Advancing cell-free DNA as a biomarker of damage to heart caused by ionizing radiation.

Exposure to diagnostic and therapeutic radiation introduces risks for development of diseases later in life by causing DNA damage in cells. Currently, there is no clinical method for determining exposure risk caused by radiation toxicity to DNA. Cell-free DNA (cfDNA), a marker of DNA damage, is currently used to assess risk for long-term effects following organ transplantation, surgery and inflammation. The goal of our proposed study is to develop cfDNA as an early biomarker for assessing risk for cardiovascular disease and cancer from radiation exposure so that strategies to mitigate the damaging effects of medical radiation can be assessed. Hearts from male and female WAG/RijCmcr rats (n = 6-10/group) were exposed to increasing doses of X-radiation (50 mGy and 3.5 Gy). Blood was collected prior to and after (15 minutes-96 hours) irradiation, and cell-free plasma was prepared. Primers and probes were designed for quantitative analysis of sequences of mitochondria (12S rRNA) and nuclear (Gapdh) cfDNA present in rat plasma using quantitative reverse transcription polymerase chain reaction (RT-qPCR). Exposure of hearts to radiation increased nuclear and mitochondrial cfDNA in a dose-dependent manner. Three point five grays from X-radiation increase cfDNA for Gapdh in plasma after 1 hour with a 15.8-fold increase (P < 0.001) after 6 hours. The earliest time nuclear and mitochondrial cfDNA increases were detected in plasma was at 60 minutes following exposure to 3.5 Gy. cfDNA has potential to advance as a biomarker of exposure to medical doses of radiation in patients.