAT1-/- mice at 3, 5, and 28 days. In mice infused with angiotensin II for >3 days, aortic rupture occurred more frequently in ApoE/STAT-/- mice (53% vs 19%, P < .05) and at earlier time points (4.0 +/- 0.5 vs 9.2 +/- 0.77 days, P < .05) vs ApoE-/- mice. SBP did not differ between the groups during angiotensin II infusion. By 28 days, aneurysms were larger in ApoE/STAT1-/- mice compared with ApoE-/- mice (2.7 +/- 0.4 vs 1.9 +/- 0.1 mm, P < .05) and were more extensive. H&E and Movat stain did not reveal differences in aortic wall structural content at baseline between ApoE-/- and ApoE/STAT1-/- mice. Both groups demonstrated equal disorganization in the aneurysmal state.

CONCLUSIONS

Phosphorylated STAT1 is elevated during aneurysmal degeneration. Its loss is associated with a higher rate of acute aortic rupture and more extensive aneurysms in a mouse model of aortic dissection. Further investigation is necessary to determine whether these observations are secondary to an underlying aortic wall abnormality or alterations in vessel wall matrix remodeling.

Peroxisome proliferator-activated receptor ligands reduce aortic dilatation in a mouse model of aortic aneurysm

OBJECTIVE

Osteopontin (OPN) is associated with human abdominal aortic aneurysms (AAA) and in vitro studies suggest that this cytokine is downregulated by peroxisome proliferator-activated receptor (PPAR) ligation. We examined the effect of two PPAR ligands within a mouse model of aortic aneurysm.

METHODS

At 11 weeks of age apolipoprotein E deficient (ApoE(-/-)) mice were given pioglitazone (n=27), fenofibrate (n=27) or vehicle (n=27) in their drinking water. From 13 weeks of age mice received angiotensin II (1 microg/kg/min) infusion via subcutaneous pumps until death or 17 weeks when the aortas were harvested and maximum aortic diameters were recorded. Suprarenal aortic segments were assessed for OPN concentration and macrophage accumulation. Saline infused mice served as negative controls (n=22).

RESULTS

Angiotensin II induced marked dilatation in the suprarenal aorta (>2-fold increase compared to controls) associated with upregulation of the cytokines OPN and macrophage infiltration. Suprarenal aortic expansion was significantly reduced by administration of pioglitazone (mean diameter 1.61+/-0.11 mm, p=0.011) and fenofibrate (mean diameter 1.51+/-0.13 mm, p=0.001) compared to the vehicle control group (mean diameter 2.10+/-0.14 mm). Immunostaining for macrophages was reduced in mice treated with pioglitazone (median staining area 6.2%, interquartile range 4.1-7.2, p<0.001) and fenofibrate (median staining area 4.0%, interquartile range 2.2-6.1, p<0.001) compared to mice receiving vehicle control (median staining area 13.2%, interquartile range 8.4-20.0).

CONCLUSION

These findings suggest the potential value of peroxisome proliferator-activated receptor ligation as a therapy for human AAAs.

Inhibition of soluble epoxide hydrolase attenuated atherosclerosis, abdominal aortic aneurysm formation, and dyslipidemia

OBJECTIVE

Epoxyeicosatrienoic acids (EETs) have been shown to have antiinflammatory effects and therefore may play a role in preventing vascular inflammatory and atherosclerotic diseases. Soluble epoxide hydrolase (s-EH) converts EETs into less bioactive dihydroxyeicosatrienoic acids. Thus, inhibition of s-EH can prevent degradation of EETs and prolong their effects. The present study aimed to test the hypothesis that inhibition of s-EH has vascular protective effects.

METHODS AND RESULTS

Six-month-old apolipoprotein E-deficient mice were chronically infused with angiotensin II (1.44 mg/kg/d) for 4 weeks to induce abdominal aortic aneurysm (AAA), accelerate atherosclerosis development and carotid artery ligation-induced vascular remodeling. The mice were treated with a novel s-EH inhibitor, AR9276 (1.5 g/L in drinking water) or vehicle for 4 weeks. The results demonstrated that AR9276 significantly reduced the rate of AAA formation and atherosclerotic lesion area, but had no effect on ligation-induced carotid artery remodeling. These effects were associated with a reduction of serum lipid, IL-6, murine IL-8-KC, and IL-1alpha, and downregulation of gene expressions of ICAM-1, VCAM-1, and IL-6 in the arterial wall.

CONCLUSIONS

The present data demonstrate that treatment with an s-EH inhibitor attenuates AAA formation and atherosclerosis development. The attendant downregulation of inflammatory mediators and lipid lowering effects may both contribute to the observed vascular protective effects.

Whole genome expression analysis within the angiotensin II-apolipoprotein E deficient mouse model of abdominal aortic aneurysm

BACKGROUND

An animal model commonly used to investigate pathways and potential therapeutic interventions relevant to abdominal aortic aneurysm (AAA) involves subcutaneous infusion of angiotensin II within the apolipoprotein E deficient mouse. The aim of this study was to investigate genes differentially expressed in aneurysms forming within this mouse model in order to assess the relevance of this model to human AAA.

RESULTS

Using microarrays we identified genes relevant to aneurysm formation within apolipoprotein E deficient mice. Firstly we investigated genes differentially expressed in the aneurysm prone segment of the suprarenal aorta in these mice. Secondly we investigated genes that were differentially expressed in the aortas of mice developing aneurysms relative to those that did not develop aneurysms in response to angiotensin II infusion. Our findings suggest that a host of inflammation and extracellular matrix remodelling pathways are upregulated within the aorta in mice developing aneurysms. Kyoto Encyclopedia of Genes and Genome categories enriched in the aortas of mice with aneurysms included cytokine-cytokine receptor interaction, leukocyte transendothelial migration, natural killer cell mediated cytotoxicity and hematopoietic cell lineage. Genes associated with extracellular matrix remodelling, such as a range of matrix metalloproteinases were also differentially expressed in relation to aneurysm formation.

CONCLUSION

This study is the first report describing whole genome expression arrays in the apolipoprotein E deficient mice in relation to aneurysm formation. The findings suggest that the pathways believed to be critical in human AAA are also relevant to aneurysm formation in this mouse model. The findings therefore support the value of this model to investigate interventions and mechanisms of human AAA.