Radioprotective action

The radioprotective action of 3,5-diamino-l,2,4-thiadiazole, its 3-toluene-p-sulfonyl derivative, and the corresponding 5-methyl-amino- and 5-anilino analogs has been determined.218 Administration of the parent compound results in 69% survival in mice after 900 r whole body X-radiation, a result that compares favorably with the effects of such established protectors as AET ([Pg.202]

Adventitious impurities in pharmaceutical and surgical supplies may act as energy transfer acceptors, scavengers, or complexants and make radiation sterilization more difficult owing to radioprotective action. 

Documented effects Fruits are a rich source of polyvitamins. Oil from the fruits is used as an analgesic and to treat bums, frostbite, eczema, persistent wounds, as well as stomach and duodenal ulcers. The oil is used during radiation treatment for esophageal cancer (Tolmachev 1976). A study of the radioprotective action of a preparation of this species resulted in an 82 % survival rate in mice that received the treatment compared to no survival in irradiated control (Goel et al. 2002). Alcoholic extracts of leaves and fruits of sea buckthorn were found to inhibit chromium-induced free radical production, apoptosis, and DNA fragmentation, and restored the anti-oxidant stams to that of control cells. These extracts also were able to arrest the chromium-induced inhibition of lymphocyte proliferation (Geetha et al. 2002). Flavonoids isolated from the plant are reported to have antioxidant, anti-ulcerogenic, and hepato-protective properties (Yue et al. 2004). 

Naslund, M., Ehrenberg, L., and Djalali-Behzad, G., 1976, Antagonism of ascorbate against the radioprotective action of cysteamine, Int. J. Radiat. Biol. 30 95-99. 

Many newer drugs have been described during the period of this report only those for which significant radioprotective action was reported can be mentioned here. 

The radioprotective properties of thiazolidines continue to be a subject of considerable interest (cf. ref. 183 for a brief list of the relevant literature).Activity has been found in simple derivatives such as 2,2-dimethyl-, 2-methy 1-2-ethyl-, and 2-phenyl-thiazolidines. Thiazolidines substituted in their 3-position with 5-halogeno-2-pyridyloxy-pentyl or -hexyl groups possess relatively high radioprotective action when administered orally. Promising activity is also shown by their thio-analogues. ... 

Other Radioprotective Chemicals. The bis-methylthio- and methylthioamino-derivatives of 1-methylquinolinium iodide and l-methylpyridinium-2-dithioacetic acid provide reasonable protection to mice at much lower doses than the aminothiols, which suggests a different mechanism of action (139). One of these compounds, the 2-(methylthio)-2-piperidino derivative of the l-methyl-2-vinyl quinolinium iodide (VQ), interacts with supercoUed plasmic DNA primarily by intercalation. Minor substitutions on the aromatic quinolinium ring system markedly influence this interaction. Like WR-1065, VQ is positively charged at physiological pH, and the DNA-binding affinities of VQ and WR-1065 appear to be similar. 

In regard to anoxia or hypoxia as a major mechanism, most recent evidence has been unfavorable, particularly for the action of amino thiols. For instance, a correlation was observed between radioprotective activity and depressive effect of thymidine uptake in DNA synthesis, whereas anoxia did not Inhibit the uptake No relation was shown between radioprotective activity and ability to Increase oxygen uptake in spleen, kidney, muscle, or red blood cells and the intracellular ox-red state in rats was unaltered even after massive doses of radiation Amino thiols, nitrite, and PAPP did not affect... 

A voluntary ALARA approach has been decided to improve radioprotection in operation, main actions undertaken are ... 

Design of compounds that are selectively active in hypoxia and also the development of nontoxic radioprotectants are active areas of current research. The concepts briefly outlined above can be found in more detail in some relatively recent reviews [15—19]. Many metals and metal complexes have been shown to modify radiation damage and what is of interest here is how these metal-based actions can be understood through, and incorporated into, the general understanding of radiation sensitization and protection. 

The radioprotecting properties of thiols and aminothiols have been known for some time and this is generally attributed to their quenching of radiation-induced radicals such as Oj. Compounds which remove endogenous thiols thus increase radical lifetime and can have sensitizing properties. This mechanism contributes to the action of, for instance, A-ethylmaleimide [90] and any thiol depletion by artificial means should indeed produce enhancement of sensitization [91]. 

PHYSIOLOGICAL ACTIVITY General comments Hallucinogenic activity Haemostatic action Radioprotective activity Control of erythroblastosis foetalis... 

Cystamine and other radioprotective disulphides react with the SH groups of proteins and glutathione from the resulting mixed disulphides, the reduced form (cysteamine) is liberated by enzyme action. 

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