Biomedical subjects

J Jarabak

Publications and source records attributed to J Jarabak.

At least 19 recordsLinked to original sources

PubMed1998

Redox cycling of polycyclic aromatic hydrocarbon o-quinones: metal ion-catalyzed oxidation of catechols bypasses inhibition by superoxide dismutase.

Several two-electron quinone reductases catalyze the redox cycling of polycyclic aromatic hydrocarbon (PAH) o-quinones. When the carbonyl reductase of human placenta catalyzes the cycling of 9,10-phenanthrenequinone in aqueous phosphate buffer, reactive oxygen species are produced. Superoxide dismutase (SOD) inhibits the cycling by more than 90%, but the addition of 1 microM Cu2+ or 15 microM ferricytochrome c (cyt c3+) completely restores the cycling rate to that of the control. Similar results are obtained for 5,6-chrysenequinone, 5,6-benz[a]anthracenequinone, 4,5-benzo[a]pyrenequinone, and 7,8-benzo[a]pyrenequinone in assay mixtures which contain dimethyl sulfoxide. The 17beta-hydroxysteroid dehydrogenase (17beta-HSD) of human placenta also catalyzes the redox cycling of these quinones, and cycling is inhibited by SOD. Although free metal ions (Cu2+ and Fe3+) inhibit the 17beta-HSD, cyt c3+ does not inhibit the enzyme. If cyt c3+ is added to assay mixtures containing SOD, cycling rates are equal to those of the corresponding controls. These experiments suggest that SOD may not protect cells from the toxic effects of PAH o-quinone cycling if certain metal ions or metal chelates are also present.

17-Hydroxysteroid Dehydrogenases↗

PubMed1997

Redox cycling of polycyclic aromatic hydrocarbon o-quinones: reversal of superoxide dismutase inhibition by ascorbate.

When redox cycling of four polycyclic aromatic hydrocarbon o-quinones is catalyzed by the 17 beta-hydroxysteroid dehydrogenase, autooxidation of the hydroquinone is a free radical chain reaction in which superoxide anion is the propagating species. Superoxide dismutase inhibits the redox cycling of these quinones, and ascorbate reverses this inhibition. Studies of the mechanism, using 9,10-phenanthrenequinone, show that ascorbate competes with superoxide dismutase for the superoxide anion; the ascorbyl radical formed then oxidizes the hydroquinone. In this mechanism, ascorbyl radical participates in chain propagation. The reversal of superoxide dismutase inhibition by ascorbate is observed when other two-electron reductases catalyze the cycling, and it occurs in the absence of metal ions. Although ascorbate is generally thought to be an antioxidant, it behaves as a prooxidant in the experiments reported here.

17-Hydroxysteroid Dehydrogenases↗

PubMed1996

Polycyclic aromatic hydrocarbon quinone-mediated oxidation reduction cycling catalysed by a human placental 17beta-hydroxysteroid dehydrogenase.

The human placental 17beta-hydroxysteroid dehydrogenase reduces a number of polycyclic aromatic hydrocarbon (PAH) o-quinones; some of the quinones undergo redox cycling at rates that approach or exceed the rate of reduction of estrone by the enzyme. The non-K-region o-quinone, 7,8-benzo[a]pyrenequinone, is the best o-quinone substrate tested. Cycling of all the quinone substrates is inhibited by superoxide dismutase; cycling is also inhibited by 17beta-estradiol and other estrogens. Since 19 alpha-estradiol is a competitive inhibitor of 9,10-phenanthrenequinone by the 17beta-hydroxysteroid dehydrogenase, it is likely that both reactions occur at the same active site on the enzyme. In the presence of the 17beta-hydroxysteroid dehydrogenase, the equilibrium between 17beta-estradiol, estrone, NADP, and NADPH is shifted by 7,8-benzo[a]pyrenequinone because the rapid redox cycling of this quinone results in the oxidation of NADPH. Unlike a number of hydroxysteroid dehydrogenases, the placental 17beta-hydroxysteroid dehydrogenase does not oxidize any of the six PAH trans-dihydrodiols tested.

17-Hydroxysteroid Dehydrogenases↗

PubMed1995

Effect of ascorbate on the DT-diaphorase-mediated redox cycling of 2-methyl-1,4-naphthoquinone.

Following the two-electron reduction of 2-methyl-1,4-naphthoquinone by rat liver DT-diaphorase (also called NAD(P)H: (quinone acceptor) oxidoreductase, EC 1.6.99.2), the hydroquinone product is slowly autoxidized to the quinone in buffered solutions at pH 7.0. The autoxidation, which generates the superoxide radical (O2-.) and other reactive oxygen species, is the rate-limiting step in the oxidation-reduction (redox) cycling of the quinone. The addition of ascorbate to these reaction mixtures increases the rate of redox cycling. Two mechanisms are proposed to explain this increase: (1) ascorbate reduces the quinone in a one-electron reduction and (2) if Fe(3+)-EDTA is present, ascorbate reduces the metal chelate in a one-electron reduction. Both mechanisms produce O2-. which initiates the free radical chain reaction that results in autoxidation of the hydroquinone. Although ascorbate may be a physiologically important antioxidant under some conditions, the studies reported here show that ascorbate is a prooxidant in the redox cycling of 2-methyl-1,4-naphthoquinone and, as such, could increase the potential toxicity of this quinone.

Animals↗

PubMed1993

Studies on three reductases which have polycyclic aromatic hydrocarbon quinones as substrates.

Unlike rodent tissues, the major quinone reductase in centrifuged homogenates of human liver and placenta is a carbonyl reductase rather than a DT-diaphorase. When reduction of polycyclic aromatic hydrocarbons is compared, there are differences between the human placental carbonyl reductase, rat liver DT-diaphorase, and Clostridium DT-diaphorase. In a buffer containing 1% albumin and 10 microM quinone, 9,10-phenanthrenequinone is reduced most rapidly by the carbonyl reductase, 2-methyl-1,4-naphthoquinone is reduced most rapidly by the rat enzyme, and 3,6-pyrenequinone is reduced most rapidly by the Clostridium enzyme. In the presence of O2, redox cycling occurs with all of the quinones that are enzyme substrates, but the rate of cycling does not necessarily correlate with that of quinone reduction. Since glutathionyl adducts of certain quinones can undergo redox cycling mediated by the human carbonyl reductase or rat DT-diaphorase, it is unlikely that the conjugation of one of these quinones with glutathione is sufficient to protect against quinone-mediated oxidative stress in cells which contain either of these enzymes. The observation that superoxide dismutase and a dismutase "mimic," 3-carboxy-2,2,5,5-tetramethylpyrrolidine-1-oxyl, inhibit the redox cycling of 9,10-phenanthrenequinone suggests a mechanism whereby cells could be protected against oxidative stress caused by certain quinones.

Alcohol Oxidoreductases↗

PubMed1992

Polycyclic aromatic hydrocarbon quinones may be either substrates for or irreversible inhibitors of the human placental NAD-linked 15-hydroxyprostaglandin dehydrogenase.

Under aerobic conditions, 9,10-phenanthrenequinone and 5,6-chyrsenequinone undergo oxidation-reduction cycling in the presence of NADH and the NAD-linked 15-hydroxyprostaglandin dehydrogenase. This results in the formation of potentially hazardous semiquinones, the superoxide anion, and H2O2. Superoxide dismutase inhibits this cycling by destroying the free radical chain propagator, the superoxide anion. Four other polycyclic aromatic hydrocarbon quinones are not substrates of the enzyme and they cause it to undergo a time-dependent inactivation. This presumably results from alkylation of the enzyme. Glutathione fully protects the enzyme against inactivation by 1,2-naphthoquinone but is only partially effective against 7,8-benzo[a]pyrenequinone. These results suggest that in tissues which contain the NAD-linked 15-hydroxyprostaglandin dehydrogenase some polycyclic aromatic hydrocarbon quinones might produce deleterious effects by undergoing redox cycling. Others might cause such effects by irreversibly inhibiting the enzyme which catalyzes the first step in prostaglandin catabolism.

Alprostadil↗

PubMed1991

Polycyclic aromatic hydrocarbon quinone-mediated oxidation reduction cycling catalyzed by a human placental NADPH-linked carbonyl reductase.

Polycyclic aromatic hydrocarbon quinones, hydroquinones, and glutathionyl adducts of quinones undergo oxidation-reduction (redox) cycling in the presence of NADPH and the NADPH-linked human placental carbonyl reductase. K-region and non-K-region o-quinones and their glutathione adducts are the best substrates of this enzyme; they are reduced to hydroquinones. Under aerobic conditions, the hydroquinones are autoxidized with the formation of potentially hazardous semiquinones and the superoxide anion. Because of these reactions it is unlikely that polycyclic aromatic hydrocarbon quinones or their glutathione adducts are inert products of detoxication in tissues that contain the carbonyl reductase or another enzyme with similar substrate specificity. If superoxide dismutase is added to reaction mixtures containing the carbonyl reductase and quinones, it inhibits redox cycling. Presumably this results from destruction of the superoxide anion which acts as a chain propagator in these reactions.

Alcohol Oxidoreductases↗

PubMed1989

Improved safety of glucagon testing for pheochromocytoma by prior alpha-receptor blockade. A controlled trial in a patient with a mixed ganglioneuroma/pheochromocytoma.

The glucagon stimulation test has been superseded in recent years by the clonidine suppression test because it can provoke dangerous increases in blood pressure in patients with pheochromocytomas. We describe the first patient in whom a pheochromocytoma was diagnosed by a glucagon test, after which the blood pressure (but not the plasma catecholamine) response to a second injection of glucagon was blocked by pretreatment with phenoxybenzamine. After the tumor (which contained both pheochromocytoma and ganglioneuroma tissue) was removed, a third glucagon test result was negative. This experience suggests that patients with normal plasma catecholamine levels who are suspected of harboring a pheochromocytoma may be accurately diagnosed, but potentially dangerous increases in blood pressure may be minimized, by performing the glucagon test after alpha-adrenergic blockade.

Adrenal Gland Neoplasms↗

PubMed1988

Inhibition of the human placental NAD- and NADP-linked 15-hydroxyprostaglandin dehydrogenases by nonsteroidal anti-inflammatory drugs.

A number of nonsteroidal anti-inflammatory drugs are non-competitive or mixed inhibitors of human placental NAD- and NADP-linked 15-hydroxyprostaglandin dehydrogenases. Cis- and trans-sulindac sulfide and cis- and trans-sulindac inhibit the NAD-linked enzyme as well or better than they inhibit various cyclooxygenases in vitro. The remainder of the compounds tested are at least one order of magnitude less effective as inhibitors of the 15-hydroxyprostaglandin dehydrogenases than they are as inhibitors of cyclooxygenases. Cis- and trans-sulindac sulfide are sufficiently strong inhibitors of the NAD-linked enzyme (Kis of 7.8 microM and 6.8 microM respectively) to raise the possibility that they might also inhibit this enzyme in vivo.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1988

Purification of the human placental NAD-linked 15-hydroxyprostaglandin dehydrogenase.

An NAD-linked 15-hydroxyprostaglandin dehydrogenase has been purified 13,100-fold from human placental tissue. The specific activity of the purified enzyme ranges from 6900 to 8300 mU/mg protein depending on the method used to determine the protein concentration. On discontinuous electrophoresis in sodium dodecyl sulfate more than 95% of the protein migrates as a single band; its estimated molecular weight is 25.5-26.0 kDa. This is half the value obtained when the molecular weight is estimated under non-denaturing conditions and suggests that the enzyme is composed of two identical or nearly identical subunits.

Electrophoresis, Polyacrylamide Gel↗

PubMed1987

Polycyclic aromatic hydrocarbon quinones and glutathione thioethers as substrates and inhibitors of the human placental NADP-linked 15-hydroxyprostaglandin dehydrogenase.

The human placental NADP-linked 15-hydroxyprostaglandin dehydrogenase catalyzes oxidoreduction at the 9- and 15-positions of many prostaglandins, but its catalytic efficiency (i.e. kcat/Km) for these reactions is low (Jarabak, J., Luncsford, A., and Berkowitz, D. (1983) Prostaglandins 26, 849-868). In the present study, we demonstrate that both K-region and non-K-region o-quinones of polycyclic aromatic hydrocarbons are excellent substrates for this enzyme. These compounds are reduced with kcat/Km values ranging from 3 to 20 X 10(6) S-1 M-1. The glutathione thioethers of menadione and toluquinone are reduced with similar catalytic efficiencies. Furthermore, these substances and certain other glutathione thioethers are potent inhibitors of prostaglandin B1 oxidation ([I50] = 7 X 10(-8) to 5 X 10(-6) M); while several glutathione thioethers also inhibit polycyclic aromatic hydrocarbon quinone reduction ([I50] = 1.7-6.5 microM). These findings raise the possibility that the potential toxicity of quinones of polycyclic aromatic hyrocarbons and other xenobiotic substances may be altered in the placenta by an oxidoreductase for which prostaglandins are relatively poor substrates. They also suggest that the presence in placental tissue of certain glutathione thioethers could influence the reduction of these quinones and other xenobiotic substances by this enzyme.

Female↗

PubMed1987

Glutathione mixed disulfide inhibitors of the human placental NADP-linked 15-hydroxyprostaglandin dehydrogenase.

Six glutathione-containing inhibitors of the human NADP-linked 15-hydroxyprostaglandin dehydrogenase have been isolated from placental homogenates. Glutathione disulfide is one of these inhibitors. Although the structures of the other five have not been fully elucidated, all are disulfides. Studies with these compounds and with other mixed disulfides have shown that the glutathione mixed disulfides of beta-mercaptopyruvate, mercaptoacetate, and beta-mercaptolactate are more effective inhibitors of the enzyme than are the glutathione-containing mixed disulfides isolated from placental homogenates. beta-Mercaptolactate is particularly noteworthy because of its low Ki (0.13 microM). The results reported here suggest that the activity of the prostaglandin dehydrogenase may be influenced in vivo by various glutathione mixed disulfides.

Disulfides↗

PubMed1987

Irreversible inhibition of the human placental NADP-linked 15-hydroxyprostaglandin dehydrogenase/9-ketoprostaglandin reductase by glutathione thiosulfonate.

Oxidation of glutathione disulfide by a mixture of performic and hydrochloric acids leads to the formation of several compounds that are stronger inhibitors than glutathione disulfide of the placental enzyme that possess both NADP-linked 15-hydroxyprostaglandin dehydrogenase and 9-ketoprostaglandin reductase activities. The only one of these inhibitors that has been identified is glutathione thiosulfonate. The others are unstable and may include glutathione sulfinyl sulfone and glutathione disulfone. Since the enzyme appears to have a glutathione binding site in close proximity to its active site and glutathione thiosulfonate reacts with free sulfhydryl groups, the effects of this thiosulfonate on the enzyme were examined in more detail. Glutathione thiosulfonate and methyl methanethiosulfonate cause a time-dependent irreversible inhibition of both the hydroxyprostaglandin dehydrogenase and the ketoprostaglandin reductase activities, presumably by reacting with a free sulfhydryl at the prostaglandin binding site. Experiments with PGA1-glutathione show that this sulfhydryl is not necessary for the catalytic activity of the enzyme as long as the substrate can bind at the glutathione site.

Binding Sites↗

PubMed1987

In vitro activity of nicotinamide adenine dinucleotide- and nicotinamide adenine dinucleotide phosphate-linked 15-hydroxyprostaglandin dehydrogenases in placentas from normotensive and preeclamptic/eclamptic pregnancies.

Concentrations of prostaglandins E2 and I2 may be decreased in preeclamptic and eclamptic pregnancies. Because these prostaglandins produce vasodilation and inhibit platelet aggregation it has been suggested that a reduction in their biosynthesis might play an important role in the pathogenesis of the hypertension and coagulation abnormalities associated with preeclampsia. Placental tissue is an extremely rich source of several enzymes that catalyze the catabolism of prostaglandins. The present study was initiated to determine whether one of these catabolic enzymes might be increased in preeclamptic/eclamptic pregnancies. The activities of the NAD- and the NADP-linked 15-hydroxyprostaglandin dehydrogenases were measured in 16 preeclamptics (mean diastolic pressure, 108 +/- 13 mmHg) and compared with 16 normotensive controls matched for age (20.8 +/- 5.43 vs. 20.6 +/- 5.16) and gestational week of delivery (34.6 +/- 5.40 vs. 35.0 +/- 5.06). These results indicate that the activity of the placental NAD-linked 15-hydroxyprostaglandin dehydrogenase is elevated in preeclampsia (40.1 +/- 31.3 vs. 14.9 +/- 8.30 mU/g tissue, P less than 0.01). If this increase were also expressed in vivo, its effect on prostaglandin metabolism could be mistaken for impaired prostacyclin biosynthesis unless both the 6-keto- and 6,15-diketo-metabolites of prostacyclin were measured.

Adolescent↗

PubMed1985

The effect of NaCl intake on 9-ketoprostaglandin reductase activity in the rabbit kidney.

Renal 9-ketoprostaglandin reductase activity from rabbits fed 0.3 g or 2.5 g NaCl per 100 g chow was measured in both centrifuged homogenates and in purified enzyme fractions. There was no salt related increase in 9-ketoprostaglandin reductase activity. PGA1-glutathione, 9, 10-phenanthrenequinone, and 4-nitrobenzaldehyde were better substrates for the purified 9-ketoprostaglandin reductases than was PGE2. Several carbonyl reductases were isolated which used PGA1-glutathione, 9, 10-phenanthrenequinone, and 4-nitrobenzaldehyde, but not PGE2, as substrates. Although PGA1-glutathione was a more faithful indicator of PGE2-related 9-ketoprostaglandin reductase activity than either 9, 10-phenanthrenequione or 4-nitrobenzaldehyde, it did not always provide an accurate estimate of that activity.

Alcohol Oxidoreductases↗

PubMed1984

Oxidation of prostacyclin and its analogs by three 15-hydroxyprostaglandin dehydrogenases.

A study of the oxidation of prostacyclin and some of its analogs by three 15-hydroxyprostaglandin dehydrogenases was undertaken to determine the structural features of these compounds which might influence their rate of enzymatic inactivation. The effect of some structural changes seemed to be determined by the substrate specificity of individual enzymes. Other changes influenced the rate of oxidation by all three enzymes similarily. Among this latter group it was noted that a 15S hydroxyl group is necessary for oxidation to occur and that steric changes in the carboxy side chain and structural changes in the epoxy ring have a greater effect on the affinity of the substrate for the enzyme than on its maximum rate of oxidation. Certain analogs of prostacyclin are not substrates for one or more of the enzymes tested. Of these, (5S)-9-deoxy-5,9 alpha-epoxy-PGF1 and its methyl ester are potent inhibitors of only the placental enzyme---an interesting case of apparent selective metabolic regulation.

Animals↗

PubMed1983

Substrate specificity of three prostaglandin dehydrogenases.

Studies on the substrate specificity, kcat/Km, and effect of inhibitors on the human placental NADP-linked 15-hydroxyprostaglandin dehydrogenase (9-ketoprostaglandin reductase) indicate that it is very similar to a human brain carbonyl reductase which also possesses 9-ketoprostaglandin reductase activity. These observations led to a comparison of three apparently homogeneous 15-hydroxyprostaglandin dehydrogenases with varying amounts of 9-ketoprostaglandin reductase activity: an NAD- and an NADP-linked enzyme from human placenta and an NADP-linked enzyme from rabbit kidney. All three enzymes are carbonyl reductases for certain non-prostaglandin compounds. The placental NAD-linked enzyme, which has no 9-ketoprostaglandin reductase activity, is the most specific of the three. Although it has carbonyl reductase activity, a comparison of the Km and kcat/Km for prostaglandin and non-prostaglandin substrates of this enzyme suggests that its most likely function is as a 15-hydroxyprostaglandin dehydrogenase. The results of similar comparisons imply that the other two enzymes may function as less specific carbonyl reductases.

Alcohol Oxidoreductases↗

PubMed1983

Virilization due to a metastasizing granulosa cell tumor.

This report describes a virilizing granulosa cell tumor in a postmenopausal woman. The tumor metastasized to the liver, urinary bladder, and spinal column. Although the bladder metastases were diagnosed initially as paraganglioma, review of the slides and the demonstration of abundant lipid within the tumor cells led to the correct diagnosis. The plasma testosterone and 17-hydroxyprogesterone levels were elevated, while the plasma 17-hydroxypregnenolone and dehydroepiandrosterone levels were normal, suggesting that the delta 4-pathway of testosterone biosynthesis was predominant in this tumor. Gonadotropin levels were suppressed and did not respond to gonadotropin-releasing hormone. Presumably, this suppression was due to an increase in the plasma testosterone level.

17-alpha-Hydroxyprogesterone↗