Augmentation of TNF-induced osteoclast differentiation by inhibition of ERK and activation of p38: Similar intracellular signaling between RANKL- and TNF-induced osteoclast differentiation

Delphinidin, one of the major anthocyanidins, prevents bone loss through the inhibition of excessive osteoclastogenesis in osteoporosis model mice

Anthocyanins, one of the flavonoid subtypes, are a large family of water-soluble phytopigments and have a wide range of health-promoting benefits. Recently, an anthocyanin-rich compound from blueberries was reported to possess protective property against bone loss in ovariectomized (OVX) animal models. However, the active ingredients in the anthocyanin compound have not been identified. Here we show that delphinidin, one of the major anthocyanidins in berries, is a potent active ingredient in anti-osteoporotic bone resorption through the suppression of osteoclast formation. In vitro examinations revealed that delphinidin treatment markedly inhibited the differentiation of RAW264.7 cells into osteoclasts compared with other anthocyanidins, cyanidin and peonidin. Oral administration of delphinidin significantly prevented bone loss in both RANKL-induced osteoporosis model mice and OVX model mice. We further provide evidence that delphinidin suppressed the activity of NF-κB, c-fos, and Nfatc1, master transcriptional factors for osteoclastogenesis. These results strongly suggest that delphinidin is the most potent inhibitor of osteoclast differentiation and will be an effective agent for preventing bone loss in postmenopausal osteoporosis.

An inhibitory role for caspase-3 at the late stage of RANKL-induced osteoclast differentiation in RAW264 cells and mouse bone marrow macrophages

Osteoclast differentiation/activation is involved in orthodontic tooth movement at the compression sites of the alveolar bone. RANKL, a member of the TNF family expressed in osteoblasts, binds to RANK, a member of the TNF receptor family expressed on preosteoclasts, resulting in differentiation of preosteoclasts into mature osteoclasts. Several members of the TNF family, such as TNF and Fas ligand, can induce apoptosis by activation of caspase-3. We have investigated whether caspase-3 be involved in the late stage of RANKL-induced osteoclast differentiation. Increased active caspase-3 was found in mouse monocytic RAW264 cells differentiated into mature osteoclasts by treatment with RANKL for 3 days. Co-treatment with Z-Asp-CH₂-DCB, a caspase-3-specific inhibitor, augmented RANKL-induced osteoclast differentiation in RAW264 cells, also seen in mouse bone marrow macrophages. This suggests that activation of caspase-3 may play an inhibitory role at the late stage of RANKL-induced osteoclast differentiation.