| With the improvement of people’s life quality and the diet structure,the prevalence of ulcerative colitis in China has been increasing,and it has became one of the diseases which could threat people’s health.Lactic acid bacteria have the potential to alleviate UC by their special physiological characteristics.However,there have some controversies in recent reports that some probiotics aggravate the colitis.Therefore,this study will evaluate the effect of live/heat-killed bacteria of L.plantarum Zhang-LL and their metabolites on DSS-induced UC in rats.In this study,Wistar rats were gavaged:PBS buffer(DSS group),live/heat-killed L.plantarum Zhang-LL(10~9 CFU/mL)and their supernatants,and positive control of L.rhamnosus LGG(10~9 CFU/mL)for 7 days,then used 5%DSS repeatedly to establish the model of chronic UC.After a 42-day gavage experiment,we evaluated the effect of live/heat-killed bacteria of L.plantarum Zhang-LL and their metabolites on UC through the rat’s morphology,colon histology,immune response system,intestinal permeability,and intestinal flora to provide a theoretical basis for the development of potential probiotics.The main results are as follows:(1)Morphological effects on UC rats:Compared with the DSS group,the L.plantarum Zhang-LL heat-killed group had the most significant effects on the rat’s behavior,weight gain,stool characteristics,and blood in the stool,and the DAI score was only 0.43 points,which was significantly lower than the DSS group 2 points.Except for the control group,L.plantarum Zhang-LL live/heat-killed group,the rats in the other groups all had individual death during the test.(2)Effect of colon histology on UC rats:The pathological section of colon tissue in DSS group showed a typical UC morphology with a histological score of 9.28.Compared with the DSS group,the degree of colonic injury was significantly reduced in each experimental group,and the L.plantarum Zhang-LL heat-killed group had the lowest degree of injury,with a histological score of 3.75 points.(3)Effect of immune response system on UC rats:Compared with the DSS group,the live/heat-killed bacteria of L.plantarum Zhang-LL and their metabolites had the tendency to down-regulate partial pro-inflammatory factors in colon and serum of rats,and to up-regulate partial anti-inflammatory factors.The L.plantarum Zhang-LL heat-killed group could significantly down-regulate pro-inflammatory cytokines(IL-6,TNF-α,IFN-γ)in the colon tissue and serum of the rats,up-regulated anti-inflammatory cytokines(IL-4,IL-10).Compared with the DSS group,the MPO content of the L.plantarum Zhang-LL live/heat-killed groups decreased significantly by 1.71 U/L and1.46 U/L,which could indicate that the L.plantarum Zhang-LL live/heat-killed bacteria can effectively alleviate the degree of neutrophil infiltration and improve the immune response ability.(4)Effect of intestinal permeability on UC rats:The expression of Claudin-1,Occludin,and ZO-1 in intestinal tissues was significantly decreased in the DSS model group.Compared with the DSS group,the expression of tight junction protein in the L.plantarum Zhang-LL heat-killed group was significantly increased 4.5 times,5.8 times and 4.1 times,which could indicate that L.plantarum Zhang-LL live/heat-killed bacteria can increase the expression of tight junction proteins to resist the invasion of pathogenic bacteria by reducing the intestinal permeability.(5)Effect of intestinal microflora on UC rats:From the similarity analysis of intestinal microbiota,it was found that ingestion of DSS will cause significant changes of intestinal microflora in rats.From the intestinal diversity analysis,compared with the control group,the Sobs index,Ace index,and Chao index in the DSS model group were significantly reduced,but there was no significant difference in the L.plantarum Zhang-LL heat-killed group,which indicated that the heat-killed bacteria of L.plantarum Zhang-LL can effectively maintain the balance of intestinal flora diversity and the stability of the intestinal flora.Further analysis showed that compared with the control group,the abundance of Faecalitalea and[Eubacterium]_fissicatena_group in the intestine of rats ingested with DSS was significantly increased,prevotellaceae_NK3B31_group and Ruminococcaceae_UCG-005were significantly decreased.Compared with the DSS group,the abundance of Ruminococcaceae_UCG-005 in the intestine of rats was significantly increased and the abundance of Faecalitalea was significantly decreased by the intervention of live/heat-killed bacteria of L.plantarum Zhang-LL and their metabolites.There was no significant difference in the abundance of these two species between the heat-killed group of L.plantarum Zhang-LL and the control group.In summary,the live/heat-killed bacteria of L.plantarum Zhang-LL can enhance immune response by up-regulating anti-inflammatory cytokines and down-regulating pro-inflammatory cytokines in rat serum and colon tissues,reduce intestinal permeability by increasing the expression of tight junction proteins,maintain intestinal flora stability by increasing intestinal flora diversity to achieve the effect of preventing chronic UC in rats.At the same time,the heat-killed bacteria of L.plantarum Zhang-LL was more effective against DSS-induced chronic ulcerative colitis in rats. |
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