The genus Achyranthes : A review on traditional uses, phytochemistry, and pharmacological activities

Achyranthes L. (Amaranthaceae), also known as Chaff Flower and Niuxi/牛膝, mainly includes two famous medicinal species namely A. bidentata and A. aspera. A. bidentata has been widely used as blood-activating and stasis-resolving medicine for the treatment of various diseases including amenorrhea, dysmenorrhea, lumbago, gonalgia, paraplegia, edema, stranguria, headache, dizziness, odontalgia, oral ulcer, hematemesis, and epistaxis. A. aspera has been widely used to treat various diseases, including gynecological disorder, asthma, ophthalmia, odontalgia, haemorrhoids, and abdominal tumor, and has been applied to difficult labour, wound healing, insect and snake bites. This review aims to provide systematically reorganized information on distributions, botanical characteristics, ethnopharmacology, chemical constituents, qualitative and quantitative analysis, pharmacological activities, and toxicity of Achyranthes species to support their therapeutic potential. The relevant information on Achyranthes species was gathered from worldwide accepted scientific databases via electronic search (Google Scholar, Web of Science, ScienceDirect, ACS Publications, PubMed, Wiley Online Library, SciFinder, CNKI). Information was also obtained from International Plant Names Index, Chinese Pharmacopoeia, Chinese herbal classic books, PhD and MSc dissertations, etc. A comprehensive analysis of literatures obtained through the above- mentioned sources confirms that the ethnomedicinal uses of Achyranthes species are mainly recorded in China, India, Korea, Pakistan, Ethiopia, Kenya, Sri Lanka, Bangladesh, Philippines, etc. Phytochemical investigations revealed that the major bioactive substances of Achyranthes plants are polysaccharides, polypeptides, triterpenoid saponins, and ketosteroids. Achyranthes plants have been shown to not only act on immune system, nervous system, bone metabolism, and reproduction, but also possess a wide range of biological activities, including blood-activating, anti-tumor, anti-inflammation, anti-arthritis, anti-oxidation, anti-aging, wound healing, etc. Toxicity studies indicated that A. bidentata and A. aspera seem non-toxic at the common therapeutic doses. A. bidentata and A. aspera are very promising to be fully utilized in the development of nutraceutical and pharmaceutical products. There are, however, needs for further in-depth studies to confirm some ethnomedicinal uses of Achyranthes plants and to elucidate the scientific connotation of the widely documented property of conducting drug downward of A. bidentata. In addition, other widespread Achyranthes species like A. japonica and A. rubrofusca ought to be studied. Likewise, systematic comparative studies of the chemical constituents of medicinal Achyranthes plants resources with the same local name are also needed. Furthermore, not only should the investigations on the structure-activity relationship of the main bioactive compounds triterpenoid saponins and ketosteroids be carried out, but the pathways of absorption, distribution, metabolism, and excretion ought to be clarified. Last but not least, there is also a need to evaluate the long-term chronic toxicity and acute toxicity in vivo of the main bioactive compounds.