On the Mechanism of Radioprotection by Cysteamine

SummaryThe i.p. administration of 150 mg/kg cysteamine leads to a transient inhibition of 3H-thymidine incorporation into DNA of liver cells in white mice. This functional suspension of DNA-synthesis is probably responsible for cysteamine-induced radioprotective effects, i.e. the acceleration of DNA restoration and the prevention of loss in liver-weight and in the total liver content of DNA, RNA and protein four and eight days after a whole-body γ-irradiation with 500 rads. Similar effects are shown after the i.p. administration of 200 mg/kg dibutyryl cyclic 3′,5′-AMP. Furthermore, cysteamine itself initiates an elevation of endogenous cyclic 3′,5′-AMP in the liver cells. So it is assumed that cysteamine-induced radioprotective effects are mediated by cyclic 3′,5′-AMP as intracellular second messenger. It is suggested that cysteamine administration leads to the formation of cyclic 3′,5′-AMP, which might induce a transient functional suspension of DNA-synthesis. In that stage the DNA should be more resistant to ionizing radiation.