The role of leptin in the etiopathogenesis of anorexia nervosa and bulimia

Repositioning leptin as a therapy for Alzheimer's disease

The data from the initial clinical trials utilizing recombinant human leptin as an obesity therapy were published in 1998. Since then, numerous studies have been described which address dosage, safety and efficacy of leptin replacement for a variety of disorders with diverse patient groups, including pediatric and adult subjects. We review the current clinical trial data, demonstrate that leptin administration is safe for long term use in humans, and summarize reported cognitive benefits. The functions of leptin in neuroprotection and cognition have been largely overlooked. Accumulating data suggest a very significant application of leptin may be a therapy for Alzheimer's disease.

Leptin as a neuroactive agent

OBJECTIVE

To review the literature regarding the role of leptin in psychiatric disorders.

METHODS

A PubMed search was undertaken using the following keywords: leptin, psychosis, affective disorders, alcohol, psychiatry, depression, dementia, and eating disorders. The articles were restricted to the English language.

RESULTS

The role of leptin in psychiatric populations has been the subject of increasing investigation. Basic science and clinical observations support a role for leptin in mediating cognition and reward processes. The role of leptin in psychiatric illnesses characterized by cognitive deficits has gained increased attention in recent years. Leptin deficiency and resistance have also been associated with eating disorders as well as affective, alcohol dependence, and psychotic disorders. The mechanisms underlining these associations remain to be determined.

CONCLUSIONS

Clinical research suggests an important role of leptin in psychiatric illnesses. Given the morbidity associated with mental illness, clinical research on the role of leptin and related novel therapeutic modalities is needed.

Psychobiology of purging disorder: reduction in circulating leptin levels in purging disorder in comparison with controls

OBJECTIVE

Purging disorder (PD), a recently recognized eating disorder syndrome, is differentiated from bulimia nervosa (BN) based on the absence of objectively large binge episodes. BN has been associated with low serum leptin levels. This study examined whether PD is also characterized by low serum leptin.

METHOD

Participants included women with PD (n = 20) or BN (n = 37), and non-eating disorder controls (n = 33). Blood samples for measurement of leptin and total ghrelin were obtained after overnight fast.

RESULTS

In comparison with control values, leptin levels were significantly decreased in PD (p < .01), as well as in BN (p < .02). Plasma ghrelin levels did not differ significantly across groups.

DISCUSSION

These results provide the first evidence that PD is associated with alteration in a neurobiological pathway influencing eating patterns and body weight. Further research is needed to assess whether low leptin levels in PD and BN are associated with restrained eating and weight suppression.

Appetite-Related Gut Peptides in Obesity and Binge Eating Disorder

The worldwide increase in obesity prevalence is a result of positive energy balance, with energy intake exceeding expenditure. The eating behavior in obesity ranges from mild passive overconsumption to excessive overeating with loss of control observed in binge eating disorder (BED). The signaling systems that underlie appetite control in BED are complex and, at this point, not well understood. The present review highlights the current knowledge of key components of the gut peptide system and examines evidence of defects in signaling that differentiate obese binge eaters from obese non-binge eaters. The signaling network underlying hunger, satiety, and metabolic status includes leptin and insulin from energy stores and cholecystokinin, glucagon-like peptide-1, peptide YY(3-36), and ghrelin from the gastrointestinal tract. Of the many gastrointestinal peptides, ghrelin is the only established appetite-stimulating one, whereas cholecystokinin, glucagon-like peptide-1, and peptide YY(3-36) promote satiety. Adipose tissue provides hormonal signals via leptin and insulin to the brain about energy stores and likely from adiponectin and resistin. Binge eating has been related to a dysfunction in the ghrelin signaling system. Moreover, the larger gastric capacity observed in BED may further reduce satiety signals and contribute to overeating.

Towards a physiologically based diagnosis of anorexia nervosa and bulimia nervosa

Diagnosis of anorexia nervosa (AN) and bulimia nervosa (BN), while including such physiological data as weight and the reproductive status of the individual, are primarily based on questionnaires and interviews that rely on self-report of both body-related concerns and eating-related behaviors. While some key components of eating disorders are psychological and thus introspective in nature, reliance on self-report for the assessment of eating-related behaviors and nutritional status lacks the objectivity that a physiologically based measure could provide. The development of a more physiologically informed diagnosis for AN and BN would provide a more objective means of diagnosing these disorders, provide a sound physiological basis for diagnosing subclinical disorders and could also aid in monitoring the effectiveness of treatments for these disorders. Empirically supported, physiologically based methods for diagnosing AN and BN are reviewed herein as well as promising physiological measures that may potentially be used in the diagnosis of AN and BN.

The impact of hyperactivity and leptin on recovery from anorexia nervosa

In anorexia nervosa (AN), hyperactivity is observed in about 80% of patients and has been associated with low leptin levels in the acute stage of AN and in anorexia animal models. To further understand the importance of this correlation in AN, we investigated the relationship between hypoleptinaemia and hyperactivity in AN patients longitudinally and assessed their predictive value for recovery.

Body weight, activity levels, and serum leptin levels were assessed in adolescents and adult AN patient groups at the start and during treatment, up to a year. In the adolescent group, initial leptin and activity levels were correlated. This negative correlation changes over time into a positive correlation with physiological recovery. Treatment outcome in both groups could be predicted by initial BMI and leptin levels but not by activity levels. No major relationship of activity with the course of recovery was detected, suggesting that in contrast to the acute stage of the disease, leptin and activity levels during the recovery process are dissociated.

Alterations in the autonomic control of heart rate variability in patients with anorexia or bulimia nervosa: correlations between sympathovagal activity, clinical features, and leptin levels

Changes in body composition, hormone secretions, and heart function with increased risk of sudden death occur in eating disorders. In this observational clinical study, we evaluated sympathovagal modulation of heart rate variability (HRV) and cardiovascular changes in response to lying-to-standing in patients with anorexia (AN) or bulimia nervosa (BN) to analyze: a) differences in autonomic activity between AN, BN, and healthy subjects; b) relationships between autonomic and cardiovascular parameters, clinical data and leptin levels in patients with eating disorders. HRV, assessed by power spectral analysis of R-R intervals, blood pressure (BP) and heart rate (HR) were studied by tilt-table test in 34 patients with AN, 16 with BN and 30 healthy controls. Autonomic and cardiovascular findings were correlated with clinical data, and serum leptin levels. Leptin levels were lowered in AN vs BN and healthy subjects (p<0.0001), but both AN and BN patients showed unbalanced sympathovagal control of HRV due to relative sympathetic failure, prevalent vagal activity, impaired sympathetic activation after tilting, independently from their actual body weight and leptin levels. No significant correlations were obtained between HRV data vs clinical data, BP and HR findings, and leptin levels in eating disorders. Body mass indices (BMI) (p<0.02), and leptin levels (p<0.04) correlated directly with BP values. Our data showed alterations of sympathovagal control of HRV in eating disorders. These changes were unrelated to body weight and BMI, diagnosis of AN or BN, and leptin levels despite the reported effects of leptin on the sympathetic activity.

Correlation between psychometric and biological parameters in anorexic and bulimic patients during and after an intensive day hospital treatment

This study describes: 1. The therapeutic effects on anorexia nervosa (AN) and bulimia nervosa (BN) patients of a psycho-nutritional intensive day-hospital program; 2. The possible correlation between the changes observed in the psychometric tests and the variations of a number of biological parameters. Forty-six female patients (24 AN and 22 BN) were assessed through a semi-structured clinical interview based on DSM-IV criteria for Eating Disorders (ED) and a number of psychometric tests (SCL-90R, BDI, EDI-2, EAT-40, BITE, BAT) at the beginning and at the end of treatment, and after a 6-month follow-up. At these three times, we also assessed the plasma level of leptin, cortisol, luteinizing hormone (LH), follicle-stimulating hormone (FSH) and 17beta-estradiol together with body mass index (BMI) and menstrual cycle. From beginning to discharge, the scores on all psychometric tests improved in the whole sample, except for the Perfectionism subscale of EDI-2 in both groups (AN and BN), the Anger-Hostility, Phobic Anxiety and Paranoid Ideation subscales of SCL-90 and the Interpersonal Distrust subscale of EDI-2 in the BN group. At follow-up, there was a worsening of the BITE scores and of a number of EDI-2 subscales, especially in the AN subgroup - with these changes correlating with the trend of BMI. In AN patients, plasma leptin levels changed from the beginning to the end of treatment and at follow-up according to BMI changes. The mean plasma leptin level in the BN subgroup was higher than in the AN one. We found a statistically significant correlation with the scores of BDI, SCL-90R Depression and Ineffectiveness subscales, EAT-40, BITE-Symptom subscale and the trend of menses dividing these patients into two subgroups (according to the plasma leptin concentration, higher or lower than the top leptin level in the anorexics). These data seem to confirm that leptin secretion doesn't correlate univocally to BMI.

Leptin treatment in activity-based anorexia

BACKGROUND

Activity-based anorexia (ABA) is considered an animal model of anorexia nervosa (AN). In ABA, scheduled feeding together with voluntary access to a running wheel results in increased running wheel activity (RWA), hypophagia, and body weight loss. Previously it was shown that leptin treatment reduced semi-starvation-induced hyperactivity in rats. The present study was performed to confirm and extend this finding, to evaluate leptin's effect on energy balance in ABA.

METHODS

The effects of chronic leptin treatment (intracerebroventricular, 4 microg/day) in ABA rats, ad libitum-fed running rats, and sedentary rats exposed to ad libitum feeding or scheduled feeding were investigated.

RESULTS

Leptin treatment decreased RWA in ABA rats. Additionally, leptin treatment reduced food intake and increased energy expenditure by thermogenesis in ABA rats. Ad libitum-fed running/sedentary rats or food-restricted sedentary rats did not reduce activity after leptin treatment, whereas all leptin-treated rats showed hypophagia. Body temperature was slightly increased in leptin-treated food-restricted sedentary rats.

CONCLUSIONS

Although leptin treatment reduced RWA in ABA rats, it also prevented hypothermia and decreased food intake. Altogether, this resulted in a stronger negative energy balance and body weight loss in leptin-treated ABA rats.

Role of leptin in energy-deprivation states: normal human physiology and clinical implications for hypothalamic amenorrhoea and anorexia nervosa

Leptin is an adipocyte-secreted hormone that plays a key part in energy homoeostasis. Advances in leptin physiology have established that the main role of this hormone is to signal energy availability in energy-deficient states. Studies in animals and human beings have shown that low concentrations of leptin are fully or partly responsible for starvation-induced changes in neuroendocrine axes, including low reproductive, thyroid, and insulin-like growth factor (IGF) hormones. Disease states such as exercise-induced hypothalamic amenorrhoea and anorexia nervosa are also associated with low concentrations of leptin and a similar spectrum of neuroendocrine abnormalities. We have recently shown in an interventional, proof-of-concept study that leptin can restore ovulatory menstrual cycles and improve reproductive, thyroid, and IGF hormones and bone markers in hypothalamic amenorrhoea. Further studies are warranted to establish the safety and effectiveness of leptin for the infertility and osteoporosis associated with hypothalamic amenorrhoea, and to clarify its role in anorexia nervosa.