Abstract: Andrographolide (ADG) is a diterpenoid isolated from Andrographis paniculata  with a wide spectrum of biological activities, including anti-inflammatory, anticancer and hepatoprotective effects. However, its poor water solubility and efflux by P-glycoprotein have resulted in lower bioavailability. In this study, ADG nanosuspensions (ADG-NS) were prepared using a wet media milling technique followed by freeze drying. D-α-Tocopheryl polyethylene glycol 1000 succinate (TPGS), a surfactant that inhibits P-glycoprotein function, and sodium lauryl sulfate were used as surface stabilizers. A Box–Behnken design was used to optimize the nanosuspension preparation. The products of these optimal preparation conditions were amorphous and possessed much faster dissolution in vitro than a coarse powder of ADG. The particle size and redispersibility index of the freeze-dried ADG-NS were 244.6±3.0 nm and 113%±1.14% (n=3), respectively. A short-term stability study indicated that the freeze-dried ADG-NS could remain highly stable as nanosuspensions during the testing period. A test of transport across a Caco-2 cell monolayer revealed that the membrane permeability (P _app) of ADG-NS was significantly higher than the permeability of the ADG coarse powder or ADG-NS without TPGS (P <0.01). Compared to the ADG coarse powder, a physical mixture, commercial dripping pills and ADG-NS without TPGS, ADG-NS exhibited significantly higher plasma exposure with significant enhancements in C _max and area under the curve of plasma concentration versus time from zero to the last sampling time (AUC_0–t ) (P <0.01). An evaluation of the anti-inflammatory effect on Carr-induced paw edema demonstrated that the ADG-NS were more effective in reducing the rate of paw swelling, producing a greater increase in the serum levels of nitric oxide (NO), Interleukin-1 (IL-1) and tumor necrosis factor-α (TNF-α) (P <0.01) and an increase in superoxide dismutase activity (P <0.05) compared to the ADG coarse powder. This study indicated that nanosuspensions could act as an effective delivery device for ADG to enhance its oral bioavailability and biological efficacy.
Keywords: andrographolide, nanosuspensions, Box–Behnken design, D-α-tocopheryl polyethylene glycol 1000 succinate, dissolution rate, oral bioavailability