Biphasic effects of the flavonoids quercetin and naringenin on the metabolic activation of 2-amino-3,5-dimethylimidazo[4,5-f]quinoline by Salmonella typhimurium TA1538 co-expressing human cytochrome P450 1A2, NADPH-cytochrome P450 reductase, and cytochrome b5

Morin hydrate ameliorates heat-induced testicular impairment in a mouse model

BACKGROUND

Heat stress is known to adversely affect testicular activity and manifest the pathogenesis of spermatogenesis. Morin hydrate is a plant-derived compound, which contains a wide range of biological activities. Thus, it is hypothesized that morin hydrate might have an ameliorative effect on heat-induced testicular impairment. There has not been any research on the impact of morin hydrate on heat-induced testicular damage.

METHODS

The experimental mice were divided into four groups, groups1 as the normal control group (CN), and the second which underwent heat stress (HS) by immersing the lower body for 15 min in a thermostatically controlled water bath kept at 43 °C (HS), and third and fourth heat-stressed followed by two different dosages of morin hydrate 10 mg/kg (HSM10) and 100 mg/kg (HSM100) for 14 days.

RESULTS

Morin hydrate treatment at 10 mg/kg improved, circulating testosterone levels (increases 3βHSD), and oxidative stress along with improvement in the testis and caput and corpus epididymis histoarchitecture, however, both doses of morin hydrate improved sperm parameters. Morin hydrate treatment significantly increases germ cell proliferation, (GCNA, BrdU staining), expression of Bcl2 and decreases expression of active caspase 3. Heat stress also decreased the expression of AR, ER- α, and ER-β, and Morin hydrate treatment increased the expression of these markers in the 10 mg/kg treatment group.

CONCLUSION

Morin hydrate ameliorates heat-induced testicular impairment modulating testosterone synthesis, germ cell proliferation, and oxidative stress. These effects could be manifested by regulating androgen and estrogen receptors. However, the two doses showed differential effects of some parameters, which requires further investigations.

Biphasic Dose-Response Induced by Phytochemicals: Experimental Evidence

Many phytochemicals demonstrate nonmonotonic dose/concentration-response termed biphasic dose-response and are considered to be hormetic compounds, i.e., they induce biologically opposite effects at different doses. In numerous articles the hormetic nature of phytochemicals is declared, however, no experimental evidence is provided. Our aim was to present the overview of the reports in which phytochemical-induced biphasic dose-response is experimentally proven. Hence, we included in the current review only articles in which the reversal of response between low and high doses/concentrations of phytochemicals for a single endpoint was documented. The majority of data on biphasic dose-response have been found for phytoestrogens; other reports described these types of effects for resveratrol, sulforaphane, and natural compounds from various chemical classes such as isoquinoline alkaloid berberine, polyacetylenes falcarinol and falcarindiol, prenylated pterocarpan glyceollin1, naphthoquinones plumbagin and naphazarin, and panaxatriol saponins. The prevailing part of the studies presented in the current review was performed on cell cultures. The most common endpoint tested was a proliferation of tumor and non-cancerous cells. Very few experiments demonstrating biphasic dose-response induced by phytochemicals were carried out on animal models. Data on the biphasic dose-response of various endpoints to phytochemicals may have a potential therapeutic or preventive implication.

Effect of Morinda citrifolia (Noni)-Enriched Diet on Hepatic Heat Shock Protein and Lipid Metabolism-Related Genes in Heat Stressed Broiler Chickens

Heat stress (HS) has been reported to alter fat deposition in broilers, however the underlying molecular mechanisms are not well-defined. The objectives of the current study were, therefore: (1) to determine the effects of acute (2 h) and chronic (3 weeks) HS on the expression of key molecular signatures involved in hepatic lipogenic and lipolytic programs, and (2) to assess if diet supplementation with dried Noni medicinal plant (0.2% of the diet) modulates these effects. Broilers (480 males, 1 d) were randomly assigned to 12 environmental chambers, subjected to two environmental conditions (heat stress, HS, 35°C vs. thermoneutral condition, TN, 24°C) and fed two diets (control vs. Noni) in a 2 × 2 factorial design. Feed intake and body weights were recorded, and blood and liver samples were collected at 2 h and 3 weeks post-heat exposure. HS depressed feed intake, reduced body weight, and up regulated the hepatic expression of heat shock protein HSP60, HSP70, HSP90 as well as key lipogenic proteins (fatty acid synthase, FASN; acetyl co-A carboxylase alpha, ACCα and ATP citrate lyase, ACLY). HS down regulated the hepatic expression of lipoprotein lipase (LPL) and hepatic triacylglycerol lipase (LIPC), but up-regulated ATGL. Although it did not affect growth performance, Noni supplementation regulated the hepatic expression of lipogenic proteins in a time- and gene-specific manner. Prior to HS, Noni increased ACLY and FASN in the acute and chronic experimental conditions, respectively. During acute HS, Noni increased ACCα, but reduced FASN and ACLY expression. Under chronic HS, Noni up regulated ACCα and FASN but it down regulated ACLY. In vitro studies, using chicken hepatocyte cell lines, showed that HS down-regulated the expression of ACCα, FASN, and ACLY. Treatment with quercetin, one bioactive ingredient in Noni, up-regulated the expression of ACCα, FASN, and ACLY under TN conditions, but it appeared to down-regulate ACCα and increase ACLY levels under HS exposure. In conclusion, our findings indicate that HS induces hepatic lipogenesis in chickens and this effect is probably mediated via HSPs. The modulation of hepatic HSP expression suggest also that Noni might be involved in modulating the stress response in chicken liver.

Molecular mechanisms of action of quercetin in cancer: recent advances

In the last few decades, the scientific community has discovered an immense potential of natural compounds in the treatment of dreadful diseases such as cancer. Besides the availability of a variety of natural bioactive molecules, efficacious cancer therapy still needs to be developed. So, to design an efficacious cancer treatment strategy, it is essential to understand the interactions of natural molecules with their respective cellular targets. Quercetin (Quer) is a naturally occurring flavonol present in many commonly consumed food items. It governs numerous intracellular targets, including the proteins involved in apoptosis, cell cycle, detoxification, antioxidant replication, and angiogenesis. The weight of available synergistic studies vigorously fortifies the utilization of Quer as a chemoprevention drug. This extensive review covers various therapeutic interactions of Quer with their recognized cellular targets involved in cancer treatment.

Influence of a Nigerian honey on CYP3A4 biotransformation of quinine in healthy volunteers

WHAT IS KNOWN AND OBJECTIVES

Some studies, howbeit with conflicting reports, have suggested that consumption of honey has a potential to modulate drug metabolizing enzymes which may result in a honey-drug interaction. Numerous studies have established that honey varies in composition, influenced by the dominant floral, processing and environmental factors. Thus, variation in honey composition may be a contributing factor to the controversial results obtained. No previous drug interaction study has been carried out with any honey from Africa. CYP 3A4 is an important enzyme in drug metabolism studies as it is involved in the metabolism of over 50% of drugs in clinical use and quinine remains very relevant in malaria treatment in the tropics, and we therefore determined whether there is potential drug interaction between a Nigerian honey and quinine, a drug whose metabolism to 3-hydroxyquinine is mediated majorly by CYP3A4.

METHODS

In a three-phase randomized crossover study with a washout period of 2 weeks between each treatment phase, ten (10) healthy volunteers received quinine sulphate tablet (600 mg single dose) alone (phase 1) or after administration of 10 ml of honey (Phase 2) and 20 mL of honey (Phase 3) twice daily for seven (7) days. Blood samples were collected at the 16th hour post-quinine administration in each phase, and quinine and its major metabolite, 3-hydroxyquinine, were analysed using a validated HPLC method.

RESULTS

After scheduled doses of honey, the mean metabolic ratios of quinine (3-hydroxyquinine/quinine) increased by 24·4% (with 10 mL of honey) and reduced by 23·9% (with 20 mL of honey) when compared to baseline. These magnitudes of alteration in the mean metabolic ratios were not significant (P > 0·05; Friedman test). The geometric mean (95% CI) for the metabolic ratio of quinine before and after honey intake at the two dose levels studied was 0·82 (0·54, 1·23) and 1·29 (0·96, 1·72), respectively, and were also not significant (P = 0·296 and 0·081 respectively; Student's t-test).

WHAT IS NEW AND CONCLUSION

This is a pioneer study on the effect of Nigerian/African honey on quinine metabolism. The findings indicated that low and high doses of honey did not significantly affect metabolism of quinine to 3-hydroxyquinine. This suggests that CYP3A4 activity is not significantly altered following low or high dose of honey, as CYP3A4 has been reported to be responsible for the conversion of quinine to 3-hydroxyquinine. In conclusion, the outcome of this study suggests that there may be no potential significant metabolic interaction between Nigerian honey and quinine administration.

Quercetin significantly inhibits the metabolism of caffeine, a substrate of cytochrome P450 1A2 unrelated to CYP1A2*1C (-2964G>A) and *1F (734C>A) gene polymorphisms

Background. Quercetin is abundant in plants and human diets. Previous studies indicated that quercetin inhibited the activity of CYP1A2, and the combination of quercetin with the substrates of CYP1A2 might produce herb-drug interactions. This research aims to determine the effects of quercetin and the CYP1A2 gene polymorphisms, namely, CYP1A2*1C  (−2964G>A) and *1F (734C>A), on the metabolism of caffeine. Method. The experiment was designed into two treatment phases separated by a 2-week washout period. Six homozygous individuals for the CYP1A2*1C/*1F (GG/AA) genotype and 6 heterozygous individuals for the CYP1A2*1C/*1F (GA/CA) genotype were enrolled in the study. Quercetin capsules (500 mg) were given to each volunteer once daily for 13 consecutive days, and after that, each subject was coadministrated 100 mg caffeine capsules with 500 mg quercetin on the 14th day. Then a series of venous blood samples were collected for HPLC analysis. Correlation was determined between pharmacokinetics of caffeine and paraxanthine with caffeine metabolite ratio. Results. Quercetin significantly affected the pharmacokinetics of caffeine and its main metabolite paraxanthine, while no differences were found in the pharmacokinetics of caffeine and paraxanthine between GG/AA and GA/CA genotype groups. Conclusion. Quercetin significantly inhibits the caffeine metabolism, which is unrelated to CYP1A2*1C (−2964G>A) and *1F (734C>A) gene polymorphisms.

Co-expression of human cytochrome b5 increases expression of cytochrome P450 3A4 in Escherichia coli by stabilizing mRNA

CYP3A4 is the most abundant cytochrome P450 in the human liver. The expression level of CYP3A4 when coexpressed with cytochrome b(5) (cyt b(5)) in Escherichia coli was 20-60% higher than that when it was expressed alone over an extended period (48-72 h). This time-dependent elevation in coexpression with cyt b(5) was a result of an increase in CYP3A4 mRNA half-life; no significant change in CYP3A4 degradation was seen in the bacterial protease fraction. These results suggest that the higher CYP3A4 levels observed upon coexpression with cyt b(5) primarily resulted from CYP3A4 mRNA stabilization by cyt b(5).

Effect of Vernonia cognata on oxidative damage induced by ethanol in rats

Free radicals production and oxidative stress play a central role in injuries caused by ethanol (EtOH) on gastric mucosal. Thus, strategies to counteract EtOH toxicity are highly desirable. This study was aimed at evaluating whether Vernonia cognata extract would reduce EtOH effects in rats. Rats received Vernonia cognata extract (0, 1 and 2 g/kg bw, by gavage) 1 hour after EtOH had been administered (0 or 70%, 0.5 mL/100 g bw, by gavage) and were killed 1 hour after Vernonia cognata extract administration. The stomach was removed for macroscopic and histopathological evaluation, as well as, oxidative stress markers such as lipoperoxidation (LPO) and non-protein thiol groups (NPSH) levels and catalase (CAT) activity. EtOH acute exposure increased LPO and decreased NPSH levels and CAT activity along with macroscopic and microscopic lesions in gastric tissue, confirming the involvement of oxidative stress in EtOH toxicity. Vernonia cognata extract attenuated oxidative and histopathological features induced by EtOH at all evaluated doses. Moreover, both studied doses of Vernonia cognata extract caused an increase in NPSH levels per se. However, only the dose of 2 g/kg reverted all macroscopic changes caused by EtOH toxicity. The protective effect of the extract could be attributed to antioxidant molecules present in the extract, such as flavonoids and phenolic acids, which were quantified by high performance liquid chromatography (HPLC). Thus, an antioxidant effect of the extract leads to a protection on gastric tissue. Our results indicate that Vernonia cognata hydroethanolic extract could have a beneficial role against EtOH toxicity by preventing oxidative stress and gastric tissue injury.

Chemopreventive compounds--view from the other side

Increasing attention is being paid to the possibility of applying chemopreventive agents for the protection of individuals from cancer risk. The beneficial potential of chemoprotective compounds is usually well documented by extensive experimental data. To assure the desired effect, these compounds are frequently concentrated to produce dietary supplements for human use. The additive and synergistic effects of other food constituents are, however, frequently ignored. Even natural chemopreventive compounds have to be considered as xenobiotics. Thus, as much attention has to be paid to their testing prior to their wide application as is usual in drug development for human treatment. Unfortunately, much of the research in this area is solely based on simplified in vitro systems that cannot take into account the complexity of biotransformation processes, e.g. chemopreventive compound-drug interaction, effect on metabolism of endogenic compounds. Hence, the predicted chemopreventive potential is not attained in respect of cancer prevention; moreover, the administration of high doses of chemopreventive compounds might be even detrimental for the human health.

Mutagenic evaluation and chemical investigation of Byrsonima intermedia A. Juss. leaf extracts

Byrsonima intermedia is a native species of the cerrado formation (tropical American savannah). In Brazil, this plant has been used for the treatment of fever, in ulcers, as a diuretic, as antiasthmatics and in skin infections. Members of the genus Byrsonima (Malpighiaceae) are employed not only in the folk medicine but also as food to make juice, jellies and liquor. The aim of this work was to evaluate the mutagenic effects of Byrsonima intermedia, common name 'murici'. Phytochemical analysis of methanol extract furnished (+)-catechin, (-)-epicatechin, quercetin-3-O-beta-d-galactopyranoside, methyl gallate, gallic acid, quercetin-3-O-alpha-l-arabinopyranoside, amentoflavone, quercetin, quercetin-3-O-(2''-O-galloyl)-beta-galactopyranoside and quercetin-3-O-(2''-O-galloyl)-alpha-arabinopyranoside. Methanol, hydromethanol and chloroform extracts were evaluated in mutagenic assay with Salmonella typhimurium (Ames test) and mice (Micronucleus test). The methanolic extract presented signs of mutagenic activity for the strains TA98 and TA100 in the Ames assay. Mutagenicity was not observed in vivo.

Acute, subacute toxicity and genotoxic effect of a hydroethanolic extract of the cashew (Anacardium occidentale L.)

Anacardium occidentale L. (Anacardiaceae), popularly known as cajueiro is a native plant to Brazil, and largely used in popular medicine to treat ulcers, hypertension and diarrhea. In the present study, acute, 30-day subacute toxicity and genotoxicity assays were carried out. The crude extract did not produce toxic symptoms in rats in doses up to 2000 mg/kg. Based on biochemical analyses of renal and hepato-biliary functions, such as the level of urea, creatinine, transaminases and alkaline phosphatase, we determined that the extract is generally tolerated by rats. This was also confirmed by hematological and histopathological exams. Genotoxicity was accessed by the Ames test in Salmonella typhimurium strains TA97, TA98, TA100, TA102 and by the bone marrow micronucleus test in mice. The extract was shown to induce frameshift, base pair substitution and damage to the chromosomes. However, this effect was less deleterious than the clastogenic effect of ciclophosphamide.

Comparison of prostate cancer cell lines for androgen receptor-mediated reporter gene assays

In order to select a better prostate cancer cell model for androgen receptor (AR)-mediated reporter gene assays, we assessed the androgen response characteristics of three cell lines, LNCaP, PC3/AR(+) and 22Rv1, in this study. Both the mRNA and the proteins of AR and glucocorticoid receptor (GR) were expressed in all three cell lines. Among the three cell lines, only in LNCaP cells, DHT concentration-dependently stimulated proliferation. DHT induced the luciferase activity in three cell lines which were transiently transfected with pMMTV-Luc, in a concentration-dependent manner. The maximum induction was 24.0-fold and 13.4-fold in 22Rv1 and in the LNCaP respectively. PC3/AR(+) were more sensitive to respond to DHT at a minimal concentration of 10(-12)M by 14.0-fold induction. The transcriptional activity induced with 10(-8)M DHT was inhibited about 50-75% in the PC3/AR(+) and 22Rv1, and 98% in the LNCaP, by vinclozolin. Dexamethasone concentration-dependently induced the luciferase activity in PC3 and 22Rv1, but not in the LNCaP. However, the response to dexamethasone in 22Rv1 was very weak compared to DHT. The (anti)androgencity of seven pyrethroids was assessed via an AR-mediated luciferase reporter assay. None of them showed the androgenic action in all three cell lines. Permethrin inhibited the DHT induced luciferase activity about 22%, 35.8% and 75.5% in 22Rv1, PC3/AR(+) and LNCaP, respectively. Based on results from in this study and cell line character, 22Rv1 cells seemed to be an appropriate model for the screening of androgenic endocrine disruptors, although it needs further studies with other steroid receptor and thyroid receptor.

Effect of the co-administration of phenobarbital, quercetin and mancozeb on nitrosomethylurea-induced pancreatic tumors in rats

We have previously shown that a single i.p. injection of nitrosomethylurea (NMU) in 3-day-old rats orally treated with the pesticide mancozeb (MZ), the flavonoid quercetin (Q) or in combination (MZ-Q) induces hyperplasia, atypical acinar cell proliferation and carcinoma in situ (CIS) in the pancreas. This work studies the effect of oral administration of phenobarbital (PB) on this model of pancreatic carcinogenesis. The animals were fed on a diet supplemented by MZ or/and Q from the 10th day of pregnancy, thorough lactation and as pups after weaning until being sacrificed at week 24. Saline injection with non-supplemented diet was used for the control group (SAL). The experimental groups were (1) SAL (control), (2) SAL-PB, (3) NMU, (4) NMU-PB, (5) MZ-NMU, (6) MZ-NMU-PB, (7) Q-NMU, (8) Q-NMU-PB, (9) MZ-Q-NMU and (10) MZ-Q-NMU-PB. Acinar cell hyperplasia was found in all groups of NMU-treated rats. Dysplastic foci (DYS) were seen in groups 3-10 at the following percentages: 19, 48, 71, 27, 71, 35, 100 and 30, respectively. CIS were recorded in groups 4 to 10 at percentages: 4, 36, 13, 11, 0, 16, 5, respectively.

CONCLUSION

Although PB, Q or MZ given alone enhance DYS lesions in NMU-treated rats, the MZ/Q/PB combined treatments may increase (mainly in males) or decrease (mainly in female) the DYS and CIS proportion. Because PB, MZ and Q influence P450 enzymes, we suggest that these enzymes play a role in the carcinogenesis process.

Cancer biology and hormesis: human tumor cell lines commonly display hormetic (biphasic) dose responses

This article assesses the nature of the dose-response relationship of human tumor cell lines with a wide range of agents including antineoplastics, toxic substances (i.e., environmental pollutants), nonneoplastic drugs, endogenous agonists, and phyto-compounds. Hormetic-like biphasic dose responses were commonly reported and demonstrated in 136 tumor cell lines from over 30 tissue types for over 120 different agents. Quantitative features of these hormetic dose responses were similar, regardless of tumor cell line or agent tested. That is, the magnitude of the responses was generally modest, with maximum stimulatory responses typically not greater than twice the control, while the width of the stimulatory concentration range was usually less than 100-fold. Particular attention was directed to possible molecular mechanisms of the biphasic nature of the dose response, as well as clinical implications in which a low concentration of chemotherapeutic agent may stimulate tumor cell proliferation. Finally, these findings further support the conclusion that hormetic dose responses are broadly generalizable, being independent of biological model, endpoint measured, and stressor agent, and represent a basic feature of biological responsiveness to chemical and physical stressors.

Flavonoids suppresses the enhancing effect of beta-carotene on DNA damage induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in A549 cells

This study investigated the individual and combined effects of beta-carotene with a common flavonoid (naringin, quercetin or rutin) on DNA damage induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a potent tobacco-related carcinogen in human. A human lung cancer cell line, A549, was pre-incubated with beta-carotene, a flavonoid, or both for 1h followed by incubation with NNK for 4 h. Then, we determined DNA strand breaks and the level of 7-methylguanine (7-mGua), a product of NNK metabolism by cytochrome P450 (CYP). We showed that beta-carotene at 20 microM significantly enhanced NNK-induced DNA strand breaks and 7-mGua levels by 90% (p < 0.05) and 70% (p < 0.05), respectively, and that the effect of beta-carotene was associated with an increased metabolism of NNK by CYP because the concomitant addition of 1-aminobenzotriazole, a CYP inhibitor, with beta-carotene to cells strongly inhibited NNK-induced DNA strand breaks. In contrast to beta-carotene, incubation of cells with naringin, quercetin or rutin added at 23 microM led to significant inhibition of NNK-induced DNA strand breaks, and the effect was in the order of quercetin > naringin > rutin. However, these flavonoids did not significantly affect the level of 7-mGua induced by NNK. Co-incubation of beta-carotene with any of these flavonoids significantly inhibited the enhancing effect of beta-carotene on NNK-induced DNA strand breaks; the effects of flavonoids were dose-dependent and were also in the order of quercetin > naringin > rutin. Co-incubation of beta-carotene with any of these flavonoids also significantly inhibited the loss of beta-carotene incorporated into the cells, and the effects of the flavonoids were also in the order of quercetin > naringin > rutin. The protective effects of these flavonoids may be attributed to their antioxidant activities because they significantly decreased intracellular ROS, and the effects were also in the order of quercetin > naringin > rutin. These in vitro results suggest that a combination of beta-carotene with naringin, rutin, or quercetin may increase the safety of beta-carotene.

Effects of hydroxyl group numbers on the B-ring of 5,7-dihydroxyflavones on the differential inhibition of human CYP 1A and CYP1B1 enzymes

Flavonoids are polyphenols composed of two aromatic rings (A, B) and a heterocyclic ring (C). In order to determine the effects of the number of hydroxyl groups in the B-ring of the flavonoids on human cytochrome P450 (CYP) 1 family enzymes, we evaluated the inhibition of CYP1A-dependent 7-ethoxyresorufin omicron-deethylation activity by chrysin, apigenin and luteolin, using bacterial membranes that co-express human CYP1A1, CYP1A2, or CYP1B1 with human NADPH-cytochrome P450 reductase. Chrysin, which possesses no hydroxyl groups in its B-ring, exhibited the most pronounced inhibitory effects on CYP1A2-dependent EROD activity, followed by apigenin and luteolin. On the contrary, CYP1A1-mediated EROD activity was most potently inhibited by luteolin, which is characterized by two hydroxyl groups in its B-ring, followed by apigenin and chrysin. However, all of the 5,7-dihydroxyflavones were determined to similarly inhibit CYP1B1 activity. Chrysin, apigenin, and luteolin exhibited a mixed-type mode of inhibition with regard to CYP1A2, CYP1B1, and CYP1A1, with apparent Ki values of 2.4, 0.5, and 2.0 microM, respectively. These findings suggested that the number of hydroxyl groups in the B-ring of 5,7-dihydroxyflavone might have some influence on the degree to which CYP1A enzymes were inhibited, but not on the degree to which CYP1B1 enzymes were inhibited.

The stimulatory role of human cytochrome b5 in the bioactivation activities of human CYP1A2, 2A6 and 2E1: a new cell expression system to study cytochrome P450 mediated biotransformation

Cytochrome b(5) (b(5)) is increasingly recognized to be of importance for specific cytochrome P450 (CYP) activities. We developed human b(5)/CYP-competent mutagenicity tester bacteria to study the role of b(5) in the bioactivation activity of human CYP. These new tester bacteria were derived from the previously engineered human CYP-competent Escherichia coli K12 tester strain MTC, containing a bi-plasmid system for the co-expression of a specific CYP form (CYP1A2, 2A6 or 2E1) with human b(5), and human NADPH cytochrome P450 reductase (RED), resulting in the strain BTC-b(5)-1A2, BTC-b(5)-2A6 and BTC-b(5)-2E1, respectively. The relative content of b(5) with CYP and RED in these three BTC-b(5)-CYP strains demonstrated physiologically relevant co-expression levels and typical CYP-specific activities could be determined with their specific chemical probes. These strains were applied in mutagenicity assays along with their corresponding b(5)-void strains to determine the effect of b(5) on the CYP1A2-, CYP2A6- and CYP2E1-mediated bioactivation of several promutagens. For CYP1A2, of the 5 compounds tested [2-aminoanthracene (2AA), 1-aminopyrene, 6-aminochrysene, 2-amino-3-methylimidazo(4,5-f)quinoline and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)], only the mutagenicity of 2AA was slightly increased ( approximately 1.5-fold) in the presence of b(5). The CYP2E1- and CYP2A6-dependent mutagenicity of N-nitrosodiethylamine increased approximately 3- and 23-fold, respectively when the bacteria contained b(5). The CYP2A6-mediated mutagenicity of NNK increased approximately 9-fold when co-expressed with b(5). The stimulatory effect of b(5) on the bioactivation of N-nitrosodi-n-propylamine was most striking. The mutagenicity of this procarcinogen was completely dependent on the co-expression of b(5) with CYP2A6 or CYP2E1. This demonstrates the prominent role of b(5) in the bioactivation of this carcinogen.