Sepsis-induced lung injury in rats increases alveolar epithelial vulnerability to stretch

Objective: Previous in vitro models have shown that cellular deformation causes dose-dependent injury and death in healthy rat alveolar epithelial cells (AECs). We compared the viability of AECs from septic rats with those from nonseptic rats after 1 hr of cyclic equibiaxial stretch. We hypothesized that sepsis would increase stretch-induced cell death. Design: Laboratory investigation. Setting: University research laboratory. Subjects: Thirty-seven male Sprague-Dawley rats weighing 240-260 g. Interventions: Anesthetized rats were subjected to cecal ligation and double puncture (2CLP) or sham laparotomy without cecal ligation or puncture (sham). After 24 or 48 hrs, AECs were isolated, seeded in custom wells, and maintained in culture for 48 hrs before study. AECs were stretched cyclically (15/min) to a 0%, 12%, 25%, or 37% change in surface area (Delta SA) for 1 hr. Cell viability, phenotypic markers, and nuclear factor-KB intracellular localization were assessed using fluorescent immunocytochemistry. Measurements and Main Results: Phase and fluorescent images were evaluated for all studies. Response to stretch was the same at 24 and 48 hrs after 2CLP. Relative to sham, 2CLP significantly increased cell death at 25 and 37% Delta SA (p <.003, analysis of variance). Relative to sham, 2CLP did not alter expression of type I or type 11 phenotypic markers. Nuclear factor-KB within the nuclear compartment was observed after 2CLP in unstretched cells and after 1 hr of cyclic stretch at 37% Delta SA. In sham, nuclear factor-KB within the nuclear compartment was seen only after stretch. Conclusions: AECs isolated from septic rats are more vulnerable to mechanical deformation injury than AECs from nonseptic animals.