Inhibitory effects ofγ-interferon on bradykinin-induced bone resorption and prostaglandin formation in cultured mouse calvarial bones

The effects of mouse recombinantγ-interferon (γ-IFN) and indomethacin on bone resorption stimulated by bradykinin, Lys-bradykinin, Met-Lys-bradykinin, des-Arg⁹-bradykinin and prostaglandin E₂ (PGE₂) have been studied using cultures of neonatal calvarial bones and analyzing the release of⁴⁵Ca from prelabelled bones as a paramenter of bone resorption. In addition, the effects ofγ-IFN and indomethacin on formation of PGE₂ in bone cultures stimulated by bradykinin was analyzed. Indomethacin (1 μmol/l) totally abolished bradykinin (1 μmol/l) induced⁴⁵Ca release. The inhibitory effect of indomethacin could be fully reversed by addition of PGE₂ (1 μmol/l).γ-IFN (1000 U/ml) almost totally inhibited⁴⁵Ca release stimulated by bradykinin (1 μmol/l), but the inhibitory effect could only be partially overcome by PGE₂.γ-IFN and indomethacin also inhibited the stimulatory effects of Lys-bradykinin, Met-Lys-bradykinin and des-Arg⁹-bradykinin (1 μmol/l) on⁴⁵Ca release. The stimulatory effects of PGE₂ (1 μmol/l) on radioactive calcium mobilization was partially inhibited byγ-IFN (1000 U/ml), whereas indomethacin (1 μmol/l) was without effect. The inhibitory effect ofγ-IFN on⁴⁵Ca release stimulated by bradykinin and PGE₂ was dose-dependent with threshold for action at 3–30 U/ml. Comparative dose-response curves showed thatγ-IFN was most potent as inhibitor of bradykinin induced⁴⁵Ca release. Bradykinin (1 μmol/l) significantly stimulated PGE₂ formation by a mechanism that was completely inhibited by indomethacin (1 μmol/l).γ-IFN (1000 U/ml) partially inhibited the stimulatory effect of bradykinin on PGE₂ formation. These data show that i)γ-IFN is a potent inhibitor of bone resorption induced by bradykinin and bradykinin analogues and ii) that the mechanism of action can be mainly explained by an inhibition of kinin induced prostaglandin biosynthesis. The results, however, also show thatγ-IFN can inhibit bone resorption by mechanisms unrelated to prostaglandin formation.