Blood-Brain Barrier Leakage Is Increased in Parkinson's Disease

Deep brain stimulation halts Parkinson's disease-related immune dysregulation in the brain and peripheral blood

Immune dysregulation in the brain and periphery is thought to contribute to the detrimental neurodegeneration that occurs in Parkinson's disease (PD). Identifying mechanisms to reverse this dysregulation is key to developing disease-altering therapeutics for this currently incurable disease. Here we utilized the longitudinal data from the Parkinson's Progression Marker Initiative to demonstrate that circulating lymphocytes progressively decline in PD and can be used to predict future motor symptom progression. Deep brain stimulation (DBS), which is used as a symptomatic treatment, could halt this progressive decline. By analyzing specific immune populations from a second cohort of patients, we could show that DBS causes a shift from the pro-inflammatory CD4+ T helper 17 cells driving neurodegeneration to anti-inflammatory CD4+ regulatory T cells. RNA-sequencing and immunohistochemistry in the brain of the A53T alpha-synuclein rat model of PD revealed that DBS also decreases neuroinflammation. These data suggest a potential disease-altering role for DBS by halting inflammatory processes.

Immune cell infiltration and modulation of the blood-brain barrier in a guinea pig model of tuberculosis: Observations without evidence of bacterial dissemination to the brain

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) infection, is a chronic inflammatory disease. Although typically associated with inflammation of the lungs and other peripheral tissues, increasing evidence has uncovered neurological consequences attributable to Mtb infection. These include deficits in memory and cognition, increased risk for neurodegenerative disease, and progressive neuropathology. Although the neurological effects of the disease, without CNS infection, have been characterized, the mechanism of neurotoxicity is unknown. We hypothesized that alterations to the blood-brain barrier (BBB) allows peripheral immune cells to enter the brain, initiating a neuroinflammatory response. To test this hypothesis, guinea pigs were exposed by aerosol to a laboratory and a clinical Mtb strain for 15 days. Following Mtb infection, proteins critical to BBB function, including claudin V and collagen IV, are modulated without evidence of bacterial dissemination to the brain. This is correlated with increased contact of astrocytic processes to vessels in the brain, as well as increased expression of the water channel protein aquaporin 4 (AQP4) on endfeet. Upon further investigation, we discovered the potential role of glial reactivity, which is increased following infection with both bacterial strains, in the progression of BBB changes and, ultimately, the permeability of peripheral immune cells into the brain. Through these data, we have obtained a preliminary understanding of the mechanisms of cellular stress in the brain following pulmonary Mtb infection which should be further investigated in future studies.

Isolation method of brain microvessels from small frozen human brain tissue for blood-brain barrier protein expression analysis

BACKGROUND

Protein expression analysis of isolated brain microvessels provides valuable insights into the function of the blood-brain barrier (BBB). However, isolation of brain microvessels from human brain tissue, particularly in small quantities, poses significant challenges. This study presents a method for isolating brain microvessels from a small amount of frozen human brain tissue, adapting techniques from an established mouse brain capillary isolation method.

METHODS

Brain microvessel fractions were obtained from approximately 0.3 g of frozen human brain tissue (frontal cortex) using a bead homogenizer for homogenization, followed by purification with a combination of cell strainers and glass beads. Protein expression in the isolated human microvessel fractions and whole-brain lysates was analyzed by western blot and proteomic analysis.

RESULTS

Microscopic imaging confirmed the successful isolation of brain microvessels from frozen human brain tissue. Protein quantification assays demonstrated that the microvessel fraction yielded sufficient protein for detailed expression analysis. Western blot analysis revealed an enrichment of BBB-selective proteins including multidrug resistance 1 (MDR1)/ATP-binding cassette sub-family B member 1 (ABCB1), glucose transporter protein type 1 (GLUT1)/solute carrier family 2 member 1 (SLC2A1), and claudin 5 (CLDN5), in the brain microvessel fraction compared to whole-brain lysates. Multiple reaction monitoring quantification of six BBB-selective proteins-MDR1, breast cancer resistance protein (BCRP)/ATP binding cassette subfamily G member 2 (ABCG2), GLUT1, monocarboxylate transporter 1 (MCT1)/solute carrier family 16 member 1 (SLC16A1), transferrin receptor, and CLDN5-revealed expression levels consistent with those observed in larger human brain samples. Sequential Window Acquisition of all Theoretical Mass Spectra (SWATH-MS)-based quantitative proteomics further demonstrated significant enrichment of human microvascular endothelial cells in the isolated fraction, corroborating the findings from mouse models.

CONCLUSIONS

We successfully developed a method for isolation of brain microvessels from a small amount of frozen human brain tissue, facilitating detailed study of BBB proteome in aging or pathological conditions. This technique provides valuable insights into BBB dysfunction in central nervous system disorders and holds potential for improving brain-targeted drug delivery strategies.

Revealing the mechanisms of blood-brain barrier in chronic neurodegenerative disease: an opportunity for therapeutic intervention

The brain microenvironment is tightly regulated, and the blood-brain barrier (BBB) plays a pivotal role in maintaining the homeostasis of the central nervous system. It effectively safeguards brain tissue from harmful substances in peripheral blood. However, both acute pathological factors and age-related biodegradation have the potential to compromise the integrity of the BBB and are associated with chronic neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD), as well as Epilepsy (EP). This association arises due to infiltration of peripheral foreign bodies including microorganisms, immune-inflammatory mediators, and plasma proteins into the central nervous system when the BBB is compromised. Nevertheless, these partial and generalized understandings do not prompt a shift from passive to active treatment approaches. Therefore, it is imperative to acquire a comprehensive and in-depth understanding of the intricate molecular mechanisms underlying vascular disease alterations associated with the onset and progression of chronic neurodegenerative disorders, as well as the subsequent homeostatic changes triggered by BBB impairment. The present article aims to systematically summarize and review recent scientific work with a specific focus on elucidating the fundamental mechanisms underlying BBB damage in AD, PD, and EP as well as their consequential impact on disease progression. These findings not only offer guidance for optimizing the physiological function of the BBB, but also provide valuable insights for developing intervention strategies aimed at early restoration of BBB structural integrity, thereby laying a solid foundation for designing drug delivery strategies centered around the BBB.

Early-life exposure to PCBs and PFAS exerts negative effects on the developing central nervous system

Persistent organic pollutants (POPs) are ubiquitous in the environment and display the capacity to bioaccumulate in living organisms, constituting a hazard to both wildlife and humans. Although restrictions have been applied to prohibit the production of several POPs since the 1960s, high levels of these compounds can still be detected in many environmental and biological matrices, due to their chemical properties and significantly long half-lives. Some POPs can be passed from mother to the fetus and can gain entry to the central nervous system (CNS), by crossing the blood-brain barrier (BBB), resulting in significant deleterious effects, including neurocognitive and psychiatric abnormalities, which may lead to long-term socio-economic burdens. A growing body of evidence obtained from clinical and experimental studies has increasingly indicated that these POPs may influence neurodevelopment through several cellular and molecular mechanisms. However, studies assessing their mechanisms of action are still incipient, requiring further research. Polychlorinated biphenyls (PCBs) and per- and polyfluoroalkyl substances (PFAS) are two of the main classes of POPs associated with disturbances in different human systems, mainly the nervous and endocrine systems. This narrative review discusses the main PCB and PFAS effects on the CNS, focusing on neuroinflammation and oxidative stress and their consequences for neural development and BBB integrity. Moreover, we propose which mechanisms could be involved in POP-induced neurodevelopmental defects. In this sense, we highlight potential cellular and molecular pathways by which these POPs can affect neurodevelopment and could be further explored to propose preventive therapies and formulate public health policies.

Investigating the causal relationship between inflammation and multiple types of hearing loss: a multi-omics approach combining Mendelian randomization and molecular docking

Background

Hearing loss affects over 10% of the global population. Inflammation is a key factor in hearing loss caused by noise, infection, and aging, damaging various hearing-related tissues (e.g., spiral ligament, stria vascularis). Mendelian randomization (MR) can help identify potential causal relationships and therapeutic targets.

Methods

We conducted MR analyses on 91 inflammatory proteins (n = 14,824) and genome-wide association study results for various hearing loss types in European ancestry populations, including sensorineural hearing loss (SNHL; ncases = 15,952, ncontrols = 196,592), sudden idiopathic hearing loss (SIHL; ncases = 1,491, ncontrols = 196,592), and other hearing loss (OHL; ncases = 4,157, ncontrols = 196,592). Additionally, hearing loss with difficulty in hearing (ncases = 14,654, ncontrols = 474,839) served as a validation set. To predict inflammatory protein-enriched pathways and tissues, we performed enrichment analysis, functional annotation, and tissue analyses using "OmicsNet2.0" and "FUMA" platforms. We also combined "CoreMine" and molecular docking to explore potential drugs targeting inflammatory proteins and investigate binding efficacy.

Results

CCL19 was identified as a common risk factor for SNHL and OHL, which was validated in the hearing loss with difficulty in hearing dataset. Tissue analysis revealed that SIHL-related inflammatory proteins were enriched in the amygdala. Multi-omics research indicated associations between inflammatory proteins and neurodegenerative diseases. Molecular docking studies suggested that Chuanxiong Rhizoma and Uncariae Ramulus Cumuncis are potential drugs for targeting CCL19.

Conclusion

This study identified CCL19 as a common risk factor for various types of hearing loss through MR analysis, highlighting the crucial role of inflammatory proteins in hearing loss. The enrichment of related inflammatory proteins in the amygdala and their association with neurodegenerative diseases provide new insights into the mechanisms of hearing loss.

Role of the transcription factor NRF2 in maintaining the integrity of the Blood-Brain Barrier

BACKGROUND

The Blood-Brain Barrier (BBB) is a complex and dynamic interface that regulates the exchange of molecules and cells between the blood and the central nervous system. It undergoes structural and functional throughout oxidative stress and inflammation, which may compromise its integrity and contribute to the pathogenesis of neurodegenerative diseases.

MAIN BODY

Maintaining BBB integrity is of utmost importance in preventing a wide range of neurological disorders. NRF2 is the main transcription factor that regulates cellular redox balance and inflammation-related gene expression. It has also demonstrated a potential role in regulating tight junction integrity and contributing to the inhibition of ECM remodeling, by reducing the expression of several metalloprotease family members involved in maintaining BBB function. Overall, we review current insights on the role of NRF2 in addressing protection against the effects of BBB dysfunction, discuss its involvement in BBB maintenance in different neuropathological diseases, as well as, some of its potential activators that have been used in vitro and in vivo animal models for preventing barrier dysfunction.

CONCLUSIONS

Thus, emerging evidence suggests that upregulation of NRF2 and its target genes could suppress oxidative stress, and neuroinflammation, restore BBB integrity, and increase its protection.

Circadian control of polycyclic aromatic hydrocarbon-induced dysregulation of endothelial tight junctions and mitochondrial bioenergetics

The study evaluates the impact of environmental toxicants, such as polycyclic aromatic hydrocarbons (PAHs), on circadian regulations and functions of brain endothelial cells, which form the main structural element of the blood-brain barrier (BBB). PAH are lipophilic and highly toxic environmental pollutants that accumulate in human and animal tissues. Environmental factors related to climate change, such as an increase in frequency and intensity of wildfires or enhanced strength of hurricanes or tropical cyclones, may lead to redistribution of these toxicants and enhanced human exposure. These natural disasters are also associated with disruption of circadian rhythms in affected populations, linking increased exposure to environmental toxicants to alterations of circadian rhythm pathways. Several vital physiological processes are coordinated by circadian rhythms, and disruption of the circadian clock can contribute to the development of several diseases. The blood-brain barrier (BBB) is crucial for protecting the brain from blood-borne harmful substances, and its integrity is influenced by circadian rhythms. Exposure of brain endothelial cells to a human and environmentally-relevant PAH mixture resulted in dose-dependent alterations of expression of critical circadian modulators, such as Clock, Bmal1, Cry1/2, and Per1/2. Moreover, silencing of the circadian Clock gene potentiated the impact of PAHs on the expression of the main tight junction genes and proteins (namely, claudin-5, occludin, JAM-2, and ZO-2), as well as mitochondrial bioenergetics. Findings from this study contribute to a better understanding of pathological influence of PAH-induced health effects, especially those related to circadian rhythm disruption.

Circulating blood circular RNA in Parkinson's Disease; from involvement in pathology to diagnostic tools in at-risk individuals

To identify circRNAs associated with Parkinson's disease (PD) we leveraged two of the largest publicly available studies with longitudinal clinical and blood transcriptomic data. We performed a cross-sectional study utilizing the last visit of each participant (N = 1848), and a longitudinal analysis that included 1166 participants with at least two time points. We identified 192 differentially expressed circRNAs, with effects that were sustained during disease, in mutation carriers, and diverse ancestry. The 192 circRNAs were leveraged to distinguish between PD and healthy participants with a ROC AUC of 0.797. Further, 71 circRNAs were sufficient to distinguish between genetic PD (AUC71 = 0.954) and, at-risk participants (AUC71 = 0.929) and healthy controls, supporting that circRNAs have the potential to aid the diagnosis of PD. Finally, we identified five circRNAs highly correlated with symptom severity. Overall, we demonstrated that circRNAs play an important role in PD and can be clinically relevant to improve diagnostic and monitoring.

A guide for blood-brain barrier models

Understanding the intricate mechanisms underlying brain-related diseases hinges on unraveling the pivotal role of the blood-brain barrier (BBB), an essential dynamic interface crucial for maintaining brain equilibrium. This review offers a comprehensive analysis of BBB physiology, delving into its cellular and molecular components while exploring a wide range of in vivo and in vitro BBB models. Notably, recent advancements in 3D cell culture techniques are explicitly discussed, as they have significantly improved the fidelity of BBB modeling by enabling the replication of physiologically relevant environments under flow conditions. Special attention is given to the cellular aspects of in vitro BBB models, alongside discussions on advances in stem cell technologies, providing valuable insights into generating robust cellular systems for BBB modeling. The diverse array of cell types used in BBB modeling, depending on their sources, is meticulously examined in this comprehensive review, scrutinizing their respective derivation protocols and implications. By synthesizing diverse approaches, this review sheds light on the improvements of BBB models to capture physiological conditions, aiding in understanding BBB interactions in health and disease conditions to foster clinical developments.

Plasma acellular transcriptome contains Parkinson's disease signatures that can inform clinical diagnosis

We aimed to identify plasma cell-free transcripts (cfRNA) associated with Parkinson's disease (PD) that also have a high predictive value to differentiate PD from healthy controls. Leveraging two independent populations from two different movement disorder centers we identified 2,188 differentially expressed cfRNAs after meta-analysis. The identified transcripts were enriched in PD relevant pathways, such as PD (p=9.26×10-4), ubiquitin-mediated proteolysis (p=7.41×10-5) and endocytosis (p=4.21×10-6). Utilizing in-house and publicly available brain, whole blood, and acellular plasma transcriptomic and proteomic PD datasets, we found significant overlap across dysregulated biological species in the different tissues and the different biological layers. We developed three predictive models containing increasing number of transcripts that can distinguish PD from healthy control with an area under the ROC Curve (AUC) ≥0.85. Finally, we showed that several of the predictive transcripts significantly correlate with symptom severity measured by UPDRS-III. Overall, we have demonstrated that cfRNA contains pathological signatures and has the potential to be utilized as biomarker to aid in PD diagnostics and monitoring.

iPSC-derived blood-brain barrier modeling reveals APOE isoform-dependent interactions with amyloid beta

BACKGROUND

Three common isoforms of the apolipoprotein E (APOE) gene - APOE2, APOE3, and APOE4 - hold varying significance in Alzheimer's Disease (AD) risk. The APOE4 allele is the strongest known genetic risk factor for late-onset Alzheimer's Disease (AD), and its expression has been shown to correlate with increased central nervous system (CNS) amyloid deposition and accelerated neurodegeneration. Conversely, APOE2 is associated with reduced AD risk and lower CNS amyloid burden. Recent clinical data have suggested that increased blood-brain barrier (BBB) leakage is commonly observed among AD patients and APOE4 carriers. However, it remains unclear how different APOE isoforms may impact AD-related pathologies at the BBB.

METHODS

To explore potential impacts of APOE genotypes on BBB properties and BBB interactions with amyloid beta, we differentiated isogenic human induced pluripotent stem cell (iPSC) lines with different APOE genotypes into both brain microvascular endothelial cell-like cells (BMEC-like cells) and brain pericyte-like cells. We then compared the effect of different APOE isoforms on BBB-related and AD-related phenotypes. Statistical significance was determined via ANOVA with Tukey's post hoc testing as appropriate.

RESULTS

Isogenic BMEC-like cells with different APOE genotypes had similar trans-endothelial electrical resistance, tight junction integrity and efflux transporter gene expression. However, recombinant APOE4 protein significantly impeded the "brain-to-blood" amyloid beta 1-40 (Aβ40) transport capabilities of BMEC-like cells, suggesting a role in diminished amyloid clearance. Conversely, APOE2 increased amyloid beta 1-42 (Aβ42) transport in the model. Furthermore, we demonstrated that APOE-mediated amyloid transport by BMEC-like cells is dependent on LRP1 and p-glycoprotein pathways, mirroring in vivo findings. Pericyte-like cells exhibited similar APOE secretion levels across genotypes, yet APOE4 pericyte-like cells showed heightened extracellular amyloid deposition, while APOE2 pericyte-like cells displayed the least amyloid deposition, an observation in line with vascular pathologies in AD patients.

CONCLUSIONS

While APOE genotype did not directly impact general BMEC or pericyte properties, APOE4 exacerbated amyloid clearance and deposition at the model BBB. Conversely, APOE2 demonstrated a potentially protective role by increasing amyloid transport and decreasing deposition. Our findings highlight that iPSC-derived BBB models can potentially capture amyloid pathologies at the BBB, motivating further development of such in vitro models in AD modeling and drug development.

The immune system in Parkinson's disease: what we know so far

Parkinson's disease is characterized neuropathologically by the degeneration of dopaminergic neurons in the ventral midbrain, the accumulation of α-synuclein (α-syn) aggregates in neurons and chronic neuroinflammation. In the past two decades, in vitro, ex vivo and in vivo studies have consistently shown the involvement of inflammatory responses mediated by microglia and astrocytes, which may be elicited by pathological α-syn or signals from affected neurons and other cell types, and are directly linked to neurodegeneration and disease development. Apart from the prominent immune alterations seen in the CNS, including the infiltration of T cells into the brain, more recent studies have demonstrated important changes in the peripheral immune profile within both the innate and adaptive compartments, particularly involving monocytes, CD4+ and CD8+ T cells. This review aims to integrate the consolidated understanding of immune-related processes underlying the pathogenesis of Parkinson's disease, focusing on both central and peripheral immune cells, neuron-glia crosstalk as well as the central-peripheral immune interaction during the development of Parkinson's disease. Our analysis seeks to provide a comprehensive view of the emerging knowledge of the mechanisms of immunity in Parkinson's disease and the implications of this for better understanding the overall pathogenesis of this disease.

Neuroinflammation and blood-brain barrier breakdown in acute, clinical intracerebral hemorrhage

Neuroinflammation is a promising therapeutic target in intracerebral hemorrhage (ICH), characterized in the brain by microglial activation and blood-brain barrier (BBB) breakdown. In this study, 36 acute, spontaneous, supratentorial ICH patients underwent dynamic contrast-enhanced MRI to measure BBB permeability (Ktrans) 1-3 days post-onset and 16 returned for [11C](R)-PK11195 PET to quantify microglial activation (BPND), 2-7 days post-onset. We first tested if these markers were increased and co-localized in the perihematomal brain and found that perihematomal Ktrans and BPND were increased vs. the contralateral brain, but regions of high Ktrans and BPND only overlapped by a mean of 4.9%. We then tested for associations of perihematomal Ktrans and BPND with clinical characteristics (age, ICH volume & location, blood pressure), other markers of inflammation (edema, IL-6, and CRP), and long-term functional outcome (90-day mRS). Lower perihematomal BPND was associated with increasing age. Lobar hemorrhage was associated with greater Ktrans than deep, but Ktrans and BPND were not associated with ICH volume, or other inflammatory markers. While perihematomal Ktrans and BPNDwere not associated with outcome, contralateral Ktrans was significantly associated with greater 90-day mRS. Exploratory analyses demonstrated that blood pressure variability over 72 h was also associated with contralateral Ktrans.

Unlocking the potential of low-molecular-weight (Poly)phenol metabolites: Protectors at the blood-brain barrier frontier

Neurodegenerative diseases (NDDs) are an increasing group of chronic and progressive neurological disorders that ultimately lead to neuronal cell failure and death. Despite all efforts throughout decades, their burden on individuals and society still casts one of the most massive socioeconomic problems worldwide. The neuronal failure observed in NDDs results from an intricacy of events, mirroring disease complexity, ranging from protein aggregation, oxidative stress, (neuro)inflammation, and even blood-brain barrier (BBB) dysfunction, ultimately leading to cognitive and motor symptoms in patients. As a result of such complex pathobiology, to date, there are still no effective treatments to treat/halt NDDs progression. Fortunately, interest in the bioavailable low molecular weight (LMW) phenolic metabolites derived from the metabolism of dietary (poly)phenols has been rising due to their multitargeted potential in attenuating multiple NDDs hallmarks. Even if not highly BBB permeant, their relatively high concentrations in the bloodstream arising from the intake of (poly)phenol-rich diets make them ideal candidates to act within the vasculature and particularly at the level of BBB. In this review, we highlight the most recent - though still scarce - studies demonstrating LMW phenolic metabolites' ability to modulate BBB homeostasis, including the improvement of tight and adherens junctional proteins, as well as their power to decrease pro-inflammatory cytokine secretion and oxidative stress levels in vitro and in vivo. Specific BBB-permeant LMW phenolic metabolites, such as simple phenolic sulfates, have been emerging as strong BBB properties boosters, pleiotropic compounds capable of improving cell fitness under oxidative and pro-inflammatory conditions. Nevertheless, further studies should be pursued to obtain a holistic overview of the promising role of LMW phenolic metabolites in NDDs prevention and management to fully harness their true therapeutic potential.

Characteristics of blood-brain barrier heterogeneity between brain regions revealed by profiling vascular and perivascular cells

The blood-brain barrier (BBB) protects the brain and maintains neuronal homeostasis. BBB properties can vary between brain regions to support regional functions, yet how BBB heterogeneity occurs is poorly understood. Here, we used single-cell and spatial transcriptomics to compare the mouse median eminence, one of the circumventricular organs that has naturally leaky blood vessels, with the cortex. We identified hundreds of molecular differences in endothelial cells (ECs) and perivascular cells, including astrocytes, pericytes and fibroblasts. Using electron microscopy and an aqueous-based tissue-clearing method, we revealed distinct anatomical specializations and interaction patterns of ECs and perivascular cells in these regions. Finally, we identified candidate regionally enriched EC-perivascular cell ligand-receptor pairs. Our results indicate that both molecular specializations in ECs and unique EC-perivascular cell interactions contribute to BBB functional heterogeneity. This platform can be used to investigate BBB heterogeneity in other regions and may facilitate the development of central nervous system region-specific therapeutics.

NX210c drug candidate peptide strengthens mouse and human blood-brain barriers

BACKGROUND

Alterations of blood-brain barrier (BBB) and blood-spinal cord barrier have been documented in various animal models of neurodegenerative diseases and in patients. Correlations of these alterations with functional deficits suggest that repairing barriers integrity may represent a disease-modifying approach to prevent neuroinflammation and neurodegeneration induced by the extravasation of blood components into the parenchyma. Here, we screened the effect of a subcommissural organ-spondin-derived peptide (NX210c), known to promote functional recovery in several models of neurological disorders, on BBB integrity in vitro and in vivo.

METHODS

In vitro, bEnd.3 endothelial cell (EC) monolayers and two different primary human BBB models containing EC, astrocytes and pericytes, in static and microfluidic conditions, were treated with NX210c (1-100 µM), or its vehicle, for 4 h and up to 5 days. Tight junction (TJ) protein levels, permeability to dextrans and transendothelial electrical resistance (TEER) were evaluated. In vivo, young and old mice (3- and 21-month-old, respectively) were treated daily intraperitoneally with NX210c at 10 mg/kg or its vehicle for 5 days and their brains collected at day 6 to measure TJ protein levels by immunohistochemistry.

RESULTS

NX210c induced an increase in claudin-5 protein expression after 24-h and 72-h treatments in mouse EC. Occludin level was also increased after a 24-h treatment. Accordingly, NX210c decreased by half the permeability of EC to a 40-kDa FITC-dextran and increased TEER. In the human static BBB model, NX210c increased by ∼ 25% the TEER from 3 to 5 days. NX210c also increased TEER in the human 3D dynamic BBB model after 4 h, which was associated with a reduced permeability to a 4-kDa FITC-dextran. In line with in vitro results, after only 5 days of daily treatments in mice, NX210c restored aging-induced reduction of claudin-5 and occludin levels in the hippocampus, and also in the cortex for occludin.

CONCLUSIONS

In summary, we have gathered preclinical data showing the capacity of NX210c to strengthen BBB integrity. Through this property, NX210c holds great promises of being a disease-modifying treatment for several neurological disorders with high unmet medical needs.

Meta-analysis of the make-up and properties of in vitro models of the healthy and diseased blood-brain barrier

In vitro models of the human blood-brain barrier (BBB) are increasingly used to develop therapeutics that can cross the BBB for treating diseases of the central nervous system. Here we report a meta-analysis of the make-up and properties of transwell and microfluidic models of the healthy BBB and of BBBs in glioblastoma, Alzheimer's disease, Parkinson's disease and inflammatory diseases. We found that the type of model, the culture method (static or dynamic), the cell types and cell ratios, and the biomaterials employed as extracellular matrix are all crucial to recapitulate the low permeability and high expression of tight-junction proteins of the BBB, and to obtain high trans-endothelial electrical resistance. Specifically, for models of the healthy BBB, the inclusion of endothelial cells and pericytes as well as physiological shear stresses (~10-20 dyne cm-2) are necessary, and when astrocytes are added, astrocytes or pericytes should outnumber endothelial cells. We expect this meta-analysis to facilitate the design of increasingly physiological models of the BBB.

Intercellular Adhesion Molecule 1 (ICAM-1): An Inflammatory Regulator with Potential Implications in Ferroptosis and Parkinson's Disease

Intercellular adhesion molecule 1 (ICAM-1/CD54), a transmembrane glycoprotein, has been considered as one of the most important adhesion molecules during leukocyte recruitment. It is encoded by the ICAM1 gene and plays a central role in inflammation. Its crucial role in many inflammatory diseases such as ulcerative colitis and rheumatoid arthritis are well established. Given that neuroinflammation, underscored by microglial activation, is a key element in neurodegenerative diseases such as Parkinson's disease (PD), we investigated whether ICAM-1 has a role in this progressive neurological condition and, if so, to elucidate the underpinning mechanisms. Specifically, we were interested in the potential interaction between ICAM-1, glial cells, and ferroptosis, an iron-dependent form of cell death that has recently been implicated in PD. We conclude that there exist direct and indirect (via glial cells and T cells) influences of ICAM-1 on ferroptosis and that further elucidation of these interactions can suggest novel intervention for this devastating disease.

Vascular Impairment, Muscle Atrophy, and Cognitive Decline: Critical Age-Related Conditions

The triad of vascular impairment, muscle atrophy, and cognitive decline represents critical age-related conditions that significantly impact health. Vascular impairment disrupts blood flow, precipitating the muscle mass reduction seen in sarcopenia and the decline in neuronal function characteristic of neurodegeneration. Our limited understanding of the intricate relationships within this triad hinders accurate diagnosis and effective treatment strategies. This review analyzes the interrelated mechanisms that contribute to these conditions, with a specific focus on oxidative stress, chronic inflammation, and impaired nutrient delivery. The aim is to understand the common pathways involved and to suggest comprehensive therapeutic approaches. Vascular dysfunctions hinder the circulation of blood and the transportation of nutrients, resulting in sarcopenia characterized by muscle atrophy and weakness. Vascular dysfunction and sarcopenia have a negative impact on physical function and quality of life. Neurodegenerative diseases exhibit comparable pathophysiological mechanisms that affect cognitive and motor functions. Preventive and therapeutic approaches encompass lifestyle adjustments, addressing oxidative stress, inflammation, and integrated therapies that focus on improving vascular and muscular well-being. Better understanding of these links can refine therapeutic strategies and yield better patient outcomes. This study emphasizes the complex interplay between vascular dysfunction, muscle degeneration, and cognitive decline, highlighting the necessity for multidisciplinary treatment approaches. Advances in this domain promise improved diagnostic accuracy, more effective therapeutic options, and enhanced preventive measures, all contributing to a higher quality of life for the elderly population.

Infiltration of immune cells to the brain and its relation to the pathogenesis of Alzheimer's and Parkinson's diseases

The neurovascular unit, composed of vascular endothelium, vascular smooth muscle, extracellular matrix components, pericytes, astrocytes, microglia, and neurons, allows the highly regulated exchange of molecules and the limited trafficking of cells to the brain through coordinated signaling activity. The passage of peripheral immune cells to the brain parenchyma is observed when there is clear damage to the barriers of this neurovascular unit, as occurs in traumatic brain injury. The possibility of leukocyte infiltration to the brain in neurodegenerative conditions has been proposed. In this review, we focus on describing the evidence for peripheral immune cell infiltration to the brain in the two most frequent neurodegenerative diseases: Alzheimer's and Parkinson's diseases. In particular, we address the mechanisms that promote the passage of these cells into the brain under such pathological conditions. We also discuss the relevance of the resulting cellular interactions, which provide evidence that the presence of peripheral immune cells in the brain is a key point in these neurodegenerative diseases.

Differentiation and regulation of CD4+ T cell subsets in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease, and its hallmark pathological features are the loss of dopaminergic (DA) neurons in the midbrain substantia nigra pars compacta (SNpc) and the accumulation of alpha-synuclein (α-syn). It has been shown that the integrity of the blood-brain barrier (BBB) is damaged in PD patients, and a large number of infiltrating T cells and inflammatory cytokines have been detected in the cerebrospinal fluid (CSF) and brain parenchyma of PD patients and PD animal models, including significant change in the number and proportion of different CD4+ T cell subsets. This suggests that the neuroinflammatory response caused by CD4+ T cells is an important risk factor for the development of PD. Here, we systematically review the differentiation of CD4+ T cell subsets, and focus on describing the functions and mechanisms of different CD4+ T cell subsets and their secreted cytokines in PD. We also summarize the current immunotherapy targeting CD4+ T cells with a view to providing assistance in the diagnosis and treatment of PD.

Inflammatory diet, gut microbiota and sensorineural hearing loss: a cross-sectional and Mendelian randomization study

Aims

Inflammatory diets can trigger chronic inflammation and affect gut microbiota. However, the relationship between dietary preferences and sensorineural hearing loss (SNHL) remains unclear. This study aims to elucidate the relationship between different dietary preferences and sensorineural deafness.

Methods

The Dietary Inflammation Index (DII) and SNHL were defined by data from the National Health and Nutrition Examination Survey (NHANES), and exploring their relationship. Using Mendelian randomization (MR) to analyze the relationship between 34 dietary preferences, 211 gut microbiota, and SNHL.

Results

Smooth curve fitting indicated that the risk of SNHL increased with increasing DII score when the DII score was greater than 5.15. MR results suggest that a diet including both oily and non-oily fish can substantially reduce the risk of SNHL. Additionally, six specific gut microbiota were found to have significant causal relationship with SNHL.

Conclusion

An inflammatory diet may increase the risk of developing SNHL. The observed relationship between fish consumption, gut microbiota, and SNHL suggests the existence of a gut-inner ear axis.

Blood-brain barrier disruption: a culprit of cognitive decline?

Cognitive decline covers a broad spectrum of disorders, not only resulting from brain diseases but also from systemic diseases, which seriously influence the quality of life and life expectancy of patients. As a highly selective anatomical and functional interface between the brain and systemic circulation, the blood-brain barrier (BBB) plays a pivotal role in maintaining brain homeostasis and normal function. The pathogenesis underlying cognitive decline may vary, nevertheless, accumulating evidences support the role of BBB disruption as the most prevalent contributing factor. This may mainly be attributed to inflammation, metabolic dysfunction, cell senescence, oxidative/nitrosative stress and excitotoxicity. However, direct evidence showing that BBB disruption causes cognitive decline is scarce, and interestingly, manipulation of the BBB opening alone may exert beneficial or detrimental neurological effects. A broad overview of the present literature shows a close relationship between BBB disruption and cognitive decline, the risk factors of BBB disruption, as well as the cellular and molecular mechanisms underlying BBB disruption. Additionally, we discussed the possible causes leading to cognitive decline by BBB disruption and potential therapeutic strategies to prevent BBB disruption or enhance BBB repair. This review aims to foster more investigations on early diagnosis, effective therapeutics, and rapid restoration against BBB disruption, which would yield better cognitive outcomes in patients with dysregulated BBB function, although their causative relationship has not yet been completely established.

Microphysiological Blood-Brain Barrier Systems for Disease Modeling and Drug Development

The blood-brain barrier (BBB) is a highly controlled microenvironment that regulates the interactions between cerebral blood and brain tissue. Due to its selectivity, many therapeutics targeting various neurological disorders are not able to penetrate into brain tissue. Pre-clinical studies using animals and other in vitro platforms have not shown the ability to fully replicate the human BBB leading to the failure of a majority of therapeutics in clinical trials. However, recent innovations in vitro and ex vivo modeling called organs-on-chips have shown the potential to create more accurate disease models for improved drug development. These microfluidic platforms induce physiological stressors on cultured cells and are able to generate more physiologically accurate BBBs compared to previous in vitro models. In this review, different approaches to create BBBs-on-chips are explored alongside their application in modeling various neurological disorders and potential therapeutic efficacy. Additionally, organs-on-chips use in BBB drug delivery studies is discussed, and advances in linking brain organs-on-chips onto multiorgan platforms to mimic organ crosstalk are reviewed.

Cellular and molecular mechanisms of the blood-brain barrier dysfunction in neurodegenerative diseases

BACKGROUND

Maintaining the structural and functional integrity of the blood-brain barrier (BBB) is vital for neuronal equilibrium and optimal brain function. Disruptions to BBB performance are implicated in the pathology of neurodegenerative diseases.

MAIN BODY

Early indicators of multiple neurodegenerative disorders in humans and animal models include impaired BBB stability, regional cerebral blood flow shortfalls, and vascular inflammation associated with BBB dysfunction. Understanding the cellular and molecular mechanisms of BBB dysfunction in brain disorders is crucial for elucidating the sustenance of neural computations under pathological conditions and for developing treatments for these diseases. This paper initially explores the cellular and molecular definition of the BBB, along with the signaling pathways regulating BBB stability, cerebral blood flow, and vascular inflammation. Subsequently, we review current insights into BBB dynamics in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis. The paper concludes by proposing a unified mechanism whereby BBB dysfunction contributes to neurodegenerative disorders, highlights potential BBB-focused therapeutic strategies and targets, and outlines lessons learned and future research directions.

CONCLUSIONS

BBB breakdown significantly impacts the development and progression of neurodegenerative diseases, and unraveling the cellular and molecular mechanisms underlying BBB dysfunction is vital to elucidate how neural computations are sustained under pathological conditions and to devise therapeutic approaches.

The impact of interleukin-6 (IL-6) and mesenchymal stem cell-derived IL-6 on neurological conditions

Interleukin-6 (IL-6) is a versatile cytokine crucial for immune response modulation, inflammation regulation, and various physiological processes in the body. Its wide-ranging functions underscore its importance in maintaining health. Dysregulated IL-6 is closely associated with many diseases, making it a key research and therapeutic target. Elevated IL-6 levels in the central nervous system worsen neuroinflammation in neurodegenerative diseases by activating microglia and astrocytes and releasing pro-inflammatory cytokines and neurotoxic molecules. Moreover, dysregulated IL-6 weakens the blood-brain barrier, exacerbating neuroinflammation and neuronal damage by allowing peripheral immune cells and inflammatory mediators to enter the brain. Mesenchymal stem cells (MSCs) show promise in modulating neuroinflammation by regulating IL-6 levels. They effectively suppress pro-inflammatory cytokines, including IL-6, while promoting anti-inflammatory factors. This therapeutic approach highlights the importance of targeting IL-6 and other inflammatory mediators to alleviate neuroinflammation and its adverse effects on neurological disorders. This review provides a comprehensive overview of IL-6's involvement in neurological disorders, examining endogenous IL-6 and IL-6 derived from MSCs. We explore IL-6's mechanisms affecting neuronal function, survival, and immune modulation in the central nervous system. Additionally, we discuss the potential of MSC-derived IL-6 in neuroregeneration and neuroprotection. By elucidating IL-6's interplay with neurological pathologies, this review offers insights into novel therapeutic strategies targeting IL-6 signaling pathways for neurological disorders.

Endothelial dysfunction in neurodegenerative disease: Is endothelial inflammation an overlooked druggable target?

Neurological diseases with a neurodegenerative component have been associated with alterations in the cerebrovasculature. At the anatomical level, these are centred around changes in cerebral blood flow and vessel organisation. At the molecular level, there is extensive expression of cellular adhesion molecules and increased release of pro-inflammatory mediators. Together, these has been found to negatively impact blood-brain barrier integrity. Systemic inflammation has been found to accelerate and exacerbate endothelial dysfunction, neuroinflammation and degeneration. Here, we review the role of cerebrovasculature dysfunction in neurodegenerative disease and discuss the potential contribution of intermittent pro-inflammatory systemic disease in causing endothelial pathology, highlighting a possible mechanism that may allow broad-spectrum therapeutic targeting in the future.

Untargeted serum metabolic profiling of diabetes mellitus among Parkinson's disease patients

Type 2 diabetes mellitus (T2DM) is a common comorbidity among Parkinson's disease (PD) patients. Yet, little is known about dysregulated pathways that are unique in PD patients with T2DM. We applied high-resolution metabolomic profiling in serum samples of 636 PD and 253 non-PD participants recruited from Central California. We conducted an initial discovery metabolome-wide association and pathway enrichment analysis. After adjusting for multiple testing, in positive (or negative) ion mode, 30 (25) metabolic features were associated with T2DM in both PD and non-PD participants, 162 (108) only in PD participants, and 32 (7) only in non-PD participants. Pathway enrichment analysis identified 17 enriched pathways associated with T2DM in both the PD and non-PD participants, 26 pathways only in PD participants, and 5 pathways only in non-PD participants. Several amino acid, nucleic acids, and fatty acid metabolisms were associated with T2DM only in the PD patient group suggesting a possible link between PD and T2DM.

Synthesis and Monoamine Oxidase Inhibitory Activity of Halogenated Flavones

Small molecule neurotransmitters containing amines are metabolized by monoamine oxidase (MAO) in the nervous system. Monoamine oxidase inhibitors are a valuable class of drugs prescribed for the management of neurological disorders, including depression. A series of halogenated flavonoids similar to the dietary flavonoid acacetin were designed as selective MAO-B inhibitors. MAO-A and -B inhibition of 36 halogenated flavones were tested. The halogens (fluorine and chlorine) were placed at positions 5 and 7 on ring A of the flavone scaffold. All compounds were selective MAO-B inhibitors with micro- and nanomolar IC50 values. Compounds 9f, 10a-c, 11a-c, 11g,h, and 11l displayed inhibitory activity toward MAO-B with IC50 values between 16 to 74 nM. We conclude that halogenated flavonoids are promising molecules in pursuit of developing new agents for neurological disorders.

Hopping the Hurdle: Strategies to Enhance the Molecular Delivery to the Brain through the Blood-Brain Barrier

Modern medicine has allowed for many advances in neurological and neurodegenerative disease (ND). However, the number of patients suffering from brain diseases is ever increasing and the treatment of brain diseases remains an issue, as drug efficacy is dramatically reduced due to the existence of the unique vascular structure, namely the blood-brain barrier (BBB). Several approaches to enhance drug delivery to the brain have been investigated but many have proven to be unsuccessful due to limited transport or damage induced in the BBB. Alternative approaches to enhance molecular delivery to the brain have been revealed in recent studies through the existence of molecular delivery pathways that regulate the passage of peripheral molecules. In this review, we present recent advancements of the basic research for these delivery pathways as well as examples of promising ventures to overcome the molecular hurdles that will enhance therapeutic interventions in the brain and potentially save the lives of millions of patients.

Neurodegenerative Etiology of Aromatic L-Amino Acid Decarboxylase Deficiency: a Novel Concept for Expanding Treatment Strategies

Aromatic l-amino acid decarboxylase deficiency (AADC-DY) is caused by one or more mutations in the DDC gene, resulting in the deficit in catecholamines and serotonin neurotransmitters. The disease has limited therapeutic options with relatively poor clinical outcomes. Accumulated evidence suggests the involvement of neurodegenerative mechanisms in the etiology of AADC-DY. In the absence of neurotransmitters' neuroprotective effects, the accumulation and the chronic presence of several neurotoxic metabolites including 4-dihydroxy-L-phenylalanine, 3-methyldopa, and homocysteine, in the brain of subjects with AADC-DY, promote oxidative stress and reduce the cellular antioxidant and methylation capacities, leading to glial activation and mitochondrial dysfunction, culminating to neuronal injury and death. These pathophysiological processes have the potential to hinder the clinical efficacy of treatments aimed at increasing neurotransmitters' synthesis and or function. This review describes in detail the mechanisms involved in AADC-DY neurodegenerative etiology, highlighting the close similarities with those involved in other neurodegenerative diseases. We then offer novel strategies for the treatment of the disease with the objective to either reduce the level of the metabolites or counteract their prooxidant and neurotoxic effects. These treatment modalities used singly or in combination, early in the course of the disease, will minimize neuronal injury, preserving the functional integrity of neurons, hence improving the clinical outcomes of both conventional and unconventional interventions in AADC-DY. These modalities may not be limited to AADC-DY but also to other metabolic disorders where a specific mutation leads to the accumulation of prooxidant and neurotoxic metabolites.

Blood-brain barrier biomarkers

The blood-brain barrier (BBB) is a dynamic interface that regulates the exchange of molecules and cells between the brain parenchyma and the peripheral blood. The BBB is mainly composed of endothelial cells, astrocytes and pericytes. The integrity of this structure is essential for maintaining brain and spinal cord homeostasis and protection from injury or disease. However, in various neurological disorders, such as traumatic brain injury, Alzheimer's disease, and multiple sclerosis, the BBB can become compromised thus allowing passage of molecules and cells in and out of the central nervous system parenchyma. These agents, however, can serve as biomarkers of BBB permeability and neuronal damage, and provide valuable information for diagnosis, prognosis and treatment. Herein, we provide an overview of the BBB and changes due to aging, and summarize current knowledge on biomarkers of BBB disruption and neurodegeneration, including permeability, cellular, molecular and imaging biomarkers. We also discuss the challenges and opportunities for developing a biomarker toolkit that can reliably assess the BBB in physiologic and pathophysiologic states.

Contribution of Direct Cerebral Vascular Transport in Brain Substance Clearance

The accumulation of harmful substances has long been recognized as a likely cause of many neurodegenerative diseases. The two classic brain clearance pathways are cerebrospinal fluid (CSF) and vascular circulation systems. Since the discovery of the glymphatic system, research on the CSF pathway has gained momentum, and impaired CSF clearance has been implicated in virtually all neurodegenerative animal models. However, the contribution of the direct participation of vascular transport across the blood-brain barrier in clearing substances is often ignored in glymphatic papers. Supportive evidence for the direct involvement of parenchymal vasculature in substance clearance is accumulated. First, multiple mechanisms have been proposed for the vascular drainage of exogenous and endogenous substances across the blood-brain barriers. Second, the "traditional" role of arachnoid villi and granulations as the main site for CSF draining into the vasculature system has been questioned. Third, MRI studies using different CSF tracers indicate that parenchymal vasculature directly participates in tracer efflux, consistent with immunohistochemical findings. Here we will review evidence in the literature that supports the direct participation of the parenchymal vascular system in substance clearance, in addition to the CSF clearance pathways.

Neuroimmune Connectomes in the Gut and Their Implications in Parkinson's Disease

The gastrointestinal tract is the largest immune organ and it receives dense innervation from intrinsic (enteric) and extrinsic (sympathetic, parasympathetic, and somatosensory) neurons. The immune and neural systems of the gut communicate with each other and their interactions shape gut defensive mechanisms and neural-controlled gut functions such as motility and secretion. Changes in neuroimmune interactions play central roles in the pathogenesis of diseases such as Parkinson's disease (PD), which is a multicentric disorder that is heterogeneous in its manifestation and pathogenesis. Non-motor and premotor symptoms of PD are common in the gastrointestinal tract and the gut is considered a potential initiation site for PD in some cases. How the enteric nervous system and neuroimmune signaling contribute to PD disease progression is an emerging area of interest. This review focuses on intestinal neuroimmune loops such as the neuroepithelial unit, enteric glial cells and their immunomodulatory effects, anti-inflammatory cholinergic signaling and the relationship between myenteric neurons and muscularis macrophages, and the role of α-synuclein in gut immunity. Special consideration is given to the discussion of intestinal neuroimmune connectomes during PD and their possible implications for various aspects of the disease.

Relationship Between Short-chain Fatty Acids and Parkinson's Disease: A Review from Pathology to Clinic

Parkinson's disease (PD) is a complicated neurodegenerative disease, characterized by the accumulation of α-synuclein (α-syn) in Lewy bodies and neurites, and massive loss of midbrain dopamine neurons. Increasing evidence suggests that gut microbiota and microbial metabolites are involved in the development of PD. Among these, short-chain fatty acids (SCFAs), the most abundant microbial metabolites, have been proven to play a key role in brain-gut communication. In this review, we analyze the role of SCFAs in the pathology of PD from multiple dimensions and summarize the alterations of SCFAs in PD patients as well as their correlation with motor and non-motor symptoms. Future research should focus on further elucidating the role of SCFAs in neuroinflammation, as well as developing novel strategies employing SCFAs and their derivatives to treat PD.

Gastrointestinal and brain barriers: unlocking gates of communication across the microbiota-gut-brain axis

Crosstalk between gut and brain has long been appreciated in health and disease, and the gut microbiota is a key player in communication between these two distant organs. Yet, the mechanisms through which the microbiota influences development and function of the gut-brain axis remain largely unknown. Barriers present in the gut and brain are specialized cellular interfaces that maintain strict homeostasis of different compartments across this axis. These barriers include the gut epithelial barrier, the blood-brain barrier and the blood-cerebrospinal fluid barrier. Barriers are ideally positioned to receive and communicate gut microbial signals constituting a gateway for gut-microbiota-brain communication. In this Review, we focus on how modulation of these barriers by the gut microbiota can constitute an important channel of communication across the gut-brain axis. Moreover, barrier malfunction upon alterations in gut microbial composition could form the basis of various conditions, including often comorbid neurological and gastrointestinal disorders. Thus, we should focus on unravelling the molecular and cellular basis of this communication and move from simplistic framing as 'leaky gut'. A mechanistic understanding of gut microbiota modulation of barriers, especially during critical windows of development, could be key to understanding the aetiology of gastrointestinal and neurological disorders.

CSF1R inhibition promotes neuroinflammation and behavioral deficits during graft-versus-host disease in mice

ABSTRACT

Chronic graft-versus-host disease (cGVHD) remains a significant complication of allogeneic hematopoietic stem cell transplantation. Central nervous system (CNS) involvement is becoming increasingly recognized, in which brain-infiltrating donor major histocompatibility complex (MHC) class II+ bone marrow-derived macrophages (BMDM) drive pathology. BMDM are also mediators of cutaneous and pulmonary cGVHD, and clinical trials assessing the efficacy of antibody blockade of colony-stimulating factor 1 receptor (CSF1R) to deplete macrophages are promising. We hypothesized that CSF1R antibody blockade may also be a useful strategy to prevent/treat CNS cGVHD. Increased blood-brain barrier permeability during acute GVHD (aGVHD) facilitated CNS antibody access and microglia depletion by anti-CSF1R treatment. However, CSF1R blockade early after transplant unexpectedly exacerbated aGVHD neuroinflammation. In established cGVHD, vascular changes and anti-CSF1R efficacy were more limited. Anti-CSF1R-treated mice retained donor BMDM, activated microglia, CD8+ and CD4+ T cells, and local cytokine expression in the brain. These findings were recapitulated in GVHD recipients, in which CSF1R was conditionally depleted in donor CX3CR1+ BMDM. Notably, inhibition of CSF1R signaling after transplant failed to reverse GVHD-induced behavioral changes. Moreover, we observed aberrant behavior in non-GVHD control recipients administered anti-CSF1R blocking antibody and naïve mice lacking CSF1R in CX3CR1+ cells, revealing a novel role for homeostatic microglia and indicating that ongoing clinical trials of CSF1R inhibition should assess neurological adverse events in patients. In contrast, transfer of Ifngr-/- grafts could reduce MHC class II+ BMDM infiltration, resulting in improved neurocognitive function. Our findings highlight unexpected neurological immune toxicity during CSF1R blockade and provide alternative targets for the treatment of cGVHD within the CNS.

CYP1B1 affects the integrity of the blood-brain barrier and oxidative stress in the striatum: An investigation of manganese-induced neurotoxicity

AIMS

Excessive influx of manganese (Mn) into the brain across the blood-brain barrier induces neurodegeneration. CYP1B1 is involved in the metabolism of arachidonic acid (AA) that affects vascular homeostasis. We aimed to investigate the effect of brain CYP1B1 on Mn-induced neurotoxicity.

METHOD

Brain Mn concentrations and α-synuclein accumulation were measured in wild-type and CYP1B1 knockout mice treated with MnCl2 (30 mg/kg) and biotin (0.2 g/kg) for 21 continuous days. Tight junctions and oxidative stress were analyzed in hCMEC/D3 and SH-SY5Y cells after the treatment with MnCl2 (200 μM) and CYP1B1-derived AA metabolites (HETEs and EETs).

RESULTS

Mn exposure inhibited brain CYP1B1, and CYP1B1 deficiency increased brain Mn concentrations and accelerated α-synuclein deposition in the striatum. CYP1B1 deficiency disrupted the integrity of the blood-brain barrier (BBB) and increased the ratio of 3, 4-dihydroxyphenylacetic acid (DOPAC) to dopamine in the striatum. HETEs attenuated Mn-induced inhibition of tight junctions by activating PPARγ in endothelial cells. Additionally, EETs attenuated Mn-induced up-regulation of the KLF/MAO-B axis and down-regulation of NRF2 in neuronal cells. Biotin up-regulated brain CYP1B1 and reduced Mn-induced neurotoxicity in mice.

CONCLUSIONS

Brain CYP1B1 plays a critical role in both cerebrovascular and dopamine homeostasis, which might serve as a novel therapeutic target for the prevention of Mn-induced neurotoxicity.

The microbiota-gut-brain axis in Huntington's disease: pathogenic mechanisms and therapeutic targets

Huntington's disease (HD) is a currently incurable neurogenerative disorder and is typically characterized by progressive movement disorder (including chorea), cognitive deficits (culminating in dementia), psychiatric abnormalities (the most common of which is depression), and peripheral symptoms (including gastrointestinal dysfunction). There are currently no approved disease-modifying therapies available for HD, with death usually occurring approximately 10-25 years after onset, but some therapies hold promising potential. HD subjects are often burdened by chronic diarrhea, constipation, esophageal and gastric inflammation, and a susceptibility to diabetes. Our understanding of the microbiota-gut-brain axis in HD is in its infancy and growing evidence from preclinical and clinical studies suggests a role of gut microbial population imbalance (gut dysbiosis) in HD pathophysiology. The gut and the brain can communicate through the enteric nervous system, immune system, vagus nerve, and microbiota-derived-metabolites including short-chain fatty acids, bile acids, and branched-chain amino acids. This review summarizes supporting evidence demonstrating the alterations in bacterial and fungal composition that may be associated with HD. We focus on mechanisms through which gut dysbiosis may compromise brain and gut health, thus triggering neuroinflammatory responses, and further highlight outcomes of attempts to modulate the gut microbiota as promising therapeutic strategies for HD. Ultimately, we discuss the dearth of data and the need for more longitudinal and translational studies in this nascent field. We suggest future directions to improve our understanding of the association between gut microbes and the pathogenesis of HD, and other 'brain and body disorders'.

Integration of National Health Insurance claims data and animal models reveals fexofenadine as a promising repurposed drug for Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a common and costly progressive neurodegenerative disease of unclear etiology. A disease-modifying approach that can directly stop or slow its progression remains a major unmet need in the treatment of PD. A clinical pharmacology-based drug repositioning strategy is a useful approach for identifying new drugs for PD.

METHODS

We analyzed claims data obtained from the National Health Insurance Service (NHIS), which covers a significant portion of the South Korean population, to investigate the association between antihistamines, a class of drugs commonly used to treat allergic symptoms by blocking H1 receptor, and PD in a real-world setting. Additionally, we validated this model using various animal models of PD such as the 6-hydroxydopmaine (6-OHDA), α-synuclein preformed fibrils (PFF) injection, and Caenorhabditis elegans (C. elegans) models. Finally, whole transcriptome data and Ingenuity Pathway Analysis (IPA) were used to elucidate drug mechanism pathways.

RESULTS

We identified fexofenadine as the most promising candidate using National Health Insurance claims data in the real world. In several animal models, including the 6-OHDA, PFF injection, and C. elegans models, fexofenadine ameliorated PD-related pathologies. RNA-seq analysis and the subsequent experiments suggested that fexofenadine is effective in PD via inhibition of peripheral immune cell infiltration into the brain.

CONCLUSION

Fexofenadine shows promise for the treatment of PD, identified through clinical data and validated in diverse animal models. This combined clinical and preclinical approach offers valuable insights for developing novel PD therapeutics.

Blood-Brain Barrier Disruption and Perivascular Spaces in Small Vessel Disease and Neurodegenerative Diseases: A Review on MRI Methods and Insights

Perivascular spaces (PVS) and blood-brain barrier (BBB) disruption are two key features of cerebral small vessel disease (cSVD) and neurodegenerative diseases that have been linked to cognitive impairment and are involved in the cerebral waste clearance system. Magnetic resonance imaging (MRI) offers the possibility to study these pathophysiological processes noninvasively in vivo. This educational review provides an overview of the MRI techniques used to assess PVS functionality and BBB disruption. MRI-visible PVS can be scored on structural images by either (subjectively) counting or (automatically) delineating the PVS. We highlight emerging (diffusion) techniques to measure proxies of perivascular fluid and its movement, which may provide a more comprehensive understanding of the role of PVS in diseases. For the measurement of BBB disruption, we explain the most commonly used MRI technique, dynamic contrast-enhanced (DCE) MRI, as well as a more recently developed technique based on arterial spin labeling (ASL). DCE MRI and ASL are thought to measure complementary characteristics of the BBB. Furthermore, we describe clinical studies that have utilized these MRI techniques in cSVD and neurodegenerative diseases, particularly Alzheimer's disease (AD). These studies demonstrate the role of PVS and BBB dysfunction in these diseases and provide insight into the large overlap, but also into the differences between cSVD and AD. Overall, MRI techniques may provide valuable insights into the pathophysiological mechanisms underlying these diseases and have the potential to be used as markers for disease progression and treatment response. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY: Stage 2.

Inflammatory bowel disease induces pathological α-synuclein aggregation in the human gut and brain

AIMS

According to Braak's hypothesis, it is plausible that Parkinson's disease (PD) originates in the enteric nervous system (ENS) and spreads to the brain through the vagus nerve. In this work, we studied whether inflammatory bowel diseases (IBDs) in humans can progress with the emergence of pathogenic α-synuclein (α-syn) in the gastrointestinal tract and midbrain dopaminergic neurons.

METHODS

We have analysed the gut and the ventral midbrain from subjects previously diagnosed with IBD and form a DSS-based rat model of gut inflammation in terms of α-syn pathology.

RESULTS

Our data support the existence of pathogenic α-syn in both the gut and the brain, thus reinforcing the potential role of the ENS as a contributing factor in PD aetiology. Additionally, we have analysed the effect of a DSS-based rat model of gut inflammation to demonstrate (i) the appearance of P-α-syn inclusions in both Auerbach's and Meissner's plexuses (gut), (ii) an increase in α-syn expression in the ventral mesencephalon (brain) and (iii) the degeneration of nigral dopaminergic neurons, which all are considered classical hallmarks in PD.

CONCLUSION

These results strongly support the plausibility of Braak's hypothesis and emphasise the significance of peripheral inflammation and the gut-brain axis in initiating α-syn aggregation and transport to the substantia nigra, resulting in neurodegeneration.

Heat Shock Protein 90 in Parkinson's Disease: Profile of a Serial Killer

Parkinson's disease (PD) is the second most common neurodegenerative disease, characterized by abnormal α-synuclein misfolding and aggregation, mitochondrial dysfunction, oxidative stress, as well as progressive death of dopaminergic neurons in the substantia nigra. Molecular chaperones play a role in stabilizing proteins and helping them achieve their proper structure. Previous studies have shown that overexpression of heat shock protein 90 (HSP90) can lead to the death of dopaminergic neurons associated with PD. Inhibiting HSP90 is considered a potential treatment approach for neurodegenerative disorders, as it may reduce protein aggregation and related toxicity, as well as suppress various forms of regulated cell death (RCD). This review provides an overview of HSP90 and its role in PD, focusing on its modulation of proteostasis and quality control of LRRK2. The review also explores the effects of HSP90 on different types of RCD, such as apoptosis, chaperone-mediated autophagy (CMA), necroptosis, and ferroptosis. Additionally, it discusses HSP90 inhibitors that have been tested in PD models. We will highlight the under-investigated neuroprotective effects of HSP90 inhibition, including modulation of oxidative stress, mitochondrial dysfunction, PINK/PARKIN, heat shock factor 1 (HSF1), histone deacetylase 6 (HDAC6), and the PHD2-HSP90 complex-mediated mitochondrial stress pathway. By examining previous literature, this review uncovers overlooked neuroprotective mechanisms and emphasizes the need for further research on HSP90 inhibitors as potential therapeutic strategies for PD. Finally, the review discusses the potential limitations and possibilities of using HSP90 inhibitors in PD therapy.

Functionalized Nanomaterials Capable of Crossing the Blood-Brain Barrier

The blood-brain barrier (BBB) is a specialized semipermeable structure that highly regulates exchanges between the central nervous system parenchyma and blood vessels. Thus, the BBB also prevents the passage of various forms of therapeutic agents, nanocarriers, and their cargos. Recently, many multidisciplinary studies focus on developing cargo-loaded nanoparticles (NPs) to overcome these challenges, which are emerging as safe and effective vehicles in neurotheranostics. In this Review, first we introduce the anatomical structure and physiological functions of the BBB. Second, we present the endogenous and exogenous transport mechanisms by which NPs cross the BBB. We report various forms of nanomaterials, carriers, and their cargos, with their detailed BBB uptake and permeability characteristics. Third, we describe the effect of regulating the size, shape, charge, and surface ligands of NPs that affect their BBB permeability, which can be exploited to enhance and promote neurotheranostics. We classify typical functionalized nanomaterials developed for BBB crossing. Fourth, we provide a comprehensive review of the recent progress in developing functional polymeric nanomaterials for applications in multimodal bioimaging, therapeutics, and drug delivery. Finally, we conclude by discussing existing challenges, directions, and future perspectives in employing functionalized nanomaterials for BBB crossing.

Circulating blood circular RNA in Parkinson's Disease; a systematic study

We aimed to identify circRNAs associated with Parkinson's disease (PD) by leveraging 1,848 participants and 1,789 circRNA from two of the largest publicly available studies with longitudinal clinical and blood transcriptomic data. To comprehensively understand changes in circRNAs we performed a cross-sectional study utilizing the last visit of each participant, and a longitudinal (mix model) analysis that included 1,166 participants with at least two time points. We identified 192 circRNAs differentially expressed in PD participants compared to healthy controls, with effects that were consistent in the mixed models, mutation carriers, and diverse ancestry. Finally, we included the 149 circRNA in a model with a ROC AUC of 0.825, showing that have the potential to aid the diagnosis of PD. Overall, we demonstrated that circRNAs play an important role in PD and can be leveraged as biomarkers.

Immunological shifts during early-stage Parkinson's disease identified with DNA methylation data on longitudinally collected blood samples

Parkinson's disease (PD) is the second most common neurodegenerative disease in the United States. Decades before motor symptoms manifest, non-motor symptoms such as hyposmia and rapid eye movement (REM) sleep behavior disorder are highly predictive of PD. Previous immune profiling studies have identified alterations to the proportions of immune cells in the blood of clinically defined PD patients. However, it remains unclear if these phenotypes manifest before the clinical diagnosis of PD. We utilized longitudinal DNA methylation (DNAm) microarray data from the Parkinson's Progression Marker's Initiative (PPMI) to perform immune profiling in clinically defined PD and prodromal PD patients (Prod). We identified previously reported changes in neutrophil, monocyte, and T cell numbers in PD patients. Additionally, we noted previously unrecognized decreases in the naive B cell compartment in the defined PD and Prod patient group. Over time, we observed the proportion of innate immune cells in PD blood increased, but the proportion of adaptive immune cells decreased. We identified decreases in T and B cell subsets associated with REM sleep disturbances and early cognitive decline. Lastly, we identified increases in B memory cells associated with both genetic (LRRK2 genotype) and infectious (cytomegalovirus seropositivity) risk factors of PD. Our analysis shows that the peripheral immune system is dynamic as the disease progresses. The study provides a platform to understand how and when peripheral immune alterations occur in PD and whether intervention at particular stages may be therapeutically advantageous.

The gut-brain axis in Parkinson's disease

There is a bi-directional communication between the gut, including the microbiota, and the brain through the autonomic nervous system. Accumulating evidence has suggested a bidirectional link between gastrointestinal inflammation and neurodegeneration, in accordance with the concept of the gut-rain axis. An abnormal microbiota-gut-brain interaction contributes to the pathogeny of Parkinson's disease. This supports the hypothesis that Parkinson's disease originates in the gut to spread to the central nervous system, in particular through the vagus nerve. Targeting the gut-to-brain axis with vagus nerve stimulation, fecal microbiota transplantation, gut-selective antibiotics, as well as drugs targeting the leaky gut might be of interest in the management of Parkinson's disease.

The Common Denominators of Parkinson's Disease Pathogenesis and Methamphetamine Abuse

The pervasiveness and mortality associated with methamphetamine abuse have doubled during the past decade, suggesting a possible worldwide substance use crisis. Epitomizing the pathophysiology and toxicology of methamphetamine abuse proclaims severe signs and symptoms of neurotoxic and neurobehavioral manifestations in both humans and animals. Most importantly, chronic use of this drug enhances the probability of developing neurodegenerative diseases manifolds. Parkinson's disease is one such neurological disorder, which significantly and evidently not only shares a number of toxic pathogenic mechanisms induced by methamphetamine exposure but is also interlinked both structurally and genetically. Methamphetamine-induced neurodegeneration involves altered dopamine homeostasis that promotes the aggregation of α-synuclein protofibrils in the dopaminergic neurons and drives these neurons to make them more vulnerable to degeneration, as recognized in Parkinson's disease. Moreover, the pathologic mechanisms such as mitochondrial dysfunction, oxidative stress, neuroinflammation and decreased neurogenesis detected in methamphetamine abusers dramatically resemble to what is observed in Parkinson's disease cases. Therefore, the present review comprehensively cumulates a holistic illustration of various genetic and molecular mechanisms putting across the notion of how methamphetamine administration and intoxication might lead to Parkinson's disease-like pathology and Parkinsonism.