Search PubMed⌕ Search

Biomedical subjects

K H Summer

Publications and source records attributed to K H Summer.

At least 55 records · Page 3Linked to original sources
PubMed1982

Elimination of thioethers following administration of naphthalene and diethylmaleate to the rhesus monkey.

As a measure of glutathione (GSH) conjugation, urinary, fecal and biliary excretion of thioethers and hepatic GSH content were measured in rhesus monkeys following administration of single doses of naphthalene and diethylmaleate (DEM). Naphthalene had little or no effect on hepatic GSH content and the excretion of thioethers into urine, feces or bile of rhesus monkeys which is similar to that observed in chimpanzees and humans and is in contrast to results obtained from rats. Apparently, conjugation of naphthalene and/or its metabolites with GSH does not play a major role in the metabolism of naphthalene in primates, whereas it is one of the major pathways in rodents. Rhesus monkeys, like chimpanzees, excreted about 13% of the various doses of DEM (30, 75 and 200 mg/kg) as thioethers into urine which is half of that excreted by rats. Six hrs after administration of 200 mg/kg DEM, the hepatic GSH content was decreased by 90% in the rhesus monkey. During the first day after this dose (200 mg/kg), the increase in the excretion of thioethers into bile corresponded to about 15% of the dose of DEM administered. Since fecal excretion of thioethers corresponded to only 1% of the dose and urinary excretion represented 12% of the dose, it appears that biliary thioethers of DEM are reabsorbed from the intestine and then excreted into urine. It appears that the rhesus monkey as well as the chimpanzee is, whereas the rat is not, a good animal model to study GSH-related conjugation reactions with predictive value for man.

Animals↗
PubMed1981

Glutathione and glutathione S-transferase activities of mammalian cells in culture.

Continuous cell cultures derived from various tissues of rat, mouse, hamster and man were assayed for their glutathione (GSH) content and glutathione S-transferase activities. GSH S-transferase activities were monitored toward the substrates 1-chloro-2,4-dinitro-benzene (CDNB), 1,2-dichloro-4-nitrobenzene (DCNB) and 1,2-epoxy-3-(p-nitrophenoxy)propane (PO). All cell lines tested contained appreciable amounts of GSH ranging from 10 to 65 nmol/mg cellular protein. Likewise, all cell lines expressed GSH S-transferase activities. However, the various cell lines differed considerably in their relative transferase activities exhibiting some degree of species-specificity.

Animals↗
PubMed1981

Threshold levels in toxicology: significance of inactivation mechanisms.

Metabolic inactivation of chemicals may prevent toxic effects of reactive intermediates when present at low levels whereas inactivation may be overcome at high levels changing dose-effect relation. This is demonstrated in various in vitro test systems: a) Monooxygenase-mediated metabolism causes formation of reactive oxygen species which induce DNA repair in lymphoblastoid cells. DNA damage is suppressed in the presence of glutathione (GSH), catalase or superoxide dismutase. b) Chloroprene is mutagenic in Salmonella typhimurium but not carcinogenic, possibly due to inactivation by GSH-conjugations. c) Chlorodinitrobenzene is not mutagenic is Salmonella typhimurium in the presence of GSH. However it is increasingly mutagenic at concentrations exceeding those of the GSH. d) Suppression of glucuronidation and sulfation in isolated hepatocytes highly increases irreversible binding of naphthalene. It is concluded that information on the metabolism of chemicals is essential for interpretation of toxicity studies in animals and their relevance to man.

Animals↗
PubMed1980

Mutagenicity testing with Salmonella microsome test.

This in vitro mutagenicity test system comprises five different strains of S. typhimurium as target cells with the rat liver S-9 fraction and appropriate co-factors for metabolic activation of the chemical tested. The bacterial tester strains detect both mutations induced by base pair substitutions and intercalation (frame shift mutations). Usually 10(8)--10(9) cells of an overnight culture or an exponentially growing culture are incubated for 2-3 days with a mixture of S-9, co-factors, soft agar and the chemical on histidine-deficient agar. The S-9 fraction is obtained from the livers of rats pretreated with 500 mg/kg chlorinated biphenyls (Clophen A-50, Aroclor 1254) to obtain high metabolic activity. For reproducibility it is essential to standardize metabolic activity and protein content of the S-9 and to use three different concentrations thereof in the test system. Since solvents inhibit metabolic activation of the chemicals they must not exceed 4% of the final 2.6 ml incubate. Several independent studies have shown that between 85 and 93% of chemical carcinogens are mutagens in the test. Regarding extrapolation to man one has to consider that the test is preferentially adapted for metabolic activation of the chemicals, whereas inactivation processes are absent or are less active than in vivo. Thus, the test provides qualitative rather than quantitative information on mutagenic effects of a chemical.

Animals↗
PubMed1980

Glutathione and glutathione S-transferases in the Salmonella mammalian-microsome mutagenicity test.

Levels of the tripeptide glutathione (GSH) and the activity of glutathione S-transferases were investigated in S9 fractions of rats and mice and in Salmonella typhymurium tester strains TA1535, TA100, TA1538 and TA98. The S9 and Salmonella typhimurium tester strains had high levels of glutathione. Compared with S9, the activity of GSH S-transferases was lower in the bacteria. However, electrophiles such as 1-chloro-2,4-dinitrobenzene (CDNB), diethyl maleate and styrene oxide were effectively bound to bacterial GSH. The mutagenicity of the direct mutagen CDNB was drastically lowered in presence of S9 fractions but not in presence of microsomes. A comparable decrease was obtained when microsomal supernatant, which contains GSH and GSH S-transferases, was added to the microsomes. Addition of GSH in excess completely abolished mutagenicity of CDNB. These results demonstrate that the conjugation of electrophiles with GSH mediated by the S9 fraction or the bacterial tester strains represents an important detoxication mechanism which may influence the results obtained with the Salmonella typhimurium mammalian-microsome mutagenicity test.

Animals↗
PubMed1980

Mutagenicity of 1-fluoro-2,4-dinitrobenzene is affected by bacterial glutathione.

Recently we have shown that Salmonella typhimurium tester strains have high levels of the tripeptide glutathione (GSH) and activity of GSH S-transferases (Summer et al., 1979). In continuation of the GSH-dependent suppression of mutagenicity of 1-chloro-2,4-dinitrobenzene in presence of S9 fraction (Summer et al., 1979), this paper is focused on the GSH-dependent detoxifying capacity of the bacterial tester strains. 1-Fluoro-2,4-dinitrobenzene (FDNB), an electrophilic agent, which is used to identify terminal amino acids in proteins (Sanger reagent), readily reacts with GSH leading to a dose-dependent depletion of bacterial GSH. Additionally, FDNB is a strong mutagen for Salmonella typhimurium TA100, TA1538, and TA98 without metabolic activation. Presumably owing to conjugation with bacterial GHS, FDNB in concentrations which were lower or equal to those of bacterial GSH were found to be not mutagenic. Accordingly, increasing amounts of bacteria in the test system require increasing amounts of FDNB for expression of mutagenicity.

Dinitrobenzenes↗
PubMed1980

UDP-glucuronosyl-, phenol sulfo-, and glutathione-S-transferase activities of mammalian cells in permanent culture.

Established cell cultures derived from mouse, rat, hamster, cat, and man were examined for the in vitro activities of UDP-glucuronosyl-, phenol sulfo-, and glutathione-S-transferases. The relative activities of the conjugation reactions differed considerably between the various cell lines: Glutathione-S-transferase activities were present in all cell lines with wide variation between different transferase forms. Phenol sulfotransferase was not detectable at all in most of the cell lines tested or was present at very low levels. In contrast, UDP-glucuronosyltransferase activity was expressed in the majority of cultures. Established cultures containing specific combinations of the various types of conjugases should be useful in examining their role in the inactivation and activation of potentially toxic chemicals.

Animals↗
PubMed1980

Contact allergy as a therapeutic tool for alopecia areata: application of squaric acid dibutylester.

Squaric acid dibutylester (SADBE), a potent contact allergen, was tested for mutagenicity in the bacterial plate incorporation assay (Ames test), in the presence and absence of mammalian microsomes. In contrast to dinitrochlorobenzene which is mutagenic in this test, SADBE was found not to be mutagenic. In 53 patients with extensive or total alopecia areata, SADBE dissolved in acetone was applied weekly to one side of the head, the other side serving as control. In 46 patients (87%), hair regrew either exclusively on the treated side, or considerably faster and denser on this side. In some patients, continuous treatment failed to maintain the response. Persistent response was observed in 37 patients (70%). These results are essentially the same as those obtained with DNCB. Therefore, contact allergy is proposed as a therapeutic concept for alopecia areata.

Adolescent↗
PubMed1979

Responses of mitochondrial superoxide dismutase, catalase and glutathione peroxidase activities to aging.

The previous observation (Eur. J. Biochem., 82 (1978) 563--567) that age-dependent accumulation of lipid peroxides follows as a consequence of increased radical formation in mitochondria has prompted an examination of the response of a set of protective enzymes to the above situation. Levels of mitochondrial catalase activity as well as selenium-dependent glutathione peroxidase activity were found to be increased with age, while superoxide dismutase activity remained unchanged. No selenium-independent glutathione peroxidase activity could be detected either in preparations from young 3-month-old controls or in preparations from 2-year-old rats. Both the relatively high and unchanged levels of reduced glutathione and kinetic considerations suggest that glutathione peroxidase is preferentially involved in lipid peroxide metabolism, while catalase predominantly metabolizes mitochondrial H2O2.

Aging↗
PubMed1979

Transport and metabolism of bromosulfophthalein by isolated rat liver cells.

Kinetics of transport and metabolism of bromosulfophthalein have been studied in isolated liver cells in a dose-dependent manner obtaining the following results. The disposition of bromosulfophthalein in suspensions of isolated liver cells is similar to the turnover in the whole liver. The initial maximal rate of uptake of bromosulfophthalein is 2--3 times faster than intracellular conjugation with glutathione. Conjugation proceeds to an equilibrium between intracellular substrate (bromosulfophthalein) and product (bromosulfophthalein-glutathione conjugate) which are both transiently accumulated in the cell. Formation of bromosulfophthalein-glutathione is accompanied by an equimolar decrease of glutathione. The bromosulfophthalein-glutathione conjugate is slowly released from the cells in an energy-dependent and saturable transport process. The maximal velocity of excretion amounts to only 6% of the maximal velocity of uptake and to 20% of the maximal velocity of conjugation. Excretion, therefore, represents the slowest step in the overall turnover.

Animals↗
PubMed1975

Hydroperoxide-metabolizing systems in rat liver.

1. Metabolism of added hydroperoxides was studied in hemoglobin-free perfused rat liver and in isolated rat hepatocytes as well as microsomal and mitochondrial fractions. 2. Perfused liver is capable of removing organic hydroperoxides [cumene and tert-butyl hydroperoxide] at rates up to 3--4 mumol X min-1 X gram liver-1. Concomitantly, there is a release of glutathione disulfide (GSSG) into the extracellular space in a relationship approx. linear with hydroperoxide infusion rates. About 30 nmol GSSG are released per mumol hydroperoxide added per min per gram liver. GSSG release is interpreted to indicate GSH peroxidase activity. 3. GSSG release is observed also with added H2O2. At rates of H2O2 infusion of about 1.5 mumol X min-1 X gram liver-1 a maximum of GSSG release is attained which, however, can be increased by inhibition of catalase with 3-amino-1,2,4-aminotriazole. 4. A contribution of the endoplasmic reticulum in addition to glutathione peroxidase in organic hydroperoxide removal is demonstrated (a) by comparison of perfused livers from untreated and phenobarbital-pretreated rats and (b) in isolated microsomal fractions, and a possible involvement of reactive iron species (e.g. cytochrome P-450-linked peroxidase activity) is discussed. 5. Hydroperoxide addition to microsomes leads to rapid and substantial lipid peroxidation as evidenced by formation of thiobarbituric-acid-reactive material (presumably malondialdehyde) and by O2 uptake. Like in other types of induction of lipid peroxidation, malondialdehyde/O2 ratios of 1/20 are observed. Cumene hydroperoxide (0.6 mM) gives rise to 4-fold higher rates of malondialdehyde formation than tert-butyl hydroperoxide (1 mM). Ethylenediamine tetraacetate does not inhibit this type of lipid peroxidation. 6. Lipid peroxidation in isolated hepatocytes upon hydroperoxide addition is much lower than in isolated microsomes or mitochondria, consistent with the presence of effective hydroperoxide-reducing systems. However, when NADPH is oxidized to the maximal extent as evidenced by dual-wavelength spectrophotometry, lipid peroxidation occurs at large amounts. 7. A dependence of hydroperoxide removal rates upon flux through the pentose phosphate pathway is suggested by a stimulatory effect of glucose in hepatocytes from fasted rats and by an increased rate of 14CO2 release from [1-14C]glucose during hydroperoxide metabolism in perfused liver.

Animals↗