Study on chemical composition, anti-inflammatory activity and quality control of the branch bark of Morus alba L.

In this study, the chemical constituents of branch bark and root bark of Morus alba L. were first qualitatively analyzed by UPLC-Q/TOF-MS. A total of 40 compounds were identified, including 20 flavonoids, 3 stilbenes, 1 phenolic acid, 1 alkaloid, 5 arylbenzofurans and 10 Diels-Alder adducts. Of these, 19 compounds were specific to the root bark, 10 to the branch bark, and 11 were common to both. Total phenolic and flavonoid contents were determined, and anti-inflammatory activities were evaluated. Ethyl acetate extracts of both significantly inhibited NO secretion, with the root bark showing a stronger effect than the branch bark. Chemical components of branch bark were further separated, and the anti-inflammatory activities of these isolated compounds were investigated. Eight compounds were isolated from the ethyl acetate extract of the branch bark of Morus alba L.. These compounds were able to inhibit the release of inflammatory factors, including NO, IL-6, and IL-1β, in a concentration-dependent manner. Among them, compounds SZP-1, SZP-6 and SZP-8 exhibited superior in vitro anti-inflammatory activity, comparable to the positive drug meloxicam at high concentrations. In addition, the quality standard of the branch bark of Morus alba L. was established for the first time according to the 2020 edition of the Chinese Pharmacopoeia. This study provides valuable insights into the medicinal value of the branch bark of Morus alba L. and promotes the comprehensive utilization of mulberry branch resources.