A systematic review of in vitro cytokine production in eating disorders

Anorexia Nervosa in vivo cytokine production: a systematic review

INTRODUCTION

The underlying psychobiology that contributes to Anorexia Nervosa (AN) onset and disease progression remains unclear. New research is emerging suggesting a possible link between inflammation and a variety of mental illnesses. Alterations of cytokines may play a role in the pathogenesis of AN. Some studies have found differences in the cytokine profile of those with AN compared to healthy controls, but results are heterogeneous. The aim of this work was to systematically review existing studies investigating in-vivo cytokine production in those with AN before and after weight restoration compared to controls.

METHODS

A comprehensive literature search of four electronic databases (PubMed, PsychInfo, EMBASE and CINAH) was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines to identify human in-vivo studies investigating the relationship between AN and cytokine production. Data extracted from included studies related to population characteristics (e.g. age, gender, mean mBMI/%IBW), cytokine measurement and relevant findings. Confounding factors (e.g. smoking status, co-morbid mental illness, menstruation status) were also collected.

RESULTS

36 studies were eligible for this systematic review of which the majority were conducted in Europe (77.8%) and involved female subjects (97.2%). Those with AN ranged in age from 13 to 47 years and had an illness duration of 3 months to 24 years. 15 candidate cytokines and 3 receptors were identified (TNF-alpha, IL-6, IL-1B, CRP, IL-2, IL-7, IL-10, IFN-γ, TNF-R2, IL-1 α, IL-15, TNF-R1, IL-17, IL-18, TGF-B1, IL-12, IL-6R and TGF-B2) exploring in-vivo levels in patients with AN and comparing to controls. TNF-alpha and IL-6 were the most extensively studied with IL-6 being significantly elevated in 4 out of 8 (50%) of longitudinal studies when comparing AN patients at baseline compared to post weight restoration. Following weight restoration, there was no difference in IL-6 levels when comparing to HC in 7 of 8 (87.5%) longitudinal studies examined.

CONCLUSIONS

The most promising cytokine potentially involved in the pathogenesis of AN appears to be IL-6, and possibly TNF-alpha pathways. The heterogeneity of clinical and methodology factors impedes the generalizability of results. Future studies may wish to address these methodological shortcomings as alterations in cytokine levels in AN could act as therapeutic targets assisting with weight restoration and psychopathology and may offer diagnostic potential.

Expression of immune-related proteins and their association with neuropeptides in adolescent patients with anorexia nervosa

Anorexia nervosa (AN) is a metabo-psychiatric disorder where alterations of cytokines, neuropeptides, neurotransmitters, and the interactions between these factors can play an important role. Thus, the primary goal of the presented study was a cross-sectional analysis of immune-related proteins in patients with AN. Moreover, the correlations between these molecules and selected neuropeptides were studied. Twenty-five adolescent inpatients girls in the acute stage of a restrictive type of AN were enrolled in the study within the first year of the disease. Additionally, thirty similar in age and height controls (CG) were also assessed. The levels of 24 immune-related proteins, including cytokines, chemokines, and proteases, were measured. Moreover, selected adipocytokines, gastrointestinal hormones, and centrally produced neuropeptides levels were determined. Finally, the correlations between these molecules were analyzed. The fasting levels of CXCL1, CXCL9, FGF2, GrB, IL1, IL6, IL8, MMP8, MMP9, CTSS were statistically lower in AN than in the CG. The concentrations of many immune-related proteins remain unchanged despite their metabolic and mental condition. Moreover, significant correlations were found between leptin and CXCL1, CXCL9, GrB, IL1, IL6, and MMP8. Leptin receptors were correlated with GrB, while resistin was associated with MMP9. Our findings suggest that the initial stage of restrictive AN among adolescents within the first year of the disease is not connected with a pro-inflammatory state. Some immune-related protein changes may be associated with altered neuropeptides, primarily leptin, its receptors, and resistin. Future research should clarify which changes are primary and secondary to weight loss and whether these changes normalize with increasing weight. This would aid in understanding the complex etiopathogenesis of AN and in the search for new methods of treatment.

Nutrient Intake and Dietary Inflammatory Potential in Current and Recovered Anorexia Nervosa

Anorexia nervosa (AN) is characterised by disrupted and restrictive eating patterns. Recent investigations and meta-analyses have found altered concentrations of inflammatory markers in people with current AN. We aimed to assess nutrient intake in participants with current or recovered AN, as compared to healthy individuals, and explore group differences in dietary inflammatory potential as a possible explanation for the observed alterations in inflammatory markers. We recruited participants with current AN (n = 51), those recovered from AN (n = 23), and healthy controls (n = 49). We used the Food Frequency Questionnaire (FFQ), to calculate a Dietary Inflammatory Index (DII^®) score and collected blood samples to measure serum concentrations of inflammatory markers. In current AN participants, we found lower intake of cholesterol, compared to HCs, and lower consumption of zinc and protein, compared to HC and recovered AN participants. A one-way ANOVA revealed no significant group differences in DII score. Multivariable regression analyses showed that DII scores were significantly associated with tumour necrosis factor (TNF)-α concentrations in our current AN sample. Our findings on nutrient intake are partially consistent with previous research. The lack of group differences in DII score, perhaps suggests that diet is not a key contributor to altered inflammatory marker concentrations in current and recovered AN. Future research would benefit from including larger samples and using multiple 24-h dietary recalls to assess dietary intake.

Role of Neuroendocrine, Immune, and Autonomic Nervous System in Anorexia Nervosa-Linked Cardiovascular Diseases

Anorexia nervosa represents a severe mental disorder associated with food avoidance and malnutrition. In patients suffering from anorexia nervosa, cardiovascular complications are the main reason leading to morbidity and mortality. However, the origin and pathological mechanisms leading to higher cardiovascular risk in anorexia nervosa are still unclear. In this aspect, the issue of exact pathological mechanisms as well as sensitive biomarkers for detection of anorexia nervosa-linked cardiovascular risk are discussed. Therefore, this review synthesised recent evidence of dysfunction in multiple neuroendocrine axes and alterations in the immune system that may represent anorexia nervosa-linked pathological mechanisms contributing to complex cardiovascular dysregulation. Further, this review is focused on identification of non-invasive biomarkers for the assessment of increased cardiovascular risk in anorexia nervosa that can be linked to a clinical application. Complex non-invasive assessment of cardiovascular autonomic regulation—cardiac vagal control (heart rate variability), sympathetic vascular activity (blood pressure variability), and cardiovascular reflex control (baroreflex sensitivity)—could represent a promising tool for early diagnosis, personalized therapy, and monitoring of therapeutic interventions in anorexia nervosa particularly at a vulnerable adolescent age.

Pharmacological treatment of eating disorders, comorbid mental health problems, malnutrition and physical health consequences

The pharmacological treatment of patients with an eating disorder (ED) often includes medications to treat their ED, comorbid mental health problems, malnutrition and the physical health problems resulting from it. The currently approved pharmacological treatment options for EDs are limited to fluoxetine for bulimia nervosa (BN) and - in some countries - lisdexamfetamine for binge eating disorder (BED). Thus, there are no approved pharmacological options for anorexia nervosa (AN), even though study results for olanzapine and dronabinol are promising. Topiramate might be an additional future option for the treatment of BN and BED. Selective serotonin reuptake inhibitors (SSRI), mirtazapine and bupropion could be considered for the treatment of comorbid unipolar depression. However, AN and BN are contraindications for bupropion. For ED patients with a manic episode, we recommend olanzapine in AN and risperidone in BN and BED; whereas for bipolar depression, olanzapine (plus fluoxetine) seems appropriate in AN and lamotrigine in BN and BED. Acute anxiety or suicidality may warrant benzodiazepine treatment with lorazepam. Proton-pump inhibitors, gastroprokinetic drugs, laxatives and hormones can alleviate certain physical health problems caused by EDs. Therapeutic drug monitoring, pharmacogenomic testing, a more restrictive use of "pro re nata" (PRN) medication, an interdisciplinary treatment approach, shared decision making (SDM) and the formulation of common treatment goals by the patients, their family or carers and clinicians could improve treatment success and safety. Novel genetic, immunological, microbiome and brain imaging research as well as new pharmacological developments like the use of psychedelics, stimulants, novel monoaminergic drugs, hormone analogues and drugs which enhance the effects of psychotherapy may extend our therapeutic options in the near future.

The Neurobiology of Eating Disorders

Eating disorders are severe psychiatric illnesses with a typical age of onset in adolescence. Brain research in youth and young adults may help us identify specific neurobiology that contributes to onset and maintenance of those disorders. This article provides a state-of-the-art review of our current understanding of the neurobiology of anorexia nervosa and bulimia nervosa. This includes brain structure and function studies to understand food restriction, binge-eating or purging behaviors, cognitive and emotional factors, as well as interoception. Binge-eating disorder and avoidant restrictive food intake disorder are also discussed, but the literature is still very small.

Brain-Behavior-Immune Interaction: Serum Cytokines and Growth Factors in Patients with Eating Disorders at Extremes of the Body Mass Index (BMI) Spectrum

Alterations of the immune system are known in eating disorders (EDs), however the importance of cytokine balance in this context has not been clarified. We compared cytokines and growth factors at opposite ends of BMI ranges, in 90 patients classified in relation to BMI, depressive and EDs comorbidities. Serum concentrations of interleukin (IL)-1α, IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α), monocyte chemoattractant protein-1 (MCP-1), vascular endothelial growth factor (VEGF), and epidermal growth factor (EGF) were determined by a biochip analyzer (Randox Labs). Differences were calculated through ANOVA. Possible predictors of higher cytokine levels were evaluated through regression analysis. IL-1α, IL-10, EGF, and IFN-γ were altered individuals with anorexia nervosa (AN) and binge eating disorder (BED). Night-eating was associated with IL-8 and EGF levels, IL-10 concentrations with post-dinner eating and negatively with sweet-eating, long fasting with higher IFN-γ levels. IL-2 increase was not linked to EDs, but to the interaction of depression and BMI. Altogether, for the first time, IL-1α, IL-10, EGF, and IFN-γ were shown to differ between AN and HCs, and between AN and individuals with obesity with or without BED. Only IL-2 was influenced by depression. Dysfunctional eating behaviors predicted abnormal concentrations of IL-10, EGF, IL-8 and IFN-γ.