Effects of radical scavengers for reactive oxygen species on vitamin K-induced phototoxicity under UVA irradiation.

Vitamin K possesses efficacy as a topical dermatological agent. However, vitamin K is phototoxic and susceptible to photodegradation. Herein, we investigated the mechanisms underlying the phototoxicity of phylloquinone (PK, vitamin K1) and menaquinone-4 (MK-4, vitamin K2) under ultraviolet A (UVA) irradiation using various reactive oxygen species (ROS) scavengers. This resulted in the production of superoxide anion radicals via type I and singlet oxygen via type II photodynamic reactions, which were quenched by the ROS scavengers: superoxide dismutase and sodium azide (NaN3). In HaCaT cells, MK-4 and PK induced the production of intracellular ROS, particularly hydrogen peroxide, in response to UVA irradiation. Furthermore, the addition of catalase successfully decreased maximum ROS levels by approximately 30%. NaN3 and catalase decreased the maximum reduction in cell viability induced by UVA-irradiated PK and MK-4 in cell viability by approximately 2-7-fold. Additionally, ROS scavengers had no effect on the photodegradation of PK or MK-4 at 373 nm. Therefore, the phototoxicities of PK and MK-4 were attributed to the generation of singlet oxygen and hydrogen peroxide, underscoring the importance of photoshielding in circumventing phototoxicity.