Serotonin and Melatonin in Human Lower Gastrointestinal Tract

TNBS colitis induces architectural changes and alpha-synuclein overexpression in mouse distal colon: A morphological study

Alpha-synuclein (α-syn) is widely expressed in presynaptic neuron terminals, and its structural alterations play an important role in the pathogenesis of Parkinson's disease (PD). Aggregated α-syn has been found in brain, in the peripheral nerves of the enteric nervous system (ENS) and in the intestinal neuroendocrine cells during synucleinopathies and inflammatory bowel disorders. In the present study, we evaluated the histomorphological features of murine colon with 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis, a common model of colitis. Thereafter, we investigated the expression of α-syn, Toll-like receptor 4 (TLR4), choline acetyltransferase (ChAT), vasoactive intestinal peptide (VIP), tyrosine hydroxylase (TH), calcitonin gene-related peptide (CGRP), and calcitonin-like receptor (CALCR). Finally, we investigated the presence of phosphorylated α-syn (pS129 α-syn) aggregates and their relationship with inflammatory cells. Colon from TNBS mice showed an increase in inflammatory cells infiltrate and significative changes in the architecture of the intestinal mucosa. α-Syn expression was significantly higher in inflamed colon. VIP was increased in both the mucosa and muscularis externa of TNBS mice, while TH, CGRP, and CALCR were significantly reduced in TNBS mice. Amyloid aggregates of pS129 α-syn were detectable in the ENS, as in the macrophages around the glands of the mucosa correlating with the markers of inflammation. This study describes - for the first time - the altered expression of α-syn and the occurrence of amyloid α-syn aggregates in the inflammatory cells under colitis, supporting the critical role of bowel inflammation in synucleinopathies and the involvement of α-syn in IBD.

Colon delivery of agomelatine nanoparticles in the treatment of TNBS induced ulcerative colitis

Agomelatine is an atypical antidepressant with a long half-life and the mechanism of action similar to melatonin. Agomelatine is a strong antioxidant and its anti-inflammatory effect has been reported in many studies. The current study aimed to evaluate the anti-inflammatory effect of agomelatine loaded in targeted nanoparticles (NPs) in an experimental colitis model induced by trinitrobenzene sulfonic acid (TNBS). Poly(1-vinylpyrrolidone)-graft-(1-triacontene) (PVP-TA) and Eudragit®-FS30D polymers were used alone and in combination as time, pH and time/pH dependent formulations respectively. The optimal formula was selected according to their physicochemical properties such as particle size, morphology, and drug release pattern. Six separate groups of rats were induced with 0.5 ml of TNBS. The designed groups were: normal, untreated, agomelatine (25 mg/kg/d), agomelatine/ Eudragit®-FS30D NPs, agomelatine/ Eudragit-FS30D/PVP-TA NPs, and dexamethasone (Dex., 1 mg/kg/d). Twenty-four hours after the last administration, colonic tissue was analyzed for macroscopic and histopathological evaluations, along with quantification of malondialdehyde (MDA) and myeloperoxidase (MPO) levels. The results showed that the PVP-TA NPs alone was not suitable regarding to release profile and particle size distribution. However, Eudragit-FS30D NPs alone and Eudragit-FS30D + PVP-TA NPs passed physicochemical evaluations and were both effective in reducing the symptoms and indices of experimental colitis. Taken together, targeted NPs of agomelatine are potentially effective in treatment of ulcerative colitis.

Microbial melatonin metabolism in the human intestine as a therapeutic target for dysbiosis and rhythm disorders

Melatonin (MT) (N-acetyl-5-methoxytryptamine) is an indoleamine recognized primarily for its crucial role in regulating sleep through circadian rhythm modulation in humans and animals. Beyond its association with the pineal gland, it is synthesized in various tissues, functioning as a hormone, tissue factor, autocoid, paracoid, and antioxidant, impacting multiple organ systems, including the gut-brain axis. However, the mechanisms of extra-pineal MT production and its role in microbiota-host interactions remain less understood. This review provides a comprehensive overview of MT, including its production, actions sites, metabolic pathways, and implications for human health. The gastrointestinal tract is highlighted as an additional source of MT, with an examination of its effects on the intestinal microbiota. This review explores whether the microbiota contributes to MT in the intestine, its relationship to food intake, and the implications for human health. Due to its impacts on the intestinal microbiota, MT may be a valuable therapeutic agent for various dysbiosis-associated conditions. Moreover, due to its influence on intestinal MT levels, the microbiota may be a possible therapeutic target for treating health disorders related to circadian rhythm dysregulation.

Nutritional and Microbial Strategies for Treating Acne, Alopecia, and Atopic Dermatitis

BACKGROUND/OBJECTIVES

Diet is one of the major determinants of the composition and function of the gut microbiome, and diverse studies have established directional connections between gut microbiome dysbiosis and skin dyshomeostasis. Furthermore, a significant link between the gut and certain skin-related disorders has been reported. This work reviews the mechanisms underlying the relationship between nutritional factors, gut microbiome, and certain skin diseases such as acne vulgaris, alopecia, and atopic dermatitis. In addition, it explores how the modulation of the gut microbiome and human skin through diet and various microbial strategies, including probiotics, synbiotics, postbiotics, and fecal microbiota transplantation, may serve as future treatments for skin diseases, possibly replacing traditional methods such as antibiotic, topical corticosteroid, and laser therapies.

RESULTS

The adequate intake of certain foods can promote a balanced gut microbiome, potentially reducing skin inflammation and improving overall skin health, while poor dietary choices may lead to worse outcomes by disrupting gut homeostasis. In this regard, diets high in antioxidants, fiber, and phytonutrients appear to be beneficial for enhancing skin health and preventing associated comorbidities. In addition, the administration of probiotics, synbiotics, and postbiotics in the treatment of cutaneous diseases has been shown to restore skin dyshomeostasis and to improve the symptoms of the reviewed skin conditions.

CONCLUSIONS

Consuming a healthy, plant-based diet can reduce skin inflammation and enhance overall skin health. Although the application of probiotics, synbiotics, and postbiotics has demonstrated promise in modulating inflammation, enhancing tissue regeneration, and inhibiting pathogenic colonization, further research is required.

Variety of Serotonin Levels in Pediatric Gastrointestinal Disorders

(1) Serotonin primarily regulates our emotions. A complex process, which includes dysfunctions in gastrointestinal motility and deregulation of the gene responsible for serotonin reuptake (SERT), is implicated in the pathophysiology of irritable bowel syndrome (IBS). This also encompasses changes in intestinal microbiota, the response to stress, the intricate interplay between the brain and the digestive tract, heightened sensitivity to visceral stimuli, and low-grade inflammation. This paper aims to investigate the effectiveness of probiotic therapy in managing gastrointestinal and neuropsychiatric symptoms related to serotonin levels, with a focus on individuals with serotonin deficiency and those with normal serotonin levels experiencing gastrointestinal disorders. (2) The study involved 135 pediatric patients aged 5-18 years with gastrointestinal disturbances, including constipation, diarrhea, and other symptoms, such as nausea, flatulence, feeling full, or gastrointestinal pain. (3) Serotonin testing was performed, and administering probiotics appeared to be effective in addressing serotonin deficiency and other gastrointestinal disorders. (4) Serotonin's pivotal role in regulating neurotransmitter secretion and its impact on neuropsychiatric health, coupled with gender differences and age-related declines, underscore the complexity of their influence on gastrointestinal and neuropsychiatric conditions.

Circadian rhythms in colonic function

A rhythmic expression of clock genes occurs within the cells of multiple organs and tissues throughout the body, termed "peripheral clocks." Peripheral clocks are subject to entrainment by a multitude of factors, many of which are directly or indirectly controlled by the light-entrainable clock located in the suprachiasmatic nucleus of the hypothalamus. Peripheral clocks occur in the gastrointestinal tract, notably the epithelia whose functions include regulation of absorption, permeability, and secretion of hormones; and in the myenteric plexus, which is the intrinsic neural network principally responsible for the coordination of muscular activity in the gut. This review focuses on the physiological circadian variation of major colonic functions and their entraining mechanisms, including colonic motility, absorption, hormone secretion, permeability, and pain signalling. Pathophysiological states such as irritable bowel syndrome and ulcerative colitis and their interactions with circadian rhythmicity are also described. Finally, the classic circadian hormone melatonin is discussed, which is expressed in the gut in greater quantities than the pineal gland, and whose exogenous use has been of therapeutic interest in treating colonic pathophysiological states, including those exacerbated by chronic circadian disruption.