Mechanism of radioprotection by δ-tocotrienol: pharmacokinetics, pharmacodynamics and modulation of signalling pathways.

OBJECTIVE: The objective of this study was to investigate the correlation between in vivo δ-tocotrienol (DT3) pharmacokinetics, pharmacodynamics and radiation protection, and to evaluate the effect of DT3 pre-treatment on radiation-induced alterations in apoptotic and autophagic pathways. METHODS: We evaluated pharmacokinetics (plasma, 0.5 to 12 h) and pharmacodynamics (peripheral blood indices; day 3, 7, 10 and 14) after a single subcutaneous injection of 300 mg kg(-1) DT3 in unirradiated CD2F1 mice. Next, we monitored 30-day post-irradiation survival (9.25 Gy) and haematopoietic recovery of DT3-treated mice (7 Gy) exposed to cobalt-60 γ-irradiation. The effects of DT3 on irradiated bone marrow apoptosis and autophagy were determined by analyses of key caspases (3, 7, 9 and 8), beclin-1 and light chain 3 conversion. RESULTS: Plasma concentration of DT3 reached ∼195 µM (Cmax) 1 h after injection (Tmax), and DT3 was eliminated from plasma 12 h later. In unirradiated mice, DT3 significantly increased white blood cells (WBCs), neutrophils, lymphocytes (day 3 post DT3 injection) and platelets (day 7) by 1.5- to 2-fold, over vehicle-treated control. DT3 pre-treatment improved 30-day survival to 100% (∼15% in control) and accelerated recovery of reticulocytes, platelets, WBCs, neutrophils, lymphocytes and monocytes in peripheral blood. DT3 reduced activation of caspase-8, caspase-3 and caspase-7, inherent to apoptosis, while increasing autophagy-related beclin-1 expression in irradiated bone marrow. CONCLUSION: These data indicate that DT3 stimulates multilineage haematopoiesis, protects against radiation-induced apoptosis downstream of the mitochondria and stimulates cytoprotective autophagy. Apart from a potent antioxidant activity, DT3 may elicit survival advantage following irradiation by enhancing haematopoiesis and modulating signalling pathways.

Tracing radiation induced genomic instability in vivo in the haemopoietic cells from fetus to adult mouse.

The present experiment was aimed at studying the delayed expression of fetal irradiation induced genomic instability in the mouse haemopoietic cells in vivo. The abdominal area of 14 day pregnant Swiss albino mice was exposed to 0-1.5 Gy of gamma radiation. Chromosomal aberrations were studied in three passages of spleen colonies (short-term repopulating stem cells, STRSC) derived from 24 h post-irradiation fetal liver cells and in the 1-20 months postpartum bone marrow (long-term repopulating stem cells, LTRSC). Irradiation produced a significant and dose-dependent increase in the aberrant metaphases in the first passage spleen colony (CFU-S1) cells, which decreased in subsequent passages and reached normal levels by the third passage (CFU-S3). Bone marrow at 1-6 months postpartum showed similar chromosomal picture in the 0 Gy control and after 0.5-1.5 Gy, but there was a clear increase in aberrant cells from 9 months postpartum in the irradiated groups. Some mice in all irradiated groups showed a 2.5- to 5-fold increase in peripheral leukocyte counts. Bone marrow of these animals exhibited severe aneuploidy, the chromosome number ranging from less than 1n to 6n at 20 months of age. Our results indicate that unstable chromosome aberrations induced in the fetal haemopoietic STRSC are eliminated during subsequent cell divisions. However, genomic instability induced in the LTRSC persists and is expressed as chromosomal aberrations at advanced ages. Induction of chromosome aneuploidy could be an early step in the chain of events leading to adult leukaemia after prenatal irradiation.

Protection against prenatal irradiation-induced genomic instability and its consequences in adult mice by Ocimum flavonoids, orientin and vicenin.

PURPOSE: To study the protective effect of orientin and vicenin against early genomic effects of foetal irradiation and their late consequences in mice. MATERIALS AND METHODS: Fourteen-day pregnant mice were exposed to 1 Gy 60Co gamma-radiation 30 min after an intraperitoneal injection of orientin or vicenin (50 microg kg(-1) body weight). Chromosomal aberrations were studied in foetal liver cells and their spleen colonies (three passages, colony-forming units-spleen CFU-S1, CFU-S2, CFU-S3) and 1-12 months post-partum bone marrow. Peripheral blood counts and solid tumours were recorded to 12 and 20 months, respectively. RESULTS: Irradiation significantly increased the percent aberrant cells and aberrations/cell in foetal liver and CFU-S1. These effects decreased in later passages of CFU-S and were not seen at 1-6 months post-partum, but increased significantly from 9 months. Total blood counts showed significant reduction from 6 months, while neutrophils increased from 3 months post-partum. Solid tumour incidence in adults increased significantly, with a decrease in age at detection. Orientin/vicenin significantly reduced the chromosomal anomalies in foetal and adult haemopoietic cells, restored blood counts to the normal range, and significantly reduced tumour incidence and delayed tumour development to control age. CONCLUSIONS: Orientin and vicenin protect against foetal irradiation-induced genomic damage and instability, thereby reducing the delayed chromosomal abnormalities and tumorigenesis in adult.

In vivo radioprotection by alpha-TMG: preliminary studies.

alpha-TMG is a novel water-soluble derivative of Vitamin E that has shown excellent antioxidant activity. The parent compound has demonstrated protection against radiation induced chromosomal damage in vivo. Hence, the preliminary experiments to determine the radioprotective activity of alpha-TMG were carried out in adult Swiss albino mice. Acute toxicity of the drug was studied taking 24h, 72 h and 30 day mortality after a single intraperitoneal injection of 500-2000 mg/kg body weight of the drug. The drug LD(50) for 24h and 72 h/30 day survival were found to be 1120 and 1000 mg/kg body weight, respectively. The optimum time of drug administration and drug dose-dependent effect on in vivo radiation protection of bone marrow chromosomes was studied in mice. Injection of 600 mg/kg of the drug 15 min before or within 5, 15 or 30min after 3Gy whole body gamma radiation resulted in a significant decrease in the aberrant metaphases percent at 24h post-irradiation; the maximum effect was seen when the drug was given immediately after irradiation. Injection of 200-800 mg/kg TMG within 5 min of irradiation with 3 Gy produced a significant dose-dependent reduction in the radiation induced percent aberrant metaphases and in the frequency of micronucleated erythrocytes at 24h after exposure, with a corresponding decrease in the different types of aberrations. The optimum dose for protection without drug toxicity was 600 mg/kg body weight. At this dose, TMG produced 70 and >60% reduction in the radiation induced percent aberrant metaphases and micronucleated erythrocytes, respectively. The high water solubility and effectiveness when administered post-irradiation favor TMG as a likely candidate for protection in case of accidental exposures.