Leptin pulsatility in formerly obese women

Metabolic surgery-induced changes of the growth hormone system relate to improved adipose tissue function

AIMS

Body weight loss improves insulin resistance and growth hormone secretion in obesity, which may be regulated by leptin according to preclinical studies. How changes in leptin, lipids and insulin sensitivity after bariatric (metabolic) surgery affect the human growth hormone system is yet unclear.

PARTICIPANTS AND METHODS

People with obesity (OBE, n = 79, BMI 50.8 ± 6.3 kg/m²) were studied before, 2, 12, 24 and 52 weeks after metabolic surgery and compared to lean healthy humans (control; CON, n = 24, BMI 24.3 ± 3.1 kg/m²). Tissue-specific insulin sensitivity was assessed by hyperinsulinemic-euglycemic clamps with D-[6,6-²H₂]glucose. Fasting leptin, growth hormone (GH), insulin-like growth factor 1 (IGF-1) and IGF-binding proteins (IGFBP1, IGFBP3) were measured using ELISA.

RESULTS

At baseline, OBE exhibited higher glycemia and leptinemia as well as pronounced peripheral, adipose tissue and hepatic insulin resistance compared to CON. GH and IGFBP1 were lower, while IGF1 was comparable between groups. At 52 weeks, OBE had lost 33% body weight and doubled their peripheral insulin sensitivity, which was paralleled by continuous increases in GH, IGF-1 and IGFBP1 as well as decrease in leptin. The rise in GH correlated with reductions in free fatty acids, adipose tissue insulin resistance and insulinemia, but not with changes in body weight, peripheral insulin sensitivity, glycemia or leptinemia. The rise in IGF-1 correlated with reduction in high-sensitive C-reactive protein.

CONCLUSION

Reversal of alterations of the GH-IGF-1 axis after surgically-induced weight loss is unlikely related to improved leptin secretion and/or insulin sensitivity, but is rather associated with restored adipose tissue function and reduced low-grade inflammation.

Glycemic control after metabolic surgery: a Granger causality and graph analysis

The purpose of this study was to examine the contribution of nonesterified fatty acids (NEFA) and incretin to insulin resistance and diabetes amelioration after malabsorptive metabolic surgery that induces steatorrhea. In fact, NEFA infusion reduces glucose-stimulated insulin secretion, and high-fat diets predict diabetes development. Six healthy controls, 11 obese subjects, and 10 type 2 diabetic (T2D) subjects were studied before and 1 mo after biliopancreatic diversion (BPD). Twenty-four-hour plasma glucose, NEFA, insulin, C-peptide, glucagon-like peptide-1 (GLP-1), and gastric inhibitory polypeptide (GIP) time courses were obtained and analyzed by Granger causality and graph analyses. Insulin sensitivity and secretion were computed by the oral glucose minimal model. Before metabolic surgery, NEFA levels had the strongest influence on the other variables in both obese and T2D subjects. After surgery, GLP-1 and C-peptide levels controlled the system in obese and T2D subjects. Twenty-four-hour GIP levels were markedly reduced after BPD. Finally, not only did GLP-1 levels play a central role, but also insulin and C-peptide levels had a comparable relevance in the network of healthy controls. After BPD, insulin sensitivity was completely normalized in both obese and T2D individuals. Increased 24-h GLP-1 circulating levels positively influenced glucose homeostasis in both obese and T2D subjects who underwent a malabsorptive bariatric operation. In the latter, the reduction of plasma GIP levels also contributed to the improvement of glucose metabolism. It is possible that the combination of a pharmaceutical treatment reducing GIP and increasing GLP-1 plasma levels will contribute to better glycemic control in T2D. The application of Granger causality and graph analyses sheds new light on the pathophysiology of metabolic surgery.

Role of cardiotrophin-1 in the regulation of metabolic circadian rhythms and adipose core clock genes in mice and characterization of 24-h circulating CT-1 profiles in normal-weight and overweight/obese subjects

Cardiotrophin (CT)-1 is a regulator of glucose and lipid homeostasis. In the present study, we analyzed whether CT-1 also acts to peripherally regulate metabolic rhythms and adipose tissue core clock genes in mice. Moreover, the circadian pattern of plasma CT-1 levels was evaluated in normal-weight and overweight subjects. The circadian rhythmicity of oxygen consumption rate (Vo₂) was disrupted in aged obese CT-1-deficient (CT-1^-/-) mice (12 mo). Although circadian rhythms of Vo₂ were conserved in young lean CT-1^-/- mice (2 mo), CT-1 deficiency caused a phase shift of the acrophase. Most of the clock genes studied (Clock, Bmal1, and Per2) displayed a circadian rhythm in adipose tissue of both wild-type (WT) and CT-1^-/- mice. However, the pattern was altered in CT-1^-/- mice toward a lower percentage of the rhythm or lower amplitude, especially for Bmal1 and Clock. Moreover, CT-1 mRNA levels in adipose tissue showed significant circadian fluctuations in young WT mice. In humans, CT-1 plasma profile exhibited a 24-h circadian rhythm in normal-weight but not in overweight subjects. The 24-h pattern of CT-1 was characterized by a pronounced increase during the night (from 02:00 to 08:00). These observations suggest a potential role for CT-1 in the regulation of metabolic circadian rhythms.-López-Yoldi, M., Stanhope, K. L., Garaulet, M., Chen, X. G., Marcos-Gómez, B., Carrasco-Benso, M. P., Santa Maria, E. M., Escoté, X., Lee, V., Nunez, M. V., Medici, V., Martínez-Ansó, E., Sáinz, N., Huerta, A. E., Laiglesia, L. M., Prieto, J., Martínez, J. A., Bustos, M., Havel, P. J., Moreno-Aliaga, M. J. Role of cardiotrophin-1 in the regulation of metabolic circadian rhythms and adipose core clock genes in mice and characterization of 24-h circulating CT-1 profiles in normal-weight and overweight/obese subjects.

Effects of supplementation with omega-3 on insulin sensitivity and non-esterified free fatty acid (NEFA) in type 2 diabetic patients

OBJECTIVE

The aim of this study was to determine the role of omega-3 supplementation on NEFA concentration, insulin sensitivity and resistance, and glucose and lipid metabolism in type 2 diabetic patients.

SUBJECTS AND METHODS

Forty-four type 2 diabetic patients were randomly recruited into two groups. Group A received 4 g/day omega-3 soft gels, and group B received a placebo for 10 wks. Blood samples were collected after 12-h fast. Physical activity records, three-day food records, and anthropometric measurements were obtained from all participants at the beginning and end of the study.

RESULTS

Omega-3 supplementation caused a significant reduction in NEFA in the intervention group compared with the placebo group (P = 0.009). Additionally, the administration of omega-3 resulted in significantly greater changes (Diff) for the intervention group in various parameters, such as insulin and Quicki indices compared with the placebo group (P < 0.05).

CONCLUSIONS

Omega-3 fatty acid supplementation in type 2 diabetic patients improved insulin sensitivity, probably due to the decrease in NEFA concentrations.

The impact of leptin on perinatal development and psychopathology

Leptin has long been associated with metabolism as it is a critical regulator of both food intake and energy expenditure, but recently, leptin dysregulation has been proposed as a mechanism of psychopathology. This review discusses the evidence supporting a role for leptin in mental health disorders and describes potential mechanisms that may underlie this association. Leptin plays a critical role in pregnancy and in fetal growth and development. Leptin's role and profile during development is examined in available human studies, and the validity of applying studies conducted in animal models to the human population are discussed. Rodents experience a postnatal leptin surge, which does not occur in humans or larger animal models. This suggests that further research using large mammal models, which have a leptin profile across pregnancy and development similar to humans, are of high importance. Maternal obesity and hyperleptinemia correlate with increased leptin levels in the umbilical cord, placenta, and fetus. Leptin levels are thought to impact fetal brain development; likely by activating proinflammatory cytokines that are known to impact many of the neurotransmitter systems that regulate behavior. Leptin is likely involved in behavioral regulation as leptin receptors are widely distributed in the brain, and leptin influences cortisol release, the mesoaccumbens dopamine pathway, serotonin synthesis, and hippocampal synaptic plasticity. In humans, both high and low levels of leptin are reported to be associated with psychopathology. This inconsistency is likely due to differences in the metabolic state of the study populations. Leptin resistance, which occurs in the obese state, may explain how both high and low levels of leptin are associated with psychopathology, as well as the comorbidity of obesity with numerous mental illnesses. Leptin resistance is likely to influence disorders such as depression and anxiety where high leptin levels have been correlated with symptomatology. Schizophrenia is also associated with both low and high leptin levels. However, as anti-psychotics pharmacotherapy induces weight gain, which elevates leptin levels, drug-naïve populations are needed for further studies. Elevated circulating leptin is consistently found in childhood neurodevelopmental disorders including autism spectrum disorders and Rhett disorder. Further, studies on the impact of leptin and leptin resistance on psychopathology and neurodevelopmental disorders are important directions for future research. Studies examining the mechanisms by which exposure to maternal obesity and hyperleptinemia during fetal development impact brain development and behavior are critical for the health of future generations.

Circadian rhythms and metabolic syndrome: from experimental genetics to human disease

The incidence of the metabolic syndrome represents a spectrum of disorders that continue to increase across the industrialized world. Both genetic and environmental factors contribute to metabolic syndrome and recent evidence has emerged to suggest that alterations in circadian systems and sleep participate in the pathogenesis of the disease. In this review, we highlight studies at the intersection of clinical medicine and experimental genetics that pinpoint how perturbations of the internal clock system, and sleep, constitute risk factors for disorders including obesity, diabetes mellitus, cardiovascular disease, thrombosis and even inflammation. An exciting aspect of the field has been the integration of behavioral and physiological approaches, and the emerging insight into both neural and peripheral tissues in disease pathogenesis. Consideration of the cell and molecular links between disorders of circadian rhythms and sleep with metabolic syndrome has begun to open new opportunities for mechanism-based therapeutics.

Metabolic endotoxemia and saturated fat contribute to circulating NGAL concentrations in subjects with insulin resistance

OBJECTIVE

Lipocalin-2 (neutrophil gelatinase-associated lipocalin, NGAL) is an innate immune system protein that has been linked to insulin resistance and obesity, but the mechanisms behind these associations are poorly known. We hypothesized that endotoxin (lipopolysaccharide, LPS) and fat intake were in the background of these associations.

DESIGN

We studied four cohorts: (1) a cross-sectional study in 194 subjects; (2) the changes in NGAL concentration induced by diet and weight loss in 36 obese women (with circadian rhythm in 8 of them); (3) the effects of acute fat intake on circulating NGAL concentration in 42 morbidly obese subjects; and (4) LPS-induced NGAL secretion ex vivo (whole blood and adipose tissue explants).

RESULTS

Serum NGAL concentration was significantly associated with fasting triglycerides and LPS-binding protein in patients with type 2 diabetes. In obese subjects, the intake of saturated fatty acids was the factor that best explained the variance of NGAL changes after weight loss (contributing independently to 14% of NGAL variance). In fact, weight loss significantly changed the circadian rhythm of NGAL. The acute increase in circulating NGAL after fat overload was significantly associated with fasting insulin (r=0.52, P<0.001), homeostasis model assessment of insulin resistance (HOMA-IR) (r=0.36, P=0.02) and post-load triglyceride concentrations (r=0.38, P=0.018). LPS-induced NGAL secretion from adipose tissue explants did not change significantly, but LPS led to a significant increase in NGAL concentration in the whole blood obtained from patients with type 2 diabetes.

CONCLUSION

Metabolic endotoxemia and saturated fat might contribute to circulating NGAL concentration in patients with insulin resistance.

Serum leptin levels in obese males during over- and underfeeding

Leptin levels in lean adults vary in response to short-term alterations in energy balance. We tested whether leptin responded to short-term changes in energy balance in obese males in a similar manner to lean individuals. We enrolled eight obese, healthy males in a 12-day study composed of four consecutive dietary treatment periods of 3 days each: baseline eucaloric feeding followed by randomized crossover periods of overfeeding (130% of total energy expenditure (TEE)) or underfeeding (70% of TEE), separated by a eucaloric (100% of TEE) washout period. We measured TEE with doubly labeled water prior to baseline. Leptin levels were measured throughout the third day of each treatment and 24-h weighted averaged were calculated. Subjects' ad libitum intake during a breakfast buffet following each treatment period was recorded. During underfeeding, leptin levels decreased by 21 +/- 6% (P < 0.01) from the previous eucaloric period. During overfeeding, leptin levels increased by 25 +/- 11% (P < 0.01) when subjects were underfed first, but did not increase (5 +/- 8%, nonsignificant (n.s.)) when subjects were overfed first. Changes in ad libitum intake from baseline were calculated for each subject after over-, under-, and eucaloric feeding and did not to correlate with the changes in mesor leptin levels from baseline (R(2) = 0.006, n.s). Leptin levels in obese males were acutely responsive to negative energy balance, but not to positive energy balance unless subjects were previously underfed. Consequently, leptin levels in obese males do not respond to changes in energy intake in a manner that would protect against weight gain.

Genes involved in mitochondrial biogenesis/function are induced in response to bilio-pancreatic diversion in morbidly obese individuals with normal glucose tolerance but not in type 2 diabetic patients

AIMS/HYPOTHESIS

The mechanisms allowing normalisation of insulin sensitivity and reversal of type 2 diabetes after bilio-pancreatic diversion (BPD) have not been elucidated. We studied whether the expression of genes relevant to mitochondrial biogenesis/function is induced in response to BPD and whether the response differs between morbidly obese patients with normal glucose tolerance (NGT) and patients with type 2 diabetes.

METHODS

The effect of stable weight reduction after BPD on metabolic variables and expression of nuclear genes encoding for mitochondrial proteins or regulators of mitochondrial function was investigated in skeletal muscle. Insulin sensitivity was assessed by euglycaemic-hyperinsulinaemic clamp and substrate oxidation by indirect calorimetry.

RESULTS

Both NGT and type 2 diabetic patients showed a net improvement of insulin sensitivity, with the latter also showing blood glucose normalisation. NGT patients had a large increase in glucose oxidation and substantial reduction in lipid oxidation. In contrast, type 2 diabetic patients had a blunted response to BPD in terms of glucose oxidation. NGT patients showed increased expression of genes encoding mitofusin 2, porin or citrate synthase; no significant changes were detected in diabetic patients. The expression of genes regulating mitochondrial activity (PGC-1beta [also known as PPARGC1B], PGC-1alpha [also known as PPARGC1A], PPARdelta [also known as PPARD], SIRT1) was induced only in NGT patients.

CONCLUSIONS/INTERPRETATION

These findings indicate that weight loss after BPD exerts a beneficial effect on insulin sensitivity via mechanisms that are independent of the expression of genes involved in mitochondrial biogenesis/activity. Furthermore, the observation that gene expression is not altered with weight loss in type 2 diabetic patients while it is induced in NGT patients suggests a heritable component.

Role of the incretin system in the remission of type 2 diabetes following bariatric surgery

AIMS

It has been observed, as a collateral outcome of bariatric surgery, that morbidly obese patients with frank type 2 diabetes mellitus or impaired glucose tolerance undergone Roux-en-Y Gastric Bypass (RYGB) or bilio-pancreatic diversion (BPD) became and remained euglycemic since surgery. But, most interestingly, the conversion to euglycemia happened within few days from the operation, long before a significant weight loss could intervene. The purpose of this viewpoint is to try to elucidate the mechanisms involved in the resolution/remission of diabetes after bariatric surgery, in particular highlighting the role played by the modifications in incretin secretion.

DATA SYNTHESIS

The effect of purely restrictive procedures in improving glucose control is directly proportional to the degree of weight loss. In contrast, either RYGB or BPD, the first a mainly restrictive and the second a quite purely malabsorptive bariatric technique, operate through a different mechanism, as a probable consequence of the small intestine bypass. The bypass of different intestinal portions covers a central role in the mechanisms of action of these two surgical procedures. In fact, while RYGB does not affect insulin resistance but increases insulin secretion via the stimulation of nutrient-mediated incretin secretion, BPD induces a full normalization of insulin resistance and, consequently, a significant reduction of insulin secretion. The insulin resistance reversion is only partially explained by the incretin level changes after BPD.

CONCLUSION

A role of incretins in type 2 diabetes improvement or resolution is ascertained although it is possible that other, not yet identified, hormone(s) can cooperate with them.

Prolactin and insulin ultradian secretion and adipose tissue lipoprotein lipase expression in severely obese women after bariatric surgery

BACKGROUND

Hyperprolactinemia is associated with obesity. Furthermore, in human adipose tissue cultured in vitro, prolactin (PRL) inhibited lipoprotein lipase (LPL) activity via functional PRL receptors.

OBJECTIVE

To study PRL and insulin ultradian rhythm and subcutaneous adipose tissue LPL mRNA and protein expressions in severely obese women before and after malabsorptive bariatric surgery.

METHODS AND PROCEDURES

Seven severely obese, fertile women were studied twice, once before and the second time 1 year after bilio-pancreatic diversion (BPD), when the weight was stable for at least 3 months. Metabolizable energy intake and 24-h energy expenditure (EE) were measured. Fourier and PULSEFIT analyses were applied to 24-h hormonal time-series to study daily fluctuations and hormonal clearance. Insulin sensitivity was assessed by euglycemic-hyperinsulinemic clamp. Quantitative-competitive reverse transcriptase-PCR and western blot analysis were used to measure LPL gene expression.

RESULTS

Spontaneous 24-h PRL secretion was significantly reduced after BPD (mean-daily release, 128.4 +/- 28.1 microg/l vs. 67.2 +/- 9.2 microg/l distribution volume (Vd/l.24 h), P = 0.02); insulin secretion also was significantly reduced (499.9 +/- 204.0 microg/Vd/l.24 h vs. 85.6 +/- 21.0 microg/Vd/l.24 h, P = 0.0001). Metabolizable energy/kg(FFM) did not change significantly after BPD. Twenty-four-hour EE, but not 24-h EE/FFM, was significantly decreased after BPD (P < 0.05). Insulin sensitivity significantly (P < 0.0001) increased after BPD from 21.41 +/- 1.92 to 68.62 +/- 5.03 micromol/kg(FFM)/min. LPL mRNA concentration (from 42.63 +/- 4.21% to 19.00 +/- 2.74% of cyclophilin mRNA, P = 0.001) as well as LPL protein level (from 8.94 +/- 2.73 to 3.16 +/- 1.05 as ratios of protein of interest vs. housekeeping protein, P = 0.038) significantly decreased after BPD. The major determinant of PRL secretion was insulin secretion, whereas the best predictors of LPL expression were insulin and PRL secretion rates.

DISCUSSION

The restriction of lipid metabolizable energy rather than weight loss seems to be responsible for both reduction in PRL circulating levels and normalization of its secretion rhythm after bariatric surgery. Furthermore, the reduced adipose tissue LPL expression, being significantly correlated with the decrease in insulin and PRL, suggests a role of hyperinsulinemia and hyperprolactinemia in inducing and sustaining obesity.

Twenty-four hour insulin secretion and beta cell NEFA oxidation in type 2 diabetic, morbidly obese patients before and after bariatric surgery

AIMS/HYPOTHESIS

We have previously demonstrated that type 2 diabetes resolves after bariatric surgery. To study the role of NEFA in the prompt normalisation of beta cell glucose sensitivity, insulin secretion and beta cell glucose and lipid metabolism were investigated by a model of nutrient-stimulated insulin secretion using a multiple-meal test.

METHODS

Hourly glucose, C-peptide and NEFA were measured in nine morbidly obese, type 2 diabetic patients before and 1 week after bariatric surgery and in six matched healthy volunteers over 24 h. A mathematical model of glucose-NEFA comodulation of insulin secretion rate (ISR) was used to compute ISR and beta-oxidation. Insulin sensitivity was measured by an OGTT minimal model.

RESULTS

Beta cell sensitivity to glucose and NEFA was doubled after surgery, while the 24 h insulin secretion decreased from 277.1 +/- 144.4 to 198.0 +/- 107.6 nmol/m(2) (p < 0.02). Insulin sensitivity was restored. The beta-oxidation rate of beta cells was completely normalised (from 0.032 +/- 0.012 x 10(-12) to 0.103 +/- 0.031 x 10(-12) mmol/min per cell, p < 0.005). The best predictor of beta cell function improvement was the duration of diabetes.

CONCLUSIONS/INTERPRETATION

Bariatric surgery in type 2 diabetes restores beta-oxidation in beta cells, doubles glucose-NEFA sensitivity and reverses diabetes. It is likely that ISR is reduced to match insulin-sensitivity normalisation, in spite of no significant reduction in NEFA levels. We hypothesise that insulin sensitivity normalisation might appear as a consequence of nutrient exclusion from proximal intestinal transit, and that secondarily the need for insulin secretion diminishes. The insulin sensitivity increase is much higher than usually obtained by insulin-sensitising agents and is independent of weight changes.

Molecular mechanisms of diabetes reversibility after bariatric surgery

OBJECTIVE

Insulin resistance is a strong biological marker of both obesity and type 2 diabetes. Abnormal fat deposition within skeletal muscle has been identified as a mechanism of obesity-associated insulin resistance. Biliopancreatic diversion (BPD), inducing a massive lipid malabsorption, leads to a reversion of type 2 diabetes. To elucidate the mechanisms of diabetes reversibility, the expression of genes involved in glucose and free fatty acids (FFAs) metabolism was investigated in skeletal muscle biopsies from obese, type 2 diabetic subjects. Peripheral insulin sensitivity and insulin secretion was also measured.

SUBJECTS

Eight Caucasian obese diabetic patients (BMI 52.1+/-1.85 kg/m(2)) were studied before and 3 years after BPD.

MEASUREMENTS

The mRNA levels were estimated by quantitative real-time reverse transcription polymerase chain reaction (RT-PCR), insulin sensitivity by the euglycemic-hyperinsulinemic clamp and insulin secretion using a model describing the relationship between insulin secretion and glucose concentration.

RESULTS

Whole-body glucose uptake (M), normalized by fat-free mass, significantly increased in post-obese subjects (P<0.0001). Total insulin output decreased (P<0.05) in association with a significant improvement of beta-cells glucose sensitivity (P<0.05). mRNA levels of FABP3 (P<0.05), FACL (P<0.05), ACC2 (P<0.05), HKII (P<0.05) and PDK4 (P<0.05) were significantly decreased, while SREBP1c mRNA increased (P<0.05) after BPD.

CONCLUSION

Reversibility of type 2 diabetes after BPD is dependent on the improvement of skeletal muscle insulin sensitivity, mediated by changes in the expression of genes regulating glucose and fatty acid metabolism in response to nutrient availability.