A common functional polymorphism in the promoter region of the microsomal triglyceride transfer protein gene influences plasma LDL levels

Association between MTTP genotype (-493G/T) polymorphism and hepatic steatosis in hepatitis C: a systematic review and meta-analysis

BACKGROUND

Hepatitis C has been associated with the development of hepatic steatosis, which increases the risk of liver cancer. The microsomal triglyceride transporter protein (MTTP), is a lipid transport protein that mediates lipid metabolism and CD1d antigen presentation. The study aimed to explore the association between MTTP genotype (-493G/T) polymorphism and hepatic steatosis in hepatitis C.

METHODS

The database "Pubmed, Cochrane library, CNKI, Web of science, Embase and CBM" were retrieved to identify the literature. The quality of the selected literature was evaluated using the "the Newcastle-Ottawa Scale" (NOS). Relevant data was extracted and analyzed using the Stata software. Heterogeneity was expressed by "Cochran's Q and I2", with I2 ≥ 50% or P < 0.05 indicating high heterogeneity. A random-effects model and subgroup analysis were conducted to identify the sources of heterogeneity. We also used "Funnel plots", "Egger's tests" and "Begg's tests" to evaluate biases in the literature.

RESULTS

The study found a significant and positive association between liver steatosis and the HCV genotype 3 with a dominant model of the MTTP genotype (-493G/T) (OR = 11.57, 95%CI: 4.467-29.962, P < 0.001). In contrast, no correlation was found between hepatic steatosis and either the recessive, homozygous or heterozygous models (OR = 1.142, P = 0.5; OR = 1.581, P = 0.081; OR = 1.029, P = 0.86). There was no significant publication biases, as measured by the Funnel plot, and the Egger's and Begg's tests. Finally, sensitivity analysis showed the obtained results are stable.

CONCLUSIONS

Dominant mutations in the T allele of the MTTP genotype (-493G/T) increase susceptibility to hepatic steatosis in patients presenting with the HCV genotype 3.

Effect of MTTP -493G/T, I128T, Q95H and Q244E polymorphisms on hepatic steatosis in patients with chronic hepatitis

BACKGROUND

Chronic hepatitis C is characterized by a progressive deterioration of liver function and is involved in metabolic complications, such as hepatic steatosis.

OBJECTIVE

The aim of this study was to investigate the role of host and viral characteristics associated with -493G/T (rs1800591), I128T (rs3816873), Q95H (rs61733139), and Q244E (rs17599091) Single Nucleotide Polymorphisms (SNPs) in the Microsomal Triglyceride Transfer Protein (MTTP) gene on hepatic steatosis in chronic hepatitis C.

METHODS

SNPs were genotyped by PCR-RFLP and analyzed in combination with host and viral characteristics by multiple logistic regression in different genetic models of inheritance.

RESULTS

The authors analyzed 236 patients with chronic hepatitis C, and 53% had hepatic steatosis. The mutated allele frequencies were > 5%, and the genotypes were in Hardy-Weinberg equilibrium (p ≥ 0.05). It was observed that patients with HCV genotype 3 infection (OR = 2.74, 95% CI 1.24‒6.06, p = 0.013), female sex (OR = 2.28, 95% CI 1.21‒4.28, p = 0.011) and moderate- and high-intensity liver inflammatory activity (A2-A3) (OR = 3.61, 95% CI 1.86‒7.01, p < 0.001) alone exhibited a higher risk of steatosis. The results of multiple logistic regression analysis for interaction showed that for the -493G/T SNP, when the GT/TT genotype (dominant model) and the GT genotype (codominant model) were each combined with HCV genotype 3 infection, an 11.51-fold (95% CI 2.08‒63.59, p = 0.005) and a 15.69-fold (95% CI 2.46‒99.85, p = 0.004) increased risk of steatosis, respectively, was observed. For the I128T SNP, when both the IT/TT genotype (dominant model) and the IT genotype (codominant model) were combined with HCV genotype 3 infection, an 8.51-fold (95% CI 1.59‒45.54, p = 0.012) and an 8.40 fold (95% CI 1.51‒46.91, p = 0.015) increased risk of steatosis, respectively, was observed.

CONCLUSION

The present study showed that the viral genotype combined with the -493G/T and I128T SNPs in the MTTP gene influences hepatic steatosis.

Impact of IL10, MTP, SOD2, and APOE Gene Polymorphisms on the Severity of Liver Fibrosis Induced by HCV Genotype 4

Complications of hepatitis C virus (HCV) chronic infection cause ~400,000 deaths worldwide annually. One complication, liver fibrosis, is influenced by host genetic factors. Genes influencing fibrosis include immune, metabolic, oxidative stress, and viral entry genes, such as interleukin 10 (IL10), microsomal triglyceride-transfer protein (MTP), superoxide dismutase-2 (SOD2), and apolipoprotein E (APOE)-encoding genes, respectively. Thus, correlating variations in these genes with HCV-induced fibrosis represents an attractive biomarker for the prognosis of fibrosis severity in chronically infected patients. Here, we aimed to test whether polymorphisms in IL10, MTP, SOD2, and APOE genes correlated with the severity of fibrosis induced by HCV genotype 4 (HCV-gt4) in a cohort of chronically infected Egyptian patients. Our results demonstrate a significant association between the severity of fibrosis and specific SNPs in IL-10, SOD2, and ApoE-encoding genes. Haplotype-combination analysis for IL10, MTP, SOD2, and APOE showed statistically significant associations between specific haplotype combinations and fibrosis severity. Identifying biomarkers correlating with the severity of HCV-gt4-induced fibrosis would significantly impact precision prophylaxis and treatment of patients at risk.

The association between SNPs rs1800591 and rs3816873 of the MTTP gene and nonalcoholic fatty liver disease: A meta-analysis

BACKGROUND/AIMS

: The role of two polymorphisms rs1800591 and rs3816873 of the microsomal triglyceride transfer protein (MTTP) gene in the development of nonalcoholic fatty liver disease (NAFLD) remains controversial. A meta-analysis was conducted to determine the correlation between these MTTP polymorphisms and NAFLD.

MATERIALS AND METHODS

: A systematic search was carried out using PubMed, Embase, and Cochrane Library to retrieve English studies that reported the relationship between MTTP polymorphisms (rs1800591 and rs3816873) and NAFLD published before February 18, 2020. Odds ratio (OR) and 95% confidence interval (CI) were used to appraise the risk of MTTP polymorphism in NAFLD.

RESULTS

: A total of 10 case-control studies, including 1388 cases and 1690 healthy subjects, were included. No significant correlation between the rs1800591 (G vs. T: OR = 1.08, 95% CI = 0.68-1.70, P = 0.76) and rs3816873 (CT + CC vs. TT: OR = 1.23, 95% CI = 0.76-2.01, P = 0.398) polymorphisms of MTTP and NAFLD was found in any of the models. However, when NASH patients confirmed by liver biopsy were extracted alone for rs1800591 polymorphism analysis, it was found that the G allele significantly increased the risk of NASH under the heterozygote model (GT vs. TT: OR = 3.16, 95% CI = 1.13-8.83, P = 0.028) and dominant model (GT + GG vs. TT: OR = 3.03, 95% CI = 1.13-8.09, P = 0.027).

CONCLUSION

The present meta-analysis revealed that the rs1800591 and rs3816873 polymorphisms of the MTTP gene are uncommon in NAFLD. However, the G allele of rs1800591 was more likely to be correlated to NASH susceptibility.

MTTP polymorphisms and hepatic steatosis in individuals chronically infected with hepatitis C virus

Polymorphisms in the microsomal triglyceride transfer protein (MTTP) gene were genotyped in individuals who were chronically infected with hepatitis C virus (HCV). In the 236 patients, the frequencies of risk alleles of the -164T/C (rs1800804), -400A/T (rs1800803) and H297Q (rs2306985) polymorphisms were 0.30, 0.41 and 0.50, respectively. A significant association between the risk alleles of the -164T/C and -400A/T polymorphisms combined with HCV genotype 3 infection and the occurrence of steatosis was detected (p = 0.004 and p = 0.032), suggesting that a combination of host and viral factors can potentially be used to predict hepatic steatosis.

Association between hepatic steatosis and MTP gene -493G/T polymorphism in the patients with HCV genotype 1 infection

AIM

Hepatitis C virus (HCV) affects approximately 250 million people worldwide. If patients are untreated, 80% of patients with chronic HCV develop liver failure, liver cirrhosis (LC), and hepatocellular carcinoma (HCC). HCV genotype 1 is the most prevalent among the infected individuals with HCV. Hepatic steatosis is known as accumulation of lipid molecules in hepatocytes, and its prevalence is approximately 55% in CHC infection. The reason of HCV-related hepatic steatosis in CHC infection is mainly HCV core protein. HCV core protein inhibits activities of microsomal triglyceride transfer protein (MTP) which is a lipid transfer protein expressed in the liver. The -493G/T polymorphism in the promoter region of MTP gene has been associated with HCV-related hepatic steatosis. This polymorphism in MTP gene influences MTP mRNA expression, therefore which might also affect lipid transfer. We evaluated the association between MTP gene polymorphism and the risk of HCV genotype 1-related hepatic steatosis.

METHODS

In the current study, MTP gene polymorphism was explored in 144 biopsy-proven chronic HCV genotype 1 patients by using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method.

RESULTS

The results showed that there were no any difference between the steatosis and the non-steatosis groups for the allele and genotype frequencies of the -493G/T polymorphism (P > .05). Moreover, MTP genotypes (GG vs. TG + TT) were not associated with BMI, fibrosis stages and the levels of biochemical parameters. Additionally, there were statistically significant differences in the biochemical parameters including triglyceride, total cholesterol, LDL, VLDL levels between the two groups (P < .05).

CONCLUSIONS

In conclusion, the current study demonstrates for the first time that MTP gene -493G/T polymorphism has not a major effect on the risk of HCV genotype 1-related hepatic steatosis in Turkish population. Further studies are imperative to clarify the association of this polymorphism with HCV genotype 1 infection in HCV-related hepatic steatosis.

MTP genetic variants associated with non-alcoholic fatty liver in metabolic syndrome patients

This study was performed for investigation the relationship between variants of MTP gene polymorphism and the development of NAFLD in patients with and without MS. The study was included 174 NAFLD patients (106 with MS and 68 without MS), and 141 healthy control subjects. The 493 G/T polymorphism of MTP gene was evaluated by PCR-RFLP method. The frequency of MTP TT genotype and T allele were significantly higher in NAFLD patients when compared to healthy controls. Moreover, a significant association in MTP gene polymorphism was observed in NAFLD patients with MS compared to NAFLD patients without MS and controls. Our study suggested that MTP 493 G/T gene polymorphism may act as susceptibility biomarker for NAFLD and MS.

Genetic variation in the microsomal triglyceride transfer protein (-493G/T) is associated with hepatic steatosis in patients infected with hepatitis C virus

Background

In chronic hepatitis C, the fibrosis progression rates are extremely variable and can be influenced by factors associated with the host, virus and environment. Among the associated metabolic factors, hepatic steatosis is characterized by an accumulation of triglycerides in hepatocytes. In the host, genetic determinants of hepatic steatosis are observed, such as single-nucleotide polymorphisms (SNPs) in the microsomal triglyceride transfer protein (MTTP) gene. The MTTP -493G/T SNP appears to play an important role in the regulation of gene expression and influences the plasma concentration of circulating low-density lipoprotein (LDL). The present study investigated the influence of this SNP in the development of hepatic steatosis in patients with chronic hepatitis C and evaluated the association of hepatic steatosis with certain characteristics of these patients and the hepatitis C virus (HCV).

Methods

Two hundred thirty-nine patients with chronic hepatitis C were genotyped for the MTTP -493G⁄T SNP by a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay. The association between hepatic steatosis and selected characteristics of the patient and virus was evaluated using bivariate and multivariate analyses.

Results

The most prevalent MTTP -493G/T genotype was GG (46%) followed by GT (43.5%) and TT (10.5%). Multivariate analysis of the total cohort revealed associations between the presence of hepatic steatosis and inflammatory activity of moderate to high intensity (P < 0.001), advanced age (P = 0.010), elevated gamma glutamyl transpeptidase (GGT) levels (P = 0.010) and low LDL levels (P = 0.022). Hepatic steatosis was also associated with the TT/GT genotype of the MTTP -493G⁄T SNP in patients infected with HCV genotype 3 (P < 0.001).

Conclusions

In chronic hepatitis C patients infected with HCV genotype 3 and with the TT/GT genotype of the MTTP -493G/T SNP, a significant increase in hepatic steatosis was observed, which may indicate that this SNP has a significant influence on the accumulation of triglycerides in hepatocytes. Furthermore, associations were observed between hepatic steatosis and inflammatory activity of moderate to high intensity, advanced age, elevated GGT and low LDL levels.

Significance of genetic polymorphisms in patients with nonalcoholic fatty liver disease

Because of recent advances in genetic research such as genome-wide association studies, the underlying genetic mechanisms of nonalcoholic fatty liver disease (NAFLD) pathophysiology have been elucidated. Here, we present a review of the current literature on the impact of genetic polymorphisms in patients with NAFLD. These genetic polymorphisms, which regulate lipid metabolism, glucose metabolism, and the renin-angiotensin system, are involved in NAFLD onset, steatosis, inflammation, fibrosis, and hepatocellular carcinoma (HCC). Among these genetic polymorphisms, many studies and meta-analyses have demonstrated that position 148 (rs738409 C/G) of the patatin-like phospholipase domain-containing protein (PNPLA3) is a genetic factor associated with NAFLD pathophysiological features, such as hepatic fat level, hepatic inflammation, fibrosis, and HCC. However, the impact of genetic polymorphisms on NAFLD pathophysiology appears to differ among ethnic groups. Therefore, further studies with larger sample sizes are needed for each ethnic group.

RNA helicase DDX3 maintains lipid homeostasis through upregulation of the microsomal triglyceride transfer protein by interacting with HNF4 and SHP

Multifunctional RNA helicase DDX3 participates in HCV infection, one of the major causes of hepatic steatosis. Here, we investigated the role of DDX3 in hepatic lipid metabolism. We found that HCV infection severely reduced DDX3 expression. Analysis of intracellular triglyceride and secreted ApoB indicated that lipid accumulations were increased while ApoB secretion were decreased in DDX3 knockdown HuH7 and HepG2 cell lines. Down-regulation of DDX3 significantly decreased protein and transcript expression of microsomal triglyceride transfer protein (MTP), a key regulator of liver lipid homeostasis. Moreover, DDX3 interacted with hepatocyte nuclear factor 4 (HNF4) and small heterodimer partner (SHP), and synergistically up-regulated HNF4-mediated transactivation of MTP promoter via its ATPase activity. Further investigation revealed that DDX3 interacted with CBP/p300 and increased the promoter binding affinity of HNF4 by enhancing HNF4 acetylation. Additionally, DDX3 partially relieved the SHP-mediated suppression on MTP promoter by competing with SHP for HNF4 binding which disrupted the inactive HNF4/SHP heterodimer while promoted the formation of the active HNF4 homodimer. Collectively, these results imply that DDX3 regulates MTP gene expression and lipid homeostasis through interplay with HNF4 and SHP, which may also reveal a novel mechanism of HCV-induced steatosis.

Drug-induced fatty liver disease: An overview of pathogenesis and management

Over the past decades, many drugs have been identified, that can potentially induce steatohepatitis in the predisposed individual. Classically this has been incriminated to amiodarone, perhexiline, and 4,4'-diethylaminoethoxyhexestrol (DH), all of which have been found to independently induce the histologic picture of non-alcoholic steatohepatitis (NASH). Pathogenetic mechanisms of hepatotoxicity although still evolving, demonstrate that mitochondrial dysfunction, deranged ATP production and fatty acid catabolism likely play an important role. Drugs like steroid hormones can exacerbate the pathogenetic mechanisms that lead to NASH, and other drugs like tamoxifen, cisplatin and irenotecan have been shown to precipitate latent fatty liver as well. Further research aiming to elucidate the pathogenesis of drug-induced steatosis and steatohepatitis is needed in order to better design therapeutic targets.

Genetic background in nonalcoholic fatty liver disease: A comprehensive review

In the Western world, nonalcoholic fatty liver disease (NAFLD) is considered as one of the most significant liver diseases of the twenty-first century. Its development is certainly driven by environmental factors, but it is also regulated by genetic background. The role of heritability has been widely demonstrated by several epidemiological, familial, and twin studies and case series, and likely reflects the wide inter-individual and inter-ethnic genetic variability in systemic metabolism and wound healing response processes. Consistent with this idea, genome-wide association studies have clearly identified Patatin-like phosholipase domain-containing 3 gene variant I148M as a major player in the development and progression of NAFLD. More recently, the transmembrane 6 superfamily member 2 E167K variant emerged as a relevant contributor in both NAFLD pathogenesis and cardiovascular outcomes. Furthermore, numerous case-control studies have been performed to elucidate the potential role of candidate genes in the pathogenesis and progression of fatty liver, although findings are sometimes contradictory. Accordingly, we performed a comprehensive literature search and review on the role of genetics in NAFLD. We emphasize the strengths and weaknesses of the available literature and outline the putative role of each genetic variant in influencing susceptibility and/or progression of the disease.

MTTP-297H polymorphism reduced serum cholesterol but increased risk of non-alcoholic fatty liver disease-a cross-sectional study

Background

Microsomal triglyceride transfer protein (MTP) works to lipidate and assemble the apoB-containing lipoproteins in liver. It closely links up the hepatic secretion of lipid to regulate serum lipid and atherosclerosis. Cases of MTTP gene mutation is characterized by abetalipoproteinemia and remarkable hepatic steatosis or cirrhosis. Several MTTP polymorphisms have been reported relating to metabolic syndrome, hyperlipidemia and steatohepatitis. We supposed the regulation of serum lipids and risk of non-alcoholic fatty liver disease (NAFLD) formation may be modified by individual susceptibility related to the MTTP polymorphisms.

Methods and results

A cross-sectional population of 1193 subjects, 1087 males and 106 females mean aged 45.9 ± 8.9 years, were enrolled without recognized secondary hyperlipidemia. Fasting serum lipid, insulin, and non-esterified fatty acid were assessed and transformed to insulin resistance index, HOMA-IR and Adipo-IR. After ruling out alcohol abuser, non-alcoholic fatty liver disease (NAFLD) was diagnosed by abdominal ultrasound. Five common MTTP polymorphisms (promoter -493G/T, E98D, I128T, N166S, and Q297H) were conducted by TaqMan assay. Multivariate regression analysis was used to estimate their impact on serum lipid and NAFLD risk. Assessment revealed a differential impact on LDL-C and non-HDL-C, which were sequentially determined by the Q297H polymorphism, insulin resistance, body mass index and age. Carriers of homozygous minor allele (297H) had significantly lower LDL-C and non-HDL-C but higher risk for NAFLD. Molecular modeling of the 297H variant demonstrated higher free energy, potentially referring to an unstable structure and functional sequence.

Conclusion

These results evidenced the MTTP polymorphisms could modulate the lipid homeostasis to determine the serum lipids and risk of NAFLD. The MTTP 297H polymorphism interacted with age, insulin resistance and BMI to decrease serum apoB containing lipoproteins (LDL-C and non-HDL-C) but increase the risk of NAFLD formation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-015-0242-6) contains supplementary material, which is available to authorized users.

Association of L-FABP T94A and MTP I128T polymorphisms with hyperlipidemia in Chinese subjects

The purpose of this study was to evaluate the relation between the L-FABP T94A and MTP I128T polymorphisms and hyperlipidemia in Chinese subjects. We recruited 390 volunteers: 201 hyperlipidemic and 189 healthy volunteers. The L-FABP T94A and MTP I128T polymorphisms were genotyped using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Anthropometry, lipid profile, and liver function of the subjects were determined. We observed that male carriers of the L-FABP A94 allele had significantly higher body weight (P = 0.012), higher body mass index (BMI) (P = 0.014), and higher plasma triacylglycerol levels (TAG) (P = 0.033) and lower ratios of high-density lipoprotein cholesterol (HDL-C) to total cholesterol (TC) (P = 0.008) than T94 homozygotes. The MTP T128 allele was associated with significantly lower serum TC (P < 0.001) and low-density lipoprotein cholesterol (LDL-C) (P < 0.001) levels in males. There was a direct correlation between the MTP T128 allele and a decreased risk of hyperlipidemia after adjusting for body mass index (OR = 0.327, 95 % CI: 0.178-0.600, P < 0.001). In conclusion, both the MTP I128T and the L-FABP T94A polymorphisms can affect serum lipid levels in the Chinese population. The MTP T128 allele offers protection against hyperlipidemia in the Chinese population.

Insights from human congenital disorders of intestinal lipid metabolism

The intestine must challenge the profuse daily flux of dietary fat that serves as a vital source of energy and as an essential component of cell membranes. The fat absorption process takes place in a series of orderly and interrelated steps, including the uptake and translocation of lipolytic products from the brush border membrane to the endoplasmic reticulum, lipid esterification, Apo synthesis, and ultimately the packaging of lipid and Apo components into chylomicrons (CMs). Deciphering inherited disorders of intracellular CM elaboration afforded new insight into the key functions of crucial intracellular proteins, such as Apo B, microsomal TG transfer protein, and Sar1b GTPase, the defects of which lead to hypobetalipoproteinemia, abetalipoproteinemia, and CM retention disease, respectively. These "experiments of nature" are characterized by fat malabsorption, steatorrhea, failure to thrive, low plasma levels of TGs and cholesterol, and deficiency of liposoluble vitamins and essential FAs. After summarizing and discussing the functions and regulation of these proteins for reader's comprehension, the current review focuses on their specific roles in malabsorptions and dyslipidemia-related intestinal fat hyperabsorption while dissecting the spectrum of clinical manifestations and managements. The influence of newly discovered proteins (proprotein convertase subtilisin/kexin type 9 and angiopoietin-like 3 protein) on fat absorption has also been provided. Finally, it is stressed how the overexpression or polymorphism status of the critical intracellular proteins promotes dyslipidemia and cardiometabolic disorders.

A polymorphism in the microsomal triglyceride transfer protein can predict the response to antiviral therapy in Egyptian patients with chronic hepatitis C virus genotype 4 infection

BACKGROUND/AIMS

A polymorphism in the microsomal triglyceride transfer protein (MTP) is associated with hepatic fibrosis, and carriers showed higher levels of steatosis, higher levels of hepatitis C virus (HCV) RNA and advanced fibrosis. The aim of this study was to study MTP expression pattern in HCV patients and impact of the MTP polymorphism on the response to antiviral therapy.

METHODS

One hundred consecutive naive HCV genotype 4 patients were recruited to receive antiviral therapy, and 40 control subjects were also recruited. Demographic, laboratory, and histopathology data were collected. DNA was isolated, and the samples were subjected to polymerase chain reaction analysis and genotyping for MTP by restriction fragment length polymorphism analysis.

RESULTS

Patients and controls were age- and sex-matched (male/female, 56/44, age, 39.2±7.8 years for patients with HCV; male/female, 18/22, age, 38.1±8.1 years for controls). MTP single nucleotide polymorphisms (SNPs) (GG, GT, TT) and alleles (G, T) in the patients versus the controls were 70%, 21%, 9% & 80.5%, 19.5% versus 10%, 87.5%, 2.5% & 53.8%, 46.3%, respectively (p=0.0001). The sustained viral response (SVR) of the patients was 60%. SNPs in MTP genotypes (GG, GT, and TT) and alleles (G and T) in the responders and nonresponders were 71.7%, 25%, 3.3% & 84.2%, 15.8% versus 67.5%, 15%, 17.5% & 75%, 25% (p=0.038 and p=0.109, respectively). A multivariate analysis showed that the GT genotype was an independent predictor of SVR (area under the curve 90% and p=0.0001).

CONCLUSIONS

MTP could be a new predictor for SVR to antiviral therapy in patients with HCV genotype 4 infection.

Genetic predisposition in NAFLD and NASH: impact on severity of liver disease and response to treatment

Liver fat deposition related to systemic insulin resistance defines non-alcoholic fatty liver disease (NAFLD) which, when associated with oxidative hepatocellular damage, inflammation, and activation of fibrogenesis, i.e. non-alcoholic steatohepatitis (NASH), can progress towards cirrhosis and hepatocellular carcinoma. Due to the epidemic of obesity, NAFLD is now the most frequent liver disease and the leading cause of altered liver enzymes in Western countries. Epidemiological, familial, and twin studies provide evidence for an element of heritability of NAFLD. Genetic modifiers of disease severity and progression have been identified through genome-wide association studies. These include the Patatin-like phosholipase domain-containing 3 (PNPLA3) gene variant I148M as a major determinant of inter-individual and ethnicity-related differences in hepatic fat content independent of insulin resistance and serum lipid concentration. Association studies confirm that the I148M polymorphism is also a strong modifier of NASH and progressive hepatic injury. Furthermore, a few large multicentre case-control studies have demonstrated a role for genetic variants implicated in insulin signalling, oxidative stress, and fibrogenesis in the progression of NAFLD towards fibrosing NASH, and confirm that hepatocellular fat accumulation and insulin resistance are key operative mechanisms closely involved in the progression of liver damage. It is now important to explore the molecular mechanisms underlying these associations between gene variants and progressive liver disease, and to evaluate their impact on the response to available therapies. It is hoped that this knowledge will offer further insights into pathogenesis, suggest novel therapeutic targets, and could help guide physicians towards individualised therapy that improves clinical outcome.

Variation in genes related to hepatic lipid metabolism and changes in waist circumference and body weight

We analysed single nucleotide polymorphisms (SNPs) tagging the genetic variability of six candidate genes (ATF6, FABP1, LPIN2, LPIN3, MLXIPL and MTTP) involved in the regulation of hepatic lipid metabolism, an important regulatory site of energy balance for associations with body mass index (BMI) and changes in weight and waist circumference. We also investigated effect modification by sex and dietary intake. Data of 6,287 individuals participating in the European prospective investigation into cancer and nutrition were included in the analyses. Data on weight and waist circumference were followed up for 6.9 ± 2.5 years. Association of 69 tagSNPs with baseline BMI and annual changes in weight as well as waist circumference were investigated using linear regression analysis. Interactions with sex, GI and intake of carbohydrates, fat as well as saturated, monounsaturated and polyunsaturated fatty acids were examined by including multiplicative SNP-covariate terms into the regression model. Neither baseline BMI nor annual weight or waist circumference changes were significantly associated with variation in the selected genes in the entire study population after correction for multiple testing. One SNP (rs1164) in LPIN2 appeared to be significantly interacting with sex (p = 0.0003) and was associated with greater annual weight gain in men (56.8 ± 23.7 g/year per allele, p = 0.02) than in women (-25.5 ± 19.8 g/year per allele, p = 0.2). With respect to gene-nutrient interaction, we could not detect any significant interactions when accounting for multiple testing. Therefore, out of our six candidate genes, LPIN2 may be considered as a candidate for further studies.

Host genetic variants in obesity-related nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a complex disease. The considerable variability in the natural history of the disease suggests an important role for genetic variants in the disease development and progression. There is evidence based on genome-wide association studies and/or candidate gene studies that genetic polymorphisms underlying insulin signaling, lipid metabolism, oxidative stress, fibrogenesis, and inflammation can predispose individuals to NAFLD. This review highlights some of the genetic variants in NAFLD.

MTTP polymorphisms and susceptibility to non-alcoholic fatty liver disease in a Han Chinese population

BACKGROUND

The microsomal triglyceride transfer protein (MTP) is required for the assembly and secretion of apolipoprotein B (ApoB)-containing lipoproteins from the liver and intestine. Previous studies showed that functional polymorphisms in the MTTP gene correspond to lower LDL levels and protect against other traits of the metabolic syndrome.

AIMS

Here, we aimed to investigate whether MTTP single nucleotide polymorphisms (SNPs) and their predicted haplotypes of linkage disequilibrium blocks contribute to non-alcoholic fatty liver disease (NAFLD) susceptibility in a Han Chinese population.

METHODS

Seven tag SNPs in the MTTP gene were selected and genotyped in a frequency-matched case-control study in a population from Fuzhou City, China. We enrolled 580 patients with NAFLD and 580 healthy controls.

RESULTS

In the multivariate logistic regression analysis, the rs1800804 (-164 T/C) was associated with an increased risk of NAFLD, while the rs1057613 A/G and rs3805335 C/T SNPs were associated with a decreased risk of NAFLD. The cumulative effect of the rs1800804 (-164 T/C), rs1057613 and rs3805335 was estimated, and a significant increased trend in the risk of NAFLD with increasing genetic risk score was observed (adjusted P(trend) = 0.014). Furthermore, the results of haplotype analysis suggested that the haplotype GC in block 1 containing the -164 C allele was associated with an increased risk of NAFLD, while haplotype TGTTC in block 2 was associated with a decreased risk of NAFLD.

CONCLUSIONS

Our data show that MTTP genetic polymorphisms influence the susceptibility to developing NAFLD independently or jointly in the Han Chinese population.

Genetic variants of microsomal triglyceride transfer protein (MTTP) are associated with metabolic syndrome in schizophrenic patients treated with atypical antipsychotics

OBJECTIVES

Promoter polymorphisms in microsomal triglyceride transfer protein (MTTP) have been associated with the various traits of metabolic syndrome (MetS) in the general population. This study investigated whether the common variants in MTTP genes were associated with MetS in schizophrenic patients treated with atypical antipsychotics.

METHOD

The study included 456 hospitalized patients diagnosed with schizophrenia, who had been treated with clozapine (n = 171), olanzapine (n = 91), or risperidone (n = 194) for at least 3 months. Patients were genotyped for the 10 MTTP single-nucleotide polymorphisms.

RESULTS

The prevalence of MetS among all subjects was 22.8%. In single-marker-based analysis, the MTTP rs1800591 (-493G>T) T-allele carriers were at double the risk for MetS relative to G/G homozygotes. In contrast, the T-allele homozygotes had considerably lower fasting high-density lipoprotein levels than that in the heterozygotes or G-allele homozygotes.

CONCLUSIONS

Our findings extend and add new information to the existing data regarding the association between MTTP genetic variants and MetS regulation during long-term atypical antipsychotic treatment. The MTTP rs1800591 T allele could be a risk factor for MetS in patients under atypical antipsychotic medication.

Microsomal triglyceride transfer protein -164 T > C gene polymorphism and risk of cardiovascular disease: results from the EPIC-Potsdam case-cohort study

Background

The microsomal triglyceride transfer protein (MTTP) is encoded by the MTTP gene that is regulated by cholesterol in humans. Previous studies investigating the effect of MTTP on ischemic heart disease have produced inconsistent results. Therefore, we have tested the hypothesis that the rare allele of the -164T > C polymorphism in MTTP alters the risk of cardiovascular disease (CVD), depending on the cholesterol levels.

Methods

The -164T > C polymorphism was genotyped in a case-cohort study (193 incident myocardial infarction (MI) and 131 incident ischemic stroke (IS) cases and 1 978 non-cases) nested within the European Prospective Investigation into Cancer and Nutrition (EPIC)–Potsdam study, comprising 27 548 middle-aged subjects. The Heinz Nixdorf Recall study (30 CVD cases and 1 188 controls) was used to replicate our findings.

Results

Genotype frequencies were not different between CVD and CVD free subjects (P = 0.79). We observed an interaction between the -164T > C polymorphism and total cholesterol levels in relation to future CVD. Corresponding stratified analyses showed a significant increased risk of CVD (HR_additve = 1.38, 95% CI: 1.07 to 1.78) for individuals with cholesterol levels <200 mg/dL in the EPIC-Potsdam study. HR_additive was 1.06, 95% CI: 0.33 to 3.40 for individuals in the Heinz Nixdorf Recall study. A borderline significant decrease in CVD risk was observed in subjects with cholesterol levels ≥200 mg/dL (HR_additve = 0.77, 95% CI: 0.58 to 1.03) in the EPIC-Potsdam study. A similar trend was observed in the independent cohort (HR_additve = 0.60, 95% CI: 0.29 to 1.25).

Conclusions

Our study suggests an interaction between MTTP -164T > C functional polymorphism with total cholesterol levels. Thereby risk allele carriers with low cholesterol levels may be predisposed to an increased risk of developing CVD, which seems to be abolished among risk allele carriers with high cholesterol levels.

Microsomal triglyceride transfer protein gene -493G/T polymorphism and its association with serum lipid levels in Bama Zhuang long-living families in China

BACKGROUND

The -493G/T polymorphism in the microsomal triglyceride transfer protein (MTP) gene is associated with lower serum low-density lipoprotein cholesterol (LDL-C) and triglyceride (TG) levels and longevity in several populations, but the results are inconsistent in different racial/ethnic groups. The current study was to investigate the plausible association of MTP -493G/T polymorphism with serum lipid levels and longevity in Zhuang long-lived families residing in Bama area, a famous home of longevity in Guangxi, China.

METHODS

The MTP -493G/T was genotyped by PCR-restriction fragment length polymorphism in 391 Bama Zhuang long-lived families (BLF, n = 1467, age 56.60 ± 29.43 years) and four control groups recruited from Bama and out-of-Bama area with or without a familial history of exceptional longevity: Bama non-long-lived families (BNLF, n = 586, age 44.81 ± 26.83 years), Bama non-Zhuang long-lived families (BNZLF, n = 444, age 52.09 ± 31.91 years), Pingguo long-lived families (PLF, n = 658, age 50.83 ± 30.30 years), and Pingguo non-long-lived families (PNLF, n = 539, age 38.74 ± 24.69 years). Correlation analyses between genotypes and serum lipid levels and longevity were then performed.

RESULTS

No particularly favorable lipoprotein and clinical phenotypes were seen in BLF as compared to general families in the same area. Instead, the levels of total cholesterol (TC), TG, LDL-C, and the prevalence of dyslipidemia were significantly higher in the three Bama families as compared to the two non-Bama families (P < 0.01 for all). There were no differences in the allelic and genotypic frequencies among the tested cohorts (P > 0.05 for all), but the TT genotype tended to enrich in the three long-lived cohorts from both areas. In addition, the individuals harboring TT genotype exhibited lower LDL-C and TC levels in the overall populations and Bama populations with a region- and sex-specific pattern. Multiple linear regression analyses unraveled that LDL-C levels were correlated with genotypes in Bama combined population, BNLF, and the total population (P < 0.05 for each) but not in Pingguo populations; TC and HDL-C levels were correlated with genotypes in Bama combined population and BLF, respectively (P < 0.05 for each).

CONCLUSIONS

MTP -493G/T polymorphism may play an important role in fashioning the serum lipid profiles of Bama populations, despite no direct association between MTP -493G/T and longevity was detected.

MTP -493G/T gene polymorphism is associated with steatosis in hepatitis C-infected patients

The reduction of hepatic microsomal transfer protein (MTP) activity results in fatty liver, worsening hepatic steatosis and fibrosis in chronic hepatitis C (CHC). The G allele of the MTP gene promoter, -493G/T, has been associated with lower transcriptional activity than the T allele. We investigated this association with metabolic and histological variables in patients with CHC. A total of 174 untreated patients with CHC were genotyped for MTP -493G/T by direct sequencing using PCR. All patients were negative for markers of Wilson's disease, hemochromatosis and autoimmune diseases and had current and past daily alcohol intake lower than 100 g/week. The sample distribution was in Hardy-Weinberg equilibrium. Among subjects with genotype 1, 56.8% of the patients with fibrosis grade 3+4 presented at least one G allele versus 34.3% of the patients with fibrosis grade 1+2 (OR = 1.8; 95%CI = 1.3-2.3). Logistic regression analysis with steatosis as the dependent variable identified genotypes GG+GT as independent protective factors against steatosis (OR = 0.4, 95%CI = 0.2-0.8; P = 0.01). The results suggest that the presence of the G allele of MTP -493G/T associated with lower hepatic MTP expression protects against steatosis in our CHC patients.

The chylomicron: relationship to atherosclerosis

The B-containing lipoproteins are the transporters of cholesterol, and the evidence suggests that the apo B48-containing postprandial chylomicron particles and the triglyceride-rich very low density lipoprotein (VLDL) particles play an important part in the development of the plaque both directly and indirectly by their impact on LDL composition. The ratio of dietary to synthesised cholesterol is variable but tightly regulated: hence intervention with diet at best reduces serum cholesterol by <20% andusually <10%. Statins are the mainstay of cholesterol reduction therapy, but they increase cholesterol absorption, an example of the relationship between synthesis and absorption. Inhibition of cholesterol absorption with Ezetimibe, an inhibitor of Niemann Pick C1-like 1 (NPC1-L1), the major regulator of cholesterol absorption, increases cholesterol synthesis and hence the value of adding an inhibitor of cholesterol absorption to an inhibitor of cholesterol synthesis. Apo B48, the structural protein of the chylomicron particle, is synthesised in abundance so that the release of these particles is dependent on the amount of cholesterol and triglyceride available in the intestine. This paper will discuss cholesterol absorption and synthesis, chylomicron formation, and the effect of postprandial lipoproteins on factors involved in atherosclerosis.

Viral genotype-specific role of PNPLA3, PPARG, MTTP, and IL28B in hepatitis C virus-associated steatosis

BACKGROUND & AIMS

Steatosis is a prominent feature of hepatitis C, especially in patients infected with genotype 3. The analysis of genetic polymorphisms influencing steatosis in chronic hepatitis C has been limited by the studies' small sample size, and important single nucleotide polymorphisms (SNPs), such as those in the patatin-like phospholipase family 3 protein (PNPLA3), were never evaluated.

METHODS

We analyzed the role of SNPs, from 19 systematically selected candidate genes, on steatosis in 626 Caucasian hepatitis C virus (HCV) infected patients. SNPs were extracted from a genome-wide association-generated dataset. Associations of alleles with the presence and/or different severity of steatosis were evaluated by univariate and multivariate logistic regression, accounting for all relevant covariates.

RESULTS

The risk of steatosis was increased by carriage of I148M in PNPLA3, but only in patients with HCV genotypes non-3 (odds ratio [OR]=1.9, 95% confidence interval [CI]=1.6-2.3, p<0.001) and similar, albeit weaker associations were found for SNPs in peroxisome proliferator-activated receptor-γ (PPARG) and interleukin-28B (IL28B). Carriage of a SNP in the microsomal triglyceride transfer protein (MTTP) increased the risk of steatosis, but only in patients with HCV genotype 3 (rs1800803, OR=3.4, 95% CI=2.4-4.9, p=0.001).

CONCLUSIONS

The rs738409 SNP in PNPLA3 is associated with an increased risk of steatosis in patients infected with HCV genotypes non-3. Host genes affect steatosis depending on the infecting HCV genotype, suggesting their interaction with viral factors.

Dyslipidaemia--hepatic and intestinal cross-talk

Cholesterol metabolism is tightly regulated with the majority of de novo cholesterol synthesis occurring in the liver and intestine. 3 Hydroxy-3-methylglutaryl coenzyme A reductase, a major enzyme involved in cholesterol synthesis, is raised in both liver and intestine in diabetic animals. Niemann PickC1-like1 protein regulates cholesterol absorption in the intestine and facilitates cholesterol transport through the liver. There is evidence to suggest that the effect of inhibition of Niemann PickC1-like1 lowers cholesterol through its effect not only in the intestine but also in the liver. ATP binding cassette proteins G5/G8 regulate cholesterol re-excretion in the intestine and in the liver, cholesterol excretion into the bile. Diabetes is associated with reduced ATP binding cassette protein G5/G8 expression in both the liver and intestine in animal models. Microsomal triglyceride transfer protein is central to the formation of the chylomicron in the intestine and VLDL in the liver. Microsomal triglyceride transfer protein mRNA is increased in diabetes in both the intestine and liver. Cross-talk between the intestine and liver is poorly documented in humans due to the difficulty in obtaining liver biopsies but animal studies are fairly consistent in showing relationships that explain in part mechanisms involved in cholesterol homeostasis.

Microsomal triglyceride transfer protein and nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease is currently one of the most common forms of liver disease, covering cases from simple steatosis without inflammation, to cases of steatohepatitis and fibrosis, and may lead to liver cirrhosis and hepatocellular carcinoma. The pathophysiology of nonalcoholic fatty liver disease is based on multiple events; changes in the secretion of lipoproteins can lead to steatosis. Liver lipid secretion is mediated by apoB100 and microsomal triglyceride transfer protein (MTP). The pharmacological suppression of MTP is suggested as a possible treatment for hyperlipidemia, although the upregulation of this protein can be a treatment for nonalcoholic steatohepatitis.

Genetic polymorphisms in non-alcoholic fatty liver disease in obese Egyptian children

BACKGROUND/AIM

Polymorphisms in the promoter of microsomal triglyceride transfer protein (MTP) lead to decreased MTP transcription, less export of triglyceride from hepatocytes, and greater intracellular triglyceride accumulation. Therefore, functional polymorphisms in MTP may be involved in determining susceptibility to nonalcoholic steatohepatitis (NASH). The aim of this study is to examine the effect of some genetic influences among a group of obese Egyptian children.

PATIENTS AND METHODS

A cross-sectional study was conducted on 76 overweight and obese children presenting to the Pediatric Endocrinology Unit, Cairo University Children's Hospital, Egypt, as well as on 20 healthy controls. Anthropometric measurements were taken for all the patients and they underwent clinical examination, ultrasonographic examination of the liver, and liver biopsy when appropriate. Liver functions, blood glucose, serum insulin, C-peptide, and lipid profile were assessed and HOMA-IR calculated. Blood samples from biopsy-proven NASH patients and controls were analyzed by polymerase chain reaction (PCR) and restriction fragment length polymorphism for the -493 G/T polymorphism in the promoter of MTP and the 1183 T/C polymorphism in the mitochondrial targeting sequence of manganese superoxide dismutase (MnSOD).

RESULTS

Eight had biopsy-proven simple steatosis and 7 had NASH. NASH patients had a much higher incidence of the MTP G/G genotype (P = 0.002, CI: 2.9-392) compared with the controls. NASH patients also had a 100% prevalence of the MnSOD T/T genotype.

CONCLUSION

Certain genotypes in MTP and MnSOD are significantly more prevalent among obese children with NASH and may be responsible for such a phenotype.

Genetic determinants of apolipoprotein B-100 kinetics

PURPOSE OF REVIEW

We review stable isotope tracer studies of apolipoprotein B-100 (apoB) kinetics concerning genetic polymorphisms and mutations that affect human lipoprotein metabolism.

RECENT FINDINGS

In obese men, the allelic combination of the apoB signal peptide, SP24, and cholesteryl ester transfer protein, CETP B1B1, is independently associated with lower VLDL apoB secretion. Microsomal triglyceride transfer protein -493G/T carriers have reduced IDL apoB and LDL apoB production as compared with controls. Mutations in cholesterol transporters (ATP-binding cassette transporter G8 and Niemann-Pick C1 Like 1) are associated with reduced VLDL apoB secretion and increased LDL apoB production and catabolism. The ATP-binding cassette transporter G8 400K variant is a significant, independent predictor of VLDL apoB secretion. Mutations in lipases (lipoprotein lipase and hepatic lipase) and transfer proteins (lecithin-cholesterol acyltransferase and cholesteryl ester transfer protein) alter their functional activity, which impact on VLDL and LDL kinetics.

SUMMARY

Mutations in genes that regulate intrahepatic apoB assembly and lipid substrate availability to the liver impact on VLDL apoB secretion. Lipoprotein tracer studies can provide functional insight into the potential impact of genetic polymorphisms in regulating apoB metabolism in humans.

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.

Allele-specific regulation of MTTP expression influences the risk of ischemic heart disease

Promoter polymorphisms in microsomal triglyceride transfer protein (MTTP) have been associated with decreased plasma lipids but an increased risk for ischemic heart disease (IHD), indicating that MTTP influences the susceptibility for IHD independent of plasma lipids. The objective of this study was to characterize the functional promoter polymorphism in MTTP predisposing to IHD and its underlying mechanism. Use of pyrosequencing technology revealed that presence of the minor alleles of the promoter polymorphisms -493G>T and -164T>C result in lower transcription of MTTP in vivo in the heart, liver, and macrophages. In vitro experiments indicated that the minor -164C allele mediates the lower gene expression and that C/EBP binds to the polymorphic region in an allele-specific manner. Furthermore, homozygous carriers of the -164C were found to have increased risk for IHD as shown in a case-control study including a total of 544 IHD patients and 544 healthy control subjects. We concluded that carriers of the minor -164C allele have lower expression of MTTP in the heart, mediated at least partly by the transcription factor CCAAT/enhancer binding protein, and that reduced concentration of MTTP in the myocardium may contribute to IHD upon ischemic damage.

Hepatic steatosis in hepatitis C is a storage disease due to HCV interaction with microsomal triglyceride transfer protein (MTP)

Liver steatosis is a frequent histological feature in patients chronically infected with hepatitis C virus (HCV). The relationship between HCV and hepatic steatosis seems to be the result of both epigenetic and genetic factors. In vivo and in vitro studies have shown that HCV can alter intrahepatic lipid metabolism by affecting lipid synthesis, oxidative stress, lipid peroxidation, insulin resistance and the assembly and secretion of VLDL. Many studies suggest that HCV-related steatosis might be the result of a direct interaction between the virus and MTP. It has been demonstrated that MTP is critical for the secretion of HCV particles and that inhibition of its lipid transfer activity reduces HCV production. However, higher degrees of hepatic steatosis were found in chronic hepatitis C patients carrying the T allele of MTP -493G/T polymorphism that seems to be associated with increased MTP transcription. We propose here that liver steatosis in hepatitis C could be a storage disease induced by the effects of the virus and of its proteins on the intracellular lipid machinery and on MTP. Available data support the hypothesis that HCV may modulate MTP expression and activity through a number of mechanisms such as inhibition of its activity and transcriptional control. Initial up regulation could favour propagation of HCV while down regulation in chronic phase could cause impairment of triglyceride secretion and excessive lipid accumulation, with abnormal lipid droplets facilitating the "storage" of virus particles for persistent infection.

Association of polymorphisms of glutamate-cystein ligase and microsomal triglyceride transfer protein genes in non-alcoholic fatty liver disease

BACKGROUND AND AIMS

Although the metabolic risk factors for non-alcoholic fatty liver disease (NAFLD) progression have been recognized, the role of genetic susceptibility remains a field to be explored. The aim of this study was to examine the frequency of two polymorphisms in Brazilian patients with biopsy-proven simple steatosis or non-alcoholic steatohepatitis (NASH): -493 G/T in the MTP gene, which codes the protein responsible for transferring triglycerides to nascent apolipoprotein B, and -129 C/T in the GCLC gene, which codes the catalytic subunit of glutamate-cystein ligase in the formation of glutathione.

METHODS

One hundred and thirty-one biopsy-proven NAFLD patients (n = 45, simple steatosis; n = 86, NASH) and 141 unrelated healthy volunteers were evaluated. Genomic DNA was extracted from peripheral blood cells, and the -129 C/T polymorphism of the GCLC gene was determined by restriction fragment length polymorphism (RFLP). The -493 G/T polymorphism of the MTP gene was determined by direct sequencing of the polymerase chain reaction products.

RESULTS

The presence of at least one T allele in the -129 C/T polymorphism of the GCLC gene was independently associated with NASH (odds ratio 12.14, 95% confidence interval 2.01-73.35; P = 0.007), whereas, the presence of at least one G allele in the -493 G/T polymorphism of the MTP gene differed slightly between biopsy-proven NASH and simple steatosis.

CONCLUSION

This difference clearly warrants further investigation in larger samples. These two polymorphisms could represent an additional factor for consideration in evaluating the risk of NAFLD progression. Further studies involving a larger population are necessary to confirm this notion.

Nutrigenetics: links between genetic background and response to Mediterranean-type diets

OBJECTIVE

It has been substantiated that the onset of most major diseases (CVD, diabetes, obesity, cancers, etc.) is modulated by the interaction between genetic traits (susceptibility) and environmental factors, especially diet. We aim to report more specific observations relating the effects of Mediterranean-type diets on cardiovascular risk factors and the genetic background of subjects.

RESULTS AND CONCLUSIONS

In the first part, general concepts about nutrigenetics are briefly presented. Human genome has, overall, only marginally changed since its origin but it is thought that minor changes (polymorphisms) of common genes that occurred during evolution are now widespread in human populations, and can alter metabolic pathways and response to diets. In the second part, we report the data obtained during the Medi-RIVAGE intervention study performed in the South-East of France. Data obtained in 169 subjects at moderate cardiovascular risk after a 3-month dietary intervention indicate that some of the twenty-three single nucleotide polymorphisms (SNP) studied exhibit interactions with diets regarding changes of particular parameters after 3-month regimens. Detailed examples are presented, such as interactions between SNP in genes coding for microsomial transfer protein (MTTP) or intestinal fatty acid binding protein (FABP2) and triglyceride, LDL-cholesterol or Framigham score lowering in responses to Mediterranean-type diets. The data provided add further evidence of the interaction between particular SNP and metabolic responses to diets. Finally, improvement in dietary recommendations by taking into account known genetic variability has been discussed.

Lipoprotein metabolism mediates the association of MTP polymorphism with beta-cell dysfunction in healthy subjects and in nondiabetic normolipidemic patients with nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) predicts incident diabetes independently of insulin resistance, adiposity and metabolic syndrome through unclear mechanisms. Dietary fat consumption and lipoperoxidative stress predispose to diabetes in the general population and to liver injury in NASH. Microsomal triglyceride transfer protein (MTP) polymorphism modulates lipoprotein metabolism in the general population and liver disease in NASH; a functional MTP polymorphism recently predicted incident diabetes independently of insulin resistance in the general population. We simultaneously assessed the impact of MTP polymorphism, diet, adipokines and lipoprotein metabolism, on glucose homeostasis in NASH. MTP -493G/T polymorphism, dietary habits, adipokines and postprandial triglyceride-rich lipoproteins, high-density lipoprotein cholesterol (HDL-C) and oxidized low-density lipoprotein (oxLDL) responses to an oral fat load, were cross-sectionally correlated to oral glucose tolerance test- and frequently sampled intravenous glucose tolerance test-derived Minimal Model indexes of glucose homeostasis in 40 nondiabetic normolipidemic patients with NASH and 40 age-,sex- and body mass index-matched healthy controls. Despite comparable insulin resistance, fasting lipids, adipokines and dietary habits, MTP GG genotype had significantly more severe beta-cell dysfunction; higher plasma Tg, FFA, intestinal and hepatic very low-density lipoprotein 1 subfractions and oxLDL responses and deeper HDL-C fall than GT/TT carriers in patients and controls. Postprandial HDL-C and oxLDL responses independently predicted beta-cell dysfunction and mediated the effect of MTP polymorphism on beta-cell function. In nondiabetic normolipidemic NASH, MTP -493G/T polymorphism modulates beta-cell function, an effect mediated by postprandial HDL-C and oxLDL metabolism. The impact of this polymorphism on the risk of diabetes and the efficacy of lipid-lowering therapies in restoring beta-cell function in NASH, even with normal fasting lipid values, warrant further investigation.

Microsomal triglyceride transfer protein gene polymorphism strongly influences circulating malondialdehyde-modified low-density lipoprotein

Microsomal triglyceride transfer protein (MTP) plays a critical role in the assembly of lipoproteins. Therefore, we studied whether MTP gene polymorphisms are associated with atherosclerosis-promoting parameters, especially metabolic profiles and endothelial function, in healthy young men. One hundred one healthy men (mean age, 30.3 years) were studied. We analyzed the 2 promoter polymorphisms (-493G/T and -400A/T) of the MTP gene. Linkage disequilibrium analysis revealed a significant but incomplete linkage disequilibrium between the 2 polymorphisms (D' = 0.74). The -493T allele carriers (n = 26) showed marked increases in their levels of malondialdehyde-modified low-density lipoprotein (mean value, 135 vs 99 U/L in the G/G carriers; P = .003) and triglycerides (2.15 vs 1.16 mmol/L, P = .014), and reduced low-density lipoprotein particle size (259.2 vs 264.3 nm, P = .023), whereas there was no difference in apolipoproteins, insulin, adiponectin, homocysteine, folate, and endothelial function assessed using ultrasound measurement of brachial artery flow-mediated vasodilation. In contrast, the -400T allele carriers (n = 61) showed a reduced endothelial function (P = .044), accompanied by elevated apolipoprotein B levels in subjects with higher triglyceride levels. These results indicate that both promoter polymorphisms may be associated with the development of atherosclerosis and cardiovascular diseases, but that the mechanism responsible may be different.

Microsomal triglyceride transfer protein polymorphism (-493G/T) is associated with hepatic steatosis in patients with chronic hepatitis C

BACKGROUND

Hepatic steatosis may promote progression of chronic hepatitis C (CHC). Microsomal triglyceride transfer protein (MTP) is required for assembly and secretion of ApoB lipoprotein and is implicated in hepatitis C virus (HCV)-related steatosis. The MTP -493G/T polymorphism may promote liver fat accumulation, but its role in HCV-related steatosis is still unclear.

METHODS

Two hundred ninety-eight CHC patients were studied and genotyped for MTP -493G/T variants. Hepatic MTP mRNA expression and activity were determined in a subgroup.

RESULTS

Patients with grades 2/3 steatosis were older, had a higher body mass index (BMI), more advanced fibrosis and lower MTP mRNA expression and carried more often HCV genotype 3 and the MTP T allele. Age, BMI, HCV-3 and MTP T allele [odds ratio (OR) 2.05; 95% confidence interval (CI) 1.2-3.53; P=0.009] were independent risk factors for steatosis grades 2/3, and in HCV genotype non-3 patients, the MTP T allele was the strongest predictor for steatosis grade 2/3 (OR 2.17; 95% CI 1.22-3.86; P=0.008). Moreover, TT carriers had higher high-density lipoprotein (65.6+/-14.6 vs 56.1+/-16.2 mg/dl; P=0.003) and apolipoprotein AI (1.80+/-0.3 vs 1.60+/-0.3 g/L; P=0.005) levels than G allele carriers.

CONCLUSIONS

Chronic hepatitis C patients with the MTP -493T allele reveal higher grades of steatosis, indicating a relevant contribution to liver fat accumulation, particularly in HCV non-3 patients.

Influence of ethnicity on histological differences in non-alcoholic fatty liver disease

BACKGROUND/AIMS

Previous studies examining ethnic differences in non-alcoholic fatty liver disease (NAFLD) are limited by small sample sizes and the lack of liver biopsy as a diagnostic modality.

METHODS

We retrospectively examined the influence of ethnicity on the biochemical and liver histological differences in NAFLD patients.

RESULTS

The proportion of African Americans (AA) in the NAFLD sample (total 238 patients; 15.1% AA) was lower than in the base population (68.2%). Median ALT (47 IU/L; p=0.05) and triglyceride (134mg/dL, p=0.002) levels were lower in AA than other ethnicities. AA showed lower degrees of steatosis [odds ratio (OR) 0.44, 95% confidence interval (CI) 0.22-0.89; p=0.02] than Whites. In contrast, Asians showed higher grades of ballooning than Whites (OR 2.67, 95% CI 1.03-6.93; p=0.04) and other ethnicities combined (OR 2.71, 95% CI 1.06-6.92; p=0.04). Hispanics showed a higher rate of Mallory bodies than Whites (OR 2.38, 95% CI 1.05-5.39; p=0.04) and other ethnicities combined (OR 2.41, 95% CI 1.09-5.34; p=0.03).

CONCLUSIONS

African Americans showed a lower degree of steatosis than Whites. In contrast, Asians and Hispanics showed higher grades of ballooning and Mallory bodies, respectively, than Whites and other ethnicities combined. These findings highlight the need for prospective studies to evaluate ethnic differences in NAFLD.

Linkage disequilibrium between four MTTP gene polymorphisms in a Mexican population

BACKGROUND

The microsomal triglyceride transfer protein plays an important role in the folding, assembling and secretion of lipoproteins that contain apoprotein B. Different polymorphisms in the MTTP gene have been associated with risk factors for coronary heart disease and diabetes, the first and fourth most common causes of death in Mexico, respectively.

AIM

The objective of this study was to assess allele, genotype and haplotype frequencies of six MTTP polymorphisms in an unselected Mexican population.

SUBJECTS AND METHODS

Six polymorphisms were analysed by DNA sequencing of polymerase chain reaction products in 155 Mexican individuals and Hardy-Weinberg equilibrium, genetic variability, linkage disequilibrium and neutrality test were evaluated.

RESULTS

The rare alleles of the six polymorphisms analysed had frequencies greater than 1% and their genotype distributions were in accordance with Hardy-Weinberg equilibrium. All three promoter and I/T 128 polymorphisms were in linkage disequilibrium. Twelve different haplotypes were observed; GATGGT (70.44%) and TTCGGC (13.91%) were the most common. Diversity patterns in this Mexican population deviate significantly from expectations of the standard neutral model for infinite allele.

CONCLUSION

The -493 G/T, -400 A/T, -164 T/C and I/T 128 polymorphisms can be useful for association studies in this population.

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.

Microsomal triglyceride transfer protein (MTP) -493G/T gene polymorphism contributes to fat liver accumulation in HCV genotype 3 infected patients

(A) A reduced activity of microsomal triglyceride transfer protein (MTP), a key enzyme of assembly/secretion of lipoproteins, is related to HCV steatosis. Host genetic background may influence development of steatosis. The aim of the study was to investigate the association between MTP-493 G/T gene polymorphism, fat liver accumulation and fibrosis progression in HCV infected patients. A total of 102 naïve patients with liver biopsy proven chronic hepatitis C were evaluated for MTP-493 G/T gene polymorphism, HCV RNA, HCV genotype, HOMA-IR, serum adiponectin, TNF-alpha and serum lipid levels. HCV genotype 3 infected patients carrying the T allele of the MTP gene polymorphism showed higher degree of steatosis than those carrying GG genotype (3.45 +/- 0.37 vs 1.30 +/- 0.45, respectively; P < 0.001). MTP'T' allele carriers also had higher HCV RNA serum levels (P < 0.01) and hepatic fibrosis (P < 0.001). Irrespective of MTP genotype, patients with HCV genotype 3 had lower levels of cholesterol, ApoB, HDL and LDL. In HCV genotype non-3 infected patients no parameters were associated with MTP gene polymorphism. In conclusion the presence of T allele of MTP-493G/T gene polymorphism predisposes patients infested with HCV genotype 3 to develop higher degree of fatty liver accumulation.

Polymorphisms of microsomal triglyceride transfer protein in different hepatitis B virus-infected patients

AIM: To identify the two polymorphisms of microsomal triglyceride transfer protein (MTP) gene in the Chinese population and to explore their correlation with both hepatitis B virus (HBV) self-limited infection and persistent infection.

METHODS: A total of 316 subjects with self-limited HBV infection and 316 patients with persistent HBV infection (195 subjects without familial history), matched with age and sex, from the Chinese Han population were enrolled in this study. Polymorphisms of MTP at the promoter region -493 and at H297Q were determined by the allele specific polymerase chain reaction (PCR).

RESULTS: The ratio of males to females was 2.13:1 for each group and the average age in the self-limited and chronic infection groups was 38.36 and 38.28 years, respectively. None of the allelic distributions deviated significantly from that predicted by the Hardy-Weinberg equilibrium. There was a linkage disequilibrium between H297Q and -493G/T (D’ = 0.77). As the χ² test was used, the genotype distribution of MTP-493G/T demonstrated a significant difference between the self-limited infection group and the entire chronic group or the chronic patients with no family history (χ² = 8.543, P = 0.015 and χ² = 7.199, P = 0.019). The allele distribution at the MTP-493 position also demonstrated a significant difference between the study groups without family history (χ² = 6.212, P = 0.013). The T allele emerged as a possible protective factor which may influence the outcomes of HBV infection (OR: 0.59; 95% CI: 0.389-0.897).

CONCLUSION: The polymorphism of the MTP gene, T allele at -493, may be involved in determining the HBV infection outcomes, of which the mechanism needs to be further investigated.

The intestine as a regulator of cholesterol homeostasis in diabetes

The chylomicron influences very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) composition but itself is atherogenic. Thus abnormalities of chylomicron production are of interest particularly in conditions such as diabetes which confer major cardiovascular risk. Intestinal function is abnormal in diabetes and is a major cause of the dyslipidaemia found in this condition. Studies have suggested that cholesterol absorption is decreased in diabetes and cholesterol synthesis increased. Molecular mechanisms involved in insulin resistance in the intestine and its effect on cholesterol homeostasis in diabetes are described. Abnormalities in triglyceride synthesis and alterations genes regulating cholesterol absorption and intestinal synthesis are discussed. In particular, increase in apolipoprotein B48 synthesis has been demonstrated in animal models of diabetes and insulin resistance. Intestinal mRNA expression of Niemann Pick C1-like 1, protein is increased in both experimental and human diabetes suggesting that an increase in cholesterol transportation does occur. mRNA expression of the ATP binding cassette proteins (ABC) G5 and G8, two proteins working in tandem to excrete cholesterol have been shown to be decreased suggesting increased delivery of cholesterol for absorption. Expression of microsomal triglyceride transfer protein, which assembles the chylomicron particle, is increased in diabetes leading to increase in both number and cholesterol content. In conclusion, diabetes is associated with considerable dysfunction of the intestine leading to abnormal chylomicron composition which may play a major part in the premature development of atherosclerosis.

Human fasting plasma concentrations of vitamin E and carotenoids, and their association with genetic variants in apo C-III, cholesteryl ester transfer protein, hepatic lipase, intestinal fatty acid binding protein and microsomal triacylglycerol transfer protein

Plasma concentrations of vitamin E and carotenoids are governed by several factors, including genetic factors. Single nucleotide polymorphisms (SNP) in some genes involved in lipid metabolism have recently been associated with fasting plasma concentrations of these fat-soluble micronutrients. To further investigate the role of genetic factors that modulate the plasma concentrations of these micronutrients, we assessed whether SNP in five candidate genes (apo C-III,CETP,hepatic lipase,I-FABPandMTP) were associated with the plasma concentrations of these micronutrients. Fasting plasma vitamin E and carotenoid concentrations were measured in 129 French Caucasian subjects (forty-eight males and eighty-one females). Candidate SNP were genotyped by PCR amplification followed by restriction fragment length polymorphisms. Plasma γ-tocopherol, α-carotene and β-carotene concentrations were significantly different (P < 0·05) in subjects who carried different SNP variants in hepatic lipase. Plasma α-tocopherol concentrations were significantly different in subjects who had different SNP variants in apo C-III and cholesteryl ester transfer protein (CETP). Plasma lycopene concentrations were significantly different (P < 0·05) in women who had different SNP variants in intestinal fatty acid binding protein (I-FABP). Finally, there was no effect of SNP variants in microsomal TAG transfer protein upon the plasma concentrations of these micronutrients. Most of the observed differences remained significant after the plasma micronutrients were adjusted for plasma TAG and cholesterol. These results suggest that apo C-III, CETP and hepatic lipase play a role in determining the plasma concentrations of tocopherols while hepatic lipase and I-FABP may modulate plasma concentrations of carotenoids.