Age and disease related changes in the translocator protein (TSPO) system in the human brain: positron emission tomography measurements with [11C]vinpocetine.

BACKGROUNDS AND PURPOSE: The main objectives of the present study were (i) to measure density changes of activated microglia and the peripheral benzodiazepine receptor/translocator protein (TSPO) system during normal ageing in the human brain with positron emission tomography (PET) using the TSPO molecular imaging biomarker [(11)C]vinpocetine and (ii) to compare the level and pattern of TSPO in Alzheimer (AD) patients with age matched healthy subjects, in order to assess the biomarker's usefulness as a diagnostic imaging marker in normal (ageing) and pathological (AD) up-regulation of microglia. METHODS AND SUBJECTS: PET measurements were made in healthy volunteers, aged between 25 and 78 years, and AD patients, aged between 67 and 82 years, using [(11)C]vinpocetine as the tracer. Global and regional quantitative parameters of tracer uptake and binding, including time activity curves (TAC) of standard uptake values (%SUV), binding affinity parameters, intensity spectrum and homogeneity of the uptake distribution were measured and analysed. RESULTS: Both %SUV and binding values increased with age linearly in the whole brain and in all brain regions. There were no significant differences between the %SUV values of the AD patients and age matched control subjects. There were, however, significant differences in %SUV values in a large number of brain regions between young subjects and old subjects, as well as young subjects and AD patients. The intensity spectrum analysis and homogeneity analysis of the voxel data show that the homogeneity of the %SUV values decreases with ageing and during the disease, whereas the centre of the intensity spectrum is shifted to higher %SUV values. These data indicate an inhomogeneous up-regulation of the TSPO system during ageing and AD. These changes were significant between the group of young subjects and old subjects, as well as young subjects and AD patients, but not between old subjects and AD patients. CONCLUSIONS: The present data indicate that [(11)C]vinpocetine may serve as a molecular imaging biomarker of the activity of the TSPO system and, consequently, of the up-regulation of microglia during ageing and in neuroinflammatory diseases. However, the global and regional brain %SUV values between AD patients and age matched controls are not different from each other. The disease specific changes, measured with [(11)C]vinpocetine in AD, are significantly different from those measured in age matched controls only if the inhomogeneities in the uptake pattern are explored with advanced mathematical techniques. For this reason, PET studies using [(11)C]vinpocetine, as molecular imaging biomarker, can efficiently visualise the activation of microglia and the up-regulation of TSPO during ageing and in diseased brains with the help of an appropriate inhomogeneity analysis of the radioligand's brain uptake pattern.

Functional neuroimaging in multiple sclerosis with radiolabelled glia markers: preliminary comparative PET studies with [11C]vinpocetine and [11C]PK11195 in patients.

With the purpose of demonstrating the use of positron emission tomography (PET) and radiolabelled glia markers to indicate regional cerebral damage, we measured with PET in four young multiplex sclerosis (MS) patients in two consecutive measurements the global and regional brain uptake as well as regional distribution and binding potential (BP) of [(11)C]vinpocetine and [(11)C]PK11195. Both ligands showed increased uptake and BP in the regions of local brain damage. However, regional BP values for [(11)C]vinpocetine were markedly higher than those for [(11)C]PK11195. This feature of the former radioligand may be related to its high brain uptake and marked affinity to the peripheral benzodiazepine receptor binding sites (PBBS), characteristic for glia cells. As local brain traumas entail reactive glia accumulation in and around the site of the damage, the present findings may indicate that [(11)C]vinpocetine marks the place or boundaries of local brain damage by binding to the PBBS present in glia cells, which, in turn, accumulate in the region of the damage. The present findings (i) confirm earlier observations with [(11)C]PK11195 as a potential glia marker in PET studies and (ii) support the working hypothesis that [(11)C]vinpocetine is a potentially useful PET marker of regional and global brain damage resulting in glia accumulation locally or globally in the human brain. The comparative analysis of the two ligands indicate that [(11)C]vinpocetine shows a number of characteristics favourable in comparison with [(11)C]PK11195.

[11C]vinpocetine: a prospective peripheral benzodiazepine receptor ligand for primate PET studies.

Vinpocetine, a synthetic derivative of the Vinca minor alkaloid vincamine, is a widely used drug in neurological practice. We tested the hypothesis that vinpocetine binds to peripheral benzodiazepine binding sites (PBBS) and is therefore a potential ligand of PBBS. Positron emission tomography (PET) measurements in two cynomolgous monkeys showed that pretreatment with vinpocetine markedly reduced the brain uptake of [11C]PK11195, a known PBBS radioligand. On the other hand, whereas pretreatment with PK11195 increased the brain uptake of [11C]vinpocetine due to the blockade of PBBS in the periphery, it significantly reduced the binding potential (BP) values of [11C]vinpocetine in the whole brain and in individual brain structures to PK11195. These findings indicate that, whereas the two ligands have different affinities to PBBS, vinpocetine is a potent ligand of PBBS, which in turn suggests that the pharmacological activity of vinpocetine may involve the regulation of glial functions.

Effects of vinpocetine on the redistribution of cerebral blood flow and glucose metabolism in chronic ischemic stroke patients: a PET study.

The pharmacological effects of the neuroprotective drug vinpocetine, administered intravenously in a 14-day long treatment regime, on the cerebral blood flow and cerebral glucose metabolism in chronic ischemic stroke patients (n=13) were studied with positron emission tomography in a double-blind design. The regional and global cerebral metabolic rates of glucose (CMRglc) and cerebral blood flow (CBF) as well as vital physiological parameters, clinical performance scales, and transcranial Doppler parameters were measured before and after the treatment period in patient groups treated with daily intravenous infusion with or without vinpocetine. While the global CMRglc values did not change markedly as a result of the infusion treatment with (n=6) or without (n=7) vinpocetine, the global CBF increased and regional CMRglc and CBF values showed marked changes in several brain structures in both cases, with more accentuated changes when the infusion contained vinpocetine. In the latter case the highest rCBF changes were observed in those structures in which the highest regional uptake of labelled vinpocetine was measured in other PET studies (thalamus and caudate nucleus: increases amounting to 36% and 37%, respectively). The findings indicate that a 2-week long intravenous vinpocetine treatment can contribute effectively to the redistribution of rCBF in chronic ischemic stroke patients. The effects are most pronounced in those brain regions with the highest uptake of the drug.

Clinical and non-clinical investigations using positron emission tomography, near infrared spectroscopy and transcranial Doppler methods on the neuroprotective drug vinpocetine: a summary of evidences.

Vinpocetine (Cavinton, Gedeon Richter, Budapest) is widely used as a neuroprotective drug in the prevention and treatment of cerebrovascular diseases. Vinpocetine is a potent inhibitor of the voltage-dependent Na(+) channels and a selective inhibitor of the Ca(2+)/caldmoduline-dependent phosphodiesterase 1. The clinical efficacy has been supported by several previous studies. Positron emission tomography (PET) is a powerful method to evaluate the fate, the site of action, the pharmacological and physiological effects of a drug in the brain and other organs. We have demonstrated in monkey that the [11C]-labelled vinpocetine rapidly enters the brain after intravenous (i.v.) injection, the maximal uptake being approximately 5% of the total injected radioactivity. The distribution pattern of vinpocetine in the brain was heterogenous, with the highest uptake in the thalamus, basal ganglia and visual cortex. These findings were confirmed in healthy humans, where the i.v. administered [11C]-labelled vinpocetine had a similar distribution pattern. The highest uptake in the brain was 3.71% of the total administered radioactivity. Quite recently, we have shown that [11C]-labelled vinpocetine administered orally to healthy human volunteers also rapidly appears in the brain and shows a similar distribution pattern, the highest uptake being 0.71% of the total administered radioactivity. In two separate sets of clinical studies where chronic ischaemic post-stroke patients were either treated with a single infusion (Study 1) or with daily vinpocetine infusion for 2 weeks (Study 2), we have shown that vinpocetine increases the regional cerebral glucose uptake and to a certain extent glucose metabolism in the so-called peri-stroke region as well as in the relatively intact brain tissue. The 2-week-long treatment also increased the regional cerebral blood flow (CBF) especially in the thalamus, basal ganglia and visual cortex of the nonsymptomatic hemisphere. We have demonstrated the cerebral perfusion-enhancing and parenchymal oxygen extraction-increasing effects of vinpocetine in subacute ischaemic stroke patients by near infrared spectroscopy (NIRS) and transcranial Doppler (TCD) methods.

Cerebral uptake of [ethyl-11C]vinpocetine and 1-[11C]ethanol in cynomolgous monkeys: a comparative preclinical PET study.

PET provides the potential to quantify the distribution of radiolabelled drugs in the human body. In cases when radiolabelled compounds undergo metabolic transformation after administration in vivo, it is necessary to examine the kinetics and distribution of both the labeled mother compound and labeled metabolites. The objective of this study was to assess the extent by which 11C-labeled ethanol, the product arising from the de-esterification of the neuroprotective drug vinpocetine (ethyl-apovincaminate), might contribute to the regional cerebral radioactivity measured by PET after the administration of [ethyl-11C]vinpocetine. In three cynomolgous monkeys PET measurements were made after intravenous bolus injection of both [11C]vinpocetine and 1-[11C]ethanol. There was a marked difference between the regional time-activity curves of [11C]ethanol and [11C]vinpocetine. The distribution pattern obtained with [11C]ethanol was similar to that observed with blood flow tracers such as [15O]water and [15O]butanol. The study shows that although [11C]ethanol may moderately contribute to the brain radioactivity distribution pattern of [11C]vinpocetine, the rapid degradation of [11C]ethanol makes it unlikely that the contribution of this metabolite is of importance. The distinct distribution patterns and kinetics of [11C]vinpocetine and [11C]ethanol also support the view, obtained from our previous observations, that vinpocetine may bind to specific sites in the monkey and human brain, especially in the thalamus.

[Cerebral uptake and regional distribution of [11C]-vinpocetin after intravenous administration to healthy men: a PET study]. / [11C]-vinpocetin agyi felvétele és regionális eloszlása egyszeri intravénás adás után emberben: PET vizsgálatok.

INTRODUCTION: Vinpocetine is a compound widely used in the prevention and treatment of cerebrovascular diseases. The exact mechanism of action of the drug is still not known. The objective of the present investigation was to determine the global uptake and regional distribution of radiolabelled vinpocetine in the human brain. Three healthy persons were examined with positron emission tomography (PET) and [11C]-vinpocetine. RESULTS: The uptake of [11C]-vinpocetine in brain was rapid and on average as a maximum 3.7% of the total radioactivity injected was in the brain 2 minutes after radioligand administration. The uptake was heterogeneously distributed among brain regions. When compared with the cerebellum, an a priori reference region, the highest regional uptake was in the thalamus, the upper brain stem, the striatum and the cortex. CONCLUSIONS: The brain regions showing increased uptake in the human brain correspond to those in which vinpocetine has previously been shown to induce elevated metabolism and blood flow by PET clinical studies in patients with chronic ischaemic post-stroke condition.

[Human positron emission tomography with oral 11C-vinpocetine]. / Pozitronemissziós tomográfiás humán vizsgálatok orálisan adott [11C]vinpocetinnel.

INTRODUCTION: Positron emission tomography (PET) is a useful tool for the investigation of certain physiological changes and for the evaluation of the distribution, and receptor binding of drugs labelled with positron emitting isotopes. Vinpocetine (ethyl-apovincaminate) is a neuroprotective drug widely used in the prevention and treatment of cerebrovascular diseases. In the clinical practice vinpocetine is usually administered to the patients in intravenous infusion followed by long-term oral treatment. Until presently human data describing vinpocetine's kinetics and brain distribution came from ex vivo (blood, plasma, liquor) and post mortem (brain autoradiography) measurements. AIM: The authors wished to investigate the kinetics and distribution of vinpocetine in the brain and body after oral administration with PET in order to prove, that PET is useful in the non-invasive in vivo determination of these parameters. METHOD: Vinpocetine was labelled with carbon-11 and the radioactivity was measured by PET in the stomach, liver, brain, colon and kidneys in healthy male volunteers. The radioactivity in the blood and urine was also determined. RESULTS: After oral administration, [11C]vinpocetine appeared immediately in the stomach and within minutes in the liver and the blood. In the blood the level of radioactivity continuously increased until the end of the measurement period, whereas the fraction of the unchanged mother compound decreased. Radioactivity uptake and distribution in the brain were demonstrable from the tenth minute after the oral administration of the labelled drug (average maximum uptake: 0.7% of the administered total dose). Brain distribution was heterogeneous (with preferences in the thalamus, basal ganglia and occipital cortex), similar to the distribution previously reported by the authors after intravenous administration. CONCLUSIONS: Vinpocetine, administered orally to human volunteers, readily entered the bloodstream from the stomach and the gastrointestinal tract and thereafter passed the blood-brain barrier and entered the brain. Radioactivity from [11C]vinpocetine was also demonstrated in the kidneys and in urine. The study demonstrates that PET might be a useful, direct and non-invasive tool to study the distribution and pharmacokinetics of orally administered labelled drugs active in the central nervous system in the living human body.

Visualising neuroinflammation in post-stroke patients: a comparative PET study with the TSPO molecular imaging biomarkers [11C]PK11195 and [11C]vinpocetine.

With the main objective of comparing the prospective diagnostic power of two 11C-labelled molecular imaging biomarkers with affinity for TSPO and used for the visualisation of activated microglia after a stroke, we measured with positron emission tomography (PET) in four post-stroke patients the regional brain uptake and binding potential of [11C]vinpocetine and [11C]PK11195. Percentage standard uptake values (%SUV) and binding potential (BPND) were used as outcome measures. The total peak brain uptake value and average global brain uptake value were higher for [11C]vinpocetine than for [11C]PK11195. The regional %SUV values were significantly higher for [11C]vinpocetine than for [11C]PK11195 in the hemispheres as well as in almost all standard brain regions. The %SUV values of [11C]vinpocetine were higher in the peri-infarct zone than in the ischaemic core, however, the difference did not prove to be significant. There was basically no difference in %SUV values between the ischaemic core and the peri-infarct zone for [11C]PK11195. The BPND values for [11C]vinpocetine were higher in all standard regions than those for [11C]PK11195, but the difference was not significant between them. The BPND values of [11C]vinpocetine were higher in the peri-infarct zone than in the ischaemic core, however, the difference did not prove to be significant. A comparative analysis of the two ligands indicates that [11C]vinpocetine shows a number of favourable characteristics over [11C]PK11195, but to demonstrate that it may serve as a prospective molecular imaging biomarker of microglia activation in post-stroke patients, further studies are required.

Evolution of microglial activation in ischaemic core and peri-infarct regions after stroke: a PET study with the TSPO molecular imaging biomarker [((11))C]vinpocetine.

Although there is increasing evidence for microglial activation after an ischaemic stroke in the infarct core and the peri-infarct region, the "evolution" of the process in stroke patients is poorly known. Using PET and [((11))C]vinpocetine, we measured the regional changes of TSPO in the brain of nine ischaemic stroke patients up to 14weeks after the insult. Already a week after stroke there was an increased radioligand uptake, indicating the up-regulation of TSPO and the presence of activated microglia, in both the ischaemic core and the peri-infarct zone. This increased activation showed a steady decrease with post stroke time. The proportion between %SUV values in the peri-infarct zone and the ischaemic core increased with time. There were no time-dependent TSPO activity changes in other regions, not affected directly by the stroke. The present observations demonstrate that increased regional microglia activation, as a consequence of stroke, can be visualised with PET, using the TSPO molecular imaging biomarker [((11))C]vinpocetine. The evolution of this microglial activation shows a time dependent decrease the gradient of which is different between the peri-infarct zone and the ischaemic core. The findings indicate an increased microglial activation in the peri-stroke region for several weeks after the insult.

Translocator protein (TSPO 18kDa) is expressed by neural stem and neuronal precursor cells.

Translocator protein 18 kDa, the peripheral benzodiazepine receptor by its earlier name, is a mitochondrial membrane protein associated with the mitochondrial permeability pore. While the function of the protein is not properly understood, it is known to play roles in necrotic and apoptotic processes of the neural tissue. In the healthy adult brain, TSPO expression is restricted to glial cells. In developing or damaged neural regions, however, TSPO appears in differentiating/regenerating neurons. Using immunocytochemical, molecular biological and cell biological techniques, we demonstrate that TSPO mRNA and protein, while missing from mature neurons, are present in neural stem cells and also in postmitotic neuronal precursors. Investigating some distinct stages of in vitro differentiation of NE-4C neural stem cells, TSPO 18 kDa was found to be repressed in a relatively late phase of neuron formation, when mature neuron-specific features appear. This timing indicates that mitochondria in fully developed neurons display specific characteristics and provides an additional marker for characterising neuronal differentiation.

Inhibition of phosphodiesterase 1 augments the pulmonary vasodilator response to inhaled nitric oxide in awake lambs with acute pulmonary hypertension.

Phosphodiesterase 1 (PDE1) modulates vascular tone and the development of tolerance to nitric oxide (NO)-releasing drugs in the systemic circulation. Any role of PDE1 in the pulmonary circulation remains largely uncertain. We measured the expression of genes encoding PDE1 isozymes in the pulmonary vasculature and examined whether or not selective inhibition of PDE1 by vinpocetine attenuates pulmonary hypertension and augments the pulmonary vasodilator response to inhaled NO in lambs. Using RT-PCR, we detected PDE1A, PDE1B, and PDE1C mRNAs in pulmonary arteries and veins isolated from healthy lambs. In 13 lambs, the thromboxane A(2) analog U-46619 was infused intravenously to increase mean pulmonary arterial pressure to 35 mmHg. Four animals received an intravenous infusion of vinpocetine at incremental doses of 0.3, 1, and 3 mg.kg(-1).h(-1). In nine lambs, inhaled NO was administered in a random order at 2, 5, 10, and 20 ppm before and after an intravenous infusion of 1 mg.kg(-1).h(-1) vinpocetine. Administration of vinpocetine did not alter pulmonary and systemic hemodynamics or transpulmonary cGMP or cAMP release. Inhaled NO selectively reduced mean pulmonary arterial pressure, pulmonary capillary pressure, and pulmonary vascular resistance index, while increasing transpulmonary cGMP release. The addition of vinpocetine enhanced pulmonary vasodilation and transpulmonary cGMP release induced by NO breathing without causing systemic vasodilation but did not prolong the duration of pulmonary vasodilation after NO inhalation was discontinued. Our findings demonstrate that selective inhibition of PDE1 augments the therapeutic efficacy of inhaled NO in an ovine model of acute chemically induced pulmonary hypertension.

Eburnamine derivatives and the brain.

The Apocynaceae plant family contains a great number of so called eburnamine-vincamine alkaloids. Quite a few of these alkaloids exert varied pharmacological activities on the cell multiplication, cardiovascular system, and brain functions. Many derivatives were also synthesized to find pharmacologically active compounds better characterized and safer to be administered than the natural plant alkaloids themselves. We concentrate on the eburnamine structures with cerebral activities in this review. Vincamine, vinburnine, vindeburnol, apovincaminate, and vinpocetine (cis-ethyl-apovincaminate) all share modulatory effects on brain circulation and neuronal homeostasis, bear antihypoxic and neuroprotective potencies to various degrees. The most eminent compound of this class of alkaloids is vinpocetine. Since its introduction to the market as a neuroprotective agent many non clinical and clinical studies proved vinpocetine's effects on calmodulin dependent phosphodiesterase E1, on sodium, calcium channels, peripheral benzodiazepine receptor, and glutamate receptors as well as its clinical usefulness in the treatment of post-ischaemic stroke disease states and various disorders of cerebrovascular origin. Lately, positron emission tomography studies proved that vinpocetine has a rapid uptake in the primate and human brain with a heterogeneous distribution pattern (preference areas: thalamus, basal ganglia, and visual cortex) both after intravenous and oral administration. Vinpocetine exerts beneficial effects in cerebral glucose metabolism and regional cerebral blood flow in chronic post-stroke patients.

Drug distribution in man: a positron emission tomography study after oral administration of the labelled neuroprotective drug vinpocetine.

Direct information on the distribution of a drug requires measurements in various tissues. Such data have until now been obtained in animals, or have indirectly been calculated from plasma measurements in humans using mathematical models. Here we suggest the use of positron emission tomography (PET) as a method to obtain direct measurements of drug distribution in the human body. The distribution in body and brain of vinpocetine, a neuroprotective drug widely used in the prevention and treatment of cerebrovascular diseases, was followed after oral administration. Vinpocetine was labelled with carbon-11 and radioactivity was measured by PET in stomach, liver, brain and kidney in six healthy volunteers. The radioactivity in blood and urine as well as the fractions of [(11)C]vinpocetine and labelled metabolites in plasma were also determined. After oral administration, [(11)C]vinpocetine appeared immediately in the stomach and within minutes in the liver and the blood. In the blood the level of radioactivity continuously increased until the end of the measurement period, whereas the fraction of the unchanged mother compound decreased. Radioactivity uptake and distribution in the brain were demonstrable from the tenth minute after the administration of the labelled drug. Brain distribution was heterogeneous, similar to the distribution previously reported after intravenous administration. These findings indicate that vinpocetine, administered orally in humans, readily enters the bloodstream from the stomach and gastrointestinal tract and, consequently, passes the blood-brain barrier and enters the brain. Radioactivity from [(11)C]vinpocetine was also demonstrated in the kidneys and in urine, indicating that at least a part of the radioactive drug and labelled metabolites is eliminated from the body through the kidneys. This study is the first to demonstrate that PET might be a useful, direct and non-invasive tool to study the distribution and pharmacokinetics of orally administered labelled CNS drugs in the living human body.