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Pseudomonas aeruginosa induces apoptosis in human endothelial cells
E Valente1, M C Assis, I M Alvim
1Department of Microbiology and Immunology, State University of Rio de Janeiro, Rio de Janeiro, Brazil.
Abstract:
Pseudomonas aeruginosa has been shown to enter into human endothelial cells in vitro. To ascertain the effects of bacterial intracellular (IC) infection, endothelial cells were exposed to PAK and PAO-1 strains for 1 h and treated with gentamicin in culture medium for different periods. P. aeruginosa induced a significant production of superoxide and hydrogen peroxide by endothelial cells. Concentrations of IC bacteria were reduced progressively with time and no viable PAO-1 was detected at 24 h after infection. However, IC infection led to killing of 32.2%+/-2.9 and 51.8%+/-3.5 of the cells infected with PAK and PAO-1, respectively, as determined by the MTT assay. By three criteria (transmission electron microscopy, DNA electrophoresis and reactivity with annexin V) infected cells exhibited features of apoptosis. Treatment of infected cells with anti-oxidants (catalase, tocopherol and N -acetyl-L-cysteine) significantly decreased the percentage of cell death. In contrast, treatment with aminoguanidine, an inhibitor of inducible NO synthase, increased significantly the killing of PAO-1 infected cells. Based on these results we speculate that in response to P. aeruginosa infection, endothelial cells increase the production of reactive oxygen intermediates to eliminate IC pathogens, but cells do not resist the oxidative stress and die by apoptosis.
Insights
Pseudomonas aeruginosa infection triggers human endothelial cells to produce reactive oxygen species, leading to cell death via apoptosis. Antioxidants reduce this cell death, while NO synthase inhibition exacerbates it.
Area of Science:
- Microbiology
- Cell Biology
- Pathology
Background:
- Pseudomonas aeruginosa is known to invade human endothelial cells in vitro.
- Understanding the consequences of intracellular bacterial infection is crucial for host defense mechanisms.
Purpose of the Study:
- To investigate the effects of intracellular Pseudomonas aeruginosa infection on human endothelial cells.
- To elucidate the mechanisms of endothelial cell death following P. aeruginosa invasion.
Main Methods:
- Endothelial cells were infected with P. aeruginosa strains (PAK and PAO-1) and treated with gentamicin.
- Bacterial load, cell viability (MTT assay), and apoptosis markers were assessed.
- Effects of antioxidants and inducible nitric oxide synthase (iNOS) inhibitor were evaluated.
Main Results:
- P. aeruginosa infection induced significant production of superoxide and hydrogen peroxide by endothelial cells.
- Intracellular bacterial concentrations decreased over time, with no viable PAO-1 detected at 24 hours.
- Infection led to significant endothelial cell death (32.2%–51.8%) exhibiting features of apoptosis.
- Antioxidant treatment reduced cell death, whereas iNOS inhibition increased it.
Conclusions:
- Endothelial cells attempt to eliminate intracellular P. aeruginosa by producing reactive oxygen intermediates.
- The host cells succumb to oxidative stress, resulting in apoptosis.
- Targeting oxidative stress pathways may offer therapeutic strategies against P. aeruginosa endothelial infections.