metallothionein and monomethylarsonic-acid

Arsenic is a pollutant that can be detected in different chemical forms in soil. However, the toxicological effects of different arsenic species on organisms have received little attention. In this study, we exposed earthworms Eisenia fetida to artificial soils contaminated by arsenite [As(III)], arsenate [As(V)], monomethylarsonate (MMA) and dimethylarsinate (DMA) for 28 and 56 days. Three biomarkers including lipid peroxidation (LPO), metallothioneins (MTs) and lysosomal membrane stability (LMS) were analyzed in the organisms. In addition, the contents of total arsenic and arsenic species in earthworms were also determined to investigate the effects of bioaccumulation and biotransformation of arsenic on biomarkers and to evaluate the dose-response relationships. The results showed that the relationship between the three biomarkers and the two inorganic arsenic species were dose dependent, and the correlation levels between the biomarkers and As(III) were higher than that between the biomarkers and As(V). Trivalent arsenic species shows more toxicity than pentavalent arsenic on the earthworms at molecular and subcellular level, including oxidative damage, MTs induction and lysosomal membrane damage. The toxicity of MMA and DMA was lower than inorganic arsenic species. However, the occurrence of demethylation of organic arsenics could lead to the generation of highly toxic inorganic arsenics and induce adverse effects on organisms. The biotransformation of highly toxic inorganic arsenics to the less toxic organic species in the earthworms was also validated in this study. The biomarker responses of the earthworm to different arsenic species found in this study could be helpful in future environment monitoring programs.

Topics: Animals; Arsenates; Arsenic; Arsenic Poisoning; Arsenicals; Arsenites; Biomarkers; Biotransformation; Cacodylic Acid; Dose-Response Relationship, Drug; Environmental Pollution; Lipid Peroxidation; Lysosomes; Metallothionein; Oligochaeta; Oxidation-Reduction; Oxidative Stress; Soil; Soil Pollutants

Inorganic arsenic [As(V)+As(III)] and its metabolites, especially the trivalent forms [monomethylarsonous acid, MMA(III), and dimethylarsinous acid, DMA(III)], are considered the forms of arsenic with the highest degree of toxicity, linked to certain types of cancer and other pathologies. The gastrointestinal mucosa is exposed to these forms of arsenic, but it is not known what toxic effect these species may have on it. The aim of the present work was to evaluate the toxicity and some mechanisms of action of inorganic arsenic and its metabolites [monomethylarsonic acid, MMA(V), dimethylarsinic acid, DMA(V), MMA(III) and DMA(III)] in intestinal epithelial cells, using the Caco-2 human cell line as a model. The results show that the pentavalent forms do not produce toxic effects on the intestinal monolayer, but the trivalent species have a different degree of toxicity. As(III) induces death mainly by necrosis, whereas only apoptotic cells are detected after exposure to MMA(III), and for DMA(III) the percentages of apoptosis and necrosis are similar. The three forms produce reactive oxygen species, accompanied by a reduction in intracellular GSH and lipid peroxidation, the latter being especially notable in the dimethylated form. They also alter the enzyme activity of glutathione peroxidase and catalase and induce expression of stress proteins and metallothioneins. The results indicate that the trivalent forms of arsenic can affect cell viability of intestinal cells by mechanisms related to the induction of oxidative stress. Further studies are needed to evaluate how the effects observed in this study affect the structure and functionality of the intestinal epithelium.

Topics: Apoptosis; Arsenicals; Caco-2 Cells; Cacodylic Acid; Carcinogens, Environmental; Cell Survival; Gene Expression; Glutathione; Heat-Shock Proteins; Herbicides; Humans; Intestinal Mucosa; Lipid Peroxidation; Metallothionein; Mitochondria; Necrosis; Oxidative Stress; Oxidoreductases; Reactive Oxygen Species

Arsenic exerts its toxicity by the generation of reactive oxygen intermediates which caused lipid peroxidation and cellular damage. Metallothioneins (MTs) have been shown to be induced by oxidative stress and act as scavengers of reactive oxygen intermediates. Thus, hepatic MT was examined in channel catfish treated with the herbicide monosodium methyl arsonate (MSMA) and compared to equal doses of trivalent and pentavalent arsenic. Fish were exposed to 0.01, 0.1, and 1.0 mg/L of each compound for 1 week by static renewal. Hepatic MT was measured by the cadmium/hemoglobin (Cd/Hb) saturation assay, ELISA using antibodies raised against the first 10 amino acids of piscine MT, and Northern blot analysis using a cDNA encoding winter flounder hepatic MT. Cd/Hb and ELISA measurements of low molecular weight fractions from the hepatic cytosolic component of fish exposed to MSMA revealed a dose dependent increase in MT. MTs and MT mRNA of fish receiving the 1.0 mg/L dose were significantly induced vs control. Responses to arsenate exposure were more variable, but showed a trend toward a dose-dependent induction of MT and MT mRNA. MT mRNA and protein also showed a dose-dependent increase with arsenite exposure with no significant differences with untreated animals. Hepatic lipid peroxidation (as determined by TBARS) and glutathione was unaltered by any of the arsenical treatments. Thus, the lack of correlation between oxidative stress and MT expression suggest MT may not be a reliable indicator of oxidative stress. In addition, the induction of hepatic MT by various forms of As does not appear to be mediated through an oxidative stress mechanism in the liver.

Topics: Animals; Arsenates; Arsenic Poisoning; Arsenicals; Arsenites; Cadmium Chloride; Copper Sulfate; Dose-Response Relationship, Drug; Enzyme-Linked Immunosorbent Assay; Glutathione; Herbicides; Ictaluridae; Lipid Peroxidation; Liver; Male; Metallothionein; Sodium Compounds; Zinc Sulfate