Induction of Single-Strand DNA Breaks in Human Cells by H 2 O 2 Formed in Near-uv (Black Light)-Irradiated Medium

Abstract

When Dulbecco's modified Eagle's medium (depleted of phenol red) was irradiated for up to 3 h by 4 to 5 W/m/sup 2/ black light, hydrogen peroxide (H/sub 2/O/sub 2/) was produced. Generation of H/sub 2/O/sub 2/ resulted from riboflavin-sensitized photooxidation of tryptophan and tyrosine. Reagent H/sub 2/O/sub 2/, or hydrogen peroxide generated in black light-exposed aqueous solutions containing riboflavin and tryptophan, induced 2 x 10/sup 4/ single-strand breaks per 10/sup 16/ daltons of DNA in intact, physiologically viable human D98/AH/sub 2/ cells. Concomitant with the single-strand breaks in the cells was loss of cellular reproductive viability. Two classes of photoproducts were identified: H/sub 2/O/sub 2/ and non-H/sub 2/O/sub 2/. The H/sub 2/O/sub 2/ component of the photoproducts was responsible for all the single-strand break induction but for only partial loss of reproductive viability. The non-H/sub 2/O/sub 2/ photoproducts, accountable for the remainder of cell lethality, caused no single-strand breaks.