Oxygen radical generation by Maillard compounds

Colorimetric cell proliferation assay for microorganisms in microtiter plate using water-soluble tetrazolium salts

A colorimetric method to assay cell proliferation of microorganisms in 96-well microtiter plates using water-soluble tetrazolium salts and electron mediators was developed. Combinations of 6 kinds of water-soluble tetrazolium salts and 27 kinds of electron mediators that considered the metabolic efficiency of microorganisms and the influence with medium components were investigated. 2-Methyl-1,4-naphthoquinone (NQ) was reduced most effectively by various species of microorganisms, and a combination of WST-8 as a water-soluble tetrazolium salt with 2-methyl-1,4-NQ repressed the increase in background due to medium components. In the presence of 2-methyl-1,4-NQ, WST-8 was reduced by microbial cells to formazan, which exhibited maximum absorbance at 460 nm. The proposed tetrazolium method could be applied to measure proliferations of various microbial cells including 3 kinds of yeast, 9 kinds of Gram-positive bacteria, and 10 kinds of Gram-negative bacteria. Linear relationships between the absorbance and viable microbial cell density were obtained in all microorganisms, suggesting that the absorbance change reflected the microbial cell proliferation.

Pathophysiological concentrations of glucose promote oxidative modification of low density lipoprotein by a superoxide-dependent pathway

Oxidized lipoproteins may be important in the pathogenesis of atherosclerosis. Because diabetic subjects are particularly prone to vascular disease, and glucose autoxidation and protein glycation generate reactive oxygen species, we explored the role of glucose in lipoprotein oxidation. Glucose enhanced low density lipoprotein (LDL) oxidation at concentrations seen in the diabetic state. Conjugated dienes, thiobarbituric acid reactive substances, electrophoretic mobility, and degradation by macrophages were increased when LDL was modified in the presence of glucose. In contrast, free lysine groups and fibroblast degradation were reduced. Although loss of reactive lysine groups could be due to either oxidative modification or nonenzymatic glycation of apolipoprotein B-100, inhibition of lipid peroxidation by the metal chelator, diethylenetriamine pentaacetic acid, blocked the changes in free lysines. Thus, glycation of lysine residues is unlikely to account for the alterations in macrophage and fibroblast uptake of LDL modified in the presence of glucose. Glucose-mediated enhancement of LDL oxidation was partially blocked by superoxide dismutase and nearly completely inhibited by butylated hydroxytoluene. These findings indicate that glucose enhances LDL lipid peroxidation by an oxidative pathway involving superoxide and raise the possibility that the chronic hyperglycemia of diabetes accelerates lipoprotein oxidation, thereby promoting diabetic vascular disease.