Pseudomonas aeruginosa induces apoptosis in human endothelial cells

Pseudomonas aeruginosa has been shown to enter into human endothelial cells in vitro. To ascertain the effects of bacterial intracellular (IC) infecti on, endothelial cells were exposed to PAK and PAO-1 strains for 1 h and tre ated with gentamicin in culture medium for different periods. P. aeruginosa induced a significant production of superoxide and hydrogen peroxide by en dothelial cells. Concentrations of IC bacteria were reduced progressively w ith time and no viable PAC-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 cell s 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 apoptos is. Treatment of infected cells with anti-oxidants (catalase, tocopherol an d 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 PAC-1 infected cells. Base d on these results we speculate that in response to P. aeruginosa infection , endothelial cells increase the production of reactive oxygen intermediate s to eliminate IC pathogens, but cells do not resist the oxidative stress a nd die by apoptosis. (C) 2000 Academic Press.