Altered thiol pattern in plasma of subjects affected by rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease which involves the synovial membrane of multiple diarthroidal joints causing damage to cartilage and bones. The damage process seems to be related to an overproduction of oxygen reactive species inducing an oxidative perturbation. Since sulfhydryl groups are primary antioxidant factors, we were interested in investigating the balance of plasma sulfhydryl/disulfides in patients with active RA compared to healthy control subjects.

Twenty-one patients with RA and 15 age-matched controls were studied. Plasmatic sulfhydryl groups and their disulfide form concentrations were measured by spectrophotometry or HPLC.

RA patients showed significantly lower levels of plasma protein sulfhydryls and cysteinyl-glycine compared to healthy controls (p < 0.001). Conversely, cystine and homocystine, and protein-bound cysteine and homocysteine were significantly increased (p < 0.005 in disulfides forms and p < 0.05 in protein mixed disulfides forms). There was a significant correlation between some clinical data (ESR, number of tender/swollen joints) and some of the parameters studied.

The results of this study indicate a biochemical disturbance of plasma sulfhydryl/disulfides balance in patients with RA compared to controls with an increase in some oxidised forms (disulfides and protein mixed disulfides) and a decrease in free thiols. The increase in total homocysteine, correlated to the higher risk of cardiovascular diseases in RA patients, is associated with higher levels of the oxidised forms, disulfides and protein-thiol mixed disulfides.