An in-depth look into a well-known herbal drug: Fingerprinting, isolation, identification, and content estimation of saponins in different Strophanthus seeds

Abstract

Seeds of Strophanthus species are known as a source of rapid-acting cardenolides. These water-soluble glycosides are listed as the sole critical constituents of this raw herbal drug. A non-standard cardioprotective medication with ouabain-containing oral remedies has become popular in Europe as a result of the withdrawal of corresponding registered drugs from the market. However, the bioequivalence of pure ouabain solutions, tinctures, and home-made extracts from Strophanthus seeds is unknown. Thus, this study aimed to update the information on the composition of Strophanthus seeds used for this purpose. The distribution of two main saponins and about 90 previously unreported compounds, tentatively identified as saponins in eleven Strophanthus species, was systematically evaluated by ultra-high-performance liquid chromatography mass spectrometry (UHPLC-MS) and -MS/MS. Seeds of S. gratus were selected to isolate the dominant unreported triterpenoids, bidesmosides of echinocystic and oleanolic acid. Their structures were established by HRMS, MS/MS, as well as by NMR techniques. The total saponin content, estimated by UHPLC-MS, was up to 1%. The detected saponins could influence the peroral bioavailability of hardly absorbable Strophanthus cardenolides and exhibit their own activity. This finding may be relevant when Strophanthus preparations (containing both saponins and cardiac glycosides) are used, particularly when homemade preparations are administered.

Strophantus (Apocynaceae): Composition and Biochemical Properties with a Focus on S. sarmentosus

“…In contrast to cardiac glycosides, triterpene glycosides were not as extensively investigated although Strophantus extracts have been used as emetic and for treatment of respiratory diseases by native Africans for long [2]. Saponins (water-soluble foam-forming plant components) are credited with emetic, secretolytic and expectorant activity.…”

“…Saponins (water-soluble foam-forming plant components) are credited with emetic, secretolytic and expectorant activity. For a recent review on Strophantus saponins and triterpene glycosides in S. gratus, see [2].…”

“…In S. sarmentosus and other Strophantus species, echinocystic acid (Figure 2) was isolated from fermented seed extract as a core structure, e.g., of bidesmoside in S. gratus [2]. Echinocystic acid as a natural extract is widely used in the treatment of inflammatory diseases and reported to alleviate ischemia/reperfusion injury via inhibiting the JNK signaling pathway in mice [47].…”

“…The genus Strophantus was described by deCandolle in 1802, but Linnaeus had already reported on S. caudatus in 1767 [1]. The plants have been used for thousands of years in traditional herbal medicine and, interestingly, also as an arrow poison [2,3]. Their ethnopharmacological significance extends to dermatological diseases and skin care [4], treatment of tuberculosis [5] and ulcers [6], anti-protozoal [7], antibacterial, antioxidant [8] and anti-inflammatory [9] activity, as well as hypoglycemic effects [10].…”

“…The cardiotoxins, which were isolated from Strophantus seeds and which were the main reason for the use of the plant extracts as a poison, gained increasing interest in Western medicine as an alternative to digitoxin, the cardiac glycoside from the foxglove, at the turn of the 19 th century [13]. They were used in purified form in clinics to treat congestive heart failure and arrhythmias for many years [2]. Practitioners of alternative medicine still advertise strophantin for its cardiotonic effects [14].…”