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H Sies

Publications and source records attributed to H Sies.

At least 253 records · Page 14Linked to original sources
PubMed1989

[Biochemistry of thiol groups: the role of glutathione].

Glutathione (GSH) comprises the bulk of the pool of free thiol groups in biological systems. Since its first description as philothione 100 years ago, there have been repeated surprises in discoveries of novel functions. Just recently the important role of thioethers with products of the lipoxygenase reaction, i.e., the leukotrienes, was revealed as mediator of physiological and pathophysiological processes. Another major function resides in detoxication, GSH being cosubstrate in the GSH-peroxidase reaction for the reduction of hydroperoxides in the defense against oxidative stress. Interest also focuses on reactions of glutathionyl radicals in protection by thiols against DNA damage resulting from ionizing radiation.

Animals↗
PubMed1989

Hepatic lipoate uptake.

Uptake of [35S]lipoate was studied in perfused rat liver and in isolated rat hepatocytes. During single-pass perfusion of [35S]lipoate about 30% of the radioactivity is retained in the liver. A substantial amount of 5,5'-dithiobis(2-nitrobenzoic acid)-reactive material appears in the effluent perfusate, while hepatic efflux of GSH is unchanged. The hepatic uptake of lipoate, the release of thiols, and also the biliary excretion of 35S-labeled compounds are suppressed by octanoate. In isolated hepatocytes the uptake of lipoate follows saturation kinetics showing a Km value of 38 microM and a Vmax of 180 pmol/mg X 10 s. The uptake is temperature-dependent; from the Arrhenius plot an activation energy of 14.8 kcal/mol at 20 microM lipoate is calculated. At high concentrations of lipoate (above 75 microM) a nonsaturable uptake component becomes predominant. Lipoate uptake is selectively inhibited by medium-chain fatty acids. Only slight inhibition is seen in the presence of long-chain fatty acids, and there is no inhibition with acetate or lactate. Substantial inhibition is also observed with acetylsalicylic acid, but not with taurocholate, bromosulfophthalein or biotin. Lipoate uptake can be inhibited by high concentrations of phloretin (200 microM) and is rather insensitive to 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (200 microM). The results indicate that hepatic uptake of lipoate at physiological concentrations is largely carrier-mediated.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1989

Chemiluminescent oxidation of ribose catalyzed by horseradish peroxidase in presence of hydrogen peroxide.

The reaction of ribose with horseradish peroxidase in the presence of H2O2 is accompanied by light emission. The detection of horseradish peroxidase Compound II (FeO2+) indicates that the enzyme participates in a normal peroxidatic cycle. Hydrogen peroxide converts horseradish peroxidase into Compound 1 (FeO2+) which in turn is converted into Compound II by abstracting a hydrogen atom from ribose forming a ribosyl radical. In aerated solutions oxygen rapidly adds to the ribosyl radical. Based on the spectral characteristics and the enhancement of the chemiluminescence by chlorophyll-a, xanthene dyes, D2O and DABCO, it is suggested that the excited species, apparently triplet carbonyls and 1O2, are formed from the biomolecular decay of the peroxyl radicals via the Russell mechanism.

Horseradish Peroxidase↗
PubMed1989

The peroxidase/oxidase activity of soybean lipoxygenase--I. Triplet excited carbonyls from the reaction with isobutanal and the effect of glutathione.

Soybean lipoxygenase shows a secondary peroxidase/oxidase activity: The aerobic reaction with isobutanal, enhanced by hydrogen peroxide as a cosubstrate, yields acetone, exhibits chemiluminescence and consumes oxygen (phi cl = 1.3 x 10(-9) photons/O2 molecule consumed). 9,10-Dibromoanthracene-2-sulfonate increases the photoemission (kET tau 0 = 2 x 10(4) M-1; phi cl = 0.9 x 10(-7) photons/O2), whereas it is diminished by sorbate, tryptophan, 2-methyl-1,4-naphthoquinone, glutathione, and superoxide dismutase. In the presence of hydrogen peroxide the lipoxygenase reaction with glutathione yields yet another excited state. From the well-known reactions promoted by horseradish-peroxidase, these features are concluded to indicate the novel activity of soybean lipoxygenase. With isobutanal as a substrate lipoxygenase acts as an oxidase and as a peroxidase. The mechanism suggested leads to photoemissive triplet excited acetone as expected from the cleavage of an intermediate dioxetane.

Aldehydes↗
PubMed1989

The peroxidase/oxidase activity of soybean lipoxygenase--II. Triplet carbonyls and red photoemission during polyunsaturated fatty acid and glutathione oxidation.

During the aerobic reaction of soybean lipoxygenase with polyunsaturated fatty acids (linoleic, linolenic, and arachidonic acid) oxygen uptake is followed by excited carbonyl photoemission. The chemiluminescence yield of phi cl = 10(-10) photons/O2 molecule consumed is enhanced 2-3 orders of magnitude by the carbonyl sensitizers 9,10-dibromo-anthracene-2-sulfonate (kET tau 0 = 10(4) M-1; phi cl = 10(-8) photons/O2) and chlorophyll-a (kET tau 0 = 10(6) M-1; phi cl = 10(-7) photons/O2), respectively. alpha,beta-Saturated triplet excited carbonyls as from 1,2-dioxetane cleavage are discussed to arise from a secondary peroxidase/oxidase reaction with aldehydes formed in the course of enzymic lipid peroxidation. When 1 mM glutathione is added to the aerobic lipoxygenase/arachidonate reaction, carbonyl emission (375-455 nm) is replaced by intense red bands (630-645 nm and 695-715 nm) resembling the characteristic spectrum of (1 delta g)O2-singlet oxygen dimol-emission. The quantum yield (phi cl = 10(-8) photons/O2) remains unaffected by chlorophyll indicating that the red emission is independent of excited carbonyls. The effect of GSH is attributed to dioxetane interception and subsequent glutathione peroxidation generating 1O2 by electron transfer from the superoxide anion radical to a peroxysulfenyl radical.

Fatty Acids↗
PubMed1989

Cytochrome P-450, reductive metabolism, and cell injury.

A variety of organic compounds such as carbon tetrachloride, halothane, gentian violet, and benznidazole are reductively metabolized to free radicals by liver microsomal cytochrome P-450. Due to the fact that this metabolic activation occurs at a site where O2 usually becomes activated during the monooxygenase cycle, there is a competition between these xenobiotics and O2 for electrons. Reductive activation occurs at a maximal rate under anaerobic conditions. Cell injury may be directly produced by the reactive metabolites. It may also result from lipid peroxidation induced by interaction of the free radicals with polyunsaturated fatty acids of membrane phospholipids. For polyhalogenated alkanes the latter process is most likely the one leading to cell death. When loss of cell viability is mediated by lipid peroxidation, a complex O2 dependence may result, characterized by a maximum loss of cell viability at oxygen partial pressures (PO2) between 1 and 10 mm Hg. These PO2 values are found in the centrilobular area of the liver lobule.

Cell Survival↗
PubMed1989

Antioxidant activity of 5-hydroxytryptophan, 5-hydroxyindole, and DOPA against microsomal lipid peroxidation and its dependence on vitamin E.

The antioxidant capacity of 5-hydroxy-tryptophan, 5-hydroxy-indole, and DOPA (3,4-dihydroxy-phenylalanine) was tested in the Fe-induced lipid peroxidation of liver microsomes of normal- and vitamin E-deficient rats, using ascorbate as a reductant. Lipid peroxidation was monitored as low-level chemiluminescence, indicative of generation of electronically-excited states arising from the recombination of secondary lipid peroxyl radicals. The lag phase (tau 0) preceding the rise in chemiluminescence intensity was used as indicator of antioxidant efficiency, in the absence (tau 0) and the presence (tau) of these polar compounds. The increase in duration of the lag phase exerted by these hydroxy compounds was expressed and quantified as the relationship: tau-tau 0. The tau-tau 0 values were considerably higher in the presence of vitamin E and almost negligible in the absence of tocopherol. It is postulated that the observed increased protection against lipid peroxidation by the above 5-hydroxy derivatives is displayed in a fashion dependent on the presence of vitamin E and probably involving recovery of the chromanoxyl radical by means of an electron-transfer process.

5-Hydroxytryptophan↗
PubMed1989

Comparative toxicology of ozone and t-butyl hydroperoxide on isolated rat lung.

Comparative studies were undertaken on the effects of ozone and t-butyl hydroperoxide (t-BuOOH) on alkane production, glutathione and lactate dehydrogenase (LDH) release from isolated rat lungs. Specifically, ethane and pentane production, as well as glutathione and LDH release were simultaneously determined at different time intervals from the isolated lung preparation in the absence and presence of toxic concentrations of ozone or t-BuOOH. When compared to control conditions, both toxic agents produced a marked decrease in the dry weight to wet weight ratios, reflecting the development of acute pulmonary edema. These toxic agents also caused a marked increase in the efflux of glutathione into the effluent. A much higher glutathione efflux into the effluent was observed during t-BuOOH perfusion in comparison to ozone exposure. In parallel with the enhancement of glutathione release a significant increase in ethane production was also observed during t-BuOOH perfusion. However, the production of either alkane by ozone inhalation was not significantly different from that in the control conditions. Unlike glutathione release, there was no marked increase of LDH release into the effluent following exposure to t-BuOOH or ozone. This suggests that the observed increase in glutathione release caused by t-BuOOH or ozone treatment was not associated with non-specific destruction of cell membrane integrity.

Air↗
PubMed1989

Relationship between free radicals and vitamins: an overview.

Aerobic metabolism entails the generation of reactive oxygen species. These include the superoxide anion radical, hydrogen peroxide, the hydroxyl radical, and singlet molecular oxygen. Further, organic alkoxyl or peroxyl radicals may be formed. In the pattern of antioxidant defense, some vitamins play a prominent role and have therefore received much attention recently in the study of the physiological or pathophysiological imbalance in the prooxidant/antioxidant equilibrium. Prooxidant states are sometimes also referred to as oxidative stress. Vitamin E in the membrane compartment and vitamin C in the aqueous compartment exhibit direct reactivity with radicals, and there are repair pathways for the tocopheryl and ascorbyl radicals that are generated. In this regard, there can be an interaction between these two vitamins. Also, glutathione (GSH) can exhibit repair capacity as well as direct reactivity with radicals. Singlet molecular oxygen is an electronically excited state of oxygen with considerable chemical reactivity. It is a non-radical compound, generated by photochemical reactions or by the process of lipid peroxidation of biomembranes, i.e., by photoexcitation or by chemiexcitation. Singlet oxygen can be inactivated by a number of biological compounds known as quenchers. beta-Carotene is the most important vitamin in this respect.

Free Radicals↗
PubMed1988

The protection by ascorbate and glutathione against microsomal lipid peroxidation is dependent on vitamin E.

Lipid peroxidation of rat liver microsomal fractions was monitored by its low-level chemiluminescence in preparations from controls and vitamin-E-deficient animals. Measurements were made (a) of the duration of the lag phase tau0 after initiation with NADPH/iron-ADP and (b) of the slope of the chemiluminescence increase. In microsomes with normal vitamin E (alpha-tocopherol) level the lag phase tau0 was substantially increased by ascorbate; in contrast, even an enhanced peroxidation was observed with ascorbate in vitamin-E-deficient microsomes. Therefore, the ascorbate-mediated protection of microsomal membranes against lipid peroxidation is dependent on vitamin E in the membrane. In vitamin E deficiency the pro-oxidant effect of ascorbate was abolished when glutathione (GSH) was present. Likewise, GSH does not prolong the lag phase tau0 in vitamin E deficiency. However, GSH (but not cysteine) exerts an antioxidant effect both in controls and in vitamin E deficiency by decreasing the slope of the chemiluminescence increase during lipid peroxidation. The involvement of GSH in an enzyme-dependent mechanism is suggested.

Animals↗
PubMed1988

Inhibition of biliary taurocholate excretion during menadione metabolism in perfused rat liver.

In perfused rat liver menadione elicits substantial oxidation in both the NADPH and GSH redox systems. Biliary excretion of GSSG is increased several-fold. Menadione derivatives appear in the bile predominantly as the menadione-S-glutathione conjugate, thiodione (60%), or as conjugates derived therefrom (17%). About 10% appear as menadione glucuronides. The excretion of taurocholate into bile is strongly inhibited upon menadione infusion. The inhibition of taurocholate excretion is small in livers with a low content of Se-GSH-peroxidase and in glutathione-depleted livers. In these livers intracellular GSSG and biliary GSSG release remain at low values, although menadione still imposes oxidative stress as indicated by an oxidation of intracellular NADPH. Under anoxic conditions menadione has little influence on both the NADPH and GSH redox systems and also on biliary taurocholate excretion. The amount of thiodione released into bile is similar to that found under normoxia, whereas the amount of glucuronidated products almost doubled. We conclude (a) that intracellular formation of GSSG by menadione occurs via the generation of hydrogen peroxide; (b) that the inhibition of biliary taurocholate excretion by menadione is related to the increased formation of glutathione disulfide; and (c) that menadione derivatives show little, if any, contribution to the inhibition of taurocholate excretion.

Adenosine Triphosphate↗
PubMed1988

Effects of 5-azacytidine and methyl-group deficiency on NAD(P)H: quinone oxidoreductase and glutathione S-transferase in liver.

Treatment with 5-azacytidine or dietary methyl-group deficiency effected DNA hypomethylation in mouse liver. With these treatments, NAD(P)H: quinone oxidoreductase (EC 1.6.99.2) and some glutathione S-transferase (EC 2.5.1.18) activities were over-expressed, lactate dehydrogenase (EC 1.1.1.27) activity was unaffected and the level of cytochrome P-450 was decreased. The 5-azacytidine induction of NAD(P)H: quinone oxidoreductase was significantly suppressed by puromycin, suggesting that increased enzyme activity results from an elevated level of enzyme-protein synthesis. Regulation at the transcriptional level was revealed by a substantial increase in mRNA of NAD(P)H: quinone oxidoreductase, as shown by Northern-blot analysis. The enzyme pattern observed with 5-azacytidine and with the (carcinogenic) dietary methyl-group deficiency resembles that found in hepatic nodules.

Animals↗
PubMed1988

Hepatic inositol release upon hormonal stimulation of perfused rat liver.

A sustained increase in the hepatic release of 3H radioactivity was shown to occur upon hormonal stimulation of perfused rat liver 15-20 h after intraperitoneal injection of 100 microCi of myo-[2-3H]inositol. Hormone-released radioactive material was analysed by t.l.c. and was found to consist predominantly of [3H]inositol, without further metabolites. Vasopressin (14 nM), phenylephrine (1.7 microM), angiotensin II (15 nM), glucagon (0.5 nM) and dibutyryl cyclic AMP (5 microM) exert maximal effects on hepatic inositol efflux after 10-15 min of stimulation. Omission of Ca2+ from the perfusion medium abolishes the hormone-dependent inositol release. LiCl (10 mM) does not significantly affect the basal release of [3H]inositol, but suppresses vasopressin- and angiotensin-triggered inositol release. Inositol efflux induced by glucagon, dibutyryl cyclic AMP and phenylephrine, however, remains essentially unchanged by LiCl infusion. This establishes a further metabolic difference between these two groups of agonists in that stimuli that act through cyclic AMP produce a stimulated outflow of inositol, but apparently without a Li+-sensitive phosphatase being involved in the overall process.

Angiotensin II↗
PubMed1988

A novel biologically active selenooorganic compound--VII. Biotransformation of ebselen in perfused rat liver.

Ebselen (PZ 51) is a selenoorganic compound with antioxidant and antiinflammatory properties, and its metabolism was studied in isolated perfused rat liver (hemoglobin-free, open system). 75Se-labelled ebselen was taken up into liver cells and radioactivity was excreted into bile. Biliary excretion of 75Se-compounds reached maximal values of 4 nmol/min per g wet wt. HPLC analysis of bile and effluent perfusate as well as identification of separated metabolites by mass spectrometry were carried out. The biliary metabolites were (a) an interesting novel Se-glucuronide, 2-glucuronylselenobenzanilide, (metabolite IV), as the major metabolite, and (b) an O-glucuronide, N-(4'-glucuronyloxyphenyl)-2-methylselenobenzanilide (metabolite III). The major effluent perfusate metabolites were Se-methylated derivatives (metabolites I and II). There was no evidence for sulfated metabolites. The selenodisulfide with glutathione, S-(2-phenyl-carbamoyl-phenylselenyl)-glutathione, was not detected, probably because of low steady-state concentrations and/or its biochemical lability. The selenium in ebselen is not bioavailable (e.g. for the synthesis of glutathione peroxidase), in contrast to selenite, for example, thus explaining the very low ebselen toxicity. However, the enzymatic steps in Se-methylation could be similar to those in the metabolism of selenite which include hydrogen selenide methylation. Se-glucuronides constitute a novel category of compounds in addition to the O-, N-, C- and S-glucuronide classes known in biology.

Animals↗
PubMed1988

Alkane production by isolated rat heart and lung.

Ethane and pentane have been measured as an index of lipid peroxidation occurring in the isolated perfused rat heart as well as lung preparations. In order to initiate lipid peroxidation cumene hydroperoxide was infused. The results show a significant enhancement of both ethane and pentane evolution from both isolated organs by cumene hydroperoxide. The production of alkanes by perfusion of high doses of cumene hydroperoxide in lungs is about one-half that of the isolated heart. Such reduced production of alkanes by the lungs can be explained by the fact that lung lipids, which contain mostly saturated fatty acids, might have resisted the peroxidative degradation. In comparison to cumene hydroperoxide, tert-butyl hydroperoxide also increased alkane production, caused a reduction of glutathione content and increased oxidized glutathione in hearts. 4-Hydroxynonenal infusion was much less effective in causing alkane release but caused profound depletion of cardiac glutathione. Paraquat had relatively insignificant effects on cardiac lipid peroxidation and glutathione content.

Animals↗