title: Effect of Dietary Maillard Reaction Products on Insulin Sensitivity, Metabolic Inflammation and Intestinal Inflammation in Mice Fed the Total Western Diet
Creators: name: Xiao, Siyu
Publisher: name: Utah State University
Year: 2020

description: Maillard reaction products (MRPs) are generated when proteins or amino acids are heated with reducing sugars. In previous studies, baking whole diet pellets at a high temperature has been the most common way to promote MRP formation. However, baking diets also induces other chemical reactions besides MRP production, for example lipid oxidation. In this study, only casein and sugars were cooked to generate MRPs. Thus, a complementary experiment was conducted to determine how baking diet pellets affects lipid oxidation.
Previous rodent studies showed MRPs either induced weight gain and or impaired glucose tolerance. On the other hand, dietary MRPs were shown to alleviate colitis induced by dextran sodium sulfate (DSS). The aim of this study was to elucidate the effects of dietary MRPs generated by a different treatment method in a different diet on weight gain, glucose metabolism and intestinal health in mice. Three groups of C57BL6/J mice (n=10/gp) were fed the Total Western Diet (TWD) with different levels of MRPs: MRP0, TWD with low level of MRPs; MRP1, TWD with medium level of MRPs, and MRP2, TWD with high level of MRPs.
Mice receiving different levels of MRPs in their diet showed no significant difference in weight gain. Mice receiving 10 days of oral administration of dextran sodium sulfate (DSS) showed no significant difference in histology and colitis score of their colons. The results of the oral glucose tolerance test (OGTT) showed that the normalized area under the curve (AUC) of blood sugar during 120 minutes of MRP2 was significantly lower than that of MRP0 (p < 0.05), indicating that increased intake of MRPs either promoted insulin secretion, increased insulin sensitivity in target tissues, or both. Alpha diversity of fecal microbiome showed significant differences at phylum level (p < 0.01) and class level (p < 0.01). Beta diversity of the cecal microbiome (p < 0.004) and the fecal microbiome (p < 0.001) showed significant differences at all taxonomic levels (OTU level, species, genus, family, order, class and phylum). Different levels of MRPs in the TWD induced significantly different taxonomic abundance of cecal microbiome at OTU level, species level and phylum level (p < 0.05), and significantly different taxonomic abundance of fecal microbiome at all other taxonomic levels except Species level (p < 0.05). Short chain fatty acids as microbial fermentation products were measured in the cecal and fecal contents using gas chromatography with flame ionization detection (GC-FID). Valeric acid, propionic acid and butyric acid in the cecal contents, along with propionic acid and valeric acid in the fecal contents were significantly different between the three groups (p < 0.05). Baking diets to promote MRP formation was shown to significantly increase lipid oxidation. This suggests that the negative effects of MRPs on glucose metabolism shown in previous studies may be actually caused by ingestion of lipid oxidation products, rather than MRPs.
In conclusion, ingestion of MRPs affected both glucose tolerance and the gut microflora. MRPs did not induce obesity in mice, nor did any of the mice show symptoms of colitis after receiving DSS for 10 days. Intake of MRPs decreased overall incremental blood glucose concentration during OGTT, indicating that it could reduce the risk of high blood glucose, which would be beneficial for health. High alpha diversity of gut microbiota is associated with healthy state according to previous human studies. Alpha diversity of fecal microbiome decreased with higher MRPs level in diet, and the significance of this observation is unclear. The microbiota composition and microbial fermentation products SCFAs in the hindgut of mice were changed by intake of MRPs. As SCFAs could play a role in the improvement of insulin sensitivity in mice, further studies should investigate possible mechanisms of this beneficial effect.