Temporal course of cerebrospinal fluid dynamics and amyloid accumulation in the aging rat brain from three to thirty months

Volumetric Changes in the Choroid Plexus Associated with Spontaneous Intracranial Hypotension in Patients with Spinal CSF Leak

BACKGROUND AND PURPOSE

The choroid plexus contains specialized ependymal cells responsible for CSF production. Recent studies have demonstrated volumetric and perfusion changes in the choroid plexus with age and neurodegenerative disorders, however, volumetric changes in the choroid plexus in low pressure states is not known. The purpose of this study is to evaluate volumetric differences in choroid plexus size in patients with spontaneous intracranial hypotension (SIH) resultant from spinal CSF leaks compared with healthy controls.

MATERIALS AND METHODS

This was a retrospective, institutional review board-approved study. Patients with MRI evidence of SIH and a spinal CSF leak diagnosed on myelography and subsequently confirmed at surgery were included in this study. All patients included in this study including age-matched healthy controls had a brain MRI performed on a either a 1.5 or 3T scanner with acquisition of 3D T1 postcontrast (eg, BRAVO, MPRAGE, etc). In all patients, the trigonum ventriculi volume, in the atria of the lateral ventricles, was contoured by using Visage-7 segmentation tools on the volumetric postcontrast T1 sequence. A basic 2-tailed t test was used to compare choroid plexus volumes between the 2 groups.

RESULTS

Thirty-four patients were included with 17 patients with SIH with spinal CSF leak and 17 healthy control patients who were age- and sex-matched. The mean age of patients was 45 years, standard deviation 14 years. The mean volume of the choroid plexus for patients with SIH with spinal CSF leak was 1.2 cm3 (standard deviation = 0.26) compared with 0.63 cm3 (standard deviation = 0.31) in the control group (P < .0001).

CONCLUSIONS

Results of this study demonstrate a higher choroid plexus volume in patients with SIH with spinal CSF leak compared with age- and sex-matched healthy controls. This likely reflects compensatory mechanisms to counteract intracranial hypotension by increasing CSF production as well as increased vascularity of the choroid plexus through expansion of the intracranial blood pool.

Near-Infrared-II Imaging Revealed Hypothermia Regulates Neuroinflammation Following Brain Injury by Increasing the Glymphatic Influx

Advanced in vivo imaging techniques have facilitated the comprehensive visual exploration of animal biological processes, leading to groundbreaking discoveries such as the glymphatic system. However, current limitations of macroscopic imaging techniques impede the precise investigation of physiological parameters regulating this specialized lymphatic transport system. While NIR-II fluorescence imaging has demonstrated advantages in peripheral lymphatic imaging, there are few reports regarding its utilization in the glymphatic system. To address this, a noninvasive transcranial macroscopic NIR-II fluorescence imaging model is developed using a cyanine dye-protein coupled nanoprobe. NIR-II imaging with high temporal and spatial resolution reveals that hypothermia can increase the glymphatic influx by reducing the flow rate of cerebrospinal fluid. In addition, respiratory rate, respiratory amplitude, and heart rate all play a role in regulating the glymphatic influx. Thus, targeting the glymphatic influx may alter the trajectory of immune inflammation following brain injury, providing therapeutic prospects for treating brain injury with mild hypothermia.

Regulation of trophic factors in the choroid plexus of aged mice

Background

The choroid plexus (CP) is an understudied tissue in the central nervous system (CNS), primarily implicated in cerebrospinal fluid (CSF) production. Additionally, CP produces numerous neurotrophic factors (NTF), which circulate to different regions of the brain. Regulation of NTF in the CP during natural aging has yet to be discovered. Here, we investigated the age and gender-specific transcription of NTFs along with the changes in the tight junctional proteins (TJPs) and water channel protein Aquaporin (AQP1).

Methods

We used male and female mice for our study. We analyzed neurotrophic factor gene expression patterns using quantitative and digital droplet PCR at three different time points: mature adult, middle-aged, and aged. Additionally, we used immunohistochemical analysis (IHC) to evaluate in vivo protein expression. We further investigated the cellular phenotype of these NTFS, TJP and water channel proteins in the mouse CP by co-labeling them with the classical vascular marker, Isolectin B4, and epithelial cell marker, plectin.

Results

Aging significantly altered the NTF's gene expression in the CP Brain-derived neurotrophic factor (BDNF), Midkine, VGF, Insulin-like growth factor (IGF1), IGF2, klotho, Erythropoietin, and its receptor were reduced in the aged CP of males and females. Vascular endothelial growth factor (VEGF) transcription was gender-specific; in males, gene expression is unchanged in the aged CP while females showed an age-dependent reduction. Age-dependent changes in VEGF localization were evident, from vasculature to epithelial cells. IGF2 and klotho localized in the basolateral membrane of the CP and showed an age-dependent reduction in epithelial cells. Water channel protein AQP1 localized in the tip of epithelial cells and showed an age-related reduction in mRNA and protein levels. TJP's JAM, CLAUDIN1, CLAUDIN2, and CLAUDIN5 were reduced in aged mice.

Conclusions

Our study highlights transcriptional level changes in the CP during aging. The age-related transcriptional changes exhibit similarities as well as gene-specific differences in the CP of males and females. Altered transcription of the water channel protein AQP1 and TJPs could be involved in reduced CSF production during aging. Importantly, reduction in the neurotrophic factors and longevity factor Klotho can play a role in regulating brain aging.

Nasopharyngeal lymphatic plexus is a hub for cerebrospinal fluid drainage

Cerebrospinal fluid (CSF) in the subarachnoid space around the brain has long been known to drain through the lymphatics to cervical lymph nodes1-17, but the connections and regulation have been challenging to identify. Here, using fluorescent CSF tracers in Prox1-GFP lymphatic reporter mice18, we found that the nasopharyngeal lymphatic plexus is a major hub for CSF outflow to deep cervical lymph nodes. This plexus had unusual valves and short lymphangions but no smooth-muscle coverage, whereas downstream deep cervical lymphatics had typical semilunar valves, long lymphangions and smooth muscle coverage that transported CSF to the deep cervical lymph nodes. α-Adrenergic and nitric oxide signalling in the smooth muscle cells regulated CSF drainage through the transport properties of deep cervical lymphatics. During ageing, the nasopharyngeal lymphatic plexus atrophied, but deep cervical lymphatics were not similarly altered, and CSF outflow could still be increased by adrenergic or nitric oxide signalling. Single-cell analysis of gene expression in lymphatic endothelial cells of the nasopharyngeal plexus of aged mice revealed increased type I interferon signalling and other inflammatory cytokines. The importance of evidence for the nasopharyngeal lymphatic plexus functioning as a CSF outflow hub is highlighted by its regression during ageing. Yet, the ageing-resistant pharmacological activation of deep cervical lymphatic transport towards lymph nodes can still increase CSF outflow, offering an approach for augmenting CSF clearance in age-related neurological conditions in which greater efflux would be beneficial.

Intracranial Pressure Dysfunction Following Severe Intracerebral Hemorrhage in Middle-Aged Rats

Rising intracranial pressure (ICP) aggravates secondary injury and heightens risk of death following intracerebral hemorrhage (ICH). Long-recognized compensatory mechanisms that lower ICP include reduced cerebrospinal fluid and venous blood volumes. Recently, we identified another compensatory mechanism in severe stroke, a decrease in cerebral parenchymal volume via widespread reductions in cell volume and extracellular space (tissue compliance). Here, we examined how age affects tissue compliance and ICP dynamics after severe ICH in rats (collagenase model). A planned comparison to historical young animal data revealed that aged SHAMs (no stroke) had significant cerebral atrophy (9% reduction, p ≤ 0.05), ventricular enlargement (9% increase, p ≤ 0.05), and smaller CA1 neuron volumes (21%, p ≤ 0.05). After ICH in aged animals, contralateral striatal neuron density and CA1 astrocyte density significantly increased (12% for neurons, 7% for astrocytes, p ≤ 0.05 vs. aged SHAMs). Unlike young animals, other regions in aged animals did not display significantly reduced cell soma volume despite a few trends. Nonetheless, overall contralateral hemisphere volume was 10% smaller in aged ICH animals compared to aged SHAMs (p ≤ 0.05). This age-dependent pattern of tissue compliance is not due to absent ICH-associated mass effect (83.2 mm3 avg. bleed volume) as aged ICH animals had significantly elevated mean and peak ICP (p ≤ 0.01), occurrence of ICP spiking events, as well as bilateral evidence of edema (e.g., 3% in injured brain, p ≤ 0.05 vs. aged SHAMs). Therefore, intracranial compliance reserve changes with age; after ICH, these and other age-related changes may cause greater fluctuation from baseline, increasing the chance of adverse outcomes like mortality.

Effect of isolated intracranial hypertension on cerebral perfusion within the phase of primary disturbances after subarachnoid hemorrhage in rats

Introduction

Elevated intracranial pressure (ICP) and blood components are the main trigger factors starting the complex pathophysiological cascade following subarachnoid hemorrhage (SAH). It is not clear whether they independently contribute to tissue damage or whether their impact cannot be differentiated from each other. We here aimed to establish a rat intracranial hypertension model that allows distinguishing the effects of these two factors and investigating the relationship between elevated ICP and hypoperfusion very early after SAH.

Methods

Blood or four different types of fluids [gelofusine, silicone oil, artificial cerebrospinal fluid (aCSF), aCSF plus xanthan (CX)] were injected into the cisterna magna in anesthetized rats, respectively. Arterial blood pressure, ICP and cerebral blood flow (CBF) were continuously measured up to 6 h after injection. Enzyme-linked immunosorbent assays were performed to measure the pro-inflammatory cytokines interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) in brain cortex and peripheral blood.

Results

Silicone oil injection caused deaths of almost all animals. Compared to blood, gelofusine resulted in lower peak ICP and lower plateau phase. Artificial CSF reached a comparable ICP peak value but failed to reach the ICP plateau of blood injection. Injection of CX with comparable viscosity as blood reproduced the ICP course of the blood injection group. Compared with the CBF course after blood injection, CX induced a comparable early global ischemia within the first minutes which was followed by a prompt return to baseline level with no further hypoperfusion despite an equal ICP course. The inflammatory response within the tissue did not differ between blood or blood-substitute injection. The systemic inflammation was significantly more pronounced in the CX injection group compared with the other fluids including blood.

Discussion

By cisterna magna injection of blood substitution fluids, we established a subarachnoid space occupying rat model that exactly mimicked the course of ICP in the first 6 h following blood injection. Fluids lacking blood components did not induce the typical prolonged hypoperfusion occurring after blood-injection in this very early phase. Our study strongly suggests that blood components rather than elevated ICP play an important role for early hypoperfusion events in SAH.

Mechanisms of cerebrospinal fluid and brain interstitial fluid production

Fluid homeostasis is fundamental for brain function with cerebral edema and hydrocephalus both being major neurological conditions. Fluid movement from blood into brain is one crucial element in cerebral fluid homeostasis. Traditionally it has been thought to occur primarily at the choroid plexus (CP) as cerebrospinal fluid (CSF) secretion due to polarized distribution of ion transporters at the CP epithelium. However, there are currently controversies as to the importance of the CP in fluid secretion, just how fluid transport occurs at that epithelium versus other sites, as well as the direction of fluid flow in the cerebral ventricles. The purpose of this review is to evaluate evidence on the movement of fluid from blood to CSF at the CP and the cerebral vasculature and how this differs from other tissues, e.g., how ion transport at the blood-brain barrier as well as the CP may drive fluid flow. It also addresses recent promising data on two potential targets for modulating CP fluid secretion, the Na+/K+/Cl- cotransporter, NKCC1, and the non-selective cation channel, transient receptor potential vanilloid 4 (TRPV4). Finally, it raises the issue that fluid secretion from blood is not constant, changing with disease and during the day. The apparent importance of NKCC1 phosphorylation and TRPV4 activity at the CP in determining fluid movement suggests that such secretion may also vary over short time frames. Such dynamic changes in CP (and potentially blood-brain barrier) function may contribute to some of the controversies over its role in brain fluid secretion.

Age- and time-of-day dependence of glymphatic function in the human brain measured via two diffusion MRI methods

Advanced age, accompanied by impaired glymphatic function, is a key risk factor for many neurodegenerative diseases. To study age-related differences in the human glymphatic system, we measured the influx and efflux activities of the glymphatic system via two non-invasive diffusion magnetic resonance imaging (MRI) methods, ultra-long echo time and low-b diffusion tensor imaging (DTI_low-b) measuring the subarachnoid space (SAS) flow along the middle cerebral artery and DTI analysis along the perivascular space (DTI-ALPS) along medullary veins in 22 healthy volunteers (aged 21-75 years). We first evaluated the circadian rhythm dependence of the glymphatic activity by repeating the MRI measurements at five time points from 8:00 to 23:00 and found no time-of-day dependence in the awake state under the current sensitivity of MRI measurements. Further test-retest analysis demonstrated high repeatability of both diffusion MRI measurements, suggesting their reliability. Additionally, the influx rate of the glymphatic system was significantly higher in participants aged >45 years than in participants aged 21-38, while the efflux rate was significantly lower in those aged >45 years. The mismatched influx and efflux activities in the glymphatic system might be due to age-related changes in arterial pulsation and aquaporin-4 polarization.

Morphological and mitochondrial changes in murine choroid plexus epithelial cells during healthy aging

BACKGROUND

Choroid plexuses (ChPs) are intraventricular structures mainly composed by specialized epithelial cells interconnected by tight junctions that establish the blood-cerebrospinal fluid (CSF) barrier. ChPs are essential to produce CSF and transport solutes from and into the brain. Deterioration of ChP function and morphology has been correlated to worsening of neurodegenerative disorders. We here map morpho-functional changes in the ChP epithelial cells during healthy aging, starting from young adult to 2-years old mice.

METHODS

We used a multi-tiered approach, including transmission electron microscopy (TEM), immunohistochemistry, RT-qPCR, Western Blot and 2-photon microscopy (2-PM) at multiple timepoints ranging from young adult to 2-years old mice.

RESULTS

We identified distinct morpho-functional modifications in epithelial cells of ChP starting from 8 to 12 months of age, which mostly remained stable up to 2 years. These changes include flattening of the epithelium, reduction of microvilli length and an augmentation of interrupted tight junctions. We also found a decrease in mitochondria density together with elongation of mitochondria in older mice. Morphological mitochondrial rearrangements were accompanied by increased superoxide levels, decreased membrane potential and decreased mitochondrial motility in aged mice. Interestingly, most of the age-related changes were not accompanied by modification of protein and/or gene expression levels and aged mitochondria effectively responded to acute pharmacological stressful stimuli.

CONCLUSIONS

Our study suggests a long-term progression of multiple morpho-functional features of the mouse choroid plexus epithelium during adulthood followed by structural remodeling during the aging process. These findings can lead to a better understanding on how functional and morphological rearrangements of ChP are correlated during aging.

Analgesic Action of Acetaminophen via Kv7 Channels

The mechanism of acetaminophen (APAP) analgesia is at least partially unknown. Previously, we showed that the APAP metabolite N-acetyl-p-benzoquinone imine (NAPQI) activated Kv7 channels in neurons in vitro, and this activation of Kv7 channels dampened neuronal firing. Here, the effect of the Kv7 channel blocker XE991 on APAP-induced analgesia was investigated in vivo. APAP had no effect on naive animals. Induction of inflammation with λ-carrageenan lowered mechanical and thermal thresholds. Systemic treatment with APAP reduced mechanical hyperalgesia, and co-application of XE991 reduced APAP's analgesic effect on mechanical pain. In a second experiment, the analgesic effect of systemic APAP was not antagonized by intrathecal XE991 application. Analysis of liver samples revealed APAP and glutathione-coupled APAP indicative of metabolization. However, there were no relevant levels of these metabolites in cerebrospinal fluid, suggesting no relevant APAP metabolite formation in the CNS. In summary, the results support an analgesic action of APAP by activating Kv7 channels at a peripheral site through formation of the metabolite NAPQI.

Cerebral Folate Metabolism in Post-Mortem Alzheimer's Disease Tissues: A Small Cohort Study

We investigated the cerebral folate system in post-mortem brains and matched cerebrospinal fluid (CSF) samples from subjects with definite Alzheimer's disease (AD) (n = 21) and neuropathologically normal brains (n = 21) using immunohistochemistry, Western blot and dot blot. In AD the CSF showed a significant decrease in 10-formyl tetrahydrofolate dehydrogenase (FDH), a critical folate binding protein and enzyme in the CSF, as well as in the main folate transporter, folate receptor alpha (FRα) and folate. In tissue, we found a switch in the pathway of folate supply to the cerebral cortex in AD compared to neurologically normal brains. FRα switched from entry through FDH-positive astrocytes in normal, to entry through glial fibrillary acidic protein (GFAP)-positive astrocytes in the AD cortex. Moreover, this switch correlated with an apparent change in metabolic direction to hypermethylation of neurons in AD. Our data suggest that the reduction in FDH in CSF prohibits FRα-folate entry via FDH-positive astrocytes and promotes entry through the GFAP pathway directly to neurons for hypermethylation. This data may explain some of the cognitive decline not attributable to the loss of neurons alone and presents a target for potential treatment.

Acute Methylglyoxal-Induced Damage in Blood-Brain Barrier and Hippocampal Tissue

Methylglyoxal (MG) is a reactive dicarbonyl compound formed mostly via the glycolytic pathway. Elevated blood glucose levels can cause MG accumulation in plasma and cerebrospinal fluid in patients with diabetes mellitus and Alzheimer's disease. Under these disease conditions, the high reactivity of MG leads to modification of proteins and other biomolecules, generating advanced glycation end products (AGEs), which are considered mediators in neurodegenerative diseases. We investigated the integrity of the blood-brain barrier (BBB) and astrocyte response in the hippocampus to acute insult induced by MG when it was intracerebroventricularly administered to rats. Seventy-two hours later, BBB integrity was lost, as assessed by the entry of Evans dye into the brain tissue and albumin in the cerebrospinal fluid, and a decrease in aquaporin-4 and connexin-43 in the hippocampal tissue. MG did not induce changes in the hippocampal contents of RAGE in this short interval, but decreased the expression of S100B, an astrocyte-secreted protein that binds RAGE. The expression of two important transcription factors of the antioxidant response, NF-κB and Nrf2, was unchanged. However, hemeoxigenase-1 was upregulated in the MG-treated group. These data corroborate the idea that hippocampal cells are targets of MG toxicity and that BBB dysfunction and specific glial alterations induced by this compound may contribute to the behavioral and cognitive alterations observed in these animals.

Revisiting Cerebrospinal Fluid Flow Direction and Rate in Physiologically Based Pharmacokinetic Model

The bidirectional pulsatile movement of cerebrospinal fluid (CSF), instead of the traditionally believed unidirectional and constant CSF circulation, has been demonstrated. In the present study, the structure and parameters of the CSF compartments were revisited in our comprehensive and validated central nervous system (CNS)-specific, physiologically based pharmacokinetic (PBPK) model of healthy rats (LeiCNS-PK3.0). The bidirectional and site-dependent CSF movement was incorporated into LeiCNS-PK3.0 to create the new LeiCNS-PK“3.1” model. The physiological CSF movement rates in healthy rats that are unavailable from the literature were estimated by fitting the PK data of sucrose, a CSF flow marker, after intra-CSF administration. The capability of LeiCNS-PK3.1 to describe the PK profiles of other molecules was compared with that of the original LeiCNS-PK3.0 model. LeiCNS-PK3.1 demonstrated superior description of the CSF PK profiles of a range of small molecules after intra-CSF administration over LeiCNS-PK3.0. LeiCNS-PK3.1 also retained the same level of predictability of CSF PK profiles in cisterna magna after intravenous administration. These results support the theory of bidirectional and site-dependent CSF movement across the entire CSF space over unidirectional and constant CSF circulation in healthy rats, pointing out the need to revisit the structures and parameters of CSF compartments in CNS-PBPK models.

Chemerin fragments show different effects on systemic blood pressure dependent on carboxyl-terminal cleavage site

Chemerin is an adipocytokine whose concentration in blood correlates positively with blood pressure (BP). We have recently revealed that acute intracerebroventricular (i.c.v.) injection of chemerin-9, an active fragment of human chemerin, increased systemic BP in normal Wistar rats, suggesting that chemerin is involved in the central nervous control of peripheral BP. After secreted as an inactive form as prochemerin, a mature form of active chemerin is produced through the cleavage of its carboxyl (C)-terminus by proteases. Although the activity of cleaved products of chemerin has been examined in vitro, in vivo effects remained to be elusive. In order to explore them, we performed acute i.c.v. injection of mouse chemerin-9 (mChemerin-9; 148F-156S), mouse chemerin-8 (mChemerin-8; 148F-155F), and mouse chemerin-7 (mChemerin-7; 148F-154A) into Wistar rats, and examined the effects on systemic BP. After chemerin fragment (1–30 nmol/head, i.c.v.) was cumulatively administered, systemic BP was measured by a cannulation method under an isoflurane anesthesia. mChemerin-9 but not mChemerin-8 and -7 induced a pressor response, which was concentration-dependent. In conclusion, we for the first time demonstrated that mChemerin-9 that corresponds to the C-terminal nine amino acids of active mouse chemerin156S increased systemic BP in rats, and also that chemerin fragments showed different effects on systemic BP dependent on how their C-terminus was cleaved.

Choroid plexus function in neurological homeostasis and disorders: The awakening of the circadian clocks and orexins

As research regarding the role of circadian rhythms, sleep, and the orexinergic system in neurodegenerative diseases is growing, it is surprising that the choroid plexus (CP) remains underappreciated in this realm. Despite its extensive role in the regulation of circadian rhythms and orexinergic signalling, as well as acting as the primary conduit between cerebrospinal fluid (CSF) and the circulatory system, providing a mechanism by which toxic waste molecules can be removed from the brain, the CP has been largely unexplored in neurodegeneration. In this review, we explore the role of the CP in maintaining brain homeostasis and circadian rhythms, regulating CSF dynamics, and how these functions change across the lifespan, from development to senescence. In addition, we examine the relationship between the CP, orexinergic signalling, and the glymphatic system, highlighting gaps in the literature and areas that require immediate exploration. Finally, we assess current knowledge, including possible therapeutic strategies, regarding the role of the CP in neurological disorders, such as traumatic brain injury, migraine, Alzheimer's disease, and multiple sclerosis.

NLRP3 inflammasome-mediated choroid plexus hypersecretion contributes to hydrocephalus after intraventricular hemorrhage via phosphorylated NKCC1 channels

Background

Hydrocephalus is a severe complication of intracerebral hemorrhage with ventricular extension (ICH-IVH) and causes cerebrospinal fluid (CSF) accumulation. The choroid plexus epithelium plays an important role in CSF secretion and constitutes the blood–CSF barrier within the brain–immune system interface. Although the NLRP3 inflammasome, as a key component of the innate immune system, promotes neuroinflammation, its role in the pathogenesis of hydrocephalus after hemorrhage has not been investigated. Therefore, this study aimed to investigate the potential mechanism of NLRP3 in hydrocephalus to discover a potential marker for targeted therapy.

Methods

A rat model of hydrocephalus after ICH-IVH was developed through autologous blood infusion in wild-type and Nlrp3^−/− rats. By studying the features and processes of the model, we investigated the relationship between the NLRP3 inflammasome and CSF hypersecretion in the choroid plexus.

Results

The ICH-IVH model rats showed ventricular dilation accompanied by CSF hypersecretion for 3 days. Based on the choroid plexus RNA-seq and proteomics results, we found that an inflammatory response was activated. The NLRP3 inflammasome was investigated, and the expression levels of NLRP3 inflammasome components reached a peak at 3 days after ICH-IVH. Inhibition of NLRP3 by an MCC950 inflammasome inhibitor or Nlrp3 knockout decreased CSF secretion and ventricular dilation and attenuated neurological deficits after ICH-IVH. The mechanism underlying the neuroprotective effects of NLRP3 inhibition involved decreased phosphorylation of NKCC1, which is a major protein that regulates CSF secretion by altering Na⁺- and K⁺-coupled water transport, via MCC950 or Nlrp3 knockout. In combination with the in vitro experiments, this experiment confirmed the involvement of the NLRP3/p-NKCC1 pathway and Na⁺ and K⁺ flux.

Conclusions

This study demonstrates that NKCC1 phosphorylation in the choroid plexus epithelium promotes NLRP3 inflammasome-mediated CSF hypersecretion and that NLRP3 plays an important role in the pathogenesis of hydrocephalus after hemorrhage. These findings provide a new therapeutic strategy for treating hydrocephalus.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02530-x.

Effects of age, amyloid, sex, and APOE ε4 on the CSF proteome in normal cognition

Introduction

It is important to understand which biological processes change with aging, and how such changes are associated with increased Alzheimer's disease (AD) risk. We studied how cerebrospinal fluid (CSF) proteomics changed with age and tested if associations depended on amyloid status, sex, and apolipoprotein E Ɛ4 genotype.

Methods

We included 277 cognitively intact individuals aged 46 to 89 years from Alzheimer's Disease Neuroimaging Initiative, European Medical Information Framework for Alzheimer's Disease Multimodal Biomarker Discovery, and Metabolic Syndrome in Men. In total, 1149 proteins were measured with liquid chromatography mass spectrometry with multiple reaction monitoring/Rules-Based Medicine, tandem mass tag mass spectrometry, and SOMAscan. We tested associations between age and protein levels in linear models and tested enrichment for Reactome pathways.

Results

Levels of 252 proteins increased with age independently of amyloid status. These proteins were associated with immune and signaling processes. Levels of 21 proteins decreased with older age exclusively in amyloid abnormal participants and these were enriched for extracellular matrix organization.

Discussion

We found amyloid-independent and -dependent CSF proteome changes with older age, perhaps representing physiological aging and early AD pathology.

Evaluation of Blood-CSF Barrier Transport by Quantitative Real Time Fluorescence Microscopy

PURPOSE

Transporters at the blood-cerebrospinal fluid (CSF) barrier (BCSFB) play active roles in removing drugs and toxins from the CSF. The goal of this study is to develop a fluorescence microscopy approach to quantitatively study the transepithelial transport processes at the murine BCSFB in real time.

METHODS

Choroid plexus (CP) tissues were isolated from mouse lateral ventricles and incubated with anionic (fluorescein-methotrexate, 8-fluorescein-cAMP) or cationic (IDT307) fluorescent probes. The CSF-to-blood transport was imaged and quantified using compartmental segmentation and digital image analysis. Real time images were captured and analyzed to obtain kinetic information and identify the rate-limiting step. The effect of transporter inhibitors was also evaluated.

RESULTS

The transport processes of fluorescent probes can be captured and analyzed digitally. The intra- and inter- animal variability were 20.4% and 25.7%, respectively. Real time analysis showed distinct transport kinetics and rate-limiting step for anionic and cationic probes. A CP efflux index was proposed to distinguish between transepithelial flux and intracellular accumulation. Rifampin and MK571 decreased the overall transepithelial transport of anionic probes by more than 90%, indicating a possible involvement of organic anion transporting polypeptides (Oatps) and multidrug resistance-associated proteins (Mrps).

CONCLUSIONS

A CP isolation method was described, and a quantitative fluorescence imaging approach was developed to evaluate CSF-to-blood transport in mouse CP. The method is consistent, reproducible, and capable of tracking real time transepithelial transport with temporal and spatial resolution. The approach can be used to evaluate transport mechanisms, assess tissue drug accumulation, and assay potential drug-drug interactions at the BCSFB.

Fluid transport in the brain

The brain harbors a unique ability to, figuratively speaking, shift its gears. During wakefulness, the brain is geared fully toward processing information and behaving, while homeostatic functions predominate during sleep. The blood-brain barrier establishes a stable environment that is optimal for neuronal function, yet the barrier imposes a physiological problem; transcapillary filtration that forms extracellular fluid in other organs is reduced to a minimum in brain. Consequently, the brain depends on a special fluid [the cerebrospinal fluid (CSF)] that is flushed into brain along the unique perivascular spaces created by astrocytic vascular endfeet. We describe this pathway, coined the term glymphatic system, based on its dependency on astrocytic vascular endfeet and their adluminal expression of aquaporin-4 water channels facing toward CSF-filled perivascular spaces. Glymphatic clearance of potentially harmful metabolic or protein waste products, such as amyloid-β, is primarily active during sleep, when its physiological drivers, the cardiac cycle, respiration, and slow vasomotion, together efficiently propel CSF inflow along periarterial spaces. The brain's extracellular space contains an abundance of proteoglycans and hyaluronan, which provide a low-resistance hydraulic conduit that rapidly can expand and shrink during the sleep-wake cycle. We describe this unique fluid system of the brain, which meets the brain's requisites to maintain homeostasis similar to peripheral organs, considering the blood-brain-barrier and the paths for formation and egress of the CSF.

Aging-Related Alterations of Glymphatic Transport in Rat: In vivo Magnetic Resonance Imaging and Kinetic Study

Objective

Impaired glymphatic waste clearance function during brain aging leads to the accumulation of metabolic waste and neurotoxic proteins (e.g., amyloid-β, tau) which contribute to neurological disorders. However, how the age-related glymphatic dysfunction exerts its effects on different cerebral regions and affects brain waste clearance remain unclear.

Methods

We investigated alterations of glymphatic transport in the aged rat brain using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and advanced kinetic modeling. Healthy young (3-4 months) and aged (18-20 months) male rats (n = 12/group) underwent the identical MRI protocol, including T2-weighted imaging and 3D T1-weighted imaging with intracisternal administration of contrast agent (Gd-DTPA). Model-derived parameters of infusion rate and clearance rate, characterizing the kinetics of cerebrospinal fluid (CSF) tracer transport via the glymphatic system, were evaluated in multiple representative brain regions. Changes in the CSF-filled cerebral ventricles were measured using contrast-induced time signal curves (TSCs) in conjunction with structural imaging.

Results

Compared to the young brain, an overall impairment of glymphatic transport function was detected in the aged brain, evidenced by the decrease in both infusion and clearance rates throughout the brain. Enlarged ventricles in parallel with reduced efficiency in CSF transport through the ventricular regions were present in the aged brain. While the age-related glymphatic dysfunction was widespread, our kinetic quantification demonstrated that its impact differed considerably among cerebral regions with the most severe effect found in olfactory bulb, indicating the heterogeneous and regional preferential alterations of glymphatic function.

Conclusion

The robust suppression of glymphatic activity in the olfactory bulb, which serves as one of major efflux routes for brain waste clearance, may underlie, in part, age-related neurodegenerative diseases associated with neurotoxic substance accumulation. Our data provide new insight into the cerebral regional vulnerability to brain functional change with aging.

The glymphatic hypothesis: the theory and the evidence

The glymphatic hypothesis proposes a mechanism for extravascular transport into and out of the brain of hydrophilic solutes unable to cross the blood-brain barrier. It suggests that there is a circulation of fluid carrying solutes inwards via periarterial routes, through the interstitium and outwards via perivenous routes. This review critically analyses the evidence surrounding the mechanisms involved in each of these stages. There is good evidence that both influx and efflux of solutes occur along periarterial routes but no evidence that the principal route of outflow is perivenous. Furthermore, periarterial inflow of fluid is unlikely to be adequate to provide the outflow that would be needed to account for solute efflux. A tenet of the hypothesis is that flow sweeps solutes through the parenchyma. However, the velocity of any possible circulatory flow within the interstitium is too small compared to diffusion to provide effective solute movement. By comparison the earlier classical hypothesis describing extravascular transport proposed fluid entry into the parenchyma across the blood-brain barrier, solute movements within the parenchyma by diffusion, and solute efflux partly by diffusion near brain surfaces and partly carried by flow along "preferred routes" including perivascular spaces, white matter tracts and subependymal spaces. It did not suggest fluid entry via periarterial routes. Evidence is still incomplete concerning the routes and fate of solutes leaving the brain. A large proportion of the solutes eliminated from the parenchyma go to lymph nodes before reaching blood but the proportions delivered directly to lymph or indirectly via CSF which then enters lymph are as yet unclear. In addition, still not understood is why and how the absence of AQP4 which is normally highly expressed on glial endfeet lining periarterial and perivenous routes reduces rates of solute elimination from the parenchyma and of solute delivery to it from remote sites of injection. Neither the glymphatic hypothesis nor the earlier classical hypothesis adequately explain how solutes and fluid move into, through and out of the brain parenchyma. Features of a more complete description are discussed. All aspects of extravascular transport require further study.

Brain Morphometry and Cognitive Performance in Normal Brain Aging: Age- and Sex-Related Structural and Functional Changes

BACKGROUND

The human brain structure undergoes considerable changes throughout life. Cognitive function can be affected either negatively or positively. It is challenging to segregate normal brain aging from the accelerated one.

OBJECTIVE

To work out a descriptive model of brain structural and functional changes in normal aging.

MATERIALS AND METHODS

By using voxel-based morphometry and lesion segmentation along with linear statistics and machine learning (ML), we analyzed the structural changes in the major brain compartments and modeled the dynamics of neurofunctional performance throughout life. We studied sex differences in lifelong dynamics of brain volumetric data with Mann-Whitney U-test. We tested the hypothesis that performance in some cognitive domains might decline as a linear function of age while other domains might have a non-linear dependence on it. We compared the volumetric changes in the major brain compartments with the dynamics of psychophysiological performance in 4 age groups. Then, we tested linear models of structural and functional decline for significant differences between the slopes in age groups with the T-test.

RESULTS

White matter hyperintensities (WMH) are not the major structural determinant of the brain normal aging. They should be viewed as signs of a disease. There is a sex difference in the speed and/or in the onset of the gray matter atrophy. It either starts earlier or goes faster in males. Marked sex difference in the proportion of total cerebrospinal fluid (CSF) and intraventricular CSF (iCSF) justifies that elderly men are more prone to age-related brain atrophy than women of the same age.

CONCLUSION

The article gives an overview and description of the conceptual structural changes in the brain compartments. The obtained data justify distinct patterns of age-related changes in the cognitive functions. Cross-life slowing of decision-making may follow the linear tendency of enlargement of the interhemispheric fissure because the center of task switching and inhibitory control is allocated within the medial wall of the frontal cortex, and its atrophy accounts for the expansion of the fissure. Free online tool at https://med-predict.com illustrates the tests and study results.

Choroid Plexus in Alzheimer’s Disease—The Current State of Knowledge

The choroid plexus (CP), located in each of the four ventricles of the brain, is formed by a monolayer of epithelial cells that surrounds a highly vascularized connective tissue with permeable capillaries. These cells are joined by tight junctions forming the blood–cerebrospinal fluid barrier (BCSFB), which strictly regulates the exchange of substances between the blood and cerebrospinal fluid (CSF). The primary purpose of the CP is to secrete CSF, but it also plays a role in the immune surveillance of the central nervous system (CNS) and in the removal of neurotoxic compounds from the CSF. According to recent findings, the CP is also involved in the modulation of the circadian cycle and neurogenesis. In diseases such as Alzheimer’s disease (AD), the function of the CP is impaired, resulting in an altered secretory, barrier, transport, and immune function. This review describes the current state of knowledge concerning the roles of the CP and BCSFB in the pathophysiology of AD and summarizes recently proposed therapies that aim to restore CP and BCSFB functions.

Cerebrospinal fluid is a significant fluid source for anoxic cerebral oedema

Cerebral edema develops after anoxic brain injury. In two models of asphyxial and asystolic cardiac arrest without resuscitation, we found that edema develops shortly after anoxia secondary to terminal depolarizations and the abnormal entry of cerebrospinal fluid (CSF). Edema severity correlated with the availability of CSF with the age-dependent increase in CSF volume worsening the severity of edema. Edema was identified primarily in brain regions bordering CSF compartments in mice and humans. The degree of ex vivo tissue swelling was predicted by an osmotic model suggesting that anoxic brain tissue possesses a high intrinsic osmotic potential. This osmotic process was temperature-dependent, proposing an additional mechanism for the beneficial effect of therapeutic hypothermia. These observations show that CSF is a primary source of edema fluid in anoxic brain. This novel insight offers a mechanistic basis for the future development of alternative strategies to prevent cerebral edema formation after cardiac arrest.

Characterization of Age-Related Differences in the Human Choroid Plexus Volume, Microstructural Integrity, and Blood Perfusion Using Multiparameter Magnetic Resonance Imaging

The choroid plexus (CP) is an important cerebral structure involved in cerebrospinal fluid production and transport of solutes into the brain. Recent studies have uncovered the involvement of the CP in neurological disorders such as Alzheimer's disease and multiple sclerosis. However, our understanding of human age-related microstructural and functional changes in the CP with aging and neuropathology is limited. In this cross-sectional study, we investigated age and sex differences in the CP structure and function using advanced quantitative magnetic resonance imaging methodology in a large cohort (n = 155) of cognitively unimpaired individuals over a wide age range between 21 and 94 years. Our analysis included volumetric measurements, relaxometry measures (T 1 and T 2), diffusion tensor imaging (DTI) measures of fractional anisotropy (FA) and mean diffusivity (MD), as well as measures of cerebral blood flow (CBF). Our results revealed that CP volume was increasing with advancing age. We conjecture that this novel observation is likely attributed to alterations in the CP microstructure or function as well as to ventriculomegaly. Indeed, we also found that CBF was lower with advanced age, while, consistent with previous studies, T 1, T 2 and MD were higher, and FA was lower with advanced age. We attribute these functional and microstructural differences to a deteriorated CP structural integrity with aging. Furthermore, our relaxometry and DTI measures were found to be associated with differences in blood perfusion revealing lower microstructural integrity with lower CBF. Finally, in agreement with literature, sex-related differences in MD and CBF were statistically significant. This work lays the foundation for ongoing investigation of the involvement of CP in neurodegeneration.

Altered Cerebrospinal Fluid Clearance and Increased Intracranial Pressure in Rats 18 h After Experimental Cortical Ischaemia

Oedema-independent intracranial pressure (ICP) rise peaks 20-22-h post-stroke in rats and may explain early neurological deterioration. Cerebrospinal fluid (CSF) volume changes may be involved. Cranial CSF clearance primarily occurs via the cervical lymphatics and movement into the spinal portion of the cranio-spinal compartment. We explored whether impaired CSF clearance at these sites could explain ICP rise after stroke. We recorded ICP at baseline and 18-h post-stroke, when we expect changes contributing to peak ICP to be present. CSF clearance was assessed in rats receiving photothrombotic stroke or sham surgery by intraventricular tracer infusion. Tracer concentration was quantified in the deep cervical lymph nodes ex vivo and tracer transit to the spinal subarachnoid space was imaged in vivo. ICP rose significantly from baseline to 18-h post-stroke in stroke vs. sham rats [median = 5 mmHg, interquartile range (IQR) = 0.1-9.43, n = 12, vs. -0.3 mmHg, IQR = -1.9-1.7, n = 10], p = 0.03. There was a bimodal distribution of rats with and without ICP rise. Tracer in the deep cervical lymph nodes was significantly lower in stroke with ICP rise (0 μg/mL, IQR = 0-0.11) and without ICP rise (0 μg/mL, IQR = 0-4.47) compared with sham rats (4.17 μg/mL, IQR = 0.74-8.51), p = 0.02. ICP rise was inversely correlated with faster CSF transit to the spinal subarachnoid space (R = -0.59, p = 0.006, Spearman's correlation). These data suggest that reduced cranial clearance of CSF via cervical lymphatics may contribute to post-stroke ICP rise, partially compensated via increased spinal CSF outflow.

A 3D flexible neural interface based on a microfluidic interconnection cable capable of chemical delivery

The demand for multifunctional neural interfaces has grown due to the need to provide a better understanding of biological mechanisms related to neurological diseases and neural networks. Direct intracerebral drug injection using microfluidic neural interfaces is an effective way to deliver drugs to the brain, and it expands the utility of drugs by bypassing the blood-brain barrier (BBB). In addition, uses of implantable neural interfacing devices have been challenging due to inevitable acute and chronic tissue responses around the electrodes, pointing to a critical issue still to be overcome. Although neural interfaces comprised of a collection of microneedles in an array have been used for various applications, it has been challenging to integrate microfluidic channels with them due to their characteristic three-dimensional structures, which differ from two-dimensionally fabricated shank-type neural probes. Here we present a method to provide such three-dimensional needle-type arrays with chemical delivery functionality. We fabricated a microfluidic interconnection cable (µFIC) and integrated it with a flexible penetrating microelectrode array (FPMA) that has a 3-dimensional structure comprised of silicon microneedle electrodes supported by a flexible array base. We successfully demonstrated chemical delivery through the developed device by recording neural signals acutely from in vivo brains before and after KCl injection. This suggests the potential of the developed microfluidic neural interface to contribute to neuroscience research by providing simultaneous signal recording and chemical delivery capabilities.

Cognitively unimpaired individuals with a low burden of Aβ pathology have a distinct CSF biomarker profile

Background

Understanding the changes that occur in the transitional stage between absent and overt amyloid-β (Aβ) pathology within the Alzheimer’s continuum is crucial to develop therapeutic and preventive strategies. The objective of this study is to test whether cognitively unimpaired individuals with a low burden of Aβ pathology have a distinct CSF, structural, and functional neuroimaging biomarker profile.

Methods

Cross-sectional study of 318 middle-aged, cognitively unimpaired individuals from the ALFA+ cohort. We measured CSF Aβ42/40, phosphorylated tau (p-tau), total tau (t-tau), neurofilament light (NfL), neurogranin, sTREM2, YKL40, GFAP, IL6, S100B, and α-synuclein. Participants also underwent cognitive assessments, APOE genotyping, structural MRI, [¹⁸F]-FDG, and [¹⁸F]-flutemetamol PET.

To ensure the robustness of our results, we used three definitions of low burden of Aβ pathology: (1) positive CSF Aβ42/40 and < 30 Centiloids in Aβ PET, (2) positive CSF Aβ42/40 and negative Aβ PET visual read, and (3) 20–40 Centiloid range in Aβ PET. We tested CSF and neuroimaging biomarker differences between the low burden group and the corresponding Aβ-negative group, adjusted by age and sex.

Results

The prevalence and demographic characteristics of the low burden group differed between the three definitions. CSF p-tau and t-tau were increased in the low burden group compared to the Aβ-negative in all definitions. CSF neurogranin was increased in the low burden group definitions 1 and 3, while CSF NfL was only increased in the low burden group definition 1. None of the defined low burden groups showed signs of atrophy or glucose hypometabolism. Instead, we found slight increases in cortical thickness and metabolism in definition 2.

Conclusions

There are biologically meaningful Aβ-downstream effects in individuals with a low burden of Aβ pathology, while structural and functional changes are still subtle or absent. These findings support considering individuals with a low burden of Aβ pathology for clinical trials.

Trial registration

NCT02485730

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00863-y.

Choroid Plexus and Drug Removal Mechanisms

Timely and efficient removal of xenobiotics and metabolites from the brain is crucial in maintaining the homeostasis and normal function of the brain. The choroid plexus (CP) forms the blood-cerebrospinal fluid barrier and vitally removes drugs and wastes from the brain through several co-existing clearance mechanisms. The CP epithelial (CPE) cells synthesize and secrete the cerebrospinal fluid (CSF). As the CSF passes through the ventricular and subarachnoid spaces and eventually drains into the general circulation, it collects and removes drugs, toxins, and metabolic wastes from the brain. This bulk flow of the CSF serves as a default and non-selective pathway for the removal of solutes and macromolecules from the brain interstitium. Besides clearance by CSF bulk flow, the CPE cells express several multispecific membrane transporters to actively transport substrates from the CSF side into the blood side. In addition, several phase I and II drug-metabolizing enzymes are expressed in the CPE cells, which enzymatically inactivate a broad spectrum of reactive or toxic substances. This review summarizes our current knowledge of the functional characteristics and key contributors to the various clearance pathways in the CP-CSF system, overviewing recent developments in our understanding of CSF flow dynamics and the functional roles of CP uptake and efflux transporters in influencing CSF drug concentrations.

Direct Measurement of Cerebrospinal Fluid Production in Mice

The emerging interest in brain fluid transport has prompted a need for techniques that provide an understanding of what factors regulate cerebrospinal fluid (CSF) production. Here, we describe a methodology for direct quantification of CSF production in awake mice. We measure CSF production by placing a catheter in a lateral ventricle, while physically blocking outflow from the 4^th ventricle. Using this methodology, we show that CSF production increases during isoflurane anesthesia, and to a lesser extent with ketamine/xylazine anesthesia, relative to the awake state. Aged mice have reduced CSF production, which is even lower in aged mice overexpressing amyloid-β. Unexpectedly, CSF production in young female mice is 30% higher than in age-matched males. Altogether, the present observations imply that a reduction in CSF production might contribute to the age-related risk of proteinopathies but that the rate of CSF production and glymphatic fluid transport are not directly linked.

Liu et al. develop a method for direct quantification of cerebrospinal fluid (CSF) production in awake mice. Using this method, the authors evaluate the effect of brain states, ages, sex, anesthetic types, and amyloid-β burden on CSF production.

Cerebrospinal fluid drainage kinetics across the cribriform plate are reduced with aging

BACKGROUND

Continuous circulation and drainage of cerebrospinal fluid (CSF) are essential for the elimination of CSF-borne metabolic products and neuronal function. While multiple CSF drainage pathways have been identified, the significance of each to normal drainage and whether there are differential changes at CSF outflow regions in the aging brain are unclear.

METHODS

Dynamic in vivo imaging of near infrared fluorescently-labeled albumin was used to simultaneously visualize the flow of CSF at outflow regions on the dorsal side (transcranial and -spinal) of the central nervous system. This was followed by kinetic analysis, which included the elimination rate constants for these regions. In addition, tracer distribution in ex vivo tissues were assessed, including the nasal/cribriform region, dorsal and ventral surfaces of the brain, spinal cord, cranial dura, skull base, optic and trigeminal nerves and cervical lymph nodes.

RESULTS

Based on the in vivo data, there was evidence of CSF elimination, as determined by the rate of clearance, from the nasal route across the cribriform plate and spinal subarachnoid space, but not from the dorsal dural regions. Using ex vivo tissue samples, the presence of tracer was confirmed in the cribriform area and olfactory regions, around pial blood vessels, spinal subarachnoid space, spinal cord and cervical lymph nodes but not for the dorsal dura, skull base or the other cranial nerves. Also, ex vivo tissues showed retention of tracer along brain fissures and regions associated with cisterns on the brain surfaces, but not in the brain parenchyma. Aging reduced CSF elimination across the cribriform plate but not that from the spinal SAS nor retention on the brain surfaces.

CONCLUSIONS

Collectively, these data show that the main CSF outflow sites were the nasal region across the cribriform plate and from the spinal regions in mice. In young adult mice, the contribution of the nasal and cribriform route to outflow was much higher than from the spinal regions. In older mice, the contribution of the nasal route to CSF outflow was reduced significantly but not for the spinal routes. This kinetic approach may have significance in determining early changes in CSF drainage in neurological disorder, age-related cognitive decline and brain diseases.

Klotho overexpression improves amyloid-β clearance and cognition in the APP/PS1 mouse model of Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent type of dementia, characterized by the presence of amyloid-β (Aβ) plaques. We previously reported that Klotho lowered Aβ levels in the brain and protected against cognitive deficits in amyloid precursor protein/presenilin 1(APP/PS1) mice. However, the underlying mechanism remains unclear. In this study, we induced intracerebral Klotho overexpression in 13-month-old APP/PS1 mice by injecting lentivirus that carried full-length mouse Klotho cDNA in the lateral ventricle of the brain. We examined the effects of Klotho overexpression on cognition, Aβ burden, Aβ-related neuropathology, microglia transformation, and Aβ transport systems in vivo. Additionally, we investigated the effects of Klotho on Aβ transport at the blood-cerebrospinal fluid barrier by knocking down Klotho in primary human choroid plexus epithelial cells (HCPEpiCs). The upregulation of Klotho levels in the brain and serum significantly ameliorated Aβ burden, neuronal and synaptic loss and cognitive deficits in aged APP/PS1 mice. Klotho treatment significantly inhibited NACHT, LRR, and PYD domain-containing protein 3 (NLRP3) and the subsequent transformation of microglia to the M2 type that may enhance microglia-mediated Aβ clearance. Meanwhile, Klotho overexpression also regulated Aβ transporter expression, which may promote Aβ transporter-mediated Aβ clearance. Moreover, the ability of HCPEpiCs to transport Aβ in vitro was also significantly impaired by Klotho knockdown. Given the neuroprotective effect of Klotho overexpression, the present findings suggest that Klotho should be further investigated as a potential therapeutic target for AD.

Central IRAK-4 kinase inhibition for the treatment of pain following nerve injury in rats

There is ample evidence for the role of the immune system in developing chronic pain following peripheral nerve injury. Especially Toll-like receptors (TLRs) and their associated signaling components and pro-inflammatory cytokines such as IL-1β, induced after injury, are involved in nociceptive processes and believed to contribute to the manifestation of chronic neuropathic pain states. Whereas the inhibition of the kinase function of IRAK-4, a central kinase downstream of TLRs and IL-1 receptors (IL-1Rs), seems efficacious in various chronic inflammatory and autoimmune models, it's role in regulating chronic neuropathic pain remained elusive to date. Here, we examined whether pharmacological inhibition of IRAK-4 kinase activity using PF-06650833 and BMS-986147, two clinical-stage kinase inhibitors, is effective for controlling persistent pain following nerve injury. Both inhibitors potently inhibited TLR-triggered cytokine release in human peripheral blood mononuclear cell (PBMC) as well as human and rat whole blood cultures. BMS-986147 showing favorable pharmacokinetic (PK) properties, significantly inhibited R848-triggered plasma TNF levels in a rat in vivo cytokine release model after single oral dosing. However, BMS-986147 dose dependently reversed cold allodynia in a rat chronic constriction injury (CCI) model following intrathecal administration only, supporting the notion that central neuro-immune modulation is beneficial for treating chronic neuropathic pain. Although both inhibitors were efficacious in inhibiting IL-1β- or TLR-triggered cytokine release in rat dorsal root ganglion cultures, only partial efficacy was reached in IL-1β-stimulated human glial cultures indicating that inhibiting IRAK-4́'s kinase function might be partially dispensable for human IL-1β driven neuroinflammation. Overall, our data demonstrate that IRAK-4 inhibitors could provide therapeutic benefit in chronic pain following nerve injury, and the central driver for efficacy in the neuropathic pain model as well as potential side effects of centrally available IRAK-4 inhibitors warrant further investigation to develop effective analgesia for patients in high unmet medical need.

CSF biomarkers in Olmsted County: Evidence of 2 subclasses and associations with demographics

OBJECTIVE

We studied interrelationships between CSF biomarkers and associations with APOE ε4 genotype, demographic variables, vascular variables, and clinical diagnosis in Olmsted County, Minnesota.

METHODS

We included 774 Mayo Clinic Study of Aging participants (693 cognitively unimpaired [CU]; 71 with mild cognitive impairment [MCI]). CSF β-amyloid 42 (Aβ42), total tau (t-tau), and hyperphosphorylated tau (p-tau) were analyzed using Aβ42 CSF, t-tau CSF, and p-tau (181P) CSF electrochemiluminescence immunoassays. Bivariate mixture models were used to evaluate latent classes. We used linear regression models to evaluate independent associations of APOE ε4, demographic factors, cardiovascular risk, and diagnosis with CSF biomarker levels. Results were weighted back to the Olmsted County population.

RESULTS

Interrelationships between CSF Aβ42 and p-tau/t-tau were consistent with 2 latent classes in the general population. In subgroup 1 (n = 547 [71%]), we found a strong positive correlation between Aβ42 and p-tau (ρ = 0.81), while the correlation was much smaller in group 2 (ρ = 0.26, n = 227 [29%]). Group 2 was associated with older age, APOE ε4 genotype, a diagnosis of MCI, and elevated amyloid PET. Overall, APOE ε4 genotype and MCI were associated with Aβ42, while age was associated with p-tau/t-tau. There were no associations with sex, education, or vascular risk.

CONCLUSION

We hypothesize the population without dementia can be subdivided into participants with and without biological Alzheimer disease (AD) based on the combination of CSF Aβ42 and p-tau/t-tau (represented also by the p-tau/t-tau/Aβ42 ratio). In those without biological AD, common factors such as CSF dynamics may cause a positive correlation between CSF Aβ42 and p-tau/t-tau, while AD leads to dissociation of these proteins.

Acute intracerebroventricular injection of chemerin-9 increases systemic blood pressure through activating sympathetic nerves via CMKLR1 in brain

Chemerin is an adipocytokine involved in inflammation and lipid metabolism via G protein-coupled receptor, chemokine-like receptor (CMKLR)1. Since the important nuclei regulating pressure (BP) exist in the brain, we examined the effects of acute intracerebroventricular (i.c.v.) injection of chemerin-9 on systemic BP and explored underlying mechanisms. We examined the effects of acute i.c.v. injection of chemerin-9 (10 nmol/head) on systemic BP by a carotid cannulation method in the control or CMKLR1 small interfering (si) RNA-treated Wistar rats (0.04 nmol, 3 days, i.c.v.). We examined protein expression of CMKLR1 around brain ventricles by Western blotting. We examined the effects of acute i.c.v. injection of chemerin-9 on serum adrenaline by a high performance liquid chromatography. In the control siRNA-treated rats, chemerin-9 significantly increased mean BP, which reached a peak at 2 to 4 min after injection. On the other hand, in the CMKLR1 siRNA-treated rats, chemerin-9 did not affect the mean BP. Protein expression of CMKLR1 specifically in subfornical organ (SFO) and paraventricular nucleus (PVN) from the CMKLR1 siRNA-treated rats decreased compared with the control siRNA-treated rats. In the control siRNA-treated rats, chemerin-9 increased serum adrenaline level. On the other hand, in the CMKLR1 siRNA-treated rats, chemerin-9 did not affect the serum adrenaline level. Further, pretreatment with prazosin, an α-adrenaline receptor blocker, significantly prevented the pressor responses induced by chemerin-9. In summary, we for the first time demonstrated that chemerin-9 stimulates the sympathetic nerves via CMKLR1 perhaps expressed in SFO and PVN, which leads to an increase in systemic BP.

Intrathecal drug delivery in the era of nanomedicine

Administration of substances directly into the cerebrospinal fluid (CSF) that surrounds the brain and spinal cord is one approach that can circumvent the blood-brain barrier to enable drug delivery to the central nervous system (CNS). However, molecules that have been administered by intrathecal injection, which includes intraventricular, intracisternal, or lumbar locations, encounter new barriers within the subarachnoid space. These barriers include relatively high rates of turnover as CSF clears and potentially inadequate delivery to tissue or cellular targets. Nanomedicine could offer a solution. In contrast to the fate of freely administered drugs, nanomedicine systems can navigate the subarachnoid space to sustain delivery of therapeutic molecules, genes, and imaging agents within the CNS. Some evidence suggests that certain nanomedicine agents can reach the parenchyma following intrathecal administration. Here, we will address the preclinical and clinical use of intrathecal nanomedicine, including nanoparticles, microparticles, dendrimers, micelles, liposomes, polyplexes, and other colloidalal materials that function to alter the distribution of molecules in tissue. Our review forms a foundational understanding of drug delivery to the CSF that can be built upon to better engineer nanomedicine for intrathecal treatment of disease.

Intrathecal Injection in A Rat Model: A Potential Route to Deliver Human Wharton's Jelly-Derived Mesenchymal Stem Cells into the Brain

Mesenchymal stem cells (MSCs) are considered as promising therapeutic agents for neurodegenerative disorders because they can reduce underlying pathology and also repair damaged tissues. Regarding the delivery of MSCs into the brain, intravenous and intra-arterial routes may be less feasible than intraparenchymal and intracerebroventricular routes due to the blood–brain barrier. Compared to the intraparenchymal or intracerebroventricular routes, however, the intrathecal route may have advantages: this route can deliver MSCs throughout the entire neuraxis and it is less invasive since brain surgery is not required. The objective of this study was to investigate the distribution of human Wharton’s jelly-derived MSCs (WJ-MSCs) injected via the intrathecal route in a rat model. WJ-MSCs (1 × 10⁶) were intrathecally injected via the L2-3 intervertebral space in 6-week-old Sprague Dawley rats. These rats were then sacrificed at varying time points: 0, 6, and 12 h following injection. At 12 h, a significant number of MSCs were detected in the brain but not in other organs. Furthermore, with a 10-fold higher dose of WJ-MSCs, there was a substantial increase in the number of cells migrating to the brain. These results suggest that the intrathecal route can be a promising route for the performance of stem cell therapy for CNS diseases.

Impact of chemical modification of sulfamidase on distribution to brain interstitial fluid and to CSF after an intravenous administration in awake, freely-moving rats

Mucopolysaccharidosis III A (MPS IIIA) is an autosomal recessive lysosomal storage disorder caused by deficiency of the enzyme sulfamidase. The disorder results in accumulation of heparan sulfate, lysosomal enlargement and cellular and organ dysfunction. Patients exhibit progressive neurodegeneration and behavioral problems and no treatment is currently available. Enzyme replacement therapy is explored as potential treatment strategy for MPS IIIA patients and to modify the disease, sulfamidase must reach the brain. The glycans of recombinant human sulfamidase (rhSulfamidase) can be chemically modified to generate CM-rhSulfamidase. The chemical modification reduced the affinity to the cation-independent mannose-6-phosphate receptor with the aim a prolonged higher concentration in circulation and thus at the blood brain barrier. The pharmacokinetic properties in serum and the distribution to brain and to cerebrospinal fluid (CSF) of chemically modified recombinant human sulfamidase (CM-rhSulfamidase) were studied and compared to those of rhSulfamidase, after a single intravenous (i.v.) 30 mg/kg dose in awake, freely-moving male Sprague Dawley rats. Distribution to brain was studied by microdialysis of the interstitial fluid in prefrontal cortex and by repeated intra-individual CSF sampling from the cisterna magna. Push-pull microdialysis facilitated sampling of brain interstitial fluid to determine large molecule concentrations in awake, freely-moving male Sprague Dawley rats. Together with repeated serum and CSF sampling, push-pull microdialysis facilitated determination of CM-rhSulfamidase and rhSulfamidase kinetics after i.v. administration by non-compartments analysis and by a population modelling approach. Chemical modification increased the area under the concentration versus time in serum, CSF and brain interstitial fluid at least 7-fold. The results and the outcome of a population modelling approach of the concentration versus time data indicated that both compounds pass the BBB with an equilibrium established fairly rapid after administration. We suggest that prolonged high serum concentrations facilitated high brain interstitial fluid concentrations, which could be favorable to reach various target cells in the brain.

Imaging the effect of the circadian light-dark cycle on the glymphatic system in awake rats

Homeostasis and the daily rhythms in brain function and temperature are coupled to the circadian light–dark cycle. MRI was used to study the redistribution of intraventricular contrast agent in awake rats during the night when they are active and during the day when at rest. Redistribution is lowest during the day and highest at night and parallels the gradients and regional variations in brain temperatures reported in the literature. The brain areas of low parenchymal redistribution are associated with high temperatures and have a high density of blood vessels that may be an essential part of the organization of the glymphatic system regulating brain temperature, blood gases, nutrients, metabolites, and waste products over the light–dark cycle.

The glymphatic system functions in the removal of potentially harmful metabolites and proteins from the brain. Dynamic, contrast-enhanced MRI was used in fully awake rats to follow the redistribution of intraventricular contrast agent entrained to the light–dark cycle and its hypothetical relationship to the sleep–waking cycle, blood flow, and brain temperature in specific brain areas. Brain areas involved in circadian timing and sleep–wake rhythms showed the lowest redistribution of contrast agent during the light phase or time of inactivity and sleep in rats. Global brain redistribution of contrast agent was heterogeneous. The redistribution was highest along the dorsal cerebrum and lowest in the midbrain/pons and along the ventral surface of the brain. This heterogeneous redistribution of contrast agent paralleled the gradients and regional variations in brain temperatures reported in the literature for awake animals. Three-dimensional quantitative ultrashort time-to-echo contrast-enhanced imaging was used to reconstruct small, medium, and large arteries and veins in the rat brain and revealed areas of lowest redistribution overlapped with this macrovasculature. This study raises new questions and theoretical considerations of the impact of the light–dark cycle, brain temperature, and blood flow on the function of the glymphatic system.

Assessment of Neurological Toxicity of Hydroxyethyl Starch 130/0.4 Injected in the Intrathecal Space in Rats

Objective

Epidural blood patch is the procedure of choice to relieve postdural puncture headache. Hydroxyethyl-starch (HES) has been proposed as a patch in some circumstances such as in the case of hematological disease due to the theoretical risk of neoplastic seeding to the central nervous system. Acute neurological HES toxicity has been excluded by a previous animal study, but the long-term neurological toxicity has not been evaluated.

Methods

Rats were randomly assigned to one of three groups: no intrathecal injection, 20 μL of intrathecal saline, or a 20-μL intrathecal HES (6% hydroxyethyl starch 130/0.4) administered via a cervical puncture. Clinical daily rat activity was measured before and after dural puncture by actinometry. The rats were killed at day 28, and the spinal cord was surgically removed and stained with hematoxylin-phloxine-saffron for gross and microscopic examination.

Results

Eleven rats underwent dural puncture without injection, 11 were injected with normal saline, and 12 received intrathecal HES. No clinical or actimetric changes (total distance traveled, number of direction changes, and number of rearings) were observed up to one month after injection. Nonspecific histopathological changes were equally observed in all groups.

Conclusions

The results of the current study indicate that intrathecal injection of HES in rats does not induce any clinical or histopathological evidence of long-term neuronal toxicity. Further safety studies in animals are warranted before HES might be considered a safe alternative to the classic epidural blood patch.

Cerebrospinal fluid dynamics and intracranial pressure elevation in neurological diseases

The fine balance between the secretion, composition, volume and turnover of cerebrospinal fluid (CSF) is strictly regulated. However, during certain neurological diseases, this balance can be disrupted. A significant disruption to the normal CSF circulation can be life threatening, leading to increased intracranial pressure (ICP), and is implicated in hydrocephalus, idiopathic intracranial hypertension, brain trauma, brain tumours and stroke. Yet, the exact cellular, molecular and physiological mechanisms that contribute to altered hydrodynamic pathways in these diseases are poorly defined or hotly debated. The traditional views and concepts of CSF secretion, flow and drainage have been challenged, also due to recent findings suggesting more complex mechanisms of brain fluid dynamics than previously proposed. This review evaluates and summarises current hypotheses of CSF dynamics and presents evidence for the role of impaired CSF dynamics in elevated ICP, alongside discussion of the proteins that are potentially involved in altered CSF physiology during neurological disease. Undoubtedly CSF secretion, absorption and drainage are important aspects of brain fluid homeostasis in maintaining a stable ICP. Traditionally, pharmacological interventions or CSF drainage have been used to reduce ICP elevation due to over production of CSF. However, these drugs are used only as a temporary solution due to their undesirable side effects. Emerging evidence suggests that pharmacological targeting of aquaporins, transient receptor potential vanilloid type 4 (TRPV4), and the Na+-K+-2Cl- cotransporter (NKCC1) merit further investigation as potential targets in neurological diseases involving impaired brain fluid dynamics and elevated ICP.

Methods for Assessing Serpins as Neuroprotective Therapeutics

As the systematic work on the pathogenesis of the white matter injury in the spinal cord models progresses, it becomes obvious that a severe and extraordinarily protracted, destructive inflammation follows the initial injury. Appropriate anti-inflammatory therapies of sufficient duration should not only inhibit but also lead to the elimination of this destructive inflammation, thus resulting in neuroprotection of the spinal cord tissue and a greater preservation of the neurologic function. While dexamethasone, a powerful, anti-inflammatory steroid analog administered continuously by subdural infusion for 7 days inhibited severe macrophage infiltration in the cavity of injury, the dose used was remarkably toxic. A 2-week-long infusion of lower doses of dexamethasone resulted in dose-dependent inhibition of macrophage infiltration and was better tolerated by the rats, but it became evident that a much longer duration of subdural administration of a powerful anti-inflammatory drug is required to eliminate myelin-rich, necrotic debris from the cavity and synthetic steroids such as dexamethasone, and methylprednisolone may be too toxic for this application. Therefore, nontoxic but powerful anti-inflammatory compounds are required for neuroprotective treatment of the spinal cord injury (SCI) and also brain trauma and stroke where the massive injury to the white matter occurs. Serpins have been associated with neurological damage. The mammalian serpin neuroserpin (SERPINI1) is reported to act in a protective manner after cerebrospinal infarction. The serine protease, tissue-type plasminogen activator (tPA), and the serpin plasminogen activator inhibitor (PAI-1, SERPINE1) are both upregulated at sites of central nervous system damage. In preliminary studies, subdural infusion of the myxomaviral serpin, Serp-1, resulted in the powerful inhibition of the macrophage infiltration of the cavity of injury, comparable to the inhibition by high dose of dexamethasone that has proven to be unduly toxic. Nontoxic, yet powerful neuroprotective, anti-inflammatory effects of Serp-1 may indicate this serpin protein as a potential attractive compound to treat SCI and similar syndromes involving massive injury to the white matter such as brain trauma and stroke. Novel methods of drug delivery, chronic subdural infusion, and novel analytic methods to measure the effectiveness of the neuroprotective serpin treatments are discussed in this chapter.

Therapeutic efficacy of the Ginkgo special extract EGb761® within the framework of the mitochondrial cascade hypothesis of Alzheimer's disease

OBJECTIVES

The mitochondrial cascade hypothesis of dementia assumes mitochondrial dysfunction as an important common pathomechanism for the whole spectrum of age-associated memory disorders from cognitive symptoms in the elderly over mild cognitive impairment to Alzheimer's dementia. Thus, a drug such as the Ginkgo special extract EGb 761^® which improves mitochondrial function should be able to ameliorate cognitive deficits over the whole aging spectrum.

METHODS

We review the most relevant publications about effects of EGb 761^® on cognition and synaptic deficits in preclinical studies as well as on cognitive deficits in man from aging to dementia.

RESULTS

EGb 761^® improves mitochondrial dysfunction and cognitive impairment over the whole spectrum of age-associated cognitive disorders in relevant animal models and in vitro experiments, and also shows clinical efficacy in improving cognition over the whole range from aging to Alzheimer's or even vascular dementia.

CONCLUSIONS

EGb 761^® shows clinical efficacy in the treatment of cognitive deficits over the whole spectrum of age-associated memory disorders. Thus, EGb 761^® can serve as an important pharmacological argument for the mitochondrial cascade hypothesis of dementia.

Cerebral Aβ40 and systemic hypertension

Mid-life hypertension and cerebral hypoperfusion may be preclinical abnormalities in people who later develop Alzheimer's disease. Although accumulation of amyloid-beta (Aβ) is characteristic of Alzheimer's disease and is associated with upregulation of the vasoconstrictor peptide endothelin-1 within the brain, it is unclear how this affects systemic arterial pressure. We have investigated whether infusion of Aβ₄₀ into ventricular cerebrospinal fluid modulates blood pressure in the Dahl salt-sensitive rat. The Dahl salt-sensitive rat develops hypertension if given a high-salt diet. Intracerebroventricular infusion of Aβ induced a progressive rise in blood pressure in rats with pre-existing hypertension produced by a high-salt diet ( p < 0.0001), but no change in blood pressure in normotensive rats. The elevation in arterial pressure in high-salt rats was associated with an increase in low frequency spectral density in systolic blood pressure, suggesting autonomic imbalance, and reduced cardiac baroreflex gain. Our results demonstrate the potential for intracerebral Aβ to exacerbate hypertension, through modulation of autonomic activity. Present findings raise the possibility that mid-life hypertension in people who subsequently develop Alzheimer's disease may in some cases be a physiological response to reduced cerebral perfusion complicating the accumulation of Aβ within the brain.

MRI investigation of glymphatic responses to Gd-DTPA infusion rates

The glymphatic system is a newly identified waste clearance pathway in brain discovered and investigated predominately using in vivo two‐photon confocal microscopy. Magnetic resonance imaging (MRI), in contrast to two‐photon confocal microscopy, provides dynamic and real‐time pictures of the glymphatic system in whole brain. We employ MRI to investigate the response of the glymphatic system to the rate of infusion of Gd‐DTPA (magnevist). Wistar rats were subjected to a surgery of inserting a tube into the cisterna magna for infusion during MRI. Three infusion rates were chosen for 20 min infusions of diluted magnevist into the cerebrospinal fluid (CSF) of rat brain. Glymphatic response was imaged using dynamic MRI 3D measurement for 5 hr. Robust correlations were found in all ventricles between the peak intensities of image enhancement and infusion rates, with additional correlations between the peak times of MRI image enhancement and infusion rates in the fourth ventricle. An infusion rate of 2.92 μL/min induced an evident accumulation of tracer in the fourth ventricle near the cisterna magna. In hippocampal tissue, image enhancements exhibited low correlation with the infusion rates. However, an infusion rate of 1.67 μL/min provided a high image enhancement, but less tracer accumulation near the cisterna magna. Contrast‐enhanced MRI provides a suitable tool for investigating image contrast infusion rate response of the glymphatic system in rat brain. Considering both T₁ and T₂^* effects in response to the infused magnevist into CSF, the infusion rate of 1.67 μL/min appears suitable for MRI study of the glymphatic system in rat.

Normal tension glaucoma: review of current understanding and mechanisms of the pathogenesis

Normal tension glaucoma (NTG) is an exception in the "glaucoma family" where the major risk factor, increased intraocular pressure, is missing. If not increased intraocular pressure, then what other causes can then lead to glaucomatous optic disc change and visual field loss in NTG? Several possibilities will be discussed. Among them a higher sensitivity to normal pressure, vascular dysregulation, an abnormally high translaminar pressure gradient and a neurodegenerative process due to impaired cerebrospinal fluid dynamics in the optic nerve sheath compartment. There are many excellent review papers published on normal tension glaucoma (NTG). The aim of this paper is therefore not to add another extensive review on NTG but rather to focus on and to discuss some possible mechanisms that are thought to be involved in the pathophysiology of NTG and to discuss the stronger and weaker aspects of each concept. The fact that several concepts exist suggests that NTG is still not very well understood and that no single mechanism on its own might adequately explain NTG.

Dual effects of brain sparing opioid in newborn rats: Analgesia and hyperalgesia

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The peripherally acting opioid loperamide produces sustained antinociception in the newborn rat.

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Loperamide minimally crosses the blood brain barrier in the newborn rat.

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Daily systemic administration of loperamide produces opioid induced hyperalgesia in the newborn rat.

Effective pain management in neonates without the unwanted central nervous system (CNS) side effects remains an unmet need. To circumvent these central effects we tested the peripherally acting (brain sparing) opioid agonist loperamide in neonate rats. Our results show that: 1) loperamide (1 mg/kg, s.c.) does not affect the thermal withdrawal latency in the normal hind paw while producing antinociception in all pups with an inflamed hind paw. 2) A dose of loperamide 5 times higher resulted in only 6.9 ng/mL of loperamide in the cerebrospinal fluid (CSF), confirming that loperamide minimally crosses the blood–brain barrier (BBB). 3) Unexpectedly, sustained administration of loperamide for 5 days resulted in a hyperalgesic behavior, as well as increased excitability (sensitization) of dorsal root ganglia (DRGs) and spinal nociceptive neurons. This indicates that opioid induced hyperalgesia (OIH) can be induced through the peripheral nervous system. Unless prevented, OIH could in itself be a limiting factor in the use of brain sparing opioids in the neonate.

Dosing, collection, and quality control issues in cerebrospinal fluid research using animal models

Cerebrospinal fluid (CSF) is a complex fluid filling the ventricular system and surrounding the brain and spinal cord. Although the bulk of CSF is created by the choroid plexus, a significant fraction derives from the interstitial fluid in the brain and spinal cord parenchyma. For this reason, CSF can often be used as a source of pharmacodynamic and prognostic biomarkers to reflect biochemical changes occurring within the brain. For instance, CSF biomarkers can be used to diagnose and track progression of disease as well as understand pharmacokinetic and pharmacodynamic relationships in clinical trials. To facilitate the use of these biomarkers in humans, studies in preclinical species are often valuable. This review summarizes methods for preclinical CSF collection for biomarkers from mice, rats, and nonhuman primates. In addition, dosing directly into CSF is increasingly being used to improve drug levels in the brain. Therefore, this review also summarizes the state of the art in CSF dosing in these preclinical species.