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

Pd-Catalyzed cascade Heck cyclization/carbonylation of indoles with aryl formates: enantioselective construction of indolo[2,1-a]isoquinolines

An efficient palladium-catalyzed cascade cyclization/carbonylation of indoles with aryl formates to access ester-functionalized indolo[2,1-a]isoquinoline scaffolds has been developed. In addition, an asymmetric variant is also achieved using a chiral phosphine ligand, affording the indolo[2,1-a]isoquinoline products in good yields and enantioselectivities.

Neuroprotective Effects of Vinpocetine Against Ischemia-Reperfusion Injury Via Inhibiting NLRP3 Inflammasome Signaling Pathway

Ischemic stroke is one of the main causes of serious disability and death worldwide. NLRP3 inflammasome is an intracellular pattern recognition receptor composed of polyprotein complex, which participates in mediating a series of inflammatory responses and is considered as a potential target for the treatment of ischemic stroke. Vinpocetine, a derivative of vincamine, has been widely used in the prevention and treatment of ischemic stroke. However, the therapeutic mechanism of vinpocetine is not clear, and its effect on NLRP3 inflammasome remains to be determined. In this study, we used the mouse model of transient middle cerebral artery occlusion (tMCAO) to simulate the occurrence of ischemic stroke. Different doses of vinpocetine (5, 10, 15 mg/kg/d) were injected intraperitoneally for 3 days after ischemia-reperfusion in mice. The effects of different doses of vinpocetine on the degree of ischemia-reperfusion injury in mice were observed by TTC staining and modified neurological severity score scale, and the optimal dose was determined. Then, based on this optimal dose, we observed the effects of vinpocetine on apoptosis, microglial proliferation and NLRP3 inflammasome. In addition, we compared the effects of vinpocetine and MCC950 (a specific inhibitor of NLRP3 inflammasome) on NLRP3 inflammasome. Our results show that vinpocetine can effectively reduce the infarct volume and promote the recovery of behavioral function in stroke mice, and the maximal beneficial effects were observed at the dose of 10 mg/kg/d. Vinpocetine can effectively inhibit the apoptosis of peri-infarct neurons, promote the expression of Bcl-2, inhibit the expression of Bax and Cleaved Caspase-3, and reduce the proliferation of peri-infarct microglia. In addition, vinpocetine, like MCC950, can reduce the expression of NLRP3 inflammasome. Therefore, vinpocetine can effectively alleviate the ischemia-reperfusion injury in mice, and the inhibition of NLRP3 inflammasome may be an important therapeutic mechanism of vinpocetine.

Phytochemicals targeting lncRNAs: A novel direction for neuroprotection in neurological disorders

Neurological disorders with various etiologies impacting the nervous system are prevalent in clinical practice. Long non-coding RNA (lncRNA) molecules are functional RNA molecules exceeding 200 nucleotides in length that do not encode proteins, but participate in essential activities. Research indicates that lncRNAs may contribute to the pathogenesis of neurological disorders, and may be potential targets for their treatment. Phytochemicals in traditional Chinese herbal medicine (CHM) have been found to exert neuroprotective effects by targeting lncRNAs and regulating gene expression and various signaling pathways. We aim to establish the development status and neuroprotective mechanism of phytochemicals that target lncRNAs through a thorough literature review. A total of 369 articles were retrieved through manual and electronic searches of PubMed, Web of Science, Scopus and CNKI databases from inception to September 2022. The search utilized combinations of natural products, lncRNAs, neurological disorders, and neuroprotective effects as keywords. The included studies, a total of 31 preclinical trials, were critically reviewed to present the current situation and the progress in phytochemical-targeted lncRNAs in neuroprotection. Phytochemicals have demonstrated neuroprotective effects in preclinical studies of various neurological disorders by regulating lncRNAs. These disorders include arteriosclerotic ischemia-reperfusion injury, ischemic/hemorrhagic stroke, Alzheimer's disease, Parkinson's disease, glioma, peripheral nerve injury, post-stroke depression, and depression. Several phytochemicals exert neuroprotective roles through mechanisms such as anti-inflammatory, antioxidant, anti-apoptosis, autophagy regulation, and antagonism of Aβ-induced neurotoxicity. Some phytochemicals targeted lncRNAs and served a neuroprotective role by regulating microRNA and mRNA expression. The emergence of lncRNAs as pathological regulators provides a novel direction for the study of phytochemicals in CHM. Elucidating the mechanism of phytochemicals regulating lncRNAs will help to identify new therapeutic targets and promote their application in precision medicine.

Vinpocetine, a PDE1 modulator, regulates markers of cerebral health, inflammation, and oxidative stress in a rat model of prenatal alcohol-induced experimental attention deficit hyperactivity disorder

Prenatal alcohol exposure (PAE) has been shown to induce symptomatology associated with attention deficit hyperactivity disorder (ADHD) by altering neurodevelopmental trajectories. Phosphodiesterase-1 (PDE1) is expressed centrally and has been used in various experimental brain conditions. We investigated the role of vinpocetine, a PDE1 inhibitor, on behavioral phenotypes and important biochemical deficits associated with a PAE rat model of ADHD. Protein markers of cerebral health (synapsin-IIa, BDNF, and pCREB), inflammation (IL-6, IL-10, and TNF-α), and oxidative stress (TBARS, GSH, and SOD) were analyzed in three brain regions (frontal cortex, striatum, and cerebellum). Hyperactivity, inattention, and anxiety introduced in the offspring due to PAE were assayed using open-field, Y-maze, and elevated plus maze, respectively. Administration of vinpocetine (10 & 20 mg/kg, p.o. [by mouth]) to PAE rat offspring for 4 weeks resulted in improvement of the behavioral profile of the animals. Additionally, levels of protein markers such as synapsin-IIa, BDNF, pCREB, IL-10, SOD, and GSH were found to be significantly increased, with a significant reduction in markers such as TNF-α, IL-6, and TBARS in selected brain regions of vinpocetine-treated animals. Vinpocetine, a selective PDE1 inhibitor, rectified behavioral phenotypes associated with ADHD, possibly by improving cerebral function, reducing brain inflammation, and reducing brain oxidative stress. This study provides preliminary analysis and suggests that the PDE1 enzyme may be an important pharmacological tool to study ADHD as a result of PAE.

Vinpocetine (A comprehensive profile)

Vinpocetine (VIN) is a herbal supplement extracted from the periwinkle plant. It is a multi-action agent, which is used to treat various neurological disorders such as Alzheimer's and Parkinson's disease. Vinpocetine has also anti-inflammatory, analgesic, antioxidant property and treats various thinking and memory problems. Currently, vinpocetine is also available in the market as a dietary supplement to enhance cognition and memory. This profile explains the physicochemical properties, methods of preparation, content of related impurities and different spectroscopical behavior of vinpocetine. It also discusses the reported methods of analysis of the drug, which include Compendial Methods, Electrochemical Methods, Spectrophotometric Methods and Chromatographic Methods of analysis. Furthermore, this profile explains the stability of the drug subjected to stress conditions of acid, alkaline and photolytic degradation. In addition, the clinical applications of the drug, its uses, side effects, dosing information, pharmacokinetics and mechanism of action are also discussed.

Strategic, feasibility, economic, and cultural aspects of Phase 0 approaches

Research conducted over the past 2 decades has enhanced the validity and expanded the applications of microdosing and other phase 0 approaches in drug development. Phase 0 approaches can accelerate drug development timelines and reduce attrition in clinical development by increasing the quality of candidates entering clinical development and by reducing the time to “go‐no‐go” decisions. This can be done by adding clinical trial data (both healthy volunteers and patients) to preclinical candidate selection, and by applying methodological and operational advantages that phase 0 have over traditional approaches. The main feature of phase 0 approaches is the limited, subtherapeutic exposure to the test article. This means a reduced risk to research volunteers, and reduced regulatory requirements, timelines, and costs of first‐in‐human (FIH) testing. Whereas many operational aspects of phase 0 approaches are similar to those of other early phase clinical development programs, they have some unique strategic, regulatory, ethical, feasibility, economic, and cultural aspects. Here, we provide a guidance to these operational aspects and include case studies to highlight their potential impact in a range of clinical development scenarios.

Vinpocetine amended prenatal valproic acid induced features of ASD possibly by altering markers of neuronal function, inflammation, and oxidative stress

Autism spectrum disorder (ASD) is a neurodevelopmental disorder with complex etiology and phenotypes. Phosphodiesterase-1 (PDE1) inhibitors are known to provide benefits in various brain conditions manifesting similar behavioral phenotypes. The pharmacological consequences of vinpocetine administration a PDE1 inhibitor in prenatal-valproic acid (pre-VPA) induced ASD related behavioral phenotypes (social behavior deficits, repetitive behavior, anxiety, hyperlocomotion, and nociception) was assessed. Also, effects on important biochemical markers of neuronal function (DCX-neurogenesis, BDNF-neuronal survival, synapsin-IIa-synaptic transmission, pCREB-neuronal transcription factor), inflammation (interleukin [IL]-6, IL-10, and TNF-α) and oxidative stress (thiobarbituric acid reactive substance [TBARS] and glutathione (GSH) were studied in important brain areas (frontal cortex, cerebral cortex, hippocampus, and striatum). Further, neuronal cell viability was determined in dentate gyrus using Nissl staining. Pre-VPA administration resulted into impaired behavior, brain biochemistry, and neuronal cell viability. Administration of vinpocetine resulted in improvements of pre-VPA impaired social behavior, repetitive behavior, anxiety, locomotion, and nociception. Also, vinpocetine resulted in a significant increase in the levels of BDNF, synapsin-IIa, DCX, pCREB/CREB, IL-10, and GSH along with significant decrease in TNF-α, IL-6, TBARS, number of pyknotic and chromatolytic cells in different brain areas of pre-VPA group. Finally, high association between behavioral parameters and biochemical parameters was observed upon Pearson's correlation analysis. Vinpocetine, a PDE1 inhibitor rectified important behavioral phenotypes related with ASD, possibly by improving neuronal function, brain inflammation and brain oxidative stress. Thus, PDE1 may be a possible target for further understanding ASD. LAY SUMMARY: ASD is a brain developmental disorder with a wide array of genetic and environmental factors. Many targets have been identified till date, but a clinical treatment is still afar. The results of this study indicate that vinpocetine administration resulted in amelioration of ASD associated symptomatology in rats, prenatally exposed to VPA. Our research adds a widely expressed brain enzyme PDE1, as a possible novel pharmacological target and opens-up a new line of enquiry for ASD treatment.

Emerging neuroprotective strategies for the treatment of ischemic stroke: An overview of clinical and preclinical studies

Stroke is the leading cause of disability and thesecond leading cause of death worldwide. With the global population aged 65 and over growing faster than all other age groups, the incidence of stroke is also increasing. In addition, there is a shift in the overall stroke burden towards younger age groups, particularly in low and middle-income countries. Stroke in most cases is caused due to an abrupt blockage of an artery (ischemic stroke), but in some instances stroke may be caused due to bleeding into brain tissue when a blood vessel ruptures (hemorrhagic stroke). Although treatment options for stroke are still limited, with the advancement in recanalization therapy using both pharmacological and mechanical thrombolysis some progress has been made in helping patients recover from ischemic stroke. However, there is still a substantial need for the development of therapeutic agents for neuroprotection in acute ischemic stroke to protect the brain from damage prior to and during recanalization, extend the therapeutic time window for intervention and further improve functional outcome. The current review has assessed the past challenges in developing neuroprotective strategies, evaluated the recent advances in clinical trials, discussed the recent initiative by the National Institute of Neurological Disorders and Stroke in USA for the search of novel neuroprotectants (Stroke Preclinical Assessment Network, SPAN) and identified emerging neuroprotectants being currently evaluated in preclinical studies. The underlying molecular mechanism of each of the neuroprotective strategies have also been summarized, which could assist in the development of future strategies for combinational therapy in stroke treatment.

A Review and Hypothesized Model of the Mechanisms That Underpin the Relationship Between Inflammation and Cognition in the Elderly

Age is associated with increased risk for several disorders including dementias, cardiovascular disease, atherosclerosis, obesity, and diabetes. Age is also associated with cognitive decline particularly in cognitive domains associated with memory and processing speed. With increasing life expectancies in many countries, the number of people experiencing age-associated cognitive impairment is increasing and therefore from both economic and social terms the amelioration or slowing of cognitive aging is an important target for future research. However, the biological causes of age associated cognitive decline are not yet, well understood. In the current review, we outline the role of inflammation in cognitive aging and describe the role of several inflammatory processes, including inflamm-aging, vascular inflammation, and neuroinflammation which have both direct effect on brain function and indirect effects on brain function via changes in cardiovascular function.

An update on vinpocetine: New discoveries and clinical implications

Vinpocetine, a derivative of the alkaloid vincamine, has been clinically used in many countries for treatment of cerebrovascular disorders such as stroke and dementia for more than 30 years. Currently, vinpocetine is also available in the market as a dietary supplement to enhance cognition and memory. Due to its excellent safety profile, increasing efforts have been put into exploring the novel therapeutic effects and mechanism of actions of vinpocetine in various cell types and disease models. Recent studies have revealed a number of novel functions of vinpocetine, including anti-inflammation, antagonizing injury-induced vascular remodeling and high-fat-diet-induced atherosclerosis, as well as attenuating pathological cardiac remodeling. These novel findings may facilitate the repositioning of vinpocetine for preventing or treating relevant disorders in humans.

The Effect of Vinpocetine on Human Cytochrome P450 Isoenzymes by Using a Cocktail Method

Vinpocetine is a derivative of the alkaloid vincamine, which had been prescribed for chronic cerebral vascular ischemia and acute ischemic stroke or used as a dietary supplement for its several different mechanisms of biological activities. However, information on the cytochrome P450 (CYP) enzyme-mediated drug metabolism has not been previously studied. The present study was performed to investigate the effects of vinpocetine on CYPs activity, and cocktail method was used, respectively. To evaluate the effects of vinpocetine on the activity of human CYP3A4, CYP2C9, CYP2C19, CYP2D6, and CYP2E1, human liver microsomes were utilized to incubate with the mixed CYPs probe substrates and the target components. The results indicate that vinpocetine exhibited weak inhibitory effect on the CYP2C9, where the IC₅₀ value is 68.96 μM, whereas the IC₅₀ values for CYP3A4, CYP2C19, CYP2D6, and CYP2E1 were all over range of 100 μM, which showed that vinpocetine had no apparent inhibitory effects on these CYPs. In conclusion, the results indicated that drugs metabolized by CYP2C9 coadministrated with vinpocetine may require attention or dose adjustment.

Vinpocetine reduces carrageenan-induced inflammatory hyperalgesia in mice by inhibiting oxidative stress, cytokine production and NF-κB activation in the paw and spinal cord

Vinpocetine is a safe nootropic agent used for neurological and cerebrovascular diseases. The anti-inflammatory activity of vinpocetine has been shown in cell based assays and animal models, leading to suggestions as to its utility in analgesia. However, the mechanisms regarding its efficacy in inflammatory pain treatment are still not completely understood. Herein, the analgesic effect of vinpocetine and its anti-inflammatory and antioxidant mechanisms were addressed in murine inflammatory pain models. Firstly, we investigated the protective effects of vinpocetine in overt pain-like behavior induced by acetic acid, phenyl-p-benzoquinone (PBQ) and formalin. The intraplantar injection of carrageenan was then used to induce inflammatory hyperalgesia. Mechanical and thermal hyperalgesia were evaluated using the electronic von Frey and the hot plate tests, respectively, with neutrophil recruitment to the paw assessed by a myeloperoxidase activity assay. A number of factors were assessed, both peripherally and in the spinal cord, including: antioxidant capacity, reduced glutathione (GSH) levels, superoxide anion, tumor necrosis factor alpha (TNF-α) and interleukin 1 beta (IL-1β) levels, as well as nuclear factor kappa B (NF-κB) activation. Vinpocetine inhibited the overt pain-like behavior induced by acetic acid, PBQ and formalin (at both phases), as well as the carrageenan-induced mechanical and thermal hyperalgesia and associated neutrophil recruitment. Both peripherally and in the spinal cord, vinpocetine also inhibited: antioxidant capacity and GSH depletion; increased superoxide anion; IL-1β and TNF-α levels; and NF-κB activation. As such, vinpocetine significantly reduces inflammatory pain by targeting oxidative stress, cytokine production and NF-κB activation at both peripheral and spinal cord levels.

Use of positron emission tomography for real-time imaging of biodistribution of green tea catechin

The aim of this study was to achieve real-time imaging of the in vivo behavior of a green tea polyphenol, catechin, by positron emission tomography (PET). Positron-labeled 4″ -[(11)C]methyl-epigallocatechin gallate ([(11)C]Me-EGCG) was orally administered to rats, and its biodistribution was imaged for 60 min by using a small animal PET system. As the result, images of [(11)C]Me-EGCG passing through the stomach into the small intestines were observed; and a portion of it was quantitatively detected in the liver. On the other hand, intravenous injection of [(11)C]Me-EGCG resulted in a temporal accumulation of the labeled catechin in the liver, after which almost all of it was transferred to the small intestines within 60 min. In the present study, we succeeded in obtaining real-time imaging of the absorption and biodistribution of [(11)C]Me-EGCG with a PET system.

Distribution and binding of 18F-labeled and 125I-labeled analogues of ACI-80, a prospective molecular imaging biomarker of disease: a whole hemisphere post mortem autoradiography study in human brains obtained from Alzheimer's disease patients

One of the major pathological landmarks of Alzheimer's disease and other neurodegenerative diseases is the presence of amyloid deposits in the brain. The early non-invasive visualization of amyloid is a major objective of recent diagnostic neuroimaging approaches, including positron emission tomography (PET), with an eye on follow-up of disease progression and/or therapy efficacy. The development of molecular imaging biomarkers with binding affinity to amyloid in the brain is therefore in the forefront of imaging biomarker and radiochemistry research. Recently, a dodecamer peptide (amino acid sequence=QSHYRHISPAQV; denominated D1 or ACI-80) was identified as a prospective ligand candidate, binding with high ex vivo affinity to L-Aβ-amyloid (K(d): 0.4 μM). In order to assess the ligand's capacity to visualize amyloid in Alzheimer's disease (AD), two (125)I labeled and three (18)F labeled analogues of the peptide were synthesized and tested in post mortem human autoradiography experiments using whole hemisphere brain slices obtained from deceased AD patients and age matched control subjects. The (18)F-labeled radioligands showed more promising visualization capacity of amyloid that the (125)I-labeled radioligands. In the case of each (18)F radioligands the grey matter uptake in the AD brains was significantly higher than that in control brains. Furthermore, the grey matter: white matter uptake ratio was over ~2, the difference being significant for each (18)F-radioligands. The regional distribution of the uptake of the various radioligands systematically shows a congruent pattern between the high uptake regions and spots in the autoradiographic images and the disease specific signals obtained in adjacent or identical brain slices labeled with histological, immunohistochemical or autoradiographic stains for amyloid deposits or activated astrocytes. The present data, using post mortem human brain autoradiography in whole hemisphere human brains obtained from deceased AD patients and age matched control subjects, support the visualization capacity of the radiolabeled ACI-80 analogues of amyloid deposits in the human brain. Further studies are warranted to explore the usefulness of the (18)F-labeled analogues as in vivo molecular imaging biomarkers in diagnostic PET studies.

Current paradigm of the 18-kDa translocator protein (TSPO) as a molecular target for PET imaging in neuroinflammation and neurodegenerative diseases

Neuroinflammation is a process characterised by drastic changes in microglial morphology and by marked upregulation of the 18-kDa translocator protein (TSPO) on the mitochondria. The continual increase in incidence of neuroinflammation and neurodegenerative diseases poses a major health issue in many countries, requiring more innovative diagnostic and monitoring tools. TSPO expression may constitute a biomarker for brain inflammation that could be monitored by using TSPO tracers as neuroimaging agents. From medical imaging perspectives, this review focuses on the current concepts related to the TSPO, and discusses briefly on the status of its PET imaging related to neuroinflammation and neurodegenerative diseases in humans.

Preparation and in vitro/in vivo evaluation of vinpocetine elementary osmotic pump system

Preparation and in vitro and in vivo evaluation of vinpocetine (VIN) elementary osmotic pump (EOP) formulations were investigated. A method for the preparation of VIN elementary osmotic pump tablet was obtained by adding organic acid additives to increase VIN solubility. VIN was used as the active pharmaceutical ingredient, lactose and mannitol as osmotic agent. Citric acid was used as increasing API solubility and without resulting in the API degradation. It is found that the VIN release rate was increasing with the citric acid amount at a constant range. Cellulose acetate 398-3 was employed as semipermeable membrane containing polyethylene glycol 6000 and diethyl-o-phthalate as pore-forming agent and plasticizer for controlling membrane permeability. In addition, a clear difference between the pharmacokinetic patterns of VIN immediate release and VIN elementary osmotic pump formulations was revealed. The area under the plasma concentration-time curve after oral administration of elementary osmotic pump formulations was equivalent to VIN immediate release formulation. Furthermore, significant differences found for mean residence time, elimination half-life, and elimination rate constant values corroborated prolonged release of VIN from elementary osmotic pump formulations. These results suggest that the VIN osmotic pump controlled release tablets have marked controlled release characters and the VIN osmotic pump controlled release tablets and the normal tablets were bioequivalent.

Vinpocetine for acute ischaemic stroke

BACKGROUND

Vasoactive and neuroprotective drugs such as vinpocetine are used to treat stroke in some countries.

OBJECTIVES

To assess the effect of vinpocetine in acute ischaemic stroke.

SEARCH STRATEGY

We searched the Cochrane Stroke Group Trials Register (last searched February 2007), MEDLINE (1966 to February 2007) and Scopus (1960 to February 2007). We also searched the Internet Stroke Center Stroke Trials Registry, Google Scholar, the science-specific search engine Scirus and Wanfang Data, the leading information provider in China. We contacted researchers in the field and four pharmaceutical companies that manufacture vinpocetine. Searches were complete to February 2007.

SELECTION CRITERIA

Unconfounded randomised trials of vinpocetine compared with placebo, or any other reference treatment, in people with acute ischaemic stroke. We included trials if treatment started no later than 14 days after stroke onset.

DATA COLLECTION AND ANALYSIS

Two review authors independently applied the inclusion criteria. One review author extracted the data, which was then checked by the second review author. We assessed trial quality. The primary outcome measure was death or dependency.

MAIN RESULTS

We included two trials, involving a total of 70 participants. Data for 63 participants were reported in the two trials combined. The rate of death or dependency did not differ between the treatment and placebo groups at one and three months. The 95% confidence intervals for the outcome measures were wide and included the possibility of both significant benefit and significant harm. No adverse effects were reported.

AUTHORS' CONCLUSIONS

There is not enough evidence to evaluate the effect of vinpocetine on survival or dependency in patients with acute ischaemic stroke.

Evaluation of reference regions for (R)-[(11)C]PK11195 studies in Alzheimer's disease and mild cognitive impairment

Inflammation in Alzheimer's disease (AD) may be assessed using (R)-[(11)C]PK11195 and positron emission tomography. Data can be analyzed using the simplified reference tissue model, provided a suitable reference region is available. This study evaluates various reference regions for analyzing (R)-[(11)C]PK11195 scans in patients with mild cognitive impairment (MCI) and probable AD. Healthy subjects (n=10, 30+/-10 years and n=10, 70+/-6 years) and patients with MCI (n=10, 74+/-6 years) and probable AD (n=9, 71+/-6 years) were included. Subjects underwent a dynamic three-dimensional (R)-[(11)C]PK11195 scan including arterial sampling. Gray matter, white matter, total cerebellum and cerebrum, and cluster analysis were evaluated as reference regions. Both plasma input binding potentials of these reference regions (BP(PLASMA)) and corresponding reference region input binding potentials of a target region (BP(SRTM)) were evaluated. Simulations were performed to assess cluster analysis performance at 5% to 15% coefficient of variation noise levels. Reasonable correlations for BP(PLASMA) (R(2)=0.52 to 0.94) and BP(SRTM) (R(2)=0.59 to 0.76) were observed between results using anatomic regions and cluster analysis. For cerebellum white matter, cerebrum white matter, and total cerebrum a considerable number of unrealistic BP(SRTM) values were observed. Cluster analysis did not extract a valid reference region in 10% of the scans. Simulations showed that potentially cluster analysis suffers from negative bias in BP(PLASMA). Most anatomic regions outperformed cluster analysis in terms of absence of both scan rejection and bias. Total cerebellum is the optimal reference region in this patient category.

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.

CEREBRAL UPTAKE OF DRUGS IN HUMANS

1. Drugs that target the central nervous system (CNS) are under-represented in the pharmacopoeia because of the difficulties of overcoming passive and active defences of the blood-brain barrier (BBB). Methods have been developed in drug discovery to make decisions about whether a compound crosses the BBB. Less is known about how the rate and extent of CNS penetration of a drug affects its clinical behaviour, largely because of past difficulties in measuring the cerebral uptake of drugs in humans. Three methods for doing so are reviewed. 2. Microdialysis is sometimes used as a clinical tool for monitoring the brain in neurointensive care and opportunistic pharmacological studies are possible. The method is relatively cheap and simple, measures free drug concentrations and is better suited to characterizing slowly changing brain drug concentrations. 3. Measuring cerebral drug uptake using positron emission tomography imaging requires the use of short-lived isotopes (labelled drug or labelled receptor ligand). Data with high spatial and temporal resolution can be collected, but the method requires expensive infrastructure. 4. Jugular bulb catheters collect pure brain venous blood and are sometimes placed for neuromonitoring. Cerebral drug uptake is inferred from the arterial to cerebral venous concentration difference. The method is relatively cheap and simple and allows global brain concentrations to be estimated. It is better suited to characterizing rapidly changing brain concentrations and effects. 5. The cerebral kinetics of a cerebro-active drug can make substantial contributions to its clinical behaviour. For example, loperamide is a peripherally acting opioid that has little CNS effect due to the active efflux transport of loperamide from the brain back into the blood by transporters including P-glycoprotein. The opioids alfentanil and fentanyl differ in their duration of action largely because of differences in their cerebral distribution volume rather than differences in systemic kinetics. The onset of anaesthesia of the intravenous anaesthetic propofol is governed almost completely by the kinetics of the first-pass passage of the drug through the brain and is more affected by changes in cerebral blood flow than hepatic clearance. 6. Continuing to exploit and develop these methods may provide new avenues to enhance the safety and efficacy of cerebro-active drugs in clinical practice.

Distribution of PK11195 binding sites in porcine brain studied by autoradiography in vitro and by positron emission tomography

The cerebral distribution of peripheral-type benzodiazepine binding sites (PBBS) in human brain has been investigated by positron emission tomography (PET) with the specific radioligand [11C]PK11195 in diverse neuropathological conditions. However, little is known about the pattern of PK11195 binding sites in healthy brain. Therefore, we used quantitative autoradiography to measure the saturation binding parameters for [3H]PK11195 in cryostat sections from young Landrace pigs. Specific binding was lowest in the cerebellar white matter (85 fmol mg(-1)) and highest in the caudate nucleus (370 fmol mg(-1)), superior colliculus (400 fmol mg(-1)), and anterior thalamic nucleus (588 fmol mg(-1)). The apparent affinity was in the range of 2-6 nM in vitro, predicting high specific binding in PET studies of living brain. However, the distribution volume (V(d), ml g(-1)) of high specific activity [11C]PK11195 was nearly homogeneous (3 ml g(-1)) throughout brain of healthy Landrace pigs, and was nearly identical in studies with lower specific activity, suggesting that factors in vivo disfavor the detection of PBBS in Landrace pigs with this radioligand. In young, adult Göttingen minipig brain, the magnitude of V(d) for [11C]PK11195 was in the range 5-10 ml g(-1), and had a heterogeneous distribution resembling the in vitro findings in Landrace pigs. There was a trend toward globally increased V(d) in a group of minipigs with acute MPTP-induced parkinsonism, but no increase in V(d) was evident in the same pigs rescanned at 2 weeks after grafting of fetal mesencephalon to the partially denervated striatum. Thus, [11C]PK11195 binding was not highly sensitive to constituitively expressed PBBS in brain of young Landrace pigs, and did not clearly demonstrate the expected microglial activation in the MPTP/xenograft model of minipigs.

Using positron emission tomography to facilitate CNS drug development

Positron emission tomography (PET) is a non-invasive technology of nuclear medicine that has sensitivity for tracing low picomolar concentrations of radiolabeled molecules in the human body. Radiolabeling a new drug to high specific radioactivity facilitates a detailed mapping of its distribution to crucial organs in humans after the administration of a "microdose" (< 1 microg), for which limited toxicology documentation is required. For drugs directed at the CNS, this method is particularly useful for confirming exposure to the brain. A different approach is to develop suitable radioligands for quantitative PET studies of drug binding to target proteins and subsequently to correlate receptor occupancy with pharmacodynamic responses. To follow disease progression and to monitor the outcome of new treatments, PEt also facilitates longitudinal studies of biomarkers of pathophysiology such as amyloid plaque load in Alzheimer's disease. Finally, combining genomic knowledge with PET neuroreceptor imaging is expected to facilitate the search for genetic predictors of drug response.

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.

[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.