Striatal dopamine transporter changes after glucose loading in humans

Hypomethylation of the dopamine transporter (DAT) gene promoter is associated with hyperphagia-related behavior in Prader-Willi syndrome: a case-control study

Prader-Willi syndrome (PWS), a neurodevelopmental disorder based on the loss of paternally derived but maternally imprinted genes on chromosome 15q11-13, is typically associated with hyperphagia-related behavior leading to massive obesity. Recently, there has been increasing evidence for dysregulated expression patterns of genes outside the PWS locus that influence the behavioral phenotype and for alterations in the dopaminergic system associated with weight regulation in PWS. In this study, we investigated the epigenetic regulation of the promoter regions of the dopamine transporter (DAT) and dopamine receptor D2 (DRD2) genes and their association with hyperphagia-related behavior in PWS. Methylation of the DAT and DRD2 promoter regions was examined by DNA bisulfite sequencing in 32 individuals with PWS and compared with a control group matched for sex, age, and body mass index (BMI). Hyperphagia-related behavior was assessed using the Hyperphagia Questionnaire for Clinical Trials (HQ-CT). Analysis by linear mixed models revealed a significant effect of factor group on mean DAT promoter methylation rate with decreased mean methylation in PWS (7.3 ± 0.4%) compared to controls (18.8 ± 0.6%), p < 0.001. In the PWS group, we further identified effects of HQ-CT score and BMI on DAT promoter methylation. Although also statistically significantly different (8.4 ± 0.2 in PWS, 10.5 ± 0.3 in controls, p < 0.001), DRD2 promoter methylation visually appeared to be evenly distributed between groups, raising concerns regarding a biological effect. Here, we provide evidence for altered epigenetic regulation of the DAT gene in PWS, which is associated with PWS-typical hyperphagia-related behaviors.

Dopamine receptor and dopamine transporter in obesity: A meta-analysis

The brain plays a major role in controlling the desire to eat. This meta-analysis aimed to assess the association between dopamine receptor (DR) availability and dopamine transporter (DAT) availability, measured using positron emission tomography, and obesity. We performed a systematic search of MEDLINE (from inception to November 2020) and EMBASE (from inception to November 2020) for articles published in English using the keywords "dopamine receptor," "dopamine transporter," "obesity," and "neuroimaging." Body mass index (BMI) and the corresponding binding potential (BP_ND ) were extracted from figures in each study using Engauge Digitizer, version 12.1, and plotted for radiopharmaceuticals and regions of interest (ROIs). Five studies involving 119 subjects with DR and five studies including 421 subjects with DAT were eligible for inclusion in this study. In overweight or obese subjects with BMI of 25 kg/m² or higher, DR availability from ¹¹ C-Racloprie was negatively associated with BMI. However, DR availability from ¹¹ C-PHNO was positively associated with BMI. DAT ratio was calculated after dividing DAT availabilities of overweight/obese BMI with mean DAT availabilities of normal BMI. The association between DAT ratio and BMI was not significant regardless of radiopharmaceuticals. In conclusion, dopamine plays a main role in the reward system with regard to obesity. Overweight and obese subjects had negative association between DR availability from ¹¹ C-Raclopride and BMI. However, the association of DR availability with BMI was dependent on radiopharmaceuticals. DAT availability did not show the significant relationship with BMI regardless of radiopharmaceuticals.

Molecular Imaging of Central Dopamine in Obesity: A Qualitative Review across Substrates and Radiotracers

Dopamine is a neurotransmitter that plays a crucial role in adaptive behavior. A wealth of studies suggests obesity-related alterations in the central dopamine system. The most direct evidence for such differences in humans comes from molecular neuroimaging studies using positron emission tomography (PET) and single-photon emission computed tomography (SPECT). The aim of the current review is to give a comprehensive overview of molecular neuroimaging studies that investigated the relation between BMI or weight status and any dopamine target in the striatal and midbrain regions of the human brain. A structured literature search was performed and a summary of the extracted findings are presented for each of the four available domains: (1) D2/D3 receptors, (2) dopamine release, (3) dopamine synthesis, and (4) dopamine transporters. Recent proposals of a nonlinear relationship between severity of obesity and dopamine imbalances are described while integrating findings within and across domains, after which limitations of the review are discussed. We conclude that despite many observed associations between obesity and substrates of the dopamine system in humans, it is unlikely that obesity can be traced back to a single dopaminergic cause or consequence. For effective personalized prevention and treatment of obesity, it will be crucial to identify possible dopamine (and non-dopamine) profiles and their functional characteristics.

Limited power of dopamine transporter mRNA mapping for predicting dopamine transporter availability

Dopamine transporters (DAT) are transmembrane proteins that translocate dopamine from the extracellular space into presynaptic neurons. We aimed to investigate the predictive power of DAT mRNA for DAT protein expression, measured using positron emission tomography (PET). We performed ¹⁸ F-FP-CIT PET scans in 35 healthy individuals. Binding potentials (BP_ND ) from the ventral striatum, caudate nucleus, putamen, and middle frontal, orbitofrontal, cingulate, parietal, and temporal cortices were measured. DAT gene expression data were obtained from the freely available Allen Human Brain Atlas derived from six healthy donors. The auto-correlation of PET-derived BP_ND s for DAT was intermediate (mean ρ² = 0.66) with ρ² ranging from 0.0811 to 1. However, the auto-correlation of mRNA expression was weak across the probes with a mean ρ² of 0.09-0.23. Cross-correlations between PET-derived BP_ND s and mRNA expression were weak with a mean ρ² ranging from 0 to 0.22 across the probes. In conclusion, we observed weak associations between DAT mRNA expression and DAT availability in human brains. Therefore, DAT mRNA mapping may have only limited predictive power for DAT availability in humans. However, the difference in distribution of DAT mRNA and DAT protein may influence this limitation. This article is protected by copyright. All rights reserved.

Serotonin transporter is negatively associated with body mass index after glucose loading in humans

Serotonin transporter (SERT) is a presynaptically localized membrane protein that regulates the serotonin transmission via its reuptake of released serotonin. We hypothesized that glucose loading may change SERT availability from brainstem in humans. An intravenous bolus injection of ¹⁸F-FP-CIT was administered after the infusion of glucose or placebo (normal saline), and the emission data were acquired over 90 mins in 33 healthy nonobese subjects. For a volume-of-interest-based analysis, an atlas involving midbrain, and pons was applied. SERT availability, binding potential (BP_ND), were measured via the simplified reference tissue method with a reference of cerebellum. For a voxel-based analysis, statistical parametric mapping 12 was used with parametric BP_ND images. BP_NDs from midbrain (p=0.8937), and pons (p=0.1115) were not different between glucose and placebo loading. Both of BP_NDs from midbrain after glucose, and placebo loading were negatively correlated with body mass index (BMI). BMI showed a trend of negative correlation with glucose-loaded BP_ND from pons, whereas, placebo-loaded BP_NDs from pons did not show any significant association with BMI. In conclusion, SERT availability was negatively correlated with BMI after glucose loading in humans. SERT might have a role in eating behavior through the action of insulin. Further studies are needed to elucidate the underlying mechanism of this phenomenon.

Striatal DAT availability does not change after supraphysiological glucose loading dose in humans

Brain dopamine neurotransmission is regulated by the dopamine transporter (DAT), which drives reuptake of extracellular dopamine into the presynaptic neurons. We hypothesized that the glucose loading dose would affect the striatal DAT availability. An i.v. bolus injection of 18F-FP-CIT was administered after infusion of low-dose glucose (300 mg/kg), high-dose glucose (600 mg/kg) or placebo (normal saline). The emission data were acquired over 90 min in 23 healthy male subjects. Substantial increases of binding potential (BPNDs) from ventral striatum (VST), caudate nucleus, and putamen were observed after low-dose glucose loading (+26.0, +87.0, and +37.8%) and after high-dose glucose loading (+10.4, +51.9, and +22.0%). BPNDs of the caudate nucleus and putamen showed significant differences (P = 0.0472 and 0.0221) after placebo, low-dose glucose, and high-dose glucose loading. BPNDs in the caudate nucleus and putamen after placebo, low-dose glucose, and high-dose glucose loading were positively intercorrelated with each other. In conclusion, striatal DAT changes after physiological glucose loading, but not after supraphysiological glucose loading in humans. DAT availabilities after placebo, low-dose glucose, high-dose glucose loading were correlated to each other in the caudate nucleus and putamen, but not in the VST. Therefore, sub-regional variability in DAT regulatory mechanisms mediated by insulin may exist in humans.

No association of Brain-derived neurotrophic factor with striatal dopamine transporter availability in healthy subjects

OBJECTIVE

Brain-derived neurotrophic factor (BDNF) is a neurotrophin that plays a key role in brain plasticity, synaptic function, neuronal survival, learning, and memory formation. We aimed to investigate the association of BDNF with dopamine transporter (DAT) availabilities measured by positron emission tomography (PET) in healthy subjects.

METHODS

Thirty-five healthy, male subjects without brain injury, neuropsychological disorders were included in this study. The emission data were acquired over 90 mins with 50 frames after injection of 18F-FP-CIT using PET. Binding potentials (BPNDs) of ventral striatum (VST), caudate nucleus, putamen were measured with the simplified reference tissue method. The serum BDNF level (pg/mL) was measured through enzyme-linked immunosorbent assay method.

RESULTS

Thirty-five healthy males with a mean age of 24.4 ± 2.7 years were included in this study. Multiple regression was done to investigate the association between striatal BPNDs from VST, caudate nucleus, putamen and serum BDNF after adjusting for age. None of striatal BPNDs from VST (p=0.8450), caudate nucleus (p=0.4783), and putamen (p=0.7994) were associated with serum BDNF.

CONCLUSION

Striatal DAT availabilities measured from PET were not associated with the serum BDNF in healthy subjects.

The association of DAT gene methylation with striatal DAT availability in healthy subjects

Background

DNA methylation inhibits gene expression by preventing transcription factors from binding to DNA. Functioning of nigrostriatal dopaminergic neurons is influenced by the expression of the dopamine transporter (DAT), and genetic variations in the gene encoding DAT contribute to differences in reward processing. We aimed to investigate the action of DAT methylation on DAT protein expression measured by positron emission tomography (PET).

Methods

The emission data were acquired over 90 min with 50 frames after injection of ¹⁸F-FP-CIT using PET. Binding potentials (BP_NDs) of ventral striatum, caudate nucleus, putamen were measured with the simplified reference tissue method. Genomic DNA was extracted from subjects’ blood sampling. Methylation of 4 regions in SLC6A3 gene was assessed using bisulfite pyrosequencing. The mean percentage of methylation (%) for each cluster was calculated by taking the average of all CpG site methylation levels measured within the cluster. Subjects were assessed with the Generalized Reward and Punishment Expectancy Scales (GRAPES) that consists of 30 items related with the reward and punishment that individuals expect for their behaviors.

Results

Thirty-five healthy males, with an age range between 20 and 30 years, and a mean age of 24.4 ± 2.7 years, were included in this study. The mean percentage of methylation (%) from cluster C showed a trend of positive correlation with DAT availability of ventral striatum (rho = 0.3712, p = 0.0281), not significant after correction for multiple comparisons, and a significant correlation with GRAPES A: reward expectancy scale (rho = 0.7178, p < 0.0001).

Conclusion

DAT methylation from peripheral blood showed a trend of positive correlation with DAT availability of ventral striatum in healthy subjects; however, it was not significant after correction for multiple comparison. The degrees of methylation from cluster C of DAT in peripheral blood were significantly correlated with reward scales of GRAPES A: reward expectancy scale. The association between DAT methylation and DAT expression needs to be investigated further.

Hedonic Rating of Sucrose Is Sub-Regionally Associated with Striatal Dopamine Transporter in Humans

BACKGROUND

Eating behavior is determined by both homeostatic and hedonic values.

OBJECTIVE

We investigated the association of hedonic value with striatal dopamine transporter (DAT) availability sub-regionally.

METHOD

An intravenous bolus injection of 18F-FP-CIT was administered after the infusion of glucose or placebo, and the emission data were acquired over 90 min. DAT availability and binding potential (BPND) were measured via the simplified reference tissue method. Subjects were assessed with sensory taste test of sucrose solutions. The "most liked" sucrose concentration (%) was determined as the hedonic rating for sucrose.

RESULTS

Twenty healthy males participated in this study. After glucose loading, BPNDs of putamen significantly increased, and those of caudate nucleus showed the increasing trend, while those of ventral striatum were not significantly different. After glucose loading, the "most liked" sucrose concentration (%) was negatively associated with BPNDs of caudate nucleus and showed the trend of positive association with those from ventral striatum. Slopes of regression lines were significantly different according to the sub-regions of striatum.

CONCLUSION

We have highlighted that striatal DAT increased after glucose loading in dorsal striatum, not in ventral striatum. These changes of striatal DAT were sub-regionally associated with the hedonic rating of sucrose from each subject.