Development of an albuminous reactive oxygen species assay for photosafety evaluation under experimental biomimetic conditions.

The generation of reactive oxygen species (ROS) from an ultraviolet (UV)-exposed chemical can be an experimental indicator of phototoxic potential. The aim of the present study was to develop a new ROS assay using serum albumin to provide photosafety assessment under experimental biomimetic conditions. To assess assay robustness, a validation study on an albuminous ROS (aROS) assay was conducted with a focus on intra- and inter-day precisions and Z'-factor reflecting both the assay signal-to-noise ratio and variation associated with signal measurements. In the aROS assay on quinine HCl (200 μM), a typical phototoxic drug, both intra- and inter-day precisions (coefficient of variation; CV) were found to be below 4%, and the Z'-factors for singlet oxygen and superoxide suggested a large separation band between samples and blank signals. To evaluate the prediction capacity, the aROS and ROS assays were applied to 21 phototoxins and 10 non-phototoxic chemicals. Upon aROS assay on these model chemicals, the individual specificity was 100%, and the positive and negative predictivities were found to be 100% and 81.8%, respectively. The aROS assay can be employed for poorly soluble chemicals for which the ROS assay is unavailable. Comparing the ROS assay data, there seemed to be a photochemical transition of some chemicals in albuminous solution. A molecular interaction between albumin and chemical was also assessed by UV and fluorescent spectroscopic analyses, and the results suggested the limited relationship between the albumin-chemical interaction and the photochemical change. The aROS assay may allow photosafety assessment of new drug entities with a wide range of applicability partly under experimental biomimetic conditions.