Beneficial properties of melatonin in an experimental model of pancreatic cancer

Pancreatic cancer is a major health problem because of the aggressiveness of the disease and the lack of effective systemic therapies. Melatonin has antioxidant activity and prevents experimental genotoxicity. However, the effect of melatonin in pancreatic cancer has not been tested. Pancreatic carcinogenesis was induced by N-nitrosobis (2-oxopropyl)amine (BOP) in Syrian hamsters. Melatonin was administered during the BOP-induction phase (12 wk) and/or following the postinduction phase (12 wk). Different parameters of oxidative stress including lipid peroxides (LPO) and antioxidants (superoxide dismutase, catalase, reduced glutathione and glutathione peroxidase) were determined in pancreatic tissue. Also, the presence of atypical hyperplasia (AH), well and moderately differentiated adenomacarcinoma (ADC-WD and ADC-MD, respectively) were studied. The administration of BOP induced an intense oxidative stress and ADC induction in the pancreas. The administration of melatonin during the induction or postinduction phase reduced LPO and improved the antioxidant status, as well as drastically reducing the presence of ADC but some AH remained. In conclusion, treatment with melatonin reduced oxidative damage and cancer nodules induced by BOP in the pancreas.     

Melatonin protects kidney grafts from ischemia/reperfusion injury through inhibition of NF-kB and apoptosis after experimental kidney transplantation

Abstract:  Free radicals are involved in pathophysiology of ischemia/reperfusion injury (IRI). Melatonin is a potent scavenger of reactive oxygen and nitrogen species. Thus, this study was designed to elucidate its effects in a model of rat kidney transplantation. Twenty Lewis rats were randomly divided into 2 groups (n = 10 animals each). Melatonin (50 mg/kg BW) dissolved in 5 mL milk was given to one group via gavage 2 hr before left donor nephrectomy. Controls were given the same volume of milk only. Kidney grafts were then transplanted into bilaterally nephrectomized syngeneic recipients after 24 hr of cold storage in Histidine–Tryptophan–Ketoglutarate solution. Both graft function and injury were assessed after transplantation through serum levels of blood urea nitrogen (BUN), creatinine, transaminases, and lactate dehydrogenase (LDH). Biopsies were taken to evaluate tubular damage, the enzymatic activity of superoxide dismutase (SOD) and lipid hydroperoxide (LPO), and the expression of NF-kBp65, inducible nitric oxide synthase (iNOS), caspase-3 as indices of oxidative stress, necrosis, and apoptosis, respectively. Melatonin improved survival ( P  < 0.01) while decreasing BUN, creatinine, transaminases, and LDH values up to 39–71% ( P  < 0.05). Melatonin significantly reduced the histological index for tubular damage, induced tissue enzymatic activity of SOD while reducing LPO. At the same time, melatonin down-regulated the expression of NF-kBp65, iNOS, and caspase-3. In conclusion, donor preconditioning with melatonin protected kidney donor grafts from IRI-induced renal dysfunction and tubular injury most likely through its anti-oxidative, anti-apoptotic and NF-kB inhibitory capacity.     

Melatonin protects against experimental reflux esophagitis

Abstract:  Reflux esophagitis (RE), a major gastrointestinal disorder results from excess exposure of the esophageal mucosa to acidic gastric juice or bile-containing duodenal contents refluxed via an incompetent lower esophageal sphincter. Recent studies implicated oxygen derived free radicals in RE induced esophageal mucosal damage resulting in mucosal inflammation. Thus, control over free radical generation and modulation of inflammatory responses might offer better therapeutic effects to counteract the severity of RE. In this context we investigated the effect of melatonin against experimental RE in rats. Melatonin pretreatment significantly reduced the haemorrhagic lesions and decreased esophageal lipid peroxidation aggravated by RE. Moreover, the depleted levels of superoxide dismutase and glutathione observed in RE were replenished by melatonin signifying its free radical scavenging properties and antioxidant effects resulting in the improvement of esophageal defense mechanism. Further melatonin repressed the upregulated levels of expression of proinflammatory cytokines like, TNF-α, IL-1β and IL-6 in RE. However, increased levels of the anti-inflammatory cytokine IL-10 remained unaltered after melatonin administration signifying its immunomodulatory effect through suppression of Th1-mediated immune responses. The involvement of receptor dependent actions of melatonin against RE were also investigated with MT2 receptor antagonist, luzindole (LUZ). LUZ failed to antagonize melatonin's protective effects against RE indicating that melatonin mediated these beneficial effects in a receptor-independent fashion. Thus, esophageal mucosal protection elicited by melatonin against experimental RE is not only dependent on its free radical scavenging activity but also mediated in part through its effect on the associated inflammatory events in a receptor-independent manner.     

The efficacy of vitamin E and melatonin as antioxidants against lipid peroxidation in rat retinal homogenates

Abstract: Free radical-induced oxidation can cause severe cell damage in biological systems. Melatonin, a pineal secretory product, is a recently identified antioxidant that protects cells from the damaging effects of free radicals. We compared the effect of melatonin and vitamin E, another antioxidant, against lipid peroxidation (LPO) in rat retinal homogenates. The aim was to characterize the antioxidative efficacy of melatonin in retina, a tissue highly susceptible to oxidative damage. The LPO product, malondialdehyde (MDA), was determined to provide an index of cell damage in vitro. After the incubation with iron(II) ions, the free radical scavenging effectiveness of four different concentrations (i.e., 0.5, 1.0, 2.0, and 4.0 mM) of vitamin E and melatonin were determined by comparing the final levels of MDA. Lipid peroxidation product levels were significantly reduced in a dose-response manner by all concentrations of vitamin E. Melatonin, in concentrations of either 2.0 or 4.0 mM, also significantly reduced LPO. Statistical analysis of the data showed that vitamin E treatment always yielded a lower level of LPO products than did the same concentration of melatonin. The concentrations of each agent required to inhibit 50% of the lipid damage (IC50) were 0.69 mM and 4.98 mM for vitamin E and melatonin, respectively. Both vitamin E and melatonin protect the retina against LPO in a dose-dependent manner. Although the IC50 value for melatonin is about 7.2 times higher than that of vitamin E, melatonin's pharmacological and physiological role in the treatment and/or prevention of certain retinal diseases in vivo should be further investigated.     

Melatonin protects from the long-term consequences of a neonatal hypoxic-ischemic brain injury in rats

Abstract:  Among the main factors responsible for perinatal brain injury, inflammation, hypoxia-ischemia and formation of free radicals (FR) appear to play key roles. Melatonin, an endogenously produced indoleamine formed in higher amounts in adults than in neonates, is a potent FR scavenger as well as an indirect antioxidant. Herein, we examined whether melatonin provides significant protection against brain damage and its long-term consequences in a neonatal model of hypoxia-ischemia (HI). Seven day-old rats were subjected to permanent legation of the right common carotid artery followed to 2.5 hrs hypoxia 3 hrs later (HI). The neuroprotective effect of melatonin was evaluated 7 days after HI, or when rats reached adulthood, using behavioral and histological analyses. A beneficial effect was observed with 5 mg/kg melatonin administered before HI. The same dose repeated three times reduced further injury. A significant protective effect was found when 15 mg/kg melatonin was given 30 min before HI or when the same dose was given after HI and administration repeated after 24 and 48 hrs. The latter schedule of administration was used to assess the long-term protective effects. Melatonin did not affect growth rate and behavior at adulthood, but significantly improved the behavioral asymmetry and learning deficits induced by HI. Consistently, brain injury was significantly attenuated in the melatonin-treated ischemic group. The present study demonstrates that melatonin administration before or after HI in immature rats has an excellent and long-lasting benefit on ischemic outcomes suggesting that the drug could represent a potentially safe approach to perinatal brain damage in humans.     

Free iron, total F2-isoprostanes and total F4-neuroprostanes in a model of neonatal hypoxic–ischemic encephalopathy: neuroprotective effect of melatonin

Abstract:   Oxidative stress due to free radical formation and initiation of abnormal oxidative reactions is involved in several diseases of newborns, such as hypoxic–ischemic encephalopathy. Melatonin, an endogenously produced indoleamine primarily formed in the pineal gland, is a potent free radical scavenger as well as an indirect antioxidant. The present study was conducted to evaluate the formation of oxidative damage mediators and the possible effect of melatonin treatment in a model of hypoxic–ischemic encephalopathy in 7-day-old rats. Pups were subjected to permanent ligation of the right common carotid artery and exposed for 2.5 hr to a nitrogen–oxygen mixture (92% and 8%, respectively) (hypoxia–ischemia, HI). Melatonin was injected intraperitoneally to a group of rats at the dose of 15 mg/kg 30 min before starting the ischemic procedure (HI–Melatonin). After 24 hr of treatment, in homogenized cerebral cortex, desferoxamine (DFO)-chelatable free iron, total F₂-isoprostanes and total F₄-neuroprostanes, originating from the free radical-catalyzed peroxidation of arachidonic and docosahexaenoic acids, respectively, were determined. HI induced a significant increase in DFO-chelatable iron, total F₂-isoprostanes and F₄-neuroprostanes in both right and left side of the cerebral cortex. In HI–Melatonin-treated animals the levels of free iron, F₂-isoprostanes, and F₄-neuroprostanes were significantly lower than that in HI rats and the values were similar to controls. These data show the important neuroprotective role of melatonin in reducing oxidative damage resulting from HI. Melatonin could represent a potential safe approach to perinatal brain damage in humans.     

Changes in iNOS activity, oxidative stress and melatonin levels in hypertensive patients treated with lacidipine

OBJECTIVE(S): To study the changes in macrophage inducible nitric oxide synthase (iNOS) activity, plasma levels of nitrite, lipid peroxidation (LPO) and melatonin in human essential hypertension before and 6 months after 4 mg/day lacidipine treatment. DESIGN: The study was carried out in a total of 25 subjects--11 healthy subjects and 14 hypertensive patients. Blood pressure and peripheral blood samples were taken before and after 6 months of lacidipine treatment (4 mg/day). METHODS: Systolic (SBP) and diastolic blood pressure (DBP), renal function, lipid and carbohydrate metabolism, renin, aldosterone and catecholamine levels were measured by routine methods. The activity of macrophage iNOS and plasma nitrite, LPO and melatonin levels were also measured. CONCLUSIONS: Besides reducing blood pressure, lacidipine treatment significantly decreased plasma LPO and macrophage iNOS activity, without changes in NO. Melatonin significantly increases in hypertensive patients, returning to control after lacidipine. Thus, lacidipine reduced blood pressure and free radicals, avoiding the oxidative damage to endothelium. It is suggested that administration of lacidipine plus melatonin may enhance the beneficial effects of each drug in essential hypertension.     

Melatonin and tryptophan counteract lipid peroxidation and modulate superoxide dismutase activity in ringdove heterophils in vivo. Effect of antigen-induced activation and age

Aging is associated with an increased production of free radicals and alterations in the mechanisms of adaptation to stress. A number of studies have shown a causal connection between age-related oxidant/antioxidant imbalance and the diminution of an organism’s melatonin levels in old age. Restoration of this rhythm may contribute to the re-stabilization of cellular homeostasis. The present work was aimed at examining the effect of the administration of melatonin or its precursor, the amino acid tryptophan, on heterophil lipid peroxidation (LPO) levels and superoxide dismutase (SOD) activity in heterophils from young (4–5 year) and old (12–14 year) ringdoves (Streptopelia risoria) under both basal and antigen-induced (stressful) conditions. Young animals were treated for 3 consecutive days with a single daily oral dose (0.25 mg) of melatonin at 1900 hours while old animals were treated for 3 consecutive days with either an oral dose (2.5 mg) of melatonin at 1900 hours or an oral capsule of 300 mg/kg body weight of l-tryptophan at 0900 hours. Non-treated old animals presented lower circulating levels of melatonin at night and higher levels of malonaldehyde (MDA) both day and night when compared to young birds. In both age groups, LPO levels were lower at night than during the day. Melatonin or tryptophan treatments significantly increased serum melatonin levels, reinforced SOD activity, and reduced MDA levels induced by the antigen. Melatonin and tryptophan may be useful agents for the treatment of disease states and processes in which an excessive production of oxidative damage occurs.     

Effect of melatonin administration on parameters related to oxidative damage in hepatocytes isolated from old Wistar rats

Aging induces changes in several organs and tissues, such as the liver, and this process might be due to oxidative damage caused by free radicals and inflammatory mediators. Melatonin is a secretory product with well-known antioxidant properties. The aim of this study was to investigate the effect of melatonin administration on age-induced alterations in hepatocytes. Twenty-two-month old male Wistar rats were treated with oral melatonin for 10 wk. At the end of the treatment, hepatocytes were isolated and cultured, and different parameters were measured in both cells and medium. Aging induced a significant increase in lipid peroxidation, nitric oxide, carbon monoxide and cyclic guanosyl-monophosphate, as well as a reduction in adenosine triphosphate content and phosphatidylcholine synthesis when compared to young animals. Melatonin administration significantly ameliorated all these age-related changes in males. Melatonin administration seems to exert beneficial effects against age-induced changes in hepatocytes.     

Melatonin-induced increased activity of the respiratory chain complexes I and IV can prevent mitochondrial damage induced by ruthenium red in vivo

Melatonin displays antioxidant and free radical scavenger properties. Due to its ability with which it enters cells, these protective effects are manifested in all subcellular compartments. Recent studies suggest a role for melatonin in mitochondrial metabolism. To study the effects of melatonin on this organelle we used ruthenium red to induce mitochondrial damage and oxidative stress. The results show that melatonin (10 mg/kg i.p.) can increase the activity of the mitochondrial respiratory complexes I and IV after its administration in vivo in a time-dependent manner; these changes correlate well with the half-life of the indole in plasma. Melatonin administration also prevented the decrease in the activity of complexes I and IV due to ruthenium red (60 microg/kg i.p.) administration. At this dose, ruthenium red did not induce lipid peroxidation but it significantly reduced the activity of the antioxidative enzyme glutathione peroxidase, an effect also counteracted by melatonin. These results suggest that melatonin modulates mitochondrial respiratory activity, an effect that may account for some of the protective properties of the indoleamine. The mitochondria-modulating role of melatonin may be of physiological significance since it seems that the indoleamine is concentrated into normal mitochondria. The data also support a pharmacological use of melatonin in drug-induced mitochondrial damage in vivo.     

Melatonin reduces apoptosis and necrosis induced by ischemia/reperfusion injury of the pancreas

The pancreas is highly susceptible to the oxidative stress induced by ischemia/reperfusion (IR) injury leading to the generation of acute pancreatitis. Melatonin has been shown to be useful in the prevention of the damage by ischemia-reperfusion in liver, brain, myocardium, gut and kidney. The aim of the study was to evaluate the cytoprotective properties of melatonin against injury induced by IR in pancreas. The obstruction of gastro-duodenal and inferior splenic arteries induced pancreatic IR in male Wistar rats. Melatonin was intraperitoneally administered before or/and after IR injury. The animals were killed at 24 and 48 hr after reperfusion and there were evaluated parameters of oxidative stress (lipoperoxides, superoxide dismutase, catalase, glutathione peroxidase and reduced glutathione), glandular endocrine and exocrine function (lipase, amylase, insulin) and cell injury (apoptosis and necrosis). The IR induced a marked enhancement of oxidative stress and impaired pancreatic function. The histological analysis showed that IR induced acute pancreatitis with the accumulation of inflammatory infiltrate, disruption of tissue structure, cell necrosis and hemorrhage. Melatonin administration before or after pancreatic IR prevented all tissue markers of oxidative stress, biochemical and histological signs of apoptosis and necrosis, and restored glandular function. No histological signs of pancreatitis were observed 48 hr after reperfusion in 80% of the animals treated with melatonin, with only a mild edematous pancreatitis being observed in the remaining rats. Preventive or therapeutic administration of melatonin protected against the induction of oxidative stress and tissue injury, and restored cell function in experimental pancreatic IR in rats.     

Aging and oxygen toxicity: Relation to changes in melatonin

Melatonin (N-acetyl-5-methoxytryptamine) is a chemical mediator produced in the pineal gland and other sites in the body. The melatonin found in the blood is derived almost exclusively from the pineal gland. Since the pineal synthesizes melatonin primarily at night, blood levels of the indole are also higher at night (5–15 fold) than during the day. Some individuals on a nightly basis produce twice as much melatonin as others of the same age. Throughout life, the melatonin rhythm gradually wanes such that, in advanced age, melatonin production is usually at a minimum. Melatonin was recently found to be a free radical scavenger and antioxidant. It has been shown, in the experimental setting, to protect against both free radical induced DNA damage and oxidative stress-mediated lipid peroxidation. Pharmacologically, melatonin has been shown to reduce oxidative damage caused by such toxins as the chemical carcinogen safrole, carbon tetrachloride, paraquat, bacterial lipopolysaccharide, kainic acid, δ-aminolevulinic and amyloid β peptide of Alzheimer’s disease as well as a model of Parkinson’s disease involving the drug 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Additionally, the oxidative damage caused by agents such as ionizing radiation and excessive exercise is reduced by melatonin. Since free radical-induced molecular injury may play a significant role in aging, melatonin’s ability to protect against it suggests a potential function of melatonin in deferring aging and age-related, free radical-based diseases. Besides its ability to abate oxidative damage, other beneficial features of melatonin may be important in combating the signs of aging; these include melatonin’s immune-stimulating function, its sleep-promoting ability, its function as an anti-viral agent, and general protective actions at the cellular level. Definitive tests of the specific functions of physiological levels of melatonin in processes of aging are currently being conducted.     

Cardiovascular diseases: protective effects of melatonin

This brief review considers some of the cardiac diseases and conditions where free radicals and related reactants are believed to be causative. The report also describes the beneficial actions of melatonin against oxidative cardiovascular disorders. Based on the data available, melatonin seems to have cardioprotective properties via its direct free radical scavenger and its indirect antioxidant activity. Melatonin efficiently interacts with various reactive oxygen and reactive nitrogen species (receptor independent actions) and it also upregulates antioxidant enzymes and downregulates pro-oxidant enzymes (receptor-dependent actions). Moreover, melatonin enters all cells and subcellular compartments and crosses morphophysiologic barriers. These findings have implications for the protective effects of melatonin against cardiac diseases induced by oxidative stress. Melatonin attenuates molecular and cellular damages resulting from cardiac ischemia/reperfusion in which destructive free radicals are involved. Anti-inflammatory and antioxidative properties of melatonin are also involved in the protection against a chronic vascular disease, atherosclerosis. The administration of melatonin, as a result of its antioxidant features, has been reported to reduce hypertension and cardiotoxicity induced by clinically used drugs. The results described herein help to clarify the beneficial effects of melatonin against these conditions and define the potential clinical applicability of melatonin in cardiovascular diseases.     

Melatonin prevents experimental liver cirrhosis induced by thioacetamide in rats

Abstract:  Liver cirrhosis is a critical stage of chronic liver diseases that can produce liver failure, portal hypertension and hepatocarcinoma. Sustained oxidative stress plays a key role in cell damage and fibrosis induced during liver cirrhosis. We evaluated the effect of oxidative stress regulation by melatonin on the development of parenchymal destruction and stellate cell activation in experimental liver cirrhosis. Melatonin was administered to rats with liver cirrhosis induced by thioacetamide (TAA) for 1 or 3 months. Liver injury was assessed by serological analysis, as well as hematoxylin-eosin staining and the in situ apoptosis detection assay in liver sections. Oxidative stress was evaluated by lipoperoxide and reduced glutathione levels, and by the measurement of catalase and superoxide dismutase activities in liver and serum respectively. The activation of stellate cells was evaluated by α -smooth muscle actin expression in liver sections. Our results showed that TAA induced oxidative stress with extensive tissue damage and enhanced α -smooth muscle actin expression in liver. Melatonin prevented the oxidative stress-related changes associated with TAA toxicity. In conclusion, the study showed that melatonin prevents the tissue damage and fibrosis associated with TAA-induced liver cirrhosis in rats.     

Dual effect of melatonin as proinflammatory and antioxidant in collagen-induced arthritis in rats

Abstract:  The aim of this study was to determine the effects of melatonin on proinflammatory status of rats with collagen-induced arthritis (CIA). CIA was induced in male Wistar rats with an emulsion of type II collagen in Freund's Incomplete Adjuvant (C-II/FIA). For 14 days, control and pinealectomized rats received a subcutaneous injection of 100  μ L melatonin (30  μ g) or vehicle (saline on 1% ethanol). Levels of cytokines interleukin (IL)-1 β and IL-6 were determined in the serum, peripheral blood mononuclear cells, and joints. Levels of anti-type II collagen antibody, nitrite/nitrate, and lipid peroxidation (LPO) were determined in the serum, joints, and brain. Treatment with melatonin significantly increased the levels of IL-1 β , IL-6, nitrite/nitrate and LPO in joints. However, melatonin significantly reduced the levels of nitrite/nitrate and LPO in serum and brain. Moreover, CIA in pinealectomized rats presented significantly reduced levels of IL-1 β and IL-6, titers of anti-type II collagen antibodies, levels of nitrite/nitrate, and LPO in joints but elevated levels in serum and brain. Melatonin has been described as a proinflammatory and antioxidant agent. In a process of inflammation as CIA, melatonin acts with a markedly proinflammatory effect at local and peripheral levels maintaining its antioxidant effect only at peripheral level.     

Melatonin improves placental efficiency and birth weight and increases the placental expression of antioxidant enzymes in undernourished pregnancy

Abstract:  Melatonin participates in circadian, seasonal and reproductive physiology. Melatonin also acts as a potent endogenous antioxidant by scavenging free radicals and upregulating antioxidant pathways. The placenta expresses melatonin receptors and melatonin protects against oxidative damage induced in rat placenta by ischemia-reperfusion. One of the most common complications in pregnancy is a reduction in fetal nutrient delivery, which is known to promote oxidative stress. However, whether melatonin protects placental function and fetal development in undernourished pregnancy is unknown. Here, we investigated the effects of maternal treatment with melatonin on placental efficiency, fetal growth, birth weight and protein expression of placental oxidative stress markers in undernourished pregnancy. On day 15 of pregnancy, rats were divided into control and undernourished pregnancy (35% reduction in food intake), with and without melatonin treatment (5 μg/mL drinking water). On day 20 of gestation, fetal biometry was carried out, the placenta was weighed and subsequently analyzed by Western blot for xanthine oxidase, heat shock protein (HSP) 27 and 70, catalase, manganese superoxide dismutase (Mn-SOD) and glutathione peroxidase 1 (GPx-1). A separate cohort was allowed to deliver to assess effects on birth weight. Maternal undernutrition led to a fall in placental efficiency, disproportionate intrauterine growth retardation and a reduction in birth weight. Maternal treatment with melatonin in undernourished pregnancy improved placental efficiency and restored birth weight, and it increased the expression of placental Mn-SOD and catalase. The data show that in pregnancy complicated by undernutrition, melatonin may improve placental efficiency and birth weight by upregulating placental antioxidant enzymes.     

Serum cholesterol and lipid peroxidation are decreased by melatonin in diet-induced hypercholesterolemic rats

The purpose of this study was to investigate the effect of melatonin, at pharmacological doses, on serum lipids of rats fed with a hypercholesterolemic diet. Therefore, different groups of animals were fed with either the regular Sanders Chow diet or a diet enriched in cholesterol. Moreover, animals were treated with or without melatonin in the drinking water for 3 months. We show that melatonin treatment did not affect the levels of cholesterol or triglycerides in rats fed with a regular diet. However, the increase in total cholesterol and low-density lipoprotein (LDL)-cholesterol induced by a cholesterol-enriched diet was reduced significantly by melatonin administration. On the other hand, melatonin administration prevented the decrease in high-density lipoprotein (HDL)-cholesterol induced by the same diet. No differences in the levels of very low-density lipoprotein (VLDL)-cholesterol and triglycerides were found. We also found that melatonin administration slightly decreased serum uric, bilirubin and increased serum glucose levels. Other biochemical parameters, including total proteins, creatinine, urea, phosphorus, calcium, glutamic oxalacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), gamma-glutamyltranspeptidase (gamma-GT), acetyl cholinesterase (AcCho), and alkaline phosphatase (ALP) were not modified by melatonin treatment. Finally, lipid peroxidation (LPO) was studied in membranes of liver, brain, spleen, and heart as an index of membrane oxidative damage. Results show that hypercholesterolemic diet did not modify the LPO status in any of the tissues studied. However, chronic melatonin administration significantly decreased LPO. Results confirm that melatonin participates in the regulation of cholesterol metabolism and in the prevention of oxidative damage to membranes.     

Melatonin increases activities of glutathione peroxidase and superoxide dismutase in fetal rat brain

Melatonin is a powerful scavenger of oxygen free radicals. In humans, melatonin is rapidly transferred from the maternal to the fetal circulation. To investigate whether or not maternal melatonin administration can protect the fetal rat brain from radical-induced damage by increasing the activities of antioxidant enzymes, we administered melatonin to pregnant rats on day 20 of gestation. Melatonin (10 mg/kg) was injected intraperitoneally at daytime (14:00 hr) and, to remove the fetuses, a laparotomy was performed at 1, 2, or 3 hr after its administration. We measured the melatonin concentration in the maternal serum and in fetal brain homogenates and determined the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in fetal brain homogenates. Melatonin administration markedly increased melatonin concentrations in the maternal serum and fetal brain homogenates, with peak levels achieved 1 hr after melatonin administration (serum: 538.2+/-160.7 pM/mL; brain homogenates: 13.8+/-2.8 pM/mg protein). Between 1 and 3 hr after melatonin administration, GSH-Px activity in fetal brain homogenates increased significantly (P<0.01). Similarly, SOD activity increased significantly between 1 and 2 hr after melatonin administration (P<0.01). These results indicate that melatonin administration to the mother increases antioxidant enzyme activities in the fetal brain and may thereby provide indirect protection against free radical injury. Thus, melatonin may potentially be useful in the treatment of neurodegenerative conditions that may involve excessive free radical production, such as fetal hypoxia and preeclampsia.     

Melatonin administration prevents cardiac and diaphragmatic mitochondrial oxidative damage in senescence-accelerated mice

Cardiac and diaphragmatic mitochondria from male SAMP8 (senescent) and SAMR1 (resistant) mice of 5 or 10 months of age were studied. Levels of lipid peroxidation (LPO), glutathione (GSH), GSH disulfide (GSSG), and GSH peroxidase and GSH reductase (GRd) activities were measured. In addition, the effect of chronic treatment with the antioxidant melatonin from 1 to 10 months of age was evaluated. Cardiac and diaphragmatic mitochondria show an age-dependent increase in LPO levels and a reduction in GSH:GSSG ratios. Chronic treatment with melatonin counteracted the age-dependent LPO increase and GSH:GSSG ratio reduction in these mitochondria. Melatonin also increased GRd activity, an effect that may account for the maintenance of the mitochondrial GSH pool. Total mitochondrial content of GSH increased after melatonin treatment. In general, the effects of age and melatonin treatment were similar in senescence-resistant mice (SAMR1) and SAMP8 cardiac and diaphragmatic mitochondria, suggesting that these mice strains display similar mitochondrial oxidative damage at the age of 10 months. The results also support the efficacy of long-term melatonin treatment in preventing the age-dependent mitochondrial oxidative stress.