Insulin sensitivity in familial hypercholesterolemia

Clinical Aspects of Genetic and Non-Genetic Cardiovascular Risk Factors in Familial Hypercholesterolemia

Familial hypercholesterolemia (FH) is the most common monogenic metabolic disorder characterized by considerably elevated low-density lipoprotein cholesterol (LDL-C) levels leading to enhanced atherogenesis, early cardiovascular disease (CVD), and premature death. However, the wide phenotypic heterogeneity in FH makes the cardiovascular risk prediction challenging in clinical practice to determine optimal therapeutic strategy. Beyond the lifetime LDL-C vascular accumulation, other genetic and non-genetic risk factors might exacerbate CVD development. Besides the most frequent variants of three genes (LDL-R, APOB, and PCSK9) in some proband variants of other genes implicated in lipid metabolism and atherogenesis are responsible for FH phenotype. Furthermore, non-genetic factors, including traditional cardiovascular risk factors, metabolic and endocrine disorders might also worsen risk profile. Although some were extensively studied previously, others, such as common endocrine disorders including thyroid disorders or polycystic ovary syndrome are not widely evaluated in FH. In this review, we summarize the most important genetic and non-genetic factors that might affect the risk prediction and therapeutic strategy in FH through the eyes of clinicians focusing on disorders that might not be in the center of FH research. The review highlights the complexity of FH care and the need of an interdisciplinary attitude to find the best therapeutic approach in FH patients.

Diabetes and Familial Hypercholesterolemia: Interplay between Lipid and Glucose Metabolism

Familial hypercholesterolemia (FH) is a genetic disease characterized by high low-density lipoprotein (LDL) cholesterol (LDL-c) concentrations that increase cardiovascular risk and cause premature death. The most frequent cause of the disease is a mutation in the LDL receptor (LDLR) gene. Diabetes is also associated with an increased risk of cardiovascular disease and mortality. People with FH seem to be protected from developing diabetes, whereas cholesterol-lowering treatments such as statins are associated with an increased risk of the disease. One of the hypotheses to explain this is based on the toxicity of LDL particles on insulin-secreting pancreatic β-cells, and their uptake by the latter, mediated by the LDLR. A healthy lifestyle and a relatively low body mass index in people with FH have also been proposed as explanations. Its association with superimposed diabetes modifies the phenotype of FH, both regarding the lipid profile and cardiovascular risk. However, findings regarding the association and interplay between these two diseases are conflicting. The present review summarizes the existing evidence and discusses knowledge gaps on the matter.

Determination of Serum Progranulin in Patients with Untreated Familial Hypercholesterolemia

Background: Familial hypercholesterolemia (FH) is an autosomal dominant trait characterized by elevated LDL-C concentrations and is associated with an increased risk of premature atherosclerosis. Progranulin (PGRN) is a multifunctional protein that is known to have various anti-atherogenic effects. To date, the use of serum PGRN in patients with FH has not been studied. Methods: In total, 81 untreated patients with heterozygous FH (HeFH) and 32 healthy control subjects were included in this study. Serum PGRN, sICAM-1, sVCAM-1, oxLDL and TNFα concentrations were determined by ELISA. Lipoprotein subfractions were detected by Lipoprint. We diagnosed FH using the Dutch Lipid Clinic Network criteria. Results: We could not find a significant difference between the PGRN concentrations of the HeFH patients and controls (37.66 ± 9.75 vs. 38.43 ± 7.74 ng/mL, ns.). We found significant positive correlations between triglyceride, TNFα, sVCAM-1, the ratio of small HDL subfraction and PGRN, while significant negative correlations were found between the ratio of large HDL subfraction and PGRN both in the whole study population and in FH patients. PGRN was predicted by sVCAM-1, logTNFα and the ratio of small HDL subfraction. Conclusions: The strong correlations between HDL subfractions, inflammatory markers and PGRN suggest that PGRN may exert its anti-atherogenic effect in HeFH through the alteration of HDL composition and the amelioration of inflammation rather than through decreasing oxidative stress.

Familial Hypercholesterolemia: Do HDL Play a Role?

Cardiovascular disease (CVD) in heterozygous familial hypercholesterolemia (HeFH), the most frequent monogenic disorder of human metabolism, is largely driven by low-density lipoprotein (LDL) cholesterol concentrations. Since the CVD rate differs considerably in this population, beyond the lifetime LDL cholesterol vascular accumulation, other classical risk factors are involved in the high cardiovascular risk of HeFH. Among other lipoprotein disturbances, alterations in the phenotype and functionality of high-density lipoproteins (HDL) have been described in HeFH patients, contributing to the presence and severity of CVD. In fact, HDL are the first defensive barrier against the burden of high LDL cholesterol levels owing to their contribution to reverse cholesterol transport as well as their antioxidant and anti-inflammatory properties, among others. In this context, the present narrative review aimed to focus on quantitative and qualitative abnormalities in HDL particles in HeFH, encompassing metabolic, genetic and epigenetic aspects.

Lipoprotein metabolism in familial hypercholesterolemia

Familial hypercholesterolemia (FH) is one of the most common genetic disorders in humans. It is an extremely atherogenic metabolic disorder characterized by lifelong elevations of circulating LDL-C levels often leading to premature cardiovascular events. In this review, we discuss the clinical phenotypes of heterozygous and homozygous FH, the genetic variants in four genes (LDLR/APOB/PCSK9/LDLRAP1) underpinning the FH phenotype as well as the most recent in vitro experimental approaches used to investigate molecular defects affecting the LDL receptor pathway. In addition, we review perturbations in the metabolism of lipoproteins other than LDL in FH, with a major focus on lipoprotein (a). Finally, we discuss the mode of action and efficacy of many of the currently approved hypocholesterolemic agents used to treat patients with FH, with a special emphasis on the treatment of phenotypically more severe forms of FH.

Insulin Resistance and Atherosclerosis: Implications for Insulin-Sensitizing Agents

Patients with type 2 diabetes mellitus (T2DM) are at high risk for macrovascular complications, which represent the major cause of mortality. Despite effective treatment of established cardiovascular (CV) risk factors (dyslipidemia, hypertension, procoagulant state), there remains a significant amount of unexplained CV risk. Insulin resistance is associated with a cluster of cardiometabolic risk factors known collectively as the insulin resistance (metabolic) syndrome (IRS). Considerable evidence, reviewed herein, suggests that insulin resistance and the IRS contribute to this unexplained CV risk in patients with T2DM. Accordingly, CV outcome trials with pioglitazone have demonstrated that this insulin-sensitizing thiazolidinedione reduces CV events in high-risk patients with T2DM. In this review the roles of insulin resistance and the IRS in the development of atherosclerotic CV disease and the impact of the insulin-sensitizing agents and of other antihyperglycemic medications on CV outcomes are discussed.

Distinct metabolic and vascular effects of dietary triglycerides and cholesterol in atherosclerotic and diabetic mouse models

Cholesterol and triglyceride-rich Western diets are typically associated with an increased occurrence of type 2 diabetes and vascular diseases. This study aimed to assess the relative impact of dietary cholesterol and triglycerides on glucose tolerance, insulin sensitivity, atherosclerotic plaque formation, and endothelial function. C57BL6 wild-type (C57) mice were compared with atherosclerotic LDLr(-/-) ApoB(100/100) (LRKOB100) and atherosclerotic/diabetic IGF-II × LDLr(-/-) ApoB(100/100) (LRKOB100/IGF) mice. Each group was fed either a standard chow diet, a 0.2% cholesterol diet, a high-fat diet (HFD), or a high-fat 0.2% cholesterol diet for 6 mo. The triglyceride-rich HFD increased body weight, glucose intolerance, and insulin resistance but did not alter endothelial function or atherosclerotic plaque formation. Dietary cholesterol, however, increased plaque formation in LRKOB100 and LRKOB100/IGF animals and decreased endothelial function regardless of genotype. However, cholesterol was not associated with an increase of insulin resistance in LRKOB100 and LRKOB100/IGF mice and, unexpectedly, was even found to reduce the insulin-resistant effect of dietary triglycerides in these animals. Our data indicate that dietary triglycerides and cholesterol have distinct metabolic and vascular effects in obese atherogenic mouse models resulting in dissociation between the impairment of glucose homeostasis and the development of atherosclerosis.

Roles of insulin, age, and asymmetric dimethylarginine on nitric oxide synthesis in vivo

We tested the effects of insulin on production of nitrous oxide (NO)-related substances (nitrites and nitrates [NOx]) after (15)N-arginine intravenous infusion and on asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) concentrations in conditions reportedly associated with altered NO availability, i.e., aging, hypertension, hypercholesterolemia, and type 2 diabetes mellitus (T2DM). A total of 26 male subjects (age 23-71 years, BMI 23-33 kg/m(2)), some of whom were affected by mixed pathologic features, were enrolled. NOx fractional synthesis rate (FSR) was lower in elderly (P < 0.015) and T2DM subjects (P < 0.03) than in matched control subjects. Hyperinsulinemia generally increased both NOx FSR and absolute synthesis rate (ASR) and reduced NOx, ADMA, and SDMA concentrations. Insulin sensitivity was impaired only in T2DM. With use of simple linear regression analysis across all subjects, age was inversely correlated with both NOx FSR (R(2) = 0.23, P < 0.015) and ASR (R(2) = 0.21, P < 0.02). NOx FSR inversely correlated with both ADMA and SDMA. With use of multiple regression analysis and various models, NOx FSR remained inversely associated with age and ADMA, whereas ASR was inversely associated with age and diabetes. No association with insulin sensitivity was found. We conclude that whole-body NOx production is decreased in aging and T2DM. Age, ADMA concentration, and T2DM, but not insulin resistance, appear as negative regulators of whole-body NOx production.

Diabetes and hypertension: the bad companions

High blood pressure is reported in over two-thirds of patients with type 2 diabetes, and its development coincides with the development of hyperglycaemia. Many pathophysiological mechanisms underlie this association. Of these mechanisms, insulin resistance in the nitric-oxide pathway; the stimulatory effect of hyperinsulinaemia on sympathetic drive, smooth muscle growth, and sodium-fluid retention; and the excitatory effect of hyperglycaemia on the renin-angiotensin-aldosterone system seem to be plausible. In patients with diabetes, hypertension confers an enhanced risk of cardiovascular disease. A blood pressure of lower than 140/85 mm Hg is a reasonable therapeutic goal in patients with type 2 diabetes according to clinical trial evidence. People with controlled diabetes have a similar cardiovascular risk to patients without diabetes but with hypertension. A renin-angiotensin system blocker combined with a thiazide-type diuretic might be the best initial antihypertensive regimen for most people with diabetes. In general, the positive effects of antihypertensive drugs on cardiovascular outcomes outweigh the negative effects of antihypertensive drugs on glucose metabolism.

Assessment and treatment of cardiovascular risk in prediabetes: impaired glucose tolerance and impaired fasting glucose

Individuals with impaired glucose tolerance (IGT) and/or impaired fasting glucose (IFG) are at high risk, not only to develop diabetes mellitus, but also to experience an adverse cardiovascular (CV) event (myocardial infarction, stroke, CV death) later in life. The underlying pathophysiologic disturbances (insulin resistance and impaired β-cell function) responsible for the development of type 2 diabetes are maximally/near maximally expressed in subjects with IGT/IFG. These individuals with so-called prediabetes manifest all of the same CV risk factors (dysglycemia, dyslipidemia, hypertension, obesity, physical inactivity, insulin resistance, procoagulant state, endothelial dysfunction, inflammation) that place patients with type 2 diabetes at high risk for macrovascular complications. The treatment of these CV risk factors should follow the same guidelines established for patients with type 2 diabetes, and should be aggressively followed to reduce future CV events.

Insulin resistance, lipotoxicity, type 2 diabetes and atherosclerosis: the missing links. The Claude Bernard Lecture 2009

Insulin resistance is a hallmark of type 2 diabetes mellitus and is associated with a metabolic and cardiovascular cluster of disorders (dyslipidaemia, hypertension, obesity [especially visceral], glucose intolerance, endothelial dysfunction), each of which is an independent risk factor for cardiovascular disease (CVD). Multiple prospective studies have documented an association between insulin resistance and accelerated CVD in patients with type 2 diabetes, as well as in non-diabetic individuals. The molecular causes of insulin resistance, i.e. impaired insulin signalling through the phosphoinositol-3 kinase pathway with intact signalling through the mitogen-activated protein kinase pathway, are responsible for the impairment in insulin-stimulated glucose metabolism and contribute to the accelerated rate of CVD in type 2 diabetes patients. The current epidemic of diabetes is being driven by the obesity epidemic, which represents a state of tissue fat overload. Accumulation of toxic lipid metabolites (fatty acyl CoA, diacylglycerol, ceramide) in muscle, liver, adipocytes, beta cells and arterial tissues contributes to insulin resistance, beta cell dysfunction and accelerated atherosclerosis, respectively, in type 2 diabetes. Treatment with thiazolidinediones mobilises fat out of tissues, leading to enhanced insulin sensitivity, improved beta cell function and decreased atherogenesis. Insulin resistance and lipotoxicity represent the missing links (beyond the classical cardiovascular risk factors) that help explain the accelerated rate of CVD in type 2 diabetic patients.

Insulin sensitivity indices of glucose and free fatty acid metabolism in obese children and adolescents in relation to serum lipids

OBJECTIVE

Most studies concerning the association between insulin resistance and the features of metabolic syndrome in obese children are based on measurement of insulin sensitivity indices (ISI) of glucose metabolism and not of fat metabolism.

METHODS

We studied fasting low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides, insulin, free fatty acids (FFA), blood glucose, ISI of glucose (homeostasis model assessment [HOMA] %S), and FFA metabolism (ISI-FFA) in 124 obese children aged 6 to 16 years. ISI-FFA was calculated based on the formula 2/(insulin x FFA + 1). Stepwise forward regression analyses were performed with triglycerides, HDL-C and LDL-C as dependent variables and age, sex, stage of puberty, body mass index, insulin, FFA, and blood glucose as independent variables. Direct multiple regression analyses were conducted with the dependent variables triglycerides, HDL-C, and LDL-C including age, sex, stage of puberty, body mass index, HOMA %S, and ISI-FFA as independent variables. Furthermore, ISI-FFA was measured in 13 normal-weight children aged 6 to 16 years.

RESULTS

ISI-FFA (median 0.30) was significantly (P < .05) reduced in obese children compared with normal-weight children (median ISI-FFA 0.64). In stepwise regression analyses, triglycerides were significantly correlated with insulin and FFA (P < .05), LDL-C levels were significantly correlated with FFA (P < .05), and HDL-C was related to stage of puberty (P < .05), whereas all other variables demonstrated no significant associations with triglycerides, LDL-C, and HDL-C levels. In contrast to HOMA %S, ISI-FFA was significantly (P < .05) related to triglycerides and LDL-C in direct multiple regression analysis.

CONCLUSIONS

Insulin resistance in respect to FFA metabolism is already detectable in childhood. Insulin sensitivity index of FFA metabolism seems to be a better tool for describing insulin resistance in lipid metabolism than ISI of glucose metabolism, because FFA and partially insulin but not glucose were related to triglycerides and LDL-C.

Insulin resistance and endothelial dysfunction

Insulin has multiple metabolic actions, including effects on blood vessels. Insulin normally increases blood flow by a mechanism which involves generation of nitric oxide (NO) via the arginine-NO pathway. Although insulin itself is a weak and physiologically unimportant vasodilatator, it appears to markedly potentiate endothelium-dependent vasodilatation. Therefore, anything that impairs insulin action in endothelial cells can be expected to be associated with endothelial dysfunction, i.e. loss of NO bioactivity in the vessel wall. Consistent with the idea that insulin resistance and endothelial dysfunction frequently coexist, all insulin-resistant conditions examined to date have been associated with endothelial dysfunction. However, the latter can also be caused by factors other than insulin resistance-such as a high concentration of low-density lipoprotein (LDL) cholesterol. Therapies which reverse insulin resistance-such as exercise, insulin and inhibitors of the renin-angiotensin-aldosterone (RAA) axis-also reverse endothelial dysfunction, which may thus be an inherent feature of insulin resistance.

Atherosclerosis seems not to be associated with hyperinsulinaemia in patients with familial hypercholesterolaemia

OBJECTIVE

To study the relationship between hyperinsulinaemia, insulin resistance, leptin and atherosclerosis in subjects with familial hypercholesterolaemia (FH).

DESIGN

Case-control cross-sectional study.

SETTING

Lipid clinic, Johannesburg Hospital, South Africa.

SUBJECTS AND METHODS

Fasting serum lipid, glucose, insulin and leptin levels were measured in 24 homozygous FH subjects; 20 FH heterozygotes without coronary artery disease (CAD); 22 heterozygotes with documented CAD; and 20 healthy normocholesterolaemic subjects. Insulin resistance was calculated using the homeostasis model assessment (HOMA) formula.

RESULTS

Mean glucose and insulin levels were similar in all 4 groups. There was no significant difference in calculated insulin resistance between any of the groups. There was also no relationship between the degree of insulin resistance and total or LDL-cholesterol levels. Using Spearman's correlation coefficient (Rs) calculated insulin resistance correlated with triglyceride (Rs = 0.27; P<0.05) and inversely with HDL-cholesterol (Rs = -0.26; P<0.05). Fasting insulin concentrations and calculated insulin resistance were similar in FH subjects with overt CAD compared to those without. Leptin levels were higher in the FH subjects with CAD. However, these subjects were older and had a larger body mass index (BMI), and when adjusted for age and BMI, only BMI correlated with leptin levels (multiple r = 0.65; P<0.001).

CONCLUSIONS

In the absence of other causes of insulin resistance, FH subjects have normal fasting insulin levels and, in general, they are not insulin resistant. Insulin resistance appears to play little role in the pathogenesis of accelerated atherosclerosis in FH.

Hepatic insulin clearance increases after weight loss in obese children and adolescents

BACKGROUND

Obesity is a rapidly increasing health problem among US youth. Hyperinsulinemia is associated with obesity and has been found to be a contributory factor for the development of cardiovascular disease in the obese. It has been suggested that hyperinsulinemia of obesity is a result of increased insulin secretion caused by insulin resistance. However, it has been shown in adults that decreased hepatic insulin clearance (HIC) is the primary cause of hyperinsulinemia in this population.

METHODS

We studied 15 obese children and adolescents (11 F, 4 M; 8.6 to 18.1 years) before and 10 weeks after their enrollment in a multidisciplinary weight reduction program, which included a protein-sparing modified fast, a moderate intensity progressive exercise program, and a behavior-modification intervention.

RESULTS

All patients lost weight (P < 0.05). Measurements of immunoreactive insulin (IRI) and C-peptide reactivity (CPR) were performed before the program and at 10 weeks. IRI levels dropped significantly, whereas CPR levels did not change. CPR/IRI molar ratios, considered an indirect estimation of HIC, rose significantly after weight loss.

CONCLUSIONS

Our data suggest that hyperinsulinemia seen in obese children and adolescents is caused by decreased HIC. The cause for this decrease remains unknown, but it is reversible upon weight loss.

Effect of a reduced-fat diet with or without pravastatin on glucose tolerance and insulin sensitivity in patients with primary hypercholesterolemia

Pharmacological treatment of hyperlipidemia may be associated with deterioration of glucose tolerance. We randomized 20 nonobese patients with primary familial hypercholesterolemia (serum total cholesterol 7.8 +/- 0.4 mM, triglycerides 1.4 +/- 0.2 mM) to an isocaloric, reduced fat (< 30%) low-cholesterol (200 mg/day) diet with placebo or pravastatin (40 mg/day). Oral glucose tolerance, endogenous insulin response to glucose, insulin sensitivity (determined by the euglycemic insulin clamp technique), hepatic glucose production (by the tritiated glucose technique), and substrate utilization (by indirect calorimetry) were measured at baseline and after 8 weeks of treatment. Ten normocholesterolemic healthy subjects, matched to the patients by age, sex, and body weight, served as the control group. Diet alone (with no change in body weight) was associated with a significant 15% decrease in both serum low density lipoprotein (LDL)-cholesterol and triglycerides (p < 0.001 for both), and a slight decrease in high density lipoprotein (HDL)-cholesterol concentrations, paralleled by reductions in Apo B, C2, C3, and E levels (p < 0.05 or less). The addition of pravastatin led to a significantly larger reduction in LDL-cholesterol (30%, p < 0.05) and an 8% increase (p < 0.02) in total HDL-cholesterol concentrations. Accordingly, the ratio of LDL:HDL cholesterol (which was 60% higher than in controls at baseline) remained unchanged in the placebo-diet group whereas it was restored to normal in the pravastatin-diet group. Glucose tolerance, insulin response, insulin-induced inhibition of hepatic glucose production and lipolysis, and insulin-mediated glucose uptake and oxidation were all slightly but not significantly improved after treatment, with no significant differences between pravastatin and placebo. In nonobese patients with primary hypercholesterolemia, pravastatin treatment in combination with an isocaloric, reduced-fat diet leads to a marked reduction in LDL-cholesterol and triglycerides levels and a normalization of the LDL:HDL ratio without affecting glucose tolerance or insulin sensitivity.