Identification and in vitro biological activities of hop proanthocyanidins: inhibition of nNOS activity and scavenging of reactive nitrogen species

Oligomeric proanthocyanidins constitute a group of water-soluble polyphenolic tannins that are present in the female inflorescences (up to 5% dry wt) of the hop plant (Humulus lupulus). Humans are exposed to hop proanthocyanidins through consumption of beer. Proanthocyanidins from hops were characterized for their chemical structure and their in vitro biological activities. Chemically, they consist mainly of oligomeric catechins ranging from dimers to octamers, with minor amounts of catechin oligomers containing one or two gallocatechin units. The chemical structures of four procyanidin dimers (B1, B2, B3, and B4) and one trimer, epicatechin-(4beta-->8)-catechin-(4alpha-->8)-catechin (TR), were elucidated using mass spectrometry, NMR spectroscopy, and chemical degradation. When tested as a mixture, the hop oligomeric proanthocyanidins (PC) were found to be potent inhibitors of neuronal nitric oxide synthase (nNOS) activity. Among the oligomers tested, procyanidin B2 was most inhibitory against nNOS activity. Procyanidin B3, catechin, and epicatechin were noninhibitory against nNOS activity. PC and the individual oligomers were all strong inhibitors of 3-morpholinosydnonimine (SIN-1)-induced oxidation of LDL, with procyanidin B3 showing the highest antioxidant activity at 0.1 microg/mL. The catechin trimer (TR) exhibited antioxidant activity more than 1 order of magnitude greater than that of alpha-tocopherol or ascorbic acid on a molar basis.

Cloning, sequencing, and characterization of CYP1A1 cDNA from leaping mullet (Liza Saliens) liver and implications for the potential functions of its conserved amino acids

A 2,037 bp CYP1A1 cDNA (GenBank AF072899) was cloned through screening of a lambdaZipLox cDNA library constructed from the liver of a leaping mullet (Liza saliens) fish captured from Izmir Bay on the Aegean coast of Turkey using rainbow trout CYP1A1 cDNA as a probe. This clone has a 130 bp 5'-flanking region, a 1,563 bp open reading frame (ORF) encoding a 521-amino acid protein (58,972 Da), and a 344 bp 3'-untranslated region without a poly (A) tail. Alignment of the deduced amino acids of CYP1A1 cDNAs showed 58% and 69-96% identities with human and 12 other fish species, respectively. Southern blot analysis suggested that this CYP1A1 cDNA was from a single-copy gene. Based on the comparison with CYP1A1 genes reported for fish and mammals, the leaping mullet CYP1A1 gene is probably split into 7 exons. The intron insertion sites were predicted. Alignment of the CYP1A1 cDNA encoded amino acids from 13 fish and 7 mammalian species disclosed differences in highly conserved amino acids between aquatic and land vertebrates. The possible associated secondary structure; conserved motifs and substrate-binding sites were discussed. The phylogenetic relationships of CYP1A1s among 13 fish species were analyzed by a distance method.

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.

Influence of prenylated and non-prenylated flavonoids on liver microsomal lipid peroxidation and oxidative injury in rat hepatocytes

Prenylated chalcones from hops and beer were compared with non-prenylated flavonoids [chalconaringenin (CN), naringenin (NG), genistein (GS) and quercetin (QC)] for their ability to inhibit lipid peroxidation in rat liver microsomes. Chalcones with prenyl- or geranyl-groups (5 and 25 microM) were more effective inhibitors of microsomal lipid peroxidation than CN, NG or GS induced by Fe(2+)/ascorbate. Prenylated chalcones were effective inhibitors of microsomal lipid peroxidation induced by Fe(3+)-ADP/NADPH and by tert-butyl hydroperoxide (TBH) but to a lesser extent compared to the Fe(2+)/ascorbate system. An increase of prenyl substituents decreased antioxidant activity in the lipid peroxidation systems. Certain flavonoids behaved as prooxidants in the iron-dependent lipid peroxidation systems. For example, at 5 microM, NG enhanced iron/ascorbate-induced lipid peroxidation whereas CN, diprenylxanthohumol and tetrahydroxanthohumol enhanced Fe(3+)-ADP/NADPH-induced lipid peroxidation. None of the flavonoids (25 microM), except QC, inhibited NADPH cytochrome P450-reductase activity of rat liver microsomes, suggesting that the mechanism of inhibition of lipid peroxidation induced by Fe(3+)-ADP/NADPH is not due to inhibition of the reductase enzyme. Chalcones exhibiting antioxidant activity against TBH-induced lipid peroxidation such as xanthohumol and 5'-prenylxanthohumol, and NG, with no antioxidant property at 5 microM concentration protected cultured rat hepatocytes from TBH toxicity. Other antioxidants (desmethylxanthohumol and CN) in the TBH system were not cytoprotective. These results demonstrate the importance of prenyl groups in the antioxidant activity of hop chalcones in the various in vitro systems of lipid peroxidation. Furthermore, the antioxidant activity of the flavonoids has little or no bearing on their ability to protect rat hepatocytes from the toxic effects of TBH.

In vitro glucuronidation of xanthohumol, a flavonoid in hop and beer, by rat and human liver microsomes

Xanthohumol (XN) is the major prenylated flavonoid of hop plants and has been detected in beer. Previous studies suggest a variety of potential cancer chemopreventive effects for XN, but there is no information on its metabolism. The aim of this study was to investigate in vitro glucuronidation of XN by rat and human liver microsomes. Using high-performance liquid chromatography, two major glucuronides of XN were found with either rat or human liver microsomes. Release of the aglycone by enzymatic hydrolysis with beta-glucuronidase followed by liquid chromatography/mass spectrometry and nuclear magnetic resonance analysis revealed that these were C-4' and C-4 monoglucuronides of XN.

In vitro biotransformation of xanthohumol, a flavonoid from hops (Humulus lupulus), by rat liver microsomes

Xanthohumol (XN) is the major prenylated flavonoid of the female inflorescences (cones) of the hop plant (Humulus lupulus). It is also a constituent of beer, the major dietary source of prenylated flavonoids. Recent studies have suggested that XN may have potential cancer-chemopreventive activity, but little is known about its metabolism. We investigated the biotransformation of XN by rat liver microsomes. Three major polar metabolites were produced by liver microsomes from either untreated rats or phenobarbital-pretreated rats as detected by reverse-phase high-performance liquid chromatography analysis. Liver microsomes from isosafrole- and beta-naphthoflavone-pretreated rats formed another major nonpolar metabolite in addition to the three polar metabolites. As determined by liquid chromatography/mass spectrometry and (1)H NMR analyses, the three major polar microsomal metabolites of XN were tentatively identified as 1) 5"-isopropyl-5"-hydroxydihydrofurano[2",3":3',4']-2',4-dihydroxy-6'-methoxychalcone; 2) 5"-(2"'-hydroxyisopropyl)-dihydrofurano[2",3":3',4']-2',4-dihydroxy-6'-methoxychalcone; and 3) a derivative of XN with an additional hydroxyl function at the B ring. The nonpolar XN metabolite was identified as dehydrocycloxanthohumol.

Oregon's Toxic Household Products Law

In 1991, Oregon became the first state in the U.S. to require the addition of an aversive agent to ethylene glycol-containing antifreeze and methanol-containing windshield wiper fluid. This new law, entitled "Toxic Household Products (THP) Act," was designed to reduce pediatric and animal poisonings from accidental ingestion of these two potentially lethal consumer automotive products. While not the stated intention of the law, addition of aversive agents to consumer automotive products could also reduce adult poisonings associated with intentional (suicides or alcoholics ingesting methanol-containing windshield wiper fluid) or accidental exposures. This law went into effect April 30, 1995, following settlement of a lawsuit brought by the Chemical Manufacturing Specialties Association (CSMA), a trade group representing the five largest manufacturers of ethylene glycol-based antifreeze in the U.S. This paper discusses the major policy issues that arose following the passage of Oregon's THP Act. Major provisions of the law are provided along with a discussion of CSMA's opposition to the Act's implementation. A description of the eventual settlement that was reached with CSMA as well as the major components of Oregon Health Division's (OHD) enforcement program are also highlighted. Data are presented for 1987 through 1998 on the number of exposures and severity of effects for pediatric cases (children < 6 years old) following exposure to both of these potentially lethal automotive products. However, because of the low incidence of exposures each year, these data are insufficient to draw any conclusions on the impact of the THP Act.

Heterologous expression of CYP2K1 and identification of the expressed protein (BV-CYP2K1) as lauric acid (omega-1)-hydroxylase and aflatoxin B1 exo-epoxidase

LMC2 is the most abundant constitutively expressed hepatic cytochrome P450 found in sexually immature rainbow trout (Onchorynchus mykiss) and is also the isozyme that activates the carcinogen aflatoxin B1 (AFB1). This P450 has been cloned, sequenced, and designated as CYP2K1. The present report describes the heterologous expression of enzymatically active CYP2K1 (BV-CYP2K1) in baculovirus Spodoptera frugiperda (Sf9) insect cells and its catalytic and immunoreactivity characterization in comparison with that of the previously purified LMC2 P450. Homogenates of Sf9 cells expressing the CYP2K1 enzyme and LMC2 both catalyzed the hydroxylation of lauric acid and the epoxidation of AFB1 in the presence of rat NADPH-cytochrome P450 reductase. Both LMC2 and BV-CYP2K1 catalyzed the oxidation of lauric acid primarily at the (omega-1) position plus small amounts at the (omega-2) position. Formation of AFB1 epoxide was shown indirectly by the appearance of an AFB1 epoxide-glutathione conjugate when P450 incubation mixtures contained AFB1, glutathione (GSH) together with mouse liver cytosol or purified rat GSH-transferase. When the AFB1 epoxide-GSH conjugate produced by BV-CYP2K1 and purified LMC2 was analyzed by HPLC using a chiral column, it had a retention time identical to that produced by CYP3A4, a human P450 known to form exclusively the AFB1 exo-epoxide. These results, therefore, confirm that the cDNA-expressed CYP2K1 protein is catalytically and immunologically identical to purified trout LMC2 and that these two enzymes produce primarily the highly carcinogenic stereoisomeric exo-epoxide form of AFB1.

Prenylflavonoids from hops inhibit the metabolic activation of the carcinogenic heterocyclic amine 2-amino-3-methylimidazo[4, 5-f]quinoline, mediated by cDNA-expressed human CYP1A2

The heterocyclic amine 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) is a potential human carcinogen found in cooked food that requires initial metabolic activation by cytochrome P450s, primarily CYP1A2. The present study was conducted to examine whether recombinant human CYP1A2 expressed in insect cells mediates the metabolic activation of IQ and whether prenylflavonoids found in hops and beer would modulate the CYP1A2-mediated activation of IQ. The cDNA-expressed human CYP1A2 was found to strongly activate IQ as measured by the Ames Salmonella assay and by the covalent binding of IQ metabolites to calf thymus DNA and protein. Inhibition studies showed that the prenylchalcone xanthohumol and the prenylflavanones 8-prenylnaringenin and isoxanthohumol strongly inhibited the mutagenic activation of IQ mediated by cDNA-expressed human CYP1A2 in the Ames Salmonella assay. The three prenylflavonoids also markedly inhibited the human CYP1A2-mediated binding of IQ to metabolites that bind to DNA. The inhibition of the metabolic activation of IQ was paralleled by the inhibition of acetanilide 4-hydroxylase activity of human CYP1A2. Thus, xanthohumol, isoxanthohumol, and prenylflavanones 8-prenylnaringenin are potent inhibitors of the metabolic activation of IQ and may have the potential to act as chemopreventive agents against cancer induced by heterocyclic amines activated by CYP1A2.

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.

Antioxidant and prooxidant actions of prenylated and nonprenylated chalcones and flavanones in vitro

Prenylated flavonoids found in hops and beer, i.e., prenylchalcones and prenylflavanones, were examined for their ability to inhibit in vitro oxidation of human low-density lipoprotein (LDL). The oxidation of LDL was assessed by the formation of conjugated dienes and thiobarbituric acid-reactive substances (TBARS) and the loss of tryptophan fluorescence. At concentrations of 5 and 25 microM, all of the prenylchalcones tested inhibited the oxidation of LDL (50 microg protein/ml) induced by 2 microM copper sulfate. The prenylflavanones showed less antioxidant activity than the prenylchalcones, both at 5 and 25 microM. At 25 microM, the nonprenylated chalcone, chalconaringenin (CN), and the nonprenylated flavanone, naringenin (NG), exerted prooxidant effects on LDL oxidation, based on TBARS formation. Xanthohumol (XN), the major prenylchalcone in hops and beer, showed high antioxidant activity in inhibiting LDL oxidation, higher than alpha-tocopherol and the isoflavone genistein but lower than the flavonol quercetin. When combined, XN and alpha-tocopherol completely inhibited copper-mediated LDL oxidation. These findings suggest that prenylchalcones and prenylflavanones found in hops and beer protect human LDL from oxidation and that prenylation antagonizes the prooxidant effects of the chalcone, CN, and the flavanone, NG.

In vitro inhibition of human P450 enzymes by prenylated flavonoids from hops, Humulus lupulus

1. Several unique flavonoid compounds have recently been isolated from hops, Humulus lupulus, and their presence has been detected in beer. Their chemical structures are similar to other plant-derived compounds, many present in the human diet, that have been shown to have cancer chemopreventive properties due, in part, to inhibition of cytochrome P450 enzymes that activate carcinogens. Additionally, preliminary studies have shown these flavonoids (at 100 microM) to be inhibitory of P450-mediated activation reactions in a variety of in vitro systems. Thus, the in vitro effects of these phytochemicals on cDNA-expressed human CYP1A1, CYP1B1, CYP1A2, CYP3A4 and CYP2E1 were currently examined by the use of diagnostic substrates and the carcinogen AFB1. 2. At 10 microM, the prenylated chalcone, xanthohumol (XN), almost completely inhibited the 7-ethoxyresorufin O-deethylase (EROD) activity of CYP1A1. At the same concentration, other hop flavonoids decreased the EROD activity by 90.8-27.0%. 3. At 10 microM, XN completely eliminated CYP1B1 EROD activity, whereas the other hop flavonoids showed varying degrees of inhibitory action ranging from 99.3 to 1.8%. 4. In contrast, the most effective inhibitors of CYP1A2 acetanilide 4-hydroxylase activity were the two prenylated flavonoids, 8-prenylnaringenin (8PN) and isoxanthohumol (IX), which produced > 90% inhibition when added at concentrations of 10 microM. 5. CYP1A2 metabolism of the carcinogen AFB1 was also inhibited by IX and 8PN as shown by decreased appearance of dihydrodiols and AFM1 as analysed by hplc. IX and 8PN also decreased covalent binding of radiolabelled AFB1 to microsomal protein in a concomitant manner. 6. XN, IX and 8PN, however, were poor inhibitors of CYP2E1 and CYP3A4 as measured by their effect on chorzoxazone hydroxylase and nifedipine oxidase activities respectively. 7. These results suggest that the hop flavonoids are potent and selective inhibitors of human cytochrome P450 and warrant further in vivo investigations.

Prenylated chalcones and flavanones as inducers of quinone reductase in mouse Hepa 1c1c7 cells

The objective of this study was to determine if prenylchalcones (open C-ring flavonoids) and prenylflavanones from hops and beer are inducers of quinone reductase (QR) in the mouse hepatoma Hepa 1c1c7 cell line. All the prenylchalcones and prenylflavanones tested were found to induce QR but not CYP1A1 in this cell line. In contrast, the synthetic chalcone, chalconaringenin, and the flavanone, naringenin, with no prenyl or geranyl groups, were ineffective in inducing QR. The hop chalcones, xanthohumol and dehydrocycloxanthohumol hydrate, also induced QR in the Ah-receptor-defective mutant cell line, Hepa 1c1c7 bp(r)c1. Thus, the prenylflavonoids represent a new class of monofunctional inducers of QR.

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.

Antiproliferative and cytotoxic effects of prenylated flavonoids from hops (Humulus lupulus) in human cancer cell lines

Six flavonoids [xanthohumol (XN), 2',4',6',4-tetrahydroxy-3'-prenylchalcone (TP); 2',4',6',4-tetrahydroxy-3'-geranylchalcone (TG); dehydrocycloxanthohumol (DX); dehydrocycloxanthohumol hydrate (DH); and isoxanthohumol (IX)] from hops (Humulus lupulus) were tested for their antiproliferative activity in human breast cancer (MCF-7), colon cancer (HT-29) and ovarian cancer (A-2780) cells in vitro. XN, DX and IX caused a dose-dependent (0.1 to 100 microM) decrease in growth of all cancer cells. After a 2-day treatment, the concentrations at which the growth of MCF-7 cells was inhibited by 50% (IC50) were 13.3, 15.7 and 15.3 microM for XN, DX and IX, respectively. After a 4-day treatment, the IC50 for XN, DX and IX were 3.47, 6.87 and 4.69 microM, respectively. HT-29 cells were more resistant than MCF-7 cells to these flavonoids. In A-2780 cells, XN was highly antiproliferative with IC50 values of 0.52 and 5.2 microM after 2 and 4 days of exposure, respectively. At 100 microM, all the hop flavonoids were cytotoxic in the three cell lines. Growth inhibition of XN- and IX-treated MCF-7 cells was confirmed by cell counting. XN and IX inhibited DNA synthesis in MCF-7 cells. As antiproliferative agents, XN (chalcone) and IX (flavanone isomer of XN) may have potential chemopreventive activity against breast and ovarian cancer in humans.

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.

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.

Species differences in the hepatic microsomal enzyme metabolism of the pyrrolizidine alkaloids

Species differences in pyrrolic metabolites and senecionine (SN) N-oxide formation among eight animal species (sheep, cattle, gerbils, rabbits, hamsters, Japanese quail, chickens, rats) varying in susceptibility to pyrrolizidine alkaloid (PA) intoxication were measured in vitro by hepatic microsomal incubations. The results suggested that there is not a strong correlation between the production of pyrrolic metabolites and susceptibility of animals to PA toxicity. The rate of PA activation in hamsters, a resistant species, measured by formation of (+/-)6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP) far exceeded the rate of SN N-oxide formation (detoxification) (DHP/N-oxide = 2.29). In contrast, SN N-oxide was the major metabolite in sheep, another resistant species, with much lower production of DHP (DHP/N-oxide = 0.26). The roles of cytochrome P450s and flavin-containing monooxygenases (FMO) in bioactivation and detoxification of pyrrolizidine alkaloids (PA) were studied in vitro using sheep and hamster hepatic microsomes. Chemical and immunochemical inhibition data suggested that the conversion of SN to DHP is catalyzed mainly by cytochrome P450s (68-82%), whereas the formation of SN N-oxide is carried out largely by FMO (55-71%). There also appeared to be a high rate of glutathione-DHP conjugation in hamster (63%) and sheep (79%) liver microsomal incubation mixtures. Therefore, low rates of pyrrole metabolite production coupled with glutathione conjugation in sheep may explain the resistance of sheep to SN, whereas the high rate of GSH-DHP conjugation may be one of the factors contributing to the resistance of hamsters to intoxication by this PA.

The roles of CYP3A and CYP2B isoforms in hepatic bioactivation and detoxification of the pyrrolizidine alkaloid senecionine in sheep and hamsters

The roles of cytochrome CYP3A and CYP2B isozymes in the bioactivation and detoxification of the pyrrolizidine alkaloid (PA) senecionine (SN) have been investigated in vitro with sheep and hamster hepatic microsomes. Our results show that the rate of SN activation measured by (+/-)-6, 7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP) formation greatly exceeded the rate of SN N-oxide formation (detoxification) in hamsters. In contrast, SN N-oxide, a detoxification product, was the major metabolite in sheep with much lower DHP production. Immunoinhibition studies with anti-sheep CYP3A and CYP2B antibodies show that members of CYP3A subfamily play the major role in the conversion of PA to pyrrolic metabolites in both species (over 90% in sheep; 68% in hamster). These enzymes also contribute 38.8 and 41. 3% of SN N-oxidation in sheep and hamsters, respectively. In contrast, CYP2B isoforms have a limited capacity toward DHP formation in both species (47% in sheep; 32% in hamster), while these enzymes catalyzed only 24.6 and 35.4% SN N-oxidation in sheep and hamster, respectively. Using triacetyloleandomycin (TAO) and gestodene, two highly selective chemical inhibitors of CYP3A isoforms, our data show that 90% of DHP formation was inhibited by either inhibitor in sheep. Gestodene appeared to be more efficient than TAO in the inhibition of DHP production in hamsters. Testosterone 6beta-hydroxylase activity, a functional marker of CYP3A, was significantly inhibited by TAO and gestodene in sheep liver microsomes and by gestodene (100 microM) in hamster liver microsomes. These results suggest that CYP3A isozymes have important roles in bioactivation and detoxification of PA in both species, whereas CYP2B subfamily members are less efficient in biotransformation of PA.