The Role Of Nitric Oxide On The Proliferation Of Human Osteoblasts (Hos Cells) Stimulated With Hydroxyapatite

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Date
2006-04
Authors
SUGIATNO, ERWAN
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Abstract
Hydroxyapatite (HA) as a ceramic material is widely used for orthopaedic and dental implants, since this biomaterial has ability to stimulate osteoblast functions in vitro and in vivo. However, the exact mechanism by which HA accelerates osteoblast function, thereby stimulating rapid bone formation, remains far from clear. It is well known that bone formation is tightly regulated by nitric oxide (NO) via its effects on osteoblast and osteoclast function. Therefore, the overall aim of the present studies was to elucidate the possible regulation of NO in HA-stimulated HOS cell proliferation. The present study used a human osteoblast cell line (HOS cells), since this cell line is known to mimic the functions of normal human osteoblasts, thereby representing the biological response of normal osteoblasts in humans. The first experiments were carried out to delineate whether HA-stimulated HOS cell proliferation is regulated by endogenous NO. The results showed that following contact with HA, elevated NO production and HOS cell proliferation were observed. Exogenous L-arginine further promoted HA-stimulated osteoblast NO production and proliferation. Furthermore, cell proliferation and NO production by HA-stimulated HOS cells in the presence of anti-human integrin a V antibody were reduced. Similarly reduction of cell proliferation and NO production by HA-stimulated HOS cells was observed when the cells were incubated with eNOS, but not nNOSand iNOS, inhibitor. Deletion of NO production by a NO scavenger resulted in suppressed HA-stimulated osteoblast proliferation. The effect of exogenous NO on HA-stimulated HOS cell proliferation was then determined. The results showed that exogenous NO up to 20 )lM enhances HAxv sumUlatea tlu:s cell prOllteration. lhe ettect ot exogenous NU on HA-stimulated HUS cell proliferation was abolished by the presence of NO scavenger but only partially reduced by eNOS inhibitor. The effect of exogenous NO on HA-stimulated HOS cells proliferation was also reduced when the cells were pre-treated with anti-human integrin aVantibody. The next experiments were to determine whether the regulation of NO on HAstimulated HOS cell proliferation was via its ability to enhance prostaglandin E2 (PGE2) production. The results showed that the production of PGE2 by HA-stimulated HOS cells was augmented by exogenous NO. The presence of NO scavenger suppressed the production of PGE2 by HA-stimulated HOS cells with or without the presence of exogenous NO. The presence of eNOS inhibitor only partially suppressed the production of PGE2 by HA-stimulated HOS cells with or without the presence of exogenous NO. Again, the production of this prostaglandin by HA-stimulated HOS cells with or without the presence of NO was reduced when the HOS cells were pretreated with anti-human integrin aV antibody. The production of this prostaglandin and cell proliferation by HA-stimulated HOS cells with or without the presence of NO was reduced when the HOS cells were pre-treated with indomethacin (a COX-l and COX-2 inhibitor) or nimesulide (a COX-2 inhibitor) but not aspirin (a COX-l inhibitor), suggesting COX2-mediated PGE2 synthesis. HA-stimulated cell proliferation with or without the presence of NO was also decreased, when HOS cells were pre-coated with anti-human EP4 receptor antibody.
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The Role Of Nitric Oxide On The Proliferation Of Human Osteoblasts , Stimulated With Hydroxyapatite
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