Pancreatic steatosis in humans: cause or marker of lipotoxicity? van Raalte, Daniël H; van der Zijl, Nynke J; Diamant, Michaela
Current opinion in clinical nutrition and metabolic care,
2010-July, 2010-Jul, 2010-07-00, 20100701, Letnik:
13, Številka:
4
Journal Article
Recenzirano
PURPOSE OF REVIEWType 2 diabetes mellitus (T2DM) is characterized by impaired insulin secretion. Chronically increased levels of plasma nonesterified fatty acids (NEFA) and triglyceride-rich ...lipoproteins impair beta-cell function, a process referred to as lipotoxicity. Furthermore, when NEFA supply exceeds metabolic capacity, lipids accumulate in nonadipose tissues, such as pancreatic islets, inducing organ dysfunction. The purpose of this review is to describe the mechanisms underlying lipotoxicity in vitro, to discuss the evidence for lipotoxicity in vivo and to address whether pancreatic lipid accumulation interferes with insulin secretion in humans.
RECENT FINDINGSAlthough numerous in-vitro studies have shown that chronically elevated NEFA levels induce beta-cell dysfunction and apoptosis, studies in humans are less conclusive. It has been acknowledged that concurrent hyperglycaemia amplifies the adverse effects of elevated plasma NEFA levels on beta-cell function; therefore glucolipotoxicity should be the preferred term. Lipid accumulation in pancreatic islets impaired beta-cell secretory capacity in leptin-deficient rodents. In humans, recent studies employing noninvasive magnetic resonance-technology and computed tomography-technology, lipid accumulation in the pancreas was increased in individuals with impaired glucose metabolism and T2DM. However, there was no clear association with beta-cell dysfunction.
SUMMARYTo date, it is difficult to provide evidence that intraislet lipid accumulation truly exists in humans and that it is indeed causal to beta-cell dysfunction. Additional research is warranted to further detail the nature and role of pancreatic lipid content in humans, its consequence for the postulated processes pertinent to glucolipotoxicity and its contribution to the progressive nature of beta-cell dysfunction in prediabetes.
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-(13)C-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.
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).
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) ((133)Xe 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.
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.
Trialregister.nl NTR721 (ISRCTN Registry: ISRCTN42786336).
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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.
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.
Metabolic syndrome (MetS) is characterized by central obesity, insulin resistance, dysglycemia, and a pro-atherogenic plasma lipid profile. MetS creates a high risk for development of type 2 diabetes ...(T2DM) and cardiovascular disease (CVD), presumably by altering inflammatory responses. Presently, it is unknown how the chronic metabolic disturbances in acute hyperglycemia, MetS and T2DM affect the immune activity of peripheral blood cells.
We performed genome-wide expression analysis of peripheral blood cells obtained from patients with T2DM (n = 6) and age-, sex- , BMI- and blood pressure-matched obese individuals with MetS (n = 4) and lean healthy normoglycemic controls (n = 3), both under fasting conditions and after controlled induction of acute hyperglycemia during a 70 min hyperglycemic clamp. Differential gene expression during fasting conditions was confirmed by real-time PCR, for which we included additional age-, sex-, BMI-, and blood pressure-matched obese individuals with (n = 4) or without (n = 4) MetS.
Pathway and Gene ontology analysis applied to baseline expression profiles of peripheral blood cells from MetS and T2DM patients revealed metabolic changes, highly similar to a reoviral infection gene signature in T2DM patients. Transcription factor binding site analysis indicated that increased HIF-1α activity, a transcription factor induced by either hypoxia or oxidative stress, is responsible for this aberrant metabolic profile in peripheral blood cells from T2DM patients. Acute hyperglycemia in healthy controls resulted in reduced expression of cytotoxicity-related genes, representing NK- and CD8(+) cells. In obese controls, MetS and especially T2DM patients, baseline expression of genes involved in cytotoxicity was already low, compared to healthy controls and did not further decrease upon acute hyperglycemia.
The reduced activity of cytotoxic genes in T2DM is explained by chronic hyperglycemia, but its acute effects are restricted to healthy controls. Genome expression of circulating leukocytes from T2DM patients differs from MetS individuals by a specific reovirus signature. Our data thus suggest a role for suppressed anti-viral capacity in the etiology of diabetes.
Matrix metalloproteinases (MMPs) may play a pathophysiological role in the development of diabetic nephropathy (DN). We hypothesized that urinary MMP activity in patients with type 2 diabetes ...mellitus (T2DM) is related to a decline in renal function. We determined MMP-2, -8 and -9 activity in 24-h urine collections in relation to risk factors for DN in T2DM patients with (UA,
n
=
27) and without albuminuria (NA,
n
=
48) and controls (CO,
n
=
28). MMP-8 and -9 levels were highest in UA patients (
P
<
0.01). Of UA patients, 93% had at least one MMP increased, compared to 78% of NA patients and 46% of CO (
P
=
0.001). Age, diabetes duration, BMI, systolic blood pressure, fasting plasma glucose, HbA1c and renal function were determinants of MMP-8 and -9 (
P
<
0.05). In summary, MMP-8 and -9 are highest in T2DM UA patients. MMP-9, showed the strongest associations with clinical parameters related to DN.
BACKGROUNDIndividuals 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.
METHODSIn 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.
RESULTSIndividuals 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.
CONCLUSIONIn 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.
Type 1 diabetes mellitus (T1DM) is associated with cerebral compromise, typically found in patients with microangiopathy. Associations between subclinical macroangiopathy and the brain, whether or ...not in the presence of microangiopathy, have not been fully explored in T1DM. We hypothesized that subclinical macroangiopathy in adult T1DM may affect the brain and interacts with microangiopathy.
In 51 asymptomatic T1DM patients with, 53 without proliferative retinopathy and 51 controls, right common carotid artery ultrasound was used to assess intima media thickness (cIMT) and distensibility (cD). Neuropsychological tests for cognitive functions, and magnetic resonance imagining for white matter integrity and functional connectivity, i.e. neuronal communication, were used.
After correction for confounders, cIMT was borderline significantly increased in all T1DM patients (P = 0.071), whereas cD was not statistically significantly altered (P = 0.45). Patients with proliferative retinopathy showed the largest increase in cIMT and decrease in cD. In all participants, after adjustment for confounders, increased cIMT was related to decreased white matter integrity (β = -0.198 P = 0.041) and decreased functional connectivity in visual areas (β = -0.195 P = 0.046). For cognition, there was a significant interaction between cIMT and the presence of proliferative retinopathy after adjustment for confounding factors (all P < 0.05). Increased cIMT was associated with lower general cognitive ability (β = -0.334; P = 0.018), information processing speed (β = -0.361; P = 0.010) and attention (β = -0.394; P = 0.005) scores in patients without, but not in patients with proliferative retinopathy.
These findings suggest that subclinical macroangiopathy may be a factor in the development of diabetes-related cognitive changes in uncomplicated T1DM, whereas in patients with advanced T1DM, proliferative retinopathy may rather be the driving force of cerebral compromise.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract We investigated whether the relation between liver fat and subclinical atherosclerosis is mediated by low-grade systemic inflammation in type 2 diabetes (T2DM) and the metabolic syndrome ...(MetS). In 16 T2DM, 36 MetS, and 21 age-matched healthy men, liver fat was quantified by1 H-MRS. Carotid intima–media thickness (cIMT) was measured by ultrasound. Differences between controls, MetS and T2DM or between high versus low liver fat content were calculated. Furthermore, the association of liver fat content, cIMT and CRP was assessed. Liver fat percentage was highest in T2DM, as compared to MetS and controls 17.5% (8.0–27.6), 8.2% (4.2–14.2) and 5.3% (2.3–7.4), respectively; P < 0.001. Subjects with high-liver fat content had increased cIMT and CRP (all P < 0.02). Liver fat content was positively associated with cIMT ( r = 0.37; P = 0.003). The association of liver fat content and cIMT disappeared after adjustment for CRP. The association between liver fat content and subclinical atherosclerosis seems mediated by low-grade inflammation, possibly due to increased hepatic production. Lowering of liver fat content may decrease CVD risk by concomitantly reducing the pro-inflammatory state in high-risk populations.
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