Opioid and tachykinin peptides, and their precursors and precursor-processing enzymes, in human cerebrospinal fluid

Human cerebrospinal fluid peptidomics

Cerebrospinal fluid (CSF) has frequently been extensively studied to explore several different central nervous system (CNS) disorders because it contains proteins, enzymes, hormones, neuropeptides and neurotransmitters that play critical regulatory roles in many different physiological processes. Individual neuropeptidergic systems in CSF have been studied. In theory, peptidomics offers a bird's-eye, comprehensive and systems-level approach to analyze all of the peptidergic systems that have been expressed in CSF at any given time. In this study, low molecular mass (M(r) < 5 kDa) peptides were isolated by ultrafiltration. The isolated peptides, with or without trypsin digestion, were preferentially enriched with a solid-phase extraction cartridge, and the peptides were separated with capillary liquid chromatography and analyzed with on-line quadrupole time-of-flight mass spectrometry (MS). In this proof-of-principle study, the 20 representative MS-characterized peptides were shown to be derived from 12 proteins, among which four proteins, amyloid-like protein 1, secretogranin I, granin-like neuroendocrine peptide precursor and neurosecretory protein VGF, have been shown elsewhere to be either associated with CNS disorders or to play a central role in the CNS. The long-term goals of this peptidomics study are to monitor the changes (amount; modifications) of CSF peptides, clarify the aberrant processing of large intact protein precursors, elucidate the molecular mechanisms of CNS disorders and find biomarkers. This analytical method is effective for the analysis of the human lumbar CSF peptidome.

Mass spectrometric analysis of neuropeptidergic systems in the human pituitary and cerebrospinal fluid

Neuropeptidergic systems have been studied in human tissues and fluids, which include the pituitary and lumbar cerebrospinal fluid, respectively. This paper reviews the qualitative and quantitative mass spectrometric analytical data obtained from three areas of study. Methionine enkephalin (ME) and beta-endorphin (BE) were quantified in the human pituitary by liquid secondary ion mass spectrometry (LSI MS)-tandem mass spectrometry. Corresponding stable isotope-incorporated synthetic peptide internal standards were used. Proenkephalin A and proopiomelanocortin produce ME and BE, respectively. The analysis of neuropeptides in macroadenomas demonstrated a decrease in both of those neuropeptidergic systems relative to controls. An analysis of prolactin-secreting microadenomas showed an increase in the proenkephalin A system. Mass spectrometry was also used to detect opioid peptide-containing proteins in the pituitary. Enzymes that process the precursors of proenkephalin A and tachykinin (substance P) neuropeptides were studied in human lumbar cerebrospinal fluid. Electrospray ionization mass spectrometry was used to characterize the molecular mass of each peptide product.

Time, life ... and mass spectrometry. New techniques to address biological questions

Within the last ten years, startling new developments in two ionization methods--matrix-assisted laser desorption (MALDI) and electrospray (ESI)--have been described by Karas et al. [M. Karas, D. Bachmann, U. Bahr, F. Hillenkamp, Int. J. Mass Spectrom. Ion Proc., 78 (1987) 53.] and by Fenn et al. [J.B. Fenn, M. Mann, C.K. Meng, S.F. Wong, C.M. Whitehouse, Science, 246 (1989) 64.], respectively. Their work demonstrated that these techniques, under appropriate experimental conditions, have high sensitivity and wide mass range, extending to hundreds of thousands of daltons and beyond, and thus can be extremely effective for the study of biopolymers. The result has been a revolution in the way that mass spectrometry experiments are carried out, a widening of the range of investigators who employ mass spectrometry in their own laboratories and a penetration of mass spectrometry into the investigation of biological phenomena that exceeds any previous expectations. Progress in improving mass spectral ionization and mass analysis methods and in interpreting and understanding the spectra is actively being pursued and exploited in many laboratories, to capitalize even further upon these advances. The results should facilitate understanding of structure-activity relationships pertinent to biology and medicine. In our laboratory, the focus of research is on oligosaccharide and glycoconjugate structural determinations, and on the improvement of methods for these important classes of compounds that relate to development, immune response, signalling, lipid and protein transport and disease. Representative examples of applications of MALDI and ESI mass spectrometry to these and other biological questions are provided herein.

Novel neuropeptide Y processing in human cerebrospinal fluid from depressed patients

In vitro processing of neuropeptide Y (NPY) in cerebrospinal fluid (CSF) of patients with depression was monitored by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Single peptide bonds in NPY were cleaved to yield N- or C-terminal fragments. Multiple cleavage to form internal peptides was unimportant. Degradation rates varied between individuals, whereas the product distributions were fairly constant. Other peptides did not evidence such proteolysis. MALDI-TOF MS will facilitate extensive investigations of NPY processing that could provide the basis for clinical assays and illuminate the pathophysiology related to depression.

Rationale for intrastriatal grafting of striatal neuroblasts in patients with Huntington's disease

Huntington's disease is a genetic disease, autosomal and dominant, that induces motor disorders, an inexorable deterioration of higher brain functions and psychiatric disturbances. At present, there are no known therapeutics against Huntington's disease. The Network of European CNS Transplantation and Restoration (NECTAR) has begun a program aimed at defining the conditions under which intrastriatal transplantation of fetal striatal cells could be attempted as an experimental treatment for Huntington's disease. This review presents the reasons why our group is considering participating in these trials. The validity of this therapeutic approach is supported by three main series of data: (i) neuropathological, clinical and imaging data indicate that Huntington's disease is, above all, a localized affection of a specific neuronal population ("medium-spiny" neurons) in the striatum; (ii) a large body of experimental results, obtained in rats and non-human primates, demonstrates that transplanted fetal striatal cells are able to integrate the host brain and to substitute for previously lesioned host striatal neurons; (iii) expertise in clinical neural transplantation has now been acquired from the treatment of patients with Parkinson's disease. These different sets of data are presented and discussed in this review. There are a number of problems which do not yet appear to be entirely resolved, nor are they likely to be using the experimental models currently available. These problems are identified and explicitly presented as working hypotheses. (1) Anatomo-functional results obtained in rodents and non-human primates with excitotoxic striatal lesions can serve as a basis for the extrapolation of what can be obtained from patients with Huntington's disease. (2). Huntington's disease can be efficiently fought by substituting degenerated striatal neurons alone. (3) Huntington's disease is due to a genetic defect which either hits the neurons that carry it directly or hits them indirectly only after several decades. Transplanted neurons, because they do not carry the gene or because they are of fetal origin, will not be rapidly affected by the ongoing disease process. Given the current state of knowledge, intracerebral transplantation appears to be the most serious opportunity (if not the only one that has been experimentally validated) for clinical improvement to be obtained in patients with Huntington's disease. The purpose of this review is to open a scientific discussion on its experimental bases before actual clinical trials start.

Sensitivity and selectivity of the electrochemical detection of the copper(II) complexes of bioactive peptides, and comparison to model studies by rotating ring-disc electrode

Post-column reaction of peptides with Cu(II) can be used for the electrochemical detection of peptides as their biuret complexes. Understanding of the behavior (sensitivity at the anode and cathode in the dual-series electrochemical detector) of the system is facilitated through the observation of the rotating ring disc voltammetry of some model compounds. In operation, the anodic signal from the oxidation of the Cu(II)-peptide to the Cu(III) form can be used to detect peptides, or the downstream cathode can be used to detect the Cu(III) form. The signals appear at about 0.4 V (anode) for tetra- and longer peptides, 0.65 V for tripeptides. The anode signal is augmented by tyrosine (oxidation at 0.4-0.5 V) and tryptophan (0.5-0.6 V). If the cathode is used as the detector in a two working electrode cell, the sensitivity depends on the stability of the Cu(III) product. This is peptide dependent, but the signal is significant and useful analytically. Twenty-three bioactive peptides in two groups, naturally electrochemically active and naturally electrochemically silent, and several model compounds have been studied. Both naturally electrochemically active peptides (contain tyrosine and/or tryptophan) and naturally electrochemically silent peptides have been studied. Chromatography with an acetonitrile gradient has been used to separate the peptides in each group. Detection limits are for non-electroactive peptides in the range of 16-100 fmol (10- microliters injection 1.6-10 nM, 100 microliters injection 0.16-1.0 nM), and for electroactive peptides in the range of 6-40 fmol (0.6-4.0 nM for a 10- microliters injection and 60-400 pM for a 100- microliters injection). A tryptic digest of bovine cytochrome c is easily seen at 100 nM.

Quantitation of N-terminally extended tachykinins in cerebrospinal fluid from healthy subjects

N-terminally extended substance P (SP) and neuropeptide K (NPK), an N-terminally extended form of neurokinin A (NKA), were determined in cerebrospinal fluid (CSF) from healthy human subjects by combined high performance liquid chromatography and radioimmunoassay. The concentrations of the peptides were similar in fresh CSF and in CSF which had been kept frozen for up to 5 months. SP and NKA were not present in measurable amounts in neither fresh CSF nor in CSF that had been frozen. On the other hand, when synthetic SP and NKA were added to approx. 2 pM concentration to fresh CSF samples, both peptides were recovered to 85 and 98%, respectively. There were no significant concentration gradients of the peptides in the first 18 ml (three consecutive 6 ml fractions) of CSF (n = 10). In contrast, we confirmed previous findings, that there are gradients of the amine metabolites 5-HIAA (P < 0.01) and HVA (P < 0.001) (n = 5). The concentrations of extended SP (expressed in SP equivalents) and NPK in the first 6 ml of CSF were 1.5 +/- 0.7 pM and 14.2 +/- 6.4 pM (mean +/- S.D., n = 10), respectively. The present results thus show that the levels of N-terminally extended SP and NKA are stable in frozen CSF samples for up to 5 months. The virtual lack of SP and NKA in CSF does not seem to be due to losses during sample preparation or storage.

Substance P inactivating enzymes in human cerebrospinal fluid

The Km and Vmax values were determined for enzymes in human lumbar cerebrospinal fluid (CSF) that inactivate synthetic substance P (SP = RPKPQQFFGLM-NH2) and produce metabolic products. For the human lumbar CSF samples analyzed in this study, Km = 2.24 +/- 0.93 mM and Vmax = 0.113 +/- 0.035 nmol/ml/min (n = 10; mean +/- SEM) for the rate of decrease of SP. HPLC analysis of the incubated synthetic peptide fragments demonstrated that the primary enzymatically produced fragment is SP(3-11), with minor amounts in decreasing order of SP(1-4), SP(1-7), and SP(1-9). Electrospray ionization mass spectrometry (ESI-MS) confirmed the appropriate molecular weights for the four peptides, SP(3-11), SP(1-4), SP(1-7), and SP(1-9). These data demonstrate that the primary enzyme in human lumbar CSF that acts on synthetic SP is a post-proline cleaving enzyme (PPCE).

Analysis of proenkephalin A, proopiomelanocortin and protachykinin neuropeptides in human lumbar cerebrospinal fluid by reversed-phase high-performance liquid chromatography, radioimmunoassay and enzymolysis

A comprehensive high-performance liquid chromatographic, radioimmunoassay, and enzymatic degradation scheme has been developed to analyze several intact neuropeptides and the corresponding peptides created by in vivo enzymolysis of precursors to study neuropeptides in human lumbar cerebrospinal fluid (CSF) and to test the hypothesis that defects in the metabolism (synthesis, degradation) of neuropeptide precursors, neuropeptides, and metabolites play a role in low back pain. CSF samples were obtained from three different patient groups: controls (C), whose low back pain was relieved without lidocaine; pharmacological responders (PR), whose pain was relieved by lidocaine and who were candidates for surgery; and pharmacological non-responders (PNR), whose pain was not relieved by lidocaine and a mid-thoracic anesthetic, and who were not candidates for surgery. The metabolic activity involved during synthesis and degradation of the peptides was assessed by measuring intact, native neuropeptide immunoreactivity in pre-incubated and post-incubated CSF samples, where samples were incubated at 37 degrees C for 1 h. Pre-incubation radioimmunoassay measurements reflected the content of intact peptides present in lumbar CSF at the time of sampling, and post-incubation measurements assayed the amount of peptide that had remained embedded within its precursors [cryptic methionine enkephalin (ME)] and that had been released by the action of CSF peptidases. Significant differences were found in post-incubation samples for the amount of proenkephalin A [ME, leucine enkephalin (LE)] and tachykinin [substance P (SP)] peptides. For example, significant differences were observed for ME-like immunoreactivity (C versus cryptic), SP-like immunoreactivity (PNR versus PR), and LE-like immunoreactivity (PR versus C). No significant differences were observed among the peptides within the pre-incubation samples.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of methionine enkephalin in human pituitary by multi-dimensional reversed-phase high-performance liquid chromatography, radioreceptor assay, radioimmunoassay, fast atom bombardment mass spectrometry, and mass spectrometry-mass spectrometry

Methionine enkephalin (ME = YGGFM) was measured in five individual human post-mortem pituitaries using four different analytical methods, with the objective of comparing the molecular specificities of the methods. Radioreceptor assay (RRA) used a receptor-rich preparation from brain and [3H]etorphine as radioligand to determine ME-like receptoractivity (ME-LR). Radioimmunoassay (RIA) measured ME-like immunoreactivity (ME-LI). Pituitary samples analyzed by RRA and RIA were purified first with a high-performance liquid chromatography (HPLC) gradient on a polymer analytical column. Fast atom bombardment mass spectrometry (FAB-MS) in two different detection modes quantified ME using the protonated molecular ion MH+ of ME at 574 a.m.u. and B/E linked-field selected reaction monitoring (SRM) to monitor the specific unimolecular metastable transition that produced the unique amino acid sequence-determining tetrapeptide fragment ion YGGFA+ from the MH+ precursor ion. Both FAB-MS methods used the deuterated internal standard YGG[2H5-F]M. Samples analyzed with FAB-MS were purified first with multi-dimensional reversed-phase HPLC. The first dimension was an ODS gradient, and the second dimension was a polymer isocratic elution. The following ME amounts were measured (mean +/- standard error of the mean): ME-LR, 7.0 +/- 1.9 micrograms g-1 tissue; ME-LI, 1.8 +/- 0.7 micrograms g-1 tissue; MH+, 2.7 +/- 0.6 micrograms g-1 tissue; SRM, 3.0 +/- 0.8 micrograms g-1 tissue. The FAB SRM method provided the highest level of molecular specificity amount these four analytical methods used to measure picomole amounts of endogenous ME in a human pituitary.

A new fluorogenic assay for tyrosine-containing peptides

A new tyrosine-specific LC assay with pre-column fluorogenic derivatization is described for Tyr-Gly as model peptide. o-Hydroxylation of the tyrosine residue with tyrosinase in the presence of ascorbic acid, followed by oxidation to the corresponding quinone by potassium ferricyanide at room temperature and condensation with 1,2-diamino-1,2-diphenylethane in the presence of acetonitrile gave a highly fluorescent species. The resulting fluorescence signal was stable over the investigated period of 5 h and exhibited a linear response curve on a reversed-phase LC system. Under optimized reaction conditions, the lower limit of detection for Tyr-Gly was 200 fmol per injection. Examination of a series of dipeptides (L-Tyr-L-X; X = Gly, Ala, Val, Leu, Phe) showed no significant influence of neighbouring amino acids on the enzymatic hydroxylation by tyrosinase. This and the formation of a highly fluorescent signal for Leu-enkephalin suggests the general feasibility of the approach for the determination of tyrosine-containing peptides.

Proenkephalin A and proopiomelanocortin peptides in human cerebrospinal fluid

Precursors to beta-endorphin (BE) and methionine enkephalin (ME), and proteolytic enzymes that cleave those BE and ME precursors to BE and ME, were determined in several milliliters of human cerebrospinal fluid. Endogenous peptides were purified by reversed-phase high-performance liquid chromatography (HPLC), and were detected with radioreceptor assay (RRA), radioimmunoassay, and mass spectrometry (MS). Total opioid receptor activity measurements and the profile of HPLC-receptor activity of human CSF samples were both used to monitor neuropeptide metabolism. MS data linked the molecular ion of ME to a unique fragment ion. A later-eluting fraction (84 min) in a 90-min HPLC gradient appeared in all HPLC-RRA profiles, contained opioid receptor activity that displaced [3H]etorphine, and the quantitative and qualitative patterns of opioid receptor activity in those profiles both changed within the few minutes that elapsed between acquiring the first and second cerebrospinal fluid samples. That 84-min fraction contained precursors to opioid peptides and was fractionated further with a more shallow 120-min HPLC gradient into three sections that displayed delta-opioid receptor-preferring activity, using [3H]ME as ligand. These three sections were hydrolyzed separately with human cerebrospinal fluid as the source for endogenous neuropeptides to yield products that correlated to immunoreactive BE in section I and immunoreactive ME in section III.