Diterpenes in Aralia cordata Rhizomes Suppress the Expression of Proinflammatory and Extracellular Matrix Degradation-Related Genes in ATDC5 Cells

Aralia cordata Thunberg (Araliaceae) is a perennial plant that grows in East Asia, including Japan. Its rhizome, called Dokukatsu in Japanese, is used as a crude drug in traditional Japanese (Kampo) medicines. Aralia rhizomes are included in several Kampo formulae, such as Dokkatsuto, which is prescribed for patients with osteoarthritis-related arthralgia, due to its analgesic and anti-inflammatory properties. However, the specific compounds responsible for these effects remain unexplored. In this study, we aimed to evaluate the anti-inflammatory properties of Aralia rhizome constituents by monitoring the production of the proinflammatory mediator nitric oxide (NO) in primary cultured rat hepatocytes. An ethyl acetate (EtOAc)-soluble fraction from an Aralia rhizome extract significantly suppressed interleukin (IL)-1β-induced NO production in rat hepatocytes. Within this fraction, we identified diterpenes, such as pimaradienoic acid (most abundant), kaurenoic acid, and pimaric acid. Among these, pimaradienoic acid markedly inhibited NO production in hepatocytes. We further investigated the effects of the EtOAc-soluble fraction on mouse chondrogenic cell line ATDC5—which produces NO in response to IL-1β and bacterial lipopolysaccharide (LPS)—and found that it inhibited NO production in ATDC5 cells treated with IL-1β and LPS. Moreover, pimaradienoic acid suppressed IL-1β-induced expression of the inducible nitric oxide synthase gene and downregulated genes involved in extracellular matrix (ECM) degradation in cartilage, specifically matrix metalloproteinase-13 (Mmp13) and a disintegrin and metalloproteinase with thrombospondin motifs-5 (Adamts5) genes. These findings suggest that pimaradienoic acid contributes to the anti-inflammatory effects of Aralia rhizomes by inhibiting NO-mediated inflammation and matrix degradation in articular cartilage during osteoarthritis.