Two-site column enzyme immunoassay for neuron-specific enolase (NSE) in human serum using monoclonal antibodies

Neuron-Specific Enolase as a Biomarker: Biochemical and Clinical Aspects

Neuron-specific enolase (NSE) is known to be a cell specific isoenzyme of the glycolytic enzyme enolase. In vertebrate organisms three isozymes of enolase, expressed by different genes, are present: enolase α is ubiquitous; enolase β is muscle-specific and enolase γ is neuron-specific. The expression of NSE, which occurs as γγ- and αγ-dimer, is a late event in neural differentiation, thus making it a useful index of neural maturation.NSE is a highly specific marker for neurons and peripheral neuroendocrine cells. As a result of the findings of NSE in specific tissues under normal conditions, increased body fluids levels of NSE may occur with malignant proliferation and thus can be of value in diagnosis, staging and treatment of related neuroendocrine tumours (NETs).NSE is currently the most reliable tumour marker in diagnosis, prognosis and follow-up of small cell lung cancer (SCLC), even though increased levels of NSE have been reported also in non-small cell lung cancer (NSCLC). The level of NSE correlates with tumour burden, number of metastatic sites and response to treatment.NSE can be also useful at diagnosis of NETs and gastroenteropancreatic (GEP)-NETs.Raised serum levels of NSE have been found in all stages of neuroblastoma, although the incidence of increased concentration is greater in widespread and metastatic disease. Moreover, NSE determination in cord blood offers an early postnatal possibility of confirming the diagnosis of neuroblastoma in newborns.NSE has been demonstrated to provide quantitative measures of brain damage and/or to improve the diagnosis and the outcome evaluation in ischaemic stroke, intracerebral hemorrhage, seizures, comatose patients after cardiopulmonary resuscitation for cardiac arrest and traumatic brain injury.Increased NSE serum levels have also been found associated with melanoma, seminoma, renal cell carcinoma, Merkel cell tumour, carcinoid tumours, dysgerminomas and immature teratomas, malignant phaechromocytoma, Guillain-Barré syndrome and Creutzfeldt-Jakob disease.

Serum time course of two brain-specific proteins, alpha(1) brain globulin and neuron-specific enolase, in tick-born encephalitis and Lyme disease

METHODS

Time courses of the serum concentrations of two brain-specific proteins (BSP), alpha(1) brain globulin (alpha(1)BG, an astroglial marker) and neuron-specific enolase (NSE), were studied in patients with severe tick-born encephalitis (TBE) and Lyme disease (LD; neuroborreliosis). The concentrations were determined on the second day of the acute phase and then on the 7th, 12th, 18th, and 23rd days. Apparent rate constants for the elimination of the BSP from blood (k(e)) were calculated with the non-linear regression.

RESULTS

In patients with TBE, the highest serum concentrations of alpha(1)BG and NSE, observed on the second day, were followed by their monotonic decrease to the normal levels reached by the 23rd day. The mean k(e) values for alpha(1)BG and NSE were found to be significantly different (0.086+/-0.003 vs. 0.057+/-0.006 day(-1), respectively; p<0.05). Higher serum levels of both BSP were observed in the more severe clinical cases and in the cases with unfavorable outcomes. Similar profiles were also observed for the serum alpha(1)BG and NSE in LD.

CONCLUSIONS

These results suggest that, in the patients examined, the blood-brain barrier was partially impaired; the quantitative parameters of the serum BSP time courses can be indicative of the extents of the neuronal and/or glial lesions.

A simple enzyme-linked immunosorbent assay (ELISA) for the neuron-specific gamma isozyme of human enolase (NSE) using monoclonal antibodies raised against synthetic peptides corresponding to isozyme sequence differences

Monoclonal antibodies specific for the gamma isozyme of human enolase (known as neuron-specific enolase or NSE) have been raised against synthetic peptides after coupling to carrier protein: the selected peptides were those corresponding to regions of amino acid sequence difference between the alpha and gamma subunits of these closely similar isozymes. This technique gave monoclonal antibodies of high specificity and affinity. Two monoclonal antibodies raised against different peptides were used to develop a double-antibody sandwich enzyme-linked immunosorbent assay (ELISA), using one as the solid-phase antibody and the other conjugated to horseradish peroxidase to detect the bound NSE. This assay provides a simple and routine method of detecting NSE in serum samples from patients with small-cell carcinoma of the lung and related tumours.

Clinical biochemistry of neuron specific enolase

The soluble brain protein 14-3-2 first described by Moore and McGregor in 1965 is now known to be a cell specific isoenzyme of the glycolytic enzyme enolase (EC 4.2.1.11), designated neuron specific enolase (NSE). It is not only a marker for all types of neurons, but also for all neuroendocrine or paraneuronal cells. The appearance of NSE is a late event in neural differentiation, thus making NSE a useful index of neural maturation. The demonstration that tumors of the nervous system and of neuroendocrine origin contain NSE has promoted the study of NSE as a possible tumor marker. Immunocytochemistry has been used to identify NSE in cytologic preparations from several types of tumors, offering useful indications for differential diagnosis. NSE levels in serum from tumor patients are not useful in the diagnosis of early stage disease. However, serum NSE levels have been shown to be helpful in the identification of advanced small cell lung cancer, neuroblastoma and several other neoplasms. The main use of serum NSE is the monitoring of chemotherapy and the detection of a relapse in these cases.