Influence of Dietary Compounds on Arsenic Metabolism and Toxicity. Part I-Animal Model Studies

Zinc as a Mechanism-Based Strategy for Mitigation of Metals Toxicity

PURPOSE OF REVIEW

Zinc is an essential micronutrient with a myriad of key roles in human health. This review summarizes mechanistic data supporting the protective effects of zinc on metal toxicity and discusses the framework for an interventional clinical trial of zinc supplementation within a metal exposed Native American community.

RECENT FINDINGS

Many metals have common underlying mechanisms of toxicity that contribute to adverse human health effects. Studies demonstrate that multiple aspects of metal toxicity can be attributed to disruption of essential zinc-dependent functions. Multiple lines of evidence suggest that zinc may confer protection against metal toxicity in human populations with mixed-metal exposures. Thinking Zinc is a mechanism-informed intervention study of zinc supplementation to test the potential benefits of zinc while maintaining a culturally responsive research approach. The current knowledge of diverse metal and zinc interactions, coupled with strong mechanistic evidence for zinc benefits in the context of toxic metal exposures, supports the hypothesis that zinc supplementation may mitigate the impact of toxic metals exposures in populations with chronic mixed metal exposures and in populations with low zinc status.

Dietary Compounds in the Prevention of Arsenic Induced Intestinal Toxicity In Vitro

Recent studies show that inorganic arsenic (As) exerts a toxic effect on the intestinal epithelium, causing a significant increase in its permeability. This disruption of the epithelial barrier may favor the entry of contaminants or toxins into the systemic circulation, thus causing toxicity not only at the intestinal level but possibly also at the systemic level. The present study conducts an in vitro evaluation of the protective effect of various dietary supplements and plant extracts against the intestinal toxicity of inorganic As. Some of these compounds were found to exert a protective effect. A significant decrease was observed in intracellular reactive oxygen/nitrogen species (10-31%), as well as a lower secretion of the pro-inflammatory cytokine IL-8 (25-41%) in the intestinal monolayers treated with the supplements and extracts, compared with those exposed only to As(III). The most effective supplements (glutathione/cysteine/vitamin C and lipoic acid) also normalized the distribution of tight junction protein zonula occludens-1, with partial restoration of the paracellular permeability and cell regeneration capacity of the intestinal epithelial cells. The results obtained show that dietary supplements and plant extracts can reduce the intestinal barrier disruption caused by inorganic As, and this may have a positive impact at both local and systemic levels.

Possible Metabolic Remodeling based on de novo Biosynthesis of L-serine in Se-Subtoxic or -Deficient Mammals

Current research studies point to an increased risk of diabetes with selenium (Se) intake beyond the physiological requirement used to prevent cancers. The existing hypothesis of "selenoprotein overexpression leads to intracellular redox imbalance" cannot clearly explain the U-shaped dose-effect relationship between Se intake and the risk of diabetes. In this review, it is speculated that metabolic remodeling based on the de novo biosynthesis of L-serine may occur in mammals at supranutritional or subtoxic levels of Se. It is also speculated that a large amount of L-serine is consumed by the body during insufficient Se intake, thus resulting in similar metabolic reprogramming. The increase in atypical ceramide and its derivatives due to the lack of L-serine may also play a role in the development of diabetes.

Metabolism of inorganic arsenic in mice carrying the human AS3MT gene and fed folate deficient or folate supplemented diet

Arsenic (+3 oxidation state) methyltransferase (AS3MT) catalyzes the S-adenosylmethionine (SAM)-dependent methylation of inorganic arsenic (iAs), yielding monomethyl‑arsenic (MAs) and dimethyl‑arsenic (DMAs) metabolites. The formation of DMAs in this pathway is considered a key mechanism for iAs detoxification. Availability of SAM for iAs methylation depends in part on dietary intake of folate. Results of population studies suggest that supplementation with folate stimulates iAs methylation, increasing DMAs and decreasing iAs and MAs proportions in urine and/or blood. The goal of the present study was to determine if folate intake affects methylation and clearance of iAs in a recently established mouse strain that expresses human AS3MT and exhibits a human-like pattern of iAs metabolism. The humanized male and female mice were fed folate-deficient (FD) or folate-supplemented (FS) diet for 6 weeks, followed by exposure to 0 ppb or 400 ppb iAs in drinking water for 5 weeks, while on the same types of diet. The concentrations and proportions of iAs, MAs and DMAs were determined in urine, liver, kidneys, and spleen. The diet-, sex- and dose-related differences were assessed by t-test or a non-parametric test; Bonferroni test was used to correct for multiple comparisons. In general, proportions of DMAs were greater and proportions of iAs were smaller in urine and tissues of FS mice as compared to FD mice. However, folate supplementation also increased MAs proportions. Notably, the folate intake had no effect on the concentrations of total arsenic either in the urine or the tissues. These results suggest that, similar to humans, folate supplementation stimulates iAs methylation in the humanized mice. However, the stimulation of iAs methylation is not associated with clearance of arsenic from tissues, possibly due to an inefficient conversion of MAs to DMAs.

To breathe or not to breathe: Inhalational exposure to heavy metals and related health risk

This study reviewed scientific literature on inhalation exposure to heavy metals (HMs) in various indoor and outdoor environments and related carcinogenic and non-carcinogenic risk. A systematic search in Web of Science, Scopus, PubMed, Embase, and Medline databases yielded 712 results and 43 articles met the requirements of the Population, Exposure, Comparator, and Outcomes (PECO) criteria. Results revealed that HM concentrations in most households exceeded the World Health Organization (WHO) guideline values, indicating moderate pollution and dominant anthropogenic emission sources of HMs. In the analyzed schools, universities, and offices low to moderate levels of air pollution with HMs were revealed, while in commercial environments high levels of air pollution were stated. The non-carcinogenic risk due to inhalation HM exposure exceeded the acceptable level of 1 in households, cafes, hospitals, restaurants, and metros. The carcinogenic risk for As and Cr in households, for Cd, Cr, Ni, As, and Co in educational environments, for Pb, Cd, Cr, and Co in offices and commercial environments, and for Ni in metros exceeded the acceptable level of 1 × 10-4. Carcinogenic risk was revealed to be higher indoors than outdoors. This review advocates for fast and effective actions to reduce HM exposure for safer breathing.

Zinc supplementation alters tissue distribution of arsenic in Mus musculus

Arsenic occurs naturally in the environment and humans can be exposed through food, drinking water and inhalation of air-borne particles. Arsenic exposure is associated with cardiovascular, pulmonary, renal, immunologic, and developmental toxicities as well as carcinogenesis. Arsenic displays dose-depen toxicities in target organs or tissues with elevated levels of arsenic. Zinc is an essential micronutrient with proposed protective benefits due to its antioxidant properties, integration into zinc-containing proteins and zinc-related immune signaling. In this study, we tested levels of arsenic and zinc in plasma, kidney, liver, and spleen as model tissues after chronic (42-day) treatment with either arsenite, zinc, or in combination. Arsenite exposure had minimal impact on tissue zinc levels with the exception of the kidney. Conversely, zinc supplementation of arsenite-exposed mice reduced the amount of arsenic detected in all tissues tested. Expression of transporters associated with zinc or arsenic influx and efflux were evaluated under each treatment condition. Significant effects of arsenite exposure on zinc transporter expression displayed tissue selectivity for liver and kidney, and was restricted to Zip10 and Zip14, respectively. Arsenite also interacted with zinc co-exposure for Zip10 expression in liver tissue. Pairwise comparisons show neither arsenite nor zinc supplementation alone significantly altered expression of transporters utilized by arsenic. However, significant interactions between arsenite and zinc were evident for Aqp7 and Mrp1 in a tissue selective manner. These findings illustrate interactions between arsenite and zinc leading to changes in tissue metal level and suggest a potential mechanism by which zinc may offer protection from arsenic toxicities.

Metabolic Changes and Their Associations with Selected Nutrients Intake in the Group of Workers Exposed to Arsenic

Arsenic (As) exposure causes numerous adverse health effects, which can be reduced by the nutrients involved in the metabolism of iAs (inorganic As). This study was carried out on two groups of copper-smelting workers: WN, workers with a urinary total arsenic (tAs) concentration within the norm (n = 75), and WH, workers with a urinary tAs concentration above the norm (n = 41). This study aimed to analyze the association between the intake level of the nutrients involved in iAs metabolism and the signal intensity of the metabolites that were affected by iAs exposure. An untargeted metabolomics analysis was carried out on urine samples using liquid chromatography-mass spectrometry, and the intake of the nutrients was analyzed based on 3-day dietary records. Compared with the WN group, five pathways (the metabolism of amino acids, carbohydrates, glycans, vitamins, and nucleotides) with twenty-five putatively annotated metabolites were found to be increased in the WH group. In the WN group, the intake of nutrients (methionine; vitamins B2, B6, and B12; folate; and zinc) was negatively associated with six metabolites (cytosine, D-glucuronic acid, N-acetyl-D-glucosamine, pyroglutamic acid, uridine, and urocanic acid), whereas in the WH group, it was associated with five metabolites (D-glucuronic acid, L-glutamic acid, N-acetyl-D-glucosamine, N-acetylneuraminic acid, and uridine). Furthermore, in the WH group, positive associations between methionine, folate, and zinc intake and the signal intensity of succinic acid and 3-mercaptolactic acid were observed. These results highlight the need to educate the participants about the intake level of the nutrients involved in iAs metabolism and may contribute to further considerations with respect to the formulation of dietary recommendations for people exposed to iAs.

Comparison Process of Blood Heavy Metals Absorption Linked to Measured Air Quality Data in Areas with High and Low Environmental Impact

Air pollution is a problem shared by the entire world population, and researchers have highlighted its adverse effects on human health in recent years. The object of this paper was the relationship between the pollutants’ concentrations measured in the air and the quantity of pollutant itself inhaled by the human body. The area chosen for the study has a high environmental impact given the significant presence on the territory of polluting activities. The Acerra area (HI) has a waste-to-energy plant and numerous industries to which polluting emissions are attributed. This area has always been the subject of study as the numbers of cancer patients are high. A survey on male patients to evaluate the heavy metals concentrations in the blood was conducted in the two areas and then linked to its values aero-dispersed. Using the air quality data measured by the monitoring networks in two zones, one with high environmental impact (HI) and one with low environmental impact (LI), the chronicle daily intake (CDI) of pollutants inhaled by a single person was calculated. The pollutants considered in this study are PM10 and four heavy metals (As, Cd, Ni, Pb) constituting the typical particulates of the areas concerned. The CDI values calculated for the two zones are significantly higher in the HI zone following the seasonal pollution trend.

Tracing of Heavy Metals Embedded in Indoor Dust Particles from the Industrial City of Asaluyeh, South of Iran

Assessment of indoor air quality is especially important, since people spend substantial amounts of time indoors, either at home or at work. This study analyzes concentrations of selected heavy metals in 40 indoor dust samples obtained from houses in the highly-industrialized Asaluyeh city, south Iran in spring and summer seasons (20 samples each). Furthermore, the health risk due to exposure to indoor air pollution is investigated for both children and adults, in a city with several oil refineries and petrochemical industries. The chemical analysis revealed that in both seasons the concentrations of heavy metals followed the order of Cr > Ni > Pb > As > Co > Cd. A significant difference was observed in the concentrations of potential toxic elements (PTEs) such as Cr, As and Ni, since the mean (±stdev) summer levels were at 60.2 ± 9.1 mg kg−1, 5.6 ± 2.7 mg kg−1 and 16.4 ± 1.9 mg kg−1, respectively, while the concentrations were significantly lower in spring (17.6 ± 9.7 mg kg−1, 3.0 ± 1.7 mg kg−1 and 13.5 ± 2.4 mg kg−1 for Cr, As and Ni, respectively). Although the hazard index (HI) values, which denote the possibility of non-carcinogenic risk due to exposure to household heavy metals, were generally low for both children and adults (HI < 1), the carcinogenic risks of arsenic and chromium were found to be above the safe limit of 1 × 10−4 for children through the ingestion pathway, indicating a high cancer risk due to household dust in Asaluyeh, especially in summer.