Background and purpose: Oxidative stress biomarkers are increased in multiple sclerosis (MS) lesions. Antioxidant defense enzymes regulate reactive oxygen species that can cause tissue injury in MS.

Methods: The study of 91 subjects included 64 relapsing-remitting MS (RR-MS; 72% female, baseline age ± SD = 44.6 ± 11 years, disease duration = 13.3 ± 8.8 years, median Expanded Disability Status Scale [EDSS] = 2.0, interquartile range = 1.8) and 27 healthy controls (HC) at baseline and 5-year follow-up (5YFU). Serum glutathione peroxidase (GPX), glutathione-S-transferase (GST), glutathione reductase (GSHR), superoxide dismutase, and paraoxonase-1 (PON1) arylesterase and paraoxonase activities were measured using kinetic enzyme assays. Total cholesterol (TC), high-density lipoprotein cholesterol, low-density lipoprotein cholesterol (LDL-C), and an apolipoprotein (Apo) panel with ApoA-I, ApoA-II, ApoB, ApoC-II, and ApoE were obtained. Serum neurofilament (sNfL) was used to assess axonal injury. Disability was measured on the EDSS.

Results: GSHR activity was lower in HC compared to RR-MS at baseline and 5YFU. GPX (p = 0.008) and PON1 arylesterase and paraoxonase activities (both p = 0.05) increased between baseline and 5YFU in HC but did not increase in RR-MS. At baseline and 5YFU, GPX and GST were associated with TC, LDL-C, and ApoA-II; GSHR was associated with ApoA-II and ApoC-II. Antioxidant enzymes were not associated with sNfL or EDSS in RR-MS.

Conclusions: RR-MS patients did not exhibit the changes in antioxidant enzyme activities over 5YFU found in HC; however, the differences were modest. Antioxidant enzyme activities are not associated with disability.