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Biomedical subjects

P Bentley

Publications and source records attributed to P Bentley.

At least 73 records · Page 4Linked to original sources
PubMed1988

Electroporation of cultured adult rat hepatocytes with the c-myc gene potentiates DNA synthesis in response to epidermal growth factor.

The human c-myc gene was introduced and transiently expressed in adult rat hepatocyte cultures by the technique of electroporation and its effect on DNA synthesis was examined. Epidermal growth factor (EGF) has been found to stimulate a wave of DNA synthesis in electroporated rat hepatocytes. Hepatocyte cultures electroporated with the c-myc gene showed a potentiation of this EGF effect exhibiting rates of DNA synthesis up to 50% greater than those of control electroporated cultures, as determined by [3H]thymidine labeling of cell nuclei. This potentiation was dependent on the amount of c-myc DNA transfected. The potentiation was due neither to an alteration in the dose-response of the stimulatory effect of EGF nor to a change in the time course of the DNA synthesis wave.

Animals↗
PubMed1988

Workplace wellness participation and the becoming of self.

This paper provides a sociological examination of workplace wellness participation as a process that occurs in two stages or levels. The existential model of self provides the theoretical orientation for this examination, and data are presented from an ethnographic study of a large workplace wellness program. The first stage or level of participation involves the establishment of a sense of competence. Competence refers to the perceived ability to 'fit in' with the program, to master the often subtle skills required for membership in the class. Once a minimal sense of competence is established, the employee may decide to join by viewing participation either as an extension of a commitment to wellness, or as a vehicle for experimenting with or establishing a new style of self, the identity of a 'well person' so highly valued in contemporary western culture. The dynamics of workplace wellness participation illustrate a more general cultural trend towards health-as-accomplishment.

Adult↗
PubMed1988

Stimulation of DNA synthesis but not of peroxisomal beta-oxidation by nafenopin in primary cultures of marmoset hepatocytes.

The effects of the peroxisome proliferator nafenopin upon primary cultures of marmoset hepatocytes have been investigated and compared to those on cultured rat hepatocytes. Nafenopin did not induce peroxisomal beta-oxidation or peroxisome proliferation but did induce replicative DNA synthesis. These findings demonstrate that peroxisome proliferation and mitogenicity are two independent properties of nafenopin and question the widely held view that primates are generally insensitive to the effects of peroxisome proliferators.

Animals↗
PubMed1987

Investigations on the mechanism of liver tumour induction by peroxisome proliferators.

Further understanding of the mechanism by which peroxisome proliferators induce liver tumours is essential to assessing the risks of such compounds to exposed humans. To this end the effects of nafenopin upon the liver have been investigated. Nafenopin was shown to induce certain drug metabolising enzymes, but sub-cellular fractions from induced animals did not form reactive metabolites which could be detected as mutagens. Nafenopin treatment slightly increased the rate of alkaline elution of hepatic nuclear DNA from polycarbonate filters. However, simultaneous administration of sodium glycolate to stimulate H2O2 production or pyrazole to inhibit catalase activity had no further effects. These findings demonstrate that nafenopin is not activated to a mutagen and argue against the hypothesis that indirect DNA damage as a result of excess H2O2 production is responsible for tumour induction.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1987

Long-term maintenance of hepatocytes in primary culture in the presence of DMSO: further characterization and effect of nafenopin, a peroxisome proliferator.

The addition of 2% dimethyl sulfoxide to adult rat hepatocytes cultured in a chemically defined medium at Day 1 after cell plating resulted in maintenance of the cytochrome P-450 content and the cyanide-insensitive palmitoyl-CoA beta-oxidation activity at 66 and 70% of the initial Day 1 values. The addition of phenobarbital, 3-methylcholanthrene, or nafenopin from Day 3 to Day 6 increased the contents of cytochrome P-450 to 128, 239, and 251%, respectively, compared to untreated controls at Day 3. In addition, nafenopin also caused a pronounced and time-dependent increase in palmitoyl-CoA beta-oxidation activity but was found to have only a weak stimulating effect on replicative DNA synthesis (2-fold) when compared to that of epidermal growth factor (6.5-fold). In the presence of dimethyl sulfoxide the hepatocyte cultures could be kept alive for more than 1 month. Exposure of such cultures to nafenopin from Day 1 do Day 37 resulted in survival which was even better than that of their untreated counterparts. This effect was accompanied by the appearance of abundant endoplasmic reticulum membranes and an increased number of peroxisomes.

Animals↗
PubMed1987

Reduced in vitro erythroid progenitor cell growth in bronchial cancer.

Peripheral blood and bone marrow were studied in 21 men with disseminated untreated bronchial cancer in an attempt to define abnormalities of erythropoiesis associated with the development of anaemia. Haemoglobin concentration at or below 13 g/dl was present in 13 cases. Marrow morphology was normal in all cases except one, in which small numbers of tumour cells were found. Clonal assay of erythroid progenitors showed a significant decrease in the number of BFU-E (p = 0.03) and CFU-E (p = 0.01) compared with cultures from normal marrow (12 subjects). The growth of granulocyte and macrophage progenitors (GM-CFCs) was similar in patients with bronchial cancer and normal subjects. When normal marrow was incubated in the presence of serum from bronchial cancer patients, no inhibitory factors could be detected either for BFU-E or CFU-E growth. In all patients circulating T8 numbers were significantly raised (p = 0.0002). Consequently, the median T4:T8 ratio in blood was 1.2, and this was significantly lower than the ratio of 1.7 found in 20 normal subjects (p = 0.036). In 18 patients the bone marrow T4:T8 ratio of 1.1 was significantly lower than the ratio of 2.9 found in seven normal subjects (p = 0.04). Total blood white cell counts, neutrophils, and monocyte numbers were also increased (p = 0.0001; p = 0.0001; p = 0.002).

Aged↗
PubMed1986

Species differences in the covalent binding of p-chloro-o-toluidine to DNA.

The covalent binding of p-chloro-o-toluidine to hepatic macromolecules was assessed in rats and mice. At all timepoints investigated covalent binding to DNA was most marked in mice, whilst binding to proteins was more pronounced in rats. Two major hydrophobic DNA-adducts were formed in both species. One of these was formed to a much greater extent (6-30 fold) in mice. Thus, species differences in the metabolism of p-chloro-o-toluidine could account for the fact that mice are more susceptible to the carcinogenic effects of this compound.

Animals↗
PubMed1986

Species differences in the toxicity of p-chloro-o-toluidine to rats and mice. Covalent binding to hepatic macromolecules and hepatic non-parenchymal cell DNA and an investigation of effects upon the incorporation of [3H] thymidine into capillary endothelial cells.

The interaction of p-[14C] chloro-o-toluidine with hepatic macromolecules of rats and mice has been investigated. At all time points after single administration the extent of binding decreased in the order protein greater than RNA greater than DNA in both species. The level of binding to mouse liver DNA was greater than that to rat liver DNA after both single and repeated administration. In vitro studies showed that mouse liver fractions catalysed the binding of p-chloro-o-toluidine to calf thymus DNA more readily than rat liver fractions. Conversely, binding to protein and RNA was more marked in the rat than in the mouse. Species differences in DNA repair rates were not observed. The results failed to demonstrate a preferential persistence of binding to mouse liver nonparenchymal cell DNA. Autoradiographic determinations did not demonstrate any effect of p-chloro-o-toluidine upon the incorporation of [3H] thymidine into subcutaneous capillary endothelial cells. The results suggest that different reactive metabolites are responsible for binding to DNA and protein, and that the pattern of reactive metabolites formed from p-chloro-o-toluidine in the mouse differs from that formed in rats.

Animals↗
PubMed1986

Pyruvate kinase isoenzymes in altered foci and carcinoma of rat liver.

Pyruvate kinase (PK) isoenzymes, rate limiting for the last steps of glycolysis, were studied in normal rat liver, putative preneoplastic foci, neoplastic nodules and hepatocellular carcinoma. These lesions were produced by an initiation-promotion protocol: treatment with a single dose of N-nitrosomorpholine (NNM) was followed by feeding diets containing phenobarbital (PB) or alpha-hexachlorocyclohexane (alpha-HCH), or basal diet. PK was demonstrated (i) by immunocytochemistry on histological sections with antibodies specifically directed against the L and M2 isoenzymes, (ii) by electrophoretic separation of isoenzymes in homogenates from liver and larger tumors, and (iii) by electrophoretic separation of isoenzymes in parenchymal and stromal cells isolated from liver and tumors. Immunocytochemistry showed decreases of L-PK (L-PK-) in hepatocytes of most of the foci, nodules and carcinomas. Most L-PK- foci showed increases in gamma-glutamyltransferase (gamma-GT) and epoxide hydrolase (EH). PB or alpha-HCH treatment further decreased expression of L-PK in foci, but not in normal liver. Cells and foci with enhanced L-PK (L-PK+) were also found after carcinogen treatment. These did not show increases of gamma-GT or EH or any distinct morphological alterations with the exception of some which were basophilic ('tigroid') in H and E stained sections. No L-PK+ tumors were found. We could not demonstrate the M2-type PK in parenchymal cells of liver or any of the lesions described above. This isoenzyme was restricted to stromal cells in normal rat liver and in all stages of carcinogenesis as shown by immunohistology and by electrophoresis of preparations from isolated cell populations. However, stromal cells from hepatocellular carcinomas exhibited a 3-fold increase of M2-PK compared with stromal cells from normal liver. These results do not support an isoenzyme shift from L to M2-PK in the course of malignant transformation of hepatocytes as suggested previously.

Animals↗
PubMed1985

Induction of hepatic drug-metabolising enzymes following treatment of rats and mice with chlordimeform.

We investigated the effects of the formamidine insecticide chlordimeform upon the activities of various hepatic drug metabolising enzymes in rats and mice. Chlordimeform treatment induced several enzyme activities. However, the extent of induction depended upon the activity studied, the sex of the animal and the species selected. Microsomal cytochrome P-450 content was elevated in both male and female rats and mice. Ethoxycoumarin O-deethylase activity was induced in male and female rats but not in mice, whilst ethylmorphine N-demethylase activity was elevated in mice, but not in rats. Benzo(a)pyrene hydroxylase activity was increased in female rats and mice, but not in males. UDP-glucuronyl transferase, glutathione S-transferase and microsomal epoxide hydrolase were induced in a dose-dependent manner in male rats, and female rats and mice, but not in male mice.

Amidines↗
PubMed1985

Metabolism of benzo(a)pyrene by subcellular fractions of rat liver: evidence for similar patterns of cytochrome P-450 in rough and smooth endoplasmic reticulum but not in nuclei and plasma membrane.

Since our earlier work (P. Stasiecki, F. Oesch, G. Bruder, E.D. Jarasch, and W.W. Franke, Eur. J. Cell Biol., 21: 79-92, 1980) had shown that carcinogen-metabolizing monooxygenase activity was present in almost all investigated cellular membranes, the possibility of differential control of the various metabolic pathways in the individual cellular membranes arose. Using high pressure liquid chromatography we have now studied the benzo(a)pyrene metabolites formed by rough and smooth endoplasmic reticulum, nuclei, and plasma membrane as well as mitochondrial fractions and investigated the metabolic cooperation between the monooxygenases and epoxide hydrolase in these fractions. Since various cytochrome P-450 isozymes catalyze the oxidative attack on the benzo(a)pyrene molecule at defined preferential sites, this analysis also provides an indirect trace of potential differences in the pattern of cytochrome P-450 isozymes present in the individual membranes. The metabolic profiles produced by the two most active fractions, smooth and rough endoplasmic reticulum, were very similar to each other but different from those produced by the other three preparations. The metabolite pattern produced by incubations containing nuclear fractions differed slightly from that produced by the fractions of endoplasmic reticulum, but plasma membrane and mitochondria produced markedly different patterns. Since the similarity of the benzo(a)pyrene metabolite pattern produced by the smooth and rough endoplasmic reticulum suggested similar cytochrome P-450 isozyme patterns in these two subfractions, they were further investigated by the use of selective inducers as well as a broad spectrum substrate, 7-ethoxy-coumarin, in the absence and presence of selective inhibitors. Treatment of animals with trans-stilbene oxide or phenobarbital (a) increased the total amount of metabolites per protein mass and time, (b) changed the pattern of metabolites, but (c) induced a pattern of metabolites which was again very similar in rough and smooth endoplasmic reticulum. Even more distinct changes were found following treatment with 3-methylcholanthrene or beta-naphthoflavone. Both of these compounds (a) preferentially induced the activity of rough endoplasmic reticulum, (b) changed the profile of metabolites, but (c) again did not disturb the similarities of the benzo(a)pyrene metabolite pattern between both fractions.(ABSTRACT TRUNCATED AT 400 WORDS)

7-Alkoxycoumarin O-Dealkylase↗
PubMed1984

Induction of cytosolic and microsomal epoxide hydrolases by the hypolipidaemic compound nafenopin in the mouse liver.

The repeated oral administration of nafenopin, a hypolipidaemic compound, at a dose of 100 mg/kg to male C57BL/6, DBA/2, Balb c and C3H mice caused an increase in the specific activity of liver cytosolic epoxide hydrolase, the activity of microsomal epoxide hydrolase was also increased in all except the C3H mice. The dose dependence and the specificity of this induction was investigated in male DBA/2 mice. In the range of 10-200 mg/kg nafenopin the induction of the two hydrolase activities was found to increase with increasing doses of the test compound. Two other cytosolic enzyme activities, lactate dehydrogenase and glutathione S-transferase, remained essentially unchanged within the dose range investigated.

Animals↗
PubMed1984

Inhibitory effect of nafenopin upon the development of diethylnitrosamine-induced enzyme-altered foci within the rat liver.

The effect of nafenopin and phenobarbitone upon the distribution of gamma-glutamyltranspeptidase activity and epoxide hydrolase antigenic sites in the liver and upon the development of enzyme-altered foci during hepatocarcinogenesis have been compared. Phenobarbitone induced gamma-glutamyltranspeptidase activity in perilobular hepatocytes. Nafenopin did not alter the distribution of this enzyme. Both compounds appeared to induce epoxide hydrolase; phenobarbitone increased the enzyme content of centrilobular cells, whilst nafenopin altered immunostaining mainly in portal regions. Hepatic lesions were induced by treating one day-old rats with diethylnitrosamine. Phenobarbitone and nafenopin were then administered in the diet upon weaning. Animals were killed after either 2, 4 or 8 weeks feeding and liver sections were stained for the two enzymes. Only sections from nitrosamine-treated animals contained enzyme-altered foci. In general, gamma-glutamyltranspeptidase-containing foci stained also for epoxide hydrolase; but many hydrolase-positive foci did not stain for gamma-glutamyltranspeptidase activity. Phenobarbitone treatment stimulated the formation of enzyme-altered foci. This effect was more marked in male animals. Nafenopin treatment suppressed the development of foci at all time points, such that less hepatic lesions were seen than in animals which received only diethylnitrosamine. The results cast doubt upon the generality of gamma-glutamyltranspeptidase as a marker for preneoplastic lesions within the liver.

Animals↗
PubMed1984

Use of primary cultures of adult rat hepatocytes to investigate mechanisms of action of nafenopin, a hepatocarcinogenic peroxisome proliferator.

The effect of nafenopin upon primary cultures of adult rat hepatocytes has been investigated. Nafenopin treatment resulted in a proliferation of peroxisomes within the cultured cells. This proliferation was the result of an increase in both the number and size of the peroxisomes. Nafenopin treatment also caused an increased level of thymidine incorporation into the cultures, which was a consequence of replicative DNA synthesis rather than DNA repair. Finally, nafenopin appeared to delay the appearance of gamma-glutamyltranspeptidase activity within the cultured cells. Consequently three effects of nafenopin upon the liver were reproduced using monolayers of adult rat hepatocytes, which suggests that this culture system may be useful to further investigate the molecular processes underlying peroxisome proliferation, and their involvement in the hepatocarcinogenicity of peroxisome proliferators.

Animals↗
PubMed1984

The hematological response to continuous ambulatory peritoneal dialysis.

Over the first three months of continuous ambulatory peritoneal dialysis (CAPD) the level of hemoglobin (Hb) rises significantly in most patients. To elucidate this further we studied the hematological response over 3 months of 8, previously non-transfused new patients treated with CAPD. Mean Hb rose by +2.78 g/dl (P less than 0.02). Mean RCM rose by 284 ml (37.7%) (P less than 0.05) and 3.7 ml/kg (29.6%) (P less than 0.05). PV fell relative to BW only, by -8.6 ml/kg (P less than 0.05). There was no significant change in serum vitamin B12 or folate concentrations or evidence of hemolysis. Plasma ferritin fell in all patients, but hematological changes of iron deficiency appeared in only one. Bio-assayable erythropoietin (EPO) levels were generally in the normal range, but inappropriately low for the degree of anemia. EPO did not change significantly apart from in two patients, one with polycystic disease. These results indicate that over the initial 3 months of therapy the majority of CAPD patients have a rise in Hb, due mainly to a rise in RCM, unrelated to changes in serum EPO level.

Adult↗
PubMed1983

Purification and characterization of a new cytosolic glutathione S-transferase (glutathione S-transferase X) from rat liver.

A hitherto unknown cytosolic glutathione S-transferase from rat liver was discovered and a method developed for its purification to apparent homogeneity. This enzyme had several properties that distinguished it from other glutathione S-transferases, and it was named glutathione S-transferase X. The purification procedure involved DEAE-cellulose chromatography, (NH4)2SO4 precipitation, affinity chromatography on Sepharose 4B to which glutathione was coupled and CM-cellulose chromatography, and allowed the isolation of glutathione S-transferases X, A, B and C in relatively large quantities suitable for the investigation of the toxicological role of these enzymes. Like glutathione S-transferase M, but unlike glutathione S-transferases AA, A, B, C, D and E, glutathione S-transferase X was retained on DEAE-cellulose. The end product, which was purified from rat liver 20 000 g supernatant about 50-fold, as determined with 1-chloro-2,4-dinitrobenzene as substrate and about 90-fold with the 1,2-dichloro-4-nitrobenzene as substrate, was judged to be homogeneous by several criteria, including sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, isoelectric focusing and immunoelectrophoresis. Results from sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and gel filtration indicated that transferase X was a dimer with Mr about 45 000 composed of subunits with Mr 23 500. The isoelectric point of glutathione S-transferase X was 6.9, which is different from those of most of the other glutathione S-transferases (AA, A, B and C). The amino acid composition of transferase X was similar to that of transferase C. Immunoelectrophoresis of glutathione S-transferases A, C and X and precipitation of various combinations of these antigens by antisera raised against glutathione S-transferase X or C revealed that the glutathione S-transferases A, C and X have different electrophoretic mobilities, and indicated that transferase X is immunologically similar to transferase C, less similar to transferase A and not cross-reactive to transferases B and E. In contrast with transferases B and AA, glutathione S-transferase X did not bind cholic acid, which, together with the determination of the Mr, shows that it does not possess subunits Ya or Yc. Glutathione S-transferase X did not catalyse the reaction of menaphthyl sulphate with glutathione, and was in this respect dissimilar to glutathione S-transferase M; however, it conjugated 1,2-dichloro-4-nitrobenzene very rapidly, in contrast with transferases AA, B, D and E, which were nearly inactive towards that substrate.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acids↗
PubMed1983

Epoxide hydrolase activity in isolated peroxisomes of mouse liver.

Using trans-stilbene oxide as substrate, the subcellular distribution of epoxide hydrolase was investigated in livers from DBA/2 mice. The highest specific activities were found in cytosolic and light mitochondrial fractions. Isopycnic subfractionation of the light mitochondrial fraction showed that the organelle-bound trans-stilbene oxide hydrolase is localized in peroxisomes.

Animals↗