Lipopolysaccharide pretreatment protects against ischemia/reperfusion injury via increase of HSP70 and inhibition of NF-κB

It has been reported that pretreatment of rats with lipopolysaccharide (LPS) increases myocardial functional recovery in ischemia/reperfusion (I/R) hearts. However, the mechanisms by which LPS induces cardioprotection against I/R injury have not been fully elucidated. In this study, we pretreated rats with LPS (1.0 mg/kg) 24 h before they were subjected to I/R injury, and then examined the roles of heat shock protein-70 (HSP70) and nucleus factor-kappa B (NF-kappa B) in LPS-induced cardioprotection. We observed that pretreatment with low-dose LPS resulted in significantly increased levels of HSP70 in the myocardium, which could dramatically inhibit NF-kappa B translocation and reduce degradation of inhibitory kappa B. Inhibition of NF-kappa B, in turn, attenuated release of inflammatory cytokines (tumor necrosis factor-alpha, interleukin (IL)-1 beta, and IL-6) and reduced apoptosis of myocardium and infarct area following I/R injury. Moreover, HSP70 could ameliorate oxidative stress following I/R injury. To further investigate whether increase of HSP70 might be responsible for protection of the myocardium against I/R injury, we co-administered the HSP70 inhibitor, quercetin, with LPS before I/R injury. We found that LPS-induced cardioprotection was attenuated by co-administration with quercetin. Herein, we concluded that increased levels of HSP70 through LPS pretreatment led to inhibition of NF-kappa B activity in the myocardium after I/R injury. Our results indicated that LPS-induced cardioprotection was mediated partly through inhibition of NF-kappa B via increase of HSP70, and LPS pretreatment could provide a means of reducing myocardial I/R injury.