Metabolism Of Benzo Research Articles

Effect of inducers on metabolism of benzo(a)pyrene invivo and invitro: Analysis by high pressure liquid chromatography

The characterisation of metabolites formed from benzo(a)pyrene (BP) by Aspergillus ochraceus TS and effect of inducers on BP metabolism are reported. The high pressure liquid chromatographic profile of BP metabolites was similar to that of mammalian microsomes furnishing diols, quinones and phenols. The production of BP-4,5-dihydrodiol (K-region diol) by Aspergillus ochraceus TS seems to be novel and provides first report on BP metabolism by eukaryotic fungi. In control, phenols and quinones were produced in excess over dihydrodiols while the induced preparation showed the reverse order. Presumably the induction effecting production of excess dihydrodiols influenced the synthesis of epoxide hydrolase. In addition, a differential increase in BP metabolism was observed with inducers of narrow and broad specificity.

Metabolism of benzo(A)pyrene by a dioxygenase enzyme system of the freshwater green alga selenastrumcapricornutum

The green alga Selenastrum capricornutum was incubated with benzo(a)-pyrene under an atmosphere of 20% (18)O2: 80% N2. The cis-11,12-dihydro-11,12-dihydroxybenzo(a)pyrene, cis-7,8-dihydro-7,8-dihydroxybenzo(a)pyrene and cis-4,5-dihydro-4,5-dihydroxybenzo(a)pyrene, were isolated by HPLC and analyzed by mass spectrometry. The metabolites produced molecular ions at m/z 290 and 286. Elemental analysis of the ion at m/z 290 gave an elemental composition of C20H14(18)O2 with 13% (18)O2 incorporation. The results indicate that S. capricornutum produces cis vicinal dihydrodiols from molecular oxygen via a dioxygenase enzyme pathway. The dioxygenase enzymes are characteristic of the bacterial metabolic pathway and unlike those of eukaryotic organisms which involve monooxygenase enzymes.

Metabolism of benzo( f)quinoline and dibenzo( a,h)acridine by liver microsomes from rats and bullheads

Metabolism of benzo( f)quinoline and dibenzo( a,h)acridine by liver microsomes from rats and bullheads

Benzo[ a]pyrene metabolism and induction of enzymealtered foci in regenerating rat liver

The metabolism of benzo[ a]pyrene (BP) in regenerating rat liver and the induction of enzyme-altered foci (EAF) in the liver of partially hepatectomized rats, treated with BP and promoted with 2-acetylaminofluorene (2-AAF)/CCl 4 was investigated. The aim was to examine factors that might be of importance for the tumorigenicity of BP in the regenerating rat liver, such as cytochrome P-450 activity and glutathione levels. In regenerating rat liver, obtained 18 h after partial hepatectomy (PH), the amount of microsomal cytochrome P-450 was reduced by 20% whereas the level of glutathione was elevated by 15% and the cytosolic glutathione transferase activity towards chlorodinitrobenzene and (±)-7β,8α-dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydro-BP (BPDE) was unaffected. Microsomes from these animals had a reduced capacity to activate (−)- trans-7,8-dihydroxy-7,8-dihydro-BP (BPD) to DNA-binding products but the pattern of BP metabolites was similar to that observed with control rat liver microsomes. Treatment of rats with 3-methylcholanthrene (MC, 50 mg/kg body wt.) increased cytochrome P-450 levels and glutathione transferase activity towards both substrates. Regenerating livers from these animals retained their cytochrome P-450 level and enzymatic activity towards BP and BPD. Regenerating rat liver microsomes from MC-treated animals were about 35 times more efficient in activating BPD than microsomes from uninduced, partially hepatectomized animals. Intraperitoneal administration of BP (50 mg/kg body wt.) 18 h after PH induced EAF in rats subsequently promoted with 2-AAF/CCl 4. Pretreatment of rats with MC 66 h before PH and 84 h before BP administration, increased the number of EAF. In accordance with results by Tsuda et al. (Cancer Res., 40 (1980) 1157–1164), these studies demonstrate that BP is tumorigenic in regenerating rat liver, despite a reduced ability of the liver to activate this compound. Furthermore, MC, an inducer of certain cytochrome P-450 species (“aryl hydrocarbon hydroxylase”), potentiates the effect of BP.

Induction of the Cytochrome P-450c gene and the metabolism of benzo(a)pyrene-7,8-diol (BP7,8-diol) in eight different human breast cancer cell lines

Induction of the Cytochrome P-450c gene and the metabolism of benzo(a)pyrene-7,8-diol (BP7,8-diol) in eight different human breast cancer cell lines

Metabolism of benzo[α] pyrene in the combined rat liver —lung perfusion system

The influence of the insertion of a liver into the perfusion circuit of a lung on the availability of benzo[ a]pyrene and benzo[ a]pyrene metabolites to the lung was examined. Perfused lungs from 5,6-benzoflavone pretreated rats release high quantities of free benzo[ a]pyrene metabolites and conjugates into the perfusion medium. The insertion of a liver taken from an untreated rat reduces the concentration of unmetabolized substrate and of free diol, quinone and phenol metabolites to less than 20% of the concentrations found in the absence of the liver. When the liver of a 5,6-benzoflavone-pretreated rat is used, substrate depletion is not much greater than in the experiments with control livers; however, the concentration of free metabolites is further reduced to one third. In lung tissue, only very low levels of benzo[ a]pyrene and greatly reduced levels of free and conjugated metabolites are found when a 5,6-benzoflavone-induced liver had been present during perfusion. These findings can explain the protective effect of the liver on covalent binding of benzo[ a]pyrene metabolites to pulmonary macro-molecules observed in previous experiments with the combined liver-lung perfusion model [Klaus et al., Biochem. Biophys. Res. Commun., 105 (1982) 596].

Stereoselective formation and hydration of benzo[ c]phenanthrene 3,4-and 5,6-epoxide enantiomers by rat liver microsomal enzymes

The K-region 5,6-epoxides, formed in the metabolism of benzo[ c]phenanthrene (BcPh) in the presence of an epoxide hydrolase inhibitor 3,3,3-trichloropropylene 1,2-oxide (TCPO) by liver microsomes from untreated, phenobarbital-treated, 3-methylcholanthrene-treated, and polychlorinated biphenyls (Aroclor 1254)-treated rats of the Sprague-Dawley and the Long-Evans strains, were found by chiral stationary phase high-performance liquid chromatography analyses to be enriched (58–72%) in the 5 S,6 R enantiomer. In the absence of TCPO, the metabolically formed BcPh trans-5,6-dihydrodiol was enriched (78–86%) in the 5 S,6 R enantiomer. The major enantiomer of the BcPh 3,4-epoxide metabolite was found to be enriched in the 3 S,4 R enantiomer which undergoes racemization under the experimental conditions. The major enantiomer of the 5,6-dihydrodiol metabolite was elucidated by the exciton chirality circular dichroism (CD) method to have a 5 S,6 R absolute stereochemistry. Absolute configurations of enantiomeric BcPh 5,6-epoxides were determined by CD spectral analyses of the enantiomeric methoxylation products derived from each of the two BcPh 5,6-epoxide enantiomers. Optically pure BcPh 5 S,6 R-epoxide was enzymatically hydrated exclusively at the C 6 position to form an optically pure BcPh 5 S,6 S-dihydrodiol. However, optically pure BcPh 5 R,6 S-epoxide was hydrated at both C 5 and C 6 positions to form a BcPh trans-5,6-dihydrodiol with a (5 S,6 S):(5 R,6 R) enantiomer ratio of 32:68.

Metabolism of benzo(a)pyrene in monolayer cultures of human bronchial epithelial cells from a series of donors

Benzo(a)pyrene [B(a)P] metabolism was measured in monolayer cultures of human bronchial epithelial cells derived from 18 specimens of explanted tissue. Bronchial epithelial cells converted B(a)P to dihydrodiols, phenols, quinone derivatives, and polyhydroxylated forms. Sulfate and glucuronide conjugates of B(a)P metabolites were also detected. Both total metabolism and distribution of metabolites showed a 10-fold or greater variation in cultures from different specimens. When the data were divided according to smoking status, however, no differences in total metabolism, extent of conjugation, or distribution of metabolites could be demonstrated between the two groups. Wide variation (over 1000-fold) in the cytotoxicity of B(a)P towards cells derived from different specimens was demonstrated but could not be directly correlated to the extent of metabolic activation. The results suggest that human bronchial epithelial cells which are newly grown from explanted tissue of smokers in culture do not demonstrate enzymatic induction. Variation among individuals observed in these studies probably represents basal differences in metabolic capability.

Effects of feeding and temperature on uptake, elimination and metabolism of benzo(a)pyrene in the bluegill sunfish ( Lepomis macrochirus)

Bluegill sunfish ( Lepomis macrochirus) were exposed to [ 14C]benzo(a)pyrene (BaP) in a flow-through system to examine the effects of temperature and feeding regime on BaP uptake and elimination and extent of biotransformation within the fish. The rate of uptake of BaP at 23°C was twice as fast in fish fed during aqueous exposure than in those denied food; however, the rate of elimination of radioactivity was 10 times greater in the fed fish. BaP was rapidly metabolized to polar and nonpolar metabolites, although 40 to 50% of the radioactivity in the fish appears to be covalently bound to cellular constituents. The rate of conversion of BaP to polar metabolites was also accelerated by feeding. Because animals in nature usually have food available, care must be exercised in using, applying, and extrapolating results of laboratory experiments in which food is withheld. Temperature is an environmental variable that had a significant effect on the uptake, elimination, and metabolic fate of organic contaminants. Both BaP uptake (5.8-fold) and 14C elimination rates (3.6-fold) at 13°C were lower than in fed fish exposed at 23°C. The metabolite profiles indicate that biotransformation of BaP is also much slower at the colder temperature.

Microspectrofluorometric comparison of benzo(a)pyrene and dibenzo(c,h)acridine metabolism in single living 3T3 fibroblasts.

The purpose of this study was to determine if dibenzo(c,h)acridine could be used as a probe for the N-heterocyclic aromatic compound detoxification system. The determination was achieved by cell population studies (histograms) using microspectrofluorimetry on single living cells. The results show a similar metabolic distribution pattern between dibenzo(c,h)acridine and benzo(a)pyrene, whereas important differences appear between 6-aminochrysene and dibenzo(c,h)acridine, respectively amine aromatic and N-heterocyclic aromatic compounds. No differences were observed in the metabolism of benzo(a)pyrene in untreated cells and those treated with constant concentrations of dibenzo(c,h)acridine. However, inhibition of dibenzo(c,h)acridine metabolism was observed in the presence of benzo(a)pyrene, indicating that this compound should be a preferential substrate for a cell detoxification system.

Metabolism of benzo[a]pyrene in the perfused rat liver: factors affecting the release of phenolic metabolites into the bile and perfusate.

The metabolism of benzo[a]pyrene (BP) to phenolic metabolites was studied in the non-recirculating perfused rat liver. After 30 min of BP (20 microM) infusion most phenols formed (78%) remained in the liver. Phenols detected in the perfusate and bile were primarily glucuronide (70%) and sulfate (20%) conjugates. When albumin was present in the perfusion buffer, release of phenols into perfusate was the predominant route of elimination from the liver. In the absence of albumin, biliary efflux of phenols predominated. Biliary concentrations of BP phenolic glucuronides and sulfates were at least 3.5-fold higher than their hepatic concentrations, suggesting an active transport of these metabolites into bile. Rates of biliary elimination of BP phenols were enhanced by the infusion of taurocholate, which displaces BP metabolites from intracellular stores. These results confirm and extend previous studies which have demonstrated that the release of BP phenols from the liver is a complex process, influenced by the availability of intracellular storage sites, biliary excretion mechanisms and the presence of carrier proteins such as albumin.

Metabolism of benzo[a]pyrene in primary cultures of human hepatocytes: dose-response over a four-log range.

Cultures of isolated human hepatocytes from three different human liver specimens were exposed for 24 h to media containing [3H]benzo[a]pyrene (BP) (0.1, 1.0, 10, 100 microM). The cells and media were harvested and extracted. Subsequent incubations of the aqueous phase with beta-glucuronidase and aryl sulfatase, followed by acetone/ethyl acetate extraction, were utilized to determine specific conjugation. Separation of the BP and its metabolites in the residues of the extracts was achieved by h.p.l.c. The capacity of human hepatocytes to metabolize BP was not saturated at up to 100 microM of BP, and the predominant metabolites produced were eluted in the void volume and were a mixture of highly polar BP forms. The next four most prevalent forms of BP metabolites were the 3-hydroxy BP, BP-4,5-dihydrodiol, BP-9,10-dihydrodiol, and BP-7,8-dihydrodiol. These metabolites all increased nearly linearly with dose. Conjugation varied for each different case, ranging from 31 to 91%, but a general trend clearly appeared; if beta-glucuronidation decreased, then sulfation increased and vice versa. BP metabolite binding to DNA was associated with the amount of unconjugated BP-7,8-dihydrodiol metabolite. BP metabolite binding to DNA was nearly linear from 0.1 to 10 microM BP; however, binding to DNA at 100 microM increased 64- to 844-fold over the binding occurring at 10 microM. Thus, human hepatocytes have a strong tendency to form highly polar BP metabolites, and total binding of BP to DNA over a four-log dose range is much less at 0.1-10 microM than one would predict from extrapolation from the high concentration (100 microM).

Metabolism of benzo[f]quinoline by rat liver microsomes.

The metabolism of [1,3-14C]benzo[f]quinoline (BfQ) by liver microsomes from control, 3-methylcholanthrene (3-MC)-pretreated and phenobarbital (PB)-pretreated rats has been investigated in order to gain insights into the effect of mixed function oxidase inducers on the types and levels of specific metabolites as formed in vitro. The rates of metabolism of BfQ by liver microsomes from control, 3-MC- and PB-pretreated rats were 0.5, 3.6 and 2.4 nmol/min/mg of respectively. The most predominant metabolite of BfQ detected with liver microsomes from 3-MC-pretreated rats was BfQ-7,8-dihydrodiol, a precursor of the bay-region diol epoxide, constituting 41% of the total ethyl acetate-extractable metabolites. Other metabolites obtained along with their relative proportions were as follows: BfQ-N-oxide, 23% 7-hydroxyBfQ, 15%; 9-hydroxyBfQ, 9%; and BfQ-9,10-dihydrodiol, 6%. BfQ-5,6-dihydrodiol, a K-region dihydrodiol, was a trace metabolite representing approximately 1.0% of the total metabolism. Liver microsomes from PB-pretreated rats oxidized BfQ primarily to BfQ-N-oxide and 9-hydroxyBfQ, which constituted 41% and 20% of the total ethyl acetate-extractable metabolites of BfQ. The relative proportions of BfQ-9,10-dihydrodiol, BfQ-7,8-dihydrodiol and 7-hydroxy-BfQ formed were 12%, 3% and 13% respectively, while the figure for BfQ-5,6-dihydrodiol was 0.5%. The profile of metabolites formed by liver microsomes from control rats was similar to that generated by microsomes from PB-pretreated rats. While benzo-ring metabolites represented a major part of the metabolism of BfQ by liver microsomes from either 3-MC- or PB-pretreated rats, these two types of microsomes exhibited a positional selectivity in the oxidation of BfQ, the former primarily attacking the 7,8-position of BfQ while the latter preferentially oxidizing the 9,10-position. The preponderance of the potentially mutagenic BfQ-7,8-dihydrodiol amongst the metabolites generated by liver microsomes from 3-MC-pretreated rats suggests a possible role for cytochrome P-450c, the major form of rat hepatic cytochrome P-450 induced by 3-MC, in the metabolic activation of BfQ.

Benzo[a]pyrene metabolism in the Mongolian gerbil: influence of chlordecone and mirex induction

1. The metabolism of benzo[a]pyrene (BP) by gerbil hepatic microsomes is increased following induction by phenobarbital (PB), chlordecone, mirex and 3-methylcholanthrene (3-MC). 2. By several criteria including the influence of alpha-naphthoflavone (alpha-NF) on BP-hydroxylase activity and BP-metabolite profiles, the cytochromes P-450 responsible for benzo[a]pyrene metabolism appear to be similar in microsomes isolated from PB-, chlordecone-, or mirex-treated gerbils. The cytochromes P-450 present in microsomes isolated from control animals and those treated with 3-MC are different from each other and from those present in PB, chlordecone, or mirex microsomes by the same criteria. 3. Of the inducers used, only PB induced microsomal epoxide hydrolase activity.

Influence of chlordecone and mirex exposure on benzo[a]pyrene metabolism of rat-liver microsomes

The metabolism of benzo[a]pyrene (BP) in hepatic microsomes isolated from rats exposed to chlordecone or mirex was compared to that of untreated rats and rats treated with 3-methylcholanthrene (3-MC) or phenobarbital (PB). Treatment with chlordecone resulted in a two- to three-fold increase in cytochrome P-450 content but the BP-hydroxylase activity per mg microsomal protein was unaffected. Addition of alpha-naphthoflavone (alpha-NF) or chlordecone caused changes in BP-hydroxylase activity indicating that chlordecone-induced cytochromes P-450 were similar to control. H.p.l.c. analyses of BP metabolites confirmed this similarity. Treatment with mirex caused a two-fold induction of cytochrome P-450, and BP-hydroxylase activity expressed per mg microsomal protein was increased 1.3-fold. Addition of chlordecone or alpha-NF caused changes in BP-hydroxylase activity, indicating differences between control and mirex-induced cytochromes P-450. H.p.l.c. analyses of BP metabolites confirmed this difference. Treatment with chlordecone or mirex increased microsomal epoxide hydrolase activity three-fold. Chlordecone accumulated in hepatic nuclei.

Benzo[a]pyrene metabolism by purified cytochrome P-450 from 3-methylcholanthrene-treated rats.

The metabolism of benzo[a]pyrene in reconstituted pulmonary mono-oxygenase systems has been studied. Metabolites formed by pulmonary cytochrome P450MC, a major form of pulmonary cytochrome P-450 isolated from 3-methylcholanthrene-treated rats, were analysed by h.p.l.c. The profiles of benzo[a]pyrene metabolites formed by the reconstituted P-450MC systems were different from that obtained with rat-lung microsomes, indicating the presence of several unknown metabolites in the reconstituted systems containing NADPH-cytochrome P-450 reductase and epoxide hydrolase. 3-Hydroxybenzo[a]pyrene was a major product formed by pulmonary cytochrome P-450MC, in the absence or presence of epoxide hydrolase. The addition of purified epoxide hydrolase to the reconstituted systems increased the formation of dihydrodihydroxy-benzo[a]pyrenes, particularly 7,8-dihydro-7,8-dihydroxybenzo[a]pyrene. The 9,10-dihydro-9,10-dihydroxybenzo[a]pyrene was the major dihydrodiol formed by pulmonary cytochrome P-450MC. By the addition of epoxide hydrolase the total amount of phenols decreased in parallel with an increased production of dihydrodiol, but the amount of quinones was not changed. Similar results concerning the related production of phenols and dihydrodiols, in the absence and presence of epoxide hydrolase, were obtained in reconstituted systems of hepatic cytochrome P-450MC, the major form of hepatic cytochrome P-450 from 3-methylcholanthrene-treated rats.

Action of xanthine-xanthine oxidase system on microsomal benzo(a)pyrene metabolism in vitro

The effect of superoxide anion-radical and other reactive oxygen species on the metabolism of benzo(a)pyrene was studied with isolated mouse liver microsomes. Reactive oxygen species were generated in vitro by xanthine-xanthine oxidase plus Fe 3+·FeEDTA and benzo(a)pyrene metabolism was followed by reverse-phase high pressure liquid chromatography. The following results were obtained: 1. 1. The reactive oxygen species induced one-electron oxidation of benzo(a)pyrene and increased production of free epoxide as well as protein-binding intermediates. 2. 2. The reactive oxygen species triggered microsomal lipid peroxidation in the presence of Fe 3+·FeEDTA. 3. 3. As a result of microsomal lipid peroxidation a decreased activity of cytochrome P-450, epoxide hydrolase and UDP-glucuronyltransferase was found. 4. 4. It is suggested that active oxygen species changed the balance between bioactivation and conjugation of benzo(a)pyrene metabolites causing accumulation of the epoxide and protein-binding intermediates. 5. 5. The role of iron ions and chelates in this process is discussed.

Human Hair Follicle Benzo[a]pyrene and Benzo[a]pyrene 7,8-diol Metabolism: Effect of Exposure to a Coal Tar-Containing Shampoo

Assay systems for the evaluation of carcinogen interaction with human tissues are essential for assessing cancer risk. Hair follicles are a readily available source of human epithelial tissue and offer an excellent system with which to study carcinogen metabolism in human populations. In this study freshly plucked human hair follicles were employed to measure the metabolism of benzo[a]pyrene (BP), benzo[a]pyrene-7,8-diol (BP 7,8-diol), and the enzyme-mediated binding of [3H]-BP to DNA. The effect of human exposure to a crude coal tar (CCT)-containing shampoo, a preparation rich in polycyclic aromatic hydrocarbons (PAHs), on these parameters was also evaluated. Twelve healthy volunteers were studied before and after shampooing their hair daily for 4 days with the CCT-containing shampoo. Wide interindividual variation was observed in basal cytochrome P-450-dependent aryl hydrocarbon hydroxylase (AHH) activity which ranged from 0.6-17.6 fmol water-soluble BP metabolites/h/hair follicle (mean +/- SE of 32 individuals was 9.7 +/- 0.9). After use of the shampoo for 4 days AHH activity increased in 10 of the 12 volunteers (50-148%) and enhancement of enzyme-mediated binding of BP to DNA was detected in most subjects. Hair follicles were shown to convert BP to several metabolic species including BP 7,8-diol, a major precursor of the ultimate carcinogenic metabolite of BP. Benzo[a]pyrene-7,8-diol itself was also metabolized by the human hair follicles in this system. Clotrimazole, a known inhibitor of the metabolism of BP as well as the carcinogenicity of the hydrocarbon in rodent skin, was found to inhibit AHH and the in vitro metabolism of BP and BP 7,8-diol in human hair follicles. Oral administration of a similar antifungal imidazole, ketoconazole at a dose of 200 mg daily for 5 days, to healthy volunteers also resulted in greater than 90% inhibition of hair follicle AHH activity. These studies indicate that hair follicles represent an accessible tissue suitable for assessing the extent of PAH carcinogen metabolism in human subjects. Furthermore, enzyme activity critical to cancer induction by PAHs was shown to be inducible following the use of a CCT-containing shampoo. This carcinogen-activating enzyme system was substantially inhibited by imidazole compounds, suggesting that they may prove effective as anticarcinogens in human populations.

Metabolism of tobacco specific carcinogens in cultured rat buccal mucosa epithelial cells.

The metabolism of tobacco carcinogens was studied in a potential target for their carcinogenic effects. Rat buccal mucosa cells metabolized several polycyclic aromatic hydrocarbons, e.g., benzo(a)pyrene, benz(b)- and benz(j)-fluoranthene, dibenz(a,j)acridine, N,N-diethylnitrosamine and protein pyrolysate products, 2-amino-3-methylimidazo(4,5-f)quinoline, and 2-amino-3,4-dimethylimidazo(4,5-f)quinoline, as measured by binding of the carcinogens to cellular DNA. The highest level of binding was seen with the nitrosamine followed by the protein pyrolysate products. There was no significant difference in the binding levels between the different polycyclic aromatic hydrocarbons. Cells treated with a non-cytotoxic dose of the non-volatile condensate fraction of regular tobacco smoke increased metabolism as measured by binding to DNA of the protein pyrolysate products, whereas the pretreatment did not have any effect on the metabolism of benzo(a)pyrene, and N,N-diethylnitrosamine. However, the profile of benzo(a)pyrene metabolites released into the media changed. The results indicate that rat buccal mucosa cells metabolize several classes of tobacco specific carcinogens, and that the metabolism is modified by continued exposure to tobacco smoke components.

Oxidative biotransformation in primary cultures of chick embryo hepatocytes: induction of cytochrome P-450 and the metabolism of benzo(a)pyrene.

Primary cultures of chick embryo hepatocytes are known to maintain their initial level of cytochrome P-450 for a number of days. To explore the possibilities of chick embryo hepatocyte cultures as a tool in drug metabolism, induction profiles of cytochrome P-450 were determined and the metabolism of benzo(a)pyrene as a model substrate was studied. Maximum induction by phenobarbitone and Aroclor 1254 is reached after 21 h and 18 h, respectively, both in the presence and absence of serum. For beta-naphthoflavone induction is maximal after 31 h in the presence and 43 h in the absence of serum. The levels of P-450 after induction are comparable to those found in vivo in rats: increases of 200% for phenobarbitone, 200% for beta-naphthoflavone and 210% for Aroclor 1254. Ethoxyresorufin-O-deethylase activities are induced by beta-naphthoflavone and Aroclor 1254, but as expected only slightly by phenobarbitone. In the absence of serum in the culture medium, for the control as well as the induced cells a plateau of activity is maintained for at least 24 h. In the presence of serum a decline in P-450 levels is observed. Especially in the case of Aroclor, an increase in porphyrin content of 320% of control values is seen at the same time. A number of representative metabolites of benzo(a)pyrene were quantitated during a 4-h incubation. Relative amounts are comparable to those observed with rat liver microsomes. As expected, beta-naphthoflavone and Aroclor induce the rate of metabolism (by 500% and 400%, respectively, in the absence of serum), but phenobarbitone has no or very little effect.(ABSTRACT TRUNCATED AT 250 WORDS)