Evaluation of excipients for enhanced intestinal absorption of Rooibos flavonoids
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Date
2017
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University of Zululand
Abstract
Aspalathin, a dihydrochalcone C-glucoside, and a major flavonoid unique to Rooibos, has been shown to ameliorate insulin resistance, improve glucose uptake in vitro and improve glycaemia in animal models. However, the poor bioavailability of aspalathin limits its potential as a nutraceutical. This study investigated the intestinal absorption of aspalathin, its flavone derivatives, orientin and isoorientin, and nothofagin, its 3-deoxy-derivative, from different green Rooibos extracts in an in vitro intestinal epithelial model, the Caco-2 cell model. Addition of excipients and a nanosome preparation of green Rooibos extract to improve absorption of these flavonoid C-glucosides was also investigated. Methods : Seven green Rooibos extracts, prepared using different solvents (60% ethanol, 80% ethanol and an aqueous extracts), were assessed for the intestinal absorption of their major flavonoids, i.e. aspalathin and its flavone derivatives, orientin and isoorientin, as well as nothofagin, the 3-deoxy-derivative of aspalathin. For testing, two samples per extract type were selected from a large set, based on their bioactivity and chemical dissimilarity. These samples were prepared from different batches of plant material. Caco-2 cells were used as an in vitro intestinal epithelial model to assess absorption of the compounds. Intestinal permeability of the compounds was quantified by analysis of the apical and basolateral samples by HPLC-DAD. The relative transport rate (Papp values) was calculated from the detected concentrations of the compounds crossing the Caco-2 monolayer from the apical to the basolateral compartment. The effect of different extract types, addition of excipients (β-cyclodextrin and inulin) and encapsulation of green Rooibos extract in a nanosome formulation on the absorption of the flavonoids was also explored. Results: At the highest soluble and non-toxic concentration of 1 mg/mL, the transport of aspalathin, nothofagin, orientin and isoorientin across the Caco-2 cell monolayer was confirmed, as these compounds were detected in the basolateral compartment by HPLC-DAD analysis. Standardization of the different extracts (n = 7) to their aspalathin equivalent concentration of 150 μM demonstrated that the transport rate of aspalathin (±1.72 x 10-06 cm/s) was not markedly altered by extract composition as determined by the extraction solvent and plant material. The rate transport was not increased by the addition of β-cyclodextrin (6.99 x 10-07 cm/s) and inulin (1.21977 x 10-06 cm/s), nor by using a nanosome (3.020 X 10-07 cm/s), implying that the strategies used in this study did not enhance intestinal absorption of aspalathin. Conclusion: This study has provided novel information about the intestinal absorption of aspalathin which was not significantly altered by extract composition as determined by extract type and plant material variation. Neither the addition of excipients nor nanosome formulation of the extract could enhance the absorption of aspalathin.
Description
A thesis submitted to the Faculty of Science and Agriculture in partial fulfillment of the Degree of Master of Science in the Department of Biochemistry and Microbiology at the University of Zululand, 2017
Keywords
rooibos flavonoid --aspalatrhin --insulin --intestines