Inhibition of Osteoclast Activation and Bone Resorption by Korean Thistle Ethanol Extracts in Receptor Activator of NF-κB Ligand-differentiated Murine Macrophages (P06-061-19)

Abstract

ObjectivesEnhanced bone resorption due to osteoclast activation cause skeletal diseases such as osteoporosis. Botanical antioxidants are being increasingly investigated for their health-promoting effects on bone. Korean thistle (Cirsium setidens Nakai), a wild perennial, is widely consumed as a food and traditional medicine in Korea and contains flavone-type flavonoids of luteolin, apigenin and acacetin with anti-inflammatory and antioxidant activities. This study examined whether Korean thistle extracts and their component acacetin inhibited osteoclast activation in receptor activator of NF-κB ligand (RANKL)-differentiated murine macrophages. MethodsRAW 264.7 murine macrophages were incubated with 10–20 μg/ml Korean thistle extracts and 20 μM acacetin for 5 days in the presence of 50 ng/ml RANKL. Tartrate-resistance acid phosphatase (TRAP) staining and its activity measurement were performed. Western blotting was done with target proteins involved in the osteoclast activation. ResultsNon-toxic Korean thistle extracts inhibited RANKL-induced formation of multinucleated osteoclasts and diminished TRAP activity enhanced in the osteoclast differentiation process. When Korean thistle extracts were treated to RANKL-exposed macrophages, the bone-resorbing activity was highly attenuated. The treatment of murine macrophages with 20 μg/ml Korean thistle extracts reduced cellular expression of carbonic anhydrase II, vacuolar-type H(+)-ATPase D2 and integrin αvβ3 elevated by RANKL, all involved in the bone resorption. Additionally, Korean thistle extracts reduced the expression of paxillin and cortactin elevated by RANKL, being concurrent with inhibition of induction of TRAF6, Src and PI3K. Korean thistle extracts blocked the formation of actin rings of osteoclasts enhanced by RANKL. Furthermore, the Korean thistle component, acacetin, diminished RANKL-promoted TRAP activity. ConclusionsKorean thistle extracts and acacetin deterred preosteoclasts from the cell-cell fusion and the organization of the cytoskeleton for bone resorption. Korean thistle and its effective flavonoid acacetin could be natural therapeutic agents combating osteoclastogenesis. Funding SourcesThis work (Grants No. C0501612) was supported by project for Cooperative R&D between Industry, Academy, and Research Institute funded Korea Ministry of SMEs and Startups in 20.