Pain modulation role of melatonin in eating disorders

From Virtual Reality to Regenerative Virtual Therapy: Some Insights from a Systematic Review Exploring Inner Body Perception in Anorexia and Bulimia Nervosa

Despite advances in our understanding of the behavioral and molecular factors that underlie the onset and maintenance of Eating Disorders (EDs), it is still necessary to optimize treatment strategies and establish their efficacy. In this context, over the past 25 years, Virtual Reality (VR) has provided creative treatments for a variety of ED symptoms, including body dissatisfaction, craving, and negative emotions. Recently, different researchers suggested that EDs may reflect a broader impairment in multisensory body integration, and a particular VR technique-VR body swapping-has been used to repair it, but with limited clinical results. In this paper, we use the results of a systematic review employing PRISMA guidelines that explore inner body perception in EDs (21 studies included), with the ultimate goal to analyze the features of multisensory impairment associated with this clinical condition and provide possible solutions. Deficits in interoception, proprioception, and vestibular signals were observed across Anorexia and Bulimia Nervosa, suggesting that: (a) alteration of inner body perception might be a crucial feature of EDs, even if further research is needed and; (b) VR, to be effective with these patients, has to simulate/modify both the external and the internal body. Following this outcome, we introduce a new therapeutic approach-Regenerative Virtual Therapy-that integrates VR with different technologies and clinical strategies to regenerate a faulty bodily experience by stimulating the multisensory brain mechanisms and promoting self-regenerative processes within the brain itself.

Sensory impairment in obese patients? Sensitivity and pain detection thresholds for electrical stimulation after surgery-induced weight loss, and comparison with a nonobese population

INTRODUCTION

Obese patients have a high prevalence of painful musculoskeletal disorders that may decrease after massive weight loss. Pain thresholds may be different in obese participants.

OBJECTIVES

To assess the sensitivity and pain detection thresholds, through the application of an electrical sensitivity, before and after massive weight loss, and to compare the thresholds obtained with those in a control population.

METHODS

The sensitivity and pain detection thresholds obtained in participants subjected to electrical stimulation were determined in 31 obese individuals (age: 40.3 ± 10.5 y) before (body mass index: 45.7 ± 6.8 kg/m) and 6 months after a mean weight loss of 32 kg induced by gastric bypass. The results obtained were compared with those for 49 nonobese control participants (38.5 ± 11.2 y; body mass index: 22.6 ± 2.6 kg/m). Body composition and metabolic biomarkers, such as leptin, adiponectin, insulin, and interleukin 6, were assessed and single-nucleotide polymorphisms of the mu opioid receptor [OPRM1 (c.118A > G) and COMT (p.Val158Met)] were genotyped in obese patients.

RESULTS

Sensitivity and pain detection thresholds (3.9 ± 1.1; 11.6 ± 6.0) were significantly higher in obese than in nonobese participants (3.1 ± 1.1; 6.0 ± 3.0), respectively (P < 0.0001), and were not affected by drastic weight loss (mean change: 32 kg). Pain thresholds in obese participants were not correlated with any of the clinical and biological variables studied. The obese participants in the highest quartile for both sensitivity and pain detection thresholds were significantly older than those in the lowest quartile.

CONCLUSIONS

Further studies are required to explore sensory dysfunction in obese individuals and to investigate the implications of this dysfunction for pain management.

Potential use of melatonergic drugs in analgesia: mechanisms of action

Melatonin is a remarkable molecule with diverse physiological functions. Some of its effects are mediated by receptors while other, like cytoprotection, seem to depend on direct and indirect scavenging of free radicals not involving receptors. Among melatonin's many effects, its antinociceptive actions have attracted attention. When given orally, intraperitoneally, locally, intrathecally or through intracerebroventricular routes, melatonin exerts antinociceptive and antiallodynic actions in a variety of animal models. These effects have been demonstrated in animal models of acute pain like the tail-flick test, formalin test or endotoxin-induced hyperalgesia as well as in models of neuropathic pain like nerve ligation. Glutamate, gamma-aminobutyric acid, and particularly, opioid neurotransmission have been demonstrated to be involved in melatonin's analgesia. Results using melatonin receptor antagonists support the participation of melatonin receptors in melatonin's analgesia. However, discrepancies between the affinity of the receptors and the very high doses of melatonin needed to cause effects in vivo raise doubts about the uniqueness of that physiopathological interpretation. Indeed, melatonin could play a role in pain through several alternative mechanisms including free radicals scavenging or nitric oxide synthase inhibition. The use of melatonin analogs like the MT(1)/MT(2) agonist ramelteon, which lacks free radical scavenging activity, could be useful to unravel the mechanism of action of melatonin in analgesia. Melatonin has a promising role as an analgesic drug that could be used for alleviating pain associated with cancer, headache or surgical procedures.

Elevated pain threshold in eating disorders: physiological and psychological factors

Several studies have found decreased pain sensitivity in patients with eating disorders but it is unclear what physiological and psychological factors are associated with this abnormality. In the present investigation, thermal pain threshold latency, somatoform dissociation, body image disturbance and physiological indices of autonomic neural system activity were measured in 39 female patients with eating disorders (21 with anorexia nervosa and 18 with bulimia nervosa) and 17 healthy women. Pain threshold was elevated in patients with eating disorders, especially those with binge-purging symptomatology. A regression analysis indicated that increased pain threshold is moderately associated with decreased peripheral skin temperature and weakly associated with lack of familiarity with one's own body. However, the between group differences in pain perception remained significant after controlling for peripheral skin temperature. Hence, elevation of pain threshold in eating disorders is a replicable finding, which is not explicable by peripheral indices of autonomic system activity or by somatoform dissociation. In future research it may be evaluated as a potential marker of broader phenotype of decreased interoceptive awareness, which may be associated with vulnerability to the development of eating disorders.

Melatonin deficiencies in women

The pineal hormone melatonin is the mediator of external light to physiologic adaptation to day and night rhythms, it regulates reproduction in animals but attempts to utilize melatonin in women for contraception have failed. Melatonin seems to be the natural hormone to facilitate sleep in insomniac patients and causes no hang over. When applied together with benzodiazepine it allows reduction of benzodiazepine without withdrawal effects. It should be applied 2 h before sleeping time in doses between 3 and 5 mg. Melatonin acts via the gamma-aminobutyric acid- and benzodiazepine receptor explaining its success in treatment of seizures in children and in adults. Constant application of benzodiazepine reduced the production of natural melatonin in rats, supporting the evidence that long-term application of benzodiazepine in humans does not restore sleeping habits but reduces natural sleeping habits even more. Low melatonin levels were seen in bulimia or neuralgia and in women with fibromyalgia; replacement reduced pain, sleeping disorders, and depression in fibromyalgia and bulimia. Melatonin profiles are a diagnostic tool to distinguish between several forms of depression, like major depression, winter depression (SAD), unipolar depression, delayed sleep phase syndrome (DSPS). In patients with a major depression success with antidepressants correlated with an increase in their melatonin profiles but only patients suffering from DSPS can be successfully treated with melatonin. In perimenopausal women melatonin administration did produce a change in LH, FSH and thyroid hormones. Some oncostatic properties are supported by cell culture work and studies in animals. In Nordic countries indigenous people suffer less from breast and prostate cancer, winter darkness seems to protect. The supposedly increased melatonin levels created the 'melatonin hypothesis'. Epidemiological studies did show that blind people indeed have half the rate of breast cancers, supporting the hypothesis. Controversial results concerning melatonin and insulin resistance and glucose tolerance have been published. In postmenopausal women application of melatonin reduced glucose tolerance and insulin sensitivity. Pregnant women should avoid melatonin, since its teratogenic effect is not known. Patients suffering from non-hormone dependent tumors, like leukemia, should avoid melanin, since tumor growth was promoted in animal experiments. It can be expected that melatonin will receive wide consideration for treatment of sleeping disturbances, jet lag, and fibromyalgia once an oral formulation becomes available in Europe.