Serum adenosine deaminase activity and its isoenzyme pattern in patients with systemic lupus erythematosus

To study the correlation between serum adenosine deaminase (ADA) activity and clinical activity in patients with systemic lupus erythematosus (SLE). The patterns of two ADA isoenzymes, ADA1 and ADA2, were also analysed in healthy controls and patients to determine the source of increased ADA activity in patients.

Total serum ADA activity (tADA) was measured spectrophotometrically. The isoenzyme pattern of ADA was analysed by the HPLC method using a specific inhibitor of ADA1, erytro-9-(2-hydroxy-3-nonyl)adenine (EHNA). Disease activity was assessed using the European Consensus Lupus Activity Measurement index (ECLAM).

Serum tADA activity was significantly increased in patients compared to healthy controls (mean +/- SD; 476.9 +/- 145.3 vs 254.0 +/- 98.9 ncat/L, p < 0.001). The isoenzyme analyses showed that the increased total ADA activity in the patients was mainly due to increased ADA2 activity (371.3 +/- 154.8 vs 214.2 +/- 47.9 ncat/L in healthy controls, p < 0.001). The mean values for ADA1 activity in the patients (64.6 +/- 37.9 ncat/L) and healthy controls (69.2 +/- 26.9 ncat/L) were similar. A strong correlation was found between serum ADA activity and disease activity as measured by ECLAM (Spearman's rank correlation coefficient 0.74, p < 0.0001, linear regression coefficient 0.68, p < 0.01).

Serum ADA activity is closely associated with SLE activity and appears to be useful as a new disease activity parameter of SLE.