ELASTASE-INDUCED MATRIX DEGRADATION IN ARTERIAL ORGAN-CULTURES - AN IN-VITRO MODEL OF ANEURYSMAL DISEASE

Purpose: Abdominal aortic aneurysms are characterized by degradation o f the extracellular matrix, induction of endogenous metalloproteinases (MMPs), and development of a chronic inflammatory infiltrate. Despite intensive analysis of end-stage tissue, aneurysm pathogenesis remains obscure. The aim of this study was to develop an in vitro model of an eurysmal disease. Methods: Porcine aortic organ cultures were preincub ated with pancreatic elastase before culture in standard conditions fo r up to 14 days. The extent of matrix degradation at various time poin ts was determined by quantitative histologic estimation of collagen an d elastin concentration. Endogenous metalloproteinase production withi n the tissue was quantified by gel enzymography and immunoblotting. A separate series of experiments was performed to investigate the effect of incorporating autologous leukocytes into the culture system. Resul ts: Although exogenous elastase was removed after 24 hours, substantia l degradation of the aortic extracellular matrix occurred in the subse quent 13 days in tissue culture. Analysis of samples preincubated with elastase (100 U/ml) for 24 hours before tissue culture demonstrated t hat elastin degradation occurred in a time-dependent manner (p < 0.001 ) and was not confined to the initial phase of exogenous elastase acti vity. Gelatin gel enzymography revealed a time-related production of m etalloproteinases (55 to 250 kDa) within the aortic tissue. The presen ce of MMPs-1, 2, 3, and 9 was determined by immunoblotting. Immunohist ochemistry identified the vascular smooth-muscle cell as the source of MMPs-1, 2, and 3. Addition of autogenous leukocytes to elastase-pretr eated tissue initiated an inflammatory infiltrate within the aortic wa ll, which further enhanced both matrix degradation and MMP production (p < 0.001). Conclusions: These data demonstrate that aortic samples p retreated with elastase before tissue culture undergo matrix degradati on with MMP production and the development of an inflammatory infiltra te. These changes mirror the pathophysiological events within establis hed aneurysms. It is suggested that this model may be useful in unders tanding early pathogenic events within aneurysmal tissue.