Blocking and suppressing mechanisms of chemoprevention by dietary constituents

Many dietary constituents are chemopreventive in animal models, and experim ents with cultured cells are revealing various potential mechanisms of acti on. Compounds classified as blocking agents can prevent, or greatly reduce, initiation of carcinogenesis, while suppressing agents affect later stages of the process by reducing cell proliferation. Many compounds have both ty pes of activity. Blocking mechanisms include alteration of drug metabolisin g activities and scavenging of reactive oxygen species. Mechanisms which su ppress tumorigenesis often involve modulation of signal transduction pathwa ys, leading to altered gene expression, cell cycle arrest or apoptosis. As our knowledge of how these dietary components affect cell biochemistry impr oves, so the likelihood of success in chemoprevention trials and in provisi on of dietary advice to the general population to optimise the chances of p reventing disease is increased. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.