Chronic Myocardial Ischemia Leads to Loss of Maximal Oxygen Consumption and Complex I Dysfunction.

BACKGROUND: Cardiomyocytes rely heavily on mitochondrial energy production through oxidative phosphorylation. Chronic myocardial ischemia may cause mitochondrial dysfunction and affect ATP formation. Metabolic changes due to ischemia alters cardiac bioenergetics and hence myocardial function and overall bioenergetic state. Here, we evaluate differences in functional status of respiratory complexes in mitochondrial isolates extracted from left atrial appendage tissue (LAA) from patients undergoing cardiac surgery, with and without chronic ischemia. METHODS: Mitochondrial isolates were extracted from LAA in ischemic coronary artery bypass grafting patients (n = 8) and non-ischemic control patients (n = 6) undergoing other cardiac surgery (valve repair/replacement). Coupling and electron transport chain assays were performed using Seahorse XFe 96 (Agilent Technologies, Santa Clara, CA) analyzer. Oxygen consumption rates were measured to calculate respiration states. RESULTS: Respiratory control rate (RCR) in ischemic patients was significantly lower than control patients (6.17 ± 0.27 vs 7.11 ± 0.31, respectively; p < 0.05). This is the result of minimal, non-significant state 3ADP and state 4O changes in chronic ischemia. Complex I respiration is diminished in ischemic tissue (99.1 ± 14.9 vs 257.8 ± 65.2 in control; p < 0.01). Maximal complex I/II respiration ratio was significantly lower in ischemic patients (58.9% ± 5.5% vs 90.9% ± 8.8%; p < 0.05), a difference that was also seen in complex I/IV ratios (p < 0.05). There was no significant difference in complex II/IV ratios between groups. CONCLUSIONS: Ischemic patients have aberrant mitochondrial function, highlighted by a lowered RCR. All ratios involving complex I were affected, suggesting that the insufficient ATP formation is predominantly due to complex I dysfunction. Complex II and IV respiration may be impaired as well, but to a lesser extent.

Improved metabolism and redox state with a novel preservation solution: implications for donor lungs after cardiac death (DCD).

Lungs donated after cardiac death (DCD) are an underutilized resource for a dwindling donor lung transplant pool. Our study investigates the potential of a novel preservation solution, Somah, to better preserve statically stored DCD lungs, for an extended time period, when compared to low-potassium dextran solution (LPD). We hypothesize that Somah is a metabolically superior organ preservation solution for hypothermic statically stored porcine DCD lungs, possibly improving lung transplant outcomes. Porcine DCD lungs (n = 3 per group) were flushed with and submerged in cold preservation solution. The lungs were stored up to 12 h, and samples were taken from lung tissue and the preservation medium throughout. Metabolomic and redox potential were analyzed using high performance liquid chromatography, mass spectrometry, and RedoxSYS®, comparing substrate and pathway utilization in both preservation solutions. Glutathione reduction was seen in Somah but not in LPD during preservation. Carnitine, carnosine, and n-acetylcarnosine levels were elevated in the Somah medium compared with LPD throughout. Biopsies of Somah exposed lungs demonstrated similar trends after 2 h, up to 12 h. Adenosine gradually decreased in Somah medium over 12 h, but not in LPD. An inversely proportional increase in inosine was found in Somah. Higher oxidative stress levels were measured in LPD. Our study suggests suboptimal metabolic preservation in lungs stored in LPD. LPD had poor antioxidant potential, cytoprotection, and an insufficient redox potential. These findings may have immediate clinical implications for human organs; however, further investigation is needed to evaluate DCD lung preservation in Somah as a viable option for transplant.

Parkinson's Disease Skin Fibroblasts Display Signature Alterations in Growth, Redox Homeostasis, Mitochondrial Function, and Autophagy.

The discovery of biomarkers for Parkinson's disease (PD) is challenging due to the heterogeneous nature of this disorder, and a poor correlation between the underlying pathology and the clinically expressed phenotype. An ideal biomarker would inform on PD-relevant pathological changes via an easily assayed biological characteristic, which reliably tracks clinical symptoms. Human dermal (skin) fibroblasts are accessible peripheral cells that constitute a patient-specific system, which potentially recapitulates the PD chronological and epigenetic aging history. Here, we compared primary skin fibroblasts obtained from individuals diagnosed with late-onset sporadic PD, and healthy age-matched controls. These fibroblasts were studied from fundamental viewpoints of growth and morphology, as well as redox, mitochondrial, and autophagic function. It was observed that fibroblasts from PD subjects had higher growth rates, and appeared distinctly different in terms of morphology and spatial organization in culture, compared to control cells. It was also found that the PD fibroblasts exhibited significantly compromised mitochondrial structure and function when assessed via morphological and oxidative phosphorylation assays. Additionally, a striking increase in baseline macroautophagy levels was seen in cells from PD subjects. Exposure of the skin fibroblasts to physiologically relevant stress, specifically ultraviolet irradiation (UVA), further exaggerated the autophagic dysfunction in the PD cells. Moreover, the PD fibroblasts accumulated higher levels of reactive oxygen species (ROS) coupled with lower cell viability upon UVA treatment. In essence, these studies highlight primary skin fibroblasts as a patient-relevant model that captures fundamental PD molecular mechanisms, and supports their potential utility to develop diagnostic and prognostic biomarkers for the disease.

The Critical Role of Bioenergetics in Donor Cardiac Allograft Preservation.

The traditional philosophy of ex vivo organ preservation has been to limit metabolic activity by storing organs in hypothermic, static conditions. This methodology cannot provide longevity of hearts for more than 4-6 h and is thereby insufficient to expand the number of available organs. Albeit at lower rate, the breakdown of ATP still occurs during hypothermia. Furthermore, cold static preservation does not prevent the permanent damage that occurs upon reperfusion known as ischemia-reperfusion (IR) injury. This damage is caused by increased reactive oxygen species (ROS) production in combination with mitochondrial permeability transition pore (mPTP) opening, highlighting the importance of mitochondria in ischemic storage. There has recently been a major paradigm shift in the field, with emerging research supporting changes in traditional storage approaches. Novel research suggests achieving metabolic homeostasis instead of attempting to limit metabolic activity which reduces IR injury and improves graft preservation. Maintaining high ATP levels and circumventing cold organ storage would be a much more sophisticated standard for organ storage and should be the focus of future research in organ preservation. Given the link between mPTP, Ca2(+), and ROS, managing Ca2(+) influx into the mitochondria during conditioning might be the next critical step towards preventing irreversible IR injury.