Chronic ethanol ingestion in rats results in an increase in hepatic microsomal dimethylnitrosamine (DMN) demethylase activity and in an increase in hepatic microsomal activation of DMN to a mutagen. These effects of ethanol on DMN metabolism were detectable in vitro at DMN concentrations as low as 0.3 to 1 mM and as high as 100 mM. This ability of ethanol to increase the rate of DMN metabolism over such a broad range of DMN concentrations is in marked contrast to the effects of other microsomal enzyme inducers, such as phenobarbital and 3-methylcholanthrene, which increase the rate of DMN metabolism only at relatively high DMN concentrations and repress its metabolism at low DMN concentrations.
A 2.1-megadalton, EcoRI-generated fragment of Bacillus subtilis phage phi 105 DNA was cloned into plasmid pUB110. The hybrid plasmid produces a biologically active product which renders B. subtilis immune to infection by phi 105.
Crown-gall tumor tissue cultures release peroxidase into the medium in response to the concentration of specific ions in the medium. This release is not due to diffusion from cut surfaces or injured cells. Calcium, magnesium, and ammonium were, in that order, most effective in increasing peroxidase release. The enzyme was demonstrated cytochemically on the cell walls and in the cytoplasm. Cell wall fractions, exhaustively washed in buffer, still contained bound peroxidase. This bound peroxidase could be released by treating the wall fractions with certain divalent cations or ammonium. The order of effectiveness for removing the enzyme from the washed cell walls is: Ca(++) approximately Sr(++) > Ba(++) > Mg(++) > NH(4) (+). These data support the thesis presented that specific ions can control the deposition of lignin on cell walls by affecting the peroxidase levels on these walls.
The seven previously identified EcoRI cleavage fragments of phi 105 DNA were ordered with respect to their sites of origin on the phage genome by marker rescue. One fragment, H, did not carry any determinants essential for replication. This fragment was totally missing in a deletion mutant which exhibited a lysogenization-defective phenotype. There is a nonessential region on the phi 105 genome which begins in fragment B, spans fragment H, and ends in fragment F. The size of the nonessential region, as estimated by alterations observed in the fragmentation patterns of deletion mutant DNAs, is approximately 2.7 X 10(6) daltons. Two new EcoRI cleavage fragments with molecular weights of approximately 0.2 X 10(6) were detected by autoradiography of 32P-labeled DNA. These small fragments were not located on the cleavage map.
The effect of chronic ethanol consumption on enzyme systems directly involved in carcinogen activation and detoxification were studied in rat upper alimentary tract tissue. Microsomal cytochrome P‐450 (P‐450) levels and glutathione levels as well as glutathione transferase and UDP‐glucuronic acid transferase (UDPGT) activities were measured in mucosa scraped from esophagus, forestomach and glandular stomach of rats which had been pair‐fed ethanol or dextrimaltose‐containing diets. Esophageal and forestomach P‐450 levels were increased in the ethanol‐fed rats. The ethanol diet also produced a small but significant increase in esophageal glutathione transferase levels. Glutathione levels and UDPGT activity were unaffected. Since P‐450 is directly involved in the activation of many chemical carcinogens, these results are consistent with the hypothesis that the increase in upper alimentary tract cancer risk associated with alcohol abuse is due, at least in part, to ethanol's altering the balance between carcinogen activation and detoxification.
To establish the role of the activity of the microsomal biotransformation system in chemical carcinogenesis, the mutagenic effect of primary (ultimate) and secondary (potential) carcinogens after exposure to isolated hepatic microsomes was studied. The principal enzyme system, suggested to be active in the metabolism of carcinogenic compounds, is the nonspecific cytochrome P-450 dependent mixed-function oxidase (1). This microsomal enzyme system is inducible by many substrates, including some environmental contaminants (2). The involvement of the microsomal enzymes in carcinogenesis is suggested by the observed increased carcinogen biotransformation in animals (3) and isolated cells (4) following exposure to inducing substrates. Most carcinogenic compounds are mutagenic for microorganisms (5). The primary are themselves mutagenic, the secondary are inactive until metabolized to a mutagenic form (6). Metabolism of primary carcinogens may reduce mutagenic and carcinogenic properties. Both types of metabolic...
Bacillus subtilis mutants with lesions in PBSX prophage genes have been isolated. One of these appears to be a regulatory mutant and is defective for mitomycin C-induced derepression of PBSX; the others are defective for phage capsid formation. All of the PBSX structural proteins are synthesized during induction of the capsid defective mutants; however, several of these proteins exhibit abnormal serological reactivity with anti-PBSX antiserum. The two head proteins X4 and X7 are not immunoprecipitable in a mutant which fails to assemble phage head structures. In the tail mutant, proteins X5 and X6 are not immunoprecipitable, tails are not assembled, and a possible tail protein precursor remains uncleaved. The noninducible mutant does not synthesize any PBSX structural proteins after exposure to mitomycin C. The mutation is specific for PBSX since ø105 and SPO2 lysogens of the mutant are inducible. All of the known PBSX-specific mutations were shown to be clustered between argC and metC on the host chromosome. In addition, the metC marker was shown to be present in multiple copies in cells induced for PBSX replication. This suggests that the derepressed prophage replicates while still integrated and that replication extends into the adjacent regions of the host chromosome.
Possible mechanisms whereby alcohol abuse and alcohol-related diseases may promote the development of cancer are analyzed. The mechanisms discussed include: (a) contact-related local effects on the upper gastrointestinal tract; (b) the presence of low levels of carcinogens in alcoholic beverages; (c) induction of microsomal enzymes involved in carcinogen metabolism; (d) various types of cellular injury produced by ethanol and its metabolites and their relationship to cancer, particularly in the liver; (e) the nutritional disturbances frequently associated with alcohol abuse. The relationship between alcohol-induced cirrhosis and hepatocellular carcinoma is also discussed, and case histories of patients seen at the Bronx Veterans Administration Medical Center with hepatocellular carcinoma in the absence of cirrhosis are reviewed. Data are presented demonstrating the induction, by chronic ethanol consumption, of microsomal enzymes which convert procarcinogens to carcinogens. These data were derived from experiments in which the ability of microsomes isolated from liver, intestine, and lung tissues of ethanol-fed and control rats to activate several test carcinogens was examined in the Ames Salmonella-mutagenicity test. The hypothesis is presented that ethanol-mediated induction of enzyme systems which activate procarcinogens to carcinogens in various tissues contributes to the enhanced incidence of cancer in the alcoholic.
