Toll-like receptor 4 (TLR4) belongs to the family of microbial associated molecular patterns. TLR4 is involved in the immune response, and also expressed in cardiomyocytes. Extensive activation of the immune response in the heart causes the release of proinflammatory cytokine mediators which depress heart function. High-mobility group box 1 (HMGB1), released following LPS or hypoxic conditions from both inflammatory cells and from cardiomyocytes, activates TLR4 signaling and induces the release of proinflammatory cytokines and chemokines. Targeting TLR4 with a decoy peptide (TLR4P) derived from TRAM TIR BB loop against TLR4 activation, was tested both in vitro and in vivo following LPS or hypoxic damage. Rat cardiomyocyte were subjected to hypoxia with and without TLR4P (20 µM). Lactate dehydrogenase (LDH), creatine kinase (CK), HMGB1 and TNFα secretion to the medium increased following hypoxia or LPS. TLR4P significantly reduced these markers. TLR4 expression in the cells was reduced (154±0.05 vs 68±0.3%, 172±0.2% vs 61±0.2%, p<0.05, respectively), and HMGB1 secretion decreased (5±1.4ng/ml vs 2.7±0.6ng/ml and 22.9±8.4ng/ml vs 7.3±3.2ng/ml, pin vivo reduced systemic inflammatory response elicited in mice by a sublethal LPS dose and protected mice against LPS challenge as seen by reduction of mortality within 24 hours from 100% to 50%survival. HMGB1 protein expression in cells and serum was decreased (230 ±0.6% vs 165±0.2%, compared to baseline, 32.2±3.7 ng/ml vs 19.3±0.4ng/ml, pin vitro and in vivo against LPS and cardiac ischemic injury.
