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Biomedical subjects

H C Pitot

Publications and source records attributed to H C Pitot.

At least 253 records · Page 14Linked to original sources
PubMed1984

The expression of the myc proto-oncogene in a dimethylsulfoxide resistant HL-60 cell line.

A cell line partially resistant to dimethylsulfoxide (DMSO) was derived from the HL-60 cell line. Cycloleucine, theophylline, sodium butyrate and elevated levels of DMSO were found to induce myeloid differentiation in this cell line while TPA induced monocytic differentiation. The levels of myc RNA and the genomic structure of the c-myc proto-oncogene were found to be the same in HL-60 and the resistant cell line. Differentiation of the DMSO resistant line was accompanied by a reduction in myc RNA levels.

Base Composition↗
PubMed1984

Effect of hypolipidemic peroxisome proliferators on unscheduled DNA synthesis in cultured hepatocytes and on mutagenesis in Salmonella.

The peroxisome proliferators Wy-14,643, BR-931, nafenopin and ciprofibrate were tested in the primary hepatocyte culture-unscheduled DNA synthesis assay and in the Ames Salmonella microsome mutagenicity assay. The amount of unscheduled DNA synthesis (UDS) in hepatocytes was determined by quantifying the amount of [3H]thymidine incorporated into DNA in the presence of hydroxyurea after isolation of nuclei from hepatocytes treated with the test agent. Wy-14,643 and BR-931 induced unscheduled DNA synthesis in rat hepatocytes, whereas nafenopin and ciprofibrate had no effect. All of the peroxisome proliferators were negative in the Ames Salmonella assay.

Animals↗
PubMed1984

The natural history and dose-response characteristics of enzyme-altered foci in rat liver following phenobarbital and diethylnitrosamine administration.

Enzyme-altered foci (EAF) were induced in the liver of female rats by 70% partial hepatectomy (PH), followed by a single intragastric administration of diethylnitrosamine (DEN) at a dose of 10 mg/kg. The stability and response of these foci to various doses of the hepatic promoting agent, phenobarbital (PB), were studied. The number of gamma-glutamyltranspeptidase-positive (GGT+) EAF resulting from PH/DEN followed by PB (0.05%) administration for 1 week, 2 weeks, 1 month, 2 months, 3 months or 4 months did not significantly change when the administration of the promoting agent was followed by a 6-month period of a diet containing no PB. These data demonstrate the stability of the foci induced by the PH/DEN/PB regimen and indicate that the increased number of foci resulting from PB promotion in the absence of overt hepatic necrosis are not reversible on removal of the promoting stimulus. Chronic administration of dose levels of PB below 0.001% in the diet failed to demonstrate an increase in the number of EAF over the number in the control animals not promoted with PB. A linear increase in the number of EAF was observed when rats were chronically fed doses of PB ranging between 0.001% and 0.05% in the diet, whereas diet concentrations of PB greater than 0.05% did not result in any further increase in the number of EAF. The number of EAF resulting from PH/DEN followed by 0.05% PB in the diet increased during the first 3-4 months of promotion. Thereafter, the number of foci did not change despite the continued administration of PB for as long as 8 months. These data suggest the presence of an apparent threshold (no effect level) for promotion by PB and demonstrate the presence of a maximal response of EAF to this promoting agent after initiation by a single dose of DEN.

Animals↗
PubMed1983

Translational and pretranslational control of ornithine aminotransferase synthesis in rat liver.

The mitochondrial matrix enzyme, ornithine aminotransferase, is induced in rat liver by the administration of a diet high in protein and by glucagon. The rate of synthesis of the enzyme is increased 100-fold in the livers of rats maintained on a 60% relative to a 0% protein diet, whereas the levels of functional and hybridizable mRNA measured by in vitro translation and through the use of a cloned cDNA probe increased by only 2- to 6-fold and 2- to 3-fold, respectively. Under conditions of glucagon induction that resulted in a 10- to 12-fold increase in the rate of enzyme synthesis, the relative level of functional ornithine aminotransferase mRNA increased by only 2-fold, and the level of hybridizable mRNA actually decreased. The rate of polypeptide chain elongation and the relative number of ornithine aminotransferase nascent chains on polysomes were 2-fold and 23-fold greater, respectively, in hepatocytes derived from 60% relative to 0% protein-fed rats. Using these data, a 23-fold increase in the translational efficiency of the mRNA was calculated. This increase, along with a 2-fold increase in the mRNA level, completely account for the 40-fold increase in the rate of ornithine aminotransferase synthesis observed in hepatocytes derived from 60% protein-fed rats. We conclude that ornithine aminotransferase synthesis is regulated at both a translational and a pretranslational level in rat liver.

Animals↗
PubMed1983

Regulation of ornithine aminotransferase mRNA levels in rat kidney by estrogen and thyroid hormone.

The regulation of the mitochondrial matrix enzyme, ornithine aminotransferase, by estrogen and triiodothyronine (T3) in rat kidney was examined using a cloned cDNA probe and in vitro translation of poly(A+) RNA. After a single, acute dose of either 17 beta-estradiol or T3, the rate of enzyme synthesis and the levels of translatable and hybridizable ornithine aminotransferase mRNA all increase in parallel. Levels of hybridizable mRNA were estimated by hybridization of randomly 32P-labeled RNA to filter-bound plasmid DNA. Maximal levels of induction by estrogen and T3 were about 15- and 3-fold, respectively. Lag times of at least 5 h and less than 3 h were observed for induction by T3 and estrogen. T3 and estrogen exert a synergistic effect in increasing ornithine aminotransferase mRNA levels. 16 h after T3 administration and 24 h after estrogen administration, a 1.6- and 13-fold increase in mRNA levels were observed. Both of these treatments in combination for the indicated time periods resulted in a 21-fold increase in ornithine aminotransferase mRNA. From the mRNA accumulation curves, half-lives of 10 to 14 h and 12 to 16 h were estimated for the mRNA after estrogen and T3 induction, respectively. These similar half-lives suggest that an increase in the rate of mRNA production is primarily responsible for the induction observed after estrogen administration.

Animals↗
PubMed1983

Inability of red beet betalain pigments to initiate or promote hepatocarcinogenesis.

A short-term bioassay was used to determine the ability of red-beet betalain pigments to initiate or promote hepatocarcinogenesis in rat liver. Female Sprague-Dawley rats were partially hepatectomized and separated into nine groups (6-11 animals/group). Four of the groups were treated with betacyanin pigment preparations (betacyanin solution after fermentation, 50 mg/kg; pure betanin, 50 mg/kg; degraded betanin, 50 mg/kg; a betacyanin diet containing 2000 ppm/kg) to evaluate their ability to initiate hepatocarcinogenesis. N-Nitrosodiethylamine (NDEA: 10 mg/kg) was used for the positive control. Another group, previously initiated with NDEA, received daily a betacyanin solution (100 ppm; 3.5 mg/rat/day) to determine the pigment's ability to promote NDEA hepatocarcinogenesis in comparison with positive and negative controls treated respectively with and without a promoting agent (0.5% phenobarbital in the diet). Animals were killed after month 6 (promotion test) or 8 (initiation test). Liver sections were stained with haematoxylin and eosin and for gamma-glutamyl transpeptidase (GGT) activity. The number of enzyme-altered foci and the percentage of liver volume so affected, were determined for each group, by scoring for GGT. Comparison of the results obtained for the experimental groups with those for positive and negative control groups indicated that the betacyanin pigments tested in this assay did not initiate or promote hepatocarcinogenesis in rat liver. These findings provide further evidence that betalain colourants may be viable alternatives for synthetic dyes currently used as food additives.

Animals↗
PubMed1983

Chemicals and cancer: initiation and promotion.

What happens during the latency period in tumorigenesis--the interval between exposure to a carcinogen and development of detectable neoplastic changes? A two-step process has been delineated: initiation, which is apparently irreversible and occurs at any carcinogen dose level, and promotion, which is dose- and time-dependent and thus may be a reversible step in tumor development.

Alcoholic Beverages↗
PubMed1983

Consequences of altered poly(ADP-ribose) metabolism on hepatocyte functions in vitro.

Cultured hepatocytes derived from adult rats were used to determine the consequences of altered poly(ADP-ribose)-metabolism on DNA repair and the expression of hepatocellular functions in vitro. Inhibition of poly(ADP-ribose)-biosynthesis affected the process of DNA repair in response to carcinogens at more than one single step. The expression of two fetal enzymes, gamma-glutamyl transpeptidase and the K-(111) type isozyme of pyruvate kinase, was inhibited in hepatocytes in which poly(ADP-ribose)-biosynthesis was suppressed with 3-aminobenzamide or other inhibitors. Our data show that cellular functions as diverse as DNA repair and gene expression are affected by the same experimental manipulations of poly(ADP-ribose)-metabolism in the same cell. This suggests that poly(ADP-ribose)-modification of chromatin proteins affects a mechanism which is involved in the regulation of more than one chromatin function.

Aminobenzoates↗
PubMed1982

In vitro synthesis and processing of a precursor to ornithine aminotransferase.

Poly(A)+ RNA was isolated from liver-free polysomes of rats maintained on a 60% casein diet by sodium dodecyl sulfate-phenol-chloroform extraction and oligo(dT)-cellulose chromatography. Poly(A)+ RNA translated in a rabbit reticulocyte lysate system produced a polypeptide of 49,000 daltons that was immunoprecipitated by monospecific, affinity-purified IgG antibodies to ornithine aminotransferase (ornithine-oxo acid aminotransferase, EC 2.6.1.13). This polypeptide is 6,000 daltons larger than mature ornithine aminotransferase when electrophoresed on sodium dodecyl sulfate polyacrylamide gels. One-dimensional peptide mapping demonstrated that this 49,000-dalton polypeptide is structurally related to ornithine aminotransferase. Furthermore, it can be processed to a polypeptide of 43,000 daltons by a rat liver mitochondrial fraction. We have concluded that this polypeptide is a precursor to ornithine aminotransferase.

Animals↗
PubMed1982

ADP-ribosyltransferase activity in cultured hepatocytes. Interactions with DNA repair.

A rapid increase in ADP-ribosyltransferase activity was observed when freshly isolated hepatocytes derived from adult rats were established in primary monolayer culture. (ADP-ribose)n-degrading activity remained constant over a period of 48 h of culture. Inhibition of ADP-ribosyltransferase activity with pyridine derivatives, 3-aminobenzamide, theophylline, or thymidine, was accompanied by an enhanced DNA repair synthesis in response to the direct-acting carcinogen, methyl methanesulfonate, or UV irradiation. Three aminobenzamides differing only in the position of the amino group exhibited the same structure-activity relationship in regard to their action on DNA repair synthesis and ADP-ribosyltransferase. Spermine treatment of hepatocytes apparently had an inverse effect on both these cellular functions. The removal of DNA strand breaks following methyl methanesulfonate treatment was accelerated by inhibitors of ADP-ribosyltransferase. The results suggest that ADP-ribosylation interacts with late stages in the process of DNA repair. This interaction apparently is dependent on the nature of damage imposed on chromatin since repair synthesis in response to a number of carcinogens is unaffected by inhibitors of ADP-ribosyltransferase.

Animals↗
PubMed1982

Cloning of DNA complementary to ornithine aminotransferase mRNA.

Free polysomes were isolated from the livers of rats maintained on a 60% casein diet to induce ornithine aminotransferase mRNA. Ornithine aminotransferase-synthesizing polysomes were immunoadsorbed using monospecific, affinity-purified antibody and Staphylococcus aureus cells. Poly(A+)RNA prepared from these polysomes by oligo(dT)-cellulose chromatography was used as a template for the synthesis of double-stranded cDNA by reverse transcriptase. Using the deoxyguanosine-5'-triphosphate-deoxycytidine-5'-triphosphate tailing method and pBR322 as a vector, recombinant molecules were produced and used to transform Escherichia coli. Two clones containing DNA complementary to ornithine aminotransferase mRNA were identified by colony hybridization and hybrid-arrest translation. A partial restriction endonuclease map of the ornithine aminotransferase cDNA inserts was constructed which spanned 1066 base pairs.

Animals↗
PubMed1982

The natural history of neoplastic development: the relation of experimental models to human cancer.

The natural history of the development of neoplasia in experimental systems may be separated into at least three different stages, those of initiation, promotion and progression. Evidence for such distinct stages has been demonstrated in at least half a dozen different experimental systems. The stage of promotion is that stage most easily modulated. The actions of promoting agents are reversible and only effective above certain threshold levels of the promoting agent. This is in contrast to the stage of initiation, which can be induced at any dose of the carcinogenic agent in an irreversible manner. Agents exhibiting both initiating and promoting activities are termed complete carcinogens while incomplete carcinogens are those capable only of initiation. Promoting agents do not initiate but may promote cells initiated by ambient environmental means, giving the appearance of complete carcinogens in standard bioassay procedures. The stages of initiation and promotion have been extensively studied in skin and liver carcinogenesis and show almost identical characteristics. A variety of promoting agents in the human environment have been demonstrated both by experimental and epidemiologic methodologies. The importance of an understanding of tumor promotion in relation to the prevention of human cancer is emphasized.

Animals↗
PubMed1982

Polyamine degradation in foetal and adult bovine serum.

1. Using protein-separative chromatographic procedures and assays specific for putrescine oxidase and spermidine oxidase, adult bovine serum was found to contain a single polyamine-degrading enzyme with substrate preferences for spermidine and spermine. Apparent Km values for these substrates were approx. 40 microM. The apparent Km for putrescine was 2 mM. With spermidine as substrate, the Ki values for aminoguanidine (AM) and methylglyoxal bis(guanylhydrazone) (MGBG) were 70 microM and 20 microM respectively. 2. Bovine serum spermidine oxidase degraded spermine to spermidine to putrescine and N8-acetylspermidine to N-acetylputrescine. Acrolein was produced in all these reactions and recovered in quantities equivalent to H2O2 recovery. 3. Spermidine oxidase activity was present in foetal bovine serum, but increased markedly after birth to levels in adult serum that were almost 100 times the activity in foetal bovine serum. 4. Putrescine oxidase, shown to be a separate enzyme from bovine serum spermidine oxidase, was present in foetal bovine serum but absent from bovine serum after birth. This enzyme displayed an apparent Km for putrescine of 2.6 microM. The enzyme was inhibited by AM and MGBG with Ki values of 20 nM. Putrescine, cadaverine and 1,3-diaminopropane proved excellent substrates for the enzyme compared with spermidine and spermine, and N-acetylputrescine was a superior substrate to N1- or N8-acetylspermidine.

Animals↗