Endotoxin stimulates hydrogen peroxide detoxifying activity in rat hepatic endothelial cells

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Abstract

The study aimed to assess the effect of lipopolysaccharide (LPS) in vivo (from Escherichia coli, 2 mg/kg body weight intraperitoneally) on the production and elimination of hydrogen peroxide (H2O2) in rat hepatic endothelial and Kupffer cells. Twenty-two hours after the injection of LPS, hepatic cells were isolated by collagenase and pronase digestion followed by centrifugal elutriation, and cell- associated H2O2 was determined by flow cytometry analysis using 2′,7′- dichloroflorescin diacetate (DCF-diacetate). LPS treatment did not alter the basal or phorbol myristate acetate-stimulated levels of H2O2- related fluorescence in endothelial cells; however, it doubled phorbol myristate acetate-stimulated fluorescence in Kupffer cells. Administration of varying concentrations of H202 (range, 10−7 - 10−4 mol/L) in vitro caused a significantly delayed increase in fluorescence in endothelial cells from endotoxemic rats as compared with cells from saline-injected animals. The 50% effective concentration of H2O2 was found at 1.1 × 10−6 and 8.1 × 10−6 mol/L on endothelial cells after saline and LPS treatment, respectively. No differences were detected in H2O2-stimulated fluorescence between resting and LPS-stimulated Kupffer cells. Administration of varying glucose concentrations in vitro significantly decreased the H2O2- stimulated fluorescence in endothelial and Kupffer cells from LPS- injected animals. Inhibition of nitric oxide synthase by in vitro administration of NG-monomethyl-L-arginine (L-NNMMA) did not alter the H2O2- or phorbol myristate acetate-stimulated responses in endothelial and Kupffer cells. As shown earlier, LPS stimulates the gene expression of GLUT1 glucose transporter, glucose-6-phosphate dehydrogenase (G6PD), superoxide dismutases, and glutathione peroxidase in hepatic endothelial cells. The present data indicate that the LPS-induced metabolic alterations are accompanied by an increased H2O2-detoxifying capacity in hepatic endothelial cells. This may represent a protective mechanism against exogenous oxidative stress caused by activated hepatic phagocytes during inflammation. Our observations are consistent with primed production of reactive oxygen species (ROS) in LPS-activated Kupffer cells.

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