The effect of dietary lipid composition on the intestinal uptake and tissue distribution of benzo[a]pyrene and phenanthrene in Atlantic salmon (Salmo salar).

Uptake of polycyclic aromatic hydrocarbons (PAHs) across the intestine is suggested to occur in association with dietary lipids. Partial replacement of fish ingredients by vegetable ingredients in aquafeeds has led to increased levels of PAHs in marine farmed fish. We therefore investigated, intestinal uptake, tissue distribution and PAH metabolism after a single dose of (14)C-benzo[a]pyrene (BaP) or (14)C-phenanthrene (PHE) given to Atlantic salmon (Salmo salar) acclimatized to a fish oil or vegetable oil based diet. Both BaP and PHE were absorbed along the intestine. Fish oil based feed increased BaP concentration in the pyloric caeca and that of PHE in the proximal intestine. In contrast, vegetable oil increased BaP concentrations in the distal intestine. Extraction of whole body autoradiograms removed PHE-associated radiolabeling almost completely from the intestinal mucosa, but not BaP-associated radiolabeling, indicating the presence of BaP metabolites bound to cellular macromolecules. This observation correlates with the increased cyp1a expression in the proximal intestine, distal intestine and liver in the BaP exposed group. Furthermore, BaP-induced cyp1a expression was higher in the distal intestine of salmon fed fish oil compared to the vegetable oil fed group. PHE had no significant effect on cyp1a expression in any of these tissues. We conclude that dietary lipid composition affects intestinal PAH uptake. Fish oil based feed increased intestinal PAH concentrations probably due to an enhanced solubility in micelles composed of fish oil fatty acids. Increased BaP accumulation in the distal intestine of vegetable oil fed fish seems to be associated with a reduced Cyp1a-mediated BaP metabolism.

Disposition of arsenobetaine in two marine fish species following administration of a single oral dose of [14C]arsenobetaine.

The distribution and excretion of arsenobetaine in fish were investigated using whole body autoradiography and liquid scintillation counting. A single dose of synthesised [(14)C]arsenobetaine was orally administered to Atlantic salmon, Salmo salar L., and Atlantic cod, Gadus morhua L. Arsenobetaine was distributed to most organs within both species. Nevertheless, there were species differences in tissue distribution and excretory pattern. The highest level of arsenobetaine in Atlantic salmon was present in muscle tissue, while high levels of arsenobetaine were found in both muscle and liver (including gall bladder) from Atlantic cod. The results suggest that the major route of excretion was via urine, which seemed to be more important in Atlantic cod than in Atlantic salmon. Elimination of arsenobetaine via bile appeared to be negligible in both species.

Cadmium accumulation and Cd-binding proteins in marine invertebrates--a radiotracer study.

Tissue and subcellular accumulation of cadmium were studied in different tissues of three marine invertebrates (blue mussel Mytilus edulis, the tunicate Ciona intestinalis and the sea star Asterias rubens) using radioactive 109Cd as a tracer. The organisms were exposed to 0.05, 2 and 50 microg Cd l(-1) for 21 days. Quantitative data were obtained by dissecting, weighing and subsequently measuring radioactivity in organs and tissues. Differences between each exposure and each tissue with regard to the amount of radioactivity and metallothionein (MT) content were evaluated. Obvious interspecies differences in Cd accumulation were observed, as well as differences between tissues of the three species. The highest concentrations of Cd in all exposure treatments were found in the hepatopancreas of M. edulis and body wall of A. rubens. Taking all treatments into account, Cd accumulation in the tunic of C. intestinalis was high compared to other tissues from this species. Over 60% of Cd was present in the S50 fraction in all treatments in all three species. Metallothionein levels were increased at the highest Cd-exposure in all species and tissues, except in branchial pharynx of C. intestinalis where the highest MT level was reached following exposure to 2 microg Cd l(-1). The most surprising finding was that even the lowest Cd exposure concentration (0.05 microg Cd l(-1)) caused MT induction in pyloric caeca of A. rubens, but there was no dose-dependent increase in MT at higher exposure levels.

Monooxygenase mediated pyrethroid detoxification in sea lice (Lepeophtheirus salmonis).

The role of monooxygenases in detoxification of the pyrethroids cypermethrin and deltamethrin was examined. Four strains of sea lice (Lepeophtheirus salmonis Krøyer) with normal or moderately reduced sensitivity towards the pyrethroids were tested in bioassays by exposure to the pyrethroid alone and in combination with an oxygenase inhibitor, piperonyl butoxide (PBO). The normal (baseline) sensitivity was considered as the sensitivity range for the two most sensitive strains. Pre-treatment with PBO elevated the sensitivity (P < 0.01) compared with groups exposed to the pyrethroid only. A positive, but not statistically significant, correlation between the activity of haem peroxidases and the pyrethroid concentration immobilizing 50% of the parasites was demonstrated (rho = 0.500 for deltamethrin and rho = 0.310 for cypermethrin). The results indicate that cytochrome P450 monooxygenases are involved in detoxification of pyrethroids in sea lice. 14C-Deltamethrin was absorbed in a lesser amount in a group of sea lice exposed to a mixture of the compound and PBO than in a group exposed to 14C-deltamethrin alone. A significant difference could be demonstrated both immediately after exposure (P < 0.01) and 24 h after exposure (P < 0.05). No significant differences were found between groups pre-treated with PBO and groups exposed to 14C-deltamethrin only. 14C-Deltamethrin was taken up mainly through the cuticle, especially the cuticle on the extremities of the ventral surface, and subsequently distributed throughout the body of the parasite.

Cell-specific CYP1A expression and benzo[a]pyrene adduct formation in gills of rainbow trout (Oncorhynchus mykiss) following CYP1A induction in the laboratory and in the field.

The effect of cytochrome P4501A (CYP1A) induction on cell-specific benzo[a]pyrene (BaP) adduct formation was studied in rainbow trout (Oncorhynchus mykiss) gills. Fish preexposed to beta-naphthoflavone (betaNF) or caged in a polluted river were exposed to waterborne 3H-benzo[a]pyrene (3H-BaP). The 3H-benzo[a]pyrene adducts in the gill filaments were localized by autoradiography and CYP1A protein by immunohistochemistry. Ethoxyresorufin O-deethylase (EROD) activity was measured using a gill filament-based ex vivo assay. Branchial 3H-BaP binding and EROD activity were enhanced by exposure to betaNF or to the river water, and completely blocked by the CYP1A inhibitor ellipticine. The predominant sites of adduct formation were in epithelium of the secondary lamellae and in epithelium of the efferent edge of the gill filament. In betaNF-exposed fish, the strongest CYP1A immunoreactivity was observed in differentiating cells and in pillar cells. In fish caged in the polluted river, strong CYP1A immunoreactivity was found in most cells in the secondary lamellae, whereas the primary lamellae were almost devoid of immunoreactivity. Our results reveal a discrepancy between the localization of CYP1A protein and BaP adducts in the gill. Consequently, other factors, such as bioavailability of waterborne polycyclic aromatic hydrocarbons (PAHs) to the target cells, are important for the localization of PAH adducts in the gill.

EROD activity in gill filaments of anadromous and marine fish as a biomarker of dioxin-like pollutants.

The applicability of a gill filament-based ethoxyresorufin O-deethylase (EROD) assay, originally developed in rainbow trout, was examined in Atlantic salmon (Salmo salar), Arctic charr (Salvelinus alpinus), Atlantic cod (Gadus morhua), saithe (Pollachius virens) and spotted wolffish (Anarhichas minor). All species but spotted wolffish showed strong EROD induction in tip pieces of gill filaments following 48 h of exposure to waterborne beta-naphthoflavone. Atlantic salmon parr, smolts held in freshwater and smolts transferred to seawater showed EROD induction of similar magnitude. Arctic charr, differing 11-fold in body weight, showed similar EROD activities as expressed per gill filament tip. Laboratory exposure of saithe to water and sediments collected at polluted sites, resulted in strong EROD induction. In conclusion, the gill filament assay seems useful for monitoring exposure to aryl hydrocarbon receptor agonists in various species. Furthermore, smoltification status, water salinity and body size proved to have minor influence on gill filament EROD activity. However, the results in spotted wolffish show that some species may be less suitable for monitoring using the gill assay. Assessment of gill filament EROD activity in fish exposed to polluted water and sediments in the laboratory proved to be an easy and cost-effective way to survey pollution with dioxin-like chemicals.

Irreversible binding of o,p'-DDD in interrenal cells of Atlantic cod (Gadus morhua).

Precision-cut tissue slices of the anterior kidney from Atlantic cod (Gadus morhua) were prepared with a Krumdieck tissue slicer and exposed to 2-(2-chlorophenyl)-2-(4-chloro-(14C)phenyl)-1,1-dichlorethane (o,p(')-[14C]DDD) in vitro. Microautoradiography revealed irreversible o,p(')-DDD-derived binding confined to the glucocorticoid producing interrenal cells (adrenocortical analogues). This cell-selective binding was confirmed by means of autoradiography at different levels of resolution on Atlantic cod administered o,p(')-[14C]DDD intragastrically. The results provide evidence for a site-specific metabolic activation and irreversible binding of o,p(')-DDD in the interrenal cells, which, in turn, may modify glucocorticoid homeostasis.

Flumequine in Atlantic salmon Salmo salar: disposition in fish held in sea water versus fresh water.

14C-labeled flumequine was administered as a single oral (5 mg kg(-1), 86 microCi kg(-1)) or intravenous (5 mg kg(-1), 82 microCi kg(-1)) dose to Atlantic salmon Salmo salar held in sea water or in fresh water. The absorption, tissue distribution and elimination were determined by means of liquid scintillation counting and whole-body autoradiography. The drug was rapidly absorbed and extensively distributed in all groups of fish. Radiolabeled compound was present in blood and muscle for more than 8 wk in the freshwater groups. In the seawater groups, however, no radioactivity was detected in the blood and muscle after 4 d and 2 wk, respectively. It was concluded that flumequine was eliminated at a substantially higher rate from Atlantic salmon in sea water than in fresh water.