Effects of atrazine on hepatic metabolism and endocrine homeostasis in rainbow trout (Oncorhynchus mykiss)

Oxidative stress response and gene expression with atrazine exposure in adult female zebrafish (Danio rerio)

Atrazine (ATZ) is the most common pesticide of freshwater ecosystems in the world. The effects of ATZ exposure on the induction of oxidative stress and the alteration of gene expression were studied in liver and ovary samples from female zebrafish (Danio rerio). Antioxidant enzyme activities (SOD and CAT), in addition to the GSH and MDA content, in the liver altered significantly; the mRNA levels for the genes encoding these antioxidant proteins, such as Cu/Zn-Sod, Mn-Sod, Cat, and Gpx, were up-regulated significantly in the liver when zebrafish were exposed to various concentrations of ATZ for 14d. However, the mRNA induction patterns were not in accordance with those of antioxidant enzyme changes in the liver and ovary. Moreover, the transcriptional expression of mitochondrial inner membrane genes related to ROS production, such as Ucp-2 and Bcl-2, were altered significantly in high ATZ treatment groups. However, the ATZ treatment did not induce any apparent changes in the transcriptional expression of CoxI, Ndi, or ATPo6, which are related to the mitochondrial respiratory chain and ATP synthesis. To our knowledge, this is the first report to study the transcriptional effects of ATZ stress on zebrafish. The information presented in this study will be helpful in fully understanding the mechanism of oxidative stress induced by ATZ in fish.

Identification of a CYP3A form (CYP3A126) in fathead minnow (Pimephales promelas) and characterisation of putative CYP3A enzyme activity

Cytochrome P450-dependent monooxygenases (CYPs) are involved in the metabolic defence against xenobiotics. Human CYP3A enzymes metabolise about 50% of all pharmaceuticals in use today. Induction of CYPs and associated xenobiotic metabolism occurs also in fish and may serve as a useful tool for biomonitoring of environmental contamination. In this study we report on the cloning of a CYP3A family gene from fathead minnows (Pimephales promelas), which has been designated as CYP3A126 by the P450 nomenclature committee (GenBank no. EU332792). The cDNA was isolated, identified and characterised by extended inverse polymerase chain reaction (PCR), an alternative to the commonly used method of rapid amplification of cDNA ends. In a fathead minnow cell line we identified a full-length cDNA sequence (1,863 base pairs (bp)) consisting of a 1,536 bp open reading frame encoding a 512 amino acid protein. Genomic analysis of the identified CYP3A isoenzyme revealed a DNA sequence consisting of 13 exons and 12 introns. CYP3A126 is also expressed in fathead minnow liver as demonstrated by reverse transcription PCR. Exposure of fathead minnow (FHM) cells with the CYP3A inducer rifampicin leads to dose-dependent increase in putative CYP3A enzyme activity. In contrast, inhibitory effects of diazepam treatment were observed on putative CYP3A enzyme activity and additionally on CYP3A126 mRNA expression. This indicates that CYP3A is active in FHM cells and that CYP3A126 is at least in part responsible for this CYP3A activity. Further investigations will show whether CYP3A126 is involved in the metabolism of environmental chemicals.

Glyphosate-based herbicides are toxic and endocrine disruptors in human cell lines

Glyphosate-based herbicides are the most widely used across the world; they are commercialized in different formulations. Their residues are frequent pollutants in the environment. In addition, these herbicides are spread on most eaten transgenic plants, modified to tolerate high levels of these compounds in their cells. Up to 400 ppm of their residues are accepted in some feed. We exposed human liver HepG2 cells, a well-known model to study xenobiotic toxicity, to four different formulations and to glyphosate, which is usually tested alone in chronic in vivo regulatory studies. We measured cytotoxicity with three assays (Alamar Blue, MTT, ToxiLight), plus genotoxicity (comet assay), anti-estrogenic (on ERalpha, ERbeta) and anti-androgenic effects (on AR) using gene reporter tests. We also checked androgen to estrogen conversion by aromatase activity and mRNA. All parameters were disrupted at sub-agricultural doses with all formulations within 24h. These effects were more dependent on the formulation than on the glyphosate concentration. First, we observed a human cell endocrine disruption from 0.5 ppm on the androgen receptor in MDA-MB453-kb2 cells for the most active formulation (R400), then from 2 ppm the transcriptional activities on both estrogen receptors were also inhibited on HepG2. Aromatase transcription and activity were disrupted from 10 ppm. Cytotoxic effects started at 10 ppm with Alamar Blue assay (the most sensitive), and DNA damages at 5 ppm. A real cell impact of glyphosate-based herbicides residues in food, feed or in the environment has thus to be considered, and their classifications as carcinogens/mutagens/reprotoxics is discussed.