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Biomedical subjects

F Oesch

Publications and source records attributed to F Oesch.

At least 433 records · Page 24Linked to original sources
PubMed1976

Epoxides derived from various polycyclic hydrocarbons as substrates of homogeneous and microsome-bound epoxide hydratase. A general assay and kinetic properties.

A general assay for epoxide hydratase using epoxides derived from polycyclic aromatic hydrocarbons as substrates is described. Addition of dimethylsulphoxide to the incubation mixture after incubation allowed unreacted epoxide and its phenolic by-product to be extracted into light petroleum whilst the product dihydrodiol remained in the aqueous phase. The product was then extracted into ethyl acetate and estimated radiochemically. This assay gave low extraction blanks (0.8-3.8%) when six K-region epoxides of polycyclic hydrocarbons were used, with high recoveries of the corresponding dihydrodiol in the ethyl acetate phase (65-89%). Radiochromatograms demonstrated that all the radioactivity in the ethyl acetate extracts of active incubations above that of boiled enzyme blanks was confined to a single band that always cochromatographed with the authentic trans-dihydrodiol. Using this assay, the kinetic parameters of six K-region epoxides were estimated. In all cases the apparent Km was low (2-5.9 muM). This is about 100-fold lower than the known apparent Km of epoxide hydratase for styrene oxide, an alkene oxide that is widely used as a substrate for epoxide hydratase. The rate of hydration varied with the substrate. Thus the maximum velocity for hydration of phenanthrene 9,10-oxide greater than 7-methylbenz[a]anthracene 5,6-oxide approximately benz[a]anthracene 5,6-oxide approximately benzo[a]pyrene 4,5-oxide greater than 3-methylcholanthrene 11,12-oxide greater than dibenz[a,h] anthracene 5,6-oxide. This relationship between the individual epoxides was found in microsomal fractions from both rat skin and rat liver, although the activity was always much lower in skin microsomes. All six arene oxides derived from polycyclic hydrocarbons were substrates for the homogeneous epoxide hydratase that was isolated from rat liver microsomal fractions using styrene oxide, an alkene oxide, as substrate to follow the purification.

Animals↗
PubMed1976

Latency of epoxide hydratase and its relationship to that of UDPglucuronyltransferase.

Epoxide hydratase activity in liver microsomal preparations from adult made rats is latent to a slight extent. Maximal activations with neutral or anionic detergents were 30-60% whilst UDPglucuronyltransferase was maximally activated by 160-830% by the same detergents. Activation of microsomal epoxide hydratase requires much higher amounts of neutral or anionic detergents than activation of microsomal UDPglucuronyltransferase. High concentrations of inorganic salt, sonication or freeze-thawing which activate microsomal UDPglucuronyltransferase have no influence on microsomal epoxide hydratase activity. From this it appears that the activation which may involve either removal of a permeability barrier or release from conformational restraint occurs more easily for UDPglucuronyltransferase than for epoxide hydratase and that the activation of microsomal epoxide hydratase requires breakage of some hydrophobic bonds between the enzyme and membrrane component(s).

Animals↗
PubMed1976

Differential control of rat microsomal "aryl hydrocarbon" monooxygenase and epoxide hydratase.

A growing body of evidence implicates epoxide metabolites of mutagenic and carcinogenic polycyclic hydrocarbons as either the only species, or one of the contributing species responsible for these adverse effects. Selective induction of epoxide hydratase(s) catalyzing the transformation of epoxides to electrophilically unreactive dihydrodiols, under conditions not leading to increases in monooxygenase(s) responsible for epoxide formation would, therefore, be of interest. All inducers of rat hepatic epoxide hydratase (determined with [7-3H]styrene oxide as substrate) which have been discovered also induced monooxygenase (determined with benzo(a)pyrene as substrate) suggesting a possible common biosynthetic control of these enzymes. The enzyme levels observed in different sexes and at different stages of the ontogenetic development, possibly dependent on endogenous inducers, strengthened this view. No sex difference is epoxide hydratase activity was observed in young rats (1 to 5 days old) while epoxide hydratase levels were about 3-fold higher in adult males than in females, which was remarkably similar to the behavior of monooxygenase. Moreover, the prenatal development of epoxide hydratase and monooxygenase appeared to be similar--although the low enzyme levels precluded accurate determinations of the latter. Although different types of known monooxygenase inducers all led to epoxide hydratase induction in adult rat liver, their effect of epoxide hydratase and monooxygenase could be dissociated by transplacental treatment. Dissociation was clearest with inducers of the polycyclic hydrocarbon type which led to great induction of monooxygenase while epoxide hydratase remained unchanged. The increases in monooxygenase activity were very different when determined by two methods based on different principles, demonstrating that at least two monooxygenases are involved in oxidative metabolism of benzo(a)pyrene, and that the control of epoxide hydratase is not under common control with either of them.

Aging↗
PubMed1975

Epoxides metabolically produced from some known carcinogens and from some clinically used drugs. I. Differences in mutagenicity.

The epoxide metabolites of two clinically used drugs and an experimental psychotropic agent, carbamazepine 10,11-oxide, cyproheptadine 10,11-oxide and cyclobenzaprine 10,11-oxide, were fully devoid of any mutagenic activity under conditions where K-region-epoxide metabolites of some known carcinogens, such as benzo(a)pyrene, proved to be potent frameshift mutational agents for Salmonella typhimurium TA 1537 and TA 1538. All epoxides tested were non-mutagenic for TA 1535, designed to detect substitution mutations. The 10,11-epoxides of the three drugs, carbamazepine, cyproheptadine and cyclobenzaprine, were not cytotoxic to any of the bacterial tester strains used, precluding that mutagenicity might have been overshadowed by cytotoxicity. When the mutagen, precursor, benzo(a)pyrene, was incubated together with TA 1537 and a mammalian microsomal preparation in the presence of a system generating the co-factor necessary for mono-oxygenase activity, activation to mutagenic species was observed which was dramatically increased in the presence of a potent epoxide hydratase inhibitor, 1,1,1-trichloropropene 2,3-oxide, suggesting epoxide(s) as the (or one of the) mutagenically active species metabolically produced in situ. None of these effects was observed with the three medical drugs. Moreover, the observation that the alkene oxide 4-phenylstyrene 7,8-oxide is mutagenic to the two strains TA 1537 and TA 1538 but the K-region arene oxide derived from 7,12-dimethylbenz(a)anthracene is inactive for the latter strain indicates that epoxidation of an aromatic double bond of a polycyclic hydrocarbon is neither a necessary nor a satisfying condition for frameshift mutagenesis to occur.

Benzopyrenes↗
PubMed1975

Nerve growth factor induces volume increase and enhances tyrosine hydroxylase synthesis in chemically axotomized sympathetic ganglia of newborn rats.

Concomitant daily treatment of newborn rats for a 2-week to 1-month period with 10 mug/g of body weight of nerve growth factor and 100 mug/g of body weight of 6-hydroxydopamine produces in the cell bodies of adrenergic neurons the characteristic effects of the growth factor but in the nerve terminals the characteristic effects of 6-hydroxydopamine. The dual opposite effects result in a striking volume increase of sympathetic ganglia which far exceeds that produced by nerve growth factor alone. The selective induction of tyrosine hydroxylase [L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2] in these chemically axotomized adrenergic neurons is even more pronounced than that produced by nerve growth factor alone in intact neurons.

Animals↗
PubMed1974

Purification and specificity of a human microsomal epoxide hydratase.

Epoxide hydratase was solubilized from human liver microsomal fractions and purified to an extent where the specific activity was 40-fold greater than that of the liver homogenate. Combination of homogenate and purified preparation showed that the increase in activity was not due to the removal of an inhibitor. Monosubstituted oxiranes with a lipophilic substituent larger than an ethyl group (isopropyl, t-butyl, n-hexyl, phenyl) readily interacted as substrates or inhibitors with this purified human epoxide hydratase, whereas those with a small substituent (methyl, ethyl, vinyl) were inactive, probably reflecting greater affinity of the former epoxides owing to lipophilic binding sites near the active site of the enzyme. In a series of oxiranes having a lipophilic substituent of sufficient size (styrene oxides), monosubstituted as well as 1,1- and cis-1,2-disubstituted oxiranes readily served as substrates or inhibitors of the enzyme, but not the trans-1,2-disubstituted, tri- or tetra-substituted oxiranes. trans-Substitution at the oxirane ring apparently prevents access of the oxirane ring to the active site by steric hindrance. Epoxide hydratase was also solubilized from microsomal fractions of rat and guinea-pig liver and purified by the same procedure. Structural requirements for effective interaction of substrates, inhibitors and activators were qualitatively identical for epoxide hydratase from the three sources. However, several quantitative differences were observed. Thus human hepatic epoxide hydratase seems to be very similar to, although not identical with, the enzyme from guinea pig or rat. Studies with epoxide hydratase from the latter two species therefore appear to be significant with respect to man. In addition, knowledge of structural requirements for epoxides to serve as substrates for human epoxide hydratase may prove useful for drug design. Compounds which need aromatic or olefinic moieties for their desired effect would not be expected to lead to accumulation of epoxides if their structure was such as to allow for a metabolically produced epoxide to be rapidly consumed by epoxide hydratase.

Adult↗
PubMed1974

Location of an isoproterenol-responsive cyclic AMP pool in adrenergic nerve cell bodies and its relationship to tyrosine 3-monooxygenase induction.

To decide whether adenosine 3':5'-cyclic monophosphate (cyclic AMP) plays a role as a second messenger in the trans-synaptic induction of tyrosine 3-monooxygenase (EC 1.14.16.2), it is desirable to discriminate between neuronal and extraneuronal changes in cyclic AMP concentration. Treatment of newborn rats with nerve growth factor antiserum or 6-hydroxydopamine, leading to destruction of 61-85% of the adrenergic nerve cell bodies in the superior cervical ganglion, led to a decrease in cyclic AMP of only 16-28%. This observation demonstrates that a relatively small portion of cyclic AMP is localized in the adrenergic neurons. However, administration of isoproterenol produced an increase (12-fold) in cyclic AMP only in this neuronal pool. Neither single nor repeated injections of isoproterenol led to induction of tyrosine monoxygenase. This, together with previous observations that experimental conditions leading to induction of the enzyme do not produce significant increases of cyclic AMP in the whole ganglion, is taken as an indication that cyclic AMP is not acting as a second messenger in the trans-synaptic induction of tyrosine monooxygenase in the rat superior cervical ganglion. In the rat adrenal medulla, treatment with reserpine led to both a shortlasting (60-90 min) increase in cyclic AMP and a subsequent induction of tyrosine monooxygenase. However, the increase in cyclic AMP was almost completely prevented (40 compared to 320%) by pretreatment of the rats with propranolol while the induction of tyrosine monooxygenase was not diminished. This observation also argues against an exclusive key-function of cyclic AMP in trans-synaptic induction of tyrosine monooxygenase in the adrenal medulla.

Adrenal Medulla↗