Glaucocalyxin A suppresses osteoclastogenesis induced by RANKL and osteoporosis induced by ovariectomy by inhibiting the NF-κB and Akt pathways.

ETHNOPHARMACOLOGICAL RELEVANCE: Glaucocalyxin A (GLA), the most abundant active component of the aboveground sections of Rabdosia japonica (Burm. f.) Hara var. glaucocalyx (Maxim.) Hara, possesses various pharmacological activities, such as antioxidant, antithrombosis, anticoagulation, antibacterial, antitumor, anti-inflammatory activities. According to previous studies, inflammation is closely associated with osteoclast differentiation and activity. Although GLA has demonstrated effective anti-inflammatory properties, its effects on osteoclast differentiation remain unclear. AIM OF THE STUDY: To examine the possible inhibitory effects of GLA and its molecular mechanisms in osteogenesis induced by RANKL as well as ovariectomy (OVX)-induced osteoporosis (OP) in mice. MATERIALS AND METHODS: Tartrate-resistant acid phosphatase (TRAP) staining, F-actin staining, and a bone resorption pit assay were applied for identifying the effects of GLA on the differentiation of osteoclasts and the function of bone resorption. The mRNA expression of the genes related to osteoclast differentiation was measured by quantitative PCR. Protein expression of nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1), c-fos and phosphorylation of inhibitor of nuclear factor kappa B (IκBα), protein kinase B (AKT), c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and p38 in RANKL-induced osteoclasts was determined using western blotting. The effect of GLA on OP was studied using a mouse model of OVX. RESULTS: At nontoxic concentrations ≤0.5 µM in vitro, GLA suppressed the formation of osteoclasts induced by RANKL with the decreased number and area size of TRAP-positive multinuclear osteoclasts, and the resorption of bone function by reducing F-actin ring number and bone resorption pit areas. It also reduced the expression of the genes specific for osteoclasts, which included genes encoding NFATc1, cathepsin K, c-fos, TRAP, vacuolar-type ATPase d2, and dendritic cell-specific transmembrane protein. Moreover, GLA repressed NF-κB and Akt pathway activation induced by RANKL. Micro-CT analysis of femur samples indicated decreased bone loss and greater trabecular bone density after GLA treatment, which showed that GLA played a protective role by inhibiting bone loss in OVX-induced OP mice in vivo. CONCLUSIONS: Our study is the first to show that GLA has significant therapeutic potential in OP, which is the disease of osteoclast increase caused by estrogen deficiency.

Vindoline Attenuates Osteoarthritis Progression Through Suppressing the NF-κB and ERK Pathways in Both Chondrocytes and Subchondral Osteoclasts.

Disruption of extracellular matrix (ECM) homeostasis and subchondral bone remodeling play significant roles in osteoarthritis (OA) pathogenesis. Vindoline (Vin), an indole alkaloid extracted from the medicinal plant Catharanthus roseus, possesses anti-inflammatory properties. According to previous studies, inflammation is closely associated with osteoclast differentiation and the disorders of the homeostasis between ECM. Although Vin has demonstrated effective anti-inflammatory properties, its effects on the progression of OA remain unclear. We hypothesized that Vin may suppress the progress of OA by suppressing osteoclastogenesis and stabilizing ECM of articular cartilage. Therefore, we investigated the effects and molecular mechanisms of Vin as a treatment for OA in vitro and in vivo. In the present study, we found that Vin significantly suppressed RANKL-induced osteoclast formation and obviously stabilized the disorders of the ECM homeostasis stimulated by IL-1ß in a dose-dependent manner. The mRNA expressions of osteoclast-specific genes were inhibited by Vin treatment. Vin also suppressed IL-1ß-induced mRNA expressions of catabolism and protected the mRNA expressions of anabolism. Moreover, Vin notably inhibited the activation of RANKL-induced and IL-1ß-induced NF-κB and ERK pathways. In vivo, Vin played a protective role by inhibiting osteoclast formation and stabilizing cartilage ECM in destabilization of the medial meniscus (DMM)-induced OA mice. Collectively, our observations provide a molecular-level basis for Vin's potential in the treatment of OA.