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E G DeMaster

Publications and source records attributed to E G DeMaster.

At least 55 records · Page 3Linked to original sources
PubMed1987

Cyanide is a product of the catalase-mediated oxidation of the alcohol deterrent agent, cyanamide.

Cyanide was detected as a product of cyanamide oxidation by bovine liver catalase in vitro under conditions that also produced an active aldehyde dehydrogenase (AlDH) inhibitor. Cyanide formation was directly related to both cyanamide and catalase concentrations and was also dependent on incubation time. The apparent Km for this reaction was 172 microM. Cyanide formation was blocked by ethanol, a known substrate for catalase Compound I. The toxic effects of cyanamide in the dog, a species with limited capacity to conjugate cyanamide by N-acetylation, may be causally related to enhancement of this catalase-mediated pathway for cyanamide metabolism.

Alcohol Deterrents↗
PubMed1987

Metabolism of cyanamide to cyanide and an inhibitor of aldehyde dehydrogenase (ALDH) by rat liver microsomes.

Rat liver microsomes, as well as purified catalase, convert the alcohol deterrent agent, cyanamide, to an active inhibitor of AlDH. Whether this enzymatic activation of cyanamide is mediated primarily by catalase present in the microsomes or involves the cytochrome P-450 enzymes is not known. We now report that cyanide is also a product of the microsomal oxidation of cyanamide. Formation of cyanide from cyanamide and rat liver microsomes was time dependent, reaching maximal levels within 5-10 min. Induction of the cytochrome P-450 enzymes by phenobarbital (PB) pretreatment doubled the yield of cyanide, while SKF-525A blocked this PB-induced increase. Administration of 3-aminotriazole (3-AT) to PB-treated rats inhibited the catalatic activity of their microsomes by 98% and substantially reduced cyanide formation. These results suggest that while catalase is responsible in major part for the oxidation of cyanamide to cyanide by uninduced microsomes, the participation of the hepatic cytochrome P-450 enzymes cannot be ruled out in PB-induced microsomes. We propose a metabolic scheme wherein N-hydroxycyanamide is the intermediate product of cyanamide oxidation, which then decomposes to yield the observed product, cyanide. By deduction, the second product of this decomposition is postulated to be nitroxyl (HNO), which may be the active AlDH inhibitor.

Aldehyde Dehydrogenase↗
PubMed1986

Differential inhibition of rat tissue catalase by cyanamide.

The relative sensitivity of rat tissue catalase to inhibition by intraperitoneally administered cyanamide was liver greater than kidney greater than heart greater than brain, whereas the activity of the erythrocyte enzyme was affected minimally. The measured ED50 values for cyanamide in these tissues were 31, 44, 107 and 680 mumoles/kg body weight for liver, kidney, heart and brain respectively. On a molar basis, cyanamide was approximately twenty times more potent than 3-amino-1,2,4-triazole (3-AT) in inhibiting hepatic catalase in vivo in the rat. Like 3-AT, cyanamide inhibited erythrocyte catalase activity in vitro in the presence of hydrogen peroxide. The apparent similarities between the inhibition of hepatic catalase by cyanamide and 3-AT in vivo suggest that cyanamide belongs to the family of 3-AT-like catalase inhibitors.

Amitrole↗
PubMed1986

Role of propiolaldehyde and other metabolites in the pargyline inhibition of rat liver aldehyde dehydrogenase.

The metabolism of pargyline proceeds by way of three separate cytochrome P-450 catalyzed N-dealkylation reactions: N-depropargylation, N-demethylation and N-debenzylation. Propiolaldehyde, a product of N-depropargylation, is a potent inhibitor of aldehyde dehydrogenase (AlDH). The formation of pargyline-derived propiolaldehyde by isolated rat liver microsomes in vitro was confirmed using gas chromatographic/mass spectrometric techniques. The measured rates of propiolaldehyde formation for uninduced and phenobarbital-induced microsomes in vitro were 0.2 +/- 0.03 and 0.9 +/- 0.2 mumole/30 min/g wet weight liver respectively. However, these rates may have been artificially low due to competition between semicarbazide, the trapping agent, and microsomal proteins for the generated propiolaldehyde. CO significantly inhibited the microsome-catalyzed N-depropargylation reaction in vitro, whereas CoCl2 pretreatment of rats partially blocked the pargyline-induced rise in blood acetaldehyde after ethanol. Inhibition of the low Km liver mitochondrial AlDH by propiolaldehyde in vitro exhibited first-order kinetics, which is consistent with irreversible inhibition. Acetaldehyde did not attenuate the inhibition of AlDH by propiolaldehyde in vitro or by pargyline in vivo. Propargyl alcohol, a substance which is metabolized to propiolaldehyde by alcohol dehydrogenase, also inhibited AlDH in vivo and caused a quantitatively similar rise in blood acetaldehyde after ethanol as pargyline. Other putative metabolites of pargyline, namely benzylamine and propargylamine, inhibited AlDH in vivo, albeit to a lesser degree than pargyline, but neither of these amines inhibited AlDH directly. Monoamine oxidase was implicated in the conversion of benzylamine to an active inhibitory species, possibly an imine. From these studies, we conclude that propiolaldehyde was the primary metabolite responsible for the pargyline inhibition of AlDH in vivo; however, certain amine metabolites may have contributed to a lesser degree by conversion to yet unknown inhibitory forms.

Aldehyde Dehydrogenase↗
PubMed1986

Acyl, N-protected alpha-aminoacyl, and peptidyl derivatives as prodrug forms of the alcohol deterrent agent cyanamide.

Cyanamide (H2NC identical to N), a potent aldehyde dehydrogenase (AlDH) inhibitor that is used therapeutically as an alcohol deterrent agent, is known to be rapidly metabolized and excreted in the urine as acetylcyanamide (1). On the basis of our observation that 1 is deacetylated to cyanamide in vivo, albeit very slightly, thereby serving as a precursor of prodrug form of the latter, several acyl derivatives of cyanamide were synthesized specifically as prodrugs, including benzoylcyanamide (2), pivaloylcyanamide (3), and 1-adamantoylcyanamide (4), as well as long- and medium-chain fatty acyl derivatives such as palmitoyl- (6), stearoyl- (7), and n-butyrylcyanamide (5). N-Protected alpha-aminoacyl and peptidyl derivatives of cyanamide were also synthesized, and these include N-carbobenzoxyglycyl- (10), hippuryl- (13), N-benzoyl-L-leucyl- (14), N-carbobenzoxyglycyl-L-leucyl- (18), N-carbobenzoxy-L-pyroglutamyl- (22), L-pyroglutamyl-L-leucyl- (19), and L-pyroglutamyl-L-phenylalanylcyanamide (20). All of these prodrugs of cyanamide raised ethanol-derived blood acetaldehyde levels in rats significantly over controls 3 h after ip drug administration, and some of these were still capable of elevating blood acetaldehyde 16 h post drug administration. A selected group of cyanamide prodrugs were also evaluated by the oral route of administration and showed nearly equivalent activity as the ip route in elevating ethanol-derived blood acetaldehyde. These results suggest potential utility of these prodrugs as deterrent agents for the treatment of alcoholism.

Acylation↗
PubMed1985

Ventricular myocardial catecholamines in primates.

We report myocardial catecholamine levels in primate ventricles assayed by high-pressure liquid chromatography with electrochemical detection. The norepinephrine content of the left ventricles of 11 monkeys (four rhesus and seven cynomolgus) was 1391 +/- 362 ng/gm (+/-SD) with a definite gradient from base (highest) to apex (lowest concentration). Dopamine and epinephrine were present in much lower concentrations (51.8 +/- 24.5 ng/gm and 59.2 +/- 20.0 ng/gm, respectively), but were similarly distributed throughout the left ventricle. There was considerable variation in norepinephrine concentration between animals, but the dopamine/norepinephrine ratio was very consistent within a given animal, averaging 3.7% +/- 1.4%. These values are probably indicative of what normal concentrations of catecholamines are likely to be in humans, and provide a basis for interpretation of results obtained in disease studies.

Animals↗
PubMed1984

The metabolic activation of cyanamide to an inhibitor of aldehyde dehydrogenase is catalyzed by catalase.

The inhibition of aldehyde dehydrogenase by cyanamide is dependent on an enzyme catalyzed conversion of the latter to an active metabolite. The following results suggest that catalase is the enzyme responsible for this bioactivation. The elevation of blood acetaldehyde elicited by cyanamide after ethanol administration to rats was attenuated more than 90 percent by pretreatment with the catalase inhibitor, 3-amino-1,2,4-triazole. This attenuation was dose dependent and was accompanied by a reduction in total hepatic catalase activity. Although hepatic catalase was also inhibited by cyanamide, a positive correlation between blood acetaldehyde and hepatic catalase activity was observed. In vitro, the activation inhibitor, 3-amino-1,2,4-triazole. This attenuation was dose dependent and was accompanied by a reduction in total hepatic catalase activity. Although hepatic catalase was also inhibited by cyanamide, a positive correlation between blood acetaldehyde and hepatic catalase activity was observed. In vitro, the activation of cyanamide was catalyzed by a) the rat liver mitochondrial subcellular fraction, b) the 50-65% ammonium sulfate mitochondrial fraction and c) purified bovine liver catalase. Cyanamide activation was inhibited by sodium azide. Since much of the hepatic catalase is localized in the peroxisomes and since peroxisomes and mitochondria cosediment, the cyanamide activating enzyme, catalase, is likely of peroxisomal and mitochondrial origin.

Acetaldehyde↗
PubMed1984

Latent inhibitors of aldehyde dehydrogenase as alcohol deterrent agents.

A series of compounds structurally related to pargyline (N-methyl-N-propargylbenzylamine, 4) were synthesized with the propargyl group replaced by a cyclopropyl, allyl, or 2,2,2-trichloroethyl group and, additionally in several cases, with the methyl group replaced by H. The rationale for their preparation was based on the expectation that, like pargyline, which gives rise to propiolaldehyde, oxidative metabolism of the above compounds by the hepatic cytochrome P-450 enzymes would lead to the generation in vivo of the aldehyde dehydrogenase (AlDH) inhibitors, cyclopropanone, acrolein, or chloral. These compounds were evaluated for inhibition of liver AlDH in vivo by measuring the elevation of ethanol-derived blood acetaldehyde in rats and in vitro by the rate of oxidation of acetaldehyde by intact and osmotically disrupted liver mitochondria. Administration of N-methyl-N-cyclopropylbenzylamine (5) and its nor-methyl analogue (8) to rats raised blood acetaldehyde levels significantly over controls at 2 h. This effect was more pronounced at 9 h, with blood acetaldehyde levels reaching 19 to 27 times control values and approaching the values induced by pargyline. Other compounds elicited significant elevations in ethanol-derived blood acetaldehyde only at 9 h. We suggest that latent inhibitors of AlDH such as 5 or 8 might be useful as alcohol deterrent agents.

Alcoholism↗
PubMed1984

Regional differences in adrenergic function within the left ventricle.

Since ischemic heart disease (IHD) is inhomogeneous, the adrenergic response of the heart to ischemia or infarction could depend on the level of adrenergic supply within specific regions of the myocardium. Therefore we quantified myocardial norepinephrine (NE) content of tissue samples from 54 different sites in the left ventricle (LV) of four normal dogs using high-pressure liquid chromatography with electrochemical detection. Up to 10-fold differences in NE content occurred within a single LV. The NE distribution followed a consistent pattern, demonstrating a gradient from apex (avg minimum value of 162 ng/g of tissue) to base (avg maximum value 844 ng/g). No epicardial-to-endocardial gradient was present. In six other dogs a similar pattern was found in myocardial uptake of radioactively labeled NE and epinephrine assessed 2 min after intravenous injection. These results suggest that areas of high tissue NE represent regions rich in adrenergic supply and high in adrenergic activity, not merely NE stored in inactive pools. Samples from a human autopsy specimen suggest that these findings can be extrapolated to humans.

Animals↗
PubMed1984

Quantitative analysis of postmortem changes in myocardial norepinephrine using HPLC with electrochemical detection.

Myocardial adrenergic function may be important in the pathophysiology of many cardiac abnormalities, and quantitative analysis of catecholamines in cardiac tissue can provide insight in the role of adrenergic neurons in specific disorders. Our purpose was to determine the stability of myocardial catecholamines postmortem to assess the validity of using postmortem samples to represent premorbid conditions and to provide information applicable to proper handling of biopsy specimens. Serial myocardial samples were obtained postmortem in rats and dogs for which norepinephrine and dopamine levels were analyzed using high-pressure liquid chromatography with electrochemical detection. No significant differences in catecholamine content were found between samples taken immediately after death and those taken 15 minutes later. Thereafter, a progressive decline in catecholamines was observed. We conclude that biopsy or postmortem samples frozen within 15 minutes of death will accurately reflect premortem catecholamine values.

Animals↗
PubMed1983

Elevated left ventricular myocardial dopamine in preterminal idiopathic dilated cardiomyopathy.

The adrenergic nervous system is chronically activated in patients with congestive heart failure (CHF). One consequence of this is depletion of the normally high levels of myocardial norepinephrine. In this study, myocardial norepinephrine and dopamine concentrations from the left ventricular walls of 3 patients undergoing cardiac transplantation for severe refractory CHF are reported. The dopamine/norepinephrine ratios were high in all 3 patients (29, 58 and 26%). This finding supports data from animal studies suggesting a change in the rate-limiting step for myocardial norepinephrine synthesis in CHF. Conversion of tyrosine to dopa by tyrosine hydroxylase is replaced as the rate-limiting step by inability to hydroxylate dopamine to norepinephrine. Thus, dopamine accumulates while norepinephrine is depleted.

Adult↗
PubMed1983

Elimination of artifactual acetaldehyde in the measurement of human blood acetaldehyde by the use of polyethylene glycol and sodium azide: normal blood acetaldehyde levels in the dog and human after ethanol.

A new procedure is described for the preparation of human blood samples for analysis of acetaldehyde and ethanol by head space gas chromatography. High concentrations of polyethylene glycol were used to remove the hemoglobin and approximately 50% of the plasma protein. Artifactual formation of acetaldehyde from ethanol was inhibited by sodium azide. Using this method, no artifactual acetaldehyde was detectable in human, dog, sheep, and rat blood when spiked with ethanol in final concentrations of 65 mM. The recovery of added acetaldehyde was approximately 80% for human dog, and sheep blood, whereas it was only 30% for rat blood. Following ethanol administration, acetaldehyde levels were determined in blood taken from the pulmonary artery and descending aorta of the dog and human, and also from the hepatic vein of the latter. The relative blood acetaldehyde concentrations at these sites were hepatic vein greater than pulmonary artery greater than descending aorta.

Acetaldehyde↗
PubMed1982

Studies on the cyanamide-ethanol interaction. Dimethylcyanamide as an inhibitor of aldehyde dehydrogenase in vivo.

Administration of dimethylcyanamide (DMC) to rats caused a marked elevation in ethanol-derived blood acetaldehyde (AcH) and depressed the specific activity of the low Km mitochondrial aldehyde dehydrogenase (AIDH) by 90% at 12-24 hr, coincident with depletion of hepatic glutathione levels. Comparison of the relative efficacy of DMC and cyanamide in elevating blood AcH measured at 2 hr and 1 hr post-drug treatment, respectively, indicated that DMC was at least one-fifth as active as cyanamide. However, since the comparison was not made at optimal times for DMC (12-24 hr), it is likely that its activity in vivo approaches that of cyanamide itself. DMC was essentially inactive in vitro as an inhibitor of the low Km AIDH isozyme in intact rat liver mitochondria. Although methylcyanamide, the product of N-demethylation of DMC, was too unstable to be prepared for this evaluation, the higher monoalkyl cyanamide, n-propylcyanamide, was synthesized chemically and was shown to be a good inhibitor of the mitochondrial enzyme in vitro. These results suggest that DMC must be N-demethylated before being converted to a reactive species that inhibits AIDH activity.

Aldehyde Dehydrogenase↗