Endotoxins stimulate generation of superoxide radicals and lipid peroxidation in blood platelets

Lipopolysaccharide (LPS, endotoxin) is an important structural constituent of the membrane of Gram-negative bacteria with a wide range of biological e ffects. It can activate blood platelets. The purpose of present study was t o determine the direct effect of endotoxins from Proteus mirabilis, differi ng significantly in their composition, on the generation of superoxide radi cals and thiobarbituric acid reactive substances (TBARS) in blood platelets . Superoxide radicals were measured by means of superoxide dismutase-inhibi table reduction of cytochrome C. The TEARS determination (malonyldialdehyde ) was used as a marker of endogenous arachidonate metabolism end thromboxan e A:! synthesis. Results demonstrate that three endotoxins (LPS S1959, LPS R110, LPS R45) after 2 min of action, even at the lowest concentration (0.0 3 mu g/10(8) platelets) stimulated the generation of TEARS and release of s uperoxide radicals. All LPS contain lipid A as a component but differ in th eir chemical composition in the polysaccharide part. It is suggested that t he observed effects of LPS on blood platelets are attributable to their lip id A portion.