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Biomedical subjects

M Metzler

Publications and source records attributed to M Metzler.

At least 109 records · Page 6Linked to original sources
PubMed1987

Metabolism of diethylstilbestrol in hamster hepatocytes.

Under certain modulating conditions the liver of the male Syrian golden hamster is a target organ for the carcinogenic effect of the synthetic estrogen diethylstilbestrol (DES). As a basis for mechanistic studies aimed at elucidating the role of metabolic activation in the process of DES-induced neoplasia, the metabolism of 14C-DES was investigated in freshly isolated hamster hepatocytes. These oxidative metabolites of DES, viz. Z,Z-dienestrol,3'-hydroxy-DES and 1-hydroxy-E-DES, were formed in 14.2, 9.1, and 0.3% yield, respectively, when hepatocytes were incubated with 50 nmol DES/mg cellular protein for 60 min. Glucuronides (4.0%) and sulfates (2.8%) of DES and of the oxidative metabolites were also found, and non-extractable binding of radioactivity to cellular protein was observed indicating the formation of reactive intermediates. The capability of hamster hepatocytes to oxidize and conjugate DES should allow the investigation of the effects of modulators on the metabolic activation of DES in this cellular system in order to help clarify the mechanisms of DES-induced hepatocarcinogenesis.

Animals↗
PubMed1987

Sex hormones and neoplasia: liver tumors in rodents.

The association of liver tumors in women and men with the use of oral contraceptives and anabolics, respectively, has drawn attention to the hepatotumorigenic effects of sex hormones. The available evidence from long-term carcinogenicity studies in various strains of mice, rats and hamsters indicates that sex hormones are hepatotumorigenic agents, although the incidence of liver tumors is, in general, low even at doses exceeding human exposure by a factor of one hundred or more. Among the three rodent species, mice appear to be the least sensitive. Under certain modulating conditions, however, a 100% incidence of hepatocellular carcinomas can be obtained with some estrogens in male Syrian golden hamsters. The mechanism of the hepatotumorigenic effect of sex hormones is far from being clear. Whereas their tumor promoting activity is generally recognized, there is recent evidence suggesting that some sex hormones may also have initiating potential. Although the incomplete understanding of the mechanisms responsible for sex hormone induced liver neoplasia seriously hampers the assessment of the human risk, it appears to be clear that sex hormones are important modulating factors determining the incidence of hepatic tumors in rodents and possibly in humans.

Androgens↗
PubMed1987

Sex hormones and neoplasia: genotoxic effects in short term assays.

The mechanism of the tumorigenic effects of sex hormones in the liver and in other organs is still unclear. Clues towards an understanding of this action of sex hormones can be gained from short-term assays suitable for revealing adverse effects at different molecular levels relevant to the process of neoplastic transformation. The available data on the effects of sex hormones indicating gene mutations, unscheduled DNA synthesis, sister chromatid exchange, chromosomal anomalies, induction of aneuploidy and cell transformation are reviewed. Although the data base is scant, in particular for androgens and progestins and in systems other than the mutational assays, it can be concluded that sex hormones, in general, fail to induce gene mutations. On the other hand, recent evidence shows that diethylstilbestrol and steroidal estrogens are capable of inducing neoplastic transformation in vitro. In this context, the induction of aneuploidy is discussed as non-mutational but genotoxic effect of estrogens responsible for the neoplastic transformation. Morphological transformation and scoring for chromosomal anomalies can provide useful endpoints for further evaluation of sex hormones with suspected carcinogenic properties.

Aneuploidy↗
PubMed1987

Site-specific covalent binding of stilbene-type and steroidal estrogens to tubulin following metabolic activation in vitro.

Both the steroidal estrogen, 2-hydroxy estradiol, and the stilbene-type estrogen, diethylstilbestrol, bind covalently and selectively to the C-terminal domain of beta-tubulin after peroxidative activation in vitro. The binding probably has to be attributed to quinonoid metabolites, as estrogens such as estradiol and hexestrol, which are unable to form quinones under these conditions, fail to bind. Albumin is not simultaneously modified, demonstrating the selectivity of the binding. The observed protein binding is discussed with respect to estrogen-induced aneuploidy and neoplastic cell transformation.

Binding Sites↗
PubMed1987

Metabolic activation of xenobiotic stilbene estrogens.

Certain stilbene estrogens, in particular diethylstilbestrol, are established carcinogens in animals and in humans. The question is raised whether the formation of reactive metabolites is part of the carcinogenic mechanism of these compounds. Some aspects of the oxidative metabolism are briefly reviewed, with special emphasis on peroxidase-mediated metabolic activation. The interaction of the reactive intermediates with nucleic acids and proteins is described and examples of the induction of genetic damage in several short-term assays are given. From the available data it is concluded that metabolic activation may play a role in the process of neoplastic cell transformation induced by stilbene estrogens.

Animals↗
PubMed1986

Indirect evidence for the metabolic dehalogenation of tetrafluorodiethylstilbestrol by rat and hamster liver and kidney microsomes. Species- and organ-dependent differences.

In order to assess the significance of the catechol pathway for the carcinogenic activity of diethylstilbestrol (DES), the stability of 3',5',3",5"-tetrafluoro-DES (TF-DES) against metabolic catechol formation was examined in vitro. A radioenzymatic assay was used for determining the estrogen hydroxylase activity of liver and kidney microsomes from male and female Syrian golden hamsters and from male Wistar rats for the substrates TF-DES, DES, estradiol-17 beta and 2-fluoro-estradiol-17 beta. With all microsomes tested, catechols were formed from TF-DES to an extent similar to or, in some cases, even exceeding that observed with DES and the steroidal estrogens. The estrogen hydroxylase activity measured for the various microsomes depended on the species, organ and substrate. Analysis by high performance liquid chromatography showed that four products were formed in the radioenzymatic assay with DES and TF-DES. These data demonstrate that the fluorine substitution present in TF-DES does not prevent catechol formation and imply that the catechol pathway must be taken into account as a putative pathway for the metabolic activation of DES.

Animals↗
PubMed1986

Identification of S-1,2,2-trichlorovinyl-N-acetylcysteine as a urinary metabolite of tetrachloroethylene: bioactivation through glutathione conjugation as a possible explanation of its nephrocarcinogenicity.

The elimination and metabolism of [14-C]-tetrachloroethylene (Tetra) was studied in female rats and mice after the oral administration of 800 mg/kg [14-C]-Tetra. Elimination of unchanged Tetra was the main pathway of elimination in both species and amounted to 91.2% of the dose in rats and 85.1% in mice. [14-C]-Carbon dioxide (CO2) was found to be a trace metabolite of [14-C]-Tetra. Only a small part of the applied dose was transformed to urinary (rats = 2.3%, mice = 7.1%) and fecal (rats = 2.0%, mice = 0.5%) metabolites. The urinary metabolites were separated and quantified by high performance liquid chromatography (HPLC) and identified by gas liquid chromatography/mass spectrometry (GC/MS). The following metabolites could be identified: oxalic acid (8.0% of urinary radioactivity in rats, 2.9% in mice), dichloroacetic acid (5.1%, 4.4%), trichloroacetic acid (54.0%, 57.8%), N-trichloroacetyl-aminoethanol (5.4%, 5.7%), trichloroethanol, free and conjugated (8.7%, 8.0%), S-1,2,2-trichlorovinyl-N-acetylcysteine (N-acetyl TCVC) (1.6%, 0.5%), and another conjugate of trichloroacetic acid (1.8%, 1.3%). The structures of the identified metabolites indicate two different pathways operative in Tetra biotransformation: cytochrome P-450-mediated epoxidation forming reactive metabolites in the liver and conjugation of Tetra with glutathione (GSH) catalyzed by glutathione transferase(s). The formation of reactive intermediates by renal processing of the glutathione conjugates may provide a molecular mechanism for the nephrotoxicity and nephrocarcinogenicity of Tetra in male rats.

Acetylcysteine↗
PubMed1986

DNA adducts of medicinal drugs: some selected examples.

A few selected medicinal drugs, diamminedichloroplatinum (II) compounds, mitomycin C, psoralens, and diethylstilbestrol are briefly reviewed with respect to the formation and biological significance of their DNA adducts. Different types of adducts, e.g., DNA intrastrand crosslinks, DNA interstrand crosslinks, or monoadducts appear to represent the critical DNA lesions of the different drugs, accounting for cytotoxicity and carcinogenicity. Thus, these examples serve to illustrate the complexity of DNA adduct formation and its biological sequelae.

Animals↗
PubMed1986

Different metabolism by mammalian and horseradish peroxidases in vitro of steroidal estrogens and their catechol metabolites.

Radioactively labeled estradiol-17 beta and 17 alpha-ethynylestradiol and their 2-hydroxy derivatives were incubated with either horseradish peroxidase or mouse uterus peroxidase, and the formation of polar products, which could not be extracted with diethyl ether, and of ether-extractable metabolites was studied. Moreover, the extent of DNA binding was determined. The different peroxidases gave rise to different products, indicating that different pathways in the metabolism of these steroidal estrogens are catalysed by the two peroxidases.

Animals↗
PubMed1986

Co-oxidation of diethylstilbestrol and structural analogs by prostaglandin synthase.

Structural analogs of diethylstilbestrol (DES) with at least one phenolic hydroxyl group are metabolized by prostaglandin H synthase (PHS) from ram seminal vesicle microsomes (RSVM) in vitro in the presence of arachidonic acid (20:4). U.v. spectroscopy revealed the formation of p-quinoid intermediates in incubations of DES, tetrafluoro-DES and dimethylstilbestrol, and tautomerization of the quinones to the respective dien-compounds which were characterized by h.p.l.c. and GC/MS. Indomethacin inhibits the formation of these metabolites which are identical to the major metabolites formed in incubations with horseradish peroxidase/hydrogen peroxide. Covalent binding to protein was observed in incubations of PHS co-substrates. Notably, formation of reactive intermediates which bind to protein is not limited to DES-analogs which form quinone intermediates: radiolabeled hexestrol and E,E-dienestrol yield protein-bound radioactive products upon incubation with RSVM and 20:4, probably via one electron-oxidation to a phenoxy radical. PHS-catalyzed metabolism of structural analogs of DES is accompanied by a concentration-dependent increase in cyclo-oxygenase activity. The measurement of the 20:4-dependent oxygen uptake rates in vitro can serve as a convenient assay for estrogenic compounds which undergo co-oxidation. At high concentrations, however, DES structural analogs can inhibit rather than stimulate PHS. The PHS-catalyzed formation of reactive intermediates from DES structural analogs and their effect on PHS may be of importance for their biological activity in estrogen target tissues with low mono-oxygenase activity.

Animals↗
PubMed1986

Possible role of oxygen radicals in cell transformation by diethylstilbestrol and related compounds.

Diethylstilbestrol (DES) and four derivatives, viz. tetrafluoro-DES, 3'-hydroxy-DES, Z,Z-dienestrol and hexestrol, were examined for their abilities to form superoxide radicals and to induce DNA strand breaks in the presence of horseradish peroxidase/hydrogen peroxide metabolism in a cell-free system. Furthermore, the induction of strand breaks by these compounds was tested in Syrian hamster embryo (SHE) cells in vitro. Formation of superoxide radicals could be demonstrated by reduction of nitro blue tetrazolium for DES but not for its derivatives. With isolated superhelical DNA, induction of strand breaks in the presence of Fe3+ was observed for DES, tetrafluoro-DES and 3'-hydroxy-DES, while hexestrol and Z,Z-dienestrol were ineffective. In SHE cells, alkaline elution technique showed that DNA strand breaks were induced by DES and all derivatives tested, although only at cytotoxic concentrations. It is concluded that DES, under conditions of peroxidative metabolism, can give rise to superoxide generation and DNA strand breaks, and that these events may play a role in the process of DES-induced cell transformation.

Animals↗
PubMed1986

Absorption, elimination and metabolism of trichloroethylene: a quantitative comparison between rats and mice.

The absorption, elimination and metabolism of 14C-trichloroethylene (Tri) was studied in adult female Wistar rats and NMRI mice after administration of 200, 20 and 2 mg/kg Tri. Dose-dependent biotransformation of Tri to metabolites was observed in both species. Induction of hepatic mono-oxygenases by phenobarbital or polychlorinated biphenyls resulted in a higher rate of biotransformation after a single oral dose of 200 mg/kg 14C-Tri to rats. An increase in radioactivity covalently bound to liver and kidney macromolecules of induced rats as compared to control rats parallels the toxic effects of Tri on these organs after induction of cytochrome P-450. The urinary metabolites were analysed by h.p.l.c. In both species, 1,1,1-trichlorocompounds (trichloroacetic acid, trichloroethanol and its glucuronide, comprising 88.9-93.5% of the radioactivity excreted in the urine) constituted the main metabolites; in addition, N-(hydroxyacetyl)-aminoethanol (4.1-7.2%), dichloroacetic acid (0.1-2.0%) and oxalic acid (0.7-1.8%) were identified. The pattern of metabolites in the 72 h urine remained constant for each species in the dose range studied and no change was induced by pretreatment. The percentage of radioactivity exhaled as 14CO2 increased with dose in mice, which may indicate dose-dependent formation of dichloroacetic acid and saturation of deactivating mechanisms for reactive intermediates in mice.

Animals↗
PubMed1986

Humeral shaft fracture with brachial artery injury.

The management of ten patients with fracture of the humeral diaphysis and concomitant injury to the brachial artery was analyzed retrospectively for examination of the factors contributing to preservation of limb viability and function. Of ten treated fractures, eight were rigidly stabilized with either a plate or an external fixation device. Seven of the vascular injuries required an interpositional graft. Three arteries were repaired with an end-to-end anastomosis. Two of these repairs failed in patients whose fractures were not rigidly stabilized, and one of these patients required amputation. Fasciotomy was performed in five cases. Seven patients retained normal or functional extremities despite ligation of the brachial artery in two individuals. Preoperative arteriography was of equivocal value, and it doubled the patient's transit time from the emergency room to surgery. The use of a temporary intraluminal vascular shunt to perfuse the limb at surgery and the semi-invasive rigid stability afforded by contemporary external fixators are important advances in the management of these complex injuries. In civilian practice, the prioritized guidelines the authors suggest for care of combined major skeletal and vascular trauma to the arm are: resuscitation of the patient; arteriogram, which is nonessential in open injuries but helpful in closed trauma; intraoperative perfusion of the limb with a temporary shunt; rigid bony stabilization; wound debridement; vascular repair with an autogenous vein graft; neurorrhaphy; and assessment of the need for fasciotomy.

Adolescent↗
PubMed1985

Nature of the macromolecular binding of diethylstilbestrol to DNA and protein following oxidation by peroxidase/hydrogen peroxide.

Incubation of [14C]diethylstilbestrol ([14C]DES) with horseradish peroxidase(HRP)/hydrogen peroxide in the presence of various polynucleotides and proteins led to macromolecular binding of radioactivity. Binding to DNA proved stable against ethanol precipitation, but was completely removed when the DNA was subjected to gel electrophoresis, caesium chloride density centrifugation, and mild hydrolysis. In contrast, binding to protein was stable in gel electrophoresis. The extent of binding did not differ significantly between proteins with and without thiol groups. These results imply that the products of peroxidase-mediated oxidation of DES bind to DNA in a strong but non-covalent manner, whereas binding to protein appears to be covalent and does not depend on the presence of thiol groups. The possible nature of the binding species is discussed.

Carbon Radioisotopes↗
PubMed1985

In vitro metabolism of diethylstilbestrol by hepatic, renal and uterine microsomes of rats and hamsters. Effects of different inducers.

In order to elucidate possible differences in the metabolism of the synthetic estrogen diethylstilbestrol (DES) by target and non-target tissues for DES carcinogenicity, the biotransformation of [14C]DES has been studied in vitro with hepatic and renal microsomes of male and female hamsters and rats, and from hamster and rat uterus. Of these tissues, only the male hamster kidney is susceptible to the carcinogenic effect of DES. Moreover, the effect of various inducers on the in vitro metabolism of DES has been investigated. It was found that male hamster kidney microsomes produced a markedly different pattern of DES metabolites as compared to renal microsomes from female hamster or male and female rats. Pretreatment with phenobarbital markedly increased oxidative DES metabolism by renal microsomes from female rat but not from male rat. Diethylstilbestrol metabolism by hepatic microsomes was different between hamster and rat, but was not sex-dependent and could not be significantly affected by pretreatment with phenobarbital, DES, 3-methylcholanthrene and 7:8-benzoflavone. The differences in DES metabolism between target and non-target organs and its modulation by inducers may help to gain further insight into the mechanism of DES tumorigenesis.

Animals↗
PubMed1985

Alkaline phosphatase. 31P NMR probes of the mechanism.

31P NMR signals from substrates and products of alkaline phosphatase have been adapted to measure the rates and product ratios for the hydrolysis and phosphotransferase reactions from pH 6 to 10. Below pH 8, glycerol is a poorer acceptor than H2O (glycerol phosphates:Pi = 0.5). Tris is a more effective acceptor below pH 8, showing a maximum acceptor efficiency at pH 8 (Tris phosphate:Pi = 2). Phosphotransferase efficiencies are in the order expected for the pKaS of the alcohol groups, Tris less than glycerol Cl, C3 less than glycerol C2. Tris and glycerol induce chemical shifts in 113Cd(II) present at the A site but not the B or C sites of the metal triad present at each active center of Cd(II)6 alkaline phosphatase, suggesting that the alcoxides of the acceptors coordinate the A site metal and become the nucleophiles attacking the phosphoseryl residue (E-P) in the second step of the mechanism. The interaction is through the oxygen of Tris. The transferase activity of the amino alcohol shows a bell-shaped pH dependency. Aliphatic alcohol acceptors show small increases in acceptor activity between pH 6 and 8, with 5-fold increases from pH 8 to 10 (at pH 10, glycerol phosphates:Pi = 2.5). 31P NMR inversion transfer has been used to measure the koff for Pi dissociation from the noncovalent enzyme complex (E . P). For the Zn(II)4 alkaline phosphatase koff is essentially pH independent at approximately 35 s-1. For Cd(II) or Mg(II) at the B site in place of Zn(II), koff less than or equal to 1 s-1 X Cl-ion, which appears to coordinate the A site metal ion, enhances koff, suggesting that both Cl- and HPO2-4 can coordinate the A site metal ion in a 5-coordinate intermediate. pH control of the alkaline phosphatase mechanism appears to reside in the stability of E-P and not the dissociation of E . P, compatible with the hypothesis that the activity-linked pKa is that of a H2O molecule coordinated to the A site metal, which in the hydroxide form becomes the nucleophile attacking the phosphoseryl group (E-P).

Alkaline Phosphatase↗