Mechanisms underlying the inhibitory effects of probucol on elastase-induced abdominal aortic aneurysm in mice

BACKGROUND AND PURPOSE

Abdominal aortic aneurysm (AAA) is a degenerative disease with irreversible and progressive dilation of the artery. But there are few options for efficacious treatment except for traditional surgery. Probucol has been widely applied to treat hyperlipidaemia and atherosclerosis in clinic, but whether it can protect against AAA remains unknown. In this study, the protective effects of probucol against AAA and its related mechanisms were explored.

EXPERIMENTAL APPROACH

The model of AAA was induced in mice by periaortic application of elastase (40 min) to the abdominal aorta. Probucol at different doses was administered by daily gavage, starting on the same day as AAA was induced, for 14 days. In vitro, cultures of rat vascular smooth muscle cells (VSMCs) were stimulated with TNF-α. Haem oxygenase (HO)-1 siRNA and HO-1 plasmid were used to regulate the expression or activity of HO-1 in the VSMCs and to clarify the effects of HO-1.

KEY RESULTS

Probucol dose-dependently prevented the development of AAA, reflected by decreased incidence of AAA, diameter of aortic dilation, elastin degradation, and infiltration of inflammatory cells. Probucol also protected VSMCs from oxidative injury and enhanced elastin biosynthesis. This anti-inflammatory effects of probucol on VSMCs were significantly decreased when HO-1 was inhibited by siRNA.

CONCLUSION AND IMPLICATIONS

Probucol protected against AAA through inhibiting the degradation of elastin induced by inflammation and oxidation and by facilitating the biosynthesis of elastin. HO-1 played a crucial role in the anti-inflammatory effects of probucol in VSMCs.

Comparison of Efficacy between Ramipril and Carvedilol on Limiting the Expansion of Abdominal Aortic Aneurysm in Mouse Model

Objective:

Abdominal aortic aneurysm (AAA) is a common condition that may be life-threatening when it is unrecognized. The aim of this study is to evaluate and compare the efficacy of ramipril and carvedilol on limiting AAA expansion in mouse model.

Methods and Results:

A total of 36 experimental AAA mouse model was induced with the continuous infusion of angiotensin II (Ang II) in 20-week-old male apolipoprotein E-deficient mice. They were randomly divided into 3 treatment groups and fed orally for 8 weeks; saline alone, ramipril (2.5 mg/30g/d), or carvedilol (3.125 mg/30g/d), respectively. Aortic diameter (AD) was measured by micro-computed tomography, and the level of biomarkers of aortic tissue such as monocyte chemoattractant protein-1 (MCP-1) and tissue inhibitor matrix metalloproteinase-1 (TIMP-1) was evaluated. After treatment, AD of both ramipril and carvedilol group was smaller than in the saline group. The percentage change of AD in both ramipril and carvedilol groups was significantly smaller than that of the saline group. Pathologic examination revealed relatively well-preserved aortic walls in the ramipril group compared to the carvedilol and saline groups. The level of MCP-1 was markedly decreased in both the ramipril and carvedilol groups compared to the saline group. The level of TIMP-1 was higher in the carvedilol group when compared to either the saline or ramipril groups.

Conclusions:

Ramipril and carvedilol treatment shows similar efficacy in limiting AAA expansion in mouse model. Future clinical research would be warranted to validate these results.

Inhibitory effects of doxycycline on the onset and progression of abdominal aortic aneurysm and its related mechanisms

The objective of this study was to investigate whether doxycycline (DOX) given at different doses and via different administration routes had protective or therapeutic effects on abdominal aortic aneurysm (AAA) induced by elastase in mice. Moreover, the anti-AAA mechanism of DOX was studied in TNF-α-stimulated vascular smooth muscle cell (VSMC) in vitro. For in vivo study, either daily administration of 30mg/kg of DOX by gavage or intraperitoneal injection of 15mg/kg DOX every other day for 14 days significantly prevented the development of AAA at its early stage. Further study showed that intraperitoneal injection of 15mg/kg DOX every other day for 7 times in total could also cure the established AAA. In vitro study showed that treating VSMCs with TNF-α together with DOX remarkably inhibited the expressions and activities of MMPs (MMP-2 and MMP-9), significantly suppressed the activation of protein kinase B (AKT) signaling pathway and mitogen-activated protein kinases (MAPKs) signal proteins, including extracellular signal-regulated kinase (ERK), c-Jun amino-terminal kinases (JNK) and p38, and downregulated mRNA levels of interleukin-6 (IL-6) and monocyte chemotactic protein 1 (MCP-1), and significantly upregulated mRNA levels of transforming growth factor beta (TGF-β), heme oxygenase 1 (HO-1) and superoxide dismutase 1 (SOD-1), indicating that DOX inhibits activities of MMPs through reducing oxidative stress, suppressing MAPKs and AKT signaling pathways and ameliorating inflammation in VSMCs, and therefore, exerts preventive as well as therapeutic effects on AAA.

Magnetically-responsive, multifunctional drug delivery nanoparticles for elastic matrix regenerative repair

Arresting or regressing growth of abdominal aortic aneurysms (AAAs), localized expansions of the abdominal aorta are contingent on inhibiting chronically overexpressed matrix metalloproteases (MMPs)-2 and -9 that disrupt elastic matrix within the aortic wall, concurrent with providing a stimulus to augmenting inherently poor auto-regeneration of these matrix structures. In a recent study we demonstrated that localized, controlled and sustained delivery of doxycycline (DOX; a tetracycline-based antibiotic) from poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs), enhances elastic matrix deposition and MMP-inhibition at a fraction of the therapeutically effective oral dose. The surface functionalization of these NPs with cationic amphiphiles, which enhances their arterial uptake, was also shown to have pro-matrix regenerative and anti-MMP effects independent of the DOX. Based on the hypothesis that the incorporation of superparamagnetic iron oxide NPs (SPIONs) within these PLGA NPs would enhance their targetability to the AAA site under an applied external magnetic field, we sought to evaluate the functional effects of NPs co-encapsulating DOX and SPIONs (DOX-SPION NPs) on elastic matrix regeneration and MMP synthesis/activity in vitro within aneurysmal smooth muscle cell (EaRASMC) cultures. The DOX-SPION NPs were mobile under an applied external magnetic field, while enhancing elastic matrix deposition 1.5-2-fold and significantly inhibiting MMP-2 synthesis and MMP-2 and -9 activities, compared to NP-untreated control cultures. These results illustrate that the multifunctional benefits of NPs are maintained following SPION co-incorporation. Additionally, preliminary studies carried out demonstrated enhanced targetability of SPION-loaded NPs within proteolytically-disrupted porcine carotid arteries ex vivo, under the influence of an applied external magnetic field. Thus, this dual-agent loaded NP system proffers a potential non-surgical option for treating small growing AAAs, via controlled and sustained drug release from multifunctional, targetable nanocarriers.

STATEMENT OF SIGNIFICANCE

Proactive screening of high risk elderly patients now enables early detection of abdominal aortic aneurysms (AAAs). There are no established drug-based therapeutic alternatives to surgery for AAAs, which is unsuitable for many elderly patients, and none which can achieve restore disrupted and lost elastic matrix in the AAA wall, which is essential to achieve growth arrest or regression. We have developed a first generation design of polymer nanoparticles (NPs) for AAA tissue localized delivery of doxycycline, a modified tetracycline drug at low micromolar doses at which it provides both pro-elastogenic and anti-proteolytic benefits that can augment elastic matrix regenerative repair. The nanocarriers themselves are also uniquely chemically functionalized on their surface to also provide them pro-elastin-regenerative & anti-matrix degradative properties. To provide an active driving force for efficient uptake of intra-lumenally infused NPs to the AAA wall, in this work, we have rendered our polymer NPs mobile in an applied magnetic field via co-incorporation of super-paramagnetic iron oxide NPs. We demonstrate that such modifications significantly improve wall uptake of the NPs with no significant changes to their physical properties and regenerative benefits. Such NPs can potentially stimulate structural repair in the AAA wall following one time infusion to delay or prevent AAA growth to rupture. The therapy can provide a non-surgical treatment option for high risk AAA patients.

Multifunctional nanoparticles for doxycycline delivery towards localized elastic matrix stabilization and regenerative repair

Abdominal aortic aneurysms (AAAs) are abnormal expansions of the aortic wall, typically characterized by chronic up-regulation of matrix metalloproteases (MMPs)-2 and -9. These MMPs degrade elastin and elastic matrix within the aortic wall, leading to a progressive loss of elasticity of the abdominal aorta as the condition progresses. Doxycycline (DOX) is a tetracycline-based antibiotic which has shown significant promise in delaying and slowing the growth of AAAs in both clinical studies and animal models. However, it has been found to inhibit elastic matrix deposition by vascular cells at dosages in the μg ml(-1) range, which is typically observed in the circulation, in addition to systemic side effects, following oral dosage. In this paper, we describe the development of DOX-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles for localized, controlled and sustained DOX delivery towards AAA therapy. Further, we demonstrate that surface functionalization of these nanoparticles with cationic amphiphiles not only imparts them with a positive charge for potentially enhanced aortic uptake, but also enables enhanced elastin binding via hydrophobic interactions, as well as up-regulating activity of the elastin crosslinking enzyme lysyl oxidase. In addition to the DOX released from the nanoparticles being effective in inhibiting MMP-2 production and activity, we also demonstrate that surface functionalization of the nanoparticles cationic amphiphiles may also play a role in MMP-2 inhibition via (i) electrostatic interactions with negatively charged residues in the active-site of MMP-2 or (ii) steric blockade of the active site on account of the presence of two dodecyl chains in the DMAB molecule. Thus, in addition to enhanced aortic uptake and retention illustrated in studies by other groups, we have demonstrated that cationic functionalization of PLGA nanoparticles enhances elastogenic outcomes by targeted binding to elastin, as well as their potential to inhibit elastolysis. These results establish their multifunctionality as a localized delivery system for AAA therapy. Overall, this delivery system has the potential to enhance regenerative outcomes at sites of proteolytic matrix disruption/degradation by enabling targeted, controlled and long-term release of therapeutic agents.

Standardization of outcome measures in clinical trials of pharmacological treatment for abdominal aortic aneurysm

An abdominal aortic aneurysm (AAA) is a common aortic wall disease with an increased prevalence in the elderly population (4-8% for those aged >65 years). Many AAAs are slow growing and remain insidious. Current standard of care for patients with small AAAs (<49 mm) is surveillance, with interventional therapy (open surgical repair or endovascular aneurysm repair) recommended for large (>50-55 mm), rapidly growing (>10 mm/year) or symptomatic AAAs. Although open surgical repair or endovascular aneurysm repair are effective, significant short- and long-term postoperative morbidity and mortality occurs. Currently, there is no pharmacological treatment specific for AAA; the need for the development of targeted pharmacological therapies based on clinically relevant and feasible outcomes acceptable to the medical community, regulatory agencies and third-party payers is high. A consensus on such end points will be critical to accelerating the development of pharmacological agents to prevent formation, arrest the expansion and reduce the rupture risk of AAA.

Abdominal aortic aneurysm: an often asymptomatic and fatal men's health issue

Men are more likely than women to develop an abdominal aortic aneurysm (AAA), a disease that is often asymptomatic and has up to a 90% risk of mortality if the aneurysm ruptures. What many men do not know is that an AAA can easily be identified through an ultrasound screening, and if the aneurysm is >5.5 cm, it can be surgically repaired to prevent a life-threatening rupture. Although current AAA screening recommendations focus on men between the ages of 65 and 75 years, who have ever smoked, recent evidence suggest many men of ages 50 to 80 years, regardless of smoking status, may also be at risk for developing an AAA. This article presents a comprehensive overview of AAA disease and summarizes current evidence-based diagnostic and treatment guidelines, the importance of educating men about this health issue, and the need for more widespread AAA ultrasound screening opportunities.

Medical treatment for small abdominal aortic aneurysms

BACKGROUND

Screening for abdominal aortic aneurysm (AAA) in selected groups is now performed in England, the USA and Sweden. Patients with aneurysms over 55 mm in diameter are generally considered for elective surgical repair. Patients with aneurysm diameters below or equal to 55 mm (termed 'small AAAs') are managed with aneurysm surveillance as there is currently insufficient evidence to recommend surgery in these cases. As more patients are screened, there will be an increasing number of small AAAs identified. There is interest in pharmaceutical interventions (for example angiotensin converting enzyme (ACE) inhibitors, antibiotics, beta-blockers, statins) which could be given to such patients to delay or reverse aneurysm expansion and reduce the need for elective surgical repair.

OBJECTIVES

To assess the effects of medical treatment on the expansion rate of small abdominal aortic aneurysms.

SEARCH METHODS

The Cochrane Peripheral Vascular Diseases Group Trials Search Co-ordinator searched the Specialised Register (May 2012) and CENTRAL (2012, Issue 5). Clinical trials databases were searched for details of ongoing or unpublished studies. The reference lists of articles retrieved by electronic searches were searched for additional citations.

SELECTION CRITERIA

We selected randomised trials in which patients with small AAAs allocated to medical treatment with the intention of retarding aneurysm expansion were compared to patients allocated to a placebo treatment, alternative medical treatment, a different regimen of the same drug or imaging surveillance alone.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted the data and assessed the risk of bias in the trials. Meta-analyses were used when heterogeneity was considered low. The two primary outcomes were the mean difference (MD) in aneurysm diameter and the odds ratio (OR) calculated to compare the number of individuals referred to AAA surgery in each group over the trial period.

MAIN RESULTS

Seven trials involving 1558 participants were included in this review; 457 were involved in four trials of antibiotic medication, and 1101 were involved in three trials of beta-blocker medication. Five of the studies were rated at a high risk of bias.Individually, all of the included trials reported non-significant differences in AAA expansion rates between their intervention and control groups.The two major drug groups were then analysed separately. For AAA expansion it was only possible to combine two of the antibiotic trials in a meta-analysis. This demonstrated that roxithromycin had a small but significant protective effect (MD -0.86 mm; 95% confidence interval (CI) -1.57 to -0.14). When referral to AAA surgery was compared (including all four antibiotic trials in the meta-analysis), non-significantly fewer patients were referred in the intervention groups (OR 0.96; 95% CI 0.59 to 1.57) than the control groups. When only the trials reporting actual elective surgery were included in a subgroup analysis, the result remained statistically non-significant (OR 1.17; 95% CI 0.57 to 2.42).For the beta-blocker trials, when all were combined in a meta-analysis, there was a very small, non-significant protective effect for propranolol on AAA expansion (MD -0.08 mm; 95% CI -0.25 to 0.10), and non-significantly fewer patients were referred to AAA surgery in the propranolol group (OR 0.74; 95% CI 0.52 to 1.05). Bronchospasm and shortness of breath were the main adverse effects from the beta-blockers. In one trial the adverse effects were reportedly so severe that the trial was stopped early after two years.

AUTHORS' CONCLUSIONS

There is some limited evidence that antibiotic medication may have a slight protective effect in retarding the expansion rates of small AAAs. The quality of the evidence makes it unclear whether this translates into fewer referrals to AAA surgery, owing mainly to the small sample sizes of the studies.Antibiotics were generally well tolerated with minimal adverse effects. Propranolol was poorly tolerated by patients in all of the beta-blocker trials and demonstrated only minimal and non-significant protective effects. Further research on beta-blockers for AAA needs to consider the use of drugs other than propranolol.In general, there is surprisingly little high quality evidence on medical treatment for small AAAs, especially in relation to the use of newer beta-blockers, ACE inhibitors and statins.

In vivo quantification of murine aortic cyclic strain, motion, and curvature: implications for abdominal aortic aneurysm growth

PURPOSE

To develop methods to quantify cyclic strain, motion, and curvature of the murine abdominal aorta in vivo.

MATERIALS AND METHODS

C57BL/6J and apoE(-/-) mice underwent three-dimensional (3D) time-of-flight MR angiography to position cardiac-gated 2D slices at four locations along the abdominal aorta where circumferential cyclic strain and lumen centroid motion were calculated. From the 3D data, a centerline through the aorta was created to quantify geometric curvature at 0.1-mm intervals. Medial elastin content was quantified with histology postmortem. The location and shape of abdominal aortic aneurysms (AAAs), created from angiotensin II infusion, were evaluated qualitatively.

RESULTS

Strain waveforms were similar at all locations and between groups. Centroid motion was significantly larger and more leftward above the renal vessels than below (P < 0.05). Maximum geometric curvature occurred slightly proximal to the right renal artery. Elastin content was similar around the circumference of the vessel. AAAs developed in the same location as the maximum curvature and grew in the same direction as vessel curvature and motion.

CONCLUSION

The methods presented provide temporally and spatially resolved data quantifying murine aortic motion and curvature in vivo. This noninvasive methodology will allow serial quantification of how these parameters influence the location and direction of AAA growth.