Design of a trial to evaluate the effect of propranolol upon abdominal aortic aneurysm expansion

Experimental techniques and models in the study of the development and treatment of abdominal aortic aneurysm

BACKGROUND

It is still unclear what initiates aneurysmal dilatation and what determines whether or not an aneurysm will continue to expand and rupture. Early detection and operative repair of an abdominal aortic aneurysm (AAA) still remains the only effective means of reducing the high mortality rate associated with the condition. Endovascular techniques are being developed in an attempt to reduce the mortality rate associated with elective repair. A variety of animal models and experimental techniques have been described in the investigation of the pathophysiology of AAA and in the development of improved endovascular surgical and pharmacological therapies. This article discusses these models and techniques, their advantages and some of the problems encountered in extrapolating experimental findings to the human condition.

METHODS

This review is based on a search of the Medline database from 1966 to March 1998 using recognized key words and text words. A further search was then conducted on references quoted within selected relevant publications.

RESULTS AND CONCLUSION

Treatment of rodent aortas with intraluminal elastase or periaortic calcium chloride creates reproducible aneurysms that have certain similarities to the human pathology; such aneurysms have been favoured in the investigation of the pathophysiology of aneurysm expansion. However, these models lack several of the prominent features of the human lesion, such as atherosclerosis and intraluminal thrombosis. The development of gene knockout mice may lead to a more analogous aneurysm formation, with associated atherosclerosis. Many large animal models have been used in the development of endovascular techniques but, in general, these do not mimic the human pathophysiology and fail to predict medium- and long-term complications.

Doxycycline inhibits elastin degradation and reduces metalloproteinase activity in a model of aneurysmal disease

PURPOSE

Abdominal aortic aneurysms are characterized by degradation of the extracellular matrix, with a reduction in the elastin concentration of the arterial media. These changes are mediated by increased levels of endogenous metalloproteinases (MMPs) within the aorta, which provide a potential therapeutic target for pharmacologic agents aimed at reducing the growth rate of small aneurysms. In this study, the ability of doxycycline--an MMP inhibitor--to reduce matrix degradation was assessed in a previously described model of aneurysmal disease that used a brief pulse of elastase to induce MMP production and elastin degradation in arterial organ cultures.

METHODS

Porcine aortic segments (n = 8) were preincubated in exogenous pancreatic elastase for 24 hours before culture in standard conditions for 13 days with both 1 and 10 mg/L doxycycline. Control segments were cultured both without doxycycline and without elastase. At the termination of culture, MMPs were extracted from the tissue and quantified by a combination of substrate gel enzymography and immunoblotting. The volume fractions of elastin and collagen were determined by stereologic analysis of sections stained with Miller's elastin and van Gieson's stain.

RESULTS

Stereologic analysis demonstrated a significant preservation of elastin in aorta treated with doxycycline 10 mg/L (p < 0.001) and demonstrated that this preservation was accompanied by a significant reduction in MMP-9 activity (p < 0.02). Immunoblotting for tissue inhibitors of metalloproteinases (TIMP-1 and TIMP-2) showed no decreased production in the doxycycline-treated groups.

CONCLUSIONS

Therapeutic ranges of doxycycline significantly inhibited elastin degradation and MMP-9 production within aortic organ cultures. These data suggest that doxycycline may have a potential application in reducing the growth rates of small abdominal aortic aneurysms.