A single-step solid phase radioimmunoassay for quantifying human carbonic anhydrase I and II in cerebrospinal fluid

Variations in the cerebrospinal fluid proteome following traumatic brain injury and subarachnoid hemorrhage

BACKGROUND

Proteomic analysis of cerebrospinal fluid (CSF) has shown great promise in identifying potential markers of injury in neurodegenerative diseases [1-13]. Here we compared CSF proteomes in healthy individuals, with patients diagnosed with traumatic brain injury (TBI) and subarachnoid hemorrhage (SAH) in order to characterize molecular biomarkers which might identify these different clinical states and describe different molecular mechanisms active in each disease state.

METHODS

Patients presenting to the Neurosurgery service at the Louisiana State University Hospital-Shreveport with an admitting diagnosis of TBI or SAH were prospectively enrolled. Patients undergoing CSF sampling for diagnostic procedures were also enrolled as controls. CSF aliquots were subjected to 2-dimensional gel electrophoresis (2D GE) and spot percentage densities analyzed. Increased or decreased spot expression (compared to controls) was defined in terms of in spot percentages, with spots showing consistent expression change across TBI or SAH specimens being followed up by Matrix-Assisted Laser Desorption/Ionization mass spectrometry (MALDI-MS). Polypeptide masses generated were matched to known standards using a search of the NCBI and/or GenPept databases for protein matches. Eight hundred fifteen separately identifiable polypeptide migration spots were identified on 2D GE gels. MALDI-MS successfully identified 13 of 22 selected 2D GE spots as recognizable polypeptides.

RESULTS

Statistically significant changes were noted in the expression of fibrinogen, carbonic anhydrase-I (CA-I), peroxiredoxin-2 (Prx-2), both α and β chains of hemoglobin, serotransferrin (Tf) and N-terminal haptoglobin (Hp) in TBI and SAH specimens, as compared to controls. The greatest mean fold change among all specimens was seen in CA-I and Hp at 30.7 and -25.7, respectively. TBI specimens trended toward greater mean increases in CA-I and Prx-2 and greater mean decreases in Hp and Tf.

CONCLUSIONS

Consistent CSF elevation of CA-I and Prx-2 with concurrent depletion of Hp and Tf may represent a useful combination of biomarkers for the prediction of severity and prognosis following brain injury.

The impact of blood contamination on the proteome of cerebrospinal fluid

Human cerebrospinal fluid (CSF) is in direct contact with the brain extracellular space. Beside the secretion of CSF by the choroid plexus the fluid also derives directly from the brain by the ependymal lining of the ventricular system and the glial membrane and from blood vessels in the arachnoid. Therefore, biochemical change in the brain may be reflected in the CSF. CSF is a potential source of protein molecular indices of central nervous system function and pathology. However, various amounts of blood contamination in CSF may arise during sample acquisition. The concentration of protein in the CSF is only 0.2 to 0.5% that of blood. Minor contamination of CSF with blood during collection of the fluid may dramatically alter the protein profile confounding the identification of potential biomarkers. We have analyzed CSF and CSF spiked with increasing amounts of whole blood using proteomic techniques. We detected at least four blood specific highly abundant proteins: hemoglobin, catalase, peroxiredoxin and carbonic anhydrase I. These proteins can be used as blood contamination markers for proteomic analysis of CSF. Proteins in blood contaminated CSF samples were less stable compared to neat CSF at 37 degrees C suggesting that blood borne protease may induce protein degradation in CSF during sample acquisition. This analysis was aimed at identification of proteins found primarily in CSF, those found primarily in blood and assessment of the impact of blood contamination on those proteins found in both fluids.

A competitive dual-label time-resolved immunofluorometric assay for simultaneous detection of carbonic anhydrase I and II in cerebrospinal fluid

Carbonic anhydrase (CA) is functionally an important enzyme in the central nervous system (CNS) where it is involved in the control of acid-base balance and regulation of the production of cerebrospinal fluid (CSF). Isoenzyme II (CAII) is the most widely distributed CA in the CNS being specifically present in CNS glial tissue and therefore it is expected to be leaked to CSF in degenerative CNS diseases. A competitive dual-labeled time-resolved immunofluorometric assay was developed for simultaneous quantification of human CAI (HCA I) and II (HCA II) in CSF. HCA I was measured to determine the blood contamination in the samples. This solid-phase immunoassay is based on competition between europium (Eu3+)- or samarium (Sm3+)-labeled antigen and the sample antigens for polyclonal rabbit antibodies which are attached to microtiter-plate wells precoated with sheep anti-rabbit IgG. The subsequent immunoassay, including the separation of free and bound HCA I and II, requires only one incubation step, after which an enhancement solution dissociates Sm3+ and Eu3+ ions from the labeled HCA I and II, respectively, into a solution where they form highly fluorescent chelates. Spectra of the fluorescent chelates in the microtitration strip wells were run on time-resolved fluorometers equipped with filters for Eu3+ (613 nm) and Sm3+ (643 nm), the fluorescence from each sample being inversely proportional to the concentration of antigens. The detection limit of the HCA II assay was 0.3 micrograms/l and that of the HCA I assay was 5.2 micrograms/l. The intra- and inter-assay imprecisions (C.V.s) were 8.0% and 8.8% for HCA I and 6.3% and 4.8% for HCA II, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The excretion of carbonic anhydrase isozymes CA I and CA II in the urine of apparently healthy subjects and in patients with kidney disease

Carbonic anhydrase isozymes CA I and CA II were assayed by a radio-immunosorbent technique in the plasma and urine of apparently healthy subjects and of patients with renal disease. The concentrations (mean +/- SD, n = 8) of CA I and CA II in the plasma of healthy subjects were 2.3 +/- 2.3 and 0.8 +/- 0.5 mg/l, respectively. The urinary excretion values were 3.8 +/- 2.0 and 3.5 +/- 1.9 micrograms/24 h, and the apparent renal clearances were 21 +/- 17 and 52 +/- 44 microliters/min, respectively, values that are similar to those of other low molecular weight proteins. CA I and CA II have mol. wt of 28,850 and 29,300, respectively, they are globular in shape and have a Stoke-Einstein radius of 25 A. They could, therefore, be expected to be filtered at the glomeruli and thereafter reabsorbed by the proximal tubules. CA II is also present in the cytoplasm of renal proximal and distal tubular cells. A study of the pattern of urinary excretion of CA I and CA II could permit detection of damage to renal tubular cells in two ways--either from defective reabsorption of filtered CA I and CA II by the proximal tubular cells, or from leakage of CA II from the proximal or distal tubules into the urine. Some patients with hypercalcuria and renal tubular acidosis showed increased excretion of these enzyme proteins and of beta 2-microglobulin (BMG) into the urine, but the prevalence was rather low (27%). Further studies of patients with more severely damaged kidneys are required.