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.     

Oxidative stress and apoptosis in fetal rat liver induced by maternal cholestasis. Protective effect of ursodeoxycholic acid

BACKGROUND/AIMS: The sensitivity of fetal rat liver to maternal obstructive cholestasis during pregnancy (OCP), and the effect of ursodeoxycholic acid (UDCA) were investigated. METHODS: UDCA was administered (i.g. 0.6 mg/kg b.wt./day) from day 14 to day 21 of pregnancy after maternal common bile duct ligation. RESULTS: Impairment in the activity of antioxidant enzymes, levels of total glutathione and GSH/GSSG ratio and the degrees of lipid peroxidation and protein carbonylation were similar in livers of OCP mothers and fetuses at term, despite hypercholanemia was milder in fetuses. Treatment of OCP rats with UDCA reduced maternal and fetal liver oxidative stress. Although maternal hypercholanemia was not corrected, fetal serum concentrations of major bile acids (except UDCA and beta-muricholic acid) were reduced. Fetal liver expression of key enzyme in bile acid synthesis, Cyp7a1, Cyp27 and Cyp8b1 was not affected by OCP or UDCA treatment. In OCP fetal livers, the relative expression of Bax-alpha and Bcl-2 and the activity of caspase-3, but not caspase-8, were increased. These changes were markedly reduced in fetuses of OCP animals treated with UDCA. CONCLUSIONS: OCP induced moderate fetal hypercholanemia but marked liver oxidative stress and apoptosis that were partly prevented by treatment of pregnant rats with UDCA.     

Melatonin rescues cardiovascular dysfunction during hypoxic development in the chick embryo

There is a search for rescue therapy against fetal origins of cardiovascular disease in pregnancy complicated by chronic fetal hypoxia, particularly following clinical diagnosis of fetal growth restriction (FGR). Melatonin protects the placenta in adverse pregnancy; however, whether melatonin protects the fetal heart and vasculature in hypoxic pregnancy independent of effects on the placenta is unknown. Whether melatonin can rescue fetal cardiovascular dysfunction when treatment commences following FGR diagnosis is also unknown. We isolated the effects of melatonin on the developing cardiovascular system of the chick embryo during hypoxic incubation. We tested the hypothesis that melatonin directly protects the fetal cardiovascular system in adverse development and that it can rescue dysfunction following FGR diagnosis. Chick embryos were incubated under normoxia or hypoxia (14% O₂) from day 1 ± melatonin treatment (1 mg/kg/day) from day 13 of incubation (term ~21 days). Melatonin in hypoxic chick embryos rescued cardiac systolic dysfunction, impaired cardiac contractility and relaxability, increased cardiac sympathetic dominance, and endothelial dysfunction in peripheral circulations. The mechanisms involved included reduced oxidative stress, enhanced antioxidant capacity and restored vascular endothelial growth factor expression, and NO bioavailability. Melatonin treatment of the chick embryo starting at day 13 of incubation, equivalent to ca. 25 wk of gestation in human pregnancy, rescues early origins of cardiovascular dysfunction during hypoxic development. Melatonin may be a suitable antioxidant candidate for translation to human therapy to protect the fetal cardiovascular system in adverse pregnancy.     

Melatonin versus vitamin E as protective treatment against oxidative stress after extra-hepatic bile duct ligation in rats

The aims of the present study were first to compare the effects of melatonin and vitamin E on the cholestasis syndrome and their protective effect on liver injury, and second, to evaluate the activity of antioxidant enzymes after treatment with these antioxidant drugs. Cholestasis was achieved in adult male Wistar rats by double ligature and section of the extra-hepatic biliary duct. Hepatic and plasma oxidative stress markers were evaluated by changes in the amount of lipid peroxides, measured as malondialdehyde (MDA) and reduced glutathione (GSH) in plasma and homogenates of hepatic tissue. Serum bilirubin, alkaline phosphatase (AP), and gamma-glutamyl-transpeptidase (GGT) were used to evaluate the severity of cholestasis, and serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were used to evaluate the hepatic injury. Both vitamin E and melatonin were administrated 1 day before and 7 days after bile duct ligation. Acute ligation of the bile duct was accompanied by a significant increased in MDA and a decrease in GSH levels in both plasma and liver, as well as a significant reduction in antioxidant enzymes activities. The overall analysis of both treatments showed that melatonin (500 microg/kg daily) offered significantly better protection against cholestasis and a superior protective effect on hepatic injury than did vitamin E (15 mg/kg daily). Although vitamin E treatment resulted in a reduction of parameters of oxidative stress, the results were significantly better after a much lower daily dose of melatonin. Moreover, melatonin treatment was associated with a significant recovery of antioxidative enzymes. In conclusion, the present paper demonstrates a correlation between the intensity of biliary tract obstruction and increased free radical generation, as well as a direct correlation between the level of oxidative stress and the biochemical markers of liver injury. Melatonin (at a much lower dose than vitamin E) was much more efficient than vitamin E in reducing the negative parameters of cholestasis, the degree of oxidative stress and provided a significantly greater hepatoprotective effect against the liver injury secondary to the acute ligation of the biliary duct.     

Melatonin for prevention of placental malperfusion and fetal compromise associated with intrauterine inflammation‐induced oxidative stress in a mouse model

Melatonin has been shown to reduce oxidative stress and mitigate hypercoagulability. We hypothesized that maternally administered melatonin may reduce placental oxidative stress and hypercoagulability associated with exposure to intrauterine inflammation (IUI) and consequently improve fetoplacental blood flow and fetal sequelae. Mice were randomized to the following groups: control (C), melatonin (M), lipopolysaccharide (LPS; a model of IUI) (L), and LPS with melatonin (ML). The expression of antioxidant mediators in the placenta was significantly decreased, while that of pro‐inflammatory mediators was significantly increased in L compared to C and ML. The systolic/diastolic ratio, resistance index, and pulsatility index in uterine artery (UtA) and umbilical artery (UA) were significantly increased in L compared with other groups when analyzed by Doppler ultrasonography. The expression of antioxidant mediators in the placenta was significantly decreased, while that of pro‐inflammatory mediators was significantly increased in L compared to C and ML. Vascular endothelial damage and thrombi formation, as evidenced by fibrin deposits, were similarly increased in L compared to other groups. Maternal pretreatment with melatonin appears to modulate maternal placental malperfusion, fetal cardiovascular compromise, and fetal neuroinflammation induced by IUI through its antioxidant properties.     

Melatonin stimulates glutathione peroxidase activity in human chorion

In preeclampsia, placental production of lipid peroxides is abnormally increased, while placental glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) activities are decreased. Administration of melatonin, a powerful scavenger of oxygen free radicals, also may protect the placenta from free radical-induced damage by increasing the activity of antioxidant enzymes. To test this hypothesis we administered melatonin to pregnant women before they underwent voluntary interruption of pregnancy between 7 and 9 wk of gestation. Melatonin (6 mg) was administered orally at 12:00 hr, and samples of chorion and maternal blood were obtained at the time of the procedure, 1, 2 or 3 hr later. We measured the melatonin concentration in maternal serum and activities of GSH-Px and SOD and levels of melatonin in chorionic homogenates. Melatonin administration was reflected by markedly increased melatonin concentrations in maternal serum and in chorion, with peak levels achieved 1 hr after melatonin administration (serum, 46.87 +/- 10.87 nM/L; chorionic homogenate, 4.36 +/- 1.56 pmol/mg protein). Between 1 and 3 hr after melatonin administration, GSH-Px activity in chorionic homogenates increased significantly (P < 0.001), with peak levels occurring at 3 hr (51.68 +/- 3.22 mU/mg protein per min, 137.3% of GSH-Px activity in untreated control subjects). No significant changes in chorionic SOD activity occurred during the 3-hr post-administration period. These results indicate that exogenous melatonin increases GSH-Px activity in the chorion and thereby may protect indirectly against free radical injury. Melatonin could be useful in treating preeclampsia and possibly other clinical states involving excessive free radical production, such as intrauterine fetal growth retardation and fetal hypoxia.     

Effect of maternal cholestasis on bile acid transfer across the rat placenta-maternal liver tandem

Cholestasis of pregnancy induces alterations in bile acid transport by human trophoblast plasma membrane (TPM) vesicles. We investigated whether maternal cholestasis affects the overall ability of the rat placenta to carry out vectorial bile acid transfer from the fetus to the mother. Complete obstructive cholestasis (OCP) was maintained during the last week of pregnancy and released at term (day 21), before experiments were performed. In situ single-pass perfusion of one placenta per rat with 250 nmol [(14)C]glycocholic acid (GC) revealed an impaired uptake in OCP rats (2.28 vs. 5.53 nmol in control rats). Approximately 100% of GC taken up by control placentas was secreted in maternal bile over 120 minutes (5.38 nmol), whereas this was only 61% (1.40 nmol) of the GC taken up by OCP placentas. When 5 nmol GC was administered through the jugular vein no significant difference between both groups in total GC bile output was found. The efficiency (V(max)/K(M)) of adenosine triphosphate (ATP)-dependent GC transport by vesicles from the maternal side of TPM was decreased (-41%) in OCP. Moreover, histological examination of the placentas suggested a reduction in the amount of functional trophoblast in the OCP group. This was consistent with a lower antipyrine diffusion across the placenta in these animals. In sum, our results indicate that maternal cholestasis affects the ability of the placenta to efficiently carry out bile acid transfer from fetal to maternal blood. Changes in both the structure and the functionality of the chorionic tissue may account for this impairment.     

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 protects against oxidative mitochondrial damage induced in rat placenta by ischemia and reperfusion

We assessed the effects of melatonin, a powerful scavenger of oxygen free radicals, on ischemia/reperfusion-induced oxidative damage to mitochondria in the rat placenta. In Wistar rats at day 19 of pregnancy, feto-placental ischemia was induced by occluding both utero-ovarian arteries for 20 min. Reperfusion was achieved by releasing the occlusion and restoring circulation for 30 min. Melatonin solution or the vehicle alone was injected intraperitoneally at dose of 10 mg/kg 1 hr before occlusion. Sham-ischemic animals were treated with vehicle. Each group consisted of 10 pregnant rats. We measured placental mitochondrial respiratory control index (RCI; a marker of mitochondrial respiratory activity), the ratio of the added adenosine 5-diphosphate (ADP) concentration to consumption of oxygen during state 3 respiration (ADP/O), and the concentration of thiobarbituric acid reactive substances (TBARS) in each group. RCI and ADP/O were significantly decreased by ischemia/reperfusion, while TBARS were increased. Melatonin prevented these changes. These results indicate that exogenous melatonin protects against ischemia/reperfusion-induced oxidative damage to mitochondria in rat placenta. Melatonin could be useful in treating preeclampsia and possibly other clinical states involving excess free radical production, such as fetal growth restriction and fetal hypoxia.     

Melatonin preserves fetal growth in rats by protecting against ischemia/reperfusion-induced oxidative/nitrosative mitochondrial damage in the placenta

We have previously demonstrated that melatonin protects against ischemia/reperfusion-induced oxidative damage to mitochondria in the fetal rat brain. The purpose of the present study was to evaluate the effects of maternally administered melatonin on ischemia/reperfusion-induced oxidative placental damage and fetal growth restriction in rats. The utero-ovarian arteries were occluded bilaterally for 30 min in rats on day 16 of pregnancy to induce fetal ischemia. Reperfusion was achieved by releasing the occlusion and restoring circulation. Melatonin solution (20 microg/mL) or the vehicle alone was administered orally during pregnancy. A sham operation was performed in control rats, which were treated with vehicle alone. Laparotomy was performed on day 20 of pregnancy and the number and weight of fetal rats and placentas were measured. Placental mitochondrial respiratory control index (RCI), a marker of mitochondrial respiratory activity, was also calculated for each group. Using immunohistochemistry, we investigated the degree of immunostaining of 8-hydroxy-2-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage, and redox factor-1(ref-1), which repairs DNA damage and acts as a redox-modifying factor in rat placenta. Predictably, the ischemia/reperfusion operation significantly decreased the weight of fetal rats and placentas and the RCI. Melatonin prevented ischemia/reperfusion-induced changes in RCI (1.55 +/- 0.05 to 1.83 +/- 0.09, P < 0.05) and fetal growth (3.04 +/- 0.17 to 3.90 +/- 0.1, P < 0.0001). Immunohistochemistry revealed significant positive staining for 8-OHdG and ref-1 following ischemia/reperfusion; these effects were also reduced by melatonin treatment. Results indicated that ischemia/reperfusion-induced oxidative placental DNA and mitochondrial damage and fetal growth restriction can be prevented by maternally administered melatonin.     

Bile acid stress in the mother and baby unit

Intrahepatic cholestasis of pregnancy (ICP) affects about 0.7% of deliveries in Britain. It is regarded as a benign condition for the mother but is associated with increased fetal mortality in late pregnancy and early delivery is advised. Ursodeoxycholic acid (UDCA) treatment is beneficial to the mother and does not appear to harm the fetus. ICP is often regarded as a disease of the maternal liver already made 'cholestatic' by high levels of circulating progesterone. We propose that ICP should be considered as a feto-maternal disease involving complex interactions between maternal and fetal bile acid metabolism across the placenta. During the late stages of gestation, when there is a rise in fetal and maternal bile acid levels, the placenta may fail to render potentially hepatotoxic bile acids water soluble and hence excretable. This might cause a vicious cycle leading to further cholestasis in the maternal liver already challenged by progesterone.     

Maternally administered melatonin differentially regulates lipopolysaccharide-induced proinflammatory and anti-inflammatory cytokines in maternal serum, amniotic fluid, fetal liver, and fetal brain

Lipopolysaccharide (LPS) has been associated with adverse developmental outcome, including intra-uterine fetal death and intra-uterine growth retardation. In the LPS model, tumor necrosis factor alpha (TNF-alpha) is the major mediator leading to intra-uterine fetal death and intra-uterine growth retardation. Interleukin (IL)-10 protects rodents against LPS-induced intra-uterine fetal death and intra-uterine growth retardation. Melatonin is an immunomodulator. In the present study, we investigated the effect of maternally administered melatonin on LPS-induced proinflammatory and anti-inflammatory cytokines in maternal serum, amniotic fluid, fetal liver and fetal brain. The time pregnant mice were injected with melatonin [5.0 mg/kg, intraperitoneal (i.p.)] 30 min before LPS (500 microg/kg, i.p.) on gestational day 17. As expected, TNF-alpha, IL-1beta, IL-6 and IL-10 were obviously increased in maternal serum and amniotic fluid in response to LPS. In addition, maternal LPS exposure significantly increased the levels of TNF-alpha, IL-1beta, IL-6 and IL-10 in fetal liver, and TNF-alpha and IL-10 in fetal brain. Melatonin pretreatment significantly attenuated LPS-evoked elevation of TNF-alpha in maternal serum. On the contrary, melatonin aggravated LPS-induced increase in IL-10 in maternal serum. Melatonin had no effect on LPS-evoked IL-1beta and IL-6 in maternal serum and amniotic fluid. Interestingly, maternally administered melatonin also significantly attenuated LPS-evoked elevation of TNF-alpha in fetal brain, whereas the indole aggravated LPS-induced increase in IL-10 in fetal liver. Taken together, these results indicate that maternally administered melatonin differentially regulates LPS-induced proinflammatory and anti-inflammatory cytokines in maternal serum, amniotic fluid, fetal liver, and fetal brain.     

Melatonin inhibits oxidative stress and apoptosis in fetal brains of hyperhomocysteinemic rat dams

Moderate hyperhomocysteinemia is a risk factor for neurodegenerative diseases and complications during pregnancy. Increased homocysteine levels during pregnancy may elevate developmental risk on fetal brain structure and function. However, little is known about the mechanism of action of homocysteine on the degeneration of the fetal brain. Hence in this study, we examined the effects of maternal hyperhomocysteinemia on oxidative stress and apoptosis in brain tissues and investigated whether administration of melatonin to the mother would prevent homocysteine-induced oxidative cerebral damage in pups. Hyperhomocysteinemia was induced in female rats by administration of methionine at a dose of 1 g/kg body weight dissolved in drinking water during pregnancy. Some animals received methionine plus 10 mg/kg/day melatonin subcutaneously throughout pregnancy. After delivery, the level of lipid peroxidation (malondialdehyde + 4-hydroxyalkenals) was determined in different subfractions of pup brains. Furthermore, DNA fragmentation, levels of Bcl-2 protein and p53 mRNA expression were determined to evaluate apoptosis. Significant elevation was found in the levels of lipid peroxidation in subcellular fractions of the brain of pups of hyperhomocysteinemic dams. Increased DNA fragmentation and p53 mRNA expression was observed in the brain of pups of homocysteine-treated rats, while a significant reduction was seen in the levels of anti-apoptotic Bcl-2 levels. Melatonin administration prevented markers of oxidative stress and biochemical signs of apoptosis. In conclusion, therapeutic administration of melatonin protects against the induction of oxidative stress and neural tissue injury and might prevent congenital malformations of fetal brain caused by maternal hyperhomocysteinemia.     

The spectrum of liver and gastrointestinal disease seen in cholestasis of pregnancy.

A mild form of intrahepatic cholestasis is an infrequent complication of pregnancy, with a spontaneous cure almost immediately after delivery and that often recurs in future pregnancies. Pruritus alters maternal well-being, and a subclinical steatorrhea may impair the patient's nutritional status; otherwise, it is a mild disease in the mother, and no maternal mortality has been attributed to it. In contrast, cholestasis of pregnancy is often identified as a risk of increased perinatal morbidity and mortality. The cause of cholestasis of pregnancy is unknown. A hereditary predisposition seems to induce in the maternal liver an abnormal reaction to female sex hormones, but some still unidentified environmental (possibly dietary) factor could also be involved in the pathogenesis of the disease. Pruritus, but not the biochemical alterations, can be alleviated by the use of cholestyramine, silymarin, or epomediol. Ursodeoxycholic acid has been beneficial in pruritus and in liver function tests; an improvement in fetal prognosis should be evaluated in future controlled studies.     

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.     

Lack of effect of melatonin on myometrial electromyographic activity in the pregnant sheep at 138-142 days gestation (term = 147 days gestation)

A 24-h rhythm has been demonstrated in fetal and maternal melatonin plasma concentrations in pregnant sheep in the last third of gestation. Melatonin in the maternal circulation can cross the placenta and is the major source of melatonin in the fetal circulation. Melatonin has been postulated to act as a prostaglandin (PG) synthetase inhibitor in the uterus. PG synthetase inhibitors decrease myometrial contractility. To assess transplacental passage of melatonin and potential influences of melatonin on uterine contractility, we infused melatonin continuously into the maternal jugular vein in seven pregnant sheep at 138-142 days gestation (term in our instrumented animals is 147 days gestation) at three infusion rates for successive 1-h periods during the late morning to late afternoon. There was no change in the total time during which the myometrium was active, as indicated by myometrial electromyographic activity or the myometrial contracture frequency during the 3 h before and after melatonin infusions and for each hour of the infusions. The MCR for melatonin in the ewe was 4128 +/- 410 ml/min (mean +/- SE; n = 7; weight, 50-70 kg). The resting maternal to fetal melatonin concentration ratio was 0.8; this ratio was maintained at 2.28 during melatonin infusion to the ewe at a wide range of maternal melatonin concentrations. Melatonin concentrations in the range of 3-200 times normal had no effect on the maternal plasma PGF2 alpha metabolite concentration, but caused a 40.4% fall in fetal plasma PGE2 (P less than 0.05). We conclude that changes in maternal and fetal plasma melatonin concentrations within the physiological range observed throughout the day do not alter myometrial contractility, but do alter fetal PGs.     

Melatonin alleviates lipopolysaccharide-induced placental cellular stress response in mice

Abstract: Melatonin protects mice from lipopolysaccharide (LPS)‐induced fetal death and intra‐uterine growth retardation. Nevertheless, its molecular mechanism remains obscure. In the present study, we investigated the effects of melatonin on LPS‐induced cellular stress in placenta. Pregnant mice were given with melatonin [5.0 mg/kg, intraperitoneal (i.p.)] 30 min before and 150 min after LPS (300 μg/kg, i.p.) on gestational day 15. Oxidative stress, endoplasmic reticulum (ER) stress, hypoxic stress, and heat stress in placenta were analyzed at 4 hr after LPS. As expected, maternal LPS administration resulted in placental glutathione (GSH) depletion and up‐regulated the expression of placental antioxidative enzymes. In addition, LPS significantly increased the level of inducible nitric oxide synthase (iNOS) and enhanced the intensity of placental 3‐nitrotyrosine residues. An ER stress, as determined by a decreased GRP78 expression, an obvious eIF2α and JNK phosphorylation, and an increased CHOP expression, were observed in placenta of pregnant mice injected with LPS. In addition, LPS significantly increased mRNA level of placental HIF‐1α, VEGF, and ET‐1, the markers of hypoxic stress. Heme oxygenase (HO)‐1, a marker of heat stress, was also up‐regulated in placenta of LPS‐treated pregnant mice. Interestingly, LPS‐induced placental oxidative stress, hypoxic stress, and ER stress were significantly alleviated when pregnant mice were given with melatonin, whereas melatonin had little effect on LPS‐evoked placental HO‐1 expression. In conclusion, maternally administered melatonin alleviates LPS‐induced cellular stress in the placenta. Melatonin may be useful as pharmacological agents to protect the fetuses against LPS‐induced intra‐uterine fetal death and intra‐uterine growth restriction.     

Hepatoprotective actions of melatonin: possible mediation by melatonin receptors

Melatonin,the hormone of darkness and messenger of the photoperiod,is also well known to exhibit strong direct and indirect antioxidant properties. Melatonin has previously been demonstrated to be a powerful organ protective substance in numerous models of injury; these beneficial effects have been attributed to the hormone’s intense radical scavenging capacity. The present report reviews the hepatoprotective potential of the pineal hormone in various models of oxidative stress in vivo,and summarizes the extensive literature showing that melatonin may be a suitable experimental substance to reduce liver damage after sepsis,hemorrhagic shock,ischemia/reperfusion,and in numerous models of toxic liver injury. Melatonin’s influence on hepatic antioxidant enzymes and other potentially relevant pathways,such as nitric oxide signaling,hepatic cytokine and heat shock protein expression,are evaluated. Based on recent literature demonstrating the functional relevance of melatonin receptor activation for hepatic organ protection,this article finally suggests that melatonin receptors could mediate the hepatoprotective actions of melatonin therapy.     

Melatonin protects against oxidative stress in granular corneal dystrophy type 2 corneal fibroblasts by mechanisms that involve membrane melatonin receptors

Considering that oxidative stress plays a role in corneal fibroblast degeneration during granular corneal dystrophy type 2 (GCD2) and melatonin is an effective antioxidant, we examined the ability of melatonin to protect against oxidative stress-induced cell death of primary cultured normal and GCD2-homozygous corneal fibroblasts. Melatonin treatment protected primary cultured normal and GCD2 corneal fibroblasts from paraquat (PQ)-induced oxidative stress and caused increased expression levels of Cu/Zn-superoxide dismutase (SOD1) and glutathione reductase (GR) in both types of cells. Interestingly, catalase expression increased in normal corneal fibroblasts, but decreased in GCD2 corneal fibroblasts after melatonin treatment. Melatonin also reduced the levels of intracellular reactive oxygen species and H(2)O(2) in both cell types. In addition, the selective melatonin receptor antagonist luzindole blocked melatonin-induced expression of SOD1 and GR. The expression levels of melatonin receptors 1A (MT1) and 1B (MT2) were significantly higher in GCD2 corneal fibroblasts than in normal cells. These results suggest that increased expression of melatonin receptors may be involved in the defense mechanisms against oxidative stress in GCD2 corneal fibroblasts, and melatonin may have potential therapeutic implications for GCD2 treatment.     

Comparative analysis of the protective effects of melatonin and vitamin E on streptozocin-induced diabetes mellitus

There is a clearly documented link between diabetic complications and lipid peroxidation. Hyperglycemia causes a reduction in levels of protective endogenous antioxidants and increases generation of free radicals. The present study was carried out to compare the protective effects of melatonin and vitamin E against streptozocin (STZ)-induced diabetes in rats. Melatonin was administered s.c. (100 microg/kg) whereas vitamin E was given i.p. (100 mg/kg) after induction of diabetes with STZ (60 mg/kg). Plasma total cholesterol, triglyceride and low density lipoprotein (LDL) levels were increased in STZ group while both melatonin and vitamin E injection caused a significant decrease in the levels of all these parameters. The lipid lowering effect of melatonin was greater than that of vitamin E. Melatonin caused a significant decrease in brain, liver and kidney tissue malondialdehyde (MDA) levels which were increased because of STZ-induced diabetes. Vitamin E also reduced elevated MDA concentrations in diabetic rat tissues, but the effect of melatonin was more potent than that of vitamin E. Furthermore, treatment of diabetic rats with melatonin increased brain and kidney glutathione peroxidase (GSH-Px) activity to the levels below that of control rats. Vitamin E was found to be less effective on GSH-Px activity levels in brain and kidney than melatonin whereas it was more potent than melatonin in liver. In summary, melatonin prevents many diabetic complications by reducing oxidative stress and protects organisms from oxidative damage and dyslipidemia. Considering the much lower molar concentration of melatonin compared with vitamin E, melatonin seems to be a more potent antioxidant, especially in the brain and kidney.