Isocratic reverse-phase HPLC separation and RIA used in the analysis of neuropeptides in brain tissue

Analysis of substance P in rat brain by means of immunoaffinity capture and matrix-assisted laser desorption/ionization time-of-flight mass-spectrometry

Interest in the analysis of low abundance neuropeptides particularly using matrix-assisted laser desorption/ionization time-of-flight mass-spectrometry (MALDI-TOF-MS) is increasing because these neuropeptides are essential to the mechanism of transportation and the metabolism. This article describes an immunoprecipitation procedure that is suitable for MALDI-MS analysis of substance P (SP), a neuropeptide, in rat brain tissues. Substance P was precipitated from brain tissue extracts by immunoprecipitation with antibodies directed against SP, and are analyzed by MALDI-TOF-MS. Mass spectrometric analysis showed a singly charged [M+H]+ ion peak that corresponded to the SP molecular mass and was observed with a detection error of 1.6%. The average mass errors between the observed and theoretical molecular mass were within the 0.11 Da range. Capillary zone electrophoresis analysis was subsequently performed, and the effects of the different separation parameters were examined. Beginning with milligram quantities of brain tissue, picomole quantities of SP could be detected using this method.

Techniques for neuropeptide determination

Because immunoassay responds to epitopes, and many molecules share the same peptide epitope, it is very difficult to obtain an accurate understanding of peptides, their creation and hydrolysis, in biological systems. Separate-and-detect approaches have merit in that the many active peptides and inactive fragments of a particular system can be separately determined. This review discusses the separation, by chromatography and capillary electrophoresis, and detection, by absorbance, fluorescence, electrochemistry, and immunoassay techniques. When separation pre-concentration is accompanied by laser-induced fluorescence or biuret-based electrochemical detection, nM-pM detection limits are obtained.

An immunoassay for Leu-enkephalin based on a C-terminal aequorin-peptide fusion

Recently we demonstrated that the fusion of an octapeptide to the C-terminus of a cysteine-free mutant of aequorin showed no inhibitory effect on the luminescence activity of the photoprotein. This observation is of particular importance when the use of aequorin as a label in the development of immunoassays for peptides whose activity lies in their C-terminal region or the epitope for antibody recognition is at their C-terminus is desired. In the case of opioid peptides, antibodies are directed toward their C-terminus as they differ from each other at this terminus. The goal of this study was to develop an immunoassay for Leu-enkephalin, a mammalian opioid peptide, using a C-terminal aequorin-peptide fusion protein. For that, the N-terminus of Leu-enkephalin was genetically fused to the C-terminus of a cysteine-free mutant of aequorin. It was observed that the C-terminal conjugated aequorin maintained its luminescence activity. An immunoassay for Leu-enkephalin was then developed using the aequorin-Leu-enkephalin fusion protein as a labeled analyte in a competitive as well as in a sequential binding mode. It was demonstrated that aequorin can be used as a label in peptide assays in which it is critical that the peptide's C-terminus be free for activity and/or for antibody recognition.

A highly sensitive and selective radioimmunoassay for the measurement of neurotensin

A highly selective and sensitive radioimmunoassay (RIA) for the detection of endogenous neurotensin (NT) has been developed. We have raised a C-terminally-directed antibody (CAb) that specifically binds 'biologically active' NT (NT and NT(8-13)) and that does not significantly cross-react with inactive NT metabolites or other bioactive peptides in the CNS. By reducing the volume of the assay to a low volume-RIA (30 microl), such that in vivo measurements can be made, we have increased the sensitivity (<0.3 fmol per tube), with inter- and intra-assay variations of 11.2 and 5.8%, respectively. Comparisons with similar methods of detecting NT have demonstrated that this RIA has a higher sensitivity than previously used RIA's and ELISA's. The data presented suggests that this sensitive RIA is a reliable method ideal for the detection of small quantities of biologically active NT.

Solid-phase extraction of arginine vasotocin and isotocin in fish samples and subsequent gradient reversed-phase high-performance liquid chromatographic separation

Gradient high-performance liquid chromatography (HPLC) preceded by a solid-phase extraction (SPE) step is described for determining arginine vasotocin and isotocin, the neurohypophysial nonapeptides, in fish plasma samples. The combination of these two methods significantly improves the separation and increases the sensitivity of the assay. The proposed assay may be a useful alternative for analysis of similar nonapeptides in plasma without the use of radioisotopes, while taking into consideration a difference in detection sensitivity.

High-performance liquid chromatographic resolution of synthetic opiate and "anti-opiate" peptides from human plasma

An assay system using reversed-phase high-performance liquid chromatographic (HPLC) resolution of synthetic anti-opioid peptides (AOPs) and opioid peptides (OPs) was developed. Samples were diluted with trifluoroacetic acid, loaded onto Sep-Pak C18 cartridges, eluted, dried, and redissolved in ethanol-acetic acid-water. Retention-time consistency was established, and high levels of synthetic AOP and OP recovery, generally higher than 80%, were achieved. In a single HPLC run synthetic enkephalins, dynorphins, and beta-endorphins were separated even when extracted from human plasma using a volatile mobile phase which yielded fractions totally compatible with quantitation by radioimmunoassay. Combining the resolution of HPLC with the sensitivity of radioimmunoassay (RIA) may facilitate simultaneous measurement of numerous neuropeptides in body fluids such as plasma and cerebrospinal fluid.

Characterization of neurotensin-like immunoreactivity in human basal ganglia: increased neurotensin levels in substantia nigra in Parkinson's disease

A method that combines high performance liquid chromatography with radioimmunoassay (HPLC/RIA) has been used to characterize neurotensin-like immunoreactivity (NT-IR) in the basal ganglia from control subjects and Parkinson's disease (PD) patients. In samples from the caudate nucleus and putamen, NT-IR eluted as two HPLC peaks. One was indistinguishable from the synthetic tridecapeptide, while the other peak corresponded to oxidized NT, as judged by its chromatographic behaviour and its reaction with the antiserum employed. There were marked discrepancies between the IR detected in crude extracts and that in HPLC purified samples. NT levels (HPLC/RIA) were unaltered in the caudate nucleus, putamen and both segments of the globus pallidus in the parkinsonian brain. In contrast, there was a two-fold increase in NT content in both zona compacta and zona reticulata of the substantia nigra in PD patients compared to controls. Degeneration of the nigrostriatal pathway and/or prolonged antiparkinsonian treatment in PD appears to alter neurotensin levels in an attempt to activate the dopaminergic nigrostriatal pathway.

Parallel alterations in Met-enkephalin and substance P levels in medial globus pallidus in Parkinson's disease patients

Met-enkephalin (Met-enk) and substance P (SP) were measured by a combined high-performance liquid chromatography/radioimmunoanalysis method in medial (GPM) and lateral globus pallidus (GPL) from controls and from Parkinson's disease (PD) patients. All patients showed a similar marked (> 90%) reduction in dopamine (DA) levels in putamen compared with controls. However, based on DA levels in the caudate nucleus, two subgroups of PD patients were differentiated. In patients with > 80% decrease in caudate nucleus DA content, there was a three-fold increase in both Met-enk and SP levels in GPM. In contrast, in patients showing an approximately 50% reduction in DA content in caudate, levels of both peptides were markedly reduced (approximately 80%). Met-enk and SP levels in GPL were unchanged in PD. These results suggest that neurons containing Met-enk and SP projecting to GPM adapt according to the extent of degeneration in the substantia nigra in PD.

Striatal neuropeptide levels in Parkinson's disease patients

Substance P (SP), Met-enkephalin (Met-enk) and cholecystokinin-8-S (CCK-8-S) were measured by a combined HPLC/RIA method in the caudate nucleus and anterior putamen from controls and from Parkinson's disease (PD) patients. SP levels were reduced in caudate in PD, but unchanged in putamen. No differences in Met-enk content were found in parkinsonians compared to controls. However, a significant correlation between DA and Met-enk levels in caudate nucleus from PD was observed. The concentration of CCK-8-S was unaltered in caudate nucleus or putamen in PD. The decrease in caudate nucleus SP levels might be related to the decrease in nigral SP levels in PD, while the reduction in Met-enk levels appears to be a feature of a subgroup of parkinsonian patients.