Anti-inflammatory drug-eluting implant model system to prevent wear particle-induced periprosthetic osteolysis

Abstract

Background: Aseptic loosening, as a consequence of an extended inflammatory reaction induced by wear particles, has been classified as one of the most common complications of total joint replacement (TJR). Despite its high incidence, no therapeutical approach has yet been found to prevent aseptic loosening, leaving revision as only effective treatment. The local delivery of anti-inflammatory drugs to modulate wear-induced inflammation has been regarded as a potential therapeutical approach to prevent aseptic-loosening.

Methods: In this context, we developed and characterized anti-inflammatory drug-eluting TiO₂ surfaces, using nanoparticles as a model for larger surfaces. The eluting surfaces were obtained by conjugating dexamethasone to carboxyl-functionalized TiO₂ particles, obtained by using either silane agents with amino or mercapto moieties.

Results: Zeta potential measurements, thermogravimetric analysis (TGA) and drug release results suggest that dexamethasone was successfully loaded onto the TiO₂ particles. Release was pH dependent and greater amounts of drug were observed from amino route functionalized surfaces. The model-system was then tested for its cytotoxic and anti-inflammatory properties in LPS-stimulated macrophages. Dexamethasone released from amino route functionalized surfaces TiO₂ particles was able to decrease LPS-induced nitric oxide (NO) and TNF-a production similarly to pure DEX at the same concentration; DEX released from mercapto route functionalized surfaces was at a too low concentration to be effective.

Conclusion: Dexamethasone released from amino functionalized titanium can offer the possibility of preventing asepting loosening of joint replacement devices.

Keywords: TJR; aseptic loosening; dexamethasone; implant; macrophages; titanium.

Figure 1

Detailed schemes of chemical reactions for dexamethasone-TiO₂ particles: 1) silane functionalization, followed by 2) carboxyl functionalization, and then 3) dexamethasone attachment, for amino and mercapto routes. Functional groups on TiO₂ particle surface are highlighted with blue color.

Figure 2

Examples of transmission electron microscopy images of different surface-modified TiO₂ particles: (A) TiO₂ particles, (B) amino-functionalized, (C) succinylated amino-functionalized, and (D) DEX-loaded TiO₂ particles. Bar represents 100 nm.

Figure 3

Zeta potentials of different surface-modified TiO₂ nanoparticle suspensions at different pH values for amino (A) route: TiO₂ bare NP (−); amino-functionalized TiO₂-NH₂ (−); succinylated amino-functionalized TiO₂-COOH (−); DEX conjugated to succinylated amino-functionalized TiO₂-COOH (−); and for mercapto (B) route: TiO₂ bare NP (−); mercapto-functionalized TiO₂-SH (−); carboxyl mercapto-functionalized TiO₂-COOH (−); DEX conjugated to succinylated mercapto-functionalized TiO₂-COOH (−). Abbreviations: DEX, dexamethasone; NP, nanoparticle.

Figure 4

Thermograms of different surface-modified TiO₂ particles prepared through amino (A) and mercapto route (B).

Figure 5

FTIR spectra of TiO₂ bare NP (−); amino-functionalized TiO₂-NH₂ (−); succinylated amino-functionalized TiO₂-COOH (−); DEX conjugated to succinylated amino-functionalized TiO₂-COOH (−); mercapto-functionalized TiO₂-SH (−); carboxyl mercapto-functionalized TiO₂-COOH (−); DEX conjugated to succinylated mercapto-functionalized TiO₂-COOH (−). Abbreviations: DEX, dexamethasone; FTIR, Fourier-transformed infrared; NP, nanoparticle.

Figure 6

Cumulative release of dexamethasone from TiO₂ particles obtained via amino route (A) and mercapto route (B) under different pH conditions.

Figure 7

Effect of DEX on cell viability of LPS-activated RAW 264.7. Notes: Cells were exposed to DEX (3.9 µg/mL) either from filtered broth collected after the first 24 hours of release (black columns) or DEX-P for 18, 24, 48, and 72 hours (light gray columns). Cellular viability was assessed by MTT assay, and 10% PBS buffer was used as positive control (dark gray columns). Abbreviations: DEX-P, dexamethasone phosphate; LPS, lipopolysaccharide.

Figure 8

Effect of DEX on NO production (percentage to NO in LPS-only control) of LPS-activated RAW 264.7. Notes: Cells were exposed to DEX (3.9 µg/mL) from filtered broth collected after the first 24 hours of release (black columns) or DEX-P (DEX equivalent 3.9 µg/mL) (gray columns) for 18, 24, 48, and 72 hours. Culture supernatants were collected and analyzed by Griess reagent. Abbreviations: DEX-P, dexamethasone phosphate; LPS, lipopolysaccharide; NO, nitric oxide.

Figure 9

Effect of DEX on TNF-a production (percentage to TNF-a in LPS-only control) of LPS-activated RAW 264.7 macrophages. Notes: Cells were exposed to DEX (3.9 µg/mL) from filtered broth collected after the first 24 hours (black columns) of release or DEX-P (DEX equivalent 3.9 µg/mL) (gray columns) for 18, 24, 48, and 72 hours. Abbreviations: DEX-P, dexamethasone phosphate; LPS, lipopolysaccharide; TNF-a, tumor necrosis factor-a.