Combined subthreshold dose inhibition of myosin light chain phosphorylation and MMP‐2 activity provides cardioprotection from ischaemic/reperfusion injury in isolated rat heart

Background and Purpose Phosphorylation and degradation of myosin light chain 1 ( MLC1 ) during myocardial ischaemia/reperfusion ( I/R ) injury is a well‐established phenomenon. It has been established that MMP ‐2 is involved in MLC1 degradation and that this degradation is increased when MLC1 is phosphorylated. We hypothesized that simultaneous inhibition of MLC1 phosphorylation and MMP ‐2 activity will protect hearts from I/R injury. As phosphorylation of MLC1 and MMP ‐2 activity is important for normal heart function, we used a cocktail consisting combination of low (subthreshold for any protective effect alone) doses of MLC kinase, MMP ‐2 inhibitors and subthreshold dose of an MLC phosphatase activator. Experimental Approach Isolated rat hearts were subjected to 20 min of global, no‐flow ischaemia and 30 min reperfusion in the absence and presence of inhibitors of MLC1 phosphorylation and degradation. Key Results The recovery of cardiac function was improved in a concentration‐dependent manner by the MLC kinase inhibitor, ML ‐7 (1–5 μM), the MLC phosphatase activator, Y ‐27632 (0.05–1 μM) or the MMP inhibitor, doxycycline ( D oxy, 1–30 μM). Co‐administration of subthreshold doses of ML ‐7 (1 μM) and Y ‐27632 (0.05 μM) showed a potential synergistic effect in protecting cardiac contractility and MLC1 levels in I/R hearts. Further combination with a subthreshold concentration of D oxy (1 μM) showed additional protection that resulted in full recovery to control levels. Conclusions and Implications The results of this study exemplify a novel low‐dose multidrug approach to pharmacological prevention of reperfusion injury that will enable a reduction of unwanted side effects and/or cytotoxicity associated with currently available MMP ‐2 and kinase inhibiting drugs.