GlyCEST: Magnetic Resonance Imaging of Glycine—Distribution in the Normal Murine Brain and Alterations in 5xFAD Mice

The glycine level in the brain is known to be altered in neuropsychiatric disorders, such as schizophrenia and Alzheimer’s disease (AD). Several studies have reported the in vivo measurement of glycine concentrations in the brain using proton magnetic resonance spectroscopy (1H-MRS), but 1H-MRS is not capable of imaging the distribution of glycine concentration with high spatial resolution. Chemical exchange saturation transfer magnetic resonance imaging (CEST-MRI) is a new technology that can detect specific molecules, including amino acids, in tissues. To validate the measurements of glycine concentrations in living tissues using CEST from glycine to water (GlyCEST), we extracted the brain tissues from mice and performed biochemical tests. In wild-type C57BL/6 mice, GlyCEST effects were found to be higher in the thalamus than in the cerebral cortex ( P < 0.0001 , paired t-test), and this result was in good agreement with the biochemical results. In 5xFAD mice, an animal model of AD, GlyCEST measurements demonstrated that glycine concentrations in the cerebral cortex ( P < 0.05 , unpaired t-test) and thalamus ( P < 0.0001 , unpaired t-test), but not in the hippocampus, were decreased compared to those in wild-type mice. These findings suggest that we have successfully applied the CEST-MRI technique to map the distribution of glycine concentrations in the murine brain. The present method also captured the changes in cerebral glycine concentrations in mice with AD. Imaging the distribution of glycine concentrations in the brain can be useful in investigating and elucidating the pathological mechanisms of neuropsychiatric disorders.

Elevation of cell-associated HIV-1 RNA transcripts in CSF CD4+ T cells, despite suppressive antiretroviral therapy, is linked to in vivo brain injury

Objective Despite effective antiretroviral therapy (ART), brain injury remains prevalent in people living with HIV-1 infection (PLHIV) possibly due to ART lacking direct inhibition of transcription with continued local production of viral transcripts and neurotoxic proteins, such as Tat, rather than cell-free whole virion toxicity. We quantified cell-associated (CA) HIV-1 RNA-transcripts in CSF and blood, in relation to proton Magnetic Resonance Spectroscopy (1H MRS) of major brain metabolites, in well characterised PLHIV. Methods RNA was extracted from cells in 16 paired samples of CSF and blood, from PLHIV on fully suppressive ART. HIV-1 CA-RNA copies were measured using the highly sensitive Double-R assay and normalized /million CD4+ T cells. 18-colour flow cytometry was used to count and analyse CD4+ T cells and monocytes in CSF and blood. The concentrations of major brain metabolites from 1H MRS in frontal white matter (FWM), posterior cingulate cortex (PCC), and caudate areas were measured. Brain injury in each voxel was defined using a composite score derived by principal component analysis. Results 14/16 CSF cell samples had quantifiable HIV-1 CA-RNA transcripts, at levels significantly higher than in their PBMCs (median 9,266 vs 185 copies /106 CD4+ T cells; p<0.0001). Higher levels of CSF transcripts were associated with greater brain injury in the FWM (Std beta=-0.73; p=0.007) and PCC (Std beta=-0.61; p=0.03). CSF cells were 91% memory T cells, equally CD4+ (median 3,605) cells and CD8+ T cells (3,632), but contained much fewer B cells (0.4 %), NK cells (2.0%) and monocytes (3.1%; 378 cells; >90% CD14+CD16+ phenotype). CXCR3+CD49d+integrin beta7-negative, CCR5+ CD4+ T cells were significantly enriched in CSF, compared with PBMC (p <0.001). Transcriptional activity in CSF cells was highly correlated with levels of transcriptional activity in CD4+ T cells in PBMC (r=0.76; p=0.002). In contrast, HIV-1 RNA in highly purified monocytes from PBMC was detected in only 6/16 samples. Conclusions Elevated HIV-1 transcripts in CSF cells were associated with in vivo brain injury, despite suppressive ART. The cellular source is most likely the predominant CXCR3+ CD49d+ integrin beta7- CCR5+ memory CD4+ T cells, not monocytes. Inhibitors of transcription to reduce local production of potentially neurotoxic proteins, should be developed.

Minority Stress and the Effects on Emotion Processing in Transgender Men and Cisgender People: A Study Combining fMRI and Proton Magnetic Resonance Spectroscopy ( 1H-MRS)

Background Minority stress via discrimination, stigmatization, and exposure to violence can lead to development of mood and anxiety disorders and underlying neurobiochemical changes. To date, the neural and neurochemical correlates of emotion processing in transgender people (and their interaction) are unknown. Methods This study combined functional magnetic resonance imaging (fMRI) and magnetic resonance spectroscopy ( 1H-MRS) to uncover the effects of anxiety and perceived stress on the neural and neurochemical substrates, specifically Choline, on emotion processing in transgender men. Thirty transgender men (TM), 30 cisgender men (CM), and 35 cisgender women (CW) passively viewed angry, neutral, happy, and surprise faces in the fMRI scanner, underwent a 1H-MRS scan and filled out mood and anxiety related questionnaires. Results As predicted, Choline levels modulated the relationship between anxiety and stress symptoms and the neural response to angry and surprise (but not happy faces) in the amygdala. This was only the case for TM but not cisgender comparisons. More generally, neural responses in the left amygdala, left middle frontal gyrus, and medial frontal gyrus to emotional faces in TM resembled that of CW. Conclusions These results provide first evidence of a critical interaction between levels of analysis and that Choline may influence neural processing of emotion in individuals prone to minority stress.

Schizophrenia Increases Variability of the Central Antioxidant System: A Meta-Analysis of Variance From MRS Studies of Glutathione

Patients with schizophrenia diverge in their clinical trajectories. Such diverge outcomes may result from the resilience provided by antioxidant response system centered on glutathione (GSH). Proton Magnetic Resonance Spectroscopy (1H-MRS) has enabled the precise in vivo measurement of intracortical GSH; but individual studies report highly variable results even when GSH levels are measured from the same brain region. This inconsistency could be due to the presence of distinct subgroups of schizophrenia with varying GSH-levels. At present, we do not know if schizophrenia increases the interindividual variability of intracortical GSH relative to matched healthy individuals. We reviewed all 1H-MRS GSH studies in schizophrenia focused on the Anterior Cingulate Cortex published until August 2021. We estimated the relative variability of ACC GSH levels in patients compared to control groups using the variability ratio (VR) and coefficient of variation ratio (CVR). The presence of schizophrenia significantly increases the variability of intracortical GSH in the ACC (logVR = 0.12; 95% CI: 0.03–0.21; log CVR = 0.15; 95% CI = 0.06–0.23). Insofar as increased within-group variability (heterogeneity) could result from the existence of subtypes, our results call for a careful examination of intracortical GSH distribution in schizophrenia to seek redox-deficient and redox-sufficient subgroups. An increase in GSH variability among patients also indicate that the within-group predictability of adaptive response to oxidative stress may be lower in schizophrenia. Uncovering the origins of this illness-related reduction in the redox system stability may provide novel treatment targets in schizophrenia.

Comparison of seven modelling algorithms for GABA-edited 1H-MRS

Edited MRS sequences are widely used for studying GABA in the human brain. Several algorithms are available for modelling these data, deriving metabolite concentration estimates through peak fitting or a linear combination of basis spectra. The present study compares seven such algorithms, using data obtained in a large multi-site study. GABA-edited (GABA+, TE = 68 ms MEGA-PRESS) data from 222 subjects at 20 sites were processed via a standardised pipeline, before modelling with FSL-MRS, Gannet, AMARES, QUEST, LCModel, Osprey and Tarquin, using standardised vendor-specific basis sets (for GE, Philips and Siemens) where appropriate. After referencing metabolite estimates (to water or creatine), systematic differences in scale were observed between datasets acquired on different vendors' hardware, presenting across algorithms. Scale differences across algorithms were also observed. Using the correlation between metabolite estimates and voxel tissue fraction as a benchmark, most algorithms were found to be similarly effective in detecting differences in GABA+. An inter-class correlation across all algorithms showed single-rater consistency for GABA+ estimates of around 0.38, indicating moderate agreement. Upon inclusion of a basis set component explicitly modelling the macromolecule signal underlying the observed 3.0 ppm GABA peaks, single-rater consistency improved to 0.44. Correlation between discrete pairs of algorithms varied, and was concerningly weak in some cases. Our findings highlight the need for consensus on appropriate modelling parameters across different algorithms, and for detailed reporting of the parameters adopted in individual studies to ensure reproducibility and meaningful comparison of outcomes between different studies.

Molecular neuroimaging of inflammation in HIV

People-with-HIV now have near-normal life expectancies due to the success of effective combination antiretroviral therapy (cART). Following cART initiation, immune recovery occurs, and opportunistic diseases become rare. Despite this, high rates of non-infectious comorbidities persist in treated people-with-HIV, hypothesised to be related to persistent immuno-activation. One such comorbidity is cognitive impairment, which may partly be driven by ongoing neuro-inflammation in otherwise effectively-treated people-with-HIV. In order to develop therapeutic interventions to address neuro-inflammation in effectively-treated people-with-HIV, a deeper understanding of the pathogenic mechanisms driving persistent neuro-inflammatory responses and the ability to better characterise and measure neuro-inflammation in the central nervous system is required. This review highlights recent advances in molecular neuroimaging techniques which have the potential to assess neuro-inflammatory responses within the central nervous system in HIV-disease. Proton magnetic resonance spectroscopy ( 1H-MRS) has been utilised to assess neuro-inflammatory responses since early in the HIV pandemic and shows promise in recent studies assessing different antiretroviral regimens. 1H-MRS is widely available in both resource-rich and some resource-constrained settings and is relatively inexpensive. Brain positron emission tomography (PET) imaging using Translocator Protein (TSPO) radioligands is a rapidly evolving field; newer TSPO-radioligands have lower signal-to-noise ratio and have the potential to localise neuro-inflammation within the brain in people-with-HIV. As HIV therapeutics evolve, people-with-HIV continue to age and develop age-related comorbidities including cognitive disorders. The use of novel neuroimaging modalities in the field is likely to advance in order to rapidly assess novel therapeutic interventions and may play a role in future clinical assessments.

The trajectory of putative astroglial dysfunction in first episode schizophrenia: a longitudinal 7-Tesla MRS study

Myo-inositol is mainly found in astroglia and its levels has been shown to be reduced in the anterior cingulate cortex (ACC) of patients with schizophrenia. We investigate the status of astroglial integrity indexed by ACC myo-inositol at the onset and over the first 6 months of treatment of first episode schizophrenia. We employed 7 T magnetic resonance spectroscopy (1H-MRS) and quantified myo-inositol spectra at the dorsal ACC in 31 participants; 21 patients with schizophrenia with median lifetime antipsychotic exposure of less than 3 days, followed up after 6 months of treatment, and 10 healthy subjects scanned twice over the same period. We studied the time by group interaction for myo-inositol after adjusting for gender and age. We report significant reduction in myo-inositol concentration in the ACC in schizophrenia at an early, untreated state of acute illness that becomes insignificant over time, after instituting early intervention. This trajectory indicates that dynamic astroglial changes are likely to operate in the early stages of schizophrenia. MRS myo-inositol may be a critical marker of amelioration of active psychosis in early stages of schizophrenia.

BIOM-14. METABOLIC BIOMARKERS OF TERT-TARGETED THERAPY FOR HUMAN GLIOBLASTOMA DETECTED BY MAGNETIC RESONANCE SPECTROSCOPY

BACKGROUND TERT promoter mutations that result in TERT expression are observed in over 80% of GBM. Moreover, the upstream transcription factor GABPB1 was recently identified as an ideal therapeutic target for tumors with TERT promoter mutations. In that context, non-invasive reliable biomarkers that can help detect TERT expression are needed. The aim of this research was to assess the value of MRS-detectable metabolic changes as biomarkers of TERT expression and TERT-targeted therapy in GBM. METHODS Genetically engineered GBM cells (NHARas/TERT) treated with TERT siRNA were compared to siCtrl-treated cells, and stable TERT and GABPB1 knock down GBM cells (U251, GBM1) were compared to shCtrl. 1H-MRS and 13C-MRS metabolic data was acquired from cell extracts using a Bruker 500MHz scanner. Hyperpolarized MRS studies of live cells used a HyperSense DNP polarizer and data was acquired using a Varian 500MHz scanner. Spectra were analyzed using Mnova and Matlab software. Multivariate data analysis was performed using SIMCA software. RESULTS Unbiased PCA analysis of 1H-MRS metabolic data showed separation of TERT or GABPB1 knock down and control cells. VIP predictive scores revealed that lactate and GSH were the top altered metabolites with a significant drop observed in both metabolites in every model following TERT silencing. Consistent with the reduction in GSH, spectrophotometric assays showed a significant drop in NADPH and NADH. 2-13C glucose flux analysis revealed that both glycolysis and PPP-related metabolites were reduced in TERT knock down cells. Hyperpolarized [1-13C]-pyruvate flux to lactate was also reduced, confirming that the glycolytic pathway was altered following TERT knock down. CONCLUSION 1H MRS-detectable lactate and GSH, combined with hyperpolarized 13C MRS-detectable metabolic fluxes, could serve as metabolic biomarkers of TERT-targeted therapy for human GBM with TERT promoter mutations. These biomarkers could be translated to the clinical, improve the monitoring of GBM patients and advance precision medicine.