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Biomedical subjects

M Calvin

Publications and source records attributed to M Calvin.

At least 37 records · Page 2Linked to original sources
PubMed1978

Biochemical basis for the acquisition of resistance to benzo[a]pyrene in clones of mouse liver cells in culture.

In a Namru mouse liver epithelial cell strain designated NMuLi, aryl hydrocarbon hydroxylase (AHH) activity peaked at 12 h post-induction with 1 microgram/ml of benzo(a)pyrene (BaP) in both confluent and growing cells. Maximal levels of AHH activity were reached on day two post-plating. This induced activity was inhibited in vitro 78% by gassing the incubation mixture with carbon monoxide for 15 s, and inhibited 93% by addition of 40 microgram/ml of 7,8 benzoflavone(BF). Induced AHH levels were higher in epithelial clones that were sensitive to the toxicity of BaP than in resistant clones. The survival fraction of clones from NMuLi and of subclones derived from a sensitive clone of NMuLi after BaP treatment was a negative exponential function of the maximal induced AHH activity in the clones. One of the clones, NMuLi cl 8, was extremely susceptible to the toxic effects of BaP, the +/-(trans)-7alpha, 8beta-dihydroxy-7,8-dihydro-BaP(7,8-diol), and the (+/-)-7alpha, 8beta-dihydroxy-9beta, 10beta-epoxy-7,8,9,10-tetrahydro-BaP (diol-epoxide), known metabolites of BaP. The toxicity of BaP and the 7,8 diol to this clone was inhibited by BF, suggesting that these cells possessed an enzyme activity inhibitable by BF that could epoxidize BaP to the 7,8 oxide and then epoxidize the resultant 7,8 diol to the diol-epoxide. Another clone derived from NMuLi, clone 7, was relatively resistant to the toxic effects of BaP and the 7,8-diol, but still extremely susceptible to the toxic effects of the diol-epoxide. The slight toxicity to BaP in this clone was inhibited by BF, but the toxicity of the 7,8-diol to this clone was not inhibited by BF. A typical cytochrome P450 inhibitor, metyrapone, had no effect on the toxicity of BaP, the 7,8-diol, or the diol-epoxide to either clone 7 or clone 8. The results suggest that these liver cells possess two enzymes that play some role in polycyclic hydrocarbon-induced toxicity. Enzyme A, a BaP-inducible enzyme that is inhibitable by BF, efficiently metabolizes BaP to the 7,8-diol and the 7,8-diol to the diol-epoxide. It is responsible for most of the hydrocarbon toxicity. Enzyme B is not inhibitable by BF and metabolizes the 7,8-diol less efficiently to the diol-epoxide or efficiently to other, less toxic products.

Animals↗
PubMed1978

Inhibition of adenocarcinoma TA3 ascites tumor growth by rifamycin derivatives.

A growth inhibitory effect on adenocarcinoma TA3 ascites tumors in LAF1/J mice resulted from the repeated IP administration of subtoxic doses of 3 rifamycin derivatives: rifampicin (Rif)1, dimethylbenzyldesmethylrifampicin (DMB), and rifazone-82 (R-82). A high-viscosity methylcellulose vehicle was found to be essential for obtaining a uniform drug suspension and a significant antitumor effect by the least water soluble derivatives, DMB and R-82. The more hydrophilic derivative, Rif, was found to have a comparable growth inhibitory effect on TA3 cells when prepared in 0.9% NaCl solution with or without added methylcellulose. Oral or SC drug injections did not have an antitumor effect. The results of this study point to the importance of vehicle and route of administration in chemotherapy trials with these compounds.

Adenocarcinoma↗
PubMed1978

Chemical carcinogenesis.

The first step in the generation of a malignancy seems to be a transformation in the genetic apparatus of a single cell. The ultimate nature of the cancer which appears is a result of the interaction of that change with the control and regulatory apparatus of the whole animal. It appears that the primary cellular change which may be induced by physical, chemical or biological agents (or a combination of them) may be something which is common to all carcinogenesis. The nature of that primary change and how it may result from the action of viruses, chemicals, and radiation (or interaction between them) is the subject of this discussion.

Animals↗
PubMed1977

DNA strand scission by benzo[a]pyrene diol epoxides.

Syn-and anti-benzo[a]pyrene diol epoxides elicit a concentration-dependent nicking of superhelical Col E1 DNA in an in vitro reaction monitored by agarose gel electrophoresis and electron microscopy. This strand scission represents less than 1 percent of the DNA modification by diol epoxide. Kinetic analysis implicates the formation of unstable phosphotriesters, hydrolysis of which nick the DNA.

Benzopyrenes↗
PubMed1977

Characterization of a photoproduct of 7,12-dimethylbenz[alpha]anthracene and its effects on chick-embryo cells in culture.

A common impurity of 7,12-dimethylbenz[alpha]anthracene was more effective than 7,12-dimethylbenz[alpha]anthracene in inducing morphological alterations, and in causing an increase in glucose uptake, DNA synthesis and cell number in chick-embryo fibroblasts. Gradual morphological transformation follows the increase in DNA synthesis after 2 days when either primary or secondary cultures are treated with 3 microgram of the compound/ml. The compound, isolated from 7,12-dimethylbenz[alpha]anthracene by alumina column chromatography, was characterized by t.l.c., mass spectroscopy, carbon-hydrogen analysis, u.v. and nuclear-magnetic-resonance spectroscopy and thermal decomposition. It was the photo-oxidation product of 7,12-dimethylbenz[alpha]anthracene, 7,12-epidioxy-7,12-dimethylbenz[alpha]anthracene. It is suggested that some of the biological effects observed after treatment of cultures with 7,12-dimethylbenz[alpha]anthracene may be due in part to the presence of the photo-oxidation product.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1977

Simultaneous peptide and oligonucleotide formation in mixtures of amino acid, nucleoside triphosphate, imidazole, and magnesium ion.

Simultaneous peptide and oligonucleotide formation was observed in reaction mixtures of amino acid, nucleoside triphosphate, imidazole, and MgCl2. At 70 degrees C in solutions that were evaporated to dryness the formation of peptide for phe and pro was greatest with CTP relative to ATP, GTP, and UTP. Lysine exhibited a preference for GTP and glycine for UTP. At ambient temperature insolution at pH 7.8, CTP was preferred by glycine, but at pH 8.7 UTP was preferred. The glycine nucleotide phosphoramidates were also detected and characterized in reactions at 40 degrees C. The glycine-reaction preference for CTP at pH 7.8 and UTP at 8.7 suggested that the basicity of the nucleoside triphosphate was involved in increasing the peptide yield. CTP near neutrality is the most basic nucleoside triphosphate and the basic anionic form UTP could facilitate peptide formation at pH 8.7. These data, together with information on the complexing of poly(C) by GTP, led to the experimentally approchable hypothesis that GTP, by forming a basic triplex between the cytosine residues adjacent to the peptidyl adenosine and aminoacyl adenosine at the termini of two proto-tRNAs, would promote peptide bond synthesis between the aminoacyl residue and peptidyl residue.

Amino Acids↗
PubMed1977

Identification of the major adducts formed by reaction of benzo(a)pyrene diol epoxide with DNA in vitro.

Covalent binding of the benzo[a]pyrene metabolite (+/-)7beta,8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene to calf thymus DNA was investigated. Enzymatic hydrolysis of the carcinogen-modified DNA and subsequent separation via reversed-phase high-pressure liquid chromatography resulted in the detection and isolation of seven distinct products. High-resolution mass spectrometry indicates that these products are covalent adducts of deoxyguanosine, deoxyadenosine, and deoxycytidine. The deoxyguanosine and deoxyadenosine adducts involve binding between the activated hydrocarbon (benzo[a]pyrene diol epoxide) and exocyclic amino groups of the respective purines.

Adenine↗
PubMed1977

Electrophoretic analysis of brain proteins from young adult and aged mice.

The purpose of this study was to electrophoretically examine proteins from mice of different ages to determine whether general changes occurred in protein levels during senescence and to relate the data to specific ageing hypotheses involving proteins. Proteins from whole brain, brain regions, soluble and ribosomal brain fractions, from young adult and senescent mice, were totally solubilized and subjected to polyacrylamide slab gel electrophoresis. The resulting gel patterns were than compared by examining the intensity of gel bands of the same migration distance. Positive controls were used to establish the high sensitivity of the electrophoretic method. For example, band intensity differences were observed when brain proteins from different species, different periods of growth and development, normal and mutant mice, and different brain regions were compared. Virtually all band intensities and therefore, corresponding brain protein concentrations were unchanged when patterns from senescent mice were compared to patterns from younger adult mice. These results provide evidence against ageing hypotheses involving: (1) progressive programmed ageing; (2) protein cross-linking, and (3) a systematic shutdown of gene activity. The few, select, protein band changes that did occur provide evidence that (1) the volume of the brain vascular system decreases with age, and (2) the brain S-100 protein concentration increases with age.

Aging↗
PubMed1976

Effect of some rifamycin derivatives on chemically-induced mammary tumors in rats.

Five rifamycin derivatives have been compared for their effectiveness in inhibiting chemically-induced mammary tumours in rats. Daily oral administration of DMB (dimethylbenzyl-desmethylrifampicin), starting 2 weeks before the carcinogen challenge, was the most effective, both in inhibiting or delaying the onset of tumours and in slowing the growth of those that occurred. The inhibitory effects of rifampin, dirifampin, RC-16(rifazacyclo16) and R-82) were less than those of DMB when administered by the same route at the same dose level.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1976

Specific positions involved in enzyme catalyzed covalent binding of benzo[a]pyrene to poly(G).

Covalent binding of benzo[a]pyrene to poly(G) was studied with the use of a radioactive assay and specifically labeled substrates to define the role of the 1, 3- and 6-positions of the hydrocarbon during this process. Binding was shown to be dependent on microsomes, NADPH, O2 and poly(G). 7, 8-Benzoflavone and 2', 2'-diethylaminoethyl-2, 2-diphenyl valerate were inhibitory w.hereas modulators of epoxide hydrase activity had little effect. 3H and 14C studies suggested a possible loss of one to two protons. Incorporation of [6-3H1]benzo[a]pyrene provided evidence that the 6-position of the hydrocarbon was not metabolized during covalent attachment to poly(G) and, furthermore, results with [1, 3, 6-3H]benzo[a]pyrene suggest that the 1- and 3-positions may not be involved either. After scaling up of the standard assay 20-fold, characterization of the tritiated BaP-poly(G) complex was carried out by hydrolysis and subsequent chromatography. Thin-layer chromatography of the isolated hydrolysis products treated with HCl or alkaline phosphatase indicated that the complex formed between BaP and poly(G) was covalently linked and composed of hydrocarbon-nucleotide(s).

Animals↗
PubMed1976

Elucidation of hydrocarbon structure in an enzyme-catalyzed benzo[a]pyrene-poly (G) covalent complex.

The carcinogen, benzo[a]pyrene, was covalently attached to poly (G) by liver microsomes from rats pretreated with 3-methylcholanthrene. The complex was hydrolyzed with enzymes or base and products were isolated by Sephadex chromatography. Absorbance and fluorescence spectra of the products fit that of red-shifted pyrene aromatic system and suggest that metabolism has occurred at the 7-, 8-, 9-, and 10-positions of the hydrocarbon. Benzanthracene or chrysene fluorescence were not observed in these preparations. Benzo[a]pyrene derivatives were synthesized and purified by high-pressure liquid chromatography. Dehydration of 7,8-dihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene resulted in the formation of small amounts of 7-oxo-7,8,9,10-tetrahydrobenzoa[a]pyrene. A 7-keto species was also observed after similar treatment of the hydrocarbon-poly(G) hydrolysis products. Evidence of dehydration at the 9,10-positions was not observed. The hydrocarbon covalently bound to poly(G) is, therefore, a derivative of 7,8-dihydroxy-7,8,9,10-tetrahydrobenzol[a]pyrene with nucleic acid substitution at C-10 or 9.

Benzopyrenes↗
PubMed1976

Inhibition of infectious Rous sarcoma virus production by rifamycin derivative.

A new rifamycin derivative, rifazone-82 (R-82), an inhibitor of viral RNA-dependent DNA polymerase, is selectively toxic to transformed chicken cells in culture. R-82 has now been shown to possess antiviral activity as well. The relatively nontoxic properties of R-82 to nontransformed cells have permitted the execution of experiments examining the effect of a rifamycin derivative on virus reproduction. Addition of low concentrations of R-82 (15 mug/ml) to cultures soon after Rous sarcoma virus infection prevents the spread of infection thoroughout the culture. This inhibition is not dependent on concomitant cellular transformation as identical results were obtained with cells infected with a transformation-defective Rous sarcoma virus. Addition of R-82 to cultures in which all the cells are infected does not substantially affect the yield of physical particles as measured by RNA-dependent DNA polymerase activity and by (3H) uridine incorporation into viral RNA. However, the infectivity of the progeny virus, as measured by focus-forming ability, is decrreased 95 to 99% by R-82 treatment.

Animals↗
PubMed1976

Quantitative studies of the toxicity of benzo(a)pyrene to a mouse liver epithelial cell strain in culture.

The toxic effects of the carcinogen benzo(a)pyrene (BaP) were studied in a well-characterized epithelial cell strain NMuLi, derived from the livers of weanling Namru mice. These cells were extremely susceptible to the toxicity, 99% dying after a 6-day exposure to BaP, 5mug/ml. The toxic effects began between 11 and 24 hr postapplication of BaP to the cells and increased exponentially with the time of treatment. The toxicity was concentration dependent in cells treated for a specific time period. The survival curves were exponential and extrapolated to a survival fraction of 1.0. The toxic effects of BaP to logarithmically growing NMuLi were inhibited 40% by 7,8 benzoflavone, and the inhibition was concentration dependent. The 7,8-benzoflavone also inhibited aryl hydrocarbon hydroxylase (AHH) from NMuLi cell homogenates and microsomes by 99%. The concentration dependence for AHH inhibition by 7,8-benzoflavone paralleled its inhibition of cellular toxicity. The toxicity of BaP to these cells increased exponentially with the number of population doublings. Hence, the toxicity was 130 times greater in exponentially growing cells than in confluent cells. Levels of AHH, the enzyme that metabolizes BaP to its cytotoxic derivatives, were only 2.4 times higher in exponentially growing than in confluent cells, suggesting that cell division was responsible for the large differential toxicity. In addition, a toxic BaP metabolite was preferentially toxic to log-phase cells. The results indicate that the metabolism of BaP by AHH to produce cytotoxic metabolites, which may cause lesions that are expressed upon cell division, is responsible for the cytotoxicity of BaP to NMuLi.

Animals↗
PubMed1975

Carcinogenesis.

An examination has been made of the major chemicals which are known to be carcinogenic, either in animals or in humans. As a result, a generalized type of chemical property seems to be a prerequisite for the carcinogenic activity. In most cases, this is some kind of reactive electrophilic intermediate produced directly from the carcinogen or from one of its immediate metabolites. This electrophilic reagent is generally a positively charged ion of some kind. In the case of the hydrocarbons it seems to be an incipient carbonium ion; in the case of nitrogen compounds, it is a corresponding nitronium ion. There are a number of possible substrate materials (nucleophilic) in a cells, but the dominant one which has been suspected is the nucleic acid component, either the DNA or the RNA. The bases of these materials all have extra pi electrons susceptible to attach by the electrophiles of the carcinogen. Such a modification, particularly of the DNA, could lead to either major or minor changes in the genetic composition of the cell. Minor changes are usually rectifiable or are not visible, and this would include a large variety of point mutations.

2-Acetylaminofluorene↗