High-Dose N-Acetyl Cysteine Associated With Reduced GFAP Levels in Phase 2 Progressive MS Study

A phase 2 trial (NCT02804594) recently published in the Multiple Sclerosis Journal reported that 4 weeks of high-dose oral N-acetyl cysteine (NAC) was associated with a significant decrease in serum glial fibrillary acidic protein (GFAP) levels in adults with progressive multiple sclerosis (MS), whereas neurofilament light chain (NfL) levels remained stable in both treatment arms.¹ The findings add to a growing body of evidence that oxidative stress may be a tractable target in the biology of disability progression independent of relapse activity.

Although 4-week intervention may have been too brief to capture any clinical effect on disability, the authors were careful to frame the biomarker results as hypothesis-generating. The differential trajectory of GFAP, a marker of astrocytic damage shown in prior work to be elevated by approximately 50% in patients experiencing progression independent of relapse activity (PIRA) compared with stable patients with MS, may carry mechanistic relevance for clinicians managing patients with primary or secondary progressive disease.

Study Overview

Senior author Emmanuelle Waubant, MD, PhD, professor of neurology at University of California, San Francisco (UCSF), and colleagues conducted the phase 2, randomized, double-blind, placebo-controlled pilot trial at the UCSF. Eligible participants were adults aged 18 to 75 years with a diagnosis of progressive MS, at least 1 year since progressive symptom onset, a Modified Fatigue Impact Scale score greater than 38, and an Expanded Disability Status Scale score of 2.0 to 6.5. Fifteen participants were randomized 2:1 to receive NAC 1250 mg 3 times daily or matching placebo for 4 weeks, with 1 participant in the placebo arm not providing blood samples, resulting in a final analytic sample of 10 patients in the NAC group and 4 in the placebo group.

Serum biomarkers were measured at baseline and week 4 using the Olink proximity extension assay, a multi-protein platform validated for use in MS populations. An a priori defined set of 20 proteins was evaluated, including NfL, GFAP, myelin oligodendrocyte glycoprotein (MOG), and interleukin-12 subunit beta (IL-12B). Changes from baseline to week 4 were compared between arms using the Wilcoxon rank-sum test; a permutation-based ANCOVA was performed as a sensitivity analysis to adjust for age imbalance between groups.

Key Findings

All told, GFAP levels declined in the NAC arm while rising in the placebo arm over the 4-week period (median change: −10.1 pg/mL vs. 39.5 pg/mL, respectively; P = .008). This difference survived age adjustment and was the primary statistically significant finding of the study. NfL levels, reflecting neuro-axonal damage, were stable and did not differ meaningfully between groups (median change: 0.25 pg/mL vs. 0.61 pg/mL; P = .777).

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MOG, a marker of myelin injury, trended toward a reduction in the NAC arm that reached nominal significance after age adjustment (median change: 0.15 pg/mL vs. 4.8 pg/mL; unadjusted P = .106; age-adjusted P = .057). IL-12B, a proposed surrogate marker of NAC's direct cellular effect, and soluble CD6 each showed directional differences that approached but did not cross the significance threshold (P = 0.054, for both).

Clinical Context

Progressive MS represents a substantial unmet need. Current disease-modifying therapies exert modest effects on PIRA, and no approved agent is specifically indicated to address the noninflammatory mechanisms, including oxidative stress, metabolic failure, and chronic demyelination, that are thought to drive disability accumulation in progressive MS.^1,2

Prior to this study, glutathione, a principal intrinsic antioxidant, has been shown to be decreased in the gray matter of MS patients relative to healthy controls by MRI spectroscopy. NAC is a precursor to glutathione synthesis, directly scavenges reactive oxygen species, and penetrates the blood-brain barrier at high oral doses, providing mechanistic rationale for its investigation in progressive disease.^3,4

Interpretation

The reduction in GFAP observed with NAC is consistent with prior post-mortem and biomarker evidence suggesting that astrocytic and oligodendroglial injury, rather than neuro-axonal loss, may be the earlier or more prominent event at the margins of slowly expanding lesions in PMS.¹ The combination of declining GFAP alongside stable NfL could reflect a biologically plausible partial attenuation of astrocytic damage before downstream axonal injury occurs. The trend toward IL-12B suppression is also consistent with prior experimental evidence that thiol antioxidants inhibit IL-12 assembly in activated myeloid cells, suggesting a potential anti-inflammatory dimension to NAC's mechanism in this context.

Limitations and Future Research

The trial enrolled only 15 participants, with 4 completing the placebo arm following one dropout, a sample size that substantially limits the precision and generalizability of all findings. The 4-week duration precludes any assessment of clinical outcomes or durable biomarker effects. Baseline age differed between arms, necessitating sensitivity analyses. Since this was an exploratory study, outcomes were not adjusted for multiple comparisons.

The ongoing NACPMS trial (NCT05122559), a phase 2 randomized, double-blind, placebo-controlled add-on trial with a larger sample and longer follow-up, is designed to provide more definitive evidence regarding NAC's neuroprotective potential in progressive MS.⁵ That trial could be better positioned to assess whether the biomarker changes observed here translate into measurable effects on disability progression.

REFERENCES
1. Schoeps VA, Murataj R, Virupakshaiah A, et al. High-dose N-acetyl cysteine reduces GFAP levels: Exploratory results from a pilot double-blind, placebo-controlled randomized trial. Mult Scler J. 2026. doi:10.1177/13524585261454840
2. Mendiola AS, Ryu JK, Bardehle S, et al. Transcriptional profiling and therapeutic targeting of oxidative stress in neuroinflammation. Nat Immunol. 2020;21:513–524.
3. Choi IY, Lee P, Adany P, et al. In vivo evidence of oxidative stress in brains of patients with progressive multiple sclerosis. Mult Scler. 2018;24(8):1029–1038.
4. Krysko KM, Bischof A, Nourbakhsh B, et al. A pilot study of oxidative pathways in MS fatigue: Randomized trial of N-acetyl cysteine. Ann Clin Transl Neurol. 2021;8(4):811–824.
5. Meier S, Willemse EAJ, Schaedelin S, et al. Serum glial fibrillary acidic protein compared with neurofilament light chain as a biomarker for disease progression in multiple sclerosis. JAMA Neurol. 2023;80:287–297.