In vitro degradation of the antimicrobial human peptide HEM-γ 130-146 in plasma analyzed by a validated quantitative LC-MS/MS procedure

In stability studies during preclinical drug development, the human antimicrobial peptide hHEM-γ 130-146 shows progressive N-terminal degradation in plasma. To determine this effect, we developed and validated a selective and quantitative μHPLC-MS/MS procedure for this compound. Following deproteinization by precipitation, reversed-phase separation is performed with a time-saving two-column design online coupled to an ion trap mass spectrometer for electrospray ionization MS detection. Using a linear calibration curve obtained with synthetic external standards ranging nearly two orders of magnitude, we achieved good precision (repeatability and reproducibility: 5-15%), accuracy (−3 to 15%), and ruggedness with a lower limit of quantification at 0.29 μg/ml plasma (0.15 μM). Because of good linearity (r2 > 0.999), the recovery (84 ± 3%) and ion suppression (86 ± 4% remaining intensity) were calculated from specifically prepared calibration curves. The developed procedure was applied to human and animal plasma samples. Incubations in the presence and absence of proteinase inhibitors revealed at least an aminopeptidase M activity for the initial N-terminal truncation of tryptophan (W130) and a putative glutaminyl-peptide cyclotransferase activity for the resulting intermediate starting with the bared glutamine residue (Q131). The calculated periods of half-change demonstrated exceeding interspecies variations, whereas the intraspecies variations were only between 20 and 30%. The current procedure is valuable as a generic method for pharmaceutical purposes, and data give important information for further development toward a potential natural drug candidate.