ABSTRACT
OBJECTIVE: Both constitutive and inducible forms of nitric oxide synthase exist in endothelial cells. Disorders that produce acute lung injury frequently release endotoxin and cytoknes, such as interferon(IFNgamma) and tumor necrosis factor (TNFalpha). Endotoxin and these cytokines likely act as important mediators of cell injury. Because nitric oxide (NO) avidly reacts with iron, it may affect the activity of key enzymes, such as mitochondrial aconitase, which contain an iron-sulfur structure as a prosthetic group. METHOD: We studied the effect of IFNgamma, TNFalpha and E. coli lipopolysaccharide(LPS) on NO production and mitochondrial aconitase activity in cultured rat lung microvascular endothelial cells(RLMVC). RESULT: Exposing RLMVC for 24 hours to IFNgamma(500 U/mL), TNFalpha(300 U/mL) and LPS(5 microgram/mL) significantly increases nitrite production to 20+/-1 micrometer compared to 0.07 micrometer in control cells(P<0.05, n=4). Cytokine treatment also reduced mitochondrial aconitase activity from 196+/-8 to 102+/-34 nmole/min/mg of cell protein(P<0.05, n=4). Treatment with the inhibitor of nitric oxide synthase N-monomethyl-L-arginine(NMMA) (0.5 mM) not only significantly blunted the cytokine-mediated increase in nitrite formation (3+/-0.5 micrometer vs 20+/-1 micrometer with cytokines, P<0.05, n=4), but also prevented the cytokine-mediated drop in aconitase activity (161+/- 24 vs. 196+/-8 nmole/min/mg of cell protein, NS). CONCLUSION: Exposing RLMVC to IFNgamma, TNFalpha and E. coli LPS substantially decreases mitochondrial aconitase activity. Nitric oxide appears to mediate this effect. Our results suggest that the excessive production of NO by endothelial cells, in response to cytokines and endotoxin, may inhibit the function of the endothelial cell itself.