Insulin reduces morbidity and mortality among critically ill patients, but the molecular mechanisms of its effect remain unknown. Insulin is a well-known inhibitor of glycogen synthase kinase-3, which may play an important role in systemic inflammation and shock. Here we investigate the role of blood glucose and glycogen synthase kinase-3β inhibition in the protective effect of insulin on the organ injury/dysfunction associated with excessive systemic inflammation.Design:
Prospective, randomized study.Setting:
University-based research laboratory.Subjects:
Eighty-five anesthetized Wistar rats.Interventions:
Rats received Escherichia coli lipopolysaccharide (1 mg/kg) and Staphylococcus aureus peptidoglycan (0.3 mg/kg) or vehicle intravenously. Insulin (1.4 units/kg intravenously) was administered in the absence or presence of continuous glucose administration (4.5 mg/kg/hr intravenously) either prophylactically or therapeutically. The potent and selective glycogen synthase kinase-3β inhibitor TDZD-8 (1 mg/kg intravenously) or vehicle (10% dimethyl sulfoxide) was administered either prophylactically or therapeutically.Measurements and Main Results:
Coadministration of lipopolysaccharide and peptidoglycan resulted in increases in the serum levels of creatinine (indicator of renal dysfunction), alanine aminotransferase, and aspartate aminotransferase (indicators of liver injury) at 6 hrs. Insulin or TDZD-8 similarly attenuated the organ injury/dysfunction caused by lipopolysaccharide and peptidoglycan when given either prophylactically or therapeutically. Continuous glucose administration had no effect on blood glucose levels or organ injury/dysfunction at 6 hrs. Treatment with insulin or TDZD-8 reduced the plasma levels of the proinflammatory cytokine interleukin-1β. In vitro, insulin or TDZD-8 caused similar reductions in the nuclear factor-κB p65 activity and similar increases in the phosphorylation of Ser9 of glycogen synthase kinase-3β.Conclusions:
Therapy with insulin or the potent and selective glycogen synthase kinase-3β inhibitor TDZD-8 reduced the organ injury/dysfunction caused by lipopolysaccharide and peptidoglycan in the rat. We propose that the inhibitory effect of insulin on the activity of glycogen synthase kinase-3β contributes to the protective effect of insulin against the organ injury/dysfunction caused by excessive systemic inflammation independently of any effects on blood glucose.