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R H Hinton

Publications and source records attributed to R H Hinton.

At least 19 recordsLinked to original sources
PubMed2001

Effects on male rats of di-(2-ethylhexyl) phthalate and di-n-hexylphthalate administered alone or in combination.

The effects of phthalate esters of branched chain alcohols, typified by di-(2-ethylhexyl)phthalate (DEHP) differ from those of esters of straight chain alcohols typified by di-n-hexyl phthalate (DnHP). The former induce liver enlargement and proliferation of hepatic peroxisomes, while the latter cause no peroxisome proliferation but cause fat accumulation in the liver. Both classes of phthalate esters are hypolipidaemic and cause thyroid changes associated with an increased rate of thyroglobulin turnover. As phthalate esters are used as mixtures, we have examined the effect of mixtures of the compounds. Groups of five male Wistar albino rats were administered either control diet or diets containing either 10000 ppm of DEHP, 10000 ppm of DnHP or 10000 ppm DEHP plus 10000 ppm DnHP for 14 days. Rats receiving diets containing DEHP showed the expected increase in relative liver weight, in "peroxisomal" fatty acid oxidation and in CYP4A1. Serum triglyceride and serum cholesterol were also reduced, and the thyroid showed the histological changes mentioned above. Rats consuming diets containing DnHP showed no increase in relative liver weight and no induction of peroxisomal fatty acid oxidation or CYP4A1. However, there was a marked accumulation of fat in the liver. The fall in serum cholesterol was similar to that in rats treated with DEHP, but the fall of serum triglyceride was more pronounced. Thyroidal changes were again observed. In general, changes in rats treated with a mixture of DEHP and DnHP were very similar to those found with rats treated with DEHP alone. The liver was enlarged, and peroxisomal fatty acid oxidation and CYP4A1 were both induced. The amount of fat in the liver was much less than in rats receiving DnHP alone. Thyroid changes were similar to those in rats receiving the individual compounds. The effect on serum cholesterol seemed additive, but the levels of serum triglyceride were intermediate between the groups receiving the single compounds.

Animals↗
PubMed1999

Liver poly(ADP-ribose)polymerase is resistant to cleavage by caspases.

In hepatocytes the DNA repair enzyme poly(ADP-ribose)polymerase (PARP) is not proteolytically cleaved during apoptosis. The reason for this was investigated using a cell-free system that consisted of isolated nuclei from hepatocytes or thymocytes and cytosolic extracts from hepatocytes or thymocytes undergoing apoptosis. It was found that liver PARP is resistant to proteolytic cleavage by the caspases present in the cytosolic extracts. Furthermore, liver PARP was not cleaved by recombinant human caspase-3. It is concluded that PARP proteolysis cannot be used as a marker for hepatocyte apoptosis.

Animals↗
PubMed1998

Fas-mediated apoptosis in mouse hepatocytes involves the processing and activation of caspases.

The mechanism of Fas antigen-induced hepatocyte apoptosis was investigated. Using a monoclonal antibody directed against the Fas antigen, apoptosis was induced in freshly isolated murine hepatocytes within 90 minutes of antibody addition as assessed by plasma membrane bleb formation, chromatin condensation, and DNA fragmentation. Pretreatment of the cells with the caspase inhibitors, N-acetyl-Asp-Glu-Val-Asp aldehyde (Ac-DEVD-CHO), benzyloxycarbonyl-Val-Ala-DL-Asp-fluoromethylketone (Z-VAD-FMK), or Z-Asp-2,6-dichlorobenzoyloxymethylketone inhibited anti-Fas-mediated apoptosis. Likewise, the serine protease inhibitors, N-tosyl-L-phenyl chloromethyl ketone (TPCK) and 3,4-dichloroisocoumarin (DCI), prevented apoptosis, whereas N-tosyl-L-lysine chloromethyl ketone (TLCK), Ac-Leu-Leu-L-norleucinal, Ac-Leu-Leu-L-methional, and trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane were without effect. Examination of CED-3/caspase-3-related caspases revealed that pro-caspases-3 (CPP32) and -7 (Mch-3alpha) were rapidly processed after Fas antigen stimulation. Caspase-7 was further cleaved to form the catalytically active subunits. In contrast, the p17 subunit of caspase-3 was not detected, indicating slow formation or rapid degradation. The activation of CED-3-related caspases was further confirmed by an increase in the rate of Z-DEVD-7-amino-4-trifluoromethylcoumarin (Z-DEVD-AFC) hydrolysis that was sensitive to Ac-DEVD-CHO and was inhibited by pretreatment of the cells with TPCK but not by DCI. In contrast, no increase in the rates of hydrolysis of Z-YVAD-AFC, a substrate for caspase-1, was detected. Investigation of the in situ proteolytic cleavage of the CED-3 related caspases substrate, poly(ADP-ribose) polymerase, revealed that this protein was not degraded in hepatocytes undergoing Fas-mediated apoptosis. Taken together, our results show that processing of caspases, in particular, caspases-7 and -3, occurs during Fas-induced apoptosis of mouse hepatocytes and suggest a role of these proteases as well as serine protease(s) in the apoptotic response.

Animals↗
PubMed1997

Bioanalysis of p-trifluoromethylmandelic acid and Mosher's acid by chiral gas chromatography and fluorine nuclear magnetic resonance to study chiral inversion: application to rat urine samples.

Methods for the nuclear magnetic resonance and gas chromatographic analysis of the enantiomers of p-trifluoromethylmandelic acid (p-TFM) and Mosher's acid (alpha-methoxy-alpha-(trifluoromethyl)phenylacetic acid) present in rat urine samples are described. Gas chromartography was performed using cyclodextrin capillary columns with both compounds analysed following derivatisation with methanolic HCl. Nuclear magnetic resonance was performed directly on the untreated urine samples following addition of beta-cyclodextrin. The methods were suitable for the determination of the individual enantiomers of the analytes in urine. Analysis of the rat urine samples indicated that the p-TFM had undergone a unidirectional enantiomeric interconversion in vivo, while the enantiomers of Mosher's acid were excreted unchanged.

Animals↗
PubMed1997

Hepatic and associated response of rats to pregnancy, lactation and simultaneous treatment with butylated hydroxytoluene.

This paper describes changes in the livers of rats fed diets containing butylated hydroxytoluene (BHT) over two generations in two separate studies. BHT did not produce tumours when tested for carcinogenicity in several studies by the conventional way. However, when BHT was given to rats in a two-generation carcinogenicity study, a high incidence of hepatic tumours was found in males but not in female rats of the F1 generation. A sequential study has been carried out to gain an insight into this unexpected finding, paying particular attention to the perinatal period. In the dose-ranging study designed to assess the tolerance of rats to BHT, groups of male and female rats (F0 generation) were fed diets calculated to deliver 0, 500, 750 and 1000 mg/kg body weight/day. Following a loading period of 5 wk the rats were mated. The BHT content of the diet was not adjusted during pregnancy and lactation. Owing to the normal increase in food consumption during lactation, intakes peaked at double the nominal value by 21 days after the birth of pups. At this time the pups (F1) were weaned onto control diet and maintained on it for 4 wk. At birth, the body weights of pups from the BHT-treated dams were comparable to those of the controls but at weaning the body weights of the pups from all three dose levels were less than those of the controls. At the termination of the experiment (4 wk after weaning), the pups from BHT-treated dams still weighed less than those from untreated controls. In the main experiment the F0 generation were fed 0, 25, 100 and 500 mg/kg body weight/day. Their offspring (F1 generation) were weaned on diets containing the same amount of BHT as the respective parents, apart from the group given the highest dose level (500 mg/kg body weight/day). This dose level was reduced to 250 mg/kg body weight/day at weaning in order to conform with previously published findings. The pups from the dams given the highest dose level were maintained on a dietary concentration of 250 mg/kg body weight/day for the entire study. A group of age-matched non-pregnant females was also studied and the results obtained compared with those from pregnant dams. Pups from all groups were examined at day 20 of gestation, at weaning (21 days after birth), and at 4 and 22 wk post-weaning. There were no effects on fertility and no increase in foetal abnormalities at any dose of BHT. Dams receiving BHT at a nominal dose of 500 mg/kg body weight/day showed liver enlargement accompained by induction of pentoxyresorufin O-depentylase and glutathione S-transferase, and proliferation of the endoplasmic reticulum. Pups from these dams were of the same weight at birth as controls but lost weight during the lactation period. This deficit was not recovered by the time the experiment was terminated. Hence, in two independent studies, the only significant finding in rats treated with BHT in utero and during lactation was that the weight gain of pups during lactation was less than expected when dams received at least 500 mg BHT/kg body weight/day. The body weight of pups did not return to normal following a return to a control diet for 4 wk. It is postulated that the retardation in weight gain of the pups could be due to inadequate milk production.

Animals↗
PubMed1996

Influence of the gut microflora and of biliary constituents on morphological changes in the small intestine in obstructive jaundice.

Increased amounts of intestinal endotoxin are absorbed in obstructive jaundice. The precise mechanism is not known but the increased absorption may arise from alterations in the luminal contents, in the intestinal flora, in the gut wall or in interactions between all three. To examine the effects of the intestinal flora we have compared the morphological changes in the small intestine in obstructive jaundice in germ free and conventional rats while the effects of bile constituents have been examined by addition of bile constituents to the diet of bile duct ligated rats. Changes in the intestine were examined, histologically, by enzyme histochemistry, and by transmission and scanning electron microscopy. The results showed no differences in response between germ free and conventional rats. Feeding of diets containing bile salts exacerbated the lesion. Feeding of diets containing cholesterol, however, reduced the degree of intestinal changes produced by cholestasis and completely antagonised the increase in damage caused by feeding of bile salts.

Animals↗
PubMed1991

Immunotoxicity of tri-n-butyltin oxide (TBTO) and tri-n-butyltin chloride (TBTC) in the rat.

In a 1-month feeding trial, pure and commercial tri-n-butyltin oxide (TBTO) and tri-n-butyltin chloride (TBTC) were fed to rats at concentrations of 5 ppm and 25 ppm. At all times, the mean body weight gain and the food consumption was significantly less in rats treated with 25 ppm pure TBTO or pure TBTC as compared to control rats or rats receiving commercial TBTO. Histological examination of the thymus of rats treated for 7 days with TBTO showed atrophy with severe lymphocytic depletion in the cortex. After 28 days of exposure, most of the lesions reversed and the thymus became markedly smaller than in control rats, both in absolute terms and in relation to body weight. Seven days of exposure to TBTO increased liver weight but this change was reversed during a further 3-week exposure. Tin concentrations were the highest in livers and kidneys. Concentrations in the thymus were less than one-fifth of hepatic values. Changes in the rats treated with the commercial TBTO were very similar. Rats treated with TBTC showed lower tin levels and less immunotoxicity as compared to those treated with TBTO.

Animals↗
PubMed1991

Evidence for and possible mechanisms of non-genotoxic carcinogenesis in rodent liver.

Doses of chemicals which induce hepatocellular necrosis usually induce hepatic tumours if the dosing is frequent and is maintained for long periods. Such necrosis is usually evident within 48 h of the first administration. Similarly, chemicals that lead to marked proliferation of peroxisomes in the liver also usually induce hepatic tumours on pretracked regular dosing. For both of these phenomena failure to produce a certain level of effect, or to maintain it for sufficiently long periods, can result in the observation of a non-carcinogenic response. The exact dose/time requirements for carcinogenicity have not been defined and may be species/strain/sex-specific. Some chemicals induce liver enlargement and mitogenesis in the absence of overt hepatotoxic effects. The early phases of hepatomegaly are associated with mitogenic effects that can be measured as cells in S-phase within the first few days of administration. The later stages of hepatomegaly appear to be associated more with cellular hypertrophy. Both effects appear to be threshold-related. Further, sustained hepatomegaly is associated with proliferation of SER and the induction of a range of liver enzymes. These changes (mitogenesis, hepatomegaly, enzyme induction), in isolation, are less definitive indicators of carcinogenicity, but they occur for a sufficient number of liver-specific carcinogens that their role as early indicators is worthy of confirmed study. The major area of study required for all possible early markers of hepatocarcinogenicity is to establish the dose and time dependence of these changes in relation to the eventual appearance of tumours. Finally, the specificity of all these markers require evaluation by the study of appropriate non-carcinogens.

Animals↗
PubMed1990

Hepatic nuclear and cytoplasmic effects following intermittent feeding of rats with di(2-ethylhexyl) phthalate.

The effects on rats of intermittent feeding with the peroxisome proliferator and hepatocarcinogen di(2-ethylhexyl) phthalate (DEHP) have been examined. Male Wistar rats were fed for alternate 7-day periods diets containing 20,000 ppm DEHP or the control diet. The rats were examined 3 days after the start or recommencement of administration of the DEHP-containing diet or after 7 days on the control diet. After the commencement or recommencement of feeding with DEHP the expected increases in liver weight and in the number of peroxisomes were found. The increase in liver: body-weight ratio in response to administration of DEHP-containing diets was greater in rats that had been previously exposed to the compound, but re-administration of DEHP had a less marked effect on the increase in peroxisome number. Morphometric analysis showed that administration of DEHP-containing diets resulted in an increase in cell number in the liver and that a fall in the cell number occurred after the rats had been returned to the control diet for 7 days. Analysis of nuclear size gave results consistent with an increase in tetraploid hepatocytes after treatment with DEHP which was reversed when the rats were returned to control diet.

Animals↗
PubMed1989

Sodium arsenite induced alterations in bilirubin excretion and heme metabolism.

The acute administration of sodium arsenite (AsIII) to rats resulted in a biphasic alteration of the hepatic cytosolic "free" heme pool. The first stage was an increase in the cytosolic "free" heme without significant effects on the content of cytochrome P-450 or on bilirubin excretion. The second stage consisted of a continuous fall of the cytosolic "free" heme and of the content of cytochrome P-450. These changes were concurrent with an eight-fold increase in heme oxygenase activity and associated with marked elevations in the biliary excretion of bilirubin. The bile was collected from chronically cannulated rats to avoid artifacts related to anesthesia or post anesthetic effects. The rapid increase in biliary excretion of labeled heme degradation products indicated an increased breakdown of newly synthesized heme. Immunoelectrophoresis of bile proteins showed an altered pattern of bile protein excretion. The increased biliary haptoglobin suggested some hemolysis, while the reduction in the free immunoglobulin A (IgA) secretory component showed an AsIII-related decreased protein transport across hepatocytes to bile. Further research is required to assess the direct role of an increased heme degradation in the genesis of the hepatotoxic effects of AsIII.

Animals↗
PubMed1988

Early changes in bile duct lining cells and hepatocytes in rats treated with alpha-naphthylisothiocyanate.

Morphological changes in bile duct lining cells precede morphological changes in hepatocytes in rats treated with 300 mg/kg body wt of alpha-naphthylisothiocyanate (ANIT). Four hours after dosing, electron microscopy showed dilation of bile ducts, loss of microvilli from bile duct epithelial cells, and an apparent opening of the tight junctions between some bile duct epithelial cells. These changes were more pronounced after 6 hr and there was in some bile duct lining cells detachment of the nuclear membrane and vacuolation of the endoplasmic reticulum. Light microscopy 6 hr after treatment with ANIT showed some portal edema and loss of gamma-glutamyl transpeptidase activity from the bile duct lining cells. By 8 hr after treatment many ducts showed clear-cut damage, with bile plugs forming and cells exfoliating into the ducts. Twenty-four hours after treatment the majority of bile ducts were destroyed but by 48 hr there was some evidence of regeneration. No tissue changes were seen at the light microscopy level in the liver parenchymal cells 4, 6, or 8 hr after treatment. At the ultrastructural level some alterations in the tight junctions between hepatocytes were seen 6 hr after treatment. No other changes were observed before this time point. By 24 hr after treatment there was focal necrosis in the parenchyma. Assay of gamma-glutamyl transpeptidase and albumin in bile gave results consistent with the histochemical evidence for the loss of activity from bile duct lining cells and for weakening of the tight junctions between hepatocytes.

1-Naphthylisothiocyanate↗
PubMed1988

Alterations in the thyroids of rats treated for long periods with di-(2-ethylhexyl) phthalate or with hypolipidaemic agents.

Treatment of rats for periods of 3 months or longer with the hypolipidaemic drugs clofibrate and fenofibrate or with the plasticiser di-(2-ethylhexyl) phthalate causes alterations in the thyroid. The colloid is shrunken and contains calcium-rich inclusions. Electron microscopy shows increases in the number and size of lysosomes, hypertrophy of the Golgi apparatus and dilation of the rough endoplasmic reticulum. These changes are consistent with persistent hyperactivity in the gland.

Animals↗
PubMed1987

The preparative isolation of endosome fractions: a review.

The endosome is an intracellular, acidic, membrane-bound, subcellular compartment to which endocytosed ligands, receptors and plasma membrane proteins are conveyed before sorting and delivery to destinations elsewhere in the cell. The preparative isolation of elements of this compartment has been achieved successfully using various appropriate combinations of density gradient ultracentrifugation, electrophoretic, gel filtration and immunoaffinity techniques. These methods for isolating endosome fractions are reviewed together with the difficulties of establishing markers for such fractions. The isolation of an endosome fraction from the pathway of polymeric IgA transcytosis in rat liver is discussed to exemplify successful isolation procedures and appropriate subcellular markers.

Animals↗
PubMed1987

Changes in plasma proteins in rats treated for short periods with hepatotoxins or with agents which induce cytochrome P450 isoenzymes.

We have compared the alterations in plasma proteins following treatment of rats with the centrilobular hepatotoxin carbon tetrachloride, the periportal hepatotoxin allyl alcohol and two inducers of hepatic microsomal drug metabolising enzymes, phenobarbitone and a mixture of polychlorinated biphenyls (Aroclor 1254). The results are compared with changes observed in animals treated with agents which caused proliferation of rat liver peroxisomes and described in an earlier publication. Our results indicate that: There is a marked induction of a minor glycoprotein which migrates as a prealbumin following treatment with both inducers of microsomal mixed function oxidases and inducers of peroxisome proliferation. There is a marked increase in a minor alpha 1-glycoprotein when there is chemically-induced mitosis in the liver but not in mitosis following liver damage. Two major alpha 1-glycoprotein are depressed in all forms of liver damage. There are indications of specific protein responses to allyl alcohol, to inducers of microsomal mixed function oxidases and to inducers of peroxisome proliferation.

1-Propanol↗
PubMed1986

Effects of mono (2-ethylhexyl) phthalate and its straight chain analogues mono-n-hexylphthalate and mono-n-octyl phthalate on lipid metabolism in isolated hepatocytes.

In cultured hepatocytes, as in vivo, mono-2-ethylhexyl phthalate (MEHP) and its straight chain analogues mono-n-hexyl phthalate (MnHP) and mono-n-octyl phthalate (MnOP) each cause accumulation of lipid but only MEHP produces significant induction of peroxisomal fatty acid oxidizing enzymes. To elucidate the mechanisms underlying this lipid accumulation we investigated the effects of these phthalates and the drug clofibric acid on fatty acid metabolism in suspensions of isolated hepatocytes. The effects were found to be markedly dependent on the nutritional state of the animals from which the hepatocytes were isolated. In hepatocytes isolated from animals fasted overnight, or animals fed ab libitum but killed at approximately 2.30 p.m., MEHP, MnHP, MnOP and clofibric acid each caused a marked rapid stimulation of fatty acid oxidation and the synthesis of triglycerides in hepatocytes when incubated in Hanks saline. Export of very low density lipoprotein (VLDL) from the cells was either unchanged or somewhat reduced. In contrast, in hepatocytes isolated from rats fed ad libitum but killed at approximately 9.30 a.m. MEHP and clofibric acid did not alter fatty acid oxidation or triglyceride synthesis, while MnOP and MnHP increased triglyceride synthesis but decreased fatty acid oxidation. The effects of fasting were largely abolished by incubations of the cells in a complete tissue culture medium (Liebowitz L-15). The results suggest that MEHP and its straight chain analogues can, either as the free acid or the CoA ester, mimic the action of fatty acids in the allosteric regulation of fatty acid metabolism.

Animals↗
PubMed1986

Time and dose study on the response of rats to the hypolipidaemic drug fenofibrate.

Groups of male Wistar albino rats were administered diets containing sufficient fenofibrate to ensure intakes of either 200, 60 or 13 mg/kg/day or sufficient clofibrate to ensure an intake of 400 mg/kg/day. Four rats from each experimental group and 6 control rats were killed, 3, 7, 14 and 28 days, 8, 12 and 20 weeks and 6, 9, 12 and 18 months after commencement of treatment. At all time points livers were subjected to histological, electron microscopic and biochemical examination, the other major abdominal organs were removed for histological examination. A more extensive necropsy was carried out on rats killed after 12 and 18 months. The major alterations were observed in the liver, although there were also morphological changes in the thyroid, pancreas and kidney after prolonged treatment. The hepatic changes followed a distinct time course. Within 24 h of offering diets containing the compounds to the rats there was accumulation of small droplets of lipid, induction of peroxisomal enzymes and of the specific cytochrome P-450 catalysing omega-hydroxylation of fatty acids and an increase in the number of mitotic figures. More slowly developing changes were loss from the centrilobular zone of fat, glycogen and of glucose 6-phosphatase activity. Here maximal changes were observed after 14 days of treatment. A still more slowly developing change was accumulation of enlarged lipid-loaded lysosomes, which was maximal at 26 weeks, accompanied by the development of lipofuscin bodies. Finally, in animals treated for 12 months or more there was evidence for increasing cell turnover as indicated by an increased number of mitotic figures, more dark cells and induction of serum alanine transaminase. The last 2 groups of changes were not observed in rats treated with 13 mg/kg/day of fenofibrate. In general the degree of change in rats treated with 400 mg/kg/day of clofibrate was similar to those found in rats treated with 60 mg/kg/day of fenofibrate.

Animals↗