Induction of cytochrome P4501 as an indicator of potential chemical carcinogenesis

Cigarette smoking enhances the metabolic activation of the polycyclic aromatic hydrocarbon phenanthrene in humans

Although it is well established that human cytochrome P450 1 family enzymes are induced by cigarette smoking through activation of the Ah receptor, it is not known whether this leads to increased metabolic activation or detoxification of carcinogenic polycyclic aromatic hydrocarbons (PAH), which are present in cigarette smoke and the general environment. We gave oral doses of deuterated phenanthrene ([D10]Phe), a non-carcinogenic surrogate of carcinogenic PAH such as benzo[a]pyrene, to smokers (N = 170, 1 or 10 μg doses) and non-smokers (N = 57, 1 μg dose). Bioactivation products (dihydrodiol and tetraol) and detoxification products (phenols) of [D10]Phe were determined in 6-h urine to obtain a comprehensive metabolic profile. Cigarette smoking increased the bioactivation of [D10]Phe and decreased its detoxification resulting in significantly different metabolic patterns between smokers and non-smokers (P < 0.01), consistent with increased cancer risk in smokers. The Phe bioactivation ratios ([D10]PheT/total [D9]OHPhe) were significantly higher (2.3 (P < 0.01) to 4.8 (P < 0.001) fold) in smokers than non-smokers. With solid human in vivo evidence, our results for the first time demonstrate that cigarette smoking enhances the metabolic activation of Phe, structurally representative of carcinogenic PAH, in humans, strongly supporting their causal role in cancers caused by smoking. The results suggest potential new methods for identifying smokers who could be at particularly high risk for cancer.

Human Family 1-4 cytochrome P450 enzymes involved in the metabolic activation of xenobiotic and physiological chemicals: an update

This is an overview of the metabolic activation of drugs, natural products, physiological compounds, and general chemicals by the catalytic activity of cytochrome P450 enzymes belonging to Families 1-4. The data were collected from > 5152 references. The total number of data entries of reactions catalyzed by P450s Families 1-4 was 7696 of which 1121 (~ 15%) were defined as bioactivation reactions of different degrees. The data were divided into groups of General Chemicals, Drugs, Natural Products, and Physiological Compounds, presented in tabular form. The metabolism and bioactivation of selected examples of each group are discussed. In most of the cases, the metabolites are directly toxic chemicals reacting with cell macromolecules, but in some cases the metabolites formed are not direct toxicants but participate as substrates in succeeding metabolic reactions (e.g., conjugation reactions), the products of which are final toxicants. We identified a high level of activation for three groups of compounds (General Chemicals, Drugs, and Natural Products) yielding activated metabolites and the generally low participation of Physiological Compounds in bioactivation reactions. In the group of General Chemicals, P450 enzymes 1A1, 1A2, and 1B1 dominate in the formation of activated metabolites. Drugs are mostly activated by the enzyme P450 3A4, and Natural Products by P450s 1A2, 2E1, and 3A4. Physiological Compounds showed no clearly dominant enzyme, but the highest numbers of activations are attributed to P450 1A, 1B1, and 3A enzymes. The results thus show, perhaps not surprisingly, that Physiological Compounds are infrequent substrates in bioactivation reactions catalyzed by P450 enzyme Families 1-4, with the exception of estrogens and arachidonic acid. The results thus provide information on the enzymes that activate specific groups of chemicals to toxic metabolites.

Bioavailability of the diterpenoid 14-deoxy-11,12-didehydroandrographolide in rats and up-regulation of hepatic drug-metabolizing enzyme and drug transporter expression

BACKGROUND

14-Deoxy-11,12-didehydroandrographolide (deAND) is the second most abundant diterpenoid in Andrographis paniculata (Burm. f.) Nees, a traditional medicine used in Asia. To date, the biological activity of deAND has not been clearly investigated.

PURPOSE

In this study, we intended to examine the modulatory effect of deAND on hepatic drug metabolism as well as its bioavailability.

STUDY DESIGN

deAND prepared from A. paniculata was orally given to Sprague-Dawley rats and changes in plasma deNAD were determined by HPLC-MS. Modulation of deAND on drug-metabolizing enzyme and drug transporter expression as well as the possible mechanism involved was examined in primary rat hepatocytes.

RESULTS

After a single oral administration of 50 mg/kg deAND to rats, the maximum plasma concentration (C_max), time to reach the C_max, area under the curve (AUC_0-24h), mean retention time, and half-life (t_1/2) of deAND were 2.65 ± 0.68 μg/ml, 0.29 ± 0.15 h, 6.30 ± 1.66 μg/ml•h, 5.55 ± 2.52 h, and 3.56 ± 1.05 h, respectively. The oral bioavailability was 3.42%. In primary rat hepatocytes treated with up to 10 μM deAND, a dose-dependent increase was noted in the expression of cytochrome P450 (CYP) 1A1/2, CYP2C6, and CYP3A1/2; UDP-glucuronosyltransferase (UGT) 1A1, NAD(P)H:quinone oxidoreductase (NQO1), π form of GSH S-transferase (GSTP), multidrug resistance-associated protein 2, p-glycoprotein, and organic anion transporter protein 2B1. Immunoblotting assay and EMSA revealed that deAND increases the nuclear translocation and DNA binding activity of aryl hydrocarbon receptor (AhR), pregnane X receptor (PXR), and nuclear factor erythroid-derived 2-related factor 2 (Nrf2). Knockdown of AhR and Nrf2 expression abolished deAND induction of CYP isozymes and UGT1A1, NQO1, and GSTP expression, respectively.

CONCLUSION

These results indicate that deAND quickly passes through enterocytes in rats and effectively up-regulates hepatic drug-metabolizing enzyme and drug transporter expression in an AhR-, PXR-, and Nrf2-dependent manner.

Development and Uses of Offline and Web-Searchable Metabolism Databases - The Case of Benzo[a]pyrene

BACKGROUND

The present work describes development of offline and web-searchable metabolism databases for drugs, other chemicals, and physiological compounds using human and model species, prompted by the large amount of data published after year 1990. The intent was to provide a rapid and accurate approach to published data to be applied both in science and to assist therapy.

METHODS

Searches for the data were done using the Pub Med database, accessing the Medline database of references and abstracts. In addition, data presented at scientific conferences (e.g., ISSX conferences) are included covering the publishing period beginning with the year 1976.

RESULTS

Application of the data is illustrated by the properties of benzo[a]pyrene (B[a]P) and its metabolites. Analysis show higher activity of P450 1A1 for activation of the (-)- isomer of trans-B[a]P-7,8-diol, while P4501B1 exerts higher activity for the (+)- isomer. P450 1A2 showed equally low activity in the metabolic activation of both isomers.

CONCLUSION

The information collected in the databases is applicable in prediction of metabolic drug-drug and/or drug-chemical interactions in clinical and environmental studies. The data on the metabolism of searched compound (exemplified by benzo[a]pyrene and its metabolites) also indicate toxicological properties of the products of specific reactions. The offline and web-searchable databases had wide range of applications (e.g. computer assisted drug design and development, optimization of clinical therapy, toxicological applications) and adjustment in everyday life styles.

Promising therapeutic potential of pterostilbene and its mechanistic insight based on preclinical evidence

Pterostilbene (PS) is a well-recognized antioxidant that primarily exists in blueberries, grapevines and heartwood of red sandalwood. Interest in this compound has been renewed in recent years, and studies have found that PS possesses an array of pharmacological properties, including chemopreventive, antiinflammatory, antidiabetic, antidyslipidemic, antiatherosclerotic and neuroprotective effects. However, the greater in vivo bioavailability of PS, as compared to resveratrol, is an added advantage for its efficacy. This review provides a summary regarding the sources, pharmacokinetic aspects and pharmacodynamics of PS, with a focus on the molecular mechanisms underlying its protective effects against cancer, brain injuries and heart disease. Studies regarding the safety profile of PS have also been included. Based on the presently available evidence, we conclude that PS represents an active phytonutrient and a potential drug with pleiotropic health applications.

Dopamine D2-Receptor Antagonists Down-Regulate CYP1A1/2 and CYP1B1 in the Rat Liver

Dopaminergic systems regulate the release of several hormones including growth hormone (GH), thyroid hormones, insulin, glucocorticoids and prolactin (PRL) that play significant roles in the regulation of various Cytochrome P450 (CYP) enzymes. The present study investigated the role of dopamine D₂-receptor-linked pathways in the regulation of CYP1A1, CYP1A2 and CYP1B1 that belong to a battery of genes controlled by the Aryl Hydrocarbon Receptor (AhR) and play a crucial role in the metabolism and toxicity of numerous environmental toxicants. Inhibition of dopamine D₂-receptors with sulpiride (SULP) significantly repressed the constitutive and benzo[a]pyrene (B[a]P)-induced CYP1A1, CYP1A2 and CYP1B expression in the rat liver. The expression of AhR, heat shock protein 90 (HSP90) and AhR nuclear translocator (ARNT) was suppressed by SULP in B[a]P-treated livers, whereas the AhRR expression was increased by the drug suggesting that the SULP-mediated repression of the CYP1 inducibility is due to inactivation of the AhR regulatory system. At signal transduction level, the D₂-mediated down-regulation of constitutive CYP1A1/2 and CYP1B1 expression appears to be mediated by activation of the insulin/PI3K/AKT pathway. PRL-linked pathways exerting a negative control on various CYPs, and inactivation of the glucocorticoid-linked pathways that positively control the AhR-regulated CYP1 genes, may also participate in the SULP-mediated repression of both, the constitutive and induced CYP1 expression. The present findings indicate that drugs acting as D₂-dopamine receptor antagonists can modify several hormone systems that regulate the expression of CYP1A1, CYP1A2 and CYP1B1, and may affect the toxicity and carcinogenicity outcome of numerous toxicants and pre-carcinogenic substances. Therefore, these drugs could be considered as a part of the strategy to reduce the risk of exposure to environmental pollutants and pre-carcinogens.

Antimutagenic and anticancer activity of Al Madinah Alhasawy mint (Mentha longifolia) leaves extract

Mentha is one of the genera of Lamiaceae family. The aim of the present study was to evaluate the antimutagenic and anticancer activity of the water and methanolic extract of Alhasawy mint (Mentha longifolia), that grown in Madina Province, western region, Saudi Arabia using three different bioassays namely; Brine shrimp bioassay, Ames mutagenicity bioassay using 3 Hist-Salmonella typhimurium strains of different mutations (TA98, TA97 and TA100) and 2 reference mutagenic drugs nitrosopiperidine (NP) and 2-amino-3-methylimidazo-quinolidine (IQ) and Mammalian cell lines bioassays using 2 different cell lines HepG2 and Vero cell lines. The plant extract showed an efficient antimutagenic activity against the studied bioassays in a directly proportional effect with concentration.

Assessment of the antimutagenic effect of Doash tea extract fractions

Origanum majorana L (Doash) is one of the traditional remedy that is used as a tea and to treat ailments, in the Kingdom of Saudi Arabia. The present study has attempted to evaluate the inhibitory action of Doash fractions on the bioactivation of selected food mutagens and direct-acting mutagens. Four Sallmonella bacterial strains (TA98, TA97, TA100 and TA1530) were used in the present study. These strains contain different mutations in the histidine operon, allowing the bacteria to detect different types of mutation. The two strains (TA98 and TA97) are capable of detecting frameshift mutations, while TA100 and TA1530 are able to detect base-pair substitutions. The liver homogenate and other subcellular fractions were prepared. Identification of Doash fractions was conducted using the high-performance liquid chromatography/mass spectrometry system. The results of the present study demonstrated that the Doash tea fraction components have the ability to reduce the in vitro mutagencity of several promutagens, which were employed in this study. Fraction No. 5 (with the highest content of solid) was the most potent inhibitor of the mutagenicity of all promutagens employed in this study. The antimutagenic effect of Doash tea extract, and its various fractions, was pronounced, indicating that the metabolism of cytochrome P450 1A2 isozyme is likely to be inhibited.

Evaluation of the in vitro antimutagenic effect of Doash tea aqueous extracts

Human carcinogens are formed mainly due to the lifestyle and diet that is followed. It is well known that dietary factors play a crucial role in the aetiology of human cancer. The new attractions of drug discovery using natural products remain an important issue in the current herbal medicine research. The present study aimed to evaluate the antimutagenic activity of the water extracts of Doash leaves against several known mutagens, both direct- and indirect-acting, belonging to different chemical classes. These classes are heterocyclic amines (HAs), polycyclic aromatic hydrocarbons and nitrosamines. The antimutagenic activity will be determined in Salmonella/microsomal system (Ames) using strains of Salmonella Typhimurium. Four Salmonella bacterial strains (TA98, TA97, TA100 and TA1530) were used in the present study. Results obtained showed that Doash extract possesses powerful antimutagenic properties, which impair the deleterious effects of various chemicals used in this study. One possible mechanism involved in this protection is the inhibition of the metabolic activation of chemical carcinogens to their reactive metabolites. We also suggest that the health benefits of Doash could be derived from the additive and synergistic combinations of the various phytochemicals present in Doash leaves. Other studies should also be conducted to determine the active components of Doash leaves, including macronutrients, micronutrients and other phytochemicals. Clinical studies should be performed before any claims that Doash consumption offers chemoprotection against cancer can be made.

In-vitro effect of flavonoids from Solidago canadensis extract on glutathione S-transferase

Solidago canadensis is typical of a flavonoid-rich herb and the effect of an aqueous ethanol extract on glutathione-S-transferase (GST) activity using HepG2 cells was compared with those of the flavonol quercetin and its glycosides quercitrin and rutin, found as major constituents. The composition of the extract was determined by HPLC and rutin was found to be the major flavonoidal component of the extract. Total GST activity was assessed using 1-chloro-2,4-dinitrobenzene as a substrate. The glycosides rutin and quercitrin gave dose-dependent increases in GST activity, with a 50% and 24.5% increase at 250 mm, respectively, while the aglycone quercetin inhibited the enzyme by 30% at 250 mm. The total extract of the herb gave an overall dose-dependent increase, the fractions corresponding to the flavonoids showed activating effects while those containing caffeic acid derivatives were inhibitory. The activity observed corresponds to that reported for similar compounds in-vivo using rats, thus the HepG2 cell line could serve as a more satisfactory method of assessing the effects of extracts and compounds on GST.

Subacute oral exposure to benzo[alpha]pyrene (B[alpha]P) increases aggressiveness and affects consummatory aspects of sexual behaviour in male mice

Benzo[alpha]pyrene (B[alpha]P) is a neurotoxic pollutant which is also able to affect some behaviour and cognitive function. Here we report that a subacute oral exposure to B[alpha]P increases aggressiveness and affects copulatory behaviour in male mice. Indeed, after 3 weeks of exposure to B[alpha]P at 0.02 and 0.2mg/kg, we have observed that B[alpha]P 0.02 mg/kg-treated male mice are more aggressive than control mice in resident-intruder test because a significant decrease in the latency time of the first attack and a significant increase in the number of attacks in B[alpha]P 0.02 mg/kg-treated mice were found. On the other hand, we have found that subacute exposure (4 weeks) to B[alpha]P, does not affect the appetitive aspects and sexual motivation in copulatory behaviour because the latency to the first mount between control and B[alpha]P-treated male mice was not significantly different. We have nevertheless, surprisingly found that B[alpha]P (0.02-0.2)mg/kg-treated mice have performed significantly more sexual behavioural acts including mounting, intromission latency and intromission frequency than control mice. Although these last results suggest that B[alpha]P improves the consummatory aspects of sexual behaviour, we cannot conclude that this neurotoxic pollutant has advantage of sexual function because B[alpha]P has been shown to alter the monoaminergic neurotransmitter system and causes endocrine dysregulation via toxic effect.

Different mechanisms of handling ingested polycyclic aromatic hydrocarbons in mammalian species: organ-specific response patterns of CYP1A1-induction after oral intake of PAH-contaminated soils

Potential effects of xenobiotics on humans are largely derived from studies with animal models. However, due to species-specific processing of xenobiotics, susceptibilities to xenobiotic-dependent adverse effects are known to differ between species. We analysed the basal expression of cytochrome P450 (CYP) enzymes in several organs of minipigs and rats, and their inducibility upon oral intake of soils containing polycyclic aromatic hydrocarbons (PAH). CYP-specific enzymatic activities were determined in duodenum, liver and kidney microsomes. Upon ingestion of PAH-contaminated soils, CYP1A1 is differentially induced in a tissue-specific and dose-dependent manner in duodenum, liver and kidney of minipigs and rats. In the duodenum, the induction response is low in rats (about 4-fold) but it is high in minipigs (8-230-fold). By contrast, induced hepatic CYP1A1-dependent EROD-activity is higher in rats than in minipigs. The dose-response profile for renal CYP1A1 parallels that in the liver of either species but EROD-activities are 10-20 times lower than in the liver. Liver microsomal CYP2E1 is only slightly modulated in its expression by ingestion of PAH-contaminated soils in both species, whereas CYP3A-dependent testosterone 2beta- and 6beta-hydroxylation is increased in liver of rats but not in minipigs. The hepatic capacity for catechol oestrogen formation, i.e., the 2-hydroxylation of 17beta-oestradiol, is markedly increased in rats but not in minipigs by ingested PAH. It is concluded that different metabolic and transport pathways are used by minipigs and rats to process ingested PAH. Whereas in minipigs the duodenum appears as the first efficient barrier, rats respond by efficient metabolism in the liver. What is not known is which response profile is operative in man.

Differential inhibition of rat and human hepatic cytochrome P450 by Andrographis paniculata extract and andrographolide

The inhibitory effect of Andrographis paniculata extract (APE) and andrographolide (AND), the most medicinally active phytochemical in the extract, on hepatic cytochrome P450s (CYPs) activities was examined using rat and human liver microsomes. For this purpose, CYP1A2-dependent ethoxyresorufin-O-deethylation, CYP2B1-dependent benzyloxyresorufin-O-dealkylation, CYP2B6-dependent bupropion hydroxylation, CYP2C-dependent tolbutamide hydroxylation, CYP2E1-dependent p-nitrophenol hydroxylation and CYP3A-dependent testosterone 6 beta-hydroxylation activities, were determined in the presence and absence of APE or AND (0-200 microM). APE inhibited ethoxyresorufin-O-deethylation activity in rat and human liver microsomes, with apparent Ki values of 8.85 and 24.46 microM, respectively. In each case, the mode of inhibition was noncompetitive. APE also inhibited tolbutamide hydroxylation both in rat and human microsomes with apparent Ki values of 8.21 and 7.51 microM, respectively and the mode of inhibition was mixed type. In addition, APE showed a competitive inhibition only on CYP3A4 in human microsomes with Ki of 25.43 microM. AND was found to be a weak inhibitor of rat CYP2E1 with a Ki of 61.1 microM but did not affect human CYP2E1. In conclusion, it cannot be excluded from the present study that APE could cause drug-drug interactions in humans through CYP3A and 2C9 inhibition.

Panax ginseng effects on DNA damage, CYP1A1 expression and histopathological changes in testes of rats exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

The effects of Panax ginseng extracts on DNA damage, expression of cytochrome P450 (CYP) 1A1 and reproductive toxicity were evaluated in the testis of rats exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxinthe (TCDD). Fifty rats were divided into five groups according to treatment with 2,3,7,8-TCDD and P. ginseng extracts. Single cell gel electrophoresis assays were performed to evaluate DNA damage that occurred in the lymphocytes of rats. Histological changes in the seminiferous tubules of the testis were determined using Johnsen's scoring system and Real Time-PCR was performed to evaluate the mRNA expression of CYP1A1. Significant pathological effects were observed in the 2,3,7,8-TCDD treated rats including a reduced seminiferous tubular diameter, an increased number of damaged tubules (maturation arrest, eosinophilic degeneration and spermatid giant cells) and increased Johnsen's score. DNA damage and the expression of CYP1A1 mRNA were significantly increased in rat testes. There were no significant differences between the control and animals treated with P. ginseng extracts. However, a significantly decreased level of DNA damage, decreased CYP1A1 expression and reduced pathological effects were observed in the 2,3,7,8-TCDD with P. ginseng extracts treated groups when compared with the TCDD treated group. In summary, our study demonstrates that 2,3,7,8-TCDD induces the pathological and genotoxical damage in rat testes, while P. ginseng extract treatment exhibits a therapeutic capacity to reduce these effects via reduction of CYP1A1 mRNA.

Inhibition of human cytochrome p450 1b1 further clarifies its role in the activation of dibenzo[a,l]pyrene in cells in culture

Metabolic activation and DNA adduct formation of the carcinogenic aromatic hydrocarbon dibenzo[a,l]pyrene (DBP) was investigated in human mammary carcinoma MCF-7 cells and human cytochrome P450 (CYP) 1B1-expressing Chinese hamster V79 cells in culture. It has been shown that DBP is metabolically activated to DNA-binding diol epoxides both in vitro and in vivo. To further establish the role of human CYP1B1 in the activation of DBP, both cell lines were cotreated with DBP and a selective chemical inhibitor of CYP1B1, 2,4,3' ,5'-tetramethoxy-stilbene (TMS). Results from DBP-DNA adduct analyses revealed the complete inhibition of DNA binding when cells were cotreated with DBP and TMS in comparison to DBP alone. Inactivation of CYP1B1 by TMS was also demonstrated through a decrease in the 7-ethoxyresorufin O-deethylase (EROD) activity in microsomes isolated from these cells. Emodin, 3-methyl-1,6,8-trihydroxyanthraquinone, an active ingredient of an herb, has been recently shown of being able to induce CYP1 gene expression. Examination of human CYP1B1 induction and EROD activity confirmed an increase in protein levels upon cotreatment with emodin and DBP. Despite increases in protein levels and enzyme activity, there was no significant change in DBP-DNA binding levels at very low substrate concentrations (17 nM). The data obtained in this study emphasize the central role of CYP1B1 in the activation of DBP in human cells in culture.

CYP1A in TCDD toxicity and in physiology-with particular reference to CYP dependent arachidonic acid metabolism and other endogenous substrates

Toxicologic and physiologic roles of CYP1A enzyme induction, the major biochemical effect of aryl hydrocarbon receptor activation by TCDD and other receptor ligands, are unknown. Evidence is presented that CYP1A exerts biologic effects via metabolism of endogenous substrates (i.e., arachidonic acid, other eicosanoids, estrogens, bilirubin, and melatonin), production of reactive oxygen, and effects on K(+) and Ca(2+) channels. These interrelated pathways may connect CYP1A induction to TCDD toxicities, including cardiotoxicity, vascular dysfunction, and wasting. They may also underlie homeostatic roles for CYP1A, especially when transiently induced by common chemical exposures and environmental conditions (i.e., tryptophan photoproducts, dietary indoles, and changes in oxygen tension).

Activation of ERK1/2 and p38 kinases by polycyclic aromatic hydrocarbons in rat liver epithelial cells is associated with induction of apoptosis

Deregulation of various signaling pathways, linked either to induction of cell proliferation or to modulation of cellular differentiation and apoptosis, has been proposed to contribute to carcinogenicity of polycyclic aromatic hydrocarbons (PAHs). In the present study, we investigated effects of the PAHs previously shown to induce cell proliferation and/or apoptosis in contact-inhibited rat liver epithelial WB-F344 cells, with an aim to define the role of mitogen-activated protein kinases in both events. We found that only strong genotoxin dibenzo[a,l]pyrene (DBalP) activated extracellular signal-regulated kinases 1 and 2 (ERK1/2) and p38 kinase, but not c-Jun N-terminal kinases (JNKs), at concentrations inducing both apoptosis and phosphorylation of p53 tumor suppressor at serine 15 residue. In contrast, the PAHs stimulating cell proliferation in WB-F344 cell line had no effect on activation of ERK1/2, p38 or JNKs. Synthetic inhibitors of ERK1/2 activation (U0126) or p38 kinase activity (SB203580) prevented both apoptosis and induction of p53 phosphorylation by DBalP. Pifithrin-alpha, inhibitor of p53 transcriptional activity, prevented induction of apoptosis and activation of ERK1/2 and p38. Taken together, our data suggest that both ERK1/2 and p38 are activated in response to DBalP and that they might be involved in regulation of cellular response to DNA damage induced by DBalP, while neither kinase is involved in the release from contact inhibition induced by PAHs.

Activation of p53 as a causal step for atherosclerosis induced by polycyclic aromatic hydrocarbons

This study was performed to prove our hypothesis that the metabolite(s) of polycyclic aromatic hydrocarbons (PAHs) caused the activation or phosphorylation of p53 via DNA damage to suppress the liver X receptor (LXR)-mediated signal transductions as a probably more direct mechanism. We found that LXR-mediated trans-activation was inhibited by 3-methylchoranthrene (MC) and doxorubicin (Dox) in HepG2 cells carrying wild-type p53, but not in Hep3B cells possessing mutant p53. The exogenous expression of wild-type p53 suppressed the LXR-mediated trans-activation in Hep3B cells. The expression of mRNA for ATP binding cassette A1 was suppressed by MC and Dox in HepG2 cells. The protein expression of retinoid X receptor (RXR), a partner of LXR to form a heterodimer, was suppressed by MC and Dox in HepG2 cells.

Effect of sulfur dioxide inhalation on CYP1A1 and CYP1A2 in rat liver and lung

Sulfur dioxide (SO2) is a ubiquitous air pollutant, presents in low concentrations in the urban air, and in higher concentrations in the working environment. In the present study, male Wistar rats were housed in exposure chambers and treated with 14.00+/-1.53, 28.00+/-2.12 and 56.00+/-4.28 mg/m3 SO2 for 6 h/day for 7 days, while control rats were exposed to filtered air in the same condition. Highly specific substrates were used as probes of cytochrome P4501A1 (CYP1A1) and cytochrome P4501A2 (CYP1A2). The mRNA levels of CYP1A1 and 1A2 were analyzed in livers and lungs by using a real-time reverse transcription-polymerase chain reaction (real-time RT-PCR) assay. Our results showed that the activities and mRNA levels of P450 were decreased in livers and lungs of rats exposed to SO2. In the liver, a decrease down to 0.68- and 0.64-fold in the CYP1A1 activity, probed by the O-deethylation of ethoxyresorufin (EROD), was observed at higher dose of SO2 (28 and 56 mg/m3); Similarly, CYP1A1 mRNA levels were reduced in livers of rats exposed to SO2 at 28 and 56 mg/m3. For livers, CYP1A2-mediated methoxyresorufin O-demethylase activity (MROD) was unaltered by SO2 at low concentrations, except for a significant decrease in the rats exposed to SO2 at 56 mg/m3 (0.79-fold); however, SO2 at higher concentrations significantly decreased levels of CYP1A2 (28 and 56 mg/m3) (p<0.05). Significant inhibition of both EROD and MROD was observed in lungs of rats exposed to SO2 at 28 and 56mg/m3. CYP1A1 activity was repressed 0.62- and 0.53-fold, while CYP1A2 activity was reduced to 0.74- and 0.55-fold in lungs, respectively. SO2 at higher concentrations (28 and 56 mg/m3) decreased significantly pulmonary CYP1A1 and 1A2 mRNA levels relative to control animals. Furthermore, the decreases of activities and mRNA levels of these P450 enzymes caused by SO2 at different concentrations in lungs and livers of rats followed linear dose-response curves. These results lead to the conclusion that SO2 exposure can reduce CYP1A1 and 1A2 in lungs and livers of rats and ROS and/or cytokines might act as mediators of this effect according to previous studies performed in mice. Reduction of hepatic and pulmonary CYPlAl and lA2 expression during SO2 exposure may be part of an adaptive response by the liver and lung to minimize cell damage.

Gene expression of drug metabolizing enzymes in adult and aged mouse liver: A modulation by immobilization stress

The role of stress in the regulation of enzymatic systems involved in the biotransformation of xenobiotics, as well as endogenous substrates in the liver was investigated using single immobilization stress as a model. Adult (3 months of age) and aged (26 months) C3H/a male mice were used. Cytochrome P450 1A1 and 1A2 (CYP1A1 and CYP1A2), glutathione S-transferase M1 (GSTM1), aryl hydrocarbon receptor (AHR), aryl hydrocarbon receptor nuclear translocator (ARNT) and catechol-O-methyltransferase (COMT) mRNA levels in the mouse liver were measured by a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) method. Excluding CYP1A1, experiments revealed significant differences in the expression of these genes between adult- and aged-control animals. The influence of stress on the expression of genes studied was shown to be higher in adult mice than in aged ones. Our results clearly demonstrate the lack of response or even the attenuation of gene expression in aged animals that may play an important role in age-related pathologies and diseases.

Occupational exposure to polycyclic aromatic hydrocarbons suppresses constitutive expression of CYP1B1 on the transcript level in human leukocytes

Expression patterns of the cytochromes P450 CYP1A1 and CYP1B1 have been analyzed on the transcript level in leukocytes of persons (n = 30) occupationally exposed to polycyclic aromatic hydrocarbons (PAH). To assess effects on expression levels results were compared with data obtained from a non-exposed control group (n = 68). CYP1B1 transcripts can be detected in all subjects of the control group but vary largely in their levels (factor 35). Statistical analysis shows that this variability is neither due to the age of the persons nor due to cigarette smoking. Furthermore, there is no difference in expression levels between genders. In contrast to CYP1B1, CYP1A1 is detectable in only 14% of the subjects. People involved in graphite electrode production and exposed to PAH show largely decreased CYP1B1 transcript levels. In 67% of the subjects, CYP1B1 is no more detectable at all. Vice versa, expression of CYP1A1 is increased in exposed persons so that 80% become positive for CYP1A1 vs. 14% of the control group. The results show that occupational exposure to PAH apparently leads to effect-relevant internal doses. Both, suppression of CYP1B1 and induction of CYP1A1 in leukocytes can be used as exposure parameters proving both enzymes to be suitable biomarkers of exposure. The suppression of CYP1B1 is an unexpected effect which needs further investigation. It is discussed that CYP1B1 and CYP1A1 indeed share a common Ah receptor mediated transcriptional regulation but that differences in promoter structure of the two genes and tissue-specific expression profiles of transcription factors may cause a differential expression behaviour.

Assessment of temporal biochemical and gene transcription changes in rat liver cytochrome P450: utility of real-time quantitative RT-PCR

PURPOSE

A conventional approach to assess cytochrome P450 (CYP) induction in preclinical animal models involves daily dosing for a least a week followed by Western blot and/or enzyme activity analysis. To evaluate the potential benefit of a third more specific and sensitive assay, real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR), with the objective of reducing the duration of the conventional 1-week study, we simultaneously assessed gene expression by qRT-PCR along with Western blots and enzyme activity assays as a time course in an in vivo model.

METHODS

Rats were dosed daily for 8 days with model inducers of CYP1A, CYP2B, CYP3A, or CYP4A. Liver P450 levels were measured after 0.5, 1, 2, 4, and 8 days of dosing by qRT-PCR, Western blot, and enzyme activity.

RESULTS

CYP1A, CYP3A, and CYP4A genes were maximally induced very rapidly (0.5-1 day), whereas the CYP2B gene was maximally induced after a lag time of 4 days. In all cases, fold changes in induction detected by qRT-PCR were greater than fold changes in protein levels and enzyme activities.

CONCLUSIONS

Maximal persistent and larger fold changes observed by qRT-PCR either preceded or occurred simultaneously with maximal sustained fold changes in protein levels as measured by Western blots and enzyme activity assays. Our data show that qRT-PCR provides increased sensitivity and specificity over conventional assays and may be key information for reliable assessment of drug-related changes in CYP induction during the transition from discovery to toxicology studies.

Cytochrome P450-dependent toxicity of environmental polycyclic aromatic hydrocarbons towards human macrophages

Polycyclic aromatic hydrocarbons (PAHs) such as benzo(a)pyrene (BP) are potent immunosuppressive environmental contaminants acting on lymphocytes and monocytes. To establish whether differentiated macrophages, which play a crucial role in innate and acquired immunity, can also constitute major cellular targets, we have characterized PAH effects towards primary human macrophages. BP-treatment was found to dramatically alter their functional capacities and to trigger a caspase- and mitochondrion-related apoptosis, associated with down-regulation of the survival factors c-FLIP(L) and Bcl-X(L) and up-regulation of the pro-apoptotic factor p53. Such deleterious effects were associated with BP metabolite production, whose inhibition by the cytochrome P-450 1A1 inhibitor alpha-naphthoflavone fully abolished BP toxicity. In contrast to BP, the related halogenated arylhydrocarbon 2,3,7,8-tetrachlorodibenzo-p-dioxin, known to be poorly metabolized if any, only minimally affected macrophages. Overall, these data provide evidence for a cytochrome P-450-dependent toxicity of PAHs towards human differentiated macrophages, which may contribute to their immunosuppressive effects.

Effect of lindane on hepatic and brain cytochrome P450s and influence of P450 modulation in lindane induced neurotoxicity

Oral administration of lindane (2.5, 5, 10 and 15 mg/kg, body weight) for 5 days was found to produce a dose-dependent increase in the activity of P450 dependent 7-ethoxyresorufin-O-deethylase (EROD), 7-pentoxyresorufin-O-dealkylase (PROD) and N-nitrosodimethylamine demethylase (NDMA-d) in rat brain and liver. A significant increase in the hepatic and brain P450 monooxygenases was also observed when the duration of exposure of low dose (2.5 mg/kg) of lindane was increased from 5 days to 15 or 21 days. As observed with different doses, the magnitude of induction in the activity of P450 monooxygenases was several fold higher in liver microsomes when compared with the brain. Western blotting studies have indicated that the increase in the P450 enzymes could be due to the increase in the expression of P450 1A1/1A2, 2B1/2B2 and 2E1 isoenzymes. In vitro studies using organic inhibitors specific for individual P450 isoenzymes and antibody inhibition experiments have further demonstrated that the increase in the activity of PROD, EROD and NDMA-d are due to the increase in the levels of P450 2B1/2B2, 1A1/1A2 and 2E1 isoenzymes, respectively. Induction studies have further shown that while pretreatment of 3-methylcholanthrene (MC), an inducer of P4501A1/1A2, did not produce any significant effect in the incidence of lindane induced convulsions, pretreatment with phenobarbital (PB), an inducer of P450 2B1/2B2 or ethanol, an inducer of P450 2E1 catalysed reactions, significantly increased the incidence of lindane induced convulsions. Similarly, when the P450-mediated metabolism of lindane was blocked by cobalt chloride incidence of convulsions was increased in animals treated with lindane indicating that lindane per se or its metabolites formed by PB or ethanol inducible P450 isoenzymes are involved in its neurobehavioral toxicity.

Effect of pretreatment of cytochrome P450 (P450) modifiers on neurobehavioral toxicity induced by deltamethrin

To investigate the involvement of cytochrome P450 (P450) enzyme induction and the effect of different P450 modifiers in the neurobehavioral toxicity of deltamethrin, deltamethrin (10 mg/kg; orally for 1 day) was administered to young male albino Wistar rats, or in rats pretreated with phenobarbital (PB; 80 mg/kg, ip for 5 days), an inducer of P450 2B1/2B2 or 3-methylcholanthrene (MC; 30 mg/kg, ip for 5 days), an inducer of P450 1A1/1A2 or cobalt chloride (CoCl(2); sc for 2 days), a depletor of P450s. The administration of PB or MC or CoCl(2) alone did not produced any symptoms of neurobehavioral toxicity. While a single oral administration of deltamethrin produced tremors in two out of 10 rats and decreased the spontaneous locomotor activity, pretreatment with MC or PB potentiated the deltamethrin induced neurobehavioral toxicity with 50% of the treated rats exhibiting tremors. Half of the animals pretreated with MC prior to exposure to deltamethrin also exhibited choreoathetosis. The decrease in the spontaneous locomotor activity was found to be much more significant in PB- or MC-pretreated animals exposed to deltamethrin. In contrast to the pretreatment with inducers, rats pretreated with CoCl(2) exhibited no symptoms of tremors or choreoathetosis, indicating that a reactive metabolite of deltamethrin is formed by P450 catalysed reactions which is involved in the neurobehavioral toxicity of deltamethrin.

Tissue-specific induction of cytochromes P450 1A1 and 1B1 by polycyclic aromatic hydrocarbons and polychlorinated biphenyls in engineered C57BL/6J mice of arylhydrocarbon receptor gene

Tissue-specific induction of mRNA of cytochrome P450 (P450 or CYP) 1A1 and 1B1 by polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) was investigated in wild and arylhydrocarbon receptor (AhR)-deficient C57BL/6J mice. Ratios of mRNA expression of CYP1A1 or CYP1B1 over beta-actin were determined and used to compare levels of expression and induction of these P450s by PAHs and PCBs in various organs. CYP1A1 mRNA was detected in control mice at very low levels in liver, lung, heart, kidney, intestine, thymus, testis, uterus, ovary, and brain and was highly induced in these organs by benzo[a]pyrene and 3,4,3',4'-tetrachlorobiphenyl in AhR(+/+) mice. In AhR(+/+) and AhR(-/-) mice, CYP1B1 mRNA was found to be constitutively expressed at significant levels in heart (the ratio of mRNAs of CYP1B1 to beta-actin was approximately 0.6), kidney ( approximately 0.8), intestine ( approximately 0.3), testis ( approximately 0.9), thymus ( approximately 0.4), uterus ( approximately 0.3), ovary ( approximately 1.4), and brain ( approximately 0.4), whereas it was low in liver and lung (the mRNA ratio to beta-actin was <0.2 in these cases). CYP1B1 in the latter two organs was highly induced by PAHs and 3,4,3',4'-tetrachlorobiphenyl in AhR(+/+) mice. The induction of CYP1B1 by PAHs and PCBs was more extensive in organs in which the constitutive expression of CYP1B1 was low. For example, CYP1B1 was induced 9-fold and 10-fold by benzo[a]pyrene and 3,4,3',4'-tetrachlorobiphenyl in livers of male and female mice, respectively, whereas in testis and ovary, the fold induction of CYP1B1 by two inducers was only 1.1 and 1.4, respectively. Liver microsomal xenobiotic oxidation activities were induced by these PAHs and PCBs in male and female AhR(+/+) mice. These results suggest that CYP1A1 and CYP1B1 are differentially regulated in their expression in extrahepatic organs of mice and could be induced by PAHs and PCBs with different extents of induction depending on the inducers used and the organs examined in AhR(+/+) mice. The findings of significant levels of constitutive expression of CYP1B1 in AhR(-/-) mice as well as AhR(+/+) mice in several organs including heart, kidney, thymus, testis, ovary, and brain in AhR(-/-) mice as well as AhR(+/+) mice are of importance in understanding the basis of toxicity and carcinogenesis by chemicals that are metabolized by CYP1B1.

Studies on the inhibition of human cytochromes P450 by selenocysteine Se-conjugates

1. To investigate whether cytochrome P450 (P450) inhibition can contribute to the chemopreventive activity of selenocysteine Se-conjugates (SeCys conjugates), 21 SeCys conjugates were screened for their inhibitory potency towards seven of the most important human P450s. 2. The majority of the SeCys conjugates produced near complete inhibition of CYP1A1 at a concentration of 250 microm. The most potent inhibitor, Se-benzyl-L-selenocysteine, displayed an IC50 of 12.8 +/- 1.2 microm. CYP2C9, -2C19 and -2D6 were moderately (50-60%) inhibited by the SeCys conjugates. CYP1A2, -2E1 and -3A4 were least inhibited. 3. Studies on the susceptibility of CYP1A1 to SeCys conjugates implicated a thiol-reactive intermediate, as evidenced by reduced inhibition levels in the presence of glutathione and N-acetyl cysteine. Uncoupling of the P450-catalytic cycle was of no importance as ROS scavengers did not influence inhibition levels. 4. P450 inhibition by two physiologically relevant metabolite classes of SeCys conjugates was also studied. N-acetylation of SeCys conjugates consistently increased the inhibitory potency towards CYP1A2, -2C19, -2E1 and -3A4. Beta-lyase catalysed bioactivation of alkyl-substituted SeCys conjugates or Se-benzyl-L-selenocysteine produced little or no additional inhibition of P450 activity. For Se-phenyl-L-selenocysteine, however, significant increases in P450 inhibition were obtained by beta-lyase pre-incubation. 5. It is concluded that the potent and relatively selective CYP1A1 inhibition exerted by SeCys conjugates may contribute to their chemopreventive activity.

Comparative study on the bioactivation mechanisms and cytotoxicity of Te-phenyl-L-tellurocysteine, Se-phenyl-L-selenocysteine, and S-phenyl-L-cysteine

Tellurium compounds are effective antioxidants and chemoprotectors, even more active than their selenium and sulfur analogues. In addition to these properties, some selenium compounds, such as selenocysteine Se-conjugates, possess significant chemopreventive and antitumor activities, and selenol metabolites are considered as active species. In the present study, we have synthesized Te-phenyl-L-tellurocysteine and evaluated its bioactivation and cytotoxicity. The activities of this compound were compared with those of the corresponding selenium and sulfur analogues. Te-Phenyl-L-tellurocysteine is bioactivated into its corresponding tellurol, as detected by GC-MS, by cysteine conjugate beta-lyase and amino acid oxidase, analogously to what has been shown previously for Se-phenyl-L-selenocysteine. The rate of beta-elimination may reflect the bond strength of the corresponding C-S, C-Se, and C-Te bond. Bioactivation of Te-phenyl-L-tellurocysteine and its selenium and sulfur analogues by oxidative enzymes was evaluated by measuring NADPH-dependent activation of hepatic mGST and inhibition of EROD. Te-Phenyl-L-tellurocysteine and Se-phenyl-L-selenocysteine displayed strong and time-dependent mGST activation, while S-phenyl-L-cysteine resulted in no significant activation. Te-Phenyl-L-tellurocysteine was also a strong inhibitor of EROD activity. In addition to EROD inhibition, Te-phenyl-L-tellurocysteine was the strongest inhibitor of several human cytochrome P450 isoenzymes followed by Se-phenyl-L-selenocysteine, while S-phenyl-L-cysteine was the weakest inhibitor. Interestingly, Te-phenyl-L-tellurocysteine selectively inhibited cytochrome P450 1A1 directly, which is, for example, responsible for the activation of several procarcinogens. Preliminary cytotoxicity studies with Te-phenyl-L-tellurocysteine in freshly isolated rat hepatocytes showed a time-dependent depletion of GSH and LDH leakage comparable with the relatively nontoxic drug paracetamol, while the selenium and sulfur analogues were nontoxic toward rat hepatocytes. In conclusion, because the chemopreventive and antitumor activities of selenium compounds are thought to be mediated via their selenol metabolites and tellurium compounds might be even more active than selenium compounds, tellurocysteine Te-conjugates might be an interesting novel class of prodrugs for the formation of biologically active tellurols.

Ontogeny of hepatic and renal systemic clearance pathways in infants: part I

Dramatic developmental changes in the physiological and biochemical processes that govern drug pharmacokinetics and pharmacodynamics occur during the first year of life. These changes may have significant consequences for the way infants respond to and deal with drugs. The ontogenesis of systemic clearance mechanisms is probably the most critical determinant of a pharmacological response in the developing infant. In recent years, advances in molecular techniques and an increased availability of fetal and infant tissues have afforded enhanced insight into the ontogeny of clearance mechanisms. Information from these studies is reviewed to highlight the dynamic and complex nature of developmental changes in clearance mechanisms in infants during the first year of life. Hepatic and renal elimination mechanisms constitute the two principal clearance pathways of the developing infant. Drug metabolising enzyme activity is primarily responsible for the hepatic clearance of many drugs. In general, when compared with adult activity levels normalised to amount of hepatic microsomal protein, hepatic cytochrome P450-mediated metabolism and the phase II reactions of glucuronidation, glutathione conjugation and acetylation are deficient in the neonate, but sulfate conjugation is an efficient pathway at birth. Parturition triggers the dramatic development of drug metabolising enzymes, and each enzyme demonstrates an independent rate and pattern of maturation. Marked interindividual variability is associated with their developmental expression, making the ontogenesis of hepatic metabolism a highly variable process. By the first year of life, most enzymes have matured to adult activity levels. When compared with adult values, renal clearance mechanisms are compromised at birth. Dramatic increases in renal function occur in the ensuing postpartum period, and by 6 months of age glomerular filtration rate normalised to bodyweight has approached adult values. Maturation of renal tubular functions exhibits a more protracted time course of development, resulting in a glomerulotubular imbalance. This imbalance exists until adult renal tubule function values are approached by 1 year of age. The ontogeny of hepatic biliary and renal tubular transport processes and their impact on the elimination of drugs remain largely unknown. The summary of the current understanding of the ontogeny of individual pathways of hepatic and renal elimination presented in this review should serve as a basis for the continued accruement of age-specific information concerning the ontogeny of clearance mechanisms in infants. Such information can only help to improve the pharmacotherapeutic management of paediatric patients.

Cytochrome P450 1B1 determines susceptibility to dibenzo[a,l]pyrene-induced tumor formation

Metabolic activation, DNA binding, and tumorigenicity of the carcinogenic polycyclic aromatic hydrocarbon dibenzo[a,l]pyrene (DB[a,l]P) catalyzed by murine cytochrome P450 (P450) enzymes were investigated. DNA binding of DB[a,l]P in human mammary carcinoma MCF-7 and human P450-expressing Chinese hamster V79 cell lines was previously shown to occur preferentially with metabolically generated fjord region DB[a,l]P-11,12-dihydrodiol 13,14-epoxides (DB[a,l]PDE). To elucidate different capabilities of murine P450 1A1 and 1B1 for metabolic activation of DB[a,l]P, V79 cell cultures stably expressing P450s 1A1 or 1B1 from mice were exposed to 10 or 100 nM DB[a,l]P. Both cell lines transformed DB[a,l]P to DNA binding intermediates. As with V79 cells expressing the corresponding human P450 enzyme [Luch et al. (1998) Chem. Res. Toxicol. 11, 686-695], murine P450 1B1-catalyzed metabolism and DNA binding proceeded exclusively through generation of fjord region DB[a,l]PDE. In addition, only DB[a,l]PDE-derived DNA adducts were found in V79 cells expressing P450 1A1 from mice. This is in contrast to our recent findings with V79 cells expressing P450 1A1 from humans or rats which catalyzed the formation of both highly polar DNA adducts as well as nonpolar DB[a,l]PDE-DNA adducts. To establish the role of P450 1B1 in DB[a,l]P-induced tumor formation in vivo, we treated P450 1B1-null and wild-type mice intragastrically and monitored survival rates and appearance of neoplasias in various organs. All wild-type mice (n = 17) used in this study developed at least one tumor at one site (tumor rate of 100%). In contrast, 5 of 13 P450 1B1-null mice were observed to be free from any tumor (tumor rate of 62%). The organ sites of tumor formation and the dignity of tumors were different between wild-type and P450 1B1-null mice. Wild-type mice were diagnosed with both benign and malignant tumors of the ovaries, lymphoid tissues, as well as with skin and endometrial hyperplasias, whereas P450 1B1-null mice developed only lung adenomas and endometrial hyperplasias. DNA binding studies using embryonic fibroblasts isolated from these animals provided further evidence that P450 1B1-catalyzed formation of fjord region DB[a,l]PDE-DNA adducts is the critical step in DB[a,l]P-mediated carcinogenesis in mice, and probably also in man.

No role of protected region B of human cytochrome P4501A2 gene (CYP1A2) as an AP-1 response element

Cytochrome P4501A2 (CYP1A2) is a member of the cytochrome P450 family of isozymes involved in the phase I drug metabolism of vertebrates. CYP1A2 is responsible for the activation of a number of aromatic amines to mutagenic and carcinogenic forms. Thus, the level of CYP1A2, which varies among different populations, may determine an individual's susceptibility to these chemicals. We have previously reported on the importance of a cis element named PRB (protected region B) in the regulation of human Cytochrome P4501A2 (CYP1A2) gene, which appeared to act as a positive regulatory element. Closer examination of the PRB sequence (-2218 to -2187 bp) revealed a putative AP-1 binding site, TGACTAA, at -2212 bp (Chung and Bresnick, 1997). To elucidate the role of AP-1 in CYP1A2 regulation, we transiently overexpressed c-Jun and c-Fos transcription factors in human hepatoma HepG2 cells, and examined their influence on the CYP1A2 promoter activity by reporter gene assays. Cotransfection of the c-Jun and the c-Fos expression vectors increased the induced transactivation by five to six fold from the CYP1A2 promoter constructs. However, deletion of the PRB element did not affect the degree of activation by the c-Jun and the c-Fos. Therefore, it is unlikely that the c-Jun and the c-Fos activate the CYP1A2 promoter through this AP-1 consensus-like sequence in the PRB region.

A high-throughput cell-based reporter gene system for measurement of CYP1A1 induction

INTRODUCTION

Enzyme induction is undesirable in new drug discovery process, with consequences spanning from auto-induction to toxicity. Cytochrome P450 (CYP) 1A1 has long been known to be one of the metabolic enzymes involved in activating many procarcinogens, the first step toward tumor formation during chemical carcinogenesis. Induction of CYP1A1 during drug treatment may predispose the patients to some risk of chemical carcinogenesis.

METHODS

Based on the signal-transduction mechanism of CYP1A1 induction, a high-throughput reporter-gene system was established by stable transformation of H4IIE cells to incorporate the luciferase gene under control of CYP1A1 promoter. This stable cell line was validated with known CYP1A1 inducers, such as 3-methylcholanthrene (3-MC), beta-naphthoflavone (beta-NF), alpha-naphthoflavone (alpha-NF) and 3-indocarbinol. Thirty in-house new chemical entities (NCEs) were then screened with this reporter-gene system, and also administered to rats to evaluate in vivo CYP1A1 induction.

RESULTS

CYP1A1 reporter gene system can be used to identify strong inducers, such as 3-MC, beta-NF and alpha-NF, and weak inducers, such as 3-indocarbinol. In vitro induction of 30 in-house compounds in reporter gene system did not correlate with in vivo induction in rat liver microsome measured by ethoxyresorufin-O-dealkylation (EROD) activity, but had a reasonable correlation with Western blot signals.

DISCUSSION

This reporter-gene system may be useful in eliminating compounds that can cause CYP1A1 induction at an early stage of drug discovery.

Human carcinogens: an evaluation study via the COMPACT and HazardExpert procedures

The results of computer-optimized molecular parametric analysis of chemical toxicity (COMPACT) and HazardExpert evaluations on 14 established human carcinogens are reported. The concordances between COMPACT and carcinogenicity (71%) and between HazardExpert and carcinogenicity (57%) are significantly improved when taken in combination, where all 14 carcinogens are correctly identified by the two systems used in conjunction. However, if a negative energy of the highest occupied molecular orbital (E(HOMO)) value is regarded as evidence of electrophilic reactivity likely to give rise to mutagenicity and carcinogenicity, then 13/14 (93%) of the carcinogens are correctly identified by combination with the COMPACT procedure alone. It is possible, therefore, to establish likely carcinogenicity arising from either P450 mediation (CYP1 and CYP2E) or compound electrophilicity via the employment of a straightforward approach to molecular and electronic structure calculation, a process that can be performed in a relatively short time frame (i.e., less than 1 hour per chemical) and at a low cost.

Juvenile sea bass liver P450, EROD induction, and erythrocytic genotoxic responses to PAH and PAH-like compounds

Sea bass were exposed, for 0, 2, 4, 6 and 8 h, to 0 or 2.7 microM beta-naphthoflavone (BNF), or to 0, 0.1, 0.3, 0.9, or 2.7 microM benzo[a]pyrene (B(a)P) and naphthalene (NAPH). Liver cytochrome P-450 content (P450) and liver ethoxyresorufin-O-deethylase activity (EROD) induction were determined as phase I biotransformation responses, whereas erythrocytic micronuclei (EMN) and erythrocytic nuclear abnormalities (ENA) tests were performed to assess genotoxic effects. Liver alanine aminotransferase activity and liver somatic index were determined, respectively, as liver damage and common health indicators. A significant increase in sea bass EROD activity began, respectively, at 2 and 4 h exposure to 2.7 microM B(a)P and 2.7 microM BNF, whereas NAPH failed to induce EROD activity. Maximal EROD activity was observed after 6 h exposure to 2.7 microM BNF (9-fold increase), 2.7 microM B(a)P (4-fold increase), and 2.7 microM NAPH (2-fold increase), indicating BNF as the most potent EROD inducer (BNF>B(a)P>NAPH). A significant increase in liver P450 content was observed at 6 h exposure to 2.7 microM BNF (6.5-fold increase), indicating BNF as the most potent P450 inducer. A significant P450 increase was observed at 8 h exposure only to 0.1 microM B(a)P (2-fold increase), whereas it slightly increased at 2 h exposure to 2.7 microM NAPH, within a wide variable range. The BNF, NAPH, and B(a)P genotoxic potential was demonstrated as sea bass EMN and ENA. B(a)P promoted at 2 h exposure a significant EMN (24-fold) and ENA (2.2-fold) increase, whereas NAPH exhibited similar results only at 8 h exposure. BNF also increased significantly sea bass EMN (8-fold) and ENA (1.5-fold) after 8 h. The results indicated B(a)P as the most genotoxic compound, followed by NAPH and BNF (B(a)P>NAPH>BNF). Despite the low liver P450 content and EROD activity induction by NAPH and B(a)P, their genotoxic potential was higher than that of BNF.

Summary of information on human CYP enzymes: human P450 metabolism data

This chapter is an update of the data on substrates, reactions, inducers, and inhibitors of human CYP enzymes published previously by Rendic and DiCarlo (1), now covering selection of the literature through 2001 in the reference section. The data are presented in a tabular form (Table 1) to provide a framework for predicting and interpreting the new P450 metabolic data. The data are formatted in an Excel format as most suitable for off-line searching and management of the Web-database. The data are presented as stated by the author(s) and in the case when several references are cited the data are presented according to the latest published information. The searchable database is available either as an Excel file (for information contact the author), or as a Web-searchable database (Human P450 Metabolism Database, www.gentest.com) enabling the readers easy and quick approach to the latest updates on human CYP metabolic reactions.

Induction by xenobiotics of phase I and phase II enzyme activities in the human keratinocyte cell line NCTC 2544

This study analyses the expression and induction of several drug-metabolising enzyme activities involved in either phase I or phase II biotransformations in NCTC 2544 human keratinocytes. The phase I activities 7-ethoxycoumarin O-deethylase (ECOD), 7-ethoxyresorufin O-deethylase (EROD) and 7-pentoxyresorufin O-depenthylase (PROD) were easily detectable in basal conditions. During incubations lasting up to 144 h in the presence of the classical cytochrome P450 inducers beta-naphthoflavone (BNF), 3-methylcholanthrene (MC) and phenobarbital (PB), a considerable and significant increase in all the three activities was observed. PROD activity was induced up to 4.5-fold after 96 h in the presence of PB. The MC-induced ECOD and EROD activities were also dose-dependently inhibited by alpha-naphothflavone, which was given to the cells during the incubation with CYP 1A1 inducers. Also the PB-induced PROD activity was decreased by the simultaneous addition of the CYP 2B inhibitor metyrapone. Both cytochrome P450 inhibitors were used at non-cytotoxic concentrations. The phase II enzymes glutathione S-transferase, aldehyde dehydrogenase and quinone reductase were all highly expressed and inducible by MC. The exposure (24 h) of the cells to four hair dyes used in cosmetic formulations resulted in a marked increase in ECOD activity. All data give sustained evidence for the suitability of NCTC 2544 cell line to skin toxicology studies.

Common and uncommon cytochrome P450 reactions related to metabolism and chemical toxicity

Cytochrome P450 (P450) enzymes catalyze a variety of reactions and convert chemicals to potentially reactive products as well as make compounds less toxic. Most of the P450 reactions are oxidations. The majority of these can be rationalized in the context of an FeO(3+) intermediate and odd electron abstraction/rebound mechanisms; however, other iron-oxygen complexes are possible and alternate chemistries can be considered. Another issue regarding P450-catalyzed reactions is the delineation of rate-limiting steps in the catalytic cycle and the contribution to reaction selectivity. In addition to the rather classical oxidations, P450s also catalyze less generally discussed reactions including reduction, desaturation, ester cleavage, ring expansion, ring formation, aldehyde scission, dehydration, ipso attack, one-electron oxidation, coupling reactions, rearrangement of fatty acid and prostaglandin hydroperoxides, and phospholipase activity. Most of these reactions are rationalized in the context of high-valent iron-oxygen intermediates and Fe(2+) reductions, but others are not and may involve acid-base catalysis. Some of these transformations are involved in the bioactivation and detoxication of xenobiotic chemicals.

Role of plant polyphenols in genomic stability

Polyphenols are a large and diverse class of compounds, many of which occur naturally in a range of food plants. The flavonoids are the largest and best-studied group of these. A range of plant polyphenols are either being actively developed or currently sold as dietary supplements and/or herbal remedies. Although, these compounds play no known role in nutrition (non-nutrients), many of them have properties including antioxidant, anti-mutagenic, anti-oestrogenic, anti-carcinogenic and anti-inflammatory effects that might potentially be beneficial in preventing disease and protecting the stability of the genome. However not all polyphenols and not all actions of individual polyphenols are necessarily beneficial. Some have mutagenic and/or pro-oxidant effects, as well as interfering with essential biochemical pathways including topoisomerase enzyme activities, prostanoid biosynthesis and signal transduction. There is a very large amount of in vitro data available, but far fewer animal studies, and these are not necessarily predictive of human effects because of differences in bacterial and hepatic metabolism of polyphenols between species. Epidemiological studies suggest that high green tea consumption in the Japanese population and moderate red wine consumption in the French population may be beneficial for heart disease and cancer, and these effects may relate to specific polyphenols. A small number of adequately controlled human intervention studies suggest that some, but not all polyphenol extracts or high polyphenol diets may lead to transitory changes in the antioxidative capacity of plasma in humans. However, none of these studies have adequately considered long-term effects on DNA or the chromosome and unequivocally associated these with polyphenol uptake. Furthermore, clinical trials have required intravenously administered polyphenols at concentrations around 1400mg/m(2) before effects are seen. These plasma concentrations are unlikely to be achieved using the dietary supplements currently available. More focused human studies are necessary before recommending specific polyphenolic supplements at specific doses in the human population.

Induced CYP1A mRNA, protein and catalytic activity in the liver of feral fish, leaping mullet, Liza saliens

In this study, we examined whether levels of P4501A mRNA expression were naturally induced in feral fish, Liza saliens, and whether CYP1A protein levels and associated enzyme activity, EROD, were also increased. Induction of mRNA was measured using a nucleic acid hybridization technique. For the hybridization studies, a new 33-mer oligonucleotide probe 5'-dCTC ATC CAG CTT CCT GTC CTC GCA GTG ATC AAT-3' was designed, which corresponded to the totally conserved amino acid motif of CYP1A protein from positions 291 to 301 among the various fish species. Results of Northern blot analysis revealed that RNA isolated from the liver of mullet collected from the highly contaminated region of Izmir Bay with a dissolved and dispersed petroleum hydrocarbon content of 12.45 microg l(-1) gave a strong hybridization signal, whereas only a weak hybridization signal was detected in the liver RNA of fish caught from the reference site containing less than 1 microg l(-1) of petroleum hydrocarbons. Similarly, fish from the contaminated site had approximately 80 times more EROD activity than the feral fish captured from the reference site. Studies using polyclonal antibodies produced against purified mullet CYP1A also showed the similar trend. In conclusion, feral leaping mullet caught from contaminated water displayed induction of CYP1A at three levels of expression, namely, mRNA, apoprotein and catalytic activity.

Protective effect of stiripentol on acetaminophen-induced hepatotoxicity in rat

Acetaminophen (APAP) is mainly eliminated at a therapeutic dose through glucuronidation and sulfatation and a small fraction is oxidized by cytochromes P450 (CYP) 2E1, 3A4, and 1A2 to N-acetyl-p-benzoquinone-imine (NAPQI), a highly reactive metabolite further conjugated with glutathione into APAP-GSH, and then metabolized to APAP-cystein and APAP-mercapturate excreted in urine. After APAP overdose, the glucuronidation and sulfatation pathways are saturated and the production of NAPQI increases, causing hepatic injury. Stiripentol (STP); (200 mg/kg), an anticonvulsant drug inhibitor of CYP1A2 and CYP3A4 in vivo in humans was tested against APAP-induced toxicity in rat in comparison with N-acetylcysteine (NAC; 100 mg/kg). The mortality rates 24 h after APAP overdose (2 x 500 mg/kg) were 63% (control), 38% (NAC), 0% (STP), and 4% (STP + NAC). The mean plasma transaminase concentrations 5 and 24 h after overdose were significantly higher in control than in STP and NAC groups. The percentage of rats without microscopic liver necrosis 5 h after APAP overdose was significantly higher in rats receiving STP (100%), NAC (83%), or STP + NAC (83%) than controls (42%). In another experiment, four similar groups were administered 50 mg/kg APAP. Plasma AUC(0-5 h) for APAP-GSH, APAP-cystein, and APAP-mercapturate as well as urine APAP-mercapturate mean amounts were significantly lower in STP animals than in the other groups. STP (200 mg/kg) inhibited NAPQI synthesis through CYP inhibition, thus preventing both liver necrosis and mortality in rats.

The discovery of RPR 200765A, a p38 MAP kinase inhibitor displaying a good oral anti-arthritic efficacy

RPR132331, a 2-(2-dioxanyl)imidazole, was identified as an inhibitor of tumour necrosis factor (TNF)alpha release from lipopolysaccharide (LPS)-stimulated human monocytes. An intensive programme of work exploring the biology, toxicity and physical chemistry of a novel series of inhibitors, derived from RPR132331, has led to the identification of RPR200765A, a development candidate for the treatment of rheumatoid arthritis (RA). RPR200765A is a potent and selective inhibitor of p38 MAP kinase (IC50 = 50 nM). It inhibits LPS-stimulated TNFalpha release both in vitro, from human monocytes (EC50 = 110 nM), and in vivo in Balb/c mice (ED50 = 6 mg/kg). At oral doses between 10 and 30 mg/kg/day it reduces the incidence and progression in the rat streptococcal cell wall (SCW) arthritis model when administered in either prophylactic or therapeutic dosing regimens. The compound, which is a mesylate salt and exists as a stable monohydrate, shows good oral bioavailabiltiy (F = 50% in the rat) and excellent chemical stability. The data from the SCW disease model suggests that RPR200765A could exhibit a profile of disease modifying activity in rheumatoid arthritis (RA) patients which is not observed with current drug therapies.

Ability of polycyclic aromatic hydrocarbons to induce 7-ethoxyresorufin-o-deethylase activity in a trout liver cell line

Along with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 24 unsubstituted polycyclic aromatic hydrocarbons (PAHs) were evaluated for their ability to induce 7-ethoxyresorufin-o-deethylase (EROD) activity in the rainbow trout liver cell line RTL-W1. When the duration and cell density of exposure were increased, the EC(50) for EROD induction was relatively constant for TCDD, but increased for PAHs. Regardless of exposure conditions, EROD activity was not induced by 9 PAHs: naphthalene, phenanthrene, anthracene, pyrene, perylene, acenaphthylene, acenaphthene, fluorene, and fluoranthene. Two PAHs, benzo[g,h,i]perylene and coronene, induced EROD activity inconsistently. The remaining 13 PAHs consistently induced EROD activity. The EC(50)s for induction exhibited approximately a 110-fold range. The order of potency, from most to least potent, was benzo[k]fluoranthene, dibenzo[a,i]pyrene, dibenzo [a,h]anthracene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene, benzo [b]fluoranthene, pentacene, benzo[b]anthracene, benzo[b] fluorene, chrysene, benzo[a]anthracene, benzo[e]pyrene, and triphenylene. When the induction potency was expressed relative to TCDD, the toxic equivalency factors (TEFs) ranged from 0.001 to 0.000 01. When expressed relative to benzo[a]pyrene, the TEFs ranged from 3.44 to 0. 03.

Influence of urethane and ketamine on rat hepatic cytochrome P450 in vivo

The aim of this study was to identify the effects of widely used laboratory anaesthetics on cytochrome (CYP) activity in male Sprague Dawley rats in vivo. The anaesthetics used were urethane and ketamine. 7-Ethoxyresorufin (EROD), 7-pentoxyresorufin (PROD), aniline and ethylmorphine were used as substrates for CYP 1A, CYP 2B, CYP 2E1 and CYP 3A, respectively. Urethane increased EROD (CYP 1A) activity by 40 % (p < 0.01), and hydroxylation of aniline (CYP 2E1) by 14 % in the early phase of anaesthesia and by 60 % (p < 0.01) in the later one. Urethane also reduced the demethylation of ethylmorphine by 37 % (p < 0.01), but did not affect CYP 2B activity significantly. Ketamine did not significantly affect CYP 1A, 2B or 2E1. However, it reduced the demethylation of ethylmorphine (i.e. CYP 3A) by 32 % (p < 0.01). From these data, we concluded that a single dose of urethane inhibits CYP 3A but increases CYP 2E1 and CYP 1A, and that a single dose of ketamine inhibits the activity of CYP 3A.

Differential expression of CYP1A1, CYP1A2, CYP1B1 in human kidney tumours

The presence of mRNA of individual members of the CYP1 gene family in normal and neoplastic kidney has been investigated by RTPCR. CYP1B1 mRNA was consistently expressed in both normal and neoplastic kidney while CYP1A1 was present in the majority of normal and neoplastic whereas CYP1A2 was infrequently expressed. Expression of the Ah receptor and Arnt which are involved in the transcriptional activation of the CYP1 genes was also studied. The Ah receptor mRNA and Arnt mRNA were consistently expressed both in kidney tumours and normal kidney. These results indicate differential expression of individual members of the CYP1 gene family in normal and neoplastic kidney and suggest that several mechanisms including the Ah receptor complex could be involved in their regulation.

Metabolic activation of dibenzo[a,l]pyrene by human cytochrome P450 1A1 and P450 1B1 expressed in V79 Chinese hamster cells

Metabolic activation of the strongly carcinogenic polycyclic aromatic hydrocarbon (PAH) dibenzo[a,l]pyrene (DB[a,l]P) and its trans-8,9-dihydrodiol (trans-8,9-diol) catalyzed by human cytochromes P450 (P450) 1A1 and 1B1 was investigated. DNA binding of DB[a,l]P in mammalian cell lines has previously been shown to be preferentially mediated by fjord region DB[a,l]P-11,12-dihydrodiol 13,14-epoxides (DB[a,l]PDE). In order to elucidate different capabilities of both P450 enzymes for metabolic activation of DB[a, l]P V79 Chinese hamster cells, stably expressing human P450s 1A1 or 1B1 have been exposed to the parent PAH or its racemic trans-8, 9-diol. For this purpose, synthesis and spectroscopic characterization of the trans-DB[a,l]P-8,9-diol and its individual enantiomers have been achieved. Both human P450-expressing cell lines were capable of transforming DB[a,l]P to its fjord region DB[a, l]PDE, but the extent of metabolism to DB[a,l]PDE catalyzed by human P450 1B1 was higher compared to human P450 1A1 at all times measured. On the other hand, cytotoxicity studies performed with the same incubation systems emerged stronger effects by DB[a,l]P and its enantiomeric trans-11,12-diols in human P450 1A1-expressing cells. Both human P450 enzymes stereospecifically catalyzed the formation of the (-)-DB[a,l]P-11,12-diol with R,R-configuration, whereas only the human P450 1A1-expressing cells form small amounts of the K-region trans-8,9-diol with high excess of the (+)-(8R, 9R)-enantiomer. Application of trans-DB[a,l]P-8,9-diol in metabolism studies revealed that this compound is converted by human P450s 1A1 and 1B1 to several diol phenols and bis-diols. However, and even at concentrations as high as 10 microM, in both cell lines the trans-DB[a,l]P-8,9-diol showed no cytotoxicity at all, suggesting that an activation of DB[a,l]P via further oxidation of the K-region trans-8,9-diol plays a minor role.

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.