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Biomedical subjects

D J van den Dobbelsteen

Publications and source records attributed to D J van den Dobbelsteen.

7 recordsLinked to original sources
PubMed2004

Genotoxicity of hormonal steroids.

Hormonal steroids have a widespread use in medicine and their side effects are continuously debated. The possible genotoxic activity of steroids has been the subject of many investigations. The natural estrogens estradiol, estrone and estriol are generally negative in the ICH core battery of tests, but several positive results have been obtained when using additional endpoints of genotoxicity. The genotoxic activity of the 4-hydroxy metabolites of estradiol and estrone is well established. The synthetic steroidal estrogens have a comparable profile of negative and positive test results. Cyproterone acetate and some of its analogues have a special position within the group of progestins. Their genotoxic potential has been established. Other progestins are generally negative in the routine tests. Anti-glucocorticoids, anti-progestins, corticosteroids, androgens, anabolics and anti-androgens appear to be devoid of genotoxic activities. The genotoxic potential of estradiol, estrone and cyproterone acetate with its analogues may play no role under normal physiological and therapeutic conditions. The metabolic conditions that are needed for the formation of DNA-reactive metabolites and oxygen radicals may not be present in humans. Epidemiological cancer data seem to support this view. The importance of thresholds in the dose-effect-relationship of genotoxicity data and their use in risk assessment is discussed.

Androgens↗
PubMed2000

Inhibition of Na+/K(+)-ATPase may be one mechanism contributing to potassium efflux and cell shrinkage in CD95-induced apoptosis.

To investigate the involvement of K+ efflux in apoptotic cell shrinkage, we monitored efflux of the K+ congener, 86Rb+, and cell volume during CD95-mediated apoptosis in Jurkat cells. An anti-CD95 antibody caused apoptosis associated with intracellular GSH depletion, a significant increase in 86Rb+ efflux, and a decrease in cell volume compared with control cells. Preincubating Jurkat cells with Val-Ala-Asp-chloromethylketone (VAD-cmk), an inhibitor of caspase proteases, prevented the observed 86Rb+ efflux and cell shrinkage induced by the anti-CD95 antibody. A wide range of inhibitors against most types of K+ channels could not inhibit CD95-mediated efflux of 86Rb+, however, the uptake of 86Rb+ by Jurkat cells was severely compromised when treated with anti-CD95 antibody. Uptake of 86Rb+ in Jurkat cells was sensitive to ouabain (a specific Na+/K(+)-ATPase inhibitor), demonstrating Na+/K(+)-ATPase dependent K+ uptake. Ouabain induced significant 86Rb+ efflux in untreated cells, as well as it seemed to compete with 86Rb+ efflux induced by the anti-CD95 antibody, supporting a role for Na+/K(+)-ATPase in the CD95-mediated 86Rb+ efflux. Ouabain treatment of Jurkat cells did not cause a reduction in cell volume, although together with the anti-CD95 antibody, ouabain potentiated CD95-mediated cell shrinkage. This suggests that the observed inhibition of Na+/K(+)-ATPase during apoptosis may also facilitate apoptotic cell shrinkage.

Amino Acid Chloromethyl Ketones↗
PubMed1996

Rapid and specific efflux of reduced glutathione during apoptosis induced by anti-Fas/APO-1 antibody.

Although human JURKAT T lymphocytes induced to undergo apoptosis with anti-Fas/APO-1 antibody were observed to rapidly lose reduced glutathione (GSH), increased concentrations of oxidized products were not detectable. Unexpectedly, the reduced tripeptide was instead quantitatively recovered in the incubation medium of the cells. As GSH loss was blocked by bromosulfophthalein and dibromosulfophthalein, known inhibitors of hepatocyte GSH transport, a specific export rather than nonspecific leakiness through plasma membranes is proposed to be responsible. Apoptosis was delayed when GSH-diethylesters were used to elevate intracellular GSH, although the high capacity of the activated efflux system quickly negated the benefit of this treatment. Stimulation of GSH efflux provides a novel mechanism whereby Fas/APO-1 ligation can deplete GSH. We speculate that it enhances the oxidative tonus of a responding cell without requiring an increase in the production of reactive oxygen species.

Apoptosis↗
PubMed1996

Intracellular redox changes during apoptosis.

In the current paradigm for apoptotic cell death, the activity of a family of proteases related to interleukin 1-beta converting enzyme (ICE) orchestrates the multiple downstream events (such as cell shrinkage and chromatin degradation) that comprise apoptosis. A variety of stimuli can induce this type of cell death. One of the most reproducible inducers is mild oxidative stress, although it is unclear how an oxidative stimulus activates ICE-like proteases. Oxidative modification of proteins and lipids have also been observed in cells undergoing apoptosis in response to non-oxidative stimuli, suggesting that intracellular oxidation may be a general feature of the effector phase of apoptosis. However, attempts to consistently detect a requirement for reactive oxygen species in apoptosis have been inconclusive. Recent experiments revealing that apoptosis is typically accompanied by a depletion of intracellular reduced glutathione (GSH) are also discussed. In JURKATT lymphocytes treated with antibodies to the Fas/APO-1 surface receptor, this depletion results from an accelerated efflux of the reduced thiol rather than any intracellular oxidation. As GSH is the most abundant cytosolic reductant, we propose that its efflux may provide a non-oxidative mechanism by which the reducing environment of apoptotic cells is lost. An increase in oxidative damage to proteins and lipids would then result even in the absence of an increase in the production of oxidants. This may explain the seemingly contradictory findings that increased oxidative stress is not required for apoptosis even though antioxidants often inhibit the process and peroxidised products accumulate in apoptotic cells.

Journal Article↗
PubMed1995

Signalling mechanisms and oxidative stress in apoptosis.

A variety of stimuli can induce cells to undergo apoptotic death. One of the most reproducible inducers is mild oxidative stress, be it via exposure to hydrogen peroxide, redox-cycling quinones or thiol-alkylating agents. Oxidative modifications of proteins and lipids have also been observed in cells undergoing apoptosis in response to non-oxidative stimuli such as glucocorticoids or topoisomerase II inhibitors. This suggests that some unidentified oxidative changes occur during apoptosis in many, if not all, cases. However, recent experiments demonstrating apparently normal apoptosis even when cells are cultured at low oxygen tensions show that reactive oxygen species cannot be essential mediators of this type of cell death. Experiments revealing that apoptosis is typically accompanied by a depletion of intracellular reduced glutathione (GSH) are also discussed. As GSH depletion will lower a cell's capacity to buffer against endogenous oxidants, we propose that it contributes to the increased oxidative damage commonly observed to accompany apoptosis. In addition, it may set a time limit on continued mitochondrial function (and thus indirectly on total ATP levels and membrane integrity) in apoptotic cells, and thereby explain the often observed 'secondary necrosis' of cells undergoing apoptosis in vitro.

Animals↗