Long-term oral melatonin administration reduces ethanol-induced increases in duodenal mucosal permeability and motility in rats

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.

Melatonin mitigates chemotherapy-induced small intestinal atrophy in rats and reduces cytotoxicity in murine intestinal organoids

Cancer continues to pose a significant global health challenge, with gastrointestinal (GI) cancers among the most prevalent and deadly forms. These cancers often lead to high mortality rates and demand the use of potent cytotoxic chemotherapeutics. For example, 5-fluorouracil (5-FU) forms the backbone of chemotherapy regimens for various GI cancers, including colorectal cancer. While these chemotherapeutics efficiently kill cancer cells, they frequently cause off-target effects such as chemotherapy-induced mucositis (CIM), characterized by debilitating symptoms like pain, nausea, and diarrhoea, necessitating medical intervention. In this study, we elucidated the potential of melatonin and misoprostol to reduce 5-FU-induced small intestinal mucositis. Morphological and cellular changes in the jejunum, along with colonic faecal water content were quantified in rats as markers for CIM. Additionally, the effects of melatonin were investigated in vitro on 5-FU treated murine intestinal organoids. The results showed that melatonin prevented villus atrophy in the rat jejunal mucosa and upheld cell viability in murine intestinal organoids. In contrast, misoprostol alone or in combination with melatonin did not significantly affect CIM caused by 5-FU. These in vivo and in vitro experiments provided promising insights that melatonin may be used as a preventive and/or adjuvant combination therapy to prevent and reduce CIM, holding the potential to enhance cancer treatment outcomes and improve patient quality-of-life.

Therapeutic applications of melatonin in disorders related to the gastrointestinal tract and control of appetite

Most animals have large amounts of the special substance melatonin, which is controlled by the light/dark cycle in the suprachiasmatic nucleus. According to what is now understood, the gastrointestinal tract (GIT) and other areas of the body are sites of melatonin production. According to recent studies, the GIT and adjacent organs depend critically on a massive amount of melatonin. Not unexpectedly, melatonin's many biological properties, such as its antioxidant, anti-inflammatory, pro-apoptotic, anti-proliferative, anti-metastasis, and antiangiogenic properties, have drawn the attention of researchers more and more. Because melatonin is an antioxidant, it produces a lot of secretions in the GIT's mucus and saliva, which shields cells from damage and promotes the development of certain GIT-related disorders. Melatonin's ability to alter cellular behavior in the GIT and other associated organs, such as the liver and pancreas, is another way that it functions. This behavior alters the secretory and metabolic activities of these cells. In this review, we attempted to shed fresh light on the many roles that melatonin plays in the various regions of the gastrointestinal tract by focusing on its activities for the first time.

Endoplasmic reticulum stress in the pathogenesis of chemotherapy-induced mucositis: Physiological mechanisms and therapeutic implications

Chemotherapy is a common and effective treatment for cancer, but these drugs are also associated with significant side effects affecting patients' well-being. One such debilitating side effect is mucositis, characterized by inflammation, ulcerations, and altered physiological functions of the gastrointestinal (GI) tract's mucosal lining. Understanding the mechanisms of chemotherapy-induced intestinal mucositis (CIM) is crucial for developing effective preventive measures and supportive care. Chemotherapeutics not only target cancer cells but also rapidly dividing cells in the GI tract. These drugs disrupt endoplasmic reticulum (ER) homeostasis, leading to ER-stress and activation of the unfolded protein response (UPR) in various intestinal epithelial cell types. The UPR triggers signaling pathways that exacerbate tissue inflammation and damage, influence the differentiation and fate of intestinal epithelial cells, and compromise the integrity of the intestinal mucosal barrier. These factors contribute significantly to mucositis development and progression. In this review, we aim to give an in-depth overview of the role of ER-stress in mucositis and its impact on GI function. This will provide valuable insights into the underlying mechanisms and highlighting potential therapeutic interventions that could improve treatment-outcomes and the quality of life of cancer patients.

Intestinal melatonin levels and gut microbiota homeostasis are independent of the pineal gland in pigs

Introduction

Melatonin (MEL) is a crucial neuroendocrine hormone primarily produced by the pineal gland. Pinealectomy (PINX) has been performed on an endogenous MEL deficiency model to investigate the functions of pineal MEL and its relationship with various diseases. However, the effect of PINX on the gastrointestinal tract (GIT) MEL levels and gut microbiome in pigs has not been previously reported.

Methods

By using a newly established pig PINX model, we detected the levels of MEL in the GIT by liquid chromatography-tandem mass spectrometry. In addition, we examined the effects of PINX on the expression of MEL synthesis enzymes, intestinal histomorphology, and the intestinal barrier. Furthermore, 16S rRNA sequencing was performed to analyze the colonic microbiome.

Results

PINX reduced serum MEL levels but did not affect GIT MEL levels. Conversely, MEL supplementation increased MEL levels in the GIT and intestinal contents. Neither PINX nor MEL supplementation had any effect on weight gain, organ coefficient, serum biochemical indexes, or MEL synthetase arylalkylamine N-acetyltransferase (AANAT) expression in the duodenum, ileum, and colon. Furthermore, no significant differences were observed in the intestinal morphology or intestinal mucosal barrier function due to the treatments. Additionally, 16S rRNA sequencing revealed that PINX had no significant impact on the composition of the intestinal microbiota. Nevertheless, MEL supplementation decreased the abundance of Fibrobacterota and increased the abundance of Actinobacteriota, Desulfobacterota, and Chloroflexi.

Conclusion

We demonstrated that synthesis of MEL in the GIT is independent of the pineal gland. PINX had no influence on intestinal MEL level and microbiota composition in pigs, while exogenous MEL alters the structure of the gut microbiota.

Oral administration of heat-inactivated Escherichia coli during suckling alleviated Salmonella typhimurium-derived intestinal injury after rat weaning

Introduction

Newly weaned animals are susceptible to a wide range of microbial infections taking a high risk of developing post-weaning diarrhea. Trained immunity is the capacity of the innate immune system to produce a stronger and non-specific response against a secondary infection after the inflammatory response caused by previous stimulus has returned to normal state. The objective of this study was to evaluate if the heat-inactivated Escherichia coli (IEC) as an immunostimulant on suckling pups elicits a protective effect on the intestine of post-weaning rats challenged with Salmonella Typhimurium (S.Typhimurium). We adapted a newborn rat model for this purpose.

Methods

Sixty newborn pups were randomly separated into two groups: IEC group (n =30) orally administrated IEC during suckling, while the CON group received orally the same dose of saline. Both of the two group challenged with various doses of S.Typhimurium after experiencing a 4-week resting period. Twelve of individuals were selected to detect the survival rate, and ten of the rest were necropsied 48 hours post-challenge.

Results and Discussion

The results showed that oral administration of IEC during suckling alleviated the injury in ileal morphology induced by post-weaning S.Typhimurium infection via increasing the levels of two tight junction proteins [zonula occluden-1 (ZO-1) and Occludin-1] and several secreted proteins (Lysozyme, Mucin-2, and SIgA) in the intestinal mucosa. Furthermore, the pre-stimulation with IEC significantly increased cytokines tumor necrosis factor-alpha (TNF- α) and interleukin-1 beta (IL-1 β) expressions in an enhanced secondary reaction way after experiencing a 4-week resting period. This implicated the possible involvement of trained immunity. The 16S rDNA sequence results showed that pre-stimulation with IEC decreased the abundance of Clostridia, Prevotella, Christensenellaceae_R-7_group and Parabacteroides after intestinal infection of S.Typhimurium. Our results confirmed that the previous oral administration of IEC had a protective effect on S.Typhimurium-induced intestinal injury in weaned rats by inducing a robust immune response. The present study suggested a new strategy for preventing intestinal infection of newborn animals.

Melatonin and inflammatory bowel disease: From basic mechanisms to clinical application

Inflammatory bowel disease is a chronic inflammatory disease and has periods of recurrence and remission. Improper immune responses to gut flora bacteria, along with genetic susceptibility, appear to be involved in causing this complex disease. It seems dysbiosis and oxidative stress may also be involved in IBD pathogenesis. A significant number of clinical studies have shown an interesting association between sleep disturbances and IBD. Studies in animal models have also shown that sleep deprivation has a significant effect on the pathogenesis of IBD and can aggravate inflammation. These interesting findings have drawn attention to melatonin, a sleep-related hormone. Melatonin is mainly produced by the pineal gland, but many tissues in the body, including the intestines, can produce it. Melatonin can have an interesting effect on the pathogenesis of IBD. Melatonin can enhance the intestinal mucosal barrier, alter the composition of intestinal bacteria in favor of bacteria with anti-inflammatory properties, regulate the immune response, alleviate inflammation and attenuate oxidative stress. It seems that, melatonin supplementation is effective in relieving inflammation and healing intestinal ulcers in IBD animal models. Some clinical studies have also shown that melatonin supplementation as an adjuvant therapy may be helpful in reducing disease activity in IBD patients. In this review article, in addition to reviewing the effects of sleep disturbances and melatonin on key mechanisms involved in the pathogenesis of IBD, we will review the findings of clinical studies regarding the effects of melatonin supplementation on IBD treatment.

Effects of melatonin on intestinal function and bacterial compositions in sucking piglets

Melatonin has been reported to affect intestinal function by targeting microbiome, morphological structure, barrier integrity and nutrient absorptive system. While the effect of melatonin on intestinal development in newborn infants is obscure, thus, this study firstly attempted to investigate the hypothesis that melatonin treatment improves intestinal development in sucking piglets. 14 healthy newborn piglets received 10 ml melatonin solution (1 mg/ml) or drinking water (n = 7) for 21 days. The results showed that oral administration of melatonin increased liver relative weight (p < 0.05) but failed to affect growth performance in sucking piglets (p > 0.05). Immunostaining jejunal samples from melatonin group showed high expressions of nnos and claudin1, indicating that melatonin improved intestinal neural development and barrier integrity. Also, melatonin promoted intestinal absorptive function evidenced by the increased serum proline concentration in melatonin-treated piglets compared with the control (p < 0.05). Gut microbiota compositions were tested by 16S rDNA sequencing and the results showed that melatonin increased the relative abundance of Actinobacteria compared with the control (p < 0.05) at the phylum level. However, Selenomonadales was markedly reduced compared with the control at the order level (p < 0.05). Gut and faecal volatile fatty acids were tested to evaluate the microbiota metabolism, but no difference was noticed in volatile fatty acid concentrations (p > 0.05). Melatonin improved intestinal development by affecting neural development, barrier integrity, nutrient absorption and microbiota in sucking piglets.

Essential Oils and Melatonin as Functional Ingredients in Dogs

Simple Summary

Phytogenics are plant-based compounds with beneficial actions in feed technology and/or animal health. These so-called plant secondary metabolites are very diverse and with wide possible applications in humans and animals. Among them, essential oils (EOs) are the most used in feed for livestock and pets. Lately, melatonin has acquired new and interesting applications in dogs. Recent studies using EOs and/or melatonin in dog feeding and their involvement in health aspects are presented.

Abstract

The use of nutraceuticals or functional ingredients is increasingly widespread in human food; their use is also widespread in animal feed. These natural compounds generally come from plant materials and comprise a wide range of substances of a very diverse chemical nature. In animals, these compounds, so-called phytogenics, are used to obtain improvements in feed production/stability and also as functional components with repercussions on animal health. Along with polyphenols, isoprenoid compounds represent a family of substances with wide applications in therapy and pet nutrition. Essential oils (EOs) are a group of complex substances with fat-soluble nature that are widely used. Melatonin is an indolic amine present in all living with amphiphilic nature. In this work, we present a review of the most relevant phytogenics (polyphenol, isoprenoid, and alkaloid compounds), their characteristics, and possible uses as nutraceuticals in dogs, with special emphasis on EOs and their regulatory aspects, applied in foods and topically. Additionally, a presentation of the importance of the use of melatonin in dogs is developed, giving physiological and practical aspects about its use in dog feeding and also in topical application, with examples and future projections. This review points to the combination of EOs and melatonin in food supplements and in the topical application as an innovative product and shows excellent perspectives aimed at addressing dysfunctions in pets, such as the treatment of stress and anxiety, sleep disorders, alopecia, and hair growth problems, among others.

Melatonin maintains the function of the blood redox system at combined ethanol-induced toxicity and subclinical inflammation in mice

BACKGROUND

The goal of this study was to assess the effect of melatonin on blood redox systems in mice simultaneously exposed to ethanol and low-dose lipopolysaccharide (LPS).

METHODS

Oxidative stress parameters were assessed in eight groups: untreated control, melatonin (10 mg kg-1, 10 days), LPS (injected once intraperitoneally at a dose of 150 μg per mouse), LPS with previous melatonin treatment, acute ethanol-induced stress (AES, 0.75 g kg-1 per day, 10 days), AES with previous melatonin treatment, LPS- and AES-induced toxicity, and melatonin treatment.

RESULTS

Both ethanol and LPS induced oxidative stress. The combination of these two factors was even more toxic to the organism. Melatonin stabilized erythrocyte membranes and decreased the high level of free radical oxidation at the initial and final stages. Furthermore, melatonin limited protein damage through maintenance in the functional ability of the blood redox system to counteract pathological conditions.

CONCLUSIONS

Melatonin limited the negative effects associated with alcohol consumption and low-intensity inflammation.

Role of melatonin in murine "restraint stress"-induced dysfunction of colonic microbiota

Intestinal diseases caused by physiological stress have become a severe public health threat worldwide. Disturbances in the gut microbiota-host relationship have been associated with irritable bowel disease (IBD), while melatonin (MT) has anti-inflammatory and antioxidant effects. The objective of this study was to investigate the mechanisms by which MT-mediated protection mitigated stress-induced intestinal microbiota dysbiosis and inflammation. We successfully established a murine restraint stress model with and without MT supplementation. Mice subjected to restraint stress had significantly elevated corticosterone (CORT) levels, decreased MT levels in their plasma, elevated colonic ROS levels and increased bacterial abundance, including Bacteroides and Tyzzerella, in their colon tract, which led to elevated expression of Toll-like receptor (TLR) 2/4, p-P65 and p-IKB. In contrast, supplementation with 20 mg/kg MT reversed the elevation of the plasma CORT levels, downregulated the colon ROS levels and inhibited the changes in the intestinal microbiota induced by restraint stress. These effects, in turn, inhibited the activities of TLR2 and TLR4, p-P65 and p-IκB, and decreased the inflammatory reaction induced by restraint stress. Our results suggested that MT may mitigate "restraint stress"-induced colonic microbiota dysbiosis and intestinal inflammation by inhibiting the activation of the NF-κB pathway.

Increasing Nrf2 Activity as a Treatment Approach in Neuropsychiatry

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor encoded by NFE2L2. Under oxidative stress, Nrf2 does not undergo its normal cytoplasmic degradation but instead travels to the nucleus, where it binds to a DNA promoter and initiates transcription of anti-oxidative genes. Nrf2 upregulation is associated with increased cellular levels of glutathione disulfide, glutathione peroxidase, glutathione transferases, thioredoxin and thioredoxin reductase. Given its key role in governing the cellular antioxidant response, upregulation of Nrf2 has been suggested as a common therapeutic target in neuropsychiatric illnesses such as major depressive disorder, bipolar disorder and schizophrenia, which are associated with chronic oxidative and nitrosative stress, characterised by elevated levels of reactive oxygen species, nitric oxide and peroxynitrite. These processes lead to extensive lipid peroxidation, protein oxidation and carbonylation, and oxidative damage to nuclear and mitochondrial DNA. Intake of N-acetylcysteine, coenzyme Q₁₀ and melatonin is accompanied by increased Nrf2 activity. N-acetylcysteine intake is associated with improved cerebral mitochondrial function, decreased central oxidative and nitrosative stress, reduced neuroinflammation, alleviation of endoplasmic reticular stress and suppression of the unfolded protein response. Coenzyme Q₁₀, which acts as a superoxide scavenger in neuroglial mitochondria, instigates mitohormesis, ameliorates lipid peroxidation in the inner mitochondrial membrane, activates uncoupling proteins, promotes mitochondrial biogenesis and has positive effects on the plasma membrane redox system. Melatonin, which scavenges mitochondrial free radicals, inhibits mitochondrial nitric oxide synthase, restores mitochondrial calcium homeostasis, deacetylates and activates mitochondrial SIRT3, ameliorates increased permeability of the blood-brain barrier and intestine and counters neuroinflammation and glutamate excitotoxicity.

Role of melatonin in intestinal mucosal injury induced by restraint stress in mice

Context: A growing body of evidence demonstrates that gastrointestinal motility disorder (GIMD) and gastric stress ulcers can be induced by restraint stress, while melatonin (MT) elicits anti-inflammation and antioxidant effects.Objective: The present study investigated the mechanisms of MT-mediated protection effects on restraint stress-induced GIMD.Materials and methods: 144 8-week-old male ICR mice were divided into four groups: control, restraint stress, restraint stress + MT and MT (positive control). 20 mg/kg MT or vehicle were intraperitoneally injected 60 min before restraint stress (10 h/day) once daily for 3 days. Biochemical parameters, intestinal mucosal integrity, tissues antioxidant ability and autophagic proteins levels were determined.Results: Mice subjected to restraint stress elevated NE level by 141.41% and decreased MT content by 38.82% in plasma. Consistent with the decrease in MT level, we observed a reduction in the antioxidant ability and an increase in autophagic proteins by 14.29-46.74% in the gut, resulting in injury to intestinal mucosa which was manifested by reductions in villus height and villus height/crypt depth (V/C) ratio, number of goblet and PCAN-positive cells, and expression of tight junction protein (ZO-1, occludin and claudin-1). In contrast, MT reversed these changes caused by restraint stress and improved the intestinal mucosal injury. However, there was no significant difference between MT (positive control) and control group.Discussion and conclusion: Our results suggest that MT effectively mitigates psychological stress-induced injury to intestinal mucosa, providing evidence demonstrating the potential for using MT as therapy against intestinal impairment associated with psychological stress.

Topical Melatonin Improves Gastric Microcirculatory Oxygenation During Hemorrhagic Shock in Dogs but Does Not Alter Barrier Integrity of Caco-2 Monolayers

Systemic administration of melatonin exerts tissue protective effects in the context of hemorrhagic shock. Intravenous application of melatonin prior to hemorrhage improves gastric microcirculatory perfusion and maintains intestinal barrier function in dogs. The aim of the present study was to analyze the effects of a topical mucosal melatonin application on gastric microcirculation during hemorrhagic shock in vivo and on mucosal barrier function in vitro. In a randomized cross-over study, six anesthetized female foxhounds received 3.3 mg melatonin or the vehicle as a bolus to the gastric and oral mucosa during physiological and hemorrhagic (-20% blood volume) conditions. Microcirculation was analyzed with reflectance spectrometry and laser doppler flowmetry. Systemic hemodynamic variables were measured with transpulmonary thermodilution. For analysis of intestinal mucosal barrier function in vitro Caco-2 monolayers were used. The transepithelial electrical resistance (TEER) and the passage of Lucifer Yellow (LY) from the apical to the basolateral compartment of Transwell chambers were measured. Potential barrier protective effects of melatonin against oxidative stress were investigated in the presence of the oxidant H₂O₂. During physiologic conditions topical application of melatonin had no effect on gastric and oral microcirculation in vivo. During hemorrhagic shock, gastric microcirculatory oxygenation (μHbO₂) was decreased from 81 ± 8% to 50 ± 15%. Topical treatment with melatonin led to a significant increase in μHbO₂ to 60 ± 13%. Topical melatonin treatment had no effect on gastric microcirculatory perfusion, oral microcirculation or systemic hemodynamics. Incubation of H₂O₂ stressed Caco-2 monolayers with melatonin did neither influence transepithelial electrical resistance nor LY translocation. Topical treatment of the gastric mucosa with melatonin attenuates the shock induced decrease in microcirculatory oxygenation. As no effects on local microcirculatory and systemic perfusion were recorded, the improved μHbO₂ is most likely caused by a modulation of local oxygen consumption. In vitro melatonin treatment did not improve intestinal barrier integrity in the context of oxidative stress. These results extend the current knowledge on melatonin's protective effects during hemorrhage in vivo. Topical application of melatonin exerts differential effects on local microcirculation compared to systemic pretreatment and might be suitable as an adjunct for resuscitation of hemorrhagic shock.

Prevention of Rat Intestinal Injury with a Drug Combination of Melatonin and Misoprostol

A healthy intestinal barrier prevents uptake of allergens and toxins, whereas intestinal permeability increases following chemotherapy and in many gastrointestinal and systemic diseases and disorders. Currently, there are no approved drugs that target and repair the intestinal epithelial barrier while there is a medical need for such treatment in gastrointestinal and related conditions. The objective of this single-pass intestinal perfusion study in rats was to investigate the preventive cytoprotective effect of three mucosal protective drugs—melatonin, misoprostol, and teduglutide—with different mechanisms of action on an acute jejunal injury induced by exposing the intestine for 15 min to the anionic surfactant, sodium dodecyl sulfate (SDS). The effect was evaluated by monitoring intestinal clearance of ⁵¹Cr-labeled ethylenediaminetetraacetate and intestinal histology before, during, and after luminal exposure to SDS. Our results showed that separate pharmacological pretreatments with luminal misoprostol and melatonin reduced acute SDS-induced intestinal injury by 47% and 58%, respectively, while their use in combination abolished this injury. This data supports further development of drug combinations for oral treatments of conditions and disorders related to a dysregulated or compromised mucosal epithelial barrier.

Melatonin alleviates oxidative stress in sleep deprived mice: Involvement of small intestinal mucosa injury

BACKGROUND

Previous research demonstrated that sleep deprivation (SD) resulted in intestinal homeostasis disorder in colon. The present study was further performed to clarify the role of melatonin in SD-induced small intestinal (SI) mucosal injury.

METHODS

We successfully established a multiplatform 72 h SD mouse model with or without melatonin supplementation to explore the improvement of melatonin in the destruction of SI induced by SD.

RESULTS

Melatonin supplementation suppressed an increase of corticosterone level and a decrease of melatonin level caused by SD. Meanwhile, we observed that melatonin supplementation in sleep deprived mice markedly reversed a decrease of the villi length/crypt depth (V/C) ratio and the number of goblet cells, PCNA positive cells, the expressions of MUC2 and tight junction proteins, as well as an upregulation of the expressions of autophagic proteins in the duodenum, jejunum and ileum. Furthermore, melatonin supplementation inverted the SD-induced the decline of antioxidant enzyme activities (T-AOC and CAT etc) and anti-inflammatory cytokines (IL-10 and IFN-γ) and the increase of oxidative product MDA, pro-inflammatory cytokines (IL-6 and TNF-α), p-P65 and p-IκB proteins in the SI.

CONCLUSIONS

These findings suggested that melatonin may be used as a probiotic agent to reverse SD-induced SI mucosa injury by suppressing oxidative stress and NF-κB pathway activation.

Melatonin Treatment Alleviates Spinal Cord Injury-Induced Gut Dysbiosis in Mice

Spinal cord injury (SCI) disturbs the autonomic nervous system and induces dysfunction in multiple organs/tissues, such as the gastrointestinal (GI) system. The neuroprotective effects of melatonin in SCI models have been reported; however, it is unclear whether the beneficial effects of melatonin are associated with alleviation of gut dysbiosis. In this study, we showed that daily intraperitoneal injection with melatonin following spinal cord contusion at thoracic level 10 in mice improved intestinal barrier integrity and GI motility, reduced expression levels of certain proinflammatory cytokines, improved animal weight gain and metabolic profiling, and promoted locomotor recovery. Analysis of gut microbiome revealed that melatonin treatment decreased the Shannon index and reshaped the composition of intestinal microbiota. Melatonin-treated SCI animals showed decreased relative abundance of Clostridiales and increased relative abundance of Lactobacillales and Lactobacillus, which correlated with alteration of cytokine (monocyte chemotactic protein 1) expression and GI barrier permeability, as well as with locomotor recovery. Experimental induction of gut dysbiosis in mice before SCI (i.e., by oral delivery of broad-spectrum antibiotics) exacerbates neurological impairment after SCI, and melatonin treatment improves locomotor performance and intestinal integrity in antibiotic-treated SCI mice. The results suggest that melatonin treatment restores SCI-induced alteration in gut microbiota composition, which may underlie the ameliorated GI function and behavioral manifestations.

Attenuating effect of melatonin on lipopolysaccharide-induced chicken small intestine inflammation

Enriched melatonin (MEL) has been found in the mammalian intestine and has been recently demonstrated to alleviate rodent colitis. In this study, the effect of MEL on lipopolysaccharide (LPS)-induced intestinal inflammations was investigated in new chicken hatchlings. The chicks were fed with a diet supplemented with MEL (12.5 mg/day) from D1 to D10. Meanwhile, the chicks in the LPS or MEL + LPS groups were injected with LPS (10 mg/kg BW, i.p.) at D10. LPS treatment for 6 h increased the expression of IL-6, IL-4, caspase-3 mRNAs and TUNEL-positive cell populations, but decreased populations of the goblet and PCNA+ cells, IgA production and the expression of MUC2 mRNA in the duodenum. Compared with the LPS group, MEL pre-feeding alleviated duodenal inflammation and decreased the expression of TNF-α mRNAs by 23.6% (P = 0.004), IL-6 mRNAs by 69.4% (P = 0.001), IL-4 mRNAs by 4.1% (P = 0.824) and caspase-3 mRNAs by 45.8% (P < 0.001). Conversely, MEL pre-feeding attenuated the LPS-induced changes of IgA production by 161.6% (P = 0.013) and PCNA+ cell populations by 172.1% (P < 0.001) in the duodenum. TLR4 mRNA was also up-regulated by LPS treatment but down-regulated by MEL pre-feeding. In conclusion, dietary MEL could attenuate LPS-induced chick duodenal inflammation by down-regulating the expression of inflammatory cytokines, promoting epithelial cell proliferation, improving the immunological barrier and inhibiting epithelial apoptosis via the mediation of TLR4.

Melatonin alleviates weanling stress in mice: Involvement of intestinal microbiota

Melatonin influences intestinal microbiota and the pathogenesis of various diseases. This study was conducted to explore whether melatonin alleviates weanling stress through intestinal microbiota in a weanling mouse model. Melatonin supplementation in weanling mice (provided in the drinking water at a dosage of 0.2 mg/mL for 2 weeks) significantly improved body weight gain (1.4 ± 0.03 g/day in melatonin group vs 1.2 ± 0.06 g/day in control group) and intestinal morphology (ie, villus length, crypt depth, and villus to crypt ratio), but had little effect on the proliferation or apoptosis of intestinal cells, the numbers of Paneth cells and goblet cells, as well as the expression of makers related to enterocytes (sucrase) and endocrine cells (chromogranin A and peptide YY) in the ileum. Melatonin supplementation had little effect on serum levels of amino acids or stress-related parameters (eg, SOD, TNF-α, and angiotensin I). 16S rRNA sequencing suggested that melatonin supplementation increased the richness indices of intestinal microbiota (observed species, Chao 1, and ACE) and shaped the composition of intestinal microbiota (eg, increase in the abundance of Lactobacillus [19 ± 3% in melatonin group vs 6 ± 2% in control group]), which was demonstrated using an ex vivo proliferation assay and colonic loop proliferation assay. Melatonin supplementation also significantly influenced the metabolism of intestinal microbiota, such as amino acid metabolism and drug metabolism. More importantly, in antibiotic-treated weanling mice and germ-free weanling mice, melatonin failed to affect body weight gain or intestinal morphology. Melatonin significantly reduced (by about 60%) the bacterial load in enterotoxigenic Escherichia coli (ETEC)-infected weanling mice, but had little effect on ETEC load in antibiotic-pretreated animals. In conclusion, melatonin affects body weight gain, intestinal morphology, and intestinal ETEC infection through intestinal microbiota in weanling mice. The findings highlight the importance of intestinal microbiota in mediating the various physiological functions of melatonin in the host.

Melatonin pretreatment improves gastric mucosal blood flow and maintains intestinal barrier function during hemorrhagic shock in dogs

OBJECTIVE

Melatonin improves hepatic perfusion after hemorrhagic shock and may reduce stress-induced gastric lesions. This study was designed to investigate whether pretreatment with melatonin may influence gastric mucosal microcirculatory perfusion (μflow), oxygenation (μHbO₂ ), or intestinal barrier function during physiological and hemorrhagic conditions in dogs.

METHODS

In a randomized crossover study, five anesthetized foxhounds received melatonin 100 μg kg^-1 or vehicle (ethanol 5%) intravenously in the absence or presence of hemorrhagic shock (60 minutes, -20% blood volume). Systemic hemodynamic variables, gastric mucosal perfusion, and oxygenation were recorded continuously; intestinal barrier function was assessed intermittently via xylose absorption.

RESULTS

During hemorrhagic shock, melatonin significantly attenuated the decrease in μflow, compared with vehicle (-19±9 vs -43±10 aU, P<.05), without influence on μHbO₂ . A significant increase in xylose absorption was detected during hemorrhage in vehicle-treated dogs, compared with sham-operated animals (13±2 vs 8±1 relative amounts, P<.05); this was absent in melatonin-treated animals (6±1 relative amounts). Melatonin did not influence macrocirculation.

CONCLUSIONS

Melatonin improves regional blood flow suggesting improved oxygen delivery in gastric mucosa during hemorrhagic shock. This could provide a mechanism for the observed protection of intestinal barrier function in dogs.

Melatonin Improves Laying Performance by Enhancing Intestinal Amino Acids Transport in Hens

The high concentration of melatonin (MEL) in the intestinal mucosa suggests that it has a special physiological function in intestine. In hens, previous studies have shown that MEL treatment promoted egg-laying performance. Considering the importance of amino acids (AA) for egg formation, we hypothesized that MEL may enhance the intestinal absorption of AA from the feed, thus promoting egg laying performance. In this study, we supplemented the hens with MEL for two consecutive weeks. The results showed that, compared with control group, feeding with 0.625 mg MEL/kg diets gave rise to higher egg laying rate (by 4.3%, P = 0.016), increased eggshell thickness (by 16.9%, P < 0.01) and albumen height (by 4.5%, P = 0.042). Meanwhile, feeding with 0.625 and 2.5 mg MEL/kg diets could significantly increase serum levels of aspartic acid, threonine, serine, glutamic acid, glycine, alanine, isoleucine, leucine, tyrosine, phenylalanine, lysine, histidine, arginine, and proline. Furthermore, a 0.625 mg MEL/kg diets could significantly increase the expression of PepT1 (by 3949.9%), B⁰AT (by 6045.9%), b^{0, +}AT (by 603.5%), and EAAT3 (by 412.7%) in the jejunum. Additionally, in the cultured intestinal crypt "organoids," treatment with 0.5 μM MEL could significantly enhance the expression of PepT1, b^{0, +}AT and EAAT3 mRNAs by 35.4%, 110.0%, and 160.1%, respectively. Detection of MEL concentration in serum and intestinal fluid suggested that lower dosage of MEL feeding was mainly acted on intestine locally, and further increased intestinal antioxidases (GPx-3, SOD-1 or PRDX-3) mRNA expression. Taken together, we demonstrated that MEL feeding in laying hens could locally promote the expression and function of AA transporter in small intestine by up-regulating antioxidases expression, and finally elevate laying performance.

Short-chain fatty acids augment rat duodenal mucosal barrier function

NEW FINDINGS

What is the central question of this study? Small intestinal epithelium is exposed to high concentrations of short-chain fatty acids (SCFAs), but their role in regulating intestinal mucosal barrier function and motility is not fully understood. What is the main finding and its importance? By perfusing the duodenal segment in anaesthetized rats, we show that acetate and propionate significantly decrease mucosal paracellular permeability and transepithelial net fluid flux and increase mucosal bicarbonate secretion. Likewise, SCFAs administered i.v. decrease mucosal permeability but decrease bicarbonate secretion. Altered luminal chemosensing or aberrant signalling in response to SCFAs might contribute to symptoms observed in patients with suppressed mucosal barrier function. Short-chain fatty acids (SCFAs) are produced by bacterial fermentation in the large intestine, particularly from diets containing fibres and carbohydrates. The small intestinal epithelium is exposed to SCFAs derived mainly from oral bacteria or food supplementation. Although luminal nutrients are important in regulation of intestinal functions, the role of SCFAs in regulation of small intestinal mucosal barrier function and motility has not been fully described. The aim of the present study was to elucidate the effects of acetate and propionate on duodenal mucosal barrier function and motility. Rats were anaesthetized with thiobarbiturate, and a 30 mm segment of proximal duodenum with an intact blood supply was perfused. The effects on duodenal bicarbonate secretion, blood-to-lumen clearance of ⁵¹ Cr-EDTA, motility and transepithelial net fluid flux were investigated. Perfusion of the duodenum with acetate or propionate significantly decreased mucosal paracellular permeability and transepithelial net fluid flux and significantly increased bicarbonate secretion. Acetate or propionate administered as an i.v. infusion decreased the mucosal paracellular permeability, but significantly decreased bicarbonate secretion. Luminal SCFAs changed the duodenal motility pattern from migrating motor complexes to fed patterns. Systemic administration of glucagon-like peptide-2 induced increases in both bicarbonate secretion and net fluid absorption, but did not change motility. Glucagon-like peptide-2 infusion during luminal perfusion of SCFAs significantly reduced the motility. In conclusion, SCFAs decreased duodenal paracellular permeability and net fluid flux. Short-chain fatty acids induced opposite effects on bicarbonate secretion after luminal and i.v. administration. Presence of SCFAs in the lumen induces fed motility patterns. Altered luminal chemosensing and aberrant signalling in response to SCFAs might contribute to symptoms observed in patients with suppressed barrier function.

Neuropeptide S reduces duodenal bicarbonate secretion and ethanol-induced increases in duodenal motility in rats

Alcohol disrupts the intestinal mucosal barrier by inducing metabolic and functional changes in epithelial cells. Recently, we showed that neuropeptide S (NPS) decreases duodenal motility and increases mucosal paracellular permeability, suggesting a role of NPS in the pathogenesis of disorders and dysfunctions in the small intestine. The aim of the present study was to investigate the effects of NPS on ethanol- and HCl-induced changes of duodenal mucosal barrier function and motility. Rats were anaesthetized with thiobarbiturate, and a 30-mm segment of the proximal duodenum with an intact blood supply was perfused in situ. The effects on duodenal bicarbonate secretion, the blood-to-lumen clearance of 51Cr-EDTA, motility and transepithelial net fluid flux were investigated. Intravenous (i.v.) administration of NPS significantly reduced duodenal mucosal bicarbonate secretion and stimulated mucosal transepithelial fluid absorption, mechanisms dependent on nitrergic signaling. NPS dose-dependently reduced ethanol-induced increases in duodenal motility. NPS (83 pmol·kg-1·min-1, i.v.) reduced the bicarbonate and fluid secretory response to luminal ethanol, whereas a 10-fold higher dose stimulated fluid secretion but did not influence bicarbonate secretion. In NPS-treated animals, duodenal perfusion of acid (pH 3) induced greater bicarbonate secretory rates than in controls. Pre-treating animals with Nω-nitro-L-arginine methyl ester (L-NAME) inhibited the effect of NPS on bicarbonate secretion. In response to luminal acid, NPS-treated animals had significantly higher paracellular permeability compared to controls, an effect that was abolished by L-NAME. Our findings demonstrate that NPS reduces basal and ethanol-induced increases in duodenal motility. In addition, NPS increases luminal alkalinization and mucosal permeability in response to luminal acid via mechanisms that are dependent on nitric oxide signaling. The data support a role for NPS in neurohumoral regulation of duodenal mucosal barrier function and motility.

Decreased melatonin secretion is associated with increased intestinal permeability and marker of endotoxemia in alcoholics

Chronic heavy alcohol use is known to cause gut leakiness and alcoholic liver disease (ALD), but only 30% of heavy drinkers develop increased intestinal permeability and ALD. The hypothesis of this study was that disruption of circadian rhythms is a potential risk factor in actively drinking alcoholics for gut leakiness and endotoxemia. We studied 20 subjects with alcohol use disorder (AD) and 17 healthy controls (HC, 6 day workers, 11 night workers). Subjects wore a wrist actiwatch for 7 days and underwent a 24-h dim light phase assessment and urine collection for intestinal permeability. The AD group had significantly less total sleep time and increased fragmentation of sleep (P < 0.05). AD also had significantly lower plasma melatonin levels compared with the HC [mean area under the curve (AUC) 322.78 ± 228.21 vs. 568.75 ± 304.26 pg/ml, P = 0.03]. In the AD group, AUC of melatonin was inversely correlated with small bowel and colonic intestinal permeability (lactulose-to-mannitol ratio, r = -0.39, P = 0.03; urinary sucralose, r = -0.47, P = 0.01). Cosinor analysis of lipopolysaccharide-binding protein (marker of endotoxemia) and lipopolysaccharide every 4 h for 24 h in HC and AD subjects had a midline estimating statistic of rhythm of 5,026.15 ± 409.56 vs. 6,818.02 ± 628.78 ng/ml (P < 0.01) and 0.09 ± 0.03 vs. 0.15 ± 0.19 EU/ml (P < 0.05), respectively. We found plasma melatonin was significantly lower in the AD group, and lower melatonin levels correlated with increased intestinal permeability and a marker of endotoxemia. Our study suggests the suppression of melatonin in AD may promote gut leakiness and endotoxemia.