Increasing evidence points to a critical involvement of oxidative stress in schizophrenia pathophysiology. Redox dysregulation, related to various mechanisms including disruption of glutathione (GSH) metabolism, may represent one hub on which converge various causal genetic and environmental risk factors during neurodevelopment, leading to structural and functional connectivity impairments¹. GSH serves as a major cellular redox regulator and antioxidant protecting cell from damages induced by reactive oxygen species. GSH deficits have been reported in cerebro-spinal fluid and medial prefrontal cortex of chronic patients². Therefore, boosting GSH levels by N-acetylcysteine (NAC), an orally bioavailable antioxidant and precursor of GSH, was hypothesized to be a neuroprotective treatment for schizophrenia. Indeed, adjunctive treatment of NAC increases plasma glutathione levels, improves negative symptoms³, mismatch negativity⁴ and EEG local synchronisation⁵ and reduces standard medication side effects. However, the effect of NAC administration on brain GSH levels has never been reported. It remains unclear whether the beneficial effects reported following add-on NAC treatment can be attributed to its postulated ability to elevate cortical GSH levels or to some other mechanism⁶. Moreover, in the previous study of glutathione-deficient schizophrenia mouse model, NAC treatment also lead to neurochemical changes including glutamate(Glu), glutamine(Gln), Gln/Glu and myo-inositol (Ins)⁷. Therefore, the aim of this study was to investigate whether the supplementation of NAC to standard medication has an impact on cerebral GSH levels and other metabolites in early psychosis (EP) patients using in vivo ¹H MRS.

24 early psychosis patients (demographic details are shown in table 1.), who met the threshold criteria for psychosis according to Comprehensive Assessment of at Risk Mental States Scale (CAARMS) participated in this study, gave informed consent prior to the study. This study was a double blind randomized controlled trial comparing NAC (2.7g/day) and placebo as an add-on therapy to standard medication (antipsychotic, mood stabilizers and/or benzodiazepine) for a period of 6 months. All subjects underwent MRS measurement visit at baseline (V1) and 6 months after NAC/placebo uptake (V2). NAC and matching placebo was provided by BioAdvantex Pharma Inc. (Mississauga, Ontario, Canada).

All MRS measurements were performed on a 3T Trio MR scanner (Siemens Medical Solutions, Erlangen, Germany) with a TEM volume coil. B₀ field inhomogeneity was optimized using first- and second-order shimming with FAST(EST)MAP. ¹H MR spectra were obtained in the voxel located in medial prefrontal cortex (mPFC) using the SPECIAL⁸ localization sequence (TE/TR=6/4000ms, VOI=20×20×25mm³, 148 averages). Metabolite concentrations were quantified with LCModel⁹ using unsuppressed water MR spectra as an internal reference. mPFC GSH, Glu, Gln, Gln/Glu and Ins levels of V1 and V2 were compared using paired t-test (two-tailed).

A representative ¹H MR spectrum of mPFC in patients and the corresponding spectral fits are shown in Figure 1. Spectral SNR and linewidth (LCModel output) were 42 ± 8, 0.038 ± 0.011ppm for V1 and 41 ± 9, 0.038 ± 0.010ppm for V2, respectively. No significant differences (paired t-test) in spectral quality (i.e. SNR and linewidth) between V1 and V2 were observed. mPFC GSH levels were well quantified with a CRLB of 11.5 ± 4.3%. A significant increase (p=0.0007) of mPFC GSH levels was observed at V2 in patients taking NAC, however such increase was absent in placebo group (Figure 2). No significant differences were observed in mPFC Glu, Gln, Gln/Glu and Ins between V1 and V2 in both placebo and NAC group.The matched spectral quality is a prerequisite for the detection of GSH alterations between groups at 3T using short TE MRS. This requirement was well satisfied in this study. Reports on the ability of NAC to cross blood-brain barrier are controversial¹⁰. This double-blind randomized controlled study validated for the first time the elevation of cerebral GSH levels in vivo using 6 months adjunctive oral administration of NAC in early psychosis patients, suggesting a good blood-brain barrier permeability with oral administration of NAC. The effect of NAC on other metabolites was not observed in the current EP patients cohort, implying that either NAC does not have normalization effect or the administration stage is already too late, i.e. all neurological alterations are not reversible. Indeed, NAC normalized most neurochemical alterations of animal models to wild-type levels at the prepubertal ages⁷. Therefore, the further investigation in young at-risk subjects may prove the beneficial treatment effect of NAC for schizophrenia.