Seminars in vascular medicine最新文献

Severe hyperhomocysteinemia is typically caused by rare enzymatic defects or by renal failure. In contrast, mild to moderate hyperhomocysteinemia chiefly results from suboptimal status of nutritional factors involved in homocysteine metabolism. Low dietary intake of folate is the most important nutritional cause of elevated homocysteine (tHcy) concentrations. Folic acid is more effective than dietary folate in lowering tHcy concentrations, and a daily dose of 400 mug of folic acid is the minimum daily dose associated with the maximum tHcy-lowering effect ( approximately 20-25% reduction). Mean fasting tHcy concentrations have dropped substantially in populations with mandatory folic acid fortification, and other B-vitamins, such as vitamin B (12), are important determinants of tHcy levels in this setting. Vitamins B (2) and B (6) have little influence on fasting tHcy concentrations, although the former may be relevant in individuals with the MTHFR 677 TT-genotype, and the latter may improve tHcy catabolism in elderly individuals. Betaine and choline can lower fasting tHcy concentrations to a similar extent as folic acid, particularly in the setting of a high intake of methionine. Consumption of tea and coffee increase tHcy concentrations by up to 20%. A high-protein meal also increases tHcy, but these changes are transient, and levels return to normal after an overnight fast. Serine and cystine also influence the methionine-induced postprandial rise in tHcy concentrations. In conclusion, alteration in dietary intake or use of folic acid supplements can substantially lower tHcy concentrations. However, it is not known whether lowering tHcy levels can reduce the risk of cardiovascular disease or cognitive decline or prevent pregnancy complications or osteoporosis.

The prevalence of obesity is increasing at an alarming rate in many parts of the world. In White populations living in the west and north of Europe, Australia, and the United States, the prevalence of obesity is similarly high in men and women. In countries with relatively low gross national product, such as those in Central and Eastern Europe, Asia, Latin-America, and Africa, the prevalence is 1.5 to 2 times higher among women than among men. Within affluent societies, the rates of obesity seem to be more common among women at older ages (65 years) and in groups with relatively low socioeconomic status. It can be tentatively concluded that obesity is particularly common in women living in relatively poor conditions.

The prevalence of obesity in industrialized countries has reached epidemic proportions, with about one in three people being obese and another one in three people being overweight and at risk of developing obesity. In recent years, obesity has gained the traditional tetrad of cardiovascular risk factors of smoking: hypertension, dyslipidemia, and dysglycemia. Attention has also focused on the importance of abdominal (or central) obesity as a determinant of cardiovascular risk, independent of the body mass index. In addition to effects on coronary artery disease, obesity has an effect on cardiovascular disease, including stroke, ventricular function, peripheral arterial disease, and venous thromboembolism. The objectives of this review are to summarize the effects of obesity on cardiovascular disease, and the possible mechanisms for these associations, and to investigate the effects of weight-loss interventions on the burden of cardiovascular disease. Large ongoing clinical outcome trials, such as the SOS study, the Look-AHEAD trial, or the SCOUT study, should provide important information on the effects of surgical and nonsurgical obesity treatment on cardiovascular morbidity and mortality.

An increased amount of deep abdominal visceral fat has generally been accepted as an important cardiovascular risk factor, and disturbances in hemostasis and fibrinolysis have been suggested to play a role. Fibrinogen and von Willebrand factor, representatives of the hemostatic system, and plasminogen activator inhibitor 1 (PAI-1), as the most important inhibitor of the fibrinolytic system, have been associated with visceral obesity, with the most convincing evidence found for the involvement of PAI-1. The association with fibrinogen and von Willebrand factor has been suggested to be merely a reflection of the association with inflammation and endothelial dysfunction. The fact that PAI-1 is secreted by adipose tissue has attracted much attention. The increase of PAI-1 in visceral obesity could be because visceral adipose tissue produces more PAI-1 compared with subcutaneous abdominal adipose tissue. The contribution of other cell types such as hepatocytes or endothelial cells is probably more important, with stimulation of PAI-1 production by different components of the metabolic syndrome. PAI-1 secretion by adipose tissue has been suggested to have a more local effect, playing a role in tissue remodeling during the development of obesity.

Deep vein thrombosis (DVT) is a disorder frequently affecting the deep veins of the lower limbs; its onset is induced by known risk factors. The main complications of DVT are pulmonary embolism and postthrombotic syndrome (PST). Clinical pulmonary embolism occurs in a high proportion of cases of untreated proximal DVT and is associated with a mortality rate of 11-23% if not treated. PST, however, is a cause of increased morbidity and disability. The natural history of DVT is a dynamic process, with both thrombolysis and thrombus extension occurring after an episode of DVT. With the introduction of duplex scanning, several clinical studies have investigated and tried to clarify the natural history of DVT, the rate of recanalization of the thrombus, and the presence of reflux and its relation to lysis of the thrombus. These and other debated issues associated with PST are reviewed here. Knowledge of the evolution of these processes could result in better understanding of PST and be applied for improvement of medical and surgical management of venous thrombosis and its complications.

Recently, adipocytes have been shown to be endocrine cells that secrete a variety of bioactive substances-the so-called adipocytokines. Among adipocytokines, tumor necrotizing factor alpha, plasminogen activator inhibitor 1, and heparin-binding epidermal growth factor-like growth factor are produced in adipocytes as well as already known organs, and they contribute to the development of vascular diseases. Visfatin is a very recently discovered visceral fat-specific protein that may be related to the development of obesity-related diseases such as diabetes mellitus and cardiovascular disease. In contrast to these adipocytokines, adiponectin, also a newfound adipose tissue-specific collagen-like protein, has been noted recently as an important antiatherogenic as well as antidiabetic protein. The function of adipocytokine secretion might be regulated dynamically by nutritional state. Visceral fat accumulation causes dysfunction of adipocytes including oversecretion of tumor necrotizing factor alpha, plasminogen activator inhibitor 1, and heparin-binding epidermal growth factor-like growth factor, as well as hyposecretion of adiponectin, which results in the development of a variety of metabolic and circulatory diseases. In this review, the importance of adipocytokines, including adiponectin, is discussed with respect to atherosclerosis.

Obesity is becoming more prevalent in the developed world because of the abundance of food and the decrease of physical activity. Obesity is a risk factor for a host of diseases from arthritis to cardiovascular disease. The precise mechanisms by which obesity promotes cardiovascular disease are not well understood but are likely to include metabolic and inflammatory responses to the increased amount of stored fat. The endothelium plays a pivotal role in maintaining vascular health. Impaired endothelial function is an independent predictor of cardiovascular disease. Most studies of vascular function in obese subjects have demonstrated impaired endothelial function. This impairment of endothelial function becomes obvious early on, long before any vascular abnormalities become clinically relevant and detectable. Better understanding of the mediators of obesity-induced endothelial dysfunction may lead to the identification of new targets for interventions that may prevent or postpone the development of obesity-related cardiovascular disease.

Leptin is synthesized and secreted primarily by adipocytes, and is present in serum in direct proportion to the amount of adipose tissue. The primary role of leptin is to provide to the central nervous system a signal of energy intake and energy stores in the body so that the hypothalamus can efficiently maintain a stable body weight. The receptor for leptin in the hypothalamus signals by activation of an associated janus kinase which phosphorylates signal transducer and activator of transcription (STAT) proteins that regulate neuronal gene expression. Genetic mutations in leptin and its receptor can result in obesity in both rodents and humans, supporting a central role for leptin in the regulation of body weight. Leptin has also been implicated in a variety of physiological processes other than body weight homeostasis. Many of these functions are mediated through the central nervous system; however, the presence of leptin receptors in tissues throughout the body suggests that leptin can also have direct effects on cells and tissues. Serum leptin levels have been associated with cardiovascular risk factors after correction for adiposity. Leptin can promote platelet aggregation, which requires expression of functional leptin receptors on the platelet. Leptin-induced increases in sympathetic nerve activity have been suggested to contribute to hypertension, and leptin has been observed to increase oxidative stress in cultured endothelial cells. Many of these pathophysiologic effects of leptin on the vasculature are most likely of importance when leptin levels are elevated in obese subjects due to resistance to the weight-reducing effects of the hormone. An improved understanding of the effects of leptin on the vasculature will provide valuable insight into the relationship between obesity and cardiovascular disease.