title: Ascorbic acid prolongs the viability and stability of isolated perfused lungs: A mechanistic study using 31P and hyperpolarized 13C nuclear magnetic resonance.
abstract: Ex vivo lung perfusion (EVLP) has recently shown promise as a means of more accurately gauging the health of lung grafts and improving graft performance post-transplant. However, reperfusion of ischemic lung promotes the depletion of high-energy compounds and a progressive loss of normal mitochondrial function, and it remains unclear how and to what extent the EVLP approach contributes to this metabolic decline. Although ascorbate has been used to mitigate the effects of ischemia-reperfusion injury, the nature of its effects during EVLP are also not clear. To address these uncertainties, this study monitored the energy status of lungs during EVLP and after the administration of ascorbate using (31)P and hyperpolarized (13)C NMR (nuclear magnetic resonance). Our experiments demonstrated that the oxidative phosphorylation capacity and pyruvate dehydrogenase flux of lungs decline during ex vivo perfusion. The addition of ascorbate to the perfusate prolonged lung viability by 80% and increased the hyperpolarized (13)C bicarbonate signal by a factor of 2.7. The effect of ascorbate is apparently due not to its antioxidant quality but rather to its ability to energize cellular respiration given that it increased the lung's energy charge significantly, whereas other antioxidants (glutathione and α-lipoic acid) did not alter energy metabolism. During ascorbate administration, inhibition of mitochondrial complex I with rotenone depressed energy charge and shifted the metabolic state of the lung toward glycolysis; reenergizing the electron transport chain with TMPD (N,N,N',N'-tetramethyl-p-phenylenediamine) recovered metabolic activity. This indicates that ascorbate slows the decline of the ex vivo perfused lung's mitochondrial activity through an independent interaction with the electron transport chain complexes.
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Hoora
authors.initials: H
authors.lastname: Shaghaghi
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Stephen
authors.initials: S
authors.lastname: Kadlecek
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Sarmad
authors.initials: S
authors.lastname: Siddiqui
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Mehrdad
authors.initials: M
authors.lastname: Pourfathi
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Hooman
authors.initials: H
authors.lastname: Hamedani
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Justin
authors.initials: J
authors.lastname: Clapp
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Harrilla
authors.initials: H
authors.lastname: Profka
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, PA 19104, USA. Electronic address: rahim.rizi@uphs.upenn.edu.
authors.forename: Rahim
authors.initials: R
authors.lastname: Rizi
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001205:Ascorbic Acid / Q000494:pharmacology*; D002250:Carbon Radioisotopes / Q000378:metabolism*; D019069:Cell Respiration / Q000187:drug effects; D004734:Energy Metabolism / Q000187:drug effects; D006019:Glycolysis / Q000187:drug effects; D008168:Lung / Q000187:drug effects / Q000502:physiology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008928:Mitochondria / Q000187:drug effects; D010084:Oxidation-Reduction; D010085:Oxidative Phosphorylation / Q000187:drug effects; D010477:Perfusion; D010759:Phosphorus Isotopes / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015427:Reperfusion Injury / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*
chemical_list: D000975:Antioxidants; D002250:Carbon Radioisotopes; D010759:Phosphorus Isotopes; D001205:Ascorbic Acid
keywords: (13)C NMR; (31)P NMR; Ascorbic acid; Energy charge; Ex vivo lung perfusion; Hyperpolarized; Ischemia–reperfusion; Metabolism; Oxidative phosphorylation