The Mechanism And Application Of Gut Remediation To Alleviate Heavy Metals Toxicity In Hosts

With the rapid development of industries,heavy metal pollution of soil in China has become increasingly serious.According to statistics,more than 16% of the cultivated land has been polluted by heavy metals,and 12 million tons of grain are contaminated annually,causing serious social problems.The traditional soil heavy metals remediation approaches such as physical,chemical,microbial,and phytoremediation are effective.However,the physicochemical methods are costly,have high technical requirements,and can cause secondary pollution.Although phytoremediation is relatively safe,few plant species can enrich heavy metals,and they grow slowly and have small aboveground biomass.Moreover,most microbial remediation technologies are still limited to the laboratory level,with a few implemented case studies.As the result,human beings are inevitably threatened by heavy metals.In recent years,many studies have shown that probiotics can be used to alleviate the toxicity of heavy metals in animals.Gut microbiota is considered to be an important "barrier" to limit the absorption of heavy metals.However,the interaction mechanism between probiotics and gut microbiota in alleviating heavy metal toxicity is not clear.In addition,its effectiveness in protecting humans from heavy metal toxicity has not been studied.Therefore,this study explored the protective mechanism of probiotics against the toxicity of heavy metals in animals,and then applied probiotics in the form of yogurt to the population exposed to heavy metals.In the human trial,the effect of probiotics on reducing the content of heavy metals in blood was evaluated,and the possible mechanism of interaction between the probiotics and gut microbiota in detoxifying heavy metals was further explored.The main results of this study are as follows:(1)Probiotic strains with heavy metals tolerance and strong antioxidant capacity were screened from a variety of traditional fermented foods.Among 9 Lactobacilli strains,Pediococcus acidlactici GR-1 isolated from Tibet Plateau had the best tolerance in the range of 100-4000 μM Cr(Ⅵ).Moreover,P.acidlactici GR-1 showed the best antioxidative capacity from three aspects(DPPH and hydroxyl radical scavenging ability,as well as total antioxidant capacity).Further,this study showed that P.acidlactici GR-1 had no Cr(Ⅵ)adsorption.Subsequently,whole-genome sequencing was performed to understand the underlying mechanism of the strong antioxidant capacity of GR-1.Therefore,P.acidlactici GR-1 was selected for subsequent animal experiments.(2)The animal model for Cr(Ⅵ)toxicity has been established.The strain GR-1with strong antioxidant but no Cr(Ⅵ)-reducing capacity was selected to apply in mice.After 4 weeks of intervention,GR-1 was able to promote fecal Cr excretion,decrease the accumulation of Cr(in liver,kidney,and small intestine),alleviate hepatic oxidative stress and injury,reduce inflammatory cytokines levels in the small intestine,and mitigate histopathological damages.The gastrointestinal tract is considered the main target organ for heavy metals absorption,but it is also the region where GR-1can work directly.Hence,further the effects of the strain on regulating the gut microbiota in Cr(Ⅵ)exposed mice and exploring the potential mechanism of P.acidilactici GR-1 against Cr(Ⅵ)toxicity were studied.The results showed that GR-1colonized in the intestinal tract of mice after 10 days of treatment and increased the Cr(Ⅵ)resistance and reduction ability of gut microbiota.16 S r RNA and metatranscriptome sequencing analysis of fecal microbiota showed that GR-1reversed Cr(Ⅵ)-induced changes in the gut microbial population and metabolic activity.Specifically,GR-1 significantly upregulated the differentially expressed genes associated with antioxidation and Cr(Ⅵ)reduction.The results indicated that,GR-1 can modulate the gut microbiota in response to Cr(Ⅵ)induced oxidative stress and protect against Cr(Ⅵ)toxicity.(3)The composition of gut microbiota was disrupted in mice first treated with antibiotics mixture,and then exposed to Cu.The results showed that the mice with disrupted gut microbiota decreased the fecal Cu excretion,whereas increased the accumulation in liver,ileum,and colon.It increased the level of oxidative stress in liver and aggravated the histopathological damages when compared with the mice having normal gut microbiota.On the other hand,P.acidilactici GR-1 treatment significantly promoted fecal Cu excretion,reduced the accumulation of Cu in tissues,alleviated liver oxidative stress,and reduced liver tissue damage in mice with normal gut microbiota as compared to the one with disrupted gut microbiota.This experiment confirmed the important role of gut microbiota in the process of toxicity alleviation caused by Cu during the application of P.acidilactici GR-1.In addition,based on the fact that P.acidilactici GR-1 has strong antioxidant ability,it can mitigate chromate toxicity in mice by alleviating oxidative stress of the gut microbiota.To further analyze the concrete mechanism,the oxidative stress-induced mice models were employed through Cu and acetaminophen exposure.The strain GR-1 or vitamin C was orally given to the intervention groups daily to test the antioxidant effect of GR-1.The results showed that both acetaminophen and Cu exposure increased the oxidative stress in the intestine,reduced the resistance of gut microbiota to Cu,and caused changes in the gut microbiota composition of mice.Strain GR-1 and vitamin C had similar effects in reversing the Cu-induced intestinal oxidative stress,increased the resistance of gut microbiota to Cu,and reduced gut microbial dysbiosis.This experiment demonstrated the protective effect of P.acidilactici GR-1 on the antioxidant function of gut microbiota against Cu.(4)A randomized,double-blind,controlled trial with 152 occupational workers from a metal industry was conducted.The participants were randomly assigned to consume either conventional yogurt or probiotic yogurt containing a heavy metal-resistant strain P.acidilactici GR-1 for 12 weeks.Assay of blood metal content indicated that consumption of probiotic yogurt led to a more significant and faster decrease in blood Cu(34.45%)and Nickel(Ni)(38.34%)levels as compared with the conventional yogurt(16.41% and 27.57%,respectively).Consumption of probiotic yogurt also significantly increased fecal Cu and Ni levels,alleviated oxidative stress in the blood,reduced inflammation,and increased fecal short-chain fatty acid levels.Furthermore,metagenomic and metabolomic studies revealed a close correlation between gut microbiota and host metabolism.Significantly enriched members and metabolites were positively correlated with the enhanced antioxidant capacity of the gut microbiota and host,while was negatively correlated with the blood metal content.In conclusion,the study demonstrated that probiotic supplementation could be an effective approach for people to combat toxic metals exposure via gut microbiota regulation.By constructing the toxic models for different heavy metals(Cr and Cu),this study explored the potential mechanism of probiotics to alleviate heavy metal-induced oxidative stress and tissue injuries by balancing the gut microbiota composition and metabolism.It will provide an effective reference in the future for a better formulation of strategies in mitigating heavy metal toxicity.