Governance of the concentration of plasma LDL: a reevaluation of the LDL receptor paradigm

Physiological Bases for the Superiority of Apolipoprotein B Over Low-Density Lipoprotein Cholesterol and Non-High-Density Lipoprotein Cholesterol as a Marker of Cardiovascular Risk

In 2019, the European Society of Cardiology/European Atherosclerosis Society stated that apolipoprotein B (apoB) was a more accurate marker of cardiovascular risk than low-density lipoprotein cholesterol (LDL-C) and non-high-density lipoprotein cholesterol. Since then, the evidence has continued to mount in favor of apoB. This review explicates the physiological mechanisms responsible for the superiority of apoB as a marker of the cardiovascular risk attributable to the atherogenic apoB lipoprotein particles chylomicron remnants, very low-density lipoprotein, and low-density lipoprotein particles. First, the nature and relative numbers of these different apoB particles will be outlined. This will make clear why low-density lipoprotein particles are almost always the major determinants of cardiovascular risk and why the concentrations of triglycerides and LDL-C may obscure this relation. Next, the mechanisms that govern the number of very low-density lipoprotein and low-density lipoprotein particles will be outlined because, except for dysbetalipoproteinemia, the total number of apoB particles determines cardiovascular risk, Then, the mechanisms that govern the cholesterol mass within very low-density lipoprotein and low-density lipoprotein particles will be reviewed because these are responsible for the discordance between the mass of cholesterol within apoB particles, measured either as LDL-C or non-high-density lipoprotein cholesterol, and the number of apoB particles measured as apoB, which creates the superior predictive power of apoB over LDL-C and non-high-density lipoprotein cholesterol. Finally, the major apoB dyslipoproteinemias will be briefly outlined. Our objective is to provide a physiological framework for health care givers to understand why apoB is a more accurate marker of cardiovascular risk than LDL-C or non-high-density lipoprotein cholesterol.

The severe hypercholesterolemia phenotype: clinical diagnosis, management, and emerging therapies

The severe hypercholesterolemia phenotype includes all patients with marked elevation of low-density lipoprotein cholesterol (LDL-C) levels. The most common cause is autosomal dominant hypercholesterolemia, an inherited disorder caused by mutations either in LDL receptor, apolipoprotein B (APOB), or proprotein convertase subtilisin kexin type 9 (PCSK9) genes. However, it is now known that many subjects with severe inherited hypercholesterolemia have no defects in these genes. These cases are caused either by mutations in genes yet to be identified or are consequences of polygenic, epigenetic, or acquired defects. Because the clinical consequences of extreme hypercholesterolemia are the same no matter the cause, the focus should be on the identification of subjects with severe hypercholesterolemia, followed by phenotypic screening of family members. Genetic screening is not necessary to diagnose or initiate treatment for the severe hypercholesterolemia phenotype. Management of severe hypercholesterolemia is based on risk factor modification and use of multiple lipid-lowering medications. Lipoprotein apheresis is indicated for coronary artery disease (CAD) patients taking maximally tolerated therapy and with LDL-C levels >200 mg/dl (>300 mg/dl if without CAD). A microsomal triglyceride transfer protein inhibitor and an antisense oligonucleotide against APOB have recently been approved for use in subjects with clinically diagnosed homozygous familial hypercholesterolemia. PCSK9 inhibitors, currently in phase II and III trials, lower LDL-C up to an additional 70% in the setting of maximally tolerated medical therapy and have the potential to reduce LDL-C to <70 mg/dl in most patients. Early identification of affected individuals and aggressive treatment should significantly reduce the burden of cardiovascular disease in society.

Pro-atherogenic lipid changes and decreased hepatic LDL receptor expression by tocilizumab in rheumatoid arthritis

OBJECTIVES

Blocking the interleukin-6 pathway by tocilizumab (TCZ) has been associated with changes in the lipoprotein profile, which could adversely impact cardiovascular (CV) risk in patients with rheumatoid arthritis (RA). In the present study, we addressed the effect of TCZ on lipoproteins in both fasting and non-fasting state in RA patients and tested the effect of TCZ on LDL receptor (LDLr) expression in vitro.

METHODS

Twenty patients with active RA and an inadequate response to TNF blockers received monthly TCZ intravenously. On week 0, 1 and 6 blood was drawn before and after an oral fat load, the lipid profiles and HDL antioxidative capacity were measured. Effects of TCZ on LDLr expression in transfected HepG2 cells were subjected.

RESULTS

After 6 weeks of TCZ, total cholesterol increased by 22% (4.8 ± 0.9 to 5.9 ± 1.3 mmol/L; p < 0.001), LDLc by 22% (3.0 ± 0.6 to 3.6 ± 0.8 mmol/L; p < 0.001) and HDLc by 17% (1.4 ± 0.4 to 1.7 ± 0.7 mmol/L; p < 0.016). Fasting triglycerides (TG) increased by 48% (1.0 ± 0.4 to 1.4 ± 0.8 mmol/L; p = 0.011), whereas postprandial incremental area under the curve TG increased by 62% (p = 0.002). Lipid changes were unrelated to the change in disease activity or inflammatory markers. No difference in HDL antioxidative capacity was found. In vitro, LDLr expression in cultured liver cells was significantly decreased following TCZ incubation (P < 0.001).

CONCLUSIONS

TCZ adversely impacts on both LDLc as well as fasting and postprandial TG in patients with RA. The changes in hepatic LDLr expression following TCZ imply that adverse lipid changes may be a direct hepatic effect of TCZ. The net effect of TCZ on CV-morbidity has to be confirmed in future clinical trials.

Diagnosis and treatment of apolipoprotein B dyslipoproteinemias

Conventionally, atherogenic dyslipidemias have been defined by elevated levels of triglyceride and/or LDL cholesterol. However, cholesterol and triglycerides are not metabolically and physically independent entities. Rather, they are constituents of the atherogenic apolipoprotein B (apoB) particles, which differ in their origin and their metabolic function. Moreover, the risk of vascular disease is not related to the plasma concentration of cholesterol or triglyceride per se, but to the number, composition and size of the apoB particles, within which the cholesterol and triglycerides are contained. After all, the entire apoB particle--rather than individual cholesterol or triglyceride molecules--enters and is trapped within the arterial wall, and this particle initiates and sustains the process that results in atherosclerosis. Accordingly, we suggest a change of name and focus from dyslipidemias to dyslipoproteinemias. Virtually all the atherogenic apoB dyslipoproteinemias can be specifically identified on the basis of plasma levels of cholesterol, triglyceride and apoB. Not only does this enable an accurate diagnosis in the individual, but the major familial dyslipoproteinemias can be identified as well. Here, we review the diagnostic algorithm for apoB dyslipoproteinemias and provide, for the first time, a treatment plan on the basis of a reduction of atherogenic lipoprotein particles rather than plasma lipids.

Regulation of plasma LDL: the apoB paradigm

The objectives of this analysis are to re-examine the foundational studies of the in vivo metabolism of plasma LDL (low-density lipoprotein) particles in humans and, based on them, to reconstruct our understanding of the governance of the concentration of plasma LDL and the maintenance of cholesterol homoeostasis in the hepatocyte. We believe that regulation of cholesterol homoeostasis within the hepatocyte is demonstrably more complex than envisioned by the LDL receptor paradigm, the conventional model to explain the regulation of plasma LDL and the fluxes of cholesterol into the liver, a model which was generated in the fibroblast but has never been fully validated in the hepatocyte. We suggest that the LDL receptor paradigm should be reconfigured as the apoB (apolipoprotein B) paradigm, which states that the rate at which LDL particles are produced is at least an important determinant of their concentration in plasma as the rate at which they are cleared from plasma and that secretion of cholesterol within VLDL (very-low-density lipoprotein) particles is an important mechanism of maintaining cholesterol homoeostasis within the hepatocyte. These two paradigms are not mutually exclusive. The LDL receptor paradigm, however, includes only one critical aspect of the regulation of plasma LDL, namely the rate at which LDL particles are cleared through the LDL receptor pathway, but ignores another - the rate at which LDL particles are added to the plasma compartment. The apoB paradigm includes both and points to a different model of how the hepatocyte achieves cholesterol homoeostasis in a complex metabolic environment.

Familial combined hyperlipidemia is associated with alterations in the cholesterol synthesis pathway

OBJECTIVE

Familial combined hyperlipidemia (FCH) is a common familial lipid disorder characterized by increases in plasma total cholesterol, triglyceride, and apolipoprotein B-100 levels. In light of prior metabolic and genetic research, our purpose was to ascertain whether FCH cases had significant abnormalities of plasma markers of cholesterol synthesis and absorption as compared to unaffected kindred members.

METHODS AND RESULTS

Plasma levels of squalene, desmosterol, and lathosterol (cholesterol synthesis markers) and campesterol, sitosterol, and cholestanol (cholesterol absorption markers) were measured by gas-liquid chromatography in 103 FCH patients and 240 normolipidemic relatives (NLR). Squalene, desmosterol, and lathosterol levels were 6% (0.078), 31%, (P<0.001) and 51% (P<0.001) higher in FCH as compared to NLR, and these differences were especially pronounced in women. An interaction with obesity was also noted for a subset of these markers. We did not observe any apparent differences for the cholesterol absorption markers among FCH patients and NLR.

CONCLUSIONS

Our data indicate that both men and women with FCH have alterations in the cholesterol synthesis pathway, resulting in 51% higher levels of lathosterol (and additionally desmosterol in women). Plasma levels of the cholesterol precursor sterol squalene were only slightly increased (6%), suggesting enhanced conversion of squalene to lathosterol in this disorder.

Diabetes, abdominal adiposity, and atherogenic dyslipoproteinemia in women compared with men

OBJECTIVE

To understand why atherogenic risk differs more between diabetic and nondiabetic women than between diabetic and nondiabetic men.

RESEARCH DESIGN AND METHODS AND RESULTS

Measures of cardiovascular risk, body composition, and serum hormones from the baseline examinations of the Insulin Resistance Atherosclerosis Study on 524 nondiabetic women, 258 diabetic women, 421 nondiabetic men, and 220 diabetic men were compared to detect greater adverse differences in women than in men. Systolic blood pressure; apolipoprotein B (apoB); total cholesterol; apoB-to-apoA-I ratio; non-HDL cholesterol; LDL particle count, small LDL, and intermediate-density lipoprotein by nuclear magnetic resonance; and C-reactive protein exhibited significant diabetes-sex interaction (P < 0.05). ApoB exhibited the most significant interaction (P = 0.0005). Age- and ethnicity-adjusted apoB means were lower in nondiabetic women than nondiabetic men (102.4 vs. 106.8 mg/dl, P < 0.05) but higher in diabetes (115.7 vs. 110.2 mg/dl, P < 0.01). Plotted against BMI, waist circumference was 6% higher and hip circumference 10% lower in diabetic than nondiabetic women (both P < 0.05), whereas the circumference measures did not differ conspicuously between diabetic and nondiabetic men.

CONCLUSIONS

In diabetic women, an elevated level of atherogenic particles, as manifested by apoB and LDL particle count, which may result from abdominal adiposity, represents a major treatable cardiovascular risk factor.

Familial combined hyperlipidaemia: how can genetic disorders be common, complex and comprehensible?

FCHL (familial combined hyperlipidaemia) is characterized by multiple phenotypes that are shaped by genes, the environment and time. A longitudinal study by Brouwers and co-workers, which appears in this issue of Clinical Science, points to the central role of the liver in defining the FCHL phenotypes and demonstrates how they vary over time in relation to energy excess. On the basis of their work and that of others, we propose that FCHL is a multiple gene/multiple pathway/multiple phenotype disease. The key feature of this model of common complex disease is that it posits testable faults in definable metabolic pathways, which supply the genetic underpinning of the disorder.

Effect of aging and obesity on the expression of dyslipidaemia in children from families with familial combined hyperlipidaemia

The aim of the present study was to delineate the mechanism(s) responsible for the increased secretion of VLDL (very-low-density lipoprotein) particles in patients with FCH (familial combined hyperlipidaemia). In 194 young adults (<25 years of age) recruited from families with FCH, we investigated how plasma lipids, (apo)lipoproteins and BMI (body mass index) varied with age. Furthermore, we performed a 5-year follow-up study of clinical and biochemical characteristics of a subset of this population (n=85) stratified by apoB (apolipoprotein B) levels (below or above the 75th percentile adjusted for age and gender). Plasma apoB concentration (r=0.45, P<0.0001), triacylglycerol (triglyceride) concentration (r=0.45, P<0.0001), LDL (low-density lipoprotein) subfraction profile (r=−0.46, P<0.0001) and BMI (r=0.51, P<0.0001) were significantly associated with age. Plasma apoB concentration in the hyperapoB group was already elevated at a young age, whereas other characteristics of FCH, as observed in adults, including triacylglycerol levels >1.5 mmol/l and/or small-dense LDL, were observed only sporadically. After the 5-year follow-up, BMI increased in both groups, and this increase was associated with changes in apoB (r=0.27, P<0.05), triacylglycerol (r=0.30, P<0.01), VLDL cholesterol (r=0.22, P<0.05), VLDL triacylglycerol (r=0.25, P<0.05) and high-density lipoprotein cholesterol (r=−0.27, P<0.05). In conclusion, we have found indirect evidence of a primary, presumably genetically determined, increase in plasma apoB concentration occurring early in life of offspring from families with FCH. However, aging-related post-maturation increases in adipose tissue mass also appear to contribute to an aggravation and/or modulation of this genetically determined apoB overproduction.

Influence of hepatic steatosis (fatty liver) on severity and composition of dyslipidemia in type 2 diabetes

OBJECTIVE

The objective of this study was to examine the associations between the severity of hepatic steatosis and dyslipidemia in type 2 diabetes, including circulating apolipoprotein B100 (apoB) concentrations and lipoprotein particle size and numbers.

RESEARCH DESIGN AND METHODS

Computed tomography imaging was used to assess hepatic fat content and adipose tissue distribution in 67 men and women with type 2 diabetes, withdrawn from antidiabetic medications preceding the study. Fasting serum lipoprotein number and size was determined by nuclear magnetic resonance. Insulin sensitivity was measured with a glucose clamp and a [6,6-(2)H(2)]glucose isotope infusion.

RESULTS

Two-thirds of the cohort had fatty liver. Hepatic steatosis correlated with serum triglycerides (r = 0.40, P < 0.01) and lower HDL cholesterol (r = -0.31, P < 0.05). ApoB and LDL cholesterol did not, being virtually identical in those with or without steatosis. The association between serum triglycerides and hepatic steatosis was largely accounted for by greater triglyceride enrichment in VLDL particles, which were larger. Severe steatosis was also associated with 70% higher small, dense LDL concentrations. Visceral obesity did not fully explain these associations, and hepatic steatosis was better correlated with triglycerides than with hyperglycemia or hepatic insulin resistance (P > 0.05).

CONCLUSIONS

The presence of hepatic steatosis in type 2 diabetes does not appear to affect apoB levels, but potentially increases atherogenesis by increasing triglycerides, reducing HDL levels, and increasing small, dense LDL.

The adipocyte life cycle hypothesis

The adipocyte life cycle hypothesis states that the metabolic properties of an adipocyte vary predictably during its life cycle: that as an adipocyte matures, it accumulates triacylglycerol (triglyceride) and becomes larger; that the rates of triacylglycerol synthesis and lipolysis are matched within adipocytes and that larger adipocytes, in general, have greater rates of triacylglycerol synthesis and, concurrently, greater rates of lipolysis and, therefore, larger adipocytes have greater rates of transmembrane fatty acid flux; and that the secretion of cytokines can also be related to adipocyte size with larger adipocytes having a more unfavourable profile of cytokine secretion than smaller adipocytes. Adipocyte location is an important modifier of this relationship and the favoured sites of adipocyte proliferation are a function of gender and the position within the life cycle of the organism at which proliferation occurs. The adipocyte life cycle hypothesis posits that the metabolic consequences of obesity depend on whether expansion of adipose tissue is achieved primarily by an increase in adipocyte number or adipocyte size. This hypothesis may explain a variety of previously unanswered clinical puzzles such as the vulnerability of many peoples from South East Asia to the adverse metabolic consequences of obesity.

Apo B versus cholesterol in estimating cardiovascular risk and in guiding therapy: report of the thirty-person/ten-country panel

There is abundant evidence that the risk of atherosclerotic vascular disease is directly related to plasma cholesterol levels. Accordingly, all of the national and transnational screening and therapeutic guidelines are based on total or LDL cholesterol. This presumes that cholesterol is the most important lipoprotein-related proatherogenic risk variable. On the contrary, risk appears to be more directly related to the number of circulating atherogenic particles that contact and enter the arterial wall than to the measured concentration of cholesterol in these lipoprotein fractions. Each of the atherogenic lipoprotein particles contains a single molecule of apolipoprotein (apo) B and therefore the concentration of apo B provides a direct measure of the number of circulating atherogenic lipoproteins. Evidence from fundamental, epidemiological and clinical trial studies indicates that apo B is superior to any of the cholesterol indices to recognize those at increased risk of vascular disease and to judge the adequacy of lipid-lowering therapy. On the basis of this evidence, we believe that apo B should be included in all guidelines as an indicator of cardiovascular risk. In addition, the present target adopted by the Canadian guideline groups of an apo B <90 mg dL(-1) in high-risk patients should be reassessed in the light of the new clinical trial results and a new ultra-low target of <80 mg dL(-1) be considered. The evidence also indicates that the apo B/apo A-I ratio is superior to any of the conventional cholesterol ratios in patients without symptomatic vascular disease or diabetes to evaluate the lipoprotein-related risk of vascular disease.

Postprandial lipemic response and lipoprotein composition in subjects with low or high cholesterol absorption efficiency

BACKGROUND

The purpose of this study was to investigate the effect of differences in cholesterol absorption efficiency on the postprandial lipemia and lipoprotein composition.

METHODS

Fifteen healthy subjects were divided into low and high cholesterol absorbers on the basis of serum cholestanol to cholesterol ratio. A high-performance liquid chromatographic method with evaporative light scattering detection was developed for quantitation of free and esterified cholesterol, triglycerides and major phospholipids from the same lipid extract in two runs utilizing the same internal standard.

RESULTS

The free cholesterol to phosphatidylcholine ratio of chylomicrons was higher in the high cholesterol absorption group. The total increase of cholesterol in combined chylomicron and very low density lipoprotein (VLDL) fraction was also higher in this group. Chylomicron free cholesterol and cholesterol ester responses correlated with fasting low density lipoprotein (LDL) cholesterol. VLDL and VLDL1 triglyceride responses correlated inversely with fasting insulin and homeostasis model assessment of insulin resistance.

CONCLUSIONS

High cholesterol absorption efficiency was seen in chylomicrons as higher cholesterol to phosphatidylcholine ratio during the postprandial peak. Chylomicron cholesterol response was linked to fasting LDL cholesterol and low VLDL triglyceride response to fasting insulin.

Statin induction of liver fatty acid-binding protein (L-FABP) gene expression is peroxisome proliferator-activated receptor-alpha-dependent

Statins are drugs widely used in humans to treat hypercholesterolemia. Statins act by inhibiting cholesterol synthesis resulting in the activation of the transcription factor sterol-responsive element-binding protein-2 that controls the expression of genes involved in cholesterol homeostasis. Statin therapy also decreases plasma triglyceride and non-esterified fatty acid levels, but the mechanism behind this effect remains more elusive. Liver fatty acid-binding protein (L-FABP) plays a role in the influx of long-chain fatty acids into hepatocytes. Here we show that L-FABP is a target for statins. In rat hepatocytes, simvastatin treatment induced L-FABP mRNA levels in a dose-dependent manner. Moreover, L-FABP promoter activity was induced by statin treatment. Progressive 5'-deletion analysis revealed that the peroxisome proliferator-activated receptor (PPAR)-responsive element located at position -67/-55 was responsible for the statin-mediated transactivation of the rat L-FABP promoter. Moreover, treatment with simvastatin and the PPARalpha agonist Wy14,649 resulted in a synergistic induction of L-FABP expression (mRNA and protein) in rat Fao hepatoma cells. This effect was also observed in vivo in wild-type mice but not in PPARalpha-null animals demonstrating the direct implication of PPARalpha in L-FABP regulation by statin treatment. Statin treatment resulted in a rise in PPARalpha mRNA levels both in vitro and in vivo and activated the mouse PPARalpha promoter in a reporter assay. Altogether, these data demonstrate that L-FABP expression is up-regulated by statins through a mechanism involving PPARalpha. Moreover, PPARalpha might be a statin target gene. These effects might contribute to the triglyceride/non-esterified fatty acid-lowering properties of statins.

Insights from apoB: from better diagnosis & therapy to the Medusa Hypothesis

This article will review six of the most important insights that have come from the measurement of apolipoprotein B (apoB). Amongst these are critical clinical advances, which include better definition of those at high risk of vascular disease and better definition of the adequacy of statin therapy. There are also major advances in our understanding of the fundamental processes that interact to cause vascular disease. These include a more precise understanding of the determinants of lipoprotein levels and lipoprotein composition in plasma and, even more importantly, an appreciation of the pivotal role excess fatty acid intake and impaired fatty acid trapping by adipose tissue play in the generation of the complex risk profile that is so common in patients with coronary disease. We have designated the constellation of hypertriglyceridemic (hyperTg) hyperapoB, dysglycemia, and elevated levels of markers of prothrombosis and inflammation--all of which are traceable to adipose tissue dysfunction--as the Medusa Hypothesis. The Medusa Hypothesis puts forward a common pathophysiology for the complex and biologically diverse array of factors that have been associated with vascular disease.

Fasting acylation-stimulating protein is predictive of postprandial triglyceride clearance

Postprandial plasma triglyceride (ppTG) and NEFA clearance were stratified by plasma acylation-stimulating protein (ASP) and gender to determine the contribution of fasting ASP in a normal population (70 men; 71 women). In the highest ASP tertile only, ASP decreased over 8 h (90 +/- 9.7 nM to 70 +/- 5.9 nM, P<0.05 males; 61.9 +/- 4.0 nM to 45.6 +/- 6.2 nM, P<0.01 females). Fasting ASP correlated positively with ppTG response. ppTG (P<0.0001, 2-way ANOVA, both genders) and NEFA levels progressively increased from lowest to highest ASP tertile, with the greatest differences in males. By stepwise multiple regression, the best prediction of ppTG was: (fasting ASP + apolipoprotein B + insulin + TG; r=0.806) for men and (fasting ASP + total cholesterol; r=0.574) for women. Leptin, body mass index, and other fasting variables did not improve the prediction. Thus, in men and women, ASP significantly predicted ppTG and NEFA clearance and, based on lower ASP, women may be more ASP sensitive than men. Plasma ASP may be useful as a fasting variable that will provide additional information regarding ppTG and NEFA clearance.

Effects on apoB-100 secretion and bile acid synthesis by redirecting cholesterol efflux from HepG2 cells

This study determined the effects of apoA-I, HDL3, or hydroxy-beta-cyclodextrin on apoB-100 secretion and bile acid synthesis by HepG2 cells. The principal observations were that: 1) ApoB-100 secretion into the medium was significantly less after the addition of any of the three agents. 2) Triglyceride mass was not significantly changed from control in the medium but was significantly, although modestly, reduced in the cells. 3) Neither free cholesterol (FC) nor cholesteryl ester (CE) mass in the medium was changed; by contrast, CE mass was reduced within the cells although FC was not. 4) Although the total mass of cholesterol in the medium was unaffected, the proportion associated with apoB-100 was reduced, whereas the proportion associated with the non-apoB-100 fraction was increased. 5) There was also an unanticipated, but substantial, increase in bile acid synthesis induced by apoA-I, HDL3, or hydroxy-beta-cyclodextrin, which was time and concentration dependent, and which was associated with marked increases in cholesterol 7 alpha-hydroxylase activity. There were no significant changes in ACAT activity and only modest increases in HMG-CoA reductase activity. These findings support previous clinical observations that an elevated apoB-100 can accompany a low HDL cholesterol in normotriglyceridemic subjects. They also point to physiologically important, although still only partially understood, metabolic relationships amongst hepatic apoB-100 secretion, cholesterol efflux, and bile acid synthesis.

Effects of dietary soybean lecithin on plasma lipid transport and hepatic cholesterol metabolism in rats

Dietary lecithin can stimulate bile formation and biliary lipid secretion, particularly cholesterol output in bile. Studies also suggested that the lecithin-rich diet might modify hepatic cholesterol homeostasis and lipoprotein metabolism. Therefore, we examined hepatic activities of 3-hydroxy-3 methylglutaryl coenzyme A reductase "HMG -CoA reductase", cholesterol 7 alpha-hydroxylase and acyl-CoA: cholesterol acyltransferase "ACAT" as well as plasma lipids and lipoprotein composition in rats fed diets enriched with 20% of soybean lecithin during 14 days. We also evaluated the content of hepatic canalicular membrane proteins involved in lipid transport to the bile (all P-glycoproteins as detected by the C 219 antibody and the sister of P-glycoprotein "spgp" or bile acid export pump) by Western blotting. As predicted, lecithin diet modified hepatic cholesterol homeostasis. The activity of hepatic HMG-CoA reductase and cholesterol 7 alpha-hydroxylase was enhanced by 30 and 12% respectively, while microsomal ACAT activity showed a dramatic decrease of 75%. As previously reported from ACAT inhibition, the plasma level and size of very low-density lipoprotein (VLDL) were significantly decreased and bile acid pool size and biliary lipid output were significantly increased. The canalicular membrane content of lipid transporters was not significantly affected by dietary lecithin. The current data on inhibition of ACAT activity and related metabolic effects by lecithin mimic the previously reported effects following drug-induced inhibition of ACAT activity, suggesting potential beneficial effects of dietary lecithin supplementation in vascular disease.

Atorvastatin treatment induced peroxisome proliferator-activated receptor alpha expression and decreased plasma nonesterified fatty acids and liver triglyceride in fructose-fed rats

We aimed to investigate the effect of atorvastatin (5 and 30 mg/kg/day for 2 weeks) on hepatic lipid metabolism in a well established model of dietary hypertriglyceridemia, the fructose-fed rat. Fructose feeding (10% fructose in drinking water for 2 weeks) induced hepatic lipogenesis and reduced peroxisome proliferator-activated receptor alpha (PPARalpha) expression and fatty acid oxidation. As a result, plasma and liver triglyceride and plasma apolipoprotein B (apoB) levels were increased. Atorvastatin, 5 and 30 mg/kg during 2 weeks, markedly reduced plasma triglyceride, but decreased apoB levels only at the highest dose tested (50%). Triglyceride biosynthetic enzymes and microsomal triglyceride transfer protein were unchanged, whereas liver PPARalpha, acyl-CoA oxidase, and carnitine palmitoyltransferase I mRNA levels (1.9-, 1.25-, and 3.4-fold, respectively) and hepatic fatty acid beta-oxidation activity (1.25-fold) were increased by atorvastatin at 30 mg/kg. Furthermore, hepatic triglyceride content (45%) and plasma nonesterified fatty acids (NEFAs) (49%) were reduced. These results show for the first time that liver triglyceride increase in fructose-fed rats is linked to decreased expression of PPARalpha, which is prevented by atorvastatin treatment. The increase in PPARalpha expression caused by atorvastatin was associated with reduced liver triglyceride and plasma NEFA levels.

Effects of atorvastatin on postprandial plasma lipoproteins in postinfarction patients with combined hyperlipidaemia

Enhanced and prolonged postprandial lipaemia is implicated in coronary and carotid artery disease. This study assessed the effects of atorvastatin, a 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor, on postprandial plasma concentrations of triglyceride-rich lipoproteins (TRLs). Sixteen middle-aged men with combined hyperlipidaemia (baseline low density lipoprotein (LDL) cholesterol and plasma triglyceride concentrations (median (interquartile range) of 4.54 (4.17-5.26)) and 2.66 (2.04-3.20) mmol/l, respectively) and previous myocardial infarction were randomised to atorvastatin 40 mg or placebo once daily for 8 weeks in a double-blind, cross-over design. The apolipoprotein (apo) B-48 and B-100 contents were determined in subfractions of TRLs as a measure of chylomicron remnant and very low density lipoprotein (VLDL) particle concentrations (expressed as mg apo B-48 or apo B-100 per litre of plasma), in the fasting state and after intake of a mixed meal. Atorvastatin treatment reduced significantly the fasting plasma concentrations of VLDL cholesterol, LDL cholesterol and VLDL triglycerides (median% change) by 29, 44 and 27%, respectively, and increased high density lipoprotein (HDL) cholesterol by 19%, compared with baseline. The postprandial plasma concentrations of large (Svedberg flotation rate (Sf) 60-400) and small (Sf 20-60) VLDLs and chylomicron remnants were almost halved compared with baseline (mean 0-6 h plasma concentrations were reduced by 48% for Sf 60-400 apo B-100, by 46% for Sf 60-400 apo B-48, by 46% for Sf 20-60 apo B-100 and by 27% for Sf 20-60 apo B-48), and the postprandial triglyceridaemia was reduced by 23% during active treatment. In conclusion, atorvastatin 40 mg once daily causes profound reductions of postprandial plasma concentrations of all TRLs in combined hyperlipidaemic patients with premature coronary artery disease.

Shifting the LDL-receptor paradigm in familial hypercholesterolemia: novel insights from recent kinetic studies of apolipoprotein B-100 metabolism

Familial hypercholesterolemia (FH) is a dominantly inherited disorder associated with elevated plasma cholesterol concentrations and premature cardiovascular disease. In addition to impaired low density lipoprotein (LDL) receptor-mediated clearance of low density lipoproteins in FH, evidence from in vitro and in vivo studies suggests that hepatic oversecretion of apoB may contribute to the hypercholesterolemia. The proposed association between apoB secretion and FH may, however, be a function of the class of LDL receptor defect. Hepatic cholesterol pools appear to regulate apoB secretion and LDL receptor activity. Therefore, therapeutic regulation of cholesterogenesis in FH may have the dual effect of reducing hepatic apoB secretion and upregulating the LDL receptor. These effects may also be genetically determined.

The role of risk factors in the development of atherosclerosis

Our understanding of risk factors for atherogenesis has changed significantly over the last decade. In addition to better grasp of the mechanism of action of the "classic" (causal) risk factors, a number of potentially important new factors has emerged. In this review we briefly summarize the evidence of the relation between atherosclerosis and the currently recognized causal risk factors, namely, age, smoking, LDL cholesterol, HDL cholesterol, hypertension, and diabetes. More emphasis has been put on description of the emerging entities such as atherogenic profile of plasma lipoproteins with discussion of LDL and HDL subclasses, Lp(a), homocysteine, and, last but not least, on the role of infection and inflammation in atherogenesis. Whenever possible, we tried to summarize the relevant lines of evidence such as epidemiological, pathological, genetic, and clinical trial data linking the specific factor with atherosclerosis.