Abstract
Astragalus mongholicus Bunge (Fabaceae) is an ancient Chinese herbal medicine, and Astragalus saponins are the main active components, which have a wide range of biological activities, such as immunomodulation, antioxidation, and neuroprotection. In this study, silver nanoparticles obtained by sodium borohydride reduction were used as the enhanced substrate to detect astragaloside I (1), astragaloside II (2), astragaloside III (3), astragaloside IV (4), isoastragaloside I (5), and isoastragaloside II (6) in the phloem, xylem, and cork by surface-enhanced Raman spectroscopy (SERS). In the SERS spectrum of Astragalus slices, the characteristic peaks were observed at 562, 671, 732, 801, 836, 950, 1,026, 1,391, and 1,584 cm−1, among which 950 cm−1 and 1,391 cm−1 were strong SERS signals. Subsequently, the metabolites of the six kinds of Astragalus saponins were identified by UPLC/ESI/Q-TOF-MS. Totally, 80, 89, and 90 metabolites were identified in rat plasma, urine, and feces, respectively. The metabolism of saponins mainly involves dehydration, deacetylation, dihydroxylation, dexylose reaction, deglycosylation, methylation, deacetylation, and glycol dehydration. Ten metabolites (1-M2, 1-M11, 2-M3, 2-M12, 3-M14, 4-M9, 5-M2, 5-M17, 6-M3, and 6-M12) were identified by comparison with reference standards. Interestingly, Astragalus saponins 1, 2, 5, and 6 were deacetylated to form astragaloside IV (4), which has been reported to have good pharmacological neuroprotective, liver protective, anticancer, and antidiabetic effects. Six kinds of active Astragalus saponins from different parts of Astragalus mongholicus were identified by SERS spectroscopy. Six kinds of active Astragalus saponins from different parts of Astragalus mongholicus were identified by SERS spectrum, and the metabolites were characterized by UPLC/ESI/Q-TOF-MS, which not only provided a new method for the identification of traditional Chinese medicine but also provided a theoretical basis for the study of the pharmacodynamic substance basis of Astragalus mongholicus saponins.
Highlights
Astragalus mongholicus Bunge is an ancient Chinese herbal medicine used as an essential ingredient in over 200 Chinese herbal formulas prescribed to treat different diseases in China and other Asian countries (Yuan et al, 2012; Sun et al, 2019)
Compound astragaloside I (1), astragaloside II (2), astragaloside III (3), astragaloside IV (4), isoastragaloside I (5), isoastragaloside II (6), and cycloastragenol were all purchased from Chengdu Monster Biological Technology Co., Ltd., and their purity was above 98%
Astragaloside IV had a Raman peak of 1,391 cm−1 (Figure 3F), but the response was very low
Summary
Astragalus mongholicus Bunge is an ancient Chinese herbal medicine used as an essential ingredient in over 200 Chinese herbal formulas prescribed to treat different diseases in China and other Asian countries (Yuan et al, 2012; Sun et al, 2019). Pharmacological studies have shown that their saponins, flavonoids, and polysaccharide phytochemicals have interesting bioactivities, such as antioxidant, antiinflammatory, immunomodulatory, antiviral, and antitumor activities (Liu et al, 2017). According to the Chinese Pharmacopeia (2020 version), astragaloside saponins (especially astragaloside IV) possess interesting pharmacological activities, and they are used as quality assessment markers for Astragalus mongholicus Bunge. More than 40 triterpenoid saponins have been obtained from Astragalus mongholicus Bunge and its related plants (Lee et al, 2017a; Song et al, 2007). Several researchers have studied the pharmacokinetic characteristics of its active components and metabolites in different crude extracts (Liu et al, 2015; Shi et al, 2015). Many potential active saponins in Astragalus mongholicus Bunge have not been studied
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