David J. W. Goon

Lowering of ethanol-derived circulating blood acetaldehyde in rats by D-penicillamine

Abstract The sulfhydryl amino acid, D-penicillamine, but not L-cysteine or L-cystine, when administered to disulfiram-treated rats 1 hour before a dose of ethanol lowered the ethanol-derived, circulating blood acetaldehyde to 10% of control values. This was accompanied by a concomitant lowering of AcH in the expired air of penicillamine-treated rats. Since blood ethanol levels were the same in saline injected controls and in sulfhydryl amino acid-treated rats, this lowering of blood acetaldehyde was not due to any malabsorption of ethanol or to inhibition of the enzyme(s) that metabolize ethanol. By administration of D-penicillamine in multiple, divided doses, blood acetaldehyde generated during ethanol metabolism was reduced an average of 70% over an 8 hour period.

Nitrosyl cyanide, a putative metabolic oxidation product of the alcohol-deterrent agent cyanamide

When incubated with catalase/glucose-glucose oxidase, 13C-labeled cyanamide gave rise not only to 13C-labeled cyanide, but also to 13C-labeled CO2. Moreover, a time-dependent formation of nitrite was observed when cyanamide was oxidized in this system. These results suggested that the initial product of cyanamide oxidation, viz. N-hydroxycyanamide, was being further oxidized by catalase/H2O2 to nitrosyl cyanide (O = N-C = N). Theoretically, nitrosyl cyanide can hydrolyze to the four end-products detected in the oxidative metabolism of cyanamide in vitro, viz. nitroxyl, cyanide, nitrite, and CO2. Accordingly, both unlabeled and 13C-labeled nitrosyl cyanide were synthesized by the low temperature (-40 to -50 degrees) nitrosylation of K-(18-crown-6)cyanide with nitrosyl tetrafluoroborate. The product, a faint blue liquid at this temperature, was transferred as a gas to phosphate-buffered solution, pH 7.4, where it was solvolyzed. Analysis of the headspace by gas chromatography showed the presence of N2O, the dimerization/dehydration product of nitroxyl, while cyanide was detected in the aqueous solution, as measured colorimetrically. [13C]CO2 was analyzed by GC/MS. An oxidative biotransformation pathway for cyanamide that accounts for all the products detected and involving both N-hydroxycyanamide and nitrosyl cyanide as tandem intermediates is proposed.

LOWERING OF BLOOD ACETALDEHYDE LEVELS AS A THERAPERTIC APPROACH TO ALCOHOLISM

Approaches that can lower blood AcH have been considered. D-Penicillamine, a metabolically inert sulfhydryl amino acid, when administered with ethanol-1−14C, condensed non-enzymatically with the AcH generated in vivo leading to the urinary excretion of 14C-labeled 2,5,5-trimethylthiazolidine-4-carboxylic acid (TTCA). Disulfiram and pargyline treatment tripled and quadrupled, respectively, the amount of TTCA excreted, whereas pyrogallol administration had no effect. Blood AcH levels were reduced 90% and AcH in expired air was reduced 75% by D-penicillamine treatment, but blood ethanol levels were unaffected. The catecholamine responses of AcH infusion to anesthetized dogs were reversed by simultaneous infusion of D-penicillamine, concomitant to a lowering of blood AcH levels caused by the trapping of AcH by D-penicillamine.

Rationale for Alcoholism Treatment Based on Inhibition of Aldehyde Dehydrogenase

It has been long recognized that certain individuals, particularly of Oriental origin, present a pronounced facial flush on consumption of only modest quantities of alcoholic beverages, thereby sustaining a natural aversion to alcohol (ethanol). These individuals lack a functional low Km hepatic mitochondrial aldehyde dehydrogenase (A1DH2) that metabolizes acetaldehyde, the first product of ethanol metabolism (1). This inborn trait observed in 40–50% of Orientals has been shown to be due to a genetic defect manifested by a point mutation on A1DH2, with the amino acid lysine replacing a glutamate residue near the C-terminal end of the enzyme (2). The consumption of ethanol by such individuals gives rise to elevated blood acetaldehyde levels and a flushing reaction reminiscent of the disulfiram-ethanol reaction (3), leading to alcohol avoidance.