Metabolism of 1-fluoropyrene and pyrene in marine flatfish and terrestrial isopods

The effect of soil pollution with petroleum-derived substances on Porcellio scaber Latr. (Crustacea, Isopoda)

Presented research aimed at investigating the effect of short-term contact with petroleum-derived substances (PDSs) on life parameters of Porcellio scaber Latr. (Isopoda) and accumulation of polycyclic aromatic hydrocarbons (PAHs) in its body. The influence of presence of P. scaber on the total petroleum hydrocarbons (TPH) content in soil was also determined. The following objects were established: control-unpolluted soil; soil polluted with petrol; soil polluted with diesel fuel and soil polluted with used engine oil. Every pollutant was used in the amounts equal to 6000 mg of fuel/kg d.m. of soil 15 months earlier. In the laboratory, survival and body mass change of P. scaber reared in investigated soils were observed. The delivered food was not contaminated with PDSs. P. scaber reveals a considerable resistance in a short (4 weeks) contact with PDSs, evidenced as high survivability (from 68% on the soil polluted with engine oil to 77% on the soil polluted with diesel fuel) and undisturbed increase in body mass (on the level similar to control). It indicates the potential usefulness of this animal as a monitoring organism. No positive correlation was observed between TPH depletion in the soils contaminated with PDSs and P. scaber presence during 4 weeks of the experiment. PAH level in P. scaber bodies was generally very low (with the highest level of anthracene 0.40 μg/g of wet mass-after 4 weeks of rearing on the diesel fuel-contaminated soil), which may confirm the thesis about considerable abilities of isopods for biotransformation of these pollutants and low susceptibility to these xenobiotic penetration through integuments. However, a tendency for accumulation for phenanthrene and anthracene in conditions of soil polluted with diesel fuel was observed respectively 0.07 and 0.21 μg/g of wet mass for phenanthrene and 0.22 and 0.40 μg/g of wet mass for anthracene, observed successively in the 2nd and 4th week of rearing.

Mechanistic insights into the specificity of human cytosolic sulfotransferase 2A1 (hSULT2A1) for hydroxylated polychlorinated biphenyls through the use of fluoro-tagged probes

Determining the relationships between the structures of substrates and inhibitors and their interactions with drug-metabolizing enzymes is of prime importance in predicting the toxic potential of new and legacy xenobiotics. Traditionally, quantitative structure activity relationship (QSAR) studies are performed with many distinct compounds. Based on the chemical properties of the tested compounds, complex relationships can be established so that models can be developed to predict toxicity of novel compounds. In this study, the use of fluorinated analogues as supplemental QSAR compounds was investigated. Substituting fluorine induces changes in electronic and steric properties of the substrate without substantially changing the chemical backbone of the substrate. In vitro assays were performed using purified human cytosolic sulfotransferase hSULT2A1 as a model enzyme. A mono-hydroxylated polychlorinated biphenyl (4-OH PCB 14) and its four possible mono-fluoro analogues were used as test compounds. Remarkable similarities were found between this approach and previously published QSAR studies for hSULT2A1. Both studies implicate the importance of dipole moment and dihedral angle as being important to PCB structure in respect to being substrates for hSULT2A1. We conclude that mono-fluorinated analogues of a target substrate can be a useful tool to study the structure activity relationships for enzyme specificity.

Identification and characterization of oxidative metabolites of 1-chloropyrene

Polycyclic aromatic hydrocarbons (PAHs) and chlorinated PAHs (ClPAHs) are ubiquitous contaminants that bind to the aryl hydrocarbon receptor (AhR) and exhibit mutagenic potential. It is difficult to monitor human exposure levels to ClPAHs because the exposure routes are complicated, and environmental concentrations are not always correlated with the levels of PAHs. Urinary PAH metabolites are useful biomarkers for evaluating PAH exposure, and ClPAH metabolites may therefore contribute to the estimation of ClPAH exposure. One of the most abundant ClPAHs present in the environment is 1-chloropyrene (ClPyr), and urinary ClPyr metabolites have the potential to be good biomarkers to evaluate the level of exposure to ClPAHs. Since the metabolic pathways involving ClPAHs are still undetermined, we investigated the effect of human cytochrome P450 enzymes on ClPyr and identified three oxidative metabolites by liquid chromatography-tandem mass spectrometry and nuclear magnetic resonance. We found that ClPyr was metabolized most efficiently by the P450 1A1 enzyme, followed by the 1B1 and 1A2 enzymes. Similar to ClPyr, these metabolites were shown to have agonist activity for the human AhR. We detected these metabolites when ClPyr reacted with a pooled human liver S9 fraction as well as in human urine samples. These results suggest that the metabolites may be used as biomarkers to evaluate the extent of exposure to ClPAHs.

Are red gourami (Colisa labiosa) low xenobiotic metabolizers? Elucidation of in vivo pharmacokinetics of pyrene as a model substrate

Red gourami (Colisa labiosa) have previously been shown to have low levels of pyrene-metabolizing activity. In this study, other pharmacokinetic factors of pyrene in C. labiosa were compared to those in Japanese medaka (Oryzias latipes). Results indicated that the two species labiosa absorbed pyrene in similar amounts. However, excretion of pyrene metabolites from C. labiosa over an 8-day period was lower than those from O. latipes. These findings show that C. labiosa has low ability to metabolize pyrene and to excrete pyrene and its metabolites from the body, and is therefore considered an accumulator of these chemicals. C. labiosa has unique characteristics with regard to pyrene pharmacokinetics. Knowledge about interspecies differences in pharmacokinetics is crucial in determining the endangered species to xenobiotic exposure.

Characterization of phase-II conjugation reaction of polycyclic aromatic hydrocarbons in fish species: unique pyrene metabolism and species specificity observed in fish species

Metabolic activity, particularly conjugation, was examined in fish by analyzing pyrene (a four-ring, polycyclic aromatic hydrocarbon) metabolites using high-performance liquid chromatography (HPLC) with fluorescence detector (FD), a mass spectrometry (MS) system, and kinetic analysis of conjugation enzymes. Fourteen fresh water fish species, including Danio rerio and Orizias latipes, were exposed to aqueous pyrene, and the resulting metabolites were collected. Identification of pyrene metabolites by HPLC/FD and ion-trap MS indicated that the major metabolites were pyrene glucuronide and pyrene sulfate in all 14 species. Differences were observed in pyrene glucuronide:pyrene sulfate ratio and in the total amount of pyrene conjugates excreted between fish species. Furthermore, a correlation was found between the amount of pyrene glucuronide present and the total amount of the pyrene metabolite eliminated. Kinetic analysis of conjugation by hepatic microsomes in vitro indicated that the differences in excreted metabolites reflected the differences in enzymatic activities.

Challenges in assessing the toxic effects of polycyclic aromatic hydrocarbons to marine organisms: a case study on the acute toxicity of pyrene to the European seabass (Dicentrarchus labrax L.)

The acute toxicity (96 h) of pyrene (PY) to European seabass (Dicentrachus labrax) juveniles assessed in a semi-static bioassay (SSB) with medium renewal at each 12h, and in a static bioassay (SB) without medium renewal was compared in laboratorial conditions (water PY concentrations: 0.07-10 mg L(-1)). Main findings in the SSB that assessed mainly the toxicity of PY and its metabolites were: increased levels of bile PY metabolites in good agreement with the profile of lipid peroxidation levels (LPO) in exposed fish relating PY exposure and oxidative damage; increased levels of PY-type compounds in the brain indicating their ability to cross the blood-brain barrier; increased levels of these substances in liver and muscle which are edible tissues for humans thus raising concern on potential adverse effects on consumers of fish from PY contaminated areas; a significant inhibition of glutathione S-transferase activity suggesting its involvement in PY detoxication as toxicant scavenger; finally, an almost complete impairment of the swimming velocity at all the PY concentrations linking sub-individual to higher population level effects. In the SB, where the overall toxicity of PY, its metabolites and environmental degradation products was evaluated, 19% and 79% of PY decay in test media was found at 12 and 96 h, respectively. In general, the effects were similar to those of SSB but with significant effects being induced at higher PY concentrations indicating that the parental compound is more toxic than its environmental degradation products. The other main differences relatively to the SSB were: increased levels of PY-type substances in the liver suggesting more accumulation in this organ. Therefore, these findings highlight the need of carefully considering experimental design options when assessing the toxicity of readily degradable substances to marine fish, and stress the importance of taking into consideration the toxicity of environmental degradation products in addition to toxic effects of the parental substance and its metabolites for marine ecological risk assessment.

Metabolites of polycyclic aromatic hydrocarbons (PAHs) in bile as biomarkers of pollution in European eel (Anguilla anguilla) from German rivers

In the light of the alarming decline of the European eel (Anguilla anguilla L.) population, there is an urgent need to define ecological indicators for eel habitat quality. Due to an increasing shortage of glass eels available for local stock enhancement, the decision of whether restocking is a valuable management tool to increase high-quality silver eel escapement to the sea needs to be evaluated. Organic contaminants, such as polycyclic aromatic hydrocarbons (PAHs), are among the major threats to fish in their habitat. Therefore, the aim of the investigation presented here was to examine metabolites of PAHs in eel bile as one possible marker for habitat quality. In total, 170 yellow eels were collected in the rivers Rhine, Ems, Weser, Elbe, Havel, Schlei, Eider, Trave, Warnow, Peene, Uecker, and Oder in 2009. PAH metabolites in eel bile were analyzed using high-performance liquid chromatography with fluorescence detection. Metabolites of pyrene and phenanthrene were investigated. Concentrations of PAH metabolites in eel bile varied significantly between several rivers, with the highest mean concentrations of 1-hydroxypyrene and 1-hydroxyphenanthrene in eel bile from the river Trave (2421 and 632 ng/ml). Moreover, huge differences in the ratio of 1-hydroxypyrene to 1-hydroxyphenanthrene, with the highest mean value in eel bile from the river Ems (7.43) and the lowest mean value in eel bile from the river Uecker (0.70), indicate different sources of PAH contamination. A comparative analysis of PAH-metabolite contamination of eels in different river systems is seen as a first step toward a classification of freshwater habitats for restocking purposes.

Phase-II conjugation ability for PAH metabolism in amphibians: characteristics and inter-species differences

The present study examines amphibian metabolic activity - particularly conjugation - by analysis of pyrene (a four ring, polycyclic aromatic hydrocarbon) metabolites using high-performance liquid chromatography (HPLC) with fluorescence detector (FD), a mass spectrometry detector (MS) system and kinetic analysis of conjugation enzymes. Six amphibian species were exposed to pyrene (dissolved in water): African claw frog (Xenopus laevis); Tago's brown frog (Rana tagoi); Montane brown frog (Rana ornativentris); Wrinkled frog (Rana rugosa); Japanese newt (Cynops pyrrhogaster); and Clouded salamander (Hynobius nebulosus); plus one fish species, medaka (Oryzias latipes); and a fresh water snail (Clithon retropictus), and the resultant metabolites were collected. Identification of pyrene metabolites by HPLC and ion-trap MS system indicated that medaka mainly excreted pyrene-1-glucuronide (PYOG), while pyrene-1-sulfate (PYOS) was the main metabolite in all amphibian species. Pyrene metabolites in amphibians were different from those in invertebrate fresh water snails. Inter-species differences were also observed in pyrene metabolism among amphibians. Metabolite analysis showed that frogs relied more strongly on sulfate conjugation than did Japanese newts and clouded salamanders. Furthermore, urodelan amphibians, newts and salamanders, excreted glucose conjugates of pyrene that were not detected in the anuran amphibians. Kinetic analysis of conjugation by hepatic microsomes and cytosols indicated that differences in excreted metabolites reflected differences in enzymatic activities. Furthermore, pyrenediol (PYDOH) glucoside sulfate was detected in the Japanese newt sample. This novel metabolite has not been reported previously to this report, in which we have identified unique characteristics of amphibians in phase II pyrene metabolism.

Bioaccumulation and biotransformation of pyrene and 1-hydroxypyrene by the marine whelk Buccinum undatum

The fates of a phenolic contaminant and its hydrocarbon precursor have rarely been compared, especially in an invertebrate species. Two groups of Buccinum undatum were exposed to equimolar amounts of pyrene and 1-hydroxypyrene over 15 d through their diets. Tissue extracts from the muscle and visceral mass were analyzed by liquid chromatography with fluorescence and mass spectrometry detection. Nine biotransformation products were detected in animals from both exposures. These included 1-hydroxypyrene, pyrene-1-sulfate, pyrene-1-glucuronide, pyrene glucose sulfate, two isomers each of pyrenediol sulfate and pyrenediol disulfate, and one isomer of pyrenediol glucuronide sulfate. These compounds represent a more complex metabolic pathway for pyrene than is typically reported. Diconjugated metabolites were as important in animals exposed to pyrene as in those exposed to 1-hydroxypyrene. Biotransformation products represented >90% of the material detected in the animals and highlight the importance of analyzing metabolites when assessing exposure. A mean of only 2 to 3% of the body burden was present in muscle compared with the visceral mass of both groups. The analytical methods were sufficiently sensitive to detect biotransformation products both in laboratory control whelks and in those sampled offshore. The tissue distribution of [(14)C]pyrene was also studied by autoradiography. Radioactivity was present primarily in the digestive and excretory system of the whelks and not in the gonads or muscle tissue.

A modified parallel artificial membrane permeability assay for evaluating the bioconcentration of highly hydrophobic chemicals in fish

Low cost in vitro tools are needed at the screening stage of assessment of bioaccumulation potential of new and existing chemicals because the number of chemical substances that needs to be tested highly exceeds the capacity of in vivo bioconcentration tests. Thus, the parallel artificial membrane permeability assay (PAMPA) system was modified to predict passive uptake/ elimination rate in fish. To overcome the difficulties associated with low aqueous solubility and high membrane affinity of highly hydrophobic chemicals, we measured the rate of permeation from the donor poly(dimethylsiloxane)(PDMS) disk to the acceptor PDMS disk through aqueous and PDMS membrane boundary layers and term the modified PAMPA system "PDMS-PAMPA". Twenty chemicals were selected for validation of PDMS-PAMPA. The measured permeability is proportional to the passive elimination rate constant in fish and was used to predict the "minimum" in vivo elimination rate constant. The in vivo data were very close to predicted values except for a few polar chemicals and metabolically active chemicals, such as pyrene and benzo[a]pyrene. Thus, PDMS-PAMPA can be an appropriate in vitro system for nonmetabolizable chemicals. Combination with metabolic clearance rates using a battery of metabolic degradation assays would enhance the applicability for metabolizable chemicals.

Humic substances modify accumulation but not biotransformation of pyrene in salmon yolk-sac fry

Humic substances may influence the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in aquatic environment. Relatively little is known how humic substances affect the biotransformation of PAHs in aquatic animals. Here we report how two different types of humic substances affected the accumulation of pyrene, a four-ringed PAH, to yolk-sac fry of landlocked salmon (Salmo salar m. sebago). The accumulation of pyrene to yolk-sac fry tissues was inversely related to humic substance concentration in a short term (72h) exposure. However, the biotransformation of pyrene was not affected by humic substances. Pyrene or humic substances did not induce CYP1A activity in yolk-sac fry tissues contrasting to beta-naphthoflavone, which was used as a positive control. Yolk-sac fry were capable to biotransform pyrene to phase I (1-hydroxypyrene) and phase II (pyrene-1-sulphate) products. Interestingly, glucuronide conjugate (i.e. pyrene-1-glucuronide) was not present in yolk-sac fry tissues. The concentration of parent pyrene and 1-hydroxypyrene remained the same throughout the experiment but the concentration of pyrene-1-sulphate more than doubled from 24 to 72h. This finding suggests that salmon yolk-sac fry are not capable to excrete phase II biotransformation products or the excretion is very slow. Further, this could indicate that early life stage toxicity of many CYP1A inducing compounds is related to accumulation of phase II conjugates in fry tissues.

Characterization of monofluorinated polycyclic aromatic compounds by 1H, 13C and 19F NMR spectroscopy

Monofluorinated polycyclic aromatic hydrocarbons (F-PAHs) have attracted much attention in analytical, environmental, toxicological and mechanistic studies because of their physico-chemical properties, which are closely similar to those of the parent PAHs. Because of this, full NMR characterization has become of interest. Complete 1H, 13C and 19F NMR chemical shifts, and also 1J(H,C), (n)J(C,F), (n)J(H,F) and (n)J(H,H) coupling constants, have been assigned for the F-PAHs 1-fluoronaphthalene, 2-fluorofluorene, 5-fluoroacenaphthylene, 2-fluorophenanthrene, 3-fluorophenanthrene, 3-fluorofluoranthene, 1-fluoropyrene, 1-fluorochrysene, 2-fluorochrysene, 3-fluorochrysene and 9-fluorobenzo[k]fluoranthene. To allow comparison with the corresponding parent PAHs, the 1H and 13C chemical shifts of acenaphthylene, phenanthrene, fluoranthene, pyrene and benzo[k]fluoranthene were determined. Chemical shift increments and the effects on the coupling constants from the fluorine substitution are discussed.

Determination of dioxin and dioxin-like compounds in sediments from UK estuaries using a bio-analytical approach: chemical-activated luciferase expression (CALUX) assay

The DR-CALUX assay has been utilised for the bio-analytical screening of a number of estuarine sediments for dioxin-like activity. Total sediment extracts (samples containing all extracted compounds) and cleaned-up extracts (samples with the most stable compounds isolated from the total extracts) were screened. The concentration of the stable dioxin-like compounds in the cleaned-up sediment extracts was between 1.0 and 106 pgTEQCALUX g(-1) dry weight. The majority of sediments contained levels of dioxin-like compounds that were above concentrations that are considered to be a low risk to aquatic organisms. The CALUX bio-analytical approach showed some disparity with the traditional analytical approach. The reasons for these differences have been identified tentatively: firstly, the DR-CALUX assay responds to all dioxin-like compounds, and secondly, it measures non-additive effects. The dioxin-like activity of compounds in sediment total extracts, which contain both labile and stable compounds, were also assessed and were six orders of magnitude higher than the cleaned-up samples. This suggests the vast majority of the total dioxin-like activity is attributable to labile compounds. Overall, the DR-CALUX assay is shown to be a useful tool in the assessment of dioxin-like activity in estuarine sediments.