The hypothalamic-pituitary-adrenal axis in obesity

Effects of very low-calorie ketogenic diet on hypothalamic-pituitary-adrenal axis and renin-angiotensin-aldosterone system

BACKGROUND

The hypothalamic-pituitary-adrenal (HPA) axis is a neuroendocrine system involved in controlling stress responses in humans under physiological and pathological conditions; cortisol is the main hormone produced by the HPA axis. It is known that calorie restriction acts as a stressor and can lead to an increase in cortisol production. Renin-angiotensin-aldosterone system (RAAS) is a complex endocrine network regulating blood pressure and hydrosaline metabolism, whose final hormonal effector is aldosterone. RAAS activation is linked to cardiometabolic diseases, such as heart failure and obesity. Obesity has become a leading worldwide pandemic, associated with serious health outcomes. Calorie restriction represents a pivotal strategy to tackle obesity. On the other hand, it is well known that an increased activity of the HPA may favour visceral adipose tissue expansion, which may jeopardize a successful diet-induced weight loss. Very low-calorie ketogenic diet (VLCKD) is a normoprotein diet with a drastic reduction of the carbohydrate content and total calorie intake. Thanks to its sustained protein content, VLCKD is extremely effective to reduce adipose tissue while preserving lean body mass and resting metabolic rate.

PURPOSE

The purpose of this narrative review is to gain more insights on the effects of VLCKD on the HPA axis and RAAS, in different phases of weight loss and in different clinical settings.

Body mass index and variability in hippocampal volume in youth with major depressive disorder

BACKGROUND

The hippocampus has been implicated in major depressive disorder (MDD), in both adults and youth. However, possible sources of variability for the hippocampus have not been well delineated. Here, we explored the relationship between body mass index (BMI) and hippocampal volume in youth with MDD.

METHODS

Twenty-two controls (9 male, 13 female, 12-24 years), 24 youth with MDD and normal BMI (12 male, 12 female, 14-24 years), and 20 youth with MDD and high BMI (14 male, 6 female, 13-22 years) underwent magnetic resonance (MR) imaging and spectroscopy (1H-MRS). Hippocampal volume was determined through manual tracing of high-resolution anatomical T1 scans, and LCModel quantified neurochemical concentrations. Intracranial volume was used as a covariate in analysis to control for effects of brain volume on hippocampus.

RESULTS

In youth with MDD and normal BMI, right hippocampal volume was reduced (p = 0.006, Bonferroni) and a trend for reduced left hippocampal volume was noted when compared to healthy controls (p = 0.054, Bonferroni). Left hippocampal volumes were negatively associated with BMI in youth with MDD and high BMI group (r = -0.593, p = 0.006). No associations were found between the right hippocampus and BMI and there were no group differences for metabolite concentrations.

LIMITATIONS

Larger sample sizes would enable researchers to explore overweight vs obese groups and effect of sex in MDD-BMI groups.

CONCLUSIONS

BMI may account for some of the variability observed in previous studies of hippocampal volume in MDD, and therefore BMI impacts should be considered in future analyses.

Pituitary Gland Functional Connectivity and BMI

The pituitary gland (PG) influences body weight through hormonal releases; however, the relation between body weight and PG’s co-activities with other brain regions remains unclear. Here, we aimed to identify (1) the functional connectivity of the PG and (2) PG functional connectivity associated with body mass index by examining resting state functional magnetic resonance imaging data. Using enhanced Nathan Kline Institute-Rockland Sample, PG functional connectivity of 494 individuals was analyzed to assess in voxel-wise fashion. A negative association was found between BMI and PG functional connectivity with the orbitofrontal cortex, hippocampus, putamen, and temporal lobe. Our results show PG dysconnectivity to these regions is associated with higher BMI and implicate that the connectivity between these dopaminergic regions and PG may be associated with body weight maintenance through feeding behavior and growth.

HPA axis dysregulation, NR3C1 polymorphisms and glucocorticoid receptor isoforms imbalance in metabolic syndrome

CONTEXT

Metabolic syndrome (MetS) shares several similarities with hypercortisolism.

OBJECTIVES

To evaluate hypothalamic-pituitary-adrenal (HPA) axis sensitivity to dexamethasone (DEX), NR3C1 single nucleotide polymorphisms (SNPs), and expression of glucocorticoid receptor (GR) isoforms and cytokines in peripheral immune cells of MetS patients and controls.

DESIGN

Prospective study with 40 MetS patients and 40 controls was conducted at the Ribeirão Preto Medical School University Hospital.

METHODS

Plasma and salivary cortisol were measured in basal conditions and after 0.25, 0.5, and 1 mg of DEX given at 2300 h. In addition, p.N363S (rs6195), p.ER22/23EK (rs6189-6190), and BclI (rs41423247) SNPs were evaluated by quantitative polymerase chain reaction allelic discrimination. Exons 3 to 9 and exon/intron boundaries of NR3C1 were sequenced. GR isoforms and cytokines (IL1B, IL2, IL4, IL6, IL8, IL10, IFNγ, TNFα) expression were assessed by quantitative polymerase chain reaction.

RESULTS

Plasma and salivary cortisol (nmol/L) after 1-mg DEX were higher in MetS patients compared with controls (PF: 70.2 ± 17.3 vs 37.9 ± 2.6, P = .02, and SF: 4.9 ± 1.7 vs 2.2 ± 0.3, P < .0001). After all DEX doses, a lower number of MetS patients suppressed plasma and salivary cortisol compared with controls. The BclI genotypic frequencies (%) differed between patients (CC:56/CG:44) and controls (CC:50/CG:32.5/GG:17.5) (P = .03). The GRβ was overexpressed (fold = 100.0; P = .002) and IL4 (fold = -265.0; P < .0001) was underexpressed in MetS.

CONCLUSION

MetS patients exhibited decreased HPA sensitivity to glucocorticoid feedback. Moreover, the BclI polymorphism lower frequency, GRβ overexpression, and IL4 underexpression might underlie the molecular mechanism of glucocorticoid resistance in MetS. Thus, HPA axis dysregulation might contribute to MetS pathogenesis.

In Obesity, HPA Axis Activity Does Not Increase with BMI, but Declines with Aging: A Meta-Analysis of Clinical Studies

Background

Obesity is one of the major public health challenges worldwide. It involves numerous endocrine disorders as etiological factors or as complications. Previous studies strongly suggested the involvement of the hypothalamic-pituitary-adrenal (HPA) axis activity in obesity, however, to date, no consistent trend in obesity-associated alterations of the HPA axis has been identified. Aging has been demonstrated to aggravate obesity and to induce abnormalities of the HPA axis. Thus, the question arises whether obesity is correlated with peripheral indicators of HPA function in adult populations.

Objectives

We aimed to meta-analyze literature data on peripheral cortisol levels as indicators of HPA activity in obesity during aging, in order to identify possible explanations for previous contradictory findings and to suggest new approaches for future clinical studies.

Data Sources

3,596 records were identified through searching of PubMed, Embase and Cochrane Library Database. Altogether 26 articles were suitable for analyses.

Study Eligibility Criteria

Empirical research papers were eligible provided that they reported data of healthy adult individuals, included body mass index (BMI) and measured at least one relevant peripheral cortisol parameter (i.e., either morning blood cortisol or 24-h urinary free cortisol).

Statistical Methods

We used random effect models in each of the meta-analyses calculating with the DerSimonian and Laird weighting methods. I-squared indicator and Q test were performed to assess heterogeneity. Meta-regression was applied to explore the effect of BMI and age on morning blood and urinary free cortisol levels. To assess publication bias Egger’s test was used.

Results

Obesity did not show any correlation with the studied peripheral cortisol values. On the other hand, peripheral cortisol levels declined with aging within the obese, but not in the non-obese groups.

Conclusions

Our analysis demonstrated that obesity or healthy aging does not lead to enhanced HPA axis activity, peripheral cortisol levels rather decline with aging.

Controversies about a common etiology for eating and mood disorders

Obesity and depression represent a growing health concern worldwide. For many years, basic science and medicine have considered obesity as a metabolic illness, while depression was classified a psychiatric disorder. Despite accumulating evidence suggesting that obesity and depression may share commonalities, the causal link between eating and mood disorders remains to be fully understood. This etiology is highly complex, consisting of multiple environmental and genetic risk factors that interact with each other. In this review, we sought to summarize the preclinical and clinical evidence supporting a common etiology for eating and mood disorders, with a particular emphasis on signaling pathways involved in the maintenance of energy balance and mood stability, among which orexigenic and anorexigenic neuropeptides, metabolic factors, stress responsive hormones, cytokines, and neurotrophic factors.

Obesity--a neuropsychological disease? Systematic review and neuropsychological model

Obesity is a global epidemic associated with a series of secondary complications and comorbid diseases such as diabetes mellitus, cardiovascular disease, sleep-breathing disorders, and certain forms of cancer. On the surface, it seems that obesity is simply the phenotypic manifestation of deliberately flawed food intake behavior with the consequence of dysbalanced energy uptake and expenditure and can easily be reversed by caloric restriction and exercise. Notwithstanding this assumption, the disappointing outcomes of long-term clinical studies based on this assumption show that the problem is much more complex. Obviously, recent studies render that specific neurocircuits involved in appetite regulation are etiologically integrated in the pathomechanism, suggesting obesity should be regarded as a neurobiological disease rather than the consequence of detrimental food intake habits. Moreover, apart from the physical manifestation of overeating, a growing body of evidence suggests a close relationship with psychological components comprising mood disturbances, altered reward perception and motivation, or addictive behavior. Given that current dietary and pharmacological strategies to overcome the burgeoning threat of the obesity problem are of limited efficacy, bear the risk of adverse side-effects, and in most cases are not curative, new concepts integratively focusing on the fundamental neurobiological and psychological mechanisms underlying overeating are urgently required. This new approach to develop preventive and therapeutic strategies would justify assigning obesity to the spectrum of neuropsychological diseases. Our objective is to give an overview on the current literature that argues for this view and, on the basis of this knowledge, to deduce an integrative model for the development of obesity originating from disturbed neuropsychological functioning.

Cortisol and the polycystic ovary syndrome

Adrenal steroidogenesis is under the control of the hypothalamic-pituitary-adrenal (HPA) axis. Furthermore, metabolic factors including insulin and obesity-related signals may play a role in the regulation of both enzymes involved in the steroidogenetic pathways, as well as in the regulation of the HPA axis. In women with the polycystic ovary syndrome (PCOS), cortisol production rate is probably normal, although adrenal androgens can be overproduced in a subset of affected women. Cortisol metabolism and regeneration from inactive glucocorticoids can also be disrupted in PCOS, thereby contributing to determining an adrenal hyperandrogenic state. Finally, overactivity of the HPA axis may be related to the high prevalence of psychopathological and eating disorders in women with PCOS, implying a maladaptive allostatic load in the adaptive mechanisms to chronic stress exposure.

The hypothalamic-pituitary-adrenal axis and sex hormones in chronic stress and obesity: pathophysiological and clinical aspects

Obesity, particularly the abdominal phenotype, has been ascribed to an individual maladaptation to chronic environmental stress exposure mediated by a dysregulation of related neuroendocrine axes. Alterations in the control and action of the hypothalamic-pituitary-adrenal axis play a major role in this context, with the participation of the sympathetic nervous system. The ability to adapt to chronic stress may differ according to sex, with specific pathophysiological events leading to the development of stress-related chronic diseases. This seems to be influenced by the regulatory effects of sex hormones, particularly androgens. Stress may also disrupt the control of feeding, with some differences according to sex. Finally, the amount of experimental data in both animals and humans may help to shed more light on specific phenotypes of obesity, strictly related to the chronic exposure to stress. This challenge may potentially imply a different pathophysiological perspective and, possibly, a specific treatment.

Obesogens, stem cells and the developmental programming of obesity

Obesogens are chemicals that directly or indirectly lead to increased fat accumulation and obesity. Obesogens have the potential to disrupt multiple metabolic signalling pathways in the developing organism that can result in permanent changes in adult physiology. Prenatal or perinatal exposure to obesogenic endocrine disrupting chemicals has been shown to predispose an organism to store more fat from the beginning of its life. For example, excess oestrogen or cortisol exposure in the womb or during early life resulted in an increased susceptibility to obesity and metabolic syndrome later in life. This review focuses on the effects of environmental chemicals, such as the model obesogen, tributyltin (TBT), on the development of obesity. We discuss evidence linking the obesogenic effects of TBT with its ability to activate the peroxisome proliferator-activated receptor gamma and stimulate adipogenesis. We also discuss how TBT and other environmental obesogens may lead to epigenetic changes that predispose exposed individuals to subsequent weight gain and obesity. This suggests that humans, who have been exposed to obesogenic chemicals during sensitive windows of development, might be pre-programmed to store increased amounts of fat, resulting in a lifelong struggle to maintain a healthy weight and exacerbating the deleterious effects of poor diet and inadequate exercise.

Levels of maternal serum corticotropin-releasing hormone (CRH) at midpregnancy in relation to maternal characteristics

BACKGROUND

Corticotropin-releasing hormone (CRH) in maternal blood originates primarily from gestational tissues and elevated levels in midpregnancy have been linked to adverse pregnancy outcomes. Investigators have hypothesized that high levels of maternal stress might lead to elevated CRH levels in pregnancy. Yet a few studies have measured maternal CRH levels among subgroups of women who experience disproportionate socioeconomic disadvantage, such as African-American and Hispanic women, and found that these groups have lower CRH levels in pregnancy. Our goal was to identify maternal characteristics related to CRH levels in midpregnancy and examine which if any of these factors help to explain race differences in CRH levels.

METHODS

The Pregnancy Outcomes and Community Health (POUCH) Study prospectively enrolled women at 15-27 weeks' gestation from 52 clinics in five Michigan communities (1998-2004). Data from the POUCH Study were used to examine maternal demographics, anthropometrics, health behaviors, and psychosocial factors (independent variables) in relation to midpregnancy blood CRH levels modeled as logCRHpg/ml (dependent variable). Analyses were conducted within a sub-cohort from the POUCH Study (671 non-Hispanic Whites, 545 African-Americans) and repeated in the sub-cohort subset with uncomplicated pregnancies (n=746). Blood levels of CRH and independent variables were ascertained at the time of enrollment. All regression models included week of enrollment as a covariate. In addition, final multivariate regression models alternately incorporated different psychosocial measures along with maternal demographics and weight. Psychosocial variables included measures of current depressive symptoms, perceived stress, coping style, hostility, mastery, anomie, and a chronic stressor (history of abuse as a child and adult).

RESULTS

In sub-cohort models, the adjusted mean log CRH level was significantly lower in African-Americans vs. non-Hispanic Whites; the difference was -0.48pg/ml (P<0.01). This difference was reduced by 21% (-0.38pg/ml, P<0.01) after inclusion of other relevant covariates. Adjusted mean log CRH levels were also lower among women with <12 years vs. >or=12 years of education (minimal difference=-0.19pg/ml, P<0.05), and among women with high levels of depressive symptoms who did not use antidepressants vs. women with lower levels of depressive symptoms and no antidepressant use (minimal difference=-0.13pg/ml, P<0.01). Log CRH levels were inversely associated with maternal weight (-0.03pg/ml per 10 pound increase, P<.05) but unrelated to smoking and all other psychosocial measures. Results were similar in the subset of women with uncomplicated pregnancies, except that lower CRH levels were also linked to higher perceived stress.

CONCLUSION

African-American women have lower blood CRH levels at midpregnancy and the race difference in CRH levels is reduced modestly after adjustment for other maternal characteristics. CRH levels were not elevated among women with high levels of perceived stress or more chronic stressors. The inverse association between CRH levels and maternal weight is likely due to a hemodilution effect. Relations among maternal CRH levels and maternal race, educational level, and depressive symptoms are difficult to explain and invite further investigation. Our results highlight a group of covariates that merit consideration in studies that address CRH in the context of pregnancy and/or post-partum complications.

Adaptive and maladaptive cortisol responses to pediatric obesity

The recent unprecedented increase of childhood obesity has led to an alarming rise in type 2 diabetes mellitus (T2D) among these children. The process underlying the progression from simple obesity to T2D is not well understood. Cortisol is a candidate factor in the pathogenesis of T2D, as it can exacerbate insulin resistance and provoke other disturbances of the metabolic syndrome. The 24-h integrated concentration (IC) of cortisol is suppressed in non-diabetic obese children compared to lean children. This difference in IC-cortisol is not due to changes in cortisol binding globulin or plasma cortisol to cortisone ratio between groups. In obese individuals, IC-cortisol suppression disappears with age after adolescence, which corresponds with increasing occurrence of T2D and other metabolic disorders of obesity. We consider the IC-cortisol levels of lean insulin sensitive children to be metabolically inappropriate for obese insulin resistant children. Thus, we hypothesize that suppression of IC-cortisol is an important adaptive response to obesity (cortisol adaptive suppression) in childhood that prevents pediatric T2D while failure to suppress IC-cortisol (cortisol suppression failure) exacerbates insulin resistance and contributes to the development of T2D. In further support of this hypothesis is early pilot data suggesting that cortisol suppression failure occurs in obese children with impaired fasting glucose levels. The mechanism(s) underlying cortisol adaptive suppression, how and why these mechanism(s) fail are unknown. Elucidation of these mechanisms may lead to interventions to prevent the development of T2D and its complications in obese individuals.

The Hypothalamic-Pituitary-Adrenal Axis Activity in Obesity and the Metabolic Syndrome

A hypothetical role of glucocorticoids in human obesity has been suggested since the abdominal obesity phenotype and syndromes of endogenous or exogenous hypercortisolism share several clinical, metabolic, and cardiovascular similarities. An emerging body of evidence indicates that both neuroendocrine dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis as well as peripheral alterations of cortisol metabolism may play a role in the pathophysiology of abdominal obesity. Major alterations of the HPA axis in vivo may be identified in different ways. They include evaluation of hormone concentrations: (a) in basal conditions, in blood, urine, or saliva samples; (b) during dynamic studies following stimulation with different neuropeptides or psychological stress challenges, or suppression with inhibiting agents of the HPA axis at different levels; and (c) after mixed meals or meals containing different nutrient compositions. In addition, alteration of peripheral cortisol metabolism can be detected by direct measurement of cortisol metabolites in urine, although this is a matter of more complex investigation. Alterations of the HPA axis in abdominal obesity are associated with insulin resistance, which suggests a direct responsibility of these hormonal alterations in the susceptibility of affected patients to develop both metabolic and cardiovascular diseases. According to available data, no single marker probably has the power to detect subtle alterations of the HPA axis in conditions, such as the abdominal obesity and the metabolic syndrome. On the contrary, they indicate the need for multiple parameters. At present, evaluation of urinary free cortisol, particularly during the night-time, and salivary-free cortisol appear to be promising for these purposes, whereas dynamic tests should be reserved for specific clinical settings, involving well-characterized patients.

Sex difference in the relationship between the hypothalamic-pituitary-adrenal axis and sex hormones in obesity

OBJECTIVE

This study was carried out to investigate the role of sex in the regulation of the hypothalamic-pituitary-adrenal (HPA) axis and its relationship with testosterone levels in male and female obesity.

RESEARCH METHODS AND PROCEDURES

Twenty-two obese men (OB-M) and 29 obese women (OB-W) participated in the study. Two groups of normal weight men (NW-M) and women (NW-W), respectively, served as controls. In basal conditions, blood concentrations of major androgens, sex hormone-binding protein, and gonadotropins were assessed, and the free androgen index (testosterone x100/sex hormone-binding globulin) was calculated. All subjects underwent a combined corticotropin-releasing hormone plus arginine-vasopressin stimulation test.

RESULTS

OB-M and NW-M had higher basal adrenal cortical tropic hormone (ACTH) and cortisol levels than their female counterparts. In addition, ACTH, but not cortisol basal, levels were significantly higher in obese than in normal weight controls in both sexes. OB-W had a higher response than OB-M to the combined corticotropin-releasing hormone plus arginine-vasopressin test of both ACTH and cortisol [expressed as incremental percentage of area under the curve (AUC%)]. The same finding was present between NW-W and NW-M. Basal luteinizing hormone levels were negatively correlated to ACTH(AUC%) in both OB-W and OB-M. In the OB-W, however, a positive correlation was found between cortisol(AUC%) and testosterone (r = 0.48; p = 0.002), whereas a tendency toward a negative correlation was present in OB-M.

DISCUSSION

In conclusion, we have shown a significant positive relationship between the activity of the HPA axis and testosterone in obese women, which suggests a partial responsibility of increased HPA axis activity in determining testosterone levels. In addition, it clearly seems that, as reported in normal weight subjects, a sex difference in the HPA axis activity still persists even in the presence of obesity.

Adipose tissue as an endocrine organ? A review of recent data related to cardiovascular complications of endocrine dysfunctions

Clinical and experimental data obtained in the last few years have modified the concept of adipose tissue as one solely directed at energy storage and release. The adipose tissue is a target organ for glucocorticoids and several studies have been carried out on the function of hypothalamic-pituitary-adrenal axis in obese subjects without conclusive results. A recent and innovative finding is that adipose tissue can produce cortisol from its inactive precursor, cortisone. The identification of leptin, a hormone synthesised by fat tissue, has ushered in the modern view of this tissue as a true endocrine organ. Leptin is produced primarily by subcutaneous and to a lesser extent by visceral adipose tissue, and has a central role in controlling body weight and, especially in regulating fat stores. Leptin is also involved in several complex functions, including physiological processes associated with puberty. Another hormone of fat tissue is angiotensinogen, which is produced in larger amounts by visceral than subcutaneous fat. Human and animals adipose tissue express a whole renin-angiotensin system (RAS). Angiotensin II, the final effector of this system is probably produced locally by adipose tissue. The function of adipose RAS is not well known. RAS can participate together with other hormones and substances, in adipocyte differentiation and fat tissue growth, but could be also involved in the pathogenesis of complications of obesity including arterial hypertension.

Depressive symptoms and bone mineral density in older men

Most studies examining the relation between depression and bone mineral density (BMD) have been limited to psychiatric patients or to community-dwelling, older women. We conducted a cross-sectional and prospective cohort study to determine whether depressive symptoms are associated with low BMD in community-dwelling, older men. We recruited 515 men 50 years of age or older from population-based listings of age-eligible men. Participants completed the Geriatric Depression Scale (short form) and were considered depressed if they scored 6 or more out of 15 possible points. BMD was measured in the spine and hip using dual energy x-ray absorptiometry in all participants, and again an average of 3.6 years later in a random subset of 100 participants. The prevalence of depressive symptoms (GDS = 6) was 3.1% (16 of 515). We found no difference in mean BMD or mean percent change in BMD per year of the hip and lumbar spine in men who had 6 or more depressive symptoms compared with men who reported 5 or fewer symptoms of depression. These findings suggest that depressive symptoms are not associated with BMD in community-dwelling, older men.

Prenatal stress and risk for psychopathology: specific effects or induction of general susceptibility?

This review focuses on prenatal stress as a risk factor for psychopathology. Evidence from animal studies is summarized, and the relevance of prenatal stress models in animals for human studies is discussed. In the offspring of prenatally stressed animals, overactivity and impaired negative feedback regulation of the hypothalamic-pituitary-adrenal axis are consistent findings and may reflect a pathophysiological mechanism involved in the development of psychopathology. Reduced activity of the opioid GABA/benzodiazepine, serotonin, and dopamine systems and increased activity of the sympathico-adrenal system have been found as well. These alterations have been linked to a diverse spectrum of psychopathology. Therefore, the evidence supports the view that exposure to prenatal stress may result in a general susceptibility to psychopathology, rather than exerting a direct effect on a specific form of psychopathology.

Body composition in patients with inflammatory bowel disease: a population-based study

OBJECTIVE

Weight loss and nutritional depletion are common features of inflammatory bowel disease. Our aim was to assess body composition in patients with Crohn's disease (CD) and ulcerative colitis (UC) and to evaluate possible differences between the patient groups and healthy subjects.

METHODS

A total of 60 patients with CD, 60 patients with UC, and 60 healthy subjects were investigated. Each group consisted of 24 men and 36 women. Body composition was measured by dual x-ray absorptiometry and Z scores were obtained by comparison to age- and sex-matched normal values.

RESULTS

Bone mineral content and lean body mass were significantly lower in patients with CD compared with patients with UC and healthy subjects. The body composition of CD men was more strongly affected than that of women. UC patients had significantly higher fat mass and body mass index than patients with CD and healthy subjects. There was no difference in the percentage of fat mass between the two patient groups. Corticosteroid treatment and smoking had a negative impact on bone mineral content and lean body mass in CD patients independently of each other.

CONCLUSIONS

CD was associated with disturbances in body composition: both bone mineral content and lean body mass were significantly reduced, especially in men with CD. Corticosteroid therapy and smoking had a significant influence on body composition in patients with CD. When studying the effects of inflammatory bowel disease on body composition and nutritional status, patients with CD and UC should be evaluated separately.

The glucocorticoid receptor gene and its association to metabolic syndrome

In recent decades, there has been an increasing interest in the role of endogenous glucocorticoids such as cortisol in the pathogenesis of metabolic syndrome. Studies in humans have suggested a positive association between obesity, hypertension, and insulin resistance, with alleles at the glucocorticoid receptor (GR) gene. For instance, the BclI polymorphism within the intron upstream of GR exon 2 has been associated with cardiovascular risk factors such as visceral obesity, hypertension, insulin resistance, and elevated cortisol concentrations. However, the location of the BclI polymorphism is not known, and the variant has so far not been compared with the wild-type receptor for its ability to be activated by glucocorticoids. Although several other mutations in the GR gene have been postulated as being relevant to the progression to type 2 diabetes and cardiovascular diseases, conflicting results makes it difficult to determine exactly what effect these GR variations have on metabolic syndrome incidence and progression. Further studies focusing on the most compelling GR mutations might offer a better understanding of metabolic syndrome pathogenesis and progression, aiding in the development of more effective treatments for this condition.

Obesity-depression associations in the population

This article summarizes data on the relationship between obesity and depression in the population. Both obesity and depression are increasingly prevalent and associated with numerous health complications including hypertension, coronary heart disease, and increased mortality. There does not appear to be a simple or single association between these disorders. Meta-analytic studies suggest no statistically significant relationship, although pooling all subjects may mask important variables that moderate or mediate potential covariations. Sociodemographic, psychosocial, and genetic factors may render certain obese individuals more prone to depression or vice versa. Physiological and behavioral variables that link obesity and depression have received limited study. There are likely multiple obesity-depression covariations in the population, rather than a single pattern of association. There is a need for longitudinal and mechanistic studies to understand casual pathways and greater collaboration between depression and obesity specialists.

Intracerebroventricular glucocorticoid infusion in normal rats: induction of parasympathetic-mediated obesity and insulin resistance

OBJECTIVE

The aims of the present study were to determine whether increased body weight resulting from intracerebroventricular (ICV) glucocorticoid (dexamethasone) infusion in normal rats is associated, as in obesity, with changes in glucose metabolism and to investigate whether the parasympathetic nervous system is involved in the glucocorticoid-induced effects.

RESEARCH METHODS AND PROCEDURES

Male Sprague-Dawley rats were infused with ICV dexamethasone (2.5 microg/d) or its vehicle for 2 days during which food intake, body weight, and basal insulinemia were measured. Euglycemic-hyperinsulinemic clamps associated with the labeled 2-deoxyglucose technique were then performed to determine the total rate of glucose disappearance and the tissue glucose use indices. Similar experiments were carried out in vagotomized rats.

RESULTS

Two days of ICV glucocorticoid infusion in normal rats resulted in increases in food intake, body weight, basal insulinemia, and produced decreases in the insulin-stimulated total rate of glucose disappearance, as well as in glucose use indices of all muscle types studied. None of these alterations was observed when glucocorticoid infusion was carried out in vagotomized rats.

DISCUSSION

These data show that central glucocorticoid infusion favors anabolic processes, such as feeding behavior, body weight gain, and insulin output, while promoting muscle insulin resistance. These effects seem to be mediated by an activation of the parasympathetic nervous system, because they all disappear when tested in vagotomized rats.

Adrenal responsiveness to high, low and very low ACTH 1-24 doses in obesity

OBJECTIVE

To investigate adrenal activity in visceral obesity in which adrenal hyperactivity has been hypothesized. This could reflect hypothalamus-pituitary alterations leading to slight hyperfunction of the adrenal. Primary adrenal hypersensitivity to ACTH drive in obesity has also been suggested. However, it has also been reported that dehydroepiondrosterone (DHEA) levels in obesity are reduced and it has been hypothesized that this could play a role in the increased cardiovascular risk in obese patients.

SUBJECTS

We have studied seven obese women with visceral adiposity (OB, age: 33.6+/-3.3 years, BMI: 33.8+/-1.3 kg/m2, WHR: 0.88+/-0.01). The results in OB were compared with those recorded in a group of age-matched normal women (NS, age: 30+/-1.3 years, BMI: 19.9+/-0.4 kg/m2, WHR: 0.76+/-0.02).

METHODS

We have studied the cortisol (F), aldosterone (A) and DHEA responses to ACTH 1-24 administered at low (LD, 0.5 microg/m2) or very low (VLD, 0.125 microg/m2) dose followed by a second challenge with supramaximal dose (HD, 250 microg).

RESULTS

Basal F, A and DHEA levels in OB were similar to those in NS. The peak F responses to ACTH were dose-related in both groups. At each dose the F peaks in OB (VLD: 495.6+/-43.9 nmol/l, HD: 722.3+/-67.7 nmol/l; LD: 519.2+/-46.0 nmol/l, HD: 729.6+/-44.7 nmol/l) were similar to those in NS (VLD: 556.7+/-45.9 nmol/l, HD: 704.8+/-20.7 nmol/l; LD: 511.8+/-22.8 nmol/l, HD: 726.7+/-26.5 nmol/l). The peak A responses to ACTH were dose-related in both groups. At each dose, the A peaks in OB (VLD: 0.55+/-0.03 pmol/l, HD: 0.79+/-0.09 pmol/l; LD: 0.63+/-0.04 pmol/l, HD: 0.78+/-0.09 pmol/l) were similar to those in NS (VLD: 0.8+/-0.10 pmol/l, HD: 0.86+/-0.09 pmol/l; LD: 0.8+/-0.10 pmol/l, HD: 0.95+/-0.12 pmol/l). The peak DHEA responses to ACTH were dose-related in both groups. At each dose the DHEA peaks in OB (VLD: 58.6+/-13.3 nmol/l, HD: 61.9+/-13.1 nmol/l; LD: 55.18+/-6.4 nmol/l, HD: 72.3+/-9.8 nmol/l) were similar to those in NS (VLD: 54.3+/-8.2 nmol/l, HD: 57.8+/-8.2 nmol/l; LD: 42.2+/-3.7 nmol/l, HD: 56.9+/-4.3 nmol/l).

CONCLUSIONS

This study shows that the cortisol, aldosterone and dehydroepiondrosterone responses to high, low and very low ACTH doses in obese women overlap with those in age-matched lean controls; these findings suggest normal sensitivity of the different zones of the adrenal cortex to ACTH in obesity.

Adipose tissue as an endocrine organ? A review of some recent data

Recent clinical and experimental data have radically modified the concept of adipose tissue as one solely devoted to energy storage and release. Adipose tissue is a target organ for glucocorticoids. Several studies of the function of the hypothalamic-pituitary-adrenal axis in obese subjects have failed to reach conclusive results. An innovative finding is that adipose tissue produces cortisol from its inactive precursor, cortisone. Identification of leptin, a hormone synthesised by adipose tissue, has ushered in the modern view that it is a true endocrine organ. Leptin is produced by subcutaneous and to a lesser extent by visceral adipose tissue. It has a central role in body weight and especially fat stores regulation, but is also involved in several complex functions, including the physiological processes associated with puberty. Angiotensinogen (AGT), another hormone synthesised in abundance by adipose tissue, is produced in larger amounts by visceral than subcutaneous fat. In addition, in man and animals adipose tissue appears to possess the whole renin-angiotensin system (RAS), suggesting that angiotensin II, the final effector of the system, is locally produced. The function of adipose RAS is not well known; besides participating, together with other hormones and substances, in adipocyte differentiation and fat tissue growth, it could be involved in the pathogenesis of the complications of obesity. All these findings have opened interesting prospects and are expected to yield further stimulating insights into the physiopathology of the adipose organ.

Food-induced cortisol secretion in relation to anthropometric, metabolic and haemodynamic variables in men

OBJECTIVE

To assess the relationships between the regulation of diurnal and food-induced cortisol secretion and anthropometric, metabolic and haemodynamic variables in middle-aged men.

SUBJECTS AND METHOD

Salivary cortisols were collected repeatedly (n = 7) over an ordinary working day (8a.m. to 11 p.m.) in a randomly selected population of 284 men, aged 51 y. A standardized lunch was provided, and an overnight low-dose dexamethasone suppression test was performed. These measurements were correlate with the anthropometric factors-body mass index, BMI, (kg/m2), waist-to-hip ratio (WHR) and abdominal sagittal diameter; the metabolic factors-fasting insulin and glucose as well as their ratio, and triglycerides; and the haemodynamic factors-systolic and diastolic blood pressures and heart rate.

RESULTS

As reported previously two principal types of salivary cortisol secretory patterns can be singled out, one characterized by high morning cortisol levels, a normal circadian rhythm and feedback regulation (dexamethasone) along with a brisk cortisol response to lunch, and another, found in a limited number of men, characterized by low morning cortisols, the absence of a circadian rhythm, a relative resistance to dexamethasone inhibition and a poor lunch-induced cortisol response. The normal cortisol secretory pattern showed negative associations with BMI (P< 0.05), WHR (P< 0.01), and blood pressures (P< 0.001). After stimulation by food intake, negative relationships were found with all obesity measurements, insulin, insulin/glucose ratio, triglycerides, blood pressures and heart rate (all P < 0.001). These results suggest that normally regulated cortisol is associated with a favourable somatic health. In contrast, after food intake cortisol secretion, based on an abnormal cortisol secretory pattern, showed consistent positive associations with obesity measurements, insulin, glucose and insulin/glucose ratio, triglycerides, blood pressures and heart rate (all P < 0.001).

CONCLUSIONS

A normal HPA axis regulation is associated with excellent health anthropometric, metabolic and haemodynamic variables, particularly visible after the physiological stimulus of food intake. This is, however, not the case in men with perturbed HPA axis function where associations in these somatic variables become exaggerated by food intake. We have previously reported that perceived stress-related cortisol is associated with abnormalities in the variables mentioned above, both with a normal and, particularly, with an abnormal function of the HPA axis. It is thus apparent that perceived stress and food intake show separate associations to somatic variables with a normally functioning HPA axis, while with an abnormal regulation of this axis both perceived stress and food intake exaggerate associations to abnormal somatic variables.

Regulation of body weight in humans

The mechanisms involved in body weight regulation in humans include genetic, physiological, and behavioral factors. Stability of body weight and body composition requires that energy intake matches energy expenditure and that nutrient balance is achieved. Human obesity is usually associated with high rates of energy expenditure. In adult individuals, protein and carbohydrate stores vary relatively little, whereas adipose tissue mass may change markedly. A feedback regulatory loop with three distinct steps has been recently identified in rodents: 1) a sensor that monitors the size of adipose tissue mass is represented by the amount of leptin synthesized by adipose cells (a protein encoded by the ob gene) which determines the plasma leptin levels; 2) hypothalamic centers, with specific leptin receptors, which receive and integrate the intensity of the signal; and 3) effector systems that influence the two determinants of energy balance, i.e., energy intake and energy expenditure. With the exception of a few very rare cases, the majority of obese human subjects have high plasma leptin levels that are related to the size of their adipose tissue mass. However, the expected regulatory responses (reduction in food intake and increase in energy expenditure) are not observed in obese individuals. Thus obese humans are resistant to the effect of endogenous leptin, despite unaltered hypothalamic leptin receptors. Whether defects in the leptin signaling cascade play a role in the development of human obesity is a field of great actual interest that needs further research. Present evidences suggest that genetic and environmental factors influence eating behavior of people prone to obesity and that diets that are high in fat or energy dense undermine body weight regulation by promoting an overconsumption of energy relative to need.

Hypothalamic-pituitary-adrenal axis and sympathetic nervous system activities in Pima Indians and Caucasians

It has been proposed that both hypercortisolism and low sympathetic nervous system (SNS) activity contribute to obesity. Because glucocorticoids inhibit SNS activity, we hypothesized that hypercortisolism and low SNS activity may be found in association in Pima Indians, a population with a high prevalence of obesity. We therefore measured indices of hypothalamic-pituitary-adrenal (HPA) axis and SNS activities in 39 nondiabetic men, 20 Pimas (age, 30+/-5 years; weight, 94+/-26 kg; 35%+/-8% body fat [mean +/- SD]) and 19 Caucasians (33+/-9 years, 91+/-23 kg, 28%+/-11% body fat). HPA axis activity was assessed by measurements of morning fasting plasma corticotropin (ACTH) and cortisol concentrations and 24-hour urinary free cortisol (UFC) excretion. SNS activity was assessed as muscle sympathetic nerve activity (MSNA) by microneurography and by measurement of catecholamines (fasting plasma concentration and 24-hour urinary excretion). Plasma ACTH and cortisol and UFC were similar in Pimas and Caucasians. MSNA was positively correlated with percent body fat (r = .49, P = .002) and was lower in Pimas compared with Caucasians after adjustment for percent body fat (24+/-9 v 31+/-10 bursts/min, P = .04). We conclude that Pima Indians, a population with a high prevalence of obesity, have lower SNS activity but normal HPA axis activity compared with Caucasians.

Pulsatile secretion of ACTH and cortisol in premenopausal women: effect of obesity and body fat distribution

OBJECTIVE

There is emerging evidence that women with visceral obesity may have hyper-responsiveness of the hypothalamic-pituitary-adrenal axis. There are no studies on basal daily secretory pattern of ACTH and cortisol in subjects with different obesity phenotypes.

DESIGN AND PATIENTS

In this study we examined daytime pulsatile secretion of ACTH and cortisol in two groups of premenopausal obese women with visceral (V-BFD) (BMI 37.1 +/- 1.7) and subcutaneous (S-BFD) (BMI 38.8 +/- 1.5) body fat distribution (measured by CT scan) and in a group of normal weight healthy controls (BMI 21.1 +/- 0.5). After an overnight fast, blood samples were taken at 15-minute intervals for 12 h (49 samples, from 0800 h until 2000 h). All women avoided breakfast but had a normal lunch and dinner, both containing similar food, energy and nutrient composition. ACTH and cortisol responses to mixed meals at noon and in the evening were also investigated.

RESULTS

Mean values of ACTH and cortisol did not differ between the groups. However, ACTH pulse frequency was significantly higher in V-BFD (P < 0.06) and S-BFD (P < 0.02) obese women than in controls, without any significant differences between the two obese subgroups. Mean ACTH pulse amplitude was lower in the V-BFD than in S-BFD obese (P < 0.02) and control (P < 0.05) groups. Cortisol episodic characteristics did not differ between V-BFD and S-BFD obese and controls. All differences in ACTH pulsatile parameters between obese and controls and between the two obese subgroups were evident only in the morning, with no further significant differences during the early and late afternoon. There were no significant differences in cortisol parameters during the three periods of the day between the various groups, apart from late afternoon cortisol pulse frequencies, which were significantly lower in V-BFD than in controls. After lunch, ACTH and cortisol levels significantly increased in all groups, but the cortisol increase tended to be more rapid in V-BFD than in the other two groups. After dinner, ACTH significantly increased in V-BFD and controls but not in the S-BFD group, whereas cortisol rose significantly in all groups, but significantly less in S-BFD than in V-BFD and controls. CortisolAUC (but not ACTHAUC) after lunch was significantly higher than after dinner in all groups. ACTH response after each meal was similar in all groups, but cortisolAUC after dinner was significantly lower in S-BFD than in V-BFD women.

CONCLUSION

This study demonstrates that in premenopausal women, obesity, particularly the visceral phenotype, is associated with several abnormalities of ACTH pulsatile secretion, particularly in the morning. On the contrary, no major differences were present in either blood concentrations, diurnal rhythm or secretory pattern of cortisol between obese and controls. The responses to meals seem to indicate a much more rapid cortisol response after lunch in women with visceral obesity and a reduced activation of the hypothalamic-pituitary-adrenal axis after dinner in women with subcutaneous obesity.

The endocrinology of obesity

Numerous endocrine alterations are associated with obesity (Table 1). The majority of the alterations are secondary to obesity and must be considered simply associated and potentially in the pathogenesis of the complications of obesity. The discovery of new endocrine peptides such as leptin that signal body fat content will increase our understanding of the regulation of body fat content. As a result, therapies will most certainly be developed that are directly targeted at the alterations in endocrine function.

Effects of glucocorticoids on energy metabolism and food intake in humans

The effect of glucocorticoid administration on energy metabolism and food intake was studied in 20 healthy, nondiabetic Caucasian male volunteers [27 +/- 5 (SD) yr, 72 +/- 9 kg, 20 +/- 7% body fat] randomly and blindly assigned to glucocorticoid (methylprednisolone, METH; n = 10) or placebo (PLAC; n = 10) treatment. Each subject was studied twice: during a weight maintenance diet and during ad libitum food intake. Energy metabolism was measured by indirect calorimetry and food intake by an automated food-selection system. Twenty-four-hour urinary norepinephrine excretion (24-h NE) was used as an estimate of sympathetic nervous system activity. During weight maintenance, METH intravenous infusion (125 mg/30 min) increased energy expenditure compared with PLAC, and after 4 days of oral therapy, METH (40 mg/day) decreased 24-h NE and increased energy expenditure compared with PLAC. During ad libitum food intake, after 4 days of METH (40 mg/day) or PLAC oral therapy, both groups increased their energy intake over weight maintenance, but the increase was significantly larger in the METH group compared with the PLAC group (4,554 +/- 1,857 vs. 2,867 +/- 846 kcal/day; P = 0.04). Our data suggest that therapeutic doses of glucocorticoids induce obesity mostly by increasing energy intake, an effect which may be related to the ability of glucocorticoids to act directly or indirectly on the central regulation of appetite.