Studies on the Reaction of Dietary Methylglyoxal and Creatine during Simulated Gastrointestinal Digestion and in Human Volunteers.

The reactive 1,2-dicarbonyl compound methylglyoxal (MGO) is consumed with food and its concentrations decrease during digestion. In the present paper, the reaction of MGO with creatine, arginine, and lysine during simulated digestion, and its reaction with creatine during the digestion in human volunteers, was studied. Therefore, simulated digestion experiments with a gastric and an intestinal phase were performed. Additionally, an intervention study with 12 subjects consuming MGO-containing Manuka honey and creatine simultaneously or separately was conducted. Derivatization with o-phenylenediamine and HPLC-UV was used to measure MGO, while creatine and glycated amino compounds were analyzed via HPLC-MS/MS. We show that MGO quickly reacts with creatine and arginine, but not lysine, during simulated digestion. Creatine reacts with 56% of MGO to form the hydroimidazolone MG-HCr, and arginine reacted with 4% of MGO to form the hydroimidazolone MG-H1. In the intervention study, urinary MG-HCr excretion is higher in subjects who consumed MGO and creatine simultaneously compared to subjects who ingested the substances separately. This demonstrates that the 1,2-dicarbonyl compound MGO reacts with amino compounds during human digestion, and glycated adducts are formed. These contribute to dietary glycation products consumed, and should be considered in studies investigating their physiological consequences.

MG-HCr, the Methylglyoxal-Derived Hydroimidazolone of Creatine, a Biomarker for the Dietary Intake of Animal Source Food.

In the course of the Maillard reaction in vivo or in food, creatine reacts with the 1,2-dicarbonyl compound methylglyoxal to N-(4-methyl-5-oxo-1-imidazolin-2-yl)sarcosine (MG-HCr). We studied whether the urinary excretion of MG-HCr is affected by its intake with meat or by the intake of creatine and subsequent in vivo formation of MG-HCr. Therefore, 24 h urine of 30 subjects with different dietary habits was analyzed with HPLC-MS/MS. The daily MG-HCr excretion via urine varied between omnivores (0.39-9.67 µmol/day, n = 24), vegetarians (0.18-0.97 µmol/day, n = 19), and vegans (0.10-0.27 µmol/day, n = 8). An intervention study with 18 subjects demonstrated the bioavailability of MG-HCr (ca. 54%) from 200 g of heated meat and its quick excretion with urine. A creatine intervention of 0.44 g did not increase MG-HCr excretion. Thus, the differences in MG-HCr excretion between different diets are mainly caused by the dietary uptake of MG-HCr. We additionally found MG-HCr in milk and egg products, where it is formed during heat treatment. This partly explains differences in MG-HCr excretion of vegetarians and vegans. Hence, MG-HCr in urine is a short-term marker for the intake of heat-processed animal source food.

Studies on the Formation of 3-Deoxyglucosone- and Methylglyoxal-Derived Hydroimidazolones of Creatine during Heat Treatment of Meat.

Dicarbonyl compounds such as methylglyoxal (MGO) and 3-deoxyglucosone (3-DG) are formed via caramelization and the Maillard reaction in food during heating or in vivo as byproducts of glycolysis. Recently, it was shown that creatine, an amino compound linked to the energy metabolism in vertebrate muscle, reacts rapidly with methylglyoxal under physiological conditions to form N-(4-methyl-5-oxo-1-imidazolin-2-yl)sarcosine (MG-HCr), a methylglyoxal-derived hydroimidazolone of creatine. Based on the observation that heated meat contains only small amounts of MGO and 3-DG when compared to many other foodstuffs, the aim of this study was to investigate a possible reaction of creatine with 3-DG and MGO in meat. From incubation mixtures consisting of 3-DG and creatine, a new hydroimidazolone of creatine, namely N-(4-butyl-1,2,3-triol-5-oxo-1-imidazolin-2-yl)sarcosine (3-DG-HCr), was isolated and characterized via spectroscopic means. To quantitate 3-DG-HCr and MG-HCr, meat and fish products were analyzed via HPLC-MS/MS using isotopically labeled standard material. Whereas samples of raw fish and meat contained only trace amounts of the hydroimidazolones (below 5 µg/kg), up to 28.3 mg/kg MG-HCr and up to 15.3 mg/kg 3-DG-HCr were found in meat and fish products. The concentrations were dependent on the heat treatment and presumably on the smoking process. In comparison to the lysine and arginine derivatives CEL, pyrraline, and MG-H1, the derivatization rate of creatine as MG-HCr and 3-DG-HCr was higher than of lysine and arginine, which clearly demonstrates the 1,2-dicarbonyl scavenging properties of creatine in meat.

Lysine-Derived Protein-Bound Heyns Compounds in Bakery Products.

Fructose and dicarbonyl compounds resulting from fructose in heated foods have been linked to pathophysiological pathways of several metabolic disorders. Up to now, very little has been known about the Maillard reaction of fructose in food. Heyns rearrangement compounds (HRCs), the first stable intermediates of the Maillard reaction between amino components and fructose, have not yet been quantitated as protein-bound products in food. Therefore, the HRCs glucosyllysine and mannosyllysine were synthesized and characterized by NMR. Protein-bound HRCs in cookies containing various sugars and in commercial bakery products were quantitated after enzymatic hydrolysis by RP-HPLC-ESI-MS/MS in the multiple reaction monitoring mode through application of the standard addition method. Protein-bound HRCs were quantitated for the first time in model cookies and in commercial bakery products containing honey, banana, and invert sugar syrup. Concentrations of HRCs from 19 to 287 mg/kg were found, which were similar to or exceeded the content of other frequently analyzed Maillard reaction products, such as N-ε-carboxymethyllysine (10-76 mg/kg), N-ε-carboxyethyllysine (2.5-53 mg/kg), and methylglyoxal-derived hydroimidazolone 1 (10-218 mg/kg) in the analyzed cookies. These results show that substantial amounts of HRCs form during food processing. Analysis of protein-bound HRCs in cookies is therefore useful to evaluate the Maillard reaction of fructose.