Realgar-derived Arsenic Compounds Induce Anti-proliferation and Apoptosis on Cultured HaCaT Keratinocytes

Our current research project focuses on the development of topical therapies from natural sources for psoriasis, a chronic immune-mediated inflammatory skin disease characterized by abnormal differentiation and hyperproliferation of keratinocytes. Previous studies conducted by our group have shown that the ethanolic extract of Realgar, a common Chinese medicinal substance, possesses potent inhibitory effect on the proliferation of the HaCaT cells, which are immortalized human epidermal keratinocytes. In the present study, three inorganic compounds derived from Realgar namely Arsenic (III) Oxide, Arsenic (V) Oxide and Arsenic Iodide were investigated for their anti-proliferative and apoptogenic effects on cultured HaCaT cells. All three arsenic compounds showed time and dose-dependent antiproliferative activities, with IC₅₀s being 2.4µM, 16.0µM and 6.8µM respectively. Flow cytometric analysis revealed that these inorganic compounds elicited anti-proliferation of HaCaT cells through the induction of apoptosis based on evidence (i) DNA cleavage detected by TUNEL assay; (ii) the appearance of sub G1 peak through the analysis of cell cycle with propidium iodide (PI) staining; (iii) quantitative analysis of apoptosis by concomitant Annexin V-GFP and PI staining; and (iv) the expression of caspase 3 proteins. In a specificity test, all three Realgar-derived inorganic compounds exhibited less cytotoxicity to HS68 than that of HaCaT cells. In conclusion, we have unambiguously demonstrated that the arsenic compounds derived from Realgar exerted potent antiproliferative action on HaCaT cells via the induction of cellular apoptosis. The findings could be used for future development of new topical agents for psoriasis treatment.

Acknowledgement: This project is funded by CUHK Direct Grant (Project Code: 2030363)