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Biomedical subjects

T F Slater

Publications and source records attributed to T F Slater.

At least 73 records · Page 4Linked to original sources
PubMed1985

Carbon tetrachloride toxicity as a model for studying free-radical mediated liver injury.

A single dose of CCl4 when administered to a rat produces centrilobular necrosis and fatty degeneration of the liver. These hepatotoxic effects of CCl4 are dependent upon its metabolic activation in the liver endoplasmic reticulum to reactive intermediates, including the trichloromethyl free radical. Positive identification of the formation of this free radical in vivo, in isolated liver cells and in microsomal suspensions in vitro has been achieved by e.s.r. spin-trapping techniques. The trichloromethyl radical has been found to be relatively unreactive in comparison with the secondarily derived peroxy radical CCl3O2., although each free radical species contributes significantly to the biological disturbances that occur. Major early perturbations produced to liver endoplasmic reticulum by exposure in vivo or in vitro to CCl4 include covalent binding and lipid peroxidation; studies of these processes occurring during CCl4 intoxication have uncovered a number of concepts of general relevance to free-radical mediated tissue injury. Lipid peroxidation produces a variety of substances that have high biological activities, including effects on cell division; many liver tumours have a much reduced rate of lipid peroxidation compared with normal liver. A discussion of this rather general feature of liver tumours is given in relation to the liver cell division that follows partial hepatectomy.

Animals↗
PubMed1985

Protein thiols in normal and neoplastic human uterine cervix.

Protein-thiol groups that react with dihydroxydinaphthyl disulphide during a 7 h incubation (so-called reactive protein thiols, PSHr) have been quantitatively measured on sections of human uterine cervix by microcytospectrophotometry. Measurements were made on areas (1 micron 2) of epithelium and adjoining stroma in samples of normal cervix, and in samples obtained from patients with dysplasia, carcinoma-in-situ and invasive cancer. The ratio of PSHr in epithelium to stroma is substantially reduced in the pathological conditions compared with normal and in apparently normal adjacent areas. Such changes in PSHr are discussed in relation to the redox balance of the tissue, and free radical disturbances previously described.

Adult↗
PubMed1985

Low rate of NADPH/ADP-iron dependent lipid peroxidation in hepatic microsomes of DBA/2 mice.

Hepatic microsomal lipid peroxidation has been studied in 4 inbred strains of mice: C57BL/6, BALB/c, AKR and DBA/2. The rates of lipid peroxidation stimulated in vitro by carbon tetrachloride, ascorbate-iron and cumene hydroperoxide were similar in all 4 strains. Lipid peroxidation induced by NADPH/ADP-iron, however, proceeded at a substantially lower rate in the hepatic microsomes of DBA/2 mice. It is suggested that this low rate of enzymic iron-induced lipid peroxidation is a factor that may be involved in the resistance of this strain of mice to experimental hepatic porphyria induced by polyhalogenated aromatic hydrocarbons.

Adenosine Diphosphate↗
PubMed1985

Separation and characterization of the aldehydic products of lipid peroxidation stimulated by carbon tetrachloride or ADP-iron in isolated rat hepatocytes and rat liver microsomal suspensions.

Carbonyl products were separated and identified in suspensions of rat liver microsomal fractions and in isolated hepatocytes, after stimulation of lipid peroxidation by incubation with the pro-oxidants CCl4 and ADP-iron. The carbonyl products were allowed to react with 2,4-dinitrophenylhydrazine, and the derivatives were extracted and separated by t.l.c. into three zones of non-polar materials, and one fraction of polar derivatives that remained at the origin. Separation of the individual non-polar hydrazones in each zone by h.p.l.c. demonstrated that zone I prepared from microsomal fraction or hepatocytes incubated with CCl4 or ADP-iron contained mainly 4-hydroxyhex-2-enal, 4-hydroxynon-2-enal and 4-hydroxynona-2,5-dienal. Zone III consisted mainly of the alkanals propanal, pentanal and hexanal, the 2-alkenals propenal, pent-2-enal, hex-2-enal, hept-2-enal, oct-2-enal and non-2-enal, the ketones butanone, pentan-2-one and pentan-3-one, and deca-2,4-dienal. Incubation of a microsomal fraction with ADP-iron was much more effective in producing malonaldehyde and other carbonyl products than an incubation with CCl4. Despite such quantitative differences, there were no obvious qualitative differences in the h.p.l.c. spectra obtained from zones I and III. However, the stoichiometric evaluation of fatty acid loss and the production of malonaldehyde and other carbonyls suggests that the pathways of lipid peroxidation triggered by CCl4 and ADP-iron are different. The accumulation of carbonyl products of lipid peroxidation in isolated hepatocytes is strongly affected by their metabolism; in particular, 4-hydroxyalkenals were found to be metabolized very rapidly. Nonetheless, both CCl4 and ADP-iron produced stimulation in the production of malonaldehyde and non-polar carbonyl production. After incubation of rat hepatocytes with CCl4 or ADP-iron it was found that approx. 50% of the total amount of non-polar carbonyls produced during incubation escaped into the external medium. This was not leakage from dead cells, as 90-95% of the hepatocytes had retained their integrity at the end of the incubation. Release of carbonyl products from cells stimulated to undergo lipid peroxidation may be a mechanism for spreading an initial intracellular disturbance to affect critical targets outside the parent cell.

Adenosine Diphosphate↗
PubMed1985

The concentrations of 6-keto-PGF1 alpha and TXB2 in plasma samples from patients with benign and malignant tumours of the breast.

Peripheral plasma concentrations of 6-keto-PGF1 alpha and TXB2 were measured in patients with benign and malignant tumours of the breast, in patients with non-gynecological diseases, and in healthy female controls. The values were significantly higher in female patients with malignant tumours of the breast than in healthy controls (146 +/- 28 vs 13 +/- 2.5 pg/ml for 6-keto-PGF1 alpha p less than 0.01 and 78 +/- 17 vs 11 +/- 2 pg/ml for TXB2, p less than 0.01). Benign tumours of the breast were also associated with significantly raised plasma levels of 6-keto-PGF1 alpha and TXB2 compared to normal controls (52 +/- 5 vs 13 +/- 2.5 pg/ml for 6-keto-PGF1 alpha, p less than 0.01 and 26 +/- 5 vs 11 +/- 2 pg/ml for TXB2, p less than 0.05). The high levels of 6-keto-PGF1 alpha and TXB2 were not found to be correlated with clinical and histopathological data. The surgical removal of the primary tumour has apparently no effect on the plasma concentrations of 6-keto-PGF1 alpha and TXB2 over a follow-up period of 9 days after operation. The lack of alterations in the ratio of TXB2:6-keto-PGF1 alpha in the cancer patients and other subjects studied before and after surgery is indicative of the regulatory power of metabolic systems to preserve the homeostatic balance.

6-Ketoprostaglandin F1 alpha↗
PubMed1985

Production of prostacyclin (PGI2) and thromboxane A2 (TXA2) by vessels draining and not-draining benign and malignant tumours of the breast.

The production of PGI2 (determined by bioassay) and TXB2 (determined by radioimmunoassay) was studied in the supernatant solutions obtained after incubation of vessel rings prepared from veins draining and not draining benign and malignant tumours of the breast. A significant increase (p less than 0.01) was found in the production of PGI2 by vessels draining the malignant tumours as compared to those not draining such tumours or vessels draining benign tumours. The changes in PGI2, and the tendency for TXB2 to be higher in vessels draining malignant tumours, were in the same direction so that they balanced out when the ratio PGI2/TXB2 was calculated: in consequence no significant changes in this ratio were found in malignant tumours as compared to the benign. A significant difference (p less than 0.01) was observed in the ratios of vessels draining tumours:vessels not draining tumours between malignant and benign tumours in relation to the production of PGI2. The present data demonstrate that the production of PGI2 by vessels draining malignant tumours of the breast is different to that obtained with vessels from patients with benign tumours, although the mechanism responsible for this difference is not known.

Adult↗
PubMed1985

Activation of chloroform and related trihalomethanes to free radical intermediates in isolated hepatocytes and in the rat in vivo as detected by the ESR-spin trapping technique.

When hepatocytes isolated from phenobarbital-induced rats were incubated with chloroform and the spin trap phenyl-t-butyl nitrone (PBN) under anaerobic conditions, a free radical-spin trap adduct was detectable by ESR spectroscopy. A similar incubation of hepatocytes in the presence of air resulted in an ESR signal that was eight times less intense than that seen under anaerobic conditions; incubation mixtures exposed to pure oxygen had no detectable adduct signal. A significant reduction in the signal intensity was also produced by the addition of cytochrome P-450 inhibitors such as SKF-525A, metyrapone and carbon monoxide, indicating that free radical formation depended upon the reductive metabolism of chloroform mediated by the mixed oxidase system. The origin of the CHCl3-derived free radical has been confirmed by using [13C]CHCl3, while the comparison between the ESR spectra obtained in the presence of deuterated chloroform (CDCl3) and bromodichloro-methane (CHBrCl2) suggests that the free radical derived from CHCl3 may be CHCl2. Free radical intermediates were also detected during the aerobic and anaerobic incubation of isolated hepatocytes with bromoform (CHBr3), and iodoform (CHI3). The intensity of the ESR signal obtained with the various trihalomethanes increases in the order CHCl3 less than CHBrCl2 less than CHBr3 less than CHI3. The formation of PBN-free radical adducts has also been observed in phenobarbital-induced rats in vivo when intoxicated with chloroform, bromoform or iodoform, suggesting that the reductive metabolism of trihalomethanes might be of relevance to their established toxicity in the whole animal.

Animals↗
PubMed1985

Platelet sensitivity to prostacyclin in normal subjects, and in patients with benign and malignant tumours of the breast.

Platelet sensitivity to prostacyclin (PG12) was determined in normal male and female subjects, and in patients with benign and malignant tumours of the breast. The IC50 overall mean values for PG12 on ADP-induced platelet aggregation were similar for normal men and women, being 0.97 +/- 0.05 ng ml-1 and 0.83 +/- 0.07 ng ml-1 respectively. However, there were significant differences in the IC50 values for women in the 1st (0.81 +/- 0.06 ng ml-1) vs. 2nd (1.37 +/- 0.13 ng ml-1) phase of the menstrual cycle; post-menopausal women gave similar values to normal males and to pre-menopausal women in the 1st phase of the cycle. No significant differences were found between normal subjects and patients with benign or malignant tumours of the breast when account was taken of the status of the patient in relation to the phase of the menstrual cycle and the menopause. The importance of the hormonal status in evaluating changes in platelet sensitivity in patients with breast cancer is strongly emphasised.

Adenosine Diphosphate↗
PubMed1985

Biochemical studies on the metabolic activation of halogenated alkanes.

This paper reviews recent investigations by Slater and colleagues into the metabolic activation of halogenated alkanes in general and carbon tetrachloride in particular. It is becoming increasingly accepted that free radical intermediates are involved in the toxicity of many such compounds through mechanisms including lipid peroxidation, covalent binding, and cofactor depletion. Here we describe the experimental approaches that are used to establish that halogenated alkanes are metabolized in animal tissues to reactive free radicals. Electron spin resonance spectroscopy is used to identify free-radical products, often using spin-trapping compounds. The generation of specific free radicals by radiolytic methods is useful in the determination of the precise reactivity of radical intermediates postulated to be injurious to the cell. The enzymic mechanism of the production of such free radicals and their subsequent reactions with biological molecules is studied with specific metabolic inhibitors and free-radical scavengers. These combined techniques provide considerable insight into the process of metabolic activation of halogenated compounds. It is readily apparent, for instance, that the local oxygen concentration at the site of activation is of crucial importance to the subsequent reactions; the formation of peroxy radical derivatives from the primary free-radical product is shown to be of great significance in relation to carbon tetrachloride and may be of general importance. However, while these studies have provided much information on the biochemical mechanisms of halogenated alkane toxicity, it is clear that many problems remain to be solved.

Aerobiosis↗
PubMed1984

Studies on human uterine cervix and rat uterus using S-, X- and Q-band electron-spin-resonance spectroscopy.

In previous studies we have reported on the detection of a strong e.s.r. signal in samples of normal human cervix; the signal is much reduced or absent in samples of invasive cancer of the cervix. In order to identify the species responsible for the strong signal, we have used X-, S- and Q-band e.s.r. spectroscopy. The major signal that is detectable in ground-up samples of cervix preserved at -196 degrees C has features consistent with the presence of a peroxy free radical. Good agreement with the experimental findings was obtained by computer simulation, using values for the g-tensor of gx = 2.002, gy = 2.005 and gz = 2.036. The peroxy radical is produced on grinding the normal cervix samples to a powder under liquid N2, and appears to be formed by modification of a pre-existing oxygen-containing complex. Control experiments eliminated the possibility that the strong signals seen in frozen powders prepared from normal cervix were artefacts only of the grinding procedure. Experiments with rats in vivo and with cervix samples in vitro are consistent with the conclusion that the peroxy radical is formed by disturbing the cyclo-oxygenase system that is involved in prostaglandin synthesis.

Animals↗
PubMed1984

The effect of the administration of cobaltic protoporphyrin IX on drug metabolism, carbon tetrachloride activation and lipid peroxidation in rat liver microsomes.

The effects of cobaltic protoporphyrin IX (CPP) administration on hepatic microsomal drug metabolism, carbon tetrachloride activation and lipid peroxidation have been investigated using male Wistar rats. CPP (125 mumol/kg, 72 h before sacrifice) profoundly decreased the levels of hepatic microsomal heme, particularly cytochrome P-450. Consequently, the associated mixed-function oxidase systems were equally strongly depressed. An unexpected finding was that CPP administration also greatly decreased the activity of NADPH/cytochrome c reductase, a result not generally found with the administration of the more widely used cytochrome P-450 depleting agents, cobaltous chloride. Activation of carbon tetrachloride, measured as covalent binding of [14C] CCl4, spin-trapping of CCl3 and CCl4-stimulated lipid peroxidation, was much lower in liver microsomes from CPP-treated rats. Other microsomal lipid peroxidation systems, utilising cumene hydroperoxide or NADPH/ADP-Fe2+, were also depressed in parallel with the decrease in microsomal enzyme activities.

Animals↗
PubMed1984

Production of prostacyclin, 6-keto-PGF1 alpha and thromboxane B2 by incubated samples of umbilical vessels: a comparison of methods for expressing the results on dry weight, wet weight, protein or DNA bases.

The production of PGI2 (determined by bioassay), and of 6-keto-PGF1 alpha and TXB2 (determined by radioimmunoassay) by samples of human umbilical vessels have been measured. The results have been calculated on four bases: dry weight, wet weight, protein and DNA. There was a higher production of PGI2 and 6-keto-PGF1 alpha by umbilical veins than by umbilical arteries; no significant difference in TXB2 production was observed between umbilical veins and arteries. The ratio of 6-keto-PGF1 alpha: TXB2 production was about 100 for the samples of veins and about 40 for the samples of arteries. The best methods of expressing the results were on the bases of protein and DNA, the latter basis being marginally the best. The least satisfactory method for expressing the results was that based on dry weight. The physiological and practical implications of the results are discussed.

6-Ketoprostaglandin F1 alpha↗
PubMed1984

Lipid peroxidation and lipid antioxidants in normal and tumor cells.

Lipid peroxidation is often low in tumor tissue as compared to the corresponding normal tissue and it has been postulated that lipid peroxidation may be associated with cell division. In this paper the various contributory factors which control the rate of microsomal lipid peroxidation in normal rat liver and in the Novikoff hepatoma have been carefully analyzed. The low rate of lipid peroxidation in the hepatoma seems to be due to a combination of factors: low levels of polyunsaturated fatty acids and of cytochrome P-450 and elevated levels of lipid-soluble antioxidant. This lipid-soluble antioxidant is principally alpha-tocopherol.

Animals↗
PubMed1984

Free radical intermediates under hypoxic conditions in the metabolism of halogenated carcinogens.

Many halogenated hydrocarbons are known to have carcinogenic potency, nevertheless, humans may be exposed to such xenobiotics for prolonged periods during industrial occupations. In this study, eight aliphatic haloalkanes, all suspected carcinogens, have been studied with respect to their metabolic activation to free radical intermediates, that may exert toxic effects when produced in vivo. The eight haloalkanes studied here are: carbon tetrachloride, chloroform, 1,2-dibromoethane, 1,1-dichloroethane, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2-trichloroethane and 1,1,2,2-tetrachloroethane. Using isolated rat hepatocytes as a model system, and electron spin resonance spectroscopy coupled to the spin trapping technique as a detection technique, it has been possible to demonstrate the formation of free radical derivatives, both under normoxic as well as under hypoxic conditions from carbon tetrachloride, chloroform, 1,1,1-tetrachloroethane and 1,1,2,2-tetrachloroethane. In contrast, free radical production was only detectable under hypoxic conditions when 1,2-dibromoethane, 1,1-dichloroethane, 1,2-dichloroethane and 1,1,2-trichloroethane were added to the hepatocyte suspensions. It is known that some xenobiotics that usually undergo oxidative pathways of metabolism can be metabolized differently when the oxygen concentration is substantially diminished. Evidence have been obtained suggesting that such different types of metabolism may be of relevance in vivo. Possible relationships between free radical production, metabolic activation, covalent binding and carcinogenic potency are discussed.

Animals↗
PubMed1983

The metabolism of halothane by hepatocytes: a comparison between free radical spin trapping and lipid peroxidation in relation to cell damage.

The technique of free radical spin trapping has been applied to demonstrate the formation of free radicals produced during the metabolism of halothane by rat liver hepatocytes under hypoxic conditions. The results obtained support previous findings that reported sex differences in the metabolic activation of halothane by rats in vivo. Cell viability under hypoxic conditions, as judged by trypan blue staining and lactate dehydrogenase release, shows a correlation with the extent of metabolism of halothane as measured by electron spin resonance spectroscopy. The extent of lipid peroxidation was measured by diene conjugation, malondialdehyde production and chemiluminescence. The latter technique allowed the demonstration of lipid peroxidation during incubations of hepatocytes under aerobic conditions. The magnitude of the aerobic chemiluminescence showed a similar sex dependency to the extent of free radical formation under hypoxic conditions. Cell viability measurements show that halothane metabolism in both hypoxic and aerobic conditions can lead to cell death. Consequently, oxidative lipid damage could be a cause of cell damage, as judged by cell viability, additional to covalent binding.

Animals↗