Gamma Low-Dose-Rate Ionizing Radiation Stimulates Adaptive Functional and Molecular Response in Human Aortic Endothelial Cells in a Threshold-, Dose-, and Dose Rate-Dependent Manner.

A central question in radiation protection research is whether low-dose and low-dose-rate (LDR) exposures to ionizing radiation play a role in progression of cardiovascular disease. The response of endothelial cells to different LDR exposures may help estimate risk of cardiovascular disease by providing the biological mechanism involved. We investigated the effect of chronic LDR radiation on functional and molecular responses of human aorta endothelial cells (HAoECs). Human aorta endothelial cells were continuously irradiated at LDR (6 mGy/h) for 15 days and analyzed at time points when the cumulative dose reached 0.05, 0.5, 1.0, and 2.0 Gy. The same doses were administered acutely at high-dose rate (HDR; 1 Gy/min). The threshold for the loss of angiogenic capacity for both LDR and HDR radiations was between 0.5 and 1.0 Gy. At 2.0 Gy, angiogenic capacity returned to normal only for HAoEC exposed to LDR radiation, associated with increased expression of antioxidant and anti-inflammatory genes. Pre-LDR, but not pre-HDR, radiation, followed by a single acute 2.0 Gy challenge dose sustained the expression of antioxidant and anti-inflammatory genes and stimulated angiogenesis. Our results suggest that dose rate is important in cellular response and that a radioadaptive response is involved for a 2.0 Gy dose at LDR.

Intrinsically impaired platelet production in some patients with persistent or chronic immune thrombocytopenia.

Persistent or chronic immune thrombocytopenias (P/C-ITP) are acquired blood disorders lasting more than 3 months or 1 year, respectively. The pathogenesis of these disorders is thought to be immunological. We hypothesized that some patients with P/C-ITP might have an intrinsic megakaryopoiesis defect. We identified a group of P/C-ITP patients with acquired isolated mild thrombocytopenia (30-100 × 10(9) /l), undetectable anti-platelet antibodies, negative autoimmune investigations and no need for treatment. We examined in vitro megakaryocyte differentiation and compared these patients' results with those of acute-ITP patients and healthy controls. No difference in proliferation, ploidy or expression of surface markers was found. In contrast, P/C-ITP patients had significantly fewer proplatelet-forming megakaryocytes. This novel observation demonstrated that some patients diagnosed with P/C-ITP have an intrinsic megakaryopoiesis defect independent of the bone-marrow environment. Further investigations are needed to dissect mechanisms underlying this impaired proplatelet formation in these patients.