Doxycycline attenuates isoproterenol-induced myocardial fibrosis and matrix metalloproteinase activity in rats.

Our objective was to investigate the effects of doxycycline, a matrix metalloproteinase (MMP) inhibitor (MMPi) on beta-agonist-induced myocardial fibrosis and MMP expression. Twenly-four Wistar-Kyoto rats were divided into 3 groups: control (CTL; n=8), isoproterenol (ISO; n=8), and isoproterenol with doxycycline (ISO+DOX; n=8). ISO and ISO+DOX rats received L-isoproterenol (2.0 mg/kg/d) for 14 d, whereas the CTL group received vehicle. In addition, ISO+DOX rats received a subcutaneous injection of doxycycline (25 mg/kg/d) for 14 d, whereas CTL and ISO rats were injected with saline. Cardiac fibrosis was evaluated via histopathological analysis. MMP-2 and -9 were analyzed by Western blotting and zymography. Compared to the control, the myocardial cross-sectional area and areas of fibrosis were increased significantly in the ISO group, but were attenuated in the ISO+DOX group. MMP-2 activity also increased significantly in the ISO group, but decreased in the ISO+DOX group. Similarly, immunoblotting showed significant increase in MMP-2 and -9 levels in the ISO group, and decreased levels in the ISO+DOX group. Our results suggest that the enhanced expression of MMPs plays a prominent role in promoting myocardial fibrosis in beta-agonist signaling pathway, and that MMP-inhibiting compounds may attenuate myocardial fibrosis.