Radiation carcinogenesis from a membrane perspective.

Abstract

Radiation damage in phospholipid membranes involves free radical chain reactions which propagate on their own. These reactions oxidize the constituent fatty acids (LH) to alkyl radicals (L) which upon oxygenation, for lipid hydroperoxides (LOOH), some of which absorb light at 232 nm. The response (R) of these membranes to irradiation from tritium (3H) in tritiated water increases with dose (D) in accordance with R = aDm, where m = 1.44 +/- 0.30 in the absence of superoxide dismutase and 0.80 +/- 0.14 in its presence. The parameter "a" is expressible in terms of dose rate (delta D/delta t) by a = c (delta D/delta t)-n, where n = 1.18 +/- 0.05 in the absence of superoxide dismutase and 0.82 +/- 0.02 in its presence. Thus, R = cDm(delta D/delta t)-n where the values of m, n depend on the presence or absence of the free radical scavenger, superoxide dismutase. From this composite relationship, the response per annum for 100-250 millirem/y is calculable and found to differ qualitatively, that is, in the absence of superoxide dismutase the response increases whereas in the enzyme's presence it decreases. The latter trend is reminiscent of the correlation between radiation dose rate and the per annum malignant rate in humans. This coincidence is interesting in that LOOH are linked in the literature to several forms of carcinogenesis.