Cardioprotective effect of metformin in lipopolysaccharide-induced sepsis via suppression of toll-like receptor 4 (TLR4) in heart

Mechanisms of cardioprotection via modulation of the immune response

Both morbidity and mortality as a result of cardiovascular disease remain significant worldwide and account for approximately 31% of annual deaths in the US. Current research is focused on novel therapeutic strategies to protect the heart during and after ischemic events and from subsequent adverse myocardial remodeling. After cardiac insult, the immune system is activated and plays an essential role in the beginning, development, and resolution of the healing cascade. Uncontrolled inflammatory responses can cause chronic disease and exacerbate progression to heart failure and therefore, constitute a major area of focus of cardiac therapies. In the present overview, we share novel insights and promising therapeutic cardioprotective strategies that target the immune response.

AMPK activation by metformin inhibits local innate immune responses in the isolated rat heart by suppression of TLR 4-related pathway

Toll like receptors (TLRs) are key players in the innate immune responses. The energy sensing enzyme, AMPK, has been implicated in the modulation of immunity. The present study investigated whether AMPK activation by metformin could contribute to the regulation of immune responses in the isolated heart via suppression of TLR4 activity, independent of circulatory immunity. Isolated Wistar rat hearts were perfused with Krebs-Henseleit buffer in the absence or presence of lipopolysaccharide (LPS; 0.2μM), LPS+metformin (10mM), and LPS+metformin+compound C (10μM). Following measurement of hemodynamic parameters, TLR4-activation related changes and TLR4 mRNA level in the heart was examined by western blotting and real-time PCR. The activation of AMPK was evaluated by measuring the ratio of p-AMPKα and p-ACC to their non-phosphorylated forms. The effluent and cardiac levels of TNF-α and IL6 were assayed by ELISA. LPS profoundly increased the levels of TLR4 mRNA, MyD88 (TLR4 adaptor protein), and NF-κB and also the release of TNF-α and IL6 from the heart. The enhancement in the TLR4 activity was associated with a significant depression of myocardial function. Metformin clearly augmented the phosphorylation of both AMPKα and ACC and in addition to improvement of cardiac performance, markedly suppressed the TLR4 activity. Antagonizing AMPK by compound C which is a selective inhibitor of AMPK pathway, considerably reversed the protective effects of metformin against the TLR4-related activity. The results of the study demonstrated the importance of TLR4-involved local immune responses in the LPS-induced myocardial dysfunction and indicated a clear link between AMPK and TLR4.