[ RadSafe ] About the recent mice study and hormesis

[Ansari, Armin (CDC/ONDIEH/NCEH)]

Dear colleagues,

I noticed several messages reporting on the recent study by Bernal et al. in the FASEB Journal, titled: Adaptive radiation-induced epigenetic alterations mitigated by antioxidants.  These messages imply that the study documents beneficial effects of low dose radiation.

I believe this conclusion may be overreaching a little bit.  All that is happening here is that as a result of radiation, the methylation pattern of DNA has changed.  This change usually results in hypomethylation, but can also result in hypermethylation.  It has been shown that radiation-induced methylation pattern depends on the genomic region of DNA and the genomic background of the cells among other things.  Even in the present study, the hypermethylation was predominant in male offsprings only.

Because the mice used in this study were already in trouble, (i.e., their agouti genes were extremely hypomethylated making them more prone to obesity and cancer), the change happened to reverse that condition for some mice.  It is likely that methylation patterns in some other genomic region of the same mice have also been altered, and we know some of these methylation changes persist.  In fact, this is one of the main mechanisms postulated for genomic instability.  

Therefore, that fact that for this one gene - already messed up because of low state of methylation - radiation did something good by chance, it provides no basis to conclude that low-dose radiation is beneficial in general.  Not from this study anyway.

Best regards,
Armin Ansari