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ePaper created 2016-06-09, 15:16:05 | version 1.38.0
Journal of Oral Science & Rehabilitation 10 Volume 2 | Issue 2/2016 bone turnover. The biological activity of osteo- clasts is bone resorption, initiated byattachment to the surface of the bone tissue and secreting protons and free radicals into the cell compart- ment formed below their ruffled border. The ac- tivity of osteoclasts is essentially regulated by the molecular triad osteoprotegerin/receptor activator of nuclear factor-kappa B/receptor ac- tivator of nuclear factor-kappa-B ligand (OPG/ RANK/RANKL). The balance and expression of this triad in bone tissue decisively influence dif- ferentiationandactivationofosteoclastsandplay an important role in coordinating osteogenesis, odontogenesis and tooth eruption. The proteins ofthistriadcanbesynthesizedbyalargenumber of cells, including bone marrow cells, dendritic cells, lymphoid cellsand endothelialcells.Osteo- blastsarethekeycelltypeinthesecretionofOPG and RANKL and, therefore, orchestrate the bone turnover. Changes in the expression balance of this triad can be responsible for hereditary bone disorders, such as familiar expansile osteolysis, expansile skeletal hyperphosphatasia and juve- nile Paget’s disease; different forms of osteopo- rosis; and other metabolic bone diseases. The OPG/RANK/RANKL triad can be modu- lated bynumerous molecules, including melato- nin.22 Melatonin suppresses osteoclastic and osteoblastic activity by interacting with this triad.23 It reduces the expression of RANK in os- teoblasts24 and RANK receptor in osteoclasts19 while increasing OPG,24 eventually preventing the appearance and activation of osteoclasts.19 This suggeststhat melatonin in pharmacological doses can inhibit bone resorption and increase bone mass bydown-regulating RANK-mediated osteoclast proliferation and activation.24 Another important aspect ofthe relationship betweenosteoclastsandmelatoninconcernsthe production offree radicals by osteoclasts during osteolysis. Osteoclasts generate high levels of superoxide anions during bone resorption that contribute to the degenerative process of the organic bone matrix. One of the most important Fig. 1 Melatonin properties. Fig. 1 Pineal gland Secretion Scavenging of free radicals BIOLOGICAL ACTIONS ANTIOXIDANT AGENT BONE METABOLISM Anti-carcinogenic Immunostimulatory agent Sleep regulator Melatonin NEUTRALIZED Peroxyl radical Hydroxyl radical E f f e c t s o f m e l a t o n i n o n b o n e