Capillary liquid chromatography-fast atom bombardment mass spectrometry using a high-resolving cation exchanger, based on a continuous chromatographic matrix. Application to studies on neuropeptide peptidases

Stellan Hjertén's contribution to the development of monolithic stationary phases

This overview is presented to celebrate the birthday of one of the luminaries of the separation science and my friend - Stellan Hjertén. He made significant contributions to a variety of areas in separation science such as electrophoresis, LC, and CEC to name just a few. Since the scope of his work was enormous, this review will focus only on a single aspect of his scientific activities, the design and applications of monolithic materials. During the years starting from 1989, Stellan Hjertén published many excellent papers concerning the preparation of acrylamide chemistry-based monoliths and their use in both micro-HPLC and CEC. The following text details his works in the field.

Preparation and characterization of alkylated polymethacrylate monolithic columns for micro-HPLC of proteins

Protein separations were carried out by micro-high performance liquid chromatography (micro-HPLC) with surface alkylated monolithic columns, which were prepared by in situ copolymerization of glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate (EGDMA) in the presence of dodecanol and toluene as porogens. First, glycidyl groups at the surface of the porous monolith were hydrolyzed with sulfuric acid. The hydroxyl groups thus formed were then reacted with n-alkyl chloride to form alkylated stationary phase. Separation performance for proteins on columns with C18 and C8 stationary phases was compared. The results showed that a poly(GMA-EGDMA) support derivatized with octadecyl moieties could achieve much better resolution than one with octyl groups. A protein mixture was separated with the octadecylated poly-(GMA-EGDMA) monolithic column, and the effluent peaks were collected and analyzed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The physical properties of the monolithic columns such as column morphology, surface area, mesopore size distribution, and column permeability were further characterized by scanning electron microscopy (SEM), multipoint BET nitrogen adsorption/desorption, and Darcy's law, respectively.

Processing of neuropeptide Y, galanin, and somatostatin in the cerebrospinal fluid of patients with Alzheimer's disease and frontotemporal dementia

Alzheimer's disease (AD) and frontotemporal dementia (FTD) are two prevalent neurodegenerative disorders for which the causes are unknown, except in rare familial cases. Several changes in neuropeptide levels as measured by radioimmunoassay (RIA) have been observed in these illnesses. Somatostatin (SOM) levels in cerebrospinal fluid (CSF) are consistently decreased in AD and FTD. Neuropeptide Y (NPY) levels are decreased in AD, but normal in FTD. Galanin (GAL) levels increase with the duration of illness in AD patients. The majority of studies of neuropeptides in CSF have not been verified by HPLC. The observed decrease in a neuropeptide level as measured by RIA may therefore reflect an altered synthesis or extracellular processing, resulting in neuropeptide fragments that may or may not be detected by RIA. Matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-MS) has been shown to be a powerful technique in the analysis of biological materials without any pre-treatment, by detecting peptides and proteins at a specific mass-to-charge (m/z) ratio. We studied the processing of the neuropeptides NPY, NPY, SOM and GAL in the cerebrospinal fluid of patients with AD (n = 3), FTD (n = 3) and controls (n = 2) using MALDI-MS. We found that considerable inter-individual variability exists in the rate of neuropeptide metabolism in CSF, as well as the number of peptide fragments formed. Certain patients showed differences in the processing of specific neuropeptides, relative to other patients and controls. This analysis of the metabolic processing of neuropeptides in CSF yielded a large amount of data for each individual studied. Further studies are required to determine the changes in neuropeptide processing that can be associated with AD and FTD. With further investigations using MALDI-MS analysis, it may be possible to identify a neuropeptide fragment or processing enzyme that can be correlated to these disease states.

Recent developments in microcolumn liquid chromatography

An overview of the most recent developments in microcolumn liquid chromatography (LC) is presented. A short theoretical discussion on chromatographic dilution and extracolumn bandbroadening is given and also the recent progress and advances in column technology and instrumentation are reviewed. However, the emphasis of this review is on miniaturized sample clean-up, sample introduction techniques and on both established and more recent detection techniques for microcolumn LC. The hyphenation of miniaturized LC columns with other techniques, specifically on multidimensional chromatography and the coupling of microcolumn LC to mass spectrometry is discussed in detail. Both the on-line and automated off-line interfacing to other separation and detection techniques will also be addressed. Finally, a number of typical microcolumn LC applications are presented in order to demonstrate the potential of microcolumn LC methods in a variety of scientific areas.

Processing of neuropeptide Y and somatostatin in human cerebrospinal fluid as monitored by radioimmunoassay and mass spectrometry

The processing of four neuropeptides, neuropeptide Y (NPY) 1-36, NPY (18-36), somatostatin (SOM) 1-28, and SOM (15-28) was studied in human cerebrospinal fluid (CSF) by using a novel combination of methods that included radioimmunoassay (RIA) and mass spectrometry. Untreated CSF samples were chromatographed using reversed-phase high pressure liquid chromatography (RP-HPLC) followed by NPY-RIA or SOM-RIA. These results were compared with those obtained by incubating CSF with exogenous synthetic peptides and directly detecting peptide fragments by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-MS). Using this combination of methods, we were able to determine the probable identities of peptides/peptide fragments recognized in radioimmunoassays. The most important NPY-immunoreactive components in CSF were found to be NPY (1-36) and NPY (3-36). Metabolic products of SOM (15-28) were found to contribute to SOM-like immunoreactivity (SOM-LI) in CSF, but SOM (1-28) only to a lesser degree. Differences in the rate of neuropeptide processing were observed. These differences depended more on the length of the peptide than its sequence. NPY (18-36) and SOM (15-28) were rapidly and extensively processed, whereas NPV (1-36) and SOM (1-28) were processed much more slowly in CSF. The production of SOM (15-28) from SOM (1-28) by enzymes in CSF was not observed. Also, the presence of a disulfide bond in the somatostatins appeared to stabilize them against enzymatic digestion of the ring structure. The results detailed in this report confirm MALDI-MS important role in studies of neuropeptide processing in CSF.

Metabolism of an insect diuretic hormone by Malpighian tubules studied by liquid chromatography coupled with electrospray ionization mass spectrometry

The larger of two diuretic hormones of the tobacco hornworm, Manduca sexta, (Mas-DH) is a peptide of 41 residues. It is one of a family of seven currently known insect diuretic hormones that are similar to the corticotropin-releasing factor-urotensin-sauvagine family of peptides. We investigated the possible inactivation of Mas-DH by incubating it in vitro with larval Malpighian tubules (Mt), the target organ of the hormone. The medium was analyzed, and degradation products were identified, using on-line microbore reversed-phase liquid chromatography coupled to electrospray ionization mass spectrometry (RPLC-ESI-MS). This sensitive technique allows identification of metabolites of Mas-DH (present at an initial level of approximately 1 microM). An accurate Mr value for a metabolite is usually sufficient for unambiguous identification. Mas-DH is cleaved by Mt proteases initially at L29-R30 and R30-A31 under our assay conditions; some Mas-DH is also oxidized, apparently at M2 and M11. The proteolysis can be inhibited by 5 mM EDTA, suggesting that divalent metals are needed for peptide cleavage. The oxidation of the hormone can be inhibited by catalase or 1 mM methionine, indicating that H2O2 or related reactive oxygen species are responsible for the oxidative degradation observed. RPLC-ESI-MS is shown here to be an elegant and efficient method for studying peptide hormone metabolism resulting from unknown proteases and pathways.

Reversed-phase high-performance liquid chromatography combined with tandem mass spectrometry in studies of a substance P-converting enzyme from human cerebrospinal fluid

The application of reversed-phase HPLC in combination with micro-electrospray mass spectrometry to study a substance P (SP)-hydrolysing endoprotease in human cerebrospinal fluid (hCSF) is reported. The enzyme was partially purified from the hCSF specimens by ion-exchange chromatography and molecular sieving. During the purification procedure the enzyme activity was monitored by measuring the formation of the SP-fragment 1-7 from SP by radioimmunoassay. Regarding its behaviour upon molecular sieve chromatography, the enzyme was suggested to be associated with an apparent molecular mass of around 100 x 10(3). In subsequent experiments using the partially purified endopeptidase, the hydrolysis of SP was demonstrated by HPLC. The reaction product mixture was resolved in several components including the N-terminal fragments 1-8, 1-7 and 1-6 and the C-terminal fragment 8-11. The identity of these fragments were confirmed by tandem mass spectrometry. It was concluded that the present SP-degrading enzyme is different from those previously identified and purified from hCSF. The applied techniques were proven to be highly efficient for the recovery and identification of the released peptide products.