Journal Article

Hormesis and dose–response-mediated mechanisms in carcinogenesis: evidence for a threshold in carcinogenicity of non-genotoxic carcinogens

Shoji Fukushima, Anna Kinoshita, Rawiwan Puatanachokchai, Masahiko Kushida, Hideki Wanibuchi and Keiichirou Morimura

in Carcinogenesis

Volume 26, issue 11, pages 1835-1845
Published in print November 2005 | ISSN: 0143-3334
Published online June 2005 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/bgi160
Hormesis and dose–response-mediated mechanisms in carcinogenesis: evidence for a threshold in carcinogenicity of non-genotoxic carcinogens

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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 using phenobarbital, 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT), α-benzene hexachloride (α-BHC) and other non-genotoxins. Furthermore, the effects of low and high doses of non-genotoxic and genotoxic compounds on carcinogenesis are compared, with especial attention to differences in mechanisms of action in animals and possible application of the dose–response concept to cancer risk assessment in humans. 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. Genotoxic agents, in contrast, cause genetic change by directly attacking DNA and inducing mutations, in addition to temporarily modulating the gene activity. Carcinogens can elicit a variety of changes via multiple genetic and epigenetic lesions, contributing to cellular carcinogenesis.

Keywords: α-BHC, α-benzene hexachloride; 2-AAF, 2-acetylaminofluorene; Cx32, connexin 32; DDT, 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane; DEN, diethylnitrosamine; GABA, gamma-aminobutyric acid; GST-P, glutathione S-transferase placental form; HCC, hepatocellular carcinoma; IR, ionizing radiation; MeIQx, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline; NOEL, no-observed effect level; 8-OHdG, 8-hydroxy-2′-deoxyguanosine; Ogg1, oxoguanine glycosylase 1; ROS, reactive oxygen species; TCDD, 2,3,7,8-tetrachlorodibenzo-p-dioxin

Journal Article.  8242 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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