Effect of heat shock and endotoxin stress on enterocyte viability apoptosis and function varies based on whether the cells are exposed to heat shock or endotoxin first.

BACKGROUND

Stress-gene responses, including the heat shock (HS) response and the acute phase response, are protective mechanisms for cells after exposure to stress. Both responses cannot occur simultaneously, and, in endothelial cells, the sequence of stress-gene expression seems to be a critical factor in whether cellular protection or injury occurs.

OBJECTIVE

To determine if the sequence of stress-gene expression affects cellular protection or injury in epithelial cells.

DESIGN

Randomized controlled in vitro study.

SETTING

University research laboratory.

SUBJECTS

Rat intestinal epithelial cell-6 (IEC-6) cells were grown on 35-mm culture dishes, chamber slides, or in a bicameral system to confluence or until tight junction integrity was established.

INTERVENTIONS

Rat IEC-6 cells were examined for viability, apoptosis, and bacterial translocation (BT) after exposure to 25-micrograms/mL lipopolysaccharide (LPS) for 18 hours to HS (43 degrees C) for 90 minutes, to LPS followed by HS, or to HS followed by LPS.

MAIN OUTCOME MEASURES

The IEC-6 cells were stained for viability and apoptosis using trypan blue and a direct immunoperoxidase detection of digoxigenin-labeled genomic DNA (Apop Tag Plus In Situ Apoptosis Detection Kit, Oncor, Gaithersburg, Md), respectively. Bacterial translocation was measured by culturing the bacteria (ie, Escherichia coli) that crossed the IEC-6 cell monolayer in the bicameral system.

RESULTS

Control cells (medium only) and cells exposed to LPS alone, HS alone, or HS followed by LPS had a viability from 92% to 98%, and the percentage of apoptotic cells ranged from 2.2% to 5.7%. In contrast, IEC-6 cells exposed to LPS followed by HS had a significantly lower viability (83%, P < .05 vs all other groups) and a higher percentage of apoptotic cells (12.2%, P < .01). At 3 hours after challenge with E coli, the LPS-exposed IEC-6 cell monolayers had significantly increased BT vs control monolayers (P < .05), while the IEC-6 cell monolayers exposed to HS followed by LPS had decreased BT (P < .05). Conversely, cells exposed to LPS followed by HS had the highest magnitude of BT (P < .01 vs all other groups).

CONCLUSIONS

These results indicate that preinduction of HS response can diminish LPS-induced cell injury, while induction of HS response after the LPS challenge (ie, the acute phase response) may lead to decreased enterocyte viability, increased apoptosis, and cellular dysfunction as manifested by BT.