The Role of MKP-1 in Insulin-Induced Cardioprotection.

Purpose: The mitogen-activated protein kinase phosphatases (MKPs) are a family of dual-specificity phosphatases that inactivate MAPKs by dephosphorylation. Impairment of MKP-1 expression in insulin resistance has been suggested to affect the cardioprotective properties of insulin. We hypothesized that manipulation of its activity during myocardial ischaemia/reperfusion of control as well as insulin-resistant rats may affect the outcome.

Methods: Hearts from 16 week dietary induced obese Wistar rats and their age matched controls were isolated, perfused in the working mode and subjected to 15 min global ischaemia / 30 min reperfusion or 35 min coronary artery ligation/ 60 min reperfusion. Hearts received insulin (1mIU/ml), a MKP-1 inhibitor (sanguinarine 2.5uM), or insulin + sanguinarine for 15 min pre- and 10 min post-ischaemia. Endpoints were functional recovery and infarct size. Hearts from control and experimental groups were freeze-clamped either immediately after removal from the animal (baseline) or at 10 min reperfusion after global ischaemia and Western blot analysis done for total and phosphorylated MKP-1.

Results: Insulin treatment significantly increased total work recovery while sanguinarine abolished the insulin-mediated protection. Insulin had no effect on infarct size while sanguinarine reduced infarct size. Insulin increased while sanguinarine attenuated phosphorylation of MKP-1 at 10 min reperfusion.

Conclusion: Inhibition of MKP-1 with sanguinarine abolished the insulin-induced improvement in functional recovery, but reduced infarct size. Although the data suggest a role for this phosphatase in insulin-induced cardioprotection, the multiple downstream effects of insulin hamper interpretation of the data obtained. In addition, the effects of sanguinarine per se in myocardial ischaemia/reperfusion need to be further elucidated.