Bioactivity of peptide analogs of the neutrophil chemoattractant, N-acetyl-proline-glycine-proline.
OBJECTIVE
The release of N-acetyl-proline-glycine-proline (PGP), a chemoattractant resulting from direct alkaline hydrolysis of corneal proteins, is believed to be the initial trigger for neutrophil invasion into the alkali-injured cornea. The purpose of this study is twofold: (1) to compare the activity of N-acetyl-PGP with the bioactivities of other similar synthetic peptides in an effort to uncover information about this chemoattractant molecule, and (2) to test these peptide analogs as potential antagonists of N-acetyl-PGP.


METHODS
The polarization assay was used to measure the potential chemotactic 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 required to produce 50% inhibition (ID50) of polarization activated by N-acetyl-PGP.


RESULTS
Peptide bioactivities (EC50) were ranked as follows: APGPR (0.34 mM) > 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 gly-pro-hyp). Peptides with no detectable bioactivity were tested as potential antagonists of neutrophil polarization induced by N-acetyl-PGP. Gly-Pro-Hyp inhibited N-acetyl-PGP activation of polarization at 20 mM (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 blocked. Using this approach, active and inactive mimetic peptides of N-acetyl-PGP were produced. The most active peptide, APGPR, was equal to or slightly greater than N-acetyl-PGP, suggesting that more potent analogs might be designed. Gly-pro-hyp was the only inactive peptide analog to inhibit the chemoattractant.
Haddox
J L
JL
The Eye Research Laboratories, Brookwood Medical Center, Birmingham, Alabama, USA.
Pfister
R R
RR
Muccio
D D
DD
Villain
M
M
Sommers
C I
CI
Chaddha
M
M
Anantharamaiah
G M
GM
Brouillette
W J
WJ
DeLucas
L J
LJ
D002630:Chemotactic Factors / Q000138:chemical synthesis / Q000494:pharmacology*; D002634:Chemotaxis, Leukocyte / Q000502:physiology*; D006801:Humans; D018375:Neutrophil Activation / Q000187:drug effects*; D009504:Neutrophils / Q000502:physiology*; D009842:Oligopeptides / Q000138:chemical synthesis / Q000494:pharmacology*; D011392:Proline / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000494:pharmacology; D013329:Structure-Activity Relationship
D002630:Chemotactic Factors; D009842:Oligopeptides; C113164:prolyl-glycyl-proline; D011392:Proline