There are a number of therapeutic targets to treat organ fibrosis that are under investigation in preclinical models. There is increasing evidence that stimulation of the angiotensin II type 2 receptor (AT2R) is a novel anti-fibrotic strategy and we have reviewed the published in vivo preclinical data relating to the effects of compound 21 (C21), which is the only nonpeptide AT2R agonist that is currently available for use in chronic preclinical studies. In particular, the differential influence of AT2R on extracellular matrix status in various preclinical fibrotic models is discussed. Collectively, these studies demonstrate that pharmacological AT2R stimulation using C21 decreases organ fibrosis, which has been most studied in the setting of cardiovascular and renal disease. In addition, AT2R-mediated anti-inflammatory effects may contribute to the beneficial AT2R-mediated anti-fibrotic effects seen in preclinical models.

We have previously shown that individual β-amino acid substitution in angiotensin (Ang) II reduced Ang II type 1 receptor (AT1R) but not Ang II type 2 receptor (AT2R)-binding and that the heptapeptide Ang III exhibited greater AT2R:AT1R selectivity than Ang II. Therefore, we hypothesized that β-amino-acid-substituted Ang III peptide analogues would yield highly selective AT2R ligands, which we have tested in binding and functional vascular assays. In competition binding experiments using either AT1R- or AT2R-transfected human embryonic kidney (HEK)-293 cells, novel β-substituted Ang III analogues lacked appreciable AT1R affinity, whereas most compounds could fully displace (125)I-Sar(1)Ile(8) Ang II from AT2R. The rank order of affinity at AT2R was CGP42112 > Ang III > β-Pro(7) Ang III=Ang II > β-Tyr(4) Ang III ≥ PD123319 >> β-Phe(8) Ang III >> β Arg(2) Ang III=β-Val(3) Ang III >> β-Ile(5) Ang III. The novel analogue β-Pro(7) Ang III was the most selective AT2R ligand tested, which was >20,000-fold more selective for AT2R than AT1R. IC50 values at AT2R from binding studies correlated with maximum vasorelaxation in mouse aortic rings. Given that β-Pro(7) Ang III was an AT2R agonist, we compared β-Pro(7) Ang III and native Ang III for their ability to reduce blood pressure in separate groups of conscious spontaneously hypertensive rats. Whereas Ang III alone increased mean arterial pressure (MAP), β-Pro(7) Ang III had no effect. During low-level AT1R blockade, both Ang III and β-Pro(7) Ang III, but not Ang II, lowered MAP (by ∼30 mmHg) at equimolar infusions (150 pmol/kg/min for 4 h) and these depressor effects were abolished by the co-administration of the AT2R antagonist PD123319. Thus, β-Pro(7) Ang III has remarkable AT2R selectivity determined in binding and functional studies and will be a valuable research tool for insight into AT2R function and for future drug development.

β(3)-amino acid based polypeptides offer a unique starting material for the design of self-assembled nanostructures such as fibres and hierarchical dendritic assemblies, due to their well-defined helical geometry in which the peptide side chains align at 120° due to the 3.0-3.1 residue pitch of the helix. In a previous work we have described the head-to-tail self-assembly of N-terminal acetylated β(3)-peptides into infinite helical nanorods that was achieved by designing a bioinspired supramolecular self-assembly motif. Here we describe the effect of consecutively more polar side chains on the self-assembly characteristics of β(3)-tetrapeptides Ac-β (3)Ala-β(3)Leu-β(3)Ile-β(3)Ala (Ac-β(3)[ALIA]), Ac-β(3)Ser-β(3)Leu-β(3)Ile-β(3)Ala (Ac-β(3)[SLIA]) and Ac-β (3)Lys-β (3)Leu-β(3)Ile-β (3)Glu (Ac-β(3)[KLIE]). β(3)-tetrapeptides complete 1 1/3 turns of the helix: thus in the oligomeric form the side chain positions shift 120° with each added monomer, forming a regular periodic pattern along the nanorod. Dynamic light scattering (DLS) measurements confirmed that these peptides self-assemble even in highly polar solvents such as water and DMSO, while diffusion-ordered NMR spectroscopy revealed the presence of a substantial monomeric population. Temperature dependence of the size distribution in DLS measurements suggests a dynamic equilibrium between monomers and oligomers. Solution casting produced distinct fibrillar deposits after evaporating the solvent. In the case of the apolar Ac-β(3)[ALIA] the longitudinal helix morphology gives rise to geometrically defined (∼70°) junctions between fibres, forming a mesh that opens up possibilities for applications e.g. in tissue scaffolding. The deposits of polar Ac-β(3)[SLIA] and Ac-β(3)[KLIE] exhibit fibres in regular parallel alignment over surface areas in the order of 10 μm.

Peptide self-assembly has been exploited to generate a multitude of biomaterials that exhibit biocompatibility due to their similarity to naturally occurring proteins. Previously, we have shown β-tripeptides self-assemble despite containing...