Bioactivity of peptide analogs of the neutrophil chemoattractant, N-acetyl-proline-glycine-proline

PURPOSE. The release of N-acetyl-proline-glycine-proline (PGP), a chemoattr actant resulting from direct alkaline hydrolysis of corneal proteins, is be lieved to be the initial trigger for neutrophil invasion into the alkali-in jured cornea. The purpose of this study is twofold: (1) to compare the acti vity of N-acetyl-PGP with the bioactivities of other similar synthetic pept ides in an effort to uncover information about this chemoattractant molecul e, and (2) to test these peptide analogs as potential antagonists of N-acet yl-PGP. METHODS. The polarization assay was used to measure the potential chemotact ic response of human neutrophils to peptides. Bioactivity was expressed as the peptide concentration required to produce 50% neutrophil polarization ( EC50). Antagonist activity was expressed as the peptide concentration requi red to produce 50% inhibition (ID50) of polarization activated by N-acetyl- PGP. RESULTS. peptide bioactivities (EC50) were ranked as follows: APGPR (0.34 m hl) > N-acetyl-PGP (0.5 mM) > N-(PGP)(4)-PGLG (3 mM) = t-Boc-PGP (3 mM) > N -acetyl-PG (3.4 mM) > N-methyl-PGP (15 mM) = PGP (15 mM) > peptides without detectable activity (t-Boc-PGP-OMe, N-acetyl-P, PG, PGG, GP, GG and gb-pro -hyp). Peptides with no detectable bioactivity were tested as potential ant agonists of neutrophil polarization induced by N-acetyl-PGP. Glp-Pro-Hyp in hibited N-acetyl-PGP activation of polarization at 20 mhl (ID50). No other synthetic peptide demonstrated a capacity for inhibition. CONCLUSIONS. The minimum requirement to elicit bioactivity was the presence of PGP alone or derivatives of PG in which the N-terminal proline is block ed. Using this approach, active and inactive mimetic peptides of N-acetyl-P GP were produced. The most active peptide, APGPR, was equal to or slightly greater than N-acetyl-PGP, suggesting that more potent analogs might be des igned. Gly-pro-hyp was the only inactive peptide analog to inhibit the the chemoattractant.