Hormesis in Carcinogenicity of Non-genotoxic Carcinogens

Abstract

Recently the idea of hormesis, a biphasic dose-response relationship in which a chemical exerts opposite effects dependent on the dose, has attracted interest in the field of carcinogenesis. With non-genotoxic agents there is considerable experimental evidence in support of hormesis and the present review highlights current knowledge of dose- response effects. In particular, several in vivo studies have provided support for the idea that non-genotoxic carcinogens may inhibit hepatocarcinogenesis at low doses. Here, we survey the examples and discuss possible mechanisms of hormesis with cytochrome P450 inducers, such as phenobarbital, 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT), α-benzene hexachloride (α-BHC), and other non-genotoxins. Epigenetic processes differentially can be affected by agents that impinge on oxidative stress, DNA repair, cell proliferation, apoptosis, intracellular communication and cell signaling. Non-genotoxic carcinogens may target nuclear receptors, cause aberrant DNA methylation at the genomic level and induce post-translational modifications at the protein level, thereby impacting on the stability or activity of key regulatory proteins, including oncoproteins and tumor suppressor proteins. Via multiple epigenetic lesions, non- genotoxic carcinogens can elicit a variety of changes contributing to cellular carcinogenesis. (J Toxicol Pathol 2006; 19: 111-122)