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 effects. It can activate blood platelets. The purpose of present study was to determine the direct effect of endotoxins from Proteus mirabilis, differing significantly in their composition, on the generation of superoxide radicals and thiobarbituric acid reactive substances (TBARS) in blood platelets. Superoxide radicals were measured by means of superoxide dismutase-inhibitable reduction of cytochrome C. The TBARS determination (malonyldialdehyde) was used as a marker of endogenous arachidonate metabolism and thromboxane A2 synthesis. Results demonstrate that three endotoxins (LPS S1959, LPS R110, LPS R45) after 2 min of action, even at the lowest concentration (0.03 microg/10(8) platelets) stimulated the generation of TBARS and release of superoxide radicals. All LPS contain lipid A as a component but differ in their chemical composition in the polysaccharide part. It is suggested that the observed effects of LPS on blood platelets are attributable to their lipid A portion.