Drug delivery across the blood–brain barrier: why is it difficult? how to measure and improve it?

Brain delivery enabled by transient blood-brain barrier disruption induced by regadenoson: a PET imaging study

BACKGROUND

Regadenoson, an agonist of adenosine A2 receptors, enables transient blood-brain barrier (BBB) disruption. The relevance of regadenoson as a pharmacological strategy for brain delivery was investigated using in vivo PET imaging in rats.

RESEARCH DESIGN AND METHODS

Kinetic modeling of brain PET data was performed to estimate the impact of regadenoson (0.05 mg.kg-1, i.v.) on BBB permeation compared with control rats (n = 4-6 per group). Three radiolabeled compounds of different sizes, which do not cross the intact BBB, were tested.

RESULTS

Regadenoson significantly increased the BBB penetration (+116 ± 13%, p < 0.001) of [18F]2-deoxy-2-fluoro-D-sorbitol ([18F]FDS, MW = 183 Da), a small-molecule marker of BBB permeability. The magnitude of the effect was different across brain regions, with a maximum increase in the striatum. Recovery of BBB integrity was observed 30 min after regadenoson injection. Regadenoson also increased the brain penetration (+72 ± 45%, p < 0.05) of a radiolabeled nanoparticle [89Zr]AGuIX (MW = 9 kDa). However, the brain kinetics of a monoclonal antibody ([89Zr]mAb, MW = 150 kDa) remained unchanged (p > 0.05).

CONCLUSIONS

PET imaging showed the features and limitations of BBB disruption induced by regadenoson in terms of extent, regional distribution, and reversibility. Nevertheless, regadenoson enables the brain delivery of small molecules or nanoparticles in rats.

A novel study of brain microvascular endothelial cells induced by astrocyte conditioned medium for constructing blood brain barrier model in vitro: A promising tool for meningitis of teleost

The blood-brain barrier (BBB) is mainly composed of specialized endothelial cells, which can resist harmful substances, transport nutrients, and maintain the stability of the brain environment. In this study, an endothelial cell line from tilapia (Oreochromis niloticus) named TVEC-01 was successfully established. During the earlier establishment phase of the cell line, the TVEC-01 cells were persistently exposed to an astrocyte-conditioned medium (ACM). TVEC-01 cells were identified as an endothelial cell line. TVEC-01 cells retained the multiple functions of endothelial cells and were capable of performing various experiments in vitro. Furthermore, TVEC-01 cells efficiently expressed BBB-related tight junctions and key efflux transporters. From the results of the qRT-PCR, we found that the TVEC-01 cell line did not gradually lose BBB characteristics after persistent and repetitive passages, which was different from the vast majority of immortalized endothelial cells. The results showed that ACM induced up-regulation of the expression levels of multiple BBB-related genes in TVEC-01 cells. We confirmed that Streptococcus agalactiae was capable of invading the TVEC-01 cells and initiating a series of immune responses, which provided a theoretical basis for S. agalactiae to break through the BBB of teleost through the transcellular traversal pathway. In summary, we have successfully constructed an endothelial cell line of teleost, named TVEC-01, which can be used in many experiments in vitro and even for constructing BBB in vitro. Moreover, it was confirmed that S. agalactiae broke through the BBB of teleost through the transcellular traversal pathway and caused meningitis.

Food-Derived Peptides: Beneficial CNS Effects and Cross-BBB Transmission Strategies

Food-derived peptides, as dietary supplements, have significant effects on promoting brain health and relieving central nervous system (CNS) diseases. However, the blood-brain barrier (BBB) greatly limits their in-brain bioavailability. Thus, overcoming the BBB to target the CNS is a major challenge for bioactive peptides in the prevention and treatment of CNS diseases. This review discusses improvement in the neuroprotective function of food-derived active peptides in CNS diseases, as well as the source of BBB penetrating peptides (BBB-shuttles) and the mechanism of transmembrane transport. Notably, this review also discusses various peptide modification methods to overcome the low permeability and stability of the BBB. Lipification, glycosylation, introduction of disulfide bonds, and cyclization are effective strategies for improving the penetration efficiency of peptides through the BBB. This review provides a new prospective for improving their neuroprotective function and developing treatments to delay or even prevent CNS diseases.

The Role of Substance P Within Traumatic Brain Injury and Implications for Therapy

This review examines the role of the neuropeptide substance P within the neuroinflammation that follows traumatic brain injury. It examines it in reference to its preferential receptor, the neurokinin-1 receptor, and explores the evidence for antagonism of this receptor in traumatic brain injury with therapeutic intent. Expression of substance P increases following traumatic brain injury. Subsequent binding to the neurokinin-1 receptor results in neurogenic inflammation, a cause of deleterious secondary effects that include an increased intracranial pressure and poor clinical outcome. In several animal models of TBI, neurokinin-1 receptor antagonism has been shown to reduce brain edema and the resultant rise in intracranial pressure. A brief overview of the history of substance P is presented, alongside an exploration into the chemistry of the neuropeptide with a relevance to its functions within the central nervous system. This review summarizes the scientific and clinical rationale for substance P antagonism as a promising therapy for human TBI.

The Bradykinin B2 Receptor Agonist (NG291) Causes Rapid Onset of Transient Blood-Brain Barrier Disruption Without Evidence of Early Brain Injury

Background: The blood–brain barrier (BBB) describes the brain’s highly specialized capillaries, which form a dynamic interface that maintains central nervous system (CNS) homeostasis. The BBB supports the CNS, in part, by preventing the entry of potentially harmful circulating molecules into the brain. However, this specialized function is challenging for the development of CNS therapeutics. Several strategies to facilitate drug delivery into the brain parenchyma via disruption of the BBB have been proposed. Bradykinin has proven effective in disrupting mechanisms across the blood–tumor barrier. Unfortunately, bradykinin has limited therapeutic value because of its short half-life and the undesirable biological activity elicited by its active metabolites.

Objective: To evaluate NG291, a stable bradykinin analog, with selective agonist activity on the bradykinin-B2 receptor and its ability to disrupt the BBB transiently.

Methods: Sprague Dawley rats and CD-1 mice were subjected to NG291 treatment (either 50 or 100 μg/kg, intravenously). Time and dose-dependent BBB disruption were evaluated by histological analysis of Evans blue (EB) extravasation. Transcellular and paracellular BBB leakage were assessed by infiltration of ^99mTc-albumin (66.5 KDa) and ¹⁴C-sucrose (340 Da) radiolabeled probes into the brains of CD-1 mice treated with NG291. NG291 influence on P-glycoprotein (P-gp) efflux pump activity was evaluated by quantifying the brain accumulation of ³H-verapamil, a known P-gp substrate, in CD-1 mice.

Results: NG291-mediated BBB disruption was localized, dose-dependent, and reversible as measured by EB extravasation. ^99mTc-albumin leakage was significantly increased by 50 μg/kg of NG291, whereas 100 μg/kg of NG291 significantly augmented both ¹⁴C-sucrose and ^99mTc-albumin leakage. NG291 enhanced P-gp efflux transporter activity and was unable to increase brain uptake of the P-gp substrate pralidoxime. NG291 did not evoke significant short-term neurotoxicity, as it did not increase brain water content, the number of Fluoro-Jade C positive cells, or astrocyte activation.

Conclusion: Our findings strongly suggest that NG291 increases BBB permeability by two different mechanisms in a dose-dependent manner and increases P-gp efflux transport. This increased permeability may facilitate the penetration into the brain of therapeutic candidates that are not P-gp substrates.

Multi-disciplinary Approach for Drug and Gene Delivery Systems to the Brain

Drug delivery into the brain has for long been a huge challenge as the blood–brain barrier (BBB) offers great resistance to entry of foreign substances (with drugs inclusive) into the brain. This barrier in healthy individuals is protective to the brain, disallowing noxious substances present in the blood to get to the brain while allowing for the exchange of small molecules into the brain by diffusion. However, BBB is disrupted under certain disease conditions, such as cerebrovascular diseases including acute ischemic stroke and intracerebral hemorrhage, and neurodegenerative disorders including multiple sclerosis (MS), Alzheimer’s disease (AD), Parkinson’s disease (PD), and cancers. This review aims to provide a broad overview of present-day strategies for brain drug delivery, emphasizing novel delivery systems. Hopefully, this review would inspire scientists and researchers in the field of drug delivery across BBB to uncover new techniques and strategies to optimize drug delivery to the brain. Considering the anatomy, physiology, and pathophysiological functioning of the BBB in health and disease conditions, this review is focused on the controversies drawn from conclusions of recently published studies on issues such as the penetrability of nanoparticles into the brain, and whether active targeted drug delivery into the brain could be achieved with the use of nanoparticles. We also extended the review to cover novel non-nanoparticle strategies such as using viral and peptide vectors and other non-invasive techniques to enhance brain uptake of drugs.

The search for brain-permeant NKCC1 inhibitors for the treatment of seizures: Pharmacokinetic-pharmacodynamic modelling of NKCC1 inhibition by azosemide, torasemide, and bumetanide in mouse brain

Because of its potent inhibitory effect on the Na⁺-K⁺-2Cl^- symporter isotype 1 (NKCC1) in brain neurons, bumetanide has been tested with varying results for treatment of seizures that potentially evolve as a consequence of abnormal NKCC1 activity. However, because of its physicochemical properties, bumetanide only poorly penetrates into the brain. We previously demonstrated that NKCC1 can be also inhibited by azosemide and torasemide, which lack the carboxyl group of bumetanide and thus should be better brain-permeable. Here we studied the brain distribution kinetics of azosemide and torasemide in comparison with bumetanide in mice and used pharmacokinetic-pharmacodynamic modelling to determine whether the drugs reach NKCC1-inhibitory brain concentrations. All three drugs hardly distributed into the brain, which seemed to be the result of probenecid-sensitive efflux transport at the blood-brain barrier. When fractions unbound in plasma and brain were determined by equilibrium dialysis, only about 6-17% of the brain drug concentration were freely available. With the systemic doses (10 mg/kg i.v.) used, free brain concentrations of bumetanide and torasemide were in the NKCC1-inhibitory concentration range, while levels of azosemide were slightly below this range. However, all three drugs exhibited free plasma levels that would be sufficient to block NKCC1 at the apical membrane of brain capillary endothelial cells. These data suggest that azosemide and torasemide are interesting alternatives to bumetanide for treatment of seizures involving abnormal NKCC1 functionality, particularly because of their longer duration of action and their lower diuretic potency, which is an advantage in patients with seizures.

A novel pharmacotherapy approach using P-glycoprotein (PGP/ABCB1) efflux inhibitor combined with ivermectin to reduce alcohol drinking and preference in mice

Alcohol use disorder (AUD) has a major national impact, affecting over 18 million people, causing approximately 88,000 deaths, and costing upward of $250 billion annually in the United States. Unfortunately, FDA-approved AUD pharmaceuticals are few, and clinical benefits are mostly ineffective in patients suffering from AUD. Therefore, the identification of novel targets and/or innovative methods for the development of safe and effective medications represents a critical public health need. Previously, we reported that avermectin compounds (ivermectin [IVM] and moxidectin [MOX]) significantly reduced ethanol intake in male and female mice. However, avermectin compounds are readily effluxed by P-glycoprotein (Pgp/ABCB1) in the blood-brain barrier (BBB), resulting in reduced retention time by the drugs in the central nervous system (CNS). As such, the doses of IVM or MOX and the time frame for significant reductions of ethanol intake are not ideal. Here we evaluate a novel combinatorial strategy involving IVM and tariquidar (TQ), a third-generation efflux inhibitor of Pgp, to reduce the dosing necessary for improving alcohol (ethanol) consumption behavior. We tested male C57BL/6J mice using a two-bottle choice study to evaluate ethanol consumption and preference. We found that injecting 10 mg/kg of TQ 30 min prior to IVM resulted in a five-fold improvement in the efficacy of IVM (dosed at 0.5 mg/kg), resulting in a significant reduction in ethanol intake and preference. Notably, the reduction by IVM was well tolerated, and no adverse effects were identified when tested at doses ranging from 0.50 mg/kg to 2.0 mg/kg. Collectively, our findings indicate that IVM, in combination with TQ, increases its efficacy in the CNS for reducing ethanol consumption. This work demonstrates a novel combinatorial drug strategy that allows new opportunities for drugs with poor CNS retention, such as IVM, to demonstrate improved potency and potentially improved safety.

PLGA nanoparticles for nose to brain delivery of Clonazepam: formulation, optimization by 32 Factorial design, in vitro and in vivo evaluation

BACKGROUND

Intranasal administration of biodegradable nanoparticles has been extensively studied for targeting the drug directly to CNS through olfactory or trigeminal route bypassing blood brain barrier.

OBJECTIVE

The objective of the present study was to optimize Clonazepam loaded PLGA nanoparticles (CLO-PNPs) by investigating the effect of process variables on the responses using 32 full factorial design.

METHODS

Effect of two independent factors-amount of PLGA and concentration of Poloxamer 188, were studied at low, medium and high levels on three dependent responses-%Entrapment efficiency, Particle size (nm) and %cumulative drug release at 24hr.

RESULTS

%EE, Particle size and %CDR at 24hr of optimized batch was 63.7%, 165.1 nm and 86.96% respectively. Nanoparticles were radiolabeled with 99mTc and biodistribution was investigated in BALB/c mice after intranasal & intravenous administrations. Significantly higher brain/blood uptake ratios and AUC values in brain following intranasal administration of CLO-PNPs indicated more effective brain targeting of CLO. Higher brain uptake of intranasal CLO-PNPs was confirmed by rabbit brain scintigraphy imaging. Histopathological study performed on goat nasal mucosa revealed no adverse response of nanoparticles. TEM image exhibited spherical shaped particles in nano range. DSC and XRD studies suggested Clonazepam encapsulation within PLGA matrix. The onset of occurrence of PTZ-induced seizures in rats was significantly delayed by intranasal nanoparticles as compared to intranasal & intravenous CLO-SOL.

CONCLUSION

This investigation exhibits rapid rate and higher extent of CLO transport in brain with intranasal CLO-PNPs suggesting a better option as compared to oral & parenteral route in management of acute status epilepticus.

The effect of baicalein-loaded Y-shaped miktoarm copolymer on spatial memory and hippocampal expression of DHCR24, SELADIN and SIRT6 genes in rat model of Alzheimer

In the present study, we successfully synthesized nanocarriers (NCs) based on Y-shaped miktoarm copolymers, Poly Ethylene Glycol-Lysine-(Poly Caprolactone)₂ (PEG-Lys-PCL₂), which were loaded by baicalein (B) through the nanoprecipitation process to assess their in-vitro and in-vivo properties. We applied various methods and measurements including proton nuclear magnetic resonance (HNMR), dynamic light scattering (DLS), differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), MTT assay, hemolysis test, lethal dose, real-time PCR, and Morris water maze. The results of DLS indicated that the size and zeta potential of the obtained NCs and B-loaded NCs were acceptable. Also, in-vivo and in-vitro biocompatibility examinations proved that miktoarm-based NCs were safe, and all rats treated with miktoarm-based NCs did not exhibit any remarkable weight loss during the experiment. The results of the Morris water maze (in-vivo test) revealed that the normal saline-treated group, as well as B-miktoarm + Scopolamine (M + B + S) and B-miktoarm-Tween80 + Scopolamine (M + B + T + S) pretreatment groups, spent more time in the target quadrant. Thus, this experiment showed that pretreatment of rats with M + B + S and M + B + T + S had the most effects on spatial memory. According to quantitative PCR analysis, we hypothesized that, in comparison with other experimental groups, pretreatment of rats with M + B + T + S could be more effective in preventing cholinergic dysfunction, brain oxidative stress and cognitive deficits which cause by Scopolamine HBr. This outcome may be partially due to the upregulation of DHCR24, SELADIN, and SIRT6 in entire of the hippocampal region of normal saline-treated and M + B + T + S pretreatment groups. These results may be because mimicking the cell membrane structure would be an excellent feature for miktoarm, and partial coating of Tween-80 can play a critical role for PEG-Lys-PCL₂-based NCs in crossing the brain cell membrane, and they can easily be uptaken by the cells. Eventually, all of the obtained data confirmed that PEG-Lys-PCL₂ miktoarm star copolymers are suitable for delivering therapeutic agents to the brain for the treatment of Alzheimer's disease (AD). Also, it seems that baicalein should be taken into account as a potent compound for the treatment of AD.

Peptide Mediated Brain Delivery of Nano- and Submicroparticles: A Synergistic Approach

The brain is a complex, regulated organ with a highly controlled access mechanism: The Blood-Brain Barrier (BBB). The selectivity of this barrier is a double-edged sword, being both its greatest strength and weakness. This weakness is evident when trying to target therapeutics against diseases within the brain. Diseases such as metastatic brain cancer have extremely poor prognosis due to the poor permeability of many therapeutics across the BBB. Peptides can be designed to target BBB receptors and gain access to the brain by transcytosis. These peptides (known as BBB-shuttles) can carry compounds, usually excluded from the brain, across the BBB. BBB-shuttles are limited by poor loading of therapeutics and degradation of the peptide and cargo. Likewise, nano- submicro- and microparticles can be fine-tuned to limit their degradation and with high loading of therapeutics. However, most nano- and microparticles' core materials completely lack efficient targeting, with a few selected materials able to cross the BBB passively. Combining the selectivity of peptides with the high loading potential of nano-, microparticles offers an exciting strategy to develop novel, targeted therapeutics towards many brain disorders and diseases. Nevertheless, at present the field is diverse, in both scope and nomenclature, often with competing or contradictory names. In this review, we will try to address some of these issues and evaluate the current state of peptide mediated nano,-microparticle transport to the brain, analyzing delivery vehicle type and peptide design, the two key components that must act synergistically for optimal therapeutic impact.

Recent prospective of surface engineered Nanoparticles in the management of Neurodegenerative disorders

Clinically, the therapeutic outcomes in neurodegenerative disorders (NDs) by drug treatment are very limited, and the most insurmountable obstacle in the treatment of NDs is the blood-brain barrier (BBB), which provides the highest level of protection from xenobiotics. A great deal of attention still needs to be paid to overcome these barriers, and surface-engineered polymeric nanoparticles are emerging as innovative tools that are able to interact with the biological system at a molecular level for the desired response. The present review covers the potential importance of surface-structure-engineered nanoparticles to overcome the BBB for good bioavailability, and the evaluation of drug therapy in NDs.

Protein-functionalized PLGA nanoparticles of lamotrigine for neuropathic pain management

Lamotrigine (LTG), a sodium and calcium channel blocker, has demonstrated efficacy for the treatment of neuropathic pain in multiple, randomized, controlled trials. However, its potential clinical applications in neuropathic pain are limited due to the risk of dose-dependent severe rashes associated with high dose and prompt dose escalation. Further, the poor pharmacokinetic profile due to non-selective distribution to organs other than brain reduces the efficacy of dosage regimen. Therefore, the aim of present investigation is to develop surface-engineered LTG nanoparticles (NPs) using transferrin and lactoferrin as ligand to deliver higher amount of drug to brain and improve the biodistribution and pharmacokinetic profile of drug with prolonged duration of action and reduced accumulation in non-target organs. The LTG NPs were prepared by nanoprecipitation and optimized by factorial design for high entrapment and optimized particle size. The optimized NPs were surface functionalized by conjugating with the lactoferrin (Lf) and transferrin (Tf) as ligands. The developed NPs were characterized for different physicochemical parameters and stability. The in vivo biodistribution showed preferential targeting to brain and reduced accumulation in non-target organs over a prolonged duration of time. Finally, partial sciatic nerve injury model was used to demonstrate the increased pharmacodynamic response as antinociceptive effect. Both biodistribution and pharmacodynamic study in mice confirmed that the approach used for LTG can help to increase clinical applications of LTG due to brain targeting and reduced side effects.

Psychotropic drugs and bruxism

INTRODUCTION

Sleep and awake bruxism is defined as 'a parafunctional activity including clenching, bracing, gnashing, and grinding of the teeth'. Some evidence suggests that bruxism may be caused by, or associated with, alterations in the CNS neurotransmission. Several classes of psychotropic drugs interfering with CNS activity may potentially contribute to bruxism. Thus, the purpose of this study was to examine relevant peer-reviewed papers to identify and describe the various classes of psychotropic substances that may cause, exacerbate or reduce bruxism as the result of their pharmacological action in CNS neurons.

AREAS COVERED

A literature search from 1980 to the present was performed using PubMed database. The term 'bruxism' was used in association with 'psychotropic', 'dopamine (DA)', 'serotonin', 'histamine', 'antipsychotics', 'antidepressants', 'antihistaminergics' and 'stimulants'.

EXPERT OPINION

Studies on the effects of DA agonists (Levo-DOPA, psychostimulants) and antagonists (antipsychotics) identified a central role of DA in the pathogenesis of pharmacologically induced bruxism. Important information from studies on drugs acting on serotonin neurotransmission (antidepressants) was recognized. Other mechanisms involving different neurotransmitters are emerging. This is the case of antihistaminergic drugs which may induce bruxism as a consequence of their disinhibitory effect on the serotonergic system.

Tissue penetration of antifungal agents

Understanding the tissue penetration of systemically administered antifungal agents is critical for a proper appreciation of their antifungal efficacy in animals and humans. Both the time course of an antifungal drug and its absolute concentrations within tissues may differ significantly from those observed in the bloodstream. In addition, tissue concentrations must also be interpreted within the context of the pathogenesis of the various invasive fungal infections, which differ significantly. There are major technical obstacles to the estimation of concentrations of antifungal agents in various tissue subcompartments, yet these agents, even those within the same class, may exhibit markedly different tissue distributions. This review explores these issues and provides a summary of tissue concentrations of 11 currently licensed systemic antifungal agents. It also explores the therapeutic implications of their distribution at various sites of infection.

Oatp58Dc contributes to blood-brain barrier function by excluding organic anions from the Drosophila brain

The blood-brain barrier (BBB) physiologically isolates the brain from the blood and, thus, plays a vital role in brain homeostasis. Ion transporters play a critical role in this process by effectively regulating access of chemicals to the brain. Organic anion-transporting polypeptides (Oatps) transport a wide range of amphipathic substrates and are involved in efflux of chemicals across the vertebrate BBB. The anatomic complexity of the vascularized vertebrate BBB, however, creates challenges for experimental analysis of these processes. The less complex structure of the Drosophila BBB facilitates measurement of solute transport. Here we investigate a physiological function for Oatp58Dc in transporting small organic anions across the BBB. We used genetic manipulation, immunocytochemistry, and molecular techniques to supplement a whole animal approach to study the BBB. For this whole animal approach, the traceable small organic anion fluorescein was injected into the hemolymph. This research shows that Oatp58Dc is involved in maintaining a chemical barrier against fluorescein permeation into the brain. Oatp58Dc expression was found in the perineurial and subperineurial glia, as well as in postmitotic neurons. We specifically targeted knockdown of Oatp58Dc expression in the perineurial and subperineurial glia to reveal that Oatp58Dc expression in the perineurial glia is necessary to maintain the barrier against fluorescein influx into the brain. Our results show that Oatp58Dc contributes to maintenance of a functional barrier against fluorescein influx past the BBB into the brain.

Blood-brain barrier unlocked

The brain is protected by a physiological blood-brain barrier (BBB) against toxins and some metabolites circulating in the blood. At the same time, the BBB limits penetration into the brain of many neuroactive drugs. Efficient ways to increase BBB permeability for delivery of drugs of different chemical nature into the brain are unknown. This work deals with delivery into the brain of 10(-2) M dopamine, a substance that does not penetrate the BBB under normal circumstances. It was studied in two independent experiments: (i) penetration of (3)H-labeled dopamine from its mixture with 10(-5) M H2O2 into hypothalamus and striatum structures of intact rat brain, and (ii) effect of unlabeled dopamine from a mixture with H(2)O(2) on the rat motor activity in a haloperidol catalepsy model. It was shown that (i) at the third minute after nasal application of the dopamine + H(2)O(2) mixture, the dopamine level increases 45-fold in the hypothalamus and almost 30-fold in the striatum and (ii) motility of animals in the catalepsy haloperidol model is recovered 90 sec after intranasal introduction of dopamine. No such effects were observed after replacement of H(2)O(2) by 0.9% NaCl solution. Thus, it was shown on the example of dopamine that its introduction into the nasal cavity simultaneously with H(2)O(2) provides for rapid delivery of the drug into the brain. These results expand our knowledge concerning the biological role of exoROS in modulating BBB permeability and may contribute to the development of a new therapeutic strategy for neurological diseases.

RNAi-based therapies for Huntington's disease: delivery challenges and opportunities

Huntington's disease (HD) is a polyglutamine neurodegenerative disease caused by a mutation in the HTT gene coding for the Huntingtin protein (HTT). Unfortunately, there is no cure for HD and there is also no known way to modify the disease progression. RNAi approaches offer the promise of a certain degree of control over the disease. However, there are several challenges in potential use of RNAi in the treatment of HD. This article will discuss the details of RNAi technology as applied to the treatment of HD, and novel approaches to overcome the drug delivery challenges.

Brainpeps: the blood-brain barrier peptide database

Peptides are able to cross the blood-brain barrier (BBB) through various mechanisms, opening new diagnostic and therapeutic avenues. However, their BBB transport data are scattered in the literature over different disciplines, using different methodologies reporting different influx or efflux aspects. Therefore, a comprehensive BBB peptide database (Brainpeps) was constructed to collect the BBB data available in the literature. Brainpeps currently contains BBB transport information with positive as well as negative results. The database is a useful tool to prioritize peptide choices for evaluating different BBB responses or studying quantitative structure-property (BBB behaviour) relationships of peptides. Because a multitude of methods have been used to assess the BBB behaviour of compounds, we classified these methods and their responses. Moreover, the relationships between the different BBB transport methods have been clarified and visualized.

Lipid nanoparticles for brain targeting I. Formulation optimization

The aim of this study was to optimize the formulation of lipid nanoparticles (NPs), intended for brain targeting, with the aid of a computer generated experimental design. The high pressure homogenization technique, selected for this purpose, was suitable to formulate the 3 investigated lipids (i.e., Softisan(®) 142, SOFT; Compritol(®) 888 ATO, COMP; cetyl palmitate, CP) into nanometre-length particles, while the computer generated experimental design helped to individuate the best preparation conditions with a small number of experimental assay. Even though all the 3 optimized formulations were suitable for intravenous infusion, CP NPs showed the smallest particle size and the appropriate thermal behaviour to be used as carriers in brain targeting applications.

Pharmaceutical and pharmacological importance of peptide transporters

Peptide transport is currently a prominent topic in membrane research. The transport proteins involved are under intense investigation because of their physiological importance in protein absorption and also because peptide transporters are possible vehicles for drug delivery. Moreover, in many tissues peptide carriers transduce peptidic signals across membranes that are relevant in information processing. The focus of this review is on the pharmaceutical relevance of the human peptide transporters PEPT1 and PEPT2. In addition to their physiological substrates, both carriers transport many β-lactam antibiotics, valaciclovir and other drugs and prodrugs because of their sterical resemblance to di- and tripeptides. The primary structure, tissue distribution and substrate specificity of PEPT1 and PEPT2 have been well characterized. However, there is a dearth of knowledge on the substrate binding sites and the three-dimensional structure of these proteins. Until this pivotal information becomes available by X-ray crystallography, the development of new drug substrates relies on classical transport studies combined with molecular modelling. In more than thirty years of research, data on the interaction of well over 700 di- and tripeptides, amino acid and peptide derivatives, drugs and prodrugs with peptide transporters have been gathered. The aim of this review is to put the reports on peptide transporter-mediated drug uptake into perspective. We also review the current knowledge on pharmacogenomics and clinical relevance of human peptide transporters. Finally, the reader's attention is drawn to other known or proposed human peptide-transporting proteins.

Risk factors for brain relapse in HER2-positive metastatic breast cancer patients

Brain relapse is a common occurrence in HER2-positive breast cancer patients. However, the factors determining the risk of brain metastasis in these patients remain to be established. The aim of this study was to assess the impact of particular clinical and pathological factors on the risk of brain relapse in HER2-positive advanced breast cancer patients. The study group included 264 consecutive HER-2 positive metastatic breast cancer patients, most of whom (210; 80%) were administered trastuzumab, usually in combination with chemotherapy. Time from the diagnosis to distant relapse ranged from 0 to 142 months (median 16 months). The most common dominant site of metastatic disease was viscera (80%), followed by soft tissue (11%) and bones (10%). After a median follow-up of 3.1 years, the symptomatic brain relapse occurred in 103 patients (39%). Median time from treatment dissemination to brain relapse was 15 months (range, 0-81 months), and the cumulative 1-year, 3-year and 5-year risk of brain relapse was 17, 42 and 55%, respectively. The average annual risk of brain relapse for surviving patients during consecutive 7 years of follow-up was 10.0% (95% CI, 6.6-13.5%). In the univariate analysis the only variable significantly related to the increased risk of brain relapse was time from initial diagnosis to distant relapse shorter than 2 years (HR = 1.55, 95% CI, 1.03-2.33, P = 0.034). Patients with dominant site of disease in soft tissue or bones tended to have lower risk of relapse (HR = 0.54 and 0.62; P = 0.098 and 0.203, respectively) compared to patients with visceral metastases. Treatment with trastuzumab was not associated with reduced risk of brain relapse (HR = 0.91, 95% CI, 0.47-1.77, P = 0.78). In the multivariate analysis, time from initial diagnosis to distant relapse shorter than 2 years remained the only significant variable related to increased risk of brain relapse (adjusted HR = 1.62, 95% CI, 1.07-2.44; P = 0.022). HER2-positive breast cancer patients remain at high and continuous risk of brain relapse for a prolonged period of time after diagnosis of disease dissemination. Short time from initial diagnosis to distant relapse is related to increased risk of brain relapse. Molecular predictors are sorely needed to better characterize patients with high probability of early brain relapse.

Equivalence-by-design: targeting in vivo drug delivery profile

In the United States (U.S.), drug products are considered therapeutically equivalent if they meet regulatory criteria of pharmaceutical equivalence and bioequivalence. These requirements can be traced back to 1977 when the U.S. Food and Drug Administration (FDA) published the regulations on bioavailability and bioequivalence. Over the years, to keep up with the advancement in science and technology, the FDA has been constantly updating the regulatory approaches to assessing and ensuring equivalence. In view of the recent growth in novel pharmaceutical dosage forms and delivery systems, this paper examines the current framework for documentation of therapeutic equivalence and explores the opportunities of further advancing equivalence methods for complex drug products. It is proposed that equivalence may be established by matching the in vivo drug delivery profile (iDDP) between drug products in comparison. This can be achieved by characterizing the iDDP of the reference formulation with application of an equivalence-by-design approach for pharmaceutical development. Critical variables can be identified to serve as in vitro markers or biomarkers for mapping the desired drug delivery profile in vivo. A multidisciplinary approach may be necessary to develop these markers for characterization of iDDPs.

The pharmacokinetics and pharmacodynamics of micafungin in experimental hematogenous Candida meningoencephalitis: implications for echinocandin therapy in neonates

BACKGROUND

Hematogenous Candida meningoencephalitis (HCME) is a relatively frequent manifestation of disseminated candidiasis in neonates and is associated with significant mortality and neurodevelopmental abnormalities. The outcome after antifungal therapy is often suboptimal, with few therapeutic options. Limited clinical data suggest that echinocandins may have role to play in the treatment of HCME.

METHODS

We studied the pharmacokinetics and pharmacodynamics of micafungin in a rabbit model of neonatal HCME and bridged the results to neonates by use of population pharmacokinetics and Monte Carlo simulation.

RESULTS

Micafungin exhibited linear plasma pharmacokinetics in the range of 0.25-16 mg/kg. Micafungin penetrated most compartments of the central nervous system (CNS), but only with doses >2 mg/kg. Micafungin was not reliably found in cerebrospinal fluid. With few exceptions, drug penetration into the various CNS subcompartments was not statistically different between infected and noninfected rabbits. A dose-microbiological response relationship was apparent in the brain, and near-maximal effect was apparent with doses of 8 mg/kg. Monte Carlo simulations revealed that near-maximal antifungal effect was attained at human neonatal doses of 12-15 mg/kg.

CONCLUSIONS

These results provide a foundation for clinical trials of micafungin in neonates with HCME and a model for antimicrobial bridging studies from bench to bedside in pediatric patients.

The role of permeability in drug ADME/PK, interactions and toxicity--presentation of a permeability-based classification system (PCS) for prediction of ADME/PK in humans

PURPOSE

The objective was to establish in vitro passive permeability (Pe) vs in vivo fraction absorbed (fa)-relationships for each passage through the human intestine, liver, renal tubuli and brain, and develop a Pe-based ADME/PK classification system (PCS).

MATERIALS AND METHODS

Pe- and intestinal fa-data were taken from an available data set. Hepatic fa was calculated based on extraction ratios of the unbound fraction of drugs (with support from animal in vivo uptake data). Renal fa (reabsorption) was estimated using renal pharmacokinetic data, and brain fa was predicted using animal in vitro and in vivo brain Pe-data. Hepatic and intestinal fa-data were used to predict bile excretion potential.

RESULTS

Relationships were established, including predicted curves for bile excretion potential and minimum oral bioavailability, and a 4-Class PCS was developed: I (very high Pe; elimination mainly by metabolism); II (high Pe) and III (intermediate Pe and incomplete fa); IV (low Pe and fa). The system enables assessment of potential drug-drug transport interactions, and drug and metabolite organ trapping.

CONCLUSIONS

The PCS and high quality Pe-data (with and without active transport) are believed to be useful for predictions and understanding of ADME/PK, elimination routes, and potential interactions and organ trapping/toxicity in humans.

Primary porcine brain microvascular endothelial cells: biochemical and functional characterisation as a model for drug transport and targeting

The blood-brain barrier (BBB) remains a significant obstacle to the delivery of therapeutic agents into the central nervous system (CNS). Primary cell cultures of brain capillary endothelial cells represent the closest possible phenotype to the in vivo BBB cell providing a convenient model for the study of transport systems and events that mediate solute delivery to the CNS. In this investigation we have characterized an in vitro primary BBB model from porcine brain microvascular endothelial capillary (PBMVEC) cells after recovery from cryopreservation of upto 12 months and studied their modulation by astrocytes. Co-cultures of PBMVECs with astrocytes (C6 astroglioma) resulted in trans-endothelial electrical resistance of up to approximately 900Omega cm2 and marked discrimination between the para- and trans- cellular markers sucrose and propranolol. Micrographs of confluent monolayers of PBMVECs showed the presence of tight junction complexes and vesicles with the morphological characteristics of either caveolae or clathrin coated pits. Extensive RT-PCR evaluation highlighted the expression of tight junction transcripts, ABC transporters, leptin receptor and select nutrient transporters. Functional studies examined the kinetics of transport of glucose, large neutral amino acids and p-glycoprotein (P-gp). Our findings indicate primary PBMVECs retain many barrier characteristics and transport pathways of the in vivo BBB. Further, primary cells can be stored as frozen stocks which can be thawed and cultured without phenotypic drift many months after isolation. Frozen PBMVECs therefore serve as a robust and convenient in vitro cell culture tool for research programs involving CNS drug delivery and targeting and in studies addressing blood-brain barrier transport mechanisms.

Structural modifications of (1S,3S)-3-amino-4-difluoromethylenecyclopentanecarboxylic acid, a potent irreversible inhibitor of GABA aminotransferase

Low brain levels of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) lead to convulsions. Inhibition of GABA aminotransferase increases the concentration of GABA and can terminate the convulsions. Earlier we reported the synthesis of (1S,3S)-3-amino-4-difluoromethylenecyclopentanecarboxylic acid (2), which is 186 times more potent an inactivator of GABA aminotransferase than the epilepsy drug S-vigabatrin. The corresponding dichloromethylene analogue of 2 (compound 3) has been made, but it shows only weak reversible inhibition of GABA aminotransferase. However, the tetrazole isostere of 2 (compound 4) has been found to be a time-dependent inactivator of GABA aminotransferase. Although it is 20 times less potent than carboxylic acid 2, it is 2.5 times more potent than S-vigabatrin. A calculation of the ClogP values indicates that 4 is the most lipophilic of the three, being 69 times more lipophilic than 2 and 55 times more lipophilic than S-vigabatrin, indicating potential for improved bioavailability.