Comparison of metabolic fate, target organs, and microbiota interactions of free and bound dietary advanced glycation end products.

Increased intake of Western diets and ultra-processed foods is accompanied by increased intake of advanced glycation end products (AGEs). AGEs can be generated exogenously in the thermal processing of food and endogenously in the human body, which associated with various chronic diseases. In food, AGEs can be divided into free and bound forms, which differ in their bioavailability, digestion, absorption, gut microbial interactions and untargeted metabolites. We summarized the measurements and contents of free and bound AGE in foods. Moreover, the ingestion, digestion, absorption, excretion, gut microbiota interactions, and metabolites and metabolic pathways between free and bound AGEs based on animal and human studies were compared. Bound AGEs were predominant in most of the selected foods, while beer and soy sauce were rich in free AGEs. Only 10%-30% of AGEs were absorbed into the systemic circulation when orally administered. The excretion of ingested free and bound AGEs was approximately 90% and 60%, respectively. Dietary free CML has a detrimental effect on gut microbiota composition, while bound AGEs have both detrimental and beneficial impacts. Free and bound dietary AGEs changed amino acid metabolism, energy metabolism and carbohydrate metabolism. And besides, bound dietary AGEs altered vitamin metabolism, and glycerolipid metabolism.

Generation of advanced glycation end products from glycated protein or fructose/glyoxal-protein adducts under in vitro simulated gastrointestinal digestion.

Advanced glycation end products (AGEs) are a heterogeneous group of compounds formed both endogenously and exogenously through reactions between reducing sugars and amino acids within the proteins. The digestive tract may also serve as a site for endogenous AGEs generation. This study examined whether additional AGEs are formed during the digestion of glycated protein diets and meal-resembling systems (dietary proteins with fructose or glyoxal). The digestion of glycated protein showed that free AGEs were gradually released, but no additional AGEs were generated. In contrast, co-digestion of dietary proteins with fructose or glyoxal resulted in the formation of additional AGEs, and the reaction substrates (fructose or glyoxal) were depleted during digestion. Additionally, the lysine released from proteins decreased, leading to a loss of nutritional value of the food during co-digestion. The formation of AGEs and the depletion of essential amino acids in the gut may have significant implications for human health.

Comparative Study of the Effects of Dietary-Free and -Bound Nε-Carboxymethyllysine on Gut Microbiota and Intestinal Barrier.

Nε-carboxymethyllysine (CML) is produced by a nonenzymatic reaction between reducing sugar and ε-amino group of lysine in food and exists as free and bound forms with varying digestibility and absorption properties in vivo, causing diverse interactions with gut microbiota. The effects of different forms of dietary CML on the gut microbiota and intestinal barrier of mice were explored. Mice were exposed to free and bound CML for 12 weeks, and colonic morphology, gut microbiota, fecal short-chain fatty acids (SCFAs), intestinal barrier, and receptor for AGE (RAGE) signaling cascades were measured. The results indicated that dietary-free CML increased the relative abundance of SCFA-producing genera including Blautia, Faecalibacterium, Agathobacter, and Roseburia. In contrast, dietary-bound CML mainly increased the relative abundance of Akkermansia. Moreover, dietary-free and -bound CML promoted the gene and protein expression of zonula occludens-1 and claudin-1. Additionally, the intake of free and bound CML caused an upregulation of RAGE expression but did not activate downstream inflammatory pathways due to the upregulation of oligosaccharyl transferase complex protein 48 (AGER1) expression, indicating a delicate balance between protective and proinflammatory effects in vivo. Dietary-free and -bound CML could modulate the gut microbiota community and increase tight-junction expression, and dietary-free CML might exert a higher potential benefit on gut microbiota and SCFAs than dietary-bound CML.

Galactooligosaccharide or 2'-Fucosyllactose Modulates Gut Microbiota and Inhibits LPS/TLR4/NF-κB Signaling Pathway to Prevent DSS-Induced Colitis Aggravated by a High-Fructose Diet in Mice.

A high-fructose diet (HFrD) has been reported to exacerbate dextran sulfate sodium (DSS)-induced colitis. 2'-Fucosyllactose (FL) and galactooligosaccharide (GOS) have been shown, respectively, to have preventive and ameliorative effects on colitis, while limited research has explored whether GOS and FL may be equally protective or preventive in mice with HFrD. Here, we evaluated the protective effects of FL and GOS on colitis exacerbated by feeding HFrD and explored the underlying mechanisms. DSS-induced colitis was studied in four randomized C57BL/6J male mice (n = 8 mice/group). Among them, three groups were fed with HFrD, and two received either GOS or FL treatment, respectively. Gut microbial composition was analyzed by 16S rDNA gene sequencing. Intestinal barrier integrity and inflammatory pathway expression were measured using qPCR, immunofluorescence, and Western blot methods. Compared to the HFrD group, GOS or FL treatment increased the α-diversity of the gut microbiota, reduced the relative abundance of Akkermansia, and increased the content of short-chain fatty acids (SCFAs), respectively. Compared with the HFrD group, GOS or FL treatment improved the loss of goblet cells and the reduction of tight junction protein expression, thereby improving intestinal barrier integrity. Also, GOS or FL inhibited the LPS/TLR4/NF-κB signaling pathway and oxidative stress to suppress the inflammatory cascade compared with the HFrD group. These findings suggest that GOS or FL intake can alleviate HFrD-exacerbated colitis, with no significant difference observed between GOS and FL treatments.

Comparison of pharmacokinetics, biodistribution, and excretion of free and bound Nε-carboxymethyllysine in rats by HPLC-MS/MS.

As a representative product of advanced glycation end products, Nɛ-carboxymethyllysine (CML) exists in free and bound forms in vivo and in food with different bioavailability. To thoroughly understand the bioavailability of free Nɛ-carboxymethyllysine (CML) and bovine serum albumin (BSA)-CML in vivo after intragastric administration, pharmacokinetics, biodistribution, and excretion of CML in rats were investigated by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Pharmacokinetics results revealed that free CML peaked at 1.83 h (1684.72 ± 78.08 ng/mL) and 1.33 h (1440.84 ± 72.48 ng/mL) in serum after intragastric administration of free CML and BSA-CML, demonstrating the higher absorption of free CML than BSA-CML. Besides, dietary free CML exhibited a relatively lower body clearance and tissue distribution than dietary BSA-CML based on the apparent volume of distribution and body clearance. Moreover, free CML was concentrated in the kidneys, indicating that kidneys were the target organ for the uptake of absorbed free CML. Additionally, the total excretion rate of CML in urine and feces were 37% and 60% after oral administration of free CML and BSA-CML. These results shed pivotal light on a better understanding of the biological effects of free and bound CML on health.

Galactooligosaccharides ameliorate dietary advanced glycation end product-induced intestinal barrier damage in C57BL/6 mice by modulation of the intestinal microbiome.

Advanced glycation end products (AGEs) are increasingly recognized as potentially pathogenic components of processed foods, and long-term consumption of dietary AGEs triggers disruption of the intestinal barrier integrity and increases the risk of chronic diseases. Galactooligosaccharides (GOS) as prebiotics can modulate the intestinal microbiota and improve the intestinal barrier integrity. In this study, we aimed to investigate whether GOS could ameliorate the intestinal barrier damage induced by AGEs. The results showed an increased number of goblet cells (AGEs vs. H-GOS, 133.4 vs. 174.7, p < 0.05) and neutral mucin area (PAS positive area, 7.29% vs. 10.05%, p < 0.05). Upregulated expressions of occludin and claudin-1 and improved intestinal barrier integrity were observed in the H-GOS group. Using 16S rRNA sequencing analysis, we found that GOS significantly reduced the high enrichment of Akkermansia (16.95% vs. 1.29%, p < 0.05) induced by dietary AGEs while increasing the content of short-chain fatty acids. Fecal microbiota transplantation (FMT) showed that AGE-induced damage to the intestinal mucus barrier was reversed in the H-GOS transplanted group. Collectively, GOS ameliorated dietary AGE-induced intestinal barrier damage by reversing the dysregulated state of the intestinal microbiota. Our study lays the foundation for further research on dietary guidelines for populations with high AGE diets.

Highland barley ß-glucan alleviated western diet-induced non-alcoholic fatty liver disease via increasing energy expenditure and regulating bile acid metabolism in mice.

Non-alcoholic fatty liver disease (NAFLD) has become a public health burden. Controlling bile acids (BAs) metabolism and energy expenditure are  potential therapies for NAFLD. Because one of the main health effects of cereal ß-glucan (BG) is its ability to lower cholesterol by interacting with BAs, BG may regulate imbalances of the metabolism of BAs during NAFLD. Therefore, by using metabolic tests coupled with the profiling of hepatic BAs, we have assessed the effect of BG from highland barley on western diet (WD) induced NAFLD mice. BG treatment prevented fat accumulation and increased adipose lipolysis. These moderating effects were associated with an increased energy expenditure. Moreover, BG-treated mice enhanced the production of hepatic BAs, which may be connected with the activation of farnesoid X receptor (FXR) signaling in the liver and inhibition of FXR signaling in the ileum. Our results suggest that BG prevents fat accumulation by increasing energy expenditure, a mechanism associated with major changes in the composition of hepatic BAs.

Comparison of tissue distribution of free and protein bound Nɛ-carboxymethyllysine after long-term oral administration to mice.

Nɛ-Carboxymethyl-lysine (CML) is a primary advanced glycation end product that exists in the body and food as free and bound forms with different bioavailability and physiological effects. To compare the uptake, tissue distribution, and fecal excretion of dietary free and bound CML, free or bound CML were administered to healthy mice at 10 mg CML kg-1 body weight per day for 12 weeks. The results demonstrated that free CML was significantly absorbed in serum and accumulated in the colon, ileum, lung, kidneys, heart, spleen, brain, and liver after intake of free and bound CML, whereas no statistical increase was found in the accumulation of bound CML in the serum, lung, spleen, kidneys, and liver. The colon was the main tissue for the accumulation of free and total CML. Moreover, the accumulation of free CML in tissues and organs was significantly correlated with free CML levels in serum. In conclusion, consumption of bound CML caused a higher uptake, accumulation, and fecal excretion of CML in the body than intake of free CML.

Hypoglycemic Effects of Lycium barbarum Polysaccharide in Type 2 Diabetes Mellitus Mice via Modulating Gut Microbiota.

This study aims to explore the molecular mechanisms of Lycium barbarum polysaccharide (LBP) in alleviating type 2 diabetes through intestinal flora modulation. A high-fat diet (HFD) combined with streptozotocin (STZ) was applied to create a diabetic model. The results indicated that LBP effectively alleviated the symptoms of hyperglycemia, hyperlipidemia, and insulin resistance in diabetic mice. A high dosage of LBP exerted better hypoglycemic effects than low and medium dosages. In diabetic mice, LBP significantly boosted the activities of CAT, SOD, and GSH-Px and reduced inflammation. The analysis of 16S rDNA disclosed that LBP notably improved the composition of intestinal flora, increasing the relative abundance of Bacteroides, Ruminococcaceae_UCG-014, Intestinimonas, Mucispirillum, Ruminococcaceae_UCG-009 and decreasing the relative abundance of Allobaculum, Dubosiella, Romboutsia. LBP significantly improved the production of short-chain fatty acids (SCFAs) in diabetic mice, which corresponded to the increase in the beneficial genus. According to Spearman's correlation analysis, Cetobacterium, Streptococcus, Ralstonia. Cetobacterium, Ruminiclostridium, and Bifidobacterium correlated positively with insulin, whereas Cetobacterium, Millionella, Clostridium_sensu_stricto_1, Streptococcus, and Ruminococcaceae_UCG_009 correlated negatively with HOMA-IR, HDL-C, ALT, AST, TC, and lipopolysaccharide (LPS). These findings suggested that the mentioned genus may be beneficial to diabetic mice's hypoglycemia and hypolipidemia. The up-regulation of peptide YY (PYY), glucagon-like peptide-1 (GLP-1), and insulin were remarkably reversed by LBP in diabetic mice. The real-time PCR (RT-PCR) analysis illustrated that LBP distinctly regulated the glucose metabolism of diabetic mice by activating the IRS/PI3K/Akt signal pathway. These results indicated that LBP effectively alleviated the hyperglycemia and hyperlipidemia of diabetic mice by modulating intestinal flora.

Dietary advanced glycation end products modify gut microbial composition and partially increase colon permeability in rats.

SCOPE: The adverse impacts of dietary advanced glycation end products (AGEs) on health are currently of interest. These compounds are inevitably formed during thermal food processing and make foods less digestible because of protein cross-linking. This study examined not only whether dietary AGEs alter cecal microbiota and their metabolites but also their effects on colon permeability. METHODS AND RESULTS: Sprague-Dawley rats were exposed to a high-AGEs diet (AGEs content was increased by heating food at 125°C/3 h) for 6, 12, or 18 weeks. Cecal microbiota was analyzed by 16S rDNA gene sequencing. Colon permeability was assessed through histopathology, immunohistochemistry and endotoxin testing. Microbial metabolites (e.g. ammonia and short-chain fatty acids (SCFAs)) were also measured. AGEs treatment reduced the diversity and richness of the microbiota, especially saccharolytic bacteria such as Ruminococcaceae and Alloprevotella, which can produce SCFAs, whereas some putatively harmful bacteria (Desulfovibrio and Bacteroides) were increased. Protein fermentation was enhanced, supported by elevated ammonia and branched-chain fatty acid levels (p < 0.05). Additionally, the colonocytes structure changed and the expression of tight junction proteins in colon were decreased. CONCLUSION: Dietary AGEs detrimentally modulate gut microbial ecology and may partially increase colon permeability, which can adversely impact host health.