| Background and objective:Neuroinflammation characterized by glial cell activation is a common pathological feature of a variety of acute and chronic brain diseases.Excessive and prolonged neuroinflammation has devastating effects on neuron/brain structure and function.Not only classic neuroinflammatory diseases such as multiple sclerosis(MS)and autoimmune encephalitis are caused by immune disorders,but similar scenarios also exist in other neurodegenerative and psychiatric diseases,such as Alzheimer’s disease(AD),Parkinson’s disease(PD),schizophrenia,autism spectrum disorders,bipolar disorder,and depression.Thus,inhibition of glial cell overactivation and neuroinflammation has become one of the important strategies for the treatment of central nervous system(CNS)diseases.Although the primary cells involved in neuroinflammation are glial cells within the CNS,the stimuli that cause glial cell activation often come from the periphery,especially the gastrointestinal tract.There is two-way communication between the gastrointestinal tract and the brain.Through the brain-gut axis,which is composed of CNS,neuroimmune and neuroendocrine systems,autonomic nervous system and intestinal microbiota,brain regulates peripheral immune function and inflammatory response,and peripheral inflammation can also be transmitted to the brain through the blood-brain barrier(BBB).Intestinal inflammation may cause a variety of common chronic diseases along its transmission route,including CNS disorders.There are at least three ways to transmit inflammatory signals between the gastrointestinal tract and the brain,namely,systemic humoral pathway,cellular immune pathway and neural pathway.Increasing evidence is showing that intestinal inflammation can damage the integrity of BBB,leading to neuroinflammation,brain aging and various CNS diseases.Inflammatory bowel disease(IBD)is a chronic recurrent intestinal inflammation caused by many factors.Clinical studies have shown that anxiety and depression are common comorbidities of IBD.Symptomatic IBD patients have higher scores of depression and anxiety than the control group.Compared with non-IBD patients,IBD patients also have a higher risk of PD.An animal experiment has confirmed that α4β7 Integrin-mediated interaction between white blood cells and cerebral vascular endothelial cells is enhanced,leading to neuroinflammation and anxiety-like behavior in the IBD mouse model.The above evidence shows that intestinal inflammation is a common risk factor for neurodegenerative and mental diseases,and regulation of peripheral and intestinal inflammation is critical for controlling neuroinflammation to provide prevention and treatment for brain diseases.Fucoidan,also known as sulfated fucans,is a complex sulphated polysaccharide derived from marine brown seaweed.Fucoidan has been known to have various biological activities such as anticoagulation,anti-tumor,anti-virus,anti-inflammation and lipid-lowering effect.Some studies have shown that oral administration of fucoidan can reduce the injury to intestinal barrier(IB)and intestinal inflammation in IBD model mice.In PD animal models,fucoidan has also been reported to improve motor function and protect dopaminergic neurons.Due to the high molecular weights of fucoidan,it is not easy to be absorbed into the blood from the intestine and may not be distributed in the brain,thus more likely to play a role in the intestine and peripheral.Recent studies have demonstrated gut microbiota dysbiosis and intestinal inflammation in the classical PD animals,so the neuroprotective effect of fucoidan may be related to the brain-gut axis.The purpose of this study is to study whether fucoidan can inhibit the brain inflammation that derive from the peripheral,thereby improving neuronal injury and brain function in the IBD mouse model.Method:The DSS colitis model is very popular in IBD research due to its rapidity,simplicity,reproducibility and controllability.In this study,mice were used to establish the classic acute ulcerative colitis(UC)model with DSS to observe the effects of oral fucoidan on intestinal and brain inflammation,neuronal damage and function.Male C57 mice aged 3 months were used to prepare acute UC model by drinking 3.5%DSS solution freely for 7 days.Fucoidan(200mg/kg)was administered by gavage once a day for a total of 14 days.Mice were pretreated with fucoidan for 7 days followed by another week of fucoidan treatment during the establishment of DSS model.The animals were divided into three groups,10 in each group,control group(normal saline gavage;free drinking of water),UC model group(normal saline gavage;free drinking of 3.5%DSS),UC treatment group(fucoidan gavage;free drinking of 3.5% DSS).On the last day of DSS treatment,elevated cross maze behavioral test was conducted.Mice were then sacrificed and blood,intestine and brain tissue were collected for further experiments:measurement of the length of colon and observation of the pathological changes of intestine by HE staining,detection of release of tumor necrosis factor(TNF)-ɑ and interleukin(IL)-6 in serum/tissues by ELISA,measurement of Iba-1 and inflammasome NLRP3 protein expression in colon tissue and cerebral cortex with Western blot,examination of TNF-ɑ,IL-6 and IL-1β gene expression in the brain by quantitative PCR(QPCR),observation of the morphology and number of microglia and neurons as well as the expression of BBB tight junction protein claudin-5 by immunofluorescence staining.Results:Fucoidan treatment improved the intestinal pathological changes caused by DSS,reduce the expression and release of inflammatory factors in the intestine and brain caused by DSS,inhibit the activation of microglia in the intestine and brain,reduce the down-regulation of BBB tight junction protein claudin-5 and the loss of neurons in the brain,and improve the anxiety-like behavior of mice caused by DSS.1.Fucoidan improves intestinal pathological changes caused by DSSThe experiment was divided into three groups: control group(C),UC model group(DSS),and fucoidan treatment group(DSS+FU).Colon tissues were taken from mice after DSS insult,and the length of the whole colon(from the lower part of ileocecal valve to the upper part of rectum)was measured.Compared with DSS group,the shortening of colon in DSS+FU group was significantly improved(p < 0.05).HE staining was used to observe the morphological changes of the intestinal mucosa.The intestinal mucosa of the control group was normal with regular arrangement of glands,while the colon tissues of mice in the DSS group were infiltrated by a large number of inflammatory cells,resulting in obvious mucosal damage and disordered arrangement of glands.The intestinal mucosa of mice treated with fucoidan was repaired to a certain extent,with significantly reduced inflammatory cells and orderly arrangement of glands.The intestinal mucosal injury score was also reduced in DSS+FU group in comparison with DSS group(p < 0.05).Immunofluorescence detection of expression of intestinal mucosal barrier-related antibodies ZO-1and Claudin-5.The results showed that the degree of intestinal mucosal barrier damage in the sugar gum treatment group was significantly lower than that in the DSS group(p< 0.01,n=3).2.Fucoidan mitigates peripheral and cerebral inflammation induced by DSS--secretion of inflammatory cytokinesELISA assay kit was used to detect protein supernatants in serum,colon tissue and cerebral cortex of mice.The results showed that increased protein expression of TNF-ɑand IL-6 in tissues elicited by DSS were significantly attenuated by fucoidan treatment,TNF-ɑ(p < 0.05)、IL-6(p < 0.01).Similar effect on serum TNF-ɑ(p < 0.05)was shown.3.Fucoidan mitigates cerebral inflammation induced by DSS –gene expression of inflammatory cytokinesThe mRNA levels of TNF-ɑ,IL-6 and IL-1β in mouse cortical tissue were tested by QPCR.The results showed that increased gene expression of TNF-ɑ(p < 0.01).,IL-6(p < 0.05).and IL-1β(p < 0.05).in the cortex elicited by DSS were significantly attenuated by fucoidan treatment.4.Fucoidan decreases NLRP3 protein expression in colonic and cerebral cortex tissues induced by DSSWestern blotting results showed that increased expression of NLRP3 in colon and brain tissue induced by DSS was significantly decreased by fucoidan,with statistical significance(p < 0.05).5.Fucoidan inhibits the activation of intestinal macrophages and microglia in the brainIba-1(ionized Ca+2 binding adapter protein 1)is a specific protein expressed by macrophages and microglia cells,and its up-regulation marks the activation of microglia.Western blotting results showed that the increased expression of Iba-1 in colon tissue of mice challenged with DSS was significantly suppressed by fucoidan treatment(p<0.01).The immunofluorescence staining of Iba-1 with colon sections showed similar result with that of Western blotting.The immunofluorescence staining of Iba-1 with cortex sections showed that DSS-induced microglia activation was attenuated by fucoidan(p < 0.01).6.Fucoidan reduces the down-regulation of BBB tight junction protein claudin-5 caused by DSS.Claudin-5,as the key protein of tight junction between vascular endothelial cells,plays an important role in regulating the integrity and permeability of BBB.The results of immunofluorescence staining showed that decreased expression of claudin-5 in the cerebral cortex of mice caused by DSS was attenuated by fucoidan treatment.(p < 0.05).7.Fucoidan mitigates neuronal injury of cerebral cortex caused by DSSNeu N immunofluorescence staining was performed on the brain sections of the mice.The results showed that the reduced number of neurons elicited by DSS was significantly mitigated by fucoidan treatment(p<0.05),with no obvious change on the morphology of neurons.8.Fucoidan improves anxiety-like behavior caused by DSS--elevated cross maze test and open field testThe results of the elevated cross maze test showed that the frequency of entry to the open arm and the time spent in the open area of DSS mice were increased by fucoidan,(p < 0.05).Conclusions:This study shows that fucoidan can improve a variety of inflammation-related changes in the intestine,peripheral blood and brain caused by DSS,including improving intestinal pathology and inflammation,reducing the level of inflammatory factors in the blood,reducing the activation of microglia and neuroinflammation in the cerebral cortex,reducing the down-regulation of BBB tight junction protein expression,and mitigating the neuronal damage in the cerebral cortex and anxiety-like behavior.This study is the first to prove that fucoidan can inhibit the neuroinflammation originating from the intestine,reduction of the intestinal inflammation and its spread to the brain through systemic humoral pathway might be one of the mechanisms for the anti-neuroinflammation effect of fucoidan. |
PDF Full Text Request