Insulin prevents oxidant-induced endothelial cell barrier dysfunction via nitric oxide–dependent pathway

BackgroundThe rigorous maintenance of normoglycemia by the administration of insulin is beneficial to critically ill patients. Because insulin induces endothelial nitric oxide (NO) release, and the constitutive release of NO maintains normal microvascular permeability, the authors postulated that insulin would prevent peroxide (H2O2)-induced endothelial barrier dysfunction, an effect dependent on endothelial NO synthase (eNOS) activity.MethodsMurine lung microvascular endothelial cells (LMEC) grown to confluence on 8 μ pore polyethylene filters were exposed to media (control), H2O2 (20 to 500 μmol/L), insulin (1 to 1,000 nmol/L) or insulin (100 nmol/L) + H2O2 (10−4mol/L). Endothelial monolayer permeability was quantitated by measuring the transendothelial electrical resistance at 15-minute intervals for 120 minutes. Other cells were exposed to H2O2 and insulin after pretreatment with a NO scavenger (PTIO), an eNOS inhibitor (L-NIO), or a phosphoinositol-3-kinase inhibitor (LY-294002).ResultsH2O2 caused a concentration- and time-dependent reduction in electrical resistance consistent with an increase in monolayer permeability. This effect was prevented by insulin. Inhibiting NO release (L-NIO, LY-294002) or scavenging NO (PTIO) abolished this protective effect.ConclusionsThese data suggest that insulin may modulate endothelial barrier function during oxidant stress by inducing the release of NO.