Xenobiotic biotransformation systems in fishes

Evaluation of the bioaccumulation potential of selected alternative brominated flame retardants in marine fish using in vitro metabolic transformation rates

The global consumption of alternative brominated flame retardants (BFRs) has increased with the restriction of the first generation BFRs such as polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecanes (HBCDs). However, many alternative BFRs are suspected to be persistent in the environment and possibly bioaccumulative after their release into the environment because of their chemical properties, which are similar to those of the already banned BFRs. In this study, the bioaccumulation potential of selected alternative BFRs (1,2-bis(2,4,6‑tribromophenoxy)ethane (BTBPE), 1,2,3,4,5,6‑hexabromobenzene (HBB), pentabromoethylbenzene (PBEB), 2,3,4,5,6‑pentabromotoluene (PBT), 2‑ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB), and 2,3,4,5‑tetrabromo-6-chlorotoluene (TBCT)) was evaluated. The in vitro depletion rate constants (k_depl) were measured for the alternative BFRs using liver S9 fractions isolated from five marine fish species (Epinephelus septemfasciatus, Konosirus punctatus, Lateolabrax japonicus, Mugil cephalus, and Sebastes schlegelii) that inhabit the oceans off the Korean coast. The measured k_depl values were converted to in vitro intrinsic clearance rate constants (CL_{in vitro}) to estimate whole-body metabolic rate constants (k_MET) using an in vitro to in vivo extrapolation (IVIVE) model. Finally, the bioconcentration factors (BCF) were determined using a one-compartment model. The transformation kinetics for obtaining k_depl agreed well with first-order chemical kinetics, regardless of initial BFR concentrations. The values of CL_{in vitro} were lower in the selected marine fish species than those in freshwater fish species, implying slower metabolic transformation. The derived BCF values based on the total concentration in water (BCF_TOT) ranged from 16 (TBB in M. cephalus) to 27,000 (HBB in K. punctatus). The BCF values for HBB and PBT were >2000 except for those in M. cephalus suggesting further investigation of BCF values of BFRs whose log K_OW is between 6 and 7.

The genome of the golden apple snail Pomacea canaliculata provides insight into stress tolerance and invasive adaptation

Background

The golden apple snail (Pomacea canaliculata) is a freshwater snail listed among the top 100 worst invasive species worldwide and a noted agricultural and quarantine pest that causes great economic losses. It is characterized by fast growth, strong stress tolerance, a high reproduction rate, and adaptation to a broad range of environments.

Results

Here, we used long-read sequencing to produce a 440-Mb high-quality, chromosome-level assembly of the P. canaliculata genome. In total, 50 Mb (11.4%) repeat sequences and 21,533 gene models were identified in the genome. The major findings of this study include the recent explosion of DNA/hAT-Charlie transposable elements, the expansion of the P450 gene family, and the constitution of the cellular homeostasis system, which contributes to ecological plasticity in stress adaptation. In addition, the high transcriptional levels of perivitelline genes in the ovary and albumen gland promote the function of nutrient supply and defense ability in eggs. Furthermore, the gut metagenome also contains diverse genes for food digestion and xenobiotic degradation.

Conclusions

These findings collectively provide novel insights into the molecular mechanisms of the ecological plasticity and high invasiveness.

Metabolic Costs of Exposure to Wastewater Effluent Lead to Compensatory Adjustments in Respiratory Physiology in Bluegill Sunfish

Municipal wastewater effluent is a major source of aquatic pollution and has potential to impact cellular energy metabolism. However, it is poorly understood whether wastewater exposure impacts whole-animal metabolism and whether this can be accommodated with adjustments in respiratory physiology. We caged bluegill sunfish (Lepomis macrochirus) for 21 days at two sites downstream (either 50 or 830 m) from a wastewater treatment plant (WWTP). Survival was reduced in fish caged at both downstream sites compared to an uncontaminated reference site. Standard rates of O₂ consumption increased in fish at contaminated sites, reflecting a metabolic cost of wastewater exposure. Several physiological adjustments accompanied this metabolic cost, including an expansion of the gill surface area available for gas exchange (reduced interlamellar cell mass), a decreased blood-O₂ affinity (which likely facilitates O₂ unloading at respiring tissues), increased respiratory capacities for oxidative phosphorylation in isolated liver mitochondria (supported by increased succinate dehydrogenase, but not citrate synthase, activity), and decreased mitochondrial emission of reactive oxygen species (ROS). We conclude that exposure to wastewater effluent invokes a metabolic cost that leads to compensatory respiratory improvements in O₂ uptake, delivery, and utilization.

Toxicological hazard induced by sucralose to environmentally relevant concentrations in common carp (Cyprinus carpio)

Sucralose (SUC) is an artificial sweetener that is now widely used in North American and Europe; it has been detected in a wide variety of aquatic environments. It is considered safe for human consumption but its effects in the ecosystem have not yet been studied in depth, since limited ecotoxicological data are available in the peer-reviewed literature. This study aimed to evaluate potential SUC-induced toxicological hazard in the blood, brain, gill, liver and muscle of Cyprinus carpio using oxidative stress biomarkers. Carps were exposed to two different environmentally relevant concentrations (0.05 and 155μgL^-1) for different exposure times (12, 24, 48, 72 and 96h). The following biomarkers were evaluated: lipid peroxidation (LPX), hydroperoxide content (HPC) and protein carbonyl content (PCC), as well as the activity of antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT). SUC was determined by high pressure liquid chromatography tandem mass spectrometry techniques (HPLC)-MS/MS. Results show a statically significant increase in LPX, HPC, PCC (P<0.05) especially in gill, brain and muscle, as well as significant changes in the activity of antioxidant enzymes in gill and muscle. Furthermore, the biomarkers employed in this study are useful in the assessment of the environmental impact of this agent on aquatic species.

A pharm-ecological perspective of terrestrial and aquatic plant-herbivore interactions

We describe some recent themes in the nutritional and chemical ecology of herbivores and the importance of a broad pharmacological view of plant nutrients and chemical defenses that we integrate as "Pharm-ecology". The central role that dose, concentration, and response to plant components (nutrients and secondary metabolites) play in herbivore foraging behavior argues for broader application of approaches derived from pharmacology to both terrestrial and aquatic plant-herbivore systems. We describe how concepts of pharmacokinetics and pharmacodynamics are used to better understand the foraging phenotype of herbivores relative to nutrient and secondary metabolites in food. Implementing these concepts into the field remains a challenge, but new modeling approaches that emphasize tradeoffs and the properties of individual animals show promise. Throughout, we highlight similarities and differences between the historic and future applications of pharm-ecological concepts in understanding the ecology and evolution of terrestrial and aquatic interactions between herbivores and plants. We offer several pharm-ecology related questions and hypotheses that could strengthen our understanding of the nutritional and chemical factors that modulate foraging behavior of herbivores across terrestrial and aquatic systems.

Genotoxic and hepatic biotransformation responses induced by the overflow of pulp mill and secondary-treated effluents on Anguilla anguilla L

Pulp and paper mill effluent compounds pollute the aquatic environment and are responsible for increased biochemical alterations and genotoxicity in aquatic organisms such as fish. Adult eels (Anguilla anguilla L) were exposed during 8, 16, 24, and 72 h to the following conditions: (1) aerated, filtered, and dechlorinated tap water (C); (2) 2.5% (v/v) sewage water previously treated with activated sludge (T); (3) bleached kraft pulp and paper mill effluent collected at the river Vouga, close to an ancient sewage outlet (Portucel), diluted in tap water [25% (E25) and 50% (E50)]; and (4) bleached kraft pulp and paper mill effluent sediment [water-soluble fraction (S)]. Liver biotransformation induced by the above conditions was measured as ethoxyresorufin-O-deethylase (EROD), cytochrome P450 (P450) (Phase I), and glutathione-S-transferase (GST) (Phase II). Genotoxicity was also determined as blood/liver DNA strand breaks and erythrocytic nuclear abnormalities (ENA) induced on European eel (A. anguilla L). Liver EROD activity was significantly increased in eels at 8 and 16 h exposure to E25, as well as at 16, 24, and 72 h exposure to E50. S exposure induced liver EROD activity only at 24h. A significant decrease in liver P450 was observed at 72 h exposure to T, whereas a significant P450 increase at 16 h was followed by a significant decrease at 24h exposure to E25. Another P450 significant increase was noticed at 72 h exposure to S. Liver GST activity (Phase II) demonstrated a significant increase at 72 h exposure to E50 and to S. A significant decrease in blood DNA integrity was observed at 72 h exposure to T and at 24 and 72 h to S. Blood DNA integrity significantly decreased at 16 and 24 h exposure to E25, as well as at 8, 16, and 24 h exposure to E50. Liver DNA integrity significantly decreased at 72 h exposure to T and at 16 h exposure to S. Moreover, liver DNA integrity was significantly decreased at 24h exposure to E25 and E50, and 72 h to E50. A. anguilla L. increased ENA frequency was detected in T at 16, 24, and 72 h, whereas in E25 and S it was observed at 8, 16, and 24 h. Furthermore, E50 ENA frequency increased at 24 h exposure.

Anguilla anguilla L. biochemical and genotoxic responses to benzo[a]pyrene

Eels (Anguilla anguilla L.) were exposed for 2, 4, 6, 8, 16, 24, 48, 72, 144, and 216 h to 0 (control), 0.3, 0.9, and 2.7 microM benzo[a]pyrene (BaP). The biotransformation induced by BaP was measured as liver ethoxyresorufin O-deethylase (EROD) activity and cytochrome P450 content, and compared with the genotoxic effects, such as erythrocytic nuclear abnormalities (ENA), and blood and liver DNA strand breaks. The liver exhibited a highly significant EROD activity increase from 2 up to 216 h exposure to 0.9 and 2.7 microM BaP, whereas 0.3 microM BaP exposure induced a significant liver EROD increase from 2 up to 144 h. Liver cytochrome P-450 content was significantly increased at 8 h to 2.7 microM BaP exposure. Liver DNA integrity was decreased at 16 h, from 8 up to 144 h and 8 up to 72 h exposure to 0.3, 0.9, and 2.7 microM BaP, respectively. A significant decrease in blood DNA integrity was observed at 48, 72, 144 h, from 8 up to 72, and from 6 up to 72 h exposure to 0.3, 0.9, and 2.7 microM BaP, respectively. The A. anguilla L. genotoxic response to BaP, measured as ENA induction, was significantly increased at 144 h exposure to 0.3 microM BaP. The intermediate BaP concentration tested (0.9 microM) induced a significant three fold ENA increase at 48 and 72 h exposure compared to their controls. The highest BaP concentration (2.7 microM) induced a significant increase in ENA frequency at 72, 144 and 216 h exposure.

Hepatic microsomal desulfuration and dearylation of chlorpyrifos and parathion in fingerling channel catfish: lack of effect from Aroclor 1254

Channel catfish were treated intraperitoneally with 100 mg Aroclor 1254/kg body weight and sacrificed at 96 h to observe the effects of this cytochrome P450 1A (CYP1A) inducer on chlorpyrifos and parathion metabolism. In the initial experiment, hepatic microsomal ethoxyresorufin-O-deethylase (EROD) activity of the Aroclor-treated fish was significantly induced but no effects on desulfuration or dearylation of chlorpyrifos or parathion were evident. In the second experiment, Aroclor 1254 did not alter total hepatic microsomal P450s content, but significantly induced hepatic EROD and CYP1A. There were no evident effects to other hepatic CYP isoforms recognized by anti-trout CYP2K1, CYP2M1 and CYP3A27. These experiments indicate that Aroclor 1254 did not induce the P450s responsible for metabolism of the phosphorothionate insecticides.

A physiologically based pharmacokinetic and pharmacodynamic model for paraoxon in rainbow trout

Trout were exposed to an aqueous solution of 75 ng/ml paraoxon for 5 days at 12 degrees C. The relationships among paraoxon concentration in water and target organs, AChE inhibition, and carboxylesterase (CaE) detoxification of paraoxon were characterized quantitatively by development of a PBPK-PD model. The PKPD model structure consisted of brain, heart, liver, kidney, and remainder of the body, which were interconnected by blood circulation. The paraoxon tissue/blood partition coefficients were: plasma/water, 1.46; liver/plasma, 5.89; brain/plasma, 3.90; heart/plasma, 2.91; kidney/plasma, 0.45; and blood/plasma, 0.91. Turnover of AChE was characterized from a dose-response study, in which its zero-order synthesis rate and first-order degradation rate constant were determined in several tissues; for brain they were 7.67 pmol/min and 7.31 x 10(-5) hr(-1). The uptake and depuration clearances of paraoxon (Cl(u) = 0.651 and Cl(d) = 0.468 ml min(-1) g body wt(-1)) were determined using a compartmental model. During continuous water exposure to paraoxon, AChE activity in the tissues declined to new steady state values that were maintained by the synthesis of new AChE. CaE was shown by simulation to be an important pathway for detoxification of paraoxon.

Pharmacokinetics of sulphadimidine in carp (Cyprinus carpio L.) and rainbow trout (Salmo gairdneri Richardson) acclimated at two different temperature levels

The influence of temperature (10 degrees C and 20 degrees C) on pharmacokinetics and metabolism of sulphadimidine (SDM) in carp and trout was studied. At 20 degrees C a significantly lower level of distribution (Vdarea) and a significantly shorter elimination half-life (T(1/2)beta) was achieved in both species compared to the 10 degrees C level. In carp the body clearance parameter (ClB(SDM)) was significantly higher at 20 degrees C compared to the value at 10 degrees C, whereas for trout this parameter was in the same order of magnitude for both temperatures. N4-acetylsulphadimidine (N4-SDM) was the main metabolite of SDM in both species at the two temperature levels. The relative N4-SDM plasma percentage in carp was significantly higher at 20 degrees C than at 10 degrees C, whereas there was in trout no significant difference. In neither species was the peak plasma concentration of N4-SDM (Cmax(N4-SDM)) significantly different at two temperatures. The corresponding peak time of this metabolite (Tmax(N4-SDM)) was significantly shorter at 20 degrees C compared to 10 degrees C in both carp and trout. In carp at both temperatures, acetylation occurs to a greater extent than hydroxylation. Only the 6-hydroxymethyl-metabolite (SCH2OH) was detected in carp, at a significant different level at the two temperatures. Concentrations of hydroxy metabolites in trout were at the detection level of the HPLC-method (0.02-micrograms/ml). The glucuronide metabolite (SOH-gluc.) was not detected in either species at the two temperatures.