Aminoguanidine (AG), a prototype agent for the preventive
therapy of
diabetic complications, reacts with the physiological alpha-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 alpha-oxoaldehydes with AG under physiological conditions pH 7.4 and 37 degrees was investigated. The rate of reaction of AG with
glyoxal was first order with respect to both reactants; the rate constant k(AG,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](k(AG,3-DG)[AG] + k(3-DG)), where k(AG,3-DG) = (3. 23 +/- 0.25) x 10(-3) M(-1) sec(-1) and k(3-DG) = (1.73 +/- 0.08) x 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-H(2)O) forms. The rate equation was d[T](o)/dt = ¿k(1)k(AG,MG)/(k(-1) + k(AG,MG)[AG]) + k(AG, MG-H(2)O)¿[MG-H(2)O][AG], where the rate constant for the reaction of AG with MG, k(AG,MG), was 178 +/- 15 M(-1) sec(-1) and for the reaction of AG with MG-H(2)O, k(AG,MG-H(2)O), was 0.102 +/- 0.001 M(-1) sec(-1); k(1) and k(-1) are the forward and reverse rate constants for
methylglyoxal dehydration MG-H(2)O right harpoon over left harpoon MG. The kinetics of these reactions were not influenced by ionic strength, but the reaction of AG with
glyoxal and with
methylglyoxal under MG-H(2)O
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-H(2)O equilibrium, and the ratio of the isomeric
triazine products varied with initial reactant concentration. AG is kinetically competent to scavenge the alpha-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.