Obesity Is Associated With Gene Expression and Imaging Markers of Iron Accumulation in Skeletal Muscle

CONTEXT

Different genetic and imaging iron markers are known to be increased in the liver, adipose tissue, and brain of obese subjects.

OBJECTIVE

We aimed to investigate these markers in human skeletal muscle. DESIGN, SETTING, PATIENTS, AND OUTCOME MEASURES: Markers of iron accumulation were measured in three different territories: Iron gene markers (TFRC1, TF, SLC11A2, FTL, FTH1, and SLC40A1) were studied in abdominal rectus abdominis (Cohort 1, n = 26) and quadriceps (Cohort 2, n = 13) muscle using real-time PCR, whereas paravertebral muscle R2* signal (as surrogate of iron content) (Cohort 3, n = 43) was evaluated by means of magnetic resonance imaging.

INTERVENTION

In a subgroup of 14 obese participants from Cohort 3, a diet-induced weight loss was performed.

RESULTS

Rectus abdominis muscle age-adjusted gene expression of SLC40A1 (ferroportin) (r = 0.47; P = .04), SLC11A2 (r = 0.50; P = .03) and CYBA (r = 0.62; P = .006) increased with body fatness. In obese participants from Cohort 1, muscle CYBA gene expression was positively correlated with serum ferritin. This association was replicated in quadriceps from obese participants (Cohort 2). Paravertebral muscle R2* was positively associated with body mass index, waist circumference, and fat mass (measured by dual-energy x-ray absorptiometry) in parallel with hepatic iron content, serum ferritin, and hepcidin. In multivariate regression analyses, obesity parameters (P < .0001) and hsCRP concentration (P < .05) contributed independently to the variance of sex-, serum hepcidin- and age-adjusted muscle R2*. Of note, weight loss intervention resulted in decreased muscle R2* (P = .02) in correlation with the change of serum ferritin (r = 0.69; P = .01).

CONCLUSIONS

These findings emphasize a significant iron accumulation in human skeletal muscle in association with obesity. The mechanisms implicated in these observations should be studied further.

Autophagy-regulating TP53INP2 mediates muscle wasting and is repressed in diabetes

A precise balance between protein degradation and synthesis is essential to preserve skeletal muscle mass. Here, we found that TP53INP2, a homolog of the Drosophila melanogaster DOR protein that regulates autophagy in cellular models, has a direct impact on skeletal muscle mass in vivo. Using different transgenic mouse models, we demonstrated that muscle-specific overexpression of Tp53inp2 reduced muscle mass, while deletion of Tp53inp2 resulted in muscle hypertrophy. TP53INP2 activated basal autophagy in skeletal muscle and sustained p62-independent autophagic degradation of ubiquitinated proteins. Animals with muscle-specific overexpression of Tp53inp2 exhibited enhanced muscle wasting in streptozotocin-induced diabetes that was dependent on autophagy; however, TP53INP2 ablation mitigated experimental diabetes-associated muscle loss. The overexpression or absence of TP53INP2 did not affect muscle wasting in response to denervation, a condition in which autophagy is blocked, further indicating that TP53INP2 alters muscle mass by activating autophagy. Moreover, TP53INP2 expression was markedly repressed in muscle from patients with type 2 diabetes and in murine models of diabetes. Our results indicate that TP53INP2 negatively regulates skeletal muscle mass through activation of autophagy. Furthermore, we propose that TP53INP2 repression is part of an adaptive mechanism aimed at preserving muscle mass under conditions in which insulin action is deficient.

Profiling of circulating microRNAs reveals common microRNAs linked to type 2 diabetes that change with insulin sensitization

OBJECTIVE

This study sought to identify the profile of circulating microRNAs (miRNAs) in type 2 diabetes (T2D) and its response to changes in insulin sensitivity.

RESEARCH DESIGN AND METHODS

The circulating miRNA profile was assessed in a pilot study of 12 men: 6 with normal glucose tolerance (NGT) and 6 T2D patients. The association of 10 circulating miRNAs with T2D was cross-sectionally validated in an extended sample of 45 NGT vs. 48 T2D subjects (65 nonobese and 28 obese men) and longitudinally in 35 T2D patients who were recruited in a randomized, double-blinded, and placebo-controlled 3-month trial of metformin treatment. Circulating miRNAs were also measured in seven healthy volunteers before and after a 6-h hyperinsulinemic-euglycemic clamp and insulin plus intralipid/heparin infusion.

RESULTS

Cross-sectional studies disclosed a marked increase of miR-140-5p, miR-142-3p, and miR-222 and decreased miR-423-5p, miR-125b, miR-192, miR-195, miR-130b, miR-532-5p, and miR-126 in T2D patients. Multiple linear regression analyses revealed that miR-140-5p and miR-423-5p contributed independently to explain 49.5% (P < 0.0001) of fasting glucose variance after controlling for confounders. A discriminant function of four miRNAs (miR-140-5p, miR-423-5p, miR-195, and miR-126) was specific for T2D with an accuracy of 89.2% (P < 0.0001). Metformin (but not placebo) led to significant changes in circulating miR-192 (49.5%; P = 0.022), miR-140-5p (-15.8%; P = 0.004), and miR-222 (-47.2%; P = 0.03), in parallel to decreased fasting glucose and HbA1c. Furthermore, while insulin infusion during clamp decreased miR-222 (-62%; P = 0.002), the intralipid/heparin mixture increased circulating miR-222 (163%; P = 0.015) and miR-140-5p (67.5%; P = 0.05).

CONCLUSIONS

This study depicts the close association between variations in circulating miRNAs and T2D and their potential relevance in insulin sensitivity.

The effect of insulin infusion on the metabolites in cerebral tissues assessed with proton magnetic resonance spectroscopy in young healthy subjects with high and low insulin sensitivity

OBJECTIVE

Insulin may play important roles in brain metabolism. Proton magnetic resonance spectroscopy ((1)H-MRS) of the central nervous system gives information on neuronal viability, cellular energy, and membrane status. To elucidate the specific role of insulin action in the brain, we estimated neurometabolites with (1)H-MRS and assessed their regulation by insulin infusion and their relationship with insulin sensitivity.

RESEARCH DESIGN AND METHODS

We studied 16 healthy young men. (1)H-MRS was performed at baseline and after 240 min of euglycemic-hyperinsulinemic clamp. Voxels were positioned in the left frontal lobe, left temporal lobe, and left thalamus. The ratios of N-acetylaspartate (NAA), choline-containing compounds (Cho), myo-inositol, and glutamate/glutamine/γ-aminobutyric acid complex (Glx) to creatine (Cr) and nonsuppressed water signal were determined. The participants were divided into subgroups of high (high IS) and low (low IS) insulin sensitivity.

RESULTS

Baseline neurometabolic substrates were not different between the groups. Insulin infusion resulted in an increase in frontal NAA/Cr and NAA/H2O and frontal and temporal Glx/Cr and Glx/H2O and a decrease in frontal Cho/Cr and temporal Cho/H2O and myo-inositol/H2O (all P < 0.05, except temporal Glx/H2O, P = 0.054, NS) in the high-IS, but not in the low-IS, group. Insulin sensitivity correlated positively with frontal NAA/Cr and NAA/H2O and temporal Glx/H2O and negatively with temporal myo-inositol/Cr and myo-inositol/H2O assessed during the second (1)H-MRS (all P < 0.05).

CONCLUSIONS

Insulin might influence cerebral metabolites, and this action is impaired in subjects with low whole-body insulin sensitivity. Thus, our results provide a potential link between insulin resistance and altered metabolism of the central nervous system.

Serum visfatin is differentially regulated by insulin and free Fatty acids in healthy men

CONTEXT

Serum visfatin is elevated in insulin-resistant states, ie, obesity, type 2 diabetes mellitus, and polycystic ovary syndrome, thus linking visfatin with the pathogenesis of insulin resistance.

OBJECTIVE

Our objective was to evaluate the effect of hyperinsulinemia and the acute elevation of free fatty acids (FFAs) on serum visfatin in humans.

DESIGN, SETTING AND SUBJECTS

We estimated serum visfatin during hyperinsulinemia and the insulin-resistant conditions caused by an acute elevation of FFAs in 19 healthy male volunteers (mean age, 25 ± 7 years; body mass index, 26 ± 4 kg/m(2)) at a university hospital.

INTERVENTIONS

Intervention included a 6-hour euglycemic-hyperinsulinemic clamp without and with Intralipid/heparin infusion.

MAIN OUTCOME MEASURES

Measurements were made of serum visfatin at baseline and at 2 and 6 hours during both clamp studies.

RESULTS

Hyperinsulinemia resulted in a significant decrease in serum visfatin concentration (P = .043). Concomitant Intralipid/heparin infusion, which caused a reduction of insulin sensitivity by 40% (P < .0001), resulted in a marked increase in serum visfatin (P < .0001), which was already observed after 2 hours of FFAs increase (P < .0001). Serum visfatin during the clamp study after 2 and 6 hours of Intralipid/heparin infusion was significantly higher than respective values during the clamp study without the elevation of FFAs (both P < .0001). The increase in serum visfatin during Intralipid/heparin infusion was positively related to body weight (r = 0.54, P = .016) and γ-glutamyltransferase activity (r = 0.56, P = .011).

CONCLUSIONS

Serum visfatin is differentially regulated by insulin and FFAs. One might hypothesize that the induction of insulin resistance by FFAs suppresses insulin inhibition of visfatin secretion, resulting in a serum visfatin increase in insulin-resistant conditions.

Impact of FTO genotypes on BMI and weight in polycystic ovary syndrome: a systematic review and meta-analysis

AIMS/HYPOTHESIS

FTO gene single nucleotide polymorphisms (SNPs) have been shown to be associated with obesity-related traits and type 2 diabetes. Several small studies have suggested a greater than expected effect of the FTO rs9939609 SNP on weight in polycystic ovary syndrome (PCOS). We therefore aimed to examine the impact of FTO genotype on BMI and weight in PCOS.

METHODS

A systematic search of medical databases (PubMed, EMBASE and Cochrane CENTRAL) was conducted up to the end of April 2011. Seven studies describing eight distinct PCOS cohorts were retrieved; seven were genotyped for SNP rs9939609 and one for SNP rs1421085. The per allele effect on BMI and body weight increase was calculated and subjected to meta-analysis.

RESULTS

A total of 2,548 women with PCOS were included in the study; 762 were TT homozygotes, 1,253 had an AT/CT genotype, and 533 were AA/CC homozygotes. Each additional copy of the effect allele (A/C) increased the BMI by a mean of 0.19 z score units (95% CI 0.13, 0.24; p = 2.26 × 10(-11)) and body weight by a mean of 0.20 z score units (95% CI 0.14, 0.26; p = 1.02 × 10(-10)). This translated into an approximately 3.3 kg/m(2) increase in BMI and an approximately 9.6 kg gain in body weight between TT and AA/CC homozygotes. The association between FTO genotypes and BMI was stronger in the cohorts with PCOS than in the general female populations from large genome-wide association studies. Deviation from an additive genetic model was observed in heavier populations.

CONCLUSIONS/INTERPRETATION

The effect of FTO SNPs on obesity-related traits in PCOS seems to be more than two times greater than the effect found in large population-based studies. This suggests an interaction between FTO and the metabolic context or polygenic background of PCOS.

Impact of the FTO gene variation on fat oxidation and its potential influence on body weight in women with polycystic ovary syndrome

CONTEXT

Polycystic ovary syndrome (PCOS) is a heterogeneous disorder where insulin resistance might be involved in the development of endocrine and metabolic abnormalities. It has recently been shown that the FTO gene modifies weight, fat mass and insulin sensitivity in women with PCOS, where its role might be larger than in other phenotypes.

OBJECTIVE

The aim of this study was to estimate the effect of a variation of the FTO gene on carbohydrate and lipid oxidation in PCOS women.

PATIENTS

The study group consisted of 65 women with PCOS and 28 healthy, normally menstruating women.

MEASUREMENTS

Clinical examination, anthropometric measurements, euglycaemic hyperinsulinaemic clamp and measurements of serum sex hormones were performed. Carbohydrate and lipid oxidation were evaluated with indirect calorimetry in the baseline state and during last 30 min of the clamp. The FTO rs9939609 polymorphism was genotyped using the restriction fragment length polymorphism method.

RESULTS

There were no differences in carbohydrate and lipid oxidation between PCOS and control women. In the PCOS group, TT homozygotes had higher baseline fat oxidation in comparison with carriers of the A allele (P = 0·018), which was not found in the control group. We did not observe the effect of the FTO gene variation on insulin-stimulated lipid oxidation and neither on the baseline nor on the insulin-stimulated carbohydrate oxidation.

CONCLUSION

Our data show that this FTO gene variation might influence the baseline lipid oxidation in PCOS patients. This might potentially be one of the mechanisms explaining the impact of the FTO gene on body weight in PCOS.

Hyperinsulinemia acutely increases serum macrophage inhibitory cytokine-1 concentration in anorexia nervosa and obesity

CONTEXT

Macrophage inhibitory cytokine-1 (MIC-1) plays a role in the regulation of cellular responses to stress signals and inflammation. MIC-1 has also been implicated in mediation of tumour-induced anorexia and weight loss. Increased serum concentrations of MIC-1 were found in patients with anorexia nervosa (AN), obesity and type 2 diabetes.

OBJECTIVE

To estimate serum MIC-1 concentration in women with AN and obese women, its regulation by hyperinsulinemia and relationship with insulin sensitivity.

PATIENTS

We examined 20 women with AN, 28 healthy normal-weight female controls and 28 obese women.

MEASUREMENTS

Serum MIC-1 concentration was measured in the fasting state and after 2-h euglycemic hyperinsulinemic clamp.

RESULTS

At baseline, serum MIC-1 was higher in AN in comparison with other groups (normal-weight, P = 0·018; obese, P = 0·01). Hyperinsulinemia resulted in a significant increase in serum MIC-1 concentration in the entire study population (P < 0·001) and in AN (P < 0·001), normal-weight (P = 0·002) and obese (P < 0·001) groups analysed separately. Postclamp serum MIC-1 was still higher in AN women in comparison with other groups (normal-weight, P = 0·012; obese, P = 0·023). When normal-weight and obese women were analysed together, with the exclusion of AN group, an inverse correlation between insulin sensitivity and the change in serum MIC-1 during the clamp was observed (r = -0·27, P = 0·042).

CONCLUSIONS

Hyperinsulinemia resulted in a significant increase in serum MIC-1 in different states of adiposity. Increased serum MIC-1 in AN women might be an additional factor responsible for weight loss in this group.

Insulin sensitivity, metabolic flexibility, and serum adiponectin concentration in women with anorexia nervosa

Anorexia nervosa (AN) is an eating disorder resulting in sustained low weight and marked decrease in fat mass. The lack of adipose tissue observed in lipodystrophies is accompanied by insulin resistance. It remains unclear if the same phenomenon would be present in AN. The objective of the study was to estimate insulin sensitivity, oxidative and nonoxidative glucose metabolism in insulin-stimulated conditions, metabolic flexibility, and serum adiponectin concentration in women with AN. We examined 21 women with AN and 24 healthy normal-weight female controls. Euglycemic hyperinsulinemic clamp, indirect calorimetry, and the measurement of serum adiponectin concentration were performed in all the subjects. We did not observe differences in insulin sensitivity, oxidative and nonoxidative glucose metabolism in insulin-stimulated conditions, and metabolic flexibility between AN and control subjects. Serum adiponectin was higher in AN women in comparison with control group (P = .002). Women with AN have normal insulin sensitivity because of the preserved response of glucose oxidation, nonoxidative glucose metabolism in response to insulin, and normal metabolic flexibility. High adiponectin concentration and normal insulin sensitivity in anorectic women suggest that in AN the adipocytes are still capable of functioning at the level that is sufficient to prevent the metabolic consequences.

Serum soluble glycoprotein 130 concentration is inversely related to insulin sensitivity in women with polycystic ovary syndrome

OBJECTIVE

Insulin resistance might play a role in the pathogenesis of polycystic ovarian syndrome (PCOS). The family of glycoprotein 130 (gp130) cytokines could influence insulin action. One of these cytokines is interleukin (IL)-6, which exerts a short-term insulin-sensitizing effect, whereas in a long-term period, it might induce insulin resistance. Some other gp130 activators are supposed to have beneficial metabolic effects. Gp130 is present in the circulation in the soluble form (sgp130), which inhibits intracellular gp130 signaling. The aim of the present study was to estimate the relation between sgp130 and insulin sensitivity in women with PCOS.

RESEARCH DESIGN AND METHODS

We studied 78 women with PCOS (35 lean and 43 obese) and 34 healthy women (18 lean and 16 obese). The euglycemic-hyperinsulinemic clamp and the measurements of serum sgp130, IL-6, soluble IL-6 receptor (sIL-6R), and sex hormones were performed.

RESULTS

Both obesity and PCOS were characterized by an increased sgp130 (P < 0.0001 and P = 0.0002, respectively). sIL-6R concentration was lower (P = 0.0036) in women with PCOS independently of obesity. Serum sgp130 was negatively correlated with insulin sensitivity when control and PCOS women were analyzed together (r = -0.36, P < 0.0001) and in the PCOS subjects separately (r = -0.34, P = 0.002). In multiple regression analysis, this correlation was significant after adjustment for BMI, waist, percent of body fat, postload glucose and insulin, triglycerides, and high-sensitive C-reactive protein.

CONCLUSIONS

Serum sgp130 is inversely and independently associated with insulin sensitivity in women with PCOS. An increased serum sgp130 in obesity and PCOS suggests an inhibition of intracellular gp130 signaling in insulin-resistant conditions.

Increased suppression of serum ghrelin concentration by hyperinsulinemia in women with anorexia nervosa

CONTEXT

Ghrelin is a peptide secreted mainly by the stomach, which has the ability to stimulate appetite and food intake. Serum ghrelin concentration decreases rapidly after a meal, probably because of the concurrent increase in serum insulin. Anorexia nervosa (AN) is an eating disorder, which is characterized by high serum ghrelin concentration; however, the regulation of circulating ghrelin by insulin in this disorder remains unclear.

OBJECTIVE

To estimate serum ghrelin concentration in the fasting state and after hyperinsulinemia in women with AN.

DESIGN AND PARTICIPANTS

We examined 19 women with AN, 26 lean healthy women, and 25 women who were overweight or obese. Serum ghrelin concentration was measured in the fasting state and after euglycemic hyperinsulinemic clamp.

RESULTS

Insulin sensitivity was similar in AN and normal-weight women, and was markedly decreased in the obese subjects. In the fasting state, serum ghrelin was higher in AN group than in other groups (normal-weight, P=0.017; obese, P=0.0001) and in normal-weight women than in obese women (P=0.044). Hyperinsulinemia resulted in a marked decrease in serum ghrelin in AN (P<0.0001) and normal-weight women (P=0.002). The fall in serum ghrelin was higher in AN group than in other groups (normal-weight, P=0.0008; obese, P=0.0001), and was related to insulin sensitivity (r=0.24, P<0.05). In multiple regression analysis, only fasting serum ghrelin and the presence of AN were independent predictors of this fall.

CONCLUSIONS

Women with AN have an increased suppression of serum ghrelin by hyperinsulinemia. This phenomenon might lead to an increased and more rapid feeling of satiety in AN.

The FTO gene modifies weight, fat mass and insulin sensitivity in women with polycystic ovary syndrome, where its role may be larger than in other phenotypes

AIM

Genome-wide association studies have shown that variation in the FTO gene predisposes to obesity and related traits that are common features of polycystic ovary syndrome (PCOS). The aim of the present study was to assess the effect of FTO variation on obesity, insulin sensitivity, and metabolic and hormonal profiles in PCOS.

METHODS

We examined 136 PCOS women (mean body mass index [BMI]: 28.28+/-6.95kg/m(2), mean age: 25.36+/-5.48 years). Anthropometric measurement, euglycaemic-hyperinsulinaemic clamp and oral glucose tolerance tests and sex hormone assessments were performed. The study group was genotyped for the FTO rs9939609 polymorphism.

RESULTS

BMI (29.0+/-6.9kg/m(2) vs 26.1+/-6.8kg/m(2); P=0.023), body weight (80.1+/-20.7kg vs 72.6+/-20.2kg; P=0.048), fat mass (29.7+/-1 6.6kg vs 24.6+/-17.7kg; P=0.045) and waist circumference (89.8+/-16.7cm vs 83.2+/-17.1cm; P=0.028) were higher in carriers of at least one copy of the A allele. Differences in these parameters were more significant when comparing AA and TT homozygotes. Women with the AA genotype also had decreased insulin sensitivity (P=0.025) and follicle-stimulating hormone (P=0.036). In logistic-regression analyses, the association of the FTO gene polymorphism with insulin sensitivity was no longer significant when BMI was included in the model.

CONCLUSION

Variation in the FTO gene modifies weight, adiposity and other measures of obesity and insulin sensitivity in PCOS. The examined FTO gene variant appears to have a greater impact on obesity and related traits in PCOS than in other phenotypes. The effect on insulin sensitivity appears to be secondary to its influence on obesity and body fat.

Insulin resistance, serum adiponectin, and proinflammatory markers in young subjects with the metabolic syndrome

Insulin resistance is the underlying metabolic abnormality in the metabolic syndrome. The low-grade chronic inflammation may be associated with metabolic risk factors and atherogenesis. The aim of our study was to establish the link between the metabolic syndrome, as defined by the National Cholesterol Education Program (NCEP) criteria, and insulin sensitivity, serum adiponectin, and parameters of chronic inflammation in young subjects. The group of 223 subjects (mean age, 25.86 +/- 5.49 years; body mass index, 28.04 +/- 6.91 kg/m2) was studied. Oral glucose tolerance test, euglycemic hyperinsulinemic clamp, and estimation of serum adiponectin and proinflammatory factors were performed. The NCEP-defined metabolic syndrome was present in 49 subjects (21.97%). The higher the number of NCEP criteria fulfilled was, the bigger were the decrease in insulin sensitivity (P < .0001) and adiponectin (P < .0001) and the increase in fasting and postload insulin (both Ps < .0001), C-reactive protein (P < .0001), interleukin 18 (P < .0001), interleukin 6 (P < .0001), and soluble tumor necrosis factor-alpha receptors sTNFR1 (P < .0001) and sTNFR2 (P < .0001) observed. Multiple regression analysis revealed that adiponectin and inflammatory factors predicted NCEP score independent of insulin sensitivity (all adjusted beta values between .16 and .32, all Ps < .01). Young subjects with metabolic syndrome demonstrate an increased inflammatory response and lower adiponectin concentration.

Serum retinol binding protein 4 is related to insulin resistance and nonoxidative glucose metabolism in lean and obese women with normal glucose tolerance

CONTEXT

Retinol-binding protein (RBP) 4 is secreted by adipose tissue and is postulated to be a determinant of insulin sensitivity. The mechanisms of RBP4 insulin desensitizing action remain unclear.

OBJECTIVE

The aim of the present study was to estimate the relationships between serum RBP4 concentration with insulin sensitivity and oxidative and nonoxidative glucose metabolism in lean and obese women.

DESIGN AND PARTICIPANTS

The study group consisted of 67 women with normal glucose tolerance, 27 lean and 40 overweight or obese. Insulin sensitivity was estimated with the euglycemic hyperinsulinemic clamp. Glucose and lipid oxidation was measured with indirect calorimetry in the basal state and during the last 30 min of the clamp. Nonoxidative glucose metabolism was calculated in insulin-stimulated conditions by subtracting glucose oxidation from total glucose metabolism.

RESULTS

There was no difference in serum RBP4 concentration between lean and obese women. Serum RBP4 was inversely related to insulin sensitivity and nonoxidative glucose metabolism in the entire group (r = -0.36, P =0.003 in both cases) and within the subgroups of lean (r = -0.41, P =0.034 and r = -0.41, P =0.031) and obese women (r = -0.41, P =0.009 and r = -0.40, P =0.01, respectively). These relationships were independent of potential confounding factors. RBP4 levels were not associated with oxidative metabolism of glucose or lipid.

CONCLUSIONS

Our data indicate that serum RBP4 is related to decreased insulin sensitivity, mostly through its association with nonoxidative glucose metabolism.

The role of skeletal muscle sphingolipids in the development of insulin resistance

Insulin resistance is an important risk factor for type 2 diabetes, obesity, cardiovascular disease, polycystic ovary syndrome and other diseases. The most important stage in the development of insulin resistance is impairment of insulin-stimulated skeletal muscle glucose uptake. There is evidence that intramyocellular lipids might be responsible for this process through inhibition of insulin signaling. One of the important intracellular lipid pools is associated with the sphingomyelin signaling pathway. The second messenger in this pathway is ceramide. In vitro data indicate that ceramide inhibits insulin signaling, mainly through inactivation of protein kinase B. In vivo data suggest that ceramide accumulation within muscle cells might be associated with the development of insulin resistance. In this review, we discuss both in vitro and in vivo evidence for the role of muscle ceramide in the impairment of insulin action with particular focus on the question whether findings from animal studies are applicable to humans. We describe problems that are unresolved so far and topics of potential interest for future research.

Increased skeletal muscle ceramide level in men at risk of developing type 2 diabetes

AIMS/HYPOTHESIS

Intramyocellular lipids, including ceramide, a second messenger in the sphingomyelin signalling pathway, might contribute to the development of insulin resistance. The aim of our study was to assess parameters of the skeletal muscle sphingomyelin signalling pathway in men at risk of developing type 2 diabetes.

METHODS

We studied 12 lean (BMI < 25 kg/m(2)) men without a family history of diabetes (control group), 12 lean male offspring of type 2 diabetic patients, and 21 men with overweight or obesity comprising 12 with NGT (obese-NGT) and nine with IGT (obese-IGT). A euglycaemic-hyperinsulinaemic clamp and a biopsy of vastus lateralis muscle were performed. Ceramide, sphingomyelin, sphinganine and sphingosine levels and sphingomyelinase and ceramidase activities were measured in muscle. Muscle diacylglycerol and triacylglycerol levels were estimated in a subgroup of 27 men (comprising men from all the above groups).

RESULTS

Compared with the control group, the lean offspring of diabetic patients and the men with overweight or obesity showed lower insulin sensitivity (all p < 0.005) and a greater muscle ceramide level (all p < 0.01). The obese-IGT group had lower insulin sensitivity (p = 0.0018) and higher muscle ceramide (p = 0.0022) than the obese-NGT group. There was lower muscle sphingosine level and alkaline ceramidase activity in offspring of diabetic patients (p = 0.038 and p = 0.031, respectively) and higher sphinganine level in the obese-NGT (p = 0.049) and obese-IGT (p = 0.002) groups than in the control group. Muscle sphingomyelin was lower (p = 0.0028) and neutral sphingomyelinase activity was higher (p = 0.00079) in the obese-IGT than in the obese-NGT group. Muscle ceramide was related to insulin sensitivity independently of other muscle lipid fractions.

CONCLUSIONS/INTERPRETATIONS

Ceramide accumulates in muscle of men at risk of developing type 2 diabetes.

Serum visfatin in relation to insulin resistance and markers of hyperandrogenism in lean and obese women with polycystic ovary syndrome

BACKGROUND

Visfatin, a protein secreted by adipose tissue, is suggested to play a role in pathogenesis of insulin resistance. In polycystic ovary syndrome (PCOS), insulin resistance might be involved in the development of endocrine and metabolic abnormalities. The aim of the study was to asses the relation between serum visfatin concentration and insulin sensitivity and markers of hyperandrogenism in lean and obese PCOS patients.

METHODS

The study group consisted of 70 women with PCOS (23 lean and 47 obese) and 45 healthy women (25 lean and 20 obese). Euglycemic hyperinsulinemic clamp and the measurements of serum visfatin, sex hormones were performed.

RESULTS

The PCOS group had lower insulin sensitivity (P=0.00049) and higher serum visfatin (P=0.047) in comparison to the control group. The decrease in insulin sensitivity was present in both the lean (P=0.019) and obese (P=0.0077) PCOS subjects, whereas increase in serum visfatin was observed only in lean PCOS subjects (P=0.012). In the whole group, serum visfatin was negatively correlated with insulin sensitivity (r=-0.27, P=0.004). This relationship was also observed in the subgroup of lean (r=-0.30, P=0.038), but not obese women. Additionally, in lean women, visfatin was associated with serum testosterone (r=0.47, P=0.002) and free androgen index (r=0.48, P=0.002), independently of other potential confounding factors.

CONCLUSIONS

Visfatin is associated with insulin resistance and markers of hyperandrogenism in lean PCOS patients.

Protection from inflammatory disease in insulin resistance: the role of mannan-binding lectin

AIMS/HYPOTHESIS

Decreased sensing of the innate immune system may lead to chronic activation of the inflammatory cascade. We hypothesised that mannan-binding lectin (MBL) deficiency may confer risk of obesity and insulin resistance.

MATERIALS AND METHODS

We performed a cross-sectional study of MBL protein concentration (n=434) and MBL2 gene mutations (exon 1) (n=759) in association with obesity, markers of inflammation and insulin action (euglycaemic clamp, n=113), and a longitudinal study of MBL protein before and after weight loss in obese patients (n=10). We also studied the effects of MBL in vitro in muscle cells and circulating MBL-A (mouse equivalent of human MBL) in a mouse model.

RESULTS

Among 434 consecutive non-diabetic men, the age-adjusted serum MBL concentration was lower in obese subjects than in lean subjects (median: 959 microg/ml [interquartile range: 116.8-2,044 microg/ml] vs 1,365 [467-2,513] microg/ml; p=0.01) and was accompanied by increased serum inflammatory markers. Insulin action correlated significantly with serum MBL (r=0.49, p<0.0001). Serum MBL concentration increased by a median of 110.2% after weight loss. The change in serum concentration of MBL was positively associated with the increase in insulin sensitivity (r=0.713, p=0.021). At least one MBL2 gene mutation was present in 48.2% of obese vs 39.3% of non-obese subjects (p=0.037). The plasma concentration of MBL-A was lower in insulin-resistant obese ob/ob mice, as was the glucose/insulin ratio. Incubation of rat soleus muscle with human MBL markedly increased fatty acid oxidation.

CONCLUSIONS/INTERPRETATION

These findings suggest that MBL, previously thought only to be involved in inflammation and immune system function, affects metabolic pathways.

Plasma levels of soluble tumor necrosis factor-alpha receptors are related to total and LDL-cholesterol in lean, but not in obese subjects

Background

Tumor necrosis factor-α (TNFα) is a mediator of insulin resistance. Plasma levels of soluble TNFα receptors (sTNFR1 and sTNFR2) probably reflect paracrine action of the cytokine. TNFα is also a regulator of lipid metabolism, however, data about impact of obesity on the relationships between TNFα and plasma lipids remain controversial.

Aim

The purpose of the present study was to examine the associations of TNFα system with plasma lipids in lean and obese subjects with normal glucose metabolism.

Methods

We examined 63 subjects, 33 lean (BMI<25 kg × m^-2) and 30 with marked overweight or obesity (BMI>27.8 kg × m^-2). Anthropometric and biochemical parameters were measured. Oral glucose tolerance test and euglycemic hyperinsulinemic clamp were also performed.

Results

Obese subjects were markedly more insulin resistant and had higher levels of both TNFα receptors. Total (TC) and LDL-cholesterol (LDL-C), triglycerides (TG) and non-esterified fatty acids (NEFA) were also higher in the obese group. In obese subjects, both receptors were significantly related to TG and HDL-cholesterol (HDL-C), while sTNFR2 was also associated with NEFA. All those correlations disappeared after controlling for insulin sensitivity. In lean subjects, both receptors were related to TC, HDL-C and LDL-C. In that group, sTNFR1 predicted values of all those parameters independently of BMI, plasma glucose and insulin, and insulin sensitivity.

Conclusion

We conclude that TNFα receptors are associated with plasma lipids in different way in lean and in obese subjects. TNFα system is probably important in determining cholesterol levels in lean subjects, while in obese this effect might be masked by other metabolic abnormalities.

Increased serum interleukin-18 concentration is associated with hypoadiponectinemia in obesity, independently of insulin resistance

OBJECTIVE

Interleukin-18 (IL-18) is a cytokine with proinflammatory and proatherogenic properties, which might be associated with the development of insulin resistance. In contrast, adiponectin, a protein secreted by adipose tissue, might exert insulin-sensitizing and antiatherogenic effects. The aim of the present study was to analyze the association between serum IL-18 and adiponectin in lean and obese subjects, in relation to insulin resistance.

DESIGN

Cross-sectional study.

SUBJECTS

One hundred and thirty individuals, 62 lean (body mass index (BMI)<25 kg/m(2), 30 men and 32 women) and 68 with overweight or obesity (BMI>25 kg/m(2), 24 men and 44 women), with normal glucose tolerance and without concomitant diseases.

MEASUREMENTS

Oral glucose tolerance test, euglycemic hyperinsulinemic clamp, serum concentrations of IL-18, IL-6, soluble tumor necrosis factor-alpha receptors and adiponectin.

RESULTS

Obese subjects had lower insulin sensitivity (M value, P=0.00029) and serum adiponectin (P=0.01) and higher levels of serum IL-18 (P=0.00055). Circulating IL-18 was negatively related to adiponectin (r=-0.31, P=0.00027) and insulin sensitivity (r=-0.33, P=0.00012). Subgroup analysis revealed that these associations were present in the obese (adiponectin, r=-0.38, P=0.0014; M, r=-0.29, P=0.016), but not in lean individuals (r=-0.17, P=0.18 and r=-0.20, P=0.12, respectively). Association of IL-18 with adiponectin remained significant after adjustment for other estimated parameters, including insulin sensitivity. Also, relationship between IL-18 and insulin sensitivity was independent of other estimated parameters.

CONCLUSION

Serum IL-18 is inversely related to serum adiponectin, independently of insulin resistance. The relationships of IL-18 with adiponectin and insulin sensitivity are influenced by the presence of overweight/obesity.

An alternative spliced variant of circulating soluble tumor necrosis factor-alpha receptor-2 is paradoxically associated with insulin action

OBJECTIVE

Serum concentrations of soluble tumor necrosis factor-alpha (TNF-alpha) receptor 2 (sTNFR2) are associated with insulin resistance. In a recent study, we provided evidence for the existence of a biologically active form of sTNFR2 produced by alternative splicing (DS-TNFR2). We aimed to evaluate whether this circulating DS-TNFR2 is associated with insulin action in humans.

DESIGN AND METHODS

Real time PCR (light cycler technology) evaluated DS-TNFR2 expression in monocytes. DS-TNFR2 was measured using a monoclonal antibody against an epitope present in TNFR2 (first 14 residues of the juxtamembrane region) but predicted to be absent in soluble proteolytic cleavage-produced TNFR2. Insulin sensitivity was measured using euglycemic hyperinsulinemic clamp (n = 76) and homeostatic model of assessment (HOMA) value in a replication study of 223 subjects.

RESULTS

Real time PCR confirmed gene expression of DS-TNFR2 in monocytes from healthy subjects. A significant and positive association was found between serum DS-TNFR2 concentration and insulin sensitivity (P = 0.032, n = 76). This association was most significant in subjects with normal glucose tolerance (r = 0.44, P = 0.002). The subjects in whom DS-TNFR2 was detectable were more insulin sensitive than those with undetectable DS-TNFR2 (42.12+/-22.08 vs 31.71+/- 16.95 micromol x kg(-1) x min(-1), P = 0.039). DS-TNFR2 was inversely associated with body mass index, waist-to-hip ratio, systolic and diastolic blood pressure, fasting serum glucose, serum triglycerides and serum uric acid concentration and with the HOMA value (P = 0.03) in the replication study. Circulating DS-TNFR2 declined with increased number of components of the metabolic syndrome.

CONCLUSION

Native sTNFR2 and DS-TNFR2 show opposite associations with insulin action. DS-TNFR2 might play a role as a counterpart of the proinflammatory environment associated with insulin resistance.

Plasma adiponectin concentration and tumor necrosis factor-alpha system activity in lean non-diabetic offspring of type 2 diabetic subjects

OBJECTIVE

There is growing evidence that adiponectin function is related to the pathogenesis of insulin resistance. Insulin resistance might be present even in lean subjects with a strong family history of type 2 diabetes. The aim of the study was to look for adiponectin's role in the pathogenesis of insulin resistance in offspring of type 2 diabetic patients, and its relation to the activity of the tumor necrosis factor (TNF)-alpha system.

RESEARCH DESIGN AND METHODS

The study was carried out in 23 lean offspring of type 2 diabetic subjects and in 23 controls matched for age, sex and body mass index. The oral glucose tolerance test for glucose and insulin estimations and hyperinsulinemic, euglycemic clamp studies were performed in all patients. The plasma concentration of adiponectin, TNF-alpha, soluble TNF receptors 1 and 2 (sTNFR1, sTNFR2), HbA1c, total cholesterol, high-density lipoprotein (HDL)-cholesterol, low-density lipoprotein-cholesterol and triglycerides were estimated.

RESULTS

The insulin sensitivity index, normalized for fat-free mass (M(ffm)) and adiponectin concentrations were markedly decreased in offspring of type 2 diabetic subjects compared with the control group (P = 0.0046 and P = 0.00058 respectively). TNF-alpha and sTNFR1 concentrations did not differ between the studied groups; however the concentration of sTNFR2 was markedly increased in the offspring of type 2 diabetic patients (P = 0.0002). Adiponectin concentration was positively correlated to the insulin sensitivity index (r = 0.34; P = 0.020) and to HDL-cholesterol (r = 0.29, P = 0.047) and was inversely related to sTNFR2 (r = -0.33, P = 0.027).

CONCLUSIONS

The obtained results suggest that adiponectin could play a role in the pathogenesis of insulin resistance in lean offspring of type 2 diabetic subjects.

Plasma adiponectin and E-selectin concentrations in patients with coronary heart disease and newly diagnosed disturbances of glucose metabolism

PURPOSE

Adiponectin is a fat derived hormone, which enhances insulin sensitivity. In experimental studies adiponectin was shown to have antiatherogenic properties by suppressing endothelial expression of adhesion molecules. Therefore, the aim of the study was to evaluate plasma adiponectin and E-selectin concentrations in patients with coronary artery disease and impaired glucose metabolism and evaluation of their relationship with selected anthropometric, biochemical and clinical parameters.

MATERIAL AND METHODS

The study group consisted of 62 patients with coronary heart disease, without previous diagnosis of diabetes mellitus (mean age 48.6 +/- 6.0 years; mean BMI 28.6 +/- 3.13 kg/m2). In the studied group the OGTT with glucose and insulin estimation was performed and insulin resistance index (HOMA-IR) was calculated. In the fasting state, the plasma adiponectin, soluble form of E-selectin, HbA1c and lipid parameters were estimated.

RESULTS

Adiponectin concentration was not different in patients with type 2 diabetes mellitus and impaired glucose tolerance (n = 36) in comparison to the group with normal glucose tolerance (n = 26). There was also no difference in adiponectin concentration in relation to atherosclerosis progression. There was no significant correlation between adiponectin and calculated insulin resistance index, while there was marked inverse correlation between adiponectin and BMI (r = -0.30; p = 0.018), body weight (r = -0.33; p = 0.008), E-selectin (r = -0.263; p = 0.039), TG concentration (r = -0.27; p = 0.036), duration of coronary heart disease (r = -0.33; p = 0.009) and borderline significance with ejection fraction (r = -0.268; p = 0.06).

CONCLUSIONS

Our study supports the hypothesis that adiponectin could be recognised as a protective protein for the development of atherosclerosis.

Homocysteine concentrations and vascular complications in patients with type 2 diabetes

OBJECTIVE

Hyperhomocysteinemia is a well known risk factor for the diseases of the cardiovascular system, which seem to be the main cause of increased mortality in patients with type 2 diabetes. The aim of the study was to evaluate the levels of homocysteine in patients with type 2 diabetes in respect to the regimen of diabetes treatment as well as the presence of diabetic complications.

METHODS

The investigation was carried out in the group of 64 patients with type 2 diabetes and in 18 healthy subjects from the control group. Clinical examination and measurements of homocysteine, folic acid, vitamin B12, glycosylated hemoglobin concentration and evaluation of parameters of the lipid metabolism, microalbuminuria and creatinine were done in both groups.

RESULTS

Homocysteine concentration was significantly higher in the group of patients with diabetes in comparison to the control group (p = 0.0007). Diabetic patients had significantly lower concentrations of folic acid (p = 0.028) and HDL cholesterol (p = 0.025) together with higher levels of systolic blood pressure (p = 0.007). In the group of patients with diabetes no differences in homocysteine levels were found in respect to diabetes treatment. Diabetic patients with coronary artery disease had significantly higher homocysteine concentration in comparison to the group with diabetes without history of coronary artery disease (p = 0.0097). Homocysteine levels correlated significantly with incidence of ischaemic heart disease (r = 0.44, p = 0.001) and microalbuminuria (r = 0.26, p = 0.019). Negative correlation was noticed in HDL concentrations (r = -0.30, p = 0.013) and the levels of folic acid (r = -0.30, p = 0.008).

CONCLUSION

Our results suggest that hyperhomocysteinemia in diabetic patients may contribute to the development of chronic complications. The influence of diabetes treatment on Hcy levels requires further observations.

Comparison of simple indices of insulin sensitivity using the euglycemic hyperinsulinemic clamp technique

BACKGROUND

Insulin resistance is an important factor in the pathogenesis of type 2 diabetes mellitus and other diseases, collectively known as "metabolic syndrome". The gold standard in measuring insulin resistance is glucose clamp, but this method is difficult to apply in large studies. Therefore, indirect indices of insulin sensitivity are proposed. The aim of the present study was to compare these simple indices with data from clamp studies.

MATERIAL/METHODS

We examined 51 obese subjects, 23 with impaired glucose tolerance (IGT), 28 with normal (obese-NGT), and 37 healthy lean controls. Insulin sensitivity was determined with the euglycemic hyperinsulinemic clamp technique. We estimated indices of insulin sensitivity: fasting plasma insulin (INS), logarithm INS (log [INS]), homeostasis model assessment (HOMA), logarithm HOMA (log [HOMA]) and quantitative insulin sensitivity check index (QUICKI).

RESULTS

With clamp technique, we demonstrated a decrease in insulin sensitivity in both obese groups vs controls, and also in IGT compared to NGT subjects. The differences were significant when we used other indices of insulin sensitivity, except those for INS, log [INS] and HOMA between the two obese groups. Indirect indices correlated with insulin sensitivity derived from clamp in the whole population and in the subgroups of control and NGT-obese subjects. In the IGT group, only the correlations with log [INS], log [HOMA] and QUICKI were significant.

CONCLUSIONS

Simple indices may give valuable information about insulin sensitivity in large studies. Indices based on log-transformed plasma glucose and insulin levels are recommended in subjects with IGT.

Relationship between insulin sensitivity and sphingomyelin signaling pathway in human skeletal muscle

In vitro studies revealed that insulin resistance might be associated with the intracellular formation of ceramide, the second messenger in the sphingomyelin signaling pathway. The aim of the present study was to examine the content and composition of fatty acids in ceramide and sphingomyelin in human muscle and to evaluate their relationships with insulin sensitivity. The study was conducted on 27 male subjects with normal glucose tolerance. Euglycemic-hyperinsulinemic clamps and biopsies of vastus lateralis muscle were performed. In 10 subjects, additional biopsies were taken after a 4-h clamp and after a clamp with concurrent Intralipid/heparin infusion. We identified 13 ceramides and sphingomyelins according to fatty acid residues. Insulin sensitivity was related to total ceramide content (r = -0.49, P = 0.01) and to ceramide consisting of palmitic (r = -0.48, P = 0.011), palmitoleic (r = -0.45, P = 0.019), mirystic (r = -0.42, P = 0.028), and nervonic acid (r = -0.39, P = 0.047). Hyperinsulinemia did not affect estimated muscle parameters. Intralipid/heparin infusion resulted in a 24.73% decrease in insulin sensitivity (P = 0.007) and a 47.81% increase in ceramide content (P = 0.005). These changes were significantly related to each other (r = -0.64, P = 0.046). A relationship with the decrease in insulin sensitivity was also observed for ceramides consisting of palmitic (r = -0.68, P = 0.03) and linoleic (r = -0.66, P = 0.038) acid. Our data indicate that the sphingomyelin signaling pathway in muscle might be an important factor determining the development of insulin resistance in humans.

Post-partum evaluation of amylin in lean patients with gestational diabetes mellitus

The aim of our study was to compare the secretion of amylin, as well as glucose, insulin and C-peptide at baseline and in response to glucagon stimulation in 26 lean women with gestational diabetes mellitus (GDM) and in 19 age- and BMI-matched pregnant women with normal glucose tolerance (NGT). Intravenous 1-mg glucagon stimulation test was performed 6 weeks after delivery. Fasting and stimulated glucose levels were significantly higher in GDM patients than in subjects with NGT ( p<0.01 at 0 and 6 min; glucose area under the curve (AUC), 604.8+/-41.8 mg/6 min vs. 572.4+/-52.4 mg/6 min, p<0.05). Insulin AUC was also markedly higher in GDM subjects than in healthy controls (373.9+/-144.2 micro IU/6 min vs. 283.7+/-139.1 micro IU/6 min, p<0.05). There was no difference in fasting C-peptide levels between the groups studied, but stimulated concentrations, as well as C-peptide AUC were significantly higher in patients with GDM ( p<0.01 at 1 min and p<0.005 at 6 min; AUC, 27.4+/-11.3 pmol/6 min vs. 18.4+/-6.9 pmol/6 min, p<0.01). Amylin levels were higher in GDM group in comparison to healthy subjects ( p<0.005 at 1 and 6 min; amylin AUC, 113.3+/-51.2 pg/6 min vs. 72.5+/-15.7 pg/6 min; p=0.14), but in contrast to the other hormones, did not rise in response to glucagon injection. In conclusion, our results provide evidence that in patients with GDM in the post-partum period, the levels of amylin, as well as the secretion of insulin and C-peptide remain elevated, when compared to women with NTG. Further investigations are needed to clarify the significance of this elevation as a predictive factor for the development of late maternal type 2 diabetes.

Plasma interleukin 8 concentrations in obese subjects with impaired glucose tolerance

BACKGROUND

Interleukin 8 (IL-8) is a cytokine with atherogenic properties. In vitro studies revealed that it is produced and secreted by human adipocytes. We recently reported that plasma IL-8 is increased in obese subjects with normal glucose tolerance (NGT). The aim of the present study was to measure plasma IL-8 concentrations in subjects with impaired glucose tolerance (IGT).

METHODS

A total of 44 subjects with marked overweight or obesity (BMI > 27.8 kg/m2), 27 with NGT and 17 with IGT, were recruited for the present study. Plasma IL-8 levels were measured in fasting state, after an oral glucose tolerance test (OGTT) and after euglycemic hyperinsulinemic clamp.

RESULTS

The studied groups did not differ in fasting IL-8 concentrations. Both OGTT and clamp resulted in a significant increase in plasma IL-8. The change in IL-8 after clamp was similar in both groups. In contrast, after OGTT plasma IL-8 levels (IL-8OGTT) were markedly higher in IGT individuals. In IGT, but not NGT group, IL-8OGTT was positively related to postload glucose and negatively to insulin sensitivity.

CONCLUSION

Plasma IL-8 concentrations after glucose load are increased in obese IGT subjects in comparison to normoglycemic weight-matched individuals. Increase in plasma IL-8 might be both insulin-mediated (during clamp) and glucose-mediated (during OGTT).

[Assessment of insulin sensitivity during exercise training program in obese women. Comparison of simple indices with hyperinsulinemic euglycemic clamp technique]

Insulin resistance is a key element of metabolic syndrome, which includes disturbances of glucose tolerance, obesity, hypertension, coronary heart disease dyslipidemia and many other defects. An important problem in scientific research is precise measurement of insulin sensitivity. The method considered "the gold standard" is glucose clamp, however, it is difficult to apply this method in large studies. Therefore, simple indices of insulin resistance are proposed. It remains unclear whether those indices are able to reflect changes occurring during insulin-sensitizing intervention. The aim of the present study was to assess the use of indirect indices for the changes in insulin sensitivity during exercise training and to compare those indices with results derived from clamp. Fourteen obese normoglycemic women participated in 12-week exercise training program, which included exercise performed on a bicycle ergometer, 5 days a week for 30 minutes. Insulin sensitivity (M/FFM value) before and after training was measured with hyperinsulinemic euglycemic clamp technique. Simple indices of insulin resistance were also assessed: fasting plasma insulin (INS), logarithm INS (log [INS]), homeostasis model assessment (HOMA), logarithm HOMA (log [HOMA]) and quantitative insulin sensitivity check index (QUICKI). Before training, all those indices were markedly related to M/FFM. After training, an increase in M/FFM was observed. None of the examined indices markedly changed after training. There was no correlations between changes of evaluated indices and in M/FFM during training, and no relationships of those parameters after training. Our study indicates that simple indices are not able to reflect changes occurring during insulin-sensitizing intervention.

Insulin resistance in the first-degree relatives of persons with type 2 diabetes

BACKGROUND

Type 2 diabetes is characterized by impaired insulin secretion and insulin resistance. Both genetic and environmental factors are thought to play a role in the pathogenesis of this disease. Obesity is associated with increased risk of type 2 diabetes, but some metabolic abnormalities may also be present in lean, predisposed subjects. The aim of the present study was to assess insulin sensitivity in lean normoglycemic offspring of parents with type 2 diabetes.

MATERIAL/METHODS

We examined 17 lean offspring (BMI<25 kg x m-2) whose parents had type 2 diabetes, and 17 age, sex and BMI-matched subjects without family history of diabetes as controls. Anthropometric and biochemical measurements, oral glucose tolerance test (OGTT), and euglycemic hyperinsulinemic clamp were performed.

RESULTS

The subjects did not differ in anthropometric measurements, and all had normal glucose tolerance according to WHO criteria. Offspring of type 2 diabetic parents were markedly more hyperinsulinemic (p<0.05) and insulin resistant (p<0.005). The ratio of the increase in insulin to the increase in glucose during the first 30 minutes of the OGTT, a crude index of first-phase insulin secretion, did not differ between groups. Insulin sensitivity was negatively related to fasting plasma insulin (r=-0.67, p<0.001) and non-esterified fatty acids (r=-0.43, p<0.02).

CONCLUSIONS

Insulin resistance is present even in young lean subjects at high risk to develop type 2 diabetes. Our data suggest that insulin resistance may be a primary abnormality in the pathogenesis of this disease.

[Insulin resistance in obese subjects with impaired glucose tolerance. Studies with hyperinsulinemic euglycemic clamp technique]

Insulin resistance is a key factor in the pathogenesis of impaired glucose tolerance (IGT) and type 2 diabetes and is also associated with greater risk for cardiovascular disease. Insulin resistance is more common in obese individuals and is considered to be the link between obesity and IGT and diabetes. The aim of the present study was to assess insulin resistance in obese subjects with IGT. We examined 57 subjects with marked overweight or obesity (BMI > > 27.8 kg x m-2), 27 with IGT and 30 with normal glucose tolerance (NGT), assessed by an oral glucose tolerance test, according to WHO criteria. Thirty lean (BMI < 25 kg x m-2) healthy subjects served as a control group. Anthropometric and biochemical parameters were measured. Insulin sensitivity was evaluated with hyperinsulinemic euglycemic clamp technique. Subjects with IGT had higher levels of glucose, insulin, non-esterified fatty acids and glycated hemoglobin than obese with NGT, all those parameters were also higher in both obese groups in comparison to controls. We showed significant differences in insulin sensitivity between the studied groups, an index of the whole-body glucose uptake was decreased in both obese groups in comparison to controls, and it was also lower in IGT than in obese NGT group. We observed marked negative correlations between insulin sensitivity and estimated anthropometric and biochemical parameters. Our study indicates that insulin resistance is an important factor determining a deterioration of glucose tolerance in subjects with overweight and obesity.

Soluble tumor necrosis factor-alpha receptors in young obese subjects with normal and impaired glucose tolerance

OBJECTIVE

Tumor necrosis factor-alpha (TNF-alpha) is a possible link between obesity and impaired glucose tolerance (IGT) and type 2 diabetes. Data about TNF-alpha and soluble forms of its receptors (sTNFR1 and sTNFR2) in IGT are controversial. The aim of the present study was to assess plasma TNF-alpha, sTNFR1, and sTNFR2 levels and to evaluate the relationships with insulin resistance in obese subjects with IGT.

RESEARCH DESIGN AND METHODS

A total of 104 subjects participated in the present study: 30 obese subjects with IGT (obese-IGT), 32 obese subjects with normal glucose tolerance (obese-NGT), and 42 lean healthy control subjects (control-NGT). Anthropometry and blood biochemical parameters were measured and euglycemic-hyperinsulinemic clamp was performed.

RESULTS

Obese-IGT subjects were more insulin resistant in comparison with obese-NGT and control-NGT groups; obese-NGT subjects were more insulin resistant than control-NGT. Plasma sTNFR1 and sTNFR2 were markedly higher in both groups of obese subjects in comparison with control-NGT and in the obese-IGT versus obese-NGT group. Plasma sTNFR1 and sTNFR2 were inversely related to insulin sensitivity. Both relationships remained significant after adjustment for age, BMI, waist girth, percent body fat, plasma glucose, insulin, nonesterified fatty acids, cholesterol, and triglycerides. Correlation between sTNFR2 and insulin sensitivity was also present in all the groups analyzed separately, but the correlation between sTNFR1 and insulin sensitivity was present only in the obese-NGT group.

CONCLUSIONS

Our data suggest that TNF-alpha receptors are increased in obese-IGT subjects and are related to insulin resistance. These findings indicate that the TNF-alpha system might contribute to the development of insulin resistance in glucose-intolerant subjects.

Plasma interleukin-8 concentrations are increased in obese subjects and related to fat mass and tumor necrosis factor-alpha system

Obesity is associated with the increased risk of cardiovascular disease; however, mechanisms responsible for such an increase are not fully understood. IL-8 is a cytokine that might have atherogenic properties. Recent in vitro studies revealed that IL-8 is produced and secreted by human adipocytes. The aim of the present study was to evaluate plasma IL-8 concentrations in obese subjects and the relationships between circulating IL-8 and anthropometric and biochemical parameters and TNF-alpha system. A total of 75 subjects with normal glucose tolerance, 35 lean and 40 obese, were recruited for this study. Plasma IL-8 levels were measured in fasting state, after an oral glucose tolerance test and after the euglycemic hyperinsulinemic clamp. A significant increase in plasma IL-8 was observed in the obese group. In simple regression analysis, performed for the initial evaluation of relationships, plasma IL-8 was related to body mass index, percentage of body fat, fat mass (FM), and soluble TNF-alpha receptor 2 (sTNFR2) in both groups and with waist-to-hip ratio and sTNFR1 in the obese. In multiple regression analysis, FM, waist-to-hip ratio, gender, sTNFR2, and low density lipoprotein cholesterol were responsible for 44% of IL-8 variability. During oral glucose tolerance testing, mean plasma IL-8 concentrations increased in both groups, whereas clamp resulted in a significant increase in plasma IL-8 only in the obese. We conclude that plasma IL-8 levels are increased in obese subjects, and are related to FM and TNF-alpha system. Increase in circulating IL-8 might be one of the factors linking obesity with greater cardiovascular risk.

Increased plasma-soluble tumor necrosis factor-alpha receptor 2 level in lean nondiabetic offspring of type 2 diabetic subjects

OBJECTIVE

Tumor necrosis factor-alpha (TNF-alpha) is one of the proposed mediators of insulin resistance, upregulated in human obesity. Insulin resistance, however, might precede the development of obesity, especially in subjects with a family history of type 2 diabetes. Therefore, the aim of the present study was to assess plasma levels of TNF-alpha and soluble forms of its receptors (soluble TNF-alpha receptors 1 [sTNFR1] and 2 [sTNFR2]) and to evaluate the relationship of the TNF-alpha system with insulin resistance in lean, nondiabetic offspring of type 2 diabetic patients.

RESEARCH DESIGN AND METHODS

We compared 20 lean offspring (BMI <25 kg/m(2), 8 men and 12 women) of type 2 diabetic patients with 20 lean subjects with no family history of diabetes, matched for age, sex, and BMI (control group). Anthropometry and blood biochemical parameters were measured, and insulin sensitivity was evaluated with the euglycemic-hyperinsulinemic clamp technique.

RESULTS

Both men and women in the offspring group were markedly more insulin-resistant and had higher plasma levels of sTNFR2 (all P < 0.05). TNF-alpha, sTNFR1, and other examined parameters did not differ between the studied groups. Both TNF-alpha receptors were related to waist-to-hip ratio (WHR), fat-free mass (FFM), plasma total cholesterol, HDL cholesterol, LDL cholesterol, and nonesterified fatty acids (NEFAs). sTNFR2, but not sTNFR1, was also associated with insulin sensitivity (r = -0.49, P = 0.001). This relationship remained significant after adjustment for WHR, FFM, plasma insulin, and NEFA.

CONCLUSIONS

TNF-alpha system might be involved in modulating insulin action before the onset of obesity in subjects at high risk for type 2 diabetes.

Circulating E-selectin, vascular cell adhesion molecule-1, and intercellular adhesion molecule-1 in men with coronary artery disease assessed by angiography and disturbances of carbohydrate metabolism

It is hypothesized that adhesion molecules could be an early predictor of coronary artery disease. Therefore we investigated the relationship between the concentrations of soluble forms of adhesion molecules and disturbances of glucose metabolism in 78 men referred for coronary angiography but with no previous history of diabetes. The group consisted of 78 men (mean age, 47.6 +/- 7.0 years; mean body mass index [BMI], 28.4 +/- 3.24 with the symptoms of angina pectoris and positive exercise test. All subjects were given a standard oral glucose tolerance test (OGTT) with glucose and insulin estimations. Fasting plasma concentrations of the soluble (s) forms of E-selectin, intercellular adhesion cell molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), triglycerides (TG), and HbA(1c) were also measured. According to the OGTT, 10.2% of the patients (n = 8) fulfilled the criteria for type 2 diabetes mellitus and 44.9% (n = 35) for impaired glucose tolerance (IGT). The highest concentrations of sE-selectin were observed in patients with type 2 diabetes mellitus and were significantly higher in comparison to the group with normal glucose tolerance and IGT. The concentration of sVCAM-1 increased with the progression of disturbances of glucose metabolism and remained the highest in type 2 diabetic patients. sICAM-1 concentration was not significantly different. sE-selectin concentration correlated significantly with fasting glucose (r = 0.23, P =.041), postload glucose (r = 0.39, P =.001), and postload insulin (r = 0.28, P =.023). sVCAM-1 was significantly related to the postload glucose concentration (r = 0.30, P =.009). A significant correlation between sICAM-1 concentration and postload insulin was also observed (r = 0.27, P =.025). This would suggest that hyperglycemia increases sE-selectin and sVCAM-1 in plasma, which reflects excessive formation of atherosclerotic plaques in patients with disturbances of glucose metabolism.

Elevated soluble intercellular adhesion molecule-1 levels in obesity: relationship to insulin resistance and tumor necrosis factor-alpha system activity

Intercellular adhesion molecule-1 (ICAM-1) is 1 of the possible factors linking obesity and diabetes with cardiovascular disease, however, the mechanism of the increase in ICAM-1 concentration in obesity remains unclear. Therefore, the aim of the present study was to assess plasma soluble ICAM-1 (sICAM-1) levels in obese subjects with normal glucose tolerance and to evaluate whether those levels may be related to insulin resistance and tumor necrosis factor-alpha (TNFalpha) system activity. The study was performed in 8 lean and 15 obese subjects. Anthropometric and biochemical parameters were measured, and insulin sensitivity was evaluated using the euglycemic hyperinsulinemic clamp technique (insulin infusion, 50 mU x kg(-1) x h(-1)). Obese subjects were markedly more hyperinsulinemic and insulin resistant and had higher plasma soluble TNF receptor 2 (sTNFR2) and sICAM-1 levels. sICAM-1 was related positively to body mass index (BMI), waist-to-hip ratio (WHR), percent of body fat, glycated hemoglobin (HbA(1c)), plasma insulin and triglycerides (TG), TNFalpha, and sTNFR2 and negatively to insulin sensitivity. Multiple regression analysis showed that only sTNFR2 and insulin sensitivity were independent predictors of sICAM-1 concentrations and were responsible for 66% of sICAM-1 variability. We conclude that an increase in plasma sICAM-1 concentration in obesity is related to TNFalpha system activation and insulin resistance.

Changes in tumor necrosis factor-alpha system and insulin sensitivity during an exercise training program in obese women with normal and impaired glucose tolerance

OBJECTIVE

Tumor necrosis factor-alpha (TNFalpha) plays an important role in the pathogenesis of insulin resistance and type 2 diabetes. Plasma levels of the soluble (s) fractions of TNFalpha receptors, especially sTNFR2, are good indicators of TNFalpha system activation in obesity. The aim of the present study was to assess the effect of exercise training on the TNFalpha system and to evaluate the relationship with changes in insulin sensitivity.

DESIGN AND METHODS

Sixteen obese women (body mass index (BMI)>27.8 kg/m(2)), 8 with normal (NGT) and 8 with impaired glucose tolerance (IGT), participated in an exercise training program which lasted for 12 weeks and included exercise performed on a bicycle ergometer at an individual intensity of 70% maximal heart rate, for 30 min, 5 days a week. Anthropometrical measurements and blood biochemical analyses were performed, and plasma TNFalpha, sTNFR1 and sTNFR2 levels were assessed. Insulin sensitivity was evaluated using the hyperinsulinemic euglycemic clamp technique (insulin infusion: 50 mU x kg(-1)xh(-1)).

RESULTS

At baseline, despite similar anthropometrical parameters, IGT subjects were markedly more insulin resistant and had higher TNFalpha and sTNFR2 concentrations. Exercise training increased insulin sensitivity and decreased TNFalpha and sTNFR2 levels, while sTNFR1 remained unchanged. The decrease in sTNFR2 was significantly related to the increase in insulin sensitivity; that relationship remained significant after adjustment for the concurrent changes in BMI, waist circumference, percentage of body fat, plasma glucose, insulin and free fatty acids.

CONCLUSIONS

Regular physical exercise decreases TNFalpha system activity and that decrease may be responsible for the concurrent increase in insulin sensitivity.

Insulin, leptin, IGF-I and insulin-dependent protein concentrations after insulin-sensitizing therapy in obese women with polycystic ovary syndrome

OBJECTIVE

To determine the clinical, hormonal and biochemical effect of 4-5 months of insulin-sensitizing therapy (hypocaloric diet+metformin) in obese patients with polycystic ovary syndrome (PCOS).

DESIGN

Prospective study.

METHODS

Twenty-three obese patients with PCOS, 19 obese patients without menstrual disturbances and 11 healthy control women were recruited from the Department of Endocrinology and Endocrine Gynecology, Medical Academy, Bialystok, Poland. Obese patients received 500 mg metformin together with hypocaloric diet three times daily for 4-5 months, after baseline study. The clinical parameters, menstrual pattern and serum concentrations of insulin, leptin, IGF-I, insulin-dependent proteins (sex hormone-binding protein (SHBG), insulin-like growth factor-binding protein-1 (IGFBP-1)), gonadotropins and sex steroids were determined before and after treatment.

RESULTS

In the baseline study, obese patients with PCOS had significantly higher insulin, testosterone and LH concentrations in comparison with the other groups. The serum leptin, IGF-I, IGFBP-1 and SHBG were not different between the two groups of obese patients, but there was a significant difference in comparison with the control group. After metformin therapy a significant reduction in BMI, % of body fat and leptin concentration were observed in both groups of obese patients. Fasting insulin, testosterone and LH concentrations decreased significantly only in the PCOS group. Six out of 11 patients in the PCOS group had more regular menstrual cycles; two patients conceived.

CONCLUSIONS

Insulin-sensitizing therapy could be considered as an additional therapeutic option in obese women with PCOS.

The effect of exercise training on glucose tolerance and skeletal muscle triacylglycerol content in rats fed with a high-fat diet

The aim of the present study was to evaluate the effect of exercise training on glucose tolerance and glycogen and triacylglycerol (TG) content in different types of skeletal muscles and in the liver of rats fed with a high-fat diet. From 8 to 11 weeks of age male Wistar rats were fed with isocaloric standard (control) or high-fat diet (HFD--59% calories as fat) and were additionally assigned to a sedentary or trained group (4 weeks of training on a treadmill). An intravenous glucose tolerance test (IVGTT) with the determination of basal and post load insulin was performed before the final tissue sampling. HFD rats developed marked hyperinsulinemia. Exercise training improved glucose tolerance and insulin response in the control group only (AUC for glucose in control sedentary vs control trained, p<0.05; AUC for insulin: control sedentary vs control trained, p<0.005). Liver glycogen was significantly lower in the HFD group (p<0.05 vs control sedentary) and did not increase after exercise training. Muscle and liver TG content was markedly higher in the HFD group in comparison to control (p<0.0001 in all cases). Exercise training increased TG content in the control group in all examined tissues except white gastrocnemius (p<0.001 in all cases compared to sedentary controls), and did not affect tissue TG in the HFD group. After exercise training there was still markedly higher tissue TG content in the HFD group vs control (p<0.0001 in all cases). We conclude that beneficial metabolic effects of training are impaired in high-fat fed rats and that training does not completely reverse metabolic disturbances in this group of animals.

The effect of a single bout of exhaustive exercise on muscle carbohydrate and lipid metabolism in a rat model of type 2 diabetes mellitus

The aim of the present study was to estimate whether a single bout of exhaustive exercise influences the glycogen and triglyceride (TG) content in red and white gastrocnemius muscle and in the liver of rats with experimental type 2 diabetes. Experiments were carried out on male Wistar rats fed from 8 to 11 weeks of age with isocaloric standard or high-fat diet (HFD) with a previous injection of low-dose of streptozotocin (STZ) or vehicle at 2 days of age (I, control group; II, HFD; III, STZ; IV, STZ + HFD). Group IV (STZ + HFD) represents a model of type 2 diabetes. Basal liver glycogen was markedly lower in all the studied groups compared to controls. Glycogen concentration after exercise fell significantly in the examined tissues in all groups in comparison to basal conditions. A significant TG accumulation in examined tissues was observed in all the studied groups in comparison to controls. Exercise decreased tissue TG content in all the groups, but it remained significantly higher in the experimental groups vs. control. We conclude that in this model of type 2 diabetes, a single bout of exercise reveals defective utilization of tissue carbohydrates and lipids.

The effect of fasting and physical exercise on plasma leptin concentrations in high-fat fed rats

The aim of our study was to estimate the effect of fasting and physical exercise on a treadmill on plasma leptin concentrations in high-fat fed rats. Male Wistar rats were injected a low dose of streptozotocin (STZ) or buffer at 2 days of age and later fed a standard or high-fat diet (HFD). Plasma leptin was measured by RIA method in all the groups studied in basal conditions, after 48h fasting, a single bout of exhaustive exercise, and 4 weeks of exercise training. Plasma leptin concentrations were markedly elevated in the HFD and STZ/HFD groups compared to the control group. The significant correlation between plasma leptin and body weight was noted. Fasting and exercise training decreased plasma leptin in similar percentage in all the groups studied. The observed decrease was greater than expected from changes in body weight. We conclude that high-fat feeding results in an increase in plasma leptin levels in rats independently of plasma insulin or daily calorie intake. High-fat fed rats have maintained leptin response to fasting and exercise training. The reduction in plasma leptin after exercise training is partly independent on changes in body weight or plasma insulin.

[The effect of obesity on ovarian function. I. Serum insulin and insulin dependent protein concentrations in obese patients with polycystic ovary syndrome]

OBJECTIVES

The aim of the present study was to estimate the role of insulin in the pathogenesis of polycystic ovary syndrome.

DESIGN

The study was carried out in 21 obese women with PCO, 18 obese women without menstrual disturbances and 9 normal-weight healthy women.

MATERIALS AND METHODS

In all patients antropomethric parameters: weight, height, % of body fat, waist and hip girths were measured and than BMI and WHR were calculated. Oral glucose tolerance test after 75 g glucose was done after overnight fast. Plasma glucose and insulin were measured in 0 min, 60 min and 120 min of the test. The concentrations of IGF-I, IGFBP-1, SHBG, LH, FSH, testosterone, cortisol, PRL, estradiol, were estimated.

RESULTS

There was statistical significant difference between plasma insulin concentrations in obese patients with PCO in comparison to obese women with normal menstrual cycle (p < 0.05) and control group (p < 0.001). The concentrations of IGFBP-1 and SHBG were similar in both groups of obese patients and differ markedly in comparison to the control group. There were significant correlation between plasma insulin and % body fat, BMI and waist girth in all studied groups.

CONCLUSIONS

We conclude that in obese women with PCO insulin influence ovarian androgen production and decreases the serum SHBG and IGFBP-1 which could contribute in the augmentation of the symptoms of PCO.

[The influence of obesity on ovarian function. II. Plasma leptin concentration in women with polycystic ovary syndrome]

OBJECTIVES

The aim of the present study was to estimate the leptin role in the pathogenesis of polycystic ovary syndrome.

DESIGN

The study was carried out in 21 obese women with PCO, 18 obese women without menstrual disturbances and 9 normal-weight healthy women.

MATERIALS AND METHODS

In all patients antropomethric parameters: weight, height, % of body fat, waist and hip girths were measured and than BMI and WHR were calculated. Plasma concentrations of leptin, insulin, LH, FSH, testosterone, cortisol, PRL, estradiol were estimated.

RESULTS

There were no statistical significant difference between plasma leptin concentrations in obese patients with PCO in comparison to obese women with normal menstrual cycle. In both groups of obese patients plasma leptin concentrations was significantly higher than in control group (p < 0.001, p < 0.001). There were significant correlation between plasma leptin and % body fat, BMI and waist girth in all studied groups.

CONCLUSIONS

We conclude that leptin is not directly involved in observed hormonal disturbances in polycystic ovary syndrome. The main predictor of plasma leptin concentrations in patients with PCO is amount of body fat.

[Levels of leptin in plasma of patients with type 2 diabetes]

Leptin, the product of ob gene is secreted by adipose tissue. It is believed that leptin plays an important role in energy balance. The secretion of leptin by adipose tissue is influenced by insulin. The aim of the present study was the estimation of plasma leptin concentrations in patients with type 2 diabetes mellitus. The study was carried out in 21 diabetic obese patients (BMI > 27.5), 8 diabetic patients with BMI < 27.5, 24 obese patients with normal glucose tolerance (BMI > 27.5) and 10 patients from the control group (BMI < 27.5). The mean leptin concentration in obese diabetic patients was 22.5 + 6.5 ng/ml and was not significantly different from that in obese patients without diabetes (24.1 + 10.3 ng/ml) but differed markedly in comparison to the normal weight diabetic patients (7.9 + 4.3 ng/ml, p < 0.01). Plasma leptin concentration correlated significantly and positively with BMI and fasting insulin in all studied groups. There was no significant correlation between leptin and glycated hemoglobin, total cholesterol and triglycerides. We conclude that serum leptin concentrations in patients with type 2 diabetes depends mainly on the amount of body fat.