The soluble transcobalamin receptor (sCD320) is present in cerebrospinal fluid and correlates to dementia-related biomarkers tau proteins and amyloid-beta.

BACKGROUND: Cellular uptake of vitamin B12 (B12) demands binding of the vitamin to transcobalamin (TC) and recognition of TC-B12 (holoTC) by the receptor CD320. Recently, we identified a soluble form of CD320 (sCD320) in human plasma. Here we present data on the occurrence of this soluble receptor in cerebrospinal fluid (CSF) and show its correlations to dementia-related biomarkers tau proteins and amyloid-beta. METHODS: We collected 223 cerebrospinal fluid samples and corresponding plasma samples (n = 46). We measured CSF and plasma sCD320, holoTC and total TC employing in-house ELISA methods and CSF phospho-tau (181P) (p-tau), total tau (t-tau) and amyloid-beta 1-42 (Aß) (n = 177) employing commercial ELISA kits (Innogenetics Company). Size exclusion chromatography was performed on a Superdex 200 column. RESULTS: The median sCD320 concentration in CSF (14 pmol/L) is around five times lower than in plasma (72 pmol/L). No correlation was observed between plasma and CSF sCD320 levels (n = 46), while the behavior upon size exclusion chromatography was the same. In CSF, sCD320 correlates to holoTC and total TC (Spearman's correlation (Rs) = 0.325, 0.232 (n = 218, 217) respectively, p < 0.01). Interestingly, sCD320 correlates to p-tau and t-tau (Rs = 0.599, 0.569 (n = 173, 176) respectively, p < 0.001) and to Aß (Rs = 0.265, p < 0.001 (n = 177)). CONCLUSION: We document for the first time the occurrence of sCD320 in human CSF. We report that the concentration of sCD320 correlates to the dementia-related biomarkers p-tau, t-tau and Aß.

Biomarkers of folate and vitamin B12 are related in blood and cerebrospinal fluid.

BACKGROUND: B-vitamins (folate, B(12)) are important micronutrients for brain function and essential cofactors for homocysteine (HCY) metabolism. Increased HCY has been related to neurological and psychiatric disorders. We studied the role of the B-vitamins in HCY metabolism in the brain. METHODS: We studied blood and cerebrospinal fluid (CSF) samples from 72 patients who underwent lumbar puncture. We measured HCY, methylmalonic acid (MMA), and cystathionine by gas chromatography-mass spectrometry; S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) by liquid chromatography-tandem mass spectrometry; and the B-vitamins by HPLC or immunoassays. RESULTS: Concentrations were lower in CSF than serum or plasma for HCY (0.09 vs 9.4 micromol/L), SAH (13.2 vs 16.8 nmol/L), cystathionine (54 vs 329 nmol/L), and holotranscobalamin (16 vs 63 pmol/L), whereas concentrations in CSF were higher for MMA (359 vs 186 nmol/L) and SAM (270 vs 113 nmol/L; all P <0.05). CSF concentrations of HCY correlated significantly with CSF folate (r = -0.46), CSF SAH (r = 0.48), CSF-albumin (r = 0.31), and age (r = 0.32). Aging was also associated with lower concentrations of CSF-folate and higher CSF-SAH. The relationship between serum and CSF folate depended on serum folate: the correlation (r) of serum and CSF-folate was 0.69 at serum folate <15.7 nmol/L. CSF concentrations of MMA and holotranscobalamin were not significantly correlated. CONCLUSIONS: CSF and serum/plasma concentrations of vitamin biomarkers are significantly correlated. Older age is associated with higher CSF-HCY and CSF-SAH and lower CSF-folate. These metabolic alterations may be important indicators of low folate status, hyperhomocysteinemia, and neurodegenerative diseases.

Cobalamin binding proteins in the human fetus.

Cobalamin binding proteins are synthesized by the fetus from at least 16-19 gestational weeks. Cerebrospinal fluid contained transcobalamin with size and isoelectric points identical to adult transcobalamin. The unsaturated cobalamin-binding capacity in the fetal cerebrospinal fluid was comparable to adult levels, that is 0.01-0.04 nmol/l, median 0.03 nmol/l, n = 4. The unsaturated cobalamin-binding capacity in serum was low compared to adult values (0.02-0.04 nmol/l, median 0.03 nmol/l, n = 4). The unsaturated cobalamin-binding capacity in at term umbilical cord serum was alike for arterial and venous blood. The values obtained was 0.14-1.03 nmol/l, median 0.66 nmol/l, n = 22, which was two thirds of the corresponding values in maternal serum: In the amniotic fluid haptocorrin, intrinsic factor and transcobalamin were identical with the adult binders regarding the size and the isoelectric point.

The interaction of human transcobalamin isopeptides in cerebrospinal fluid and plasma with cobalamin and the cellular acceptor.

By isoelectric focusing, transcobalamin from human cerebrospinal fluid was separated into the phenotypes X, M, MX, SX and MS. The corresponding plasma transcobalamins were of identical phenotypes. The unsaturated cobalamin-binding capacity in the cerebrospinal fluid was 0.12-0.54 nmol.1(-1), median 0.23 nmol.1(-1); no difference in binding capacity was found between the individual phenotypes. The isopeptides M, X and S bound cyano[57Co]cobalamin from pH 6 to 10. The apparent affinity constant was the same for all the isopeptides (0.4.10(12) l.mol-1, pH 7.4). The isopeptide-cobalamin complexes bound to acceptors on human placenta membranes with an apparent affinity constant of 11.10(9) l.mol-1, pH 7.4.

Isoelectric focusing of rabbit transcobalamin from serum and cerebrospinal fluid.

Isoelectric focusing in agarose gel separated rabbit transcobalamin into five to eight isopeptides with isoelectric point (pI) 5.4-6.8. Three different sets of patterns were observed in serum samples from 34 rabbits and in cerebrospinal fluid samples from 10 rabbits as a given pattern in serum corresponded to a given pattern in cerebrospinal fluid. Serum contained higher substance concentrations of acidic isopeptides than cerebrospinal fluid. No correlation was found between the isopeptide patterns and the unsaturated cobalamin-binding capacity. The unsaturated cobalamin-binding capacity of cerebrospinal fluid was high in relation to the protein concentration (0.5-1.3 nmol/l) compared to that of serum (6.6-22.8 nmol/l). The data suggest synthesis of transcobalamin into the cerebrospinal fluid.

Cobalamin binding proteins (haptocorrin and transcobalamin) in human cerebrospinal fluid.

The unsaturated cobalamin binding capacity of transcobalamin and haptocorrin was studied in cerebrospinal fluid (CSF) and plasma (P) from 37 reference individuals. These comprised 27 males and 10 females who underwent minor surgery in spinal anaesthesia. The 5th and 95th percentiles were as follows: P-Transcobalamin 300-870 pmol/l (median 550 pmol/l); CSF-Transcobalamin 90-540 pmol/l (median 194 pmol/l); P-Haptocorrin 75-290 pmol/l (median 159 pmol/l); CSF-Haptocorrin 10-41 pmol/l (median 21 pmol/l). No sex difference was found between the levels of haptocorrin or transcobalamin in plasma or cerebrospinal fluid. A positive correlation between P-Transcobalamin and CSF-Transcobalamin was found, whereas no correlation between P-Haptocorrin and CSF-Haptocorrin values was found. The plasma/CSF ratios of transcobalamin, haptocorrin, albumin and IgG indicated that the binders may be synthetized into the cerebrospinal fluid or are actively being transported into the cerebrospinal fluid.