Mechanism of Escherichia coli alpha-hemolysin-induced injury to isolated renal tubular cells.

Alpha-hemolysin (AH) is a 110,000-dalton protein secreted extracellularly by certain Escherichia coli. This protein is an acknowledged virulence factor for E coli and recently has been implicated as an important determinant in the pathogenesis of E coli pyelonephritis. Recombinant engineered strains of E coli were used that varied only in their ability to secrete AH extracellularly. The effect of AH on vital dye exclusion, oxygen consumption rate (QO2) adenosine triphosphate (ATP) levels, superoxide (O2-) and hydrogen peroxide (H2O2) production in preparations of isolated rat cortical renal tubular cells (RTCs) was assessed. Approximately 5-10 pg of AH dramatically stimulated QO2 by nearly 150%. This was associated with a marked increase in production of O2- and H2O2, to 13.9 +/- 1.7 and 13.2 +/- 2.1 nM/mg cell protein, respectively (P less than 0.05), as well as a 38% decrease in cellular ATP. These biochemical effects were all seen after a 30-minute exposure to AH and by 120 minutes were associated with 15.7% +/- 1.1% of RTCs that were unable to exclude vital dye. The effect of AH on QO2 and O2- formation was prevented by pretreatment of RTCs with ouabain, which indicates that the effect of AH on oxygen metabolism is linked to Na-K ATPase activity. However, when ouabain-treated RTCs were exposed to AH, ATP remained depressed despite the inhibition of QO2 and O2- production. In contrast, in ouabain-pretreated RTCs, cell membrane integrity was dramatically protected, because only 2.4% +/- 0.4% of RTCs were not unable to exclude vital dye. Thus, the data demonstrate that E coli AH provokes at least two biochemical events that may be injurious to RTC: increased oxygen intermediates (O2- and H2O2 and ATP depletion. These findings with ouabain suggest that the first mechanism of injury may be a more proximate cause of cell death. Moreover, the data suggest that endogenous production of reactive oxygen molecules may be critical modulators of RTC membrane injury.