Melatonin protects against gastric ulceration and increases the efficacy of ranitidine and omeprazole in reducing gastric damage

Melatonin protects against ketorolac induced gastric mucosal toxic injuries through molecular mechanism associated with the modulation of Arylakylamine N-Acetyltransferase (AANAT) activity

Ketorolac tromethamine (KT), is a widely used non-steroidal anti-inflammatory drug (NSAID) for treating moderate to severe pain. However, the use of KT has been restricted due to its highly toxic attributes that lead to severe gastric ulceration and bleeding. The protective effects of exogenous melatonin (MT) has been reported in conditions associated with gastro-intestinal disorders. This study aims at exploring the role of gastric endogenous MT level and it's metabolizing enzyme AANAT, at the onset of ketorolac mediated toxicities in the gastric mucosa. Gastric mucosal damage was induced in experimental rats by oral administration of graded doses of KT, where 50 mg/kg b.w. of KT was observed to incur maximum gastric lesions. However, gastric damages were found to be protected in rats, pre-treated with 60 mg/kg b.w. of MT. Post-sacrifice, mean ulcer index, oxidative status, total melatonin levels and enzyme activities associated with MT biosynthesis and catabolism were estimated. The results reveal that KT decreases AANAT activity with a concomitant decline in endogenous MT level which cumulatively aggravates gastric toxicity. Moreover, exogenous MT administration has been found to be protective in ameliorating this ulcerogenic process in rats, challenged with KT. Biochemical and histo-pathological observations revealed the reduction in oxidative stress level and replenishment of depleted gastric MT levels in MT pre-treated animals, which might be the causative factors in conferring protection to the gastric tissues and residing mitochondria. The results revealed a correlation between depleted gastric MT level and ulcer formation, which unveiled a novel ulcerogenic mechanism. This may bring forth future therapeutic relevance for treating patients suffering from KT mediated acute gastric toxicities.

Gut melatonin: A potent candidate in the diversified journey of melatonin research

After being discovered from the bovine pineal gland by Aaron Lerner and co-workers in the year 1958, various distinguished researchers have reported melatonin (5-methoxy-N-acetyl-tryptamine) from several extra-pineal sources, including the gastrointestinal tract (GIT). In the year 1974, Raikhlin and Kvetnoy first detected this molecule in the gastrointestinal tissue. Later, within the last 45 years, many renowned investigators found that the GIT is a rich source of melatonin, in addition to the pineal gland. In the carp gut, the estimation of Arylalkylamine-N-acetyltransferase (AANAT) mRNA/protein levels, which is the rate-determining enzyme for melatonin biosynthesis in the pineal gland, confirmed the endogenous synthesis of melatonin. The remarkable feature of the pineal gland melatonin is its rhythmic synthesis with a peak at dark-phase and lowest at light-phase in synchronization with seasonal environmental light-dark (LD) cycle. Recent studies on carp demonstrated that the melatonin concentrations and the AANAT protein intensities in different gut segments underwent significant daily fluctuations. However, compared to the melatonin rhythm in the pineal gland, the melatonin profiles in gut tissue displayed daily rhythm in parallel with the feeding cycle of the carp, irrespective of LD conditions of the environment. Notably, in carp, the temporal pattern of the gut melatoninergic system found to vary with the environmental non-photic signal(s), such as food entrainment factors (viz. availability of food, timing of food supply, number(s) of feed per day, quality of food) those act as the most dependable synchronizer(s) in daily rhythm characteristics of gut melatonin and AANAT. Thereby in this review, it appears meaningful to highlight the existing data on the mode of synthesis of melatonin in cells of the digestive tract, and most importantly, the regulation of its synthesis. Finally, in comparison with the dynamic actions of melatonin derived from the pineal gland, this review will lead to underline the role of gut-derived melatonin in a variety of physiological functions.

Agomelatine prevents indomethacin-induced gastric ulcer in rats

BACKGROUND

Gastric ulcer is a very common gastrointestinal disease that may be dangerous and even may lead to death. The current study was conducted to detect the prophylactic effects of agomelatine on indomethacin-induced gastric ulcer.

METHODS

In this study, a total of 5 groups were created as the sham, ulcer, omeprazole, agomelatine 1 mg/kg and agomelatine 5 mg/kg groups. The effects of agomelatine on indomethacin-induced gastric injury were investigated. Total antioxidant and oxidant levels; the oxidant parameters like oxidative stress index and the inflammation markers such as tumor necrosis factor-α, interleukin-1β, interleukin-6 and interleukin-10 levels in stomach tissue were determined by ELISA. In addition, the gastric mucosal injury occurred in stomach wall was examined with histopathological methods.

RESULTS

While the levels of the inflammatory markers, total oxidant status and oxidative stress index increased at an obvious level especially in the indomethacin group, the total antioxidant status levels decreased. It was observed that these parameters were improved at a significant level in agomelatine 1 mg/kg and agomelatine 5 mg/kg groups when compared to ulcer group; and the results were similar to omeprazole group. It was also observed that our histopathological findings were consistent with all our other results.

CONCLUSIONS

The results of this study showed that agomelatine usage in indomethacin-induced gastric ulcer model provides beneficial results.

Petroselinum Crispum is Effective in Reducing Stress-Induced Gastric Oxidative Damage

Background:

Oxidative stress has been shown to play a principal role in the pathogenesis of stress-induced gastric injury. Parsley (Petroselinum crispum) contains many antioxidants such as flavanoids, carotenoids and ascorbic acid.

Aims:

In this study, the histopathological and biochemical results of nutrition with a parsley-rich diet in terms of eliminating stress-induced oxidative gastric injury were evaluated.

Study Design:

Animal experimentation

Methods:

Forty male Wistar albino rats were divided into five groups: control, stress, stress + standard diet, stress + parsley-added diet and stress + lansoprazole (LPZ) groups. Subjects were exposed to 72 hours of fasting and later immobilized and exposed to the cold at +4 degrees for 8 hours to create a severe stress condition. Samples from the animals’ stomachs were arranged for microscopic and biochemical examinations.

Results:

Gastric mucosal injury was obvious in rats exposed to stress. The histopathologic damage score of the stress group (7.00±0.57) was higher than that of the control group (1.50±0.22) (p<0.05). Significant differences in histopathologic damage score were found between the stress and stress + parsley-added diet groups (p<0.05), the stress and stress + standard diet groups (p<0.05), and the stress and stress + LPZ groups (p<0.05). The mean tissue malondialdehyde levels of the stress + parsley-added group and the stress + LPZ group were lower than that of the stress group (p<0.05). Parsley supported the cellular antioxidant system by increasing the mean tissue glutathione level (53.31±9.50) and superoxide dismutase (15.18±1.05) and catalase (16.68±2.29) activities.

Conclusion:

Oral administration of parsley is effective in reducing stress-induced gastric injury by supporting the cellular antioxidant defence system.

The preventive effect of β3 adrenoceptor stimulation against experimentally induced reflux esophagitis

A β3 adrenoceptor agonist plays an important regulatory role in stimulation of thermogenesis and lipolysis and it appears to have anti-ulcer and spasmolytic effects. So the present aim was to examine the effect of BRL 37344 (a selective B3 adrenoceptor agonist) on reflux esophagitis.

METHODS

Forty-eight rats were divided into twelve sham-operated with BRL 37344 and/or omeprazole with or without indomethacin. RE was induced in rats, then gastric acid output, pH, plasma nitric oxide (NO), esophageal PGE2, malondialdehyde (MDA) and reduced glutathione (GSH) were measured and the esophageal injury was assessed by macroscopic damage score.

RESULTS

Pretreatment with BRL significantly increased plasma NO, GSH, decreased acid output, esophageal MDA and esophageal injury in comparison to pretreatment. In addition, there was a no significant increase in esophageal PGE2.

CONCLUSION

It can be concluded that BRL 37344 has an anti-oxidant protective effect in rats with RE.

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

AIM

Increased intestinal epithelial permeability is associated with intestinal inflammation and dysfunction. The aim of the present study was to investigate the role of long-term oral melatonin administration on ethanol-induced increases in duodenal mucosal permeability and hypermotility.

METHODS

Male Sprague-Dawley rats were administered melatonin in their tap water (0.1 mg mL(-1) or 0.5 mg mL(-1) ) for 2 or 4 weeks. After the treatment period, the rats were anaesthetized with Inactin(®) , and a 30-mm duodenal segment was perfused in situ. The effects on duodenal mucosal paracellular permeability, bicarbonate secretion, fluid flux and motor activity were studied. The expression levels of the tight junction components, zona occludens (ZO)-1, ZO-2, and ZO-3, claudin-2, claudin-3, claudin-4, occludin, and myosin light chain kinase and of the melatonin receptors MT1 and MT2 were assessed using qRT-PCR.

RESULTS

Melatonin administration for 2 weeks significantly reduced the basal paracellular permeability, an effect that was absent after 4 weeks. Perfusing the duodenal segment with 15% ethanol induced marked increases in duodenal paracellular permeability, bicarbonate secretion and motor activity. Melatonin for 2 weeks dose-dependently reduced ethanol-induced increases in permeability and motor activity. Four weeks of melatonin administration reduced the ethanol-induced increases in duodenal motility and bicarbonate secretion but had no effect on the increases in permeability. Two weeks of melatonin administration upregulated the expression of MT1 and MT2 , although both were downregulated after 4 weeks. Melatonin downregulated the expression of ZO-3 and upregulated the expression of claudin-2, even as all other mRNA-levels investigated were unaffected.

CONCLUSION

Although further studies are needed, our data demonstrate that melatonin administration markedly improves duodenal barrier functions, suggesting its utility in clinical applications when intestinal barrier functions are compromised.

Protective effect of antioxidant rich aqueous curry leaf (Murraya koenigii) extract against gastro-toxic effects of piroxicam in male Wistar rats

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Piroxicam causes gastric ulceration through oxidative stress.

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Curry leaf extract protects against piroxicam induced gastric injury.

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Antioxidant mechanism(s) are involved in such protection.

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The extract may have future therapeutic potential.

Piroxicam (chemically 4-hydroxy-2-methyl-N-2-pyridinyl-2H-1,2-benzothiazine-3-carboxamide), a classical non-steroidal anti-inflammatory drug (NSAID) is orally administered to arthritic patients. Inhibition of prostaglandin E₂ (PGE₂) synthesis and subsequent free hydroxyl radical generation in vivo exert gastro-toxic side effects on piroxicam treatment. Leaves of curry plant are rich in antioxidants with prolific free radical scavenging activities. This led us to investigate the efficiency of the use of curry leaves in ameliorating piroxicam induced gastric damage. Piroxicam was orally (30 mg per kg body weight) administered in male albino Wistar rats to generate gastric ulcers. These rats were orally fed with graded doses of aqueous extract of curry or Murraya koenigii leaves (Cu LE) prior to piroxicam administration. Oxidative stress biomarkers, activities of antioxidant and pro-oxidant enzymes, mucin content and nature, PGE₂ level, activities of mitochondrial enzymes and histomorphology of gastric tissues were studied. Piroxicam treatment altered all the above mentioned parameters whereas, curry leaf extract pre-treated animals were protected against piroxicam induced alterations. Hence, the protective action of the antioxidant rich Cu LE was investigated to propose a new combination therapy or dietary management to arthritic patients using piroxicam.

Melatonin decreases duodenal epithelial paracellular permeability via a nicotinic receptor-dependent pathway in rats in vivo

Intestinal epithelial intercellular tight junctions (TJs) provide a rate-limiting barrier restricting passive transepithelial movement of solutes. TJs are highly dynamic areas, and their permeability is changed in response to various stimuli. Defects in the intestinal epithelial TJ barrier may contribute to intestinal inflammation or leaky gut. The gastrointestinal tract may be the largest extrapineal source of endogenous melatonin. Melatonin released from the duodenal mucosa is a potent stimulant of duodenal mucosal bicarbonate secretion (DBS). The aim of this study was to elucidate the role of melatonin in regulating duodenal mucosal barrier functions, including mucosal permeability, DBS, net fluid flux, and duodenal motor activity, in the living animal. Rats were anesthetized with thiobarbiturate, and a ~30-mm segment of the proximal duodenum with an intact blood supply was perfused in situ. Melatonin and the selective melatonin receptor antagonist luzindole were perfused luminally or given intravenously. Effects on permeability (blood-to-lumen clearance of (51)Cr-EDTA), DBS, mucosal net fluid flux, and duodenal motility were monitored. Luminal melatonin caused a rapid decrease in paracellular permeability and an increase in DBS, but had no effect on duodenal motor activity or net fluid flux. Luzindole did not influence any of the basal parameters studied, but significantly inhibited the effects of melatonin. The nonselective and noncompetitive nicotinic acetylcholine receptor antagonist mecamylamine abolished the effect of melatonin on duodenal permeability and reduced that on DBS. In conclusion, these findings provide evidence that melatonin significantly decreases duodenal mucosal paracellular permeability and increases DBS. The data support the important role of melatonin in the neurohumoral regulation of duodenal mucosal barrier.

New perspectives in melatonin uses

This review summarizes the metabolism, secretion, regulation and sites of action of melatonin. An updated description of the melatonin receptors, including their signal transduction mechanisms, distribution and characterization of receptor genes, is given. Special emphasis is focused on the clinical aspects and potential uses of melatonin in the sleep-wake rhythms, in the immune function, in cancer therapy, in neuroprotection against oxidative damage and antioxidant activities in different tissues. Finally, combined effects of melatonin with other drugs are discussed.

Secretion of melatonin and 6-sulfatoxymelatonin urinary excretion in functional dyspepsia

AIM: To evaluate blood concentration of melatonin and urinary excretion of its metabolite, 6-sulfatoxymelatonin (6-OHMS), in functional dyspepsia (FD).

METHODS: Ninety individuals were enrolled in the study: 30 in each study group: patients with postprandial distress syndrome (PDS), epigastric pain syndrome (EPS), and controls. Blood samples were drawn at 02:00 and 09:00 h and 24-h urine collection was performed. Serum melatonin and urinary 6-OHMS concentrations were measured by enzyme-linked immunosorbent assay.

RESULTS: Serum melatonin concentration at night and in the morning was significantly (P < 0.001) higher in PDS patients [at 02:00 h-93.3 pg/mL, quartile range (QR): 79.8-116.2; at 09.00 h-14.3 pg/mL, QR: 7.06-19.0] than in EPS (57.2 pg/mL, QR: 42.6-73.1; 8.1 pg/mL, QR: 4.1-9.3) and control patients (57.7 pg/mL, QR: 51.2-62.5; 8.1 pg/mL, QR: 5.4-10.3). A similar relationship was observed for urinary 6-OHMS excretion. Patients with severe PDS symptoms had a higher melatonin concentration than these with moderate syndromes, whereas patients with severe EPS had a lower urinary 6-OHMS excretion than patients with moderate symptoms.

CONCLUSION: Evaluation of melatonin serum concentrations and 24-h urinary 6-OHMS excretion are useful methods for differential diagnosis of various clinical forms of FD.

Melatonin or L-tryptophan accelerates healing of gastroduodenal ulcers in patients treated with omeprazole

Melatonin and L-tryptophan (Trp) are highly gastroprotective in humans, but no study has assessed their impact on healing of chronic gastroduodenal ulcers in humans. Three groups (A, B and C) of 14 idiopathic patients in each treatment group with gastroduodenal chronic ulcers were treated with omeprazole (20 mg twice daily) combined either with placebo (group A), melatonin (group B) or with Trp (group C). The rate of ulcer healing was determined by gastroduodenoscopy at day 0, 7, 14 and 21 after initiation of therapy. Plasma melatonin, gastrin, ghrelin and leptin were measured by RIA. On day 7, omeprazole by itself (group A) had not healed any ulcers, but four ulcers were healed with omeprazole plus melatonin and two with omeprazole plus tryptophan. At day 21, all ulcers were healed in patients treated with melatonin or Trp, but only 10-12 ulcers were healed in placebo-treated patients. After treatment with omeprazole plus melatonin (group B) or Trp (group C), plasma melatonin levels rose several-fold above initial values. Plasma gastrin level also rose significantly during treatment with omeprazole plus melatonin or Trp, but it was also significantly increased in patients treated with omeprazole plus placebo. Plasma ghrelin levels did not change significantly after treatment with melatonin or Trp, while plasma leptin increased significantly in patients treated with melatonin or Trp but not with placebo. We conclude that melatonin or Trp, when added to omeprazole treatment, accelerates ulcer healing and this likely depends mainly upon the significant increments in plasma melatonin.

A protective effect of melatonin on intestinal permeability is induced by diclofenac via regulation of mitochondrial function in mice

AIM

This study investigated the effect of intragastrically administered melatonin on intestinal mucosal permeability induced by diclofenac in mice.

METHODS

Intestinal mucosal permeability was induced in mice by intragastric administration of diclofenac (2.5 mg/kg). Melatonin was given intragastrically (10 mg/kg) once per day for 3 d after diclofenac administration. The small intestine was examined macroscopically and microscopically for pathologic injury to the intestinal mucosa. Intestinal mucosal permeability was evaluated by Evans blue and FITC-dextran methods. Mitochondrial functional parameters, including mitochondrial membrane potential, mitochondrial ATPase and succinate dehydrogenase (SDH) activity, were assessed. The malondialdehyde (MDA) and myeloperoxidase (MPO) levels were determined from small intestinal mucosal homogenates.

RESULTS

As compared with control mice, the permeability, pathologic score, MDA and MPO levels and ulceration of the intestinal mucosa were increased significantly by diclofenac treatment, and a broadened junctional complex and enlarged intercellular space were observed by transmission electron microscopy (TEM). Melatonin treatment significantly reduced the intestinal mucosal permeability, pathologic score, MDA, and MPO levels and ulceration of the intestinal mucosa. By TEM, the small intestine villus morphology and intercellular spaces were nearly normal in melatonin-treated mice. At the level of the mitochondria, melatonin treatment significantly restored the activities of ATPase and SDH.

CONCLUSION

The intestinal damage and increased intestinal permeability induced by diclofenac in mice was limited by melatonin; moreover, melatonin preserved several aspects of mitochondrial function.

Melatonin protects against isoproterenol-induced myocardial injury in the rat: antioxidative mechanisms

The present study was undertaken to explore the protective effect of melatonin against isoproterenol bitartrate (ISO)-induced myocardial injury in rat. Treatment of rats with ISO increased the level of lipid peroxidation products and decreased the reduced glutathione levels in cardiac tissue indicating that this synthetic catecholamine induces oxidative damage following oxidative stress. Pretreatment of ISO-injected rats with melatonin at a dose of 10 mg/kg body weight, i.p. prevented these changes. Additionally, melatonin also restored the activities and the levels of antioxidant enzymes which were found to be altered by ISO treatment. Treatment of rats with ISO resulted into an increased generation of hydroxyl radicals with melatonin pretreatment significantly reducing their production. Finally, treatment of rats with ISO caused a lowering of systolic pressure with reduced cardiac output and diastolic dysfunction whereas melatonin pretreatment significantly restored many of these parameters to normal. The findings document melatonin's ability to provide cardio protection at a low pharmacological dose. Melatonin has virtually no toxicity which raises the possibility of this indole being a therapeutic treatment for ischemic heart disease.

The potential therapeutic effect of melatonin in Gastro-Esophageal Reflux Disease

Background

Gastro-Esophageal Reflux Disease (GERD) defined as a condition that develops when the reflux of stomach contents causes troublesome symptoms and/or complications. Many drugs are used for the treatment of GERD such as omeprazole (a proton pump inhibitor) which is a widely used antiulcer drug demonstrated to protect against esophageal mucosal injury. Melatonin has been found to protect the gastrointestinal mucosa from oxidative damage caused by reactive oxygen species in different experimental ulcer models. The aim of this study is to evaluate the role of exogenous melatonin in the treatment of reflux disease in humans either alone or in combination with omeprazole therapy.

Methods

36 persons were divided into 4 groups (control subjects, patients with reflux disease treated with melatonin alone, omeprazole alone and a combination of melatonin and omeprazole for 4 and 8 weeks) Each group consisted of 9 persons. Persons were subjected to thorough history taking, clinical examination, and investigations including laboratory, endoscopic, record of esophageal motility, pH-metry, basal acid output and serum gastrin.

Results

Melatonin has a role in the improvement of Gastro-esophageal reflux disease when used alone or in combination with omeprazole. Meanwhile, omeprazole alone is better used in the treatment of GERD than melatonin alone.

Conclusion

The present study showed that oral melatonin is a promising therapeutic agent for the treatment of GERD. It is an effective line of treatment in relieving epigastric pain and heartburn. However, further studies are required to confirm the efficacy and long-term safety of melatonin before being recommended for routine clinical use.

Trial Registration

QA13NCT00915616

Influence of astragaloside on gastric mucosal oxygen free radicals and melatonin receptors of rats with stress ulcer

AIM: To investigate the effects of astragaloside (AST) on gene expression of melatonin receptor and oxygen free radical in gastric mucosa of rat with stress ulcer.

METHODS: A total of 48 experimental animals were equally divided into 4 groups: the control group, the model group, the AST group and the ranitidine group. The stress ulcer model was established using water immersion and restraint. The SOD activity, the MDA contents were determined using colorimetry, and the expression of melatonin receptors 1 and 2 were detected in gastric mucosa using RT-PCR.

RESULTS: Compared with the control group, the model group showed increased ulcer index and elevated MDA contents, decreased SOD activity and down-regulated mRNA expression of melatonin receptors in damaged gastric mucosa. After administration of AST, the gastric mucosal ulcer index decreased significantly (6.75 ± 4.10 vs 16.83 ± 4.96, P < 0.01) and MDA contents were relieved obviously (0.45 ± 0.07 vs 0.79 ± 0.36, P < 0.05). The SOD activity (110.62 ± 26.42 vs 71.74 ± 22.20, P< 0.05) and the expression of melatonin receptor1, 2 mRNA were significantly elevated (0.86 ± 0.12 vs 0.54 ± 0.05, 0.79 ± 0.14 vs 0.50 ± 0.10, both P < 0.01).

CONCLUSION: AST could prevent the gastric mucosal damage of rats with stress ulcer. And the mechanism of the gastric mucosal protection is perhaps concerned with regulating melatonin receptor and lessening the injury of oxygen free radicals.

Dynamic physiological and molecular changes in gastric ulcer healing achieved by melatonin and its precursor L-tryptophan in rats

Following induction of gastric ulcer in rats by serosal application of acetic acid, local mucosal necrosis ensues accompanied by a reduction in mucosal microcirculation and by almost immediate expression of inducible nitric oxide (NO) synthase (iNOS) and proinflammatory cytokines. Daily application of melatonin (20 mg/kg) or l-tryptophan (100 mg/kg) accelerates ulcer healing by affecting the cyclooxygenase-2 (COX-2)-prostaglandin (PG) system with excessive production of protective PG, especially in later period of ulcer healing. Furthermore, expression of hypoxia inducible factor, vascular-endothelial growth factor, an activation of cNOS-NO system and the stimulation of sensory nerves with the expression and release of calcitonin gene related peptide (CGRP) appear to aid the restoration of mucosal repair and microcirculation in the ulcer bed. The enhanced expression of the melatonin MT(2) receptors (MT(2)-R) combined with overexpression of key enzymes involved in biosynthesis of melatonin such as N-acetyltransferase and hydroxyindole-O-methyltransferase contribute to the acceleration of ulcer healing by this indole. Melatonin-induced acceleration of ulcer healing is also mediated by release of gastrin and ghrelin, the most potent stimulants of gastric mucosal cell proliferation and mucosal repair. These sequential steps in ulcer healing accelerated by melatonin can be interfered with by the blockade of MT(2)R, COX-2/PG and cNOS/NO systems, and by reduction in the inflammatory iNOS/NO system. Thus, melatonin and its precursor l-tryptophan, trigger the cascade of molecular events leading to the functional improvement in ulcer healing.

Melatonin as pharmacologic support in burn patients: a proposed solution to thermal injury-related lymphocytopenia and oxidative damage

OBJECTIVE

To review the data that support the clinical use of melatonin in the treatment of burn patients, with special emphasis on the stimulation of the oxidative defense system, the immune system, circadian rhythm of sleep/wakefulness, and the reduction in the toxicity of therapeutic agents used in the treatment of burn victims.

DATA SOURCE

A MEDLINE/PubMed search from 1975 to July 2006 was conducted.

STUDY SELECTION

The screening of the literature was examined using the key words: burn patients, lymphocytopenia, skin oxidative stress, antioxidant, melatonin, and free radicals.

DATA EXTRACTION AND SYNTHESIS

Thermal injury often causes damage to multiple organs remote from the original burn wound and may lead to multiple organ failure. Animal models and burn patients exhibit elevated free radical generation that may be causative in the local wound response and in the development of burn shock and distant organ injury. The suppression of nonspecific resistance and the disturbance in the adaptive immune system makes burn patients vulnerable to infections. Moreover, there is loss of sleep and the toxicity produced by drugs habitually used in the clinic for burn patients. Melatonin is a powerful antioxidant and is a potent protective agent against damage after experimental thermal injury. Some actions of melatonin as a potential supportive pharmacologic agent in burn patients include its: role as a scavenger of both oxygen and nitrogen-based reactants, stimulation of the activities of a variety of antioxidative enzymes, reduction in proinflammatory cytokines, inhibition of adhesion molecules, chronobiotic effects, and reduction in the toxicity of the drugs used in protocols to treat thermal injury patients.

CONCLUSIONS

These combined actions of melatonin, along with its low toxicity and its ability to penetrate all morphophysiologic membranes, could make it a ubiquitously acting and highly beneficial molecule in burn patients.

Therapeutic effect of melatonin in patients with functional dyspepsia

BACKGROUND AND GOAL

Melatonin may inhibit reactive oxygen species-related pathogenesis in the alimentary tract by neutralizing free radicals. In the present study we assessed the potential protective action of melatonin in ulcerlike dyspepsia.

STUDY

Sixty patients aged 19 to 39 years with the diagnosis of functional dyspepsia according to the Rome Criteria II and no Helicobacter pylori infection were involved in the study. Melatonin, at a dose of 5 mg (n=30), or placebo (n=30) were taken in the evening for a period of 12 weeks. At this time, patients were on an equivalent diet and were only to take an alkaline drug in case of the abdominal pain.

RESULTS

After 12 weeks, the dyspeptic symptoms completely subsided in 17 patients in the melatonin-treatment group (56.6%). In other 9 individuals (30.0%) a partial improvement in health was achieved, especially in the frequency and intensity of nocturnal pain. After placebo, the majority of patients (93.3%) did not experience any improvement in symptoms. Multivariate analysis indicated that melatonin (odds ratio 95.86, 95% confidence interval 3.72-2469.37, P<0.01) correlated independently with significantly improved patients health. H. pylori past infection decreased positive effect of melatonin in ulcerlike dyspepsia.

CONCLUSIONS

Melatonin can be considered as an auxiliary drug in the treatment of ulcerlike dyspepsia.

The potential of melatonin in reducing morbidity-mortality after craniocerebral trauma

Craniocerebral trauma (CCT) is the most frequent cause of morbidity-mortality as a result of an accident. The probable origins and etiologies are multifactorial and include free radical formation and oxidative stress, the suppression of nonspecific resistance, lymphocytopenia (disorder in the adhesion and activation of cells), opportunistic infections, regional macro and microcirculatory alterations, disruptive sleep-wake cycles and toxicity caused by therapeutic agents. These pathogenic factors contribute to the unfavorable development of clinical symptoms as the disease progresses. Melatonin (N-acetyl-5-methoxytryptamine) is an indoleamine endogenously produced in the pineal gland and in other organs and it is protective agent against damage following CCT. Some of the actions of melatonin that support its pharmacological use after CCT include its role as a scavenger of both oxygen and nitrogen-based reactants, stimulation of the activities of a variety of antioxidative enzymes (e.g. superoxide dismutase, glutathione peroxidase, glutathione reductase and catalase), inhibition of pro-inflammatory cytokines and activation-adhesion molecules which consequently reduces lymphocytopenia and infections by opportunistic organisms. The chronobiotic capacity of melatonin may also reset the natural circadian rhythm of sleep and wakefulness. Melatonin reduces the toxicity of the drugs used in the treatment of CCT and increases their efficacy. Finally, melatonin crosses the blood-brain barrier and reduces contusion volume and stabilizes cellular membranes preventing vasospasm and apoptosis of endothelial cells that occurs as a result of CCT.

Melatonin protects against oxidative damage and restores expression of GLUT4 gene in the hyperthyroid rat heart

To understand the mechanism of cardiovascular dysfunction in the hyperthyroid condition, the role of oxidative stress was examined in rats treated with 3,5,3'-triiodo-l-thyronine (T3). Treatment of rats daily with T3 (8 microg/100 g BW) for 15 days resulted in an increase in heart weight to body weight ratio, which was ameliorated by antioxidants, melatonin (2 mg/100 g BW) or vitamin E (4 mg/100 g BW). Both melatonin and vitamin E also inhibited rises of lipid peroxidation and hydroxyl radical generation and prevented the inhibition of Cu,Zn-superoxide dismutase in the hypertrophic heart. The expression of the glucose transporter, GLUT4, was reduced in response to T3, which was completely restored by melatonin and partially by vitamin E. However, neither antioxidant prevented down regulation of peroxisome proliferator-activated receptor-alpha in the hyperthyroid heart. Furthermore, the reduced level of myocyte enhancer factor-2, a regulator of GLUT4 transcription was restored completely by melatonin and partially by vitamin E treatment. Glucose uptake in hypertrophic left ventricular cells was also restored by these antioxidants. The expression of B-type natriuretic peptide, a marker of heart failure, was significantly increased by T3 and ameliorated by melatonin or vitamin E treatments. In general, the beneficial effects of melatonin given as a co-treatment with T3 were better than those induced by vitamin E. These data show that melatonin ameliorates hypertrophic growth of the myocardium induced by hyperthyroidism and provide an insight into the mechanism of reactive oxygen species-mediated down regulation of metabolically important genes such as GLUT4 in the heart.

Regression of gastroesophageal reflux disease symptoms using dietary supplementation with melatonin, vitamins and aminoacids: comparison with omeprazole

The prevalence of gastroesophageal reflux disease (GERD) is increasing. GERD is a chronic disease and its treatment is problematic. It may present with various symptoms including heartburn, regurgitation, dysphagia, coughing, hoarseness or chest pain. The aim of this study was to investigate if a dietary supplementation containing: melatonin, l-tryptophan, vitamin B6, folic acid, vitamin B12, methionine and betaine would help patients with GERD, and to compare the preparation with 20 mg omeprazole. Melatonin has known inhibitory activities on gastric acid secretion and nitric oxide biosynthesis. Nitric oxide has an important role in the transient lower esophageal sphincter relaxation (TLESR), which is a major mechanism of reflux in patients with GERD. Others biocompounds of the formula display anti-inflammatory and analgesic effects. A single blind randomized study was performed in which 176 patients underwent treatment using the supplement cited above (group A) and 175 received treatment of 20 mg omeprazole (group B). Symptoms were recorded in a diary and changes in severity of symptoms noted. All patients of the group A (100%) reported a complete regression of symptoms after 40 days of treatment. On the other hand, 115 subjects (65.7%) of the omeprazole reported regression of symptoms in the same period. There was statiscally significant difference between the groups (P < 0.05). This formulation promotes regression of GERD symptoms with no significant side effects.

Melatonin modulates acid/base transport in human pancreatic carcinoma cells

Melatonin was found to improve pancreatic organ function in diseased animals. To study whether pancreatic bicarbonate secretion is stimulated by melatonin, investigations were done in two human ductal pancreatic adenocarcinoma cell lines MIA PaCa-2 (MIA) and PANC-1 (PANC). Using the fluorescence pH-sensor BCECF-AM, we monitored melatonin effects on basal intracellular pH (pH(i)), and on pH(i) recovery after intracellular alkalinization produced by the removal of extracellular HCO(3) (-)/CO(2). Exposure to 1 microM melatonin for 24 hrs and presence of the indoleamine during the experiment increases the basal pH(i). Moreover, pHi recovery and HCO(3) (-) secretion are facilitated after the alkaline load. These findings are in line with the observed increase in mRNA expression of the Na(+)/HCO(3) (-)-cotransporter SLC4A4b for the uptake and the Cl(-)/HCO(3) (-)-exchanger SLC26A6 for the secretion of HCO(3) (-). The reduction in Na(+)/H(+)- exchanger SLC9A1 mRNA would favor pH(i) recovery after alkalinization, but it does not explain the initial increase in pHi. This controversial effect and the requirement for continuous presence of melatonin throughout the experiment suggest that nontranscriptional signalling may contribute to the effects of melatonin on acid/base movements. In summary, we show a stimulatory effect of melatonin on bicarbonate secretion in the pancreatic cancer cell lines which may help to prevent duodenal damage.

Effects of melatonin administration on intestinal adaptive response after massive bowel resection in rats

This study evaluates whether melatonin can improve the structure of the small intestine and enhance adaptation in an experimental model of short bowel syndrome. Thirty Sprague-Dawley rats were divided randomly into three experimental groups of 10 animals each. In one group, only laparotomy was performed and these rats served as the sham-control group (G1). The remaining 20 rats underwent 90% small bowel resection (SBR) and formed the two experimental groups: the SBR/untreated group (G2), and the SBR/melatonin-treated group (G3). Rats in the SBR/untreated group received no therapeutic treatment. Rats in the SBR/melatonin-treated group received melatonin intraperitoneally for 3 weeks. The animals were weighed daily. All rats underwent relaparotomy on day 21 of the experiment. Remnant small bowel was excised and evaluated for villus height, total mucosal thickness, and crypt cell mitosis. After the 90% SBR, all animals suffered from diarrhea and weight loss between the first and the sixth postoperative days. The body weight of the SBR/melatonin group showed significant increases at the beginning of postoperative day 10 and day 21 in comparison to that of the SBR/untreated group. The rats treated with melatonin had significantly greater villus height and crypt cell mitosis compared to the sham-control group and the SBR/untreated group. In addition, the mucosal thickness was significantly increased in the SBR/melatonin-treated group compared to the SBR/untreated rats. These observations suggest that melatonin treatment increases villus height, total mucosal thickness, and crypt cell mitosis after massive SBR and it may exert a considerable effect on the mucosal adaptive response in short bowel syndrome in rats.

Protective effect of melatonin and omeprazole against alendronat-induced gastric damage

Alendronate causes serious gastrointestinal adverse effects. We aimed to investigate if free radicals have any role in the damage induced by alendronate and if melatonin or omeprazole is protective against this damage. Rats were administered 20 mg/kg alendronate by gavage for 4 days, either alone or following treatment with melatonin or omeprazole. On the last day, following drug administration, pilor ligation was performed, and 2 hr later rats were killed and stomachs were removed. Gastric acidity and tissue ulcer index values, lipid peroxidation, and myeloperoxidase and glutathione levels, as well as the histologic appearance of the stomach tissues, were determined. Chronic oral administration of alendronate induced significant gastric damage, increasing lipid peroxidation and myeloperoxidase activity, while tissue glutathione levels decreased. Treatment with omeprazole or melatonin prevented this damage as well as the changes in biochemical parameters, and melatonin appeared to be more efficient than omeprazole in protecting the mucosa. Intraperitoneal administration of alendronate did not cause much gastric irritation. Findings of the present study suggest that alendronate induces oxidative gastric damage by a local irritant effect and that melatonin and omeprazole are protective against this damage due to their antioxidant properties.

Salivary thiocyanate/nitrite inhibits hydroxylation of 2-hydroxybenzoic acid induced by hydrogen peroxide/Fe(II) systems under acidic conditions: possibility of thiocyanate/nitrite-dependent scavenging of hydroxyl radical in the stomach

Formation of OH radicals in the stomach is possible by Fenton-type reactions, as gastric juice contains ascorbic acid (AA), iron ions and H2O2. An objective of the present study is to elucidate the effects of salivary SCN- and NO2- on the hydroxylation of salicylic acid which was induced by H2O2/Fe(II) and AA/H2O2/Fe(II) systems. Thiocyanate ion inhibited the hydroxylation of salicylic acid by the above systems in acidic buffer solutions and in acidified saliva. The inhibition by SCN- was deduced to be due to SCN- -dependent scavenging of OH radicals. Nitrite ion could enhance the SCN- -dependent inhibition of the hydroxylation induced by AA/H2O2/Fe(II) systems. The enhancement was suggested to be due to scavenging of OH radicals by NO which was formed by the reactions among AA, HNO2 and SCN- contained in the reaction mixture. The concentrations of SCN- and NO2-, which were effective for the inhibition, were in ranges of their normal salivary concentrations. These results suggest that salivary SCN- can cooperate with NO2- to protect stomach from OH radicals formed by AA/H2O2/Fe(II) systems under acidic conditions.

Melatonin protects against piroxicam-induced gastric ulceration

The antiulcer effect of melatonin on gastric lesions caused by piroxicam was studied with the intent of determining the mechanism of action of this agent. Melatonin dose-dependently lowered piroxicam and indomethacin-induced gastric damage with more than 90% inhibition at a dose of 60 mg/kg BW. Increased lipid peroxidation, augmented protein oxidation and decreased glutathione content of the gastric tissue following piroxicam treatment indicated a possible involvement of oxidative stress in this nonsteroidal anti-inflammatory drug (NSAID)-induced gastropathy. Pretreatment of rats with melatonin prevented these changes. Oral administration of piroxicam to rats caused a threefold increase in the tissue levels of hydroxyl radical generation, a change significantly attenuated by melatonin. Furthermore, a decrease in the activity of gastric peroxidase and an increase in the activity of gastric superoxide dismutase(s) (SOD) because of piroxicam treatment was attenuated by melatonin pretreatment indicating that the indole possibly exerts its gastroprotective effects through its direct as well as indirect antioxidant activities. The results of the present studies also reveal that melatonin may influence the expression of Cu-Zn SOD, catalase, cyclooxygenase as well as alpha-actinin whose levels were found to be altered, following piroxicam treatment. The current studies, therefore, document melatonin's gastroprotective ability against piroxicam-induced gastric damage and the findings raise the possibility of melatonin being considered as a co-therapy with piroxicam or other NSAIDs in reducing the gastropathy when long-term use of these nonsteroidal agents are unavoidable.

Melatonin, xanthurenic acid, resveratrol, EGCG, vitamin C and alpha-lipoic acid differentially reduce oxidative DNA damage induced by Fenton reagents: a study of their individual and synergistic actions

DNA damage generated by oxygen-derived free radicals is related to mutagenesis, carcinogenesis and aging. In the last several years, hundreds of publications have confirmed that melatonin is a potent endogenous free radical scavenger. In the present in vitro study, we have examined the efficacy of three polyphenolic antioxidants, i.e. xanthurenic acid, resveratrol (3,4',5-trihydroxy-trans-stilbene) and (-)-epigallocatechin-3-gallate (EGCG) and two classical non-polyphenolic antioxidants, i.e. vitamin C (ascorbic acid) and alpha-lipoic acid (LA, 1,2-dithiolane-3-pentanoic acid) in inhibiting *OH-induced oxidative DNA damage. We compared the efficacy of these five antioxidants with the effectiveness of melatonin (N-acetyl-5-methoxytryptamine) and we also investigated the possible synergistic effects of melatonin with the other five molecules. Using high performance liquid chromatography (HPLC), the formation of 8-hydroxy-2-deoxyguanosine (8-OH-dG) in purified calf thymus DNA treated with the Fenton reagents, chromium(III) (as CrCl3) plus hydrogen peroxide (H2O2) (Cr(III)/H2O2), was measured in the presence or absence of the antioxidants alone or in combination with melatonin. 8-OH-dG is considered a biomarker of oxidative DNA damage. Among the antioxidants tested, melatonin was the most effective of these with an IC50 = 3.6 +/- 0.1 micro m. For the other antioxidants the IC50 values were as follows: xanthurenic acid (IC50 = 7.9 +/- 0.3), resveratrol (IC50 = 10.9 +/- 0.3), EGCG (IC50 = 5.7 +/- 0.3), vitamin C (IC50 = 16.9 +/- 0.5) and LA (IC50 = 38.8 +/- 0.7). These values differ from that of melatonin with a P < 0.01. Melatonin (1 micro M) reversed the pro-oxidant effect of resveratrol (0.5 micro M) and vitamin C (0.5 micro M), had an antagonistic effect when used in combination with EGCG (1 micro M) and it exhibited synergism in combination with vitamin C (0.5 micro M) and with LA (5 micro M).

Melatonin in the duodenal lumen is a potent stimulant of mucosal bicarbonate secretion

Melatonin, originating from intestinal enterochromaffin cells, mediates vagal and sympathetic neural stimulation of the HCO secretion by the duodenal mucosa. This alkaline secretion is considered the first line of mucosal defense against hydrochloric acid discharged from the stomach. We have studied whether luminally applied melatonin stimulates the protective secretion and whether a melatonin pathway is involved in acid-induced stimulation of the secretion. Rats were anaesthetized (Inactin) and a 12-mm segment of proximal duodenum with an intact blood supply was cannulated in situ. Mucosal HCO secretion (pH-stat) and the mean arterial blood pressure were continuously recorded. Luminal melatonin at a concentration of 1.0 micro m increased (P < 0.05) the secretion from 7.20 +/- 1.35 to 13.20 +/- 1.51 micro Eq/cm/hr. The MT2 selective antagonist luzindole (600 nmol/kg, i.v.) had no effect on basal HCO secretion, but inhibited (P < 0.05) secretion stimulated by luminal melatonin. Hexamethonium (10 mg/kg i.v. followed by continuous i.v. infusion at a rate of 10 mg/kg/hr), abolishes neurally mediated rises in secretion and also inhibited (P < 0.05) the stimulation by luminal melatonin. Exposure of the lumen to acid containing perfusate (pH 2.0) for 5 min increased (P < 0.05) the HCO secretion from 5.85 +/- 0.82 to 12.35 +/- 1.51 micro Eq/cm/hr, and luzindole significantly inhibited (P < 0.05) this rise in secretion. The study thus demonstrates that luminal melatonin is a potent stimulant of duodenal HCO secretion and, furthermore, strongly suggests melatonin as an important mediator of acid-induced secretion.

Melatonin: reducing the toxicity and increasing the efficacy of drugs

Melatonin (N-acetyl-5-methoxytryptamine) is a molecule with a very wide phylogenetic distribution from plants to man. In vertebrates, melatonin was initially thought to be exclusively of pineal origin recent studies have shown, however, that melatonin synthesis may occur in a variety of cells and organs. The concentration of melatonin within body fluids and subcellular compartments varies widely, with blood levels of the indole being lower than those at many other sites. Thus, when defining what constitutes a physiological level of melatonin, it must be defined relative to a specific compartment. Melatonin has been shown to have a variety of functions, and research in the last decade has proven the indole to be both a direct free radical scavenger and indirect antioxidant. Because of these actions, and possibly others that remain to be defined, melatonin has been shown to reduce the toxicity and increase the efficacy of a large number of drugs whose side effects are well documented. Herein, we summarize the beneficial effects of melatonin when combined with the following drugs: doxorubicin, cisplatin, epirubicin, cytarabine, bleomycin, gentamicin, ciclosporin, indometacin, acetylsalicylic acid, ranitidine, omeprazole, isoniazid, iron and erythropoietin, phenobarbital, carbamazepine, haloperidol, caposide-50, morphine, cyclophosphamide and L-cysteine. While the majority of these studies were conducted using animals, a number of the investigations also used man. Considering the low toxicity of melatonin and its ability to reduce the side effects and increase the efficacy of these drugs, its use as a combination therapy with these agents seems important and worthy of pursuit.