ACCUMULATION OF CARBONYLS ACCELERATES THE FORMATION OF PENTOSIDINE, AN ADVANCED GLYCATION END-PRODUCT - CARBONYL STRESS IN UREMIA

Advanced glycation end product (AGE) formation is related to hyperglyc emia in diabetes but not in uremia, because plasma AGE levels do not d iffer between diabetic and nondiabetic hemodialysis patients. The mech anism of this phenomenon remains elusive. Previously, it was suggested that elevation of AGE levels in uremia might result from the accumula tion of unknown AGE precursors. The present study evaluates the in vit ro generation of pentosidine, a well identified AGE structure. Plasma samples from healthy subjects and nondiabetic hemodialysis patients we re incubated under air for several weeks. Pentosidine levels were dete rmined al:intervals by HPLC assay. Pentosidine rose to a much larger e xtent in uremic than in control plasma. Pentosidine yield, i.e., the c hange in pentosidine level between 0 and 4 wk divided by 28 d, average d 0.172 nmol/ml per d in uremic versus 0.072 nmol/ml per d in control plasma (P < 0.01). The difference in pentosidine yield between uremic and control plasma was maintained in samples ultrafiltrated through a filter with a 5000-Da cutoff value and fortified with human serum albu min (0.099 versus 0.064 nmol/ml per d; P < 0.05). Pentosidine yield wa s higher in pre- than in postdialysis plasma samples (0.223 versus 0.1 53 nmol/ml per d; P < 0.05). These results suggest that a large fracti on of the pentosidine precursors accumulated in uremic plasma have a l ower than 5000 Da molecular weight. Addition of aminoguanidine and OPB -9195, which inhibit the Maillard reaction, lowered pentosidine yield in both uremic and control plasma. When ultrafiltrated plasma was expo sed to 2,4-dinitrophenylhydrazine, the yield of hydrazones, formed by interaction with carbonyl groups, was markedly higher in uremic than i n control plasma. These observations strongly suggest that the pentosi dine precursors accumulated in uremic plasma are carbonyl compounds. T hese precursors are unrelated to glucose or ascorbic acid, whose conce ntration is either normal or lowered in uremic plasma. They are also u nrelated to 3-deoxyglucosone, a glucose-derived dicarbonyl compound wh ose level is raised in uremic plasma: Its addition to normal plasma fa ils to increase pentosidine yield. This study reports an elevated leve l of reactive carbonyl compounds (''carbonyl stress'') in uremic plasm a. Most have a lower than 5000 Da molecular weight and are thus partly removed by hemodialysis. Their effect on pentosidine generation can b e inhibited by aminoguanidine or OPB-9195. Carbonyl stress might contr ibute to AGE modification of proteins and thus to clinically relevant complications of uremia.