Regulatory Mechanism Of Gracilaria Lemaneiformis On Gut Microbiota And Its Structure-activity Relationship

Gracilaria lemaneiformis,one of the marine red algae,distributes widely in the marine environment,and is a valuable food that always used as improver of digestion and enhancer of immunity.Some polysaccharides from Gracilaria lemaneiformis(GLPs)are shown to have various activities,but the effects of GLPs on diet-induced obesity and the underlying mechanisms are unclear.This study indicated that dietary supplementation with GLPs reduced weight gain and improved body composition in high fat diet(HFD)-fed mice without reduced food consumption.Fat accumulation in the liver and adipose tissues was reduced by GLPs,and the damage of HFD on the intestine was also repaired.These effects were associated with the modulation of the gut microbiota,resulting in a specific microbiota that similar to normal microbiota.Changes in the gut microbiota improved nutrient utilization,and inhibited the expression of lipid-related genes via short chain fatty acids-activated pathway.Polysaccharides are shown to play various beneficial effects on the human health,but its action mechanisms are unclear,which could be attributed to a lack of recognition of polysaccharides metabolism.This study indicated that polysaccharides of Gracilaria lemaneiformis(GLPs)can tolerate the inner environment of the upper digestive tract,but it can be metabolized by the gut microbiota,and thus improved the gut microbiota composition and increased the abundance of the Bacteroides genus within the phylum of Bacteroidetes.To elucidate the underlying mechanisms,main Bacteroides species were isolated from the gut microbiota,and their abilities on GLPs utilization were fully evaluated.Different Bacteroides species exhibited differing ability on GLPs utilization,and the Bacteroides strain unable to live in GLPs can proliferate via a network of GLPs utilization among intestinal symbionts.It provided a basis for study of the modulatory mechanisms of polysaccharides and their specificity on the gut microbiota.Higher MW,poor solubility and higher viscosity of natural GLPs limit their biological applications in several fields.In the present study,we investigated the effects of Gracilaria lemaneiformis Polysaccharides-derived oligosaccharides on high-fat diet induced obese mice,via analyzing the gut microbiota composition by pyrosequencing,and evaluating theexpression of lipid-related genes and SCFAs production.Fat accumulation in the liver and adipose tissues was reduced by D-GLPs.These effects were associated with the modulation of the gut microbiota,resulting in a specific microbiota that similar to normal microbiota.Changes in the gut microbiota improved nutrient utilization,and inhibited the expression of cholesterol metabolism-related genes.suggesting that D-GLPs can be developed as food supplement to improve metabolic syndrome and intestinal diseases.