Geranyl Acetate Attenuates Para-phenylenediamine-induced Cytotoxicity, DNA Damage, Apoptosis, and Inflammation in HaCaT Keratinocytes.

Background: As consumer demand for cosmetic products that enhance physical appearance continues to rise, the global oxidative hair dye market is experiencing steady growth. Para-phenylenediamine (PPD), a key ingredient in most oxidative hair dyes, is widely used due to its efficacy and low cost. However, its high chemical reactivity has been consistently linked to adverse effects, including allergic contact dermatitis (ACD), eczema, carcinogenicity, and genotoxicity. Objectives: Given the concerns over the long-term use of conventional therapies such as topical corticosteroids (TCS) and calcineurin inhibitors, this study aimed to identify a plant-derived compound with protective properties in a keratinocyte model of PPD-induced toxicity. Methods: To assess the cytoprotective potential of 14 selected plant metabolites, water-soluble tetrazolium salt-1 (WST-1) and lactate dehydrogenase (LDH) assays were performed. Western blotting and reverse transcription-polymerase chain reaction were used to evaluate the anti-apoptotic, anti-DNA damage, and anti-inflammatory effects of geranyl acetate (GA), the most promising candidate. Results: Among the 14 tested plant metabolites, GA was identified as the most effective compound in mitigating cytotoxicity in HaCaT keratinocytes. Co-treatment with GA significantly attenuated PPD-induced phosphorylation of p53 and MAPK, indicating inhibition of the DNA damage response (DDR) pathway. Further experiments revealed that GA suppressed the upregulation of apoptosis-related proteins [p53 upregulated modulator of apoptosis (PUMA), B-cell lymphoma 2 (BCL-2)-associated X protein (BAX), cytochrome c, and cleaved poly (ADP-ribose) polymerase (PARP)]. Moreover, GA treatment decreased the phosphorylation of signal transducer and activator of transcription 3 (STAT3) and NF-κB p65, thereby downregulating five pro-inflammatory cytokines [interleukin (IL)-1α, IL-1β, IL-6, tumor necrosis factor (TNF)-α, and IL-24] and five chemokines [C-C motif chemokine ligand (CCL) 5/RANTES, CCL20/MIP-3α, CCL26/eotaxin-3, C-X-C motif chemokine ligand (CXCL) 1/GRO-α, and CXCL8/IL-8], confirming its anti-inflammatory efficacy. Conclusions: Collectively, this study suggests GA as a promising plant-derived metabolite with cytoprotective, genoprotective, anti-apoptotic, and anti-inflammatory effects in PPD-stimulated HaCaT cells.