Identification of substance P metabolites using a combination of reversed-phase high-performance liquid chromatography and capillary electrophoresis

Investigation of the metabolism of substance P at the blood-brain barrier using LC-MS/MS

Substance P (SP) has been associated with pain and depression as well as neurodegenerative diseases. Many of these diverse actions of SP can potentially be attributed to SP metabolites generated at the blood-brain barrier (BBB). In this study, the metabolism of SP was investigated using an in vitro model of the BBB and LC-MS/MS. Substance P metabolism was found to be non-saturable in the concentration range of 100 nM to 10 microM, with approximately 70% of the peptide remaining intact after 5 h. The major metabolites of SP were identified by MS as 3-11 and 5-11. Two previously unreported metabolites, 5-11 and 6-11, were also found in our studies. Several additional minor SP metabolites, including 1-9 and 2-11, were also identified. A profile of the SP metabolites generated by the BBB over time was obtained. The results from the present study provide a better understanding of the role of the blood-brain barrier in the pharmacology of SP.

A surface plasmon resonance sensor for substance P using gold-modified calmodulin and melittin

A surface plasmon resonance (SPR) biosensor for the quantification of a neuropeptide substance P (SP) is described based on an inhibition assay using Au colloid-modified calmodulin (Au-CaM) and a target peptide melittin immobilized on carboxymethylated dextran. The modification of CaM with streptavidin Au colloids was achieved in a sample solution by the amine coupling method. The SPR signal sharply increased, corresponding to the formation of a Ca2+-Au-CaM-melittin complex on the sensor surface, and approached a steady state within 5 min. When SP was added to a sample solution, the SPR signal was decreased, due to the formation of a Ca2+-Au-CaM-SP complex in the sample solution. The modification of CaM with streptavidin Au colloids was effective for enhancing the SPR signal for SP. A decrease in the SPR signal was observed for SP in the concentration range from 0.10 to 5.0 microM, whose lower limit was ten-times superior to that (1.0 microM) with unmodified CaM. The response was highly selective to SP and the selectivity was in the order of SP >> neurokinin A > neurokinin B > neurotransmitters (glycine, GABA, L-glutamate, acetylcholine, norepinephrine, 5HT) - substance P fragment (1 - 7). The potential use of the present sensor for the quantification of SP in mouse brain extracts is demonstrated.

Sample preparation for peptides and proteins in biological matrices prior to liquid chromatography and capillary zone electrophoresis

The determination of peptides and proteins in a biological matrix normally includes a sample-preparation step to obtain a sample that can be injected into a separation system in such a way that peptides and proteins of interest can be determined qualitatively and/or quantitatively. This can be a rather challenging, labourious and/or time-consuming process. The extract obtained after sample preparation is further separated using a compatible separation system. Liquid chromatography (LC) is the generally applied technique for this purpose, but capillary zone electrophoresis (CZE) is an alternative, providing fast, versatile and efficient separations. In this review, the recent developments in the combination of sample-preparation procedures with LC and CZE, for the determination of peptides and proteins, will be discussed. Emphasis will be on purification from and determination in complex biological matrices (plasma, cell lysates, etc.) of these compounds and little attention will be paid to the proteomics area. Additional focus will be put on sample-preparation conditions, which can be 'hard' or 'soft', and on selectivity issues. Selectivity issues will be addressed in combination with the used separation technique and a comparison between LC and CZE will be made.

Further evidence on the anxiogenic-like effect of substance P evaluated in the elevated plus-maze in rats

Substance P (SP) and its preferred NK1 receptor are widely expressed throughout the fear-processing pathways of the brain and its role in the modulation of experimental anxiety has been demonstrated. SP, like other peptides, are cleaved by peptidases in two fragments: C-terminal (SP 6-11) and N-terminal (SP 1-7) that could be responsible for its anxiogenic-like response. In this study we investigate the effects of i.c.v. micro-injections of SP free acid (SPfa), which is resistant to enzymatic cleavage, the influence of the pretreatment with peptidase inhibitors (PIs), thiorphan and/or phosphoramidon, as well as the effects of SP 6-11 and SP 1-7 and the participation of NK1 and NK2 receptors on their behavioral effects. Adult male Wistar rats were treated with 10 pmol solutions of SP 6-11, SP 1-7 or 1 and 10 pmol of SPfa and evaluated in the elevated plus maze (EPM) test. Other experimental groups received thiorphan 0.2 pmol, phosphoramidon 2 pmol or both PIs 30 min prior SP 1-11, 10 pmol i.c.v. The C-terminal fragment (SP 6-11, 10 pmol) and SPfa (1 pmol) promoted an anxiogenic-like profile of action similar to 10 pmol of SP 1-11, i.e., a decrease of entries and time spent on the open arms, whereas the N-terminal fragment (SP 1-7) was inactive at the EPM. The effect of SP 6-11 was inhibited by pretreatment (100 pmol) with NK1 (FK 888) and NK2 (SR 48968) antagonists. Moreover, both PIs enhanced the SP effect when used alone, but their combination produced an apparent reversion of anxiogenic-like effect produced by SP. Altogether, our results give further support to the SP role in the modulation of experimental anxiety in rats.

In vivo metabolism and clearance of substance P and co-expressed tachykinins in rat striatum

Neurons expressing the preprotachykinin A gene, which encodes the sequences of substance P, neurokinin A, neuropeptide gamma and neuropeptide K, exemplify peptide co-existence. Furthermore, there is also evidence that substance P fragments have biological activity. However, the relative contribution of each of these peptides to tachykinin signalling is still poorly understood. An important factor which will determine the characteristics of the signal mediated by co-localised peptides is their clearance from the extracellular space. The striatum, in which tachykinins are present and exert neuromodulatory roles, can be used as a model to investigate this aspect. Therefore, in this study we characterised in vivo in the striatum the metabolism and clearance of substance P and of the other three co-expressed peptides. After intrastriatal administration of 1 pmol, tritiated substance P disappeared too rapidly for metabolites to be detected. However, when 10 nmol substance P and 1 pmol tritiated substance P were co-injected, substance P(1-4) and substance P(1-7), which are biologically active, were detected as major metabolites. Under these conditions, the rate of decay of tritiated substance P was 0.2 nmol/min. The effects of the peptidase inhibitors thiorphan, bestatin and captopril suggested that neutral endopeptidase 24.11 and aminopeptidases were involved in primary substance P cleavages, whereas angiotensin-converting enzyme was involved in secondary cleavages. The monitoring of the decay of unlabelled substance P by high-performance liquid chromatography gave a rate of 0.16 nmol/min. Using high-performance liquid chromatography with capillary electrophoresis, the rates of decay of 10 nmol neurokinin A or neuropeptide gamma were five and seven times faster than that of substance P. In contrast, over the time course of the experiment, no significant decay of neuropeptide K was detected. These results show that substance P disappears rapidly from the extracellular space, and supports the formation in vivo of major N-terminal active substance P metabolites. Our study also highlights significant differences in the clearance of co-expressed tachykinins and suggests that certain species may disappear relatively slowly from the extracellular space, and thus may make a significant temporal and spatial contribution to signalling.

Investigation of the metabolism of substance P at the blood-brain barrier using capillary electrophoresis with laser-induced fluorescence detection

Substance P (SP) metabolism was investigated upon exposure to a monolayer of bovine brain microvessel endothelial cells (BBMECs), a cell culture model of the blood-brain barrier. SP was incubated with the BBMECs and its metabolism was followed as a function of time over a 5-h period. The resulting samples were derivatized with naphthalene-2,3-dicarboxaldehyde (NDA)/cyanide, separated, and detected using cyclodextrin-modified electrokinetic chromatography with laser-induced fluorescence detection (CDMEKC-LIF). Upon exposure to the BBMEC monolayer, SP rapidly degraded to produce the N-terminal (1-9), (1-4) and (1-7) and C-terminal (2-11) and (3-11) fragments. These results were compared with those in an earlier report from our laboratory, where SP metabolism was investigated in vivo by microdialysis sampling in rat striatum.

Investigation of the metabolism of substance P in rat striatum by microdialysis sampling and capillary electrophoresis with laser-induced fluorescence detection

The metabolism of substance P (SP) was investigated in rat striatum using in vivo microdialysis. Substance P was perfused for 5 h at 0.2 microl/min, and its metabolism was followed for over 13 h. The resulting samples were derivatized precolumn with naphthalene-2,3-dicarboxaldehyde (NDA)/cyanide, separated and detected by cyclodextrin-modified electrokinetic chromatography with laser-induced fluorescence detection (CDMEKC-LIF). Substance P rapidly degraded to form the fragments (3-11), (1-9), (1-4) and, to a lesser extent, (1-7). The metabolites reached steady-state levels 2-3 h after addition of SP.

Coupling continuous separation techniques to capillary electrophoresis

One of the weak points of capillary electrophoresis is the need to implement rigorously sample pretreatment because its great impact on the quality of the qualitative and quantitative results provided. One of the approaches to solve this problem is through the symbiosis of automatic continuous flow systems (CFSs) and capillary electrophoresis (CE). In this review a systematic approach to CFS-CE coupling is presented and discussed. The design of the corresponding interface depends on three factors, namely: (a) the characteristics of the CFS involved which can be non-chromatographic and chromatographic; (b) the type of CE equipment: laboratory-made or commercially available; and (c) the type of connection which can be in-line (on-capillary), on-line or mixed off/on-line. These are the basic criteria to qualify the hyphenation of CFS (solid-phase extraction, dialysis, gas diffusion, evaporation, direct leaching) with CE described so far and applied to determine a variety of analytes in many different types of samples. A critical discussion allows one to demonstrate that this symbiosis is an important topic in research and development, besides separation and detection, to consolidate CE as a routine analytical tool.

Capillary electrophoresis of peptides

This article gives a review of the recent developments in capillary electrophoresis (CE) of peptides. New approaches to the theoretical description of electromigration behavior of peptides are described, and methodological aspects of CE separations of peptides such as selection of separation conditions, sample treatment, suppression of peptide adsorption to the capillary wall and specificities of CE separation modes are discussed. Progress in application of high performance detection schemes, namely laser-induced fluorescence and mass spectrometry, in peptide separations by CE is presented. Applications of different CE techniques, zone electrophoresis, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography and electrochromatography to peptide analysis, preparation and physicochemical characterization are demonstrated.