Photosensitization and phototoxicity mechanism of diclofenac sodium (NSAID) under ambient UVR exposure.

Diclofenac sodium (DS) is used for pain, inflammation and musculoskeletal disorders. Despite its absorption of UV radiation, the phototoxic potential and molecular mechanisms in keratinocytes under UVA and UVB exposures are largely unexplored. In this study, we have employed a comprehensive array of in-silico, in-chemico, and in-vitro approaches to assess DS's photostability, phototoxic, and photogenotoxic properties under UV irradiation. Our findings indicate that DS undergoes photodegradation, forming 3 photoproducts. Further, docking studies revealed DS's affinity for DNA and Bax, implicating DNA damage and initiation of programmed cell death pathways. MTT and NRU assays demonstrated a concentration-dependent phototoxic response to UVA and UVB exposures. DCFH₂-DA and DHE staining confirmed that DS significantly elevates ROS under UVR. Photogenotoxicity was evidenced by comet assay, while clastogenic activity was confirmed through micronucleus and chromosomal aberration assays. Gene expression analysis showed upregulation of apoptotic marker genes including Bax, Bcl2, Casp9, Apaf1, Casp3, and Cyt C in keratinocytes treated with DS under UV irradiation. Our results showed that DS exhibits both photogenotoxic and photoclastogenic activities, coupled with ROS-induced programmed cell death, elucidating the molecular basis of its phototoxicity. These insights are crucial for understanding the mechanisms behind NSAID-induced phototoxic skin diseases under environmental UVR exposure.