Association of Cathepsin K and Tartrate- Resistant Acid Phosphatase-5b in Different Stages of Rheumatoid Arthritis Patients in South Indian Population

The aim of the study was to identify effective biomarkers of changes in bone mineral density (BMD) at different stages of rheumatoid arthritis patients from South Indian population, using disease activity score in 28 joints (DAS28) which is being used as a measurement for assessing disease activity in patients with rheumatoid arthritis. The study was carried out in 92 rheumatoid arthritis patients. Serum level of tartrateresistant acid phosphatase-5b (TRAP-5b) and cathepsin K was measured using ELISA. Serum rheumatoid factor (RF) and C-reactive protein (CRP) was recorded by the attending rheumatologists. The C-reactive protein (CRP) was quantified using a latex immunoturbidimetric method. The rheumatoid arthritis (RA) was measured by turbidimetric immunoassay method. The bone mineral density (BMD) T-score was calculated according to WHO guidelines. Reverse transcription PCR (RT-PCR) was used to determine the expression of cathepsin K. The rheumatoid arthritis (RA) patients were categorized into three groups based on the DAS28 score as inactive (DAS ≤ 3.2), moderately active (DAS > 3.2 ≤ 5.1) and very active (DAS > 5.1) at the time of admission. Out of 92 patients, 16 (17.4%) patients had inactive disease condition, 42 (45.6%) patients had moderately active disease condition and 34 (37%) patients had very active disease condition. The mean BMD was significantly lower in very active (0.28 ± 0.04; p < 0.001) as compared with moderately active (0.71 ± 0.13; p < 0.001) and inactive (1.21 ± 0.14). TRAP5b and cathepsin K showed significant increases in very active group (p < 0.001) as compared with moderately active (p < 0.001) and inactive groups. In conclusion, The biomarker TRAP-5b and cathepsin K identified in this study may become a new and highly specific biomarker for rheumatoid arthritis