Automated Dicentric Aberration Scoring for Triage Dose Assessment: 60Co Gamma Ray Dose-response at Different Dose Rates.

The objective of this study was to establish radiation dose-response calibration curves using automated dicentric scoring to support rapid and accurate cytogenetic triage dose-assessment. Blood was drawn from healthy human volunteers and exposed to Co gamma rays at several dose rates (i.e., 1.0, 0.6, and 0.1 Gy min). After radiation, the blood was placed for 2 h in a 37 °C incubator for repair. Blood was then cultured in complete media to which a mitogen (i.e., phytoghemagglutinin, concentration 4%) was added for 48 h. Colcemid was added to the culture at a final concentration of 0.2 µg mL after 24 h for the purpose of arresting first-division metaphase mitotics. Cells were harvested at the end of 48 h. Samples were processed using an automated metaphase harvester and automated microscope metaphase finder equipped with a suite of software including a specialized automated dicentric scoring application. The data obtained were used to create dose-response tables of dicentric yields. The null hypothesis that the data is Poisson-distributed could not be rejected at the significance level of α = 0.05 using results from a Shiny R Studio application (goodness-of-fit Poisson). Calibration curves based on linear-quadratic fits for Co gamma rays at the three different dose rates were generated using these data. The calibration curves were used to detect blind test cases. In conclusion, using the automated harvester and automated microscope metaphase finder with associated automated dicentric scoring software demonstrates high-throughput with suitable accuracy for triage radiation dose assessment.

Gamma-tocotrienol protects hematopoietic stem and progenitor cells in mice after total-body irradiation.

We analyzed the radioprotective effects of gamma-tocotrienol (GT3) on hematopoietic stem cells (HSCs) and progenitor cells (HPCs) in sublethally irradiated mice. Flow cytometry analysis indicated that radiation depleted HPCs (c-Kit(+), Lin(-)) to 40% at days 2 and 4 after total-body irradiation (TBI) in all treatment groups. The HPC numbers in GT3-treated mice recovered almost completely (90%) at day 7 but remained depleted in vehicle-treated mice (30%) even at day 13 after TBI. An in vitro colony-forming assay on sorted HSCs (Lin(-), Sca1(+), c-Kit(+)) indicated that TBI reduced the number of colonies to 40% and 50% at day 17 and 60, respectively, in vehicle-treated groups compared to unirradiated controls (naïve). GT3-treated irradiated mice maintained higher numbers of colonies (86% and 80% compared to naïve mice), thereby preserving the self-renewable capacity of HSCs. Histopathology of sternal bone marrow indicated more regenerative microfoci for myeloid cells and megakaryocytes and higher overall cellularity in GT3-treated mice compared to vehicle controls at days 7 and 13 after TBI. GT3 treatment also reduced the frequency of micronucleated erythrocytes significantly in irradiated mice. Our results demonstrate that GT3 protected hematopoietic tissue by preserving the HSCs and HPCs and by preventing persistent DNA damage.

Gamma-tocotrienol, a tocol antioxidant as a potent radioprotector.

PURPOSE: To assess the radioprotective potential of gamma-tocotrienol. MATERIALS AND METHODS: To optimise its dose and time regimen, gamma-tocotrienol (GT3) was injected subcutaneously (SC) at different doses into male CD2F1 mice [LD(50/30) (lethal radiation dose that results in the mortality of 50% mice in 30 days) radiation dose of 8.6 Gy with vehicle]. The mice were given 10.5, 11 and 11.5 Gy cobalt-60 radiation, and 30-day survival-protection was determined. Time optimisation was done by SC administration of GT3 at different intervals before irradiation. Dose reduction factor (DRF) was determined by probit analysis using mortality as the end point at six radiation doses. Protection from radiation induced pancytopenia was determined by enumerating peripheral blood cells from mice given GT3 and irradiated at 7 Gy. RESULTS: At an optimal dose of 200 mg/kg given SC 24 h before irradiation, GT3 had a DRF of 1.29. GT3 accelerated the recovery of total white blood cells, neutrophils, monocytes, platelets, and reticulocytes in irradiated mice, compared to vehicle-injected, irradiated controls. CONCLUSION: GT3 is a radioprotectant having a higher DRF than any other tocols. The protection it provides close to the gastro-intestinal range indicate that GT3 can be considered as an ideal radioprotectant meriting further drug development stages for the ultimate use in humans.