In vitro activation of human fibroblasts by retrieved titanium alloy wear debris

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Abstract
Titanium-aluminum-vanadium wear particles isolated from the soft-tissue membrane of a failed total hip arthroplasty were added to human fibroblasts in cell culture. The cellular response to particle challenge was determined by assaying for levels of interleukin-1β, interleukin-6, tumor necrosis factor-α, prostaglandin E2, basic fibroblast growth factor, platelet-derived growth factor-AB, and transforming growth factor-β. Collagenase and gelatinase activities were analyzed by zymography and [3H]collagen degradation. Cell viability was assessed by measuring the uptake of [3H]thymidine. Over the range of particle concentrations tested, cell viability, as demonstrated by [3H]thymidine uptake, remained unaffected. Fibroblasts exhibited a dose-dependent release of interleukin-6 in response to exposure to titanium-aluminum-vanadium particles. At 6 and 48 hours, the highest concentration of titanium alloy particles (0.189% [vol/vol]) resulted in 7-fold and 16-fold increases in interleukin-6 release, respectively, when compared with negative controls. Neither interleukin-1β nor tumor necrosis factor-α was detected in the culture medium at any particle concentration tested for both dermal and foreskin fibroblasts. The pattern of prostaglandin E2 release by fibroblasts mirrored the pattern of interleukin-6 release. Fibroblasts exposed to the highest concentration of titanium alloy particles showed an increase in collagenase activity, starting at 12 hours. When medium samples were treated with amino phenylmercuric acetate to activate latent enzymes, a statistically significant increase in collagenase activity was observed as early as 6 hours (p < 0.001). Substrate gel analysis of medium from fibroblasts stimulated by high particle concentrations also showed an increase in gelatinolytic activity when compared with unstimulated controls. Analysis of medium samples for growth factors showed an increase in basic fibroblast growth factor at low particle concentrations, beginning at 12 hours. Levels of platelet-derived growth factor-AB and transforming growth factor-β were not detectable in the controls or at any particle concentration tested. The results of this study showed that fibroblasts exposed to titanium alloy wear particles become activated and release proinflammatory mediators that influence bone metabolism. These data support the hypothesis that direct activation of fibroblasts by particulate wear may play a role in particle-mediated osteolysis. Fibroblast activation coupled with the biologic response of macrophages to wear debris in the loosening membrane may have a synergistic effect on pathologic bone resorption.