Comparison of the anti-inflammatory activities of furanocoumarins from the roots of Angelica dahurica
Background: The roots of Angelica dahurica Bentham et Hooker filius ex Franchet et Savatier (Apiaceae) have traditionally been used for inflammatory skin diseases. A. dahurica roots (Byakushi) contain furanocoumarins, such as imperatorin and byakangelicin. To elucidate which constituents are responsible for the anti-inflammatory effects, we evaluated the potency of crude A. dahurica root extract fractions by monitoring the production of the inflammatory mediator nitric oxide (NO) in hepatocytes.
Methods: The dried roots of A. dahurica were collected in South Korea and extracted with methanol. The resulting extract was fractionated into ethyl acetate (EtOAc)-soluble, n-butanol-soluble, and water-soluble fractions. Primary cultured rat hepatocytes were treated with interleukin (IL)-1β and each fraction for 8 h, and then the NO production and lactate dehydrogenase activity in the medium were measured. The expression of inducible nitric oxide synthase (iNOS) was detected by Western blotting, and its mRNA expression level was measured by quantitative reverse transcription-polymerase chain reaction.
Results: Among the three fractions, the EtOAc-soluble fraction markedly suppressed NO production without showing cytotoxicity and decreased iNOS expression in hepatocytes. From this hydrophobic fraction, we isolated five furanocoumarins: isoimperatorin, imperatorin, phellopterin, oxypeucedanin, and oxypeucedanin methanolate. Phellopterin and oxypeucedanin methanolate significantly suppressed NO production and reduced the mRNA expression of iNOS and tumor necrosis factor α. In contrast, the other three constituents did not affect NO production. Comparison of their chemical structures suggests that a methoxy group at carbon 5 and a side chain at carbon 8 in the furanocoumarin skeleton may be essential for NO production suppression.
Conclusion: These data imply that phellopterin and oxypeucedanin methanolate, which are hydrophobic furanocoumarins, may contribute to the anti-inflammatory effects of A. dahurica roots by suppressing iNOS gene expression.
Keywords: Inflammation, nitric oxide, hepatocyte, coumarin, Kampo medicine
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