In order to understand the intracellular signaling pathway involving the c-fos gene expression that is caused by Titanium-particles, we analyzed the involvement of Rac, cytosolic phospholipase A2, and eicosanoids (e.g. leukotriene B4 and prostaglandin E2) as well as c-fos.

We tested whether or not Titanium-particles activate a c-fos serum response element in Rat-2 fibroblasts. To measure the activity of the c-fos serum response element, we analyzed the serum response element using a luciferase reporter system. The luciferase activity was measured using a scintillation spectrophotometer. Next, we analyzed the involvement of Rac and the eicosanoid synthesis mechanisms which are downstream mediators of Rac in the c-fos serum response element activation cascade.

Titanium-particles cause an activation of the c-fos serum response element and this activation was selectively repressed by RacN17 and by pretreatment of the inhibitors of cytosolic phospholipase A2, cyclooxygenase or 5-lipoxygenase. Eicosanoid synthesis was increased in a Rac-dependent manner in response to the presence of Titanium- particles.

'Rac, a member of G-protein, which is involved in the eicosanoid synthesis' may play a critical role in the Titanium-induced signaling cascade. Thus, we speculated that the 'Rac-cytosolic phospholipase A2-eicosanoids-c-fos cascade' may be a possible mechanism that produces eicosanoid synthesis caused by Titanium-particles in the periprosthetic osteolytic process.