Presentation: Peripheral Blood Leukocyte Gene Expression as Biomarkers of Disease in Knee Osteoarthritis (OA) (2007)

846 Peripheral Blood Leukocyte Gene Expression as Biomarkers of Disease in Knee Osteoarthritis (OA)

Purpose: OA is a degenerative joint disease affecting millions of people. The diarthrodial joint’s diseased tissues produce local low grade inflammation which eventually leads to chronic pain, loss of cartilage and function. Circulating blood cells are dynamic and act as sensors reflecting the status of disease in the body. In the current study we explored the possibilities of using transcriptome expression profiling of peripheral blood cells as biomarkers for detecting knee osteoarthritis.
Results: We recruited 24 controls and 45 OA patients. Peripheral Blood Mononuclear Cells (PBMCs) were isolated using a Ficoll gradient and were used for RNA isolation for gene expression profiling using the Affymetrix U133A chip, representing over 25,000 genes. From these we selected 17 controls and 19 OA patients, frequency-matched for sex, ethnicity, age, and BMI for further analysis. Raw data from array scans were normalized using the Affy package from Bioconductor (www.bioconductor.org) and analyzed further using R (www.r-project.org). Using three different methods for gene identification including the Significant Analysis of Microarrays (SAM) method, we identified a set of 175 genes which were significantly up- or down-regulated in OA PBMC at a False Discovery Rate (FDR) of 5% and with at least a 1.5 fold change. Among the most significant genes were junB, CDC42, Granulin, MMP-9 and cyclin D2. Using the method of cross-validation, we estimated that this gene expression pattern has sensitivity of 89% and specificity of 76%. Using cluster analysis, we found that our group of OA patients falls into two distinct classes, OA1 (overexpressors) and OA2, based on levels of cytokine expression such as IL-1β (up 6.56 fold), IL-8 (up 2 fold), COX-2 (up 2.75 fold), and chemokines GRO2 (up 5.37 fold), macrophage inflammatory protein 1-alpha (up 6 fold) and MIP-1beta (up 2.75 fold). The two groups of OA did not differ significantly with respect to the number of affected joints, pain scores, BMI and other demographic or clinical characteristics. The differential over-expression of these inflammatory genes (IL-1β and IL-8) in OA subgroups were further validated using TaqMan real time PCR and showed significance of p<0.02. These data clearly indicate that a subgroup of OA patients expressing elevated levels of cytokine genes may be at risk for osteoarthritis progression.
Conclusion: These findings reflect that PBMCs may act as sensors of the OA disease process in the microenvironment of knee joints. Circulating blood cell based transcriptome profiles may be used as diagnostic tools to predict OA disease activity and possibly predict risk for progression.

 S. Krasnokutsky, None; M. Attur, None; I. Belitskaya-Levy, None; J. Greenberg, None; J. Samuels, None; S. Smiles, None; S.H. Lee, None; J. Patel, None; H.E. Al-Mussawir, None; S.B. Abramson, None.