Paul J Thornalley, A. Yurek-George, O. Argirov
Jul 1, 2000
Citations
4
Influential Citations
174
Citations
Quality indicators
Journal
Biochemical pharmacology
Abstract
Abstract Aminoguanidine (AG), a prototype agent for the preventive therapy of diabetic complications, reacts with the physiological α-oxoaldehydes glyoxal, methylglyoxal, and 3-deoxyglucosone (3-DG) to form 3-amino-1,2,4-triazine derivatives (T) and prevent glycation by these agents in vitro and in vivo. The reaction kinetics of these α-oxoaldehydes with AG under physiological conditions pH 7.4 and 37° was investigated. The rate of reaction of AG with glyoxal was first order with respect to both reactants; the rate constant kAG,G was 0.892 ± 0.037 M−1 sec−1. The kinetics of the reaction of AG with 3-DG were more complex: the rate equation was d[T]o/dt (initial rate of T formation) = [3-DG](kAG,3-DG[AG] + k3-DG), where kAG,3-DG = (3.23 ± 0.25) × 10−3 M−1 sec−1 and k3-DG = (1.73 ± 0.08) × 10−5 sec−1. The kinetics of the reaction of AG with methylglyoxal were consistent with the reaction of both unhydrated (MG) and monohydrate (MG-H2O) forms. The rate equation was d[T]o/dt = {k1kAG,MG/(k−1 + kAG,MG[AG]) + kAG,MG-H2O}[MG-H2O][AG], where the rate constant for the reaction of AG with MG, kAG,MG, was 178 ± 15 M−1 sec−1 and for the reaction of AG with MG-H2O, kAG,MG-H2O, was 0.102 ± 0.001 M−1 sec−1; k1 and k−1 are the forward and reverse rate constants for methylglyoxal dehydration MG-H2O ⇌ MG. The kinetics of these reactions were not influenced by ionic strength, but the reaction of AG with glyoxal and with methylglyoxal under MG-H2O dehydration rate-limited conditions increased with increasing phosphate buffer concentration. Kinetic modelling indicated that the rapid reaction of AG with the MG perturbed the MG/MG-H2O equilibrium, and the ratio of the isomeric triazine products varied with initial reactant concentration. AG is kinetically competent to scavenge the α-oxoaldehydes studied and decrease related advanced glycated endproduct (AGE) formation in vivo. This effect is limited, however, by the rapid renal elimination of AG. Decreased AGE formation is implicated in the prevention of microvascular complications of diabetes by AG.