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W Levin

Publications and source records attributed to W Levin.

At least 181 records · Page 10Linked to original sources
PubMed1982

Purification, characterization and regulation of five rat hepatic microsomal cytochrome P-450 isozymes.

1. Five hepatic microsomal cytochrome P-450 isozymes (cytochromes P-450a, P-450b, P-450c, P-450d, P-450e) have been purified to apparent homogeneity from immature male rats treated with various xenobiotics. 2. The unique electrophoretic properties, substrate specificities and spectral characteristics of these haemoproteins have been compared and contrasted. 3. Structural studies of these cytochrome P-450 isozymes have included NH2-terminal amino acid sequence analyses, as well as electrophoretic profiles of limited proteolytic digests and cyanogen bromide fragments of the haemoproteins. 4. Specific antibodies have been prepared against four of the isozymes and used to evaluate immunochemical relationships among these cytochrome P-450s by Ouchterlony double-diffusion analyses. 5. The levels of some of these cytochrome P-450 isozymes have been quantified immunologically in hepatic microsomal preparations from untreated rats and following induction by phenobarbital, 3-methylcholanthrene or Aroclor 1254. 6. Antibodies directed against cytochromes P-450a and P-450b have been used to establish the presence of more than one 7 alpha- and 16 alpha-testosterone hydroxylase in rat hepatic microsomes. The relative contributions of cytochromes P-450c and P-450d to the overall microsomal metabolism of benzo[a]pyrene have been evaluated using antibodies to these haemoproteins.

Amino Acid Sequence↗
PubMed1982

Metabolism and tumorigenicity of 7-, 8-, 9-, and 10-fluorobenzo(a)pyrenes.

The skin tumor-initiating activities of 7-, 8-, 9-, and 10-fluorobenzo(a)pyrenes have been compared to that of benzo(a)pyrene in female Sencar mice after 16 weeks of promotion with 12-O-tetradecanoylphorbol-13-acetate. Single initiating doses of 200 or 400 nmol of each hydrocarbon were tested, and the mice were treated twice weekly with 3.2 nmol of the promoter. Under these conditions, benzo(a)pyrene caused an average of 2.9 and 5.7 papillomas/mouse, respectively, whereas none of the four fluorinated hydrocarbons had significant tumor-initiating activity. Examination of the hepatic metabolism of 7- and 8-fluorobenzo(a)pyrene revealed that a 7,8-dihydrodiol was not detected as a metabolite; thus, the bay-region diol-epoxide pathway known to be responsible for the tumorigenic activity of benzo(a)pyrene is blocked. Although 7,8-dihydrodiols are formed from 9- and 10-fluorobenzo(a)pyrene, these dihydrodiols with fluorine substituted on the 9,10-double bond may not be converted to diol-epoxides by the cytochrome P-450 system, or such fluorinated 7,8-diol-9,10-epoxides may not be tumorigenic.

Animals↗
PubMed1982

Pettigrew technique of inducing whole-body hyperthermia.

The current use of heated wax as a surface contact heating source to induce whole-body hyperthermia (WBH) in the anesthetized patient is described. Heated anesthetic gases and epidural block are no longer routinely used. Hemodynamic, physiological, and biochemical changes are described. Deaths due to cardiac arrhythmias, disseminated intravascular coagulopathy, and liver failure have occurred rarely. Other complications included peripheral nerve palsies, mental disorientation, subclinical liver damage, decubitus ulceration, anemia, circumoral herpes simplex, lethargy, and anorexia. Transverse myelitis and coma occurred in 2 patients who had previously received high-dose irradiation to the spinal cord and cerebral region, respectively. The 232 patients in 4 centers have undergone 682 heating sessions. The method to produce prolonged WBH of 41.8 degrees C is simple and reliable.

Body Temperature↗
PubMed1982

Mouse skin tumor-initiating activity of 5-, 7-, and 12-methyl- and fluorine-substituted benz[a]anthracenes.

As an approach for elucidation of structure activity relationships that underlie the exceptionally large difference in carcinogenic activity between benz[a]anthracene and 7,12-dimethylbenz[a]anthracene (7,12-DMBA), 11 methyl- and/or fluorine-substituted benz[a]anthracenes were evaluated for tumor-initiating activity on mouse skin. Outbred CD-1 and outbred Sencar mice received a single topical application of the hydrocarbons followed by twice weekly applications of the tumor promoter 12-O-tetradecanoylphorbol 13-acetate for 16-26 weeks. 7,12-DMBA was almost two orders of magnitude more active as a tumor-initiator than 7- and 12-methylbenz[a]anthracene. Methyl substitution at the 7- and 7,12-positions of benz[a]anthracene was significantly more effective in the enhancement of tumorigenic activity than fluorine substitution at these positions. Although 7-fluorobenz[a]anthracene, 12-fluorobenz[a]anthracene, and 7,12-difluorobenz[a]anthracene had only 0.15, 0.26, and less than 0.005 times the tumor-initiating activity of their respective methyl-substituted derivatives, they were severalfold more active than benz[a]anthracene. 7-Fluorobenz[a]anthracene was slightly less active than 12-fluorobenz[a]anthracene, whereas 7-methylbenz[a]anthracene was about twofold more than 12-methylbenz[a]anthracene. For 7,12-di-substituted benz[a]anthracenes, 7-methyl-12-fluorobenz[a]anthracene was more than twice as tumorigenic as 7-fluoro-12-methylbenz[a]anthracene, but each was individually more active than 7-methylbenz[a]anthracene and 12-methylbenz[a]anthracene, respectively. Both fluorinated compounds were much less active than 7,12-DMBA. Substitution of fluorine or methyl at the 5-position of 7-methylbenz[a]anthracene and substitution of fluorine at the 5-position of 12-methylbenz[a]anthracene dramatically reduced their tumorigenic activity.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1982

Human liver microsomal epoxide hydrolase. Correlation of immunochemical quantitation with catalytic activity.

Human liver microsomal epoxide hydrolase was purified to apparent homogeneity as judged by a single protein-staining band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Sheep antibody to human liver epoxide hydrolase reacted with the enzyme in detergent-solubilized human liver microsomes, giving a single immunoprecipitin band which formed a line of identity with the pure human enzyme. Antibody against the human enzyme reacted well with epoxide hydrolase in detergent-solubilized monkey liver microsomes by the Ouchterlony test but less strongly cross-reacted with the enzyme from rat liver and several other species. The antibody produced against purified human liver epoxide hydrolase precipitated the enzyme but did not inhibit catalytic activity, reminiscent of the relationship of rat liver epoxide hydrolase to its antibody. The absolute level of epoxide hydrolase in liver microsomal samples from 11 human subjects, as measured by a radial immunodiffusion assay, varied 3.4-fold whereas the rate of hydration of octene oxide varied 2.9-fold. The excellent correlation of the amounts of epoxide hydrolase determined catalytically or immunochemically (r = 0.99) indicated that interindividual variation in octene oxide hydration rates by human liver microsomes is a consequence of differences in amount of epoxide hydrolase protein which is present, and not the result of differences in levels of endogenous modulators of catalytic activity.

Epoxide Hydrolases↗
PubMed1982

Mutagenicity of the optical isomers of the diastereomeric bay-region chrysene 1,3-diol-3,4-epoxides in bacterial and mammalian cells.

The mutagenic activities of the four optically pure (+)- and (-)-enantiomers of the two diastereomeric bay-region chrysene 1,2-diol-3,4-epoxides were evaluated in histidine-dependent strains of Salmonella typhimurium and in cultured Chinese hamster V79 cells. In strain TA98 of S. typhimurium, (-)-1 alpha, 2 beta-dihydroxy-3 beta, 4 beta-epoxy-1,2,3,4-tetrahydrochrysene was 5 to 10 times more active than the other three optical isomers. However, in strain TA100 of S. typhimurium and in Chinese hamster V79 cells, (+)-1 beta, 2 alpha-dihydroxy-3 alpha, 4 alpha-epoxy-1,2,3,4-tetrahydrochrysene was the most mutagenic diol-epoxide and was from 5 to 40 times more active than the other three optical isomers. The bay-region (+)- and (-)-3,4-epoxy-1,2,3,4-tetrahydrochrysene isomers has identical mutagenic activities in all three systems. These studies indicate that the presence and orientation of the hydroxyl groups play an important role in modulating the mutagenic activity of bay-region epoxides of chrysene in both bacterial and mammalian cells.

Animals↗
PubMed1981

Enantioselectivity of microsomal epoxide hydrolase toward arene oxide substrates.

The enantioselectivity of native and purified hepatic microsomal epoxide hydrolase toward one symmetrical arene oxide, phenanthrene 9,10-oxide, and the resolved enantiomers of the three chiral arene oxide substrates, benzo[a]pyrene 4,5- and 7,8-oxide and benzo[a]anthracene 5,6-oxide was examined. A model lipid system of nonionic detergent micelles was used to solubilize both substrates and products. The enantioselectivity of purified epoxide hydrolase in micellar solution was essentially the same as the microsomal enzyme in the absence of detergent. Regioselectivity of the enzyme was determined by a gas chromatographic-mass spectrometric procedure in which bis-trifluoroacetates of the dihydrodiols were pyrolyzed to trifluoroacetylphenols to locate the position of the enzyme-catalyzed incorporation of 18O from H218O into the dihydrodiol. Correlation of the enantio- and regioselectivity data with the known absolute configurations of the dihydrodiols permitted the assignment of the (4S,5R) and (5S,6R) absolute configurations to (+)-benzo[a]pyrene 4,5- and (+)-benzo[a]anthracene 5,6-oxide, respectively. A kinetic analysis of the hydration of arene oxide substrates in micellar solution is presented. The kinetic discrimination of the enzyme toward substrate enantiomers and the product enantioselectivity of the enzyme are discussed in terms of possible molecular deformations occurring in the transition state and the ability of the enzyme to bind and stabilize these transition states.

Animals↗
PubMed1981

Regulation of three forms of cytochrome P-450 and epoxide hydrolase in rat liver microsomes. Effects of age, sex, and induction.

A procedure for the preparation of monospecific antibody directed against rat liver microsomal cytochrome P-45-a is described. This antibody, together with monospecific antibodies to cytochromes P-450b and P-450c, has been used to show that these three forms of cytochrome P-450 are distinct and share no common antigenic determinants. These antibodies (a) give single immunoprecipitin bands with detergent-solubilized microsomes; (b) do not cross-react with the purified heterologous antigens in Ouchterlony double diffusion analyses; (c) have no effect on catalytic activity of the heterologous antigens but completely inhibit the enzymatic activity of the homologous antigens; and (d) remove only the homologous antigen from detergent-solubilized microsomes when covalently bound to a solid support. With radial immunodiffusion assay, we have quantitated these three forms of cytochrome P-450 in liver microsomes after treatment of rats with seven different inducers of cytochrome P-450. The levels of these cytochrome P-450 isozymes vary independently and are also regulated by the age and sex of the animal. The antibodies have also been used to assess the contribution of cytochromes P-450a, P-450b, and P-450c in the metabolism of xenobiotics by rat liver microsomes. A large proportion of benzo(a)pyrene metabolism and testosterone 16 alpha-hydroxylation in microsomes from untreated rats is not catalyzed by cytochromes P-450a, P-450b, and P-450c. Epoxide hydrolase, another microsomal enzyme involved in the metabolism of xenobiotics, was also quantitated by radial immunodiffusion after prior treatment of rats with microsomal enzyme inducers. The inductions of epoxide hydrolase varies independently of the induction of cytochromes P-450a, P-450b, and P-450c.

Aging↗
PubMed1981

Highly tumorigenic bay-region diol epoxides from the weak carcinogen benzo[c]phenanthrene.

In the four years since its inception, the bay-region theory has proved highly successful in predicting which diol epoxide of a polycyclic aromatic hydrocarbon would have the highest tumorigenic activity. The present studies on benzo[c]phenanthrene have shown this hydrocarbon to be unique. It is the first hydrocarbon for which the bay-region diol epoxide that has its benzylic hydroxyl group and epoxide oxygen cis (isomer-1 series) has significant tumorigenic activity. Additionally, its bay-region diol epoxides are the most tumorigenic diol epoxides yet tested on mouse skin despite their expected and observed very low chemical reactivity. Perhaps some unique feature of the shape of benzo[c]phenanthrene can account for the remarkable biological activity of its bay-region diol epoxides. The high degree of crowding in the bay-region of benzo[c]phenanthrene may be such a contributing factor. It is know, for example, that methyl-substitution in the bay-region but not on the critical benzo-ring enhances the tumorigenic activity of 7,12-dimethylbenzo[a]anthracene relative to 7-methylbenzo[a]anthracene (Newman, 1976), of 5-methylchrysene relative to chrysene (Hecht et al., 1974), and of 11-methylbenzo[a]pyrene relative to benzo[a]pyrene (Iyer et al., 1980). Steric crowding in the bay-region of benzo[c]phenanthrene (Hirshfeld, 1963) and 7,12-dimethylbenzo[a]anthracene has been shown by x-ray crystallography to cause out-of-plane deformation of their aromatic ring systems.

Animals↗
PubMed1981

Regio- and stereoselectivity of hepatic cytochrome P-450 toward polycyclic aromatic hydrocarbon substrates.

Although the cytochrome P-450 system shows broad substrate specificity toward the PAH, it also has regio- and stereoselectivity. Of the PAH substrates yet studied, phenanthrene is metabolized most efficiently, whereas chrysene and DBA are much more slowly turned over. Interestingly, the cytochrome P-450 system and epoxide hydrolase favor the formation of dihydrodiols with R,R configuration. The predominant enantiomers of the dihydrodiols with the bay-region double bond, as well as bay-region diol epoxides derived from phenanthrene, chrysene, BA and B[a]P, are superimposable when their bay-regions are aligned (Fig. 3). These metabolically favored isomers of the dihydrodiols and bay-region diol epoxides are also the more carcinogenic isomers when derived from carcinogenic polycyclic hydrocarbons.

Animals↗