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M Berggren

Publications and source records attributed to M Berggren.

53 records · Page 3Linked to original sources
PubMed1984

Glutathione biosynthesis in the isolated perfused rat lung: utilization of extracellular glutathione.

The isolated perfused rat lung catalyzed the biosynthesis of GSH when the sulfur amino acids cysteine or N-acetylcysteine, but not methionine, were supplied in the perfusion medium. The lung also had the capacity to utilize extracellular GSH for this purpose. Replenishment of intracellular GSH in perfused lungs from diethylmaleate-treated rats was pronounced even at 25 microM GSH in the perfusion medium. The utilization of extracellular GSH is probably primarily through extracellular break-down and resynthesis rather than direct uptake as indicated by the inhibitory effect of the gamma-glutamylcysteine synthetase inhibitor, buthionine sulfoximine and the gamma-glutamyl transferase inhibitor, anthglutin. The results indicate that the lung in addition to the kidney may utilize circulating plasma GSH.

Acetylcysteine↗
PubMed1983

Oxidation of glutathione by free radical intermediates formed during peroxidase-catalyzed N-demethylation reactions.

Horseradish peroxidase-catalyzed N-demethylation of aminopyrine and dimethylaniline results in generation of free radical intermediates which can interact with glutathione (GSH) to form a glutathione radical. This can either dimerize to yield glutathione disulfide or react with O2 to form oxygenated products of glutathione. Ethylmorphine is not a substrate in the peroxidase-mediated reaction, and free radical intermediates which react with GSH, are not formed from aminopyrine and dimethylaniline when the horseradish peroxidase/H2O2 system is replaced by liver microsomes and NADPH. Therefore, it appears unlikely that formation of free radical intermediates can be responsible for the depletion of GSH observed during N-demethylation of several drugs in isolated liver cells.

Animals↗
PubMed1982

Elevation of conjugation capacity in isolated hepatocytes from BHA-treated mice.

Using harmol and paracetamol as the substrates, the elevation of conjugation reactions by BHA feeding and their significance towards the protective effects of this antioxidant has been studied with hepatocytes obtained from mice. With both substrates, an almost five fold elevation of the glucuronidation was observed. However, there was no change in the rate of sulfate conjugation. The rate of glutathione conjugate formation with paracetamol was also not enhanced, even though both the GSH level and glutathione S-transferase activities were increased. Finally, BHA administration afforded no protective effect against the hepatotoxic effects of paracetamol, even when the production of reactive paracetamol metabolites was increased by 3-methylcholanthrene pretreatment.

Acetaminophen↗
PubMed1982

Prostaglandin synthetase catalyzed activation of paracetamol.

Prostaglandin synthetase has the ability to catalyze the metabolism of paracetamol to a reactive metabolite, which binds to protein and reduced glutathione (GSH). This was demonstrated with microsomes isolated from both sheep seminal vesicles (SSV) and rabbit kidney medulla. The activation of paracetamol occurred through cooxygenation during prostaglandin biosynthesis, the peroxidase activity of this enzyme being responsible for the reaction. In addition to being metabolized, paracetamol also stimulated the rate of prostaglandin biosynthesis probably by serving as a potent hydrogen donor. The metabolism of paracetamol to a reactive metabolite most likely involved the formation of a paracetamol radical species. This was indicated by an inhibitory effect of the antioxidant, butylated hydroxyanisole, as well as by a very rapid oxidation of GSH during the course of the prostaglandin synthetase catalyzed reaction. Whether this paracetamol radical is further oxidized to the quinone imine prior to reacting with GSH or protein, remains to be established. The ultimate reactive metabolite is evidently the same as that formed with liver microsomes and NADPH since the glutathione conjugates were apparently identical. The rate of paracetamol activation by SSV microsomes was, however, more than 100 times that by liver microsomes and furthermore the apparent Km was considerably lower. Finally, N-OH paracetamol was shown to be activated by prostaglandin synthetase in the presence of arachidonic acid to a metabolite apparently different from that formed from paracetamol.

Acetaminophen↗
PubMed1978

Uptake of glucuronides into isolated hepatocytes and their effects on glucuronide and sulphate conjugation.

Uptake studies, using radioactive labelled glucuronides, have demonstrated the ability of 4-nitrophenyl glucuronide and phenolphthalein glucuronide to enter isolated rat hepatocytes. Of these glucuronides 4-nitrophenyl glucuronide was distributed in a similar manner to O-methylglucose, whereas phenolphthalein glucuronide was bound to cellular constituents. Phenolphthalein glucuronide had an effect on theconjugation of harmol in the isolated hepatocytes when glucuronidation was found to be markedly inhibited and sulphation slightly stimulated. The glucuronidation of 4-nitrophenol, 4-methylumbelliferone and harmol in native microsomes was inhibited by phenolphthalein glucuronide. 4-Nitrophenyl glucuronide and also naphthyl glucuronide were without effect both in hepatocytes and microsomes. In control hepatocytes harmine was metabolized to form harmolsulphate mainly. Phenolphthalein glucuronide only affected this metabolic pattern to a minor extent. However, in hepatocytes from phenobarbital treated rats, where the rate of harmine metabolism is increased about five times and the main metabolite is harmol glucuronide, phenolphthalein glucuronide inhibited the formation of the conjugate with a concomitant increase in free harmol.

Animals↗
PubMed1971

Mechanism of inhibition of microsomal mixed-function oxidation by the gut-contents inhibitor of the southern armyworm (Prodenia eridania).

A potent inhibitor of microsomal mixed-function oxidation reactions in insects had previously been isolated and partially purified from the gut contents of Prodenia eridania and shown to be associated with proteinase activity. Incubation of rat liver microsomal fraction with low concentrations of this inhibitor led to solubilization of NADPH-cytochrome c reductase, which was paralleled by the inactivation of reduction of cytochrome P-450 by NADPH and by the inhibition of NADPH-linked benzo[3,4]pyrene hydroxylation and aminopyrine demethylation. There was little or no effect on cytochromes b(5) and P-450, nor was the capacity of the latter catalyst to combine with exogenous substrates decreased. Contrary to the findings with NADPH, preincubation of microsomal fraction with the inhibitor did not cause a significant decrease in the rate of cytochrome P-450 reduction by NADH, supporting the assumption that different catalysts are involved in the electron transfer from NADH and NADPH to cytochrome P-450. The findings indicate the importance of taking the possible presence of endogenous inhibitors into consideration when evaluating low or absent mixed-function oxidation activities found in insect systems in vitro.

Animals↗
PubMedDate not supplied

Gastrointestinal metabolism of N-acetylcysteine in the rat, including an assay for sulfite in biological systems.

The intestinal metabolism of N-acetylcysteine was studied in the rat. Isolated intestinal epithelial cells were shown to rapidly deacetylate [14C]-N-acetylcysteine to [14C]-cysteine, with slight oxidation of the latter to disulfide species. The cells did not accumulate reduced or oxidized cysteine, and N-acetylcysteine itself was not detected either free or in oxidized species intracellularly. Further metabolism of this NAC-derived cysteine to inorganic sulfite or glutathione was not detected. Following the administration of [14C]-N-acetylcysteine (50 mg/kg; 25 microCi) in vivo into the ilium, small quantities of both reduced and oxidized [14C]-N-acetylcysteine were demonstrated in hepatic portal vein plasma. [14C]-cysteine and inorganic sulfite were demonstrated as the major metabolites of N-acetylcysteine. These were present in the portal vein plasma at levels five and three times greater than the parent drug, respectively, 30 min after dosing. Additionally, [14C]-glutathione was shown to be a minor metabolite of N-acetylcysteine accumulating in portal vein plasma. These results may provide an explanation for the apparent low bioavailability of N-acetylcysteine when administered orally in humans and are discussed in terms of the origins of the protective effect of the drug in cases of paracetamol intoxication in humans.

Acetylcysteine↗
PubMedDate not supplied

Isolated rat hepatocytes as an experimental tool in the study of cell injury. Effect of anoxia.

Rat hepatocytes were isolated by liver perfusion in the presence of collagenase and hyaluronidase and incubated in the absence or presence of oxygen. As a result of anoxia, there was a gradual increase in plasma membrane permeability, noted as an increase in succinate-stimulated oxygen uptake, a decrease in trypan blue exclusion frequency, a leakage of cytosolic lactate dehydrogenase activity and an increased proportion of swollen and disrupted cells. After anaerobic incubation for 30 minutes--but not for 60 minutes--there were signs of recovery from anoxic cell injury upon re-oxygenation. The changes in plasma membrane permeability properties in anoxia seemed to be preceded by a marked decrease in cellular ATP level; aerobic incubation of hepatocytes in the presence of an uncoupler of phosphorylation from respiration led to a similar decrease in cellular ATP concentration followed by similar disturbances in plasma membrane permeability properties. It is suggested that a distrubed plasma membrane function caused by a decreased energy level is of primary importance for the initiation of cell death in anoxia.

Adenosine Triphosphate↗
PubMedDate not supplied

Hydroperoxide-induced broncho- and vasoconstriction in the isolated rat lung.

The effects of different hydroperoxides on lung mechanics and perfusate flow rate and their mechanisms of action were studied in isolated perfused rat lungs. The administration of hydrogen peroxide, t-butyl hydroperoxide, cumene hydroperoxide, linoleic acid hydroperoxide, and linoleic acid ethylester hydroperoxide (0.1-2 mM) to the perfusate caused a marked decrease in lung compliance, conductance, and perfusate flow rate, with constriction strength of t-butyl hydroperoxide greater than hydrogen peroxide greater than cumene hydroperoxide greater than linoleic acid ethylester hydroperoxide greater than linoleic acid hydroperoxide. Although the hydroperoxides probably had to enter lung cells to exert their effects, no relationship was found between constriction strength and amount of hydroperoxide taken up by the lung. Reduced sensitivity was apparent after repeated dosing, depending on the length of time between dosing. The addition of the iron chelator Desferal (1 mM) had no effect on the hydroperoxide-induced broncho- and vasoconstriction, although free iron was reduced by 50% in the lungs. The administration of the antioxidants diphenyl-p-phenylenediamine (50 microM) or butylated hydroxyanisole (200 microM) to the perfusate 20 min prior to the hydroperoxide attenuated the hydroperoxide-induced effects as well as arachidonic acid-induced broncho- and vasoconstriction. Our findings have shown that hydroperoxides that can enter the lung cells will also induce both vaso- and bronchoconstriction in the isolated perfused rat lung.

Animals↗
PubMedDate not supplied

A multiwell assay for inhibitors of phosphatidylinositol-3-kinase and the identification of natural product inhibitors.

A convenient and reliable multisample assay for the screening of inhibitors of the growth factor signalling enzyme phosphatidylinositol-3-kinase (PtdIns-3-K) has been developed. Four natural product inhibitors of Ptdlns-3-K have been identified with IC50 values for hypericin 0.18 microM, emodin 3.3 microM, asperuloside 2.0 microM and uttronin A 1.1 microM.

Animals↗
PubMedDate not supplied

Thioredoxin and thioredoxin reductase gene expression in human tumors and cell lines, and the effects of serum stimulation and hypoxia.

Thioredoxin and thioredoxin reductase are redox proteins that have been implicated in the control of cell proliferation and transformation. We report the levels and activity of these proteins and their mRNAs in human primary tumors and tumor cell lines. Half of human primary colorectal carcinomas (5/10) examined had increased thioredoxin mRNA, of 3- to over 100-fold, compared to adjacent normal colonic mucosa from the same subject. Thioredoxin reductase protein and activity were increased an average of 2-fold in human colorectal tumors compared to normal mucosa. A number of human hematologic and solid tumor cell lines were studied and showed a 10-fold range of thioredoxin mRNA and a 23-fold range of thioredoxin reductase mRNA. Increased proliferation and hypoxia are factors that might contribute to the increased expression in solid tumors. We found that serum stimulation of growth arrested MCF-7 breast cancer cells caused a 59% increase in thioredoxin mRNA and a 62% increase in thioredoxin reductase mRNA by 24 hours. Exposure of HT-20 colon cancer cells to hypoxia resulted in a 14-fold increase in thioredoxin mRNA by 16 hours, and a transient 4-fold increase in thioredoxin reductase mRNA at 1 hour that had returned to control levels by 8 hours. Cancer cells were found to release thioredoxin into the medium at rates between 1 to 2 pmole/10(6) cells/3 hours. The rate of secretion was not, however, related to cellular-levels of thioredoxin. The results of the study show that the expression of thioredoxin and thioredoxin reductase are increased several fold in some human solid tumors compared to normal tissue. Secretion of thioredoxin, which is known to have a direct growth stimulating activity, by human tumor cells might lead to the stimulation of cancer cell growth.

Cell Hypoxia↗
PubMedDate not supplied

Cellular thioredoxin reductase activity is regulated by selenium.

Selenium (Se) is an essential trace element and has been reported to decrease the incidence of some human cancers. We have investigated the effects of Se on thioredoxin reductase, a selenocysteine containing flavoenzyme, in HT-29 human colon cancer cells grown in serum-free medium. Sodium selenite and other Se containing compounds produced a time and concentration dependent increase in intracellular thioredoxin reductase activity and protein levels. Selenite was the most active of the Se compounds examined: 1 microM selenite produced a 28-fold increase in thioredoxin reductase activity by 1 day and 10 microM selenite over a 60-fold increase by 5 days. The activity of a related non-selenocysteine containing flavoenzyme glutathione reductase was not increased by selenite. Selenite, but not the other Se containing compounds inhibited cell growth at concentrations above 2 microM. The results show that Se can produce large increases in cell thioredoxin reductase activity.

Blotting, Western↗