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Studies of irradiated bacterial spores in aqueous suspension indicate that the sensitization of spores by oxygen can depend on three chemical processes. One of these processes involves reactions of hydroxyl radicals; the other two apparently do not.

Friend erythroleukaemia cells (FELC) in vitro were used to examine the effects of ionizing radiation on differentiation and proliferation of mammalian cells. Results suggest that X-rays can affect differentiation in two different ways. First, X-rays inactivate the ability of these cells to respond to an external trigger of differentiation, e.g., dimethyl sulphoxide. Second, X-rays themselves trigger a partial differentiation response, in the absence of any other external trigger. The radiation-induced lesions leading to these two end-points are not repaired in split-dose experiments, unlike those lesions which lead to loss of cell proliferative capacity. The profile of soluble FELC proteins, as analysed by isoelectric focusing, was also affected by irradiation. These effects of ionizing radiation on the expression of genetic information in mammalian cells have important implications for radiobiology, particularly at low doses where acute lethal effects are minimal.

p-Nitroacetophenone (PNAP) sensitizes Bacillus megaterium spores under anoxic conditions to the lethal effects of 50 kVp X-rays. Concentrations between approximately 5 X 10(-4) M and 3-8 X 10(-3) M produce the maximum effect, an increase of about 30 per cent over the anoxic response when the spores are irradiated in water. Compounds that scavenge -OH decrease, but cannot completely eliminate, this maximum amount of sensitization. These results indicate that PNAP acts to increase spores' radiation sensitivity through two separable types of chemical reactions: one which involves -OH and one which does not. Possible mechanisms responsible for these two components of damage are discussed. In these experiments 1/15 M phosphate buffer acts in several unexpected ways. This concentration itself increased the anoxic spore response by about 9 per cent (relative to the anoxic response in water). In addition, although the maximum amounts of sensitization were the same, the amounts of sensitization from lower PNAP concentrations differed when the suspending fluid was buffer instead of water. An interaction was also seen during the PNAP-t-butanol experiments; again, the responses at low PNAP concentrations were different in buffer and in water. No mechanisms for these actions of this buffer were suggested, although somewhat similar effects may occur with other organisms. Clearly, such effects must be recognized and evaluated before quantitative analyses of the actions of sensitivity-modifying agents can be completed.

Oxygen (O2) sensitizes bacterial cells in at least two mechanistically different ways, depending on the specific O2 concentration present during irradiation. Based on previous work from this laboratory, it has been proposed that nitrous oxide (N2O) and low concentrations of O2 share a common mechanism for damage. This mechanism, involving the production of superoxide anion radicals (O2-), is different from that which causes damage at high O2 concentrations. Others, however, have presented evidence that N2O and O2 (usually tested only at high concentrations) act in different ways to sensitize bacterial cells. We have now measured the radiation sensitivity in mixtures of N2O and O2 to observe additivity patterns and to determine if these two agents have any common processes for sensitization. We found that some low O2 concentrations do not increase the response in N2O, although they can have significant sensitizing effects in N2. This lack of additivity is taken as evidence for a common mechanism of damage from N2O and low concentrations of O2. In contrast, damage from high concentrations of O2 is additive to the damage from N2O. The greatest sensitivity, observed with a gas mixture of about 15 per cent O2/85 per cent N2O, is equivalent to the response in 100 per cent N2 plus the maximum amount of damage O2 can cause plus the maximum amount of damage N2O can cause. This additivity is taken as evidence that N2O and high concentrations of O2 sensitize in different ways. Thus, O2 is known to sensitize these bacteria in at least two different ways; one of these is apparently also the way N2O sensitizes.

Six cases of toxic myopathy and/or neuropathy with chloroquine and/or hydroxychloroquine therapy are described. Two patients had unique clinical and pathologic evidence of cardiomyopathy secondary to chloroquine or hydroxychloroquine therapy. One patient had polyneuropathy secondary to chloroquine toxicity. This may be the first documentation of several features of chloroquine/hydroxychloroquine toxicity: morphologic changes in human peripheral nerve in chloroquine toxicity; chloroquine/hydroxychloroquine cardiomyopathy diagnosed by endomyocardial biopsy; and hydroxychloroquine myotoxicity. Chloroquine is a neuromyotoxin that affects nerves and cardiac and skeletal muscles. Discontinuation of chloroquine and hydroxychloroquine resulted in marked improvement in most cases. The reversibility of the symptoms emphasizes the importance of recognizing potential signs of nerve, muscle, and cardiac toxicity in patients being treated with chloroquine or hydroxychloroquine.

Previous work with procaryotic cells has identified one kind of lethal damage from ionizing radiation which occurs only within a specific range of low O2 concentrations, about 10(-6) to 10(-4) M. Within this range, protection can occur in three ways: through the enzymatic decomposition of hydrogen peroxide (H2O2) by added catalase, through the enzymatic degradation of superoxide anion radicals (.O2-) by added superoxide dismutase (SOD), and through scavenging hydroxyl radicals (.OH) by various additives. These results indicate that three radiolytic products, H2O2, .OH, and .O2- (and/or the conjugate acid, the perhydroxyl radical, .HO2) are involved in this single kind of radiation-induced damage. Although the radiolytic productions of H2O2 and .O2- are strongly enhanced in higher O2 concentrations, neither enzyme protects when these air-equilibrated bacteria are irradiated. These experiments address this apparent contradiction and focus on the specific issue of why the addition of SOD protects at low but not at high O2 concentrations. We propose that, at a given O2 concentration, .O2- (and/or .HO2) may either react (with some cellular component?) to cause damage or react (with itself) to form hydrogen peroxide (H2O2). The specific O2 concentration during irradiation would determine the relative rates of these competing reactions and therefore the O2 concentration itself would establish whether or not we will observe damage from .O2-.

Although there are ambiguities about these results and their interpretations, this unambiguous experimental observation was made: the two kinds of experiments designed to measure deoxygenation times did not give the same answer, for a given N2 flushing rate, unless t-butanol was present. The addition of t-butanol caused large changes in the positions of the survival curve breakpoints, but only small changes in the 'times to anoxia' in the pre-irradiation glushing experiments. Although careful additional work is needed, these initial results suggest that in the spore, the survival curve breakpoint probably does not represent the dose at which anoxia is reached unless t-butanol is present.

E. coli B/r have been used to study radiation sensitization by nitrous oxide (N2O). Cells suspended in Sörensen's phosphate buffer show a large amount of sensitization by N2O (relative to the response in 100% N2). Cells in McIlvaine's phosphate-citric acid buffer, however, show no sensitization by N2O. Sensitization in Sörensen's buffer can be prevented by hydroxyl radical (.OH) removal or by catalase. Chemical assays for the amounts of H2O2 formed under various conditions provide the basis for the conclusion that the high concentration of the citrate ion in McIlvaine's buffer does not allow the build-up of H2O2. Sensitization by N2O requires that both H2O2 and OH radicals be present.

Spores of Bacillus megaterium were irradiated in suspension with 50 kVp X-rays under three reference conditions: in anoxia (i.e., 100 per cent N2); in anoxia with 2mM p-nitroacetophenone (PNAP), a concentration that shows the maximum amount of sensitization by this agent; and in air. The responses were then measured when different concentrations of an hydroxyl radical scavenger were also present. Allyl alcohol, t-amyl alcohol, t-butanol, ethanol, glycerol, the formate ion, and methanol were the -OH scavengers that were used. A comparison of the effects these additives have on the three reference responses provides indirect, comparative information on the sensitizing processes of PNAP and O2. Neither t-amyl alcohol nor t-butanol affects the response in air or N2 alone. Both these additives, however, can reduce the sensitization from PNAP slightly. The other additives have significant protective effects under the three conditions. In general, the additives have similar effects in air and in 100 per cent N2 but much greater protective effects in PNAP. Although the sensitizing mechanisms are not identified by these experiments, the effects of O2 and PNAP, as judged by the desensitizing actions of these additives, appear quite different.

Replicate plasma samples from wild Microtus pennsylvanicus were typed by gradient polyacrylamide gel electrophoresis for the transferrin and leucine aminopeptidase polymorphisms. Phenotypes remained the same through major seasonal changes in reproductive activity and environmental conditions. Possible explanations for the anomalous phenotypic variation seen in Microtus ochrogaster [McGovern M., and Tracy, C. R. (1981). Oecologia 51:276] are discussed.

Oxygen is a potent sensitizer of cells exposed to ionizing radiation, and, although the exact chemical mechanisms are not fully understood, some evidence suggests that this sensitization may involve the formation of superoxide anion radicals (.O-2) [F. Lavelle, A. M. Michelson, and L. Dimitrijevic, Biochem. Biophys. Res. Commun. 55, 350-357 (1973); A. Petkau and W. S. Chelack, Int. J. Radiat. Biol. 26, 421-426 (1974); L. W. Oberley, A. L. Lindgren, S. A. Baker, and R. H. Stevens, Radiat. Res. 68, 320-328 (1976)] To test this hypothesis, we compared the sensitivity of Chinese hamster V79 cells irradiated in O2/N2 and O2/N2O gas mixtures with and without the addition of other radical scavenging agents. In these tests, although oxygen was present, be blocked the radiation-induced reactions of O2 which produce .O-2. We found that the total amount of biological damage depends simply on the concentration of O2 that is present; the overall sensitivity is not reduced when .O-2 cannot be formed. Thus radiation sensitization by O2--at least of this cell line--does not require the formation of superoxide anion radicals.

The anoxic sensitization of bacterial spores by added H2O2 has been studied. Two mechanistic pathways for damage from H2O2 were found; one of these requires the presence of OH radicals. For this kind of damage, the relationship between H2O2 and OH appears to be that they are reactants. O-2 (and/or HO2), the product of such a reaction, is likely the agent which actually causes damage. These results with reagent H2O2 are compared with results of experiments in which H2O2 and OH are present as radiolytic products.