OBJECTIVETo compare the effects of matrix metalloproteinase (MMP) inhibitor doxycycline, losartan, and their combination on the expression of MMP-8, 13, tissue inhibitor of MMP-1, 2 (TIMP-1, 2), and collagen remodeling in the noninfarcted myocardium after acute myocardial infarction (AMI) in rats.

METHODSTwo hundred and fifty-four AMI rats, induced by left coronary ligation, were randomly assigned to the following groups: (1) AMI controls group (n = 64); (2) doxycycline group (30 mg x kg(-1) x d(-1), n = 63); (3) losartan group (10 mg x kg(-1) x d(-1), n = 62); (4) concomitant doxycycline and losartan group (30 and 10 mg x kg(-1) x d(-1) respectively, n = 65); and (5) Sham-operated rats (n = 30), which were randomly selected to serve as noninfarction controls. Each group was further divided into three subgroups of 1, 2, and 4 weeks that received treatment. After the completion of treatment, the rats were killed. The mRNA and protein expression of MMPs and TIMPs in the noninfarcted myocardium were quantified by RT-PCR and Western blot, respectively. The type I and type III collagen volume fraction (CVF) of the noninfarced myocardium were assessed immunohistochemically.

RESULTSNo significant difference existed in myocardial infarction sizes among the 12 subgroups of AMI controls and the three treatment groups (42%-48%, all P > 0.05). Compared with sham operated rats, the mRNA and protein expression of MMP-8 and 13 significantly increased by 39%-183% in all three subgroups of AMI controls (all P < 0.05), except both of their mRNA expressions in 2-week subgroups; the mRNA and protein levels of TIMP-1 increased only in 1-week subgroup of AMI controls by 104% and 67%, respectively (both P < 0.05); the mRNA of TIMP-2 increased in all 1, 2, and 4-week subgroups by 144%-232% (all P < 0.05), but its protein expression lagged and only enhanced in 2 and 4-week subgroups of AMI controls by 231% and 332%, respectively (both P < 0.05). Meanwhile, both type I and type III CVF of noninfarcted myocardium significantly increased in all three subgroups of AMI controls (type I CVF: 3.01%-5.64% vs 1.53%-1.67%, P < 0.01-0.001; type III CVF: 2.19%-4.42% vs 1.46%-1.59%, P < 0.05-0.001), with type I CVF being higher in 4-week than in 1 and 2-week subgroups (5.64% vs 3.01% and 3.02% respectively, all P < 0.05). Compared with AMI controls, all three kinds of treatment significantly reduced the increased mRNA and protein expressions of MMP-8, 13 and TIMP-1, 2 after AMI by 14%-60% (all P < 0.05), as well as type I/III CVF in their 2 and 4-week subgroups (type I CVF: 1.56%-2.38% vs 3.02%-5.64%, P < 0.05-0.001; type III CVF: 1.92%-2.65% vs 4.19%-4.42%, P < 0.05-0.01), except for doxycycline's effect on type III CVF in any of its three subgroups (all P > 0.05). Among the three treatment groups, significant differences existed in the above mentioned indicators only at some subgroup levels (all P < 0.05).

CONCLUSIONSLike losartan, doxycycline can also suppress the enhanced mRNA and protein expression of MMP-8, 13 and TIMP-1, 2, and reduce type I collagen deposition in the noninfarcted myocardium after AMI in rats. However, it has no effect on type III collagen deposition.