Molecular specificity of 5-androstenediol as a systemic radioprotectant in mice.

We compared in vivo radioprotective efficacy of 5-androstenediol (5-AED) to that of ten other steroids: 17alpha-androstenediol, dehydroepiandrosterone, 5-androstenetriol (AET), 4-androstenedione (AND), testosterone, estradiol, fluasterone, 16alpha-bromoepiandrosterone, 16alpha-fluoro-androst-5-en-17alpha-ol (alpha-fluorohydrin, AFH), and 16alpha-fluoro-androst-5-en-17beta-ol (beta-fluorohydrin). Steroids were administered 24 or 48 hr before, or 1 hr after, whole-body gamma-irradiation. Two days after irradiation at 3 Gy, blood elements were counted. In addition, after irradiation at 9-12.5 Gy, survival was recorded for 30 days. The results showed radioprotective efficacy was specific for 5-AED. One other steroid, AFH, demonstrated appreciable survival effects but was less efficacious than 5-AED. AND and AET produced slight enhancement of survival in some experiments. This is the first demonstration that the prophylactic window for survival enhancement by 1 subcutaneous (s.c.) injection of 5-AED is as long as 48 hr in mice. Moreover, the results indicate that 1 s.c. injection of 5-AED 1 hr after irradiation is much less effective than 1 injection 24-48 hr before irradiation. Comparing the molecular features of steroids with radioprotective efficacy leads to the following conclusions: 1) these effects are due to interaction with specific receptors, since s.c. injection of extremely similar molecules with the same physicochemical properties as 5-AED were not radioprotective; 2) the 17-hydroxyl group is essential; 3) this group must be in the beta configuration in the absence of nearby side groups; 4) a halogen atom at 16 changes the 17-hydroxyl specificity to alpha; 5) the 3beta-hydroxyl group is not essential; 6) addition of a 7beta-hydroxyl group is deleterious; and 7) the effects are not due to activation of sex steroid receptors.

Radioprotection by N-palmitoylated nonapeptide of human interleukin-1beta.

Interleukin-1beta (IL-1beta) is a cytokine involved in homeostatic processes of the immune system and specifically in inflammatory reactions. The nonapeptide of human IL-1beta (VQGEESNDK, position 163-171) has been shown to retain adjuvant and immunostimulatory activities of the native molecule without any inflammatory and pyrogenic properties. A lipophilic derivative of IL-1beta nonapeptide having a palmitoyl residue at the amino terminus was synthesized in order to determine the effects of such structural modification on its bioactivities. The structurally modified peptide derivative, palmitoylated peptide, significantly protected C3H/HeN mice against potentially lethal doses of ionizing radiation. The dose reduction factor was found to be 1.07. Hematological studies show improved recovery of red blood cells and platelets in irradiated and palmitoylated peptide treated mice as compared with the untreated and irradiated group. These results suggest the importance of the derivatization of small peptides of radioprotective, but toxic cytokines in order to enhance radioprotective activity while reducing unwanted toxic side effects.

Effects of anesthesia and vehicle injection on circulating blood elements in C3H/HeN male mice.

The induction and maintenance of general anesthesia can lead to profound alterations of many organ systems, especially the cardiovascular, pulmonary, and nervous systems. Moreover, distinct from their cardiopulmonary effects, certain anesthetics can induce physiologic and behavioral changes, which may persist after recovery from anesthesia. Knowledge of the effects of anesthesia and anesthetic agents on hematologic measurements is important. Although the effects of anesthesia were clinically unapparent, the effect on levels of circulating blood elements was an important determinant for the results of our study. We sought to evaluate the effect of anesthesia and vehicle injection on the levels of circulating blood elements in C3H/HeN male mice. We used an automated hematology system to obtain complete blood counts with differentials in anesthetized and unanesthetized mice receiving subcutaneous injections of polyethylene glycol (PEG-400). Two days after a 30-min exposure to isoflurane anesthesia, mean white blood cell counts had deceased by 15.4%, mean neutrophil counts had decreased by 26.9%, and mean platelet counts by 11.2% compared with levels in unanesthetized mice. Our results indicate that the effect of anesthesia is an important consideration when circulating blood elements in mice must be measured.

New strategies for the prevention of radiation injury: possible implications for countering radiation hazards of long-term space travel.

New strategies for the prevention of radiation injuries are currently being explored with the ultimate aim of developing globally radioprotective, nontoxic pharmacologics. The prophylactic treatments under review encompass such diverse pharmacologic classes as novel immunomodulators, nutritional antioxidants, and cytokines. An immunomodulator that shows promise is 5-androstenediol (AED), a well-tolerated, long-acting androstene steroid with broad-spectrum radioprotective attributes that include not only protection against acute tissue injury, but also reduced susceptibility to infectious agents, as well as reduced rates of neoplastic transformation. Other potentially useful radioprotectants currently under study include the nutraceutical vitamin E and analogs, a chemically-engineered cytokine, interleukin-1beta, and a sustained-release formulation of an aminothiol, amifostine. Results suggest that a new paradigm is evolving for the prophylaxes of radiation injuries, based on use of newly identified, nontoxic, broad-spectrum prophylactic agents whose protective action may be leveraged by subsequent postexposure use of cytokines with organ-specific reparative functions.

High-dose antibiotic therapy is superior to a 3-drug combination of prostanoids and lipid A derivative in protecting irradiated canines.

There is an urgent need to develop non-toxic radioprotectors. We tested the efficacy of a 3-drug combination (3-DC) of iloprost, misoprostol, and 3D-MPL (3-deacylated monophosphoryl lipid A) and the effects of postirradiation clinical support with high doses of antibiotics and blood transfusion. Canines were given 3-DC or the vehicle and exposed to 3.4 Gy or 4.1 Gy of 60Co radiation. Canines irradiated at 4.1 Gy were also given clinical support, which consisted of blood transfusion and antibiotics (gentamicin, and cefoxitin or cephalexin). Peripheral blood cell profile and 60-day survival were used as indices of protection. At 3.4 Gy, 3-DC- or vehicle-treated canines without postirradiation clinical support survived only for 10 to 12 days. Fifty percent of the canines treated with 3-DC or vehicle and provided postirradiation clinical support survived 4.1-Gy irradiation. Survival of canines treated with vehicle before irradiation significantly correlated with postirradiation antibiotic treatments, but not with blood transfusion. The recovery profile of peripheral blood cells in 4.1 Gy-irradiated canines treated with vehicle and antibiotics was better than drug-treated canines. These results indicate that therapy with high doses of intramuscular aminoglycoside antibiotic (gentamicin) and an oral cephalosporin (cephalexin) enhanced survival of irradiated canines. Although blood transfusion correlated with survival of 3-DC treated canines, there were no additional survivors with 3-DC treated canines than the controls.

Radioprotective efficacy and acute toxicity of 5-androstenediol after subcutaneous or oral administration in mice.

We previously showed that one subcutaneous (sc) injection of 5-androstene-3beta,17beta-diol (AED) stimulated the innate immune system in mice and prevented mortality due to hemopoietic suppression after whole-body ionizing irradiation with gamma rays. In the present study, we tested whether there was any significant toxicity in mice that might hinder development of this steroid for human use. There were no indications of toxicity in chemical analyses of serum after sc doses as high as 4000 mg/kg. At this dose, 2 of 54 mice died when given AED alone. When 4800 mg/kg was given orally, no deaths resulted. The only adverse findings attributed to AED administration were 1) a moderate elevation of granulocytes in abdominal organs and fat after sc injections of 320 mg/kg; and 2) occasional wasting of skin over the injection site in female B6D2F1 but not male C3H/HeN mice. Significant weight loss (6%) was observed after sc injections of 320 mg/kg but not 160 or 80 mg/kg. When male C3H/HeN mice were injected sc with AED at doses of 0-200 mg/kg 24 h before whole body gamma-irradiation (9 Gy), a significant improvement in survival was observed at doses as low as 5 mg/kg. Oral administration of AED produced significant survival enhancement at a dose of 1600 mg/kg. We conclude that the radioprotective efficacy of AED is accompanied by low toxicity.