Bacterial endotoxin (lipopolysaccharide) stimulates the rate of iron oxidation

Bacterial endotoxin (lipopolysaccharide) has affinity for a number of catio ns, including iron. Previous investigations have demonstrated that lipopoly saccharide can affect the oxidation rate of iron; heme-bound ferrous iron i n hemoglobin is oxidized to ferric iron when hemoglobin binds lipopolysacch aride. In the present study, we directly examined the interaction between l ipopolysaccharide and iron. Lipopolysaccharide caused a concentration-depen dent increase in the rate of iron oxidation, with up to a 23-fold increase in oxidation in the presence of 200 mug/ml Escherichia coli lipopolysacchar ide. This effect was seen both with several carbohydrate-rich smooth lipopo lysaccharides and also with carbohydrate-poor rough lipopolysaccharide. Ext ensively deacylated rough lipopolysaccharide had no effect, suggesting a ro le of the fatty acid components of lipopolysaccharide in this process. Puri fied lipid A produced inconsistent results: some preparations stimulated ir on oxidation and others did not. A series of sugars, starches and a prepara tion of purified O-chain polysaccharide (the carbohydrate portion of the li popolysaccharide macro-molecule) had no effect on the rate of iron oxidatio n, whereas phospholipid-enriched brain tissue extracts (similar to the lipi d A component of lipopolysaccharide) stimulated oxidation. We conclude that the lipid moiety of bacterial lipopolysaccharide is responsible for the st imulation of iron oxidation. This process may contribute to the ability of lipopolysaccharide to cause oxidation of heme-bound iron in hemoglobin.