Altered Cholesterol Metabolism and Hypocholesterolemia in Patients with Single Ventricle following Fontan Palliation.

OBJECTIVE: To assess whether an abnormality in cholesterol absorption or synthesis may be associated with hypocholesterolemia in patients with single ventricle anatomy following Fontan palliation. STUDY DESIGN: This is a cross-sectional study of 21 patients with hypocholesterolemia following Fontan procedure and age/sex-matched healthy controls, with median age of 13.4 (IQR 10.6-16.1) years. Laboratory values of several biomarkers, including phytosterols and 5-α-cholestanol (for cholesterol absorption) and lathosterol (for cholesterol biosynthesis), as well as cholesterol levels, inflammatory markers, and indices of liver function were compared between patients following Fontan procedure and controls. RESULTS: The Fontan cohort had significantly lower total cholesterol (mean 117 ± SD 13.9, vs 128 ± 19.2 mg/dL, P = .03) and free cholesterol (35.5 ± 4.5 vs 39.2 ± 5.4 mg/dL, P = .02) compared with control patients. There was an increase in normalized 5-α-cholestanol (1.51 ± 0.6 vs 1.14 ± 0.37 µg/mL, P = .02), and a significantly lower lathosterol/5-α-cholestanol ratio (0.70 ± 0.38 vs 1.11 ± 0.76, P = .04). There was a strong correlation (r = 0.78, P < .0001) between lathosterol and cholesterol levels in the Fontan cohort, not seen in controls (r = 0.47, P = .04). The Fontan cohort also had significantly higher C-reactive protein, transaminases, total bilirubin, and gamma-glutamyl transferase levels. CONCLUSIONS: Patients with hypocholesterolemia following Fontan procedure have evidence of increased cholesterol absorption and decreased cholesterol synthesis. As cholesterol absorption efficiency is a regulated process, this finding suggests an upregulation of cholesterol absorption as a result of decreased cholesterol production. In the setting of elevated liver indices and possible inflammation, this finding supports a growing body of data suggesting development of liver disease in patients receiving Fontan.

Controversy on high density lipoprotein raising therapy.

Decreased high density lipoproteins (HDL) plasma levels are a recognized independent risk factor for atherosclerotic cardiovascular disease. Attempts were therefore initiated to pharmacologically raise plasma HDL cholesterol, and the most impressive increase was obtained by inhibiting cholesteryl ester transfer protein (CETP) by means of the synthetic compound torcetrapib. Clinical trials were however disappointing, as torcetrapib increased mortality and did not reduce the progression of atherosclerosis. According to some view, it was claimed that CETP inhibition is unfavourable and that development of this class of compounds should be abandoned. Controversy nevertheless stimulated research on HDL structure, heterogeneity and functions which are not limited to reverse cholesterol transport and exert antioxidant and antiinflammatory actions. It could also be demonstrated that the deleterious effects of torcetrapib are compound specific, including its tight binding to CETP on HDL particles, thereby blocking both neutral lipids and phospholipid transfer from HDL to other lipoproteins, and would also exert an off-target effect by increasing plasma sodium and decreasing potasium concentrations (an aldosterone-like effect). As the structure of CETP was elucidated, it became possible to design CETP inhibitors that lack such off-target toxicity and may successfully slow the progression of atherosclerosis. Noteworthy, mice and rats naturally lacking CETP are resistant to diet induced atherosclerosis, while rabbits with high CETP levels are very susceptible. Families with deficient activity and exceptional longevity had also been reported.

Monogenic pediatric dyslipidemias: classification, genetics and clinical spectrum.

Monogenic disorders that cause abnormal levels of plasma cholesterol and triglycerides have received much attention due to their role in metabolic dysfunction and cardiovascular disease. While these disorders often present clinically during adulthood, some present most commonly in the pediatric population and can have serious consequences if misdiagnosed or untreated. This review provides an overview of monogenic lipid disorders that present with unusually high or low levels of plasma cholesterol and/or triglycerides during infancy, childhood and adolescence. Biochemical and genetic findings, clinical presentation and treatment options are discussed with an emphasis upon recent advances in our understanding and management of these monogenic disorders.

Secondary prevention in coronary heart disease patients with low HDL: which options do we have?

Low levels of high-density lipoprotein cholesterol (HDL-C) are frequently encountered in patients with coronary artery disease (CAD), most often in combination with elevated triglycerides as part of a dysmetabolic syndrome. Although no large secondary prevention trials with statin therapy with special emphasis on low HDL-C have been performed, some guidance can be extracted from a number of post-hoc analyses on how to treat patients with low levels of HDL-C. In terms of risk reduction, statin therapy appears to be at least as effective in patients with low compared to normal HDL-C levels. Fibrate therapy seems only effective when low HDL-C coincides with a level of low-density lipoprotein cholesterol (LDL-C) in the low-normal range. Before considering combination therapy of statins with fibrates, much emphasis should be put on dietary changes, weight reduction, smoking cessation and regular exercise, since these measures are effective tools to raise HDL-C levels. Moreover, one should be aware of the fact that combination therapy of statins and fibrates is not evidence-based and confers some potential risk of myopathy. Future therapy options may include CETP (cholesterol ester transfer protein) inhibitors, but these agents are still in an experimental phase. As most patients with low HDL-C levels share features of the dysmetabolic syndrome, one could also consider a combination therapy of statins and ACE-inhibitors, since this combination is not only safe, but the individual preventive effects of these compounds appear to be cumulative.

High-density lipoprotein cholesterol: an updated view.

New insights into low high-density lipoprotein cholesterol identify promising new directions for coronary heart disease prevention. The ATP-binding-cassette A1 gene has been identified as an important defect in genetic disorders of this lipid fraction. Recent studies indicate a benefit in treating patients with low levels of high-density lipoprotein cholesterol and suggest new clinical recommendations.

Pharmacological management of high triglycerides and low high-density lipoprotein cholesterol.

Elevated serum triglycerides and low high-density lipoprotein (HDL) cholesterol are part of a metabolic syndrome that is increasingly being recognized as an important risk factor for cardiovascular disease. Several classes of pharmacological agents including fibrates, niacin and statins, can modify the triglyceride-HDL axis. Fibrates in particular have recently been shown in clinical trials not only to increase HDL, but also to reduce cardiovascular mortality in secondary prevention. More research is needed to further define the role of fibrates when used alone and in combination with statins in high-risk individuals.

Correction of hypoalphalipoproteinemia in LDL receptor-deficient rabbits by lecithin:cholesterol acyltransferase.

Familial hypercholesterolemia (FH), a disease caused by a variety of mutations in the low density lipoprotein receptor (LDLr) gene, leads not only to elevated LDL-cholesterol (C) concentrations but to reduced high density lipoprotein (HDL)-C and apolipoprotein (apo) A-I concentrations as well. The reductions in HDL-C and apoA-I are the consequence of the combined metabolic defects of increased apoA-I catabolism and decreased apoA-I synthesis. The present studies were designed to test the hypothesis that overexpression of human lecithin:cholesterol acyltransferase (hLCAT), a pivotal enzyme involved in HDL metabolism, in LDLr defective rabbits would increase HDL-C and apoA-I concentrations. Two groups of hLCAT transgenic rabbits were established: 1) hLCAT+/LDLr heterozygotes (LDLr+/-) and 2) hLCAT+/LDLr homozygotes (LDLr-/-). Data for hLCAT+ rabbits were compared to those of nontransgenic (hLCAT-) rabbits of the same LDLr status. In LDLr+/- rabbits, HDL-C and apoA-I concentrations (mg/dl), respectively, were significantly greater in hLCAT+ (62 +/- 8, 59 +/- 4) relative to hLCAT- rabbits (21 +/- 1, 26 +/- 2). This was, likewise, the case when hLCAT+/ LDLr-/- (27 +/- 2, 19 +/- 6) and hLCAT-/LDLr-/- (5 +/- 1, 6 +/- 2) rabbits were compared. Kinetic experiments demonstrated that the fractional catabolic rate (FCR, d(-1)) of apoA-I was substantially delayed in hLCAT+ (0.376 +/- 0.025) versus hLCAT- (0.588) LDLr+/- rabbits, as well as in hLCAT+ (0.666 +/- 0.033) versus hLCAT- (1.194 +/- 0.138) LDLr-/- rabbits. ApoA-I production rate (PR, mg x kg x d(-1)) was greater in both hLCAT+/LDLr+/- (10 +/- 2 vs. 6) and hLCAT+/LDLr-/- (9 +/- 1 vs. 4 +/- 1) rabbits. Significant correlations (P < 0.02) were observed between plasma LCAT activity and HDL-C (r = 0.857), apoA-I FCR (r = -0.774), and apoA-I PR (r = 0.771), while HDL-C correlated with both apoA-I FCR (-0.812) and PR (0.751). In summary, these data indicate that hLCAT overexpression in LDLr defective rabbits increases HDL-C and apoA-I concentrations by both decreasing apoA-I catabolism and increasing apoA-I synthesis, thus correcting the metabolic defects responsible for the hypoalphalipoproteinemia observed in LDLr deficiency.

[How I study a patient with a low concentration of HDL cholesterol]. / Comment j'explore ... un sujet avec une concentration basse de cholestérol HDL.

A decrease in plasma HDL cholesterol concentration is considered as a major cardiovascular risk factor and is a prevalent lipid abnormality among patients with coronary heart disease. This condition is most often observed in the presence of hypertriglyceridaemia, generally linked to the insulin resistance syndrome, but may also be associated to elevated LDL cholesterol level or even be present alone (hypoalphalipoproteinaemia). The decision to treat a patient with low HDL level depends on the individual overall cardiovascular risk which should be evaluated as carefully as possible. The investigation should look for causes which may favour this metabolic condition, such as bad life habits or possible pharmacological interferences.

Dyslipidemias and the secondary prevention of coronary heart disease.

Dyslipidemias in patients with coronary heart disease confer a greater risk of ischemic cardiac events than comparable dyslipidemias in people free of disease. A major dyslipidemia can be diagnosed in more than 80% of patients with established premature coronary heart disease. These dyslipidemias constitute not only elevations of low-density lipoprotein cholesterol (hypercholesterolemia) but also indicate abnormalities in the metabolism of triglyceride-rich lipoproteins, high-density lipoproteins, and lipoprotein(a). Clinical trials have demonstrated that therapy to lower low-density lipoprotein levels can delay angiographic progression of coronary stenoses and reduce recurrent cardiac event rates. These clinical benefits from low-density lipoprotein cholesterol lowering may occur as early as 6 to 12 months after initiation of therapy. Intervention strategies for dyslipidemias are directed toward lowering the low-density lipoprotein cholesterol fraction to 90 to 100 mg/dl. This approach begins with dietary modification, weight loss, smoking cessation, and aerobic exercise. Patients with hypercholesterolemia refractory to nonpharmacologic intervention require lipid-lowering agents. The choice of lipid-lowering medications is influenced by concomitant abnormalities of lipoprotein metabolism, such as hypertriglyceridemia or hypoalphalipoproteinemia. Treatment of primary dyslipidemias other than hypercholesterolemia may be warranted in the presence of other cardiac risk factors; however, a broader spectrum of clinical trial data is needed to support or refute this contention.

Management of dyslipidemia in IDDM patients.

Patients with insulin-dependent diabetes mellitus (IDDM) are at an increased risk for coronary heart disease. Factors that may enhance the risk include dyslipidemia, hypertension, and hyperglycemia. Until recently, the importance of dyslipidemia in IDDM was ignored because the prevalence of high cholesterol levels was similar to that in the nondiabetic population. However, unique abnormalities in the composition and metabolism of lipoproteins may occur in IDDM patients. Management of IDDM patients, therefore, should include control of dyslipidemia as well as control of hyperglycemia and hypertension. The therapeutic goals for serum cholesterol reduction in IDDM patients should be lower than that for nondiabetic patients, and the goals for children should be even lower than those for adults. Both very-low-density lipoprotein and low-density lipoprotein (LDL) levels should be the targets for therapeutic interventions and not just the LDL alone. Because of the unique features of dyslipidemia in IDDM patients, the therapeutic options may not be the same as that for nondiabetic patients. Hyperglycemia should be controlled by matching daily energy intake and activity with appropriately timed doses of insulin. The diets should be low in saturated fats and cholesterol. If dyslipidemia persists despite diet and hyperglycemia management, drug therapy may be initiated. For IDDM children > or = 10 years of age with elevated LDL-cholesterol levels, the first-line therapy should be bile acid sequestrants. For adults with IDDM, bile acid sequestrants also may be the drugs of choice, particularly for normotriglyceridemic patients. Nicotinic acid therapy should be avoided. Among other drugs, hydroxymethyl-glutaryl coenzyme A reductase inhibitors may be preferable for patients with elevated LDL cholesterol and borderline hypertriglyceridemia. Fibric acid derivatives should be used for markedly hypertriglyceridemic patients. The role of probucol for dyslipidemia in IDDM patients is not clear.

Low levels of high-density lipoprotein cholesterol (hypoalphalipoproteinemia). An approach to management.

Clinical management of dyslipidemias has focused primarily on the low-density lipoprotein cholesterol (LDL-C) fraction; however, lipid disorders accompanied by low levels of high-density lipoprotein cholesterol (HDL-C) (hypoalphalipoproteinemia) are common, particularly among subjects with the diagnosis of coronary artery disease prior to age 55 years. The therapeutic objectives for high-risk subjects with dyslipidemias is directed initially toward reduction of the LDL-C fraction; thereafter, aggressive efforts aimed at raising the HDL-C fraction may be warranted. Strategies for raising the HDL-C fraction start with hygienic measures that include aerobic exercise, weight loss, smoking cessation, withdrawal of agents secondarily lowering HDL-C, and estrogen replacement. Pharmacotherapy selected according to the dyslipidemia that accompanies the HDL-C disorder is indicated for subjects who manifest premature coronary artery disease or who have a familial history of coronary artery disease and hypoalphalipoproteinemia.

A clinical overview of dyslipidemias: treatment strategies.

The strong epidemiologic relationship between specific lipoprotein levels (such as elevated low-density lipoprotein cholesterol or decreased high-density lipoprotein cholesterol) and the future development of coronary heart disease has been well documented. Within the past several years, landmark clinical trials have clearly demonstrated that the incidence of coronary heart disease events is reduced when lipoprotein abnormalities are corrected via pharmacologic therapy. These findings have prompted clinicians to become more vigilant with regard to recognition of dyslipidemias and institution of treatment. This review focuses on the more common primary and secondary dyslipidemias and the currently available lipid-lowering therapies for each disorder. Results of recent coronary angiographic trials are discussed, and implications for the medical management of established coronary heart disease are assessed.

Diagnosis and management of familial dyslipoproteinemia in children and adolescents.

CAD results from atherosclerosis, a chronic disease process that has its origin in childhood. Children and adolescents can be at higher risk for CAD by virtue of being from families with premature CAD or familial dyslipoproteinemias. The plasma lipid and lipoprotein levels result from a number of complex metabolic processes that are under the control of genetic and environmental (e.g., diet) influences. The normal ranges of plasma lipids and lipoproteins in children are known, and children and adolescents with dyslipoproteinemia are ordinarily defined as those having levels of plasma total, LDL, or triglyceride above the 95th percentile or with a low HDL cholesterol below the 5th percentile. Children of a parent with documented dyslipoproteinemia or with family history of premature CAD may be screened in the fasting state any time after 2 years of age. Following the exclusion of secondary causes of dyslipoproteinemia, the diagnosis of primary dyslipoproteinemia can be made. Lipoprotein patterns are not diagnostic for a given genotype. Efforts to determine further the biochemical defects responsible for a given phenotype have led to the investigation of gene coding for the apolipoproteins, the key enzymes in the lipoproteins pathways (LPL, HDL, and LCAT) and the receptors that process lipoproteins, such as the LDL receptor and the chylomicron remnant receptor. From a practical standpoint, the diagnosis of the kind of dyslipoproteinemia in a child will depend upon the nature and severity of the dyslipoproteinemia, both in the child (or adolescent) and in parents and siblings. Marked increases in plasma total and LDL cholesterol in the child and in at least one of the parents often reflect the presence of familial hypercholesterolemia, an inherited dominant condition due to a defect in the LDL receptor gene. The triglyceride levels are often normal. If the child has a different dyslipoproteinemia pattern from siblings and parents, then the diagnosis of familial combined hyperlipidemia or hyperapobetalipoproteinemia should be considered. Most children with mild or borderline elevations in total and LDL cholesterol will have polygenic hypercholesterolemia. Triglyceride problems in children and adolescents are relatively uncommon, particularly the more severe hypertriglyceridemia such as that found in lipoprotein lipase and apoC-II deficiency, dysbetalipoproteinemia, and type V hyperlipoproteinemia. High levels of Lp(a) lipoprotein, in isolation or in combination with other dyslipoproteinemia, accelerate risk for CAD. Low levels of HDL cholesterol in the absence of other abnormalities suggest the diagnosis of hypoalphalipoproteinemia.(ABSTRACT TRUNCATED AT 400 WORDS)

Dyslipoproteinemia and diabetes.

Lipoprotein changes in diabetes are discussed from both a pathophysiologic and clinical viewpoint. Though differences in concentrations are often small and vary according to the type of diabetes, other changes in lipoprotein metabolism are presented. The interrelationships between diabetes, insulin, and heart disease are also discussed, with the central role of insulin being stressed. Finally, the clinical management of lipid disorders in diabetes is addressed.