Peroxynitrite Protects Neurons against Nitric Oxide-mediated Apoptosis

Abstract

Peroxynitrite is thought to be a nitric oxide-derived neurotoxic effector molecule involved in the disruption of key energy-related metabolic targets. To assess the consequences of such interference in cellular glucose metabolism and viability, we studied the possible modulatory role played by peroxynitrite in glucose oxidation in neurons and astrocytes in primary culture. Here, we report that peroxynitrite triggered rapid stimulation of pentose phosphate pathway (PPP) activity and the accumulation of NADPH, an essential cofactor for glutathione regeneration. In contrast to peroxynitrite, nitric oxide elicited NADPH depletion, glutathione oxidation, and apoptotic cell death in neurons, but not in astrocytes. These events were noticeably counteracted by pretreatment of neurons with peroxynitrite. In an attempt to elucidate the mechanism responsible for this PPP stimulation and neuroprotection, we found evidence consistent with both exogenous and endogenous peroxynitrite-mediated activation of glucose-6-phosphate dehydrogenase (G6PD), an enzyme that catalyzes the first rate-limiting step in the PPP. Moreover, functional overexpression of the G6PD gene in stably transformed PC12 cells induced NADPH accumulation and offered remarkable resistance against nitric oxide-mediated apoptosis, whereas G6PD gene-targeted antisense inhibition depleted NADPH levels and exacerbated cellular vulnerability. In light of these results, we suggest that G6PD activation represents a novel role for peroxynitrite in neuroprotection against nitric oxidemediated apoptosis.

Linking glycolysis with oxidative stress in neural cells: a regulatory role for nitric oxide

“…Since peroxynitrite is formed spontaneously from NO and O 2 ᭹− [6], it could be surmised that peroxynitrite would be the factor that mediates such NO-derived protective responses. Taken together, the results of García-Nogales et al [44] may provide a clue for understanding the existing controversy concerning the role of NO formation in neuronal death/survival decisions.…”

“…Moreover, incubation of astrocytes with peroxynitrite triggers a rapid activation of PPP and NADPH accumulation [44] through a mechanism involving stimulation of G6PD (glucose-6-phosphate dehydrogenase) activity [44]. Furthermore, pre-treatment of neurons with peroxynitrite completely (although transiently) prevents neuronal death through a mechanism involving GSH regeneration from GSSG [44].…”

Nitrosative Stress, Hypernitrosylation, and Autoimmune Responses to Nitrosylated Proteins: New Pathways in Neuroprogressive Disorders Including Depression and Chronic Fatigue Syndrome

“…Under pathological conditions, ROS and RNS may cause GSH depletion by its oxidation to GSSG [94,95]. In an environment of O&NS, oxidation of NADPH to NAD+ impairs GSH recycling and may cause permanent GSH depletion [96,97]. Excessive O&NS may also deplete GSH by another mechanism, namely via the activation of efflux transporters in the plasma membrane called multidrug resistance-associated proteins (MRAPs) [93,98,99].…”

Mitochondrial dysfunction in glial cells: Implications for neuronal homeostasis and survival

“…Astrocytes contain higher levels of endogenous antioxidants and antioxidant systems that include NADPH and G6PD (glucose-6-phosphate dehydrogenase). Astrocytes’ resistance to oxidative damage is explained by the activation of the antioxidant response via the nuclear factor erythroid-2-related factor 2 (Nrf2) transcription factor (Garcia-Nogales et al 2003; Shih et al 2003). Both neurons and astrocytes can synthesize GSH, but neurons depend on the supply of GSH precursors from astrocytes (Figure 1.3).…”