Anti-inflammatory effects of hydrophobic constituents in the extract of the root cortex of Paeonia suffruticosa

Background: The root cortex of Paeonia suffruticosa Andrews (Paeoniaceae), which is also called moutan bark, is known as Botanpi in Japan. This crude drug has been used in several Kampo formulas, such as Daiobotanpito, to treat menstrual disturbance and constipation by improving blood stasis and suppressing inflammation. However, the anti-inflammatory effect has not been well studied.Objective: To clarify the anti-inflammatory effects of moutan bark, we isolated its constituents and investigated their activity.Methods: Moutan bark was extracted and successively fractionated with ethyl acetate (EtOAc) and n-butanol. The constituents were analyzed using HPLC. The production of nitric oxide (NO), an inflammatory mediator, was measured in interleukin (IL)-1β-treated rat hepatocytes to identify active fractions or constituents.Results: The EtOAc-soluble fraction of moutan bark extract significantly inhibited NO production. Three hydrophobic constituents were isolated from this fraction and identified as paeonol (1), 1,2,3,4,6-pentagalloyl-β-D-glucose (β-PGG; 2), and methyl gallate (3). Paeonol and paeoniflorin (4) were abundantly present in the EtOAc-soluble fraction and n-butanol-soluble fraction, respectively. The hydrophobic constituents suppressed NO production without exerting cytotoxicity and reduced the protein and mRNA levels of inducible nitric oxide synthase in IL-1β-treated hepatocytes; β-PGG showed the highest potency. Furthermore, β-PGG, methyl gallate, and paeonol decreased the mRNA levels of tumor necrosis factor α and IL-1 receptor type 1, which are involved in inflammation.Conclusion: These results suggest that hydrophobic constituents of moutan bark, such as β-PGG, methyl gallate, and paeonol, are involved in the anti-inflammatory effects of moutan bark.Keywords: Galloylglucose, tannin, nitric oxide, Kampo medicine, cytokine.