Conventional and nanomaterial-based techniques to increase the bioavailability of therapeutic natural products: a review

Natural products have been widely explored since ancient times to heal human diseases. Due to their biological activities and relative safety, natural products have found applications in functional foods, medicine, pharmaceuticals and nutraceuticals. However, applications are often limited by poor aqueous solubility, instability and poor bioavailability following oral administration. For instance, many natural products exhibit excellent in vitro pharmacological activity, and no or less in vivo activity as a result of poor gastrointestinal absorption. Here we review techniques and materials for bioavailability enhancement such as particle size reduction, surfactant use, pH change, solid dispersion, cyclodextrin complexation, phytosome technology, solid-lipid nanoparticles, liposome and polymeric nanoparticles. Natural substances include quercetin, naringenin, curcumin, hesperetin, andrographolide, ellagic acid, resveratrol, bilobalide sinomenine, genistein, ginkgolide and glycyrrhizin. The clinical use of piperine as bio-enhancer with rifampicin is key achievement in the treatment of tuberculosis.