Glucocorticoids inhibit interconversion of 7-hydroxy and 7-oxo metabolites of dehydroepiandrosterone: a role for 11beta-hydroxysteroid dehydrogenases?

The cytochrome p450-dependent formation and subsequent interconversion of dehydroepiandrosterone (DHEA) metabolites 7 alpha-hydroxy-DHEA (7 alpha-OH-DHEA), 7 beta-hydroxy-DHEA (7 beta-OH-DHEA), and 7-oxo-DHEA was observed in human, pig, and rat liver microsomal fractions. Rat liver mitochondria and nuclei also converted DHEA to 7 alpha-OH-DHEA and 7-oxo-DHEA, but at a lower rate. With NADP(+), and less so with NAD(+), rat, pig, and human liver microsomes and rat liver mitochondria and nuclei converted 7 alpha-OH-DHEA to 7-oxo-DHEA. This reaction was inhibited by corticosterone and the 11 beta-hydroxysteroid dehydrogenase (11 betaHSD) inhibitor carbenoxolone (CBX). The conversion of 7 alpha-OH-DHEA to 7-oxo-DHEA by rat kidney occurred at higher rates with NAD(+) than with NADP(+) and was inhibited by corticosterone. With NADPH, 7-oxo-DHEA was converted to unidentified hydroxylated metabolites and low levels of 7 alpha-OH-DHEA by rat liver microsomes. In contrast, pig liver microsomal fractions reduced 7-oxo-DHEA to nearly equal amounts of 7 alpha- and 7 beta-OH-DHEA, while human fractions produced mainly 7 beta-OH-DHEA. Dehydrocorticosterone inhibited the reduction to both isomers by pig liver microsomes, but only to 7 alpha-OH-DHEA by human microsomes; CBX inhibited both reactions. Rat kidney did not reduce 7-oxo-DHEA with either NADPH or NADH. These results demonstrate that DHEA is first converted in liver to 7 alpha-OH-DHEA, which is subsequently oxidized to 7-oxo-DHEA in both liver and kidney. In liver, interconversion of 7-oxo-DHEA and 7-OH-DHEA isomers is largely catalyzed by 11 betaHSD1, while in kidney 11 betaHSD2 (NAD(+)-dependent) and 11 betaHSD3 (NADP(+)-dependent) likely catalyze the unidirectional oxidation of 7 alpha-hydroxy-DHEA to 7-oxo-DHEA. Distinct species-specific routes of metabolism of DHEA and the interconversion of its metabolites obviate extrapolation of animal studies to humans.     

Oxidation of γ-Hydroxybutyrate to Succinic Semialdehyde by a Mitochondrial Pyridine Nucleotide-Independent Enzyme

An antibody that inhibits over 95% of the cytosolic NADP+-dependent gamma-hydroxybutyrate (GHB) dehydrogenase activity of either rat brain or kidney was found to inhibit only approximately 50% of the conversion of [1-14C]GHB to 14CO2 by rat kidney homogenate. A similar result was obtained with sodium valproate, a potent inhibitor of GHB dehydrogenase. The mitochondrial fraction from rat brain and kidney was found to catalyze the conversion of [1-14C]GHB to 14CO2. The dialyzed mitochondrial fraction also catalyzed the oxidation of GHB to succinic semialdehyde (SSA) in a reaction that did not require added NAD+ or NADP+ and which was not inhibited by sodium valproate. The enzyme from the mitochondrial fraction which converts GHB to SSA appears to be distinct from the NADP+-dependent cytosolic oxidoreductase which catalyzes this reaction.     

NAD+-15-hydroxyprostaglandin dehydrogenase distribution in rat kidney.

Rat kidney NAD+-dependent 15-hydroxyprostaglandin dehydrogenase (PGDH) was measured in zones and substructure of the rat kidney nephron. This was accomplished utilizing an assay procedure based upon determining the amount of prostaglandin E1 present before and after the reaction with the 15-hydroxyprostaglandin dehydrogenase contained in the tissue sample. The enzyme activity was assayed in freeze dried, quick frozen rat kidney sections and its distribution within the rat kidney was determined. In kidney zones, it was localized to medullary rays and inner cortex. In kidney substructure, activity was highest in collecting tubule, pars recti tubule, distal convoluted tubule and the ascending limb of Henle (14.2, 11.5, 6.4 and 9.2 mM kg-1hr-1, respectively). Activity in glomeruli, proximal convoluted tubule and small arteries was lower (2.1, 2.8 and 2.1 mM kg-1hr-1, respectively). The assay procedure was verified by established assays (spectrophotometric, fluorometric and radiometric TLC) which are often used in homogenate and purified PGDH preparations.     

The effect of pyrazines on the metabolism of tryptophan and nicotinamide adenine dinucleotide in the rat. Evidence of the formation of a potent inhibitor of aminocarboxy-muconate-semialdehyde decarboxylase from pyrazinamide

The intraperitoneal or oral administration of pyrazinamide and pyrazinoic acid (pyrazine 2-carboxylic acid) resulted in a marked increase of the NAD content in rat liver. The injections of pyrazine and pyrazine 2,3-dicarboxylic acid exhibited no significant effect on the hepatic NAD content. The boiled extract obtained from liver and kidney of rat injected with either pyrazinamide or pyrazinoic acid exhibited a potent inhibitory effect on the aminocarboxymuconate-semialdehyde decarboxylase (EC 4.1.1.45) activity in either lier or kidney, although pyrazinamide or pyrazinoic acid per se did not inhibit the enzyme activity. The unknown inhibitor of aminocarboxymuconate-semialdehyde decarboxylase was dialysable and heat-stable, and mostly excreted in urine by 6 and 12 h after injected of pyrazinoic acid and pyrazinamide, respectively. Pyrazine 2,3-dicarboxylic acid, pyrazine, nicotinamide, nicotinic acid, tryptophan, anthranilic acid, 5-hydroxyanthranilic acid and quinolinic acid exhibited no significant effect on the aminocarboxymuconate-semialdehyde decarboxylase activity in liver and kidney at the concentration of 1 mM in the reaction mixture. The expired 14CO2 from L-[benzen ring-U-14C]tryptophan was markedly decreased by the pyrazinamide injection, while the urinary excretion of 14C-labeled metabolites from L-tryptophan, mainly quinolinic acid, was markedly increased. These results suggest that the glutarate pathway of L-tryptophan was strongly inhibited by the inhibitor produced after the administration of pyrazinoic acid and pyrazinamide. Pyrazinamide but not pyrazinoic acid also exhibited a significant inhibition of the nuclear enzyme poly(ADP-ribose) synthetase in rat liver.     

The effect of pyrazines on the metabolism of tryptophan and nicotinamide adenine dinucleotide in the rat Evidence of the formation of a potent inhibitor of aminocarboxy-muconate-semialdehyde decarboxylase from pyrazinamide

The intraperitoneal or oral administration of pyrazinamide and pyrazinoic acid (pyrazine 2-carboxylic acid) resulted in a marked increase of the NAD content in rat liver. The injections of pyrazine and pyrazine 2,3-dicarboxylic acid exhibited no significant effect on the hepatic NAD content. The boiled extract obtained from liver and kidney of rat injected with either pyrazinamide or pyrazinoic acid exhibited a potent inhibitory effect on the aminocarboxymuconate-semialdehyde decarboxylase (EC 4.1.1.45) activity in either liver or kidney, although pyrazinamide or pyrazinoic acid per se did not inhibit the enzyme activity. The unknown inhibitor of aminocarboxymuconate-semialdehyde decarboxylase was dialysable and heat-stable, and mostly excreted in urine by 6 and 12 h after injection of pyrazinoic acid and pyrazinamide, respectively. Pyrazine 2,3-dicarboxylic acid, pyrazine, nicotinamide, nicotinic acid, tryptophan, anthranilic acid, 5-hydroxyanthranilic acid and quinolinic acid exhibited no significant effect on the aminocarboxymuconate-semialdehyde decarboxylase activity in liver and kidney at the concentration of 1 mM in the reaction mixture. The expired ¹⁴CO₂ from l-[benzen ring-U-¹⁴C]tryptophan was markedly decreased by the pyrazinamide injection, while the urinary excretion of ¹⁴C-labeled metabolites from l-tryptophan, mainly quinolinic acid, was markedly increased. These results suggest that the glutarate pathway of l-tryptophan was strongly inhibited by the inhibitor produced after the administration of pyrazinoic acid and pyrazinamide. Pyrazinamide but not pyrazinoic acid also exhibited a significant inhibition of the nuclear enzyme poly(ADP-ribose) synthetase in rat liver.     

Side-chain metabolism of propranolol: involvement of monoamine oxidase and mitochondrial aldehyde dehydrogenase in the metabolism of N-desisopropylpropranolol to naphthoxylactic acid in rat liver

We examined the metabolism of N-desisopropylpropranolol (NDP), which is generated from propranolol (PL) by side-chain N-desisopropylation, to naphthoxylactic acid (NLA) in rat liver. S(-)-NDP (S-NDP) and R(+)-NDP (R-NDP) were enantioselectively metabolized to NLA in isolated rat hepatocytes and in an enzyme reaction system of rat liver mitochondria with cofactor NAD+. Furthermore, the clearance profiles of NDP enantiomers were examined in an enzyme reaction system of rat liver mitochondria without NAD+. The amounts of S-NDP remaining in the incubation medium were similar to those of R-NDP, suggesting that monoamine oxidase (MAO) catalyzes the deamination of NDP to the aldehyde intermediate, but fails to deaminate enantioselectively S-NDP or R-NDP. Cyanamide, a potent inhibitor of aldehyde dehydrogenase (ALDH), markedly decreased the formation of NLA from racemic NDP in the enzyme reaction system of rat liver mitochondria with NAD+. When rat liver cytosol and microsomes were added to this enzyme reaction system, no significant alterations were observed in the amount of NLA generated from racemic NDP. We concluded that MAO deaminates NDP to an aldehyde intermediate, and that mitochondrial ALDH subsequently catalyzes the enantioselective metabolism of the aldehyde intermediate to NLA in rat liver.     

A new biosynthetic route of porphyrin precursors in common between animals and plants

An additional enzyme, 4-oxo-5-hydroxyvalerate (OHV) dehydrogenase was identified and characterized. This enzyme catalyzes the conversion of OHV to 4,5-dioxovalerate, a direct precursor of 5-aminolevulinate. The enzyme was partially purified from rat liver supernatant as two isoenzyme (ca. 40,000 and 70,000 dalton). 5-Aminolevulinate was formed from OHV via 4,5-dioxovalerate by this dehydrogenase and alanine-4,5-dioxovalerate aminotransferase (EC 2.6.1.43). This dehydrogenase required NADP of NAD as a hydrogen acceptor. The enzyme was heat sensitive and catalyzed the reaction reversibly. The dehydrogenase was present in the high speed supernatants of liver and kidney of rat, rabbit and human, and that of spinach leaf.     

Homotropic regulation of dihydrolipoyl dehydrogenase from bovine kidney

Dihydrolipoyl dehydrogenase from bovine kidney catalyzes NAD-linked redox reaction of lipoamide. Hates of the catalyzed reaction were studied in both directions. Saturation curves for NAD and lipoamide are nonhyperbolic, suggesting homotropic cooperative interactions of these substrates with the enzyme. The cooperative effect was analyzed by Hill plots according to the diagnostic procedure of Levitzki and Koshland. Dihydrolipoyl dehydrogenase is subject to homotropic regulation in which NAD acts as a negative cooperative effector, whereas lipoamide acts as a positive cooperative effector. At high concentrations, dihydrolipoamide normalizes the saturation curve of NAD, while NADH tends to enhance the cooperative interaction of lipoamide with the enzyme.     

Interrelations of NAD and adenosine transformation in the rat liver

The interrelationship of NAD and adenosine (inosine) conversions in the rat liver is investigated. The ratio of products of NAD+ conversions (ADP-ribose, inosine, hypoxanthine and ribose phosphates) are established. AMP and adenosine are not detected, which indicates an availability of different activities of the corresponding enzymes. It is shown that under conditions of the high inorganic phosphate concentration (33 mM) ribose-1-phosphate, formed in the purine nucleoside phosphorylase reaction, is accumulated due to the phosphoribomutase inhibition, but in the presence of NAD+ the utilization of ribose phosphate increases significantly. Nicotinamide inhibits the NAD+-glycohydrolase reaction in the system containing 33 mM phosphate, NAD+ and adenosine and simultaneously it lowers the utilization of ribose.     

Mitochondrial calcium release as induced by Hg2+

Addition of Hg2+ to mitochondria of rat kidney induces efflux of intramitochondrial Ca2+. This reaction is accompanied by a diminution of the NAD(P)H/NAD(P) ratio and a decrease of the internal negative membrane potential. These effects were enhanced by dithiothreitol. The binding of mercuric ions to mitochondria saturates with a maximal binding of 9 nmol min-1 mg-1. The stoichiometry between Ca2+ released and Hg2+ bound showed that in the presence of dithiothreitol, the binding of approximately 1 nmol of Hg2+/mg of protein suffices to induce the release of the accumulated Ca2+. In the electrophoretic analysis of Hg-labeled mitochondrial proteins it was found that 203Hg2+ bound mainly to proteins that have molecular masses of 20 and 30 kDa. It is proposed that Hg2+-induced Ca2+ release is due to modification of--SH groups of these latter proteins.     

The 11beta hydroxysteroid dehydrogenase 2 exists as an inactive dimer

The 11beta-hydroxysteroid dehydrogenase types 1 and 2 enzymes (11beta-HSD1 and 11beta-HSD2), modulate glucocorticoid occupation of the mineralocorticoid and glucocorticoid receptors by interconverting corticosterone and cortisol to the inactive metabolites 11-dehydrocorticosterone and cortisone within the target cells. The NAD(+)-dependent 11-HSD 2 in the kidney inactivates corticosterone and cortisol, allowing aldosterone, which is not metabolized, access to the receptor. Studies of the kinetics of 11-HSD 2 activity in the rat kidney have produced inconsistent results. Western blots done in the absence of the reducing agent beta-mercaptoethanol showed two bands with approximate MW of 40 and 80 kDa. When beta-mercaptoethanol was used, only the 40 kDa was detected, indicating that under non-denaturing conditions a significant proportion of the 11beta-HSD 2 exists as a dimer. NAD(+)-dependent conversion of 3H-corticosterone by 20 microg of microsomal protein increased approximately 10 fold with the addition of 5 mM DTT concentration. NADP(+)-dependent activity with 20 microg of microsomal protein was very low and did not change significantly when using DTT. In the presence of DTT, the predominant 11-HSD activity in the rat kidney is NAD(+)-dependent with a K(m) of 15.1 nM, similar to that of the cloned and expressed enzyme. These data suggest that dimerization and subsequent enzyme inactivation occur when protocols promoting oxidation of this protein are used.     

Ethanol and leucine oxidation--II. Leucine oxidation by rat tissue in vitro

The effect of ethanol upon leucine oxidation by rat tissues in vitro is reported. The activities of branched chain amino acid aminotransferase and 2-oxo acid dehydrogenase were decreased by chronic administration of ethanol (20% v/v solution as drinking water for 35 d) in muscle and kidney but were increased, although not significantly, in liver. Acute administration of ethanol (8 g kg-1 body-weight 0.73) did not affect enzyme activities. Tissue NAD+:NADH ratios, calculated from lactate:pyruvate ratios, were significantly decreased in the liver and kidney of rats receiving ethanol acutely. These data are consistent with the view that ethanol decreases leucine oxidation by decreasing availability of NAD+ when given acutely and by decreasing enzyme activity when administered chronically.     

Histochemical Detection of Quinone Reductase Activity In Situ Using LY 83583 Reduction and Oxidation

Abstract: The application of enzymatic staining techniques, using tetrazolium dyes, to aldehyde-treated brain sections has revealed the presence of NADPH-diaphorase activity attributed to nitric oxide synthase. When evaluating the specificity of the putative guanylyl cyclase inhibitor LY 83583, a robust and novel staining pattern was noted in epithelial, endothelial, and astrocytic cells when LY 83583 was included in the NADPH-diaphorase histochemical reaction. This LY 83583-dependent staining could be blocked by the NAD(P)H:quinone oxidoreductase inhibitor dicumarol. Based on its quinone structure, we hypothesized that LY 83583 was a substrate for the enzyme NAD(P)H:quinone oxidoreductase. Transfection of human embryonic kidney 293 cells with the rat liver isoform of NAD(P)H:quinone oxidoreductase resulted in robust NADPH- and LY 83583-dependent staining that was completely blocked by dicumarol and was not observed in untransfected cells. Analysis of transfected cell extracts and brain homogenates indicated that LY 83583 was a substrate for NAD(P)H:quinone oxidoreductase, with a K _m similar to the well-characterized substrate menadione. Sensitivity of the nitroblue tetrazolium reduction to superoxide dismutase indicated that the reduction of LY 83583 by NAD(P)H:quinone oxidoreductase leads to superoxide generation. The localization of NAD(P)H:quinone oxidoreductase activity to astrocytic cells suggests a role for glia in combating oxidative insults to brain and in activating quinone-like drugs such as LY 83583.     

Characterization of the effects of Ca2+ on the intramitochondrial Ca2+-sensitive dehydrogenases within intact rat-kidney mitochondria

The regulatory properties of the Ca2+-sensitive intramitochondrial enzymes (pyruvate dehydrogenase phosphate phosphatase, NAD+-isocitrate dehydrogenase and 2-oxoglutarate dehydrogenase) in extracts of rat kidney mitochondria were found to be essentially similar to those described previously for other mammalian tissues; in particular each enzyme could be activated severalfold by Ca2+ with half-maximal effects (K0.5 values) of about 1 microM and effective ranges of approx. 0.1-10 microM Ca2+. In intact mitochondria prepared from whole rat kidneys incubated in a KCl-based medium containing respiratory substrates, the amount of active, nonphosphorylated pyruvate dehydrogenase could be increased severalfold by increases in extramitochondrial [Ca2+]; these effects could be blocked by ruthenium red. Similarly, Ca2+-dependent activations of NAD+-isocitrate dehydrogenase and 2-oxoglutarate dehydrogenase could be demonstrated in intact, fully coupled, rat kidney mitochondria by either following O2 uptake (in the presence of ADP) and NAD(P)H reduction (in the absence of ADP) on presentation of non-saturating concentrations of either threo-Ds-isocitrate or 2-oxoglutarate, respectively, under appropriate conditions, or for the latter enzyme only, also by following 14CO2 production from 2-oxo[1-14C]glutarate (in the absence or presence of ADP). Effects of Na+ (as a promoter of egress) and Mg2+ (as an inhibitor of uptake) on Ca2+-transport by rat kidney mitochondria could be readily demonstrated by assaying for the Ca2+-sensitive properties of the intramitochondrial Ca2+-sensitive dehydrogenases within intact rat kidney mitochondria. In the presence of physiological concentrations of Na+ (10 mM) and Mg2+ (2 mM), activation of the enzymes was achieved by increases in extramitochondrial [Ca2+] within the expected physiological range (0.05-5 microM) and with apparent K0.5 values in the approximate range of 300-500 nM. The implications of these results on the role of the Ca2+-transport system of kidney mitochondria are discussed.     

Increase in enzyme activities of prostaglandin biosynthesis and catabolism by acute ureteral ligation in rat kidney

Acute ureteral obstruction increased cyclooxygenase, thromboxane and prostacyclin synthases and NAD+-linked 15-hydroxyprostaglandin dehydrogenase activities in rat kidney. Significant increase in prostaglandin biosynthetic and catabolic activities may mediate some pathological consequences found in obstructive nephropathy.     

The action of tellurite, a reagent for thiol groups, on mitochondria oxidative processes

Tellurite, a reagent for thiol groups, added to rat kidney, or liver mitochondria at the concentration of 1 mM, selectively inhibits the oxidation of NAD dependent substrates (pyruvate, α-ketoglutarate, glutamate, etc.) without affecting the oxidation of succinate, α-glycerophosphate and ascorbate. Moreover NADH oxidation by rat heart or by aged liver mitochondria is not affected by tellurite.     

Interactions between dehydroepiandrosterone and glucocorticoid metabolism in pig kidney: nuclear and microsomal 11beta-hydroxysteroid dehydrogenases

The 11beta-hydroxysteroid dehydrogenase type 1 (11betaHSD1) activates glucocorticoids (GC) by reversibly converting 11-keto-GC to 11-hydroxy-GC, while 11betaHSD2 and 11betaHSD3 only catalyzes the reverse reaction. Recently, rat and human 11betaHSDs were shown to interconvert 7alpha- and 7beta-hydroxy-dehydroepiandrosterone (7alpha- or 7beta-OH-DHEA) with 7-oxo-DHEA. We report that pig kidney microsomes (PKMc) and nuclei (PKN) oxidize 7alpha-OH-DHEA to 7-oxo-DHEA at higher rates with NAD+, than with NADP+. Corticosterone (CS), dehydrocoticosterone (DHC), 11alpha- and 11beta-hydroxyprogesterone, and carbenoxolone completely inhibited these reactions, while 7-oxo-DHEA only inhibited the NAD+-dependent reaction. Conversely, CS oxidation was not inhibited by 7alpha-OH-DHEA or 7-oxo-DHEA. PKMc and PKN did not convert 7-oxo-DHEA to 7-OH-DHEA with either NADPH or NADH. Finally, PKN contained a high affinity, NADPH-dependent 11betaHSD that reduces DHC to CS. The GC effects on interconversion of DHEA metabolites may have clinical significance, since DHEA and its 7-oxidized derivatives have been proposed for treatment of human autoimmune and inflammatory disorders.     

Properties and Structure of a Novel Peptide Antibiotic No. 1907

There are three NAD biosynthetic pathways: the nicotinic acid-NAD, nicotinamide-NAD, and quinolinic acid (derived from tryptophan)-NAD pathways. To discover the main pathways of NAD biosyntheses in various tissues of the rat, the tissue distribution of nicotinamidase, quinolinate phosphoribosyltransferase, nicotinate phosphoribosyltransferase, nicotinamide phosphoribosyl-transferase, nicotinamide mononucleotide adenylyltransferase, and NAD⁺ synthetase were investigated. All of the tissues could synthesize NAD from nicotinamide, judging from that the activities of nicotinamide phosphoribosyltransferase and NMN adenylyltransferase detected in all of the tissues. From nicotinic acid, only liver, kidneys, and heart could. Liver and kidney can also synthesize NAD de novo from quinolinic acid.     

Mechanisms of poly(ADP-ribose) polymerase catalysis; mono-ADP-ribosylation of poly(ADP-ribose) polymerase at nanomolar concentrations of NAD

Calf thymus and rat liver poly(ADP-ribose) polymerase enzymes, and the polymerase present in extracts of rat liver nuclei synthesize unstable mono-ADP-ribose protein adducts at 100 nM or lower NAD concentrations. The isolated enzyme-mono-ADP-ribose adduct hydrolyses to ADP-ribose and enzyme protein at pH values slightly above 7.0 indicating a continuous release of ADP-ribose from NAD through this enzyme-bound intermediate under physiological conditions. NH2OH at pH 7.0 hydrolyses the mono-ADP-ribose enzyme adduct. Desamino NAD and some other homologs at nanomolar concentrations act as 'forward' activators of the initiating mono-ADP-ribosylation reaction. These NAD analogs at micromolar concentrations do not affect polymer formation that takes place at micromolar NAD concentrations. Benzamides at nanomolar concentrations also activate mono-ADP-ribosylation of the enzyme, but at higher concentrations inhibit elongation at micromolar NAD as substrate. In nuclei, the enzyme molecule extensively auto-ADP-ribosylates itself, whereas histones are trans-ADP-ribosylated to a much lower extent. The unstable mono-ADP-ribose enzyme adduct represents an initiator intermediate in poly ADP-ribosylation.     

Cytochemical localization of glutaraldehyde-resistant NAD(P)H-oxidase in rat hepatocytes

NAD(P)H-oxidase activity was demonstrated in glutaraldehyde-fixed rat hepatocytes by a cerium technique. The activity was observed exclusively on the bile-canalicular plasma membrane of hepatocyte. No reaction product was formed in the absence of NAD(P)H as the substrate. The reaction was inhibited by pCMB (surface sulfhydryl group specific reagent), by heating, by anaerobic incubation and by catalase (H2O2 scavenger), but it was not inhibited by KCN or NaN3. The present results show that bile-canalicular plasma membrane produces H2O2 and the cerium technique for demonstration of H2O2 is therefore an useful method for the subcellular localization of NAD(P)H-oxidase activity in the glutaraldehyde-fixed hepatocyte.