Uptake Transporters at the Blood-Brain Barrier and Their Role in Brain Drug Disposition

Nanomedicine in the treatment of Alzheimer's disease: bypassing the blood-brain barrier with cutting-edge nanotechnology

Alzheimer's disease (AD) remains a formidable challenge in the field of neurodegenerative disorders, necessitating innovative therapeutic strategies. Nanomedicine, leveraging nanomaterials, has emerged as a promising avenue for AD treatment, with a key emphasis on overcoming the blood-brain barrier (BBB) to enhance drug delivery efficiency. This review provides a comprehensive analysis of recent advancements in the application of nanomaterials for AD therapy, highlighting their unique properties and functions. The blood-brain barrier, a complex physiological barrier, poses a significant hurdle for traditional drug delivery to the brain. Nanomedicine addresses this challenge by utilizing various nanomaterials such as liposomes, polymeric nanoparticles, and metal nanoparticles. These nanocarriers enable improved drug bioavailability, sustained release, and targeted delivery to specific brain regions affected by AD pathology. The review discusses the diverse range of nanomaterials employed in AD treatment, exploring their capacity to encapsulate therapeutic agents, modulate drug release kinetics, and enhance drug stability. Additionally, the multifunctionality of nanomaterials allows for simultaneous imaging and therapy, facilitating early diagnosis and intervention. Key aspects covered include the interaction of nanomaterials with Aβ aggregates, the role of antioxidants in mitigating oxidative stress, and the potential of nanomedicine in alleviating neuroinflammation associated with AD. Furthermore, the safety, biocompatibility, and toxicity profiles of various nanomaterials are scrutinized to ensure their clinical applicability. In conclusion, this review underscores the pivotal role of nanomedicine and nanomaterials in revolutionizing AD treatment strategies. By specifically addressing BBB challenges, these innovative approaches offer new avenues for targeted drug delivery and improved therapeutic outcomes in the complex landscape of Alzheimer's disease.

Targeted and Untargeted Proteomics-based Comparison of Adenoviral Infected hCMEC/D3 and hBMEC as a Human Brain Endothelial Cells to Study the OATP2B1 Transporter

The blood-brain barrier (BBB) is essential for central nervous system (CNS) homeostasis by regulating permeability between the bloodstream and brain. This study evaluates the immortalized human brain capillary endothelial cell lines hCMEC/D3 and hBMEC for their use as a brain endothelial cells to investigate the OATP2B1 transporter following adenoviral infection. We assessed the impact of adenoviral-mediated OATP2B1 expression on BBB marker proteins and transporters using targeted and untargeted mass spectrometry-based proteomics. Targeted proteomics identified measurable levels of endothelial markers PECAM1 and CDH5 in hCMEC/D3, whereas these markers were undetectable in hBMEC. Both cell lines exhibited similar Pgp levels, while BCRP was absent in hCMEC/D3. The expression of uptake transporters was also evaluated, revealing comparable levels of GLUT1, ENT1, MCT1 and OAT7 in hCMEC/D3 and hBMEC. Although OATP2B1 levels did not significantly increase post-infection in targeted proteomics, untargeted proteomics confirmed enhanced OATP2B1 expression. Other BBB markers and transporters remained unaffected in both cell lines. Notably, hCMEC/D3 demonstrated a stronger BBB phenotype, indicated by higher expression of BBB markers and transporters, while adenoviral infection was more effective in hBMEC. The differences between targeted and untargeted proteomics underscore the need for diverse methods to verify protein expression levels. This comparative analysis provides insights into the strengths and limitations of hCMEC/D3 and hBMEC for BBB research, particularly regarding drug transport mechanisms.

ROS Regulation in CNS Disorder Therapy: Unveiling the Dual Roles of Nanomedicine

The treatment of brain diseases has always been the focus of attention. Due to the presence of the blood-brain barrier (BBB), most small molecule drugs are difficult to reach the brain, leading to undesirable therapeutic outcomes. Recently, nanomedicines that can cross the BBB and precisely target lesion sites have emerged as thrilling tools to enhance the early diagnosis and treat various intractable brain disorders. Extensive research has shown that reactive oxygen species (ROS) play a crucial role in the occurrence and progression of brain diseases, including brain tumors and neurodegenerative diseases (NDDs) such as Alzheimer's disease, Parkinson's disease, stroke, or traumatic brain injury, making ROS a potential therapeutic target. In this review, on the structure and function of BBB as well as the mechanisms are first elaborated through which nanomedicine traverses it. Then, recent studies on ROS production are summarized through photodynamic therapy (PDT), chemodynamic therapy (CDT), and sonodynamic therapy (SDT) for treating brain tumors, and ROS depletion for treating NDDs. This provides valuable guidance for the future design of ROS-targeted nanomedicines for brain disease treatment. The ongoing challenges and future perspectives in developing nanomedicine-based ROS management for brain diseases are also discussed and outlined.

Pregnenolone Sulfate Permeation at the Blood-Brain Barrier is Independent of OATP2B1-In Vivo and In Vitro Insights

Sulfated steroids such as pregnenolone sulfate (PregS) are important for neuronal development and cognitive functions. Given the hydrophilic sulfate moiety, it is assumed that PregS requires an active transport mechanism to cross the blood-brain barrier (BBB). The human organic anion transporting polypeptide (OATP)2B1 has been previously shown to transport sulfated steroids and is therefore a proposed candidate for the transport of PregS. In this study, we aimed to investigate the role of OATP2B1 in the uptake of PregS in the brain. Tritium-labeled PregS was intravenously administered to humanized (SLCO2B1+/+), knockout (rSlco2b1-/-), and wildtype (WT) rats. Accumulation of the radiotracer was analyzed in rat brain, liver, small intestine, kidney, heart, and muscle. Moreover, transporter expression in brain microvessels was assessed through targeted proteomics and Western blot analysis. The involvement of hOATP2B1 in PregS transport across the BBB was further studied using a hBMEC-based in vitro BBB model. Our results indicated no significant difference in accumulation of the radiotracer among the different rat genotypes in the brain or in other tissues. In line with what we observed in the rat model, the subsequent in vitro study showed no involvement of hOATP2B1 in the transport of PregS. Taken together, our findings highlight the species-specific differences in transporter expression and suggest that OATP2B1 does not mediate PregS uptake across the BBB.

Brain endothelial permeability, transport, and flow assessed over 10 orders of magnitude using the in situ brain perfusion technique

BACKGROUND

Cerebral blood flow normally places a limit on the magnitude of brain vascular permeability (P) that can be measured in vivo. At normal cerebral blood flow, this limit falls at the lower end of lipophilicity for most FDA-approved CNS drugs. In this study, we report on two methods that can be used to overcome this limitation and measure brain vascular permeability values that are up to ~1000 times higher using the in situ brain perfusion technique.

METHODS

Rat brain was perfused with physiological saline at increased flow rate and in the presence of various concentrations of plasma protein, serum albumin or alpha-acid glycoprotein. Plasma protein was added to the saline perfusion fluid to lower extraction into the measurable range using the Crone Renkin "diffusion-flow" equation to calculate brain PoS.

RESULTS

Cerebrovascular Po was determined for 125 solutes, of which 78 showed little or no evidence of active efflux transport. Fifty of the solutes were in the lipophilicity zone (Log Poct 1-5) of most FDA-approved CNS drugs. Care was taken to ensure the integrity of the brain vasculature during perfusion and to measure flow accurately using markers that had been verified for the flow rates. The results showed a linear relationship between Log Po and Log Poct over ~10 orders of magnitude with values for diazepam, estradiol, testosterone, and other agents that exceed prior published values by fivefold to 200-fold.

CONCLUSIONS

The results show that brain vascular permeability can be measured directly in vivo for highly lipophilic solutes and the PS values obtained match reasonably with that predicted by the Crone-Renkin flow diffusion equation with care taken to validate the accuracy for the component measurements and with no need to invoke "enhanced" or "induced" dissociation.

Rare Diseases Linked to Mutations in Vitamin Transporters Expressed in the Human Blood-Brain Barrier

Recent advances have significantly enhanced our understanding of the role of membrane transporters in drug disposition, particularly focusing on their influence on pharmacokinetics, and consequently, pharmacodynamics. The relevance of these transporters in clinical pharmacology is well acknowledged. Recent research has also underscored the critical role of membrane transporters as targets in human diseases, including their involvement in rare genetic disorders. This review focuses on transporters for water-soluble B vitamins, such as thiamine, riboflavin, and biotin, essential cofactors for metabolic enzymes. Mutations in transporters, such as SLC19A3 (thiamine), SLC52A2, and SLC52A3 (riboflavin), and SLC5A6 (multiple B vitamins including pantothenic acid and biotin) are linked to severe neurological disorders due to their role in the blood-brain barrier, which is crucial for brain vitamin supply. Current treatments, mainly involving vitamin supplementation, often result in variable response. This review also provides a short perspective on the role of the transporters in the blood-cerebrospinal fluid barrier and highlights the potential development of pharmacologic treatments for rare disorders associated with mutations in these transporters.

An extended substrate spectrum of the proton organic cation antiporter and relation to other cation transporters

Most central nervous system (CNS) active drugs are organic cations, which need carrier proteins for efficient transfer through the blood-brain barrier (BBB). A genetically still unidentified proton organic cation (H+/OC) antiporter is found in several tissues, including endothelial cells of the BBB. We characterized the substrate spectrum of the H+/OC antiporter and the overlap in substrate spectrum with OCTN1, OCTN2 or OCT3 by screening 87 potential substrates for transport activity. Based on high antiport rates, 45 of the tested substances were substrates of the H+/OC antiporter. They included antidepressants (like tranylcypromine or nortriptyline), antipsychotics (like levomepromazine) and local anaesthetics. Concentration-dependent transport was confirmed for 38 of the substrates. Transport uptake depending on a pH gradient across the cell membrane confirmed that 43 drugs were indeed substrates of the H+/OC antiporter. However, the patterns of pH dependence differed between the substrates, possibly indicating different modes of transport or the existence of multiple antiporter proteins. The substrate overlap between the H+/OC antiporter and OCTN1, OCTN2 or OCT3 was minimal, indicating that the latter three are not the proteins underlying the H+/OC antiporter activity. Overall, about 50% of positively charged drugs may be substrates of the antiporter, which may be the most important membrane transport protein for many drugs.

Unraveling the secrets: Evolution of resistance mediated by membrane proteins

Membrane protein-mediated resistance is a multidisciplinary challenge that spans fields such as medicine, agriculture, and environmental science. Understanding its complexity and devising innovative strategies are crucial for treating diseases like cancer and managing resistant pests in agriculture. This paper explores the dual nature of resistance mechanisms across different organisms: On one hand, animals, bacteria, fungi, plants, and insects exhibit convergent evolution, leading to the development of similar resistance mechanisms. On the other hand, influenced by diverse environmental pressures and structural differences among organisms, they also demonstrate divergent resistance characteristics. Membrane protein-mediated resistance mechanisms are prevalent across animals, bacteria, fungi, plants, and insects, reflecting their shared survival strategies evolved through convergent evolution to address similar survival challenges. However, variations in ecological environments and biological characteristics result in differing responses to resistance. Therefore, examining these differences not only enhances our understanding of adaptive resistance mechanisms but also provides crucial theoretical support and insights for addressing drug resistance and advancing pharmaceutical development.

The role of interferon beta in neurological diseases and its potential therapeutic relevance

Interferon beta (IFNβ) is a member of the type-1 interferon family and has various immunomodulatory functions in neuropathological conditions. Although the level of IFNβ is low under healthy conditions, it is increased during inflammatory processes to protect the central nervous system (CNS). In particular, microglia and astrocytes are the main sources of IFNβ upon inflammatory insult in the CNS. The protective effects of IFNβ are well characterized in reducing the progression of multiple sclerosis (MS); however, little is understood about its effects in other neurological/neurodegenerative diseases. In this review, different types of IFNs and their signaling pathways will be described. Then we will focus on the potential role and therapeutic effect of IFNβ in several CNS-related diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, stroke, spinal cord injury, prion disease and spinocerebellar ataxia 7.

Blood-Nanoparticle Interactions Create a Brain Delivery Superhighway for Doxorubicin

Purpose

This study investigated the brain targeting mechanism of doxorubicin-loaded polybutyl cyanoacrylate (PBCA) nanoparticles, particularly their interactions with the blood-brain barrier (BBB). The BBB protects the brain from drugs in the bloodstream and represents a crucial obstacle in the treatment of brain cancer.

Methods

An advanced computer model analyzed the brain delivery of two distinct formulations, Doxil® and surfactant-coated PBCA nanoparticles. Computational learning was combined with in vitro release and cell interaction studies to comprehend the underlying brain delivery pathways.

Results

Our analysis yielded a surprising discovery regarding the brain delivery mechanism of PBCA nanoparticles. While Doxil® exhibited the expected behavior, accumulating in the brain through extravasation in tumor tissue, PBCA nanoparticles employed a unique and previously uncharacterized mechanism. They underwent cell hitchhiking, resulting in a remarkable more than 1000-fold increase in brain permeation rate compared to Doxil® (2.59 × 10-4 vs 0.32 h-1).

Conclusion

The nonspecific binding to blood cells facilitated and intensified interactions of surfactant-coated PBCA nanoparticles with the vascular endothelium, leading to enhanced transcytosis. Consequently, the significant increase in circulation time in the bloodstream, coupled with improved receptor interactions, contributes to this remarkable uptake of doxorubicin into the brain.

Accurate prediction of Kp,uu,brain based on experimental measurement of Kp,brain and computed physicochemical properties of candidate compounds in CNS drug discovery

A mathematical equation model was developed by building the relationship between the fu,b/fu,p ratio and the computed physicochemical properties of candidate compounds, thereby predicting Kp,uu,brain based on a single experimentally measured Kp,brain value. A total of 256 compounds and 36 marketed published drugs including acidic, basic, neutral, zwitterionic, CNS-penetrant, and non-CNS penetrant compounds with diverse structures and physicochemical properties were involved in this study. A strong correlation was demonstrated between the fu,b/fu,p ratio and physicochemical parameters (CLogP and ionized fraction). The model showed good performance in both internal and external validations. The percentages of compounds with Kp,uu,brain predictions within 2-fold variability were 80.0 %-83.3 %, and more than 90 % were within a 3-fold variability. Meanwhile, "black box" QSAR models constructed by machine learning approaches for predicting fu,b/fu,p ratio based on the chemical descriptors are also presented, and the ANN model displayed the highest accuracy with an RMSE value of 0.27 and 86.7 % of the test set drugs fell within a 2-fold window of linear regression. These models demonstrated strong predictive power and could be helpful tools for evaluating the Kp,uu,brain by a single measurement parameter of Kp,brain during lead optimization for CNS penetration evaluation and ranking CNS drug candidate molecules in the early stages of CNS drug discovery.

Blood-brain barrier transporters: a translational consideration for CNS delivery of neurotherapeutics

INTRODUCTION

Successful neuropharmacology requires optimization of CNS drug delivery and, by extension, free drug concentrations at brain molecular targets. Detailed assessment of blood-brain barrier (BBB) physiological characteristics is necessary to achieve this goal. The 'next frontier' in CNS drug delivery is targeting BBB uptake transporters, an approach that requires evaluation of brain endothelial cell transport processes so that effective drug accumulation and improved therapeutic efficacy can occur.

AREAS COVERED

BBB permeability of drugs is governed by tight junction protein complexes (i.e., physical barrier) and transporters/enzymes (i.e., biochemical barrier). For most therapeutics, a component of blood-to-brain transport involves passive transcellular diffusion. Small molecule drugs that do not possess acceptable physicochemical characteristics for passive permeability may utilize putative membrane transporters for CNS uptake. While both uptake and efflux transport mechanisms are expressed at the brain microvascular endothelium, uptake transporters can be targeted for optimization of brain drug delivery and improved treatment of neurological disease states.

EXPERT OPINION

Uptake transporters represent a unique opportunity to optimize brain drug delivery by leveraging the endogenous biology of the BBB. A rigorous understanding of these transporters is required to improve translation from the bench to clinical trials and stimulate the development of new treatment paradigms for neurological diseases.