Esterification and hydrolysis of vitamin A in the liver of brook trout (Salvelinus fontinalis) and the influence of a coplanar polychlorinated biphenyl

Dietary vitamin A supplementation ameliorates the effects of poly-aromatic hydrocarbons in Atlantic salmon (Salmo salar)

Several studies have reported on the interaction between vitamin A (VA) and aryl hydrocarbon receptor (AhR)-binding toxicants, including poly-aromatic hydrocarbons (PAHs). In aquaculture, the use of plant oils in novel aquafeeds can increase PAH levels while simultaneously lowering natural VA background levels, causing the need to supplement plant oil-based feeds with synthetic VA. To study dietary VA-PAH interactions, Atlantic salmon (initial weight 195±0.15g) were fed four identical plant-based diets that were supplemented with PAHs (100 and 10mgkg(-1) benzo[a]pyrene (BaP) and phenanthrene (Phe), respectively) or VA (retinyl acetate 8721IUkg(-1)) separately or combined for 2.5 months in a 2×2 factorial design, with triplicate net-pens per diet. Dietary PAH significantly reduced hepatic VA storage, and VA-enriched diets restored hepatic VA. There was a significant PAH-VA interaction effect on hepatic BaP, but not Phe, accumulation, with reduced hepatic BaP concentrations in fish fed VA+PAH compared to fish fed PAH alone. Concurrently, PAH and VA significantly interacted in their effects on CYP1A phase I biotransformation as observed from increased ethoxyresorufin-O-deethylase (EROD) activity, increased CYP1A protein concentration, and elevated transcription (cyp1a1 gene expression) in fish fed PAH+VA compared to PAH alone. Dietary VA supplementation alone had no significant effect on CYP1A phase I biotransformation. Metabolomic assessment showed that dietary VA caused a restoration of metabolic intermediates involved in energy metabolism that were affected by dietary PAH. Moreover, a PAH-induced growth inhibition was partially ameliorated by dietary VA supplementation. In conclusion, dietary VA interacted with PAH toxicity on the level of CYP1A-mediated detoxification, hepatic PAH accumulation, energy allocation, and growth.

Waterborne cadmium and nickel impact oxidative stress responses and retinoid metabolism in yellow perch

In this experiment, we studied the transcriptional and functional (enzymatic) responses of yellow perch (Perca flavescens) to metal stress, with a focus on oxidative stress and vitamin A metabolism. Juvenile yellow perch were exposed to two environmentally relevant concentrations of waterborne cadmium (Cd) and nickel (Ni) for a period of 6 weeks. Kidney Cd and Ni bioaccumulation significantly increased with increasing metal exposure. The major retinoid metabolites analyzed in liver and muscle decreased with metal exposure except at high Cd exposure where no variation was reported in liver. A decrease in free plasma dehydroretinol was also observed with metal exposure. In the liver of Cd-exposed fish, both epidermal retinol dehydrogenase 2 transcription level and corresponding enzyme activities retinyl ester hydrolase and lecithin dehydroretinyl acyl transferase increased. In contrast, muscle epidermal retinol dehydrogenase 2 transcription level decreased with Cd exposure. Among antioxidant defences, liver transcription levels of catalase, microsomal glutathione-S-transferase-3 and glucose-6-phosphate dehydrogenase were generally enhanced in Cd-exposed fish and this up-regulation was accompanied by an increase in the activities of corresponding enzymes, except for microsomal glutathione-S-transferase. No consistent pattern in antioxidant defence responses was observed between molecular and biochemical response when fish were exposed to Ni, suggesting a non-synchronous response of antioxidant defence in fish exposed to waterborne Ni. There was a general lack of consistency between muscle transcription level and enzyme activities analyzed. The overall findings from this investigation highlight the usefulness of transcriptional and biochemical endpoints in the identification of oxidative stress and vitamin A metabolism impairment biomarkers and the potential use of multi-level biological approaches when assessing environmental risk in fish.

Contrasting retinoid and thyroid hormone status in differentially-contaminated northern fulmar colonies from the Canadian Arctic, Svalbard and the Faroe Islands

The northern fulmar (Fulmarus glacialis) has previously been shown to accumulate a wide range, and occasionally high concentrations of organochlorines (OCs) (e.g., PCBs, chlorobenzenes, DDT- and chlordane-related compounds, dioxins and furans). The present study aimed to investigate, using a meta-analysis approach, the variations in cytochrome P450 (CYP) 1A-like enzyme induction based on ethoxyresorufin O-deethylase activity (EROD) and selected physiological variables (retinoids and thyroid hormones) in northern fulmar breeding in three differentially OC-exposed populations: Nunavut (Canadian Arctic), Svalbard (Norwegian Arctic) and the Faroe Islands. Substantially higher (roughly two-fold) OC levels were uncovered in the liver of this long-lived fulmarine petrel breeding in the Faroe Islands relative to Svalbard and Nunavut. Liver levels of PCDDs, PCDFs and non-ortho PCBs in Faroe Islands fulmars were amongst the highest reported thus far in any seabirds from the northern regions. Positive correlations were depicted in combined fulmars (all three populations) between hepatic EROD activity and concentrations of OCs, in which strongest associations were found for dioxin-like compound (PCDFs and PCDDs) and TEQ concentrations. Moreover, moderate to strong positive correlations were found between liver OC concentrations and plasma total thyroxin (TT(4)) levels and TT(4)/total triiodothyronine (TT(3)) level ratios, as well as strong negative correlations between the same suite of OCs and plasma TT(3) levels. Hepatic OC concentrations (PCBs, PCDDs, PCDFs, HCB, p,p'-DDE and oxychlordane) also were positively correlated with hepatic retinyl palmitate levels which, in turn, were associated with a significant decrease in plasma retinol levels and somewhat unchanged liver retinol levels. The present meta-analysis investigation on northern fulmar breeding in three geographically-distant sites illustrated that OC exposure (mainly PCBs and dioxins/furans) may be associated with modulation of the thyroid and retinoid homeostasis. However, the impact of confounding environmental factors (e.g., temperature and nutritional status) on current physiological variable variations could not be ruled out, and thus any cause-effect linkages between thyroid and retinoid system perturbation and OC exposure cannot be ascertained.

Effects of polychlorobiphenyls, polybromodiphenylethers, organochlorine pesticides and their metabolites on vitamin A status in lactating grey seals

Polychlorobiphenyls (PCBs), polybromodiphenylethers (PBDEs) and organochlorine pesticides (OCPs), such as dichlorodiphenyltrichloroethane (DDT) and hexachlorobenzene (HCB), are considered as endocrine disruptors in laboratory and wild animals. This study investigated whether these compounds and their hydroxylated metabolites (HO-PCBs and HO-PBDEs) may affect the homoeostasis of vitamin A, a dietary hormone, in the blubber and serum of twenty lactating grey seals sampled at early and late lactation on the Isle of May, Scotland. The effect of naturally produced compounds such as the methoxylated (MeO)-PBDEs was also examined. Vitamin A levels in inner blubber (37±9 μg/g wet weight (ww) and 92±32 μg/g ww at early and late lactation, respectively) and serum (408±143 and 390±98 ng/ml at early and late lactation, respectively) appeared to be positively related to ΣPCBs, ΣPBDEs and several individual PCB and PBDE congeners in inner blubber and serum. These findings may suggest enhanced mobilisation of hepatic retinoid stores and redistribution in the blubber, a storage site for vitamin A in marine mammals. We have also reported that serum concentrations of ΣHO-PCBs and 4-OH-CB107 tended to increase with circulating vitamin A levels. Although the direction of the relationships may sometimes differ from those reported in the literature, our results are in agreement with previous findings highlighting a disruption of vitamin A homoeostasis in the blubber and bloodstream following exposure to environmental pollutants. The fact that vitamin A and PCBs appeared to share common mechanisms of mobilisation and transfer during lactation in grey seals (Debier et al., 2004; Vanden Berghe et al., 2010) may also play a role in the different relationships observed between vitamin A and lipophilic pollutants.

Effects of p,p'-DDE on retinoid homeostasis and sex hormones of adult male European common frogs (Rana temporaria)

Reports of declining numbers of species and individuals of amphibians in most parts of the world have caused great concern. Several causative factors have been linked to this amphibian decline, and increased environmental pollution related to pesticide use seems to be one important factor. Persistent organic pollutants may act as endocrine disrupters, and thereby exert adverse effects on development (metamorphosis, growth and sexual differentiation) in amphibians. During periodic events, such as spring snowmelt, amphibians may be exposed to acute high levels of pesticides. 1,1,1-Trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and its metabolite 1,1-dichloro-2,2-bis(p-chlorophenyl)ethene (p,p'-DDE) is a pesticide that is still found in wetlands and soils. In order to study the effects of p,p'-DDE on susceptible amphibian endocrine systems, adult male European common frogs (Rana temporaria) were exposed to different doses of p,p'-DDE (0, 0.01, 0.1, 1 and 10 mg p,p'-DDE/kg body mass) for 14 d and sex hormone levels (testosterone and 17beta-estradiol) in plasma and retinoid concentrations (retinol and retinyl palmitate) in liver were determined. The results showed a significant variation in the liver retinol concentration at increasing doses of p,p'-DDE, suggesting that p,p'-DDE may interfere in the hepatic metabolism of retinol in adult frogs. Lack of effects on sex hormones may indicate that after arousal from hibernation males are relatively resistant to adverse reproductive effects of p,p'-DDE.