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Increased formation of methylglyoxal in clinical diabetes mellitus and metabolism by the glyoxalase system has been linked to the development of clinical complications of diabetes: retinopathy, neuropathy and nephropathy. Aminoguanidine has been proposed as a prophylactic agent for preventive therapy of diabetic complications. Methylglyoxal reacted with aminoguanidine under physiological conditions to form two isomeric triazines, 3-amino-5-methyl-1,2,4-triazine and 3-amino-6-methyl-1,2,4-triazine. The mean second order rate constant for the reaction of methylglyoxal with aminoguanidine, kMG.AG = 0.39 +/- 0.06 M-1 sec-1 at pH 7.4 and 37 degrees. Under these conditions, no methylglyoxal bisguanylhydrazone was detected. Aminoguanidine prevented the irreversible modification of human plasma protein by a physiological concentration of methylglyoxal (1 microM); the median inhibitory concentration IC50 value of aminoguanidine was 203 +/- 16 microM (N = 28). The scavenging of methylglyoxal by aminoguanidine may contribute to the beneficial effects of aminoguanidine in the prevention of vascular pathogenesis in diabetes.

Diethyl esters of the glutathione S-conjugate S-p-bromobenzylglutathione, an inhibitor of glyoxalase I, and S-p-nitrobenzoxycarbonylglutathione, an inhibitor of glyoxalase II, induced growth arrest and toxicity in human leukaemia 60 cells in culture. The median growth inhibitory concentration IC50 values were 8.3 microM (95% C.I. 7.0-9.9 microM) for S-p-bromobenzylglutathione diethyl ester and 56 microM (95% C.I. 36-86 microM) for p-nitrobenzoxycarbonylglutathione. Monoethyl ester and unesterified derivatives were inactive. The diethyl ester derivatives were also toxic to mature human neutrophils under the same culture conditions where the respective median toxic concentration IC50 values were 39.7 (95% C.I. 35.4-44.5 microM) and 127 (95% C.I. 123-132 microM) microM. Diester derivatives may be of future interest in studying the cytotoxicity of glutathione S-conjugates and for the development of cytotoxic anti-tumour agents.