Downregulation of cerebrospinal fluid production in patients with chronic hydrocephalus

The Role of Choroid Plexus in Hydrocephalus from the Perspective of Structure and Function: a Therapeutic Target

Hydrocephalus is one of the most common neurological diseases, characterized by abnormal excessive accumulation of cerebrospinal fluid (CSF) in the ventricular system. Its pathophysiological mechanism is believed to be related to the imbalance of CSF circulation and homeostasis. As the main source of CSF secretion, the choroid plexus is closely related to hydrocephalus. The choroid plexus is a specialized vascularized tissue located within the cerebral ventricles. It has multiple physiological functions including regulating CSF, immune response, endocrine metabolism, etc. Strategies that reduce choroid plexus CSF secretion have been shown to be effective in the treatment of hydrocephalus. However, the role of other physiological functions of the choroid plexus in hydrocephalus is still unclear. Recent studies on the choroid plexus and the blood-CSF barrier have deepened our understanding of the structure and function of the choroid plexus. The idea of targeting the choroid plexus to treat hydrocephalus has spawned many branches: choroid plexus epithelial cells, choroid plexus immune cells, choroid plexus peptides, and choroid plexus cilia, etc. This review introduces the basic structure and function of the choroid plexus, summarizes their changes in hydrocephalus, and analyzes the possibility of the choroid plexus as a therapeutic target for hydrocephalus.

CSF production rate, resistance to reabsorption, and intracranial pressure: a systematic review and meta-analysis

Davson's equation relates the state of stable intracranial pressure (ICP) to the production rate of CSF (IF) and resistance to CSF outflow (ROUT). Both parameters are assumed to be independent of ICP, but results are conflicting. The objective is to define the relationship between ICP, IF and ROUT using a systematic literature review. Medline and Embase were searched from inception up to 12 February 2024. Experimental studies exploring the association between ICP, IF, and ROUT were included. Individual measurements of ICP, IF and/or ROUT were extracted from tables or graphs, alongside descriptive parameters (population, ICP measurement site, disease, and computational method). Linear regression and mixed effects models were applied. From 1304 references, 25 articles were included in our meta-analysis. IF is approximately constant across all pathologies independent of the ICP level, population, disease, ICP measurement site and the measurement/estimation method. Conversely, ICP was positively correlated with ROUT. The intercorrelation, however, differed by population, disease, ICP measurement site and estimation method. Additionally, IF derived from Davson's Equation compared with the measured IF were similar for patients with hydrocephalus but differed for patients with acute brain injury. Davson's Equation describes the various components of cerebrospinal fluid dynamics. The results underline important caveats for its use in patients with acute brain injury wherein the estimated values differ from the measured ones. Overall, additional metrics describing the cerebrovascular system or the underlying disease have to be taken into account for more accurate estimations.

A Lumped Parameter Model Suggests That Infusion Studies Overestimate the Cerebrospinal Fluid Outflow Resistance in Normal Pressure Hydrocephalus

BACKGROUND/OBJECTIVES

Cerebrospinal infusion studies indicate that cerebrospinal fluid outflow resistance (Rout) is elevated in normal pressure hydrocephalus (NPH). These studies assume that the cerebrospinal formation rate (CSFfr) does not vary during the infusion. If the CSFfr were to increase during the infusion then the Rout would be overestimated. Previous estimates of the CSFfr in NPH have suggested a low figure. More recent estimates of the CSFfr suggest that it is increased, indicating it probably varies with measurement technique. This would bring the estimation of Rout into doubt. A previous paper using a lumped parameter model suggested the CSFfr could vary with the capillary transmural pressure (TMP) in this disease, suggesting a possible solution to this problem. The current study investigates the possibility that the intracranial pressure manipulation occurring during an infusion study may vary the capillary TMP and CSFfr.

METHODS

A lumped parameter model previously developed to describe the hydrodynamics of NPH was modified to investigate the effect of CSF pressure manipulation during infusion studies and to describe how the CSFfr could vary depending on the technique used.

RESULTS

The model indicates the capillary transmural pressure is normal in NPH and increases during an infusion study. CSF drainage at the end of an infusion study similarly increases the capillary TMP and, presumably, the CSFfr by increasing the interstitial fluid production.

CONCLUSIONS

The model suggests that infusion studies and draining CSF increases the CSFfr in NPH compared to earlier techniques. Allowing for an increase in the CSFfr suggests that infusion overestimates the Rout by between 23 and 33%. This study indicates that further research may be required into the utility and accuracy of infusion studies and their ability to diagnose NPH.

A lumped parameter modelling study of cerebral autoregulation in normal pressure hydrocephalus suggests the brain chooses to be ischemic

Normal pressure hydrocephalus (NPH) is associated with a reduction in cerebral blood flow and an ischemic metabolic state. Ischemia should exhaust the available autoregulation in an attempt to correct the metabolic imbalance. There is evidence of some retained autoregulation reserve in NPH. The aim of this study is to model the cerebral autoregulation in NPH to discover a solution to this apparent paradox. A lumped parameter model was developed utilizing the known limits of autoregulation in man. The model was tested by predicting the cerebral blood volume changes which would be brought about by changes in resistance. NPH and the post shunt state were then modeled using the known constraints provided from the literature. The model successfully predicted the cerebral blood volume changes brought about by altering the cerebral perfusion pressure to the limit of autoregulation. The model suggests that NPH is associated with a balanced increase in resistance within the arterial and venous outflow segments. The arterial resistance decreased after modelling shunt insertion. The model suggests that the cerebral blood flow is actively limited in NPH by arteriolar constriction. This may occur to minimize the rise in ICP by reducing the apparent CSF formation rate.

CSF formation rate-a potential glymphatic flow parameter in hydrocephalus?

BACKGROUND

Studies indicate that brain clearance via the glymphatic system is impaired in idiopathic normal pressure hydrocephalus (INPH). This has been suggested to result from reduced cerebrospinal fluid (CSF) turnover, which could be caused by a reduced CSF formation rate. The aim of this study was to determine the formation rate of CSF in a cohort of patients investigated for INPH and compare this to a historical control cohort.

METHODS

CSF formation rate was estimated in 135 (75 ± 6 years old, 64/71 men/women) patients undergoing investigation for INPH. A semiautomatic CSF infusion investigation (via lumbar puncture) was performed. CSF formation rate was assessed by downregulating and steadily maintaining CSF pressure at a zero level. During the last 10 min, the required outflow to maintain zero pressure, i.e., CSF formation rate, was continuously measured. The values were compared to those of a historical reference cohort from a study by Ekstedt in 1978.

RESULTS

Mean CSF formation rate was 0.45 ± 0.15 ml/min (N = 135), equivalent to 27 ± 9 ml/hour. There was no difference in the mean (p = 0.362) or variance (p = 0.498) of CSF formation rate between the subjects that were diagnosed as INPH (N = 86) and those who were not (N = 43). The CSF formation rate in INPH was statistically higher than in the reference cohort (0.46 ± 0.15 vs. 0.40 ± 0.08 ml/min, p = 0.005), but the small difference was probably not physiologically relevant. There was no correlation between CSF formation rate and baseline CSF pressure (r = 0.136, p = 0.115, N = 135) or age (-0.02, p = 0.803, N = 135).

CONCLUSIONS

The average CSF formation rate in INPH was not decreased compared to the healthy reference cohort, which does not support reduced CSF turnover. This emphasizes the need to further investigate the source and routes of the flow in the glymphatic system and the cause of the suggested impaired glymphatic clearance in INPH.

Association between cerebrospinal fluid pressure and cognition in patients with Alzheimer's disease and Lewy body dementia

BACKGROUND

The relationship between cerebrospinal fluid pressure (CSFP) and cognition has received little research attention. The purpose of this study was to explore the relationship between CSFP and cognition in patients with Alzheimer's disease (AD) and patients with Lewy body dementia (LBD).

METHOD

We included 178 participants, including 137 patients with AD and 41 patients with LBD (including dementia with Lewy bodies (DLBs) and Parkinson's disease dementia (PDD)). CSFP was measured by lumbar puncture, and a patient-reported history and laboratory test data were collected. Logistic and linear regression analyses were used to evaluate the associations between CSFP and cognition, the cerebrospinal fluid (CSF) / serum albumin ratio (Qalb), and CSF biomarkers of AD.

RESULTS

The mean age of the included patients was 63.58 ± 8.77 years old, and the mean CSFP was 121 ± 33.72 mmH2O. A total of 76.9% of the patients had a CSFP distribution of [90-170) mmH2O, 46 patients (25.8%) had severe dementia, 83 patients (46.6%) had moderate dementia, 28 patients (15.7%) had mild dementia, and 21 patients (11.8%) had mild cognitive impairment (MCI) (including 16 patients with MCI due to AD and 5 patients with MCI due to LBD). In all patients (p value < 0.001) and in patients with AD (p value = 0.01), the mean cerebrospinal fluid pressure (CSFP) was higher in patients with MCI than in patients with dementia. In multivariate analysis, in all patients (OR: 6.37, 95% confidential interval (CI): 1.76-23.04, p = 0.005) and patients with AD (odds ratio (OR): 5.43, 95% CI: 1.41-20.87, p = 0.005), a CSFP in the lowest quartile ([50-90) mmH2O) was associated with a higher level of severe dementia than a CSFP in the highest quartile ([170-210) mmH2O). In addition, there was a significant linear correlation between CSFP and the Mini-Mental State Examination (MMSE) score in all patients with dementia (r = 0.43, p = 0.04, Durbin-Watson test (D-W test) = 0.75).

CONCLUSION

In patients with AD, the mean cerebrospinal fluid pressure was higher in patients with MCI than in patients with dementia, and the decrease in CSFP was related to a more serious dementia level. However, no such relationship was found in patients with LBD.

Modelling of the dilated sagittal sinuses found in multiple sclerosis suggests increased wall stiffness may be a contributing factor

The cross-sectional area of the superior sagittal sinus (SSS) is larger in multiple sclerosis than normal and correlates with disease severity and progression. The sinus could be enlarged due to a decrease in the pressure difference between the lumen and the subarachnoid space, an increase in wall thickness or increased wall stiffness. The cross-sectional area of the SSS and straight sinus (ST) were measured in 103 patients with multiple sclerosis and compared to 50 controls. The cross-sectional area of the SSS and ST were increased by 20% and 13% compared to the controls (p = 0.005 and 0.02 respectively). The deflection of the wall of the sinus was estimated. The change in pressure gradient, wall thickness or elastic modulus between groups was calculated by modelling the walls as simply supported beams. To account for these findings, the modelling suggests either a 70% reduction in transmural venous pressure or a 2.4 fold increase in SSS wall stiffness plus an 11% increase in wall thickness or a combination of changes. An increase in sinus pressure, although the most straight forward possibility to account for the change in sinus size may exist in only a minority of patients. An increase in sinus wall stiffness and thickness may need further investigation.

The emergence of the calvarial hematopoietic niche in health and disease

The diploë region of skull has recently been discovered to act as a myeloid cell reservoir to the underlying meninges. The presence of ossified vascular channels traversing the inner skull of cortex provides a passageway for the cells to traffic from the niche, and CNS-derived antigens traveling through cerebrospinal fluid in a perivascular manner reaches the niche to signal myeloid cell egress. This review will highlight the recent findings establishing this burgeoning field along with the known role this niche plays in CNS aging and disease. It will further highlight the anatomical routes and physiological properties of the vascular structures these cells use for trafficking, spanning from skull to brain parenchyma.

Rodent models of senile normal-pressure hydrocephalus

Cerebrospinal fluid (CSF) and its drainage are crucial in clearing metabolic waste and maintaining the microenvironment of the central nervous system for proper functioning. Normal-pressure hydrocephalus (NPH) is a serious neurological disorder of the elderly with obstruction of CSF flow outside the cerebral ventricles, causing ventriculomegaly. The stasis of CSF in NPH compromises brain functioning. Although treatable, often with shunt implantation for drainage, the outcome depends highly on early diagnosis, which, however, is challenging. The initial symptoms of NPH are hard to be aware of and the complete symptoms overlap with those of other neurological diseases. Ventriculomegaly is not specific to NPH as well. The lack of knowledge on the initial stages in its development and throughout its progression further deters early diagnosis. Thus, we are in dire need for an appropriate animal model for researches into a more thorough understanding of its development and pathophysiology so that we can enhance the diagnosis and therapeutic strategies to improve the prognosis of NPH following treatment. With this, we review the few currently available experimental rodent NPH models for these animals are smaller in sizes, easier in maintenance, and having a rapid life cycle. Among these, a parietal convexity subarachnoid space kaolin injection adult rat model appears promising as it shows a slow onset of ventriculomegaly in association with cognitive and motor disabilities resembling the elderly NPH in humans.

Molecular Mechanisms and Risk Factors for the Pathogenesis of Hydrocephalus

Hydrocephalus is a neurological condition due to the aberrant circulation and/or obstruction of cerebrospinal fluid (CSF) flow with consequent enlargement of cerebral ventricular cavities. However, it is noticed that a lot of patients may still go through symptomatic progression despite standard shunting procedures, suggesting that hydrocephalus is far more complicated than a simple CSF circulative/obstructive disorder. Growing evidence indicates that genetic factors play a fundamental role in the pathogenesis of some hydrocephalus. Although the genetic research of hydrocephalus in humans is limited, many genetic loci of hydrocephalus have been defined in animal models. In general, the molecular abnormalities involved in the pathogenesis of hydrocephalus include brain development and ependymal cell dysfunction, apoptosis, inflammation, free radical generation, blood flow, and cerebral metabolism. Moreover, recent studies have indicated that the molecular abnormalities relevant to aberrant cerebral glymphatic drainage turn into an attractive subject in the CSF circulation disorder. Furthermore, the prevalent risk factors could facilitate the development of hydrocephalus. In this review, we elicited some possible fundamental molecular mechanisms and facilitating risk factors involved in the pathogenesis of hydrocephalus, and aimed to widen the diagnosis and therapeutic strategies for hydrocephalus management. Such knowledge could be used to improve patient care in different ways, such as early precise diagnosis and effective therapeutic regimens.

Lumbar cerebrospinal fluid-to-brain extracellular fluid surrogacy is context-specific: insights from LeiCNS-PK3.0 simulations

Predicting brain pharmacokinetics is critical for central nervous system (CNS) drug development yet difficult due to ethical restrictions of human brain sampling. CNS pharmacokinetic (PK) profiles are often altered in CNS diseases due to disease-specific pathophysiology. We previously published a comprehensive CNS physiologically-based PK (PBPK) model that predicted the PK profiles of small drugs at brain and cerebrospinal fluid compartments. Here, we improved this model with brain non-specific binding and pH effect on drug ionization and passive transport. We refer to this improved model as Leiden CNS PBPK predictor V3.0 (LeiCNS-PK3.0). LeiCNS-PK3.0 predicted the unbound drug concentrations of brain ECF and CSF compartments in rats and humans with less than two-fold error. We then applied LeiCNS-PK3.0 to study the effect of altered cerebrospinal fluid (CSF) dynamics, CSF volume and flow, on brain extracellular fluid (ECF) pharmacokinetics. The effect of altered CSF dynamics was simulated using LeiCNS-PK3.0 for six drugs and the resulting drug exposure at brain ECF and lumbar CSF were compared. Simulation results showed that altered CSF dynamics changed the CSF PK profiles, but not the brain ECF profiles, irrespective of the drug's physicochemical properties. Our analysis supports the notion that lumbar CSF drug concentration is not an accurate surrogate of brain ECF, particularly in CNS diseases. Systems approaches account for multiple levels of CNS complexity and are better suited to predict brain PK.

Protein tyrosine phosphatase receptor type Q in cerebrospinal fluid reflects ependymal cell dysfunction and is a potential biomarker for adult chronic hydrocephalus

BACKGROUND AND PURPOSE

Protein tyrosine phosphatase receptor type Q (PTPRQ) was extracted from the cerebrospinal fluid (CSF) of patients with probable idiopathic normal-pressure hydrocephalus (iNPH) by proteome analysis. We aimed to assess the feasibility of using CSF PTPRQ concentrations for the additional diagnostic criterion of iNPH in Japanese and Finnish populations.

METHODS

We compared PTPRQ concentrations among patients with probable iNPH and neurologically healthy individuals (normal control [NC] group), patients with normal-pressure hydrocephalus (NPH) of acquired and congenital/developmental aetiologies, patients with Alzheimer's disease and patients with Parkinson's disease in a Japanese analysis cohort. A corresponding iNPH group and NC group in a Finnish cohort was used for validation. Patients in the Finnish cohort who underwent biopsy were classified into two groups based on amyloid and/or tau deposition. We measured PTPRQ expression levels in autopsied brain specimens of iNPH patients and the NC group.

RESULTS

Cerebrospinal fluid PTPRQ concentrations in the patients with NPH of idiopathic, acquired and congenital/developmental aetiologies were significantly higher than those in the NC group and those with Parkinson's disease, but iNPH showed no significant differences when compared with those in the Alzheimer's disease group. For the patients with iNPH, the area under the receiver-operating characteristic curve was 0.860 in the Japanese iNPH and 0.849 in the Finnish iNPH cohorts. Immunostaining and in situ hybridization revealed PTPRQ expression in the ependymal cells and choroid plexus. It is highly possible that the elevated PTPRQ levels in the CSF are related to ependymal dysfunction from ventricular expansion.

CONCLUSIONS

Cerebrospinal fluid PTPRQ levels indicated the validity of this assay for auxiliary diagnosis of adult chronic hydrocephalus.

Delayed clearance of cerebrospinal fluid tracer from choroid plexus in idiopathic normal pressure hydrocephalus

Impaired clearance of amyloid-β from choroid plexus is one proposed mechanism behind amyloid deposition in Alzheimer's disease. The present study examined whether clearance from choroid plexus of a cerebrospinal fluid tracer, serving as a surrogate marker of a metabolic waste product, is altered in idiopathic normal pressure hydrocephalus (iNPH), one sub-type of dementia. In a prospective observational study of close to healthy individuals (reference cohort; REF) and individuals with iNPH, we performed standardized T1-weighted magnetic resonance imaging scans before and through 24 h after intrathecal administration of a cerebrospinal fluid tracer (the magnetic resonance imaging contrast agent gadobutrol). Changes in normalized T1 signal within the choroid plexus and cerebrospinal fluid of lateral ventricles were quantified using FreeSurfer. The normalized T1 signal increased to maximum within choroid plexus and cerebrospinal fluid of lateral ventricles 6-9 h after intrathecal gadobutrol in both the REF and iNPH cohorts (enrichment phase). Peak difference in normalized T1 signals between REF and iNPH individuals occurred after 24 h (clearance phase). The results gave evidence for gadobutrol resorption from cerebrospinal fluid by choroid plexus, but with delay in iNPH patients. Whether choroid plexus has a role in iNPH pathogenesis in terms of delayed clearance of amyloid-β remains to be shown.

Inflammation in acquired hydrocephalus: pathogenic mechanisms and therapeutic targets

Hydrocephalus is the most common neurosurgical disorder worldwide and is characterized by enlargement of the cerebrospinal fluid (CSF)-filled brain ventricles resulting from failed CSF homeostasis. Since the 1840s, physicians have observed inflammation in the brain and the CSF spaces in both posthaemorrhagic hydrocephalus (PHH) and postinfectious hydrocephalus (PIH). Reparative inflammation is an important protective response that eliminates foreign organisms, damaged cells and physical irritants; however, inappropriately triggered or sustained inflammation can respectively initiate or propagate disease. Recent data have begun to uncover the molecular mechanisms by which inflammation - driven by Toll-like receptor 4-regulated cytokines, immune cells and signalling pathways - contributes to the pathogenesis of hydrocephalus. We propose that therapeutic approaches that target inflammatory mediators in both PHH and PIH could address the multiple drivers of disease, including choroid plexus CSF hypersecretion, ependymal denudation, and damage and scarring of intraventricular and parenchymal (glia-lymphatic) CSF pathways. Here, we review the evidence for a prominent role of inflammation in the pathogenic mechanism of PHH and PIH and highlight promising targets for therapeutic intervention. Focusing research efforts on inflammation could shift our view of hydrocephalus from that of a lifelong neurosurgical disorder to that of a preventable neuroinflammatory condition.

Accuracy and safety of 1-day external lumbar drainage of CSF for shunt selection in patients with idiopathic normal pressure hydrocephalus

OBJECTIVE

Three to five days of external lumbar drainage (ELD) of CSF is a test for ventriculoperitoneal shunt (VPS) selection in idiopathic normal pressure hydrocephalus (iNPH). The accuracy and complication rates of a shorter (1-day) ELD procedure were analyzed.

METHODS

Data of patients with iNPH who underwent 1-day ELD to be selected to undergo VPS placement with a programmable valve in the period from 2005 to 2015 were reviewed. Patients experiencing VPS complications, valve malfunctioning, or with less than 1 year of follow-up were excluded. The ability of 1-day ELD to predict VPS outcome at 1- and 12-month follow-up was assessed by calculating sensitivity, specificity, and positive and negative predictive values.

RESULTS

Of 93 patients who underwent 1-day ELD, 3 did not complete the procedure. Of the remaining 90 patients, 2 experienced transient nerve root irritation. Twenty-four patients had negative test outcomes and 66 had positive test outcomes. Nine negative-outcome patients had intraprocedural headache, which showed 37.5% sensitivity (95% confidence interval [CI] 19.5%-59.2%) and 100% specificity (95% CI 93.1%-100%) as predictors of negative 1-day ELD outcome. Sixty-eight patients (6 with negative and 62 with positive outcomes) underwent VPS insertion, which was successful in 0 and 58 patients, respectively, at 1-month follow-up. Test sensitivity and specificity in predicting surgical outcome at 1-month follow-up were 100% (95% CI 92.3%-100%) and 60% (95% CI 27.4%-86.3%), respectively, with 94.1% accuracy (95% CI 85.6-98.4%). Among the 1-day ELD-positive patients, 2 showed no clinical benefit at 12 months follow-up. Test sensitivity and specificity in predicting surgical outcome at 12-month follow-up was 100% (95% CI 92.5%-100%) and 75.0% (95% CI 35.6%-95.5%), respectively, with 97.1% (95% CI 89.8%-99.6%) accuracy.

CONCLUSIONS

One-day ELD is a reliable tool in iNPH management, with low complication risk and short trial duration. The test is very consistent in predicting who will have a positive outcome with VPS placement, given the high chance of successful outcome at 1- and 12-month follow-up; negative-outcome patients have a high risk of unsuccessful surgery. Intraprocedural headache is prognostic of 1-day ELD negative outcome.

Cerebrospinal fluid volumetric net flow rate and direction in idiopathic normal pressure hydrocephalus

The aim of the present study was to examine cerebrospinal fluid (CSF) volumetric net flow rate and direction at the cranio-cervical junction (CCJ) and cerebral aqueduct in individuals with idiopathic normal pressure hydrocephalus (iNPH) using cardiac-gated phase-contrast magnetic resonance imaging (PC-MRI). An in-depth, pixel-by-pixel analysis of regions of interest from the CCJ and cerebral aqueduct, respectively, was done in 26 iNPH individuals, and in 4 healthy subjects for validation purposes. Results from patients were compared with over-night measurements of static and pulsatile intracranial pressure (ICP). In iNPH, CSF net flow at CCJ was cranially directed in 17/22 as well as in 4/4 healthy subjects. Estimated daily CSF volumetric net flow rate at CCJ was 6.9 ± 9.9 L/24 h in iNPH patients and 4.5 ± 5.0 L/24 h in healthy individuals. Within the cerebral aqueduct, the CSF net flow was antegrade in 7/21 iNPH patients and in 4/4 healthy subjects, while it was retrograde (i.e. towards ventricles) in 14/21 iNPH patients. Estimated daily CSF volumetric net flow rate in cerebral aqueduct was 1.1 ± 2.2 L/24 h in iNPH while 295 ± 53 mL/24 h in healthy individuals. Magnitude of cranially directed CSF net flow in cerebral aqueduct was highest in iNPH individuals with signs of impaired intracranial compliance. The study results indicate CSF flow volumes and direction that are profoundly different from previously assumed. We hypothesize that spinal CSF formation may serve to buffer increased demand for CSF flow through the glymphatic system during sleep and during deep inspiration to compensate for venous outflow.

Comparative transcriptomics of choroid plexus in Alzheimer's disease, frontotemporal dementia and Huntington's disease: implications for CSF homeostasis

BACKGROUND

In Alzheimer's disease, there are striking changes in CSF composition that relate to altered choroid plexus (CP) function. Studying CP tissue gene expression at the blood-cerebrospinal fluid barrier could provide further insight into the epithelial and stromal responses to neurodegenerative disease states.

METHODS

Transcriptome-wide Affymetrix microarrays were used to determine disease-related changes in gene expression in human CP. RNA from post-mortem samples of the entire lateral ventricular choroid plexus was extracted from 6 healthy controls (Ctrl), 7 patients with advanced (Braak and Braak stage III-VI) Alzheimer's disease (AD), 4 with frontotemporal dementia (FTD) and 3 with Huntington's disease (HuD). Statistics and agglomerative clustering were accomplished with MathWorks, MatLab; and gene set annotations by comparing input sets to GeneGo ( http://www.genego.com ) and Ingenuity ( http://www.ingenuity.com ) pathway sets. Bonferroni-corrected hypergeometric p-values of < 0.1 were considered a significant overlap between sets.

RESULTS

Pronounced differences in gene expression occurred in CP of advanced AD patients vs. Ctrls. Metabolic and immune-related pathways including acute phase response, cytokine, cell adhesion, interferons, and JAK-STAT as well as mTOR were significantly enriched among the genes upregulated. Methionine degradation, claudin-5 and protein translation genes were downregulated. Many gene expression changes in AD patients were observed in FTD and HuD (e.g., claudin-5, tight junction downregulation), but there were significant differences between the disease groups. In AD and HuD (but not FTD), several neuroimmune-modulating interferons were significantly enriched (e.g., in AD: IFI-TM1, IFN-AR1, IFN-AR2, and IFN-GR2). AD-associated expression changes, but not those in HuD and FTD, were enriched for upregulation of VEGF signaling and immune response proteins, e.g., interleukins. HuD and FTD patients distinctively displayed upregulated cadherin-mediated adhesion.

CONCLUSIONS

Our transcript data for human CP tissue provides genomic and mechanistic insight for differential expression in AD vs. FTD vs. HuD for stromal as well as epithelial components. These choroidal transcriptome characterizations elucidate immune activation, tissue functional resiliency, and CSF metabolic homeostasis. The BCSFB undergoes harmful, but also important functional and adaptive changes in neurodegenerative diseases; accordingly, the enriched JAK-STAT and mTOR pathways, respectively, likely help the CP in adaptive transcription and epithelial repair and/or replacement when harmed by neurodegeneration pathophysiology. We anticipate that these precise CP translational data will facilitate pharmacologic/transgenic therapies to alleviate dementia.

Spaceflight-Induced Intracranial Hypertension and Visual Impairment: Pathophysiology and Countermeasures

Visual impairment intracranial pressure (VIIP) syndrome is considered an unexplained major risk for future long-duration spaceflight. NASA recently redefined this syndrome as Spaceflight-Associated Neuro-ocular Syndrome (SANS). Evidence thus reviewed supports that chronic, mildly elevated intracranial pressure (ICP) in space (as opposed to more variable ICP with posture and activity on Earth) is largely accounted for by loss of hydrostatic pressures and altered hemodynamics in the intracranial circulation and the cerebrospinal fluid system. In space, an elevated pressure gradient across the lamina cribrosa, caused by a chronic but mildly elevated ICP, likely elicits adaptations of multiple structures and fluid systems in the eye which manifest themselves as the VIIP syndrome. A chronic mismatch between ICP and intraocular pressure (IOP) in space may acclimate the optic nerve head, lamina cribrosa, and optic nerve subarachnoid space to a condition that is maladaptive to Earth, all contributing to the pathogenesis of space VIIP syndrome. Relevant findings help to evaluate whether artificial gravity is an appropriate countermeasure to prevent this seemingly adverse effect of long-duration spaceflight.

Aging alters mRNA expression of amyloid transporter genes at the blood-brain barrier

Decreased clearance of potentially toxic metabolites, due to aging changes, likely plays a significant role in the accumulation of amyloid-beta (Aβ) peptides and other macromolecules in the brain of the elderly and in the patients with Alzheimer's disease (AD). Aging is the single most important risk factor for AD development. Aβ transport receptor proteins expressed at the blood-brain barrier are significantly altered with age: the efflux transporters lipoprotein receptor-related protein 1 and P-glycoprotein are reduced, whereas the influx transporter receptor for advanced glycation end products is increased. These receptors play an important role in maintaining brain biochemical homeostasis. We now report that, in a rat model of aging, gene transcription is altered in aging, as measured by Aβ receptor gene messenger RNA (mRNA) at 3, 6, 9, 12, 15, 20, 30, and 36 months. Gene mRNA expression from isolated cerebral microvessels was measured by quantitative polymerase chain reaction. Lipoprotein receptor-related protein 1 and P-glycoprotein mRNA were significantly reduced in aging, and receptor for advanced glycation end products was increased, in parallel with the changes seen in receptor protein expression. Transcriptional changes appear to play a role in aging alterations in blood-brain barrier receptor expression and Aβ accumulation.

Transport across the choroid plexus epithelium

The choroid plexus epithelium is a secretory epithelium par excellence. However, this is perhaps not the most prominent reason for the massive interest in this modest-sized tissue residing inside the brain ventricles. Most likely, the dominant reason for extensive studies of the choroid plexus is the identification of this epithelium as the source of the majority of intraventricular cerebrospinal fluid. This finding has direct relevance for studies of diseases and conditions with deranged central fluid volume or ionic balance. While the concept is supported by the vast majority of the literature, the implication of the choroid plexus in secretion of the cerebrospinal fluid was recently challenged once again. Three newer and promising areas of current choroid plexus-related investigations are as follows: 1) the choroid plexus epithelium as the source of mediators necessary for central nervous system development, 2) the choroid plexus as a route for microorganisms and immune cells into the central nervous system, and 3) the choroid plexus as a potential route for drug delivery into the central nervous system, bypassing the blood-brain barrier. Thus, the purpose of this review is to highlight current active areas of research in the choroid plexus physiology and a few matters of continuous controversy.

Current concepts on the pathophysiology of idiopathic chronic adult hydrocephalus: Are we facing another neurodegenerative disease?

INTRODUCTION

Since its description five decades ago, the pathophysiology of idiopathic chronic adult hydrocephalus (iCAH) has been traditionally related to the effect that ventricular dilatation exerts on the structures surrounding the ventricular system. However, altered cerebral blood flow, especially a reduction in the CSF turnover rate, are starting to be considered the main pathophysiological elements of this disease.

DEVELOPMENT

Compression of the pyramidal tract, the frontostriatal and frontoreticular circuits, and the paraventricular fibres of the superior longitudinal fasciculus have all been reported in iCAH. At the level of the corpus callosum, gliosis replaces a number of commissural tracts. Cerebral blood flow is also altered, showing a periventricular watershed region limited by the subependymal arteries and the perforating branches of the major arteries of the anterior cerebral circulation. The CSF turnover rate is decreased by 75%, leading to the reduced clearance of neurotoxins and the interruption of neuroendocrine and paracrine signalling in the CSF.

CONCLUSIONS

iCAH presents as a complex nosological entity, in which the effects of subcortical microangiopathy and reduced CSF turnover play a key role. According to its pathophysiology, it is simpler to think of iCAH more as a neurodegenerative disease, such as Alzheimer disease or Binswanger disease than as the classical concept of hydrocephalus.

Fabrication of three-dimensional hydrogel scaffolds for modeling shunt failure by tissue obstruction in hydrocephalus

Background

Shunt obstruction in the treatment of hydrocephalus is poorly understood, is multi-factorial, and in many cases is modeled ineffectively. Several mechanisms may be responsible, one of which involves shunt infiltration by reactive cells from the brain parenchyma. This has not been modeled in culture and cannot be consistently examined in vivo without a large sample size.

Methods

We have developed and tested a three-dimensional in vitro model of astrocyte migration and proliferation around clinical grade ventricular catheters and into catheter holes that mimics the development of cellular outgrowth from the parenchyma that may contribute to shunt obstruction.

Results

Cell attachment and growth was observed on shunt catheters for as long as 80 days with at least 77 % viability until 51 days. The model can be used to study cellular attachment to ventricular catheters under both static and pulsatile flow conditions, which better mimic physiological cerebrospinal fluid dynamics and shunt system flow rates (0.25 mL/min, 100 pulses/min). Pulsatile flow through the ventricular catheter decreased cell attachment/growth by 63 % after 18 h. Under both conditions it was possible to observe cells accumulating around and in shunt catheter holes.

Conclusions

Alone or in combination with previously-published culture models of shunt obstruction, this model serves as a relevant test bed to analyze mechanisms of shunt failure and to test catheter modifications that will prevent cell attachment and growth.

Cerebrospinal fluid biomarkers for prognosis of long-term cognitive treatment outcomes in patients with idiopathic normal pressure hydrocephalus

The prognosis of cognitive improvement after cerebrospinal fluid (CSF) shunting in idiopathic normal pressure hydrocephalus (iNPH) remains uncertain, with no reports on CSF biomarkers related to long-term cognitive prognosis. We performed a preliminary study of CSF biomarker protein levels for cognitive outcome prognostication of two-year outcomes after shunt treated iNPH in 36 patients (13 women) with a median age of 75years (IQR 69-78). CSF biomarkers included soluble amyloid precursor proteins (sAPP, sAPPα, sAPPβ), amyloid β (Aβ)1-38, Aβ1-42 and phosphorylated tau (p-tau), lipocalin-type prostaglandin D synthase (L-PGDS)/β-trace, and cystatin C. The results clearly showed that p-tau levels (sensitivity of 71.4%, specificity of 77.8%, cut-off value of 22.0pg/mL), Aβ1-38/Aβ1-42 ratio (77.8%, 81%, 3.58), and the Aβ1-42/p-tau ratio (76%, 72.7%, 14.6) in preoperative CSF have the potential to determine postoperative prognosis. Improved cognition may be associated with the improvement in CSF circulation after LPS, which likely induces cystatin C and L-PGDS and switches synthesis from Aβ1-42 to Aβ1-38.

The Glymphatic System: A Beginner's Guide

The glymphatic system is a recently discovered macroscopic waste clearance system that utilizes a unique system of perivascular tunnels, formed by astroglial cells, to promote efficient elimination of soluble proteins and metabolites from the central nervous system. Besides waste elimination, the glymphatic system also facilitates  brain-wide distribution of several compounds, including glucose, lipids, amino acids, growth factors, and neuromodulators. Intriguingly, the glymphatic system function mainly during sleep and is largely disengaged during wakefulness. The biological need for sleep across all species may therefore reflect that the brain must enter a state of activity that enables elimination of potentially neurotoxic waste products, including β-amyloid. Since the concept of the glymphatic system is relatively new, we will here review its basic structural elements, organization, regulation, and functions. We will also discuss recent studies indicating that glymphatic function is suppressed in various diseases and that failure of glymphatic function in turn might contribute to pathology in neurodegenerative disorders, traumatic brain injury and stroke.

Kaolin-induced chronic hydrocephalus accelerates amyloid deposition and vascular disease in transgenic rats expressing high levels of human APP

BACKGROUND

Normal pressure hydrocephalus (NPH) is most common in the elderly and has a high co-morbidity with Alzheimer's disease (AD) and cerebrovascular disease (CVD). To understand the relationship between NPH, AD and CVD, we investigated how chronic hydrocephalus impacts brain amyloid-beta peptide (Aβ) accumulation and vascular pathology in an AD transgenic rodent model. Previously we showed that the altered CSF physiology produced by kaolin-hydrocephalus in older wild-type Sprague-Dawley rats increased Aβ and hyperphosphorylated Tau (Silverberg et. al. Brain Res. 2010, 1317:286-296). We postulated that hydrocephalus would similarly affect an AD rat model.

METHODS

Thirty-five transgenic rats (tgAPP21) that express high levels of human APP and naturally overproduce Aβ40 were used. Six- (n = 7) and twelve-month-old (n = 9) rats had hydrocephalus induced by cisternal kaolin injection. We analyzed Aβ burden (Aβ40, Aβ42 and oligomeric Aβ) and vascular integrity (Masson trichrome and Verhoeff-Van Gieson) by immunohistochemistry and chemical staining at 10 weeks (n = 8) and 6 months (n = 5) post hydrocephalus induction. We also analyzed whether the vascular pathology seen in tgAPP21 rats, which develop amyloid angiopathy, was accelerated by hydrocephalus. Age-matched naïve and sham-operated tgAPP21 rats served as controls (n = 19).

RESULTS

In hydrocephalic tgAPP21 rats, compared to naïve and sham-operated controls, there was increased Aβ 40 and oligomeric Aβ in hippocampal and cortical neurons at 10 weeks and 6 months post-hydrocephalus induction. No dense-core amyloid plaques were seen, but diffuse Aβ immunoreactivity was evident in neurons. Vascular pathology was accelerated by the induction of hydrocephalus compared to controls. In the six-month-old rats, subtle degenerative changes were noted in vessel walls at 10 weeks post-kaolin, whereas at six months post-kaolin and in the 12-month-old hydrocephalic rats more pronounced amyloid angiopathic changes were seen, with frequent large areas of infarction noted.

CONCLUSIONS

Kaolin-hydrocephalus can accelerate intraneuronal Aβ40 accumulation and vascular pathology in tgAPP21 rats. In addition, disrupted CSF production and reduced CSF turnover results in impaired Aβ clearance and accelerated vascular pathology in chronic hydrocephalus. The high co-morbidity seen in NPH, AD and CVD is likely not to be an age-related coincidence, but rather a convergence of pathologies related to diminished CSF clearance.

Cerebrospinal fluid absorption block at the vertex in chronic hydrocephalus: obstructed arachnoid granulations or elevated venous pressure?

Background

The lack of absorption of CSF at the vertex in chronic hydrocephalus has been ascribed to an elevation in the arachnoid granulation outflow resistance (R_out). The CSF infusion studies measuring R_out are dependent on venous sinus pressure but little is known about the changes in pressure which occur throughout life or with the development of hydrocephalus.

Methods

Twenty patients with chronic hydrocephalus underwent MR venography and MR flow quantification techniques. The venous outflow pressure was estimated from the sinus blood flow and the cross-sectional area of the transverse sinuses. Adult controls as well as a normal young cohort were selected to estimate the change in sinus pressure which occurs throughout life and following the development of hydrocephalus. Significance was tested with a Student’s t-test.

Results

The size of the transverse sinuses was unchanged from the 1^st to the 5^th decade of life, indicating a stable outflow resistance. However, the blood flow was reduced by 42%, indicating a likely similar reduction in pressure gradient across the sinuses. The sinuses of hydrocephalus patients were 38% smaller than matched controls, indicating a 2.5 times increase in resistance. Despite the 24% reduction in blood flow, a significant increase in sinus pressure is suggested.

Conclusions

The size of the venous sinuses normally does not change over the age range investigated but sinus pressure is reduced proportional to an age-related blood flow reduction. Hydrocephalus is associated with much smaller sinuses than normal and an elevation in venous pressure may explain the lack of CSF absorption into the arachnoid granulations in chronic hydrocephalus.

Cerebrospinal Fluid Secretion by the Choroid Plexus

The choroid plexus epithelium is a cuboidal cell monolayer, which produces the majority of the cerebrospinal fluid. The concerted action of a variety of integral membrane proteins mediates the transepithelial movement of solutes and water across the epithelium. Secretion by the choroid plexus is characterized by an extremely high rate and by the unusual cellular polarization of well-known epithelial transport proteins. This review focuses on the specific ion and water transport by the choroid plexus cells, and then attempts to integrate the action of specific transport proteins to formulate a model of cerebrospinal fluid secretion. Significant emphasis is placed on the concept of isotonic fluid transport across epithelia, as there is still surprisingly little consensus on the basic biophysics of this phenomenon. The role of the choroid plexus in the regulation of fluid and electrolyte balance in the central nervous system is discussed, and choroid plexus dysfunctions are described in a very diverse set of clinical conditions such as aging, Alzheimer's disease, brain edema, neoplasms, and hydrocephalus. Although the choroid plexus may only have an indirect influence on the pathogenesis of these conditions, the ability to modify epithelial function may be an important component of future therapies.

Senescent changes in cerebrospinal fluid circulatory physiology and their role in the pathogenesis of normal-tension glaucoma

PURPOSE

To evaluate the evidence supporting a role for senescent changes in cerebrospinal fluid (CSF) circulatory physiology in the pathogenesis of normal-tension glaucoma (NTG).

DESIGN

Literature review and personal perspective of the authors.

METHODS

Analysis of selected articles in the peer-reviewed literature with interpretation and perspective.

RESULTS

Recent studies have reported that intracranial pressure is lower in patients with NTG when compared with patients with primary open-angle glaucoma and nonglaucomatous control subjects. It has been suggested that a low intracranial pressure in patients with normal intraocular pressure could lead to glaucomatous damage. This low intracranial pressure, leading to an abnormally high trans-lamina cribrosa pressure difference, could result in barotraumatically induced optic nerve damage at the lamina cribrosa. However, several experimental studies do not support the speculation that low intracranial pressure and the resulting pressure-dependent effects cause bowing back of the lamina cribrosa and optic disc cupping. On the other hand, CSF production and turnover have been shown to be decreased in aging and in pathologic conditions, such as Alzheimer disease and normal pressure hydrocephalus. Interestingly, recent studies have revealed that both Alzheimer disease patients and patients with normal pressure hydrocephalus may have a higher risk of developing glaucoma. Therefore, we believe that CSF circulatory failure, ultimately resulting in reduced neurotoxin clearance along the optic nerves, could be an alternative explanation as to why glaucoma develops in patients with low intracranial pressure.

CONCLUSIONS

On the basis of the evidence available from the peer-reviewed literature, our tentative conclusion is that age-related changes in CSF circulatory physiology and the subsequent decrease in CSF turnover, with diminished clearance of toxic substances, can account for, at least in part, the pathogenesis of NTG. It should be stressed that for the moment at least, the present hypothesis remains unproven. Further research will be necessary to determine the possible role of CSF circulatory dysfunction in NTG. If confirmed, this hypothesis could provide new, important insights into the pathogenesis of NTG.

Ventricle equilibrium position in healthy and normal pressure hydrocephalus brains using an analytical model

The driving force that causes enlargement of the ventricles remains unclear in case of normal pressure hydrocephalus (NPH). Both healthy and NPH brain conditions are characterized by a low transparenchymal pressure drop, typically 1 mm Hg. The present paper proposes an analytical model for normal and NPH brains using Darcy's and Biot's equations and simplifying the brain geometry to a hollow sphere with an internal and external radius. Self-consistent solutions for the large deformation problem that is associated with large ventricle dilation are presented and the notion of equilibrium or stable ventricle position is highlighted for both healthy and NPH conditions. The influence of different biomechanical parameters on the stable ventricle geometry is assessed and it is shown that both CSF seepage through the ependyma and parenchymal permeability play a key role. Although very simple, the present model is able to predict the onset and development of NPH conditions as a deviation from healthy conditions.

Increased blood-cerebrospinal fluid transfer of albumin in advanced Parkinson's disease

BACKGROUND

Alterations in blood-brain barrier permeability have been proposed to represent a relevant factor contributing to Parkinson's disease progression. However, few studies have addressed this issue in patients at different stages of disease.

METHODS

Albumin was measured in cerebrospinal fluid and serum samples obtained from 73 non-demented subjects with idiopathic Parkinson's disease and 47 age-matched control subjects. The albumin ratio (AR) was calculated to assess blood-cerebrospinal fluid and blood-brain barrier function. The group of patients with Parkinson's disease included 46 subjects with Hoehn-Yahr staging between 1 and 2 and 27, with a score ranging from 2.5 to 4.

RESULTS

Statistically significant differences in albumin ratio were found between patients with advanced disease, and both early-stage and unaffected groups. Conversely, early-phase patients did not differ from healthy subjects. Additionally, dopaminergic treatment seems to exert a possible effect on AR values.

CONCLUSIONS

Our study demonstrates that possible dysfunction of the blood-cerebrospinal fluid barrier, blood-brain barrier, or both, characterize Parkinson's disease progression. The associations between clinical scores, treatments and biochemical findings suggest a progressive impairment of barrier integrity during the course of the disease.

Hydrocephalus and aquaporins: the role of aquaporin-1

INTRODUCTION

Aquaporins (AQPs) are membrane proteins that facilitate water and small solute movement in tissues. Hydrocephalus is a major central nervous system disorder associated with defective cerebrospinal fluid (CSF) turnover. Aquaporin-1 (AQP1) is a water channel located mainly at the choroid plexus epithelium and plays an active role in CSF production. The aim of this study is to review the pertinent literature concerning the role of aquaporin-1 in the pathophysiology of hydrocephalus.

METHODS

We performed a MEDLINE search using the terms aquaporin AND hydrocephalus. The results of the search were further refined to exclude studies not related to aquaporin-1.

RESULTS

Five studies were identified. Three of these studies utilized an animal model, while only two studies referred to a few human cases of hydrocephalus. Most of the studies indicate that there is a down-regulation of AQP1 expression in choroid plexus in models of hydrocephalus. A small series of human choroid plexus tumors showed that AQP1 expression is up-regulated. In cases of human choroid plexus tumors, there are indications that AQP1 may have alternative physiologic roles, but it is not clear whether this is associated with a specific type of hydrocephalus or the genetic burden of the tumor.

CONCLUSION

There has been a paucity of research on the link between aquaporins and hydrocephalus. Most studies have relied on animal models. An adaptive and protective role of AQP1 as a regulator of CSF production is proposed in the pathophysiology of hydrocephalus. Further research is needed to clarify if this association exists in humans.

Genes involved in cerebrospinal fluid production as candidate genes for late-onset Alzheimer's disease: a hypothesis

In rare patients with autosomal dominant, early-onset Alzheimer's disease (AD), pathogenic mutations in the genes encoding β-amyloid precursor protein, and the γ-secretase-complex components presenilin-1 and presenilin-2 appear to result in β-amyloid (Aβ) overproduction. The pathological accumulation of Aβ in the far more common late-onset AD is more likely to be the result of deficient clearance of Aβ. There is evidence that production and turnover of cerebrospinal fluid (CSF) help to clear toxic molecules such as Aβ from the interstitial fluid space of the brain to the bloodstream. CSF production and turnover have been shown to be decreased in aging and in pathological conditions, such as normal pressure hydrocephalus and AD. Reduced formation of CSF, with diminished clearance of Aβ, may play an important role in the onset and progression of AD. If reduced CSF turnover is a risk factor for AD, then its incidence ought to be increased under conditions of CSF circulatory failure. In this paper, the authors hypothesize that genes and variations of genes involved in the CSF production and absorption may contribute to the pathogenesis of late-onset AD.

Does drainage hole size influence adhesion on ventricular catheters?

PURPOSE

Ventricular catheter drainage holes of shunt systems used to treat hydrocephalus obstruct with tissue commonly comprising monocytes/macrophages, astrocytes, and giant cells. Despite high rates of obstruction, very few studies have manipulated drainage hole orientation, number, position, or diameter. By altering the hole diameter but maintaining a constant hole surface area, we manipulated shear stress through the holes, which we hypothesized would change the degree of macrophage and astrocyte attachment.

METHODS

First, a hole fabrication method was chosen from two fabrication techniques including punched holes in catheter tubing and constructed holes using nanofabrication techniques.

RESULTS

Punched holes were chosen to vary hole size from 282 to 975 μm because (1) samples were geometrically similar to commercially available ventricular catheters without significant microscopic differences in roughness values and (2) total macrophage and astrocyte adhesion on the punched holes was not significantly different from adhesion on the commercially available catheters. Overall adhesion from least to most adherent appeared to follow 975 < 754 ≈ 500 < 282-μm hole diameter for macrophages and 975 < 500 < 754 < 282 for astrocytes with an obvious dependency on catheter orientation with respect to the horizontal; a dependency to the proximity of the hole to the catheter tip was not observed.

CONCLUSION

This study suggests that macrophage and astrocyte adhesion generally decreases with increasing hole diameter under flow conditions and underscores the necessity for future work to examine how hole diameter impacts inflammatory-based shunt obstruction.

Amyloid-beta transporter expression at the blood-CSF barrier is age-dependent

Background

Age is the major risk factor for many neurodegenerative diseases, including Alzheimer's disease (AD). There is an accumulation of amyloid-beta peptides (Aβ) in both the AD brain and the normal aging brain. Clearance of Aβ from the brain occurs via active transport at the blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (BCSFB). With increasing age, the expression of the Aβ efflux transporters is decreased and the Aβ influx transporter expression is increased at the BBB, adding to the amyloid burden in the brain. Expression of the Aβ transporters at the choroid plexus (CP) epithelium as a function of aging was the subject of this study.

Methods

This project investigated the changes in expression of the Aβ transporters, the low density lipoprotein receptor-related protein-1 (LRP-1), P-glycoprotein (P-gp), LRP-2 (megalin) and the receptor for advanced glycation end-products (RAGE) at the BCSFB in Brown-Norway/Fischer rats at ages 3, 6, 9, 12, 20, 30 and 36 months, using real time RT-PCR to measure transporter mRNA expression, and immunohistochemistry (IHC) to measure transporter protein in isolated rat CP.

Results

There was an increase in the transcription of the Aβ efflux transporters, LRP-1 and P-gp, no change in RAGE expression and a decrease in LRP-2, the CP epithelium influx transporter, at the BCSFB with aging. Decreased Aβ42 concentration in the CP, as measured by quantitative IHC, was associated with these Aβ transporter alterations.

Conclusions

Age-dependent alterations in the CP Aβ transporters are associated with a decrease in Aβ42 accumulation in the CP, and are reciprocal to the changes seen in these transporters at the BBB, suggesting a possible compensatory role for the BCSFB in Aβ clearance in aging.

Targeting the choroid plexus-CSF-brain nexus using peptides identified by phage display

Drug delivery to the central nervous system requires the use of specific portals to enable drug entry into the brain and, as such, there is a growing need to identify processes that can enable drug transfer across both blood-brain and blood-cerebrospinal fluid barriers. Phage display is a powerful combinatorial technique that identifies specific peptides that can confer new activities to inactive particles. Identification of these peptides is directly dependent on the specific screening strategies used for their selection and retrieval. This chapter describes three selection strategies, which can be used to identify peptides that target the choroid plexus (CP) directly or for drug translocation across the CP and into cerebrospinal fluid.

Choroidal Proteins Involved in Cerebrospinal Fluid Production may be Potential Drug Targets for Alzheimer's Disease Therapy

Alzheimer’s disease is known to be the most common form of dementia in the elderly. It is clinically characterized by impairment of cognitive functions, as well as changes in personality, behavioral disturbances and an impaired ability to perform activities of daily living. To date, there are no effective ways to cure or reverse the disease. Genetic studies of early-onset familial Alzheimer’s disease cases revealed causative mutations in the genes encoding β-amyloid precursor protein and the γ-secretase-complex components presenilin-1 and presenilin-2, supporting an important role of β-amyloid in the pathogenesis of Alzheimer’s disease. Compromised function of the choroid plexus and defective cerebrospinal fluid production and turnover, with diminished clearance of β-amyloid, may play an important role in late-onset forms of Alzheimer’s disease. If reduced cerebrospinal fluid turnover is a risk factor for Alzheimer’s disease, then therapeutic strategies to improve cerebrospinal fluid flow are reasonable. However, the role of deficient cerebrospinal fluid dynamics in Alzheimer’s disease and the relevance of choroidal proteins as potential therapeutic targets to enhance cerebrospinal fluid turnover have received relatively little research attention. In this paper, we discuss several choroidal proteins, such as Na⁺-K⁺ ATPase, carbonic anhydrase, and aquaporin 1, that may be targets for pharmacological up-regulation of cerebrospinal fluid formation. The search for potentially beneficial drugs useful to ameliorate Alzheimer’s disease by facilitating cerebrospinal fluid production and turnover may be an important area for future research. However, the ultimate utility of such modulators in the management of Alzheimer’s disease remains to be determined. Here, we hypothesize that caffeine, the most commonly used psychoactive drug in the world, may be an attractive therapeutic candidate for treatment of Alzheimer’s disease since long-term caffeine consumption may augment cerebrospinal fluid production. Other potential mechanisms of cognitive protection by caffeine have been suggested by recent studies.

Hydrocephalus and aquaporins: lessons learned from the bench

PURPOSE

Hydrocephalus is a common disorder of defective cerebrospinal fluid (CSF) turnover. The identification of the aquaporin water channels (AQPs) led to the study of their role in the composition of biological fluids including CSF. The purpose of this study is to review the potential role of aquaporins in the pathogenesis, compensation, and possibly treatment of hydrocephalus.

METHODS

We performed a MEDLINE search using the terms "aquaporin AND hydrocephalus." The search returned a total of 20 titles. Eleven studies fulfilled the criteria for this review.

RESULTS

Most studies were performed in animal models. The expression of AQPs in hydrocephalus is significantly altered. Aquaporin-1 levels at the choroid plexus are decreased in most models of hydrocephalus while CSF production and intracranial pressure are reduced in AQP1 knockout mice. In contrast, the expression of AQP4 in hydrocephalus is increased at its sites of expression. Aquaporin-4 knockout mice show a decreased clearance of brain edema via blood-CSF and blood-brain barrier (BBB) pathways and decreased survival in hydrocephalus models.

CONCLUSIONS

Aquaporin-1 is highly expressed at the choroid plexus and is related to CSF production. Aquaporin-4 is expressed at the ependyma, glia limitans, and at the perivascular end feet processes of astrocytes of the BBB, facilitating the water movement across these tissue interfaces. The observations obtained from animal studies and few cases in humans indicate an adaptive and protective role of AQPs in hydrocephalus by decreasing CSF production and increasing edema clearance. Aquaporins are attractive targets for the pharmaceutical treatment of hydrocephalus.

The distributional nexus of choroid plexus to cerebrospinal fluid, ependyma and brain: toxicologic/pathologic phenomena, periventricular destabilization, and lesion spread

Bordering the ventricular cerebrospinal fluid (CSF) are epithelial cells of choroid plexus (CP), ependyma and circumventricular organs (CVOs) that contain homeostatic transporters for mediating secretion/reabsorption. The distributional pathway ("nexus") of CP-CSF-ependyma-brain furnishes peptides, hormones, and micronutrients to periventricular regions. In disease/toxicity, this nexus becomes a conduit for infectious and xenobiotic agents. The sleeping sickness trypanosome (a protozoan) disrupts CP and downstream CSF-brain. Piperamide is anti-trypanosomic but distorts CP epithelial ultrastructure by engendering hydropic vacuoles; this reflects phospholipidosis and altered lysosomal metabolism. CP swelling by vacuolation may occlude CSF flow. Toxic drug tools delineate injuries to choroidal compartments: cyclophosphamide (vasculature), methylcellulose (interstitium), and piperazine (epithelium). Structurally perturbed CP allows solutes to penetrate the ventricles. There, CSF-borne pathogens and xenobiotics may permeate the ependyma to harm neurogenic stem cell niches. Amoscanate, an anti-helmintic, potently injures rodent ependyma. Ependymal/brain regions near CP are vulnerable to CSF-borne toxicants; this proximity factor links regional barrier breakdown to nearby periventricular pathology. Diverse diseases (e.g., African sleeping sickness, multiple sclerosis) take early root in choroidal, circumventricular, or perivascular loci. Toxicokinetics informs on pathogen, anti-parasitic agent, and auto-antibody distribution along the CSF nexus. CVOs are susceptible to plasma-borne toxicants/pathogens. Countering the physico-chemical and pathogenic insults to the homeostasis-mediating ventricle-bordering cells sustains brain health and fluid balance.

Shunt dependence: myths and facts

INTRODUCTION

Chronically shunted patients are believed to be unable to have a shunt-free life. Nevertheless, sometimes shunt removal is possible after an endoscopic third ventriculostomy, even after long periods of cerebral spinal fluid diversion.

RESULTS AND DISCUSSION

We perform a literature review that leads to a discussion of this subject in the light of the current medical knowledge.

The physical chemistry of brain and neural cell membranes: an overview

The formation of cell membranes through the physical-chemical interaction of two hydrophilic colloidal fluids is applied to the formation of the membranes of brain and neural cells. Also described is the membrane mechanism of transfer of ions and compounds necessary for brain and neural cell functions into the cerebrospinal fluid through the blood-brain barrier. Changes in the cerebrospinal fluid giving rise to degradation of brain and neural cells and the formation of precipitates within the brain are considered. Monitoring of electrolyte changes in metabolic fluids is shown to be a possible method of predicting the onset of degenerate brain conditions.

Mechanical contributions to astrocyte adhesion using a novel in vitro model of catheter obstruction

Drainage and diversion of cerebrospinal fluid (CSF) through shunt systems is the most common treatment for hydrocephalus, but complications due to tissue obstruction of the catheter occur in up to 61% of patients. Although shunt systems have undergone limited technological advancements to resist mammalian cell adhesion, there is a need to further reduce adhesion that can exacerbate obstruction. The high intrinsic variability in clinical studies and an inability to predict chronic adhesion of host cells in vitro while maintaining the environmental conditions observed in hydrocephalus have impeded progress. We designed the hydrocephalus shunt catheter bioreactor (HSCB) to measure inflammatory cell adhesion under experimentally manipulated conditions of CSF pressure, pulsation rate, and flow rates. For a 20-h period, astrocytes were perfused through the pulsatile flow system, and adhesion on silicone catheters was recorded. These results were compared with those obtained under static cell culture conditions. Astrocyte adhesion was significantly increased under conditions of increased flow rate (0.25 and 0.30 mL/min), and a trend toward increased adhesion was observed under conditions of elevated pressure and pulsation rate. Because the HSCB represents physiologic conditions more accurately than static cell culture, our results suggest that standard static cell culturing techniques are insufficient to model inflammatory cell adhesion on catheters used in the treatment of hydrocephalus and that changes to the ventricular microenvironment can alter the mechanisms of cellular adhesion. The HSCB represents a relevant test system and is an effective model system for the analysis of cellular adhesion and occlusion of shunt catheters.

More advanced Alzheimer's disease may be associated with a decrease in cerebrospinal fluid pressure

In a recent article, elevated cerebrospinal fluid pressure (CSFP) consistent with very early normal pressure hydrocephalus (NPH), was found in a small subset of Alzheimer's disease (AD) patients (possible AD-NPH hybrids) enrolled in a clinical trial for chronic low-flow cerebrospinal fluid drainage. Also in the same study, was another interesting finding that merits further discussion: a substantial proportion of AD patients had very low CSFP. Based on the characteristics of these subjects, we hypothesize that more advanced AD may be associated with a decrease in CSFP. Reduced CSFP among a group of AD patients could provide a clue towards a better understanding of the high rate of comorbidity reported between AD and glaucoma since it has been shown that mean CSFP is lower in subjects with primary open-angle glaucoma. This could result in an abnormally high trans-lamina cribrosa pressure difference and lead to glaucomatous damage.