Complementary positron emission tomographic studies of the striatal dopaminergic system in Parkinson's disease.

OBJECTIVE: To assess the relationship between striatal dopa decarboxylase capacity, D2 dopamine receptor binding, and energy metabolism in Parkinson's disease (PD). DESIGN: Positron emission tomographic (PET) studies of glucose and dopa metabolism and D2 dopamine receptor binding in the caudate nucleus and putamen of patients with PD at different Hoehn and Yahr (HY) stages using PET and the tracers 18F-fluorodeoxyglucose (FDG), 6-18F-fluoro-L-dopa (FDOPA), and 11C-raclopride (RACLO). SETTING: Positron emission tomography research program at the Paul Scherrer Institute. SUBJECTS: Twenty patients with PD at different stages of the disease (HY stages I through IV; five patients for each stage) compared with separate groups of age-matched healthy subjects. MAIN OUTCOME MEASURES: Influx constant (Ki) for specific FDOPA uptake; uptake index ratio for RACLO binding to D2 dopamine receptors; normalized to global FDG metabolic rate for glucose consumption; and semiquantitative score for assessment of tremor, rigidity, and bradykinesia in PD. RESULTS: Patients with PD at HY stages I to II (hereafter HY-I-II PD) revealed reduced FDOPA metabolism, particularly in the putamen. The FDOPA uptake in the putamen and caudate nucleus declined with increasing HY staging and scoring for bradykinesia and rigidity. Putamen RACLO binding to D2 dopamine receptors was up-regulated in patients with HY-I-II PD but declined toward control values, with increasing disease severity. Putamen side-to-side asymmetries of FDOPA metabolism and RACLO binding revealed a significant correlation. Putamen FDG metabolism showed a relative increase in all patients with PD. CONCLUSIONS: Our results show that FDOPA, RACLO, and FDG PET measurements provide complementary information to characterize metabolic and receptor changes in the striatum of PD with different degrees of motor disability. The FDOPA uptake reflects the best motor-related pathologic features, as indicated by the significant correlation between Ki values and clinical scores. The significant association between RACLO and FDOPA in the putamen suggests that D2 dopamine receptor changes are related to the reduction of presynaptic dopaminergic nerve terminals. Putamen FDG increase is probably the result of more complex feedback mechanisms that are primarily induced by striatal dopamine deficiency.

Cerebral 6-[18F]fluoro-L-DOPA uptake in rhesus monkey: pharmacological influence of aromatic amino acid decarboxylase (AAAD) and catechol-O-methyltransferase (COMT) inhibition.

FDOPA/PET scans were performed in one rhesus monkey to study the influence of three catechol-O-methyltransferase (COMT) inhibitors (CGP 28014, OR-611 and Ro 40-7592) on FDOPA pharmacokinetics. COMT inhibitors were administered in combination with carbidopa, a peripherally acting inhibitor of the aromatic amino acid decarboxylase (AAAD). FDOPA was administered intravenously and its metabolic fate in plasma was determined using an HPLC system with an on-line gamma-gamma coincidence detector. Cerebral tracer uptake was assessed in the striatum and in a non-dopaminergic brain region (occipital cortex). In the periphery, the pharmacokinetic efficiency of FDOPA was increased due to the combined inhibition of COMT and AAAD activity. All three COMT inhibitors reduced the FDOPA methylation rate constant in plasma, with complete suppression obtained in the case of Ro 40-7592. In the brain, specific 18F radioactivity (striatal minus brain reference radioactivity) increased as a result of the increase in FDOPA plasma availability following the administration of COMT and AAAD inhibitors. We established a significant linear correlation between striatal radioactivity and FDOPA plasma levels (r = 0.924 +/- 0.048, P < 0.0001 for total striatal and r = 0.948 +/- 0.054, P < 0.0001 for specific striatal radioactivity). Using plasma FDOPA radioactivity as input, we found that the striatal FDOPA uptake rate constant KiFD was not changed by any of the inhibitors. Thus, the enhancement of striatal radioactivity after application of enzyme inhibitors is a consequence of the increase in plasma FDOPA that becomes available for conversion to fluorodopamine in the striatal dopaminergic nerve terminals. By contrast, using the radioactivity in a non-dopaminergic region (cortex) as input, we found that the striatal FDOPA uptake rate constant Ki(ref) was significantly (P < 0.0001) increased following pretreatment with COMT inhibitors. Our analysis demonstrated that Ki(ref) and the 3-OMFD contribution to the cerebral radioactivity were inversely correlated.

Noninvasive dopamine determination by reversed phase HPLC in the medium of free-floating roller tube cultures of rat fetal ventral mesencephalon: a tool to assess dopaminergic tissue prior to grafting.

The low availability of dopamine containing neurons for grafting in Parkinson's disease is a general problem. Free-floating roller tube (FFRT) cultures allow storage of fetal mesencephalic tissue prior to transplantation. Preoperative functional testing permits to select an optimized set of individual cultures for transplantation. Rat fetal ventral mesencephali (E13) were dissected out and divided into four equally sized pieces each and individually prepared as FFRT cultures. After 4, 8, 12, and 16 days in vitro (DIV) the medium of each culture was collected during routine medium change and immediately stabilized. Dopamine was extracted and probes were determined with reversed phase HPLC using electro-chemical detection. After 16 DIV cultures were fixed and cell counts performed in tyrosine hydroxylase (TH)-immunostained serial sections. The mean dopamine content +/- SEM In culture conditioned media was at 4 DIV: 21 +/- 2 pg, n = 38; at 8 DIV: 37 +/- 4 pg, n = 40; at 12 DIV: 52 +/- 7 pg, n = 38; and at 16 DIV: 39 +/- 5 pg, n = 38. In all cultures devoid of dopamine after 4 and 8 DIV (12.5%) levels remained below detectability at 12 and 16 DIV. Cultures derived from the rostral mesencephalon showed significantly higher dopamine values than those from the caudal mesencephalon at 12 DIV. The mean number of TH-immunoreactive (-ir) cells/culture +/- SEM after 16 DIV was 556 +/- 51, n = 40. The correlation between TH-ir cell number (CN) and dopamine content of rostrally derived cultures at 16 DIV was: CN = 7.4 (dopamine [pg]) + 248; R = 0.75; n = 19; p < 0.001. No dopamine was present in cultures without TH-ir cells. These results demonstrate that sequential noninvasive screening of dopamine in single cultures is feasible and that the dopamine content is correlated to the number of surviving TH-ir cells. This permits to select cultures rich in dopaminergic neurons for transplantation.

Positron emission tomography in drug evaluation: influence of three different catechol-O-methyltransferase inhibitors on metabolism of [NCA] 6-[18F]fluoro-L-dopa in rhesus monkey.

We compared the influence of three different catechol-O-methyltransferase (COMT) inhibitors (CGP 28014, OR-611 and Ro 40-7592) on the metabolism of no-carrier-added (NCA) 6-[18F]fluoro-L-dopa (6-FDOPA) in one Rhesus monkey. All three COMT inhibitors improved 6-FDOPA availability in plasma, increased the specific uptake in the brain and thus improved 6-FDOPA uptake measurements using positron emission tomography (PET). Best results were obtained with Ro 40-7592.

Side effects of the catechol-O-methyl-transferase inhibitor Ro 40-7592 in rabbits.

Catechol-O-methyl-transferase inhibitors are promising drugs in Parkinson's disease since these drugs enhance levodopa effects and increase their duration. However, since these compounds block a pathway for the peripheral metabolism of catecholamines, they may also produce side effects related to elevation of catecholamines in plasma. We investigated the adverse effects of Ro 40-7592 in rabbits and the relationship of Ro 40-7592 to norepinephrine plasma levels. Intravenous administration of Ro 40-7592 in rabbits induced elevation of norepinephrine plasma levels in old animals after bolus injection of a dose three times the highest dose actually recommended to be taken orally by humans. Though Ro 40-7592 appears safe for humans, special precautions may be needed in patients with a high risk of adrenergic hyperactivity.

Long-term intracerebral infusion of fibroblast growth factors restores motility and enhances F-DOPA uptake in parkinsonian monkeys.

Fibroblast growth factors (FGFs) are important for dopamine neurons in health and disease. Acidic (aFGF) and basic (bFGF) fibroblast growth factors increase the survival and growth of dopamine cells. Nigrostriatal dopamine neurons, the target cells for degeneration in Parkinson's disease, display receptors for basic fibroblast growth factor and these receptors are decreased in the brain of parkinsonian patients. We have investigated the effects of long-term intrastriatal infusion of FGFs in hemiparkinsonian monkeys. All animals were lesioned with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 0.4mgkg(-1), into the left internal carotid artery. The monkeys that had persistent asymmetric akinesia and contralateral rotation induced by apomorphine, were selected for chronic, unilateral, intracerebral infusion of neurotrophic factors or vehicle into the striatum ipsilateral to the lesion. Two animals received intrastriatal aFGF or bFGF, 2mugweek(-1), for 6 months. The controls received intrastriatal saline or intraventricular epidermal growth factor (EGF). F-DOPA positron emission tomography scans were performed in each animal before and after the intracerebral infusion of neurotrophic factors. We measured the tyrosine hydroxylase (TH) immunoreactive neurons in the substantia nigra and terminals in the striatum and evaluated the pathological complications related to the treatment or the delivery system. All four animals had, after the lesion with MPTP, a transient but incomplete recovery of akinesia. This period of spontaneous improvement was followed by a progressive deterioration of motor behaviour during the following months. The monkeys treated with FGFs, however, recovered quickly and persistently during the intracerebral infusion. F-DOPA uptake, prior to the intracerebral infusion, was greatly reduced in the lesioned striatum. The post-infusion F-DOPA scans revealed a 60% reduction respect to baseline in the lesioned striatum of the saline and EGF-infused animals. In the animals infused with FGFs, the post-infusion F-DOPA uptake increased more than 400% in the lesioned (and infused) striatum and around 200-300% in the contralateral side, with respect to the pre-infusion scan. The number of TH-positive cells in the substantia nigra correlated well with the uptake of F-DOPA in the post-infusion scan. No severe side-effects were present. Intrastriatal infusion of FGFs restores motor behaviour and increases F-DOPA striatal uptake in hemiparkinsonian monkeys.

Vitrectomy results for diffuse diabetic macular edema with and without inner limiting membrane removal.

PURPOSE: To determine whether vitrectomy for diffuse diabetic macular edema with and without internal limiting membrane (ILM) peeling is equally effective in reducing edema. METHODS: The authors retrospectively analyzed the surgical outcomes in 73 eyes of 52 patients with diffuse diabetic macular edema. Eighteen eyes (Group A) underwent three-port pars plana vitrectomy with posterior hyaloid membrane (PHM) removal, while 55 eyes (Group B) had pars plana vitrectomy with additional ILM peeling after PHM removal. RESULTS: Intraoperatively, the posterior hyaloid was found to be attached to the macula in all eyes. In Group A, macular edema resolved completely in 8 eyes (44.4%) with improvement of visual acuity (VA). In Group B, VA improved in 38 eyes (69.1%) with complete resolution of edema. The results of this study indicated that vitrectomy effectively reduced macular edema but eyes with ILM peeling (Group B) presented better results than those without ILM peeling. Another important factor related to the outcome seems to be the level of glycosylated hemoglobin (HbA1c). CONCLUSIONS: In eyes with diffuse diabetic macular edema vitrectomy seems to be effective, but additional ILM peeling presented better results.

Complementary PET studies of striatal neuronal function in the differential diagnosis between multiple system atrophy and Parkinson's disease.

We used PET with the tracers [18F]fluorodeoxyglucose (FDG), [18F]fluorodopa (FDOPA) and [11C]raclopride (RACLO) to study striatal glucose and dopa metabolism, and dopamine D2 receptor binding, respectively, in nine patients with multiple system atrophy. Ten patients with classical Parkinson's disease were investigated with the same three PET tracers' and three separate groups, each of 10 healthy subjects, served as control populations. We found that striatal FDOPA values separated all healthy subjects from patients with parkinsonism but they were not useful in distinguishing multiple system atrophy from Parkinson's disease. Conversely, striatal RACLO as well as FDG values discriminated all multiple system atrophy from Parkinson's disease patients as well as from healthy control subjects. Metabolic and receptor binding decrements in the putamen of multiple system atrophy patients were significantly correlated. Stepwise regression analysis revealed that a linear combination of putamen RACLO and FDOPA values accurately predicted clinical measures of disease severity in the multiple system atrophy group. Our findings suggest that striatal FDG and particularly RACLO are sensitive and effective measures of striatal function and may help characterizing patients with multiple system atrophy. In contrast, FDOPA measurements are accurate in detecting abnormalities of the nigrostriatal dopaminergic system but may not distinguish among different forms of parkinsonism.

Brain tumor iron uptake measured with positron emission tomography and 52Fe-citrate.

Iron and transferrin are required for DNA synthesis and cell division. Cellular iron uptake is mediated by transferrin receptors. In order to investigate whether iron uptake in brain tumors is associated with their histological grade, we studied 24 patients (5 astrocytoma, 11 glioblastoma, 8 meningioma) using positron emission tomography and 52Fe-citrate. Tracer uptake from blood into brain and tumor tissue was assessed 1. using multiple time graphical analysis yielding a measure for unidirectional net tracer uptake (Ki) and 2.) testing a one- and two-tissue kinetic compartment model, where K1 denotes tracer uptake from blood into tissue, k2 efflux from tissue into plasma, and k3 specific tracer binding. In the plasma, 52Fe was bound to a 80 kD protein (transferrin). Ki (in units of 10(-5)/min) was higher in glioblastomas (Ki mean +/- SD 13.6 +/- 6.1) compared with astrocytomas (4.8 +/- 3.5, Mann Whitney p = 0.015) and contralateral brain (2.2 +/- 0.9, Mann Whitney p = 0.009). Highest values were found in meningiomas (no blood-brain barrier (BBB); Ki 33.4 +/- 16.5, Mann Whitney p = 0.008 compared with glioblastomas). Among the compartment models, fitting with K1 and regional plasma volume explained the data best (one-tissue model), data fits were not significantly improved by addition of a k2 or k3 parameter. K1 and Ki values were significantly correlated (Spearman Rank, p = 0.0006). We conclude that 52Fe accumulation in tumors is governed by tracer uptake at the BBB, and does not reflect number of transferrin receptors at the level of tumor cells.