The role of hypoleptinemia in the psychological and behavioral adaptation to starvation: implications for anorexia nervosa

Leptin replacement therapy in the management of lipodystrophy syndromes

Lipodystrophy syndromes are rare diseases of genetic or acquired origin, characterized by quantitative and qualitative defects in adipose tissue. The metabolic consequences of lipodystrophy syndromes, such as insulin resistant diabetes, hypertriglyceridemia and hepatic steatosis, are frequently very difficult to treat, resulting in significant risks of acute and/or chronic complications and of decreased quality of life. The production of leptin by lipodystrophic adipose tissue is decreased, more severely in generalized forms of lipodystrophy, where adipose tissue is absent from almost all body fat depots, than in partial forms of the disease, where lipoatrophy affects only some parts of the body and can be associated with increased body fat in other anatomical regions. Several lines of evidence in preclinical and clinical models have shown that leptin replacement therapy could improve the metabolic complications of lipodystrophy syndromes. Metreleptin, a recombinant leptin analogue, was approved as an orphan drug to treat the metabolic complications of leptin deficiency in patients with generalized lipodystrophy in the USA or with either generalized or partial lipodystrophy in Japan and Europe. In this brief review, we will discuss the benefits and limitations of this therapy, and the new expectations arising from the recent development of a therapeutic monoclonal antibody able to activate the leptin receptor.

Dynamic Amygdala Nuclei Alterations in Relation to Weight Status in Anorexia Nervosa Are Mediated by Leptin

OBJECTIVE

The amygdaloid complex is a subcortical limbic group of distinct nuclei. In a previous patient-control study, differential amygdala nuclei alterations were found in acute anorexia nervosa (AN); rostral-medial nuclei involved in fear and reward processing were substantially reduced in volume and associated with hypoleptinemia, a key neuroendocrine characteristic of AN. Here, longitudinal amygdala nuclei alterations in AN were investigated in relation to weight status and their associations with leptin levels.

METHOD

T1-weighted structural magnetic resonance imaging scans were longitudinally processed with FreeSurfer. Amygdala nuclei volumes in young female patients with acute AN before and after short-term weight restoration (n = 110, >14% body mass index increase over 3 months) and female participants with a history of AN (n = 79, long-term [mean 5 years] weight recovered) were compared with female healthy control participants (n = 271) using linear mixed effects models.

RESULTS

Rostral-medially clustered amygdala nuclei volumes, accessory basal, cortical, medial nuclei, and corticoamygdaloid transition, increased during short-term weight restoration (Cohen's d range 0.18-0.30). However, volumetric normalization across nuclei was heterogeneous. Right cortical, medial nuclei, bilateral corticoamygdaloid transitions, and anterior amygdaloid areas were only partially normalized following short-term weight restoration. Right anterior amygdaloid area remained reduced after long-term weight recovery compared with control participants (d = 0.36). Leptin increase, accompanying short-term weight restoration, mediated the effect of weight gain on volumetric increase in left corticoamygdaloid transition and bilateral medial nuclei.

CONCLUSION

Rostral-medially clustered amygdala nuclei show pronounced volumetric increase but incomplete normalization in AN during and after short-term weight restoration. Leptin increase may be relevant for the recovery of specific amygdala nuclei in addition to nutritional rehabilitation, indicating links between amygdala substructure and leptin dynamics of potential pathophysiological and clinical relevance in AN.

PLAIN LANGUAGE SUMMARY

The amygdala plays a critical role in processing fearful and rewarding stimuli, and alterations in the amygdala are associated with anorexia nervosa. In this study, the authors measured amygdala nuclei volumes in female patients with acute anorexia nervosa undergoing weight-restoration treatment (n = 110), long-term weight-recovered individuals with anorexia (n = 79), and healthy control participants (n = 271). Structural magnetic resonance imaging revealed that volumes of specific nuclei, clustered in the rostral-medial amygdala, were substantially reduced in acute anorexia nervosa and only partially normalized following weight restoration treatment. Residual reductions in volume persisted even after long-term weight-recovery, compared to healthy control participants. Short-term weight restoration was associated with increases in the neurohormone leptin, and increasing leptin levels were found to mediate the positive impact of weight gain on increased amygdala volume over the treatment course.

DIVERSITY & INCLUSION STATEMENT

We worked to ensure race, ethnic, and/or other types of diversity in the recruitment of human participants. We worked to ensure that the study questionnaires were prepared in an inclusive way. One or more of the authors of this paper received support from a program designed to increase minority representation in science. We actively worked to promote sex and gender balance in our author group. We actively worked to promote inclusion of historically underrepresented racial and/or ethnic groups in science in our author group. While citing references scientifically relevant for this work, we also actively worked to promote sex and gender balance in our reference list. While citing references scientifically relevant for this work, we also actively worked to promote inclusion of historically underrepresented racial and/or ethnic groups in science in our reference list. The author list of this paper includes contributors from the location and/or community where the research was conducted who participated in the data collection, design, analysis, and/or interpretation of the work.

Does hypoleptinemia trigger entrapment in anorexia nervosa? Etiological and clinical considerations

Based on the recent observation that human recombinant leptin (r-Met-hu-leptin; metreleptin) may induce a profound alleviation of the complex symptomatology of patients with anorexia nervosa (AN), we examine the implications for our conceptualisation of this eating disorder. Hypoleptinemia as a core endocrine feature of AN serves as a central and peripheral trigger of tissue-specific adaptations to starvation. In this narrative review, we argue that leptin deficiency may explain many of the puzzling features of this eating disorder. Weight loss can be viewed as a two-step process, with only the second step entailing hypoleptinemia and thereby the entrapment characteristic of AN. We discuss the central and peripheral distribution of leptin receptors and consider possible functional implications of hypoleptinemia. We contrast the slow psychological recovery of patients with AN and of people who experienced starvation upon weight recovery with the rapid onset of improvements upon off-label metreleptin treatment. Characteristics of the sex and age dependent secretion of leptin may contribute to the elevated vulnerability of young females to develop AN.

Anorexia-Induced Hypoleptinemia Drives Adaptations in the JAK2/STAT3 Pathway in the Ventral and Dorsal Hippocampus of Female Rats

Leptin is an appetite-regulating adipokine that is reduced in patients with anorexia nervosa (AN), a psychiatric disorder characterized by self-imposed starvation, and has been linked to hyperactivity, a hallmark of AN. However, it remains unknown how leptin receptor (LepR) and its JAK2-STAT3 downstream pathway in extrahypothalamic brain areas, such as the dorsal (dHip) and ventral (vHip) hippocampus, crucial for spatial memory and emotion regulation, may contribute to the maintenance of AN behaviors. Taking advantage of the activity-based anorexia (ABA) model (i.e., the combination of food restriction and physical activity), we observed reduced leptin plasma levels in adolescent female ABA rats at the acute phase of the disorder [post-natal day (PND) 42], while the levels increased over control levels following a 7-day recovery period (PND49). The analysis of the intracellular leptin pathway revealed that ABA rats showed an overall decrease of the LepR/JAK2/STAT3 signaling in dHip at both time points, while in vHip we observed a transition from hypo- (PND42) to hyperactivation (PND49) of the pathway. These changes might add knowledge on starvation-induced fluctuations in leptin levels and in hippocampal leptin signaling as initial drivers of the transition from adaptative mechanisms to starvation toward the maintenance of aberrant behaviors typical of AN patients, such as perpetuating restraint over eating.

Unexpected identification of obesity-associated mutations in LEP and MC4R genes in patients with anorexia nervosa

Mutations leading to a reduced or loss of function in genes of the leptin-melanocortin system confer a risk for monogenic forms of obesity. Yet, gain of function variants in the melanocortin-4-receptor (MC4R) gene predispose to a lower BMI. In individuals with reduced body weight, we thus expected mutations leading to an enhanced function in the respective genes, like leptin (LEP) and MC4R. Therefore, we have Sanger sequenced the coding regions of LEP and MC4R in 462 female patients with anorexia nervosa (AN), and 445 healthy-lean controls. In total, we have observed four and eight variants in LEP and MC4R, respectively. Previous studies showed different functional in vitro effects for the detected frameshift and non-synonymous variants: (1) LEP: reduced/loss of function (p.Val94Met), (2) MC4R: gain of function (p.Val103Ile, p.Ile251Leu), reduced or loss of function (p.Thr112Met, p.Ser127Leu, p.Leu211fsX) and without functional in vitro data (p.Val50Leut). In LEP, the variant p.Val94Met was detected in one patient with AN. For MC4R variants, one patient with AN carried the frameshift variant p.Leu211fsX. One patient with AN was heterozygous for two variants at the MC4R (p.Val103Ile and p.Ser127Leu). All other functionally relevant variants were detected in similar frequencies in patients with AN and lean individuals.

The Diagnosis and Treatment of Anorexia Nervosa in Childhood and Adolescence

BACKGROUND

Anorexia nervosa (AN) is a serious disease with a lifetime prevalence of up to 3.6% in women and 0.3% in men. Abnormally low weight and the associated starvation partly account for its somatic and mental manifestations.

METHODS

This review is based on publications retrieved by a selective search concerning AN in childhood and adolescence.

RESULTS

The peak age of onset of AN is 15.5 years. The frequency of inpatient treatment for AN rose by 40% during the COVID pandemic, indicating the importance of environmental factors; the heritability of AN is estimated at 0.5. The ICD-11 sets the threshold for AN-associated underweight at the fifth percentile for age of the body mass index, as long as the remaining diagnostic criteria are met. The main goal of the multiprofessional treatment of AN is the return to normal body weight, which is a central prerequisite for regaining somatic and mental health. The mean duration of AN is 3.4 years, and approximately twothirds of patients recover from the disease over the long term.

CONCLUSION

Marked weight loss in childhood and adolescence can trigger AN in the presence of a predisposition to this disease. Patients and their families should receive psychoeducation regarding the symptoms of starvation and their overlap with those of AN. Important objectives are to shorten the duration of the illness, minimize mortality and the risk of chronic illness, and to identify pharmacological approaches to treatment.

Differential longitudinal changes of hippocampal subfields in patients with anorexia nervosa

BACKGROUND

Anorexia nervosa (AN) is a mental disorder characterized by dietary restriction, fear of gaining weight, and distorted body image. Recent studies indicate that the hippocampus, crucial for learning and memory, may be affected in AN, yet subfield-specific effects remain unclear. We investigated hippocampal subfield alterations in acute AN, changes following weight restoration, and their associations with leptin levels.

METHODS

T1-weighted magnetic resonance imaging scans were processed using FreeSurfer. We compared 22 left and right hemispheric hippocampal subfield volumes cross-sectionally and longitudinally in females with acute AN (n = 165 at baseline, n = 110 after partial weight restoration), healthy female controls (HCs; n = 271), and females after long-term recovery from AN (n = 79) using linear models.

RESULTS

We found that most hippocampal subfield volumes were significantly reduced in patients with AN compared with HCs (~-3.9%). Certain areas such as the subiculum exhibited no significant reduction in the acute state of AN, while other areas, such as the hippocampal tail, showed strong decreases (~-9%). Following short-term weight recovery, most subfields increased in volume. Comparisons between participants after long-term weight-recovery and HC yielded no differences. The hippocampal tail volume was positively associated with leptin levels in AN independent of body mass index.

CONCLUSIONS

Our study provides evidence of differential volumetric differences in hippocampal subfields between individuals with AN and HC and almost complete normalization after weight rehabilitation. These alterations are spatially inhomogeneous and more pronounced compared with other major mental disorders (e.g. major depressive disorder and schizophrenia). We provide novel insights linking hypoleptinemia to hippocampal subfield alterations hinting towards clinical relevance of leptin normalization in AN recovery.

Longitudinal analysis of the gut microbiome in adolescent patients with anorexia nervosa: microbiome-related factors associated with clinical outcome

There is mounting evidence regarding the role of gut microbiota in anorexia nervosa (AN). Previous studies have reported that patients with AN show dysbiosis compared to healthy controls (HCs); however, the underlying mechanisms are unclear, and data on influencing factors and longitudinal course of microbiome changes are scarce. Here, we present longitudinal data of 57 adolescent inpatients diagnosed with AN at up to nine time points (including a 1-year follow-up examination) and compare these to up to six time points in 34 HCs. 16S rRNA gene sequencing was used to investigate the microbiome composition of fecal samples, and data on food intake, weight change, hormonal recovery (leptin levels), and clinical outcomes were recorded. Differences in microbiome composition compared to HCs were greatest during acute starvation and in the low-weight group, while diminishing with weight gain and especially weight recovery at the 1-year follow-up. Illness duration and prior weight loss were strongly associated with microbiome composition at hospital admission, whereas microbial changes during treatment were associated with kilocalories consumed, weight gain, and hormonal recovery. The microbiome at admission was prognostic for hospital readmission, and a higher abundance of Sutterella was associated with a higher body weight at the 1-year follow-up. Identifying these clinically important factors further underlines the potential relevance of gut microbial changes and may help elucidate the underlying pathophysiology of gut-brain interactions in AN. The characterization of prognostically relevant taxa could be useful to stratify patients at admission and to potentially identify candidate taxa for future supplementation studies aimed at improving AN treatment.

Case report: Rapid improvements of anorexia nervosa and probable myalgic encephalomyelitis/chronic fatigue syndrome upon metreleptin treatment during two dosing episodes

A comorbidity of anorexia nervosa (AN) and myalgic encephalomyelitis (ME/CSF) is uncommon. A 17 years-old male adolescent with possible onset of ME/CFS after an Epstein Barr Virus infection (EBV) and later onset of AN during a second period of weight loss was twice treated off-label with metreleptin for 15 and 11 days, respectively. As in previous cases, eating disorder specific cognitions and mood improved. Interestingly, fatigue and post-exertional muscle pain (P-EMP) improved, too. We discuss potential mechanisms. Treatment with metreleptin may prove beneficial in AN and in ME/CSF associated with substantial weight loss.

Similarities and differences regarding acute anorexia nervosa and semi-starvation: does behavioral thermoregulation play a central role?

Objective

To clarify the association between acute anorexia nervosa (AN) and semi-starvation (SS) by focusing on similarities and differences in physiology, mood, and behavior.

Method

A comparison of published literature between these two groups.

Results

Both groups show similar hormonal and metabolic changes in response to caloric restriction and extreme weight loss (~25%). Associated changes result in a reduced body temperature (Tcore-low). Maintenance of body temperature within a specific range is crucial to survival. However, both groups cannot activate autonomic strategies to maintain their Tcore-low, such as increasing metabolic rate, constricting skin blood vessels, or shivering. Furthermore, Tcore-low increases the individuals' "coldness sensations" throughout the body, hence the frequent reports from ANs and SSs of "feeling cold." To eliminate these uncomfortable "coldness sensations" and, importantly, to maintain Tcore-low, ANs, and SSs "select" different thermoregulatory behavioral strategies. It is proposed that the primary differences between AN and SS, based on genetics, now manifest due to the "selection" of different thermo-regulatory behaviors. AN patients (ANs) "select" hyperactive behavior (HyAc), which increases internal metabolic heat and thus assists with maintaining Tcore-low; in harmony with hyperactive behavior is a lively mood. Also related to this elevated arousal pattern, ANs experience disrupted sleep. In contrast, SS individuals "select" a passive thermo-behavioral strategy, "shallow torpor," which includes reduced activity, resulting in energy conservation. In addition, this inactivity aids in the retention of generated metabolic heat. Corresponding to this lethargic behavior, SS individuals display a listless mood and increased sleep.

Conclusion

Initial similarities between the two are attributable to physiological changes related to extreme weight loss. Differences are most likely attributable to genetically programmed "selection" of alternate thermoregulatory strategies, primarily to maintain Tcore-low. However, if acute AN is prolonged and evolves into a chronic condition, AN will more closely align with starvation and more precisely reflect SS symptomology.

Case report: clinical improvements observed in first off-label metreleptin treatment of a patient with atypical anorexia nervosa

Off-label metreleptin treatment resulted in cognitive, emotional and behavioral improvements of patients with anorexia nervosa, who presented with hypoleptinemia. We now report a case study of a 16-year-old female patient with atypical anorexia nervosa who was treated off-label with metreleptin for 11 days. She had lost 21 kg over 6 months. Her body mass index at referral for inpatient treatment was 20 kg/m2, her serum leptin level was just within the normal range (2.4 ng/ml). Dosing resulted in prominent improvements of mood and weight phobia entailing a comparatively brief inpatient treatment. The observed improvements are similar to those observed in patients with AN, suggesting overlapping mechanisms with respect to clinical effects induced by elevations of absolute or relative hypoleptinemia. Randomized controlled trials are warranted for both eating disorders.

Explicating the role of amygdala substructure alterations in the link between hypoleptinemia and rumination in anorexia nervosa

OBJECTIVE

The amygdaloid complex plays a pivotal role in emotion processing and has been associated with rumination transdiagnostically. In anorexia nervosa (AN), we previously observed differential reductions of amygdala nuclei volumes (rostral-medial cluster substantially affected) and, in another study, elevated food-/weight-related rumination. Both amygdala volumes and rumination frequency correlated with characteristically suppressed leptin levels in AN. Thus, we hypothesized that amygdala nuclei alterations might be associated with AN-related rumination and potentially mediate the leptin-rumination relationship in AN.

METHODS

Rumination (food-/weight-related) was assessed using ecological momentary assessment for a 14-day period. We employed frequentist and Bayesian linear mixed effects models in females with AN (n = 51, 12-29 years, majority admitted to inpatient treatment) and age-matched healthy females (n = 51) to investigate associations between rostral-medial amygdala nuclei volume alterations (accessory basal, cortical, medial nuclei, corticoamygdaloid transitions) and rumination. We analyzed mediation effects using multi-level structural equation models.

RESULTS

Reduced right accessory basal and cortical nuclei volumes predicted more frequent weight-related rumination in AN; both nuclei fully mediated the effect of leptin on weight-related rumination. In contrast, we found robust evidence for the absence of amygdala nuclei volume effects on rumination in healthy females.

CONCLUSION

This study provides first evidence for the relevance of specific amygdala substructure reductions regarding cognitive symptom severity in AN and points toward novel mechanistic insight into the relationship between hypoleptinemia and rumination, which might involve the amygdaloid complex. Our findings in AN may have important clinical value with respect to understanding the beneficial neuropsychiatric effects of leptin (treatment) in AN and potentially other psychiatric conditions such as depression.

Differential alterations of amygdala nuclei volumes in acutely ill patients with anorexia nervosa and their associations with leptin levels

BACKGROUND

The amygdala is a subcortical limbic structure consisting of histologically and functionally distinct subregions. New automated structural magnetic resonance imaging (MRI) segmentation tools facilitate the in vivo study of individual amygdala nuclei in clinical populations such as patients with anorexia nervosa (AN) who show symptoms indicative of limbic dysregulation. This study is the first to investigate amygdala nuclei volumes in AN, their relationships with leptin, a key indicator of AN-related neuroendocrine alterations, and further clinical measures.

METHODS

T1-weighted MRI scans were subsegmented and multi-stage quality controlled using FreeSurfer. Left/right hemispheric amygdala nuclei volumes were cross-sectionally compared between females with AN (n = 168, 12-29 years) and age-matched healthy females (n = 168) applying general linear models. Associations with plasma leptin, body mass index (BMI), illness duration, and psychiatric symptoms were analyzed via robust linear regression.

RESULTS

Globally, most amygdala nuclei volumes in both hemispheres were reduced in AN v. healthy control participants. Importantly, four specific nuclei (accessory basal, cortical, medial nuclei, corticoamygdaloid transition in the rostral-medial amygdala) showed greater volumetric reduction even relative to reductions of whole amygdala and total subcortical gray matter volumes, whereas basal, lateral, and paralaminar nuclei were less reduced. All rostral-medially clustered nuclei were positively associated with leptin in AN independent of BMI. Amygdala nuclei volumes were not associated with illness duration or psychiatric symptom severity in AN.

CONCLUSIONS

In AN, amygdala nuclei are altered to different degrees. Severe volume loss in rostral-medially clustered nuclei, collectively involved in olfactory/food-related reward processing, may represent a structural correlate of AN-related symptoms. Hypoleptinemia might be linked to rostral-medial amygdala alterations.

Current Discoveries and Future Implications of Eating Disorders

Eating disorders (EDs) are characterized by severe disturbances in eating behaviors and can sometimes be fatal. Eating disorders are also associated with distressing thoughts and emotions. They can be severe conditions affecting physical, psychological, and social functions. Preoccupation with food, body weight, and shape may also play an important role in the regulation of eating disorders. Common eating disorders have three major types: anorexia nervosa (AN), bulimia nervosa (BN), and binge eating disorder (BED). In some cases, EDs can have serious consequences for an individual's physical and mental health. These disorders often develop during adolescence or early adulthood and affect both males and females, although they are more commonly diagnosed in young adult females. Treatment for EDs typically involves a combination of therapy, nutrition counseling, and medical care. In this narrative review, the authors summarized what is known of EDs and discussed the future directions that may be worth exploring in this emerging area.

The Role of Leptin in Rodent and Human Sleep: A Transdiagnostic Approach with a Particular Focus on Anorexia Nervosa

This narrative review addressed to both clinicians and researchers aims to assess the role of hypoleptinemia in disordered sleep with a particular focus on patients with anorexia nervosa (AN). After introducing circadian rhythms and the regulation of circulating leptin, we summarize the literature on disordered sleep in patients with AN and in fasting subjects in general. We highlight novel single-case reports of substantially improved sleep within days after initiation of off-label metreleptin treatment. These beneficial effects are set in relationship to current knowledge of disordered sleep in animal models of an impaired leptin signaling. Specifically, both absolute and relative hypoleptinemia play a major role in animal models for insomnia, obstructive sleep apnea and obesity hypoventilation syndrome. We pinpoint future research required to complement our understanding of the role of leptin in sleep in patients with acute AN. Moreover, within the section clinical applications we speculate that human recombinant leptin may be useful for the treatment of treatment-resistant sleep-wake disorders, which are associated with (relative) hypoleptinemia. Overall, we stress the role of the hormone leptin in sleep.

"Your mind doesn't have room for anything else": a qualitative study of perceptions of cognitive functioning during and after recovery from anorexia nervosa

BACKGROUND

Past research has indicated the presence of cognitive difficulties in individuals with anorexia nervosa (AN), although it is unclear how these are experienced in real life. Moreover, it is unclear how and whether the experience of cognitive difficulties changes in nature and intensity over the course of the illness and following recovery.

METHODS

Twenty-one female participants (AN = 11; recovered AN = 10) participated in online semi-structured interviews, utilising open-ended questions and exploring topics relating to their experiences of their cognitive function, changes over time and their perspectives on the future. Reflexive thematic analysis was conducted on the resulting transcripts.

RESULTS

Six themes were identified, centred around the effects of the illness on mental and physical function, cognition, adaptation to living with the illness, similarities between AN and other psychopathology, tentative optimism for the future and recovery as a representation of liberation. Whilst respondents with AN appeared to perform remarkably well in their professional and educational lives, the cognitive difficulties were described as significantly impacting their ability to engage in life, particularly in the context of leisure and socialising. Respondents recovered from AN noted the importance of developing a non-AN identity as well as better emotion-regulation skills as central to recovery.

CONCLUSIONS

Whilst people with AN may be able to adapt their lives to the demands of the illness, they report significant cognitive difficulties that interfere with their engagement in many aspects of daily life. This should be considered by professionals working in the clinical management of AN. Treatments focused on ameliorating cognitive difficulties, and promoting emotional regulation and identity in AN are warranted.

Increased Habit Frequency in the Daily Lives of Patients with Acute Anorexia Nervosa

Strict eating routines and frequent rigid behavior patterns are commonly observed in patients with anorexia nervosa (AN). A recent theory proposes that while these behaviors may have been reinforced initially, they later become habitual. To date, however, research has been overly focused on eating-disorder (ED)-related habits. Over the course of seven days, we applied an ecological momentary assessment (EMA) to investigate the habit frequency and strength of ED-specific (food intake) and ED-unspecific (hygiene) habits in the daily lives of a sample of n = 57 AN and n = 57 healthy controls (HC). The results of the hierarchical models revealed that habits were significantly more likely in patients compared with HC for both categories, independently. Furthermore, a lower body mass index (BMI) was associated with increased habit frequency in AN. Our study strengthens the habit theory of AN by showing the relevance of habits beyond ED-specific behavioral domains. This also supports the development of innovative therapeutic interventions targeting habitual behavior in EDs.