Effect of acute-phase and heat-shock stress on apoptosis in intestinal epithelial cells (Caco-2)

Objectives: a) To determine if the sequence of exposure of intestinal epithelial cells to heat-shock or acute-phase stimuli would affect whether cellular protection or injury would occur; and b) to determine if the effects of a thermally induced heat-shock response can be mimicked by sodium arsenite, a nonthermal inducer of the heat-shock response. Design: In vitro controlled study. Setting: Institutional laboratories. Subjects: Caco-2 human intestinal cell line. Interventions: Human intestinal epithelial cells (Caco-2) were grown on 35 mm culture dishes, chamber slides, or in a bicameral culture system to confluence or until tight junction integrity was established. The cells were examined for viability, apoptosis, and bacterial translocation after exposure to a series of insults. Measurements and Main Results: Control Caco-2 cells (medium only) and cells exposed to arsenite or to LPS alone had an apoptotic cell rate of 5.7%, 7.9%, and 8.6%, respectively. However, Caco-2 cells exposed to the cytokines IL-1 beta and IL-6 had a significantly higher rate of apoptosis (22.1%, p < .01 vs. other groups). Caco-2 cells exposed to arsenite followed by LPS had 6.7% apoptotic cells, while cells exposed to LPS followed by arsenite had a significantly greater number of apoptotic cells (19.7%, p < .05). In addition, cells exposed to cytokines followed by arsenite had a higher apoptotic rate than cells exposed to arsenite followed by cytokines 128.4% vs. 10.6%, p < .01). Similar results were seen when cell viability was quantitated. At 3 hrs after challenge with Escherichia coli, the cytokine exposed Caco-2 monolayers had a significantly increased rate of bacterial passage across the Caco-2 monolayer than control monolayers (p < .05), while the Caco-2 monolayers exposed to arsenite followed by cytokines or arsenite alone had a decreased rate of bacterial passage (p < .05). Conversely, cells exposed to cytokines or LPS before arsenite had the highest number of bacteria crossing the monolayer (p < .05). Conclusions: These results indicate that preinduction of a heat-shock response (arsenite) can protect against cytokine or LPS-induced apoptosis and enterocyte dysfunction, as manifested by the passage of E, coli across an intact enterocyte monolayer. In contrast, the induction of a heat shock response after exposure to acute-phase response inducers (cytokines and LPS) may result in decreased enterocyte viability, increased apoptosis, and cellular dysfunction.