Materials and methods
Ninety-five (95) participants were recruited – 36 with schizophrenia,
27 with methamphetamine-induced psychosis, and 32 healthy controls
(Table 1). All participants underwent the Diagnostic and Statistical
Manual IV – Text Revision (DSM-IV-TR) Structured Clinical Interview For
DSM-IV-TR Axis I Disorders (SCID) to assess eligibility. Additional
clinical questionnaires were completed with all participants, which
include the Positive and Negative Syndrome Scale (PANSS), Clinical
Global Impressions scale (GGI), Global Assessment of Functioning scale
(GAF) and a subjective questionnaire on drug abuse, the
Kreek-McHugh-Schluger-Kellogg scale (KMSK). Participants were excluded
during screening for chronic medical illnesses known to affect metabolic
processes (e.g., hyper/hypo thyroidism, diabetes type I or II, etc.),
illnesses where the immune system is dysfunctional or compromised (e.g.,
HIV, lupus), major brain trauma, and intellectual disability.
Additionally, female participants were excluded if there was current or
recent pregnancy, or if they were breastfeeding. The study was approved
by the Human Research Ethics Committee, Faculty of Health Sciences of
the University of Cape Town – HREC Reference Number: 062/2017 and was
conducted in accordance with the Declaration of Helsinki .
Additional screening for MRI brain imaging for all participants included
ensuring that participants were not claustrophobic or had any form of
foreign material in their bodies which could interfere with the MRI
scanning process.
***Table 1***
All participants underwent magnetic resonance imaging on a Siemens Skyra
3 Tesla scanner with a 32-channel head coil. A high-resolution
Magnetization Prepared Rapid Acquisition Gradient Echo (MPRAGE)
structural image was acquired and was used for placement of single-voxel
spectroscopy (SVS) voxels located in the anterior cingulate cortex (ACC)
(Figure 1) and left thalamus (Figure 1) as well as chemical-shift
imaging (CSI) 2-dimensional voxel grid (Figure 2). Single voxel
spectroscopy (SVS) of the ACC and left thalamus were acquired for
standard metabolites (PRESS, TE = 30 ms, TR = 2000 ms, 128 averages,
delta = -2.6 ppm delta frequency, VOI 20 x 20 mm with a thickness of
15mm, scan time 4:40, with unsuppressed water MRS spectra for the same
volume, two averages were acquired). An additional SVS sequence was
acquired for the ACC, with parameters optimized for glutamate /
glutamine separation (Schubert et al., 2004). The parameters used for
this sequence were similar to that of the sequence for standard
metabolites, except for the echo time, which was increased to 80
milliseconds (PRESS, TE = 80 ms, TR = 2000 ms, 128 averages, delta =
-2.6 ppm delta frequency, VOI 20 x 20 mm with a thickness of 15mm, scan
time 8:56, with unsuppressed water MRS spectra for the same volume, two
averages were acquired). Partial volume correction was applied to SVS
voxels to obtain absolute neurometabolite concentrations. This was
achieved with combination of LCModel and MRSParVolCo software. The 2D
CSI 1H-MRS slice was acquired (PRESS, TE = 30 ms, TR=2000 ms, Hamming
filter, 2 averages, delta = -2.7 ppm delta frequency, weighted phase
encoding, FOV = 256 × 256 mm, voxel size 10 × 8 mm, thickness 15 mm,
automated CHESS water suppression, scan time 10:52). The slice was
positioned to include, bilaterally, the dorsolateral prefrontal cortex
(DLPFC), anterior cingulate cortex (ACC), frontal white matter (FWM)
located between the DLPFC and ACC. Neurometabolites examined were
glutamatergic neurometabolites (glutamate (Glu), glutamine (Gln) and
glutamate with glutamine (Glx)), neuroinflammatory neurometabolite
(myo-inositol (mI)) and neuronal integrity markers (n-acetyl-aspartate
(NAA), and n-acetyl aspartate with n-acetyl-aspartyl glutamate
(NAA+NAAG)). CSI neurometabolites are reported in relation to creatine
with phosphocreatine (Cr+PCr).
***Figure 1***