Validated multi-component CZE-UV procedure for the quantification of human hemorphin LVV-H7 in plasma stability studies

Hemorphins-From Discovery to Functions and Pharmacology

During the last three decades, a variety of different studies on bioactive peptides that are opioid receptor ligands, have been carried out, with regard to their isolation and identification, as well as their molecular functions in living organisms. Thus, in this review, we would like to summarize the present state-of-the art concerning hemorphins, methodological aspects of their identification, and their potential role as therapeutic agents. We have collected and discussed articles describing hemorphins, from their discovery up until now, thus presenting a very wide spectrum of their characteristic and applications. One of the major assets of the present paper is a combination of analytical and pharmacological aspects of peptides described by a team who participated in the initial research on hemorphins. This review is, in part, focused on the analysis of endogenous opioid peptides in biological samples using advanced techniques, description of the identification of synthetic/endogenous hemorphins, their involvement in pharmacology, learning, pain and other function. Finally, the part regarding hemorphin analogues and their synthesis, has been added.

Development and validation of a capillary electrophoresis tandem mass spectrometry analytical method for the determination of Leu-Val-Val- and Val-Val-hemorphin-7 peptides in cerebrospinal fluid

A CE-tandem MS method was optimised and validated for selective and specific determination of LVV- and VV-hemorphin-7 peptides in cerebrospinal fluid. These two small peptides originate from haemoglobin beta chains. They possess relevant biological activity and recently a potential biomarker role in posterior cranial fossa paediatric brain tumour disease was evidenced. The separation was optimised using formic acid as background electrolyte and a water/methanol mixture, containing 0.1% (v/v) formic acid, as sheath liquid. The two peptides, differing in only one amino acid of the sequence at the N-terminal side were baseline separated in less than 15 min. The method allowed a very reduced and rapid sample pretreatment and was successfully applied to hemorphins determination in patient samples without matrix interferences. The method successfully passed bioanalytical validation showing linearity, accuracy and precision data on cerebrospinal fluid matrix within the acceptable values. The analysis of cerebrospinal fluid of patients affected by different posterior cranial fossa tumour forms confirmed our previous findings showing the absence of hemorphins in the pre-surgical cerebrospinal fluid and their presence in the post-ones and controls. The present method saves costs and time due to capillary electrophoresis miniaturisation and to the absence of chromatographic column and gradient elution and allows numerous injections per sample starting from few microlitres of cerebrospinal fluid.

Kinetic studies on aminopeptidase M-mediated degradation of human hemorphin LVV-H7 and its N-terminally truncated products

The human hemorphin LVV-H7 belongs to the class of micro-opiod receptor-binding peptides, which also exhibits significant affinity to insulin-regulated aminopeptidase (IRAP) thereby affecting IRAP inhibition. The inhibitory potency towards IRAP is of pharmaceutical interest for the treatment of Alzheimer's disease. Consecutive N-terminal cleavage of the first two amino acid residues of LVV-H7 affects a drastic increase of the binding affinity (V-H7) but ultimately leads to its complete abolition after cleavage of the next amino acid residue (H7). Therefore, we investigated LVV-H7 truncation by aminopeptidase M (AP-M) identified as a LVV-H7 degrading enzyme potentially regulating hemorphin activity towards IRAP in vivo. Using a selective quantitative multi-component capillary zone electrophoretic method (CZE-UV), we analyzed the AP-M-mediated subsequent proteolysis of the hemorphins LVV-H7 (L32-F41), VV-H7 (V33-F41), and V-H7 (V34-F41) in vitro. Incubations were carried out with synthetic hemorphins applied as single substrates or in combination. Maximum velocities (V(max)), catalytic constants (turnover numbers, kcat), and specific enzyme activities (EA) were calculated. L32 cleavage from LVV-H7 happens more than two-times faster (kcat: 140 min(-1) +/- 9%, EA: 1.0 U/mg +/- 9%) than V33 cleavage from VV-H7 (kcat: 61 min(-1) +/- 10%, EA: 0.43 U/mg +/- 10%) or V32 deletion from V-H7 (kcat: 62 min(-1) +/- 8%, EA: 0.46 U/mg +/- 8%). In contrast, we showed that H7 (Y35-F41) was neither degraded by porcine AP-M nor did it act as an inhibitor for this enzyme. Determined turnover numbers were in the same dimension as those reported for dynorphin degradation. This is the first time that AP-M-mediated truncation of natural underivatized LVV-H7 and its physiological metabolites was analyzed to determine kinetic parameters useful for understanding hemorphin processing and designing hemorphin-derived drug candidates.

Quantification of angiotensin-converting-enzyme-mediated degradation of human chemerin 145-154 in plasma by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry

Chemerin is a chemoattractive protein acting as a ligand for the G-protein-coupled receptor ChemR23/CMKLR1 and plays an important role in the innate and adaptive immunity. Proteolytic processing of its C terminus is essential for receptor binding and physiological activity. Therefore, we investigated the plasma stability of the decapeptide chemerin 145-154 (P(145)-F(154)) corresponding to the C terminus of the physiologically active chemerin variant E(21)-F(154) from human hemofiltrate. For monitoring concentration-time profiles and degradation products we developed a novel matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry procedure using an internal peptide standard (hemorphin LVV-H7) for quantification. The linear range covers 2.5 orders of magnitude in the lower micromolar concentration range (lower limit of quantification 0.312 microg/ml, 0.25 microM) characterized by satisfactory reproducibility (CV < or =9%), accuracy (< or =10%), ruggedness, and recovery (98%). We found that chemerin 145-154 is C-terminally truncated in human citrate plasma by the cleavage of the penultimate dipeptidyl residue. N-terminal truncation was not observed. In contrast to citrate plasma, no degradation was detected in ethylenediammetetraacetate (EDTA) plasma. We identified angiotensin-converting-enzyme (ACE) to be responsible for C-terminal truncation, which could be completely inhibited by EDTA and captopril. These results are relevant to clarify the natural processing of chemerin and the potential involvement of ACE in mediating the immune response.