Nature Clinical Practice. Cardiovascular Medicine最新文献

Antihypertensive drugs that inhibit the renin-angiotensin system (RAS) have been proposed to have additional benefits beyond their classic effects on the cardiovascular system, including reducing the risk of new-onset diabetes. Whether RAS inhibitors vary in ability to protect against new-onset diabetes is, however, unknown. The angiotensin II type 1 receptor (AT(1)) blocker telmisartan has been discovered to also activate the peroxisome proliferator-activated receptor-gamma (PPARgamma), an established antidiabetic drug target. In patients with hypertension and biochemical features of the metabolic syndrome, telmisartan has had beneficial effects on lipid and glucose metabolism. As a selective modulator of PPARgamma, telmisartan does not cause the side effects of fluid retention and weight gain associated with conventional thiazolidinedione ligands of PPARgamma. These observations raise the possibility that combined AT(1) receptor blockade and selective PPARgamma modulation with molecules such as telmisartan could provide greater protection from new-onset diabetes and cardiovascular disease than drugs that target either the RAS or PPARgamma alone. The cardioprotective and antidiabetic effects of telmisartan are being assessed in two large clinical trials, the ONgoing Telmisartan Alone in combination with Ramipril Global Endpoint Trial (ONTARGET) and the Telmisartan Randomised AssessmeNt Study in ACE-I iNtolerant subjects with cardiovascular Disease (TRANSCEND).

Cardiovascular risk profiling and therapy have traditionally been based on established risk factors, such as age, smoking, sex, hypertension, dyslipidemia, body weight, and diabetes mellitus. Despite optimum therapy, cardiovascular mortality and morbidity remain high. Attention is being devoted, therefore, to identifying new risk factors that can also be used as therapeutic targets. Renal dysfunction manifesting as low glomerular filtration rate, albuminuria, or anemia is a strong risk factor for cardiovascular disease and is prevalent in the general population and among patients with cardiovascular disease. Epidemiological data suggest that 10-11% of the general population have low glomerular filtration rates, 5-7% have increased urinary albumin excretion, and 5-10% have anemia. Each of these features represents an independent but additive cardiovascular risk. Treatments for all these indications can reduce cardiovascular mortality and morbidity as well as renal risk. Such findings suggest that treatment should be directed towards improving renal function in order to achieve optimum cardiovascular benefit. Such a strategy would offer the possibility of multiorgan therapy in diseases characterized by multiorgan impairment, such as type 2 diabetes. I present the evidence that renal dysfunction is a common and powerful cardiovascular risk factor and that treatment strategies intervening in the renin-angiotensin-aldosterone system can be used to target albuminuria and reduce cardiovascular and renal risk.

Much controversy has surrounded both the pathological basis and the clinical utility of the metabolic syndrome. Key questions still revolve around the definition of this syndrome, its utility as a predictor of cardiovascular risk, and the treatment implications of diagnosis. The metabolic syndrome is associated with increased cardiovascular risk. However, the metabolic syndrome clearly underperforms compared with other, established prediction equations, such as the Framingham Risk Score and SCORE (Systemic COronary Risk Evaluation). Differences arise because the components are highly correlated (whereas other tools specifically include independent predictors) and because diagnosis is based on dichotomized variables. These facts, together with uncertain pathophysiology, mean that the metabolic syndrome in its current manifestation has limited utility for the diagnosis and treatment of cardiovascular disease. The syndrome has, however, served and continues to serve a useful purpose in raising awareness of the metabolic consequences of obesity, and as a spur for research into metabolic risk factor interactions.

Since its conception, the metabolic syndrome has received worldwide recognition as a useful clinical aid for predicting cardiovascular risk. The earliest definition, which included risk factors such as insulin resistance, hyperglycemia, hypertension, and cholesterol, has undergone many transformations. Two revisions have focused on visceral adiposity as an essential component of the syndrome, particularly in Asian populations. The Japanese national guidelines have also suggested that abnormalities in adipose tissue metabolism are an underlying molecular cause of the syndrome. In addition, emerging evidence suggests that lowering the threshold of waist circumference in Asian populations increases the prevalence of the metabolic syndrome. Inevitably, this widening of the threshold will capture more patients at risk of cardiovascular events. The aim of this Article is to consider the country-specific impact of the metabolic syndrome, using the evolution of the definition in Japan as a model.

Obesity greatly increases risk of cardiovascular disease, metabolic syndrome, and diabetes mellitus. Most obese patients are unable to sustain appreciable weight loss; the body has a natural tendency to return to its previous weight. Although bariatric surgery is effective, it is not without risk. Until better treatments for obesity are available, management remains focused on lifestyle changes, drug therapy, and treating the metabolic complications of obesity. The main cause of metabolic dysfunction in obesity is visceral fat. Fat deposition in and around organs, skeletal muscle, and other tissues is thought to occur when subcutaneous adipose tissue stores are full. Creation of additional adipose-tissue stores is prevented by the mature adipocytes, which inhibit the differentiation of preadipocytes in a negative feedback loop. This inhibition is mediated, in part, by the renin-angiotensin system. Indeed, angiotensin II blockade has been shown to promote adipogenesis in vitro. Clinical studies are currently underway to investigate whether the angiotensin-II-receptor blocker telmisartan can stimulate adipogenesis, with the aim of diverting intramuscular fat back into adipose tissue and thereby restoring insulin sensitivity. If this effect can be demonstrated in humans, this type of agent might become the treatment of choice for obese or overweight people at risk of type 2 diabetes.

A substantial need exists for new treatments to prevent and treat cardiac dysfunction. In the 1990s, there was great hope for gene therapy in this regard. Since that time, the focus has switched to cell therapy-in particular, therapy-with the aim of inducing myocardial regeneration. Individually, gene and cell therapies still have substantial promise. Ultimately, however, the convergence of both techniques might be necessary to achieve improvements in cardiac function and more successful clinical outcomes in patients with cardiac dysfunction. This approach has already been adopted for treatment of malignancies. Several gene products are currently being studied, including growth factors and chemokines that can modulate the survival and function of cardiac myocytes following an ischemic event and influence remodeling of the left ventricle. However, several issues remain, including the optimization and characterization of cell types, selection of vectors for gene transfer, and identification of appropriate strategies for delivery. Here, we review the potential and need for cell-based gene therapy for the prevention and treatment of cardiac dysfunction and attempt to discuss the unresolved issues.

For decades, it has been widely accepted that the heart is a terminally differentiated organ that is unable to regenerate. Studies of recipients of hearts donated by other humans have shed light on the regenerative potential of the human heart. Investigators have been able to trace the Y chromosome by fluorescence in situ hybridization or polymerase chain reaction, or both, in sex-mismatched heart recipients. Cardiac chimerism has been reported, with concentrations of chimeric cells ranging from 0.04% to 10.0%. Cardiac chimerism after bone marrow or progenitor cell transplantation has also been reported to a low extent (approximately 0.20%), suggesting that a fraction of the extracardiac cells that colonize the myocardium are of bone marrow origin. Cardiac chimerism after pregnancy with male offspring (fetal cell microchimerism) has also been demonstrated. Cells of fetal origin have been shown to be capable of differentiating into myocardial cells. Collectively, we show that chimerism studies provide a proof of concept of a process that it is likely to be part of normal cardiac homeostasis in humans but apparently insufficient for cardiac repair in diseased hearts.

The concept of an intrinsic regenerative capacity of the adult mammalian myocardium owing to the presence of cardiac stem cells (CSCs) in the atria and ventricles is starting to be accepted by the cardiovascular research community. The identification of this cell population has improved the prospects for developing successful clinical protocols for human myocardial regeneration. In the normal adult myocardium, only a small fraction of CSCs undergo amplification and differentiation to replace the parenchymal cells lost by normal wear and tear. Physiological or pathological stimuli cause substantial activation of CSCs, which is mediated by a paracrine feedback loop between myocytes and CSCs. In response to stress, the myocytes produce growth factors and cytokines, for which CSCs have receptors, and autocrine, self-sustaining activation of growth-factor production is simultaneously triggered in the CSCs. These findings from human and animal studies led us to test whether in situ activation of CSCs by growth factors would be as effective as transplantation of CSCs into the regenerating myocardium after ischemia in an animal model that has relevance to humans. In a porcine model, we produced extensive and functionally relevant myocardial regeneration. Here, we discuss the properties of endogenous myocardial stem cells that might be exploited to produce clinical myocardial regeneration without the need for cell transplantation.

Cellular cardiomyoplasty (myogenic cell grafting) is actively being explored as a novel method to regenerate damaged myocardium. The adult human heart contains small populations of indigenous committed cardiac stem cells or multipotent cardiac progenitor cells, identified by their cell-surface expression of c-kit (the receptor for stem cell factor), P-glycoprotein (a member of the multidrug resistance protein family), and Sca-1 (stem cell antigen 1, a mouse hematopoietic stem cell marker) or a Sca-1-like protein. Cardiac stem cells represent a logical source to exploit in cardiac regeneration therapy because, unlike other adult stem cells, they are likely to be intrinsically programmed to generate cardiac tissue in vitro and to increase cardiac tissue viability in vitro. Cardiac stem cell therapy could, therefore, change the fundamental approach to the treatment of heart disease.