Relation Between Post-Myocardial Infarct Remodelling and Gelatinase Activity in Patients Enrolled in the TIPTOP Trial

In pre-clinical studies, matrix metalloproteinase (MMP) inhibition, particularly gelatinases (MMP-2 and -9), attenuated post-myocardial infarct (MI) remodelling.1 However, synthetic inhibitors of MMPs in the clinical setting have yielded disappointing results.2 For the first time, the TIPTOP trial3 showed that a timely short-term treatment with doxycycline, the most potent MMP inhibitor of the tetracycline, is able to reduce 6-month left ventricular (LV) remodelling in patients with a first ST-elevation MI (STEMI) and LV dysfunction [LV ejection fraction (LVEF) < 40%]. Based on the plasma profile of total MMP concentrations and their tissue inhibitors (TIMPs), it has been hypothesized that this may be due to a favourable modulation of MMP activity by TIMP-2.4 Thus, using the stored plasma samples of the TIPTOP patients,4 we now evaluated the relationship between MMP-2 and -9 activities and LV remodelling. The TIPTOP trial has already been described in detail.3, 4 In brief, it was a prospective, phase 2, randomized, open-label trial, with blinded outcome assessment, in which 110 STEMI patients were randomized to receive doxycycline [100 mg oral dose immediately after primary percutaneous coronary intervention (pPCI), then twice daily for 7 days], or standard care. For MMP analysis, blood samples were collected at baseline, and at post-MI days 1, 7, 30 and 180. LV remodelling was assessed by two-dimensional echocardiography on admission and at 6 months. For the present analysis, gelatinase activity was analysed by zymography in polyacrylamide gels containing gelatin as a substrate by an independent blind off-site laboratory. Statistical analyses were conducted using SPSS software (version 19; IBM Corp., Somers, NY, USA) after transformation of not normally distributed variables. Univariate linear regression was used to assess the relationship between plasma values of collagenase activities at each measurement time, and changes (Δ) of LV end-diastolic volume index (LVEDVi) from baseline to 6 months. ANOVA followed by Bonferroni post-hoc test was used to analyse the interaction between doxycycline and MMP-2 activity on ΔLVEDVi. Differences between groups for continuous variables were analysed using Student's t-test. Multivariate regression analysis was performed to evaluate the independent association between MMP-2 activity and ΔLVEDVi. The significant variables in the univariate analysis (the variables tested are all those listed in Figure 1) were entered into the multivariate model. A P-value of <0.05 was considered statistically significant. As previously reported,4 blood samples were available in 106 of 110 (96%) patients enrolled in the TIPTOP trial. The characteristics of the study population are shown in Figure 1. From baseline to 1 month, MMP-2 activity significantly correlated with ΔLVEDVi (baseline: P < 0.05; 24 h and day 7: P < 0.01, 1 month: P < 0.001). ANOVA showed an interaction between doxycycline and MMP-2 activity (median values) on ΔLVEDVi at 24 h, and day 7 (F = 5.40, P = 0.022 and F = 4.95, P = 0.029, respectively). According to the median value of the sum of MMP-2 activity detected at baseline, 24 h and day 7 (Σ MMP-2), i.e. during active treatment with doxycycline, patients were divided into two groups: low MMP-2 activity (group 1) and high MMP-2 activity (group 2), respectively. Group 2 showed more severe remodelling than group 1 (ΔLVEDVi: 7.3 ± 17 mL vs. 0.9 ± 12 mL, P = 0.010; ΔLV end-systolic volume index: 1.4 ± 14 mL vs. −5.1 ± 10 mL, P = 0.006; ΔLVEF: 7 ± 11% vs. 13 ± 11%, P = 0.013) (Figure 1). Finally, Σ MMP-2 was independently associated with LVEDVi changes (P = 0.007), together with troponin I peak (P = 0.000), baseline LVEDVi (P = 0.017), and doxycycline (P = 0.031). Because of its design, the findings of this study should be considered only hypothesis generating. However, some interesting considerations can be done. First, according to pre-clinical studies,1, 5 high plasma MMP-2 activity after a large STEMI likely reflects the initiation of structural remodelling that is manifested in the later post-MI period as LV dilatation/dysfunction. This occurs despite pPCI, persistent infarct-related artery patency and a well-timed anti-remodelling therapy with renin–angiotensin–aldosterone inhibitors and beta-blockers, which also have pleiotropic effects in reducing MMPs.6 Noteworthy, plasma MMP-2 activity correlated with LV dilatation independently of the major known factors affecting LV remodelling. Thus, limiting the MMP activation continues to be a potential and intriguing target. The lack of correlation between MMP-9 and LV dilatation we observed is difficult to interpret. Wagner et al.7 demonstrated a correlation between plasma MMP-9 activity early after STEMI and ΔLVEDVi at 2-year follow-up. Perhaps our follow-up is too short to highlight this relationship. Second, from 24 h to day 7 after index STEMI we observed a significant interaction between doxycycline and MMP-2 activity on 6-month LV dilatation. Of note, in this same time frame TIMP-2 levels resulted elevated with doxycycline treatment.4 Obviously, whether TIMP-2 is a key substrate for the favourable effects of doxycycline requires ad hoc studies.8 Third, unexpectedly we did not observe any differences in plasma collagenase activities between treatment groups. This likely depends on the absence of serial measures documenting successful inhibition. Furthermore, plasma MMPs are only a surrogate marker for local myocardial levels, and we cannot rule out an MMP inhibitory effect of doxycycline at myocardial level. The main limitations of this study coincide with those of the main study.3 More specific limitations are the absence of serial measurements of plasma gelatinase activity, and evaluation of gelatinases only; finally, we cannot exclude that different methods based on direct measurement of MMP-2 and -9 activities (i.e. fluorimetric immunoassay) might provide different results. Conflict of interest: none declared.