Biotoxicity Assessment Of Dietary Advanced Glycation End Products

Advanced glycation end products(AGEs) are a group of heterogeneous compounds that are formed through nonenzymatic reactions between reactive carbonyl group in reducing suagrs such as glucose and free amino groups in proteins, lipids and nucleic acids. In recent years, chronic diseases related to endogenous AGEs level have attracted more attention. Food contains a large amount of AGEs produced during the cooking or thermal processing, and thus becomes an important environmental source of AGEs in vivo. So far studies on the biological effects of exogenous AGEs on the health of organisms are scarce and are controversial. Therefore, this study explored the biological effects of Nε?(Carboxymethyl)lysine(CML), a typical biomarker of AGEs, on the healthy adult and young rats, aiming to clearly elucidate whether dietary CML is harmful to bodies.Firstly, the study thoroughly investigated the effects of chronic intake of free CML(60mg/kg body weight/d) on tissues in healthy adult SD rats fed a normal diet. Results indicated that the protein-bound CML contents in tissues of rats were increased in different degrees, particularly in the kidney, heart, and liver, follow by the lungs(P<0.05). No statistical increase was found in the spleen and pancreas. Moreover, serum blood urea nitrogen(BUN), creatinine(CREA), alanine aminotransferase(ALT) and aspartate aminotransferase(AST) values increased significantly(P<0.05), confirming that the liver and kidney functions were impaired. Whereas no obvious changes were seen in fasting blood glucose(FBG) level and energy expenditure of rats. Furthermore, GC-TOF/MS analyses of endogenous metabolites in plasma and urine of these adult SD rats were performed. Results indicated that endogenous metabolites such as 3-hydroxycapric acid and guanidinosuccinic acid levels were elevated significantly, confirming that the liver and kidney functions of these rats were damaged. Meanwhile, these rats’ energy metabolism, carbohydrate metabolism and amino acid metabolism had been disordered.Secondly, the study thoroughly investigated the effects of chronic intake of free CML(60mg/kg body weight/d) on tissues in healthy adult SD rats fed a high-fat diet. Results indicated that the protein-bound CML in tissues studied had accumulated to various degrees. Protein-bound CML levels in the kidney, heart, lung, pancreas, and muscle increased significantly(P<0.05), particularly in pancreas(when compared to rats fed a normal diet). Whereas no differences were seen in the liver and spleen. Meanwhile, serum low-density lipoprotein cholesterol(LDL-C) value, FBG and energy expenditure levels were elevated obviously(P<0.05). We put forward, for the first time, the possible combination of free CML and tissue proteins by covalent bonds. Furthermoer, GC-TOF/MS analysis of endogenous metabolites in plasma and urine of these adult SD rats were performed. Results showed that guanidinosuccinic acid level was elevated and arachidonic acid level was reduced, indicating that the kidney function of these rats were impaired. Increased methionine sulfoxide level indicated that the oxidative stress level in vivo had rised. Meanwhile, chronic intake of free CML would impact these rats’ amino acid metabolism and lipid metabolism.Finally, the study thoroughly investigated the effects of different doses of free CML(low dose 1.5g CML/kg normal chow, medium dose 4.5g CML/kg normal chow, high dose 13.5g CML/kg normal chow) on tissues in healthy young SD rats. Results indicated that with increase of free CML intake, there was a dose-dependent increase in the protein-bound CML level in tissues and proteinuria level. Moreover, a dose-dependent decrease was seen in serum total protein(TP) and albumin(ALB) values as well as in the liver/body weight ratio, confirming that the liver and kidney functions might have been impaired. Meanwhile, intake of free CML overdose could disturb hematological parameters. While no obvious change was found in FBG level and energy expenditure of young rats. Furthermore, comparative analyses of endogenous metabolites in serum and urine of young SD rats between control group and high dose CML group were performed by GC-TOF/MS. Results indicated that endogenous metabolite N-acetylserotonin level was increased in young rats in high dose CML group, proving that the elevated oxidative stress level occurred in these young rats bodies. In addition, these young rats’ nucleotide metabolism, amino acid metabolism, lipid metabolism, metabolism of cofactors and vitamins, carbohydrate metabolism, translation and energy metabolism have been disordered.Based on the above research results, this study suggests that under a normal diet, chronic intake of a large amount of free CML would affect the liver and kidney functions for healthy rats, particularly for adult rats whose liver and kidney functions could be damaged. A high-fat diet would affect healthy rats’ blood glucose level, and intake of a large amount of free CML could accelerate the rise of blood glucose in rats. No matter which type of diet, chronic intake of a large amount of free CML would cause oxidative stress in healthy rats, and thus to pose a potential risk of the development of a series of chronic diseases including type 2 diabetes. This study could provide a basically theoretical reference for people who recognize the potential risk of chronic intake of foods rich in AGEs. This will be a positive guidence for people to improve their bad eating habit.