Melatonin plays a protective role in postburn rodent gut pathophysiology

The potential influence of melatonin on mitochondrial quality control: a review

Mitochondria are critical for cellular energetic metabolism, intracellular signaling orchestration and programmed death regulation. Therefore, mitochondrial dysfunction is associated with various pathogeneses. The maintenance of mitochondrial homeostasis and functional recovery after injury are coordinated by mitochondrial biogenesis, dynamics and autophagy, which are collectively referred to as mitochondrial quality control. There is increasing evidence that mitochondria are important targets for melatonin to exert protective effects under pathological conditions. Melatonin, an evolutionarily conserved tryptophan metabolite, can be synthesized, transported and metabolized in mitochondria. In this review, we summarize the important role of melatonin in the damaged mitochondria elimination and mitochondrial energy supply recovery by regulating mitochondrial quality control, which may provide new strategies for clinical treatment of mitochondria-related diseases.

Melatonin: Manager of psychosomatic and metabolic disorders in polymorbid cardiovascular pathology

Objectives

To investigate the relationship between changes in circadian patterns of melatonin and clinical manifestations of polymorbid cardiovascular pathology (PCVP) in young men and to analyze the effectiveness of their complex treatment.

Materials and methods

We made the immunohistochemical (IHC) analysis of epiphysis tissues from autopsies of 25 men aged 32–44 with PCVP and metabolic syndrome (MS) who had died as a result of ischemic cardiomyopathy (IC) and 25 persons after the car accident as a control group. Then, 93 young men aged 35–44 with PCVP, metabolic syndrome, and depressive spectrum disorders (DSD) were divided into three groups: (1) standard therapy; (2) standard therapy and psychotherapy sessions; (3) standard therapy in combination with psychotherapeutic and psychophysiological visual and auditory correction sessions. The control group included 24 conditionally healthy male volunteers. Before and after the treatment, we studied the anthropometric status, lipid and carbohydrate metabolism indicators, the level of urinary 6-hydroxymelatonin sulfate, the degree of nocturnal decrease in blood pressure (BP), and the relationship of these indicators with circadian variations of melatonin excretion.

Results

Young polymorbid patients who died from IC have a lower expression of melatonin type 1 and 2 receptors. All patients with PCVP showed a decrease in the nocturnal melatonin excretion fraction and a correlation with higher severity of depressive (r = −0.72) and anxiety (r = −0.66) symptoms. Reduced values of the 6-hydroxymelatonin sulfate (6-SM) in the 1st (r = 0.45), 2nd (r = 0.39), and 3rd (r = 0.51) groups before treatment was associated with periods of increased BP. The achievement of melatonin excretion reference values and normalization of biochemical parameters of carbohydrate and lipid metabolism, daily BP profile, and psychophysiological state were noted in all three patients’ groups, with a more pronounced effect in group 3.

Conclusion

Low nocturnal melatonin excretion levels are associated with greater severity of clinical symptoms and a higher risk of death in patients with PCVP. Therefore, comprehensive therapy may be more effective for correcting this disease.

Melatonin Attenuates Sepsis-Induced Small-Intestine Injury by Upregulating SIRT3-Mediated Oxidative-Stress Inhibition, Mitochondrial Protection, and Autophagy Induction

Melatonin reportedly alleviates sepsis-induced multi-organ injury by inducing autophagy and activating class III deacetylase Sirtuin family members (SIRT1-7). However, whether melatonin attenuates small-intestine injury along with the precise underlying mechanism remain to be elucidated. To investigate this, we employed cecal ligation and puncture (CLP)- or endotoxemia-induced sepsis mouse models and confirmed that melatonin treatment significantly prolonged the survival time of mice and ameliorated multiple-organ injury (lung/liver/kidney/small intestine) following sepsis. Melatonin partially protected the intestinal barrier function and restored SIRT1 and SIRT3 activity/protein expression in the small intestine. Mechanistically, melatonin treatment enhanced NF-κB deacetylation and subsequently reduced the inflammatory response and decreased the TNF-α, IL-6, and IL-10 serum levels; these effects were abolished by SIRT1 inhibition with the selective blocker, Ex527. Correspondingly, melatonin treatment triggered SOD2 deacetylation and increased SOD2 activity and subsequently reduced oxidative stress; this amelioration of oxidative stress by melatonin was blocked by the SIRT3-selective inhibitor, 3-TYP, and was independent of SIRT1. We confirmed this mechanistic effect in a CLP-induced sepsis model of intestinal SIRT3 conditional-knockout mice, and found that melatonin preserved mitochondrial function and induced autophagy of small-intestine epithelial cells; these effects were dependent on SIRT3 activation. This study has shown, to the best of our knowledge, for the first time that melatonin alleviates sepsis-induced small-intestine injury, at least partially, by upregulating SIRT3-mediated oxidative-stress inhibition, mitochondrial-function protection, and autophagy induction.

Protective Effects of Melatonin against Severe Burn-Induced Distant Organ Injury: A Systematic Review and Meta-Analysis of Experimental Studies

Extensive burns result in a local wound response and distant-organ injury (DOI) caused by oxidative-stress and inflammation. Melatonin (MT) shows promise in alleviating oxidative-stress and inflammation, but its role in thermal injury is largely unexplored. The present systematic review and meta-analysis were designed to assess the effects of MT on oxidative-stress and inflammatory markers against severe burn-induced DOI. Mean difference (MD)/standard mean difference (SMD) with 95% confidence interval (CI) were estimated using fixed-effect/random-effects models. Eighteen experimental studies met the inclusion criteria. Compared with the control group, MT significantly decreased the levels of malondialdehyde (SMD, −1.03; 95% CI, −1.30, −0.76, p < 0.00001) and 4-hydroxynonenal (MD, −1.06; 95% CI, −1.57, −0.56, p < 0.0001). Additionally, MT increased the levels of glutathione (SMD, 1.94; 95% CI, 1.27, 2.61, p < 0.00001) and superoxide-dismutase (SMD, 0.76; 95% CI, 0.08, 1.45, p = 0.03). Finally, MT significantly decreased the levels of tumor necrosis factor-α (SMD, −1.34; 95% CI, −1.92 to −0.77; p < 0.00001) and C-reactive protein (MD, −12.67; 95% CI, −16.72 to −8.62; p < 0.00001). Meta-analysis indicates that severe burn followed by immediate MT (10 mg/kg) intervention shows significant beneficial effects after 24-h against DOI by regulating oxidative-stress and the inflammatory response.

Rumen-Protected 5-Hydroxytryptophan Improves Sheep Melatonin Synthesis in the Pineal Gland and Intestinal Tract

BACKGROUND Based on the extensive biological effects of melatonin (MLT), it is beneficial to increase the MLT content in the bodies of animals at a specific physiological stage. This study was conducted to investigate the effect of a diet supplemented with rumen-protected (RP) 5-hydroxytryptophan (5-HTP) on the pineal gland and intestinal tract MLT synthesis of sheep. MATERIAL AND METHODS Eighteen Kazakh sheep were assigned randomly to 3 diet groups: control group (CT, corn-soybean meal basal diet), CT+111 group (111 mg/kg BW RP 5-HTP), and CT+222 group (222 mg/kg BW RP 5-HTP). The gene expressions of aromatic amino acid decarboxylase (AADC), arylalkylamine N-acetyltransferase (AA-NAT), hydroxyindole-O-methyltransferase (HIOMT), monoamine oxidase A (MAOA), and the intermediates of MLT synthesis were observed from the pineal gland and intestinal tract by the reverse transcription (RT)-PCR method. The 5-HTP, 5-HT, N-acetylserotonin (NAS), MLT, and 5-hydroxyindole acetic acid (5-HIAA) contents in the pineal gland and intestinal tract were analyzed by ultra-high-performance liquid chromatography-tandem mass spectrometry. RESULTS The study showed that the pineal gland HIOMT expression (P<0.05), MLT (P<0.05) and 5-HIAA (P<0.05) levels in the 222 mg/kg group significantly increased compared to those in the CT and CT+111 mg/kg groups. In addition, the AADC (P<0.01) and AA-NAT (P<0.05) gene expression levels in the duodenum and jejunum were increased by the supplementation of RP 5-HTP. CONCLUSIONS Rumen-protected 5-hydroxytryptophan promoted melatonin synthesis in the pineal gland and intestinal tract during the natural light period.

Sodium butyrate protects mice from the development of the early signs of non-alcoholic fatty liver disease: role of melatonin and lipid peroxidation

Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver diseases worldwide with universally accepted treatments still lacking. Oral supplementation of sodium butyrate (SoB) has been suggested to attenuate liver damage of various aetiologies. Our study aimed to further delineate mechanisms involved in the SoB-dependent hepatic protection using a mouse model of fructose-induced NAFLD and in in vitro models. C57BL/6J mice were either pair-fed a fructose-enriched liquid diet ±0·6 g/kg body weight per d SoB or standard chow for 6 weeks. Markers of liver damage, intestinal barrier function, glucose metabolism, toll-like receptor-4 (TLR-4) and melatonin signalling were determined in mice. Differentiated human carcinoma colon-2 (Caco-2) and J774A.1 cells were used to determine molecular mechanisms involved in the effects of SoB. Despite having no effects on markers of intestinal barrier function and glucose metabolism or body weight gain, SoB supplementation significantly attenuated fructose-induced hepatic TAG accumulation and inflammation. The protective effects of SoB were associated with significantly lower expression of markers of the TLR-4-dependent signalling cascade, concentrations of inducible nitric oxide synthase (iNOS) protein and 4-hydroxynonenal protein adducts in liver. Treatment with SoB increased melatonin levels and expression of enzymes involved in melatonin synthesis in duodenal tissue and Caco-2 cells. Moreover, treatment with melatonin significantly attenuated lipopolysaccharide-induced expression of iNOS and nitrate levels in J774A.1 cells. Taken together, our results indicated that the protective effects of SoB on the development of fructose-induced NAFLD in mice are associated with an increased duodenal melatonin synthesis and attenuation of iNOS induction in liver.

Gut melatonin response to microbial infection in carp Catla catla

The purpose of present study was to demonstrate the response of gut melatoninergic system to Aeromonas hydrophila infection for 3 or 6 days and search for its correlation with the activity of different antioxidative and digestive enzymes to focus their interplay under pathophysiological conditions in carp (Catla catla). Microscopic study of gut in infected fish revealed degenerative changes in the tunica mucosa and lamina propria layers with sloughed off epithelial cells in the lumen. The activity of each digestive enzyme was reduced, but the levels of melatonin, arylalkylamine-N-acetyl transferase protein, the key regulator of melatonin biosynthesis, and different enzymatic antioxidants in gut were gradually and significantly increased with the progress of infection. Gut melatonin concentrations in A. hydrophila challenged carp by showing a positive correlation with the activity of each antioxidative enzyme, and a negative correlation with different digestive enzymes argued in favor of their functional relation, at least, during pathological stress. Moreover, parallel changes in the gut and serum melatonin titers indicated possible contribution of gut to circulating melatonin. Collectively, present carp study provided the first data to suggest that endogenous gut melatonin may be implicated to the mechanism of response to microbial infections in any fish species.

Animal models in burn research

Burn injury is a severe form of trauma affecting more than 2 million people in North America each year. Burn trauma is not a single pathophysiological event but a devastating injury that causes structural and functional deficits in numerous organ systems. Due to its complexity and the involvement of multiple organs, in vitro experiments cannot capture this complexity nor address the pathophysiology. In the past two decades, a number of burn animal models have been developed to replicate the various aspects of burn injury, to elucidate the pathophysiology, and to explore potential treatment interventions. Understanding the advantages and limitations of these animal models is essential for the design and development of treatments that are clinically relevant to humans. This review aims to highlight the common animal models of burn injury in order to provide investigators with a better understanding of the benefits and limitations of these models for translational applications. While many animal models of burn exist, we limit our discussion to the skin healing of mouse, rat, and pig. Additionally, we briefly explain hypermetabolic characteristics of burn injury and the animal model utilized to study this phenomena. Finally, we discuss the economic costs associated with each of these models in order to guide decisions of choosing the appropriate animal model for burn research.

Evidence for simvastatin anti-inflammatory actions based on quantitative analyses of NETosis and other inflammation/oxidation markers

Simvastatin (SMV) has been shown to exhibit promising anti-inflammatory properties alongside its classic cholesterol lowering action. We tested these emerging effects in a major thermal injury mouse model (3rd degree scald, ~20% TBSA) with previously documented, inflammation-mediated intestinal defects. Neutrophil extracellular traps (NETs) inflammation measurement methods were used alongside classic gut mucosa inflammation and leakiness measurements with exogenous melatonin treatment as a positive control. Our hypothesis is that simvastatin has protective therapeutic effects against early postburn gut mucosa inflammation and leakiness. To test this hypothesis, we compared untreated thermal injury (TI) adult male mice with TI littermates treated with simvastatin (0.2 mg/kg i.p., TI + SMV) immediately following burn injury and two hours before being sacrificed the day after; melatonin-treated (Mel) (1.86 mg/kg i.p., TI + Mel) mice were compared as a positive control. Mice were assessed for the following: (1) tissue oxidation and neutrophil infiltration in terminal ileum mucosa using classic carbonyl, Gr-1, and myeloperoxidase immunohistochemical or biochemical assays, (2) NETosis in terminal ileum and colon mucosa homogenates and peritoneal and fluid blood samples utilizing flow cytometric analyses of the surrogate NETosis biomarkers, picogreen and Gr-1, and (3) transepithelial gut leakiness as measured in terminal ileum and colon with FITC-dextran and transepithelial electrical resistance (TEER). Our results reveal that simvastatin and melatonin exhibit consistently comparable therapeutic protective effects against the following: (1) gut mucosa oxidative stress as revealed in the terminal ileum by markers of protein carbonylation as well as myeloperoxidase (MPO) and Gr-1 infiltration, (2) NETosis as revealed in the gut milieu, peritoneal lavage and plasma utilizing picogreen and Gr-1 flow cytometry and microscopy, and (3) transepithelial gut leakiness as assessed in the ileum and colon by FITC-dextran leakiness and TEER. Thus, simvastatin exhibits strong acute anti-inflammatory actions associated with marked decreases in gut tissue and systemic NETosis and decreased gut mucosa leakiness.

Expression of melatonin synthesizing enzymes in Helicobacter pylori infected gastric mucosa

Helicobacter pylori colonization of gastric mucosa causes pain of unknown etiology in about 15-20% of infected subjects. The aim of the present work was to determine the level of expression of enzymes involved in the synthesis of melatonin in gastric mucosa of asymptomatic and symptomatic H. pylori infected patients. To diagnose H. pylori infection, histological analysis and the urea breath test (UBT C13) were performed. The levels of mRNA expression of arylalkylamine-N-acetyltransferase (AA-NAT) and acetylserotonin methyltransferase (ASMT) were estimated in gastric mucosa with RT-PCR. The level of AA-NAT expression and AMST was decreased in H. pylori infected patients and was increased after H. pylori eradication. We conclude that decreased expression of melatonin synthesizing enzymes, AA-NAT and ASMT, in patients with symptomatic H. pylori infection returns to normal level after H. pylori eradication.

Melatonin inhibits alcohol-induced increases in duodenal mucosal permeability in rats in vivo

Increased intestinal permeability is often associated with epithelial inflammation, leaky gut, or other pathological conditions in the gastrointestinal tract. We recently found that melatonin decreases basal duodenal mucosal permeability, suggesting a mucosal protective mode of action of this agent. The aim of the present study was to elucidate the effects of melatonin on ethanol-, wine-, and HCl-induced changes of duodenal mucosal paracellular permeability and motility. Rats were anesthetized with thiobarbiturate and a ~30-mm segment of the proximal duodenum was perfused in situ. Effects on duodenal mucosal paracellular permeability, assessed by measuring the blood-to-lumen clearance of ⁵¹Cr-EDTA, motility, and morphology, were investigated. Perfusing the duodenal segment with ethanol (10 or 15% alcohol by volume), red wine, or HCl (25-100 mM) induced concentration-dependent increases in paracellular permeability. Luminal ethanol and wine increased, whereas HCl transiently decreased duodenal motility. Administration of melatonin significantly reduced ethanol- and wine-induced increases in permeability by a mechanism abolished by the nicotinic receptor antagonists hexamethonium (iv) or mecamylamine (luminally). Signs of mucosal injury (edema and beginning of desquamation of the epithelium) in response to ethanol exposure were seen only in a few villi, an effect that was histologically not changed by melatonin. Melatonin did not affect HCl-induced increases in mucosal permeability or decreases in motility. Our results show that melatonin reduces ethanol- and wine-induced increases in duodenal paracellular permeability partly via an enteric inhibitory nicotinic-receptor dependent neural pathway. In addition, melatonin inhibits ethanol-induced increases in duodenal motor activity. These results suggest that melatonin may serve important gastrointestinal barrier functions.

Preclinical efficacy of melatonin to reduce methotrexate-induced oxidative stress and small intestinal damage in rats

BACKGROUND

Methotrexate is widely used as a chemotherapeutic agent for leukemia and other malignancies. The efficacy of this drug is often limited by mucositis and intestinal injury, which are the major causes of morbidity in children and adults.

AIM

The present study investigates whether melatonin, a powerful antioxidant, could have a protective effect.

METHOD

Rats were pretreated with melatonin (20 and 40 mg/kg body weight) daily 1 h before methotrexate (7 mg/kg body weight) administration for three consecutive days. After the final dose of methotrexate, the rats were sacrificed and the small intestine was used for light microscopy and biochemical assays. Intestinal homogenates were used for assay of oxidative stress parameters malondialdehyde and protein carbonyl content, and myeloperoxidase activity, a marker of neutrophil infiltration as well as for the activities of the antioxidant enzymes.

RESULT

Pretreatment with melatonin had a dose-dependent protective effect on methotrexate (MTX)-induced alterations in small intestinal morphology. Morphology was saved to some extent with 20 mg melatonin pretreatment and near normal morphology was achieved with 40 mg melatonin pretreatment. Biochemically, pretreatment with melatonin significantly attenuated MTX-induced oxidative stress (P < 0.01 for MDA, P < 0.001 for protein carbonyl content) and restored the activities of the antioxidant enzymes (glutathione reductase P < 0.05, superoxide dismutase P < 0.01).

CONCLUSION

The results of the present study demonstrate that supplementation by exogenous melatonin significantly reduces MTX-induced small intestinal damage, indicating that it may be beneficial in ameliorating MTX-induced enteritis in humans.

Melatonin Protection against Burn-Induced Hepatic Injury by Down-Regulation and Nuclear Factor Kappa B Activation

Melatonin exhibits a wide variety of biological activity including antioxidant and anti-inflammatory effects. We have previously reported its protective effect on hepatic oxidative hepatic injury in burns. In this study, we investigated the role of nuclear factor kappa B (NF-kB) in melatonin-mediated protection against liver injury by using the burned-rat model. Melatonin (N-acetyl-5-methoxytriptamin, 10mg/kg (-1), i.p.) was administered immediately and 12 hours after thermal skin injury. Hepatic NF-kB expression was determined by Western blotting. TNF-α level in liver homogenate was quantified using enzyme-linked immunosorbent assay (ELISA) kit. Plasma aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were determined to assess liver injury at the 24th hour after burns. Thermal skin injury caused significant elevation of hepatic NF-kB expression by 48%, TNF-α level by 55% and plasma AST and ALT activities by 2- and 3-fold, respectively, in comparison with normal control rats. Treatment with melatonin decreased significantly elevated hepatic NF-kB activity and TNF-α, maintaining the levels close to the control values Melatonin suppressed the elevation of plasma AST and ALT activities (p<0.001), which remained significantly increased compared to controls. In conclusion, thermal skin injury causes hepatic NF-kB activation that may mediate the release of hepatic TNF-α and contribute to liver damage. Melatonin protects against burn-induced hepatic injury as to a certain extent this effect may result from the suppression of NF-kB-mediated inflammatory response.