Distribution volume ratio of serotonin and dopamine transporters in euthymic patients with a history of major depression - a dual-isotope SPECT study

Dopamine in major depressive disorder: A systematic review and meta-analysis of in vivo imaging studies

BACKGROUND

Major depressive disorder (MDD) is a leading cause of global disability. Several lines of evidence implicate the dopamine system in its pathophysiology. However, the magnitude and consistency of the findings are unknown. We address this by systematically reviewing in vivo imaging evidence for dopamine measures in MDD and meta-analysing these where there are sufficient studies.

METHODS

Studies investigating the dopaminergic system using positron emission tomography or single photon emission computed tomography in MDD and a control group were included. Demographic, clinical and imaging measures were extracted from each study, and meta-analyses and sensitivity analyses were conducted.

RESULTS

We identified 43 studies including 662 patients and 801 controls. Meta-analysis of 38 studies showed no difference in mean or mean variability of striatal D2/3 receptor availability (g = 0.06, p = 0.620), or combined dopamine synthesis and release capacity (g = 0.19, p = 0.309). Dopamine transporter (DAT) availability was lower in the MDD group in studies using DAT selective tracers (g = -0.56, p = 0.006), but not when tracers with an affinity for serotonin transporters were included (g = -0.21, p = 0.420). Subgroup analysis showed greater dopamine release (g = 0.49, p = 0.030), but no difference in dopamine synthesis capacity (g = -0.21, p = 0.434) in the MDD group. Striatal D1 receptor availability was lower in patients with MDD in two studies.

CONCLUSIONS

The meta-analysis indicates striatal DAT availability is lower, but D2/3 receptor availability is not altered in people with MDD compared to healthy controls. There may be greater dopamine release and lower striatal D1 receptors in MDD, although further studies are warranted. We discuss factors associated with these findings, discrepancies with preclinical literature and implications for future research.

Current and potential roles of immuno-PET/-SPECT in CAR T-cell therapy

Chimeric antigen receptor (CAR) T-cell therapies have evolved as breakthrough treatment options for the management of hematological malignancies and are also being developed as therapeutics for solid tumors. However, despite the impressive patient responses from CD19-directed CAR T-cell therapies, ~ 40%-60% of these patients' cancers eventually relapse, with variable prognosis. Such relapses may occur due to a combination of molecular resistance mechanisms, including antigen loss or mutations, T-cell exhaustion, and progression of the immunosuppressive tumor microenvironment. This class of therapeutics is also associated with certain unique toxicities, such as cytokine release syndrome, immune effector cell-associated neurotoxicity syndrome, and other "on-target, off-tumor" toxicities, as well as anaphylactic effects. Furthermore, manufacturing limitations and challenges associated with solid tumor infiltration have delayed extensive applications. The molecular imaging modalities of immunological positron emission tomography and single-photon emission computed tomography (immuno-PET/-SPECT) offer a target-specific and highly sensitive, quantitative, non-invasive platform for longitudinal detection of dynamic variations in target antigen expression in the body. Leveraging these imaging strategies as guidance tools for use with CAR T-cell therapies may enable the timely identification of resistance mechanisms and/or toxic events when they occur, permitting effective therapeutic interventions. In addition, the utilization of these approaches in tracking the CAR T-cell pharmacokinetics during product development and optimization may help to assess their efficacy and accordingly to predict treatment outcomes. In this review, we focus on current challenges and potential opportunities in the application of immuno-PET/-SPECT imaging strategies to address the challenges encountered with CAR T-cell therapies.

Altered levels of dopamine transporter in the frontal pole and the striatum in mood disorders: A postmortem study

Dopamine dysregulation is known to play a major role in the pathophysiology of major depressive disorders (MDD) and bipolar disorders (BD). The dopamine transporter (DAT) plays a critical role in regulating dopamine concentration at the synaptic cleft and therefore could have an important role in the molecular pathology of MDD and BD. To test this hypothesis, we measured levels of [³H]mazindol binding to DAT in Brodmann's area (BA) 10, BA 17 as well as in the dorsal and ventral striatum from 15 controls, 15 patients with MDD and 15 patients with BD, obtained postmortem, using in situ radioligand binding with autoradiography. Compared to controls, levels of [³H]mazindol binding to DAT was significantly higher in BA10 from patients with MDD but not BD. There was no significant difference in [³H]mazindol binding to DAT in BA 17 or the dorsal and ventral striatum from patients with MDD or BD. In addition, levels of [³H]mazindol binding show no correlation with donor age, postmortem interval, tissue pH, sex or duration of illness. In conclusion, our data suggest that changes in levels of DAT may be selectively affecting dopamine homeostasis in BA 10 in patients with MDD.

Multi-molecule imaging and inter-molecular imaging in nuclear medicine

Multi-molecule imaging and inter-molecular imaging are not fully implemented yet, however, can become an alternative in nuclear medicine. In this review article, we present arguments demonstrating that the advent of the Compton positron emission tomography (Compton-PET) system and the invention of the quantum chemical sensing method with double photon emission imaging (DPEI) provide realistic perspectives for visualizing inter-molecular and multi-molecule in nuclear medicine with MeV photon. In particular, the pH change of InCl3 solutions can be detected and visualized in a three-dimensional image by combining the hyperfine electric quadrupole interaction sensing and DPEI. Moreover, chemical states, such as chelating, can be detected through angular correlation sensing. We argue that multi-molecule and chemical sensing could be a realistic stream of research in future nuclear medicine.

Serotonin Modulates the Correlations between Obsessive-compulsive Trait and Heart Rate Variability in Normal Healthy Subjects: A SPECT Study with [123I]ADAM and Heart Rate Variability Measurement

Objective

The impact of serotonergic system on obsessive-compulsive disorder (OCD) is well studied. However, the correlation between OC presentations and autonomic nervous system (ANS) is still unclear. Furthermore, whether the correlation might be modulated by serotonin is also uncertain.

Methods

We recruited eighty-nine healthy subjects. Serotonin transporter (SERT) availability by [¹²³I]ADAM and heart rate variability (HRV) tests were measured. Symptoms checklist-90 was measured for the OC presentations. The interaction between HRV and SERT availability were calculated and the correlation between HRV and OC symptoms were analyzed after stratified SERT level into two groups, split at medium.

Results

The interactions were significant in the factors of low frequency (LF), high frequency (HF), and root mean square of successive differences (RMSSD). Furthermore, the significantly negative correlations between OC symptoms and the above HRV indexes existed only in subjects with higher SERT availability.

Conclusion

OC symptoms might be correlated with ANS regulations in subjects with higher SERT availability.

Examining the Feasibility of Quantifying Receptor Availability Using Cross-Modality Paired-Agent Imaging

Purpose

The ability to noninvasively quantify receptor availability (RA) in solid tumors is an aspirational goal of molecular imaging, often challenged by the influence of non-specific accumulation of the contrast agent. Paired-agent imaging (PAI) techniques aim to compensate for this effect by imaging the kinetics of a targeted agent and an untargeted isotype, often simultaneously, and comparing the kinetics of the two agents to estimate RA. This is usually accomplished using two spectrally distinct fluorescent agents, limiting the technique to superficial tissues and/or preclinical applications. Applying the approach in humans using conventional imaging modalities is generally infeasible since most modalities are unable to routinely image multiple agents simultaneously. We examine the ability of PAI to be implemented in a cross-modality paradigm, in which the targeted and untargeted agent kinetics are imaged with different modalities and used to recover receptor availability.

Procedures

Eighteen mice bearing orthotopic brain tumors were administered a solution containing three contrast agents: (1) a fluorescent agent targeted to epidermal growth factor receptor (EGFR), (2) an untargeted fluorescent isotype, and (3) a gadolinium-based contrast agent (GBCA) for MRI imaging. The kinetics of all three agents were imaged for 1 h after administration using an MRI-coupled fluorescence tomography system. Paired-agent receptor availability was computed using (1) the conventional all-optical approach using the targeted and untargeted optical agent images and (2) the cross-modality approach using the targeted optical and untargeted MRI-GBCA images. Receptor availability estimates between the two methods were compared.

Results

Receptor availability values using the cross-modality approach were highly correlated to the conventional, single-modality approach (r = 0.94; p < 0.00001).

Conclusion

These results suggest that cross-modality paired-agent imaging for quantifying receptor availability is feasible. Ultimately, cross-modality paired-agent imaging could facilitate rapid, noninvasive receptor availability quantification in humans using hybrid clinical imaging modalities.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11307-021-01629-6.

Simultaneous SPECT imaging with 123I and 125I - a practical approach to assessing a drug and its carrier at the same time with dual imaging

Radiolabeling of a drug with radioactive iodine is a good method to determine its pharmacokinetics and biodistribution in vivo that only minimally alters its physicochemical properties. With dual labeling, using the two radioactive iodine isotopes ¹²³I and ¹²⁵I, two different drugs can be evaluated at the same time, or one can follow both a drug and its drug delivery system using a single photon emission computed tomography (SPECT) imager. One difficulty is that the two radioisotopes have overlapping gamma spectra. Our aim was therefore to develop a technique that overcomes this problem and allows for quantitative analysis of the two radioisotopes present at varied isotope ratios. For this purpose, we developed a simple method that included scatter and attenuation corrections and fully compensated for ¹²³I/¹²⁵I crosstalk, and then tested it in phantom measurements. The method was applied to the study of an orally administered lipid formulation for the delivery of fenofibrate in rats. To directly compare a traditional study, where fenofibrate was determined in plasma samples to SPECT imaging with ¹²³I-labeled fenofibrate and ¹²⁵I-labeled triolein over 24 h, the drug concentrations were converted to standardized uptake values (SUVs), an unusual unit for pharmaceutical scientists, but the standard unit for radiologists. A generally good agreement between the traditional and the radioactive imaging method was found in the pharmacokinetics and biodistribution results. Small differences are discussed in detail. Overall, SPECT imaging is an excellent method to pilot a new formulation with just a few animals, replaces blood sampling, and can very quickly highlight potential administration problems, the excretion pathways and the kinetics. Furthermore, dual labeling with the two radioisotopes ¹²³I and ¹²⁵I clearly shows if a drug and its drug delivery system stay together when traveling through the body, if slow drug release takes place, and where degradation/excretion of the components occurs.

Simultaneous multi-nuclide imaging via double-photon coincidence method with parallel hole collimators

Multi-tracer imaging can provide useful information in the definitive diagnosis and research of medical, biological, and pharmaceutical sciences. Single-photon emission computed tomography (SPECT) is one of the nuclear medicine imaging modalities widely used for diagnosis or medical research and has a multi-tracer imaging capability. One of the drawbacks of multi-tracer imaging is crosstalk from other gamma rays, which affects the reconstructed image. Scattering correction methods, such as the dual- and triple-energy window methods, are used for conventional SPECT imaging to reduce the background caused by the crosstalk. This study proposes another crosstalk reduction method. Some nuclides emit two or more gamma rays through intermediate levels. Thus, detecting these gamma rays with the coincidence method allows us to distinguish a true gamma ray signal and a background signal. The nuclide position can be estimated at the intersection of two gamma rays using collimators. We demonstrate herein simultaneous ¹¹¹In and ¹⁷⁷Lu imaging via the double-photon coincidence method using GAGG detectors and parallel hole collimators. The double-photon coincidence method greatly reduces the background caused by other gamma rays and offers higher-quality images than does conventional imaging.

Imaging of inflammatory cellular protagonists in human atherosclerosis: a dual-isotope SPECT approach

Purpose

Atherosclerotic plaque development and progression signifies a complex inflammatory disease mediated by a multitude of proinflammatory leukocyte subsets. Using single photon emission computed tomography (SPECT) coupled with computed tomography (CT), this study tested a new dual-isotope acquisition protocol to assess each radiotracer’s capability to identify plaque phenotype and inflammation levels pertaining to leukocytes expressing leukocyte function-associated antigen-1 (LFA-1) and the leukocyte subset of proinflammatory macrophages expressing somatostatin receptor subtype-2 (SST₂). Individual radiotracer uptake was quantified and the presence of corresponding immunohistological cell markers was assessed.

Methods

Human symptomatic carotid plaque segments were obtained from endarterectomy. Segments were incubated in dual-isotope radiotracers [¹¹¹In]In-DOTA-butylamino-NorBIRT ([¹¹¹In]In-Danbirt) and [^99mTc]Tc-[N^0–1₄,Asp⁰,Tyr³]-octreotate ([^99mTc]Tc-Demotate 2) before scanning with SPECT/CT. Plaque phenotype was classified as pathological intimal thickening, fibrous cap atheroma or fibrocalcific using histology sections based on distinct morphological characteristics. Plaque segments were subsequently immuno-stained with LFA-1 and SST₂ and quantified in terms of positive area fraction and compared against the corresponding SPECT images.

Results

Focal uptake of co-localising dual-radiotracers identified the heterogeneous distribution of inflamed regions in the plaques which co-localised with positive immuno-stained regions of LFA-1 and SST₂. [¹¹¹In]In-Danbirt and [^99mTc]Tc-Demotate 2 uptake demonstrated a significant positive correlation (r = 0.651; p = 0.001). Fibrous cap atheroma plaque phenotype correlated with the highest [¹¹¹In]In-Danbirt and [^99mTc]Tc-Demotate 2 uptake compared with fibrocalcific plaques and pathological intimal thickening phenotypes, in line with the immunohistological analyses.

Conclusion

A dual-isotope acquisition protocol permits the imaging of multiple leukocyte subsets and the pro-inflammatory macrophages simultaneously in atherosclerotic plaque tissue. [¹¹¹In]In-Danbirt may have added value for assessing the total inflammation levels in atherosclerotic plaques in addition to classifying plaque phenotype.

Dual-isotope imaging allows in vivo immunohistochemistry using radiolabelled antibodies in tumours

While radiolabelled antibodies have found great utility as PET and SPECT imaging agents in oncological investigations, a notable shortcoming of these agents is their propensity to accumulate non-specifically within tumour tissue. The degree of this non-specific contribution to overall tumour uptake is highly variable and can ultimately lead to false conclusions. Therefore, in an effort to obtain a reliable measure of inter-individual differences in non-specific tumour uptake of radiolabelled antibodies, we demonstrate that the use of dual-isotope imaging overcomes this issue, enables true quantification of epitope expression levels, and allows non-invasive in vivo immunohistochemistry. The approach involves co-administration of (i) an antigen-targeting antibody labelled with zirconium-89 (89Zr), and (ii) an isotype-matched non-specific control IgG antibody labelled with indium-111 (111In). As an example, the anti-HER2 antibody trastuzumab was radiolabelled with 89Zr, and co-administered intravenously together with its 111In-labelled non-specific counterpart to mice bearing human breast cancer xenografts with differing HER2 expression levels (MDA-MB-468 [HER2-negative], MDA-MB-231 [low-HER2], MDA-MB-231/H2N [medium-HER2], and SKBR3 [high-HER2]). Simultaneous PET/SPECT imaging using a MILabs Vector4 small animal scanner revealed stark differences in the intratumoural distribution of [89Zr]Zr-trastuzumab and [111In]In-IgG, highlighting regions of HER2-mediated uptake and non-specific uptake, respectively. Normalisation of the tumour uptake values and tumour-to-blood ratios obtained with [89Zr]Zr-trastuzumab against those obtained with [111In]In-IgG yielded values which were most strongly correlated (R = 0.94; P = 0.02) with HER2 expression levels for each breast cancer type determined by Western blot and in vitro saturation binding assays, but not non-normalised uptake values. Normalised intratumoural distribution of [89Zr]Zr-trastuzumab correlated well with intratumoural heterogeneity HER2 expression.

Factors related to metabolic parameters in medicated patients with major depressive disorder--a naturalistic study

The aim of this study was to examine the metabolic parameters, including body mass index (BMI), homeostasis model assessment-estimated insulin resistance (HOMA-IR), homeostasis model assessment-estimated pancreatic β-cell function (HOMA-β), and lipid plasma level, in medicated patients with major depressive disorder (MDD) and to assess factors related to metabolic parameters in patients with MDD. 121 patients with MDD and 63 controls were recruited. The Hamilton Depression Rating Scale (HDRS), Wisconsin Card Sorting Test (WCST), Continuous Performance Test (CPT), and Finger-Tapping Test (FTT), were administered. BMI, HOMA-IR, and HOMA-β were calculated as modifiable metabolic parameters. The FTT results and BMI in depressed patients were significantly poorer and lower, respectively, than those of the controls. However, no significant differences were noted between MDD patients and controls included metabolic parameters and other neuropsychological tests. Among depressed patients, higher BMI is significantly related with lower education, no tobacco use, and male. The result demonstrated metabolic parameters could be neutral among medicated patients with MDD, particularly in non-elderly Asian individuals. The deficits of psychomotor speed could be more prominent than other cognitive alterations in patient with MDD.

Neurotoxicity of carbon monoxide targets caudate-mediated dopaminergic system

The clinical features of parkinsonism in carbon monoxide (CO) intoxication have been associated with striatal-related neuronal networks. As parkinsonian and neuropsychiatric features are both related to presynaptic dopaminergic integrity, the aim of this study was to explore the clinical significance of ^99mTcTRODAT-1 in grading neurobehavioral scores and parkinsonian severity in CO intoxication. We enrolled 64 patients with CO intoxication, including 29 with parkinsonism (parkinsonism[+] group) and 35 without (parkinsonism[-] group). All of the patients received ^99mTcTRODAT-1 neuroimaging evaluations, comprehensive neurobehavioral tests and assessments of the severity of parkinsonism using Unified Parkinson's Disease Rating Scale (UPDRS)-part III motor score. Univariate and multivariate regression analyses were used to test the predictive factors and scores for a diagnosis of parkinsonism and its severity. The parkinsonism(+) group had significantly lower cognitive scores and higher neuropsychiatric total scores compared with the parkinsonism(-) group, both of which were independently related to the severity of parkinsonism. ^99mTcTRODAT-1 regional caudate signals were correlated with tremors at rest, action or postural tremors of the hands, bradykinesia and hypokinesia, and visuospatial, verbal fluency, abstract thinking and digit backwards scores. Scores of the neurobehavioral tests and UPDRS items were highly correlated (p<0.01). Our results validated the initial hypothesis in that neurobehavioral deficits and parkinsonian symptoms were highly related. This association was independent of demographic factors and initial carboxyhemoglobin level. Within the presynaptic dopaminergic circuit, the clinical role of the caudate in mediating the clinical symptoms in CO intoxication may outweigh the putamen.

Neurobiology of Chronic Stress-Related Psychiatric Disorders: Evidence from Molecular Imaging Studies

Chronic stress accounts for billions of dollars of economic loss annually in the United States alone, and is recognized as a major source of disability and mortality worldwide. Robust evidence suggests that chronic stress plays a significant role in the onset of severe and impairing psychiatric conditions, including major depressive disorder, bipolar disorder, and posttraumatic stress disorder. Application of molecular imaging techniques such as positron emission tomography and single photon emission computed tomography in recent years has begun to provide insight into the molecular mechanisms by which chronic stress confers risk for these disorders. The present paper provides a comprehensive review and synthesis of all positron emission tomography and single photon emission computed tomography imaging publications focused on the examination of molecular targets in individuals with major depressive disorder, posttraumatic stress disorder, or bipolar disorder to date. Critical discussion of discrepant findings and broad strengths and weaknesses of the current body of literature is provided. Recommended future directions for the field of molecular imaging to further elucidate the neurobiological substrates of chronic stress-related disorders are also discussed. This article is part of the inaugural issue for the journal focused on various aspects of chronic stress.

One-step preparation of [(18)F]FPBM for PET imaging of serotonin transporter (SERT) in the brain

Serotonin transporters (SERT) in the brain play an important role in normal brain function. Selective serotonin reuptake inhibitors such as fluoxetine, sertraline, paroxetine, escitalopram, etc., specifically target SERT binding in the brain. Development of SERT imaging agents may be useful for studying the function of SERT by in vivo imaging. A one-step preparation of [(18)F]FPBM, 2-(2'-(dimethylamino)methyl)-4'-(3-([(18)F]fluoropropoxy)phenylthio)benzenamine, for positron emission tomography (PET) imaging of SERT binding in the brain was achieved. An active OTs intermediate, 9, was reacted with [(18)F]F(-)/K222 to produce [(18)F]FPBM in one step and in high radiochemical yield. This labeling reaction was evaluated and optimized under different temperatures, bases, solvents, and varying amounts of precursor 9. The radiolabeling reaction led to the desired [(18)F]FPBM in one step and the crude product was purified by HPLC purification to give no-carrier-added [(18)F]FPBM (radiochemical yield, 24-33%, decay corrected; radiochemical purity >99%). PET imaging studies in normal monkeys (n=4) showed fast, pronounced uptakes in the midbrain and thalamus, regions known to be rich in SERT binding sites. A displacement experiment with escitalopram (5mg/kg iv injection at 30min after [(18)F]FPBM injection) showed a rapid and complete reversal of SERT binding, suggesting that binding by [(18)F]FPBM was highly specific and reversible. A one-step radiolabeling method coupled with HPLC purification for preparation of [(18)F]FPBM was developed. Imaging studies suggest that it is feasible to use this method to prepare [(18)F]FPBM for in vivo PET imaging of SERT binding in the brain.

Changes of dopamine transporter availability in depressed patients with and without anhedonia: a 123I-N-ω-fluoropropyl-carbomethoxy-3β- (4-Iodophenyl)tropane SPECT study

BACKGROUND/AIMS

Dopamine is an important neurotransmitter involved in the pathophysiology of depression and anhedonia. Dopamine transporters (DAT) may play a crucial role in the pathophysiology of dopaminergic transmission. We investigated the relationship between striatal DAT availability and depression, pointing out possible correlations with anhedonia and treatment outcomes.

METHODS

Ten depressed patients with anhedonia, 10 depressed patients without anhedonia and 20 healthy controls underwent single photon emission computed tomography using (123)I-FP-CIT [(123)I-N-ω-fluoropropyl-carbomethoxy-3β-(4-iodophenyl)tropane]. Psychometric measures included the Snaith-Hamilton Pleasure Scale and the Hamilton Depression Rating Scale. A further assessment of DAT availability was performed in the 10 patients with marked anhedonia after a 3-month pharmacological treatment.

RESULTS

Depressed patients with and without anhedonia showed significantly lower (123)I-FP-CIT binding ratios in the bilateral striatum, caudate and putamen. No significant changes were detected after treatment in the 10 patients with marked anhedonia. When considering clinical outcomes, subjects with remission of depression showed a significant reduction of (123)I-FP-CIT binding ratios in all regions at baseline, but after treatment no differences were found any longer.

CONCLUSIONS

We suppose that a hypofunction of the striatal dopaminergic system may be a 'state' feature of a depressive condition as a whole rather than anhedonia itself. On the other hand, some anhedonic features mainly represent an enduring trait that persists independently of mood state.

Probing the Serotonin Transporter Availability Among Male Cigarette Smokers: A SPECT Study With [123I] ADAM

OBJECTIVE

Genetic studies have suggested that the serotonin transporter (SERT) could be associated with cigarette smoking. However, evidence from neuroimaging is scarce. The aim of the present study was to examine the SERT availability among cigarette smokers by using single-photon emission computed tomography (SPECT).

METHODS

Sixteen male smokers and 32 controls were enrolled. The SERT availability was measured by SPECT with a radiotracer, [I] ADAM, which is highly sensitive and specific to SERT.

RESULTS

No significant difference in SERT availability was found between 2 groups in the midbrain (smokers: 2.12 ± 0.70, nonsmokers: 2.13 ± 0.63; P = 0.86), basal ganglia (smokers: 0.83 ± 0.30, nonsmokers:0.90 ± 0.39; P = 0.95), or thalamus (smokers: 1.14 ± 0.41, nonsmokers: 1.20 ± 0.38; P = 0.88). No significant association was found between the SERT availability, and either the breath carbon monoxide level or the score of the Fagerström Test for Nicotine Dependence.

CONCLUSIONS

Whether the SERT availability in the brain is altered in smokers remains unclear.

Baseline symptom severity predicts serotonin transporter change during psychotherapy in patients with major depression

AIMS

The role of the serotonin transporter (SERT) in the pathophysiology of depression is unclear and only a few follow-up studies exist. Our aim was to measure changes in SERT availability during psychodynamic psychotherapy in patients with major depression over a follow-up time of 12 or 18 months.

METHODS

The patients were studied with iodine-123 labelled 2β-carbomethoxy-3β-(4-iodophenyl) serial single-photon emission tomography imaging and clinical rating scales of symptoms.

RESULTS

Changes in SERT availability had no correlation with the change of symptoms, but the change of SERT availability during psychotherapy in the midbrain was predicted by the baseline severity of the clinical symptoms measured by the Symptom Checklist Depression Scale and the Symptom Checklist Global Severity Index. With cut-off values applied, it was found that SERT availabilities increased in patients with high baseline symptoms, and decreased in patients with low baseline symptoms.

CONCLUSIONS

Together with our earlier finding of decreased SERT in patients with depression, these results indicate a state-dependent and possibly a compensatory role of decreased SERT availability in depression.

Serotonin transporter availability may moderate the association between perceiving stress and depressive tendencies - A SPECT with 5-HTTLPR genotyping study

It was found that serotonin transporter (SERT) gene (5-HTTLPR) polymorphism may moderate the association between perceiving stress and depressive tendency. Although SERT availability in the central nervous system could be associated with 5-HTTLPR polymorphism, whether SERT availability moderates the association between stress and depressive tendency is unclear. This study aimed to investigate whether there is a SERT availability×environmental stress interaction effect, as well as a gene-by-environmental (G×E) interaction effect, using single-photon emission computed tomography (SPECT) with a serotonin transporter radiotracer, [(123)I]ADAM. 87 healthy volunteers were enrolled. The SERT availability was approximated using SPECT with [(123)I]ADAM. Stress and depressive tendencies were measured by the Recent Life Change Questionnaire (RLCQ) and the Taiwanese Depression Questionnaire (TDQ), respectively. A significant interaction of sex×RLCQ×thalamic SERT availability on the TDQ was found, and this effect was robust after controlling for the effect of the SS genotype. The interaction of RLCQ×thalamic SERT availability on the TDQ was significant among males. In particular, a significant association between RLCQ and TDQ (Spearman correlation, ρ=0.64, p<0.01) was found among male subjects with a lower level of thalamic SERT availability. SERT availability may play a role in depressive tendency when under perceived stress among healthy individuals, independent of G×E. This finding provides new evidence that confirms the role of the serotonergic system in the association between stress and depression. Males with lower levels of SERT availability may be more vulnerable to the effects of negative life events.

Which demographic variables are necessary to correct in neuroimaging studies of serotonin transporter availability? A SPECT study with [¹²³I]ADAM

Previous studies have shown that many demographic variables influence serotonin transporter (SERT) availability as assessed by single photon emission computed tomography (SPECT). The aim of this study was to explore which demographic variables influenced the SERT availability most in a SPECT study with [(123)I]ADAM. Ninety-five healthy volunteers were recruited. Age, sex, smoking, alcohol intake, educational level, body mass index, seasonal change, and SERT availability were recorded and then analyzed by multivariate linear regression. Age was the only variable that was significantly associated with SERT availability (calculate: (midbrain-cerebellum)/cerebellum). Furthermore, the inverse correlation of age and SERT availability may be present only before the age of 47. Age should be a covariate in SERT-related neuroimaging analyses, particularly in participants under the age of 47 years.

Molecular imaging of striatal dopamine transporters in major depression--a meta-analysis

BACKGROUND

Increasing studies have revealed the dopamine transporter (DAT) availability altered in striatum associated with major depression. However, the results remain inconsistent.

METHODS

To assess the alteration of striatal DAT availability in major depression, we performed a meta-analysis based on 12 case-control molecular imaging studies, including a total of 209 depressed patients and 314 healthy controls. Hedges׳ g and corresponding 95% confidence intervals (CIs) for striatal DAT availability in major depression compared with controls were estimated.

RESULTS

Our meta-analysis revealed no evidence for the alteration of striatal DAT availability in major depression (Hedges׳ g=0.09, CI 95% from -0.43 to 0.61, P=0.73). Meta-regression analyses suggested that there were no moderating effects for age, gender, year of publication, sample size, medication exposures and severity of depression on the hedges׳g values for striatal DAT availability.

LIMITATIONS

The results should be treated with caution because of the significant heterogeneity and the potential interference of confounding factors in this meta-analysis.

CONCLUSIONS

Our results showed no altered striatal DAT availability in major depression and indicated that striatal DAT may not implicated in the pathophysiology of major depression.

Disproportionate Reduction of Serotonin Transporter May Predict the Response and Adherence to Antidepressants in Patients with Major Depressive Disorder: A Positron Emission Tomography Study with 4-[18F]-ADAM

BACKGROUND

Many lines of evidence suggest the role of serotonin transporter (SERT)-mediated reuptake of serotonin in the pathophysiology and treatment of major depressive disorder (MDD). This study aimed to examine whether the pretreatment of SERT binding potential or SERT binding ratio between terminal projection regions relative to the midbrain raphe nuclei was associated with treatment outcomes to SERT-targeted antidepressants.

METHODS

We recruited 39 antidepressant-naïve patients with MDD and 39 heathy controls. Positron emission tomography with N,N-dimethyl-2-(2-amino-4-[(18)F]fluorophenylthio)benzylamine (4-[(18)F]-ADAM) was used to measure in vivo SERT availability prior to antidepressant treatment. The 21-item Hamilton Depression Rating Scale (HDRS) was use to assess the severity of depression from baseline to week 6. All the patients with MDD had HDRS scores of 18 or more.

RESULTS

Pretreatment SERT binding in the thalamus and striatum positively correlated with an early reduction in HDRS scores at week 3. Nonresponders and dropout patients showed a proportionate reduction in SERT binding in the terminal projection regions and midbrain compared to healthy controls. In contrast, a disproportionate reduction in SERT binding in the terminal projection regions relative to midbrain was observed in responders.

CONCLUSIONS

The results of this study suggested that a disproportionate reduction in SERT binding between terminal projection regions and midbrain may predict better treatment outcomes in patients with MDD.

Biomarker approaches in major depressive disorder evaluated in the context of current hypotheses

Major depressive disorder is a heterogeneous disorder, mostly diagnosed on the basis of symptomatic criteria alone. It would be of great help when specific biomarkers for various subtypes and symptom clusters of depression become available to assist in diagnosis and subtyping of depression, and to enable monitoring and prognosis of treatment response. However, currently known biomarkers do not reach sufficient sensitivity and specificity, and often the relation to underlying pathophysiology is unclear. In this review, we evaluate various biomarker approaches in terms of scientific merit and clinical applicability. Finally, we discuss how combined biomarker approaches in both preclinical and clinical studies can help to make the connection between the clinical manifestations of depression and the underlying pathophysiology.

Positive association between neuroticism and working memory in healthy female volunteers

OBJECTIVES

Neuroticism is an important personality trait that is often associated with mental disorders. It has been reported that lower levels of neuroticism are associated with better cognitive function later in life; however, the concurrent association is unclear.

METHODS

A total of 184 healthy participants, 84 males and 100 females, completed the Wechsler Memory Scale-Revised version and the 24-item neuroticism subscale of the Maudsley personality inventory.

RESULTS

The neuroticism score was found to be positively associated with verbal memory, general memory, and delayed recall, particularly among healthy females, independent of the effect of age.

CONCLUSION

The mechanisms of this association remain to be elucidated. Clinicians should pay additional attention to this phenomenon.

Serotonin and mental disorders: a concise review on molecular neuroimaging evidence

Serotonin is one of the most important neurotransmitters influencing mental health and, thus, is a potential target for pharmaco-logical treatments. Functional neuroimaging techniques, such as positron-emission tomography (PET) and single photon emission computed tomography (SPECT), could provide persuasive evidence for the association between mental disorders and serotonin. In this concise review, we focus on evidence of the links between serotonin and major depressive disorders, as well as other mood disorders, anxiety disorders, schizophrenia, addiction, attention deficit hyperactivity disorder (ADHD), and autism.

Sex-specific associations between plasma oxytocin levels and schizotypal personality features in healthy individuals

OBJECTIVES

Oxytocin (OT) has been shown to play a crucial role in the biology of social interaction. Sex differences associated with this neuropeptide system have been reported. OT may serves as an indicator of interpersonal stress, especially in women. The aim of this study was to investigate the sex-specific associations between plasma OT levels and schizotypal personality features, especially in interpersonal dimension, in healthy individuals.

METHODS

Ninety six healthy participants, including 41 males and 55 females, were recruited. Fasting blood samples were analyzed by enzyme immunoassay of OT. The Schizotypal Personality Questionnaire (SPQ) was administered. Mann-Whitney U test was used to test the difference between male and female. Spearman's ρ correlation analysis (two-tailed) was carried out to examine the association between OT level and SPQ score.

RESULTS

The results showed that OT level was significantly positively correlated with total score and interpersonal dysfunction dimensional scores of the SPQ only in females.

CONCLUSIONS

Although the causal relationship remains unclear, our findings provide further evidence to support the sexual dimorphic role of OT in interpersonal biology. Moreover, the effect of sex difference also is taken into consideration.

Imaging studies on dopamine transporter and depression: a review of literature and suggestions for future research

We review the conflicting results from imaging studies of dopamine transporter availability in depressed patients and also discuss the heterogeneity of the variables involved. Major depression includes diverse clinical manifestations and in recent years there has been an increasing interest in the identification of homogeneous phenotypes and different clinical subtypes of depression, e.g. anhedonic depression, retarded depression, etc. In addition, the use of different radioligands and imaging techniques, diverse rating scales, together with the lack of control of clinical variables (clinical course, recent or past use of substances of abuse, etc.) make it difficult to clearly identify neuronal regions or networks with consistently abnormal structures or functions in major depressive disorder. It is probably necessary to build a shared approach between clinicians and researchers in order to identify standardized procedures to better understand the role of the dopamine transporter in depression. We outline a list of major issues and also suggest some standardized procedures in collecting clinical and imaging data on major depressed patients. Our aim is to delineate a possible "modus operandi" that would be a proposal for neuroreceptor studies on major depression.

Lower availability of midbrain serotonin transporter between healthy subjects with and without a family history of major depressive disorder - a preliminary two-ligand SPECT study

PURPOSE

Serotonin transporter (SERT) and dopamine transporter (DAT) levels differ in patients with major depressive disorder (MDD) who are in a depressed state in comparison with healthy controls. In addition, a family history of depression is a potent risk factor for developing depression, and inherited vulnerability to serotonergic and dopaminergic dysfunction is suspected in this. The aim of this study was to examine the availabilities of midbrain SERT and striatal DAT in healthy subjects with and without a first-degree family history of MDD.

METHODS

Eight healthy subjects with first-degree relatives with MDD and 16 sex- and age-matched healthy controls were recruited. The availabilities of SERT and DAT were approximated using SPECT, employing [¹²³I] 2-((2-((dimethylamino) methyl) phenyl)thio)-5-iodophenylamine (ADAM) and [(⁹⁹m)Tc] TRODAT-1 as the ligands, respectively. There are missing data for one participant with a first-degree family history of MDD from the ADAM study, due to a lack of the radio-ligand at the time of experiment.

RESULTS

SERT availability in the midbrain was significantly lower in subjects with a first-degree family history of MDD than in healthy subjects. However, DAT availability was no different between two groups.

CONCLUSIONS

The results with regard to the midbrain SERT level suggest the heritability of MDD.

Serotonin transporter availability in the midbrain and perceived social support in healthy volunteers

OBJECTIVE

Serotonin modulates human behavior and emotion. Recent evidence implies that a higher level of serotonergic activity could be associated with a higher level of perceived social support. This study aimed to examine the correlation between serotonin transporter (SERT) availability and perceived social support scores in healthy volunteers.

METHODS

111 healthy participants, 50 males and 61 females, were enrolled from the community and completed the Measurement of Support Function questionnaire. Single photon emission computed tomography (SPECT) with [(123)I] ADAM was performed to examine SERT availability.

RESULTS

Perceived social support was positively correlated with SERT availability (Spearman's ρ=0.29, p<0.01; χ(2)=7.57, p<0.01), particularly in males (Spearman's ρ=0.37, p<0 .01; χ(2)=11.77, p<0.01). Censored regressions indicated that these associations are not influenced by a ceiling effect and remained significant after controlling the effect of age.

CONCLUSIONS

This result confirmed the correlation between perceived social support and central serotonergic activity. However, this correlation was present only in males.

SPECT imaging of fibrin using fibrin-binding peptides

Noninvasive detection of fibrin in vivo using diagnostic imaging modalities may improve clinical decision-making on possible therapeutic options in atherosclerosis, cancer and thrombus-related pathologies such as pulmonary embolism and deep venous thrombosis. The aim of this study was to assess the potential of a novel (111)In-labeled fibrin-binding peptide (FibPep) to visualize thrombi in mice noninvasively using single-photon emission computed tomography (SPECT). FibPep and a negative control peptide (NCFibPep) were synthesized and their fibrin-binding properties were assessed in vitro. FibPep showed enhanced binding compared with NCFibPep to both fibrin and blood clots. FibPep bound to fibrin with a dissociation constant (K(d)) of 0.8 μ m, whereas NCFibPep displayed at least a 100-fold lower affinity towards fibrin. A FeCl3 -injury carotid artery thrombosis mouse model was used to evaluate the peptides in vivo. FibPep and NCFibPep displayed rapid blood clearance and were eliminated via the renal pathway. In vivo SPECT imaging using FibPep allowed clear visualization of thrombi. Ex vivo biodistribution showed significantly increased uptake of FibPep in the thrombus-containing carotid in comparison to the noninjured carotid (5.7 ± 0.7 and 0.6 ± 0.4% injected dose per gram (%ID g(-1)), respectively; p < 0.01; n = 4), whereas nonspecific NCFibPep did not (0.4 ± 0.2 and 0.3 ± 0.0%ID g(-1), respectively; n = 4). In conclusion, FibPep displayed high affinity towards fibrin in vitro and rapid blood clearance in vivo, and allowed sensitive detection of thrombi using SPECT imaging. Therefore, this particular imaging approach may provide a new tool to diagnose and monitor diseases such as atherosclerosis and cancer.

Change over time in brain serotonin transporter binding in major depression: effects of therapy measured with [(123) I]-ADAM SPECT

Several studies have reported low brain serotonin transporter (SERT) binding in individuals with major depression. We hypothesized that the SERT standardized uptake ratio (SUR) values using [(123) I]-ADAM single photon emission computed tomography would increase in depressed subjects who responded to cognitive behavior therapy (CBT) compared to CBT nonresponders. [(123) I]-ADAM scans were acquired before and after 12 weeks of CBT from 20 depressed subjects and on two occasions 12 weeks apart from 10 nondepressed, healthy volunteers. The primary outcome measure was change over time in SUR values in the midbrain, medial temporal lobe, and basal ganglia regions. Depressed subjects demonstrated low pretreatment mean SUR values that significantly increased over time in the midbrain (P = .011), right medial temporal lobe (P = .008), and left medial temporal lobe (P = .000) regions. Treatment responders showed a significant increase over time in SUR values in left medial temporal lobe (P = .029) and right medial temporal lobe (P = .007) regions. Partial and nonresponder subjects also showed a significant increase over time in SUR values in the left medial temporal region (P = .040) (vs. healthy volunteers), but to a lesser degree. The findings suggest that low pretreatment SERT binding may increase over time in some depressed individuals who experience symptom improvement.

The interaction between dopamine transporter function, gender differences, and possible laterality in depression

The Dopamine Transporter (DAT) can reflect the general state of striatal dopamine activity. This current study examined the role of DAT in depressed patients before and after bupropion treatment. Twenty-three patients with major depression were treated with bupropion for 8 weeks. Before and after the treatment, they and 20 normal subjects received the radioligand (99m)Tc-TRODAT-1 single photon emission tomography scan (SPECT). Subjects were assessed with the Hamilton Depression Rating Scale. All DAT images were spatially normalized to an averaged brain template, and the specific binding ratios of the striatum, caudate, and putamen were calculated according the formulae of: [region counts] / [occipital counts] - 1. Depressed patients had greater DAT availability on both sides of the striatum. DAT binding was significantly decreased in the striatum after bupropion treatment. Women had higher initial and final DAT binding in the right and left caudate when compared to depressed men. DAT binding decreased in all areas of the brain in women after successful antidepressant treatment, but only in the right caudate of men. Depressed patients had a greater availability of DAT; it was decreased after bupropion treatment.Women seemed to have more DAT availability.

Dual-isotope 111In/177Lu SPECT imaging as a tool in molecular imaging tracer design

The synthesis, design and subsequent pre-clinical testing of new molecular imaging tracers are topic of extensive research in healthcare. Quantitative dual-isotope SPECT imaging is proposed here as a tool in the design and validation of such tracers, as it can be used to quantify and compare the biodistribution of a specific ligand and its nonspecific control ligand, labeled with two different radionuclides, in the same animal. Since the biodistribution results are not blurred by experimental or physiological inter-animal variations, this approach allows determination of the ligand's net targeting effect. However, dual-isotope quantification is complicated by crosstalk between the two radionuclides used and the radionuclides should not influence the biodistribution of the tracer. Here, we developed a quantitative dual-isotope SPECT protocol using combined (111)Indium and (177)Lutetium and tested this tool for a well-known angiogenesis-specific ligand (cRGD peptide) in comparison to a potential nonspecific control (cRAD peptide). Dual-isotope SPECT imaging of the peptides showed a similar organ and tumor uptake to single-isotope studies (cRGDfK-DOTA, 1.5 ± 0.8%ID cm(-3); cRADfK-DOTA, 0.2 ± 0.1%ID cm(-3)), but with higher statistical relevance (p-value 0.007, n = 8). This demonstrated that, for the same relevance, seven animals were required in case of a single-isotope test design as compared with only three animals when a dual-isotope test was used. Interchanging radionuclides did not influence the biodistribution of the peptides. Dual-isotope SPECT after simultaneous injection of (111)In and (177)Lu-labeled cRGD and cRAD was shown to be a valuable method for paired testing of the in vivo target specificity of ligands in molecular imaging tracer design.

Low brain serotonin transporter binding in major depressive disorder

We examined midbrain, medial temporal lobe, and basal ganglia serotonin transporter (SERT) distribution volume ratio (DVR) values in subjects with major depressive disorder versus healthy volunteers using a selective SERT radioligand and single photon emission computed tomography (SPECT). We hypothesized that the DVR value for SERT binding would be lower in depressed versus non-depressed subjects. [(123)I]-ADAM SPECT scans were acquired from 20 drug free, depressed subjects and 20 drug-free depressed subjects and 10 drug-free healthy volunteers. The primary outcome measure was the DVR value for [(123)I]-ADAM uptake in the midbrain, medial temporal lobe, and basal ganglia regions. Depressed subjects demonstrated significantly lower DVR values in the midbrain, right and left medial temporal lobe, and right and left basal ganglia. There was significant probability that lower DVR values could distinguish between depressed and non-depressed subjects in the midbrain, medial temporal lobe, and the right and left basal ganglia. These findings confirm prior observations of lower SERT binding in depression, and suggest that low SERT binding may represent a putative biomarker of depression. Future studies are needed to confirm these observations.

Key players in major and bipolar depression--a retrospective analysis of in vivo imaging studies

In the present study, we evaluated the contribution of the individual synaptic constituents of all assessed neurotransmitter systems by subjecting all available in vivo imaging studies on patients with unipolar major depressive disorder (MDD) and bipolar depression (BD) to a retrospective analysis. In acute MDD, findings revealed significant increases of prefrontal and frontal DA synthesis, decreases of thalamic and midbrain SERT, increases of insular SERT, decreases of midbrain 5-HT(1A) receptors and decreases of prefrontal, frontal, occipital and cingulate 5-HT(2A) receptors, whereas, in remission, decreases of striatal D₂ receptors, midbrain SERT, frontal, parietal, temporal, occipital and cingulate 5-HT(1A) receptors and parietal 5-HT(2A) receptors were observed. In BD, findings indicated a trend towards increased striatal D₂ receptors in depression and mania, decreased striatal DA synthesis in remission and decreased frontal D₁ receptors in all three conditions. Additionally, there is some evidence that ventrostriatal and hippocampal SERT may be decreased in depression, whereas in remission and mania elevations of thalamic and midbrain SERT, respectively, were observed. Moreover, in depression, limbic 5-HT(1A) receptors were elevated, whereas in mania a decrease of both cortical and limbic 5-HT(2A) receptor binding was observed. Furthermore, in depression, prefrontal, frontal, occipital and cingulate M2 receptor binding was found to be reduced. From this, a complex pattern of dysregulations within and between neurotransmitter systems may be derived, which is likely to be causally linked not only with the subtype and duration of disease but also with the predominance of individual symptoms and with the kind and duration of pharmacological treatment(s).

Association between somatization subscale score and serotonin transporter availability in healthy volunteers--a single photon emission computed tomography study with [¹²³I] ADAM

RATIONALE AND OBJECTIVE

Serotonin is one of the key neuromodulators involved in fundamental cerebral functions and behaviors. Previous study has demonstrated that somatization symptoms are probably associated with central serotonergic circuits, which are implicated in anxiety and nociception regulation. This study aims to examine the correlation between somatization subscale score and serotonin transporter (SERT) availability in healthy volunteers.

METHODS

Sixty-four healthy participants, 26 males and 38 females, were enrolled from the community and were administered the single somatization subscale of the Chinese symptom checklist 90 revised (SCL90-R). Single photon emission computed tomography with [(123)I] 2-((2-((dimethylamino)methyl)phenyl)thio)-5-iodophenylamine was also performed to examine SERT availability.

RESULTS

The somatization scores were negatively correlated with SERT availability (Spearman's ρ = -0.35, p = 0.005), particularly in males (Spearman's ρ = -0.54, p = 0.004).

CONCLUSION

This result reconfirmed the correlation between central serotonergic activity and the intensity of somatization symptoms, even in healthy participants. However, a gender difference exists in this correlation.