Harpagoside Inhibits RANKL-Induced Osteoclastogenesis via Syk-Btk-PLCγ2-Ca²⁺ Signaling Pathway and Prevents Inflammation-Mediated Bone Loss

Abstract

Harpagoside (HAR) is a natural compound isolated from Harpagophytum procumbens (devil's claw) that is reported to have anti-inflammatory effects; however, these effects have not been investigated in the context of bone development. The current study describes for the first time that HAR inhibits receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclastogenesis in vitro and suppresses inflammation-induced bone loss in a mouse model. HAR also inhibited the formation of osteoclasts from mouse bone marrow macrophages (BMMs) in a dose-dependent manner as well as the activity of mature osteoclasts, including filamentous actin (F-actin) ring formation and bone matrix breakdown. This involved a HAR-induced decrease in extracellular signal-regulated kinase (ERK) and c-jun N-terminal kinase (JNK) phosphorylation, leading to the inhibition of Syk-Btk-PLCγ2-Ca(2+) in RANKL-dependent early signaling, as well as the activation of c-Fos and nuclear factor of activated T cells cytoplasmic 1 (NFATc1), which resulted in the down-regulation of various target genes. Consistent with these in vitro results, HAR blocked lipopolysaccharide (LPS)-induced bone loss in an inflammatory osteoporosis model. However, HAR did not prevent ovariectomy-mediated bone erosion in a postmenopausal osteoporosis model. These results suggest that HAR is a valuable agent against inflammation-related bone disorders but not osteoporosis induced by hormonal abnormalities.

Devil's claw (Harpagophytum procumbens) and chronic inflammatory diseases: A concise overview on preclinical and clinical data

“…An imbalance of this process leads to the onset of osteoporosis, a multifactorial age-related disease characterized by increased bone fragility, with a major incidence in women ( Conversely, Chung et al (2016) showed that harpagoside, in addition to the stimulating osteoblast proliferation activity, was also able to restore OVX-induced destruction of trabecular bone. Actually, this contrasting result, compared with the findings of Kim et al (2015), could be related, albeit partially, to significant differences in study design. Indeed, although the oral dose of harpagoside (2-10 mg/kg) was the same in both studies, the duration of treatment, in Chung's paradigm (12 weeks), was much longer compared with Kim's study (4 weeks), thus affecting pharmacological response, in vivo.…”

“…Intriguingly, experimental studies also suggested the potential application of devil's claw as protective agent in osteoporosis. Chung et al () showed harpagide efficacy in exerting protective activity against bone loss in ovariectomized (OVX) mice, an animal model largely used to reproduce estrogen insufficiency‐related postmenopausal osteoporosis (Kim et al, ). Particularly, harpagide was found effective in stimulating osteoblast and blunting RANKL‐induced osteoclast differentiation.…”

“…Harpagoside displayed protective effects on bone, as well. Kim et al () showed harpagoside effectiveness in blunting both RANKL‐induced osteoclastogenesis and inflammation‐induced bone loss. On the other hand, harpagoside did not prevent bone erosion in OVX‐mice, thus supporting its potential use against inflammation‐related bone disorders, but not osteoporosis induced by hormonal imbalance.…”

Sitagliptin, An Anti-diabetic Drug, Suppresses Estrogen Deficiency-Induced OsteoporosisIn Vivo and Inhibits RANKL-Induced Osteoclast Formation and Bone Resorption In Vitro

“…The RANKL–RANK axis also stimulates the Ca 2+ –NFATc1 signaling pathway by activating PLCγ. During osteoclastogenesis, activated PLCγ hydrolyzes phosphatidylinositol-4,5-biphosphate (PIP2) to inositol-1,4,5-triphosphate (IP3), thereby upregulating both the intracellular Ca 2+ and the NFATc1 activation (Negishi-Koga and Takayanagi, 2009; Hwang and Putney, 2011; Kim et al, 2014, 2015). Oxidative stress stimuli transmitted by increased intracellular production of ROS could play as the secondary messengers in RANKL-induced osteoclast signaling pathways (Lee et al, 2005).…”

Antiinflammatory effect of herbal preparations on adjuvant arthritis in rats

“…With the aging of the global population, such diseases as rheumatoid arthritis (RA), osteoarthritis, and other bone metabolic disorders are increasingly impacting public health as well as the economy (1,2). Because current treatments for arthritis are inefficient, produce substantial side effects, and tend to be expensive, natural products, which are devoid of such disadvantages, offer novel treatment opportunities (3).…”