metallothionein and arsenic-acid

A comparative analysis of toxicities of both arsenic forms (arsenite and arsenate) in the model eukaryotic microorganism Tetrahymena thermophila (ciliate protozoa) has shown the presence of various detoxification mechanisms and cellular effects comparable to those of animal cells under arsenic stress. In the wild type strain SB1969 arsenate is almost 2.5 times more toxic than arsenite. According to the concentration addition model used in binary metallic mixtures their toxicities show an additive effect. Using fluorescent assays and flow cytometry, it has been detected that As(V) generates elevated levels of ROS/RNS compared to As(III). Both produce the same levels of superoxide anion, but As(V) also causes greater increases in hydrogen peroxide and peroxynitrite. The mitochondrial membrane potential is affected by both As(V) and As(III), and electron microscopy has also revealed that mitochondria are the main target of both arsenic ionic forms. Fusion/fission and swelling mitochondrial and mitophagy, together with macroautophagy, vacuolization and mucocyst extruction are mainly associated to As(V) toxicity, while As(III) induces an extensive lipid metabolism dysfunction (adipotropic effect). Quantitative RT-PCR analysis of some genes encoding antioxidant proteins or enzymes has shown that glutathione and thioredoxin metabolisms are involved in the response to arsenic stress. Likewise, the function of metallothioneins seems to be crucial in arsenic detoxification processes, after using both metallothionein knockout and knockdown strains and cells overexpressing metallothionein genes from this ciliate. The analysis of the differential toxicity of As(III) and As(V) shown in this study provides cytological and molecular tools to be used as biomarkers for each of the two arsenic ionic forms.

Topics: Animals; Arsenates; Arsenic; Arsenites; Metallothionein; Tetrahymena thermophila

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

This study aimed at investigating the individual and interactive effects of cadmium (Cd) and arsenate (AsV) in Gammarus pulex (Crustacea, Amphipoda) through the use of several biomarkers. Individuals were exposed for 240 h to two concentrations of AsV or Cd alone, and all the possible binary mixtures of these concentrations of AsV and Cd in a complete factorial design. The pattern of the biomarkers' responses to Cd and AsV alone or in mixture was similar in Gammarus pulex, even if the response intensity varied depending on the tested conditions. G. pulex responded to contamination with increased mobilization of the detoxification systems [i.e. γ-glutamyl-cystein ligase activity (GCL), reduced glutathione content (GSH) and metallothionein concentrations (MT)]. This response seems to imply changes in energy reserve utilization (total lipids and proteins are used prior to glycogen reserves), but also a possible energy reallocation from locomotion to detoxification processes. The observed increase in lipid peroxidation could be relied to the increasing gammarid mortality, despite the higher mobilization of detoxification systems. Even if the outcome of the complex interactions between AsV and Cd remains difficult to unravel, such studies are critically important for better assessing the effects of stressors on organisms, populations and communities in a multi-contamination context of ecosystems.

Topics: Amphipoda; Animals; Arsenates; Behavior, Animal; Biomarkers; Cadmium; Lipid Peroxidation; Lipids; Metallothionein; Mortality; Proteins; Water Pollutants, Chemical

A method combining gel filtration chromatography (GFC), protease digestion, and ion pair chromatography with inductively coupled plasma mass spectrometry detection was developed for the determination of arsenic species bound to proteins. The method was first established by examining the interactions of two model proteins, metallothionein (MT) and hemoglobin, with three reactive trivalent arsenic species. It was then successfully applied to the speciation of arsenic in red blood cells of rats. Inorganic arsenite (iAs(III)), monomethylarsonous acid (MMA(III)), and dimethylarsinous acid (DMA(III)) were efficiently released from the proteins by protease digestion at pH 8.0, with the recovery ranging from 93% to 106%. There was no oxidation of iAs(III) or MMA(III) during the protease digestion process. Up to 61% DMA(III) (the least stable arsenic species) was unchanged, and the rest was oxidized to the pentavalent dimethylarsinic acid (DMA(V)). The arsenic species in the red blood cells of control rats was present as DMA(III) complex with hemoglobin. The method enabling the determination of the specific arsenic species that bind to cellular proteins is potentially useful for studying arsenic distribution, metabolism, and toxicity.

Topics: Animals; Arsenates; Arsenic; Arsenites; Chromatography; Hemoglobins; Humans; Mass Spectrometry; Metallothionein; Peptide Hydrolases; Protein Binding; Rats