Metabolism and transport of drugs and xenobiotics

Individuals are continuously exposed to myriad of foreign compounds derived from the diet, environmental pollutants and drugs (xenobiotics). Metabolic enzymes in the body usually convert xenobiotics to more water-soluble and less harmful metabolites although enzymatic reactions may also produce reactive, toxic products. Transport proteins aid in transfer of xenobiotics and their metabolites across cell membranes and excrete them out of the body. Exposure to xenobiotics can either block the activity of metabolic enzymes and transporters (inhibition) or enhance their expression levels (induction).