Mechanisms of protection by melatonin against acetaminophen-induced liver injury in mice

Contributing roles of mitochondrial dysfunction and hepatocyte apoptosis in liver diseases through oxidative stress, post-translational modifications, inflammation, and intestinal barrier dysfunction

This review provides an update on recent findings from basic, translational, and clinical studies on the molecular mechanisms of mitochondrial dysfunction and apoptosis of hepatocytes in multiple liver diseases, including but not limited to alcohol-associated liver disease (ALD), metabolic dysfunction-associated steatotic liver disease (MASLD), and drug-induced liver injury (DILI). While the ethanol-inducible cytochrome P450-2E1 (CYP2E1) is mainly responsible for oxidizing binge alcohol via the microsomal ethanol oxidizing system, it is also responsible for metabolizing many xenobiotics, including pollutants, chemicals, drugs, and specific diets abundant in n-6 fatty acids, into toxic metabolites in many organs, including the liver, causing pathological insults through organelles such as mitochondria and endoplasmic reticula. Oxidative imbalances (oxidative stress) in mitochondria promote the covalent modifications of lipids, proteins, and nucleic acids through enzymatic and non-enzymatic mechanisms. Excessive changes stimulate various post-translational modifications (PTMs) of mitochondrial proteins, transcription factors, and histones. Increased PTMs of mitochondrial proteins inactivate many enzymes involved in the reduction of oxidative species, fatty acid metabolism, and mitophagy pathways, leading to mitochondrial dysfunction, energy depletion, and apoptosis. Unique from other organelles, mitochondria control many signaling cascades involved in bioenergetics (fat metabolism), inflammation, and apoptosis/necrosis of hepatocytes. When mitochondrial homeostasis is shifted, these pathways become altered or shut down, likely contributing to the death of hepatocytes with activation of inflammation and hepatic stellate cells, causing liver fibrosis and cirrhosis. This review will encapsulate how mitochondrial dysfunction contributes to hepatocyte apoptosis in several types of liver diseases in order to provide recommendations for targeted therapeutics.

Application of Melatonin with N-Acetylcysteine Exceeds Traditional Treatment for Acetaminophen-Induced Hepatotoxicity

Acetaminophen (APAP) overdose is one of the leading causes of acute liver damage. Given N-acetylcysteine (NAC) and melatonin (MLT) both have an attenuated value for APAP-induced liver toxification, where an optimized integrated treatment has not been well deciphered. Here, by giving a single dose of APAP (500 mg/kg) to wild-type male mice, combined with a single dose of 500 mg/kg NAC or 100 mg/kg MLT separately as the therapeutic method, this study aimed to investigate the effects of NAC and melatonin (MLT) alone or combined on acetaminophen (APAP)-induced liver injury. In this study, NAC and MLT both partially have an alleviated function in APAP-challenged liver injury. However, MLT's add-on role strengthens the hepatoprotective effect of NAC on APAP-induced liver damage and resolute the inflammatory infiltration. Meanwhile, the combination of two reagents attenuates the decreased glutathione (GSH) and activation of the p38/JNK pathway. The combination of MLT and NAC can further ameliorate APAP-induced liver injury, which provides a novel strategy for drug-induced liver injury (DILI).

The effects of mitochondrial transplantation in acetaminophen-induced liver toxicity in rats

AIMS

Acetaminophen (APAP) toxicity is one of the leading causes of acute liver injury-related death and liver failure worldwide. In many studies, mitochondrial dysfunction has been identified as an important cause of damage in APAP toxicity. Therefore, our study aimed to investigate the possible effects of mitochondrial transplantation on liver damage due to APAP toxicity.

MAIN METHODS

APAP toxicity model was implemented by administering a toxic dose of APAP. To demonstrate the efficiency of mitochondria transplantation, it was compared with N-acetylcysteine (NAC) application, which is now clinically accepted. Mitochondrial transplantation was carried out by delivering mitochondria to the liver via the portal circulation, which was injected into the spleen. In our study, the rats were randomly divided into 6 groups as Sham, APAP, Control 1, APAP+mito, Control 2, and APAP+NAC. In the end of the experiment, histological and biochemical analysis were performed and the biodistribution of the transplanted mitochondria to target cells were also shown.

KEY FINDINGS

Successful mitochondrial transplantation was confirmed and mitochondrial transplantation improved the liver histological structure to a similar level with healthy rats. Moreover, plasma ALT levels, apoptotic cells, and total oxidant levels were decreased. It was also observed that NAC treatment increased GSH levels to the highest level among the groups. However, mitochondrial transplantation was more effective than NAC application in terms of histological and functional improvement.

SIGNIFICANCE

It has been evaluated that mitochondrial transplantation can be used as an important alternative or adjunctive treatment method in liver damage caused by toxic dose APAP intake.

Effects of Melatonin on Liver Injuries and Diseases

Liver injuries and diseases are serious health problems worldwide. Various factors, such as chemical pollutants, drugs, and alcohol, could induce liver injuries. Liver diseases involve a wide range of liver pathologies, including hepatic steatosis, fatty liver, hepatitis, fibrosis, cirrhosis, and hepatocarcinoma. Despite all the studies performed up to now, therapy choices for liver injuries and diseases are very few. Therefore, the search for a new treatment that could safely and effectively block or reverse liver injuries and diseases remains a priority. Melatonin is a well-known natural antioxidant, and has many bioactivities. There are numerous studies investigating the effects of melatonin on liver injuries and diseases, and melatonin could regulate various molecular pathways, such as inflammation, proliferation, apoptosis, metastasis, and autophagy in different pathophysiological situations. Melatonin could be used for preventing and treating liver injuries and diseases. Herein, we conduct a review summarizing the potential roles of melatonin in liver injuries and diseases, paying special attention to the mechanisms of action.

The protective effects of carvacrol and thymol against paracetamol-induced toxicity on human hepatocellular carcinoma cell lines (HepG2)

Acetaminophen (APAP) overdose could induce liver damage and lead to acute liver failure. The treatment of APAP overdoses could be improved by new therapeutic strategies. Thymus spp., which has many beneficial effects and has been used in folk medicine, is one such potential strategy. In the present study, the hepatoprotective activity of the main constituents of Thymus spp., carvacrol and thymol, were evaluated in light of APAP-induced hepatotoxicity. We hoped to understand the hepatoprotective mechanism of these agents on the antioxidant system and pro-inflammatory cytokines in vitro. Dose-dependent effects of thymol and carvacrol (25, 50, and 100 µM) were tested on cultured HepG2 cells. N-Acetylcysteine (NAC) was tested as positive control. We showed that APAP inhibited HepG2 cell growth by inducing inflammation and oxidative stress. Incubating APAP-exposed HepG2 cells with carvacrol and thymol for 24 h ameliorated this inflammation and oxidative stress. We also evaluated alanine transaminase and lactate dehydrogenase levels of HepG2 cells. We found that thymol and carvacrol protected against APAP-induced toxicity in HepG2 cells by increasing antioxidant activity and reducing pro-inflammatory cytokines, such as tumor necrosis factor α and interleukin 1β. Taking together high-dose thymol and carvacrol treatment has an effect close to NAC treatment in APAP toxicity, but thymol has better treatment effect than carvacrol.

An indole derivative protects against acetaminophen-induced liver injury by directly binding to N-acetyl-p-benzoquinone imine in mice

AIMS

Acetaminophen (APAP)-induced liver injury is mainly due to the excessive formation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) through the formation of a reactive intermediate, N-acetyl-p-benzoquinone imine (NAPQI), in both humans and rodents. Here, we show that the indole-derived synthetic compound has a protective effect against APAP-induced liver injury in C57Bl/6 mice model.

RESULTS

NecroX-7 decreased tert-butylhydroperoxide (t-BHP)- and APAP-induced cell death and ROS/RNS formation in HepG2 human hepatocarcinoma and primary mouse hepatocytes. In mice, NecroX-7 decreased APAP-induced phosphorylation of c-Jun N-terminal kinase (JNK) and 3-nitrotyrosine (3-NT) formation, and also protected mice from APAP-induced liver injury and lethality by binding directly to NAPQI. The binding of NecroX-7 to NAPQI did not require any of cofactors or proteins. NecroX-7 could only scavenge NAPQI when hepatocellular GSH levels were very low.

INNOVATION

NecroX-7 is an indole-derived potent antioxidant molecule, which can be bound to some types of radicals and especially NAPQI. It is well known that the NAPQI is a major intermediate of APAP, which causes necrosis of hepatocytes in rodents and humans. Thus, blocking NAPQI formation or eliminating NAPQI are novel strategies for the treatment or prevention of APAP-induced liver injury instead of GSH replenishment.

CONCLUSION

Our data suggest that the indole-derivative, NecroX-7, directly binds to NAPQI when hepatic GSH levels are very low and the NAPQI-NecroX-7 complex is secreted to the blood from the liver. NecroX-7 shows more preventive and similar therapeutic effects against APAP-induced liver injury when compared to the effect of N-acetylcysteine in C57Bl/6 mice.

Agomelatine

Paracetamol was shown to induce hepatotoxicity or more severe fatal acute hepatic damage. Agomelatine, commonly known as melatonin receptor agonist, is a new antidepressant, which resynchronizes circadian rhythms with subjective and objective improvements in sleep quality and architecture, as melatonin does. In the present study, it was aimed to evaluate the hepatoprotective activity of agomelatine on paracetamol-induced hepatotoxicity and to understand the relationship between the hepatoprotective mechanism of agomelatine and antioxidant system and proinflammatory cytokines. A total of 42 rats were divided into 7 groups as each composed of 6 rats: (1) intact, (2) 40 mg/kg agomelatine, (3) 140 mg/kg N-acetylcysteine (NAC), (4) 2 g/kg paracetamol, (5) 2 g/kg paracetamol + 140 mg/kg NAC, (6) 2 g/kg paracetamol + 20 mg/kg agomelatine, and (7) 2 g/kg paracetamol + 40 mg/kg agomelatine groups. Paracetamol-induced hepatotoxicity was applied and liver and blood samples were analyzed histopathologically and biochemically. There were statistically significant increases in the activities of aspartate aminotransferase, alanine aminotransferase, levels of tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) and 8-iso-prostane, and decreases in the activity of superoxide dismutase and level of glutathione in the group treated with paracetamol. Administration of agomelatine and NAC separately reversed these changes significantly. In conclusion, agomelatine administration protects liver cells from paracetamol-induced hepatotoxicity via antioxidant activity and reduced proinflammatory cytokines, such as TNF-α and IL-6.

Garlic and cardioprotection: insights into the molecular mechanisms

Garlic is widely recognized for its immense therapeutic potential. Garlic has been shown to exert its beneficial effects against a wide spectrum of diseases, including cancer, diabetes, and microbial infections, as well as immunological and cardiovascular disorders. Most of the research on garlic has indicated that garlic and its active compounds are effective in reducing cardiovascular and metabolic risk by normalizing abnormal plasma lipids, oxidized low density lipoproteins, abnormal platelet aggregation, high blood pressure, and cardiac injury. Some of the beneficial effects of dietary garlic against cardiovascular disorders are mediated via the generation of hydrogen sulfide and nitric oxide in cardiomyocytes and endothelial cells. Garlic has the potential to protect the heart against myocardial infarction, doxorubicin-induced cardiotoxicity, arrhythmia, hypertrophy, and ischemia-reperfusion injury. The induction of cardiac endogenous antioxidants and the reduction of lipid peroxidation by garlic has been reported by several different groups. Other mechanisms, such as regulating ion channels, modulating Akt signaling pathways, histone deacetylase inhibition, and cytochrome P450 inhibition, could be responsible for the cardioprotective effect of garlic. Although several mechanisms have been identified for the cardioprotective effect of garlic, there is a need for further research to identify the specific molecular mechanism of cardioprotection in different cardiac diseases.

Melatonin protects against apoptosis-inducing factor (AIF)-dependent cell death during acetaminophen-induced acute liver failure

Acetaminophen (APAP) overdose is the most frequent cause of acute liver failure and is primarily caused by cytochrome P450 (CYP) 2E1-driven conversion of APAP into hepatotoxic metabolites. Several reports showed that melatonin attenuated APAP-induced acute liver failure. Nevertheless, the exact mechanism remains obscure. In the present study, we investigated the effects of melatonin on apoptosis-inducing factor (AIF)-dependent cell death in APAP-induced acute liver failure. Mice were intraperitoneally (i.p.) injected with different doses of melatonin (1.25, 5, 20 mg/kg) 30 min before APAP (300 mg/kg, i.p.). As expected, melatonin significantly alleviated APAP-induced cell death, as determined by TdT-mediated dUTP-biotin nick end labeling (TUNEL) assay. Further analysis showed that melatonin significantly attenuated APAP-induced activation of the serine/threonine kinase receptor interacting protein 1 (RIP1). In addition, melatonin inhibited APAP-induced hepatic c-Jun N-terminal kinase (JNK) phosphorylation and mitochondrial Bax translocation. Correspondingly, melatonin inhibited APAP-induced translocation of AIF from mitochondria to nuclei. Interestingly, no changes were induced by melatonin on hepatic CYP2E1 expression. In addition, melatonin had little effect on APAP-induced hepatic glutathione (GSH) depletion. In conclusion, melatonin protects against AIF-dependent cell death during APAP-induced acute liver failure through its direct inhibition of hepatic RIP1 and subsequent JNK phosphorylation and mitochondrial Bax translocation.

HSP70 immune reactivity and TUNEL positivity in the liver of toluene-inhaled and melatonin-treated rats

Toluene is a clear, colorless and volatile hydrocarbon that is metabolized in liver, produced free oxygen radicals and can mediate cellular damage. Melatonin which is a pineal gland hormone is a very potent antioxidant. It can make the cellular membrane more durable against oxidative attacks and protect nuclear DNA from oxidative damage. This study aimed to investigate heat shock protein (HSP)70 immune reactivity and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) positivity (apoptotic activity) in the liver of toluene-inhaled and melatonin-treated rats. A total of 21 adult male Wistar albino rats were divided at random into 3 equal groups. Animals in group I were designated as control. The rats in group II were exposed to toluene (3000 ppm/1 h/day) for 30 days, while the rats in group III were treated with melatonin (10 mg/kg/day, intraperitoneally) plus toluene inhalation. At the end of the 30-day experimental period, all rats were killed by decapitation. Then the liver tissues of rats were removed and tissue specimens were embedded in paraffin blocks. The specimens were stained with periodic acid-schiff (PAS) following routine histological procedures. Sections obtained from paraffin blocks were used for immune detection of TUNEL and HSP70. In light microscopic observations of tissues from toluene-inhaled rats, massive hepatocyte degeneration, ballooning degeneration and decreased PAS positivity were observed. Increased TUNEL positivity and HSP70 immune reactivity were determined in toluene-inhaled group and melatonin treatment decreased all these adverse effects.

Geranylgeranylacetone ameliorates inflammatory response to lipopolysaccharide (LPS) in murine macrophages: inhibition of LPS binding to the cell surface

We investigated whether pretreatment with geranylgeranylacetone (GGA), a potent heat shock protein (HSP) inducer, could inhibit proinflammatory cytokine liberation and nitric oxide (NO) production in lipopolysaccharide (LPS)-treated murine macrophages. The levels of NO and tumor necrosis factor-α (TNF-α) released from murine macrophage RAW 264 cells were increased dose- and time-dependently following treatment with LPS (1 µg/ml). GGA (80 µM) treatment 2 h before LPS addition significantly suppressed TNF-α and NO productions at 12 h and 24 h after LPS, respectively, indicating that GGA inhibits activation of macrophages. However, replacement by fresh culture medium before LPS treatment abolished the inhibitory effect of GGA on NO production in LPS-treated cells. Furthermore, GGA inhibited both HSP70 and inducible NO synthase expressions induced by LPS treatment despite an HSP inducer. When it was examined whether GGA interacts with LPS and/or affects expression of Toll-like receptor 4 (TLR4) and CD14 on the cell surface, GGA inhibited the binding of LPS to the cell surface, while GGA did not affect TLR4 and CD14 expressions. These results indicate that GGA suppresses the binding of LPS to the cell surface of macrophages, resulting in inhibiting signal transduction downstream of TLR4.

Melatonin combats molecular terrorism at the mitochondrial level

The intracellular environmental is a hostile one. Free radicals and related oxygen and nitrogen-based oxidizing agents persistently pulverize and damage molecules in the vicinity of where they are formed. The mitochondria especially are subjected to frequent and abundant oxidative abuse. The carnage that is left in the wake of these oxygen and nitrogen-related reactants is referred to as oxidative damage or oxidative stress. When mitochondrial electron transport complex inhibitors are used, e.g., rotenone, 1-methyl-1-phenyl-1,2,3,6-tetrahydropyridine, 3-nitropropionic acid or cyanide, pandemonium breaks loose within mitochondria as electron leakage leads to the generation of massive amounts of free radicals and related toxicants. The resulting oxidative stress initiates a series of events that leads to cellular apoptosis. To alleviate mitochondrial destruction and the associated cellular implosion, the cell has at its disposal a variety of free radical scavengers and antioxidants. Among these are melatonin and its metabolites. While melatonin stimulates several antioxidative enzymes it, as well as its metabolites (cyclic 3-hydroxymelatonin, N¹-acetyl-N²-formyl-5-methoxykynuramine and N¹-acetyl-5-methoxykynuramine), likewise effectively neutralize free radicals. The resulting cascade of reactions greatly magnifies melatonin's efficacy in reducing oxidative stress and apoptosis even in the presence of mitochondrial electron transport inhibitors. The actions of melatonin at the mitochondrial level are a consequence of melatonin and/or any of its metabolites. Thus, the molecular terrorism meted out by reactive oxygen and nitrogen species is held in check by melatonin and its derivatives.

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.

Polaprezinc Protects Mice against Endotoxin Shock

Polaprezinc (PZ), a chelate compound consisting of zinc and l-carnosine (Car), is an anti-ulcer drug developed in Japan. In the present study, we investigated whether PZ suppresses mortality, pulmonary inflammation, and plasma nitric oxide (NO) and tumor necrosis factor (TNF)-α levels in endotoxin shock mice after peritoneal injection of lipopolysaccharide (LPS), and how PZ protects against LPS-induced endotoxin shock. PZ pretreatment inhibited the decrease in the survival rate of mice after LPS injection. PZ inhibited the increases in plasma NO as well as TNF-α after LPS. Compatibly, PZ suppressed LPS-induced inducible NO synthase mRNA transcription in the mouse lungs. PZ also improved LPS-induced lung injury. However, PZ did not enhance the induction of heat shock protein (HSP) 70 in the mouse lungs after LPS. Pretreatment of RAW264 cells with PZ suppressed the production of NO and TNF-α after LPS addition. This inhibition likely resulted from the inhibitory effect of PZ on LPS-mediated nuclear factor-κB (NF-κB) activation. Zinc sulfate, but not Car, suppressed NO production after LPS. These results indicate that PZ, in particular its zinc subcomponent, inhibits LPS-induced endotoxin shock via the inhibition of NF-κB activation and subsequent induction of proinflammatory products such as NO and TNF-α, but not HSP induction.

Melatonin Inhibits Benzene-Induced Lipid Peroxidation in Rat Liver

We studied the antioxidative role of melatonin against benzene toxicity in rat liver. The inhibition of mitochondrial and microsomal lipid peroxidation differed between 24-hour (single-dose), 15-day, and 30-day treatments. Inhibition of mitochondrial lipid peroxidation was the highest after the single dose of melatonin, whereas highest microsomal inhibition was recorded after 30 days of melatonin treatment. No significant difference was recorded between 15-day and 30-day treatments. Cytochrome P 4502E1 (CYP 4502E1) activity declined after the single-dose and 15-day melatonin treatment in the benzene-treated group, but it rose again, though not significantly after 30 days of treatment. Liver histopathology generally supported these findings. Phenol concentration in the urine samples declined in melatonin and benzene-treated rats. Our results show that melatonin affects CYP 4502E1, which is responsible for benzene metabolism. Inhibition of its metabolism correlated with lower lipid peroxidation. In conclusion, melatonin was found to be protective against lipid peroxidation induced by benzene.

Zinc Supplementation with Polaprezinc Protects Mouse Hepatocytes against Acetaminophen-Induced Toxicity via Induction of Heat Shock Protein 70

Polaprezinc, a chelate compound consisting of zinc and l-carnosine, is clinically used as a medicine for gastric ulcers. It has been shown that induction of heat shock protein (HSP) is involved in protective effects of polaprezinc against gastric mucosal injury. In the present study, we investigated whether polaprezinc and its components could induce HSP70 and prevent acetaminophen (APAP) toxicity in mouse primary cultured hepatocytes. Hepatocytes were treated with polaprezinc, zinc sulfate or l-carnosine at the concentration of 100 microM for 9 h, and then exposed to 10 mM APAP. Polaprezinc or zinc sulfate increased cellular HSP70 expression. However, l-carnosine had no influence on it. Pretreatment of the cells with polaprezinc or zinc sulfate significantly suppressed cell death as well as cellular lipid peroxidation after APAP treatment. In contrast, pretreatment with polaprezinc did not affect decrease in intracellular glutathione after APAP. Furthermore, treatment with KNK437, an HSP inhibitor, attenuated increase in HSP70 expression induced by polaprezinc, and abolished protective effect of polaprezinc on cell death after APAP. These results suggested that polaprezinc, in particular its zinc component, induces HSP70 expression in mouse primary cultured hepatocytes, and inhibits lipid peroxidation after APAP treatment, resulting in protection against APAP toxicity.

The hepatic microcirculation: mechanistic contributions and therapeutic targets in liver injury and repair

The complex functions of the liver in biosynthesis, metabolism, clearance, and host defense are tightly dependent on an adequate microcirculation. To guarantee hepatic homeostasis, this requires not only a sufficient nutritive perfusion and oxygen supply, but also a balanced vasomotor control and an appropriate cell-cell communication. Deteriorations of the hepatic homeostasis, as observed in ischemia/reperfusion, cold preservation and transplantation, septic organ failure, and hepatic resection-induced hyperperfusion, are associated with a high morbidity and mortality. During the last two decades, experimental studies have demonstrated that microcirculatory disorders are determinants for organ failure in these disease states. Disorders include 1) a dysregulation of the vasomotor control with a deterioration of the endothelin-nitric oxide balance, an arterial and sinusoidal constriction, and a shutdown of the microcirculation as well as 2) an overwhelming inflammatory response with microvascular leukocyte accumulation, platelet adherence, and Kupffer cell activation. Within the sequelae of events, proinflammatory mediators, such as reactive oxygen species and tumor necrosis factor-alpha, are the key players, causing the microvascular dysfunction and perfusion failure. This review covers the morphological and functional characterization of the hepatic microcirculation, the mechanistic contributions in surgical disease states, and the therapeutic targets to attenuate tissue injury and organ dysfunction. It also indicates future directions to translate the knowledge achieved from experimental studies into clinical practice. By this, the use of the recently introduced techniques to monitor the hepatic microcirculation in humans, such as near-infrared spectroscopy or orthogonal polarized spectral imaging, may allow an early initiation of treatment, which should benefit the final outcome of these critically ill patients.

Effect of resveratrol and melatonin on oxidative stress enzymes, regeneration, and hepatocyte ultrastructure in rats subjected to 70% partial hepatectomy

AIM

We sought to compare the antioxidant effects of resveratrol (R) and melatonin (M) after 70% partial hepatectomy (PH) as evidenced by ultrastructural alterations and effects on hepatocyte proliferation and apoptosis.

METHODS

Twenty-six male Wistar albino rats were randomized into four groups: group A (n = 8) resveratrol (R); group B (n = 8) melatonin (M); group C (n = 5) control PH; group D (n = 5) sham operated animals. The rats that received either R or M were sacrificed a week after PH. The malondialdehyde, glutathione, glutathione S-transferase, and nitric oxide levels were estimated in liver homogenates. The morphological changes were investigated using light and electron microscopy (EM). Cell proliferation was detected by immunohistochemical staining with monoclonal antibodies to Ki-67. Apoptosis was detected by the transferase-mediated dUTP nick end-labeling method.

RESULTS

PH induced hepatic LP, decreased GSH and NO, and inhibited GST activity (P < .05). R and M completely prevented PH-induced lipid peroxidation, decreased hepatic GSH and NO levels (P < .05). The inhibition of GST activity was prevented by R (P < .05), but not with M (P > .05). In the PH group EM showed severe morphological changes: mitochondrial degeneration, vacuoles, lipid droplets, and myelin-like figures. In both the R and M groups, morphological alterations repaired protective effects more prominently in the R group. Ki-67 indices (KI) were increased in the PH group and decreased in both R and M groups (P < .001). In the M group, KI was the lowest, but the difference compared with R was not significant (P > .05). Apoptosis was slightly increased in PH, but in either the R or M groups, apoptosis was intensively increased (P < .001). Increased apoptosis was greatest in the M group and the difference compared with the R group was statistically significant (P < .05).

CONCLUSION

R and M suppressed PH-induced oxidative damage, attenuated proliferation, and stimulated apoptosis. When we compared R and M, R showed more potent antioxidative effects and was morphologically more protective to hepatocytes. Antiproliferative effects of M were more potent. Because of their potent antioxidative effects, R and M can be effective for oxidative damage like ischemia-reperfusion injury; however, because of the adverse effects on proliferation and apoptosis more studies are needed in states in which regeneration is critical.

Protective effect of melatonin on Ca2+ homeostasis and contractility in acute cholecystitis

Impaired Ca2+ homeostasis and smooth muscle contractility co-exist in acute cholecystitis (AC) leading to gallbladder dysfunction. There is no pharmacological treatment for this pathological condition. Our aim was to evaluate the effects of melatonin treatment on Ca2+ signaling pathways and contractility altered by cholecystitis. [Ca2+]i was determined by epifluorescence microscopy in fura-2 loaded isolated gallbladder smooth muscle cells, and isometric tension was recorded from gallbladder muscle strips. Malondialdehyde (MDA) and reduced glutathione (GSH) contents were determined by spectrophotometry and cycloxygenase-2 (COX-2) expression was quantified by western blot. Melatonin was tested in two experimental groups, one of which underwent common bile duct ligation for 2 days and another that was later de-ligated for 2 days. Inflammation-induced impairment of Ca2+ responses to cholecystokinin and caffeine were recovered by melatonin treatment (30 mg/kg). This treatment also ameliorated the detrimental effects of AC on Ca2+ influx through both L-type and capacitative Ca2+ channels, and it was effective in preserving the pharmacological phenotype of these channels. Despite its effects on Ca2+ homeostasis, melatonin did not improve contractility. After de-ligation, Ca2+ influx and contractility were still impaired, but both were recovered by melatonin. These effects of melatonin were associated to a reduction of MDA levels, an increase in GSH content and a decrease in COX-2 expression. These findings indicate that melatonin restores Ca2+ homeostasis during AC and resolves inflammation. In addition, this indoleamine helps in the subsequent recovery of functionality.

Melatonin pretreatment improves liver function and hepatic perfusion after hemorrhagic shock

Exogenous administration of pineal hormone melatonin (MEL) has been demonstrated to attenuate organ damage in models of I/R and inflammation by antioxidative effects. However, specific organ-protective effects of MEL with respect to hemorrhagic shock have not been investigated yet. In the present study, we evaluated the role of MEL pretreatment for hepatic perfusion, redox state, and function after hemorrhage and resuscitation, with emphasis on MEL receptor activation. In a model of hemorrhagic shock (MAP 35 +/- 5 mmHg for 90 min) and reperfusion (2 h), we measured nicotinamide adenine dinucleotide phosphate (reduced form; NADPH) autofluorescence, hepatic microcirculation, and hepatocellular injury by intravital microscopy, as well as plasma disappearance rate of indocyanine green (PDRICG) as a sensitive maker of liver function in rat. Pretreatment with 10 mg kg(-1) MEL (i.v.) 15 min before induction of hemorrhage resulted in a significantly improved PDR(ICG) compared with controls (MEL/shock, 15.02% min(-1) +/- 2.9 SD vs. vehicle/shock, 6.18 +/- 4.6 SD; P = 0.001). Intravital microscopy after reperfusion revealed an improved hepatic perfusion index, redox state, and reduced hepatocellular injury in pretreated animals compared with the vehicle group. Melatonin receptor antagonist luzindole (LZN; 2.5 mg kg(-1)) almost completely abolished the protective effects of MEL pretreatment with respect to liver function (MEL + LZN/shock PDR(ICG), 7.31% min(-1) +/- 3.4 SD). Beneficial effects regarding hepatic perfusion, redox state, and cellular injury were not influenced by LZN, indicating that they may depend on antioxidative effects of MEL. However, liver function after hemorrhage is effectively maintained by MEL pretreatment via receptor-dependent pathways.

Melatonin receptors mediate improvements of liver function but not of hepatic perfusion and integrity after hemorrhagic shock in rats

OBJECTIVE

Melatonin has been demonstrated to attenuate organ damage in models of ischemia and reperfusion. Melatonin treatment before hemorrhagic shock has been shown to improve liver function and hepatic perfusion. Proposed mechanisms of the pineal hormone involve direct inactivation of reactive oxygen species and induction of antioxidative enzymes. However, recent evidence suggests a strong influence of melatonin receptor activation for these effects. Specific protection of organ function by melatonin after hemorrhage has not been investigated yet. In this study, we evaluated whether melatonin therapy after hemorrhagic shock improves liver function and hepatic perfusion, with emphasis on melatonin receptor activation.

DESIGN

Prospective, randomized, controlled study.

SETTING

University research laboratory.

SUBJECTS

Male Sprague-Dawley rats, 200-300 g (n = 10 per group).

INTERVENTIONS

Animals underwent hemorrhagic shock (mean arterial pressure, 35 +/- 5 mm Hg for 90 mins) and were resuscitated with shed blood and Ringer's solution. At the end of shock, animals were treated with either melatonin (10 mg/kg, intravenously), melatonin receptor antagonist luzindole (2.5 mg/kg, intravenously) plus melatonin (10 mg/kg, intravenously), luzindole alone (2.5 mg/kg, intravenously), or vehicle.

MEASUREMENTS AND MAIN RESULTS

After 2 hrs of reperfusion, either liver function was assessed by plasma disappearance rate of indocyanine green or intravital microscopy of the liver was performed for evaluation of hepatic perfusion, hepatocellular redox state, and hepatic integrity. Compared with vehicle controls, melatonin therapy after hemorrhagic shock significantly improved plasma disappearance rate of indocyanine green, hepatic redox state, hepatocellular injury, and hepatic perfusion index. Coadministration of luzindole completely abolished the protective effect with respect to liver function only, and improvements regarding hepatic redox state, perfusion, and integrity were comparable with melatonin treatment alone.

CONCLUSIONS

Melatonin therapy after hemorrhagic shock improves liver function, hepatic perfusion, redox state, and hepatic integrity. With respect to liver function, beneficial effects of the pineal hormone seem to be dependent on melatonin receptor activation.

Chemotactic effect of melatonin on leukocytes

Melatonin seems to be an important stimulatory factor of the immune system. This indolamine is capable of inducing activation of leukocytes. Tissue leukocyte infiltration is a key feature of inflammatory and immune responses; however, there is no information about the effect of melatonin on leukocyte chemotaxis. Therefore, the aim of this study was to examine the in vitro and in vivo effects of melatonin on leukocyte chemotaxis, on modulation of leukocyte chemotaxis to other chemoattractants and on the in vivo induction of leukocyte chemokines. Neutrophils and mononuclear leukocytes (PBMC) were isolated by a discontinuous gradient on Hystopaque. Chemotaxis was performed in blind well Boyden's chambers. In vivo chemotaxis was determined after intraperitoneal injection of melatonin into rats. Leukocyte chemotactic response and leukocyte chemokine expression were determined in human volunteers treated with 20 mg daily of melatonin. Increased neutrophils and PBMC chemotaxis in response to 1.2 nm melatonin was observed in vitro. Peritoneal leukocytes were found increased after melatonin injection. Humans treated with melatonin showed an increased neutrophil chemotactic response to a physiological chemoattractant and increased expression of intracellular chemokines; however, decreased chemotactic response and no chemokine expression were observed in PBMC. These data suggest that melatonin could have a relevant role during the tissue leukocyte infiltration in inflammatory and immune responses.