Evidence for high density lipoproteins as the major apolipoprotein A-IV-containing fraction in normal human serum

Transcriptomic and metabolomic responses induced in the livers of growing pigs by a short-term intravenous infusion of sodium butyrate

Previous studies showed that butyrate played benefit roles in the health and metabolism of animals. However, little information on the effects of butyrate on the metabolism of piglets at the extraintestinal level is available. The present study investigated transcriptomic and metabolomic responses in the livers of pigs to evaluate the effects of intravenous sodium butyrate (SB) on the body's metabolism at the extraintestinal level. A total of 12 Duroc×Landrace×Large White growing barrows (60 days of age) fitted with jugular vein cannula were randomly allocated to either the SB group or the control (CO) group. Pigs in the SB group were intravenously infused with 10 ml SB (200 mmol/l) for 7 days, whereas pigs in the CO group were treated with the same amount of saline. The livers of pigs were collected for gene expression and metabolome analyses. The RNA sequencing (RNA-Seq) analysis showed that the mRNA expression of Acyl-CoA synthetase long-chain family member 1 (ACSL1), carnitine palmitoyltransferase 1A (CPT1A), acetyl-CoA acyltransferase 2 (ACAA2) and phosphoenolpyruvate carboxykinase 1 (PCK1) were downregulated (Q<0.05), whereas fatty acid binding protein 1 (FABP1) and cytochrome P450 family 7 subfamily A member 1 (CYP7A1) were upregulated (P<0.05) by SB treatment, indicating a decrease in fatty acid oxidation and gluconeogenesis and an increase in fatty acid transportation and cholesterol metabolism. Gas chromatography-mass spectrometry analysis showed that raffinose was enriched in the SB group compared with the CO group, indicating a decrease in metabolism of galactose. Moreover, SB treatment significantly decreased the concentration of blood cholesterol. The results suggest that a short-term intravenous infusion of SB could modulate hepatic lipid metabolism by decreasing fatty acid oxidation and increasing fatty acid transportation and cholesterol metabolism.

Human leucine zipper protein promotes hepatic steatosis via induction of apolipoprotein A-IV

The molecular mechanism of stress-induced hepatic steatosis is not well known. Human leucine zipper protein (LZIP) regulates the expression of genes involved in inflammation, cell migration, and stress response. The aim of this study was to determine the regulatory role of LZIP in stress-induced hepatic steatosis. We used a microarray analysis to identify LZIP-induced genes involved in hepatic lipid metabolism. LZIP increased the expression of apolipoprotein A-IV (APOA4) mRNA. In the presence of stress inducer, APOA4 promoter analysis was performed, and LZIP-induced lipid accumulation was monitored in mouse primary cells and human tissues. Under Golgi stress conditions, LZIP underwent proteolytic cleavage and was phosphorylated by AKT to protect against proteasome degradation. The stabilized N-terminal LZIP was translocated to the nucleus, where it directly bound to the APOA4 promoter, leading to APOA4 induction. LZIP-induced APOA4 expression resulted in increased absorption of surrounding free fatty acids. LZIP also promoted hepatic steatosis in mouse liver. Both LZIP and APOA4 were highly expressed in human steatosis samples. Our findings indicate that LZIP is a novel modulator of APOA4 expression and hepatic lipid metabolism. LZIP might be a therapeutic target for developing treatment strategies for hepatic steatosis and related metabolic diseases.-Kang, M., Kim, J., An, H.-T., Ko, J. Human leucine zipper protein promotes hepatic steatosis via induction of apolipoprotein A-IV.

Transcriptional regulation of apolipoprotein A-IV by the transcription factor CREBH

cAMP responsive element-binding protein H (CREBH) is an endoplasmic reticulum (ER) anchored transcription factor that is highly expressed in the liver and small intestine and implicated in nutrient metabolism and proinflammatory response. ApoA-IV is a glycoprotein secreted primarily by the intestine and to a lesser degree by the liver. ApoA-IV expression is suppressed in CREBH-deficient mice and strongly induced by enforced expression of the constitutively active form of CREBH, indicating that CREBH is the major transcription factor regulating Apoa4 gene expression. Here, we show that CREBH directly controls Apoa4 expression through two tandem CREBH binding sites (5'-CCACGTTG-3') located on the promoter, which are conserved between human and mouse. Chromatin immunoprecipitation and electrophoretic mobility-shift assays demonstrated specific association of CREBH with the CREBH binding sites. We also demonstrated that a substantial amount of CREBH protein was basally processed to the active nuclear form in normal mouse liver, which was further increased in steatosis induced by high-fat diet or fasting, increasing apoA-IV expression. However, we failed to find significant activation of CREBH in response to ER stress, arguing against the critical role of CREBH in ER stress response.

Effects of elaidic acid on lipid metabolism in HepG2 cells, investigated by an integrated approach of lipidomics, transcriptomics and proteomics

Trans fatty acid consumption in the human diet can cause adverse health effects, such as cardiovascular disease, which is associated with higher total cholesterol, a higher low density lipoprotein-cholesterol level and a decreased high density lipoprotein-cholesterol level. The aim of the study was to elucidate the hepatic response to the most abundant trans fatty acid in the human diet, elaidic acid, to help explain clinical findings on the relationship between trans fatty acids and cardiovascular disease. The human HepG2 cell line was used as a model to investigate the hepatic response to elaidic acid in a combined proteomic, transcriptomic and lipidomic approach. We found many of the proteins responsible for cholesterol synthesis up-regulated together with several proteins involved in the esterification and hepatic import/export of cholesterol. Furthermore, a profound remodeling of the cellular membrane occurred at the phospholipid level. Our findings contribute to the explanation on how trans fatty acids from the diet can cause modifications in plasma cholesterol levels by inducing abundance changes in several hepatic proteins and the hepatic membrane composition.

Cholesterol-secreting and statin-responsive hepatocytes from human ES and iPS cells to model hepatic involvement in cardiovascular health

Hepatocytes play a central and crucial role in cholesterol and lipid homeostasis, and their proper function is of key importance for cardiovascular health. In particular, hepatocytes (especially periportal hepatocytes) endogenously synthesize large amounts of cholesterol and secrete it into circulating blood via apolipoprotein particles. Cholesterol-secreting hepatocytes are also the clinically-relevant cells targeted by statin treatment in vivo. The study of cholesterol homeostasis is largely restricted to the use of animal models and immortalized cell lines that do not recapitulate those key aspects of normal human hepatocyte function that result from genetic variation of individuals within a population. Hepatocyte-like cells (HLCs) derived from human embryonic and induced pluripotent stem cells can provide a cell culture model for the study of cholesterol homeostasis, dyslipidemias, the action of statins and other pharmaceuticals important for cardiovascular health. We have analyzed expression of core components for cholesterol homeostasis in untreated human iPS cells and in response to pravastatin. Here we show the production of differentiated cells resembling periportal hepatocytes from human pluripotent stem cells. These cells express a broad range of apolipoproteins required for secretion and elimination of serum cholesterol, actively secrete cholesterol into the medium, and respond functionally to statin treatment by reduced cholesterol secretion. Our research shows that HLCs derived from human pluripotent cells provide a robust cell culture system for the investigation of the hepatic contribution to human cholesterol homeostasis at both cellular and molecular levels. Importantly, it permits for the first time to also functionally assess the impact of genetic polymorphisms on cholesterol homeostasis. Finally, the system will also be useful for mechanistic studies of heritable dyslipidemias, drug discovery, and investigation of modes of action of cholesterol-modulatory drugs.

ApoA-IV promotes the biogenesis of apoA-IV-containing HDL particles with the participation of ABCA1 and LCAT

The objective of this study was to establish the role of apoA-IV, ABCA1, and LCAT in the biogenesis of apoA-IV-containing HDL (HDL-A-IV) using different mouse models. Adenovirus-mediated gene transfer of apoA-IV in apoA-I(-/-) mice did not change plasma lipid levels. ApoA-IV floated in the HDL2/HDL3 region, promoted the formation of spherical HDL particles as determined by electron microscopy, and generated mostly α- and a few pre-β-like HDL subpopulations. Gene transfer of apoA-IV in apoA-I(-/-) × apoE(-/-) mice increased plasma cholesterol and triglyceride levels, and 80% of the protein was distributed in the VLDL/IDL/LDL region. This treatment likewise generated α- and pre-β-like HDL subpopulations. Spherical and α-migrating HDL particles were not detectable following gene transfer of apoA-IV in ABCA1(-/-) or LCAT(-/-) mice. Coexpression of apoA-IV and LCAT in apoA-I(-/-) mice restored the formation of HDL-A-IV. Lipid-free apoA-IV and reconstituted HDL-A-IV promoted ABCA1 and scavenger receptor BI (SR-BI)-mediated cholesterol efflux, respectively, as efficiently as apoA-I and apoE. Our findings are consistent with a novel function of apoA-IV in the biogenesis of discrete HDL-A-IV particles with the participation of ABCA1 and LCAT, and may explain previously reported anti-inflammatory and atheroprotective properties of apoA-IV.

Predictive value of different HDL particles for the protection against or risk of coronary heart disease

The inverse relationship between plasma HDL levels and the risk of developing coronary heart disease is well established. The underlying mechanisms of this relationship are poorly understood, largely because HDL consist of several functionally distinct subpopulations of particles that are continuously being interconverted from one to another. This review commences with an outline of what is known about the origins of individual HDL subpopulations, how their distribution is regulated, and describes strategies that are currently available for isolating them. We then summarise what is known about the functionality of specific HDL subpopulations, and how these findings might impact on cardiovascular risk. The final section highlights major gaps in existing knowledge of HDL functionality, and suggests how these deficiencies might be addressed. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).

Structure and function of the apoA-IV T347S and Q360H common variants

Human apolipoprotein A-IV (apoA-IV) is involved in chylomicron assembly and secretion, and in reverse cholesterol transport. Several apoA-IV isoforms exist, the most common in Caucasian populations being apoA-IV-1a (T347S) and apoA-IV-2 (Q360H). The objective of the present study was to investigate the impact of these common aminoacid substitutions on the ability of apoA-IV to bind lipids, to promote cell cholesterol efflux via ABCA1, and to maintain endothelial homeostasis. Recombinant forms of wild-type apoA-IV, apoA-IV Q360H, and apoA-IV T347S were produced in Escherichia coli. ApoA-IV Q360H and apoA-IV T347S showed a slightly higher alpha-helical content compared to wild-type apoA-IV, and associated with phospholipids faster than wild-type apoA-IV. The capacity to promote ABCA1-mediated cholesterol efflux was significantly greater for the apoA-IV T347S than the other apoA-IV isoforms. No differences were observed in the ability of apoA-IV isoforms to inhibit the production of VCAM-1 and IL-6 in TNFalpha-stimulated endothelial cells. In conclusion, the apoA-IV T347S common variant has increased lipid binding properties and cholesterol efflux capacity, while the apoA-IV Q360H variant has only slightly increased lipid binding properties. The two common aminoacid substitutions have no effect on the ability of apoA-IV to maintain endothelial homeostasis.

Modulation of apolipoprotein A-IV lipid binding by an interaction between the N and C termini

Apolipoprotein A-IV (apoA-IV) is a 376-amino acid exchangeable apolipoprotein made in the small intestine of humans. Although it has many proposed roles in vascular disease, satiety, and chylomicron metabolism, there is no known structural basis for these functions. The ability to associate with lipids may be a key step in apoA-IV functionality. We recently identified a single amino acid, Phe(334), which seems to inhibit the lipid binding capability of apoA-IV. We also found that an intact N terminus was necessary for increased lipid binding of Phe(334) mutants. Here, we identify Trp(12) and Phe(15) as the N-terminal amino acids required for the fast lipid binding seen with the F334A mutant. Furthermore, we found that individual disruption of putative amphipathic alpha-helices 3-11 had little effect on lipid binding, suggesting that the N terminus of apoA-IV may be the operational site for initial lipid binding. We also provide three independent pieces of experimental evidence supporting a direct intramolecular interaction between sequences near amino acids 12/15 and 334. This interaction could represent a unique "switch" mechanism by which apoA-IV changes lipid avidity in vivo.

Response of ApoA-IV in pigs to long-term increased dietary oil intake and to the degree of unsaturation of the fatty acids

ApoA-IV is a protein constituent of HDL particles; the gene coding for it is a member of the ApoA-I–ApoC-III–ApoA-IV cluster. To investigate the effects of the quantity and the degree of saturation of dietary lipid on the long-term response of this Apo, and on the hypothetical coordinated regulation of the clusterin vivo, pigs were fed isoenergetic, cholesterol-free, low-lipid or lipid-enriched diets (containing either extra olive oil (rich in MUFA) or sunflower oil (rich inn−6 PUFA)) for 42 d. In animals fed on the control diet, ApoA-IV was mainly associated with plasma lipoproteins. An increase in plasma ApoA-IV concentration, mainly in the lipoprotein-free fraction, was induced by the lipid-enriched diets, independent of the degree of saturation of the fatty acids involved. The latter diets also led to increases in hepatic ApoA-I, ApoA-IV and ApoC-III mRNA levels, more so with the sunflower oil-rich diet. The present results show that porcine plasma ApoA-IV levels and their association with lipoproteins are very sensitive to increases in dietary lipids, independent of the degree of fatty acid saturation. Furthermore, hepatic expression of RNA appears to be coordinated along with that of the other members of the gene cluster.

Accelerated atherosclerosis in apolipoprotein E-deficient mice fed Western diets containing palm oil compared with extra virgin olive oils: a role for small, dense high-density lipoproteins

To test the hypothesis that extra virgin olive oils from different cultivars added to Western diets might behave differently than palm oil in the development of atherosclerosis, apoE-deficient mice were fed diets containing different cultivars of olive oil for 10 weeks. Female mice were assigned randomly to one of the following five groups: (1-4) fed chow diets supplemented with 0.15% (w/w) cholesterol and 20% (w/w) extra virgin olive oil from the Arbequina, Picual, Cornicabra, or Empeltre cultivars, and (5) fed a chow diet supplemented with 0.15% cholesterol and 20% palm oil. Compared to diets containing palm oil, a Western diet supplemented with one of several varieties of extra virgin olive oil decreased atherosclerosis lesions, reduced plaque size, and decreased macrophage recruitment. Unexpectedly, total plasma paraoxonase activity, apoA-I, plasma triglycerides, and cholesterol played minor roles in the regulation of differential aortic lesion development. Extra virgin olive oil induced a cholesterol-poor, apoA-IV-enriched lipoparticle that has enhanced arylesterase and antioxidant activities, which is closely associated with reductions in atherosclerotic lesions. Given the anti-atherogenic properties of extra virgin olive oil evident in animal models fed a Western diet, clinical trials are needed to establish whether these oils are a safe and effective means of treating atherosclerosis.

Apolipoprotein A-IV is regulated by nutritional and metabolic stress: involvement of glucocorticoids, HNF-4 alpha, and PGC-1 alpha

Apolipoprotein A-IV (apoA-IV) is a 46 kDa glycoprotein that associates with triglyceride-rich and high density lipoproteins. Blood levels of apoA-IV generally correlate with triglyceride levels and are increased in diabetic patients. This study investigated the mechanisms regulating the in vivo expression of apoA-IV in the liver and intestine of mice in response to changes in nutritional status. Fasting markedly increased liver and ileal apoA-IV mRNA and plasma protein concentrations. This induction was associated with increased serum glucocorticoid levels and was abolished by adrenalectomy. Treatment with dexamethasone increased apoA-IV expression in adrenalectomized mice. Marked increases of apoA-IV expression were also observed in two murine models of diabetes. Reporter gene analysis of the murine and human apoA-IV/C-III promoters revealed a conserved cooperative activation by the hepatic nuclear factor-4 alpha (HNF-4 alpha) and the peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1 alpha) but no evidence of a direct regulatory role for the glucocorticoid receptor. Consistent with these in vitro data, induction of apoA-IV in response to fasting was accompanied by increases in HNF-4 alpha and PGC-1 alpha expression and was abolished in liver-specific HNF-4 alpha-deficient mice. Together, these results indicate that the induction of apoA-IV expression in fasting and diabetes likely involves PGC-1 alpha-mediated coactivation of HNF-4 alpha in addition to glucocorticoid-dependent actions.

Immunohistochemical localization of apolipoprotein A-IV in human kidney tissue

BACKGROUND

Apolipoprotein A-IV (ApoA-IV) is a 46 kD glycoprotein thought to protect against atherosclerosis. It is synthesized primarily in epithelial cells of the small intestine. Elevated plasma concentrations of ApoA-IV in patients with chronic kidney disease suggest that the human kidney is involved in ApoA-IV metabolism.

METHODS

To investigate whether the human kidney directly metabolizes ApoA-IV and which kidney tissue compartment is involved therein, ApoA-IV was localized by immunohistochemistry in 28 healthy kidney tissue samples obtained from patients undergoing nephrectomy. ApoA-IV mRNA expression was analyzed by real-time polymerase chain reaction (PCR) to exclude de novo synthesis in the kidney.

RESULTS

ApoA-IV immunostaining was detected in proximal and distal tubular cells, capillaries and blood vessels but not inside glomeruli. ApoA-IV was predominantly found in the brush border of proximal tubules and in intracellular granules and various plasma membrane domains of both proximal and distal tubules. mRNA expression analysis revealed that no ApoA-IV was produced in the kidney.

CONCLUSION

The immunoreactivity of ApoA-IV observed in kidney tubular cells suggests a direct role of the human kidney in ApoA-IV metabolism. The granular staining pattern probably represents lysosomes degrading ApoA-IV. The additional ApoA-IV localization in distal tubules suggests a rescue function to reabsorb otherwise escaping ApoA-IV in case proximal tubules cannot reabsorb all ApoA-IV. Since no mRNA expression could be detected in any kidney cells, the observed ApoA-IV immunoreactivity represents uptake and not de novo synthesis of ApoA-IV.

Immune-regulation of the apolipoprotein A-I/C-III/A-IV gene cluster in experimental inflammation

Apolipoprotein A-IV is a member of the apo A-I/C-III/A-IV gene cluster. In order to investigate its hypothetical coordinated regulation, an acute phase was induced in pigs by turpentine oil injection. The hepatic expression of the gene cluster as well as the plasma levels of apolipoproteins were monitored at different time periods. Furthermore, the involvement of the inflammatory mediators' interleukins 1 and 6 and tumor necrosis factor in the regulation of this gene cluster was tested in cultured pig hepatocytes, incubated with those mediators and apo A-I/C-III/A-IV gene cluster expression at the mRNA level was measured. In response to turpentine oil-induced inflammation, a decreased hepatic apo A-IV mRNA expression was observed (independent of apo A-I and apo C-III mRNA) not correlating with the plasma protein levels. The distribution of plasma apo A-IV experienced a shift from HDL to larger particles. In contrast, the changes in apo A-I and apo C-III mRNA were reflected in their corresponding plasma levels. Addition of cytokines to cultured pig hepatocytes also decreased apo A-IV and apo A-I mRNA levels. All these results show that the down-regulation of apolipoprotein A-I and A-IV messages in the liver may be mediated by interleukin 6 and TNF-alpha. The well-known HDL decrease found in many different acute-phase responses also appears in the pig due to the decreased expression of apolipoprotein A-I and the enlargement of the apolipoprotein A-IV-containing HDL.

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.

Cloning, characterization and comparative analysis of pig plasma apolipoprotein A-IV

Pig apolipoprotein (apo) A-IV cDNA was cloned, characterized and compared to the human ortholog. Mature porcine apo A-IV consists of 362 amino acids and displays a 75.6% sequence identity with human protein. Pig apo A-IV is the smallest reported mammalian apo A-IV because it lacks the repeated motifs of glutamine and glutamic acid at the carboxyl terminus. A phylogenic tree of apo A-IV mammalian proteins reveals that porcine apo A-IV is more closely related to humans and primates than to rodents. This protein is highly hydrophobic and is mainly associated with lipoproteins.

Postprandial changes in the distribution of apolipoprotein AIV between apolipoprotein B- and non apolipoprotein B-containing lipoproteins in obese women

Plasma apolipoprotein AIV (apo AIV) level has been shown to be a good marker of triglyceride changes after a high-fat diet. However, the distribution of apo AIV between apo B- and non-apo B-containing lipoproteins (Lp) during the postprandial state has not been described as well as the influence of obesity on this distribution. Our aim was to study the influence of parameters related to obesity and insulin resistance on the postprandial changes in apo AIV-containing Lp after a high-fat meal in obese women. Twenty-three overweight or obese women (body mass index [BMI] ranging from 29.1 and 64.0 kg.1 m(-2)), for whom blood samples were taken after fasting overnight, participated in the study. Thirteen of these obese women were given a fatty meal and, in this case, blood samples were taken at fast and 30 minutes, 1, 2, 4, and 6 hours after ingestion of the fat meal. Apo AIV-containing particle families, Lp B:AIVf (family [f] of particles containing at least apo B and apo AIV) and Lp AIV non-Bf (family [f] of particles containing apo AIV, but free of apo B) were quantified by sandwich enzyme-linked immunosorbent assay (ELISA). When fasting, Lp B:AIVf and Lp AIV non-Bf did not correlate with any of the parameters related to obesity and insulin resistance, if one excepts a positive correlation between HDL-cholesterol (HDL-C) and Lp AIV non-Bf. Postprandial lipemia was associated with a trend towards an increase in the plasma levels of apo AIV-containing Lp 6 hours after fat ingestion. The postprandial peak of Lp B:AIVf and Lp AIV non-Bf occurred 2 hours after the triglyceride peak. The distribution between apo B- and non-apo B-containing Lp did not change after ingestion of the fat meal, if one excepts a tendancy towards a lower ratio of bound and nonbound forms at 8 hours. Fasting plasma Lp B:AIVf concentration correlated with the area under the curve (AUC) of plasma triglycerides (beta = 0.11, P <.02). In a multivariate analysis, BMI (beta = 51.85, P <.001), fasting triglycerides (beta = 431.08, P <.01), and low-density lipoprotein-cholesterol (LDL-C) (beta = 2638.57, P <.005) were independent and positive determinants of the AUC of Lp AIV non-Bf, while waist circumference (beta = -23.94, P <.001), cholesterol (beta = -1655.02, P <.01), and systolic blood pressure (beta = -6.34, P <.05) were negative and independent determinants of this AUC. Fasting Lp B:AIVf may represent a good marker of the postprandial triglyceride increase in obese women. Changes in apo AIV concentrations in apo B- and non-apo B-containing Lp after a fat meal depend mainly on the degree of obesity rather than on insulin resistance. This effect is more obvious for Lp AIV non-Bf than for Lp B:AIVf.

Plasma distribution of apoA-IV in patients with coronary artery disease and healthy controls

Recent studies showed lower apolipoprotein A-IV (apoA-IV) plasma concentrations in patients with coronary artery disease (CAD). The actual distribution of the antiatherogenic apoA-IV in human plasma, however, is discussed controversially and it was never investigated in CAD patients. We therefore developed a gentle technique to separate the various apoA-IV-containing plasma fractions. Using a combination of precipitation of all lipoproteins with 40% phosphotungstic acid and 4 M MgCl2, as well as immunoprecipitation of all apoA-I-containing particles with an anti-apoA-I antibody, we obtained three fractions of apoA-IV: lipid-free apoA-IV (about 4% of total apoA-IV), apoA-IV associated with apoA-I (LpA-I:A-IV, 12%), and apoA-I-unbound but lipoprotein-containing apoA-IV (LpA-IV, 84%). We compared these three apoA-IV fractions between 52 patients with a history of CAD and 52 age- and sex-matched healthy controls. Patients had significantly lower apoA-IV levels when compared to controls (10.28 +/- 3.67 mg/dl vs. 11.85 +/- 2.82 mg/dl, P = 0.029), but no major differences for the three plasma apoA-IV fractions. We conclude that our gentle separation method reveals a different distribution of apoA-IV than in many earlier studies. No major differences exist in the apoA-IV plasma distribution pattern between CAD patients and controls. Therefore, the antiatherogenic effect of apoA-IV has to be explained by other functional properties of apoA-IV (e.g., the antioxidative characteristics).

Apo A-IV: an update on regulation and physiologic functions

Apolipoprotein (apo) A-IV, first identified 28 years ago as a plasma lipoprotein moiety, is now known to participate in the regulation of various metabolic pathways. It is synthesized primarily in the enterocytes of the small intestine during fat absorption. After entry into the bloodstream, the 46-kDa glycoprotein apo A-IV appears associated with chylomicrons, high-density lipoproteins, and in the lipoprotein-free fraction. It has a role in lipid absorption, transport and metabolism, and may act as a post-prandial satiety signal, an anti-oxidant and a major factor in the prevention of atherosclerosis. After summarizing and discussing these functions for reader's comprehension, the current review focuses on the regulation of apo A-IV by nutrients, biliary components, drugs, hormones and gastrointestinal peptides. The understanding of the involved mechanisms that underline apo A-IV regulation may in the long run allow us to switch on its gene, which may confer multiple beneficial effects, including the protection from atherosclerosis.

Cladistic analysis of human apolipoprotein a4 polymorphisms in relation to quantitative plasma lipid risk factors of coronary heart disease

Genetic variation in several genes involved in lipid metabolism is known to affect population variation in quantitative lipid risk factor profiles for coronary heart disease (CHD). The apolipoprotein A-IV gene (APOA4) is one such candidate gene. We genotyped five polymorphisms in the APOA4 gene (codon 127, codon 130, codon347, codon 360 and 3' VNTR) and investigated their impact on plasma lipid trait levels in three populations comprising 604 U.S. non-Hispanic Whites (NHWs), 408 U.S. Hispanics and 708 Nigerian Blacks. Cladistic analysis was carried out to identify 5-site haplotypes that were associated with significant phenotypic differences in each population. The distribution of APOA4 genotypes was significantly different between ethnic groups. The Africans were monomorphic for two of the five sites (codons 130 and 360), but possess a unique 12 bp insertion that was not observed in NHWs and Hispanics. Due to linkage disequilibrium between the sites, only 6 haplotypes were observed in NHWs and Hispanics, and 4 in Africans. Several gender-and ethnic-specific associations between genotypes and plasma lipid traits were observed when single sites were used. Several haplotypes were identified by cladistic analysis that may carry functional mutations that affect plasma lipid trait levels.

Quantitative Measurement of Lipoprotein Particles Containing Both Apolipoprotein AIV and Apolipoprotein B in Human Plasma by a Noncompetitive ELISA

Background: A reliable method for plasma would be useful to investigate the role of apolipoprotein (apo) AIV when associated with apo B-containing or triglyceride-rich lipoproteins.

Method: We used a sandwich ELISA to quantify lipoprotein B:AIV particles (Lp B:AIVf; lipoproteins containing at least apo B and apo AIV) in plasma. The method used microtiter plates coated with purified anti-apo B immunoglobulins that selectively retained apo B-containing particles. Lipoproteins containing both apo B and apo AIV were distinguished from those containing only apo B by use of a peroxidase-labeled anti-apo AIV antibody. These subspecies were revealed by ABTS® reagent and further quantified by spectrophotometry. Results were expressed in mg/L apo AIV associated with apo B. This method was applied to samples with different cholesterol and triglyceride concentrations.

Results: The developed sandwich ELISA method identified and quantified Lp B:AIVf in plasma samples. Within- and between-run CVs were ∼10%, and analytical recoveries were 95–107%. Results were not significantly influenced by addition of triglycerides or by storage at −20 °C (up to 9 months). Under these conditions, plasma Lp B:AIVf concentrations were statistically higher in hypercholesterolemic and mixed hyperlipidemic individuals (53 ± 13 mg/L; P &lt;0.001 and 70 ± 18 mg/L; P &lt;0.001, respectively) than in normolipidemic individuals (43 ± 12 mg/L). Lp B:AIVf concentration appeared to be well correlated with total cholesterol, triglycerides, LDL-cholesterol, and apo B. These results were in contrast to total apo AIV, which was not different between dyslipidemic and normolipidemic individuals.

Conclusions: The developed ELISA method for Lp B:AIVf in plasma combines specificity, reliability, and speed. The increase in Lp B:AIVf concentrations in various dyslipidemic states, together with a lack of change in total apo AIV concentrations, suggests a redistribution of apo AIV toward apo B-containing lipoproteins when these lipoproteins accumulate.

Effects of apolipoprotein A-IV genotype on glucose and plasma lipoprotein levels

The effects of apolipoprotein (apo) A-IV genotype on serum glucose, total cholesterol, low density lipoprotein (LDL) cholesterol, high density lipoprotein (HDL) cholesterol, triglyceride and glucose concentrations were ascertained in a population of 373 men and 361 women with a mean age of about 57 years. Subjects were evaluated at entry into a lifestyle intervention program. Apolipoprotein A-IV genotype variations at residues 347 and 360 were examined, as these mutations affect the sequence of apo A-IV, a major protein constituent of intestinal triglyceride-rich lipoprotein and HDL. With regard to the apo A-IV 360 mutation, 16.4% of the females and 13.4% of the males carried the apo A-IV 2-allele, almost entirely in the heterozygous state. No effect of the apo A-IV 1/2 genotype was observed in either men or women on total cholesterol, LDL cholesterol, HDL cholesterol, triglyceride, the total cholesterol (TC)/HDL ratio, or on A-I, A-IV and apo B levels. This was also the case for the apo A-IV 347 mutation. However, women with the apo A-IV 360 1/2 genotype had significantly (p < 0.005) higher glucose levels (105.5 mg/dl) compared with the 1/1 wild-type (94.0 mg/dl). All analyses were also adjusted for age, body mass index, medications, alcohol use and cigarette smoking. The prevalence of the 347 mutation was somewhat higher than the 360 mutation, with 29% of the females and 32.0% of the males being heterozygous for this mutation, and 3.9% of the females and 5.4% of the males being homozygous for this mutation. These data are consistent with the concept that the apo A-IV 360 and 347 genotypes have no significant effect on apo A-IV levels and other lipid parameters in either gender. However, apo A-IV 360 1/2 genotype did have a significant effect on serum glucose levels in women.

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.

Human apolipoprotein A-IV metabolism within triglyceride-rich lipoproteins and plasma

In order to investigate the metabolism of apo A-IV within TRL and plasma, we assessed TRL and plasma apo A-IV kinetics in 19 and 4 subjects, respectively, consuming an average US diet for a 6-week period. At the end of this diet study, each subject received a primed-constant infusion of deuterated leucine over a 15 h time period with hourly feeding, and blood samples were drawn at 10 time points. TRL was separated by ultracentrifugation. Apo A-IV was isolated by immunoprecipitation and/or SDS-PAGE. Apo A-IV concentrations were determined by immunoelectrophoresis. Stable isotope tracer/tracee ratios were measured by gas chromatography/mass spectrometry, and the data were analyzed by multicompartmental modeling. The mean concentrations of plasma and TRL apo A-IV during the isotope infusion period were 21.0+/-3.2 and 0.66+/-0.25 mg/dl, respectively, and these values were 11.5 and 30.5% higher than those of fasting samples. The mean TRL and plasma apo A-IV residence times (RT) were 1.97+/-0.57 and 2.71+/-0.65 days, and transport rates (TR) were 0.17+/-0.19 and 3.90+/-1.24 mg/kg per day, respectively. There were significant correlations between TRL apo A-IV concentrations and TR (r(2)=0.79, P<0.001), and between TRL apo A-IV pool size and TRL cholesterol levels (r(2)=0.29, P=0.02). Our data indicated that; (1) TRL apo A-IV has a RT of 1.97 days which is similar to that earlier reported for HDL apo A-IV; (2) Apo A-IV recirculates between TRL and other slowly turning over pools; (3) the primary determinant of TRL apo A-IV levels is its TR; and (4) there is no correlation between TRL apo A-IV and apo B48 fractional catabolism in TRL.

Low apolipoprotein A-IV plasma concentrations in men with coronary artery disease

OBJECTIVES

The objective of this study was to evaluate the relation between apolipoprotein A-IV (apoA-IV) plasma concentrations and coronary artery disease (CAD).

BACKGROUND

Experimental in vitro and in vivo studies favor apoA-IV to be protective against the development of atherosclerosis. Mice that overexpress either human or mouse apoA-IV demonstrated a significant reduction of aortic atherosclerotic lesions compared with control mice. Data on apoA-IV plasma concentrations and CAD in humans are lacking.

METHODS

We determined in two independent case-control studies of a Caucasian and an Asian Indian population whether apoA-IV plasma concentrations are related to the presence of angiographically assessed CAD.

RESULTS

Plasma apoA-IV levels were significantly lower in 114 male Caucasian subjects with angiographically defined CAD when compared with 114 age-adjusted male controls (10.2 +/-3.8 mg/dL vs. 15.1 +/- 4.0 mg/dL, p < 0.001). Logistic regression analysis indicated that the association between apoA-IV levels and CAD was independent of the high-density lipoprotein cholesterol and triglyceride concentrations. The inverse relationship between plasma levels of apoA-IV and the presence of CAD was confirmed in an independent sample of 68 male Asian Indians with angiographically documented CAD and 68 age-matched controls.

CONCLUSIONS

The results of this cross-sectional study demonstrate for the first time an association between low apoA-IV concentrations and CAD in humans and suggest that apoA-IV may play an antiatherogenic role in humans.

Effects of age, gender, and lifestyle factors on plasma apolipoprotein A-IV concentrations

Apolipoprotein (apo) A-IV is a protein component of triglyceride (TG)-rich lipoproteins and high density lipoproteins (HDL). Plasma apo A-IV levels were measured by immunoelectrophoresis and these values were related to other biological variables in 723 middle aged and elderly men and women (more than 90% of them were Caucasian) prior to participation in a lifestyle modification program. Apo A-IV may play an important function in regulating lipid absorption, reverse cholesterol transport, and food intake. The data are consistent with the following concepts: (1) apo A-IV levels are significantly and positively correlated with age (r = 0.159, P < 0.05) in all subjects, with plasma apo A-I levels in both men (r = 0.194, P < 0.001) and women (r = 0.213, P < 0.001), and with apo E (r=0.111, P<0.05) and TG levels (r =0.120, P <0.05) in men; (2) apo A-IV levels are inversely correlated with body mass index (r = 0.170, P <0.05) in women; (3) female subjects on hormone replacement therapy have significantly lower plasma apo A-IV levels (by 4.1%, P < 0.05) than normal controls; (4) diabetic subjects have significantly higher apo A-IV levels (by 21%, P < 0.01) than normal subjects; (5) there is no significant effect of smoking, alcohol intake, and apo A-IV-1/2 genotype on apo A-IV levels. The data indicate that plasma apo A-IV levels are significantly affected by age, diabetes, and hormone replacement therapy.

Common apolipoprotein A-IV variants are associated with differences in body mass index levels and percentage body fat

OBJECTIVE

To determine the relationship between two common apoA-IV variants (Thr347-->Ser; Gln360-->His), and body mass index (BMI) and percentage body fat.

DESIGN

Cross-sectional study.

SUBJECTS

Eight-hundred and forty-eight subjects screened for participation in ongoing clinical studies.

MEASUREMENTS

ApoA-IV genotype, body mass index, waist-to-hip ratio and percentage body fat by bioelectric impedance.

RESULTS

Participants had an average age of 41+/-12 y and an average BMI of 28.2+/-5.5 kg/m2. Individuals homozygous for the Ser347 allele had higher BMI (32.3+/-6.6 vs 28.6+/-5.3 kg/m2; P<0.01) and percentage body fat (36.9+/-7.8 vs 31.0+/-9.6%; P<0.05) compared with individuals homozygous for Thr347. In contrast, the presence of at least one copy of the His360 allele was associated with lower BMI (27.2+/-5.0 vs 28.4+/-5.6 kg/m2; P<0.05) and percentage body fat (28.6+/-8.2 vs 30.7+/-9.1%; P<0.05). The genotype effects persisted after normalization of the data for the potential confounding effects of gender, age and race. When grouped by BMI percentile, the frequency of the Ser347/Ser347 genotype increased while the frequency of the His360 allele decreased with increasing BMI.

CONCLUSIONS

These data suggest a role for apoA-IV in fat storage or mobilization and that genetic variations in the apoA-IV gene may play a role in the development of obesity.

Human ApoA-IV overexpression in transgenic mice induces cAMP-stimulated cholesterol efflux from J774 macrophages to whole serum

The role of apolipoprotein A-IV (apoA-IV) in lipoprotein metabolism has not been established. The aim of the present study was to investigate the role of apoA-IV in reverse cholesterol transport by comparing cellular cholesterol efflux to serum or serum fractions from control mice and from mice transgenic for human apoA-IV (HuA-IVTg mice). When Fu5AH hepatoma cells were used, the cholesterol efflux to serum from either control or transgenic mice was similar. When control J774 macrophage cells were used, a comparison of efflux to serum or lipoprotein-deficient serum (LPDS) failed to demonstrate any differences between control and transgenic mice. In contrast, when the J774 cells were pretreated with cAMP, there was a stimulation of efflux to whole serum or LPDS from HuA-IVTg mice. cAMP treatment had no effect on efflux to serum or LPDS from control mice. Pretreatment of the cells with cAMP did not enhance the efflux response to high density lipoprotein isolated from HuA-IVTg mouse serum. Our results suggest that apoA-IV, unassociated with high density lipoprotein particles, is responsible for enhanced cholesterol efflux. This study illustrates the role of lipid-free apolipoproteins in mediating cellular cholesterol efflux with use of a biological fluid and is potentially of physiological relevance, especially in apolipoprotein-rich extravascular fluids.

360His polymorphism of the apolipoproteinA-IV gene and plasma lipid response to energy restricted diets in overweight subjects

Obesity is commonly associated with high rates of cardiovascular disease (CVD). Weight loss in obese subjects reduces risk factors for CVD but this response is not uniform. Genetic factors could be involved in this variability. The 360His polymorphism of apolipoproteinA-IV (apoA-IV) influences the lipid response to fat intake, but it is unclear whether this polymorphism could contribute to lipid variability during weight loss. Therefore, we assessed the effects of an energy restricted diet (6.3 MJ) for 12 weeks on weight loss and plasma lipids according to apoA-IV genotype in 186 overweight/obese subjects (BMI mean 33+/-4.3, range 25.0-48.0 kg/m(2)). The frequency of the 360His allele was 0.083. Energy restriction for 12 weeks resulted in an average weight loss of 8. 25+/-0.28 kg. HDL-C increased 5.4% in subjects with the apoA-IV-1/1 genotype with weight loss compared to a 2.6% decrease in apoA-IV-1/2 subjects (P=0.035). This was more apparent when only the subjects with type 2 diabetes (n=57) were analyzed (P=0.003). ApoA-IV genotype was not related to change in total cholesterol, LDL-C or triglyceride concentrations. Therefore, weight loss as a treatment to reduce CVD risk factors may be more effective in subjects with the apoA-IV-1/1 variant as compared to those with the apoA-IV-1/2 variant, especially in subjects with type 2 diabetes.

Effect of 347-serine mutation in apoprotein A-IV on plasma LDL cholesterol response to dietary fat

Lipid response to dietary fat and cholesterol is, to a large extent, genetically controlled. Apoprotein (apo) A-IV has been related to fat absorption and to the activation of some of the enzymes involved in lipid metabolism. One mutation has been described in the apo A-IV gene that causes substitution of Ser for Thr at position 347. To study the influence of this mutation on the plasma LDL cholesterol (LDL-C) response in diets of various fat content and fatty acid saturation, 41 healthy male subjects were studied, 25 of whom were homozygous for the Thr allele (347Thr) and the rest who were either homozygous (n = 2) or heterozygous carriers of the Ser allele (347Ser). They consumed three consecutive diets, each of 4 weeks' duration: one rich in saturated fat (SFA diet: 38% fat, 20% saturated), a National Cholesterol Education Program (NCEP) type 1 diet (28% fat, 10% saturated), and a third rich in monounsaturated fat (MUFA diet; 38% fat, 22% monounsaturated). Carriers of the 347Ser allele presented a greater decrease in total cholesterol (-0.7 vs -0.44 mmol/L, P < .034), LDL-C (-0.62 vs -0.31 mmol/L, P < .012), and apo B (-14 vs -8 mg/dL, P < .01) levels when they were switched from the SFA to the NCEP type 1 diet than homozygous carriers of the 347Thr allele. The change from the NCEP type 1 to the MUFA diet resulted in a greater increase in total cholesterol (0.18 vs -0.05 mmol/L, P < .028) and apo B (5 vs -1 mg/dL, P < .006) levels in the 347Ser than in the 347Thr individuals. In a previous study, we demonstrated that the G-->A polymorphism at position -76 of the gene promoter of apo A-I affects the LDL-C response to dietary fat. We therefore decided to study the effect of the interaction between these mutations on this response. We found that both mutations have an additive effect on total cholesterol, LDL-C, and apo B dietary-induced changes. Our results suggest that total cholesterol and LDL-C response to dietary fat is influenced by the 347Ser mutation of apo A-IV.

Influence of two apo A4 polymorphisms at codons 347 and 360 on non-fasting plasma lipoprotein-lipids and apolipoproteins in Asian Indians

Apolipoprotein A-IV (apo A-IV, protein; apo A4, gene) is a major constituent of triglyceride-rich and high-density lipoprotein particles and may, therefore, play an important role in lipid metabolism. We studied the distribution of two apo A4 polymorphisms at codons 347 (alleles A and T) and 360 (alleles 1 and 2) in relation to plasma lipoprotein-lipid and apolipoprotein levels in 176 non-fasting male blood donors from New Delhi, Northern India. The frequencies of the T allele at codon 347 and the 2 allele at codon 360 were 0.12 and 0.03 respectively. Carriers of the T allele (AT and TT genotypes) had significantly lower plasma total cholesterol (P = 0.04) and low density lipoprotein (LDL)-cholesterol (P = 0.02) levels than individuals homozygous for the A allele (AA genotype). The codon 347 polymorphism explained 2.2 and 2.6% of the phenotypic variation in total cholesterol and LDL-cholesterol, respectively. The 2 allele at codon 360 was associated with marginally reduced plasma LDL-cholesterol (P = 0.09) and increased triglyceride (P = 0.05) levels compared to the 1 allele. To further elucidate the combined effects of the two polymorphism we constructed two-site haplotypes. The haplotype data showed a stronger influence and explained 3.0 and 5.2% of the phenotypic variation in total cholesterol and LDL-cholesterol, respectively. The two uncommon haplotypes, T1 and A2, were associated with 24.2 and 23.5 mg/dl lower total cholesterol and 22.5 and 42.0 mg/dl lower LDL-cholesterol levels, respectively. The accentuated effect of apo A4 polymorphisms on non-fasting plasma cholesterol suggest that apo A-IV may play an important role in regulating the postprandial metabolism of lipoproteins.

Control of synthesis and secretion of intestinal apolipoprotein A-IV by lipid

Apolipoprotein (apo) A-IV, a component of intestinally secreted, triacylglycerol-rich lipoproteins, has recently been proposed as a physiological controller of gastric function and food intake. Thus, it is important to understand the mechanisms involved in the control of expression, synthesis and secretion of apo A-IV. Apo A-IV is a member of a closely linked, multigene cluster which includes apolipoproteins A-I and C-III. Expression and synthesis of apo A-IV display marked variability with regard to species, tissue, stage of development and response to hormones, but intestinal apo A-IV is consistently stimulated by dietary lipid. The precise molecular mechanisms underlying the response of apo A-IV to lipid have not been clearly defined. Most evidence supports the hypothesis that some aspect of lipid transport is necessary for the apo A-IV response, but only part of this response may be due to a direct effect of intestinal lipid: recent findings suggest a connection between intestinal production of apo A-IV and hormonal and/or neural factors associated with operation of the "ileal brake." Thus, apo A-IV may play an integrative role in the modulation of both upper gastrointestinal function and ingestive behavior.

Postprandial lipaemia is associated with increased levels of apolipoprotein A-IV in the triacylglycerol-rich fraction and decreased levels in the denser plasma fractions

Apolipoprotein (apo) A-IV is primarily associated with HDL or with the lipoprotein-free fraction of plasma, and in small amounts with chylomicrons and VLDL. The aim of the present study was to assess the effect of a fatty meal on the postprandial variation in plasma apo A-IV and on its distribution among lipoprotein fractions following absorption of fat. Twenty healthy male subjects participated in the study. After an overnight fast, subjects were given a fatty breakfast containing 1 g fat/kg body weight (% energy: fat 65, carbohydrate 20; protein 15). Blood samples were taken every hour during the next 10 h. Apo A-IV was measured by ELISA. Postprandial lipaemia was associated with a moderate, although significant, increase in the plasma levels of apo A-IV. Apo A-IV increased from the median baseline value of 0.15 g/l to 0.165 g/l (median +17%; P < 0.01) 5 h after fat ingestion. The postprandial peak of apo A-IV occurred 1 h after the triacylglycerol peak. There were no statistically significant correlations between baseline lipids, baseline apo A-IV and postprandial changes in apo A-IV levels, or between postprandial changes in lipids and apo A-IV at any time. To assess apo A-IV distribution among lipoproteins, plasma was fractionated by fast performance liquid chromatography at baseline and 3, 6 and 10 h postprandially. There was a substantial heterogeneity in the apo A-IV distribution among lipoproteins following the fatty meal. At 3 h after fat ingestion, apo A-IV levels increased in the triacyglycerol-rich lipoprotein (TRL) fraction and decreased in the denser plasma fraction. At 6 h after the fatty meal, apo A-IV was still present in the TRL but was decreased in the HDL fractions. The findings of the present study support the concept that apo A-IV particles transfer from the denser plasma fraction to TRL during postprandial lipaemia.

Interstitial fluid apolipoprotein A-II: an association with the occurrence of myocardial infarction

A sample of male patients aged 25-64 years, survivors of myocardial infarction (MI) taken from the Lille MONICA register, and age-matched control subjects from the general population were recruited in Lille and its surroundings in the North of France. Diabetics and subjects taking hypolipidemic drugs were excluded from the analysis, so that 73 MI and 144 control subjects were included. Lipids, apolipoprotein (apo) A-I, apo A-II, apo A-IV and apo B, and apo A-I-containing particles such as lipoproteins containing both apo A-I and apo A-II (LpA-I:A-II) and those containing apo A-I but not apo A-II (LpA-I) were measured in interstitial fluid by applying mild suction, and in plasma. Univariate analysis showed that plasma triglycerides, very low density lipoprotein (VLDL)-cholesterol and apo B were significantly higher, while high density lipoprotein (HDL)-cholesterol, apo A-I, LpA-I and LpA-I:A-II were lower in MI survivors compared to controls after adjustment for age, body mass index (BMI), alcohol and tobacco consumption. In interstitial fluid, cholesterol and apo A-II were higher in MI than in controls before adjustment for covariates. However, after adjustment, triglycerides became significant while cholesterol and apo A-II remained significantly higher in MI, at 43.8 and 7.5 mg/dl, respectively, than in control subjects, at 38.6 and 5.9 mg/dl, respectively. Taking into account only the plasma parameters, the multivariate analysis reveals that triglycerides and apo A-I appear to be independent factors indicative of the presence of a MI. When plasma and interstitial fluid parameters were taken together in the multivariate analysis, the measurement of apo A-II in interstitial fluid increased the level of prediction of MI over the information provided by the plasma parameters. These data raise the possibility that interstitial fluid apo A-II levels may be associated with the occurrence of MI.

Protection against atherogenesis in mice mediated by human apolipoprotein A-IV

Apolipoproteins are protein constituents of plasma lipid transport particles. Human apolipoprotein A-IV (apoA-IV) was expressed in the liver of C57BL/6 mice and mice deficient in apoE, both of which are prone to atherosclerosis, to investigate whether apoA-IV protects against this disease. In transgenic C57BL/6 mice on an atherogenic diet, the serum concentration of high density lipoprotein (HDL) cholesterol increased by 35 percent, whereas the concentration of endogenous apoA-I decreased by 29 percent, relative to those in transgenic mice on a normal diet. Expression of human apoA-IV in apoE-deficient mice on a normal diet resulted in an even more severe atherogenic lipoprotein profile, without affecting the concentration of HDL cholesterol, than that in nontransgenic apoE-deficient mice. However, transgenic mice of both backgrounds showed a substantial reduction in the size of atherosclerotic lesions. Thus, apoA-IV appears to protect against atherosclerosis by a mechanism that does not involve an increase in HDL cholesterol concentration.

Activation of human plasma cholesteryl ester transfer protein by human apolipoprotein A-IV

Function of apolipoprotein (apo) A-IV was studied for its role in cholesteryl ester transfer protein (CETP; lipid transfer protein, LTP) reaction between lipid microemulsions having the diameter of low density lipoprotein, being compared to apoA-I. CETP hardly catalyzed lipid transfer without apolipoproteins. ApoA-IV bound to the surface of the microemulsion in equilibrium with a similar affinity to that of other helical apolipoproteins, and activated the transfer reaction by CETP of cholesteryl ester, triacylglycerol and phosphatidylcholine between the emulsions. The rate of the transfer reaction of cholesteryl ester and triacylglycerol was directly proportional to the amount of the bound apoA-IV to the surface of the emulsion. For phosphatidylcholine, activation was less effective until 40% of total binding capacity of lipid emulsion was occupied by the apolipoprotein. Cholesteryl ester was highly preferred by CETP over triacylglycerol when equal amount of these lipids was present in the core of the apoA-IV-activated emulsion, resulting in almost no triacylglycerol transfer. However, when the emulsion has the core exclusively of triacylglycerol, triacylglycerol was transferred by CETP with the rate in the same order as that of cholesteryl ester transfer. These findings were all comparable to the results with apoA-I, and also consistent with our previous observation for other amphiphilic helical apolipoproteins such as apoA-II, E and C-III.

Two novel apolipoprotein A-IV variants in individuals with familial combined hyperlipidemia and diminished levels of lipoprotein lipase activity

It has been suggested that apo A-IV may play a role in modulating the activation of lipoprotein lipase (LPL) by apo C-II (Goldberg et al., 1990). Therefore, the role of genetic variation at the apolipoprotein A-IV locus in familial combined hyperlipidemia (FCHL) was investigated. A subset of FCHL patients with half the level of plasma LPL activity was screened by single-strand conformation polymorphism (SSCP) for variants in the apolipoprotein A-IV gene. Two of 20 such individuals were found to be heterozygous carriers of previously undescribed amino acid substitutions: S158L and R 244Q substitutions, designated A-IV-Seattle-1 and A-IV-Seattle-2, respectively. These substitutions were not detected among 20 other FCHL patients with normal LPL levels and among 97 unselected medical students. The finding of these two alleles among only the 20 patients with FCHL with reduced levels of LPL suggests an association with this phenotype. It is hypothesized that these two alleles may contribute, along with alleles of other genes or environmental factors, to the development of FCHL. A third previously undescribed variant (A141S) was observed in four (two homozygotes and two heterozygotes) of the 97 medical students.

HDL heterogeneity and atherosclerosis

High-density lipoprotein (HDL), the most abundant human plasma lipoprotein, plays a major role in reverse cholesterol transport, which recycles cholesterol from peripheral cells to the liver. HDL constitutes a heterogeneous group of particles differing in density, size, electrophoretic mobility, and apolipoprotein content. HDL can therefore be fractionated into discrete subclasses by different techniques according to their physicochemical properties. The clinical significance of HDL differs with the subclasses, especially with respect to coronary heart disease, alcohol intake, longevity, dyslipoproteinemia, dietary fat content, and hypolipidemic drugs. Because of their structural and functional diversity, HDL subclasses generate considerable hope that they may help to improve the identification of individuals at an increased risk of developing coronary heart disease.

Lipoproteins containing apolipoprotein A-IV but not apolipoprotein A-I take up and esterify cell-derived cholesterol in plasma

Two-dimensional nondenaturing polyacrylamide gradient gel electrophoresis (2D-PAGGE) identifies distinct apoA-I-or apoE-containing subclasses of high-density lipoproteins (HDLs), each of which plays a different role in reverse cholesterol transport. In this study we used 2D-PAGGE to investigate the role of apoA-IV-containing lipoproteins in reverse cholesterol transport in native plasma. Incubation of 2D electrophoretograms with anti-apoA-IV antibodies identified up to three subclasses of particles. The smaller particle subclasses, LpA-IV-1 and LpA-IV-2, were found in every plasma sample. The largest particle subclass, LpA-IV-3, was observed in fewer than 10% of the plasmas analyzed. 2D-PAGGE of apoA-I-deficient plasma and apoA-I-depleted plasma and anti-apoA-I immunosubtracting 2D-PAGGE of normal plasma revealed that LpA-IV-1 and LpA-IV-2 do not contain apoA-I. The importance of LpA-IV-1 and LpA-IV-2 for uptake and esterification of cell-derived cholesterol was investigated using pulse-chase incubations of plasma with [3H]cholesterol-labeled fibroblasts followed by anti-apoA-I immunosubtracting 2D-PAGGE. During 1-minute pulse incubation with cells, [3H]cholesterol was taken up by gamma-LpE > LpA-IV-1 > pre-beta 1-LpA-I > LpA-IV-2 (">" denotes "more than"). During subsequent chase incubation without cells, proportionately less radioactivity disappeared from LpA-IV-1 and LpA-IV-2 than from pre-beta 1-LpA-I and gamma-LpE. During 5-minute pulse incubations, radioactive cholesteryl esters were formed in pre-beta 3-LpA-I > alpha-LpA-I > LpA-IV-1 > LpA-IV-2. The fractional estertification rate was highest in pre-beta 2-LpA-I and lowest in alpha-LpA-I.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of subpopulations of lipoprotein particles isolated from human cerebrospinal fluid

The aim of the present study was to define lipoprotein complexes within cerebrospinal fluid (CSF) in terms of their apolipoprotein composition, using fractionation procedures considered optimal for maintaining lipoprotein structural integrity. Five apolipoproteins were identified, namely apolipoproteins A-I, A-IV, D, E and J. These were differentially distributed amongst lipoprotein particles of which three major subpopulations were identified. CSF-LpAI (20.1 +/- 3.8 nm) was enriched in apolipoprotein A-I and contained the major proportion (> 50%) of apolipoproteins D, E and J. CSF-LpE, of similar size to CSF-LpAI (20.2 +/- 3.1 nm), was composed principally of apolipoprotein E, with minor quantities of apolipoproteins A-I, A-IV, D and J. Elimination of these particles from cerebrospinal fluid by immunoabsorption revealed a third subpopulation of significantly greater diameter (32.0 +/- 6.8 nm). The majority (62%) of apolipoprotein A-IV was also present in this fraction. The study demonstrates the structural and size heterogeneity of lipoproteins in cerebrospinal fluid. This may reflect the lipid transport processes within the central nervous system.

Genetic but not diet-induced hypercholesterolemia causes low apolipoprotein A-IV level in rabbit sera

The present report describes a competitive enzyme immunoassay for rabbit apolipoprotein A-IV (apo A-IV). This assay was applied to the determination of its concentration and distribution in sera from normolipidemic and hyperlipidemic rabbits. The assay was sufficiently sensitive to study this 42-kDa protein in lipoproteins fractionated from 200 microliters of serum by FPLC gel filtration. In normolipidemic sera (n = 8), apo A-IV concentration was 5.32 +/- 0.76 mg/dl. A diet rich in cholesterol (0.5%), which induced an 18-fold increase in serum cholesterol, did not significantly alter apo A-IV concentration (6.65 +/- 1.52 mg/dl, n = 8). By contrast, genetically induced hypercholesterolemia (Watanabe heritable hyperlipidemia, WHHL mutation) caused a significantly reduced level of apo A-IV (3.8 +/- 1.14 mg/dl, n = 7). In each of the groups studied, apo A-IV was distributed in two distinct pools; a high-density lipoprotein-(HDL) associated pool and a lipoprotein-free pool. However, compared to normal, the distribution of apo A-IV in WHHL rabbit sera was shifted towards the lipoprotein-free pool. Consistent with previously reported observations on apo A-I, these results are compatible with the hypothesis of an impaired reverse transport of cholesterol in WHHL rabbits, an animal model for familial hypercholesterolemia.

Apolipoprotein A-IV polymorphism in the Hungarian population: gene frequencies, effect on lipid levels, and sequence of two new variants

The genetic polymorphism of human apolipoprotein A-IV was investigated in Hungarian blood donors (n = 202) by isoelectric focusing (IEF) of plasma samples followed by immunoblotting. The frequency of apo A-IV alleles was f(A-IV1) = 0.95, f(A-IV2) = 0.039 and f(A-IV3) = 0.002. This frequency distribution is significantly different from other Caucasian populations (P < 0.05). The association of apo A-IV phenotypes with HDL-cholesterol concentration which was previously described for two other European populations was only of borderline significance (P = 0.08). Three previously undescribed apo A-IV variants, designated Budapest-1, Budapest-2 and Budapest-3, were detected by IEF. The mutant proteins are not associated with alterations in the lipid/lipoprotein concentrations in heterozygotes. DNA-sequencing revealed two point mutations (Arg285-->Cys and Thr347-->Ser) in exon 3 of apo A-IV-Budapest-1 and a Glu-->Lys substitution at position 24 in exon 2 of apo A-IV-Budapest-2.