Specific expression of cytochrome P4501A1 gene in gill, intestine and liver of tilapia exposed to coastal sediments

Toxicological effects of persistent organic pollutants (POPs) in aquatic ec osystems lead to the deterioration of water quality and adversely affect fi sh and human health. The highly lipophilic nature of these pollutants may e nter fish through the diet or by water-borne exposure. In monitoring contam ination in aquatic systems, induction of the cytochrome P450 1A1 (CYP1A1) g ene of fish has been evaluated as a sensitive, 'early warning' method. The objective of the present study was to characterize the induction of the gen e in fish upon exposure to coastal sediments and to determine its specific expression in liver and extrahepatic organs (i.e. gill and intestine) in wh ich the toxicological effects to the corresponding tissues could be address ed. Sediment samples were collected from different sites, including Victori a Harbour (VS), Ma Wan (MW), Tsim Bei Tsui (TBT) and Mai Po (MP). The sampl es were analyzed for polychlorinated biphenyls (PCBs) and polycyclic aromat ic hydrocarbons (PAHs). CYP1A1 mRNA expression was measured in juvenile til apia exposed experimentally to coastal sediment for 3 and 7 days. A negativ e control group of fish maintained in seawater was used. Using the primer d ropping polymerase chain reaction technique, gill, intestinal and hepatic C YP1A1 mRNAs were quantified. Chemical analysis shows that the samples from VS contaminated with the highest concentration of PCBs (45.24 p.p.b.) and P AHs (1663.7 p.p.b.), followed by MW (16.01 and 347.7 p.p.b.), TBT (14.48 an d 235.2 p.p.b.) and NIP (14.60 and 242.2 p.p.b.). Fish exposed to sediments were contaminated with various levels of PCBs (VS, 64.14-72.06 p.p.b., MP, 27.06-31.62 p.p.b., TBT, 27.29-33.92 p.p.b.; MW, 16.05-17.76 p.p.b.) and P AHs (VS, 124.7-304.9 p.p.b.; MP, 97.57-164.1 p.p.b., TBT, 25.38-98 p.p.b.; MW, 24.07-68.13 p.p.b.). The control fish displayed moderate expression of CYP1A1 mRNA in liver (1.45 arbitrary units), gill (1.21 arbitrary units) an d intestine (0.56 arbitrary units). Following sediment exposure, there was a large increase in CYP1A1 mRNA in intestine and liver but no significant c hanges in gill tissues. In the first 3 days, there was anywhere from 34-96 and 69-156% induction of the CYP1A1 transcripts in intestine and liver. res pectively. Following 7 days of exposure, a continued induction of high leve l of CYP1A1 mRNA in intestine (73-157%) was observed. The induction of CYP1 A1 in liver and intestine provided a defensive mechanism against POPs enter ing from the external environment. (C) 2000 Elsevier Science B.V. All right s reserved.