Reaction of melatonin with hemoglobin-derived oxoferryl radicals and inhibition of the hydroperoxide-induced hemoglobin denaturation in red blood cells

Stimulation of Hemolysis and Eryptosis by β-Caryophyllene Oxide

BACKGROUND

Eryptosis stimulated by anticancer drugs can lead to anemia in patients. β-caryophyllene oxide (CPO) is an anticancer sesquiterpene present in various plants; however, its effect on the structure and function of human red blood cells (RBCs) remains unexplored. The aim of this study was to investigate the hemolytic and eryptotic activities and underlying molecular mechanisms of CPO in human RBCs.

METHODS

Cells were treated with 10-100 μM of CPO for 24 h at 37 °C, and hemolysis, LDH, AST, and AChE activities were photometrically assayed. Flow cytometry was employed to determine changes in cell volume from FSC, phosphatidylserine (PS) externalization by annexin-V-FITC, intracellular calcium by Fluo4/AM, and oxidative stress by 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA). Cells were also cotreated with CPO and specific signaling inhibitors and antihemolytic agents. Furthermore, whole blood was exposed to CPO to assess its toxicity to other peripheral blood cells.

RESULTS

CPO induced concentration-responsive hemolysis with LDH and AST leakage, in addition to PS exposure, cell shrinkage, Ca2+ accumulation, oxidative stress, and reduced AChE activity. The toxicity of CPO was ameliorated by D4476, staurosporin, and necrosulfonamide. ATP and PEG 8000 protected the cells from hemolysis, while urea and isotonic sucrose had opposite effects.

CONCLUSIONS

CPO stimulates hemolysis and eryptosis through energy depletion, Ca2+ buildup, oxidative stress, and the signaling mediators casein kinase 1α, protein kinase C, and mixed lineage kinase domain-like pseudokinase. Development of CPO as an anticancer therapeutic must be approached with prudence to mitigate adverse effects on RBCs using eryptosis inhibitors, Ca2+ channel blockers, and antioxidants.

Mancozeb-induced cytotoxicity in human erythrocytes: enhanced generation of reactive species, hemoglobin oxidation, diminished antioxidant power, membrane damage and morphological changes

Mancozeb is an ethylene bis-dithiocarbamate fungicide extensively used in agriculture to safeguard crops from various fungal diseases. The general population is exposed to mancozeb through consumption of contaminated food or water. Here, we have investigated the effect of mancozeb on isolated human erythrocytes under in vitro conditions. Erythrocytes were treated with different concentrations of mancozeb (0, 5, 10, 25, 50, 100 μM) and incubated for 24 h at 37 °C. Analysis of biochemical parameters and cell morphology showed dose-dependent toxicity of mancozeb in human erythrocytes. Mancozeb treatment caused hemoglobin oxidation and heme degradation. Protein and lipid oxidation were enhanced, while a significant decrease was seen in reduced glutathione and total sulfhydryl content. A significant increase in the generation of reactive oxygen and nitrogen species was detected in mancozeb-treated erythrocytes. The antioxidant capacity and the activity of key antioxidant enzymes were greatly diminished, while crucial metabolic pathways were inhibited in erythrocytes. Damage to the erythrocyte membrane on mancozeb treatment was apparent from increased cell lysis and osmotic fragility, along with the impairment of the plasma membrane redox system. Mancozeb also caused morphological alterations and transformed the normal discoid-shaped erythrocytes into echinocytes and stomatocytes. Thus, mancozeb induces oxidative stress in human erythrocytes, impairs the antioxidant defense system, oxidizes cellular components, that will adversely affect erythrocyte structure and function.

Oxidative Stress and Inflammation in COVID-19-Associated Sepsis: The Potential Role of Anti-Oxidant Therapy in Avoiding Disease Progression

Since the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak emerged, countless efforts are being made worldwide to understand the molecular mechanisms underlying the coronavirus disease 2019 (COVID-19) in an attempt to identify the specific clinical characteristics of critically ill COVID-19 patients involved in its pathogenesis and provide therapeutic alternatives to minimize COVID-19 severity. Recently, COVID-19 has been closely related to sepsis, which suggests that most deceases in intensive care units (ICU) may be a direct consequence of SARS-CoV-2 infection-induced sepsis. Understanding oxidative stress and the molecular inflammation mechanisms contributing to COVID-19 progression to severe phenotypes such as sepsis is a current clinical need in the effort to improve therapies in SARS-CoV-2 infected patients. This article aims to review the molecular pathogenesis of SARS-CoV-2 and its relationship with oxidative stress and inflammation, which can contribute to sepsis progression. We also provide an overview of potential antioxidant therapies and active clinical trials that might prevent disease progression or reduce its severity.

COVID-19: hemoglobin, iron, and hypoxia beyond inflammation. A narrative review

Coronavirus disease-19 (COVID-19) has been regarded as an infective-inflammatory disease, which affects mainly lungs. More recently, a multi-organ involvement has been highlighted, with different pathways of injury. A hemoglobinopathy, hypoxia and cell iron overload might have a possible additional role. Scientific literature has pointed out two potential pathophysiological mechanisms: i) severe acute respiratory syndrome-coronavirus-2 (SARS-CoV- 2) interaction with hemoglobin molecule, through CD147, CD26 and other receptors located on erythrocyte and/or blood cell precursors; ii) hepcidin-mimetic action of a viral spike protein, inducing ferroportin blockage. In this translational medicinebased narrative review, the following pathologic metabolic pathways, deriving from hemoglobin denaturation and iron metabolism dysregulation, are highlighted: i) decrease of functioning hemoglobin quote; ii) iron overload in cell/tissue (hyperferritinemia); iii) release of free toxic circulating heme; iv) hypoxemia and systemic hypoxia; v) reduction of nitric oxide; vi) coagulation activation; vii) ferroptosis with oxidative stress and lipoperoxidation; viii) mitochondrial degeneration and apoptosis. A few clinical syndromes may follow, such as pulmonary edema based on arterial vasoconstriction and altered alveolo-capillary barrier, sideroblastic-like anemia, endotheliitis, vasospastic acrosyndrome, and arterio- venous thromboembolism. We speculated that in COVID-19, beyond the classical pulmonary immune-inflammation view, the occurrence of an oxygen-deprived blood disease, with iron metabolism dysregulation, should be taken in consideration. A more comprehensive diagnostic/therapeutic approach to COVID-19 is proposed, including potential adjuvant interventions aimed at improving hemoglobin dysfunction, iron over-deposit and generalized hypoxic state.

Dietary Sources and Bioactivities of Melatonin

Insomnia is a serious worldwide health threat, affecting nearly one third of the general population. Melatonin has been reported to improve sleep efficiency and it was found that eating melatonin-rich foods could assist sleep. During the last decades, melatonin has been widely identified and qualified in various foods from fungi to animals and plants. Eggs and fish are higher melatonin-containing food groups in animal foods, whereas in plant foods, nuts are with the highest content of melatonin. Some kinds of mushrooms, cereals and germinated legumes or seeds are also good dietary sources of melatonin. It has been proved that the melatonin concentration in human serum could significantly increase after the consumption of melatonin containing food. Furthermore, studies show that melatonin exhibits many bioactivities, such as antioxidant activity, anti-inflammatory characteristics, boosting immunity, anticancer activity, cardiovascular protection, anti-diabetic, anti-obese, neuroprotective and anti-aging activity. This review summaries the dietary sources and bioactivities of melatonin, with special attention paid to the mechanisms of action.

Free radical scavenging activity of silibinin in nitrite-induced hemoglobin oxidation and membrane fragility models

Free radical formation in heme proteins is recognized as a factor in mediating the toxicity of many drugs. Xenobiotics and drug therapy-related toxicity, due to oxidative modification of hemoglobin (Hb), has been attributed in part to the uncontrolled oxidative reactions. A variety of antioxidant strategies to ameliorate potential oxidative damage in vivo have been suggested. The present study was designed to evaluate the dose-response relationship of the free radical scavenging properties of silibinin dihemisuccinate (SDH) in nitrite-induced Hb oxidation in vitro and in vivo. Different concentrations of SDH were added, before and after different intervals of inducing Hb oxidation in erythrocytes lysate, and formation of methemoglobin (MetHb) was monitored spectrophotometrically; the same approach was utilized to evaluate the effect of the same doses of SDH on the integrity of erythrocytes after induction of hemolysis. Moreover, the most effective dose of SDH was administered in rats before challenge with toxic dose of sodium nitrite, and MetHb formation was monitored as mentioned before. The results showed that in both in vitro and in vivo models, SDH successfully attenuates Hb oxidation after challenge with sodium nitrite; this protective effect was not related to the stage of the catalytic stage of Hb oxidation, though the effect was more prominent when the compound was administered before nitrite. In conclusion, SDH can effectively, in concentration-dependent pattern, attenuate sodium nitrite-induced Hb oxidation and maintain integrity of red blood cells both in vitro and in vivo.

Neuroprotection by melatonin after germinal matrix hemorrhage in neonatal rats

BACKGROUND

Germinal matrix hemorrhage (GMH) is a devastating neurological disorder of very low birth weight premature infants that leads to post-hemorrhagic hydrocephalus, cerebral palsy, and mental retardation. Melatonin is a potent antioxidant known to reverse free-radical mediated injury in the brain. This study investigated the effect of melatonin treatment after GMH injury.

METHODS

Clostridial collagenase was infused into the right germinal matrix region of neonatal rats with stereotaxic technique. Cognitive function, sensorimotor ability, cerebral, cardiac and splenic growths were measured in juvenile animals.

RESULTS

Systemic melatonin treatment ameliorated cognitive and sensorimotor dysfunction at the juvenile developmental stage. This hormone also normalized brain atrophy, splenomegaly, and cardiac hypertrophy consequences at 1 month after injury.

CONCLUSION

This study supports the role of free radicals in acute neonatal hemorrhagic brain injury. Melatonin is an effective antioxidant that can protect the infant's brain from the post-hemorrhagic consequences of mental retardation and cerebral palsy. Further mechanistic studies are warranted to determine the mechanisms behind these neuroprotective effects.

Interactions of anionic surfactants with methemoglobin

Interactions of two anionic surfactants, sodium dodecyl sulphate (SDS) and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) at concentrations below and above critical micelle concentration with methemoglobin (metHb) have been investigated by conventional as well as by stopped-flow absorption and fluorescence spectroscopy. The absorption spectra of metHb in AOT reverse micelles have been also analyzed. Both surfactants in their monomeric form convert metHb to reversible hemichrome. This is connected with a diminution of peroxidase-like activity of metHb and with an increase of the susceptibility of heme for a damage by H(2)O(2). In micellar solutions of AOT and SDS as well as in AOT reverse micelles pentacoordinated ferric species seems to be the predominant form of this protein. It has been concluded, basing on a kinetic analysis, that conformational changes in the heme environment of metHb as induced by both surfactants occur independently of the alterations in the tertiary structure of this protein.

Protective effect of melatonin upon neuropathology, striatal function, and memory ability after intracerebral hemorrhage in rats

Since free radicals play a role in the mechanisms of brain injury after hemorrhagic stroke, the effect of melatonin (a potent antioxidant and free-radical scavenger) on outcomes was investigated after intracerebral hemorrhage (ICH) in rats. ICH was induced by clostridial collagenase infusion into the right caudate putamen, and several time points and doses of melatonin were studied. Brain edema and neurological function at 24 h were unchanged in comparison with vehicle-treated groups, in spite of oxidative stress reductions. Repeated treatment with the lower dose of melatonin (5 mg/kg) given at 1 h and every 24 h thereafter for 3 days after ICH, led to normalization of striatal function and memory ability over the course of 8 weeks, and less brain atrophy 2 weeks later. These results suggest that melatonin is safe for use after ICH, reduces oxidative stress, provides brain protection, and could be used for future investigations of free radical mechanisms after cerebral hemorrhage.

Melatonin protects the cytochrome P450 system through a novel antioxidant mechanism

Melatonin, an endogenous hormone, is used as an antioxidant drug in doses quite higher than the endogenous circulating levels of this hormone. Hepatic endoplasmic reticulum contains the cytochrome P450 (CYP450) system, which catalyzes one biotransformation pathway of melatonin; this organelle is also one of the main sources of reactive oxygen species in cells. Therefore, we proposed that the antioxidant activity of this hormone may have a biological relevance in the organelle where it is biotransformed. To evaluate this postulate, we used Fe(3+)/ascorbate, an oxygen free radical generating system that leads to lipid peroxidation, loss of protein-thiol content, and activation of UDP-glucuronyltransferase in rat liver microsomes. We found that mM concentrations of melatonin prevented all these oxidative phenomena. We also found that Fe(3+)/ascorbate leads to structural alterations in the CYP450 monooxygenase, the enzyme that binds the substrate in the CYP450 system catalytic cycle, probably through direct oxidation of the protein, and also inhibited p-nitroanisole O-demethylation, a reaction catalyzed by the CYP450 system. Notably, melatonin prevented both phenomena at microM concentrations. We provide evidence suggesting that melatonin may be oxidized by oxygen free radicals. Thus, we postulate that melatonin may be acting as an oxygen free radical scavenger, and Fe(3+)/ascorbate-modified melatonin would be directly protecting the CYP450 system through an additional specific mechanism. Pharmacological relevance of this phenomenon is discussed.

Kynuramines, metabolites of melatonin and other indoles: the resurrection of an almost forgotten class of biogenic amines

Kynuramines represent their own class of biogenic amines. They are formed either by decarboxylation of kynurenines or pyrrole ring cleavage of indoleamines. N(2)-formylated compounds formed in this last reaction can be deformylated either enzymatically by arylamine formamidases or hemoperoxidases, or photochemically. The earlier literature mainly focussed on cardiovascular effects of kynuramine, 5-hydroxykynuramine and their N(1),N(1)-dimethylated analogs, including indirect effects via release of catecholamines or acetylcholine and interference with serotonin receptors. After the discovery of N(1)-acetyl-N(2)-formyl-5-methoxykynuramine (AFMK) and N(1)-acetyl-5-methoxykynuramine (AMK) as major brain metabolites of melatonin, these compounds became of particular interest. They were shown to be produced enzymatically, pseudoenzymatically, by various free radical-mediated and via photochemical processes. In recent years, AFMK and AMK were shown to scavenge reactive oxygen and nitrogen species, thereby forming several newly discovered 3-indolinone, cinnolinone and quinazoline compounds, and to protect tissues from damage by reactive intermediates in various models. AMK is of special interest due to its properties as a potent cyclooxygenase inhibitor, NO scavenger forming a stable nitrosation product, inhibitor and/or downregulator of neuronal and inducible NO synthases, and a mitochondrial metabolism modulator. AMK easily interacts with aromates, forms adducts with tyrosyl and tryptophanyl residues, and may modify proteins.

Effect of melatonin on the blood oxygen transport during hypothermia and rewarming in rats

PURPOSE

We aimed to study effect of melatonin on the blood oxygen transport during hypothermia and rewarming in rats.

MATERIAL/METHODS

Cold exposure was performed on male rats (body weight 220-270 g, n=48) for 120 minutes under the box water temperature of 19 degrees C; rewarming took the next 120 min, with a mean rate of 0.06 degrees C/min. Melatonin was administered intraperitoneally 30 min before the cold exposure (bolus doses of 0.1, 1 or 10 mg/kg, or 1 mg/kg*day for 4 days). Haemoglobin-oxygen affinity was evaluated by p50 (blood pO2 at its 50% O2 saturation) determined by the "mixing" method at 37 degrees C, pH 7.4 and pCO2 40 mm Hg (p50stand) and at actual pH, pCO2 and temperature (p50act).

RESULTS

After hypothermia and rewarming, the values of p50stand and p50act were 31.5+/-0.28 and 30.2+/-0.61 mm Hg, respectively. The 0.1 mg/kg of melatonin virtually did not change these values, whereas the larger doses increased them. This effect was maximal after the prolonged (4 days) melatonin administration: p50stand rose by 5.4% (p<0.05) and p50act--by 12.9 (p<0.05) compared with rats without the melatonin treatment. Melatonin affected the mechanisms of O2 transport by decreasing the haemoglobin-oxygen affinity (shifting the oxygen dissociation curve of haemoglobin rightwards) and promoting the tissue oxygenation, thereby enhancing the body's resistance to cold.

CONCLUSIONS

The melatonin effect mediated by haemoglobin-oxygen affinity change may be used for the correction of metabolic disorders and the improvement of the body's resistance to low environmental temperature.

Potential role of tryptophan derivatives in stress responses characterized by the generation of reactive oxygen and nitrogen species

To face physicochemical and biological stresses, living organisms evolved endogenous chemical responses based on gas exchange with the atmosphere and on formation of nitric oxide (NO(*)) and oxygen derivatives. The combination of these species generates a complex network of variable extension in space and time, characterized by the nature and level of the reactive oxygen (ROS) and nitrogen species (RNS) and of their organic and inorganic scavengers. Among the latter, this review focusses on natural 3-substituted indolic structures. Tryptophan-derived indoles are unsensitive to NO(*), oxygen and superoxide anion (O(2)(*-)), but react directly with other ROS/RNS giving various derivatives, most of which have been characterized. Though the detection of some products like kynurenine and nitroderivatives can be performed in vitro and in vivo, it is more difficult for others, e.g., 1-nitroso-indolic compounds. In vitro chemical studies only reveal the strong likelihood of their in vivo generation and biological effects can be a sign of their transient formation. Knowing that 1-nitrosoindoles are NO donors and nitrosating agents indicating they can thus act both as mutagens and protectors, the necessity for a thorough evaluation of indole-containing drugs in accordance with the level of the oxidative stress in a given pathology is highlighted.

Interactions between melatonin and nicotinamide nucleotide: NADH preservation in cells and in cell-free systems by melatonin

Interactions of melatonin and nicotinamide adenine dinucleotide (NADH) have been studied in different experimental models including NADH-promoted oxyhemoglobin oxidation, vanadate-induced NADH oxidation and paraquat-induced NADH depletion in cultured PC12 cells. Our findings indicate that melatonin preserves NADH levels under oxidative stress both in cell-free systems and in cultured PC12 cells. These interactions likely involve electron donation by melatonin and reduction of the NAD radical. As a result, the NAD radical is recycled to NADH and melatonin is oxidized to N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK). NADH is a central molecule at the crossroads between energy metabolism and the antioxidant defense system in organisms. Recycling of NADH by melatonin might improve the efficiency of NADH as an energy carrier and as an antioxidant. Interactions between melatonin and NADH may be implicated in mitochondrial metabolism.

Rat, caprine, equine and bovine erythrocyte ghosts exposed to t-butyl hydroperoxide as a model to study lipid peroxidation using a chemiluminescence assay

The aim of the present study was to analyze the time-course of t-butyl hydroperoxide-induced changes in lipid peroxidation, fatty acid composition and chemiluminescence intensity in rat, caprine, equine and bovine erythrocyte ghosts. A relatively high content of arachidonic acid (C20:4 n6) and docosahexaenoic acid (C22:6 n3) was characteristic of the rat erythrocyte ghosts. The fatty acid composition of native erythrocyte ghosts obtained from caprine, equine and bovine was characterized by a high content of oleic acid (C18:1 n9) and a low content of the peroxidable polyunsaturated fatty acids (C20:4 n6 and C22:6 n3). The proportion of linoleic acid (C18:2 n6) was higher in equine and bovine compared to rat and caprine. Increase in lipid peroxidation in rat erythrocyte ghosts was maximal within 12 min of incubation, t-butyl hydroperoxide concentration dependent and was paralleled by a decrease in C18:2 n6, C20:4 n6 and C22:6 n3 and an increase in chemiluminescence formation. Polyunsaturated fatty acids (PUFAs) present in rat erythrocyte ghosts exhibit the highest sensitivity to oxidative damaged and their sensitivity increases as a power function of the number of double bonds per fatty acid molecule. Light emission in caprine, equine and bovine erythrocyte ghosts was very low, t-butyl hydroperoxide concentration-dependent but changes in fatty acid composition were not observed. The main conclusion of this work is that a low unsaturation degree of fatty acids in erythrocyte ghosts of caprine, equine and bovine prevent the lipid peroxidation on those membranes when they are incubated with t-butyl hydroperoxide.

Oxygen therapeutics: can we tame haemoglobin?

Chemically modified or genetically engineered haemoglobins (Hbs) developed as oxygen therapeutics (often termed 'blood substitutes') are designed to correct oxygen deficit due to ischaemia in a variety of clinical settings. These modifications are intended to stabilize Hb outside its natural environment--red blood cells--in a functional tetrameric and/or polymeric form. Uncontrolled haem-mediated oxidative reactions of cell-free Hb and its reactions with various oxidant/antioxidant and cell signalling systems have emerged as an important pathway of toxicity. Current protective strategies designed to produce safe Hb-based products are focused on controlling or suppressing the 'radical' nature of Hb while retaining its oxygen-carrying function.

Protective effect of melatonin against mitochondrial injury induced by ischemia and reperfusion of rat liver

Melatonin, a pineal secretory product, is a potent scavenger of a variety of free radicals. The aim of this study was to investigate the effect of melatonin on the prevention of mitochondrial injury induced by hepatic ischemia and reperfusion. Rats were subjected to 70 min of hepatic ischemia and 2 h of reperfusion. Fifteen minutes prior to ischemia and at reperfusion, animals received vehicle or melatonin (10 mg/kg body weight) intraperitoneally. In the vehicle-treated animals, the respiratory control index, ADP/O, State 3 respiration and dinitrophenol-induced uncoupled respiration decreased markedly after ischemia/reperfusion and were restored by melatonin administration. Similarly, pH change coupled with mitochondrial energy transfer was suppressed by ischemia/reperfusion with the effects being reduced by melatonin treatment. Mitochondrial lipid peroxidation was elevated in the ischemic/reperfused vehicle-treated livers, but this elevation was attenuated by melatonin. Mitochondrial glutathione peroxidase activity decreased in the vehicle-treated group with this decrease being reduced by melatonin treatment. Electron microscopic studies demonstrated that treatment with melatonin restored to near normal the ischemia/reperfusion-induced disorganization of mitochondrial structure. Melatonin protects against mitochondrial injury which reduces mitochondrial oxidative stress and improves ischemia/reperfusion-induced hepatic energy metabolism.

Acutely administered melatonin restores hepatic mitochondrial physiology in old mice

Damage to mitochondria as a result of the intrinsic generation of free radicals is theoretically involved in the processes of cellular aging. Herein, we investigated whether acutely administered melatonin, due to its free radical scavenging activity, would influence mitochondrial metabolism. Mitochondrial respiratory activity and respiratory chain complex I and IV activities in liver mitochondria from a strain of senescence-accelerated-prone mice (SAMP8) and a strain of senescence-accelerated-resistant mice (SAMR1) were measured when the animals were 12 months of age. Respiratory control index (RCI), ADP/O ratio, State 3 respiration and dinitrophenol (DNP)-dependent uncoupled respiration were significantly lower in SAMP8 than in SAMR1. In contrast, State 4 respiration was significantly higher in SAMP8 than in SAMR1. Activities of complexes I and IV in SAMP8 were significantly lower than in SAMR1. Melatonin administration (10mg/kg body weight, intraperitoneally) 1h prior to sacrifice significantly increased RCI, ADP/O ratio, State 3 respiration and DNP-induced uncoupled respiration in SAMP8 while also significantly reducing State 4 respiration in SAMP8. The injection of melatonin also significantly increased complex I activity in both mouse strains and complex IV activity in the liver of SAMP8 mice. These results document an age-related decrease in hepatic mitochondrial function in SAM which can be modified by an acute pharmacological injection of melatonin; the indole stimulated mitochondrial respiratory chain activity which would likely reduce deteriorative oxidative changes in mitochondria that normally occur in advanced age.

Melatonin and pinoline prevent aluminium-induced lipid peroxidation in rat synaptosomes

The serum concentrations of aluminum, a metal potentially involved in the pathogenesis of Alzheimer's disease, increase with age. Also, intense and prolonged exposure to aluminum may result in dementia. Melatonin and pinoline are two well known antioxidants that efficiently reduce lipid peroxidation due to oxidative stress. Herein, we investigated the effects of melatonin and pinoline in preventing aluminum promotion of lipid peroxidation when the metal was combined with FeCl3 and ascorbic acid in rat synaptosomal membranes. Lipid peroxidation was estimated by quantifying malondialdehyde (MDA) and 4-hydroxyalkenal (4-HDA) concentrations in the membrane suspension. Under the experimental conditions used herein, the addition of aluminum (0.0001 to 1 mmol/L) enhanced MDA + 4-HDA formation in the synaptosomes. Melatonin and pinoline reduced, in a concentration-dependent manner, lipid peroxidation due to aluminum, FeCl3 and ascorbic acid in the synaptosomal membranes. These results suggest that the indoleamine melatonin and the beta-carboline pinoline may potentially act as neuroprotectant agents in the therapy of those diseases with elevated aluminum concentrations in the tissues.

Hepatic mitochondrial dysfunction in senescence-accelerated mice: correction by long-term, orally administered physiological levels of melatonin

Mitochondrial oxidative damage from free radicals may be a factor underlying aging. We investigated whether long-term administration of physiological levels of melatonin, a direct free radical scavenger and indirect antioxidant, influences mitochondrial respiratory activity in liver of senescence-accelerated mice (SAM). Liver was obtained in the middle of dark period of the daily light:dark cycle from SAMP8, a strain of mice prone to accelerated senescence, and from SAMR1, a senescence-resistant strain, at 6 and 12 months of age. Respiratory control index (RCI), adenosine-5-diphosphate (ADP)/O ratio, State 3 respiration and dinitophenol (DNP)-dependent uncoupled respiration exhibited significant age-associated decreases in SAMP8. SAMP8 also showed significant age-associated reductions in respiratory chain complex I and IV activities. No age-related effects were found in these parameters in SAMR1. Daily oral melatonin administration (2 microg/mL of drinking fluid) beginning at 7 months of age significantly increased RCI, State 3 respiration, DNP-dependent uncoupled respiration, and complex I and IV activities in both mouse strains when they were 12 months old. These results reveal age-related reductions in mitochondrial function in SAM mice which are modified by melatonin; the most likely explanation for the corrective actions of melatonin relate to its antioxidative actions in mitochondria and other portions of the cell. The implication of the findings is that melatonin may be beneficial during aging as it reduces the deteriorative oxidative changes in mitochondria and other portions of the cell associated with advanced age.

Protective effect of melatonin against cytotoxic actions of malondialdehyde: an in vitro study on human erythrocytes

Malondialdehyde (MDA), a by-product of the oxidation of polyunsaturated fatty acids, is strongly cytotoxic. Here we report the in vitro ability of melatonin to protect intact human erythrocytes against the damage induced by the exposure to MDA. MDA at 20 microM caused marked variations in the red blood cell (RBC) membrane. High molecular weight fluorescent adducts were formed within minutes with membrane proteins. A 6-hr incubation led to the oxidation of membrane lipids, as reflected by the formation of conjugated diene (CD) lipid hydroperoxides and oxidation of vitamin E, and to an increase of the high molecular weight fluorescent adducts, which were an indication of MDA finally generated in the cells. Functional damage to the membrane was evident as a leakage of K+ ions into the incubation medium, and an increased resistance to osmotic lysis. A time-dependent hemolysis was observed by exposure of RBCs to 20 microM MDA for 6-12 hr. Melatonin was not a substrate for MDA, therefore it was not able to prevent the early formation of the adducts from the reaction of the MDA in the medium with membrane proteins. Melatonin, however, concentration-dependent prevented the formation of CD lipid hydroperoxides. As a consequence of counteracting the membrane lipid oxidation, the indoleamine prevented the loss of vitamin E and the increase of the fluorescent proteinaceous adducts observed after a 6-hr exposure to MDA. Melatonin also inhibited the K+ loss and returned to normal the osmotic resistance of the erythrocyte in the osmotic fragility test. By protecting membrane lipids and proteins, melatonin effectively prevented the MDA-induced time-dependent hemolysis. In the light of the known radical scavenging properties of melatonin, mechanisms of the cytoprotective effects of melatonin in our system are discussed.

Melatonin protects hepatic mitochondrial respiratory chain activity in senescence-accelerated mice

Mitochondrial oxidative damage from free radicals may be a factor underlying aging, and melatonin, a powerful free radical scavenger, may participate in mitochondrial metabolism. We measured respiratory chain complex I and IV activities in liver mitochondria from a strain of senescence-accelerated prone mice (SAMP8) and a strain of senescence-accelerated resistant mice (SAMR1) at age 3, 6, and 12 months. No age-associated effects were found in either complex I and IV activities, thiobarbituric acid-reactive substances (TBARS), or glutathione peroxidase (GPx) activity in SAMRI. In contrast, SAMP8 showed significant age-associated decreases in complex I and IV activities. While no age effect was found in TBARS in SAMP8, TBARS levels in SAMP8 were significantly more abundant than in SAMRI. GPx activity in SAMP8 decreased significantly by 12 months. Daily oral melatonin administration (2 microg/mL of drinking fluid) beginning when the mice were 7 months old significantly increased complex I and IV activity, decreased TBARS, and increased GPx activities in both SAMRI and SAMP8 at 12 months. The implication of the findings is that melatonin may be beneficial during aging as it reduced the deteriorative oxidative changes in mitochondria and other portions of the cell associated with advanced age.