| Large accumulation of the heavy metal Cadmium(Cd)in rice and its transfer through the food chain is not only a problem of environmental pollution but also a threat to food safety.Long-term exposure to dietary cadmium will lead to health risks and increase physical diseases hazards.Therefore,it is of great significance to study the exposure hazards of Cd in dietary rice flour substrate to the body and conduct scientific and effective dietary intervention.This paper studied the effects of Cd-contaminated rice flour exposure on gut microbiota and metabolism in adult female Sprague Dawley(SD)rats,screened out microorganisms/metabolites-biomarkers related to Cd exposure,and further combined with saccharomyces cerevisiae intervention to explore and analyze the intervention mechanism of saccharomyces cerevisiae to promote the excretion of Cd in rice flour.The main research contents and conclusions are as follows:Firstly,16S rRNA sequencing analysis of cecum contents of rats showed that long-term exposure to Cd in rice flour substrate significantly changed microbial diversity and distribution composition in rats.The number,diversity and composition of gut microbiota species in Cd-contaminated brown rice flour group(cBR-test)were more significant than those in Cd-contaminated white rice flour group(cWR-test).According to the linear discriminant analysis,compared with cBR-con,the marker bacteria of cBR-test were selected as Monoglobus,Romboutsia,Desulfovibrio,CIEAF 020 and Eubacterium xylanophilum;compared with cWR-con,the marker bacteria of cWR-test were RF39 and Christensenellaceae R7.And the prediction of gut microbiota function found that the metabolic pathways of the top 10 relative abundance in cBR-test and cWR-test were the same,but the abundance trend was different.In addition,there were significant differences(p<0.05)in abundance expression of functional genes of 5 metabolic pathways in the cBRtest,which were Carbon fixation in photosynthetic organisms,Galactose metabolism,Alanine,aspartate and glutamate metabolism,Biofilm formation-Vibrio cholerae and TCA cycle.In the second place,using Ultra High Performance Liquid Chromatography-Mass Spectrometry(UHPLC-MS)non-targeted metabolomics,we studied the effects of long-term consumption of Cd-contaminated rice flour on serum differential metabolites and related metabolic pathways of SD rats.The results showed that lipids and lipid molecules were mainly affected by Cd exposure in rats.Second,in both the cBR-test and cWR-test groups,the expression levels of y-CEHC and 6-Hydroxy 5-methoxyindole glucuronide(6-H-5-Mig)were significantly up-regulated(p<0.05).In addition,compared with cBR-con,four metabolic pathways including lysine degradation metabolism,alanine,aspartic acid and glutamic acid metabolism,phenylalanine metabolism and glycerophospholipid metabolism were affected after intaking Cd-contaminated brown rice flour in rats.Compared with cWRcon,two metabolic pathways of caffeine metabolism and β-alanine metabolism were affected after the ingestion of Cd-contaminated brown rice flour.Spearman correlation analysis showed that y-CEHC and 6-H-5-Mig had no significant correlation with different species in cBR-test.In the cWR-test,6-H-5-Mig showed a significant negative correlation with Clostridia UCG-014(p<0.05),a significant positive correlation with Allobaculum(p<0.05),and no significant correlation with other species.At the same time,there was no significant difference in the correlation between y-CEHC and each species.Finally,the effects of two saccharomyces cerevisiae on absorption and excretion of Cd exposure in young rats were studied by in vitro and in vivo digestion experiments.The animal experiment of saccharomyces cerevisiae interfering with Cd excretion showed that the two saccharomyces cerevisiae could significantly promote Cd excretion through feces after rats ingested Cd-contaminated white rice flour.Among them,saccharomyces cerevisiae Danbaoli had a better effect on promoting Cd excretion in vitro than saccharomyces cerevisiae Fali.When rats ingested Cd-contaminated white rice flour and saccharomyces cerevisiae at the same time,the Cd excretion rate of rats ingested saccharomyces cerevisiae Danbaoli could reach 20.47%,while the Cd excretion rate of saccharomyces cerevisiae Fali could reach 16.65%.When ingestion of Cd-contaminated white rice flour for a period of time and then ingestion of saccharomyces cerevisiae in the later intervention,the excretion rate of Cd by saccharomyces cerevisiae Danbaoli reached 16.80%and that by saccharomyces cerevisiae Fali reached 17.06%.The in vitro study on the mechanism of inhibiting Cd absorption and promoting excretion of saccharomyces cerevisiae showed that when saccharomyces cerevisiae supplemental level was greater than 0.1 g,the content of Cd ion in the digestive supernieces decreased with the increase of saccharomyces cerevisiae supplemental level during the whole digestion stage.When the supplemental level of saccharomyces cerevisiae was about 0.05 g,saccharomyces cerevisiae could promote the release of Cd in digestive system and significantly increase the content of Cd in supernatant.In addition,there was no significant difference in the growth of saccharomyces cerevisiae at relatively low supplemental levels(0.05 g and 0.1 g).When the saccharomyces cerevisiae supplemental level was 0.2 g or 0.3 g,the two saccharomyces cerevisiae in the early and middle stages of digestion(2 h～3 h)were in the rapid growth stage,and Cd was adsorbed at the late stage of digestion(3 h～4 h),and their growth was inhibited by Cd.The characterization analysis showed that the adsorption of Cd in the digestive juices of white rice flour by saccharomyces cerevisiae Danbaoli and saccharomyces cerevisiae Fali was mainly on the cell surface,and a small part of Cd was absorbed in the cell interior.The apparent effect of Cd adsorbed in the interior of saccharomyces cerevisiae was mainly manifested as morphological deformation of saccharomyces cerevisiae cells and vacuoles in the cells.Through the comprehensive analysis method of gut microbiota and metabolomics,it is true that gut microbiota and metabolic activities were significantly affected under long-term Cd exposure in young organisms.Meanwhile,microbial/metabolite biomarkers are expected to indicate the harm of dietary Cd exposure to body health,and it was further revealed that saccharomyces cerevisiae effectively interfered with dietary Cd in the body through the adsorption of Cd in the rice flour substrate in the form of fecal Cd,and provided a feasible scheme for accurate assessment of dietary Cd exposure and how to reduce the harm caused by dietary Cd absorption. |
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