The relationship between osteoclastogenic and anti-osteoclastogenic pro-inflammatory cytokines differs in human osteoporotic and osteoarthritic bone tissues

Background: Pro-inflammatory cytokines possess osteoclastogenic or anti-osteoclastogenic activities. They influence osteoclasts directly or via the receptor activator of nuclear factor kappa B (RANK), RANK ligand (RANKL) and osteoprotegerin (OPG) system. Recent evidence suggests that inflammation may play a role in osteoporosis (OP) and osteoarthritis (OA). We aimed therefore to determine whether there is a difference between both groups: first, in the expression of the osteoclastogenic and anti-osteoclastogenic cytokines, second, in correlation of these cytokines with bone mineral density (BMD) and levels of bone turnover markers (BTM) and third, in correlation between the expression of these cytokines and osteoclast specific genes and RANK/RANKL/OPG genes. Methods: Human bone samples from 54 age and sex matched patients with OP or OA were collected during hip arthroplasty surgery. The expression of 25 genes encoding pro-inflammatory cytokines, their receptors, osteoclast specific genes and RANK/RANKL/OPG genes was measured using quantitative real-time PCR. Total hip, femoral neck and lumbar spine BMD and BTM in blood samples were measured. The comparison between OP and OA was assessed using Student's t-test or Mann-Whitney U test and correlations between gene expression, BMD and BTM were determined using nonparametric correlation. Results: The results demonstrated a higher expression of interleukin (IL)-6 and IL-1 alpha in OP, and interferon (IFN)-gamma in OA (p < 0.0005). Negative correlations of total hip BMD with tumor necrosis factor-alpha (TNF-alpha) in OA and with RANKL/RANK in OP were found (p < 0.05). Significant correlations with BTM were shown for IL-1 alpha and IFN-gamma in OP (rho = 0.608 and -0.634) and for TNF-alpha, IL-6 and transforming growth factor-beta 1 (TGF-beta 1) in OA (rho = 0.591, -0.521 and 0.636). Results showed OP specific negative correlations (IFN-gamma with ITGB3, IFN-beta 1 with CTSK, tartrate resistant acid phosphatase (TRAP), CALCR, RANK, RANKL, IL-1 alpha with CTSK, OPG, IL-17A with CALCR) and positive (TGF-beta 1 with CTSK, TRAP, RANK), and OA specific negative (IL-1 alpha with osteoclast associated immunoglobulin-like receptor (OSCAR), TNF-alpha with RANK, RANKL, OPG) and positive (IL-6 with RANK, RANKL, OPG) correlations. Conclusions: Our results demonstrate that the relationship between osteoclastogenic and anti-osteoclastogenic pro-inflammatory cytokines differs in human OP and OA bone and could present an important factor for characteristics of OP and OA bone phenotypes.