High-performance liquid chromatography and diode-array detection for the identification of peptides containing aromatic amino acids in studies of endorphin-degrading activity in human cerebrospinal fluid

Quantitative analysis of a model opioid peptide and its cyclic prodrugs in rat plasma using high-performance liquid chromatography with fluorescence and tandem mass spectrometric detection

Two analytical methods were developed for quantitative determination of DADLE (H(2)N-Tyr-D-Ala-Gly-Phe-D-Leu-COOH) and its two cyclic prodrugs in rat plasma. For high-performance liquid chromatography with fluorescence detection (LC-FLU), precolumn derivatization of DADLE was accomplished by labeling the N-terminal amino group with the reagent naphthalene-2,3-dicarboxaldehyde in the presence of cyanide (NDA/CN) to form a highly fluorescent 1-cyanobenz[f]isoindole (CBI) derivative. A multi-dimensional LC system was employed to improve selectivity, and solid-phase extraction (SPE) was used for plasma sample preparation. The cyclic prodrugs were converted to DADLE prior to their derivatization. With fluorescence detection after derivatization, the limit of quantitation (LOQ) was 6 ng ml(-1) for the analysis of DADLE, and good linearity was observed up to 6000 ng ml(-1) in rat plasma. Quantitative analysis of DADLE and its cyclic prodrugs was also performed using liquid chromatography interfaced to electrospray ionization tandem mass spectrometry (LC-ESI-MS-MS). Chromatographic separation was achieved on a C(18) column using gradient elution in a water-acetonitrile system containing 0.1% (v/v) formic acid. The tandem mass spectrometric analysis was performed in the multiple reaction monitoring mode using internal standardization to improve assay precision and accuracy. For plasma sample pretreatment, acetonitrile was added first to precipitate proteins and SPE was used to minimize matrix effects. Using LC-ESI-MS-MS, the LOQ was 0.5 ng ml(-1) for DADLE and 2 to 5 ng ml(-1) for its prodrugs. Good linearity was observed from the LOQ up to 1000 ng ml(-1) for all compounds. For the analysis of DADLE, both analytical methods showed good precision, accuracy and stability. However, for prodrug analysis, LC-FLU showed some sensitivity and accuracy problems, while the LC-ESI-MS-MS method provided consistent and satisfactory results. In conclusion, LC-ESI-MS-MS is the method of choice for the analysis of DADLE and its cyclic prodrugs in rat plasma samples due to its good selectivity, high sensitivity, and fast analysis. Its application was demonstrated through biodisposition and bioconversion studies of the coumarinic acid-based prodrug after intravenous administration in rats.

Opioid peptides derived from hemoglobin: hemorphins

Investigation of hemoglobin peptic hydrolysate has revealed the presence of biologically active peptides with affinity for opioid receptors. Two peptides, VV-hemorphin-7 and LVV-hemorphin-7, were resolved by a combination of size exclusion and reversed phase HPLC. A new spectroscopic method based on the second order derivative spectra analysis of aromatic amino acids has been developed. This method allows qualitative and quantitative evaluation of hemorphins generated by peptic hemoglobin hydrolysis. Using this method, a kinetic study of hemorphins appearance has been undertaken. In this paper, we also evidenced the generation of VV-hemorphin-7 from globin by peritoneal macrophages. In regard to this result, the putative physiological role of hemorphins is discussed.

Kinetics of appearance of hemorphins from bovine hemoglobin peptic hydrolysates by a direct coupling of reversed-phase high-performance liquid chromatography and electrospray ionization mass spectrometry

Reversed-phase high-performance liquid chromatography coupled with electrospray ionization mass spectrometry was used to improve the preparation of three opioid peptides (Leu-Val-Val-hemorphin-7, Val-Val-hemorphin-7 and Val-Val-hemorphin-4) resulting from bovine hemoglobin peptic hydrolysates. Optimal conditions for the preparation of these peptides were determined thanks to their kinetic studies of appearance in the course of peptic hydrolyses as a function of degree of hydrolysis of hemoglobin. We propose a low degree of hydrolysis (3%) to prepare Leu-Val-Val-hemorphin-7, a mean degree of hydrolysis (11%) to prepare Val-Val-hemorphin-7 and a high degree of hydrolysis (21%) to prepare Val-Val-hemorphin-4.

Elevated cerebrospinal fluid substance P-like immunoreactivity in patients with painful osteoarthritis, but not in patients with rhizopatic pain from a herniated lumbar disc

Cerebrospinal fluid (CSF) levels of substance P like immunoreactivity (SPLI) were determined in 11 patients with painful osteoarthritis in hip or knee, 9 patients with rhizopatic pain from a herniated lumbar disc, and in 9 healthy volunteers without pain. The patients with osteoarthritis had increased levels of SPLI in CSF (p < 0.001) compared to the controls. A positive correlation was also seen between the CSF SPLI and the degree of pain. At a second lumbar puncture 5 months after operation, SPLI had decreased, but was still significantly higher than in the controls. No difference in CSF SPLI was seen in the patients with herniated lumbar disc compared to the controls, neither before treatment, nor at follow up CSF postoperatively. The results suggest that nociceptive joint pain is consistent with increased SPLI in CSF. Differences in SPLI in CSF may be useful to differentiate pain from various origin, and may also increase our understanding of different pain mechanisms.

Isolation of haemorphin-related peptides from filter membranes collected in connection with haemofiltration of human subjects

This paper describes the extraction and isolation from dialysis filters of two peptides containing the opioid active sequence haemorphin-7. The filter devices were obtained from uraemic patients subjected to haemofiltration. Following acidic extraction of the filter membranes the peptides were purified by size-exclusion, ion-exchange chromatography and finally by reversed-phase chromatography using different columns and different chromatographic systems. The purification was guided by radioimmunoassay and the structure of the final products was elucidated by N-terminal sequencing and fast-atom bombardment mass spectrometry as well as micro-electrospray mass spectrometry. The isolated peptides were suggested to be identical to fragments 1-41 and 32-41 of the beta-chain of human haemoglobin.

Spectroscopic characterization by photodiode array detection of human urinary and amniotic protein HC subpopulations fractionated by anion-exchange and size-exclusion high-performance liquid chromatography

A procedure for spectroscopic characterization and partial fractionation of human protein HC populations by high-performance liquid chromatography-photodiode array ultraviolet-visible detection is reported. Human protein HC from urine or amniotic fluid fractionated by anion-exchange HPLC in a protein Pak DEAE 5PW appeared to be heterogeneous as judged by the asymmetric elution pattern, consisting of a continuous irregular broad peak with several shoulders distributed along the whole chromatogram. Selected fractions containing shoulders were rechromatographed and finally six symmetrical homogeneous peaks with different retention times were obtained from each protein HC preparation. The direct automatic absorption spectra analyses at each peak maximum, indicated that all of the homogeneous peaks seemed to be protein HC, all of them associated to the same chromophore although with different stoichiometry ratios. Isoelectric focusing showed that each peak was composed of a limited number of subpopulations of protein HC with different isoelectric points. Size microheterogeneity has been also demonstrated in both urinary and amniotic protein HC preparations by a combination of size-exclusion HPLC on a TSK 3000 SW6 column and photodiode array detection. Partial fractionation of human albumin on an analytical anion-exchange Mono-Q PC 1.6/5 column, has allowed the identification of heterogeneous chromophore-containing populations displaying significant absorption in the visible region in resemblance to that of protein HC.

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).

Met-enkephalin-Arg6-Phe7 in spinal cord and brain following traumatic injury to the spinal cord: influence of p-chlorophenylalanine. An experimental study in the rat using radioimmunoassay technique

The possibility that trauma to the dorsal horn may affect the release and distribution of enkephalin was examined using the opioid peptide Met-Enk-Arg6-Phe7 (MEAP) as a marker in a rat model. The peptide content of samples of spinal cord and whole brain was measured using a radioimmunoassay (RIA) technique. In addition, the possible functional relation between this peptide and serotonin was evaluated using a pharmacological approach that included depletion of endogenous serotonin. A focal trauma to the right dorsal horn in the T10-11 segments (2 mm deep and 5 mm long) markedly modified the content of MEAP of the adjacent rostral and caudal segments of the cord, as well as the content of MEAP of the brain. Depletion of serotonin with p-CPA (an inhibitor of the synthesis of serotonin) significantly elevated the content of MEAP in the whole brain without affecting the regions of the spinal cord (except T9 level which showed a 25% decrease from an intact control group). Trauma to the spinal cord in the serotonin-depleted animals did not alter the content of MEAP further, as compared to a p-CPA-treated but untraumatized group. These results indicate that enkephalin (i) participates in the pathophysiology of spinal cord trauma and (ii) suggest that the peptide is somehow functionally related with serotonin.

Strategies for peak-purity assessment in liquid chromatography

One of the key requirements for the validation of chromatographic methods is to determine the purity of a chromatographic peak. Statistical modelling of the chromatographic process suggests that overlapping components are highly probable in a chromatogram. Hence extensive efforts have been directed at the development of sensitive, reliable and robust methods to assess peak purity. This is especially the case in the pharmaceutical industry, where liquid chromatography (LC) is widely utilized and the demands on method validation are justifiably high. On-line multiwavelength absorptiometric detection is often used to generate the additional data required to facilitate peak-purity assessment in LC. This approach, using photodiode-array technology, is directly compatible with the aqueous-based reversed-phase LC solvents used extensively in drug analysis. Consequently, this work highlights many of the peak-purity algorithms, which may be applied using LC with diode-array detection. The relative merits of the individual techniques are discussed, and a rationale is developed for their application.

Dynorphin A content in the rat brain and spinal cord after a localized trauma to the spinal cord and its modification with p-chlorophenylalanine. An experimental study using radioimmunoassay technique

The distribution of dynorphin A in the spinal cord and brain of normal rats and of rats subjected to a focal injury of the spinal cord was examined in a rat model using a radioimmunoassay (RIA) technique. The validity of RIA was checked by high performance liquid chromatography (HPLC). Furthermore, the possibility that the peptide is somehow functionally related with endogenous 5-hydroxytryptamine (5-HT, serotonin), was also evaluated using a pharmacological approach. In normal animals, the peptide content was very similar in the spinal cord segments (T9, T10-11, and T12) examined whereas, the dynorphin content of the whole brain was about two-fold higher compared with that in the spinal cord. A focal injury to the spinal cord in the right dorsal horn (about 1.5 mm deep, 2.5 mm long and 1.5 mm to the right of the midline) of the lower thoracic cord (T10-11) in urethane anaesthetised animals significantly altered the peptide content in the whole brain as well as in the spinal cord. Thus, a decrease in the peptide level in whole brain, T10-11 and in the T12 segments of the spinal cord was observed 1 and 2 h after trauma. At 5 h, the peptide had accumulated markedly in the T9 segment (about a two-fold increase) as compared with the controls. At this time, the peptide content had been restored in the T10-11 and T12 segments. On the other hand, the whole brain dynorphin level continued to remain low (by 55%) as compared to the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Application of photodiode array detection and fast atom bombardment mass spectrometry for the identification of the arginine residue in neuropeptides

Chemical derivatization by phenylglyoxal (PGX) was applied to the identification of arginine in the neuropeptides dynorphin A (1-6) and substance P. The obtained products were separated on a short reversed phase C18 column and analysed on-line with the photodiode array UV technique. The selective attachment of a chromogenic molecule into the arginine residue resulted in significant change in the absorbance spectra around 250 nm, depending on the number of PGX molecules attracted. Further analysis employed fast atom bombardment mass spectrometry (FAB MS) and C-terminal sequencing for detailed verification of the derivatives formed during modification with PGX. The results clearly demonstrated that the photodiode array technique, when combined with chemical modification of certain amino acids, provides new possibilities for the analysis of peptide structures.

Approach to studying proteinase specificity by continuous-flow fast atom bombardment mass spectrometry and high-performance liquid chromatography combined with photodiode-array ultraviolet detection

Fast atom bombardment mass spectrometry (FAB-MS) and high-performance liquid chromatography using a photodiode-array ultraviolet detector were applied to study a dynorphin-converting endopeptidase from the human pituitary gland. The specificity of the enzyme was tested towards various opioid peptides derived from the prodynorphin precursor, i.e. dynorphin A, dynorphin B and alpha-neoendorphin. Peptide fragments were analysed directly by continuous-flow FAB-MS and those containing aromatic amino acids were detected independently by the photodiode-array ultraviolet detector. The results obtained suggest a similar processing of these structure-related substrates and it appears that the enzyme recognizes the dibasic stretch in their sequence. It is also clear from this study that the combination of the above techniques provides a powerful tool for studies of enzymatic conversion among the prodynorphin-derived peptides and it should be applicable to studies of similar mechanisms in other peptide systems.

Analysis of tyrosine- and methionine-containing neuropeptides by fast atom bombardment mass spectrometry

A simple and unambiguous method for the detection of the amino acids tyrosine and methionine in peptide structures has been developed. The procedure, which was applied in studies of opioid peptides, is based on continuous-flow fast atom bombardment mass spectrometry (CF-FAB-MS) following chemical modification of the residue to be analyzed. Thus, for the detection of tyrosine, modification reactions such as acetylation or non-radioactive iodination were performed prior to analysis by CF-FAB-MS. O-Acetylation of the tyrosine residue with N-acetylimidazole was accompanied by a shift of 42 Da in the molecular mass of the peptide under investigation. This modification was reversed by treatment with hydroxylamine hydrochloride. Incorporation of iodine resulted in a molecular weight shift of 126 Da per iodine atom. Methionine residues were detected in methionine-enkephalin-containing peptides following S-oxidation with hydrogen peroxide. The procedures described may have a wide application in peptide chemistry, particularly for the identification of peptide fragments containing the above residues, e.g. in studies of processing or degradation of the enkephalins or other neuropeptides (e.g. endorphins and tachykinins).

Inhibition of proteases with enkephalin-analogue inhibitors

N-peptidyl-O-acyl hydroxylamines have proven to be effective and selective mechanism-based inhibitors of serine and cysteine proteases as demonstrated using enzymes with specificities for hydrophobic amino acids at the cleavage site. Here, we report for the first time the inhibition of proteases able to accommodate cationic amino acid side chains in their binding pockets using compounds of this inhibitor class. Trypsin and papain are inactivated by enkephalin-analogue diacyl hydroxylamines in a time-dependent and irreversible manner exhibiting second-order rate constants in the range of 100-1000 M-1.s-1. In contrast, human cerebrospinal fluid dynorphin-converting enzyme (hCSFDCE) is inhibited only moderately by these inhibitors. Mechanistic implications have been derived.

Fast atom bombardment mass spectrometric analysis of arginine-containing neuropeptides

A new procedure using fast atom bombardment mass spectrometry for the determination of arginine residues in neuropeptides is described. The technique is based on the modification of the arginine side-group with 1,2-cyclohexanedione. This novel procedure may have a potential use in the study of neuropeptides and their processing and degrading enzymes.

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.

Aminopeptidase in human CSF which degrades delta-sleep inducing peptide (DSIP)

This study describes the purification and characterization of an aminopeptidase from human cerebrospinal fluid capable of degrading delta-sleep-inducing-peptide (DSIP). The enzyme has an apparent molecular weight of approximately 80,000 dalton. It is sensitive towards amastatin, bestatin and EDTA and is optimally active at neutral pH. The recovered enzyme was also found to degrade other neuropeptides, e.g., the enkephalins.

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

Opioid and tachykinin neuropeptides, which were derived from two biological sources (intact, and released from their corresponding precursors by the action of human cerebrospinal fluid (CSF) neuropeptidases), were characterized in human CSF by using a combination of post-high-performance liquid chromatographic (HPLC) detection techniques. Peptides were separated using gradient and isocratic reversed-phase HPLC. Radioimmunoassay measured immunoreactivity corresponding to several different individual neuropeptides including methionine enkephalin, leucine enkephalin, substance P and beta-endorphin. Commercial enzymes (trypsin, carboxypeptidase B) were used to release methionine- and leucine-enkephalin from precursors. Human CSF also served as a source of endogenous neuropeptidases. Mass spectrometry produced fragment ions that corroborated the amino acid sequence of methionine enkephalin and of substance P derived from both sources (intact, from precursors). These results demonstrated the presence of endogenous intact neuropeptides, several different neuropeptide-containing precursors and appropriate precursor-processing enzymes in human CSF for precursors of methionine enkephalin, leucine enkephalin, beta-endorphin1-31 and substance P.

Determination of leucine enkephalin and methionine enkephalin in equine cerebrospinal fluid by microbore high-performance liquid chromatography and capillary zone electrophoresis coupled to tandem mass spectrometry

The performance of microbore high-performance liquid chromatography and capillary zone electrophoresis, both equipped with on-line tandem mass spectrometric detection capability, was evaluated critically for the determination of endogenous amounts of leucine enkephalin and methionine enkephalin in equine cerebrospinal fluid. Using an identical sample clean-up and enrichment procedure, capillary zone electrophoresis-mass spectrometry is limited in its concentration detection capacity owing to its much smaller injection volume. Leucine enkephalin was identified in post-mortem equine cerebrospinal fluid at the 1-5 ng/ml level by liquid chromatography-mass spectrometry.

Application of high performance liquid chromatography combined with diode-array detection for analysis of proteins and peptides in human cerebrospinal fluid

Different strategies for HPLC separation, including molecular sieving, ion-exchange, and hydrophobic interaction as well as reversed phase chromatography, were used to study molecular components in human cerebrospinal fluid (CSF). The separations were followed by photodiode-array UV detection, which is a recently developed technique allowing a direct and rapid discrimination between peptides and proteins differing in their content of aromatic amino acids. By the various HPLC techniques in conjunction with diode-array detection it was possible to identify and characterize several protein and peptide components present in CSF. The procedure also allowed quantitative analysis of CSF proteins using minute amounts of the fluid.

High-performance liquid chromatography and photodiode-array detection of the human protein HC (human complex-forming glycoprotein heterogeneous in charge), a chromophore-associated protein

Photodiode-array ultraviolet-visible detection has been adapted to our high-performance liquid chromatographic system for the analysis and the characterization of the unknown yellow-brown chromophore associated with the human complex-forming glycoprotein, heterogeneous in charge (Protein HC). By using several post-experiment data processing modes, such as multichromatograms, automatic spectrum analyses or three-dimensional plots, the technique allows a direct verification of purity, quantification, as well as the identification of Protein HC without the necessity for further analytical systems. At least thirteen different shoulders in the absorption spectrum in the visible region between 300 and 480 nm have been identified for urinary Protein HC. However, no chromophore was found to be associated with Protein HC complexed with immunoglobulin A (HC-IgA complex). Comparison of spectra between plasma or urinary protein HC allows one to distinguish spectral differences in its chromophore, at least in the range from 300 to 480 nm. The technique was useful for easy identification of chromophore-containing peptides from the digested Protein HC.

Substance P synthesis by enzymatic fragment condensation using product-directed antibodies as molecular traps

This paper describes the enzyme catalyzed synthesis of the undecapeptide substance P from its non-associated fragments (1-7) and (8-11) or (1-8) and (9-11). The fragment condensation was mediated by the use of product specific antibodies as molecular traps. As catalyst a previously purified endopeptidase was used which specifically hydrolyzes substance P at the Phe7-Phe8 and Phe8-Gly9 bonds. The synthesis was performed in analytical scale and product formation was guided by reversed phase HPLC combined with radioimmunoassay. It appeared that the substance P fragments (1-8) and (9-11) were condensed to a larger extent than (1-7) and (8-11). This observation may well result from the higher affinity of the antibodies observed for substance P (8-11) as compared to that found for the other fragments. Increased concentration of the antibodies also seemed to result in enhanced resynthesis of substance P.