Peptide agonists and antagonists of a novel pathway in neutrophilic inflammation

There is a well established role for the activity of neutrophils in several inflammatory disease states, including chronic obstructive pulmonary disease and acute lung injury. The recruitment of this leukocyte subtype from the bloodstream into peripheral tissue is a multistep process primarily thought to be mediated by the action of chemokines released by macrophages or epithelia. It has recently been shown, however, that a small peptide having the sequence acetyl-proline-glycine-proline (PGP) has activating and chemotactic activity on neutrophils and is generated in vivo in a model of neutrophilic inflammation. In the current work, we confirm the activities of PGP on neutrophils, show that the peptide is active through the CXCR1 and CXCR2 chemokine receptors which are abundant on neutrophils and ligated by chemokines like interleukin-8 (IL-8), and prove that PGP can induce pulmonary neutrophilia when delivered into the lungs. We attribute this activity to structural similarities seen between the PGP peptide and an important binding domain exclusive to these chemokines active on neutrophils. We show that the PGP peptide is generated in vivo in lung during the 24 h following the exposure to aerosolized lipopolysaccharide, a procedure used to induce acute lung injury in experimental animal models. Furthermore, long-term peptide administration can cause pathology in mice that is analogous to that seen in human chronic obstructive pulmonary disease, namely increased alveolar diameter and hypertrophy of the right ventricle of the heart. Using complementary peptide technology and the Molecular Recognition Theory, we have developed a peptide drug, RTR, which has been shown to block the biological effects of PGP and interact with the peptide in solution. We show here that RTR can also suppress neutrophil chemotaxis to CXC ligands like IL-8. Additionally, RTR decreases the neutrophil burden in the lung after exposure to the PGP peptide or LPS, presumably by the blocking of the activities of the small peptides and chemokines which both signal through the CXCR pathway. Finally, in the long term PGP exposure model concurrent RTR treatment prevents the histopathological changes seen when PGP alone is administered.