Modulation of mitochondrion-mediated oxidative stress by nitric oxide in human placental trophoblastic cells

Intracellular hydroperoxide generation in cultured human placental trophoblastic cells (HPTCs) was quantitatively monitored in the presence or absence of an NO synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L- NAME, 1 mM), by digital microfluorography with use of carboxydichlorofluorescein, a hydroperoxide-sensitive fluorogenic probe. In the absence of L-NAME, HPTCs displayed a time-dependent gradual elevation of the fluorescence, suggesting the ability to produce oxidants spontaneously. In the presence of L-NAME, however, the fluorescent response in these cells increased further; the oxidative impact elicited by L-NAME treatment for 30 min was equivalent to that induced by application of 230 μM tert-butyl hydroperoxide for 5 min. This oxidative process was completely blocked by rotenone, a reagent that interferes with electron entry into complex I of the mitochondrial respiratory chain. On the other hand, antimycin A, which blocks mitochondria at the distal site of the ubiquinone pool, potentiated the L- NAME-induced oxidative change. These findings suggest that constitutive levels of nitric oxide production contribute to regulation of mitochondrion- derived intracellular oxidant generation in HPTCs.