1. ¹Department of Microbiology and Immunology, State University of Rio de Janeiro, Brazil
2. ²Department of Medical Microbiology, Federal University of Rio de Janeiro, Brazil
3. ³Department of Biochemistry, State University of Rio de Janeiro, Brazil

Correspondence: Maria-Cristina Plotkowski, Department of Microbiology and Immunology, Faculdade de Ciências Médicas - UERJ, Avenida. 28 de Setembro, 87 fundos, 3° andar. 20 551-030, Rio de Janeiro, Brazil. Email: mcplot@uerj.br

Received 13 October 2003; Accepted 23 February 2004; Published online 28 July 2004.

Abstract

We have previously shown that human umbilical vein endothelial cells (HUVEC) can be activated by IFN plus TNF to kill intracellular (IC) Pseudomonas aeruginosa through production of reactive oxygen intermediate, but the cumulative effects of cytokine activation and bacterial infection on host cells has not been extensively addressed. In this study we investigated the fate of IFN plus TNF-activated HUVEC that have harboured IC bacteria for up to 24 h. At 10 h, the endothelial cell killing of P. aeruginosa isolates exceeded 90%. IC bacteria enhanced the expression of inducible nitric oxide synthase (iNOS) and induced overproduction of NO and superoxide by infected HUVEC. P. aeruginosa IC infection also induced a slight decrease in the cellular level of reduced glutathione (GSH). Overproduction of NO correlated with a marked peroxidation of plasma membrane lipids and decline in HUVEC viability. Treatment of cells with the antioxidant -lipoic acid significantly increased the survival of infected cells. Our data suggest that with the failure of adequate scavenger mechanisms, oxidant radicals overproduced in response to bacterial infection were highly toxic to host cells. Therefore, instead of contributing to defence against infectious agents, the upregulation of free radicals production by endothelial cells in response to cytokine activation would be detrimental to the host.