Physiology, Pharmacology and Pathology of the Blood-Brain Barrier (Handbook of Experimental Pharmacology, 273)

This book presents a comprehensive collection of current knowledge and leading research about the blood-brain barrier. The chapters are organized in four main parts providing basic information and novel insights about the physiology of the blood-brain barrier, the challenges related to finding and developing drugs crossing the blood-brain barrier, experimental methods to study the blood-brain barrier and the role of the blood-brain barrier in disease mechanisms and its consequences for drug development. In the first part the readers will discover the structure, function and developmental aspects of the blood-brain barrier and gain novel insights into the complexity and functionality of the neurovascular unit and energy metabolism of brain endothelial cells. Chapters of the second part focus on translational challenges from the bench to the bedside in CNS drug development, shed light on the importance to understand the brain distribution of drugs related to their efficacy, elaborate on general pharmacokinetic considerations for CNS drugs and introduce current and novel drug delivery strategies to overcome the blood-brain barrier. The experimental part of the book covers mathematical and in vitro models as well as animal and human methods in blood-brain barrier research. Specific emphasis is set on the description of the methods, the role of species differences for data interpretation, novel human models based on stem cells with the potential for personalized medicine and technical considerations and tips helpful for readers interested in working with these models. In the fourth part particular attentions is given to the blood-brain barrier, its changes and participation during disease progression. Chapters summarize alterations of the blood-brain barrier that are present in common disorders such as Alzheimer’s disease, multiple sclerosis, stroke, traumatic brain injury, epilepsy and brain tumors. Present therapies will be discussed and the consequences for novel treatment approaches that need to bypass the blood-brain-barrier will be explored. In addition, experts discuss the question in how far changes at the blood-brain barrier are causally linked to disease progressions and consequently could serve as therapeutic targets. This collection is designed to appeal to a wide readership from students through basic and applied scientist to pharmacologists, medical doctors and stakeholders from the pharmaceutical industry and regulatory affairs. Due its comprehensive content the book has the potential to become a standard work in the field of blood-brain barrier research. Preface Contents Part I: Background on the Blood-Brain Barrier Structure and Function of the Blood-Brain Barrier (BBB) 1 Background on the BBB Structure and Function 1.1 Definition of the BBB 1.2 Molecular Composition of BCEC Junctions 1.3 Transport and Metabolic Barrier 1.4 BBB Formation and Maintenance 1.5 Transport at the BBB 2 Vessel and BBB Heterogeneity in the CNS 2.1 Circumventricular Organs (CVOs) 2.1.1 Common Features of CVOs Endothelial Cells Organization of the NVU Barrier Heterogeneity Within the CVOs 2.1.2 Fluid and Sodium Homeostasis 2.2 Barrier Properties in the Choroid Plexus 2.3 Barrier Properties in the Cerebellum vs. Cortex 2.4 Blood-Spinal Cord Barrier 2.5 BBB at Sites of Adult Neurogenesis 3 Neurovascular Coupling 3.1 Neuronal Activity 4 Outlook References New Insights in the Complexity and Functionality of the Neurovascular Unit 1 Introduction 2 Intricate Interplay Between Blood Vessels and Brain Parenchyma During Brain Development 3 Structural Diversity of the Neurovascular Unit 4 Revisiting the Complexity of the Neurovascular Unit: The Cellular Composition and Function 4.1 Endothelial Cells 4.2 Mural Cells: Pericytes and Vascular Smooth Muscle Cells 4.3 Astrocytes 4.4 Microglia 4.5 Perivascular Macrophages 4.6 Perivascular Fibroblast-Like Cells 5 Gut-Brain Axis Regulating Integrity and Function of Neurovascular Unit 6 Conclusion References Brain Endothelial Cells: Metabolic Flux and Energy Metabolism 1 Introduction 2 Materials and Methods 2.1 Cell Culture 2.2 Extracellular Flux Analysis 2.3 Day Prior to Assay 2.4 Day of Assay 2.5 Mitochondrial Stress Test 2.6 Glycolytic Rate Assay 2.7 ATP Rate Assays 2.8 Calculations 3 Results 3.1 OCR and ECAR Measurements Reveal Glycolytic Nature of Brain Endothelial Cells 4 Discussion References Part II: Challenges with Findings Drugs to Cross the Blood-Brain Barrier Considerations When Developing Blood-Brain Barrier Crossing Drug Delivery Technology 1 Biological Barriers to CNS Drug Delivery Box 1 The BBB Glycocalyx 2 Carrier Transport and Receptor-Mediated Transcytosis at the BBB 3 Lessons from Neurotrophic Pathogens 4 BBB-Crossing Adeno-Associated Virus Capsids 5 Confirming and Identifying New Targets 6 Considerations for In Vivo Validation Studies 7 Manufacturing Considerations and Challenges 8 Concluding Remarks References Brain Distribution of Drugs: Brain Morphology, Delivery Routes, and Species Differences 1 Introduction 2 The Prominent Role of Distribution 3 Brain Heterogeneity 3.1 Anatomical Differences and Regional Heterogeneity 3.2 Different Cellular Types 3.3 Biochemical Heterogeneity 3.4 Transporters Heterogeneity 4 Fluids and Dynamics 5 Barriers in the CNS 5.1 The Blood-Brain Barrier 5.2 The Brain ECF-ICF Barrier 5.3 The CSF-ECF Barrier 5.4 The Blood-CSF Barrier 6 Delivery Routes 7 Neuropharmacokinetic Imaging and Interspecies Differences 7.1 Variability in Transporter Expression/Activity at the BBB 7.2 Variability in Brain Target Expression/Distribution 8 Conclusions References Brain Distribution of Drugs: Pharmacokinetic Considerations 1 Introduction to CNS Drug Distribution 2 Key Parameters for Characterization of CNS Drug Distribution Key Definitions 2.1 Drug Transport Across CNS Barriers with Focus on BBB and BCSFB 2.1.1 Unbound Brain to Plasma Concentration Ratio, Kp,uu,brain Underlying Principles Current and Emerging Methodologies Applications in Drug Development 2.1.2 Unbound CSF to Plasma Concentration Ratio, Kp,uu,CSF Underlying Principles Current and Emerging Methodologies Applications in Drug Development 2.2 Drug Distribution within the Brain Parenchyma 2.2.1 Unbound Volume of Distribution in the Brain, Vu,brain Underlying Principles Current and Emerging Methodologies Applications in Drug Development 2.2.2 Fraction of Unbound Drug in the Brain, fu,brain Underlying Principles Current and Emerging Methodologies Applications in Drug Development 2.2.3 Unbound Intracellular to Extracellular Concentration Ratio, Kp,uu,cell Underlying Principles Current and Emerging Methodologies Applications in Drug Development 3 Small vs Large Molecules: Pharmacokinetic Differences 4 Optimization of Experimental Design for Neuropharmacokinetic Studies 5 Conclusions and Future Directions References Drug Delivery Strategies to Overcome the Blood-Brain Barrier (BBB) 1 Introduction 2 Drug Delivery and Blood-Brain Barrier Function 3 Delivery of ``Small Molecules ́ ́ to the Brain 4 The Efflux Transporter Inhibition Concept 5 Receptor-Mediated Uptake of Therapeutic Antibodies 6 Peptides as Brain Drug Delivery Vectors 6.1 Cell-Penetrating Peptides as Brain Drug Delivery Vectors 6.2 Blood-Brain Barrier Receptor Targeting Peptides for Brain Drug Delivery 7 Viral Delivery to the Brain 7.1 Targeting Viral Vectors to the Brain 7.2 Mechanisms of Underlying Brain Delivery of Viral Vectors 8 Invasive Delivery; Osmosis and Ultrasound 9 Conclusions and Perspectives References Part III: Experimental Methods to Study Drug Transport across the Blood-Brain Barrier In Vitro and In Vivo Transport Studies Using Blood-Brain Barrier In Vitro Models: A Critical Review and Guidelines 1 Introduction 2 In Vitro Permeability Measurements 2.1 Apparent Permeability Coefficient 2.2 Endothelial Permeability Coefficient 2.3 Efflux Ratio as a Measurement of Active Efflux 3 Permeability Studies to Measure Barrier Tightness 3.1 Factors Influencing BBB Permeability Results 3.2 Importance of Recovery Values 3.3 Importance of the Materials Used in the Permeability Assay 3.4 Influence of Mechanical Forces 3.5 Plasma Protein Binding and Brain Tissue Binding 3.6 Example of Normalization: Diazepam 4 Transendothelial Electrical Resistance Measurements 5 Conclusion References Human Blood-Brain-Barrier In Vitro Models: Overview and Applications 1 Introduction 2 Key Features of BBB Endothelial Cells and Their Models 3 Sourcing Brain Endothelial Cells 3.1 Primary and Immortalised Cultures of Cerebral Endothelial Cells 3.2 IPSC Derived Endothelial Cells 4 The Importance of the BBB Niche 4.1 Astrocytes and Pericytes 4.2 Extracellular Matrix 5 Types of In Vitro BBB Models 5.1 Transwell Models 5.2 Dynamic Models 5.3 Organoid-Like Models 5.4 Extracellular Matrix-Based 3D BBB Models 6 Applications of BBB Models 6.1 Disease Mechanism and Target Discovery 6.2 Toxicology 6.3 BBB Barrier and Transport Function 7 Limitations and Challenges for Current Brain Capillary Endothelial Cell Differentiation Protocols 8 Conclusions References In Vivo Studies of Drug BBB Transport: Translational Challenges and the Role of Brain Imaging 1 Introduction to In Vivo Assessment of Drug Transport Across the BBB 2 Methods to Study BBB Drug Transport In Vivo 2.1 Brain Microdialysis 2.2 Molecular Brain Imaging 2.3 Two-Photon Laser Scanning Fluorescence Microscopy 2.4 CSF Sampling 2.5 Combined In Vivo-In Vitro Assessment: The Combinatory Mapping Approach 3 In Vivo Models of Disease 3.1 Chemically Induced Models 3.2 Genetically Modified Models 4 Translational Aspects of BBB Drug Transport 5 Conclusions and Future Directions References Part IV: The Blood-Brain Barrier and Diseases: Novel Treatment Approaches from a Blood-Brain Barrier Perspective The Blood-Brain Barrier in Alzheimer ́s Disease 1 Amyloid Dynamics at the Blood-Brain Barrier 2 P-gp- and LRP1-Mediated Aβ Transport Across the Blood-Brain Barrier 3 RAGE-Mediated Aβ Transport Across the Blood-Brain Barrier 4 Transmission of Aβ Protein Pathology Via Peripheral Blood Sources 5 Changes of Blood-Brain Barrier Function in Alzheimer ́s Disease 6 Current Treatment Approaches 7 Summary and Future Perspectives References Blood-Brain Barrier Mechanisms in Stroke and Trauma 1 Pathophysiology of BBB Disruption After Brain Injury 1.1 Time Course of BBB Dysregulation 1.1.1 Time Course of BBB Dysregulation in TBI 1.1.2 Time Course of BBB Dysregulation in Stroke 1.2 Cell-Cell Interactions in BBB Dysregulation 1.2.1 Endothelial-Pericyte Interactions 1.2.2 Endothelial-Astrocyte Interactions 1.3 Common Events in BBB Dysregulation After TBI and Stroke 1.3.1 Gene Expression 1.3.2 Immune Response 1.3.3 Inflammation 1.3.4 Edema 1.3.5 Cell Death 2 Molecular Mechanisms of BBB Dysfunction in Stroke and TBI 2.1 Paracellular Mechanisms 2.1.1 Down-Regulated Expression of Junctional Proteins 2.1.2 Translocation of Junctional Proteins 2.2 Transcellular Mechanisms 2.2.1 BBB Transporters Nutrient Transporters ABC Transporters 2.2.2 Transcytosis 3 Therapeutic Interventions for BBB Dysfunction After TBI and Stroke 3.1 Antioxidant BBB Therapies for TBI and Stroke 3.2 Anti-inflammatory BBB Therapies for TBI and Stroke 4 Conclusions References Brain Barriers and Multiple Sclerosis: Novel Treatment Approaches from a Brain Barriers Perspective 1 Introduction 2 The Brain Barriers (Fig. 1) 2.1 The Endothelial Blood-Brain Barrier (BBB) 2.2 Glia Limitans 2.3 Choroid Plexus and Blood-Cerebrospinal Fluid Barrier (BCSFB) 2.4 Additional Brain Barriers 3 Cell Trafficking Across Brain Barriers 3.1 Immune Cell Trafficking Across the BBB 3.2 Immune Cell Trafficking Across the Glia Limitans 3.3 Immune Cell Trafficking via the Choroid Plexus 3.4 Immune Cell Trafficking Across Additional Barriers 4 Mechanisms of Brain Barriers Impairment in MS 4.1 BBB 4.2 The Glia Limitans 4.3 Blood-Cerebrospinal Fluid Barrier (BCSFB) of the Choroid Plexus 4.4 Arachnoid Barrier 5 Therapeutic Strategies Targeting Brain Barriers 5.1 Current MS Therapies Directly Targeting Brain Barriers 5.1.1 BBB Stabilizing Effects 5.2 Current MS Therapies Indirectly Targeting the Brain Barriers 6 Future Directions for Direct or Indirect Therapeutic Targeting of the Brain Barriers for Treating MS 6.1 Direct Targeting Approaches 6.2 Indirect Targeting Approaches 7 Conclusions and Outlook Glossary References Epilepsy and Alterations of the Blood-Brain Barrier: Cause or Consequence of Epileptic Seizures or Both? 1 Introduction 2 Morphological Alterations of the BBB in Epilepsy 3 Why Do Seizures Alter the Morphology and Functionality of the BBB? 4 Impairment of BBB Function in Epilepsy, Leading to Increased Brain Uptake of Xenobiotics and Albumin 5 Increased Efflux Transport at the BBB in Epilepsy, Leading to Decreased Brain Uptake of Antiepileptic Drugs: a Role in Drug ... 6 Impairment of Barrier Function of the BBB in Epilepsy, Leading to Invasion of Inflammatory Cells Into the Brain 7 Impairment of Barrier Function of the BBB Following Brain Injury: Role in the Development of Epilepsy? 8 Conclusions References Novel Treatment Approaches for Brain Tumour from a Blood-Brain Barrier Perspective 1 BBB Basics 2 BBB and BBTB 3 Current Chemotherapeutic Drugs for Brain Tumour 4 Current Strategies for Overcoming the BBB/BBTB 4.1 Convection-Enhanced Delivery by Direct Injection 4.2 Implantation of Wafers, Gels, and Microchips 4.3 Inhibition of Drug Efflux Transporters 4.4 Non-invasive BBB/BBTB Permeability Enhancement 4.4.1 Osmotic BBB/BBTB Opening 4.4.2 Focused Ultrasound-Induced BBB Opening References