The redox pathway ofS-nitrosoglutathione, glutathione and nitric oxide in cell to neuron communications

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Abstract
Recent results demonstrated that S-nitrosoglutathione (GSNO) and nitric oxide (·NO) protect brain dopamine neurons from hydroxyl radical (·OH)-induced oxidative stress in vivo because they are potent antioxidants. GSNO and ·NO terminate oxidant stress in the brain by (i) inhibiting iron-stimulated hydroxyl radicals formation or the Fenton reaction, (ii) terminating lipid peroxidation, (iii) augmenting the antioxidative potency of glutathione (GSH), (iv) mediating neuroprotective action of brain-derived neurotrophin (BDNF), and (v) inhibiting cysteinyl proteases. In fact, GSNO — S-nitrosylated GSH — is approximately 100 times more potent than the classical antioxidant GSH. In addition, S-nitrosylation of cysteine residues by GSNO inactivates caspase-3 and HIV-1 protease, and prevents apoptosis and neurotoxicity. GSNO-induced antiplatelet aggregation is also mediated by S-nitrosylation of clotting factor XIII. Thus the elucidation of chemical reactions involved in this GSNO pathway (GSH → GS· + ·NO → [GSNO] → GSSG + ·NO → GSH) is necessary for understanding the biology of ·NO, especially its beneficial antioxidative and neuroprotective effects in the CNS. GSNO is most likely generated in the endothelial and astroglial cells during oxidative stress because these cells contain mM GSH and nitric oxide synthase. Furthermore, the transfer of GSH and ·NO to neurons via this GSNO pathway may facilitate cell to neuron communications, including not only the activation of guanylyl cyclase, but also the nitrosylation of iron complexes, iron containing enzymes, and cysteinyl proteases. GSNO annihilates free radicals and promotes neuroprotection via its c-GMP-independent nitrosylation actions. This putative pathway of GSNO/GSH/·NO may provide new molecular insights for the redox cycling of GSH and GSSG in the CNS.