Long-term dynamics of serum α-MSH and α-MSH-binding immunoglobulins with a link to gut microbiota composition in patients with anorexia nervosa.

INTRODUCTION: Immunoglobulins (Ig) reactive with α-melanocyte-stimulating hormone (α-MSH), an anorexigenic neuropeptide, are present in humans and were previously associated with eating disorders. In this longitudinal study involving patients with anorexia nervosa (AN), we determined whether α-MSH in serum is bound to IgG and analyzed long-term dynamics of both α-MSH peptide and α-MSH-reactive Ig in relation to changes in BMI and gut microbiota composition. METHODS: The study included 64 adolescents with a restrictive form of AN, whose serum samples were collected at hospital admission, discharge, and during a 1-year follow-up visit, and 41 healthy controls, all females. RESULTS: We found that in both study groups, approximately 40% of serum α-MSH was reversibly bound to IgG and that levels of α-MSH-reactive IgG, but not of α-MSH peptide in patients with AN were low at hospital admission, but recovered 1-year later. Total IgG levels were also low at admission. Moreover, BMI-standard deviation score (SDS) correlated positively with α-MSH IgG in both groups studied, but negatively with α-MSH peptide only in controls. Significant correlations between the abundance of specific bacterial taxa in the gut microbiota and α-MSH peptide and IgG levels were found in both study groups, but they were more frequent in controls. CONCLUSION/DISCUSSION: We conclude that IgG in the blood plays a role as an α-MSH binding protein, whose characteristics are associated with BMI in both patients with AN and controls. Furthermore, the study suggests that low production of α-MSH-reactive IgG during the starvation phase in patients with AN may be related to altered gut microbiota composition.

Functional role of immunoglobulin G as an oxytocin-carrier protein.

It has been long-time known that oxytocin in plasma is bound to a carrier protein, a common feature of circulating peptide hormones, however, the nature of such protein was uncertain. A recent study revealed that about 60% of oxytocin present in plasma is bound to immunoglobulin G (IgG) and that oxytocin-binding IgG plays a role of a functional oxytocin carrier protein. Here, we review the historical background and methodology leading to this discovery. Moreover, we review the data showing the functional role of oxytocin-binding IgG in the modulation of oxytocin signaling relevant to the regulation of motivated behavior and several neuropsychiatric disorders. Furthermore, the possible role of gut microbiota in the origin of such IgG is discussed and the relevant new therapeutic strategies for the enhancement of oxytocin signaling are presented.

Immunoglobulin G is a natural oxytocin carrier which modulates oxytocin receptor signaling: relevance to aggressive behavior in humans.

Oxytocin is a neuropeptide produced mainly in the hypothalamus and secreted in the CNS and blood. In the brain, it plays a major role in promoting social interactions. Here we show that in human plasma about 60% of oxytocin is naturally bound to IgG which modulates oxytocin receptor signaling. Further, we found that IgG of violent aggressive inmates were characterized by lower affinity for oxytocin, causing decreased oxytocin carrier capacity and reduced receptor activation as compared to men from the general population. Moreover, peripheral administration of oxytocin together with human oxytocin-reactive IgG to resident mice in a resident-intruder test, reduced c-fos activation in several brain regions involved in the regulation of aggressive/defensive behavior correlating with the attack number and duration. We conclude that IgG is a natural oxytocin carrier protein modulating oxytocin receptor signaling which can be relevant to the biological mechanisms of aggressive behavior.

Protein Extract of a Probiotic Strain of Hafnia alvei and Bacterial ClpB Protein Improve Glucose Tolerance in Mice.

A commercial strain of Hafnia alvei (H. alvei) 4597 bacteria was shown to reduce food intake and promote weight loss, effects possibly induced by the bacterial protein ClpB, an antigen-mimetic of the anorexigenic α-melanocyte-stimulating hormone. A decrease in the basal plasma glucose levels was also observed in overweight fasted humans and mice receiving H. alvei. However, it is not known whether H. alvei influences sweet taste preference and whether its protein extract or ClpB are sufficient to increase glucose tolerance; these are the objectives tested in the present study. C57BL/6J male mice were kept under standard diet and were gavaged daily for 17 days with a suspension of H. alvei (4.5 × 107 CFU/animal) or with H. alvei total protein extract (5 µg/animal) or saline as a control. Sweet taste preference was analyzed via a brief-access licking test with sucrose solution. Glucose tolerance tests (GTT) were performed after the intraperitoneal (IP) or intragastric (IG) glucose administration at the 9th and 15th days of gavage, respectively. The expression of regulatory peptides' mRNA levels was assayed in the hypothalamus. In another experiment performed in non-treated C57BL/6J male mice, effects of acute IP administration of recombinant ClpB protein on glucose tolerance were studied by both IP- and IG-GTT. Mice treated with the H. alvei protein extract showed an improved glucose tolerance in IP-GTT but not in IG-GTT. Both groups treated with H. alvei bacteria or protein extract showed a reduction of pancreatic tissue weight but without significant changes to basal plasma insulin. No significant effects of H. alvei bacteria or its total protein extract administration were observed on the sweet taste preference, insulin tolerance and expression of regulatory peptides' mRNA in the hypothalamus. Acute administration of ClpB in non-treated mice increased glucose tolerance during the IP-GTT but not the IG-GTT, and reduced basal plasma glucose levels. We conclude that both the H. alvei protein extract introduced orally and the ClpB protein administered via IP improve glucose tolerance probably by acting at the glucose postabsorptive level. Moreover, H. alvei probiotic does not seem to influence the sweet taste preference. These results justify future testing of both the H. alvei protein extract and ClpB protein in animal models of diabetes.

Lactobacillus salivarius and Lactobacillus gasseri supplementation reduces stress-induced sugar craving in mice.

OBJECTIVE: Increased intake of sweets or sugar craving may occur in response to chronic stress representing a risk factor for development of eating disorders and obesity. However, no safe treatment of stress-induced sugar craving is available. In this study we analysed effects of two Lactobacillus strains on food and sucrose intake in mice before and during their exposure to a chronic mild stress (CMS). RESEARCH METHODS & PROCEDURES: C57Bl6 mice were gavaged daily for 27 days with a mix of L. salivarius (LS) LS7892 and L. gasseri (LG) LG6410 strains or with 0.9% NaCl as a control. Following 10 days of gavage, mice were individually placed into the Modular Phenotypic cages, and after 7 days of acclimation were exposed to a CMS model for 10 days. Food, water and 2% sucrose intakes as well as meal pattern were monitored. Anxiety and depressive-like behaviour were analysed by standard tests. RESULTS: Exposure of mice to CMS was accompanied by increased size of sucrose intake in the control group likely reflecting the stress-induced sugar craving. A consistent, about 20% lower total sucrose intake, was observed in the Lactobacilli-treated group during stress which was mainly due to a reduced number of intakes. Lactobacilli treatment also modified the meal pattern before and during the CMS, showing a decrease of meal number and an increase of meal size with a tendency of reduced total daily food intake. Mild anti-depressive behavioural effects of the Lactobacilli mix were also present. CONCLUSION: Supplementation of mice with LS LS7892 and LG LG6410 decreases sugar consumption suggesting a potential utility of these strains against stress-induced sugar craving.

Blood Levels of Neuropeptide 26RFa in Relation to Anxiety and Aggressive Behavior in Humans-An Exploratory Study.

26RFa, also referred to as QRFP, is a hypothalamic neuropeptide mainly known for its role in the regulation of appetite and glucose metabolism. Its possible relevance to emotional regulation is largely unexplored. To address this, in the present exploratory study, we analyzed the plasma concentrations of 26RFa in humans characterized by different levels of anxiety and aggressive behavior. For this purpose, the study included 13 prison inmates who have committed violent crimes and 19 age-matched healthy men from the general population as controls. Anxiety, depression and aggressive behavior were evaluated in both groups using standard questionnaires. The inmate group was characterized by increased aggression and anxiety compared to the controls. We found that the mean plasma levels of 26RFa did not significantly differ between the inmates and the controls. However, several high outliers were present only in the inmate group. The plasma levels of 26RFa correlated positively with the anxiety scores in all the studied subjects and controls. After removing the high outliers in the inmate group, positive correlations of 26RFa with anxiety and a subscale of hostility in the aggression scale were also recorded in this group. No significant correlations of 26RFa with depression scores or other parameters of aggressive behavior were found. Thus, the present results did not support an involvement of 26RFa in aggressive behavior in humans but pointed to a link between this neuropeptide and anxiety. Nevertheless, considering the exploratory nature of the present study, this conclusion should be verified in a larger cohort, including the clinical degree of anxiety.

Plasma enterobacterial ClpB levels and ClpB- and α-MSH-reactive immunoglobulins in lung cancer patients with and without anorexia.

OBJECTIVES: Anorexia represents a common and debilitating clinical problem in patients with several forms of cancer, in particular lung cancer, but its mechanisms are not completely understood. Recently, the caseinolytic-protease-B (ClpB) homologue protein, produced by common gut bacteria, such as Escherichia coli, was identified as an antigen-mimetic of α-melanocyte-stimulating hormone (α-MSH), an anorexigenic neuropeptide. ClpB was previously detected in human plasma and displayed satietogenic properties; however, its possible relevance to cancer anorexia has not yet been investigated. METHODS: To address this question, we analyzed plasma ClpB concentrations as well as levels and affinities of anti-ClpB and α-MSH-reactive antibodies in patients with lung cancer with and without anorexia as compared with body mass index-matched healthy controls with normal appetite. RESULTS: We found that plasma ClpB concentrations were significantly lower in non-anorexic patients with cancer than those of the control group (P = 0.028). In contrast, patients with cancer and anorexia had lower levels of anti-ClpB immunoglobulins (Ig)M (P < 0.0001) and of both α-MSH IgM and IgG (P < 0.05) with respect to controls. Moreover, in patients with cancer and anorexia, anti-ClpB IgG showed a trend of lower affinities compared with non-anorexic patients (P = 0.05). CONCLUSIONS: Taken together, the results revealed a reduced humoral immune response to ClpB in patients with cancer and anorexia, which may lead to an enhanced satietogenic effect of this enterobacterial protein contributing to the mechanisms of reduced appetite.