Inflammatory changes associated with periarticular pure gold bead implants were studied in dogs involved in a clinical trial investigating motor dysfunction and chronic pain owing to hip joint dysplasia and osteoarthritis. Gold beads were percutaneously implanted via a needle into different locations surrounding the greater trochanter of the femur. Nine dogs with implants were necropsied. In all examined animals, characteristic histologic lesions were observed in the tissue surrounding the gold implants-namely, a fibrous capsule composed of concentric fibroblasts intermixed with a variable number of inflammatory cells and a paucicellular innermost layer of collagen with a few fibrocyte-like cells in empty lacunae. Lymphocytes dominated the inflammatory infiltrate, with rarely observed macrophages present in close proximity to the implant site. No giant cells were observed. Immunohistochemistry showed mixed populations of lymphocytes, both CD3 positive (T cells) and CD79a positive (B cells), which in some cases formed lymphoid follicles. Diffuse inflammatory changes were present to a minor extent in the perimysium and surrounding fascia. The inflammation observed in dogs is similar to that observed with gold implants in humans. It is possible that the clinically beneficial effect of gold beads for chronic osteoarthritis depends on sustained localized inflammation with localized release of soluble mediators. The encapsulation of the implant by a paucicellular and poorly vascularized fibrous capsule may help prevent an exaggerated inflammatory reaction by sequestering the gold bead from the surrounding tissue.
Keywords
B cells, dogs, gold implants, immunohistochemistry, inflammation, osteoarthritis, T cellsThe parenteral therapeutic use of gold salts (chrysotherapy) is well known in human medicine and has been used in cases of rheumatoid arthritis. 23 The mechanisms behind the anti-inflammatory effect of monovalent gold salts and its metabolites, such as Au 3þ , Au(CN) 2 -, and metallic gold, is incompletely understood.5 One proposed mechanism of action for Au þ is due to binding with thiolate and thioether ligands on proteins.5 This is thought to inhibit presentation of complexed antigen to T cells, activity of certain transcription factors, and enzymes such as protein tyrosine phosphatase in T cells, protein kinase C in neutrophils and T cells, and proteins important for B cell differentiation. Au(CN) 2 -is an effective inhibitor of the respiratory burst of neutrophils and monocytes; it also inhibits the proliferation of lymphocytes.
5A more recent therapeutic application of gold is the implantation of gold beads directly into a painful anatomic region, such as the periarticular tissue of arthritic joints. This technique is derived from acupuncture and has been used in veterinary medicine for the past decade, largely as a treatment in canine hip dysplasia.10 A recent double-blind, placebocontrolled clinical trial performed by Jaeger et al showed that the performance of dogs with hip joint osteoarthritis s...