Correlation of Serum Levels of Adenosine Deaminase Activity and Its Isoenzymes with Disease Activity in Rheumatoid Arthritis

Objective: Adenosine deaminase (ADA) is involved in purine metabolism and plays a significant role in the mechanisms of the immune system. The aim of this study was to investigate the correlation between the activity of total ADA (tADA) and isoenzymes ADA1 and ADA2 and clinical activity in patients with rheumatoid arthritis (RA).

Methods: The study comprised 37 patients with rheumatoid arthritis and 30 healthy controls. Total serum ADA activity was measured spectrophotometrically. The isoenzyme pattern of ADA was analyzed using erytro-9-(2-hydroxy-3-nonyl) adenine (EHNA). Disease activity was assessed using DAS criterion.

Results: The means of tADA, ADA1 and ADA2 levels were found to be 22.7 +/- 5.9, 3.9 +/- 2.0 and 18.8 +/- 4.9 IU/L in patients with RA, and 15.1 +/- 4.4, 4.1 +/- 1.2 and 11.0 +/- 3.7 IU/L in healthy control subjects. When compared to the healthy controls, serum tADA and ADA2 levels were significantly higher (p < 0.001) in patients with RA, but the decrease of ADA1 level was not statistically significant (p > 0.05). There was a strong correlation (r = 0.527, p < 0.001) between serum tADA level and disease activity by DAS (Pearson's rank correlation), and no correlation between tADA and CRP or ESR in the patient groups (p > 0.05).

Conclusion: Serum tADA and ADA2 activity is closely associated with RA and these non-invasive investigations can be used as biochemical markers for inflammation. These may provide additional information regarding disease activity along with the traditional indices such as ESR and CRP.