The influence of the choroid plexus on the concentration of prealbumin in CSF

Neural cell adhesion molecule (NCAM) and prealbumin in cerebrospinal fluid from depressed patients

The size of the soluble form of the human cerebrospinal fluid (CSF) neural cell adhesion molecule, NCAM-sol, was by gel permeation chromatography estimated to 160-250 kDa. Within the CSF the concentration of NCAM-sol was found about 15-25% increased in lumbar fluid and 25% increased in ventricular fluid, both compared to cisternal fluid. Whereas prealbumin was found evenly distributed in CSF, albumin was relatively enriched in lumbar fluid. The concentrations of NCAM-sol and prealbumin were measured in lumbar CSF from psychiatric patients. Prealbumin was increased 7.2% and NCAM-sol was decreased 15.1% in depressed patients. The changes were partially normalized during recovery from the depression. The findings can be explained by hypothesizing that endogenous depression is associated with an increased choroid plexus activity and CSF production.

The evolution of transthyretin synthesis in the choroid plexus

Choroid plexus has the highest concentration of transthyretin (TTR) mRNA in the body, 4.4 microg TTR mRNA/g wet weight tissue, compared with 0.39 microg in the liver. The proportion of TTR to total protein synthesis in choroid plexus is 12%. All newly synthesized TTR is secreted towards the ventricles. Net transfer of T4 occurs only towards the ventricle and depends on ongoing protein synthesis. Thyroxine-binding globulin (TBG), TTR and albumin form a "buffering" system for plasma [T4] because of their overlapping affinities and on/off rates for L-thyroxine (T4)-binding. The individual components of this network determining T4 distribution are functionally highly redundant. Absence of TBG (humans), or TTR (mice), or albumin (humans, rats) is not associated with hypothyroidism. Natural selection is based on small, inheritable alterations improving function. The study of these alterations can identify function. TTR genes were cloned and sequenced for a large number of vertebrate species. Systematic, stepwise changes during evolution occurred only in the N-terminal region, which became shorter and more hydrophilic. Simultaneously, a change in function occurred: TTR affinities for T4 are higher in mammals than in reptiles and birds. L-triiodothyronine (T3) affinities show the opposite trend. This favors site-specific regulation of thyroid hormones by tissue-specific deiodinases in the brain.

Structure and expression of the transthyretin gene in the choroid plexus: a model for the study of the mechanism of evolution

Thyroid hormones are key regulators of brain differentiation and function. They permeate strongly into lipid membranes. However, a substantial portion of thyroid hormone is retained in the intravascular/extracellular compartments by binding to plasma proteins. In the brain, transthyretin is the most important of these proteins. This transthyretin is synthesized in the epithelial cells of the choroid plexus and exclusively secreted towards the brain. A net movement of thyroid hormones from the blood to the brain ensues. During evolution, transthyretin synthesis in the choroid plexus and the beginnings of a neocortex first appeared at the stage of the stem reptiles. The affinity of transthyretin for thyroxine increased and that for triiodothyronine decreased during evolution. This could augment the importance of deiodination for regulation of metabolism and gene expression by thyroid hormones in the brain. Successive shifts of the splice site at the 5' end of exon 2 of transthyretin precursor mRNA in the 3' direction led to a shortening of the N-terminal sections and to an increase in hydrophilicity of the N-terminal regions of transthyretin. This shift can be explained by a sequence of single base mutations. It could be an example for a molecular mechanism of positive Darwinian evolution. The selection pressure, which led to the expression of the transthyretin gene in the choroid plexus during evolution, might have been the maintenance of thyroid hormone homeostasis in the extracellular compartment of the brain in the presence of the greatly increasing volume of the lipid phase.

Affinity capillary electrophoresis is a powerful tool to identify transthyretin binding drugs for potential therapeutic use in amyloidosis

In this work we used affinity capillary electrophoresis (ACE) to investigate the extent of interaction between a pool of drugs and wild-type transthyretin. After qualitative preliminary screening, attention was focused on the most promising molecules, flufenamic acid and flurbiprofen, which underwent a further stage of investigation, the determination of the binding constants, and, when possible, the assessment of the number of binding sites by ACE, frontal analysis (FA) capillary electrophoresis (CE) and parallel ultrafiltration (UF) experiments. Furthermore, our data demonstrate that FA CE is a suitable technique for identifying fibril ligands. This represents a novel CE application of pharmaceutical interest.

Cerebrospinal fluid soluble L-selectin (sCD62L) in meningoencephalitis

The leucocyte adhesion molecule L-selectin (CD62L) is rapidly cleaved off proteolytically after cell activation, generating soluble L-selectin (sCD62L) molecules. sCD62L concentrations were determined in 185 cerebrospinal fluid (CSF) samples obtained from children aged 1 month to 17 years. In 36 CSF samples of children with meningoencephalitis, sCD62L was significantly higher (median 209 fmol/ml) than in samples of children with other febrile diseases (n = 67, median 50 fmol/ml) or non-febrile disorders (n = 82, median 44 fmol/ml). There was a positive correlation between CSF protein and CSF sCD62L (rS = 0.68), suggesting that a disturbed blood-brain barrier contributes to raised sCD62L concentrations in the CSF. However, the CSF sCD62L/protein ratio of children with meningoencephalitis was significantly higher than in children with other febrile diseases or non-febrile disorders, indicating that sCD62L concentrations in children with meningoencephalitis were higher than expected from plasma leakage alone. It is concluded that both an impaired blood-brain barrier and the generation of sCD62L by infiltrating leucocytes contribute to raised CSF sCD62L concentrations in children with meningoencephalitis.

The crystal structure of transthyretin from chicken

The crystal structure of chicken transthyretin has been solved at 290-pm resolution by molecular-replacement techniques. Transthyretin is the protein component of the amyloid fibrils found in patients suffering from either familial amyloidotic polyneuropathy or senile systemic amyloidosis. Familial amyloidotic polyneuropathy is an autosomal dominant hereditary type of amyloidosis which involves transthyretin with either one or two amino acid substitutions. The three-dimensional structure of chicken transthyretin was determined in order to compare a non-amyloidogenic, species-variant transthyretin with wild-type and mutant transthyretin molecules. Of the 31 chicken-to-human residue differences, 9 occur at positions which in human transthyretin give rise to amyloidogenic variants although none corresponds to the appropriate side-chain substitutions. The model of chicken transthyretin has been refined to an R-factor of 19.9%. The overall fold of the protein is that of an all-beta protein. Compared with wild-type human transthyretin the avian transthyretin shows quite large differences in the region known to be involved in binding to retinol-binding protein, it has a much shorter helical component than the human protein and some of the monomer-monomer interactions are different.

Analysis of cerebrospinal fluid proteins by electrophoresis

The cerebrospinal fluid (CSF) is a specific ultrafiltrate of plasma, which surrounds the brain and spinal cord. The study of its proteins and their alteration may yield useful information on several neurological diseases. By using various electrophoretic separation techniques, several CSF proteins have been identified derived from plasma or from brain. Different one-dimensional methods, such as agarose gel electrophoresis and isoelectric focusing, are of similar value in identifying the non-specific oligoclonal bands, which are mainly helpful in the diagnosis of multiple sclerosis and other inflammatory diseases. Isoelectric focusing has a greater resolution than other one-dimensional methods, and it yields additional data about disease-associated proteins occurring in Alzheimer's disease, Huntington's chorea and amyotrophic lateral sclerosis. Silver-stained two-dimensional gels provide more information about the complex protein composition of CSF, particularly about proteins produced in the brain, such as apolipoprotein E and neuron-specific enolase. For the detection of oligoclonal antibodies, the investigation of protein changes revealed by Parkinson's disease, schizophrenia and Creutzfeldt-Jakob disease, and the analysis of CSF immune complexes, two-dimensional electrophoresis has a greater sensitivity.

Alterations in prealbumin concentration after adrenal autotransplantation for Parkinson's disease

The cerebrospinal fluid of eight patients with Parkinson's disease who underwent adrenal medullary autotransplantation was analyzed using SDS-polyacrylamide gel electrophoresis. A protein, subsequently identified as prealbumin, was noted to change in concentration over the intraoperative to 18-month postoperative time course. The qualitative changes observed on visual inspection were confirmed and quantified using laser densitometry. The concentration of prealbumin increased by an average of 90% when the intraoperative and 12-month samples were compared. This increase persisted at 18 months. The ratio of prealbumin to albumin also increased from intraoperative to 12 months by an average of 56%. This suggests that the increases in PA are the result of choroid plexus activation rather than a nonspecific breakdown of the blood-brain barrier. Given the association of prealbumin with other nervous system diseases, as well as its known ability to bind multiple substances, these findings may have important implications. Alterations in prealbumin may be responsible for the improvement seen in some patients who receive adrenal medullary autotransplants. Alternatively, prealbumin may be implicated in the pathophysiology of Parkinson's disease.

The contribution from the choroid plexus and the periventricular CNS to amino acids and proteins in the human CSF

During neurosurgery the freshly secreted extracellular fluid (ECF) from the choroid plexus was sampled with small pieces of application paper in three patients with intractable epilepsy. The samples were analyzed for free amino acids and for soluble proteins. The results were compared with corresponding data on extracellular fluid from the brain surface obtained with dialysis-perfusion as well as with the cerebrospinal fluid (CSF) acquired by lumbar punction. The dialysis data were calibrated against the paper results. The choroid plexus secretion had a high concentration of transthyretin as well as of an unidentified protein with an isoelectric point of 7.4. The cortical ECF exhibited high concentrations of tau-globulin and gamma-trace protein. Among the amino acids, glutamine had lower concentration in the choroid plexus secretion and higher concentrations in the ECF of the brain compared to the CSF. The amino acid derivative ethanolamine exhibited a similar pattern. This was interpreted to demonstrate that these compounds enter the CSF from the brain tissue. In contrast, alanine, serine, and taurine had a lower concentration in the CSF than in the plexus secretion which suggests that they are removed from the CSF by brain tissue.

Reduced prealbumin (transthyretin) in CSF of severely demented patients with Alzheimer's disease

Prealbumin (transthyretin) quantified in CSF was negatively correlated with degree of dementia in 24 patients with dementia of Alzheimer type (DAT). There was neither a significant correlation between prealbumin in serum and degree of dementia nor between prealbumin in CSF and number of T lymphocytes in serum. There was no such relationship in 7 patients with multi-infarct dementia. Prealbumin was also quantified in 4 non-demented control groups, one consisting of 14 age- and sex-matched neurological patients, 17 with MS, 6 with ALS and 10 patients who had had a subarachnoid hemorrhage. Prealbumin was significantly lower in the last group. The study suggests that there may be a relationship between prealbumin levels in cerebrospinal fluid and degree of dementia. It is suggested that this may be caused by affection of the choroid plexus.

Variant transthyretin in cerebrospinal fluid in familial amyloidotic polyneuropathy

Structurally abnormal transthyretin is a precursor protein of amyloid fibrils in type I familial amyloidotic polyneuropathy (FAP). This variant transthyretin has an amino acid substitution of methionine for valine at position 30. The purpose of this study was to clarify whether this variant transthyretin also circulates in the cerebrospinal fluid (CSF) of patients with type I FAP. CSF transthyretin of the patients was purified and its primary structure determined. Sequence determination indicated that transthyretin consisted of a mixture of normal and variant transthyretin. Variant transthyretin was present in the CSF of all 5 Japanese FAP patients studied. The CSF concentration of variant transthyretin was high (0.72 +/- 0.15 mg/dl, mean +/- S.D.), suggesting that variant transthyretin is synthesized in the choroid plexus. Variant transthyretin was not present in any of 20 controls. The CSF concentration of total transthyretin in FAP patients was 1.74 +/- 0.42 mg/dl, which was not significantly different from controls.

Localization of immunoreactive transthyretin (prealbumin) and of transthyretin mRNA in fetal and adult rat brain

We used a combination of immunohistochemical and molecular-biological techniques to investigate the localization of transthyretin (TTR) in the brains of adult and fetal rats. The immunohistochemical studies employed antibodies purified by immunosorbent affinity chromatography, permitting the specific staining and localization of TTR using the unlabeled peroxidase-antiperoxidase method. TTR mRNA levels were measured by Northern-blot analysis of poly (A+) RNA, followed by hybridization to 32P-labeled TTR cDNA; TTR mRNA was localized in brain tissue sections by in situ hybridization. Immunoreactive TTR was found to be specifically localized in the choroid plexus epithelial cells of adult rat brain. High levels of TTR mRNA were found in poly (A+) RNA samples obtained from the choroid plexus. In addition, the specific localization of TTR mRNA in the epithelial cells of the choroid plexus was demonstrated by in situ hybridization. Neither immunoreactive TTR nor TTR mRNA were found in other regions of adult rat brains. The levels of TTR mRNA in the choroid plexus were at least 30 times higher than those observed in the adult liver. Immunoreactive TTR was observed in the brains of fetal rats on as early as the 11th day of gestation. This immunoreactive TTR was localized in the tela choroidea, the developmental forerunner of the choroid plexus. Immunoreactive TTR was also observed in the fetal choroid plexus as it began to form (14th day of gestation) as well as in the more completely developed choroid plexus (18th day of gestation).(ABSTRACT TRUNCATED AT 250 WORDS)

High prealbumin and transferrin mRNA levels in the choroid plexus of rat brain

Expression of plasma protein genes in various parts of the rat brain was studied by hybridizing radioactive cDNA to RNA in cytoplasmic extracts. No mRNA could be detected in brain for the beta subunit of fibrinogen, major acute phase alpha 1-protein, alpha 1-acid glycoprotein and albumin. However, per g tissue, the choroid plexus contained at least 100 times larger amounts of prealbumin mRNA than the liver and about the same amount of transferrin mRNA as liver. No prealbumin mRNA was found in other areas of the brain. The results obtained suggest very active synthesis of prealbumin in choroid plexus, which would be an important link in the transport of thyroid hormones from the blood to the brain via the cerebrospinal fluid.