Molecular imaging for depressive disorders

Progress in the application of molecular imaging in psychiatric disorders

Psychiatric disorders have always attracted a lot of attention from researchers due to the difficulties in their diagnoses and treatments. Molecular imaging, as an emerging technology, has played an important role in the researchers of various diseases. In recent years, molecular imaging techniques including magnetic resonance spectroscopy, nuclear medicine imaging, and fluorescence imaging have been widely used in the study of psychiatric disorders. This review will briefly summarize the progression of molecular imaging in psychiatric disorders.

Immunological Disturbances and Neuroimaging Findings in Major Depressive Disorder (MDD) and Alcohol Use Disorder (AUD) Comorbid Patients

Mood disorders and Major Depressive Disorder, in particular, appear to be some of the most common psychiatric disorders with a high rate of comorbidity most frequently of anxiety or substance abuse disorders (alcohol use disorder). In both cases - MDD and AUD, a number of immunological disturbances are observed, such as chronic mild inflammation response, increased level of cytokines, hypercortisolaemia, which lead to specific changes in brain neurotransmitter functions. Some of the contemporary brain imaging techniques are functional magnetic resonance imaging (fMRI) and magnetic spectroscopy which are most commonly used to assess the brain metabolism and functional connectivity changes such as altered responses to emotional stimuli in MDD or overactivation of ventromedial prefrontal areas during delayed and underactivation of dorsolateral prefrontal regions during impulsive reward decisions in AUD and dysfunction of gamma-aminobutyric acid (GABA) and/or glutamate neurotransmitter systems, low NAA and myo-Inositol in both MDD and AUD.

Synaptic Microenvironment in Depressive Disorder: Insights from Synaptic Plasticity

Depression is a major disease that can affect both mental and physical health, limits psychosocial functioning and diminishes the quality of life. But its complex pathogenesis remains poorly understood. The dynamic changes of synaptic structure and function, known as synaptic plasticity, occur with the changes of different cellular microenvironment and are closely related to learning and memory function. Accumulating evidence implies that synaptic plasticity is integrally involved in the pathological changes of mood disorders, especially in depressive disorder. However, the complex dynamic process of synaptic plasticity is influenced by many factors. Here, we reviewed and discussed various factors affecting synaptic plasticity in depression, and proposed a specific framework named synaptic microenvironment, which may be critical for synaptic plasticity under pathological conditions. Based on this concept, we will show how we understand the balance between the synaptic microenvironment and the synaptic plasticity network in depression. Finally, we point out the clinical significance of the synaptic microenvironment in depression.

The rise and fall of MRI studies in major depressive disorder

Structural and functional brain alterations are common in patients with major depressive disorder (MDD). In this review, we assessed the recent literature (1995-2018) on the structural and functional magnetic resonance imaging (MRI) studies of MDD. Despite the growing number of MRI studies on MDD, reverse inference is not possible as MRI scans cannot be used to aid in the diagnosis or treatment planning of patients with MDD. Hence, researchers must develop "bridges" to overcome the reverse inference fallacy in order to build effective tools for MDD diagnostics. From our findings, we proposed that the "bridges" may be built using multidisciplinary technologies, such as artificial intelligence, multimodality imaging, and nanotheranostics, allowing for the further study of MDD at the biological level. In return, the "bridges" will aid in the development of future diagnostics for MDD and other mental disorders.

General technical remarks on 1HMRS translational research in 7T

Purpose

The aim of the work was to share the practical experience of preclinical and clinical proton magnetic resonance spectroscopy (¹HMRS) studies conducted using a 7-Tesla magnetic field strength scanner, taking into account the specificity of both settings in the context of translational research.

Material and methods

¹HMRS volunteer studies conducted using a Discovery 950 GE 7T scanner, were carried out with PRESS sequence, and a VOI measuring 2.0 × 2.0 × 2.0 cm³ placed in the white matter at the parietal occipital lobe. Rodent spectra obtained using a 7T Bruker were measured with PRESS, with a VOI 2.0 × 2.0 × 5.5 mm³ placed over the hippocampus.

Results

¹HMRS data from humans and rats show that the brain spectra obtained in the same field are characterised by a similar neurochemical structure and spectral resolution. Spectra obtained from rats demonstrate the following metabolites: NAA, Glu, Gln, Ins, Cho, Cr, PCr, Tau, GABA, Lac, NAAG, and Asp. In turn, spectra from humans allowed estimation of the following metabolites: Ala, NAA, Glu, Gln, Ins, Cho, Cr, PCr, Tau, GABA, Lac, NAAG, and Asp. Signals from Gln, Glu with chemical shift around 2.4 ppm, from Cr, PCr, and GABA at 3 ppm, and signals from Cho and Tau at approximately 3.2 ppm, can be properly separated and estimated both in humans and in rats.

Conclusions

These results are promising in terms of broadening the knowledge of many neurological diseases by inducing them on animal models and then transferring this knowledge to clinical practice. In spite of this, important distinctions in the technical aspects and methodological differences of high-field ¹HMRS in both preclinical and clinical conditions should be taken into account.

Positron emission tomography imaging of the γ-aminobutyric acid system

In this review, we summarize the recent development of positron emission tomography (PET) radioligands for γ-aminobutyric acid A (GABA_A) receptors and their potential to measure changes in endogenous GABA levels and highlight the clinical and translational applications of GABA-sensitive PET radioligands. We review the basic physiology of the GABA system with a focus on the importance of GABA_A receptors in the brain and specifically the benzodiazepine binding site. Challenges for the development of central nervous system radioligands and particularly for radioligands with increased GABA sensitivity are outlined, as well as the status of established benzodiazepine site PET radioligands and agonist GABA_A radioligands. We underline the challenge of using allosteric interactions to measure GABA concentrations and review the current state of PET imaging of changes in GABA levels. We conclude that PET tracers with increased GABA sensitivity are required to efficiently measure GABA release and that such a tool could be broadly applied to assess GABA transmission in vivo across several disorders.

Serotonin 1A receptor density measured by F18-Mefway PET/CT in mesiotemporal cortex and raphe does not discriminate therapeutic response in patients with major depressive episode

BACKGROUND

More than 50% of patients with major depressive episode (MDE) fail to respond to initial treatment with first line pharmacological therapy. Altered receptor and serotonin transporter function are considered to be associated with mental disorders. Our investigation aimed on the density of the HT1A receptor in mesiotemporal cortex (MTC) and raphe measured by F18-Mefway in patients with MDD.

METHODS

Patients with untreated clinically suspected major depressive episode were recruited from June 2012 to May 2014. 49 patients were included into the study: 36 patients (73%) were identified as responders, whereas 13 (27%) were non-responders. Gender distribution was 26 men (56%) and 23 women (44%). For treatment, only a standard medication of a selective serotonin reuptake inhibitor (SSRI) with escitalopram in a range of 10-20 mg/day was permitted. Responders were defined by improvement of the MADRS>50%. Visually MTC had the highest uptake of F18-Mefway among all brain regions, an asymmetry could not be observed in any patient. An elliptical region was drawn over the amygdala and hippocampus area and a small circular region was drawn over the raphe nuclei. All data were calculated related to (unspecific) cerebellar uptake.

RESULTS

The quotient of the right MTC was 5.00 [4.33; 5.50] in all patients, in responders 5.00 [4.00; 5.75] and in non-responders 5.00 [4.50; 5.50] (P=0.56). The quotient of the left MTC presented with a median level of 4.50 [4.50; 5.50] in all persons. The responders had 4.50 [4.50; 5.75] which was not statistically significant to the data of the non-responders with 5.00 [4.50; 5.50] at P=0.64. The raphe had a median quotient of 2.50 [2.00; 3.00] in all and the cohort of responders, whereas non-responders had 2.50 [2.00; 2.50] (P=0.61). Also the absolute values of SUV in the three brain regions were not statistically different between the cohorts. Additionally, we did not find any sex-related differences in our patient group.

CONCLUSIONS

Serotonin 1A receptor density can be assessed efficiently by F18-Mefway and PET-CT in patients with MDE. The method can be estimated as a possible tool for clinical and academic investigation, marked tracer uptake can constantly be observed at MTC and the raphe. Anyhow, under conditions of real life in patient care, it is not possible to distinguish patients with a good prognosis who will respond to standard SSRI therapy from non-responders who would benefit from a different therapeutic approach starting earlier.

Targeted Superparamagnetic Iron Oxide Nanoparticles for In Vivo Magnetic Resonance Imaging of T-Cells in Rheumatoid Arthritis

PURPOSE

The purpose of the study is to develop a targeted nanoparticle platform for T cell labeling and tracking in vivo.

PROCEDURES

Through carboxylation of the polyethylene glycol (PEG) surface of SPION, carboxylated-PEG-SPION (IOPC) was generated as a precursor for further conjugation with the targeting probe. The IOPC could readily cross-link with a variety of amide-containing molecules by exploiting the reaction between 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide and N-hydroxysuccinimide. The subsequent conjugation of monoclonal anti-CD3 antibody with IOPC made it possible to construct a magnetic resonance imaging (MRI) contrast agente (CA) that targets T cells, named IOPC-CD3.

RESULTS

IOPC-CD3 was found to have high transverse relaxivity, good targeting selectivity, and good safety profile in vitro. The utility of this newly synthesized CA was explored in an in vivo rodent collagen-induced arthritis (CIA) model of rheumatoid arthritis. Serial MRI experiments revealed a selective decrease in the signal-to-noise ratio of the femoral growth plates of CIA rats infused with IOPC-CD3, with this finding being consistent with immunohistochemical results showing the accumulation of T cells and iron oxide nanoparticles in the corresponding region.

CONCLUSIONS

Together with the abovementioned desirable features, these results indicate that IOPC-CD3 offers a promising prospect for a wide range of cellular and molecular MRI applications.

Clinical neuroimaging markers of response to treatment in mood disorders

Mood disorders (MD) are important and frequent psychiatric illness. The management of patients affected by these conditions represents an important factor of disability as well as a significant social and economic burden. The "in-vivo" studies can help researchers to understand the first developmental events of the pathology and to identify the molecular and non-molecular targets of therapies. However, they have strong limitations due to the fact that human brain circuitry can not be reproduced in animal models. In addition, these neural pathways are difficult to be selectively studied with the modern imaging (such as Magnetic Resonance and Positron Emitted Tomography/Computed Tomography) and non-imaging (such as electroencephalography, magnetoencephalography, transcranial magnetic stimulation and evoked potentials) methods. In comparison with other methods, the "in-vivo" imaging investigations have higher temporal and spatial resolution compared to the "in-vivo" non-imaging techniques. All these factors make difficult to fully understand the aetiology and pathophysiology of these disorders, and consequently hinder the analysis of the effects of pharmacological and non-pharmacological therapies, which have been demonstrated effective in clinical settings. In this review, we will focus our attention on the current state of the art of imaging in the assessment of treatment efficacy in MD. We will analyse briefly the actual classification of MD; then we will focus on the "in vivo" imaging methods used in research and clinical activity, the current knowledge about the neural models at the base of MD. Finally the last part of the review will focus on the analysis of the main markers of response to treatment.

Prefrontal inositol levels and implicit decision-making in healthy individuals and depressed patients

Risky decision-making is found in several mental disorders and is associated with deleterious consequences. Current research aims at understanding the biological underpinnings of this complex cognitive function and the basis of individual variability. We used 3T proton Magnetic Resonance Spectroscopy to measure in vivo glutamate, GABA, N-acetyl-aspartate (NAA), and myo-inositol levels at rest in the right dorsal prefrontal cortex of 54 participants, comprising 24 unmedicated depressed patients and 30 healthy individuals. Participants were also tested with the Iowa Gambling Task (IGT), a classical measure of value-based decision-making. No group differences were found in terms of compound levels or decision-making performance. However, high inositol levels were associated with lower decision-making scores independently from group, notably during the initial stage of the task when explicit rules are still unknown and decisions are largely based on implicit processes (whole sample: F=4.0; p=0.02), with a large effect size (Cohen׳s d=0.8, 95% [0.2-1.5]). This effect was stronger when explicit knowledge was taken into account, with explicit knowledge showing an independent effect on performance. There was no association with other compounds. This study suggests, for the first time, a role for the inositol pathway on the implicit learning component of decision-making, without any direct effect on the explicit component. Hypothesized mechanisms implicate intracellular calcium modulation and subsequent synaptic plasticity. These findings represent a first step in the understanding of the biochemical mechanisms underlying decision-making and the identification of therapeutic targets. They also emphasize a dimensional approach in the study of the neurobiological determinants of mental disorders.

Applications of blood-based protein biomarker strategies in the study of psychiatric disorders

Major psychiatric disorders such as schizophrenia, major depressive and bipolar disorders are severe, chronic and debilitating, and are associated with high disease burden and healthcare costs. Currently, diagnoses of these disorders rely on interview-based assessments of subjective self-reported symptoms. Early diagnosis is difficult, misdiagnosis is a frequent occurrence and there are no objective tests that aid in the prediction of individual responses to treatment. Consequently, validated biomarkers are urgently needed to help address these unmet clinical needs. Historically, psychiatric disorders are viewed as brain disorders and consequently only a few researchers have as yet evaluated systemic changes in psychiatric patients. However, promising research has begun to challenge this concept and there is an increasing awareness that disease-related changes can be traced in the peripheral system which may even be involved in the precipitation of disease onset and course. Converging evidence from molecular profiling analysis of blood serum/plasma have revealed robust molecular changes in psychiatric patients, suggesting that these disorders may be detectable in other systems of the body such as the circulating blood. In this review, we discuss the current clinical needs in psychiatry, highlight the importance of biomarkers in the field, and review a representative selection of biomarker studies to highlight opportunities for the implementation of personalized medicine approaches in the field of psychiatry. It is anticipated that the implementation of validated biomarker tests will not only improve the diagnosis and more effective treatment of psychiatric patients, but also improve prognosis and disease outcome.