Novel antiosteoclastogenic activity of phloretin antagonizing RANKL-induced osteoclast differentiation of murine macrophages.
METHODS
Bone-remodeling imbalance resulting in more bone resorption than bone formation is known to cause skeletal diseases such as osteoporosis. Phloretin, a natural dihydrochalcone compound largely present in apple peels, possesses antiphotoaging, and antiinflammatory activity.


RESULTS
Phloretin inhibited receptor activator of NF-κB ligand (RANKL)-induced formation of multinucleated osteoclasts and diminished bone resorption area produced during the osteoclast differentiation process. It was also found that ≥ 10 μM phloretin reduced RANKL-enhanced tartrate-resistance acid phosphatase activity and matrix metalloproteinase-9 secretion in a dose-dependent manner. The phloretin treatment retarded RANKL-induced expression of carbonic anhydrase II, vacuolar-type H(+) -ATPase D2 and β3 integrin, all involved in the bone resorption. Furthermore, submicromolar phloretin diminished the expression and secretion of cathepsin K elevated by RANKL, being concurrent with inhibition of TRAF6 induction and NF-κB activation. RANKL-induced activation of nuclear factor of activated T cells c1 (NFATc1) and microphthalmia-associated transcription factor was also suppressed by phloretin.


CONCLUSIONS
These results demonstrate that the inhibition of osteoclast differentiation and bone resorption by phloretin entail a disturbance of TRAF6-NFATc1-NF-κB pathway triggered by RANKL. Therefore, phloretin may be a potential therapeutic agent targeting osteoclast differentiation and bone resorption in skeletal diseases such as osteoporosis.
Department of Food Science and Nutrition, Hallym University, Chuncheon, Korea.
Jung-Lye
JL
Kim
Min-Kyung
MK
Kang
Ju-Hyun
JH
Gong
Sin-Hye
SH
Park
Seon-Young
SY
Han
Young-Hee
YH
Kang
D000135:Acid Phosphatase / Q000378:metabolism; D000818:Animals; D001862:Bone Resorption; D002256:Carbonic Anhydrases / Q000378:metabolism; D056657:Cathepsin K / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D007527:Isoenzymes / Q000378:metabolism; D008264:Macrophages / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D051379:Mice; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D050778:NFATC Transcription Factors / Q000378:metabolism; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010693:Phloretin / Q000494:pharmacology*; D053245:RANK Ligand / Q000037:antagonists & inhibitors*; D000077385:Silybin; D012838:Silymarin / Q000494:pharmacology; D048029:TNF Receptor-Associated Factor 6 / Q000235:genetics / Q000378:metabolism; D000071681:Tartrate-Resistant Acid Phosphatase; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism
D007527:Isoenzymes; D016328:NF-kappa B; D050778:NFATC Transcription Factors; C494005:Nfatc1 protein, mouse; D053245:RANK Ligand; D012838:Silymarin; D048029:TNF Receptor-Associated Factor 6; C505689:Tnfsf11 protein, mouse; D000077385:Silybin; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase; D056657:Cathepsin K; C534132:Ctsk protein, mouse; D020780:Matrix Metalloproteinase 9; D025262:Vacuolar Proton-Translocating ATPases; D002256:Carbonic Anhydrases; D010693:Phloretin