Biological principles for the effects of ethanol

Biological principles for the effects of ethanol are deduced from a study of some 60 different cell types ranging from bacteria, yeasts, and fungi to animal and plant cells. The direct effects of ethanol against metabolic pathways appears to be minimal, and the observed effects are more a reflection of ethanol metabolism rather than ethanol per se. Roles for NAD/NADH imbalances, acetaldehyde accumulation, and for the deactivation (i.e., switching off)of replicative processes emerge as central mechanisms. In the yeast-ethanol fermentation, it is suggested that the ability to avoid acetaldehyde accumulation is a prerequisite to so-called ethanol tolerance. Membrane-related effects due to ethanol are also involved. However, the spectrum of these effects may be such that different loci are involved at different ethanol concentrations. These effects are due to the polar, dielectric, and hydrogen-bond interactions of ethanol with membrane proteins and with the surface groups of the membrane. Competition for, and displacement of, bound cellular water will also occur. The so-called lipophilic effects of ethanol are shown to be minimal. Strategies and mechanisms for ethanol tolerance are discussed.