Comparison of the physicochemical characteristics and flavonoid release profiles of Sutherlandia frutescens phytosomes versus liposomes
Sutherlandia frutescens is a traditional plant medicine widely used in South Africa. Traditionally, the leaves of S. frutescens are mainly used as a tea, but these traditional dosage forms have several disadvantages, including that they are not particularly convenient to prepare and store, encourage dosage inaccuracy and are highly susceptible to microbial contamination. To solve these problems, dried aqueous extract forms, e.g. freeze dried aqueous extract (FDAE) of S. frutescens were prepared, but they, in turn, may still suffer from instability and contain mainly hydrophilic phytoconstituents that are poorly absorbed and delivered for in vivo activity. Modified forms of the FDAE, i.e. the active phytopharmaceutical ingredient (API), may be a better solution. Therefore this study sought to prepare liposomes and phytosomes of the freeze dried aqueous extract of Sutherlandia frutescens, as a means of increasing the total the surface area of the API, thus improving its release and dissolution in gastrointestinal fluids. Liposomes and phytosomes of the FDAE of Sutherlandia frutescens obtained were prepared using a thin film hydration method at ratios of lecithin: S. frutescens (3:1) and phosphatidylcholine: S. frutescens (2:1) respectively. The physical characteristics (i.e. particle size, size distribution, zeta potential, and morphology), of flavonoid glycosides (i.e. sutherlandins A to D; API) as well as content and release profiles of each dosage form (i.e. FDAE liposome or phytosomes) at pH 1.2 and pH 6.8 was determined. A validated HPLC assay was used to determine and compare the flavonoid glycoside content and release profiles of the liposomes and phytosomes. Both liposomes and phytosomes were successfully prepared, in moderate yields (± 30 %, and ± 50 %, respectively), using the thin film hydration method. The liposomes had a significantly smaller size, lower size distribution, higher zeta potential and better stability than the phytosomes (p < 0.05). The phytosomes, however, had significantly higher flavonoid glycoside encapsulation efficiency than the liposomes (±50 % vs ±26 %; p < 0.01). In addition, the release at 120 minutes, of flavonoid glycosides from the liposomes (63%, 58%, 76% and 46% % at pH 1.2, and 78%, 76%, 87% and 89 % at pH 6.8 for sutherlandins A, B, C and D, respectively) was significantly higher and faster than that of the phytosomes (52%, 41%, 51% and 39 % at pH 1.2, and 31% 31%, 33%and 45% % at pH 6.8, for sutherlandins A, B, C and D, respectively). The differences in release were likely due to differences in particle size and size distribution of the two modified API forms. Overall, liposomes and phytosomes can be considered promising vehicles for delayed delivery of herbal crude extracts. Based on its characteristics (i.e. narrower size distribution, and better stability), the liposomes were preferred compared to the phytosomes offering a better kinetic release profile. The phytosomes had higher encapsulation than the liposomes that may be due to complex formation between the API and the lipid.