| Chronic neutrophilic inflammation is a hallmark of numerous pulmonary diseases. It is commonly associated with declining lung function, collagen turnover, and increased protease activity. Our laboratory has recently published several articles describing a biologically active collagen breakdown product, proline-glycine-proline (PGP) and its more active amino-terminus acetylated form, N-alpha-PGP. PGP acts via classical chemokine receptors CXCR1 and 2 to draw neutrophils (PMNs) into sites of inflammation in what is potentially a feed-forward mechanism of disease. The tri-peptide appears to be a bio-marker in certain clinical diseases like cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). The present work first details PMN proteases and their mechanism of release, with an emphasis on their role in inflammation. A closer examination is taken of a serine protease, prolyl endopeptidase (PE), that performs the final proteolytic cleavage of PGP from collagen fragments. These experiments detail for the first time that PE is present and active in PMNs. In turn demonstrating that neutrophils contain all of the necessary enzymes to take intact collagen and produce PGP, indicating a possible feed-forward mechanism of PMN inflammation. Additionally, another model of chronic neutrophilic inflammation in pulmonary disease, bronchiolitis obliterans syndrome (BOS) is examined to determine if PGP is a potential mediator of aspects of this condition. Indeed, it appears that at the time of diagnosis of BOS, or chronic rejection of lung transplant, there is an increase in the both the proteases responsible for its production, and PGP itself. Moreover, there is a shift from the traditional PMN chemokine, interleukin-8 (IL-8) to PGP playing the more prominent role in neutrophil migration. Finally, we describe an extremely novel concept of a dual PE inhibitor and CXCR antagonist activity residing in a single compound, benzyloxycarbonyl-proline-prolinal (ZPP). We show that ZPP is capable of blocking both PE activity and generation of PGP, but also CXCR mediated PMN recruitment and directly competes with IL-8 for binding. This work advances the concept of a self sustaining mechanism of chronic neutrophilic inflammation and introduces a novel concept for potential therapeutics directed at blunting the condition. |
