Leukotriene C4-induced radioprotection: the role of hypoxia.

Pretreatment of mice with leukotriene C4 (LTC4), a biological mediator that can cause marked contraction of vascular, tracheal, and bronchial smooth muscles, enhances radiation survival. Optimal protection is observed with 10 micrograms LTC4 per mouse (400 micrograms/kg body wt) administered subcutaneously 5 to 10 min prior to irradiation. Pretreatment with 10 micrograms LTC4 increases the LD50/30 from 8.36 Gy in mice receiving saline to 15.7 Gy, providing a dose reduction factor of 1.9. Enhanced survival of mice was observed with doses of 50 micrograms LTD4/mouse, but not with LTE4. Fifteen minutes after administration of 10 micrograms LTC4, the breathing rate is reduced by 33%, the blood paO2 by 20%, the paCO2 by 29%, and the HCO3- by 43%. Whole blood lactate increased by 288% at this same time. The period over which the elevation in blood lactate occurs is similar to the times for optimal radioprotection. These data coupled with the finding that protection was eliminated when irradiation occurred in an enriched oxygen atmosphere indicate that hypoxia plays a role in leukotriene C4-induced animal radiation survival. High-performance liquid chromatography and tissue distribution analyses support a role for an indirect mechanism since the highest levels of LTC4 in the tissues do not correlate with the peak time for radioprotection.     

Protection of mice against mixed fission neutron-gamma (n: gamma = 1:1) irradiation by WR-2721, 16,16-dimethyl PGE2, and the combination of both agents

The survival of mice after whole-body exposure to a modified fission neutron-gamma field (n: gamma = 1:1) was used to examine radiation protection by WR-2721, 16,16-dimethyl PGE2(DiPGE2), and the combination of both agents. Administration of WR-2721 (453 mg/kg) increased the LD50/30 from 5.24 to 7.17 Gy (DMF = 1.37), whereas pretreatment with DiPGE2 (1.6 mg/kg) increased the LD50/30 to 5.77 Gy (dose modification factor (DMF) = 1.10). The combination of 453 mg/kg WR-2721 and 0.4 mg/kg DiPGE2 resulted in an LD50/30 of 7.33 Gy, yielding a DMF of 1.39. However, no significant difference in protection was obtained with the combination of the two agents compared to that seen with WR-2721 alone.     

Water soluble vitamin E (TMG) as a radioprotector

Tocopherol monoglucoside (TMG), a water soluble derivative of vitamin E offers protection against deleterious effects of ionizing radiation, both under in vivo and in vitro conditions, to biological systems. TMG was found to be a potent antioxidant and an effective free radical scavenger. It forms a phenoxyl radical similar to trolox upon reaction with various one-electron oxidants. TMG protected DNA from radiation-induced strand breaks. It also protected thymine glycol formation induced by gamma-radiation. Gamma-radiation-induced loss of viability of EL-tumor cells and peroxidation of lipids in microsomal and mitochondrial membranes were prevented by TMG. TMG was nontoxic to mice when administered orally up to 7.0 g/kg body weight. The LD50 dose of TMG for ip administration in mice was 1.15 g/kg body wt. In rats, following oral and ip administration of TMG, the absorption (distribution) half lives were 5.8 and 3.0 min respectively and elimination half lives were 6.7 and 3.1 min respectively. Embryonic mortality resulting from exposure of pregnant mice to ionizing radiation (2 Gy) was reduced by 75% by ip administration of TMG (0.6 g/kg, body wt) prior to irradiation. TMG offered protection to mice against whole body gamma-radiation-induced lethality and weight loss. The LD50(30) of mice increased from 6 to 6.72 Gy upon post irradiation administration of a single dose of TMG (0.6 g/kg, body wt) by ip.     

Medical-prophylactic properties of the low-molecular-weight chitosan at environmental radiation injury

The possibility of the successful modification of radiation injury by chitosan with low molecular weight (10 kDa) has been established under experimental conditions. The survival of mice increased up to 72.7 and 44.7% respectively at intravenous and intramuscular injection 30 min before gamma-irradiation with a dose 8 Gy (LD97). In guinea pigs the effect was 50-52.6% at intravenous and 40% at intramuscular administration 1-3 h after irradiation with a dose 5 Gy (LD90). Radioprotective efficiency of 10 kDa chitosan is close to that of high-molecular-weight (65-70 kDa) preceding (medicine RS-10 and RS-11).     

Radiation protection of murine intestine by WR-2721, 16,16-dimethyl prostaglandin E2, and the combination of both agents

The survival of murine intestinal clonogenic cells (ICC) and the survival of mice after whole-body exposure to 137Cs irradiation were used to measure radiation protection by ethiophos (WR-2721), 16,16-dimethyl prostaglandin E2, and the combination of the two. Doses from 2 to 12.5 mg/mouse of WR-2721 increased cell survival linearly from 3.2 +/- 0.3 in controls given 15.0 Gy to 93.1 +/- 5.2 per jejunal circumference. In contrast, 16,16-dm PGE2 increased ICC survival at 15.0 Gy rapidly from 1 to 10 micrograms/mouse, followed by a plateau up to 100 micrograms/mouse. Animal survival at 6 days (LD50/6) increased from 16.3 +/- 0.4 Gy (95% confidence limits) in controls to 20.3 +/- 0.6 Gy in the PG-treated animals. WR-2721 increased the LD50/6 to 26.1 +/- 1.4 Gy. The dose modification factors were 1.25 and 1.60, respectively. The combination of agents increased ICC survival above that seen with each agent alone up to 8 mg WR-2721, above which no additional protection was seen. Animals given 10 micrograms PG plus 10 mg WR-2721 survived longer than with either agent given alone. The LD50/6 was 36.3 +/- 1.8 Gy for a dose modification factor (DMF) of 2.23. In addition, the slope of the probit curve was reduced from those of each agent alone. PG-induced changes in villus epithelial cell morphology and survival may account, in part, for these observations. The results suggest that either the mechanisms for these two types of radiation protectors are different or they act on separate subcellular targets which are critical to survival from radiation injury.     

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.     

The modifying action of the Japanese pagoda tree (Sophora japonica) and pantocrine in radiation lesions

A study was made of the effect of Sophora japonica and pantocrine on irradiated (2.5 Gy) human lymphoblastoid cells. The radioprotective effect was manifested with the preparations injected separately after irradiation. The highest radioprotective effect was produced by the mixture of the preparations, the injection 15 min after irradiation being more effective than preinjection. The protective effect of the agents was studied on mongrel mice after the administration thereof for the purposes of protection protection-and-treatment and treatment. Sophora japonica and pantocrine were shown to increase the survival rate of lethally exposed mice (LD90/30) when administered in a combination 5-15 min before irradiation and when used for the purposes of protection--and--treatment: 53.3% and 50% of animals, respectively, survived by day 30 following irradiation. DMF was 1.25.     

Metallothionein induction as a potent means of radiation protection in mice

A striking resistance to lethal damage from a single dose of 6-8 Gy of X rays has been found in mice which had received various pretreatments to induce metallothionein (MT) synthesis in the liver prior to irradiation. Mice were injected with manganese (10 mg Mn/kg) or cadmium (3 mg Cd/kg) salt subcutaneously, or a patch of dorsal skin (2 X 2 cm2) was excised 1 or 2 days prior to irradiation. The increased tolerance of these mice to radiation was established by a marked decrease of mortality rate, an increase of mean survival time, a reduction of weight loss, and a smaller decrease in the number of leukocytes as compared with the control group. The LD50/30 for control mice was 6.3 Gy, while the corresponding values for the groups pretreated with Mn, Cd, and skin excision were 7.5, 7.7, and 7.9 Gy, respectively. The normal level of MT in mouse liver was approximately 25 micrograms/g tissue. This level increased 2.5- to 3-fold 24 h after 6.3 Gy irradiation. The MT levels of mice pretreated with Cd, Mn, and skin excision were increased 8-, 5-, and 7-fold, respectively, prior to irradiation as compared with the preirradiation control. These results indicate that the induction of MT in mouse liver is a significant factor in the mechanism of protection against radiation.     

Radiomodifying properties of the synthetic analog of prostaglandin F2 alpha-estrofan

Estrofan (0.1 to 5 mg/kg) administered to rats and mice 5 min prior to gamma irradiation with doses of 8.5 to 9.5 Gy (LD90/30) increases the survival rate up to 30-40 per cent. The drug is ineffective when administered 30 and 60 min before irradiation.     

The radioprotective effect of extracts of Archangelica officinalis Hoffm. and Ledum palustre L. on mice

A single injection of Archangelica officinalis Hoffm. and Ledum palustre L. extracts to mice 5-15 min before irradiation with a median lethal dose increased their survival rate. The most favourable effect was produced by a combination of the two preparations: by day 30 100% of animals survived after a dose of 6 Gy (LD50/30); 70% survived after a dose of 7.5 Gy (LD90/30), and 25% after a dose of 8 Gy (LD100/12). DMF for the extract mixture was 1.48.     

Role of Rubia cordifolia Linn. in radiation protection

The radioprotective potential of alcoholic extract of root of R. cordifolia, was studied by survival, hemopoietic cell protection and micronucleus assay. The LD50 value for the alcoholic root extract was found to be 1200 mg/kg body weight at 72 hr post irradiation. A significant radiation protection (67%) as assessed by increased animal survival was observed when R. cordifolia (RC) extract was administered intraperitoneally, 90 min. before the radiation exposure. Besides, the extract also inhibited radiation induced lipid peroxidation measured by the inhibition of thiobarbituric acid reactive substance (TBARS). The RC extract at a selected dose of 460 mg/kg body weight was effective in protecting the radiation induced suppression of endogenous colony forming units in spleen. A significant inhibition of radiation (2 Gy) induced micronuclei formation was observed when RC extract was administered 90 min prior to irradiation. Thus, it appears that the alcoholic root extract of R. cordifolia provides significant protection against radiation induced lipid peroxidation, hemopoietic injury and genotoxicity. The mechanism of action of RC extract appears to be through its anti-oxidant, metal chelation and anti-inflammatory property.     

Protection by WR-3689 against gamma-ray-induced intestinal damage: comparative effect on clonogenic cell survival, mouse survival, and DNA damage

The aminophosphorothioate WR-3689 was characterized for its ability to protect mouse jejunal cells in vivo from single doses of X or gamma radiation. First, the effect of the drug on the survival of jejunal stem cells was examined using a clonogenic end point, the crypt microcolony assay. When WR-3689 was administered 30 min prior to whole-body irradiation, the number of surviving crypt cells was markedly increased at all doses of the drug, although protection began to level out at doses larger than 600 mg/kg. Protection was maximal when the drug was given 30 min before whole-body irradiation and declined rapidly with both shorter and longer intervals. Protection factors (PFs) were obtained by measuring survival curves for clonogenic crypt cells as a function of radiation dose; WR-3689 given 30 min before whole-body irradiation protected jejunum in the microcolony assay with a PF of 1.26 +/- 0.02, 1.50 +/- 0.10, and 1.65 +/- 0.10 at doses of 200, 400, and 800 mg/kg, respectively. Next, the effect of WR-3689 on the survival of jejunal stem cells was determined by assaying the survival of mice given X-ray doses to the whole abdomen in the range leading to death from the gastrointestinal syndrome. The PFs based on the LD50 values for 11-day survival were 1.31 +/- 0.05 (200 mg/kg) and 1.48 +/- 0.05 (400 mg/kg). Crypt-cell survival and animal survival were thus modified to a similar extent by this agent. Finally, the effect of WR-3689 on the induction of DNA single-strand breaks (SSBs) in jejunal cells was measured using an adaptation of the alkaline elution methodology. In mice treated with WR-3689 (400 or 800 mg/kg) 30 min prior to whole-body irradiation with 10 Gy there was no significant reduction in the number of DNA SSBs induced either in samples of the jejunum or in the cycling crypt cells, providing further evidence that there is no simple relationship between the modification of DNA SSBs and the survival of jejunal stem cells.     

Effect of Pseudomonas contamination or antibiotic decontamination of the GI tract on acute radiation lethality after neutron or gamma irradiation

The influence of antibiotic decontamination of Pseudomonas contamination of the GI tract prior to whole-body neutron or gamma irradiation was studied. It was observed that for fission neutron doses greater than 5.5 Gy, cyclotron-produced neutron doses greater than 6.7 Gy, and 137Cs gamma-ray doses greater than 14.4 Gy, the median survival time of untreated rats was relatively constant at 4.2 to 4.5 days, indicating death was due to intestinal injury. Within the dose range of 3.5 to 5.5 Gy of fission neutrons, 4.9 to 6.7 Gy of cyclotron-produced neutrons, and 9.6 to 14.4 Gy of gamma rays, median survival time of these animals was inversely related to dose and varied from 12 to 4.6 days. This change in survival time with dose reflects a transition in the mechanisms of acute radiation death from pure hematopoietic, to a combination of intestinal and hematopoietic, to pure intestinal death. Decontamination of the GI tract with antibiotics prior to irradiation increased median survival time 1 to 5 days in this transitional dose range. Contamination of the intestinal flora with Pseudomonas aeruginosa prior to irradiation reduced median survival time 1 to 5 days in the same radiation dose range. Pseudomonas-contaminated animals irradiated within this transitional dose range had maximum concentrations of total bacteria and Pseudomonas in their livers at the time of death. However, liver bacteria concentration was usually higher in gamma-irradiated animals, due to a smaller contribution of hematopoietic injury in neutron-irradiated animals. The effects of both decontamination of the GI tract and Pseudomonas contamination of the GI tract were negligible in the range of doses in which median survival time was dose independent, i.e., in the pure "intestinal death" dose range. Finally, despite the marked changes in survival time produced by decontamination or Pseudomonas contamination in the "transitional dose range," these treatments had little effect on ultimate survival after irradiation as measured by the LD50/5 day and the LD50/30 day end points. The implications of these results with respect to treatment of acute radiation injury after whole-body irradiation are discussed.     

Multi-endpoint biological monitoring of phosphine workers

5-Aminosalicylic acid (5ASA), a prescribed drug for ulcerative colitis, is a potent scavenger of oxygen-derived free radicals. The present study was undertaken to ascertain its ability to protect against radiation-induced damage. The drug dose-dependent effect, optimum time of drug administration and radiation dose-dependent effect (0-4 Gy) on in vivo radiation protection against micronuclei induction in polychromatic erythrocytes (PCE) and normochromatic erythrocytes (NCE) were studied in the bone marrow of mice. Intraperitoneal injection of 10-125 mg/kg of the drug 30 min before whole body irradiation with 3 Gy produced a significant reduction in the frequency of micronucleated erythrocytes at 24 h after exposure. The optimum dose for protection without drug toxicity was 25 mg/kg body weight. Injection of 25 mg/kg of the drug 60 or 30 min before or within 15 min after 3 Gy whole body gamma-irradiation resulted in a significant decrease in the radiation-induced PCE and NCE with micronuclei (MPCE and MNCE) and an increase in the ratio of PCE to NCE (P/N), at 24 h post-irradiation. Maximum effect was seen when the drug was administered 30 min before irradiation. Therefore, to study the radiation dose-response, mice were pre-treated with 25 mg/kg of 5ASA 30 min before 1-4 Gy of gamma-irradiation. Radiation increased the MN frequency linearly (r(2)=0.99) with dose. Pre-treatment with 5ASA significantly reduced the MN counts to 40-50% of the radiation (RT) alone values, giving a dose modification factor (DMF) of 2.02 (MPCE) and 2.53 (MNCE). Irradiation resulted in a dose-dependent decline in the P/N ratio at all the doses of radiation studied. 5ASA produced a significant increase in the P/N ratio from that of irradiated controls, at all doses of radiations tested. These results show that 5ASA protect mice against radiation-induced MN formation and mitotic arrest.     

Effect of gemcitabine on the tolerance of the lung to single-dose irradiation in C3H mice.

In an early phase II trial combining gemcitabine (dFdC) and radiotherapy for lung carcinomas, severe pulmonary toxicity was observed. In this framework, the objective of this study was to investigate the effect of dFdC on the tolerance of the lungs of C3H mice to single-dose irradiation. The thoraxes of C3H mice were irradiated with a graded single dose of 8 MV photons; dFdC (150 mg/kg) or saline (control animals) was administered i.p. 3 or 48 h prior to irradiation. Lung tolerance was assessed by the LD50 at 7-180 days after irradiation. For irradiation alone, the LD50 reached 14.45 Gy (95% CI 13.33-15.66 Gy). With a 3-h interval between administration of dFdC and irradiation, the LD50 reached 13.29 (95% CI 12.26-14.44 Gy); the corresponding value with a 48-h interval reached 13.01 Gy (95% CI 11.92-14.20 Gy). Our data also suggested a possible effect of dFdC on radiation-induced esophageal toxicity. dFdC has a minimal effect on lung tolerance after single-dose irradiation. However, a proper phase I-II trial should be designed before any routine use of combined dFdC and radiotherapy in the thoracic region.     

Changes in the sensitivity of mice to the action of gamma irradiation by Viscum album L. polysaccharides]

The influence of water-soluble polysaccharides of Viscum album L. on the survival of mice subjected to whole-body gamma-irradiation has been investigated. Polysaccharides were shown to exert a radioprotective effect which was a function of both the radiation dose and the drug dose and time of its injection. The maximum radioprotective efficacy of polysaccharides was observed after their injection 15 min before irradiation. A single intraperitoneal administration of polysaccharides (25 mg/kg) before irradiation with LD50/30 and LD100/10-12 increased the 60-day survival rate up to 95% and 27% respectively. The postirradiation injection of polysaccharides prevented death of 80% of mice given LD50 and increased the average life expectancy of animals irradiated with absolutely lethal doses.     

Luplatex and its radioprotective properties

In experimental conditions the radioprotective properties of the placental complex Luplatex created in Scientific production complex "Biotechindustry" was studied. In experiments on mice F1(CBA x C57Bl) it was shown that Luplatex injected intraperitoneally in dose 0.5 ml 5-10 min before or after whole body gamma-irradiation with 8 Gy (LD80/30) increased the survival up to 40% as compared to the control group. In white mice protected by oral administration of Luplatex 30 min before exposure to 7.5 Gy, which is absolute minimal lethal dose for this type of mice (LD100/30), the effect was 48.3%.     

Cyclic nucleotides and lipids in the realization of the radioprotective effect of ceruloplasmin

Ceruloplasmin administered 60 min before irradiation diminished cAMP and cGMP levels, which were increased by irradiation at LD50 and LD100, and normalized cAMP/cGMP ratio in the rat liver during the first 24 h following irradiation with a dose of 6.24 Gy. The content of phospholipids increased and that of cholesterol decreased under the effect of ceruloplasmin leading to normalization of the molar cholesterol/phospholipid ratio in the rat liver on the 7th day of radiation sickness (LD50, 6.24 Gy).     

The effects of gamma irradiation on the survival and development of Clonorchis sinensis metacercariae

The effects of gamma irradiation on the survival and development of C. sinensis metacercariae were studied to evaluate the feasibility of irradiation as a control measure for clonorchiasis. Pseudorasbora parva were collected at an endemic river of clonorchiasis and were used for irradiation of the fluke in three schemes. The first (Scheme 1) was irradiation of the isolated metacercariae from the fish followed by infection to experimental rats. The second (Scheme 2) was irradiation of the fish, and then the metacercariae were isolated and infected to rats. The third (Scheme 3) was irradiation on the rat livers after infection with normal metacercariae. Irradiation doses varied from 5 to 100 Gy for Schemes 1 and 2, and 10 to 25 Gy for Scheme 3. The rats were sacrificed 2 to 6 weeks after infection. In Scheme 1, the metacercariae irradiated at 50 Gy failed to survive in the rats after 2 or 6 weeks. However, 1 to 44% of the metacercariae irradiated at 5-30 Gy survived. The estimated LD50 of Scheme 1 was 16.5 Gy. The flukes irradiated in Scheme 2 survived better than those in Scheme 1. The average worm recovery rate in 50 Gy was 28%(7-39% individually). Increasing the dose up to 100 Gy brought a remarkably low survival rate of an average 1%(0-3% individually). The LD50 of Scheme 2 was 47.5 Gy. Worm recovery rates in the 10 Gy group of Scheme 3 were 21-39%, and those in the 25 Gy group were 2% and 34%. Although the metacercariae were irradiated, all of the recovered worms were morphologically normal.(ABSTRACT TRUNCATED AT 250 WORDS)     

Trehalose dimycolate enhances survival of fission neutron-irradiated mice and Klebsiella pneumoniae-challenged irradiated mice

The survival of B6D2F1 female mice exposed to lethal doses of fission neutron radiation is increased when trehalose dimycolate (TDM) preparations are given either 1 h after exposure or 1 day before exposure to radiation. TDM in an emulsion of squalene, Tween 80, and saline was the most effective formulation for increasing the 30-day survival of mice when given 1 day before (90%) or 1 h after (88%) exposure to radiation. An aqueous suspension of a synthetic analog of TDM was less effective at increasing 30-day survival (60%) when given 1 day prior to radiation exposure and not effective when given 1 h after radiation. Mice receiving a sublethal dose (3.5 Gy) of fission neutron radiation and either the TDM emulsion or synthetic TDM 1 h after irradiation were substantially more resistant to challenge with 10, 100, 1000, or 5000 times the LD50/30 dose of Klebsiella pneumoniae than untreated mice.