Cystic fibrosis (CF) is a multifactorial disease in which dysfunction of
protease-
antiprotease balance plays a key role. The current CF
therapy relies on dornase α, hypertonic saline, and
antibiotics and does not address the high
neutrophil elastase (NE) activity observed in the lung and sputum of CF patients. Our hypothesis is that variants of
heparin, which potently inhibit NE but are not
anticoagulant, would help restore the
protease-
antiprotease balance in CF. To realize this concept, we studied molecular principles governing the effectiveness of different heparins, especially 2-O,3-O-desulfated
heparin (ODSH), in the presence of sputum components and therapeutic agents. Using sputa from CF patients and an NE activity assay, we found that heparins are ineffective if used in the absence of dornase. This is true even when
mucolytics, such as DTT or
N-acetylcysteine, were used. Computational modeling suggested that ODSH and
DNA compete for binding to an overlapping allosteric site on NE, which reduces the anti-NE potential of ODSH. NE inhibition of both
DNA and ODSH is chain length-dependent, but ODSH chains exhibit higher potency per unit residue length. Likewise, ODSH chains exhibit higher NE inhibition potential compared with
DNA chains in the presence of saline. These studies suggest fundamental differences in
DNA and ODSH recognition and inhibition of NE despite engaging overlapping sites and offer unique insights into molecular principles that could be used in developing
antiprotease agents in the presence of current treatments, such as dornase and hypertonic saline.