Transporter-mediated permeation of drugs across the blood-brain barrier

Large-scale next generation sequencing based analysis of SLCO1B1 pharmacogenetics variants in the Saudi population

BACKGROUND

SLCO1B1 plays an important role in mediating hepatic clearance of many different drugs including statins, angiotensin-converting enzyme inhibitors, chemotherapeutic agents and antibiotics. Several variants in SLCO1B1 have been shown to have a clinically significant impact, in relation to efficacy of these medications. This study provides a comprehensive overview of SLCO1B1 variation in Saudi individuals, one of the largest Arab populations in the Middle East.

METHODS

The dataset of 11,889 (9,961 exomes and 1,928 pharmacogenetic gene panel) Saudi nationals, was used to determine the presence and frequencies of SLCO1B1 variants, as described by the Clinical Pharmacogenetic Implementation Consortium (CPIC).

RESULTS

We identified 141 previously described SNPs, of which rs2306283 (50%) and rs4149056 (28%), were the most common. In addition, we observed six alleles [*15 (24.7%) followed by *20 (8.04%), *14 (5.86%), *5 (3.84%), *31 (0.21%) and *9 (0.03%)] predicted to be clinically actionable. Allele diplotype to phenotype conversion revealed 41 OATP1B1 diplotypes. We estimated the burden of rare, and novel predicted deleterious variants, resulting from 17 such alterations.

CONCLUSIONS

The data we present, from one of the largest Arab cohorts studied to date, provides the most comprehensive overview of SLCO1B1 variants, and the subsequent OATP1B1 activity of this ethnic group, which thus far remains relatively underrepresented in available international genomic databases. We believe that the presented data provides a basis for further clinical investigations and the application of personalized statin drug therapy guidance in Arabs.

Masson pine pollen aqueous extract ameliorates cadmium-induced kidney damage in rats

Introduction: Cadmium (Cd) is a hazardous environmental pollutant present in soil, water, and food. Accumulation of Cd in organisms can cause systematic injury and damage to the kidney. The Masson pine pollen aqueous extract (MPPAE) has attracted increasing attention due to its antioxidant activity and ability to enhance immunity. Methods: In this study, we investigated the potential of MPPAE to protect against Cd-induced kidney damage in rats and the underlying mechanism. The transcriptome and metabolome of rats with Cd-induced kidney damage, following treatment with MPPAE, were explored. Results: The concentrations of superoxide dismutase (SOD) and malondialdehyde (MDA) were both significantly altered after treatment with MPPAE. Furthermore, sequencing and analysis of the transcriptome and metabolome of rats with Cd-induced kidney damage, following treatment with MPPAE, revealed differential expression of numerous genes and metabolites compared with the untreated control rats. These differentially expressed genes (DEGs) included detoxification-related genes such as cytochrome P450 and the transporter. The differentially expressed metabolites (DEMs) included 4-hydroxybenzoic acid, L-ascorbate, and ciliatine. Conjoint transcriptome and metabolome analysis showed that several DEGs were correlated with DEMs. Conclusion: These preliminary findings indicate the potential of MPPAE for the treatment of toxic metal poisoning.

Optimization of Nasal Liposome Formulation of Venlafaxine Hydrochloride using a Box-Behnken Experimental Design

Background

Intranasal administration is among the most effective alternatives to deliver drugs directly to the brain and prevent first-pass metabolism. Venlafaxine-loaded liposomes are biocompatible carriers that enhance transport qualities over the nasal mucosa.

Objective

This research aimed to develop, formulate, characterize, and observe the prepared formulation.

Methods

The formulation was developed using the thin-film hydration technique. The response surface plot interrelationship between three independent variables are lipid, cholesterol and polymer and four dependent variables such as particle size, percentage entrapment efficiency, and percentage drug release were ascertained using the Box-Behnken design.

Results

The drug-release chitosan-coated liposomes were reported to have a particle size distribution, entanglement efficiency, and 84%, respectively, of 191 ± 34.71 nm, 94 ± 2.71% and 94 ± 2.71%. According to in vitro investigations, liposomes as a delivery system for the nasal route provided a more sustained drug release than the oral dosing form.

Conclusions

The intranasal administration of venlafaxine liposomal vesicles effectively enhanced the absolute bioavailability, retention time, and brain delivery of venlafaxine.

Nanoparticle Strategies to Improve the Delivery of Anticancer Drugs across the Blood-Brain Barrier to Treat Brain Tumors

Primary brain and central nervous system (CNS) tumors are a diverse group of neoplasms that occur within the brain and spinal cord. Although significant advances in our understanding of the intricate biological underpinnings of CNS neoplasm tumorigenesis and progression have been made, the translation of these discoveries into effective therapies has been stymied by the unique challenges presented by these tumors' exquisitely sensitive location and the body's own defense mechanisms (e.g., the brain-CSF barrier and blood-brain barrier), which normally protect the CNS from toxic insult. These barriers effectively prevent the delivery of therapeutics to the site of disease. To overcome these obstacles, new methods for therapeutic delivery are being developed, with one such approach being the utilization of nanoparticles. Here, we will cover the current state of the field with a particular focus on the challenges posed by the BBB, the different nanoparticle classes which are under development for targeted CNS tumor therapeutics delivery, and strategies which have been developed to bypass the BBB and enable effective therapeutics delivery to the site of disease.

Current Update on Transcellular Brain Drug Delivery

It is well known that the presence of a blood-brain barrier (BBB) makes drug delivery to the brain more challenging. There are various mechanistic routes through which therapeutic molecules travel and deliver the drug across the BBB. Among all the routes, the transcellular route is widely explored to deliver therapeutics. Advances in nanotechnology have encouraged scientists to develop novel formulations for brain drug delivery. In this article, we have broadly discussed the BBB as a limitation for brain drug delivery and ways to solve it using novel techniques such as nanomedicine, nose-to-brain drug delivery, and peptide as a drug delivery carrier. In addition, the article will help to understand the different factors governing the permeability of the BBB, as well as various formulation-related factors and the body clearance of the drug delivered into the brain.

Overcoming the shortcomings of peptide-based therapeutics

Peptides have traditionally been perceived as poor drug candidates due to unfavorable characteristics mainly regarding their pharmacokinetic behavior, including plasma stability, membrane permeability and circulation half-life. Nonetheless, in recent years, general strategies to tackle those shortcomings have been established, and peptides are subsequently gaining increasing interest as drugs due to their unique ability to combine the advantages of antibodies and small molecules. Macrocyclic peptides are a special focus of drug development efforts due to their ability to address so called ‘undruggable’ targets characterized by large and flat protein surfaces lacking binding pockets. Here, the main strategies developed to date for adapting peptides for clinical use are summarized, which may soon help usher in an age highly shaped by peptide-based therapeutics. Nonetheless, limited membrane permeability is still to overcome before peptide therapeutics will be broadly accepted.

Characterization of Aripiprazole Uptake Transporter in the Blood-Brain Barrier Model hCMEC/D3 Cells by Targeted siRNA Screening

AIM

Identification of blood-brain barrier (BBB) uptake transporters is a major challenge in the research and development of central nervous system (CNS) drugs. However, conventional methods that consider known drug uptake characteristics have failed at identifying the responsible transporter molecule. The present study aimed at identifying aripiprazole uptake transporters in BBB model hCMEC/D3 cells using a knockdown screening study targeting various transporters, including uncharacterized ones.

METHODS

We evaluated the effect of 214 types of siRNA targeting transporters on the uptake of aripiprazole, an atypical antipsychotic drug, in hCMEC/D3 cells. Aripiprazole uptake was determined using Xenopus oocytes expressing the candidate genes extracted from the siRNA screening assay.

RESULTS

The estimated unbound brain to plasma concentration ratio (K_p,uu,brain) of aripiprazole was estimated as 0.67 in wild-type mice and 1.94 in abcb1a/1b/abcg2 knockout mice, suggesting the involvement of both uptake and efflux transporters in BBB permeation. According to siRNA knockdown screening studies, organic cation/carnitine transporter 2 (OCTN2) and long-chain fatty acid transporter 1 (FATP1) were identified as candidate genes. The uptake of aripiprazole by hCMEC/D3 cells was decreased by OCTN2 inhibitors, but not by FATP1 inhibitors. A partially increased uptake of aripiprazole was observed in OCTN2-expressing Xenopus oocytes. Finally, to evaluate transporter-mediated BBB permeation of drugs, the reported and estimated K_p,uu,brain values were summarized.

CONCLUSIONS

A knockdown screening study in combination with K_p,uu,brain values showed that aripiprazole was a potential substrate of OCTN2. The technique described in this study can be applied to identifying novel BBB transporters for CNS drugs.

Phytochemical and Over-The-Counter Drug Interactions: Involvement of Phase I and II Drug-Metabolizing Enzymes and Phase III Transporters

Consumption of plant-derived natural products and over-the-counter (OTC) drugs is increasing on a global scale, and studies of phytochemical-OTC drug interactions are becoming more significant. The intake of dietary plants and herbs rich in phytochemicals may affect drug-metabolizing enzymes (DMEs) and transporters. These effects may lead to alterations in pharmacokinetics and pharmacodynamics of OTC drugs when concomitantly administered. Some phytochemical-drug interactions benefit patients through enhanced efficacy, but many interactions cause adverse effects. This review discusses possible mechanisms of phytochemical-OTC drug interactions mediated by phase I and II DMEs and phase III transporters. In addition, current information is summarized for interactions between phytochemicals derived from fruits, vegetables, and herbs and OTC drugs, and counseling is provided on appropriate and safe use of OTC drugs.

Therapeutic targeting of membrane-associated proteins in central nervous system tumors

The activity of the most complex system, the central nervous system (CNS) is profoundly regulated by a huge number of membrane-associated proteins (MAP). A minor change stimulates immense chemical changes and the elicited response is organized by MAP, which acts as a receptor of that chemical or channel enabling the flow of ions. Slight changes in the activity or expression of these MAPs lead to severe consequences such as cognitive disorders, memory loss, or cancer. CNS tumors are heterogeneous in nature and hard-to-treat due to random mutations in MAPs; like as overexpression of EGFRvIII/TGFβR/VEGFR, change in adhesion molecules α5β3 integrin/SEMA3A, imbalance in ion channel proteins, etc. Extensive research is under process for developing new therapeutic approaches using these proteins such as targeted cytotoxic radiotherapy, drug-delivery, and prodrug activation, blocking of receptors like GluA1, developing viral vector against cell surface receptor. The combinatorial approach of these strategies along with the conventional one might be more potential. Henceforth, our review focuses on in-depth analysis regarding MAPs aiming for a better understanding for developing an efficient therapeutic approach for targeting CNS tumors.

Receptor-Mediated Muscle Homeostasis as a Target for Sarcopenia Therapeutics

Sarcopenia is a disease characterized by age-related decline of skeletal muscle mass and function. The molecular mechanisms of the pathophysiology of sarcopenia form a complex network due to the involvement of multiple interconnected signaling pathways. Therefore, signaling receptors are major targets in pharmacological strategies in general. To provide a rationale for pharmacological interventions for sarcopenia, we herein describe several druggable signaling receptors based on their role in skeletal muscle homeostasis and changes in their activity with aging. A brief overview is presented of the efficacy of corresponding drug candidates under clinical trials. Strategies targeting the androgen receptor, vitamin D receptor, Insulin-like growth factor-1 receptor, and ghrelin receptor primarily focus on promoting anabolic action using natural ligands or mimetics. Strategies involving activin receptors and angiotensin receptors focus on inhibiting catabolic action. This review may help to select specific targets or combinations of targets in the future.

Implementation of a Skull-Conformal Phased Array for Transcranial Focused Ultrasound Therapy

OBJECTIVE

To implement a skull-conformal phased array for ultrasound-guided transcranial focused ultrasound therapy with improved patient comfort.

METHODS

Using patient-specific computed tomography and MRI neuroimaging data, tightly-conforming helmet scaffolds were designed computationally. The helmet scaffolds were designed to hold reusable transducer modules at near-normal incidence in an optimal configuration for the treatment location(s) of interest. Numerical simulations of trans-skull ultrasound propagation were performed to evaluate different conformal array designs and to compare with hemispherical arrays similar to those employed clinically. A 4096-element phased array was constructed by 3D printing a helmet scaffold optimised for an ex vivo human skullcap, and its performance was evaluated via benchtop and in vivo experiments.

RESULTS

Acoustic field measurements confirmed the system's ability to focus through human skull bone using simulation-based transcranial aberration corrections. Preliminary in vivo testing demonstrated safe trans-human skull blood-brain barrier (BBB) opening in rodents.

CONCLUSION

Patient-specific conformal ultrasound phased arrays appear to be a feasible and safe approach for conducting transcranial BBB opening procedures.

SIGNIFICANCE

Skull-conformal phased arrays stand to improve patient comfort and have the potential to accelerate the adoption of transcranial FUS therapy by improving access to the technology.

Rethinking CRITID Procedure of Brain Targeting Drug Delivery: Circulation, Blood Brain Barrier Recognition, Intracellular Transport, Diseased Cell Targeting, Internalization, and Drug Release

The past decades have witnessed great progress in nanoparticle (NP)-based brain-targeting drug delivery systems, while their therapeutic potentials are yet to be fully exploited given that the majority of them are lost during the delivery process. Rational design of brain-targeting drug delivery systems requires a deep understanding of the entire delivery process along with the issues that they may encounter. Herein, this review first analyzes the typical delivery process of a systemically administrated NPs-based brain-targeting drug delivery system and proposes a six-step CRITID delivery cascade: circulation in systemic blood, recognizing receptor on blood-brain barrier (BBB), intracellular transport, diseased cell targeting after entering into parenchyma, internalization by diseased cells, and finally intracellular drug release. By dissecting the entire delivery process into six steps, this review seeks to provide a deep understanding of the issues that may restrict the delivery efficiency of brain-targeting drug delivery systems as well as the specific requirements that may guarantee minimal loss at each step. Currently developed strategies used for troubleshooting these issues are reviewed and some state-of-the-art design features meeting these requirements are highlighted. The CRITID delivery cascade can serve as a guideline for designing more efficient and specific brain-targeting drug delivery systems.

Partitioning of Aβ Peptide Fragments into Blood-Brain Barrier Mimetic Bilayer

We used all-atom replica-exchange umbrella sampling molecular dynamics simulations to investigate the partitioning of the charged tetrapeptide KLVF and its neutral apolar counterpart VVIA into the blood-brain barrier (BBB)-mimetic bilayer. Our findings allowed us to reconstruct the partitioning mechanism for these two Aβ peptide fragments. Despite dissimilar sequences, their permeation shares significant common features. Computations of free energies and permeabilities show that partitioning of both peptides is highly unfavorable, ruling out passive transport. The peptides experience multiple rotational transitions within the bilayer and typically cause considerable lipid disorder and bilayer thinning. Near the bilayer midplane, they lose almost entirely their solvation shell and the interactions with the lipid headgroups. The peptides cause complex reorganization within the proximal bilayer region. Upon insertion, they induce striking cholesterol influx reversed by its depletion and the influx of DMPC when the peptides reach the midplane. The differences in partitioning mechanisms are due to the much higher polarity of KLVF peptide, the permeation of which is more unfavorable and which exclusively assumes vertical orientations within the bilayer. In contrast, VVIA positions itself flat between the leaflets, causing minor disorder and even thickening of the BBB-mimetic bilayer. Due to the high density of the cholesterol-rich BBB bilayer, the unfavorable work associated with the peptide insertion provides a significant, but not dominant, contribution to the partition free energy, which is still governed by dehydration and loss of peptide-headgroup interactions. Comparison with experiments indicates that KLVF and VVIA permeation is similar to that of proline tetrapeptide, mannitol, or cimetidine, all of which exhibit no passive transport.

Targeting receptor-ligand chemistry for drug delivery across blood-brain barrier in brain diseases

The blood-brain barrier (BBB) is composed of a layer of endothelial cells that is interspersed with a series of tight junctions and characterized by the absence of fenestrations. The permeability of this barrier is controlled by junctions such as tight junctions and adherent junctions as well as several cells such as astrocytes, pericytes, vascular endothelial cells, neurons, microglia, and efflux transporters with relatively enhanced expression. It plays a major role in maintaining homeostasis in the brain and exerts a protective regulatory control on the influx and efflux of molecules. However, it proves to be a challenge for drug delivery strategies that target brain diseases like Dementia, Parkinson's Disease, Alzheimer's Disease, Brain Cancer or Stroke, Huntington's Disease, Lou Gehrig's Disease, etc. Conventional modes of drug delivery are invasive and have been known to contribute to a "leaky BBB", recent studies have highlighted the efficiency and relative safety of receptor-mediated drug delivery. Several receptors are exhibited on the BBB, and actively participate in nutrient uptake, and recognize specific ligands that modulate the process of endocytosis. The strategy employed in receptor-mediated drug delivery exploits this process of "tricking" the receptors into internalizing ligands that are conjugated to carrier systems like liposomes, nanoparticles, monoclonal antibodies, enzymes etc. These in turn are modified with drug molecules, therefore leading to delivery to desired target cells in brain tissue. This review comprehensively explores each of those receptors that can be modified to serve such purposes as well as the currently employed strategies that have led to increased cellular uptake and transport efficiency.

The uses of resveratrol for neurological diseases treatment and insights for nanotechnology based-drug delivery systems

Neurological disorders have been growing in recent years and are highly prevalent globally. Resveratrol (RES) is a natural product from plant sources such as grape skins. This compound has shown biological activity in many diseases, in particular, those that act on the central nervous system. The mechanism of action and the key points in neurological disorders were described and show the targeted mechanism of action. Due to the insolubility of this compound; the use of nanotechnology-based systems has been proposed for the incorporation of RES and RES-loaded nanocarriers have been designed for intranasal administration, oral or parenteral routes to deliver it to the brain. In general, these nanosystems have shown to be effective in many studies, pharmacological and pharmacokinetic assays, as well as some cell studies. The outcomes show that RES has been reported in human clinical trials for some neurological diseases, although no studies were performed in humans using nanocarriers, animal and/or cellular models have been reported to show good results regarding therapeutics on neurological diseases. Thus, the use of this nutraceutical has shown true for neurological diseases and its loading into nanocarriers displaying good results on the stability, delivery and targeting to the brain.

'Prodrug-Like' Acetylmannosamine Modified Liposomes Loaded With Arsenic Trioxide for the Treatment of Orthotopic Glioma in Mice

Glioma is one of the fatal intracranial cancers that is a huge challenge to decrease the death rate currently. The deep penetration and high accumulation of therapeutic inorganic ions into the tumor site are extremely impeded due to the existence of physiological barriers, which limits to widen the indication of some drugs such as arsenic trioxide. The previous data have confirmed that the mannose substrate (MAN) without acetyl groups facilitates vesicles to go into the brain. Given that deacetylation of Ac₄MAN groups on the surface of liposomes under the enzyme incubation occurred, namely 'prodrug-like' features of vesicles, the liposomes could more easily penetrate the BBB, target the glioma site, release arsenic trioxide, and inhibit the growth of glioma cells in the brain. Besides, the possibility of Ac₄MAN binding to Gluts could be reduced due to the steric hindrance of acetyl groups, decreasing the off-target effects of vesicles. Here, we developed 'prodrug-like' arsenic trioxide (As₂O₃, ATO)-loaded liposomes inserted with distearoyl phospho-ethanolamine-polyethylene glycol-1000-p-carboxylpheny-α-d-acetylmannosamine (DSPE-PEG-1000-Ac₄MAN), which was named Ac₄MAN-ATO-LIP. Cytotoxic experiments of liposomes indicated that the toxicity of Ac₄MAN-ATO-LIP was lower than that of free ATO but stronger than that of ATO-LIP (without insertion of DSPE-PEG-1000-Ac₄MAN). The uptake of vesicles by U87 glioma cells displayed that the cellular uptake of Ac₄MAN-Rho-LIP (labeled by rhodamine) was remarkably improved, compared with Rho-LIP. The in vivo biodistribution results showed the superiority of Ac₄MAN-Rho-LIP in enhanced intracranial accumulation. Furthermore, the treatment of orthotopic glioma in Balb/c nude mice with Ac₄MAN-ATO-LIP elongated the survival time of the animals than that with physiological saline, free ATO, or ATO-LIP, respectively. All the results suggested that the Ac₄MAN-ATO-LIP had stronger anti-glioma effects as well as lower toxicities, and may be a promising approach for the treatment of brain cancer.

Simvastatin-chitosan-citicoline conjugates nanoparticles as the co-delivery system in Alzheimer susceptible patients

The main goal of this study was the preparation and characterization of a chitosan-based system for co-delivery of simvastatin and citicoline to overcome simvastatin unwanted side effects in Alzheimer's disease. This conjugated complex was synthesized in three steps, and ¹HNMR, FTIR, and UV-Vis spectroscopy confirmed its success. The simvastatin conjugation rate to chitosan was 1.67 times more than citicoline. X-ray diffraction results showed that the crystalline property of both drugs converted to an amorphous state during the synthesis of the conjugated form. Further, SEM images revealed that the developed nanoparticles have a spherical shape with a size between 100 and 300 nm. Another characterization test was RBC hemolysis, with the lowest value at 6.04% and the highest value at 89.56% and became much lower after preparing nanoparticles using the ionotropic technique. TEM characterized the nanoparticles and showed that the gelation technique stabilized the particles.

Weak correlations between serum and cerebrospinal fluid levels of estradiol, progesterone and testosterone in males

Background

Neuroactive steroids seem to be implicated in a variety of neurophysiological and behavioral processes, such as sleep, learning, memory, stress, feeding and aging. Numerous studies have also addressed this implication in various cerebral disorders and diseases. Yet, the correlation and association between steroids in the periphery, e.g. blood, and the central compartments, e.g. cerebrospinal fluid (CSF), have not yet been comprehensively assessed. As the brain is not directly accessible, and the collection of human CSF usually requires invasive procedures, easier accessible compartments, such as blood, have always attracted attention. However, studies in humans are scarce. In the present study we determined estradiol, progesterone and testosterone levels in CSF and serum of 22 males without cerebral disorders or diseases.

Results

Samples were taken under conditions corresponding closest to basal conditions with patients expecting only spinal anesthesia and minor surgery. All samples per patient were collected concomitantly. Total estradiol, progesterone and testosterone concentrations were measured by electro-chemiluminescence immunoassay. The strength of correlation was assessed by Spearman’s rank correlation coefficient. Correlation analysis revealed merely weak to very weak correlations for estradiol, progesterone and testosterone respectively between the CSF and serum compartments.

Conclusions

Total steroid levels of estradiol, progesterone and testosterone in CSF and serum of males without neurological disorders were determined. Weak to very weak correlations between CSF and serum were found thus suggesting that concentrations in the periphery do not parallel concentrations in the central compartments. Further research is needed to clarify to what extent and under which conditions serum levels of estradiol, progesterone and testosterone may possibly serve as a biomarker reflecting the respective concentrations in the CSF or in the brain.

Bioformulative concepts on intracellular organ specific bioavailability

Bioavailability is an ancient but effective terminology by which the entire therapeutic efficacy of a drug directly or indirectly relays. Despite considering general plasma bioavailability, specific organ/tissue bioavailability will pave the path to broad spectrum dose calculation. Clear knowledge and calculative vision on bioavailability can improve the research and organ-targeting phenomenon. This article comprises a detailed introduction on bioavailability along with regulatory aspects, kinetic data and novel bioformulative approaches to achieve improved organ specific bioavailability, which may not be readily related to blood plasma bioavailability.

Blood-brain barrier receptors and transporters: an insight on their function and how to exploit them through nanotechnology

INTRODUCTION

The blood-brain barrier (BBB) is a highly limiting barrier that prevents the brain from contacting with several circulating molecules, including harmful agents. However, certain systemic nutrients and macromolecules are able to cross the BBB and reach the brain parenchyma, involving the interaction with multiple receptors and/or transporters at the BBB surface. Nanotechnology allows the creation of drug vehicles, functionalized with targeting ligands for binding specific BBB receptors and/or transporters, hence triggering the transport through this biobarrier.

AREAS COVERED

This review focuses the BBB receptors/transporters to be exploited in regard to their overall structure and biologic function, as well as their role in the development of strategies envisaging drug delivery to the brain. Then, the interplay between the targeting of these BBB receptors/transporters and nanotechnology is explored, as they can increase by several-fold the effectiveness of brain-targeted therapies.

EXPERT OPINION

Nanomedicine may be particularly useful in brain drug delivery, mainly due to the possibility of functionalizing nanoparticles to target specific receptors/transporters. Since the BBB is endowed with numerous receptors and transporters responsible for regulating the proper metabolic activity of the brain, their targeting can be a promising bypass strategy to circumvent the hurdle that the BBB represents for brain drug delivery.

Evaluating the safety profile of focused ultrasound and microbubble-mediated treatments to increase blood-brain barrier permeability

INTRODUCTION

Treatment of several diseases of the brain are complicated by the presence of the skull and the blood-brain barrier (BBB). Focused ultrasound (FUS) and microbubble (MB)-mediated BBB treatment is a minimally invasive method to transiently increase the permeability of blood vessels in targeted brain areas. It can be used as a general delivery system to increase the concentration of therapeutic agents in the brain parenchyma.

AREAS COVERED

Over the past two decades, the safety of using FUS+MBs to deliver agents across the BBB has been interrogated through various methods of imaging, histology, biochemical assays, and behavior analyses. Here we provide an overview of the factors that affect the safety profile of these treatments, describe methods by which FUS+MB treatments are controlled, and discuss data that have informed the assessment of treatment risks.

EXPERT OPINION

There remains a need to assess the risks associated with clinically relevant treatment strategies, specifically repeated FUS+MB treatments, with and without therapeutic agent delivery. Additionally, efforts to develop metrics by which FUS+MB treatments can be easily compared across studies would facilitate a more rapid consensus on the risks associated with this intervention.

Angiopep-2-Conjugated "Core-Shell" Hybrid Nanovehicles for Targeted and pH-Triggered Delivery of Arsenic Trioxide into Glioma

The poor capability of drugs to permeate through the blood-brain barrier (BBB) and further release inside glioma greatly limits the curative effects of glioma chemotherapies. In this study, we prepared angiopep-2-conjugated liposome-silica hybrid nanovehicles for targeted delivery and increased the permeation of arsenic trioxide (ATO) in glioma. Polyacrylic acid (PAA) was grafted on mesoporous silica nanoparticles (MSN) for pH-sensitive release and supporting the lipid membrane. The prepared "core-shell" nanovehicles (ANG-LP-PAA-MSN) were characterized with uniform size, high drug loading efficiency (8.19 ± 0.51%), and superior pH-sensitive release feature. From the experiments, the enhanced targeted delivery of ATO by ANG-LP-PAA-MSN (ANG-LP-PAA-MSN@ATO) was evidenced by the improvement of transport, enhanced cellular uptake, and apoptosis in vitro. In addition, the pharmacokinetic study was creatively carried out through the blood-glioma synchronous microdialysis and revealed that the half-life ( t_1/2) of blood and glioma tissue in the ANG-LP-PAA-MSN@ATO treatment group was extended by 1.65 and 2.34 times compared with the ATO solution group (ATO-Sol). The targeting efficiency of ANG-LP-PAA-MSN@ATO (24.96%) was dramatically stronger than that of the ATO-Sol (5.94%). Importantly, ANG-LP-PAA-MSN@ATO had a higher accumulation (4.6 ± 2.6% ID per g) in tumor tissues and showed a better therapeutic efficacy in intracranial C6 glioma bearing rats. Taken together, the blood-glioma synchronous microdialysis was successful used for the pharmacokinetic study and real-time monitoring of drug concentrations in blood and glioma; ANG-LP-PAA-MSN could be a promising targeted drug delivery system for glioma therapy.

Penetration of PFASs Across the Blood Cerebrospinal Fluid Barrier and Its Determinants in Humans

Laboratory studies indicate that exposure to perfluoroalkyl and polyfluoroalkyl substances (PFASs) can induce neurobehavioral effects in animals. However, the penetration of PFASs across the brain barrier and its determining factors are yet to be clarified in humans. We studied PFAS levels in 223 matched-pair serum and cerebrospinal fluid (CSF) samples from hospital in-patients using UPLC/MS/MS. Among the 21 target analytes, PFOA, PFOS, and 6:2 Cl-PFESA were dominant in serum, with mean concentrations of 7.4, 6.8, and 6.2 ng/mL, respectively, contributing 79% to the total PFAS burden in serum. In CSF, PFOA, PFOS, and 6:2 Cl-PFESA were again the dominant PFASs, with mean concentrations of 0.078, 0.028, and 0.051 ng/mL contributing 36%, 13%, and 24%, respectively, to the total PFAS burden in CSF. Furthermore, PFAS penetration ( R_PFAS, PFAS_CSF/PFAS_serum) was positively correlated with the barrier permeability index R_Alb (Albumin_CSF/Albumin_serum), indicating that barrier integrity was the main determinant of PFAS penetration across the blood-CSF barrier. Positive associations between the R_PFAS values of the main PFASs and serum C-reactive protein were observed, implying that inflammation facilitates the penetration of PFASs across the brain barrier.

The Role of Combined Penetration Enhancers in Nasal Microspheres on In Vivo Drug Bioavailability

Microspheres based on both methyl-β-cyclodextrins and chitosan were prepared by spray-drying as nasal formulations of a model polar drug to analyze, firstly, how the composition of the carrier affects drug permeation across synthetic membranes and, secondly, how it induces systemic or brain delivery of the drug. Microparticles with different weight ratios of the two penetration enhancers (10⁻90, 50⁻50, 90⁻10) were characterized with respect to morphology, size, structural composition, water uptake, and the in vitro drug permeation profile. The leader formulation (weight ratio of 50⁻50) was then nasally administered to rats; systemic and cerebrospinal fluid (CSF) drug concentrations were analyzed by high performance liquid chromatography (HPLC) over time. Microspheres obtained with a single enhancer, methyl-β-cyclodextrins or chitosan, were administered in vivo as a comparison. The in vitro properties of combined microspheres appeared modified with regard to the polymeric matrix ratio. In vivo results suggest that the optimal drug distribution between CSF and bloodstream can be easily obtained by varying the amount of these two penetration enhancers studied in the matrix of nasal microspheres.

Targeting central nervous system pathologies with nanomedicines

One of the major challenges in drug development is the delivery of therapeutics to the central nervous system (CNS). The blood-brain barrier (BBB), which modulates the passage of molecules from the CNS, presents a formidable obstacle that limits brain uptake of therapeutics and, therefore, impedes the treatment of multiple neurological pathologies. Targeted nanocarriers present an excellent opportunity for drug delivery into the brain leveraging on endogenous receptors to transport therapeutics across the BBB endothelium. Receptor-mediated transport endows multiple benefits over other conventional delivery methods such as the transient permeabilization of the BBB or the direct depositioning of intracranial depots. Herein, different strategies for nanocarrier targeting to the CNS are discussed, highlighting the challenges and recent developments.

Nucleobase and Nucleoside Analogues: Resistance and Re-Sensitisation at the Level of Pharmacokinetics, Pharmacodynamics and Metabolism

Antimetabolites, in particular nucleobase and nucleoside analogues, are cytotoxic drugs that, starting from the small field of paediatric oncology, in combination with other chemotherapeutics, have revolutionised clinical oncology and transformed cancer into a curable disease. However, even though combination chemotherapy, together with radiation, surgery and immunotherapy, can nowadays cure almost all types of cancer, we still fail to achieve this for a substantial proportion of patients. The understanding of differences in metabolism, pharmacokinetics, pharmacodynamics, and tumour biology between patients that can be cured and patients that cannot, builds the scientific basis for rational therapy improvements. Here, we summarise current knowledge of how tumour-specific and patient-specific factors can dictate resistance to nucleobase/nucleoside analogues, and which strategies of re-sensitisation exist. We revisit well-established hurdles to treatment efficacy, like the blood-brain barrier and reduced deoxycytidine kinase activity, but will also discuss the role of novel resistance factors, such as SAMHD1. A comprehensive appreciation of the complex mechanisms that underpin the failure of chemotherapy will hopefully inform future strategies of personalised medicine.

Tyr1-ψ[( Z)CF═CH]-Gly2 Fluorinated Peptidomimetic Improves Distribution and Metabolism Properties of Leu-Enkephalin

Opioid peptides are key regulators in cellular and intercellular physiological responses, and could be therapeutically useful for modulating several pathological conditions. Unfortunately, the use of peptide-based agonists to target centrally located opioid receptors is limited by poor physicochemical (PC), distribution, metabolic, and pharmacokinetic (DMPK) properties that restrict penetration across the blood-brain barrier via passive diffusion. To address these problems, the present paper exploits fluorinated peptidomimetics to simultaneously modify PC and DMPK properties, thus facilitating entry into the central nervous system. As an initial example, the present paper exploited the Tyr¹-ψ[( Z)CF═CH]-Gly² peptidomimetic to improve PC druglike characteristics (computational), plasma and microsomal degradation, and systemic and CNS distribution of Leu-enkephalin (Tyr-Gly-Gly-Phe-Leu). Thus, the fluoroalkene replacement transformed an instable in vitro tool compound into a stable and centrally distributed in vivo probe. In contrast, the Tyr¹-ψ[CF₃CH₂-NH]-Gly² peptidomimetic decreased stability by accelerating proteolysis at the Gly³-Phe⁴ position.

Intranasal rifampicin for Alzheimer's disease prevention

Introduction

Oral rifampicin has been shown to significantly reduce amyloid β (Aβ) and tau pathologies in mice. However, it shows occasional adverse effects such as liver injury in humans, making its use difficult for a long period.

Methods

To explore safer rifampicin treatment, APP_OSK mice, a model of Alzheimer's disease, were treated with rifampicin for 1 month via oral, intranasal, and subcutaneous administration, and its therapeutic efficacy and safety were compared.

Results

Intranasal or subcutaneous administration of rifampicin improved memory more effectively than oral administration. The improvement of memory was accompanied with the reduction of neuropathologies, including Aβ oligomer accumulation, tau abnormal phosphorylation, and synapse loss. Serum levels of a liver enzyme significantly rose only by oral administration. Pharmacokinetic study revealed that the level of rifampicin in the brain was highest with intranasal administration.

Discussion

Considering its easiness and noninvasiveness, intranasal administration would be the best way for long-term dosing of rifampicin.

Bioreducible Polymeric Nanoparticles Containing Multiplexed Cancer Stem Cell Regulating miRNAs Inhibit Glioblastoma Growth and Prolong Survival

Despite our growing molecular-level understanding of glioblastoma (GBM), treatment modalities remain limited. Recent developments in the mechanisms of cell fate regulation and nanomedicine provide new avenues by which to treat and manage brain tumors via the delivery of molecular therapeutics. Here, we have developed bioreducible poly(β-amino ester) nanoparticles that demonstrate high intracellular delivery efficacy, low cytotoxicity, escape from endosomes, and promotion of cytosol-targeted environmentally triggered cargo release for miRNA delivery to tumor-propagating human cancer stem cells. In this report, we combined this nanobiotechnology with newly discovered cancer stem cell inhibiting miRNAs to develop self-assembled miRNA-containing polymeric nanoparticles (nano-miRs) to treat gliomas. We show that these nano-miRs effectively intracellularly deliver single and combination miRNA mimics that inhibit the stem cell phenotype of human GBM cells in vitro. Following direct intratumoral infusion, these nano-miRs were found to distribute through the tumors, inhibit the growth of established orthotopic human GBM xenografts, and cooperatively enhance the response to standard-of-care γ radiation. Co-delivery of two miRNAs, miR-148a and miR-296-5p, within the bioreducible nano-miR particles enabled long-term survival from GBM in mice.

In vitro P-glycoprotein activity does not completely explain in vivo efficacy of novel centrally effective oxime acetylcholinesterase reactivators

Novel-substituted phenoxyalkyl pyridinium oxime acetylcholinesterase (AChE) reactivators (US patent 9,227,937) that showed convincing evidence of penetration into the brains of intact rats were developed by our laboratories. The oximes separated into three groups based on their levels of brain AChE reactivation following exposure of rats to the sarin surrogate nitrophenyl isopropyl methylphosphonate (NIMP). P-glycoprotein (P-gp) is a major blood-brain barrier (BBB) transporter and requires ATP for efflux. To determine if P-gp affinity screening could be used to reduce animal use, we measured in vitro oxime-stimulated ATPase activity to see if the in vivo reactivation efficacies related to the oximes' functions as P-gp substrates. High efficacy oximes were expected to be poor P-gp substrates, thus remaining in the brain longer. The high efficacy oximes (24-35% brain AChE reactivation) were worse P-gp substrates than the low efficacy oximes (0-7% brain AChE reactivation). However, the oxime group with medium in vivo reactivation of 10-17% were even worse P-gp substrates than the high efficacy group so their reactivation ability was not reflected by P-gp export. The results suggest that in vitro P-gp ATPase activity can remove the low efficacy oximes from in vivo testing, but is not sufficient to differentiate between the top two tiers.

Dopamine and Levodopa Prodrugs for the Treatment of Parkinson's Disease

Background: Parkinson's disease is an aggressive and progressive neurodegenerative disorder that depletes dopamine (DA) in the central nervous system. Dopamine replacement therapy, mainly through actual dopamine and its original prodrug l-dopa (LD), faces many challenges such as poor blood brain barrier penetration and decreased response to therapy with time. Methods: The prodrugs described herein are ester, amide, dimeric amide, carrier-mediated, peptide transport-mediated, cyclic, chemical delivery systems and enzyme-models prodrugs designed and made by chemical means, and their bioavailability was studied in animals. Results: A promising ester prodrug for intranasal delivery has been developed. LD methyl ester is currently in Phase III clinical trials. A series of amide prodrugs were synthesized with better stability than ester prodrugs. Both amide and dimeric amide prodrugs offer enhanced blood brain barrier (BBB) penetration and better pharmacokinetics. Attaching LD to sugars has been used to exploit glucose transport mechanisms into the brain. Conclusions: Till now, no DA prodrug has reached the pharmaceutical market, nevertheless, the future of utilizing prodrugs for the treatment of PD seems to be bright. For instance, LD ester prodrugs have demonstrated an adequate intranasal delivery of LD, thus enabling the absorption of therapeutic agents to the brain. Most of the amide, cyclic, peptidyl or chemical delivery systems of DA prodrugs demonstrated enhanced pharmacokinetic properties.

Remodeling the blood-brain barrier microenvironment by natural products for brain tumor therapy

Brain tumor incidence shows an upward trend in recent years; brain tumors account for 5% of adult tumors, while in children, this figure has increased to 70%. Moreover, 20%-30% of malignant tumors will eventually metastasize into the brain. Both benign and malignant tumors can cause an increase in intracranial pressure and brain tissue compression, leading to central nervous system (CNS) damage which endangers the patients' lives. Despite the many approaches to treating brain tumors and the progress that has been made, only modest gains in survival time of brain tumor patients have been achieved. At present, chemotherapy is the treatment of choice for many cancers, but the special structure of the blood-brain barrier (BBB) limits most chemotherapeutic agents from passing through the BBB and penetrating into tumors in the brain. The BBB microenvironment contains numerous cell types, including endothelial cells, astrocytes, peripheral cells and microglia, and extracellular matrix (ECM). Many chemical components of natural products are reported to regulate the BBB microenvironment near brain tumors and assist in their treatment. This review focuses on the composition and function of the BBB microenvironment under both physiological and pathological conditions, and the current research progress in regulating the BBB microenvironment by natural products to promote the treatment of brain tumors.

The effects of dietary and herbal phytochemicals on drug transporters

Membrane transporter proteins (the ABC transporters and SLC transporters) play pivotal roles in drug absorption and disposition, and thus determine their efficacy and safety. Accumulating evidence suggests that the expression and activity of these transporters may be modulated by various phytochemicals (PCs) found in diets rich in plants and herbs. PC absorption and disposition are also subject to the function of membrane transporter and drug metabolizing enzymes. PC-drug interactions may involve multiple major drug transporters (and metabolizing enzymes) in the body, leading to alterations in the pharmacokinetics of substrate drugs, and thus their efficacy and toxicity. This review summarizes the reported in vitro and in vivo interactions between common dietary PCs and the major drug transporters. The oral absorption, distribution into pharmacological sanctuaries and excretion of substrate drugs and PCs are considered, along with their possible interactions with the ABC and SLC transporters which influence these processes.

Organic cation transporter 1 (OCT1) is involved in pentamidine transport at the human and mouse blood-brain barrier (BBB)

Pentamidine is an effective trypanocidal drug used against stage 1 Human African Trypanosomiasis (HAT). At the blood-brain barrier (BBB), it accumulates inside the endothelial cells but has limited entry into the brain. This study examined transporters involved in pentamidine transport at the human and mouse BBB using hCMEC/D3 and bEnd.3 cell lines, respectively. Results revealed that both cell lines expressed the organic cation transporters (OCT1, OCT2 and OCT3), however, P-gp was only expressed in hCMEC/D3 cells. Polarised expression of OCT1 was also observed. Functional assays found that ATP depletion significantly increased [³H]pentamidine accumulation in hCMEC/D3 cells (***p<0.001) but not in bEnd.3 cells. Incubation with unlabelled pentamidine significantly decreased accumulation in hCMEC/D3 and bEnd.3 cells after 120 minutes (***p<0.001). Treating both cell lines with haloperidol and amantadine also decreased [³H]pentamidine accumulation significantly (***p<0.001 and **p<0.01 respectively). However, prazosin treatment decreased [³H]pentamidine accumulation only in hCMEC/D3 cells (*p<0.05), and not bEnd.3 cells. Furthermore, the presence of OCTN, MATE, PMAT, ENT or CNT inhibitors/substrates had no significant effect on the accumulation of [³H]pentamidine in both cell lines. From the data, we conclude that pentamidine interacts with multiple transporters, is taken into brain endothelial cells by OCT1 transporter and is extruded into the blood by ATP-dependent mechanisms. These interactions along with the predominant presence of OCT1 in the luminal membrane of the BBB contribute to the limited entry of pentamidine into the brain. This information is of key importance to the development of pentamidine based combination therapies which could be used to treat CNS stage HAT by improving CNS delivery, efficacy against trypanosomes and safety profile of pentamidine.

Evaluation of red and near infrared fluorescent silver nanoclusters as potential in vivo indicators of tight junction opening

A double fluorescence probe strategy based on silver nanoclusters for study of the TJ structure change.

Exploring tight junction alteration using double fluorescent probe combination of lanthanide complex with gold nanoclusters

Tight junctions play a key role in restricting or regulating passage of liquids, ions and large solutes through various biological barriers by the paracellular route. Changes in paracellular permeation indicate alteration of the tight junction. However, it is very difficult to obtain the structural change information by measuring paracellular flux based on transepithelial electrical resistance or using fluorescein-labeled dextrans. Here we show that the BSA and GSH stabilized gold nanoclusters exhibit marginal cytotoxicity and pass through the MDCK monolayer exclusively through the paracellular pathway. We propose a double fluorescence probe strategy, the combination of a proven paracellular indicator (europium complex) with fluorescent gold nanoclusters. We calculate changes of structural parameters in tight junctions based on determination of the diffusion coefficients of the probes. Two different types of tight junction openers are used to validate our strategy. Results show that EDTA disrupts tight junction structures and induces large and smooth paracellular pore paths with an average radius of 17 nm, but vanadyl complexes induce paths with the radius of 6 nm. The work suggests that the double fluorescence probe strategy is a useful and convenient approach for in vitro investigation of tight junction structural alternations caused by pharmacological or pathological events.

Distribution of polymer nanoparticles by convection-enhanced delivery to brain tumors

Glioblastoma multiforme (GBM) is a fatal brain tumor characterized by infiltration beyond the margins of the main tumor mass and local recurrence after surgery. The blood-brain barrier (BBB) poses the most significant hurdle to brain tumor treatment. Convection-enhanced delivery (CED) allows for local administration of agents, overcoming the restrictions of the BBB. Recently, polymer nanoparticles have been demonstrated to penetrate readily through the healthy brain when delivered by CED, and size has been shown to be a critical factor for nanoparticle penetration. Because these brain-penetrating nanoparticles (BPNPs) have high potential for treatment of intracranial tumors since they offer the potential for cell targeting and controlled drug release after administration, here we investigated the intratumoral CED infusions of PLGA BPNPs in animals bearing either U87 or RG2 intracranial tumors. We demonstrate that the overall volume of distribution of these BPNPs was similar to that observed in healthy brains; however, the presence of tumors resulted in asymmetric and heterogeneous distribution patterns, with substantial leakage into the peritumoral tissue. Together, our results suggest that CED of BPNPs should be optimized by accounting for tumor geometry, in terms of location, size and presence of necrotic regions, to determine the ideal infusion site and parameters for individual tumors.

Glucose Transporters at the Blood-Brain Barrier: Function, Regulation and Gateways for Drug Delivery

Glucose transporters (GLUTs) at the blood-brain barrier maintain the continuous high glucose and energy demands of the brain. They also act as therapeutic targets and provide routes of entry for drug delivery to the brain and central nervous system for treatment of neurological and neurovascular conditions and brain tumours. This article first describes the distribution, function and regulation of glucose transporters at the blood-brain barrier, the major ones being the sodium-independent facilitative transporters GLUT1 and GLUT3. Other GLUTs and sodium-dependent transporters (SGLTs) have also been identified at lower levels and under various physiological conditions. It then considers the effects on glucose transporter expression and distribution of hypoglycemia and hyperglycemia associated with diabetes and oxygen/glucose deprivation associated with cerebral ischemia. A reduction in glucose transporters at the blood-brain barrier that occurs before the onset of the main pathophysiological changes and symptoms of Alzheimer's disease is a potential causative effect in the vascular hypothesis of the disease. Mutations in glucose transporters, notably those identified in GLUT1 deficiency syndrome, and some recreational drug compounds also alter the expression and/or activity of glucose transporters at the blood-brain barrier. Approaches for drug delivery across the blood-brain barrier include the pro-drug strategy whereby drug molecules are conjugated to glucose transporter substrates or encapsulated in nano-enabled delivery systems (e.g. liposomes, micelles, nanoparticles) that are functionalised to target glucose transporters. Finally, the continuous development of blood-brain barrier in vitro models is important for studying glucose transporter function, effects of disease conditions and interactions with drugs and xenobiotics.