Potential epigenetic biomarkers of obesity-related insulin resistance in human whole-blood

Obesity can increase the risk of complex metabolic diseases, including insulin resistance. Moreover, obesity can be caused by environmental and genetic factors. However, the epigenetic mechanisms of obesity are not well defined. Therefore, the identification of novel epigenetic biomarkers of obesity allows for a more complete understanding of the disease and its underlying insulin resistance. The aim of our study was to identify DNA methylation changes in whole-blood that were strongly associated with obesity and insulin resistance. Whole-blood was obtained from lean (n = 10; BMI = 23.6 ± 0.7 kg/m²) and obese (n = 10; BMI = 34.4 ± 1.3 kg/m²) participants in combination with euglycemic hyperinsulinemic clamps to assess insulin sensitivity. We performed reduced representation bisulfite sequencing on genomic DNA isolated from the blood. We identified 49 differentially methylated cytosines (DMCs; q < 0.05) that were altered in obese compared with lean participants. We identified 2 sites (Chr.21:46,957,981 and Chr.21:46,957,915) in the 5’ untranslated region of solute carrier family 19 member 1 (SLC19A1) with decreased methylation in obese participants (lean 0.73 ± 0.11 vs. obese 0.09 ± 0.05; lean 0.68 ± 0.10 vs. obese 0.09 ± 0.05, respectively). These 2 DMCs identified by obesity were also significantly predicted by insulin sensitivity (r = 0.68, P = 0.003; r = 0.66; P = 0.004). In addition, we performed a differentially methylated region (DMR) analysis and demonstrated a decrease in methylation of Chr.21:46,957,915–46,958,001 in SLC19A1 of ?34.9% (70.4% lean vs. 35.5% obese). The decrease in whole-blood SLC19A1 methylation in our obese participants was similar to the change observed in skeletal muscle (Chr.21:46,957,981, lean 0.70 ± 0.09 vs. obese 0.31 ± 0.11 and Chr.21:46,957,915, lean 0.72 ± 0.11 vs. obese 0.31 ± 0.13). Pyrosequencing analysis further demonstrated a decrease in methylation at Chr.21:46,957,915 in both whole-blood (lean 0.71 ± 0.10 vs. obese 0.18 ± 0.06) and skeletal muscle (lean 0.71 ± 0.10 vs. obese 0.30 ± 0.11). Our findings demonstrate a new potential epigenetic biomarker, SLC19A1, for obesity and its underlying insulin resistance.     

Baroreflex sensitivity in obesity: relationship with cardiac autonomic nervous system activity

Objective: The aim of this study was to test the hypothesis that baroreflex sensitivity (BRS), assessed by indirect measurement of aortic pressure, is blunted in obesity. Additionally, the potential effect of cardiac autonomic nervous system (ANS) activity, aortic compliance, and metabolic parameters on BRS of obese subjects was investigated. Research Methods and Procedures: A group of 30 women with BMI >30 kg/m² and a group of 30 controls with BMI <25 kg/m² were examined. BRS was estimated by the sequence technique, cardiac ANS activity by short‐term spectral analysis of heart rate variability (HRV), and aortic compliance by the method of applanation tonometry. Results: BRS was lower in obese women (9.18 ± 3.77 vs. 19.63 ± 9.16 ms/mm Hg, p < 0.001). The median values (interquartile range) of the power of both the high‐frequency and low‐frequency components of the HRV were higher in the lean than in the obese participants [1079.2 (202.7 to 1716.9) vs. 224.1 (72.7 to 539.6) msec², p = 0.001 and 411.8 (199.3 to 798.0) vs. 235.8 (99.4 to 424.5) msec², p = 0.01 respectively]. Low‐to‐high‐frequency ratio values were higher in the obese subjects [0.82 (0.47 to 2.1) vs. 0.57 (0.28 to 0.89), p = 0.02]. Aortic augmentation values were not significantly different between lean and obese subjects. Multivariate analysis demonstrated a significant and independent association between BRS and age (p = 0.003), BMI (p < 0.001), and high‐frequency power of HRV (p < 0.001). These variables explained 72% of the variation of BRS values. Discussion: BRS is severely reduced in obese subjects. BMI, age, and the parasympathetic nervous system activity are the main determinants of BRS. Baroreflex behavior is of clinical relevance because an attenuated BRS represents a negative prognostic factor in cardiovascular diseases, which are common in obesity.     

Skeletal muscle fat oxidation is increased in African-American and white women after 10 days of endurance exercise training

Objective: Obesity is associated with lower rates of skeletal muscle fatty acid oxidation (FAO), which is linked to insulin resistance. FAO is reduced further in obese African‐American (AAW) vs. white women (CW) and may also be lower in lean AAW vs. CW. In lean CW, endurance exercise training (EET) elevates the oxidative capacity of skeletal muscle. Therefore, we determined whether EET would elevate skeletal muscle FAO similarly in AAW and CW with a lower lipid oxidative capacity. Research Methods and Procedures: In vitro rates of FAO were assessed in rectus abdominus muscle strips using [1‐¹⁴C] palmitate (Pal) from lean AAW [BMI = 24.2 ± 0.9 (standard error) kg/m²] and CW (23.6 ± 0.8 kg/m²) undergoing voluntary abdominal surgery. Lean AAW (22 ± 0.9 kg/m²) and CW (24 ± 0.8 kg/m²) and obese AAW (36 ± 1.2 kg/m²) and CW (40 ± 1.3 kg/m²) underwent 10 consecutive days of EET on a cycle ergometer (60 min/d, 75% peak oxygen uptake). FAO was measured in vastus lateralis homogenates as captured ¹⁴CO₂ using [1‐¹⁴C] Pal, palmitoyl‐CoA (Pal‐CoA), and palmityl‐carnitine (Pal‐Car). Results: Muscle strip experiments showed suppressed rates of FAO (p = 0.03) in lean AAW vs. CW. EET increased the rates of skeletal muscle Pal oxidation (p = 0.05) in both lean AAW and CW. In obese subjects, Pre‐EET Pal (but not Pal‐CoA or Pal‐Car) oxidation was lower (p = 0.05) in AAW vs. CW. EET increased Pal oxidation 100% in obese AAW (p < 0.05) and 59% (p < 0.05) in obese CW. Similar increases (p < 0.05) in post‐EET FAO were observed for Pal‐CoA and Pal‐Car in both groups. Discussion: Both lean and obese AAW possess a lower capacity for skeletal muscle FAO, but EET increases FAO similarly in both AAW and CW. These data suggest the use of EET for treatment against obesity and diabetes for both AAW and CW.     

Oxidant Stress in Healthy Normal‐weight,Overweight, and Obese Individuals

This study was undertaken to investigate the association among BMI and lipid hydroperoxide (LH), total antioxidant status (TAS), superoxide dismutase (SOD), and reduced glutathione (GSH). Ninety (n = 90) healthy males and females (n = 23/67) (29 normal weight (BMI: 22.74 ± 0.25 kg/m²), 36 overweight (BMI: 27.18 ± 0.23 kg/m²), and 25 obese (33.78 ± 0.48 kg/m²)) participated in the study. Data collected included anthropometric measures, fasting blood glucose, lipid profile, LH, TAS, and enzymatic antioxidants (SOD, and reduced GSH). The results of the study showed that obese individuals had significantly increased LH levels compared to normal‐weight individuals (obese vs. normal weight (0.88 ± 0.05 vs. 0.67 ± 0.03 µmol/l, P < 0.01)) but the increased levels were not significantly different when compared to the overweight group (obese vs. overweight (0.88 ± 0.05 vs. 0.79 ± 0.05 µmol/l)). No other consistent significant differences in TAS, SOD, and GSH were identified between groups. This study concluded that only obesity and not moderate overweight elevates LH levels. Furthermore, the levels of TAS, SOD, and GSH in obesity do not explain the increased LH levels observed in obesity.     

Association of childhood sexual abuse with obesity in a community sample of lesbians

Objective: Our goal was to examine the association between childhood sexual abuse (CSA) and obesity in a community‐based sample of self‐identified lesbians. Research Methods and Procedures: A diverse sample of women who self‐identified as lesbian was recruited from the greater Chicago metropolitan area. Women (n = 416) were interviewed about sexual abuse experiences that occurred before the age of 18. Self‐reported height and weight were used to calculate BMI and categorize women as normal‐weight (<25.0 kg/m²), overweight (25.0 to 29.9 kg/m²), obese (30.0 to 39.9 kg/m²), or severely obese (≥40 kg/m²). The relationship between CSA and BMI was examined using multinomial logistic regression analysis. Results: Overall, 31% of women in the sample reported CSA, and 57% had BMI ≥25.0 kg/m². Mean BMI was 27.8 (±7.2) kg/m² and was significantly higher among women who reported CSA than among those who did not report CSA (29.4 vs. 27.1, p < 0.01). CSA was significantly related to weight status; 39% of women who reported CSA compared with 25% of women who did not report CSA were obese (p = 0.004). After adjusting for age, race/ethnicity, and education, women who reported CSA were more likely to be obese (odds ratio, 1.9; 95% confidence interval, 1.1–3.4) or severely obese (odds ratio, 2.3; 95% confidence interval, 1.1–5.2). Discussion: Our findings, in conjunction with the available literature, suggest that CSA may be an important risk factor for obesity. Understanding CSA as a factor that may contribute to weight gain or act as a barrier to weight loss or maintenance in lesbians, a high‐risk group for both CSA and obesity, is important for developing successful obesity interventions for this group of women.     

Ghrelin Does Not Influence Gastric Emptying in Obese Subjects

Objective: To evaluate the relationship between fasting plasma concentrations of ghrelin and gastric emptying in obese individuals compared with lean subjects. Research Methods and Procedures: We included 20 obese patients (9 men and 11 women, BMI > 30 kg/m²) and 16 nonobese control subjects (7 men and 9 women, BMI ≤ 25 kg/m²). Gastric emptying of solids (egg sandwich labeled with radionuclide) was measured at 120 minutes with (99m)Tc‐single photon emission computed tomography imaging. Ghrelin and leptin were analyzed by radioimmunoassay and ELISA methods, respectively. Results: The gastric half‐emptying time was similar in obese men and women (67.8 ± 14.79 vs. 66.6 ± 13.56 minutes) but significantly shorter (p < 0.001) than in the control population (men: 88.09 ± 11.72 minutes; women: 97.25 ± 10.31 minutes). Ghrelin levels were significantly lower in obese subjects (131.37 ± 47.67 vs. 306.3 ± 45.52 pg/mL; p < 0.0001 in men and 162.13 ± 32.95 vs. 272.8 ± 47.77 pg/mL; p < 0.0001 in women). A negative correlation between gastric emptying and fasting ghrelin levels was observed only in lean subjects (y = ?0.2391x + 157.9; R² = 0.95). Also, in the lean group, ghrelin was the only significant independent determinant of gastric emptying, explaining 98% of the variance (adjusted R²) in a multiple regression analysis. Discussion: This report shows that, in humans, gastric emptying is faster in obese subjects than in lean controls and that, whereas ghrelin is the best determinant of gastric kinetics in healthy controls, this action is lost in obesity.     

Adapted Changes in Left Ventricular Structure and Function in Severe Uncomplicated Obesity

Objective: A massive amount of fat tissue, as that observed in obese subjects with BMI over 50 kg/m², could affect cardiac morphology and performance, but few data on this issue are available. We sought to evaluate cardiac structure and function in uncomplicated severely obese subjects. Research Methods and Procedures: We studied 55 uncomplicated severely obese patients, 40 women, 15 men, mean age 35.5 ± 10.2 years, BMI 51.2 ± 8.8 kg/m², range 43 to 81 kg/m², with a history of fat excess of at least 10 years, and 55 age‐matched normal‐weight subjects (40 women, 15 men, mean BMI 23.8 ± 1.2 kg/m²) as a control group. Each subject underwent an echocardiogram to evaluate left ventricular (LV) mass and geometry and systolic and diastolic function. Results: Severely obese subjects showed greater LV mass and indexed LV mass than normal‐weight subjects (p < 0.01 for all parameters). Nevertheless, LV mass was appropriate for sex, height^2.7, and stroke work in most (77%) uncomplicated severely obese subjects. In addition, no significant difference in LV mass indices and LV mass appropriateness between obese subjects with BMI ≥ 50 kg/m² and those with BMI ≤ 50 kg/m² was found. Obese subjects also showed higher ejection fraction and midwall shortening than normal‐weight subjects (p = 0.05 and p < 0.01, respectively), suggesting a hyperdynamic systolic function. No significant difference in systolic performance between obese subjects with BMI ≥ 50 kg/m² and those with BMI ≤ 50 kg/m² was seen. Discussion: Our data show that uncomplicated severe obesity, despite the massive fat tissue amount, is associated largely with adapted and appropriate changes in cardiac structure and function.     

Higher protein intake preserves lean mass and satiety with weight loss in pre-obese and obese women

Objective: To examine the effects of dietary protein and obesity classification on energy‐restriction‐induced changes in weight, body composition, appetite, mood, and cardiovascular and kidney health. Research Methods and Procedures: Forty‐six women, ages 28 to 80, BMI 26 to 37 kg/m², followed a 12‐week 750‐kcal/d energy‐deficit diet containing higher protein (HP, 30% protein) or normal protein (NP, 18% protein) and were retrospectively subgrouped according to obesity classification [pre‐obese (POB), BMI = 26 to 29.9 kg/m²; obese (OB), BMI = 30 to 37 kg/m²). Results: All subjects lost weight, fat mass, and lean body mass (LBM; p < 0.001). With comparable weight loss, LBM losses were less in HP vs. NP (?1.5 ± 0.3 vs. ?2.8 ± 0.5 kg; p < 0.05) and POB vs. OB (?1.2 ± 0.3 vs. ?2.9 ± 0.4 kg; p < 0.005). The main effects of protein and obesity on LBM changes were independent and additive; POB‐HP lost less LBM vs. OB‐NP (p < 0.05). The energy‐restriction‐induced decline in satiety was less pronounced in HP vs. NP (p < 0.005). Perceived pleasure increased with HP and decreased with NP (p < 0.05). Lipid‐lipoprotein profile and blood pressure improved and kidney function minimally changed with energy restriction (p < 0.05), independently of protein intake. Discussion: Consuming a higher‐protein diet and accomplishing weight loss before becoming obese help women preserve LBM. Use of a higher‐protein diet also improves perceptions of satiety and pleasure during energy restriction.     

Prevalence of Uncomplicated Obesity in an Italian Obese Population

Objective: The existence of healthy obese subjects has been suggested but not clearly reported. We sought to address the prevalence of uncomplicated obesity and adverse risk factors in a large Italian obese population. Research Methods and Procedures: This was a cross‐sectional study of a population of consecutive Italian obese subjects. We studied 681 obese subjects (514 women and 167 men), with a mean age of 41.1 ± 13.9 years (range, 16 to 77 years), mean BMI of 40.2 ± 7.6 kg/m² (range, 30 to 89.8 kg/m²), and a history of obesity for 20.5 ± 7 years (range, 10.5 to 30 years). Anthropometric, metabolic, cardiac, and obesity‐related risk factors were evaluated. Results: The prevalence of uncomplicated subjects was 27.5%, independent of BMI and duration of obesity. The youngest group of obese subjects showed a higher, but not statistically significantly higher, prevalence of uncomplicated obesity. No statistical difference for the prevalence of impaired fasting glucose, glucose intolerance, high triglycerides, high total cholesterol, low‐density lipoprotein cholesterol, and high‐density lipoprotein cholesterol among BMI categories (from mild to extremely severe obesity degree) was found. Obese subjects with BMI >50 kg/m² showed a higher prevalence of high blood pressure only when they were compared with the group with a BMI of 30 to 35 kg/m² (p < 0.01). Obese subjects with BMI >40 kg/m² showed a higher prevalence of hyperinsulinemia than subjects with BMI 30 to 35 kg/m² (p < 0.01). Discussion: This study shows that a substantial part of an Italian obese population has uncomplicated obesity, and the prevalence of adverse risk factors in this sample is unexpectedly low and partially independent of obesity degree. Uncomplicated obesity could represent a well‐defined clinical entity.     

Association Between the 4 bp Proinsulin Gene Insertion Polymorphism (IVS‐69) and Body Composition in Black South African Women

The objective of the study was to examine the association between a functional 4 bp proinsulin gene insertion polymorphism (IVS‐69), fasting insulin concentrations, and body composition in black South African women. Body composition, body fat distribution, fasting glucose and insulin concentrations, and IVS‐69 genotype were measured in 115 normal‐weight (BMI <25 kg/m²) and 138 obese (BMI ≥30 kg/m²) premenopausal women. The frequency of the insertion allele was significantly higher in the class 2 obese (BMI ≥35kg/m²) compared with the normal‐weight group (P = 0.029). Obese subjects with the insertion allele had greater fat mass (42.3 ± 0.9 vs. 38.9 ± 0.9 kg, P = 0.034) and fat‐free soft tissue mass (47.4 ± 0.6 vs. 45.1 ± 0.6 kg, P = 0.014), and more abdominal subcutaneous adipose tissue (SAT, 595 ± 17 vs. 531 ± 17 cm², P = 0.025) but not visceral fat (P = 0.739), than obese homozygotes for the wild‐type allele. Only SAT was greater in normal‐weight subjects with the insertion allele (P = 0.048). There were no differences in fasting insulin or glucose levels between subjects with the insertion allele or homozygotes for the wild‐type allele in the normal‐weight or obese groups. In conclusion, the 4 bp proinsulin gene insertion allele is associated with extreme obesity, reflected by greater fat‐free soft tissue mass and fat mass, particularly SAT, in obese black South African women.     

Sitting and Supine Esophageal Pressures in Overweight and Obese Subjects

Esophageal pressure (P_Es) can be used to approximate pleural pressure (P_pl) and might be clinically useful, particularly in the obese e.g., to guide mechanical ventilator settings in critical illness. However, mediastinal artifact (the difference between true P_pl and P_Es) may limit acceptance of the measurement, and reproducibility of P_Es measurements remains unknown. Therefore, we aimed to assess the effect of body posture on P_Es in a cohort of obese, but healthy subjects, some of whom had multiple measurements, to address the clinical robustness of esophageal manometry. Twenty‐five overweight and obese subjects (BMI > 25 kg/m²) and 11 control lean subjects (BMI < 25 kg/m²) underwent esophageal manometry with pressures measured seated and supine. Twenty overweight and obese subjects had measurements repeated after ～1 to 2 weeks. Anthropometric data and sitting and supine spirometry were recorded. The average end‐expiratory P_Es sitting and supine were greater in the overweight and obese group than the lean group (sitting ?0.1 ± 2.1 vs. ?3.3 ± 1.2 cmH₂O, supine 9.3 ± 3.3 vs. 6.9 ± 2.8 cmH₂O, respectively). The mean differences between repeated measurements were small (?0.3 ± 1.7 cmH₂O sitting and ?0.1 ± 1.5 cmH₂O supine). P_Es correlated with a number of anthropometric and spirometric variables. In conclusion, P_Es are slightly greater in overweight and obese subjects than lean subjects; but changes with position are similar in both groups. These data indicate that mediastinal weight and postural effects on P_Es are within a clinically acceptable range, and suggest that esophageal manometry can be used to inform clinical decision making across wide range of body types.     

Insulin Resistance in Nondiabetic Morbidly Obese Patients: Effect of Bariatric Surgery

Objective: To evaluate insulin action on substrate use and insulinemia in nondiabetic class III obese patients before and after weight loss induced by bariatric surgery. Research Methods and Procedures: Thirteen obese patients (four men/nine women; BMI = 56.3 ± 2.7 kg/m²) and 13 lean subjects (five men/eight women; BMI = 22.4 ± 0.5 kg/m²) underwent euglycemic clamp, oral glucose tolerance test, and indirect calorimetry. The study was carried out before (Study I) and after (～40% relative to initial body weight; Study II) weight loss induced by Roux‐en‐Y Gastric bypass with silastic ring surgery. Results: The obese patients were insulin resistant (whole‐body glucose use = 19.7 ± 1.5 vs. 51.5 ± 2.4 μmol/min per kilogram fat‐free mass, p < 0.0001) and hyperinsulinemic in the fasting state (332 ± 86 vs. 85 ± 5 pM, p < 0.0001) and during the oral glucose tolerance test compared with the lean subjects. Fasting plasma insulin normalized after weight loss, whereas whole‐body glucose use increased (35.5 ± 3.7 μmol/min per kilogram fat‐free mass, p < 0.05 vs. Study I). The higher insulin clearance of obese did not change during the follow‐up period. Insulin‐induced glucose oxidation and nonoxidative glucose disposal were lower in the obese compared with the lean group (all p < 0.05). In Study II, the former increased slightly, whereas nonoxidative glucose disposal reached values similar to those of the control group. Fasting lipid oxidation was higher in the obese than in the control group and did not change significantly in Study II. The insulin effect on lipid oxidation was slightly improved (p = 0.01 vs. Study I). Discussion: The rapid weight loss after surgery in obese class III patients normalized insulinemia and improved insulin sensitivity almost entirely due to glucose storage, whereas fasting lipid oxidation remained high.     

Effects of Insulin on Ketogenesis Following Fasting in Lean and Obese Men

The ketone bodies (KBs) D‐3‐hydroxybutyrate (D‐3HB) and acetoacetate (AcAc) play a role in starvation and have been associated with insulin resistance. The dose–response relationship between insulin and KBs was demonstrated to be shifted to the right in type 2 diabetes patients. However, KB levels have also been reported to be decreased in obesity. We investigated the metabolic adaptation to fasting with respect to glucose and KB metabolism in lean and obese men without type 2 diabetes using stable glucose and D‐3HB isotopes in a two‐step pancreatic clamp after 38 h of fasting. We found that D‐3HB fluxes in the basal state were higher in lean compared to obese men: 15.2 (10.7–27.1) vs. 7.0 (3.5–15.1) µmol/kg lean body mass (LBM)·min, respectively, P < 0.01. No differences were found in KB fluxes between lean and obese volunteers during the pancreatic clamp (step 1: 6.9 (1.8–12.0) vs. 7.4 (4.2–17.8) µmol/kg LBM·min, respectively; and step 2: 2.9 (0–7.2) vs. 3.4 (0.85–18.7) µmol/kg LBM·min, respectively), despite similar plasma insulin levels. Meanwhile, peripheral glucose uptake was higher in lean compared to obese men (step 1: 15.2 (12.3–25.6) vs. 14.7 (11.9–22.7) µmol/kg LBM·min, respectively, P ≤ 0.05; and step 2: 12.5 (7.0–17.3) vs. 10.8 (5.2–15.0) µmol/kg LBM·min, respectively, P ≤ 0.01). These data show that obese subjects who display insulin resistance on insulin‐mediated peripheral glucose uptake have the same sensitivity for the insulin‐mediated suppression of ketogenesis. This implies differential insulin sensitivity of intermediary metabolism in obesity.     

Traditional Anthropometric Parameters Still Predict Metabolic Disorders in Women With Severe Obesity

It is well established that fat distribution rather than the total quantity of fat is the major determinant of cardiovascular risk in overweight subjects. However, it is not known whether the concept of fat distribution still makes sense in severely obese subjects. Particularly, the role of visceral fat accumulation and/or of adipocyte hypertrophy in insulin resistance (IR) has not been studied in this population. Therefore, the aim of this study was to clarify the determinants of metabolic disorders in severely obese women. We performed a cross‐sectional study in 237 severely obese women (BMI >35 kg/m²). We assessed total body fat mass and fat distribution by anthropometric measurements (BMI and waist‐to‐hip ratio (WHR)) and by dual‐energy X‐ray absorptiometry (DXA). In 22 women, we measured subcutaneous and visceral adipocyte size on surgical biopsies. Mean BMI was 44 ± 7 kg/m² (range 35–77), mean age 37 ± 11 years (range 18–61). Lipid parameters (triglycerides, high‐density lipoprotein cholesterol) and IR markers (fasting insulin and homeostasis model assessment (HOMA) index) correlated with fat distribution, whereas inflammatory parameters (C‐reactive protein, fibrinogen) correlated only with total fat mass. An association was observed between android fat distribution and adipocyte hypertrophy. Visceral adipocyte hypertrophy was associated with both IR and hypertension, whereas subcutaneous fat‐cell size was linked only to hypertension. Our results obtained in a large cohort of women showed that fat distribution still predicts metabolic abnormalities in severe obesity. Furthermore, we found a cluster of associations among fat distribution, metabolic syndrome (MS), and adipocyte hypertrophy.     

Alterations in fatty acid kinetics in obese adolescents with increased intrahepatic triglyceride content

Objective: It has been hypothesized that excessive fatty acid availability contributes to steatosis and the metabolic abnormalities associated with nonalcoholic fatty liver disease (NAFLD). The purpose of this study was to evaluate whether adipose tissue lipolytic activity and the rate of fatty acid release into plasma are increased in obese adolescents with NAFLD. Methods: Palmitate kinetics were determined in obese adolescents with normal (n = 9; BMI = 37 ± 2 kg/m²; intrahepatic triglyceride (IHTG) ≤5.5% of liver volume) and increased (n = 9; BMI = 36 ± 2 kg/m²; IHTG ≥ 10% of liver volume) IHTG content during the basal state (postabsorptive condition) and during physiological hyperinsulinemia (postprandial condition). Both groups were matched on body weight, BMI, percent body fat, age, sex, and Tanner stage. The hyperinsulinemic‐euglycemic clamp procedure, in conjunction with a deuterated palmitate tracer infusion, was used to determine free‐fatty acid (FFA) kinetics, and magnetic resonance spectroscopy was used to determine IHTG content. Results: The rate of whole‐body palmitate release into plasma was greater in subjects with NAFLD than those with normal IHTG content during basal conditions, (87 ± 7 vs. 127 ± 13 µmol/min; P < 0.01) and during physiological hyperinsulinemia, (24 ± 2 vs. 44 ± 8 µmol/min; P < 0.01). Discussion: These results demonstrate that adipose tissue lipolytic activity is increased in obese adolescents with NAFLD and results in an increase in the rate of fatty acid release into plasma throughout the day. This continual excess in fatty acid flux supports the hypothesis that adipose insulin resistance is involved in the pathogenesis of steatosis and contributes to the metabolic complications associated with NAFLD.     

Influence of Excess Fat on Cardiac Morphology and Function: Study in Uncomplicated Obesity

Objective: To evaluate whether or not “uncomplicated” obesity (without associated comorbidities) is really associated with cardiac abnormalities. Research Methods and Procedures: We evaluated cardiac parameters in obese subjects with long‐term obesity, normal glucose tolerance, normal blood pressure, and regular plasma lipids. We selected 75 obese patients [body mass index (BMI) >30 kg/m²], who included 58 women and 17 men (mean age, 33.7 ± 11.9 years; BMI, 37.8 ± 5.5 kg/m²) with a ≥10‐year history of excess fat, and 60 age‐matched normal‐weight controls, who included 47 women and 13 men (mean age, 32.7 ± 10.4 years; BMI, 23.1 ± 1.4 kg/m²). Each subject underwent an oral glucose tolerance test to exclude impaired glucose tolerance or diabetes mellitus, bioelectrical impedance analysis to calculate fat mass and fat‐free mass, and echocardiography. Results: Obese patients presented diastolic function impairment, hyperkinetic systole, and greater aortic root and left atrium compared with normal subjects. No statistically significant differences between obese subjects and normal subjects were found in indexed left ventricular mass (LVM/body surface area, LVM/height^2.7, and LVM/fat‐free mass_kg), and no changes in left ventricular geometry were observed. No statistically significant differences in cardiac parameters between extreme (BMI > 40 kg/m²) and mild obesity (BMI < 35 kg/m²) were observed. Discussion: In conclusion, our data showed that obesity, in the absence of glucose intolerance, hypertension, and dyslipidemia, seems to be associated only with an impairment of diastolic function and hyperkinetic systole, and not with left ventricular hypertrophy.     

Alteration of Amine Oxidase Activity in the Adipose Tissue of Obese Subjects

Objective: To explore the activity of monoamine oxidases (MAOs) and semicarbazide‐sensitive amine oxidases (SSAOs) in adipose tissue and blood of lean and moderately obese subjects and to study whether there is a link between these hydrogen peroxide‐generating enzymes and blood markers of oxidative stress. Research Methods and Procedures: Nine obese male subjects (BMI 32.6 ± 0.4 kg/m²) and nine controls (BMI 23.4 ± 0.5) of 24‐ to 40‐year‐old subjects were included in the study. MAO and SSAO activities were measured on microbiopsies of abdominal subcutaneous adipose tissue by quantifying ¹⁴C‐tyramine and ¹⁴C‐benzylamine oxidation. Levels of soluble SSAO, lipid peroxidation products, and antioxidant agents were measured in plasma, whereas cytoprotective enzymes were determined in blood lysates. Results: The high MAO activity found in adipose tissue was diminished by one‐half in obese subjects (maximum initial velocity of 1.2 vs. 2.3 nmol tyramine oxidized/mg protein/min). There was no change in SSAO activity, either under its adipose tissue‐bound or plasma‐soluble form. Plasma levels of lipid peroxidation products and antioxidant vitamins remained unmodified, as well as erythrocyte antioxidant enzymes, whereas circulating triglycerides, insulin, and leptin were increased. Discussion: Although they already exhibited several signs of endocrino‐metabolic disorders, the obese men did not exhibit the increase in blood markers of oxidative stress or the decrease in antioxidant defenses reported to occur in very obese or diabetic subjects. The reduced MAO and the unchanged SSAO activities found in obesity suggest that these hydrogen peroxide‐generating enzymes expressed in adipocytes are probably not involved in the onset of the oxidative stress found in severe obesity and/or in its complications.     

High Serum Leptin Is Associated with Attenuated Coronary Vasoreactivity

Objective: Hyperleptinemia, a hallmark of obesity, appears to be a risk factor for coronary artery disease. However, although leptin is a vasoactive hormone, no studies addressing leptin's effect on coronary perfusion have been performed. We examined the association between circulating leptin concentration and coronary vasoreactivity in young obese and nonobese males. Research Methods and Procedures: Myocardial blood flow was quantitated in 10 obese men (age 31 ± 7 years, BMI 34 ± 2 kg/m²) and 10 healthy matched nonobese men (age 33 ± 8 years, BMI 24 ± 2 kg/m²) using positron emission tomography and O‐15‐water. The measurements were performed basally and during adenosine infusion (140 μg/kg per minute). Results: Serum leptin was significantly higher in obese than nonobese subjects (10.3 ± 5.6 vs. 4.3 ± 2.5 ng/mL, p < 0.01). Basal myocardial blood flow was not significantly different between obese and nonobese subjects. Adenosine‐stimulated flow was blunted in obese (3.2 ± 0.6 mL/g per minute) when compared with nonobese subjects (4.0 ± 1.1 mL/g per minute, p < 0.05). Serum leptin concentration was inversely associated with adenosine‐stimulated flow in study subjects (r = ?0.50, p < 0.05). This association was no longer observed after adjustment for obesity and/or hyperinsulinemia. Discussion: Hyperleptinemia and reduced coronary vasoreactivity occur concomitantly in young obese but otherwise healthy men. Moreover, the adenosine‐stimulated myocardial flow is inversely related to prevailing concentration of serum leptin. Although this relationship appears to be explained by obesity and/or hyperinsulinemia, leptin might have a role in regulation of myocardial blood supply.     

Effect of Obesity on Growth‐related Oncogene Factor‐α, Thrombopoietin,and Tissue Inhibitor Metalloproteinase‐1 Serum Levels

We have recently identified several adipokines as oversecreted by omental adipose tissue (AT) of obese subjects: two chemokines (growth‐related oncogene factor‐α (GRO‐α), macrophage inflammatory protein‐1β (MIP‐1β)), a tissue inhibitor of metalloproteinases‐1 (TIMP‐1), an interleukin‐7 (IL‐7) and a megakaryocytic growth‐factor (thrombopoietin (TPO)). These adipokines are involved in insulin resistance and atherosclerosis. The objectives of this study were to determine whether the circulating levels of these adipokines were increased in obesity and to identify the responsible factors. A cross‐sectional study including 32 lean (BMI (kg/m²) <25), 15 overweight (BMI: 25–29.9), 11 obese (BMI: 30–39.9), and 17 severely obese (BMI >40) age‐matched women was carried out. Serum adipokine levels, insulin sensitivity, and substrate oxidation were measured by ELISA, euglycemic–hyperinsulinemic clamp, and indirect calorimetry, respectively. Circulating levels of GRO‐α, TPO, and TIMP‐1 were higher in obese and/or severely obese women than in lean ones (+30, 55, and 20%, respectively). Serum levels of these adipokines positively correlated with insulinemia or glycemia, and negatively with insulin sensitivity. TIMP‐1 also positively correlated with blood pressure, and TPO with triglyceride levels. Multiple regression analysis showed that fat mass per se was an independent determinant of GRO‐α, TPO, and TIMP‐1 levels, suggesting that hypertrophied adipocytes and recruited macrophages in expanded AT mainly contribute to this hyperadipokinemia. Insulinemia, glycemia and resistance of glucose oxidation to insulin were additional predictors for TPO. Circulating GRO‐α, TPO, and TIMP‐1 levels are increased in obesity. This may be partially due to augmented adiposity per se and to hyperinsulinemia/insulin resistance. These high systemic levels may in turn worsen/promote insulin resistance and cardiovascular disease.     

Associations among SPARC mRNA expression in adipose tissue,serum SPARC concentration and metabolic parameters in Korean women

Objective: Secreted protein acidic and rich in cysteine (SPARC) is expressed in most tissues and is also secreted by adipocytes. The associations of SPARC mRNA expression in visceral adipose tissue (VAT), subcutaneous abdominal adipose tissue (SAT), serum SPARC concentration, and metabolic parameters in Korean women are investigated. Design and Methods: This is a cross‐sectional study. Fifty‐eight women were recruited, of whom 15 women who underwent bariatric surgery for morbid obesity (BMI mean ± SD: 40.2±5.7 kg/m²), 16 who underwent metabolic surgery for type 2 diabetes (BMI: 28.9±4.5 kg/m²), and, as a control group, 27 who underwent gynecological surgery (BMI: 22.7±2.4 kg/m²). Anthropometric variables, metabolic parameters, SPARC mRNA expression in adipose tissue, and serum SPARC concentration were measured. Results: In all subjects, SPARC mRNA expression was significantly higher in SAT than in VAT. Serum SPARC concentrations (mean ± SE) in morbidly obese subjects, subjects with type 2 diabetes, and normal weight subjects were 267.3±40.2 ng/mL, 130.4±33.0 ng/mL, and 53.1±2.8 ng/mL, respectively. SPARC mRNA in SAT was significantly correlated with BMI, whereas SPARC mRNA in VAT was significantly correlated with BMI and VAT area. Serum SPARC concentration was significantly correlated with BMI, waist circumference, total adipose tissue area, and SAT area. After BMI adjustment, serum SPARC concentration was significantly correlated with fasting insulin concentration and HOMA‐IR score. Multivariate regression analysis showed that BMI and HOMA‐IR were independently associated with serum SPARC concentration. Conclusions: Serum SPARC concentration is significantly correlated with obesity indices and might be influenced by insulin resistance. These findings suggest that SPARC may contribute to the metabolic dysregulation associated with obesity in humans.