Visceral fat accumulation and insulin resistance are important factors in nonalcoholic fatty liver disease

Background Nonalcoholic fatty liver diseases are often associated with obesity, insulin resistance, and excessive visceral fat accumulation. The aims of this study were (1) to evaluate the relationship between the severity of fatty liver and visceral fat accumulation in nonalcoholic fatty liver diseases, and (2) to investigate the relationships of fatty liver with biochemical data and insulin resistance. Methods One hundred twenty-nine subjects (63 women) with fatty liver diagnosed by ultrasonography were enrolled. Subjects positive for hepatitis B virus, hepatitis C virus, or autoimmune antibodies and those whose alcohol intake was over 20 g/day were excluded. The visceral fat area at the umbilical level and the liver–spleen ratio were evaluated by computed tomography. Results The severity of fatty liver evaluated by ultrasonography showed a significant positive relationship with the visceral fat area and waist circumstance (fatty liver severity: mild, 92.0 ± 30.9 cm²; moderate, 122.1 ± 32.6 cm²; severe, 161.0 ± 48.4 cm²; P < 0.0001). The visceral fat area and liver–spleen ratio were negatively correlated (r = −0.605, P < 0.0001). The severity of fatty liver showed strong positive relationships with serum aspartate aminotransferase, alanine aminotransferase, fasting plasma glucose, fasting plasma insulin, and insulin resistance. The severity of fatty liver was positively related to the visceral fat area in 49 nonobese subjects (body mass index <25). Conclusions The severity of fatty liver was positively correlated with visceral fat accumulation and insulin resistance in both obese and nonobese subjects, suggesting that hepatic fat infiltration in nonalcoholic fatty liver disease may be influenced by visceral fat accumulation regardless of body mass index.     

Exercise training reduces fatty acid availability and improves the insulin sensitivity of glucose metabolism

Aims/hypothesis It is not known whether the beneficial effects of exercise training on insulin sensitivity are due to changes in hepatic and peripheral insulin sensitivity or whether the changes in insulin sensitivity can be explained by adaptive changes in fatty acid metabolism, changes in visceral fat or changes in liver and muscle triacylglycerol content. We investigated the effects of 6 weeks of supervised exercise in sedentary men on these variables. Subjects and methods We randomised 17 sedentary overweight male subjects (age 50 ± 2.6 years, BMI 27.6 ± 0.5 kg/m²) to a 6-week exercise programme (n = 10) or control group (n = 7). The insulin sensitivity of palmitic acid production rate (Ra), glycerol Ra, endogenous glucose Ra (EGP), glucose uptake and glucose metabolic clearance rate were measured at 0 and 6 weeks with a two-step hyperinsulinaemic–euglycaemic clamp [step 1, 0.3 (low dose); step 2, 1.5 (high dose) mU kg⁻¹ min⁻¹]. In the exercise group subjects were studied >72 h after the last training session. Liver and skeletal muscle triacylglycerol content was measured by magnetic resonance spectroscopy and visceral adipose tissue by cross-sectional computer tomography scanning. Results After 6 weeks, fasting glycerol, palmitic acid Ra (p = 0.003, p = 0.042) and NEFA concentration (p = 0.005) were decreased in the exercise group with no change in the control group. The effects of low-dose insulin on EGP and of high-dose insulin on glucose uptake and metabolic clearance rate were enhanced in the exercise group but not in the control group (p = 0.026; p = 0.007 and p = 0.04). There was no change in muscle triacylglycerol and liver fat in either group. Conclusions/interpretation Decreased availability of circulating NEFA may contribute to the observed improvement in the insulin sensitivity of EGP and glucose uptake following 6 weeks of moderate exercise. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible to authorised users.     

Differential effects of fatness,fitness and physical activity energy expenditure on whole-body,liver and fat insulin sensitivity

Aims/hypothesis The relative contributions of fitness (maximal oxygen uptake), physical activity energy expenditure (PAEE) and fatness to whole-body, liver and fat insulin sensitivity is uncertain. The aim of this study was to determine whether fitness and PAEE are associated with whole-body, liver and fat insulin sensitivity independently of body fat. Materials and methods We recruited 25 men (mean [SD] age 53 [6] years). Whole-body (M value) and liver (percentage suppression of endogenous glucose output) insulin sensitivity were estimated using a hyperinsulinaemic–euglycaemic clamp. Insulin sensitivity in fat (insulin sensitivity index for NEFA) was estimated during an OGTT. Total and truncal fat were measured by dual-energy X-ray absorptiometry, fitness by treadmill, and PAEE (n = 21) by 3 day heart rate monitoring and Baecke questionnaire. Results In univariate analyses, fatness was strongly associated with insulin sensitivity (whole-body, liver and fat). Fitness was associated with whole-body (r = 0.53, p < 0.007) and liver (0.42, p = 0.04) insulin sensitivity, while PAEE was associated with liver insulin sensitivity (r = 0.55, p = 0.01). Regression models were established to describe associations between fatness, fitness and physical activity and measures of insulin sensitivity (whole-body, fat and liver) as outcomes. Only fatness was independently associated with whole-body insulin sensitivity (B coefficient −0.01, p = 0.001). Fitness was not associated with any outcome. Only PAEE was independently associated with liver insulin sensitivity (B coefficient 13.5, p = 0.02). Conclusions/interpretation Fatness explains most of the variance in whole-body insulin sensitivity. In contrast, PAEE explains most of the variance in liver insulin sensitivity.     

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 ¹H-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. N. Stefan and A. Peter contributed equally to this work.     

A common variant in PNPLA3, which encodes adiponutrin, is associated with liver fat content in humans

Aims/hypothesis  It has recently been suggested that the rs738409 G allele in PNPLA3, which encodes adiponutrin, is strongly associated with increased liver fat content in three different ethnic groups. The aims of the present study were as follows: (1) to try to replicate these findings in European individuals with quantitative measures of hepatic fat content; (2) to study whether the polymorphism influences hepatic and adipose tissue insulin sensitivity; and (3) to investigate whether PNPLA3 expression is altered in the human fatty liver. Methods  We genotyped 291 Finnish individuals in whom liver fat had been measured using proton magnetic resonance spectroscopy. Hepatic PNPLA3 expression was measured in 32 participants. Hepatic and adipose tissue insulin sensitivities were measured using a euglycaemic–hyperinsulinaemic (insulin infusion 0.3 mU kg⁻¹ min⁻¹) clamp technique combined with infusion of [3-³H]glucose in 109 participants. Results  The rs738409 G allele in PNPLA3 was associated with increased quantitative measures of liver fat content (p = 0.011) and serum aspartate aminotransferase concentrations (p = 0.002) independently of age, sex and BMI. Fasting serum insulin and hepatic and adipose tissue insulin sensitivity were related to liver fat content independently of genotype status. PNPLA3 mRNA expression in the liver was positively related to obesity (r = 0.62, p < 0.0001) and to liver fat content (r = 0.58, p = 0.025) in participants who were not morbidly obese (BMI < 40 kg/m²). Conclusions/interpretation  A common variant in PNPLA3 increases the risk of hepatic steatosis in humans. A. Kotronen and L. E. Johansson contributed equally to this study.     

Improved glucose tolerance in mice receiving intraperitoneal transplantation of normal fat tissue

Aims/hypothesis The association between increased (visceral) fat mass, insulin resistance and type 2 diabetes mellitus is well known. Yet, it is unclear whether the mere increase in intra-abdominal fat mass, or rather functional alterations in fat tissue in obesity contribute to the development of insulin resistance in obese patients. Here we attempted to isolate the metabolic effect of increased fat mass by fat tissue transplantation. Methods Epididymal fat pads were removed from male C57Bl6/J mice and transplanted intraperitoneally into male littermates (recipients), increasing the combined perigonadal fat mass by 50% (p < 0.005). At 4 and 8 weeks post-transplantation, glucose and insulin tolerance tests were performed, and insulin, NEFA and adipokines measured. Results Circulating levels of NEFA, adiponectin and leptin were not significantly different between transplanted and sham-operated control mice, while results of the postprandial insulin tolerance test were similar between the two groups. In contrast, under fasting conditions, the mere increase in intra-abdominal fat mass resulted in decreased plasma glucose levels (6.9 ± 0.4 vs 8.1 ± 0.3 mmol/l, p = 0.03) and a ∼20% lower AUC in the glucose tolerance test (p = 0.02) in transplanted mice. Homeostasis model assessment of insulin resistance (HOMA-IR) was 4.1 ± 0.4 in transplanted mice (vs 6.2 ± 0.7 in sham-operated controls) (p = 0.02), suggesting improved insulin sensitivity. Linear regression modelling revealed that while total body weight positively correlated, as expected, with HOMA-IR (β: 0.728, p = 0.006), higher transplanted fat mass correlated with lower HOMA-IR (β: −0.505, p = 0.031). Conclusions/interpretation Increasing intra-abdominal fat mass by transplantation of fat from normal mice improved, rather than impaired, fasting glucose tolerance and insulin sensitivity, achieving an effect opposite to the expected metabolic consequence of increased visceral fat in obesity.     

Tissue specificity of insulin resistance in humans: fat in the liver rather than muscle is associated with features of the metabolic syndrome

Aims/hypothesis The aim of this study was to investigate whether intrahepatic and intramyocellular fat are related to insulin resistance in these respective tissues or to the metabolic syndrome. Methods Hepatic (insulin 1.8 pmol kg⁻¹ min⁻¹ combined with [3-³H]glucose) and muscle (insulin 6.0 pmol kg⁻¹ min⁻¹) insulin sensitivity were measured on separate occasions in 45 non-diabetic men (age 42 ± 1 years, BMI 26.2 ± 0.6 kg/m²) using the euglycaemic–hyperinsulinaemic clamp. Liver fat and intramyocellular lipid (IMCL) were measured by proton magnetic resonance spectroscopy and body composition by magnetic resonance imaging. We also determined fasting serum insulin and adiponectin concentrations, components of the metabolic syndrome and maximal oxygen consumption. Results In participants with high [median 12.0% (interquartile range 5.7–18.5%)] vs low [2.0% (1.0–2.0%)] liver fat, fasting serum triacylglycerols (1.6 ± 0.2 vs 1.0 ± 0.1 mmol/l, p = 0.002) and fasting serum insulin (55 ± 4 vs 32 ± 2 pmol/l, p < 0.0001) were increased and serum HDL-cholesterol (1.26 ± 0.1 vs 1.48 ± 0.1 mmol/l, p = 0.02) and fasting serum adiponectin (9.5 ± 1.2 vs 12.2 ± 1.2 μg/ml, p = 0.05) decreased. In participants with high [19.5% (16.0–26.0%)] vs low [5.0% (2.3–7.5%)] IMCL, these parameters were comparable. Liver fat was higher in participants with [10.5% (3.0–18.0%)] than in those without [2.0% (1.5–6.0%), p = 0.010] the metabolic syndrome, even independently of obesity, while IMCL was comparable. Insulin suppression of glucose rate of appearance and serum NEFA was significantly impaired in the high liver fat group. Conclusions/interpretation Fat accumulation in the liver rather than in skeletal muscle is associated with features of the metabolic syndrome, i.e. increased fasting serum triacylglycerols and decreased fasting serum HDL-cholesterol, as well as with hyperinsulinaemia and low adiponectin.     

Eradicating hepatitis C virus ameliorates insulin resistance without change in adipose depots

Chronic hepatitis C (CHC) is associated with lipid‐related changes and insulin resistance; the latter predicts response to antiviral therapy, liver disease progression and the risk of diabetes. We sought to determine whether insulin sensitivity improves following CHC viral eradication after antiviral therapy and whether this is accompanied by changes in fat depots or adipokine levels. We compared 8 normoglycaemic men with CHC (genotype 1 or 3) before and at least 6 months post viral eradication and 15 hepatitis C antibody negative controls using an intravenous glucose tolerance test and two‐step hyperinsulinaemic–euglycaemic clamp with [6,6‐²H₂] glucose to assess peripheral and hepatic insulin sensitivity. Magnetic resonance imaging and spectroscopy quantified abdominal fat compartments, liver and intramyocellular lipid. Peripheral insulin sensitivity improved (glucose infusion rate during high‐dose insulin increased from 10.1 ± 1.6 to 12 ± 2.1 mg/kg/min/, P = 0.025), with no change in hepatic insulin response following successful viral eradication, without any accompanying change in muscle, liver or abdominal fat depots. There was corresponding improvement in incremental glycaemic response to intravenous glucose (pretreatment: 62.1 ± 8.3 vs post‐treatment: 56.1 ± 8.5 mm , P = 0.008). Insulin sensitivity after viral clearance was comparable to matched controls without CHC. Post therapy, liver enzyme levels decreased but, interestingly, levels of glucagon, fatty acid–binding protein and lipocalin‐2 remained elevated. Eradication of the hepatitis C virus improves insulin sensitivity without alteration in fat depots, adipokine or glucagon levels, consistent with a direct link of the virus with insulin resistance.     

The common SLC30A8 Arg325Trp variant is associated with reduced first-phase insulin release in 846 non-diabetic offspring of type 2 diabetes patients—the EUGENE2 study

Aims/hypothesis A recent genome-wide association study identified the SLC30A8 rs13266634 polymorphism encoding an Arg325Trp polymorphism in the zinc transporter protein member 8 (ZnT-8) to be associated with type 2 diabetes. Here, we investigate whether the polymorphism is related to altered insulin release in response to intravenous and oral glucose loads in non-diabetic offspring of type 2 diabetic patients. Methods We genotyped SLC30A8 rs13266634 in 846 non-diabetic offspring of type 2 diabetic patients from five different white populations: Danish (n = 271), Finnish (n  = 217), German (n = 149), Italian (n  = 109) and Swedish (n  = 100). Participants were subjected to both IVGTTs and OGTTs, and measurements of insulin sensitivity. Results Homozygous carriers of the major type 2 diabetes C risk-allele showed a 19% decrease in first-phase insulin release (0–10 min) measured during the IVGTT (CC 3,624 ± 3,197; CT 3,763 ± 2,674; TT 4,478 ± 3,032 pmol l⁻¹ min⁻¹, mean ± SD; p = 0.007). We found no significant genotype effect on insulin release measured during the OGTT or on estimates of insulin sensitivity. Conclusions/interpretation Of European non-diabetic offspring of type 2 diabetes patients, 46% are homozygous carriers of the Arg325Trp polymorphism in ZnT-8, which is known to associate with type 2 diabetes. These diabetes-prone offspring are characterised by a 19% decrease in first-phase insulin release following an intravenous glucose load, suggesting a role for this variant in the pathogenesis of pancreatic beta cell dysfunction. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Elevated serum levels of visfatin in gestational diabetes: a comparative study across various degrees of glucose tolerance

Aims/hypothesis Concentrations of visfatin are increased in insulin-resistant conditions, but the relationship between visfatin and insulin and/or insulin resistance indices in pregnancy remains unclear. Insulin resistance in pregnancy is further accentuated in women with gestational diabetes mellitus (GDM). Thus we assessed serum levels of visfatin in pregnant women with varying degrees of glucose tolerance. Materials and methods Fasting visfatin levels were measured at 28 weeks of gestation in 51 women divided according to their response to a 50-g glucose challenge test (GCT) and a 75-g OGTT: control subjects (n = 20) had normal responses to both a GCT and an OGTT; the intermediate group (IG; n = 15) had a false-positive GCT, but a normal OGTT; the GDM group (n = 16) had abnormal GCTs and OGTTs. Results There were no age or BMI differences between analysed groups. Across the subgroups there was a progressive increase in glucose and insulin at 120 min of the OGTT (p < 0.01). This was accompanied by an increase in visfatin, from 76.8 ± 14.1 ng/ml in the control subjects, to 84.0 ± 14.7 ng/ml in the IG group and 93.1 ± 12.3 ng/ml in the GDM group (p < 0.01 for GDM vs control subjects). There was a positive correlation between visfatin and fasting insulin (r = 0.38, p = 0.007) and insulin at 120 min of the OGTT (r = 0.39, p = 0.006). Conclusions/interpretation An increase in fasting visfatin, the levels of which correlate with both fasting and post-glucose-load insulin concentrations, accompanies worsening glucose tolerance in the third trimester of pregnancy. However, the significance of these findings, and in particular the role of visfatin in the regulation of insulin sensitivity during pregnancy, remains to be elucidated. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users. G. M. Prelevic and H. S. Randeva are both senior authors.     

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, β = −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; β = −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.     

Variations in the four and a half LIM domains 1 gene (<Emphasis Type="Italic">FHL1</Emphasis>) are associated with fasting insulin and insulin sensitivity responses to regular exercise

Aims/hypothesis The expression of the four and a half LIM domains 1 gene (FHL1) is increased in the muscle of individuals who show an improvement in insulin sensitivity index (S _I) after 20 weeks of exercise training. The aim of the present study was to investigate associations between three FHL1 single nucleotide polymorphisms (SNPs) and variables derived from an IVGTT, both in the sedentary state and in response to exercise training, in participants in the HERITAGE Family Study. Materials and methods SNPs were typed using fluorescence polarisation methodology. Analyses were performed separately by sex and in black and white individuals. Results In black participants, no associations were found with any of the SNPs. In white women (n = 207), SNP rs9018 was associated with the disposition index (D _I), which is calculated as S _I generated from the MINMOD program (×10⁻⁴ min⁻¹[μU/ml]⁻¹) multiplied by acute insulin response to glucose (AIR_g; pmol/l × 10 min), and the glucose disappearance index (K _g) training responses (p = 0.016 and p = 0.008, respectively). In white men (n = 222), all SNPs were associated with fasting glucose levels (p ≤ 0.05) and SNP rs2180062 with the insulin sensitivity index (S _I) (p = 0.04) in the sedentary state. Two SNPs were associated with fasting insulin training response. Fasting insulin decreased to a greater extent in carriers of the rs2180062 C allele (p = 0.01) and rs9018 T allele (p = 0.04). With exercise training, S _I (×10⁻⁴ min⁻¹[μU/ml]⁻¹: 0.68 ± 0.20 vs −0.77 ± 0.44, p = 0.046), D _I (319 ± 123 vs –528 ± 260, p = 0.006) and K _g (per 100 min: 0.09 ± 0.04 vs −0.14 ± 0.8, p = 0.03) improved more in the C allele carriers at rs2180062 than in the T allele carriers. Conclusions/interpretation Fasting insulin and S _I responses to exercise training were associated with DNA sequence variation in FHL1 in white men. Whether these associations exist only in white men remains to be investigated. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Non-esterified fatty acid concentrations are independently associated with hepatic steatosis in obese subjects

Aims/hypothesis We tested the hypothesis that NEFA concentrations are higher in obese subjects with fatty liver than in obese subjects without fatty liver. Materials and methods We recruited 22 obese (BMI>30 kg/m²) men aged 42–64 years, in whom liver fat was assessed by ultrasound and classified into categories of no, mild to moderate and severe fatty liver by two independent radiologists. Regional and visceral abdominal fat were assessed by dual-energy X-ray absorptiometry and magnetic resonance imaging, and endogenous glucose production, whole-body glucose disposal during an insulin clamp, and NEFA concentrations were measured, along with NEFA suppression (percent (%) suppression and insulin sensitivity index for NEFA during an OGTT). Results Seven subjects had no evidence of fatty liver, nine had mild or moderate fatty liver and six had severe fatty liver. The amount of visceral fat was not associated with the degree of fatty liver. Whole-body glucose disposal was inversely associated with fatty liver (38.4, 26.5 and 23.9 μmol kg⁻¹ min⁻¹ for the groups with no fatty liver, mild to moderate fatty liver and severe fatty liver, respectively, p=0.004). NEFA suppression during the OGTT was decreased (62.5, 50.8 and 41%, p=0.03, for no, mild to moderate, and severe fatty liver, respectively) and the insulin sensitivity index for NEFA was decreased (0.80, 0.40 and 0.34, p<0.0001). Regression modelling suggested that NEFA concentrations were associated with fatty liver independently of whole-body glucose production and disposal measurements. Conclusions/interpretation In obese men, NEFA concentrations during an OGTT are associated with fatty liver independently of classic measures of insulin sensitivity determined by the hyperinsulinaemic clamp. The contribution to this association by factors regulating NEFA concentrations requires further study.     

Markers of de novo lipogenesis in adipose tissue: associations with small adipocytes and insulin sensitivity in humans

Aims/hypothesis  Previous studies have shown relationships between fatty acid ratios in adipose tissue triacylglycerol (TG), adipocyte size and measures of insulin sensitivity. We hypothesised that variations in adipose tissue de novo lipogenesis (DNL) in relation to adiposity might explain some of these observations. Methods  In a cross-sectional study, subcutaneous abdominal adipose tissue biopsies from 59 people were examined in relation to fasting and post-glucose insulin sensitivity. Adipocyte size, TG fatty acid composition and mRNA expression of lipogenic genes were determined. Results  We found strong positive relationships between adipose tissue TG content of the fatty acids myristic acid (14:0) and stearic acid (18:0) with insulin sensitivity (HOMA model) (p < 0.01 for each), and inverse relationships with adipocyte size (p < 0.01, p < 0.05, respectively). Variation in 18:0 content was the determinant of the adipose tissue TG 18:1 n-9/18:0 ratio, which correlated negatively with insulin sensitivity (p < 0.01), as observed previously. Adipose tissue 18:0 content correlated positively with the mRNA expression of lipogenic genes (e.g. FASN, p < 0.01). Lipogenic gene expression (a composite measure derived from principal components analysis) was inversely correlated with adipocyte cell size (p < 0.001). There was no relationship between dietary saturated fatty acid intake and adipose tissue 18:0 content. Conclusions/interpretation  Our data suggest a physiological mechanism whereby DNL is downregulated as adipocytes expand. Taken together with other data, they also suggest that hepatic and adipose tissue DNL are not regulated in parallel. We also confirm a strong relationship between small adipocytes and insulin sensitivity, which is independent of BMI. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Direct rosiglitazone-induced modifications in insulin secretion, action and clearance: a single-dose hyperglycaemic clamp study

Aims/hypothesis In addition to the improvement in insulin sensitivity, it has been shown that thiazolidinediones modulate beta cell function and insulin clearance in type 2 diabetic subjects. However, interactions between all these actions, and confounding factors due to co-morbidities and co-treatments in diabetic individuals, complicate the identification of specific effects. The aim of this pilot study was to investigate the potential acute effects of rosiglitazone on beta cell function and insulin sensitivity by the hyperglycaemic clamp technique in healthy volunteers. Subjects and methods Twelve healthy men were included in a randomised, double-blind crossover study. Rosiglitazone (8 mg) or placebo was given orally 45 min before the hyperglycaemic clamp (10 mmol/l for 2 h). Results The second phase of the insulin response was significantly decreased by rosiglitazone: 13,066 ± 1,531 vs 16,316 ± 2,813 pmol l⁻¹ 110 min in controls (p < 0.05), without change in the first phase. Serum C-peptide was not modified. Rosiglitazone treatment significantly increased insulin clearance (molar ratio of the C-peptide to insulin AUCs: 12.80 ± 1.34 vs 11.38 ± .33, p < 0.05) and the insulin sensitivity index (12.0 ± 1.5 vs 8.5 ± 1.1 μmol m⁻² min⁻¹ pmol⁻¹l, p < 0.01). Conclusions/interpretation The present results show that a single dose of rosiglitazone rapidly increases insulin clearance and insulin sensitivity index in healthy volunteers, with no direct effect on insulin secretion. The precise mechanisms mediating these actions remain to be determined. ClinicalTrials.gov ID no.: NCT00285142     

Liver fat and lipid oxidation in humans

Background: Studies in animals show that changes in hepatic fatty acid oxidation alter liver fat content. Human data regarding whole‐body and hepatic lipid oxidation are controversial and based on studies of only a few subjects. Aims: We examined whether whole‐body and hepatic lipid oxidation are altered in subjects with non‐alcoholic fatty liver disease (NAFLD) compared with controls. Methods: In vivo measurements of rates of substrate oxidation and insulin sensitivity (using the euglycaemic hyperinsulinaemic clamp technique in combination with indirect calorimetry and infusion of [3‐³H]glucose) were performed in subjects with NAFLD [mean liver fat 14.0% (interquartile range 7.5–20.5%), n=29] and in control subjects [1.6% (1.0–3.0%), n=29]. Liver fat was measured using proton magnetic resonance spectroscopy. Plasma concentrations of 3‐hydroxybutyrate (3‐OHB) were measured as markers of hepatic lipid oxidation. Results: In the basal state, substrate oxidation rates and serum 3‐OHB concentrations were comparable in subjects with and without NAFLD. Plasma 3‐OHB concentrations were similarly suppressed by insulin in both the groups. During the insulin infusion, whole‐body lipid oxidation was inversely correlated with insulin‐stimulated glucose disposal (r=?0.48, P<0.0001), which was lower in subjects with NAFLD [3.7±0.2 mg/(kg fat‐free mass min)] than in the control subjects [5.0±0.3 mg/(kg fat‐free mass min), P=0.0008]. Conclusions: Hepatic lipid oxidation is unchanged in NAFLD. Whole‐body lipid oxidation is increased because of peripheral insulin resistance. These data imply that alterations in hepatic fatty acid oxidation do not contribute to liver fat content in humans.     

Effect of short-term ACE inhibitor treatment on peripheral insulin sensitivity in obese insulin-resistant subjects

Aims/hypothesis This study was designed to investigate the effect of short-term ACE inhibitor treatment on insulin sensitivity and to examine possible underlying metabolic and haemodynamic effects in obese insulin-resistant subjects.Methods A randomised, double-blind placebo-controlled trial was performed in 18 obese insulin-resistant men (age, 53 ± 2 years; BMI, 32.6 ± 0.8 kg/m²; homeostasis model assessment of insulin resistance, 5.6 ± 0.5; systolic blood pressure [SBP], 140.8 ± 3.2; diastolic blood pressure [DBP], 88.8 ± 1.6 mmHg), who were free of any medication. The aim was to examine the effects of 2 weeks of ACE inhibitor treatment (ramipril, 5 mg/day) on insulin sensitivity, forearm blood flow, substrate fluxes across the forearm, whole-body substrate oxidation and intramuscular triacylglycerol (IMTG) content.Results Ramipril treatment decreased ACE activity compared with placebo (−22.0 ± 1.7 vs 0.2 ± 1.1 U/l, respectively, p < 0.001), resulting in a significantly reduced blood pressure (SBP, −10.8 ± 2.1 vs −2.7 ± 2.0 mmHg, respectively, p = 0.01; DBP, −10.1 ± 1.3 vs −4.2 ± 2.1 mmHg, respectively, p = 0.03). Ramipril treatment had no effect on whole-body insulin-mediated glucose disposal (before: 17.9 ± 2.0, after: 19.1 ± 2.4 μmol kg body weight⁻¹ min⁻¹, p = 0.44), insulin-mediated glucose uptake across the forearm (before: 1.82 ± 0.39, after: 1.92 ± 0.29 μmol 100 ml forearm tissue⁻¹ min⁻¹, p = 0.81) and IMTG content (before: 45.4 ± 18.8, after: 48.8 ± 27.5 μmol/mg dry muscle, p = 0.92). Furthermore, the increase in carbohydrate oxidation (p < 0.001) and forearm blood flow (p < 0.01), and the decrease in fat oxidation (p < 0.001) during insulin stimulation were not significantly different between treatments.Conclusions/interpretation Short-term ramipril treatment adequately reduced ACE activity and blood pressure, but had no significant effects on insulin sensitivity, forearm blood flow, substrate fluxes across the forearm, whole-body substrate oxidation and IMTG content in obese insulin-resistant subjects.     

Women and men have similar amounts of liver and intra-abdominal fat,despite more subcutaneous fat in women: implications for sex differences in markers of cardiovascular risk

Aims/hypothesis Fat accumulation in the liver has been shown to be closely correlated with hepatic insulin resistance and features of insulin resistance, also independently of body weight. It remains to be established how fat in the liver correlates with that in other depots, and whether any association differs between men and women.Methods Liver fat (assessed using proton spectroscopy), intra-abdominal and subcutaneous fat (measured using magnetic resonance imaging) and markers of insulin resistance, including serum adiponectin, were determined in 132 non-diabetic subjects: 66 men (age 41±1 years) and 66 women (age 42±1 years).Results Although the women had almost twice as much subcutaneous fat as the men (5045±207 vs 2610±144 cm³, p<0.0001), amounts of intra-abdominal fat (1305±80 vs 1552±111 cm³, NS) and liver fat (6.7±0.8 vs 8.9±1.2%, NS) were similar. In this study, no sex differences were observed with respect to serum insulin, adiponectin, triglyceride and HDL cholesterol concentrations. Of all measures of body composition, liver fat was best correlated with serum insulin (r=0.58, p<0.001), with no difference observed between men and women. Serum adiponectin was inversely correlated with liver fat content (r=–0.21, p<0.05). Multiple linear regression analysis revealed that intra-abdominal fat was significantly associated with liver fat, independently of serum adiponectin and subcutaneous fat. Liver fat, but not intra-abdominal fat, significantly explained the variation in serum insulin concentrations.Conclusions/interpretation Intra-abdominal fat is independently associated with liver fat, whereas subcutaneous fat is not. Liver fat, but not intra-abdominal fat, is independently associated with serum insulin. Men and women with similar amounts of intra-abdominal and liver fat do not exhibit sex differences in markers of insulin resistance (serum insulin, triglycerides, HDL cholesterol and adiponectin).Abbreviations ALT alanine aminotransferase - AST aspartate aminotransferase - GGT gamma glutamyl transferase - MRI magnetic resonance imaging - NAFLD non-alcoholic fatty liver disease - SNP single nucleotide polymorphism     

A comparison of twice-daily exenatide and biphasic insulin aspart in patients with type 2 diabetes who were suboptimally controlled with sulfonylurea and metformin: a non-inferiority study

Aims/hypothesis The aim of this 52-week, open-label, non-inferiority trial was to compare the safety and efficacy of exenatide (an incretin mimetic) with that of biphasic insulin aspart. Materials and methods Patients on metformin and a sulfonylurea were randomised to exenatide (n = 253; 5 μg twice daily for 4 weeks, 10 μg thereafter) or biphasic insulin aspart (n = 248; twice-daily doses titrated for optimal glucose control), while continuing with metformin and sulfonylurea treatment. Results Glycaemic control achieved with exenatide was non-inferior to that achieved with biphasic insulin aspart (mean±SEM, HbA_1c change: exenatide −1.04 ± 0.07%, biphasic insulin aspart −0.89 ± 0.06%; difference −0.15 [95% CI −0.32 to 0.01]%). Exenatide-treated patients lost weight, while patients treated with biphasic insulin aspart gained weight [between-group difference −5.4 (95% CI −5.9 to −5.0) kg]. Both treatments reduced fasting serum glucose (exenatide −1.8 ± 0.2 mmol/l, p < 0.001; biphasic insulin aspart −1.7 ± 0.2 mmol/l, p < 0.001). Greater reductions in postprandial glucose excursions following morning (p < 0.001), midday (p = 0.002) and evening meals (p < 0.001) were observed with exenatide. The withdrawal rate was 21.3% (54/253) for exenatide and 10.1% (25/248) for biphasic insulin aspart. Nausea (33% incidence, 3.5% discontinuation) was the most common adverse event observed with exenatide. Conclusions/interpretation Exenatide treatment resulted in HbA_1c reduction similar to biphasic insulin aspart and provided better postprandial glycaemic control, making it a potential alternative for the treatment of type 2 diabetes. Treatment with biphasic insulin aspart was associated with weight gain and lower risk of adverse gastrointestinal events. Although the availability of glucose-lowering agents associated with weight reduction may be considered a therapeutic advance, the long-term implications of progressive weight reduction observed with exenatide have yet to be defined. Electronic supplementary material A list of the site investigators is available as electronic supplementary material in the online version of this article at and is accessible to authorised users.     

Relationship between basal metabolic rate and cortisol secretion throughout pregnancy

The role of cortisol in mediating basal metabolic rate (BMR) changes that accompany the adjustment of maternal body weight (BW) and body composition during pregnancy is unknown. We tested whether increase in BMR during pregnancy is explained by variations in cortisol secretion. Longitudinal changes in BW, fat mass (FM), fat-free mass (FFM), BMR, hormonal, and metabolic parameters in 31 parous Caucasian women at gestational weeks 12, 26, and 36 were examined. Individual differences (Δ) between the last and the first measurement occasions for each variable were calculated. By gestational week 36, BW and BMR increased while both FFM/FM and BMR/BW ratio decreased (P < 0.001 for all) suggesting higher proportion of FM accretion. Cortisol, leptin, and insulin-like growth factor-1 (IGF-1) concentration rose, whereas non-placental growth hormone (GH) and thyroid hormones declined (P < 0.001 for all). Insulin resistance changed; basal glucose (P < 0.001) and ghrelin (P < 0.014) declined, whereas insulin (P < 0.001), homeostatic model index (HOMA-IR) (P = 0.041), and free fatty acid (FFA) concentration (P = 0.007) increased. The elevation in BMR showed inverse correlations with ΔBW (r = 0.37, P = 0.047) and Δcortisol (r = −0.53, P = 0.004). Significant portion (51.6%) of the variation in BMR change was explained by increases of cortisol (27.1%), FFA (13.4%), and free triiodothyronine (11.1%). In conclusion, the changes in maternal cortisol concentration are in relationship with changes in BMR and BW, further suggesting that increased cortisol secretion during pregnancy could be linked with the maintenance of maternal BW and body composition.