Excessive activity of osteoclasts contributes to skeletal diseases such as
osteoporosis and
osteolysis. However, current drugs targeting osteoclast have various deficiencies, placing natural compounds as substitutions of great potential.
Roburic acid (RA) is a
triterpenoid exacted from
Radix Gentianae Macrophyllae, which exhibits inhibitory effects on
inflammation and oxidation. By employing an in vitro osteoclastogenesis model, this study investigates the effects and mechanisms of RA on intracellular signaling induced by receptor activator of nuclear factor-κB
ligand (RANKL). As expected, RA at a concentration scope from 1 to 10 μM dampened the osteoclast differentiation of bone marrow macrophages (BMMs) but without cell toxicity. Interestingly, RA showed no effect on osteoblastogenesis in vitro. Furthermore, RA mitigated
F-actin ring formation,
hydroxyapatite resorption, and gene expression in osteoclasts. Mechanistically, RA suppressed
TNF receptor-associated factor 6 (
TRAF6), the crucial adaptor
protein following RANKL-RANK binding. On the one hand, RA downregulated the nuclear factor-κB (NF-κB) activity, extracellular regulated
protein kinases (ERK) phosphorylation, and calcium oscillations. On the other hand, RA upregulated the antioxidative response element (ARE) response and the
protein expression of
heme oxygenase (HO)-1. These upstream alterations eventually led to the suppression of the nuclear factor of activated T cells 1 (NFATc1) activity and the expression of
proteins involved in osteoclastogenesis and
bone resorption. Furthermore, by using an ovariectomized (OVX) mice model, RA was found to have
therapeutic effects against bone loss. On account of these findings, RA could be used to restrain osteoclasts for treating
osteoporosis and other osteolytic diseases.