Use of Nonspecific Protease Inhibitors in Research: An Underestimated Problem

Substrate-like novel inhibitors of prolyl specific oligo peptidase for neurodegenerative disorders

Prolyl specific oligopeptidase (POP), is one of the highly expressed enzymes in the brain and is a prime target to treat disorders related to the central nervous system. Here, we describe the structure-based design of the tacrine derivatives, selective, and brain-permeable POP inhibitors. These compounds inactivate POP in-vitro specifically and sustainably at very low concentrations (nano molar). Among this series, compound 6b (IC50 = 0.81 ± 0.04 µM) exhibited most potent inhibition. Furthermore, kinetic study revealed that these molecules target active site of POP which is further confirmed by in-silico molecular interaction analysis. The computational docking results indicates that the compounds are well fitted in the active site with high binding score (i.e., > -7 to > -4 kcal/mol) where Trp595, Arg643, Tyr473, and Ser554 plays important role in binding with the active compounds. The molecular dynamic simulation of most active compounds (6a, 6b, 6d, and 6f) displayed higher free energy binding, when compared to the standard drug in MM-PBSA based binding free energy calculation. In addition, the predicted pharmacokinetic profile suggests that these compounds can serve as excellent inhibitors upon additional optimization which makes them prime choice for further investigation.Communicated by Ramaswamy H. Sarma.

The C-terminal cleavage of angiotensin II and III is mediated by prolyl carboxypeptidase in human umbilical vein and aortic endothelial cells

The renin-angiotensin system, with the octapeptide angiotensin II as key player, is important in the renal, cardiac and vascular physiology. Prolyl carboxypeptidase (PRCP), prolyl endopeptidase (PREP) and angiotensin converting enzyme 2 (ACE2) are reported to be involved in the conversion of angiotensin II to angiotensin (1-7). Previous investigations showed that the processing of angiotensin II is cell- and species-specific and little is known about its conversion in human endothelial cells. Therefore, we aimed to investigate the C-terminal processing of angiotensin II and III in comparison to the processing of des-Arg⁹-bradykinin in human endothelial cells. To this end, human umbilical vein and aortic endothelial cells (HUVEC and HAoEC) were incubated with the peptides for different time periods. Mass spectrometry analysis was performed on the supernatants to check for cleavage products. Contribution of PRCP, ACE2 and PREP to the peptide cleavage was evaluated by use of the selective inhibitors compound 8o, DX600 and KYP-2047. The use of these selective inhibitors revealed that the C-terminal cleavage of angiotensin II and III was PRCP-dependent in HUVEC and HAoEC. In contrast, the C-terminal cleavage of des-Arg⁹-bradykinin was PRCP-dependent in HUVEC and PRCP- and ACE2-dependent in HAoEC. With this study, we contribute to a better understanding of the processing of peptides involved in the alternative renin-angiotensin system. We conclude that PRCP is the main enzyme for the C-terminal processing of angiotensin peptides in human umbilical vein and aortic endothelial cells. For the first time the contribution of PRCP was investigated by use of a selective PRCP-inhibitor.