| The Laminaria japonica polysaccharide,a major bioactive substance of this common sea vegetable,has been proved to ameliorate insulin resistance induced by high fat diet(HFD)in our previous study.As we know,lipopolysaccharides(LPS)produced by gut microbiota contribute to the formation of insulin resistance.Based on this fact,the aim of the current study is to uncover the underlying mechanism of a known structure and clear biological activity Laminaria japonica polysaccharide(LJP61A)reduces insulin resistance in HFD mice via modulating the composition of the gut microbiota.The main results were obtained as follows:(1)LJP61A reduces insulin resistance in HFD mice: In the model mice,HFD decreased insulin sensitivity and glucose tolerance and induced insulin resistance.The experiments of insulin tolerance test and oral glucose tolerance test indicated that LJP61 A reversed the decrease of insulin sensitivity and glucose tolerance induced by high fat diet.In addition,the fasting glucose,fasting insulin and HOMA-IR were significantly decreased by LJP61 A.Furthermore,western blot analysis showed that LJP61 A decreased the expression of p-AKT and p-IRS1 in liver and adipose.These results suggested that LJP61 A reduced insulin resistance induced by HFD.(2)LJP61A reduces inflammation in HFD-fed mice: HFD induced the excessive secretion of inflammatory cytokines and made the body produce sustained low inflammation,which plays a key role in the formation of insulin resistance.The effect of LJP61 A on systemic inflammation was studied using an insulin resistance model of C57 BL mice induced by HFD.The results of RT-qPCR showed that LJP61 A significantly improved the abnormal mRNA expressions of TNF-α,IL-6,IL-10,IL-1β and PAI-1 in liver and adipose tissue.Meanwhile,the serum mRNA expressions of TNF-α,IL-6 and IL-1β,the downstream effector molecules of NF-κB and MAPK signaling,were decrease by LJP61 A.The western blot analysis showed that LJP61 A decreased the phosphorylation of NF-κB p65,JNK,IκB,ERK1/2 and P38 MAPK in high fat diet mice,indicating that LJP61 A inhibited the NF-κB signaling pathway,as well as MAPK signaling pathway via suppressing the activation of JNK,ERK1/2 and P38.These results indicated that LJP61 A could inhibit inflammation in HFD-fed mice.(3)LJP61A maintains intestinal integrity and reduces endotoxemia in HFD mice: In the model group,HFD increased intestinal permeability,resulting in endotoxemia and chronic inflammation.The current results showed that LJP61 A significantly increased theexpression of Occludin and ZO-1 in intestine tissue.In the meantime,the RT-qPCR analysis displayed that LJP61 A significantly increased the mRNA expression of Occludin and ZO-1.Furthermore,LJP61 A significantly inhibited the serum level of LPS and the protein expression of TLR4 in liver and adipose.These results indicated that LJP61 A could reduce intestinal permeability and endotoxemia in HFD mice.(4)LJP61A modulates the gut microbiota of HFD-fed mice : HFD could induce the imbalance of gut microbiota and reduce the amount of probiotics,leading to the change of intestinal tightness.The results in the current study showed that HFD diet significantly increased the ratio of Bacteroides to Firmicutes.When the dosage of LJP61 A reached 200mg/kg/day,the level of Firmicutes was lowest among the experimental groups,while the level of Bacteroides was the highest.In addition,LJP61 A enriched relative abundance of some beneficial bacterial species,such as Akkermansia,Bifidobacterium,Lactobacillus.Collectively,these results show that LJP61 A modulates the gut microbiota in the HFD-fed mice,resulting in a microbiota composition which is similar to that of LFD-fed mice.In conclusion,LJP61 A ameliorated inflammation,endotoxemia and intestinal integrity via the regulation of gut microbiota,leading to the inhibition of insulin resistance. |
