Metabolic activation of pioglitazone identified from rat and human liver microsomes and freshly isolated hepatocytes.

Pioglitazone is in the class of compounds known as the thiazolidinediones and is used to treat type 2 diabetes mellitus. The first in its class compound, troglitazone, was withdrawn from the U.S.

Aminoguanidine and the effects of modified LDL on cultured retinal capillary cells.

Purpose: Compared with normal low density lipoprotein (N-LDL), LDL minimally modified in vitro by glycation, minimal oxidation, or glycoxidation (G-, MO-, GO-LDL) decreases survival of cultured retinal capillary endothelial cells and pericytes. Similar modifications occurring in vivo in diabetes may contribute to retinopathy. The goal of this study was to determine whether low concentrations of aminoguanidine might prevent cytotoxic modification of LDL and/or protect retinal capillary cells from previously modified LDL.

Age-dependent increase in ortho-tyrosine and methionine sulfoxide in human skin collagen is not accelerated in diabetes. Evidence against a generalized increase in oxidative stress in diabetes.

The glycoxidation products Nepsilon-(carboxymethyl)lysine and pentosidine increase in skin collagen with age and at an accelerated rate in diabetes. Their age-adjusted concentrations in skin collagen are correlated with the severity of diabetic complications. To determine the relative roles of increased glycation and/or oxidation in the accelerated formation of glycoxidation products in diabetes, we measured levels of amino acid oxidation products, distinct from glycoxidative modifications of amino acids, as independent indicators of oxidative stress and damage to collagen in aging and diabetes.

New biomarkers of Maillard reaction damage to proteins.

The amount of advanced glycation end-products (AGE) in tissue proteins increases in diabetes mellitus, and the concentration of a subclass of AGEs, known as glycoxidation products, also increases with chronological age in proteins. The rate of accumulation of glycoxidation products is accelerated in diabetes and age-adjusted concentrations of two glycoxidation products, N epsilon-(carboxymethyl)lysine (CML) and pentosidine, correlate with the severity of complication in diabetic patients. Although AGEs and glycoxidation products are implicated in the development of diabetic complications, these compounds are present at only trace concentrations in tissue proteins and account for only a fraction of the chemical modifications in AGE proteins prepared in vitro.

Pathways of formation of glycoxidation products during glycation of collagen.

Glycoxidation products (GOPs), such as N epsilon-(carboxymethyl)lysine (CML) and pentosidine, are formed during reaction of glucose with protein under oxidative conditions in vitro. It is uncertain whether these GOPs are derived from oxidation of Amadori adducts on protein or from oxidation of glucose or intermediates formed prior to the Amadori rearrangement. To address this question, we reacted collagen with 250 mM glucose in 200 mM phosphate buffer, pH 7.

Toxicity of mildly modified low-density lipoproteins to cultured retinal capillary endothelial cells and pericytes.

To investigate the role of modified low-density lipoproteins (LDL) in the pathogenesis of diabetic retinopathy, we studied the cytotoxicity of normal and mildly modified human LDL to bovine retinal capillary endothelial cells and pericytes in vitro. Pooled LDL was incubated (in phosphate-buffered saline-EDTA, 3 days, 37 degrees C) under 1) nitrogen with additional chelating agents and 2) air, to prepare normal and minimally oxidized LDL, respectively. Similar conditions, but with the addition of 50 mM D-glucose, were used to prepare glycated and glycoxidized LDL.

Oxidized amino acids in lens protein with age. Measurement of o-tyrosine and dityrosine in the aging human lens.

The concentrations of ortho-tyrosine (o-Tyr) and dityrosine (DT) were measured in noncataractous human lenses in order to assess the role of protein oxidation reactions in the aging of lens proteins. The measurements were conducted by selected ion monitoring-gas chromatography/mass spectrometry using deuterium-labeled internal standards, which provided both high sensitivity and specificity for the quantitation of o-Tyr and DT. Between ages 1 and 78 years, the o-Tyr concentration in lens proteins varied from 0.

Formation of o-tyrosine and dityrosine in proteins during radiolytic and metal-catalyzed oxidation.

To evaluate their usefulness as chemical indicators of cumulative oxidative damage to proteins, we studied the kinetics and extent of formation of ortho-tyrosine (o-Tyr), dityrosine (DT), and dityrosine-like fluorescence (Ex = 317 nm, Em = 407 nm) in the model proteins RNase and lysozyme exposed to radiolytic and metal-catalyzed (H2O2/Cu2+) oxidation (MCO). Although there were protein-dependent differences, o-Tyr, DT, and fluorescence increased coordinately during oxidation of the proteins in both oxidation systems. The contribution of DT to total dityrosine-like fluorescence in oxidized proteins varied from 2-100%, depending on the protein, type of oxidation, and extent of oxidative damage.