Endotoxin infusion in rats induces apoptotic and survival pathways in hearts

Inflammatory mediators of sepsis induce apoptosis in many cell lines. We tested the hypothesis that lipopolysaccharide (LPS) injection in vivo results in induction of early apoptotic and survival pathways as well as evidence of late-stage apoptosis in the heart. Hearts were collected from control rats and at 6, 12, and 24 h after LPS injection (4 mg/kg). Activation of an apoptotic pathway was identified by a 1,000-fold increase in caspase-3 activity at 24 h (P < 0.05). Confirmation of these results occurred when terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining identified myocardial cells undergoing DNA fragmentation with significant levels at 24 h post-LPS injection. LPS also caused early proapoptotic mRNA (Bax) to increase (16% at 24 h, P < 0.05), whereas the Bax protein initially decreased (35% at 6 h, P < 0.05) and then returned to baseline values by 24 h. Six hours after LPS injection, Bcl-2 (early prosurvival) mRNA levels increased, whereas its protein levels decreased (70%, P < 0.05) and then returned to baseline levels by 24 h. Mitochondrial cytochrome c levels decreased, suggestive of mitochondrial involvement. Thus involvement of proapoptotic and prosurvival pathways in the heart occurs during a septic inflammatory response.