Protection against radiation-induced degradation of DNA bases by polyamines

Polyamines have been reported to protect DNA against the formation of radia tion-induced strand breaks and crosslinks to proteins. The present study wa s aimed at investigating the protective effect of spermine, spermidine and putrescine against the degradation of DNA bases upon exposure to gamma rays in aerated aqueous solution. The yield of 8-oxo-7,8-dihydroguanine and 5-h ydroxycytosine was found to decrease for concentrations of spermine and spe rmidine greater than 0.1 mM, A protection factor of 10 was observed for a c oncentration of 1 mM of the latter two polyamines. Putrescine afforded a lo wer protection, In addition, the formation yield of a series of radiation-i nduced degradation products of the purine and pyrimidine bases was determin ed within DNA in the presence or absence of spermine. The protection factor was within the same range for all the lesions measured. The latter observa tion ruled out the possibility of degradation of DNA by radiation-induced p olyamine peroxyl radicals. This was confirmed by studies involving radiolys is of DMSO and decomposition of 2,2'-azobis(2-methyl-propionamidine) as sou rces of alkylperoxyl radicals. Therefore, it is likely that the polyamine-m ediated protection against the radiation-induced degradation of DNA bases i s due to the compaction of the DNA structure and the reduction in the acces sibility of DNA to (OH)-O-. rather than by scavenging (OH)-O-. in the bulk solution or in the vicinity of the DNA, (C) 2000 by Radiation Research Soci ety.