C.C.M. Moors

Ectopic Fat Storage in the Pancreas, Liver, and Abdominal Fat Depots: Impact on β-Cell Function in Individuals with Impaired Glucose Metabolism

CONTEXT Pancreatic fat content (PFC) may have deleterious effects on β-cell function. OBJECTIVE We hypothesized that ectopic fat deposition, in particular pancreatic fat accumulation, is related to β-cell dysfunction in individuals with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT). DESIGN, SETTING AND PARTICIPANTS This was a cross-sectional study in 64 age- and body mass index-matched individuals, with normal glucose tolerance (NGT; n = 16, 60% males), IFG (n = 29, 52% males), or IFG/IGT (n = 19, 63% males) was conducted. INTERVENTION AND MAIN OUTCOME MEASURES Participants underwent the following: 1) a combined hyperinsulinemic-euglycemic and hyperglycemic clamp, with subsequent arginine stimulation to quantify insulin sensitivity and β-cell function; 2) proton-magnetic resonance spectroscopy to assess PFC and liver fat content (LFC); and 3) magnetic resonance imaging to quantify visceral (VAT) and sc (SAT) adipose tissue. The disposition index (DI; insulin sensitivity adjusted β-cell function) was assessed. RESULTS IFG and IFG/IGT were more insulin resistant (P < 0.001) compared with NGT. Individuals with IFG/IGT had the lowest values of glucose- and arginine-stimulated C-peptide secretion (both P < 0.03) and DI (P < 0.001), relative to IFG and NGT. PFC and LFC gradually increased between NGT, IFG, and IFG/IGT (P = 0.02 and P = 0.01, respectively), whereas VAT and SAT were similar between groups. No direct associations were found between PFC, LFC, VAT, and SAT and C-peptide secretion. The DI was inversely correlated with PFC, LFC, and VAT (all P < 0.05). CONCLUSIONS PFC was increased in individuals with IFG and/or IGT, without a direct relation with β-cell function.

Valsartan Improves {beta}-Cell Function and Insulin Sensitivity in Subjects With Impaired Glucose Metabolism: A randomized controlled trial

OBJECTIVE Recently, the Nateglinide and Valsartan in Impaired Glucose Tolerance Outcomes Research Trial demonstrated that treatment with the angiotensin receptor blocker (ARB) valsartan for 5 years resulted in a relative reduction of 14% in the incidence of type 2 diabetes in subjects with impaired glucose metabolism (IGM). We investigated whether improvements in β-cell function and/or insulin sensitivity underlie these preventive effects of the ARB valsartan in the onset of type 2 diabetes. RESEARCH DESIGN AND METHODS In this randomized controlled, double-blind, two-center study, the effects of 26 weeks of valsartan (320 mg daily; n = 40) or placebo (n = 39) on β-cell function and insulin sensitivity were assessed in subjects with impaired fasting glucose and/or impaired glucose tolerance, using a combined hyperinsulinemic-euglycemic and hyperglycemic clamp with subsequent arginine stimulation and a 2-h 75-g oral glucose tolerance test (OGTT). Treatment effects were analyzed using ANCOVA, adjusting for center, glucometabolic status, and sex. RESULTS Valsartan increased first-phase (P = 0.028) and second-phase (P = 0.002) glucose-stimulated insulin secretion compared with placebo, whereas the enhanced arginine-stimulated insulin secretion was comparable between groups (P = 0.25). In addition, valsartan increased the OGTT-derived insulinogenic index (representing first-phase insulin secretion after an oral glucose load; P = 0.027). Clamp-derived insulin sensitivity was significantly increased with valsartan compared with placebo (P = 0.049). Valsartan treatment significantly decreased systolic and diastolic blood pressure compared with placebo (P < 0.001). BMI remained unchanged in both treatment groups (P = 0.89). CONCLUSIONS Twenty-six weeks of valsartan treatment increased glucose-stimulated insulin release and insulin sensitivity in normotensive subjects with IGM. These findings may partly explain the beneficial effects of valsartan in the reduced incidence of type 2 diabetes.

PUFAs acutely affect triacylglycerol-derived skeletal muscle fatty acid uptake and increase postprandial insulin sensitivity

BACKGROUND Dietary fat quality may influence skeletal muscle lipid processing and fat accumulation, thereby modulating insulin sensitivity. OBJECTIVE The objective was to examine the acute effects of meals with various fatty acid (FA) compositions on skeletal muscle FA processing and postprandial insulin sensitivity in obese, insulin-resistant men. DESIGN In a single-blind, randomized, crossover study, 10 insulin-resistant men consumed 3 high-fat mixed meals (2.6 MJ), which were high in SFAs, MUFAs, or PUFAs. Fasting and postprandial skeletal muscle FA processing was examined by measuring differences in arteriovenous concentrations across the forearm muscle. [²H₂]Palmitate was infused intravenously to label endogenous triacylglycerol and FFAs in the circulation, and [U-¹³C]palmitate was added to the meal to label chylomicron-triacylglycerol. Skeletal muscle biopsy samples were taken to assess intramuscular lipid metabolism and gene expression. RESULTS Insulin and glucose responses (AUC) after the SFA meal were significantly higher than those after the PUFA meal (P = 0.006 and 0.033, respectively). Uptake of triacylglycerol-derived FAs was lower in the postprandial phase after the PUFA meal than after the other meals (AUC₆₀₋₂₄₀; P = 0.02). The fractional synthetic rate of the triacylglycerol, diacylglycerol, and phospholipid pool was higher after the MUFA meal than after the SFA meal. PUFA induced less transcriptional downregulation of oxidative pathways than did the other meals. CONCLUSION PUFAs reduced triacylglycerol-derived skeletal muscle FA uptake, which was accompanied by higher postprandial insulin sensitivity, a more transcriptional oxidative phenotype, and altered intramyocellular lipid partitioning and may therefore be protective against the development of insulin resistance.

Does interference with the renin-angiotensin system protect against diabetes? Evidence and mechanisms

Agents interfering with the renin–angiotensin system (RAS) were consistently shown to lower the incidence of type 2 diabetes mellitus (T2DM), as compared to other antihypertensive drugs, in hypertensive high‐risk populations. The mechanisms underlying this protective effect of RAS blockade using angiotensin‐converting enzyme inhibitors or angiotensin‐receptor blockers on glucose metabolism are not fully understood. In this article, we will review the evidence from randomized controlled trials and discuss the proposed mechanisms as to how RAS interference may delay the onset of T2DM. In particular, as T2DM is characterized by β‐cell dysfunction and obesity‐related insulin resistance, we address the mechanisms that underlie RAS blockade‐induced improvement in β‐cell function and insulin sensitivity.

Valsartan Improves Adipose Tissue Function in Humans with Impaired Glucose Metabolism: A Randomized Placebo-Controlled Double-Blind Trial

Background Blockade of the renin-angiotensin system (RAS) reduces the incidence of type 2 diabetes mellitus. In rodents, it has been demonstrated that RAS blockade improved adipose tissue (AT) function and glucose homeostasis. However, the effects of long-term RAS blockade on AT function have not been investigated in humans. Therefore, we examined whether 26-wks treatment with the angiotensin II type 1 receptor blocker valsartan affects AT function in humans with impaired glucose metabolism (IGM). Methodology/Principal Findings We performed a randomized, double-blind, placebo-controlled parallel-group study, in which 38 subjects with IGM were treated with valsartan (VAL, 320 mg/d) or placebo (PLB) for 26 weeks. Before and after treatment, an abdominal subcutaneous AT biopsy was collected for measurement of adipocyte size and AT gene/protein expression of angiogenesis/capillarization, adipogenesis, lipolytic and inflammatory cell markers. Furthermore, we evaluated fasting and postprandial AT blood flow (ATBF) (133Xe wash-out), systemic inflammation and insulin sensitivity (hyperinsulinemic-euglycemic clamp). VAL treatment markedly reduced adipocyte size (P<0.001), with a shift toward a higher proportion of small adipocytes. In addition, fasting (P = 0.043) and postprandial ATBF (P = 0.049) were increased, whereas gene expression of angiogenesis/capillarization, adipogenesis and macrophage infiltration markers in AT was significantly decreased after VAL compared with PLB treatment. Interestingly, the change in adipocyte size was associated with alterations in insulin sensitivity and reduced AT gene expression of macrophage infiltration markers. VAL did not alter plasma monocyte-chemoattractant protein (MCP)-1, TNF-α, adiponectin and leptin concentrations. Conclusions/Significance 26-wks VAL treatment markedly reduced abdominal subcutaneous adipocyte size and AT macrophage infiltration markers, and increased ATBF in IGM subjects. The VAL-induced decrease in adipocyte size was associated with reduced expression of macrophage infiltration markers in AT. Our findings suggest that interventions targeting the RAS may improve AT function, thereby contributing to a reduced risk of developing cardiovascular disease and type 2 diabetes. Trial Registration Trialregister.nl NTR721 (ISRCTN Registry: ISRCTN42786336)

Impaired insulin sensitivity is accompanied by disturbances in skeletal muscle fatty acid handling in subjects with impaired glucose metabolism

Objective:To determine insulin sensitivity and skeletal muscle fatty acid (FA) handling at baseline and after a high-fat mixed meal in impaired fasting glucose (IFG), impaired glucose tolerance (IGT), IFG/IGT and normal glucose tolerance (NGT) subjects.Design:In this multi-center study, insulin sensitivity and β-cell function were assessed (n=102), using a euglycemic-hyperinsulinemic and hyperglycemic clamp with additional arginine stimulation and a 75 g oral glucose tolerance test. Fasting and postprandial skeletal muscle FA handling was examined in a substudy using the forearm balance technique (n=35).Subjects:A total of 102 subjects with IFG (n=48), IGT (n=12), IFG/IGT (n=26) and NGT (n=16).Results:IFG, IGT and IFG/IGT subjects had lower insulin sensitivity with no differences between groups, and lower impaired β-cell function compared with NGT controls. The early postprandial increase in triacylglycerol (TAG) concentration was higher (iAUC0−2 h IFG: 238.4±26.5, IGT: 234.0±41.0 and NGT: 82.6±13.8 μmol l−1 min−1, both P<0.05) and early TAG extraction was increased (AUC0−2 h IFG: 56.8±9.0, IGT: 52.2±12.0 and NGT: 3.8±15.4 nmol·100 ml−1 min−1, P<0.05 and P=0.057, respectively) in both IFG and IGT subjects.Conclusion:IFG, IGT and IFG/IGT subjects have lower insulin sensitivity and impaired β-cell function compared with age- and BMI-matched NGT controls. The increased postprandial TAG response and higher muscle TAG extraction in both IFG and IGT compared with NGT may lead to ectopic fat accumulation in the skeletal muscle, thereby contributing to insulin resistance.

Altered Skeletal Muscle Fatty Acid Handling in Subjects with Impaired Glucose Tolerance as Compared to Impaired Fasting Glucose

Altered skeletal muscle fatty acid (FA) metabolism contributes to insulin resistance. Here, we compared skeletal muscle FA handling between subjects with impaired fasting glucose (IFG; n = 12 (7 males)) and impaired glucose tolerance (IGT; n = 14 (7 males)) by measuring arterio-venous concentration differences across forearm muscle. [2H2]-palmitate was infused intravenously, labeling circulating endogenous triacylglycerol (TAG) and free fatty acids (FFA), whereas [U-13C]-palmitate was incorporated in a high-fat mixed-meal, labeling chylomicron-TAG. Skeletal muscle biopsies were taken to determine muscle TAG, diacylglycerol (DAG), FFA, and phospholipid content, their fractional synthetic rate (FSR) and degree of saturation, and gene expression. Insulin sensitivity was assessed using a hyperinsulinemic-euglycemic clamp. Net skeletal muscle glucose uptake was lower (p = 0.018) and peripheral insulin sensitivity tended to be reduced (p = 0.064) in IGT as compared to IFG subjects. Furthermore, IGT showed higher skeletal muscle extraction of VLDL-TAG (p = 0.043), higher muscle TAG content (p = 0.025), higher saturation of FFA (p = 0.004), lower saturation of TAG (p = 0.017) and a tendency towards a lower TAG FSR (p = 0.073) and a lower saturation of DAG (p = 0.059) versus IFG individuals. Muscle oxidative gene expression was lower in IGT subjects. In conclusion, increased liver-derived TAG extraction and reduced lipid turnover of saturated FA, rather than DAG content, in skeletal muscle accompany the more pronounced insulin resistance in IGT versus IFG subjects.

Valsartan-induced improvement in insulin sensitivity is not paralleled by changes in microvascular function in individuals with impaired glucose metabolism

Background Individuals with impaired glucose metabolism (IGM) are at high risk of developing type 2 diabetes (T2DM). The renin–angiotensin system (RAS) is activated in insulin-resistant states and its inhibition resulted in delayed onset of T2DM. The underlying mechanisms may include improvement in microvascular structure and function, which may increase glucose and insulin delivery to insulin-sensitive tissues. We hypothesized that functional and structural capillary density is impaired in insulin-resistant individuals with IGM and that treatment with the angiotensin-receptor blocker valsartan (VAL) will improve insulin sensitivity and microvascular function. Methods In this randomized controlled trial, individuals with IGM (n = 48) underwent a hyperinsulinaemic-euglycaemic clamp to assess insulin sensitivity (M-value) and capillaroscopy to examine baseline skin capillary density (BCD), capillary density after arterial occlusion (PRH) and capillary density during venous occlusion (VEN) before and after 26 weeks of VAL or placebo (PLB). Sixteen BMI-matched individuals with normal glucose metabolism (NGM) served as controls. Results Individuals with IGM were more insulin resistant (P < 0.001) and had impaired microvascular function compared with those with NGM (all P < 0.01). Univariate associations were found for microvascular function (BCD, PRH, VEN) and M-value (all P < 0.005). The relations were independent of age, sex and BMI. VAL improved insulin sensitivity (P = 0.034) and lowered blood pressure as compared with PLB, whereas microvascular function remained unchanged. Conclusion In insulin-resistant individuals with IGM, impaired functional and structural capillary density was inversely associated with insulin sensitivity. VAL improved insulin sensitivity without affecting the functional and structural capillary density, indicating that other mechanisms may be stronger determinants in the VAL-mediated insulin-sensitizing effect.

The Effects of Long-Term Valsartan Treatment on Skeletal Muscle Fatty Acid Handling in Humans With Impaired Glucose Metabolism

CONTEXT Blocking the renin-angiotensin system reduces the incidence of type 2 diabetes mellitus in humans with impaired glucose metabolism (IGM). Nevertheless, underlying mechanisms remain to be established. OBJECTIVE The purpose of this study was to investigate the effects of the angiotensin II type 1 receptor blocker valsartan (VAL) on skeletal muscle fatty acid (FA) handling in subjects with IGM. DESIGN/SETTING This was a randomized, double-blind placebo-controlled trial at Maastricht University Medical Center. INTERVENTION/MAIN OUTCOMES/PARTICIPANTS: Fasting and postprandial skeletal muscle FA handling were assessed at baseline and after 26 weeks of treatment with VAL or placebo in 26 subjects with IGM. Fasting and postprandial skeletal muscle FA handling were determined by combining the forearm balance technique with stable isotopes of palmitate. [²H₂]-Palmitate was infused iv to label endogenous triacylglycerol (TAG) and free fatty acid (FFA) in the circulation, and [U-¹³C]-palmitate was incorporated in a high-fat mixed meal (2.6 MJ, 61% energy from fat) to label chylomicron TAG. Muscle biopsy samples were taken to determine im TAG, diacylglycerol (DAG), FFA, and phospholipid contents, their fractional synthetic rates and degree of saturation, and mRNA expression of oxidative genes. RESULTS VAL decreased saturation of im TAG and DAG fractions but did not affect net muscle uptake of [²H₂]-palmitate, very low-density lipoprotein ([²H₂])-TAG and chylomicron ([U-¹³C])-TAG, and muscle mRNA expression. VAL decreased FA spillover, as estimated by circulating [U-¹³C]-palmitate, and FFA rate of appearance and tended to decrease chylomicron TAG concentrations. CONCLUSIONS VAL treatment for 26 weeks decreased saturation of skeletal muscle TAG and DAG stores, suggesting altered intramuscular lipid partitioning of FA. The VAL-induced reduction in postprandial FA spillover, endogenous lipolysis, and chylomicron TAG concentrations indicate improved adipose tissue lipid buffering capacity.

PS9 - 45. Differences in skeletal muscle fatty acid handling between subjects with impaired fasting glucose and impaired glucose tolerance

Impairments in skeletal muscle (SM) fatty acid (FA) handling may contribute to insulin resistance and type 2 diabetes mellitus. The objective of the present study was to determine fasting and postprandial SM FA handling in subjects with impaired fasting glucose (IFG) (n=12) and combined IFG/impaired glucose tolerance (IGT) (n=14).