Plasma thiol/disulphide homeostasis changes in patients with restless legs syndrome

Objectives: Restless legs syndrome (RLS) is a common neurological condition. Oxidative stress plays an important role in its pathogenesis. Thiol-disulphide homeostasis (TDH) is a new biomarker of oxidative stress. We studied plasma TDH to determine whether TDH could be used as a new biomarker for RLS and evaluated correlations between TDH and various disease severity rating scales. Methods: A total of 25 RLS patients and 25 healthy controls were included into the study. TDH status was determined using an automated spectrophotometric analysis method and correlations were analyzed between the TDH status and various disease rating scales in the RLS patients. Results: Plasma total (401 +/- 27 mu mol/L) and native thiol (354 +/- 30 mu mol/L) levels were significantly lower, but disulphide level (24 +/- 6 itmol/L) was significantly (<0.0001) higher in the RLS patients compared to the controls (455 +/- 36, 424 +/- 37, 15 +/- 5 mu mol/L, respectively). The disulphide/native thiol and disulphide/total thiol ratios increased, in contrast, native thiol/total thiol ratio decreased significantly in the RLS patients compared to the healthy controls (<0.0001). The disulphide levels correlated positively with age and various rating scores of the RLS patients. International Restless Legs Syndrome Study Group (IRL SSG) rating score and age correlated negatively with the total and native thiol levels. Conclusions: Our findings indicate increased oxidative stress in the RLS patients reflected by decreased native and total thiol, and increased disulphide levels and positive correlations between the disulphide levels and various rating scores. We suggest dynamic TDH status to be used as a novel biomarker for the diagnosis and follow-up of the RLS patients.