Seminars in vascular medicine最新文献

Familial combined hyperlipidemia (FCH) is the most common inherited hyperlipidemia in humans, affecting 1 to 3% of the adult population and up to 20% of patients with premature myocardial infarction. FCH is traditionally diagnosed by total plasma cholesterol and/or triglyceride levels above the 90th percentile adjusted for age and gender; however, the diagnosis of FCH based on these diagnostic criteria is inconsistent in 26% of the subjects over a five-year period, emphasizing the need for re-evaluation of the diagnostic criteria for FCH. Recently, a nomogram was developed based on absolute apolipoprotein B levels in combination with triglyceride and total cholesterol levels adjusted for both age and gender to simply and accurately diagnose FCH. When percentiles of triglyceride and total cholesterol adjusted for age and gender are not available in a population, the definition of FCH can be established based on hypertriglyceridemia (> 1.5 mmol/l) and hyperapoB (> 1200 mg/l). Standardized and simple diagnostic criteria are necessary to further delineate the pathogenesis of FCH. Several metabolic pathways have been suggested to be important in causing the FCH phenotype including hepatic VLDL overproduction either with or without impaired clearance of triglyceride-rich lipoproteins from plasma. The presence of insulin resistance and obesity in FCH patients further contribute to the expression of the lipidphenotype. A disturbed adipose tissue metabolism that results in an increased plasma free fatty acid pool may be the culprit in the pathogenesis of FCH.

In humans, apolipoprotein E (apoE) is a polymorphic protein of which three common isoforms can be distinguished, designated apoE2, apoE3, and apoE4. This genetic variation is associated with different plasma lipoprotein levels, different response to diet and lipid-lowering therapy, and a variable risk for cardiovascular disease and Alzheimer's disease. An example of an apoE-mediated, autosomal recessive, lipid disorder is familial dysbetalipoproteinemia (FD), caused by mutations in the apolipoprotein E gene. Homozygosity for APOE*2 (1 in 170 persons) causes FD or type III hyperlipoproteinemia in less than 20% of the adult APOE*2 homozygotes. Less common, dominant negative mutations may also cause the disorder. The patients may present with typical skin lesions and elevated plasma levels of cholesterol and triglycerides, mainly in very-low-density lipoprotein remnants and intermediate-density lipoproteins. The disorder is associated with peripheral and coronary artery disease. Additional gene and environmental factors are necessary for the expression of this hyperlipoproteinemia. Hyperinsulinemia and defects in genes involved in the hydrolysis of triglycerides are associated with this lipid disorder. Diet and weight reduction are effective but usually not sufficient to normalize the lipid levels. Additional therapy with statins or fibrates is necessary and effective in most patients.

Patients with familial hypercholesterolemia (FH) or familial defective apolipoprotein B (FDB) have severely increased low-density lipoprotein (LDL)-cholesterol levels and increased risk for premature coronary artery disease (CAD). Previous data on FDB patients were collected in patients referred to lipid clinics and were therefore subject to referral bias. We assessed the clinical phenotype of FDB in a population free from selection on CAD to compare the atherosclerotic burden with that of heterozygous FH. The study population was actively recruited in a large-scale screening program for inherited hypercholesterolemia in which FH and FDB heterozygotes were diagnosed by standard molecular techniques. Patients with FH and FDB had significantly higher plasma total cholesterol and LDL-cholesterol levels compared with their unaffected relatives. As with previous findings in FH, in FDB 19% of the carriers and 17% of the noncarriers of apoB mutations would have been misdiagnosed by cholesterol measurement alone, taking the age- and sex-specific 95th percentile as the diagnostic criterion. In FH patients the CAD risk was 8.5 relative to unaffected family members, whereas FDB patients had a 2.7-fold higher risk of CAD than unaffected relatives. FDB patients, free from clinical selection bias, do show lower total and LDL-cholesterol levels and lower CAD risk compared with FH heterozygotes. However, FDB patients are still exposed to a substantially higher CAD risk compared with unaffected relatives.

Familial hypercholesterolemia (FH) is a codominant disorder due to a variety of mutations of the low-density lipoprotein (LDL) receptor gene that result in an elevation of plasma LDL-cholesterol (LDL-C). Plasma levels of LDL-C show large interindividual variation even in subjects carrying the same mutation of the LDL receptor gene. This variability may be due to genetic factors (modifier genes). Several surveys indicate that the overall contribution of common polymorphisms of modifier genes (such as the genes encoding apolipoproteins E and B) to this variability is less than 10%. In contrast, beta-thalassemia has a profound LDL-lowering effect. This was documented in FH patients identified on the island of Sardinia, in Italy, where 12% of the inhabitants are carriers of beta-thalassemia due to a single mutation (Q39X) of the beta-globin gene that abolishes the synthesis of beta-globin chain of hemoglobin (beta(o)-thalassemia). Plasma LDL-C in FH heterozygotes carrying the beta(o)-thalassemia trait is 25% lower than in noncarriers, regardless of the LDL receptor gene mutation. It is likely that this effect is due to two main mechanisms: (1) increased uptake of LDL by the bone marrow to provide cholesterol for the increased proliferation of erythroid progenitor cells and (2) increased production of inflammatory cytokines that reduce the hepatic secretion and increase the catabolism of LDL. In view of its LDL-C-lowering effect, beta-thalassemia trait may protect FH heterozygotes against premature coronary atherosclerosis.

As part of the acute phase reaction, lipid metabolism is significantly altered in patients with unstable coronary syndromes. The clinical relevance and the mechanisms underlying this phenomenon are discussed in this article. Cholesterol reduction takes place in the first hours of an acute coronary event; thus, plasma levels determined at this point should be interpreted with caution. This reduction may be just a consequence of the inflammatory response, or it may be also related to an increase in cellular uptake of cholesterol for tissue repair and hormonal synthesis. A synergistic effect between this predisposition to cholesterol reduction and statin therapy appears to exist during acute coronary syndromes. Triglyceride changes are variable during acute coronary syndromes, and recent data indicate that the pattern of triglyceride variation is a potential risk marker in those patients, possibly because it reflects neurohumoral changes related to the acute phase.

Ghrelin, a 28-amino acid peptide mainly produced by the stomach, is a natural ligand of the type 1a growth hormone secretagogue receptor (GHS-R1a) that also binds synthetic peptidyl and nonpeptidyl GHSs. GHS-R1a and various GHS-R1a-related receptor subtypes are widely distributed in central and peripheral tissues, particularly in the cardiovascular system. In agreement with this distribution of GHS-R, ghrelin and synthetic GHSs exert a wide spectrum of actions, including cardiac and vascular activities. Ghrelin, as well as peptidyl and nonpeptidyl GHSs, is able to increase cardiac performances both in animals and in humans and to exert protective effects on ischemia/reperfusion injury of isolated rat heart. Moreover, both ghrelin and synthetic GHSs have been shown as able to act as survival factors, protecting cardiomyocytes and endothelial cells from doxorubicin-induced apoptosis. Despite the fact that the neuroendocrine actions of ghrelin are dependent on its acylation in serine 3, these cardiovascular effects are exerted by unacylated as well as by acylated ghrelin. This evidence indicates that these actions are not likely to be mediated by a type 1a GHS-R, which, by definition, binds acylated ghrelin only. However, synthetic peptidyl GHSs, but not nonpeptidyl, and even ghrelin itself are able to reduce atherosclerotic lesion development in apolipoprotein-E-deficient mice. This action seems to be mediated by a specific receptor for synthetic peptidyl GHSs only, identified as CD36, a multifunctional B-type scavenger receptor involved in atherogenesis and mainly expressed in cardiomyocytes and microvascular endothelial cells. Thus, there are similarities, but also differences, between ghrelin and synthetic GHSs, in terms of cardiac actions that are likely to be related to the existence of multiple GHS-R subtypes that mediate the cardiovascular actions of the above substances. These actions indicate their potential pharmacotherapeutic implications in cardiovascular diseases.

Lp(a) appears to be one of the most atherogenic lipoproteins. It consists of an low-density lipoprotein core in addition to a covalently bound glycoprotein, apo(a). Apo(a) exists in numerous polymorphic forms. The size of the polymorphism is mediated by the variable number of kringle-4 Type 2 repeats found in apo(a). Plasma Lp(a) levels are determined to more than 90% by genetic factors. Plasma Lp(a) levels in healthy individuals correlate significantly highly with apo(a) biosynthesis, and not with its catabolism. There are several hormones that are known to have a strong effect on Lp(a) metabolism. In certain diseases, such as kidney disease, the Lp(a) catabolism is impaired, leading to elevations that are up to a fivefold increase. Lp(a) levels rise with age but are otherwise only little influenced by diet and lifestyle. There is no safe and efficient way of treating individuals with elevated plasma Lp(a) concentrations. Most of the lipid-lowering drugs have either no significant influence on Lp(a) or exhibit a variable effect in patients with different forms of primary and secondary hyperlipoproteinemia.

Hypothyroidism is a common condition and recent epidemiological studies demonstrated that up to 10 percent of subjects may display its subclinical form. Despite the well-known relationship between overt hypothyroidism and cardiovascular disease, few studies demonstrating such a link are available. However, the relationship between hypothyroidism and a variety of cardiovascular risk factors is now well established. Recent data on new cardiovascular risk factors that were shown to be associated with hypotyroidism are reviewed. Haemostatic and fibrinolytic parameters are disturbed differently according to the stage of hypothyroidism. C-reactive protein levels are higher in patients with overt and subclinical hypotyroidism compared to euthyroid patients. In contrast, elevation of homocysteine values was demonstrated only in overt hypothyroidism. Although no randomized controlled trial evaluated the potential benefits of levothyroxine substitution on the risk to suffer major coronary events in patients with subclinical hypothyroidism, there is growing evidence that this disorder is mainly characterized by a high risk of cardiovascular disease.

Coronary artery bypass grafting is an effective treatment for myocardial ischaemia and is particularly important in patients with multivessel disease and diabetes. However, up to 40% of saphenous vein grafts will occlude within 10 years of surgery. The predominant mechanisms for saphenous vein graft disease are thrombosis, intimal hyperplasia, and accelerated atherosclerosis. The pathology of these changes and the role of key factors such as nitric oxide, cellular proliferation, and the role of hypercholesterolemia and hypertriglyceridaemia, are reviewed. Saphenous vein graft disease is among the first cardiovascular conditions to show significant benefit from gene therapy and promises to show remarkable developments in the near future.