Immunoassay of dithymidine cyclobutane dimers in nanogram quantities of DNA

Immunological assays for DNA photoproducts, which have been in use for a number of years, provide a rapid means for quantifying photodamage in DNA. Radioimmunoassays (RIA) are capable of measuring photoproducts in microgram quantities (1-10 micrograms) of DNA extracted from biological samples, e.g., animal skin or cultured cells. We have refined an indirect enzyme-linked immunosorbent assay (ELISA) for the analysis of cyclobutadithymidine (T-T) photoproducts in nanogram quantities (3-100 ng) of DNA. T-T photoproducts were detectable in 30 ng DNA irradiated with a minimum of 10 J/m2 of 254 nm ultraviolet light (UV). The efficiency of T-T induction in DNA was approximately 4000-fold lower per unit dose using a solar-simulating UV radiation source (290-400 nm) than with 254 nm radiation. The assay was used to measure T-T photoproducts induced by solar-simulated UV radiation in hamster skin and human skin and should be useful for the routine analysis of photoproducts in small amounts of DNA (500-1000 ng) available from human skin biopsies.