Hippuric acid and 3‐(3‐hydroxyphenyl) propionic acid inhibit murine osteoclastogenesis through RANKL‐RANK independent pathway

Nutritional factors influence bone development. Previous studies demonstrated that bone mass significantly increased with suppressed bone resorption in early life of rats fed with AIN‐93G semi‐purified diets supplemented with 10% whole blueberry (BB) powder for 2 weeks. However, the effects of increased phenolic acids in animal serum due to this diet on bone and bone resorption were unclear. This in vitro and in ex vivo study examined the effects of phenolic hippuric acid (HA) and 3‐(3‐hydroxyphenyl) propionic acid (3‐3‐PPA) on osteoclastic cell differentiation and bone resorption. We cultured murine osteoclast (macrophage) cell line, RAW 264.7 cells, and hematopoietic osteoclast progenitor cells (isolated from 4‐week‐old C57BL6/J mice) with 50 ng/ml of receptor activator of nuclear factor κ‐Β ligand (RANKL). Morphologic studies showed decreased osteoclast number with treatment of 2.5% mouse serum from BB diet–fed animals compared with those treated with serum from standard casein diet–fed mice in both RAW 264.7 cell and primary cell cultures. HA and 3‐3‐PPA, but not 3–4‐PPA, had dose‐dependent suppressive effects on osteoclastogenesis and osteoclast resorptive activity in Corning osteo‐assay plates. Signaling pathway analysis showed that after pretreatment with HA or 3‐3‐PPA, RANKL‐stimulated increase of osteoclastogenic markers, such as nuclear factor of activated T‐cells, cytoplasmic 1 and matrix metallopeptidase 9 gene/protein expression were blunted. Inhibitory effects of HA and 3‐3‐PPA on osteoclastogenesis utilized RANKL/RANK independent mediators. The study revealed that HA and 3‐3‐PPA significantly inhibited osteoclastogenesis and bone osteoclastic resorptive activity.