Comparison of the DNA-damaging property of photosensitised riboflavin via singlet oxygen (1O2) and superoxide radical O2-. mechanisms.

Riboflavin was found to generate singlet oxygen (1O2) and superoxide anion radicals O2-. on exposure to UV-A (320-400 nm) and UV-B (290-320 nm) light. Studies with deoxyguanosine (dGuo) showed that 1O2 was largely responsible for riboflavin-sensitised photodegradation of the guanine base of DNA and RNA. Azide ions (N-3) and 1,4 diazabicyclo-[2.2.2]-octane (DABCO) produced over 90% inhibition of dGuo photo oxidation, whereas superoxide dismutase did not show any noticeable quenching effect under similar conditions. Photo oxidation of dGuo by riboflavin and UV radiation is of significant importance from the point of view of cell-damaging reactions by activated oxygen species produced by the synergistic action of sunlight and chemical agents. It is now known that activated oxygen species are responsible for skin photosensitisation, tumor promotion and carcinogenic properties.