Metallothionein in radiation exposure: its induction and protective role

Since its discovery about 40 years ago, there has been a wide interdiscipli nary research interest in metallothionein (MT) on its physiological and tox icological aspects. Functionally, MT is involved not only in metal detoxifi cation and homeostasis, but also in scavenging free radicals during oxidati ve damage. Among over 4500 publications which can be retrieved by Medline s earch: only about 50 reports have been published on the relationship of MT with ionizing and UV radiation. In this review, we have evaluated criticall y the published data on the induced synthesis of MT by radiation, and the p otential functions of MT in radiation induced cell damage. MT mRNA expressi on or MT synthesis was found to be induced by exposure of cells in vitro or tissues in vivo to ionizing or UV radiation. In most of the studies in ani mals and tissue cultures, high doses of ionizing radiation were used to ind uce MT, and, therefore, it is difficult to extrapolate these results to low level of repeated exposures to radiation in humans. Induced synthesis of M T is considered as one of the mechanisms involved in the adaptive response to low dose radiation exposure. The presence of MT in normal cells may prov ide protective effects from radiation-induced genotoxicity and cytotoxicity . However, in tumor cells, the presence of MT can result in drug and radiat ion resistance as well. These effects are modulated by other cellular facto rs, besides MT, such as antioxidants, and by the cell cycle stages in cell proliferation and differentiation. (C) 1999 Elsevier Science Ireland Ltd. A ll rights reserved.