Lemieux 2011 Abstract Bordeaux

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Lemieux H, Semsroth S, Antretter H, Hoefer D, Gnaiger E (2011) Increased OXPHOS capacity after cold preservation of the human heart – a paradox resolved by a dyscoupling mechanism. MiP2011

Link: http://www.mitophysiology.org

Lemieux H, Semsroth S, Antretter H, Hoefer D, Gnaiger E (2011)

Event: MiP2011

The large apparent excess capacity of the electron transfer-pathway in the human heart provides a scope for compensation of partial dyscoupling between oxidation and phosphorylation. Under these conditions, the increase of respiration in the OXPHOS state at constant ET capacity indicates a mitochondrial dysfunction after cold preservation of human heart tissue, which contrasts to mitochondrial injuries involved in ischemic and dilated cardiomyopathies.


O2k-Network Lab: AT Innsbruck Gnaiger E, CA Edmonton Lemieux H


Labels:

Stress:Ischemia-reperfusion  Organism: Human  Tissue;cell: Heart 

Enzyme: Complex I, Complex II;succinate dehydrogenase, Complex III  Regulation: Substrate  Coupling state: OXPHOS 

HRR: Oxygraph-2k 


Full abstract

Cold storage of the human heart is limited to 3-6 h for organ transplantation. In a rat transplant model, multiple mitochondrial injuries correlate with cardiac dysfunction after cold preservation and transplantation [1]. We addressed the question if cold storage of human cardiac tissue reflects the short organ preservation time and if the resulting mitochondrial pathology is comparable to heart disease.

Tissue samples (right atrial appendage of heart disease patients, HD; left and right ventricle and atrial appendage of explanted hearts of chronic heart failure patients, CHF) were stored in cardioplegic solution (Custodiol®) on ice from 1 to 150 h. Substrate-uncoupler-inhibitor-titration (SUIT) protocols were applied on permeabilized fibres using high-resolution respirometry (Oroboros O2k; 37 °C) for functional mitochondrial diagnosis. Replicate measurements (n=5 to 24) were made per time point in a high-throughput approach (10 chambers). Each measurement consisted of sequential SUIT-induced coupling and substrate control states. Tissue-specific respiratory flux was expressed per wet weight [pmol O2∙s-1∙mg-1] (+-SE) and as flux control ratios by internal normalization for oxygen flux in a reference state [2].

OXPHOS capacity (saturating [ADP]) with Complex I-related substrates (CI; pyruvate+malate; 36 +- 2 pmol∙s-1∙mg-1), and ET-pathway capacity (ET-pathway; non-coupled state after FCCP titration) with succinate+rotenone (CII; 43 +- 2 pmol∙s-1∙mg-1) and with a physiological substrate cocktail (CI+II; pyruvate+malate+glutamate+succinate; 93 +- 8 pmol∙s-1∙mg-1) were stable up to 9 h cold storage of the right atrial appendage. ET capacity was preserved, but OXPHOS capacity even increased after 16 to 150 h cold storage.

The increase of OXPHOS capacity upon cold preservation was unexpected. It is a paradigm of bioenergetics to view an increase of OXPHOS capacity as a positive response, for instance induced by physical exercise. In line with this paradigm, OXPHOS and ET capacities of cardiac mitochondria of CHF patients were significantly decreased, with a specific decline of CI-linked respiration and fatty acid oxidation capacity.

OXPHOS capacity of the healthy human heart was strongly limited by the phosphorylation system, as shown by the two-fold increase of CI- or CI+II-linked respiration upon uncoupler titration of ADP-stimulated mitochondria. The uncoupler titration induces a transition from the partially coupled OXPHOS state (P) to the non-coupled ET state (E). The correspondingly low P/E flux ratio (CI) was 0.48 +- 0.03 in healthy controls, and declined further to 0.42 +- 0.01 and 0.41 +- 0.02 in HD and CHF patients. This indicated a specific defect of the phosphorylation system, while coupling of OXPHOS was preserved. Cold storage beyond 12 hours, however, induced significant uncoupling (dyscoupling), as shown by an increase of CI-linked LEAK respiration (L; in the absence of ADP). This dyscoupling remained apparent in the OXPHOS state by an increase of oxygen consumption (increase of OXPHOS capacity) compensating for the increased proton leak or slip, or for increased electron leak or cation cycling. The higher energy demand was not paralleled by increased phosphorylation, but required a larger share of the apparent ET-pathway excess capacity, such that the P/E flux ratio (CI+II) increased from 0.66 to 0.96 after 150 h cold storage, approaching the theoretical maximum of 1.0. Integrity of the outer mitochondrial membrane was maintained for 16 h, but cytochrome c stimulation was significant after 140 h of preservation (2.7±0.9, 2.9±1.9, 3.2±1.8, 3.9±1.3 and 5.6±0.6 % stimulation at 1, 12, 16, 64 and 140 h, respectively).

The large apparent excess capacity of the electron transfer-pathway in the human heart provides a scope for compensation of partial dyscoupling between oxidation and phosphorylation. Under these conditions, the increase of respiration in the OXPHOS state at constant ET capacity indicates a mitochondrial dysfunction after cold preservation of human heart tissue, which contrasts to mitochondrial injuries involved in ischemic and dilated cardiomyopathies.

Supported by the National Sciences and Engineering Research Council (Canada), Fonds Québécois de la Recherche sur la Nature et les Techologies (Quebec, Canada; postdoctoral fellowships to H. Lemieux), Oroboros Instruments (Innsbruck, Austria); contribution to MitoCom Tyrol.

1. Kuznetsov AV, Schneeberger S, Seiler R, Brandacher G, Mark W, Steurer W, Saks V, Usson Y, Margreiter R, Gnaiger E (2004) Mitochondrial defects and heterogeneous cytochrome c release after cardiac cold ischemia and reperfusion. Am. J. Physiol. Heart Circ. Physiol. 286: H1633–H1641.

2. Gnaiger E (2009) Capacity of oxidative phosphorylation in human skeletal muscle. New perspectives of mitochondrial physiology. Int. J. Biochem. Cell Biol. 41: 1837–1845.