HAPTOGLOBIN-STIMULATED BONE-RESORPTION IN NEONATAL MOUSE CALVARIAL BONES INVITRO

Objective. To study the in vitro effects of human haptoglobin (Hp) on bone resorption and prostanoid formation. Methods. Parietal bones were dissected out from neonatal mice that had been injected with Ca-45, and were cultured in chemically defined medium with or without test substances. Bone resorption was assessed by analysis of Ca-45 release. Prostanoid formation was quantified by analysis of the amount of prostaglandin E2 (PGE2) in culture medium. Results. Hp phenotype 2-1, in quantities greater-than-or-equal-to 0.17 mg/ml, stimulated the release of Ca-45 and the biosynthesis of PGE2, in a time- and dose-dependent manner. Hp-induced PGE2 formation was abolished by indomethacin and flurbiprofen, whereas the stimulation of Ca-45 release was only partially reduced. Conclusion. These observations suggest that the acute-phase reactant Hp may contribute, by a humoral mechanism, to the bone resorption seen in chronic inflammatory processes.