Nitric oxide release by macrophages in response to particulate wear debris Arun S. Shanbhag, William Macaulay, Maja Stefanovic-Racic, Harry E. Rubash Musculoskeletal Research Center, Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania 15213 Received 2 June 1997; accepted 21 January 1998 Abstract: At the interface between a prosthetic implant and bone, macrophage interaction with particulate wear de- bris is a key event in the initiation of localized bone resorp- tion, leading to aseptic loosening of the prostheses. Numer- ous investigators have reported that macrophages release a variety of cytokines and mediators including tumor necrosis factor, interleukin-1, prostaglandin E 2 , and interleukin-6 when they are stimulated with particulate wear debris. In this study, we have demonstrated that macrophages stimu- lated with particulate debris are also capable of releasing in copious amounts a key inflammatory chemical, nitric oxide. This release of nitric oxide was dependent upon the period of culture and the type and dosage of the challenging par- ticles. Titanium-alloy particles were the most stimulatory, followed by commercially pure titanium and polymethyl- methacrylate. While the role of nitric oxide in osteolysis is not clearly understood, the literature suggests that it may be a key mediator in inhibiting DNA synthesis, in cell prolif- eration, and in stimulating PGE 2 release. This finding en- hances our understanding of the sequence of events occur- ring at the bone–implant interface during wear debris– mediated osteolysis, and exposes potential avenues to interrupt this sequence. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 497–503, 1998. Key words: nitric oxide; cell–particle interactions; titanium alloy; polymethylmethacrylate; osteolysis; aseptic loosening; wear debris INTRODUCTION Aseptic loosening with associated periprosthetic bone resorption is currently the leading cause of fail- ure of total hip replacements (THR). 1–4 The com- ponents retrieved during revision surgery are surrounded by a granulomatous tissue consisting of macrophages and foreign-body giant cells with phagocytized wear debris. 5–8 Willert and Semlitsch 9 were among the first to suggest that macrophages stimulated by wear debris initiated an inflammatory cascade which leads to granulomatous tissue replac- ing periprosthetic bone and eventually resulting in component loosening. To confirm this hypothesis, sev- eral investigators have demonstrated that macro- phages and peripheral blood monocytes, when stimu- lated in vitro with wear debris, release significant amounts of inflammatory mediators such as interleu- kin-1 (IL-1), IL-1, IL-6, prostaglandin E 2 (PGE 2 ), collagenase, and tumor necrosis factor- (TNF-). 10–14 Many of these proinflammatory mediators are in- volved in various aspects of osteoclast maturation and are capable of stimulating bone resorption. 15–17 We suggest that nitric oxide may also be a key mediator in particle disease. Nitric oxide is a small molecule synthesized from the amino acid L-arginine by a family of enzymes called the nitric oxide synthases (NOS). 18–20 Nitric ox- ide has gained importance because it is a multifunc- tional and intercellular messenger that participates in a variety of physiological processes. 19,21 For instance, nitric oxide in the vascular endothelium is responsible for the regulation of blood pressure and the control of platelet aggregation, and may also regulate cardiac muscle contractility. 18,19 In the central nervous system, nitric oxide is a neurotransmitter involved in memory and motor function. 22 In the peripheral nervous sys- tem, nitric oxide is involved in the modulation of re- laxation of the gastrointestinal tract and bladder. Mac- rophages and peripheral blood monocytes also release nitric oxide during host defense and immunological reactions. 20 Nitric oxide can be elicited from macro- phages activated by either cell wall lipopolysaccharide (endotoxin) or inflammatory mediators such as IL-1 Correspondence to: A. S. Shanbhag; 1126 GRJ, Massachu- setts General Hospital, Harvard Medical School, 55 Fruit St, Boston, MA 02114; e-mail: shanbhag@helix.mgh. harvard.edu Contract grant sponsor: Ferguson Foundation for Ortho- paedic Research Contract grant sponsor: University of Pittsburgh Medical Center © 1998 John Wiley & Sons, Inc. CCC 0021-9304/98/030497-07