indoxam and Shock--Septic

Phospholipase A2 receptor (PLA2R) is a type I transmembrane glycoprotein related to the C-type animal lectin family and mediates a variety of biological responses elicited by group IB secretory phospholipase A2 (sPLA2-IB). In the present study, we have shown the evidence that a novel type of sPLA2, sPLA2-X, also acts as one of the high-affinity ligands for mouse PLA2R. We then generated PLA2R-deficient mice and found that the knockout mice exhibited the resistance to an endotoxic shock with reduced plasma levels of proinflammatory cytokines, such as TNF-alpha and IL-1 beta. In situ hybridization analysis revealed that the expression of PLA2R transcript was markedly enhanced in type II alveolar epithelial cells and a subset of splenic lymphocytes in accordance with the elevated expression of sPLA2-IB and TNF-alpha mRNAs during endotoxic shock. In addition, the elevated expression level of TNF-alpha transcript was significantly reduced by the deficiency of PLA2R, suggesting that PLA2R plays a role in the regulation of TNF-alpha expression in these cell types. We then synthesized a specific sPLA2 inhibitor, indoxam, which blocked the binding of sPLA2-IB and X to PLA2R. Indoxam was found to suppress the elevation of the plasma level of TNF-alpha and prolonged the survival of endotoxin-challenged mice. The inhibitory effects of indoxam were abolished by the deficiency of PLA2R, demonstrating the involvement of PLA2R in the progression of endotoxic shock. We also detected and characterized a soluble form of PLA2R protein in the plasma of mouse with anti-PLA2R antibody, and showed its potential role as an endogenous sPLA2 inhibitor. Taken together, a series of studies with PLA2R-knockout mice have elucidated a critical role of PLA2R in the regulation of the development of endotoxic shock.

Topics: Animals; Carbamates; Disease Models, Animal; Enzyme Inhibitors; Group II Phospholipases A2; Group X Phospholipases A2; Humans; Indolizines; Mice; Mice, Knockout; Phospholipases A; Phospholipases A2; Receptors, Cell Surface; Receptors, Phospholipase A2; Shock, Septic; Solubility; Tumor Necrosis Factor-alpha

Endotoxic shock is a systemic inflammatory process, involving a variety of proinflammatory mediators. Two types of secretory phospholipase A2 (sPLA2) have been implicated in this process. Group IB sPLA2 (PLA2-IB) binds to the PLA2 receptor (PLA2R), and PLA2R-deficient mice exhibit resistance to endotoxin-induced lethality with reduced plasma levels of proinflammatory cytokines, such as TNF-alpha. Group IIA sPLA2 (PLA2-IIA) is found in many tissues and cell types, and local and systemic levels are elevated under numerous inflammatory conditions including sepsis. In this study, we investigated the effect of a specific sPLA2 inhibitor, indoxam, on murine endotoxic shock. Indoxam suppressed the elevation of plasma TNF-alpha with a similar potency in PLA2-IIA-expressing and PLA2-IIA-deficient mice after LPS challenge. In PLA2-IIA-deficient mice, indoxam also suppressed the elevation of plasma IL-1beta, IL-6 and NO, and prolonged survival after LPS challenge. Indoxam was found to block the PLA2-IB binding to murine PLA2R with a high potency (Ki=30 nM). The inhibitory effects of indoxam on the LPS-induced elevation of plasma TNF-alpha levels could not be observed in mice deficient in PLA2R. These findings suggest that indoxam blocks the production of proinflammatory cytokines during endotoxemia through PLA2-IIA-independent mechanisms, possibly via blockade of the PLA2R function.

Topics: Animals; Carbamates; Carrier Proteins; Enzyme Inhibitors; Female; Group II Phospholipases A2; Indolizines; Interleukin-1; Interleukin-6; Lipopolysaccharides; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Phospholipases A; Phospholipases A2; Receptors, Cell Surface; Receptors, Phospholipase A2; Shock, Septic; Tumor Necrosis Factor-alpha