Glyoxalase I deficiency is associated with an unusual level of advanced glycation end products in a hemodialysis patient

Background. Advanced glycation of proteins and their attendant advanced gly cation end products (AGES) contribute to the complications associated with diabetes mellitus or uremia. Regulatory mechanisms of AGE formation in vivo remain an issue of particular interest. We investigated a role of the glyo xalase detoxification system of precursor reactive carbonyl compounds (RCOs ) in the in vivo AGE formation. Methods. Plasma levels of AGES [pentosidine and N-epsilon-carboxymethyllysi ne (CML)], their RCO precursors, D-lactate (the final product resulting fro m the glyoxalase detoxification pathway), as well as of various compounds k nown to generate AGE precursors and surrogate markers for oxidative stress (antioxidant enzymes and glutathione), were measured in both hemodialysis ( HD) patients and normal subjects. The activity and protein expression of gl yoxalase I, an enzyme essential for the detoxification of alpha -oxoaldehyd es, in red blood cells (RBC) were also examined. Results. In one 69-year-old lady who had been on hemodialysis (HD) for thre e years and had suffered from recurrent cardiovascular complications despit e the absence of significant risk factors, plasma levels of pentosidine (77 .3 +/- 2.4 pmol/mg protein) and CML (330.8 +/- 8.2 pmol/mg protein) were ma rkedly elevated as compared to other HD patients (N = 20:26.6 +/- 11.8 pmol /mg protein for pentosidine and 224.4 +/- 51.7 pmol/mg protein for CML). Th e plasma level of RCO precursors for pentosidine and CML was also higher in this patient than in other HD patients. Further investigation disclosed a very low activity in RBC of glyoxalase I (1.5 +/- 0.4 mU/10(6) RBC), as com pared to other HD patients (3.9 +/- 0.6 mU/10(6) RBC) or normal subjects (4 .0 +/- 0.6 mU/10(6) RBC). The glyoxalase I protein level, assessed in RBC b y immunoblot analysis with a specific antibody, was markedly lower than tha t observed in HD patients and normal subjects. The causes of this deficienc y remain unknown. Nucleotide sequencing of the products of reverse transcri ption-polymerase chain reaction from the patient's mononuclear cells reveal ed no genetic mutation within the coding region of the glyoxalase I gene. P lasma D-lactate level was also in the lower range (0.18 +/- 0.03 mg/dL) of the values measured in the other HD patients (0.27 +/- 0.09 mg/dL) and norm al subjects (0.35 +/- 0.12 mg/dL). The plasma levels of various compounds k nown to generate AGE precursors (glucose, lipids and ascorbic acid) were ei ther normal or low. The surrogate markers for oxidative stress such as anti oxidant enzymes (glutathione peroxidases and superoxide dismutase) and glut athione were all within the range observed in the other HD patients. Conclusion. The unusually high levels of AGES in this patient implicate a d eficient glyoxalase detoxification of RCO precursors. The present clinical observation implicates, to our knowledge for the first time, the glyoxalase detoxification system and, in particular, glyoxalase in the actual level o f AGES in a uremic patient.