The chronic ingestion of diets containing different proteins produces marked variations in brain tryptophan levels and serotonin synthesis in the rat. Neurochem Res. 2011;36:559-565. [PMID: 21207140 DOI: 10.1007/s11064-010-0382-1]

The anorexic effect of DL-fenfluramine is dependent on animals' habituation to different food types

Background

As rates of obesity and diabetes have increased dramatically over the past few decades, the use of anti-obesity drugs has now become a routine therapeutic measure. However, the pharmacological effects of chronic use of these drugs in humans frequently lead to reduced efficacy in reducing appetite and body weight through as-yet-unidentified mechanisms. An example of this can be found in animal studies where the appetite suppressant DL-fenfluramine (FEN) is chronically administered and its tolerance develops in animals and humans. The appetite effects of FEN are typically measured in several animal studies by the feeding changes in a balanced standard diet. To determine whether FEN differentially altered appetite suppression in animals with long-term expression with different macronutrient diet compositions, its anorexic effects were measured specifically in male rats that had previously been chronically maintained on normal chow (NC) or a high-fat and high-carbohydrate western diet (WD).

Methods

Three experiments were conducted by feeding the animals either NC or WD for 1 month to habituate them with their diet. Animals maintained on either NC or WD were subsequently offered both diet options ad libitum for a 2- or 7-day adaptation period while receiving daily systemic FEN treatment.

Results

The results suggested that long-term habituated food affected the food preference of animals and their appetite even after chronic systemic FEN administration. Therefore, the effectiveness and success or failure of repeated use of chronic anti-obesity drugs may depend on habituated food type.

Conclusion

The appetite suppressant effect was found to be determined by the palatability of a specific macronutrient and the habituated food rather than by a change in the concentration of the administered FEN. This results in a critical analysis of the rationale for taking medication considering the patient's past dietary habits to achieve successful weight loss.

Duodenal infusion of soy protein hydrolysate activates cAMP signaling and hypothalamic neurotransmitter synthesis in pigs

An increased soy protein hydrolysate (SPH) level promoted hypothalamic acetylcholine, dopamine, and brain-derived neurotrophic factor (BDNF) synthesis.

Fecal incontinence as a moderator between dietary intake and depressive symptoms among a sample of older adults obtained from the National Health and Nutrition Examination Survey (NHANES)

OBJECTIVES

Many studies have established a relationship between diet and mental health, as well as the importance of bowel health. Further, with increased evidence of a gut-brain bidirectional relationship, an indication of dysbiosis as a potential moderator between diet and depression may be a viable target for future interventions. The current study investigated the relationship between diet and depressive symptoms (DS) among older adults, as well as gender, and whether a symptom of dysbiosis, fecal incontinence severity (FIS), moderated this relationship.

METHOD

Using moderated regressions, we examined whether FIS moderates the relationship between diet and DS while controlling for covariates in the overall sample (N = 1918), as well as among the male (n = 841) and female sample (n = 1077). The dietary variables were reduced using a factor analysis.

RESULTS

Results indicated significant moderating effects of FIS between Component 4 and polyunsaturated fatty acids (PFA) in the overall sample. Component 4, protein, carbohydrates, and alcohol were significant in males only while PFA only in females. Further analysis of protein/carbohydrate ratio groups indicated significant differences within males. Higher scores of FIS were related to higher DS and less consumption of Component 4 nutrients, PFA, and protein. Males that consumed higher protein and carbohydrates resulted in lower DS with increased FIS.

CONCLUSION

Outcomes from the current study provide further evidence of the importance of healthy bowel function and the potential of modifying the diet to improve DS in older adults.

Biscuits with No Added Sugar Containing Stevia, Coffee Fibre and Fructooligosaccharides Modifies α-Glucosidase Activity and the Release of GLP-1 from HuTu-80 Cells and Serotonin from Caco-2 Cells after In Vitro Digestion

This study assessed the in vitro effects of the bioaccessible food components released during the simulated human digestion of a coffee fibre-containing biscuit (CFB) on α-glucosidase activity, antioxidant capacity and satiety hormones. Digest of CFB presented a significantly (p < 0.05) lower amount of sugar (68.6 mg/g) and a higher antioxidant capacity (15.1 mg chlorogenic acid eq./g) than that of a sucrose-containing biscuit (SCB). The CFB significantly reduced (p < 0.05) α-glucosidase activity (IC50 = 3.3 mg/mL) compared to the SCB (IC50 = 6.2 mg/mL). Serotonin and glucagon-like peptide-1 (GLP-1) release by differentiated Caco-2 and HuTu-80 cells, respectively, was stimulated by the CFB (355% at a concentration of 0.5 mg/mL and 278% at a concentration of 0.05 mg/mL) to the same order of magnitude as those of the SCB. To summarize, the CFB was demonstrated to reduce monosaccharide bioaccessibility, to inhibit a diabetes-related digestive enzyme, and to improve the release of satiety hormones.

Dietary protein ingested before and during short photoperiods makes an impact on affect-related behaviours and plasma composition of amino acids in mice

In mammals, short photoperiod is associated with high depression- and anxiety-like behaviours with low levels of the brain serotonin and its precursor tryptophan (Trp). Because the brain Trp levels are regulated by its ratio to large neutral amino acids (Trp:LNAA) in circulation, this study elucidated whether diets of various protein sources that contain different Trp:LNAA affect depression- and anxiety-like behaviours in C57BL/6J mice under short-day conditions (SD). In the control mice on a casein diet, time spent in the central area in the open field test (OFT) was lower in the mice under SD than in those under long-day conditions (LD), indicating that SD exposure induces anxiety-like behaviour. The SD-induced anxiety-like behaviour was countered by an α-lactalbumin diet given under SD. In the mice that were on a gluten diet before transition to SD, the time spent in the central area in the OFT under SD was higher than that in the SD control mice. Alternatively, mice that ingested soya protein before the transition to SD had lower immobility in the forced swim test, a depression-like behaviour, compared with the SD control. Analysis of Trp:LNAA revealed lower Trp:LNAA in the SD control compared with the LD control, which was counteracted by an α-lactalbumin diet under SD. Furthermore, mice on gluten or soya protein diets before transition to SD exhibited high Trp:LNAA levels in plasma under SD. In conclusion, ingestion of specific proteins at different times relative to photoperiodic transition may modulate anxiety- and/or depression-like behaviours, partially through changes in plasma Trp:LNAA.

Simplified dietary acute tryptophan depletion: effects of a novel amino acid mixture on the neurochemistry of C57BL/6J mice

BACKGROUND

Diet and nutrition can impact on the biological processes underpinning neuropsychiatric disorders. Amino acid (AA) mixtures lacking a specific neurotransmitter precursor can change the levels of brain serotonin (5-HT) or dopamine (DA) in the central nervous system. The availability of these substances within the brain is determined by the blood-brain barrier (BBB) that restricts the access of peripheral AA into the brain. AA mixtures lacking tryptophan (TRP) compete with endogenous TRP for uptake into the brain across the BBB, which in turn leads to a decrease in central nervous 5-HT synthesis.

OBJECTIVE

The present study compared the effects of a simplified acute tryptophan depletion (SATD) mixture in mice on blood and brain serotonergic and dopaminergic metabolites to those of a commonly used acute tryptophan depletion mixture (ATD Moja-De) and its TRP-balanced control (BAL).

DESIGN

The SATD formula is composed of only three large neutral AAs: phenylalanine (PHE), leucine (LEU), and isoleucine (ILE). BAL, ATD Moja-De, or SATD formulas were delivered to adult male C57BL/6J mice by gavage. TRP, monoamines, and their metabolites were quantified in blood and brain regions (hippocampus, frontal cortex, amygdala, caudate putamen, and nucleus accumbens).

RESULTS

Both ATD Moja-De and SATD significantly decreased levels of serum and brain TRP, as well as brain 5-HIAA and 5-HT compared with BAL. SATD reduced HVA levels in caudate but did not alter total DA levels or DOPAC. SATD decreased TRP and serotonergic metabolites comparably to ATD Moja-De administration.

CONCLUSION

A simplified and more palatable combination of AAs can manipulate serotonergic function and might be useful to reveal underlying monoamine-related mechanisms contributing to different neuropsychiatric disorders.

Food allergy in irritable bowel syndrome: The case of non-celiac wheat sensitivity

Irritable bowel syndrome (IBS) is one of the most common gastrointestinal disorders, having a prevalence of 12%-30% in the general population. Most patients with IBS attribute their symptoms to adverse food reactions. We review the role of diet in the pathogenesis of IBS and the importance of dietary factors in the management of these patients. The MEDLINE electronic database (1966 to Jan 2015) was searched using the following keywords: "food", "diet", "food allergy", "food hypersensitivity", "food intolerance", "IBS", "epidemiology", "pathogenesis", "pathophysiology", "diagnosis", "treatment". We found 153 eligible papers; 80 were excluded because: not written in English, exclusive biochemical and experimental research, case reports, reviews, and research otherwise not relevant to our specific interest. We selected 73 papers: 43 original papers, 26 reviews and 4 letters to the editor. These papers focused on IBS pathogenesis, the association between IBS and atopy, and between IBS and food allergy, the relationship between IBS and non-celiac wheat sensitivity, the role of diet in IBS. Pending further scientific evidence, a cautious approach is advisable but the concept of food allergy should be included as a possible cause of IBS, and a dietary approach may have a place in the routine clinical management of IBS.

Importance of serotonin (5-HT) and its precursor l-tryptophan for homeostasis and function of skeletal muscle in rats. A morphological and endocrinological study

Serotonin (5-HT) is a neurotransmitter, synthesized in serotonergic neurons of the central nervous system and in enterochromaffin cells of the gastrointestinal tract, which is involved in the regulation of several body functions, including muscle tissue development and growth and its contractile response. l-Tryptophan (l-Trp) is an essential amino acid and precursor of 5-HT. The aim of the present study was to better understand the mechanisms that govern neuroendocrine homeostasis of muscle tissue and emphasize the importance of a diet, complete in all its elements, referring specifically to the essential amino acids such as l-Trp, crucial in several neuroendocrine functions.We analyzed the possible consequences of l-Trp-free diet on 5-HT production and on skeletal muscle morphology and function in young female rats. We also evaluated the eventual alterations of hormone production such as growth hormone (GH), thyroid stimulating hormone (TSH) and thyroid hormones (T3 and T4) that control and regulate growth, metabolism and efficiency of the skeletal muscle. Our results showed a strong decrease of 5-HT, GH, TSH, T3 and T4 levels associated to a clear difference in body weight between experimental and control rats. Moreover, the muscle samples of experimental rats showed histological and ultrastructural alterations. These findings thus supported a strong link between l-Trp, serotonergic system, hormone secretion and morphology of skeletal muscle tissue and thus, the importance of a balanced daily diet.

Non-celiac gluten sensitivity: literature review

BACKGROUND

A significant percentage of the general population report problems caused by wheat and/or gluten ingestion, even though they do not have celiac disease (CD) or wheat allergy (WA), because they test negative both for CD-specific serology and histopathology and for immunoglobulin E (IgE)-mediated assays. Most patients report both gastrointestinal and nongastrointestinal symptoms, and all report improvement of symptoms on a gluten-free diet. This clinical condition has been named non-celiac gluten sensitivity (NCGS).

AIM

We attempt to define the current pathogenic, clinical, and diagnostic criteria of this "new" disease, to provide a practical view that might be useful to evaluate, diagnose, and manage NCGS patients.

METHODS

We reviewed the international literature through PubMed and Medline, using the search terms "wheat (hyper)sensitivity," "wheat allergy," "wheat intolerance," "gluten (hyper)sensitivity," and "gluten intolerance," and we discuss current knowledge about NCGS.

RESULTS

It has been demonstrated that patients suffering from NCGS are a heterogeneous group, composed of several subgroups, each characterized by different pathogenesis, clinical history, and, probably, clinical course. NCGS diagnosis can be reached only by excluding CD and WA. Recent evidence shows that a personal history of food allergy in infancy, coexistent atopy, positive for immunoglobulin G (IgG) antigliadin antibodies and flow cytometric basophil activation test, with wheat and duodenal and/or ileum-colon intraepithelial and lamina propria eosinophil counts, could be useful to identify NCGS patients.

CONCLUSIONS

Future research should aim to identify reliable biomarkers for NCGS diagnosis and to better define the different NCGS subgroups. Key teaching points: • Most patients report both gastrointestinal and nongastrointestinal symptoms, and all agree that there is an improvement of symptoms on a gluten-free diet. • NCGS diagnosis can be reached only by excluding celiac disease and wheat allergy. • Patients suffering from NCGS are a heterogeneous group, composed of several subgroups, each characterized by different pathogenesis, clinical history, and, probably, clinical course. • A personal history of food allergy in infancy, coexistent atopy, positive IgG antigliadin antibodies (AGA) and flow cytometric basophil activation test, with wheat and duodenal and/or ileum-colon intraepithelial and lamina propria eosinophil counts, could be useful to identify NCGS patients. • Future research should aim to identify reliable biomarkers for NCGS diagnosis and to better define the different NCGS subgroup.

Parkinson's disease: no milk today?

Several prospective epidemiological studies on large cohorts have consistently reported an association between milk intake and a higher incidence of Parkinson’s disease (PD). Pesticide contamination of milk and milk’s urate-lowering effects have been put forward as risk factors to explain epidemiological data. This has led to considerable uncertainty among physicians and avoidance of dairy products by PD patients. However, neither factor stands up to the rational and detailed examination of the literature carried out in this mini-review. We suggest that changes in eating behavior related to pre-motor PD are an alternative potential explanation of correlations observed between milk intake and PD occurrence. Despite clear-cut associations between milk intake and PD incidence, there is no rational explanation for milk being a risk factor for PD. Based on current knowledge, limiting the consumption of dairy products does not seem to be a reasonable strategy in the prevention of the development and progression of PD.

Serotonin (5HT) expression in rat pups treated with high-tryptophan diet during fetal and early postnatal development

Serotonin (5HT) is a neurotransmitter synthesized in serotonergic neurons of the central nervous system and in the enterochromaffin cells of the gastrointestinal tract. 5HT regulates growth and maturation of some cerebral regions in the developing brain as well as the secretion of pituitary growth hormone. This hormone is necessary for development and growth through the stimulation of insulin-like growth factor synthesis. The precursor of 5HT, tryptophan (Trp), is an essential amino acid, since the human organism is unable to synthesize it and it is assumed only through diet. The aim of our study was to analyze how a high-tryptophan diet in pregnant rats affects growth and survival of pups until weaning. We monitored the number and weight of pups until weaning. Then, we detected serotonin and growth hormone levels in whole blood by ELISA of surviving pups at the end of the lactation period. We also analyzed by means of immunohistochemistry and Western blot the expression of serotonin in rat gastric tissue and the morphological structure of skeletal muscle tissue of both control and experimental pups. Hyperserotonemia and very low levels of growth hormone were detected in experimental pups compared to controls. Immunohistochemistry demonstrated a strong serotonin expression in stomach samples confirming that a high intake of tryptophan increases the production of serotonin in enterochromaffin cells, thereby resulting in hyperserotonemia in pups. These data were also strengthened by Western blot analysis. Histological alterations of skeletal muscle fibers in experimental pups were found and showed that in experimental samples the muscle tissue demonstrated deleterious alterations, being less developed and defined. Our data suggest that a high-tryptophan diet in pregnant rats induces hyperserotonemia in the fetus. Hyperserotonemia results in an excess of serotonin in the brain where it has a negative influence on development of serotonergic neurons and consequently on growth hormone production.

Effects of high-tryptophan diet on pre- and postnatal development in rats: a morphological study

PURPOSE

Tryptophan is an essential amino acid, precursor of serotonin. Serotonin (5HT) regulates the secretion of pituitary growth hormone (GH), which in turn stimulates the liver to produce insulin-like growth factor-I (IGF-I) that is necessary for development and growth. The aim of our study was to investigate the effects of an excess of tryptophan in the diet of pregnant rats on the differentiation of skeletal muscle tissue.

METHODS

We conducted an immunohistochemical study on the IGF-I expression in hepatic and muscle tissues in offspring, and then, we associated this molecular data with morphological effects on the structure of the muscle fibers and hepatic tissue at different postnatal weeks, from birth to sexual maturity. Measurements of 5HT, GH in blood, and of tryptophan hydroxylase (Tph) activity in gastrointestinal tracts tissue were also taken.

RESULTS

Hyperserotonemia and higher values of Tph activity were detected in both pregnant rats and pups. Very low levels of GH were detected in experimental pups. Morphological alterations of the muscle fibers and lower IGF-I expression in hepatic and muscle tissue in pups were found.

CONCLUSIONS

Our data suggest that an excess of tryptophan in the diet causes hyperserotonemia in fetus. Hyperserotonemia results in an excess of serotonin in the brain where it has an adverse effect on the development of serotonergic neurons. The affected neurons do not regulate optimally the secretion of pituitary GH that consequently decreases. This limits stimulation in the liver to produce IGF-I, crucial for development and growth of pups.

Brain responses to high-protein diets

Proteins are suspected to have a greater satiating effect than the other 2 macronutrients. After protein consumption, peptide hormones released from the gastrointestinal tract (mainly anorexigenic gut peptides such as cholecystokinin, glucagon peptide 1, and peptide YY) communicate information about the energy status to the brain. These hormones and vagal afferents control food intake by acting on brain regions involved in energy homeostasis such as the brainstem and the hypothalamus. In fact, a high-protein diet leads to greater activation than a normal-protein diet in the nucleus tractus solitarius and in the arcuate nucleus. More specifically, neural mechanisms triggered particularly by leucine consumption involve 2 cellular energy sensors: the mammalian target of rapamycin and AMP-activated protein kinase. In addition, reward and motivation aspects of eating behavior, controlled mainly by neurons present in limbic regions, play an important role in the reduced hedonic response of a high-protein diet. This review examines how metabolic signals emanating from the gastrointestinal tract after protein ingestion target the brain to control feeding, energy expenditure, and hormones. Understanding the functional roles of brain areas involved in the satiating effect of proteins and their interactions will demonstrate how homeostasis and reward are integrated with the signals from peripheral organs after protein consumption.