Kinetics and mechanism of the reaction of aminoguanidine with the α-oxoaldehydes glyoxal, methylglyoxal, and 3-deoxyglucosone under physiological conditions

doi:10.1016/S0006-2952(00)00287-2

Biochemical Pharmacology

Volume 60, Issue 1, July 2000, Pages 55-65

https://doi.org/10.1016/S0006-2952(00)00287-2 Get rights and content

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 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) × 10⁻³ M⁻¹ sec⁻¹ and k_3-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 = {k₁k_AG,MG/(k₋₁ + k_AG,MG[AG]) + k_AG,MG-H₂O}[MG-H₂O][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-H₂O, k_AG,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.

Section snippets

Materials

Glyoxal (40% aqueous solution), AG hydrochloride, and 3-amino-1,2,4-triazine were purchased from Sigma. Methylglyoxal was prepared by acid hydrolysis of methylglyoxal dimethyl acetal, purified by fractional distillation under reduced pressure as described previously [13]. 3-DG was prepared and purified as described [14].

3-Amino-1,2,4-triazine derivatives were prepared by incubating glyoxal, methylglyoxal, and 3-DG (20 mM) with 20 mM AG hydrochloride in 50 mM sodium phosphate buffer in D₂O, pD

Spectrophotometric study of the formation of 3-amino-1,2,4-triazine derivatives by the reaction of AG with α-oxoaldehydes

When glyoxal, methylglyoxal, and 3-DG reacted with AG in 50 mM sodium phosphate buffer, pH 7.4 and 37°, there was a increase in UV absorbance at ca. 225 and 320 nm. This was characteristic of the formation of the 3-amino-1,2,4-triazine products 7, 8. The rate of reaction was much slower with 3-DG compared to that of glyoxal and methylglyoxal. To view the reaction progress, therefore, UV spectra were recorded at 1800-sec (30-min) intervals over 21,600 sec (6 hr) for 50 μM α-oxoaldehyde with 200

Discussion

The kinetics of the reaction of α-oxoaldehydes with AG are complicated by interaction with unhydrated, monohydrate, and (where applicable) hemiacetal forms of the α-oxoaldehyde (Fig. 4). The hydrazino group of AG is the most reactive group of AG with α-oxoaldehydes. The interaction of the hydrazino group with the free aldehyde form of α-oxoaldehydes forms an initial aldimino adduct (Fig. 4, VIIIa and VIIIb) that cyclises to form the 5-alkyl-substituted 3-amino-1,2,4-triazine derivative. The

Acknowledgements

P.J.T. thanks the Medical Research Council (U.K.) for support for the research programme.

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Kinetics and mechanism of the reaction of aminoguanidine with the α-oxoaldehydes glyoxal, methylglyoxal, and 3-deoxyglucosone under physiological conditions

Abstract

Section snippets

Materials

Spectrophotometric study of the formation of 3-amino-1,2,4-triazine derivatives by the reaction of AG with α-oxoaldehydes

Discussion

Acknowledgements

Biochem Pharmacol

Carbohydr Res

Anal Chim Acta

Carbohydr Res

J Biol Chem

Mol Aspects Med

Arch Biochem Biophys

Biochem Pharmacol

Biochem Pharmacol

Leuk Res

Biochem Biophys Res Commun

Microvasc Res

Maillard reaction products and their relation to complications in insulin-dependent diabetes mellitus

J Clin Invest

Role of glycation in modification of lens crystallins in diabetic and nondiabetic senile cataracts

Diabetes

Advanced glycation end products contribute to amyloidosis in Alzheimer disease

Proc Natl Acad Sci USA

β2-Microglobulin modified with advanced glycation end products is a major component of haemodialysis-associated amyloidosis

J Clin Invest

Exogenous advanced glycosylation end products induce complex vascular dysfunction in normal animalsA model for diabetic and aging complications

Proc Natl Acad Sci U S A

Mechanism of inhibition of advanced glycosylation by aminoguanidine in vitro

J Carbohydr Chem

Advanced glycation end products and their receptors co-localise in rat organs susceptible to diabetic vascular injury

Diabetologia

Aminoguanidine treatment inhibits the development of experimental diabetic retinopathy

Proc Natl Acad Sci U S A

β₂-Microglobulin modified with advanced glycation end products is a major component of haemodialysis-associated amyloidosis