Evaluation of photostability and phototoxicity of esterified derivatives of ubiquinol-10 and their application as prodrugs of reduced coenzyme Q10 for topical administration.

Ubiquinol-10 (UqH-10), the fully reduced form of ubiquinone-10 (Uq-10, coenzyme Q10 ), is an antioxidant and is involved in energy production. However, physicochemical disadvantages, such as rapid oxidation, water-insolubility, photoinstability, and phototoxicity, limit its application. We previously reported that UqH-10 1,4-bis-N,N-dimethylglycinate improved the oxidation susceptibility and poor bioavailability of UqH-10 in rats. Herein, we evaluated the photochemical properties of UqH-esterified derivatives (N,N-dimethylglycinate, hemi-succinate, ethylsuccinate, and hemi-glutarate). Photostability was examined by irradiation using artificial sunlight and monochromatic light. The concentration of each compound was determined using LC-MS/MS. Phototoxicity was assessed by singlet oxygen and superoxide assays. Delivery of UqH-10 via UqH-esters to the HaCaT human keratinocyte cell line was determined using LC-MS/MS. UqH-esters showed higher photostability to artificial sunlight than Uq-10 and UqH-10. Uq-10 and UqH-10 were rapidly degraded by monochromatic light at 279 nm, whereas UqH-esters were more stable. UVA and/or UVB irradiation generated high levels of singlet oxygen and superoxide in Uq-10, whereas UqH-esters were unreactive. Additionally, UqH-esters effectively delivered UqH-10 to HaCaT cells following efficient uptake in their ester forms and ester bond hydrolysis in the cells. In conclusion, UqH-ester derivatives exhibit higher photostability and lower phototoxicity compared with Uq-10 and UqH-10.