Comparative in vitro degradation of the human hemorphin LVV‐H7 in mammalian plasma analysed by capillary zone electrophoresis and mass spectrometry

The human hemorphin LVV‐H7 (L 32 VVYPWTQRF 41 ) is a hemoglobin‐β, ‐γ, ‐δ or ‐ε chain derived cationic decapeptide of the µ‐opioid receptor binding family. It exhibits potential pharmacological value relevant, for example, for blood pressure regulation, learning performance and Alzheimer's disease. The regulatory potency is strictly dependent on the length of the amino acid sequence which is sensitive towards proteinases from tissues and plasma. To analyse LVV‐H7 in vitro degradation in mammalian plasma, a novel multi‐component quantitative capillary zone electrophoretic (CZE) procedure was applied, combined with qualitative metabolite profiling by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS). In all types of plasma, LVV‐H7 was N ‐terminally truncated generating four metabolites (M1–M4) with an intact C ‐terminus: M1 (V 33 VYPWTQRF 41 ), M2 (V 34 YPWTQRF 41 ), M3 (Y 35 PWTQRF 41 ) and M4 (W 37 TQRF 41 ). In EDTA plasma these degradation products were detected exclusively, whereas in citrate and heparin plasma four further metabolites appeared resulting from additional C ‐terminal cleavage of the dipeptide R 40 F 41 : M5 (L 32 VVYPWTQ 39 ), M6 (V 33 VYPWTQ 39 ), M7 (V 34 YPWTQ 39 ) and M8 (Y 35 PWTQ 39 ). In the presence of selective proteinase inhibitors aminopeptidase M and angiotensin‐converting enzyme (for N ‐ and C ‐terminal truncation, respectively) were identified as plasma enzymes responsible for hemorphin degradation. Furthermore, striking inter‐mammalian species distinctions were detected revealing strongly differing degradation velocities but similar metabolite patterns. Copyright © 2007 John Wiley & Sons, Ltd.