Emerging ideas: can erythromycin reduce the risk of aseptic loosening?

Osteoblastic differentiation and bactericidal activity are enhanced by erythromycin released from PCL/PLGA-PVA coaxial nanofibers

Prosthesis with antibiotic-eluting nanofibrous (NF) coating represents coating alternative to prevent periprosthetic joint infection (PJI). In this study, four formulas of erythromycin (EM)-embedded both in core and sheath components of coaxial PCL/PLGA-PVA NF coatings were developed: EM 0 (no EM), EM 100 (100 μg/mL), EM500 (500 μg/mL) and EM1000 (1000 μg/mL). EM doping altered the physicochemical and structural properties of NFs to some extent, including the increase of NF porosity and surface wettability. A sustained EM release from EM-NFs for >4 weeks was observed. Eluents collected from EM-NFs showed strong zone of inhibition (ZOI) to Staphylococcus aureus growth and the sizes of ZOI positively related to the amount of EM released. EM-NFs were nontoxic to rat bone marrow stem cells (rBMSCs). Cell growth was significantly enhanced when comparing rBMSCs cultured on EM-NFs (EM0 and EM 100) to those cultured on NF-free control. Cell differentiation (ALP activity) was notably enhanced by EM100, compared to control and EM0. Eluents from EM-NFs on rBMSCs were also investigated. The presence of 10% EM-NF eluents inhibited the growth of rBMSCs, which was proportional to the amount of EM doped. The ALP activity was notably enhanced by eluents from EM-NFs with the highest activity in EM100 compared to control and EM0. Our data indicate that EM-doped PCL/PLGA-PVA coaxial NF coatings have a great potential to be applied as a new implant coating matrices. Further in vivo testing in animal models is currently planned that should represent the first step in predicting the clinical outcomes of EM-eluting NF coating approach.

Properties of erythromycin-loaded polymeric dicalcium phosphate dehydrate bone graft substitute

A self-setting, injectable polymeric dicalcium phosphate dehydrate bone graft substitute that is mechanically strong and has excellent cohesion was developed. We assessed the performance of erythromycin-loaded polymeric dicalcium phosphate dehydrate cement. Its properties include drug release, growth inhibition against Staphylococcus aureus and biocompatibility with osteoblastic MC3T3 cells. The impact of erythromycin loading on cement injectability, setting time, and mechanical strength were also evaluated. A sustained, low burst release of erythromycin was observed. Eluents collected from erythromycin-loaded cement showed a considerable zone of inhibition for up to 28 days. Direct contact of erythromycin-loaded cement discs with agar plate showed a similarly sizable zone of inhibition for up to 22 days. Degraded ceramic residues had strong zones of inhibition as well. While the erythromycin-loaded cement was injectable, a notable delay of the setting time was observed (49.2 ± 6.8 min) as compared with control (drug-free cement, 12.2 ± 2.6 min). A slight increase in compressive strength (60.83 ± 6.28 MPa) was observed in erythromycin-loaded cement as compared with control (59.41 ± 6.48 MPa). Erythromycin-loaded cement was biocompatible although reduced cell growth was observed in the presence of the cement eluent. We propose that the bactericidal efficacy of erythromycin-loaded cement was caused by the combined effects of erythromycin released and exposed on the contact surface of degrading ceramics. Our data may elucidate the future application of polymeric dicalcium phosphate dehydrate bone graft substitute for the treatment of orthopedic infections and opportunities to use other antibiotics and applications considering its comparable handling and mechanical strength to poly (methyl methacrylate) cements.

Apoptotic pathways of macrophages within osteolytic interface membrane in periprosthestic osteolysis after total hip replacement

Macrophage apoptosis in interface membrane, which occurs through either death receptor, mitochondrion, or endoplasmic reticulum (ER) stress pathways, has been suggested to play an important role in promoting osteolysis. However, how and why macrophage apoptosis originates and the correlation among these apoptotic pathways is not yet clear. The objective of this study was to identify the apoptotic mechanism of macrophages, and to explore the relationship between the apoptotic pathways and progression of osteolysis. Transmission electron microscopy (TEM) was utilized to analyze the tissue ultrastructure of wear particles, and in situ apoptotic macrophage identification was performed by TUNEL staining. We analyzed the expression of the key biomarkers of apoptotic pathways via immunohistochemistry and Western blotting. Our results demonstrated that the majority of wear particles within osteolytic interface membrane was in the 30-60 nm range, and that macrophage apoptotic ratio increased along with osteolysis progression. Normal hip dysplasia and mechanical loosening of tissues showed low expression levels of biomarkers for ER stress (Ca²⁺ , JNK, cleaved Caspase-4, IRE1-α, Grp78/Bip, and CHOP), mitochondrion (Bcl-2, Bax, and Cytochrome c), and death receptor (Fas and cleaved Caspase-8) pathways, while osteolytic interface membrane tissues expressed high levels of these biomarkers. In addition, we found that the ER stress intensity was in complete conformity with mitochondrial dysfunction and was consistent with the results of death receptor activation. Thus, our findings suggested that wear particles generated at implant interface can accelerate macrophage apoptosis through changes in apoptotic pathways and ultimately aggravate the symptom of osteolysis. These data represent a preferential apoptotic signaling pathway of macrophages as specific target points for the prevention and therapeutic modulation of periprosthetic osteolysis.