d‐amino acid modification protects N‐Acetyl‐seryl‐aspartyl‐lysyl‐proline from physiological hydroxylation and increases its antifibrotic effects on hepatic fibrosis

Abstract

N‐Acetyl‐seryl‐aspartyl‐lysyl‐proline (Ac‐SDKP) is a critical negative regulator of fibrosis development in the liver. However, its extremely short half‐life in vivo greatly compromises its potential applications. Here, we report an Ac‐SDKP analog peptide with d‐amino acid replacement (Ac‐SDDKDP). The stability of Ac‐SDDKDP and its prevention of liver fibrosis were investigated in vitro and in vivo. The stabilities of Ac‐SDKP and Ac‐SDDKDP exposed to angiotensin‐1‐converting enzyme (ACE) and their half‐lives in rats and human sera were determined by high‐performance liquid chromatography. The inhibitory effects of Ac‐SDKP and Ac‐SDDKDP on the proliferation and activation of hepatic stellate cells (HSC‐T6) were evaluated using the Cell Counting Kit‐8, Western blotting, reverse transcription quantitative polymerase chain reaction, and immunofluorescence assays. Finally, the protective effects of Ac‐SDKP and Ac‐SDDKDP on carbon tetrachloride (CCl4)‐induced liver fibrosis in rats were compared. d‐Amino acid replacement significantly enhanced the stability of the peptide to ACE and prolonged the half‐life of Ac‐SDKP in rats and human sera. The Ac‐SDKP‐mediated inhibition of HSC‐T6 cell proliferation was well preserved, and Ac‐SDDKDP exerted inhibitory effects comparable to Ac‐SDKP on α‐smooth muscle actin (α‐SMA), collagen I and III expression, and phosphorylated‐Smad‐2 expression. After intraperitoneal (i.p.) administration, Ac‐SDDKDP exhibited significantly greater protection than Ac‐SDKP against CCl4‐induced liver fibrosis in rats. The serum alanine aminotransferase, aspartate aminotransferase, albumin, and total protein levels of the Ac‐SDDKDP‐treated rats were significantly lower than those of the Ac‐SDKP‐treated rats. α‐SMA, CD45, and collagen I and III expression, as well as Smad‐2 phosphorylation were significantly attenuated in the livers of the Ac‐SDDKDP‐treated rats compared to those of the Ac‐SDKP‐treated rats. Furthermore, we showed that the Ac‐SDDKDP concentration in the rat liver increased to a physiological level of 60 min after i.p. administration, although i.p. administration of Ac‐SDKP failed to enhance the peptide concentration in the rat liver. Our findings indicate that d‐amino acid replacement is a simple and effective method to enhance the stability of Ac‐SDKP. Ac‐SDDKDP represents potential application of Ac‐SDKP in fibrosis treatment and provides a new potential treatment strategy for liver fibrosis. © 2019 IUBMB Life, 71(9):1302–1312, 2019

A long‐acting isomer of Ac‐SDKP attenuates pulmonary fibrosis through SRPK1‐mediated PI3K/AKT and Smad2 pathway inhibition

“…These findings are in line with our previous observations that Ac-SD D K D P more effectively protects against cardiac fibrosis F I G U R E 4 Legend on next page. and hepatic fibrosis than Ac-SDKP, 25,26 indicating that Ac-SD D K D P is a promising potential candidate for the treatment of fibrotic diseases.…”

“…To develop Ac‐SDKP into a clinically available antifibrotic drug, we modified Ac‐SDKP by replacing L‐isomers of Asp and Lys with D‐isomers to extend its half‐life. Previously, we reported that the Ac‐SDKP analog peptide Ac‐SD D K D P exhibits better resistance to ACE‐mediated degradation and a longer half‐life than Ac‐SKDP in rat and human sera 26 . In the current study, we compared the protective effects of Ac‐SDKP and Ac‐SD D K D P on HFL‐1 cells and a BLM‐induced IPF model and explored the mechanisms underlying the antifibrotic effects of these peptides in an effort to provide a foundation for the clinical treatment of IPF.…”

“…The half‐life of Ac‐SD D K D P in rats is more than 10 times higher than that of Ac‐SDKP. The protective effect of Ac‐SD D K D P in cardiac fibrosis and hepatic fibrosis is more effective than that of Ac‐SDKP 25,26 …”

“…The protective effect of Ac-SD D K D P in cardiac fibrosis and hepatic fibrosis is more effective than that of Ac-SDKP. 25,26 To expand the applications of Ac-SD D K D P and to offer a candidate drug for IPF, the ability of Ac-SD D K D P to inhibit the proliferation and α-SMA and collagen production of HFL-1 s was evaluated in the present study. The antifibrotic activity of Ac-SD D K D P in C57BL/6 mice with bleomycin (BLM)-induced idiopathic pulmonary fibrosis was also evaluated.…”

<p>Synthesis and Identification of a Novel Peptide, Ac-SDK (Biotin) Proline, That Can Elicit Anti-Fibrosis Effects in Rats Suffering from Silicosis</p>

“…Zhuo et al used 125 I-labeled 3-(p-hydroxyphenyl)-propionic acid (Hpp)-Aca-SDKP (a biologically active analog of Ac-SDKP) to detect localization of binding sites for Ac-SDKP receptors in rat cardiac fibroblasts 33 Zhang et al protected Ac-SDKP from physiologic hydroxylation through modification of d-amino acids and enhanced its anti-fibrotic effect upon liver fibrosis. 34 In the present study, to protect its original anti-fibrotic activity, 17 biotin was labeled on the K side-chain of Ac-SDKP to form Ac-B ( Figure 7A). Biotin branches cause steric hindrance, which reduces the efficiency of degradation by ACE-1, thereby increasing the Ac-B concentration in plasma.…”