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Endothelial cell killing by neutrophils. Synergistic interaction of oxygen products and proteases
J Varani1, I Ginsburg, L Schuger
1Department of Pathology, University of Michigan Medical School, Ann Arbor 48109.
Abstract:
Killing of rat pulmonary artery endothelial cells by activated polymorphonuclear leukocytes (PMNs), as measured at 4 hours, is catalase sensitive, iron dependent, and unaffected by addition of protease inhibitors. If the time course for exposure of endothelial cells to activated PMNs is extended to 18 hours, progressive injury occurs. Endothelial cell injury resulting at 18 hours is partially inhibited by catalase and partially inhibited by soybean trypsin inhibitor. Together, these two inhibitors function synergistically to protect the cells from injury. Exposure of endothelial cells to reagent H2O2 and purified proteolytic enzymes (trypsin, chymotrypsin, elastase, and cathepsin G) mimics the effects of activated PMNs: H2O2 alone is cytotoxic with maximal killing achieved by 4 hours; proteolytic enzymes produce cytotoxicity only at high concentrations and only after prolonged incubation (longer than 8 hours); and, in combination, H2O2 and proteolytic enzymes act synergistically. These data provide compelling evidence that PMN-mediated injury of endothelial cells involves interaction between oxygen products and proteases.
Insights
Activated white blood cells (PMNs) injure lung endothelial cells through a combination of oxygen products and proteases. This interaction causes progressive cell damage over time, highlighting a dual mechanism in inflammatory injury.
Area of Science:
- Cell Biology
- Immunology
- Pulmonary Medicine
Background:
- Pulmonary artery endothelial cells are vital for lung function.
- Activated polymorphonuclear leukocytes (PMNs) can cause endothelial cell injury.
- The precise mechanisms of PMN-induced endothelial cell damage are not fully understood.
Purpose of the Study:
- To investigate the mechanisms of PMN-mediated injury to rat pulmonary artery endothelial cells.
- To determine the roles of oxygen products and proteases in this injury process.
Main Methods:
- Endothelial cells were exposed to activated PMNs for 4 and 18 hours.
- Cell viability was assessed in the presence of catalase and protease inhibitors (soybean trypsin inhibitor).
- The effects of hydrogen peroxide (H2O2) and purified proteases (trypsin, chymotrypsin, elastase, cathepsin G) were evaluated.
Main Results:
- Short-term (4 hours) PMN-induced injury was catalase-sensitive and iron-dependent, unaffected by protease inhibitors.
- Long-term (18 hours) PMN-induced injury was partially inhibited by catalase and soybean trypsin inhibitor, showing synergistic protection.
- H2O2 was cytotoxic within 4 hours, while proteases required prolonged incubation; both acted synergistically with H2O2.
Conclusions:
- PMN-mediated endothelial cell injury involves a synergistic interaction between oxygen products and proteases.
- This dual mechanism contributes to progressive endothelial cell damage in inflammatory conditions.
- Understanding this interaction may inform therapeutic strategies for lung injury.