Pharmacotherapy in Clinical Trials for Abdominal Aortic Aneurysms: A Systematic Review and Meta-Analysis

A Novel Method for the Rat Model of Abdominal Aortic Aneurysm Induced by Retroperitoneal Implantation of an Osmotic Pump System With Lipopolysaccharide

BACKGROUND

Few methods can cocurrently mimic the pathological characteristics and nature history of human abdominal aortic aneurysms (AAAs), especially for the exist of the self-healing tendency of rodents. This study tested a novel method for the AAA rat model induced by retroperitoneal implantation of an osmotic pump system with lipopolysaccharide (LPS) based on the hypothesis that chronic inflammation of perivascular adipose tissue directly influenced the development and progression of AAAs.

METHODS

20 male Sprague-Dawley rats (10-month-old) fed with the Paigen diet were randomly divided into 4 groups: the blank group ×2, the sham group ×4, the empty capsule group ×4, and the LPS capsule group ×10. The LPS capsule group received implantations of the ALZET® osmotic pump capsule with LPS (3.6 μg/day) parallel to the abdominal aorta through a retroperitoneal approach. Two weeks later, 6 rats were randomly selected from the LPS capsule group to form the anti-inflammatory group and received implantations of another osmotic pump capsule with interleukin (IL)-10 (75 ng/day) through the same approach. The changes in abdominal aortic diameter were observed by ultrasound every 2 weeks, and samples were harvested for histopathologic and immunohistochemical analysis 6 weeks later.

RESULTS

Within the 6 weeks after modeling, the LPS capsule group showed sustained and significant aortic dilatation (P < 0.01), while the anti-inflammatory group showed a rapid and obvious shrinkage 2 weeks after the IL-10 osmotic pump capsule implantation (P < 0.01). The LPS capsule group presented excellent pathological mimicking of human AAAs and showed severe medial degeneration with the least elastic content among the 5 groups at the end of the sixth week (P < 0.05). Notably, the anti-inflammatory group showed perfect medial preservation with the most elastic content (P < 0.05) and the highest elastin/collagen ratio (P < 0.01) at the end of the study. Matrix metalloproteinases (MMP) 2 and 9 and toll-like receptor 2 showed strong expression in the LPS capsule group at the end of the sixth week, which was significantly higher than that in the blank group and sham group. Interestingly, the anti-inflammatory group showed a slightly higher MMP9 expression than the LPS capsule group though there was no statistical difference between them.

CONCLUSIONS

This novel method for the rat AAA model induced by retroperitoneal implantation of an osmotic pump capsule with LPS can concurrently mimic the histological characteristics and natural history of human AAAs. Further studies were needed to improve the osmotic pump system.

Influence of cardiometabolic medications on abdominal aortic aneurysm growth in the UK Aneurysm Growth Study: metformin and angiotensin-converting enzyme inhibitors associated with slower aneurysm growth

BACKGROUND

There is a clinical need for treatments that can slow or prevent the growth of an abdominal aortic aneurysm, not only to reduce the need for surgery, but to provide a means to treat those who cannot undergo surgery.

METHODS

Analysis of the UK Aneurysm Growth Study (UKAGS) prospective cohort was conducted to test for an association between cardiometabolic medications and the growth of an abdominal aortic aneurysm above 30 mm in diameter, using linear mixed-effect models.

RESULTS

A total of 3670 male participants with data available on abdominal aortic aneurysm growth, smoking status, co-morbidities, and medication history were included. The mean age at recruitment was 69.5 years, the median number of surveillance scans was 6, and the mean(s.e.) unadjusted abdominal aortic aneurysm growth rate was 1.75(0.03) mm/year. In a multivariate linear mixed-effect model, smoking (mean(s.e.) +0.305(0.07) mm/year, P = 0.00003) and antiplatelet use (mean(s.e.) +0.235(0.06) mm/year, P = 0.00018) were found to be associated with more rapid abdominal aortic aneurysm growth, whilst metformin was strongly associated with slower abdominal aortic aneurysm growth (mean(s.e.) -0.38(0.1) mm/year, P = 0.00019), as were angiotensin-converting enzyme inhibitors (mean(s.e.) -0.243(0.07) mm/year, P = 0.0004), angiotensin II receptor antagonists (mean(s.e.) -0.253(0.08) mm/year, P = 0.00255), and thiazides/related diuretics (mean(s.e.) -0.307(0.09) mm/year, P = 0.00078).

CONCLUSION

The strong association of metformin with slower abdominal aortic aneurysm growth highlights the importance of the ongoing clinical trials assessing the effectiveness of metformin with regard to the prevention of abdominal aortic aneurysm growth and/or rupture. The association of angiotensin-converting enzyme inhibitors, angiotensin II receptor antagonists, and diuretics with slower abdominal aortic aneurysm growth points to the possibility that optimization of cardiovascular risk management as part of abdominal aortic aneurysm surveillance may have the secondary benefit of also reducing abdominal aortic aneurysm growth rates.

Effect of Hydralazine on Angiotensin II-Induced Abdominal Aortic Aneurysm in Apolipoprotein E-Deficient Mice

The rupture of an abdominal aortic aneurysm (AAA) causes about 200,000 deaths worldwide each year. However, there are currently no effective drug therapies to prevent AAA formation or, when present, to decrease progression and rupture, highlighting an urgent need for more research in this field. Increased vascular inflammation and enhanced apoptosis of vascular smooth muscle cells (VSMCs) are implicated in AAA formation. Here, we investigated whether hydralazine, which has anti-inflammatory and anti-apoptotic properties, inhibited AAA formation and pathological hallmarks. In cultured VSMCs, hydralazine (100 μM) inhibited the increase in inflammatory gene expression and apoptosis induced by acrolein and hydrogen peroxide, two oxidants that may play a role in AAA pathogenesis. The anti-apoptotic effect of hydralazine was associated with a decrease in caspase 8 gene expression. In a mouse model of AAA induced by subcutaneous angiotensin II infusion (1 µg/kg body weight/min) for 28 days in apolipoprotein E-deficient mice, hydralazine treatment (24 mg/kg/day) significantly decreased AAA incidence from 80% to 20% and suprarenal aortic diameter by 32% from 2.26 mm to 1.53 mm. Hydralazine treatment also significantly increased the survival rate from 60% to 100%. In conclusion, hydralazine inhibited AAA formation and rupture in a mouse model, which was associated with its anti-inflammatory and anti-apoptotic properties.

Insulin Dependence is Associated with Poor Long-Term Outcomes Following AAA Repair

BACKGROUND

While prior studies have confirmed the protective effect of diabetes on abdominal aortic aneurysm (AAA) development, much less is known about the effect of diabetes, and in particular insulin dependence, on outcomes following AAA repair. In this study, we aim to evaluate the role of insulin-dependent diabetes on short-term and long-term outcomes following open and endovascular AAA repair.

METHODS

The Vascular Implant Surveillance and Interventional Outcomes Network (VISION), a registry linking the Vascular Quality Initiative (VQI) data with Medicare claims, was queried for patients who underwent open or endovascular AAA repair from 2011 to the present. Exclusion criteria were unknown diabetes status, prior aortic intervention, maximum aneurysm diameter <45 mm at presentation, and Medicare Advantage coverage due to inconsistent follow-up. Patients were stratified based on diabetes status (no diabetes versus diabetes) and insulin dependence (no diabetes or non-insulin-dependent diabetes versus insulin-dependent diabetes).

RESULTS

Of the 38,437 cases in the VISION endovascular aortic aneurysm (EVAR) and open aortic aneurysm repair (OAR) databases, 21,943 met inclusion criteria. Perioperative outcomes after OAR were comparable between diabetic and nondiabetic patients. However, diabetic patients undergoing EVAR were significantly more likely to have a postoperative myocardial infarction (1.0% vs 0.6%, P = 0.04) and have a 30-day readmission (10.9% vs 8.8%, P < 0.001). Insulin-dependent diabetic patients were more likely to require a 30-day readmission after OAR (24.5% vs 13.5%, P = 0.02) and EVAR (15.1% vs 9.0%, P < 0.001); however, only insulin-dependent diabetes mellitus (IDDM) patients undergoing EVAR experienced higher rates of postoperative myocardial infarction (1.9% vs 0.7%, P < 0.01). After propensity score matching, patients with IDDM undergoing EVAR were additionally at increased risk of mortality at 1-year, 3-year, and 5-year follow-up with the highest risk occurring at the 1-year mark (hazard ratio 1.79, P < 0.0001), while IDDM patients undergoing OAR were only at a significantly increased risk of mortality at 5-year follow-up (hazard ratio 1.90, P = 0.01).

CONCLUSIONS

Patients with insulin-dependent diabetes have greater than 14% one-year mortality following open or endovascular aneurysm repair, compared to 8% for all others. Our findings raise questions about whether insulin-dependent diabetics should have a higher size threshold for prophylactic repair, although further studies are needed to address this question and consider the influence of glycemic control on these outcomes.

Novel pharmacological approaches in abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a severe vascular disease and a major public health issue with an unmet medical need for therapy. This disease is featured by a progressive dilation of the abdominal aorta, boosted by atherosclerosis, ageing, and smoking as major risk factors. Aneurysm growth increases the risk of aortic rupture, a life-threatening emergency with high mortality rates. Despite the increasing progress in our knowledge about the etiopathology of AAA, an effective pharmacological treatment against this disorder remains elusive and surgical repair is still the unique available therapeutic approach for high-risk patients. Meanwhile, there is no medical alternative for patients with small aneurysms but close surveillance. Clinical trials assessing the efficacy of antihypertensive agents, statins, doxycycline, or anti-platelet drugs, among others, failed to demonstrate a clear benefit limiting AAA growth, while data from ongoing clinical trials addressing the benefit of metformin on aneurysm progression are eagerly awaited. Recent preclinical studies have postulated new therapeutic targets and pharmacological strategies paving the way for the implementation of future clinical studies exploring these novel therapeutic strategies. This review summarises some of the most relevant clinical and preclinical studies in search of new therapeutic approaches for AAA.

Double-edged sword of diabetes mellitus for abdominal aortic aneurysm

INTRODUCTION

Diabetes mellitus (DM) has been proved to contribute to multiple comorbidities that are risk factors for abdominal aortic aneurysm (AAA). Remarkably, evidences from epidemiologic studies have demonstrated a negative association between the two disease states. On the other hand, hyperglycemic state was linked to post-operative morbidities following AAA repair. This review aims to provide a thorough picture on the double-edged nature of DM and major hypoglycemic medications on prevalence, growth rate and rupture of AAA, as well as DM-associated prognosis post AAA repair.

METHODS

We performed a comprehensive search in electronic databases to look for literatures demonstrating the association between DM and AAA. The primary focus of the literature search was on the impact of DM on the morbidity, enlargement and rupture rate, as well as post-operative complications of AAA. The role of antidiabetic medications was also explored.

RESULTS

Retrospective epidemiological studies and large database researches associated the presence of DM with decreased prevalence, slower expansion and limited rupture rate of AAA. Major hypoglycemic drugs exert similar protective effect as DM against AAA by targeting pathological hallmarks involved in AAA formation and progression, which were demonstrated predominantly by animal studies. Nevertheless, presence of DM or postoperative hyperglycemia was linked to poorer short-term and long-term prognosis, primarily due to greater risk of infection, longer duration of hospital stays and death.

CONCLUSION

While DM is a positive factor in the formation and progression of AAA, it is also associated with higher risk of negative outcomes following AAA repair. Concomitant use of antidiabetic medications may contribute to the protective mechanism of DM in AAA, but further studies are still warranted to explore their role following AAA repair.