Parental exposure to the herbicide diuron results in oxidative DNA damage to germinal cells of the Pacific oyster Crassostrea gigas

Unveiling the nexus between parental exposure to toxicants and heritable spermiotoxicity - Is life history a shield or a shadow?

The knowledge on parental experiences is critical to predict how organisms react to environmental challenges. So, the DNA integrity of Procambarus clarkii spermatozoa exposed ex vivo to the herbicide penoxsulam (Px) or ethyl methanesulfonate (EMS; model genotoxicant) was assessed with and without the influence of in vivo parental exposure to the same agents. The parental exposure alone did not affect the DNA of unexposed spermatozoa. However, the history of Px exposure increased the vulnerability to oxidative lesions in Px-exposed offspring. Otherwise, parental exposure to EMS allowed the development of protection mechanisms expressed when F₁ was also exposed to EMS, unveiling life history as a shield. The parental exposure to a different agent adverse and decisively affected Px spermiotoxic potential, pointing out life history as a shadow to progeny. Given the complexity of the aquatic contamination scenarios, involving mixtures, the spermiotoxicity of Px to wild P. clarkii populations emerged as probable.

Improving knowledge on genotoxicity dynamics in somatic and germ cells of crayfish (Procambarus clarkii)

The harmful effects of pesticides can be extended beyond the exposure time scale. Appraisals combining exposure and long-term post-exposure periods appear as an unavoidable approach in pesticide risk assessment, thus allowing a better understanding of the real impact of agrochemicals in non-target organisms. This study aimed to evaluate the progression of genetic damage in somatic and germ tissues of the crayfish Procambarus clarkii, also seeking for gender-specificities, following exposure (7 days) to penoxsulam (23 μg L^-1 ) and a post-exposure (70 days) period. The same approach was applied to the model genotoxicant ethyl methanesulfonate (EMS; 5 mg L^-1 ) as a complementary mean to improve knowledge on genotoxicity dynamics (induction vs. recovery). Penoxsulam induced DNA damage in all tested tissues, disclosing tissue- and gender-specificities, where females showed to be more vulnerable than males in the gills, while males demonstrated higher susceptibility in what concerns internal organs, that is, hepatopancreas and gonad. Crayfish were unable to recover from the DNA damage induced by EMS in gills and hepatopancreas (both genders) as well as in spermatozoa. The genotoxicity in the hepatopancreas was only perceptible in the post-exposure period. Oxidative DNA lesions were identified in hepatopancreas and spermatozoa of EMS-exposed crayfish. The spermatozoa proved to be the most vulnerable cell type. It became clear that the characterization of the genotoxic hazard of a given agent must integrate a complete set of information, addressing different types of DNA damage, tissue- and gender-specificities, as well as a long-term appraisal of temporal progression of damage.

Genotoxic and epigenetic effects of diuron in the Pacific oyster: in vitro evidence of interaction between DNA damage and DNA methylation

Recently, research has contributed to better knowledge on the occurrence of pesticides in coastal water by identifying frequently detected substances, their concentration range and their acute and chronic toxicity for organisms. Pesticide pollution is of particular concern in France due to important agricultural activities and presence of several exoreic catchment areas that vehicle pesticides up to coastal waters, impacting non-target marine species. Several ecotoxicology questions remain to be addressed concerning the long-term effects of chronic pesticide exposure and the mechanisms involved in adaptation to chemical stress. In the present study, we brought new insights on the genetic and epigenetic effects of the herbicide diuron in oyster genitors. During gametogenesis, we exposed Crassostrea gigas to environmentally realistic herbicide concentrations (0.2-0.3 μg L^-1 during two 7-day periods at half-course and end of gametogenesis). Diuron exposure was shown to decrease global DNA methylation and total methyltransferase activity in whole oyster tissue; this is consistent with the previous observation of a significant decrease in DNMT1 gene expression. Diuron effect seemed to be tissue-specific; hypermethylation was detected in the digestive gland, whereas diuron exposure had no effect on gill and gonad tissue. The genotoxicity of diuron was confirmed by the detection of one adduct in gonad DNA. By using in vitro approaches and human DNMT1 (DNMT1 has not been purified yet in bivalves), the presence of DNA lesions (adduct, 8-oxodGuo) was shown to interfere with DNMT1 activity, indicating a complex interaction between DNA damage and DNA methylation. Based on our results, we propose mechanisms to explain the effect of diuron exposure on DNA methylation, a widespread epigenetic mark.

Assessment of oxidative DNA damage, oxidative stress responses and histopathological alterations in gill and liver tissues of Oncorhynchus mykiss treated with linuron

We investigated changes in 8-hydroxy-2-deoxyguanosine (8-OHdG) activity which is a product of oxidative DNA damage, histopathological changes and antioxidant responses in liver and gill tissues of rainbow trout, following a 21-day exposure to three different concentrations of linuron (30 µg/L, 120 µg/L and 240 µg/L). Our results indicated that linuron concentrations caused an increase in LPO levels of liver and gill tissues (p < 0.05). While linuron induced both increases and decreases in GSH levels and SOD activity, CAT activity was decreased by all concentrations of linuron (p < 0.05). The immunopositivity of 8-OHdG was detected in the hepatocytes of liver and in the epithelial and chloride cells of the secondary lamellae of the gill tissues. Our results suggested that linuron could cause oxidative DNA damage by causing an increase in 8-OHdG activity in tissues, and it induces histopathological damage and alterations in the antioxidant parameters of the tissues.

DNA of crayfish spermatozoa as a target of waterborne pesticides - An ex vivo approach as a tool to short-term spermiotoxicity screening

The spermiotoxic properties of aquatic contaminants might be the cause of low fertilization rate and decreased prolificacy, affecting the success of the impacted populations. The genotoxic potential of pesticides in spermatozoa as an undesirable effect on non-target organisms, namely aquatic invertebrates with external fertilization, emerges as a key question in ecogenotoxicological research. Thus, this study aimed to clarify if DNA integrity of red swamp crayfish (Procambarus clarkii) spermatozoa is affected by waterborne pesticides at environmentally relevant concentrations. By adopting an ex vivo approach, six pesticides were addressed in a short-term assay: herbicides glyphosate (9 and 90 μg L^-1) and penoxsulam (2.3 and 23 μg L^-1); insecticides dimethoate (2.4 and 24 μg L^-1) and imidacloprid (13.1 and 131 μg L^-1); fungicides pyrimethanil (2.2 and 22 μg L^-1) and imazalil (16 and 160 μg L^-1). Genotoxicity was observed in higher concentrations of glyphosate, penoxsulam, dimethoate, pyrimethanil, and imazalil. Imidacloprid was the only pesticide that did not cause non-specific DNA damage, although displaying pro-oxidant properties. Overall, the present study demonstrated the suitability of the ex vivo approach on spermiotoxicity screening, highlighting the potential ecological impact of pesticides on non-target species, such as P. clarkii, compromising sperm DNA integrity and, subsequently, the population success.

Antagonistic Interactions between Benzo[a]pyrene and Fullerene (C60) in Toxicological Response of Marine Mussels

This study aimed to assess the ecotoxicological effects of the interaction of fullerene (C60) and benzo[a]pyrene (B[a]P) on the marine mussel, Mytilus galloprovincialis. The uptake of nC60, B[a]P and mixtures of nC60 and B[a]P into tissues was confirmed by Gas Chromatography-Mass Spectrometry (GC-MS), Liquid Chromatography-High Resolution Mass Spectrometry (LC-HRMS) and Inductively Coupled Plasma Mass Spectrometer (ICP-MS). Biomarkers of DNA damage as well as proteomics analysis were applied to unravel the interactive effect of B[a]P and C60. Antagonistic responses were observed at the genotoxic and proteomic level. Differentially expressed proteins (DEPs) were only identified in the B[a]P single exposure and the B[a]P mixture exposure groups containing 1 mg/L of C60, the majority of which were downregulated (~52%). No DEPs were identified at any of the concentrations of nC60 (p < 0.05, 1% FDR). Using DEPs identified at a threshold of (p < 0.05; B[a]P and B[a]P mixture with nC60), gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis indicated that these proteins were enriched with a broad spectrum of biological processes and pathways, including those broadly associated with protein processing, cellular processes and environmental information processing. Among those significantly enriched pathways, the ribosome was consistently the top enriched term irrespective of treatment or concentration and plays an important role as the site of biological protein synthesis and translation. Our results demonstrate the complex multi-modal response to environmental stressors in M. galloprovincialis.

Effects of Antifouling Biocides on Molecular and Biochemical Defense System in the Gill of the Pacific Oyster Crassostrea gigas

Antifouling biocides such as organotin compounds and their alternatives are potent toxicants in marine ecosystems. In this study, we employed several molecular and biochemical response systems of the Pacific oyster Crassostrea gigas to understand a potential mode of action of antifouling biocides (i.e. tributyltin (TBT), diuron and irgarol) after exposure to different concentrations (0.01, 0.1, and 1 μg L^-1) for 96 h. As a result, all the three antifouling biocides strongly induced the antioxidant defense system. TBT reduced both enzymatic activity and mRNA expression of Na⁺/K⁺-ATPase and acetylcholinesterase (AChE). Lower levels of both Na⁺/K⁺-ATPase activity and AChE mRNA expression were observed in the diuron-exposed oysters compared to the control, while the irgarol treatment reduced only the transcriptional expression of AChE gene. We also analyzed transcript profile of heat shock protein (Hsp) superfamily in same experimental conditions. All antifouling biocides tested in this study significantly modulated mRNA expression of Hsp superfamily with strong induction of Hsp70 family. Taken together, overall results indicate that representative organotin TBT and alternatives have potential hazardous effects on the gill of C. gigas within relatively short time period. Our results also suggest that analyzing a series of molecular and biochemical parameters can be a way of understanding and uncovering the mode of action of emerging antifouling biocides. In particular, it was revealed that Pacific oysters have different sensitivities depend on the antifouling biocides.