The Effects Of Lactobacillus Plantarum CCFM639 On Alleviating Aluminium Toxicity And Its Protective Mechanisms

Although aluminum(Al)is not an essential element in mammals,it widely exists in nature(the most abundant metal in the earth's crust)and frequently used in daily life.Al accumulates in most of the mammalian tissues and causes tissue injuries and a variety of adverse physiological effects,especially for the brain.Chelation therapy can alleviate Al toxicity by promoting Al excretion,but it has unavoidable side effects and deficient in safety.Lactic acid bacteria are classified as GRAS(generally regarded as safe).It has been reported that LAB can bind toxic metals,maintain the balance of gut function and have a positive effect on nervous system and behavioural performance by microbiome-gut-brain axis.Therefore,LAB has potential as a therapeutic dietary strategy against Al toxicity.In this study,we selected probiotic LAB strains with good abilities to alleviate Al toxicity and explore the related protective mechanism,further excavate the function of LAB and seek the new approaches and solutions to alleviate Al toxicity by using dietary strategies.Firstly,the screening model for potential LAB strain need be established in vitro.The ideal LAB strain should have excellent Al-binding ability,good abilities to tolerate Al and simulated GI tract conditions,and outstanding antioxidative capacity.Among 30 LAB strains,Lactobacillus plantarum CCFM639 had the best binding capacity at both 5 and 50 mg/L initial Al concentrations with 64.54% and 26.83% of Al decrease,respectively.Moreover,L.plantarum CCFM639 showed the best Al resistance ability among all the tested strains with an MIC of more than 2048 mg/L.L.plantarum CCFM639 had good resistance to simulated gastric juice and intestinal juice,which the survival rates were 90.69% and 91.86%,respectively.The principal component analysis(PCA)was performed to analyze correlations among the four antioxidative parameters of the tested strains,and further principal component analysis showed L.plantarum CCFM639 had the highest antioxidative capacity.Therefore,L.plantarum CCFM639 was selected for the following studies as its excellent performance.We used fourier transform infrared spectroscopy(FTIR),transmission(TEM)and scanning electron microscope(SEM)and whole genome sequenceto analyze the adsorption mechanisms of L.plantarum CCFM639.The results showed that multiple functional groups on the strain surface and functional genes involved in the Al binding and alleviating Al toxicity,respectively.The protective effects of L.plantarum CCFM639 agianst Al toxicity were evaluated in the acute and chronic animal models.In the acute model,L.plantarum CCFM639 treatment was able to reduce the mortality of mice,promote fecal Al excretion,decrease accumulation of Al in tissues,alleviate oxidative stress and histopathologicay.Furthermore,L.plantarum CCFM639 treatment also effectively alleviated chronic Al toxicity in mice and tilapia,including decrease of Al accumulation in tissues,regulation of the trace element levels,recovery of oxidative stress and physiological and biochemical changes,and finally alleviation of pathological injuries.Additionally,L.plantarum CCFM639 completely avoid the Al-induced mortality of tilapia.The intestinal tract is the organ that Lactobacillus can work directly,and it is also the main absorption organ for Al.Hence,it is necessary to study the effects of the strain on regulating the intestinal barrier and intestinal function in Al exposure model and explore the concrete protective mechanism of L.plantarum CCFM639 against Al toxicity.In the batch culture fermentation model,Al exposure reduced the numbers of Bifidobacteria and Lactobacilli,and increased the numbers of Baceroides,Clostridia and Enterobacteriaceae.L.plantarum CCFM639 can elevate the probiotics number significantly,especially for Bifidobacteria and Lactobacilli.The results of metabolite analysis showed that L.plantarum CCFM639 increased the levels of butyrate and lactate dramaticlly.In the HT-29 cell and chronic Al exposure mice models,Al exposure impaired the intestinal barrier and increased the intestinal permeability,which may caused by oxidative stress,proinflammatory response and the damage of TJ proteins.L.plantarum CCFM639 treatment can alleviate oxidative stress and inflammation,maintaining the integrity of TJ proteins and decrease intestinal permeability.In the chronic Al exposure tilapia model,Al increased Bacteroidetes abundance and decreased Firmicutes abundance in the gut microbiota at the phyla level.At the genus level,Al increased abundance of Flavobacterium,Enterovibrio,Porphyromonadaceae and Comamonadaceaeand,and decreased abundance of Plesiomonas and Deefgea.Dietary L.plantarum CCFM639 supplementation elevated Lactobacilli level in tilapia feces and Deefgea abundance in the gut microbiota,and reduced Comamonadaceae abundance.The results showed that L.plantarum CCFM639 can adjust the structure and composition of the gut microbiota in the tilapia with the incerase of probiotic number and decrease of harmful bacteria number.In the chronic Al exposure mice model,the correlation between L.plantarum CCFM639 and Al-induced abnormal behavior was analyzed.The mice in Al only group showed poor learning and memory performance,object recognition disorder and anxiety-like behaviour,while oral administration of L.plantarum CCFM639 can improve these adverse effects.Moreover,Al exposure decreased GSH levels,and SOD,GPx,CAT activities,increased AchE activity,the levels of pro-inflammatory cytokine,A?1-40 and A?1-42,altered trace element levels and breaked TJ proteins in the brain samples.Administration of L.plantarum CCFM639 reversed these alterations significantly.The results showed that the strain can alleviate brain damage and abnormal behavior induced by chronic Al exposure.The reasons may be that the strain can adjust the gut barrier,gut microbiota and metabolite levels,and ultimately achieve protection effects by brain-gut axis.