Melatonin reduces protein and lipid oxidative damage induced by homocysteine in rat brain homogenates

Age-dependent effect of continuous 'artificial light at night' on circadian rhythm in male rats: neuroprotective role of melatonin

Circadian disruption due to artificial light at night (ALAN) is an alarming threat to modern society. In the present study we evaluated the protective effect of melatonin on age dependent redox insults and neurochemical deficits induced by ALAN in the brain of chronodisrupted rat model. Young (3 months) and old (22 months) male Wistar rats were exposed to ALAN along with melatonin supplementation (10 mg Kg^-1, oral) for 10 days. Results demonstrated significant increment in the pro-oxidant biomarkers: reactive oxygen species, lipid hydroperoxidation, protein carbonyl, nitric oxide while suppression in the total thiol, ferric reducing antioxidant potential level, superoxide dismutase and catalase activities in the brain of ALAN exposed groups with higher amplitude in aged rats. Further these oxidative modifications were protected by subsequent administration of melatonin. Mitochondrial complexes (C-I to C-IV) activity was significantly altered in young and old ALAN exposed groups with melatonin showing protective effect. Histopathological analysis show dense cytosolic staining and neuronal degeneration in cerebral cortex and different hippocampus regions with greater extent in old ALAN rats effectively moderated by melatonin supplementation. RT-PCR data analysis revealed melatonin effectively downregulated neuroinflammatory (IL-6, TNF α) and neurodegenerative marker (Ngb) while upregulating the aging (Sirt 1) gene expression in both young and old melatonin supplemented ALAN exposed groups. Our results may help in understanding the degree of ALAN induced photo-oxidative damage in neuronal redox homeostasis during aging. We also show that melatonin supplementation might provide a basis for amelioration of oxidative disturbances to improve circadian entrainment in aged populations.

Melatonin as a Reducer of Neuro- and Vasculotoxic Oxidative Stress Induced by Homocysteine

The antioxidant properties of melatonin can be successfully used to reduce the effects of oxidative stress caused by homocysteine. The beneficial actions of melatonin are mainly due to its ability to inhibit the generation of the hydroxyl radical during the oxidation of homocysteine. Melatonin protects endothelial cells, neurons, and glia against the action of oxygen radicals generated by homocysteine and prevents the structural changes in cells that lead to impaired contractility of blood vessels and neuronal degeneration. It can be, therefore, assumed that the results obtained in experiments performed mainly in the in vitro models and occasionally in animal models may clear the way to clinical applications of melatonin in patients with hyperhomocysteinemia, who exhibit a higher risk of developing neurodegenerative diseases (e.g., Parkinson’s disease or Alzheimer’s disease) and cardiovascular diseases of atherothrombotic etiology. However, the results that have been obtained so far are scarce and have seldom been performed on advanced in vivo models. All findings predominately originate from the use of in vitro models and the scarcity of clinical evidence is huge. Thus, this mini-review should be considered as a summary of the outcomes of the initial research in the field concerning the use of melatonin as a possibly efficient attenuator of oxidative stress induced by homocysteine.

Homocysteine and Age-Related Central Nervous System Diseases: Role of Inflammation

Hyperhomocysteinemia (HHcy) is remarkably common among the aging population. The relation between HHcy and the development of neurodegenerative diseases, such as Alzheimer's disease (AD) and eye diseases, and age-related macular degeneration (AMD) and diabetic retinopathy (DR) in elderly people, has been established. Disruption of the blood barrier function of the brain and retina is one of the most important underlying mechanisms associated with HHcy-induced neurodegenerative and retinal disorders. Impairment of the barrier function triggers inflammatory events that worsen disease pathology. Studies have shown that AD patients also suffer from visual impairments. As an extension of the central nervous system, the retina has been suggested as a prominent site of AD pathology. This review highlights inflammation as a possible underlying mechanism of HHcy-induced barrier dysfunction and neurovascular injury in aging diseases accompanied by HHcy, focusing on AD.

Effects of melatonin on morphology and development of primordial follicles during in vitro culture of bovine ovarian tissue

This study aims to investigate the effect of melatonin on activation, growth and morphology of bovine primordial follicles, as well as on stromal cells density in ovarian tissues after in vitro culture. Ovarian fragments were cultured in α-MEM⁺ alone or supplemented with melatonin (250, 500, 1,000 or 2,000 pM) for a period of six days. Non-cultured and cultured tissues were processed for histological analysis; according to developmental stages, follicles were classified as primordial or growing follicles. These follicles were further classified as morphologically normal or degenerated. Ovarian stromal cell density was also evaluated. The percentages of primordial and developing follicles, as well as those classified of normal follicles, were compared by Fisher's exact test, and the differences were considered significant when p < .05. The results showed that the presence of 1,000 and 2,000 pM melatonin in culture medium promoted a reduction in the percentage of primordial follicles and an increase in the percentage of development follicles, when compared to follicles cultured in control medium. On the other hand, the presence of 250 or 500 pM melatonin did not show a significant effect on the percentage of primordial and developing follicles. Besides that, the presence of 500, 1,000 and 2,000 pM melatonin maintained the percentage of normal follicles similar to those seen uncultured control. Moreover, tissues cultured in presence of 1,000 pM melatonin showed a higher percentage of normal follicles when compared to follicles cultured in the presence of 250 pM melatonin. It was observed a similar profile of stromal density in both uncultured tissues and those cultured in vitro in the presence of melatonin. In conclusion, melatonin (1,000 and 2,000 pM) promotes bovine primordial follicles activation and maintains the stromal cell density during in vitro culture of ovarian cortical tissue.

Melatonin Treatment Ameliorates Hyperhomocysteinemia-Induced Impairment of Erectile Function in a Rat Model

BACKGROUND

Hyperhomocysteinemia (HHcy) has been reported to be strongly correlated with the occurrence of erectile dysfunction (ED), but the mechanisms are not fully understood. Moreover, whether melatonin could be a potential treatment of HHcy-induced ED needs to be elucidated.

AIM

The aim of this study was to investigate the effects of melatonin on HHcy-induced ED and the potential mechanisms via modulating oxidative stress and apoptosis.

METHODS

The Sprague-Dawley (SD) rat model of HHcy was induced by 7% methionine (Met)-rich diets. 36 male SD rats were randomly distributed into 3 groups (n = 12 per group): control group, 7% Met group, and 7% Met + melatonin (Mel; 10 mg/kg, intraperitoneal injection) treatment group. After 4 weeks, the erectile function of all rats was evaluated by electrical stimulation of the cavernous nerve. Histologic and molecular alterations of the corpus cavernosum were also analyzed by immunofluorescence, immunohistochemistry, enzyme-linked immunosorbent assay, Western blotting, and polymerase chain reaction.

OUTCOMES

HHcy-induced ED rat models were successfully established, and Mel could preserve erectile function mainly through inhibiting oxidative stress via the Erk1/2/Nrf2/HO-1 signaling pathway and suppression of apoptosis.

RESULTS

Erectile function was significantly reduced in the rats with HHcy compared with that in the control group and was ameliorated in the HHcy rats treated with Mel. Compared with the control group, the rats in the HHcy group showed the following: (1) higher levels of total plasma homocysteine; (2) fewer neuronal nitric oxide synthase-positive cells in the corpus cavernous; (3) higher levels of reactive oxygen species and malondialdehyde, higher expression levels of nicotinamide adenine dinucleotide phosphate oxidase, and lower activities of superoxide dismutase, indicating an overactivated oxidative stress; (4) lower expression levels of Erk1/2/Nrf2/HO-1 signaling pathway components; and (5) higher levels of apoptosis, as determined by the expression levels of Bax, Bcl-2, and caspase 3. Mel treatment improved the erectile response, as well as histologic and molecular alterations.

CLINICAL TRANSLATION

Our study on a rodent model of HHcy provided evidence that Mel could be a potential therapeutic method for HHcy-related ED.

CONCLUSIONS

Mel treatment improves erectile function in rats with HHcy probably by potential antioxidative stress activity. This finding provides evidence for a potential new therapy for HHcy-induced ED. Tang Z, Song J, Yu, Z, et al. Melatonin Treatment Ameliorates Hyperhomocysteinemia-Induced Impairment of Erectile Function in a Rat Model. J Sex Med 2019;16:1506-1517.

NQO2 inhibition relieves reactive oxygen species effects on mouse oocyte meiotic maturation and embryo development

NRH: quinone oxidoreductase 2 (NQO2) is a cytosolic and ubiquitously expressed flavoprotein that catalyzes the two-electron reduction of quinone to hydroquinones. Herein, we assessed the protein expression, subcellular localization, and possible functions of NQO2 in mouse oocyte meiotic maturation and embryo development. Western blot analysis detected high and stable protein expression of NQO2 in mouse oocytes during meiotic progression. Immunofluorescence illustrated NQO2 distribution on nuclear membrane, chromosomes, and meiotic spindles. Microtubule poisons treatment (nocodazole and taxol) showed that filamentous assembly of NQO2 and its co-localization with microtubules require microtubule integrity and normal dynamics. Increased levels of NQO2, reactive oxygen species (ROS), malondialdehyde (MDA), and autophagy protein Beclin1 expression were detected in oocytes cultured with ROS stimulator vitamin K3 (VK3), combined with decreased antioxidant glutathione (GSH). These oocytes were arrested at metaphase I with abnormal spindle structure and chromosome configuration. However, this impact was counteracted by melatonin or NQO2 inhibitor S29434, and the spindle configuration and first polar body extrusion were restored. Similarly, morpholino oligo-induced NQO2 knockdown suppressed ROS, MDA, and Beclin1, instead increased GSH in oocytes under VK3. Supplementary S29434 or melatonin limited changes in NQO2, ROS, MDA, Beclin1, and GSH during in vitro aging of ovulated oocytes, thereby maintaining spindle structure, as well as ordered chromosome separation and embryo development potential after parthenogenetic activation with SrCl2. Taken together, NQO2 is involved in ROS generation and subsequent cytotoxicity in oocytes, and its inhibition can restore oocyte maturation and embryo development, suggesting NQO2 as a pharmacological target for infertility cure.

Melatonin attenuates homocysteine-induced injury in human umbilical vein endothelial cells

Homocysteine (Hcy) is a major risk factor for vascular disease and is closely associated with endothelial dysfunction. Melatonin is a neurohormone that is mostly produced by the pineal gland. Studies have reported that melatonin exhibits neuroprotective effects in several neurodegenerative disorders. The aim of the current study was to investigate the possible protective effect of melatonin against Hcy-induced endothelial cell apoptosis in human umbilical vein endothelial cells (HUVECs) and to explore the underlying mechanisms. HUVECs were exposed to Hcy in the presence or absence of melatonin. The effect of melatonin on viability was examined by MTT assay. Intracellular reactive oxygen species (ROS) levels were determined by 2',7'-dichlorofluorescein diacetate (DCF-DA). Further, expression of Bax, Bcl-2, and caspase-3 was analyzed by Western blot analysis. Lipid peroxidation (LPO) levels, total antioxidant power (TAP), and total thiol molecules were also evaluated. The results of this study revealed that melatonin significantly prevented Hcy-induced loss in cell viability in HUVECs. It was found that ROS significantly increased in the presence of Hcy, whereas melatonin reduced ROS production. Melatonin also downregulated Bax, upregulated Bcl-2, and decreased the expression and activity of caspase-3. Hcy increased the levels of LPO, and this effect was significantly attenuated by melatonin. Melatonin also increased the levels of TAP and total thiol molecules. It was concluded that melatonin played a protective role against Hcy-induced endothelium cell apoptosis through inhibition of ROS accumulation and the mitochondrial-dependent apoptotic pathway.

The potential physiological crosstalk and interrelationship between two sovereign endogenous amines, melatonin and homocysteine

The antioxidant melatonin and the non-proteinogenic excitotoxic amino acid homocysteine (Hcy) are very distinct but related reciprocally to each other in their mode of action. The elevated Hcy level has been implicated in several disease pathologies ranging from cardio- and cerebro-vascular diseases to neurodegeneration owing largely to its free radical generating potency. Interestingly, melatonin administration potentially normalizes the elevated Hcy level, thereby protecting the cells from the undesired Hcy-induced excitotoxicity and cell death. However, the exact mechanism and between them remain obscure. Through literature survey we have found an indistinct but a vital link between melatonin and Hcy i.e., the existence of reciprocal regulation between them, and this aspect has been thoroughly described herein. In this review, we focus on all the possibilities of co-regulation of melatonin and Hcy at the level of their production and metabolism both in basal and in pathological conditions, and appraised the potential of melatonin in ameliorating homocysteinemia-induced cellular stresses. Also, we have summarized the differential mode of action of melatonin and Hcy on health and disease states.

Endoplasmic Reticulum Stress Plays a Key Role in Rotenone-Induced Apoptotic Death of Neurons

Rotenone, a pesticide, causes neurotoxicity via the mitochondrial complex-I inhibition. The present study was conducted to evaluate the role of endoplasmic reticulum (ER) stress in rotenone-induced neuronal death. Cell viability, cytotoxicity, reactive oxygen species (ROS) generation, nitrite level, mitochondrial membrane potential (MMP), and DNA damage were assessed in rotenone-treated neuro-2A cells. Protein levels of ER stress markers glucose regulated protein 78 (GRP78), growth arrest- and DNA damage-inducible gene 153 (GADD153), and phosphorylation of eukaryotic translation initiation factor 2 subunit α (eIF2-α) were estimated to assess the ER stress. To confirm the apoptotic death of neurons, mRNA levels of caspase-9, caspase-12 and caspase-3 were estimated. Further, to confirm the involvement of ER stress, neuro-2A cells were pretreated with ER stress inhibitor salubrinal. Co-treatment of antioxidant melatonin was also given to assess the role of oxidative stress in rotenone-induced apoptosis. Rotenone (0.1, 0.5, and 1 μM) treatment to neurons caused significantly decreased cell viability, increased cytotoxicity, increased ROS generation, increased expression of GRP78 and GADD, DNA damage and activation of caspase-12 and caspase-3 which were significantly attenuated by pretreatment of salubrinal (25 μM). Rotenone-induced dephosphorylation of eIF2α was also inhibited with salubrinal treatment. However, pretreatment of salubrinal did not affect the rotenone-induced increased nitrite levels, decreased MMP and caspase-9 activation. Co-treatment of antioxidant melatonin (1 mM) did not offer attenuation against rotenone-induced increased expression of caspase-9, caspase-12 and caspase-3. In conclusion, results indicated that ER stress plays a key role in rotenone-induced neuronal death, rather than oxidative stress. Graphical Abstract Pictorial presentation showed the involvement of endoplasmic reticulum (ER) stress, increased reactive oxygen species (ROS), nitrite level, decreased mitochondrial membrane potential (MMP), caspase activation and DNA damage in neuronal cells after rotenone treatment. ER stress inhibitor-salubrinal showed significant attenuation against most of the rotenone-induced adverse effects reflecting its key involvement in rotenone-induced neuronal death.

Astrocyte activation: a key step in rotenone induced cytotoxicity and DNA damage

Astrocytes are the most abundant glial cells, which provide metabolic support for neurons. Rotenone is a botanical pesticide of natural origin, known to exhibit neurotoxic potential via inhibition of mitochondrial complex-I. This study was carried out to explore the effect of rotenone on C6 cells. The cell line C6 derived from rat glioma cells represents astrocyte-like cell. C6 cells were treated with rotenone (0.1, 1 and 10 μM) for 4 h. The effect of rotenone was studied on cell survival (MTT reduction and PI uptake); free radicals (ROS and RNS) and DNA damage (comet assay and Hoechst staining). The glial cell activation and apoptotic cell death was evaluated by expression of Glial fibrillary acidic protein (GFAP) and caspase-3 respectively. The treatment with rotenone resulted in decreased cell survival and increased free radical generation. Altered nuclear morphology and DNA damage were evident following rotenone treatment in Hoechst staining and Comet assay. Rotenone elevated expression of GFAP and caspase-3 that indicates glial cell activation and apoptosis, respectively. We further studied the effect of melatonin, an antioxidant, on the observed toxic effects. Co-incubation of antioxidant, melatonin (300 μM), significantly suppressed rotenone induced above-mentioned effects in C6 cells. Inhibitory effects of melatonin suggest that free radicals play a major role in rotenone induced astrocyte activation and cellular toxicity leading to apoptosis of astroglial cells.

Rotenone-induced apoptosis and role of calcium: a study on Neuro-2a cells

Rotenone causes cytotoxicity in astrocytic cell culture by glial activation, which is linked to free radical generation. The present study is an investigation to explore whether rotenone could also cause cellular toxicity in mouse neuroblastoma cells (Neuro-2a) under treatment similar to astroglial cells. The effect of rotenone (0.1, 1, and 10 μM) on mitochondrial dehydrogenase enzyme activity by MTT reduction assay, PI uptake, total reactive oxygen species (ROS)/superoxide levels, nitrite levels, extent of DNA damage (by comet assay), and nuclear morphological alteration by Hoechst staining was studied. Caspase-3 and Ca⁺²/calmodulin-dependent protein kinase II (CaMKIIα) gene expression was determined to evaluate the apoptotic cell death and calcium kinase, respectively. Calcium level was estimated fluorometrically using fura-2A stain. Rotenone decreased mitochondrial dehydrogenase enzyme activity and generated ROS, superoxide, and nitrite. Rotenone treatment impaired cell intactness and nuclear morphology as depicted by PI uptake and chromosomal condensation of Neuro-2a cells, respectively. In addition, rotenone resulted in increased intracellular Ca⁺² level, caspase-3, and CaMKIIα expression. Furthermore, co-exposure of melatonin (300 μM), an antioxidant to cell culture, significantly suppressed the rotenone-induced decreased mitochondrial dehydrogenase enzyme activity, elevated ROS and RNS. However, melatonin was found ineffective to counteract rotenone-induced increased PI uptake, altered morphological changes, DNA damage, elevated Ca⁺², and increased expression of caspase-3 and CaMKIIα. The study indicates that intracellular calcium rather than oxidative stress is a major factor for rotenone-induced apoptosis in neuronal cells.

The role of melatonin as an antioxidant in the follicle

Melatonin (N-acetyl-5-methoxytryptamine) is secreted during the dark hours at night by pineal gland, and it regulates a variety of important central and peripheral actions related to circadian rhythms and reproduction. It has been believed that melatonin regulates ovarian function by the regulation of gonadotropin release in the hypothalamus-pituitary gland axis via its specific receptors. In addition to the receptor mediated action, the discovery of melatonin as a direct free radical scavenger has greatly broadened the understanding of melatonin's mechanisms which benefit reproductive physiology. Higher concentrations of melatonin have been found in human preovulatory follicular fluid compared to serum, and there is growing evidence of the direct effects of melatonin on ovarian function especially oocyte maturation and embryo development. Many scientists have focused on the direct role of melatonin on oocyte maturation and embryo development as an anti-oxidant to reduce oxidative stress induced by reactive oxygen species, which are produced during ovulation process. The beneficial effects of melatonin administration on oocyte maturation and embryo development have been confirmed by in vitro and in vivo experiments in animals. This review also discusses the first application of melatonin to the clinical treatment of infertile women and confirms that melatonin administration reduces intrafollicular oxidative damage and increase fertilization rates. This review summarizes our recent works and new findings related to the reported beneficial effects of melatonin on reproductive physiology in its role as a reducer of oxidative stress, especially on oocyte maturation and embryo development.

Evaluating the toxicity of environmental concentrations of waterborne chromium (VI) to a model teleost, Oncorhynchus mykiss: a comparative study of in vivo and in vitro

Toxic effects of environmental concentrations (50, 100, and 200μg/L) of waterborne chromium (VI) were evaluated in rainbow trout by comparison of in vitro and in vivo assays. Multiple biomarkers were measured including oxidative stress indices and antioxidant response parameters in liver and brain, as well as Na(+)-K(+)-ATPase in gill. Superoxide dismutase (SOD) and glutathione reductase (GR) activities were significantly induced (1.54-fold and 1.37-fold, respectively) in fish brain in vivo, but no significant differences were observed in any other biomarker or in vivo test group. Oxidative stress was apparent in vitro as significantly higher levels of oxidative indices, with the highest induction of TBARS and CP found in brain at 200μg/L Cr(VI) (2.41-fold and 1.95-fold, respectively), and SOD and GR activities and reduced glutathione in brain were significantly inhibited (65%, 44%, and 36%, respectively). In vitro Na(+)-K(+)-ATPase activity in gill was also significantly inhibited at concentrations of 100 and 200μg/L (69% and 45%, respectively). Short-term exposure to environmental concentrations of Cr(VI) does not therefore evoke marked effects in fish in vivo. Based on the present results, a set of in vitro tests with tissue homogenate can be evoked more remarkable effects by the lower concentrations of Cr(VI) than in vivo, which could provide some useful information and might be a potential alternative approach for monitoring heavy metal pollution in aquatic environments. However, it needs more detailed studies in other area, such as hormonal response or genotoxicity, before these findings could be applied in the field investigation.

Effect of a human pharmaceutical carbamazepine on antioxidant responses in brain of a model teleost in vitro: an efficient approach to biomonitoring

Residual pharmaceuticals are generally recognized as relevant sources of aquatic environmental pollutants. In this study, the effects of carbamazepine (CBZ) on the antioxidant defense system in the brain of rainbow trout in vitro were studied. The brain homogenates were incubated with various concentrations of CBZ (1.0 µg l⁻¹, 0.2 mg l⁻¹ or 2.0 mg l⁻¹) for 0, 60, 120 min. After incubation, oxidative stress indices (lipid peroxidation and carbonyl protein), antioxidant enzymes (superoxide dismutase, glutathione reductase and glutathione peroxidase) and nonenzymatic antioxidant (reduced glutathione) in each samples were measured. Based on the results, the brain homogenates performed adaptive responses to CBZ-induced stress at environmental concentration (1.0 µg l⁻¹). With increased CBZ concentrations (0.2 or 2.0 mg l⁻¹), oxidative stress was apparent as reflected by the significant higher levels of oxidative indices, together with the significant inhibition of all antioxidant enzymes activities and reduced glutathione content. Compared with previous studies in vivo, the brain homogenates showed more sensitive antioxidant responses to CBZ stress. In conclusion, the brain homogenates of rainbow trout could be used as an efficient model system in aquatic risk assessment, but more detailed laboratory studies are needed before these findings could be established as special biomarkers for monitoring residual pharmaceuticals in aquatic environment.

Effects of antenatal, postpartum and post-weaning melatonin supplementation on blood pressure and renal antioxidant enzyme activities in spontaneously hypertensive rats

Although melatonin lowers blood pressure in spontaneously hypertensive rats (SHR), its effect following antenatal and postpartum supplementation on the subsequent development of hypertension in SHR pups remains unknown. To investigate this, SHR dams were given melatonin in drinking water (10 mg/kg body weight/day) from day 1 of pregnancy until day 21 postpartum. After weaning, a group of male pups continued to receive melatonin till the age of 16 weeks (Mel-SHR), while no further melatonin was given to another group of male pups (Maternal-Mel-SHR). Controls received plain drinking water. Systolic blood pressure (SBP) was measured at 4, 6, 8, 12 and 16 weeks of age, after which the kidneys were collected for analysis of antioxidant enzyme profiles. SBP was significantly lower till the age of 8 weeks in Maternal-Mel-SHR and Mel-SHR than that in the controls, after which no significant difference was evident in SBP between the controls and Maternal-Mel-SHR. SBP in Mel-SHR was lower than that in controls and Maternal-Mel-SHR at 12 and 16 weeks of age. Renal glutathione peroxidase (GPx) and glutathione s-transferase (GST) activities, levels of total glutathione and relative GPx-1 protein were significantly higher in Mel-SHR. GPx protein was however significantly higher in Mel-SHR. No significant differences were evident between the three groups in the activities of superoxide dismutase, catalase and glutathione reductase. In conclusion, it appears that while antenatal and postpartum melatonin supplementation decreases the rate of rise in blood pressure in SHR offspring, it however does not alter the tendency of offspring of SHR to develop hypertension.

Melatonin protects against taurolithocholic-induced oxidative stress in rat liver

Cholestasis, encountered in a variety of clinical disorders, is characterized by intracellular accumulation of toxic bile acids in the liver. Furthermore, oxidative stress plays an important role in the pathogenesis of bile acids. Taurolithocholic acid (TLC) was revealed in previous studies as the most pro-oxidative bile acid. Melatonin, a well-known antioxidant, is a safe and widely used therapeutic agent. Herein, we investigated the hepatoprotective role of melatonin on lipid and protein oxidation induced by TLC alone and in combination with FeCl(3) and ascorbic acid in rat liver homogenates and hepatic membranes. The lipid peroxidation products, malondialdehyde and 4-hydroxyalkenals (MDA + 4-HDA), and carbonyl levels were quantified as indices of oxidative damage to hepatic lipids and proteins, respectively. In the current study, the rise in MDA + 4-HDA levels induced by TLC was inhibited by melatonin in a concentration-dependent manner in both liver homogenates and in hepatic membranes. Melatonin also had protective effects against structural damage to proteins induced by TLC in membranes. These results suggest that the indoleamine melatonin may potentially act as a protective agent in the therapy of those diseases that involve bile acid toxicity.

Neurotoxins: free radical mechanisms and melatonin protection

Toxins that pass through the blood-brain barrier put neurons and glia in peril. The damage inflicted is usually a consequence of the ability of these toxic agents to induce free radical generation within cells but especially at the level of the mitochondria. The elevated production of oxygen and nitrogen-based radicals and related non-radical products leads to the oxidation of essential macromolecules including lipids, proteins and DNA. The resultant damage is referred to as oxidative and nitrosative stress and, when the molecular destruction is sufficiently severe, it causes apoptosis or necrosis of neurons and glia. Loss of brain cells compromises the functions of the central nervous system expressed as motor, sensory and cognitive deficits and psychological alterations. In this survey we summarize the publications related to the following neurotoxins and the protective actions of melatonin: aminolevulinic acid, cyanide, domoic acid, kainic acid, metals, methamphetamine, polychlorinated biphenyls, rotenone, toluene and 6-hydroxydopamine. Given the potent direct free radical scavenging activities of melatonin and its metabolites, their ability to indirectly stimulate antioxidative enzymes and their efficacy in reducing electron leakage from mitochondria, it would be expected that these molecules would protect the brain from oxidative and nitrosative molecular mutilation. The studies summarized in this review indicate that this is indeed the case, an action that is obviously assisted by the fact that melatonin readily crosses the blood brain barrier.

Melatonin and structurally-related compounds protect synaptosomal membranes from free radical damage

Since biological membranes are composed of lipids and proteins we tested the in vitro antioxidant properties of several indoleamines from the tryptophan metabolic pathway in the pineal gland against oxidative damage to lipids and proteins of synaptosomes isolated from the rat brain. Free radicals were generated by incubation with 0.1 mM FeCl₃, and 0.1 mM ascorbic acid. Levels of malondialdehyde (MDA) plus 4-hydroxyalkenal (4-HDA), and carbonyl content in the proteins were measured as indices of oxidative damage to lipids and proteins, respectively. Pinoline was the most powerful antioxidant evaluated, with melatonin, N-acetylserotonin, 5-hydroxytryptophan, 5-methoxytryptamine, 5-methoxytryptophol, and tryptoline also acting as antioxidants.

Melatonin and Trolox ameliorate duodenal LPS-induced disturbances and oxidative stress

BACKGROUND AND AIMS

Lipopolysaccharide evokes gastrointestinal motility disturbances and oxidative stress. The aims of the present study were to investigate the effect of melatonin and Trolox in the actions of lipopolysaccharide on duodenal contractility and on lipid peroxidation in rabbit duodenum.

METHODS

The in vitro duodenal contractility studies were carried out in organ bath and the levels of malondialdehyde were assayed by spectrophotometry. Duodenal segments were incubated with lipopolysaccharide (0.3 microg mL(-1)).

RESULTS

Lipopolysaccharide decreased acetylcholine-induced contractions and increased malondialdehyde and 4-hydroxyalkenals concentrations in homogenates of duodenum. Melatonin reduced the amplitude of spontaneous contractions in duodenal muscle. Acetylcholine-induced contractions were not altered by melatonin in longitudinal and circular muscles. Trolox decreased the amplitude of spontaneous contractions of duodenal muscle. Trolox (1.2 or 4 mM) did not alter acetylcholine-induced contractions in duodenal muscle, but the concentration of 12 mM diminished the frequency of contractions and acetylcholine-induced contractions. Melatonin (0.3 mM) or Trolox (4 mM) diminished malondialdehyde and 4-hydroxyalkenals levels induced by lipopolysaccharide in the duodenum.

CONCLUSIONS

Melatonin and Trolox reduce oxidative stress induced by lipopolysaccharide and ameliorate the effect of lipopolysaccharide on duodenal contractility.

Effect of selected antioxidants in beta-cyfluthrin-induced oxidative stress in human erythrocytes in vitro

beta-Cyfluthrin is one of the most widely used type II pyrethroid in agriculture. The aim of this study was to examine (1) the possibility of beta-cyfluthrin to induce oxidative stress in human erythrocytes in vitro and its effect on catalase (CAT) and superoxide dismutase (SOD) activities as well as (2) the role of melatonin (MEL; 2mM), its precursor--N-acetylserotonin (NAS; 1mM), quercetin (Q; 80 microM) and rutin (R; 80 microM) in alleviating the cytotoxic effects of beta-cyfluthrin. Erythrocytes were divided into portions. The first portion was incubated for 4h at 37 degrees C with different concentrations (0, 43, 215, 1075 ppm) of beta-cyfluthrin. The other portions were preincubated with selected antioxidant, respectively for 30 min and followed by beta-cyfluthrin incubation for 4h. Malondialdehyde (MDA) concentrations, CAT and SOD activities, as well as haemolysis percentage (H) were measured in all treatment portions of erythrocytes. It could be concluded that the in vitro toxicity of beta-cyfluthrin may be associated with oxidative stress. Significant reduction in the activities of CAT was observed at all beta-cyfluthrin concentrations, while SOD activities were significantly decreased only in erythrocytes incubated with the highest beta-cyfluthrin concentration. SOD activity of the non-pretreated erythrocytes exposed to the lowest dose of beta-cyfluthrin was significantly greater when compared to comparably beta-cyfluthrin-exposed antioxidant pretreated cells. The highest concentration of beta-cyfluthrin has caused over 35% haemolysis, and the lowest concentration about 15%. MEL pretreatment had no effect on H and MDA induction by beta-cyfluthrin. NAS, Q and R reduced H and MDA level, but could not prevent induction of these parameters. Compared to other antioxidants NAS appeared to maintain better the CAT activity at control levels for all doses of beta-cyfluthrin. Pretreatment with Q was found to protect against the decrease in SOD activity induced by beta-cyfluthrin.

Protective effect of melatonin against mitomycin C-induced genotoxic damage in peripheral blood of rats

Mitomycin C (MMC) generates free radicals when metabolized. We investigated the effect of melatonin against MMC-induced genotoxicity in polychromatic erythrocytes and MMC-induced lipid peroxidation in brain and liver homogenates. Rats (N = 36) were classified into 4 groups: control, melatonin, MMC, and MMC + melatonin. Melatonin and MMC doses of 10 mg/kg and 2 mg/kg, respectively, were injected intraperitoneally. Peripheral blood samples were collected at 0, 24, 48, 72, and 96 hours posttreatment and homogenates were obtained at 96 hours posttreatment. The number of micronucleated polychromatic erythrocytes (MN-PCE) per 1000 PCE was used as a genotoxic marker. Malondialdehyde (MDA) plus 4-hydroxyalkenal (4-HDA) levels were used as an index of lipid peroxidation. The MMC group showed a significant increase in MN-PCE at 24, 48, 72, and 96 hours that was significantly reduced with melatonin begin coadministrated. No significant differences were found in lipid peroxidation. Our results indicate that MMC-induced genotoxicity can be reduced by melatonin.