The protective effect of human renal sinus fat on glomerular cells is reversed by the hepatokine fetuin-A.

Renal sinus fat (RSF) is a perivascular fat compartment located around renal arteries. In this in vitro and in vivo study we hypothesized that the hepatokine fetuin-A may impair renal function in non alcoholic fatty liver disease (NAFLD) by altering inflammatory signalling in RSF. To study effects of the crosstalk between fetuin-A, RSF and kidney, human renal sinus fat cells (RSFC) were isolated and cocultured with human endothelial cells (EC) or podocytes (PO). RSFC caused downregulation of proinflammatory and upregulation of regenerative factors in cocultured EC and PO, indicating a protective influence of RFSC. However, fetuin-A inverted these benign effects of RSFC from an anti- to a proinflammatory status. RSF was quantified by magnetic resonance imaging and liver fat content by 1H-MR spectroscopy in 449 individuals at risk for type 2 diabetes. Impaired renal function was determined via urinary albumin/creatinine-ratio (uACR). RSF did not correlate with uACR in subjects without NAFLD (n = 212, p = 0.94), but correlated positively in subjects with NAFLD (n = 105, p = 0.0005). Estimated glomerular filtration rate (eGRF) was inversely correlated with RSF, suggesting lower eGFR for subjects with higher RSF (r = 0.24, p < 0.0001). In conclusion, our data suggest that in the presence of NAFLD elevated fetuin-A levels may impair renal function by RSF-induced proinflammatory signalling in glomerular cells.

An extended fatty liver index to predict non-alcoholic fatty liver disease.

BACKGROUND: In clinical practice, there is a strong interest in non-invasive markers of non-alcoholic fatty liver disease (NAFLD). Our hypothesis was that the fold-change in plasma triglycerides (TG) during a 2-h oral glucose tolerance test (fold-change TGOGTT) in concert with blood glucose and lipid parameters, and the rs738409 C>G single nucleotide polymorphism (SNP) in PNPLA3 might improve the power of the widely used fatty liver index (FLI) to predict NAFLD. METHODS: The liver fat content of 330 subjects was quantified by 1H-magnetic resonance spectroscopy. Blood parameters were measured during fasting and after a 2-h OGTT. A subgroup of 213 subjects underwent these measurements before and after 9 months of a lifestyle intervention. RESULTS: The fold-change TGOGTT was closely associated with liver fat content (r=0.51, P<0.0001), but had less power to predict NAFLD (AUROC=0.75) than the FLI (AUROC=0.79). Not only was the fold-change TGOGTT independently associated with liver fat content and NAFLD, but so also were the 2-h blood glucose level and rs738409 C>G SNP in PNPLA3. In fact, a novel index (extended FLI) generated from these and the usual FLI parameters considerably increased its power to predict NAFLD (AUROC=0.79-0.86). The extended FLI also increased the power to predict changes in liver fat content with a lifestyle intervention (n=213; standardized beta coefficient: 0.23-0.29). CONCLUSION: This study has provided novel data confirming that the OGTT-derived fold-change TGOGTT and 2-h glucose level, together with the rs738409 C>G SNP in PNPLA3, allow calculation of an extended FLI that considerably improves its power to predict NAFLD.

Intramyocellular lipids and their dynamics assessed by 1 H magnetic resonance spectroscopy.

This report provides an overview on the present knowledge on intramyocellular lipids (IMCL) and their dynamics in the course of interventions with physical activity of variable type and intensity in different population groups, as accessible by examinations using non-invasive volume-selective 1 H magnetic resonance spectroscopy (1 H MRS). IMCL serve as energy source in skeletal muscle for fat oxidation in the mitochondria and became intensively studied after discovery of their relation with insulin sensitivity. While baseline levels of IMCL concentration have been shown to be mainly dependent on the metabolic status (insulin sensitivity), on the level of training and on fibre composition in the muscles, studies applying different physical activity protocols revealed the dynamic of their depletion and replenishment. From the findings in human studies, it can be concluded that IMCL levels are potentially useful markers for monitoring metabolic adaptation of skeletal muscle to sportive activities and training.

[Liver volume, intrahepatic fat and body weight in the course of a lifestyle interventional study: Analysis with quantitative MR-based methods]. / Lebervolumen, Leberfettanteil und Körpergewicht im Verlauf einer Lebensstilinterventionsstudie : Eine Analyse mit quantitativen MR-basierten Methoden.

OBJECTIVES: The aim of this study was to investigate potential associations between changes in liver volume, the amount of intrahepatic lipids (IHL) and body weight during lifestyle interventions. MATERIAL AND METHODS: In a prospective study 150 patients with an increased risk for developing type 2 diabetes mellitus were included who followed a caloric restriction diet for 6 months. In the retrospective analysis 18 women and 9 men (age range 22-71 years) with an average body mass index (BMI) of 32 kg/m(2) were enrolled. The liver volume was determined at the beginning and after 6 months by three-dimensional magnetic resonance imaging (3D-MRI, echo gradient, opposed-phase) and IHLs were quantified by volume-selective MR spectroscopy in single voxel stimulated echo acquisition mode (STEAM). Univariable and multivariable correlation analyses between changes of liver volume (Δliver volume), intrahepatic lipids (ΔIHL) and body weight (ΔBW) were performed. RESULTS: Univariable correlation analysis in the whole study cohort showed associations between ΔIHL and ΔBW (r = 0.69; p < 0.0001), ΔIHL and Δliver volume (r = 0.66; p = 0.0002) as well as ΔBW and Δliver volume (r = 0.5; p = 0.0073). Multivariable correlation analysis revealed that changes of liver volume are primarily determined by changes in IHL independent of changes in body weight (ß = 0.0272; 95% CI: 0.0155-0.034; p < 0.0001). CONCLUSION: Changes of liver volume during lifestyle interventions are independent of changes of body weight primarily determined by changes of IHL. These results show the reversibility of augmented liver volume in steatosis if it is possible to reduce IHLs during lifestyle interventions.

Plasminogen activator inhibitor-1, monocyte chemoattractant protein-1, e-selectin and C-reactive protein levels in response to 4-week very-high-fructose or -glucose diets.

BACKGROUND/OBJECTIVES: High intake of added sweeteners is considered to have a causal role in the pathogenesis of cardiometabolic disorders. Especially, high-fructose intake is regarded as potentially harmful to cardiometabolic health. It may cause not only weight gain but also low-grade inflammation, which represents an independent risk factor for developing type 2 diabetes and cardiovascular disease. In particular, fructose has been suggested to induce plasminogen activator inhibitor-1 (PAI-1) expression in the liver and to increase circulating inflammatory cytokines. We therefore aimed to investigate, whether high-fructose diet has an impact on PAI-1, monocyte chemoattractant protein-1 (MCP-1), e-selectin and C-reactive protein (CRP) concentrations in healthy humans. SUBJECTS/METHODS: We studied 20 participants (12 males and 8 females) of the TUebingen FRuctose Or Glucose study. This is an exploratory, parallel, prospective, randomized, single-blinded, outpatient, hypercaloric, intervention study. The participants had a mean age of 30.9 ± 2.1 years and a mean body mass index of 26.0 ± 0.5 kg/m(2) and they received 150 g of either fructose or glucose per day for 4 weeks. RESULTS: There were neither significant changes of PAI-1, MCP-1, e-selectin and CRP after fructose (n=10) and glucose (n=10) intervention nor treatment effects (all P>0.2). Moreover, we did not observe longitudinal associations of the inflammatory parameters with triglycerides, liver fat, visceral fat and body weight in the fructose group. CONCLUSIONS: Temporary high-fructose intake does not seem to cause inflammation in apparently healthy people in this secondary analysis of a small feeding trial.

Rapid improvement of hepatic steatosis after initiation of leptin substitution in a leptin-deficient girl.

BACKGROUND: Leptin deficiency is associated with severe obesity and metabolic disturbances. Increased liver fat content has been reported in only one case beforehand, even though hepatic steatosis is a typical comorbidity of common obesity. It is also frequent in patients with lipodystrophy where it resolves under leptin therapy. SUBJECT AND METHODS: In 2010, we reported a leptin-deficient patient with a novel homozygous mutation in the leptin gene and severe hepatic steatosis. We have now studied serum changes and changes in liver fat content during the substitution with recombinant methionyl human leptin. RESULTS: After 23 weeks of leptin substitution, elevated transaminases, total cholesterol and low-density lipoprotein levels normalized. After 62 weeks, homeostasis model assessment of insulin resistance improved from 10.7 to 6.0 and body fat mass dropped from 50.2 to 37.8%. Liver fat content was drastically reduced from 49.7 to 9.4%. The first changes in liver fat content were detectable after 3 days of therapy. CONCLUSION: Our patient showed a remarkable reduction of liver fat content during the treatment with recombinant methionyl human leptin. These changes occurred rapidly after initiation of the substitution, which implies that leptin has a direct effect on hepatic lipid metabolism in humans as it is seen in rodents.

Exercise-induced albuminuria is associated with perivascular renal sinus fat in individuals at increased risk of type 2 diabetes.

AIMS/HYPOTHESIS: Microalbuminuria represents an established surrogate marker of early diabetic nephropathy and glomerular microangiopathy. Increasing evidence is emerging of a role of perivascular adipose tissue (PVAT) as an important link between obesity, insulin resistance and both macro- and microangiopathy. It is not known whether perivascular renal sinus fat (RSF) has an impact on microalbuminuria in the prediabetic stage. We investigated whether RSF quantified by MRI is associated with microalbuminuria before or after exercise. METHODS: Non-diabetic individuals at increased risk of type 2 diabetes were recruited into the Tübingen Lifestyle Intervention Program (TULIP); 146 participants took part in the analysis. RSF was measured in axial MRI sections at the level of the renal artery. Urine was collected before and after exercise stress testing. RESULTS: Participants (age 47 ± 12 years; mean ± SD) reached a mean exercise load of 176 ± 49 W, with a mean arterial peak pressure (MAPP) of 112 ± 14 mmHg. After adjusting for sex, age, visceral adipose tissue (VAT) and MAPP during exercise, RSF was significantly associated with postexercise albumin/creatinine ratio (ACR; p = 0.006). No association between RSF and baseline BP could be observed after adjusting for confounders (p = 0.26), and there was no association between RSF and baseline ACR either (p = 0.2). CONCLUSIONS: RSF is associated with exercise-induced albuminuria independently of sex, age, VAT and MAPP in a non-diabetic cohort at diabetic risk. We conclude that PVAT in the renal sinus may play a role in the pathogenesis of microalbuminuria.

The secretion pattern of perivascular fat cells is different from that of subcutaneous and visceral fat cells.

AIMS/HYPOTHESIS: We have previously found that the mass of perivascular adipose tissue (PVAT) correlates negatively with insulin sensitivity and post-ischaemic increase in blood flow. To understand how PVAT communicates with vascular vessels, interactions between perivascular, subcutaneous and visceral fat cells with endothelial cells (ECs) were examined with regard to inflammatory, metabolic and angiogenic proteins. To test for possible in vivo relevance of these findings, circulating levels of the predominant secretion product, hepatocyte growth factor (HGF), was measured in individuals carefully phenotyped for fat distribution patterns. METHODS: Mono- and co-cultures of human primary fat cells with ECs were performed. mRNA expression and protein production were studied using Luminex, cytokine array, RealTime Ready and ELISA systems. Effects of HGF on vascular cells were determined by WST assays. In patients, HGF levels were measured by ELISA, and the mass of different fat compartments was determined by whole-body MRI. RESULTS: In contrast with other fat cell types, PVAT cells released higher amounts of angiogenic factors, e.g. HGF, acidic fibroblast growth factor, thrombospondin-1, serpin-E1, monocyte chemotactic protein-1 and insulin-like growth factor-binding protein -3. Cocultures showed different expression profiles from monocultures, and mature adipocytes differed from pre-adipocytes. HGF was preferentially released by PVAT cells and stimulated EC growth and smooth muscle cell cytokine release. Finally, in 95 patients, only PVAT, not visceral or subcutaneous mass, correlated independently with serum HGF levels (p = 0.03; r = 0.225). CONCLUSIONS: Perivascular (pre-)adipocytes differ substantially from other fat cells with regard to mRNA expression and protein production of angiogenic factors. This may contribute to fat tissue growth and atherosclerotic plaque complications. Higher levels of angiogenic factors, such as HGF, in patients with increased perivascular fat mass may have pathological relevance.

High cerebral insulin sensitivity is associated with loss of body fat during lifestyle intervention.

AIMS/HYPOTHESIS: Loss of weight and body fat are major targets in lifestyle interventions to prevent diabetes. In the brain, insulin modulates eating behaviour and weight control, resulting in a negative energy balance. This study aimed to test whether cerebral insulin sensitivity facilitates reduction of body weight and body fat by lifestyle intervention in humans. METHODS: The study was performed as an additional arm of the TUebingen Lifestyle Intervention Program (TULIP). In 28 non-diabetic individuals (14 female/14 male; mean ± SE age 42 ± 2 years; mean ± SE BMI 29.9 ± 0.8 kg/m²), we measured cerebrocortical insulin sensitivity by using magnetoencephalography before lifestyle intervention. Total and visceral fat were measured by using MRI at baseline and after 9 months and 2 years of lifestyle intervention. RESULTS: Insulin-stimulated cerebrocortical theta activity at baseline correlated with a reduction in total adipose tissue (r = -0.59, p = 0.014) and visceral adipose tissue (r = -0.76, p = 0.001) after 9 months of lifestyle intervention, accompanied by a statistical trend for reduction in body weight change (r = -0.37, p = 0.069). Similar results were obtained after 2 years. CONCLUSIONS/INTERPRETATION: Our results suggest that high insulin sensitivity of the human brain facilitates loss of body weight and body fat during lifestyle intervention.

Visceral obesity modulates the impact of apolipoprotein C3 gene variants on liver fat content.

OBJECTIVE: It has not been solved whether subjects carrying the minor alleles of the -455T>C or -482C>T single nucleotide polymorphisms (SNPs) in the apolipoprotein-C3-gene (APOC3) have an increased risk for developing fatty liver and insulin resistance. We investigated the relationships of the SNPs with hepatic APOC3 expression and hypothesized that visceral obesity may modulate the effects of these SNPs on liver fat and insulin sensitivity (IS). METHODS: APOC3 mRNA expression and triglyceride content were determined in liver biopsies from 50 subjects. In a separate group (N=330) liver fat was measured by (1)H-magnetic resonance spectroscopy. IS was estimated during an oral glucose tolerance test (OGTT) and the euglycemic, hyperinsulinemic clamp (N=222). RESULTS: APOC3 mRNA correlated positively with triglyceride content in liver biopsies (r=0.29, P=0.036). Carriers of the minor alleles (-455C and -482T) tended to have higher hepatic APOC3 mRNA expression (1.80 (0.45-3.56) vs 0.77 (0.40-1.64), P=0.09), but not higher triglyceride content (P=0.76). In 330 subjects the genotype did not correlate with liver fat (P=0.97) or IS (OGTT: P=0.41; clamp: P=0.99). However, a significant interaction of the genotype with waist circumference in determining liver fat was detected (P=0.02) in which minor allele carriers had higher liver fat only in the lowest tertile of waist circumference (P=0.01). In agreement, during a 9-month lifestyle intervention the minor allele carriers of the SNP -482C>T in the lowest tertile also had less decrease in liver fat (P=0.04). CONCLUSIONS: APOC3 mRNA expression is increased in fatty liver and is regulated by SNPs in APOC3. The impact of the APOC3 SNPs on fatty liver is small and depends on visceral obesity.

Effects of a lifestyle intervention in metabolically benign and malign obesity.

AIMS/HYPOTHESIS: We and others recently characterised metabolically benign or healthy obesity (MHO). In the present study we investigated whether a lifestyle intervention is sufficient to place obese insulin-resistant (OIR) individuals in a position where the possible metabolic consequences are similar to those for MHO individuals. METHODS: A total of 262 non-diabetic individuals participated in a 9 month lifestyle intervention programme. Obese individuals (BMI ≥ 30.0 kg/m(2)) were stratified, based on their insulin sensitivity (IS) estimated from an OGTT, into MHO (IS in the upper quartile, n = 26) and OIR (IS in the lower three quartiles, n = 77). Total body and visceral fat were measured by magnetic resonance (MR) tomography and liver fat by (1)H-MR spectroscopy. RESULTS: During the intervention, visceral fat decreased significantly in both groups (both p ≤ 0.009), whereas total body and liver fat decreased only in the OIR group (p < 0.0001; MHO p = 0.12 for total body fat and p = 0.47 for liver fat). IS improved in the OIR group (p < 0.0001), but remained essentially unchanged in the MHO group (p = 0.30). However, despite the significant increase in the OIR group, IS at follow-up barely exceeded 50% of the IS of the MHO group (OIR 9.30 ± 0.53 arbitrary units [AU]; MHO 16.41 ± 1.05 AU; p < 0.0001). CONCLUSIONS/INTERPRETATION: IS improves during the lifestyle intervention in OIR individuals. However, it does not reach a level where adequate protection from type 2 diabetes and cardiovascular disease is expected. Thus, stratification of obese individuals based on their metabolic phenotype is important to identify those who are likely to need early pharmacological treatment in addition to the lifestyle intervention.

Reducing visceral adipose tissue mass is essential for improving endothelial function in type 2 diabetes prone individuals.

OBJECTIVE: In obesity, particularly increased visceral- (VAT), but not total (TAT) adipose tissue mass is a major source of proinflammatory cytokine expression and secretion. VAT, more than TAT, is associated with endothelial dysfunction (ED), which is an accepted risk factor for atherosclerosis. Consequently, we hypothesized that during a lifestyle intervention specifically a decrease in VAT, rather than TAT, is associated with improved ED and vascular adhesion molecules in type 2 diabetes prone subjects. METHODS: Analyses were done in 189 individuals (age: 45.4±0.8 years) at increased risk of type 2 diabetes, who underwent a 9-month lifestyle intervention. ED expressed as flow mediated dilation (FMD) of the brachial artery, sE-selectin, sV-CAM, sI-CAM, TAT and VAT (measured by magnetic resonance tomography) was determined. RESULTS: There was a mean decrease in body weight (-3%, p<0.0001), TAT (-7.6%, p<0.0001) and VAT (-12.5%, p<0.0001), while FMD increased (+9.1%, p=0.04). The change in FMD was not associated with change in body weight (p=0.35) or TAT (p=0.21) but with a decrease in VAT (r=-0.19, p=0.009). In a post hoc analysis, the subjects were divided by the median change in VAT into responders and non-responders. FMD increased only in the responders (from 6.2±0.4% to 8.0±0.5%, p=0.0005) but not in the non-responders (p=0.15). Also sE-selectin significantly decreased only in the responders (from 54±4 ng/ml to 47±3 ng/ml; p=0.03). CONCLUSION: During a lifestyle intervention, not weight loss or decrease in TAT, but decrease in VAT is associated with improved ED in individuals prone to type 2 diabetes. Therefore, primary cardiovascular prevention should focus specifically on reducing VAT rather than body weight alone.

The impact of liver fat vs visceral fat in determining categories of prediabetes.

AIMS/HYPOTHESIS: Impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) are risk factors for type 2 diabetes and cardiovascular disease; however, their impact on these endpoints differs. Because liver fat and visceral fat are important determinants of glucose and lipid metabolism, we investigated whether these fat compartments and their humoral products, the adipokine adiponectin and the hepatokine fetuin-A, differ in their impact on the glucose categories. METHODS: In 330 individuals at risk of type 2 diabetes, glucose tolerance status was determined by a 2 h 75 g OGTT. Total-body and visceral fat were precisely quantified by magnetic resonance (MR) tomography and liver fat by (1)H-MR spectroscopy. RESULTS: A total of 210 individuals had normal glucose tolerance (NGT), 41 isolated IFG, 43 isolated IGT and 36 IFG+IGT. Total-body fat was not different (p = 0.51), although a small but continuous increase in visceral fat was found among the categories after adjustment for age and sex (NGT: 3.07 +/- 0.10 kg; IFG: 3.11 +/- 0.21 kg; IGT: 3.61 +/- 0.21 kg; IFG+IGT: 3.84 +/- 0.23 kg [SEs], p = 0.03). A larger difference was found for liver fat (NGT: 4.73 +/- 0.42%; IFG: 5.86 +/- 0.92%; IGT: 8.65 +/- 0.92%; IFG + IGT: 11.11 +/- 1.01%, p < 0.0001). The differences among the categories were small for adiponectin (p = 0.14), but larger for fetuin-A (p = 0.015). Among fat compartments, liver fat (p < 0.0001) and among circulating variables fetuin-A (p = 0.016) were the strongest determinants of the categories. CONCLUSIONS/INTERPRETATION: Liver fat, more than visceral fat, strongly increases when glycaemia and glucose tolerance move from NGT to isolated IFG, isolated IGT and IFG+IGT. Because liver-derived circulating fetuin-A determines, although weakly, prediabetes categories, it is worth searching for hepatokines more strongly predicting prediabetes.

AHSG gene variation is not associated with regional body fat distribution--a magnetic resonance study.

Obesity-resistance in AHSG-knockout mice indicate an important role of alpha2-Heremans-Schmid glycoprotein/fetuin-A (AHSG) in the development of obesity. We studied whether genetic variation within AHSG affects whole-body adiposity and regional fat distribution in humans. We genotyped 321 subjects at increased risk for type 2 diabetes for five single nucleotide polymorphisms (SNP) rs2248690, rs4831, rs2070635, rs4917, and rs1071592. Body fat distribution and ectopic hepatic and intramyocellular lipids were assessed by magnetic resonance techniques. AHSG levels were determined by immunoturbidimetry. The five chosen SNPs covered 100% of common genetic variation (minor allele frequency >/=0.05) within AHSG (r (2)>/=0.8). All SNPs were significantly associated with AHSG levels (p<0.0001), except for rs4831 (p=0.9) after adjustment for gender, age, and body mass index (BMI). AHSG levels were associated with liver fat content (p=0.0160) and BMI (p=0.0247) after adjustment for gender and age. While rs2248690 was nominally associated with BMI in the dominant model (p=0.0432), none of the SNPs was associated with regional fat distribution. Common genetic variation within AHSG does not appear to influence regional body fat distribution, but may affect whole-body adiposity in humans.

The L162V polymorphism of the peroxisome proliferator activated receptor alpha gene (PPARA) is not associated with type 2 diabetes, BMI or body fat composition.

BACKGROUND: The L162V single nucleotide polymorphism in PPARA is suggested to play an important role in the pathogenesis of type 2 diabetes, obesity, and body fat composition. However, clinical evidence is controversial. OBJECTIVE: Our aim was to investigate the relationships of the L162V SNP with type 2 diabetes, pre-diabetes phenotypes, adiposity, and plasma lipid levels. In addition, we studied the associations of the L162V SNP with body fat composition, intramyocellular lipids, and liver fat content. Furthermore, we examined if the L162V SNP was associated with changes in BMI, insulin secretion, insulin resistance, body fat composition, intramyocellular lipids, and liver fat content in response to lifestyle intervention. MATERIAL AND METHODS: Data from two large cross sectional studies, the combined TULIP/TUEF cohorts, and the LURIC study were analysed. Prospective data were obtained from TULIP participants who underwent a lifestyle intervention. A total of 4,779 subjects were studied. BMI was measured in all subjects. Type 2 diabetes was diagnosed in a subgroup of the LURIC study. In the TULIP study total body fat, non-visceral adipose tissue, and visceral adipose tissue were measured with magnetic resonance tomography. Liver fat and intramyocellular lipid content were quantified with (1)H magnetic resonance spectroscopy. Insulin sensitivity and insulin secretion were estimated from oral glucose tolerance testing. RESULTS: The L162V SNP was neither associated with type 2 diabetes or BMI nor with body fat composition, intramyocellular lipids or liver fat content. CONCLUSIONS: According to our study, the L162V SNP does not have a strong impact on the pathogenesis of type 2 diabetes or obesity.

High cardiorespiratory fitness is an independent predictor of the reduction in liver fat during a lifestyle intervention in non-alcoholic fatty liver disease.

OBJECTIVE: Lifestyle intervention with diet modification and increase in physical activity is effective for reducing hepatic steatosis in patients with non-alcoholic fatty liver disease (NAFLD). However, for a similar weight loss, there is a large variability in the change in liver fat. We hypothesised that cardiorespiratory fitness may predict the response to the intervention. DESIGN: Longitudinal study with increase in physical activity and diet modification. SETTING: University teaching hospital. PATIENTS: 50 adults with NAFLD and 120 controls at risk for metabolic diseases. MAIN OUTCOME MEASURES: Total-, subcutaneous abdominal- and visceral adipose tissue by magnetic resonance tomography, liver fat by 1HMR spectroscopy and cardiorespiratory fitness (VO(2,max)) by a maximal cycle exercise test at baseline and after 9 months of follow-up. RESULTS: In all subjects total-, subcutaneous abdominal- and visceral adipose tissue decreased and fitness increased (all p<0.0001) during the intervention. The most pronounced changes were found for liver fat (-31%, p<0.0001). Among the parameters predicting the change in liver fat, fitness at baseline emerged as the strongest factor, independently of total- and visceral adipose tissue as well as exercise intensity (p = 0.005). In the group of subjects with NAFLD at baseline, a resolution of NAFLD was found in 20 individuals. For 1 standard deviation increase in VO(2,max) at baseline the odds ratio for resolution of NAFLD was 2.79 (95% confidence interval, 1.43-6.33). CONCLUSIONS: Cardiorespiratory fitness, independently of total adiposity, body fat distribution and exercise intensity, determines liver fat content in humans, suggesting that fitness and liver fat are causally related to each other. Moreover, measurement of fitness at baseline predicts the effectiveness of a lifestyle intervention in reducing hepatic steatosis in patients with NAFLD.

Perivascular fatty tissue at the brachial artery is linked to insulin resistance but not to local endothelial dysfunction.

AIMS/HYPOTHESIS: Different ectopic fat depots, such as visceral or hepatic fat, are known to affect whole body insulin sensitivity. It has recently been hypothesised that differences in perivascular adipose tissue (PVAT) mass around resistance vessels may also contribute to insulin resistance, possibly via direct vascular effects leading to reduced capillary cross-sectional area in the muscle, which in turn affects muscular blood flow and glucose uptake. Based on this, the aim of the present study was to test whether PVAT around conduit arteries (i.e. the brachial artery) influences NO bioavailability, expressed as flow-mediated dilation (FMD), or insulin sensitivity in humans in vivo. METHODS: Insulin sensitivity was measured by OGTT in all 95 participants (59 women, 36 men; median age 47 years, range 19-66 years) and by the gold standard, a euglycaemic-hyperinsulinaemic clamp, in a randomly selected subgroup of 33 participants. Quantification of the different fat compartments, including PVAT around the brachial artery, was achieved by high-resolution magnetic resonance imaging (1.5 T). Blood flow and FMD were measured at the brachial artery using high-resolution (13 MHz) ultrasound, after 5 min of forearm occlusion. RESULTS: PVAT was negatively correlated with insulin sensitivity and the post-ischaemic increase in blood flow. The association between PVAT and insulin sensitivity (r = -0.54, beta = -0.37, p = 0.009) was independent of age, sex, visceral adipose tissue, liver fat, BMI and further cardiovascular risk factors. No correlation could be detected between PVAT and local endothelial function. However, we observed an independent association between PVAT and post-ischaemic increase in blood flow (r = -0.241; beta = -1.69; p = 0.02). CONCLUSIONS/INTERPRETATION: PVAT seems to play an independent role in the pathogenesis of insulin resistance. This may be due to direct vascular effects influencing muscular blood flow.

Low hepatic stearoyl-CoA desaturase 1 activity is associated with fatty liver and insulin resistance in obese humans.

AIMS/HYPOTHESIS: Stearoyl-CoA desaturase 1 (SCD1) is the rate-limiting enzyme in monounsaturated fatty acid synthesis. It is imperative for the assembly of VLDL particles, which transport triacylglycerol (TG) from liver to adipose tissue and other sites. We aimed to determine the role of hepatic SCD1 activity in human glucose and lipid metabolism. METHODS: We studied 54 people participating in a lifestyle intervention programme with diet modification and increased physical activity. Insulin sensitivity was determined during a euglycaemic-hyperinsulinaemic clamp and estimated from an OGTT. Liver fat was quantified by (1)H-magnetic resonance spectroscopy at baseline and after 9 months of intervention. The pattern of fatty acids in serum VLDL-TGs was determined by ultracentrifugation followed by thin layer and gas chromatography, with the 18:1 n-9: 18:0 ratio providing an index of hepatic SCD1 activity. RESULTS: The hepatic SCD1 activity index correlated negatively with liver fat (r= -0.29, p=0.04) and positively with insulin sensitivity, both OGTT-derived (r=0.42, p=0.003) and clamp-derived (r=0.27, p=0.07). These correlations depended on overall adiposity. They were absent in leaner participants (n=27, liver fat: p=0.34, insulin sensitivity [OGTT]: p=0.75, insulin sensitivity [clamp]: p=0.24), but were strong in obese individuals (n=27, p=0.004, p=0.0002 and p=0.006, respectively). Furthermore, during intervention a high SCD1 activity index at baseline predicted a decrease in liver fat only in obese participants (r= -0.46, p=0.02). CONCLUSIONS/INTERPRETATION: Our data suggest that high hepatic SCD1 activity may regulate fat accumulation in the liver and possibly protects from insulin resistance in obesity.

Role of AMP-activated protein kinase gamma 3 genetic variability in glucose and lipid metabolism in non-diabetic whites.

AIMS/HYPOTHESIS: AMP-activated protein kinase (AMPK) is a heterotrimeric enzyme that acts as an intracellular fuel sensor, directing multiple metabolic pathways in a catabolic direction in times of nutrient shortage. In humans, three different gamma-subunits (gamma(1), gamma(2), gamma(3)) have been identified as AMPK regulators. The AMPKgamma3 (protein kinase, AMP-activated, gamma 3 non-catalytic subunit, PRKAG3) isoform plays a role in gene regulation in glucose/lipid metabolism and skeletal muscle glycogen content. We investigated whether PRKAG3, in addition to being expressed in skeletal muscle, is also expressed in human liver. We also investigated whether genetic variance in PRKAG3 is associated with glucose and/or lipid metabolism in non-diabetic whites. MATERIALS AND METHODS: After sequencing a screening cohort (n = 50) in the PRKAG3 locus, we genotyped 1061 participants for frequently found single nucleotide polymorphisms (SNPs). Association analyses between genotypes/haplotypes and metabolic traits were carried out. RESULTS: We detected PRKAG3 expression in human liver and skeletal muscle. Two SNPs (rs692243, rs6436094) with minor allele frequencies of 0.16 and 0.26 respectively and in moderate linkage disequilibrium (D' = 0.92; r (2) = 0.47) were found. rs692243 (C/G) confers a Pro71Ala mutation, while rs6436094 (A/G) is located in the 3' untranslated region. No associations with prediabetic traits such as body fat distribution, insulin resistance or insulin secretion were found (p > 0.15 for all). However, the minor alleles of both SNPs were significantly associated with higher serum LDL-cholesterol and apolipoprotein (Apo) B-100 levels (rs692243: CG:LDL 4.3%, ApoB-100 3.4%; GG:LDL 7.6%, ApoB-100 5.4%; p = 0.008 and p = 0.01 respectively; rs6436094: AG:LDL 3.3%, ApoB-100 1.7%; GG:LDL 11.3%, ApoB-100 11.1%; p = 0.009 and p = 0.05 respectively; dominant model). The GG/GG diplotype homozygous for both minor SNP alleles displayed the highest LDL-cholesterol among all frequent diplotypes (p = 0.059). CONCLUSIONS/INTERPRETATION: While genetic variability in PRKAG3 does not seem to have a major effect on glucose metabolism, it may play an important role in lipoprotein metabolism in humans.

Gender specific correlations of adrenal gland size and body fat distribution: a whole body MRI study.

OBJECTIVE: The aim of this study was to investigate the gender specific correlations of stress related tissues [adrenal gland volume (AV), visceral fat] and alimentary dependent fat compartments with cortisol concentrations in healthy male and female subjects. METHODS: Fourteen men and 13 women were examined. Fat compartments [whole body fat, visceral adipose tissue (VAT) and subcutaneous adipose tissue (SCAT)] were determined using whole body MRI. Adrenal gland volume was assessed by a 3D MR data set. The salivary cortisol was determined at 9 AM and 4 PM. RESULTS: Men had significantly more visceral fat and less subcutaneous fat than women. Adrenal gland size correlated significantly with the visceral and subcutaneous fat in women (r=0.7, p=0.008), but not in men (r=0.2, p=0.4). There was a negative correlation between the decrease of cortisol between 9 AM and 4 PM with VAT (r=-0.451, p=0.027) in the whole group. DISCUSSION: The high correlation between the adrenal gland volume and VAT in women underlines the link between hypothalamic-pituitary-adrenal (HPA) axis, stress, and circadian cortisol rhythm, respectively, and an increased abdominal fat volume. The lack of correlation between visceral fat and adrenal volume in men points to an additional influence of sex hormones.