Lipid-induced mononuclear cell cytokine secretion in the development of metabolic aberration and androgen excess in polycystic ovary syndrome

STUDY QUESTION

What is the effect of saturated fat ingestion on mononuclear cell (MNC) TNFα, IL-6 and IL-1β secretion and circulating IL-6 levels in women with polycystic ovary syndrome (PCOS)?

SUMMARY ANSWER

Women with PCOS exhibit increases in MNC-derived TNFα, IL-6 and IL-1β secretion and circulating IL-6 following saturated fat ingestion even in the absence of obesity, and these increases are linked to metabolic aberration and androgen excess.

WHAT IS KNOWN ALREADY

Cytokine excess and metabolic aberration is often present in PCOS.

STUDY DESIGN, SIZE, DURATION

A cross-sectional design was used in this study of 38 reproductive-age women.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Groups of 19 reproductive-age women with PCOS (10 lean, 9 obese) and 19 ovulatory controls (10 lean, 9 obese) participated in this study that was performed at a tertiary academic medical centre. TNFα, IL-6 and IL-1β secretion was measured from cultured MNC, and IL-6 was measured in plasma from blood sampling while fasting and 2, 3 and 5 h after saturated fat ingestion. Insulin sensitivity was determined using the Matsuda index following an oral glucose tolerance test. Androgen secretion was evaluated with blood sampling while fasting and 24, 48 and 72 h after an HCG injection.

MAIN RESULTS AND THE ROLE OF CHANCE

Lean and obese women with PCOS exhibited lipid-induced incremental AUC increases in MNC-derived TNFα (489-611%), IL-6 (333-398%) and IL-1β (560-695%) secretion and in plasma IL-6 levels (426-474%), in contrast with lean control subjects. In both PCOS groups, insulin sensitivity was lower (42-49%) and androgen secretion after HCG injection was greater (63-110%) compared with control subjects. The MNC-derived TNFα, IL-6 and IL-1β and circulating IL-6 responses were inversely associated with insulin sensitivity and directly associated with fasting lipids and androgen secretion after HCG injection.

LIMITATIONS, REASONS FOR CAUTION

The sample size of each of the four study groups was modest following group assignment of subjects by body mass.

WIDER IMPLICATIONS OF THE FINDINGS

This study showcases the unique pro-inflammatory contribution of circulating MNC in the development of metabolic aberration and androgen excess in PCOS.

STUDY FUNDING/COMPETING INTEREST(S)

This research was supported by grant R01 DK107605 to F.G. from the National Institutes of Health, the Indiana Clinical and Translational Sciences Institute Clinical Research Center which is funded in part by grant UL1TR002529 from the National Institutes of Health, National Center for Advancing Translational Sciences, Clinical and Translational Sciences Award, and the Indiana University Center for Diabetes and Metabolic Diseases funded by grant P30 DK097512 from the National Institutes of Health. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. No conflicts of interest, financial or otherwise, are declared by the authors.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov NCT01489319.

Changes in Weight and Glucose Can Protect Against Progression in Early Diabetes Independent of Improvements in β-Cell Function

CONTEXT

Evidence-based strategies to prevent progression of dysglycemia in newly diagnosed type 2 diabetes are needed.

OBJECTIVE

To undertake a secondary analysis of the Early Diabetes Intervention Program (EDIP) in order to understand the features that were protective against worsening glycemia.

DESIGN

EDIP was a randomized, placebo-controlled trial.

SETTING

Two university diabetes centers.

PATIENTS

A total of 219 overweight individuals with fasting glucose < 7.8 mmol/L and 2-hour oral glucose tolerance test (OGTT) glucose > 11.1 mmol/L.

INTERVENTIONS

Acarbose versus placebo, on a background of dietary recommendations, with quarterly visits to assess glycemia and intervention adherence for up to 5 years.

MAIN OUTCOME MEASURES

Progression of fasting glucose ≥ 7.8 mmol/L on two consecutive quarterly visits. Cox proportional hazards modeling and ANOVA were performed to evaluate determinants of progression.

RESULTS

Progression-free status was associated with reductions in weight, fasting glucose, 2-hour OGTT glucose, and increases in the high-density lipoprotein/triglyceride ratio. The reduction in fasting glucose was the only effect that remained significantly associated with progression-free status in multivariable Cox modeling. The reduction in fasting glucose was in turn primarily associated with reductions in weight and in 2-hour OGTT glucose. Acarbose treatment did not explain these changes.

CONCLUSIONS

In early diabetes, reductions in glucose, driven by reductions in weight, can delay progressive metabolic worsening. These observations underscore the importance of lifestyle management including weight loss as a tool to mitigate worsening of glycemia in newly diagnosed diabetes.

Assessment of myocardial metabolic flexibility and work efficiency in human type 2 diabetes using 16-[18F]fluoro-4-thiapalmitate, a novel PET fatty acid tracer

Altered myocardial fuel selection likely underlies cardiac disease risk in diabetes, affecting oxygen demand and myocardial metabolic flexibility. We investigated myocardial fuel selection and metabolic flexibility in human type 2 diabetes mellitus (T2DM), using positron emission tomography to measure rates of myocardial fatty acid oxidation {16-[(18)F]fluoro-4-thia-palmitate (FTP)} and myocardial perfusion and total oxidation ([(11)C]acetate). Participants underwent paired studies under fasting conditions, comparing 3-h insulin + glucose euglycemic clamp conditions (120 mU·m(-2)·min(-1)) to 3-h saline infusion. Lean controls (n = 10) were compared with glycemically controlled volunteers with T2DM (n = 8). Insulin augmented heart rate, blood pressure, and stroke index in both groups (all P < 0.01) and significantly increased myocardial oxygen consumption (P = 0.04) and perfusion (P = 0.01) in both groups. Insulin suppressed available nonesterified fatty acids (P < 0.0001), but fatty acid concentrations were higher in T2DM under both conditions (P < 0.001). Insulin-induced suppression of fatty acid oxidation was seen in both groups (P < 0.0001). However, fatty acid oxidation rates were higher under both conditions in T2DM (P = 0.003). Myocardial work efficiency was lower in T2DM (P = 0.006) and decreased in both groups with the insulin-induced increase in work and shift in fuel utilization (P = 0.01). Augmented fatty acid oxidation is present under baseline and insulin-treated conditions in T2DM, with impaired insulin-induced shifts away from fatty acid oxidation. This is accompanied by reduced work efficiency, possibly due to greater oxygen consumption with fatty acid metabolism. These observations suggest that improved fatty acid suppression, or reductions in myocardial fatty acid uptake and retention, could be therapeutic targets to improve myocardial ischemia tolerance in T2DM.

Failure of hyperglycemia and hyperinsulinemia to compensate for impaired metabolic response to an oral glucose load

OBJECTIVE

To evaluate whether the augmented insulin and glucose response to a glucose challenge is sufficient to compensate for defects in glucose utilization in obesity and type 2 diabetes, using a breath test measurement of integrated glucose metabolism.

METHODS

Non-obese, obese normoglycemic and obese type 2 diabetic subjects were studied on 2 consecutive days. A 75g oral glucose load spiked with ¹³C-glucose was administered, measuring exhaled breath ¹³CO₂ as an integrated measure of glucose metabolism and oxidation. A hyperinsulinemic euglycemic clamp was performed, measuring whole body glucose disposal rate. Body composition was measured by DEXA. Multivariable analyses were performed to evaluate the determinants of the breath ¹³CO₂.

RESULTS

Breath ¹³CO₂ was reduced in obese and type 2 diabetic subjects despite hyperglycemia and hyperinsulinemia. The primary determinants of breath response were lean mass, fat mass, fasting FFA concentrations, and OGTT glucose excursion. Multiple approaches to analysis showed that hyperglycemia and hyperinsulinemia were not sufficient to compensate for the defect in glucose metabolism in obesity and diabetes.

CONCLUSIONS

Augmented insulin and glucose responses during an OGTT are not sufficient to overcome the underlying defects in glucose metabolism in obesity and diabetes.

Effect of acarbose to delay progression of carotid intima-media thickness in early diabetes

BACKGROUND

The anti-diabetic agent acarbose reduces postprandial glucose excursions. We have evaluated the effect of randomized treatment with acarbose on the progression of carotid intima-media thickness (IMT) in early diabetes.

METHODS

The Early Diabetes Intervention Program was a randomized trial of acarbose versus placebo in 219 participants with early diabetes characterized by glucose values over 11.1 mmol/L 2 h after a 75 g oral glucose load and a mean HbA1c of 6.3%. IMT was measured at baseline and yearly. Follow-up was discontinued if participants progressed to the study glucose endpoints; IMT readings were available for a median of 2 years, with 72 subjects followed for 5 years.

RESULTS

Progressive increases in IMT were seen in both treatment groups, but progression was reduced in participants randomized to acarbose (p = 0.047). In age, sex and smoking-adjusted analyses, IMT progression was associated with greater fasting and oral glucose tolerance test-excursion glucose, fasting insulin, cholesterol and glycated low-density lipoprotein concentrations. IMT progression was reduced with study-related changes in weight, insulin and non-esterified fatty acids; these features were more strongly associated with reduced IMT progression than acarbose treatment. Despite strong associations of baseline glycemia with IMT progression, study-related changes in glucose were not important determinants of IMT progression.

CONCLUSIONS

Acarbose can delay progression of carotid intima-media thickness in early diabetes defined by an oral glucose tolerance test. Glucose, weight, insulin and lipids contributed to risk of progression but reductions in glycemia were not major determinants of reduced rate of IMT progression. Vascular benefits of acarbose may be independent of its glycemic effects.

Effects of losartan on whole body, skeletal muscle and vascular insulin responses in obesity/insulin resistance without hypertension

AIMS

Renin-angiotensin system antagonists have been found to improve glucose metabolism in obese hypertensive and type 2 diabetic subjects. The mechanism of these effects is not well understood. We hypothesized that the angiotensin receptor antagonist losartan would improve insulin-mediated vasodilation, and thereby improve insulin-stimulated glucose uptake in skeletal muscle of insulin-resistant subjects.

METHODS

We studied subjects with obesity and insulin resistance but without hypertension, hypercholesterolaemia or dysglycaemia [age 39.0 ± 9.6 yr (mean ± SD), body mass index (BMI) 33.2 ± 5.9 kg/m(2) , BP 115.8 ± 12.2/70.9 ± 7.2 mmHg, LDL 2.1 ± 0.5 mmol/l]. Subjects were randomized to 12 weeks' double-blind treatment with losartan 100 mg once daily (n = 9) or matching placebo (n = 8). Before and after treatment, under hyperinsulinaemic euglycaemic clamp conditions we measured whole-body insulin-stimulated glucose disposal, insulin-mediated vasodilation, and insulin-stimulated leg glucose uptake by the limb balance technique.

RESULTS

Whole-body insulin-stimulated glucose disposal was not significantly increased by losartan. Insulin-mediated vasodilation was augmented following both treatments [increase in leg vascular conductance: pretreatment 0.7 ± 0.3 l/min/mmHg (losartan, mean ± SEM) and 0.9 ± 0.3 (placebo), posttreatment 1.0 ± 0.4 (losartan) and 1.3 ± 0.6 (placebo)] but not different between treatment groups (p = 0.53). Insulin's action to augment nitric oxide (NO) production and to augment endothelium-dependent vasodilation was also not improved. Leg glucose uptake was not significantly changed by treatments, and not different between groups (p = 0.11).

CONCLUSIONS

These findings argue against the hypothesis that losartan might improve skeletal muscle glucose metabolism by improving insulin-mediated vasodilation in normotensive insulin-resistant obese subjects. The metabolic benefits of angiotensin receptor blockers may require the presence of hypertension in addition to obesity-associated insulin resistance.

Fat-induced membrane cholesterol accrual provokes cortical filamentous actin destabilisation and glucose transport dysfunction in skeletal muscle

AIMS/HYPOTHESIS

Diminished cortical filamentous actin (F-actin) has been implicated in skeletal muscle insulin resistance, yet the mechanism(s) is unknown. Here we tested the hypothesis that changes in membrane cholesterol could be a causative factor, as organised F-actin structure emanates from cholesterol-enriched raft microdomains at the plasma membrane.

METHODS

Skeletal muscle samples from high-fat-fed animals and insulin-sensitive and insulin-resistant human participants were evaluated. The study also used L6 myotubes to directly determine the impact of fatty acids (FAs) on membrane/cytoskeletal variables and insulin action.

RESULTS

High-fat-fed insulin-resistant animals displayed elevated levels of membrane cholesterol and reduced F-actin structure compared with normal chow-fed animals. Moreover, human muscle biopsies revealed an inverse correlation between membrane cholesterol and whole-body glucose disposal. Palmitate-induced insulin-resistant myotubes displayed membrane cholesterol accrual and F-actin loss. Cholesterol lowering protected against the palmitate-induced defects, whereas characteristically measured defects in insulin signalling were not corrected. Conversely, cholesterol loading of L6 myotube membranes provoked a palmitate-like cytoskeletal/GLUT4 derangement. Mechanistically, we observed a palmitate-induced increase in O-linked glycosylation, an end-product of the hexosamine biosynthesis pathway (HBP). Consistent with HBP activity affecting the transcription of various genes, we observed an increase in Hmgcr, a gene that encodes 3-hydroxy-3-methyl-glutaryl coenzyme A reductase, the rate-limiting enzyme in cholesterol synthesis. In line with increased HBP activity transcriptionally provoking a membrane cholesterol-based insulin-resistant state, HBP inhibition attenuated Hmgcr expression and prevented membrane cholesterol accrual, F-actin loss and GLUT4/glucose transport dysfunction.

CONCLUSIONS/INTERPRETATION

Our results suggest a novel cholesterolgenic-based mechanism of FA-induced membrane/cytoskeletal disorder and insulin resistance.

mRNA concentrations of MIF in subcutaneous abdominal adipose cells are associated with adipocyte size and insulin action

Objective

To determine whether the mRNA concentrations of inflammation response genes in isolated adipocytes and in cultured preadipocytes are related to adipocyte size and in vivo insulin action in obese individuals.

Design

Cross-sectional inpatient study.

Subjects

Obese Pima Indians with normal glucose tolerance.

Measurements

Adipocyte diameter (by microscope technique; n=29), expression of candidate genes (by quantitative real-time PCR) in freshly isolated adipocytes (monocyte chemoattractant protein [MCP] 1 and MCP2, macrophage inflammatory protein [MIP] 1α, MIP1β and MIP2, macrophage migration inhibitory factor [MIF], tumor necrosis factor alpha, interleukin [IL] 6 and IL8; n=22) and cultured preadipocytes (MCP1, MIP1α, MIF, IL6 and matrix metalloproteinase 2; n=33) from subcutaneous abdominal adipose tissue (by aspiration biopsy, n=34), body fat by dual-energy X-ray absorptiometry, glucose tolerance by 75-gram oral glucose tolerance test, and insulin action by euglycemic-hyperinsulinemic clamp (insulin infusion rate 40 mU/m².min)(all n=34).

Results

MIF was the only gene whose expression in both freshly isolated adipocytes and cultured preadipocytes was positively associated with adipocytes diameter and negatively associated with peripheral and hepatic insulin action (all P<0.05). In multivariate analysis, the association between adipocyte MIF mRNA concentrations and adipocytes diameter was independent of percent body fat (P=0.03), whereas adipocyte MIF mRNA concentrations but not adipocytes diameter independently predicted peripheral insulin action. The mRNA expression concentrations of MIF gene in adipocytes were not associated with plasma concentrations of MIF, but were negatively associated with plasma adiponectin concentrations (P=0.004). In multivariate analysis, adipocyte MIF RNA concentrations (P=0.03) but not plasma adiponectin concentrations (P=0.4) remained a significant predictor of insulin action.

Conclusions

Increased expression of MIF gene in adipose cells may be an important link between obesity characterized by enlarged adipocytes and insulin resistance in normal glucose tolerant people.

Expression of the thermogenic nuclear hormone receptor coactivator PGC-1alpha is reduced in the adipose tissue of morbidly obese subjects

Peroxisome proliferator-activated receptor gamma coactivator 1alpha (PGC1alpha) is an accessory protein which can potentiate the transcriptional activation function of many nuclear hormone receptors. Its tissue distribution and physiological studies suggest that its principal in vivo roles are to promote cold-induced thermogenesis, mitochondrial biogenesis, hepatic gluconeogenesis, and fatty acid beta-oxidation. It is expressed in the white adipose tissue of both humans and rodents, and in rodents it has been suggested to mediate in part the leptin-induced conversion of white adipocytes from fat storing to fat oxidising cells. In this study, quantitative real-time PCR has been used in human tissue to demonstrate that (1) PGC1alpha mRNA levels in subcutaneous fat are three-fold lower in morbidly obese than in slim subjects; (2) there are no differences in PGC1alpha mRNA between omental and subcutaneous mature adipocytes; (3) there is a robust induction of PGC1alpha expression during subcutaneous human preadipocyte differentiation ex vivo. Whether low PGC1alpha expression is a prelude to the development of obesity, or a consequence of that obesity, attempts to upregulate endogenous white adipose tissue expression may prove a valuable new avenue to explore in obesity therapy.

Serum leptin responses after acute resistance exercise protocols

This study examined the acute effects of maximum strength (MS), muscular hypertrophy (MH), and strength endurance (SE) resistance exercise protocols on serum leptin. Ten young lean men (age = 23 +/- 4 yr; body weight = 79.6 +/- 5.2 kg; body fat = 10.2 +/- 3.9%) participated in MS [4 sets x 5 repetitions (reps) at 88% of 1 repetition maximum (1 RM) with 3 min of rest between sets], MH (4 sets x 10 reps at 75% of 1 RM with 2 min of rest between sets), SE (4 sets x 15 reps at 60% of 1 RM with 1 min of rest between sets), and control (C) sessions. Blood samples were collected before and immediately after exercise and after 30 min of recovery. Serum leptin at 30 min of recovery exhibited similar reductions from baseline after the MS (-20 +/- 5%), MH (-20 +/- 4%), and SE (-15 +/- 6%) protocols that were comparable to fasting-induced reduction in the C session (-12 +/- 3%) (P < 0.05). Furthermore, no differences were found in serum leptin among the MS, MH, SE, and C sessions immediately after exercise and at 30 min of recovery (P > 0.05). Cortisol was higher (P < 0.05) after the MH and SE protocols than after the MS and C sessions. Glucose and growth hormone were higher (P < 0.05) after exercise in the MS, MH, and SE protocols than after the C session. In conclusion, typical resistance exercise protocols designed for development of MS, MH, and SE did not result in serum leptin changes when sampled immediately or 30 min postexercise.

Leptin levels in type 2 diabetes: associations with measures of insulin resistance and insulin secretion

Interactions between leptin and insulin have been shown previously, in vitro and in vivo. In this study, we evaluate the associations of leptin levels with insulin secretion and insulin sensitivity in type 2 diabetes. Fasting leptin levels, HbA 1c, glucose, insulin, C-peptide, intact and des-31,32-proinsulin were measured in 100 non-insulin-treated type 2 diabetic patients. Glucose, insulin and C-peptide were measured 2 hours after an oral glucose load. Insulin resistance and beta-cell function were calculated using HOMA. Leptin levels were found to be associated with all measures of beta-cell secretion: with fasting and 2 hours insulin and C-peptide, with intact and des-31,32-proinsulin concentrations, and with beta-cell secretion estimated with HOMA. This association was independent of age and body fat in women, but in men, associations with insulin and C-peptide weakened after controlling for fat mass, whereas those with intact and des-31,32-proinsulin disappeared. Fasting insulin and C-peptide levels were also significant in multiple regression analyses, besides gender and fat mass. Insulin resistance, as assessed by HOMA, was strongly correlated with leptin, also after correction for age and fat mass in both genders. We conclude that, besides fat mass and gender - the main determinants for leptin levels in type 2 diabetic subjects as in healthy subjects - insulin secretion and the degree of insulin resistance also seem to contribute significantly to leptin levels.

Polymorphisms in the leptin receptor gene, body composition and fat distribution in overweight and obese women

OBJECTIVE

Leptin is an adipocyte-secreted hormone involved in body weight regulation, acting through the leptin receptor, localised centrally in the hypothalamus as well as peripherally, amongst others on adipose tissue. The aim of this study was to evaluate whether polymorphisms in the leptin receptor (LEPR) gene were related to obesity and body fat distribution phenotypes, such as waist and hip circumferences and the amount of visceral and subcutaneous fat.

METHODS

Three known LEPR polymorphisms, Lys109Arg, Gln223Arg and Lys656Asn, were typed on genomic DNA of 280 overweight and obese women (body mass index (BMI)>25), aged 18-60 y. General linear model (GLM) analyses were performed in 198 pre- and 82 postmenopausal women, adjusting the data for age and menopausal state, plus fat mass for the fat distribution phenotypes.

RESULTS

No associations were found between the LEPR polymorphisms and BMI or fat mass. In postmenopausal women, carriers of the Asn656 allele had increased hip circumference (P=0.03), total abdominal fat (P=0.03) and subcutaneous fat (P=0.04) measured by CT scan. Total abdominal fat was also higher in Gln223Gln homozygotes (P=0.04). Also in postmenopausal women, leptin levels were higher in Lys109Lys homozygotes (P=0.02).

CONCLUSION

In conclusion, polymorphisms in the leptin receptor gene are associated with levels of abdominal fat in postmenopausal overweight women. Since body fat distribution variables were adjusted for fat mass, these results suggest that DNA sequence variations in the leptin receptor gene play a role in fat topography and may be involved in the predisposition to abdominal obesity.

Regulation of leptin production

Fat mass is the primary determinant of serum leptin in humans with energy intake and gender also having significant effects. Gender influences leptin production through the reproductive hormones. Glucose metabolism links food intake to leptin production and hexosamine biosynthesis appears to play a significant role in this process. Catecholamines inhibit leptin production and the sympathetic nervous system has been proposed to be the efferent arm of the leptin signal transduction pathway between adipose tissue and the central nervous system. Additional regulators of leptin production include glucocorticoids, cytokines and agonists of PPAR gamma. In addition to adipose tissue, leptin is produced in several other places including placenta, bone marrow, stomach, muscle and perhaps brain, thus increasing the number of potential regulatory roles for this hormone. Future work will be needed to fully elucidate the mechanisms regulating leptin synthesis/release in each tissue as well as its regulatory functions.

Resistin / Fizz3 expression in relation to obesity and peroxisome proliferator-activated receptor-gamma action in humans

Recent studies in murine models suggest that resistin (also called Fizz3 [1]), a novel cysteine-rich protein secreted by adipocytes, may represent the long-sought link between obesity and insulin resistance (2). Furthermore, peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists appear to inhibit resistin expression in murine adipocytes, providing a possible explanation for the mode of action of this class of insulin sensitizers (2). Using a fluorescent real-time reverse transcriptase-polymerase chain reaction-based assay, we found that resistin mRNA levels in whole adipose tissue samples were increased in morbidly obese humans compared with lean control subjects. However, in freshly isolated human adipocytes, resistin mRNA levels were very low and showed no correlation with BMI. Resistin mRNA was undetectable in preadipocytes, endothelial cells, and vascular smooth muscle cells, but it was readily detectable in circulating mononuclear cells. Although exposure of human mononuclear cells to PPAR-gamma agonists markedly upregulated fatty acid-binding protein-4 expression, these agents had no effect on mononuclear cell resistin expression. Finally, resistin mRNA was undetectable in adipocytes from a severely insulin-resistant subject with a dominant-negative mutation in PPAR-gamma (3). We conclude that the recently described relationships of murine resistin/Fizz3 expression with obesity, insulin resistance, and PPAR-gamma action may not readily translate to humans. Further studies of this novel class of proteins are needed to clarify their roles in human metabolism.

Hexosamines regulate leptin production in human subcutaneous adipocytes

The hexosamine biosynthetic pathway has recently been proposed as a mechanism through which cells "sense" nutrient flux to regulate leptin release. This study was undertaken to examine the regulation of leptin production by hexosamines in human adipocytes. Adipose tissue UDP-N-acetylglucosamine, an end product of hexosamine biosynthesis, was elevated 3.2-fold, and ob messenger ribonucleic acid was elevated 2-fold in the sc adipose tissue of 17 obese [body mass index (BMI), 41.3+/-12.0 kg/m2; age, 31+/-5 yr] subjects compared to 14 lean (BMI, 23.4+/-1.6 kg/m2; age, 33+/-11 yr) subjects. Serum leptin was increased 2.7-fold in the obese subjects. A significant positive relationship was found between adipose tissue UDP-N-acetylglucosamine and BMI (Spearman correlation = 0.576; P = 0.0007) and between UDP-N-acetylglucosamine and serum leptin (Spearman correlation = 0.4650; P = 0.0145). Treatment of isolated sc adipocytes with 1 mmol/L glucosamine, an intermediate product in UDP-N-acetylglucosamine biosynthesis, increased leptin release 21.4+/-17.6% (mean +/- SD) over control (P = 0.0365) and 74.5+/-82.8% over control (P = 0.0271) in adipocytes from lean (BMI, 23.2+/-1.6 kg/m2; n = 6) and obese (BMI, 55.4+/-13.0 kg/m2,; n = 9) subjects, respectively, by 48 h of culture. Inhibition of UDP-N-acetylglucosamine biosynthesis with 6-diazo-5-oxo-norleucine reduced glucose-stimulated leptin release from cultured adipocytes 21.8+/-32.4% (P = 0.0395; n = 12) and ob gene expression 19.9+/-18.9% (P = 0.0208; n = 8) by 48 h of treatment. These findings suggest that hexosamine biosynthesis regulates leptin production in human adipose tissue.

Human leptin: from an adipocyte hormone to an endocrine mediator

Leptin is a mainly adipocyte-secreted protein that was discovered 5 years ago. Most of the research following this discovery focused on the role of leptin in body weight regulation, aiming to illuminate the pathophysiology of human obesity. However, more and more data are emerging that leptin is not only important in the regulation of food intake and energy balance, but that it also has a function as a metabolic and neuroendocrine hormone. It is now clear that it is especially involved in glucose metabolism, as well as in normal sexual maturation and reproduction. Besides this, interactions with the hypothalamic-pituitary-adrenal, thyroid and GH axes and even with haematopoiesis and the immune system have also been described. It has been shown that leptin secretion by the adipocyte is partly regulated by other hormones, such as insulin, cortisol, and sex steroids, mainly testosterone. Also, other hormones like thyroid hormone and GH are possibly involved in leptin synthesis. Leptin itself exerts effects on different endocrine axes, mainly on the hypothalamic-pituitary-gonadal axis and on insulin metabolism, but also on the hypothalamic-pituitary-adrenal, thyroid and GH axes. Leptin may thus be considered a new endocrine mediator, besides its obvious role in body weight regulation.

Intensity of acute exercise does not affect serum leptin concentrations in young men

PURPOSE

We examined the effects of exercise intensity on serum leptin levels.

METHODS

Seven men (age = 27.0 yr; height = 178.3 cm; weight = 82.2 kg) were tested on a control (C) day and on 5 exercise days (EX). Subjects exercised (30 min) at the following intensities: 25% and 75% of the difference between the lactate threshold (LT) and rest (0.25 LT, 0.75 LT), at LT, and at 25% and 75% of the difference between LT and VO2peak (1.25 LT, 1.75 LT).

RESULTS

Kcal expended during the exercise bouts ranged from 150 +/- 11 kcal (0.25 LT) to 529 +/- 45 kcal (1.75 LT), whereas exercise + 3.5 h recovery kcal ranged from 310 +/- 14 kcal (0.25 LT) to 722 +/- 51 kcal (1.75 LT). Leptin area under the curve (AUC) (Q 10-min samples) for all six conditions (C + 5 Ex) was calculated for baseline (0700-0900 h) and for exercise + recovery (0900-1300 h). Leptin AUC for baseline ranged from 243 +/- 33 to 291 +/- 56 ng x mL(-1) x min; for exercise + recovery results ranged from 424 +/- 56 to 542 +/- 99 ng x mL(-1) x min. No differences were observed among conditions within either the baseline or exercise + recovery time frames. Regression analysis confirmed positive relationships between serum leptin concentrations and percentage body fat (r = 0.94) and fat mass (r = 0.93, P < 0.01).

CONCLUSION

We conclude that 30 min of acute exercise, at varying intensity of exercise and caloric expenditure, does not affect serum leptin concentrations during exercise or for the first 3.5 hours of recovery in healthy young men.

Leptin production in adipocytes from morbidly obese subjects: stimulation by dexamethasone, inhibition with troglitazone, and influence of gender

This study examined the regulation of leptin production by dexamethasone and troglitazone. Subcutaneous and omental adipose tissue was obtained during bariatric surgical procedures (30 women and 16 men; body mass index, 52.5 +/- 1.7 kg/m2, age, 39 +/- 2 yr), and adipocytes were cultured in suspension. Subcutaneous adipocytes from females released significantly more leptin than did omental cells from the same subject (P < 0.05), but basal leptin release was not different in adipocytes from these depots in males. Dexamethasone (0.1 micromol/L) significantly increased leptin release within 24 h from sc (135 +/- 13% of control) and omental (227 +/- 53%) adipocytes of females, but not males. Dexamethasone-stimulated leptin production at 48 h was significantly greater in the omental adipocytes of females (398 +/- 64% of control) than in sc adipocytes of females (207 +/- 21%) or the omental (211 +/- 33%) and sc (180 +/- 23%) adipocytes of males. Troglitazone (10 micromol/L; 48 h) significantly inhibited dexamethasone-stimulated leptin release in sc (57 +/- 10.7% inhibition) and omental adipocytes (134 +/- 26% inhibition). There was no gender-related difference in the effect of troglitazone to inhibit dexamethasone-stimulated leptin release. Troglitazone significantly inhibited basal leptin production from omental adipocytes by 15.0 +/- 5.2%. The effect of dexamethasone and troglitazone to regulate leptin release was mediated through changes in ob gene expression, but did not involve changes in glucose uptake or metabolism to lactate. The data suggest that adipocytes from females are more responsive to the stimulatory effect of dexamethasone in vitro than are adipocytes from males. If adipocytes from females are more responsive to relevant in vivo stimuli for leptin secretion such as insulin or glucose, this could contribute to the gender difference in serum leptin. The data also suggest that leptin release from omental adipocytes may be more responsive to hormonal and nutrient regulation in vivo than are sc adipocytes.

Hexosamines stimulate leptin production in transgenic mice

Hexosamine flux has been shown to mediate aspects of nutrient sensing in insulin sensitive tissues and has been hypothesized to represent a satiety signal that results in shunting of fuel toward storage as fat. It has been recently reported that in vitro treatment of fat and muscle cells with hexosamines and acute glucosamine infusion in intact rats stimulate leptin secretion. In order to investigate the effects of chronic, physiologic increases in hexosamine flux on leptin we have examined leptin mRNA and serum leptin in mice overexpressing the rate-limiting enzyme for hexosamine synthesis, GFA, in muscle and fat. Increased levels of UDP-N-acetylglucosamine, the principal end-product of the hexosamine pathway were seen in transgenic fat, consistent with the overexpression of GFA. After overnight fasting, the transgenic mice were hyperleptinemic compared to littermate controls (4.5+/-0.5 ng/ml in transgenic, 2.8+/-0.2 in control, p = 0.005) despite equal body weights. In the random-fed state, the leptin levels of control mice increased to 4.1+/-0.5 ng/ml (p = 0.01) whereas the leptin levels in the transgenics did not increase any further (3.7+/-0.4 ng/ml). Leptin mRNA levels were also increased in transgenic fat (2.7+/-0.6 in transgenic compared to 0.8+/-0.2 in control, arbitrary units normalized to actin, p < 0.007). Despite increased leptin, the transgenic animals did not have lower body fat content. We conclude that hexosamine flux in fat regulates leptin synthesis and secretion.

Localization of leptin receptor-like immunoreactivity in the corticotropes, somatotropes, and gonadotropes in the ovine anterior pituitary

Leptin is a secreted product of the adipocytes that regulates a variety of functions. The presence of the leptin receptor (LR) has been demonstrated in the endocrine and neuroendocrine tissue, but only limited information is available regarding cell-specific expression in the anterior pituitary gland. We have used double-label immunofluorescence histochemistry to study the distribution of LR-like immunoreactivity (LR-ir) in the corticotropes, somatotropes, and gonadotropes of the ovine anterior pituitary. LR-ir was found in 34% of cells in the pars distalis and 94% of the cells in the pars tuberalis. In the pars distalis, LR-ir was present in 27% of corticotropes, 69% of somatotropes, and 29% of gonadotropes. In contrast, 90% of the gonadotropes in the pars tuberalis were immunopositive for LR. There was no alteration in the number of gonadotropes containing LR-ir during the various phases of the estrous cycle (n = 3/group) in the pars distalis (luteal phase, 36%; follicular phase, 32%; and estrous phase, 32%). In conclusion, we show that, in the pars distalis, LR-ir is expressed to a greater extent in the somatotropes than in the gonadotropes or corticotropes. This is in accordance with the documented effects of leptin on pituitary GH secretion. The differential expression of LR-ir between the gonadotropes of the pars distalis and pars tuberalis probably reflects the different phenotypes of the cells in these two regions. Lower levels of LR-ir expression in gonadotropes and corticotropes of the pars distalis may suggest that leptin does not substantially influence these particular cells, at least in this species.

Tumor necrosis factor-alpha inhibits leptin production in subcutaneous and omental adipocytes from morbidly obese humans

This study was undertaken to examine the regulation of leptin production from human adipocytes by tumor necrosis factor-alpha (TNFalpha). Adipocytes were isolated from adipose tissue obtained during bariatric surgical procedures (17 women and 3 men; body mass index, 52.5 +/- 2.4 kg/m2; age, 40 +/- 3 yr) and cultured in suspension. Leptin release from sc adipocytes was inhibited 17.7 +/- 5.2% (P < 0.01), 21.6 +/- 4.3% (P < 0.005), and 37.1 +/- 7.2% (P < 0.05) by 1, 10, and 100 ng/mL TNFalpha, respectively, after 48 h in culture. At 100 ng/mL, significant inhibition of leptin release (25.8 +/- 9.7%; P < 0.05) was detected by 24 h. TNFalpha (10 ng/mL) had no effect on dexamethasone (0.1 micromol/L)-stimulated leptin production in sc adipocytes. In omental adipocytes TNFalpha inhibited leptin release 21.0 +/- 9.6% and 40.8 +/- 6.3% at 10 and 100 ng/mL by 48 h (P < 0.05). Significant inhibition ofleptin release from omental adipocytes was observed at 24 h with 100 ng/mL TNFalpha (P < 0.05). Anti-TNFalpha antibody completely blocked TNFalpha inhibition of leptin release. The ob messenger ribonucleic acid was significantly reduced (23.6 +/- 5.9%) after 48 h of TNFalpha (100 ng/mL) treatment (P < 0.025). TNFalpha had no effect on glucose uptake or lactate production in sc and omental adipocytes. The data suggest that the direct paracrine effect of adipose-derived TNFalpha is inhibition of leptin production.

Serum leptin during recovery following maximal incremental and prolonged exercise

This study investigated the delayed circulating leptin response to maximal and prolonged treadmill exercise. Six healthy untrained males performed three sessions after an overnight fast: control, maximal exercise, and prolonged exercise at 50% of maximal oxygen consumption. Blood samples were collected prior to exercise, at the end of exercise, and at 60, 120, 180, and 240 min following exercise and control sessions. Blood samples were analyzed for serum leptin, insulin, glucose, free fatty acids, and glycerol. Hemoglobin and hematocrit were measured to correct for plasma volume changes. Resting energy expenditure (REE) and body fat (BF) were also assessed. Immediately at the end of maximal and prolonged exercise, and during the 4 hours of recovery, serum leptin levels did not change significantly compared to their respective baseline values. At 240 min of recovery serum leptin decreased 7% and 9% (p>0.05) from the baseline in the maximal and prolonged sessions, respectively. In the control experiment serum leptin decreased 27% from the baseline at 240 min of the recovery (p < 0.05). No significant differences were found in leptin values between the control and exercise sessions. Control serum leptin was positively correlated (p < 0.05) to BF (r = 0.88) and glucose (r=0.96), and negatively correlated to REE (r= -0.81). In conclusion, maximal or prolonged exercise do not appear to have an influence on circulating serum leptin in the delayed (4 hr) post exercise recovery period.

Leptin secretion in Cushing's syndrome: preservation of diurnal rhythm and absent response to corticotropin-releasing hormone

The normal inverse relationship between leptin and cortisol is lost in chronic hypercortisolism. We studied this apparent dysregulation in patients with Cushing's syndrome to investigate 1) the effect of chronic hypercortisolemia on the circadian rhythm of leptin secretion, 2) the response of leptin after administration of CRH, and 3) the short term effect of curative surgery on leptin. The preoperative morning leptin concentration was 54.2 +/- 8.1 ng/mL, and the nighttime value was 68.6 +/- 9.8 ng/mL, reflecting a mean rise of 32.8 +/- 7.6%, similar to the nocturnal increase observed in normal subjects. By contrast, cortisol's diurnal variation (21.8 +/- 1.7 vs. 16.9 +/- 1.1 mg/dL) was blunted. In women, but not men, body mass index correlated with leptin (P = 0.001). Preoperative ACTH and cortisol (both P < 0.0001), but not leptin levels increased after CRH. Ten days after surgery, basal cortisol values were subnormal (1.1 +/- 0.6 mg/dL), but leptin levels remained unchanged and did not increase after CRH. Body mass index and insulin also remained unchanged. Insulin, but not age, urinary free cortisol, or plasma cortisol correlated with leptin (P < 0.05). In summary, patients with Cushing's syndrome have moderately elevated leptin levels that maintain an intact circadian rhythm but do not respond to acute or subacute alterations of cortisol.

Weight loss and leptin changes in individuals with type 2 diabetes

OBJECTIVE

To identify variables associated with leptin change in subjects with type 2 diabetes after 3 weeks and 20 weeks of weight loss.

RESEARCH METHODS AND PROCEDURES

Subjects with type 2 diabetes treated with diet or sulfonylureas (n = 54) were enrolled in a 20-week behavioral weight control program. Sulfonylureas were stopped > or =2 weeks before study entry. Seven subjects who restarted sulfonylureas after week 3 had their data analyzed separately after this point.

RESULTS

Leptin, fasting plasma glucose, and insulin levels were measured at baseline and at 3, 10, and 20 weeks. After 3 weeks, subjects lost 2.7+/-2.0 kg (p<0.001), and had significant decreases in leptin (5.2+/-7.0 ng/mL, p<0.001), fasting plasma glucose (1.8+/-1.8 mmol/L, p<0.001), and insulin (23+/-60 pmol/L, p<0.03). Between week 3 and week 20, subjects lost an additional 6.3+/-4.4 kg (p<0.001), but had no further changes in leptin. The primary determinants of leptin change at all time-points were weight loss and initial leptin level. Changes in insulin were not related to changes in leptin after controlling for the effects of weight loss. At week 20, more recent weight loss (week 10 to week 20) was as strong a predictor of overall change in leptin as overall weight loss (baseline to 20 week). Subjects who restarted sulfonylureas had an increase in both leptin levels (+1.9+/-9.0 ng/mL, p<0.05) and insulin levels (+23+/-65 pmol/L, p<0.05), despite significant overall weight loss (-7.4+/-4.0 kg, p<0.01). Initial changes in leptin (0 weeks to 3 weeks) did not affect subsequent ability to lose weight.

DISCUSSION

Both short- and long-term changes in weight had an effect on leptin changes in individuals with type 2 diabetes. Although physiological insulin changes did not independently influence changes in leptin concentration with weight loss, increases in insulin levels with sulfonylurea therapy were associated with increases in leptin levels despite weight loss.

Clinical endocrinology of human leptin

Since the discovery of leptin, a boom of scientific knowledge became available about the OB-protein gene and its role and significance in weight regulation. Both from animal and human research data, serum leptin can probably be considered as one of the best biological markers to reflect total body fat, and this finding is true over a wide range of body mass indexes (BMIs) and in different pathologies: in normal weight, anorexic and obese subjects; in non insulin-dependent diabetes mellitus (NIDDM) patients, PCO women, Prader-Willi children and subjects with hypogonadism and growth hormone deficiency. Gender differences clearly exist, probably related to sex hormone differences, and from fat distribution studies it could be shown that subcutaneous fat is much more related to serum leptin concentrations than visceral fat: also leptin messenger-RNA (m-RNA) expression is significantly higher in subcutaneous fat from human obese subjects. Leptin is not only correlated to a series of endocrine parameters such as insulin, insulin-like growth factor, (IGF) and SHBG, it seems involved as a mediator in some endocrine mechanisms (onset of puberty, insulin secretion, etc) as well. Weight loss will reduce human leptin concentrations, whereas the administration of human recombinant leptin seems to show only limited effects.

Serum leptin levels in women throughout pregnancy and the postpartum period and in women suffering spontaneous abortion

OBJECTIVE

In pregnancy, important changes occur in the body weight of the mother, caused by sodium and water retention and by an increase in body fat tissue, but the mechanisms that regulate maternal and foetal changes in fat mass are poorly understood. Leptin is a hormone produced by adipocytes in order to regulate food intake and energy expenditure at the hypothalamic level in man. In order to verify whether leptin participates in the changes in body composition during pregnancy and postpartum, 630 healthy women were studied at specific time periods and leptin and auxological parameters were determined.

DESIGN

A cross-sectional study in which leptin levels were measured in women at specific time periods related to pregnancy. Each woman was assessed only once.

PATIENTS

630 women participated in the study, and were divided into categories as follows: Group A, 29 internal controls, with no previous or current pregnancy; Group B, 73 women in the first trimester of pregnancy; Group C, 60 women in the 24 h before delivery; Group D, 212 women in the 24 h postpartum; Group E, 93 women in the eightH postpartum week (2 months group); Group F, 71 women in the sixteenth postpartum week (4 months group); Group G, 20 women in the sixth month postpartum; Group H, 23 women one year postpartum; Group I, 20 women two years postpartum; finally Group J, of 29 women who had suffered spontaneous abortion in the first trimester of pregnancy and were studied in the 24 h after the stillborn delivery.

MEASUREMENTS

Serum leptin levels were measured in duplicate by radioimmunoassay using commercial kits. Height and weight was measured and BMI (kg/m2) calculated.

RESULTS

Compared with serum leptin in the control group (11.7 +/- 1.0 micrograms/l), a non significant (NS) increase was observed in the first trimester of pregnancy (14.3 +/- 1.4 micrograms/l), with no parallel changes in body weight. A reduction in leptin occurred in the 24 h after delivery (9.4 +/- 1.4 micrograms/l, P = 0.02). After delivery a progressive increase in leptin concentrations was observed, 13.3 +/- 1.5 micrograms/l at two months (NS) and 17.4 +/- 2.6 micrograms/l at four months (P = 0.035 vs controls). Afterwards leptin values decreased towards normal values at 6, 12 and 24 months after delivery 14.4 +/- 1.8 micrograms/l; 12.9 +/- 1.6 micrograms/l; and 10.1 +/- 1.1 micrograms/l respectively (all NS). With the exception of the postpartum group, a significant correlation was observed between leptin concentrations and body weight or BMI in each group of women studied. In the women who suffered spontaneous abortion in the first trimester of pregnancy a reduction in leptin levels occurred (8.8 +/- 1.0 micrograms/l, P = 0.001 vs first trimester group).

CONCLUSION

Serum leptin concentrations rose slightly during pregnancy, fell following delivery and subsequently increased during the first six months postpartum. These variations were unrelated to changes in body composition, and may be responsible for the postpartum weight gain observed in some women. Abnormally low serum leptin levels were observed in women suffering spontaneous abortion in the first trimester of pregnancy.

Association of leptin and hunger-satiety ratings in obese women

OBJECTIVE

To measure leptin, insulin and cholecystokinin (CCK) concentrations in obese women on calorie restriction and to determine their correlation with hunger-satiety ratings. Although it has been proposed to play a role in appetite regulation, the effects of physiological concentrations of these hormones on hunger-satiety in humans have not yet been well established.

DESIGN

Prospective metabolic study. A two week 'wash-in period' followed by a three-week observation period, during which each subject underwent six measurements of satiety, blood parameters and body weight.

SETTING

Energy Metabolism Research Unit, Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, Alabama, USA.

SUBJECTS

22 moderately to severely overweight women (mean age: 45 +/- 8 y; body mass index (BMI): 33 +/- 6 kg/m2).

INTERVENTION

Energy restriction, in the form of a 3.3 MJ (800 kcal) diet during five weeks.

MAIN OUTCOME MEASUREMENTS

Fasting blood levels of leptin, insulin, glucose and CCK, fasting hunger-satiety scores and body weight.

RESULTS

The mean (+/- s.d.) fasting serum leptin concentration at the beginning of the observation period was 26.1 +/- 15.9 ng/ml (range: 6.7-59.8 ng/ml). Leptin concentrations correlated positively with body weight (P < 0.0001). Furthermore, reductions in body weight were associated with decreases in fasting leptin levels (P = 0.002). Leptin concentrations correlated with serum levels of insulin (P = 0.0001) and CCK (P = 0.06), but in multivariate analysis including insulin, CCK and glucose, only leptin had a significant relationship with satiety (P = 0.04). This relationship was linear.

CONCLUSIONS

These results confirm the association between leptin levels, body weight and serum insulin. We also showed that higher serum leptin levels correlated with greater feelings of fullness, a relationship which was not blunted in the more obese subjects. These findings suggest that leptin is a satiety hormone that reduces appetite, even in obese individuals, and that weight gain must be due to other factors, overriding this feed-back regulation.

Effect of obesity on estradiol level, and its relationship to leptin, bone maturation, and bone mineral density in children

The purpose of this study was to investigate 24-h estradiol and leptin levels in obese and nonobese children to further understand the roles of estradiol and leptin in obesity and puberty. We measured serum estradiol, leptin, insulin, glucose, and GH levels every hour for 24 h in 18 obese (12 females and 6 males) and 30 nonobese (11 females and 19 males) prepubertal and early pubertal (stages 1-2) children. Bone age and dual energy x-ray absortiometry (DEXA) were obtained upon completion of the 24-h study. Obese children were significantly younger than nonobese children, with no difference in pubertal stage, height, or bone age between the 2 groups. Obese children had greater bone age to chronological age ratios than nonobese children, indicating a more advanced rate of bone maturation. Mean 24-h estradiol levels correlated significantly with chronological age and bone age as well as with insulin-like growth factor I, insulin-like growth factor-binding protein-3, dehydroepiandrosterone sulfate, mean 24-h GH, and lean body mass. Mean 24-h estradiol levels did not differ between obese and nonobese children [1.65+/-1.47 us. 2.75+/-3.30 pmol/L (0.45+/-0.40 vs. 0.75+/-0.90 pg/mL), respectively]. Similar mean 24-h estradiol levels in obese and nonobese children are consistent with the increased bone maturation of the obese children. Estradiol did not correlate significantly with DEXA fat mass, body mass index, or arm fat measures of adiposity. Obese children had higher 24-h mean leptin concentrations than nonobese children (28.6+/-17.4 vs. 6.8+/-7.1 ng/mL; P < 0.001). Leptin concentrations positively correlated with DEXA fat mass, body mass index, and arm fat measurement of adiposity. Girls had higher 24-h mean leptin levels than boys when controlling for adiposity. Estradiol and leptin concentrations fluctuated over a 24-h period in both groups, with all children having higher leptin concentrations at night and higher estradiol concentrations in the morning. This diurnal rhythm was of a similar pattern, but at higher levels for leptin and lower levels for estradiol in the obese children compared to nonobese children. There was no significant correlation between estradiol and leptin levels. Bone mineral density, as measured by DEXA, did not differ between obese and nonobese children. Similar bone mineral density values in obese and nonobese children are consistent with the increased bone maturation of the obese children. Bone mineral density was not correlated with estradiol or leptin level in these children. In conclusion, obese children had similar estradiol levels and equivalent bone ages at a younger chronological age than nonobese children. Leptin was higher in these obese children, but did not correlate with estradiol level or bone age. These findings suggest that the role of leptin in both obesity and pubertal development is not directly correlated with the estradiol level.

Acute changes in free-fatty acids (FFA) do not alter serum leptin levels

Leptin, the product of the ob gene, is a recently discovered hormone secreted by adipocytes. Serum leptin concentrations increase in correlation with the percentage of body fat, but besides that little is known about the physiological actions of leptin in humans. The aim of this study was to assess the influence of changes in circulating free-fatty acids on serum leptin levels. Increases in plasma FFA levels (p < 0.02) were obtained in a group of normal subjects following the administration of intralipid plus heparin (250 ml 10% Intralipid plus 5000 U heparin). FFA reduction was achieved through the administration of acipimox (250 mg, orally, at 0 min and at 210 min), a lipid-lowering drug devoid of side effects, to a group of normal (p < 0.02) and obese subjects (p < 0.05). An increase in circulating FFA levels in normal subjects (n = 6), following administration of a lipid-heparin infusion, failed to modify plasma leptin levels as assessed by the area under the curve (AUC; mean +/- SE 892 +/- 168 for placebo vs 896 +/- 260 following intralipid plus heparin). Similarly, whereas acipimox pretreatment induced a reduction in FFA levels compared to placebo in normal (n = 6) and obese subjects (n = 8), it also failed to modify plasma leptin levels at any time-point studied. The results indicate that short-term reduction or increase in circulating FFA are not associated to changes in plasma leptin levels.

Effect of hydrolyzed guar fiber on fasting and postprandial satiety and satiety hormones: a double-blind, placebo-controlled trial during controlled weight loss

OBJECTIVE

To evaluate the effects of a completely soluble fiber on fasting and postprandial hormone levels, respiratory quotient (RQ) and subjective ratings of satiety during a controlled weight-loss program.

DESIGN

In a five-week prospective, randomized, double-blind study, a 3.3 MJ (800 kcal)/d diet was provided during a two-week wash-in period. Then, during the intervention weeks, separated by a one-week wash-out period, a 3.3 MJ (800 kcal) formula containing either 20 g fiber or placebo daily, was given in a cross-over design and on days 1, 3 and 7 of the intervention weeks (weeks 3 and 5) measurements were taken after an overnight fast.

SUBJECTS

25 obese but otherwise healthy females (age: 46+/-6 y, body mass index (BMI): 35+/-6 kg/m2) were studied.

MEASUREMENTS

Body weight; hunger/satiety ratings; glucose, insulin, cholecystokinin (CCK) and leptin concentrations; RQ during the intervention weeks.

RESULTS

In the fasting state, the supplement had no effect on any of the measured parameters, including blood concentrations of glucose, insulin, CCK, and leptin, RQ and satiety ratings. In the 2 h postprandial period following the test meal, none of the measured parameters differed significantly from that following the non-fiber-supplemented meal, except for the CCK response. CCK demonstrated an overall higher concentration after the fiber-supplemented meal (P=0.007), even after adjustment for age, weight, height and treatment sequence. The postprandial peak in CCK also occurred earlier (at 15 min vs 30 min) after completion of the fiber-supplemented meal.

CONCLUSIONS

The results indicated that a hydrolyzed guar gum fiber supplement produced a heightened postprandial CCK response, but did not alter other satiety hormones or increase satiety ratings, in either the fasting or the postprandial state.

Interaction between leptin and neuropeptide Y on in vivo growth hormone secretion

Leptin, the product of the ob gene, is a recently discovered hormone secreted by adipocytes that regulates food intake and energy expenditure. Leptin has recently been shown to play a stimulatory role on GH secretion. The aim of the present study was to investigate whether leptin regulation of GH secretion was mediated by hypothalamic neuropeptide Y (NPY). We assessed the effect of leptin administration (10 microg, i.c.v.) and/or NPY (4 microg, i.c. v.) on fasted rats. Furthermore we administered leptin antiserum (10 microl, i.c.v.), anti-NPY serum (5 microl, i.c.v.) or normal rabbit serum (10 microl, i.c.v.) to freely moving fed rats. Spontaneous GH secretion was assessed over 6 h with blood samples taken every 15 min. Fed rats treated with anti-NPY serum exhibited a normal ultradian GH rhythm. However, administration of anti-NPY serum (5 microl, i.c.v., at 120 min) completely reversed the suppression induced by antileptin serum (10 microl, i.c.v., at 0 min) on plasma GH levels (area under the curve, AUC, 168 +/- 72 vs. 1,287 +/- 430 ng/ml/6 h; p < 0.01). In fasted rats, following NPY administration, GH levels remained suppressed throughout the 6 h studied. Besides, NPY administration completely blunted leptin-induced GH secretion as assessed by the AUC (28.5 +/- 11 vs. 520 +/- 220 ng/ml/6 h; p < 0. 01). Thus, it is possible that NPY mediates the effects of leptin on GH secretion. Alternatively, leptin and NPY could act through parallel pathways to alter GH release with NPY overcoming the stimulatory effect exerted by leptin on plasma GH levels.

The Ob protein (leptin) and the kidney

Mutation of the Ob gene, which encodes for leptin, or mutation of the leptin receptor leads to obesity in mice. Humans, for the most part, have a positive correlation of leptin with body fat mass suggesting possible defects in leptin effector mechanisms that may contribute to obesity. As patients on hemodialysis have difficulty with appetite, we investigated whether leptin is cleared by the kidney and is elevated in hemodialysis patients. In patients with intact renal function there was a net renal uptake of 12% of circulating leptin, whereas in patients with renal insufficiency there was no renal uptake of leptin. In a separate cohort of 36 patients with end-stage renal disease (ESRD), peripheral leptin levels factored for body mass index was increased by fourfold as compared to a group of healthy controls (N = 338). The leptin receptor exists in a long and short form, with the long form primarily expressed in the hypothalamus but also in the lungs and kidneys of the mouse. Further studies are necessary to clarify the role of leptin in regulating appetite in patients with ESRD and the role of leptin in directly affecting kidney function via its receptors.

A new paradigm for type 2 diabetes mellitus: could it be a disease of the foregut?

SUMMARY BACKGROUND DATA

We previously reported, in a study of 608 patients, that the gastric bypass operation (GB) controls type 2 diabetes mellitus in the morbidly obese patient more effectively than any medical therapy. Further, we showed for the first time that it was possible to reduce the mortality from diabetes; GB reduced the chance of dying from 4.5% per year to 1% per year. This control of diabetes has been ascribed to the weight loss induced by the operation. These studies, in weight-stable women, were designed to determine whether weight loss was really the important factor.

METHODS

Fasting plasma insulin, fasting plasma glucose, minimal model-derived insulin sensitivity and leptin levels were measured in carefully matched cohorts: six women who had undergone GB and had been stable at their lowered weight 24 to 30 months after surgery versus a control group of six women who did not undergo surgery and were similarly weight-stable. The two groups were matched in age, percentage of fat, body mass index, waist circumference, and aerobic capacity.

RESULTS

Even though the two groups of patients were closely matched in weight, age, percentage of fat, and even aerobic capacity, and with both groups maintaining stable weights, the surgical group demonstrated significantly lower levels of serum leptin, fasting plasma insulin, and fasting plasma glucose compared to the control group. Similarly, minimal model-derived insulin sensitivity was significantly higher in the surgical group. Finally, self-reported food intake was significantly lower in the surgical group.

CONCLUSIONS

Weight loss is not the reason why GB controls diabetes mellitus. Instead, bypassing the foregut and reducing food intake produce the profound long-term alterations in glucose metabolism and insulin action. These findings suggest that our current paradigms of type 2 diabetes mellitus deserve review. The critical lesion may lie in abnormal signals from the gut.

Relationship of leptin concentration to gender, menopause, age, diabetes, and fat mass in African Americans

This investigation was designed to determine the relationship of leptin concentration to gender, sex hormones, menopause, age, diabetes, and fat mass in African Americans. Participants included 101 African Americans, 38 men (mean age, 34.2 +/- 7.4 years), 29 age-matched premenopausal women (mean age, 32.6 +/- 3.7 years), and 36 postmenopausal women (mean age, 57.8 +/- 5.9 years). The women were not taking exogenous sex hormones, and 12 subjects were diabetic. Percent body fat was calculated with the Siri formula, fat mass (FM) was calculated as weight x percent body fat, and Fat-free mass (FFM) was calculated as weight minus FM. Fasting plasma was assayed for leptin, estradiol, free testosterone, glucose, and insulin concentrations. The nondiabetics had an oral glucose tolerance test (OGTT). The diabetics compared with the non-diabetics had a higher central fat index (p=0.04) but otherwise were similar to nondiabetics in all parameters measured. Body mass index, percent body fat, and FM were greater in women than men (p<0.001). Leptin concentrations in men, premenopausal, and postmenopausal women were: 7.51 +/- 8.5, 33.9 +/- 17.3, 31.4 +/- 22.3 ng/mL. Leptin/FM x 100 in the three groups were: 28.9 +/- 16.1, 98.65 +/- 44.9, 77.1 +/- 44.5 ng/mL/kg. The gender difference in leptin concentration and leptin/FM was significant (p<0.001), but the difference between premenopausal and postmenopausal women was not. In each group, weight, percent body fat, and FM were highly correlated with leptin concentration. Multiple regression analyses with leptin concentration as the dependent variable and age, diabetic status, percent body fat, weight, FM, FFM, estradiol, and free testosterone concentrations as independent variables demonstrated that the determinants of leptin concentration in men was weight only (R=0.83, p<0.001), in premenopausal women it was FM only (R=0.57, p<0.001), and in postmenopausal women it was weight only (R=0.67, p<0.001). With diabetics excluded, the multiple regression analysis was repeated with fasting insulin concentration and the area under the insulin curve during the OGTT included as independent variables. The results for this multiple regression analyses were the same as the first. Therefore, leptin concentration in African Americans is determined by gender and fat mass. Menopause, age, and diabetes do not affect leptin concentration.

Serum leptin levels and energy expenditure in normal weight women

To investigate whether circulating leptin levels are associated with energy expenditure in healthy humans, doubly labeled water energy measurements and food intake assessment were carried out in 27 women (mean age, 48.6 years; weight, 61.9 kg; body mass index, 23.2). Energy expenditure was determined over 13 days. Food intake was measured by 7-day food records. Leptin was measured by radioimmunoassay. Leptin level was strongly associated with percentage body fat (r = 0.59; p < 0.001), fat mass (r = 0.60; p < 0.001), and body mass index (r = 0.41; p = 0.03), but no correlation was observed with energy expenditure (r = 0.02; p = 0.93). After controlling for percentage body fat, a positive association of leptin level with energy expenditure of marginal significance (p = 0.06) was observed. There were no significant univariate associations of age, physical activity, lean body mass, height, or dietary variables with leptin level. When controlling for body fat, a significant positive correlation was observed for percent energy from carbohydrate and negative correlations with dietary fat and alcohol intake. These findings confirm previous associations between leptin and body fat content and suggest a relationship between serum leptin and energy expenditure level in healthy humans.Key words: leptin, energy expenditure, body composition, diet.

Serum leptin levels and energy expenditure in normal weight women

To investigate whether circulating leptin levels are associated with energy expenditure in healthy humans, doubly labeled water energy measurements and food intake assessment were carried out in 27 women (mean age, 48.6 years; weight, 61.9 kg; body mass index, 23.2). Energy expenditure was determined over 13 days. Food intake was measured by 7-day food records. Leptin was measured by radioimmunoassay. Leptin level was strongly associated with percentage body fat (r = 0.59; p < 0.001), fat mass (r = 0.60; p < 0.001), and body mass index (r = 0.41; p = 0.03), but no correlation was observed with energy expenditure (r = 0.02; p = 0.93). After controlling for percentage body fat, a positive association of leptin level with energy expenditure of marginal significance (p = 0.06) was observed. There were no significant univariate associations of age, physical activity, lean body mass, height, or dietary variables with leptin level. When controlling for body fat, a significant positive correlation was observed for percent energy from carbohydrate and negative correlations with dietary fat and alcohol intake. These findings confirm previous associations between leptin and body fat content and suggest a relationship between serum leptin and energy expenditure level in healthy humans.

Weight regulation, leptin and growth hormone

Leptin, the product of the adipose tissue-specific ob gene, is a newly recognized hormone involved in the regulation of metabolism and body composition. Leptin appears to provide information to the central nervous system on the amount of energy stored in the adipose tissue. Serum leptin levels are highly correlated with body fat mass in adults, children and newborns. Obese individuals have significantly higher circulating leptin than normal, lean subjects. In addition, females have higher serum leptin than males with equivalent fat mass. Although leptin correlates with fat mass, circulating concentrations are altered by extremes in energy intake, such as fasting and overfeeding. Defects in leptin or its receptor in the hypothalamus lead to the development of obesity in several rodent models; however, no such deleterious defects have been identified in humans to date. Taken together, these observations suggest that humans may be resistant to their endogenous leptin levels. Despite this, studies in rodents demonstrating that leptin administration can cause weight loss in both ob/ob mice, and in normal weight controls suggest that leptin may be useful in the treatment of human obesity. This review will summarize the current understanding of leptin and its role in the regulation of body composition. In addition, the interaction of leptin with other metabolic hormones including growth hormone will be discussed.

Short- and long-term changes in serum leptin dieting obese women: effects of caloric restriction and weight loss

This study examined the effects of caloric restriction and weight loss on serum leptin concentrations in 49 obese women who participated in a 40-week weight loss program. During the first 12 weeks, half the subjects were provided a 1000 kcal/day low-calorie diet (LCD), compromised of portion-controlled foods, whereas the other half were prescribed a 1200 kcal/day balanced deficit diet (BDD) consisting of self-selected table foods. Thereafter, subjects in both conditions were instructed to consume approximately 1200-1800 kcal/day of self-selected foods, depending on their desired weight change. During the first 6 weeks, weight and serum leptin fell significantly more (P < 0.05) in women in the LCD condition than in the BDD condition. In the former group, the 55% reduction in baseline leptin was 10 times greater than the relative reduction in body weight. Stepwise multiple regression analysis revealed that degree of caloric restriction, but not weight loss, contribution significantly to the variance in the change in leptin at week 6. By contrast, long-term changes in leptin, when subjects had increased their calorie intake, were more strongly related to changes in weight and fat. At week 40, for example, weight loss account for 47% of the variance in the change in leptin. Serum leptin and body fat remained highly correlated after weight loss (r = 0.79, P < 0.001), as before (r = 0.66, P < 0.001). After treatment, however, we observed a greater-than-expected reduction in serum leptin concentrations, as expressed per kilogram of body fat. The significance of this finding remains to be determined.

Leptin plasma levels in healthy Spanish children and adolescents, children with obesity, and adolescents with anorexia nervosa and bulimia nervosa

OBJECTIVES

(1) To investigate normal circulating levels of leptin in children at various stages of pubertal maturation (Tanner stages) according to sex; and (2) to analyze serum leptin levels in pediatric patients with eating disorders (obesity, anorexia nervosa, and bulimia nervosa).

STUDY DESIGN

Fasting leptin levels were studied in normal healthy boys and girls throughout development. Obese pediatric subjects and patients with anorexia nervosa were studied at the time of diagnosis and after 6 months and 1 year of treatment for weight reduction or weight recuperation, respectively. Patients with bulimia nervosa were studied at the moment of diagnosis.

RESULTS

Leptin levels in both boys and girls vary significantly depending on the maturational stage, being low in both sexes at Tanner stage I and rising significantly by Tanner stage III. In girls, there was a further increase by Tanner stage V and a significant decrease in boys, resulting in a sexual dimorphism in Tanner V subjects. In obese prepubertal patients, leptin levels were significantly elevated at the time of diagnosis and declined significantly with weight loss (ANOVA: p < 0.0001). In anorexia nervosa patients' leptin levels are significantly reduced compared with age- and sex-matched controls (p < 0.0001). These levels remain significantly lower even after recovery of at least 10% of the original body weight and 1 year later. In patients with bulimia leptin levels were reduced at the time of diagnosis but were significantly higher than in patients with anorexia.

CONCLUSION

In normal pediatric subjects leptin levels are highly correlated with the body mass index, but this is not the case in eating disorders, where the body mass index is either significantly elevated or reduced. Both age and sex should be taken into consideration when analyzing serum leptin levels.

Influence of endogenous leptin tone on the estrous cycle and luteinizing hormone pulsatility in female rats

Recent data indicate that leptin may well play an important regulatory role in the hypothalamo-pituitary-gonadal axis. In order to further unravel the mechanisms by which leptin acts, we have studied the effect of treatment (8 days) of leptin antiserum (5 microl daily; i.c.v.) on LH pulsatility and estrous cycle in adult female rats. The administration of leptin antiserum led to a marked decrease in LH pulsatility as assessed by the area under the curve (13.5 +/- 4.7 ng/ml) in comparison to rats treated with normal rabbit serum (114 f 53 ng/ml; p < 0.01). Furthermore, rats treated with leptin antiserum showed an impairment of reproductive function as shown by the fact that all rats remained in anestrus. In conclusion, these data show that leptin markedly influences LH secretion and the estrous cycle in the female rat.

Leptin and the regulation of body weight

Leptin has received considerable attention as a newly recognized metabolic hormone and for its potential for therapeutic use in the treatment of human obesity. Furthermore, defects in the leptin signal pathway that result in obesity in animal models have raised the possibility of a similar etiology for obesity in humans. This review will summarize the current findings on leptin in both humans and rodents. These findings will be discussed with respect to our view of the physiology and potential for pathophysiology in leptin-mediated regulation of body weight and composition.