Study of the effects of metformin on Toll like receptor 4 (TLR-4) expression and activity in the isolated rat heart

Abstract

Introduction: 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. Aims: In this work, the potential of AMPK activation by metformin in regulation of immune responses in myocard and lung tissue and also in the isolated rat heart were investigated. Methods: TLR-4 expression was evaluated by real-time PCR. The MyD88 and NF-κB content and also P-AMPKα and P-ACC were evaluated by western blot. The levels of TNF-α and IL-6 were assayed by ELISA method. Results: LPS profoundly upregulated TLR-4 expression in the heart and lung tissue and increased the tissue levels of MyD88 and NF-κB and release of TNF-α and IL-6. The enhancement in TLR-4 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 TLR-4 activity. Antagonizing AMPK by compound C considerably reversed the protective effects of metformin against TLR-4 activity in isolated heart. Histological examinations of lung tissue revealed that metformin remarkably attenuated congestion and inflammatory cellular infiltration into the alveolar walls and also decreased MPO activity by 37% (P < 0.05). Conclusion: The results of the study demonstrated the importance of local immune response in the LPS-induced myocardial dysfunction and indicated a link between AMPK and TLR-4. Furthermore, these results suggest that metformin exhibits protective effects in sepsis by suppression of TLR-4 activity, at least in part through pathways involving AMPK activation.