Expression of melatonin synthesizing enzymes in Helicobacter pylori infected gastric mucosa

Melatonin for gastric cancer treatment: where do we stand?

Gastric cancer (GC) is the third leading reason of death in men and the fourth in women. Studies have documented an inhibitory function of melatonin on the proliferation, progression and invasion of GC cells. MicroRNAs (miRNAs) are small, non-coding RNAs that play an important function in regulation of biological processes and gene expression of the cells. Some studies reported that melatonin can suppress the progression of GC by regulating the exosomal miRNAs. Thus, melatonin represents a promising potential therapeutic agent for subjects with GC. Herein, we evaluate the existing data of both in vivo and in vitro studies to clarify the molecular processes involved in the therapeutic effects of melatonin in GC. The data emphasize the critical function of melatonin in several signaling ways by which it may inhibit cancer cell proliferation, decrease chemo-resistance, induce apoptosis as well as limit invasion, angiogenesis, and metastasis. This review provides a resource that identifies some of the mechanisms by which melatonin controls GC enlargement. In light of the findings, melatonin should be considered a novel and testable therapeutic mediator for GC treatment.

Neuromodulators as Interdomain Signaling Molecules Capable of Occupying Effector Binding Sites in Bacterial Transcription Factors

Hormones and neurotransmitters are important components of inter-kingdom signaling systems that ensure the coexistence of eukaryotes with their microbial community. Their ability to affect bacterial physiology, metabolism, and gene expression was evidenced by various experimental approaches, but direct penetration into bacteria has only recently been reported. This opened the possibility of considering neuromodulators as potential effectors of bacterial ligand-dependent regulatory proteins. Here, we assessed the validity of this assumption for the neurotransmitters epinephrine, dopamine, and norepinephrine and two hormones (melatonin and serotonin). Using flexible molecular docking for transcription factors with ligand-dependent activity, we assessed the ability of neuromodulators to occupy their effector binding sites. For many transcription factors, including the global regulator of carbohydrate metabolism, CRP, and the key regulator of lactose assimilation, LacI, this ability was predicted based on the analysis of several 3D models. By occupying the ligand binding site, neuromodulators can sterically hinder the interaction of the target proteins with the natural effectors or even replace them. The data obtained suggest that the direct modulation of the activity of at least some bacterial transcriptional factors by neuromodulators is possible. Therefore, the natural hormonal background may be a factor that preadapts bacteria to the habitat through direct perception of host signaling molecules.

Melatonin-Microbiome Two-Sided Interaction in Dysbiosis-Associated Conditions

Melatonin is a pineal indolamine, allegedly known as a circadian rhythm regulator, and an antioxidative and immunomodulatory molecule. In both experimental and clinical trials, melatonin has been shown to have positive effects in various pathologies, as a modulator of important biochemical pathways including inflammation, oxidative stress, cell injury, apoptosis, and energy metabolism. The gut represents one of melatonin's most abundant extra pineal sources, with a 400-times-higher concentration than the pineal gland. The importance of the gut microbial community-namely, the gut microbiota, in multiple critical functions of the organism- has been extensively studied throughout time, and its imbalance has been associated with a variety of human pathologies. Recent studies highlight a possible gut microbiota-modulating role of melatonin, with possible implications for the treatment of these pathologies. Consequently, melatonin might prove to be a valuable and versatile therapeutic agent, as it is well known to elicit positive functions on the microbiota in many dysbiosis-associated conditions, such as inflammatory bowel disease, chronodisruption-induced dysbiosis, obesity, and neuropsychiatric disorders. This review intends to lay the basis for a deeper comprehension of melatonin, gut microbiota, and host-health subtle interactions.

Long-Term Vitamin D Deficiency Results in the Inhibition of Cell Proliferation and Alteration of Multiple Gastric Epithelial Cell Lineages in Mice

Over one billion people globally are vitamin D (VD) deficient. Studies on the biological roles of VD are numerous but very little on the stomach. This project aims to understand how gastric homeostasis is affected by VD deficiency caused by prolonged exposure to darkness alone or combined with VD deficient diet. Three groups of C57/BL6 mice were subjected to different light exposure conditions and diets for 12 months (n = 8−12/group): control—12 h/12 h light/dark SDL (Standard Diet/Light), 24 h dark SDD (Standard Diet/Dark), and 24 h dark VDD (VD deficient diet/Dark). Stomach samples were collected for different multi-label lectin-/immuno-histochemical and qRT-PCR analyses, and the serum for LC-MS-MS. We found that the membrane VD receptor is expressed widely in the stomach when compared to nuclear VD receptors. Compared to SDL, VDD mice developed mucous cell expansion with increased mucins-mRNA (3.27 ± 2.73 (p < 0.05)) increased apoptotic cells, 15 ± 7 (p ≤ 0.001)); decreased cell proliferation, 4 ± 4 (p < 0.05)) and decreased acid secretion 33 ± 2 μEq/kg (p ≤ 0.0001)). Interestingly, mice exposed to full darkness developed mild VD deficiency with higher VD epimer levels: 11.9 ± 2.08 ng/mL (p ≤ 0.0001)), expansion in zymogenic cell number (16 ± 3 (p ≤ 0.01)), and a reduction in acid secretion (18 ± 2 μEq/kg (p ≤ 0.0001)). In conclusion, changes in light exposure or VD levels have serious physiological effects on the gastric mucosa, which should be considered during the management of gastric disorders.

Transcriptional effects of melatonin on the gut commensal bacterium Klebsiella aerogenes

Klebsiella (nee Enterobacter) aerogenes is the first human gut commensal bacterium with a documented sensitivity to the pineal/gastrointestinal hormone melatonin. Exogenous melatonin specifically increases the size of macrocolonies on semisolid agar and synchronizes the circadian clock of K. aerogenes in a concentration dependent manner. However, the mechanisms driving these phenomena are unknown. In this study, we applied RNA sequencing to identify melatonin sensitive transcripts during culture maturation. This work demonstrates that the majority of melatonin sensitive genes are growth stage specific. Melatonin exposure induced differential gene expression of 81 transcripts during exponential growth and 30 during early stationary phase. This indole molecule affects genes related to biofilm formation, fimbria biogenesis, transcriptional regulators, carbohydrate transport and metabolism, phosphotransferase systems (PTS), stress response, metal ion binding and transport. Differential expression of biofilm and fimbria-related genes may be responsible for the observed differences in macrocolony area. These data suggest that melatonin enhances Klebsiella aerogenes host colonization.

Bacteriostatic Potential of Melatonin: Therapeutic Standing and Mechanistic Insights

Diseases caused by pathogenic bacteria in animals (e.g., bacterial pneumonia, meningitis and sepsis) and plants (e.g., bacterial wilt, angular spot and canker) lead to high prevalence and mortality, and decomposition of plant leaves, respectively. Melatonin, an endogenous molecule, is highly pleiotropic, and accumulating evidence supports the notion that melatonin's actions in bacterial infection deserve particular attention. Here, we summarize the antibacterial effects of melatonin in vitro, in animals as well as plants, and discuss the potential mechanisms. Melatonin exerts antibacterial activities not only on classic gram-negative and -positive bacteria, but also on members of other bacterial groups, such as Mycobacterium tuberculosis. Protective actions against bacterial infections can occur at different levels. Direct actions of melatonin may occur only at very high concentrations, which is at the borderline of practical applicability. However, various indirect functions comprise activation of hosts' defense mechanisms or, in sepsis, attenuation of bacterially induced inflammation. In plants, its antibacterial functions involve the mitogen-activated protein kinase (MAPK) pathway; in animals, protection by melatonin against bacterially induced damage is associated with inhibition or activation of various signaling pathways, including key regulators such as NF-κB, STAT-1, Nrf2, NLRP3 inflammasome, MAPK and TLR-2/4. Moreover, melatonin can reduce formation of reactive oxygen and nitrogen species (ROS, RNS), promote detoxification and protect mitochondrial damage. Altogether, we propose that melatonin could be an effective approach against various pathogenic bacterial infections.

The value of melatonin supplementation in postmenopausal women with Helicobacter pylori-associated dyspepsia

BACKGROUND

Dyspeptic syndrome is particularly common in postmenopausal women in the form of epigastric pain. The aim of the study was to assess the role of melatonin in chronic dyspepsia in this group of women, and examine the role of Helicobacter infection.

METHODS

The study comprised 152 subjects including 30 healthy women (Group I), 60 women with asymptomatic H.pylori infection (Group II), and 64 women with H. pylori infection with chronic dyspepsia (Group III). Endoscopic examination was performed, as well as histological assessment of gastric end duodenal mucosa, urease breath test (UBT-13C), and immunoenzymatic assessment of serum 17-β-estradiol, follicle stimulating hormone and melatonin, and urinary 6-sulfatoxymelatonin. In Group III, 14-day antibacterial treatment was introduced with pantoprazole, amoxicillin and levofloxacin followed a six-month treatment with placebo in 32 women (Group IIIa), and melatonin 1 mg/morning and 3 mg/at bedtime in the other 32 women (Group IIIb).

RESULTS

No significant differences were found between serum level of female hormone. Serum melatonin levels were similar between Group I (12.5 ± 2.72 pg/ml) and Group II (10.5 ± 3.73 pg/ml; p > 0,05). The level was significantly lower in Group III (5.72 ± 1.42 pg/ml; p < 0.001). Eradication of H.pylori was obtained in 75.0% women in Group IIIa, and in 84.3% in Group IIIb (p > 0.05). After six months, dyspeptic symptoms resolved in 43.7% patients in Group IIIa and 84.3% in Group IIIb (p < 0.001).

CONCLUSION

Melatonin supplementation is useful in treating H. pylori-associated dyspepsia, particularly in postmenopausal women with lower levels of this hormone.

TRIAL REGISTRATION

NCT04352062, date of registration: 15.04.2020.

Melatonin and gastrointestinal cancers: Current evidence based on underlying signaling pathways

Gastrointestinal (GI) cancers, leading causes of cancer-related deaths, have been serious challenging human diseases up to now. Because of high rates of mortality, late-stage diagnosis, metastasis to distant locations, and low effectiveness and adverse events of routine standard therapies, the quality of life and survival time are low in patients with GI cancers. Hence, many efforts need to be done to explore and find novel efficient treatments. Beneficial effects of melatonin have been reported in a wide variety of human diseases. Melatonin has antioxidant, anti-inflammatory, antimicrobial, and anticancer effects. Various studies have showed the regulatory effects of melatonin on apoptotsis, autophagy and angiogenesis; these properties result in the inhibition of invasion, migration, and proliferation of GI cancer cells in vivo and in vitro. Together, this review suggests that melatonin in combination with anticancer agents may improve the efficacy of routine medicine and survival rate of patients with cancer.

Expression of tryptophan hydroxylase in gastric mucosa in symptomatic and asymptomatic Helicobacter pylori infection

INTRODUCTION

Helicobacter pylori infection induces clinical symptoms in 15-20% of subjects, and the reason for this variation is still not clear. The aim of the present study is to evaluate the expression of tryptophan hydroxylase (TpH-1) in gastric mucosa of patients with symptomatic and asymptomatic H. pylori infection in relation to the intensity of bacterial colonization and severity of dyspeptic symptoms.

MATERIAL AND METHODS

Ninety subjects (aged 35-49 years) were enrolled in the study and separated into 3 groups of 30 subjects each. Group I - healthy volunteers without H. pylori infection, group II - subjects with asymptomatic H. pylori infection, group III - H. pylori-infected patients with dyspeptic symptoms, mainly fasting and nocturnal epigastric pain. To diagnose H. pylori infection the urea breath test (UBT-13C) and histological analysis were performed. The level of mRNA expression of tryptophan hydroxylase (TpH-1) was estimated in gastric mucosa with RT-PCR.

RESULTS

The expression of this enzyme in antral mucosa was 2.69 ±0.97 in group I, 2.28 ±0.69 in group II (p > 0.05) and 4.40 ±1.64 in group III (p < 0.001). The levels of expression of TpH-1 in gastric body mucosa were 2.16 ±0.70, 1.57 ±0.52 (p > 0.05) and 3.40 ±1.51 (p < 0.001), respectively. In group III a positive correlation was found between intensity of H. pylori colonization and TpH-1 expression as well as between TpH-1 expression and severity of dyspeptic symptoms.

CONCLUSIONS

Increased expression of TpH-1 in gastric mucosa plays a role in pathogenesis of chronic dyspepsia.

Melatonin mediated Foxp3-downregulation decreases cytokines production via the TLR2 and TLR4 pathways in H. pylori infected mice

Melatonin has important immuno-regulatory effects in inflammatory disorders but its specific role in Helicobacter pylori induced gastritis remains unclear. The aim of our study was to analyze the activity of melatonin against H. pylori induced gastritis in vivo, and explore the underlying mechanisms. The H. pylori infected mice showed extensive inflammatory cell infiltration in the gastric mucosa and submucosa, along with significantly reduced spleen and thymus weight. However, 2 and 6 weeks of treatment with 25 and 50 mg/kg melatonin restored the thymus weights relative to that of the untreated mice. TLR2 was upregulated in the gastric mucosa of the infected mice, which was restored to normal levels after 2 and 6 weeks of melatonin treatment. In contrast, TLR4 levels were similar between the treated and untreated mice. Furthermore, melatonin treatment restored spleen Foxp3 and serum TGF-β1 levels that were respectively increased and decreased in the infected mice. H. pylori infected mice also showed a decrease in the serum levels of IL-2, IL-6, IL-10, IL-17, IFN-γ and TFN-α following 2 and 6 weeks of melatonin treatment compared to the untreated mice. Melatonin treatment also resulted in decreased CD4+CD25+Foxp3+ Treg cell count in the spleen. The expression of TLR2, MyD88, p-ERK, p-p38, p65, p50 and Foxp3 in the gastric tissues were lower in the untreated mice compared to mice treated with melatonin for 2 weeks. However, the expression levels evened out after 6 weeks of treatment. Taken together, melatonin alleviates H. pylori induced gastritis by regulating TGF-β1 and Foxp3 expression via the TLR2 and TLR4 pathways.

Utilizing melatonin to combat bacterial infections and septic injury

Melatonin, also known as N-acetyl-5-methoxytryptamine, is a ubiquitously acting molecule that is produced by the pineal gland and other organs of animals, including humans. As melatonin and its metabolites are potent antioxidants and free radical scavengers, they are protective against a variety of disorders. Moreover, multiple molecular targets of melatonin have been identified, and its actions are both receptor-mediated and receptor-independent. Recent studies have shown that melatonin may be useful in fighting against sepsis and septic injury due to its antioxidative and anti-inflammatory actions; the results generally indicate a promising therapeutic application for melatonin in the treatment of sepsis. To provide a comprehensive understanding regarding the protective effects of melatonin against septic injury, in the present review we have evaluated the published literature in which melatonin has been used to treat experimental and clinical sepsis. Firstly, we present the evidence from studies that have used melatonin to resist bacterial pathogens. Secondly, we illustrate the protective effect of melatonin against septic injury and discuss the possible mechanisms. Finally, the potential directions for future melatonin research against sepsis are summarized.

Gingival, plasma and salivary levels of melatonin in periodontally healthy individuals and chronic periodontitis patients: a pilot study

INTRODUCTION

Periodontal disease is an inflammatory condition affecting tooth supporting structures in which dysregulated immune response and oxidative stress mediate tissue destruction. Melatonin, the pineal gland hormone is a regulator of circadian rhythm, an antioxidant and an immunomodulator. Previous studies have shown lowered melatonin levels in saliva, plasma and gingival crevicular fluid (GCF) of patients with periodontal disease. Till date no study has assessed the melatonin levels in gingival tissues.

MATERIALS AND METHODS

Five healthy individuals and 15 chronic periodontitis patients were recruited for this pilot study. 5ml of whole saliva, 2 ml peripheral blood and gingival tissue samples were obtained from each individual at 8.00 am in fasting state. Melatonin assay was performed with a commercially available ELISA kit. Statistical analysis was done to assess the difference in mean melatonin levels among the groups.

RESULTS

No statistically significant difference was found in mean melatonin levels between healthy individuals and chronic periodontitis patients in saliva (p=.266) and plasma (p=.933) samples, whereas in gingival tissue samples (p=.015), the melatonin levels were significantly lowered in chronic periodontitis patients compared to healthy individuals.

CONCLUSION

This study demonstrates the presence of melatonin in gingival tissue. Furthermore, melatonin levels are lowered in gingival tissues of chronic periodontitis patients.

Effects of melatonin on oxidative stress, and resistance to bacterial, parasitic, and viral infections: a review

Melatonin, a hormone secreted by the pineal gland, works directly and indirectly as a free radical scavenger. Its other physiological or pharmacological activities could be dependent or independent of receptors located in different cells, organs, and tissues. In addition to its role in promoting sleep and circadian rhythms regulation, it has important immunomodulatory, antioxidant, and neuroprotective effects suggesting that this indole must be considered as a therapeutic alternative against infections. The aim of this review is to describe the effects of melatonin on oxidative stress and the resistance to bacterial (Klebsiella pneumoniae, Helicobacter pylori, Mycobacterium tuberculosis, and Clostridium perfringens), viral (Venezuelan equine encephalomyelitis virus and respiratory syncytial virus), and parasitic (Plasmodium spp., Entamoeba histolytica, Trypanosoma cruzi, Toxoplasma gondii, and Opisthorchis viverrini) infections.