Dopa Uptake Research Articles

Functional connectivity of the cortico-subcortical sensorimotor loop is modulated by the severity of nigrostriatal dopaminergic denervation in Parkinson’s Disease

To assess if the severity of nigrostriatal innervation loss affects the functional connectivity (FC) of the sensorimotor cortico-striato-thalamic-cortical loop (CSTCL) in Parkinson’s Disease (PD), Resting-State functional MRI and 18F-DOPA PET data, simultaneously acquired on a hybrid PET/MRI scanner, were retrospectively analyzed in 39 PD and 16 essential tremor patients. Correlations between posterior Putamen DOPA Uptake (pPDU) and the FC of the main CSTCL hubs were assessed separately in the two groups, analyzing the differences between the two groups by a group-by-pPDU interaction analysis of the resulting clusters’ FC. Unlike in essential tremor, in PD patients pPDU correlated inversely with the FC of the thalamus with the sensorimotor cortices, and of the postcentral gyrus with the dorsal cerebellum, and directly with the FC of pre- and post-central gyri with both the superior and middle temporal gyri and the paracentral lobule, and of the caudate with the superior parietal cortex. The interaction analysis confirmed the significance of the difference between the two groups in these correlations. In PD patients, the post-central cortex FC, in the clusters correlating directly with pPDU, negatively correlated with both UPDRS motor examination score and Hoehn and Yahr stage, independent of the pPDU, suggesting that these FC changes contribute to motor impairment. In PD, nigrostriatal innervation loss correlates with a decrease in the FC within the sensorimotor network and between the sensorimotor network and the superior temporal cortices, possibly contributing to motor impairment, and with a strengthening of the thalamo-cortical FC, that may represent ineffective compensatory phenomena.

Imaging synaptic dopamine availability in individuals at clinical high-risk for psychosis: a [11C]-(+)-PHNO PET with methylphenidate challenge study.

Patients at clinical high-risk (CHR) for psychosis show elevations in [18F]DOPA uptake, an estimate of dopamine (DA) synthesis capacity, in the striatum predictive of conversion to schizophrenia. Intrasynaptic DA levels can be inferred from imaging the change in radiotracer binding at D2 receptors due to a pharmacological challenge. Here, we used methylphenidate, a DA reuptake inhibitor, and [11C]-(+)-PHNO, to measure synaptic DA availability in CHR both in striatal and extra-striatal brain regions. Fourteen unmedicated, nonsubstance using CHR individuals and 14 matched control subjects participated in the study. Subjects underwent two [11C]-(+)-PHNO scans, one at baseline and one following administration of a single oral dose (60 mg) of methylphenidate. [11C]-(+)-PHNO BPND, the binding potential relative to the nondisplaceable compartment, was derived using the simplified reference tissue model with cerebellum as reference tissue. The percent change in BPND between scans, ΔBPND, was computed as an index of synaptic DA availability, and group comparisons were performed with a linear mixed model. An overall trend was found for greater synaptic DA availability (∆BPND) in CHR than controls (p = 0.06). This was driven entirely by ∆BPND in ventral striatum (-34 ± 14% in CHR, -20 ± 12% in HC; p = 0.023). There were no significant group differences in any other brain region. There were no significant differences in DA transmission in any striatal region between converters and nonconverters, although this finding is limited by the small sample size (N = 2). There was a strong and negative correlation between ΔBPND in VST and severity of negative symptoms at baseline in the CHR group (r = -0.66, p < 0.01). We show abnormally increased DA availability in the VST in CHR and an inverse relationship with negative symptoms. Our results suggest a potential early role for mesolimbic dopamine overactivity in CHR. Longitudinal studies are needed to ascertain the significance of the differential topography observed here with the [18F]DOPA literature.

Extended Treatment with Glial Cell Line-Derived Neurotrophic Factor in Parkinson’s Disease

Background:Intraputamenal glial cell line-derived neurotrophic factor (GDNF), administered every 4 weeks to patients with moderately advanced Parkinson’s disease, did not show significant clinical improvements against placebo at 40 weeks, although it significantly increased [18F]DOPA uptake throughout the entire putamen.Objective:This open-label extension study explored the effects of continued (prior GDNF patients) or new (prior placebo patients) exposure to GDNF for another 40 weeks.Methods:Using the infusion protocol of the parent study, all patients received GDNF without disclosing prior treatment allocations (GDNF or placebo). The primary outcome was the percentage change from baseline to Week 80 in the OFF state Unified Parkinson’s Disease Rating Scale (UPDRS) motor score.Results:All 41 parent study participants were enrolled. The primary outcome decreased by 26.7±20.7% in patients on GDNF for 80 weeks (GDNF/GDNF; N = 21) and 27.6±23.6% in patients on placebo for 40 weeks followed by GDNF for 40 weeks (placebo/GDNF, N = 20; least squares mean difference: 0.4%, 95% CI: –13.9, 14.6, p = 0.96). Secondary endpoints did not show significant differences between the groups at Week 80 either. Prespecified comparisons between GDNF/GDNF at Week 80 and placebo/GDNF at Week 40 showed significant differences for mean OFF state UPDRS motor (–9.6±6.7 vs. –3.8±4.2 points, p = 0.0108) and activities of daily living score (–6.9±5.5 vs. –1.0±3.7 points, p = 0.0003). No treatment-emergent safety concerns were identified.Conclusions:The aggregate study results, from the parent and open-label extension suggest that future testing with GDNF will likely require an 80- rather than a 40-week randomized treatment period and/or a higher dose.

Suspicious for recurrent low and high grade glioma and indeterminate MRI: the role of 18F-DOPA PET/CT

1691 Objectives: ACKGROUND. The aim of present study was to assess the role of 18F-FDOPA PET/CT in patients who had a suspicious forrecurrent low and high grade glioma but with an indeterminate MRI.MATERIALS AND METHODS . From a monocentric database, we retrospectively analyzed 21 patients (median age: 60 yrs;19-80) who underwent 18F- DOPA PET/CT for the restaging of low and high grade glioma. All PET/CT images werere-examined by two nuclear medicine physicians. Both visual and semiquantitative analysis was used for the interpretation ofimages. At visual analysis, PET/CT was defined as positive in case of a DOPA uptake in the lesion (identified by MRI) higherthan controlateral striatum uptake. For the semiquantitative analysis, the ratios between SUVmax of the lesion and SUVmax ofthe striatum (T/S)/normal brain tissue (T/B) equal to 1 and 2 respectively were used. Clinical reassessment consisted of standardevaluation including MRI and assessment of neurological symptoms. The agreement between visual and semiquantitativeanalysis was obtained by k statistical analysis. Diagnostic performance was calculated by standard methods.RESULTS. Six patients had a low grade glioma and 14 a high grade. At visual analysis, 15 (75%) patients had a positive PET/CTresult, in particular 4 with a low grade glioma and 11 with a high grade (67% and 79%, respectively). Based onsemiquantitative analysis, 14 (70%) and 14 (70%) patients had a positive PET/CT, respectively for T/S and T/B. The agreementbetween visual and semiquantitative analysis was 88% (p

Reproducibility of PET measurement for presynaptic dopaminergic functions using L-[β-11C]DOPA and [18F]FE-PE2I in humans

Recent PET studies have indicated altered presynaptic function and relation with psychotic symptoms in patients with schizophrenia. The L-[β-(11)C]DOPA uptake rate reflects the dopamine synthesis capacity (kref), whereas the nondisplaceable binding potential (BPND) of [(18)F]FE-PE2I reflects the dopamine transporter availability. Although the kref values of L-[β-(11)C]DOPA and the BPND of [(18)F]FE-PE2I can be potential markers for evaluating the severity of positive symptoms, test-retest reproducibility has not been confirmed. The purpose of this study was to investigate the test-retest reproducibility of kref values of L-[β-(11)C]DOPA and that of BPND of [(18)F]FE-PE2I in the striatum and midbrain in healthy humans. Twelve healthy male volunteers underwent two PET studies on separate days. Each PET study comprised two PET scans, one with L-[β-(11)C]DOPA and the other with [(18)F]FE-PE2I. Volumes of interest were defined for the caudate, putamen, midbrain, and thalamus. Test-retest reproducibility was assessed in terms of intrasubject variability (absolute variability) and reliability [intraclass correlation coefficient (ICC)]. The absolute variability values of kref and BPND were 4.8-25.7% on average for the caudate, putamen, midbrain, and thalamus. The ICC values of the kref values of L-[β-(11)C]DOPA were 0.78, 0.71, 0.77, and 0.77 for the caudate, putamen, midbrain, and thalamus, respectively. The ICC values of the BPND of [(18)F]FE-PE2I were 0.83, 0.88, 0.71, and 0.70 for the caudate, putamen, midbrain, and thalamus, respectively. We found good test-retest reproducibility for the kref values of L-[β-(11)C]DOPA and that for the BPND of [(18)F]FE-PE2I in the striatum and midbrain, indicating the reliability of clinical investigation using PET with L-[β-(11)C]DOPA and [(18)F]FE-PE2I.

Does human presynaptic striatal dopamine function predict social conformity?

Socially desirable responding (SDR) is a personality trait which reflects either a tendency to present oneself in an overly positive manner to others, consistent with social conformity (impression management (IM)), or the tendency to view one's own behaviour in an overly positive light (self-deceptive enhancement (SDE)). Neurochemical imaging studies report an inverse relationship between SDR and dorsal striatal dopamine D₂/₃ receptor availability. This may reflect an association between SDR and D₂/₃ receptor expression, synaptic dopamine levels or a combination of the two. In this study, we used a [¹⁸F]-DOPA positron emission tomography (PET) image database to investigate whether SDR is associated with presynaptic dopamine function. Striatal [¹⁸F]-DOPA uptake, (k(i)(cer), min⁻¹), was determined in two independent healthy participant cohorts (n=27 and 19), by Patlak analysis using a cerebellar reference region. SDR was assessed using the revised Eysenck Personality Questionnaire (EPQ-R) Lie scale, and IM and SDE were measured using the Paulhus Deception Scales. No significant associations were detected between Lie, SDE or IM scores and striatal [¹⁸F]-DOPA k(i)(cer). These results indicate that presynaptic striatal dopamine function is not associated with social conformity and suggests that social conformity may be associated with striatal D₂/₃ receptor expression rather than with synaptic dopamine levels.

On the use of [18F]DOPA as an imaging biomarker for transplanted islet mass

Islet transplantation is being developed as a potential cure for patients with type 1 diabetes. There is a need for non-invasive imaging techniques for the quantification of transplanted islets, as current transplantation sites are associated with a substantial loss of islet viability. The dopaminergic metabolic pathway is present in the islets; therefore, we propose Fluorine-18 labeled L-3,4-dihydroxyphenylalanine ([18F]DOPA) as a biomarker for transplanted islet mass. The expression of enzymes involved in the dopaminergic metabolic pathway was investigated in both native and transplanted human islets. The specific uptake of [18F]DOPA in islets and immortalized beta cells was studied in vitro by selective blocking of dopa decarboxylase (DDC). Initial in vivo PET imaging of viable subcutaneous human islets was performed using [18F]DOPA. DDC and vesicular monoamine transporter 2 are co-localized with insulin in the native human pancreas, and the expression is retained after transplantation. Islet uptake of the [18F]DOPA could be modulated by inhibiting DDC, indicating that the uptake followed the normal dopaminergic metabolic pathway. In vivo imaging revealed [18F]DOPA uptake at the site of the functional islet graft. Based on the in vitro and in vivo results presented in this study, we propose to further validate [18F]DOPA-PET as a sensitive imaging modality for imaging extrahepatically transplanted islets.

Benefits of putaminal GDNF infusion in Parkinson disease are maintained after GDNF cessation

We previously reported clinical improvement, increase in putamen [(18)F]-dopa uptake on PET imaging, and neuropathologic evidence of sprouting of dopaminergic fibers following chronic intraputaminal delivery of glial cell line-derived neurotrophic factor (GDNF) in idiopathic Parkinson disease (PD).(1-3) We now provide clinical and PET evidence of persistent efficacy lasting for at least 3 years following cessation of GDNF infusion in a patient with PD. This is a single-case observational study, providing Class IV evidence.

The Second Revision of the Dopamine Theory of Schizophrenia: Implications for Treatment and Drug Development

In this edition of Biological Psychiatry, Egerton et al. (1) from the Institute of Psychiatry at King’s College in London published the results of an imaging study measuring dopamine (DA) synthesis capacity in subjects presenting potentially prodromal symptoms of schizophrenia. Subjects fulfilled clinical criteria associated with a 20% to 40% risk of presenting a psychotic episode within 1 to 3 years (2), a condition labeled as ultra-high risk (UHR). Compared with matched control subjects, striatal DA synthesis capacity (measured with positron emission tomography as the uptake of [F]DOPA) was increased in UHR subjects. Analysis of striatal functional subdivisions showed that the [F] DOPA uptake was increased in the associative striatum (AST) and not in the ventral striatum (VST). This outcome confirms an earlier result from the same group in a smaller cohort (3) and suggests that abnormalities of DA function in the AST precede the emergence of psychotic symptoms in UHR subjects. The authors should be complimented for having submitted their initial findings to the rigor of replication in an independent cohort. As pointed out by the authors, replication of a clinical finding by the same investigators does carry less weight than independent replication. Nonetheless, replication studies are extremely important and might not be given enough attention and credit in the field. Given that the recruitment criteria, clinical evaluation, and imaging technique were maintained between the two studies, the data can be pooled, and this combined analysis will be especially important for the follow-up studies. Based on the UHR criteria, it is anticipated that 20% to 40% of these subjects will present a psychotic episode within 2 years and that this episode might be the first psychotic manifestation of a chronic psychotic disorder such as schizophrenia. In the follow-up of the first cohort, the authors observed that increased [F]DOPA uptake at baseline was associated with higher risk of psychotic transition within 3 years. It will be very important to ascertain if the prognostic value of elevated [F]DOPA uptake in the AST is replicated in this larger cohort. This result provides an important contribution to a large body of imaging work performed over the last decade that generated a remarkably consistent picture of alteration of DA function in schizophrenia [reviewed in (4,5)]. Using either [F]DOPA uptake or competition studies between endogenous DA and DA D2 receptor ligands, several groups have documented that schizophrenia is associated with increases in striatal presynaptic DA function, at least during the period of psychotic exacerbation, and that this increase is associated with the severity and acuity of psychotic symptoms. This DA dysregulation does not appear to be a

Substantia nigra hyperechogenicity in healthy controls: a [18Fluoro] Dopa-PET follow-up study

In order to assess nigrostriatal function over time in healthy subjects with substantia nigra hyperechogenicity (SN+) believed to be at higher risk for Parkinson's disease (PD), ten healthy SN+ subjects underwent [(18)Fluoro] Dopa positron emission tomography (PET) twice-at baseline and after a mean of 7.3 years. Neurological examination took place at study inclusion followed by a structured telephone interview focusing on early Parkinsonian symptoms at the time point of second PET study and 3.5 years later. The [(18)Fluoro] Dopa uptake remained unchanged in eight of ten participants. In the other two subjects marked unilateral reduction of putaminal [(18)Fluoro] Dopa uptake ratios appeared over the time, followed by complaints of a clinically manifest PD in one. We suggest that the progressive pathological PET findings in 20 % and PD conversion in 10 % of our cohort may be in accordance with the presumed proportion of SN+ individuals eventually developing PD based on SN+ prevalence of 10 % within the healthy population, being ten times higher than PD prevalence in the age of over 60 years. Our findings hint towards a significance of SN+ indicating a high risk for PD in some extrapyramidally healthy SN+ individuals.

Motor behavior correlates with striatal [18F]-DOPA uptake in MPTP-lesioned primates

The MPTP-lesioned monkey is considered as the best animal model for Parkinson’s disease (PD). It has damage to dopaminergic cell groups and motor dysfunction similar to that seen in PD. Correlations between these two parameters have been described but there is a lack of formal statistical analyses on dopaminergic function as assessed by [18F]-F-DOPA PET and objectively rated motor behavior in longitudinal experiments.Eight rhesus monkeys received two MPTP infusions: first in one carotid artery, and after eight weeks in the other. Motor behavior and [18F]-F-DOPA uptake were measured at three stages: baseline, unilateral and bilateral. We correlated movement with radiotracer uptake across these three stages. MPTP caused the expected parkinsonian motor signs which were accompanied by lower radioactivity concentrations in the striatum. There were significant correlations between dopaminergic function and behavior.In conclusion, striatal [18F]-F-DOPA uptake correlates inversely with the severity of motor impairment in MPTP-lesioned non-human primates. Both behavioral scoring and [18F]-F-DOPA PET scans are useful and sensitive methods to monitor dopaminergic degeneration within subjects.

Increase of oxidative stress by a novel PINK1 mutation, P209A

Mutation in the human PTEN-induced protein kinase 1 (PINK1) gene is responsible for the second most common form of recessive Parkinson disease (PD). We have identified a single heterozygous PINK1 mutation, P209A, from a cohort of 68 patients with early onset PD. From age 31, this patient developed an asymmetric bradykinesia with rigidity that was L-DOPA responsive. An [18F]-fluorodopa PET scan showed reduced DOPA uptake in the bilateral basal ganglia. The H2O2-induced cell death, ROS production, and caspase-3 activation in SH-SY5Y cells were enhanced by the transfection of the PINK1 P209A mutant. The heme oxygenase-1 (HO-1) induction in response to H2O2 and MPP+ treatment was impaired by the overexpression of the PINK1 P209A mutant. In addition, SOD2 induction after TNFα treatment was also inhibited by the PINK1 P209A mutation. Akt and ERK are involved in HO-1 induction after oxidative stress. The phosphorylation of Akt and ERK after exposure to H2O2 or MPP+ was also inhibited in PINK1 P209A mutant cells compared with empty-vector-transfected cells. These results indicate a novel pathway by which the P209A defect in the PINK1 kinase domain inhibits oxidative stress-induced HO-1 and SOD2 induction, which may accelerate the neurodegeneration in PD with PINK1 defect.

Dopamine Synthesis Capacity in Patients With Treatment-Resistant Schizophrenia

Elevated presynaptic striatal dopaminergic function is a robust feature of schizophrenia. However, the relationship between this dopamine abnormality and the response to dopamine-blocking antipsychotic treatments is unclear. The authors tested the hypothesis that in patients with schizophrenia the response to antipsychotic treatment would be related to the severity of presynaptic dopamine dysfunction, as indexed using [(18)F]-DOPA uptake positron emission tomography (PET). Twelve patients with treatment-resistant schizophrenia, twelve patients with schizophrenia who had responded to antipsychotics, and twelve healthy volunteers matched for gender, age, ethnicity, weight, and cigarette smoking underwent [(18)F]-DOPA PET scanning. [(18)F]-DOPA influx rate constants (K(i)(cer) values) were measured in the striatum and its functional subdivisions. Patients who had responded to antipsychotic treatment showed significantly higher K(i)(cer) striatal values than did patients with treatment-resistant illness (effect size=1.11) and healthy volunteers (effect size=1.12). The elevated [(18)F]-DOPA uptake was most marked in the associative (effect size=1.31) and the limbic (effect size=1.04) striatal subdivisions. There were no significant differences between patients with treatment-resistant illness and healthy volunteers in the whole striatum or any of its subdivisions. In some patients with schizophrenia, antipsychotic treatment may be ineffective because they do not exhibit the elevation in dopamine synthesis capacity that is classically associated with the disorder; this may reflect a different underlying pathophysiology or a differential effect of antipsychotic treatment.

α2C-Adrenoceptors modulatel-DOPA uptake in opossum kidney cells and in the mouse kidney

Targeted deletion or selective pharmacological inhibition of α(2C)-adrenoceptors in mice results in increased brain tissue levels of dopamine and its precursor l-3,4-dihydroxyphenylalanine (l-DOPA), without significant changes in l-DOPA synthesis. l-DOPA uptake is considered the rate-limiting step in dopamine synthesis in the kidney. Since α(2C)-adrenoceptors may influence the transport of l-DOPA, we investigated the effect of α(2C)-adrenoceptor activation on l-DOPA uptake in a kidney cell line (opossum kidney cells). l-DOPA and dopamine kidney tissue levels in α(2C)-adrenoceptor knockout (α(2C)KO) mice and in mice treated with the selective α(2C)-adrenoceptor antagonist JP-1302 were also evaluated. The α(2)-adrenoceptor agonist medetomidine (0.1-1,000 nM) produced a concentration-dependent decrease in l-DOPA uptake in opossum kidney cells (IC(50): 2.5 ± 0.5 nM and maximal effect: 28 ± 5% of inhibition). This effect was abolished by a preincubation with JP-1302 (300 nM). Furthermore, the effect of medetomidine (100 nM) was abolished by a preincubation with U-0126 (10 μM), a MEK1/2 inhibitor. Kidney tissue levels of l-DOPA were significantly higher in α(2C)KO mice compared with wild-type mice (wild-type mice: 58 ± 2 pmol/g tissue and α(2C)KO mice: 81 ± 15 pmol/g tissue, P < 0.05) and in mice treated with JP-1302 (3 μmol/kg body wt) compared with control mice (control mice: 62 ± 2 pmol/g tissue and JP-1302-treated mice: 75 ± 1 pmol/g tissue, P < 0.05), both without significant changes in dopamine kidney tissue levels. However, mice treated with JP-1302 on a high-salt diet presented significantly higher dopamine levels in the kidney and urine compared with control animals on a high-salt diet. In conclusion, in a kidney cell line, α(2C)-adrenoceptor activation inhibits l-DOPA uptake, and in mice, deletion or blockade of α(2C)-adrenoceptors increases l-DOPA kidney tissue levels.

Caste differences in dopamine-related substances and dopamine supply in the brains of honeybees (Apis mellifera L.)

We determined the mechanisms underlying caste differences in the brain levels of dopamine-related substances in adult honeybees (Apis mellifera L.). Brain levels of dopamine, DOPA (a dopamine precursor), and N-acetyldopamine (a dopamine metabolite, NADA) were significantly higher in three-day-old virgin queens than same-aged workers. Caste differences in dopamine and NADA levels were also found in the hemolymph. The in vitro enzymatic activities of DOPA decarboxylase (DDC) during dopamine synthesis in brains were not significantly different between castes. The DDC activity in adult queens was mainly found in the brain, but with lower levels of activity detected in the mandibular glands, salivary glands and ovaries. Oral application of DOPA to workers led to DOPA uptake in the brain and significantly higher dopamine and NADA levels in the brain, suggesting that dopamine synthesis could be controlled by the amount of DDC substrate. Royal jelly samples taken from queen cells had a >25-fold higher concentration of dopamine compared with honey samples collected from honey cells. However, oral application of the same concentration of dopamine did not significantly enhance the brain levels of dopamine and NADA. These results suggest that the higher levels of brain dopamine in queens compared with workers can be explained by the higher level of DDC substrate, rather than DDC activity in the brain and other tissues of queens as well as exogenous dopamine in the royal jelly.

Is There an Optimal Scan Time for 6-[F-18]Fluoro-L-DOPA PET in Pheochromocytomas and Paragangliomas?

To define the appropriate scan time for fluorine-18-labeled dihydroxyphenylalanine (F-18 DOPA) PET in oncological imaging of pheochromocytomas and paragangliomas. F-18 DOPA PET examinations were performed in 9 patients with 7 pheochromocytomas and 4 head and neck paragangliomas using a dedicated PET scanner. The acquisition started with a dynamic single-bed scan in the tumor region over the first 60 minutes after tracer injection followed by a late time whole-body scan at approximately 130 minutes. Standard uptake values (SUVs) were calculated in tumors, surrounding background, and adjacent normal tissues of relevance. Furthermore, kinetic analysis was performed using a 2-compartment model with rate constants for uptake (K1'), release (k2'), metabolism (k3'), and reverse reaction (k4') for region of interest and pixel-wise analysis. All tumors show a marked increased F-18 DOPA uptake, which was visually detectable and distinguishable from the surrounding tissue. The SUV is significantly lower in neck paraganglioma compared with abdominal pheochromocytomas. Mean time-activity curves of F-18 DOPA in tumors show a rapid uptake of the tracer. Already 2 minutes after the injection, the activity in the tumor is beyond that of the blood pool. The average maximum value (SUVmean = 8.2) has already been reached after 20 minutes. Afterward, a very slight decrease of the tumor SUV starts, which still amounts to 80% of the maximum value after 132 minutes. Due to the continuous decrease of activity in the background tissue, the tumor-to-background ratio of SUVs shows a constant increase within the entire period of examination. The mean values of apparent kinetic constants obtained by region of interest analysis averaged over all tumors are as follows: K1' = 2.89 ± 2.56 min(-1), k2' = 2.59 ± 2.81 min(-1), k3' = 0.301 ± 0.395 min(-1), and k4' = 0.044 ± 0.043 min(-1). Pheochromocytoma and paraganglioma take up F-18 DOPA very quickly. At best, the acquisition for static clinical PET imaging of paraganglioma with F-18 DOPA can start at 20 minutes postinjection for maximum uptake in tumors. Separation of tumor, background, and adjacent normal tissues is feasible due to their differences in SUV values and kinetics. The kinetic analysis demonstrates an F-18 DOPA accumulation within the tumor due to considerable differences between the rate constants of uptake and metabolism. Second, in contradiction to healthy brain, paraganglionic tumors show a reversible F-18 DOPA metabolism.

Usefulness of [18F]-DA and [18F]-DOPA for PET imaging in a mouse model of pheochromocytoma

To evaluate the usefulness of [(18)F]-6-fluorodopamine ([(18)F]-DA) and [(18)F]-L-6-fluoro-3,4-dihydroxyphenylalanine ([(18)F]-DOPA) positron emission tomography (PET) in the detection of subcutaneous (s.c.) and metastatic pheochromocytoma in mice; to assess the expression of the norepinephrine transporter (NET) and vesicular monoamine transporters 1 and 2 (VMAT1 and VMAT2), all important for [(18)F]-DA and [(18)F]-DOPA uptake. Furthermore, to compare tumor detection by micro-computed tomography (microCT) to magnetic resonance imaging (MRI) in individual mouse. SUV(max) values were calculated from [(18)F]-DA and [(18)F]-DOPA PET, tumor-to-liver ratios (TLR) were obtained and expression of NET, VMAT1 and VMAT2 was evaluated. [(18)F]-DA detected less metastatic lesions compared to [(18)F]-DOPA. TLR values for liver metastases were 2.26-2.71 for [(18)F]-DOPA and 1.83-2.83 for [(18)F]-DA. A limited uptake of [(18)F]-DA was found in s.c. tumors (TLR = 0.22-0.27) compared to [(18)F]-DOPA (TLR = 1.56-2.24). Overall, NET and VMAT2 were expressed in all organ and s.c. tumors. However, s.c. tumors lacked expression of VMAT1. We confirmed [(18)F]-DA's high affinity for the NET for its uptake and VMAT1 and VMAT2 for its storage and retention in pheochromocytoma cell vesicles. In contrast, [(18)F]-DOPA was found to utilize only VMAT2. MRI was superior in the detection of all organ tumors compared to microCT and PET. [(18)F]-DOPA had overall better sensitivity than [(18)F]-DA for the detection of metastases. Subcutaneous tumors were localized only with [(18)F]-DOPA, a finding that may reflect differences in expression of VMAT1 and VMAT2, perhaps similar to some patients with pheochromocytoma where [(18)F]-DOPA provides better visualization of lesions than [(18)F]-DA.

Altered Relationship Between Hippocampal Glutamate Levels and Striatal Dopamine Function in Subjects at Ultra High Risk of Psychosis

Animal models of psychosis propose that striatal hyperdopaminergia is driven by abnormalities in hippocampal glutamatergic neurotransmission, but this has never been tested in humans. Sixteen individuals with an at-risk mental state for psychosis (ARMS) and 12 control subjects underwent proton magnetic resonance spectroscopy to estimate hippocampal glutamate and [18F]DOPA positron emission tomography to index striatal dopamine function. The relationship between hippocampal glutamate and striatal dopamine, as well as their relationship with prodromal symptoms, was determined using linear regression. In ARMS subjects, but not controls, there was a significant negative relationship between hippocampal glutamate levels and striatal [18F]DOPA uptake (p = .03). Within the ARMS sample, striatal [18F]DOPA uptake was correlated with severity of abnormal beliefs (p = .03), there was a trend for hippocampal glutamate levels to be correlated with disordered speech (p = .06) and a trend for the interaction between hippocampal glutamate and [18F]DOPA uptake to predict later transition to psychosis (p = .07). The relationship between hippocampal glutamate and striatal dopamine systems is altered in people at high risk of psychosis, and the degree to which it is changed may be related to the risk of transition to psychosis. Pharmacologic modulation of the glutamate system before the onset of psychosis might ameliorate this risk.

Molecular and functional identification of large neutral amino acid transporters LAT1 and LAT2 and their pharmacological relevance at the blood-brain barrier.

We present here the evidence of molecular and functional expression of LAT1 and LAT2, subunits of the large neutral amino acid transporter system L, in cultured brain capillary endothelial cells of the rat. By means of the RT-PCR method, transcripts of LAT1, LAT2 and heavy chain of 4F2 antigen (4F2hc) were detected in rat primary cultured brain capillary endothelial cells (BCECs) and immortalized subline, RBEC1. The uptake properties of RBEC1, such as [3H]leucine and L-[3H]DOPA uptake, were similar to those of primary cultured BCECs. So, RBEC1 may retain almost native properties of the large neutral amino acid uptake activities. [3H]Leucine uptake by RBEC1 showed two saturable components and the Km values of the high- and low-affinity components were 8.92+/-3.18 and 119+/-45 microM, respectively. The Km value of the high-affinity component agreed well with that of LAT1 and the amino acid transport selectivity of RBEC1 was similar to that of LAT1. Therefore, it is suggested that LAT1 is important at the blood-brain barrier of rats. Additionally, the Km value of the low-affinity component was similar to that of LAT2. These observations indicate that LAT1 and LAT2 are involved as transporters for large neutral amino acids at the blood-brain barrier. Additionally, we concluded that RBEC1 is useful as an in-vitro model for evaluation of the pharmacological relevance of system L at the blood-brain barrier.

Signaling cascade of insulin-induced stimulation of l-dopa uptake in renal proximal tubule cells

The inward l-dihydroxyphenylalanine (L-dopa) transport supplies renal proximal tubule cells (PTCs) with the precursor for dopamine synthesis. We have previously described insulin-induced stimulation of L-dopa uptake into PTCs. In the present paper we examined insulin-related signaling pathways involved in the increase of l-dopa transport into isolated rat PTCs. Insulin (50-500 microU/ml) increased L-dopa uptake by PTCs, reaching the maximal increment (60% over the control) at 200 microU/ml. At this concentration, insulin also increased insulin receptor tyrosine phosphorylation. Both effects were abrogated by the tyrosine kinase inhibitor genistein (5 microM). In line, inhibition of the protein tyrosine phosphatase by pervanadate (0.2-100 microM) caused a concentration-dependent increase in both the uptake of L-dopa (up to 400%) and protein tyrosine phosphorylation. A synergistic effect between pervanadate and insulin on L-dopa uptake was observed only when threshold (0.2 microM), but not maximal (5 microM), concentrations of pervanadate were assayed. Insulin-induced stimulation of L-dopa uptake was also abolished by inhibition of phosphatidylinositol 3-kinase (PI3K; 100 nM wortmannin, and 25 microM LY-294002) and protein kinase C (PKC; 1 microM RO-318220). Insulin-induced activation of PKC-zeta was confirmed in vitro by its translocation from the cytosol to the membrane fraction, and in vivo by immunohistochemistry studies. Insulin caused a wortmannin-sensitive increase in Akt/protein kinase B (Akt/PKB) phosphorylation and a dose-dependent translocation of Akt/PKB to the membrane fraction. Our findings suggest that insulin activates PKC-zeta, and Akt/PKB downstream of PI3K, and that these pathways contribute to the insulin-induced increase of L-dopa uptake into PTCs.