Probing Angiotensin Converting Enzyme (ACE) Domain-Dependent Inhibition of Onopordia, Isolated from Onopordon acanthium L., Using a Continuous Fluorescent Assay

Background: Somatic ACE is a two-domain protein, C and N which are resulted from gene duplication. Presence of two active sites with particular properties, demonstrates functional significance of each domain. Increased levels of circulating N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), could be the result of ACE N-domain selective inhibition. Moreover, ACE C-domain specific inhibitors are able to inactivate bradykinin and inhibit the conversion of angiotensin I to angiotensin II in order to regulate blood pressure as well as reduced side effect profiles. Methods: The present study was designed to determine ACE domain specificity of the novel ACE inhibitor, onopordia which was recently isolated from Onopordon acanthium L. The ACE inhibition activity was determined using Abz-SDK (Dnp)P-OH and Abz-LFK(Dnp)-OH as ACE domain selective substrates. IC50 values of onopordia determined and compared with those of captopril as the standard. Results: IC50 values of onopordia for ACE N and C- domains were 180 µM and 244 µM respectively which demonstrated approximately similar affinity of the mentioned compound to ACE C and N-domains. A pharmacophore model was further generated based on onopordia interactions with the relevant ACE domain active sites. Conclusion: According to onopordia interactions in the ACE C and N-domain active sits, it is a potential to generate more potent and also specific inhibitor based on this new scaffold by doing accurate adjustments. Therefore, this study provides the molecular basis for further designing ACE inhibitors, which are new therapeutics in combating tissue fibrosis diseases.