Melatonin protects against pro-oxidant enzymes and reduces lipid peroxidation in distinct membranes induced by the hydroxyl and ascorbyl radicals and by peroxynitrite

Melatonin facts: Lack of evidence that melatonin is a radical scavenger in living systems

Melatonin is a small natural compound, so called a neuro-hormone that is synthesized mainly in pineal gland in animals. Its main role is to master the clock of the body, under the surveillance of light. In other words, it transfers the information concerning night and day to the peripheral organs which, without it, could not "know" which part of the circadian rhythm the body is in. Besides its main circadian and circannual rhythms mastering, melatonin is reported to be a radical scavenger and/or an antioxidant. Because radical scavengers are chemical species able to neutralize highly reactive and toxic species such as reactive oxygen species, one would like to transfer this property to living system, despite impossibilities already largely reported in the literature. In the present commentary, we refresh the memory of the readers with this notion of radical scavenger, and review the possible evidence that melatonin could be an in vivo radical scavenger, while we only marginally discuss here the fact that melatonin is a molecular antioxidant, a feature that merits a review on its own. We conclude four things: (i) the evidence that melatonin is a scavenger in acellular systems is overwhelming and could not be doubted; (ii) the transposition of this property in living (animal) systems is (a) theoretically impossible and (b) not proven in any system reported in the literature where most of the time, the delay of the action of melatonin is over several hours, thus signing a probable induction of cellular enzymatic antioxidant defenses; (iii) this last fact needs a confirmation through the discovery of a nuclear factor-a key relay in induction processes-that binds melatonin and is activated by it and (iv) we also gather the very important description of the radical scavenging capacity of melatonin in acellular systems that is now proven and shared by many other double bond-bearing molecules. We finally discussed briefly on the reason-scientific or else-that led this description, and the consequences of this claim, in research, in physiology, in pathology, but most disturbingly in therapeutics where a vast amount of money, hope, and patient bien-être are at stake.

NOX4 as a critical effector mediating neuroinflammatory cytokines, myeloperoxidase and osteopontin, specifically in astrocytes in the hippocampus in Parkinson's disease

Oxidative stress and mitochondrial dysfunction have been believed to play an important role in the pathogenesis of aging and neurodegenerative diseases, including Parkinson's disease (PD). The excess of reactive oxygen species (ROS) increases with age and causes a redox imbalance, which contributes to the neurotoxicity of PD. Accumulating evidence suggests that NADPH oxidase (NOX)-derived ROS, especially NOX4, belong to the NOX family and is one of the major isoforms expressed in the central nervous system (CNS), associated with the progression of PD. We have previously shown that NOX4 activation regulates ferroptosis via astrocytic mitochondrial dysfunction. We have previously shown that activation of NOX4 regulates ferroptosis through mitochondrial dysfunction in astrocytes. However, it remains unclear why an increase in NOX4 in neurodegenerative diseases leads to astrocyte cell death by certain mediators. Therefore, this study was designed to evaluate how NOX4 in the hippocampus is involved in PD by comparing an MPTP-induced PD mouse model compared to human PD patients. We could detect that the hippocampus was dominantly associated with elevated levels of NOX4 and α-synuclein during PD and the neuroinflammatory cytokines, myeloperoxidase (MPO) and osteopontin (OPN), were upregulated particularly in astrocytes. Intriguingly, NOX4 suggested a direct intercorrelation with MPO and OPN in the hippocampus. Upregulation of MPO and OPN induces mitochondrial dysfunction by suppressing five protein complexes in the mitochondrial electron transport system (ETC) and increases the level of 4-HNE leading to ferroptosis in human astrocytes. Overall, our findings indicate that the elevation of NOX4 cooperated with the MPO and OPN inflammatory cytokines through mitochondrial aberration in hippocampal astrocytes during PD.

Reactive oxygen species and ovarian diseases: Antioxidant strategies

Reactive oxygen species (ROS) are mainly produced in mitochondria and are involved in various physiological activities of the ovary through signaling and are critical for regulating the ovarian cycle. Notably, the imbalance between ROS generation and the antioxidant defense system contributes to the development of ovarian diseases. These contradictory effects have critical implications for potential antioxidant strategies that aim to scavenge excessive ROS. However, much remains to be learned about how ROS causes various ovarian diseases to the application of antioxidant therapy for ovarian diseases. Here, we review the mechanisms of ROS generation and maintenance of homeostasis in the ovary and its associated physiological effects. Additionally, we have highlighted the pathological mechanisms of ROS in ovarian diseases and potential antioxidant strategies for treatment.

Benefits of the Neurogenic Potential of Melatonin for Treating Neurological and Neuropsychiatric Disorders

There are several neurological diseases under which processes related to adult brain neurogenesis, such cell proliferation, neural differentiation and neuronal maturation, are affected. Melatonin can exert a relevant benefit for treating neurological disorders, given its well-known antioxidant and anti-inflammatory properties as well as its pro-survival effects. In addition, melatonin is able to modulate cell proliferation and neural differentiation processes in neural stem/progenitor cells while improving neuronal maturation of neural precursor cells and newly created postmitotic neurons. Thus, melatonin shows relevant pro-neurogenic properties that may have benefits for neurological conditions associated with impairments in adult brain neurogenesis. For instance, the anti-aging properties of melatonin seem to be linked to its neurogenic properties. Modulation of neurogenesis by melatonin is beneficial under conditions of stress, anxiety and depression as well as for the ischemic brain or after a brain stroke. Pro-neurogenic actions of melatonin may also be beneficial for treating dementias, after a traumatic brain injury, and under conditions of epilepsy, schizophrenia and amyotrophic lateral sclerosis. Melatonin may represent a pro-neurogenic treatment effective for retarding the progression of neuropathology associated with Down syndrome. Finally, more studies are necessary to elucidate the benefits of melatonin treatments under brain disorders related to impairments in glucose and insulin homeostasis.

Melatonin as Modulator for Sulfur and Nitrogen Mustard-Induced Inflammation, Oxidative Stress and DNA Damage: Molecular Therapeutics

Sulfur and nitrogen mustards, bis(2-chloroethyl)sulfide and tertiary bis(2-chloroethyl) amines, respectively, are vesicant warfare agents with alkylating activity. Moreover, oxidative/nitrosative stress, inflammatory response induction, metalloproteinases activation, DNA damage or calcium disruption are some of the toxicological mechanisms of sulfur and nitrogen mustard-induced injury that affects the cell integrity and function. In this review, we not only propose melatonin as a therapeutic option in order to counteract and modulate several pathways involved in physiopathological mechanisms activated after exposure to mustards, but also for the first time, we predict whether metabolites of melatonin, cyclic-3-hydroxymelatonin, N1-acetyl-N2-formyl-5-methoxykynuramine, and N1-acetyl-5-methoxykynuramine could be capable of exerting a scavenger action and neutralize the toxic damage induced by these blister agents. NLRP3 inflammasome is activated in response to a wide variety of infectious stimuli or cellular stressors, however, although the precise mechanisms leading to activation are not known, mustards are postulated as activators. In this regard, melatonin, through its anti-inflammatory action and NLRP3 inflammasome modulation could exert a protective effect in the pathophysiology and management of sulfur and nitrogen mustard-induced injury. The ability of melatonin to attenuate sulfur and nitrogen mustard-induced toxicity and its high safety profile make melatonin a suitable molecule to be a part of medical countermeasures against blister agents poisoning in the near future.

The mechanisms and roles of melatonin in gastrointestinal cancer

Gastrointestinal (GI) cancer is a global health problem with wide lesions and numerous cases. The increased morbidity and mortality of GI cancer is a socio-economic challenge for decades to come. Melatonin, a nature indolamine, exerts a crucial role in molecular interactions involved in multiple functional and physiological processes. Increasing evidence indicates that melatonin can modulate GI tract, decrease the occurrence of GI cancer, and enhance the sensitivity to chemoradiotherapy. However, little is known about the exact role of melatonin in anti-carcinogenesis. In this review, we discuss the action of the beneficial effects of melatonin in GI carcinogenesis. Furthermore, we compile the understanding of the role of melatonin in GI cancer, including esophageal cancer (EC), gastric cancer (GC), hepatocellular carcinoma (HCC), colorectal cancer (CRC), and pancreatic cancer (PC). In addition, the potential therapeutic application and clinical evaluation of melatonin in GI cancer are also discussed.

Citrulline protects human retinal pigment epithelium from hydrogen peroxide and iron/ascorbate induced damages

Oxidative stress plays an important role in the ageing of the retina and in the pathogenesis of retinal diseases such as age‐related macular degeneration (ARMD). Hydrogen peroxide is a reactive oxygen species generated by the photo‐excited lipofuscin that accumulates during ageing in the retinal pigment epithelium (RPE), and the age‐related accumulation of lipofuscin is associated with ARMD. Iron also accumulates with age in the RPE that may contribute to ARMD as an important source of oxidative stress. The aim of this work was to investigate the effects of L‐Citrulline (CIT), a naturally occurring amino acid with known antioxidant properties, on oxidative stressed cultured RPE cells. Human RPE (ARPE‐19) cells were exposed to hydrogen peroxide (H₂O₂) or iron/ascorbate (I/A) for 4 h, either in the presence of CIT or after 24 h of pretreatment. Here, we show that supplementation with CIT protects ARPE‐19 cells against H₂O₂ and I/A. CIT improves cell metabolic activity, decreases ROS production, limits lipid peroxidation, reduces cell death and attenuates IL‐8 secretion. Our study evidences that CIT is able to protect human RPE cells from oxidative damage and suggests potential protective effect for the treatment of retinal diseases associated with oxidative stress.

Ecotoxicological risk assessment of pentachlorophenol, an emerging DBP to plants: evaluation of oxidative stress and antioxidant responses

Chlorophenols are not only noticed in an effluvium of industries but also can emerge from the water treatment plants for domestic supply which poses a high threat for crop production and human health. Therefore, research on their risks to ecosystem and human health via ecotoxicological tests to derivate permissible environmental contaminant concentrations is necessary. The chlorophenols produced in the course of chlorination of potable water is an outcome of natural carboxylic acids/organic material and those chlorophenols occurred as emerging disinfection byproducts (EDBPs). Among chlorophenols, pentachlorophenol (PCP) has been recently identified as one of the important EDBPs. The main objective was to evaluate the PCP-induced genotoxicity and the oxidative damage in two plant species, i.e., Allium cepa and Vigna radiata. Genotoxicity of PCP was examined at three selected concentrations based on EC₅₀ (half-maximal effective concentrations) values in both the plants along with the defense mechanism. EC₅₀ value for A. cepa and V. radiata was 0.7 mg/L and 35 mg/L. Root length inhibition, DNA laddering, lipid peroxidation, H₂O₂ content, and antioxidant enzymatic assays evaluated revealed a dose-dependent response. PCP influenced defense enzyme glutathione peroxidase (GPX) and ascorbate peroxidase (APX) action in both plants and showed deprivement of catalase (CAT) with the increase of PCP concentrations. PCP-invaded toxicity management by these plants implied that A. cepa is more sensitive than V. radiata regarding PCP-induced toxicity.

Molecular Mechanisms and Genetics of Oxidative Stress in Alzheimer's Disease

Alzheimer’s disease is the most common neurodegenerative disorder that can cause dementia in elderly over 60 years of age. One of the disease hallmarks is oxidative stress which interconnects with other processes such as amyloid-β deposition, tau hyperphosphorylation, and tangle formation. This review discusses current thoughts on molecular mechanisms that may relate oxidative stress to Alzheimer’s disease and identifies genetic factors observed from in vitro, in vivo, and clinical studies that may be associated with Alzheimer’s disease-related oxidative stress.

Hormones and oxidative stress: an overview

In aerobes, oxygen is essential for maintenance of life. However, incomplete reduction of oxygen leads to generation of reactive oxygen species. These oxidants oxidise biological macromolecules present in their vicinity and thereby impair cellular functions causing oxidative stress (OS). Aerobes have evolved both enzymatic and nonenzymatic antioxidant defences to protect themselves from OS. Although hormones as means of biological coordination involve in regulation of physiological activities of tissues by regulating metabolism, any change in their normal titre leads to pathophysiological states. While, hormones such as melatonin, insulin, oestrogen, progesterone display antioxidant features, thyroid hormone, corticosteroids and catecholamines elicit free radical generation and OS, and the role of testosterone in inducing OS is debateable. This review is an attempt to understand the impact of free radical generation and cross talk between the hormones modulating antioxidant defence system under various pathophysiological conditions.

Role of Melatonin to Enhance Phytoremediation Capacity

Phytoremediation is a green technology that aims to take up pollutants from soil or water. Metals are one of the targets of these techniques due to their high toxicity in biological systems, including plants and animals. Their elimination or, at least, decrease will help keep them from being incorporated in the trophic chain and thus reaching animal and human food. The metal removal efficiency of plants is closely related to their growth rate, tolerance, and their adaptability to different environments. Melatonin (N-acetyl-5-methoxytryptamine) is a ubiquitous molecule present in animals, plants, fungi, and bacteria. In plants, it plays an important role related to antioxidant activity, but also as an important redox network regulator. Thus, melatonin has been defined as a biostimulator of plant growth, especially under environmental stress conditions, whether abiotic (water deficit and waterlogging, extreme temperature, UV radiation, salinity, alkalinity, specific mineral deficit/excess, metals and other toxic compounds, etc.) or biotic (bacteria, fungi, and viruses). Exogenous melatonin treated plants have been seen to have a high tolerance to stressors, minimizing possible harmful effects through the control of reactive oxygen species (ROS) levels and activating antioxidative responses. Furthermore, important gene expression changes in stress specific transcription factors have been demonstrated. Melatonin is capable of mobilizing toxic metals, through phytochelatins, transporting this, while sequestration adds to the biostimulator effect of melatonin on plants, improving plant tolerance against toxic pollutants. Furthermore, melatonin improves the uptake of nitrogen (N), phosphorus (P), and sulfur (S) in stress situations, enhancing cell metabolism. In light of the above, the application of melatonin seems to be a useful option for clearing toxic pollutants from the environment by improving phytoremediation. Interestingly, a variety of stressors induce melatonin biosynthesis in plants, and the study of this endogenous response in hyperaccumulator plants may be even more interesting as a natural response of the phytoremediation of diverse plants.

Dietary Melatonin Supplementation Could Be a Promising Preventing/Therapeutic Approach for a Variety of Liver Diseases

In the therapeutic strategies, the role of diet is a well-established factor that can also have an important role in liver diseases. Melatonin, identified in animals, has many antioxidant properties and it was after discovered also in plants, named phytomelatonin. These substances have a positive effect during aging and in pathological conditions too. In particular, it is important to underline that the amount of melatonin produced by pineal gland in human decreases during lifetime and its reduction in blood could be related to pathological conditions in which mitochondria and oxidative stress play a pivotal role. Moreover, it has been indicated that melatonin/phytomelatonin containing foods may provide dietary melatonin, so their ingestion through balanced diets could be sufficient to confer health benefits. In this review, the classification of liver diseases and an overview of the most important aspects of melatonin/phytomelatonin, concerning the differences among their synthesis, their presence in foods and their role in health and diseases, are summarized. The findings suggest that melatonin/phytomelatonin supplementation with diet should be considered important in preventing different disease settings, in particular in liver. Currently, more studies are needed to strengthen the potential beneficial effects of melatonin/phytomelatonin in liver diseases and to better clarify the molecular mechanisms of action.

Effects of melatonin on oxidative stress parameters and pathohistological changes in rat skeletal muscle tissue following carbon tetrachloride application

Animal models demonstrating skeletal muscle (SM) disorders are rarely investigated, although these disorders accompany liver disorders and can occur during prolonged exercise/training. In cases of SM disorders exogenous antioxidants, such as melatonin, could help by generally improving tissues antioxidant capacities. We aimed to analyze the potential of melatonin in preventing biochemical and structural changes in rat biceps muscle (BM) occurring after an acute exposure to carbon tetrachloride (CCl₄). Biceps muscles obtained from male Wistar rats belonging to different experimental groups were biochemically (determination of tissue MDA, total antioxidant capacity, GSH, CAT, SOD and GPx activities) and pathologically analyzed. Also, serum levels of potassium, LHD and CK were analyzed in all experimental animals. The obtained results were statically compared with those from vehicle-treated control group. The applied melatonin prevented potassium and intracellular enzyme leakage (CK and LDH) that was induced by CCl₄, as well as an increase in tissue MDA. From a panel of determined oxidative stress parameters melatonin was able to statistically significantly prevent changes in total antioxidative capacity and in CAT, SOD and GPx activities induced by CCl₄. Microscopic analysis of BM from the animals exposed to CCl₄ revealed significant muscle fiber disorganization and massive inflammatory cell infiltration. All these changes were significantly ameliorated in the group that received melatonin prior to CCl₄. Changes in serum and tissue biochemical parameters accompanied the observed pathological changes, which demonstrated a significant influence of melatonin in preventing skeletal muscle damage induced by CCl₄.

Pre- vs. post-treatment with melatonin in CCl4-induced liver damage: Oxidative stress inferred from biochemical and pathohistological studies

AIMS

The present study was designed to compare the ameliorating potential of pre- and post-treatments with melatonin, a potent natural antioxidant, in the carbon tetrachloride-induced rat liver damage model by tracking changes in enzymatic and non-enzymatic liver tissue defense parameters, as well as in the occurring pathohistological changes.

MAIN METHODS

Rats from two experimental groups were treated with melatonin before and after CCl₄ administration, while the controls, negative and positive, received vehicle/melatonin and CCl₄, respectively. Serum levels of transaminases, alkaline phosphates, γ-GT, bilirubin, and albumin, as well as a wide panel of oxidative stress-related parameters in liver tissue, were determined in all experimental animals. Liver tissue specimens were stained with hematoxylin and eosin and further evaluated for morphological changes.

KEY FINDINGS

Both pre- and post-treatment with melatonin prevented a CCl₄-induced increase in serum (ALT, AST, and γ-GT) and tissue (MDA and XO) liver damage markers and a decrease in the tissue total antioxidant capacity, in both enzymatic and non-enzymatic systems. The intensity of pathological changes, hepatocyte vacuolar degeneration, necrosis and inflammatory cell infiltration, was suppressed by the treatment with melatonin.

SIGNIFICANCE

In conclusion, melatonin, especially as a post-intoxication treatment, attenuated CCl₄-induced liver oxidative damage, increased liver antioxidant capacities and improved liver microscopic appearance. The results are of interest due to the great protective potential of melatonin that was even demonstrated to be stronger if applied after the tissue damage.

Melatonin and its relationship to plant hormones

BACKGROUND

Plant melatonin appears to be a multi-regulatory molecule, similar to those observed in animals, with many specific functions in plant physiology. In recent years, the number of studies on melatonin in plants has increased significantly. One of the most studied actions of melatonin in plants is its effect on biotic and abiotic stress, such as that produced by drought, extreme temperatures, salinity, chemical pollution and UV radiation, among others.

SCOPE

This review looks at studies in which some aspects of the relationship between melatonin and the plant hormones auxin, cytokinin, gibberellins, abscisic acid, ethylene, jasmonic acid and salicylic acid are presented. The effects that some melatonin treatments have on endogenous plant hormone levels, their related genes (biosynthesis, catabolism, receptors and transcription factors) and the physiological actions induced by melatonin, mainly in stress conditions, are discussed.

CONCLUSIONS

Melatonin is an important modulator of gene expression related to plant hormones, e.g. in auxin carrier proteins, as well as in metabolism of indole-3-acetic acid (IAA), gibberellins, cytokinins, abscisic acid and ethylene. Most of the studies performed have dealt with the auxin-like activity of melatonin which, in a similar way to IAA, is able to induce growth in shoots and roots and stimulate root generation, giving rise to new lateral and adventitious roots. Melatonin is also able to delay senescence, protecting photosynthetic systems and related sub-cellular structures and processes. Also, its role in fruit ripening and post-harvest processes as a gene regulator of ethylene-related factors is relevant. Another decisive aspect is its role in the pathogen-plant interaction. Melatonin appears to act as a key molecule in the plant immune response, together with other well-known molecules such as nitric oxide and hormones, such as jasmonic acid and salicylic acid. In this sense, the discovery of elevated levels of melatonin in endophytic organisms associated with plants has thrown light on a possible novel form of communication between beneficial endophytes and host plants via melatonin.

Melatonin as a mitochondrial protector in neurodegenerative diseases

Mitochondria are crucial organelles as their role in cellular energy production of eukaryotes. Because the brain cells demand high energy for maintaining their normal activities, disturbances in mitochondrial physiology may lead to neuropathological events underlying neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease and Huntington's disease. Melatonin is an endogenous compound with a variety of physiological roles. In addition, it possesses potent antioxidant properties which effectively play protective roles in several pathological conditions. Several lines of evidence also reveal roles of melatonin in mitochondrial protection, which could prevent development and progression of neurodegeneration. Since the mitochondrial dysfunction is a primary event in neurodegeneration, the neuroprotection afforded by melatonin is thereby more effective in early stages of the diseases. This article reviews mechanisms which melatonin exerts its protective roles on mitochondria as a potential therapeutic strategy against neurodegenerative disorders.

Mitochondrial bioenergetics decay in aging: beneficial effect of melatonin

Aging is a biological process characterized by progressive decline in physiological functions, increased oxidative stress, reduced capacity to respond to stresses, and increased risk of contracting age-associated disorders. Mitochondria are referred to as the powerhouse of the cell through their role in the oxidative phosphorylation to generate ATP. These organelles contribute to the aging process, mainly through impairment of electron transport chain activity, opening of the mitochondrial permeability transition pore and increased oxidative stress. These events lead to damage to proteins, lipids and mitochondrial DNA. Cardiolipin, a phospholipid of the inner mitochondrial membrane, plays a pivotal role in several mitochondrial bioenergetic processes as well as in mitochondrial-dependent steps of apoptosis and in mitochondrial membrane stability and dynamics. Cardiolipin alterations are associated with mitochondrial bienergetics decline in multiple tissues in a variety of physiopathological conditions, as well as in the aging process. Melatonin, the major product of the pineal gland, is considered an effective protector of mitochondrial bioenergetic function. Melatonin preserves mitochondrial function by preventing cardiolipin oxidation and this may explain, at least in part, the protective role of this compound in mitochondrial physiopathology and aging. Here, mechanisms through which melatonin exerts its protective role against mitochondrial dysfunction associated with aging and age-associated disorders are discussed.

Selective and sensitive visualization of endogenous nitric oxide in living cells and animals by a Si-rhodamine deoxylactam-based near-infrared fluorescent probe

A Si-rhodamine deoxylactam-based near-infrared fluorescent probe has been successfully developed for the imaging of endogenous NO in living cells and mouse models.

Nitric oxide (NO) is a fundamental signaling molecule that regulates virtually every critical cellular function, and it is also a potent mediator of cellular damage in a wide range of conditions mainly via its secondary metabolite peroxynitrite (ONOO^–). In this work, we present an o-phenylenediamine (OPD)-locked Si-rhodamine deoxylactam, i.e.deOxy-DALSiR, as a near-infrared fluorescent probe for the selective and sensitive detection of NO in living cells and bodies. Not only could the probe overcome the limitations suffered by widely used and commercialized OPD-type fluorescent NO probes, such as the possible interferences by dehydroascorbic acid/ascorbic acid/methylglyoxal (DHA/AA/MGO), pH-sensitive fluorescence output, and short excitation and emission wavelengths, but it can also avoid serious interference from cysteine (Cys) found in the rhodamine lactam-based fluorescent NO probes developed later. What’s more, the probe is fairly sensitive for NO, as evidenced by its rapid fluorescence response rate (within seconds), huge fluorescence off–on ratio (6300-fold), and ultra-low detection limit (0.12 nM). Its effectiveness and practicability have been demonstrated by the successful imaging of endogenous NO in RAW 264.7 macrophages, pancreatic β-cells, and endothelial EA.hy926 cells, as well as in inflamed and diabetic mouse models.

Effects of Melatonin on Colchicine-Treated PLBs of Dendrobium sonia-28 Orchid

Dendrobium hybrid orchid is popular in orchid commercial industry due to its short life cycle and ability to produce various types of flower colours. This study was conducted to identify the morphological, biochemical and scanning electron microscopy (SEM) analysis in the Dendrobium sonia-28 orchid plants. In this study, 0.05 and 0.075 % of colchicine-treated Dendrobium sonia-28 (4-week-old culture) protocorm-like bodies (PLBs) were treated in different concentrations of melatonin (MEL) posttreatments (0, 0.05, 0.1, 0.5, 1, 5 and 10 μM). Morphological parameters such as number of shoots, growth index and number of PLBs were determined. In the 0.05 and 0.075 % of colchicine-treated PLBs which were posttreated with 0.05 μM MEL resulted in the highest value of the morphological parameters tested based on the number of shoots (84.5 and 96.67), growth index (16.94 and 12.15) and number of PLBs (126.5 and 162.33), respectively. SEM analysis of the 0.05 μM MEL posttreatment on both the colchicine-treated regenerated PLBs showed irregular cell lineages, and some damages occurred on the stomata. This condition might be due to the effect of plasmolyzing occurred in the cell causing irregular cell lineages.

Fast-response and highly selective fluorescent probes for biological signaling molecule NO based on N-nitrosation of electron-rich aromatic secondary amines

Nitric oxide (NO) is a ubiquitous biological messenger molecule, and plays the active roles in the regulation of various physiological processes. Although numerous NO fluorescent probes have also been successfully developed in the past ten years, it still remains challenging to increase the response rate for NO while having the high selectivity and sensitivity. In this work, a simple N-nitrosation reaction of the electron-rich aromatic secondary amine with NO under aerobic condition has been utilized for the first time to construct fluorescent probe for NO. The resulting probe 1, containing a N-benzyl-4-hydroxyaniline moiety as reaction group and a BODIPY dye as fluorescence reporter, could detect NO with the fast fluorescence off-on response (within seconds), high sensitivity (nM level), and excellent selectivity over various reactive oxygen species (ROS) as well as dehydroascorbic acid (DHA), ascorbic acid (AA), and methylglyoxal (MGO). Even in the presence of glutathione (GSH, a high reactive biothiol for NO), the probe still works well for NO. Further, a mitochondria-targetable probe 2 was exploited by introducing a targeted triphenylphosphonium cation into probe 1 scaffold. It's excellent NO sensing performance as well as its ability to specifically target mitochondria and image NO there have been nicely demonstrated. With the two probes, the basal and stimulation-induced NO in RAW264.7 murine macrophages as well as the endogenous NO in endothelial cells after oxygen-glucose deprivation (OGD) have been successfully visualized.

Visualizing peroxynitrite fluxes in endothelial cells reveals the dynamic progression of brain vascular injury

Accumulating evidence suggests that formation of peroxynitrite (ONOO(-)) in the cerebral vasculature contributes to the progression of ischemic damage, while the underlying molecular mechanisms remain elusive. To fully understand ONOO(-) biology, efficient tools that can realize the real-time tracing of endogenous ONOO(-) fluxes are indispensable. While a few ONOO(-) fluorescent probes have been reported, direct visualization of ONOO(-) fluxes in the cerebral vasculature of live mice remains a challenge. Herein, we present a fluorescent switch-on probe (NP3) for ONOO(-) imaging. NP3 exhibits good specificity, fast response, and high sensitivity toward ONOO(-) both in vitro and in vivo. Moreover, NP3 is two-photon excitable and readily blood-brain barrier penetrable. These desired photophysical and pharmacokinetic properties endow NP3 with the capability to monitor brain vascular ONOO(-) generation after injury with excellent temporal and spatial resolution. As a proof of concept, NP3 has enabled the direct visualization of neurovascular ONOO(-) formation in ischemia progression in live mouse brain by use of two-photon laser scanning microscopy. Due to these favorable properties, NP3 holds great promise for visualizing endogenous peroxynitrite fluxes in a variety of pathophysiological progressions in vitro and in vivo.

Caenorhabditis elegans as an alternative in vivo model to determine oral uptake, nanotoxicity, and efficacy of melatonin-loaded lipid-core nanocapsules on paraquat damage

Caenorhabditis elegans is an alternative in vivo model that is being successfully used to assess the pharmacological and toxic effects of drugs. The exponential growth of nanotechnology requires the use of alternative in vivo models to assess the toxic effects of theses nanomaterials. The use of polymeric nanocapsules has shown promising results for drug delivery. Moreover, these formulations have not been used in cases of intoxication, such as in treatment of paraquat (PQ) poisoning. Thus, the use of drugs with properties improved by nanotechnology is a promising approach to overcome the toxic effects of PQ. This research aimed to evaluate the absorption of rhodamine B-labeled melatonin (Mel)-loaded lipid-core nanocapsules (LNC) by C. elegans, the application of this model in nanotoxicology, and the protection of Mel-LNC against PQ damage. The formulations were prepared by self-assembly and characterized by particle sizing, zeta potential, drug content, and encapsulation efficiency. The results demonstrated that the formulations had narrow size distributions. Rhodamine B-labeled Mel-LNC were orally absorbed and distributed in the worms. The toxicity assessment of LNC showed a lethal dose 50% near the highest dose tested, indicating low toxicity of the nanocapsules. Moreover, pretreatment with Mel-LNC significantly increased the survival rate, reduced the reactive oxygen species, and maintained the development in C. elegans exposed to PQ compared to those worms that were either untreated or pretreated with free Mel. These results demonstrated for the first time the uptake and distribution of Mel-LNC by a nematode, and indicate that while LNC is not toxic, Mel-LNC prevents the effects of PQ poisoning. Thus, C. elegans may be an interesting alternative model to test the nanocapsules toxicity and efficacy.

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

INTRODUCTION

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Theoretical insight into the antioxidant properties of melatonin and derivatives

Density functional theory calculations on melatonin, metabolites and synthetic derivatives thereof, and a range of other biological antioxidant molecules are presented, with a view to understanding the antioxidant ability of these molecules. After testing of the necessary calculations, we show that melatonin lies close to vitamin E on a donor-acceptor map, indicating that it should be an excellent electron donor but a poor acceptor. The neutral radical metabolite of melatonin is predicted to be an even better donor, whereas other metabolites and synthetic derivatives should retain antioxidant ability but are less powerful than the parent. QSAR models of antioxidant activity, measured in two different assays, are presented. We show that octanol-water partition coefficient is an excellent predictor of activity in lipophilic media, while properties related to electron donor/acceptor power give good fits against activity in aqueous media.

Melatonin ameliorates vascular endothelial dysfunction, inflammation, and atherosclerosis by suppressing the TLR4/NF-κB system in high-fat-fed rabbits

Vascular endothelial dysfunction (VED) and inflammation contribute to the initiation and progression of atherosclerosis. Melatonin (MLT) normalizes lipid profile, improves endothelial function, and possesses anti-inflammatory properties. However, the precise mechanisms are still unclear. This study investigated whether MLT could ameliorate VED, inflammation, and atherosclerosis by suppressing the Toll-like receptor 4 (TLR4)/nuclear factor kappa B (NF-κB) system in high-fat-fed rabbits. Rabbits were randomly divided into three groups that received a standard diet (control group), high-cholesterol diet (atherosclerosis group), or high-cholesterol diet plus 10 mg/kg/day MLT (MLT group) for 12 wk. After treatment, high-fat diet significantly increased serum lipid and inflammatory markers in rabbits in atherosclerosis group compared with that in control group. In addition, high-fat diet also induced VED and typical atherosclerotic plaque formation and increased intima/media thickness ratio, which were significantly improved by MLT therapy as demonstrated in MLT group. Histological and immunoblot analysis further showed that high-fat diet enhanced the expressions of TLR4, myeloid differentiation primary response protein (MyD88), and NF-κB p65, but decreased inhibitor of NF-κB (IκB) expression. By contrast, MLT therapy decreased the expressions of TLR4, MyD88, and NF-κB p65 and increased IκB expression. This study has demonstrated that MLT ameliorates lipid metabolism, VED, and inflammation and inhibits the progression of atherosclerosis in high-fat-fed rabbits. Moreover, our study indicates for the first time that suppression of the TLR4/NF-κB system in local vasculature with atherosclerotic damage is important for the protective effects of MLT.

Effect of melatonin on the functional recovery from experimental traumatic compression of the spinal cord

Spinal cord injury is an extremely severe condition with no available effective therapies. We examined the effect of melatonin on traumatic compression of the spinal cord. Sixty male adult Wistar rats were divided into three groups: sham-operated animals and animals with 35 and 50% spinal cord compression with a polycarbonate rod spacer. Each group was divided into two subgroups, each receiving an injection of vehicle or melatonin (2.5 mg/kg, intraperitoneal) 5 min prior to and 1, 2, 3, and 4 h after injury. Functional recovery was monitored weekly by the open-field test, the Basso, Beattie and Bresnahan locomotor scale and the inclined plane test. Histological changes of the spinal cord were examined 35 days after injury. Motor scores were progressively lower as spacer size increased according to the motor scale and inclined plane test evaluation at all times of assessment. The results of the two tests were correlated. The open-field test presented similar results with a less pronounced difference between the 35 and 50% compression groups. The injured groups presented functional recovery that was more evident in the first and second weeks. Animals receiving melatonin treatment presented more pronounced functional recovery than vehicle-treated animals as measured by the motor scale or inclined plane. NADPH-d histochemistry revealed integrity of the spinal cord thoracic segment in sham-operated animals and confirmed the severity of the lesion after spinal cord narrowing. The results obtained after experimental compression of the spinal cord support the hypothesis that melatonin may be considered for use in clinical practice because of its protective effect on the secondary wave of neuronal death following the primary wave after spinal cord injury.

N-(Phenoxyalkyl)amides as MT(1) and MT(2) ligands: antioxidant properties and inhibition of Ca(2+)/CaM-dependent kinase II

Recently a series of chiral N-(phenoxyalkyl)amides have been reported as potent MT(1) and MT(2) melatonergic ligands. Some of these compounds were selected and tested for their antioxidant properties by measuring their reducing effect against oxidation of 2',7'-dichlorodihydrofluorescein (DCFH) in the DCFH-diacetate (DCFH-DA) assay. Among the tested compounds, N-[2-(3-methoxyphenoxy)propyl]butanamide displayed potent antioxidant activity that was stereoselective, the (R)-enantiomer performing as the eutomer. This compound displayed strong cytoprotective activity against H(2)O(2)-induced cytotoxicity resulting slightly more active than melatonin, and performed as Ca(2+)/calmodulin-dependent kinase II (CaMKII) inhibitor, too.

The antioxidant behaviour of melatonin and structural analogues during lipid peroxidation depends not only on their functional groups but also on the assay system

There is no general agreement yet on the antioxidant effect of pineal indoles against lipid peroxidation. Accordingly, the main goal of the present work was to study the antioxidant activity of melatonin (MLT), N-acetylserotonin (NAS), 5-HO-tryptophan (5HO-TRP) and 5-methoxytryptamine (5MTP) in two different lipid systems with high content of polyunsaturated fatty acids (PUFAs): triglycerides (rich in 20:5 n-3, 22:6 n-3) dissolved in chloroform and sonicated liposomes made of retinal lipids (rich in 22:6 n-3). In the triglyceride-chloroform-system the peroxidation reaction was initiated by cumene hydroperoxide (CHP) whereas liposomes were peroxidized with Fe(2+). The techniques employed at the present work were: (1) TBARS production, (2) DPPH assay, (3) determination of conjugated dienes production and (4) analysis of fatty acid profile by GC-MS. Butylated hydroxytoluene (BHT) was employed as a reference because of its well known antioxidant capacity. Our results showed that MLT and 5MTP were unable to protect PUFAs against lipid peroxidation in both systems, whereas NAS and 5HO-TRP were better antioxidants that BHT in the triglyceride-system but ineffective in the liposome-system. We conclude that the antioxidant behaviour of pineal indoles depends not only on their functional groups but also on the assay system and could be explained by the polar paradox theory.

Hydrogels containing redispersible spray-dried melatonin-loaded nanocapsules: a formulation for transdermal-controlled delivery

The aim of the present study was to develop a transdermal system for controlled delivery of melatonin combining three strategies: nanoencapsulation of melatonin, drying of melatonin-loaded nanocapsules, and incorporation of nanocapsules in a hydrophilic gel. Nanocapsules were prepared by interfacial deposition of the polymer and were spray-dried using water-soluble excipients. In vitro drug release profiles were evaluated by the dialysis bag method, and skin permeation studies were carried out using Franz cells with porcine skin as the membrane. The use of 10% (w/v) water-soluble excipients (lactose or maltodextrin) as spray-drying adjuvants furnished redispersible powders (redispersibility index approximately 1.0) suitable for incorporation into hydrogels. All formulations showed a better controlled in vitro release of melatonin compared with the melatonin solution. The best controlled release results were achieved with hydrogels prepared with dried nanocapsules (hydrogels > redispersed dried nanocapsules > nanocapsule suspension > melatonin solution). The skin permeation studies demonstrated a significant modulation of the transdermal melatonin permeation for hydrogels prepared with redispersible nanocapsules. In this way, the additive effect of the different approaches used in this study (nanoencapsulation, spray-drying, and preparation of semisolid dosage forms) allows not only the control of melatonin release, but also transdermal permeation.

The importance of oxidative stress in patients with chronic renal failure whose hypertension is treated with peritoneal dialysis

Increased oxidative stress is a well-known phenomenon in dialysis patients. However, the contribution of hypertension to the oxidative stress in peritoneal dialysis patients has not yet been assessed. The present study aimed to investigate if hypertension had an additional effect on oxidative stress in peritoneal dialysis patients. A total of 50 patients treated with peritoneal dialysis were divided into two groups: The patients with mean of last three blood pressure results as 135/90 mmHg and above were considered hypertensive, the patients with lower blood pressure were considered normotensive. The control group included 25 healthy individuals. Serum malondialdehyde (MDA), advanced oxidation protein product (AOPP), myeloperoxidase (MPO), catalase (CAT) and glutathione peroxidase (GSH-Px) levels were measured in all groups. MDA level, an indicator of lipid peroxidation, was significantly higher in the hypertensive group compared to the control group, while the increase in the normotensive group was not significant. However, the difference between the hypertensive and normotensive groups was significant. The levels of AOPP, an indicator of protein oxidation level, and MPO, an indicator of neutrophil activation, were not different between the groups, while the activities of antioxidant CAT and GSH-Px decreased in both normotensive and hypertensive groups compared to the control group, and there was no significant difference between the patient groups. This study shows that both normotensive and hypertensive peritoneal dialysis patients have increased-oxidative stress and decreased antioxidant levels and hypertension might have an additional effect on oxidative stress by increasing MDA level in peritoneal dialysis patients.

Influence of melatonin on the order of phosphatidylcholine-based membranes

The effect of melatonin was evaluated on three phosphatidylcholine-based membrane models. Changes in liposome dynamics were monitored by fluorescence, following the response of the probe merocyanine-540, as well as by differential scanning calorimetry (DSC). Langmuir monolayers were investigated using molecular area measurements, as well as by Brewster angle microscopy (BAM). Mica-supported bilayers were observed via atomic force microscopy (AFM). Fluorescence results demonstrating that melatonin increases the affinity between MC-540 and lipid molecules possibly because of an increase in the membrane fluidity in liposomes. DSC analyses showed that melatonin promoted a reduction in enthalpy in the lipid nonpolar chains. Melatonin also promoted an increase in the molecular area of Langmuir monolayers, as well as a decrease in membrane thickness. Consequently, melatonin appeared to induce re-ordering effects in liposome and Langmuir monolayers. AFM images of bilayers immobilized on mica suggested that melatonin induced a gel state predominance or a delay in the main phase transition. At experimental conditions, melatonin interacted actively with all membranes models tested and induced changes in their physico-chemical properties. The data presented here may contribute to the understanding of melatonin physiologic properties, as well as the development of therapeutic advanced systems, such as drug delivery systems and biosensors.

Melatonin, cardiolipin and mitochondrial bioenergetics in health and disease

Melatonin is a natural occurring compound with well-known antioxidant properties. Melatonin is ubiquitously distributed and because of its small size and amphiphilic nature, it is able to reach easily all cellular and subcellular compartments. The highest intracellular melatonin concentrations are found in mitochondria, raising the possibility of functional significance for this targeting with involvement in situ in mitochondrial activities. Mitochondria, the powerhouse of the cell, are considered to be the most important cellular organelles to contribute to degenerative processes mainly through respiratory chain dysfunction and formation of reactive oxygen species, leading to damage to mitochondrial proteins, lipids and DNA. Therefore, protecting mitochondria from oxidative damage could be an effective therapeutic strategy against cellular degenerative processes. Many of the beneficial effects of melatonin administration may depend on its effect on mitochondrial physiology. Cardiolipin, a phospholipid located at the level of inner mitochondrial membrane is known to be intimately involved in several mitochondrial bioenergetic processes as well as in mitochondrial-dependent steps of apoptosis. Alterations to cardiolipin structure, content and acyl chain composition have been associated with mitochondrial dysfunction in multiple tissues in several physiopathological situations and aging. Recently, melatonin was reported to protect the mitochondria from oxidative damage by preventing cardiolipin oxidation and this may explain, at least in part, the beneficial effect of this molecule in mitochondrial physiopathology. In this review, we discuss the role of melatonin in preventing mitochondrial dysfunction and disease.

Melatonin ameliorates cerulein-induced pancreatitis by the modulation of nuclear erythroid 2-related factor 2 and nuclear factor-kappaB in rats

Melatonin exhibits a wide variety of biological effects, including antioxidant and anti-inflammatory functions. Its antioxidant role impedes the etiopathogenesis of pancreatitis, but little is known about the signaling pathway of melatonin in the induction of antioxidant enzymes in acute pancreatitis (AP). The aim of this study was to determine whether melatonin could prevent cerulein-induced AP through nuclear factor erythroid 2-related factor 2 (Nrf2) and curtail inflammation by inhibition of NF-kappaB. AP was induced by two intraperitoneal (i.p.) injections of cerulein at 2 h intervals (50 microg/kg) in Sprague-Dawley rats. Melatonin (10 or 50 mg/kg/daily, i.p.) was administered 24 h before each injection of cerulein. The rats were killed 12 h after the last injection. Acinar cell degeneration, pancreatic edema, and inflammatory infiltration were significantly different in cerulein- and melatonin-treated rats. Melatonin significantly reduced amylase, lipase, MPO, and MDA levels, and increased antioxidant enzyme activities including SOD and GPx, which were decreased in AP (P < 0.05). Melatonin increased the expression of NQO1, HO-1, and SOD2 when compared with the cerulein-induced AP group (P < 0.05). In addition, melatonin increased Nrf2 expression, and reduced expressions of tumor necrosis factor-alpha, IL-1beta, IL-6, IL-8, and iNOS. The elevated nuclear binding of NF-kappaB in the cerulein-induced pancreatitis group was inhibited by melatonin. These results show that melatonin increases antioxidant enzymes and Nrf2 expression, and limits inflammatory mediators in cerulein-induced AP. It is proposed that melatonin may play an important role in oxidative stress via the Nrf2 pathway in parallel with reduction of inflammation by NF-kappaB inhibition.

Preparation of drug-loaded polymeric nanoparticles and evaluation of the antioxidant activity against lipid peroxidation

Antioxidants have been found to be effective as prophylatic and therapeutic agents for different diseases such as diabetes, cancer, and neurodegenerative disorders. However, antioxidant substances can present poor solubility in water, inefficient permeability, gastrointestinal degradation, first-pass effect, and/or instability during storage. These drawbacks can be potentially circumvented by encapsulating the susceptible antioxidants. Polymeric nanoparticles (nanocapsules or nanospheres) have been used to improve the drug efficacy and release. Our group has shown that the in vitro antioxidant effect of melatonin against lipid peroxidation in microsomes and liposomes can be improved by encapsulation of the antioxidant drug in polymeric nanoparticles.

Effects of melatonin and acetylsalicylic acid against hepatic oxidative stress after bile duct ligation in rat

The aim of this study was to assess the effect of melatonin and acetylsalicylic acid (ASA) on hepatic damage induced by bile duct ligation (BDL).

MATERIAL AND METHODS

Male Sprague-Dawley rats were subjected to either sham operation or common BDL before treatment with ASA, melatonin or vehicle. Hepatic superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) enzyme activities and reduced glutathione (GSH), malondialdehyde (MDA) and nitric oxide (NO) levels were evaluated.

RESULTS

Our results have indicated that BDL caused a significant increase in lipid peroxidation whereas a statistically insignificant decrease in GSH level and some of the antioxidant enzyme activities. Both MEL and ASA administrations, either separately or together, decreased MDA whereas co-administration of MEL with ASA increased GSH levels in BDL rats.

CONCLUSIONS

CAT activity and MEL level decreased in the liver tissues of rats with BDL after administration of either melatonin alone or with ASA. However, melatonin and ASA administration increases liver tissue GSH levels in BDL ligated rats

Melatonin: an established antioxidant worthy of use in clinical trials

Oxidative stress plays a key role in the pathogenesis of aging and many metabolic diseases; therefore, an effective antioxidant therapy would be of great importance in these circumstances. Nutritional, environmental, and chemical factors can induce the overproduction of the superoxide anion radical in both the cytosol and mitochondria. This is the first and key event that leads to the activation of pathways involved in the development of several metabolic diseases that are related to oxidative stress. As oxidation of essential molecules continues, it turns to nitrooxidative stress because of the involvement of nitric oxide in pathogenic processes. Once peroxynitrite forms, it damages via two distinctive mechanisms. First, it has direct toxic effects leading to lipid peroxidation, protein oxidation, and DNA damage. This mechanism involves the induction of several transcription factors leading to cytokine-induced chronic inflammation. Classic antioxidants, including vitamins A, C, and E, have often failed to exhibit beneficial effects in metabolic diseases and aging. Melatonin is a multifunctional indolamine that counteracts virtually all pathophysiologic steps and displays significant beneficial actions against peroxynitrite-induced cellular toxicity. This protection is related to melatonin's antioxidative and antiinflammatory properties. Melatonin has the capability of scavenging both oxygen- and nitrogen-based reactants, including those formed from peroxynitrite, and blocking transcriptional factors, which induce proinflammatory cytokines. Accumulating evidence suggests that this nontoxic indolamine may be useful either as a sole treatment or in conjunction with other treatments for inhibiting the biohazardous actions of nitrooxidative stress.

Melatonin reduces oxidative stress induced by chronic exposure of microwave radiation from mobile phones in rat brain

PURPOSE

The aim of the study was to evaluate the intensity of oxidative stress in the brain of animals chronically exposed to mobile phones and potential protective effects of melatonin in reducing oxidative stress and brain injury.

MATERIALS AND METHODS

Experiments were performed on Wistar rats exposed to microwave radiation during 20, 40 and 60 days. Four groups were formed: I group (control)- animals treated by saline, intraperitoneally (i.p.) applied daily during follow up, II group (Mel)- rats treated daily with melatonin (2 mg kg(-1) body weight i.p.), III group (MWs)- microwave exposed rats, IV group (MWs + Mel)- MWs exposed rats treated with melatonin (2 mg kg(-1) body weight i.p.). The microwave radiation was produced by a mobile test phone (SAR = 0.043-0.135 W/kg).

RESULTS

A significant increase in the brain tissue malondialdehyde (MDA) and carbonyl group concentration was registered during exposure. Decreased activity of catalase (CAT) and increased activity of xanthine oxidase (XO) remained after 40 and 60 days of exposure to mobile phones. Melatonin treatment significantly prevented the increase in the MDA content and XO activity in the brain tissue after 40 days of exposure while it was unable to prevent the decrease of CAT activity and increase of carbonyl group contents.

CONCLUSION

We demonstrated two important findings; that mobile phones caused oxidative damage biochemically by increasing the levels of MDA, carbonyl groups, XO activity and decreasing CAT activity; and that treatment with the melatonin significantly prevented oxidative damage in the brain.

Flavonols from Pterogyne nitens and their evaluation as myeloperoxidase inhibitors

A myeloperoxidase inhibitory kaempferol derivative, namely pterogynoside (1), was isolated from fruits of Pterogyne nitens, along with six known flavonols, kaempferol, afzelin, kaempferitrin, quercetin, isoquercetrin and rutin. The structures of all compounds were elucidated primarily from 1D and 2D NMR spectroscopic analyses, as well as by high resolution mass spectrometry. All flavonols were screened to identify secondary metabolites as potential myeloperoxidase (MPO) inhibitors, and at concentrations of 0.50-50nM, quercetin (5), isoquercitrin (6) and rutin (7) exhibited strong inhibitory effects with IC50 values of 1.22+/-0.01, 3.75+/-0.02 and 3.60+/-0.02, respectively. The MPO activity detected for the new derivative 1 was markedly decreased (IC(50) 10.3+/-0.03) when compared with known flavonols 5-7, and interestingly increased when tested against ABTS scavenging activity.

Protective effects of melatonin on renal failure in pinealectomized rats

AIM

The purpose of the current study was to investigate the effects melatonin on renal function.

METHODS

The histological appearance of the kidney and malondialdehyde, nitric oxide, glutathione and superoxide dismutase contents were determined. Serum creatinine and blood urea nitrogen levels were also assayed. Rats were divided as: Sham, pinealectomized (Px) and pinealectomized and treated with melatonin.

RESULTS

In Px group, malondialdehyde and nitric oxide levels were elevated when compared with the sham group. The Px group exhibited reduced superoxide dismutase activity and glutathione content. All of these harmful changes were restored by melatonin. Melatonin also ameliorated serum creatinine and blood urea nitrogen levels related to renal injury. The score for glomerular, tubular and interstitial changes was significantly higher in the Px group. Melatonin supplementation significantly reduced these parameters.

CONCLUSIONS

This protective effect may be associated with both melatonin's lipophilic and hydrophilic effects, thus providing on-site protection against free radical mediated damage.

Melatonin location in egg phosphatidylcholine liposomes: possible relation to its antioxidant mechanisms

Although it is known that the antioxidant properties of melatonin can be modulated by its effect on membrane fluidity, there are few studies on this subject reported in the literature and they are controversial. In this study, viscosimetry and nuclear magnetic resonance (NMR) techniques were used to determine melatonin's effect and location on egg phosphatidylcholine bilayers mobility. Melatonin decreases the dynamic viscosity of the lipid dispersion. (31)P-NMR line width analysis indicated that melatonin induces a slight but uniform restriction of the lipid motional freedom in the polar head. However, melatonin changes in choline (13)C dynamics was only observed through chemical shift analysis. On the other hand, melatonin can induce an increase in the lipid nonpolar chain mobility, as observed by (13)C and (1)H relaxation time analysis. These results suggest the interfacial location of melatonin in the membrane. Additionally, the results of the analysis of the lipid (1)H-fitted exponential relaxation times suggest that melatonin promotes a molecular rearrangement of the bilayers. The melatonin effect and location in the lipid membrane may explain its antioxidant properties against lipid peroxidation induced by reactive species.

Melatonin attenuates lipopolysaccharide (LPS)-induced apoptotic liver damage in d-galactosamine-sensitized mice

D-Galactosamine (GalN) depletes UTP primarily in liver, resulting in decreased RNA synthesis in hepatocytes. When given together with a sublethal dose of lipopolysaccharide (LPS), GalN highly sensitizes animals to produce apoptotic liver injury with severe hepatic congestion, resulting in rapid death. Melatonin is a cytokine modulator, antioxidant and anti-apoptotic agent. In the present study, we investigated the effect of melatonin on LPS-induced apoptotic liver damage in GalN-sensitized mice. Female CD-1 mice were intraperitoneally (i.p.) injected with melatonin (5.0mg/kg) 30min before GalN/LPS (700mg10microg/kg, i.p.), another two doses of melatonin (2.5mg/kg, i.p.) being administered 1 and 2h after GalN/LPS. Results showed that serum alanine aminotransferase (ALT) activities were markedly increased 8h after GalN/LPS treatment, massive hemorrhage being observed in histological sections of liver from GalN/LPS-treated mice. Melatonin significantly attenuated GalN/LPS-induced elevation of serum ALT. In parallel, melatonin distinctly improved GalN/LPS-induced congestion. Additional experiment showed that melatonin significantly attenuated GalN/LPS-induced hepatic apoptosis, measured by inhibition of caspase-3 activities and attenuation of DNA laddering. Furthermore, melatonin markedly increased hepatic Se-dependent glutathione peroxidase (GSH-Px) and glutathione reductase (GSH-Rd) activities and attenuated hepatic glutathione (GSH) depletion in GalN/LPS-treated mice. Increases in serum tumor necrosis factor alpha (TNF-alpha), which were observed in GalN/LPS-treated mice, were significantly reduced by melatonin. However, melatonin had no effect on LPS-evoked nitric oxide production in GalN-sensitized mice. Taken together, these results indicate that melatonin protected against LPS-induced liver damage in GalN-sensitized mice through its strong ROS-scavenging, antiinflammatory and antiapoptotic effects.