Biomedical subjects

F Oesch

Publications and source records attributed to F Oesch.

At least 253 records · Page 14Linked to original sources

PubMed1988

Time-dependence and differential induction of rat and guinea pig peroxisomal beta-oxidation, palmitoyl-CoA hydrolase, cytosolic and microsomal epoxide hydrolase after treatment with hypolipidemic drugs.

Fischer-344 rats and Hartley guinea pigs received a diet containing 0.01% (w/w), 0.05% (w/w), or 0.25% (w/w) of the hypolipidemic drug fenofibrate. Rats were treated for 4, 7, 14, or 21 days, and a clear dose-dependent and weak time-dependent increase in liver/body weight ratio was observed. The specific activity of peroxisomal beta-oxidation increased linearly with time at all concentrations used. A dose-dependent increase in cEH was observed, but the activity remained constant after treatment for 7 days. Enhancement of palmitoyl-CoA hydrolase was dose-dependent, but was similar at all 4 time points investigated. In contrast to the other enzyme activities, mEH was not or only minimally (less than 1.5-fold) induced. In contrast to the rat, treatment of guinea pigs with fenofibrate for 1 week did not change liver weight or enzyme activities. Prolonged treatment of guinea pigs (4 weeks) with fenofibrate did not result in an increase in enzyme activities. This was also observed with clofibrate whereas tiadenol caused a slight increase in enzyme activities (1.5- to 2.6-fold). In contrast to the guinea pig each of the three hypolipidemic drugs led to an increase in enzyme activities in the rat liver after treatment for 1 week.

Animals↗

PubMed1988

Effect of antibodies against cytochrome P-450 on demethylation and denitrosation of N-nitrosodimethylamine and N-nitrosomethylaniline.

Rat liver microsomes which were induced either with ethanol or PB were incubated with NDMA or NMA. Formaldehyde generation and nitrite formation were measured as metabolic parameters for oxidative bioactivation and denitrosation, respectively. The influence of antiserum PB3a1 and PB22 containing antibodies against the corresponding cytochrome P-450 species on both metabolic functions was investigated. The results showed that the influence on formaldehyde production and denitrosation varied independently in that both parameters were either not affected, or influenced in an opposite way, or inhibited to a different degree. Especially remarkable was the 80% inhibition of formaldehyde generation accompanied by no change in the nitrite formation by antiserum PB3a in ethanol-induced microsomes when NDMA was used as substrate. The 80% inhibition of formaldehyde production by antiserum PB3a was in contrast to no inhibition by antiserum PB2 under the same conditions. Denitrosation of NMA by PB-induced microsomes was inhibited by antiserum PB3a, but activated by antiserum PB2. It is concluded that oxidative demethylation and reductive denitrosation can be mediated by different cytochrome P-450 forms.

Animals↗

PubMed1988

Microsomal metabolism of picene.

Picene, a polycyclic aromatic hydrocarbon (PAH) of environmental relevance has recently been predicted to be carcinogenic, based on quantum mechanical calculation, although in several animal studies no carcinogenicity could be detected. In order to find out if the metabolism of this PAH can provide an explanation for its lack of carcinogenicity, picene was incubated with the hepatic microsomal fraction of Sprague-Dawley rats, which had been pretreated with Aroclor 1254. Sixteen ethyl acetate-extractable metabolites could be separated by reversed-phase high-performance liquid chromatography. Comparison of the chromatographic behavior and the UV and mass spectral properties of the metabolites with those of synthetic derivatives of picene allowed the identification of trans-1,2-, -3,4-, -5,6-dihydrodiol as well as 2- and 4-phenol as microsomal metabolites of picene. At a substrate concentration of 2.7 microM and an amount of 68 micrograms microsomal protein per ml incubation volume, 4-picenol was the main microsomal metabolite with 32.2% of total metabolic conversion, followed by the 1,2-(bay-region)dihydrodiol with 16.7%, the 3,4-(M-region)dihydrodiol with 15.9%, 2-picenol with 9.1% and the 5,6-(K-region)dihydrodiol with 1.6%. In this respect the metabolism of picene is not significantly different from that of the carcinogenic PAH benzo[a]pyrene and dibenz[a,h]anthracene. The M-region dihydrodiols, potential precursors of electrophilically reactive dihydrodiol bay-region epoxides, are formed from all three PAHs at 11-16% of total metabolic conversion. From the 2.8- to 4.4-fold lower amounts of polar and water-soluble metabolites of picene as compared to dibenz[a,h]anthracene and benzo[a]pyrene it is deduced that dihydrodiol epoxides are generated from picene to a much smaller extent than from the two carcinogenic PAHs. The lacking carcinogenicity of picene could therefore result from the inability of microsomal enzymes to transform its M-region dihydrodiol to dihydrodiol bay-region epoxides in amounts necessary to initiate carcinogenesis.

Animals↗

PubMed1988

Contact-dependent regulation of growth of diploid human fibroblasts is dependent upon the presence of terminal galactose residues on plasma membrane glycoproteins.

The growth of diploid human fibroblasts has previously been shown to be regulated mainly by the extent of cell-cell contacts [R. J. Wieser and F. Oesch (1986) J. Cell Biol. 103, 361], these contacts being effective only when terminal, beta-glycosidically linked galactose residues were present on plasma membrane glycoproteins. These studies, in which a high cell density in sparse cell cultures has been mimicked by the addition of immobilized plasma membrane glycoproteins, have been further extended to investigate the role of terminal galactose residues directly in cell cultures. The studies presented herein show that (i) culturing human fibroblasts in the presence of beta-galactosidase resulted in an approximately twofold higher saturation density, as well as a twofold higher proliferation rate at high cell densities when compared to the rates found in control cultures. (ii) The presence of alpha-lactalbumin in the culture medium, which acts as a modifier of the activity of galactosyltransferase, had the same effect as beta-galactosidase. (iii) Addition of the lectin I from Bandeiraea simplicifolia (BS I), which is specific for terminal galactose residues, resulted in an increase in the proliferation rate of cell cultures at high cell densities, while the proliferation was not affected at low cell densities. These data show that the presence of terminal, beta-glycosidically linked galactose is vital for the efficient growth control of normal cells.

Cells, Cultured↗

PubMed1988

Antimutagenesis by shift in monooxygenase isoenzymes and induction of epoxide hydrolase.

The widely occurring aromatic and olefinic structural elements can be transformed into epoxides by microsomal monooxygenases. These epoxides may react with nucleophilic centers in the cell and thereby covalently bind to DNA, RNA and protein. Such a reaction may lead to cytotoxicity, allergy, mutagenicity and/or carcinogenicity, depending on the properties of the epoxide in question. An important contributing factor is the presence and relative activity of enzymes controlling the concentration of such epoxides. There are several microsomal monooxygenases which differ in activity and substrate specificity. On individual substrates individual cytochromes P-450 often preferentially attack at one specific site different from that attacked by others. Some of these pathways lead to reactive products, others are detoxification pathways. Also important are the enzymes which metabolize epoxides, such as epoxide hydrolases and glutathione transferases. Such enzymes can act as inactivating and in some specific cases also as co-activating enzymes. Moreover, precursor-sequestering enzymes such as dihydrodiol dehydrogenase, glucuronosyl transferases and sulfotransferases are important for the control of reactive epoxides. These enzymes themselves are subject to control by many endogenous and exogenous factors. By virtue of their contribution to the control of mutagenic metabolites such modulators can exert antimutagenic activity. An especially interesting antimutagen, whose mechanism of antimutagenic action is modulation of mutagen-metabolizing enzymes, is trans-stilbene oxide. This agent selectively induces the synthesis of some specific cytochrome P-450 isoenzymes at the expense of others, so that the metabolism of benzo[a]pyrene is shifted from the route leading to the highly mutagenic 7,8-dihydrodiol 9,10-epoxides to the route leading to the much less mutagenic 4,5-epoxide. Moreover, the same agent potently induces microsomal epoxide hydrolase which inactivates the latter epoxide. The combined effects lead to a drastic antimutagenic effect, the molecular mechanism of which is given by these changes in mutagen-metabolizing enzymes.

Animals↗

PubMed1988

Contact-dependent inhibition of growth of normal diploid human fibroblasts by plasma membrane glycoproteins.

Homeostasis in vivo is maintained by a highly complex network of positive and negative signals. At the cellular level, this regulatory microenvironment can be divided, in a simplified fashion, into two major compartments: the humoral compartment, including compounds such as hormones, growth factors and nutrients, and the contact-environment compartment, including cell-cell and cell-matrix interactions. At least in cultures of diploid, non-transformed cells, cell-cell and cell-matrix interactions have been shown to be of major importance for the regulation of growth as well as of differentiation. Although until now the glycoprotein involved in the contact-dependent inhibition of growth has not been fully characterized, our studies give evidence for the involvement of a plasma membrane glycoprotein with an apparent molecular weight of approximately 80 kDa in the growth regulation of diploid human fibroblasts. The important characteristic of this glycoprotein is: the biologically active determinant resides in terminal, beta-glycosidically linked galactose residues on N-glycosidically linked glycans. From our studies, a receptor has to be postulated which, in addition to the galactose residues, has additional structural requirements for the specific binding of this glycoprotein, since other glycoproteins carrying terminal, beta-glycosidically linked galactose-residues are without biological activity. The postulated receptor is suggested to be defective in tumor cells, since these cells are no longer able to respond to cell-cell contacts with stopped proliferation, although they are able to inhibit growth of non-transformed cells. The inability of a tumor cell to recognize and to bind to the specific glycoprotein would result in a release from growth inhibition, leading to clonal growth of these cells. Further detailed studies on the structure and the regulation of the glycoprotein, as well as an attempt to isolate the postulated receptor, should lead to a better understanding of the complex pattern of growth regulation of normal cells.

Animals↗

PubMed1988

Stable expression of rat cytochrome P-450IIB1 cDNA in Chinese hamster cells (V79) and metabolic activation of aflatoxin B1.

V79 Chinese hamster fibroblasts are widely used for mutagenicity testing but have the serious limitation that they do not express cytochromes P-450, which are needed for the activation of many promutagens to mutagenic metabolites. A full-length cDNA clone encoding the monooxygenase cytochrome P-450IIB1 under control of the simian virus 40 early promoter was constructed and cointroduced with the selection marker neomycin phosphotransferase (conferring resistance to G418) into V79 Chinese hamster cells. G418-resistant cells were selected, established as cell lines, and tested for cytochrome P-450IIB1 expression and enzymatic activity. Two cell lines (SD1 and SD3) were found that stably produce cytochrome P-450IIB1. Although purified cytochromes P-450 possess monooxygenase activity only after reconstitution with cytochrome P-450 reductase and phospholipid, the gene product of the construct exhibited this activity. This implies that the gene product is intracellularly localized in a way that allows access to the required components. If compared with V79 cells, the mutation rate for the hypoxanthine phosphoribosyltransferase (HPRT) locus in SD1 cells is markedly increased when exposed to aflatoxin B1, which is activated by this enzyme.

Aflatoxin B1↗

PubMed1988

Effect of modifying agents on the phenotypic expression of cytochrome P-450, glutathione S-transferase molecular forms, microsomal epoxide hydrolase, glucose-6-phosphate dehydrogenase and gamma-glutamyltranspeptidase in rat liver preneoplastic lesions.

The expression of A and P forms of glutathione S-transferase (GST-A and P), two cytochrome P-450 isoenzymes (P-450 PB3a and P-450 MC2), microsomal epoxide hydrolase (mEHb), glucose-6-phosphate dehydrogenase (G6PD) and gamma-glutamyltranspeptidase (gamma-GT) was compared in preneoplastic liver lesions and background parenchyma of F344 rats post-treated with butylated hydroxyanisole (BHA), ethoxyquin (EQ) or acetaminophen (AAP). These latter three compounds have been shown to inhibit hepatocarcinogenesis after initial treatment with N-ethyl-N-hydroxyethylnitrosamine (EHEN) and a significant decrease in the number of enzyme-altered foci and nodules positive for GST-P, GST-A, G6PD and gamma-GT and negative for P-450 PB3a, P-450 MC2 was associated with their administration. Whereas in the foci case the decrease was most prominent for non-discrete (heterogeneous) type lesions, the results of quantitation of nodules revealed a most significant alteration in the discrete homogeneously staining population. This indicates that BHA, EQ and AAP have the potential to inhibit the growth of the phenotypically stable lesions thought most likely to be the immediate precursors of hepatocellular carcinomas. The two anti-oxidants were associated with periportal increase of all enzymes investigated, whereas AAP induced GST species and mEHb in the perivenular zone. Irrespective of slightly elevated enzyme levels in surrounding parenchyma, mEHb antibody binding levels within lesions showed a reciprocal shift from positive to negative in rats treated with BHA, EQ and AAP.

Animals↗

PubMed1988

12-O-tetradecanoylphorbol-13-acetate releases human diploid fibroblasts from contact-dependent inhibition of growth.

Treatment of human diploid fibroblasts at varying cell densities with 12-O-tetradecanoylphorbol-13-acetate (TPA) (10(-7) M) resulted in a bimodal response of proliferation rate: while at low cell densities (3 x 10(3)-1.5 x 10(4) cells/cm2) TPA inhibited the proliferation by up to 50%, at high cell densities (1-1.6 x 10(5) cells/cm2) a 2-fold higher proliferation rate as in untreated cultures was observed. When sparsely seeded normal diploid fibroblasts were grown in the presence of immobilized plasma membrane glycoproteins, as in confluent cell cultures strongly decreased proliferation and enhanced collagen type III synthesis is found. Using this test system, it emerged that the addition of plasma membrane proteins from untreated as well as from TPA-treated fibroblasts to untreated fibroblasts resulted in a strong inhibition of proliferation rate. In contrast, the addition of either untreated or TPA-treated plasma membrane proteins to cell cultured in the presence of TPA had no effect on growth. It is suggested that TPA treatment of normal diploid cells in culture results in a loss of responsiveness against cell-cell contacts, leading to an escape from the contact-dependent inhibition of growth.

Cell Division↗

PubMed1988

Metabolic perspectives on in vitro toxicity tests.

1. The toxic effects of chemicals arise either from the chemical itself or from metabolites. In either event, the concentration of the molecular species responsible for toxicity is under the control of metabolism. This metabolism is highly variable between animals and humans, and in human populations may exhibit substantial inter-individual differences. The range of human variability can be covered by resorting to a number of animal models. 2. For many purposes, it is desirable to have in vitro procedures to allow detailed examination of mechanisms, but for a long time it was commonly the case that results from in vitro systems were misleading. It was realised that this problem arose at least in part from the absence of appropriate metabolism in many in vitro systems, and to overcome this, it has become common to add metabolizing enzymes in the form of the so-called S9 fraction--the 9000 g supernatant containing both microsomal and cytosolic enzymes--of rat liver. These enzyme preparations contain both the cytochrome P-450 mono-oxygenases and the obligatory NADPH-generating system. This system is thereby optimized for the mono-oxygenase reactions which are frequently responsible for the metabolic activation of toxic chemicals. 3. It is extremely important to appreciate that such systems are highly artificial, being far removed from the situation operating in the intact cell and the whole body. The levels of reactive metabolites in the whole cell are determined by the balance between activating and inactivating enzyme systems. When the S9 fraction is used for metabolism, the detoxication enzymes are essentially inactive, so that a misleading emphasis is thrown upon metabolic activation. Although the inactivating enzymes, such as the glutathione S-transferases, the sulphotransferases and the glucuronosyltransferases, are present in the S9 fraction, their cofactors are diluted so far below the relevant Km values as to render them completely inoperative. This absence of metabolic inactivation in in vitro test systems very commonly underlies observed discrepancies between the results of bacterial mutagenicity tests and carcinogenicity studies in whole animals. 4. Present and future demands upon the toxicologist require the use of rapid in vitro tests for the screening of chemicals, the results of which have predictive value for in vivo adverse effects, e.g. general toxicity, carcinogenicity or mutagenicity. The key role of metabolic information in such procedures is illustrated in this report with reference to the series of methylated derivatives of the polycyclic aromatic hydrocarbon benz(a)anthracene.(ABSTRACT TRUNCATED AT 400 WORDS)

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1988

Effects of dietary zinc deficiency on the activity of enzymes associated with phase I and II of drug metabolism in Fischer-344 rats: activities of drug metabolising enzymes in zinc deficiency.

A study was undertaken to assay the various phase I and phase II drug metabolising enzymes in zinc deficiency. Male weanling Fischer rats were subjected to zinc deficiency for a period of 7 weeks. Zinc levels in the control and deficient diets were 30 mg and 1.1 mg/kg diet, respectively. At the end of the experimental period, the activities of various hepatic cytosolic and microsomal enzymes were estimated. It was observed that the activities of microsomal epoxide hydrolase (with benz(a)pyrene 4-5 oxide as substrate), uridine diphospho glucuronyl transferase (with 1-naphthol as substrate) and cytosolic glutathione-S-transferase (with chlorodinitrobenzene as substrate) were altered exclusively due to zinc deficiency. There was a change in the activities of the following enzymes, which could be due either to zinc deficiency and/or food restriction: 1) aryl hydrocarbon hydroxylase; 2) cytochrome b; 3) cytochrome c; and 4) cytochrome b5. Other enzymes studied, i.e., cytosolic epoxide hydrolases, microsomal EHSTO, and UDPGT testosterone were not different in the control and experimental groups. The results are discussed in relation to the activation of carcinogens and neoplastic formation in zinc deficiency.

Animals↗

PubMed1987

Differential induction of cytochrome P-450 by the enantiomers of trans-stilbene oxide.

Optically pure (+)- and (-)-trans-stilbene oxide (TSO) enantiomers were administered to immature male Sprague-Dawley rats. (+)-TSO was the more potent inducer of liver microsomal cytochrome P-450-dependent monooxygenases. The greater potency of (+)-TSO may be explained on the basis of stereoselective metabolism since a far greater concentration of TSO was found in liver microsomes of (+)-TSO-treated rats. Furthermore, of the enzymes known to metabolize TSO, cytosolic epoxide hydrolase turned over the (-)-TSO enantiomer at a faster rate, consistent with the greater persistence of the (+)-enantiomer. Although this report is of chiral effects in potency of enzyme induction, stereoselective metabolism (i.e. disposition) rather than inherent structural characteristics (recognition) may be responsible for these effects.

Animals↗

PubMed1987

Effect of unbalanced diets on incorporation of delta-aminolevulinic acid into cytochrome P-450.

The in vivo syntheses of two liver microsomal cytochromes P-450 PB3a, P-450 UT50 [(1987) Eur. J. Biochem., submitted] (Mr 50,000, 52,000) have been estimated by measuring the specific activity 2 h after i.p. administration of delta-[3H]aminolevulinic acid to male Sprague Dawley rats. The animals were fed either a standard rat chow (5% lard, 22% casein) or unbalanced diets (high lipid, 30% lard or low protein, 6% casein) with or without 50 ppm Phenoclor DP6. The high-lipid diet supported a more rapid body weight gain but had little impact on cytochrome P-450 content, expressed either per whole liver or per mg microsomal protein, and on the incorporation of the precursor into cytochrome P-450. The latter was determined by measuring the radioactivity incorporated into the cytochrome P-450 fraction, partially purified by affinity chromatography, as well as into two cytochrome P-450 isozymes (Mr 50,000 or 52,000) purified by DEAE-52 cellulose ion-exchange chromatography. The low-protein diet, on the other hand, severely depressed body weight gain and cytochrome P-450 content as well as incorporation of radioactivity, the lower-Mr cytochrome (Mr 50,000) being particularly affected. However, when a potent inducer, Phenoclor DP6, was added to the low-protein diet, cytochrome synthesis was restored indicating that the effect was reversible.

Aminolevulinic Acid↗

PubMed1987

Development of cytochrome P-450-altered preneoplastic and neoplastic lesions during nitrosamine-induced hepatocarcinogenesis in the rat.

The expression of four cytochrome (cyt.) P-450 isoenzymes has been studied in preneoplastic and neoplastic lesions during the course of nitrosamine-induced hepatocarcinogenesis in the female Wistar rat. Following exposure to diethylnitrosamine (50 or 100 ppm in the drinking water) for 10 days, animals were taken sequentially, and the livers were analyzed for the evolution of adenosine triphosphatase deficient focal lesions. These lesions were subdivided into different phenotypes with regard to their cyt. P-450 isoenzyme expression using serial frozen sections. Our results demonstrate that about 40% of the adenosine triphosphatase-deficient lesions show concomitant alterations in their cyt. P-450 isoenzyme contents. Of these lesions, islets which are characterized by decreased levels of at least three cyt. P-450 isoenzymes show a dramatic increase in their volumetric fraction of liver tissue with progression of time. Although only very few lesions express this phenotype, the contribution to the volumetric fraction of islet tissue raises from about 2% at 10 weeks to about 60% at 35 weeks after cessation of diethylnitrosamine treatment. By contrast, lesions which express less than two alterations in cyt. P-450 isoenzyme levels develop relatively slowly. Similar results were obtained when animals were exposed continuously to diethylnitrosamine for a period of up to 8 weeks. Following treatment of islet-bearing animals with phenobarbital, an induction of cyt. P-450 isoenzymes and NADPH-cyt. P-450-reductase was observed within preneoplastic and neoplastic lesions. This induction was most pronounced in large, expansively growing nodules, a type of lesion which displayed decreased levels of these enzymes in livers of animals not treated with phenobarbital. The elevation of the cyt. P-450 isoenzymes disappeared within 2 to 3 weeks after cessation of inducer treatment. Our results indicate that a high proportion of rapidly growing lesions has assumed a constitutive deficiency in cyt. P-450 isoenzyme expression during nitrosamine-induced hepatocarcinogenesis. This deficiency, however, is not an irreversible quality, since individual cyt. P-450 isoenzymes can be markedly induced by treatment with an enzyme inducer like phenobarbital. Thus, the observed decrease in cyt. P-450 expression during development of malignancy does not result from alterations in the cyt. P-450 encoding structural genes but may rather be related to abnormalities in the function of regulatory systems of a higher order which may play a central role in the maintenance of cell homeostasis.

Animals↗

PubMed1987

Mutagenicity experiments on agroclavines, new natural antineoplastic compounds.

Agroclavine, an alkaloid produced by some species of fungi and dicotyledon plants, and its 1-alkylated derivatives are potentially useful as antineoplastic drugs, since they exert potent and selective cytostatic effects. In the present study, we have investigated agroclavine and its 1-propyl and 1-pentyl derivatives for mutagenicity. The genetic end point studied was the reversion of strains of Salmonella typhimurium (TA 100, TA 98, TA 1537) and Escherichia coli (WP2 uvrA), auxotrophic for histidine and tryptophan, respectively. The compounds were tested directly and in the presence of a mammalian xenobiotic-metabolizing system. In the direct test, agroclavine and the two alkylated derivatives examined exhibited substantial bacteriotoxicity but no mutagenicity. Addition of NADPH-fortified postmitochondrial supernatant fraction of rat liver homogenate led to a clear-cut decrease in bacteriotoxicity and to the formation of mutagenic products. Each compound was effective in all three strains of S. typhimurium used. In E. coli only spurious effects were seen. 1-Pentylagroclavine, the most hydrophobic compound in the series, was the strongest mutagen. Agroclavine, the least hydrophobic compound, was the weakest. The mutagenic potencies and efficacies of all these test compounds were much weaker than those of the positive controls, which were known mutagens and carcinogens. Moreover, the differential effect of metabolism by liver enzymes demonstrates that the toxicity and mutagenicity of agroclavine and its derivatives are caused by different chemical species. Hence, it may be possible to develop derivatives that are cytotoxic but not mutagenic.

Animals↗

PubMed1987

Rat hepatocyte-mediated bacterial mutagenicity in relation to the carcinogenic potency of benz(a)anthracene, benzo(a)pyrene, and twenty-five methylated derivatives.

7,12-Dimethylbenz(a)anthracene, benz(a)anthracene, and benzo(a)pyrene as well as the 24 monomethylbenzo(a)pyrenes (MBPs) and monomethylbenz(a)anthracenes (MBAs), compounds which differ in carcinogenicity from very potent to apparently inactive, were investigated for mutagenicity (reversion to histidine prototrophy) in Salmonella typhimurium TA100 using either intact or NADPH-fortified homogenized rat hepatocytes for metabolic activation. In both systems, all 27 hydrocarbons showed positive responses. Their mutagenic potency in the homogenate-mediated test varied in a narrow range and did not correlate detectably with their reported activity in carcinogenicity experiments. When the cell homogenate was replaced by intact cells, the maximal mutagenic effects were weaker by factors of 1 to 14, depending on the compound, and were seen only at higher substrate concentrations. The differences between cell- and homogenate-mediated mutagenicity were small with the strong carcinogens 7,12-dimethylbenz(a)anthracene 7-MBA, 12-MBA, benzo(a)pyrene, 1-MBP, and 11-MBP. The differences were large with the apparent noncarcinogens and those weak carcinogens that were strongly mutagenic in the homogenate-mediated test. As a result of this differential reduction in activity, the cell-mediated mutagenicity did not correlate with the homogenate-mediated mutagenicity but correlated approximately with the carcinogenic potency. The lowest effects in the cell-mediated experiments were seen with 7-, 8-, 9- and 10-MBP, 2-MBA, and 3-MBA. In these compounds, the methyl group is attached to a carbon of the terminal angular benzo ring, and therefore bay-region diol-epoxides, if formed at all, additionally would carry a methyl group on one of the oxidized positions. On the other hand, among all the compounds tested 7,12-dimethylbenz(a)anthracene, 12-MBA, and 11-MBP, which have the methyl group attached in the bay-region position opposite the terminal benzo ring, showed the highest mutagenic efficacies in the cell-mediated test, as compared to those observed in the homogenate-mediated test. These structure-activity relationships and the previously reported observation that among various promutagenic benzo(a)pyrene metabolites only the 7,8-dihydrodiol was strongly mutagenic in the cell-mediated test would suggest that in the cell-mediated bacterial mutagenicity test, bay-region diol-epoxides are the ultimate mutagens which are preferentially detected.

Animals↗

PubMed1987

Isoenzyme-specific phosphorylation of cytochromes P-450 and other drug metabolizing enzymes.

A series of fourteen cytochrome P-450 isoenzymes was treated with three different protein kinases and found to divide into isoenzymes phosphorylated by both the cyclic AMP-dependent kinase and the calcium-phospholipid-dependent kinase (P-450 PB 3a and PB 2e), by none of these kinases (P-450 PB 1b, MC 1b, UT 1, and thromboxane synthase), and by either the cyclic AMP-dependent kinase (P-450 LM 2, PB 2d, and PB 3b) or the calcium-phospholipid-dependent kinase (P-450 PB 1a, PB 2a, MC 1a, LM 3c, and LM 4). Other components of the monooxygenase system, cytochrome P-450 reductase, cytochrome b5, cytochrome b5 reductase as well as microsomal epoxide hydrolase, were poor substrates for the kinases employed. On the other hand, glutathione transferases 1-2 and 4-4, but not 3-3, were relatively good substrates for the calcium-phospholipid-dependent kinase.

Animals↗

PubMed1987

Concomitant induction of cytosolic but not microsomal epoxide hydrolase with peroxisomal beta-oxidation by various hypolipidemic compounds.

The effects of two cholesterol-lowering (probucol and 1-benzyl-imidazole), three triglyceride- and cholesterol-lowering (clofibrate, tiadenol and fenofibrate) and one triglyceride-lowering (acetylsalicylic acid) compounds on the specific activities of two lipid-metabolizing enzymes (cyanide-insensitive peroxisomal beta-oxidation and palmitoyl-CoA hydrolase) and two xenobiotic metabolizing enzymes (cytosolic (cEH) and microsomal epoxide hydrolase (mEHb] from the livers of male Fischer F-344 rats were investigated. With the exception of probucol and acetylsalicylic acid, all compounds tested caused a dose-dependent hepatomegaly. Taken on a weight basis fenofibrate was the most effective inducer, causing a 20-fold induction of peroxisomal beta-oxidation, a 13-fold induction of cEH activity and a 16-fold induction of palmitoyl-CoA hydrolase activity. The other compounds with triglyceride-lowering activity also induced cEH as well as peroxisomal beta-oxidation and palmitoyl-CoA hydrolase activity. The potency of each individual drug was similar for induction of cEH activity as compared with that of peroxisomal beta-oxidation and palmitoyl-CoA hydrolase activity, but very dissimilar for mEHb, which upon treatment with any of the triglyceride-lowering compounds was either not or only minimally (less than 1.5-fold) induced. 1-Benzylimidazole possessing exclusively cholesterol-lowering activity increased mEHb much more than either cEH or peroxisomal beta-oxidation. The absence of an enhancement of cEH activity in in vitro studies confirmed that the increase in enzyme activity by the test compounds is not caused by activation. cEH activity was also induced in the kidney but only about 2-fold by fenofibrate, tiadenol and acetylsalicylic acid.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗