Genetic polymorphisms in ethanol metabolism: issues and goals for physiologically based pharmacokinetic modeling

Chronic exposure to excessive ethanol consumption has adverse effects on virtually all organs and tissues in the body, including but not limited to the liver, pancreas, reproductive organs, central nervous system, and the fetus. Exposure to ethanol can also enhance the toxicity of other chemicals. Not all persons exposed to the same amount of ethanol experience the same degree of adverse effects. For example, only 12% to 13% of alcohol abusers develop cirrhosis. Possible factors which may alter susceptibility include age, sex, nutritional status, health status (i.e., smokers) and race. Some of these factors affect susceptibility because they alter ethanol metabolism, which occurs primarily in the liver by alcohol dehydrogenase (ADH). Genetic polymorphisms for ADH partially account for the observed differences in ethanol elimination rates among various populations but the relative contribution to susceptibility is not completely understood. Incorporation of the kinetic parameters associated with ADH polymorphisms into a physiologically based pharmacokinetic (PBPK) model for ethanol will aid in assessing the relative contribution to susceptibility. The specific information required to develop this model includes Km and Kcat values for each ADH isoform and the amount of each isoform present in the liver. Blood ethanol concentrations (BEC) from various populations with known ADH phenotypes are also necessary to validate the model. The impact of inclusion of these data on PBPK model predictions was examined using available information from adult white and African American males.