Angiotensin-Converting Enzyme N-Terminal Inactivation Alleviates Bleomycin-Induced Lung Injury

Abstract

Bleomycin has potent anti-oncogenic properties for several neoplasms, but drug administration is limited by bleomycin-induced lung fibrosis. Inhibition of the renin-angiotensin system has been suggested to decrease bleomycin toxicity, but the efficacy of such strategies remains uncertain and somewhat contradictory. Our hypothesis is that, besides angiotensin II, other substrates of angiotensin-converting enzyme (ACE), such as the tetrapeptide N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP), play a significant role in controlling fibrosis. We studied bleomycin-induced lung injury in normotensive mice, termed N-KO and C-KO, which have point mutations inactivating either the N- or C-terminal catalytic sites of ACE, respectively. N-KO, but not C-KO mice, have a marked resistance to bleomycin lung injury as assessed by lung histology and hydroxyproline content. To determine the importance of the ACE N-terminal peptide substrate AcSDKP in the resistance to bleomycin injury, N-KO mice were treated with S-17092, a prolyl-oligopeptidase inhibitor that inhibits the formation of AcSDKP. In response to bleomycin injection, S-17092-treated N-KO mice developed lung fibrosis similar to wild-type mice. In contrast, the administration of AcSDKP to wild-type mice reduced lung fibrosis due to bleomycin administration. This study shows that the inactivation of the N-terminal catalytic site of ACE significantly reduced bleomycin-induced lung fibrosis and implicates AcSDKP in the mechanism of protection. These data suggest a possible means to increase tolerance to bleomycin and to treat fibrosing lung diseases.

Preventive and therapeutic effects of thymosin β4 N-terminal fragment Ac-SDKP in the bleomycin model of pulmonary fibrosis

“…Accordingly, Zuo and colleagues showed that Ac-SDKP has anti-fibrotic effects in both early and late stages of renal fibrosis induced by unilateral ureteral obstruction whereas Tβ4 alone has context- and time-dependent effects on renal fibrosis [9]. Furthermore, the current results are in agreement with observations of a previously published study showing that accumulation of endogenous Ac-SDKP in ACE N-terminal catalytic site-KO mice alleviates BLEO-induced lung injury, in particular fibrosis [19]. Similarly, exogenous Ac-SDKP has been shown to inhibit pulmonary fibrosis in rats with SiO2-induced silicosis [10, 11].…”

Increased Angiotensin II–Induced Hypertension and Inflammatory Cytokines in Mice Lacking Angiotensin-Converting Enzyme N Domain Activity

“…To address this, we studied N-KO mice treated with angiotensin II in which POP activity was blocked by daily S-17092 injection, but in which AcSDKP levels were increased by minipump infusion of 1.5 mg/kg/day of peptide, a dose consistent with previous studies. 19 These mice were compared to equivalent N-KO mice treated with angiotensin II and S-17092 but without AcSDKP supplementation (Fig. 6).…”

“…6 We treated N-KO mice with S-17092 using conditions previously shown to reduce plasma AcSDKP levels to WT levels. 19 With POP inhibition, N-KO macrophage production of TNFα in response to LPS was restored to WT levels. Further, POP inhibition reduced the angiotensin II-mediated elevation of blood pressure in N-KO mice to the levels seen in WT mice.…”

Effects of thymosin β4 and its N-terminal fragment Ac-SDKP on TGF-β-treated human lung fibroblasts and in the mouse model of bleomycin-induced lung fibrosis

“…Moreover, using ex vivo human lung fibroblasts treated with TGF-b, we have investigated the properties of Tb4 and the peptide derived from its aminoterminal end, N-acetyl-serylaspartyl-lysyl-proline (Ac-SDKP). Ac-SDKP was implicated in the mechanism of protection from bleomycin-induced lung injury achieved by ACE N-terminal genetic inactivation [9], and it was shown to mediate the antifibrogenic effects of ACE inhibitors on both heart and kidney fibrosis [10,11] and to inhibit pulmonary inflammation and fibrosis in SiO 2 -induced silicosis [12,13].…”