Experimental TLR4 inhibition improves intestinal microcirculation in endotoxemic rats

Introduction: Toll like receptor 4 (TLR4) represents a critical cellular link for endotoxin-induced pathology. The aim of this study was to evaluate the potential role of TLR4 inhibition on the intestinal microcirculation during experimental endotoxemia. Materials and methods: The intestinal microcirculation was studied by intravital microscopy in four groups of Lewis rats (n = 10 per group): healthy controls (CON group), endotoxemic animals (15. mg/kg lipopolysaccharide, LPS group), endotoxemic animals treated with a TLR4 antagonist (1. mg/kg CRX-526, LPS. +. CRX526 group), and controls treated with CRX-526 (C-CRX526 group). Plasma samples were obtained for cytokine measurements at the end of the experiments. Results: Endotoxemia significantly increased leukocyte adhesion in intestinal submucosal venules (e.g., V1 venules: CON 20.4±6.5n/mm², LPS 237.5±36.2n/mm², p<0.05) and reduced capillary perfusion of the intestinal wall (e.g., longitudinal muscular layer: CON 112.5±5.9cm/cm², LPS 71.3±11.0cm/cm², p<0.05) at 2h. TLR4 inhibition significantly reduced endotoxemia-associated leukocyte adhesion (V1 venules: 104.3±7.8n/mm²) and improved capillary perfusion (longitudinal muscular layer: 111.0±12.3cm/cm²). Cytokine release was not significantly affected. Conclusions: The TLR4 pathway may be a target in clinical Gram-negative sepsis since administration of the TLR4 antagonist CRX-526 improved intestinal microcirculation parameters in experimental endotoxemia.