Apolipoprotein AV

Association between different metabolic phenotypes of obesity and thyroid disorders among Chinese adults: a nationwide cross-sectional study

Background

Increased body mass index (BMI) and metabolic abnormalities both have potential associations with thyroid disease. The aim of this study was to investigate the correlation between different metabolic phenotypes of obesity and thyroid disorders using nationwide data from China.

Methods

Data were collected from a cross-sectional survey called the Thyroid Disorders, Iodine Status, and Diabetes Epidemiological Survey conducted between 2015 and 2017 in China. A total of 69007 subjects aged 18 years or older were defined and divided into six groups on the basis of BMI and metabolic health status: metabolically healthy normal weight (MHNW), metabolically unhealthy normal weight (MUNW), metabolically healthy overweight (MHOW), metabolically unhealthy overweight (MUOW), metabolically healthy obesity (MHO), and metabolically unhealthy obesity (MUO). We estimated the odds ratios (ORs) and confidence intervals [CIs] for different thyroid disorders according to metabolic phenotypes using multivariate logistic regression models.

Results

In our study, we found that the prevalence of subclinical hypothyroidism was almost as high in the MUNW group as in the MUO group, the prevalence of overt hyperthyroidism was highest in the MUNW group and Graves' disease was highest in the MHO group. Our results also suggested that the prevalence of goiter and thyroid nodules increased with increased BMI values and that the MUO group had the highest incidence. Multivariate logistic regression analysis indicated that subjects with unhealthy metabolic phenotypes (MUNW, MUOW, and MUO) all had an increased risk of subclinical hypothyroidism, regardless of their BMI. MUNW subjects had an approximately 1.6-fold higher risk of overt hyperthyroidism and a 1.8-fold higher risk of Graves' disease than their metabolically healthy counterparts (MHNW). The present study also demonstrated that the MUO group had the highest risk of goiter and thyroid nodules among the metabolic phenotypes of obesity.

Conclusion

Based on our study, we found that metabolic abnormalities and obesity play different roles in various thyroid diseases. Metabolically unhealthy individuals, both with and without obesity, have a higher risk of thyroid disorders than metabolically healthy individuals without obesity.

Alterations in sorting and secretion of hepatic apoA5 induce hypertriglyceridemia due to short-term use of olanzapine

Long-term use of olanzapine, an antipsychotic drug, induces hypertriglyceridemia, resulting in a higher risk of cardiovascular disease. However, the effects and underlying mechanisms of short-term use of olanzapine on circulating triglyceride levels remain poorly understood. Here, the role of apolipoprotein A5 (apoA5), a regulator of triglyceride metabolism, was investigated in olanzapine-induced hypertriglyceridemia. Our multi-center clinical study recruited 36 schizophrenia patients who received short-term (8 weeks) of olanzapine. Besides, female C57BL/6J mice were treated with olanzapine (3 mg/kg/day versus 6 mg/kg/day) for 6 weeks. We demonstrated that short-term use of olanzapine increased plasma triglyceride and decreased plasma apoA5 levels in the patients and mice, with a negative correlation between the two factors. However, no obesity was observed in the patients and mice. Interestingly, olanzapine increased hepatic apoA5 protein in the mice, without significant changes in hepatic Apoa5 mRNA. Consistently, in vitro studies indicated that olanzapine increased medium triglyceride levels and decreased medium apoA5 levels in a dose-dependent manner in human HepG2 cells and primary mouse hepatocytes. Whereas the olanzapine treatment increased hepatic apoA5 protein in vitro, without effects on hepatic APOA5 mRNA. Of note, olanzapine increased the co-localization between apoA5 protein and accumulated lipid droplets in hepatocytes, as opposed to at the hepatocellular plasma membrane, in mouse liver as demonstrated by fluorescence staining. Therefore, our study indicated that short-term use of olanzapine induced hypertriglyceridemia due to defects of sorting and secretion of hepatic apoA5.

Olanzapine leads to nonalcoholic fatty liver disease through the apolipoprotein A5 pathway

The antipsychotic drug olanzapine was reported to induce nonalcoholic fatty liver disease (NAFLD), whereas the underlying mechanism remains incompletely understood. This study investigated whether apolipoprotein A5 (apoA5) and sortilin, two interactive factors involved in NAFLD pathogenesis, are implicated in olanzapine-induced NAFLD. In our study, at week 8, olanzapine treatment successfully induced hepatic steatosis in female C57 BL/6 J mice, which was independent of body weight gain. Likewise, olanzapine effectively mediated hepatocyte steatosis in HepG2 cells characterized by substantially elevated intracellular lipid droplets. Increased plasma triglyceride concentration and decreased plasma apoA5 levels were observed in mice treated with 8-week olanzapine. Surprisingly, olanzapine markedly enhanced hepatic apoA5 protein levels in mice, without a significant effect on rodent hepatic ApoA5 mRNA. Our in vitro study showed that olanzapine reduced apoA5 protein levels in the medium and enhanced apoA5 protein levels in hepatocytes, whereas this drug exerted no effect on hepatocyte APOA5 mRNA. By transfecting APOA5 siRNA into HepG2 cells, it was demonstrated that APOA5 knockdown effectively reversed olanzapine-induced hepatocyte steatosis in vitro. In addition, olanzapine drastically increased sortilin mRNA and protein levels in vivo and in vitro. Interestingly, SORT1 knockdown reduced intracellular apoA5 protein levels and increased medium apoA5 protein levels in vitro, without affecting intracellular APOA5 mRNA levels. Furthermore, SORT1 knockdown greatly ameliorated hepatocyte steatosis in vitro. This study provides the first evidence that sortilin inhibits the hepatic apoA5 secretion that is attributable to olanzapine-induced NAFLD, which provides new insight into effective strategies against NAFLD for patients with schizophrenia administered olanzapine.

Lipidomic differentiation of Graves' ophthalmopathy in plasma and urine from Graves' disease patients

Approximately 50% of patients with Graves' disease (GD) develop retracted eyelids with bulging eyes, known as Graves' ophthalmopathy (GO). However, no simple diagnostic blood marker for distinguishing GO from GD has been developed yet. The objective of this study was to conduct comprehensive profiling of lipids using plasma and urine samples from patients with GD and GO undergoing antithyroid therapy using nanoflow ultrahigh performance liquid chromatography electrospray ionization tandem mass spectrometry. Plasma (n = 86) and urine (n = 75) samples were collected from 23 patients with GD without GO, 31 patients with GO, and 32 healthy controls. Among 389 plasma and 273 urinary lipids that were structurally identified, 281 plasma and 191 urinary lipids were quantified in selected reaction monitoring mode. High-abundance lipids were significantly altered, indicating that the development of GD is evidently related to altered lipid metabolism in both plasma and urine. Several urinary lysophosphatidylcholine species were found to be increased (3- to 10-fold) in both GD and GO. While the overall lipid profiles between GD and GO were similar, significant changes (area under receiver operating curve > 0.8) in GO vs. GD were observed in a few lipid profiles: 58:7-TG and (16:1,18:0)-DG from plasma, 16:1-PC and 50:1-TG from urine, and d18:1-S1P from both plasma and urine samples. An altered metabolism of lipids associated with the additional development of ophthalmopathy was confirmed with the discovery of several candidate markers. These can be suggested as candidate markers for differentiating the state of GO and GD patients based on plasma or urinary lipidomic analysis. Graphical abstract.

Association Between Thyroid Function and Development of Different Obesity Phenotypes in Euthyroid Adults: A Nine-Year Follow-Up

BACKGROUND

Considering inconsistent and conflicting data on associations of thyroid function, within the reference range, with anthropometric measures and metabolic syndrome, this study aimed to investigate the relationship between thyroid function and different obesity phenotypes over nine years of follow-up.

METHODS

This study was conducted on 1938 individuals from an ongoing population-based cohort study, the Tehran Thyroid Study. Participants were categorized into four obesity phenotypes based on body mass index and metabolic status. To investigate the associations of thyrotropin and free thyroxine (fT4) with incidence of different obesity phenotypes across the study period, a multivariate approach based on a generalized estimating equation method was used.

RESULTS

At baseline, individuals with the metabolically healthy normal weight (MHNW) phenotype had higher serum fT4 levels (1.2 ± 0.16 ng/dL vs. 1.14 ± 0.14 ng/dL, 1.16 ± 0.14 ng/dL, and 1.17 ± 0.15 ng/dL in metabolically healthy obese [MHO], metabolically unhealthy normal weight, and metabolically unhealthy obese individuals, respectively). The results of the generalized estimating equation analysis after multivariate adjustment for age, sex, smoking, physical activity, education level, thyroid peroxidase antibody status, and homeostasis model assessment-insulin resistance showed that each 1 ng/dL increment in fT4 levels within the reference range was accompanied with a 1.65-fold [confidence interval (CI) 1.09-2.5] increase of developing the MHNW phenotype during 9.2 years of follow-up. Moreover, each 1.0 ng/dL increment in fT4 within the reference range was associated with a 50% decreased risk of developing the MHO phenotype (odds ratio = 0.50 [CI 0.32-0.76]). Meanwhile, a significant positive association was found between serum thyrotropin levels and development of the metabolically unhealthy normal weight phenotype (odds ratio = 1.22 [CI 1.01-1.48]).

CONCLUSIONS

Serum fT4 concentrations within the reference range are associated with the development of some obesity phenotypes, including the MHNW and MHO phenotypes, after consideration of potential confounders.

Thyroid, cortisol and growth hormone levels in adult Nigerians with metabolic syndrome

Introduction

The similarities in presentation of cortisol excess, growth hormone deficiency, hypothyroidism and metabolic syndrome suggest that subtle abnormalities of these endocrine hormones may play a causal role in the development of metabolic syndrome. The aim of this study is to determine the levels of cortisol, thyroid and growth hormones in adult Nigerians with metabolic syndrome and determine the relationship between levels of these hormones and components of the syndrome.

Methods

This was a case control study conducted at the Lagos University Teaching Hospital, Lagos, Nigeria. Participants were fifty adult men and women with the metabolic syndrome, and fifty, age and sex matched males and females without the metabolic syndrome. Metabolic syndrome was defined based on the NCEP-ATPIII criteria. Written Informed consent was obtained from the participants. Socio demographic and clinical data were collected using a structured questionnaire. Venous blood was collected after an over-night fast. The Ethics committee of the Lagos University Teaching Hospital, Lagos, Nigeria, approved the study protocol. Comparison of continuous variables was done using the Student's t test. Correlation analysis was employed to determine the associations between variables. Statistical significance was set at P<0.05.

Results

Triiodotyronine (T3) was significantly decreased (p<0.001) and thyroxine (T4 ) significantly increased ( p<0.001) in metabolic syndrome compared to healthy controls. T3 correlated positively and significantly with waist circumference (p=0.004), glucose (p= 0.002), total cholesterol ( p=0.001) and LDL- cholesterol ( p<0.001 ) and negatively with body mass index ( p<0.001 )and triglyceride ( p=0.026). T4 had a negative significant correlation with waist circumference (p=0.004). Cortisol and growth hormone levels were similar in metabolic syndrome and controls. Cortisol however had a positive significant correlation with waist/hip ratio (p<0.001) while growth hormone correlated positively with HDL ( p=0.023)and negatively with diastolic blood pressure (p=0.049).

Conclusion

Thyroid hormones T3 and T4 were associated with metabolic syndrome. The thyroid hormones, cortisol and growth hormones correlated with components of the syndrome. A therapeutic role may exit for these hormones in the management of metabolic syndrome and related disorders.

A Study of the Extended Lipid Profile including Oxidized LDL, Small Dense LDL, Lipoprotein (a) and Apolipoproteins in the Assessment of Cardiovascular Risk in Hypothyroid Patients

INTRODUCTION

Hypothyroidism is one of the most common metabolic disorders associated with dyslipidemia which poses a higher risk of Coronary Artery Disease (CAD) in such patients. Biochemical markers which can pick up the risk promptly are becoming imperative now-a-days and thus the assessment beyond the conventional lipid profile is the need of the hour.

AIMS

To assess the association of non-conventional lipid parameters like small dense Low Density Lipoprotein (sd LDL), oxidized Low Density Lipoprotein (ox LDL), Apolipoprotein A (Apo A1), Apolipoprotein B (Apo B) and Lipoprotein (a) {Lp(a)} in hypothyroid patients and compare their values with the conventional lipid parameters such as Total Cholesterol (TC), Triglyceride (TG), Low-Density Lipoprotein Cholesterol (LDL-C) and High-Density Lipoprotein Cholesterol (HDL-C).

MATERIALS AND METHODS

One hundred and thirty clinically proven patients of hypothyroidism aged 20-60 years and equal number of age and gender matched healthy individuals were included in this case control study. Serum sd LDL, ox LDL, Apo A1, Apo B, Lp (a), lipid profile, Thyroid Stimulating Hormone (TSH), Free Triiodothyronine (FT3) and Free Tetraiodothyronine (FT4) levels were measured in both the groups. The data was recorded and analysed on SPSS system. The results of cases and controls were compared by student t-test and one-way ANOVA. All the parameters were correlated with TSH by Pearson's correlation.

RESULTS

We found significantly high levels of sd LDL, ox LDL, Apo B, Lp (a), TC, TG, LDL-C in cases as compared to the controls. Ox LDL has shown maximum correlation with serum TSH (p<0.0001, r=0.801) followed by sd LDL (p<0.0001, r=0.792), Apo B (p<0.001, r=0.783) and LDL-C (p<0.001, r=0.741). Moreover, ox LDL and sd LDL were found to be increased in normolipidemic hypothyroid patients thereby giving a strong supportive evidence that estimation of these parameters can become fundamental in prompt identification of the high risk patients of CAD in hypothyroid population.

CONCLUSION

Non-conventional lipid parameters appear to be better markers for the assessment of cardiovascular risk in hypothyroidism and might help in the designing of the effective treatment protocols and areas of intervention by the clinicians as well as researchers.

APOA5 Q97X mutation identified through homozygosity mapping causes severe hypertriglyceridemia in a Chilean consanguineous family

Background

Severe hypertriglyceridemia (HTG) has been linked to defects in LPL, APOC2, APOA5, LMF1 and GBIHBP1 genes. However, a number of severe HTG cases are probably caused by as yet unidentified mutations. Very high triglyceride plasma levels (>112 mmol/L at diagnosis) were found in two sisters of a Chilean consanguineous family, which is strongly suggestive of a recessive highly penetrant mutation. The aim of this study was to determine the genetic locus responsible for the severe HTG in this family.

Methods

We carried out a genome-wide linkage study with nearly 300,000 biallelic markers (Illumina Human CytoSNP-12 panel). Using the homozygosity mapping strategy, we searched for chromosome regions with excess of homozygous genotypes in the affected cases compared to non-affected relatives.

Results

A large homozygous segment was found in the long arm of chromosome 11, with more than 2,500 consecutive homozygous SNP shared by the proband with her affected sister, and containing the APOA5/A4/C3/A1 cluster. Direct sequencing of the APOA5 gene revealed a known homozygous nonsense Q97X mutation (p.Gln97Ter) found in both affected sisters but not in non-affected relatives nor in a sample of unrelated controls.

Conclusion

The Q97X mutation of the APOA5 gene in homozygous status is responsible for the severe hypertriglyceridemia in this family. We have shown that homozygosity mapping correctly pinpointed the genomic region containing the gene responsible for severe hypertriglyceridemia in this consanguineous Chilean family.

Nutrigenomics: a case for the common soil between cardiovascular disease and cancer

The border between health and disease is often set by a complex equilibrium between two elements, genetics on one hand, lifestyle on the other, To know it better, means to give new weapons, often crucial, in the hands of the doctors and their patients. It also means to adjust therapies, to find out which drug is good for a patient and which prevention strategy will work better for him/her. Nutrigenomics is an approach to individualize or personalize food and nutrition, and ultimately health, by tailoring the food to the individual genotype. In this review, we present the interaction between certain genetic polymorphisms and diet and increased cardiovascular or cancer risk. It is, indeed, now clear that a large number of bioactive food components may provide risk or protection at several stages of both atherosclerosis and cancer formation processes. We are giving here few examples of gene-food interactions relevant for both the risk of cardiovascular disease and cancer, since a common soil could exist in the genesis of cardiovascular disease and of some types of cancer (mainly gastrointestinal tract and hormone-dependent).

The paradox of ApoA5 modulation of triglycerides: evidence from clinical and basic research

Apolipoprotein A5 (ApoA5) is a key regulator of plasma triglycerides (TG), even though its plasma concentration is very low compared to other known apoproteins. Over the years, researchers have attempted to elucidate the molecular mechanisms by which ApoA5 regulates plasma TG in vivo. Though still under debate, two theories broadly describe how ApoA5 modulates TG levels: (i) ApoA5 enhances the catabolism of TG-rich lipoproteins and (ii) it inhibits the rate of production of very low-density lipoprotein (VLDL), the major carrier of TGs. This review will summarize the basic and clinical studies that describe the importance of ApoA5 in TG metabolism. Population studies conducted in various countries have demonstrated an association between single nucleotide polymorphisms (SNPs) in ApoA5 and the increased risk to cardiovascular disease and metabolic syndrome (including diabetes and obesity). ApoA5 is also highly expressed during liver regeneration and is an acute phase protein associated with HDL, which is independent of its effects on TG metabolism.

CONCLUSION

Despite considerable evidences available from clinical and basic research studies on the role of ApoA5 in TG metabolism and its indirect link to metabolic diseases, additional investigations are needed to understand the paradoxical role of this important apoprotein is modulated by both diet and its polymorphism variants.

Rat chromosome 8 confers protection against dyslipidemia caused by a high-fat/low-carbohydrate diet

BACKGROUND/AIMS

Recent studies have highlighted the importance of gene by diet interactions in contributing to risk factors of metabolic syndrome. We used a consomic rat panel, in which a chromosome of the Brown Norway (BN) strain is introgressed onto the background of the Dahl salt-sentitive (SS) strain, to test the hypothesis that these animals will be useful for dissecting gene by diet interactions involved in metabolic syndrome.

METHODS

We placed the parental SS and BN strains on a low-fat/high-carbohydrate (LF) or high-fat/low-carbohydrate (HF) diet for 22 weeks and measured several indices of metabolic syndrome. We then investigated the effect of diet in eight consomic rat strains.

RESULTS

We show that the HF diet resulted in significantly increased levels of fasting plasma cholesterol and triglycerides in the SS strain, with no effect in the BN. Both strains responded to the HF diet with slight increases in body weight. SSBN8 was the only consomic strain that resembled that of the BN, with low levels of fasting cholesterol and triglycerides even on the HF diet.

CONCLUSIONS

These results indicate that BN chromosome 8 harbors a gene or genes that confer protection against dyslipidemia caused by the HF diet.

Synthesis of recombinant high density lipoprotein with apolipoprotein A-I and apolipoprotein A-V

It has been shown that apolipoprotein A-V (apoA-V) over-expression significantly lowers plasma triglyceride levels and decreases atherosclerotic lesion development. To assess the feasibility of recombinant high density lipoprotein (rHDL) reconstituted with apoA-V and apolipoprotein A-I (apoA-I) as a therapeutic agent for hyperlipidemic disorder and atherosclerosis, a series of rHDL were synthesized in vitro with various mass ratios of recombinant apoA-I and apoA-V. It is interesting to find that apoA-V of rHDL had no effect on lipoprotein lipase (LPL) activation in vitro and very low density lipoprotein (VLDL) clearance in HepG2 cells and in vivo. By contrast, LPL activation and VLDL clearance were inhibited by the addition of apoA-V to rHDL. Furthermore, the apoA-V of rHDL could not redistribute from rHDL to VLDL after incubation at 37°C for 30 min. These findings suggest that an increase of apoA-V in rHDL could not play a role in VLDL clearance in vitro and in vivo, which could, at least in part, attribute to the lost redistribution of apoA-V from rHDL to VLDL and LPL binding ability of apoA-V in rHDL. The therapeutic application of rHDL reconstituted with apoA-V and apoA-I might need the construction of rHDL from which apoA-V could freely redistribute to VLDL.

Effects of thyroid dysfunction on lipid profile

Thyroid dysfunction has a great impact on lipids as well as a number of other cardiovascular risk factors. Hypothyroidism is relatively common and is associated with an unfavorable effect on lipids. Substitution therapy is beneficial for patients with overt hypothyroidism, improving lipid profile. However, whether subclinical hypothyroidism should be treated or not is a matter of debate. On the other hand, hyperthyroidism can be associated with acquired hypocholesterolemia or unexplained improvement of lipid profile. Overall, thyroid dysfunction should be taken into account when evaluating and treating dyslipidemic patients.

A triglyceride-raising APOA5 genetic variant is negatively associated with obesity and BMI in the Chinese population

Apolipoprotein A-V (apo A-V) exerts a potent triglyceride (TG)-lowering effect through enhanced intravascular TG-hydrolysis with increased uptake of TG-derived free fatty acids into muscle and adipose tissue. Genetic variants in the APOA5 gene were strongly associated with plasma TG concentrations. The aim of this study was to examine whether APOA5 genetic variation was associated with obesity. We genotyped the missense c.553 G>T polymorphism (p.G185C) in the APOA5 gene in 1,085 Chinese (333 obese subjects and 752 nonobese controls). We analyzed the association between the c.553 G>T polymorphism and obesity and related metabolic phenotypes. The T allele at the c.553 G>T polymorphism was associated with higher plasma TG concentrations. Each additional T allele was associated with an increased TG concentration of 53.5 mg/dl (95% confidence interval (CI) 29.6-76.0, P < 0.0001). However, the T allele was associated lower risk of obesity (odds ratio (OR), 0.48; 95% CI 0.32-0.73, P = 0.0004). Each additional copy of the T allele was associated with a BMI decrease of 0.73 kg/m(2) (95% CI 0.26-1.16, P = 0.002), equivalent to 2.11 kg in a person 1.7 m tall. We may then conclude that the TG-raising APOA5 genetic variant was associated with a decrease in BMI and reduced risk of obesity in the Chinese population.

Interactions between the APOA5 -1131T>C and the FEN1 10154G>T polymorphisms on ω6 polyunsaturated fatty acids in serum phospholipids and coronary artery disease

We determined the contribution of the combination of FEN1 10154G>T with the most significant association in the analysis of plasma arachidonic acid (AA, 20:4ω6) and the APOA5-1131T>C on phospholipid ω6PUFA and coronary artery disease (CAD). Patients with CAD (n = 807, 27-81 years of age) and healthy controls (n = 1123) were genotyped for FEN1 10154G>T and APOA5-1131T>C. We found a significant interaction between these two genes for CAD risk (P = 0.007) adjusted for confounding factors. APOA5-1131C allele carriers had a higher CAD risk [odds ratio (OR):1.484, 95% confidence interval (CI):1.31-1.96; P = 0.005] compared with APOA5-1131TT individuals in the FEN1 10154GG genotype group but not in the FEN1 10154T allele group (OR:1.096, 95%CI:0.84-1.43; P = 0.504). Significant interactions between these two genes were also observed for the AA proportion (P = 0.04) and the ratio of AA/linoleic acid (LA, 18:2ω6) (P = 0.004) in serum phospholipids of controls. The APOA5-1131C allele was associated with lower AA (P = 0.027) and AA/LA (P = 0.014) only in controls carrying the FEN1 10154T allele. In conclusion, the interaction between these genes suggests that the FEN1 10154T variant allele decreases AA and AA/LA in the serum phospholipids of carriers of the APOA5-1131C allele, but contributes no significant increase in CAD risk for this population subset despite their increased triglylcerides and decreased apoA5.

Molecular cloning, expression and polymorphism of the porcine apolipoprotein A5 gene in a Jinhua × Pietrain F2 reference population

As a newly described member of the apolipoprotein gene family, apolipoprotein A5 (APOA5) has been suggested to play a key role in the triglyceride metabolism in both human and mice. The aim of this study was to identify the porcine (Sus scrofa) APOA5 gene, determine its mRNA and its mutations that are associated with lipid accumulation. The porcine APOA5 cDNA was amplified by reverse transcriptase polymerase chain reaction using the information of the mouse or other mammals. It had been determined that the open reading frame of the porcine APOA5 gene consists of 1092 bp, which encodes a predicted protein composed of 363 amino acids with a similarity to bovine (80.43%) and to human (78.47%). The expression analysis indicated that the porcine APOA5 gene was expressed in hypophysis, fat and liver. Twelve single nucleotide polymorphisms (SNPs), including 4 SNPs in the 5' end, 1 SNP in second intron, 1 SNP in third exon and 6 SNPs in the 3' end, were identified in the porcine APOA5 gene and genotyped on the Jinhua × Pietrain F2 reference population, it had revealed that the SNP of C1834T was significantly associated with average backfat thickness and leaf fat weight (P < 0.01 and P < 0.05, respectively). In conclusion, this study has got basic information of the porcine APOA5 gene and provides evidence that the APOA5 gene could be a potential candidate gene for fat deposition.

Atheroprotective effect of human apolipoprotein A5 in a mouse model of mixed dyslipidemia

Hypertriglyceridemia is an independent risk factor for coronary artery disease. Because apolipoprotein (Apo)A5 regulates plasma triglyceride levels, we investigated the impact of human (h)ApoA5 on atherogenesis. The influence of hApoA5 transgenic expression was studied in the ApoE2 knock-in mouse model of mixed dyslipidemia. Our results demonstrate that hApoA5 lowers plasma triglyceride levels in Western diet-fed ApoE2 knock-in mice. Moreover, atherosclerotic lesion development was significantly decreased in the hApoA5 transgenic mice. Finally, pharmacologic activation of hApoA5 expression by the peroxisome proliferator-activated receptor-alpha agonist fenofibrate resulted in an enhanced atheroprotection. These results identify an atheroprotective role of hApoA5 in a mouse model of mixed dyslipidemia.

Apolipoprotein A-V gene polymorphisms in subjects with metabolic syndrome

BACKGROUND

Genetic variation at the apolipoprotein A-V locus, recently discovered proximal to the APOA1/C3/A4 gene cluster, is associated with elevated triglyceride concentrations, a risk factor for atherosclerosis.

METHODS

The goal of our study was to determine the association of two apolipoprotein A-V (APOA5) gene polymorphisms in a group of urban Romanian subjects with the prevalence of the metabolic syndrome. For this purpose, we assayed -1.131T>C and c.56C>G polymorphisms for 279 subjects divided into three groups: a control group, a metabolic syndrome group and a cardiovascular disease group. Then we correlated the minor allele frequencies with body mass index and biochemical parameters.

RESULTS

We obtained higher frequency for -1.131C compared to c.56G alleles, both mainly distributed in overweight subjects. Body mass index and triglyceride levels were higher in -1.131C allele carriers in metabolic syndrome patients, but were not significantly different in c.56G carriers compared to those with the native gene. Metabolic syndrome -1.131C homozygotes presented lower high-density lipoprotein cholesterol and higher glucose levels compared to subjects with the native gene. Total cholesterol, low-density lipoprotein cholesterol and insulin were not different between -1.131C or c.56G allele carriers and those with the native gene.

CONCLUSIONS

Our results demonstrate an independent risk for -1.131T>C APOA5 gene polymorphisms in the development of metabolic syndrome.

GPIHBP1: an endothelial cell molecule important for the lipolytic processing of chylomicrons

PURPOSE OF REVIEW

To summarize recent data indicating that glycosylphosphatidylinositol-anchored high density lipoprotein-binding protein 1 (GPIHBP1) plays a key role in the lipolytic processing of chylomicrons.

RECENT FINDINGS

Lipoprotein lipase hydrolyses triglycerides in chylomicrons at the luminal surface of the capillaries in heart, adipose tissue, and skeletal muscle. The endothelial cell molecule that facilitates the lipolytic processing of chylomicrons has never been clearly defined. Mice lacking GPIHBP1 manifest chylomicronemia, with plasma triglyceride levels as high as 5000 mg/dl. In wild-type mice, GPIHBP1 is expressed on the luminal surface of capillaries in heart, adipose tissue, and skeletal muscle. Cells transfected with GPIHBP1 bind both chylomicrons and lipoprotein lipase avidly.

SUMMARY

The chylomicronemia in Gpihbp1-deficient mice, the fact that GPIHBP1 is located within the lumen of capillaries, and the fact that GPIHBP1 binds lipoprotein lipase and chylomicrons suggest that GPIHBP1 is a key platform for the lipolytic processing of triglyceride-rich lipoproteins.

Effects of apoA-V on HDL and VLDL metabolism in APOC3 transgenic mice

Apolipoprotein A-V (apoA-V) and apoC-III are exchangeable constituents of VLDL and HDL. ApoA-V counteracts the effect of apoC-III on triglyceride (TG) metabolism with poorly defined mechanisms. To better understand the effects of apoA-V on TG and cholesterol metabolism, we delivered apoA-V cDNA into livers of hypertriglyceridemic APOC3 transgenic mice by adenovirus-mediated gene transfer. In response to hepatic apoA-V production, plasma TG levels were reduced significantly as a result of enhanced VLDL catabolism without alternations in VLDL production. This effect was associated with reduced apoC-III content in VLDL. Increased apoA-V production also resulted in decreased apoC-III and increased apoA-I content in HDL. Furthermore, apoA-V-enriched HDL was associated with enhanced LCAT activity and increased cholesterol efflux. This effect, along with apoE enrichment in HDL, contributed to HDL core expansion and alpha-HDL formation, accounting for significant increases in both the number and size of HDL particles. As a result, apoA-V-treated APOC3 transgenic mice exhibited decreased VLDL-cholesterol and increased HDL-cholesterol levels. ApoA-V-mediated reduction of apoC-III content in VLDL represents an important mechanism by which apoA-V acts to ameliorate hypertriglyceridemia in adult APOC3 transgenic mice. In addition, increased apoA-V levels accounted for cholesterol redistribution from VLDL to larger HDL particles. These data suggest that in addition to its TG-lowering effect, apoA-V plays a significant role in modulating HDL maturation and cholesterol metabolism.

Marked decrease of apolipoprotein A-V in both diabetic and nondiabetic patients with end-stage renal disease

Apolipoprotein (apo) A-V has been the focus of significant attention as a potential modulator of plasma triglyceride (TG) in spite of its very low plasma concentration. TG levels are frequently elevated in patients with end-stage renal disease (ESRD), which is associated with a high prevalence of cardiovascular disease among them. We measured plasma apo A-V levels in 20 control subjects and 70 patients with diabetic and nondiabetic ESRD to investigate whether low apo A-V levels could be involved in the pathogenesis of the hyper-TG in ESRD. The plasma TG levels were significantly elevated in diabetic patients with ESRD, whereas those in nondiabetic ESRD patients remained similar to those in the controls. High-density lipoprotein cholesterol levels were significantly lower in the patients with ESRD than in the controls, irrespective of the presence of diabetes. Apo A-V levels measured by an enzyme-linked immunosorbent assay were markedly reduced to 40% to 44% of the control levels in both diabetic and nondiabetic patients with ESRD. The apo A-V levels were not correlated with TG in the overall study population, but they were positively correlated with high-density lipoprotein cholesterol. These results suggest that reduced apo A-V levels do not necessarily lead to hyper-TG in ESRD, but we are unable to exclude the possibility that low apo A-V plays a role in raising the TG level in diabetic ESRD.

Apolipoprotein A-V, triglycerides and risk of coronary artery disease: the prospective Epic-Norfolk Population Study

In mouse models, apolipoprotein A-V (apoA-V) exhibits triglyceride (TG)-lowering effects. We investigated the apoA-V/TG relationship and the association of apoA-V with coronary artery disease (CAD) risk by determining serum apoA-V levels and genotypes in a nested case-control (n = 1,034/2,031) study. Both univariate and multivariate apoA-V levels showed no association with future CAD (P = 0.4 and 0.5, respectively). Unexpectedly, there was a significant positive correlation between serum apoA-V and TG in men and women (r = 0.36 and 0.28, respectively, P < 0.001 each) but a negative correlation between apoA-V and LPL mass (r = -0.14 and -0.12 for men and women respectively, P < 0.001 each). The frequency of the c.56C>G polymorphism did not differ between cases and controls despite significant positive association of c.56G with both apoA-V and TG levels. For -1131T>C, the minor allele was significantly associated with lower apoA-V yet higher TG levels and was overrepresented in cases (P = 0.047). The association of -1131T>C with CAD risk, however, was independent of apoA-V levels and likely acts through linkage disequilibrium with APOC3 variants. The positive correlation of apoA-V levels with TG levels, negative correlation with LPL levels, and lack of association with CAD risk highlight the need for further human studies to clarify the role of apoA-V.

Dietary intake of n-6 fatty acids modulates effect of apolipoprotein A5 gene on plasma fasting triglycerides, remnant lipoprotein concentrations, and lipoprotein particle size: the Framingham Heart Study

BACKGROUND

Apolipoprotein A5 gene (APOA5) variation is associated with plasma triglycerides (TGs). However, little is known about whether dietary fat modulates this association.

METHODS AND RESULTS

We investigated the interaction between APOA5 gene variation and dietary fat in determining plasma fasting TGs, remnant-like particle (RLP) concentrations, and lipoprotein particle size in 1001 men and 1147 women who were Framingham Heart Study participants. Polymorphisms -1131T>C and 56C>G, representing 2 independent haplotypes, were analyzed. Significant gene-diet interactions between the -1131T>C polymorphism and polyunsaturated fatty acid (PUFA) intake were found (P<0.001) in determining fasting TGs, RLP concentrations, and particle size, but these interactions were not found for the 56C>G polymorphism. The -1131C allele was associated with higher fasting TGs and RLP concentrations (P<0.01) in only the subjects consuming a high-PUFA diet (>6% of total energy). No heterogeneity by sex was found. These interactions showed a dose-response effect when PUFA intake was considered as a continuous variable (P<0.01). Similar interactions were found for the sizes of VLDL and LDL particles. Only in carriers of the -1131C allele did the size of these particles increase (VLDL) or decrease (LDL) as PUFA intake increased (P<0.01). We further analyzed the effects of n-6 and n-3 fatty acids and found that the PUFA-APOA5 interactions were specific for dietary n-6 fatty acids.

CONCLUSIONS

Higher n-6 (but not n-3) PUFA intake increased fasting TGs, RLP concentrations, and VLDL size and decreased LDL size in APOA5 -1131C carriers, suggesting that n-6 PUFA-rich diets are related to a more atherogenic lipid profile in these subjects.