Characterization of xenobiotic-metabolizing cytochrome P450 (CYP) forms in ringed and grey seals from the Baltic Sea and reference sites

Hepatic phase I and II biotransformation responses and contaminant exposure in long-finned pilot whales from the Northeastern Atlantic

Faroe Island pilot whales have been documented to have high body burdens of organohalogen contaminants (OHCs), including polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), but low burdens of their respective hydroxylated metabolites (OH-PCBs and OH-PBDEs). The present study investigated the hepatic expression and/or catalytic activities of phase I and II biotransformation enzymes in relation to hepatic concentrations of target OHCs, including OH-PCBs and OH-PBDEs, in long-finned pilot whales (Globicephala melas) from the Northeastern Atlantic. CYP1A, 2B, 2E and 3A protein expressions were identified in juveniles and adult males, but not in adult females. Ethoxyresorufin-O-deethylase (EROD) activity was significantly lower in adult females than in juveniles and adult males. Using multivariate analyses to investigate relationships between biological responses and OHC concentrations, a positive relationship was identified between EROD and OHCs. The activity levels of phase II conjugating enzymes (uridine 5'-diphospho-glucuronosyltransferase [UDPGT], and glutathione S-transferase [GST]) were low. The analyses of mRNA expression did not show correlative relationships with OHC concentrations, but cyp1a and ahr transcripts were positively correlated with EROD activity. We suggest that the low concentrations of OH-PCBs and OH-PBDEs reported in pilot whales is probably due to the identified low phase I biotransformation activities in the species.

Selective transfer of persistent organic pollutants and their metabolites in grey seals during lactation

Twenty grey seal (Halichoerus grypus) mother-pup pairs from the colony of the Isle of May (Scotland) were sampled at early and late lactation in order to study the transfer of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and their metabolites (HO-PCBs and HO-PBDEs) as well as organochlorine pesticides (OCPs), such as DDT and metabolites (DDXs) and hexachlorobenzene (HCB). The transfer of the naturally produced MeO-PBDEs was also investigated. Generally, concentrations (on a lipid weight basis) of the sum of PCBs, PBDEs and DDXs tended to be higher in all tissues at late lactation (for maternal outer blubber ΣPCBs=3860±2091 ng/g, ΣPBDEs=120±74 ng/g and ΣDDXs=559±207 ng/g; for maternal inner blubber ΣPCBs=4229±3274 ng/g, ΣPBDEs=148±118 ng/g and ΣDDXs=704±353 ng/g; for maternal serum ΣPCBs=1271±796 ng/g, ΣPBDEs=27±16 ng/g and ΣDDXs=242±125 ng/g; for milk ΣPCBs=1190±747 ng/g, ΣPBDEs=55±36 ng/g and ΣDDXs=357±160 ng/g; for pup serum ΣPCBs=1451±901 ng/g, ΣPBDEs=48±31 ng/g and ΣDDXs=395±201 ng/g). In all tissues, ΣMeO-PBDEs were found at very low levels or even undetected and their concentrations appeared to increase at late lactation only in maternal inner blubber (2.7±1.3 to 5.3±2.9 ng/g for early and late lactation, respectively) and milk (0.6±0.3 to 1.1±0.5 ng/g for early and late lactation, respectively). The transfer from inner blubber to maternal serum was selective and strongly depended on the log K(ow) value of the compounds, with less lipophilic compounds being more efficiently released. Only a limited amount of HO-PCBs was transferred during lactation as 4-HO-CB-107 was the only metabolite detected in milk (29 to 40 pg/g lw). On the contrary, most of HO-PCB metabolites found in maternal serum were also detected in pup serum. These findings suggest not only a transplacental transfer of HO-PCBs from mothers to pups but also the possibility of endogenous biotransformation in suckling pups or accumulation of undetectable low amounts from milk.

Cytochrome P450 CYP2 genes in the common cormorant: Evolutionary relationships with 130 diapsid CYP2 clan sequences and chemical effects on their expression

Cytochrome P450 CYP2 family enzymes are important in a variety of physiological and toxicological processes. CYP2 genes are highly diverse and orthologous relationships remain clouded among CYP2s in different taxa. Sequence and expression analyses of CYP2 genes in diapsids including birds and reptiles may improve understanding of this CYP family. We sought CYP2 genes in a liver cDNA library of the common cormorant (Phalacrocorax carbo), and in the genomes of other diapsids, chicken (Gallus gallus), zebra finch (Taeniopygia guttata), and anole lizard (Anolis carolinensis), for phylogenetic and/or syntenic analyses. Screening of the cDNA library yielded four CYP2 cDNA clones that were phylogenetically classified as CYP2C45, CYP2J25, CYP2AC1, and CYP2AF1. There are numerous newly identified diapsid CYP2 genes that include genes related to the human CYP2Cs, CYP2D6, CYP2G2P, CYP2J2, CYP2R1, CYP2U1, CYP2W1, CYP2AB1P, and CYP2AC1P. Syntenic relationships show that avian CYP2Hs are orthologous to CYP2C62P in humans, CYP2C23 in rats, and Cyp2c44 in mice, and suggest that avian CYP2Hs, along with human CYP2C62P and mouse Cyp2c44, could be renamed as CYP2C23, based upon the nomenclature rules. Analysis of sequence and synteny identifies cormorant and finch CYPs that are apparent orthologs of phenobarbital-inducible chicken CYP2C45. Transcripts of all four cormorant CYP2 genes were detected in the liver of birds from Lake Biwa, Japan. The transcript levels bore no significant relationship to levels of chlorinated organic pollutants in the liver, including polychlorinated biphenyls and dichlorodiphenyltrichloroethane and its metabolites. In contrast, concentrations of perfluorooctane sulfonate and perfluorononanoic acid were negatively correlated with levels of CYP2C45 and/or CYP2J25, suggesting down-regulation of expression by these environmental pollutants. This study expands our view of the phylogeny and evolution of CYP2s, and provides evolutionary insight into the chemical regulation of CYP2 gene expression in diapsids including birds.

Concentrations, patterns and metabolites of organochlorine pesticides in relation to xenobiotic phase I and II enzyme activities in ringed seals (Phoca hispida) from Svalbard and the Baltic Sea

The present study investigates the concentrations and patterns of organochlorine pesticides (OCPs) and their metabolites in liver and plasma of two ringed seal populations (Phoca hispida): lower contaminated Svalbard population and more contaminated Baltic Sea population. Among OCPs, p,p'-DDE and sum-chlordanes were the highest in concentration. With increasing hepatic contaminant concentrations and activities of xenobiotic-metabolizing enzymes, the concentrations of 3-methylsulfonyl-p,p'-DDE and the concentration ratios of pentachlorophenol/hexachlorobenzene increased, and the toxaphene pattern shifted more towards persistent Parlar-26 and -50 and less towards more biodegradable Parlar-44. Relative concentrations of the chlordane metabolites, oxychlordane and -heptachlorepoxide, to sum-chlordanes were higher in the seals from Svalbard compared to the seals from the Baltic, while the trend was opposite for cis- and trans-nonachlor. The observed differences in the OCP patterns in the seals from the two populations are probably related to the catalytic activity of xenobiotic-metabolizing enzymes, and also to differences in dietary exposure.

Identification and hepatic expression profiles of cytochrome P450 1–4 isozymes in common minke whales (Balaenoptera acutorostrata)

Full-length cDNA sequences of cytochrome P450 (CYP) 2C78, 2E1, 3A72, 4A35 and 4V6 isozymes were isolated from a hepatic cDNA library of common minke whale (Balaenoptera acutorostrata). The deduced amino acid sequences of minke whale CYP2C78, 2E1, 3A72, 4A35 and 4V6 showed high identities with cattle CYP2C86 (83%), pig CYP2E1 (85%), sheep CYP3A24 (82%), pig CYP4A21 (80%), and human CYP4V2 (76%), respectively. To investigate whether or not these CYP expression levels are altered by contamination of organochlorine contaminants (OCs), mRNA levels of these CYPs in the liver of common minke whale were measured using a quantitative real-time RT-PCR method, and the quantified mRNA levels were employed for the statistical analysis with the residue levels of OCs including PCBs, DDTs (p,p'-DDT, p,p'-DDD and p,p'-DDE), chlordanes (cis-chlordane, trans-chlordane, cis-nonachlor, trans-nonachlor and oxychlordane), HCHs (alpha-, beta- and gamma-isomers) and hexachlorobenzene that have already been reported elsewhere. Spearman's rank correlation analyses showed no significant correlation between CYP expression levels and each OC level in the common minke whale liver, implying that these environmental chemicals have no potential to alter the expression levels of these CYPs or the residue levels encountered in the whale livers may not reach their transcriptional regulation levels. This suggests that the expression of individual CYPs in the whale liver may be at basal level. Relationships among hepatic mRNA expression levels of these CYP2-4 isozymes together with CYP1A1 and CYP1A2 were also examined. Significant positive correlations were detected among mRNA expression levels of individual CYP isozymes in most cases. These associations indicate that the transcriptional regulation of these CYPs examined in this study may be reciprocally related. CYP1A1 levels showed a positive correlation with CYP1A2 levels (r=0.64, p<0.01) indicating that both CYP isozymes were regulated by aryl hydrocarbon receptor activated by endogenous ligands. A strong positive correlation between CYP2C78 and 3A72 (r=0.90, p<0.001) suggests that expression of these CYP isozymes may be under a regulation mechanism of cross-talk in which specific nuclear receptors such as constitutive androstane receptor and pregnane X receptor are involved. The present study indicates that minke whale from the North Pacific may be a model species to investigate the mechanism of basal regulation of these CYPs.

Accumulation of dietary organochlorines and vitamins in Baltic seals

We studied the accumulation of polychlorinated biphenyls (PCBs), 1,1,1.trichloro-2,2-bis[p-chlorophenyl]ethane (DDT) and its metabolites, and vitamins A and E in the top levels of the Baltic Sea food web. The investigation focused on the transfer of contaminants and vitamins to the ringed seal (Phoca hispida baltica) and the grey seal (Halichoerus grypus) from their main prey species. The trophic level of the seals was investigated using stable isotopes of nitrogen and the results indicated that both species of Baltic seal feed at approximately the same level. PCBs accumulated to a greater extent in the grey seal than in the ringed seal. Biomagnification factors for DDT compounds were similar for both species of Baltic seal (85-140). Differences in observed DDT levels were due to different prey selection by the two species, while differences in PCB levels indicated a species-specific metabolic system. There was a clearly greater accumulation of DDT compounds than of PCBs in both species of seal. The supply of dietary vitamin A was normally above the recommended level in all the seal populations studied. Low levels of hepatic vitamin A in the Baltic seals could therefore indicate the toxic effects of a high level of persistent organic pollutants on vitamin A dynamics, at least in the ringed seal. In the grey seals, low hepatic vitamin A levels could also be explained by lower levels of dietary vitamin A, compared to the reference grey seals, as it is not known if seals can store unlimited amounts of vitamin A. The greater uptake of vitamin E by Baltic seals, compared to seals in the reference areas, demonstrated by elevated levels of vitamin E in the blubber, could be a response to oxidative stress caused by the high contaminant load. These results further support our previous hypothesis that the toxic effects of environmental contaminants could be causing the observed divergence in vitamin levels between the Baltic seals and the reference seal populations.

Contaminant exposure and effects in Baltic ringed and grey seals as assessed by biomarkers

The Baltic Sea ecosystem has suffered from a heavy pollutant load for more than three decades. Persistent organic pollutants (POPs) and heavy metals have been of most concern due to their persistence and toxic properties. Ringed seals (Phoca hispida baltica) and grey seals (Halichoerus grypus) living in the Baltic Sea have been suffering from pathological impairments, including reproductive disturbances, which have resulted in a depressed reproductive capacity. We investigated several biochemical parameters as potential biomarkers for exposure to and effects of the contaminant load in the Baltic seals. Seals from less polluted areas were used as reference material in terms of the pollution load. In both Baltic seal populations, the levels of some biochemical parameters diverged from those in the reference seals, and some of these showed a clear correlation with the individual contaminant load. Of the potential bioindicators, we propose cytochrome P4501A activity and vitamin E levels, in blubber or plasma, as exposure biomarkers for polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) in both species. The arylhydrocarbon receptor-mediated chemical-activated luciferase gene expression (CALUX) response reflects the whole PCB and DDT burden in ringed seals. Retinyl palmitate (vitamin A) levels showed a negative correlation with the individual POP load, and is proposed as potential effect biomarkers for the depletion of the vitamin A stores. As the nutritional levels of both vitamin A and E have an impact on the vitamin levels in the seals, more information on the dietary vitamin levels is needed before any conclusions can be drawn. As the relationship between biochemical parameters and contaminants varied between the two species, species-specific characteristics has to be considered when monitoring the health status and possible toxic effects of the contaminant load in ringed and grey seals.