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Biomedical subjects

E G DeMaster

Publications and source records attributed to E G DeMaster.

At least 73 records · Page 4Linked to original sources
PubMed1980

Microsomal N-depropargylation of pargyline to propiolaldehyde, an irreversible inhibitor of mitochondrial aldehyde dehydrogenase.

Rat liver microsomes catalyzed the conversion of pargyline (N-methyl-N-propargylbenzylamine) to propiolaldehyde, a potent inhibitor of the low Km mitochondrial aldehyde dehydrogenase (AlDH) isozyme. The involvement of cytochrome P-450 in vivo was shown indirectly by (a) the ability of SKF-525A to block pargyline-induced acetaldehydemia, (b) the prolongation of phenobarbital sleeping time by pargyline, and (c) the enhancement of pargyline-induced acetaldehydemia by phenobarbital pretreatment. Propiolaldehyde was isolated as its semicarbazone by incubating pargyline with either phenobarbital-induced or uninduced rat liver microsomes and an NADPH-generating system, the latter being required for propiolaldehyde formation. In vitro studies with liver mitochondria showed that propiolaldehyde inhibition of AlDH was temperature- and time-dependent and irreversible. We propose that the cytochrome P-450 catalyzed conversion of pargyline to its active metabolite, propiolaldehyde, proceeds via a mechanism involving N-depropargylation, viz., hydroxylation of pargyline alpha to the acetylenic bond forming a carbinolamine intermediate, followed by dissociation.

Aldehyde Oxidoreductases↗
PubMed1980

Structural requirements for the sequestration of metabolically generated acetaldehyde.

Of a series of polyfunctional compounds containing amino, hydroxyl, or mercapto groups in conjunction with the carboxyl group, only the 1,2- or 1,3-disubstituted aminothiols, namely, D-(-)-penicillamine (1), L-cysteine (2), L-cysteinyl-L-valine (3), mercaptoethylglycine (4), and DL-homocysteine (12), showed any propensity to sequester acetaldehyde (AcH) when tested in vitro in a buffered system at pH 7.5. In vivo, however, only D-(-)-penicillamine (1) was effective in lowering ethanol-derived blood AcH in rats that had been treated with disulfiram and ethanol. These results suggest that, in addition to the functionality in the molecule, pharmacokinetic and metabolic factors must also be considered when designing AcH-sequestering agents for use in vivo.

Acetaldehyde↗
PubMed1980

Metabolic depropargylation and its relationship to aldehyde dehydrogenase inhibition in vivo.

The relationship between metabolic depropargylation in vitro to inhibition of the low Km aldehyde dehydrogenase (AIDH) of rat liver mitochondria in vivo was determined for a number of compounds bearing a propargyl substituent on nitrogen or oxygen. Only those compounds which enzymatically released the highly reactive alpha, beta-acetylenic aldehyde, propioladehyde, when incubated in vitro with phenobarbital-induced rat liver microsomes, e.g., tripropargylamine (4), pargyline (1a), and N-propargylbenzylamine (1b), significantly elevated blood acetaldehyde levels when administered in vivo. Mitochondrial AIDH activity in these animals was corresponding reduced to less than or equal to 20% that of control animals. Compounds that did not inhibit mitochondrial AlDH activity to this degree did not produce significant levels of propiolaldehyde when incubated with microsomes. Thus, for this series of compounds, metabolic depropargylation is a requirement for AlDH inhibitory activity in vivo.

Acetaldehyde↗
PubMed1980

Effect of pargyline on hepatic glutathione levels in rats treated acutely and chronically with ethanol.

A single dose of pargyline severely depleted hepatic reduced glutathione (GSH) levels in the rat. Ethanol administration, acute or chronic, had no effect on hepatic GSH levels; nor did such administration exacerbate the pargyline mediated GSH depletion. However a single dose of ethanol given one hour after pargyline administration enhanced the rate of recovery of hepatic GSH.

Alcoholism↗
PubMed1978

2,5,5-Trimethylthiazolidine-4-carboxylic acid, a D(-)-penicillamine-directed pseudometabolite of ethanol. Detoxication mechanism for acetaldehyde.

A directed detoxication mechanism for acetaldehyde (AcH) is described wherein ethanol-derived AcH, circulating in the blood of rats given ethanol-1-14C and disulfiram or pargyline, was sequestered by condensation with administered D(-)-penicillamine (1). The product of this condensation, 2,5,5-trimethylthiazolidine-4-carboxylic acid (3), which was excreted in the urine without acetyl conjugation, was quantitatively determined by inverse isotope dilution measurements. Acetylation of the urine permitted the isolation of the corresponding N-acetyl derivative in crystalline form. The chirality of 3 was deduced by NMR analysis to be 72% 2S, 4S and 28% 2R, 4S. Although acetylation selectively acetylated the predominant isomer, this acetylated derivative was identical in all respects with a chemically synthesized product. This suggests that the in vivo condensation of AcH and 1 is not enzyme mediated.

Acetaldehyde↗
PubMed1978

Inhibition of aldehyde dehydrogenase by propiolaldehyde, a possible metabolite of pargyline.

Pargyline (Eutonyl) inhibited aldehyde dehydrogenase (AlDH) in vivo in rats as adduced by the elevation of ethanol-derived blood acetaldehyde (AcH), but had no effect in vitro on the enzyme in intact mitochondria. SKF-525A, an inhibitor of the hepatic microsomal P-450 enzyme system, completely prevented the pargyline-induced elevation of blood AcH in vivo, further implicating a metabolite of pargyline as the active inhibitor of AlDH. Of the potential pargyline metabolites tested, N-benzylpropargylamine and propargyl alcohol--like pargyline itself--readily inhibited AlDH in vivo but were without effect on the enzyme in vitro. These data implicated propiolaldehyde, a theoretically possible product of metabolism of all three of the above compounds, as the active metabolite responsible for AlDH inhibition. Indeed, propiolaldehyde at a concentration of 200 micron essentially completely inhibited the low Km AlDH of intact rat liver mitochondria.

Acetylcholine↗
PubMed1977

Disulfiram-induced acetonemia in the rat and man.

Disulfiram treatment caused marked elevations of circulating blood acetone levels in rat and man. In the rat, disulfiram (0.59 g/kg, p.o.) given singly or for three consecutive days increased the fasting blood acetone levels 5- and 25-fold, fespectively. Circulating acetone levels were also estimated noninvasively in man by measuring acetone in the expired air. A 15-fold increase in the expired air acetone levels was observed in a group of five male non-fasting subjects taking disulfiram (250 mg daily) for a minimum of one month, when compared to control subjects.

Acetone↗
PubMedDate not supplied

Catalase mediated conversion of cyanamide to an inhibitor of aldehyde dehydrogenase.

A minor pathway for cyanamide metabolism catalyzed by catalase is responsible for the conversion of cyanamide to an inhibitor of aldehyde dehydrogenase. Catalase itself is also inhibited by cyanamide. Both the activation of cyanamide by catalase and the inhibition of catalase by cyanamide were blocked in vivo by ethanol pretreatment, suggesting that these two processes are closely linked. Like other catalase oxidation reactions, the catalase mediated activation of cyanamide was inhibited by 3-amino-1,2,4-triazole in vivo and sodium azide in vitro. The relative formation of the active cyanamide metabolite was assessed in vitro by following the loss of yeast aldehyde dehydrogenase activity with time. Inhibition of the yeast enzyme by activated cyanamide was dependent on NAD+ or NADP+, a requirement not fulfilled by NADH or NADPH. Although H2O2 inhibited yeast aldehyde dehydrogenase in vitro and cyanamide inhibited hepatic catalase in vivo, the possible in hepatic H2O2 concentration following cyanamide administration does not account for the effects of cyanamide on ethanol metabolism. While the cyanamide activating enzyme has been identified as catalase, the reaction products of this reaction and, in particular, the structure of the active metabolite involved in the inhibition of aldehyde dehydrogenase remain unknown.

Aldehyde Dehydrogenase↗
PubMedDate not supplied

Structure vs. activity in the sulfonylurea-mediated disulfiram-ethanol reaction.

The oral hypoglycemic agents, chlorpropamide (CP) and tolbutamide (TB) are known to elicit a clinical disulfiram-ethanol reaction (DER) when consumed with alcohol. In rats, this DER is manifested in vivo by the elevation of blood acetaldehyde (AcH) levels, a consequence of the inhibition of hepatic aldehyde dehydrogenase (AIDH). Administration of CP or TB to rats (1.0 mmol/kg, IP), followed by ethanol one hour before sacrifice, raised blood AcH levels 12- and 2-times that of control animals, respectively for CP and TB when measured at 3 hours, and 20-fold and 8-fold at 16 hours post drug administration. CP and TB had no effect on AIDH activity when incubated with either intact or osmotically disrupted rat liver mitochondria, indicating that a metabolite of CP or TB is responsible for the inhibition of AIDH in vivo. Hydrolysis products of CP, the 2'-hydroxylated products of CP, tolpropamide and tolethamide, or the 3'-hydroxylated analogs of CP and tolpropamide, were uniformly inactive in elevating ethanol-derived blood AcH. Pretreatment of rats with 3-amino-1,2,4-triazole or SKF-525A had no effect on the elevation of blood AcH mediated by CP or TB, while phenobarbital pretreatment decreased blood AcH by 69%. Although our results clearly indicated that side chain hydroxylation and subsequent oxidation do not play a role in AIDH inhibition by CP or TB, the nature of the side chain attached to the sulfonylurea moiety appears to influence this inhibitory activity in vivo. Thus, the order of activity in the homologous series was, chlorpropamide greater than chlorbutamide greater than chlorethamide much greater than chlormethamide, chlorisopropamide = 0.

Aldehyde Dehydrogenase↗
PubMedDate not supplied

An N-hydroxylated derivative of cyanamide that inhibits yeast aldehyde dehydrogenase.

A stable, N,O-dibenzoyl derivative (DBHC) of N-hydroxycyanamide, the latter the postulated bioactivation product of the alcohol deterrent agent, cyanamide, has been synthesized. DBHC was an effective inhibitor of yeast aldehyde dehydrogenase (AIDH) in vitro and inhibited this enzyme in a concentration-dependent manner with an IC50 of 25 microM. Hydrolysis of the benzoate moiety of DBHC with dilute NaOH gave rise to the formation of nitroxyl (HN = O), detected by gas chromatography as nitrous oxide (N2O), the end-product of nitroxyl dimerization and disproportionation. It is postulated that the nitroxyl liberated by esterase action on DBHC by yeast AIDH may be the reactive species that inhibits AIDH.

Aldehyde Dehydrogenase↗
PubMedDate not supplied

The formation of stable acetaldehyde-hemoglobin adducts in a red blood cell model.

The formation of stable hemoglobin adducts was examined (in the absence of an added reducing agent) in metabolizing red blood cells (RBCs) exposed to micromolar concentrations of acetaldehyde for up to 48 hours in vitro. The rapid disappearance of acetaldehyde due to oxidation by RBC aldehyde dehydrogenase was prevented by pretreating the cells with the inhibitor cyanamide. The RBCs remained viable for 48 hours (37 degrees C) as determined by cell hemolysis and glycolytic activity. [14C]acetaldehyde-modified hemoglobin was assessed in untreated and in cyanamide-pretreated cells. In untreated cells, after 3 hours of exposure to 50 and 200 nmol/ml of [14C]acetaldehyde, the molar ratios of acetaldehyde to hemoglobin were 0.00069 and 0.0038, respectively; [14C]acetaldehyde concentrations decreased to less than 4% of the initial levels within 3 hours. In cyanamide-pretreated RBCs, the molar ratios of acetaldehyde bound to hemoglobin ranged from 0.0013 after 3 hours of exposure to 20 nmol/ml [14C]acetaldehyde up to 0.039 after 48 hours of exposure to 200 nmol/ml [14C]acetaldehyde. Following tryptic digestion of [14C]acetaldehyde-hemoglobin and separation of peptides by high-performance liquid chromatography, significant incorporation of [14C]acetaldehyde was observed in nine peptides. Modifications of the labeled peptides remain to be characterized.

Acetaldehyde↗