Application of SSH and quantitative real time PCR to construction of gene expression profiles from scallop Chlamys farreri in response to exposure to tetrabromobisphenol A

Effects of BαP and TBBPA on multixenobiotic resistance (MXR) related efflux transporter activity and gene expressions in gill cells of scallop Chlamys farreri

The multixenobiotic resistance mechanism (MXR) provides aquatic organisms with the capacity to adapt to polluted environments, which can be inhibited by chemosensitizers. In the present study, the effect of two typical marine persistent organic pollutants, benzo(a)pyrene (BaP) and tetrabromobisphenol A (TBBPA), on the most relevant ABC transporters, ABCB1, ABCC1, and ABCG2 of scallop Chlamys farreri was tested. MXR transporter efflux activity of cultured gill cells of the scallops was evaluated by measuring the intracellular fluorescent intensity of Calcein-AM and rhodamine 123 with flow cytometry. The results showed that ABCB1 and ABCC1 transporters demonstrated increased activity compared with ABCG2 in mediating MXR efflux activity. BaP and TBBPA were able to suppress the efflux transporter activity of ABC transporters significantly, of which BaP revealed block effects by acting on the ABCB1 transporter. Additionally, exposure of BaP and TBBPA only significantly upregulated the expression level of ABCC1 gene. This study demonstrated the promising utility of efflux transporter activity in conjunction with biomarkers such as mRNA levels in identification of chemosensitizer.

Multi-biomarker approach in the scallop Chlamys farreri to assess PAHs pollution in Qingdao coastal areas of China

A multi-biomarker approach was conducted in the scallop Chlamys farreri from three sites, denoted here as S1, S2, and S3, in Qingdao coastal areas of China in March, June, September and December 2014 to assess pollution from polycyclic aromatic hydrocarbons (PAHs) and to select appropriate biomarkers. A suite of biological responses of the gills and digestive glands of the scallops was assayed, including: (i) phase I detoxification enzymes of 7-ethoxyresorufin-O-deethylase (EROD), epoxide hydrolase (EH), and dihydrodiol dehydrogenase (DD) and phase II detoxification enzymes of glutathione-S-transferase (GST) and sulfotransferase (SULT); (ii) antioxidant enzymes: catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx); (iii) oxidative damage parameters: lipid peroxidation (LPO) expressed by malondialdehyde (MDA) contents, protein carbonylation (PC) and DNA damage (F value); and (iv) the metabolism-related genes of EH, DD, GST, SULT and SOD. Simultaneously, the concentrations of total PAHs along with 16 types of PAHs previously identified by the US Environmental Protection Agency (USEPA) and environmental parameters, including temperature and salinity together with pH, were measured. Using Principle Component Analysis (PCA), it was revealed that S2 was the most PAH-contaminated site, while S1 was identified as the least PAH-polluted site, which was consistent with the results utilizing the Biomarker Response Index (BRI); in other words, the biological health status of S2 was worse than S1 and S3. Moreover, the most suitable biomarkers to assess PAH pollution in Qingdao coastal areas proved to be DD mRNA expression and the F value in both the gills and digestive glands for the total PAHs, DD activity and PC contents or PC and MDA contents in the gills or digestive glands for 5 + 6 rings PAHs and DD mRNA expression in both the gills and digestive glands for 2 + 3 rings and 4 rings PAHs. Moreover, this study highlighted the possible use of the scallop Chlamys farreri for studying contamination due to PAHs and provided valuable information on environmental assessment.

Bioaccumulation and detoxification responses in the scallop Chlamys farreri exposed to tetrabromobisphenol A (TBBPA)

Tetrabromobisphenol A (TBBPA) is currently the most widely used brominated flame retardant (BFR). In this study, the bioaccumulation of TBBPA and its consequent detoxification responses were examined in the scallop Chlamys farreri over 10 days' exposure. Chemical analysis showed that C. farreri absorbed TBBPA rapidly and an approximate steady state was achieved within 6 days. The mRNA expression levels of three important genes involved in aryl hydrocarbon receptor (AhR) pathway were down-regulated upon TBBPA exposure. Both CYP3A and CYP4 showed time-dependent responses to TBBPA exposure. Glutathione-S-transferase (GST) activity and gene expression level, and UDP-glucuronosyltransferase (UGT) activity were increased in time- and dose-dependent manners, confirming their role in the phase II metabolism of TBBPA. The TBBPA-elicited down-regulation of the P-glycoprotein (Pgp) gene was observed in all treatments. This study provides a preliminary basis for studying TBBPA detoxification mechanisms of marine bivalves.

Deep sequencing of the scallop Chlamys farreri transcriptome response to tetrabromobisphenol A (TBBPA) stress

Tetrabromobisphenol-A (TBBPA) is currently the most widely used brominated flame retardant (BFR) and has been proven to have a very high toxicity to aquatic organisms including bivalves. However, molecular responses to TBBPA in bivalve remain largely unknown. Novel high-throughput deep sequencing technology has been a powerful tool for looking at molecular responses to toxicological stressors in organisms. Using Illumina's digital gene expression (DGE) system, we investigated TBBPA-induced transcriptome response in the digestive gland tissue of scallop Chlamys farreri. In total, 173 and 266 genes were identified as significantly up- or down-regulated, respectively. Functional analysis based on gene ontology (GO) classification system and Kyoto Encyclopedia of Genes and Genomes (KEGG) database revealed that TBBPA significantly altered the expression of genes involved in stress response, detoxification, antioxidation, and innate immunity which were extensively discussed. In particular, evidence for the endocrine disrupting effect of TBBPA on bivalve was first obtained in this study. Quantitative real-time PCR was performed to ascertain the mRNA expression of several genes identified by the DGE analysis. The results of this study may serve as a basis for future research on molecular mechanism of toxic effects of TBBPA on marine bivalves.

Response of detoxification gene mRNA expression and selection of molecular biomarkers in the clam Ruditapes philippinarum exposed to benzo[a]pyrene

Benzo[a]pyrene (B[a]P) has a high carcinogenic potential. B[a]P concentrations and molecular biomarkers (mRNA expressions of Pgp, AhR, CYP4, CYP414A1, GST-pi, GST-S2, Cu/Zn-SOD and Mn-SOD) were assayed in gills and digestive glands of the clam Ruditapes philippinarum exposed to 0.03, 0.3 and 3 μg/L B[a]P for 21 days and then exposed to natural seawater for 15 days. Results showed that B[a]P was rapidly accumulated in and then eliminated from tissues of the clams. All gene mRNA expressions in the treated groups were induced significantly with the exception of CYP414A1 and Cu/Zn-SOD in the 0.03 μg/L B[a]P group. According to correlation analysis, mRNA expressions of AhR, GST-pi and Mn-SOD in gills and GST-pi in digestive glands had good correlations with B[a]P concentrations and could be used as molecular biomarkers of B[a]P exposure. This study investigated the molecular response of the genes mentioned above and selected useful molecular biomarkers for B[a]P pollution monitoring.