Familial apolipoprotein A-I, C-III, and A-IV deficiency and premature atherosclerosis due to deletion of a gene complex on chromosome 11

The pleiotropic effects of high-density lipoproteins and apolipoprotein A-I

The high density lipoprotein (HDL) fraction of human plasma consists of multiple subpopulations of spherical particles that are structurally uniform, but heterogeneous in terms of size, composition and function. Numerous epidemiological studies have established that an elevated high density lipoprotein cholesterol (HDL-C) level is associated with decreased cardiovascular risk. However, with several recent randomised clinical trials of HDL-C raising agents failing to reduce cardiovascular events, contemporary research is transitioning towards clinical development of the cardioprotective functions of HDLs and the identification of functions that can be exploited for treatment of other diseases. This review describes the origins of HDLs and the causes of their compositional and functional heterogeneity. It then summarises current knowledge of how cardioprotective and other functions of HDLs are regulated. The final section of the review summarises recent advances in the clinical development of HDL-targeted therapies.

Changes in the Proteome Profile of People Achieving Remission of Type 2 Diabetes after Bariatric Surgery

Bariatric surgery (BS) results in metabolic pathway recalibration. We have identified potential biomarkers in plasma of people achieving type 2 diabetes mellitus (T2DM) remission after BS. Longitudinal analysis was performed on plasma from 10 individuals following Roux-en-Y gastric bypass (n = 7) or sleeve gastrectomy (n = 3). Sequential window acquisition of all theoretical fragment ion spectra mass spectrometry (SWATH-MS) was done on samples taken at 4 months before (baseline) and 6 and 12 months after BS. Four hundred sixty-seven proteins were quantified by SWATH-MS. Principal component analysis resolved samples from distinct time points after selection of key discriminatory proteins: 25 proteins were differentially expressed between baseline and 6 months post-surgery; 39 proteins between baseline and 12 months. Eight proteins (SHBG, TF, PRG4, APOA4, LRG1, HSPA4, EPHX2 and PGLYRP) were significantly different to baseline at both 6 and 12 months post-surgery. The panel of proteins identified as consistently different included peptides related to insulin sensitivity (SHBG increase), systemic inflammation (TF and HSPA4-both decreased) and lipid metabolism (APOA4 decreased). We found significant changes in the proteome for eight proteins at 6- and 12-months post-BS, and several of these are key components in metabolic and inflammatory pathways. These may represent potential biomarkers of remission of T2DM.

Genome-Wide Association Study of the Postprandial Triglyceride Response Yields Common Genetic Variation in LIPC (Hepatic Lipase)

BACKGROUND

The increase in serum triglyceride (TG) concentrations in response to a meal is considered a risk factor for cardiovascular disease. We aimed to elucidate the genetics of the postprandial TG response through genome-wide association studies (GWAS).

METHODS

Participants of the NEO (Netherlands Epidemiology of Obesity) study (n=5630) consumed a liquid mixed meal after an overnight fast. GWAS of fasting and postprandial serum TG at 150 minutes were performed. To identify genetic variation of postprandial TG independent of fasting TG, we calculated the TG response at 150 minutes by the residuals of a nonlinear regression that predicted TG at 150 minutes as a function of fasting TG. Association analyses were adjusted for age, sex, and principal components in a linear regression model. Next, using the identified variants as determinants, we performed linear regression analyses on the residuals of the postprandial response of 149 nuclear magnetic resonance-based metabolite measures.

RESULTS

GWAS of fasting TG and postprandial serum TG at 150 minutes resulted in completely overlapping loci, replicating previous GWAS. From GWAS of the TG response, we identified rs7350789-A (allele frequency=0.36), mapping to hepatic lipase (LIPC), to be associated with a smaller increase in TG concentrations at 150 minutes (β=-0.11; P-value=5.1×10^-8). Rs7350789-A was associated with responses of 33 metabolite measures (P-value <1.34×10^-3), mainly smaller increases of the TG-component in almost all HDL (high-density lipoprotein) subparticles (HDL-TG), a smaller decrease of HDL diameter and smaller increases of most components of VLDL (very low density lipoprotein) subparticles.

CONCLUSIONS

GWAS of the TG response identified a variant near LIPC as a main contributor to postprandial TG metabolism independent of fasting TG concentrations, resulting in smaller increases of HDL-TG and VLDL subparticles.

LCAT, ApoD, and ApoA1 Expression and Review of Cholesterol Deposition in the Cornea

Lecithin:cholesterol acyltransferase (LCAT) is an enzyme secreted by the liver and circulates with high-density lipoprotein (HDL) in the blood. The enzyme esterifies plasma cholesterol and increases the capacity of HDL to carry and potentially remove cholesterol from tissues. Cholesterol accumulates within the extracellular connective tissue matrix of the cornea stroma in individuals with genetic deficiency of LCAT. LCAT can be activated by apolipoproteins (Apo) including ApoD and ApoA1. ApoA1 also mediates cellular synthesis of HDL. This study examined the expression of LCAT by epithelial cells, keratocytes, and endothelial cells, the cell types that comprise from anterior to posterior the three layers of the cornea. LCAT and ApoD were immunolocalized to all three cell types within the cornea, while ApoA1 was immunolocalized to keratocytes and endothelium but not epithelium. In situ hybridization was used to detect LCAT, ApoD, and ApoA1 mRNA to learn what cell types within the cornea synthesize these proteins. No corneal cells showed mRNA for ApoA1. Keratocytes and endothelium both showed ApoD mRNA, but epithelium did not. Epithelium and endothelium both showed LCAT mRNA, but despite the presence of LCAT protein in keratocytes, keratocytes did not show LCAT mRNA. RNA sequencing analysis of serum-cultured dedifferentiated keratocytes (commonly referred to as corneal stromal fibroblasts) revealed the presence of both LCAT and ApoD (but not ApoA1) mRNA, which was accompanied by their respective proteins detected by immunolabeling of the cultured keratocytes and Western blot analysis of keratocyte lysates. The results indicate that keratocytes in vivo show both ApoA1 and LCAT proteins, but do not synthesize these proteins. Rather, keratocytes in vivo must take up ApoA1 and LCAT from the corneal interstitial tissue fluid.

Genetic and secondary causes of severe HDL deficiency and cardiovascular disease

We assessed secondary and genetic causes of severe HDL deficiency in 258,252 subjects, of whom 370 men (0.33%) and 144 women (0.099%) had HDL cholesterol levels <20 mg/dl. We excluded 206 subjects (40.1%) with significant elevations of triglycerides, C-reactive protein, glycosylated hemoglobin, myeloperoxidase, or liver enzymes and men receiving testosterone. We sequenced 23 lipid-related genes in 201 (65.3%) of 308 eligible subjects. Mutations (23 novel) and selected variants were found at the following gene loci: 1) ABCA1 (26.9%): 2 homozygotes, 7 compound or double heterozygotes, 30 heterozygotes, and 2 homozygotes and 13 heterozygotes with variants rs9282541/p.R230C or rs111292742/c.-279C>G; 2) LCAT (12.4%): 1 homozygote, 3 compound heterozygotes, 13 heterozygotes, and 8 heterozygotes with variant rs4986970/p.S232T; 3) APOA1 (5.0%): 1 homozygote and 9 heterozygotes; and 4) LPL (4.5%): 1 heterozygote and 8 heterozygotes with variant rs268/p.N318S. In addition, 4.5% had other mutations, and 46.8% had no mutations. Atherosclerotic cardiovascular disease (ASCVD) prevalence rates in the ABCA1, LCAT, APOA1, LPL, and mutation-negative groups were 37.0%, 4.0%, 40.0%, 11.1%, and 6.4%, respectively. Severe HDL deficiency is uncommon, with 40.1% having secondary causes and 48.8% of the subjects sequenced having ABCA1, LCAT, APOA1, or LPL mutations or variants, with the highest ASCVD prevalence rates being observed in the ABCA1 and APOA1 groups.

Protein biomarkers for the prediction of cardiovascular disease in type 2 diabetes

AIMS/HYPOTHESIS

We selected the most informative protein biomarkers for the prediction of incident cardiovascular disease (CVD) in people with type 2 diabetes.

METHODS

In this nested case-control study we measured 42 candidate CVD biomarkers in 1,123 incident CVD cases and 1,187 controls with type 2 diabetes selected from five European centres. Combinations of biomarkers were selected using cross-validated logistic regression models. Model prediction was assessed using the area under the receiver operating characteristic curve (AUROC).

RESULTS

Sixteen biomarkers showed univariate associations with incident CVD. The most predictive subset selected by forward selection methods contained six biomarkers: N-terminal pro-B-type natriuretic peptide (OR 1.69 per 1 SD, 95% CI 1.47, 1.95), high-sensitivity troponin T (OR 1.29, 95% CI 1.11, 1.51), IL-6 (OR 1.13, 95% CI 1.02, 1.25), IL-15 (OR 1.15, 95% CI 1.01, 1.31), apolipoprotein C-III (OR 0.79, 95% CI 0.70, 0.88) and soluble receptor for AGE (OR 0.84, 95% CI 0.76, 0.94). The prediction of CVD beyond clinical covariates improved from an AUROC of 0.66 to 0.72 (AUROC for Framingham Risk Score covariates 0.59). In addition to the biomarkers, the most important clinical covariates for improving prediction beyond the Framingham covariates were estimated GFR, insulin therapy and HbA1c.

CONCLUSIONS/INTERPRETATION

We identified six protein biomarkers that in combination with clinical covariates improved the prediction of our model beyond the Framingham Score covariates. Biomarkers can contribute to improved prediction of CVD in diabetes but clinical data including measures of renal function and diabetes-specific factors not included in the Framingham Risk Score are also needed.

ApoA-IV: current and emerging roles in intestinal lipid metabolism, glucose homeostasis, and satiety

Apolipoprotein A-IV (apoA-IV) is secreted by the small intestine on chylomicrons into intestinal lymph in response to fat absorption. Many physiological functions have been ascribed to apoA-IV, including a role in chylomicron assembly and lipid metabolism, a mediator of reverse-cholesterol transport, an acute satiety factor, a regulator of gastric function, and, finally, a modulator of blood glucose homeostasis. The purpose of this review is to update our current view of intestinal apoA-IV synthesis and secretion and the physiological roles of apoA-IV in lipid metabolism and energy homeostasis, and to underscore the potential for intestinal apoA-IV to serve as a therapeutic target for the treatment of diabetes and obesity-related disease.

Alpinumisoflavone and abyssinone V 4'-methylether derived from Erythrina lysistemon (Fabaceae) promote HDL-cholesterol synthesis and prevent cholesterol gallstone formation in ovariectomized rats

OBJECTIVES

Erythrina lysistemon was found to improve lipid profile in ovariectomized rats. Alpinumisoflavone (AIF) and abyssinone V 4'-methylether (AME) derived from this plant induced analogous effects on lipid profile and decreased atherogenic risks. To highlight the molecular mechanism of action of these natural products, we evaluated their effects on the expression of some estrogen-sensitive genes associated with cholesterol synthesis (Esr1 and Apoa1) and cholesterol clearance (Ldlr, Scarb1 and Cyp7a1).

METHODS

Ovariectomized rats were subcutaneously treated for three consecutive days with either compound at the daily dose of 0.1, 1 and 10 mg/kg body weight (BW). Animals were sacrificed thereafter and their liver was collected. The mRNA of genes of interest was analysed by quantitative real-time polymerase chain reaction.

KEY FINDINGS

Both compounds downregulated the mRNA expression of Esr1, a gene associated with cholesterogenesis and cholesterol gallstone formation. AME leaned the Apoa1/Scarb1 balance in favour of Apoa1, an effect promoting high-density lipoprotein (HDL)-cholesterol formation. It also upregulated the mRNA expression of Ldlr at 1 mg/kg/BW per day (25%) and 10 mg/kg/BW per day (133.17%), an effect favouring the clearance of low-density lipoprotein (LDL)-cholesterol. Both compounds may also promote the conversion of cholesterol into bile acids as they upregulated Cyp7a1 mRNA expression.

CONCLUSION

AIF and AME atheroprotective effects may result from their ability to upregulate mechanisms promoting HDL-cholesterol and bile acid formation.

Apolipoprotein A-IV: a protein intimately involved in metabolism

The purpose of this review is to summarize our current understanding of the physiological roles of apoA-IV in metabolism, and to underscore the potential for apoA-IV to be a focus for new therapies aimed at the treatment of diabetes and obesity-related disorders. ApoA-IV is primarily synthesized by the small intestine, attached to chylomicrons by enterocytes, and secreted into intestinal lymph during fat absorption. In circulation, apoA-IV is associated with HDL and chylomicron remnants, but a large portion is lipoprotein free. Due to its anti-oxidative and anti-inflammatory properties, and because it can mediate reverse-cholesterol transport, proposed functions of circulating apoA-IV have been related to protection from cardiovascular disease. This review, however, focuses primarily on several properties of apoA-IV that impact other metabolic functions related to food intake, obesity, and diabetes. In addition to participating in triglyceride absorption, apoA-IV can act as an acute satiation factor through both peripheral and central routes of action. It also modulates glucose homeostasis through incretin-like effects on insulin secretion, and by moderating hepatic glucose production. While apoA-IV receptors remain to be conclusively identified, the latter modes of action suggest that this protein holds therapeutic promise for treating metabolic disease.

Treating low high-density lipoprotein cholesterol: what is the evidence?

Epidemiological studies have shown an inverse association between high-density lipoprotein cholesterol (HDL-C) and cardiovascular disease (CVD) risk. However, genetic and interventional studies have failed to consistently support this relationship. There is an increasing body of evidence that the function of HDL, including its antiatherogenic properties and its reverse cholesterol transport activity, has a greater impact on CVD risk compared with levels of HDL alone. Targeting HDL has become a growing interest. Nevertheless, raising HDL pharmacologically has failed to show a considerable, if any, impact on cardiovascular outcome. Efforts should focus on improving HDL quality in addition to raising HDL levels when developing new therapies. Ongoing and future research will help determine the most safe and effective approach to improve cardiovascular outcome and establish the safety, efficacy and impact on atherosclerosis of the emerging HDL-raising therapies.

Identification of differentially expressed proteins in the aqueous humor of primary congenital glaucoma

Primary Congenital Glaucoma (PCG) is an autosomal recessive disease caused by an abnormal development of the anterior chamber angle. Although, PCG has been linked to several genetic loci, the role that the genes at these loci or their encoded proteins play in the pathophysiology of PCG and development of the anterior chamber is not known. To identify proteins that may be altered in PCG and that may help in understanding the underlying pathophysiology of the disease, we took a global proteomics approach. Tryptic digests of the complex mixtures of proteins in aqueous humor were analyzed using Liquid Chromatography/Mass Spectrometry (LC-MS/MS). Proteins were identified by searching the data against the human subset of the UniProt database. The proteomes of aqueous humor in PCG (n = 7) and patients undergoing cataract surgery as control (n = 4) were compared based on the scan counts of comparable proteins. Using stringent filtering criteria, Apolipoprotein A-IV (APOA-IV), Albumin and Antithrombin 3 (ANT3) were detected at significantly higher levels in PCG AH compared to control, whereas Transthyretin (TTR), Prostaglandin-H2 D-isomerase (PTGDS), Opticin (OPT) and Interphotoreceptor Retinoid Binding Protein (IRBP) were detected at significantly lower levels. Many of these proteins play a role in retinoic acid (RA) binding/transport and have been implicated in the pathogenesis of neurodegenerative diseases such as Alzheimer's (AD). It is possible that similar to AD, the pathologic changes in PCG during development could be influenced by the availability of RA in the anterior chamber.

Genetic causes of high and low serum HDL-cholesterol

Plasma levels of HDL cholesterol (HDL-C) have a strong inherited basis with heritability estimates of 40-60%. The well-established inverse relationship between plasma HDL-C levels and the risk of coronary artery disease (CAD) has led to an extensive search for genetic factors influencing HDL-C concentrations. Over the past 30 years, candidate gene, genome-wide linkage, and most recently genome-wide association (GWA) studies have identified several genetic variations for plasma HDL-C levels. However, the functional role of several of these variants remains unknown, and they do not always correlate with CAD. In this review, we will first summarize what is known about HDL metabolism, monogenic disorders associated with both low and high HDL-C levels, and candidate gene studies. Then we will focus this review on recent genetic findings from the GWA studies and future strategies to elucidate the remaining substantial proportion of HDL-C heritability. Comprehensive investigation of the genetic factors conferring to low and high HDL-C levels using integrative approaches is important to unravel novel pathways and their relations to CAD, so that more effective means of diagnosis, treatment, and prevention will be identified.

Effects of variations in the APOA1/C3/A4/A5 gene cluster on different parameters of postprandial lipid metabolism in healthy young men

The APOA1/C3/A4/A5 gene cluster encodes important regulators of fasting lipids, but the majority of lipid metabolism takes place in the postprandial state and knowledge about gene regulation in this state is scarce. With the aim of characterizing possible regulators of lipid metabolism, we studied the effects of nine single nucleotide polymorphisms (SNPs) during postprandial lipid metabolism. Eighty-eight healthy young men were genotyped for APOA1 -2630 (rs613808), APOA1 -2803 (rs2727784), APOA1 -3012 (rs11216158), APOC3 -640 (rs2542052), APOC3 -2886 (rs2542051), APOC3 G34G (rs4520), APOA4 N147S (rs5104), APOA4 T29T (rs5092), and A4A5_inter (rs1263177) and were fed a saturated fatty acid-rich meal (1g fat/kg of weight with 60% fat, 15% protein and 25% carbohydrate). Serial blood samples were extracted for 11 h after the meal. Total cholesterol and fractions [HDL-cholesterol, LDL-cholesterol, trifacylglycerols (TGs) in plasma, TG-rich lipoproteins (TRLs) (large TRLs and small TRLs), apolipoprotein A-I and apolipoprotein B] were determined. APOA1 -2803 homozygotes for the minor allele and A4A5_inter carriers showed a limited degree of postprandial lipemia. Carriers of the rare alleles of APOA4 N147S and APOA4 T29T had lower APOA1 plasma concentration during this state. APOC3 -640 was associated with altered TG kinetics but not its magnitude. We have identified new associations between SNPs in the APOA1/C3/A4/A5 gene cluster and altered postprandial lipid metabolism.

Architectural roles of multiple chromatin insulators at the human apolipoprotein gene cluster

Long-range regulatory elements and higher-order chromatin structure coordinate the expression of multiple genes in cluster, and CTCF/cohesin-mediated chromatin insulator may be a key in this regulation. The human apolipoprotein (APO) A1/C3/A4/A5 gene region, whose alterations increase the risk of dyslipidemia and atherosclerosis, is partitioned at least by three CTCF-enriched sites and three cohesin protein RAD21-enriched sites (two overlap with the CTCF sites), resulting in the formation of two transcribed chromatin loops by interactions between insulators. The C3 enhancer and APOC3/A4/A5 promoters reside in the same loop, where the APOC3/A4 promoters are pointed towards the C3 enhancer, whereas the APOA1 promoter is present in the different loop. The depletion of either CTCF or RAD21 disrupts the chromatin loop structure, together with significant changes in the APO expression and the localization of transcription factor hepatocyte nuclear factor (HNF)-4alpha and transcriptionally active form of RNA polymerase II at the APO promoters. Thus, CTCF/cohesin-mediated insulators maintain the chromatin loop formation and the localization of transcriptional apparatus at the promoters, suggesting an essential role of chromatin insulation in controlling the expression of clustered genes.

A null mutation in human APOC3 confers a favorable plasma lipid profile and apparent cardioprotection

Apolipoprotein C-III (apoC-III) inhibits triglyceride hydrolysis and has been implicated in coronary artery disease. Through a genome-wide association study, we have found that about 5% of the Lancaster Amish are heterozygous carriers of a null mutation (R19X) in the gene encoding apoC-III (APOC3) and, as a result, express half the amount of apoC-III present in noncarriers. Mutation carriers compared with noncarriers had lower fasting and postprandial serum triglycerides, higher levels of HDL-cholesterol and lower levels of LDL-cholesterol. Subclinical atherosclerosis, as measured by coronary artery calcification, was less common in carriers than noncarriers, which suggests that lifelong deficiency of apoC-III has a cardioprotective effect.

Clinical presentation, laboratory values, and coronary heart disease risk in marked high-density lipoprotein-deficiency states

Our purpose is to provide a framework for diagnosing the inherited causes of marked high-density lipoprotein (HDL) deficiency (HDL cholesterol levels <10 mg/dL in the absence of severe hypertriglyceridemia or liver disease) and to provide information about coronary heart disease (CHD) risk for such cases. Published articles in the literature on severe HDL deficiencies were used as sources. If apolipoprotein (Apo) A-I is not present in plasma, then three forms of ApoA-I deficiency, all with premature CHD,and normal low-density lipoprotein (LDL) cholesterol levels have been described: ApoA-I/C-III/A-IV deficiency with fat malabsorption, ApoA-I/C-III deficiency with planar xanthomas, and ApoA-I deficiency with planar and tubero-eruptive xanthomas (pictured in this review for the first time). If ApoA-I is present in plasma at a concentration <10 mg/dL, with LDL cholesterol that is about 50% of normal and mild hypertriglyceridemia, a possible diagnosis is Tangier disease due to mutations at the adenosine triphosphate binding cassette protein A1 (ABCA1) gene locus. These patients may develop premature CHD and peripheral neuropathy, and have evidence of cholesteryl ester-laden macrophages in their liver, spleen, tonsils, and Schwann cells, as well as other tissues. The third form of severe HDL deficiency is characterized by plasma ApoA-I levels <40 mg/dL, moderate hypertriglyceridemia, and decreased LDL cholesterol, and the finding that most of the cholesterol in plasma is in the free rather than the esterified form, due to a deficiency in lecithin:cholesterol acyltransferase activity. These patients have marked corneal opacification and splenomegaly, and are at increased risk of developing renal failure, but have no clear evidence of premature CHD. Marked HDL deficiency has different etiologies and is generally associated with early CHD risk.

An ABC of apolipoprotein C-III: a clinically useful new cardiovascular risk factor?

BACKGROUND

Hypertriglyceridaemia, commonly found in subjects with obesity and type 2 diabetes mellitus, is associated with increased risk of coronary heart disease (CHD). Apolipoprotein C-III (apoC-III) plays an important role in regulating the metabolism of triglyceride-rich lipoproteins (TRLs) and may provide a new approach to assessing hypertriglyceridaemia.

AIMS

We review the role of apoC-III in regulating TRL metabolism and address the potential importance of apoC-III in clinical practice.

DISCUSSION

Hypertriglyceridaemia is chiefly a consequence of alterations in the kinetics of TRLs, including overproduction and delayed clearance of very-low density lipoprotein (VLDL). ApoC-III is an inhibitor of lipoprotein lipase and of TRLs remnant uptake by hepatic lipoprotein receptors. Elevated apoC-III, usually resulting from hepatic overproduction of VLDL apoC-III, may cause accumulation of plasma TRLs leading to hypertriglyceridaemia. The results from recent observational studies demonstrate that apoC-III is a strong predictor of risk for CHD, but this chiefly relates to apoC-III in apoB-containing lipoproteins. Lifestyle and pharmacological intervention can correct hypertriglyceridaemia by a mechanism of action that regulates apoC-III transport.

CONCLUSIONS

Targeting apoC-III metabolism may therefore be an important, new therapeutic approach to managing dyslipidaemia and CHD risk in obesity, insulin resistance and type 2 diabetes mellitus. However, further work is required to establish the practical aspects of measuring apoC-III in routine laboratory service and the precise therapeutic targets for serum total apoC-III and/or apoC-III in apoB-containing lipoproteins. While showing much promise as a potentially useful cardiovascular risk factor, apoC-III is not yet ready for prime time use in clinical practice.

Dietary, physiological, genetic and pathological influences on postprandial lipid metabolism

Most of diurnal time is spent in a postprandial state due to successive meal intakes during the day. As long as the meals contain enough fat, a transient increase in triacylglycerolaemia and a change in lipoprotein pattern occurs. The extent and kinetics of such postprandial changes are highly variable and are modulated by numerous factors. This review focuses on factors affecting postprandial lipoprotein metabolism and genes, their variability and their relationship with intermediate phenotypes and risk of CHD. Postprandial lipoprotein metabolism is modulated by background dietary pattern as well as meal composition (fat amount and type, carbohydrate, protein, fibre, alcohol) and several lifestyle conditions (physical activity, tobacco use), physiological factors (age, gender, menopausal status) and pathological conditions (obesity, insulin resistance, diabetes mellitus). The roles of many genes have been explored in order to establish the possible implications of their variability in lipid metabolism and CHD risk. The postprandial lipid response has been shown to be modified by polymorphisms within the genes for apo A-I, A-IV, A-V, E, B, C-I and C-III, lipoprotein lipase, hepatic lipase, fatty acid binding and transport proteins, microsomal triglyceride transfer protein and scavenger receptor class B type I. Overall, the variability in postprandial response is important and complex, and the interactions between nutrients or dietary or meal compositions and gene variants need further investigation. The extent of present knowledge and needs for future studies are discussed in light of ongoing developments in nutrigenetics.

Apolipoproteins AI and B as therapeutic targets

Currently the apolipoprotein B:AI ratio integrates information about the potential for cardiovascular disease (CVD) risk reduction better than any other lipid or lipoprotein index. Certainly it could, with benefit, replace serum cholesterol and HDL cholesterol in the estimation of CVD risk. Defining the therapeutic target of statin therapy in terms of serum apolipoprotein B (apo B) rather than LDL cholesterol could also help to optimize statin treatment. Deciding whether a therapeutic response is adequate also requires knowledge of whether there is persisting hypertriglyceridaemia, because this gives an indication of whether small dense LDL is likely to have been satisfactorily reduced. Raising low levels of HDL, probably best measured as apo AI, may also prove to be an important aim of treatment. This is, however, a more complex issue and also depends on the mechanism by which a particular therapy alters HDL levels and on whether the capacity of HDL to perform its anti-inflammatory and antioxidative functions is restored. A meta-analysis of randomized clinical trials of statins in which apo B and apo AI have been reported could provide valuable information.

Human genetics of variation in high-density lipoprotein cholesterol

Longitudinal population studies have confirmed plasma levels of high-density lipoprotein (HDL) cholesterol to be an important inverse coronary risk factor. Although environmental influences are known to regulate HDL cholesterol levels, genetic factors are also known to be important, and over 25 candidate genes have been proposed to be associated with variation in HDL cholesterol levels. A variety of monogenic conditions of extremely low or high HDL cholesterol has helped to delineate the physiology of HDL cholesterol metabolism in humans, which has led to the development of new therapeutic approaches to HDL cholesterol. However, most causes of genetic variation in HDL cholesterol in the general population are likely oligogenic or polygenic. We review the monogenic disorders associated with both high and low HDL cholesterol and the relevance of mutations and polymorphisms in these genes to variation in HDL cholesterol levels in the general population.

Characterization of a new mouse model for human apolipoprotein A-I/C-III/A-IV deficiency

Human data raised the possibility that coronary heart disease is associated with mutations in the apolipoprotein gene cluster APOA1/C3/A4 that result in multideficiency of cluster-encoded apolipoproteins and hypoalphalipoproteinemia. To test this hypothesis, we generated a mouse model for human apolipoprotein A-I (apoA-I)/C-III/A-IV deficiency. Homozygous mutants (Apoa1/c3/a4(-/-)) lacking the three cluster-encoded apolipoproteins were viable and fertile. In addition, feeding behavior and growth were apparently normal. Total cholesterol (TC), high density lipoprotein cholesterol (HDLc), and triglyceride levels in the plasma of fasted mutants fed a regular chow were 32% (P < 0.001), 17% (P < 0.001), and 70% (P < 0.01), respectively, those of wild-type mice. When fed a high-fat Western-type (HFW) diet, Apoa1/c3/a4(-/-) mice showed a further decrease in HDLc concentration and a moderate increase in TC, essentially in non-HDL fraction. The capacity of Apoa1/c3/a4(-/-) plasma to promote cholesterol efflux in vitro was decreased to 75% (P < 0.001), and LCAT activity was decreased by 38% (P < 0.01). Despite the very low total plasma cholesterol, the imbalance in lipoprotein distribution caused small but detectable aortic lesions in one-third of Apoa1/c3/a4(-/-) mice fed a HFW diet. In contrast, none of the wild-type mice had lesions. These results demonstrate that Apoa1/c3/a4(-/-) mice display clinical features similar to human apoA-I/C-III/A-IV deficiency (i.e., marked hypoalphalipoproteinemia) and provide further support for the apoa1/c3/a4 gene cluster as a minor susceptibility locus for atherosclerosis in mice.

Associations between plasma lipid parameters and APOC3 and APOA4 genotypes in a healthy population are independent of dietary cholesterol intake

To determine whether APOC3 and APOA4 genotypes influence plasma cholesterol fluctuations following a high cholesterol diet, a healthy population of 40 men and 51 women were studied. The crossover intervention randomly assigned participants to an EGG (640 mg/d cholesterol) or placebo (0 mg/d cholesterol) diet for 30 days, with a 3-week washout between periods. Allele-specific oligonucleotide hybridization was utilized to determine the presence or absence of APOC3 and APOA4 polymorphisms. Differences in plasma cholesterol between hyper- and hypo-responders were not influenced by genotype. However, an interaction (P < 0.0001) did exist between APOA4 allele, diet and gender with regard to triglycerides (TG). While female carriers of the APOA4(347) S allele had lower TG concentrations than those with the common T/T allele, males with the S allele had higher concentrations. The APOC3 SstI polymorphism analysis revealed that heterozygous carriers of the S2 allele had higher (P < 0.05) plasma apo C-III and TG concentrations, regardless of gender or dietary period. In addition, carriers of the S2 allele had smaller LDL peak particle diameter than those having the common APOC3 genotype. The presence of individual alleles in this population was associated with differences in plasma lipids and LDL size. However, these relationships were independent of dietary cholesterol.

Differential effects of HDL subpopulations on cellular ABCA1- and SR-BI-mediated cholesterol efflux

Our objective was to evaluate the associations of individual apolipoprotein A-I (apoA-I)-containing HDL subpopulation levels with ABCA1- and scavenger receptor class B type I (SR-BI)-mediated cellular cholesterol efflux. HDL subpopulations were measured by nondenaturing two-dimensional gel electrophoresis from 105 male subjects selected with various levels of apoA-I in pre-beta-1, alpha-1, and alpha-3 HDL particles. ApoB-containing lipoprotein-depleted serum was incubated with [(3)H]cholesterol-labeled cells to measure efflux. The difference in efflux between control and ABCA1-upregulated J774 macrophages was taken as a measure of ABCA1-mediated efflux. SR-BI-mediated efflux was determined using cholesterol-labeled Fu5AH hepatoma cells. Fractional efflux values obtained from these two cell systems were correlated with the levels of individual HDL subpopulations. A multivariate analysis showed that two HDL subspecies correlated significantly with ABCA1-mediated efflux: small, lipid-poor pre-beta-1 particles (P=0.0022) and intermediate-sized alpha-2 particles (P=0.0477). With regard to SR-BI-mediated efflux, multivariate analysis revealed significant correlations with alpha-2 (P=0.0004), alpha-1 (P=0.0030), pre-beta-1 (P=0.0056), and alpha-3 (P=0.0127) HDL particles. These data demonstrate that the small, lipid-poor pre-beta-1 HDL has the strongest association with ABCA1-mediated cholesterol even in the presence of all other HDL subpopulations. Cholesterol efflux via the SR-BI pathway is associated with several HDL subpopulations with different apolipoprotein composition, lipid content, and size.

Association of the apolipoprotein A-IV: 360 Gln/His polymorphism with cerebrovascular disease, obesity, and depression in a Brazilian elderly population

The identification of genetic polymorphisms as risk factors for complex diseases can be relevant for their prevention, diagnosis, and prognosis. The apolipoprotein A-IV: 360 Gln/His polymorphism was investigated in 383 elderly individuals, who were participants of a longitudinal study commenced in 1991. The major morbidities that affect elderly people, such as cardiovascular diseases, diabetes, low cognitive function, depression, and obesity, were extensively investigated. DNA was isolated from blood cells, amplified by PCR, and digested with Fnu4HI. In this population the frequency of the His allele was 0.056 and the genotypes were distributed according to Hardy-Weinberg equilibrium. Logistic regression analysis showed a significant association between the presence of His allele and cerebrovascular disease and/or transitory ischemic attack (odds ratio) (OR = 3.070, P = 0.027), obesity (OR = 2.241, P = 0.047), and depression (OR = 2.879, P = 0.005). This study indicates that the presence of the rare allele in elderly people can play a significant role in the occurrence of multifactorial diseases. This is the first study analyzing this polymorphism in elderly people in Brazil. More studies should be encouraged to elucidate the mechanisms involved in these diseases.

Genetic determinants of low high-density lipoprotein cholesterol

PURPOSE OF REVIEW

High-density lipoprotein cholesterol (HDL-C) has been well established as an inverse predictor of coronary heart disease (CHD), and in recent years, investigations have focused on the genetic regulation of high-density lipoprotein. Although numerous candidate genes contribute to the low HDL-C phenotype, their impact on CHD is heterogeneous, reflecting diverse gene-gene interactions and gene-environmental relationships. This review summarizes recent data involving HDL regulatory genes and their role in atherothrombosis.

RECENT FINDINGS

The primary genetic determinants associated with relative HDL-C deficiency states are the ATP binding cassette protein, ABCA1; apolipoprotein (APO) A1; and lecithin cholesteryl acyl transferase. Other potentially important candidates invoked in low HDL-C syndromes in humans include APOC3, lipoprotein lipase, sphingomyelin phosphodiesterase 1, and glucocerebrosidase. Molecular variation in ABCAI and APOAI and, in selected cases, lecithin cholesteryl acyl transferase deficiency have been associated with increased CHD, whereas two notable variants, APOAIMilano and APOAIParis, are associated with reduced risk.

SUMMARY

Low HDL-C syndromes have generally been correlated with an increased risk of CHD. However, single-gene abnormalities responsible for HDL-C deficiency states may have variable effects on atherothrombotic risk.

Association of apo A-IV 360 (Gln → His) polymorphism with plasma lipids and lipoproteins: the Framingham Offspring Study

The effect of a common apolipoprotein (apo) A-IV polymorphism (substitution of histidine for glutamine at position 360) on plasma lipid, lipoprotein cholesterol and lipoprotein(a) (Lp(a)) levels, and on low-density lipoprotein (LDL) particle size was examined by genotyping in 2322 Caucasian men and women (mean age: 48.9+/-10.1 years) participating in the Framingham Offspring Study (FOS). The relative frequencies of the apo A-IV-Gln (apo A-IV-1) and the apo A-IV-His (apo A-IV-2) alleles were 0.932 and 0.068, respectively, and were in Hardy-Weinberg equilibrium. No effect of the apo A-IV-2 genotype was observed on plasma triglyceride, total and lipoprotein cholesterol, and LDL particle size in either men or women after adjustment for age and body mass index. To avoid a possible interaction between the apo E genotype and the apo A-IV genotype, subgroup analyses were undertaken in 1,414 male and female subjects with the apo E3/3 genotype. Among women in this group there was a significant effect of the apo A-IV-2 allele on triglyceride levels (p=0.046). This effect was no longer significant after adjustment for age and BMI (p=0.074). No significant allele effect on other lipoprotein levels, including Lp(a), was noted in apo E3/3 men or women. We have also conducted a meta-analysis of our own data and of other studies found in the literature, indicating a significant lowering effect of apo A-IV-2 on plasma triglycerides, but no effects on other parameters. In conclusion, the apo A-IV-2 allele is associated with a modest reduction in plasma triglyceride levels in the general population.

A novel apoA-I mutation (L178P) leads to endothelial dysfunction, increased arterial wall thickness, and premature coronary artery disease

OBJECTIVES

We investigated the consequences of an apolipoprotein A-I (apoA-I) gene defect with regard to lipid metabolism, endothelial function, arterial wall thickness, and coronary artery disease (CAD) risk.

BACKGROUND

Due to limited numbers of carriers of the apoA-I defects, data on the consequences of such defects have remained inconclusive.

METHODS

Lipids and lipoproteins were measured in 54 apoA-I (L178P) carriers and 147 nonaffected siblings. Flow-mediated dilation (FMD) was assessed in 29 carriers and 45 noncarriers, and carotid intima-media thickness (IMT) could be determined in 33 heterozygotes and 40 controls. Moreover, CAD risk was evaluated for all apoA-I mutation carriers.

RESULTS

Heterozygotes exhibited lower plasma levels of apoA-I (-50%; p < 0.0001) and high-density lipoprotein cholesterol (-63%; p < 0.0001). In addition, carriers had impaired FMD (p = 0.012) and increased carotid IMT (p < 0.001), whereas multivariate analysis revealed that heterozygotes had a striking 24-fold increase in CAD risk (p = 0.003).

CONCLUSIONS

Heterozygosity for a novel apoA-I mutation underlies a detrimental lipoprotein profile that is associated with endothelial dysfunction, accelerated carotid arterial wall thickening, and severely enhanced CAD risk. Importantly, the extent of atherosclerosis in these subjects was similar to the burden of premature arterial wall abnormalities seen in patients with familial hypercholesterolemia. These data illustrate the pivotal role in humans of apoA-I in the protection against CAD.

Apolipoproteins A-IV and A-V are acute-phase proteins in mouse HDL

BACKGROUND

Infection and inflammation are associated with atherosclerosis. During infection and inflammation, HDL decreases and there are changes in the levels of several HDL-associated proteins. To identify changes in the protein composition of HDL during infection and inflammation, a proteomic approach was utilized.

METHODS AND RESULTS

Using two-dimensional gel electrophoresis and mass spectrometry, we found the expected increases in apolipoprotein (apo) SAA and apo E, as well as a decrease in apo A-I on HDL isolated from mice injected with endotoxin. We identified apo A-IV and apo A-V as positive acute-phase proteins in mouse HDL. We also found an increase in hepatic mRNA levels of apo A-IV and apo A-V after injection of endotoxin. Interleukin-6 increased apo A-IV and apo A-V mRNA levels in Hep3B cells. Additionally, we demonstrated that the protein levels of apo A-II in acute-phase HDL and the hepatic mRNA levels of apo A-II were decreased.

CONCLUSIONS

Apo A-IV and A-V are positive acute-phase proteins that increase in the serum during inflammation while apo A-II is a negative acute-phase protein in mice. Similar to other positive and negative acute-phase proteins, changes in hepatic production account for the changes in serum levels. However, the changes in apo A-IV and apo A-V, two apolipoproteins whose activities are not fully understood, may serve functions other than regulating lipid metabolism during the acute-phase response (APR). Coupled with the other changes in HDL proteins that occur, these changes are likely to alter the functional properties of HDL perhaps increasing the risk of atherosclerosis.

Treating low HDL—From bench to bedside

The inverse relationship between the plasma high-density lipoprotein cholesterol (HDL-C) and the risk of coronary heart disease (CHD) is well recognized in the general population. However, the development of effective therapeutics targeting HDL continues to be challenging, which is due in part to the heterogeneity of its structure and composition and the complexity of its metabolism. In this paper, we review a number of recent advances in our understanding of HDL metabolism and its role in atherogenesis. We discuss the HDL-C raising effect of a selected number of currently available lipid-modifying drugs and on a selected number of novel HDL-targeted therapeutic strategies under development.

apoA-IV tagged with the ER retention signal KDEL perturbs the intracellular trafficking and secretion of apoB

To examine the role of apolipoprotein A-IV (apoA-IV) in the intracellular trafficking and secretion of apoB, COS cells were cotransfected with microsomal triglyceride transfer protein (MTP), apoB-41 (amino terminal 41% of apoB), and either native apoA-IV or apoA-IV modified with the carboxy-terminal endoplasmic reticulum (ER) retention signal, KDEL (apoA-IV-KDEL). As expected, apoA-IV-KDEL was inefficiently secreted relative to native apoA-IV. Coexpression of apoB-41 with apoA-IV-KDEL reduced the secretion of apoB-41 by approximately 80%. The apoA-IV-KDEL effect was specific, as neither KDEL-modified forms of human serum albumin or apoA-I affected apoB-41 secretion. Similar results were observed in McA-RH7777 rat hepatoma cells, which express endogenous MTP. The full inhibitory effect of apoA-IV-KDEL on apoB secretion was observed only for forms of apoB containing a minimum of the amino-terminal 25% of the protein (apoB-25). However, apoA-IV-KDEL inhibited the secretion of both lipid-associated and lipid-poor forms of apoB-25. Dual-label immunofluorescence microscopy of cells transfected with native apoA-IV and apoB-25 revealed that both apolipoproteins were localized to the ER and Golgi, as expected. However, when apoA-IV-KDEL was cotransfected with apoB-25, both proteins localized primarily to the ER. These data suggest that apoA-IV may physically interact with apoB in the secretory pathway, perhaps reflecting a role in modulating the process of triglyceride-rich lipoprotein assembly and secretion.

Regulation of apoA-I gene expression: mechanism of action of estrogen and genistein

We have previously shown that 17-beta-estradiol (E2) and genistein increase the expression of apolipoprotein A-I (apoA-I), the major protein component of HDL, in Hep G2 cells. To elucidate the mechanism mediating the increase in apoA-I gene expression by these compounds, plasmid constructs containing serial deletions of the apoA-I promoter region were generated. The smallest region maintaining response to E2 and genistein spanned the -220 to -148 sequence, and the estrogen antagonist ICI182,780 completely inhibited the E2 and genistein effect. Nuclear extracts from cells treated with E2 and genistein showed increased binding to site B oligonucleotide (-169 to -146), and nuclear extracts from genistein-treated cells showed increased binding to an early growth response factor 1 (Egr-1) oligonucleotide compared to control cells. An increase in the concentrations of Egr-1 and hepatocyte nuclear factor-3beta was observed in nuclear extracts of cells treated with both compounds compared to control cells. Treatment with a specific inhibitor of mitogen-activated protein (MAP) kinase, but not with other inhibitors, abolished the stimulation of apoA-I gene expression by E2 and genistein. These results indicate that the MAP kinase pathway is involved in the regulation of apoA-I gene expression by genistein and E2, possibly through downstream regulation of transcription factors binding to the promoter region.

Apolipoprotein A-I deficiency results in markedly increased atherosclerosis in mice lacking the LDL receptor

OBJECTIVE

An inverse and independent association between plasma levels of apolipoprotein (apo) A-I and coronary heart disease in humans is well established. ApoA-I is the primary protein component of HDL and is thought to play an important role in mediating several of the atheroprotective effects of HDL. However, studies of the effects of apoA-I deficiency on the development of atherosclerosis in mice have not been definitive. We examined the effects of apoA-I deficiency on plasma lipids and atherosclerosis in LDL receptor-deficient mice fed a chow diet for up to 22 months.

METHODS AND RESULTS

Both apoA-I-deficient (apoA-I-/-)/LDL receptor-deficient (LDLR-/-) and LDLR-/- mice had a similar moderate elevation of non-HDL cholesterol (non-HDL-C). Unlike previous studies of apoA-I deficiency in which the HDL-C levels were extremely low, the apoA-I-/-/LDLR-/- mice in this study had substantial levels of HDL-C that were similar to wild-type mice. Despite similar levels of non-HDL-C and substantial levels of HDL-C, apoA-I-/-/LDLR-/- mice develop significantly more atherosclerosis (up to a 5-fold increase) and oxidant stress (39% increase) than LDLR-/- mice.

CONCLUSIONS

These results demonstrate that despite normal levels of HDL-C, apoA-I deficiency is associated with a significant loss of protection from the formation of atherosclerosis in LDLR-/- mice fed a chow diet.

High-density lipoprotein subpopulations in pathologic conditions

The role of low-density lipoprotein (LDL) cholesterol in coronary artery disease (CAD) and the impact of therapeutic agents on LDL cholesterol are well established. Less is known about the role of high-density lipoprotein (HDL) cholesterol and even less about the role of the different HDL subspecies in CAD. HDL particles vary in size and density, mainly because of differences in the number of apolipoprotein (apo) particles and the amount of cholesterol ester in the core of HDL. Apo A-I is essential and, together with lipid, sufficient for the formation of HDL particles. Apo A-I-containing HDL particles play a primary role in cholesterol efflux from membranes, at least in part through interactions with the adenosine triphosphate-binding cassette transporter A1 (ABCA1). Patients with Tangier disease have mutations in the gene encoding ABCA1, which result in functionally impaired protein, a marked deficiency in HDL cholesterol, and a high risk of premature CAD. Our studies of apo A-I-containing HDL subpopulations in various patient populations reveal that patients homozygous for Tangier disease have only the pre-beta(1) HDL subspecies. Tangier heterozygotes are severely depleted in the larger alpha- and pre-alpha-mobility subspecies. Patients with low HDL cholesterol levels and those with CAD also show deficiencies in the alpha(1) and pre-alpha(1-3) HDL subspecies. The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) increase the levels of the large alpha(1) and pre-alpha(1) subpopulations and decrease the level of the small alpha(3) subpopulation. Thus, atorvastatin, for example, significantly moves the distribution of HDL particles toward normal, followed by simvastatin, pravastatin, and lovastatin in decreasing order of efficiency. A new statin, rosuvastatin, produces greater increases in HDL cholesterol than atorvastatin, but its effect on HDL particle distribution is yet to be determined.

ABCA1(Alabama): a novel variant associated with HDL deficiency and premature coronary artery disease

The ATP-binding cassette transporter, ABCA1, is a member of the ABC superfamily of proteins involved in the active transport of substrates across cellular membranes. Recent studies have implicated mutations in ABCA1 as the cause of Tangier disease (TD) and familial hypoalphalipoproteinemia (FHA). To evaluate the molecular basis of low high density lipoprotein (HDL) in a family with premature coronary artery disease, single strand conformational polymorphism analysis was performed for all coding regions and splice site junctions of ABCA1 with the genomic DNA of the proband. The proband and affected individuals were heterozygotes for C254T with proline converted to leucine (P85L). This mutation was not identified in over 400 chromosomes of healthy subjects. In the FHA kindred, family members heterozygous for the ABCA1 variant also exhibited corresponding low levels of HDL cholesterol. These data confirm recent data that a single defective allele in ABCA1 may be associated with reduced HDL cholesterol and FHA.

Apolipoprotein A-I deficiency with accumulated risk for CHD but no symptoms of CHD

We evaluated a 69-year-old Japanese woman with apolipoprotein (apo) A-I deficiency, high levels of low-density lipoprotein (LDL)-cholesterol, hypertension and impaired glucose tolerance. The patient had corneal opacity, but neither xanthomas, xanthelasma, nor tonsillar hypertrophy. She was not symptomatic for coronary heart disease (CHD), and had normal electrocardiograms at rest and exercise using a cycle ergometer. She had severely reduced levels of high-density lipoprotein (HDL)-cholesterol (0.10-0.18 mmol/l) and no apo A-I (<0.6 mg/dl). LDL-cholesterol and apo B as well as apo E were increased even under treatment with 10 mg pravastatin per day. Gel filtration chromatography revealed that in addition to VLDL and LDL fractions, she had apo A-II rich and apo E rich fractions, which were present in the HDL fraction separated by ultracentrifugation. A cytosine deletion was identified by genomic DNA sequencing of the apo A-I gene of the patient at the third base of codon 184 in the fourth exon, which led to a frame shift mutation and early termination at codon 200. This patient is the oldest among those with apo A-I deficiency reported in the literature, and she had no symptoms of CHD despite the accumulated risk for the disease.

Fructose intake increases hyperlipidemia and modifies apolipoprotein expression in apolipoprotein AI-CIII-AIV transgenic mice

Fructose intake has increased steadily during the past two decades. The objective of this study was to determine the effect of fructose intake on lipid metabolism in apolipoprotein (apo) AI-CIII-AIV transgenic (Tg) mice that have severe hypertriglyceridemia and moderate hypercholesterolemia. Tg and control mice were fed for 9 mo a commercial nonpurified diet and had free access to water or 250 g/L fructose solution. In Tg mice, fructose intake increased triglycerides and cholesterol but did not induce insulin resistance. There were no differences in human hepatic apo AI and apo CIII mRNA levels in fructose-fed mice compared with untreated mice, but apo AIV mRNA was greater, indicating a differential expression of the apo AI and apo AIV genes in response to dietary perturbations. Interestingly, the plasma concentration of the three human apolipoproteins was enhanced in fructose-fed Tg mice compared with untreated Tg mice. Our data suggest that long-term fructose consumption had strong adverse effects in this hyperlipidemic mouse model.

Lipoproteins, nutrition, and heart disease

This article reviews the current status of our knowledge of lipoproteins, nutrition, and coronary heart disease (CHD). Special emphasis is placed on CHD risk assessment, dietary intervention studies, diet-gene interactions, and current dietary guidelines and the contributions of my laboratory to these areas. CHD remains a major cause of death and disability, and risk factors include age, sex, hypertension, smoking, diabetes, elevated serum LDL cholesterol, and low HDL cholesterol. Emerging independent risk factors include elevated serum concentrations of lipoprotein(a), remnant lipoproteins, and homocysteine. The cornerstone of CHD prevention is lifestyle modification. Dietary intervention studies support the concepts that restricting saturated fat and cholesterol and increasing the intake of essential fatty acids, especially n - 3 fatty acids, reduces CHD risk. The variability in LDL-cholesterol response to diet is large, related in part to APOE and APOA4 genotype. The use of antioxidants in intervention studies has not been shown to reduce CHD risk. Compliance with dietary recommendations remains a major problem, and directly altering the food supply may be the most effective way to ensure compliance. The available data indicate that the recommendation to use fats, oils, and sugars sparingly for CHD prevention should be modified to a recommendation to use animal, dairy, and hydrogenated fats; tropical oils; egg yolks; and sugars sparingly and to increase the use of vegetables, fruit, and whole grains.

Effects of a National Cholesterol Education Program Step II Diet on apolipoprotein A-IV metabolism within triacylglycerol-rich lipoproteins and plasma

BACKGROUND

Apolipoprotein (apo) A-IV is a major component of triacylglycerol-rich lipoprotein (TRL) apolipoproteins.

OBJECTIVE

We investigated the effects of dietary saturated fat and cholesterol restriction on the metabolism of TRL and plasma apo A-IV.

DESIGN

We assessed TRL and plasma apo A-IV kinetics in 16 and 4 subjects, respectively, consuming an average US (baseline) diet for 6 wk and a National Cholesterol Education Program Step II diet for 24 wk, respectively. At the end of each diet period, all subjects received a primed, constant infusion of deuterated leucine for 15 h with hourly feeding. Ratios of stable-isotope tracer to tracee were measured by using gas chromatography-mass spectrometry, and kinetic data were modeled by using SAAM II.

RESULTS

Mean apo A-IV concentrations during the isotope infusion period were 6.9 +/- 2.6 mg/L in TRL and 2.2 +/- 3.2 mg/L in plasma with the baseline diet; these values were 37.7% (P < 0.001) and 19.4% (P < 0.01) lower with the Step II diet. Similar changes were observed in the fasting state between the 2 diets. The mean apo A-IV secretion rate decreased significantly from baseline by 59.6% in TRLs and by 40.2% in plasma. Significant correlations were observed between TRL apo A-IV concentrations and the secretion rate (r = 0.94, P < 0.001) and between TRL apo A-IV pool size and TRL-cholesterol concentrations (r = 0.48, P < 0.01).

CONCLUSIONS

Our data indicate that the National Cholesterol Education Program Step II diet significantly decreases TRL and plasma apo A-IV concentrations compared with the average US diet and that this decrease is due to a decreased secretion rate.

Expression of human apolipoprotein A-I/C-III/A-IV gene cluster in mice reduces atherogenesis in response to a high fat-high cholesterol diet

We have previously generated transgenic (Tg) mice expressing the human apolipoprotein (apo) A-I/C-III/A-IV gene cluster. This expression induced hyperlipidemia but reduced atherosclerotic lesions in genetically modified mice lacking apoE. Atherosclerosis is a multifactorial process and environmental factors such as diet play significant roles in its development. We examined here how an atherogenic diet influences the expression of the human genes and the characteristics of the Tg mice. Our results indicate that a high fat-high cholesterol diet up-regulates the intestinal expression of the three genes and the concentration of the three proteins in plasma. Cholesterol concentration was highly increased in the non-high density lipoprotein (HDL) fraction, and less, although significantly, in the HDL fraction. Tgs showed a 65% reduction in diet-induced aortic lesions compared with non-Tg mice. Atherogenic diet increases the expression of the genes encoding the scavenger receptor class B type I (SR-BI) and ATP binding cassette transporter 1 (ABCA1) proteins. As cholesterol efflux mediated by SR-BI or by ABCA1 was enhanced in Tg mice fed an atherogenic diet, we can hypothesize that increased reverse cholesterol transport is the basis of the protective mechanism observed in these animals. In conclusion, we present evidence that the expression of the human gene cluster in mice protects against atherogenesis in response to an atherogenic diet.

The apolipoprotein A-IV-360His polymorphism determines the dietary fat clearance in normal subjects

Apolipoprotein IV (apo A-IV) has been related to fat absorption and to the activation of some of the enzymes involved in lipid metabolism. Several polymorphic sites within the gene locus for apo A-IV have been detected. Previous studies have shown that the A-IV-2 isoform produces a different plasma lipid response after the consumption of diets with different fat and cholesterol content. The present study was designed to evaluate whether the apo A-IV 360His polymorphism could explain, at least in part, the interindividual variability observed during postprandial lipemia. Fifty-one healthy male volunteers (42 homozygous for the apo A-IV 360Gln allele (Gln/Gln) and nine carriers of the A-IV-360His allele), homozygous for the apo E3 allele, were subjected to a vitamin A-fat load test consisting of 1 g of fat/kg body weight and 60000 IU of vitamin A. Blood was drawn at time 0 and every hour for 11 h. Plasma cholesterol (C), triacylglycerol (TG), and C, TG, apo B-100, apo B-48, apo A-IV and retinyl palmitate (RP) were determined in lipoprotein fractions. Data of postprandial lipemia revealed that subjects with the apo A-IV 360His allele had significantly greater postprandial levels in small triacylglycerol rich lipoproteins (TRL)-C (P<0.02), small TRL-TG (P<0.01) and large TRL-TG (P<0.05) than apo A-IV 360Gln/Gln subjects. In conclusion, the modifications observed in postprandial lipoprotein metabolism in subjects with the A-IV 360His allele could be involved in the different low density lipoprotein (LDL)-C responses observed in these subjects following a diet rich in cholesterol and saturated fats.