Accumulation and Transport of Roxarsone, Arsenobetaine, and Inorganic Arsenic Using the Human Immortalized Caco-2 Cell Line

Arsenic contribution of poultry manure towards soils and food plants contamination and associated cancer risk in Khyber Pakhtunkhwa, Pakistan

Exposure to high level of arsenic (As) through the ingestion of contaminated soil, dust and food plants can pose health risk to humans. This study investigates the total arsenic (As), arsenobetaine (AsB), monomethylarsenate (MMA), dimethylarsenate (DMA), arsenite (As³⁺) and arsenate (As⁵⁺) concentrations in poultry feed, manure, agricultural soils and food plants collected from Khyber Pakhtunkhwa Province, Pakistan. The total mean As concentrations in the edible parts of food plants ranged from 0.096 mg kg^-1 to 1.25 mg kg^-1 with percentile (P) values (P25-0.039, P50-0.0765, P75-0.165 1 mg kg^-1 to P25-0.95, P50-1.23, P75-1.6 1 mg kg^-1) and exceeded the food safety limit (0.1 mg kg^-1) of Food & Agriculture Organization (FAO) and World Health Organization (WHO) in all plant species except Pisum sativum (pea) and Mentha arvensis (mint). The risk to human health was assessed through the average daily intake (ADI), hazards quotient (HQ), health risk index (HRI) and lifetime cancer risk (LTCR). The highest average daily intake of As via the ingestion of Malva neglecta (mallow, a leafy plant) was observed for adults and children. The ADI for adults and children (2.36 × 10^-4 mg kg^-1 day^-1 and 6.33 × 10^-4 mg kg^-1 day^-1) was about 13% and 5%, respectively, of the Bench Mark Dose Limit (BMDL_0.5) of 3.00 × 10^-3 mg kg^-1 day^-1 set by WHO. The HRI was 3 times more in the children (2.1) than the adults (0.79), posing non-cancer health risks (health risk index > 1) for children. The LTCR values were slightly higher (1.53 × 10^-4) relative to USEPA and WHO limits (1 × 10^-6 to 1 × 10^-4) for children whereas a minimal cancer risk was observed for adults via consumption of selected food plants. The results showed that poultry manure can contaminate food plants that may lead to cancer and non-cancer risks in agricultural areas, Pakistan. Thus, it is important to minimize As concentration in poultry feed to safeguard human health and environment from adverse effects.

Exposure to Environmental Arsenic and Emerging Risk of Alzheimer's Disease: Perspective Mechanisms, Management Strategy, and Future Directions

Alzheimer’s disease (AD) is one of the most prevailing neurodegenerative diseases, characterized by memory dysfunction and the presence of hyperphosphorylated tau and amyloid β (Aβ) aggregates in multiple brain regions, including the hippocampus and cortex. The exact etiology of AD has not yet been confirmed. However, epidemiological reports suggest that populations who were exposed to environmental hazards are more likely to develop AD than those who were not. Arsenic (As) is a naturally occurring environmental risk factor abundant in the Earth’s crust, and human exposure to As predominantly occurs through drinking water. Convincing evidence suggests that As causes neurotoxicity and impairs memory and cognition, although the hypothesis and molecular mechanism of As-associated pathobiology in AD are not yet clear. However, exposure to As and its metabolites leads to various pathogenic events such as oxidative stress, inflammation, mitochondrial dysfunctions, ER stress, apoptosis, impaired protein homeostasis, and abnormal calcium signaling. Evidence has indicated that As exposure induces alterations that coincide with most of the biochemical, pathological, and clinical developments of AD. Here, we overview existing literature to gain insights into the plausible mechanisms that underlie As-induced neurotoxicity and the subsequent neurological deficits in AD. Prospective strategies for the prevention and management of arsenic exposure and neurotoxicity have also been discussed.

Bioavailability of arsenic, cadmium, lead and mercury as measured by intestinal permeability

In this study, the intestinal permeability of metal(loid)s (MLs) such as arsenic (As), cadmium (Cd), lead (Pb) and mercury (Hg) was examined, as influenced by gut microbes and chelating agents using an in vitro gastrointestinal/Caco-2 cell intestinal epithelium model. The results showed that in the presence of gut microbes or chelating agents, there was a significant decrease in the permeability of MLs (As-7.5%, Cd-6.3%, Pb-7.9% and Hg-8.2%) as measured by apparent permeability coefficient value (Papp), with differences in ML retention and complexation amongst the chelants and the gut microbes. The decrease in ML permeability varied amongst the MLs. Chelating agents reduce intestinal absorption of MLs by forming complexes thereby making them less permeable. In the case of gut bacteria, the decrease in the intestinal permeability of MLs may be associated to a direct protection of the intestinal barrier against the MLs or indirect intestinal ML sequestration by the gut bacteria through adsorption on bacterial surface. Thus, both gut microbes and chelating agents can be used to decrease the intestinal permeability of MLs, thereby mitigating their toxicity.

Selective solid-phase extraction of four phenylarsonic compounds from feeds, edible chicken and pork with tailoring imprinted polymer

The novel molecularly imprinted microspheres for four phenylarsonic compounds have been firstly prepared with the reversible addition-fragmentation chain transfer polymerization in a suspension system. The resulting polymeric microspheres were characterized by infrared spectrum, scanning electron microscope and differential scanning calorimetry. With serial adsorption experiments, the polymeric microspheres showed highly specific molecular recognition, fast mass transfer rate and robust adsorption of the substrates. Then, the imprinted polymer was used as the solid-phase extraction adsorbent to extract the phenylarsonic compounds from the feeds, edible chicken and pork. The cartridge was washed with 2 mL ethyl acetate and eluted with 3 mL of methanol- acetic acid (90:10, v/v). The recoveries of the molecularly imprinted solid-phase extraction (MISPE) column ranged from 83.4% to 95.1%. This work provided a versatile approach for the specific extraction of the organoarsenic compounds from complicated matrices and exhibited a bright future for the application of MISPE column.

Reduction of Organoarsenical Herbicides and Antimicrobial Growth Promoters by the Legume Symbiont Sinorhizobium meliloti

Massive amounts of methyl [e.g., methylarsenate, MAs(V)] and aromatic arsenicals [e.g., roxarsone (4-hydroxy-3-nitrophenylarsonate, Rox(V)] have been utilized as herbicides for weed control and growth promotors for poultry and swine, respectively. The majority of these organoarsenicals degrade into more toxic inorganic species. Here, we demonstrate that the legume symbiont Sinorhizobium meliloti both reduces MAs(V) to MAs(III) and catalyzes sequential two-step reduction of nitro and arsenate groups in Rox(V), producing the highly toxic trivalent amino aromatic derivative 4-hydroxy-3-aminophenylarsenite (HAPA(III)). The existence of this process suggests that S. meliloti possesses the ability to transform pentavalent methyl and aromatic arsenicals into antibiotics to provide a competitive advantage over other microbes, which would be a critical process for the synthetic aromatic arsenicals to function as antimicrobial growth promoters. The activated trivalent aromatic arsenicals are degraded into less-toxic inorganic species by an MAs(III)-demethylating aerobe, suggesting that environmental aromatic arsenicals also undergo a multiple-step degradation pathway, in analogy with the previously reported demethylation pathway of the methylarsenate herbicide. We further show that an FAD-NADPH-dependent nitroreductase encoded by mdaB gene catalyzes nitroreduction of roxarsone both in vivo and in vitro. Our results demonstrate that environmental organoarsenicals trigger competition between members of microbial communities, resulting in gradual degradation of organoarsenicals and contamination by inorganic arsenic.

Use of a Mouse Model and Human Umbilical Vein Endothelial Cells to Investigate the Effect of Arsenic Exposure on Vascular Endothelial Function and the Associated Role of Calpains

BACKGROUND

Arsenic (As) is a well-known environmental contaminant. Chronic exposure to As is known to increase the risk of cardiovascular diseases, including atherosclerosis, hypertension, diabetes, and stroke. However, the detailed mechanisms by which As causes vascular dysfunction involving endothelial integrity and permeability is unclear.

OBJECTIVES

Our goal was to investigate how exposure to As leads to endothelial dysfunction.

METHODS

Arsenic trioxide (ATO) was used to investigate the effects and mechanisms by which exposure to As leads to endothelial dysfunction using a mouse model and cultured endothelial cell monolayers.

RESULTS

Compared with the controls, mice exposed chronically to As (10 ppb in drinking water supplied by ATO) exhibited greater vascular permeability to Evans blue dye and fluorescein isothiocyanate-labeled bovine serum albumin (FITC-BSA). In addition, endothelial monolayers treated with ATO ([Formula: see text] As) exhibited greater intracellular gaps and permeability to low-density lipoprotein or transmigrating THP-1 cells. Furthermore, activity and protein levels of calpain-1 (CAPN-1) were significantly higher in aortas and human umbilical vein endothelial cells (HUVECs) treated with ATO. These results were consistent with effects of ATO treatment and included a rapid increase of intracellular calcium ([Formula: see text]) and higher levels of CAPN-1 in the plasma membrane. Endothelial cell dysfunction and the proteolytic disorganization of vascular endothelial cadherin (VE-cadherin) in HUVECs in response to ATO were partially mitigated by treatment with a CAPN-1 inhibitor (ALLM) but not a CAPN-2 inhibitor (Z-LLY-FMK).

CONCLUSIONS

This study found that in mice and HUVEC models, exposure to ATO led to CAPN-1 activation by increasing [Formula: see text] and CAPN-1 translocation to the plasma membrane. The study also suggested that inhibitor treatment may have a role in preventing the vascular endothelial dysfunction associated with As exposure. The findings presented herein suggest that As-induced endothelial dysfunction involves the hyperactivation of the CAPN proteolytic system. https://doi.org/10.1289/EHP4538.

Salivary and Gut Microbiomes Play a Significant Role in in Vitro Oral Bioaccessibility, Biotransformation, and Intestinal Absorption of Arsenic from Food

The release of a toxicant from a food matrix during the gastrointestinal digestion is a crucial determinant of the toxicant's oral bioavailability. We present a modified setup of the human simulator of the gut microbial ecosystem (SHIME), with four sequential gastrointestinal reactors (oral, stomach, small intestine, and colon), including the salivary and colonic microbiomes. Naturally arsenic-containing rice, mussels, and nori seaweed were digested in the presence of microorganisms and in vitro oral bioaccessibility, bioavailability, and metabolism of arsenic species were evaluated following analysis by using HPLC/mass spectrometry. When food matrices were digested with salivary bacteria, the soluble arsenic in the gastric digestion stage increased for mussel and nori samples, but no coincidence impact was found in the small intestinal and colonic digestion stages. However, the simulated small intestinal absorption of arsenic was increased in all food matrices (1.2-2.7 fold higher) following digestion with salivary microorganisms. No significant transformation of the arsenic species occurred except for the arsenosugars present in mussels and nori. In those samples, conversions between the oxo arsenosugars were observed in the small intestinal digestion stage whereupon the thioxo analogs became major metabolites. These results expand our knowledge on the likely metabolism and oral bioavailabiltiy of arsenic during human digestion, and provide valuable information for future risk assessments of dietary arsenic.

Metabolism of a Phenylarsenical in Human Hepatic Cells and Identification of a New Arsenic Metabolite

Environmental contamination and human consumption of chickens could result in potential exposure to Roxarsone (3-nitro-4-hydroxyphenylarsonic acid), an organic arsenical that has been used as a chicken feed additive in many countries. However, little is known about the metabolism of Roxarsone in humans. The objective of this research was to investigate the metabolism of Roxarsone in human liver cells and to identify new arsenic metabolites of toxicological significance. Human primary hepatocytes and hepatocellular carcinoma HepG2 cells were treated with 20 or 100 μM Roxarsone. Arsenic species were characterized using a strategy of complementary chromatography and mass spectrometry. The results showed that Roxarsone was metabolized to more than 10 arsenic species in human hepatic cells. A new metabolite was identified as a thiolated Roxarsone. The 24 h IC₅₀ values of thiolated Roxarsone for A549 lung cancer cells and T24 bladder cancer cells were 380 ± 80 and 42 ± 10 μM, respectively, more toxic than Roxarsone, whose 24 h IC₅₀ values for A549 and T24 were 9300 ± 1600 and 6800 ± 740 μM, respectively. The identification and toxicological studies of the new arsenic metabolite are useful for understanding the fate of arsenic species and assessing the potential impact of human exposure to Roxarsone.

Identifying Plant Stress Responses to Roxarsone in Soybean Root Exudates: New Insights from Two-Dimensional Correlation Spectroscopy

Roxarsone (ROX) is an organoarsenic feed additive of increasing interest used in the poultry industry. Soybean responses to ROX stress were investigated in root exudates (REs) using two-dimensional correlation spectroscopy (2D-COS) with fluorescence and Fourier transform infrared spectra. Environmentally relevant ROX concentrations caused negligible toxicity to crop growth and photosynthesis activity but blackened soybean roots at high concentrations. 2D-COS analysis revealed that the protein-like fluorophore and C═C and C═O, aliphatic OH, and polysaccharide C-O-H moieties in soybean REs were most sensitive to ROX stress. Heterospectral 2D-COS results suggested that aromatic, amide I, quinone, ketone, and aliphatic functional groups were the foundational components of protein-like and short-wavelength excited humic-like fluorophores in soybean REs. Carboxyl and phenolic moieties were related to the long-wavelength excited humic-like fluorophore. Overall, 2D-COS combined with molecular-based spectral analysis of REs provided an innovative approach to characterize the physiological responses of crops to contaminants at sublethal levels.

Comparison of Translocation and Transformation from Soil to Rice and Metabolism in Rats for Four Arsenic Species

Arsenic (As) is ubiquitously present in the environment. The toxicity of As is related to its forms. This study was designed to compare the translocation and transformation of four As species from soil to rice, and metabolism in rats for four arsenic species. A set of 26550 data was obtained from pot experiments of rice plants grown in soil fortified with four As species, and 4050 data were obtained from rat experiments in which 81 rats were administered with the four As species. The total As in grain from the methyl arsenate fortified soil was 6.1, 4.9, and 5.2 times that from As(III), As(V), and dimethyl arsenate fortified soil, respectively. The total As in husk was 1.2-7.8 times greater than that in grain. After oral administration of each As species to rats, 83-96% was accumulatively excreted via feces and urine, while 0.1-16% was detected in blood. The translocation, transformation, and metabolism of different forms of arsenic vary greatly.

Cellular arsenic transport pathways in mammals

Natural contamination of drinking water with arsenic results in the exposure of millions of people world-wide to unacceptable levels of this metalloid. This is a serious global health problem because arsenic is a Group 1 (proven) human carcinogen and chronic exposure is known to cause skin, lung, and bladder tumors. Furthermore, arsenic exposure can result in a myriad of other adverse health effects including diseases of the cardiovascular, respiratory, neurological, reproductive, and endocrine systems. In addition to chronic environmental exposure to arsenic, arsenic trioxide is approved for the clinical treatment of acute promyelocytic leukemia, and is in clinical trials for other hematological malignancies as well as solid tumors. Considerable inter-individual variability in susceptibility to arsenic-induced disease and toxicity exists, and the reasons for such differences are incompletely understood. Transport pathways that influence the cellular uptake and export of arsenic contribute to regulating its cellular, tissue, and ultimately body levels. In the current review, membrane proteins (including phosphate transporters, aquaglyceroporin channels, solute carrier proteins, and ATP-binding cassette transporters) shown experimentally to contribute to the passage of inorganic, methylated, and/or glutathionylated arsenic species across cellular membranes are discussed. Furthermore, what is known about arsenic transporters in organs involved in absorption, distribution, and metabolism and how transport pathways contribute to arsenic elimination are described.