Oxidative Stress in the Central Nervous System: Monitoring the Metabolic Response using the Pentose Phosphate Pathway

Abstract

We propose that monitoring the activity of the pentose phosphate pathway (PPP) may provide an opportunity to obtain unique information regarding the metabolic response to oxidative stress since glutathione peroxidase activity is coupled, via glutathione reductase, to the PPP enzyme glucoses-phosphate dehydrogenase. PPP activity was quantitated from data obtained from gas chromatography/mass spectrometry analysis of released lactate following metabolic degradation of (1,6-¹³C₂,6,6-²H₂)glucose. The feasibility of this approach for in vitro studies is shown using cultured rat 9L gliosarcoma cells, primary mixed cerebrocortical and primary astrocytic cultures and in vivo using intracerebral microdialysis. Exposure of 9L gliosarcoma cells to increasing concentrations of phenazine methosulfate, diamide and H₂O₂ correlated with increasing stimulation of the PPP, revealing the coupling of the PPP to the glutathione pathway. In all cultured cell types, the activity of the PPP was stimulated in a concentration-dependent fashion by exposure to H₂O₂. In primary mixed and purified astrocytic cultures, PPP activity was stimulated with H₂O₂ from 2.0 to 22.5 and from 5.9 to 66.7%, respectively. H₂O₂-induced neuronal injury was evident before saturation of the PPP occurred. H₂O₂ toxicity was attenuated when neurons were preincubated with the iron chelator, deferoxamine, and did not occur until saturation of the PPP. In vivo measurements of PPP activity in the conscious rat forebrain revealed basal levels of 4.5%, which was stimulated to 16.9 and 35.7% when 1 mM H₂O₂ and 500 µM phenazine methosulfate were added to the perfusion solution, respectively. We conclude that monitoring the activity of the PPP both in vitro and in vivo can provide a unique perspective from which the metabolic response to oxidative stress can be evaluated.

Amyloid-β Aggregates Cause Alterations of Astrocytic Metabolic Phenotype: Impact on Neuronal Viability

“…Nevertheless, astrocytes do not show signs of overt oxidative stress in our conditions, since neither an increase in the intracellular oxidized form of GSH, a change in the total intracellular GSH content, nor a loss of cellular viability could be observed. In contrast, these observations argue in favor of a cellular response mounted against pro-oxidative stimuli to provide sufficient NADPHreducing equivalents (Ben Yoseph et al, 1994;Rahman et al, 2000). Interestingly, we have recently described a similar mechanism following proinflammatory cytokines treatment of astrocytes (Gavillet et al, 2008).…”

Induction of a Futile Embden-Meyerhof-Parnas Pathway in Deinococcus radiodurans by Mn: Possible Role of the Pentose Phosphate Pathway in Cell Survival

“…PPP is essential for cell maintenance (2,4,10,24). The products of PPP, ribose-5-P (R5P), glyceraldehyde-3-P (G3P), and NADPH ϩ , are precursors for all deoxyribonucleotide triphosphates.…”

Rapid clearance of tertiary butyl hydroperoxide by cultured astroglial cells via oxidation of glutathione

“…At least in cell culture experiments, it was demonstrated that astroglial cells protect neurons (Desagher et al, 1996;Langeveld et al, 1995) and oligodendrocytes (Noble et al, 1994) against H 2 O 2 toxicity. Neurons are more vulnerable against damaging compounds such as H 2 O 2 or peroxynitrite than cultured astroglial cells (Ben-Yoseph et al, 1994;Bolanos et al, 1995). One reason for this vulnerability might be that neurons in culture contain glutathione at a lower concentration than astroglial cells (Bolanos et al, 1995).…”

“…As in other cells and tissues, the pentose phosphate pathway (PPP) appears to be the predominant source in brain cells for generation of NADPH, which subsequently is necessary for the regeneration of GSH (Hotta, 1962;Hotta and Seventko, 1968). It was demonstrated in cell cultures that during the detoxification of H 2 O 2 , the PPP was more strongly activated in astroglial cells than in neurons (Ben-Yoseph et al, 1994) and, therefore, GPx appears to exert a key function in the detoxification of H 2 O 2 and peroxides by astroglial cells. At least for the detoxification of H 2 O 2 by cultured astroglial cells it has recently been demonstrated that glutathione is quickly oxidized after application of this compound and that both enzymes, GPx and catalase, are involved in the detoxification of H 2 O 2 by these cells .…”