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Tocols are a family of eight isomers consisting of four tocopherols and four tocotrienols that exist in four isomeric forms: alpha (alpha), beta (beta), gamma (gamma), and delta (delta). Recently, tocols were found to have important and unique biological effects on nutrition and health other than antioxidant properties and are, therefore, now receiving increased attention. We have demonstrated the radioprotective efficacy of various tocol analogs and some of their esters. Three forms of tocols - alpha-tocopherol, alpha-tocopherol succinate, and gamma-tocotrienol - significantly protected mice against lethal gamma irradiation when administered subcutaneously 24 h before irradiation. The radioprotective effects of tocols on survival were associated with peripheral blood cell recovery after radiation induced cytopenia. Hematopoietic cytokines are known to promote the proliferation and differentiation of blood cell progenitors. Therefore, we hypothesized that peripheral blood cell recovery is preceded by hematopoietic cytokine induction. To test this hypothesis and compare the various radioprotective and non-radioprotective analogs, we measured serum cytokines using a sandwich ELISA, Luminex, and cytokine array in mice treated with various tocols (alpha-tocopherol succinate, alpha-tocopherol, delta-tocopherol, gamma- tocopherol, gamma-tocotrienol, and tocopherol acetate). Among the serum cytokines measured, ELISA and Luminex studies indicated that alpha-tocopherol, alpha-tocopherol succinate, and gamma-tocotrienol increased G-CSF levels in mice. Alpha-tocopherol succinate was most effective in stimulating G-CSF. IL-6 was detected by Luminex in sera samples from mice treated with the above three analogs. The results of the cytokine array suggest that other cytokines and chemokines in addition to G-CSF and IL-6 are induced. Since G-CSF, IL-6, and certain chemokines are important hematopoietic factors, these results support our hypothesis that the protection of mice from radiation-induced hematopoietic death is mediated by cytokines and chemokines. These studies may indicate that alpha-tocopherol succinate can be used as an adjunct in cancer chemotherapy, where neutropenia is a serious problem with threatening infectious complications.

Nitric oxide (NO) is involved in producing damage after exposure to radiation and also in the toxicity associated with bacterial endotoxin (lipopolysaccharide, LPS). We have evaluated different radioprotective thiols for their effects on LPS-stimulated NO production in mouse macrophage cells, RAW 264.7. Our results indicate that although thiols inhibited NO production in general, the degree of inhibition depended upon the thiol compound. Long-chain aminothiols like WR-1065 [N-(2-mercaptoethyl)-1,3-diaminopropane] exerted a strong inhibition; but its parent drug, amifostine, which protects mice against radiation lethality, was not as effective as WR-1065. Diethyl dithiocarbamate, which is less effective than amifostine as a radioprotector, strongly inhibited NO production from macrophages. These results indicate that the radioprotective potential of sulfhydryl compounds is not related to its ability to inhibit NO production by macrophages and suggest that some of the thiol radioprotectors may effectively ameliorate the fatal symptoms of hypotensive shock, associated with endotoxin (LPS)-induced NO production.

In attempting to evaluate the possible health consequences of chronic ionizing radiation exposure during extended space travel (e.g., Mars Mission), ground-based experimental studies of the clinical and pathological responses of canines under low daily doses of 60Co gamma irradiation (0.3-26.3 cGy d-1) have been examined. Specific reference was given to responses of the blood forming system. Results suggest that the daily dose rate of 7.5 cGy d-1 represents a threshold below which the hematopoietic system can retain either partial or full trilineal cell-producing capacity (erythropoiesis, myelopoiesis, and megakaryopoiesis) for extended periods of exposure (>1 yr). Trilineal capacity was fully retained for several years of exposure at the lowest dose-rate tested (0.3 cGy d-1) but was completely lost within several hundred days at the highest dose-rate (26.3 cGy d-1). Retention of hematopoietic capacity under chronic exposure has been demonstrated to be mediated by hematopoietic progenitors with acquired radioresistance and repair functions, altered cytogenetics, and cell-cycle characteristics. Radiological, biological, and temporal parameters responsible for these vital acquisitions by hematopoietic progenitors have been partially characterized. These parameters, along with threshold responses, are described and discussed in relation to potential health risks of the space traveler under chronic stress of low-dose irradiation., (Published by Elsevier Science Ltd on behalf of COSPAR.)

The capacity of the hematopoietic system to repair constantly accruing cellular damage under chronic, low daily dose gamma irradiation is essential for the maintenance of a functional hematopoietic system, and, in turn, long term survival. In certain individuals, however, such continuous cycles of damage and repair provide an essential inductive environment for selected types of hematopathologies, e.g., myeloid leukemia (ML). In our laboratory we have been studying temporal and causal relationships between hematopoietic capacity, associated repair functions, and propensities for hematologic disease in canines under variable levels of chronic radiation stress (0.3-26.3 cGy d-1). Results indicate that the maximum exposure rate tolerated by the hematopoietic system is highly individual-specific (three major responding subgroups identified) and is based largely on the degree to which repair capacity, and, in turn, hematopoietic restoration, is augmented under chronic exposure. In low-tolerance individuals (prone to aplastic anemia, subgroup 1), the failure to augment basic repair functions seemingly results in a progressive accumulation of genetic and cellular damage within vital progenitorial marrow compartments (particularly marked within erythroid compartments) that results in loss of reproductive capacity and ultimately in collapse of the hematopoietic system. The high-tolerance individuals (radioaccomodated and either prone- or not prone to ML, subgroup 2 & 3) appear to minimize the accumulating damage effect of daily exposures by extending repair functions, which preserves reproductive integrity and fosters regenerative hematopoietic responses. As the strength of the regenerative response manifests the extent of repair augmentation, the relatively strong response of high- tolerance individuals progressing to patent ML suggests an insufficiency of repair quality rather than repair quantity. The kinetics of these repair-mediated, regenerative hematopoietic responses within the major subgroups are under study and should provide useful insights into the nature of hematopoietic accommodation (or its failure) under greatly extended periods of chronic, low-daily-dose ionizing radiation exposure.

Trypanosoma brucei gambiense has been observed growing in extravascular sites throughout a solid Ehrlich ascites tumor (EAT) in Microtus montanus. These trypanosomes appear in clusters in the tumor. The possible importance of this observation to the host-parasite relationship is discussed.

Aplastic anemia and myelogenous leukemia are prominent pathologic effects in beagles exposed to continuous, daily, low-dose gamma irradiation. In the present work, granulocyte reserves and related mobilization functions have been sequentially assessed by the endotoxin stress assay during the preclinical and clinical phases of these hemopoietic disorders. Characteristic patterns of granulocyte reserve mobilization are described that reflect given stages of pathologic progression. For radiation-induced leukemia, a five stage pattern has been proposed. In contrast, a simple pattern of progressive, time-dependent contraction of granulocyte reserves and mobilization capacity was noted in the development of terminal aplastic anemia. Early preclinical phases of radiation-induced leukemia appear to involve an extensive depletion of the granulocyte reserves ((phase I) during the first approximately 200 days of exposure followed by a partial renewal of the reserves and associated mobilization functions approximately 200 and 400 days (phase II). Sustained, subnormal granulocyte mobilizations (phase III) following endotoxin stress typify the responses of dogs during the intermediate phase, whereas late preclinical, preleukemic stages (phase IV) are characterized by a further expansion of the reserves and in the mobilization capacities, particularly of the less mature granulocytes. Such late alterations in the pattern of granulocyte mobilization, together with other noted cellular aberrancies in the peripheral blood and marrow, appear to indicate leukemia (phase V) onset.