The genus Tragopogon (Asteraceae): A review of its traditional uses, phytochemistry, and pharmacological properties.

Abstract

Species of Tragopogon are used in traditional medicine, and consumed as vegetables across the world. In terms of the medicinal uses of Tragopogon, different species have found use in traditional medicine, including uses for wound-healing, treatment of gastrointestinal and hepatic complaints, cancer, kidney and liver dysfunction, inflamed skin and certain cutaneous diseases, as well as constipation, fatigue and anoxia. The aim of this review is to highlight and critically summarize those species of the genus that have been studied as a source of interesting lead compounds, and their traditional uses and bioactivities. A comprehensive and systematic review of literature on traditional uses, phytochemicals and pharmacological properties of the genus Tragopogon was carried out. Information was retrieved from secondary databases such as Scopus, Chemical Abstracts Services (Scifinder), Pubmed, Google Scholar and ScienceDirect, in addition to primary sources including books, PhD and MSc dissertations, and official websites. Species names were validated using "The Plant List" (www.theplantlist.org). The taxa of the genus Tragopogon are known for their local and traditional uses as medicine for treatment of various diseases, and have been consumed as vegetables and snacks for generations in Eurasia, the Mediterranean, Caucasus, Europe and North America. From the approximately 110 species of Tragopogon, only twelve species have been scientifically evaluated for their bioactivity and/or phytochemical composition. Tragopogon species are a rich source of phytochemical constituents and among those that have been identified are 19 flavonoids, 35 terpenoids, seven bibenzyl derivatives, five benzylphtalides, six stilbenes, nine dihydroisocoumarin derivatives, nine phenylmethane derivatives, three hydroxyphenylacetic acid derivatives, four phenylpropane derivatives, four esters of phenylpropanoic acids, a coumarin derivative, and a spermine derivative. Various extracts of the taxa, in addition to the isolated compounds, demonstrated pharmacological properties such as antitumor, antimicrobial, anti-inflammatory and enzyme inhibitory activities, in addition to hepatoprotective, antihyperlipidaemic and wound-healing properties. This review highlights the traditional uses, phytochemistry and pharmacological properties of the few studied taxa of the genus Tragopogon. Some of the reviewed papers were not of an appropriate methodological standard. For instance, phytochemical profiles were not determined, and the fundamental requirements of the pharmacological properties were not defined such as including appropriate positive and negative controls, and calculating the MIC values. Furthermore, these studies did not provide an in depth evaluation of bioactivity of the extracts and the isolated compounds or in vivo experiments which could indicate therapeutic relevance. From a phytopharmacological point of view, this review recommends more high quality evidence-based research on Tragopogon species for further development of plant-derived remedies and compounds.