Preoperative treatment with doxycycline reduces aortic wall expression andactivation of matrix metalloproteinases in patients with abdominal aortic aneurysms

Purpose: Matrix metalloproteinases (MMPs) are considered to play a central role in the pathogenesis of abdominal aortic aneurysms (AAAs). Doxycycline (Dox) has direct MMP-inhibiting properties in vitro, and it effectively sup presses the development of elastase-induced AAAs in rodents. The purpose of this study was to determine if treatment with Dox suppresses MMPs within h uman aneurysm tissue and to elucidate the molecular mechanisms underlying t his effect. Methods: Aneurysm tissues were obtained from 15 patients with an AAA, eight of whom had been treated with Dox before surgery (100 mg orally twice a da y for 7 days). Protein extracts were examined by means of gelatin zymograph y and immunoblot analysis, and RNA was examined by means of reverse transcr iption-polymerase chain reaction (RT-PCR). The effects of Dox on MMP produc tion were further examined in human THP-1 mononuclear phagocytes in vitro. Results: NO detectable difference was found between groups by using substra te zymography as a means of assessing total MMP activity, but Dox treatment was associated with a slight (24.4%) reduction in the activated fraction o f 72-kDa gelatinase (MMP-2; P < .05), In contrast, a 2.5-fold reduction in the amount of extractable 92-kDa gelatinase (MMP-9) protein in Dox-treated patients was revealed by means of immunoblot analysis (P < .05). Also, a 5. 5-fold (81.9%) reduction in MMP-9 messenger RNA (mRNA) in Dox-treated patie nts was demonstrated by means of quantitative competitive RT-PCR (mean +/- SE, mol MMP-9/mol beta-actin: 1.3 +/- 0.5 vs 7.2 +/- 3.1; p < .04). There w as no significant difference between groups in the relative expression of M MP-2 protein or mRNA. In cultured THP-1 monocytes stimulated with phorbol e ster, the expression of MMP-9 protein and mRNA were both decreased after ex posure to relevant concentrations of Dox in vitro. Conclusion: In addition to its recognized effects as a direct MMP antagonis t, Dox may influence connective tissue degradation within human aneurysm ti ssue by reducing monocyte/macrophage expression of MMP-9 mRNA and by suppre ssing the post-translational processing (activation) of proMMP-2. Through t his complementary combination of mechanisms, treatment with Dox may be a pa rticularly effective strategy for achieving MMP inhibition in patients with an AAA.