Cadmium chloride exhibits a profound toxic effect on bacterial microflora of the mice gastrointestinal tract

Oral exposure to benzalkonium chlorides in male and female mice reveals alteration of the gut microbiome and bile acid profile

Benzalkonium chlorides (BACs) are commonly used disinfectants in a variety of consumer and food-processing settings, and the COVID-19 pandemic has led to increased usage of BACs. The prevalence of BACs raises the concern that BAC exposure could disrupt the gastrointestinal microbiota, thus interfering with the beneficial functions of the microbes. We hypothesize that BAC exposure can alter the gut microbiome diversity and composition, which will disrupt bile acid homeostasis along the gut-liver axis. In this study, male and female mice were exposed orally to d7-C12- and d7-C16-BACs at 120 µg/g/day for one week. UPLC-MS/MS analysis of liver, blood, and fecal samples of BAC-treated mice demonstrated the absorption and metabolism of BACs. Both parent BACs and their metabolites were detected in all exposed samples. Additionally, 16S rRNA sequencing was carried out on the bacterial DNA isolated from the cecum intestinal content. For female mice, and to a lesser extent in males, we found that treatment with either d7-C12- or d7-C16-BAC led to decreased alpha diversity and differential composition of gut bacteria with notably decreased actinobacteria phylum. Lastly, through a targeted bile acid quantitation analysis, we observed decreases in secondary bile acids in BAC-treated mice, which was more pronounced in the female mice. This finding is supported by decreases in bacteria known to metabolize primary bile acids into secondary bile acids, such as the families of Ruminococcaceae and Lachnospiraceae. Together, these data signify the potential impact of BACs on human health through disturbance of the gut microbiome and gut-liver interactions.

Interplay between fluorine and cadmium on intestinal accumulation, oxidative stress, permeability and inflammatory response in rats

Fluorine (F) and Cadmium (Cd) have given rise to public concern regarding their adverse impacts on the environment and human beings. Yet, the toxic interplay between F and Cd on the intestine is still vague. Aiming to investigate the role of F on Cd-damaged intestine, a total of five groups of 30 SD rats were picked at random to be gavaged for 90 days: Control group (Ultra-pure water), Cd (Cd 1 mg/kg), Cd+LF (Cd 1 mg/kg+F 15 mg/kg), Cd+MF (Cd 1 mg/kg+F 45 mg/kg), and Cd+HF (Cd 1 mg/kg+F 75 mg/kg). It demonstrated that Cd enriched in the intestine and disordered intestinal barrier of rats. Interestingly, two side effects of F were observed resisting to the Cd toxicity. The Cd levels in colon contents were attenuated by 45.45 %, 28.11 %, and 19.54 % by F supplement, respectively. In the Cd+LF group, SOD, GSH-Px, and CAT activities elevated by 0.93, 1.76, and 1.78 times, respectively, and the MDA content reduced 0.67 times; the expressions of NQO1, SOD2, and GSH-Px mRNA markedly enhanced, as well as the Keap1 mRNA significantly decreased. Nevertheless, all indexes above in the Cd+HF group showed the opposite trends. Furthermore, LPS levels decreased by 45.93 % for the Cd+LF group and increased by 12.70 % in that the Cd+HF group. The ZO-1 expression in the Cd+LF group increased, whereas the Cd+HF group's expressions of Claudin-1, Occludin, and ZO-1 were all diminished by 35.46 %, 27.23 %, and 16.32 %, respectively. Moreover, the levels of TNF-α, IL-1β and TLR-4 decreased and IL-10 level promoted, while all showed opposite trends in the Cd+HF group. Collectively, it indicated there is a twofold interplay between F and Cd on intestinal damage and mainly depends on F dosages.

Epigallocatechin-3-gallate mitigates cadmium-induced intestinal damage through modulation of the microbiota-tryptophan-aryl hydrocarbon receptor pathway

Early studies have shown that the gut microbiota is a critical target during cadmium exposure. The prebiotic activity of epigallocatechin-3-gallate (EGCG) plays an essential role in treating intestinal inflammation and damage. However, the exact intestinal barrier protection mechanism of EGCG against cadmium exposure remains unclear. In this experiment, four-week-old mice were exposed to cadmium (5 mg kg-1) for four weeks. Through 16 S rDNA analysis, we found that cadmium disrupted the gut microbiota and inhibited the indole metabolism pathway of tryptophan (TRP), which serves as the principal microbial production route for endogenous ligands to activate the aryl hydrocarbon receptor (AhR). Additionally, cadmium downregulated the intestinal AhR signaling pathway and harmed the intestinal barrier function. Treatment with EGCG (20 mg kg-1) and the AhR agonist 6-Formylindolo[3,2-b] carbazole (FICZ) (1 μg/d) significantly activated the AhR pathway and alleviated intestinal barrier injury. Notably, EGCG partially restored the gut microbiota and upregulated the TRP-indole metabolism pathway to increase the level of indole-related AhR agonists. Our findings demonstrate that cadmium dysregulates common gut microbiota to disrupt TRP metabolism, impairing the AhR signaling pathway and intestinal barrier. EGCG reduces cadmium-induced intestinal functional impairment by intervening in the intestinal microbiota to metabolize AhR agonists. This study offers insights into the toxic mechanisms of environmental cadmium and a potential mechanism to protect the intestinal barrier with EGCG.

Cadmium exposure induces changes in gut microbial composition and metabolic function in long-tailed dwarf hamsters, Cricetulus longicaudatus

Numerous studies have demonstrated that exposure to cadmium disrupts the diversity and composition of the gut microbiota, resulting in damage to organ tissue. However, there remains a lack of comprehensive understanding regarding the broader ecological reality associated with this phenomenon. In this study, we conducted a thorough evaluation of the effects of different concentrations of Cd (6, 12, 24, and 48 mg/L) over a period of 35 consecutive days on the organ viscera and the gut microbiota of long-tailed dwarf hamsters, Cricetulus longicaudatus (Rodentia: Cricetidae), using histopathological analysis, 16S rDNA, and metagenome sequencing. Our findings revealed that the results suggest that Cd exposure induced liver, spleen, and kidney damage, potentially leading to increased intestinal permeability and inflammation. These alterations were accompanied by significant perturbations in the gut microbiota composition, particularly affecting potentially pathogenic bacteria such as Prevotella and Treponema within the gut ecosystem. Consequently, host susceptibility to underlying diseases was heightened due to these changes. Notably though, Cd exposure did not significantly impact the overall structure of the gut microbiota itself. Additionally, Cd exposure induced significant changes in the metabolic functions, with the pathways related to disease and environmental information processing notably enhanced, possibly indicating stronger innate defense mechanisms against external injuries among wild mammals exposed to Cd. This study offers a novel approach to comprehensively evaluate the significant impact of Cd pollution on ecosystems by investigating both structural and functional alterations in the digestive system, as well as disruptions in intestinal flora among wild mammals.

Oral Exposure to Benzalkonium Chlorides in Male and Female Mice Reveals Sex-Dependent Alteration of the Gut Microbiome and Bile Acid Profile

Benzalkonium chlorides (BACs) are commonly used disinfectants in a variety of consumer and food-processing settings, and the COVID-19 pandemic has led to increased usage of BACs. The prevalence of BACs raises the concern that BAC exposure could disrupt the gastrointestinal microbiota, thus interfering with the beneficial functions of the microbes. We hypothesize that BAC exposure can alter the gut microbiome diversity and composition, which will disrupt bile acid homeostasis along the gut-liver axis. In this study, male and female mice were exposed orally to d 7 -C12- and d 7 -C16-BACs at 120 µg/g/day for one week. UPLC-MS/MS analysis of liver, blood, and fecal samples of BAC-treated mice demonstrated the absorption and metabolism of BACs. Both parent BACs and their metabolites were detected in all exposed samples. Additionally, 16S rRNA sequencing was carried out on the bacterial DNA isolated from the cecum intestinal content. For female mice, and to a lesser extent in males, we found that treatment with either d 7 -C12- or d 7 -C16-BAC led to decreased alpha diversity and differential composition of gut bacteria with notably decreased actinobacteria phylum. Lastly, through a targeted bile acid quantitation analysis, we observed decreases in secondary bile acids in BAC-treated mice, which was more pronounced in the female mice. This finding is supported by decreases in bacteria known to metabolize primary bile acids into secondary bile acids, such as the families of Ruminococcaceae and Lachnospiraceae. Together, these data signify the potential impact of BACs on human health through disturbance of the gut microbiome and gut-liver interactions.

Probiotics Pediococcus acidilactici GR-1 promotes the functional strains and remodels gut microbiota to reduce the Cr(VI) toxicity in a dual-chamber simulated intestinal system

Numerous animal studies have demonstrated the toxicity of hexavalent chromium [Cr(VI)] and the bioremediative effects of probiotics on the composition and functions of gut microbiota. Since the precise mechanisms of Cr(VI) detoxification and its interactions with human gut microbiota were unknown, a novel dual-chamber simulated intestinal (DCSI) system was developed to maintain both the stability of the simulated system and the composition of the gut microbiota. Probiotic GR-1 was found to regulate intestinal gut microbiota, thereby reducing the toxicity of Cr(VI) within the DCSI system. The results indicate that Cr(VI) levels were reduced from 2.260 ± 0.2438 μg/g to 1.7086 ± 0.1950 μg/g in the gut microbiota cell pellet, and Cr(VI) permeability decreased from 0.5521 ± 0.1132 μg/L to 0.3681 ± 0.0178 μg/L after 48 h in simulated gut fluid. Additionally, the removal rate of 1,1-Diphenyl-2-picrylhydrazyl (DPPH), reducibility (Vitamin C), and total antioxidant capacity (T-AOC) increased by 50.83%, 31.70%, and 27.56%, respectively, following probiotic treatment. The increase in antioxidant capacity correlated with total Cr removal (P < 0.05, r from -0.80 to 0.73). 16S rRNA sequencing analysis showed that gut microbiota composition was reshaped by the addition of probiotics, which regulated the recovery of the functional gut microbiota to normal levels, rather than restoring the entire gut microbiota composition for community function. Thus, this study not only demonstrates the feasibility and stability of culturing gut microbiota but also offers a new biotechnological approach to synthesizing functional communities with functional strains for environmental risk management.

The hidden threat: Environmental toxins and their effects on gut microbiota

The human gut microbiota (GM), which consists of a complex and diverse ecosystem of bacteria, plays a vital role in overall wellness. However, the delicate balance of this intricate system is being compromised by the widespread presence of environmental toxins. The intricate connection between contaminants in the environment and human well-being has garnered significant attention in recent times. Although many environmental pollutants and their toxicity have been identified and studied in laboratory settings and animal models, there is insufficient data concerning their relevance to human physiology. Consequently, research on the toxicity of environmental toxins in GM has gained prominence in recent years. Various factors, such as air pollution, chemicals, heavy metals, and pesticides, have a detrimental impact on the composition and functioning of the GM. This comprehensive review aims to comprehend the toxic effects of numerous environmental pollutants, including antibiotics, endocrine-disrupting chemicals, heavy metals, and pesticides, on GM by examining recent research findings. The current analysis concludes that different types of environmental toxins can lead to GM dysbiosis and have various potential adverse effects on the well-being of animals. We investigate the alterations to the GM composition induced by contaminants and their impact on overall well-being, providing a fresh perspective on research related to pollutant exposure.

Selenium attenuated food borne cadmium-induced intestinal inflammation in red swamp crayfish (Procambarus clarkii) via regulating PI3K/Akt/NF-κB pathway

Selenium (Se), an indispensable micronutrient for living organisms, has been extensively studied for its heavy metal-detoxifying properties in diverse biological systems and tissues. Nevertheless, it is not entirely certain whether Se can effectively protect against Cadmium (Cd)-induced gut inflammation, especially in aquatic animals. In this study, we employed various approaches, including transcriptome profiling, histological examinations, assessment of antioxidant enzyme activities, and analysis of gut microbiota composition to investigate the effects on crayfish growth and intestinal health after exposure to dietary Cd (15 mg kg-1 diet) and Se (15 mg kg-1 diet) individually or in combination for 8 weeks. The results revealed that dietary Cd exposure resulted in reduced body weight and survival rates, along with an increased occurrence of intestinal inflammation. Nevertheless, Se supplementation proved effective in mitigating the adverse effects of Cd on growth and gut health. Se exhibited a remarkable ability to counteract the disruption of gut antioxidant abilities induced by dietary Cd, as evidenced by the observed increases in ROS and MDA contents, decrease in GSH levels, and inhibition of antioxidative enzyme activities. At the concentration of 6 mg kg-1 in the diet, Se was found beneficial for maintaining gut microbiota richness and diversity. Among them, Flavobacterium, Thermomonas, and Chloronema displayed a weak negative correlation with the rate of gut inflammation. Meanwhile, the levels of short chain fatty acids (SCFAs), including acetic acid (AA) and butanoic acid (BA), showed a significant increase in the Se-Cd group compared to the Cd-only group. Furthermore, transcriptome analysis exhibited significant responses of the PI3K/Akt and NF-κB pathways following crayfish exposure to dietary Se and Cd, either separately or in combination. In short, this study provides a new evidence regarding the molecular mechanisms through which Se could regulate the PI3K/Akt and NF-κB pathways, either directly or indirectly via ROS and SCFAs, thereby alleviating Cd-induced gut inflammation in crayfish.

Delineating the protective action of cordycepin against cadmium induced oxidative stress and gut inflammation through downregulation of NF-κB pathway

Cadmium (Cd) exposure is known to cause gut inflammation. In this study, we investigated the protective effects of cordycepin, a natural compound with pharmacological properties, against gut inflammation induced by Cd exposure. Using zebrafish larvae and colon cell line models, we examined the impact of cordycepin on Cd-induced toxicity and inflammation. Zebrafish larvae were exposed to Cd (2 µg/mL) and treated with different concentrations of cordycepin (12.5, 25 and 50 µg/mL). Cordycepin treatment significantly reduced Cd-induced embryotoxicity in zebrafish larvae. It also alleviated Cd-induced oxidative stress by reducing reactive oxygen species (ROS), lipid peroxidation and apoptosis. Furthermore, cordycepin treatment normalized the levels of liver-related biomarkers affected due to Cd exposure. Additionally, cordycepin (50 µg/mL) demonstrated a significant reduction in Cd bioaccumulation and downregulated the expression of inflammatory genes in both zebrafish larval gut and colon cell lines. These findings suggest that cordycepin could be an effective agent against Cd-induced gut inflammation.

Selenium-enriched crude polysaccharide from Rosa roxburghii Tratt ameliorates cadmium-induced acute kidney injury in mice by modulating intestinal microorganisms

Cadmium is a toxic heavy metal that can cause serious damage to the body. It can trigger the oxidative stress response and damage various organs of the body (kidney, liver, brain, lung, testis, etc.). Selenium polysaccharides are considered to possess better antioxidant, immune regulation, and heavy metal removal activities than other polysaccharides, But few reports focused on Selenium Polysaccharides in Rosa roxburghii Tratt. The purpose of this study was to isolate crude polysaccharides (RRP), and crude Selenium polysaccharides (SeRRP) from Rosa roxburghii Tratt fruit and determine their structure, antioxidant activity, and protective effects on cadmium-exposed mice (PONY-2020-FL-62). Results showed that SeRRP had lower half-maximal inhibitory concentration (IC50) and higher superoxide dismutase (SOD) activity. The intake of food and body weight decreased, while the kidney index and liver index increased significantly after acute cadmium exposure. Most significantly, SeRRP ameliorates kidney injury by improving the kidney index. Furthermore, changes in the gut microbiota may be related to SeRRP or RRP. SeRRP and RRP decreased the Firmicutes/Bacteroidetes ratio, and increased the abundance of beneficial bacteria (Lachnospiraceae, Muribaculaceae, and Ruminococcaceae, etc.). These findings indicate that SeRRP and RRP have the potential to be functional food against oxidant and heavy metal exposure.

Reduction of bioavailability and phytotoxicity effect of cadmium in soil by microbial-induced carbonate precipitation using metabolites of ureolytic bacterium Ochrobactrum sp. POC9

The application of ureolytic bacteria for bioremediation of soil contaminated with heavy metals, including cadmium (Cd), allows for the efficient immobilization of heavy metals by precipitation or coprecipitation with carbonates. Microbially-induced carbonate precipitation process may be useful also in the case of the cultivation of crop plants in various agricultural soils with trace but legally permissible Cd concentrations, which may be still uptaken by plants. This study aimed to investigate the influence of soil supplementation with metabolites containing carbonates (MCC) produced by the ureolytic bacterium Ochrobactrum sp. POC9 on the Cd mobility in the soil as well as on the Cd uptake efficiency and general condition of crop plants (Petroselinum crispum). In the frame of the conducted studies (i) carbonate productivity of the POC9 strain, (ii) the efficiency of Cd immobilization in soil supplemented with MCC, (iii) crystallization of cadmium carbonate in the soil enriched with MCC, (iv) the effect of MCC on the physico-chemical and microbiological properties of soil, and (v) the effect of changes in soil properties on the morphology, growth rate, and Cd-uptake efficiency of crop plants were investigated. The experiments were conducted in soil contaminated with a low concentration of Cd to simulate the natural environmental conditions. Soil supplementation with MCC significantly reduced the bioavailability of Cd in soil with regard to control variants by about 27-65% (depending on the volume of MCC) and reduced the Cd uptake by plants by about 86% and 74% in shoots and roots, respectively. Furthermore, due to the decrease in soil toxicity and improvement of soil nutrition with other metabolites produced during the urea degradation (MCC), some microbiological properties of soil (quantity and activity of soil microorganisms), as well as the general condition of plants, were also significantly improved. Soil supplementation with MCC enabled efficient Cd stabilization and significantly reduced its toxicity for soil microbiota and plants. Thus, MCC produced by POC9 strain may be used not only as an effective Cd immobilizer in soil but also as a microbe and plant stimulators.

Orally Administrated Lactiplantibacillus plantarum BGAN8-Derived EPS-AN8 Ameliorates Cd Hazards in Rats

Cadmium (Cd) is a highly toxic metal that is distributed worldwide. Exposure to it is correlated with a vast number of diseases and organism malfunctions. Exopolysaccharides (EPS) derived from Lactiplantibacillus plantarum BGAN8, EPS-AN8, previously showed great potential for the in vitro protection of intestinal cells from this metal. Here, we investigated the potential of food supplemented with EPS-AN8 to protect rats from the hazardous effects of Cd exposure. After thirty days of exposure to lower (5 ppm) and higher (50 ppm)-Cd doses, the administration of EPS-AN8 led to decreased Cd content in the kidneys, liver, and blood compared to only Cd-treated groups, whereas the fecal Cd content was strongly enriched. In addition, EPS-AN8 reversed Cd-provoked effects on the most significant parameters of oxidative stress (MDA, CAT, GST, and GSH) and inflammation (IL-1β, TNF-α, and IFN-γ) in the duodenum. Moreover, micrographs of the duodenum were in line with these findings. As the gut microbiota has an important role in maintaining homeostasis, we used 16S rRNA amplicon sequencing and investigated the effects of Cd and EPS-AN8 on one part of the microbiota presented in the duodenum. Although Cd decreased the growth of lactobacilli and mostly favored the blooming of opportunistic pathogen bacteria, parallel intake of EPS-AN8 reversed those changes. Therefore, our results imply that EPS-AN8 might be extremely noteworthy in combatting this toxic environmental pollutant.

Threonine Facilitates Cd Excretion by Increasing the Abundance of Gut Escherichia coli in Cd-Exposed Mice

Cadmium (Cd) can easily enter the body through the food chain and threaten health since Cd pollution is prevalent in the environment. Gut microbiota is necessary for the reduction of metal ions. To reduce Cd-induced harmful impacts and Cd accumulation in the body, we investigated the effect of amino acids on gut microbiota and Cd excretion in (fecal Cd) Cd-exposed mice. The screening of 20 amino acids showed that threonine (Thr) effectively increased fecal Cd, and reduced Cd-induced intestinal structural damage. The abundance of Escherichia-Shigella genus and KF843036_g significantly increased after the oral administration of Thr. As the type species of the Escherichia-Shigella genus, Escherichia coli exhibited high similarity to KF843036_g species and significantly decreased Cd-induced gut damage. Cd contents in the liver, kidney, and gut of Cd-exposed mice were also significantly (p < 0.05) decreased after E. coli treatment, while the contents in the feces were increased. The results demonstrated the potential roles that gut E. coli might play in Thr-mediated Cd excretion in Cd-exposed mice. The findings may provide important data for better understanding the molecular biological mechanism of Thr in reducing Cd accumulation in the body.

Impact of Heavy Metal Toxicity on the Gut Microbiota and Its Relationship with Metabolites and Future Probiotics Strategy: a Review

The gut microbiota has a vital role in the maintenance of intestinal homeostasis. Several studies have revealed that environmental exposure to pollutants such as heavy metals may contribute to the progression of extensive list of diseases which may further lead to perturbations in the gut leading to dysbiosis. This manuscript critically reviews the alterations in the gut microbiota composition and function upon exposure to various toxic heavy metals prevalent in the environment. The disturbance in gut microbial ecology also affects the microbial metabolic profile which may alter the speciation state and bioavailability heavy metals thus affecting metal uptake-absorption/detoxification mechanisms associated to heavy metal metabolism. The toxic effects of various heavy metals either in single or in multimetallic combination and the gut microbiota associated host health and disease condition need a comprehensive assessment with important consideration for therapeutic and protective strategies against the damage to gut microbiota.

Oleic Acid Facilitates Cd Excretion by Increasing the Abundance of Burkholderia in Cd-Exposed Mice

As a global pollutant, cadmium (Cd) can easily enter the body through food chains, threatening human health. Most Cd is initially absorbed in the gut, with the gut microbiota playing a pivotal role in reducing Cd absorption and accumulation. This study assessed the effects of three fatty acids on Cd accumulation and toxicity in Cd-exposed mice. The results showed that oleic acid (OA) was the most effective in facilitating Cd excretion in mice among these fatty acids. The use of OA led to reduced Cd accumulation in the organs and increased Cd content in the feces. The metagenomic analysis of the gut microbiota showed that the genus Burkholderia was the most significantly restored by OA in Cd-exposed mice. Burkholderia cepacia, as the type species for the genus Burkholderia, also exhibited strong Cd tolerance after treatment with OA. Furthermore, the electron microscopy analysis showed that most of the Cd was adsorbed on the surface of B. cepacia, where the extracellular polymeric substances (EPSs) secreted by B. cepacia play a key role, displaying a strong capacity for Cd adsorption. The peak at 2355 cm^-1 and the total sulfhydryl group content of EPSs showed significant increases following co-treatment with Cd and OA. The results demonstrated the potential roles that gut Burkholderia may play in OA-mediated Cd excretion in mice.

Interactions of semiconductor Cd-based quantum dots and Cd2+ with gut bacteria isolated from wild Salmo trutta fry

Background

With the rapid development of nanotechnology, more and more nanoproducts are being released into the environment where they may both pose ecological risks and be toxic to living organisms. The ecotoxicological impact of quantum dots (QDs), a class of nanoparticles (NPs), on aquatic organisms is becoming an emerging issue, this due to their nano-specific properties, to the physico-chemical transformation in the environment and to the possible release of toxic metals from their structure such as Cd.

Methods

In this work, (i) spectroscopic measurements of commercially available Cd-based QDs (CdSe/ZnS-COOH) were made at various pH values (5.0 and 7.0) to study their interactions (at a concentration of 4 nm) with various strains of Gram-positive and Gram-negative gut bacteria after short-term exposure and (ii) the antibacterial efficacy of QDs and Cd²⁺ (at a concentration 0.09-3.56 mM) against gut bacteria isolated from wild freshwater Salmo trutta fry was studied at different temperatures (15 °C and 25 °C) and pH values (5.0 and 7.0) by applying a well-established disc diffusion assay.

Results

Twenty-six gut bacterial isolates from wild Salmo trutta fry were identified as Aeromonas spp., A. popoffii, A. salmonicida, A. sobria, Carnobacterium maltaromaticum, Buttiauxella sp., Listeria sp., Microbacterium sp., Shewanella putrefaciens and Serratia sp. Cd-based (CdSe/ZnS-COOH) QDs at a concentration of 4 nm were found to be stable in aqueous media (with pH 7.0) or starting to form aggregates (at pH 5.0), thus, apparently, did not release heavy metals (HMs) into the media over 48 h in conditions of light or dark and did not show antibacterial efficacy on the gut bacteria isolated from wild Salmo trutta fry after short-term (9 h and 48 h) incubations. Cd²⁺ was found to produce significant dose-dependent toxic effects on bacterial growth, and the size of the inhibition zones on some of the tested strains significantly correlated with temperature. The most sensitive and the most resistant to Cd²⁺ were the Gram-positive bacteria, for which the minimum inhibitory concentration (MIC) values of Cd²⁺ were 0.09-0.27 mM and 3.11-3.29 mM respectively and varied significantly between the tested temperatures (15 °C and 25 °C). The MIC values of Cd²⁺ for the Gram-negative bacteria (18 out of 22 strains) ranged from 0.44 to 0.71 mM and did not differ significantly between the tested temperatures. Among the selected Gram-positive and Gram-negative strains, those with the higher sensitivity towards Cd²⁺ also revealed relatively stronger signals of QDs photoluminescence (PL) when transferred after incubation into fresh medium without QDs. In addition, the formation of endogenous metalloporphyrins observed spectroscopically in some bacterial strains indicates certain differences in metabolic activity that may play a protective role against potential oxidative damage.

Differential toxicity of potentially toxic elements to human gut microbes

Specific microorganisms in the human gut (i.e., gut microbes) provide mutually beneficial outcomes such as microbial balance by inhibiting the growth of pathogenic organisms, immune system modulation, fermentation of ingested products, and vitamin production. The intake of contaminants including potenially toxic elements (PTEs) can occur through food, air, water and some medicines. The gut microbes not only can be affected by environmental contaminants but they themselves can alter the speciation and bioavailability of these contaminants. This research work was designed to demonstrate the relationship between increasing level of selected PTEs including As, Cd, Pb and Hg on the growth of selected gut microbes. The toxicity of above mentioned PTEs to three gut bacteria (Lactobacillus rhamnosus, Lactobacillus acidophilus and Escherichia coli) was examined. While the toxicity of all the cationic PTEs including Cd, Pb and Hg towards gut bacteria decreased with increasing pH, the anionic As species exhibited an opposite effect. The order of toxicity was Hg > Cd > Pb > As(III)>As(V) for E. coli; and Hg > Cd > As(III)>Pb > As(V) for the two Lactobacillus sp. Arsenite (AsIII) showed higher toxicity than arsenate (AsV) to gut bacteria. While As is an anion, Cd, Pb and Hg are cations and hence their binding capacity to the bacterial cell wall varied based on the charge dependent functional groups. However, the toxic effects of PTEs for a bacteria are controlled by their speciation and bioavailability.

Pathophysiological effects of cadmium(II) on human health-a critical review

Cadmium(II) is an omnipresent environmental toxicant emitted from various industrial sources and by anthropogenic sources such as smoking. Cadmium(II) enters our body through various sources including contaminated food and drinks and from active or passive smoking. It spares no organs in our body and the calamities it invites include primarily nephrotoxicity, osteotoxicity, teratogenicity, endocrine disruption, hepatotoxicity and carcinogenicity above all. It brings about a bolt from the blue in the cellular biochemistry by generating reactive oxygen species (ROS), disrupting the factors involved in the repair of DNA lesions and many other toxic nuisances otherwise by modulating the cell signalling machinery and acting as a potent carcinogen above all. In this review, we have tried to decipher some of the mechanisms played by cadmium(II) in exhibiting its toxic effects on various system of our body.

Probiotics and gut microbiome - Prospects and challenges in remediating heavy metal toxicity

The gut microbiome, often referred to as "super organ", comprises up to a hundred trillion microorganisms, and the species diversity may vary from person to person. They perform a decisive role in diverse biological functions related to metabolism, immunity and neurological responses. However, the microbiome is sensitive to environmental pollutants, especially heavy metals. There is continuous interaction between heavy metals and the microbiome. Heavy metal exposure retards the growth and changes the structure of the phyla involved in the gut microbiome. Meanwhile, the gut microbiome tries to detoxify the heavy metals by altering the physiological conditions, intestinal permeability, enhancing enzymes for metabolizing heavy metals. This review summarizes the effect of heavy metals in altering the gut microbiome, the mechanism by which gut microbiota detoxifies heavy metals, diseases developed due to heavy metal-induced dysbiosis of the gut microbiome, and the usage of probiotics along with advancements in developing improved recombinant probiotic strains for the remediation of heavy metal toxicity.

Protective Effects of Lactobacillus plantarum CCFM8610 against Acute Toxicity Caused by Different Food-Derived Forms of Cadmium in Mice

Cadmium (Cd) is an environmental pollutant that is toxic to almost every human organ. Oral supplementation with lactic acid bacteria (LAB) has been reported to alleviate cadmium toxicity. However, research on the mitigation of cadmium toxicity by LAB is still limited to inorganic cadmium, which is not representative of the varied forms of cadmium ingested daily. In this study, different foodborne forms of cadmium were adopted to establish an in vivo toxicity model, including cadmium–glutathione, cadmium–citrate, and cadmium–metallothionein. The ability of Lactobacillus plantarum CCFM8610 to reduce the toxic effects of these forms of cadmium was further investigated. The 16S rRNA gene sequencing and metabolomics technologies based on liquid chromatography with tandem mass spectrometry (LC–MS/MS) were adopted for the exploration of relevant protective mechanisms. The results demonstrated that the consumption of CCFM8610 can reduce the content of cadmium in mice and relieve the oxidative stress caused by different food–derived forms of cadmium, indicating that CCFM8610 has a promising effect on the remediation of the toxic effects of cadmium food poisoning. Meanwhile, protective effects on gut microflora and serum metabolites might be an important mechanism for probiotics to alleviate cadmium toxicity. This study provides a theoretical basis for the application of L. plantarum CCFM8610 to alleviate human cadmium poisoning.

Effects of cadmium on organ function, gut microbiota and its metabolomics profile in adolescent rats

Cadmium (Cd) exposure in adult animals can result in multi-organ damages and gut microbiota disturbance. However, Cd's consequences on health and gut microbiota during adolescence are obscure. In the present study, three-week-old SD rats were exposed to Cd at doses of 0, 0.25, 1, and 4 mg/kg body weight for eight weeks, and the changes of liver, kidney, and ovary function, as well as gut microbiota and its metabolomics profile, were analyzed. After transplantation of fecal bacteria from the 4 mg/kg Cd-treated group into age-matched rats (4 mg/kg-Cd recipients), the organ function and inflammatory reaction were evaluated. The results indicated that Cd perturbed gut microbiota composition, significantly decreased the abundance of Prevotella and Lachnoclostridium but increased Escherichia coli_Shigella. The fecal metabolome profile was altered and was closely correlated with some specific genera. These changes were accompanied by the inflammatory response, dyslipidemia, kidney dysfunction, and abnormal estrogen level. In 4 mg/kg-Cd recipients, the serum triglyceride (TG), lipopolysaccharide (LPS), and inflammatory cytokines were increased with the expressions of IL-1β, IL-6, TNF-α genes up-regulated in liver and kidney. Overall, this study demonstrated that Cd exposure during adolescence could cause disturbance of gut microbiota, dysfunction of liver, kidney, and ovary, which may be correlated with the activation of Cd-induced inflammatory response.

Gut microbiota of homologous Chinese soft-shell turtles (Pelodiscus sinensis) in different habitats

Background

Chinese soft-shell turtle (Pelodiscus sinensis) is an important commercial species for their high nutritional value and unique taste, but it has been a vulnerable species due to habitat loss. In this study, homologous juvenile turtles were allocated to lake, pond and paddy field to investigate the habitat effects on turtles.

Results

The growth, morphology and gut microbial communities were monitored during the 4 months cultural period. It showed higher growth rate of turtles in paddy field and pond. The appearance, visceral coefficients, gut morphology and microbial communities in turtles were distinct among different habitats. The microbial community richness on Chao1 was obviously lower in initial turtle guts from greenhouses, whereas it was relative higher in turtle guts sampled from paddy fields than ponds and lake. Significant differences on dominant microbes were found among initial and subsequent samples from different habitats. Firmicutes was the most abundant phylum in the guts of turtles sampled from the greenhouse initially, while Proteobacteria was the most abundant phylum after cultivation in different habitats, followed by Bacteroidetes. The microbial composition were distinct in different habitats at 60d, and the appearance of dominant phyla and genera was more driven by sampling time than habitats at 120d. Both the sampling time and habitats affected the appearance of dominant phyla and genera during the cultivation. The functional predictions indicated that both habitat type and sampling time had significant effects on metabolic pathways, especially amino acid and carbohydrate metabolism.

Conclusions

The turtles could adapt to natural lakes, artificial ponds and paddy fields. The gut microbial abundance was different among the habitats and sampling time. The species of microbes were significantly more diverse in paddy field specimens than in those from ponds and lakes. Rice-turtle coculture is a potential ecological and economic farming mode that plays important roles in wild turtle protection and food security.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02209-y.

Gut microbes modulate bioaccessibility of lead in soil

Metabolic uptake of lead (Pb) is controlled by its bioaccessibility. Most studies have examined bioaccessibility of Pb in the absence of gut microbes, which play an important role in the metabolic uptake of nutrients and metal(loid)s in intestine. In this study, we examined the effect of three gut microbes, from various locations in the gut, on the bioaccessibility of soil ingested Pb. The gut microbes include Lactobacillus acidophilus, Lactobacillus rhamnosus and Escherichia coli. Lead toxicity to these three microbes was also examined at various pH values. Bioaccessibility of Pb was measured using gastric and intestinal extractions. Both Pb spiked and Pb-contaminated shooting range field soils were used to measure Pb bioaccessibility in the presence and absence of gut microbes. The results indicated that Pb toxicity to gut microbes, as measured by LD₅₀ value, decreased with increasing pH, and was higher for Lactobacillus species. Gut microbes decreased the bioaccessible Pb; the effect was more pronounced at low pH, mimicking gastric conditions than in conditions closer to the intestine. Lead adsorption by these microbes increased at the higher pH tested, and E. coli adsorbed higher amounts of Pb than did the Lactobacillus species. The effect of gut microbes on reducing Pb bioaccessibility may be attributed to microbially-induced immobilization of Pb through adsorption, precipitation, and complexation reactions. The study demonstrates that bioaccessibility and subsequently bioavailability of metal(loid)s can be modulated by gut microbes, and it is important to undertake bioaccessibility measurements in the presence of gut microbes.

Bioaccumulation of trace elements affects chick body condition and gut microbiome in greater flamingos

Elevated concentrations of trace elements represent a major concern to wetland ecosystems, since river estuaries are geochemical endpoints that accumulate pollution. Although the negative impact of environmental exposure of highly toxic elements such as Pb and Hg has received substantial attention, we still lack a comprehensive understanding of the effects that these and other common trace elements have on natural populations. We used greater flamingos as a study system within three sites that represent a gradient of pollution. Controlling for environmental sediment exposure, we assessed if signatures of bioaccumulation in feathers for ten trace elements (As, Cd, Cr, Cu, Hg, Ni, Pb, Se, Sn and Zn) are associated with two known proxies of health: body condition and the gut bacterial microbiome. We found evidence of an adverse effect of Se, Hg, and Pb bioaccumulation on body condition. Furthermore, bioaccumulation of the elements As, Cu, Se, Pb and Zn influenced different aspects of the gut microbiome. Bioaccumulation of Se led to a shift in the microbiome composition, largely driven by an enrichment of Bacteroides plebeius, which is linked to the breakdown of sulphated polysaccharides of algae. Bacteroides plebeius was negatively associated with chick body condition, suggesting an adverse effect of a microalgae diet rich in Se. Pb bioaccumulation was linked with a decrease in microbial diversity (adjusted-R² = 10.4%) and an increase in heterogeneity of the microbial community (adjusted-R² = 10.5%), an indication of impaired gut homeostasis. As, Cu and Zn had more nuanced effects on gut microbiome heterogeneity according to breeding site and bioaccumulation concentration. Our results therefore suggest that in addition to well-studied elements, bioaccumulation of poorly studied elements also adversely affect health of natural populations.

Protection Mechanisms Underlying Oral Administration of Chlorogenic Acid against Cadmium-Induced Hepatorenal Injury Related to Regulating Intestinal Flora Balance

Cadmium (Cd) is a heavy metal, which is widely used in the industry and daily life. It has a long half-life, so large amounts of Cd can accumulate in humans and become toxic. Chlorogenic acid (CGA) can eliminate free radicals and inhibit lipid peroxidation and is mainly used to prevent metal toxicity. In the present study, mice are given CGA by intraperitoneal injection or gavage, respectively, to explore the mechanism of preventing Cd toxicity. In acute Cd-exposed mice, CGA treatment (ip) alleviated Cd-induced oxidative damage and reduced the production of NO and MPO in the liver and kidney tissues, while TLR4 expression levels did not change significantly. After 8 weeks of Cd exposure, CGA administration (gavage) significantly alleviated gut dysbiosis by decreasing the Firmicutes to Bacteroidetes ratio, enhancing the relative abundances of bacteria, including Ruminiclostridium_9, Alloprevotella, and Rikenella, and inhibiting the activation of the TLR4/MyD88/NF-κB signaling pathway. These findings suggested that protection mechanisms underlying the oral administration of CGA against the Cd-induced hepatorenal injury was related to the regulation of the intestinal flora balance. CGA can be used as an effective component in daily diet to prevent Cd toxicity.

Gut microbiota: A target for heavy metal toxicity and a probiotic protective strategy

There is growing epidemiological evidence that heavy metals (HMs) may contribute to the progression of various metabolic diseases and that the etiology and progression of these diseases is partly due to HM-induced perturbations of the gut microbiota. Importantly, the gut microbiota are the first line of defense against the toxic effects of HMs, and there is a bidirectional relationship between the two. Thus, HM exposure alters the composition and metabolic profile of the gut microbiota at the functional level, and in turn, the gut microbiota alter the uptake and metabolism of HMs by acting as a physical barrier to HM absorption and by altering the pH, oxidative balance, and concentrations of detoxification enzymes or proteins involved in HM metabolism. Moreover, the gut microbiota can affect the integrity of the intestinal barrier, which may also in turn affect the absorption of HMs. Specifically, probiotic have been shown to reduce the absorption of HMs in the intestinal tract via the enhancement of intestinal HM sequestration, detoxification of HMs in the gut, changing the expression of metal transporter proteins, and maintaining the gut barrier function. This review is a summary of the bidirectional relationship between HMs and gut microbiota and of the probiotic-based protective strategies against HM-induced gut dysbiosis, with reference to strategies used in the food industry or for medically alleviating HM toxicity.

Interactions between Environmental Exposures and the Microbiome: Implications for Fetal Programming

Decades of population-based health outcomes data highlight the importance of understanding how environmental exposures in pregnancy affect maternal and neonatal outcomes. Animal model research and epidemiological studies have revealed that such exposures are able to alter fetal programming through stable changes in the epigenome, including altered DNA methylation patterns and histone modifications in the developing fetus and infant. It is similarly known that while microbes can biotransform environmental chemicals via conjugation and de-conjugation, specific exposures can also alter the community profile and function of the human microbiome. In this review, we consider how alterations to the maternal and or fetal/infant microbiome through environmental exposures could directly and indirectly alter fetal programming. We highlight two specific environmental exposures, cadmium (Cd) and polycyclic aromatic hydrocarbons (PAHs), and outline their effects on the developing fetus and the perinatal (maternal and fetal/infant) microbiome. We further consider how chemical exposures in the setting of natural disasters may be of particular importance to environmental health.

Amelioration of Cd-induced bioaccumulation, oxidative stress and intestinal microbiota by Bacillus cereus in Carassius auratus gibelio

The heavy metal cadmium (Cd) is a hazardous pollutant known to exert various toxic effects and other sublethal to lethal effects on aquatic organisms, and can be commonly found in environment. The genus Bacillus was one of dominant probiotics, which was commonly used in aquaculture. The aim of this study was to evaluate the effects of dietary administration of Bacillus cereus (B. cereus) on bioaccumulation, oxidative stress and intestinal microbiota of Carassius auratus gibelio (C. gibelio) after Cd exposure. Fish were exposed for 4 weeks to waterborne Cd at 0, 1 and 2 mg/L and/or dietary B. cereus at 10⁸ cfu/g. At 2 and 4 weeks, the fish were sampled and bioaccumulation, antioxidant activity and intestinal microbiota were assessed. Waterborne Cd exposure caused marked alterations in the composition of the microbiota. Dietary supplementation with B. cereus can reverse the changes in the composition of intestinal microbiota in Cd exposure and increase the abundance of Bacteroides, Akkermansia, Cetobacterium in the 0 and 1 mg/L Cd. The results obtained indicate that B. cereus can provide a significant protective effect on the toxicity of cadmium by inhibiting alterations in the levels of bioaccumulation and antioxidant enzyme including Superoxide dismutase (SOD), catalase (CAT), total antioxidant (T-AOC), glutathione (GSH), malonaldehyde (MDA) and Glutathione-S-transferase (GST). The present findings imply that dietary supplement of B. cereus can effectively protect C.gibelio to combat cadmium toxicity.

The effects of cadmium exposure in the induction of inflammation

Inflammation is a physiological process essential for maintaining homeostatic mechanisms in human, but however, exaggerated inflammatory responses are closely related to many chronic diseases. Cadmium (Cd) is a heavy metal with high toxicity when present in food, water and air has the potential of eliciting inflammatory reactions, with a major health risk to human. This review aimed to elucidate on the major routes of Cd exposure, the main organs affected by the exposure, the degree of toxicity as well as the roles of the toxic effects on the immune system which results to inflammatory responses. Immune modulation by Cd may cause serious adverse health effects in humans. Various studies have highlighted the ability of Cd as an environmental pollutant involved in the modulation of the innate, adaptive and mucosal immune responses in relations to the release of chemokine, gene expression, and susceptibility to microbial infections.

Effects of single and combined toxic exposures on the gut microbiome: Current knowledge and future directions

Human populations are chronically exposed to mixtures of toxic chemicals. Predicting the health effects of these mixtures require a large amount of information on the mode of action of their components. Xenobiotic metabolism by bacteria inhabiting the gastrointestinal tract has a major influence on human health. Our review aims to explore the literature for studies looking to characterize the different modes of action and outcomes of major chemical pollutants, and some components of cosmetics and food additives, on gut microbial communities in order to facilitate an estimation of their potential mixture effects. We identified good evidence that exposure to heavy metals, pesticides, nanoparticles, polycyclic aromatic hydrocarbons, dioxins, furans, polychlorinated biphenyls, and non-caloric artificial sweeteners affect the gut microbiome and which is associated with the development of metabolic, malignant, inflammatory, or immune diseases. Answering the question 'Who is there?' is not sufficient to define the mode of action of a toxicant in predictive modeling of mixture effects. Therefore, we recommend that new studies focus to simulate real-life exposure to diverse chemicals (toxicants, cosmetic/food additives), including as mixtures, and which combine metagenomics, metatranscriptomics and metabolomic analytical methods achieving in that way a comprehensive evaluation of effects on human health.

The Multifactorial Etiopathogeneses Interplay of Inflammatory Bowel Disease: An Overview

The gastrointestinal system where inflammatory bowel disease occurs is central to the immune system where the innate and the adaptive/acquired immune systems are balanced in interactions with gut microbes under homeostasis conditions. This article overviews the high-throughput research screening on multifactorial interplay between genetic risk factors, the intestinal microbiota, urbanization, modernization, Westernization, the environmental influences and immune responses in the etiopathogenesis of inflammatory bowel disease in humans. Inflammatory bowel disease is an expensive multifactorial debilitating disease that affects thousands new people annually worldwide with no known etiology or cure. The conservative therapeutics focus on the established pathology where the immune dysfunction and gut injury have already happened but do not preclude or delay the progression. Inflammatory bowel disease is evolving globally and has become a global emergence disease. It is largely known to be a disease in industrial-urbanized societies attributed to modernization and Westernized lifestyle associated with environmental factors to genetically susceptible individuals with determined failure to process certain commensal antigens. In the developing nations, increasing incidence and prevalence of inflammatory bowel disease (IBD) has been associated with rapid urbanization, modernization and Westernization of the population. In summary, there are identified multiple associations to host exposures potentiating the landscape risk hazards of inflammatory bowel disease trigger, that include: Western life-style and diet, host genetics, altered innate and/or acquired/adaptive host immune responses, early-life microbiota exposure, change in microbiome symbiotic relationship (dysbiosis/dysbacteriosis), pollution, changing hygiene status, socioeconomic status and several other environmental factors have long-standing effects/influence tolerance. The ongoing multipronged robotic studies on gut microbiota composition disparate patterns between the rural vs. urban locations may help elucidate and better understand the contribution of microbiome disciplines/ecology and evolutionary biology in potentially protecting against the development of inflammatory bowel disease.

A Review on Gut Remediation of Selected Environmental Contaminants: Possible Roles of Probiotics and Gut Microbiota

Various environmental contaminants including heavy metals, pesticides and antibiotics can contaminate food and water, leading to adverse effects on human health, such as inflammation, oxidative stress and intestinal disorder. Therefore, remediation of the toxicity of foodborne contaminants in human has become a primary concern. Some probiotic bacteria, mainly Lactobacilli, have received a great attention due to their ability to reduce the toxicity of several contaminants. For instance, Lactobacilli can reduce the accumulation and toxicity of selective heavy metals and pesticides in animal tissues by inhibiting intestinal absorption of contaminants and enhancing intestinal barrier function. Probiotics have also shown to decrease the risk of antibiotic-associated diarrhea possibly via competing and producing antagonistic compounds against pathogenic bacteria. Furthermore, probiotics can improve immune function by enhancing the gut microbiota mediated anti-inflammation. Thus, these probiotic bacteria are promising candidates for protecting body against foodborne contaminants-induced toxicity. Study on the mechanism of these beneficial bacterial strains during remediation processes and particularly their interaction with host gut microbiota is an active field of research. This review summarizes the current understanding of the remediation mechanisms of some probiotics and the combined effects of probiotics and gut microbiota on remediation of foodborne contaminants in vivo.

Lactobacillus brevis 23017 Relieves Mercury Toxicity in the Colon by Modulation of Oxidative Stress and Inflammation Through the Interplay of MAPK and NF-κB Signaling Cascades

Aims: Lactobacillus strains have protective effects against heavy metals while relieving oxidative stress and modulating the immune response. Mechanisms that ameliorate heavy metal toxicity and the relationship between probiotics and gut barrier protection in the process of heavy metal pathogenesis was poorly understood. Methods and Results: In this study, Lactobacillus brevis 23017 (LAB, L. brevis 23017), a selected probiotics strain with strong mercury binding capacities, was applied to evaluate the efficiency against mercury toxicity in a mouse model. Histopathological results along with HE stains show that L. brevis 23017 protects the integrity of the small intestinal villus, which slows weight loss in response to Hg exposure. The qRT-PCR results demonstrate that L. brevis 23017 maintains a normal mucosal barrier via modulation of tight junction proteins. Importantly, the present study demonstrates that L. brevis 23017 effectively ameliorates injury of the small intestine by reducing intestinal inflammation and alleviating oxidative stress in animal models. Moreover, L. brevis 23017 blocks oxidative stress and inflammation through MAPK and NF-κB pathways, as shown by western blot. Conclusions: Together, these results reveal that L. brevis 23017 may have applications in the prevention and treatment of oral Hg exposure with fermented functional foods by protecting gut health in daily life.

Urbanization and the gut microbiota in health and inflammatory bowel disease

In the 21st century, urbanization represents a major demographic shift in developed and developing countries. Rapid urbanization in the developing world has been associated with an increasing incidence of several autoimmune diseases, including IBD. Patients with IBD exhibit a decrease in the diversity and richness of the gut microbiota, while urbanization attenuates the gut microbial diversity and might have a role in the pathogenesis of IBD. Environmental exposures during urbanization, including Westernization of diet, increased antibiotic use, pollution, improved hygiene status and early-life microbial exposure, have been shown to affect the gut microbiota. The disparate patterns of the gut microbiota composition in rural and urban areas offer an opportunity to understand the contribution of a 'rural microbiome' in potentially protecting against the development of IBD. This Perspective discusses the effect of urbanization and its surrogates on the gut microbiome (bacteriome, virome, mycobiome and helminths) in both human health and IBD and how such changes might be associated with the development of IBD.

Gut as a target for cadmium toxicity

The primary objective of the present study was to review the impact of Cd exposure on gut microbiota and intestinal physiology, as well as to estimate whether gut may be considered as the target for Cd toxicity. The review is based on literature search in available databases. The existing data demonstrate that the impact of Cd on gut physiology is two-sided. First, Cd exposure induces a significant alteration of bacterial populations and their relative abundance in gut (increased Bacteroidetes-to-Firmicutes ratio), accompanied by increased lipopolysaccharide (LPS) production, reflecting changed metabolic activity of the intestinal microbiome. Second, in intestinal wall Cd exposure induces inflammatory response and cell damage including disruption of tight junctions, ultimately leading to increased gut permeability. Together with increased LPS production, impaired barrier function causes endotoxinemia and systemic inflammation. Hypothetically, Cd-induced increase gut permeability may also result in increased bacterial translocation. On the one hand, bacteriolysis may be associated with aggravation of endotoxemia. At the same time, together with Cd-induced impairment of macrophage inflammatory response, increased bacterial translocation may result in increased susceptibility to infections. Such a supposition is generally in agreement with the finding of higher susceptibility of Cd-exposed mice to infections. The changed microbiome metabolic activity and LPS-induced systemic inflammation may have a significant impact on target organs. The efficiency of probiotics in at least partial prevention of the local (intestinal) and systemic toxic effects of cadmium confirms the role of altered gut physiology in Cd toxicity. Therefore, probiotic treatment may be considered as the one of the strategies for prevention of Cd toxicity in parallel with chelation, antioxidant, and anti-inflammatory therapy.

Bile Acids and Cancer: Direct and Environmental-Dependent Effects

Bile acids (BAs) regulate the absorption of fat-soluble vitamins, cholesterol and lipids but have also a key role as singalling molecules and in the modulation of epithelial cell proliferation, gene expression and metabolism. These homeostatic pathways, when disrupted, are able to promote local inflammation, systemic metabolic disorders and, ultimately, cancer. The effect of hydrophobic BAs, in particular, can be linked with cancer in several digestive (mainly oesophagus, stomach, liver, pancreas, biliary tract, colon) and extra-digestive organs (i.e. prostate, breast) through a complex series of mechanisms including direct oxidative stress with DNA damage, apoptosis, epigenetic factors regulating gene expression, reduced/increased expression of nuclear receptors (mainly farnesoid X receptor, FXR) and altered composition of gut microbiota, also acting as a common interface between environmental factors (including diet, lifestyle, exposure to toxics) and the molecular events promoting cancerogenesis. Primary prevention strategies (i.e. changes in dietary habits and lifestyle, reduced exposure to environmental toxics) mainly able to modulate gut microbiota and the epigenome, and the therapeutic use of hydrophilic BAs to counterbalance the negative effects of the more hydrophobic BAs might be, in the near future, part of useful tools for cancer prevention and management.

Effects of subchronic oral toxic metal exposure on the intestinal microbiota of mice

Oral exposure to toxic metals such as cadmium (Cd), lead (Pb), copper (Cu) and aluminum (Al) can induce various adverse health effects in humans and animals. However, the effects of these metals on the gut microbiota have received limited attention. The present study demonstrated that long-term toxic metal exposure altered the intestinal microbiota of mice in a metal-specific and time-dependent manner. Subchronic oral Cu exposure for eight weeks caused a profound decline in gut microbial diversity in mice, whereas no significant changes were observed in groups treated with other metals. Cd exposure significantly increased the relative abundances of organisms from the genera Alistipes and Odoribacter and caused marked decreases in Mollicutes and unclassified Ruminococcaceae. Pb exposure significantly decreased the abundances of eight genera: unclassified and uncultured Ruminococcaceae, unclassified Lachnospiraceae, Ruminiclostridium_9, Rikenellaceae_RC9_gut_group, Oscillibacter, Anaerotruncus and Lachnoclostridium. Cu exposure affected abundances of the genera Alistipes, Bacteroides, Ruminococcaceae_UCG-014, Allobaculum, Mollicutes_RF9_norank, Rikenellaceae_RC9_gut_group, Ruminococcaceae_unclassified and Turicibacter. Al exposure increased the abundance of Odoribacter and decreased that of Anaerotruncus. Exposure to any metal for eight weeks significantly decreased the abundance of Akkermansia. These results provide a new understanding regarding the role of toxic metals in the pathogenesis of intestinal and systemic disorders in the host within the gut microbiota framework.

Cytoprotective effects of dietary flavonoids against cadmium-induced toxicity

Cadmium (Cd) damages the liver, kidney, bones, reproductive system, and other organs. Flavonoids, such as anthocyanins and flavonols, which are commonly found in plant foods, have shown protective effects against Cd-induced damage. The cytoprotective effects of flavonoids against Cd-induced diseases are mainly attributable to three mechanisms. First, flavonoids clear reactive oxygen species, thereby reducing lipid peroxide production and improving the activity of antioxidation enzymes. Second, flavonoids chelate Cd, thus reducing the accumulation of Cd and altering the levels of other essential metal ions in vivo. Third, flavonoids reduce DNA damage and inhibit apoptosis. In addition, flavonoids were found to inhibit inflammation and fibrosis and improve glycometabolism and the secretion of reproductive hormones. We introduce the daily dosage and absorption rate of flavonoids and then focus on their bioactive effects against Cd-induced toxicity and reveal the underlying metabolic pathway, which provides a basis for further study of the nutritional prevention of Cd-induced injury. In particular, a better understanding is needed of the structure-activity relationship of flavonoids against Cd toxicity, which has not yet been reported.

Multi-Omics Reveals that Lead Exposure Disturbs Gut Microbiome Development, Key Metabolites, and Metabolic Pathways

Lead exposure remains a global public health issue, and the recent Flint water crisis has renewed public concern about lead toxicity. The toxicity of lead has been well established in a variety of systems and organs. The gut microbiome has been shown to be highly involved in many critical physiological processes, including food digestion, immune system development, and metabolic homeostasis. However, despite the key role of the gut microbiome in human health, the functional impact of lead exposure on the gut microbiome has not been studied. The aim of this study is to define gut microbiome toxicity induced by lead exposure in C57BL/6 mice using multiomics approaches, including 16S rRNA sequencing, whole genome metagenomics sequencing, and gas chromatography-mass spectrometry (GC-MS) metabolomics. 16S rRNA sequencing revealed that lead exposure altered the gut microbiome trajectory and phylogenetic diversity. Metagenomics sequencing and metabolomics profiling showed that numerous metabolic pathways, including vitamin E, bile acids, nitrogen metabolism, energy metabolism, oxidative stress, and the defense/detoxification mechanism, were significantly disturbed by lead exposure. These perturbed molecules and pathways may have important implications for lead toxicity in the host. Taken together, these results demonstrated that lead exposure not only altered the gut microbiome community structures/diversity but also greatly affected metabolic functions, leading to gut microbiome toxicity.

Two stable variants of Burkholderia pseudomallei strain MSHR5848 express broadly divergent in vitro phenotypes associated with their virulence differences

Burkholderia pseudomallei (Bp), the agent of melioidosis, causes disease ranging from acute and rapidly fatal to protracted and chronic. Bp is highly infectious by aerosol, can cause severe disease with nonspecific symptoms, and is naturally resistant to multiple antibiotics. However, no vaccine exists. Unlike many Bp strains, which exhibit random variability in traits such as colony morphology, Bp strain MSHR5848 exhibited two distinct and relatively stable colony morphologies on sheep blood agar plates: a smooth, glossy, pale yellow colony and a flat, rough, white colony. Passage of the two variants, designated "Smooth" and "Rough", under standard laboratory conditions produced cultures composed of > 99.9% of the single corresponding type; however, both could switch to the other type at different frequencies when incubated in certain nutritionally stringent or stressful growth conditions. These MSHR5848 derivatives were extensively characterized to identify variant-associated differences. Microscopic and colony morphology differences on six differential media were observed and only the Rough variant metabolized sugars in selective agar. Antimicrobial susceptibilities and lipopolysaccharide (LPS) features were characterized and phenotype microarray profiles revealed distinct metabolic and susceptibility disparities between the variants. Results using the phenotype microarray system narrowed the 1,920 substrates to a subset which differentiated the two variants. Smooth grew more rapidly in vitro than Rough, yet the latter exhibited a nearly 10-fold lower lethal dose for mice than Smooth. Finally, the Smooth variant was phagocytosed and replicated to a greater extent and was more cytotoxic than Rough in macrophages. In contrast, multiple locus sequence type (MLST) analysis, ribotyping, and whole genome sequence analysis demonstrated the variants' genetic conservation; only a single consistent genetic difference between the two was identified for further study. These distinct differences shown by two variants of a Bp strain will be leveraged to better understand the mechanism of Bp phenotypic variability and to possibly identify in vitro markers of infection.

Efficacy of indigenous probiotic Lactobacillus strains to reduce cadmium bioaccessibility - An in vitro digestion model

The toxic heavy metal cadmium (Cd) appears as one of the major global threats to human and animal health. Human being and aquatic life are exposed to Cd by breathing, eating, or drinking when industrial effluents released into environment. The study was aimed to identify cadmium-binding Lactobacillus strain to reduce its bioaccessibility in in vitro digestion model. In this context, forty-eight lactobacilli strains isolated and characterized from fermented dairy products and human origin were screened for their Cd biosorption potential using Flame Atomic Absorption Spectroscopy (FAAS). The present study revealed that Cd biosorption potential of 48 lactobacilli strains ranged from 1.0832 ± 0.012 to 3.562 ± 0.03 mg Cd g^-1 of cells from initial 10 mg L^-1 cadmium chloride (CdCl₂) aqueous solution. Lactobacillus plantarum strain HD 48 demonstrated highest biosorption of 3.562 ± 0.03 mg Cd g^-1 of cells. Lactobacilli-Cd complex stability indicated its strong stability as even after three washes with Milli-Q water metal desorption was nonsignificant (p < 0.05) and further studies to delineate the influence of Cd (100 mg L^-1 CdCl₂) on their growth. Moreover, these strains were able to reduce Cd bioaccessibility in the in vitro digestion model in the range of 24.71 to 41.62 %. Transmission electron microscopy (TEM) investigations on Cd bioadsorption also revealed its surface associated bioadsorption phenomenon. These findings depicted that probiotic strain L. plantarum HD 48 was found to be endowed with remarkable Cd biosorption ability as well as reduction in its bioaccessibility. These results suggest that probiotic strain L. plantarum HD 48 has immense potential to sequester Cd from aqueous solution which could be further explored as a potent source to diminish body Cd burden.

The gut microbiota: a major player in the toxicity of environmental pollutants?

Exposure to environmental chemicals has been linked to various health disorders, including obesity, type 2 diabetes, cancer and dysregulation of the immune and reproductive systems, whereas the gastrointestinal microbiota critically contributes to a variety of host metabolic and immune functions. We aimed to evaluate the bidirectional relationship between gut bacteria and environmental pollutants and to assess the toxicological relevance of the bacteria-xenobiotic interplay for the host. We examined studies using isolated bacteria, faecal or caecal suspensions-germ-free or antibiotic-treated animals-as well as animals reassociated with a microbiota exposed to environmental chemicals. The literature indicates that gut microbes have an extensive capacity to metabolise environmental chemicals that can be classified in five core enzymatic families (azoreductases, nitroreductases, β-glucuronidases, sulfatases and β-lyases) unequivocally involved in the metabolism of >30 environmental contaminants. There is clear evidence that bacteria-dependent metabolism of pollutants modulates the toxicity for the host. Conversely, environmental contaminants from various chemical families have been shown to alter the composition and/or the metabolic activity of the gastrointestinal bacteria, which may be an important factor contributing to shape an individual's microbiotype. The physiological consequences of these alterations have not been studied in details but pollutant-induced alterations of the gut bacteria are likely to contribute to their toxicity. In conclusion, there is a body of evidence suggesting that gut microbiota are a major, yet underestimated element that must be considered to fully evaluate the toxicity of environmental contaminants.

Toxic trace elements at gastrointestinal level

Many trace elements are considered essential [iron (Fe), zinc (Zn), copper (Cu)], whereas others may be harmful [lead (Pb), cadmium (Cd), mercury (Hg), arsenic (As)], depending on their concentration and chemical form. In most cases, the diet is the main pathway by which they enter our organism. The presence of toxic trace elements in food has been known for a long time, and many of the food matrices that carry them have been identified. This has led to the appearance of legislation and recommendations concerning consumption. Given that the main route of exposure is oral, passage through the gastrointestinal tract plays a fundamental role in their entry into the organism, where they exert their toxic effect. Although the digestive system can be considered to be of crucial importance in their toxicity, in most cases we do not know the events that occur during the passage of these elements through the gastrointestinal tract and of ascertaining whether they may have some kind of toxic effect on it. The aim of this review is to summarize available information on this subject, concentrating on the toxic trace elements that are of greatest interest for organizations concerned with food safety and health: Pb, Cd, Hg and As.

Impact of Cadmium Exposure on the Association between Lipopolysaccharide and Metabolic Syndrome

Cadmium (Cd) is an environmental contaminant that has a direct impact on the gut microbiome. Perturbations in the gut microbiome have been linked to metabolic disorders associated with inflammation generated by lipopolysaccharide (LPS). We investigated the impact of Cd on the association between LPS and metabolic syndrome. The study population consisted of 200 apparently healthy subjects (30–64 years of age; 96 men, 104 women). Serum LPS and blood Cd concentrations were measured by ELISA and graphite furnace-atomic absorption spectrophotometry (GF-AAS), respectively. The highest LPS quartile was associated with a greater prevalence of metabolic syndrome in men. There was a significant association between LPS activity and metabolic syndrome in men with blood Cd concentrations higher than the 50th percentile (OR = 3.05, 95% CI = 1.39–6.70); however, this relationship was not significant in men with blood Cd concentrations lower than the 50th percentile. The results of this study provide evidence for a strong association between high LPS activity and the prevalence of metabolic syndrome in men with relatively high blood Cd concentrations. Therefore, exposure to Cd may potentiate the association between LPS and metabolic syndrome in men.