Research On The Effect Of Food Additive κ-carrageenan On Intestinal And Metabolism

Carrageenan(CGN),a sulfated polysaccharide derived from marine red algae,is widely used in food processing,pharmaceutical and daily chemical industries.The market demand of carrageenan for the food industry is increasing at a rate of 5%-7% per year.In 2014,global carrageenan consumption reached 205,000 tons.As China’s food processing industries are adopting western processing model,almost all processed foods contain carrageenan.In 2016,the European Food Safety Authority calculated that the per capita daily consumption of carrageenan was 75 mg/kg/day,so is that safe? International academe and official institutions have always been controversial about the safety of carrageenan.Some scholars have found that carrageenan can induce inflammatory bowel disease and glucose metabolism disorders,and others believe that carrageenan is harmless.So far,the official agencies usually adopt the latter.Is this choice correct? In view of the irreversible growth trend of processed foods,the intake of carrageenan will still increase,therefore the conclusion and mechanism of whether carrageenan is safe or not needs to be resolved.Intestinal,the largest immune organ of the human body,hosts a large number and a wide variety of microbiota,forming a unified whole with the host.Gut microbiota disorders are closely related to inflammatory bowel disease(IBD).Food additives effect the composition of gut microbiota,while gut microbiota also effect the metabolism and immunity of the host.At present,the interaction among food additives,gut microbiota and host is not clear.In order to clarify the relationship between carrageenan and gut microbiota,we used healthy adult male C57BL/6 mice as experimental models,mice were fed with different concentrations of κ-carrageenan,then feces were collected and analyzed based on 16 S r RNA and metagenome to evaluate the effects of carrageenan on gut microbiota.According to enterotype analysis,we found that the control group were clustered into Prevotella(enterotype 2),the driving microbiota of enterotype 2 have the ability to produce short chain fatty acids,which plays a key role to keep the intestinal complete.Mice of low & medium concentration groups were clustered into Bacteroides and Ruminococcus(enterotype 1 and 3)while high concentration group were clustered into Ruminococcus(enterotype 3).The driving microbiota of enterotype1 and 3 could degrade polysaccharide and mucin,respectively.Univariate analysis of phylum level showed that Bacteroides increased significantly,Proteobacteria decreased significantly,while the relative abundance of Firmicutes did not change significantly.At the genus level,the abundance of Comamonas,Parasutterella and Escherichia genus increased significantly,while the content of Mucispirillum,Akkermansia muciniphila,Lactobacillus,Ruminococcaceae decreased significantly.In order to investigate the effect of κ-CGN on intestinal barrier function,we used Cytometric Bead Array,Fluorescence in situ hybridization,Western Blot and HE staining techniques to find that inflammatory factors of κ-CGN treatment groups had little significance compared with control group.Congestion,edema and ulcers of intestinal tissue were not found.But it’s clear found that κ-CGN treatment induce intestinal permeability increased,intestinal mucus layer became thinner and the distance between microbiota and intestinal epithelial cells decreased.Furthermore,it was speculated that κ-CGN may be an inflammation adjuvant,which interferes with the composition and stability of the gut microbiota to form a weak pro-inflammatory intestinal environment.In order to verify the above speculation,we constructed an IBD model by using Citrobacter rodentium to evaluate the proinflammatory effect of κ-CGN.It was found that C.rodentium could induce inflammation in the colon tissue of mice,and κ-CGN further aggravated the intestinal damage induced by C.rodentium.We used germ free and fecal microbiota transplantation assays to verify the role of gut microbiota in the κ-CGN synergistic inflammation mechanism.The results showed that after90 days of oral administration,the mucosal layer thickness and intestinal mucin content of germ free mice fed with of κ-CGN did not change much.The intestinal permeability of FMT mice significantly increased,the mucus layer thickness decreased,and symptom of C.rodentium-induced IBD significantly aggravated.In the study of the effect of κ-CGN on glucose metabolism in mice,we found that κ-CGN induced blood glucose increased in mice.We found that κ-CGN could bind to the insulin receptor,thereby inhibiting the insulin-PI3K/AKT signaling pathway and leading to glucose transport of GLUT4,and GYS ability and glycogen synthesis ability are reduced,which eventually lead to increased blood glucose.In summary,this study indicated that carrageenan may be used as an adjuvant for inflammation,by changing the abundance and composition of gut microbiota,resulting in changes in microbiota metabolism,thinning of intestinal mucosa and increased intestinal permeability.This weak pro-inflammatory environment is formed in the intestinal,which ultimately aggravates the IBD induced by C.rodentium.At the same time,κ-CGN can also bind to insulin receptors,effecting insulin-mediated glucose metabolism.This research provides a new perspective for resolving the disputes of carrageenan safety and will promote the reevaluation of carrageenan in the food additive industry.