Current Pharmaceutical Design - Volume 14, Issue 25, 2008

The concept of metabolic modulation has an important part in the treatment of cardiovascular disease. It is now clear that ischemic heart disease, heart failure and diabetic cardiomyopathy have in common a derangement of cardiac metabolism shifted towards a greater utilization of free fatty acids and a reduced efficiency of the Krebs cycle. Over the past decades, several dugs that have been shown to improve cardiac metabolism in patients with ischemic heart disease and more recently in those with heart failure. These drugs include carnitine palmitoyl transferase (CPT)- I and/or -II inhibitors, such as etomoxir and perhexiline, essential amino acids, and long-chain 3- ketoacyl coenzyme A thiolase (LC3-KAT) inhibitors, such as trimetazidine and ranolazine. Some of these drugs are believed to work by partially inhibiting the oxidation of fatty acids in ischemic myocytes, others by improving the efficiency of the Krebs cycle. Since the oxidation of glucose is more energy efficient than fatty acid oxidation it becomes clear that enhancement of glucose metabolism should be pursued when oxygen availability is limited in underperfused cardiac tissue and in failing cardiomyocytes. Most of the drugs modulating cardiac metabolism are approved for the treatment of angina pectoris in most of Europe, Asia and Australia but not in the United States. On the contrary, ranolazine that was thought to be a metabolic agent but that now is supposed to have a different, yet not clear, mechanism of action, is approved for use in the United States but not in Europe. In this issue of Current Pharmaceutical Design, the metabolic basis of myocardial ischemia and dysfunction and the rationale for metabolic therapy in ischemic heart disease and heart failure are carefully reviewed by international experts who have mostly contributed in this area of research and matured a sound clinical experience.Yoshimura et al. [1] discuss the metabolic changes that occur in patients with diabetes mellitus and some of the metabolic therapeutic options currently available. Karastergiou and Kaski [2] discuss in depth the medical management of the diabetic patient with ischemic heart disease and highlight the need of optimization of cardiac metabolism. Vitale et al. [3] analyse the effects of drugs (e.g., dichloroacetate, L-carnitine, propionyl L-carnitine, CPT-I and LC3-KAT inhibitors) that may optimize the cardiac metabolism in patients with diabetes mellitus. Rosano et al. [4] review the metabolic changes that occur during myocardial ischemia, with related therapeutic implications, whereas Chagas et al. [5] review the importance of modulation of cardiac metabolism in patients with ischemic heart disease and the use of pharmacological strategies to improve the cardiac metabolism by the activation of pyruvate dehydrogenase (e.g., dichloroacetate), reduction of cellular uptake of free fatty acids (e.g., glucose and insulin), inhibition of mitochondrial transport of free fatty acids by CPT-I inhibitors (e.g., perhexiline and etomoxir), and inhibition of beta-oxidation of free fatty acids by LC3-KAT inhibitors (e.g., trimetazidine and, possibly, ranolazine). Heart failure is often the late stage of chronic ischemic heart disease. Dalla Libera et al. [6] review the pathophysiological and molecular (e.g., cardiomyocyte apoptosis) phenomena responsible for contractile dysfunction in heart failure, whereas Fragasso et al.[7] examine the possible effect of modulation of cardiac metabolism in patients with heart failure by acting on different metabolic pathways (e.g., inhibition of free fatty acids oxidation, xantineoxidase inhibition, mitochondrial metabolic oxidation). Marazzi et al. [8] analyze the role of amino acids in the modulation of cardiac metabolism during myocardial ischemia and heart failure by multiple actions they can provide (e.g., improvement of the oxidative stress by counteracting the action of radical oxygen species; positive action on endothelial function; increase of protein synthetic efficiency of myocardial cells by regulating gene expression; modulation of hormonal activity). Finally, Fazio et al. [9] critically revise the literature data on the possible role of statins (mainly, their pleiotropic effects) in preventing the progression of congestive heart failure in patients with metabolic syndrome. We wish to thank all the authors for their important contributions. It is our hope that this issue may represent a useful guide for a reasoned approach to metabolic therapy in patients with ischemic heart disease and/or heart failure.

Diabetes mellitus is one of the most common chronic illnesses throughout the world. Diabetic cardiomyopathy is a specific syndrome, consisting of cardiomegaly, left ventricular dysfunction, electrical remodeling of the ventricle, and symptoms of congestive heart failure, that is seen in diabetic patients in the absence of other predisposing factors. Many researchers have suggested that inhibition of the renin-angiotensin-aldosterone system and the sympathetic nervous system may exert a therapeutic effect in individuals with diabetic cardiomyopathy. Indeed, angiotensin II and aldosterone blockade may be effective, partly because aldosterone blockade down-regulates Na+/H+ exchanger 1 activity. Further study of the alterations in ion channel physiology in the context of diabetic cardiomyocytes may be of benefit.

The prevalence of type 2 diabetes is rising at an alarming rate worldwide. Coronary artery disease (CAD) is the leading cause of morbidity and mortality in the diabetic population. Future CAD risk should be routinely assessed in patients with diabetes as specific subgroups might benefit from information derived from cardiac stress testing and other diagnostic procedures. Risk factor control is of paramount importance in all cases and it usually requires sustained lifestyle modifications, coupled with pharmacological interventions. Statins and angiotensin-converting enzyme (ACE) inhibitors are the first-line agents for the treatment of dyslipidaemia and hypertension, respectively. Microvascular, but not macrovascular, complications of diabetes are effectively prevented by good glycaemic control. Metformin is considered the first-choice agent in overweight diabetic subjects, while the role of thiazolidinediones is currently the focus of medical research. The diagnosis of acute coronary events in patients with diabetes is often challenging because of the high prevalence of silent ischaemia in these subjects. All acute cardiac events need to be promptly treated and myocardial reperfusion attempted without delay. Maintaining glucose levels as close to normal as possible, during and shortly after an acute event, improves prognosis in patients with diabetes. Risk factor control remains the cornerstone of secondary prevention; beta-blockers, ACE-inhibitors and antiplatelet agents confer additional symptomatic and survival benefit. Similar therapeutic principles also apply to patients with type 1 diabetes. This article addresses the complex problem of managing patients with diabetes and coronary artery disease.

Cardiovascular disease is a major health problem in all over the world. The prevalence of type 2 diabetes mellitus has been rapidly increasing, together with the risk for cardiovascular events. Patients with diabetes, and/or with insulin resistance as well, have an impaired myocardial metabolism of glucose and free fatty acids (FFA) and accelerated and diffuse atherogenesis, with involvement of peripheral coronary segments. Significant metabolic alterations in diabetic patients are the decreased utilization of glucose and the increase in muscular and myocardial FFA uptake and oxidation, occurring as a consequence of the mismatch between blood supply and cardiac metabolic requirements. These metabolic changes are responsible both for the increased susceptibility of the diabetic heart to myocardial ischemia and for a greater decrease of myocardial performance for a given amount of ischemia, compared to non diabetic hearts. A therapeutic approach aimed at an improvement of cardiac metabolism, through manipulations of the utilization of metabolic substrates, may improve myocardial ischemia and left ventricular function. Modulation of myocardial FFA metabolism, in addition to optimal medical therapy, should be the key target for metabolic interventions in patients with coronary artery disease and diabetes. In diabetic patients the effects of modulation of FFA metabolism should be even greater than those observed in patients without diabetes.

Myocardial ischemia occurs for a mismatch between blood flow and metabolic requirements, when the rate of oxygen and metabolic substrates delivery to the myocardium is insufficient to meet the myocardial energy requirements for a given myocardial workload. During ischemia, substantial changes occur in cardiac energy metabolism, as a consequence of the reduced oxygen availability. Some of these metabolic changes are beneficial and may help the heart adapt to the ischemic condition. However, most of the changes are maladaptive and contribute to the severity of the ischemic injury leading stunned or hibernating myocardium, cell death and ultimately to contractile disfuction. Dramatic changes in cardiac metabolism and contractile function, also occur during myocardial reperfusion as a consequence of the generation of oxygen free radicals, loss of cation homeostasis, depletion of energy stores, and changes in subcellular activities. The reperfusion injury may cause in the death of cardiac myocytes that were still viable immediately before myocardial reperfusion. This form of myocardial injury, by itself can induce cardiomyocyte death and increase infarct size. During acute ischemia the relative substrate concentration is the prime factor defining preference and utilization rate. Allosteric enzyme regulation and protein phosphorylation cascades, partially controlled by hormones such as insulin, modulate the concentration effect; together they provide short-term adjustments of cardiac energy metabolism. The expression of metabolic genes is also dynamically regulated in response to developmental and (patho)physiological conditions, leading to long-term adjustments. Specific nuclear receptor transcription factors and co-activators regulate the expression of these genes. Understanding the functional role of these changes is critical for developing the concept of metabolic intervention for heart disease. The paper will review the alterations in energy metabolism that occur during acute and chronic ischemia.

Metabolic modulation during myocardial ischemia is possible by the use of specific drugs, which may induce a shift from free fatty acid towards predominantly glucose utilization by the myocardium to increase ATP generation per unit oxygen consumption. Three agents (trimetazidine, ranolazine, and perhexiline) have well-documented anti-ischaemic effects. However, perhexiline, the most potent agent currently available, requires plasma-level monitoring to avoid hepatoneuro- toxicity. Besides, the long-term safety of trimetazidine and ranolazine has yet to be established. In addition to their effect in ischemia, the potential use of these drugs in chronic heart failure is gaining recognition as clinical and experimental data are showing the improvement of myocardial function following treatment with several of them, even in the absence of ischemia. Future applications for this line of treatment is promising and deserves additional research. In particular, large, randomised, controlled trials investigating the effects of these agents on mortality and hospitalization rates due to coronary artery disease are needed.

The purpose of this review is to enlighten the mechanisms of skeletal muscle dysfunction in heart failure. The muscle hypothesis suggests that chronic heart failure (CHF) symptoms, dyspnoea and fatigue are due to skeletal muscle alterations. Hyperventilation due to altered ergoreflex seems to be the cause of shortness of breath. Qualitative and quantitative changes occurring in the skeletal muscle, such as muscle wastage and shift from slow to fast fibers type, are likely to be responsible for fatigue. Mechanisms leading to muscle wastage in chronic heart failure, include cytokine-triggered skeletal muscle apoptosis, but also ubiquitin/proteasome and non-ubiquitin-dependent pathways. The regulation of fibre type involves the growth hormone/insulin-like growth factor 1/calcineurin/ transcriptional coactivator PGC1 cascade. The imbalance between protein synthesis and degradation plays an important role. Protein degradation can occur through ubiquitin-dependent and non-ubiquit-independent pathways. Systems controlling ubiquitin/ proteasome activation have been described. These are triggered by tumour necrosis factor and growth hormone/ insulin-like growth factor 1. However, an important role is played by apoptosis. In humans, and experimental models of heart failure, programmed cell death has been found in skeletal muscle and interstitial cells. Apoptosis is triggered by tumour necrosis factor and in vitro experiments have shown that it can be induced by its second messenger sphingosine. Apoptosis correlates with the severity of the heart failure syndrome. It involves activation of caspases 3 and 9 and mitochondrial cytochrome c release. Sarcomeric protein oxidation and its consequent contractile impairment can form another cause of skeletal muscle dysfunction in CHF.

Alterations of cardiac metabolism can be present in several cardiac syndromes. Heart failure may itself promote metabolic changes such as insulin resistance, in part through neurohumoral activation, and determining an increased utilization of non-carbohydrate substrates for energy production. In fact, fasting blood ketone bodies as well as fat oxidation have been shown to be increased in patients with heart failure. The result is depletion of myocardial ATP, phosphocreatine and creatine kinase with decreased efficiency of mechanical work. A direct approach to manipulate cardiac energy metabolism consists in modifying substrate utilization by the failing heart. To date, the most effective metabolic treatments include several pharmacological agents, such as trimetazidine and perhexiline, that directly inhibit fatty acid oxidation. These agents have been originally adopted to increase the ischemic threshold in patients with effort angina. However, the results of current research is supporting the concept that shifting the energy substrate preference away from fatty acid metabolism and toward glucose metabolism could be an effective adjunctive treatment in patients with heart failure, in terms of left ventricular function and glucose metabolism improvement. In fact, these agents have also been shown to improve overall glucose metabolism in diabetic patients with left ventricular dysfunction. In this paper, the recent literature on the beneficial therapeutic effects of modulation of cardiac metabolic substrates utilization in patients with heart failure is reviewed and discussed.

During ischemia and heart failure, myocardial cells suffer for chronic energy starvation resulting in metabolic and contractile dysfunction. In normal conditions fatty acids, glucose, and lactate are the principal oxidative fuels in myocardium, while amino acids serve a minor role as an oxidative fuel. However, in pathological conditions, myocardial uptake of several amino acids increases significantly as a consequence of a metabolic remodelling. Amino acids are involved in a variety of key biochemical and physiological activities, that counteract the deleterious cellular effects of reduced oxygen availability. Several amino acids are a direct source of substrate for energy production, and they modulate the activity of some enzymes involved in the glucose metabolism. They increase contractile performance both in isolated animal and human myocardium. Furthermore, amino acids improve the oxidative stress counteracting the action of radical oxygen species, being either precursors of glutathione synthesis, or of substrate of nitric oxide biosynthesis; they act on endothelial function and increase protein synthetic efficiency of myocardial cells by regulating gene expression and modulating hormonal activity. An amount of studies have demonstrated that amino acids administration, on patients with ischemic heart disease and heart failure, can improve several clinical endpoints. Here, we present an overview of the principal effects of the most experienced amino acids and of amino acid derivatives on ischemia and heart failure.

Heart Failure (CHF) is a very important public health problem in the world and certainly one of the most common debilitating diseases and cause of mortality. Current knowledge underlines that incidence rates are also influenced by the coexisting pathologic conditions that accelerate the development of disease or increase its severity. Important scientific evidence is emerging to demonstrate a strong correlation between HF and the metabolic syndrome (MetS). Hypolipemia- inducing medication offers the opportunity to discuss the possible existence of pharmacological substances that in addition to their specific targets have several demonstrated pleiotropic effects that could be beneficial in HF. Although several trials investigated statins treatment effects on HF in general, some evidence exists about the role that these drugs can have in the progression of the disease in the specific category of HF patients affected by MetS. In this review the possible positive effects of the statins treatment in this specific subset of patients are discussed.

Nitric oxide (NO) is a well-recognized anti-atherogenic factor; it inhibits the inflammatory-proliferative processes in atherosclerosis. Indeed, endothelial dysfunction due to reduced synthesis and/or bioavailability of NO is thought to be an early step in the course of atherosclerotic cardiovascular disease (CVD). NO is synthesized from L-arginine via the action of NO synthase (NOS), which is known to be blocked by endogenous L-arginine analogues such as asymmetric dimethylarginine (ADMA), a naturally occurring amino acid found in plasma and various types of tissues. Recently, it has been demonstrated that plasma levels of ADMA are elevated in patients with diabetes. These findings suggest that the elevated ADMA in diabetes could contribute to acceleration atherosclerosis in this population. Further, since ADMA is mainly metabolized by dimethylarginine dimethylaminohydrolase (DDAH), it is conceivable that the inhibition of ADMA via up-regulation of DDAH may be a novel therapeutic target for the prevention of CVD in patients with diabetes. In this paper, we review the pathophysiological role of ADMA and DDAH system for accelerated atherosclerosis in diabetes and the therapeutic utility of ADMA suppression in CVD in diabetes.

RNA virus infections cause immense human disease burdens globally, and few effective antiviral drugs are available for their treatment. Peptide-conjugated phosphorodiamidate morpholino oligomers (PPMO) are nuclease resistant and water-soluble single-stranded-DNA-analogues that can enter cells readily and act as steric-blocking antisense agents through stable duplex formation with complementary RNA. Recently there have been a number of publications documenting sequence-specific and dose-dependent inhibition of non-retroviral RNA virus infections by PPMO in both cell culture and murine experimental systems. PPMO have suppressed viral titers by several orders of magnitude in cell cultures, and have reduced viral replication in and/or increased survivorship of mice experimentally infected with poliovirus, coxsackievirus B3, dengue virus, West Nile virus, Venezuelan Equine encephalitis virus, respiratory syncytial virus, Ebola virus and influenza A virus. Along with evaluating PPMO efficacy and toxicity, these studies also explored PPMO mechanism of action, pharmacologic properties and the generation and characterization of resistant virus. Effective PPMO target sites in viral RNA have included regions of highly conserved sequence thought to be important in the pre-initiation or initiation of translation, or in long-range RNA-RNA interactions involved in viral RNA synthesis. These studies provide guidance for the design of steric-blocking antisense agents against RNA viruses, insights into viral molecular biology and novel strategies for the development of antiviral therapeutics. The purpose of this review is to summarize notable findings from the reports documenting antiviral activity by PPMO, with a focus on the specific regions of viral RNA that provided the most effective targets for PPMO-based inhibition of viral replication.