PSEUDOMONAS PRODUCTS, OXYGEN RADICALS, AND LUNG INJURY

Pseudomonas aeruginosa causes acute and chronic infections of the lung
and other sites resulting in marked tissue damage. Formation of reactive
oxygen species such as superoxide (O2) hydrogen peroxide (H2O2), and
hydroxyl radical (OH) has been increasingly implicated in tissue injury
associated with a wide array of human pathology. OH, generated via the
iron (Fe)-catalyzed reaction of O2 and H2O2, is the most reactive of the
oxygen free radical. Recent work from our laboratory has suggested that
three compounds actively secreted by P. aeruginosa may alone, or in
conjunction with neutrophil (PMN)-derived O2/H2O2, lead to OH generation
and subsequent tissue injury. These P. aeruginosa-derived products are:
pyochelin, a P. aeruginosa siderophore (Fe-chelator) which P. aeruginosa
employs to acquire microenvironmental FE and which we found is an
effective OH catalyst; pseudomonas elastase, aP. aeruginosa protease
which we found cleaves the human Fe-binding protein transferrin to form
new Fe chelates capable of catalyzing OH production; and pyocyanin aP
aeruginosa product which can undergo cell-mediated aerobic redox cycling
which results in the generation of O2 and H2O2. The goal of the work
proposed is to investigate the potential specific aims have been targeted
for study. Aim 1 will assess whether the iron-pyochelin complex,
ferripyochelin (Fe-derived O2 and H2O2 by inducing the generation of OH
near the cell membrane. Aim 2 will determine what oxidant species are
generated during the interaction of Fe-pyochelin with O2/H2O2 what
features of the pyochelin molecule serve to promote its ability to
enhance O2/H2O2-cell injury, and whether a copper-pyochelin enhances
pyocyanin-mediated cytotoxicity by catalyzing OH generation. Aim 4 will
determine if pseudomonas elastase cleavage of transferrin also enhances
O2/H2O mediated injury of pulmonary epithelial and endothelial cells
through OH catalysis. Aim 5 will investigate whether the generation of
oxidants by these P aeruginosa products alters endothelial cell function
a as to further promote tissue injury by: increasing neutrophil adherence
to endothelial cells by modulating the expression of adherence ligands
or platelet activating factor (PAF) on the endothelial cell surface:
decreasing endothelial cell prostacyclin production: or increasing
endothelial cell release of pro-inflammatory cytokines such as TNF an
dIL-1. Thus, these studies will explore novel and previously unexplored
mechanisms whereby P. aeruginosa-derived products could contribute to
lung injury by inducing the production of toxic oxygen species. Such
information could eventually result in the design of new therapeutic
intervention to decrease the morbidity and mortality of infections of the
lung and other organs with P. aeruginosa and related bacterial pathogens.