title: Antioxidant and bone repair properties of quercetin-functionalized hydroxyapatite: An in vitro osteoblast-osteoclast-endothelial cell co-culture study.
abstract: Quercetin (3,3',4',5,7-pentahydroxy-flavone) is a flavonoid known for its pharmacological activities, which include antioxidant and anti-inflammatory properties, as well as possible beneficial action on diseases involving bone loss. In this work, we explored the possibility to functionalize hydroxyapatite (HA) with quercetin in order to obtain new materials for bone repair through local administration of the flavonoid. HA was synthesized in presence of different concentrations of quercetin according to two different procedures: direct synthesis and phase transition from monetite. Direct synthesis lead to composite nanocrystals containing up to 3.1 wt% quercetin, which provokes a reduction of the crystals mean dimensions and of the length of the coherently scattering domains. Synthesis conditions provoke a partial oxidation of quercetin and, as a consequence, a significant reduction of its radical scavenging activity (RSA). On the other hand, synthesis through phase transition yields samples containing up to 1.3 wt% of quercetin incorporated into hydroxyapatite, with minor structural modifications, which exhibit relevant anti-oxidant activities, as testified by their high RSA levels, (slightly lower than that of pure quercetin). The biological response to these materials was tested using an innovative triculture model involving osteoblast, osteoclast and endothelial cells, in order to mimic bone microenvironment. The results show that the presence of quercetin in the composite materials enhances human osteoblast-like MG63 proliferation and differentiation, whereas it downregulates osteoclastogenesis of osteoclast precursors 2T-110, and supports proliferation and differentiation of human umbilical vein endothelial cells (HUVEC).
  
  
  CONCLUSIONS
  The pharmacological activities of the flavonoid quercetin include anti-oxidant and antiinflammatory properties, as well as capability to prevent bone loss. In this paper, we demonstrate that it is possible to synthesize hydroxyapatite functionalized with different amounts of quercetin and obtain new composite materials which display both the good bioactivity of the inorganic phase and the therapeutic properties of the flavonoid. The innovative in vitro model developed in this study, which involves co-culture of osteoblast, osteoclast and endothelial cells, allows to state that the new materials exert a beneficial action onto bone repair microenvironment, stimulating osteoblast proliferation and activity, downregulating osteoclastogenesis, and supporting microangiogenetic processes necessary for new bone formation.
authors.affiliation: Department of Chemistry "G. Ciamician", University of Bologna, via Selmi 2, 40126 Bologna, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Forte
authors.affiliation: Laboratory of Preclinical and Surgical Studies, Research Institute Codivilla Putti - Rizzoli Orthopaedic Institute, via di Barbiano, 40126 Bologna, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Torricelli
authors.affiliation: Department of Chemistry "G. Ciamician", University of Bologna, via Selmi 2, 40126 Bologna, Italy. Electronic address: elisa.boanini@unibo.it.
authors.forename: Elisa
authors.initials: E
authors.lastname: Boanini
authors.affiliation: ISOF-CNR, c/o Department of Chemistry "G. Ciamician", Bologna, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Gazzano
authors.affiliation: Department of Chemistry "G. Ciamician", University of Bologna, via Selmi 2, 40126 Bologna, Italy.
authors.forename: Katia
authors.initials: K
authors.lastname: Rubini
authors.affiliation: Laboratory of Preclinical and Surgical Studies, Research Institute Codivilla Putti - Rizzoli Orthopaedic Institute, via di Barbiano, 40126 Bologna, Italy.
authors.forename: Milena
authors.initials: M
authors.lastname: Fini
authors.affiliation: Department of Chemistry "G. Ciamician", University of Bologna, via Selmi 2, 40126 Bologna, Italy.
authors.forename: Adriana
authors.initials: A
authors.lastname: Bigi
mesh_terms: D000975:Antioxidants / Q000494:pharmacology*; D015415:Biomarkers / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D018920:Coculture Techniques / Q000379:methods*; D003460:Crystallization; D017886:Durapatite / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D016166:Free Radical Scavengers / Q000737:chemistry; D061307:Human Umbilical Vein Endothelial Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D010006:Osteoblasts / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D010010:Osteoclasts / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D044367:Phase Transition / Q000187:drug effects; D011794:Quercetin / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D013056:Spectrophotometry, Ultraviolet; D014945:Wound Healing / Q000187:drug effects*; D014961:X-Ray Diffraction
chemical_list: D000975:Antioxidants; D015415:Biomarkers; D016166:Free Radical Scavengers; D017886:Durapatite; D011794:Quercetin
keywords: Endothelial cell; Hydroxyapatite; Osteoblast; Osteoclast; Quercetin