Pharmacological implications of the spleen in sepsis

Background

Our previous studies indicated that nicotine attenuated systemic inflammation, and improved survival in both lethal endotoxemia and cecal ligation and puncture [1].

Materials and methods

Here we analyzed the pathophysiological and pharmacological implications of the spleen in experimental sepsis. Acetylcholine and nicotine inhibit the production of TNF and HMGB1 from lipopolysaccharide-treated RAW264.7 macrophage-like cells in a concentration-dependent manner. Nicotine inhibits the production of these cytokine macrophage-like cells through a mechanism dependent on the α₇-nicotine acetylcholine receptor (nAChR). From a physiological perspective, our studies indicate that the spleen has a significant expression of the α₇nAChR. To study the implications of the splenic α₇nAChR in the therapeutic potential of nicotine in sepsis, we analyzed the effects of treatment with nicotine in splenectomized mice. Adult male 8–12-week-old BALB/c mice (25–30 g) were splenectomized and 7 days later subjected to cecal ligation and puncture to induce polymicrobial peritonitis. Control sham animals underwent laparotomy without splenectomy. Administration of nicotine (400 mg/kg, i.p.) or vehicle injection (1 × PBS, i.p.) began 24 hours after surgery, and thereafter twice a day for 3 days. Animals were euthanized after 44 hours for serum cytokine analysis.

Results

Treatment with nicotine improved survival in sham mice but it worsened the survival of splenectomized mice. Nicotine inhibited the production of TNF and HMGB1 from lipopolysaccharide-treated macrophages differentiated from peripheral blood mononuclear cells. However, in vivo, nicotine attenuated serum TNF levels in sham mice but not in splenectomized mice with polymicrobial peritonitis. There were no differences in serum TNF, IL-12, IFNγ or IL-10 levels between vehicle-treated or nicotine-treated splenectomized animals. Unlike systemic TNF, circulating HMGB1 levels correlated with the increased mortality induced by nicotine in splenectomized mice. Treatment with nicotine increased circulating serum HMGB1 levels in splenectomized mice with experimental sepsis.

Conclusion

These results suggest that the spleen has major pharmacological implications for the treatment of sepsis.