Striatal neurometabolite levels in patients with schizophrenia undergoing long-term antipsychotic treatment: A proton magnetic resonance spectroscopy and reliability study

Meta-analysis and open-source database for in vivo brain Magnetic Resonance spectroscopy in health and disease

Proton (1H) Magnetic Resonance Spectroscopy (MRS) is a non-invasive tool capable of quantifying brain metabolite concentrations in vivo. Prioritization of standardization and accessibility in the field has led to the development of universal pulse sequences, methodological consensus recommendations, and the development of open-source analysis software packages. One on-going challenge is methodological validation with ground-truth data. As ground-truths are rarely available for in vivo measurements, data simulations have become an important tool. The diverse literature of metabolite measurements has made it challenging to define ranges to be used within simulations. Especially for the development of deep learning and machine learning algorithms, simulations must be able to produce accurate spectra capturing all the nuances of in vivo data. Therefore, we sought to determine the physiological ranges and relaxation rates of brain metabolites which can be used both in data simulations and as reference estimates. Using the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, we've identified relevant MRS research articles and created an open-source database containing methods, results, and other article information as a resource. Using this database, expectation values and ranges for metabolite concentrations and T2 relaxation times are established based upon a meta-analyses of healthy and diseased brains.

Meta-analytic evidence of elevated choline, reduced N-acetylaspartate, and normal creatine in schizophrenia and their moderation by measurement quality, echo time, and medication status

BACKGROUND

Brain metabolite abnormalities measured with magnetic resonance spectroscopy (MRS) provide insight into pathological processes in schizophrenia. Prior meta-analyses have not yet answered important questions about the influence of clinical and technical factors on neurometabolite abnormalities and brain region differences. To address these gaps, we performed an updated meta-analysis of N-acetylaspartate (NAA), choline, and creatine levels in patients with schizophrenia and assessed the moderating effects of medication status, echo time, measurement quality, and other factors.

METHODS

We searched citations from three earlier meta-analyses and the PubMed database after the most recent meta-analysis to identify studies for screening. In total, 113 publications reporting 366 regional metabolite datasets met our inclusion criteria and reported findings in medial prefrontal cortex (MPFC), dorsolateral prefrontal cortex, frontal white matter, hippocampus, thalamus, and basal ganglia from a total of 4445 patient and 3944 control observations.

RESULTS

Patients with schizophrenia had reduced NAA in five of the six brain regions, with a statistically significant sparing of the basal ganglia. Patients had elevated choline in the basal ganglia and both prefrontal cortical regions. Patient creatine levels were normal in all six regions. In some regions, the NAA and choline differences were greater in studies enrolling predominantly medicated patients compared to studies enrolling predominantly unmedicated patients. Patient NAA levels were more reduced in hippocampus and frontal white matter in studies using longer echo times than those using shorter echo times. MPFC choline and NAA abnormalities were greater in studies reporting better metabolite measurement quality.

CONCLUSIONS

Choline is elevated in the basal ganglia and prefrontal cortical regions, suggesting regionally increased membrane turnover or glial activation in schizophrenia. The basal ganglia are significantly spared from the well-established widespread reduction of NAA in schizophrenia suggesting a regional difference in disease-associated factors affecting NAA. The echo time findings agree with prior reports and suggest microstructural changes cause faster NAA T2 relaxation in hippocampus and frontal white matter in schizophrenia. Separating the effects of medication status and illness chronicity on NAA and choline abnormalities will require further patient-level studies. Metabolite measurement quality was shown to be a critical factor in MRS studies of schizophrenia.

Meta-analysis and Open-source Database for In Vivo Brain Magnetic Resonance Spectroscopy in Health and Disease

Proton ( 1 H) Magnetic Resonance Spectroscopy (MRS) is a non-invasive tool capable of quantifying brain metabolite concentrations in vivo . Prioritization of standardization and accessibility in the field has led to the development of universal pulse sequences, methodological consensus recommendations, and the development of open-source analysis software packages. One on-going challenge is methodological validation with ground-truth data. As ground-truths are rarely available for in vivo measurements, data simulations have become an important tool. The diverse literature of metabolite measurements has made it challenging to define ranges to be used within simulations. Especially for the development of deep learning and machine learning algorithms, simulations must be able to produce accurate spectra capturing all the nuances of in vivo data. Therefore, we sought to determine the physiological ranges and relaxation rates of brain metabolites which can be used both in data simulations and as reference estimates. Using the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, we've identified relevant MRS research articles and created an open-source database containing methods, results, and other article information as a resource. Using this database, expectation values and ranges for metabolite concentrations and T 2 relaxation times are established based upon a meta-analyses of healthy and diseased brains.

Gamma-aminobutyric acid (GABA) levels in the midcingulate cortex and clozapine response in patients with treatment-resistant schizophrenia: A proton magnetic resonance spectroscopy (1 H-MRS) study

BACKGROUND

Gamma-Aminobutyric Acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system. GABAergic dysfunction has been implicated in the pathophysiology of schizophrenia. Clozapine, the only approved drug for treatment-resistant schizophrenia (TRS), involves the GABAergic system as one of its targets. However, no studies have investigated the relationship between brain GABA levels, as measured by proton magnetic resonance spectroscopy (¹ H-MRS), and clozapine response in patients with TRS.

METHODS

This study enrolled patients with TRS who did not respond to clozapine (ultra-resistant schizophrenia: URS) and who responded to clozapine (non-URS), patients with schizophrenia who responded to first-line antipsychotics (first-line responders: FLR), and healthy controls (HCs). We measured GABA levels in the midcingulate cortex (MCC) using 3T ¹ H-MRS and compared these levels among the groups. The associations between GABA levels and symptom severity were also explored within the patient groups.

RESULTS

A total of 98 participants (URS: n = 22; non-URS: n = 25; FLR: n = 16; HCs: n = 35) completed the study. We found overall group differences in MCC GABA levels (F(3,86) = 3.25, P = 0.04). Specifically, patients with URS showed higher GABA levels compared to those with non-URS (F(1,52) = 8.40, P = 0.03, Cohen's d = 0.84). MCC GABA levels showed no associations with any of the symptom severity scores within each group or the entire patient group.

CONCLUSION

Our study is the first to report elevated GABA levels in the MCC in patients with schizophrenia resistant to clozapine treatment compared with those responsive to clozapine. Longitudinal studies are required to evaluate if GABA levels are a suitable biomarker to predict clozapine resistance.

Treatment-resistant schizophrenia: Addressing white matter integrity, intracortical glutamate levels, clinical and cognitive profiles between early- and adult-onset patients

BACKGROUND

Treatment-resistance in schizophrenia is 30-40%. Its neurobiology remains unclear; to explore it, we conducted a combined spectrometry/tractography/cognitive battery and psychopathological rating study on patients with treatment-resistant schizophrenia (TRS), dividing the sample into early-onset (N = 21) and adult-onset TRS (N = 20). Previous studies did not differentiate between early- (onset 13-18 years) and adult-onset (>18 years at formal diagnosis of schizophrenia) TRS.

METHODS

We evaluated cross-sectionally 41 TRS patients (26 male and 15 female) and 20 matched healthy controls (HCs) with psychopathological and cognitive testing prior to participating in brain imaging scanning using magnetic resonance spectroscopy and diffusion tensor imaging to determine the relationship between their symptoms and their glutamate levels and white matter integrity.

RESULTS

TRS patients scored lower than HCs on all cognitive domains; early-onset patients performed better than adult-onset patients only on the Symbol Coding domain. TRS correlated with symptom severity, especially negative symptoms. Glutamate levels and glutamate/creatine were increased in anterior cingulate cortex. Diffusion tensor imaging showed low fractional anisotropy in TRS patients in specific white matter tracts compared to HCs (bilateral anterior thalamic radiation, cortico-spinal tract, forceps minor, inferior fronto-occipital fasciculus, inferior longitudinal fasciculus, superior longitudinal fasciculus, and right uncinate fasciculus).

CONCLUSIONS

We identified specific magnetic resonance spectroscopy and diffusion tensor imaging alterations in TRS patients. Adult-onset TRS differed little from early-onset TRS on most measures; this points to alterations being present since the outset of schizophrenia and may constitute a biological signature of treatment-resistance.

Transdiagnostic role of glutamate and white matter damage in neuropsychiatric disorders: A Systematic Review

Neuropsychiatric disorders including generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD), major depressive disorder (MDD), bipolar disorder (BD), and schizophrenia (SZ) have been considered distinct categories of diseases despite their overlapping characteristics and symptomatology. We aimed to provide an in-depth review elucidating the role of glutamate/Glx and white matter (WM) abnormalities in these disorders from a transdiagnostic perspective. The PubMed online database was searched for studies published between 2010 and 2021. After careful screening, 401 studies were included. The findings point to decreased levels of glutamate in the Anterior Cingulate Cortex in both SZ and BD, whereas Glx is elevated in the Hippocampus in SZ and MDD. With regard to WM abnormalities, the Corpus Callosum and superior Longitudinal Fascicle were the most consistently identified brain regions showing decreased fractional anisotropy (FA) across all the reviewed disorders, except GAD. Additionally, the Uncinate Fasciculus displayed decreased FA in all disorders, except OCD. Decreased FA was also found in the inferior Longitudinal Fasciculus, inferior Fronto-Occipital Fasciculus, Thalamic Radiation, and Corona Radiata in SZ, BD, and MDD. Decreased FA in the Fornix and Corticospinal Tract were found in BD and SZ patients. The Cingulum and Anterior Limb of Internal Capsule exhibited decreased FA in MDD and SZ patients. The results suggest a gradual increase in severity from GAD to SZ defined by the number of brain regions with WM abnormality which may be partially caused by abnormal glutamate levels. WM damage could thus be considered a potential marker of some of the main neuropsychiatric disorders.

Glutamatergic and GABAergic metabolite levels in schizophrenia-spectrum disorders: a meta-analysis of 1H-magnetic resonance spectroscopy studies

BACKGROUND

The glutamate (Glu) and gamma aminobutyric acid (GABA) hypotheses of schizophrenia were proposed in the 1980s. However, current findings on those metabolite levels in schizophrenia have been inconsistent, and the relationship between their abnormalities and the pathophysiology of schizophrenia remains unclear. To summarize the nature of the alterations of glutamatergic and GABAergic systems in schizophrenia, we conducted meta-analyses of proton magnetic resonance spectroscopy (¹H-MRS) studies examining these metabolite levels.

METHODS

A systematic literature search was conducted using Embase, Medline, PsycINFO, and PubMed. Original studies that compared four metabolite levels (Glu, glutamine [Gln], Glx [Glu+Gln], and GABA), as measured by ¹H-MRS, between individuals at high risk for psychosis, patients with first-episode psychosis, or patients with schizophrenia and healthy controls (HC) were included. A random-effects model was used to calculate the effect sizes for group differences in these metabolite levels of 18 regions of interest between the whole group or schizophrenia group and HC. Subgroup analysis and meta-regression were performed based on the status of antipsychotic treatment, illness stage, treatment resistance, and magnetic field strength.

RESULTS

One-hundred-thirty-four studies met the eligibility criteria, totaling 7993 participants with SZ-spectrum disorders and 8744 HC. 14 out of 18 ROIs had enough numbers of studies to examine the group difference in the metabolite levels. In the whole group, Glx levels in the basal ganglia (g = 0.32; 95% CIs: 0.18-0.45) were elevated. Subgroup analyses showed elevated Glx levels in the hippocampus (g = 0.47; 95% CIs: 0.21-0.73) and dorsolateral prefrontal cortex (g = 0.25; 95% CIs: 0.05-0.44) in unmedicated patients than HC. GABA levels in the MCC were decreased in the first-episode psychosis group compared with HC (g = -0.40; 95% CIs: -0.62 to -0.17). Treatment-resistant schizophrenia (TRS) group had elevated Glx and Glu levels in the MCC (Glx: g = 0.7; 95% CIs: 0.38-1.01; Glu: g = 0.63; 95% CIs: 0.31-0.94) while MCC Glu levels were decreased in the patient group except TRS (g = -0.17; 95% CIs: -0.33 to -0.01).

CONCLUSIONS

Increased glutamatergic metabolite levels and reduced GABA levels indicate that the disruption of excitatory/inhibitory balance may be related to the pathophysiology of schizophrenia-spectrum disorders.

Proton Magnetic Resonance Spectroscopy of N-acetyl Aspartate in Chronic Schizophrenia, First Episode of Psychosis and High-Risk of Psychosis: A Systematic Review and Meta-Analysis

N-acetyl-aspartate (NAA) is a readily measured marker of neuronal metabolism. Previous analyses in schizophrenia have shown NAA levels are low in frontal, temporal and thalamic regions, but may be underpowered to detect effects in other regions, in high-risk states and in first episode psychosis. We searched for magnetic resonance spectroscopy studies comparing NAA in chronic schizophrenia, first episode psychosis and high risk of psychosis to controls. 182 studies were included and meta-analysed using a random-effects model for each region and illness stage. NAA levels were significantly lower than controls in the frontal lobe [Hedge's g = -0.36, p < 0.001], hippocampus [-0.52, p < 0.001], temporal lobe [-0.35, p = 0.031], thalamus [-0.32, p = 0.012] and parietal lobe [-0.25, p = 0.028] in chronic schizophrenia, and lower than controls in the frontal lobe [-0.26, p = 0.002], anterior cingulate cortex [-0.24, p = 0.016] and thalamus [-0.28, p = 0.028] in first episode psychosis. NAA was lower in high-risk of psychosis in the hippocampus [-0.20, p = 0.049]. In schizophrenia, NAA alterations appear to begin in hippocampus, frontal cortex and thalamus, and extend later to many other regions.

Glutamatergic neurometabolites and cortical thickness in treatment-resistant schizophrenia: Implications for glutamate-mediated excitotoxicity

Treatment-resistant schizophrenia may be related to structural brain alterations. However, the mechanisms underlying these changes remain unclear. The present study had two main aims: (1) to explore differences in cortical thickness between patients with treatment-resistant schizophrenia non-responsive to clozapine (ultra-treatment-resistant schizophrenia, UTRS), patients with treatment-resistant schizophrenia responsive to clozapine (Cloz-Resp), patients responsive to first-line non-clozapine antipsychotics (FL-Resp), and healthy controls (HCs); and (2) to test our hypothesis of structural compromise as a manifestation of neurotoxic effects from elevated glutamate (Glu) (i.e. glutamate-mediated excitotoxicity) by examining the relationships between glutamatergic neurometabolite levels (Glu and glutamate + glutamine (Glx)) in the dorsal anterior cingulate cortex (dACC) and cortical thickness. T1-weighted images and ¹H-MRS data were obtained from UTRS (n = 24), Cloz-Resp (n = 25), FL-Resp (n = 19), and HCs (n = 26). Vertex-wise analyses showed that patients with UTRS had widespread cortical thinning in the bilateral frontal, temporal, parietal, and occipital gyri compared to HCs and FL-Resp patients. In the patient group, negative associations were found between dACC Glx levels and cortical thickness in the right dorsolateral prefrontal cortex after correcting for multiple comparisons and controlling for age, sex, antipsychotic dose, and illness severity. In conclusion, glutamate-mediated excitotoxicity may be one of the mechanisms underlying structural compromise seen in treatment-resistant schizophrenia. Future studies should longitudinally examine the associations between glutamatergic neurometabolite levels and cortical thickness in the context of treatment and illness progression.

Levels of glutamatergic neurometabolites in patients with severe treatment-resistant schizophrenia: a proton magnetic resonance spectroscopy study

Approximately 30% of patients with schizophrenia do not respond to antipsychotics and are thus considered to have treatment-resistant schizophrenia (TRS). To date, only four studies have examined glutamatergic neurometabolite levels using proton magnetic resonance spectroscopy (¹H-MRS) in patients with TRS, collectively suggesting that glutamatergic dysfunction may be implicated in the pathophysiology of TRS. Notably, the TRS patient population in these studies had mild-to-moderate illness severity, which is not entirely reflective of what is observed in clinical practice. In this present work, we compared glutamate + glutamine (Glx) levels in the dorsal anterior cingulate cortex (dACC) and caudate among patients with TRS, patients with non-TRS, and healthy controls (HCs), using 3T ¹H-MRS (PRESS, TE = 35 ms). TRS criteria were defined by severe positive symptoms (i.e., ≥5 on 2 Positive and Negative Syndrome Scale (PANSS)-positive symptom items or ≥4 on 3 PANSS-positive symptom items), despite standard antipsychotic treatment. A total of 95 participants were included (29 TRS patients [PANSS = 111.2 ± 20.4], 33 non-TRS patients [PANSS = 49.8 ± 13.7], and 33 HCs). dACC Glx levels were higher in the TRS group vs. HCs (group effect: F[2,75] = 4.74, p = 0.011; TRS vs. HCs: p = 0.012). No group differences were identified in the caudate. There were no associations between Glx levels and clinical severity in either patient group. Our results are suggestive of greater heterogeneity in TRS relative to non-TRS with respect to dACC Glx levels, necessitating further research to determine biological subtypes of TRS.

The effect of spinal manipulation on brain neurometabolites in chronic nonspecific low back pain patients: a randomized clinical trial

BACKGROUND

In patients with chronic nonspecific low back pain (NCLBP), brain function changes due to the neuroplastic changes in different regions.

AIM

The current study aimed to evaluate the brain metabolite changes after spinal manipulation, using proton magnetic resonance spectroscopy (¹H-MRS).

METHODS

In the current study, 25 patients with NCLBP aged 20-50 years were enrolled. Patients were randomly assigned to lumbopelvic manipulation or sham. Patients were evaluated before and 5 weeks after treatment by the Numerical Rating Scale (NRS), the Oswestry Disability Index (ODI), and ¹H-MRS.

RESULTS

After treatment, severity of pain and functional disability were significantly reduced in the treatment group vs. sham group (p < 0.05). After treatment, N-acetyl aspartate (NAA) in thalamus, insula, dorsolateral prefrontal cortex (DLPFC) regions, as well as choline (Cho) in the thalamus, insula, and somatosensory cortex (SSC) regions, had increased significantly in the treatment group compared with the sham group (p < 0.05). A significant increase was further observed in NAA in thalamus, anterior cingulate cortex (ACC), and SCC regions along with Cho metabolite in thalamus and SCC regions after treatment in the treatment group compared with the baseline measures (p < 0.05). Also, a significant increase was observed in Glx (glutamate and glutamine) levels of thalamus (p = 0.03). There was no significant difference in terms of brain metabolites at baseline and after treatment in the sham group.

CONCLUSION

In the patient with low back pain, spinal manipulation affects the central nervous system and changes the brain metabolites. Consequently, pain and functional disability are reduced.

Using proton magnetic resonance spectroscopic imaging to study glutamatergic alterations in patients with schizophrenia: A systematic review

The glutamate hypothesis of schizophrenia posits aberrant glutamatergic activity in patients with schizophrenia. Levels of glutamate and glutamine can be detected and quantified in vivo by proton magnetic resonance spectroscopy. A related technique, proton magnetic resonance spectroscopic imaging (¹H-MRSI), is particularly useful as it simultaneously collects multiple spectra, across multiple voxels, from a single acquisition. The primary aim of this study was to review and discuss the use of ¹H-MRSI to measure levels of glutamate and glutamine in patients with schizophrenia. Additionally, the advantages and disadvantages of using ¹H-MRSI to examine schizophrenia pathophysiology are discussed. A literature search was conducted through Ovid. English language studies utilizing ¹H-MRSI to measure glutamate and glutamine in patients with schizophrenia were identified. Six studies met the inclusion criteria. The included studies provide inconclusive support for glutamatergic elevations within frontal brain regions in patients with schizophrenia. The key benefit of employing ¹H-MRSI to examine schizophrenia pathophysiology appears to be its broader spatial coverage. Future ¹H-MRSI studies utilizing large sample sizes and longitudinal study designs are necessitated to further our understanding of glutamatergic alterations in patients with schizophrenia.

Enhanced Dopamine in Prodromal Schizophrenia (EDiPS): a new animal model of relevance to schizophrenia

One of the most robust neurochemical abnormalities reported in patients living with schizophrenia is an increase in dopamine (DA) synthesis and release in the dorsal striatum (DS). Importantly, it appears that this increase progresses as a patient transitions from a prodromal stage to the clinical diagnosis of schizophrenia. Here we have recreated this pathophysiology in an animal model by increasing the capacity for DA synthesis preferentially within the DS. To achieve this we administer a genetic construct containing the rate-limiting enzymes in DA synthesis—tyrosine hydroxylase (TH), and GTP cyclohydrolase 1 (GCH1) (packaged within an adeno-associated virus)—into the substantia nigra pars compacta (SNpc) of adolescent animals. We refer to this model as “Enhanced Dopamine in Prodromal Schizophrenia” (EDiPS). We first confirmed that the TH enzyme is preferentially increased in the DS. As adults, EDiPS animals release significantly more DA in the DS following a low dose of amphetamine (AMPH), have increased AMPH-induced hyperlocomotion and show deficits in pre-pulse inhibition (PPI). The glutamatergic response to AMPH is also altered, again in the DS. EDiPS represents an ideal experimental platform to (a) understand how a preferential increase in DA synthesis capacity in the DS relates to “positive” symptoms in schizophrenia; (b) understand how manipulation of DS DA may influence other neurotransmitter systems shown to be altered in patients with schizophrenia; (c) allow researchers to follow an “at risk”-like disease course from adolescence to adulthood; and (d) ultimately allow trials of putative prophylactic agents to prevent disease onset in vulnerable populations.