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RESEARCH PRODUCT

Nonenzymatic glycation reaction of folate with reducing sugars: A case study on [6S]-5-methyltetrahydrofolate and fructose

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In the Maillard reaction, free amino groups react with reducing sugars to form nonenzymatic glycation products. It has recently been shown that in the presence of reducing sugars (i.e. fructose) folic acid is subjected to a non-enzymatic glycation reaction, which may represent an important pathway of folate degradation besides the established oxidative degradation pathways. In the current study, the thermal stability of [6S]-5-methyltetrahydrofolic acid ([6S]-5-CH3H4PteGlu, 0.4µM), the predominant naturally occuring folate derivate, was investigated on a qualitative and kinetic basis in the presence of different fructose concentrations (0-3M) in milliQ water (8.11ppm O2). Samples were isothermally treated and subsequently residual concentrations of [6S]-5-CH3H4PteGlu were determined with RP-HPLC using fluorescence and UVVIS detection with external calibration curves. Kinetic parameters were estimated using linear regression analysis. Addition of fructose (44µM - 3M) prior to thermal treatment (40-100°C, 15 min) resulted in destabilisation of [6S]-5-CH3H4Pteglu depending on the fructose concentration and the severity of the treatment. Thermal degradation kinetics (40-90°C of [6S]-5-CH3H4PteGlu with or without addition of fructose (1.5M) could be described by first order reaction kinetics. Addition of fructose (1.5M) prior to thermal treatments influenced (i) the estimated degradation rate constants, and influenced (ii) the estimated temperature dependence of the rate constants, resulting in a higher [6S]-5-CH3H4PteGlu instability. MS analysis of a heated (90°C, 120min) [6S]-5-CH3H4PteGlu solution (0.4µM [6S]-5-CH3H4PteGlu, 1.5M fructose) showed a folate degradation product with m/e 532, suggesting that natural folates are probably subjected to a similar non-enzymatic glycation reaction with fructose as has previously been shown for folic acid.