Determination Of Ages In Bread Crust, Effect Of Free And Protein-bound States Of Dietary AGEs On Healthy Rat Liver And Kidney

Advanced glycation end products(AGEs) are the compounds formed by nonenzymatic Maillard reaction or lipid oxidation reaction during thermal processing and storage of food,which can be divided into free AGEs and protein-bound AGEs according to molecular weight of bounded protein. AGEs have been tied to increased risks of diabetes, cardiovascular diseases and pancreatic cancer. However, studies were scarcely conducted on the health effects of dietary AGEs in free and protein-bound states.In order to access different fractions, bread crust were removed manually and digested with pronase E solution. The insoluble fraction obtained was then weighed, lyophilized,homogenised and stored at-20 ℃ until used for CML analysis and diet formulation. The soluble fractionwas subjected to ultrafiltration. The fraction named as high molecular weight(HMW) contained compounds of which molecular mass higher than 20 k Da was retained by20 k Da ultrafiltration membrane. The compounds with mass less than 5 k Da was filtered by 5k Da ultrafiltration membrane as low molecular weight(LMW) fraction. The fraction of molecular mass between 5k Da and 20 k Da was named middle molecular weight components(MMW). AGEs analysis and chromatic value of these fractions were conducted.Then AIN-93 G purified diet was applied for laboratory rodents as the control diet. The bread crust was added to the AIN-93 G diet to the final concentration of 10%(w/w) as Bread Crust(BC) group. The insoluble fraction produced by digesting bread crust with pronase E was also added to the AIN-93 G diet in the same proportion. GL(glucose-lysine) group was produced by adding 3% of GL sample from a glucose-lysine(GL) model system to the AIN-93 G diet.Healthy Sprague-Dawley(SD) rats were used as experimental animals fed individually by dietary AGEs(BC diet), protein-bound AGEs(Insoluble diet) and free AGEs(GL diet) for 12 weeks. After sacrifice, we evaluated the kidney and liver injury caused by dietary AGEs with free and protein-bound states and AGEs accumulation in tissues of healthy rats. The conclusions were as follows:(1) Compared with bread crumb, the L* value of bread crust decreased while a* and b*values increased b* values significantly. Fluorescent AGEs, CML and browning degree of the insoluble fraction were lower than the soluble components of LMW, MMW and HMW. Thefluorescent AGEs of MMW(724.02 AU/g) was the highest. CML level of HMW was 2.5 fold of the insoluble group.(2)There was no significant(p>0.05) in the rise of total cholesterol, triglyceride and the decrease of high-density lipoprotein cholesterol among rats feed by three different diets. An increase was seen in the low density lipoprotein cholesterol of rats feed by three AGEs diets,whereas only the GL group achieved significant rise compared with control group. Different bound states of AGEs diets induced dyslipidemia in healthy rats. While the fasting blood glucose levels of rats remained within the normal range.(3) Different bound states of AGEs diets increased AGEs accumulation in the tissue of rats. Kidneys, heart and liver are vital organs in accumulating of dietary AGEs compared with lung and spleen. The accumulation of free states of AGEs in tissue was higher than protein-bound states of AGEs, which possibly due to the weaker absorption and bioavailability of protein-bound CML in vivo.(4)Compared with control group, BUN, CREA, ALT and AST values of rats increased significantly(p<0.05) after three AGEs diets administration for 12 weeks. The ALT and AST levels of GL group rats liver function were higher than that of BC group and insoluble group.The BUN level of BC group and insoluble group was lower than GL group. The contents of SOD and MDA in liver and kidney of the three groups were increased, and the level of GSH decreased. Among them, there was a slight increase in the SOD content in the kidneys of the three groups, while there was no significant difference compared to control group(p>0.05).The content of MDA in liver and kidneys of BC group was significantly higher than that in the other two AGEs diets groups. The content of GSH in GL group was significantly lower than that in BC group and insoluble group(p<0.05). The content of IL-6 and TNF-α in liver and kidneys of rats were increased in different degrees after three AGEs diets administration for 12 weeks. The levels of IL-6 in liver and kidneys of GL group were significantly higher than that in control group. The content of TNF-α in kidney of BC group and insoluble group was slightly higher than that in control group, although no significance was shown(p>0.05).The long term feeding of dietary AGEs in different bound states caused a certain degree of damage on the liver and kidney of rats, which lead to oxidative stress and inflammation in liver and kidney.