AY-NH2

AY-NH2 is a selective agonist of PAR4 with EC50 value of 11 μM [1].

Protease-activated receptor-4 (PAR4) is a member of PARs and plays an important role in mediating cellular effects of thrombin through acting G-proteins i, 12/13 (Rho and Ras activation) and q (calcium signaling) [2].

AY-NH2 is a potent PAR4 agonist and has a higher (~10 fold) activity than GYPGKF-NH2. Using rat platelet aggregation assay, it was shown that AY-NH2 had highly platelet aggregation ability than GY-NH2 and GF-NH2 [1]. When tested with platelet-rich plasma harvested from wild-type C57BL6 mice, AY-NH2 treatment exhibited highly agonist activity on PAR4 while had no effect on other PARs [3].

In male Wistar rats model of paw oedema, i.pl. injection of AY-NH2 markedly reduced the nociceptive score in response to both noxious and non-noxious mechanical stimuli, thus inhibiting carrageenan-induced mechanical hyperalgesia and allodynia [4].

References:
[1].  Hollenberg, M.D., et al., Proteinase-activated receptor-4: evaluation of tethered ligand-derived peptides as probes for receptor function and as inflammatory agonists in vivo. Br J Pharmacol, 2004. 143(4): p. 443-54.
[2].  Yu, G., et al., Increased expression of protease-activated receptor 4 and Trefoil factor 2 in human colorectal cancer. PLoS One, 2015. 10(4): p. e0122678.
[3].  Faruqi, T.R., et al., Structure-function analysis of protease-activated receptor 4 tethered ligand peptides. Determinants of specificity and utility in assays of receptor function. J Biol Chem, 2000. 275(26): p. 19728-34.
[4].   Asfaha, S., et al., Protease-activated receptor-4: a novel mechanism of inflammatory pain modulation. Br J Pharmacol, 2007. 150(2): p. 176-85.

Proteinase-activated receptor 4 (PAR4): activation and inhibition of rat platelet aggregation by PAR4-derived peptides.[Pubmed:11405248]

Can J Physiol Pharmacol. 2001 May;79(5):439-42.

We studied the actions of receptor-activating peptide analogues (PAR4APs), modeled on the proteolytically-revealed tethered ligand sequence of murine proteinase-activated receptor-4 (PAR4), in a rat platelet aggregation assay. The PAR4APs GYPGKF-NH2 (GY-NH2) and AYPGKF-NH2 (AY-NH2) were able to cause aggregation with EC50 values of about 40 microM and 15 microM, respectively. The reverse human PAR4 sequence (VQGPYG-NH2, YG-NH2) and the PAR1AP SFLLR-NH2, did not cause aggregation. In contrast, trans-cinnamoyl-YPGKF-NH2 (tcY-NH2) did not cause aggregation but blocked aggregation caused by GY-NH2, AY-NH2, and thrombin without affecting ADP-mediated aggregation. We conclude that in contrast to the PAR1AP, the PAR4APs GY-NH2 and AY-NH2 activate rat platelets via a PAR4-related receptor and that peptide analogues modeled on the PAR4 tethered activating sequence can serve as useful agonist and antagonist probes for assessing the consequence of activating PAR4 either by PAR4APs or thrombin in rat tissue preparations.

Proteinase-activated receptor-4: evaluation of tethered ligand-derived peptides as probes for receptor function and as inflammatory agonists in vivo.[Pubmed:15451771]

Br J Pharmacol. 2004 Oct;143(4):443-54.

1. We evaluated the ability of a number of peptides based on the tethered ligand sequences of human, rat and murine proteinase-activated receptor-4 (PAR(4)), to serve as receptor-activating probes or antagonists for bioassays carried out in vitro and for in vivo models of inflammation. 2. In a rat PAR(4)-dependent platelet aggregation assay, the relative potencies of the active sequences (AYPGKF-NH(2)>GYPGKF-NH(2)>GYPGFK-NH(2)>GFPGKP-NH(2)) were consistent with an activation of PAR(4). 3. In the aggregation assay, the reverse or partial reverse-sequence peptides (VQGPYG-NH(2), YAPGKF-NH(2) and FKGPYA-NH(2)) were inactive, while trans-cinnamoyl (Tc)-YPGKF-NH(2), Tc-APGKF-NH(2) and N-palmitoyl-SGRRYGHALR-NH(2) (pepducin P4pal-10) were antagonists. 4. However, in an endothelium-dependent NO-mediated rat aorta (RA) relaxation assay and in a gastric longitudinal muscle (LM) contraction assay, these antagonist peptides were agonists as were most other peptides, with distinct orders of potencies that differed for both the RA and LM assays and from the platelet assay. 5. We conclude that PAR(4)-derived tethered ligand peptide agonists can act at receptors other than PAR(4) and that a judicious choice of ligands is required to probe for PAR(4) function in bioassay systems and in particular for in vivo models. 6. By selecting from these peptides the ones most reliably reflecting PAR(4) activation (AYPGKF-NH(2) as a standard agonist; YAPGKF-NH(2) as a PAR(4)-inactive standard), we were able to establish an inflammatory role for the PAR(4)-activating peptides acting via a non-neurogenic mechanism in a rat paw oedema model.

Structure-function analysis of protease-activated receptor 4 tethered ligand peptides. Determinants of specificity and utility in assays of receptor function.[Pubmed:10779527]

J Biol Chem. 2000 Jun 30;275(26):19728-34.

Thrombin activates protease-activated receptors (PARs) by specific cleavage of their amino-terminal exodomains to unmask a tethered ligand that binds intramolecularly to the body of the receptor to effect transmembrane signaling. Peptides that mimic such ligands are valuable as agonists for probing PAR function, but the tethered ligand peptide for PAR4, GYPGKF, lacks potency and is of limited utility. In a structure-activity analysis of PAR4 peptides, AYPGKF was approximately 10-fold more potent than GYPGKF and, unlike GYPGKF, elicited PAR4-mediated responses comparable in magnitude to those elicited by thrombin. AYPGKF was relatively specific for PAR4 in part due to the tyrosine at position 2; substitution of phenylalanine or p-fluorophenylalanine at this position produced peptides that activated both PAR1 and PAR4. Because human platelets express both PAR1 and PAR4, it might be desirable to inhibit both receptors. Identifying a single agonist for both receptors raises the possibility that a single antagonist for both receptors might be developed. The AYPGKF peptide is a useful new tool for probing PAR4 function. For example, AYPGKF activated and desensitized PAR4 in platelets and, like thrombin, triggered phosphoinositide hydrolysis but not inhibition of adenylyl cyclase in PAR4-expressing cells. The latter shows that, unlike PAR1, PAR4 couples to G(q) and not G(i).

PAR-4 Agonist Peptide, amide (PAR-4-AP; AY-NH2) is a proteinase-activated receptor-4 (PAR-4) agonist, which has no effect on either PAR-1 or PAR-2 and whose effects are blocked by a PAR-4 antagonist.

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