The consistent observation of a reduction of the elastin concentration in abdominal aortic aneurysms (AAAs) has led us to investigate in AAA specimens two metalloproteinases that display elastase activity, MMP₂ (gelatinase A/72 kDa) and MMP₉ (gelatinase B/92 kDa).

Samples of full-thickness aortic wall, adherent thrombus, and serum were collected in 10 patients with AAAs. Samples of normal aortic wall and serum were taken from 6 age-matched control patients. Quantitative gelatin-zymography and gelatinolytic soluble assays after acetyl-phenyl mercuric acid activation were performed on serum and tissue extracts, and the results were expressed in units on a comparative wet-weight basis. Histologic analysis was performed in parallel to score the inflammatory infiltrate.

The luminal and parietal parts of the thrombus contained, respectively, 20- and 10-fold more gelatinolytic activity than the serum. The predominate form was MMP₉. Although the total gelatinolytic activity was in the same range both in AAAs and in normal walls, a significantly higher proportion of MMP₉ was found in the aneurysmal aortic walls. Furthermore, a significant proportion of MMP₉ was under its processed active form, which was never observed in normal samples. A significantly higher proportion of MMP₂ was also present as processed active form in AAA wall. This latter parameter positively correlated with the inflammatory score.

The presence of activated MMP₉ and MMP₂ might contribute to the degradation of the extracellular matrix proteins that occurs during the development of aneurysms. (J Vasc Surg 1996;24:127-33.)