The effects of cobalt chromium upon macrophages.

The purpose of this study was to elucidate the mechanisms by which cobalt chromium particulate wear debris contribute to the aseptic loosening of total joint prostheses. Incubation of macrophages with cobalt chromium led to release of tumor necrosis factor-alpha (TNF-alpha) and prostaglandin E2 (PGE2), but did not lead to release of interleukin-1 beta (IL-1 beta) or interleukin 6 (IL-6). Exposure of macrophages cocultured with osteoblasts to cobalt chromium also led to significant release of TNF-alpha and PGE2, but did not lead to significant IL-6 or IL-1 beta production. The release of PGE2 in the coculture system was greater than that detected when macrophages were exposed to cobalt chromium without the osteoblast contribution. Exposure of radiolabeled calvaria to media from macrophages incubated with cobalt chromium in coculture with osteoblasts led to release of 45Ca. In contrast, exposure of radiolabeled calvaria to media from isolated macrophages incubated with these particles did not result in release of 45Ca. Exposure of macrophages to cobalt chromium was toxic, as reflected by release of the intracellular enzyme lactate dehydrogenase. Macrophages play a role in the initiation of bone resorption at the interface through the phagocytosis of cobalt chromium particles and subsequent release of TNF-alpha and PGE2. The presence of osteoblasts at the interface may be required for amplification of the inflammatory response and ultimately for bone resorption.

Effects of polyethylene on macrophages.

A system was developed to expose macrophages to polyethylene in vitro. Exposure of macrophages to these particles in isolation led to the release of tumor necrosis factor alpha and prostaglandin E2. Exposure of macrophages in co-culture with osteoblasts to polyethylene particles increased the release of prostaglandin E2 and also led to the release of interleukin-6. Incubation of radiolabelled calvariae with conditioned medium from macrophages exposed to polyethylene particles alone or to particles in co-culture with osteoblasts led to bone resorption reflected by release of 45Ca. Incubation with pamidronate was effective in inhibiting resorption stimulated by conditioned medium from macrophages exposed to these particles alone or in co-culture with osteoblasts. This demonstrates that pamidronate, or other bisphosphonates, may be effective in inhibiting bone resorption at the implant/bone interface in association with the macrophage response to particulate polyethylene. Further investigation into the possible use of pamidronate or other bis-phosphonates in the treatment of aseptic loosening is warranted.

Inflammatory response to implant particulates in a macrophage/osteoblast coculture model.

The purpose of this study was to further define the cellular response to titanium and polymethylmethacrylate (PMMA) particles in aseptic loosening, and to determine if the use of pamidronate may be effective in inhibiting bone resorption associated with this response. Macrophages and osteoblasts were cocultured to simulate the environment around an aseptically loose prosthesis. Macrophages were plated on the bottom of six well plates and osteoblasts were plated on culture dish inserts, and placed into the wells with the macrophages. Incubation of macrophages with PMMA in this system led to release of prostaglandin E (PGE2), granulocyte macrophage-colony stimulating factor (GM-CSF), and interleukin-6 (IL-6). Incubation with titanium led to release of tumor necrosis factor (TNF) and IL-6. Exposure of calvaria to media from cells exposed to either PMMA or titanium led to release of calcium 45. Incubation of calvaria with pamidronate was able to inhibit release of calcium 45 associated with exposure to the macrophage/osteoblast/particle conditioned medium. Bone resorption at the interface between implant and bone is a consistent feature leading to loosening of orthopedic implants. By inhibiting bone resorption associated with the inflammatory response to implant particulates, pamidronate or other bisphosphonates may have clinical utility in the treatment or prevention or aseptic loosening.

Surgical treatment of pathologic hip lesions in patients with metastatic disease.

Impending and pathologic fractures about the hip due to metastatic tumors are debilitating to patients secondary to pain and loss of mobility. The results of internal fixation of impending or complete pathologic fracture about the hip in 29 patients undergoing 32 procedures were retrospectively reviewed. Operative procedures included total hip arthroplasty with protrusio cup acetabular reconstruction in 5 patients, bipolar hip replacement in 7 patients, compression screw and sideplate in 6 patients, placement of reconstruction intramedullary nail in 12 patients, proximal femoral replacement in 1 patient, and placement of pins and polymethylmethacrylate in 1 patient. Every patient in this series had relief of pain postoperatively, and all had improved ambulation. There were no operative or anesthesia related complications, no intraoperative or perioperative deaths, an no failures of fixation. A single postoperative complication occurred in a patient in whom a sacral decubitus developed that resolved with local wound care. This study shows that operative fixation of pathologic hip lesions can be performed with low morbidity and mortality in a debilitated patient population with good results postoperatively.

In vitro studies on the role of titanium in aseptic loosening.

This study was designed to define the role titanium debris plays in aseptic loosening. Macrophages exposed to commercially pure titanium (1-3 microns) exhibit the same mediator profile as those exposed to polymethylmethacrylate. This response consists of increased release of tumor necrosis factor but not prostaglandin E 2 or interleukin-1. Osteoblasts increase production of prostaglandin E 2 when exposed to media from titanium stimulated macrophages but not interleukin-6 or granulocyte macrophage colony stimulating factor. Media from macrophages exposed to titanium did not lead to bone resorption, as measured by calcium 45 release, in organ culture. The cellular response to titanium is characterized by release of tumor necrosis factor from macrophages and prostaglandin E 2 from osteoblasts exposed to the macrophage conditioned medium. A comparison of the results of this study with those of others involving exposure of macrophages in tissue culture suggests that titanium may not be as inflammatory as other particles in the aseptically loose joint.

Detection of bony metastases of androgen-independent prostate cancer by PET-FDG.

Fourteen F-18 fluorodeoxyglucose (FDG) studies were carried out in 13 patients known to have bony metastases from carcinoma of the prostate. One patient was newly diagnosed. The remaining patients had various types of therapy and were considered hormonally resistant. The average age was 67. All patients had extensive bony metastases shown on the conventional Tc99m-MDP bone scans. Only about 18% of bony lesions apparent on the conventional bone scans showed corresponding increase of FDG uptake. Anatomical correlation was performed by using co-registered images of SPECT and PET in the same area. The positive FDG uptake was not related to the duration of illness, level of PSA, previous therapy, and magnitude of disease involvement. It appears that only a small percentage of bony metastases is associated with increased glycolysis. It is possible that other metabolic processes are more important than glycolysis for providing prostate cancer with a source of energy and nutrients.

Pharmacologic inhibition of particulate-induced bone resorption.

In this study, a rat calvaria/macrophage co-culture model was used to study the effects of various agents upon bone resorption induced by macrophage exposure to bone cement particles. The experimental group consisted of calvaria bone disks set in tissue culture medium on stainless-steel platforms into wells with macrophages adherent to the bottom which are exposed to the particles. Tumor necrosis factor alpha (TNF-alpha), prostaglandin E2 (PGE2), and calcium 45 (Ca45 were released in significant amounts in this system. Interleukin 1 alpha (IL-1 alpha) was not detected. Indomethacin inhibited the production of PGE2, but did not affect TNF release or inhibit the release of Ca45. Anti-TNF antibody neutralized the presence of TNF to undetectable levels, but did not affect PGE2 release or inhibit Ca45 release. The addition of calcitonin did not inhibit Ca45 release by calvaria. In contrast, the addition of disodium pamidronate, a member of the bisphosphonate family, was effective in inhibiting the release of Ca45 even after 96 h of incubation. In prior studies, incubation of calvaria in conditioned medium from macrophages exposed to cement particles led to resorption through a mechanism which is dependent upon TNF production by macrophages, and PGE2 production by cells in bone. In this two-way system, in which macrophages and cells in bone are allowed to interact, this dependency was no longer evident. Pamidronate was the only agent tested which suppressed the increase in bone resorption associated with macrophage exposure to bone cement particles to levels which were not significantly different from unexposed calvaria. By delaying or preventing bone resorption associated with macrophage exposure to bone cement particles, bisphosphonates may have a clinical role in cemented joint arthroplasty by decreasing the rate or incidence of aseptic loosening and prolonging implant longevity.

Role of tumor necrosis factor alpha in particulate-induced bone resorption.

The purpose of this study was to determine the role of tumor necrosis factor alpha in bone resorption secondary to mediator release from macrophages exposed to cement particles. The J774 mouse macrophage cell line was exposed to polymethylmethacrylate particles for 24 hours and the resulting conditioned medium was analyzed for prostaglandin E2, tumor necrosis factor alpha, interleukin-1 alpha and beta, and the ability to stimulate release of prostaglandin E2 and 45Ca from radiolabeled mouse calvaria. Macrophage exposure to polymethylmethacrylate particles led to a 9-fold increase in release of tumor necrosis factor alpha (p < 0.01), but did not lead to a significant increase in release of prostaglandin E2, interleukin-1 alpha, or interleukin-1 beta when compared to unexposed cells. Exposure of the macrophages to polymethylmethacrylate particles over a time course from 30 minutes to 96 hours led to an increase in the release of tumor necrosis factor alpha that was initially detected at 30 minutes and was maximum at 48 hours. Incubation of the macrophage-polymethylmethacrylate conditioned medium with rat calvaria significantly increased the release of 45Ca and prostaglandin E2 from the bone. To study the role of release of tumor necrosis factor alpha in bone resorption, the macrophage-polymethylmethacrylate conditioned medium was then preincubated with anti-tumor necrosis factor alpha antibody prior to exposure of the conditioned medium to the calvaria. This preincubation was successful in significantly inhibiting 45Ca release by calvaria (p <0.01) to levels that were not significantly different from the levels of release by unexposed calvaria. Tumor necrosis factor alpha appears to play a critical role in initiating particulate-induced bone resorption. Exposure of macrophages to polymethylmethacrylate particles leads to a significant release of tumor necrosis factor alpha in a time-dependent fashion. This macrophage-polymethylmethacrylate conditioned medium stimulated release of prostaglandin E2 and bone resorption in bone organ culture. The addition of anti-tumor necrosis factor alpha antibody to this in vitro system inhibited the bone resorption stimulated by the macrophage-polymethylmethacrylate conditioned medium and partially suppressed the production of prostaglandin E2. The sequence of events in this model for particulate-induced bone resorption appears to be initiated by the production of tumor necrosis factor alpha by the macrophage, followed by production of prostaglandin E2 by cells in bone, and then by bone resorption.

Mechanisms of cellular recruitment in aseptic loosening of prosthetic joint implants.

The association of macrophages engaged in polymethylmethacrylate (PMMA) particle phagocytosis with pockets of inflammatory cells is a pathognomonic feature of the aseptically loose interface not present at the well-fixed interface. The mechanism by which the presence of PMMA particles leads to cellular recruitment, bone resorption, and ultimate loosening is poorly understood. Granulocyte macrophage colony stimulating factor (GM-CSF) and interleukin 6 (IL-6), cytokines released by osteoblasts, stimulate the recruitment of macrophages into sites of inflammation. We show that exposure of macrophages to PMMA particles stimulated release of tumor necrosis factor (TNF), but no increase in prostaglandin E2 (PGE-2) or interleukin 1. Incubation of osteoblasts with conditioned medium from macrophages exposed to PMMA particles led to release of GM-CSF, IL-6, and PGE-2. Incubation of the PMMA/macrophage medium with antibodies to TNF prior to osteoblast exposure inhibited release of GM-CSF, IL-6, and PGE-2 by the osteoblasts. Our data demonstrate that exposure of macrophages to PMMA particles leads to the release of TNF which then stimulates osteoblasts to produce GM-CSF, IL-6 and PGE-2. Based upon the results of this study , we propose that the process of cellular recruitment in aseptic loosening is initiated when the mechanical failure of the cement mantle leads to the production of PMMA particles. These particles are phagocytized by macrophages leading to the production of TNF. TNF stimulates surrounding osteoblasts to produce GM-CSF, IL-6, and PGE-2 which leads to recruitment of macrophages and osteoclasts into the area of the bone-cement interface. The recruitment of these cells potentiates this process leading to bone resorption and ultimately, clinical loosening of prosthetic joint implants.

Polymethylmethacrylate-stimulated macrophages increase rat osteoclast precursor recruitment through their effect on osteoblasts in vitro.

An in vitro rat osteoclast precursor model was employed to study the role of macrophages in the osteolysis associated with aseptic loosening of cemented total joint replacements. Bone resorption at the bone-bone cement interface may involve the release of mediators by macrophages in response to phagocytosis of polymethylmethacrylate particles. Two potential pathways for the macrophage-directed bone resorption were studied. An indirect pathway was investigated in which the macrophage response to cement particles was used to stimulate rat osteosarcoma (ROS) 17/2.8 osteoblasts. Osteoblast-soluble factors then were added to osteoclast precursors. In the direct pathway, osteoclast precursors were exposed directly to macrophage-soluble factors released in response to phagocytosis of cement particles. Osteoclast precursors were identified after adherence to polished human dentin slices. Acid phosphatase-positive osteoclasts were counted using light microscopy at x200 magnification. In the indirect pathway, where the macrophage response was mediated through the rat osteosarcoma osteoblasts, a significant increase in the recruitment of osteoclast precursors was observed. In the direct pathway, when the macrophage-conditioned medium was allowed to interact directly with osteoclast precursors, the adherence of the precursors was significantly decreased. This demonstrates that the macrophage mediators released following phagocytosis of polymethylmethacrylate particles affect the release of soluble factors from osteoblasts. In turn, these osteoblast factors stimulate recruitment of osteoclast precursors to calcified tissue. Evidence from this in vitro model reveals that macrophage-soluble factors, in the absence of an osteoblast contribution, decrease the adherence of osteoclast precursors to calcified substrate. We propose that bone resorption at the aseptically loose interface of cemented arthroplasty may be mediated, at least in part, by soluble factors secreted by osteoblasts responding to macrophages that have phagocytosed particles of polymethylmethacrylate cement.

Mediator interactions in macrophage/particulate bone resorption.

The purpose of this study was to examine the mechanism by which mediators released from macrophages exposed to cement particles may interact with cells in bone to ultimately lead to bone resorption. Macrophages were exposed to cement particles, and then this conditioned medium was exposed to rat calvarial bones in vitro. The macrophage conditioned medium contained increased levels of tumor necrosis factor, but not interleukin 1 or prostaglandin E2. Exposure of this medium to the calvaria led to release of prostaglandin E2 by the calvaria, but not tumor necrosis factor or interleukin 1. Bone resorption was assessed by measuring the release of calcium 45 from the newborn rat calvarial bones. At 48, 72, and 96 h of incubation, the macrophage/cement particle-conditioned medium led to the release of both prostaglandin E2 and calcium 45 from the calvaria. To determine whether the release of calcium 45 was dependent on prostaglandin E2 production by the cells in bone, the calvaria were incubated with 600 ng/ml of indomethacin in addition to the macrophage-conditioned medium. The addition of indomethacin was effective in inhibiting both prostaglandin E2 and calcium 45 release from the calvaria, even after 96 h of exposure to the macrophage-conditioned medium. This study suggests that tumor necrosis factor produced in association with macrophage/cement particle osteolysis arises from macrophages and not cells in bone, and that prostaglandin E2 originates from cells in bone and not from macrophages. Interleukin 1 was not found to be produced by macrophages or bone, and appears to have a lesser role.(ABSTRACT TRUNCATED AT 250 WORDS)