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F Oesch

Publications and source records attributed to F Oesch.

At least 343 records · Page 19Linked to original sources
PubMed1983

Studies on the subunit composition of rat liver glutathione S-transferases.

Native glutathione S-transferases are composed of subunits with apparent molecular weights of 25,000, 23,500, or 22,000 which form either homo- or heterodimers. Glutathione S-transferases A, C, and X which contain two subunits with molecular weights of 23,500 yielded similar but nonidentical proteolytic fragmentation patterns. Fragments unique to the subunits of the homodimers A and X were present in decreased intensities in the patterns of form C. Two-dimensional electrophoresis under denaturing conditions showed single nonoverlapping spots for transferases A and X, while form C yielded two spots corresponding in position to those obtained from forms A and X. Renaturation of dissociated glutathione S-transferase C yielded enzymatically active transferases A, C, and X. These results indicate that form C is a heterodimer composed of one subunit from the homodimeric transferases A and X. This was substantiated by NH2-terminal sequence analysis showing extensive NH2-terminal homology amongst all three forms. However, in the positions where forms A and X yielded different residues, both amino acids were detected in the sequence of form C, indicating that the two subunits of Mr = 23,500 are the products of two different genes. NH2-terminal sequence analysis of the heterodimeric glutathione S-transferase B which is composed of subunits with molecular weights of 22,000 and 25,000 revealed a single unique sequence which bore no resemblance to the sequences of either forms A or X. Despite the identical NH2-terminal sequences, proteolytic fragmentation of the separated subunits showed markedly different fragmentation patterns. This indicates that two different mRNAs code for these two subunits.

Amino Acid Sequence↗
PubMed1983

The influence of dimethylbiguanide on phenprocoumon elimination and its mode of action. A drug interaction study.

This study was based on the clinical observation of a higher phenprocoumon requirement in these diabetic patients simultaneously treated with phenprocoumon (Marcoumar) and dimethylbiguanide (DMB), and of a drug interaction observed in a patient. These higher requirements of phenprocoumon, suggesting an increased elimination, could have been due to an enhancement of liver microsomal enzyme activity and/or an increase in liver blood flow. Various studies were performed to test this hypothesis. The clinically suggested higher phenprocoumon requirement was proven by a drug observation study. Hence a higher tablet consumption of phenprocoumon and a diminished anticoagulatory effect was found after treatment with DMB in doses of between 1 and 3 g. An increased elimination of phenprocoumon following DMB administration was also found in a pharmacokinetic study. The activity of the liver microsomal enzyme system, investigated in animal and man, showed no changes in the liver microsomal enzymes in animal studies or the in vivo parameters of liver microsomal enzyme activity in patients. Measuring liver blood flow in dogs, utilizing the indocyanine green clearance method, an increased flow of about 33% was observed. As changes in liver blood flow can increase the metabolism of some highly lipid soluble drugs, the increased metabolism of phenprocoumon during DMB treatment could be related to the increase in liver blood flow and not to changes in liver microsomal enzyme activity.(ABSTRACT TRUNCATED AT 250 WORDS)

4-Hydroxycoumarins↗
PubMed1983

Use of monoclonal and polyclonal antibodies as structural and topographical probes for hepatic epoxide hydrolase.

Monoclonal antibodies have been prepared against rat liver epoxide hydrolase (EH), some of which gave precipitation lines on immunodiffusion against pure EH suggesting the presence of repetitive structural domains on the enzyme. Using ELISA, with polyclonal antibodies to rat and rabbit liver EH, reactivity and therefore structural similarities between EH of all species tested, including human, were observed. This was in contrast to immunodiffusion results demonstrating the limitations of the latter technique. Using monoclonal antibodies in ELISA, greatest structural similarity was between rat, mouse, and Syrian hamster EH and relatively little between rat and human. Two of the antibodies reacted with nearly all species tested and may be directed towards critical sites on the enzyme. This and most of the EH molecule would appear to be localised on the cytoplasmic surface of the endoplasmic reticulum.

Animals↗
PubMed1983

Microsomal epoxide hydrolase in different rat strains.

Epoxide hydrolase activity was determined in hepatic microsomes of adult males of 22 rat strains. The specific activity varied between 4.3 and 12.7 nmole styrene glycol/mg protein per min. The enzyme in F344, DA and Sprague--Dawley rats, strains with low, high and intermediate activity, respectively, was studied in more detail. No differences in substrate specificity and pH-dependence of the activity were observed between the strains with high and low activity, and immunoprecipitation by antibodies raised against microsomal epoxide hydrolase purified from Sprague--Dawley rats showed that the amounts of enzyme protein in microsomes from DA and F344 rats correlated with the activities. These results indicate quantitative rather than qualitative differences in epoxide hydrolase. The enzyme activity was inherited in an autosomal and codominant manner. The hepatic activity in females (about 78% of that in males) and, with the limitation that only few situations were studied, the trans-stilbene oxide-induced activity were under the same genetic control as the basal hepatic activity in males. In contrast, some extrahepatic tissues showed strain differences in epoxide hydrolase activity which contrasted with those found in liver. Hence, the enzyme activity in one tissue cannot serve as a reliable guide to the relative activity in another tissue, unless a specific correlation between the two tissues has been established. Although the strain differences in activity were not very large in themselves, in combination with inter-individual variation, sex differences and effects of the enzyme inducer transstilbene oxide they led to a 20-fold variation in hepatic epoxide hydrolase activity among the rats investigated in the present study.

Animals↗
PubMed1983

Mutagenicity of glutathione and cysteine in the Ames test.

Postmitochondrial supernatant from rat liver and kidney homogenates transformed cysteine into a mutagen that reverted bacteria of the strain Salmonella typhimurium TA100 to histidine independence. Glutathione was also activated by kidney postmitochondrial supernatant but not by liver preparations. Hence, important endogenous compounds of mammals are positive in the most commonly used short-term test for carcinogenicity and mutagenicity. Glutathione is positive in the test even at concentrations found in mammalian tissues.

Animals↗
PubMed1983

Determination of epoxide hydrolase activity in whole cells (human lymphocytes) and activation by benzoflavones.

Epoxide hydrolase (epoxide hydratase, epoxide hydrase, E.C. 3.3.2.3) activity so far has only been measured in subcellular preparations. We show here that, with the highly lipophilic substrate (3H)-benzo(a)pyrene 4,5-oxide, the activity can be determined in intact cells. Whole human lymphocytes hydrolyze it at a similar rate to that in lymphocyte homogenate. We have previously reported that cultivation of lymphocytes in a medium containing 5,6-benzoflavone leads to an increase in epoxide hydrolase activity. We now demonstrate that this stimulation is due to enzyme activation and that enzyme induction does not contribute to this increase to any measurable extent. Moreover, both 5,6-benzoflavone and 7,8-benzoflavone activate epoxide hydrolase. This activation occurs not only in cell homogenate, but also - with a similar concentration-response relationship - in whole lymphocytes. Hence measurement of epoxide hydrolase activity in subcellular preparations reflects the activity in these intact cells. Furthermore, insofar as a concentration of 1 microM of the benzoflavones is sufficient to cause a measurable (10 to 20%) activation, it appears likely that foreign compounds can activate epoxide hydrolase in man.

Benzoflavones↗
PubMed1983

Bacterial mutagenicity investigation of epoxides: drugs, drug metabolites, steroids and pesticides.

Although it has been observed that many epoxides are ultimate mutagens, surprisingly little is known about epoxides to which man may be extensively exposed, e.g., physiological compounds, drugs, drug metabolites and pesticides. We have now investigated 35 such and related epoxides for mutagenicity, using reversion of his- Salmonella typhimurium TA98 and TA100 as biological end-point. None of the tested steroids (12 compounds), vitamin K epoxides (3 compounds) and pesticides (dieldrin, endrin, HEOM (1,2,3,4,9,9-hexachloro-6,7-epoxy-1,4,4a,5,6,7,8, 8a-octahydro-1,4-methanonaphthalene), heptachlor epoxide) showed any mutagenic activity. Negative results were also obtained with the antibiotics oleandomycin, anti-capsin and asperlin, the cardiotonic drug resibufogenin, the widely used parasympatholytic drugs butylscopolamine and scopolamine, the sedatives valtratum, didovaltratum and acevaltratum, the tranquilizer oxanamide as well as with the drug metabolites carbamazepine 10,11-oxide and diethylstilbestrol alpha,beta-oxide. Three barbiturate epoxides, formed by metabolism of allobarbital, alphenal and secobarbital, caused weak but reproducible mutagenic effects at high concentrations. The cytostatic agent ethoglucide was the only drug having substantial mutagenic activity. Its mutagenic potency was similar to those of the control epoxides styrene 7,8-oxide, p-bromostyrene 7,8-oxide and m-bromostyrene 7,8-oxide, but much lower than those of benzo[a]pyrene 4,5-oxide, benzo[e]pyrene 4,5-oxide and 7,12-dimethylbenz[a]anthracene 5,6-oxide. Some epoxides were also tested in other Salmonella typhimurium strains or in the presence of rat-liver S9 mix. Positive results were only obtained with compounds that had already been detected as mutagens in the direct test with strain TA100.

Animals↗
PubMed1983

Phosphorylation of cytochrome-P-450-dependent monooxygenase components.

Most chemical carcinogens require activation by polysubstrate monooxygenase. The phosphorylation of essential components of this cytochrome P-450 monooxygenase system, isolated from rabbit liver microsomes, cytochrome P-450 (LM2) and cytochrome reductase, was tested using two different protein kinases. One of the kinases, a cyclic AMP-independent phosvitin kinase (kinase P), was inactive in all systems tested. However, the catalytic subunit of a cyclic AMP-dependent protein kinase (kinase C) catalyzed phosphoryl group transfer to both proteins, but to different extents. Cytochrome P-450 was phosphorylated when added as sole component and also when in the presence of P-450 reductase and phosphatidylcholine. In contrast, the weak phosphorylation of P-450 reductase was reduced considerably in a complete reconstituted system containing P-450 and phosphatidylcholine. The inclusion of kinase P did not alter these results which excludes the possibility that these kinases participate in a sequential phosphorylation mechanism. The monooxygenase constituents themselves were without kinase activity. When hepatic microsomes were isolated in presence of the phosphatase inhibitor sodium fluoride no significant change in monooxygenase (7-ethoxycoumarin O-deethylation) activity was observed, whilst after preincubation with either acid or alkaline phosphatase a significant reduction in monooxygenase activity was measured. Thus, cytochrome P-450 (LM2) is phosphorylatable by protein kinase C and the catalytic activity of polysubstrate monooxygenase decreases after preincubation of microsomes with phosphatases.

Acid Phosphatase↗
PubMed1983

Vinylidene chloride: changes in drug-metabolizing enzymes, mutagenicity and relation to its targets for carcinogenesis.

Results of various studies have shown that male Swiss Webster mice are more susceptible to toxic effects of vinylidene chloride (VDC) than are females of the same mouse strain, females and males of the C57BL mouse strain, Chinese hamsters and rats. The main targets of toxicity are kidney and liver. The kidney of male Swiss Webster mice is the only organ where VDC unambiguously induces tumours. In the present study we have investigated the ability of NADPH-foritifed postmitochondrial supernatant fractions (S-9 mix) of kidney and liver from susceptible and nonsusceptible animals to activate VDC to a bacterial mutagen. The following sequence of activating potencies was observed: mouse liver (both strains and sexes) and Chinese hamster liver greater than rat liver greater than human liver greater than Chinese hamster kidney greater than kidney from male mice of both strains greater than kidney from rats and female mice. The last two preparations only occasionally showed weak activation of VDC. Addition of purified microsomal epoxide hydrolase to S-9 mix did not affect the mutagenicity of VDC; addition of glutathione reduced the mutagenicity up to 50%. Pretreatment of animals (male rats, male and female Swiss Webster mice) with VDC did not potentiate the ability of the subcellular preparations to activate this compound. In fact, in some cases, a weaker activation was observed. Following this treatment, microsomal 7-ethoxy-coumarin O-dealkylase was decreased in mouse kidney and in rat liver. The enzyme was not affected in mouse liver and was not measurable in rat kidney. Microsomal epoxide hydrolase activity (with styrene 7,8-oxide as substrate) was not affected in mouse liver and rat kidney. In the kidney of male mice treated with a high concentration of VDC, epoxide hydrolase activity was decreased initially, but after longer treatment, in some cases a weak increase above control was noticed. A stronger increase in activity of epoxide hydrolase was observed in the rat liver and the kidney of female mice. Cytosolic glutathione transferase activity (with 2,4-dinitrochlorobenzene as substrate) was not affected by the VDC treatment in the liver of male mice, but was decreased in the kidney of male mice, and was elevated in the kidney and liver of rats and of female mice. The different effects of VDC on this enzyme may be one of the reasons for the differences in susceptibility towards the toxic and carcinogenic actions of this compound in different species, strains and sexes.

Animals↗
PubMed1983

Inactivation of a diol-epoxide and a K-region epoxide with high efficiency by glutathione transferase X.

Four glutathione transferases (EC 2.5.1.18), glutathione transferases A, B, and C and a hitherto unknown form, termed X, were purified to apparent homogeneity from rat liver cytosol. They were investigated for their abilities to inactivate two mutagenic epoxides derived from the polycyclic aromatic hydrocarbon benz(a)anthracene, the K-region epoxide benz(a)anthracene 5,6-oxide and the diol-epoxide r-8,t-9-dihydroxy-t-10,11-oxy-8,9,10, 11-tetrahydrobenz(a)anthracene. Mutagenic activity was determined using Salmonella typhimurium his- strain TA100. Glutathione alone had little if any influence on the mutagenicity of the diol-epoxide but significantly decreased the mutagenic effect of the K-region epoxide. This inactivation was enhanced by the addition of glutathione transferases. Both epoxides were inactivated by glutathione in the presence of each of the four enzymes, but with varying efficiencies. Inactivation of the K-region epoxide (in terms of its mutagenicity in the presence of glutathione) required extremely little enzyme, about 1000 times less than for the diol-epoxide. On a molar basis, glutathione transferase X (followed by C greater than A greater than or equal to B) was clearly the most efficient enzyme in inactivating both substrates and also more efficient than were three other purified enzymes (microsomal epoxide hydrolase, cytosolic epoxide hydrolase, and dihydrodiol dehydrogenase) previously investigated in this test system. Taking into account the amounts of enzyme present in rat liver, the glutathione transferases C and X were most effective in inactivating the epoxides examined. Thus, the newly discovered glutathione transferase X appears to be of substantial significance in the inactivation of two structural prototypes of epoxides derived from polycyclic aromatic hydrocarbons, a K-region epoxide and a non-bay-region vicinal diol-epoxide.

Animals↗
PubMed1982

Inactivation of a diol epoxide by dihydrodiol dehydrogenase but not by two epoxide hydrolases.

The mutagenicity of r-8,t-9-dihydroxy-t-10, 11-oxy-8,9,10,11-tetrahydrobenz[a]anthracene (BA-8,9-diol 10, 11-oxide) toward Salmonella typhimurium TA 100 is not decreased by the presence of large amounts of highly purified microsomal or cytosolic epoxide hydrolase. However, highly purified dihydrodiol dehydrogenase inactivates this diol epoxide, which is a major DNA-binding metabolite of benz[a]anthracene. The K-region epoxide, benz[a]anthracene 5,6-oxide (BA 5,6-oxide) is efficiently inactivated by microsomal epoxide hydrolase, is much less readily inactivated by cytosolic epoxide hydrolase, and is not inactivated by dihydrodiol dehydrogenase. This inactivation of a diol epoxide by dihydrodiol dehydrogenase points to a new significance of this enzyme and a new level of control for diol epoxides.

Alcohol Oxidoreductases↗
PubMed1982

Immuno-electron-microscopic studies on the subcellular distribution of rat liver epoxide hydrolase and the effect of phenobarbitone and 2-acetamidofluorene treatment.

The distribution of rat liver epoxide hydrolase in various subcellular fractions was investigated by immuno-electron-microscopy. Ferritin-linked monospecific anti-(epoxide hydrolase) immunoglobulins bound specifically to the cytoplasmic surfaces of total microsomal preparations and smooth and rough microsomal fractions as well as the nuclear envelope. Specific binding was not observed when the ferritin conjugates were incubated with peroxisomes, lysosomes and mitochondria. The average specific ferritin load of the individual subcellular fractions correlated well with the measured epoxide hydrolase activities. This correlation was observed with fractions prepared from control, phenobarbitone-treated and 2-acetamidofluorene-treated rats.

2-Acetylaminofluorene↗
PubMed1982

Effects of lindane treatment on drug metabolizing enzymes and liver weight of CF1 mice in which it evoked hepatomas and in non-susceptible rodents.

In CF1 mice lindane treatment led to a significant increase in liver tumor incidence whilst in Osborne-Mendel rats it was not carcinogenic. Although somewhat less clear, the test in B6C3F1 mice led to the conclusion that under the conditions of the bioassay lindane was not carcinogenic for this strain. In this study, the specific activities of some enzymes which are thought to be involved in the metabolism of lindane were studied in these different strains in order to investigate whether differences exist in the activities of these enzymes. Because the enzyme pattern may change after lindane treatment during the carcinogenicity studies, we also investigated the enzyme activities in animals treated for 3 days or 3 months with various doses of lindane. The influence of lindane treatment on the relative liver weight was also determined. B6C3F1 mice showed no increase in absolute or relative liver weight even after 3 months of treatment with the highest tolerated dose of lindane. However, in the susceptible CF1 strain lindane led to a large increase of the absolute and relative liver weight in both sexes, whilst a smaller increase was observed in Osborne-Mendel rats. Basal glutathione-S-transferase activity was higher in males than in females in all three strains, bearing no apparent relationship to susceptibility for tumor formation. However, after treatment with the highest dose of lindane a 5-6-fold induction of this enzyme activity was observed in female CF1 mice, which then together with the male CF1 mice had a higher glutathione-S-transferase activity than untreated and treated B6C3F1 mice and Osborne-Mendel rats. Whether lindane or one of its metabolites is activated by conjugation with glutathione remains to be established. After treatment of the animals with high doses of lindane detergent-treated rat liver microsomes showed a higher UDP-glucuronosyltransferase activity than mouse liver microsomes. This high activity could lead to a rapid conjugation of phenols derived from lindane. The most striking difference observed in this study was the fact that together with the larger increase in absolute and relative liver weight, untreated and treated CF1 mice showed higher monooxygenase activity and, after treatment with lindane, lower epoxide hydrolase activity than rats. Whether the high monooxygenase and rather low epoxide hydrolase activity will lead to an accumulation of reactive epoxides derived from lindane remains to be clarified.

7-Alkoxycoumarin O-Dealkylase↗