Concepts needed to understand potential health effects of chronic low-level radiation exposures: Role of adult stem cells and modulated cell–cell communication

To understand the extremely relevant, but complex, process of potential low-level ionizing radiation-induced health effects, particularly, cancer, both research-derived factual results and theoretical concepts must be generated and tested. To date, due to the difficulties of (a) generating epidemiological statistically rigorous and unambiguous data at extremely low levels; (b) deriving any mechanistic understanding from epidemiological data; (c) doing enough animal experiments due to cost and even relevancy of results to human beings; (d) using dubious molecular, biochemical, cellular in vitro assays, due to limitations, artifacts and misinterpretation of results; and (e) potently lack of appropriate paradigms and concepts needed to interpret results of chronic low-level exposures, the usual default tactic to assume extrapolation down from high-level exposures, using a non-threshold, linear model seems to defy facts and concepts that are known about carcinogenesis to date. The objective of this short analysis is to point out that several important concepts, namely, the role of adult stem cells as the “target” cells for carcinogenesis, the role of cell–cell communication, and oxidative stress as an intra-cellular signal transducer must be considered in the risk assessment of chronic low-level radiation exposure. In fact, the relatively new concepts of the “adaptive response,” the “bystander effects” and “genomic instability” must be carefully integrated with the stem cell, cell–cell communication and oxidative stress-signaling concepts.