Gut Microbiota Control the Bioavailability and Metabolism of Organoarsenicals of Seaweeds in Mice after Oral Ingestion

Gut Dysbiosis Exacerbates Intestinal Absorption of Cadmium and Arsenic from Cocontaminated Rice in Mice Due to Impaired Intestinal Barrier Functions

Globally, humans face gut microbiota dysbiosis; however, its impact on the bioavailability of cadmium (Cd) and arsenic (As) from rice consumption─a major source of human exposure to these metals─remains unclear. In this study, we compared Cd and As accumulation in the liver and kidneys of mice with disrupted gut microbiota (administered cefoperazone sodium), restored microbiota (administered probiotics and prebiotics following antibiotic exposure), and normal microbiota, all after consuming cocontaminated rice. Compared to normal mice, microbiota-disrupted mice exhibited 30.9-119% and 30.0-100% (p < 0.05) higher Cd and As levels in tissues after a 3 week exposure period. The increased Cd and As bioavailability was not due to changes in the duodenal expression of Cd-related transporters or As speciation biotransformation in the intestine. Instead, it was primarily attributed to a damaged mucus layer and depleted tight junctions associated with gut dysbiosis, which increased intestinal permeability. These mechanisms were confirmed by observing 34.3-74.3% and 25.0-75.0% (p < 0.05) lower Cd and As levels in the tissues of microbiota-restored mice with rebuilt intestinal barrier functions. This study enhances our understanding of the increased risk of dietary metal(loid) exposure in individuals with gut microbiota dysbiosis due to impaired intestinal barrier functions.

Host-microbiota interplay in arsenic metabolism: Implications on host glucose homeostasis

Arsenic (As), a naturally occurring element with unique properties, has been recognized as the largest mass poisoning in the world by the World Health Organization (WHO). Approximately 200 million people worldwide are exposed to toxic levels of arsenic due to natural and anthropogenic activities. This widespread exposure necessitates a deeper understanding of microbe-arsenic interactions and their potential influence on host exposure and health risks. It is a major causative factor for metabolic diseases, including diabetes. Arsenic exposure has been linked to dysfunction in various cell types and tissues, notably affecting pancreatic islet cells. Numerous mechanisms have been identified to be responsible for arsenic exposure under both in vitro and in vivo conditions. These mechanisms contribute to the regulation of processes underlying diabetes etiology, such as glucose-stimulated insulin secretion from pancreatic beta cells. Unlike other toxic elements, arsenic undergoes metabolism by living organisms, including microbes, plants, and animals. Other toxic elements like Lead (Pb) and mercury (Hg) are generally not metabolized in the same way as Arsenic in microbes, plants and animals. In this review, we strive to initiate a dialogue by reviewing known aspects of microbe-arsenic interactions and placing it in the context of the potential for influencing host exposure and health risks. This review provides an up-to-date insight into arsenic metabolism by the human body and its associated microbiota, as well as the deciphered molecular pathways linking the different species of arsenic in the etiology of diabetes. Additionally, the future perspectives of mitigation and detoxification of arsenic in translational medicine and limitations in current scenarios are discussed. The comprehensive review presented here underscores the importance of exploring the complex interplay between arsenic metabolism, host-microbiota interactions, and their implications on glucose homeostasis and metabolic diseases. It emphasizes the need for continued research to develop effective strategies for mitigating arsenic-related health risks and fostering better translational medicine approaches.

A comprehensive review on arsenic exposure and risk assessment in infants and young children diets: Health implications and mitigation interventions in a global perspective

The early stages of human development are critical for growth, and exposure to arsenic, particularly through the placenta and dietary sources, poses significant health risks. Despite extensive research, significant gaps remain in our comprehension of regional disparities in arsenic exposure and its cumulative impacts during these developmental stages. We hypothesize that infants in certain regions are at greater risk of arsenic exposure and its associated health complications. This review aims to fill these gaps by providing a comprehensive synthesis of epidemiological evidence related to arsenic exposure during early life, with an emphasis on the underlying mechanisms of arsenic toxicity that contribute to adverse health outcomes, including neurodevelopmental impairments, immune dysfunction, cardiovascular diseases, and cancer. Further, by systematically comparing dietary arsenic exposure in infants across Asia, the Americas, and Europe, our findings reveal that infants in Bangladesh, Pakistan, and India, exposed to levels significantly exceeding the health reference value range of 0.3-8 µg/kg/day, are particularly vulnerable to dietary inorganic arsenic. This comparative analysis not only highlights geographic disparities in exposure but also underscores the variability in regulatory frameworks. Finally, the review identifies early life as a critical window for dietary arsenic exposure and offers evidence-based recommendations for mitigating arsenic contamination in infant foods. These strategies include improved agricultural practices, dietary modifications, stricter regulatory limits on arsenic in infant products, and encouragement of low-arsenic dietary alternatives. Our work establishes the framework for future research and policy development aimed at reducing the burden of arsenic exposure from source to table and effectively addressing this significant public health challenge.

Cadmium bioavailability in market nori and kelp: A comparison with rice and mechanisms underlying reduction in rice cadmium bioavailability with nori and kelp consumption

Seaweeds, despite being rich in beneficial substances, also contain toxic metals such as cadmium (Cd), leading to ongoing debates about their health impacts. This study assessed the risk of Cd exposure from consuming nori and kelp, as well as the potential benefits of these seaweeds in mitigating Cd exposure from rice, using mouse bioassays. The results indicated that all test nori samples (n = 35) had Cd concentration exceeding 1.2 μg g-1, while the majority of kelp samples (18 out of 24) contained <0.5 μg g-1. When mixed with Cd-free rice at a 5 % (w/w) ratio and administered to mice for 14 days, kelp samples with 0.36 and 0.50 μg g-1 Cd (Kelp-0.36 and Kelp-0.50) did not result in Cd accumulation in the liver or kidneys. Conversely, nori samples with 1.30 and 1.67 μg g-1 Cd (Nori-1.30 and Nori-1.67) led to significant Cd accumulation, highlighting the exposure risk associated with nori. This risk was further emphasized by a doubling of Cd accumulation in the tissues of mice fed sushi containing nori compared to those fed sushi without nori. However, the Cd accumulation from consuming Nori-1.30 and Nori-1.67 was comparable to that from rice with a lower Cd concentration (0.93 μg g-1), suggesting a lower bioavailability of Cd in nori than in rice. More promisingly, when consumed with Cd-containing rice at a 5 % (w/w) ratio, Kelp-0.36, Kelp-0.50, Nori-1.30, and Nori-1.67 reduced the accumulation of rice Cd in mouse tissues by 25.8 %-48.1 %, primarily by increasing the relative abundances of Bacteroides in the gut of mice and enhancing fecal output, which in turn increased the excretion of rice-derived Cd by 1.46-1.54 times. These findings suggest that kelp consumption may be relatively safe, while caution is advised for nori. Moreover, regular consumption of specific amounts of seaweeds, particularly kelp, could help to reduce Cd exposure from rice.

Bio-accessibility and bio-availability evaluation of each arsenic species existing in various edible seaweeds in vitro and in vivo for arsenic risk assessment

Seaweeds consumption is one of main internal exposure sources of arsenic for human. However, the absence of representative bio-availabilities of arsenic species makes the accurate assessment of arsenic health risk originating from seaweeds consumption impossible. Herein, the arsenic species in various seaweeds collected from Fujian of China were investigated, and the bio-accessibilities/bio-availabilities of arsenic species existing in seaweeds were evaluated in vitro and in vivo. Results revealed that in vitro bio-availabilities of arsenic species presenting in seaweeds, which obtained with Caco-2 cells, were lower than those of pure arsenic standards, and varied with order of inorganic arsenic (iAs) > dimethylarsinic acid (DMA) ≈ arsenobetaine (AsB) > arsenosugars. During gastrointestinal digestion of mice, As5+ was partly methylated into monomethylarsonic acid (MMA) and DMA, which makes the in vivo bioavailability of iAs (⁓31.8 %) obtained with mouse metabolic experiment is much higher than its in vitro bio-availability (⁓10.3 %). The in vivo bio-availabilities of DMA and total arsenic (tAs) are similar to their in vitro bio-availabilities. As the dominant arsenic species in most seaweeds, arsenosugars have an ⁓0.0 % of in vivo bioavailability and only a ⁓3.7 % of in vitro bioavailability. The simulated calculation of target hazard quotient (THQ) and target cancer risk (TR) revealed that the arsenic risk originating from seaweeds was greatly degraded by taking into consideration of arsenic species and bio-availabilities, and all seaweeds collected from Fujian are safety for consumption. The simulated calculation also revealed that arsenic risk of seaweeds can be also more accurately assessed based on tAs together with bioavailability, which provides a simple but accurate and protective method for the risk assessment of arsenic originating from seaweeds. Our work provides the possible representative bio-availabilities of arsenic species presenting in seaweeds for accurately assessing arsenic risk of seaweeds, and novel insights into the bio-availabilities of arsenic in animal.

Biotransformation of roxarsone by earthworms and subsequent risk of soil arsenic release: The role of gut bacteria

The organoarsenical feed additive roxarsone (ROX) is a ubiquitous threat due to the unpredictable levels of arsenic (As) released by soil bacteria. The earthworms representing soil fauna communities provide hotspots for As biotransformation genes (ABGs). Nonetheless, the role of gut bacteria in this regard is unclear. In this study, the changes in As speciation, bacterial ABGs, and communities were analyzed in a ROX-contaminated soil (50 mg/kg As in ROX form) containing the earthworm Eisenia feotida. (RE vs. R treatment). After 56 d, earthworms reduced the levels of both ROX and total As by 59 % and 17 %, respectively. The available As content was 10 % lower in the RE than in R treatment. Under ROX stress, the total ABG abundance was upregulated in both earthworm gut and soil, with synergistic effects observed following RE treatment. Besides, the enrichment of arsM and arsB genes in earthworm gut suggested that gut bacteria may facilitate As removal by enhancing As methylation and transport function in soil. However, the bacteria carrying ABGs were not associated with the ABG abundance in earthworm gut indicating the unique strategies of earthworm gut bacteria compared with soil bacteria due to different microenvironments. Based on a well-fit structural equation model (P = 0.120), we concluded that gut bacteria indirectly contribute to ROX transformation and As detoxification by modifying soil ABGs. The positive findings of earthworm-induced ROX transformation shed light on the role of As biomonitoring and bioremediation in organoarsenical-contaminated environments.

Dietary Galactooligosaccharides Supplementation as a Gut Microbiota-Regulating Approach to Lower Early Life Arsenic Exposure

Prebiotics may stimulate beneficial gut microorganisms. However, it remains unclear whether they can lower the oral bioavailability of early life arsenic (As) exposure via regulating gut microbiota and altering As biotransformation along the gastrointestinal (GI) tract. In this study, weanling mice were exposed to arsenate (iAsV) via diet (7.5 μg As g-1) amended with fructooligosaccharides (FOS), galactooligosaccharides (GOS), and inulin individually at 1% and 5% (w/w). Compared to As exposure control mice, As concentrations in mouse blood, liver, and kidneys and As urinary excretion factor (UEF) were reduced by 43.7%-74.1% when treated with 5% GOS. The decrease corresponded to a significant proliferation of Akkermansia and Psychrobacter, reduced percentage of inorganic arsenite (iAsIII) and iAsV by 47.4% and 65.4%, and increased proportion of DMAV in intestinal contents by 101% in the guts of mice treated with 5% GOS compared to the As control group. In contrast, FOS and inulin either at l% or 5% did not reduce As concentration in mouse blood, liver, and kidneys or As UEF. These results suggest that GOS supplementation may be a gut microbiota-regulating approach to lower early life As exposure via stimulating the growth of Akkermansia and Psychrobacter and enhancing As methylation in the GI tract.

Effects of Dietary Intake of Arsenosugars and Other Organic Arsenic Species on Studies of Arsenic Methylation Efficiency in Humans

Extensive research has used dimethylarsinic acid (DMA) in urine as a marker of arsenic methylation. The premise is that humans methylate inorganic arsenicals to monomethylarsonic acid (MMA) and DMA and excrete these arsenic species into the urine. However, DMA in urine not only comes from the methylation of inorganic arsenic but also could be a result of metabolism of other arsenic species, such as arsenosugars and arsenolipids. Most environmental health and epidemiological studies of arsenic methylation might have overlooked confounding factors that contribute to DMA in urine. Here we critically evaluate reported studies that used methylation indexes, concentration ratios of methylated arsenicals, or the percentage of DMA in urine as markers of arsenic methylation efficiency. Dietary intake of arsenosugars potentially confounds the calculation and interpretation of the arsenic methylation efficiencies. Many studies have not considered incidental dietary intake of arsenosugars, arsenolipids, and other organic arsenic species. Future studies should consider the dietary intake of diverse arsenic species and their potential effect on the urinary concentrations of DMA.