White matter brain lesions in midlife familial hypercholesterolemic patients at 3-Tesla magnetic resonance imaging

BACKGROUND

Patients with hypercholesterolemia of 60 years and older have an increased risk for white matter brain lesions and dementia.

PURPOSE

To investigate whether patients with familial hypercholesterolemia (FH) develop white matter lesions at 3-Tesla (T) MRI as early as in midlife.

MATERIAL AND METHODS

Non-diabetic, nonsmoking, and non-hypertensive heterozygous FH patients on treatment with maximally tolerated dose of a statin for more than 5 years (n = 14) and matched controls (n = 22) aged 25 to 60 years of age were studied. Imaging was performed at 3T with a fluid-attenuated T2-weighted MR pulse sequence and a T1-weighted spin-echo pulse sequence following 10 ml of i.v. gadopentetate dimeglumine. Images were evaluated by two independent readers. Fasting blood samples were taken. Student's t test was employed at P<0.05.

RESULTS

Three volunteers and one FH patient had white matter lesions (P<0.53). No other evidence of past ischemic stroke was observed. Mean total serum cholesterol and low-density lipoprotein (LDL) cholesterol were significantly higher in the FH group (6.0+/-1.1 vs. 5.1+/-0.9 mmol/l, P<0.02 and 4.1+/-0.9 vs. 3.1+/-0.8 mmol/l, P<0.004, respectively).

CONCLUSION

Heterozygous FH patients on statin treatment in the age range of 25 to 60 years are not at increased risk of white matter lesions at 3T MRI.

Atorvastatin affects leukocyte gene expression in dyslipidemia patients: in vivo regulation of hemostasis, inflammation and apoptosis

BACKGROUND

The beneficial effect of HMG-CoA reductase inhibitors (statins) on coronary artery disease has been linked to mechanisms beyond their lipid-lowering effect. However the existence of direct, lipid-independent effects of statin in humans is still controversial.

OBJECTIVE

To investigate the early effect of atorvastatin on peripheral blood mononuclear cells (PBMC) in dyslipidemic patients using gene arrays.

PATIENTS AND METHODS

Eleven male patients with primary hyperlipidemia received 20 mg atorvastatin daily for 4 weeks. Blood was collected at baseline, 12 h, 36 h, 1 and 4 weeks after the start of treatment.

RESULTS

Human microarrays containing 12 650 genes were used to study the effect of atorvastatin on PBMC gene expression at all time-points. Two hundred and forty genes were significantly regulated by atorvastatin treatment, several of which are involved in hemostasis, inflammation and other processes critical to atherosclerosis. Different patterns of response over time suggested both lipid-dependent and independent effects of atorvastatin on gene expression.

CONCLUSIONS

This study demonstrates for the first time that atorvastatin regulates gene expression in PBMC in man before changes in the lipid profile are detectable in serum. Using blood leukocytes as a pharmacogenomic surrogate, we have identified new in vivo targets of atorvastatin treatment.

New prospects for lipid-lowering drugs

The advent of 3-hydroxy-methylglutaryl Co-enzyme A (HMG-CoA) reductase inhibitors has dramatically improved the treatment of dyslipidaemia and the prevention of atherosclerosis over the past 10 years. Similar but less marked benefit had previously been demonstrated for fibrates and bile acid sequestrants, which were first introduced over 30 years ago and are still in use. The discovery that fibrates are ligands for peroxisome proliferator activated receptors (PPARs) may lead to innovations in the future. However, most of the compounds now undergoing clinical trials are either HMG-CoA reductase inhibitors or bile acid sequestrants, which is indicative of the current emphasis on lowering low density lipoprotein (LDL) cholesterol. Drugs in an earlier stage of development include inhibitors of squalene synthase, which have yet to fulfil their initial promise, and of acylcholesterolacyltransferase (ACAT) and microsomal triglyceride transfer protein (MTP). Most of the earlier ACAT inhibitors were poorly absorbed, but compounds with better bioavailability hold considerable promise by virtue of their ability to inhibit ACAT in liver and arterial wall macrophages. MTP inhibitors have the potential to drastically reduce apolipoprotein B (apoB) secretion, but safety issues could negate this advantage. Thus, despite the impact of statins, the development of new lipid-modulating drugs continues to be a dynamic field of research.

Established and emerging coronary risk factors in patients with heterozygous familial hypercholesterolaemia

OBJECTIVES

To assess the clinical and biochemical factors associated with inter-individual variation in susceptibility to coronary artery disease (CAD) in treated heterozygous familial hypercholesterolaemia.

DESIGN

A cross sectional study was conducted of 410 patients recruited from six lipid clinics in the UK.

RESULTS

CAD was documented in 104 of the 211 men and in 55 of the 199 women with mean ages of onset of 43.1 and 46.5 years, respectively. CAD was significantly more common in men (49% v 28%, p < 0.001) and in patients who had smoked cigarettes versus patients who had never smoked (51% v 28%, p < 0.001). After adjusting for age, sex, and current smoking status, there were no significant differences between patients with or without CAD in lipoprotein(a), homocysteine, fibrinogen, plasminogen activator inhibitor-1, white blood cell count, body mass index, glucose, triglyceride or total cholesterol. However, high density lipoprotein (HDL) cholesterol concentrations were significantly lower in those with CAD (6%, 95% confidence interval (CI) 1% to 11%, p = 0.03) and this difference was greater in women than men (12% v 2%, p = 0.041).

CONCLUSIONS

These results indicate that emerging coronary risk factors appear not to be associated with CAD in adults with treated familial hypercholesterolaemia, but the strong association with smoking suggests that patients should be identified early in childhood and discouraged from ever starting to smoke.

Genetics of familial combined hyperlipidemia and risk of coronary heart disease

Coronary heart disease is the leading cause of death in developed countries. This alarming statistic is partly attributable to lifestyle, and partly due to the genetic factors that make humans highly susceptible to atherosclerotic vascular disease. The principal metabolic causes of atherosclerosis include hyperlipidemia, hypertension, obesity, insulin resistance and diabetes mellitus. Here we discuss the aetiology of familial combined hyperlipidemia (FCHL), a highly atherogenic disorder affecting 1-2% of the Western world. Genome-wide linkage studies indicate that more than three genes contribute to the pernicious lipid profile of FCHL, and that these genes reside within the 1q21-23, 11p14.1-q12.1 and 16q22-24.1 chromosomal regions. Other loci include 1p31, 6q16.1-16.3 and 8p23.3-22, but the linkage data for these are not yet persuasive. Combined linkage and association analyses provide compelling evidence for the involvement of two distinct alleles at the APOA1/C3/A4/A5 gene cluster in the transmission of FCHL. An important lesson arising from the study of a complex genetic disorder, such as FCHL, that lacks a consensus on diagnostic criteria, is that an understanding of complex genetic disorders can derive from comparative analyses of genome-wide linkage data generated from conditions that share phenotypic overlap. The identification of potential genetic overlap between FCHL and the Metabolic Syndrome, which is estimated to affect 47 million Americans, promises to deliver new targets for reducing the risk of important conditions such as cardiovascular disease and stroke.

The genes and proteins of atherogenic lipoprotein production

Dietary fat provides a major source of nutrition, but may in excess lead to obesity, insulin resistance, high blood cholesterol levels and atherosclerosis. Here we report molecular events that co-ordinate whole-body lipid homoeostasis from insects to humans, viewed in the context of rare and common genetic disorders of apolipoprotein B-containing lipoprotein production.

Treatment with atorvastatin alters the ratio of interleukin-12/interleukin-10 gene expression [corrected]

BACKGROUND

Statins have been shown to have pleiotropic effects extending beyond their ability to lower cholesterol.

MATERIAL AND METHODS

Seventeen patients with heterozygous familial hypercholesterolaemia participated in a single-blind placebo controlled study. The patients underwent three treatment regimens: placebo (4 weeks), atorvastatin 10 mg day(-1) (4 weeks) and atorvastatin 40 mg day(-1) (12 weeks). Following each treatment period, serum lipids and plasma mevalonic acid were measured, mononuclear leukocytes were isolated and total RNA was prepared. The content of mRNA for IL-12p35 and IL-10 was assayed, blinded, by real-time quantitative polymerase chain reactions.

RESULTS

Treatment of the subjects with atorvastatin decreased the abundance of IL-12p35 mRNA in mononuclear cells, but did not alter that of IL-10, so that the ratio of the IL-12p35 to IL-10 mRNA content was significantly reduced (P < 0.0026). The IL-12p35/IL-10 ratio correlated significantly with plasma mevalonic acid concentrations but not with serum LDL concentrations.

CONCLUSIONS

This study provides evidence that atorvastatin exerts an immunomodulatory effect in vivo, characterized by a decrease in the ratio of IL-12 mRNA to IL-10 mRNA in leukocytes. The immunomodulatory effect of statins, in addition to their cholesterol-lowering properties, may contribute to the rapid cardiovascular benefit observed during treatment with statins and reduced the rate of rejection in patients with solid organ transplantation.

Determinants of Variable Response to Statin Treatment in Patients With Refractory Familial Hypercholesterolemia

Abstract —Interindividual variability in low density lipoprotein (LDL) cholesterol (LDL-C) response during treatment with statins is well documented but poorly understood. To investigate potential metabolic and genetic determinants of statin responsiveness, 19 patients with refractory heterozygous familial hypercholesterolemia were sequentially treated with placebo, atorvastatin (10 mg/d), bile acid sequestrant, and the 2 combined, each for 4 weeks. Levels of LDL-C, mevalonic acid (MVA), 7-α-OH-4-cholesten-3-one, and leukocyte LDL receptor and hydroxymethylglutaryl coenzyme A reductase mRNA were determined after each treatment period. Atorvastatin (10 mg/d) reduced LDL-C by an overall mean of 32.5%. Above-average responders (ΔLDL-C −39.5%) had higher basal MVA levels (34.4±6.1 μmol/L) than did below-average responders (ΔLDL-C −23.6%, P <0.02; basal MVA 26.3±6.1 μmol/L, P <0.01). Fewer good responders compared with the poor responders had an apolipoprotein E4 allele (3 of 11 versus 6 of 8, respectively; P <0.05). There were no baseline differences between them in 7-α-OH-4-cholesten-3-one, hydroxymethylglutaryl coenzyme A reductase mRNA, or LDL receptor mRNA, but the latter increased in the good responders on combination therapy ( P <0.05). Severe mutations were not more common in poor than in good responders. We conclude that poor responders to statins have a low basal rate of cholesterol synthesis that may be secondary to a genetically determined increase in cholesterol absorption, possibly mediated by apolipoprotein E4. If so, statin responsiveness could be enhanced by reducing dietary cholesterol intake or inhibiting absorption.

Novel lipid-regulating drugs

This review describes the major developments in lipid-regulating drugs during the past two years. Most of the novel compounds that have been launched or were in their final stages of development during this period are aimed primarily at lowering low-density lipoprotein (LDL)-cholesterol. These include bile acid sequestrants, HMG-CoA reductase inhibitors and a cholesterol absorption inhibitor. In addition, there have been preclinical reports suggesting the potential usefulness of orally bioavailable inhibitors of cholesterol ester transfer protein in plasma and of acylcoA:cholesterol acyltransferase in monocyte-macrophages. The recent discovery of the roles of the scavenger receptor class B Type 1 and ATP-binding cassette transporter 1 in high-density lipoprotein (HDL)-cholesterol transport may shift the trend of future developments away from compounds that lower LDL to those aimed at promoting HDL turnover.

Characterization of a novel cellular defect in patients with phenotypic homozygous familial hypercholesterolemia

Familial hypercholesterolemia (FH) is characterized by a raised concentration of LDL in plasma that results in a significantly increased risk of premature atherosclerosis. In FH, impaired removal of LDL from the circulation results from inherited mutations in the LDL receptor gene or, more rarely, in the gene for apo B, the ligand for the LDL receptor. We have identified two unrelated clinically homozygous FH patients whose cells exhibit no measurable degradation of LDL in culture. Extensive analysis of DNA and mRNA revealed no defect in the LDL receptor, and alleles of the LDL receptor or apo B genes do not cosegregate with hypercholesterolemia in these families. FACS((R)) analysis of binding and uptake of fluorescent LDL or anti-LDL receptor antibodies showed that LDL receptors are on the cell surface and bind LDL normally, but fail to be internalized, suggesting that some component of endocytosis through clathrin-coated pits is defective. Internalization of the transferrin receptor occurs normally, suggesting that the defective gene product may interact specifically with the LDL receptor internalization signal. Identification of the defective gene will aid genetic diagnosis of other hypercholesterolemic patients and elucidate the mechanism by which LDL receptors are internalized.

Reduction in visceral adipose tissue is associated with improvement in apolipoprotein B-100 metabolism in obese men

We investigated the effect of reduction in visceral obesity on the kinetics of apolipoprotein B-100 (apoB) metabolism in a controlled dietary intervention study in 26 obese men. Hepatic secretion of very low density lipoprotein (VLDL) apoB was measured using a primed, constant, infusion of 1-[13C]leucine. In seven men receiving the reduction diet, intermediate density lipoprotein (IDL) and low density lipoprotein (LDL) apoB kinetics were also determined. ApoB isotopic enrichment was measured using gas chromatography-mass spectrometry, and SAAM-II was used to estimate the fractional turnover rates. Subcutaneous and visceral adipose tissues at the L3 vertebra were quantified by magnetic resonance imaging. With weight reduction there was a significant decrease (P < 0.05) in body mass index, waist circumference, and visceral adipose tissue. The plasma concentrations of total cholesterol, triglyceride, insulin, and lathosterol also significantly decreased (P < 0.05). Compared with weight maintenance, weight reduction significantly decreased the VLDL apoB concentration, pool size, and hepatic secretion of VLDL apoB (delta+2.5+/-4.6 vs. delta-14.7+/-4.0 mg/kg fat free mass-day; P = 0.010), but did not significantly alter its fractional catabolism. Weight reduction was also associated with an increased fractional catabolic rate of LDL apoB (0.24+/-0.07 vs. 0.54+/-0.10 pools/day; P = 0.002) and conversion of VLDL to LDL apoB (11.7+/-2.5% vs. 56.3+/-11.4%; P = 0.008). A change in hepatic VLDL apoB secretion was significantly correlated with a change in visceral adipose tissue area (r = 0.59; P = 0.043), but not plasma concentrations of insulin, free fatty acids, or lathosterol. The data support the hypothesis that a reduction in visceral adipose tissue is associated with a decrease in the hepatic secretion of VLDL apoB, and this may be due to a decrease in portal lipid substrate supply. Weight reduction may also increase the fractional catabolism of LDL apoB, but this requires further evaluation.

Effect of inhibiting HMG-CoA reductase on 7 alpha-hydroxy-4-cholesten-3-one, a marker of bile acid synthesis: contrasting findings in patients with and without prior up-regulation of the latter pathway

BACKGROUND

Atorvastatin is a potent inhibitor of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase, but its effect on bile acid synthesis is unknown. The objectives of the study were to determine the effect of atorvastatin on bile acid synthesis in patients in whom this process had not been or had been previously up-regulated by pharmacological or surgical means.

MATERIALS AND METHODS

Four patients with heterozygous familial hypercholesterolaemia (FH) and partial ileal bypass (PIB) and 19 FH heterozygotes without PIB were treated with placebo, atorvastatin 10 mg and atorvastatin 40 mg daily, each regimen for 4 weeks. The non-PIB group was subsequently treated with bile acid (BA) sequestrant 8-16 g daily followed by co-administration of atorvastatin 10 mg, each for 4 weeks. Plasma 7 alpha-hydroxy-4-cholesten-3-one (7 alpha-HCO), a well-validated marker of BA synthesis was measured using high-performance liquid chromatography with UV detection.

RESULTS

The plasma 7 alpha-HCO concentration was tenfold higher with placebo in the PIB than in the non-PIB group (418.5 ng mL-1 vs. 39.6 ng mL-1 p = 0.0001). Levels decreased in PIB patients treated with atorvastatin 10 mg and 40 mg daily (350.1 ng mL-1 and 174.0 ng mL-1, P = 0.007 respectively) but did not change significantly in the non-PIB group (44.7 ng mL-1 and 28.3 ng mL-1 respectively). Administration of BA sequestrant to non-PIB patients increased 7 alpha-HCO to 197.4 ng mL-1; this decreased to 106.0 ng mL-1 during co-administration of atorvastatin 10 mg daily (P = 0.0001).

CONCLUSION

Atorvastatin decreases the rate of BA synthesis only if the latter is up-regulated by PIB or BA sequestrants, presumably by limiting the supply of newly synthesized free cholesterol.

Effects of growth hormone (GH) replacement therapy on very low density lipoprotein apolipoprotein B100 kinetics in patients with adult GH deficiency: a stable isotope study

Patients with adult GH deficiency are often dyslipidemic and may have an increased risk of cardiovascular disease. The secretion and clearance of very low density lipoprotein apolipoprotein B 100 (VLDL apoB) are important determinants of plasma lipid concentrations. This study examined the effect of GH replacement therapy on VLDL apoB metabolism using a stable isotope turnover technique. VLDL apoB kinetics were determined in 14 adult patients with GH deficiency before and after 3 months GH or placebo treatment in a randomized double blind, placebo-controlled study using a primed constant [1-(13)C]leucine infusion. VLDL apoB enrichment was determined by gas chromatography-mass spectrometry. GH replacement therapy increased plasma insulin-like growth factor I concentrations 2.9 +/- 0.5-fold (P < 0.001), fasting insulin concentrations 1.8 +/- 0.6-fold (P < 0.04), and hemoglobin A1C from 5.0 +/- 0.2% to 5.3 +/- 0.2% (mean +/- SEM; P < 0.001). It decreased fat mass by 3.4 +/- 1.3 kg (P < 0.05) and increased lean body mass by 3.5 +/- 0.8 kg (P < 0.01). The total cholesterol concentration (P < 0.02), the low density lipoprotein cholesterol concentration (P < 0.02), and the VLDL cholesterol/VLDL apoB ratio (P < 0.005) decreased. GH therapy did not significantly change the VLDL apoB pool size, but increased the VLDL apoB secretion rate from 9.2 +/- 2.0 to 25.9 +/- 10.3 mg/kg x day (P < 0.01) and the MCR from 11.5 +/- 2.7 to 20.3 +/- 3.2 mL/min (P < 0.03). No significant changes were observed in the placebo group. This study suggests that GH replacement therapy improves lipid profile by increasing the removal of VLDL apoB. Although GH therapy stimulates VLDL apoB secretion, this is offset by the increase in the VLDL apoB clearance rate, which we postulate is due to its effects in up-regulating low density lipoprotein receptors and modifying VLDL composition.

Extent and severity of atherosclerotic involvement of the aortic valve and root in familial hypercholesterolaemia

OBJECTIVE

To compare the frequency of valvar and supravalvar aortic stenosis in homozygous and heterozygous familial hypercholesterolaemia (FH).

DESIGN

Analysis of life time cholesterol exposure and prevalence of aortic atherosclerosis in 84 consecutive cases attending a lipid clinic.

SETTING

A tertiary referral centre in London.

PATIENTS

Outpatients with FH (six homozygous, 78 heterozygous).

INTERVENTIONS

Maintenance of lipid lowering treatment.

MAIN OUTCOME MEASURES

Calculated cholesterol x years score (CYS) and echocardiographic measurement of aortic root diameter, aortic valve thickness, and transaortic gradient.

RESULTS

Four homozygotes with a mean (SD) CYS of 387 (124) mmol/1 x years had severe aortic stenosis (treatment started after seven years of age), whereas the other two had echocardiographic evidence of supravalvar thickening but no aortic valve stenosis (treatment started before three years of age). On multivariate analysis, mean transaortic gradient correlated significantly with CYS (mean = 523 (175) mmol/1 x years) in heterozygotes (p = 0.0001), but only two had severe aortic valve and root involvement.

CONCLUSIONS

In patients with familial hypercholesterolaemia, aortic stenosis is common in homozygotes, and aortic root involvement is always present despite the lower CYS than in heterozygotes. It appears to be determined by short term exposure to high cholesterol concentrations in early life. Conversely, aortic root and valve involvement are rare in heterozygotes and occur only with severe, prolonged hypercholesterolaemia, possibly accelerating age related degenerative effects.

Cholesterol synthesis is increased in mixed hyperlipidaemia

We showed previously that hypertriglyceridaemia, but not hypercholesterolaemia, is correlated with increases in cholesterol synthesis and apolipoprotein B secretion in patients with secondary hypertriglyceridaemia. The aim of the present study was to compare the rate of cholesterol synthesis, using fasting plasma mevalonic acid (MVA) as an index, in patients with primary mixed hyperlipidaemia (type IIb phenotype, n=45) and primary hypercholesterolaemia (type IIa phenotype, n=92). LDL cholesterol was significantly higher in types IIa (6.38+/-0.18 mmol/l) and IIb (5.89+/-0.25 mmol/l) compared to 40 normolipidaemic controls (2. 99+/-0.1 mmol/l, P<0.0001), whereas serum triglyceride was higher in type IIb (2.62 (range 2.2-3.0) mmol/l) than type IIa (1.22 (range 0. 85-1.60) mmol/l, P<0.001) and controls (0.90 (range 0.68-1.24) mmol/l, P<0.001). Similarly, MVA was higher in type IIb (7.0+/-0.46 ng/ml) than IIa (5.6+/-0.23 ng/ml, P<0.0) and controls (5.6+/-0.36 ng/ml, P<0.05). Plasma MVA correlated positively with serum triglyceride (r=0.22, P=0.004) and negatively with LDL cholesterol (r=-0.21, P=0.014). These results are in accordance with previous observations that VLDL-apolipoprotein B secretion and cholesterol synthesis are linked and demonstrate that the latter is increased in mixed hyperlipidaemia.

Use of cholesterol precursors to assess changes in cholesterol synthesis under non-steady-state conditions

BACKGROUND

Quantification of plasma levels of an early and late intermediate on the cholesterol pathway, mevalonic acid (MVA) and lathosterol respectively, provides a useful method of estimating cholesterol synthesis in humans. The aim of this study was to assess further their roles as indices of cholesterol synthesis under non-steady-state conditions.

METHODS

The short-term effects of pharmacological inhibition of 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase on both variables were determined in four normolipidaemic subjects during and after treatment with simvastatin 20 mg daily. Plasma MVA was measured using gas chromatography-mass spectrometry, and lathosterol using gas chromatography.

RESULTS

A single dose of 20 mg of simvastatin decreased plasma MVA after 2 h and decreased the lathosterol-cholesterol (L/C) ratio after 4 h. Treatment with simvastatin 20 mg daily for 9 days decreased both variables by approximately 50%, the nadir of plasma MVA occurring on the second day and of the L/C ratio on the fifth day, and resulted in a 39% reduction in low-density lipoprotein (LDL)-cholesterol. After discontinuing simvastatin, there were rebounds in plasma MVA and the L/C ratio to above basal levels but not in LDL cholesterol or apolipoprotein B (apoB), the latter continuing to decrease for a further 2 days.

CONCLUSION

These results suggest that simvastatin rapidly down-regulates cholesterol synthesis, which is then up-regulated when the drug is withdrawn.

HMG-CoA reductase is not the site of the primary defect in phytosterolemia

Phytosterolemia is an autosomal recessive disorder characterized by the excessive absorption, reduced excretion, and consequent high tissue and plasma levels of plant sterols, by the presence of tendon xanthomas, and by premature atherosclerosis. Low HMG-CoA reductase (HRase) activity and mass have been reported in liver and mononuclear leucocytes and low mRNA levels in liver from phytosterolemic subjects. These results led to the proposal that the primary defect in this condition involves the HRase gene locus. We examined this hypothesis in phytosterolemic subjects and heterozygous parents from four unrelated families. A variable number tandem repeat (VNTR) polymorphism of the HRase gene in the three informative families and a ScrFI restriction fragment length polymorphism (RFLP) within intron 2 of the gene in one of these families, segregated independently of the disease phenotype. Biological parentage was confirmed in the family in whom both polymorphisms failed to segregate with the disorder. These results conclusively exclude the HRase gene locus as the site of the primary defect in phytosterolemia. The study was extended by examining plasma levels of mevalonic acid and lathosterol, both markers of cholesterol biosynthesis, in response to cholestyramine, a bile acid sequestrant that is known to up-regulate HRase. Oral administration of cholestyramine resulted in a substantial (7.7-fold) increase in mevaIonic acid levels in two phytosterolemic subjects, compared with a 2.2-fold rise in their obligate heterozygote parents and a 2.3-fold increase in three healthy control subjects. The lathosterol/cholesterol (L/C) ratio showed a quantitatively similar response. Baseline levels of mevalonate and the L/C ratio were low in the phytosterolemic patients in conformity with reports of reduced cholesterol biosynthesis and HRase activity in this disorder. These functional data provide support for the concept that the primary defect in phytosterolemia does not affect a trans gene locus responsible for the constitutive expression or regulation of HMG-CoA reductase.

Hepatic secretion of very-low-density lipoprotein apolipoprotein B-100 studied with a stable isotope technique in men with visceral obesity

OBJECTIVE

To test the hypothesis that the hepatic secretion of very-low-density lipoprotein (VLDL) apolipoprotein B-100 (apoB) is increased in men with visceral obesity and to examine whether the oversecretion of this apolipoprotein is related to insulin resistance and increased hepatic availability of lipid substrates.

SUBJECTS

16 obese men (body mass index (BMI) > 30 kg/m2, waist circumference > 100 cm) and 16 non-obese, age matched men, were studied.

MEASUREMENTS

The hepatic secretion of VLDL apoB was measured using a primed (1 mg/kg), constant (1 mg/kg/h), intravenous infusion of 1-[13C]-leucine. Isotopic enrichment of VLDL apoB was determined using gas-chromatography mass spectrometry and a multi-compartmental model (SAAM-II) was used to estimate the fractional turnover rate of VLDL apoB.

RESULTS

Plasma concentrations of total cholesterol, triglyceride, glucose, insulin, mevalonic acid and lathosterol, as well as dietary fat intake, were significantly higher (P < 0.05) in obese than control subjects. The obese subjects had significantly lower high-density-lipoprotein cholesterol (P < 0.01). VLDL apoB pool size and hepatic secretion rate (mg/kg fat free mass/d) were significantly higher in the obese than non-obese subjects (P < 0.02). The fractional catabolic rate of VLDL apoB was lower in the obese subjects compared with controls, but the difference did not attain conventional significance (P=0.053). In pooled analysis, there was a significant positive association (P < 0.05) between VLDL apoB secretion rate (mg/kg fat free mass/d) and waist-to-hip ratio (WHR), waist circumference, and fasting plasma triglyceride, insulin and glucose concentrations. In multiple linear regression analysis, the association between VLDL apoB secretion and fasting insulin concentration was independent of age, apolipoprotein E (apoE) genotype, mevalonic acid concentration, free fatty acid concentration and fat intake.

CONCLUSION

Our findings are consistent with the hypothesis that in visceral obesity, insulin resistance and the associated increased lipid substrate supply to the liver contribute to hepatic oversecretion of apoB; expansion in the VLDL apoB pool size may also be due to a catabolic defect related to insulin resistance.

The effect of cholesterol reduction with fluvastatin on aortic compliance, coronary calcification and carotid intimal-medial thickness: a pilot study

BACKGROUND

Regression of atheroma with reduction of cholesterol levels is recognized to occur, but less is known about reversal of sclerosis. Non-invasive indices of sclerosis have largely been based on carotid ultrasound measurements.

OBJECTIVE

To measure aortic compliance, coronary calcification and carotid intimal-medial thickness during reduction of cholesterol level in patients with and without coronary artery disease.

METHODS

We studied 64 hypercholesterolaemic patients, 24 with and 40 without coronary artery disease. All were administered fluvastatin for 1 year. Aortic compliance was assessed using magnetic resonance and coronary calcification score was determined by electron beam computed tomography. Carotid intimal-medial thickness in 34 patients was measured by carotid ultrasound means.

RESULTS

There was a rise in high-density lipoprotein cholesterol level and falls in total cholesterol level, low-density lipoprotein cholesterol level, low: high-density lipoprotein ratio, triglyceride level and very-low-density lipoprotein cholesterol level. Coronary artery disease patients had a higher coronary calcification score (442 +/- 551) than did other patients (269 +/- 724, P = 0.0002). For both groups there was a small rise in coronary calcification score during the study. Mean aortic compliance rose and blood pressure and carotid intimal-medial thickness fell. Analysis revealed significant correlations between change in mean aortic compliance and changes in high-density lipoprotein level (r = 0.3, P = 0.036), very-low-density lipoprotein level (r = -0.31, P = 0.038) and low: high-density lipoprotein ratio (r = -0.35, P = 0.014). There was no significant difference in these changes between the two patient groups.

CONCLUSION

An improvement in aortic compliance over 1 year indicates that increase in high-density lipoprotein level, decrease in very-low-density lipoprotein level and improvement in low: high-density lipoprotein ratio caused by administration of fluvastatin beneficially influenced vascular pathophysiology in hypercholesterolaemic patients with and without coronary artery disease. In those patients studied with carotid ultrasound means, carotid intimal-medial thickness decreased from 1.09 to 0.87 mm (P = 0.004), corroborating these results.

Upregulation of cholesterol synthesis after acute reduction of low density lipoprotein by apheresis in normocholesterolaemic subjects: evidence for a threshold effect

The influence of low density lipoproteins (LDL) in the plasma on the regulation of cholesterol biosynthesis is not clear. We studied the changes in plasma mevalonic acid (MVA) concentration and the lathosterol/cholesterol (L/C) ratio, which are well established indices of whole body cholesterol synthesis, in four normocholesterolaemic subjects after each had undergone LDL apheresis on two occasions. LDL apheresis of 75% of the calculated plasma volume reduced LDL-cholesterol by 44% to 1.5 +/- 0.2 mmol/l without changing plasma MVA levels or L/C ratios. Apheresis of 125% of the calculated plasma volume decreased plasma LDL-cholesterol by 69% to 0.9 +/- 0.2 mmol/l, with significant increases in plasma MVA and L/C ratio on the day after the procedure. These results imply that LDL-cholesterol is an integral part of the sterol regulatory pool and suggest that plasma levels cannot be lowered below 1-1.4 mmol/l in normal subjects without upregulating cholesterol biosynthesis.

Direct association between the hepatic secretion of very-low-density lipoprotein apolipoprotein B-100 and plasma mevalonic acid and lathosterol concentrations in man

Apolipoprotein B-100 (apo B) is the principal structural and functional protein of the pro-atherogenic lipoproteins, but its homeostasis in man has not been clearly established. The hepatic availability of cholesterol substrate may be a determining factor. We examined whether there was a direct correlation between plasma concentrations of mevalonic acid (MVA) and lathosterol (indices of in vivo cholesterol synthesis) and hepatic secretion of very-low-density lipoprotein (VLDL) apo B in 13 normolipidaemic, healthy male subjects. The secretion of VLDL apo B was measured using a primed constant intravenous infusion of 1-[13C]-leucine (1 mg/kg per h) over 8 h. Gas-chromatography mass spectrometry (GCMS) was used to derive isotopic enrichment of apo B and fractional turnover rate was calculated using a monoexponential function. There was a highly significant positive correlation between the absolute secretion rate (ASR) of VLDL apo B and the plasma concentrations of mevalonic acid (r = 0.72, P = 0.005) and lathosterol (r = 0.81, P = 0.001) and the lathosterol:cholesterol ratio (r = 0.79, P = 0.001). In multiple regression analysis, these correlations remained significant after adjusting for waist circumference, age, apolipoprotein E genotype and dietary fat intake. The data further support the notion that the availability of cholesterol substrate regulates the hepatic secretion rate of apo B.

Decreased production of low density lipoprotein by atorvastatin after apheresis in homozygous familial hypercholesterolemia

Apheresis only partially controls raised low density lipoprotein cholesterol levels in patients with homozygous familial hypercholesterolemia, who usually respond poorly to lipid-lowering drugs. The efficacy and mechanism of action of a new 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, atorvastatin, was therefore investigated in seven homozygotes undergoing apheresis. One receptor-negative and six receptor-defective homozygotes undergoing plasma exchange or LDL apheresis every 2 weeks were studied during 2 months each on placebo and on atorvastatin 80 mg daily. Changes in plasma lipids and mevalonic acid, an index of cholesterol synthesis, were measured and the kinetics of the rebound of low density lipoprotein cholesterol and apolipoprotein B after apheresis were analyzed. All subjects had significant improvements on atorvastatin. Mean decreases in low density lipoprotein cholesterol were 31% greater both pre- and post-apheresis on atorvastatin compared with placebo, accompanied by a 63% decrease in mevalonic acid. Percentage changes in low density lipoprotein cholesterol and mevalonic acid were closely correlated (r = 0.89, P = 0.007). The mean production rates of low density lipoprotein cholesterol and apolipoprotein B were 21% and 25% lower, respectively, on atorvastatin than on placebo (P < 0.005 and <0.02) but changes in mean fractional clearance rates were not statistically significant. We conclude that atorvastatin enhances the efficacy of plasma exchange and low density lipoprotein apheresis in patients who lack low density lipoprotein receptors. This effect appears to be due to marked inhibition of cholesterol synthesis which results in a decreased rate of production of low density lipoprotein.

Inhibition of cholesterogenesis decreases hepatic secretion of apoB-100 in normolipidemic subjects

We examined the effect of simvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, on the kinetics of very low-density lipoprotein apolipoprotein B-100 (VLDL apoB) in 13 normolipidemic men in a placebo-controlled crossover study. Simvastatin significantly decreased the plasma concentrations of low-density lipoprotein (LDL) cholesterol by 36%, triglycerides by 26%, mevalonic acid by 34%, and lathosterol by 32%. Hepatic secretion of VLDL apoB was measured using a primed constant intravenous infusion of [1-13C]leucine with monitoring of isotopic enrichment of apoB by gas chromatography-mass spectrometry; fractional turnover rate was derived using a monoexponential function. Simvastatin decreased VLDL apoB pool size by 53% and the hepatic secretion rate of VLDL apoB by 46% but did not significantly alter its fractional catabolism. The change in hepatic VLDL apoB secretion was significantly and independently correlated with changes in plasma mevalonic acid and lathosterol concentrations and the lathosterol-to-cholesterol ratio. The data support the hypothesis that the rate of de novo cholesterol synthesis directly regulates the hepatic secretion of VLDL apoB in normal subjects.

Prolonged inhibition of cholesterol synthesis explains the efficacy of atorvastatin

HMG-CoA reductase inhibitors or statins are effective in both the primary and secondary prevention of coronary heart disease, the extent of benefit being proportional to the reduction in low density lipoprotein (LDL) cholesterol achieved. Atorvastatin, a newly licensed compound, reportedly lowers LDL with greater efficacy than other statins. The mechanism of this action was, therefore, explored in twenty patients with refractory familial hypercholesterolemia who received in a single-blind sequence simvastatin 40 mg/day, placebo and atorvastatin 10 mg/day each for 4 weeks. At the end of the placebo period the effects of single 40-mg doses of simvastatin and atorvastatin on plasma levels and urinary excretion of mevalonic acid, indices of HMG-CoA reductase activity, were compared. Administration of atorvastatin 10 mg daily for 1 month lowered LDL cholesterol by 32.5%, compared with placebo (P = 0.0001), which was 4.5% less than the decrease after simvastatin 40 mg daily (P = 0.33). The area under the plasma curve and urinary mevalonic acid/ creatinine ratio were both significantly less during the 24 h after a single dose of atorvastatin 40 mg than after a single dose of simvastatin 40 mg (P < 0.01). These findings suggest that the greater efficacy of atorvastatin compared with simvastatin is due to more prolonged inhibition of HMG-CoA reductase, presumably reflecting longer residence of atorvastatin or its active metabolites in the liver.

Apolipoprotein E1-Hammersmith (Lys146-->Asn;Arg147-->Trp), due to a dinucleotide substitution, is associated with early manifestation of dominant type III hyperlipoproteinaemia

Apolipoprotein E (apoE) is one of the major protein constituents of chylomicron and very low density lipoprotein (VLDL) remnants and plays a central role as a ligand in the receptor-mediated uptake of these particles by the liver. Here we describe a new variant of apoE, apoE1-Hammersmith, which is associated with dominantly expressed type III hyperlipidaemia. The propositus, aged 26, developed tubero-eruptive xanthomas at the age of 3, her daughter developed similar lesions at age 7 but her son, aged 3, shows no clinical abnormality so far. All three cases had an apoE3E1 phenotype and a broad beta band on lipoprotein electrophoresis. Cysteamine modification resulted in a shift of apoE1 to the apoE2 isoform position, indicating that the mutation leading to apoE1-Hammersmith occurred on an apoE3 background. ApoE genotyping confirmed these results. Sequence analysis of DNA of the propositus was performed for exons 3 and 4 and revealed a dinucleotide substitution causing two amino acid changes at adjacent positions (Lys146-->Asn) and (Arg147-->Trp).

Acute hyperinsulinaemia decreases cholesterol synthesis less in subjects with non-insulin-dependent diabetes mellitus than in non-diabetic subjects

To investigate the effect of insulin on cholesterol synthesis in vivo we measured plasma mevalonic acid (MVA) concentrations using gas chromatography-mass spectrometry in six non-obese patients with non-insulin-dependent diabetes mellitus (NIDDM) [four men, two women; age 57.5 +/- 2.2 years (mean +/- SEM); glycated haemoglobin (HbA1) 8.5 +/- 0.5%; total cholesterol (TC) 5.7 +/- 0.5 mmol L-1, triglyceride (TG) 3.8 +/- 0.9 mmol L-1] and six non-diabetic, sex- and age-matched control subjects (age 55.7 +/- 2.8 years; HbA1 6.5 +/- 0.1%; TC 5.4 +/- 0.3 mmol L-1, TG 1.2 +/- 0.1 mmol L-1). Subjects were studied twice: during 13-h hyperinsulinaemic (1 mu kg-1 min-1), euglycaemic (5 mmol L-1) clamp and during a saline infusion. Baseline MVA concentration was significantly higher in diabetic patients than in control subjects (9.8 +/- 0.7 ng mL-1 vs. 5.6 +/- 0.9 ng mL-1, P = 0.004). At the end of each study, MVA concentration, expressed as a percentage of baseline, was significantly lower during the hyperinsulinaemic, euglycaemic clamp than during the saline study in both the diabetic (54.4 +/- 5.3% vs. 69.6 +/- 6.3%, P = 0.036) and control subjects (30.5 +/- 3.4% vs. 61.7 +/- 6.0%, P = 0.01). However, the decrease in MVA during the hyperinsulinaemic clamp study was more marked in the control subjects than in the diabetic subjects (P = 0.03). A significant positive correlation was found between percentage decrease of MVA and non-esterified fatty acids following the insulin clamp in NIDDM (r = 0.83, P = 0.04). We conclude that acute hyperinsulinaemia decreases cholesterol synthesis less in subjects with NIDDM than in non-diabetic subjects and that this phenomenon, together with increased basal cholesterol synthesis in NIDDM, may in part be due to insulin resistance.

Role of cholesterol in regulating apolipoprotein B secretion by the liver

The review examines the evidence that the supply of cholesterol available for incorporation into nascent lipoprotein particles exerts a regulatory influence on apolipoprotein (apo) B secretion by the liver. Support for this hypothesis comes both from in vitro experiments and from recent observations in normal subjects and patients with dyslipidemia associated with familial hypercholesterolemia, obesity, noninsulin dependent diabetes mellitus, growth hormone deficiency and cholesteryl ester storage disease. The findings do not negate a role for triglyceride synthesis in determining apoB secretion in very low density lipoprotein, but the inhibitory effects on the latter process of pharmacological blockade of cholesterol synthesis or esterification suggest that it is conditional upon an adequate supply of cholesteryl ester.

The extracranial carotid artery in familial hypercholesterolaemia: relationship of intimal-medial thickness and plaque morphology with plasma lipids and coronary heart disease

BACKGROUND

Increased frequency of coronary heart disease in familial hypercholesterolaemia is well documented but the association with carotid atherosclerosis is less well established. The ultrasound appearances of the carotid arteries in familial hypercholesterolaemia patients without symptomatic cerebrovascular disease were therefore investigated.

METHODS

59 patients (34 men, 25 women; mean age 46.6 (+/-12.1 years) were prospectively studied using ultrasound examination of the extracranial carotid vessels. Intimal-medial thickness was measured 1 cm proximal to the carotid bulb and morphology of plaque was classified as heterogeneous or homogeneous according to echogenicity.

RESULTS

44 (75.0%) of the patients had carotid artery disease. On stepwise logistic regression, significant predictors of the presence of carotid artery disease were age (P = 0.014), serum triglycerides at time of examination (P = 0.013), coexistent coronary heart disease (P = 0.03) and the cholesterol-years score (CYS) (P = 0.015). Heterogeneous carotid plaque was associated with a higher plasma level of Lp(a) (P = 0.035), TG (P = 0.024), CYS (P = 0.0003) and the presence of CHD (P = 0.001). Matched pairs (n = 22) of patients, where the only variable was Lp(a), showed a marked increase in heterogeneous plaque frequency in those with high Lp(a) levels (P < 0.03).

CONCLUSION

Asymptomatic carotid artery disease occurs in a high proportion of familial hypercholesterolaemia patients. The presence of heterogeneous carotid plaque is significantly associated with the presence of coronary heart disease, the calculated cholesterol-years score, hypertriglyceridaemia and raised levels of Lp(a).

Plasma mevalonic acid, an index of cholesterol synthesis in vivo, and responsiveness to HMG-CoA reductase inhibitors in familial hypercholesterolaemia

Fasting plasma mevalonic acid (MVA), an indicator of in vivo cholesterol synthesis, was measured in 35 patients with familial hypercholesterolaemia (FH) of whom 7 were treated with pravastatin 10-40 mg/day, 7 with simvastatin 10-40 mg/day and 21 with atorvastatin 80 mg/day. Reductions in low density lipoprotein (LDL) cholesterol and MVA on maximal dose therapy differed significantly between the three drugs: 34.7%, 42.9% and 54.0% (P = 0.0001), and 31.6%, 48.9% and 58.8% (P = 0.004), respectively. Patients on atorvastatin were subdivided according to whether their reduction in LDL cholesterol on treatment was above or below the mean percentage change for the whole group. Basal values of LDL cholesterol did not differ significantly, but above average responders had a significantly higher mean pre-treatment level of MVA (6.2 +/- 0.60 vs. 4.3 +/- 0.61 ng/ml, P < 0.05) than below average responders. When all three drug groups were pooled above average responders showed a significantly greater absolute decrease in MVA on treatment than below average responders (3.85 +/- 0.48 vs. 2.33 +/- 0.40 ng/ml, P < 0.05). However, there was no significant correlation between the magnitude of the decreases in LDL cholesterol and MVA. These findings suggest that FH patients who responded well to statins had a higher basal level of plasma MVA, i.e. a higher rate of cholesterol synthesis, which was more susceptible to pharmacological inhibition. The more marked cholesterol lowering effect of atorvastatin 80 mg/day presumably reflects, at least in part, its ability to inhibit HMG-CoA reductase to a greater extent than maximal recommended doses of pravastatin and simvastatin of 40 mg/day.

Acute and chronic effects on cholesterol biosynthesis of LDL-apheresis with or without concomitant HMG-CoA reductase inhibitor therapy

To determine the acute and long-term effects of low density lipoprotein (LDL) reduction on cholesterol biosynthesis, we studied changes in the cholesterol precursors mevalonic acid (MVA) and lathosterol in patients with heterozygous familial hypercholesterolemia undergoing LDL-apheresis. Long-term LDL-apheresis in eight patients resulted in slight but insignificant increases in plasma MVA levels and lathosterol/cholesterol (L/C) ratios over 18 months. In short-term studies, six patients not on drugs and six patients treated with lovastatin or pravastatin had blood taken immediately before and after LDL-apheresis, and afterwards on days 1, 2, 3, 5, and 7. Plasma L/C ratios and MVA concentration did not change significantly on the first day after LDL-apheresis in those not on statin therapy (1.11 +/- 0.08 vs. 1.40 +/- 0.18, and 9.2 +/- 1.3 vs. 9.1 +/- 0.6 ng/ml, respectively) but increased in the statin-treated group (from 0.78 +/- 0.09 to 1.55 +/- 0.21, P = 0.003 and from 5.0 +/- 0.7 to 11.0 +/- 1.6 ng/ml, P = 0.008, respectively). There was no clear correlation between the changes in either of these precursors and the extent of reduction of total cholesterol by LDL-apheresis, but there was a strong inverse correlation with the post-apheresis LDL-cholesterol level (r = -0.77, P = 0.002 for L/C ratio; r = -0.75, P = 0.003 for MVA). Post-apheresis changes in L/C ratio and MVA were mutually correlated (r = 0.68. P = 0.01). We conclude that LDL-apheresis stimulates cholesterol biosynthesis transiently despite concomitant therapy with an HMG-CoA reductase inhibitor, the degree of stimulation being inversely related to the level to which the LDL-cholesterol was reduced.

Drug therapy after very-low-calorie diets

Very-low-calorie diets (VLCDs) are effective at reducing weight, even in patients who have often failed with conventional diets. Maintaining weight lost by means of a VLCD remains a clinical challenge. Attempts to prevent weight regain by dietary reeducation or by more formal behavior-modification techniques are not easily applicable to large numbers of patients and are not always successful; the use of drugs to maintain and improve upon initial VLCD success could be of real clinical value. Pharmacological treatment of obesity has evolved in recent years with the development and licensing of potent serotonin agonists, such as dexfenfluramine (dF), acting as nonstimulant anorectic agents. Thermogenic drugs are not yet as advanced in clinical development and evaluation but offer the prospect of increasing energy output in the reduced obese patient. Drugs used to treat obesity need to be effective, to be safe, not to exhibit drug tolerance, and ideally, to be shown to reduce morbidity or mortality from obesity, particularly because treatment will need to be prolonged. Such requirements are not unique for treating obesity, they are similar for drugs used to treat other metabolic diseases such as hypercholesterolemia or diabetes. VLCD followed by dF has been shown to be effective. A double-blind trial randomized 45 patients who had successfully completed 8 wk of treatment on the Cambridge diet to either placebo or dF 15 mg twice daily for 26 wk. Patients continued on a diet giving 60-75% of daily energy needs.(ABSTRACT TRUNCATED AT 250 WORDS)