Effect of Endogenous Nitric Oxide on Mitochondrial Respiration of Rat Hepatocytes In Vitro and In Vivo

Abstract

Nitric oxide, a highly reactive radical, was recently identified as an intermediate of L-arginine metabolism in mammalian cells. We have shown that nitric oxide synthesis is induced in vitro in cultured hepatocytes by supernatants from activated Kupffer cells or in vivo by injecting rats with nonviable Corynebacterium parvum. In both cases, nitric oxide biosynthesis in hepatocytes was associated with suppression of total protein synthesis. This study attempts to determine the effect of nitric oxide biosynthesis on the activity of specific hepatocytic mitochondrial enzymes and to determine whether inhibition of protein synthesis is caused by suppression of energy metabolism. Exposure of hepatocytes to supernatants from activated Kupffer cells led to a 30% decrease of aconitase (Krebs cycle) and complex I (mitochondrial electron transport chain) activity. Using NG-monomethyl-L-arginine, an inhibitor of nitric oxide synthesis, we demonstrated that the inhibition of mitochondrial aconitase activity was due, in part, to the action of nitric oxide. In contrast, in vivo nitric oxide synthesis of hepatocytes from Corynebacterium parvum-treated animals had no effect on mitochondrial respiration. This suggests that inhibition of protein synthesis by nitric oxide is not likely to be mediated by inhibition of energy metabolism.

Magnetometric Evaluation for the Effects of Silicon Carbide Whiskers on Alveolar Macrophages.

“…Nitric oxide inhibits irreversibly the enzymes for ATP production by mitochondrial respiration 32,33) . Leanderson 34) suggested that nitric oxide is present on the surface of SiC.…”

Thymic Dendritic Cells Express Inducible Nitric Oxide Synthase and Generate Nitric Oxide in Response to Self- and Alloantigens

“…Although mechanisms of NO-mediated apoptosis are still controversial, activation of tumor suppressor protein p53 (70), inhibition of the proteasome (70), impairment of mithocondrial function and energy depletion (71), direct DNA damage by deamination and cross-linking of DNA (72), and activation of caspase cascade (67,68), all have been proposed. Preliminary experiments in our laboratory showing that exposure of DP thymocytes to exogenous NO activates caspases 3 and 6 and particularly caspase 8 (S. Aiello, M. Noris, and G. Remuzzi, unpublished observations) support a role for caspase cascade activation in NO-induced DP thymocyte apoptosis.…”

Does Nitric Oxide Regulate Smooth Muscle Cell Proliferation?

“…The most convincing evidence that growth inhibition of smooth muscle cells by NO is not due to cytotoxicity is the reversibility of inhibition with removal of NO. DNA synthesis and cell growth resume following removal of NO donors [17, 18] and inhibition of smooth muscle cell growth occurs without changes in protein synthesis or mitochondrial respiration [17], two cellular processes shown to be inhibited by NO in other cell types [1, 19]. It is possible that smooth muscle cells have relatively increased resistance to NO cytotoxicity because of their constant exposure to NO from tonic endothelial eNOS activity in vivo.…”

“…NO inhibits protein synthesis and cellular respiration in other cell types [19] and this has been hypothesized [1] as a mechanism of growth inhibition as both these functions are necessary for progression through G1 phase of the cell cycle. Our studies, however, have shown that neither of these functions are inhibited by concentrations of NO donors that inhibit 90% of smooth muscle cell proliferation [17].…”