Stability and ultraviolet A photostability of silymarin polyphenols and its consequences for practical use in dermatology
Pavel Kosina, Alena Ryšavá, Jitka Vostálová, Barbora Papoušková, David Biedermann, Jitka Ulrichová, Alena Rajnochová Svobodová
Silymarin (SM), a complex mixture of polyphenols, flavonolignans and flavonoids, isolated from milk thistle seeds (Silybum marianum L. Gaertn., Asteraceae), is widely accepted as a phytomedicine for the treatment of numerous diseases of various etiology. Thanks to its manifold biological properties, i.e. anti-oxidant, anti-inflammatory, immunomodulatory, and regenerative attributes, SM is of interest for dermatological applications. The stability of SM components for dermal use in aqueous environments of varying pH, as well as their photostability after UVA irradiation, were studied here using UV/VIS spectroscopy and HPLC-MS. Isosilybin, silychristin and silydianin were found to be stable and UVA photostable. Silybin and mainly taxifolin were unstable in aqueous solutions but both were UVA photostable. Quercetin and 2,3-dehydrosilybin were unstable and dosedependent UVA-induced degradation was also found. The main UVA-induced degradation product of 2,3-dehydrosilybin (C24H19O10, m/z 467.0978) in aqueous solutions was detected by UHPLC-HRMS analysis and MSE spectra. The main UVA photodegradation product of 2,3-dehydrosilybin has a similar structural motif to the minor quercetin photoproduct (C14H9O7, m/z 289.0348), newly identified in this study.
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