title: Alterations in energy/redox metabolism induced by mitochondrial and environmental toxins: a specific role for glucose-6-phosphate-dehydrogenase and the pentose phosphate pathway in paraquat toxicity.
abstract: Parkinson's disease (PD) is a multifactorial disorder with a complex etiology including genetic risk factors, environmental exposures, and aging. While energy failure and oxidative stress have largely been associated with the loss of dopaminergic cells in PD and the toxicity induced by mitochondrial/environmental toxins, very little is known regarding the alterations in energy metabolism associated with mitochondrial dysfunction and their causative role in cell death progression. In this study, we investigated the alterations in the energy/redox-metabolome in dopaminergic cells exposed to environmental/mitochondrial toxins (paraquat, rotenone, 1-methyl-4-phenylpyridinium [MPP+], and 6-hydroxydopamine [6-OHDA]) in order to identify common and/or different mechanisms of toxicity. A combined metabolomics approach using nuclear magnetic resonance (NMR) and direct-infusion electrospray ionization mass spectrometry (DI-ESI-MS) was used to identify unique metabolic profile changes in response to these neurotoxins. Paraquat exposure induced the most profound alterations in the pentose phosphate pathway (PPP) metabolome. 13C-glucose flux analysis corroborated that PPP metabolites such as glucose-6-phosphate, fructose-6-phosphate, glucono-1,5-lactone, and erythrose-4-phosphate were increased by paraquat treatment, which was paralleled by inhibition of glycolysis and the TCA cycle. Proteomic analysis also found an increase in the expression of glucose-6-phosphate dehydrogenase (G6PD), which supplies reducing equivalents by regenerating nicotinamide adenine dinucleotide phosphate (NADPH) levels. Overexpression of G6PD selectively increased paraquat toxicity, while its inhibition with 6-aminonicotinamide inhibited paraquat-induced oxidative stress and cell death. These results suggest that paraquat "hijacks" the PPP to increase NADPH reducing equivalents and stimulate paraquat redox cycling, oxidative stress, and cell death. Our study clearly demonstrates that alterations in energy metabolism, which are specific for distinct mitochondiral/environmental toxins, are not bystanders to energy failure but also contribute significant to cell death progression.
authors.affiliation: Departments of †Chemistry and ‡Biochemistry, §Redox Biology Center, and ∥School of Veterinary Medicine and Biomedical Sciences, University of Nebraska-Lincoln , Lincoln, Nebraska 68588, United States.
authors.forename: Shulei
authors.initials: S
authors.lastname: Lei
authors.forename: Laura
authors.initials: L
authors.lastname: Zavala-Flores
authors.forename: Aracely
authors.initials: A
authors.lastname: Garcia-Garcia
authors.forename: Renu
authors.initials: R
authors.lastname: Nandakumar
authors.forename: Yuting
authors.initials: Y
authors.lastname: Huang
authors.forename: Nandakumar
authors.initials: N
authors.lastname: Madayiputhiya
authors.forename: Robert C
authors.initials: RC
authors.lastname: Stanton
authors.forename: Eric D
authors.initials: ED
authors.lastname: Dodds
authors.forename: Robert
authors.initials: R
authors.lastname: Powers
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Franco
mesh_terms: D015655:1-Methyl-4-phenylpyridinium / Q000633:toxicity; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor / Q000187:drug effects; D004298:Dopamine / Q000378:metabolism; D004734:Energy Metabolism / Q000187:drug effects*; D004785:Environmental Pollutants / Q000633:toxicity*; D005260:Female; D005954:Glucosephosphate Dehydrogenase / Q000378:metabolism*; D006019:Glycolysis / Q000187:drug effects; D006540:Herbicides / Q000633:toxicity; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D055442:Metabolome / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D010084:Oxidation-Reduction; D016627:Oxidopamine / Q000633:toxicity; D010269:Paraquat / Q000633:toxicity*; D010427:Pentose Phosphate Pathway / Q000187:drug effects*; D012402:Rotenone / Q000633:toxicity; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D004785:Environmental Pollutants; D006540:Herbicides; D012402:Rotenone; D016627:Oxidopamine; D005954:Glucosephosphate Dehydrogenase; D010269:Paraquat; D015655:1-Methyl-4-phenylpyridinium; D004298:Dopamine