Oxidative stress-mediated DNA fragmentation involved in STING-dependent apoptosis in human keratinocytes by 5-amino-2-methylphenol under ambient UVB exposure

Permanent hair dyes are widely used cosmetic products, but they can pose health risks due to their potential to cause DNA damage, inflammation, and allergic reactions. 5-Amino-2-methylphenol (5AMP), a widely used coupler with documented skin sensitization, absorbs UVB, but its photochemical behaviour is insufficiently characterized and remains unassessed in regulatory phototoxicity reports. Preliminary data showed that 5AMP undergoes UVB-induced photodegradation, forming a new photoproduct confirmed by LC-MS/MS. Still, its potential to induce phototoxicity upon simultaneous skin contact and UV exposure remained unknown. We therefore investigated its phototoxicity and underlying mechanisms. In this study, we examined the phototoxic potential of 5AMP at two concentrations (5 and 10 µg/ml) in human keratinocytes under environmentally relevant UVB dose (0.018-2.16 J/cm²). Photosensitized 5AMP generated superoxide anion radicals via a type-I photodynamic mechanism, resulting in increased intracellular and mitochondrial ROS. Oxidative stress induced by photosensitized 5AMP disrupted mitochondrial membrane potential and induced DNA damage, culminating in Apoptosis. Pretreatment with NAC/SOD mitigated photosensitized 5AMP-induced Apoptosis. Further investigation into the molecular mechanisms revealed that the upregulation of cGAS, STING, and downstream gene expression triggered IFNβ production. Treatment with H151, an inhibitor of STING, significantly reduces IFNβ expression and cell death, confirming its key role in the phototoxicity mechanism. Therefore, we conclude that oxidative stress and subsequent cGAS-STING activation play a key role in photosensitized 5AMP-induced Apoptosis. These insights into the mechanisms uncovered a critical gap in the safety assessment of photolabile hair dye ingredients under environmental UVB/sunlight exposure and underscore the need for safer alternatives.

DNA damage; Keratinocytes; Oxidative stress; Permanent hair dye; Phototoxicity.