Triterpene saponin constituents from roots of Bupleurum falcatum: Hepatoprotective effects on D-galactosamine-induced cell damage

Bupleurum falcatum L. [Apiaceae] is cultivated in Asia, and its root part, Bupleuri Radix (“Saiko" in Japanese), is one of the most important natural medicines in Japan. In the Japanese Pharmacopoeia XVI, the root has been used for anti-inflammatory, anti-pyretic, and anti-hepatotoxic effects in the treatments of common cold, fever, and hepatitis [1]. We have found that MeOH extract of the roots of B. falcatum showed inhibitory activity in D-galactisamine (D-GalN)-induced cell damage in hepatocytes. Through bioassay-guided separation, several triterpene saponins were identified as the bioactive constituents. Furthermore, hepatoprotective effects of major active saponins against D-GalN/lipopolysaccharide (LPS)-induced liver injury in mice were also examined. From the MeOH extract of the roots of B. falcatum cultivated in Sichuan province, China, a new and 17 known saponins were isolated. Hepatocytes were isolated from Wister rat by a collagenase perfusion method. The cell suspension at 4 × 10⁴ cells in 100 µl William's E medium (containing 10% FBS) was inoculated in a 96-well microplate and pre-incubated for 4h at 37 °C under 5% CO₂ atmosphere. After pre-incubation, 100 µl of fresh medium containing D-GalN (1 mM) with the test sample was added to the medium. After 44h incubation, cell viability was assessed by MTT colorimetric assay. The structure of a new saponin [1] was determined on the basis of spectroscopic properties and chemical evidence. Among the isolates, saikosaponins b₃ and b₄, and bupleuroside IX significantly inhibited cell damage in hepatocytes. In addition, major saikosaponins, such as saikosaponins a, c, and d, were found to significantly inhibit the liver injury. The data demonstrated that saponin constituents from B. falcatum roots could protect against D-GalN and D-GalN/LPS-induced liver injury.

Keywords: Bupleurum falcatum, D-galactosamine, D-GalN/LPS, liver failure.

References:

[1] Nakahara Y, Okawa M, Kinjo J, Nohara T. Oleanene glycosides of the aerial parts and seeds of Bupleurum falcatum and the aerial parts of Bupleurum rotundifolium, and their evaluation as anti-hepatitis agents. Chem Pharm Bull 2011; 59: 1329 – 1339