-Whether the myocardium in non-ischemic heart failure experiences oxygen-limitation remains a lon... more -Whether the myocardium in non-ischemic heart failure experiences oxygen-limitation remains a long-standing controversy. We addressed this question in patients with Dilated Cardiomyopathy (DCM) using a dual approach: First, we tested the changes in myocardial oxygenation between rest and stress states, using oxygenation-sensitive CMR. Secondly, we sought to assess the functional consequences of oxygen limitation at rest by measuring myocardial energetics before and after short-term oxygen supplementation. -Twenty six subjects (14 DCM; 12 normal) underwent cardiac MRI at 3 Tesla to assess cardiac volumes, function, oxygenation and first-pass perfusion (0.03 mmol/kg Gd-DTPA bolus) at stress and rest (4-6 minutes i.v. adenosine, 140μg/kg/min). Signal intensity change (SIΔ) and myocardial perfusion reserve index (MPRI) were measured from oxygenation and perfusion images, respectively. Furthermore, the effect of oxygen supplementation on resting myocardial energy metabolism was tested using (31)P MR spectroscopy, measuring PCr/ATP ratios in both groups at baseline and after 4 hours of oxygen via facemask in the DCM group. During stress there were equivalent rises in rate pressure product in both groups (DCM 76±15%, normal 79±9%, P=0.84). MPRI was significantly reduced in DCM (1.51 ± 0.11 vs. normal 1.86±0.10, P=0.03). However, there was no difference in oxygenation between groups: SI∆ in DCM 17±3% vs. normal 20±2% (P=0.38). Furthermore, at a LV segmental level, there was no correlation between oxygenation-sensitive SI∆ and MPRI (R=0.06, P=0.43). Resting PCr/ATP was reduced in DCM (1.66±0.07 vs normal 2.12±0.06, P=0.002). With oxygen supplementation, there was no change in PCr/ATP (1.61±0.08, P=0.58, Δ-0.04±0.05). There was also no effect of oxygen on systolic function (EF pre oxygen 34±1%, post oxygen 36±2%, P=0.46; Δ 2±1%). -Our results demonstrate dissociation between microvascular dysfunction and oxygenation in DCM, suggesting that the impairment of perfusion is not sufficient to cause deoxygenation during stress. Cardiac energetics are unaffected by oxygen supplementation, indicating the absence of relevant myocardial hypoxia at rest. Our study suggests that novel treatments for non-ischemic heart failure should focus on efforts to directly target cardiomyocyte function and metabolism rather than oxygen delivery and microvascular function.
Hypertrophic cardiomyopathy (HCM) is the commonest cause of sudden cardiac death in the young, wi... more Hypertrophic cardiomyopathy (HCM) is the commonest cause of sudden cardiac death in the young, with an excess of exercise-related deaths. The HCM sarcomere mutations increase the energy cost of contraction and impaired resting cardiac energetics has been documented by measurement of phosphocreatine/ATP (PCr/ATP) using (31)Phosphorus MR Spectroscopy ((31)P MRS). We hypothesized that cardiac energetics are further impaired acutely during exercise in HCM and that this would have important functional consequences. (31)P MRS was performed in 35 HCM patients and 20 age- and gender-matched normal volunteers at rest and during leg exercise with 2.5 kg ankle weights. Peak left-ventricular filling rates (PFRs) and myocardial perfusion reserve (MPRI) were calculated during adenosine stress. Resting PCr/ATP was significantly reduced in HCM (HCM: 1.71 ± 0.35, normal 2.14 ± 0.35 P < 0.0001). During exercise, there was a further reduction in PCr/ATP in HCM (1.56 ± 0.29, P = 0.02 compared with r...
Neuronal glucose uptake was thought to be independent of insulin, being facilitated by glucose tr... more Neuronal glucose uptake was thought to be independent of insulin, being facilitated by glucose transporters GLUT1 and GLUT3, which do not require insulin signaling. However, it is now known that components of the insulin-mediated glucose uptake pathway, including neuronal insulin synthesis and the insulindependent glucose transporter GLUT4, are present in brain tissue, particularly in the hippocampus. There is considerable recent evidence that insulin signaling is crucial to optimal hippocampal function. The physiological basis, however, is not clear. We propose that while noninsulin-dependent GLUT1 and GLUT3 transport is adequate for resting needs, the surge in energy use during sustained cognitive activity requires the additional induction of insulin-signaled GLUT4 transport. We studied hippocampal high-energy phosphate metabolism in eight healthy volunteers, using a lipid infusion protocol to inhibit insulin signaling. Contrary to conventional wisdom, it is now known that free fatty acids do cross the blood-brain barrier in significant amounts. Energy metabolism within the hippocampus was assessed during standardized cognitive activity. 31 Phosphorus magnetic resonance spectroscopy was used to determine the phosphocreatine (PCr)-to-adenosine triphosphate (ATP) ratio. This ratio reflects cellular energy production in relation to concurrent cellular energy expenditure. With lipid infusion, the ratio was significantly reduced during cognitive activity (PCr/ATP 1.0 AE 0.4 compared with 1.4 AE 0.4 before infusion, P = 0.01). Without lipid infusion, there was no reduction in the ratio during cognitive activity (PCr/ ATP 1.5 AE 0.3 compared with 1.4 AE 0.4, P = 0.57). This provides supporting evidence for a physiological role for insulin signaling in facilitating increased neuronal glucose uptake during sustained cognitive activity. Loss of this response, as may occur in type 2 diabetes, would lead to insufficient neuronal energy availability during cognitive activity.
In the current work, we labelled human hematopoietic stem cells with polymeric nanoparticles (NPs... more In the current work, we labelled human hematopoietic stem cells with polymeric nanoparticles (NPs) that can be tracked by Magnetic Resonance Imaging (MRI) and studied their effect on cell metabolism, proliferation, secretomics, genomics and differentiation. We showed that NPs had no effect on the stem cell differentiation program but affected their paracrine activity.
Hypoxia causes left ventricular dysfunction in the human heart, but the biochemical mechanism is ... more Hypoxia causes left ventricular dysfunction in the human heart, but the biochemical mechanism is poorly understood. Here, we tested whether short-term normobaric hypoxia leads to changes in cardiac energetics and early cardiac dysfunction. Healthy male volunteers (n=12, age 24 ± 2 yr) were exposed to normobaric hypoxia in a purpose-built hypoxic chamber. The partial pressure of oxygen during end-tidal expiration (P(ET)o₂) was kept between 50 and 60 mmHg, and peripheral oxygen saturation (Sao₂) was kept above 80%. Cardiac morphology and function were assessed using magnetic resonance imaging and echocardiography, both before and after 20 h of hypoxic exposure, and high-energy phosphate metabolism [measured as the phosphocreatine (PCr)/ATP ratio] was measured using ³¹P magnetic resonance spectroscopy. During hypoxia, P(ET)o₂ and Sao₂ averaged 55 ± 1 mmHg and 83.6 ± 0.4%, respectively. Hypoxia caused a 15% reduction in cardiac PCr/ATP (from 2.0 ± 0.1 to 1.7 ± 0.1, P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.01) and reduced diastolic function (measured as E/E&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;, rising from 6.1 ± 0.4 to 7.5 ± 0.7, P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.01). Normobaric hypoxia causes a rapid decrease in high-energy phosphate metabolism in the human cardiac left ventricle, which may lead to a decline in diastolic function. These findings are important in understanding the response of normal individuals to environmental hypoxia, and to situations in which disease reduces cardiac oxygen delivery.
Efficiency, defined as the amount of work produced for a given amount of oxygen consumed, is a ke... more Efficiency, defined as the amount of work produced for a given amount of oxygen consumed, is a key determinant of endurance capacity, and can be altered by metabolic substrate supply, in that fatty acid oxidation is less efficient than glucose oxidation. It is unclear, however, whether consumption of a high-fat diet would be detrimental or beneficial for endurance capacity, due to purported glycogen-sparing properties. In addition, a high-fat diet over several months leads to cognitive impairment. Here, we tested the hypothesis that short-term ingestion of a high-fat diet (55% kcal from fat) would impair exercise capacity and cognitive function in rats, compared with a control chow diet (7.5% kcal from fat) via mitochondrial uncoupling and energy deprivation. We found that rats ran 35% less far on a treadmill and showed cognitive impairment in a maze test with 9 d of high-fat feeding, with respiratory uncoupling in skeletal muscle mitochondria, associated with increased uncoupling protein (UCP3) levels. Our results suggest that high-fat feeding, even over short periods of time, alters skeletal muscle UCP3 expression, affecting energy production and physical performance. Optimization of nutrition to maximize the efficiency of mitochondrial ATP production could improve energetics in athletes and patients with metabolic abnormalities.-Murray, A. J., Knight, N. S., Cochlin, L. E., McAleese, S., Deacon, R. M. J., Rawlins, J. N. P., Clarke, K. Deterioration of physical performance and cognitive function in rats with short-term high-fat feeding. FASEB J. 23, 4353-4360 (2009). www.fasebj.org
Proceedings of the National Academy of Sciences, 2008
The advent of hyperpolarized 13 C magnetic resonance (MR) has provided new potential for the real... more The advent of hyperpolarized 13 C magnetic resonance (MR) has provided new potential for the real-time visualization of in vivo metabolic processes. The aim of this work was to use hyperpolarized [1-13 C]pyruvate as a metabolic tracer to assess noninvasively the flux through the mitochondrial enzyme complex pyruvate dehydrogenase (PDH) in the rat heart, by measuring the production of bicarbonate (H 13 CO 3 ؊ ), a byproduct of the PDH-catalyzed conversion of [1-13 C]pyruvate to acetyl-CoA. By noninvasively observing a 74% decrease in H 13 CO 3 ؊ production in fasted rats compared with fed controls, we have demonstrated that hyperpolarized 13 C MR is sensitive to physiological perturbations in PDH flux. Further, we evaluated the ability of the hyperpolarized 13 C MR technique to monitor disease progression by examining PDH flux before and 5 days after streptozotocin induction of type 1 diabetes. We detected decreased H 13 CO 3 ؊ production with the onset of diabetes that correlated with disease severity. These observations were supported by in vitro investigations of PDH activity as reported in the literature and provided evidence that flux through the PDH enzyme complex can be monitored noninvasively, in vivo, by using hyperpolarized 13 C MR. cardiac metabolism ͉ diabetes ͉ fasting ͉ DNP
Short-term consumption of a high-fat diet impairs exercise capacity in both rats and humans, and ... more Short-term consumption of a high-fat diet impairs exercise capacity in both rats and humans, and increases expression of the mitochondrial uncoupling protein, UCP3, in rodent cardiac and skeletal muscle via activation of the transcription factor, peroxisome proliferator-activated receptor α (PPARα). Unlike long-chain fatty acids however, medium-chain fatty acids do not activate PPARα and do not increase muscle UCP3 expression. We therefore investigated exercise performance and cardiac mitochondrial function in rats fed a chow diet (7.5% kcal from fat), a long-chain triglyceride (LCT) rich diet (46% kcal from LCTs) or a medium-chain triglyceride (MCT) rich diet (46% kcal from MCTs). Rats fed the LCT-rich diet for 15 days ran 55% less far than they did at baseline, whereas rats fed the chow or MCT-rich diets neither improved nor worsened in their exercise capacities. Moreover, consumption of an LCT-rich diet increased cardiac UCP3 expression by 35% and decreased oxidative phosphorylation efficiency, whereas consumption of the MCT-rich diet altered neither UCP3 expression nor oxidative phosphorylation efficiency. Our results suggest that the negative effects of short-term high-fat feeding on exercise performance are predominantly mediated by long-chain rather than medium-chain fatty acids, possibly via PPARα-dependent upregulation of UCP3.
Many diseases of the heart are characterised by changes in substrate utilisation, which is regula... more Many diseases of the heart are characterised by changes in substrate utilisation, which is regulated in part by the activity of the enzyme pyruvate dehydrogenase (PDH). Consequently, there is much interest in the in vivo evaluation of PDH activity in a range of physiological and pathological states to obtain information on the metabolic mechanisms of cardiac diseases. Hyperpolarised [1-13 C]pyruvate, detected using MRS, is a novel technique for the noninvasive evaluation of PDH flux. PDH flux has been assumed to directly reflect in vivo PDH activity, although to date this assumption remains unproven. Control animals and animals undergoing interventions known to modulate PDH activity, namely high fat feeding and dichloroacetate infusion, were used to investigate the relationship between in vivo hyperpolarised MRS measurements of PDH flux and ex vivo measurements of PDH enzyme activity (PDH a ). Further, the plasma concentrations of pyruvate and other important metabolites were evaluated following pyruvate infusion to assess the metabolic consequences of pyruvate infusion during hyperpolarised MRS experiments. Hyperpolarised MRS measurements of PDH flux correlated significantly with ex vivo measurements of PDH a, confirming that PDH activity influences directly the in vivo flux of hyperpolarised pyruvate through cardiac PDH. The maximum plasma concentration of pyruvate reached during hyperpolarised MRS experiments was approximately 250 mM, equivalent to physiological pyruvate concentrations reached during exercise or with dietary interventions. The concentrations of other metabolites, including lactate, glucose and b-hydroxybutyrate, did not vary during the 60 s following pyruvate infusion. Hence, during the 60-s data acquisition period, metabolism was minimally affected by pyruvate infusion.
Hyperpolarized 13 C-labeled substrates directly provide a source of magnetic resonance (MR) signa... more Hyperpolarized 13 C-labeled substrates directly provide a source of magnetic resonance (MR) signal to observe the substrates' real-time uptake and enzymatic conversion. The aim of this study was to optimize the concentration of hyperpolarized [1-13 C]pyruvate infused as a metabolic tracer, by observing the mitochondrial conversion of pyruvate to H 13 CO 3 ØŠ in heart tissue. Hyperpolarized pyruvate was infused into rats at concentrations between 20 mM and 80 mM and the relationships between [1-13 C]lactate, [1-13 C]alanine, and H 13 CO 3 ØŠ production and the infused pyruvate concentration were investigated. H 13 CO 3 ØŠ production reached saturation above 40 mM infused pyruvate concentration, indicating that hyperpolarized MR experiments performed at this concentration maximize the H 13 CO 3 ØŠ signal with minimal alterations to in vivo substrate composition. Additionally, the linear dependence of alanine production on pyruvate concentration confirmed that hyperpolarized MR methods in the heart reveal enzyme activity, rather than cellular uptake. H 13 CO 3 ØŠ production demonstrated evidence of sigmoidal enzyme kinetics, a reflection of the allosteric nature of the pyruvate dehydrogenase (PDH) enzyme complex. This protocol could be useful to optimize the infused concentration of other hyperpolarized metabolites in different organs, to ensure adequate MR signal with minimum metabolic perturbation.
Journal of Cardiovascular Magnetic Resonance, 2013
Background: T1 mapping allows direct in-vivo quantitation of microscopic changes in the myocardiu... more Background: T1 mapping allows direct in-vivo quantitation of microscopic changes in the myocardium, providing new diagnostic insights into cardiac disease. Existing methods require long breath holds that are demanding for many cardiac patients. In this work we propose and validate a novel, clinically applicable, pulse sequence for myocardial T1-mapping that is compatible with typical limits for end-expiration breath-holding in patients. Materials and methods: The Shortened MOdified Look-Locker Inversion recovery (ShMOLLI) method uses sequential inversion recovery measurements within a single short breath-hold. Full recovery of the longitudinal magnetisation between sequential inversion pulses is not achieved, but conditional interpretation of samples for reconstruction of T1-maps is used to yield accurate measurements, and this algorithm is implemented directly on the scanner. We performed computer simulations for 100 ms<T1 < 2.7 s and heart rates 40-100 bpm followed by phantom validation at 1.5T and 3T. In-vivo myocardial T1-mapping using this method and the previous goldstandard (MOLLI) was performed in 10 healthy volunteers at 1.5T and 3T, 4 volunteers with contrast injection at 1.5T, and 4 patients with recent myocardial infarction (MI) at 3T.
Journal of Cardiovascular Magnetic Resonance, 2012
This work demonstrates that cardiac energetcics is further impaired during exercise in hypertroph... more This work demonstrates that cardiac energetcics is further impaired during exercise in hypertrophic cardiomyopathy. This may be a possible reason for exercise related death in HCM.
on behalf of the Caudwell Xtreme Everest 2009 Investigators. Oral Coenzyme Q supplementation does... more on behalf of the Caudwell Xtreme Everest 2009 Investigators. Oral Coenzyme Q supplementation does not prevent cardiac alterations during a high altitude trek to Everest Base Camp. High Alt Med Biol 15:000-000, 2014.-Exposure to high altitude is associated with sustained, but reversible, changes in cardiac mass, diastolic function, and high-energy phosphate metabolism. Whilst the underlying mechanisms remain elusive, tissue hypoxia increases generation of reactive oxygen species (ROS), which can stabilize hypoxia-inducible factor (HIF) transcription factors, bringing about transcriptional changes that suppress oxidative phosphorylation and activate autophagy. We therefore investigated whether oral supplementation with an antioxidant, Coenzyme Q10, prevented the cardiac perturbations associated with altitude exposure. Twenty-three volunteers (10 male, 13 female, 46 -3 years) were recruited from the 2009 Caudwell Xtreme Everest Research Treks and studied before, and within 48 h of return from, a 17-day trek to Everest Base Camp, with subjects receiving either no intervention (controls) or 300 mg Coenzyme Q10 per day throughout altitude exposure. Cardiac magnetic resonance imaging and echocardiography were used to assess cardiac morphology and function. Following altitude exposure, body mass fell by 3 kg in all subjects ( p < 0.001), associated with a loss of body fat and a fall in BMI. Post-trek, left ventricular mass had decreased by 11% in controls ( p < 0.05) and by 16% in Coenzyme Q10-treated subjects ( p < 0.001), whereas mitral inflow E/A had decreased by 18% in controls ( p < 0.05) and by 21% in Coenzyme Q10-treated subjects ( p < 0.05). Coenzyme Q10 supplementation did not, therefore, prevent the loss of left ventricular mass or change in diastolic function that occurred following a trek to Everest Base Camp.
-Whether the myocardium in non-ischemic heart failure experiences oxygen-limitation remains a lon... more -Whether the myocardium in non-ischemic heart failure experiences oxygen-limitation remains a long-standing controversy. We addressed this question in patients with Dilated Cardiomyopathy (DCM) using a dual approach: First, we tested the changes in myocardial oxygenation between rest and stress states, using oxygenation-sensitive CMR. Secondly, we sought to assess the functional consequences of oxygen limitation at rest by measuring myocardial energetics before and after short-term oxygen supplementation. -Twenty six subjects (14 DCM; 12 normal) underwent cardiac MRI at 3 Tesla to assess cardiac volumes, function, oxygenation and first-pass perfusion (0.03 mmol/kg Gd-DTPA bolus) at stress and rest (4-6 minutes i.v. adenosine, 140μg/kg/min). Signal intensity change (SIΔ) and myocardial perfusion reserve index (MPRI) were measured from oxygenation and perfusion images, respectively. Furthermore, the effect of oxygen supplementation on resting myocardial energy metabolism was tested using (31)P MR spectroscopy, measuring PCr/ATP ratios in both groups at baseline and after 4 hours of oxygen via facemask in the DCM group. During stress there were equivalent rises in rate pressure product in both groups (DCM 76±15%, normal 79±9%, P=0.84). MPRI was significantly reduced in DCM (1.51 ± 0.11 vs. normal 1.86±0.10, P=0.03). However, there was no difference in oxygenation between groups: SI∆ in DCM 17±3% vs. normal 20±2% (P=0.38). Furthermore, at a LV segmental level, there was no correlation between oxygenation-sensitive SI∆ and MPRI (R=0.06, P=0.43). Resting PCr/ATP was reduced in DCM (1.66±0.07 vs normal 2.12±0.06, P=0.002). With oxygen supplementation, there was no change in PCr/ATP (1.61±0.08, P=0.58, Δ-0.04±0.05). There was also no effect of oxygen on systolic function (EF pre oxygen 34±1%, post oxygen 36±2%, P=0.46; Δ 2±1%). -Our results demonstrate dissociation between microvascular dysfunction and oxygenation in DCM, suggesting that the impairment of perfusion is not sufficient to cause deoxygenation during stress. Cardiac energetics are unaffected by oxygen supplementation, indicating the absence of relevant myocardial hypoxia at rest. Our study suggests that novel treatments for non-ischemic heart failure should focus on efforts to directly target cardiomyocyte function and metabolism rather than oxygen delivery and microvascular function.
Hypertrophic cardiomyopathy (HCM) is the commonest cause of sudden cardiac death in the young, wi... more Hypertrophic cardiomyopathy (HCM) is the commonest cause of sudden cardiac death in the young, with an excess of exercise-related deaths. The HCM sarcomere mutations increase the energy cost of contraction and impaired resting cardiac energetics has been documented by measurement of phosphocreatine/ATP (PCr/ATP) using (31)Phosphorus MR Spectroscopy ((31)P MRS). We hypothesized that cardiac energetics are further impaired acutely during exercise in HCM and that this would have important functional consequences. (31)P MRS was performed in 35 HCM patients and 20 age- and gender-matched normal volunteers at rest and during leg exercise with 2.5 kg ankle weights. Peak left-ventricular filling rates (PFRs) and myocardial perfusion reserve (MPRI) were calculated during adenosine stress. Resting PCr/ATP was significantly reduced in HCM (HCM: 1.71 ± 0.35, normal 2.14 ± 0.35 P < 0.0001). During exercise, there was a further reduction in PCr/ATP in HCM (1.56 ± 0.29, P = 0.02 compared with r...
Neuronal glucose uptake was thought to be independent of insulin, being facilitated by glucose tr... more Neuronal glucose uptake was thought to be independent of insulin, being facilitated by glucose transporters GLUT1 and GLUT3, which do not require insulin signaling. However, it is now known that components of the insulin-mediated glucose uptake pathway, including neuronal insulin synthesis and the insulindependent glucose transporter GLUT4, are present in brain tissue, particularly in the hippocampus. There is considerable recent evidence that insulin signaling is crucial to optimal hippocampal function. The physiological basis, however, is not clear. We propose that while noninsulin-dependent GLUT1 and GLUT3 transport is adequate for resting needs, the surge in energy use during sustained cognitive activity requires the additional induction of insulin-signaled GLUT4 transport. We studied hippocampal high-energy phosphate metabolism in eight healthy volunteers, using a lipid infusion protocol to inhibit insulin signaling. Contrary to conventional wisdom, it is now known that free fatty acids do cross the blood-brain barrier in significant amounts. Energy metabolism within the hippocampus was assessed during standardized cognitive activity. 31 Phosphorus magnetic resonance spectroscopy was used to determine the phosphocreatine (PCr)-to-adenosine triphosphate (ATP) ratio. This ratio reflects cellular energy production in relation to concurrent cellular energy expenditure. With lipid infusion, the ratio was significantly reduced during cognitive activity (PCr/ATP 1.0 AE 0.4 compared with 1.4 AE 0.4 before infusion, P = 0.01). Without lipid infusion, there was no reduction in the ratio during cognitive activity (PCr/ ATP 1.5 AE 0.3 compared with 1.4 AE 0.4, P = 0.57). This provides supporting evidence for a physiological role for insulin signaling in facilitating increased neuronal glucose uptake during sustained cognitive activity. Loss of this response, as may occur in type 2 diabetes, would lead to insufficient neuronal energy availability during cognitive activity.
In the current work, we labelled human hematopoietic stem cells with polymeric nanoparticles (NPs... more In the current work, we labelled human hematopoietic stem cells with polymeric nanoparticles (NPs) that can be tracked by Magnetic Resonance Imaging (MRI) and studied their effect on cell metabolism, proliferation, secretomics, genomics and differentiation. We showed that NPs had no effect on the stem cell differentiation program but affected their paracrine activity.
Hypoxia causes left ventricular dysfunction in the human heart, but the biochemical mechanism is ... more Hypoxia causes left ventricular dysfunction in the human heart, but the biochemical mechanism is poorly understood. Here, we tested whether short-term normobaric hypoxia leads to changes in cardiac energetics and early cardiac dysfunction. Healthy male volunteers (n=12, age 24 ± 2 yr) were exposed to normobaric hypoxia in a purpose-built hypoxic chamber. The partial pressure of oxygen during end-tidal expiration (P(ET)o₂) was kept between 50 and 60 mmHg, and peripheral oxygen saturation (Sao₂) was kept above 80%. Cardiac morphology and function were assessed using magnetic resonance imaging and echocardiography, both before and after 20 h of hypoxic exposure, and high-energy phosphate metabolism [measured as the phosphocreatine (PCr)/ATP ratio] was measured using ³¹P magnetic resonance spectroscopy. During hypoxia, P(ET)o₂ and Sao₂ averaged 55 ± 1 mmHg and 83.6 ± 0.4%, respectively. Hypoxia caused a 15% reduction in cardiac PCr/ATP (from 2.0 ± 0.1 to 1.7 ± 0.1, P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.01) and reduced diastolic function (measured as E/E&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;, rising from 6.1 ± 0.4 to 7.5 ± 0.7, P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.01). Normobaric hypoxia causes a rapid decrease in high-energy phosphate metabolism in the human cardiac left ventricle, which may lead to a decline in diastolic function. These findings are important in understanding the response of normal individuals to environmental hypoxia, and to situations in which disease reduces cardiac oxygen delivery.
Efficiency, defined as the amount of work produced for a given amount of oxygen consumed, is a ke... more Efficiency, defined as the amount of work produced for a given amount of oxygen consumed, is a key determinant of endurance capacity, and can be altered by metabolic substrate supply, in that fatty acid oxidation is less efficient than glucose oxidation. It is unclear, however, whether consumption of a high-fat diet would be detrimental or beneficial for endurance capacity, due to purported glycogen-sparing properties. In addition, a high-fat diet over several months leads to cognitive impairment. Here, we tested the hypothesis that short-term ingestion of a high-fat diet (55% kcal from fat) would impair exercise capacity and cognitive function in rats, compared with a control chow diet (7.5% kcal from fat) via mitochondrial uncoupling and energy deprivation. We found that rats ran 35% less far on a treadmill and showed cognitive impairment in a maze test with 9 d of high-fat feeding, with respiratory uncoupling in skeletal muscle mitochondria, associated with increased uncoupling protein (UCP3) levels. Our results suggest that high-fat feeding, even over short periods of time, alters skeletal muscle UCP3 expression, affecting energy production and physical performance. Optimization of nutrition to maximize the efficiency of mitochondrial ATP production could improve energetics in athletes and patients with metabolic abnormalities.-Murray, A. J., Knight, N. S., Cochlin, L. E., McAleese, S., Deacon, R. M. J., Rawlins, J. N. P., Clarke, K. Deterioration of physical performance and cognitive function in rats with short-term high-fat feeding. FASEB J. 23, 4353-4360 (2009). www.fasebj.org
Proceedings of the National Academy of Sciences, 2008
The advent of hyperpolarized 13 C magnetic resonance (MR) has provided new potential for the real... more The advent of hyperpolarized 13 C magnetic resonance (MR) has provided new potential for the real-time visualization of in vivo metabolic processes. The aim of this work was to use hyperpolarized [1-13 C]pyruvate as a metabolic tracer to assess noninvasively the flux through the mitochondrial enzyme complex pyruvate dehydrogenase (PDH) in the rat heart, by measuring the production of bicarbonate (H 13 CO 3 ؊ ), a byproduct of the PDH-catalyzed conversion of [1-13 C]pyruvate to acetyl-CoA. By noninvasively observing a 74% decrease in H 13 CO 3 ؊ production in fasted rats compared with fed controls, we have demonstrated that hyperpolarized 13 C MR is sensitive to physiological perturbations in PDH flux. Further, we evaluated the ability of the hyperpolarized 13 C MR technique to monitor disease progression by examining PDH flux before and 5 days after streptozotocin induction of type 1 diabetes. We detected decreased H 13 CO 3 ؊ production with the onset of diabetes that correlated with disease severity. These observations were supported by in vitro investigations of PDH activity as reported in the literature and provided evidence that flux through the PDH enzyme complex can be monitored noninvasively, in vivo, by using hyperpolarized 13 C MR. cardiac metabolism ͉ diabetes ͉ fasting ͉ DNP
Short-term consumption of a high-fat diet impairs exercise capacity in both rats and humans, and ... more Short-term consumption of a high-fat diet impairs exercise capacity in both rats and humans, and increases expression of the mitochondrial uncoupling protein, UCP3, in rodent cardiac and skeletal muscle via activation of the transcription factor, peroxisome proliferator-activated receptor α (PPARα). Unlike long-chain fatty acids however, medium-chain fatty acids do not activate PPARα and do not increase muscle UCP3 expression. We therefore investigated exercise performance and cardiac mitochondrial function in rats fed a chow diet (7.5% kcal from fat), a long-chain triglyceride (LCT) rich diet (46% kcal from LCTs) or a medium-chain triglyceride (MCT) rich diet (46% kcal from MCTs). Rats fed the LCT-rich diet for 15 days ran 55% less far than they did at baseline, whereas rats fed the chow or MCT-rich diets neither improved nor worsened in their exercise capacities. Moreover, consumption of an LCT-rich diet increased cardiac UCP3 expression by 35% and decreased oxidative phosphorylation efficiency, whereas consumption of the MCT-rich diet altered neither UCP3 expression nor oxidative phosphorylation efficiency. Our results suggest that the negative effects of short-term high-fat feeding on exercise performance are predominantly mediated by long-chain rather than medium-chain fatty acids, possibly via PPARα-dependent upregulation of UCP3.
Many diseases of the heart are characterised by changes in substrate utilisation, which is regula... more Many diseases of the heart are characterised by changes in substrate utilisation, which is regulated in part by the activity of the enzyme pyruvate dehydrogenase (PDH). Consequently, there is much interest in the in vivo evaluation of PDH activity in a range of physiological and pathological states to obtain information on the metabolic mechanisms of cardiac diseases. Hyperpolarised [1-13 C]pyruvate, detected using MRS, is a novel technique for the noninvasive evaluation of PDH flux. PDH flux has been assumed to directly reflect in vivo PDH activity, although to date this assumption remains unproven. Control animals and animals undergoing interventions known to modulate PDH activity, namely high fat feeding and dichloroacetate infusion, were used to investigate the relationship between in vivo hyperpolarised MRS measurements of PDH flux and ex vivo measurements of PDH enzyme activity (PDH a ). Further, the plasma concentrations of pyruvate and other important metabolites were evaluated following pyruvate infusion to assess the metabolic consequences of pyruvate infusion during hyperpolarised MRS experiments. Hyperpolarised MRS measurements of PDH flux correlated significantly with ex vivo measurements of PDH a, confirming that PDH activity influences directly the in vivo flux of hyperpolarised pyruvate through cardiac PDH. The maximum plasma concentration of pyruvate reached during hyperpolarised MRS experiments was approximately 250 mM, equivalent to physiological pyruvate concentrations reached during exercise or with dietary interventions. The concentrations of other metabolites, including lactate, glucose and b-hydroxybutyrate, did not vary during the 60 s following pyruvate infusion. Hence, during the 60-s data acquisition period, metabolism was minimally affected by pyruvate infusion.
Hyperpolarized 13 C-labeled substrates directly provide a source of magnetic resonance (MR) signa... more Hyperpolarized 13 C-labeled substrates directly provide a source of magnetic resonance (MR) signal to observe the substrates' real-time uptake and enzymatic conversion. The aim of this study was to optimize the concentration of hyperpolarized [1-13 C]pyruvate infused as a metabolic tracer, by observing the mitochondrial conversion of pyruvate to H 13 CO 3 ØŠ in heart tissue. Hyperpolarized pyruvate was infused into rats at concentrations between 20 mM and 80 mM and the relationships between [1-13 C]lactate, [1-13 C]alanine, and H 13 CO 3 ØŠ production and the infused pyruvate concentration were investigated. H 13 CO 3 ØŠ production reached saturation above 40 mM infused pyruvate concentration, indicating that hyperpolarized MR experiments performed at this concentration maximize the H 13 CO 3 ØŠ signal with minimal alterations to in vivo substrate composition. Additionally, the linear dependence of alanine production on pyruvate concentration confirmed that hyperpolarized MR methods in the heart reveal enzyme activity, rather than cellular uptake. H 13 CO 3 ØŠ production demonstrated evidence of sigmoidal enzyme kinetics, a reflection of the allosteric nature of the pyruvate dehydrogenase (PDH) enzyme complex. This protocol could be useful to optimize the infused concentration of other hyperpolarized metabolites in different organs, to ensure adequate MR signal with minimum metabolic perturbation.
Journal of Cardiovascular Magnetic Resonance, 2013
Background: T1 mapping allows direct in-vivo quantitation of microscopic changes in the myocardiu... more Background: T1 mapping allows direct in-vivo quantitation of microscopic changes in the myocardium, providing new diagnostic insights into cardiac disease. Existing methods require long breath holds that are demanding for many cardiac patients. In this work we propose and validate a novel, clinically applicable, pulse sequence for myocardial T1-mapping that is compatible with typical limits for end-expiration breath-holding in patients. Materials and methods: The Shortened MOdified Look-Locker Inversion recovery (ShMOLLI) method uses sequential inversion recovery measurements within a single short breath-hold. Full recovery of the longitudinal magnetisation between sequential inversion pulses is not achieved, but conditional interpretation of samples for reconstruction of T1-maps is used to yield accurate measurements, and this algorithm is implemented directly on the scanner. We performed computer simulations for 100 ms<T1 < 2.7 s and heart rates 40-100 bpm followed by phantom validation at 1.5T and 3T. In-vivo myocardial T1-mapping using this method and the previous goldstandard (MOLLI) was performed in 10 healthy volunteers at 1.5T and 3T, 4 volunteers with contrast injection at 1.5T, and 4 patients with recent myocardial infarction (MI) at 3T.
Journal of Cardiovascular Magnetic Resonance, 2012
This work demonstrates that cardiac energetcics is further impaired during exercise in hypertroph... more This work demonstrates that cardiac energetcics is further impaired during exercise in hypertrophic cardiomyopathy. This may be a possible reason for exercise related death in HCM.
on behalf of the Caudwell Xtreme Everest 2009 Investigators. Oral Coenzyme Q supplementation does... more on behalf of the Caudwell Xtreme Everest 2009 Investigators. Oral Coenzyme Q supplementation does not prevent cardiac alterations during a high altitude trek to Everest Base Camp. High Alt Med Biol 15:000-000, 2014.-Exposure to high altitude is associated with sustained, but reversible, changes in cardiac mass, diastolic function, and high-energy phosphate metabolism. Whilst the underlying mechanisms remain elusive, tissue hypoxia increases generation of reactive oxygen species (ROS), which can stabilize hypoxia-inducible factor (HIF) transcription factors, bringing about transcriptional changes that suppress oxidative phosphorylation and activate autophagy. We therefore investigated whether oral supplementation with an antioxidant, Coenzyme Q10, prevented the cardiac perturbations associated with altitude exposure. Twenty-three volunteers (10 male, 13 female, 46 -3 years) were recruited from the 2009 Caudwell Xtreme Everest Research Treks and studied before, and within 48 h of return from, a 17-day trek to Everest Base Camp, with subjects receiving either no intervention (controls) or 300 mg Coenzyme Q10 per day throughout altitude exposure. Cardiac magnetic resonance imaging and echocardiography were used to assess cardiac morphology and function. Following altitude exposure, body mass fell by 3 kg in all subjects ( p < 0.001), associated with a loss of body fat and a fall in BMI. Post-trek, left ventricular mass had decreased by 11% in controls ( p < 0.05) and by 16% in Coenzyme Q10-treated subjects ( p < 0.001), whereas mitral inflow E/A had decreased by 18% in controls ( p < 0.05) and by 21% in Coenzyme Q10-treated subjects ( p < 0.05). Coenzyme Q10 supplementation did not, therefore, prevent the loss of left ventricular mass or change in diastolic function that occurred following a trek to Everest Base Camp.
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