An in vitro study on the non-enzymatic glycation of melamine and serum albumin by reducing sugars

Glycation is a non-enzymatic reaction with reactants including a reducing sugar and a free amino containing molecule such as protein, amino acids, DNA, RNA and lipids. In the initial phase of glycation, the carbonyl group of the reducing carbohydrate condenses with the free amino groups on the target biomolecule to form reversible glycosylamines, which are then converted to more stable Amadori products. Once formed, these Amadori products can with time undergo dehydration, cyclization, oxidation, and rearrangement to form a polymorphic group of compounds collectively referred to as Advanced Glycation Endproducts (AGEs). The accumulation of AGEs in vivo has been implicated as a major pathogenic process in diabetic complications including diabetic cataract formation, retinopathy and neurological diseases, as well as other health disorders, such as Alzheimer’s disease (AD). Chapter one reviewed the chemistry of glycation and the formation of AGEs in a mechanical perspective. The role of AGEs in the pathogenesis of diabetic nephropathy, diabetic neuropathy, diabetic retinopathy and Alzheimer’s disease were considered. Here we also reviewed the potential inhibitors against glycation published to date, focusing on some novel potential AGE inhibitors such as zinc and gold nanoparticles. The purpose of the study described in chapter two was to investigate the susceptibility of the amine groups of melamine to glycation by milk sugars and sugar metabolites. Dairy products adulterated with melamine have been recently blamed for the death of at least several infants and the sickening of countless children in China. The presented study described the non-enzymatic glycation of melamine with milk sugar D-galactose and several sugar metabolites including methylglyoxal, glyoxal and DL-glyceraldehyde. The chemical structures of melamine AGEs were characterized by electrospray mass spectrometry. The factors influencing the rate and extent of melamine’s glycation were also evaluated. The third part of the dissertation described a study on anti-glycation effect of gold nanoparticles (GNPs). In this study we showed that certain sizes of spherical GNPs exhibit an inhibitory effect on the formation of AGEs when Bovine Serum Albumin (BSA) was glycated by D-ribose. A combination of UV spectrometry, HPLC and circular dichroism showed that only GNPs with size ranging from 2nm to 20nm inhibited the formation of BSA AGEs. The inhibition effect of GNPs was correlated to the overall surface area of nanoparticles in the solution. GNPs with higher surface areas were found to be better inhibitors of glycation, whereas those with low surface areas were less effective inhibitors. The inhibitory effect of GNPs on non-enzymatic glycation reactions may be due to the covalent bonding between gold atoms on the surface of GNP and ϵ amino groups of L-lysine residue on protein. In chapter four, we evaluated the effect of UVC radiation on glycation of Human Serum Albumin (HSA). In this study, we found that exposure to UVC radiation accelerated the glycation level of HSA and promoted the formation of AGEs, which may be stimulated by the generation of ROS by UVC radiation. A combination of several analytical methods including UV spectrometry, HPLC, and MALDI-TOF were used to evaluate the glycation level of HSA at 37 °C under neutral pH in the presence of D-glucose in vitro. This study warrants further investigation as there have been few reports on the correlation between the UVC radiation of proteins and their enhanced glycation by a reducing sugar