Erinne R. Dabkowski

Dietary fat and heart failure: moving from lipotoxicity to lipoprotection.

There is growing evidence suggesting that dietary fat intake affects the development and progression of heart failure. Studies in rodents show that in the absence of obesity, replacing refined carbohydrate with fat can attenuate or prevent ventricular expansion and contractile dysfunction in response to hypertension, infarction, or genetic cardiomyopathy. Relatively low intake of n-3 polyunsaturated fatty acids from marine sources alters cardiac membrane phospholipid fatty acid composition, decreases the onset of new heart failure, and slows the progression of established heart failure. This effect is associated with decreased inflammation and improved resistance to mitochondrial permeability transition. High intake of saturated, monounsaturated, or n-6 polyunsaturated fatty acids has also shown beneficial effects in rodent studies. The underlying mechanisms are complex, and a more thorough understanding is needed of the effects on cardiac phospholipids, lipid metabolites, and metabolic flux in the normal and failing heart. In summary, manipulation of dietary fat intake shows promise in the prevention and treatment of heart failure. Clinical studies generally support high intake of n-3 polyunsaturated fatty acids from marine sources to prevent and treat heart failure. Additional clinical and animals studies are needed to determine the optimal diet in terms of saturated, monounsaturated, and n-6 polyunsaturated fatty acids intake for this vulnerable patient population.

Cardiomyocyte-specific perilipin 5 overexpression leads to myocardial steatosis and modest cardiac dysfunction.

Presence of ectopic lipid droplets (LDs) in cardiac muscle is associated to lipotoxicity and tissue dysfunction. However, presence of LDs in heart is also observed in physiological conditions, such as when cellular energy needs and energy production from mitochondria fatty acid β-oxidation are high (fasting). This suggests that development of tissue lipotoxicity and dysfunction is not simply due to the presence of LDs in cardiac muscle but due at least in part to alterations in LD function. To examine the function of cardiac LDs, we obtained transgenic mice with heart-specific perilipin 5 (Plin5) overexpression (MHC-Plin5), a member of the perilipin protein family. Hearts from MHC-Plin5 mice expressed at least 4-fold higher levels of plin5 and exhibited a 3.5-fold increase in triglyceride content versus nontransgenic littermates. Chronic cardiac excess of LDs was found to result in mild heart dysfunction with decreased expression of peroxisome proliferator-activated receptor (PPAR)α target genes, decreased mitochondria function, and left ventricular concentric hypertrophia. Lack of more severe heart function complications may have been prevented by a strong increased expression of oxidative-induced genes via NF-E2-related factor 2 antioxidative pathway. Perilipin 5 regulates the formation and stabilization of cardiac LDs, and it promotes cardiac steatosis without major heart function impairment.

Update on lipids and mitochondrial function: impact of dietary n-3 polyunsaturated fatty acids.

Purpose of reviewRecent evidence has linked n-3 polyunsaturated fatty acid (PUFA) supplementation with dramatic alterations of mitochondrial phospholipid membranes and favorable changes in mitochondrial function. In the present review, we examine the novel effects of n-3 PUFA on mitochondria, with an emphasis on cardiac mitochondrial phospholipids. Recent findingsThere is growing evidence that dietary n-3 PUFA, particularly docosahexaenoic acid (DHA), has profound effects on mitochondrial membrane phospholipid composition and mitochondrial function. Supplementation with n-3 PUFA increases membrane phospholipid DHA and depletes arachidonic acid, and can increase cardiolipin, a tetra-acyl phospholipid that is unique to mitochondrial and essential for optimal mitochondrial function. Recent studies show that supplementation with DHA decreases propensity for cardiac mitochondria to undergo permeability transition, a catastrophic event often leading to cell death. This finding provides a potential mechanism for the cardioprotective effect of DHA. Interestingly, other n-3 PUFAs that modify membrane composition to a lesser extent have substantially less of an effect on mitochondria and do not appear to directly protect the heart. SummaryCurrent data support a role for n-3 PUFA supplementation, particularly DHA, on mitochondria that are strongly associated with changes in mitochondrial phospholipid composition.

Assessment of cardiac proteome dynamics with heavy water: Slower protein synthesis rates in interfibrillar than subsarcolemmal mitochondria

Traditional proteomics provides static assessment of protein content, but not synthetic rates. Recently, proteome dynamics with heavy water ((2)H2O) was introduced, where (2)H labels amino acids that are incorporated into proteins, and the synthesis rate of individual proteins is calculated using mass isotopomer distribution analysis. We refine this approach with a novel algorithm and rigorous selection criteria that improve the accuracy and precision of the calculation of synthesis rates and use it to measure protein kinetics in spatially distinct cardiac mitochondrial subpopulations. Subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM) were isolated from adult rats, which were given (2)H2O in the drinking water for up to 60 days. Plasma (2)H2O and myocardial (2)H-enrichment of amino acids were stable throughout the experimental protocol. Multiple tryptic peptides were identified from 28 proteins in both SSM and IFM and showed a time-dependent increase in heavy mass isotopomers that was consistent within a given protein. Mitochondrial protein synthesis was relatively slow (average half-life of 30 days, 2.4% per day). Although the synthesis rates for individual proteins were correlated between IFM and SSM (R(2) = 0.84; P < 0.0001), values in IFM were 15% less than SSM (P < 0.001). In conclusion, administration of (2)H2O results in stable enrichment of the cardiac precursor amino acid pool, with the use of refined analytical and computational methods coupled with cell fractionation one can measure synthesis rates for cardiac proteins in subcellular compartments in vivo, and protein synthesis is slower in mitochondria located among the myofibrils than in the subsarcolemmal region.

Cardiac mitochondrial proteome dynamics with heavy water reveals stable rate of mitochondrial protein synthesis in heart failure despite decline in mitochondrial oxidative capacity

We recently developed a method to measure mitochondrial proteome dynamics with heavy water ((2)H2O)-based metabolic labeling and high resolution mass spectrometry. We reported the half-lives and synthesis rates of several proteins in the two cardiac mitochondrial subpopulations, subsarcolemmal and interfibrillar (SSM and IFM), in Sprague Dawley rats. In the present study, we tested the hypothesis that the mitochondrial protein synthesis rate is reduced in heart failure, with possible differential changes in SSM versus IFM. Six to seven week old male Sprague Dawley rats underwent transverse aortic constriction (TAC) and developed moderate heart failure after 22weeks. Heart failure and sham rats of the same age received heavy water (5% in drinking water) for up to 80days. Cardiac SSM and IFM were isolated from both groups and the proteins were separated by 1D gel electrophoresis. Heart failure reduced protein content and increased the turnover rate of several proteins involved in fatty acid oxidation, electron transport chain and ATP synthesis, while it decreased the turnover of other proteins, including pyruvate dehydrogenase subunit in IFM, but not in SSM. Because of these bidirectional changes, the average overall half-life of proteins was not altered by heart failure in both SSM and IFM. The kinetic measurements of individual mitochondrial proteins presented in this study may contribute to a better understanding of the mechanisms responsible for mitochondrial alterations in the failing heart.

Marine n3 polyunsaturated fatty acids enhance resistance to mitochondrial permeability transition in heart failure but do not improve survival

Mitochondrial dysfunction in heart failure includes greater susceptibility to mitochondrial permeability transition (MPT), which may worsen cardiac function and decrease survival. Treatment with a mixture of the n3 polyunsaturated fatty acids (n3 PUFAs) docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) is beneficial in heart failure patients and increases resistance to MPT in animal models. We assessed whether DHA and EPA have similar effects when given individually, and whether they prolong survival in heart failure. Male δ-sarcoglycan null cardiomyopathic hamsters were untreated or given either DHA, EPA, or a 1:1 mixture of DHA + EPA at 2.1% of energy intake. Treatment did not prolong survival: mean survival was 298 ± 15 days in untreated hamsters and 335 ± 17, 328 ± 14, and 311 ± 15 days with DHA, EPA, and DHA + EPA, respectively (n = 27-32/group). A subgroup of cardiomyopathic hamsters treated for 26 wk had impaired left ventricular function and increased cardiomyocyte apoptosis compared with normal hamsters, which was unaffected by n3 PUFA treatment. Evaluation of oxidative phosphorylation in isolated subsarcolemmal and interfibrillar mitochondria with substrates for complex I or II showed no effect of n3 PUFA treatment. On the other hand, interfibrillar mitochondria from cardiomyopathic hamsters were significantly more sensitive to Ca(2+)-induced MPT, which was completely normalized by treatment with DHA and partially corrected by EPA. In conclusion, treatment with DHA or EPA normalizes Ca(2+)-induced MPT in cardiomyopathic hamsters but does not prolong survival or improve cardiac function. This suggest that greater susceptibility to MPT is not a contributor to cardiac pathology and poor survival in heart failure.

Chronic Hypoxia Impairs Cytochrome Oxidase Activity Via Oxidative Stress in Selected Fetal Guinea Pig Organs

We hypothesized that chronic hypoxia disrupts mitochondrial function via oxidative stress in fetal organs. Pregnant guinea pig sows were exposed to either normoxia or hypoxia (10.5% O2, 14 days) in the presence or absence of the antioxidant, N-acetylcysteine (NAC). Near-term anesthetized fetuses were delivered via hysterotomy, and fetal livers, hearts, lungs, and forebrains harvested. We quantified the effects of chronic hypoxia on cytochrome oxidase (CCO) activity and 2 factors known to regulate CCO activity: malondialdehyde (MDA) and CCO subunit 4 (COX4). Hypoxia increased the MDA levels in fetal liver, heart, and lung with a corresponding reduction in CCO activity, prevented by prenatal NAC. The COX4 expression paralleled CCO activity in fetal liver and lung, but was unaltered in fetal hearts due to hypoxia. Hypoxia reduced the brain COX4 expression despite having no effect on CCO activity. This study identifies the mitochondrion as an important target site in tissue-specific oxidative stress for the induction of fetal hypoxic injury.

Enhanced resistance to permeability transition in interfibrillar cardiac mitochondria in dogs: effects of aging and long-term aldosterone infusion

Functional differences between subsarcolemmal and interfibrillar cardiac mitochondria (SSM and IFM) have been observed with aging and pathological conditions in rodents. Results are contradictory, and there is little information from large animal models. We assessed the respiratory function and resistance to mitochondrial permeability transition (MPT) in SSM and IFM from healthy young (1 yr) and old (8 yr) female beagles and in old beagles with hypertension and left ventricular (LV) wall thickening induced by 16 wk of aldosterone infusion. MPT was assessed in SSM and IFM by Ca(2+) retention and swelling. Healthy young and old beagles had similar mitochondrial structure, respiratory function, and Ca(2+)-induced MPT within SSM and IFM subpopulations. On the other hand, oxidative capacity and resistance to Ca(2+)-induced MPT were significantly greater in IFM compared with SSM in all groups. Old beagles treated with aldosterone had greater LV wall thickness and worse diastolic filling but normal LV chamber volume and systolic function. Treatment with aldosterone did not alter mitochondrial respiratory function but accelerated Ca(2+)-induced MPT in SSM, but not IFM, compared with healthy old and young beagles. In conclusion, in a large animal model, oxidative capacity and resistance to MPT were greater in IFM than in SSM. Furthermore, aldosterone infusion increased susceptibility to MPT in SSM, but not IFM. Together this suggests that SSM are less resilient to acute stress than IFM in the healthy heart and are more susceptible to the development of pathology with chronic stress.

MitoQ improves mitochondrial dysfunction in heart failure induced by pressure overload

ABSTRACT Heart failure remains a major public‐health problem with an increase in the number of patients worsening from this disease. Despite current medical therapy, the condition still has a poor prognosis. Heart failure is complex but mitochondrial dysfunction seems to be an important target to improve cardiac function directly. Our goal was to analyze the effects of MitoQ (100 &mgr;M in drinking water) on the development and progression of heart failure induced by pressure overload after 14 weeks. The main findings are that pressure overload‐induced heart failure in rats decreased cardiac function in vivo that was not altered by MitoQ. However, we observed a reduction in right ventricular hypertrophy and lung congestion in heart failure animals treated with MitoQ. Heart failure also decreased total mitochondrial protein content, mitochondrial membrane potential in the intermyofibrillar mitochondria. MitoQ restored membrane potential in IFM but did not restore mitochondrial protein content. These alterations are associated with the impairment of basal and stimulated mitochondrial respiration in IFM and SSM induced by heart failure. Moreover, MitoQ restored mitochondrial respiration in heart failure induced by pressure overload. We also detected higher levels of hydrogen peroxide production in heart failure and MitoQ restored the increase in ROS production. MitoQ was also able to improve mitochondrial calcium retention capacity, mainly in the SSM whereas in the IFM we observed a small alteration. In summary, MitoQ improves mitochondrial dysfunction in heart failure induced by pressure overload, by decreasing hydrogen peroxide formation, improving mitochondrial respiration and improving mPTP opening. Graphical abstract Figure. No Caption available.

Dietary saturated fat and docosahexaenoic acid differentially effect cardiac mitochondrial phospholipid fatty acyl composition and Ca2+ uptake, without altering permeability transition or left ventricular function

High saturated fat diets improve cardiac function and survival in rodent models of heart failure, which may be mediated by changes in mitochondrial function. Dietary supplementation with the n3‐polyunsaturated fatty acid docosahexaenoic acid (DHA, 22:6n3) is also beneficial in heart failure and can affect mitochondrial function. Saturated fatty acids and DHA likely have opposing effects on mitochondrial phospholipid fatty acyl side chain composition and mitochondrial membrane function, though a direct comparison has not been previously reported. We fed healthy adult rats a standard low‐fat diet (11% of energy intake from fat), a low‐fat diet supplemented with DHA (2.3% of energy intake) or a high‐fat diet comprised of long chain saturated fatty acids (45% fat) for 6 weeks. There were no differences among the three diets in cardiac mass or function, mitochondrial respiration, or Ca2+‐induced mitochondrial permeability transition. On the other hand, there were dramatic differences in mitochondrial phospholipid fatty acyl side chains. Dietary supplementation with DHA increased DHA from 7% to ~25% of total phospholipid fatty acids in mitochondrial membranes, and caused a proportional depletion of arachidonic acid (20:4n6). The saturated fat diet increased saturated fat and DHA in mitochondria and decreased linoleate (18:2n6), which corresponded to a decrease in Ca2+ uptake by isolated mitochondria compared to the other diet groups. In conclusion, despite dramatic changes in mitochondrial phospholipid fatty acyl side chain composition by both the DHA and high saturated fat diets, there were no effects on mitochondrial respiration, permeability transition, or cardiac function.