Intestinal fatty acid binding protein and microsomal triglyceride transfer protein polymorphisms in French-Canadian youth

From Congenital Disorders of Fat Malabsorption to Understanding Intra-Enterocyte Mechanisms Behind Chylomicron Assembly and Secretion

During the last two decades, a large body of information on the events responsible for intestinal fat digestion and absorption has been accumulated. In particular, many groups have extensively focused on the absorptive phase in order to highlight the critical "players" and the main mechanisms orchestrating the assembly and secretion of chylomicrons (CM) as essential vehicles of alimentary lipids. The major aim of this article is to review understanding derived from basic science and clinical conditions associated with impaired packaging and export of CM. We have particularly insisted on inborn metabolic pathways in humans as well as on genetically modified animal models (recapitulating pathological features). The ultimate goal of this approach is that "experiments of nature" and in vivo model strategy collectively allow gaining novel mechanistic insight and filling the gap between the underlying genetic defect and the apparent clinical phenotype. Thus, uncovering the cause of disease contributes not only to understanding normal physiologic pathway, but also to capturing disorder onset, progression, treatment and prognosis.

Associations of the lipid genetic variants Thr54 ( FABP2) and -493T ( MTTP) with total cholesterol and low-density lipoprotein cholesterol levels in Mexican subjects

Objective Mexico has one of the world's highest rates of obesity, which is influenced by lipid-genetic and lifestyle factors. This study aimed to determine whether FABP2 (Ala54Thr) and MTTP (-493 G/T) genetic polymorphisms are associated with metabolic disorders in Mexican subjects. Methods A total of 523 subjects participated in a cross-sectional study. Genotyping for FABP2 and MTTP was performed using real-time RT-PCR. Biochemical and anthropometric data were evaluated. Results The genetically at-risk group (Thr54/-493T) was associated with significantly higher total and low-density lipoprotein cholesterol levels (difference between genetically at-risk group and wild-type group: 10.6 mg/dL and 8.94 mg/dL, respectively). Carriers within the genetically at-risk group had a significantly higher prevalence rate of hypercholesterolaemia (42.5% vs. 32.0%) and higher LDL-C levels (37.6% vs. 26.4%) than did non-carriers. Conclusions Subjects who are genetically at risk (Thr54/-493T) have higher total cholesterol levels, low-density lipoprotein cholesterol levels, and prevalence rate of hypercholesterolaemia. These findings highlight the importance of basing nutritional intervention strategies for preventing and treating chronic diseases on individual genetic characteristics.

Association of MTTP gene variants with pediatric NAFLD: A candidate-gene-based analysis of single nucleotide variations in obese children

Objective

We used targeted next-generation sequencing to investigate whether genetic variants of lipid metabolism-related genes are associated with increased susceptibility to nonalcoholic fatty liver disease (NAFLD) in obese children.

Methods

A cohort of 100 obese children aged 6 to 18 years were divided into NAFLD and non-NAFLD groups and subjected to hepatic ultrasound, anthropometric, and biochemical analyses. We evaluated the association of genetic variants with NAFLD susceptibility by investigating the single nucleotide polymorphisms in each of 36 lipid-metabolism-related genes. The panel genes were assembled for target region sequencing. Correlations between single nucleotide variations, biochemical markers, and clinical phenotypes were analyzed.

Results

97 variants in the 36 target genes per child were uncovered. Twenty-six variants in 16 genes were more prevalent in NAFLD subjects than in in-house controls. The mutation rate of MTTP rs2306986 and SLC6A2 rs3743788 was significantly higher in NAFLD subjects than in non-NAFLD subjects (OR: 3.879; P = 0.004; OR: 6.667, P = 0.005). Logistic regression analysis indicated the MTTP variant rs2306986 was an independent risk factor for NAFLD (OR: 23.468, P = 0.044).

Conclusions

The results of this study, examining a cohort of obese children, suggest that the genetic variation at MTTP rs2306986 was associated with higher susceptibility to NAFLD. This may contribute to the altered lipid metabolism by disruption of assembly and secretion of lipoprotein, leading to reducing fat export from the involved hepatocytes.

Polymorphism Ala54Thr of fatty acid-binding protein 2 gene is not associated with stroke risk in Han population of Hunan China

Background

It is still unclear which genetic factors have a role in stroke. Studies have found that Ala54Thr of Fatty Acid-Binding Protein 2 (FABP2) was associated with stroke risk. This study aimed to determine whether polymorphism Ala54Thr of FABP2 is associated with stroke risk in the Hunan Han population of China.

Material/Methods

A total of 206 cerebral infarction (CI) patients, 185 cerebral hemorrhage (CH) patients, and 172 controls were enrolled in this study. Ala54Thr genotyping was done by polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP).

Results

No significant difference was observed in genotypic distribution of FABP2 Ala54Thr between the stroke group (CI subgroup, CH subgroup included) and control group. In the stroke group, plasma triglycerides (TG) levels of subjects who carried Ala/Thr, Thr/Thr were significantly higher than those carrying Ala/Ala. In the control group, blood lipids were not significantly different among 3 genotypes of Ala54Thr. There was no significant difference in blood pressure and fasting blood sugar between the stroke group and controls.

Conclusions

Our study showed that Ala54Thr of FABP2 may be not associated with stroke risk but may be associated with plasma TG level of stroke patients from a Hunan Han population of China.

Circulating levels of fatty acid-binding protein family and metabolic phenotype in the general population

Objective

Fatty acid-binding proteins (FABPs) are a family of 14-15-kDa proteins, and some FABPs have been to be used as biomarkers of tissue injury by leak from cells. However, recent studies have shown that FABPs can be secreted from cells into circulation. Here we examined determinants and roles of circulating FABPs in a general population.

Methods

From the database of the Tanno-Sobetsu Study, a study with a population-based cohort design, data in 2011 for 296 subjects on no medication were retrieved, and FABP1∼5 in their serum samples were assayed.

Results

Level of FABP4, but not the other isoforms, showed a gender difference, being higher in females than in males. Levels of all FABPs were negatively correlated with estimated glomerular filtration rate (eGFR), but a distinct pattern of correlation with other clinical parameters was observed for each FABP isoform; significant correlates were alanine aminotransferase (ALT), blood pressure (BP), and brain natriuretic peptide (BNP) for FABP1, none besides eGFR for FABP2, age, BP, and BNP for FABP3, age, waist circumference (WC), BP, BNP, lipid variables, high-sensitivity C-reactive protein (hsCRP), and HOMA-R for FABP4, and age, WC, BP, ALT, BNP, and HOMA-R for FABP5. FABP4 is the most strongly related to metabolic markers among FABPs. In a multivariate regression analysis, FABP4 level was an independent predictor of HOMA-R after adjustment of age, gender, WC, BP, HDL cholesterol, and hsCRP.

Conclusions

Each FABP isoform level showed a distinct pattern of correlation with clinical parameters, although levels of all FABPs were negatively determined by renal function. Circulating FABP4 appears to be a useful biomarker for detecting pre-clinical stage of metabolic syndrome, especially insulin resistance, in the general population.

Proteomic and bioinformatics analyses of mouse liver microsomes

Microsomes are derived mostly from endoplasmic reticulum and are an ideal target to investigate compound metabolism, membrane-bound enzyme functions, lipid-protein interactions, and drug-drug interactions. To better understand the molecular mechanisms of the liver and its diseases, mouse liver microsomes were isolated and enriched with differential centrifugation and sucrose gradient centrifugation, and microsome membrane proteins were further extracted from isolated microsomal fractions by the carbonate method. The enriched microsome proteins were arrayed with two-dimensional gel electrophoresis (2DE) and carbonate-extracted microsome membrane proteins with one-dimensional gel electrophoresis (1DE). A total of 183 2DE-arrayed proteins and 99 1DE-separated proteins were identified with tandem mass spectrometry. A total of 259 nonredundant microsomal proteins were obtained and represent the proteomic profile of mouse liver microsomes, including 62 definite microsome membrane proteins. The comprehensive bioinformatics analyses revealed the functional categories of those microsome proteins and provided clues into biological functions of the liver. The systematic analyses of the proteomic profile of mouse liver microsomes not only reveal essential, valuable information about the biological function of the liver, but they also provide important reference data to analyze liver disease-related microsome proteins for biomarker discovery and mechanism clarification of liver disease.

Fatty acid-binding protein-2 genotype influences lipid and lipoprotein response to eicosapentaenoic acid supplementation in hypertriglyceridemic subjects

OBJECTIVE

The blood lipid-lowering effects of eicosapentaenoic acid (EPA) on hypertriglyceridemic subjects with different fatty acid-binding protein-2 (FABP2) genotypes have not, to our knowledge, been previously studied.

METHODS

Twenty-three FABP2 Ala54 and 23 Thr54 carriers with hypertriglyceridemia (triacylglycerol level >200mg/dL) were enrolled in this study. Participants took 2g of pure EPA daily for 8 wk. Fasting blood lipid and lipoprotein profiles were determined and changes from baseline were measured.

RESULTS

Blood lipids and lipoprotein responses of the FABP2 genotypes differed after EPA supplementation. Changes from baseline for triacylglycerol (19.2% decrease for Ala54 and 60.5% for Thr54, P<0.001), very low-density lipoprotein (20.0% decrease for Ala54 and 60.5% for Thr54, P<0.001), apolipoprotein CIII (22.8% decrease for Ala54 and 36.4% for Thr54, P<0.01), and high-density lipoprotein cholesterol (17.6% increase for Ala54 and 30.7% for Thr54, P<0.01) differed significantly between the two carrier groups. However, changes in total cholesterol, low-density lipoprotein cholesterol, and apolipoprotein B were not significant. EPA supplementation increased plasma EPA in Ala54 and Thr54 carriers. Although EPA supplementation increased the level of plasma EPA in both carrier groups, this effect was more pronounced in the Thr54 carriers.

CONCLUSION

Therefore, EPA consumption has more favorable effects on blood lipids of hypertriglyceridemics with Thr54 genotype rather than those with Ala54. The level of plasma EPA increases after EPA supplementation. Because the FABP2 Thr54 polymorphism appears to be prevalent in hypertriglyceridemic subjects, increasing EPA intake in these subjects could be an effective strategy for reducing blood triacylglycerol concentration.

Cholesterol absorption status and fasting plasma cholesterol are modulated by the microsomal triacylglycerol transfer protein -493 G/T polymorphism and the usual diet in women

An important inter-individual variability in cholesterol absorption has been reported. It could result from polymorphisms in genes coding for proteins involved in the absorption process and in interaction with dietary intakes. To assess whether the extent of cholesterol absorption or synthesis is modified in adult women according to the -493 G/T polymorphism in the microsomal triglyceride transfer protein gene (MTP) and/or the habitual diet. Cholestanol and sitosterol, as well as desmosterol and lathosterol, surrogate markers of cholesterol absorption or synthesis, respectively, were analyzed in the fasting plasma of 69 middle-aged women under a Western-type diet (WD) and after 3 months on a low-saturated fat, low-cholesterol/Mediterranean-type diet (LFLCD). Genotypes for MTP -493G/T polymorphism were determined. Under an usual WD, subjects homozygous for the MTP -493 T allele exhibited higher (P < 0.05) fasting serum concentrations of cholestanol (199.0 ± 30.0 vs. 133 ± 7.4 × 10(2 )mmol/mol cholesterol) and lathosterol (188.7 ± 21.8 vs. 147.6 ± 9.1 × 10(2) mmol/mol cholesterol), as well as total cholesterol (7.32 ± 0.22 vs. 6.63 ± 0.12 mmol/l) compared to G carrier subjects. After 3 months on a LFLCD, level of absorption markers decreased in TT subjects with no change in synthesis ones, leading to values comparable to those measured in G carriers. The lowering of plasma total and LDL cholesterol due to dietary change was 2.4- and 2.3-fold greater in TT women than in G carriers. The polymorphism -493G/T in MTP modulates the level of cholesterol absorption but not synthesis in women under a WD, an effect abolished under a prudent LFLCD.

MTTP variants and body mass index, waist circumference and serum cholesterol level: Association analyses in 7582 participants of the KORA study cohort

The microsomal triglyceride transfer protein (MTTP) is a key regulator in the assembly and secretion of chylomicrons and very low density lipoprotein (VLDL) in the intestine and in liver. Associations between MTTP variants and traits of the metabolic syndrome are carried out in relatively small cohorts and are not consistent. We analysed MTTP polymorphisms in 7582 participants of the KORA study cohort. Seven htSNPs covering a 52kb region of the MTTP locus and two cSNPs (I128T, H297Q) were selected. A MTTP haplotype containing the minor allele of H297Q showed a significant decrease of -0.636 (95% CI: -1.226, -0.046; p=0.035) BMI units in females but not in males. In comparison to homozygous H-carriers for the major allele of the MTTP H297Q polymorphism, homozygous Q297Q carriers showed a significant decrease in BMI of -0.425B MI units (95% CI: -0.74, -0.12; p=0.007), in waist circumference of -0.990 cm (95% CI: 1.74, -0.24; p=0.01) and in total cholesterol of -0.039 mmol/l (95% CI: -0.07, 0; p=0.03). Heterozygous Q-carriers displayed a reduction in BMI of -0.183 BMI unit (95% CI: -0.33, -0.04; p=0.012), in waist circumference of -0.45 cm (95% CI: 0.8, -0.1; p=0.01) and in total cholesterol of -0.103 mmol/l (95% CI: -0.18, -0.03; p=0.01). Gender stratified statistics revealed a significant reduction of -0.657 BMI units (95% CI: -1.14, -0.18; p=0.007), -1.437 cm waist circumference (95% CI: -2.55, -0.32; p=0.01) and -0.052 mmol/l total cholesterol (95% CI: -0.1, -0.01; p=0.03) for females homozygous for the Q297Q polymorphism. Females carrying the Q-allele showed a decrease of -0.259 BMI unit (95% CI: -0.48, -0.04; p=0.023), -0.662 cm waist circumference (95% CI: -1.18, -0.14; p=0.01) and -0.111 mmol/l total cholesterol (95% CI: -0.21, -0.01; p=0.03). Our association analysis in a large population based study cohort provides evidence that the minor allele of the MTTP H297Q polymorphism is associated with lower BMI, waist circumference and total cholesterol in females but not in males.

Establishment and characterization of monoclonal and polyclonal antibodies against human intestinal fatty acid-binding protein (I-FABP) using synthetic regional peptides and recombinant I-FABP

We have succeeded in raising highly specific anti-human intestinal fatty acid-binding protein (I-FABP) monoclonal antibodies by immunizing animals with three synthetic regional peptides, i.e., the amino terminal (RP-1: N-acetylated 1-19-cysteine), middle portion (RP-2: cysteinyl-91-107) and carboxylic terminal (RP-3: cysteinyl-121-131) regions of human I-FABP, and the whole I-FABP molecule as antigens. We also raised a polyclonal antibody by immunizing with a recombinant (r) I-FABP. To ascertain the specificity of these antibodies for human I-FABP, the immunological reactivity of each was examined by a binding assay using rI-FABP, partially purified native I-FABP and related proteins such as liver-type (L)-FABP, heart-type (H)-FABP, as well as the regional peptides as reactants, and by Western blot analysis. In addition, the expression and distribution of I-FABP in the human gastrointestinal tract were investigated by an immunohistochemical technique using a carboxylic terminal region-specific monoclonal antibody, 8F9, and a polyclonal antibody, DN-R2. Our results indicated that both the monoclonal and polyclonal antibodies established in this study were highly specific for I-FABP, but not for L-FABP and H-FABP. Especially, the monoclonal antibodies raised against the regional peptides, showed regional specificity for the I-FABP molecule. Immunoreactivity of I-FABP was demonstrated in the mucosal epithelium of the jejunum and ileum by immunohistochemical staining, and the immunoreactivity was based on the presence of the whole I-FABP molecule but not the presence of any precursors or degradation products containing a carboxylic terminal fragment. It is concluded that some of these monoclonal and polyclonal antibodies, such as 8F9, 4205, and DN-R2, will be suitable for use in research on the immunochemistry and clinical chemistry of I-FABP because those antibodies can recognize both types of native and denatured I-FABP. In order to detect I-FABP in blood samples, it is essential to use this type of antibody, reactive to native type of I-FABP. It is anticipated that, in the near future, such a method for measuring I-FABP will be developed as a useful tool for diagnosing intestinal ischemia by using some of these antibodies.

Genetic links between diabetes mellitus and coronary atherosclerosis

Diabetes mellitus is one of the most common endocrine disorders. It affects almost 6% of the world's population, and its prevalence continues to increase. The causes of diabetes mellitus are multifactorial, and in the general population both genetic and environmental factors contribute evenly to its development. Several genes have been consistently associated with type 2 diabetes mellitus; however, it is not clear how many of those translate into increased cardiovascular disease risk. Recent evidence suggests that genetic variation at the CALPN10, FABP4, GK, GST, PPARA, and PPARG loci may confer higher cardiovascular disease risk in patients with type 2 diabetes mellitus. However, the evidence is scattered and inconclusive and its translation into practical clinical testing will require studies properly designed to examine not only simple genetic associations but also gene-gene and gene-environment interactions.

Intestinal fatty acid binding protein regulates mitochondrion beta-oxidation and cholesterol uptake

The role of intestinal fatty acid binding protein (I-FABP) in lipid metabolism remains elusive. To address this issue, normal human intestinal epithelial cells (HIEC-6) were transfected with cDNA to overexpress I-FABP and compared with cells treated with empty pQCXIP vector. I-FABP overexpression stimulated mitochondrial [U-14C]oleate oxidation to CO2 and acid-soluble metabolites via mechanisms including the upregulation of protein expression and the activity of carnitine palmitoyltransferase 1, a critical enzyme controlling the entry of fatty acid (FA) into mitochondria, and increased activity of 3-hydroxyacyl-CoA dehydrogenase, a mitochondrial beta-oxidation enzyme. On the other hand, the gene and protein expression of the key enzymes FA synthase and acetyl-coenzyme A carboxylase 2 was decreased, suggesting diminished lipogenesis. Furthermore, I-FABP overexpression caused a decline in [14C]free cholesterol (CHOL) incorporation. Accordingly, a significant lessening was observed in the gene expression of Niemann Pick C1-Like 1, a mediator of CHOL uptake, along with an increase in the transcripts and protein content of ABCA1 and ABCG5/ABCG8, acting as CHOL efflux pumps. Furthermore, I-FABP overexpression resulted in increased levels of mRNA, protein mass, and activity of HMG-CoA reductase, the rate-limiting step in CHOL synthesis. Scrutiny of the nuclear receptors revealed augmented peroxisome proliferator-activated receptor alpha,gamma and reduced liver X receptor-alpha in HIEC-6 overexpressing I-FABP. Finally, I-FABP overexpression did not influence acyl-coenzyme A oxidase 1, which catalyzes the first rate-limiting step in peroxisomal FA beta-oxidation. Overall, our data suggest that I-FABP may influence mitochondrial FA oxidation and CHOL transport by regulating gene expression and interaction with nuclear receptors.

Sex-specific association of fatty acid binding protein 2 and microsomal triacylglycerol transfer protein variants with response to dietary lipid changes in the 3-mo Medi-RIVAGE primary intervention study

BACKGROUND

The dietary guidelines targeted at reducing cardiovascular risk lead to largely heterogeneous responses in which genetic determinants are largely involved.

OBJECTIVES

We evaluated the effect of fatty acid binding protein 2 (FABP2) Ala54Thr and microsomal triacylglycerol transfer protein (MTTP) -493G/T allelic variations on plasma lipid markers, at baseline and on the response to the 3-mo Medi-RIVAGE primary prevention study.

DESIGN

Subjects with moderate cardiovascular disease risk (n = 169) were advised to reduce total and saturated dietary fats and to increase intake of monounsaturated and polyunsaturated fats. They were genotyped for FABP2 Ala54Thr and MTTP -493G/T allelic variations, and plasma was processed for cardiovascular risk marker analyses.

RESULTS

At baseline, men and women homozygous for Thr54 presented a significant opposite profile for plasma oleic acid (18:1), triacylglycerol-rich lipoprotein (TRL) cholesterol, and TRL phospholipids. In addition, all Thr/Thr men presented higher 18:1 values than did women. For the MTTP -493G/T polymorphism, although all TT subjects presented high apolipoprotein B-48, a genotype x sex interaction was present for palmitic acid, linolenic acid, eicosatrienoic acid, and insulin. The prudent diet clearly improved plasma lipid markers. FABP2 genotype did not interact much with the amplitude of the response. However, for MTTP polymorphism, men homozygous for the T allele displayed a significantly more pronounced response than did men carrying the G allele, which is particularly evident by their larger decrease in the Framingham score.

CONCLUSIONS

These 2 polymorphic loci are thus differently associated with the baseline lipid markers as well as with the response to nutritional recommendations, but both presented a marked sex-specific profile, with the response to diet being particularly efficient in men homozygous for the MTTP -493T allele.

Cytogenetic mapping of eight genes encoding fatty acid binding proteins (FABPs) in the pig genome

In the present study cytogenetic localization of eight fatty acid binding protein genes in the pig genome was shown. BAC clones, containing sequences of selected genes (FABP1, FABP2, FABP3, FABP4, FABP5, FABP6, FABP7 and FABP8) were derived from porcine BAC libraries and mapped by FISH to porcine chromosomes (SSC) 3q12, 8q25, 6q26, 4q12, 4q12, 16q22, 1p22 and 4q12, respectively. Detailed analyses of regions containing gene clusters (FABP4, FABP5, FABP8) in chromosome 4 were performed and their order was established. It was shown that these three genes are located beyond the FAT1 region. Assignment of the FABP genes to chromosome regions harboring quantitative trait loci (QTL) for fat deposition is discussed.

Loss of intestinal fatty acid binding protein increases the susceptibility of male mice to high fat diet-induced fatty liver

Mice lacking I-FABP (encoded by the Fabp2 gene) exhibit a gender dimorphic response to a high fat/cholesterol diet challenge characterized by hepatomegaly in male I-FABP-deficient mice. In this study, we determined if this gender-specific modification of liver mass in mice lacking I-FABP is attributable to the high fat content of the diet alone and whether hepatic Fabp1 gene (encodes L-FABP) expression contributes to this difference. Wild-type and Fabp2-/- mice of both genders were fed a diet enriched with either polyunsaturated or saturated fatty acids (PUFA or SFA, respectively) in the absence of cholesterol. Male Fabp2-/- mice, but not female Fabp2-/- mice, exhibited increased liver mass and hepatic triacylglycerol (TG) deposition as compared to corresponding wild-type mice. In wild-type mice that were fed the standard chow diet, there was no difference in the concentration of hepatic L-FABP protein between males and females although the loss of I-FABP did cause a slight reduction of hepatic L-FABP abundance in both genders. The hepatic L-FABP mRNA abundance in both male and female wild-type and Fabp2-/- mice was higher in the PUFA-fed group than in the SFA-fed group, and was correlated with L-FABP protein abundance. No correlation between hepatic L-FABP protein abundance and hepatic TG concentration was found. The results obtained demonstrate that loss of I-FABP renders male mice sensitive to high fat diet-induced fatty liver, and this effect is independent of hepatic L-FABP.

Identification of a functional polymorphism at the adipose fatty acid binding protein gene (FABP4) and demonstration of its association with cardiovascular disease: a path to follow

Fatty acid binding proteins (FABPs) are proteins that reversibly bind fatty acids and other lipids. So far, nine tissue-specific cytoplasmic FABPs have been identified. Adipose tissue FABP (FABP4) has been suggested to be a bridge between inflammation and other pathways related to the metabolic syndrome. In this regard, genetic variability at the FABP4 locus has been shown to be associated with plasma lipid levels, type 2 diabetes, and coronary heart disease risk.

[Correlation of FABP2-A54T polymorphism and the metabolic syndrome in Maros County of Romania]

OBJECTIVE

The FABP2 (intestinal fatty acid-binding protein) gene is expressed in the intestinal epithelial cells and codes for a protein involved in the fatty acid metabolism. We investigated the association of the A54T polymorphism of the FABP2 gene with the metabolic syndrome defined according to the diagnostic criteria recommended by the IDF in 2005, in our region (Marosvásárhely - Tg. Mures, Romania).

RESEARCH DESIGN AND METHODS

A case-control study was carried out on 144 metabolic syndrome patients and 73 healthy persons with similar age and lifestyle. Insulin resistance was measured by the HOMA and QUICKI indices, and gene polymorphism was analyzed with PCR followed by restriction enzyme digestion with Hha I.

RESULTS

The T54 allele was more frequent in the metabolic syndrome group than in controls (35.71% vs. 28.08%, p < 0.05). In the presence of the T54 allele we have noticed a slight but statistically significant risk, more marked in the case of TT homozygotes (TT vs. AT + AA: OR = 4.31, CI 95% 1.21-5.29, p = 0.015 and TT vs. AA: OR = 4.61, CI95%: 1.24-7.03, p = 0.0195). No significant differences of the followed metabolic parameters were observed between persons having different genotypes in the two study groups.

CONCLUSIONS

These results suggest that the FABP2 T54 allele may have a minor contribution to the metabolic syndrome in our region.

Functional analysis of promoter variants in the microsomal triglyceride transfer protein (MTTP) gene

The microsomal triglyceride transfer protein (MTTP) is required for the assembly and secretion of apolipoprotein B (apoB)-containing lipoproteins from the intestine and liver. According to this function, polymorphic sites in the MTTP gene showed associations to low-density lipoprotein (LDL) cholesterol and related traits of the metabolic syndrome. Here we studied the functional impact of common MTTP promoter polymorphisms rs1800804:T>C (-164T>C), rs1800803:A>T (-400A>T), and rs1800591:G>T (-493G>T) using gene-reporter assays in intestinal Caco-2 and liver Huh-7 cells. Significant results were obtained in Huh-7 cells. The common MTTP promoter haplotype -164T/-400A/-493G showed about two-fold lower activity than the rare haplotype -164C/-400T/-493T. MTTP promoter mutant constructs -164T/-400A/-493T and -164T/-400T/-493T exhibited similar activity than the common haplotype. Activities of mutants -164C/-400A/-493G and -164C/-400A/-493T resembled the rare MTTP promoter haplotype. Electrophoretic mobility shift assays (EMSAs) revealed higher binding capacity of the transcriptional factor Sterol regulatory element binding protein1a (SREBP1a) to the -164T probe in comparison to the -164C probe. In conclusion, our study indicates that the polymorphism -164T>C mediates different activities of common MTTP promoter haplotypes via SREBP1a. This suggested that the already described SREBP-dependent modulation of MTTP expression by diet is more effective in -164T than in -164C carriers.

A common functional exon polymorphism in the microsomal triglyceride transfer protein gene is associated with type 2 diabetes, impaired glucose metabolism and insulin levels

The microsomal triglyceride transfer protein (MTP) is required for the assembly and secretion of apolipoprotein B-containing lipoproteins. Emerging evidence has indicated that the functional MTP exon polymorphism I128T is associated with dyslipidemia and other traits of the insulin-resistance syndrome, and the T128 variant seems to confer a reduced stability of MTP, resulting in reduced binding of LDL particles. The aim of the study was to elucidate the association of this MTP polymorphism with parameters of postprandial metabolism. A total of 716 male subjects from a postprandially characterized cohort (MICK) and a nested case-control study (EPIC) of 190 incident type 2 diabetes cases and 380 sex- or age-matched controls were genotyped for the I128T exon polymorphism. In comparison to homozygote subjects of the wild allele, carriers of the less common allele of the MTP T128 genotype showed significantly lower postprandial insulin levels (P=0.017), lower diastolic blood pressure (P=0.049) and had a lower prevalence of impaired glucose metabolism and diabetes type 2 (P=0.03) in the MICK. Consistent with this, we found a lower incidence of type 2 diabetes in male subjects of the nested case-control study in the T128 genotype (P=0.007). These results suggest that the rare allele of the MTP I128T polymorphism may be protective against impaired glucose tolerance, type 2 diabetes and other parameters of the metabolic syndrome.

The multigene family of fatty acid-binding proteins (FABPs): function, structure and polymorphism

Fatty acid-binding proteins (FABPs) are members of the superfamily of lipid-binding proteins (LBP). So far 9 different FABPs, with tissue-specific distribution, have been identified: L (liver), I (intestinal), H (muscle and heart), A (adipocyte), E (epidermal), Il (ileal), B (brain), M (myelin) and T (testis). The primary role of all the FABP family members is regulation of fatty acid uptake and intracellular transport. The structure of all FABPs is similar - the basic motif characterizing these proteins is beta-barrel, and a single ligand (e.g. a fatty acid, cholesterol, or retinoid) is bound in its internal water-filled cavity. Despite the wide variance in the protein sequence, the gene structure is identical. The FABP genes consist of 4 exons and 3 introns and a few of them are located in the same chromosomal region. For example, A-FABP, E-FABP and M-FABP create a gene cluster. Because of their physiological properties some FABP genes were tested in order to identify mutations altering lipid metabolism. Furthermore, the porcine A-FABP and H-FABP were studied as candidate genes with major effect on fatness traits.