Search PubMed⌕ Search

Biomedical subjects

H Sies

Publications and source records attributed to H Sies.

At least 361 records · Page 20Linked to original sources
PubMed1981

Hepatic calcium efflux during cytochrome P-450-dependent drug oxidations at the endoplasmic reticulum in intact liver.

During metabolism of (type I) drugs by cytochrome P-450-dependent monooxygenase of the endoplasmic reticulum, the NADPH/NADP+ ratio in rat liver selectively decreases to approximately one-half of the control values, whereas the NADH/NAD+ ratio remains practically unaffected [Sies, H. & Brauser, B. (1970) Eur. J. Biochem. 15, 521-540]. In view of the observations with isolated mitochondria [Lehninger, A. L., Vercesi, A. & Bababunmi, E. A. (1978) Proc. Natl. Acad. Sci. USA 75, 1690-1694] of stimulated Ca2+ efflux upon nicotinamide nucleotide oxidation, the selective oxidation of NADPH in cytosol and mitochondria during drug oxidations was considered a useful experimental tool for the determination of whether the oxidation of NADPH or of NADH is responsible for Ca2+ efflux. With perfused livers from phenobarbital-treated rats, Ca2+ efflux was demonstrated, amounting to 8 nmol/min per gram of liver (wet weight), with aminopyrine, ethylmorphine, or hexobarbital as drug substrates. Drug-associated Ca2+ release was diminished when the inhibitor metyrapone was also present, or when drug oxidation was suppressed during N2 anoxia or in the presence of antimycin A in livers from fasted rats. Ca2+ efflux was elicited also by infusion of the thiol oxidant diamide, and by t-butyl hydroperoxide. However whereas Ca2+ efflux elicited by these compounds was restricted upon addition of the thiol dithioerythritol, there was little, if any, sensitivity of the drug-associated Ca2+ efflux to the thiol. Further mitochondrial oxidation of NADPH by addition of ammonium chloride had no effect on drug-associated Ca2+ efflux. Prior addition of the alpha-agonist phenylephrine suppressed the Ca2+ release by drug addition. While the molecular mechanism involved in Ca2+ efflux from liver mitochondria and from hepatocytes as well as the regulatory significance are not yet known, it is concluded from the present experiments that in case of nicotinamide nucleotide-linked Ca2+ efflux the oxidation of NADPH may suffice, with oxidation of NADH not being a requirement.

Animals↗
PubMed1981

Low-level chemiluminescence of isolated hepatocytes.

1. Oxygenation of isolated hepatocytes leads to an increased emission of low level chemiluminescence and to an accumulation of malondialdehyde, both occurring after a lag phase of about 20--40 min. 2. Spectral analysis of oxygen-induced chemiluminescence of isolated hepatocytes showed three bands at 460, 560 and 640 nm, with two shoulders at 525 and 615 nm. Singlet molecular oxygen, formed during the free radical process accompanying lipid peroxidation, is identified as the main source of light emission, on the basis of comparison with spectra of singlet oxygen produced in chemical systems [Khan, A. U. and Kasha, M. (1963) J. Am. Chem. Soc. 92, 3293--3300]. 3. Hepatocytes from phenobarbital-pretreated rats, or glutathione-depleted hepatocytes showed a threefold increase in both maximal chemiluminescence intensity and malondialdehyde accumulated, as compared with control cells, whereas the lag phase was not modified by the pretreatments. 4. Glutathione-depleted hepatocytes did not show any increase in spontaneous lipid peroxidation as reflected by either malondialdehyde accumulation or chemiluminescence. A dissociation between both parameters was observed on addition of dithioerythritol: chemiluminescence intensity decreased while the malondialdehyde content remained unaltered. 5. It is concluded from these experiments that low-level chemiluminescence emitted from hepatocytes at wavelengths beyond 600 nm ('red band') monitors the steady-state concentration of singlet molecular oxygen, providing a useful tool to examine oxygen-dependent radical damage. Continuous monitoring of singlet oxygen levels affords an advantage over parameters measuring accumulative effects.

Animals↗
PubMed1980

Mitochondrial and cytosolic ATP/ADP ratios in isolated hepatocytes. A comparison of the digitonin method and the non-aqueous fractionation procedure.

The ratio of ATP content/ADP content in the mitochondrial matrix was found to be 2.07 +/- 0.21 and 2.26 +/- 0.22 as determined with six different preparations of isolated hepatocytes subfractionated with the digitonin and non-aqueous-fractionation procedures, respectively. In contrast, the mitochondrial matrix ATP/ADP determined with isolated haemoglobin-free perfused liver by using the non-aqueous-fractionation procedure was about 0.2, whereas the cytosolic values obtained with isolated cells and with the intact organ were similar. It is concluded that the relatively higher ATP/ADP ratio in the mitochondrial matrix of isolated hepatocytes represents a biochemical difference due to properties of the model rather than a methodological artifact.

Adenosine Diphosphate↗
PubMed1980

Deficient metabolic utilization of hydrogen peroxide in Trypanosoma cruzi.

The glutathione peroxidase-glutathione reductase system, an alternative pathway for metabolic utilization of H2O2 [Chance, Sies & Boveris (1979) Physiol. Rev. 59, 527-605], was investigated in Trypanosoma cruzi, an organism lacking catalase and deficient in peroxidase [Boveris & Stoppani (1977) Experientia 33, 1306-1308]. The presence of glutathione (4.9 +/- 0.7 nmol of reduced glutathione/10(8) cells) and NADPH-dependent glutathione reductase (5.3 +/- 0.4 munit/10(8) cells) was demonstrated in the cytosolic fraction of the parasite, but with H2O2 as substrate glutathione peroxidase activity could not be demonstrated in the same extracts. With t-butyl hydroperoxide or cumene hydroperoxide as substrate, a very low NADPH-dependent glutathione peroxidase activity was detected (equivalent to 0.3-0.5 munit of peroxidase/10(8) cells, or about 10% of glutathione reductase activity). Blank reactions of the glutathione peroxidase assay (non-enzymic oxidation of glutathione by hydroperoxides and enzymic oxidation of NADPH) hampered accurate measurement of peroxidase activity. The presence of superoxide dismutase and ascorbate peroxidase activity in, as well as the absence of catalase from, epimastigote extracts was confirmed. Ascorbate peroxidase activity was cyanide-sensitive and heat-labile, but no activity could be demonstrated with diaminobenzidine, pyrogallol or guaiacol as electron donor. The summarized results support the view that T. cruzi epimastigotes lack an adequate enzyme defence against H2O2 and H2O2-related free radicals.

Animals↗
PubMed1980

The role of pH and the lack of a requirement for hydorgencarbonate in the regulation of hepatic glutamine metabolism.

The rate of net glutamine degradation in non-recirculating perfused rat liver was estimated by the release of urea, ammonia and alanine in steady states of operation of glutaminase. Corrected for a slight intracellular accumulation of glutamate, accounting for 7% of the flux at 5mM glutamine, the estimated glutaminase activity agrees well with measurements of glutamine removal described in the literature for recirculating perfusion experiments. Glutaminase activity was decreased when the perfusate pH was lowered (i) by infusion of hydrochloric acid, (ii) by increasing the CO2 concentration, or (iii) by decreasing the hydrogencarbonate concentration. Conversely, it was increased when the perfusate pH was increased by infusion of sodium hydroxide or by increasing the hydrogencarbonate concentration. However, glutaminase activity did not depend on medium hydrogencarbonate. When the hydrogencarbonate buffer system was replaced by DMO or by Hepes equilibrated with O2 (no CO2 present), there was practically no change in the observed rates. These results, obtained in an iso-pH system, are in contrast to recent suggestions of a role of hydrogencarbonate in the regulation of glutamine metabolism based on results from incubations of isolated mitochondria or hepatocytes. It is concluded that the conservation of glutamine by the inhibition of hepatic glutaminase, which provides glutamine for the pH regulation by renal glutaminase, can be increased not only in metabolic acidosis but also in respiratory acidosis associated with high hydrogencarbonate concentration.

Alanine↗