Plasma Flt3-ligand as a Biomarker for Radiation Exposure

Abstract

There is a need to identify minimally invasive biomarkers that can be used to accurately and quickly determine radiation exposure. Radiation biodosimeters have applications in clinical medicine and for population screening following a nuclear or radiological event. In this study, we evaluated the efficacy of fms-like tyrosine kinase ligand (Flt3-L) as a biomarker for radiation exposure in plasma from whole body irradiated mice. Ten week old female C57BL6 mice received a single whole body irradiation dose of 1-8 Gy from a Pantak X-ray source at a dose rate of 2.28 Gy/min. Plasma was collected by cardiac puncture at 6, 24, 48 and 72hr post-IR as well as 1-3 weeks post-irradiation. Flt3-L levels were determined via a commercially available ELISA assay (R&D Systems). Data was pooled to generate a linear regression model and cluster dendrogram correlating plasma Flt3-L levels with radiation dose. At doses of 1, 4 and 8 Gy, Flt-3L levels were greater than control and the level of Flt3-L increased proportionally to the irradiation dose. At 24hr post-IR 1Gy averaged 376 pg/ml Flt3-L, 4Gy 947 pg/ml and 8Gy 1350 pg/ml Flt3-L. At 48hr post-IR, the averaged Flt3-L levels were 1Gy 730 pg/ml, 4Gy 1608 pg/ml and 8Gy 2100 pg/ml. Flt3-L at 72hr post-IR was 1Gy 632 pg/ml, 4Gy 1579 pg/ml and 8Gy 2065 pg/ml. Differences in Flt3-L levels were statistically significant at each dose and at all time points. The problem arises from overlap between Flt3-L averages from different dose groups at different time points where an outlier from one group might fall into the wrong dose category if dose calculation is based solely on Flt3-L levels without a known time point of irradiation. To reduce this error we looked at Flt3-L level trends over different time points post-IR. Samples were taken serially from the same mouse at 24hr and 72 hr. The Flt3-L trend over two sequential time points further validated the dose received. If Flt3-L levels remained constant the exposure was 1Gy or less, but if Flt3-L increased from 24hr to 72hr we could assume the mouse received a dose equal to or greater than 4Gy. This method reduced the false dose rate when determining radiation exposure when time of irradiation was unknown. Flt3-L levels at 24, 48 and 72 hrs were used to generate a mathematical model for determination of unknown radiation dose. In a blind study, the working model differentiated mice groups into dose received cohorts of 1, 4 or 8 Gy based on plasma Flt3-L levels irrespective of time of irradiation. Plasma Flt3-L levels at 24, 48 and 72 hrs consistently predicted radiation dose received in mice. Plasma Flt3-L has potential application as a radiation biodosimeter in mammalian systems.