翻译下面的英文Due to their hydrophobic nature, pentacyclic triterpenoids are almost insoluble in water. They are classified in the biopharmaceutical classification system as class IV drugs as their pharmacological effects are limited due to their low solubility in water and potential difficulty in permeating biological membranes [78]. For these reasons, some new approaches have been introduced to enhance their biopharmaceutical properties, particularly drug delivery technologies. At present, nano-emulsions, mesoporous silica nanoparticles, solid lipid nanoparticles, liposomes, niossomal gels and solid dispersions have been proposed quite successfully [79]; however, most of these studies were performed in experimental animals, and research in humans is very scarce, despite the great therapeutic potential of these natural biocompounds.
Table 1 summarizes the current knowledge of OA pharmacokinetics in humans after oral single-dose administration. Song et al. [80] reported the results of a pharmacokinetic study performed with 18 healthy male Chinese volunteers, in which the participants received a single dose of 40 mg OA (capsule preparation). Venous blood samples were collected for 48 h, and the plasma was analyzed for OA contents. The area under the plasma OA concentration–time curve (AUC) was determined in 124.3 ± 106.7 ng h/mL, with a peak OA concentration of 12.1 ± 6.8 ng/mL, which was registered at 5.2 ± 2.9 h after the OA intake. Later on, a randomized, crossover and self-control study was carried out with 18 healthy Chinese male volunteers, who received 20 mg OA orally, formulated as normal tablets and dispersible tablets [81]. The resulting pharmacokinetic parameters included AUC values of 112.2 ± 56.6 and 109.7 ± 41.6 ng h/mL, for normal and dispersible tablets, respectively, and OA peak concentrations of 18.9 ± 8.0 and 17.8 ± 7.5 ng/mL, which were recorded at 2.9 ± 1.2 and 2.5 ± 1.0 h after the triterpene administration. In 2015, Rada et al. informed on a pharmacokinetic study developed with nine adult men, who were administered 30 mg OA dissolved in 70 g of pomace olive oil. The reported AUC value was 3181.9 ± 894.3 ng h/mL, with an OA maximum concentration of 598.2 ± 176.7 ng/mL, achieved at 3.0 ± 0.8 h after the intake of the OA-containing oil. The administered OA dose revealed a distribution volume of 81.4 ± 9.7 L, and removal half-lives of 4.6 ± 1.1 h. The 30 mg OA oral dose yielded a total clearance of 35.1 ± 4.2 L/h [82]. More recently, de la Torre et al. [83] reported that an administration of 4.7 mg of OA within 30 mL of olive oil to 12 individuals led to a maximum concentration of 5.1 ± 2.1 ng/mL in plasma 4 h after the intake.