Evaluation of blood-brain barrier transport and CNS drug metabolism in diseased and control brain after intravenous L-DOPA in a unilateral rat model of Parkinson's disease

L-DOPA Promotes Functional Proliferation Through GPR143, Specific L-DOPA Receptor of Astrocytes

l-3,4-Dihydroxyphenylalanine (levodopa and L-DOPA in this text), alongside dopamine, boasts high biocompatibility, prompting industrial demand for its use as a coating material. Indeed, the effectiveness of L-DOPA is steadily rising as it serves as an oral therapeutic agent for neurodegenerative brain diseases, particularly Parkinson's disease (PD). However, the effects of L-DOPA on the growth and function of astrocytes, the main glial cells, and the most numerous glial cells in the brain, are unknown. Here, we investigated whether L-DOPA is possible as a coating material on cover glass and polystyrene for rat primary astrocytes. The coating state of L-DOPA on the cover glass and polystyrene was characterized by X-ray photoelectron spectroscopy (XPS) and static water contact angle (WCA). Interestingly, L-DOPA coated on the cover glass promoted the proliferation of astrocytes but not neurons. Furthermore, L-DOPA coated on the cover glass, as opposed to polystyrene, facilitated the proliferation of the astrocytes. The astrocytes grown on L-DOPA-coated cover glasses exhibited functional receptor-activated Ca2+ transients through the activation of protease-activated receptor subtype 1 (PAR-1), recognized as an astrocytic functional marker. However, cover glass coated with 0, 500, 1000, 2000, and 4000 μg/mL L-DOPA maintained astrocyte viability, while supplementation with 500 and 1000 μM L-DOPA significantly decreased astrocyte viability. This suggests that treatments with free 500 and 1000 μM L-DOPA significantly reduced the number of astrocytes. Both Pimozide, an inhibitor of G protein-coupled receptor 143 (GPR143), also known as Ocular albinism type 1 (OA1), and CCG2046, an inhibitor of regulator of G protein signaling 4 (RGS4), reduced the viability of astrocytes on cover glass coated with L-DOPA compared to astrocytes on cover glass coated with poly-d-lysine (PDL). This suggests that L-DOPA promotes astrocyte proliferation through activation of the GPR143 signaling pathway. These findings imply that L-DOPA proliferates functional astrocytes through the activation of GPR143. These results are the first report that L-DOPA coating cover glass proliferates rat primary astrocytes with the activation of GPR143. The discovery that levodopa enhances cell adhesion can significantly influence research in multiple ways. It provides insights into cell behavior, disease mechanisms, and potential therapeutic applications in tissue engineering and regenerative medicine. Additionally, it offers opportunities to explore novel approaches for improving cell-based therapies and tissue regeneration. Overall, this finding opens up new avenues for research, with broad implications across various scientific fields.

Enhanced Myocardial Adenylyl Cyclase Activity Alters Heart-Brain Communication

BACKGROUND

The central nervous system's influence on cardiac function is well described; however, direct evidence for signaling from heart to brain remains sparse. Mice with cardiac-selective overexpression of adenylyl cyclase type 8 (TGAC8) display elevated heart rate/contractility and altered neuroautonomic surveillance.

OBJECTIVES

In this study the authors tested whether elevated adenylyl cyclase type 8-dependent signaling at the cardiac cell level affects brain activity and behavior.

METHODS

A telemetry system was used to record electrocardiogram (ECG) and electroencephalogram (EEG) in TGAC8 and wild-type mice simultaneously. The Granger causality statistical approach evaluated variations in the ECG/EEG relationship. Mouse behavior was assessed via elevated plus maze, open field, light-dark box, and fear conditioning tests. Transcriptomic and proteomic analyses were performed on brain tissue lysates.

RESULTS

Behavioral testing revealed increased locomotor activity in TGAC8 that included a greater total distance traveled (+43%; P < 0.01), a higher average speed (+38%; P < 0.01), and a reduced freezing time (-45%; P < 0.01). Dual-lead telemetry recording confirmed a persistent heart rate elevation with a corresponding reduction in ECG-R-waves interval variability and revealed increased EEG-gamma activity in TGAC8 vs wild-type. Bioinformatic assessment of hippocampal tissue indicated upregulation of dopamine 5, gamma-aminobutyric acid A, and metabotropic glutamate 1/5 receptors, major players in gamma activity generation. Granger causality analyses of ECG and EEG recordings showed a marked increase in informational flow between the TGAC8 heart and brain.

CONCLUSIONS

Perturbed signals arising from the heart cause changes in brain activity, altering mouse behavior. More specifically, the brain interprets augmented myocardial humoral/functional output as a "sustained exercise-like" situation and responds by activating central nervous system output controlling locomotion.

The Therapeutic Potential of Salidroside for Parkinson's Disease

Parkinson's disease (PD), a neurological disorder, is characterized by the progressive loss of dopaminergic (DA) neurons in the substantia nigra. Its incidence increases with age. Salidroside, a phenolic compound extracted from Sedum roseum, reportedly has multiple biological and pharmacological activities in the nervous system. However, its effects on PD remain unclear. In this review, we summarize the effects of salidroside on PD with regard to DA metabolism, neuronal protection, and glial activation. In addition, we summarize the susceptibility genes and their underlying mechanisms related to antioxidation, inflammation, and autophagy by regulating mitochondrial function, ubiquitin, and multiple signaling pathways involving NF-κB, mTOR, and PI3K/Akt. Although recent studies were based on animal and cellular experiments, this review provides evidence for further clinical utilization of salidroside for PD.

The Pathological Mechanism Between the Intestine and Brain in the Early Stage of Parkinson's Disease

Parkinson's disease (PD) is the second most common chronic progressive neurodegenerative disease. The main pathological features are progressive degeneration of neurons and abnormal accumulation of α-synuclein. At present, the pathogenesis of PD is not completely clear, and many changes in the intestinal tract may be the early pathogenic factors of PD. These changes affect the central nervous system (CNS) through both nervous and humoral pathways. α-Synuclein deposited in the intestinal nerve migrates upward along the vagus nerve to the brain. Inflammation and immune regulation mediated by intestinal immune cells may be involved, affecting the CNS through local blood circulation. In addition, microorganisms and their metabolites may also affect the progression of PD. Therefore, paying attention to the multiple changes in the intestinal tract may provide new insight for the early diagnosis and treatment of PD.

Understanding the Blood-Brain Barrier and Beyond: Challenges and Opportunities for Novel CNS Therapeutics

This review addresses questions on how to accomplish successful central nervous system (CNS) drug delivery (i.e., having the right concentration at the right CNS site, at the right time), by understanding the rate and extent of blood‐brain barrier (BBB) transport and intra‐CNS distribution in relation to CNS target site(s) exposure. To this end, we need to obtain and integrate quantitative and connected data on BBB using the Combinatory Mapping Approach that includes in vivo and ex vivo animal measurements, and the physiologically based comprehensive LEICNSPK3.0 mathematical model that can translate from animals to humans. For small molecules, slow diffusional BBB transport and active influx and efflux BBB transport determine the differences between plasma and CNS pharmacokinetics. Obviously, active efflux is important for limiting CNS drug delivery. Furthermore, liposomal formulations of small molecules may to a certain extent circumvent active influx and efflux at the BBB. Interestingly, for CNS pathologies, despite all reported disease associated BBB and CNS functional changes in animals and humans, integrative studies typically show a lack of changes on CNS drug delivery for the small molecules. In contrast, the understanding of the complex vesicle‐based BBB transport modes that are important for CNS delivery of large molecules is in progress, and their BBB transport seems to be significantly affected by CNS diseases. In conclusion, today, CNS drug delivery of small drugs can be well assessed and understood by integrative approaches, although there is still quite a long way to go to understand CNS drug delivery of large molecules.

Particulate levodopa nose-to-brain delivery targets dopamine to the brain with no plasma exposure

Levodopa (L-DOPA) is an oral Parkinson's Disease drug that generates the active metabolite - dopamine (DA) in vivo. However, oral L-DOPA exhibits low oral bioavailability, limited brain uptake, peripheral DA-mediated side effects and its poor brain bioavailability can lead to long-term complications. Here we show that L-DOPA forms stable (for at least 5 months) 300 nm nanoparticles when encapsulated within N-palmitoyl-N-monomethyl-N,N-dimethyl-N,N,N-trimethyl-6-O-glycolchitosan (GCPQ). A nano-in-microparticle GCPQ-L-DOPA formulation (D₅₀ = 7.2 µm), prepared by spray-drying, was stable for one month when stored at room and refrigeration temperatures and was capable of producing the original GCPQ-L-DOPA nanoparticles upon aqueous reconstitution. Nasal administration of reconstituted GCPQ-L-DOPA nanoparticles to rats resulted in significantly higher DA levels in the brain (C_max of 94 ng g^-1 above baseline levels 2 h post-dosing) when compared to nasal administration of L-DOPA alone, with DA being undetectable in the brain with the latter. Furthermore, nasal GCPQ-L-DOPA resulted in higher levels of L-DOPA in the plasma (a 17-fold increase in the Cmax, when compared to L-DOPA alone) with DA undetectable in the plasma from both formulations. These data provide evidence of effective delivery of DA to the brain with the GCPQ-L-DOPA formulation.

Tuneable manganese oxide nanoparticle based theranostic agents for potential diagnosis and drug delivery

Among various magnetic nanoparticles, manganese oxide nanoparticles are considered as established T 1 magnetic resonance imaging (MRI) contrast agents for preclinical research. The implications of their degradation properties and use as therapeutic carriers in drug delivery systems have not been explored. In addition, how the chemical composition and size of manganese oxide nanoparticles, as well as the surrounding environment, influence their degradation and MRI contrast properties (T 1 vs. T 2) have not been studied in great detail. A fundamental understanding of their characteristic properties, such as degradation, is highly desirable for developing simultaneous diagnosis and therapeutic solutions. Here, we demonstrate how the precursor type and reaction environment affect the size and chemical composition of manganese oxide nanoparticles and evaluate their influence on the nanoparticle degradability and release of the drug l-3,4-dihydroxyphenylalanine (l-dopa). The results show that the degradation rate (and the associated release of drug l-dopa molecules) of manganese oxide nanoparticles depends on their size, composition and the surrounding environment (aqueous or biometric fluid). The dependence of MRI relaxivities of manganese oxide nanoparticles on the size, chemical composition and nanoparticle degradation in water is also established. A preliminary cell viability study reveals the cytocompatible properties of l-dopa functionalized manganese oxide nanoparticles. Overall, this work provides new insights into smartly designed manganese oxide nanoparticles with multitasking capabilities to target bioimaging and therapeutic applications.

Mass spectrometry imaging identifies abnormally elevated brain l-DOPA levels and extrastriatal monoaminergic dysregulation in l-DOPA-induced dyskinesia

l-DOPA treatment for Parkinson's disease frequently leads to dyskinesias, the pathophysiology of which is poorly understood. We used MALDI-MSI to map the distribution of l-DOPA and monoaminergic pathways in brains of dyskinetic and nondyskinetic primates. We report elevated levels of l-DOPA, and its metabolite 3-O-methyldopa, in all measured brain regions of dyskinetic animals and increases in dopamine and metabolites in all regions analyzed except the striatum. In dyskinesia, dopamine levels correlated well with l-DOPA levels in extrastriatal regions, such as hippocampus, amygdala, bed nucleus of the stria terminalis, and cortical areas, but not in the striatum. Our results demonstrate that l-DOPA-induced dyskinesia is linked to a dysregulation of l-DOPA metabolism throughout the brain. The inability of extrastriatal brain areas to regulate the formation of dopamine during l-DOPA treatment introduces the potential of dopamine or even l-DOPA itself to modulate neuronal signaling widely across the brain, resulting in unwanted side effects.

Progress toward the development of a microchip electrophoresis separation-based sensor with electrochemical detection for on-line in vivo monitoring of catecholamines

The development of a separation-based sensor for catecholamines based on microdialysis (MD) coupled to microchip electrophoresis (ME) with electrochemical (EC) detection is described. The device consists of a pyrolyzed photoresist film working electrode and a poly(dimethylsiloxane) microchip with a flow-gated sample injection interface. The chip was partially reversibly sealed to the glass substrate by selectively exposing only the top section of the chip to plasma. This partially reversible chip/electrode integration process not only allows the reuse of the working electrode but also greatly enhanced the reproducibility of electrode alignment with the separation channel. The developed MD-ME-EC system was then tested using l-DOPA, 3-O-MD, HVA, DOPAC, and dopamine standards, which were separated in less than 100 seconds using a background electrolyte consisting of 15 mM sodium phosphate (pH 7.4), 15 mM sodium dodecyl sulfate, and 2.5 mM boric acid. A potential of +1.0 V vs. Ag/AgCl was used for amperometric detection of the analytes. The device was evaluated for on-line monitoring of the conversion of l-DOPA to dopamine in vitro and for monitoring dopamine release in an anesthetized rat in vivo following high K+ stimulation. The system was able to detect stimulated dopamine release in vivo but not endogenous levels of dopamine.

Single dose pharmacokinetics of intravenous 3,4-dihydroxyphenylacetic acid and 3-hydroxyphenylacetic acid in rats

3,4-Dihydroxyphenylacetic acid (DOPAC) and 3-hydroxyphenylacetic acid (3-HPAA) are intestinal metabolites of the dietary flavonoid quercetin. DOPAC reportedly showed anxiolytic activity after i.p. administration in rats. The fate of these metabolites after consumption, and the pharmacological properties of 3-HPAA in the body are largely unknown. The aim of the current study was to characterize pharmacokinetic properties of DOPAC and 3-HPAA after intravenous bolus application in rats. UHPLC-MS/MS methods for quantification of DOPAC and 3-HPAA levels in lithium heparin Sprague Dawley rat plasma were developed and validated according to international regulatory guidelines. Non-compartmental and compartmental analyses were performed. Pharmacokinetic profiles of DOPAC and 3-HPAA followed a two-compartment body model, with a fast distribution into peripheral tissues (half-lives of 3.27-5.26 min) and rapid elimination from the body (half-lives of 18.4-33.3 min).

Blood-Based Biomarkers of Quinpirole Pharmacology: Cluster-Based PK/PD and Metabolomics to Unravel the Underlying Dynamics in Rat Plasma and Brain

A key challenge in the development of central nervous system drugs is the availability of drug target specific blood-based biomarkers. As a new approach, we applied cluster-based pharmacokinetic/pharmacodynamic (PK/PD) analysis in brain extracellular fluid (brainECF ) and plasma simultaneously after 0, 0.17, and 0.86 mg/kg of the dopamine D2/3 agonist quinpirole (QP) in rats. We measured 76 biogenic amines in plasma and brainECF after single and 8-day administration, to be analyzed by cluster-based PK/PD analysis. Multiple concentration-effect relations were observed with potencies ranging from 0.001-383 nM. Many biomarker responses seem to distribute over the blood-brain barrier (BBB). Effects were observed for dopamine and glutamate signaling in brainECF , and branched-chain amino acid metabolism and immune signaling in plasma. Altogether, we showed for the first time how cluster-based PK/PD could describe a systems-response across plasma and brain, thereby identifying potential blood-based biomarkers. This concept is envisioned to provide an important connection between drug discovery and early drug development.

Scaling behavior of drug transport and absorption in in silico cerebral capillary networks

Drug delivery to the brain is challenging due to the presence of the blood-brain barrier. Mathematical modeling and simulation are essential tools for the deeper understanding of transport processes in the blood, across the blood-brain barrier and within the tissue. Here we present a mathematical model for drug delivery through capillary networks with increasingly complex topologies with the goal to understand the scaling behavior of model predictions on a coarse-to-fine sequence of grids. We apply our model to the delivery of L-Dopa, the primary drug used in the therapy of Parkinson’s Disease. Our model replicates observed blood flow rates and ratios between plasma and tissue concentrations. We propose an optimal network grain size for the simulation of tissue volumes of 1 cm³ that allows to make reliable predictions with reasonable computational costs.

Age-associated physiological and pathological changes at the blood-brain barrier: A review

The age-associated decline of the neurological and cognitive functions becomes more and more serious challenge for the developed countries with the increasing number of aged populations. The morphological and biochemical changes in the aging brain are the subjects of many extended research projects worldwide for a long time. However, the crucial role of the blood-brain barrier (BBB) impairment and disruption in the pathological processes in age-associated neurodegenerative disorders received special attention just for a few years. This article gives an overview on the major elements of the blood-brain barrier and its supporting mechanisms and also on their alterations during development, physiological aging process and age-associated neurodegenerative disorders (Alzheimer's disease, multiple sclerosis, Parkinson's disease, pharmacoresistant epilepsy). Besides the morphological alterations of the cellular elements (endothelial cells, astrocytes, pericytes, microglia, neuronal elements) of the BBB and neurovascular unit, the changes of the barrier at molecular level (tight junction proteins, adheres junction proteins, membrane transporters, basal lamina, extracellular matrix) are also summarized. The recognition of new players and initiators of the process of neurodegeneration at the level of the BBB may offer new avenues for novel therapeutic approaches for the treatment of numerous chronic neurodegenerative disorders currently without effective medication.

Delivery and tracking of quantum dot peptide bioconjugates in an intact developing avian brain

Luminescent semiconductor ∼9.5 nm nanoparticles (quantum dots: QDs) have intrinsic physiochemical and optical properties which enable us to begin to understand the mechanisms of nanoparticle mediated chemical/drug delivery. Here, we demonstrate the ability of CdSe/ZnS core/shell QDs surface functionalized with a zwitterionic compact ligand to deliver a cell-penetrating lipopeptide to the developing chick embryo brain without any apparent toxicity. Functionalized QDs were conjugated to the palmitoylated peptide WGDap(Palmitoyl)VKIKKP9GGH6, previously shown to uniquely facilitate endosomal escape, and microinjected into the embryonic chick spinal cord canal at embryo day 4 (E4). We were subsequently able to follow the labeling of spinal cord extension into the ventricles, migratory neuroblasts, maturing brain cells, and complex structures such as the choroid plexus. QD intensity extended throughout the brain, and peaked between E8 and E11 when fluorescence was concentrated in the choroid plexus before declining to hatching (E21/P0). We observed no abnormalities in embryonic patterning or embryo survival, and mRNA in situ hybridization confirmed that, at key developmental stages, the expression pattern of genes associated with different brain cell types (brain lipid binding protein, Sox-2, proteolipid protein and Class III-β-Tubulin) all showed a normal labeling pattern and intensity. Our findings suggest that we can use chemically modified QDs to identify and track neural stem cells as they migrate, that the choroid plexus clears these injected QDs/nanoparticles from the brain after E15, and that they can deliver drugs and peptides to the developing brain.

Agile delivery of protein therapeutics to CNS

A variety of therapeutic proteins have shown potential to treat central nervous system (CNS) disorders. Challenge to deliver these protein molecules to the brain is well known. Proteins administered through parenteral routes are often excluded from the brain because of their poor bioavailability and the existence of the blood-brain barrier (BBB). Barriers also exist to proteins administered through non-parenteral routes that bypass the BBB. Several strategies have shown promise in delivering proteins to the brain. This review, first, describes the physiology and pathology of the BBB that underscore the rationale and needs of each strategy to be applied. Second, major classes of protein therapeutics along with some key factors that affect their delivery outcomes are presented. Third, different routes of protein administration (parenteral, central intracerebroventricular and intraparenchymal, intranasal and intrathecal) are discussed along with key barriers to CNS delivery associated with each route. Finally, current delivery strategies involving chemical modification of proteins and use of particle-based carriers are overviewed using examples from literature and our own work. Whereas most of these studies are in the early stage, some provide proof of mechanism of increased protein delivery to the brain in relevant models of CNS diseases, while in few cases proof of concept had been attained in clinical studies. This review will be useful to broad audience of students, academicians and industry professionals who consider critical issues of protein delivery to the brain and aim developing and studying effective brain delivery systems for protein therapeutics.

Application of population pharmacokinetics for preclinical safety and efficacy studies

From the beginning of the 1980s, population PK has been primarily used in clinical development and only in the last decade has it been convincingly applied in a preclinical setting. Sparse sampling and covariate analyses are key features of preclinical popPK, useful for toxicology and efficacy studies in animals to assemble data obtained from different studies; for describing individual PK and PD; for building mechanistic models; and for performing interspecies scaling-up of disposition and efficacy. Application in disease models, mainly in behavioral and neurological models, allows the quantitative description of PK and PD without frequent blood sampling and recurrent physiological measurements, which are the critical and compromising perturbations of experimental systems. A preclinical population approach to PK and PD, by its versatility and possibility of simulating ‘what if’ scenarios, offers a unique and potent tool in the development of new drugs, in particular biologics.

Targeting caspase-3 as dual therapeutic benefits by RNAi facilitating brain-targeted nanoparticles in a rat model of Parkinson's disease

The activation of caspase-3 is an important hallmark in Parkinson’s disease. It could induce neuron death by apoptosis and microglia activation by inflammation. As a result, inhibition the activation of caspase-3 would exert synergistic dual effect in brain in order to prevent the progress of Parkinson’s disease. Silencing caspase-3 genes by RNA interference could inhibit the activation of caspase-3. We developed a brain-targeted gene delivery system based on non-viral gene vector, dendrigraft poly-L-lysines. A rabies virus glycoprotein peptide with 29 amino-acid linked to dendrigraft poly-L-lysines could render gene vectors the ability to get across the blood brain barrier by specific receptor mediated transcytosis. The resultant brain-targeted vector was complexed with caspase-3 short hairpin RNA coding plasmid DNA, yielding nanoparticles. In vivo imaging analysis indicated the targeted nanoparticles could accumulate in brain more efficiently than non-targeted ones. A multiple dosing regimen by weekly intravenous administration of the nanoparticles could reduce activated casapse-3 levels, significantly improve locomotor activity and rescue dopaminergic neuronal loss and in Parkinson’s disease rats’ brain. These results indicated the rabies virus glycoprotein peptide modified brain-targeted nanoparticles were promising gene delivery system for RNA interference to achieve anti-apoptotic and anti-inflammation synergistic therapeutic effects by down-regulation the expression and activation of caspase-3.

The mastermind approach to CNS drug therapy: translational prediction of human brain distribution, target site kinetics, and therapeutic effects

Despite enormous advances in CNS research, CNS disorders remain the world's leading cause of disability. This accounts for more hospitalizations and prolonged care than almost all other diseases combined, and indicates a high unmet need for good CNS drugs and drug therapies.Following dosing, not only the chemical properties of the drug and blood-brain barrier (BBB) transport, but also many other processes will ultimately determine brain target site kinetics and consequently the CNS effects. The rate and extent of all these processes are regulated dynamically, and thus condition dependent. Therefore, heterogenious conditions such as species, gender, genetic background, tissue, age, diet, disease, drug treatment etc., result in considerable inter-individual and intra-individual variation, often encountered in CNS drug therapy.For effective therapy, drugs should access the CNS "at the right place, at the right time, and at the right concentration". To improve CNS therapies and drug development, details of inter-species and inter-condition variations are needed to enable target site pharmacokinetics and associated CNS effects to be translated between species and between disease states. Specifically, such studies need to include information about unbound drug concentrations which drive the effects. To date the only technique that can obtain unbound drug concentrations in brain is microdialysis. This (minimally) invasive technique cannot be readily applied to humans, and we need to rely on translational approaches to predict human brain distribution, target site kinetics, and therapeutic effects of CNS drugs.In this review the term "Mastermind approach" is introduced, for strategic and systematic CNS drug research using advanced preclinical experimental designs and mathematical modeling. In this way, knowledge can be obtained about the contributions and variability of individual processes on the causal path between drug dosing and CNS effect in animals that can be translated to the human situation. On the basis of a few advanced preclinical microdialysis based investigations it will be shown that the "Mastermind approach" has a high potential for the prediction of human CNS drug effects.