Photosensitized irreversible binding of estrone to protein via a hydroperoxide intermediate: An explanation of (photo-)allergic side-effects of estrogens

After irradiation (γ>425 nm) for 15 min of a solution of [4- 14C]-estrone, albumin and the photosensitizer hematoporphyrin in phosphate buffer, more than 30% of the radioactivity could not be extracted. When the protein was added after irradiation, irreversible binding also occurred. Sephadex gel filtration showed that the radiolabel was bound to albumin as well as to the photosensitizer. A 10β-hydroperoxide is the reactive intermediate in this binding. Inasmuch as phenolic steroids coupled to proteins have been used for the induction of estrogenic-specific antibodies, the irreversible binding observed between estrone and albumin by photosensitization might be an explanation for (photo)allergic disorders associated with estrogens.