Melatonin protects liver from intestine ischemia reperfusion injury in rats

Protective and therapeutic potential of melatonin against intestinal diseases: updated review of current data based on molecular mechanisms

INTRODUCTION

Intestinal diseases, a leading global cause of mortality and morbidity, carry a substantial socioeconomic burden. Small and large intestines play pivotal roles in gastrointestinal physiology and food digestion. Pathological conditions, such as gut dysbiosis, inflammation, cancer, therapy-related complications, ulcers, and ischemia, necessitate the urgent exploration of safe and effective complementary therapeutic strategies for optimal intestinal health.

AREAS COVERED

This article evaluates the potential therapeutic effects of melatonin, a molecule with a wide range of physiological actions, on intestinal diseases including inflammatory bowel disease, irritable bowel syndrome, colon cancer, gastric/duodenal ulcers and other intestinal disorders.

EXPERT OPINION

Due to anti-inflammatory and antioxidant properties as well as various biological actions, melatonin could be a therapeutic option for improving digestive disorders. However, more researches are needed to fully understand the potential benefits and risks of using melatonin for digestive disorders.

Low Serum Melatonin Levels Prior to Liver Transplantation in Patients with Hepatocellular Carcinoma are Associated with Lower Survival after Liver Transplantation

Melatonin administration has been associated with different benefits in animals and patients suffering from liver diseases. However, there is no published data about circulating melatonin levels in patients with hepatocellular carcinoma (HCC) who underwent liver transplantation (LT). Thus, the objective of this observational and retrospective study was to determine whether patients with HCC with lower serum melatonin levels prior to LT have a higher risk of one-year mortality after LT. We measured serum levels of melatonin, malondialdehyde (to assess lipid peroxidation), and total antioxidant capacity (to assess antioxidant state) before LT. One-year surviving LT patients (n = 129) showed higher serum levels of melatonin (p = 0.001) and total antioxidant capacity (p = 0.001) and lower serum levels of malondialheyde (p = 0.01) than non-surviving LT patients (n = 16). Logistic regression analysis showed that high serum melatonin levels prior to LT were associated with lower one-year LT mortality (odds ratio = 0.525; 95% confidence interval (CI) = 0.331–0.834; p = 0.006). We found an association between serum levels of melatonin with serum levels of malondialheyde (rho = −0.22; p = 0.01) and total antioxidant capacity (rho = 0.21; p = 0.01). Thus, the novel findings of our study were the association between high serum melatonin levels prior to LT and survival at first year after LT and the association between serum levels of melatonin with malondialheyde and total antioxidant capacity.

The beneficial effect of melatonin in brain endothelial cells against oxygen-glucose deprivation followed by reperfusion-induced injury

Melatonin has a cellular protective effect in cerebrovascular and neurodegenerative diseases. Protection of brain endothelial cells against hypoxia and oxidative stress is important for treatment of central nervous system (CNS) diseases, since brain endothelial cells constitute the blood brain barrier (BBB). In the present study, we investigated the protective effect of melatonin against oxygen-glucose deprivation, followed by reperfusion- (OGD/R-) induced injury, in bEnd.3 cells. The effect of melatonin was examined by western blot analysis, cell viability assays, measurement of intracellular reactive oxygen species (ROS), and immunocytochemistry (ICC). Our results showed that treatment with melatonin prevents cell death and degradation of tight junction protein in the setting of OGD/R-induced injury. In response to OGD/R injury of bEnd.3 cells, melatonin activates Akt, which promotes cell survival, and attenuates phosphorylation of JNK, which triggers apoptosis. Thus, melatonin protects bEnd.3 cells against OGD/R-induced injury.

Role of progesterone in melatonin-mediated protection against acute kidney injury

BACKGROUND

Melatonin is released by pineal gland and maintains circadian rhythm in the body. It has been reported as renoprotective agent because of its antioxidant property. Recently, a cross talk between progesterone and melatonin has been observed in various preclinical studies. The present study investigated the involvement of progesterone receptors in melatonin-mediated protection against ischemia reperfusion induced acute kidney injury (AKI) in rats.

MATERIALS AND METHODS

The rats were subjected to bilateral renal ischemia for 40 min followed by reperfusion for 24 h to induce AKI. The AKI was assessed by measuring creatinine clearance, serum urea, uric acid level, potassium level, fractional excretion of sodium, lactate dehydrogenase activity, and microproteinuria. The oxidative stress in renal tissues was assessed by quantification of myeloperoxidase activity, thiobarbituric acid reactive substances, superoxide anion generation, reduced glutathione level, and catalase activity. The hematoxylin-eosin staining was carried out to observe histopathologic changes in renal tissues. The melatonin (4 and 10 mg/kg, intraperitoneally) and progesterone receptor antagonist mifepristone (5 mg/kg, intraperitoneally) were used in the present study.

RESULTS

The renal ischemia reperfusion induced AKI as indicated by significant change in serum, urinary, and tissue parameters that was ameliorated by prior treatment with melatonin. No significant difference in serum progesterone level was observed between various groups used in the present study. The prior administration of mifepristone abolished melatonin-mediated protection against AKI.

CONCLUSIONS

It is concluded that melatonin treatment affords protection against ischemia reperfusion induced AKI. Moreover, progesterone receptors are essentially involved in mediating protective role of melatonin against AKI in rats.

Melatonin protection against burn-induced liver injury. A review

Severe thermal injury may be complicated by dysfunction of organs distant from the original burn wound, including the liver, and represents a serious clinical problem. Although pathophysiology of burn-induced liver injury remains unclear, increasing evidence implicate activation of inflammatory response, oxidative stress, endothelial dysfunction and microcirculatory disorders as the main mechanisms of hepatic injury. Several studies suggest melatonin as a multifunctional indolamine that counteracts some of the pathophysiologic steps and displays significant beneficial effects against burn-induced cellular injury. This review summarizes the role of melatonin in restricting the burn-induced hepatic injury and focuses on its effects on oxidative stress, inflammatory response, endothelial dysfunction and microcirculatory disorders as well as on signaling pathways such as regulation of nuclear erythroid 2-related factor 2 (Nrf2) and nuclear factor-kappaB (NF-kB). Further studies are necessary to elucidate the modulating effect of melatonin on the transcription factor responsible for the regulation of the pro-inflammatory and antioxidant genes involved in burn injuries.

A review of the molecular aspects of melatonin's anti-inflammatory actions: recent insights and new perspectives

Melatonin is a highly evolutionary conserved endogenous molecule that is mainly produced by the pineal gland, but also by other nonendocrine organs, of most mammals including man. In the recent years, a variety of anti-inflammatory and antioxidant effects have been observed when melatonin is applied exogenously under both in vivo and in vitro conditions. A number of studies suggest that this indole may exert its anti-inflammatory effects through the regulation of different molecular pathways. It has been documented that melatonin inhibits the expression of the isoforms of inducible nitric oxide synthase and cyclooxygenase and limits the production of excessive amounts of nitric oxide, prostanoids, and leukotrienes, as well as other mediators of the inflammatory process such as cytokines, chemokines, and adhesion molecules. Melatonin's anti-inflammatory effects are related to the modulation of a number of transcription factors such as nuclear factor kappa B, hypoxia-inducible factor, nuclear factor erythroid 2-related factor 2, and others. Melatonin's effects on the DNA-binding capacity of transcription factors may be regulated through the inhibition of protein kinases involved in signal transduction, such as mitogen-activated protein kinases. This review summarizes recent research data focusing on the modulation of the expression of different inflammatory mediators by melatonin and the effects on cell signaling pathways responsible for the indole's anti-inflammatory activity. Although there are a numerous published reports that have analyzed melatonin's anti-inflammatory properties, further studies are necessary to elucidate its complex regulatory mechanisms in different cellular types and tissues.

Intestinal ischemia/reperfusion enhances microglial activation and induces cerebral injury and memory dysfunction in rats

OBJECTIVE

The mortality of critically ill patients associated with intestinal ischemia/reperfusion remains very high, which results from multiorgan dysfunction or failure due to intestinal injury induced by intestinal ischemia/reperfusion. This study was carried out to investigate whether intestinal ischemia/reperfusion can cause cerebral injury and concomitant memory dysfunction, and explore the potential mechanisms.

DESIGN

Prospective, controlled, and randomized animal study.

SETTING

University research laboratory.

SUBJECTS

Male, adult Sprague-Dawley rats (weighing 250-300 g).

INTERVENTIONS

Intestinal ischemia/reperfusion was established by clamping the superior mesenteric artery for 90 mins followed by different reperfusion durations (2, 6, 12, 24, or 48 hrs). The sham surgical preparation including isolation of the superior mesenteric artery without occlusion was performed as control.

MEASUREMENTS AND MAIN RESULTS

In comparison with sham control, intestinal ischemia/reperfusion caused severe intestinal injury, accompanied by notable cerebral damage evidenced by increased wet-to-dry brain weight ratio reflecting brain edema and neuronal cell apoptosis manifested by increased apoptotic cell number and cleaved caspase-3 protein expressions. All these changes were concomitant with reduced survival rates as well as impaired memory function determined by Morris water maze test at 24 and 48 hrs after reperfusion. In addition, intestinal ischemia/reperfusion resulted in significant increases in the levels of tumor necrosis factor-α and interleukin-6 both in the serum and in cortices and hippocampal Cornu Ammonis area 1 regions, concomitant with the activation of microglia, a key cellular mediator involved in neuroinflammation and neurodegeneration, which was evidenced by increased protein expressions of ionized calcium binding adaptor molecule 1. Furthermore, the releases of reactive oxygen species evidenced by increased malondialdehyde levels and decreased superoxide dismutase activities in cortices and hippocampal Cornu Ammonis area 1 regions were found after reperfusion.

CONCLUSIONS

These findings indicate that intestinal ischemia/reperfusion-induced intestinal injury can lead to cerebral damage and memory dysfunction partly via microglia activation which further facilitates oxidative injury, inflammatory response, and neuronal cell apoptosis.

Radiation protection following nuclear power accidents: a survey of putative mechanisms involved in the radioprotective actions of taurine during and after radiation exposure

There are several animal experiments showing that high doses of ionizing radiation lead to strongly enhanced leakage of taurine from damaged cells into the extracellular fluid, followed by enhanced urinary excretion. This radiation-induced taurine depletion can itself have various harmful effects (as will also be the case when taurine depletion is due to other causes, such as alcohol abuse or cancer therapy with cytotoxic drugs), but taurine supplementation has been shown to have radioprotective effects apparently going beyond what might be expected just as a consequence of correcting the harmful consequences of taurine deficiency per se. The mechanisms accounting for the radioprotective effects of taurine are, however, very incompletely understood. In this article an attempt is made to survey various mechanisms that potentially might be involved as parts of the explanation for the overall beneficial effect of high levels of taurine that has been found in experiments with animals or isolated cells exposed to high doses of ionizing radiation. It is proposed that taurine may have radioprotective effects by a combination of several mechanisms: (1) during the exposure to ionizing radiation by functioning as an antioxidant, but perhaps more because it counteracts the prooxidant catalytic effect of iron rather than functioning as an important scavenger of harmful molecules itself, (2) after the ionizing radiation exposure by helping to reduce the intensity of the post-traumatic inflammatory response, and thus reducing the extent of tissue damage that develops because of severe inflammation rather than as a direct effect of the ionizing radiation per se, (3) by functioning as a growth factor helping to enhance the growth rate of leukocytes and leukocyte progenitor cells and perhaps also of other rapidly proliferating cell types, such as enterocyte progenitor cells, which may be important for immunological recovery and perhaps also for rapid repair of various damaged tissues, especially in the intestines, and (4) by functioning as an antifibrogenic agent. A detailed discussion is given of possible mechanisms involved both in the antioxidant effects of taurine, in its anti-inflammatory effects and in its role as a growth factor for leukocytes and nerve cells, which might be closely related to its role as an osmolyte important for cellular volume regulation because of the close connection between cell volume regulation and the regulation of protein synthesis as well as cellular protein degradation. While taurine supplementation alone would be expected to exert a therapeutic effect far better than negligible in patients that have been exposed to high doses of ionizing radiation, it may on theoretical grounds be expected that much better results may be obtained by using taurine as part of a multifactorial treatment strategy, where it may interact synergistically with several other nutrients, hormones or other drugs for optimizing antioxidant protection and minimizing harmful posttraumatic inflammatory reactions, while using other nutrients to optimize DNA and tissue repair processes, and using a combination of good diet, immunostimulatory hormones and perhaps other nontoxic immunostimulants (such as beta-glucans) for optimizing the recovery of antiviral and antibacterial immune functions. Similar multifactorial treatment strategies may presumably be helpful in several other disease situations (including severe infectious diseases and severe asthma) as well as for treatment of acute intoxications or acute injuries (both mechanical ones and severe burns) where severely enhanced oxidative and/or nitrative stress and/or too much secretion of vasodilatory neuropeptides from C-fibres are important parts of the pathogenetic mechanisms that may lead to the death of the patient. Some case histories (with discussion of some of those mechanisms that may have been responsible for the observed therapeutic outcome) are given for illustration of the likely validity of these concepts and their relevance both for treatment of severe infections and non-infectious inflammatory diseases such as asthma and rheumatoid arthritis.

Hepatoprotective actions of melatonin: Possible mediation by melatonin receptors

Melatonin, the hormone of darkness and messenger of the photoperiod, is also well known to exhibit strong direct and indirect antioxidant properties. Melatonin has previously been demonstrated to be a powerful organ protective substance in numerous models of injury; these beneficial effects have been attributed to the hormone’s intense radical scavenging capacity. The present report reviews the hepatoprotective potential of the pineal hormone in various models of oxidative stress in vivo, and summarizes the extensive literature showing that melatonin may be a suitable experimental substance to reduce liver damage after sepsis, hemorrhagic shock, ischemia/reperfusion, and in numerous models of toxic liver injury. Melatonin’s influence on hepatic antioxidant enzymes and other potentially relevant pathways, such as nitric oxide signaling, hepatic cytokine and heat shock protein expression, are evaluated. Based on recent literature demonstrating the functional relevance of melatonin receptor activation for hepatic organ protection, this article finally suggests that melatonin receptors could mediate the hepatoprotective actions of melatonin therapy.

Hepatoprotective actions of melatonin: possible mediation by melatonin receptors

Melatonin, the hormone of darkness and messenger of the photoperiod, is also well known to exhibit strong direct and indirect antioxidant properties. Melatonin has previously been demonstrated to be a powerful organ protective substance in numerous models of injury; these beneficial effects have been attributed to the hormone's intense radical scavenging capacity. The present report reviews the hepatoprotective potential of the pineal hormone in various models of oxidative stress in vivo, and summarizes the extensive literature showing that melatonin may be a suitable experimental substance to reduce liver damage after sepsis, hemorrhagic shock, ischemia/reperfusion, and in numerous models of toxic liver injury. Melatonin's influence on hepatic antioxidant enzymes and other potentially relevant pathways, such as nitric oxide signaling, hepatic cytokine and heat shock protein expression, are evaluated. Based on recent literature demonstrating the functional relevance of melatonin receptor activation for hepatic organ protection, this article finally suggests that melatonin receptors could mediate the hepatoprotective actions of melatonin therapy.

Sulforaphane protects liver injury induced by intestinal ischemia reperfusion through Nrf2-ARE pathway

AIM: To investigate the effect of sulforaphane (SFN) on regulation of NF-E2-related factor-2 (Nrf2)-antioxidant response element (ARE) pathway in liver injury induced by intestinal ischemia/reperfusion (I/R).

METHODS: Rats were divided randomly into four experimental groups: control, SFN control, intestinal I/R and SFN pretreatment groups (n = 8 in each group). The intestinal I/R model was established by clamping the superior mesenteric artery for 1 h and 2 h reperfusion. In the SFN pretreatment group, surgery was performed as in the intestinal I/R group, with intraperitoneal administration of 3 mg/kg SFN 1 h before the operation. Intestine and liver histology was investigated. Serum levels of aspartate aminotransferase (AST), and alanine aminotransferase (ALT) were measured. Liver tissue superoxide dismutase (SOD), myeloperoxidase (MPO), glutathione (GSH) and glutathione peroxidase (GSH-Px) activity were assayed. The liver transcription factor Nrf2 and heme oxygenase-1 (HO-1) were determined by immunohistochemical analysis and Western blotting analysis.

RESULTS: Intestinal I/R induced intestinal and liver injury, characterized by histological changes as well as a significant increase in serum AST and ALT levels (AST: 260.13 ± 40.17 U/L vs 186.00 ± 24.21 U/L, P < 0.01; ALT: 139.63 ± 11.35 U/L vs 48.38 ± 10.73 U/L, P < 0.01), all of which were reduced by pretreatment with SFN, respectively (AST: 260.13 ± 40.17 U/L vs 216.63 ± 22.65 U/L, P < 0.05; ALT: 139.63 ± 11.35 U/L vs 97.63 ± 15.56 U/L, P < 0.01). The activity of SOD in the liver tissue decreased after intestinal I/R (P < 0.01), which was enhanced by SFN pretreatment (P < 0.05). In addition, compared with the control group, SFN markedly reduced liver tissue MPO activity (P < 0.05) and elevated liver tissue GSH and GSH-Px activity (P < 0.05, P < 0.05), which was in parallel with the increased level of liver Nrf2 and HO-1 expression.

CONCLUSION: SFN pretreatment attenuates liver injury induced by intestinal I/R in rats, attributable to the antioxidant effect through Nrf2-ARE pathway.