Akebia quinata and Akebia trifoliata - a review of phytochemical composition, ethnopharmacological approaches and biological studies

'Akebia stem' (Akebiae caulis) is one of the newest raw materials officially introduced into therapeutic practice from traditional Chinese medicine. A monograph on this material appeared for the first time in 2018 in Supplement 9.6 to the 9th edition of the European Pharmacopoeia. In the latest 10th edition of the European Pharmacopoeia, the monograph remained unchanged. The 'Akebia stem' monograph allows the use, as a raw material, of Akebia quinata (Houtt.) Decne., A. trifoliata (Thunb.) Koidz, or a mixture of the two species. The aim of this work is a detailed review of the scientific literature on the genus Akebia (family Lardizabalaceae), with particular emphasis on A. quinata and A. trifoliata, providing information on the botanical, ecological, and chemical characteristics of these species. Professional research on their biological activity has been reviewed. The attention is given to phytochemistry and cosmetology. The traditional use of Akebia species and their potential use in medicine and cosmetology are assessed. In addition, individual papers describing biotechnology research on in vitro cultures of the two Akebia species are presented. The presented botanical, ecological, phytochemical and biotechnological characterization is based on a thorough review of published scientific research. It is a compilation and evaluation of data on the chemical composition and biological activities of these Akebia species. This critical review of phytochemical studies demonstrates that triterpenoid saponins are dominant secondary metabolites of these species. A comparative analysis of phytochemical studies on A. quinata and A. trifoliata stems, roots, fruits, and seeds showed differences in metabolites based on the plant parts and species. The triterpenoid saponins mutongsaponin C and saponin Pj1 have been found only in A. trifoliata, whereas the phenolic glycoside 2-(3,4-dihydroxyphenyl)-ethyl-O-β-D-glucopyranoside has been found only in A. quinata. Biological activity studies of A. quinata stem, leaf and/or fruit extracts have confirmed diuretic, hepatoregenerative, neuroprotective, analgesic, anti-inflammatory, and anti-obesity effects and an influence on ethanol metabolism. Different action profiles have been demonstrated for A. trifoliata stem, leaf and/or fruit extracts. Studies have proven the antibacterial and anticancer (liver and stomach) effects of these species. This review presents potential phytopharmacological applications of both species and detailed data on their broad applications in cosmetology. Attention is also drawn to information on the safety of using Akebia. Finally, an overview of biotechnology research on both species is presented. This review provides comprehensive knowledge about the ethnopharmacological use of Akebia species. Moreover, new findings on the differences in the chemical composition and biological activity profiles are underlined.