Changes in the anti-inflammatory activity of aurone and chalcone class flavonoids from Cotinus coggygria extracts after complexation with cyclodextrins

Abstract

Aurones and chalcones are less studied flavonoid classes with emerging therapeutical potential. Using the heartwood of European smoke tree (Cotinus coggygria Scop. syn Rhus cotinus L.) which contains aurones (sulfuretin, S) and chalcones (butein, B) [1], the aim of the present research was to obtain cyclodextrin (CDX) derivatives with enhanced water solubility and improved biological activity. Following steps were performed: 1) A flavonoid-enriched extract was prepared and standardized to its content in S, B, fustin, 2,3-dihydroquercetagetin, and quercetin using an established HPLC method [1]; 2) C. coggygria extract, S and B were each complexed through kneading with hydroxypropyl-beta cyclodextrin (HPBCD) and randomely methylated beta-cyclodextrin (RAMEB). A molar ratio of CDX: flavonoid = 2:1 was employed; 3) Formation of CDX complexes was confirmed by DSC, FT-IR and Karl Fisher titration techniques; 4) Anti-inflammatory effects of C. coggygria extract, S, B, and their CDX complexes were assessed in the model of the mouse ear edema (SKH1 male mice). Corneometry was used to measure the hydration level of the stratum corneum, this level being inversely correlated with skin irritation. Results showed that the noncomplexed extract, B, and S reduced inflammation with 50%, 33% and 50%, respectively. They are as well capable to lessen (with 26%, 97% and 30%, respectively) the skin dehydration induced by TPA. Complexation with CDXs enhances the anti-inflammatory effect of B (maximal for HPBCD) and S (maximal for RAMEB), but reduces it in case of the extract. These findings encourage further development of S- and B-CDX derivatives with improved biological effects.