Abstract
Introduction: UHMWPE wear particles induce osteolysis and loosening of total joint replacements. Much effort has been directed at reducing the wear volume of UHMWPE, such as crosslinking treatments [1]. Recently, interest in UHMWPE with vitamin E (VE) has increased due to its improved wear resistance in knee prostheses [2], as well as improved mechanical properties. The aim of this study was to culture human peripheral blood mononuclear cells (PBMNCs) with known volumes of clinically relevant wear debris from UHMWPE with and without VE in order to quantify and compare their respective biological activities.
Methods: For UHMWPE with VE, GUR1050 UHMWPE powder was mixed with VE at 0.3% (w/w) and 3% (w/w) using a screw cone mixer. The wear rates were evaluated using a six-station multidirectional pin on plate wear simulator against a smooth CoCr plate (Ra 0.01–0.03 micrometres), in 25% bovine serum, under a load of 160N and a frequency of 1 Hz. Endotoxin-free clinically relevant wear debris was generated aseptically for cell culture studies, using a single-station multidirectional pin on plate wear rig housed in a class II safety cabinet. PBMNCs were isolated from blood collected from three healthy donors then cultured with debris at particle volume (μm3) to cell number ratios of 100:1 using the agarose gel technique [3]. Cells without particles were used as the negative control, and LPS at 200 ng/ml was the positive control. Cell viability was assessed by ATP-Lite assay, and TNF-alpha, interleukin (IL)-1beta, IL-6 and IL-8 were measured by ELISA at 12 and 24 h.
Results: The 3% VE UHMWPE was found to have a higher wear rate than both the Virgin and the 0.3% VE UHMWPE, although there were no significant differences. Particle size and volume distributions were similar for all materials, with the mode of the frequency distributions being in the 0.1–1 micron size range. Cell viability was not adversely affected by any of the treatments. Cells cultured with virgin UHMWPE debris secreted significantly higher quantities (P< 0.05) of TNF-alpha compared to debris from both the 0.3% and the 3% VE UHMWPE, which released comparable levels of TNF-alpha to the cell only control group. The results for the other cytokines, IL-1beta, IL-6 and IL-8, and for the two additional donors showed similar trends as the results for TNF-alpha.
Discussion: The biological response to wear particles is strongly influenced by particle size and volume [3]. Cells cultured with wear debris of UHMWPE containing VE released very low levels of cytokines in comparison with virgin UHMWPE, even there were no significant differences in particle size. Differences in the chemical composition of the particles or different rates of protein adsorption may explain these differences. VE has anti-inflammatory properties, which may act by free radical scavenging. VE has been shown to reduce production of reactive oxygen species and pro-inflammatory cytokines such as TNF-alpha and IL-1beta from monocytes [4]. The anti-inflammatory effects of UHMWPE particles containing VE are currently being investigated.
Correspondence should be addressed to Miss B.E. Scammell at the Division of Orthopaedic & Accident Surgery, Queen’s Medical Centre, Nottingham, NG7 2UH, England
References
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