Abstract: D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS), an inhibitor of P-glycoprotein (P-gp) with low toxicity and irritation, and the natural phytochemical quillaja saponin (QS), with a strong emulsifying effect, were selected for mixing with ethoxylated hydrogenated castor oil (RH40) as emulsifiers to prepare TPGS-QS microemulsion with ethyl oleate as an oil phase and isopropanol as a co-emulsifier. The morphology, particle size and zeta potential of emulsion droplets were observed by optical microscopy (OM), transmission electron microscopy (TEM) and laser particle size analyzer. The optimal microemulsion formulation consisted of a mixture of ethyl oleate, 0.02% TPGS, 1.5% QS, RH40 and isopropanol at a ratio of 30:6.6:6.6:39.4:17.5 (m/m). All solutions were prepared with purified water. The microemulsion was yellowish, clear and transparent in appearance with strong fluidity, and it was identified as an O/W-type emulsion with uniform spherical droplets. In addition, its average particle size was (48.89 ± 0.08) nm, and its zeta potential was (–4.513 ± 0.564) mV. The α-glycosidase inhibitory activity, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity, 2,2’-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) cation radical scavenging capacity and iron reducing power of TPGS-QS microemulsion was tested, and its in vitro cytotoxicity on HepG2 and Caco-2 cells was evaluated through MTT assay. The half-maximal inhibitory concentration against α-glycosidase was 67.15 mg/mL, and the emulsion had antioxidant activity. It hardly affected the normal growth of cells, but even had a promoting effect on cell proliferation within a certain concentration range.

Key words: D-α-tocopheryl polyethylene glycol 1000 succinate; quillaja saponin; microemulsion; antioxidant; cytotoxicity