Total energy expenditure and the level of physical activity correlate with plasma leptin concentrations in five-year-old children

Leptin Resistance Does Not Facilitate Migratory Fattening in Ruby-Throated Hummingbirds (Archilochus Colubris)

In mammals, leptin is an important energy homeostasis hormone produced by adipose tissue. Circulating leptin concentrations correlate positively with fat mass and act in a negative feedback fashion to inhibit food intake and increase energy expenditure, thereby preventing fat gain. For some species, leptin resistance is advantageous during times of year where fat gain is necessary (e.g., prior to hibernation). While the function of leptin in birds remains controversial, seasonal leptin resistance may similarly benefit migratory species. Here, we used the ruby-throated hummingbird (Archilochus colubris) to test the hypothesis that leptin resistance promotes fattening prior to migration. We predicted that during the migratory fattening period, leptin levels should correlate positively with fat mass but should not inhibit food intake or increase energy expenditure, resulting in fattening. We tracked the body (fat) mass, the concentration of leptin-like protein in the urine, and the food intake of 12 captive hummingbirds from August 2021 to January 2022. In a subset of hummingbirds, we also quantified voluntary physical activity as a proxy for energy expenditure. We found remarkable age-related variation in fattening strategies, with juveniles doubling their body fat by mid-September and adults exhibiting only a 50% increase. Changes in fat mass were strongly associated with increased food intake and reduced voluntary activity. However, we found no correlation between leptin-like protein concentration and fat mass, food intake, or voluntary activity. Since increased torpor use has been shown to accelerate migratory fattening in ruby-throated hummingbirds, we also hypothesized that leptin is a mediator of torpor use. In an experimental manipulation of circulating leptin, however, we found no change in torpor use, body fat, or food intake. Overall, our findings suggest that leptin may not act as an adipostat in hummingbirds, nor does leptin resistance regulate how hummingbirds fatten prior to migration.

Restlessness and an Increased Urge to Move (Drive for Activity) in Anorexia Nervosa May Strengthen Personal Motivation to Maintain Caloric Restriction and May Augment Body Awareness and Proprioception: A Lesson From Leptin Administration in Anorexia Nervosa

Anorexia nervosa (AN), a disorder of voluntary food restriction leading to severe weight loss in female adolescents, remains an enigma. In particular, the appropriation of the starved thin body into the self-concept in AN is a process insufficiently researched and still poorly understood. Healthy humans undergoing starvation experience a slowing of movements and avoid voluntary exercise. By contrast, AN tends to be not infrequently associated with voluntary, sometimes excessive and/or compulsive exercise. Such deliberate exercise, not reported in starvation, seems to be facilitated by an increased urge for movement and physical restlessness, particular to AN. The increased urge to move would reflect spontaneous daily activity, the energy expended for everything that is not sleeping, eating, or voluntary exercise. Our hypothesis is that the starvation-induced increased urge to move and restlessness may promote the development of AN. Reversal of the fasting state, by either high caloric food or by leptin administration, would be expected to reduce restlessness and the increased urge to move along with improvement in other symptoms in AN. This review explores the idea that such restless activation in AN, in itself and through accelerating body weight loss, might foster the integration of the starving body into the self-concept by (1) enhancing the person’s sense of self-control and sense of achievement and (2) through invigorating proprioception and through intensifying the perception of the changing body shape. (3) Tentative evidence from studies piloting leptin administration in chronic AN patients which support this hypothesis is reviewed. The findings show that short term administration of high doses of leptin indeed mitigated depressive feelings, inner tension, intrusive thoughts of food, and the increased urge to be physically active, easing the way to recovery, yet had little influence on the patients’ personal commitment to remain at a low weight. Full recovery then requires resolution of the individuals’ personal unresolved psychological conflicts through psychotherapy and frequently needs specialized treatment approaches to address psychiatric co-morbidities. AN might be conceptualized as a hereditary form of starvation resistance, facilitated by the effects of starvation on fitness allowing for an exceptionally intense personal commitment to perpetuate food restriction.

The association of appetite and hormones (leptin, ghrelin, and Insulin) with resting metabolic rate in overweight/ obese women: a case-control study

Objective

Low resting metabolic rate (RMR), as a risk factor for weight gain and obesity, can be influenced by many factors. Empirical research has confirmed the role of appetite and related hormones in obesity and energy intake. This study aimed to investigate the relationship between appetite and related hormones in overweight or obese Iranian women with normal and hypo RMR.

Methods

This case–control study was conducted on 42 Iranian adult women (21 cases, and 21 controls), aged 18–48 years. An impedance body analyzer was used to obtain the body composition and an indirect calorimeter was used to assess the RMR. The Flint questionnaire was used to assess appetite, dietary intake, and physical activity were assessed by FFQ and IPAQ questionnaires respectively, and ELISA kits were used to assess leptin, ghrelin, and insulin hormones.

Results

The results of the study demonstrated a negative association between ghrelin hormone level (β = -0.34, 95%CI = -61.70,-3.86, P-value = 0.027) and RMR, and a positive association between insulin hormone level (β = 0.48, 95%CI = 9.38–34.35, P-value = 0.001) and RMR. Also, results of the appetite questionnaire showed that, in general, both appetite (β = 0.32, 95%CI = -0.10–2.99 P-value = 0.044) and hunger variable (β = 0.30, 95%CI = 0.04–5.87, P-value = 0.047) have a positive association with RMR. There was no significant association between leptin levels and RMR.

Conclusion

It is evident that appetite and related hormones have a potential role in promoting a normal RMR.

ADORA1-driven brain-sympathetic neuro-adipose connections control body weight and adipose lipid metabolism

It is essential to elucidate brain-adipocyte interactions in order to tackle obesity and its comorbidities, as the precise control of brain-adipose tissue cross-talk is crucial for energy and glucose homeostasis. Recent studies show that in the peripheral adipose tissue, adenosine induces adipogenesis through peripheral adenosine A₁ receptor (pADORA₁) signaling; however, it remains unclear whether systemic and adipose tissue metabolism would also be under the control of central (c) ADORA₁ signaling. Here, we use tissue-specific pharmacology and metabolic tools to clarify the roles of cADORA₁ signaling in energy and adipocyte physiology. We found that cADORA₁ signaling reduces body weight while also inducing adipose tissue lipolysis. cADORA₁ signaling also increases adipose tissue sympathetic norepinephrine content. In contrast, pADORA₁ signaling facilitates a high-fat diet-induced obesity (DIO). We propose here a novel mechanism in which cADORA₁ and pADORA₁ signaling hinder and aggravate DIO, respectively.

Resting Energy Expenditure Is Not Altered in Children and Adolescents with Obesity. Effect of Age and Gender and Association with Serum Leptin Levels

In children and adolescents, obesity does not seem to depend on a reduction of resting energy expenditure (REE). Moreover, in this young population, the interactions between either age and obesity or between age and gender, or the role of leptin on REE are not clearly understood. To compare the levels of REE in children and adolescents we studied 181 Caucasian individuals (62% girls) classified on the basis of age- and sex-specific body mass index (BMI) percentile as healthy weight (n = 50), with overweight (n = 34), or with obesity (n = 97) and in different age groups: 8-10 (n = 38), 11-13 (n = 50), and 14-17 years (n = 93). REE was measured by indirect calorimetry and body composition by air displacement plethysmography. Statistically significant differences in REE/fat-free mass (FFM) regarding obesity or gender were not observed. Absolute REE increases with age (p < 0.001), but REE/FFM decreases (p < 0.001) and there is an interaction between gender and age (p < 0.001) on absolute REE showing that the age-related increase is more marked in boys than in girls, in line with a higher FFM. Interestingly, the effect of obesity on absolute REE is not observed in the 8-10 year-old group, in which serum leptin concentrations correlate with the REE/FFM (r = 0.48; p = 0.011). In conclusion, REE/FFM is not affected by obesity or gender, while the effect of age on absolute REE is gender-dependent and leptin may influence the REE/FFM in 8-10 year-olds.

Physical Fitness and Its Relationship to Plasma Leptin, Leptin Soluble Receptor, and Free Leptin Index in a Saudi Population: A Comparison Between Diabetic and Non-Diabetic Individuals

Background

Low physical activity is considered to be a risk factor for type 2 diabetes mellitus (T2DM). One theory suggest that leptin resistance is involved in the pathophysiology of impaired glucose metabolism. In this study we aimed to assess the correlation of physical fitness scores (PFS) with serum total leptin (TL), serum leptin soluble receptor (LSR), and free leptin index (FLI) in a group of Saudi patients with T2DM.

Material/Methods

This cross-sectional study involved 115 subjects: 52 healthy control subjects and 63 patients with T2DM. All subjects underwent body composition analysis. Blood samples were analyzed for fasting blood glucose (FBG), glycosylated hemoglobin (HbA1c), serum total leptin (TL), and serum leptin soluble receptor (LSR). Based on ideal body composition and our previous studies, physical fitness scores (PFS) were recorded for each subject.

Results

In patients with T2DM, levels of LSR were positively correlated with PFS (r=0.281, p=0.025), while the levels of TL (r=−0.425, p=0.001) and FLI (r=−0.439, p=0.001) were negatively correlated with PFS. In control subjects, TL and FLI levels were negatively correlated (r=−0.612, p=0.001and r=−0.543, p=0.001 respectively) with PFS. In linear regression analysis, after adjustment for age and BMI, TL and FLI were independent predictors of PFS.

Conclusions

Serum TL and FLI were negatively correlated while LSR was positively correlated with PFS in patients with T2DM. Therefore, they may be important biomarkers for predicting the outcomes of physical fitness and exercise programs.

The hyperleptinemia state can downregulate cardiorespiratory fitness and energy expenditure in obese women

INTRODUCTION

In general, in obese people a state of hyperleptinemia may impair both energy balance and the inflammatory process. However, it has not been fully investigated whether there is a relationship between hyperleptinemia and cardiorespiratory fitness (CRF) and resting energy expenditure (REE), in obese women.

METHODS

83 obese women were enrolled in this cross-sectional study. Anthropometric measures, body composition, REE, CRF and serum concentration of leptin were measured. Pearson's correlation coefficient was performed to examine the relationship between circulating leptin level and other clinical variables. Multiple regression analysis was applied to determine predictors of REE and CRF. Effects were considered significant at p≤0.05.

RESULTS

The most important finding in the present study is that the hyperleptinemia state was inversely correlated with CRF (r=-0.382, p=0.001) and REE (r=-0.447, p<0.001). Moreover, a positive correlation with fat mass was confirmed (r=0.419, p<0.001). In addition, hyperleptinemia was an independent negative predictor of REE (r²=-2.649, p=0.010) and CRF (r²=-2.335, p=0.023).

CONCLUSION

Together our results may suggest a vicious cycle between the state of hyperleptinemia and a decrease in energy expenditure and cardiorespiratory fitness in obese women, which can impair whole body energy homeostasis. This information is important to contribute to clinical practices.

Role of leptin in energy expenditure: the hypothalamic perspective

The adipocyte-derived hormone leptin is a peripheral signal that informs the brain about the metabolic status of an organism. Although traditionally viewed as an appetite-suppressing hormone, studies in the past decade have highlighted the role of leptin in energy expenditure. Leptin has been shown to increase energy expenditure in particular through its effects on the cardiovascular system and brown adipose tissue (BAT) thermogenesis via the hypothalamus. The current review summarizes the role of leptin signaling in various hypothalamic nuclei and its effects on the sympathetic nervous system to influence blood pressure, heart rate, and BAT thermogenesis. Specifically, the role of leptin signaling on three different hypothalamic nuclei, the dorsomedial hypothalamus, the ventromedial hypothalamus, and the arcuate nucleus, is reviewed. It is known that all of these brain regions influence the sympathetic nervous system activity and thereby regulate BAT thermogenesis and the cardiovascular system. Thus the current work focuses on how leptin signaling in specific neuronal populations within these hypothalamic nuclei influences certain aspects of energy expenditure.

Response to the Commentary: "Methodological Considerations for Analysing the Relation of Physical Activity with Leptin Levels in Children: Comment on the Study by Cicchella et al. (2013)" by David Jiménez-Pavon

This is a response to commentary by Jiménez-Pavon (2015) on the relationships of leptin levels with children's physical activity. The present response suggests actigraphs are superior to questionnaires for measuring children's physical activity. Cicchella, Stefanelli, Jurimae, Saar and Purge (2013) pointed out some interesting methodological issues related to the relationships of leptin and physical activity in normal weight children. The questions dealt with the reliability of the questionnaires in assessing physical activity in children, choices of the cut-off points for considering levels of physical activity as moderate or intense, and the association of leptin with PA levels. Some considerations in Jiménez-Pavon (2015) remain unclear.

METHODOLOGICAL CONSIDERATIONS TO ANALYZE THE RELATION OF PHYSICAL ACTIVITY WITH LEPTIN LEVELS IN CHILDREN: COMMENT ON CICCHELLA, ET AL. (2013)

A positive correlation was found between self-reported physical activity, leptin level, and Tanner stage 2 in children aged 10 to 12 years. However, several methodological considerations on the accuracy for assessing physical activity, misclassification of physical activity levels and weight status, the inclusion of possible confounds, and interpretation of the current findings should be examined to clarify the final interpretation.

Levels of adiponectin and leptin at onset of type 1 diabetes have changed over time in children and adolescents

Adiponectin and leptin are proteins secreted by the adipose tissue and have an influence on insulin sensitivity and on inflammatory markers. Altered levels could play a part in the pathogenesis of type 1 diabetes mellitus. We determined adiponectin and leptin levels over a nine-year period in children with type 1 diabetes mellitus (T1D) in relation to the increasing incidence of T1D, and studied the impact of patient status, age, gender and body mass index (BMI). Data were derived from a population-based registry of diabetic children (DanDiabKids) from 1997 to 2005. Children with newly diagnosed T1D (n = 482) were included, and healthy siblings (n = 479) were chosen as a control group. Leptin levels were significantly higher in recent years (in both patients and siblings), whereas for adiponectin, the levels were lower in recent years in the patient group. Leptin levels were lower in children with T1D (RR 0.74, p = 0.003) and in males (RR 0.52, p < 0.001) and increasing with age in both groups. For adiponectin, there was a negative association between level and age in patients. Both adipokines showed a significant correlation with BMI and lower levels in children with blood samples taken within the first 2 days after initiation of insulin treatment. There has been a change in leptin and adiponectin levels in children with or without T1D from 1997 to 2005. This is not explained by changes in BMI and may reflect changes in other factors like diet or physical activity.

Moderate physical activity correlates with elevated leptin in physically active 10-12-year-old boys with normal BMI

The aim of this study is to examine the relations between physical activity of differing intensity and duration with body energy-balance hormone leptin in 10-12-year-old boys (N = 94) who participated in moderate-to-vigorous physical activity at least four to five times per week. The boys reported their physical activity using a questionnaire. They had normal body mass index (BMI, kg/ m2), and were at Tanner Stage 2 of development. Boys were divided into three subgroups by leptin levels: normal serum leptin (M +/- .5 SD, n = 44, 1.2-3.9 ng/ml), low leptin (< or = M - .5 SD; n = 31, < 1.2 ng/ml), and high leptin (> or = M + .5 SD; n = 19, > 3.9 ng/ml). There were significant differences between subgroups in anthropometric parameters and serum leptin levels, but not in physical activity. A significant correlation was found between leptin and moderate physical activity of at least five times per week for at least 30 minutes each time in the high leptin group (r = .61). In conclusion, the correlations between physical activity and leptin are weak; only moderate physical activity was correlated with leptin levels in the high leptin

Obesity-Related Hormones in Low-Income Preschool-Age Children: Implications for School Readiness

Mechanisms underlying socioeconomic disparities in school readiness and health outcomes, particularly obesity, among preschool-aged children are complex and poorly understood. Obesity can induce changes in proteins in the circulation that contribute to the negative impact of obesity on health; such changes may relate to cognitive and emotion regulation skills important for school readiness. We investigated obesity-related hormones, body mass index (BMI), and school readiness in a pilot study of low-income preschoolers attending Head Start (participating in a larger parent study). We found that the adipokine leptin was related to preschoolers' BMI z-score, the appetite-regulating hormones ghrelin and glucagon-like peptide 1 (GLP-1), and pro-inflammatory cytokines typically associated with early life stress; and that some of these obesity-related biomarkers were in turn related to emotion regulation. Future work should evaluate how obesity may affect multiple domains of development, and consider modeling common physiological pathways related to stress, health, and school readiness.

The associations between peak O2 consumption and leptin in 10- to 12-year-old boys

The aim of this study was to assess the associations of circulating levels of leptin with the peak O(2) consumption (VO(2)peak ) in 10- to 12-year-old boys of different BMI selected by Cole et al. (BMJ, 320,2000,1-6): total group (n = 248), normal (n = 190), overweight (n = 34) and obese (n = 24). We hypothesized that there is a close relationship in overweight and obese subgroups of boys with relative VO(2)peak kg (-1) (ml min(-1) kg(-1)) and leptin. Most of the subjects were Tanner stage 2. Peak O(2) consumption was measured directly using an increasing incremental protocol until volitional exhaustion on an electronically braked cycle ergometer. The expired gas was sampled continuously breadth-by-breadth mode for the measurement of oxygen consumption (MetaMax, Germany). Blood samples were obtained after an overnight fast from an antecubital vein for leptin measurements. Peak O(2) consumption (l min(-1)) was higher or lower (ml min(-1) kg(-1)) in overweight and obese groups, compared with normal BMI group. Leptin was higher in overweight and obese groups, compared with normal BMI group. Peak O(2) consumption (l min(-1)) correlated significantly with leptin only in total group (n = 248, r = 0·196). Contrary, relative VO(2)peak kg (-1) correlated significantly and negatively with leptin. The relationship was highest on the total group (r = -0·674). We can conclude that leptin first of all correlated negatively with relative peak O(2) consumption. Absolute VO(2)peak correlated with leptin only in total group.

Leptin predicts a decline in moderate to vigorous physical activity in minority female children at risk for obesity

What is already known about this subject Physical activity declines as children enter puberty. Leptin is cross-sectionally associated with physical activity, but there are conflicting findings on the magnitude and direction of this association. Leptin concentrations fluctuate during puberty, and may impact energy balance. What this study adds Leptin predicts the decline in physical activity during the start of puberty independent of central adiposity. Based on a median split of leptin, girls with low leptin levels have higher levels of physical activity than girls with high leptin levels at the start of puberty. Leptin levels at the start of puberty may provide a biological basis for the age-related physical activity decline in girls.

BACKGROUND

Leptin may influence moderate to vigorous physical activity (MVPA) at the start of puberty. The direction and magnitude of this association are unclear.

OBJECTIVES

To determine the effect of baseline leptin on MVPA over 1 year in minority girls at high risk for obesity.

METHODS

Data came from TRANSITIONS, a longitudinal observational study on the age-related MVPA decline. Fifty peripubertal girls aged 8-11 years at baseline participated. Baseline leptin (ng mL(-1) ) was collected via a duplicated assay using a double antibody radio immune assay. MVPA (min d(-1) ) was measured using accelerometers for at least four 10-h days on a quarterly basis for up to 1 year.

RESULTS

Continuous leptin was negatively related to MVPA (P = 0.001) independent of central adiposity at baseline and predicted the MVPA decline over 1 year (P = 0.002). For descriptive purposes, baseline leptin was dichotomized at the sample median into 'high leptin' and 'low leptin' categories to determine whether MVPA trajectories differed between these groups. Girls with 'low leptin' at baseline had significantly higher levels of MPVA at baseline, visit 1 and visit 2 compared to girls with 'high leptin'.

CONCLUSIONS

High leptin levels predicted nearly a 12.6% decline in MVPA over 1 year. These findings provide support for the biological basis of declining MVPA as girls enter puberty.

Associations of physical activity and fitness with adipocytokines in adolescents: the AFINOS Study

BACKGROUND AND AIMS

Adipocytokines may have a key role in the development of atherosclerosis and type 2 diabetes. The purpose of this study was to examine the independent and joint associations of physical activity (PA), cardiorespiratory fitness (CRF) and muscular fitness (MF) with adiponectin and leptin in adolescents.

METHODS AND RESULTS

A sample of 198 adolescents (96 girls), aged 13-17-year, was selected. Participants completed anthropometric measurements (height, weight, and waist circumference) and percentage of body fat (%BF) was estimated by bioelectrical impedance. PA was measured by accelerometer for 7-day. The 20-m shuttle-run test was used to assess CRF and two MF tests (handgrip strength and standing broad jump) were used to create an MF score. A cluster score of health status (0-3 risks) was created. Serum adiponectin and plasma leptin were also determined. Regression analyses controlling for age, sex, pubertal status and waist circumference showed that PA was not significantly associated with adiponectin and vigorous PA showed a significant inverse association with leptin. Both CRF and MF were significantly and inversely associated with adiponectin and leptin. Further analyses revealed that the 'healthy' group (0 risks) had significantly lower adiponectin and leptin than 'medium-healthy' (1 risk) and 'unhealthy' (2-3 risks) status groups.

CONCLUSIONS

PA, CRF and MF are inversely and jointly associated with adiponectin and leptin concentrations in adolescents.

Physical activity is correlated with serum leptin independent of obesity: results of the national surveillance of risk factors of noncommunicable diseases in Iran (SuRFNCD-2007)

Reports on the relationship between leptin and physical activity (PA) at the population level are scarce. The present study examined the relationship between serum leptin concentrations and PA in a nationally representative sample of 3001 Iranian adults aged 25 to 64 years. Data of our third national surveillance of risk factors of noncommunicable diseases were analyzed. Using the Global Physical Activity Questionnaire, the duration and intensity of PA were evaluated in 3 domains: work, commuting, and recreation. Total PA was calculated using metabolic equivalents for PA intensity. Serum leptin was measured with an enzyme-linked immunosorbent assay. After adjustment for age, area of residence, smoking, body mass index, and waist circumference, total PA (r = -0.129, P = .038 in men and r = -0.226, P = .006 in women), the duration of vigorous-intensity activity (r = -0.120, P = .044 in men and r = -0.154, P = .019 in women), the duration of moderate-intensity activity (r = -0.114, P = .047 in men and r = -0.160, P = .018 in women), and time spent on sedentary behaviors (r = 0.194, P = .014 in men and r = -0.204, P = .007 in women) were significantly correlated with serum leptin. In both sexes, participants in higher categories of PA had significantly lower serum leptin levels. In conclusion, our results demonstrated an inverse association between leptin concentrations and PA independent of age, sex, smoking, and body adiposity. Our results point to the regulatory effects of PA on serum leptin.

Locomotor activity and gait in aged mice deficient for type IX collagen

Osteoarthritis (OA) is a risk factor for physical inactivity and impaired mobility, but it is not well understood how these locomotor behaviors are affected by the age of onset of OA and disease severity. Male mice homozygous for a Col9a1 gene inactivation (Col9a1(-/-)) develop early onset knee OA, increased tactile pain sensitivity, and gait alterations by 9 mo of age. We hypothesized that aged Col9a1(-/-) mice would reduce joint pain by adopting locomotor behaviors that reduce both the magnitude and daily frequency of joint loading. We tested this hypothesis by evaluating gait and spontaneous locomotor activity in 15- to 17-mo-old male Col9a1(-/-) (n = 5) and Col9a1(+/+)(WT) (n = 5) mice using well-controlled measures of voluntary activity in overground and running wheel conditions, as well as studies of gait in a velocity-controlled treadmill. We found no difference due to genotype in freely chosen locomotor velocity, stride frequency, hindfoot duty factor, dark phase activity time, or dark-phase travel distance during overground, running wheel, or speed-matched treadmill locomotion. Interpretation of these findings is potentially confounded by the observation that WT mice have greater knee OA than Col9a1(-/-) mice in the lateral tibial plateau by 17 mo of age. When accounting for individual differences in knee OA, functional locomotor impairments in aged Col9a1(-/-) and WT mice are manifested as reductions in total locomotor activity levels (e.g., both distance traveled and time active), particularly for wheel running. These results support the concept that current disease status, rather than age of disease onset, is the primary determinant of impaired locomotor activity with aging.

Association of plasma leptin levels with maternal body weight and body mass index in premature and term newborns

BACKGROUND

Leptin plays an important role in the regulation of body weight and energy metabolism in adults; its role in neonates also needs to be explored. The current study aims to determine the correlation between serum leptin concentrations and anthropometric variables in newborns and their mothers, and to examine the effects of sex, gestational age and antenatal steroid use on neonatal leptin levels.

METHODS

This was a retrospective study. Blood samples were collected from 55 newborns within 24 hours of birth. Plasma leptin levels were measured by immunometric assay. The relationship between neonatal leptin levels and anthropometric parameters was determined using Pearson's correlation and further evaluated by linear regression analysis.

RESULTS

Neonatal leptin was significantly correlated with maternal body weight (p < 0.002) and maternal body mass index (BMI) (p < 0.001). However, it was not correlated with gestational age (p = 0.130), birth weight (p = 0.097), or birth BMI (p = 0.336). The leptin levels in premature newborns (gestational age < 37 weeks; 0.69 +/- 1.82ng/mL) were significantly less than those in term newborns (gestational age > or = 37 weeks; 2.09 +/- 2.30 ng/mL, p = 0.031). There were no significant differences between sexes (p = 0.277) or in relation to antenatal steroid use (p = 0.611).

CONCLUSION

Neonatal serum leptin concentrations within 24 hours of birth correlated with maternal body weight and BMI, especially in premature newborns. Premature newborns had significantly lower leptin levels than full-term newborns.

Characterization and expression of Ailuropoda melanoleuca leptin (ob gene)

Leptin, an adipocyte-derived hormone, plays important roles in metabolism and reproduction. In this article, we report the cloning, expression, and identification of the giant panda leptin (gLeptin) gene and its variants. The gLeptin cDNA was 504 bp long, encoding a precursor peptide of 167 amino acids including 21 residues of signal peptide. A short variant of gLeptin was 501 bp long, encoding a 166-aa peptide and also including a 21-aa signal peptide. Giant panda leptin was 99.4%, 94.6%, and 92.8% identical to that of black bear, dog, and cat, respectively, but was only 81.4% and 80.8% identical to that of human and rat. The cloned gLeptin gene was expressed in Escherichia coli, with expression confirmed by Western blotting and MALDI-TOF-TOF MS PMF. After purification, renaturation, and condensation, the gLeptin protein was injected into Kunming mice. The recombinant gLeptin significantly inhibited food intake by 41.8% and reduced body weight by 5.1% in the mice.

A high-sugar/low-fiber meal compared with a low-sugar/high-fiber meal leads to higher leptin and physical activity levels in overweight Latina females

Acute effects of high-sugar/low-fiber meals vs low-sugar/high-fiber meals on hormones and behavior were studied in 10 overweight Latina females, age 11 to 12 years, using a crossover design. In this exploratory pilot study, participants arrived fasted at an observation laboratory on two occasions and randomly received either a high-sugar/low-fiber meal or a low-sugar/high-fiber meal at each visit. Glucose, insulin, and leptin were assayed from serum drawn at 0, 15, 30, 60, 90, and 120 minutes. Ad libitum snacks were provided at 120 minutes. Physical activity was measured using an observational system that provides data on time spent lying down, sitting, standing, walking, and in vigorous activity. Data were collected between March 2005 and July 2006. In the high-sugar/low-fiber condition, glucose and leptin levels decreased more slowly, glucose levels were higher at 60 minutes (111.2 mg/dL vs 95.4 mg/dL, P=0.03), and leptin levels were higher at 90 minutes (49.3 ng/mL vs 46.7 ng/mL, P=0.017) than in the low-sugar/high-fiber condition. Meals did not affect insulin or ad libitum dietary intake. Sitting, standing, lying down, and vigorous activity differed by condition, but not walking. Participants were significantly more active in the first 30 to 60 minutes after the high-sugar/low-fiber meal, but after 60 minutes there was a trend for activity to be lower after the high-sugar/low-fiber meal vs the low-sugar/high-fiber meal. High-sugar meals sustain glucose and leptin levels longer, which may play an important role in modulating levels of physical activity in this group at high risk for obesity-related disease.

Responses of the hypothalamopituitary adrenal axis and the sympathoadrenal system to isolation/restraint stress in sheep of different adiposity

There is evidence that levels of adipose tissue can influence responses of the hypothalamopituitary-adrenal (HPA) axis to stress in humans and rats but this has not been explored in sheep. Also, little is known about the sympathoadrenal responses to stress in individuals with relatively different levels of adipose tissue. We tested the hypothesis that the stress-induced activation of the HPA axis and sympathoadrenal system is lower in ovariectomized ewes with low levels of body fat (lean) than ovariectomized ewes with high levels of body fat (fat). Ewes underwent dietary manipulation for 3 months to yield a group of lean ewes (n = 7) with a mean (+/-SEM) live weight of 39.1 +/- 0.9 kg and body fat of 8.9 +/- 0.6% and fat ewes (n = 7) with a mean (+/-SEM) live weight of 69.0 +/- 1.8 kg and body fat of 31.7 +/- 3.4%. Fat ewes also had higher circulating concentrations of leptin than lean ewes. Blood samples were collected every 15 min over 8 h when no stress was imposed (control day) and on a separate day when 4 h of isolation/restraint was imposed after 4 h of pretreatment sampling (stress day). Plasma concentrations of adrenocorticotropic hormone (ACTH), cortisol, epinephrine and norepinephrine did not change significantly over the control day and did not differ between lean and fat ewes. Stress did not affect plasma leptin levels. All stress hormones increased significantly during isolation/restraint stress. The ACTH, cortisol and epinephrine responses were greater in fat ewes than lean ewes but norepinephrine responses were similar. Our results suggest that relative levels of adipose tissue influence the stress-induced activity of the hypothalamopituitary-adrenal axis and some aspects of the sympathoadrenal system with fat animals having higher responses than lean animals.

Further investigations on the role of diet-induced thermogenesis in the regulation of feed intake in chickens: comparison of adult cockerels of lines selected for high or low residual feed intake

The main objective of this study was to investigate the role of diet-induced thermogenesis (DIT) in feed intake regulation in cockerels selected for high (R+) or low (R-) residual feed intake. The selection criterion was defined as the difference between observed feed intake and feed intake predicted by regression between feed intake and BW, BW gain, and egg mass production. Furthermore, the effect of genotype on postprandial oxidation of U-(13)C(6)-glucose, decarboxylation of 1-(13)C(1)-Leu, and key metabolites and hormones was analyzed. Thirty 24-wk-old cockerels of both lines were kept in battery cages under standard conditions on a commercial diet. Three cockerels per genotype were examined twice weekly from wk 30 through 34 in open-circuit respiratory cells. After adaptation, cockerels were feed deprived for 24 h and heat production was measured. During the subsequent 7-h refeeding period, DIT and feed intake, as well as glucose oxidation and Leu decarboxylation were assessed by using breath tests. Blood samples were collected after fasting and refeeding. Finally, 10 animals per genotype were killed to record abdominal fat weight. Body composition of 6 different chickens per genotype was determined by using dual-energy x-ray absorptiometry. During feed deprivation, the R+ cockerels had a significantly higher heat production than their R- counterparts, which was even more pronounced during refeeding. Consequently, the R+ cockerels had a significantly increased DIT and a higher feed intake than the R- cockerels. Thus, no evidence of a feedback effect of DIT on feed intake was observed. The oxidation of U-(13)C(6)-glucose was significantly higher in the R+ cockerels, confirming their higher respiratory quotient values and the augmented fat deposition in the R- chickens, as assessed by abdominal fat weight and dual-energy x-ray absorptiometry measurements. No significant genotype effect on 1-(13)C(1)-Leu decarboxylation was observed, despite increased circulating uric acid levels in the R+ chickens. Genotype did not influence plasma levels of triglycerides, free fatty acids, glucose, triiodothyronine, or thyroxine after refeeding, whereas plasma leptin levels were significantly higher in the R+ cockerels.

Adipokine response in diabetics and nondiabetics following the Roux-en-Y gastric bypass: a preliminary study

INTRODUCTION

The adipocyte influences eating behavior and metabolism via cytokine secretion. We report our findings of adipokine secretion in a cohort of diabetic and nondiabetic morbidly obese patients before and after Roux-en-Y gastric bypass (RYGB).

METHODS

Ten morbidly obese subjects who underwent uncomplicated RYGB were studied: five were diabetic and nine were female. Nonfasting plasma levels of adiponectin, resistin, leptin, and tumor necrosis factor-alpha were determined preoperatively and 6 mo postoperatively. C-reactive protein (CRP) was followed as a marker of the metabolic syndrome.

RESULTS

The patient age was 42 +/- 11 y, and the preoperative BMI was 50 +/- 6 kg/m(2). The 6 mo BMI fell to 33 +/- 5 kg/m(2) (P < 0.0001), and there were no differences between diabetics and nondiabetics with respect to amount of weight loss. In nondiabetic patients, there were significant increases compared with preoperative levels for adiponectin, resistin, and tumor necrosis factor-alpha; leptin was significantly decreased while CRP was unchanged. CRP and leptin levels were both significantly lower (P < 0.05), while all other protein levels were unchanged in diabetic patients.

CONCLUSIONS

At 6 mo postoperation, RYGB significantly altered most adipokine levels for nondiabetic patients. Only CRP and leptin were changed in diabetic patients. All patients lost a significant amount of weight over 6 mo, suggesting a different metabolic effect between nondiabetic and diabetic patients after RYGB.

Physical activity energy expenditure may mediate the relationship between plasma leptin levels and worsening insulin resistance independently of adiposity

Leptin regulates a constellation of neuroendocrine processes that control energy homeostasis. The infusion of leptin in rodents lacking endogenous leptin promotes physical activity energy expenditure (PAEE) and improves insulin signaling, whereas hyperleptinemia is associated with physical inactivity and insulin resistance (IR). We tested whether baseline leptin levels predict changes in PAEE and IR over time, independent of obesity. We also assessed whether the relationship between leptin and change in IR is mediated by PAEE. The population consisted of 288 nondiabetic UK Caucasian adults (mean age: 49.4 yr; SD: 0.7 yr), in whom leptin, insulin, glucose, PAEE (via heart rate monitoring with individual calibration by indirect calorimetry), and anthropometric characteristics had been measured at baseline and 5 yr later. In linear regression models, baseline leptin levels inversely predicted follow-up PAEE ( P = 0.033). On average, individuals with low leptin levels (below sex-specific median) increased their daily activity 35% more during the 5-yr follow-up period than those with above-median leptin levels. Baseline leptin level also predicted worsening IR (fasting, 30-min, and 2-h insulins, and homeostasis model assessment-IR; all P < 0.01). Associations were independent of potential confounders, such as adiposity, age, and sex. Including baseline PAEE as a cofactor in the leptin-insulin models reduced the strength (1–4% reduction) and significance of the associations, suggesting that PAEE mediates the leptin-insulin relationships. Hyperleptinemia predicts a relative decline in PAEE and worsening insulin resistance, possibly via shared molecular pathways.

Postprandial changes in leptin concentrations of cerebrospinal fluid in dogs during development of obesity

OBJECTIVE

To evaluate postprandial changes in the leptin concentration of CSF in dogs during development of obesity.

ANIMALS

4 male Beagles.

PROCEDURES

Weight gain was induced and assessments were made when the dogs were in thin, optimal, and obese body conditions (BCs). The fat area at the level of the L3 vertebra was measured via computed tomography to assess the degree of obesity. Dogs were evaluated in fed and unfed states. Dogs in the fed state received food at 9 AM. Blood and CSF samples were collected at 8 AM, 4 PM, and 10 PM.

RESULTS

Baseline CSF leptin concentrations in the thin, optimal, and obese dogs were 24.3 +/- 2.7 pg/mL, 86.1 +/- 14.7 pg/mL, and 116.2 +/- 47.3 pg/mL, respectively. In the thin BC, CSF leptin concentration transiently increased at 4 PM. In the optimal BC, baseline CSF leptin concentration was maintained until 10 PM. In the obese BC, CSF leptin concentration increased from baseline value at 4 PM and 10 PM. Correlation between CSF leptin concentration and fat area was good at all time points. There was a significant negative correlation between the CSF leptin concentration-to-serum leptin concentration ratio and fat area at 4 PM; this correlation was not significant at 8 AM and 10 PM.

CONCLUSIONS AND CLINICAL RELEVANCE

Decreased transport of leptin at the blood-brain barrier may be 1 mechanism of leptin resistance in dogs. However, leptin resistance at the blood-brain barrier may not be important in development of obesity in dogs.

Neuroendocrine mechanisms of innate states of attenuated responsiveness of the hypothalamo-pituitary adrenal axis to stress

Neuroendocrine responses to stress vary between sexes and reproductive states and are influenced by the type of stressor. Stress responses are attenuated in some physiological states, such as lactation and conditions of low visceral adipose tissue. Moreover, some individuals within a species characteristically display reduced stress responses. The neuroendocrine mechanisms for stress hyporesponsiveness are likely to include reduced synthesis and secretion of corticotropin releasing hormone (CRH) and arginine vasopressin (AVP) from the hypothalamus as a result of enhanced glucocorticoid negative feedback and/or reduced noradrenergic stimulatory input from the brain stem. A major limitation of research to date is the lack of direct measures of CRH and AVP secretion. Attenuated stress responsiveness is also commonly associated with reduced pituitary responsiveness to CRH and AVP. The possible roles of inhibitory central inputs to CRH and AVP neurons and of oxytocin and prolactin in attenuating the HPA axis responses to stress are unknown.

Leptin: a potential biomarker for childhood obesity?

Leptin, a hormone made by adipocytes, is an important circulating signal for the regulation of body weight. A review of the scientific literature (PubMed Search 1994 to 2005) for studies examining the relationship among leptin, pediatric obesity and the impact of exercise intervention programmes on leptin concentrations are summarized. The potential utility of leptin as a biomarker for identifying children at risk of obesity is discussed. This literature review demonstrated that (1) leptin directly interacts with the hypothalamus for energy balance regulation; (2) the measurement of free, bound and total leptin as well as soluble leptin receptor concentration are critical for our understanding of obesity in children; and (3) leptin concentration may be an important factor for determining intervention programme responsiveness in pediatric obesity.

Leptin cDNA cloning and its mRNA expression in plateau pikas (Ochotona curzoniae) from different altitudes on Qinghai-Tibet Plateau

Leptin, an adipocyte-derived hormone, plays an important role in body energy homeostasis. Plateau pika (Ochotona curzoniae), an endemic and keystone species living only at 3000-5000 m above sea level on Qinghai-Tibet Plateau, is a typically high hypoxia and low temperature tolerant mammal with high resting metabolic rate (RMR), non-shivering thermogenesis (NST), and high ratio of oxygen utilization to cope with harsh plateau environment. To explore the molecular mechanism of ecological acclimation in plateau pika, we first cloned pika leptin cDNA and compared its mRNA expression in different altitudes (3200 and 3900 m) using real-time RT-PCR (Taqman probe) technology. The full-length pika leptin cDNA was 3015 with 504 bp open-reading frame encoding the precursor peptide of 167 amino acids including 21 residues of signal peptide. Pika leptin was 70-72% homologous to that of other species and was of similarly structural characteristics with other species. The pika-specific genetic diversity in leptin sequence occurred at twenty sites. With the increase in altitude, there were larger fat store and high level of ob gene expression in plateau pika. Our results indicated that leptin is sensitive to cold and hypoxia plateau environment and may play one of important roles in pika's ecological adaptation to harsh plateau environment.

Individual differences in physical activity are closely associated with changes in body weight in adult female rhesus monkeys (Macaca mulatta)

The increased prevalence of overweight adults has serious health consequences. Epidemiological studies suggest an association between low activity and being overweight; however, few studies have objectively measured activity during a period of weight gain, so it is unknown whether low activity is a cause or consequence of being overweight. To determine whether individual differences in adult weight gain are linked to an individual's activity level, we measured activity, via accelerometry, over a prolonged period (9 mo) in 18 adult female rhesus monkeys. Weight, food intake, metabolic rate, and activity were first monitored over a 3-mo period. During this period, there was mild but significant weight gain (5.5 +/- 0.88%; t =-6.3, df = 17, P < 0.0001), whereas caloric intake and activity remained stable. Metabolic rate increased, as expected, with weight gain. Activity level correlated with weight gain (r = -0.52, P = 0.04), and the most active monkeys gained less weight than the least active monkeys (t = -2.74, df = 8, P = 0.03). Moreover, there was an eightfold difference in activity between the most and least active monkeys, and initial activity of each monkey was highly correlated with their activity after 9 mo (r = 0.85, P < 0.0001). In contrast, food intake did not correlate with weight gain, and there was no difference in weight gain between monkeys with the highest vs. lowest caloric intake, total metabolic rate, or basal metabolic rate. We conclude that physical activity is a particularly important factor contributing to weight change in adulthood and that there are large, but stable, differences in physical activity among individuals.

Potential role of leptin in increase of fatty acid synthase gene expression in chicken liver

Leptin is reported to have direct effects on lipogenesis in peripheral tissues that are independent of its central effects on food intake and body weight. These experiments have been mainly carried out in rodents (different models of obesity) in which lipogenesis occurs in both adipose tissue and liver. Such effects are unknown in birds in which lipogenesis occurs essentially in the liver. In this study, leptin gene expression and circulating leptin levels were examined in two chicken lines, selected for high (FL) or low (LL) abdominal fat pad size, at different nutritional states (fasted and fed state). In addition, effects of recombinant chicken leptin on liver metabolism were investigated. Hepatic leptin and fatty acid synthase (FAS) gene expression and plasma leptin levels were significantly higher in FL than in LL chickens (P < 0.05). In both lines, fasting significantly reduced hepatic leptin and FAS mRNA levels (P < 0.05). Continuous administration of recombinant chicken leptin (8 microg/kg/h) during 6 h significantly inhibited food intake (51%) and increased leptinemia (23-fold) compared to untreated group. Despite the decrease of food intake, leptin significantly induced the expression of FAS in chicken liver. These changes were accompanied by a significant down-regulation of leptin receptor gene expression, however SREBP-1, the main transcription factor of lipogenic genes, remained unchanged. This result suggests a local potential role of leptin in the regulation of avian hepatic lipogenesis, and explain, at least partly, the metabolic changes evolved during the divergent selection of FL and LL chickens.

Polymorphisms in the leptin and leptin receptor genes in relation to resting metabolic rate and respiratory quotient in the Québec Family Study

BACKGROUND

Leptin (LEP) is an endocrine hormone that participates in many metabolic pathways, including those associated with the central regulation of energy homeostasis.

OBJECTIVE

We examined the associations between polymorphisms in the LEP and leptin receptor (LEPR) genes and resting metabolic rate (RMR) and respiratory quotient (RQ) in the Quebec Family Study.

METHODS AND SUBJECTS

Three polymorphisms in LEPR (K109R, Q223R and K656N) and one in LEP (19A > G) were genotyped in 678 subjects. RMR, RQ at rest and RQ while sitting, standing and walking at 4.5 km/h (RQ45) were adjusted for age, sex, fat mass and fat-free mass.

RESULTS

RQ45 was associated with the LEPR-K109R (P = 0.004) and Q223R (P = 0.03) polymorphisms, and RMR showed association with the LEPR-K656N polymorphism (P = 0.006). For the LEP-19A > G polymorphism, no significant associations were observed. However, LEP-A19A homozygotes who were carriers of the LEPR N656 allele had a significantly lower RQ45 compared to other genotype combinations (P for interaction=0.003).

CONCLUSION

These findings suggest that DNA sequence variation in the LEPR gene contributes to human variation in RMR and in the relative rates of substrate oxidation during low-intensity exercise in steady state but not in a resting state.

Relationships between physical activity and plasma leptin levels in healthy children: the Fleurbaix-Laventie Ville Santé II Study

OBJECTIVE

To study the relationships between physical activity and plasma leptin levels in children from a population-based study, taking into account puberty stages.

DESIGN

Subjects were part of the Fleurbaix-Laventie Ville Santé (FLVS) II Study, a longitudinal study on the determinants of weight gain in children and their parents. At baseline examination, 253 girls and 257 boys aged 8-18 y were examined.

MEASUREMENTS

: Height and weight were measured, adiposity was assessed by the sum of four skinfold thicknesses (SSK). Pubertal stage was assigned according to Tanner. Leisure-time physical activity (LTPA) was assessed by the Modifiable Activity Questionnaire and ambulatory activity by pedometer recording over a week. A fasting blood sample was obtained to determine plasma leptin and insulin levels.

RESULTS

Plasma leptin was higher in girls compared to boys (8.3 (1.6-36.5) ng/ml vs 2.2 (0.1-15.3) ng/ml, P<0.001). Multivariate analyses were performed with leptin as dependent variable, and number of steps by day, Tanner stage, insulin and SSK as independent variables. In girls, leptin was negatively correlated to number of steps/day (P<0.001) and positively to SSK (P<0.001) and insulinemia (P<0.001). In boys, leptin was correlated to insulinemia (P<0.001), SSK (P<0.001), Tanner stage (P<.0001), but not to physical activity.

CONCLUSION

Physical activity is negatively related to leptin levels in girls only and this association is independent of fasting plasma insulin. In children, fasting insulinemia remains associated with leptin levels after taking into account adiposity, physical activity and Tanner stage.

Serum leptin concentration poorly reflects growth and energy and nutrient intake in young children

OBJECTIVE

We studied whether the serum leptin concentration at age 2 years predicts changes in relative body weight by age 8 and whether the serum leptin concentration is associated with intake of energy and nutrients at age 5.

METHODS

A total of 156 8-year-old participants of the Special Turku Coronary Risk Factor Intervention Project were chosen to represent children whose relative weight decreased, was stable, or increased during the preceding 6 years. Their serum leptin concentrations were measured in samples collected when they were 2 years. Serum leptin was also measured in 100 5-year-old children in the Special Turku Coronary Risk Factor Intervention Project whose energy and nutrient intakes were analyzed using 4-day food records.

RESULTS

The boys whose relative weight decreased (n = 25), was stable (n = 28), or increased (n = 26) between 2 and 8 years of age had similar serum leptin concentrations at the age of 2 years. The girls whose relative weight decreased (n = 27) had higher serum leptin concentrations at 2 years than the girls whose relative weight remained stable (n = 26) but only when the leptin values were not adjusted for body mass index. The serum leptin concentration was higher in 5-year-old girls than in 5-year-old boys even when adjusted for body mass index. Serum leptin correlated with relative weight in girls and boys (r = 0.65 and r = 0.45, respectively). Serum leptin concentration adjusted for relative weight correlated poorly with intakes of energy, fat, saturated fat, carbohydrates, sucrose, and protein.

CONCLUSIONS

Serum leptin concentrations at age 2 poorly predicted changes in relative body weight during the following 6 years and poorly reflected the intake of energy or major nutrients at age 5.

Plasma leptin and exercise: recent findings

It is established that plasma leptin is associated with satiety and that leptin stimulates lipid metabolism, and increases energy expenditure. These effects implicate leptin as a major regulator of energy homeostasis, which may serve to limit excess energy storage. As plasma leptin concentrations are tightly coupled with fat mass in humans, decreases in adipose mass with weight loss coincide with decreased concentrations of circulating leptin. However, due to many confounding factors, the effects of exercise on circulating leptin are less clear. The data from investigations examining single exercise bouts suggest that serum leptin concentrations are unaltered by short duration (41 minutes or less), non-exhaustive exercise, but may be affected by short duration, exhaustive exercise. More convincingly, studies investigating long duration exercise bouts indicate that serum leptin concentrations are reduced with exercise durations ranging from one to multiple hours. These findings raise speculation that exercise-associated reductions in leptin may be due to alterations in nutrient availability or nutrient flux at the level of the adipocytes, the primary site of leptin production and secretion. Thus, one purpose of this review is to discuss the effects of exercise on circulating leptin concentrations with special emphasis on studies that have examined single exercise bouts that are associated with high levels of energy expenditure and energy deficit. In addition, a 'nutrient sensing pathway' (the hexosamine biosynthetic pathway), which regulates leptin gene expression, will be discussed as a possible mechanism by which exercise-induced energy deficit may modulate serum leptin concentrations.

Leptin and cytokines levels in children with failure to thrive

BACKGROUND

The majority of cases of failure to thrive (FTT) are non-organic. Many of these patients present with significant decreased caloric intake. It appears as if the appetite regulation center in the hypothalamus is not attuned to the calorie requirements of the infant.

OBJECTIVE

Our hypothesis was that some cases of non-organic FTT might be caused by abnormalities in hunger/satiety control secondary to neuroendocrine or cytokine imbalance. The aim of this study was to investigate which hormonal/cytokine profiles could be assigned to a defined category of FTT, namely organic, psychosocial and idiopathic subgroups.

STUDY DESIGN

34 patients were enrolled and 32 completed the study (12 controls, 12 idiopathic FTT, 5 organic FTT, and 3 psychosocial FTT). Each child was assessed by a pediatric gastroenterologist, dietician, and social worker and underwent appropriate laboratory investigation during which leptin, IL1, IL6 and TNF-alpha levels were determined. The Mann-Whitney U test was used to compare the groups.

RESULTS

IL6 was the only cytokine that showed significant differences between FTT patients (4.06 +/- 6.3 pg/ml) and normal controls (0.0 pg/ml (p = 0.028). Leptin values were significantly higher in the normal control group (1632 +/- 483 pg/ml) as compared to FTT patients (685 +/- 687 pg/ml) (p = 0.001).

CONCLUSIONS

Our results indicate that leptin does not play a role in the pathogenesis of anorexia in children with FTT. It is however, possible that IL6 may be an important factor in the etiology of anorexia in patients with FTT.

Effect of lifestyle changes on whole-body protein turnover in obese adolescents

OBJECTIVE

To investigate the effect of lifestyle changes on whole-body protein turnover (WBPT) in obese adolescents.

DESIGN/METHODS

Randomized and controlled nonpharmacological intervention study of WBPT in obese adolescents using stable isotope dilution techniques.

SUBJECTS AND MEASUREMENTS

We studied a total of 21 adolescents (11 boys and 10 girls, matched for their pubertal status) of which 15 were obese (age=15.8+/-0.4 y old and BMI=38.6+/-3.3 kg/m(2)) and six were lean controls (age=16.0+/-0.4 y old and BMI=21.3+/-1.2 kg/m(2)). The obese subjects were subjected to a randomized controlled lifestyle intervention program that involved moderate physical activity and diet changes for 3 months. A group of lean age-matched subjects was also studied at baseline to compare the WBPT in obese and lean adolescents. The studies were performed during a primed, continuous infusion of L-[1-(13)C]leucine. Leucine appearance rate (Leu Ra) was used as an index of whole protein breakdown and the nonoxidative portion of leucine disposal (NOLD) as an index of whole-body protein synthesis.

RESULTS

The obese groups showed significantly higher body mass index (BMI), fat mass (FM), percent body fat (%BF), fat-free mass (FFM), resting energy expenditure (REE) and WBPT compared to the lean controls. The intervention program resulted in a redistribution of the parameters of body composition without apparent changes in BMI or body weight. There was a significant decrease in WBPT in the obese intervention group, but not in the obese control group. Insulin levels also decreased significantly in the obese group after intervention but not in the obese control group, whereas the glucose concentrations remained normal in all groups at baseline and also after intervention/or control.

CONCLUSIONS

Results from the current study suggest: (i). abonormalities of protein metabolism occur early in the clinical course of obesity and (ii). these abnormalities are modifiable by moderate lifestyle changes in obese adolescents. The mechanism for these changes in WBPT in obese adolescents as well as their impact on specific cardiovascular risk factors and turnover of specific proteins will require further investigation.

Genetic contributions to body weight in mice: relationship of exploratory behavior to weight

OBJECTIVE

The A/J and C57BL/6J mouse strains differ markedly in their exploratory behavior and their weight gain on a high-fat diet. We examined the genetic contributions of exploratory behavior to body weight and tested for shared, pleiotropic loci influencing energy homeostasis.

RESEARCH METHODS AND PROCEDURES

Segregating (AxB6)F2 intercross (n = 514) and (B6AF1xA/J)N2 backcross (N = 223) populations were studied, phenotyping for weight and exploratory behaviors. Relationships among traits were analyzed by correlations. Weight traits were dissected with a genome-wide scan.

RESULTS

Modest correlations were found between exploratory behaviors and weight, explaining 2% to 14% of the variance. Quantitative trait loci (QTL) for body weight at 8 weeks (wgt8), 10 weeks (wgt10), and 2-week weight gain (difference between weeks 8 and 10) on a 6% fat diet were mapped. Two QTL on chromosome 1 (peaks at 66 cM and 100 cM; Bw8q1) affected wgt8 [likelihood of the odds ratio (Lod), 3.0 and 4.4] and wgt10 (Lod, 2.2 and 3.4), respectively. In the backcross, a significant QTL on chromosome 4 (peak at 66 cM; Bw8q2) affected wgt 8 (Lod, 3.3) and wgt10 (Lod, 3.1). For 2-week weight gain, suggestive QTL were mapped on chromosomes 4 and 6. The chromosome 6 QTL region overlaps a human 7q locus for obesity. A search for between-strain sequence polymorphisms in the leptin and NPY genes was unrevealing.

DISCUSSION

In mice, loci influencing exploratory activity play a modest role in body-weight regulation. Some forms of obesity may emerge from loci regulating normal body weight.

Influence of physical training on plasma leptin in obese youths

Little is known about the effects of different intensities of physical training on plasma leptin. This study examined the effect of two intensities of physical training on leptin in obese teenagers, and explored correlates at baseline and in response to 8 months of physical training. The participants were 55 obese youths 12-16 years of age who completed both baseline and posttesting. The youths were randomized to engage in lifestyle education only (LSE), moderate-intensity physical training and LSE, or high-intensity physical training and LSE. Baseline leptin was positively associated with fat mass. Girls had higher leptin levels at lower levels of fasting insulin than boys. The 8-mo physical training doses prescribed to obese teenagers did not result in significant group differences in mean change in leptin, although there was large variability in individual response. The change in leptin was inversely associated with baseline leptin and change in cardiovascular fitness. Diet, physical activity level, visceral adiposity, and glucose concentrations were not associated with leptin, neither at baseline nor in response to physical training. At baseline, total fat mass rather than visceral adiposity was associated with higher leptin levels. Over the 8-mo intervention period, regardless of group membership, youths who had the lowest increase in cardiovascular fitness tended to have the highest increase in leptin.

Leptin response to short-term fasting in sympathectomized men: role of the SNS

We studied plasma leptin levels in six people with high-lesion spinal cord injury [SCI; body mass index (BMI) 25.9 +/- 1.5 kg/m(2), age 37 +/- 3.0 yr] and six able-bodied (AB) controls (BMI 29.1 +/- 1.9 kg/m(2), age 35 +/- 3.5 yr) before and after 12, 24, and 36 h of fasting. The plasma leptin levels significantly decreased during 36 h fasting by 48.8 +/- 4.5% (pre: 11.3 +/- 2.3, post: 6.2 +/- 1.5 ng/ml) and 38.6 +/- 7.9% (pre: 7.6 +/- 5.0, post: 4.2 +/- 1.0 ng/ml) in SCI and AB, respectively. Plasma leptin started to decrease at 24 h of fasting in the SCI group, whereas plasma leptin started to decrease at 12 h of fasting in the AB group. The current study demonstrated that plasma leptin decreased with fasting in both SCI and AB groups, with the leptin decrease being delayed in the SCI group. The delayed leptin response to fasting in the SCI group may be because of increased fat mass (%body fat, SCI: 33.8 +/- 3.0, AB: 24.1 +/- 2.9) and sympathetic nervous system dysfunction.

Plasma adiponectin levels are not associated with fat oxidation in humans

OBJECTIVE

To test the hypothesis that low adiponectin is associated with low fat oxidation in humans.

RESEARCH METHODS AND PROCEDURES

We measured plasma adiponectin concentrations in 75 healthy, nondiabetic Pima Indians (age, 28 +/- 7 years; 55 men and 20 women; body fat, 29.7 +/- 7.5%) and 18 whites [(age, 33 +/- 8 years; 14 men and 4 women; body fat, 28.2 +/- 10.8% (means +/- SD)] whose body composition was measured by DXA and 24-hour energy expenditure (24-hour EE) by a respiratory chamber. Respiratory quotient (an estimate of whole-body carbohydrate/lipid oxidation rate) was calculated over 24 hours (24-hour RQ).

RESULTS

Before correlational analyses, waist-to-thigh ratio (WTR) and percentage of body fat (PFAT) were adjusted for age, sex, and race; 24-hour EE was adjusted for fat mass and fat-free mass, and 24-hour RQ were adjusted for energy balance. Plasma adiponectin concentrations were negatively correlated with WTR (r = -0.42, p < 0.0001) and PFAT (r = -0.46, p < 0.0001). There was no correlation between plasma adiponectin concentrations and 24-hour RQ, (r = 0.09, p = 0.36) before or after adjustment for PFAT (r = 0.001, p = 0.99, respectively, partial correlation), and no correlation was found between plasma adiponectin concentrations and 24-hour EE (r = -0.12, p = 0.27).

DISCUSSION

Our cross-sectional data do not suggest physiological concentrations of fasting plasma adiponectin play a role in the regulation of whole-body fat oxidation or energy expenditure in resting conditions. Whether administration of adiponectin to individuals with low levels of this hormone will increase their fat oxidation rates/energy expenditure remains to be established.

Assessing risk factors for obesity between childhood and adolescence: II. Energy metabolism and physical activity

OBJECTIVE

To assess the effect of energy expenditure, including resting metabolic rate (RMR), total energy expenditure (TEE), and activity energy expenditure (AEE), as well as substrate oxidation (respiratory quotient [RQ]), on the development of obesity in a large cohort of Native American children with a high propensity for obesity.

METHODS

During the summer months of 1992 to 1995 and again 5 years later, 138 (65 boys and 73 girls) 5-year-old Pima Indian children were studied. At baseline and follow-up, height and weight were measured; body composition was assessed with the use of 18O dilution; RMR and RQ were assessed with the use of indirect calorimetry; TEE was measured with the use of the doubly-labeled water method; and AEE was calculated (TEE - [RMR + 0.1 x TEE]). In addition, an activity questionnaire was used to assess participation in sporting activities as well as television viewing during the previous year. Linear regression models were used to assess the effects of the baseline variables on the development of obesity.

RESULTS

Pima Indian children were markedly overweight at both 5 and 10 years of age. Cross-sectionally, percentage of body fat and body weight at 5 and 10 years of age were negatively correlated with sports participation and positively correlated with television viewing. Most important, there was a marked change in the correlation between body size and activity between 5 and 10 years of age: at age 5 years, weight was positively correlated with AEE and PAL, but at age 10 years, the correlation with AEE was lost and that with PAL was negative. However, prospectively, none of the variables measured at baseline was a predictor of percentage of body fat at age 10 years after adjustment for percentage of body fat at age 5 years.

CONCLUSIONS

At age 5 years, obesity is associated with decreased participation in sports and increased television viewing but not with a decreased PAL. At age 10 years, obesity is associated with decreased participation in sports, increased television viewing, and a decreased PAL, suggesting that a decrease in PAL in free-living conditions seems to follow, not precede, the development of obesity.

Assessing risk factors for obesity between childhood and adolescence: I. Birth weight, childhood adiposity, parental obesity, insulin, and leptin

OBJECTIVE

To assess the effects of body weight, body composition, parental obesity, and metabolic variables on the development of obesity in a large cohort of 5-year-old Native American children with a high propensity for obesity.

METHODS

During the summer months of 1992 to 1995 and again 5 years later, 138 (65 boys and 73 girls) 5-year-old Pima Indian children were studied. Height; weight; body composition; parental obesity; and fasting plasma insulin, glucose, and leptin concentrations were determined at baseline and follow-up. Linear regression models were used to assess the effect of the baseline variables on the development of obesity.

RESULTS

At both 5 and 10 years of age, Pima Indian children were heavier and fatter than an age- and gender-matched reference population. All anthropometric and metabolic variables tracked strongly from 5 to 10 years of age (r > or = 0.70). The most significant determinant of percentage of body fat at 10 years of age was percentage of body fat at 5 years of age (R(2) = 0.53). The combined effect of high maternal body mass index, elevated fasting plasma leptin concentrations, and low fasting plasma insulin concentrations at baseline explained an additional 4% of the total variance in adiposity at follow-up.

CONCLUSIONS

Although parental obesity and metabolic variables such as insulinemia and leptinemia at baseline account for a small percentage of the variance in adiposity at follow-up, early childhood obesity is the dominant predictor of obesity 5 years later. These results suggest that strategies to prevent childhood obesity must be initiated at a very early age.

Leptin levels, leptin receptor gene polymorphisms, and energy metabolism in women

OBJECTIVE

Resting metabolic rate (RMR) is mainly determined by fat-free mass and additionally by age, sex, hormones, and possibly genetic differences. We evaluated whether leptin levels and polymorphisms in the leptin receptor (LEPR) gene were associated with energy expenditure phenotypes.

METHODS

RMR, body composition, and leptin levels were measured in 125 overweight and obese women. Three LEPR polymorphisms, Lys109Arg, Gln223Arg, and Lys656Asn, were typed on genomic DNA of another group of 192 women in whom RMR was measured. Fat, protein, and carbohydrate oxidation were calculated for 103 of these subjects. In 38 subjects, glucose-induced thermogenesis was measured over 3 hours.

RESULTS

In the first study group, a negative correlation between RMR and leptin levels was found after controlling for fat and fat-free mass. In multiple regression analysis, leptin contributed significantly to RMR, independent of body composition. In the second study group, RMR was not associated with LEPR polymorphisms. Differences in substrate oxidation rates were found among genotypes at the Lys656Asn site. In fasting conditions, Lys656Lys showed a trend to oxidize more carbohydrates and less fat than Asn656 carriers, a trend which became significant after the glucose load when carbohydrate oxidation rate in Lys656Lys was 15% higher than in Asn656 carriers (p = 0.04), and fat oxidation rate was 44% lower (p = 0.02).

DISCUSSION

These results suggest that DNA sequence variations in the LEPR gene could affect substrate oxidation. We hypothesize that this might be caused by differences in glucose levels, leading to differences in glucose oxidation rates.

Diurnal leptin rhythms in children treated with prednisolone once daily in the morning or in the evening

Serum leptin levels exhibit a marked diurnal variation in children. The aim of the present study was to investigate whether the timing of administration of exogenous glucocorticoids, which have been found to increase serum leptin, affects the diurnal rhythm. Four girls and four boys aged 10.6 to 15.8 (mean 13.2) years with asthma were studied. The design was an open 2-period cross-over trial with a 1-day run in, two 4-day periods of prednisolone 5 mg in the morning or in the evening, with a 3-week washout in between treatment periods. During run in and on the last day of the prednisolone periods a fasting blood sample was drawn at 08.00 h, and thereafter samples were obtained every 2 h throughout the day until 08.00 h the next morning. Serum leptin was measured by a specific radioimmunoassay. During all periods, leptin levels were low during the day with a nadir at 10.00 h (run-in [mean +/- SEM]: 3.9+/-1.28; morning prednisolone: 5.2+/-1.58; evening prednisolone: 5.7+/-2.02 microg/l). Increases in leptin levels were detected from 20.00 h with zeniths at 24.00 h (run in: 7.2+/-1.86; evening prednisolone: 9.2+/-2.36 microg/l) and 02.00 h (morning prednisolone: 9.4+/-1.78 microg/l) (F = 115.5; p <0.01). As compared to run in, leptin levels were increased at all time points during prednisolone treatment in the morning (F = 16.0, p = 0.01) and in the evening (F = 12.6, p = 0.01). No statistically significant differences were found in leptin levels during prednisolone in the morning or in the evening (F = 0.44, p = 0.53). Therefore, the timing of administration of exogenous glucocorticoids does not affect diurnal leptin rhythms in children.

Plasma leptin and exercise: recent findings

The cloning of murine and human obese genes in 1994, and the subsequent identification that the product of the obese gene, leptin, is secreted from adipose tissue, stimulated a tremendous amount of interdisciplinary interest in adipose tissue endocrinology and the potential role of this tissue in the regulation of energy balance. Exercise, with concomitant changes in fuel flux, systemic hormone levels and energy expenditure, may contribute to the regulation of plasma leptin levels and presumably, leptin action. The initial work characterising the leptin-exercise relationship was equivocal. Cross-sectional studies provided some mixed evidence regarding the relationship between aerobic capacity or habitual physical activity and plasma leptin. In contrast, studies on acute bouts of exercise and exercise training interventions have, with few exceptions, suggested that exercise does not alter systemic leptin independent of changes in fat mass. In general, these studies did not carefully control for energy balance, and sampled only a single fasting plasma leptin level. Two recent studies utilising experimental designs in which energy balance was controlled and 24-hour profiles of plasma leptin were determined have provided the most compelling evidence to date of the interaction between exercise, energy balance and systemic leptin in humans. These studies provide a clear explanation for the apparent lack of an acute effect of exercise on systemic leptin and underscore the importance of clearly defining the balance between energy intake and energy expenditure when studying the physiology of leptin. The aim of this brief review is to provide an overview of the interaction between energy expenditure during physical activity and systemic leptin level. Special emphasis will be placed on those studies in which energy intake/balance was carefully controlled.

Serum leptin levels in alcoholic liver cirrhosis: relationship with gender, nutritional status, liver function and energy metabolism

OBJECTIVE

To determine serum leptin levels in alcoholic liver cirrhosis and the relationship with gender, nutritional status, liver function, energy metabolism, inflammatory state and refeeding.

SUBJECTS

Thirty-seven hospitalized alcoholic cirrhotic patients (M/F: 24/13), 27 hospitalized patients at risk of malnutrition but with normal liver function (M/F: 15/12) as control patients, and 31 healthy control subjects (M/F: 17/14) participated.

DESIGN

Liver function was assessed from Child-Pugh classification; anthropometric parameters and resting energy expenditure (REE) were measured; caloric intake was evaluated over 5 days; and serum leptin and insulin were assayed. The same protocol was performed after 1 month refeeding in 22 patients. Healthy subjects were studied as controls for anthropometric parameters and serum leptin levels.

RESULTS

Serum leptin levels were higher in male cirrhotic patients than in the other two male groups (P=0.0079) and in the same range in the female groups. They were higher in female than in male subjects in the three groups. In female cirrhotic patients, logarithmically transformed serum leptin levels correlated significantly with fat mass (P=0.0043), insulin levels (P=0.0072), REE (P=0.0133), bilirubin levels (P<0.0001), prothrombin time (P=0.0003) and Pugh score (P=0.0266) in simple regression analysis and with insulin levels (P=0.0137), but not with fat mass (P=0.0761), Pugh score (P=0.4472) and REE (P=0.4576) in multiple regression analysis. In the male cirrhotic and control patients, log (leptin) levels correlated with CRP (C reactive protein) (r=0.365, P=0.0223). Log (leptin) levels did not correlate with caloric intake in any of the groups. Leptin levels (P<0.05) and fat mass (P<0.02) increased with refeeding while liver function improved (P<0.01).

CONCLUSION

There is a gender difference in regulation of serum leptin level in alcoholic liver cirrhosis. Insulin level is the best determinant of leptin level in female patients while inflammatory state related to alcoholic hepatitis seems to have a greater influence in male patients. Although leptin levels positively correlated with REE in female patients, there is no evidence that leptin reduces caloric intake and fat stores in these patients.

Estrogen deficiency causes central leptin insensitivity and increased hypothalamic neuropeptide Y

OBJECTIVE

Altered fat distribution is a consequence of menopause, but the mechanisms responsible are unknown. Estrogen insufficiency in humans can be modeled using ovariectomized rats. We have shown that increased adiposity in these rats is due to reduced physical activity and transient hyperphagia, and can be reversed with 17beta-estradiol treatment. The aims of this study were to examine whether this altered energy balance is associated with circulating leptin insufficiency, central leptin insensitivity, decreased hypothalamic leptin receptor (Ob-Rb) expression, and/or increased hypothalamic neuropeptide Y (NPY).

METHODS

Plasma leptin levels, adipose tissue ob gene expression, energy balance responses to i.c.v. leptin, hypothalamic Ob-Rb expression and NPY concentration in five separate hypothalamic regions were measured in adult female rats after either ovariectomy or sham operations.

RESULTS

Obesity was not associated with hypoleptinemia or decreased ob gene expression in ovariectomized rats; however, it was associated with insensitivity to central leptin administration. Food intake was less suppressed and spontaneous physical activity was less stimulated by leptin. This was not due to decreased hypothalamic Ob-Rb expression. NPY concentration in the paraventricular nucleus of the hypothalamus was elevated in the ovariectomized rats, consistent with leptin insensitivity; however this effect was transient and disappeared as body fat and leptin levels increased further and hyperphagia normalized.

CONCLUSION

Impaired central leptin sensitivity and overproduction of NPY may contribute to excess fat accumulation caused by estrogen deficiency.

Leptin and obesity in mother-child pairs

Defects in the leptin gene or the leptin receptor may be a genetic cause of obesity, but little is known about the familial associations of leptin and obesity. This study compared plasma leptin and measures of obesity in a sample of 248 subjects (124 mother-offspring pairs); 34% were African American and 66% were white. Youth were aged 12 to 16 years. Plasma leptin and body mass index (BMI) were higher in mothers than in their offspring and, among the offspring, higher in girls than boys, even after correcting for BMI or body fat. Racial differences in leptin were present in both mothers and youth when adjusting for percentage body fat but disappeared when adjusting for BMI. In univariate analyses of the associations between mothers and offspring, BMI was associated with leptin in all groups but was most strongly associated in white pairs and in mother-son pairs. In multiple regression analyses, when adjusting for BMI, significant predictors of leptin levelfor the boys and girls together were gender, BMI, and pubertal status of the offspring; in girls only BMI was significant (R2 = 0.72), and in boys the significant predictors were their BMI (R2 = 0.66) followed by their pubertal status (R2 = 0.06) and the leptin level of their mothers (R2 = 0.02). When adjusting for body fat, the predictors were the offspring's percentage bodyfat (R2 = 0. 67) and mother's leptin (R2 = 0.03), with similar results in gender-specific analyses. The authors conclude that leptin levels of youth are most closely associated with their degree of obesity or body fat; mother's leptin and, for boys only, pubertal status also play a small role. Although the small association between maternal leptin on leptin in their offspring could be due to either heredity or shared environment, the results of this study suggest that individual obesity and environmental factors are important predictors of leptin levels in children.

Leptin levels are associated with fat oxidation and dietary-induced weight loss in obesity

OBJECTIVE

To examine the relationship between fasting plasma leptin and 24-hour energy expenditure (EE), substrate oxidation, and spontaneous physical activity (SPA) in obese subjects before and after a major weight reduction compared with normal weight controls. To test fasting plasma leptin, substrate oxidations, and SPA as predictive markers of success during a standardized weight loss intervention.

RESEARCH METHODS AND PROCEDURES

Twenty-one nondiabetic obese (body mass index: 33.9 to 43.8 kg/m(2)) and 13 lean (body mass index: 20.4 to 24.7 kg/m(2)) men matched for age and height were included in the study. All obese subjects were reexamined after a mean weight loss of 19.2 kg (95% confidence interval: 15.1-23.4 kg) achieved by 16 weeks of dietary intervention followed by 8 weeks of weight stability. Twenty-four-hour EE and substrate oxidations were measured by whole-body indirect calorimetry. SPA was assessed by microwave radar.

RESULTS

In lean subjects, leptin adjusted for fat mass (FM) was correlated to 24-hour EE before (r = -0.56, p < 0.05) but not after adjustment for fat free mass. In obese subjects, leptin correlated inversely with 24-hour and resting nonprotein respiratory quotient (r = -0.47, p < 0.05 and r = -0.50, p < 0.05) both before and after adjustments for energy balance. Baseline plasma leptin concentration, adjusted for differences in FM, was inversely related to the size of weight loss after 8 weeks (r = -0.41, p = 0.07), 16 weeks (r = -0.51, p < 0.05), and 24 weeks (r = -0.50, p < 0.05).

DISCUSSION

The present study suggests that leptin may have a stimulating effect on fat oxidation in obese subjects. A low leptin level for a given FM was associated with a greater weight loss, suggesting that obese subjects with greater leptin sensitivities are more successful in reducing weight.