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W Levin

Publications and source records attributed to W Levin.

At least 163 records · Page 9Linked to original sources
PubMed1983

Fluorine substitution as a probe for the role of the 6-position of benzo[a]pyrene in carcinogenesis.

The tumorigenic activities of benzo[a]pyrene (BP) and 6-fluorobenzo[a]pyrene (6-F-BP) were compared to determine whether an unsubstituted 6-position is important for the carcinogenic effect of BP. Highly purified samples of 6-F-BP and BP had similar activities for the induction of lung adenomas in Swiss Webster mice treated before weaning. The 6-fluoro derivative, however, had about one-half as much activity as BP for the initiation of skin papillomas in CD-1 mice. Similarly, 6-F-BP (approximately equal to 90% purity) had about one-half the activity of BP for the induction of skin tumors in C57BL/6J mice given repetitive treatments of the hydrocarbons and for the induction of sarcomas in C3H/fCum mice given a single sc injection. 6-F-BP (approximately equal to 90% purity) had activity similar to that of BP for induction of sarcomas at the sc injection site in Fischer 344 rats. These results and related data indicate the need for detailed metabolic studies whenever fluorine substitution is used as a probe to assess the role of the unsubstituted position in the carcinogenicity of the parent compound.

Animals↗
PubMed1983

Mutagenicity of the enantiomers of the diastereomeric bay-region benz(a)anthracene 3,4-diol-1,2-epoxides in bacterial and mammalian cells.

Enantiomers of the diastereomeric pair of bay-region benz(a)anthracene 3,4-diol-1,2-epoxides in which the benzylic 4-hydroxyl group and epoxide oxygen are either cis (isomer 1) or trans (isomer 2) were evaluated for mutagenic activity in two histidine-dependent strains of Salmonella typhimurium, as well as in an 8-azaguanine-sensitive Chinese hamster cell line. In strain TA 98 of S. typhimurium, the diol-epoxide with (1S,2R,3R,4S) absolute configuration [(-)-diol-epoxide 2] was the most active isomer, although there was less than a 3-fold difference in the mutagenicity of the four diol-epoxides. However, in strain TA 100 of S. typhimurium, the enantiomeric diol-epoxide with (1R,2S,3S,4R) absolute configuration [(+)-diol-epoxide 2] was the most active diol-epoxide, and the two isomers with (3S,4R) absolute configuration [(-)-diol-epoxide 1 and (+)-diol-epoxide 2] were three to eight times more active than were the two isomers with (3R,4S) configuration. The highest degree of sensitivity to absolute configuration was observed in Chinese hamster V79 cells, in which the (1R,2S,3S,4R) isomer [(+)-diol-epoxide 2] was from three to 20 times more mutagenic than were the other three isomers. This metabolically predominant (+)-diol-epoxide 2 isomer, which has high activity in strain TA 100 of S. typhimurium and the Chinese hamster V79 cells, has the same absolute configuration as do the bay-region diol-epoxide isomers of benzo(a)pyrene and chrysene that have been shown previously to be exceptionally mutagenic to mammalian cells and highly tumorigenic in mice. Analysis of the mutagenic activity of the (+)- and (-)-isomers of the 1,2- and 3,4-tetrahydroepoxides of benz(a)anthracene revealed only small enantiomeric differences in strain TA 98 of S. typhimurium (2.5 fold) and little, if any, differences (less than 1.5-fold) in the other two mutagenicity systems. However, the extent to which the four tetrahydroepoxides were converted to nonmutagenic products by homogeneous microsomal epoxide hydrolase (EC 3.3.2.3) indicated marked differences in the stereoselectivity of the enzyme. (-)-(3R,4S)-Epoxy-1,2,3,4-tetrahydrobenz(a)anthracene appears to be an exceptionally good substrate for epoxide hydrolase.

Animals↗
PubMed1983

The natural history of radiation-induced proctosigmoiditis: an analysis of 88 patients.

The records of 88 patients with radiation-induced proctosigmoidosis seen over an eight year period were reviewed. Eighty-four (95 per cent) had been irradiated for a gynaecological malignancy. The peak incidence of bleeding occurred after a latent period of nine months from the time of irradiation. Twenty-five subjects (28 per cent) had associated injury to the urinary tract. A wide spectrum of radiological abnormalities found on barium enema is described. Twenty-four patients (27 per cent) underwent operations for radiation-induced injury to the colon and urinary tract. Operations on the bowel were attended by a high complication rate (79%). A clinical classification based on bowel symptoms is presented. Those whose only symptom was low grade rectal bleeding (Group I) had the most favourable outcome and of these, 35 per cent stopped bleeding spontaneously by six months. Patients who required frequent transfusions (Group II) had an increasing mortality rate with the passage of time. Patients whose predominant symptoms were pain and bowel dysfunction (Group III) had the highest death rate but some did well after an operative procedure.

Adult↗
PubMed1983

Regioselectivity and stereoselectivity in the metabolism of trans-1,2-dihydroxy-1,2-dihydrobenz[a]anthracene by rat liver microsomes.

Metabolism of [3H]-(+/-)-trans-1,2-dihydroxy-1,2-dihydrobenz[a] anthracene by liver microsomes isolated from control, phenobarbital-treated, and 3-methylcholanthrene-treated Long-Evans rats and from 3-methylcholanthrene-treated Sprague-Dawley rats was examined. Liver microsomes from both control and phenobarbital-treated rats metabolized the dihydrodiol at a rate of 0.5 nmol/nmole of cytochrome P450 per minute, whereas prior treatment of rats with 3-methylcholanthrene stimulated the rate of metabolism by 4-fold. Prior treatment of the rats caused marked differences in the regio- and stereoselectivity of the metabolism of this pseudo-diaxial dihydrodiol. In each case, the major metabolites were three bis-dihydrodiols and a pair of diastereomeric 1,2-diol-3,4-epoxides in which the benzylic 1-hydroxyl group is either cis or trans to the epoxide oxygen (diol epoxides-1 and -2, respectively). The presence of the diol epoxides in the incubation medium was inferred from the identification of their corresponding tetraols, which arise by hydrolysis of the diol epoxides on chromatography. Hepatic microsomes from control and phenobarbital-treated rats metabolized the 1,2-dihydrodiol predominantly to 1,2-diol-3,4-epoxides (68-85% of the total metabolites) whereas bis-dihydrodiols represented 28% and 13% of the total metabolites, respectively. In contrast, liver microsomes from 3-methylcholanthrene-treated rats of either strain metabolized the 1,2-dihydrodiol primarily to isomeric bis-dihydrodiols (51-56% of total metabolites), with diol epoxides accounting for only 36-38% of the total metabolites. Bis-dihydrodiol-1 (32-35% of the total metabolites) was formed in greater amounts (2- to 4-fold) than either bis-dihydrodiols-2 or -3, which were formed in about equal amounts and have identical absorption spectra. The ratio of the diastereomeric 1,2-diol-3,4-epoxides-1 and -2 was highly dependent upon the preparation used. For microsomes from control and phenobarbital-treated rats, this ratio was between 3:1 and 4:1 whereas microsomes from 3-methylcholanthrene-treated rats (greater than 70% cytochrome P-450c) gave a ratio of between 1:1.5 and 1:2. The basis for this ratio in the latter case was explained by examination of the products formed from the (+)-(1S,2S)-and (-)-(1R,2R)-enantiomers of the dihydrodiol on metabolism by a highly purified system reconstituted with cytochrome P-450c. The (-)-isomer is a 3-fold better substrate than the (+)-isomer and forms only the diol epoxide-2 diastereomer, whereas the (+)-isomer forms much more diol epoxide-1 than diol epoxide-2 diastereomer.

Animals↗
PubMed1983

Tumor-initiating activity of benz[c]acridine and twelve of its derivatives on mouse skin.

Benz[c]acridine (B[c]ACR) and 12 of its derivatives, including the 5 metabolically possible trans-dihydrodiols, the diastereomeric bay-region diol-epoxides, 2 non-bay-region diol-epoxides, and the K-region arene oxide, were tested for tumor-initiating activity on mouse skin. A single topical application of 0.4 to 2.5 mumol of compound was followed 12 days later by twice-weekly applications of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate for 25 weeks. B[c]ACR was a weak tumor initiator on mouse skin, producing a 37% tumor incidence and 1.33 tumors/mouse at the 2.5-mumol dose. Of the five metabolically possible trans-dihydrodiols of B[c]ACR, only trans-3,4-dihydroxy-3,4-dihydro-B[c]ACR had significant tumor-initiating activity. This compound was at least 6-fold more active than was the parent compound at the three doses tested. The diastereomeric bay-region diol-epoxides, in which the epoxide oxygen is either cis(isomer 1) or trans (isomer 2) to the benzylic hydroxyl group, each had significant tumor-initiating activity, although isomer 2 was at least 5-fold more active than was isomer 1 and had activity equal to that of its potential metabolic precursor, trans-3,4-dihydroxy-3,4-dihydro-B[c]ACR. Two non-bay-region diol-epoxides (isomer 2 of the 8,9-diol-10,11-epoxide and the 10,11-diol-8,9-epoxide) and the 5,6-arene oxide (K-region) were inactive at the doses tested. 3,4-Dihydro-B[c]ACR, the potential metabolic precursor of a bay-region tetrahydroepoxide, was the most potent tumor initiator analyzed in the present study. At an initiating dose of 0.4 mumol, this compound produced a 97% tumor incidence and 7.90 tumors/mouse after 15 weeks of promotion with 12-O-tetradecanoylphorbol-13-acetate. These results suggest that B[c]ACR, the N-12 analogue of benz[a]anthracene, undergoes metabolic activation to an ultimate carcinogenic metabolite via formation of a bay-region diol-epoxide, as has already been demonstrated for benz[a]anthracene.

Acridines↗
PubMed1982

Comparisons of highly purified hepatic microsomal cytochromes P-450 from Holtzman and Long-Evans rats.

The present study describes the purification and characterization of strain variant forms of a major phenobarbital-inducible microsomal hemoprotein, cytochrome P-450b, from Holtzman and Long-Evans rats. The strain variant hemoproteins cannot be resolved by sodium dodecyl sulfate gel electrophoresis, but can be partially separated in two-dimensional isoelectric focusing SDS gels. If, however, sodium tetradecyl sulfate is incorporated into the one-dimensional gel system, separation of the cytochromes P-450b is achieved. Minor structural differences are detected in the peptides of the cytochromes P-450b following limited proteolysis by Staphylococcus aureus V8 protease, cleavage by cyanogen bromide, or reverse-phase high-pressure liquid chromatography of tryptic peptides. The strain variant cytochromes P-450b are immunochemically and spectrally indistinguishable. The optical spectra of the ferric and ferrous hemoproteins are identical, as are the CO- and ethylisocyanide-reduced difference spectra. Ferrous cytochromes P-450b from both rat strains effectively bind metyrapone with equivalent affinities. In addition, the cytochromes P-450b do not differ in their catalytic activities toward benzphetamine, hexobarbital, benzo [a]pyrene, zoxazolamine, 7-ethoxycoumarin, estradiol-17 beta and testosterone. Cytochrome P-450c, the predominant isozyme inducible in rat liver by 3-methylcholanthrene, was purified from Holtzman and Long-Evans rats. Cytochromes P-450c from both rat strains are indistinguishable based on electrophoretic, immunological, spectral and catalytic properties. Minor structural differences in the cytochromes P-450c were revealed in the reverse-phase high-pressure liquid chromatographic profiles of the tryptic peptides of these hemoproteins, but not in the peptides generated by limited proteolysis or cleavage with cyanogen bromide.

Animals↗
PubMed1982

Polypeptide patterns of hepatic microsomes from Long-Evans rats treated with different xenobiotics.

Two-dimensional gel electrophoresis was used to analyze hepatic microsomal polypeptides after treatment of immature, male Long-Evans rats with 3-methylcholanthrene, pregnenolone-16 alpha-carbonitrile, isosafrole, SKF-525A, Aroclor-1254, gamma-chlordane, or trans-stilbene oxide. Epoxide hydrolase and cytochromes P-450a, P-450bLE, P-450c, P-450d, and P-450e were all identified as resolved polypeptides in these electrophoretograms. Idiosyncratic polypeptide patterns characterized the microsomal preparations following treatment of rats with each inducing agent. Immunochemically identical cytochromes P-450bLE and P-450e were always present at the same relative levels even though their total amount varied 3-fold after induction by isosafrole, SKF-525A, Aroclor-1254, gamma-chlordane, and trans-stilbene oxide. Cytochromes P-450c and P-450d were coinduced by 3-methylcholanthrene, isosafrole, and Aroclor-1254, but their relative amounts varied. Pregnenolone-16 alpha-carbonitrile treatment resulted in an increase of a single major microsomal polypeptide which was also induced by phenobarbital, isosafrole, SKF-525A, Aroclor-1254, and trans-stilbene oxide. Only one polypeptide was identified as epoxide hydrolase in all of the microsomes analyzed. The results suggest that the levels of cytochromes P-450bLE and P-450e may be subject to coordinate control, whereas the other cytochromes P-450 are independently regulated.

Animals↗
PubMed1982

Multiple, immunoidentical forms of phenobarbital-induced rat liver cytochromes P-450 are encoded by different mRNAs.

It was shown previously that four immunochemically identical forms of phenobarbital-induced hepatic cytochrome P-450 exist in unique combinations which characterize different strains and colonies of rats (Vlasuk, G. P., Ghrayeb, J., Ryan, D. E., Reik, L., Thomas, P. E., Levin, W., and Walz, F. G., Jr. (1982) Biochemistry 21, 789-798). One colony of Long-Evans rats exhibited only cytochromes P-450bLE and P-450e among these immunorelated enzymes; whereas, one colony of Holtzman rats was characterized by cytochromes P-450bH and P-450e. After phenobarbital treatment, hepatic poly(A)+-mRNA was isolated from these groups of rats and translated in vitro. The 35S-labeled products were immunoisolated with antibody to cytochrome P-450bLE and analyzed by two-dimensional gel electrophoresis. The results indicated that the products synthesized in vitro correspond exactly to the two particular forms of the enzyme that characterize liver microsomes from each of these groups of rats. It is concluded that different structural genes encode these immunorelated forms of cytochrome P-450 and that significant post-translational processing of their polypeptide products does not occur in vivo.

Animals↗
PubMed1982

Multiplicity strain differences, and topology of phenobarbital-induced cytochromes P-450 in rat liver microsomes.

The multiplicity of phenobarbital-induced cytochromes P-450 in live microsomes from male rats was investigated by using two-dimensional gel electrophoresis, peptide fingerprinting, and immunoaffinity chromatography. Two colonies each of Holtzman and Long-Evans rats were studied. Four molecular forms of phenobarbital-induced cytochromes P-450 were distinguished as polypeptides (designated PB3, variant PB3, PB4, and PB5) which showed apparent immunochemical identity and greater than or equal to 95% fingerprint homology. Two of these polypeptides corresponded to cytochrome P-450b [Ryan, D., Thomas, P. E., Korzeniowski, D., & Levin, W. (1979) J. Biol. Chem. 254, 1365-1374] and cytochrome P-450e [Ryan, D., & Levin, W. (1981) Fed. Proc., Fed. Am. Soc. Exp. Biol. 40, 1640] which had been purified from Long-Evans rats (variant PB3 and PB5, respectively). Each rat colony was characterized by unique combinations of two or three of these immunochemically related forms of cytochromes P-450. Cytochrome P-450e was present in rats from all four colonies, but cytochrome P-450b was only found in Long-Evans rats. Polypeptide PB3 was only found in the two colonies of Holtzman rats, whereas polypeptide PB4 was present in one colony each of Holtzman and Long-Evans rats. In addition to these forms of cytochrome P-450, rats from each colony also evidenced three other major phenobarbital-induced polypeptides which gave unique fingerprints, and one of these was identified as representing epoxide hydrolase. Proteolytic digestion studies of intact microsomes demonstrated that the four immunochemically identical forms of cytochrome P-450 were partially exposed on the outer (cytoplasmic) surface of microsomes. However, polypeptide PB3 was characterized by the greatest rate of proteolytic degradation. These results clearly demonstrate that phenobarbital-induced cytochromes P-450 include microheterogeneous proteins which show remarkable variations related to rat strains and/or colony.

Animals↗