A heterogenous, pore-vesicle membrane model for protein transfer from blood to cerebrospinal fluid at the choroid plexus

CSF proteomic profiles of neurodegeneration biomarkers in Alzheimer's disease

INTRODUCTION

We aimed to unravel the underlying pathophysiology of the neurodegeneration (N) markers neurogranin (Ng), neurofilament light (NfL), and hippocampal volume (HCV), in Alzheimer's disease (AD) using cerebrospinal fluid (CSF) proteomics.

METHODS

Individuals without dementia were classified as A+ (CSF amyloid beta [Aβ]42), T+ (CSF phosphorylated tau181), and N+ or N- based on Ng, NfL, or HCV separately. CSF proteomics were generated and compared between groups using analysis of covariance.

RESULTS

Only a few individuals were A+T+Ng-. A+T+Ng+ and A+T+NfL+ showed different proteomic profiles compared to A+T+Ng- and A+T+NfL-, respectively. Both Ng+ and NfL+ were associated with neuroplasticity, though in opposite directions. Compared to A+T+HCV-, A+T+HCV+ showed few proteomic changes, associated with oxidative stress.

DISCUSSION

Different N markers are associated with distinct neurodegenerative processes and should not be equated. N markers may differentially complement disease staging beyond amyloid and tau. Our findings suggest that Ng may not be an optimal N marker, given its low incongruency with tau pathophysiology.

HIGHLIGHTS

In Alzheimer's disease, neurogranin (Ng)+, neurofilament light (NfL)+, and hippocampal volume (HCV)+ showed differential protein expression in cerebrospinal fluid. Ng+ and NfL+ were associated with neuroplasticity, although in opposite directions. HCV+ showed few proteomic changes, related to oxidative stress. Neurodegeneration (N) markers may differentially refine disease staging beyond amyloid and tau. Ng might not be an optimal N marker, as it relates more closely to tau.

Cerebrospinal fluid tau levels are associated with abnormal neuronal plasticity markers in Alzheimer's disease

Background

Increased total tau (t-tau) in cerebrospinal fluid (CSF) is a key characteristic of Alzheimer’s disease (AD) and is considered to result from neurodegeneration. T-tau levels, however, can be increased in very early disease stages, when neurodegeneration is limited, and can be normal in advanced disease stages. This suggests that t-tau levels may be driven by other mechanisms as well. Because tau pathophysiology is emerging as treatment target for AD, we aimed to clarify molecular processes associated with CSF t-tau levels.

Methods

We performed a proteomic, genomic, and imaging study in 1380 individuals with AD, in the preclinical, prodromal, and mild dementia stage, and 380 controls from the Alzheimer’s Disease Neuroimaging Initiative and EMIF-AD Multimodality Biomarker Discovery study.

Results

We found that, relative to controls, AD individuals with increased t-tau had increased CSF concentrations of over 400 proteins enriched for neuronal plasticity processes. In contrast, AD individuals with normal t-tau had decreased levels of these plasticity proteins and showed increased concentrations of proteins indicative of blood–brain barrier and blood-CSF barrier dysfunction, relative to controls. The distinct proteomic profiles were already present in the preclinical AD stage and persisted in prodromal and dementia stages implying that they reflect disease traits rather than disease states. Dysregulated plasticity proteins were associated with SUZ12 and REST signaling, suggesting aberrant gene repression. GWAS analyses contrasting AD individuals with and without increased t-tau highlighted several genes involved in the regulation of gene expression. Targeted analyses of SNP rs9877502 in GMNC, associated with t-tau levels previously, correlated in individuals with AD with CSF concentrations of 591 plasticity associated proteins. The number of APOE-e4 alleles, however, was not associated with the concentration of plasticity related proteins.

Conclusions

CSF t-tau levels in AD are associated with altered levels of proteins involved in neuronal plasticity and blood–brain and blood-CSF barrier dysfunction. Future trials may need to stratify on CSF t-tau status, as AD individuals with increased t-tau and normal t-tau are likely to respond differently to treatment, given their opposite CSF proteomic profiles.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13024-022-00521-3.

Macrophage compartmentalization in the brain and cerebrospinal fluid system

Macrophages reside within the diverse anatomical compartments of the central nervous system (CNS). Within each compartment, these phagocytes are exposed to unique combinations of niche signals and mechanical stimuli that instruct their tissue-specific identities. Whereas most CNS macrophages are tissue-embedded, the macrophages of the cerebrospinal fluid (CSF) system are bathed in an oscillating liquid. Studies using multiomics technologies have recently uncovered the transcriptomic and proteomic profiles of CSF macrophages, enhancing our understanding of their cellular characteristics in both rodents and humans. Here, we review the relationships between CNS macrophage populations, with a focus on the origins, phenotypes, and functions of CSF macrophages in health and disease.

Cerebrospinal fluid total tau levels indicate aberrant neuronal plasticity in Alzheimer's disease

Alzheimer's disease (AD) is characterised by abnormal amyloid beta and tau processing. Previous studies reported that cerebrospinal fluid (CSF) total tau (t-tau) levels vary between patients. Here we show that CSF t-tau variability is associated with distinct impairments in neuronal plasticity mediated by gene repression factors SUZ12 and REST. AD individuals with abnormal t-tau levels have increased CSF concentrations of plasticity proteins regulated by SUZ12 and REST. AD individuals with normal t-tau, on the contrary, have decreased concentrations of these plasticity proteins and increased concentrations in proteins associated with blood-brain and blood CSF-barrier dysfunction. Genomic analyses suggested that t-tau levels in part depend on genes involved in gene expression. The distinct plasticity abnormalities in AD as signaled by t-tau urge the need for personalised treatment.

Targeting the Choroid Plexuses for Protein Drug Delivery

Delivery of therapeutic agents to the central nervous system is challenged by the barriers in place to regulate brain homeostasis. This is especially true for protein therapeutics. Targeting the barrier formed by the choroid plexuses at the interfaces of the systemic circulation and ventricular system may be a surrogate brain delivery strategy to circumvent the blood-brain barrier. Heterogenous cell populations located at the choroid plexuses provide diverse functions in regulating the exchange of material within the ventricular space. Receptor-mediated transcytosis may be a promising mechanism to deliver protein therapeutics across the tight junctions formed by choroid plexus epithelial cells. However, cerebrospinal fluid flow and other barriers formed by ependymal cells and perivascular spaces should also be considered for evaluation of protein therapeutic disposition. Various preclinical methods have been applied to delineate protein transport across the choroid plexuses, including imaging strategies, ventriculocisternal perfusions, and primary choroid plexus epithelial cell models. When used in combination with simultaneous measures of cerebrospinal fluid dynamics, they can yield important insight into pharmacokinetic properties within the brain. This review aims to provide an overview of the choroid plexuses and ventricular system to address their function as a barrier to pharmaceutical interventions and relevance for central nervous system drug delivery of protein therapeutics. Protein therapeutics targeting the ventricular system may provide new approaches in treating central nervous system diseases.

Cerebrospinal fluid Plasmodium falciparum histidine-rich protein-2 in pediatric cerebral malaria

BACKGROUND

Cerebral malaria (CM) causes a rapidly developing coma, and remains a major contributor to morbidity and mortality in malaria-endemic regions. This study sought to determine the relationship between cerebrospinal fluid (CSF) Plasmodium falciparum histidine rich protein-2 (PfHRP-2) and clinical, laboratory and radiographic features in a cohort of children with retinopathy-positive CM.

METHODS

Patients included in the study were admitted (2009-2013) to the Pediatric Research Ward (Queen Elizabeth Central Hospital, Blantyre, Malawi) meeting World Health Organization criteria for CM with findings of malarial retinopathy. Enzyme-linked immunosorbent assay was used to determine plasma and CSF PfHRP-2 levels. Wilcoxon rank-sum tests and multivariable logistic regression analysis assessed the association of clinical and radiographic characteristics with the primary outcome of death during hospitalization.

RESULTS

In this cohort of 94 patients, median age was 44 (interquartile range 29-62) months, 53 (56.4%) patients were male, 6 (7%) were HIV-infected, and 10 (11%) died during hospitalization. Elevated concentrations of plasma lactate (p = 0.005) and CSF PfHRP-2 (p = 0.04) were significantly associated with death. On multivariable analysis, higher PfHRP-2 in the CSF was associated with death (odds ratio 9.00, 95% confidence interval 1.44-56.42) while plasma PfHRP-2 was not (odds ratio 2.05, 95% confidence interval 0.45-9.35).

CONCLUSIONS

Elevation of CSF, but not plasma PfHRP-2, is associated with death in this paediatric CM cohort. PfHRP-2 egress into the CSF may represent alteration of blood brain barrier permeability related to the sequestration of parasitized erythrocytes in the cerebral microvasculature.

Cerebrospinal fluid total protein in idiopathic intracranial hypertension

OBJECTIVE

To evaluate the relationship between CSF total protein concentration (CSF protein) and CSF opening pressure in idiopathic intracranial hypertension (IIH), and to explore the association of age, gender, race, BMI, and Humphrey visual field mean deviation (HVF MD) with CSF total protein.

METHODS

The medical records of all IIH patients seen between 1989 and 2016 at one institution were systematically reviewed for demographics, CSF opening pressure, CSF contents, and HVF MD (at initial evaluation and most recent follow-up). Linear regression of CSF protein on CSF opening pressure was performed also considering BMI, age, gender, race, HVF MD, and year of lumbar puncture.

RESULTS

We included 266 IIH patients (13 pre-pubertal children, 35 post-pubertal children, 218 adults). There was a negative linear association between CSF opening pressure and CSF protein: CSF protein decreased by 0.18mg/dL for each 1cm H₂O increase in CSF opening pressure (p<0.001). After controlling for CSF opening pressure, mean CSF protein was 4.1mg/dL higher in white patients than in black patients (p<0.001). Multivariable analysis found that CSF opening pressure (p=0.007), white race (p<0.001), and HVF MD (most recent follow-up, worst eye, p=0.05) remained independently associated with CSF protein controlling for year of lumbar puncture and age.

CONCLUSIONS

There was a negative association between CSF protein and CSF opening pressure. After controlling for CSF opening pressure, CSF protein was higher in white patients and unaffected by age, gender, or BMI. Our findings help clarify inconsistent results of prior studies, but do not really help clarify IIH pathophysiology.

Pathways of polyunsaturated fatty acid utilization: implications for brain function in neuropsychiatric health and disease

Essential polyunsaturated fatty acids (PUFAs) have profound effects on brain development and function. Abnormalities of PUFA status have been implicated in neuropsychiatric diseases such as major depression, bipolar disorder, schizophrenia, Alzheimer's disease, and attention deficit hyperactivity disorder. Pathophysiologic mechanisms could involve not only suboptimal PUFA intake, but also metabolic and genetic abnormalities, defective hepatic metabolism, and problems with diffusion and transport. This article provides an overview of physiologic factors regulating PUFA utilization, highlighting their relevance to neuropsychiatric disease.

What are lipoproteins doing in the brain?

Lipoproteins in plasma transport lipids between tissues, however, only high-density lipoproteins (HDL) appear to traverse the blood-brain barrier (BBB); thus, lipoproteins found in the brain must be produced within the central nervous system. Apolipoproteins E (ApoE) and ApoJ are the most abundant apolipoproteins in the brain, are mostly synthesized by astrocytes, and are found on HDL. In the hippocampus and other brain regions, lipoproteins help to regulate neurobehavioral functions by processes that are lipoprotein receptor-mediated. Moreover, lipoproteins and their receptors also have roles in the regulation of body weight and energy balance, acting through lipoprotein lipase (LPL) and the low-density lipoprotein (LDL) receptor-related protein (LRP). Thus, understanding lipoproteins and their metabolism in the brain provides a new opportunity with potential therapeutic relevance.

The blood-cerebrospinal fluid barrier: structure and functional significance

The choroid plexus (CP) of the blood-CSF barrier (BCSFB) displays fundamentally different properties than blood-brain barrier (BBB). With brisk blood flow (10 × brain) and highly permeable capillaries, the human CP provides the CNS with a high turnover rate of fluid (∼400,000 μL/day) containing micronutrients, peptides, and hormones for neuronal networks. Renal-like basement membranes in microvessel walls and underneath the epithelium filter large proteins such as ferritin and immunoglobulins. Type IV collagen (α3, α4, and α5) in the subepithelial basement membrane confers kidney-like permselectivity. As in the glomerulus, so also in CP, the basolateral membrane utrophin A and colocalized dystrophin impart structural stability, transmembrane signaling, and ion/water homeostasis. Extensive infoldings of the plasma-facing basal labyrinth together with lush microvilli at the CSF-facing membrane afford surface area, as great as that at BBB, for epithelial solute and water exchange. CSF formation occurs by basolateral carrier-mediated uptake of Na+, Cl-, and HCO3-, followed by apical release via ion channel conductance and osmotic flow of water through AQP1 channels. Transcellular epithelial active transport and secretion are energized and channeled via a highly dense organelle network of mitochondria, endoplasmic reticulum, and Golgi; bleb formation occurs at the CSF surface. Claudin-2 in tight junctions helps to modulate the lower electrical resistance and greater permeability in CP than at BBB. Still, ratio analyses of influx coefficients (Kin) for radiolabeled solutes indicate that paracellular diffusion of small nonelectrolytes (e.g., urea and mannitol) through tight junctions is restricted; molecular sieving is proportional to solute size. Protein/peptide movement across BCSFB is greatly limited, occurring by paracellular leaks through incomplete tight junctions and low-capacity transcellular pinocytosis/exocytosis. Steady-state concentration ratios, CSF/plasma, ranging from 0.003 for IgG to 0.80 for urea, provide insight on plasma solute penetrability, barrier permeability, and CSF sink action to clear substances from CNS.

Cerebrospinal fluid levels of soluble CD14 in inflammatory and non-inflammatory diseases of the CNS: upregulation during bacterial infections and viral meningitis

The CD14 antigen, an important cell surface molecule of monocytic cells, is involved in cellular activation: it binds lipopolysaccharide and other cellular lipid structures. Brain macrophages play a pivotal role during inflammatory reactions of the CNS parenchyma, ventricles and meninges. A soluble form of CD14 (sCD14) was measured in paired cerebrospinal fluid (CSF) and serum samples from 91 patients with different neurological diseases. Mean levels of circulating sCD14 in CSF in a control group of 22 patients with neurologic complaints but no neurological deficit on clinical examination were 0.19 +/- 0.06 (mean +/- SD) mg/l. The CSF/blood ratios of sCD14 was 49 +/- 16 x 10(-3), while those of albumin were 4.4 +/- 1.4 x 10(-3). These extremely high CSF/blood ratios of the sCD14 molecule compared to albumin indicate a local cerebral production. No significant changes in CSF sCD14 levels were found in patients with non-inflammatory neurological diseases (NID). In contrast, CSF sCD14 levels were markedly elevated during acute meningitis, but there was no direct correlation between sCD14 and monocyte count in the CSF. Thus, sCD14 could not originate in the CSF compartment from monocytes alone. The highest values for sCD14 were found in CSF during infections with various pathogens such as Staphylococcus aureus or Listeria monocytogenes. While sCD14 serum levels dramatically increased during acute bacterial meningitis, sCD14 ratios did not correlate with albumin ratios during the course of disease. Therefore, increased CSF sCD14 may originate from cerebral production by activated or infiltrated macrophages rather than passive diffusion from the blood, while elevated sCD14 serum levels resulted from enhanced local production. Increased CSF and serum sCD14 values were also observed in meningitis caused by viral infection. As in bacterial meningitis, sCD14 in CSF specimens did not correlate with the function of the blood/CSF barrier. Repeated lumbar punctures revealed a normalization of CSF sCD14 levels during clinical recovery. These results provide the first evidence for local production of sCD14 within the CNS. Our findings further indicate that sCD14 in CSF is a reliable marker for activation of macrophages within the CNS during inflammatory processes.

Flow cytometry of cerebrospinal fluid (CSF) lymphocytes: alterations of blood/CSF ratios of lymphocyte subsets in inflammation disorders of human central nervous system (CNS)

Flow cytometry was adapted to measure lymphocytes in human cerebrospinal fluid (CSF). The method was sufficiently precise, reproducible and accurate despite low cell counts. In lumbar CSF of controls with 500 to 3500 (10(3)/l) leukocytes, lymphocyte counts correlated with those in corresponding venous blood: blood/CSF ratios of approximately 2000 : 1 were found for total T cells (CD3+) and CD3+ HLA-DR-, CD3+4+, CD3+8+ subsets, ratios were increased for the lymphocyte subsets CD3+ HLA-DR+ < or = CD3+16+56+ < CD16+56+3- < CD8+3- << CD19+; CD8+4+ ratio was half of CD3+ ratio. Data indicate selective barriers (blood-brain and blood-CSF barriers) to blood lymphocyte subsets which favor the transfer of T subsets. Correlation of the subset ratios to the CD3+ ratio indicates distinct barrier properties which changed differently with acute and subacute inflammations and neuroimmunological diseases of central nervous system (CNS) in lumbar or ventricular CSF, but not with simple protein barrier disturbance. HLA DR+ T ratios were higher than HLA DR- T ratios only with controls and some neuroimmunological diseases. Lymphocyte barrier characteristics were related to protein leakage situated at the same barriers, indicating for the lymphocyte subsets selective transfer routes in control subjects and non-selective routes in patients with CNS inflammation where altered ratios revealed a mixture of both routes.

Prospective study of neurological responses to treatment with macrophage-targeted glucocerebrosidase in patients with type 3 Gaucher's disease

We prospectively evaluated the clinical and biochemical responses to enzyme-replacement therapy (ERT) with macrophage-targeted glucocerebrosidase (Ceredase) infusions in 5 patients (age, 3.5-8.5 years) with type 3 Gaucher's disease. The patients were followed for up to 5 years. Enzyme dosage ranged from 120 to 480 U/kg of body weight/month. Systemic manifestations of the disease regressed in all patients. Neurological deficits remained stable in 3 patients and slightly improved in 1. One patient developed myoclonic encephalopathy. Cognitive deterioration occurred in 1 patient and electroencephalographic deterioration in 2. Sequential cerebrospinal fluid (CSF) samples were obtained during the first 3 years of treatment in 3 patients and were analyzed for biochemical markers of disease burden. Glucocerebroside and psychosine levels were not elevated in these specimens, whereas chitotriosidase and quinolinic acid were elevated in 2 patients. Progressive decrease in the CSF levels of these latter macrophage markers during 3 years of treatment implies a decreased number of Gaucher cells in the cerebral perivascular space. Similar changes were not observed in the patient who had a poor neurological outcome. In conclusion, ERT reverses systemic manifestations of type 3 Gaucher's disease and appears to reduce the burden of Gaucher cells in the brain-CSF compartment in some patients.

Intracarotid infusion of RMP-7, a bradykinin analog: a method for selective drug delivery to brain tumors

The bradykinin analog, RMP-7, was investigated for its ability to selectively increase uptake of molecular tracers in RG2 glial tumors. When infused in low doses (0.1 microgram/kg/min) through the intracarotid artery ipsilateral to RG2 gliomas in rats, RMP-7 significantly increased the permeability of tumor capillaries to methotrexate and to four other tracers of varying molecular weights, compared to intracarotid infusion of vehicle alone. Tracers used to examine permeability included radiolabeled alpha-aminoisobutyric acid (M(r) 103 D), sucrose (M(r) 342 D), methotrexate (M(r) 454.5 D), inulin (M(r) 5000 D), and dextran (M(r) 70,000 D). Permeability was expressed as the unidirectional transfer constant, Ki (microliters/gm/min). The permeability (Ki) of tumors in the RMP-7 group compared to the vehicle control group was as follows: alpha-aminoisobutyric acid, 35.3 +/- 9.11 versus 12.7 +/- 4.56 (p < 0.001); sucrose, 16.5 +/- 3.83 versus 9.28 +/- 3.12 (p < 0.05); methotrexate, 26.3 +/- 10.3 versus 8.98 +/- 6.78 (p < 0.005); inulin, 13.5 +/- 3.23 versus 6.55 +/- 4.32 (p < 0.005); dextran, 15.2 +/- 3.42 versus 1.47 +/- 1.24 (p < 0.001). The permeability of RG2 gliomas to high-molecular-weight dextran (70,000 D) was 10.3-fold higher in the RMP-7 group than in the vehicle control group. Intracarotid infusion of RMP-7 did not significantly increase the blood volume in tumor or brain tissue. The permeability of normal brain capillaries was unaffected by intracarotid infusion of 0.1 microgram/kg/min RMP-7 relative to that achieved in tumor. These data support the idea that intracarotid infusion of RMP-7 will be a useful technique for selective delivery of antitumor compounds to brain tumors.

Alloalbumin in cerebrospinal fluid: report of a case and remarks on physiopathology

Alloalbumin Tagliacozzo (313 Lys------Asn) was detected in the cerebrospinal fluid of a 27-yr-old woman. We studied this rare finding by means of high-resolution electrophoresis, isoelectric focusing, and immunofixation. We herein discuss the importance of molecular mass versus superficial electrical charge in the transfer of plasma proteins through the blood-brain barrier.

Release from live choroid plexus of apical fragments and electrophoretic characterization of their synthetic products

Protein synthesis and secretion by the choroid plexus (CP) has been implicated as a major source of certain proteins in cerebrospinal fluid (CSF), such as transthyretin. The suggestion that proteins are elaborated from CP through apocrine secretion has been borne out by the presence of newly labeled proteins in apical protrusions from CP (Agnew et al.: Cell and Tissue Research 208:261-281, 1980a). When the protrusions (aposomes) separate from the cells, they continue to incorporate labeled amino acids (Gudeman et al.: Tissue and Cell 19:101-109, 1987). In the present work the formation of aposomes in live CP explants indicated that these spheroids were not the result of fixation. Aposomes were also identified within rat CSF by immunohistochemistry with monoclonal directed against aposomes as well as with anti-transthyretin serum. The protein product of aposomes was characterized by 2-dimensional SDS-PAGE and compared to the protein products of whole CP tissue. Paradoxically, transthyretin, a heavily labeled protein in the tissue, was virtually undetected in the aposome synthetic profile. However, four other proteins were expressed in relatively equivalent amounts by the aposomes. The presence of mRNA in aposomes was detected with a poly dT probe, and the presence of actin was revealed by phalloidin staining of aposomes. These studies provide a more comprehensive definition of aposomes, but the functions of their secreted proteins remains to be determined.

Protein secretion by choroid plexus: isolated apical fragments synthesize protein in vitro

Protein synthesis was studied in the isolated rat choroid plexus. When the choroid plexus was studied by transmission electron microscopy, membrane-bound structures were often observed in the ventricular space. These structures appear to bud from the apical surface of the epithelial cells. In the present study, we attempted to isolate these membrane-bound cellular fragments from the choroid plexus and to determine their ability to synthesize proteins. The apical fragments (aposomes) were isolated from the choroid plexus by allowing tissue explants to incubate in media (37 degrees C) for 1 h. The tissue was removed and the media, now containing aposomes, was incubated with [S35]methionine (100 microCi). The media was collected and analysed by SDS-PAGE followed by fluorography. Parallel [S35]methionine incubations were done with whole tissue explants. The SDS-PAGE protein derived from the aposomes was similar to the profile derived from the tissue. In addition, proteins detected in CSF had relative molecular weights comparable to the products synthesized by aposomes. These observations suggest that aposomes provide an additional route of entry for proteins into CSF.

Correlation between protein data in normal lumbar CSF and morphological findings of choroid plexus epithelium: a biochemical corroboration of barrier transport via tight junction pores

Specific "reference areas" were derived from relationships between the proteins prealbumin, albumin, alpha 1-acid glycoprotein, alpha 2-macroglobulin, total transferrin, IgG, IgA, IgM, and the corresponding total protein in normal lumbar CSF samples. The procedure for calculating the boundary lines of these reference areas was carried out on the basis of double standard deviations in subgroups with total protein differences of 50 ml/l within the whole range of 150-400 ml/l CSF. The resulting biochemical data, hydrodynamic radii of the individual proteins investigated, and van Deurs' and Koehler's morphological findings on the existence of pores in the barrier-forming tight junctions of the choroid plexus epithelium could be surprisingly well correlated with one another, although these morphological findings were obtained in choroid plexus of the rat brain. The correlation allowed the conclusion that proteins undergo ultrafiltration via a pattern of tight junction pores with various diameters. However, the molecular mechanism seems to include an additional facilitating component.

Blood-cerebrospinal fluid barrier permeability to serum IgG subfractions and measurement of intrathecal IgG synthesis

CSF/serum gradients of IgG subfractions separated by isoelectric focusing (IF) have been measured by high resolving laser densitometry. In patients with normal blood-CSF barrier permeability (N.25) and with barrier damage due to acute idiopathic polyneuropathy (N.15) and to medullary compression (N.17), the CSF/serum gradients of IgG subfractions were negatively correlated with their pI. This electrostatic selectivity appeared to be reverted in barrier damage due to acute meningoencephalitis (N.15). In a series of multiple sclerosis patients (N.31), the CSF/serum gradients of IgG subfractions lacking CSF oligoclonal bands have been used to assess the overall barrier permeability to serum IgG. All intra-BCB synthesized IgG subfractions could be measured by densitometry, whereas with other quantitative formulae, 23-26% of the results were false negatives; the total intrathecal IgG amount ranged from 0.01 to 11 mg/dl. The most frequent and prominent fractions appeared to be cathodic. Electrostatic and steric barrier selectivity must be taken into account when the amount of intrathecal IgG synthesis has to be measured.

Basal infolding density in the normal pigmented rat

A variation in retinal pigment epithelial (RPE) basal infolding (BI) density in normal rats was observed and quantified. Serial electron micrographs of the midequatorial region of all quadrants from both eyes of litter-mate pigmented rats, 58 days old, were prepared. The lengths of BI and Bruch's membrane (BM) were determined by tracing enlarged micrographs to a Zeiss MOP-3 analyser. BI density per unit length of BM was assessed over the choriocapillary (CC) lumen, nucleated cytoplasma and intercapillary septum (ICS), and expressed as the dimensionless ratio BI/BM. Fenestrae were counted. The average BI/BM was 8.7; the BI/BM over the ICS, 6.1, was significantly lower than over the CC, 10.7 (P less than 0.001). BI/BM over the lumen and nucleated CC cytoplasm was the same. The number of fenestrae was not strongly associated with BI density (R2: 0.33). These data support the notion that the density of BI is related to diffusion within BM and is proportional to the distance from the CC lumen.

Compartmental analysis of cerebrospinal fluid transfer and absorption in simulated hydrocephalus

A mathematical model of the cerebrospinal fluid (CSF) flow dynamics found in hydrocephalic infants with myelomeningocele lesions was constructed using criteria obtained from analogous clinical situations where 125I-labelled and 131I-labelled ortho-iodobenzoyl-amino-acetic acid (hippuran) had been employed to measure CSF flow dynamics. The quantitative results from this study allowed clinical data to be assessed and the importance of various CSF transfer mechanisms to be discussed. Our mathematical model indicates that the majority of radiopharmaceutical passes from the cerebral reservoir (the ventricles) into the blood. Experimental evidence indicates that the principal mechanism responsible for this movement is the bulk flow of CSF between its sites of production in the choroid plexus and absorption by the arachnoid villi.

Acute changes in blood-CSF barrier permselectivity to serum proteins after intrathecal methotrexate and CNS irradiation

Ten children affected by acute lymphoblastic leukaemia without CNS involvement were treated with a CNS prophylaxis protocol. Intrathecal methotrexate and CNS irradiation (60Co) administered at different times both induced an increase in blood-CSF barrier permeability to serum proteins (albumin, IgG, alpha 2 macroglobulin). The relationship between permeability coefficients of proteins was analysed by theoretical porous or vesicular blood-CSF barrier models. The analysis indicated that both therapeutic procedures affect endothelial pinocytosis. An increase in radius of pinocytotic vesicles from 400 to 1500 A seemed the most relevant change. The damage of endothelial barrier permselectivity could be involved in acute and late delayed toxic effects of intrathecal methotrexate and of CNS irradiation.

Heterogeneous models for blood-cerebrospinal fluid barrier permeability to serum proteins in normal and abnormal cerebrospinal fluid/serum protein concentration gradients

Cerebrospinal fluid (CSF)/serum concentration gradients (Q) of individual proteins (albumin, IgG, alpha 2-macroglobulin) have been studied in controls and in patients in whom the lumbar CSF flow is altered (medullary compression) or the blood-CSF barrier (BCB) function impaired (acute idiopathic polyneuropathy and acute meningoencephalitis). The analysis of relationships among protein Q has been performed by total and multiple regressions and the actual BCB permeability to individual proteins has been interpreted according to the accepted theoretical porous or vesicular BCB models. The exponential Q-IgG vs. Q-albumin total regression, and the poor Q-alpha 2-macroglobulin vs. Q-albumin regression found in controls, together with the different multiple regressions among proteins and the high Q-IgG vs. Q-albumin partial regression coefficients found in medullary compression, acute idiopathic polyneuropathy and acute meningoencephalitis, indicated that different permeability mechanisms can be postulated. Heterogeneous, fairly independent permeability BCB mechanisms maintain the normal CSF/serum protein concentration gradient. Pinocytotic vesicles or pores of radius exceeding 1000-1500 A, probably located at the capillary endothelium, account for the main serum-derived CSF protein fraction(s) with large hydrodynamic radius (R). A more selective endothelial vesicular transport with a radius of 250 A transfers a negligible amount of protein from serum into CSF. Proteins with small R also enter the CSF through a set of selective pores of radius 120 A, probably at the level of the choroidal epithelium. Pinocytotic vesicles with a radius of 250 A and increased rate of formation induce the accumulation of proteins below an obstruction of lumbar CSF flow. An increased formation rate of vesicles with a radius of 450 A can explain the increased capillary permeability in nerve roots in acute idiopathic polyneuropathy. Loss of selectivity was the main feature of BCB in acute meningoencephalitis, and it seemed to be due to pores or vesicles with a radius larger than 1000-1500 A. The heterogeneity of BCB mechanisms must be taken into account when the intrathecal synthesis of a protein, also derived from serum (for example IgG), has to be measured.

Differential blood-brain barrier permeabilities to [14C]sucrose and [3H]inulin after osmotic opening in the rat

The blood-brain barrier (B-BB) in 3-month-old rats was opened unilaterally by infusing 1.8 m L(+)arabinose in water into the internal carotid artery through a catheter in the external carotid. Two poorly penetrating uncharged test radiotracers of differing molecular weight and size, [14C]sucrose (340 daltons, radius 5 A) and [3H]inulin (5500 daltons, radius 15 A), were simultaneously injected i.v. in untreated rats, or rats at 1, 30, or 50 min after infusion of hypertonic arabinose solution. Evans-blue solution was injected 5 min prior to osmotic treatment as a visual indicator of barrier integrity. In regions of uninfused control brains, the [14C]sucrose permeability-surface area (PA) product approximated 10(-5) s-1, whereas PA was not measurable for [3H]inulin. In arabinose-infused animals, PA products on the ipsilateral hemisphere for both [14C]sucrose and [3H]inulin were markedly elevated 6 min after infusion, but decreased by 35 and 55 min. In nearly all regions, statistically significant differences were not found between 6-min [14C]sucrose- and [3H]inulin-PA values (P greater than 0.05). However, at 35 and 55 min in most regions, the PA for [3H]inulin was significantly lower (P less than 0.05) than PA for [14C]sucrose. The results indicated that the B-BB closed more rapidly to larger than to smaller molecules after osmotic treatment and were consistent with a pore model for osmotic B-BB opening.

Use of high-performance liquid chromatography to study the caeruloplasmin-catalysed oxidation of biogenic amines. I. Single substrate systems

Reversed-phase ion-pair chromatography was used to monitor the oxidation of four biogenic amines (adrenaline, noradrenaline, dopamine and 5-hydroxytryptamine) by the copper-containing protein, caeruloplasmin. The methods are reproducible and sufficiently rapid to permit the handling of plasma sample batches. Kinetic parameters obtained using the method are in good agreement with those obtained by more traditional means of enzyme assay. Finally, the results support the view that more than one site on the enzyme, whether binding or oxidative, may be involved in the oxidation of biogenic amines, and the possible implications of this are briefly discussed.

Study of protein characteristics that influence entry into the cerebrospinal fluid of normal mice and mice with encephalitis

Entry of proteins into the cerebrospinal (CSF) from the blood is partially determined by the size of the protein. To determine whether other characteristics of proteins influence CSF entry, proteins or protein fragments were iodinated, inoculated intravenously, and serum and CSF were sampled at later times. The Fc fragment of immunoglobulin G (IgG) did not enter the CSF significantly better than the Fab fragment suggesting that choroidal Fc receptors are not of importance for selective immunoglobulin entry. To determine the role of protein charge on entry, bovine serum albumin [isoelectric point (pI) = 3.9] was chemically altered to provide an albumin with an average pI of 6 (A-6) and another with a pI of 8.5 (A-8). All albumins were of the same size on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A-8 entered the CSF approximately 10-fold better than the native albumin. A-6 was intermediate, entering approximately twofold better. At the time of increased CSF protein concentration during an acute viral encephalitis these differences were narrowed but not eliminated. It is concluded that charge is an important determinant of protein entry into the CSF.

Protein synthesis and transport by the rat choroid plexus and ependyma: an autoradiographic study

Light (LM-ARG) and electron microscope (EM-ARG) autoradiographs were preapred from immature rat choriod plexus and ependyma at 5, 10, 30, and 60 min and 16 h following intraperitoneal administration of [3H]labeled amino acid mixtures. Intracellular protein synthesis and transport were ascertained in lateral and fourth ventricle choroid plexus epithelium by quantitative EN-ARG at the several post-injection intervals. ARG were also prepared from choriod plexuses cultured for one day, pulse labeled for one hour and reincubated for various periods in nonradioactive media. Significant labeling of both attached and free apical protrusions (blebs) was observed in both choroid plexus and ependyma in vivo and in choroid plexus in vitro. This phenomenon was interpreted as a physiologically significant mechanism for protein trasport (apocrine secretion) by epithelia into the cerebrospinal fluid (CSF).

The tight junctions of rabbit choroid plexus and ciliary body epithelia. A comparative study using the double replica freeze-fracture technique

The spatial arrangement of tight junctions in choroid plexus and ciliary body rabbit epithelia has been determined by studying freeze-fracture complementary replicas. In the choroid plexus epithelium, the interruptions of the junctional P-face fibrils were measured to be 14% in their total length. In the ciliary body epithelium, where the fibrils were found to be more fragmented than in the choroid plexus, the P-face fibril interruption accounted for 12% of the total length of the zonulae occludentes sealing the non-pigmented cells and 30% in the focal linear tight junctions connecting the non-pigmented cells at their apices. In both epithelia, the interruptions of the ridges are precisely complemented by particles or short bars of similar length found in the E-face furrows. Consequently, it is possible to conclude that the junctional fibrils are continuous in these two epithelia. For the zonulae occludentes, this continuity appears to be inconsistent with the 'leaky' properties of these epithelia shown by some physiological investigations.