Highly sensitive enzyme immunoassay for human brain aldolase C

New astroglial injury-defined biomarkers for neurotrauma assessment

Traumatic brain injury (TBI) is an expanding public health epidemic with pathophysiology that is difficult to diagnose and thus treat. TBI biomarkers should assess patients across severities and reveal pathophysiology, but currently, their kinetics and specificity are unclear. No single ideal TBI biomarker exists. We identified new candidates from a TBI CSF proteome by selecting trauma-released, astrocyte-enriched proteins including aldolase C (ALDOC), its 38kD breakdown product (BDP), brain lipid binding protein (BLBP), astrocytic phosphoprotein (PEA15), glutamine synthetase (GS) and new 18-25kD-GFAP-BDPs. Their levels increased over four orders of magnitude in severe TBI CSF. First post-injury week, ALDOC levels were markedly high and stable. Short-lived BLBP and PEA15 related to injury progression. ALDOC, BLBP and PEA15 appeared hyper-acutely and were similarly robust in severe and mild TBI blood; 25kD-GFAP-BDP appeared overnight after TBI and was rarely present after mild TBI. Using a human culture trauma model, we investigated biomarker kinetics. Wounded (mechanoporated) astrocytes released ALDOC, BLBP and PEA15 acutely. Delayed cell death corresponded with GFAP release and proteolysis into small GFAP-BDPs. Associating biomarkers with cellular injury stages produced astroglial injury-defined (AID) biomarkers that facilitate TBI assessment, as neurological deficits are rooted not only in death of CNS cells, but also in their functional compromise.

Aldolase C/Zebrin II is Released to the Extracellular Space after Stroke and Inhibits the Network Activity of Cortical Neurons

Cell death after stroke involves apoptotic, autophagocytic and necrotic mechanisms which may cause the release of cytosolic proteins to the extracellular space. Aldolase C (AldC) is the brain specific isoform of the glycolytic enzyme fructose-1,6-bisphosphate aldolase. According to its characteristic striped expression pattern in the adult cerebellum AldC is also termed zebrin II. Here, we demonstrate release of AldC into the cerebrospinal fluid (CSF) after stroke in vivo. Studies with cell cultures confirmed that AldC is released to the extracellular space after hypoxia. Moreover, addition of purified recombinant AldC to networks of cortical neurons plated on multielectrode arrays reversibly inhibited the spontaneous generation of action potentials at AldC concentrations which can be expected to occur after lesions of the human cerebral cortex. This mechanism could be relevant in the pathogenesis of the electrophysiological changes in the penumbra region after stroke.

Aldolase C in neuroendocrine tumors: an immunohistochemical study

The expression of cerebral type aldolase C was investigated immunohistochemically in six varieties of neuroendocrine (n = 57) and six types of non-endocrine tumor (n = 76) using the avidin-biotin complex method. Aldolase C expression in the neuroendocrine tumors was also compared with those of chromogranin and gamma enolase. Aldolase C was detected in all the islet cell (7/7) and carcinoid tumors (10/10), thyroid medullary carcinomas (7/7), and pheochromocytomas (10/10), as well as in the majority of neuronal tumors (8/10) and bronchial small cell carcinomas (10/13). Chromogranin immunoreactivity was restricted to the tumors with abundant neuroendocrine granules. Gamma enolase positivity was generally similar to that of aldolase C, but there were some differences. Amongst the bronchial small cell carcinomas, three tumors negative for gamma enolase were positive for aldolase C, while another three tumors were positive for gamma enolase only. However all the small cell carcinomas were positive for at least one of these two enzymes. Aldolase C was detected in 28 (37%) of the 76 non-endocrine tumors and tended to be expressed preferentially in the differentiated portions of these tumors. Although aldolase C was expressed in many bronchial squamous cell carcinomas, the immunoreactivity was localized mainly in keratinizing foci and the less differentiated parts of these tumors expressed the enzyme only occasionally. Thus aldolase C, in conjunction with other neuroendocrine-associated markers, may be of value in identifying tumors of neuroendocrine type.

Elevated levels of serum aldolase A in patients with renal cell carcinoma

To clarify whether serum aldolase A is a useful biomarker for renal cell carcinoma (RCC), we determined serum levels of the aldolase A isozyme by an enzyme immunoassay in patients suffering from RCC, other urological tumors, and benign urological diseases. Forty-six of 126 patients with RCC (37%) had elevated serum aldolase A. The positive rates were 23% in stage I, 40% in stage II, 63% in stage III, and 46% in stage IV. In 10 (83%) of 12 patients whose serum levels had been elevated preoperatively, these were reduced to within the normal range after nephrectomy. Four of 7 patients (57%) with progressive disease had elevated levels of aldolase A. In contrast, the positive rates were only 9.9% in 71 patients with other urological tumors and 5.8% in 52 cases of benign urological diseases. High concentrations of aldolase A isozyme in RCC tissues might be reflected in elevated serum levels. The present findings indicate that serum aldolase A is a useful biomarker for monitoring the clinical course of patients with RCC.

An immunochemical and immunohistochemical study of aldolase isozymes in renal cell carcinoma

To assess changes in aldolase isozyme patterns (A, B, and C) in renal cell carcinoma (RCC) tissues and to evaluate whether serum aldolase A might be a useful marker for RCC, quantitative analysis by enzyme immunoassay and immunohistochemical localization were performed. Concentrations of aldolase A in RCC (7300 +/- 6300 ng./mg. protein n = 26) were significantly higher than those of normal cortex (720 +/- 410 ng./mg. protein, n = 14, p less than 0.01); concentrations of aldolase C in RCC (48.0 +/- 8.0 ng./mg. protein) were also significantly higher than those of normal cortex (8.7 +/- 4.7 ng./mg. protein, p less than 0.01). On the other hand, concentrations of aldolase B in normal cortex were 18,100 +/- 10,100 ng./mg. protein (n = 14), whereas the values in RCC were only 130 +/- 270 ng./mg. protein, a significant lowering (p less than 0.01). Immunohistochemically, aldolases A and C were found localized in all RCC tissues (n = 10); aldolase B was faintly stained in only a few tumor cells of two cases (20%). Levels of serum aldolase A were elevated (greater than 300 ng./ml.) in 30 (75%) of 40 patients with RCC as compared to three (6.3%) of 48 individuals with urogenital benign diseases and in seven (21%) of 34 cases with non-RCC urogenital malignancies. Since it is generally accepted that RCC are derived from renal proximal tubules, these findings indicate that aldolase B, the predominant isozyme in the normal case, changes into aldolases A and C during carcinogenesis and that serum aldolase A could be a new useful biomarker for RCC.

Immunochemical and immunohistochemical studies on three aldolase isozymes in human lung cancer

The aldolase isozymes A, B, and C in tumor tissues (63) and sera (104) of patients with lung cancer were determined with an enzyme immunoassay system, compared with normal lung tissues (13), and the sera of normal healthy subjects (100). Tissue aldolase A and C concentrations were enhanced in 83% (52/63) and 51% (32/63) of patients with lung cancer, respectively, regardless of histologic type or stage (P less than 0.01). But aldolase B was not elevated in tissue levels. In the sera of patients with lung cancer, there were no significant elevations of the isozymes. Immunohistochemically aldolase A and C stained more intensely in the cytoplasm of lung cancer cells than those in normal tissues. These results indicate lung cancer cells contain enhanced tissue levels of aldolase A and C.

Sensitive enzyme immunoassay for human aldolase A

A sensitive sandwich-type enzyme immunoassay for the aldolase isozyme, A4, was developed using purified antibodies specific to the A subunit of aldolase. The antibodies were raised in sheep being immunized with purified aldolase A4 and then purified by immunoaffinity chromatography on a column of aldolase A4-coupled Sepharose. The assay system consisted of polystyrene balls with immobilized antibody F(ab')2 fragments and the same antibody F(ab')2 fragments labeled with beta-D-galactosidase from Escherichia coli. The assay was sensitive enough to detect 10 pg/tube of aldolase A4. The assay was specific to the A subunit of aldolase (aldolase A). It cross-reacted about 40% to aldolase A3C, 7% to A2C2 and 0.3% to AC3, but not cross-reacted with C4 nor B4. Coefficients of variation in intra- and inter-assay were less than 16%. Serum aldolase A levels were determined in healthy adults, which were about 200 ng/ml. The distribution and concentrations of immunoreactive aldolase A in various human tissues were also determined. High concentrations of aldolase A were found in skeletal muscle, heart muscle, cerebrum and lymphatic tissue.

Human brain-type glycogen phosphorylase: quantitative localization in human tissues determined with an immunoassay system

Glycogen phosphorylase (EC 2.4.1.1) from human brain tissue was purified to homogeneity. Antisera were developed in rabbits with purified phosphorylase as the immunogen. Antibodies were first affinity-purified with a column of brain phosphorylase-coupled Sepharose, and then the antibody fraction was adsorbed with a column of muscle phosphorylase-coupled Sepharose to remove antibodies reactive also with muscle phosphorylase. By using the specific antibodies, a sandwich-type immunoassay system for measurement of brain phosphorylase was prepared. The assay system consisted of polystyrene balls with immobilized antibrain phosphorylase F(ab')2 fragments and the same antibody Fab' fragments labeled with beta-D-galactosidase from Escherichia coli. The assay was sensitive and specific to the brain phosphorylase. The minimum detection limit of the assay was 0.1 ng/assay tube, and the cross-reactivity of the assay with muscle phosphorylase was less than 1%. Tissue concentrations of immunoreactive brain-type phosphorylase were estimated. The phosphorylase was present in the heart at as high a level as in the brain. The immunoreactivity for brain phosphorylase was distributed widely at a significant concentration in various peripheral tissues, such as the digestive tract, bladder, aorta, liver, and testis. Immunohistochemical localization of brain phosphorylase in the CNS revealed that the enzyme is present in most astrocytes and amyloid bodies, as well as in some neurons in the cerebral cortex and Golgi cells in the cerebellar cortex.

Sensitive enzyme immunoassay for human aldolase B

A highly sensitive enzyme immunoassay system for measurement of aldolase B subunit (aldolase B) was established. Antisera were raised in rabbits by injecting aldolase B4 purified from human liver, and specific antibodies to aldolase B were purified by the use of a column of aldolase B4-coupled Sepharose. The purified antibody IgG was digested with pepsin to obtain the F(ab)' fragments. The antibody F(ab)' fragments were immobilized noncovalently on polystyrene balls, and the same antibody Fab' fragments were labeled with beta-D-galactosidase from Escherichia coli. The sandwich-type assay system using these reagents was sensitive and specific to aldolase B, showing no cross-reactivity with aldolase-A or aldolase-C. The minimum detection limit of the assay was 3 pg aldolase B4/assay tube. The immunoreactive aldolase B was present at high levels in the liver and kidney, and considerably in the small intestine. It was detected in all the tissues examined. Immunohistochemically, aldolase B is localized in hepatocytes, proximal renal tubular cells and epithelial cells of small intestine. Serum levels of aldolase B in healthy subjects were ranged from 33 to 202 ng/ml.

Aldolase C is localized in neuroendocrine cells

To elucidate the localization of the subunit C of aldolase (aldolase C) in peripheral neuroendocrine cells, we made an immunohistochemical study with monospecific antibodies against human aldolase C. Aldolase C was found to be localized in various types of neuroendocrine cells; in the pituitary gland, thyroid, pancreas, adrenal gland, bronchus, and gastrointestinal tract.

A three-parameter Langmuir-type model for fitting standard curves of sandwich enzyme immunoassays with special attention to the alpha-fetoprotein assay

In a simplified approach to the reaction kinetics of enzyme-linked immunoassays, a Langmuir-type equation y = [ax/(b + x)] + c was derived. This model proved to be superior to logit-log and semilog models in the curve-fitting of standard curves. An assay for alpha-fetoprotein developed in our laboratory with a sensitivity of 2 g/liter and a between-day coefficient of variation of about 15% was used for comparison of the different models. The proposed model has the advantage that it is based on the law of mass action and that blank determinations can be included in the calculation of the curves without giving a disproportionate bias.