Activated protein C protects vascular endothelial cells from apoptosis in malaria and in sepsis

In malaria and sepsis, apoptotic endothelial damage is preventable in vitro by antioxidants and protease inhibitors. Activated protein C, which has anti-apoptotic effects, improves survival in sepsis. Therefore, we studied whether activated protein C prevents endothelial cell apoptosis, induced by serum from patients with malaria or sepsis.

Endothelial cells were incubated with patient sera (Plasmodium falciparum malaria, Escherichia coli sepsis, Staphylococcus aureus sepsis) or culture supernatants of the respective organisms, with or without neutrophils. Activated protein C was used to reduce endothelial cell apoptosis in vitro. The proportion of apoptotic endothelial cells was determined by TUNEL staining.

The apoptosis-inducing effect of patient sera or culture supernatants (P. falciparum, E. coli, S. aureus) on endothelial cells was augmented by neutrophils and reduced by activated protein C in the presence of neutrophils. Pre-incubating either endothelial cells or neutrophils with activated protein C also reduced the endothelial cell apoptosis rate. The pro-apoptotic effect of P. falciparum supernatant was reduced by pan-caspase inhibitor and caspase 8 inhibitor, but not by caspase 9 inhibitor. The pro-apoptotic effect of E. coli and S. aureus supernatants was also reduced by caspase 9 inhibitor.

Activated protein C protects vascular endothelial cells from apoptosis triggered by patient sera or culture supernatants in combination with neutrophils. It seems to act both on neutrophils and on endothelial cells. Activated protein C blocks caspase-8-dependent apoptosis, which accounts for endothelial damage in sepsis and malaria. Therefore, activated protein C might offer clinical benefit not only in sepsis but also in malaria.