Diurnal and ultradian rhythmicity of plasma leptin: effects of gender and adiposity

Harnessing the Power of Leptin: The Biochemical Link Connecting Obesity, Diabetes, and Cognitive Decline

In this review, the current understanding of leptin’s role in energy balance, glycemic regulation, and cognitive function is examined, and its involvement in maintaining the homeostatic “harmony” of these physiologies is explored. The effects of exercise on circulating leptin levels are summarized, and the results of clinical application of leptin to metabolic disease and neurologic dysfunction are reviewed. Finally, pre-clinical evidence is presented which suggests that synthetic peptide leptin mimetics may be useful in resolving not only the leptin resistance associated with common obesity and other elements of metabolic syndrome, but also the peripheral insulin resistance characterizing type 2 diabetes mellitus, and the central insulin resistance associated with certain neurologic deficits in humans.

Role of breakfast skipping, depression, and other risk factors for obesity: The Youth Risk Behavior Surveillance System

Background and objectives: Obesity among adolescents is a significant public health concern in the United States. The prevalence of obesity has increased from 13.0% in 2011 to 15.5% in 2019. The association between breakfast skipping and obesity is still controversial, and a mediator role of depression in this association is limited. The purpose of this study was to investigate the independent association between breakfast skipping and obesity and to investigate the mediator role of depressive symptomology between breakfast skipping and obesity prevalence. Materials and methods: In this cross-sectional study, data were extracted from the CDC's Youth Risk Behavior Surveillance System (YRBSS) for 9th to 12th graders from 2011 through 2020. SAS version 9.4 was used to analyze the data using proc survey frequency and proc survey logistic regression models. The adjusted odds ratios (aORs) with 95% confidence intervals (CI) were estimated. The Sobel test also was performed to test the mediator role of self-reported depression. Results: Of the 56,320 adolescents, 13.7% did not eat breakfast, 14.1% were obese, and 15.1% had depressive symptomology. Breakfast non-eaters was associated with a 24% increased odds of obesity (aOR: 1.24; 95% CI: 1.14 to 1.36) after adjusting for race/ethnicity, gender, grade level, and behavioral risk factors. A mediator role of self-reported depression was noted using the regression model and Sobel test (z = 3.90, S.E. = 0.02, p< 0.0001) between breakfast skipping and obesity. Conclusions: Breakfast skipping was independently associated with obesity. Self-reported depression was identified as a mediator factor. Therefore, the mental health condition also needs to be addressed in the prevention of obesity among adolescents. IMC J Med Sci 2022; 16(2): 001 *Correspondence: Azad R. Bhuiyan, Department of Epidemiology and Biostatistics, School of Public Health, College of Health Sciences, Jackson State University, Jackson, MS 39213, USA. Email: azad.r.bhuiyan@jsums.edu

Neurohumoral Profiles and Childhood Adversity of Patients with Multisomatoform Disorder and Pain as the Leading Bodily Symptom

Objective

Patients suffering from chronic pain often present with multifactorial underlying conditions, sometimes without concrete pathological physical findings. Functional somatic syndromes (FSS) and somatoform disorders show a high prevalence of 8-20% and are often associated with adverse childhood experiences (ACE) and chronic stress. As many different FSS have overlapping symptoms, the concept of multisomatoform disorder (MSD) has been introduced as an encompassing concept. We hypothesize that a common neurohumoral profile is present in patients with MSD that is distinct from gender- and age-matched controls and thus provides insight into possible common underlying mechanisms.

Design

In 151 patients with MSD (138 females) and 149 matched controls (131 females), we determined ACE by the Childhood Trauma Questionnaire (CTQ) and chronic stress by the Trier Inventory for Chronic Stress (TICS). Furthermore, the serum levels of leptin, FSH, LH, cortisol, DHEA-S, and IGF-1 have been assessed.

Results

There were significant differences in the levels of leptin, FSH, IGF-1, and cortisol between patients and controls, mainly driven by female participants. Levels of leptin were significantly correlated with BMI in patients, in controls, and in the female subgroup. This correlation was exaggerated in female patients when compared to female controls. Both CTQ and TICS predicted MSD directly and indirectly through the levels of leptin.

Conclusion

There is evidence of a distinct neurohumoral profile in female patients with MSD when compared to matched healthy controls, similar to what has been demonstrated in other chronic pain states. The observed profile can be taken as possible evidence for a dysregulated response to chronic stress and metabolic balance as well as a state of hypocortisolism and HPA-axis dysfunction. ACE and chronic stress play a major role in the development of MSD and altered neurohumoral profile.

Seasonal differences in clock gene expression levels in buccal epithelial cells of obese men: a pilot study

Various biological processes show seasonal variations in humans, including important metabolic pathways. Seasonal changes in gene expression may affect annual differences in human immunity. We hypothesized that seasonal changes occur in clock gene expression levels that are associated with body mass index. Six non-obese men and five obese men participated in summer and winter. Two milliliters of saliva were collected, and total RNA was isolated from buccal epithelial cells in saliva. The clock gene expression levels of CLOCK, BMAL1, PER1, CRY2, REV-ERB-α, and REV-ERB-ß were examined by real-time PCR. Blood samples were measured HbA1c, glucose, insulin, adiponectin, IL-6, and TNF-α. Participants were asked about their sleeping hours and seasonal pattern. In the present study, CLOCK, BMAL1, and REV-ERB-β gene expression levels were significantly lower in winter than in summer; BMAL1 expression level was significantly lower in obese men than in non-obese. Concentrations of adiponectin and insulin were significantly different between obese and non-obese. No significant seasonal effects were observed in HbA1c, glucose, insulin, adiponectin, IL-6, or TNF-α concentrations. Sleep duration did not significantly differ between summer and winter. The short photoperiod during winter might contribute to seasonal alterations in the expression of clock genes in men. In the present results, revealed seasonal differences in clock gene expression levels might be associated with obesity. These results also showed the potential for measuring clock gene expression in a non-invasive manner using saliva samples.

Adipose tissue in health and disease

Adipose, or fat, tissue (AT) was once considered an inert tissue that primarily existed to store lipids, and was not historically recognized as an important organ in the regulation and maintenance of health. With the rise of obesity and more rigorous research, AT is now recognized as a highly complex metabolic organ involved in a host of important physiological functions, including glucose homeostasis and a multitude of endocrine capabilities. AT dysfunction has been implicated in several disease states, most notably obesity, metabolic syndrome and type 2 diabetes. The study of AT has provided useful insight in developing strategies to combat these highly prevalent metabolic diseases. This review highlights the major functions of adipose tissue and the consequences that can occur when disruption of these functions leads to systemic metabolic dysfunction.

Dietary Options for Rodents in the Study of Obesity

Obesity and its associated metabolic diseases are currently a priority research area. The increase in global prevalence at different ages is having an enormous economic and health impact. Genetic and environmental factors play a crucial role in the development of obesity, and diet is one of the main factors that contributes directly to the obesogenic phenotype. Scientific evidence has shown that increased fat intake is associated with the increase in body weight that triggers obesity. Rodent animal models have been extremely useful in the study of obesity since weight gain can easily be induced with a high-fat diet. Here, we review the dietary patterns and physiological mechanisms involved in the dynamics of energy balance. We report the main dietary options for the study of obesity and the variables to consider in the use of a high-fat diet, and assess the progression of obesity and diet-induced thermogenesis.

Evaluation of leptin concentration in Gingival Crevicular Fluid (GCF) during orthodontic tooth movement and its correlation to the rate of tooth movement

OBJECTIVES:

Leptin, a polypeptide which is related to body fat regulation, is also found to have a role in the inflammatory reaction. The aim of this study is to assess the concentration of leptin in Gingival Crevicular Fluid (GCF) during orthodontic force application and to correlate its concentration to rate of tooth movement.

METHODS:

Twenty orthodontic patients (10 males and 10 females) were selected for the study. Leptin concentration was measured at T0, before force application; T1, one hour after force application; T2, one day after force application; T3, one week after force application; T4, one month after force application. GCF was collected using filter paper strips from the distal aspect of gingival sulcus of the right maxillary canine distalized by an active lace-backs of tooth movement was measured on dental casts, before and one month after force application. One-way ANOVA with Bonferroni correction and Pearson's correlation test were used to analyze the data.

RESULTS:

The mean GCF leptin concentration increased from T0 to T1, rose to a peak at T2, then declined to a minimum value at T3 and then increased to a value at T4, closer to the base line value (T0), and it was statistically significant (P < 0.05). There was positive correlation of the overall mean leptin concentration to rate of tooth movement (correlation coefficient = 0.634).

CONCLUSION:

There was a biphasic change in GCF leptin concentration during one cycle of orthodontic force application. There was a positive correlation between the GCF leptin concentration and rate of tooth movement.

Evidence for a Coupled Oscillator Model of Endocrine Ultradian Rhythms

Whereas long-period temporal structures in endocrine dynamics have been well studied, endocrine rhythms on the scale of hours are relatively unexplored. The study of these ultradian rhythms (URs) has remained nascent, in part, because a theoretical framework unifying ultradian patterns across systems has not been established. The present overview proposes a conceptual coupled oscillator network model of URs in which oscillating hormonal outputs, or nodes, are connected by edges representing the strength of node-node coupling. We propose that variable-strength coupling exists both within and across classic hormonal axes. Because coupled oscillators synchronize, such a model implies that changes across hormonal systems could be inferred by surveying accessible nodes in the network. This implication would at once simplify the study of URs and open new avenues of exploration into conditions affecting coupling. In support of this proposed framework, we review mammalian evidence for (1) URs of the gut-brain axis and the hypothalamo-pituitary-thyroid, -adrenal, and -gonadal axes, (2) UR coupling within and across these axes; and (3) the relation of these URs to body temperature. URs across these systems exhibit behavior broadly consistent with a coupled oscillator network, maintaining both consistent URs and coupling within and across axes. This model may aid the exploration of mammalian physiology at high temporal resolution and improve the understanding of endocrine system dynamics within individuals.

Serum Leptin, Obestatin, and Ghrelin Levels and Gastric Emptying Rates of Liquid and Solid Meals in Non-obese Rats with Roux-en-Y Bypass Surgery or Prosthesis Placement: Implications for the Role of Vagal Afferents

BACKGROUND

The present study aimed to investigate the effects of Roux-en-Y gastric bypass (RYGB) and prosthesis placement on gastric emptying rate in conjunction with serum ghrelin-obestatin-leptin responses in non-obese rats with intact or denervated afferent innervation.

METHODS

Under anesthesia, male Sprague-Dawley rats underwent either sham operation, RYGB, prosthesis, and/or Gregory cannula placement. Three weeks later, liquid or solid gastric emptying tests were performed and serum ghrelin, leptin and obestatin levels were measured.

RESULTS

Both prosthesis placement and RYGB surgery delayed non-nutrient liquid emptying; while solid nutrient emptying was delayed only by RYGB. Nutrient-dependent (acid, hyperosmolal and peptone) delay in liquid emptying was abolished in rats with prosthesis. By vagal afferent denervation, delayed liquid emptying was abolished, while solid emptying was further delayed in rats with prosthesis. Ghrelin and obestatin levels were depressed in prosthesis-placed rats, but RYGB surgery had no impact on both levels. Leptin level was elevated in solid-food-given rats with prosthesis, but not changed in RYGB group, while it was reduced following liquid meal. All the changes observed in ghrelin, obestatin, or leptin levels in response to meal ingestion were reversed with vagal afferent denervation.

CONCLUSIONS

Both RYGB and prosthesis placement had delaying effects on gastric emptying rate of non-obese rats. Our results indicate that the short-term changes in gastric motility and hormone responses induced by volume reduction are reversed by afferent denervation, suggesting that sparing the vagal innervation could be essential for reaching optimum motility and hormone changes expected after bariatric surgery.

Different Intestinal Microbial Profile in Over-Weight and Obese Subjects Consuming a Diet with Low Content of Fiber and Antioxidants

Obesity has been related to an increased risk of multiple diseases in which oxidative stress and inflammation play a role. Gut microbiota has emerged as a mediator in this interaction, providing new mechanistic insights at the interface between fat metabolism dysregulation and obesity development. Our aim was to analyze the interrelationship among obesity, diet, oxidative stress, inflammation and the intestinal microbiota in 68 healthy adults (29.4% normal-weight). Diet was assessed through a food frequency questionnaire and converted into nutrients and dietary compounds using food composition tables. The intestinal microbiota was assessed by quantitative PCR, fecal short chain fatty acids by gas chromatography and serum biomarkers by standard protocols. Higher levels of malondialdehyde (MDA), C reactive protein (CRP), serum leptin, glucose, fat percentage and the intestinal Lactobacillus group were found in the obese people. Cluster analysis of body mass index, fat mass, glucose, LDL/HDL ratio, leptin, MDA and CRP classified the subjects into two groups. The levels of the intestinal Bacteroides-Prevotella-Porphyromonas group were lower in the cluster and linked to a higher pro-oxidant and pro-inflammatory status, whose individuals also had lower intake of fruits, dried fruits, and fish. These results could be useful for designing strategies targeted to obesity prevention.

Interleukin-7 Plasma Levels in Human Differentiate Anorexia Nervosa, Constitutional Thinness and Healthy Obesity

Introduction

Interleukin-7 (IL-7) is a cytokine involved in energy homeostasis as demonstrated in rodents. Anorexia nervosa is characterized by restrained eating behavior despite adaptive orexigenic regulation profile including high ghrelin plasma levels. Constitutional thinness is a physiological condition of resistance to weight gain with physiological anorexigenic profile including high Peptide YY plasma level. Healthy obesity can be considered as a physiological state of resistance to weight loss with opposite appetite regulating profile to constitutional thinness including low Peptide YY plasma level. No studies in IL-7 are yet available in those populations. Therefore we evaluated circadian plasma levels of IL-7 in anorexia nervosa compared to constitutional thinness, healthy obese and control females.

Materials and Methods

10 restrictive-type anorexia nervosa women, 5 bingeing/purging anorexia nervosa woman, 5 recovered restrictive anorexia nervosa women, 4 bulimic females, 10 constitutional thinness women, 7 healthy obese females, and 10 normal weight women controls were enrolled in this cross-sectional study, performed in endocrinology unit and academic laboratory. Twelve-point circadian profiles of plasma IL-7 levels were measured in each subject.

Results

24h mean IL-7 plasma levels (pg/ml, mean±SEM) were decreased in restrictive-type anorexia nervosa (123.4±14.4, p<0.0037), bingeing/purging anorexia nervosa (24.2±5.6, p<0.001), recovered restrictive anorexia nervosa (64.2±16.1, p = 0.01) and healthy obese patients (51±3.2, p<0.001) compared to controls (187.7±28.6). Bulimic patients (197.4±42.7) and constitutional thinness patients (264.3±35.8) were similar to controls.

Conclusions

Low IL-7 is part of the adaptive profile in restrictive-type anorexia nervosa, confirming its difference with constitutional thinness. Healthy obesity, with low IL-7, is once again in mirror image of constitutional thinness with normal high IL-7.

Impact of leptin on memory function and hippocampal structure in mild cognitive impairment

Metabolic changes have been suggested to contribute to dementia and its precursor mild cognitive impairment (MCI), yet previous results particularly for the "satiety hormone" leptin are mixed. Therefore, we aimed to determine if MCI patients show systematic differences in leptin, independent of sex, adipose mass, age, and glucose and lipid metabolism, and whether leptin levels correlated with memory performance and hippocampal integrity. Forty MCI patients (20 females, aged 67 years ± 7 SD) were compared to 40 healthy controls (HC) that were pair-wise matched for sex, age, and body fat. Memory performance was assessed using the auditory verbal learning test. Volume and microstructure of the hippocampus were determined using 3T-neuroimaging. Fasting serum markers of leptin, glucose and lipid metabolism, and other confounding factors were assayed. MCI patients, compared with HC, showed lower serum leptin, independent of sex, age, and body fat (P < 0.001). Glucose and lipid markers did not attenuate these results. Moreover, MCI patients exhibited poorer memory and lower volume and microstructural integrity within hippocampal subfields. While leptin and memory were not significantly correlated, mediation analyses indicated that lower leptin contributed to poorer memory through its negative effect on right hippocampus volume and left hippocampus microstructure. We demonstrated that MCI is associated with lower serum leptin independent of sex, age, body fat, glucose, and lipid metabolism. Our data further suggest that inefficient leptin signaling could partly contribute to decreases in memory performance through changes in hippocampus structure, a hypothesis that should now be verified in longitudinal studies. Hum Brain Mapp 37:4539-4549, 2016. © 2016 Wiley Periodicals, Inc.

Stimulants for the Control of Hedonic Appetite

The focus of this paper is treatment of obesity in relation to the management of hedonic appetite. Obesity is a complex condition which may be potentiated by excessive reward seeking in combination with executive functioning deficits that impair cognitive control of behavior. Stimulant medications address both reward deficiency and enhance motivation, as well as suppressing appetite. They have long been recognized to be effective for treating obesity. However, stimulants can be abused for their euphoric effect. They induce euphoria via the same neural pathway that underlies their therapeutic effect in obesity. For this reason they have generally not been endorsed for use in obesity. Among the stimulants, only phentermine (either alone or in combination with topiramate) and bupropion (which has stimulant-like properties and is used in combination with naltrexone), are approved by the United States Food and Drug Administration (FDA) for obesity, although dexamphetamine and methylpenidate are approved and widely used for treating attention deficit hyperactivity disorder (ADHD) in adults and children. Experience gained over many years in the treatment of ADHD demonstrates that with careful dose titration, stimulants can be used safely. In obesity, improvement in mood and executive functioning could assist with the lifestyle changes necessary for weight control, acting synergistically with appetite suppression. The obesity crisis has reached the stage that strong consideration should be given to adequate utilization of this effective and inexpensive class of drug.

Association of Leptin with Body Pain in Women

Leptin, an appetite-regulatory hormone, is also known to act as a proinflammatory adipokine. One of the effects of increased systemic leptin concentrations may be greater sensitivity to pain. We report the results of two studies examining the association between leptin and pain: a small pilot longitudinal study, followed by a large cross-sectional study. In Study 1, three women with physician-diagnosed fibromyalgia provided blood draws daily for 25 consecutive days, as well as daily self-reported musculoskeletal pain. Daily fluctuations in serum leptin were positively associated with pain across all three participants (F (1,63) = 12.8, p < 0.001), with leptin predicting ∼49% of the pain variance. In Study 2, the relationship between leptin and body pain was examined in a retrospective cross-sectional analysis of 5676 generally healthy postmenopausal women from the Women's Health Initiative. Leptin levels obtained from single blood draws were tested for a relationship with self-reported body pain. Body mass index (BMI) was also included as a predictor of pain. Both leptin and BMI were found to be independently associated with self-reported pain (p = 0.001 and p < 0.001, respectively), with higher leptin levels and greater BMI each being associated with greater pain. Leptin appears to be a predictor of body pain both within- and between-individuals and may be a driver of generalized pain states such as fibromyalgia.

Stimulant medication effects on growth and bone age in children with attention-deficit/hyperactivity disorder: a prospective cohort study

Stimulant medication is known to cause transient weight loss and slowing down of growth, but whether it delays physical maturation is unclear. We studied growth and bone age over the first 3 years of treatment in children with attention-deficit/hyperactivity disorder (patients) compared with healthy siblings (controls). Bone age was estimated blindly by two independent radiologists using Tanner and Whitehouse version 3. Dexamphetamine or methylphenidate was titrated and continued when clinically indicated. Forty out of 73 patients, together with 22 controls, completed the study. There were no significant growth differences between the two groups at baseline. Despite slower growth on treatment [5.1 cm/year, 95% confidence interval (CI): 4.7-5.5, vs. 6.3 cm/year, 95% CI: 5.7-6.8, P=0.002; and 2.7 kg/year, 95% CI: 2.1-3.3, vs. 4.4 kg/year, 95% CI: 3.5-5.3, P=0.005], the patients showed no significant maturational delay (RUS score: 49 U/year, 95% CI: 44-55, vs. 55 U/year, 95% CI: 47-63, P=0.27). A subgroup of patients underwent serial biochemistry and dual-energy X-ray absorptiometry, recording a significant reduction in fat (5.61±3.56-4.22±3.09 kg, P<0.001) and leptin (3.88±2.87-2.57±1.94 ng/ml, P=0.017). The pattern of change in height z-score over time was modified by the dose of medication (P for interaction=0.024). We found no medication effect on the rate of maturation, which was instead predicted by baseline leptin (P=0.035 controlling for age and sex).

Leptin Level and Skipping Breakfast: The National Health and Nutrition Examination Survey III (NHANES III)

Skipping breakfast is a common dietary habit considered to be unhealthy. However, the mechanisms underlying skipping breakfast have not been fully explored. Leptin is a hormone that regulates food intake and energy storage and secretes in a diurnal rhythm with lowest levels in the morning. We examined the association between the serum leptin level and skipping breakfast in 5714 adults in the U.S. National Health and Nutrition Examination Survey III, 1988-1994. We defined breakfast as any food or beverage consumed between 5:00 a.m. and 10:00 a.m. using a single 24-h recall. Skipped breakfast was seen in 13.1%. In the logistic regression models with and without adjusting for adiposity and sex, leptin levels were not associated with skipping breakfast. After adjusting for age, race/ethnicity, and time of venipuncture, the association remained insignificant. After further adjusting for potential confounders: physical activity, alcohol intake, smoking and diabetes and after further adjusting for: dietary factors, insulin and glucose levels, there was a 9% and 11%-12%, respectively, statistically significantly higher likelihood of skipping breakfast if the leptin level was more than 50% greater. Further investigation into the biological reasons for skipping breakfast may be useful for promoting healthy lifestyles.

Evidence for abnormal cytokine expression in Gulf War Illness: A preliminary analysis of daily immune monitoring data

Background

Gulf War Illness (GWI) is a clinically heterogeneous chronic condition that affects many veterans of the 1990–1991 Persian Gulf War. One of the most prevalent and debilitating symptoms of GWI is abnormal fatigue. The mechanisms underlying GWI generally, and fatigue symptoms specifically, have yet to be conclusively identified, although immune system abnormalities are suspected to be involved. The first goal of this immune monitoring study was to determine if GWI is associated with higher absolute levels and daily variability of pro-inflammatory immune factors. The second goal was to explore the relationship between day-to-day immune marker fluctuations and daily self-reported fatigue severity.

Methods

We recruited veterans with GWI and healthy veteran control (HV) participants to provide self-reported fatigue severity data and blood samples, over 25 consecutive days. We profiled inflammatory processes by using a longitudinal, daily immune-monitoring approach. For each day, serum cytokine and chemokine concentrations were determined using multiplex assays.

Results

Seven veterans with GWI and eight healthy veteran control (HV) participants completed the study protocol. We found that GWI was associated with higher variability in the expression of eotaxin-1 (p < 0.001). For GWI participants, higher fatigue severity days were associated with greater IL-1β (p = 0.008) and IL-15 (p < 0.001).

Conclusions

Our findings provide preliminary evidence that the immune system is involved in the pathophysiology of GWI. Longitudinal immune profiling approaches may be helpful in discovering targets for novel therapies in conditions such as GWI.

Effect of extended morning fasting upon ad libitum lunch intake and associated metabolic and hormonal responses in obese adults

Background/Objectives:

Breakfast omission is positively associated with obesity and increased risk of disease. However, little is known about the acute effects of extended morning fasting upon subsequent energy intake and associated metabolic/regulatory factors in obese adults.

Subjects/Methods:

In a randomised cross-over design, 24 obese men (n=8) and women (n=16) extended their overnight fast by omitting breakfast consumption or ingesting a typical carbohydrate-rich breakfast of 2183±393 kJ (521±94 kcal), before an ad libitum pasta lunch 3 h later. Blood samples were obtained throughout the day until 3 h post lunch and analysed for hormones implicated in appetite regulation, along with metabolic outcomes and subjective appetite measures.

Results:

Lunch intake was unaffected by extended morning fasting (difference=218 kJ, 95% confidence interval −54 kJ, 490 kJ; P=0.1) resulting in lower total intake in the fasting trial (difference=−1964 kJ, 95% confidence interval −1645 kJ, −2281 kJ; P<0.01). Systemic concentrations of peptide tyrosine–tyrosine and leptin were lower during the afternoon following morning fasting (P⩽0.06). Plasma-acylated ghrelin concentrations were also lower following the ad libitum lunch in the fasting trial (P<0.05) but this effect was not apparent for total ghrelin (P⩾0.1). Serum insulin concentrations were greater throughout the afternoon in the fasting trial (P=0.05), with plasma glucose also greater 1 h after lunch (P<0.01). Extended morning fasting did not result in greater appetite ratings after lunch, with some tendency for lower appetite 3 h post lunch (P=0.09).

Conclusions:

We demonstrate for the first time that, in obese adults, extended morning fasting does not cause compensatory intake during an ad libitum lunch nor does it increase appetite during the afternoon. Morning fasting reduced satiety hormone responses to a subsequent lunch meal but counterintuitively also reduced concentrations of the appetite-stimulating hormone-acylated ghrelin during the afternoon relative to lunch consumed after breakfast.

Carbohydrate-rich breakfast attenuates glycaemic, insulinaemic and ghrelin response to ad libitum lunch relative to morning fasting in lean adults

Breakfast omission is associated with obesity and CVD/diabetes, but the acute effects of extended morning fasting upon subsequent energy intake and metabolic/hormonal responses have received less attention. In a randomised cross-over design, thirty-five lean men (n 14) and women (n 21) extended their overnight fast or ingested a typical carbohydrate-rich breakfast in quantities relative to RMR (i.e. 1963 (sd 238) kJ), before an ad libitum lunch 3 h later. Blood samples were obtained hourly throughout the day until 3 h post-lunch, with subjective appetite measures assessed. Lunch intake was greater following extended fasting (640 (sd 1042) kJ, P< 0.01) but incompletely compensated for the omitted breakfast, with total intake lower than the breakfast trial (3887 (sd 1326) v. 5213 (sd 1590) kJ, P< 0.001). Systemic concentrations of peptide tyrosine-tyrosine and leptin were greater during the afternoon following breakfast (both P< 0.05) but neither acylated/total ghrelin concentrations were suppressed by the ad libitum lunch in the breakfast trial, remaining greater than the morning fasting trial throughout the afternoon (all P< 0.05). Insulin concentrations were greater during the afternoon in the morning fasting trial (all P< 0.01). There were no differences between trials in subjective appetite during the afternoon. In conclusion, morning fasting caused incomplete energy compensation at an ad libitum lunch. Breakfast increased some anorectic hormones during the afternoon but paradoxically abolished ghrelin suppression by the second meal. Extending morning fasting until lunch altered subsequent metabolic and hormonal responses but without greater appetite during the afternoon. The present study clarifies the impact of acute breakfast omission and adds novel insights into second-meal metabolism.

High prevalence of esophageal dysmotility in asymptomatic obese patients

BACKGROUND

Obesity is an important health problem affecting >500 million people worldwide. Esophageal dysmotility is a gastrointestinal pathology associated with obesity; however, its prevalence and characteristics remain unclear. Esophageal dysmotilities have a high prevalence among obese patients regardless of gastrointestinal symptoms.

OBJECTIVE

To identify the prevalence of esophageal dysmotility among obese patients. The secondary goals were to characterize these pathologies in obese patients and identify risk factors.

METHOD

A prospective study from January 2009 to March 2010 at the University of Montreal Hospital Centre (Montreal, Quebec) was performed. Every patient scheduled for bariatric surgery underwent preoperatory esophageal manometry and was included in the study. Manometry was performed according to a standardized protocol with the following measures: superior esophageal sphincter - coordination and release during deglutition; esophageal body - presence, propagation, length, amplitude and type of esophageal waves of contraction; lower esophageal sphincter - localization, tone, release, intragastic pressure and intraesophageal pressure. All reference values were those used in the digestive motility laboratory. A gastrointestinal symptoms questionnaire was completed on the day manometry was performed. Chart reviews were performed to identify comorbidities and treatments that could influence the results.

RESULTS

A total of 53 patients were included (mean [± SD] age 43 ± 10 years; mean body mass index 46 ± 7 kg/m; 70% female). Esophageal manometry revealed dysmotility in 51% (n=27) of the patients. This dysmotility involved the esophageal body in 74% (n=20) of the patients and the inferior sphincter in 11% (n=3). Mixed dysmotility (body and inferior sphincter) was found in 15% (n=4) of cases. The esophageal body dysmotilities were hypomotility in 85% (n=23) of the patients, either from insignificant waves (74% [n=20]), nonpropagated waves (11% [n=3]) or low-amplitude waves (33% [n=9]). Gastroesophageal symptoms were found in 66% (n=35) of obese patients, including heartburn (66% [n=23]), regurgitation (26% [n=9]), dysphagia (43% [n=15]), chest pain (6% [n=2]) and dyspepsia (26% [n=9]). Among symptomatic patients, 51% (n=18) had normal manometry and 49% (n=17) had abnormal manometry (statistically nonsignificant). Among asymptomatic patients (n=18), 44% (n=8) had normal manometry and 56% (n=10) had abnormal manometry (statistically nonsignificant). Furthermore, no statistical differences were found between the normal manometry group and the abnormal manometry group with regard to medication intake or comorbidities.

CONCLUSION

Esophageal dysmotilities had a high prevalence in obese patients. Gastrointestinal symptoms cannot predict the presence of esophageal dysmotility. Hypomotility of the esophageal body is the most common dysmotility, especially from the absence of significant waves.

The impact of leptin on perinatal development and psychopathology

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

Physiological responses to food intake throughout the day

Circadian rhythms act to optimise many aspects of our biology and thereby ensure that physiological processes are occurring at the most appropriate time. The importance of this temporal control is demonstrated by the strong associations between circadian disruption, morbidity and disease pathology. There is now a wealth of evidence linking the circadian timing system to metabolic physiology and nutrition. Relationships between these processes are often reciprocal, such that the circadian system drives temporal changes in metabolic pathways and changes in metabolic/nutritional status alter core molecular components of circadian rhythms. Examples of metabolic rhythms include daily changes in glucose homeostasis, insulin sensitivity and postprandial response. Time of day alters lipid and glucose profiles following individual meals whereas, over a longer time scale, meal timing regulates adiposity and body weight; these changes may occur via the ability of timed feeding to synchronise local circadian rhythms in metabolically active tissues. Much of the work in this research field has utilised animal and cellular model systems. Although these studies are highly informative and persuasive, there is a largely unmet need to translate basic biological data to humans. The results of such translational studies may open up possibilities for using timed dietary manipulations to help restore circadian synchrony and downstream physiology. Given the large number of individuals with disrupted rhythms due to, for example, shift work, jet-lag, sleep disorders and blindness, such dietary manipulations could provide widespread improvements in health and also economic performance.

Diurnal intermittent fasting during Ramadan: the effects on leptin and ghrelin levels

We aimed to assess the effect of Islamic intermittent fasting, during and outside of Ramadan, on plasma levels of leptin and ghrelin while controlling for several potential confounding variables. Eight healthy male volunteers with a mean age of 26.6±4.9 years reported to the sleep disorders center (SDC) at King Saud University on four occasions: 1) adaptation; 2) 4 weeks before Ramadan while performing Islamic fasting for 1 week (baseline fasting) (BLF); 3) 1 week before Ramadan (non-fasting baseline) (BL); and 4) during the second week of Ramadan while fasting. Plasma leptin and ghrelin levels were measured using enzyme-linked immunoassays at 22:00, 02:00, 04:00, 06:00, and 11:00. During BLF, there were significant reductions in plasma leptin concentrations at 22:00 and 02:00 compared with the baseline concentrations (at 22:00: 194.2±177.2 vs. 146.7±174.5; at 02:00: 203.8±189.5 vs. 168.1±178.1; p<0.05). During Ramadan, there was a significant reduction in plasma leptin levels at 22:00 (194.2±177.2 vs. 132.6±130.4, p<0.05). No significant difference in plasma ghrelin concentrations was detected during the BL, BLF, or Ramadan periods. Cosinor analyses of leptin and ghrelin plasma levels revealed no significant changes in the acrophases of the hormones during the three periods. The nocturnal reduction in plasma leptin levels during fasting may be the result of the changes in meal times during fasting.

Leptin: a biomarker for sleep disorders?

Leptin, a pleiotropic protein hormone produced mainly by fat cells, regulates metabolic activity and many other physiological functions. The intrinsic circadian rhythm of blood leptin is modulated by gender, development, feeding, fasting, sleep, obesity, and endocrine disorders. Hyperleptinemia is implicated in leptin resistance. To determine the specificity and sensitivity of leptin concentrations in sleep disorders, we summarize here the alterations of leptin in four conditions in animal and human studies: short duration of sleep, sleep fragmentation, obstructive sleep apnea (OSA), and after use of continuous positive airway pressure (CPAP) to treat OSA. The presence and causes of contradictory findings are discussed. Though sustained insufficient sleep lowers fasting blood leptin and therefore probably contributes to increased appetite, obesity and OSA independently result in hyperleptinemia. Successful treatment of OSA by CPAP is predicted to decrease hyperleptinemia, making leptin an ancillary biomarker for treatment efficacy. Current controversies also call for translational studies to determine how sleep disorders regulate leptin homeostasis and how the information can be used to improve sleep treatment.

Diminished leptin signaling can alter circadian rhythm of metabolic activity and feeding

Leptin, a hormone mainly produced by fat cells, shows cell-specific effects to regulate feeding and metabolic activities. We propose that an important feature of metabolic dysregulation resulting in obesity is the loss of the circadian rhythm of biopotentials. This was tested in the pan-leptin receptor knockout (POKO) mice newly generated in our laboratory. In the POKO mice, leptin no longer induced pSTAT-3 signaling after intracerebroventricular injection. Three basic phenotypes were observed: the heterozygotes had similar weight and adiposity as the wild-type (WT) mice (>60% of the mice); the homozygotes were either fatter (∼30%), or rarely leaner (<5%) than the WT mice. By early adulthood, the POKO mice had higher average body weight and adiposity than their respective same-sex WT littermate controls, and this was consistent among different batches. The homozygote fat POKO showed significant reduction of midline estimating statistic of rhythm of circadian parameters, and shifts of ultradian rhythms. The blunted circadian rhythm of these extremely obese POKO mice was also seen in their physical inactivity, longer feeding bouts, and higher food intake. The extent of obesity correlated with the blunted circadian amplitude, accumulative metabolic and locomotor activities, and the severity of hyperphagia. This contrasts with the heterozygote POKO mice which showed little obesity and metabolic disturbance, and only subtle changes of the circadian rhythm of metabolic activity without alterations in feeding behavior. The results provide a novel aspect of leptin resistance, almost manifesting as an "all or none" phenomenon.

Daily cytokine fluctuations, driven by leptin, are associated with fatigue severity in chronic fatigue syndrome: evidence of inflammatory pathology

Background

Chronic fatigue syndrome (CFS) is a debilitating disorder characterized by persistent fatigue that is not alleviated by rest. The lack of a clearly identified underlying mechanism has hindered the development of effective treatments. Studies have demonstrated elevated levels of inflammatory factors in patients with CFS, but findings are contradictory across studies and no biomarkers have been consistently supported. Single time-point approaches potentially overlook important features of CFS, such as fluctuations in fatigue severity. We have observed that individuals with CFS demonstrate significant day-to-day variability in their fatigue severity.

Methods

Therefore, to complement previous studies, we implemented a novel longitudinal study design to investigate the role of cytokines in CFS pathophysiology. Ten women meeting the Fukuda diagnostic criteria for CFS and ten healthy age- and body mass index (BMI)-matched women underwent 25 consecutive days of blood draws and self-reporting of symptom severity. A 51-plex cytokine panel via Luminex was performed for each of the 500 serum samples collected. Our primary hypothesis was that daily fatigue severity would be significantly correlated with the inflammatory adipokine leptin, in the women with CFS and not in the healthy control women. As a post-hoc analysis, a machine learning algorithm using all 51 cytokines was implemented to determine whether immune factors could distinguish high from low fatigue days.

Results

Self-reported fatigue severity was significantly correlated with leptin levels in six of the participants with CFS and one healthy control, supporting our primary hypothesis. The machine learning algorithm distinguished high from low fatigue days in the CFS group with 78.3% accuracy.

Conclusions

Our results support the role of cytokines in the pathophysiology of CFS.

Circadian rhythms, metabolism, and insulin sensitivity: transcriptional networks in animal models

Homeostatic systems have adapted to respond to the diurnal light/dark cycle. Numerous physiological pathways, including metabolism, are coordinated by this 24-h cycle. Animals with mutations in clock genes show abnormal glucose and lipid metabolism, indicating a critical relationship between the circadian clock and metabolism. Energy homeostasis is achieved through circadian regulation of the expression and activity of several key metabolic enzymes. Temporal organization of tissue metabolism is coordinated by reciprocal cross-talk between the core clock mechanism and key metabolic enzymes and transcriptional activators. The aim of this review is to define the role of the circadian clock in the regulation of insulin sensitivity by describing the interconnection between the circadian clock and metabolic pathways.

Stimulation of leptin secretion by insulin

Leptin has a crucial role in regulating food intake and maintaining metabolic homeostasis. Although little is known about the process of leptin secretion, insulin, which has an important role in the metabolism of glucose and lipids, is believed to regulate leptin secretion through a posttranscriptional mechanism in the short term, and via glucose metabolism in the long term. The gastric mucosa secretes leptin, but this mechanism has not been completely elucidated. Understanding the mechanism of insulin-regulated leptin secretion could lead to the development of new treatment methods for obesity and its comorbidities, which are serious public health concerns.

Circadian rhythms and obesity in mammals

Obesity has become a serious public health problem and a major risk factor for the development of illnesses, such as insulin resistance and hypertension. Attempts to understand the causes of obesity and develop new therapeutic strategies have mostly focused on caloric intake and energy expenditure. Recent studies have shown that the circadian clock controls energy homeostasis by regulating the circadian expression and/or activity of enzymes, hormones, and transport systems involved in metabolism. Moreover, disruption of circadian rhythms leads to obesity and metabolic disorders. Therefore, it is plausible that resetting of the circadian clock can be used as a new approach to attenuate obesity. Feeding regimens, such as restricted feeding (RF), calorie restriction (CR), and intermittent fasting (IF), provide a time cue and reset the circadian clock and lead to better health. In contrast, high-fat (HF) diet leads to disrupted circadian expression of metabolic factors and obesity. This paper focuses on circadian rhythms and their link to obesity.

Obesity and appetite control

Obesity is one of the major challenges to human health worldwide; however, there are currently no effective pharmacological interventions for obesity. Recent studies have improved our understanding of energy homeostasis by identifying sophisticated neurohumoral networks which convey signals between the brain and gut in order to control food intake. The hypothalamus is a key region which possesses reciprocal connections between the higher cortical centres such as reward-related limbic pathways, and the brainstem. Furthermore, the hypothalamus integrates a number of peripheral signals which modulate food intake and energy expenditure. Gut hormones, such as peptide YY, pancreatic polypeptide, glucagon-like peptide-1, oxyntomodulin, and ghrelin, are modulated by acute food ingestion. In contrast, adiposity signals such as leptin and insulin are implicated in both short- and long-term energy homeostasis. In this paper, we focus on the role of gut hormones and their related neuronal networks (the gut-brain axis) in appetite control, and their potentials as novel therapies for obesity.

Obesity and appetite control

Obesity is one of the major challenges to human health worldwide; however, there are currently no effective pharmacological interventions for obesity. Recent studies have improved our understanding of energy homeostasis by identifying sophisticated neurohumoral networks which convey signals between the brain and gut in order to control food intake. The hypothalamus is a key region which possesses reciprocal connections between the higher cortical centres such as reward-related limbic pathways, and the brainstem. Furthermore, the hypothalamus integrates a number of peripheral signals which modulate food intake and energy expenditure. Gut hormones, such as peptide YY, pancreatic polypeptide, glucagon-like peptide-1, oxyntomodulin, and ghrelin, are modulated by acute food ingestion. In contrast, adiposity signals such as leptin and insulin are implicated in both short- and long-term energy homeostasis. In this paper, we focus on the role of gut hormones and their related neuronal networks (the gut-brain axis) in appetite control, and their potentials as novel therapies for obesity.

Site-specific circadian expression of leptin and its receptor in human adipose tissue

INTRODUCTION

Circadian variability of circulating leptin levels has been well established over the last decade. However, the circadian behavior of leptin in human adipose tissue remains unknown. This also applies to the soluble leptin receptor.

OBJECTIVE

We investigated the ex vivo circadian behavior of leptin and its receptor expression in human adipose tissue (AT).

SUBJECTS AND METHODS

Visceral and subcutaneous abdominal AT biopsies (n = 6) were obtained from morbid obese women (BMI ≥ 40 kg/m²). Anthropometric variables and fasting plasma glucose, leptin, lipids and lipoprotein concentrations were determined. In order to investigate rhythmic expression pattern of leptin and its receptor, AT explants were cultured during 24-h and gene expression was analyzed at the following times: 08:00, 14:00, 20:00, 02:00 h, using quantitative real-time PCR.

RESULTS

Leptin expression showed an oscillatory pattern that was consistent with circadian rhythm in cultured AT. Similar patterns were noted for the leptin receptor. Leptin showed its achrophase (maximum expression) during the night, which might be associated to a lower degree of fat accumulation and higher mobilization. When comparing both fat depots, visceral AT anticipated its expression towards afternoon and evening hours. Interestingly, leptin plasma values were associated with decreased amplitude of LEP rhythm. This association was lost when adjusting for waist circumference.

CONCLUSION

Circadian rhythmicity has been demonstrated in leptin and its receptor in human AT cultures in a site-specific manner. This new knowledge paves the way for a better understanding of the autocrine/paracrine role of leptin in human AT.

Daily rhythms of plasma melatonin, but not plasma leptin or leptin mRNA, vary between lean, obese and type 2 diabetic men

Melatonin and leptin exhibit daily rhythms that may contribute towards changes in metabolic physiology. It remains unclear, however, whether this rhythmicity is altered in obesity or type 2 diabetes (T2DM). We tested the hypothesis that 24-hour profiles of melatonin, leptin and leptin mRNA are altered by metabolic status in laboratory conditions. Men between 45–65 years old were recruited into lean, obese-non-diabetic or obese-T2DM groups. Volunteers followed strict sleep-wake and dietary regimes for 1 week before the laboratory study. They were then maintained in controlled light-dark conditions, semi-recumbent posture and fed hourly iso-energetic drinks during wake periods. Hourly blood samples were collected for hormone analysis. Subcutaneous adipose biopsies were collected 6-hourly for gene expression analysis. Although there was no effect of subject group on the timing of dim light melatonin onset (DLMO), nocturnal plasma melatonin concentration was significantly higher in obese-non-diabetic subjects compared to weight-matched T2DM subjects (p<0.01) and lean controls (p<0.05). Two T2DM subjects failed to produce any detectable melatonin, although did exhibit plasma cortisol rhythms comparable to others in the group. Consistent with the literature, there was a significant (p<0.001) effect of subject group on absolute plasma leptin concentration and, when expressed relative to an individual’s 24-hour mean, plasma leptin showed significant (p<0.001) diurnal variation. However, there was no difference in amplitude or timing of leptin rhythms between experimental groups. There was also no significant effect of time on leptin mRNA expression. Despite an overall effect (p<0.05) of experimental group, post-hoc analysis revealed no significant pair-wise effects of group on leptin mRNA expression. Altered plasma melatonin rhythms in weight-matched T2DM and non-diabetic individuals supports a possible role of melatonin in T2DM aetiology. However, neither obesity nor T2DM changed 24-hour rhythms of plasma leptin relative to cycle mean, or expression of subcutaneous adipose leptin gene expression, compared with lean subjects.

Chronobiological Effects on Obesity

The development of obesity is the consequence of a multitude of complex interactions between both genetic and environmental factors. It has been suggested that the dramatic increase in the prevalence of obesity over the past 30 years has been the result of environmental changes that have enabled the full realization of genetic susceptibility present in the population. Among the many environmental alterations that have occurred in our recent history is the ever-increasing dyssynchrony between natural cycles of light/dark and altered patterns of sleep/wake and eating behavior associated with our "24-hour" lifestyle. An extensive research literature has established clear links between increased risk for obesity and both sleep deprivation and shift work, and our understanding of the consequences of such dyssynchrony at the molecular level is beginning to emerge. Studies linking alterations in cellular circadian clocks to metabolic dysfunction point to the increasing importance of chronobiology in obesity etiology.

Timing of fructose intake: an important regulator of adiposity

1. Overconsumption of fructose produces glucose intolerance, autonomic abnormalities and renal dysfunction and may be related to the worldwide epidemic of obesity and diabetes. 2. Experiments were conducted to determine whether the time period (light or dark) of fructose consumption influenced the pathological consequences. C57BL mice were given standard chow and assigned to one of three groups: (i) control (n = 10), which received water over a 24 h period; (ii) FL (n = 11), which received 10% fructose solution during the 12 h light period; and (iii) FD (n = 11), which received 10% fructose solution during the 12 h dark period. 3. There was a time related increase in body weight for all groups (P < 0.01, 2 vs 6 wks). There was a greater increase in body fat in the FL group compared with the control and FD groups. The changes in adiposity occurred even though the total caloric intake was not significantly different among the groups (approximately 18 kcal/day). Total fluid (water + fructose) consumption was greater in the FD and FL groups compared with control at 6 weeks. Significant increases were noted for plasma insulin and leptin at 8 weeks, with highest levels in the FL compared with FD group (P < 0.05). There were no significant changes in glucose, glucose tolerance, cholesterol, triglycerides or adiponectin. 4. The results of the present study suggest that there is a mismatch in caloric consumption, metabolism and adiposity as related to the light-dark cycle of fructose consumption. These findings have clinical implications in the control of bodyweight, abdominal fat accumulation and Type 2 diabetes.

Sexual dimorphism in clock genes expression in human adipose tissue

BACKGROUND

This study was carried out to investigate whether sex-related differences exist in the adipocyte expression of clock genes from subcutaneous abdominal and visceral fat depots in severely obese patients.

METHODS

We investigated 16 morbidly obese patients, eight men and eight women (mean age 45 ± 20 years; mean BMI 46 ± 6 kg/m(2)), undergoing laparoscopic gastric bypass surgery. Biopsies were taken as paired samples [subcutaneous and visceral adipose tissue (AT)] at the beginning of the surgical process at 11:00 h in the morning. Metabolic syndrome features such as waist circumference, plasma glucose, triglycerides, total cholesterol, high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) were also studied. The expression of clock genes (PER2, BMAL1, and CRY1) was measured by quantitative real-time PCR, Western blot, and immunohistochemical analysis.

RESULTS

Gene expression was significantly higher in women than in men for the three genes studied in both ATs (P < 0.05). In visceral fat, these differences were more marked. (P < 0.001). Western blot analysis partially confirmed these results since statistical differences were observed for PER2 in both ATs and for CRY1 in subcutaneous adipose tissue. There were no differences in BMAL1 protein expression. Interestingly, clock gene expression level was correlated with LDL-C and HDL-C (P < 0.05). Moreover, we found significant associations with body fat mass in women and with age in men.

CONCLUSIONS

Clock genes expression is sex dependent in human adipose tissue from morbidly obese subjects and correlates to a decreased in metabolic syndrome-related traits. These preliminary results make necessary to go deep into the knowledge of the molecular basis of the sexual dimorphism in chronobiology.

The gut hormones in appetite regulation

Obesity has received much attention worldwide in association with an increased risk of cardiovascular diseases, diabetes, and cancer. At present, bariatric surgery is the only effective treatment for obesity in which long-term weight loss is achieved in patients. By contrast, pharmacological interventions for obesity are usually followed by weight regain. Although the exact mechanisms of long-term weight loss following bariatric surgery are yet to be fully elucidated, several gut hormones have been implicated. Gut hormones play a critical role in relaying signals of nutritional and energy status from the gut to the central nervous system, in order to regulate food intake. Cholecystokinin, peptide YY, pancreatic polypeptide, glucagon-like peptide-1, and oxyntomodulin act through distinct yet synergistic mechanisms to suppress appetite, whereas ghrelin stimulates food intake. Here, we discuss the role of gut hormones in the regulation of food intake and body weight.

Rhythmic leptin is required for weight gain from circadian desynchronized feeding in the mouse

The neuroendocrine and metabolic effects of leptin have been extensively researched since the discovery, and the later identification, of the leptin gene mutated within the ob/ob mouse. Leptin is required for optimal health in a number of physiological systems (e.g. fertility, bone density, body weight regulation). Despite the extensive leptin literature and many observations of leptin's cyclical pattern over the 24-hour day, few studies have specifically examined how the circadian rhythm of leptin may be essential to leptin signaling and health. Here we present data indicating that a rhythmic leptin profile (e.g. 1 peak every 24 hours) leads to excessive weight gain during desynchronized feeding whereas non-rhythmic leptin provided in a continuous manner does not lead to excessive body weight gain under similar feeding conditions. This study suggests that feeding time can interact with leptin's endogenous rhythm to influence metabolic signals, specifically leading to excessive body weight gains during 'wrongly' timed feeding.

The fall in leptin concentration is a major determinant of the metabolic adaptation induced by caloric restriction independently of the changes in leptin circadian rhythms

CONTEXT

Leptin is involved in the hormonal regulation of the reproductive, somatotropic, thyroid, and autonomic axes and ultimately in the regulation of energy balance. In parallel to the metabolic adaptation observed in response to caloric restriction (CR), plasma leptin concentrations are substantially decreased, suggesting a role for this hormone in the drop in energy expenditure beyond that predicted by the changes in body composition (metabolic adaptation).

AIM

The aim of the study was to explore the changes in 24-h leptin circadian rhythm in response to CR and to investigate the relationship between these changes and metabolic adaptation.

DESIGN

In a randomized, controlled trial (Comprehensive Assessment of Long-Term Effects of Reducing Intake of Energy), 48 subjects were assigned to a control group or one of three CR groups for 6 months. Leptin concentration was assessed every 30 min for 24 h, and leptin circadian variations were fitted by Cosinor analysis. Sedentary energy expenditure and urinary catecholamine excretion were measured for 24 h in a metabolic chamber.

RESULTS

Six months of CR decreased body weight by -11.4 ± 0.6% (mean ± sem; P < 0.001). Mean 24-h circulating leptin concentration decreased by -44 ± 3% (P < 0.001), whereas leptin diurnal amplitude slightly increased over the 6 months of CR. CR caused a metabolic adaptation of -126 ± 25 kcal/d (P <0.001) and a significant decrease in urinary norepinephrine (-13 ± 3%) and T(3) concentrations (10 ± 2%). The metabolic adaptation was significantly and independently related to the changes in 24-h leptin (r(2) = 0 .22, P < 0.01) but not to the changes in leptin amplitude.

CONCLUSION

Our results confirm an important role for leptin as an independent determinant of the metabolic adaptation in response to CR.

The impact of sleep disturbances on adipocyte function and lipid metabolism

Classically, sleep has been considered to serve an essential restorative function for the brain. However, there are an increasing number of studies linking decreased sleep quantity and/or quality in humans to an increased obesity and diabetes risk. Reductions in sleep quantity or quality lead to an increase in hunger and appetite, which chronically could predispose an individual to obesity. Carefully controlled studies have shown that two nights of insufficient sleep is causally linked to a decrease in disposition index, the most commonly used predictor of an individual's diabetes risk, and impairments in glucose tolerance and insulin sensitivity. Thus, sleep appears to play a critical role in modulating energy metabolism in peripheral tissues. Here we will discuss recent work implicating adipose tissue as a potential direct target of disruption of sleep quality, and explore the potential mechanistic links between sleep, adipose tissue and the global control of energy metabolism in humans.

Body weight, metabolism and clock genes

Biological rhythms are present in the lives of almost all organisms ranging from plants to more evolved creatures. These oscillations allow the anticipation of many physiological and behavioral mechanisms thus enabling coordination of rhythms in a timely manner, adaption to environmental changes and more efficient organization of the cellular processes responsible for survival of both the individual and the species. Many components of energy homeostasis exhibit circadian rhythms, which are regulated by central (suprachiasmatic nucleus) and peripheral (located in other tissues) circadian clocks. Adipocyte plays an important role in the regulation of energy homeostasis, the signaling of satiety and cellular differentiation and proliferation. Also, the adipocyte circadian clock is probably involved in the control of many of these functions. Thus, circadian clocks are implicated in the control of energy balance, feeding behavior and consequently in the regulation of body weight. In this regard, alterations in clock genes and rhythms can interfere with the complex mechanism of metabolic and hormonal anticipation, contributing to multifactorial diseases such as obesity and diabetes. The aim of this review was to define circadian clocks by describing their functioning and role in the whole body and in adipocyte metabolism, as well as their influence on body weight control and the development of obesity.

Higher habitual intake of dietary fat and carbohydrates are associated with lower leptin and higher ghrelin concentrations in overweight and obese postmenopausal women with elevated insulin levels

A highly regulated homeostatic system governs body weight; however, it is possible that this system might be impaired by the sustained intake of highly palatable foods. Short-term feeding studies suggest that the appetite-stimulating hormone ghrelin is suppressed less effectively by dietary fat intake, and diets high in sucrose decrease levels of the adipose hormone leptin. We hypothesized that higher habitual intake of dietary fat and carbohydrate (CHO) would be associated with elevated concentrations of circulating plasma ghrelin and lower circulating leptin in humans, a hormonal profile that could promote weight gain. To test our hypothesis, we examined the cross-sectional associations of ghrelin and leptin with the habitual macronutrient intake of 165 healthy overweight and obese sedentary women and tested the modifying role of insulin in these associations. We observed a significant inverse association between leptin concentrations and percentage energy from CHO independent of body mass index, percentage body fat, age, and intraabdominal fat (beta = -0.11 P = .04). No significant associations were observed between ghrelin and macronutrients or their subtypes among the total cohort. Among women with insulin concentrations at or greater than the median, we found a statistically significant positive association between intake of saturated fat and ghrelin concentrations, as well as additional statistically significant associations between leptin concentrations and macronutrients not observed among the total cohort. Our results provide some evidence that diets higher in fat and CHO are associated with a hormonal profile (ie, lower leptin and higher ghrelin concentrations), which could enhance weight gain, particularly among individuals with higher circulating insulin concentrations.

Influence of weeks of circadian misalignment on leptin levels

The neurobiology of circadian, wakefulness-sleep, and feeding systems interact to influence energy homeostasis. Sleep and circadian disruptions are reported to be associated with increased risk of diabetes and obesity, yet the roles of energy balance hormones in these associations are largely unknown. Therefore, in the current study we aimed to assess the influence of several weeks of circadian misalignment (sleep and wakefulness occurring at an inappropriate biological time) on the anorexigenic adipocyte hormone leptin. We utilized data from a previous study designed to assess physiological and cognitive consequences of changes in day length and light exposure as may occur during space fight, including exploration class space missions and exposure to the Martian Sol (day length). We hypothesized that circadian misalignment during an exploration class spaceflight simulation would reduce leptin levels. Following a three-week ~8 hours per night home sleep schedule, 14 healthy participants lived in the laboratory for more than one month. After baseline data collection, participants were scheduled to either 24.0 or 24.6 hours of wakefulness-sleep schedules for 25 days. Changes in the phase of the circadian melatonin rhythm, sleep, and leptin levels were assessed. Half of participants analyzed exhibited circadian misalignment with an average change in phase angle from baseline of ~4 hours and these participants showed reduced leptin levels, sleep latency, stage 2 and total sleep time (7.3 to 6.6 hours) and increased wakefulness after sleep onset (all P < 0.05). The control group remained synchronized and showed significant increases in sleep latency and leptin levels. Our findings indicate that weeks of circadian misalignment, such as that which occurs in circadian sleep disorders, alters leptin levels and therefore may have implications for appetite and energy balance.

Serum leptin levels, hormone levels, and hot flashes in midlife women

OBJECTIVE

To examine the associations between serum leptin levels, sex steroid hormone levels, and hot flashes in normal weight and obese midlife women.

DESIGN

Cross-sectional study.

SETTING

University clinic.

PATIENT(S)

201 Caucasian, nonsmoking women aged 45 to 54 years with a body mass index of <25 kg/m2 or >or=30 kg/m2.

INTERVENTION(S)

Questionnaire, fasting blood samples.

MAIN OUTCOME MEASURE(S)

Serum leptin and sex steroid hormone levels.

RESULT(S)

Correlation and regression models were performed to examine associations between leptin levels, hormone levels, and hot flashes. Leptin levels were associated with BMI, with "ever experiencing hot flashes" (questionnaire), with hot flashes within the last 30 days, and with duration of hot flashes (>1 year, P=.03). Leptin was positively correlated with testosterone, free testosterone index, and free estrogen index and inversely associated with levels of sex hormone-binding globulin. In women with a body mass index>or=30 kg/m2, leptin levels no longer correlated with testosterone levels.

CONCLUSION(S)

Serum leptin levels are associated with the occurrence and duration of hot flashes in midlife women; however, no correlation was found between leptin and serum estradiol.

Growth hormone/insulin-like growth factor I axis, glucose metabolism, and lypolisis but not leptin show some degree of refractoriness to short-term fasting in acromegaly

Starvation exerts critical influence on somatotroph and leptin secretion. Fasting enhances GH levels in normal subjects, but not in GH hyposecretory states, while it always inhibits leptin secretion. We aimed to clarify the GH/IGF-I and metabolic response to short-term fasting in a GH hypersecretory state such as acromegaly. To this goal, in 8 active acromegalic (ACRO) and in 7 normal women (NS) we evaluated mean GH (mGHc), leptin (mLEPc), insulin (mINSc), glucose (mGLUc) concentrations as well as IGF-I, IGF binding protein (IGFBP)-3, IGFBP-1, and free fatty acid (FFA) levels before and after 36-h fasting. Before fasting, mGHc, IGF-I, mINSc, mGLUc, and FFA levels in ACRO were higher (p<0.01) than in NS. IGFBP-3, IGFBP-1, and mLEPc were similar in ACRO and in NS. Fasting clearly (p<0.02) increased mGHc in NS only. After 36-h fasting, significant IGF-I reduction was recorded in NS only (p<0.03). IGFBP-3 did not change both in ACRO and NS. IGFBP-1 significantly increased (p<0.05) after fasting in both groups but in ACRO were lower (p<0.03) than in NS. Fasting decreased (p<0.03) mLEPc, mGLUc, and mINSc in ACRO as well as in NS; mINSc and mGLUc after fasting in ACRO persisted higher (p<0.005) than in NS. FFA levels were increased by fasting in NS (p<0.02), but not in ACRO. This study shows that GH/IGF-I axis, glucose metabolism, and lypolisis but not leptin display some degree of refractoriness to short-term fasting in acromegaly. The lack of any GH response to fasting in acromegaly would likely reflect neuroendocrine alterations secondary to the GH hypersecretory state. On the other hand, the lack of somatotropic response and the peculiarly blunted metabolic reaction to short-term fasting would partially reflect the delayed adaptation of insulin resistance to starvation.

Effect of specific allergen inhalation on serum adiponectin in human asthma

BACKGROUND

Adiponectin is associated with asthma. The direction of this association is not known in humans. In mice, this association is bidirectional: allergen inhalation affects serum adiponectin, and exogenous adiponectin administration affects asthma. We sought to evaluate whether allergen inhalation affects serum adiponectin in human asthma.

METHODS

This study included eight sensitized subjects with mild asthma and six healthy control subjects. Asthmatic subjects were challenged with inhaled specific allergen (positive allergen skin test), methacholine, and irrelevant allergen (negative allergen skin test). Control subjects were challenged with irrelevant allergen. Sequential serum samples were obtained before and nine times after each challenge. Serum adiponectin- (primary outcome), leptin-, adiponectin-to-leptin ratio-, eotaxin-, and tumor necrosis factor-alpha-response curves, area under the curves, and baseline and peak concentrations were evaluated. Statistical analysis used repeated-measures analysis of variance and paired t tests.

RESULTS

There were no significant differences in outcome measures among the challenges in asthmatic subjects or when compared to control subjects. Type II error is an unlikely explanation for these findings because the study was adequately powered to detect changes in serum adiponectin, as reported in the literature. Further, pooled data showed that serum adiponectin diurnal variation curves were lower in asthmatic subjects than in control subjects.

CONCLUSIONS

Serum adiponectin concentrations are lower in asthmatic subjects than in control subjects. Specific allergen inhalation in asthmatic subjects does not acutely affect serum adiponectin concentrations. The reverse association (ie, effect of adiponectin on asthma) needs further study. If future studies prove adiponectin to be a protective factor for asthma, modulating adiponectin may open a new approach toward managing asthma.

Comprehensive analysis of circadian periodic pattern in plant transcriptome

Background

Circadian rhythm is a crucial factor in orchestration of plant physiology, keeping it in synchrony with the daylight cycle. Previous studies have reported that up to 16% of plant transcriptome are circadially expressed.

Results

Our studies of mammalian gene expression revealed circadian baseline oscillation in nearly 100% of genes. Here we present a comprehensive analysis of periodicity in two independent data sets. Application of the advanced algorithms and analytic approached already tested on animal data reveals oscillation in almost every gene of Arabidopsis thaliana.

Conclusion

This study indicates an even more pervasive role of oscillation in molecular physiology of plants than previously believed. Earlier studies have dramatically underestimated the prevalence of circadian oscillation in plant gene expression.

Circadian mechanisms in murine and human bone marrow mesenchymal stem cells following dexamethasone exposure

A core group of regulatory factors control circadian rhythms in mammalian cells. While the suprachiasmatic nucleus in the brain serves as the central core circadian oscillator, circadian clocks also exist within peripheral tissues and cells. A growing body of evidence has demonstrated that >20% of expressed mRNAs in bone and adipose tissues oscillate in a circadian manner. The current manuscript reports evidence of the core circadian transcriptional apparatus within primary cultures of murine and human bone marrow-derived mesenchymal stem cells (BMSCs). Exposure of confluent, quiescent BMSCs to dexamethasone synchronized the oscillating expression of the mRNAs encoding the albumin D binding protein (dbp), brain-muscle arnt-like 1 (bmal1), period 3 (per3), rev-erb alpha (Rev A), and rev-erb beta (Rev B). The genes displayed a mean oscillatory period of 22.2 to 24.3 h. The acrophase or peak expression of mRNAs encoding "positive" (bmal1) and "negative" (per3) components of the circadian regulatory apparatus were out of phase with each other by approximately 8-12 h, consistent with in vivo observations. In vivo, phosphyrylation by glycogen synthase kinase 3beta (GSK3beta) is known to regulate the turnover of per3 and components of the core circadian regulatory apparatus. In vitro addition of lithium chloride, a GSK3beta inhibitor, significantly shifted the acrophase of all genes by 4.2-4.7 h oscillation in BMSCs; however, only the male murine BMSCs displayed a significant increase in the length of the period of oscillation. We conclude that human and murine BMSCs represent a valid in vitro model for the analysis of circadian mechanisms in bone metabolism and stem cell biology.

Twenty-four-hour endocrine and metabolic profiles following consumption of high-fructose corn syrup-, sucrose-, fructose-, and glucose-sweetened beverages with meals

BACKGROUND

We have reported that, compared with glucose-sweetened beverages, consuming fructose-sweetened beverages with meals results in lower 24-h circulating glucose, insulin, and leptin concentrations and elevated triacylglycerol (TG). However, pure fructose and glucose are not commonly used as sweeteners. High-fructose corn syrup (HFCS) has replaced sucrose as the predominant sweetener in beverages in the United States.

OBJECTIVE

We compared the metabolic/endocrine effects of HFCS with sucrose and, in a subset of subjects, with pure fructose and glucose.

DESIGN

Thirty-four men and women consumed 3 isocaloric meals with either sucrose- or HFCS-sweetened beverages, and blood samples were collected over 24 h. Eight of the male subjects were also studied when fructose- or glucose-sweetened beverages were consumed.

RESULTS

In 34 subjects, 24-h glucose, insulin, leptin, ghrelin, and TG profiles were similar between days that sucrose or HFCS was consumed. Postprandial TG excursions after HFCS or sucrose were larger in men than in women. In the men in whom the effects of 4 sweeteners were compared, the 24-h glucose and insulin responses induced by HFCS and sucrose were intermediate between the lower responses during consumption of fructose and the higher responses during glucose. Unexpectedly, postprandial TG profiles after HFCS or sucrose were not intermediate but comparably high as after pure fructose.

CONCLUSIONS

Sucrose and HFCS do not have substantially different short-term endocrine/metabolic effects. In male subjects, short-term consumption of sucrose and HFCS resulted in postprandial TG responses comparable to those induced by fructose.

48-h glucose infusion in humans: effect on hormonal responses, hunger and food intake

Experimentally-induced hyperglycemia by prolonged glucose infusion allows investigation of the effects of sustained stimulation of the pancreatic beta-cell on insulin secretion and sensitivity. Hormonal responses to a meal following prolonged glucose infusions have not been investigated. To determine if a 48-h glucose infusion alters hormonal responses to a test meal as well as food intake and hunger in normal weight individuals, 16 subjects (8 men, 8 women, age 18-30 years, mean BMI=21.7+/-1.6 kg/m2) were infused for 48 h with either saline (50 ml/h) or 15% glucose (200 mg/m2/min). Subjects ingested a 600 kcal mixed nutrient meal 3 h after infusion termination. Blood samples were taken during the 48 h and for 4 h following food ingestion. The 48-h glucose infusion elicited a metabolic profile of a glucose intolerant obese subjects, with increased plasma glucose, insulin and leptin (all P<0.01) and increased HOMA-IR (P<0.001). During meal ingestion, early insulin secretion was increased (P<0.05) but post-prandial glucose (P<0.01) and insulin (P<0.01) excursions were lower following the glucose infusion. Post-prandial plasma triglyceride concentrations were increased after glucose compared with saline. Food intake and hunger ratings were not different between the two conditions. Plasma leptin levels were inversely correlated with hunger (P<0.03) in both conditions and with food intake (P<0.003) during the glucose condition only. Thus, a 48-h glucose infusion does not impair post-prandial hormonal responses, alter food intake or hunger in normal weight subjects. The glucose-induced increases in plasma leptin result in a stronger inverse relationship between plasma leptin and hunger as well as food intake. These data are the first to demonstrate a relationship between leptin and hunger in normal weight, non-calorically restricted human subjects.