Effects of phenobarbital and 3-methylcholanthrene administration on glutathione-S-epoxide transferase activity in rat liver

Mechanisms of induction of cytosolic and microsomal glutathione transferase (GST) genes by xenobiotics and pro-inflammatory agents

Glutathione transferase (GST) isoezymes are encoded by three separate families of genes (designated cytosolic, microsomal and mitochondrial transferases), with distinct evolutionary origins, that provide mammalian species with protection against electrophiles and oxidative stressors in the environment. Members of the cytosolic class Alpha, Mu, Pi and Theta GST, and also certain microsomal transferases (MGST2 and MGST3), are up-regulated by a diverse spectrum of foreign compounds typified by phenobarbital, 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene, pregnenolone-16α-carbonitrile, 3-methylcholanthrene, 2,3,7,8-tetrachloro-dibenzo-p-dioxin, β-naphthoflavone, butylated hydroxyanisole, ethoxyquin, oltipraz, fumaric acid, sulforaphane, coumarin, 1-[2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole, 12-O-tetradecanoylphorbol-13-acetate, dexamethasone and thiazolidinediones. Collectively, these compounds induce gene expression through the constitutive androstane receptor (CAR), the pregnane X receptor (PXR), the aryl hydrocarbon receptor (AhR), NF-E2-related factor 2 (Nrf2), peroxisome proliferator-activated receptor-γ (PPARγ) and CAATT/enhancer binding protein (C/EBP) β. The microsomal T family includes 5-lipoxygenase activating protein (FLAP), leukotriene C(4) synthase (LTC4S) and prostaglandin E(2) synthase (PGES-1), and these are up-regulated by tumour necrosis factor-α, lipopolysaccharide and transforming growth factor-β. Induction of genes encoding FLAP, LTC4S and PGES-1 is mediated by the transcription factors C/EBPα, C/EBPδ, C/EBPϵ, nuclear factor-κB and early growth response-1. In this article we have reviewed the literature describing the mechanisms by which cytosolic and microsomal GST are up-regulated by xenobiotics, drugs, cytokines and endotoxin. We discuss cross-talk between the different induction mechanisms, and have employed bioinformatics to identify cis-elements in the upstream regions of GST genes to which the various transcription factors mentioned above may be recruited.

Isolation and characterization of a novel glutathione S-transferase-activating peptide from the oriental medicinal plant Phellodendron amurense

The aim of this study was to elucidate the characteristics of glutathione S-transferase (GST)-activating compounds from medicinal plants. Among 265 kinds of medicinal plants, Phellodendron amurense showed the highest GST activity at 174.8%. The GST-activating compound of P. amurense was maximally extracted when treated with distilled water at 30 degrees C for 12 h. The compound was purified by ultrafiltration, Sephadex G-10 gel filtration chromatography, and reverse-phase HPLC. The purified GST-activating compound from P. amurense was a novel tetrapeptide with an amino acid sequence of Ala-Pro-Trp-Cys and its molecular weight was estimated to be 476 Da. It also displayed a clear detoxicative effect in 1-chloro-2,4-dinitrobenzene treated mice at a dosage of mg/kg body weight.

Effects of Inducers of Drug Metabolism on Cytosolic GlutathioneS-transferase Activity in Rat Hepatoma-derived Fa32 Cells

Established Fa32 cells, derived from a rat hepatoma, were investigated for their glutathione S-transferase (GST) induction capacity, which is an important characteristic of the detoxification capacity in normal liver. The cells were exposed to inducers of drug metabolism for 3 days in complete medium (containing 10% fetal calf serum). Neither dimethyl sulphoxide nor dimethyl formamide could be used as a vehicle to transport the inducers into the cells, because they also interacted with GST. Phenobarbital, butylated hydroxyanisole, allyl isothio-cyanate and dimethyl fumarate (but not fumaric acid) all effectively increased the total specific GST activity. None of the test chemicals produced a very pronounced induction of specific GST subunits, but subunit 2 and subunit 8 were increased more than the others. The effects of inducers of drug metabolism on the GST activity in Fa32 cells are comparable with those in rat liver. These cells can therefore be used as a valuable alternative model for GST-dependent metabolic interactions in rat liver.

Influence of metabolism in skin on dosimetry after topical exposure

Metabolism of chemicals occurs in skin and therefore should be taken into account when one determines topical exposure dose. Skin metabolism is difficult to measure in vivo because biological specimens may also contain metabolites from other tissues. Metabolism in skin during percutaneous absorption can be studied with viable skin in flow-through diffusion cells. Several compounds metabolized by microsomal enzymes in skin (benzo[a]pyrene and 7-ethoxycoumarin) penetrated human and hairless guinea pig skin predominantly unmetabolized. However, compounds containing a primary amino group (p-aminobenzoic acid, benzocaine, and azo color reduction products) were substrates for acetyltransferase activity in skin and were substantially metabolized during absorption. A physiologically based pharmacokinetic model has been developed with an input equation, allowing modeling after topical exposure. Plasma concentrations in the hairless guinea pig were accurately predicted for the model compound, benzoic acid, from in vitro absorption, metabolism, and other pharmacokinetic parameters.

Conjugation of microsome generated and synthetic aflatoxin B1-8,9 epoxide and styrene oxide to glutathione by purified glutathione S-transferases from hamster and mouse livers

Glutathione (GSH) conjugation of microsome-mediated and synthetic aflatoxin B1 (AFB1)-epoxide and styrene oxide has been studied with purified glutathione transferases (GSTs) from mouse and hamster liver cytosols. In hamster, with microsomally activated epoxide, the alpha group of GSTs show about 10-fold more activity than the mu group. With the synthetic AFB1 epoxide, the mu enzymes designated H3B and C show considerable activity although less than alpha, whereas H3A and D demonstrate similar ranges of activity as the alpha group. The pi class of GST could not be assayed due to its absence in the hamster liver. The mouse liver cytosols show 3.6-fold greater activity than hamster cytosol in microsome mediated assay system. The mouse alpha and mu enzymes have similar levels of activity in the microsome mediated system; this activity could not be determined with the pi GST due to shortage of this enzyme. The alpha group has 2- and 5-fold higher activity than mu and pi group of GSTs, respectively, with the synthetic epoxide of AFB1. With styrene oxide, the purified GSTs from hamster liver show total loss of activity whereas in the mouse alpha, mu and pi classes of GSTs have similar range of activity as the cytosol. The role of alpha and mu isozymes of GST in rendering these animals resistant to hepatocarcinogenecity is suggested.

Effect of intratracheally administered lindane on aldrin and benzo(a)pyrene contents in lungs of rats

Pretreatment with lindane resulted in inhibition of benzo(a)pyrene hydroxylase activity in the lungs of rats. The enzyme activity tended to return to normal 5 days after the administration of lindane. Studies with benzo(a)pyrene and aldrin indicated reduced elimination of these compounds from the lungs of lindane-treated animals, suggesting that lindane may alter the clearance of certain substances or compounds from lungs. The delayed clearance of these compounds from lungs may be an indirect effect of lindane related to inhibition of certain metabolizing enzymes.

Effect of dietary fat on the induction of hepatic microsomal cytochrome P450 isozymes by phenobarbital

Dietary polyunsaturated fatty acid is needed for optimal induction of cytochrome P450. In this study we quantitated cytochrome P450 hemoproteins in male Sprague-Dawley rats that were starved for 36 hr and then refed a fat-free diet (FF) or a diet containing 20% corn oil for 4 days. Some received phenobarbital (Pb) sodium (80 mg/kg, i.p., daily) for 3 days prior to decapitation. Microsomal cytochrome P450 levels were measured by carbon monoxide binding spectra, and the P450 isozymes separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis were quantitated by gel scanner. Cytochrome P450 PB-B was quantitated by a Western blot technique. Rats fed FF diet and administered Pb had only 21% more microsomal P450 than non-induced controls, whereas rats fed 20% corn oil diet had 59% more P450 and Pb-treated rats fed 20% corn oil diet had 181% more P450 than FF controls. Analysis of gels showed 32, 59 and 124% more P450 protein, respectively, in FF Pb, corn oil control or corn oil Pb groups than in FF controls. Cytochrome P450 PB-B was not detected in non-induced groups, but quantitation by Western blot yielded 0.32 and 0.70 nmol/mg protein, respectively, in FF Pb and corn oil Pb groups. Our findings suggest that deprivation of dietary fat reduces the total amount of cytochrome P450 hemoprotein and its inducibility by Pb through decreased P450 hemoprotein synthesis. The limiting factor(s) restricting synthesis of new cytochrome P450 hemoproteins in rats refed a diet devoid of fat may be the inability to respond to the inducer (Pb) or the paucity of utilizable fatty acids needed for synthesis of the phospholipid matrix of the endoplasmic reticulum necessary for the support and proper juxtapositioning of these protein molecules.

Effect of aflatoxin B1 treatment in vivo on the in vitro activity of hepatic and extrahepatic glutathione S-transferase

The effect of aflatoxin B1 (AFB1) on the glutathione S-transferase activity (GST) and on non-protein thiol levels of different tissues was studied in adult male Wistar rats. Animals received a single dose of the toxin (100 or 500 micrograms/kg body wt., p.o.), and were studied 6 or 24 h after administration. GST was determined in liver, renal cortex, duodenum, jejunum-ileum and distal ileum, using 3 substrates: 1-chloro-2,4-dinitrobenzene (CDNB), trans-4-phenyl-3-buten-2-one (PBO) and 1,2-epoxyethylbenzene (STOX). The non-protein thiol content of all tissues tested increased with the lowest dose at 6 h, returning to normal values at 24 h, while the higher dose produced a significant decrease in reduced thiol levels at 6 h, returning to normal values at 24 h. AFB1 administration induced, independently of dose and tissue, total GST (CDNB) and epoxide-transferase activity (STOX) while A--C-type transferases (PBO) were inhibited. Almost all activities returned to normal values at 24 h. In cases of enzyme induction there was in general an increase in Vmax and a decrease in apparent Km. The opposite was seen in cases of inhibition. In conclusion, the results provide evidence that extrahepatic GST could be important in the overall process of detoxification of AFB1. The behavior seen in hepatic and extrahepatic tissues revealed the functions of catalysis (B-type transferases) and covalent bond formation, as well as inactivation by probable AFB1 metabolites (A--C-type transferases).

Simultaneous determination of cytosolic glutathione S-transferase and microsomal epoxide hydrolase activity toward benzo[a]pyrene-4,5-oxide by high-performance liquid chromatography

Cytosolic glutathione S-transferase (GST) and microsomal epoxide hydrolase (EH) are important detoxification enzymes for many epoxide xenobiotics. We have developed a rapid, simple, and convenient HPLC assay which measures both of these enzyme activities toward benzo[a]pyrene-4,5-oxide (BaPO) in tissue homogenates. Tissue fractions were incubated at 37 degrees C in the presence of 5 mM glutathione. Reactions were initiated by addition of BaPO and terminated by the addition of ice-cold acetonitrile containing 2-methoxynaphthalene as an internal standard. Samples were analyzed directly on a 15-cm C18 reverse-phase column at room temperature, with a ternary solvent program which utilized 0.01% ammonium phosphate buffer (pH 3.5), acetonitrile, and water. The uv absorbance (260 nm) was monitored. Baseline resolution of BaPO, BaPO-GSH, and BaPO-diol and the internal standard was accomplished in 10 min. In rat hepatic S9, production of both BaPO-GSH and BaPO-diol was linear with time and protein up to 15 min and 500 micrograms/ml, respectively. Coefficients of variation for replicate analyses were 2.7 and 3.7% for GST and EH activities in S9, respectively. With fluorescence detection (ex, 241; em, 389 nm), this assay was sensitive enough to measure GST and EH activities in mononuclear leukocytes (MNL). GST and EH activities in 109 human MNL samples were 142 +/- 74 (mean +/- SD; range 21-435) pmol/mg/min and 19 +/- 9 (mean +/- SD; range 3-59) pmol/mg/min, respectively. These results demonstrate the simplicity, high sensitivity, and applicability of this assay for a broad range of tissues.

Sex and species differences in glutathione S-transferase activities

Glutathione S-transferases (GSTs) are one of the important enzymes in terms of not only drug metabolism but also physiological functions. The marked sex difference in GST activity has been found in rat and mouse liver cytosol, and such differences in rat liver are suggested to be primarily due to the differences in the subunit composition of GSTs in both sexes. In addition, GST activities of rat liver cytosol are known to be largely influenced by treatment with inducers such as phenobarbital and 3-methylcholanthrene and various hormones. GSTs are widely distributed in mammalian species, and multiplicity of GST has been demonstrated so far. The present review also describes multiple forms of GST from the viewpoint of enzymology and immunology.

Induction of ornithine decarboxylase and S-adenosylmethionine decarboxylase by sulfobromophthalein in rats

The administration of sulfobromophthalein (BSP, 0.5 mmol/kg, ip.) increased ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC) activities to 30-fold and 5-fold, respectively, of the controls at 12 hr in the liver of rats. Parallel to the increase in ODC, there was an increase in hepatic putrescine content. However, spermine content tended to decrease. BSP increased ODC and SAMDC activities and putrescine content, but decreased spermine content, in a dose-dependent manner. Pretreatment of rats with actinomycin D and cycloheximide almost completely blocked the BSP-mediated increase of ODC and SAMDC activities. Pretreatment with glutathione (GSH) failed to inhibit BSP-mediated increase of ODC and SAMDC activities. In addition, the administration of BSP-GSH conjugate (0.5 mmol/kg, iv.) did not produce the increase of ODC and SAMDC activities. Pretreatment with phenobarbital and 3-methylcholanthrene did not inhibit BSP-mediated increase of ODC and SAMDC. The results indicate that BSP could cause changes in hepatic polyamine content due to the induction of ODC and SAMDC.

Positive correlation exists between glutathione S-transferase activity and aflatoxin formation in Aspergillus flavus

The presence of glutathione (GSH) S-transferase activity, using 1-chloro-2, 4-dinitrobenzene (CDNB) as a substrate, has been established in the cytosolic fraction of the toxigenic (aflatoxin producing) and nontoxigenic strains of Aspergillus flavus. Significant differences in the GSH S-transferase activity were observed between the toxigenic and non-toxigenic strains. A positive correlation has been demonstrated for the first time between aflatoxin formation and a biochemical parameter, namely GSH S-transferase activity. The evidence in support of A. flavus GSH S-transferase induction by endogenous aflatoxins is as follows: (i) the age-related production of aflatoxin follows the same pattern as the cytosolic GSH S-transferase activity profile; (ii) significantly higher enzyme activity was associated with mycelia of a toxigenic strain grown in medium supporting high aflatoxin production (sucrose-low-salts medium) while the enzyme activity was low in medium producing less aflatoxin (glucose-ammonium nitrate medium). The GSH S-transferase activity of the non-toxigenic strain was hardly affected by a change in the medium as it produces no aflatoxins; and (iii) the toxigenic strain demonstrated significantly higher apparent Vmax. with no change in Km as compared with the non-toxigenic strain. This indicates that the enzyme induction by endogenous aflatoxins is similar to the action of phenobarbitol and other inducing drugs (Kaplowitz et al., 1975).

Modulation of the cytotoxicity and mutagenicity of benzo[a]pyrene and benzo[a]pyrene 7,8-diol by glutathione and glutathione S-transferases in mammalian cells (CHO/HGPRT assay)

Biologically reactive metabolites of benzo[a]pyrene (BP) and benzo[a]-pyrene 7,8-diol (BP-diol), formed by the mixed-function oxidase (MFO) system, are substrates for conjugation and detoxication by glutathione (GSH) when catalyzed by glutathione S-transferases (GSHT). We have investigated the detoxication of BP- and BP-diol-induced cytotoxicity and mutagenicity with GSH by supplementing the S9 mix used in the Chinese hamster ovary cells/hypoxanthine-guanine phosphoribosyltransferase (CHO/HGPRT) assay with GSH (6.5 mM) or GSH plus GSHT. The addition of GSH to the S9 mix resulted in a reduction of BP- and BP-diol induced cytotoxicity. GSH plus GSHT eliminated BP-induced cytotoxicity and reduced the mutagenicity of BP. GSH inhibited the mutagenicity at low (essentially non-lethal) concentrations of BP-diol, but did not do so at toxic concentrations. GSH plus GSHT inhibited the cytotoxicity and mutagenicity of BP-diol at concentrations not affected by GSH alone. These studies indicate that biochemical mechanisms of detoxication can affect the biological activity of a carcinogen, such as BP or BP-diol as profoundly as bioactivation by the MFO system.

Difference in the effects of phenobarbital and 3-methylcholanthrene treatment on subunit composition of hepatic glutathione S-transferase in male and female rats

Male rats more than seven weeks old showed significantly higher activity of hepatic cytosolic glutathione S-transferase (GST) than females. This sex-related difference in GST activities might be explained by the difference in subunit composition of the enzymes between males and females. The relative proportion of subunit composition of GST between adult male and female rats was as follows: Ya, female greater than male; Yb(Yb'), male much greater than female; Yc, female greater than male. Since phenobarbital (60 mg/kg, i.p. for seven days) induced the Yb subunit as well as Ya subunit, the enzyme activity was more increased in males than in females and the sex difference became more marked. 3-Methylcholanthrene (20 mg/kg, i.p. three times) caused an increase of Ya subunit alone, and then the increased extent was greater in females than in males, and resulted in the disappearance of sex difference.

Mechanistic aspects on chemical induction of spindle disturbances and abnormal chromosome numbers

Work on the chemical induction of spindle disturbances and abnormal chromosome numbers, and work on the composition and biochemistry of the spindle are reviewed. Some early investigations have shown that there is an unspecific mechanism for chemical induction of spindle disturbances. This mechanism is based on the interaction of compounds with cellular hydrophobic compartments. Some compounds act differently and are more active than predicted from their lipophilic character. Selected compounds of that kind and their possible mechanisms of action are discussed. Changes in sulfhydryl and ATP levels, oxidative damage of membranes and impaired control of cytoplasmic Ca2+ levels are discussed in this context.

Transcriptional regulation of rat liver glutathione S-transferase genes by phenobarbital and 3-methylcholanthrene

The relative rates of transcription of the rat liver glutathione S-transferase Ya-Yc and Yb genes were determined in purified liver nuclei isolated at different times after phenobarbital or 3-methylcholanthrene administration. The transcriptional rates of the Ya-Yc and Yb genes were elevated approximately fivefold 8 and 6 h, respectively, after phenobarbital administration. In contrast, the transcriptional rates of the Ya-Yc genes were elevated approximately eightfold at 16 h after 3-methylcholanthrene administration, whereas the transcriptional rates of the Yb genes were elevated approximately fivefold at 6 h after the administration of this xenobiotic. The elevation in transcriptional activity of the glutathione S-transferase genes is sufficient to account for the increase in glutathione S-transferase mRNA levels determined previously by RNA blot hybridization [C. B. Pickett, C. A. Telakowski-Hopkins, G. J-F. Ding, L. Argenbright, and A. Y. H. Lu (1984) J. Biol. Chem. 259, 5182-5188]. Therefore, it appears that phenobarbital and 3-methylcholanthrene elevate the level of the rat liver glutathione S-transferases primarily by augmenting the transcriptional rates of their respective genes.

Increased glutathione in cultured hepatocytes associated with induction of cytochrome P-450. Lack of effect of glutathione depletion on induction of cytochrome P-450 and delta-aminolevulinate synthase

Cellular glutathione concentrations in primary cultures of chick embryo hepatocytes were 15.3 +/- 5.3 nmoles/mg protein (mean +/- S.D.) and remained stable for up to 3 days in culture. The presence of insulin was not essential for the maintenance of glutathione concentrations. Induction of cytochrome P-450 by phenobarbital-like inducers (2-propyl-2-isopropylacetamide, 2-allyl-2-isopropylacetamide, and 2,4,5,2',4',5'-hexabromobiphenyl) was accompanied by 2- to 3-fold increases in glutathione concentrations and by increased glucuronidation of phenol red. The 3-methylcholanthrene-like inducers of cytochrome P-450 (beta-naphthoflavone and 3,4,3',4'-tetrachlorobiphenyl) did not have these effects. Glutathione was rapidly depleted to 15-30% of control levels in hepatocytes treated with buthionine sulfoximine, an inhibitor of gamma-glutamylcysteine synthase. No toxicity was observed with glutathione depletion. Glutathione depletion did not affect the ability of 2-propyl-2-isopropylacetamide to induce cytochrome P-450, glucuronidation of phenol red, or delta-aminolevulinate synthase.

Enhancement of glutathione S-transferase activity in rat liver by repeated administration of propylthiouracil

Treatment of rats with propylthiouracil for one to two weeks caused an increase in glutathione S-transferase (GST) activity of the liver cytosol, but not of the particulate fraction. Increased GST activity was reversed two weeks after discontinuing PTU administration. Activation of the enzyme was inversely proportional to the decrease in leukocytes. Repeated administration of PTU increased the Vmax of the enzyme without affecting the Km value for the substrate 1-chloro-2,4-dinitrobenzene, whereas both the Km and Vmax for glutathione (GSH) were increased by PTU treatment. GSH content and GSH peroxidase activity were not affected by PTU, but this resulted in an increase in glucose 6-phosphate dehydrogenase activity. PTU treatment caused increase in GST activity using 1-chloro-2,4-dinitrobenzene, 1,2-dichloro-4-nitrobenzene, p-nitrobenzyl chloride, and benzalacetone as substrates; enzyme activity towards chlorodinitrobenzene was the highest.

Induction of mouse liver glutathione S-transferase by ethanol

The induction of hepatic glutathione S-transferase by ethanol was investigated in male Swiss-Webster mice using a liquid diet. After a 7-day feeding period, mice that received 18, 27 or 36% of their calories as ethanol exhibited significant increases in the specific activity of glutathione S-transferase when 1,2-dichloro-4-nitrobenzene (DCNB), p-nitrobenzylchloride (NBC) and 1,2-epoxy-3-(p-nitrophenoxy)propane (ENP) were used as substrates. The observed increases in activity appeared to be related to the concentration of ethanol in the diet. Thus, mice fed a diet with 36% of the calories as ethanol exhibited the greatest increase in specific activity (DCNB, 75%; NBC, 60%, ENP, 34%). Pair-fed mice demonstrated similar changes in enzymatic activity. A time-course study indicated a 4-day feeding period was not sufficient to elicit significant induction, but a significant increase was apparent by day 7. This increase was maintained or increased through day 14. By comparison, 0.5 mg of phenobarbital/ml of diet produced a greater increase in enzymatic activity (DCNB, 449%; NBC, 227%; ENP, 219%). These results suggest that ethanol does induce glutathione S-transferase, but it is a relatively poor inducer of this enzyme.

Metabolic activation of promutagens, detectable in Ames' Salmonella assay, by 5000 X g supernatant of rat ventral prostate

Induction of aryl hydrocarbon hydroxylase (AHH) and 7-ethoxyresorufin-O-deethylase (7-EOD) activities as well as of benzo[a]pyrene (BP) metabolite formation in rat prostatic microsomes has been demonstrated after treatment with beta-naphthoflavone (BNF). The capacity to convert promutagenic compounds to ultimate mutagenic metabolites in the Ames' Salmonella assay by 5000 X g supernatant of rat ventral prostate was investigated. Male rats were treated with BNF, polychlorinated biphenyls (PCB; Arochlor 1254), phenobarbital (PB) and the vehicle, corn oil. PCB or BNF pretreatment increased the AHH- and 7-EOD activities 100-200-fold in the rat prostate 5000 X g supernatant (S-5 fraction). Epoxide hydrolase (EH) and glutathione-S-transferase (GST) activities were not affected while UDP-glucuronosyltransferase (UDP-GT) was increased 2.2- and 2.5-fold by PCB and BNF, respectively. PB did not significantly affect any of the enzyme activities measured. A dose-dependent increase in mutagenic response versus amount of 5000 X g supernatant and promutagen (aflatoxin B1 (AFB), 2-aminofluorene (2-AF), BP) was observed. The most pronounced activation was obtained with S-5 fraction from BNF- or PCB-treated rats. The great sensitivity of prostatic AHH to certain inducers and the capacity of the prostate to produce mutagenic metabolites might be of importance for initiation of prostatic cancer by environmental factors.

Tissue differences in the ontogeny of inducibility of drug-metabolizing enzymes by 3-methylcholanthrene in the rabbit

1. The effects of treatment of rabbits of different ages with 3-methylcholanthrene on cytochrome P-450 content, and benzo[a]pyrene hydroxylase, epoxide hydrolase, glutathione S-epoxide transferase, 1-naphthol glucuronyl transferase and morphine glucuronyl transferase activities of liver, kidney and lung have been investigated. 2. The cytochrome P-450 content of liver and kidney was inducible at all ages, whereas that of lung was inducible up to only seven days old. Benzo[a]pyrene hydroxylase activity was inducible more than two-fold in kidney at all ages, but in liver and lung up to only seven days old. 3. Epoxide hydrolase activity was inducible, only in liver and lung of younger animals, to an extent of less than 50%. 4. Glutathione S-epoxide transferase activity was inducible, in the liver of young animals and in the kidney of adult animals, to extents of less than 50%. 5. Both 1-naphthol and morphine glucuronly transferase activities were significantly induced in the liver of animals up to three days old, the former being induced to the greater extent. These enzymes were not studied in kidney or lung. 6. It is concluded that 3-methylcholanthrene treatment of rabbits has tissue-specific and age-specific effects on various drug-metabolizing enzyme.

Evidence that coal tar is a mixed inducer of microsomal drug-metabolizing enzymes

Topical application of coal tar (U.S.P.) to neonatal rats resulted in the induction of hepatic cytosolic glutathione-S-transferase and microsomal epoxide hydrolase and aminopyrine N-demethylase activities. Analogous to the effect of the polychlorinated biphenyl Aroclor 1254, treatment of neonatal rats with coal tar resulted in a one nm shift to the blue region in the wavelength maximum of the hepatic microsomal hemoprotein cytochrome P-450. These results demonstrate that therapeutic coal tar contains both type I and type II inducers of hepatic drug-metabolizing enzymes.

Studies on the induction of glutathione S-transferases in mouse liver

The induction of glutathione S-transferase activity by phenobarbital was studied in the male mouse. Ion-exchange chromatography and density gradient isoelectric focusing were used to characterize the induction. Two transferases were separated by column chromatography, one peak was induced by phenobarbital while the other peak was unaffected. Three peaks of transferase activity were observed when control or induced cytosol was applied and eluted from a density gradient isoelectric focusing column. The induced F2 peak had twice the activity of the F2 control. The amount of activity in the peak labeled F3 was unaltered with PB treatment. It appears that at least one transferase is more inducible by phenobarbital than the others.

Xenobiotic biotransformation in wild birds: activity, induction, characterization and comparison with rat and mouse microsomal enzymes

1. Benzo[a]pyrene hydroxylase, aminopyrine demethylase and glutathione S-transferase activities in hepatic and extrahepatic tissues of five wild birds, rat and mouse were compared. 2. Hepatic benzo[a]pyrene hydroxylase of wild pigeon was at least three times higher than that of rat or mouse. Hepatic aminopyrine demethylase and GSH S-transferase activities of wild birds were lower than those of rodents. 3. Renal GSH S-transferase of wild birds was 2-3 times more than in rat and mouse. 4. Avian benzo[a]pyrene hydroxylase activity of hepatic and renal tissue was linear up to 3.0 mg enzyme protein with pH optima of 7.4 and 7.2, at 42 degrees C. Apparent Km values were 11.76 and 3.33 microM respectively. 5. Hepatic enzyme activity was induced four-fold by 3-methylcholanthrene and about two-fold by phenobarbitone administration.

Differences in inducibility of particulate and cytosolic rat liver glutathione S-transferase activities

1. Rat liver mitochondrial microsomal glutathione (GSH) S-transferase activities with 1-chloro-2,4-dinitrobenzene as substrate were 11.0 and 11.6%, and with 1,2-dichloro-4-nitrobenzene as substrate were 27.7 and 15.4%, of the corresponding cytosolic activities respectively. 2. Marked difference in inducibility of cytosolic and particulate GSH S-transferase activities were seen after pretreatment of animals with enzyme-inducing agents. 3-Methylcholanthrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin enhanced cytosolic GSH S-transferase activity only. Phenobarbital induced the cytosolic and microsomal enzymes only.

Glutathione-S-transferase activity in the brain: species, sex, regional, and age differences

Glutathione-S-transferase activity in the brain of male mammals (rat and mouse) was found to be relatively lower than in that of females. In contrast, the male aves (pigeon, kite, vulture, and crow) exhibited comparatively higher activity in brain glutathione-S-transferase than the corresponding females. Postnatal development of cytosolic glutathione-S-transferase activity in the rat brain was also investigated. The day-7 rats showed a low activity of 48 nmol/min/mg protein that gradually increased 3.2-fold over the age of 28 days. No striking differences in brain enzyme activities were observed between the 35- and 90-day-old rats. Discrete brain regions of immature rats were found to possess considerable but lower quantities of glutathione-S-transferase activity than those of the adults. The activity increased with the onset of development and attained a steady state after 21 days of age.

Induction of hepatic drug metabolizing enzymes in mammals by pesticides: A review

The induction of drug metabolizing enzymes in mammals is summarized including both enzymes of the cytochrome P-450-dependent microsomal mixed function oxidase system and glutathione S-transferases. Particular emphasis is placed on the role of pesticides as inducers, the early work being summarized while investigations carried out at North Carolina States University are considered in greater detail. Finally, the possible significance of induction is considered.

The major metabolite of aflatoxin B1 in the rat is a glutathione conjugate

[14C]aflatoxin B1 (AFB1) was injected i.p. into female Wistar rats. Half of the dose was eliminated into the bile mostly as polar non-extractable metabolites. Among these a glutathione conjugate was the main component. The same conjugate was formed when rat liver postmitochondrial supernatant was incubated with AFB1 and [3H]glutathione. The conjugate was purified by ion exchange chromatography, gel-filtration and thin layer chromatography (TLC). It was tentatively identified as 2,3-dihydro-2-(S-glutathionyl)-3-hydroxy aflatoxin B1 (AFB1-GSH-conjugate). This structure was derived mainly from amino acid analysis, ultraviolet spectra and the enzymatic requirements for its formation in in vitro experiments. In the rat this detoxification product of the potentially ultimate reactive AFB1-epoxide constitutes about 10% of the administered dose and thus underlines the quantitative importance of this activating pathway.