Bone marrow fat unsaturation in young adults is not affected by present or childhood obesity, but increases with age: A pilot study

OBJECTIVES

Obesity increases bone marrow fat (BMF) content. The association between early obesity and bone marrow fatty acid composition is unknown. We measured BMF unsaturation index (UI) in normal-weight and overweight young adults with a known weight status in early childhood and tested the relationship between BMF UI and exercise history, glycemic state, and other clinical characteristics.

METHODS

The study included 18 normal-weight (BMI <25 kg/m(2); 2 males, 16 females) and 17 overweight (BMI ≥25 kg/m(2); 9 males, 8 females) young adults aged 15-27 years. BMF UI was assessed with magnetic resonance proton spectroscopy optimized to reduce water interference. Exercise information was obtained with a pedometer accompanied with the history of recent physical activity. Blood samples (insulin, glucose, HbA1c) and body characteristics (BMI, waist-to-hip ratio, body fat composition) were assessed.

RESULTS

BMF UI was not affected by obesity at the time of study or before age 7 years. BMF UI increased with age in normal-weight and overweight subjects (R=0.408, p=0.015) but did not associate with gender, physical activity or body fat composition; a suggestive association was observed with glucose (R=-0.289, p=0.10).

CONCLUSIONS

The association of BMF UI with age in early adulthood may represent normal maturation of bone marrow. There was a trend toward an association with blood glucose, warranting further studies.

DNA methylation and gene expression patterns in adipose tissue differ significantly within young adult monozygotic BMI-discordant twin pairs

BACKGROUND

Little is known about epigenetic alterations associated with subcutaneous adipose tissue (SAT) in obesity. Our aim was to study genome-wide DNA methylation and gene expression differences in SAT in monozygotic (MZ) twin pairs who are discordant for body mass index (BMI). This design completely matches lean and obese groups for genetic background, age, gender and shared environment.

METHODS

14We analyzed DNA methylome and gene expression from SAT, together with body composition (magnetic resonance imaging/spectroscopy) and glucose tolerance test, lipids and C-reactive protein from 26 rare BMI-discordant (intrapair difference in BMI ⩾3 kg m(-2)) MZ twin pairs identified from 10 birth cohorts of young adult Finnish twins.

RESULTS

We found 17 novel obesity-associated genes that were differentially methylated across the genome between heavy and lean co-twins. Nine of them were also differentially expressed. Pathway analyses indicated that dysregulation of SAT in obesity includes a paradoxical downregulation of lipo/adipogenesis and upregulation of inflammation and extracellular matrix remodeling. Furthermore, CpG sites whose methylation correlated with metabolically harmful fat depots (intra-abdominal and liver fat) also correlated with measures of insulin resistance, dyslipidemia and low-grade inflammation, thus suggesting that epigenetic alterations in SAT are associated with the development of unhealthy obesity.

CONCLUSION

This is the first study in BMI-discordant MZ twin pairs reporting genome-wide DNA methylation and expression profiles in SAT. We found a number of novel genes and pathways whose methylation and expression patterns differ within the twin pairs, suggesting that the pathological adaptation of SAT to obesity is, at least in part, epigenetically regulated.

Impaired Mitochondrial Biogenesis in Adipose Tissue in Acquired Obesity

Low mitochondrial number and activity have been suggested as underlying factors in obesity, type 2 diabetes, and metabolic syndrome. However, the stage at which mitochondrial dysfunction manifests in adipose tissue after the onset of obesity remains unknown. Here we examined subcutaneous adipose tissue (SAT) samples from healthy monozygotic twin pairs, 22.8-36.2 years of age, who were discordant (ΔBMI >3 kg/m(2), mean length of discordance 6.3 ± 0.3 years, n = 26) and concordant (ΔBMI <3 kg/m(2), n = 14) for body weight, and assessed their detailed mitochondrial metabolic characteristics: mitochondrial-related transcriptomes with dysregulated pathways, mitochondrial DNA (mtDNA) amount, mtDNA-encoded transcripts, and mitochondrial oxidative phosphorylation (OXPHOS) protein levels. We report global expressional downregulation of mitochondrial oxidative pathways with concomitant downregulation of mtDNA amount, mtDNA-dependent translation system, and protein levels of the OXPHOS machinery in the obese compared with the lean co-twins. Pathway analysis indicated downshifting of fatty acid oxidation, ketone body production and breakdown, and the tricarboxylic acid cycle, which inversely correlated with adiposity, insulin resistance, and inflammatory cytokines. Our results suggest that mitochondrial biogenesis, oxidative metabolic pathways, and OXPHOS proteins in SAT are downregulated in acquired obesity, and are associated with metabolic disturbances already at the preclinical stage.

Paradoxical dissociation between hepatic fat content and de novo lipogenesis due to PNPLA3 sequence variant

CONTEXT

Nonalcoholic fatty liver disease (NAFLD) is an emerging epidemic disease characterized by increased hepatic fat, due to an imbalance between synthesis and removal of hepatic lipids. In particular, increased hepatic de novo lipogenesis (DNL) is a key feature associated with NAFLD. The genetic variations I148M in PNPLA3 and E167K in TM6SF2 confer susceptibility to NAFLD.

OBJECTIVE

Here we aimed to investigate the contribution of DNL to liver fat accumulation in the PNPLA3 I148M or TM6SF2 E167K genetic determinants of NAFLD.

PATIENTS AND METHODS

The PNPLA3 I148M and TM6SF2 E167K were genotyped in two well-characterized cohorts of Europeans. In the first cohort (Helsinki cohort; n = 88), we directly quantified hepatic DNL using deuterated water. In the second cohort (Milan cohort; n = 63), we quantified the hepatic expression of SREBP1c that we have found previously associated with increased fat content. Liver fat was measured by magnetic resonance proton spectroscopy in the Helsinki cohort, and by histological assessment of liver biopsies in the Milan cohort.

RESULTS

PNPLA3 148M was associated with lower DNL and expression of the lipogenic transcription factor SREBP1c despite substantial increased hepatic fat content.

CONCLUSIONS

Our data show a paradoxical dissociation between hepatic DNL and hepatic fat content due to the PNPLA3 148M allele indicating that increased DNL is not a key feature in all individuals with hepatic steatosis, and reinforces the contribution of decreased mobilization of hepatic triglycerides for hepatic lipid accumulation in subject with the PNPLA3 148M allele.

Genome-wide blood DNA methylation alterations at regulatory elements and heterochromatic regions in monozygotic twins discordant for obesity and liver fat

Background

The current epidemic of obesity and associated diseases calls for swift actions to better understand the mechanisms by which genetics and environmental factors affect metabolic health in humans. Monozygotic (MZ) twin pairs showing discordance for obesity suggest that epigenetic influences represent one such mechanism. We studied genome-wide leukocyte DNA methylation variation in 30 clinically healthy young adult MZ twin pairs discordant for body mass index (BMI; average within-pair BMI difference: 5.4 ± 2.0 kg/m²).

Results

There were no differentially methylated cytosine-guanine (CpG) sites between the co-twins discordant for BMI. However, stratification of the twin pairs based on the level of liver fat accumulation revealed two epigenetically highly different groups. Significant DNA methylation differences (n = 1,236 CpG sites (CpGs)) between the co-twins were only observed if the heavier co-twins had excessive liver fat (n = 13 twin pairs). This unhealthy pattern of obesity was coupled with insulin resistance and low-grade inflammation. The differentially methylated CpGs included 23 genes known to be associated with obesity, liver fat, type 2 diabetes mellitus (T2DM) and metabolic syndrome, and potential novel metabolic genes. Differentially methylated CpG sites were overrepresented at promoters, insulators, and heterochromatic and repressed regions. Based on predictions by overlapping histone marks, repressed and weakly transcribed sites were significantly more often hypomethylated, whereas sites with strong enhancers and active promoters were hypermethylated. Further, significant clustering of differentially methylated genes in vitamin, amino acid, fatty acid, sulfur, and renin-angiotensin metabolism pathways was observed.

Conclusions

The methylome in leukocytes is altered in obesity associated with metabolic disturbances, and our findings indicate several novel candidate genes and pathways in obesity and obesity-related complications.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-015-0073-5) contains supplementary material, which is available to authorized users.

Liver fat content and hepatic insulin sensitivity in overweight patients with type 1 diabetes

OBJECTIVES

Patients with type 1 diabetes mellitus (T1DM) lack the portal/peripheral insulin gradient, which might diminish insulin stimulation of hepatic lipogenesis and protect against development of nonalcoholic fatty liver disease (NAFLD). We compared liver fat content and insulin sensitivity of hepatic glucose production and lipolysis between overweight T1DM patients and nondiabetic subjects.

MATERIALS AND METHODS

We compared 32 overweight adult T1DM patients and 32 nondiabetic subjects matched for age, body mass index (BMI), and gender. Liver fat content was measured using proton magnetic resonance spectroscopy ((1)H-MRS), body composition by magnetic resonance imaging, and insulin sensitivity using the euglycemic-hyperinsulinemic clamp technique (insulin 0.4 mU/kg · min combined with infusion of D-[3-(3)H]glucose). We also hypothesized that low liver fat might protect from obesity-associated increases in insulin requirements and, therefore, determined insulin requirements across BMI categories in 3164 T1DM patients.

RESULTS

Liver fat content was significantly lower in T1DM patients than in nondiabetic subjects (0.6% [25th-75th quartiles, 0.3%-1.1%] vs 9.0% [3.0%-18.0%]; P < .001). The endogenous rate of glucose production (R(a)) during euglycemic hyperinsulinemia was significantly lower (0.4 [-0.7 to 0.8] mg/kg fat-free mass · min vs 0.9 [0.2-1.6] fat-free mass · min; P = .012) and the percent suppression of endogenous Ra by insulin was significantly greater (89% [78%-112%] vs 77% [50%-94%]; p = .009) in T1DM patients than in nondiabetic subjects. Serum nonesterified fatty acid concentrations during euglycemic hyperinsulinemia were significantly lower (78.5 [33.0-155.0] vs 306 [200.0-438.0] μmol/L; P < .001) and the percent suppression of nonesterified fatty acids significantly higher (89.1% [78.6%-93.3%] vs 51.4% [36.5%-71.1%]; P < .001) in T1DM patients than in nondiabetic subjects. Insulin doses were similar across BMI categories.

CONCLUSIONS

T1DM patients might be protected from steatosis and hepatic insulin resistance. Obesity may not increase insulin requirements in T1DM.

Impact of non-alcoholic fatty liver disease on liver volume in humans

AIM

Knowledge of liver volume is needed in the preoperative screening of liver transplant donors and in pharmacokinetic studies. In previous studies, bodyweight, surface area, age and sex have been identified as predictors of total liver volume, but the impact of non-alcoholic fatty liver disease (NAFLD) independent of body size on liver volume has not been determined. We examined whether and to what extent liver fat due to NAFLD influences liver volume.

METHODS

We quantified the percentage of liver fat by proton magnetic resonance spectroscopy ((1) H-MRS) and liver total, lean and fat volumes using magnetic resonance imaging (MRI) in 112 subjects (62 women, 50 men), who were characterized with respect to metabolic parameters associated with NAFLD.

RESULTS

Of the subjects, 45% had NAFLD (liver fat 12.5 ± 4.5% vs 1.8 ± 1.6%, NAFLD vs no NAFLD, P < 0.001). Total liver volume was 29% higher in subjects with NAFLD (1.91 ± 0.45 L) than in those with no NAFLD (1.49 ± 0.31 L, P < 0.001). In multiple linear regression analysis, the percentage of liver fat and bodyweight independently explained variation in total liver volume (r(2)  = 0.42, P < 0.001). The r-values for the relationship between metabolic parameters and the total liver fat volume were not significantly better than those between metabolic parameters and the percentage of liver fat.

CONCLUSION

Both bodyweight and NAFLD increase liver volume independent of each other. Measurement of liver fat by (1) H-MRS allows accurate quantification of NAFLD and calculation of total liver volume.

Measuring short-term liver metabolism non-invasively: postprandial and post-exercise ¹H and ³¹P MR spectroscopy

OBJECT

The objective of this study was to determine the effects of a standardized fat rich meal and subsequent exercise on liver fat content by ¹H MRS and on liver adenosine triphosphate (ATP) content by ³¹P MRS in healthy subjects.

MATERIALS AND METHODS

Hepatic ¹H and proton decoupled ³¹P MRS were performed on nine healthy subjects on a clinical 3.0 T MR imager three times during a day: after (1) an overnight fast, (2) a following standardized fat rich meal and (3) a subsequent exercise session. Blood parameters were followed during the day to serve as a reference to MRS.

RESULTS

Liver fat content increased gradually over the day (p = 0.0001) with an overall increase of 30 %. Also γ-NTP changed significantly over the day (p = 0.005). γ-NTP/tP decreased by 9 % (p = 0.019, post hoc) from the postprandial to the post-exercise state.

CONCLUSION

Our study shows that in vivo MRS can depict short lived physiological changes; entering of fat into liver cells and consumption of ATP during exercise can be measured non-invasively in healthy subjects. The physiological state may have an impact on fat and energy metabolite levels. Hepatic ¹H and ³¹P MRS studies should be performed under standardized conditions.

Metabolome and fecal microbiota in monozygotic twin pairs discordant for weight: a Big Mac challenge

Postprandial responses to food are complex, involving both genetic and environmental factors. We studied postprandial responses to a Big Mac meal challenge in monozygotic co-twins highly discordant for body weight. This unique design allows assessment of the contribution of obesity, independent of genetic liability. Comprehensive metabolic profiling using 3 analytical platforms was applied to fasting and postprandial serum samples from 16 healthy monozygotic twin pairs discordant for weight (body mass index difference >3 kg/m(2)). Nine concordant monozygotic pairs were examined as control pairs. Fecal samples were analyzed to assess diversity of the major bacterial groups by using 5 different validated bacterial group specific denaturing gradient gel electrophoresis methods. No differences in fecal bacterial diversity were detected when comparing co-twins discordant for weight (ANOVA, P<0.05). We found that within-pair similarity is a dominant factor in the metabolic postprandial response, independent of acquired obesity. Branched chain amino acids were increased in heavier as compared with leaner co-twins in the fasting state, but their levels converged postprandially (paired t tests, FDR q<0.05). We also found that specific bacterial groups were associated with postprandial changes of specific metabolites. Our findings underline important roles of genetic and early life factors in the regulation of postprandial metabolite levels.

Effects of dietary interventions on liver volume in humans

OBJECTIVE

To compare effects of similar weight loss induced either by a short-term low-carbohydrate or by a long-term hypocaloric diet, and to determine effects of high carbohydrate overfeeding on liver total, lean, and fat volumes.

METHODS

Liver total, lean, and fat volumes were measured before and after (i) a 6-day low-carbohydrate diet (n = 17), (ii) a 7-month standard hypocaloric diet (n = 26), and (iii) a 3-week high-carbohydrate diet (n = 17), by combining magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy ((1) H-MRS) techniques.

RESULTS

At baseline, three groups were comparable with respect to age, body mass index, liver volumes and the liver fat content. Body weight decreased similarly by the short-term and long-term hypocaloric diets. Liver total volume decreased significantly more during the short-term low-carbohydrate (-22 ± 2%) than the long-term (-7 ± 2%) hypocaloric diet (P < 0.001). This was due to a greater decrease in liver lean volume in the short-term (-20 ± 2%) than the long-term (-4 ± 2%) weight loss group (P < 0.001). Decreases in liver fat were comparable. Liver volume increased by 9 ± 3% due to overfeeding (P< 0.02 for before vs. after).

CONCLUSIONS

These data support the use of a short-term low-carbohydrate diet whenever a reduction in liver volume is desirable. Overeating carbohydrate is harmful because it increases liver volume.

Electrocardiographic changes associated with insulin resistance

BACKGROUND AND AIM

Cardiac steatosis has been related to increased risk of heart disease. We investigated the association between cardiac steatosis, electrocardiographic (ECG) abnormalities, and individual components of the metabolic syndrome (MetS).

METHODS AND RESULTS

A 12-lead ECG and laboratory data were examined in 31 men with the MetS and in 38 men without the MetS. Myocardial triglyceride (MTG) content was measured with 1.5 T magnetic resonance (MR) spectroscopy and epicardial and pericardial fat by MR imaging. MTG content, epicardial and pericardial fat depots were higher in men with the MetS compared with subjects without the MetS (p < 0.001). The heart rate was increased (p < 0.001), the PR interval was longer (p < 0.044), the frontal plane QRS axis shifted to the left (p < 0.001), and the QRS voltage (p < 0.001) was lower in subjects with the MetS. The frontal plane QRS axis and the QRS voltage were inversely correlated with MTG content, waist circumference (WC), body mass index (BMI), TGs, and fasting blood glucose. High-density lipoprotein cholesterol correlated positively and measures of insulin resistance negatively with the QRS voltage. MTG content and hypertriglyceridemia were determinants of the frontal plane QRS and WC and hyperglycemia were predictors of the QRS voltage.

CONCLUSION

The MetS and cardiac steatosis appear to associate with multiple changes on 12-lead ECG. The frontal plane QRS axis is shifted to the left and the QRS voltage is lower in subjects with the MetS. Standard ECG criteria may underestimate the presence of left ventricular hypertrophy in obese subjects with cardiometabolic risk factors.

Adipocyte morphology and implications for metabolic derangements in acquired obesity

BACKGROUND

Adipocyte size and number have been suggested to predict the development of metabolic complications in obesity. However, the genetic and environmental determinants behind this phenomenon remain unclear.

METHODS

We studied this question in rare-weight discordant (intra-pair difference (Δ) body mass index (BMI) 3-10 kg m(-2), n=15) and concordant (ΔBMI 0-2 kg m(-)(2), n=5) young adult (22-35 years) monozygotic twin pairs identified from 10 birth cohorts of Finnish twins (n=5 500 pairs). Subcutaneous abdominal adipocyte size from surgical biopsies was measured under a light microscope. Adipocyte number was calculated from cell size and total body fat (D × A).

RESULTS

The concordant pairs were remarkably similar for adipocyte size and number (intra-class correlations 0.91-0.92, P<0.01), suggesting a strong genetic control of these measures. In the discordant pairs, the obese co-twins (BMI 30.6 ± 0.9 kg m(-2)) had significantly larger adipocytes (volume 547 ± 59 pl), than the lean co-twins (24.9 ± 0.9 kg m(-)(2); 356 ± 34 pl, P<0.001). In 8/15 pairs, the obese co-twins had less adipocytes than their co-twins. These hypoplastic obese twins had significantly higher liver fat (spectroscopy), homeostatic model assessment-index, C-reactive protein and low-density lipoprotein cholesterol than their lean co-twins. Hyperplastic obesity was observed in the rest (7/15) of the pairs, obese and lean co-twins having similar metabolic measures. In all pairs, Δadipocyte volume correlated positively and Δcell number correlated negatively with Δhomeostatic model assessment-index and Δlow-density lipoprotein, independent of Δbody fat. Transcripts most significantly correlating with Δadipocyte volume were related to a reduced mitochondrial function, membrane modifications, to DNA damage and cell death.

CONCLUSIONS

Together, hypertrophy and hypoplasia in acquired obesity are related to metabolic dysfunction, possibly through disturbances in mitochondrial function and increased cell death within the adipose tissue.

GLP-1 responses are heritable and blunted in acquired obesity with high liver fat and insulin resistance

OBJECTIVE Impaired incretin response represents an early and uniform defect in type 2 diabetes, but the contributions of genes and the environment are poorly characterized. RESEARCH DESIGN AND METHODS We studied 35 monozygotic (MZ) and 75 dizygotic (DZ) twin pairs (discordant and concordant for obesity) to determine the heritability of glucagon-like peptide 1 (GLP-1) responses to an oral glucose tolerance test (OGTT) and the influence of acquired obesity to GLP-1, glucose-dependent insulinotropic peptide (GIP), and peptide YY (PYY) during OGTT or meal test. RESULTS The heritability of GLP-1 area under the curve was 67% (95% CI 45-80). Cotwins from weight-concordant MZ and DZ pairs and weight-discordant MZ pairs but concordant for liver fat content demonstrated similar glucose, insulin, and incretin profiles after the OGTT and meal tests. In contrast, higher insulin responses and blunted 60-min GLP-1 responses during the OGTT were observed in the heavier as compared with leaner MZ cotwins discordant for BMI, liver fat, and insulin sensitivity. Blunted GLP-1 response to OGTT was observed in heavier as compared with leaner DZ cotwins discordant for obesity and insulin sensitivity. CONCLUSIONS Whereas the GLP-1 response to the OGTT is heritable, an acquired unhealthy pattern of obesity characterized by liver fat accumulation and insulin resistance is closely related to impaired GLP-1 response in young adults.

Characterising metabolically healthy obesity in weight-discordant monozygotic twins

AIMS/HYPOTHESIS

Not all obese individuals display the metabolic disturbances commonly associated with excess fat accumulation. Mechanisms maintaining this 'metabolically healthy obesity' (MHO) are as yet unknown. We aimed to study different fat depots and transcriptional pathways in subcutaneous adipose tissue (SAT) as related to the MHO phenomenon.

METHODS

Sixteen rare young adult obesity-discordant monozygotic (MZ) twin pairs (intra-pair difference (∆) in BMI ≥ 3 kg/m(2)), aged 22.8-35.8 years, were examined for detailed characteristics of metabolic health (subcutaneous, intra-abdominal and liver fat [magnetic resonance imaging/spectroscopy]), OGTT, lipids, adipokines and C-reactive protein (CRP). Affymetrix U133 Plus 2.0 chips were used to analyse transcriptomics pathways related to mitochondrial function and inflammation in SAT.

RESULTS

Based on liver fat accumulation, two metabolically different subgroups emerged. In half (8/16) of the pairs (∆weight 17.1 ± 2.0 kg), the obese co-twin had significantly higher liver fat (∆718%), 78% increase in AUC insulin during OGTT and CRP, significantly more disturbance in the lipid profile and greater tendency for hypertension compared with the lean co-twin. In these obese co-twins, SAT expression of mitochondrial oxidative phosphorylation, branched-chain amino acid catabolism, fatty acid oxidation and adipocyte differentiation pathways were downregulated and chronic inflammation upregulated. In the other eight pairs (∆weight 17.4 ± 2.8 kg), the obese co-twin did not differ from the non-obese co-twin in liver fat (∆8%), insulin sensitivity, CRP, lipids, blood pressure or SAT transcriptomics.

CONCLUSIONS/INTERPRETATION

Our results suggest that maintenance of high mitochondrial transcription and lack of inflammation in SAT are associated with low liver fat and MHO.

Genetic variation in SULF2 is associated with postprandial clearance of triglyceride-rich remnant particles and triglyceride levels in healthy subjects

Context

Nonfasting (postprandial) triglyceride concentrations have emerged as a clinically significant cardiovascular disease risk factor that results from accumulation of remnant triglyceride-rich lipoproteins (TRLs) in the circulation. The remnant TRLs are cleared from the circulation by hepatic uptake, but the specific mechanisms involved are unclear. The syndecan-1 heparan sulfate proteoglycan (HSPG) pathway is important for the hepatic clearance of remnant TRLs in mice, but its relevance in humans is unclear.

Objective

We sought to determine whether polymorphisms of the genes responsible for HSPG assembly and disassembly contribute to atherogenic dyslipoproteinemias in humans.

Patients And Design

We performed an oral fat load in 68 healthy subjects. Lipoproteins (chylomicrons and very low density lipoproteins 1 and 2) were isolated from blood, and the area under curve and incremental area under curve for postprandial variables were calculated. Single nucleotide polymorphisms in genes encoding syndecan-1 and enzymes involved in the synthesis or degradation of HSPG were genotyped in the study subjects.

Results

Our results indicate that the genetic variation rs2281279 in SULF2 associates with postprandial clearance of remnant TRLs and triglyceride levels in healthy subjects. Furthermore, the SNP rs2281279 in SULF2 associates with hepatic SULF2 mRNA levels.

Conclusions

In humans, mild but clinically relevant postprandial hyperlipidemia due to reduced hepatic clearance of remnant TRLs may result from genetic polymorphisms that affect hepatic HSPG.

Cardiac steatosis and left ventricular function in men with metabolic syndrome

BACKGROUND

Ectopic accumulation of fat accompanies visceral obesity with detrimental effects. Lipid oversupply to cardiomyocytes leads to cardiac steatosis, and in animal studies lipotoxicity has been associated with impaired left ventricular (LV) function. In humans, studies have yielded inconclusive results. The aim of the study was to evaluate the role of epicardial, pericardial and myocardial fat depots on LV structure and function in male subjects with metabolic syndrome (MetS).

METHODS

A study population of 37 men with MetS and 38 men without MetS underwent cardiovascular magnetic resonance and proton magnetic spectroscopy at 1.5 T to assess LV function, epicardial and pericardial fat area and myocardial triglyceride (TG) content.

RESULTS

All three fat deposits were greater in the MetS than in the control group (p <0.001). LV diastolic dysfunction was associated with MetS as measured by absolute (471 mL/s vs. 667 mL/s, p = 0.002) and normalized (3.37 s⁻¹ vs. 3.75 s⁻¹, p = 0.02) LV early diastolic peak filling rate and the ratio of early diastole (68% vs. 78%, p = 0.001). The amount of epicardial and pericardial fat correlated inversely with LV diastolic function. However, myocardial TG content was not independently associated with LV diastolic dysfunction.

CONCLUSIONS

In MetS, accumulation of epicardial and pericardial fat is linked to the severity of structural and functional alterations of the heart. The role of increased intramyocardial TG in MetS is more complex and merits further study.

Acquired liver fat is a key determinant of serum lipid alterations in healthy monozygotic twins

OBJECTIVE

The effects of acquired obesity on lipid profile and lipoprotein composition in rare BMI-discordant monozygotic (MZ) twin pairs were studied.

DESIGN AND METHODS

Abdominal fat distribution, liver fat (magnetic resonance imaging and spectroscopy), fasting serum lipid profile (ultracentrifugation, gradient gel-electrophoresis, and colorimetric enzymatic methods), and lifestyle factors (questionnaires and diaries) were assessed in 15 BMI-discordant (within-pair difference [Δ] in BMI >3 kg/m2) and nin concordant (ΔBMI <3 kg/m2) MZ twin pairs, identified from two nationwide cohorts of Finnish twins.

RESULTS

Despite a strong similarity of MZ twins in lipid parameters (intra-class correlations 0.42-0.90, P < 0.05), concentrations of apolipoprotein B (ApoB), intermediate-density lipoprotein cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein 3a% (HDL3a%), and HDL3c% were higher (P < 0.05) and those of HDL cholesterol, HDL2-C, and HDL2b% were lower (P < 0.01) in the heavier co-twins of BMI-discordant pairs. The composition of lipoprotein particles was similar in the co-twins. When BMI-discordant pairs were further divided into liver fat-discordant and concordant (based on median for Δliver fat, 2.6%), the adverse lipid profile was only seen in those heavy co-twins who also had high liver fat. Conversely, BMI-discordant pairs concordant for liver fat did not differ significantly in lipid parameters. In multivariate analyses controlling for Δsubcutaneous, Δintra-abdominal fat, sex, Δsmoking and Δphysical activity, Δliver fat was the only independent variable explaining the variation in ΔApoB, Δtotal cholesterol, and ΔLDL-C concentration.

CONCLUSIONS

Several pro-atherogenic changes in the amounts of lipids but not in the composition of lipoprotein particles were observed in acquired obesity. In particular, accumulation of liver fat was associated with lipid disturbances, independent of genetic effects.

Adipocyte size is associated with NAFLD independent of obesity, fat distribution, and PNPLA3 genotype

OBJECTIVE

Adipocyte hypertrophy has been suggested to be causally linked with inflammation and systemic insulin resistance. The aim of the study was to determine whether increased adipocyte size is associated with increased liver fat content due to nonalcoholic fatty liver disease (NAFLD) in humans independent of obesity, fat distribution and genetic variation in the patatin-like phospholipase domain-containing 3 gene (PNPLA3; adiponutrin) at rs738409.

DESIGN AND METHODS

One hundred nineteen non-diabetic subjects in a cross-sectional study with a median age of 39 years, mean ± SD BMI of 30.0 ± 5.7 kg m(-2) were studied. Abdominal subcutaneous (SC) adipocyte size, liver fat [proton magnetic resonance spectroscopy ((1) H-MRS)], intra-abdominal (IA), and abdominal SC adipose tissue volumes [magnetic resonance imaging (MRI)] and the PNPLA3 genotype at rs738409 were determined. Univariate and multiple linear regression analysis were used to identify independent predictors of liver fat content.

RESULTS

In multiple linear regression analysis, age, gender, BMI, the IA/SC ratio, and PNPLA3 genotype explained 42% of variation in liver fat content. Addition of adipocyte size (P < 0.0001) to the model increased the percent of explanation to 53%. Thus, 21% of known variation in liver fat could be explained by adipocyte size alone.

CONCLUSIONS

Increased adipocyte size highly significantly contributes to liver fat accumulation independent of other causes.

Adipose tissue is inflamed in NAFLD due to obesity but not in NAFLD due to genetic variation in PNPLA3

AIMS/HYPOTHESIS

The rs738409 C>G single-nucleotide polymorphism in PNPLA3 leads to a missense mutation (I148M) which increases liver fat but does not cause insulin resistance. We hypothesised that patients with non-alcoholic fatty liver disease (NAFLD) due to the PNPLA3 variant ('PNPLA3 NAFLD' = PNPLA3-148MM) do not have adipose tissue (AT) inflammation in contrast with those with NAFLD due to obesity ('obese NAFLD').

METHODS

Biopsy specimens of AT were taken, and PNPLA3 genotype and liver fat ((1)H-magnetic resonance spectroscopy) were determined in 82 volunteers, who were divided into groups based on either median BMI (obese 36.2 ± 0.7 kg/m(2); non-obese 26.0 ± 0.4 kg/m(2)) or PNPLA3 genotype. All groups were similar with respect to age and sex. The PNPLA3 subgroups were equally obese (PNPLA3-148MM, 31.1 ± 1.3 kg/m(2); PNPLA3-148II, 31.2 ± 0.8 kg/m(2)), while the obese and non-obese subgroups had similar PNPLA3 genotype distribution. Gene expression of proinflammatory (MCP-1, CD68) and anti-inflammatory (Twist1, ADIPOQ) markers was measured using quantitative real-time RT-PCR.

RESULTS

Liver fat was similarly increased in obese NAFLD (9.5 ± 1.3% vs 5.1 ± 0.9%, obese vs non-obese, p = 0.007) and PNPLA3 NAFLD (11.4 ± 1.7% vs 5.3 ± 0.8%, PNPLA3-148MM vs PNPLA3-148II, p < 0.001). Fasting serum insulin was higher in the obese than the non-obese group (76 ± 6 vs 47 ± 6 pmol/l, p < 0.001), but similar in PNPLA3-148MM and PNPLA3-148II (60 ± 8 vs 62 ± 5 pmol/l, NS). In obese vs non-obese, MCP-1 and CD68 mRNAs were upregulated, whereas those of Twist1 and ADIPOQ were significantly downregulated. AT gene expression of MCP-1, CD68, Twist1 and ADIPOQ was similar in PNPLA3-148MM and PNPLA3-148II groups.

CONCLUSIONS/INTERPRETATION

PNPLA3 NAFLD is characterised by an increase in liver fat but no insulin resistance or AT inflammation, while obese NAFLD has all three of these features.

Cardiac steatosis associates with visceral obesity in nondiabetic obese men

BACKGROUND

Liver fat and visceral adiposity are involved in the development of the metabolic syndrome (MetS). Ectopic fat accumulation within and around the heart has been related to increased risk of heart disease. The aim of this study was to explore components of cardiac steatosis and their relationship to intra-abdominal ectopic fat deposits and cardiometabolic risk factors in nondiabetic obese men.

METHODS

Myocardial and hepatic triglyceride (TG) contents were measured with 1.5 T magnetic resonance spectroscopy, and visceral adipose (VAT), abdominal subcutaneous tissue (SAT), epicardial and pericardial fat by magnetic resonance imaging in 37 men with the MetS and in 40 men without the MetS.

RESULTS

Myocardial and hepatic TG contents, VAT, SAT, epicardial fat volumes, and pericardial fat volumes were higher in men with the MetS compared with subjects without the MetS (P < .001). All components of cardiac steatosis correlated with SAT, VAT, and hepatic TG content and the correlations seemed to be strongest with VAT. Myocardial TG content, epicardial fat, pericardial fat, VAT, and hepatic TG content correlated with waist circumference, body mass index, high-density lipoprotein cholesterol TGs, very low-density lipoprotein-1 TGs, and the insulin-resistance homeostasis model assessment index. VAT was a predictor of TGs, high-density lipoprotein cholesterol, and measures of glucose metabolism, whereas age and SAT were determinants of blood pressure parameters.

CONCLUSIONS

We suggest that visceral obesity is the best predictor of epicardial and pericardial fat in abdominally obese subjects. Myocardial TG content may present a separate entity that is influenced by factors beyond visceral adiposity.

Effect of short-term carbohydrate overfeeding and long-term weight loss on liver fat in overweight humans

BACKGROUND

Cross-sectional studies have identified a high intake of simple sugars as an important dietary factor predicting nonalcoholic fatty liver disease (NAFLD).

OBJECTIVE

We examined whether overfeeding overweight subjects with simple sugars increases liver fat and de novo lipogenesis (DNL) and whether this is reversible by weight loss.

DESIGN

Sixteen subjects [BMI (kg/m²): 30.6 ± 1.2] were placed on a hypercaloric diet (>1000 kcal simple carbohydrates/d) for 3 wk and, thereafter, on a hypocaloric diet for 6 mo. The subjects were genotyped for rs739409 in the PNPLA3 gene. Before and after overfeeding and after hypocaloric diet, metabolic variables and liver fat (measured by proton magnetic resonance spectroscopy) were measured. The ratio of palmitate (16:0) to linoleate (18:2n-6) in serum and VLDL triglycerides was used as an index of DNL.

RESULTS

Carbohydrate overfeeding increased weight (±SEM) by 2% (1.8 ± 0.3 kg; P < 0.0001) and liver fat by 27% from 9.2 ± 1.9% to 11.7 ± 1.9% (P = 0.005). DNL increased in proportion to the increase in liver fat and serum triglycerides in subjects with PNPLA3-148IIbut not PNPLA3-148MM. During the hypocaloric diet, the subjects lost 4% of their weight (3.2 ± 0.6 kg; P < 0.0001) and 25% of their liver fat content (from 11.7 ± 1.9% to 8.8 ± 1.8%; P < 0.05).

CONCLUSIONS

Carbohydrate overfeeding for 3 wk induced a >10-fold greater relative change in liver fat (27%) than in body weight (2%). The increase in liver fat was proportional to that in DNL. Weight loss restores liver fat to normal. These data indicate that the human fatty liver avidly accumulates fat during carbohydrate overfeeding and support a role for DNL in the pathogenesis of NAFLD. This trial was registered at www.hus.fi as 235780.

Genetic variation in PNPLA3 but not APOC3 influences liver fat in non-alcoholic fatty liver disease

BACKGROUND AND AIM

A recent study in Indian subjects suggested common variants in apolipoprotein C3 (APOC3) (T-455C at rs2854116 and C-482T at rs2854117) to contribute to non-alcoholic fatty liver disease (NAFLD), plasma apoC3 and triglyceride concentrations. Our aim was to determine the contribution of genetic variation in APOC3 on liver fat content and plasma triglyceride and apoC3 concentrations in a larger European cohort.

METHODS

A total of 417 Finnish individuals were genotyped for rs2854116 and rs2854117 in APOC3 and the known rs738409 in patatin-like phospholipase domain-containing protein 3 (PNPLA3) influencing liver fat. Plasma apoC3 concentration was measured enzymatically, and liver fat by proton magnetic resonance spectroscopy.

RESULTS

APOC3 wild-type homozygotes and variant allele (T-455C or C-482T or both) carriers did not differ with regard to liver fat, apoC3 concentrations, triglyceride-, high density lipoprotein-, fasting plasma glucose, insulin-, alanine aminotransferase- and aspartate aminotransferase-concentrations, nor was there a difference in prevalence of NAFLD. In contrast, carriers of the PNPLA3 GG genotype at rs738409 had a 2.7-fold (median 11.3%) higher liver fat than those with the CC (median 4.2%) genotype. The PNPLA3 rs738409 was also an independent predictor of liver fat, together with age, gender, and body mass index.

CONCLUSION

Genetic variants in PNPLA3 but not APOC3 contribute to the variance in liver fat content due to NAFLD.

Decrease in circulating fibroblast growth factor 21 after an oral fat load is related to postprandial triglyceride-rich lipoproteins and liver fat

BACKGROUND

Elevated levels of circulating fibroblast growth factor 21 (FGF21) are commonly encountered in type 2 diabetes, dyslipidemia, and non-alcoholic fatty liver disease, all of which share exaggerated postprandial lipemia as a common proatherogenic feature. How FGF21 responds to an oral fat load in man is unknown.

METHODS

We measured liver fat contents and subcutaneous and visceral fat volumes in 47 healthy subjects, who also underwent an oral fat load with measurements of plasma FGF21 and free fatty acid (FFA). Triglyceride (TG), apolipoprotein B-48 (apoB-48), and apoB-100 concentrations were measured in triglyceride-rich lipoprotein (TRL) fractions.

RESULTS

When compared with fasting levels, the concentration of FGF21 decreased significantly at 4 h (P < 0.05) and tended to return to fasting levels at 8 h after an oral fat load. Fasting and postprandial FGF21 correlated significantly with liver fat as well as with TRLs in the chylomicron and especially in very low-density lipoprotein 1 (VLDL1) and VLDL2 fractions representing remnant particles, but not with FFA. Subjects with increased liver fat (>5%, n = 12) showed impaired suppression of FGF21 at 4 h (P < 0.05) and at 8 h (P=0.01) and demonstrated higher postprandial TG area under the curve in plasma and TRL fractions (P ≤ 0.032) compared with those with normal liver fat (≤ 5%, n = 35).

CONCLUSIONS

We observed a significant decrease of FGF21 concentration after an oral fat load. Fasting and postprandial FGF21 levels were closely related to large VLDL and remnants, but not to plasma FFA. Our pilot findings suggest that the postprandial accumulation of TRL remnants and liver fat may modulate postprandial FGF21 levels.

Body electrical loss analysis (BELA) in the assessment of visceral fat: a demonstration

Background

Body electrical loss analysis (BELA) is a new non-invasive way to assess visceral fat depot size through the use of electromagnetism. BELA has worked well in phantom measurements, but the technology is not yet fully validated.

Methods

Ten volunteers (5 men and 5 women, age: 22-60 y, BMI: 21-30 kg/m², waist circumference: 73-108 cm) were measured with the BELA instrument and with cross-sectional magnetic resonance imaging (MRI) at the navel level, navel +5 cm and navel -5 cm. The BELA signal was compared with visceral and subcutaneous fat areas calculated from the MR images.

Results

The BELA signal did not correlate with subcutaneous fat area at any level, but correlated significantly with visceral fat area at the navel level and navel +5 cm. The correlation was best at level of navel +5 cm (R² = 0.74, P < 0.005, SEE = 29.7 cm², LOOCV = 40.1 cm²), where SEE is the standard error of the estimate and LOOCV is the root mean squared error of leave-one-out style cross-validation. The average estimate of repeatability of the BELA signal observed through the study was ±9.6 %. One of the volunteers had an exceptionally large amount of visceral fat, which was underestimated by BELA.

Conclusions

The correlation of the BELA signal with the visceral but not with the subcutaneous fat area as measured by MRI is promising. The lack of correlation with the subcutaneous fat suggests that subcutaneous fat has a minor influence to the BELA signal. Further research will show if it is possible to develop a reliable low-cost method for the assessment of visceral fat either using BELA only or combining it, for example, with bioelectrical impedance measurement. The combination of these measurements may help assessing visceral fat in a large scale of body composition. Before large-scale clinical testing and ROC analysis, the initial BELA instrumentation requires improvements. The accuracy of the present equipment is not sufficient for such new technology.

Dual metabolic defects are required to produce hypertriglyceridemia in obese subjects

OBJECTIVE

Obesity increases the risk of cardiovascular disease and premature death. However, not all obese subjects develop the metabolic abnormalities associated with obesity. The aim of this study was to clarify the mechanisms that induce dyslipidemia in obese subjects.

METHODS AND RESULTS

Stable isotope tracers were used to elucidate the pathophysiology of the dyslipidemia in hypertriglyceridemic (n=14) and normotriglyceridemic (n=14) obese men (with comparable body mass index and visceral fat volume) and in normotriglyceridemic nonobese men (n=10). Liver fat was determined using proton magnetic resonance spectroscopy, and subcutaneous abdominal and visceral fat were measured by magnetic resonance imaging. Serum triglycerides in obese subjects were increased by the combination of increased secretion and severely impaired clearance of triglyceride-rich very-low-density lipoprotein(1) particles. Furthermore, increased liver and subcutaneous abdominal fat were linked to increased secretion of very-low-density lipoprotein 1 particles, whereas increased plasma levels of apolipoprotein C-III were associated with impaired clearance in obese hypertriglyceridemic subjects.

CONCLUSIONS

Dual metabolic defects are required to produce hypertriglyceridemia in obese subjects with similar levels of visceral adiposity. The results emphasize the clinical importance of assessing hypertriglyceridemic waist in obese subjects to identify subjects at high cardiometabolic risk.

Genetic variation in PNPLA3 (adiponutrin) confers sensitivity to weight loss-induced decrease in liver fat in humans

BACKGROUND

The rs738409 C→G single nucleotide polymorphism in the patatin-like phospholipase domain-containing 3 (PNPLA3; adiponutrin) leads to a missense mutation (I148M), which is associated with increased liver fat but not insulin resistance. The I148M mutation impedes triglyceride hydrolysis in vitro, and its carriers have an increased risk of developing severe liver disease.

OBJECTIVE

We explored whether the rs738409 PNPLA3 G allele influences the ability of weight loss to decrease liver fat or change insulin sensitivity.

DESIGN

We recruited 8 subjects who were homozygous for the rs738409 PNPLA3 G allele (PNPLA3-148MM) and 10 who were homozygous for the rs738409 PNPLA3 C allele (PNPLA3-148II). To allow comparison of changes in liver fat, the groups were matched with respect to baseline age, sex, body mass index, and liver fat. The subjects were placed on a hypocaloric low-carbohydrate diet for 6 d. Liver fat content (proton magnetic resonance spectroscopy), whole-body insulin sensitivity of glucose metabolism (euglycemic clamp technique), and lipolysis ([(2)H(5)]glycerol infusion) were measured before and after the diet.

RESULTS

At baseline, fasting serum insulin and C-peptide concentrations were significantly lower in the PNPLA3-148MM group than in the PNPLA3-148II group, as predicted by study design. Weight loss was not significantly different between groups (PNPLA3-148MM: -3.1 ± 0.5 kg; PNPLA3-148II: -3.1 ± 0.4 kg). Liver fat decreased by 45% in the PNPLA3-148MM group (P < 0.001) and by 18% in the PNPLA3-148II group (P < 0.01).

CONCLUSION

Weight loss is effective in decreasing liver fat in subjects who are homozygous for the rs738409 PNPLA3 G or C allele. This trial was registered at www.hus.fi as 233775.

Long-TE 1H MRS suggests that liver fat is more saturated than subcutaneous and visceral fat

Cross-talk between adipose tissue and liver is disturbed in the metabolic syndrome. Moreover, the relative fatty acid composition of adipose and liver fat is poorly characterized. Long-TE (1)H MRS can determine the unsaturation and polyunsaturation of adipose tissue. The aim of this study was to use long-TE (1)H MRS to determine the composition of liver fat and its relation to adipose tissue composition. Sixteen subjects with increased liver fat (>5%) were recruited for the study. Using TE = 200  ms, we were able to resolve the olefinic (=CH, 5.3  ppm) and water (H(2)O, 4.7  ppm) resonances in liver spectra and to obtain a repeatable estimate of liver fat unsaturation (coefficient of variation, 2.3%). With TE = 135  ms, the diallylic (=C-CH(2)-C=, 2.8  ppm) resonance was detectable in subjects with a liver fat content above 15%. Long-TE (1)H MRS was also used to determine the unsaturation in subcutaneous (n = 16) and visceral (n = 11) adipose tissue in the same subjects. Liver fat was more saturated (double bonds per fatty acid chain, 0.812 ± 0.022) than subcutaneous (double bonds per fatty acid chain, 0.862 ± 0.022, p < 0.0004) or visceral (double bonds per fatty acid chain, 0.865 ± 0.033, p < 0.0004) fat. Liver fat unsaturation correlated with subcutaneous unsaturation (R = 0.837, p < 0.0001) and visceral unsaturation (R = 0.879, p < 0.0004). The present study introduces a new noninvasive method for the assessment of the composition of liver fat. The results suggest that liver fat is more saturated than subcutaneous or visceral adipose tissue, which may be attributed to differences in de novo lipogenesis.

Increased coagulation factor VIII, IX, XI and XII activities in non-alcoholic fatty liver disease

BACKGROUND AND AIMS

Obesity and the metabolic syndrome are established risk factors of venous thromboembolism. As most coagulation factors are produced exclusively by the liver and non-alcoholic fatty liver disease (NAFLD) is tightly related to metabolic disorders, we aimed at studying the association of liver fat with various coagulation factor activities.

METHODS

Plasma prothrombin (PT) and activated partial thromboplastin time, activities of vWF:RCo, FVII, FVIII, FIX, FXI, FXII, FXIII, fibrinogen and D-dimer concentrations were measured in 54 subjects with and 44 without NAFLD diagnosed by proton magnetic resonance spectroscopy. Subjects were recruited retrospectively for metabolic studies in our laboratory. The body composition and features of insulin resistance were measured in all subjects.

RESULTS

FVIII (107±30 vs. 84±22%, P<0.001), FIX (110±14 vs. 94±16%, P<0.001), FXI (109±16 vs. 96±19%, P=0.001) and FXII (113±21 vs. 99±32%, P=0.002) activities were consistently elevated in subjects with as compared with those without NAFLD. Liver fat percentage was positively related to FVIII (r=0.28, P=0.005), FIX (r=0.36, P=0.0003), FXI (r=0.29, P=0.004) and FXII (r=0.30, P=0.003) activities, again independent of age, gender and body mass index (BMI). PT%, vWF:RCo activity and fibrinogen were higher in subjects with as compared with those without NAFLD, but this difference disappeared after adjusting for age, gender and BMI.

CONCLUSION

FVIII, FIX, FXI and FXII activities are increased in human NAFLD and correlate with the features of insulin resistance. The relationships between NAFLD and these coagulation factors are independent of age, gender and BMI, suggesting that the fatty liver can contribute to the risk of thrombosis.

Liver fat but not other adiposity measures influence circulating FGF21 levels in healthy young adult twins

CONTEXT

Emerging as an important metabolic regulator, fibroblast growth factor 21 (FGF21) has gained considerable interest in diabetes and obesity research. The circulating FGF21 concentration is fairly low in normal individuals, but elevated hormone levels may associate with obesity. The determining factors of FGF21 levels in humans are not clear.

OBJECTIVE

Our objective was to study the influence of genetic and acquired components to serum FGF21 variability in healthy young adult twins.

DESIGN AND PARTICIPANTS

Fasting serum FGF21, lipids, body fat, and oral glucose tolerance test were investigated in 46 monozygotic (MZ) and 75 dizygotic twin pairs aged 22.8-33.1 yr. Subcutaneous, intraabdominal, and liver fat content were measured by magnetic resonance imaging/spectroscopy in a subsample of 24 MZ pairs.

RESULTS

Genetic factors contributed moderately (heritability 40%) to circulating serum FGF21 levels. Subjects with high FGF21 concentrations (≥ 250 pg/ml, n = 30) had higher fasting triglycerides, insulin, homeostasis model assessment index, and area under the curve glucose and lower high-density lipoprotein cholesterol but similar measures of overall adiposity (body mass index, body fat percent) than subjects with lower FGF21 (<100 pg/ml, n = 148). Importantly, in the MZ subsample, higher liver fat but not sc or intraabdominal fat content was found in subjects with high FGF21. Furthermore, in analyses controlling for genetic/familial effects in twin pairs, within-pair differences in liver fat (MZ) and triglycerides (dizygotic pairs) were the major acquired factors that correlated with differences in FGF21 concentrations.

CONCLUSIONS

Genetic factors influence serum FGF21 levels. Of the acquired components, high liver fat and triglycerides rather than overall adiposity associate with high FGF21 levels.

Cholesterol synthesis is increased and absorption decreased in non-alcoholic fatty liver disease independent of obesity

BACKGROUND & AIMS

Non-alcoholic fatty liver disease (NAFLD) is associated with impaired glucose and lipoprotein metabolism. However, the metabolism of cholesterol in NAFLD remains unexplored. We investigated how fatty liver influences cholesterol metabolism in 242 non-diabetic subjects.

METHODS

Liver fat content was measured with proton magnetic resonance spectroscopy. Cholesterol metabolism was assayed with serum non-cholesterol sterols, surrogate markers of cholesterol synthesis and absorption. The analyses were performed with gas-liquid chromatography.

RESULTS

A total of 114 subjects had NAFLD and 128 subjects had normal liver fat content. Non-cholesterol sterols reflecting cholesterol synthesis (cholestenol, desmosterol, and lathosterol) were higher, and those reflecting cholesterol absorption (cholestanol and plant sterols) were lower in subjects with NAFLD than in controls, independent of body mass index. Liver fat content was positively associated with markers of cholesterol synthesis (r = from 0.262 to 0.344, p < 0.001 for all) and inversely associated with markers of cholesterol absorption (r = from -0.299 to -0.336, p < 0.001 for all). In the entire study group, synthesis and absorption markers were interrelated, indicating that the homeostasis of cholesterol metabolism was maintained. LDL cholesterol was similar in the two groups.

CONCLUSIONS

We demonstrated that although LDL cholesterol concentrations are unchanged, cholesterol metabolism in NAFLD is characterized by increased synthesis and diminished absorption of cholesterol. These changes are associated with liver fat content independent of body weight.

Comparison of the relative contributions of intra-abdominal and liver fat to components of the metabolic syndrome

Abdominally obese individuals with the metabolic syndrome often have excess fat deposition both intra-abdominally (IA) and in the liver, but the relative contribution of these two deposits to variation in components of the metabolic syndrome remains unclear. We determined the mutually independent quantitative contributions of IA and liver fat to components of the syndrome, fasting serum (fS) insulin, and liver enzymes and measures of hepatic insulin sensitivity in 356 subjects (mean age 42 years, mean BMI 29.7 kg/m²) in whom liver fat and abdominal fat volumes were measured. IA and liver fat contents were correlated (r = 0.65, P < 0.0001). In multivariate linear regression analyses including either liver or IA fat, liver fat or IA fat explained variation in fS-triglyceride (TG) and high-density lipoprotein (HDL) cholesterol, plasma glucose, insulin and liver enzyme concentrations, and hepatic insulin sensitivity independent of age, gender, subcutaneous (SC) fat, and/or lean body mass (LBM). Including both liver and IA fat, liver and IA fat both explained variation in TG, HDL cholesterol, insulin and hepatic insulin sensitivity independent of each other and of age, gender, SC fat, and LBM. Liver fat independently predicted glucose and liver enzymes. SC fat and age explained variation in blood pressure. In conclusion, both IA and liver fat independently of each other explain variation in serum TG, HDL cholesterol, insulin concentrations and hepatic insulin sensitivity, thus supporting that both fat depots are important predictors of these components of the metabolic syndrome.

Association of intramyocellular, intraperitoneal and liver fat with glucose tolerance in severely obese adolescents

OBJECTIVE

Impaired glucose tolerance (IGT) is common among obese adolescents. The aim of the present study was to investigate the association between glucose tolerance and intramyocellular, intra-abdominal and liver fat in adolescents presenting with early-onset severe obesity.

DESIGN AND METHODS

We studied 21 adolescents (mean age 13.5 years, range 11.5-15.9 years) referred to secondary care due to severe obesity (relative weight for height > +60% or body mass index > 98th percentile for age and sex, before the age of 10 years) and their eight non-obese siblings (mean age 14.4 years, range 11.8-16.7 years). All subjects underwent oral glucose tolerance tests, followed by magnetic resonance spectroscopy (MRS) to measure the intramyocellular fat content in mainly oxidative soleus and mainly glycolytic tibialis anterior muscles. MRS was also used to measure liver fat. Abdominal fat (subcutaneous, intraperitoneal and retroperitoneal) was measured using MR imaging.

RESULTS

Compared with their non-obese siblings, the obese adolescents had increased fat deposition in all anatomic locations studied. Eight obese adolescents had IGT, and they also had increased intramyocellular fat in the soleus (P=0.03) and increased intraperitoneal fat (P=0.04) compared with obese subjects with normal glucose tolerance (NGT). In contrast, no significant difference was seen between obese adolescents with NGT and IGT in liver fat (P=0.9) or intramyocellular fat in the tibialis anterior (P=0.13). In logistic regression analysis, increased soleus intramyocellular fat and intraperitoneal fat were significant predictors of IGT.

CONCLUSIONS

IGT in obese adolescents is associated with increased intramyocellular and intraperitoneal fat rather than liver fat.

Characterizing human adipose tissue lipids by long echo time 1H-MRS in vivo at 1.5 Tesla: validation by gas chromatography

The aim of this study was to investigate the use of (1)H-MRS with various echo times to characterize subcutaneous human adipose tissue (SAT) triglyceride composition and to validate the findings with fatty acid (FA) analysis of SAT biopsies by gas chromatography (GC). (1)H-MRS spectra were acquired with a 1.5 Tesla clinical imager from the SAT of 17 healthy volunteers, with 10 undergoing SAT biopsy. Spectra were localized with PRESS and a series of echo times; 30, 50, 80, 135, 200, 300 and 540 ms were acquired with TR = 3000 ms. Prior knowledge from phantom measurements was used to construct AMARES fitting models for the lipid spectra. SAT FA composition were compared with serum lipid levels and subject characteristics in 17 subjects.Long TE (135, 200 ms) spectra corresponded better with the GC data than short TE (30, 50 ms) spectra. TE = 135 ms was found optimal for determining diallylic content (R = 0.952, p < 0.001) and TE = 200 ms was optimal for determining olefinic content (R = 0.800, p < 0.01). The improved performance of long TE spectra is a result of an improved baseline and better peak separation, due to J-modulation and suppression of water. The peak position of the diallylic resonance correlated with the average double bond content of polyunsatured fatty acids with R = 0.899 (p < 0.005). The apparent T(2) of the methylene resonance displayed relatively small inter-individual variation, 88.1 +/- 1.1 ms (mean +/- SD). The outer methyl triplet line of omega-3 PUFA at 1.08 ppm could be readily detected and quantitated from spectra obtained at TE = 540. The omega-3 resonance correlated with the omega-3 content determined by GC with R = 0.737 (p < 0.05, n = 8). Age correlated significantly with SAT diallylic content (R = 0.569, p = 0.017, n = 17), but serum lipid levels showed no apparent relation to SAT FA composition. We conclude that long TE (1)H-MRS provides a robust non-invasive method for characterizing adipose tissue triglycerides in vivo.

Evidence for abnormal glucose uptake or metabolism in thalamus during acute hyperglycaemia in type 1 diabetes--a 1H MRS study

Acute hyperglycaemia impairs cognitive function. It is however not known, whether different brain regions are equally exposed to glucose during acute hyperglycemia or whether the brain is able to adjust its glucose uptake or metabolism in response to blood glucose fluctuation. We studied the effect of acute hyperglycaemia on the brain glucose concentration in seven men with type 1 diabetes with daily glucose fluctuations of 11 +/- 3 mmol/l, and in eleven age-matched non-diabetic men. Glucose was quantified with proton magnetic resonance spectroscopy in three different brain regions at baseline (fasting glycaemia) and twice during a 2 h hyperglycaemic clamp with plasma glucose increase of 12 mmol/l. The increase in brain glucose during acute hyperglycaemia in the non-diabetic group was: cortex (2.7 +/- 0.9 mmol/l) > thalamus (2.3 +/- 0.7 mmol/l) > white matter (1.7 +/- 0.7 mmol/l, P = 0.021 vs. cortex) and in the diabetic group: cortex (2.0 +/- 0.7 mmol/l) > white matter (1.3 +/- 0.7 mmol/l) > thalamus (1.1 +/- 0.4 mmol/l, P = 0.010 vs. cortex). In the diabetic group, the glucose increase in the thalamus was attenuated compared to the non-diabetic participants (P = 0.011). In conclusion, the increase of glucose during acute hyperglycaemia seems to be dependent on the brain tissue type. The high exposure of cortex to excess glucose and the altered glucose uptake or metabolism in the thalamus may thus contribute to hyperglycaemia related cognitive dysfunction.

PRESS echo time behavior of triglyceride resonances at 1.5T: detecting omega-3 fatty acids in adipose tissue in vivo

AIM

This study investigated the impact of fatty acid (FA) composition on the echo time behavior of triglyceride resonances in a clinical setting. The feasibility of (1)H NMR spectroscopy to detect these resonances was also evaluated in human adipose tissue in vivo.

METHOD

Ten edible oils chosen to cover a wide spectrum of FA compositions were used as phantom material. The detailed FA composition and intrinsic proton spectra of the oils were characterized by gas chromatography and high-resolution (1)H NMR spectroscopy (11.7T), respectively. The detailed echo time behavior of the oils were subsequently measured by (1)H NMR spectroscopy in a clinical scanner (1.5T) using PRESS. The effect of temperature was investigated in five oils.

RESULTS

The olefinic (5.3 ppm) and diallylic (2.8 ppm) resonances exhibited distinct J-modulation patterns independent of oil FA composition. The methylene resonance (1.3 ppm) displayed an exponential decay, with the apparent T(2) showing a weak positive correlation with oil unsaturation (R=0.628, P=0.052), probably a result of changes in viscosity. For the methyl resonance (0.9 ppm), oils high in omega-3 FA displayed a markedly different J-modulation pattern compared to non-omega-3 oils. The characteristic J-modulation of the omega-3 methyl group could be attributed to the phase behavior of the omega-3 methyl triplet signal (all triplet lines in-phase at TE of 135 ms), a result of the omega-3 methyl end forming a first order spin system. The omega-3 methyl outer triplet line at 1.08ppm of the TE=140 ms spectrum was found to be useful for determining the omega-3 content of the oils (R=0.999, standard error of estimate (SE) 0.80). The olefinic and diallylic proton resonance (measured at TE=50 ms) areas correlated with the olefinic (R=0.993, SE 0.33) and diallylic (R=0.997, SE 0.19) proton contents calculated from the GC data. Information derived from long echo time spectra (TE=200) demonstrated good correlations to GC data and showed no change with increasing temperature (and T(2)). In (1)H NMR spectra (1.5T) of adipose tissue in five healthy subjects, the analytically important olefinic and diallylic resonances were clearly resolved with a coefficient of variation of 1.6% and 8.4%, respectively, for repeated measurements. The characteristic phase behavior of the omega-3 methyl outer triplet line at 1.08 ppm could also be detected at very long echo times (470 and 540 ms).

CONCLUSION

Fatty acid composition has an impact on the echo time behavior of triglyceride resonances. Long TE spectra can resolve omega-3 FA in adipose tissue in vivo. These findings will benefit long TE studies of tissue lipids.

Role of insulin as a negative regulator of plasma endocannabinoid levels in obese and nonobese subjects

OBJECTIVE

Endocannabinoids (ECs) control metabolism via cannabinoid receptors type 1 (CB1). Their plasma levels are elevated in overweight type 2 diabetes (T2D) and in obese patients, and decrease postprandially in normoweight individuals. We investigated in two different cohorts of nonobese or obese volunteers whether oral glucose in glucose tolerance tests (OGTT) or acute insulin infusion during euglycemic hyperinsulinemic clamp affect plasma EC levels.

DESIGN AND METHODS

OGTT was performed in ten obese hyperinsulinemic patients (body mass index (BMI)=35.8 kg/m2, fasting insulin=14.83 mU/l), and ten normoweight normoinsulinemic volunteers (BMI=21.9 kg/m2, fasting insulin=7.2 mU/l). Insulin clamp was performed in 19 mostly nonobese men (BMI=25.8 kg/m2) with varying degrees of liver fat and plasma triglycerides (TGs), with (n=7) or without T2D. Plasma levels of ECs (anandamide and 2-arachidonoylglycerol (2-AG)) were measured by liquid chromatography-mass spectrometry, before and 60 and 180 min after OGTT, and before and 240 and 480 min after insulin or saline infusion.

RESULTS

Oral glucose load decreased anandamide plasma levels to an extent inversely correlated with BMI, waist circumference, subcutaneous fat, fasting insulin and total glucose, and insulin areas under the curve during the OGTT, and nonsignificantly in obese volunteers. Insulin infusion decreased anandamide levels to an extent that weakly, but significantly, correlated negatively with TGs, liver fat and fasting insulin, and positively with high density lipoprotein cholesterol. OGTT decreased 2-AG levels to a lower extent and in a way weakly inversely correlated with fasting insulin.

CONCLUSIONS

We suggest that insulin reduces EC levels in a way inversely related to anthropometric and metabolic predictors of insulin resistance and dyslipidemia.

Acquisition-weighted MRSI for detection and quantification of BNCT 10B-carrier L-p-boronophenylalanine-fructose complex, a phantom study

Proton magnetic resonance spectroscopy (1H MRS) is a potential method to detect and quantify a boron neutron capture therapy 10B-carrier compound, L-p-boronophenylalanine (BPA), in the brain. However, optimal positioning of MRS voxel to capture tissue with maximal BPA concentration can be challenging. Three dimensional proton magnetic resonance spectroscopic imaging (3D 1H MRSI) provides spectral data covering a large spatial volume, which is a major advantage in detecting and quantifying BPA. BPA detection limit in phantom conditions was determined at 1.5 T using a 3D 1H MRSI protocol with clinically acceptable nominal spatial resolution and duration. Quantification tests for aqueous phantom were performed using both single voxel MRS and 3D MRSI. In 3D MRSI, BPA detection limit was approximately 1.0 mM and BPA quantification accuracy was better than +/-5%. The results suggest that MRSI would be a feasible method for in vivo BPA evaluation in clinical conditions.

Prediction of non-alcoholic fatty liver disease and liver fat using metabolic and genetic factors

BACKGROUND & AIMS

Our aims were to develop a method to accurately predict non-alcoholic fatty liver disease (NAFLD) and liver fat content based on routinely available clinical and laboratory data and to test whether knowledge of the recently discovered genetic variant in the PNPLA3 gene (rs738409) increases accuracy of the prediction.

METHODS

Liver fat content was measured using proton magnetic resonance spectroscopy in 470 subjects, who were randomly divided into estimation (two thirds of the subjects, n = 313) and validation (one third of the subjects, n = 157) groups. Multivariate logistic and linear regression analyses were used to create an NAFLD liver fat score to diagnose NAFLD and liver fat equation to estimate liver fat percentage in each individual.

RESULTS

The presence of the metabolic syndrome and type 2 diabetes, fasting serum (fS) insulin, fS-aspartate aminotransferase (AST), and the AST/alanine aminotransferase ratio were independent predictors of NAFLD. The score had an area under the receiver operating characteristic curve of 0.87 in the estimation and 0.86 in the validation group. The optimal cut-off point of -0.640 predicted increased liver fat content with sensitivity of 86% and specificity of 71%. Addition of the genetic information to the score improved the accuracy of the prediction by only <1%. Using the same variables, we developed a liver fat equation from which liver fat percentage of each individual could be estimated.

CONCLUSIONS

The NAFLD liver fat score and liver fat equation provide simple and noninvasive tools to predict NAFLD and liver fat content.

Hyperglycaemia is associated with changes in the regional concentrations of glucose and myo-inositol within the brain

AIMS/HYPOTHESIS

The aim of the study was to assess the effect of hyperglycaemia on regional concentrations of glucose and other substrates within the brain in non-diabetic individuals and in patients with type 1 diabetes.

METHODS

The brain metabolites of 17 men with type 1 diabetes and 12 age-matched non-diabetic men (22-43 years old) were studied after an overnight fast (plasma glucose 9.2 +/- 3.0 vs 4.8 +/- 0.5 mmol/l, respectively). N-Acetylaspartate (NAA), creatine, choline, myo-inositol (mI) and glucose in the frontal cortex, frontal white matter and thalamus were quantified with proton magnetic resonance spectroscopy.

RESULTS

In the non-diabetic participants, the glucose level was 47% higher (p < 0.01) in the frontal cortex than in the frontal white matter. In contrast, this regional variation was not observed in the diabetic participants, in whom the glucose level in the frontal white matter was 64% higher (p < 0.001) and in the frontal cortex 25% higher (p = 0.033) than that of the non-diabetic participants. In the diabetic participants, the glucose level in each of the three regions studied correlated with fasting plasma glucose (r = 0.88-0.67, p < 0.01). In addition, in the diabetic participants, mI was 20% higher (p < 0.001) and NAA 6% lower (p = 0.037) in the frontal white matter, and mI was 8% higher (p = 0.042) in the frontal cortex, than in the non-diabetic participants.

CONCLUSIONS/INTERPRETATION

In type 1 diabetes, hyperglycaemia is associated with accumulation of glucose and mI in the cortex and in the white matter.

Risk for metabolic syndrome predisposes to alterations in the thalamic metabolism

Risk factors for the metabolic syndrome (MetS) affect brain function and associate with asymptomatic brain infarctions in healthy individuals. We studied whether MetS risk factors alter cerebral metabolism. Eighteen non-smoking men (36 +/- 6years) were stratified into two groups according to their risk of developing the MetS. Individuals in the Risk group had a family history of type 2 diabetes, were pre-obese, had mild hypertension and higher fasting plasma glucose and serum insulin compared to the Control group with no risk factors. N-acetyl aspartate, choline, total creatine (tCr), myo-inositol, and glucose were studied in the thalamus, frontal cortex, and frontal white matter with proton magnetic resonance spectroscopy. The plasma glucose was 13% higher (p < 0.01) in the Risk group, but the brain glucose levels were comparable between the groups. In the Control group, the thalamic tCr correlated with the thalamic glucose level (r = 0.81, p = 0.015). In the Risk group, the tCr was 17% higher (p = 0.006) and correlated with the fasting plasma glucose concentration (r = 0.78, p = 0.013), but not with the thalamic glucose level. In conclusion, the increased tCr level in the Risk group suggests that a family history of type 2 diabetes together with MetS risk factors alters thalamic energy metabolism.

Postprandial lipemia associates with liver fat content

CONTEXT/OBJECTIVE

Postprandial lipemia and low adiponectin represent novel risk factors for vascular disease. This study aimed to determine whether liver fat content and adiponectin are predictors of postprandial triglyceride (TG)-rich lipoproteins (TRL).

PATIENTS/INTERVENTIONS

Twenty-nine men were allocated into subgroups with either low (< or =5%) or high (>5%) liver fat measured with magnetic resonance proton spectroscopy. Subjects underwent an oral fat tolerance test with measurements of postprandial TG, cholesterol, apolipoprotein B-48 (apoB-48), and apoB-100 in TRL fractions, a euglycemic hyperinsulinemic clamp, and determination of abdominal fat volumes by magnetic resonance imaging.

RESULTS

Subjects with high liver fat displayed increased response of postprandial lipids in plasma, chylomicron, and very-low-density lipoprotein 1 (VLDL1) (Svedberg flotation rate 60-400) fractions. Liver fat correlated positively with postprandial responses (area under the curve) of TG (r = 0.597; P = 0.001), cholesterol (r = 0.546; P = 0.002), apoB-48 (r = 0.556; P = 0.002), and apoB-100 (r = 0.42; P = 0.023) in the VLDL1 fraction. Respective incremental areas under the curve correlated significantly with liver fat. Fasting adiponectin levels were inversely correlated with both postprandial lipids and liver fat content. Liver fat remained the only independent correlate in a multiple linear regression analysis for chylomicron and VLDL1 responses.

CONCLUSIONS

Liver fat content is a close correlate of postprandial lipids predicting the responses of TRL in chylomicrons and VLDL1 better than measures of glucose metabolism or body adiposity. Low adiponectin concentration is closely linked to high liver fat content and impaired TRL metabolism. High liver fat content associated with postprandial lipemia represents potential risk factors for cardiovascular disease.