Anthony L. Fitzhugh

Diazeniumdiolates:: Pro- and antioxidant applications of the “NONOates”

Diazeniumdiolates are compounds containing the X-[N(O)NO](-) structural unit that as a class offer many advantages as tools for probing the roles of nitric oxide (NO) in biological redox processes. Available examples in which X is a secondary amine group spontaneously generate up to two molecules of NO per [N(O)NO](-) unit when dissolved in aqueous media; their half-lives range from 2 s (for X = L-prolyl) to 20 h [for X = (H(2)NCH(2)CH(2))(2)N] at pH 7. 4 and 37 degrees C, and are in general relatively little influenced by medium effects or metabolism. When X = O(-) (Angelis salt), first-order dissociation produces NO(-) rather than NO, but the ion becomes an NO source on 1-electron oxidation; diazeniumdiolate-derived NO can also be used to generate reactive nitrogen/oxygen species with higher nitrogen oxidation states (+3 and +4) in the presence of selected oxidizing agents. The advantages of diazeniumdiolates in biomedical research are briefly illustrated with examples from the recent literature probing NOs role in inhibiting oxidative drug metabolism, radical-induced lipid oxidation, the cytotoxicity of reactive oxygen species, and ischemia-induced vascular reoxygenation injury. Future work with this compound class should provide further insight into the mechanisms of NOs involvement in pro- and antioxidant processes, and may well lead to important medicinal advances, including reversal of cerebral vasospasm and radiosensitization of hypoxic tumors.

l-Tyrosine and nitric oxide synergize to prevent cytotoxic effects of superoxide

We found previously that the nitric oxide donor DEA/NO enhanced lipid peroxidation, DNA fragmentation, and cytotoxicity in human bronchial epithelial cells (BEAS-2B) when they were cultured in LHC-8 medium containing the superoxide-generating system hypoxanthine/xanthine oxidase (HX/XO). We have now discovered that DEA/NOs prooxidant action can be reversed by raising the L-tyrosine concentration from 30 to 400 microM. DEA/NO also protected the cells when they were cultured in Dulbeccos Modified Eagles Medium (DMEM), whose standard concentration of L-tyrosine is 400 microM. Similar trends were seen with the colon adenoma cell line CaCo-2. Since HPLC analysis of cell-free DMEM or LHC-8 containing 400 microM L-tyrosine, DEA/NO, and HX/XO revealed no evidence of L-tyrosine nitration, our data suggest the existence of an as-yet uncharacterized mechanism by which L-tyrosine can influence the biochemical and toxicological effects of reactive nitrogen species.

Diazeniumdiolates (Formerly NONOates) in Cardiovascular Research and Potential Clinical Applications

Nitric oxide (NO·) is a crucial messenger in biological systems. This simple diatomic molecule functions as an important protective, regulatory, and signaling agent involved in homeostatic regulation of blood pressure and platelet aggregation, neurotransmission, and immune response (1,2). The protective nature of NO· makes this compound an appealing therapeutic target to treat or prevent disorders characterized by NO· deficiency such as vasospasm and thrombosis. In fact, inhaled NO· gas produces selective pulmonary vasodilation and thus can be used to treat disorders such as adult respiratory distress syndrome (3,4). Administration of exogenous NO· by inhalation can be a successful way of reducing pulmonary vascular resistance in children with persistent pulmonary hypertension of the newborn (5,6).