Effect of nonenzymatic glycation of albumin and superoxide dismutase by glucuronic acid and suprofen acyl glucuronide on their functions in vitro

Acyl glucuronides bind irreversibly to plasma proteins, and one mechanism p roposed for this covalent binding is similar to that for glycation of prote in by reducing sugars. Because glycation of protein by glucose and other re ducing sugars can alter protein function, this lead to the hypothesis that the glycation of proteins by acyl glucuronides may cause similar effects. W hen human serum albumin (HSA) was incubated with 0.5 M glucose for 5 days, the unbound fractions of diazepam and warfarin were increased by 41 and 35% , respectively, less than that caused by glucuronic acid which increased th e unbound fractions by 90% for diazepam and 420% for warfarin. When HSA was incubated with suprofen glucuronide (SG) at a much lower concentration of 0.005 M for only 24 h, the effects on the unbound fractions of diazepam and warfarin to HSA were altered dramatically with increases of 340 and 230%, respectively. After incubation of superoxide dismutase (SOD) with 0.5 or 1 M reducing sugars for 14 days, the enzyme activity decreased to 82 and 61% of initial levels at day 14, respectively, whereas glucuronic acid almost c ompletely inactivated the enzyme activity over the same period. Even at a v ery low concentration (0.005 M) of SG, SOD activity was reduced significant ly to 11% of initial levels by day 14, which was comparable to the effect b y 0.5 and 1.0 M concentrations of glucuronic acid. Sodium dodecyl sulfate p olyacrylamide gel electrophoresis and matrix associated laser desorption:io nization time of flight mass spectrometry indicated that several equivalent s of reducing sugars or SG became attached to albumin after incubation. The se results suggest that acyl glucuronides may affect the function of protei ns by the formation of glycated protein in vivo and may be associated with the toxicity of xenobiotics metabolized to labile acyl glucuronides. (C) 19 99 Elsevier Science Ireland Ltd. All rights reserved.