Nitric oxide produced in rat liver mitochondria causes oxidative stress and impairment of respiration after transient hypoxia

Nitric oxide (NO) is produced in mam‐ mals by different isoforms of NO synthase (NOS), in‐ cluding the constitutive mitochondrial enzyme (mtNOS). Here we demonstrate that the concentration of NO resulting from a mitochondrial NOS activity increases under hypoxic conditions in isolated rat liver mitochon‐ dria. We show that mitochondrially derived NO medi‐ ates the impairment of active (state 3) respiration as measured in the presence of the substrates glutamate and malate after reoxygenation. Simultaneously, NO induces oxidative stress in mitochondria, characterized by an increase in the amount of protein carbonyls and a decrease in glutathione (GSH). Both the accumulation of oxidative stress markers during and the im‐ paired respiration after reoxygenation were prevented by blocking NO production with the NOS inhibitor L‐NAME. These observations suggest that mitochon‐ dria are exposed to high amounts of NO generated by a mitochondrial NOS upon hypoxia/reoxygenation. Such increased NO levels, in turn, inhibit mitochon‐ drial respiration and may cause oxidative stress that leads to irreversible impairment of mitochondria.— Schild, L., Reinheckel, T., Reiser, M., Horn, T. F. W., Wolf, G., Augustin, W. Nitric oxide produced in rat liver mitochondria causes oxidative stress and impair‐ ment of respiration after transient hypoxia. FASEB J. 17, 2194‐2201 (2003)