Granulins are a family of protein growth factors that are involved in cell proliferation. An orthologue of granulin from the human parasitic liver fluke Opisthorchis viverrini, known as Ov-GRN-1, induces angiogenesis and accelerates wound repair. Recombinant Ov-GRN-1 production is complex and poses an obstacle for clinical development. To identify the bioactive region(s) of Ov-GRN-1, four truncated N-terminal analogues were synthesized and characterized structurally using NMR spectroscopy. Peptides that contained only two native disulfide bonds lack the characteristic granulin β-hairpin structure. Remarkably, the introduction of a non-native disulfide bond was critical for formation of β-hairpin structure. Despite this structural difference, both two and three disulfide-bonded peptides drove proliferation of a human cholangiocyte cell line and demonstrated potent wound healing in mice. Peptides derived from Ov-GRN-1 are leads for novel wound healing therapeutics, as they are likely less immunogenic than the full-length protein and more convenient to produce.

Edited by Wolfgang PetiInflammatory bowel diseases (IBDs) are a set of complex and debilitating diseases for which there is no satisfactory treatment. Recent studies have shown that small peptides show promise for reducing inflammation in models of IBD. However, these small peptides are likely to be unstable and rapidly cleared from the circulation, and therefore, if not modified for better stability, represent non-viable drug leads. We hypothesized that improving the stability of these peptides by grafting them into a stable cyclic peptide scaffold may enhance their therapeutic potential. Using this approach, we have designed a novel cyclic peptide that comprises a small bioactive peptide from the annexin A1 protein grafted into a sunflower trypsin inhibitor cyclic scaffold. We used native chemical ligation to synthesize the grafted cyclic peptide. This engineered cyclic peptide maintained the overall fold of the naturally occurring cyclic peptide, was more effective at reducing inflammation in a mouse model of acute colitis than the bioactive peptide alone, and showed enhanced stability in human serum. Our findings suggest that the use of cyclic peptides as structural backbones offers a promising approach for the treatment of IBD and potentially other chronic inflammatory conditions. Inflammatory bowel diseases (IBDs)3 are a set of chronic inflammatory disorders of the gastrointestinal tract; the two major forms are ulcerative colitis and Crohn's disease (1). Although there are several medications on the market for IBD, they generally only provide temporary relief, and 70% of IBD patients require surgical intervention (2). Because the current treatments are not satisfactory, new drug leads are being sought from a range of sources, including small molecules from plants and bioactive regions of larger proteins (3-6).Intriguingly, several small peptides, some comprising only three residues, have been shown to be effective in the treatment of experimental colitis in mice (7-11). One example is a tripeptide (MC-12) derived from annexin A1, a calcium-dependent phospholipid-binding, anti-inflammatory protein (12). Annexin A1 mediates expression of cytokines such as TNF-␣, IL-6, and IL-10. It is required for the inhibition of NF-B activity by anti-inflammatory drugs (13) and has recently been shown to be a potential biomarker of therapeutic efficacy for IBD (14). The N-terminal region of annexin A1 comprising residues 2-26 (Ac2-26) has been well studied (15, 16) and appears to have the same biological effects as the full-length protein (17). Analysis of a series of peptides based on the N-terminal sequence of annexin A1 showed that MC-12 (Ac-Gln-Ala-Trp) was the most potent inhibitor of NF-B activity in SW480 cells (13).Small peptides such as MC-12 are likely to be unstable and not viable drug leads, supported by the finding that high doses (25 mg/kg) of MC-12 were required to elicit an in vivo response in mouse colitis models, and it was more effective when injected compared with oral administration (18). Improving t...

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