Purification and characterization of hepatic steroid hydroxylases from untreated rainbow trout

Structure and Toxicity Characterization of Alkyl Hydroxylated Metabolites of 6PPD-Q

Distinct from other nontoxic phenyl-p-phenylenediamine (PPD) quinones, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q) was recently discovered to be regioselectively metabolized to alkyl hydroxylated metabolites (alkyl-OH-6PPD-Q) in rainbow trout. It remains unknown whether the unique alkyl-OH-6PPD-Q contributes to the toxicity of 6PPD-Q. To test this, we herein synthesized chemical standards of alkyl-OH-6PPD-Q isomers and investigated their metabolic formation mechanism and toxicity. The predominant alkyl-OH-6PPD-Q was confirmed to be hydroxylated on the C4 tertiary carbon (C4-OH-6PPD-Q). The formation of C4-OH-6PPD-Q was only observed in microsomal but not in cytosolic fractions of rainbow trout (O. mykiss) liver S9. A general cytochrome P450 (CYP450) inhibitor fluoxetine inhibited the formation of hydroxylated metabolites of 6PPD-Q, supporting that CYP450 catalyzed the hydroxylation. This well-explained the compound- and regio-selective formation of C4-OH-6PPD-Q, due to the weak C-H bond on the C4 tertiary carbon. Surprisingly, while cytotoxicity was observed for 6PPD-Q and C3-OH-6PPD-Q in a coho salmon (O. kisutch) embryo (CSE-119) cell line, no toxicity was observed for C4-OH-6PPD-Q. To further confirm this under physiologically relevant conditions, we fractionated 6PPD-Q metabolites formed in the liver microsome of rainbow trout. Cytotoxicity was observed for the fraction of 6PPD-Q, but not the fraction of C4-OH-6PPD-Q. In summary, this study highlighted the C4 tertiary carbon as the key moiety for both metabolism and toxicity of 6PPD-Q and confirmed that alkyl hydroxylation is a detoxification pathway for 6PPD-Q.

The detoxification ability of sex-role reversed seahorses determines the sexual dimorphism in immune responses to benzo[a]pyrene exposure

Sexual dimorphism in immune responses is an essential factor in environmental adaptation. However, the mechanisms involved remain obscure owing to the scarcity of data from sex-role-reversed species in stressed conditions. Benzo[a]pyrene (BaP) is one of the most pervasive and carcinogenic organic pollutants in coastal environments. In this study, we evaluated the potential effects on renal immunotoxicity of the sex-role-reversed lined seahorse (Hippocampus erectus) toward environmental concentrations BaP exposure. Our results discovered the presence of different energy-immunity trade-off strategies adopted by female and male seahorses during BaP exposure. BaP induced more severe renal damage in female seahorses in a concentration-dependent manner. BaP biotransformation and detoxification in seahorses resemble those in mammals. Benzo[a]pyrene-7,8-dihydrodiol-9,10-oxide (BPDE) and 9-hydroxybenzo[a]pyrene (9-OH-BaP) formed DNA adducts and disrupted Ca2+ homeostasis may together attribute the renal immunotoxicity. Sexual dimorphisms in detoxification of both BPDE and 9-OH-BaP, and in regulation of Ca2+, autophagy and inflammation, mainly determined the extent of renal damage. Moreover, the mechanism of sex hormones regulated sexual dimorphism in immune responses needs to be further elucidated. Collectively, these findings contribute to the understanding of sexual dimorphism in the immunotoxicity induced by BaP exposure in seahorses, which may attribute to the dramatic decline in the biodiversity of the genus.

Effects of salinity acclimation on the expression and activity of Phase I enzymes (CYP450 and FMOs) in coho salmon (Oncorhynchus kisutch)

Phase I biotransformation enzymes are critically important in the disposition of xenobiotics within biota and are regulated by multiple environmental cues, particularly in anadromous fish species. Given the importance of these enzyme systems in xenobiotic/endogenous chemical bioactivation and detoxification, the current study was designed to better characterize the expression of Phase I biotransformation enzymes in coho salmon (Oncorhynchus kisutch) and the effects of salinity acclimation on those enzymes. Livers, gills, and olfactory tissues were collected from coho salmon (O. kisutch) after they had undergone acclimation from freshwater to various salinity regimes of seawater (8, 16 and 32 g/L). Using immunoblot techniques coupled with testosterone hydroxylase catalytic activities, 4 orthologs of cytochrome P450 (CYP1A, CYP2K1, CYP2M1, and CYP3A27) were measured in each tissue. Also, the expression of 2 transcripts of flavin-containing monooxygenases (FMO A and B) and associated activities were measured. With the exception of CYP1A, which was down-regulated in liver, protein expression of the other 3 enzymes was induced at higher salinity, with the greatest increase observed in CYP2M1 from olfactory tissues. In liver and gills, 6β- and 16β-hydroxylation of testosterone was also significantly increased after hypersaline acclimation. Similarly, FMO A was up-regulated in all 3 tissues in a salinity-dependent pattern, whereas FMO B mRNA was down-regulated. FMO-catalyzed benzydamine N-oxygenase and methyl p-tolyl sulfoxidation were significantly induced in liver and gills by hypersalinity, but was either unchanged or not detected in olfactory tissues. These data demonstrate that environmental conditions may significantly alter the toxicity of environmental chemicals in salmon during freshwater/saltwater acclimation.

Genomic and phenotypic response of hornyhead turbot exposed to municipal wastewater effluents

Laboratory tests with marine flatfish were conducted to investigate associations among gene expression, higher biological responses and wastewater effluent exposure. In the present study, male hornyhead turbot (Pleuronichthys verticalis) were exposed to environmentally realistic (0.5%) and higher (5%) concentrations of chemically enhanced advanced-primary (PL) and full-secondary treated (HTP) effluents from two southern California wastewater treatment plants (WWTP). Hepatic gene expression was examined using a custom low-density microarray. Alterations in gene expression (vs. controls) were observed in fish exposed to both effluent types. Fish exposed to 0.5% PL effluent showed changes in genes involved in the metabolism of xenobiotics, steroids, and lipids, among other processes. Fish exposed to 5% PL effluent showed expression changes in genes involved in carbohydrate metabolism, stress responses, xenobiotic metabolism, and steroid synthesis, among others. Exposure to 5% HTP effluent changed the expression of genes involved in lipid, glutathione and xenobiotic metabolism, as well as immune responses. Although no concentration-dependent patterns of response to effluent exposure were found, significant Spearman correlations were observed between the expression of 22 genes and molecular and/or higher biological responses. These results indicate that microarray gene expression data correspond to higher biological responses and should be incorporated in studies assessing fish health after exposure to complex environmental mixtures.

Effects of exposure to 17α-ethynylestradiol during sexual differentiation on the transcriptome of the African clawed frog (Xenopus laevis)

Exposure to estrogens during the period of sexual differentiation is known to adversely affect the development of testes in African clawed frogs (Xenopus laevis), but little is known about molecular changes that coincide with the development of altered phenotypes. Therefore, the transcriptome-level effects of exposure to 17α-ethynylestradiol (EE2) during sexual differentiation of X. laevis were evaluated by use of Illumina sequencing coupled with RNA-Seq expression analysis. Overall, a number of processes were affected by 17α-ethynylestradiol, including steroid biosynthesis, thyroid hormone signaling and metabolism, testicular development, and spermatogenesis. Some of the altered pathways, such as thyroid hormone signaling and testicular development, could be linked with biological effects on metamorphosis and gonadal phenotypes, respectively, that were observed in frogs that were exposed to 17α-ethynylestradiol throughout metamorphosis and the early postmetamorphic period. Thus, early changes at the transcriptome-level were predictive of pathologies that did not manifest until later in development. To validate the quantitative capacity of RNA-Seq, a subset of transcripts identified to have altered abundances in individuals exposed to 17α-ethynylestradiol was also evaluated by use of quantitative polymerase chain reaction (qPCR). While small sample sizes (n = 3) limited the ability to draw conclusions pertaining to differences in qPCR-derived abundances of transcripts between control and exposed tadpoles, there was a significant relationship (r(2) = 0.78) between fold-changes for RNA-Seq and qPCR.

Steroid catabolism in marine and freshwater fish

Steroids play important roles in regulating many physiological functions in marine and freshwater fish. Levels of active steroid in blood and tissues are determined by the balance between synthetic and catabolic processes. This review examines what is known about pathways of catabolism of steroids, primarily sex steroids, in marine and freshwater fish. Cytochrome P450 (P450) isoforms present in hepatic microsomes catalyze steroid hydroxylation to metabolites with lower or no activity at estrogen or androgen receptors. Important pathways of steroid catabolism to readily excreted metabolites are glucuronidation and sulfonation of hydroxyl groups. Estradiol, testosterone, DHEA and hydroxylated metabolites of these and other steroids readily form glucuronide and sulfate conjugates in those fish species where these pathways have been examined. Little is known, however, of the structure and function of the UDP-glucuronosyltransferase (UGT) and sulfotransferase (SULT) enzymes involved in steroid conjugation in fish. Glucuronide and sulfate conjugates of steroids may be transported into and out of cells by organic anion transporter proteins and multi-drug resistance proteins, and there is growing evidence that these proteins play important roles in steroid conjugate transport and elimination. Induction or inhibition of any of these pathways by environmental chemicals can result in alteration of the natural balance of steroid hormones and could lead to disruption of the endocrine system. Recent studies in this area are presented, with particular focus on phase II (conjugative) pathways.

Does exposure to testosterone significantly alter endogenous metabolism in the marine mussel Mytilus galloprovincialis?

Mussels (Mytilus galloprovincialis) were exposed to different concentrations of testosterone (T: 20, 200 and 2000ng/L) in a semi-static water regime (1-day dosing intervals) for up to 5 days in an attempt to see whether endogenous steroid levels and steroid metabolism were altered by exogenous exposure to testosterone. Whole tissue levels of total testosterone (free+esterified) sharply increased in a concentration-dependent manner, from 2ng/g in controls to 290ng/g in organisms exposed to the highest concentration. In contrast, levels of free testosterone were only significantly elevated at the high-exposure group (5-fold increase with respect to controls). Increased activity of palmitoyl-CoA:testosterone acyltransferase (ATAT) was detected in organisms exposed to the highest concentration of testosterone, while those exposed to low and medium concentrations showed significant alterations in their polyunsaturated fatty acid profiles. The obtained results suggest that esterification of the excess of T with fatty acids might act as a homeostatic mechanism to maintain endogenous levels of free T stable. Interestingly, a decrease in CYP3A-like activity was detected in T-exposed mussels together with a significant decrease in the metabolism of the androgen precursor androstenedione to dihydrotestosterone (5α-DHT). Overall, the work contributes to the better knowledge of androgen metabolism in mussels.

Investigation of EROD, CYP1A immunopositive proteins and SOD in haemocytes of Chamelea gallina and their role in response to B[a]P

CYP1A sub-family represents the main form of cytochrome P450 involved in benzo[a]pyrene (B[a]P) detoxification, but there are no clear evidences about its presence in invertebrates. 7-Ethoxy resorufin O-deethylase (EROD) activity is strictly related to CYP1A presence, at the same time P450-dependent oxidative metabolism leads to reactive oxygen species (ROS) production, thought to be an important mechanism of pollutant-mediated toxicity in aquatic organisms. Superoxide dismutases (SODs), EROD and CYP1A activities and/or expressions were detected in haemocytes of pooled clams (Chamelea gallina) and cell-free haemolymph after 24 h, 7 and 12 days of exposure to 0.5 mg/L of B[a]P. After 24 h, B[a]P content was maximum in whole tissues. A 61 kDa band was recognized in haemocytes and cell-free haemolymph by polyclonal anti-fish CYP1A, while 53.5 and 63.8 kDa CYP1A immunopositive proteins were discriminate without differences of expression. Differently, EROD, MnSOD activity/expression and ECSOD expression decreased in haemocytes and haemolymph. C. gallina immune system presents an interesting response dose/time exposure of B[a]P and the 7 days condition highlights the major effects of xenobiotic action. The identification of basal EROD levels supports the possible presence of the CYP1A, never identified in C. gallina and more specifically never isolated in immune cells, as confirmed by CYP1A-immunopositive proteins identification.

Mechanisms of fenthion activation in rainbow trout (Oncorhynchus mykiss) acclimated to hypersaline environments

Previous studies in rainbow trout have shown that acclimation to hypersaline environments enhances the toxicity to thioether organophosphate and carbamate pesticides. In order to determine the role of biotransformation in this process, the metabolism of the thioether organophosphate biocide, fenthion was evaluated in microsomes from gills, liver and olfactory tissues in rainbow trout (Oncorhynchus mykiss) acclimated to freshwater and 17 per thousand salinity. Hypersalinity acclimation increased the formation of fenoxon and fenoxon sulfoxide from fenthion in liver microsomes from rainbow trout, but not in gills or in olfactory tissues. NADPH-dependent and independent hydrolysis was observed in all tissues, but only NADPH-dependent fenthion cleavage was differentially modulated by hypersalinity in liver (inhibited) and gills (induced). Enantiomers of fenthion sulfoxide (65% and 35% R- and S-fenthion sulfoxide, respectively) were formed in liver and gills. The predominant pathway of fenthion activation in freshwater appears to be initiated through initial formation of fenoxon which may be subsequently converted to the most toxic metabolite fenoxon R-sulfoxide. However, in hypersaline conditions both fenoxon and fenthion sulfoxide formation may precede fenoxon sulfoxide formation. Stereochemical evaluation of sulfoxide formation, cytochrome P450 inhibition studies with ketoconazole and immunoblots indicated that CYP3A27 was primarily involved in the enhancement of fenthion activation in hypersaline-acclimated fish with limited contribution of FMO to initial sulfoxidation.

Purification of CYP2B-like protein from feral leaping mullet (Liza saliens) liver microsomes and its biocatalytic, molecular, and immunological characterization

In this study, CYP2B-immunoreactive protein was purified to electrophoretic homogeneity from the liver microsomes of leaping mullet. The purified cytochrome P450 (CYP) gave a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis having a M(r) of 49,300 Da. Absolute absorption spectrum of the purified CYP showed a maximum at 417 nm and CO-difference spectrum of dithionite-reduced cytochrome P450 gave a peak at 450 nm. The purified CYP was found to be active in N-demethylation of benzphetamine, erythromycin, and ethylmorphine, and O-dealkylation of pentoxyresorufin in the reconstituted system. However, it was unable to catalyze O-dealkylation of ethoxyresorufin, methoxyresorufin, benzyloxyresorufin, and hydroxylation of lauric acid and aniline. The purified CYP showed strong cross-reactivity with anti-sheep lung CYP2B, a homologue of CYP2B4. N-terminal amino acid sequence of the mullet P450 had the highest degree of homology with CYP2Bs among the known CYPs. Spectral, electrophoretic, immunochemical, N-terminal amino acid sequence, and biocatalytic properties of the purified CYP are most similar to those of mammalian cytochrome P4502B. All these data indicate that the purified CYP is certainly 2B-like. In this study, we not only purified biocatalytically active CYP2B-like protein from fish, but also demonstrated detailed functional properties of CYP2B-like protein for the first time.

Ketoconazole, an antifungal imidazole, increases the sensitivity of rainbow trout to 17alpha-ethynylestradiol exposure

This study focuses on effects of two classes of xenobiotics, azole fungicides and xenoestrogens, both of which have been detected in the aquatic environment. We hypothesize that azoles and estrogenic compounds are metabolized by cytochrome P450 (CYP) enzymes, and in particular CYP1A and CYP3A, to more readily excreted metabolites. We exposed rainbow trout (Oncorhynchus mykiss) to two different pharmaceutical representatives of theses two classes, such as the imidazole ketoconazole and the synthetic estrogen analogue, 17alpha-ethynylestradiol (EE(2)). Juvenile rainbow trout were i.p. injected with a single low dose of EE(2) (2.5 microg/kg), alone or in combination with ketoconazole (100mg/kg). Hepatic microsomal CYP1A and CYP3A protein expressions were analyzed in Western blots using polyclonal antibodies (PAb) and enhanced cheminoluminescence. CYP1A activities were analyzed using the ethoxyresorufin-O-deethylase (EROD) assay and CYP3A activities were analyzed using the benzyloxy-4-[trifluoromethyl]-coumarin-O-debenzyloxylase (BFCOD) assay. Plasma vitellogenin (vtg) and sex steroid hormones (i.e. 17beta-estradiol, testosterone and 11-keto-testosterone) were analyzed using commercially available ELISA-kits. The vtg mRNA expression was analyzed using quantitative (Q)-PCR. The dose of EE(2) selected had little or no effect on the estrogen receptor (ER) mediated vtg induction. However, in combination with ketoconazole this threshold-dose of EE(2) resulted in significantly elevated plasma vtg levels, 6 days post injection. Exposure to ketoconazole resulted in up to nine-fold induction of CYP1A after 3 days. However, this nine-fold induction was not reflected on the CYP1A catalytic activity, where exposure to ketoconazole resulted only in a two-fold increase in activity. Ketoconazole increased CYP3A protein levels 1.5-fold and decreased BFCOD activities by 80% at days 3 and 6. Treatment with ketoconazole and EE(2) alone and in combination had no significant effect on sex steroid hormones, compared to vehicle-treated fish. This study demonstrates that exposure to ketoconazole compromises the function of key enzymes involved in metabolic clearance of xenobiotics and steroids, and increases the sensitivity to EE(2) exposure in juvenile rainbow trout.

Characterization of Phase I biotransformation enzymes in coho salmon (Oncorhynchus kisutch)

Wild stocks of Pacific salmon in the Northwestern United States have declined in recent years, and the major factors contributing to these losses include water pollution and loss of habitat. In salmon, sublethal chemical exposures may impact critical behaviors (such as homing, feeding, predator-avoidance) that are important for species survival. Therefore, understanding the potential for these species to biotransform organic compounds within sensitive target tissues such as liver, gills and olfactory region can help estimate or predict their susceptibility to pollutants. In this study, we used real-time quantitative polymerase chain reaction (Q-PCR), Western blotting, and catalytic assays to characterize the expression of Phase I biotransformation enzymes in coho salmon (Oncorhynchus kisutch), a sensitive species in the Pacific Northwest. Gene expression analysis using Q-PCR assays developed for coho genes revealed the presence of the predominant cytochrome P450 mRNAs (CYP1A, CYP2K1, CYP2M1, CYP3A27) in the olfactory rosettes and provided quantitative mRNA expression levels in coho liver and gills. Q-PCR analysis revealed relatively high expression of the major CYP isoforms in the liver and olfactory rosettes, which was generally confirmed by Western blotting. Extrahepatic CYP expression was generally higher in the olfactory rosettes as compared to the gills. Catalytic studies demonstrated functional CYP1A-dependent ethoxyresorufin-O-deethylase, CYP2-dependent pentoxyresorufin-O-dealkylase, CYP2K1-dependent testosterone 16beta-hydroxylase, and CYP3A27-dependent testosterone 6beta-hydroxylase activities in liver, but not at detectable levels in gills. In contrast, flavin-containing monooxygenase (FMO)-dependent thiourea S-oxidase activity was readily observed in the gills and was substantially higher than that observed in liver. Collectively, the results of this study suggest that the olfactory rosettes are important sites of extrahepatic biotransformation in coho salmon, and that tissue specific-differences in Phase I metabolism may lead to contrasting tissue-specific biotransformation capabilities in this species.

Seasonal testosterone UDP-glucuronosyltransferase activity and biliary steroids in Eurasian perch: response to leachate exposure

In previous studies there was evidence of endocrine disruption in fish in waterways contaminated with leachate from a Swedish landfill. Symptoms included fewer sexually mature (SM) female perch (Perca fluviatilis), distinct sores, reduced gonadosomatic index, and decreased plasma androgen levels. Based on previous findings it was hypothesized that the decrease in plasma androgen concentrations could have been caused by increased steroid excretion. Therefore, testosterone UDP-glucuronosyl transferase (UDPGT) activity and biliary steroids were measured in SM and sexually immature (SIM) female perch during one reproductive cycle. UDPGT activity in exposed fish did not differ from reference fish and was similar in both SM and SIM female perch. Since androgen levels in SIM fish usually are much lower than in SM fish, this indicates expression of testosterone UDPGT irrespective of substrate availability. There was no general increase in biliary steroids in exposed female perch. Biliary steroid levels correlated with corresponding plasma steroid levels. In conclusion, the reduced androgen levels in exposed female perch are most likely not caused by increased steroid excretion.

Presence and inducibility by beta-naphthoflavone of CYP1A1, CYP1B1 and phase II enzymes in Trematomus bernacchii, an Antarctic fish

This study investigated some aspects of xenobiotic metabolism in the Nototheniidae Trematomus bernacchii, a key sentinel species for monitoring Antarctic ecosystems. After laboratory exposure to beta-naphthoflavone (betaNF), basal levels and time-course induction of CYP1A, CYP1B and CYP3A were measured as enzymatic activities, immunoreactive protein content and mRNA expression in liver, gills, intestine and heart. Additional analyses in the liver included enzymatic activities of testosterone hydroxylase, (omega)- and (omega-1)-lauric acid hydroxylase and some phase II enzymes related to the AhR battery genes, DT-diaphorase, glutathione S-transferases and UDP-glucuronyl transferases. Responsiveness of hepatic CYP1A1 after exposure to betaNF demonstrated an higher sensitivity of MEROD than EROD activity and long lasting expression of mRNA still induced after 20 days from the treatment. Testosterone metabolism, oxidation of lauric acid and activities of phase II enzymes were not affected by betaNF indicating that their modulation is not mediated by Ah receptor. Induction of CYP1A was more limited in gills and absent in intestine and heart. The first nucleotide sequence for CYP1B1 in an Antarctic fish has been obtained, revealing a homology of 89% and 72% respectively to CYP1B1 of plaice and CYP1B2 of carp. Constitutive expression of CYP1B1 was restricted to gills where it was also induced by betaNF. Obtained results represent an additional contribution to the ecotoxicological characterization of T. bernacchii and further support the use of biomarkers for early detection of chemical pollution in Antarctica.

Expression and characterization of cytochrome P450 2X1 in channel catfish (Ictalurus punctatus)

Previous studies in channel catfish identified a novel cDNA encoding the cytochrome P450 isoform, CYP2X1. To characterize the substrate specificity of CYP2X1, the 57 kDa protein was expressed in Sf9 cells. Microsomes from Sf9 cells transfected with CYP2X1 demonstrated a maximum carbon monoxide-reduced difference spectrum at 450 nm and catalyzed aminopyrine and benzphetamine demethylase activity with catalytic efficiency (Vmax/Km) values of 0.82 pmol/nmol P450/min and 4.39 pmol/nmol P450/min, respectively. However, enzymatic activity was not observed following incubation with p-nitrophenol, benzyloxyresorufin or pentoxyresorufin. Expression of CYP2X1 transcription was significantly elevated in the gills and liver relative to that detected in brain, kidney and heart. In the brain, liver and heart, intraperitoneal injections with clofibric acid, ethanol, pyridine and rifampin failed to alter expression of CYP2X1 mRNA. In kidney, pyridine significantly suppressed the expression of CYP2X1 transcription (p < or = 0.05). These results indicate CYP2X1 displays minimal catalytic activities consistent with other piscine CYP2 isoforms, and unique tissue expression and regulation patterns in juvenile channel catfish.

Exposure to p,p'-DDE or dieldrin during the reproductive season alters hepatic CYP expression in largemouth bass (Micropterus salmoides)

Largemouth bass (LMB) in Central Florida living on sites with high levels of organochlorine pesticides (OCPs) have exhibited poor reproductive success and altered steroid profiles. The mechanism underlying these changes is unknown, however changes in the rate of steroid metabolism could alter steroid homeostasis. Members of the CYP2 and CYP3A families play a significant role in the metabolism of many xenobiotics and endogenous compounds, including sex steroids. Therefore, the goal of this study was to identify members of the CYP2 and CYP3A families in LMB and characterize the effects of OCP exposure on their expression. Full-length clones of two CYP3A isoforms were obtained from LMB liver, CYP3A68 and 3A69, which exhibited significant sequence divergence. Full-length clones for CYP2N14 and CYP2P11 were also obtained from LMB liver. Steady-state mRNA levels of each of these CYPs increased in both sexes between early reproductive phase (December) and peak reproductive phase (March). Expression of CYP3A68 and CYP2P11 was sexually dimorphic during peak reproductive phase with 2-fold higher expression in females and males, respectively. Foodborne exposure to 46 ppm p,p'-DDE or 0.8 ppm dieldrin for 30 days did not have a significant effect on expression of CYPs. However, 4 months exposure to p,p'-DDE induced CYP3A68 and 3A69 expression in both sexes, while dieldrin produced weak induction of CYP3A68 and suppressed CYP3A69 expression in females, but had no effect on males. Neither p,p'-DDE nor dieldrin significantly altered the expression of CYP2P11 or CYP2N14. This work demonstrates that there are significant changes in CYP expression that occur during LMB reproduction which can be modified by exposure to OCPs.

CYP2K6 from zebrafish (Danio rerio): cloning, mapping, developmental/tissue expression, and aflatoxin B1 activation by baculovirus expressed enzyme

A full-length zebrafish (Danio rerio) cytochrome P450 (CYP) 2K6 cDNA, was obtained (GenBank accession No. AF283813) through polymerase chain reaction cloning using degenerated primers based on a consensus CYP2 sequence and the heme-binding domain. This first CYP2K family member cloned from zebrafish had 1861 bp which contained 27 bp of 5'-untranslated region (5'-UTR), an open reading frame (ORF) of 1518 bp, and a 300 bp 3'-UTR with a poly A tail. The deduced 506 amino acid sequence of CYP2K6 had 63%, 62% and 59% identity with rainbow trout CYP2K1, CYP2K4 and CYP2K3, respectively; and 45%, 42%, and 42% identity with rabbit CYP2C1, human CYP2C19 and mouse CYP2C39, respectively. CYP2K6 mapped to 107.49cR on LG3 using the LN54 radiation hybrid panel. Its mRNA was detected at 5 days post-fertilization and in the adult liver and ovary among nine tissues examined. The ORF, including the 27 bp of the 5'-UTR, was cloned into pFastBac donor vector and then transferred into the baculovirus genome (bacmid DNA) in DH10Bac competent cells. The recombinant bacmid DNA was used to infect Spodoptera frugiperda insect cells to express the CYP2K6 protein (Bv-2K6). As its ortholog, rainbow trout Bv-2K1 [Yang, Y.H., Miranda, C.L., Henderson, M.C., Wang-Buhler, J.-L., Buhler, D.R., 2000. Heterologous expression of CYP2K1 and identification of the expressed protein (Bv-2K1) as lauric acid (omega-1)-hydroxylase and aflatoxin B1 exo-epoxidase. Drug Metab. Disp. 28,1279-83.], Bv-2K6 also catalyzed the conversion of aflatoxin B1 (AFB1) to its exo-8,9-epoxide as assessed by the trapping of a glutathione (GSH) adduct in the presence of a specific mouse alpha class glutathione S-transferase. The identity of the AFB1-GSH adduct was verified by liquid chromatography-mass spectrometry (LC-MS) and mass spectrometry-mass spectrometry (MS-MS) analysis. Although rainbow trout Bv-2K1 was capable of oxidizing lauric acid, zebrafish Bv-2K6 protein showed no activity against this substrate.

Effects of nonylphenol on hepatic testosterone metabolism and the expression of acute phase proteins in winter flounder (Pleuronectes americanus): comparison to the effects of Saint John's Wort

4-Nonylphenol (4-NP), a major by-product of alkylphenol ethoxylates, is used in several industries and as a consequence is quite common in rivers, estuaries and other aquatic environments that receive sewage discharges or are near offshore oil platforms. 4-NP is an environmental estrogen that also binds human and rodent Pregnane X-receptor (PXR), the orphan nuclear receptor that controls the expression of several detoxication genes in mammals, including several CYP3A and CYP2B family members. These P450s preferentially hydroxylate testosterone in the 6beta- and 16beta-positions, respectively. In this study, the effects of 4-NP on testosterone metabolism and hepatic CYP3A induction were compared to the effects of St. John's Wort (SJW), a well established mammalian PXR agonist, in winter flounder. Male winter flounder (Pleuronectes americanus) were injected with 100 mg/kg/day 4-NP or 500 mg/kg/day SJW or both (S and N) every 24 h. Forty-eight hours after the initial injections, flounder were euthanized. Western blots and testosterone 6beta-hydroxylation indicated that CYP3A was increased 50% by 4-NP, but was not affected by SJW. Testosterone 16beta-hydroxylase activity was also significantly increased in flounder treated with 4-NP (2.8 x), but not with SJW. This is not consistent with our hypothesis that both SJW and 4-NP would induce CYP3A. Subtractive hybridization was performed between control and 4-NP treated hepatic mRNA samples to isolate differentially expressed genes. Subtractive hybridization indicated that several acute phase proteins were altered by 4-NP. Quantitative real-time PCR (Q-PCR) confirmed 4-NP altered the expression of complement components C8b, cathepsin L, C-type lectin domain, FK506 binding protein 2 precursor (FKBP2) and an EST (expressed sequence tag). SJW and 4-NP treated flounder demonstrated similar induction profiles for the EST, cathepsin L and FKBP2, suggesting that SJW was at a sufficient dose to alter gene expression but not induce P450s. In conclusion, testosterone hydroxylase activity and Western blots indicate that SJW did not activate detoxication pathways in a similar manner to 4-NP.

Cytochrome p450 induction and gonadal status alteration in common carp (Cyprinus carpio) associated with the discharge of dioxin contaminated effluent to the Hikiji River, Kanagawa Prefecture, Japan

Accumulations of polychlorinated dibenzo-p-dioxins, dibenzofurans and coplanar polychlorinated biphenyls were analyzed in common carp (Cyprinus carpio) collected in the Hikiji River, Kanagawa Prefecture, Japan in which dioxin contaminated effluent was released during the period starting from November 1992 to March 2000. Higher levels of 2,3,7,8-tetrachlorinated dibenzo-p-dioxin toxic equivalents were observed in carps collected downstream to the dioxin release site (contaminated site) than the reference site. Modulations of cytochrome p450 (CYP) enzyme in liver, serum estrogen concentration and gonadal somatic index (GSI) were also measured as biomarkers for the contaminants. Total CYP content in livers was markedly higher in male and female carps from the contaminated site relative to the reference site fish. The expression level of the cytochrome p450 1A and Ethoxyresorufin O-deethylase activity were significantly higher in female carps from the contaminated site than from the reference site. A lower level of plasma estrogen was observed in carps from the contaminated site. The GSI in female carps from the contaminated site was smaller than that recorded at the reference site. The present study indicates that dioxins released to the Hikiji River might induce the CYP enzyme and inhibit the reproductive functions in common carps dwelling downstream from the release site.

Cloning, tissue distribution, and functional studies of a new cytochrome P450 3A subfamily member, CYP3A45, from rainbow trout (Oncorhynchus mykiss) intestinal ceca

In trout and mammals, the major extrahepatic expression site for CYP3A forms is in the intestine. A cDNA encoding a new CYP3A subfamily member was isolated from rainbow trout intestinal ceca by reverse transcriptase-polymerase chain reaction (RT-PCR), followed by rapid amplification of cDNA ends (RACE)-PCR. In a set of two primers for PCR, a consensus sequence in the highly conserved regions in 17 CYP3A sequences was used for one primer, and the second primer was designed based on adapter sequence ligated on the 5(') and 3(') cDNA ends. The 3(') and 5(') end nucleotide sequences of RACE-PCR products were used for the priming sites for the full-length cDNA in RT-PCR. The resulting 2615-bp cDNA contained an open reading frame of 1554 bp encoding a 518-amino acid residue protein (M(r)=59057.13, pI=6.15) with 26 amino acid differences from that of the previously cloned rainbow trout CYP3A27. The cDNA was assigned as CYP3A45 by the P450 Nomenclature Committee. The deduced amino acid sequence of rainbow trout CYP3A45 was 94% identical with trout CYP3A27, 72% with killifish CYP3A56, and 71% with both medaka CYP3A40 and killifish CYP3A30 in positional alignment comparisons. Northern blotting by a CYP3A45-specific nucleotide probe showed that the major expression site was the intestinal ceca rather than the liver in both male and female trout. Recombinant baculovirus containing a CYP3A45 cDNA (Bv-3A45) was constructed under polyhedrin promoter of the Autographa californica nuclear polyhedrosis virus and used to express CYP3A45 protein in Spodoptera frugiperda cells. The Western blot showed that the expressed CYP3A45 protein comigrated with purified LMC5 P450 and was recognized by anti-LMC5 polyclonal antibodies. The expressed CYP3A45 showed catalytic activities for the 6 beta-, 2 beta-, and 16 beta-hydroxytestosterones of 1.76, 0.193, and 0.078 nmol/min/nmol CYP3A45, respectively. In summary, a second form of CYP3A with steroid hydroxylase activity, CYP3A45, has been cloned from rainbow trout and the major site of expression was in the intestinal tissues.

Inhibition of cytochrome p450 enzymes by enrofloxacin in the sea bass (Dicentrarchus labrax)

Currently, there are no reports on the effects of enrofloxacin (EF), a fluoroquinolone antibiotic, on the cytochrome p450 enzymes in fish, although its use as antimicrobial agent in aquaculture has been put forward. Therefore, the in vivo and in vitro effects of EF on hepatic p450 enzymes of sea bass, a widespread food-producing fish, have been evaluated. Sea bass pretreated with a single dose of EF (3 mg/kg i.p.) or with three daily doses of EF (1 mg/kg i.p.) markedly depressed the microsomal N-demethylation of aminopyrine, erythromycin, the O-deethylation of 7-ethoxycoumarin, ethoxyresorufin and the 6beta-testosterone hydroxylase. In vitro experiments showed that EF at 10 microM inhibited the above-mentioned activities and, in particular, the erythromycin N-demethylase (ERND) and 6beta-testosterone-hydroxylase, likely dependant on a p450 3A isoform. When the nature of ERND inhibition by EF was specifically studied with sea bass liver microsomes, it was found that EF is a potent mechanism-based inhibitor, with K(i) of 3.7 microM and a K(inact) of 0.045 min(-1). An immunoblot analysis with anti p450 3A27 of trout showed that the p450 3A isoform, constitutively expressed in sea bass, is particularly susceptible to inactivation by EF. In vitro experiments with sea bass microsomes have also demonstrated that EF is oxidative deethylated by the p450 system to ciprofloxacin (CF) and that this compound maintains the ability to inactivate the p450 enzymes. The mechanism by which EF or CF inactivate the p450 enzymes has not been studied but an attack of p450 on the cyclopropan ring, present, both in EF and CF structure, with the formation of electrophilic intermediates (i.e. radicals) has been postulated. In conclusion, the EF seems to be a powerful inhibitor of p450s in the sea bass. Therefore, the clinical use of this antibiotic in aquaculture has to be considered with caution.

Functional properties of a rainbow trout CYP3A27 expressed by recombinant baculovirus in insect cells

Cytochrome p450 3A27 (CYP3A27) is highly expressed in liver and intestine of rainbow trout (Oncorhynchus mykiss). In many animal species, the intestine and liver are responsible for the first-pass metabolism of a wide range of xenobiotics. To help determine its physiological role, the catalytic capabilities of CYP3A27 protein were examined. An open reading frame of CYP3A27 in pFastBac donor plasmid was transferred to the baculovirus genome (bacmid DNA) through Tn7 site-specific transposition in DH10Bac competent cells. The CYP3A27 cDNA was positioned under the control of the polyhedrin promoter of the Autographa californica nuclear polyhedrosis virus. The recombinant baculovirus containing a full-length CYP3A27 cDNA (Bv-3A27) was then transfected into Spodoptera frugiperda (Sf9) insect cells for overexpression of CYP3A27 protein. The expressed CYP3A27 protein (714 pmol/mg total protein) exhibited a maximum CO-reduced spectrum at 450 nm at 72 h postinfection after addition of 1 micro g/ml exogenous hemin. The expressed CYP3A27 protein comigrated with the purified trout LMC5 cytochrome p450 (p450) and was recognized by anti-p450 LMC5 IgG on Western blot analysis. The expressed CYP3A27 protein was reconstituted with human NADPH-cytochrome p450 reductase and cytochrome b(5). The reconstitution system showed catalytic activities for the 6 beta-, 2 beta-, and 16 beta-hydroxylation of testosterone at 1.428, 0.043, 0.034 nmol/min/nmol CYP3A27, respectively, and the dehydrogenation of nifedipine at 50 pmol/min/nmol CYP3A27. The present results demonstrated that the baculovirus system is useful for the production of the functional aquatic CYP3A form and that CYP3A27 has the capability to metabolize steroid hormone as reported for mammalian CYP3A forms.

Status and opportunities for genomics research with rainbow trout

The rainbow trout (Oncorhynchus mykiss) is one of the most widely studied of model fish species. Extensive basic biological information has been collected for this species, which because of their large size relative to other model fish species are particularly suitable for studies requiring ample quantities of specific cells and tissue types. Rainbow trout have been widely utilized for research in carcinogenesis, toxicology, comparative immunology, disease ecology, physiology and nutrition. They are distinctive in having evolved from a relatively recent tetraploid event, resulting in a high incidence of duplicated genes. Natural populations are available and have been well characterized for chromosomal, protein, molecular and quantitative genetic variation. Their ease of culture, and experimental and aquacultural significance has led to the development of clonal lines and the widespread application of transgenic technology to this species. Numerous microsatellites have been isolated and two relatively detailed genetic maps have been developed. Extensive sequencing of expressed sequence tags has begun and four BAC libraries have been developed. The development and analysis of additional genomic sequence data will provide distinctive opportunities to address problems in areas such as evolution of the immune system and duplicate genes.

Immunohistochemical localization and differential expression of cytochrome P450 3A27 in the gastrointestinal tract of rainbow trout

In mammals the cytochrome P450 3A (CYP3A) subfamily isoforms are primarily expressed in liver and intestines with lesser amounts found in other tissues. The aim of this study was to examine the cellular localization and the expression pattern of CYP3A27 in the gastrointestinal tract (GI tract) of a freshwater teleost species, the rainbow trout (Oncorhynchus mykiss), a fish model used extensively for toxicological and carcinogenesis research. Using an avidin biotinylated enzyme complex and 3,3'-diaminobenzidine staining, strong cytoplasmic immunohistochemical staining was observed for CYP3A27 protein in hepatocytes and in enterocytes of the intestinal ceca and the proximal descending intestine when probed with a polyclonal antibody raised against rainbow trout P450 LMC5, a CYP3A protein. The intensity of epithelial staining decreased distally along the GI tract with faint staining observed in the epithelial cells examined near the vent. Western blot analysis was supportive of the immunohistochemistry results. Northern blot analysis also demonstrated that CYP3A27 mRNA was expressed along the entire GI tract. The major area of CYP3A27 mRNA expression was in the intestinal ceca, followed by the proximal descending intestine, at levels that were about three- to five-fold and two- to four-fold, respectively, greater than seen in the liver of the fish studied. Monooxygenase activities of intestinal ceca microsomes against testosterone and progesterone confirmed the presence of active CYP3A enzyme in this tissue. These results suggest that the intestine of rainbow trout may possesses substantial capacity for first-pass metabolism of xenobiotics by CYP3A27, which makes it an excellent model in which to study the consequence of such metabolism.

Fish as model in pharmacological and biological research

Fish represent the oldest and most diverse classes of vertebrates, comprising around the 48% of the known member species in the subphylum Vertebrata. There are many scientific fields that use fish as models in research, including respiratory and cardiovascular research, cell culture, ecotoxicology, ageing, pharmacological and genetic studies.

Effects of beta-naphthoflavone on the cytochrome P450 system, and phase II enzymes in gilthead seabream (Sparus aurata)

The effect of beta-naphthoflavone (beta-NF) on several catalytic activities of cytochrome P450 (CYP) and phase II enzymes putatively controlled by [Ah]-receptor activation in the liver, heart and kidney of gilthead seabream, was investigated. In the liver, beta-NF treatment [intraperitoneal injection (i.p.) 50 mg/kg] resulted in an increase of CYP content, immunoreactive CYP 1A and methoxyresorufin-O-demethylase (MEROD), pentoxyresorufin O-depentylase (PROD) and ethoxyresorufin-O-deethylase (EROD) activities. However, beta-NF had no effect on any of the hepatic phase II enzymes examined (benzaldehyde dehydrogenase, propionaldehyde dehydrogenase, glutathione S-transferase, UDP-glucuronyl-transferase, DT-diaphorase). Single i.p. injection of 10 mg/kg beta-NF showed a maximal induction of CYP 1A-like protein and EROD activity after 3-7 days. CYP 1A and EROD returned to control levels 18-days post-treatment. beta-NF injection also caused a rapid increase of a single band size of mRNA recognized by a CYP 1A1 cDNA fragment from sea bass (Dicentrarchus labrax). Expression of mRNA preceded the increase of EROD activity and declined rapidly by 96 h. Dose-response experiments demonstrated that EROD was significantly enhanced in liver by a single injection of 0.3 mg/kg beta-NF and was the most sensitive measurement for CYP 1A-like induction. beta-NF treatments also increased the expression of CYP 1A-like protein, mRNA and EROD, but not MEROD and PROD activities in heart and kidney.

Effects of prochloraz and nonylphenol diethoxylate on hepatic biotransformation enzymes in trout: a comparative in vitro/in vivo-assessment using cultured hepatocytes

The suitability of cultured rainbow trout hepatocytes as a model system for the assessment of xenobiotic effects on hepatic biotransformation enzymes in fish was examined. Two model water pollutants, the imidazole fungicide prochloraz and the alkylphenolic compound nonylphenol diethoxylate (NP2EO), were investigated in a comparative in vitro/in vivo approach. Biotransformation enzymes were measured in cultured rainbow trout hepatocytes following exposure to xenobiotics in vitro, or in the liver of juvenile rainbow trout (Oncorhynchus mykiss) exposed in vivo. The patterns of biochemical responses to the model pollutants were generally similar between in vitro and in vivo investigations. Levels of cytochrome P4501A (CYP1A) protein and the catalytic activity of the CYP1A-dependent enzyme 7-ethoxyresorufin-O-deethylase (EROD) were induced in vitro after 24 h of exposure to 1.0 microM prochloraz. In vitro, higher prochloraz concentrations induced only the levels of CYP1A above control levels, but not EROD activity. In vivo exposure of juvenile trout to 0.27 microM prochloraz resulted in an induction of CYP1A and EROD after 7 and 14 days, while 0.027 microM prochloraz had no effects. In vitro, the 6beta- and 16beta-hydroxylation of testosterone was significantly decreased by 1.0-3.0 microM prochloraz, while in vivo these variables were significantly inhibited after exposure to 0.27 microM prochloraz for 7 and 14 days. NP2EO did not affect EROD activity in vitro. In vivo, EROD activity and CYP1A remained unchanged following 7 days of exposure to 0.32 or 1.30 microM NP2EO. NP2EO (15-50 microM) inhibited the 16beta-hydroxylation and glucuronidation of testosterone in vitro. In vivo, 7 days of exposure to 0.32 or 1.30 microM NP2EO resulted in a significant inhibition of the 6beta- and 16beta-hydroxylation of testosterone. The good qualitative correspondence between in vitro and in vivo results indicates that studies using trout hepatocytes allow the identification of biochemical targets of xenobiotic effects in fish liver. However, more research is needed before quantitative predictions, e.g. of effective concentrations, can be made from in vitro investigations.

Biological functions of trout pavement-like gill cells in primary culture on solid support: pH(i) regulation, cell volume regulation and xenobiotic biotransformation

This review presents results obtained on rainbow trout gill cells in primary culture on solid support. Ultrastructural analysis showed that cultured gill cells displayed features of pavement cells in situ. Several biological functions have been investigated on these cultured cells. First, it was shown that their intracellular pH at rest and after acidosis is regulated by a Na+/H+ exchanger. Second, gill cells in primary culture can regulate their volume after a cell swelling. Intracellular calcium appears to be involved in this regulation. The effects of different xenobiotics on the capacity of gill cells to regulate their volume are presented. Third, cultured pavement cells contain biotransformation enzymes to metabolize xenobiotics. All these results demonstrate that gill cells in primary culture on solid support represent a promising in vitro model for the study of pavement cells physiology. In conclusion, applications of this culture are discussed and compared with the permeable filter method, together with the limitations and prospects of this in vitro model on solid support.

Effects of 17beta-estradiol and testosterone on hepatic mRNA/protein levels and catalytic activities of CYP2M1, CYP2K1, and CYP3A27 in rainbow trout (Oncorhynchus mykiss)

There is growing concern that exposure to chemicals in the environment can disrupt the endocrine systems of wildlife and humans, causing reproductive problems or other adverse effects. The expression of many cytochrome P450s (CYPs) is under hormonal control, hence, levels of these enzymes can be affected by exposure to endocrine-disrupting chemicals. Previous research has reported that treatment of fish and other animals with the estrogenic and androgenic hormones 17beta-estradiol (E2) and testosterone (T) alters the P450 content or enzyme activities in the treated animals. However, the results of many of these studies are either incomplete or in disagreement and in most cases the effect on specific P450 forms has not been determined. Therefore, to better understand the effects of gonadal hormones on the expression of P450s and their associated enzyme activities, it was of interest to undertake a comprehensive investigation of the transcriptional and translational expression of three constitutive hepatic P450s in the rainbow trout (Oncorhynchus mykiss) following hormone exposure. Accordingly, juvenile trout were injected intraperitoneally with propylene glycol vehicle and the most active estrogenic and androgenic hormones E2 (3 mg/kg) or T (3 mg/kg) on days 1, 4, 7, 13, and 15 and euthanized on day 19. After treatment with E2, hepatic microsomes showed significantly lower levels (percentage of control) in total P450 contents (52%), lauric acid hydroxylase (32%), and 6beta-progesterone hydroxylase activities (27%), [(3)H]aflatoxin-DNA binding (31%), and the protein levels of individual cytochrome P450s (CYPs) LMC1 (CYP2M1), LMC2, (CYP2K1), and LMC5 (CYP3A27) (average for three isoforms a reduction to 29% of control values) with only minor differences between sexes. Treatment with T had either no effect or resulted in small increases in total P450 in males (42%), in lauric acid hydroxylase in females (24%), and in 6beta-progesterone hydroxylase activity in males (21%). Biological variabilities among fish were high and a polymorphic or new LMC2-like form was detected at about 52 kDa in some liver microsomal samples after exposure of fish to either hormone. Female liver RNAs were analyzed through Northern blots and an average decrease of 94% in CYP2 M1, CYP2K1, and CYP3A27 mRNA levels occurred in the E2-treated trout. In livers from T-treated trout, the changes of mRNA levels of CYP2M1 and CYP3A27 were negligible, but CYP2K1 mRNA level decreased by about 60%. Additional CYP2K1 cDNA hybridizable mRNAs were seen in some fish as faint bands at about 2.8 kb for both hormone treatments. Results of this study, therefore, indicated that E2 down-regulated while T produced small but variable effects on the hepatic mRNA/protein levels of CYP2K1, CYP2M1, and CYP3A27 in juvenile rainbow trout. This study, therefore, suggests that exposure of fish and other wildlife to environmental endocrine disruptors, especially estrogen mimics, can adversely affect a number of physiological processes through mechanisms involving altered levels of expression of specific P450 isozymes.

Effect of the dietary brominated phenol, lanasol, on chemical biotransformation enzymes in the gumboot chiton Cryptochiton stelleri (Middendorf, 1846)

The effects of diet and other non-anthropogenic stressors on biochemical defenses and their relationship to susceptibility have been largely ignored in wildlife populations. Lanosol is a compound found in relatively high amounts in various marine species of Rhodophyta, including Odonthalia dentata. While previous studies demonstrated that lanosol is a feeding deterrent to several marine herbivores, Cryptochiton stelleri readily feeds upon O. dentata. To examine the effects of lanosol on the profile of biochemical defenses in C. stelleri, chitons were gavaged daily with 0, 1, 2.5, 5, or 10 mg/kg of lanosol. After three days of exposure, digestive gland microsomes were probed for expression of homologous isoforms of cytochromes P450 (CYP1A, CYP3A, and CYP2) and phase II enzymatic activities. Expression of a 43 kDa CYP3A-like protein was increased by approximately 45%, over control following 2.5, 5, and 10 mg/kg treatments. Estradiol hydroxylase activity tended to increase with the dose of lanosol. UDP-glucuronosyl transferase activity was highly variable but appeared to increase at the two highest treatments, while sulfotranserase activity was significantly decreased at the three highest doses. Kinetic studies of GST activity showed lanosol is a non-competitive inhibitor of both CDNB and GSH in the GST-mediated conjugation reaction. These results show that dietary exposure to the brominated-phenol, lanosol, may alter expression and activity of some phase I and II biotransformation enzymes in chitons, potentially providing a dietary advantage for the species.

Identification and characterization of a cDNA encoding cytochrome P450 3A from the fresh water teleost medaka (Oryzias latipes)

A new member of the CYP3A gene family has been cloned from the teleost fish medaka (Oryzias latipes) by reverse-transcriptase polymerase chain reaction (RT-PCR). Degenerate primers homologous to highly conserved regions of known CYP3A sequences were used for initial RT-PCRs. Individual PCR products were cloned, sequenced, and identified as those belonging to the cytochrome P450 superfamily based on amino acid sequence similarity and the presence of the highly conserved heme-binding region. PCR products were subsequently used as probes to screen a complementary DNA library. A full-length cDNA clone was identified containing a 1758-base-pair (bp) insert with an open reading frame encoding a single peptide of 500 amino acids. Comparisons of the deduced amino acid sequence to other known cytochrome P450 sequences indicate that this gene product is most similar to the CYP3A gene family and has been designated as CYP3A38 by the cytochrome P450 nomenclature committee. Northern blot analysis identified two abundant CYP3A related transcripts in liver of both male and female adults and demonstrated quantitative differences in abundance according to gender. Similarly, Western blot analysis demonstrated the presence of two abundant cytochrome P450 related proteins in liver of both male and female adults. These results suggests that O. latipes contains multiple forms of CYP3A. Heterologous expression of CYP3A38 cDNA in HEK 293 cells produced a single protein that was reactive with anti-scup P450A (CYP3A) polyclonal antibody. Microsomes of HEK 293 cells expressing recombinant CYP3A38 protein actively catalyzed the hydroxylation of testosterone.

Xenobiotic and steroid biotransformation activities in rainbow trout gill epithelial cells in culture

The biotransformation of xenobiotics and steroids was investigated in cultured respiratory epithelial cells from rainbow trout (Oncorhynchus mykiss) gills. As a first approach, ethoxyresorufin-O-deethylase (EROD), chosen as a marker of CYP1A activity, was measured in monolayers of adherent cells. The induction of this enzyme was studied in cells exposed to beta-naphthoflavone (BNF) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in concentrations ranging from 10(-6) to 10(-12) M. After 24 h, TCDD showed a maximal induction at a concentration of 10(-9) M while BNF showed a maximal induction at a concentration of 10(-7) M. Concurrently, a variety of substrates involved in cytochrome P450-dependent metabolism as well as phase II reactions, namely ethoxycoumarin, aniline and testosterone were incubated with cultured gill cells for 2 or 8 h and with freshly isolated hepatocytes for comparison. Our results revealed a significant cytochrome P450-dependent activity in gill cells with ethoxycoumarin and aniline, but no hydroxylation was observed with testosterone as substrate. No trace of sulfate conjugate was detected. With 2.5 µM aniline as substrate, 2-hydroxyaniline accounted for 32.1% of the radioactivity after 2 h incubation whereas acetanilide amounted to 6.4%. Significant differences were found between gill cells and isolated hepatocytes in the capacity of these systems to conduct oxidative and conjugating metabolic pathways. Qualitatively, the main difference was observed for testosterone which is hydroxylated in position 6beta and 16beta and conjugated to glucuronic acid in liver cells, whereas reductive biotransformation giving rise to dihydrotestosterone and androstanediol and traces of androstenedione were observed in gill cells. Quantitatively, the biotransformation activity in gill epithelial cells, expressed as pmol/h per mg protein, was between 1.5 and 14% of the activity level observed in isolated hepatocytes, depending on the substrate.

Immunochemical analysis of liver microsomal cytochromes P450 of the American alligator, Alligator mississippiensis

Ten antibodies raised against various mammalian and fish cytochromes P450 (CYP) enzymes were used to probe the effects of xenobiotic pretreatment on liver microsomes of the American alligator, Alligator mississippiensis. Pretreatment with phenobarbital (PB), 3-methylcholanthrene (3MC), and PB plus 3MC elicited significant induction of multiple CYP enzymes in alligator, as detected by antibodies to CYP1A, CYP2B, CYP2C, CYP2E, CYP2K, and CYP3A. In contrast to the rat, 3MC treatment induced alligator liver microsomes that were immunoreactive with antibodies to CYP2 family enzymes. Induction of CYP enzymes was not as apparent with the Aroclor 1254 (ARO), and 2,2',4,4' tetrachlorobiphenyl (TCB) pretreatment used; fewer CYP enzymes primarily detected with antibodies against CYP2C or CYP2E were observed. Clofibrate (CLO; 80 mg/kg Days 1-4), markedly induced CYP4A in rat but this induction was not apparent in alligator. A purified PB-induced alligator liver microsomal CYP enzyme cross-reacted with several antibodies raised against CYP2 family enzymes but did not cross-react with antibodies raised against other CYP families. This indicates the PB-inducible CYP in alligator shares some epitope homology with several CYP2-family enzymes from other animals. These experiments demonstrate the usefulness and limitations of using antibodies across phylogenetic classes. While indicating the presence of CYP enzymes that have epitope homology with CYP1A, CYP2, CYP3 and CYP4 enzymes in alligator, it remains to be established whether these CYP forms are alligator orthologues of mammalian enzymes. In all cases, the relative abundance of alligator liver microsomal CYP as determined by immunoblot analysis appeared lower than found in rat. The presence and induction of CYP indicated by immunochemical analysis, corroborated previously reported enzymatic studies of the same microsomal preparations (Ertl et al., 1998a). Thus, increases in CYP protein by the various inducers employed were paralled by the increases in CYP enzyme-specific or selective activities, e.g., induction of CYP1A protein corresponded with induction of EROD.

Immunochemical approaches to studies of CYP1A localization and induction by xenobiotics in fish

There is an increasing understanding that polynuclear aromatic hydrocarbons (PAHs) and organochlorine compounds (like polychlorinated biphenyls (PCBs), certain pesticides and dioxins) in the aquatic environment may lead to physiological and pathological effects such as immunological disturbances, effects on reproduction and development, and even neoplasms. Exposure to pollutants may have consequences at all levels in the biological organization, from the cellular level over effects on the individual organism, population, to the entire ecosystem. The cytochrome P450 system (CYP or P450) has an essential function in the biotransformation of endogenous and exogenous compounds. The fact that many different environmental pollutants induce de novo synthesis of cytochrome P450 1A (CYP1A) proteins in fish, gives these enzymes an interesting position in aquatic toxicology. Many investigations concerning the CYP1A system in fish have been performed over the last two decades, demonstrating its usefulness as a biomarker for aquatic pollution. A general overview of the biochemical and toxicological aspects concerning the cytochrome P450 system will be given here, followed by a more detailed description of CYP1A induction responses in fish. Ecotoxicological consequences of CYP1A induction and the use of immunochemical techniques for CYP1A detection as a biomarker in environmental monitoring will be discussed.

Tissue-specific induction and inactivation of cytochrome P450 catalysing lauric acid hydroxylation in the sea bass, Dicentrarchus labrax

Microsomal cytochrome P450-dependent lauric acid hydroxylase activities were characterized in liver, kidney, and intestinal mucosa of the sea bass (Dicentrarchus labrax). Microsomes from these organs generated (omega-1)-hydroxylauric acid and a mixture of positional isomers including (omega)-, (omega-2)-, (omega-3)- and (omega-4)-hydroxylauric acids, which were identified by RP-HPLC and GC-MS analysis. Peroxisome proliferators, such as clofibrate and especially di(2-ethylhexyl) phthalate, increased kidney microsomal lauric acid hydroxylase activities. The synthesis of 11-hydroxylauric acid was enhanced 5.3-fold in kidney microsomes. Liver microsomal lauric acid hydroxylase activities were weakly affected and no significant induction was found in small intestine microsomes from clofibrate or di(2-ethylhexyl) phthalate-treated fish. The differences in lauric acid metabolisation and the tissue-specific induction by peroxisome proliferators suggest the involvement of several P450s in this reaction. Incubations of liver and kidney microsomes with lauric acid analogues (11- or 10-dodecynoic acids) resulted in a time- and concentration-dependent loss of lauric acid hydroxylase activities. The induction of these activities in fish by phthalates, which are widely-distributed environmental pollutants, may be taken into consideration for the development of new biomarkers.

Cloning, sequencing, and tissue expression of CYP3A27, a new member of the CYP3A subfamily from embryonic and adult rainbow trout livers

Screening of lambdagt11 and lambdagt22A cDNA libraries of livers from adult females and embryos of rainbow trout (Oncorhynchus mykiss), respectively, using rabbit anti-rainbow trout cytochrome P450 LMC5 polyclonal antibodies showed that there were identical cDNAs of 1802-bp nucleotides with open reading frames coding for proteins containing 518 amino acids (59,206 Da, pI = 6.39). The cDNA was assigned CYP3A27 by the P450 Nomenclature Committee to represent the first CYP3A subfamily member reported for aquatic species. The deduced N-terminal sequence of CYP3A27 was in agreement with 8 of the first 12 confirmed amino acid residues from Edman degradation of LMC5, a P450 previously isolated from juvenile trout liver. In similarity comparisons between species by positional alignment, the deduced amino acid sequence of rainbow trout CYP3A27 was 56.4% identical with dog CYP3A12, 56.0% with monkey CYP3A8, 54.9% with human CYP3A4, 54.7% with rat CYP3A9, and 54.2% with sheep CYP3A24. Marked differences in sex, age, and tissue expression of CYP3A27 in rainbow trout were observed at the mRNA level as shown by Northern blots. The major extrahepatic expression site for CYP3A27 was upper small intestine. Females expressed considerably more CYP3A27 mRNA than male in the fish examined. Southern blot analysis of restriction enzyme-digested rainbow trout genomic DNA demonstrated that multiple CYP3A27-related genes exist in rainbow trout.

Cytochrome P450-dependent metabolic pathways and glucuronidation in trout liver slices

We investigated the capacity of trout precision-cut liver slices to metabolize xenobiotics and steroids. As a first approach, liver slices were compared with freshly isolated trout hepatocytes, using 7-ethoxycoumarin (7-EC) and testosterone as substrates. Trout liver slices and freshly isolated hepatocytes had a similar capacity for conducting cytochrome P450-dependent metabolism, as indicated by the rate of oxidative metabolism of 7-EC and testosterone, and by the metabolic profile of these substrates. A lower rate of glucuronidation in slices compared with hepatocytes was observed with testosterone (50 microM), whereas the opposite situation occurred with 7-EC used at higher concentration (100 microM). In a second step, we investigated the effect of beta-naphthoflavone on 7-EC and testosterone biotransformation, using slices maintained in culture for 24 h, with or without the inducer added. The results were compared with the metabolic rates of these substrates incubated with liver slices originating from trout pretreated in vivo with beta-naphthoflavone. Cytochrome P450-mediated rates of 7-EC dealkylation and testosterone hydroxylation decreased to 38 and 55% of the control value, respectively, when incubations were performed in 24-h cultured slices instead of freshly cut slices. Exposure of the slices to 50 microM beta-naphthoflavone resulted in about 3 times higher deethylation rate of 7-EC. A similar value was obtained when treatment occurred in vivo. As demonstrated in rat by several authors, liver slices seem a useful and simple tool for studying the metabolic pathways of xenobiotics and steroids and for the assessment of inducers of the CYP1A1 family.

Immunochemical characterization of hepatic cytochrome P450 isozymes in the channel catfish: assessment of sexual, developmental and treatment-related effects

The profiles of immunoreactive proteins recognized by antibodies raised against purified trout P-450 isoforms (CYP1A1, CYP2M1 and CYP2K1) were examined in channel catfish liver by Western blot analysis. Gender differences in basal expression of these isoforms, as well as responses to known inducers of mammalian isoforms (ethanol, beta-naphthoflavone and clofibric acid) and early life stage (3 and 6 months) profiles are described. Two similar protein bands were detected by Western blotting in mature untreated catfish with CYP2K1 and CYP2M1 antibodies. A third band is detected by anti-2K1 in fish treated with beta-naphthoflavone; this band was verified as CYP1A, with about twice the level of expression in males versus females. No difference between sexes was seen in the expression of the 51-kDa CYP2-reactive bands; however, a significant difference (female > male) was seen in the lower molecular weight CYP2 band (47-kDa). Ethanol treatment caused a dose-dependent decrease in the 47-kDa CYP2-reactive isoforms but no change in the 51-kDa band. Clofibric acid treatment caused an increase in both the 51-kDa CYP2 protein as well as in liver somatic index. Age-dependent changes in isoform expression were also detected in CYP2-reactive forms, with a novel protein (53-kDa) detected in 3-month-old fish. The results from this study provide insight into the regulation of constitutive catfish CYP isoforms and prepares a foundation for further examination of the biotransformation capabilities of an important aquatic species.

Rainbow trout cytochrome P450s: purification, molecular aspects, metabolic activity, induction and role in environmental monitoring

Cytochromes P450 (P450s or CYPs) constitute a superfamily of heme-thiolate proteins that play important roles in oxidative metabolism of endogenous and exogenous compounds. This review provides some limited history but addresses mainly the research progress on the cytochrome P450s in rainbow trout (Oncorhynchus mykiss), their purification, structures at the primary level, role in metabolism, responses to chemicals and environmental pollutants, application to biomonitoring and the effect of various factors on their expression or activities. Information obtained to date suggests that the rainbow trout P450 systems are as complex as those seen in mammals. Fourteen P450s have been purified from liver or trunk kidney to relatively high specific content. cDNAs belonging to seven different P450 families have been documented from trout liver, kidney and ovary. Two CYP1A genes, nine cDNAs containing open reading frames, and a cDNA fragment were entered into GenBank. Among them, CYP2K1, CYP2K3, CYP2K4, CYP2M1, CYP3A27 and CYP4T1 are the most recently described forms. CYP2K1, CYP2M1 and CYP4T1 represent newly identified P450 subfamilies first described in the rainbow trout. In many cases, the cloned rainbow trout P450s have subsequently been expressed in heterologous expressions systems such as COS-7 cells, yeast and baculovirus infected insect cells. Some of the overexpressed P450 isoforms have been partially characterized. Potential future research directions are discussed.

Induction of lauric acid hydroxylase activity in catfish and bluegill by peroxisome proliferating agents

In mammals, sensitivity to peroxisome proliferation by peroxisome proliferating agents (PPAs) appears to be correlated with inducibility of lauric acid hydroxylase activity. Bluegill and catfish have been shown to respond to PPAs by induction of lauric acid hydroxylase immunoreactive proteins (Haasch, 1996). In this investigation, induction of lauric acid hydroxylase activity was confirmed by HPLC and mass spectral analysis of specific hydroxylation products and possible species-specific differences in metabolism were investigated. Male bluegill, channel catfish and rat, were administered the model PPAs, clofibrate (200 mg kg-1, i.p.), ciprofibrate (100 mg kg-1, i.p.), or olive oil as vehicle control (both sexes of catfish), 48 h prior to hepatic, trunk kidney (catfish only) or kidney (rat) microsome preparation. In general, total metabolism of lauric acid was similar in all species, but female catfish metabolize lauric acid to a greater extent than males. Ciprofibrate treatment produced significant induction of omega- and omega-6 hydroxylation in male catfish kidney. In male bluegill liver, omega-, omega-4 and omega-5 hydroxylations were significantly induced by clofibrate treatment. The data indicate that induction of lauric acid hydroxylase cytochrome(s) P450 occurs in PPA-exposed fish which may be a consideration for environmentally-exposed responsive species.

Biochemical markers for differentiation of exposures to nonplanar polychlorinated biphenyls, organochlorine pesticides, or 2,3,7, 8-tetrachlorodibenzo-p-dioxin in trout liver

The effects of a single intraperitoneal dose of the prototypical contaminant nonplanar 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153, 50 mg/kg), p,p'-DDE (50 mg/kg), or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, 200 ng/kg) on the activities of hepatic detoxification enzymes were examined in the liver of immature rainbow trout (Oncorhynchus mykiss). Different modulations of the tested xenobiotics on microsomal cytochrome P450-dependent testosterone hydroxylase activities were found: PCB 153 specifically induced 16beta-hydroxylase activity, whereas p,p'-DDE decreased cytochrome P4503A-dependent 6beta-hydroxylation as well as 16alpha- and 2alpha-hydroxylation. TCDD did not modulate testosterone hydroxylase activities, but a strong induction of cytochrome P4501A activity was observed after TCDD administration; hence, cytochrome P4501A is not involved in the hydroxylation of testosterone. Trout hepatic microsomal glutathione S-transferase (GST) activity, enhanced by all the xenobiotics tested, was found to be a sensitive nonspecific biochemical marker of oxidative stress; cytosolic glutathione reductase was a less sensitive indicator of oxidative stress and was induced significantly only by treatment with p,p'-DDE. Cytosolic GST activity toward ethacrynic acid (GST-ETHA) was induced by PCB 153 or p,p'-DDE, but not by TCDD. Modulations of hepatic microsomal testosterone hydroxylase activities and induction of GST-ETHA appeared to be suitable biochemical markers of acute exposure to nonplanar PCBs and organochlorines that do not induce cytochrome P4501A enzymes in rainbow trout, whereas microsomal GST and cytosolic glutathione reductase may become early biochemical indicators of oxidative stress.

CYP2M1: cloning, sequencing, and expression of a new cytochrome P450 from rainbow trout liver with fatty acid (omega-6)-hydroxylation activity

A cDNA clone was isolated from a female rainbow trout liver lambda g tau 11 library using polyclonal antibodies raised against rainbow trout cytochrome P450 LMC1. This 2149-nucleotide clone contained an open reading frame encoding a protein of 499 amino acids with a calculated M(r) of 56,850 Da. On the basis of cytochrome P450 (P450) amino acid sequence comparisons, this rainbow trout P450 was assigned by the P450 Nomenclature Committee to a new P450 subfamily designated as CYP2M1. Northern blot results suggest that the expression of CYP2M1 at the transcriptional level was generally sex, tissue, and age specific. By use of a full-length CYP2M1 cDNA probe, it was observed that this cDNA hybridized strongly to a single 2.2-kb transcript in juvenile female rainbow trout trunk kidney and in liver from juvenile and sexually mature trout from both sexes. Negligible amounts of mRNA hybridizable to CYP2M1 cDNA were found in the juvenile and sexually mature male trunk kidney. cDNA-directed expression in COS-7 cells and of recombinant baculovirus in insect cells produced a protein that was reactive with rabbit anti-trout P450 LMC1 polyclonal antibody and exhibited the unique (omega-6)-hydroxylation toward lauric acid previously observed with rainbow trout P450 LMC1.

Expression of CYP2M1, CYP2K1, and CYP3A27 in brain, blood, small intestine, and other tissues of rainbow trout

Expression of five constitutive forms of cytochrome P450 [(LMC1 (CYP2M1), LMC2 (CYP2K1), LMC3, LMC4, and LMC5 (CYP3A27)] in selected tissues from sexually immature 2-year old female and male rainbow trout (Oncorhynchus mykiss) were examined at the translational level by Western blot using polyclonal antibodies raised in rabbits against those purified trout hepatic P450s. Tissues examined were from brain, liver, muscle, blood, head kidney, trunk kidney, upper intestine, stomach, heart, and gonad (ovary or testis). The results showed that the liver was the major organ for expression of all the trout P450s studied. Trunk kidney was the secondary expression site except for LMC5. Selective translational expression of these P450 isoforms or similar proteins was observed for LCM1 and LMC5 in brain; for LMC2 and LMC5 in female upper intestine; and for LMC2 in blood plasma of the fish studied under the experimental and sampling conditions.

Xenobiotics and xenoestrogens in fish: modulation of cytochrome P450 and carcinogenesis

As is the case with mammals, an ever-increasing number of cytochromes P450 (CYPs) are being characterized from fish. The focus of work on fish CYPs has been primarily on environmental induction of CYP1A by pollutants such as the polycyclic aromatic hydrocarbons, polychlorinated biphenyls, dioxins and dibenzofurans. This response has been the basis for a sensitive biomonitoring tool of ecosystem health for a number of years. Studies have documented a correlation between CYP1A induction, pollutant levels and tumor incidence, especially in bottom-dwelling species. The rainbow trout has been utilized as a tumor model to document the role of CYP1A modulation in the inhibition or promotion of cancer. Fish are also very responsive to the class of chemicals known as xenoestrogens. Recent evidence is presented documenting the modulation of CYPs by xenoestrogens and their potential role as modulators of the tumor response. In this paper, we summarize the current knowledge concerning the occurrence of CYPs in fish and focus on the role of CYP1A induction in environmental monitoring of various genotoxic carcinogens and in the modulation of cancer in the trout model. Finally, the important class of aquatic pollutants known as xenoestrogens have now been shown to modulate CYP levels perhaps leading to alterations in tumor response or other adverse effects.

Evaluation of chemicals as inhibitors of trout cytochrome P450s

This study examined the ability of several inhibitors of mammalian cytochrome P450s to affect hepatic P450-mediated monooxygenase activities in microsomes from beta-naphthoflavone (BNF)-treated rainbow trout. Three monooxygenase activities, namely, lauric acid (omega-1)-hydroxylase (LA-OH), 7,12-dimethylbenz[a]anthracene hydroxylase (DMBA-OH), and progesterone 6beta-hydroxylase (PROG-OH) activities were used as functional markers for trout hepatic CYP2K1, CYP1A1, and CYP3A27, respectively. The chemicals that were examined for their inhibitory effects were reversible, quasi-irreversible, or irreversible inhibitors of mammalian P450. At 100 microM concentration, the reversible inhibitors (ketoconazole, miconazole, and clotrimazole) were most potent in inhibiting LA-OH activity. These imidazole compounds, as well as ellipticine, parathion, and alpha-naphthoflavone, were the strongest inhibitors of DMBA-OH and PROG-OH activities. In addition, isosafrole, piperonyl butoxide, gestodene, 17alpha-ethynylestradiol, 1-aminobenzotriazole, and 5,8,11,14-eicosatetraynoic acid strongly inhibited PROG-OH activity. The global inhibitors, metyrapone, chloramphenicol, and allylisopropylacetamide, had very little or no inhibitory effect on trout LA-OH and DMBA-OH activities. Triacetyloleandomycin, a CYP3A inhibitor, did not affect PROG-OH activity catalyzed by trout CYP3A27. Diethyldithiocarbamate was an activator of LA-OH activity. None of the above enzyme activities was selectively inhibited by any of the chemicals when used at a concentration of 100 microM. There was no difference in the inhibition of LA-OH activities by representative P450 inhibitors between liver microsomes from untreated trout and BNF-treated trout. The results of this study suggest that inhibition data from mammalian studies could not be directly extrapolated to trout and likely other fish species and that care must be observed when mammalian P450 inhibitors are used to determine the participation of P450s in the metabolism and toxicity of xenobiotics in nonmammalian species.

Purification and characterization of constituent androstenedione 15 alpha-hydroxylase (cytochrome P450(15 alpha AD)) from mouse liver. Sex- and tissue-dependent expression

Hepatic microsomal androstenedione 15 alpha-hydroxylase (i.e.cytochrome P450(15)alpha AD was purified from female CD-1 mice. Protein purification was monitored in eluates from Fractogel, DEAE-Sephacel, and hydroxylapatite columns at heme absorbing 417 nm, by cytochrome P450 content, reactivity to monoclonal antibody against female-specific rat cytochrome P450 2C12, and androstenedione 15 alpha-hydroxylase activity. The catalytic activity for androgens of the purified cytochrome P450(15)alpha AD, exhibiting a high degree of regioselectivity and stereospecificity, was restricted to the 7 alpha- and 15 alpha-hydroxylation of androstenedione, representing, respectively, > 5% and > 93% of the total metabolites. Polyclonal antibodies against cytochrome P450(15)alpha AD exhibited a concentration-dependent and very selective inhibition of hepatic microsomal androstenedione 7 alpha- and 15 alpha-hydroxylation and a 60% inhibition of benzphetamine demethylation, the latter drug appearing to be a much more effective substrate than androgens. Cytochrome P450(15)alpha AD accounted for about 3% of the total P450 in female mouse liver microsomes. The apparent subunit molecular weight of P450(15)alpha AD was 53,000, and the protein appeared as a single band or sodium dodecyl sulfate-polyacrylamide gels. The isoform was intensely expressed in both liver and lung of CD-1 female mice and was female-predominant in the livers of five or eight strains examined; it was sex-independent in the remaining three strains. Amino-terminal sequence analysis indicates that cytochrome P450(15)alpha AD is a member of the murine cytochrome P450 2c subfamily.

Immunochemical relationships of cytochrome P4503A-like proteins in teleost fish

Multiple P450 proteins have been purified from several teleost species, including rainbow trout (Oncorhynchus mykiss), scup (Stenotomus chrysops) and Atlantic cod (Gadus morhua). Identity, relationships and/or functions have been established in these fish species for the cytochrome P4501 As. Information about the structure, function, regulation and relationships of other piscine cytochrome P450 (CYP) proteins is sparse. In the present study we have focused on constitutively expressed CYP forms, P450con and LMC5 isolated from rainbow trout, P450A from scup, and P450b from Atlantic cod, and we consider evidence for the relationship of these proteins to mammalian members of the CYP3A subfamily. Reciprocal western blot analysis shows that P450con and LMC5, isolated from rainbow trout in two different laboratories, are closely related and ostensibly identical proteins. These trout proteins show specific reciprocal cross-reactivity with scup P450A, and polyclonal antibodies (PAb) to the trout and scup proteins both recognize cod P450b, indicating that rainbow trout P450con/LMC5, scup P450A and cod P450b are immunochemically-related proteins. In analyses of liver microsomes of trout, scup and cod, PAb to trout P450con/LMC5 and scup P450A recognize only bands that are identical in migration to the CYP proteins purified from these species, and which were used as immunogens. These CYP proteins purified from fish are each immunochemically-related to mammalian CYP3A proteins, showing recognition by PAb to human CYP3A4 and to rat CYP3A1. PAb to the mammalian CYP3As also recognize the same bands in liver microsomes from these fish species as seen by PAb to the fish proteins. These results strongly suggest that these fish proteins are members of theCYP3 gene family and probably theCYP3A subfamily. Although sequence analysis is required before their designation in the CYP3A subfamily can be confirmed and specified, we refer to these as CYP3A-like. Immunoblot analyses of hepatic microsomes from other fish species with PAb to scup P450A and trout P450con show that multiple CYP3A-like proteins are expressed in liver of several species, including killifish (Fundulus heteroclitus) and winter flounder (Pleuronectes americanus). Important questions still remain to be addressed concerning CYP3A structure, multiplicity, physiological function, regulation and metabolism of endogenous as well as exogenous substrates in fish.