In vitro evaluation of the enzyme inhibition and membrane permeation properties of benzophenones extracted from honeybush

Abstract

Tea prepared from the honeybush (Cyclopia spp.) plant has become a popular beverage and has been shown to possess medicinal properties. Honeybush plants contain phytochemicals that can contribute to the prevention of certain diseases. One mechanism through which glucose and fat uptake can be controlled by honeybush tea is enzyme inhibition in the gastrointestinal tract. The aim of this study was to determine the enzyme inhibition (i.e. lipase and α-glucosidase) effect of crude honeybush extracts, benzophenone rich fractions and xanthone rich fractions from Cyclopia genistoides. The in vitro permeation of marker molecules (i.e. benzophenone and xanthone molecules) after application of the crude extracts and fractions across excised intestinal epithelial tissues was also investigated. In addition, a non-effervescent, floating gastro-retentive drug delivery system containing honeybush extract was developed and evaluated. The lipase and α-glucosidase inhibition activity of the crude extracts and isolated rich fractions was determined through various fluorometric methods. The transport experiments were conducted across excised pig intestinal tissues in Sweetana Grass diffusion chambers. Gastro-retentive tablets were compressed from beads consisting of low-density polymers (i.e. polypropylene and polystyrene divinylbenzene), which were prepared by means of extrusion spheronisation. The tablets were evaluated in terms of buoyancy, disintegration, friability, hardness and dissolution. Samples obtained from the transport and dissolution experiments were analysed by means of ultra-high performance liquid chromatography (UHPLC). The crude extract ARC188 has presented with better inhibition against the rat α-glucosidase and pig lipase enzymes (IC50 = 150 μg/ml and IC50 = 198 μg/ml, respectively) than the crude extract ARC189 (IC50 = 186 μg/ml and IC50 = 730 μg/ml, respectively). In addition, the crude extracts and fractions presented with better inhibitory activity against the α-glucosidase than against the lipase. Relatively low transport in the apical-to-basolateral (A-B) direction was obtained for the honeybush marker molecules across excised pig intestinal tissues from both the crude extracts (ARC188 Papp: 3-β-D-glucopyranosyl-4-β-D-glucopyranosyloxyiriflophenone (IDG) = 4.95x10-7 cm/s; 3-β-D-glucopyranosyliriflophenone (I3G) = 2.38x10-7 cm/s; mangiferin = 2.09x10-7 cm/s and isomangiferin = 3.49x10-7 cm/s; ARC189 Papp: IDG = 1.00x10-7 cm/s; I3G = 3.18x10-7 cm/s; mangiferin = 3.92x10-7 cm/s and isomangiferin = 5.40x10-7 cm/s), but efflux transport occurred in almost all the groups showing higher Papp values for the basolateral-to-apical (B-A) direction (ARC188 Papp: IDG = 6.74x10-7 cm/s; I3G = 4.52x10-7 cm/s; mangiferin = 3.00x10-7 cm/s and isomangiferin = 4.55x10-7 cm/s; ARC189 Papp: IDG = 1.10x10-7 cm/s; I3G = 1.22x10-7 cm/s; mangiferin = 3.90x10-7 cm/s and isomangiferin = 6.44x10-7 cm/s). A gastro-retentive dosage form was successfully produced that showed acceptable buoyancy and release of marker molecules. The relatively low intestinal epithelial permeation of phytochemicals from honeybush is beneficial for local effects in the gastrointestinal tract and may prevent downstream side effects, while the moderate enzyme inhibition combined with a gastro-retentive delivery system has potential in preventing and alleviating diseases such as diabetes mellitus type 2 and obesity