Mitochondrial DNA integrity and function are critical for endothelium-dependent vasodilation in rats with metabolic syndrome.

Endothelial dysfunction in diabetes is generally attributed to oxidative stress, but this view is challenged by observations showing antioxidants do not eliminate diabetic vasculopathy. As an alternative to oxidative stress-induced dysfunction, we interrogated if impaired mitochondrial function in endothelial cells is central to endothelial dysfunction in the metabolic syndrome. We observed reduced coronary arteriolar vasodilation to the endothelium-dependent dilator, acetylcholine (Ach), in Zucker Obese Fatty rats (ZOF, 34 ± 15% [mean ± standard deviation] 10-3 M) compared to Zucker Lean rats (ZLN, 98 ± 11%). This reduction in dilation occurred concomitantly with mitochondrial DNA (mtDNA) strand lesions and reduced mitochondrial complex activities in the endothelium of ZOF versus ZLN. To demonstrate endothelial dysfunction is linked to impaired mitochondrial function, administration of a cell-permeable, mitochondria-directed endonuclease (mt-tat-EndoIII), to repair oxidatively modified DNA in ZOF, restored mitochondrial function and vasodilation to Ach (94 ± 13%). Conversely, administration of a cell-permeable, mitochondria-directed exonuclease (mt-tat-ExoIII) produced mtDNA strand breaks in ZLN, reduced mitochondrial complex activities and vasodilation to Ach in ZLN (42 ± 16%). To demonstrate that mitochondrial function is central to endothelium-dependent vasodilation, we introduced (via electroporation) liver mitochondria (from ZLN) into the endothelium of a mesenteric vessel from ZOF and restored endothelium-dependent dilation to vasoactive intestinal peptide (VIP at 10-5 M, 4 ± 3% vasodilation before mitochondrial transfer and 48 ± 36% after transfer). Finally, to demonstrate mitochondrial function is key to endothelium-dependent dilation, we administered oligomycin (mitochondrial ATP synthase inhibitor) and observed a reduction in endothelium-dependent dilation. We conclude that mitochondrial function is critical for endothelium-dependent vasodilation.

Myocardial ischemia: From disease to syndrome.

Although current guidelines on the management of stable coronary artery disease acknowledge that multiple mechanisms may precipitate myocardial ischemia, recommended diagnostic, prognostic and therapeutic algorithms are still focused on obstructive epicardial atherosclerotic lesions, and little progress has been made in identifying management strategies for non-atherosclerotic causes of myocardial ischemia. The purpose of this consensus paper is three-fold: 1) to marshal scientific evidence that obstructive atherosclerosis can co-exist with other mechanisms of ischemic heart disease (IHD); 2) to explore how the awareness of multiple precipitating mechanisms could impact on pre-test probability, provocative test results and treatment strategies; and 3) to stimulate a more comprehensive approach to chronic myocardial ischemic syndromes, consistent with the new understanding of this condition.

Echo-derived peak cardiac power output-to-left ventricular mass with cardiopulmonary exercise testing predicts outcome in patients with heart failure and depressed systolic function.

AIMS: Peak cardiac power output-to-mass (CPOM) represents a measure of the rate at which cardiac work is delivered respect to the potential energy stored in left ventricular (LV) mass. We studied the value of CPOM and cardiopulmonary exercise test (CPET) in risk stratification of patients with heart failure (HF). MATERIALS AND RESULTS: We studied 159 patients with chronic HF (mean rest LV ejection fraction 30%) undergoing CPET and exercise stress echocardiography. CPOM was calculated as the product of a constant (K = 2.22 × 10-1) with cardiac output (CO) and the mean blood pressure (MBP), divided by LV mass (M), and expressed in the unit of W/100 g: CPOM = [K × CO (L/min) × MBP (mmHg)]/LVM(g). Patients were followed-up for the primary endpoint, including all-cause death, ventricular assist device implantation, and heart transplantation, and the secondary endpoint that comprised hospitalization for HF. In multivariate Cox regression analyses, peak CPOM was selected as the most powerful independent predictor of both primary and secondary endpoint [hazard ratio (HR) 0.004, 95% confidence interval (CI) 0.004-0.3; P = 0.002 and HR 0.09, 95% CI 0.02-0.55; P = 0.009]. Sixty-month survival free from the combined endpoint was 85% in those exhibiting oxygen consumption (VO2) > 14 mL/min/kg and peak CPOM > 0.6 W/100 g. Peak VO2 ≤ 14 mL/min/kg provided incremental prognostic value over demographic and clinical variables, brain natriuretic peptide, and resting echocardiographic parameters (χ2 from 58 to 64; P = 0.04), that was further increased by peak CPOM ≤ 0.6 W/100 g (χ2 77; P < 0.001). CONCLUSION: Peak CPOM and peak VO2 showed independent and incremental prognostic values in patients with chronic HF.

Trimetazidine and Other Metabolic Modifiers.

Treatment goals for people with chronic angina should focus on the relief of symptoms and improving mortality rates so the patient can feel better and live longer. The traditional haemodynamic approach to ischaemic heart disease was based on the assumption that increasing oxygen supply and decreasing oxygen demand would improve symptoms. However, data from clinical trials, show that about one third of people continue to have angina despite a successful percutaneous coronary intervention and medical therapy. Moreover, several trials on chronic stable angina therapy and revascularisation have failed to show benefits in terms of primary outcome (survival, cardiovascular death, all-cause mortality), symptom relief or echocardiographic parameters. Failure to significantly improve quality of life and prognosis may be attributed in part to a limited understanding of ischaemic heart disease, by neglecting the fact that ischaemia is a metabolic disorder. Shifting cardiac metabolism from free fatty acids towards glucose is a promising approach for the treatment of patients with stable angina, independent of the underlying disease (macrovascular and/or microvascular disease). Cardiac metabolic modulators open the way to a greater understanding of ischaemic heart disease and its common clinical manifestations as an energetic disorder rather than an imbalance between the demand and supply of oxygen and metabolites.

Pharmacological Agents Targeting Myocardial Metabolism for the Management of Chronic Stable Angina : an Update.

Despite continuous advances in myocardial revascularization procedures and intracoronary devices, patients with ischemic heart disease (IHD) still experience worse prognosis and poor quality of life (QoL). Indeed, chronic stable angina (CSA) is a common disease with a large burden on healthcare costs. Traditionally, CSA is interpreted as episodes of reversible myocardial ischemia related to the presence of stable coronary artery plaque causing myocardial demand/supply mismatch when myocardial oxygen consumption increases. Accordingly, revascularization procedures are performed with the aim to remove the flow limiting stenosis, whereas traditional medical therapy (hemodynamic agents) aims at reducing myocardial oxygen demands. However, although effective, none of these treatment strategies or their combination is either able to confer symptomatic relief in all patients, nor to reduce mortality. Failure to significantly improve QoL and prognosis may be attributed at least in part to this "restrictive" understanding of IHD. Despite for many years myocardial metabolic derangement has been overlooked, recently it has gained increased attention with the development of new pharmacological agents (metabolic modulators) able to influence myocardial substrate selection and utilization thus improving cardiac efficiency. Shifting cardiac metabolism from free fatty acids (FA) towards glucose is a promising approach for the treatment of patients with stable angina, independently of the underling disease (macrovascular and/or microvascular disease). In this sense cardiac metabolic modulators open the way to a "revolutionary" understanding of ischemic heart disease and its common clinical manifestations, where myocardial ischemia is no longer considered as the mere oxygen and metabolites demand/supply unbalance, but as an energetic disorder. Keeping in mind such an alternative approach to the disease, development of new pharmacological agents directed toward multiple metabolic targets is mandatory.

Stress Testing After Complete and Successful Coronary Revascularization.

BACKGROUND: Noninvasive stress tests play a determinant role in the initial management of patients with chronic angina. Nonetheless, their use in the same patient population is considered inappropriate within 2 years after percutaneous coronary intervention (PCI). Indeed, early abnormal results correlate less well with angiographic control and are attributed to a number of confounding factors. We prospectively assessed prevalence and impact on the quality of life of abnormal stress test results in a highly selected patient population. METHODS: Patients with no cardiac comorbidities who underwent successful and complete PCI with stenting for typical angina and had an abnormal exercise stress test (EST) under guideline-directed medical treatment were administered the Seattle Angina Questionnaire (SAQ). Clinical evaluation, EST, and the SAQ were repeated at 1, 6, and 12 months after the index PCI. RESULTS: One hundred ninety-eight patients qualified and were included in the study (mean age, 64 years; 79% men). Although the majority had normal EST results or an increased threshold to angina, at 1 month after the index PCI, 29% of patients still had an abnormal result. At 6 and 12 months, 31% and 29% of patients had abnormal results, respectively. Quality-of-life assessment by the SAQ showed consistent results, with persistent angina in one third of patients. Control angiography documented a critical lesion, attributable to in-stent coronary restenosis, in only 8% of patients. CONCLUSIONS: When stress testing is systematically performed after PCI, the prevalence of abnormal results is high and is associated with impaired quality of life. Prognostic significance along with the underlying pathophysiological mechanisms of such findings should be investigated.

Impaired coronary metabolic dilation in the metabolic syndrome is linked to mitochondrial dysfunction and mitochondrial DNA damage.

Mitochondrial dysfunction in obesity and diabetes can be caused by excessive production of free radicals, which can damage mitochondrial DNA. Because mitochondrial DNA plays a key role in the production of ATP necessary for cardiac work, we hypothesized that mitochondrial dysfunction, induced by mitochondrial DNA damage, uncouples coronary blood flow from cardiac work. Myocardial blood flow (contrast echocardiography) was measured in Zucker lean (ZLN) and obese fatty (ZOF) rats during increased cardiac metabolism (product of heart rate and arterial pressure, i.v. norepinephrine). In ZLN increased metabolism augmented coronary blood flow, but in ZOF metabolic hyperemia was attenuated. Mitochondrial respiration was impaired and ROS production was greater in ZOF than ZLN. These were associated with mitochondrial DNA (mtDNA) damage in ZOF. To determine if coronary metabolic dilation, the hyperemic response induced by heightened cardiac metabolism, is linked to mitochondrial function we introduced recombinant proteins (intravenously or intraperitoneally) in ZLN and ZOF to fragment or repair mtDNA, respectively. Repair of mtDNA damage restored mitochondrial function and metabolic dilation, and reduced ROS production in ZOF; whereas induction of mtDNA damage in ZLN reduced mitochondrial function, increased ROS production, and attenuated metabolic dilation. Adequate metabolic dilation was also associated with the extracellular release of ADP, ATP, and H2O2 by cardiac myocytes; whereas myocytes from rats with impaired dilation released only H2O2. In conclusion, our results suggest that mitochondrial function plays a seminal role in connecting myocardial blood flow to metabolism, and integrity of mtDNA is central to this process.

Prediction of Post Percutaneous Coronary Intervention Myocardial Ischaemia.

Following revascularisation the majority of patients obtain symptom relief and improved quality of life. However, myocardial ischaemia may recur or persist in a significant patient subset. Symptom recurrence is usually attributed to inaccurate evaluation of epicardial stenosis, incomplete revascularisation or stent failure and disease progression. However, technological advances with modern imaging and/or physiological evaluation of epicardial plaques have not solved this issue. Conversely, recent clinical studies have shown that abnormal coronary vasomotion and increased myocardial resistance are frequent determinants of post-percutaneous coronary intervention (PCI) myocardial ischaemia. Strategies to enhance prediction of post-PCI angina include proper selection of patients undergoing revascularisation, construction of clinical prediction models, and further invasive evaluation at the time of coronary angiography in those with high likelihood.

Pharmacological approaches to coronary microvascular dysfunction.

In recent decades coronary microvascular dysfunction has been increasingly identified as a relevant contributor to several cardiovascular conditions. Indeed, coronary microvascular abnormalities have been recognized in patients suffering acute myocardial infarction, chronic stable angina and cardiomyopathies, and also in patients with hypertension, obesity and diabetes. In this review, we will examine pathophysiological information needed to understand pharmacological approaches to coronary microvascular dysfunction in these different clinical contexts. Well-established drugs and new pharmacological agents, including those for which only preclinical data are available, will be covered in detail.

BCNU-induced gR2 defect mediates S-glutathionylation of Complex I and respiratory uncoupling in myocardium.

A deficiency of mitochondrial glutathione reductase (or GR2) is capable of adversely affecting the reduction of GSSG and increasing mitochondrial oxidative stress. BCNU [1,3-bis (2-chloroethyl)-1-nitrosourea] is an anticancer agent and known inhibitor of cytosolic GR ex vivo and in vivo. Here we tested the hypothesis that a BCNU-induced GR2 defect contributes to mitochondrial dysfunction and subsequent impairment of heart function. Intraperitoneal administration of BCNU (40 mg/kg) specifically inhibited GR2 activity by 79.8 ± 2.7% in the mitochondria of rat heart. However, BCNU treatment modestly enhanced the activities of mitochondrial Complex I and other ETC components. The cardiac function of BCNU-treated rats was analyzed by echocardiography, revealing a systolic dysfunction associated with decreased ejection fraction, decreased cardiac output, and an increase in left ventricular internal dimension and left ventricular volume in systole. The respiratory control index of isolated mitochondria from the myocardium was moderately decreased after BCNU treatment, whereas NADH-linked uncoupling of oxygen consumption was significantly enhanced. Extracellular flux analysis to measure the fatty acid oxidation of myocytes indicated a 20% enhancement after BCNU treatment. When the mitochondria were immunoblotted with antibodies against GSH and UCP3, both protein S-glutathionylation of Complex I and expression of UCP3 were significantly up-regulated. Overexpression of SOD2 in the myocardium significantly reversed BCNU-induced GR2 inhibition and mitochondrial impairment. In conclusion, BCNU-mediated cardiotoxicity is characterized by the GR2 deficiency that negatively regulates heart function by impairing mitochondrial integrity, increasing oxidative stress with Complex I S-glutathionylation, and enhancing uncoupling of mitochondrial respiration.

Defining the role of high-dose statins in PCI.

Several studies have reported a significant reduction in morbidity and mortality in patients with acute coronary syndrome (ACS) or in patients with stable ischemic heart disease with the use of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins). Based on these findings, current guidelines recommend the use of statin therapy before hospital discharge for all patients with ACS regardless of the baseline low-density lipoprotein level. Statins are also recommended to patients at high risk for cardiovascular disease. Statins have been introduced in the clinical arena to reduce the low-density lipoprotein (LDL) cholesterol level that is associated with coronary atherosclerosis; however, a growing body of evidence suggests that other mechanisms of action beyond the modification of the lipid profile may come into action. In particular, statins exert antiinflammatory effects, modulate endothelial function, and inhibit the thrombotic signaling cascade. All together the non-LDL cholesterol-lowering effects of statins are called pleiotropic effects. In this article we will review the evidence supporting the use of high-dose statins in patients undergoing percutaneous coronary intervention, and we will also attempt to highlight the possible mechanisms of action.

Ultrasound assessment of the force-frequency relationship from the law of conservation of momentum in patients with left ventricular dysfunction.

Measurement of force-frequency relationship (FFR) is useful in the evaluation of heart rate-dependent contractile dysfunction. The purpose of this study was to evaluate a new Doppler-derived method for assessing FFR. Doppler velocity spectra at the left ventricular (LV) outflow tract was used to estimate mean blood flow velocity (mBFV), ejection time (ET) and velocity-time integral. LV ejection force (LVF) was then calculated according to the law of conservation of momentum: 1060 kg/m³ × (mBFV[m/sec]/ET [s]) × Stroke volume (mL). A symptom-limited, graded, bicycle semi-supine exercise test was performed in 56 patients with LV dysfunction (LV ejection fraction = 27 ± 6%). Measurements were obtained at baseline and serially during the test. The change in FFR was defined as up-sloping when the peak LVF was higher than the baseline value. The change was biphasic when the trend was initially up-sloping, then down-sloping; it was flat or negative when peak LVF was less than the baseline value. LVF was 30 ± 12 mN in patients with up-sloping FFR (n = 39) and 15 ± 6 mN in those with biphasic or flat FFR (n = 17; p < 0.0001). The ultrasound assessment of the FFR was highly concordant with a previously validated method based on pressure-end-systolic volume index ratio (κ = 0.75; 95% confidence interval, 0.55-94.0). The evaluation of the LVF using Doppler is an alternative method for the assessment of FFR during stress echocardiography in patients with LV dysfunction.

Therapy against ischemic injury.

The advent of reperfusion therapy constituted a historical change for the management of myocardial infarction (MI) patients. However, shortly after, experimental models recognized an intrinsic damage, related to reperfusion itself, which was termed as ischemiareperfusion injury (IRI). Clinical studies attribute IRI a significant burden of morbidity and mortality observed in patients undergoing successful epicardial reperfusion. Several mechanisms have been identified and, as many strategies, have been investigated to address the phenomenon. In this review we will discuss the current evidence for IRI, pharmacological and non-pharmacological preventive strategies adopted both in experimental models and in clinical practice. Finally, we will try to provide a critical appraisal to the lack of consistent benefit observed in translational medicine.

Microvascular function/dysfunction downstream a coronary stenosis.

For decades coronary macrovascular atherosclerosis has been considered the principal manifestation of coronary heart disease, with most of our effort dedicated to identifying and removal of coronary stenosis. However, growing body of literature indicates that coronary microcirculation also contributes substantially to the pathophysiology of cardiovascular disease. An understanding of mechanisms regulating microvascular function is of critical importance in understanding its role in disease, especially because these regulatory mechanisms vary substantially across species, vascular bed and due to comorbidities. Indeed, the most obvious consequence of coronary stenosis is that it may limit blood supply to the dependent myocardium to the point of causing ischaemia during exercise or even at rest. However, this flow limiting effect is not only due to the passive hydraulic effect of a narrowed conduit, but also to active responses in the coronary microcirculation triggered by the presence of an epicardial stenosis. To understand this problem it is important to review the inter-related mechanisms that regulate flow to the left ventricular wall and modulate transmural distribution of flow. These regulatory mechanisms operate hierarchically and are heterogeneously distributed along the coronary vascular tree. It is also important to discuss the effect of myocardial performance in modulating both blood flow demands and coronary resistance. Some of the interactions between coronary stenosis and microcirculation are transient, like those documented in acute coronary syndromes or during percutaneous interventions. However, microcirculatory remodeling may be triggered by a chronic coronary stenosis, leading to a sustained impairment of blood supply even after successful removal of the epicardial stenosis. A deeper understanding of these phenomena may explain paradoxical findings in patients undergoing coronary revascularization, particularly when functional tests are used in their assessment. These aspects are discussed in detail in this review.

The left ventricle as a mechanical engine: from Leonardo da Vinci to the echocardiographic assessment of peak power output-to-left ventricular mass.

The interpretation of the heart as a mechanical engine dates back to the teachings of Leonardo da Vinci, who was the first to apply the laws of mechanics to the function of the heart. Similar to any mechanical engine, whose performance is proportional to the power generated with respect to weight, the left ventricle can be viewed as a power generator whose performance can be related to left ventricular mass. Stress echocardiography may provide valuable information on the relationship between cardiac performance and recruited left ventricular mass that may be used in distinguishing between adaptive and maladaptive left ventricular remodeling. Peak power output-to-mass, obtained during exercise or pharmacological stress echocardiography, is a measure that reflects the number of watts that are developed by 100 g of left ventricular mass under maximal stimulation. Power output-to-mass may be calculated as left ventricular power output per 100 g of left ventricular mass: 100× left ventricular power output divided by left ventricular mass (W/100 g). A simplified formula to calculate power output-to-mass is as follows: 0.222 × cardiac output (l/min) × mean blood pressure (mmHg)/left ventricular mass (g). When the integrity of myocardial structure is compromised, a mismatch becomes apparent between maximal cardiac power output and left ventricular mass; when this occurs, a reduction of the peak power output-to-mass index is observed.

The second law of thermodynamics and the heart.

The second law of thermodynamics explains the phenomenon of irreversibility and the increasing entropic trend of nature. Similar to human-made machines, living structures are subjected to entropy generation, becoming 'worn' and 'damaged' from use. However, they have the possibility of eluding or deferring these processes. According to nonequilibrium thermodynamics, the heart could be considered as an open dissipative system, since it has the potential to offset the body's increasing entropic burden by using energy to export entropy to the surroundings. By organizing the tissues' molecules in order to perform external work as a result of its ability to provide oxygen and nutrients and remove waste products, the heart maintains the organization of the living structure and acts as an open dissipative system. However, the increase in tissues' randomness and disorder as a result of a number of disease states may be responsible for the intervening cardiac damage and entropy generation. This effect is known as the 'Dorian Gray effect' of the heart. Technical advances, including MRI and 3D echocardiography, may provide a means to improve the understanding of thermodynamic aspects of cardiovascular physiology and heart disease.