title: Disruption of pyridine nucleotide redox status during oxidative challenge at normal and low-glucose states: implications for cellular adenosine triphosphate, mitochondrial respiratory activity, and reducing capacity in colon epithelial cells.
abstract: We recently demonstrated that menadione (MQ), a redox cycling quinone, mediated the loss of mitochondrial glutathione/glutathione disulfide redox balance. In this study, we showed that MQ significantly disrupted cellular pyridine nucleotide (NAD(+)/NADH, NADP(+)/NADPH) redox balance that compromised cellular ATP, mitochondrial respiratory activity, and NADPH-dependent reducing capacity in colonic epithelial cells, a scenario that was exaggerated by low glucose. In the cytosol, MQ induced NAD(+) loss concurrent with increased NADP(+) and NAD kinase activity, but decreased NADPH. In the mitochondria, NADH loss occurred in conjunction with increased nicotinamide nucleotide transhydrogenase activity and NADP(+), and decreased NADPH. These results are consistent with cytosolic NAD(+)-to-NADP(+) and mitochondrial NADH-to-NADPH shifts, but compromised NADPH availability. Thus, despite the sacrifice of NAD(+)/NADH in favor of NADPH generation, steady-state NADPH levels were not maintained during MQ challenge. Impairments of cellular bioenergetics were evidenced by ATP losses and increased mitochondrial O(2) dependence of pyridine nucleotide oxidation-reduction; half-maximal oxidation (P(50)) was 10-fold higher in low glucose, which was lowered by glutamate or succinate supplementation. This exaggerated O(2) dependence is consistent with increased O(2) diversion to nonmitochondrial O(2) consumption by MQ-semiquinone redox cycling secondary to decreased NADPH-dependent MQ detoxication at low glucose, a situation that was corrected by glucose-sparing mitochondrial substrates.
authors.affiliation: Department of Molecular and Cellular Physiology, Louisiana State University, Health Sciences Center, Shreveport, Louisiana, USA.
authors.forename: Magdalena L
authors.initials: ML
authors.lastname: Circu
authors.forename: Ronald E
authors.initials: RE
authors.lastname: Maloney
authors.forename: Tak Yee
authors.initials: TY
authors.lastname: Aw
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D019069:Cell Respiration; D003106:Colon / Q000166:cytology / Q000378:metabolism*; D003593:Cytoplasm / Q000201:enzymology; D057075:Enzyme Assays; D004847:Epithelial Cells / Q000378:metabolism*; D005947:Glucose / Q000172:deficiency / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism; D019803:Glutathione Disulfide / Q000378:metabolism; D019073:HT29 Cells; D006706:Homeostasis; D006801:Humans; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism; D019344:Lactic Acid / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D009243:NAD / Q000378:metabolism*; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D009249:NADP / Q000378:metabolism*; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010101:Oxygen Consumption; D024483:Vitamin K 3 / Q000494:pharmacology
chemical_list: D009243:NAD; D019344:Lactic Acid; D009249:NADP; D024483:Vitamin K 3; D000255:Adenosine Triphosphate; D009247:NADH, NADPH Oxidoreductases; D005978:Glutathione; D005947:Glucose; D019803:Glutathione Disulfide