rxp-407 and goralatide

Angiotensin I-converting enzyme (ACE) inhibitors can affect hematopoiesis by several mechanisms including inhibition of angiotensin II formation and increasing plasma concentrations of AcSDKP (acetyl-N-Ser-Asp-Lys-Pro), an ACE substrate and a negative regulator of hematopoiesis. We tested whether ACE inhibition could decrease the hematopoietic toxicity of lethal or sublethal irradiation protocols. In all cases, short treatment with the ACE inhibitor perindopril protected against irradiation-induced death. ACE inhibition accelerated hematopoietic recovery and led to a significant increase in platelet and red cell counts. Pretreatment with perindopril increased bone marrow cellularity and the number of hematopoietic progenitors (granulocyte macrophage colony-forming unit [CFU-GM], erythroid burst-forming unit [BFU-E], and megakaryocyte colony-forming unit [CFU-MK]) from day 7 to 28 after irradiation. Perindopril also increased the number of hematopoietic stem cells with at least a short-term reconstitutive activity in animals that recovered from irradiation. To determine the mechanism of action involved, we evaluated the effects of increasing AcSDKP plasma concentrations and of an angiotensin II type 1 (AT1) receptor antagonist (telmisartan) on radioprotection. We found that the AT1-receptor antagonism mediated similar radioprotection as the ACE inhibitor. These results suggest that ACE inhibitors and AT1-receptor antagonists could be used to decrease the hematopoietic toxicity of irradiation.

Topics: Angiotensin-Converting Enzyme Inhibitors; Animals; Blood Cells; Bone Marrow; Dose-Response Relationship, Radiation; Drug Evaluation, Preclinical; Female; Hematopoiesis; Hematopoietic Stem Cells; Mice; Mice, Inbred C57BL; Oligopeptides; Peptidyl-Dipeptidase A; Perindopril; Phosphinic Acids; Radiation-Protective Agents; Survival Rate; Whole-Body Irradiation

Somatic angiotensin-converting enzyme (ACE) contains two homologous domains, each bearing a functional active site. The in vivo contribution of each active site to the release of angiotensin II (Ang II) and the inactivation of bradykinin (BK) is still unknown. To gain insights into the functional roles of these two active sites, the in vitro and in vivo effects of compounds able to selectively inhibit only one active site of ACE were determined, using radiolabeled Ang I or BK, as physiological substrates of ACE. In vitro studies indicated that a full inhibition of the Ang I and BK cleavage requires a blockade of the two ACE active sites. In contrast, in vivo experiments in mice demonstrated that the selective inhibition of either the N-domain or the C-domain of ACE by these inhibitors prevents the conversion of Ang I to Ang II, while BK protection requires the inhibition of the two ACE active sites. Thus, in vivo, the cleavage of Ang I and BK by ACE appears to obey to different mechanisms. Remarkably, in vivo the conversion of Ang I seems to involve the two active sites of ACE, free of inhibitor. Based on these findings, it might be suggested that the gene duplication of ACE in vertebrates may represent a means for regulating the cleavage of Ang I differently from that of BK.

Topics: Angiotensin I; Angiotensin II; Angiotensin-Converting Enzyme Inhibitors; Animals; Binding Sites; Bradykinin; Dose-Response Relationship, Drug; Drug Stability; Humans; Male; Mice; Mice, Inbred C57BL; Oligopeptides; Peptidyl-Dipeptidase A; Phosphinic Acids; Substrate Specificity

By screening phosphinic peptide libraries, we recently reported the discovery of RXP407 (Ac-Asp-PheY(PO2-CH2)LAla-Ala-NH2), a potent N-domain-selective inhibitor of recombinant human angiotensin-converting enzyme (ACE). Preliminary studies to evaluate the in vivo activity of RXP407 in rat led us to suspect possible differences in the binding property of RXP407 between human and rat ACE. The aim of the present study was thus to determine the potency of RXP407 toward rat and mouse ACEs, as compared to non-recombinant human ACE, and to assess the efficacy of this inhibitor in discriminating between the N- and C-domains of these ACE enzymes. By comparing the ability of RXP407 to block purified somatic and germinal ACE from mice, RXP407 was shown to be a potent N-domain-selective inhibitor of mouse somatic ACE, a behavior similar to that observed with human somatic ACE. In contrast, RXP407 appeared less potent toward purified ACE from rat and furthermore was unable to block ACE activity present in crude rat plasma. This study demonstrated that for further evaluation of the in vivo efficacy of RXP407, mice rather than rats should be used as the animal model. Thus, following the change in the Ac-S-D-K-P plasmatic levels, after i.v. injection of RXP407 to mice, will permit the potency and selectivity of this novel ACE inhibitor to be assessed.

Topics: Angiotensin-Converting Enzyme Inhibitors; Animals; Drug Interactions; Growth Inhibitors; Humans; Hydrolysis; Male; Mice; Oligopeptides; Peptidyl-Dipeptidase A; Phosphinic Acids; Rats; Species Specificity; Testis

The phosphinic peptide RXP 407 has recently been identified as the first potent selective inhibitor of the N-active site (domain) of angiotensin-converting enzyme (ACE) in vitro. The aim of this study was to probe the in vivo efficacy of this new ACE inhibitor and to assess its effect on the metabolism of AcSDKP and angiotensin I. In mice infused with increasing doses of RXP 407 (0.1--30 mg/kg/30 min), plasma concentrations of AcSDKP, a physiological substrate of the N-domain, increased significantly and dose dependently toward a plateau 4 to 6 times the basal levels. RXP 407 significantly and dose dependently inhibited ex vivo plasma ACE N-domain activity, whereas it had no inhibitory activity toward the ACE C-domain. RXP 407 (10 mg/kg) did not inhibit the pressor response to an i.v. angiotensin I bolus injection in mice. In contrast, lisinopril infusion (5 and 10 mg/kg/30 min) affected the metabolism of both AcSDKP and angiotensin I. Thus, RXP 407 is the first ACE inhibitor that might be used to control selectively AcSDKP metabolism with no effect on blood pressure regulation.

Topics: Angiotensin I; Angiotensin-Converting Enzyme Inhibitors; Animals; Blood Pressure; Dose-Response Relationship, Drug; Hydrolysis; Indicators and Reagents; Lisinopril; Male; Mice; Oligopeptides; Peptidyl-Dipeptidase A; Phosphinic Acids; Time Factors