Comparative assessment of in vitro and in vivo toxicity of azinphos methyl and its commercial formulation

Biochemical Studies to Understand Teratogenicity and Lethality Outcomes in Modified-FETAX

The frog embryo teratogenesis assay-Xenopus (FETAX) is a standardized test used to assess the toxic and teratogenic effects of xenobiotics. With this test, toxic and/or teratogenic concentrations of xenobiotic substances can be determined using morphological parameters such as lethality, length, and malformations in stage 8-11 Xenopus laevis embryos after 96 h exposure. These parameters enable the determination of the median lethal and effective concentrations (LC50 and EC50), minimum concentration to inhibit growth (MCIG), and teratogenic index of the tested chemical to reveal the short-term effects of relatively high concentrations. On the other hand, although FETAX provides quantitative and qualitative data on teratogenicity and toxicity, the biochemical and molecular mechanisms of these effects cannot be explained. Recent studies have tried to elucidate the mechanisms causing malformations and to explain the underlying causes of toxicity and teratogenicity by biochemical marker analysis. This chapter describes methods to analyze modified-FETAX and some detoxification and oxidative stress-related biomarkers during the early embryonic development of X. laevis.

Toxicological impact of organophosphorus Chlorpyrifos 48%EC pesticide on hemocytes, biochemical disruption, and molecular changes in Biomphalaria alexandrina snails

Organophosphorus pesticides like Chlorpyrifos 48%EC were widely used to control agricultural pests. The present study aimed to evaluate the toxic effects of Chlorpyrifos 48%EC on B. alexandrina snails, the intermediate host of Schistosoma mansoni. After exposure of snails to serial concentrations to determine the LC₅₀, thirty snails for each sublethal concentration (LC₁₀ 2.1 and LC₂₅ 5.6 mg/l) in each group were exposed for 24 h followed by another 24 h for recovery. After recovery random samples were collected from hemolymph and tissue to measure the impacts on Phagocytic index, histological, biochemical, and molecular parameters. The current results showed a toxic effect of Chlorpyrifos 48%EC on adult B. alexandrina snails after 24 h of exposure at LC₅₀ 9.6 mg/l. After exposure to the sub-lethal concentrations of this pesticide, it decreased the total number of hemocytes and the percentage of small cells, while increased the percentage of hyalinocytes. The granulocyte percentage was increased after exposure to LC₁₀, while after LC₂₅, it was decreased compared to the control group. Also, the light microscopical examination showed that some granulocytes have plenty of granules, vacuoles and filopodia. Some hyalinocytes were contained shrinked nuclei, incomplete cell division and forming pseudopodia. Besides, the phagocytic index of hemocytes was significantly increased than control in all treated groups. Also, these sub-lethal concentrations increased MDA and SOD activities, while, tissue NO, GST and TAC contents were significantly decreased after exposure. Levels of Testosterone (T) and Estradiol (E) were increased significantly after exposure compared with control group. The present results showed that the concentration of DNA and RNA was highly decreased after exposure to LC₁₀, ₂₅ than the control group. Therefore, B. alexandrina snails could be used as a bio monitor of the chemical pollution. Besides, this pesticide could reduce the transmission of schistosomiasis as it altered the biological system of these snails.

A comparative study of enzymatic and immunological parameters in Planorbarius corneus and Biomphalaria glabrata exposed to the organophosphate chlorpyrifos

This study aimed to investigate the acute effects of chlorpyrifos on biomarkers related to neurotoxicity and immunotoxicity in two allopatric freshwater gastropod species belonging to the family Planorbidae. For this purpose, Planorbarius corneus and Biomphalaria glabrata were exposed to chlorpyrifos (active ingredient or commercial formulation) for 48 h at environmentally realistic concentrations (1 and 7.5 μg L^-1). Basal acetylcholinesterase activity in soft tissues and hemolymph was almost one order of magnitude higher in P. corneus than in B. glabrata. However, upon chlorpyrifos exposure, statistically significant inhibition of enzymatic activity was registered in both species. Acetylcholinesterase was more sensitive to inhibition in soft tissues than in hemolymph. The highest inhibition was observed in the B. glabrata soft tissues exposed to the commercial formulation (88 % at 1 μg L^-1 and 93 % at 7.5 μg L^-1). Hemocyte number and lysosomal membrane stability did not show significant changes with respect to controls in any of the exposed groups. Superoxide anion generation was diminished (21-46 %) in P. corneus hemocytes exposed to the active ingredient and in B. glabrata hemocytes exposed to the active ingredient or the formulation. In contrast, hemocyte phagocytic activity increased in all exposed groups. Phagocytosis was most stimulated (89 %) in hemocytes sampled from B. glabrata treated with 7.5 μg L^-1 chlorpyrifos. Altogether the results suggest that the freshwater gastropods P. corneus and B. glabrata are suitable model animals for environmental monitoring studies in the Northern Hemisphere and Latin America, respectively. Furthermore, these results add information on the relevance of testing pesticide formulations and on the usefulness of acetylcholinesterase inhibition and immunological parameters as biomarkers of the acute effects of chlorpyrifos in these species.

Effect of diet on carboxylesterase activity of tadpoles (Rhinella arenarum) exposed to chlorpyrifos

An outdoor microcosm was performed with tadpoles (Rhinella arenarum) exposed to 125μgL^-1 chlorpyrifos and fed two types of food, i.e., lettuce (Lactuca sativa) and a formulated commercial pellet. Acetylcholinesterase (AChE) and carboxylesterase (CbE) activities were measured in liver and intestine after 10 days of pesticide exposure. Non-exposed tadpoles fed lettuce had an intestinal AChE activity almost two-fold higher than that of pellet-fed tadpoles. No significant differences were observed, however, in liver AChE activity between diets. Likewise, intestinal CbE activity - measured using two substrates, i.e. 1-naphthyl acetate (1-NA) and 4-nitrophenyl valerate (4-NPV) - was higher in tadpoles fed lettuce than in those fed pellets. However, the diet-dependent response of liver CbE activity was opposite to that in the intestine. Chlorpyrifos caused a significant inhibition of both esterase activities, which was tissue- and diet-specific. The highest inhibition degree was found in the intestinal AChE and CbE activities of lettuce-fed tadpoles (42-78% of controls) compared with pellet-fed tadpoles (<60%). Although chlorpyrifos significantly inhibited liver CbE activity of the group fed lettuce, this effect was not observed in the group fed pellets. In general, intestinal CbE activity was more sensitive to chlorpyrifos inhibition than AChE activity. This finding, together with the high levels of basal CbE activity found in the intestine, may be understood as a detoxification system able to reduce intestinal OP uptake. Moreover, the results of this study suggest that diet is a determinant factor in toxicity testing with tadpoles to assess OP toxicity, because it modulates levels of this potential detoxifying enzyme activity.

Endocrine activities and cellular stress responses in the marsh frog Pelophylax ridibundus exposed to cobalt, zinc and their organic nanocomplexes

Metal-containing materials are extensively used in industry, personal care products and medicine, and their release in the environment causes concern for the potential impacts on aquatic organisms. We assessed endocrine disrupting potential of N-vinyl-2-pyrrolidone-based nanoparticles (Me-PSs) containing cobalt (Co(2+)) or zinc (Zn(2+)), using the marsh frog Pelophylax ridibundus as a model. Adult males were exposed for 14 days to waterborne Co(2+) (50μg/L), Zn(2+) (100μg/L) or corresponding concentrations of Co-PS, Zn-PS, or parental polymeric compound (PS). The indices of thyroid activity, vitellogenesis, cytochrome P450-dependent monooxygenases activity (EROD) and cytotoxicity markers were evaluated. Exposure to Co(2+) led to the elevation of serum thyrotropin (TSH) and hepatic deiodinase activities accompanied by the up-regulation of EROD activity. In contrast, the action of the polymer-containing substances (Co-PS, Zn-PS and PS) as well as free Zn(2+) caused a prominent decrease of EROD activity and a decrease in serum cortisol and TSH concentrations. Exposures to Zn(2+), Zn-PS and PS upregulated vitellogenesis in males. All exposures except Co(2+) caused neurotoxicity as indicated by the depletion of cholinesterase. These results demonstrate toxicity of Co- and Zn-containing Me-PSs and their parental compounds (Zn(2+) and PS) in frogs and indicate distinct mechanisms of Co(2+) action. Broad disruption of the hormonal pathways and reduced capacity for organic xenobiotic detoxification may have deleterious impacts on amphibian populations from habitats exposed to metallorganic pollution.

Assessment of water pollution in the Brazilian Pampa biome by means of stress biomarkers in tadpoles of the leaf frog Phyllomedusa iheringii (Anura: Hylidae)

The Brazilian Pampa biome is currently under constant threat due to increase of agriculture and improper management of urban effluents. Studies with a focus on the assessment of impacts caused by human activities in this biome are scarce. In the present study, we measured stress-related biomarkers in tadpoles of the leaf frog Phyllomedusa iheringii, an endemic species to the Pampa biome, and tested its suitability as a bioindicator for the assessment of potential aquatic contamination in selected ponds (S1 and S2) nearby agricultural areas in comparison to a reference site. A significant decrease in acetylcholinesterase activity was observed in S2 when compared to S1 and reference. The levels of total-hydroperoxides were increased in S2 site. In parallel, increased activity of the antioxidant enzymes catalase, superoxide dismutase and glutathione S-transferase were observed in S2 when compared to S1 and reference. Further studies are necessary in order to correlate the changes observed here with different chemical stressors in water, as well as to elucidate mechanisms of toxicity induced by pesticides in amphibian species endemic to the Pampa biome. Nevertheless, our study validates Phyllomedusa iheringii as a valuable bioindicator in environmental studies.