Involvement of HSP70 and HO-1 in the protective effects of raloxifene on multiple organ dysfunction syndrome by endotoxemia in ovariectomized rats.

OBJECTIVE: Accumulating evidence demonstrates that raloxifene, a selective estrogen receptor modulator, possesses anti-inflammatory action. This study evaluates the preventive effects of long-term treatment of raloxifene on acute inflammation and multiple organ dysfunction syndrome (MODS) in ovariectomized (OVX) rats with endotoxemia and its underlying mechanism of action.

METHODS: Adult female rats were OVX bilaterally to induce estrogen insufficiency. OVX rats were administered with raloxifene (1 mg/kg, gavage, once daily) for 8 weeks, beginning 1 week after surgery, followed by induction of sepsis via intravenous infusion of lipopolysaccharides (LPS; 30 mg/kg) for 4 hours. LPS-activated RAW 264.7 cells were used to investigate the mechanism of raloxifene.

RESULTS: Ovariectomy amplified the endotoxemia-induced hypotensive effect, MODS, and superoxide anion production in the myocardium. The levels of inducible nitric oxide synthase, high mobility group box 1, and nuclear factor-κB p65 protein increased in OVX rats 6 hours after LPS initiation. Raloxifene mitigated MODS, together with reduced inducible nitric oxide synthase induction and fewer superoxide anions in organs. Raloxifene induced high levels of heat shock protein 70 (HSP70) and heme oxygenase 1 (HO-1), which are associated with an increase in the transcription factor heat shock factor-1 and Nrf-2, respectively. Pretreatment with quercetin, an inhibitor of HSP70, or SnPP, an inhibitor of HO-1, reversed the protective effects of raloxifene in septic OVX rats and LPS-activated macrophages.

CONCLUSIONS: Long-term treatment with raloxifene reduces the severity of sepsis in OVX rats, attributed from up-regulation of HSP70 and HO-1 to exert the antioxidant and anti-inflammatory capacities. These findings provide new insights into bacterial infection during menopause and the molecular mechanism of raloxifene.