Bioactivity-Guided Isolation and Identification of Antiadipogenic Compounds in Shiya Tea (Leaves of Adinandra nitida).

Obesity is a worldwide epidemic contributing to a higher risk of developing maladies such as type 2 diabetes, heart disease, and cancer. Shiya tea (leaves of Adinandra nitida), a traditional Chinese tea, is widely consumed due to its palatable flavor and various curative effects, such as reducing blood pressure and blood lipids, as well as anti-inflammation, etc. However, no relevant research on the antiobesity effects of Shiya tea has been reported. In particular, no health-benefiting compounds, other than flavonoids, in Shiya tea have been reported. Thus, 3T3-L1 preadipocytes have been used as a bioactivity-guided identification model to verify the inhibitory effects of Shiya tea on adipogenesis, as well as to identify antiadipogenic compounds. Four triterpenoid saponins (1-4), including one new compound (2α,3α-dihydroxyursolic acid 28- O-β-d-glucopyranosyl ester, compound 1), and a flavonoid (5) have been identified using NMR (1D and 2D NMR) and liquid chromatography (LC)-MS techniques. Compound 1, the major antiadipogenic constituent with an IC₅₀ value of 27.6 μg/mL, has been identified for the first time in Shiya tea. To understand the structure-activity relationship, three hydrolytic compounds (1s, 2s, and 5s) were obtained to provide an inhibitory effect on lipid accumulation during 3T3-L1 adipocyte differentiation. The inhibitory effect of the triterpenoid (1s) possessing no sugar group decreased significantly, while the flavonoid (5s) also without a sugar group showed increased activity. In addition, the hydroxyl group position may also play a role in inhibitory efficacy.