The effect of Escherichia coli-derived lipopolysaccharides on plasma levels of malondialdehyde and 3-nitrotyrosine.

The aim of this study was to determine the effect of Escherichia coli (E. coli)-derived lipopolysaccharide on rat plasma low density lipoprotein (LDL), malondialdehyde and 3-nitrotyrosine levels (an indicator of protein nitration). Six hours after intraperitoneal administration of E.coli, plasma LDL was measured electrophoretically and malondialdehyde level was measured by spectrophotometric method. Plasma malondialdehyde was significantly (p<0.001) elevated in E. coli-injected rats (4.97 +/- 1.33; n=10) in comparison to control animals (1.83 +/- 0.5; n=10). In addition, plasma 3-nitrotyrosine level, determined by reverse-phase HPLC, was also increased in the infected group (2.84 +/- 1.17 to 0.22 +/- 0.13; n=10). This increase was statistically significant (p<0.001). An increased level of oxidation of lipids and 3-nitrotyrosine was observed as a result of free radical-mediated damage in plasma. In conclusion, asymptomatic infections may increase the risk of atherosclerosis by inducing free radical formation and a consequent increase in the oxidation of LDL.

The effects of peroxynitrite on erythrocytes.

Endotoxin-induced peroxynitrite formation has been demonstrated in plasma. The aim of this study is to evaluate whether this has an effect on erythrocytes. For this purpose erythrocyte 3-nitrotyrosine (3-NT) level, Na+-K+ ATPase and glutathione peroxidase activities were measured both in vivo and in vitro. In vivo peroxynitrite formation was induced in rats by intraperitoneal Escherichia coli (E.coli) injection. Erythrocytes were directly incubated with peroxynitrite in the in vitro experiment. 3-NT levels were measured by reverse-phase HPLC, glutathione peroxidase, and Na+-K+ ATPase activities were measured by spectrophotometric techniques. There was a marked increase in the 3-NT levels in both experiments. However, glutathione peroxidase activity was significantly increased in in vivo experiments, while decreasing in in vitro conditions. Although Na+-K+ ATPase activities were significantly reduced by peroxynitrite in vitro, Na+-K+ ATPase activities were similar in control and E.coli-injected rat erythrocytes. Although nitrating effect of peroxynitrite does not seem to be preventable by endogenous antioxidants, this effect of peroxynitrite may not endanger erythrocytes if the oxidative damage of peroxynitrite is prevented.