Immunohistochemical evidence for an increased oxidative stress and carbonyl modification of proteins in diabetic glomerular lesions

Advanced glycation end products (AGE) include a variety of protein adducts whose accumulation has been implicated in tissue damage associated with dia betic nephropathy (DN). It was recently demonstrated that among AGE, glycox idation products, whose formation is closely linked to oxidation, such as c arboxymethyllysine (CML) and pentosidine, accumulate in expanded mesangial matrix and nodular lesions in DN, in colocalization with malondialdehyde-ly sine (MDA-lysine), a lipoxidation product, whereas pyrraline, another AGE s tructure whose deposition is rather independent from oxidative stress, was not found within diabetic glomeruli. Because CML, pentosidine, and MDA-lysi ne are all formed under oxidative stress by carbonyl amine chemistry betwee n protein amino group and carbonyl compounds, their colocalization suggests a local oxidative stress and increased protein carbonyl modification in di abetic glomerular lesions. To address this hypothesis, human renal tissues from patients with DN or IgA nephropathy were examined with specific antibo dies to characterize most, if not all, carbonyl modifications of proteins b y autoxidation products of carbohydrates, lipids, and amino acids: CML (der ived from carbohydrates, lipids, and amino acid), pentosidine (derived from carbohydrates), MDA-lysine (derived from lipids), 4-hydroxynonenal-protein adduct (derived from lipids), and acrolein-protein adduct (derived from li pids and amino acid). All of the protein adducts were identified in expande d mesangial matrix and nodular lesions in DN. In IgA nephropathy, another p rimary glomerular disease leading to end-stage renal failure, despite posit ive staining for MDA-lysine and 4-hydroxynonenal-protein adduct in the expa nded mesangial area, CML, pentosidine, and acrolein-protein adduct immunore activities were only faint in glomeruli. These data suggest a broad derange ment in nonenzymatic biochemistry in diabetic glomerular lesions, and impli cate an increased local oxidative stress and carbonyl modification of prote ins in diabetic glomerular tissue damage ("carbonyl stress").