Various crystalline forms of realgar exhibit differentiated anti-abscess and anticancer effects based on a PXRD analysis and biological evaluation.

Ethnopharmacological relevance: Realgar is a mineral medicine with a long history that can be used externally or internally. It is often used to treat skin diseases and leukemia in clinical practice. Realgar exhibits a polycrystalline phenomenon, and it remains unknown whether there is a difference in the efficacies of the different realgar crystalline forms.

Purpose: The aim of this study is to investigate the pharmacodynamic differences of the different realgar crystalline forms (α-As₄S₄ and β-As₄S₄) using in vivo and in vitro experiments.

Material and methods: The in realgar crystalline patterns were initially identified using a powder x-ray diffractometer (PXRD). The antimicrobial activities of α-As₄S₄ and β-As₄S₄ were then assessed in vitro to elucidate their effectiveness against bacteria. Transdermal absorption and pharmacokinetic experiments were used to investigate the variances in the bioavailabilities between the in vitro and in vivo conditions. The effects of α-As₄S₄ and β-As₄S₄ for skin abscess healing were studied in mice using a subcutaneous injection of Staphylococcus aureus (S. aureus). HL-60 cells were exposed to a serum that contained different crystalline forms of realgar to evaluate the potential differences in the therapeutic effects of α-As₄S₄ and β-As₄S₄ on leukemia.

Results: Realgar is composed of α-As₄S₄ and β-As₄S₄ crystalline forms. The soluble arsenic content in α-As₄S₄ generally exceeded that of β-As₄S₄, and the antimicrobial activity showed a positive correlation with the soluble arsenic content. α-As₄S₄ demonstrated a higher in vivo and in vitro bioavailability and a faster elimination rate in vivo compared to β-As₄S₄. The pharmacodynamic experimental investigations showed that α-As₄S₄ exhibited a superior healing effect on subcutaneous abscesses. Furthermore, serum pharmacology experiments revealed that α-As₄S₄ induced significantly higher membrane damage and apoptosis in HL-60 cells compared to β-As₄S₄.

Conclusion: The different realgar crystalline forms had distinct pharmacodynamics. α-As₄S₄ demonstrated higher bioavailability in vitro and in vivo and superior effects on skin abscess healing compared to β-As₄S₄. It also possessed anti-leukemia properties. It is the first time to report the differences in the efficacy between two crystalline forms of realgar, which is helpful to improve the knowledge of the real chemical substances for realgar.