Phenanthrene (PHE), a major component of crude oil, is one of the most abundant polycyclic aromatic hydrocarbons (PAHs) in aquatic ecosystems, and is readily bioavailable to marine organisms. Understanding the toxicity of PAHs in animals requires knowledge of the systems for xenobiotic biotransformation and antioxidant defence and these are poorly understood in bivalves. We report, for the first time, new transcripts and tissue-specific transcription in gill and digestive gland from the oyster Crassostrea brasiliana following 24h exposure to 100 and 1000μgL-1 PHE, a model PAH. Six new cytochrome P450 (CYP) and four new glutathione S-transferase (GST) genes were analysed by means of quantitative reverse transcription PCR (qRT-PCR). Different antioxidant endpoints, including both enzymatic and non-enzymatic parameters, were assessed as potential biomarkers of oxidative stress. GST activity was measured as an indicator of phase II biotransformation. Rapid clearance of PHE was associated with upregulation of both phase I and II genes, with more pronounced effects in the gill at 1000μgL-1 PHE. After 24h of exposure, PHE also caused impairment of the antioxidant system, decreasing non-protein thiols and glutathione levels. On the other hand, no change in antioxidant enzymes was observed. PHE treatment (100μgL-1) significantly decreased GST activity in the gill of exposed oysters. Both CYP and GST were transcribed in a tissue-specific manner, reflecting the importance of the gill in the detoxification of PAHs. Likewise, the antioxidant parameters followed a similar pattern. The data provide strong evidence that these genes play key roles in C. brasiliana biotransformation of PHE and highlight the importance of gill in xenobiotic metabolism.
Bibliographical noteFunding Information:
This work was supported by CNPq (National Council for Research Development), INCT–TA (National Institute of Science and Technology–Aquatic Toxicology) and FAPESC (Foundation for the Support of Scientific and Technological Research in the State of Santa Catarina). The provided scholarships are sincerely appreciated (KHL, TSD, RT from Capes). ACDB and ALD are CNPq research fellows. We would like to thank M.Sc. Marília N. Siebert and Mariana C. Naldi for the assistance during experiments. We are grateful to Dr. Cláudio M.R. Melo and to M.Sc. Carlos H.A.M. Gomes for supplying the oysters used in this study.
- Antioxidant parameters