Metabolites of ethanol as markers of alcohol abuse : glutathione consumption and methionine kinetics in humans

In the course of the present doctoral studies two projects related to research in
alcoholism and relevant for the postgraduate formation of a pharmacist were pursued:
one project dealt with the development of analytical tools applicable to the identification
of subjects abusing ethanol. The other, more pathophysiologically oriented project,
addressed aspects of glutathione turnover of toxicological relevance for alcoholics.
The aims of the first project were to establish analytical tools for the measurement of
direct metabolites of alcohol, in particular of ethyl-glucuronide and ethyl-lysine for
subsequent clinical studies using these metabolites as markers for excessive alcohol
consumption. Several approaches to measure these metabolites were explored and
adapted to locally available instruments. As proof of principle the present work
demonstrates that ethyl-lysine is detectable by a chromatographic method in animals and
humans consuming alcohol. Future studies will have to demonstrate the potential clinical
utility of this marker of alcohol exposure for the identification of subjects consuming
excessive amounts of alcohol. The aim of the second project was to estimate the contribution of methionine-derived
cysteine to glutathione synthesis in humans. The project originated in the observation
that subjects abusing alcohol are more susceptible to the hepatotoxic effects of
paracetamol. Since methionine homeostasis is disturbed in chronic alcoholics as evidenced
by higher circulating concentrations of methionine and homocysteine and by the impaired
activity of several enzymes involved in the methionine cycle, an impaired ability to supply
adequate amounts of cysteine generated from methionine via the transsulfuration
pathway for the resynthesis of glutathione may be one explanation for the higher
susceptibility of alcoholics. Prior to probing the methionine cycle, i.e. the formation of Sadenosylmethionine
from methionine, transmethylation and transsulfuration reactions and
finally remethylation of homocysteine back to methionine, in alcoholic subjects, a
quantitative analysis of the utilization of methionine for glutathione synthesis in healthy
subjects under physiological conditions and in situations of a drug-induced stress on the
glutathione pool was essential. The pharmacokinetic analysis of labelled methionine in
healthy subjects shows that the stress on the glutathione pool stemming from the
administration of two grams of paracetamol does not have a measurable effect on the disposition of methionine. It is therefore unlikely that a potentially impaired utilization of
methionine for glutathione synthesis in alcoholic subjects can be demonstrated by the
present approach and different options to probe the methionine cycle in alcoholics will
have to be explored.