Saurolactam inhibits osteoclast differentiation and stimulates apoptosis of mature osteoclasts

Abstract

The receptor activator of nuclear factor-kappaB ligand (RANKL) plays a critical role in the differentiation and bone resorptive activity of osteoclasts. Recently, the development of anti-resorptive agents from natural substances has become a subject of interest. Therefore, we evaluated the effects of 222 natural compounds on the RANKL-induced tartrate-resistance acid phosphatase (TRAP; a marker for osteoclast differentiation) activity and multinucleated osteoclast formation in RAW264.7 murine macrophage cells. We found that saurolactam was one of the compounds inhibiting the RANKL-induced osteoclastogenesis; it significantly inhibited the RANKL-induced TRAP activity and formation of multinucleated osteoclasts without any cytotoxicity. Interestingly, saurolactam prevented RANKL-induced activation of MAP kinases and NF-kappaB, and mRNA expression of osteoclast-related genes and transcription factors (c-Fos, Fra-2, and NFATc1). We also observed the inhibitory effect of saurolactam on the differentiation of mouse bone marrow-derived macrophages into osteoclasts. Furthermore, saurolactam inhibited the bone resorptive activity of mature osteoclasts with the induction of apoptotic signaling cascade and the inhibition of survival signaling pathways such as c-Src/PI3K/Akt, Ras/ERK, and JNK/c-Jun. In conclusion, although further studies are needed to determine the precise mechanism and biological efficacy of saurolactam in osteoclast-mediated bone disorders, our results demonstrate that saurolactam potentially inhibits osteoclast differentiation by preventing the activation of MAP kinases and transcription factors that consequently affect the regulation of genes required for osteoclastogenesis, and the bone resorptive activity of mature osteoclasts by inhibiting osteoclast survival-related signaling pathways and triggering the apoptotic signaling cascade.

Sinomenine induces apoptosis in RAW 264.7 cell-derived osteoclasts in vitro via caspase-3 activation

“…The cells were fixed with 10% formalin for 5 min, permeabilized with 0.1% Triton X-100 for 5 min and washed again with PBS. The actin rings were then stained with 50 mg/mL phalloidin-FITC for 1 h under light protection [15] . After two washes with PBS, the nuclei were stained with DAPI.…”

6,4′-Dihydroxy-7-methoxyflavanone Inhibits Osteoclast Differentiation and Function

“…Recently, several studies have suggested that natural source of small molecules prevent osteoporosis by modulate osteoclastogenesis. For example, saurolactam, sauchinone isolated from Saururus chinensis 33,34) inhibited bone destruction and osteoclast formation caused by lipopolysaccharide in an animal model. Baicalein isolated from Scutellaria baicalensis 35) inhibited osteoclast differentiation and induced apoptosis of mature osteoclasts to inhibit bone resorption.…”

Decursin inhibits osteoclastogenesis by downregulating NFATc1 and blocking fusion of pre-osteoclasts

“…Many natural products have been reported to suppress osteoclastogenesis and bone resorption [17,18]. Angelica gigas NAKAI (AGN) and its substances have been reported to exhibit several biological activities including anti-tumor, anti-nociceptive, anti-bacterial, and anti-inflammatory activity [19][20][21][22][23].…”