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Introduction: The incidence in the central nervous system diseases has increased with a growing elderly population. Unfortunately, conventional treatments used to treat the mentioned diseases are frequently ineffective due to the presence of the blood brain barrier., Aim: To illustrate the blood-brain barrier properties that limit drug transport into the brain and the main strategies employed to treat neurologic disorders., Development: The blood-brain barrier is mainly composed of a specialized microvascular endothelium and of glial cells. It constitutes a valuable tool to separate the central nervous system from the rest of the body. Nevertheless, it also represents an obstacle to the delivery of therapeutic drugs to the brain., Conclusions: To be effective, drugs must reach their target in the brain. On one hand, therapeutic agents could be designed to be able to cross the blood brain barrier. On the other hand, drug delivery systems could be employed to facilitate the therapeutic agents' entry into the central nervous system. In vivo models of neurological diseases, in addition to in vitro models of the blood brain barrier, have been widely employed for the evaluation of drugs utilized to treat central nervous system diseases.

Introduction: Concomitant use of anti-epileptic drugs (AEDs) and Chinese herbal medicines (CHMs) is increasing globally. However, information summarizing how CHMs might alter the CNS effects of AEDs is lacking., Areas Covered: A systematic review of the English-language articles in evidence-based databases was performed. It identified CHMs that interact with AEDs and lead to alterations in the CNS effects of AEDs. This review provides a descriptive summary of the existing information on CHM-induced changes of both the therapeutic and adverse CNS effects of AEDs, including i) anti-epileptic effect, ii) sedative effect, iii) anxiolytic effect and iv) memory impairment effect. The proposed mechanisms behind the interactions are also summarized., Expert Opinion: Despite the popularity of both AEDs and CHMs, the availability of information on CHM-AED interactions that could result in altered CNS outcomes is considerably limited. Moreover, there are some insufficiencies in the study designs of the identified reports. More research, including both mechanistic and human studies, with improved study design is necessary to ensure the safety and efficacy of combinational use of AEDs with CHMs.

Today the CNS drug development poses serious challenges for developers given the low probability of success and the disproportionately high investment costs. This review demonstrates how predictive models can provide quantitative criteria for increasing the efficiency of drug development in CNS. Predictive models can be applied to characterize, understand, and predict a drug's PK and PD behavior; to quantify uncertainty of information about that behavior; to identify factors that could affect the outcomes of a clinical trial through Clinical Trial Simulation (CTS), to identify prognostic factors that could affect the disease progression, to implement optimal and adaptive clinical trial and finally to control the level of placebo response by implementing study designs that minimizes the impact of placebo on study outcomes., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Reduced NMDA receptor functioning is hypothesized to underlie the cognitive and negative symptoms associated with schizophrenia. However, because direct activation of the NMDA receptor is accompanied by neurotoxicity, mechanisms that activate the glycine co-agonist site on the NMDA receptor could carry greater therapeutic potential. In the current study, the effects of two glycine transporter 1 (GlyT1) inhibitors, RG1678 and ORG25935, were characterized in the object-retrieval detour (ORD) task in scopolamine-impaired rhesus monkeys and, using positron emission tomography (PET), the GlyT1 occupancy to efficacy relationship of each compound was established. Scopolamine exerted a significant decrease in accuracy in the ORD task. Lower doses of RG1678 (0.3 and 1.0 mg/kg, p.o.) significantly attenuated the impact of scopolamine, whereas the highest dose tested (1.8 mg/kg) did not. The predicted GlyT1 occupancies of RG1678 at the effective doses were ~10 and 30 %. ORG25935 (0.1, 0.3, and 1 mg/kg, p.o.) also significantly attenuated the impact of scopolamine on the ORD task, whereas 3 mg/kg did not. The predicted GlyT1 occupancies of ORG25935 at the effective doses ranged from 16 to 80 %. These data suggest that GlyT1 inhibitors have the potential to improve performance on prefrontal cortex-dependent tests such as the ORD task, but that efficacy is lost when higher occupancies are achieved. Importantly, recent Ph2B data published by Roche suggests that low but not high doses of RG1678 improved negative symptoms in patients with schizophrenia, highlighting the potential translational nature of the current preclinical findings.

With an ageing population and increasing prevalence of central-nervous system (CNS) disorders new approaches are required to sustain the development and successful delivery of therapeutics into the brain and CNS. CNS drug delivery is challenging due to the impermeable nature of the brain microvascular endothelial cells that form the blood-brain barrier (BBB) and which prevent the entry of a wide range of therapeutics into the brain. This review examines the role intranasal delivery may play in achieving direct brain delivery, for small molecular weight drugs, macromolecular therapeutics and cell-based therapeutics, by exploitation of the olfactory and trigeminal nerve pathways. This approach is thought to deliver drugs into the brain and CNS through bypassing the BBB. Details of the mechanism of transfer of administrated therapeutics, the pathways that lead to brain deposition, with a specific focus on therapeutic pharmacokinetics, and examples of successful CNS delivery will be explored.

Receptor occupancy studies are becoming commonplace for verifying drug mechanism of action and selecting early development candidates. Positron emission tomography (PET) has been applied to pharmacodynamic (PD) studies in several therapeutic areas including neurology, cardiology, and oncology. Prospective use of PET to define dosing requirements has been proposed particularly for central nervous system (CNS)-targeted drugs; however, correlations with clinical outcomes have been mostly anecdotal and not causally established.

Background: Brain disorders, their prevalence and central nervous system (CNS) targeting are now at the rise. However, complexities of blood brain barrier (BBB) have limited the success of CNS targeting. Basic criteria necessary for passive diffusion were believed to influence the CNS drug delivery. However, often, BBB transportation has differed from the dogma of basic criteria., Purpose: This communication resets the extent to which basic criteria influence the brain delivery, through commanding examples. Further, it appraises the intervention of ABC transporters in BBB transportation, with a special emphasis on P-glycoprotein; and also brings forth the successful CNS transportation of therapeutics achieved through chimeric peptide technology. As a right path to travel, it flickers light on the novel CNS molecular drug targets/biomarkers which are specially expressed by diseased cells., Conclusion: Screening for right molecular target is of great importance for cost and time effective drug discovery process. The principle of chimeric peptide technology should be applied for CNS targeting; and every diseased cell should be screened for its biomarker. Thanks to glycan/lectin arrays technique which scans expression pattern of transporter and their possible ligands, and paves way for a new dimensional research.

The blood-brain barrier (BBB) is a physical and metabolic entity that isolates the brain from the systemic circulation. The barrier consists of tight junctions between endothelial cells that contain egress transporters and catabolic enzymes. To cross the BBB, a drug must possess the appropriate physicochemical properties to achieve a sufficient time-concentration profile in brain interstitial fluid (ISF). In this overview, we review techniques to measure BBB permeation, which is evidenced by the free concentration of compound in brain ISF over time. We consider a number of measurement techniques, including in vivo microdialysis and brain receptor occupancy following perfusion. Consideration is also given to the endothelial and nonendothelial cell systems used to assess both the BBB permeation of a test compound and its interactions with egress transporters, and computer models employed for predicting passive permeation and the probability of interactions with BBB transporters., (Copyright © 2013 John Wiley & Sons, Inc.)

Quantitative systems pharmacology (QSP) is a recent addition to the modeling and simulation toolbox for drug discovery and development and is based upon mathematical modeling of biophysical realistic biological processes in the disease area of interest. The combination of preclinical neurophysiology information with clinical data on pathology, imaging and clinical scales makes it a real translational tool. We will discuss the specific characteristics of QSP and where it differs from PK/PD modeling, such as the ability to provide support in target validation, clinical candidate selection and multi-target MedChem projects. In clinical development the approach can provide additional and unique evaluation of the effect of comedications, genotypes and disease states (patient populations) even before the initiation of actual trials. A powerful property is the ability to perform failure analysis. By giving examples from the CNS R&D field in schizophrenia and Alzheimer's disease, we will illustrate how this approach can make a difference for CNS R&D projects.

Positron emission tomography (PET) is increasingly used in drug discovery and development for evaluation of CNS drug disposition and for studies of disease biomarkers to monitor drug effects on brain pathology. The quantitative analysis of PET data is based on kinetic modeling of radioactivity concentrations in plasma and brain tissue compartments. A number of quantitative methods of analysis have been developed that allow the determination of parameters describing drug pharmacokinetics and interaction with target binding sites in the brain. The optimal method of quantification depends on the properties of the radiolabeled drug or radioligand and the binding site studied. We here review the most frequently used methods for quantification of PET data in relation to CNS drug discovery and development. The utility of PET kinetic modeling in the development of novel CNS drugs is illustrated by examples from studies of the brain kinetic properties of radiolabeled drug molecules.

The unbound drug concentration in brain parenchyma is considered to be the relevant driver for interaction with central nervous system (CNS) biological targets. Drug levels in cerebrospinal fluid (C_CSF) are frequently used surrogates for the unbound concentrations in brain. For drugs actively transported across the blood-brain barrier (BBB), C_CSF differs from unbound plasma concentration (Cu_p) to an extent that is commonly unknown. In this study, the relationship between CSF-to-unbound plasma drug partitioning in rats and the mouse Pgp (Mdr1a) efflux ratio (ER) obtained from in vitro transcellular studies has been investigated for a set of 61 CNS compounds exhibiting substantial diversity in chemical structure and physico-chemical properties. In order to understand the in vitro-in vivo extrapolation of Pgp efflux, a mechanistic model was derived relating in vivo CNS distribution kinetics to in vitro active transport. The model was applied to predict C_CSF from Cu_p and ER data for 19 proprietary Roche CNS drug candidates. The calculated CSF concentrations were correlated with CNS pharmacodynamic responses observed in rodent models. The correlation between in vitro and in vivo potency for different pharmacological endpoints indicated that the predicted C_CSF is a valuable surrogate of the concentration at the target site. Overall, C_CSF proved superior description of PK/PD data than unbound plasma or total brain concentration for Mdr1a substrates. Predicted C_CSF can be used as a default approach to understand the PK/PD relationships in CNS efficacy models and can support the extrapolation of efficacious brain exposure for new drug candidates from rodent to man., (Copyright © 2013 Elsevier Inc. All rights reserved.)

The ability to deliver drug molecules effectively across the blood-brain barrier into the brain is important in the development of central nervous system (CNS) therapies. Cerebral microdialysis is the only existing technique for sampling molecules from the brain extracellular fluid (ECF; also termed interstitial fluid), the compartment to which the astrocytes and neurones are directly exposed. Plasma levels of drugs are often poor predictors of CNS activity. While cerebrospinal fluid (CSF) levels of drugs are often used as evidence of delivery of drug to brain, the CSF is a different compartment to the ECF. The continuous nature of microdialysis sampling of the ECF is ideal for pharmacokinetic (PK) studies, and can give valuable PK information of variations with time in drug concentrations of brain ECF versus plasma. The microdialysis technique needs careful calibration for relative recovery (extraction efficiency) of the drug if absolute quantification is required. Besides the drug, other molecules can be analysed in the microdialysates for information on downstream targets and/or energy metabolism in the brain. Cerebral microdialysis is an invasive technique, so is only useable in patients requiring neurocritical care, neurosurgery or brain biopsy. Application of results to wider patient populations, and to those with different pathologies or degrees of pathology, obviously demands caution. Nevertheless, microdialysis data can provide valuable guidelines for designing CNS therapies, and play an important role in small phase II clinical trials. In this review, we focus on the role of cerebral microdialysis in recent clinical studies of antimicrobial agents, drugs for tumour therapy, neuroprotective agents and anticonvulsants.

Human cerebrospinal fluid (CSF) sampling is of high value as the only general applicable methodology to obtain information on free drug concentrations in individual human brain. As the ultimate interest is in the free drug concentration at the CNS target site, the question is what CSF concentrations may tell us in that respect. Studies have been performed in rats and other animals for which concentrations in brain extracellular fluid (brain ECF) as a target site for many drugs, have been compared to (cisterna magna) CSF concentrations, at presumed steady state conditions,. The data indicated that CSF drug concentrations provided a rather good indication of, but not a reliable measure for predicting brain ECF concentrations. Furthermore, comparing rat with human CSF concentrations, human CSF concentrations tend to be higher and display much more variability. However, this comparison of CSF concentrations cannot be a direct one, as humans probably had a disease for which CSF was collected in the first place, while the rats were healthy. In order to be able to more accurately predict human brain ECF concentrations, understanding of the complexity of the CNS in terms of intrabrain pharmacokinetic relationships and the influence of CNS disorders on brain pharmacokinetics needs to be increased. This can be achieved by expanding a currently existing preclinically derived physiologically based pharmacokinetic model for brain distribution. This model has been shown to successfully predict data obtained for human lumbar CSF concentrations of acetaminophen which renders trust in the model prediction of human brain ECF concentrations. This model should further evolute by inclusion of influences of drug properties, fluid flows, transporter functionalities and different disease conditions. Finally the model should include measures of target site engagement and CNS effects, to ultimately learn about concentrations that best predict particular target site concentrations, via human CSF concentrations.

Achieving sufficient brain penetration to elicit efficacy in humans is one of the most challenging tasks for scientists in CNS Drug Discovery. Substantial progress has been made in the past decade in understanding the factors influencing the rate and extent of brain distribution via a variety of in vivo, in vitro and in silico methodologies, and hence, predict their likelihood of success in man. This purpose of this review is to summarize the current approaches with a special focus on parameters related to free drug concentrations in brain which are the most pharmacologically relevant for the majority of CNS disease targets. Due to the dynamic and complex nature of this targeted organ, it is inevitable that these approaches have not been able to provide a fully comprehensive assessment of brain distribution and are expected to evolve further in the years to come.

Drug delivery across the brain-blood interfaces is a complex process involving physicochemical drug properties, transporters, enzymes, and barrier dysfunction in diseased conditions. Intact blood-brain barrier (BBB) limits the entry of potentially harmful compounds into the brain but may also reduce the CNS permeability of therapeutic agents. BBB permeability is typically assessed by measuring brain-to-plasma ratio in rodents (referred to as B/P ratio, BB, or Kp, often calculated as logBB), an approach that suffers significant limitations as discussed in the present review. Kp is not a permeability measurement but a partition coefficient mainly driven by the relative binding to plasma and brain tissue components including lipids, phospholipids, and proteins. Compounds with high Kp are often lipophilic with low free fraction available to mediate CNS activities. Efforts should be more concentrated on measuring pharmacologically relevant free drug concentrations at the target site. Using healthy rodents to predict brain penetration in patients might be biased due to species differences in BBB-related parameters such as transporter expression and functional activities. In addition, pathophysiological conditions such as aging, multiple sclerosis, and Alzheimer's and Parkinson's diseases have been described to affect BBB permeability, with barrier leakage and altered transporter activity. The impact of these species differences and disease states on drug delivery to the brain is largely overlooked. More data are needed to better understand their clinical implication in order to design more appropriate screening strategies and ultimately better mitigate the risk for failure in late stage development.

Presently, there are no effective treatments for several diseases involving the CNS, which is protected by the blood-brain, blood-CSF, and blood-arachnoid barriers. Traversing any of these barriers is difficult, especially for macromolecular drugs and particulates. However, there is significant experimental evidence that large molecules can be delivered to the CNS through the cerebrospinal fluid (CSF). The flux of the interstitial fluid in the CNS parenchyma, as well as the macro flux of CSF in the leptomeningeal space, are believed to be generally opposite to the desirable direction of CNS-targeted drug delivery. On the other hand, the available data suggest that the layer of pia mater lining the CNS surface is not continuous, and the continuity of the leptomeningeal space (LMS) with the perivascular spaces penetrating into the parenchyma provides an unexplored avenue for drug transport deep into the brain via CSF. The published data generally do not support the view that macromolecule transport from the LMS to CNS is hindered by the interstitial and CSF fluxes. The data strongly suggest that leptomeningeal transport depends on the location and volume of the administered bolus and consists of four processes: (i) pulsation-assisted convectional transport of the solutes with CSF, (ii) active "pumping" of CSF into the periarterial spaces, (iii) solute transport from the latter to and within the parenchyma, and (iv) neuronal uptake and axonal transport. The final outcome will depend on the drug molecule behavior in each of these processes, which have not been studied systematically. The data available to date suggest that many macromolecules and nanoparticles can be delivered to CNS in biologically significant amounts (>1% of the administered dose); mechanistic investigation of macromolecule and particle behavior in CSF may result in a significantly more efficient leptomeningeal drug delivery than previously thought.

Aims: Dried blood spots (DBS) alongside micro-analytical techniques are a potential solution to the challenges of performing pharmacokinetic (PK) studies in children. However, DBS methods have received little formal evaluation in clinical settings relevant to children. The aim of the present study was to determine a PK model for caffeine using a 'DBS/microvolume platform' in preterm infants., Methods: DBS samples were collected prospectively from premature babies receiving caffeine for treatment of apnoea of prematurity. A non-linear mixed effects approach was used to develop a population PK model from measured DBS caffeine concentrations. Caffeine PK parameter estimates based on DBS data were then compared with plasma estimates for agreement., Results: Three hundred and thirty-eight DBS cards for caffeine measurement were collected from 67 preterm infants (birth weight 0.6-2.11 kg). 88% of cards obtained were of acceptable quality and no child had more than 10 DBS samples or more than 0.5 ml of blood taken over the study period. There was good agreement between PK parameters estimated using caffeine concentrations from DBS samples (CL = 7.3 ml h⁻¹  kg⁻¹; V = 593 ml kg⁻¹; t(½) = 57 h) and historical caffeine PK parameter estimates based on plasma samples (CL = 4.9-7.9 ml h⁻¹  kg⁻¹; V = 640-970 ml kg⁻¹; t(½) = 101-144 h). We also found that changes in blood haematocrit may significantly confound estimates of caffeine PK parameters based on DBS data., Conclusions: This study demonstrates that DBS methods can be applied to PK studies in a vulnerable population group and are a practical alternative to wet matrix sampling techniques., (© 2012 The Authors. British Journal of Clinical Pharmacology © 2012 The British Pharmacological Society.)

In order to reach their pharmacologic targets, successful central nervous system (CNS) drug candidates have to cross a complex protective barrier separating brain from the blood. Being able to predict a priori which molecules can successfully penetrate this barrier could be of significant value in CNS drug discovery. Herein we report a new computational approach that combines two mechanism-based models, for passive permeation and for active efflux by P-glycoprotein, to provide insight into the multiparameter optimization problem of designing small molecules able to access the CNS. Our results indicate that this approach is capable of distinguishing compounds with high/low efflux ratios as well as CNS+/CNS- compounds and provides advantage over estimating P-glycoprotein efflux or passive permeability alone when trying to predict these emergent properties. We also demonstrate that this method could be useful for rank-ordering chemically similar compounds and that it can provide detailed mechanistic insight into the relationship between chemical structure and efflux ratios and/or CNS penetration, offering guidance as to how compounds could be modified to improve their access into the brain.

This Perspective provides important concepts about the blood-brain barrier (BBB) in drug discovery and how they should be applied effectively in designing successful CNS drugs. Key parameters for brain penetration are discussed, including unbound brain concentration, unbound brain-to-plasma ratio, BBB permeability, fraction unbound in brain and plasma, and transporters. Results from a retrospective analysis of 32 Pfizer CNS clinical drug candidates are described. Frequently encountered misconceptions about brain penetration in drug discovery programs are clarified. Strategies and guidance are provided to enhance or minimize brain exposure for CNS or peripheral targets, respectively. Recommendations for screening methodologies and a cascade in assessing brain penetration potential are presented.

Anise (Pimpinella anisum L.; Apiaceae) and its essential oil have been widely used in folk medicine, pharmacy and food industry. Since there are some data about the impact of anise on functions of central nervous system (CNS), the issue of possible interactions with drugs acting in CNS should be considered. This survey aimed to examine the influence of aniseed essential oil (EO) intake on the effects of drugs that act in CNS. The chemical profile of essential oil determined by GC-MS revealed as the main components: trans-anethole (88.49%), γ-himachalene (3.13%), cis-isoeugenol (1.99%), and linalool (1.79%). The effects of codeine, diazepam, midazolam, pentobarbital, imipramine and fluoxetine were tested in mice after 5days of peroral pretreatment with human equivalent dose of aniseed EO (0.3mg/kg). The intake of EO led to significant increase of analgesic effect of codeine. The motor impairment caused by midazolam was enhanced in the group treated by EO. The application of diazepam decreased the number and percentage of entries in open arm in elevated maze plus test in the group pretreated with EO indicating augmented effect of drug on motor activity. EO pretreatment caused significant shortage of pentobarbital induced sleeping time when compared to control. The decrease in antidepressant effect of imipramine and fluoxetine was diminished by the pretreatment with aniseed EO. Based on the results of this study we conclude that concomitant intake of aniseed EO preparations and drugs that act on CNS should be avoided due to potential herb-drug interactions, which also need further clinical confirmation., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Purpose: To develop a computational model for predicting CNS drug exposure using a novel in vivo dataset., Methods: The brain-to-plasma (B:P) ratio of 43 diverse compounds was assessed following intravenous administration to Swiss Outbred mice. B:P ratios were subjected to PLS modeling using calculated molecular descriptors. The obtained results were transferred to a qualitative setting in which compounds predicted to have a B:P ratio > 0.3 were sorted as high CNS exposure compounds and those below this value were sorted as low CNS exposure compounds. The model was challenged with an external test set consisting of 251 compounds for which semi-quantitative values of CNS exposure were available in the literature., Results: The dataset ranged more than 1700-fold in B:P ratio, with 16 and 27 compounds being sorted as low and high CNS exposure drugs, respectively. The model was a one principal component model based on five descriptors reflecting molecular shape, electronegativity, polarisability and charge transfer, and allowed 74% of the compounds in the training set and 76% of the test set to be predicted correctly., Conclusion: A qualitative computational model has been developed which accurately classifies compounds as being high or low CNS exposure drugs based on rapidly calculated molecular descriptors.

Introduction: Adverse drug reactions (ADRs) continue to be one of the major causes of failure in drug development while limiting the clinical utilities of many drugs. Contribution of the metabolites formed in vivo to ADRs could be more significant than we might have expected., Areas Covered: This review focuses on the relationship between regioselectivity in biotransformation and the ADRs of drugs acting on the central nervous system (CNS). "Regioselectivity" is defined as an exclusively or significantly preferential metabolic reaction at one (or several) site(s) on the substrate molecule. Several CNS drugs and toxicants, of which the metabolites play pivotal roles in ADRs, are summarized in details with the highlight on the roles of metabolism in both toxification and detoxification. The article also discusses in silico predictions of regioselectivity and the formation of toxic metabolites which are becoming increasingly important., Expert Opinion: Researchers working on CNS drugs face particular challenges in predicting drug metabolism and potential toxicities of their metabolites. A number of factors contribute to the difficulty of accurate prediction of metabolite disposition in the human brain. Better knowledge of regioselectivity in biotransformation and elucidation of the relationships between biotransformations and ADRs would definitely help designing new compounds with lower bioactivation potentials and rejuvenating the older drugs whose clinical applications are restricted by their ADRs. Administrating drugs by alternative routes such as the intranasal, transdermal, sublingual, and buccal routes could also be a strategy to reduce unwanted metabolite formations.

This study reports on the successful use of magnetic albumin nanosphere (MAN), consisting of maghemite nanoparticles hosted by albumin-based nanosphere, to target different sites within the central nervous system (CNS). Ultrastructural analysis by transmission electron microscopy (TEM) of the material collected from the mice was performed in the time window of 30 minutes up to 30 days after administration. Evidence found that the administered MAN was initially internalized and transported by erythrocytes across the blood-brain-barrier and transferred to glial cells and neuropils before internalization by neurons, mainly in the cerebellum. We hypothesize that the efficiency of MAN in crossing the BBB with no pathological alterations is due to the synergistic effect of its two main components, the iron-based nanosized particles and the hosting albumin-based nanospheres. We found that the MAN in targeting the CNS represents an important step towards the design of nanosized materials for clinical and diagnostic applications.

beta-Asarone has significant pharmacological effects on the central nervous system. As a potential therapeutic agent to manage brain diseases, analysis of the pharmacokinetics of beta-asarone in brain is necessary. We used cardio-perfusion method to exclude the beta-asarone in the brain blood. The brain was divided into five regions: hippocampus, cortex, brain stem, thalamus and cerebellum, and pharmacokinetic differences were investigated. We found that concentration-time profile of beta-asarone in blood, hippocampus, cortex, brain stem and cerebellum could be adequately described by a first-order equation, consistent with a linear two-compartmental model, but a first-order equation with a linear one-compartmental model in thalamus. The half lives of beta-asarone in blood, hippocampus, cortex, brain stem, thalamus and cerebellum were 1.3801, 1.300, 1.937, 7.142, 2.832 and 8.149 h, respectively. Gender differences do not significantly influence plasma pharmacokinetics of beta-asarone.

The main obstacle in the treatment of central nervous system diseases is represented by a limited passage of diagnostic and therapeutic agents across the blood-brain barrier, which separates the blood stream from the cerebral parenchyma and maintains the homeostasis of the brain. The growing knowledge about the brain capillary endothelium and the discovery of specific mechanisms for the uptake of substances enables the development of various strategies to enhance the drug delivery rate into the brain. Among the different strategies, nanoparticles are promising candidates for drug delivery to the brain due to their potential in encapsulating drugs and thereby disguising their permeation limiting characteristics. Furthermore a surface functionalization of many nanoparticles can easily be achieved allowing the active targeting of nanoparticles to the brain. For this non-invasive approach, the surface functionalization of nanoparticles with biomolecules has shown promising potential for effective drug delivery to the brain. This review indexes the main classes of biomolecules used for the surface functionalization of nanoparticles and discusses their potential as drug delivery systems for an enhanced passage of diagnostic and therapeutic agents into the brain parenchyma.

In modeling blood-brain barrier (BBB) passage, in silico models have yielded ~80% prediction accuracy, and are currently used in early drug discovery. Being derived from molecular structural information only, these models do not take into account the biological factors responsible for the in vivo outcome. Passive permeability and P-glycoprotein (Pgp, ABCB1) efflux have been successfully recognized to impact xenobiotic extrusion from the brain, as Pgp is known to play a role in limiting the BBB penetration of oral drugs in humans. However, these two properties alone fail to explain the BBB penetration for a significant number of marketed central nervous system (CNS) agents. The Biopharmaceutics Drug Disposition Classification System (BDDCS) has proved useful in predicting drug disposition in the human body, particularly in the liver and intestine. Here we discuss the value of using BDDCS to improve BBB predictions of oral drugs. BDDCS class membership was integrated with in vitro Pgp efflux and in silico permeability data to create a simple 3-step classification tree that accurately predicted CNS disposition for more than 90% of 153 drugs in our data set. About 98% of BDDCS class 1 drugs were found to markedly distribute throughout the brain; this includes a number of BDDCS class 1 drugs shown to be Pgp substrates. This new perspective provides a further interpretation of how Pgp influences the sedative effects of H1-histamine receptor antagonists., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Neurodegenerative disorders are expected to strike social and health care systems of developed countries heavily in the coming decades. Alzheimer's and Parkinson's diseases (AD/PD) are the most prevalent neurodegenerative pathologies, and currently their available therapy is only symptomatic. However, innovative potential drugs are actively under development, though their efficacy is sometimes limited by poor brain bioavailability and/or sustained peripheral degradation. To partly overcome these constraints, the development of drug delivery devices made by biocompatible and easily administrable materials might be a great adjuvant. In particular, materials science can provide a powerful tool to design hydrogels and nanoparticles as basic components of more complex nanocomposites that might ameliorate drug or cell delivery in AD/PD. This kind of approach is particularly promising for intranasal delivery, which might increase brain targeting of neuroprotective molecules or proteins. Here we review these issues, with a focus on nanoparticles as nanocomponents able to carry and tune drug release in the central nervous system, without ignoring warnings concerning their potential toxicity.

Radix Scutellariae is the dried root of the medicinal plant Scutellariae baicalensis Georgi. It exhibits a variety of therapeutic effects and has a long history of application in traditional formulations as well as in modern herbal medications. It has been confirmed that flavonoids are the most abundant constituents and induce these therapeutic effects. Six flavones are proven to be the major bioactive flavones in Radix Scutellariae existing in the forms of aglycones (baicalein, wogonin, oroxylin A) and glycosides (baicalin, wogonoside, oroxylin A-7-glucuronide). All six flavones are pharmacologically active and show great potential in the treatment of inflammation, cancers and virus-related diseases. The current review covers the preparation of the herb Radix Scutellariae, quantification of its major bioactive ingredients, and pharmacological effects of the proposed six bioactive flavones. In addition, this review summarizes the pharmacokinetic profiles of the bioactive flavones reported so far that could be used for further improvement of their pharmacokinetic study. Moreover, due to abundant co-occurring bioactive components in Radix Scutellariae, our review further documents the pharmacokinetic interactions among them., (Copyright © 2011 John Wiley & Sons, Ltd.)

In neurology, as in any other clinical specialty, there is a need to develop treatment strategies that allow stratification of therapies to optimize efficacy and minimize toxicity. Pharmacogenomics is one such method for therapy optimization: it aims to elucidate the relationship between human genome sequence variation and differential drug responses. Approaches have focused on candidate approaches investigating absorption-, distribution-, metabolism, and elimination (ADME)-related genes (pharmacokinetic pathways), and potential drug targets (pharmacodynamic pathways). To date, however, only few genetic variants have been incorporated into clinical algorithms. Unfortunately, a large number of studies have thrown up contradictory results due to a number of deficiencies, including small sample sizes, inadequate phenotyping, and genotyping strategies. Thus, there still exists an urgent need to establish biomarkers that could help to select for patients with an optimal benefit to risk relationship. Here we review recent advances, and limitations, in pharmacogenomics for agents used in neuroimmunology, neurodegenerative diseases, ischemic stroke, epilepsy, and primary headaches. Further work is still required in all of these areas, which really needs to progress on several fronts, including better standardized phenotyping, appropriate sample sizes through multicenter collaborations and judicious use of new technological advances such as genome-wide approaches, next generation sequencing and systems biology. In time, this is likely to lead to improvements in the benefit-harm balance of neurological therapies, cost efficiency, and identification of new drugs., (Copyright © 2011 American Neurological Association.)

The constant decline in drug discovery productivity despite the continuous growth in R&D investments has been on the table for many years and is driving changes in the current business model. We have focused our attention on what appears to be by far the major cause of attrition, the intrinsic quality of drug candidates; with the assumption that candidate quality can be designed and assessed at a rather early stage in drug discovery we have developed tools such as CNS chemical space mapping through PLS analysis, Drug Efficiency (DRUG(eff)) and the mechanistic PK/PD hypothesis. We also introduced best practices that were found extremely valuable which will be discussed in this article., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Drug penetration into the central nervous system (CNS) is controlled by the blood-brain barrier (BBB). Even though a number of strategies to circumvent the BBB and to improve drug access have been developed, drug resistance in CNS diseases remains an unmet clinical problem. We here review the mechanisms by which a healthy or pathological BBB influences drug distribution in the brain, with emphasis on the role of P450 metabolic enzymes and multi-drug transporter (MDT) proteins. In addition to the classic hepatic and gut biotransformation pathways, CNS expression of P450 enzymes may bear pharmacokinetic and pharmacodynamic significance exerting a metabolic activity and transforming parent drugs into specific products. We propose these mechanisms to play a major role in CNS drug resistant pathologies including refractory forms of epilepsy. Changes in the cerebrovascular hemodynamic conditions can affect expression of P450 enzymes and MDT proteins. This should be taken into account when developing in vitro experimental approaches to reproduce the physiological or pathological properties of the BBB. Finally, a link between P450 and MDT expression in the diseased brain and cell survival is discussed.

Distribution over the blood-brain barrier (BBB) is an important parameter to consider for compounds that will be synthesized in a drug discovery project. Drugs that aim at targets in the central nervous system (CNS) must pass the BBB. In contrast, drugs that act peripherally are often optimised to minimize the risk of CNS side effects by restricting their potential to reach the brain. Historically, most prediction methods have focused on the total compound distribution between the blood plasma and the brain. However, recently it has been proposed that the unbound brain-to-plasma concentration ratio (K(p,uu,brain)) is more relevant. In the current study, quantitative K(p,uu,brain) prediction models have been built on a set of 173 in-house compounds by using various machine learning algorithms. The best model was shown to be reasonably predictive for the test set of 73 compounds (R(2)=0.58). When used for qualitative prediction the model shows an accuracy of 0.85 (Kappa=0.68). An additional external test set containing 111 marketed CNS active drugs was also classified with the model and 89% of these drugs were correctly predicted as having high brain exposure., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Renal excretion is an important elimination pathway for substances associated with forensic toxicology, such as medicines, agricultural chemicals, and industrial chemicals. This study aimed to elucidate the renal elimination pathway of substances using culture cells stably expressing the human organic anion transporter 1 (hOAT1) gene. Substances tested were diazepam, triazolam, haloperidol, amitriptyline, mianserin, bromovalerylurea, phenobarbital, acetaminophen, acetylsalicylic acid, lidocaine, aconitine, atropine, caffeine, nicotine, malathion, dichlorvos, fenitrothion, chlorpyrifosmethyl, paraquat, diquat, potassium cyanide, sodium arsenite, sodium azide, o-cresol, and probenecid (control, a representative inhibitor of hOAT1). Results demonstrated that diazepam, triazolam, amitriptyline, mianserin, malathion, fenitrothion, chlorpyrifosmethyl, and probenecid significantly inhibited representative substrates of hOAT1 and para-aminohippuric acid uptake by hOAT1. IC(50) values of the aforementioned substances were 133.3, 185.2, 354.1, 312.6, 114.2, 26.6, 191.5, and 7.9μM, respectively. Ki values were 83.5, 86.0, 573.9, 99.0, 134.0, 51.2, 324.6, and 9.1μM, respectively. In conclusion, the current results suggest that fenitrothion and chlorpyrifosmethyl are transported with pharmacokinetics indicative of hOAT1 involvement in the human kidney., (2011 Elsevier Ireland Ltd. All rights reserved.)

Significant efforts through genomic approaches have been dedicated toward the identification of novel protein-protein interactions as promising therapeutic targets for indications such as Alzheimer's disease, Parkinson's disease and neuropsychiatric disorders. Additionally, the number of biotherapeutic agents entering the Pharmaceutical sector continues to increase and according to EvaluatePharma's "World Preview 2014" report, "the compounded annual growth rate of biologics is expected to be 8.5 percent from 2008-2014, eight to 10 times greater than the growth rate of small molecules". However, there are limited examples of success in developing biotherapeutic modalities for central nervous system (CNS) diseases in the drug development pipeline. A primary reason for the lack of application of biotherapeutics to neuroscience targets, is that the blood-brain barrier (BBB) isolates and protects CNS structures creating a unique biochemically and immunologically privileged environment, therefore passage of macromolecules across this barrier has additional challenges. An understanding of the anatomical and physiological properties of this barrier with respect to penetration of biotherapeutics is presented in this review document. In this summary, recent advances in biotherapeutic delivery mechanisms across the BBB including transcranial brain drug delivery, focused ultrasound technology, nasal delivery, absorptive endocytosis, and receptor mediated endocytosis are evaluated using an industrial perspective. With acknowledgement that each approach has advantages and disadvantages, this review discusses the opportunities and challenges that are encountered during application of these methods across a variety of therapeutic areas such as, pain, obesity, neuroscience, and oncology. Utilizing an industrial perspective, including consideration of cost of goods and commercial feasibility for these approaches, this review highlights technology features which would enable industry investments toward novel BBB delivery technologies for biologics. Through continued development and improvement of such technology, new therapeutic options to treat and potentially cure central nervous system diseases could eventually evolve.

The blood-brain barrier (BBB) is a regulatory interface between the circulation and the central nervous system (CNS). Therapy of neurological diseases is limited due to restricted penetration of pharmacons across the BBB. Models for screening the brain penetration of drug candidates are needed early in drug discovery. Culture-based models are useful tools for both basic research on BBB, and testing the permeability of new therapeutical molecules. This review focuses on patented in vitro BBB models and their potential application in CNS drug discovery. Cell culture models using primary and immortalized brain endothelial cells of non-human and human origin, in co-culture or mono-culture setting, in static or dynamic conditions are discussed, as well as methods to induce BBB properties in such in vitro models. The aim of these models is to reproduce as many aspects as possible of the in vivo BBB. All models should show some elements of general endothelial and specific BBB properties, like physiologically realistic cell architecture, restrictive paracellular pathway, and functional expression of transport mechanisms. Though no "ideal in vitro BBB model" has been constructed yet, the currently available models provide valuable information on BBB permeability and are useful tools in CNS drug discovery.

Phase I clinical trials have traditionally been focused on populations of normal healthy volunteers with the goal of determining the safety, tolerability, and pharmacokinetic profile of new investigational agents. As CNS drug development shifts its focus to the development of novel molecular entities, this approach will undergo an evolution. In this first part of a two-part series, the authors describe the traditional Phase I approach as well as challenges facing CNS drug development. The second half of the series will propose modifications to the traditional phase I design, including the incorporation of different populations, bio-marker surrogates, and adaptive designs.

In vitro blood-brain barrier (BBB) models help predict brain uptake of potential central nervous system drug candidates. Current in vitro models are composed of brain microvascular endothelial cells (BMEC) that are isolated from rat, bovine, or porcine. However, most in vivo studies on drug transport through the BBB are performed in small laboratory animals, specially mouse and thus murine in vitro BBB models serve as better surrogates to correlate with these studies. Here we describe the functional characterization of a reproducible in vitro model composed of murine BMEC co-cultured with rat primary astrocytes in the presence of biochemical inducing agents. The co-cultures presented high TEER and low sodium fluorescein permeability. Expression of specific BBB tight junction proteins (occludin, claudin-5, ZO-1) and the functionality of transporters (Pgp, GLUT1) were detected by immunocytochemistry and Western blotting. These results indicated a 2.5-fold increase in the expression levels of these proteins in the presence of astrocytes. In addition, a high correlation coefficient (0.98) was obtained between the permeability of a series of hydrophobic and hydrophilic drugs and their corresponding in vivo values. These results together establish the utility of this murine model for future drug transport, pathological, and pharmacological characterizations of the BBB., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Two simple multiple linear regression models were proposed to calculate the logarithm of the blood to brain concentration ratio (log BB) of drugs or drug-like compounds. The drugs were classified into two groups according to their ionization state in blood, and the significant parameters were selected using the train sets for each group. For un-ionizable compounds, the logarithm of distribution coefficient in octanol-water in pH 7.4 (log D(7.4)) and molecular weight are the significant parameters, whereas for ionizable compounds, log D(7.4) and number of hydrogen bond acceptor are significant parameters. The developed models were validated and their prediction capabilities checked using an external dataset of 25 compounds. In addition to the acceptable prediction errors, comparison of the external data analysis results with previously proposed models confirmed superior prediction capability of newly developed models.

According to the World Health Organization Central nervous system disorders are the major medical challenge of the 21st Century, yet treatments for many CNS disorders are either inadequate or absent. One reason is the existence of the blood-brain barrier, which strictly limits the access of substances to the brain. A key element of the barrier function is the expression of ABC export proteins in the luminal membrane of brain microvessel endothelial cells. Understanding the signaling cascades and the response to endogenous and exogenous stimuli, which lead to altered expression or function of the transporters as well as subsequent modulation of the transporters, may offer novel strategies to overcome the barrier and to improve drug delivery to the brain. This review gives a short overview about structure of the key elements of the blood-brain barrier with emphasis on ABC transporters. An insight into regulation of function and expression of these transport proteins is given and the involvement of these transporters in CNS diseases is discussed.

The pharmacokinetics, tissue distribution, metabolism, and excretion of ginsenosides Rg(1) were studied in Wistar rats, by measuring the concentrations of Rg(1) and its metabolites in the blood, tissues, bile, urine, and feces after dosing. After intravenous (i.v.) administration, the elimination half-lives of Rg(1) and its metabolites were 1.82, 5.87, and 6.87 h, and the area under the curves were 1595.7, 597.5, and 805.6 ng·h/mL, respectively. After oral administration, the elimination half-lives of Rg(1) and its metabolites were 2.25, 6.73, 5.44, and 5.06 h, and the area under the curves were 2363.5, 4185.5, 3774.3, and 396.2 ng·h/mL, respectively. After i.v. administration, Rg(1) and its metabolites were well distributed to the tissues analyzed except for the brain. The maximum concentration of Rg(1) was reached in all tissues at 5 min post dose, and it was eliminated from most of the tissues except for the kidney faster than it was eliminated from the blood. The maximum concentration of the metabolites was reached in all tissues between 4 and 6 h post dose. After i.v. administration, the recovery of the Rg(1) prototype in the urine and bile was 27.96% and 60.77%, respectively. The metabolism of Rg(1) in the intestine was via a hydrolization pathway, with the 6- and 20-glucoside bond hydrolyzed gradually under the catalysis of β-glucosaccharase, and then the metabolites were reabsorbed into the blood. Finally, the total recovery of the Rg(1) prototype and its metabolites in the urine and feces were 51.31% and 47.46%, respectively.

It remains a challenge to deliver effective concentrations of therapeutics into CNS pathologies, which is primarily due to the fact that current and investigational CNS therapeutics are suboptimally-sized to accumulate to effective concentrations in individual diseased CNS tissue cells. The blood-CNS barrier of blood capillary microvasculature within neuropathologic tissues is known to be permeable to lipid-insoluble macromolecules in a wide-spectrum of neuropathologies. In the case of CNS solid tumor tissue blood capillaries, the physiological upper limit of pore size to the transcapillary passage of spherical lipid-insoluble macromolecules is approximately 12 nanometers, and systemically administered imageable dendrimer nanoparticles within the 7 to 10 nanometer size range accumulate to therapeutic concentrations in solid tumors since this size range of particles maintain peak blood concentrations for several hours. In preliminary pre-clinical studies, it has recently been shown that one intravenous dose of small molecule chemotherapy-conjugated imageable dendrimer nanoparticles within the 7 to 10 nanometer size range, with doxorubicin bound to the particle exterior via acid-labile covalent linkages, is effective at regressing orthotopic rodent malignant gliomas. Although it is foreseeable that such drug-conjugated imageable nanoparticles within the 7 to 10 nanometer size range will be effective theranostic agents for the concurrent treatment (i.e. neutron capture therapy) and imaging (i.e. magnetic resonance) of solid tumor disease, the issue of maintaining a neutralized particle exterior following the attachment of cationic drugs will need to be addressed to eliminate cationic charge-mediated nanoparticle toxicity to blood capillary walls. In this review, the ultrastructural basis for blood capillary microvascular permeability to lipid-insoluble macromolecules is discussed, and the importance of delineating the precise physiologic upper limits of pore size in the blood capillary microvasculature of other CNS pathologies, including neurodegenerative, inflammatory and ischemic CNS diseases, is emphasized. The discussion herein will serve as guide for the future development of optimally-sized, non-toxic and non-immunogenic lipid-insoluble systemic therapies, which should be the focus of future patent applications and patents on CNS drug development.

Functional neuroimaging has the potential to improve the decision-making process in the development of new drugs. With the high cost of failure of compounds in later stages of development, there is a need to establish, early in man, reliable measures of drug activity and efficacy in the brain. Functional magnetic resonance imaging (FMRI) is a tool for serially examining normal and pathological brain function at the systems level. FMRI is helping us to understand therapeutic mechanisms and can provide clinically relevant markers of disease responses to drugs. An analysis of the value of FMRI to aid decision-making requires an appreciation of the techniques and their validation, a task that has begun and which necessitates an investment of its own., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

The dissolution mechanism of soluble salts of poorly soluble bases can be complex because both the dissolution of the salt and precipitation of the free base can occur depending on the experimental conditions and properties of the molecule. The dissolution of three soluble salts of poorly soluble bases is described in this paper. Two of these compounds precipitate as free base under normal stomach pH conditions (pH from 2-4) during dissolution. This free base precipitation is a result of formation of free base on the surface of the dissolving salt. Diffusion Layer modulated (DLM) solids are defined and presented that can effectively counteract this precipitation mechanism. These DLM materials employ excipients in order to modify the pH or solubility conditions at the surface of the dissolving salt to minimize precipitation of the free base that can occur. Rotating disk dissolution data is presented which shows how these formulated solids can act to improve the dissolution profile for these materials.