Melatonin inhibits vasospastic action of hydrogen peroxide in human umbilical artery

The reduction of melatonin levels is associated with the development of preeclampsia: a meta-analysis

OBJECTIVE

The aim of this analysis was to demonstrate the association between melatonin levels and the development of preeclampsia.

METHODS

Standardized mean difference (SMD) with 95% confidence interval (CI) was calculated using a random effects model.

RESULTS

The pooled SMD between case and control was 1.40 (95% CI: 0.26, 2.55; P = 0.02). And the pooled SMD between mild PE and severe PE was 5.25 (95% CI: 1.5, 9.01; P = 0.006).

CONCLUSION

The meta-analysis illustrated that melatonin concentration was significantly lower in women with preeclampsia, and correlated with the severity of the disease.

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.

Salivary melatonin levels and sleep-wake rhythms in pregnant women with hypertensive and glucose metabolic disorders: A prospective analysis

In preeclampsia and gestational diabetes, the sympathetic nerves are activated, leading to disrupted sleep. Melatonin, which transmits information to regulate the sleep-wake rhythm and other such biorhythms, has been implicated in insulin resistance, antioxidant behaviors, and metabolic syndrome. In addition, its reduced secretion increases the risk of hypertension and diabetes. The aim of this study was to elucidate the features of melatonin secretion, sleep quality, and sleep-wake rhythms in pregnant women with complications. Fifty-eight pregnant women with pregnancy complications (hypertensive or glucose metabolic disorders) and 40 healthy pregnant women completed questionnaires, including sleep logs and the Pittsburgh Sleep Quality Index (PSQI), during the second to third trimesters. Their salivary melatonin levels were also measured. Pregnant women with complications had significantly lower morning (p < 0.001), daytime (p < 0.01), evening (p < 0.001), night (p < 0.01), daily mean (p < 0.001), peak (p < 0.001), and bottom (p < 0.01) melatonin values than healthy pregnant women. Pregnant women with complications also had significantly smaller melatonin amplitudes than healthy pregnant women (p < 0.001). Among pregnant women with complications, the duration (p < 0.05) and frequency (p < 0.01) of wake after sleep-onset were significantly greater in the poor sleep group than in the favorable sleep group which was divided by PSQI cutoff value. Pregnant women with hypertensive or glucose metabolic disorder complications had smaller circadian variation in salivary melatonin secretion, and their values were lower throughout the day than healthy pregnant women.

Melatonin: a "Higgs boson" in human reproduction

As the Higgs boson could be a key to unlocking mysteries regarding our Universe, melatonin, a somewhat mysterious substance secreted by the pineal gland primarily at night, might be a crucial factor in regulating numerous processes in human reproduction. Melatonin is a powerful antioxidant which has an essential role in controlling several physiological reactions, as well as biological rhythms throughout human reproductive life. Melatonin, which is referred to as a hormone, but also as an autocoid, a chronobiotic, a hypnotic, an immunomodulator and a biological modifier, plays a crucial part in establishing homeostatic, neurohumoral balance and circadian rhythm in the body through synergic actions with other hormones and neuropeptides. This paper aims to analyze the effects of melatonin on the reproductive function, as well as to shed light on immunological and oncostatic properties of one of the most powerful hormones.

The protective role of melatonin in experimental hypoxic brain damage

BACKGROUND

It is known that oxygen-derived free radicals play an important role in the pathogenesis of brain injury. Melatonin is a powerful scavenger of the oxygen free radicals. In this study, the protective effect of melatonin against the damage inflicted by reactive oxygen species during brain hypoxia was investigated in newborn rats using biochemical parameters.

METHODS

For biochemical analyses, the levels of lipid peroxidation product (malondialdehyde ([MDA]), levels of reduced glutathione (GSH) and the activities of superoxide dismutase (SOD) and catalase (CAT) were estimated.

RESULTS

After the third day of brain hypoxia, the brain levels of MDA increased. Pretreatment of animals with melatonin abolished the rise in MDA induced by hypoxia. GSH concentration did not increase by pretreatment with melatonin. Additionally, the activities of two antioxidative enzymes (SOD and CAT) decreased after the experimental period with melatonin only preventing the change of CAT. The activity of SOD was not influenced by melatonin administration as expected.

CONCLUSION

In this experimental study, exogenously administered melatonin effectively protected against brain injury by oxidative stress. This protective effect of melatonin may be due to its direct scavenger activity and activation of CAT. Thus, melatonin may potentially be useful in the treatment of neurodegenerative conditions that may involve free radical production, such as perinatal hypoxia.

Melatonin as a new drug for improving oocyte quality

Background:  Although recent technical advances have benefited infertile couples, inadequate embryo development as a result of poor quality oocytes still contributes to infertility. The purpose of the present study was to evaluate melatonin as a drug for improving oocyte quality in such cases. Methods:  Twenty-seven women from whom fewer than three fertilized embryos were grown and who failed to fall pregnant in previous treatment cycles were enrolled in the current prospective clinical study. Subjects took 1 mg or 3 mg tablets of melatonin orally at 22:00 h from the fifth day of the previous menstrual cycle to the day they were injected with human chorionic gonadotropin. The numbers of mature follicles, retrieved oocytes, degenerate oocytes, and fertilized embryos were compared to their previous data without melatonin (the control cycle). Results:  Intrafollicular melatonin concentrations were significantly increased, and intrafollicular lipid peroxide concentrations showed a tendency towards lower levels in the 3 mg melatonin treatment cycles compared with the control cycles. The number of degenerate oocytes was significantly reduced, and the number of fertilized embryos showed a tendency towards an increase in the 3 mg cycle compared to the control cycle. Three women succeeded in falling pregnant. Conclusion:  Melatonin is likely to become the drug of choice for improving oocyte quality in women who cannot fall pregnant because of poor quality oocytes. (Reprod Med Biol 2003; 2: 139-144).

Effect of prenatal melatonin exposure on gonadotropins and prolactin secretion in male and female rat pups

We evaluated whether melatonin administration to pregnant rats during the final week of pregnancy affects prepubertal secretion of luteinizing hormone (LH), follicle stimulating hormone (FSH), and prolactin in offspring. Melatonin was administered in the drinking water from day 14 to delivery. LH, FSH and prolactin concentrations were determined in plasma sampled from offspring between 5 and 30 days in the dark portion of the diurnal cycle. Administration of 2 or 20 microg/ml melatonin did not affect LH or FSH in male or female offspring. The 20-microg/ml dose caused a significant increase in prolactin in males and females at day 15. In contrast, melatonin, 2 or 20 microg/ml, decreased prolactin at days 25 and 30 in females and day 25 in males. Thus, prenatal melatonin exposure alters prolactin secretion, but not that of LH and FSH in infantile and prepubertal male and female rats.

Weak vasoconstrictor activity of melatonin in human umbilical artery: relation to nitric oxide-scavenging action

We evaluated the nitric oxide (NO)-scavenging property of melatonin, demonstrated in a recent in vitro study, on vascular reactivity in the human umbilical artery. Helical sections of human umbilical artery were prepared following elective Cesarean deliveries near term. Changes in maximal tension induced by prostaglandin F(2 alpha)(5 x 10(-5) M) were measured in artery sections with an intact endothelium. Melatonin at concentrations higher than 10(-6) M increased prostaglandin F(2 alpha)-induced vascular tension. The vasospastic effect of melatonin was much less than that of L-N(G)-monomethylarginine (L-NMA, 2 x 10(-4) M), an inhibitor of NO synthesis (2.8+/-1.4%, 9.1+/-1.7%, 16.5+/-2.5%, and 29.6+/-5.9% of the L-NMA effect at melatonin concentrations of 10(-8), 10(-7), 10(-6), and 10(-5) M, respectively). Removal of the endothelium significantly reduced the vasoconstrictive effect of melatonin. Treatment with L-NMA (2 x 10(-4) M) prior to addition of prostaglandin F(2 alpha) also significantly reduced the vasoconstrictive effect of melatonin (10(-5) M). Treatments with melatonin (10(-5) M) did not affect calcium ionophore A 23187-induced relaxation or 5-hydroxytryptamine-induced constriction. The findings indicate that melatonin may potentiate vascular tension in human umbilical artery by scavenging endogenous endothelial NO, but not by inhibiting NO synthesis. However, the NO-scavenging vasoconstrictive effect of melatonin may be negligible at physiologic concentrations and very weak at pharmacologic concentrations below 10(-7) M.

Protective effect of melatonin against homocysteine-induced vasoconstriction of human umbilical artery

Hyperhomocysteinemia is a major and independent risk factor for vascular disease. Oxidative stress is a possible mechanism for homocysteine (Hcy)-induced endothelial dysfunction. Herein, we evaluated the antioxidant property of melatonin (MLT) in relation to the vasoconstrictive effect of Hcy on the human umbilical artery. In an initial experiment in a cell-free system, a micromolar concentration of iron was found to catalyze oxygen-dependent oxidation of Hcy. MLT (10 or 100 microM) did not affect oxygen-dependent oxidation of Hcy. Next, smooth muscle contraction induced by prostaglandin F(2alpha) (10 microM) was measured in arterial strips. Hcy (10 to 500 microM) increased this vascular tension in a concentration-dependent manner (P < 0.0001). Addition of Fe(2+) (10 microM) significantly potentiated the Hcy effect. Removal of endothelium (P < 0.05), pretreatment with a nitric oxide (NO) synthesis inhibitor (l-N(G)-monomethylarginine, 200 microM, P < 0.001), or pretreatment with a hydroxyl radical ((*)OH) scavenger (mannitol, 10 mM, P < 0.001) significantly attenuated contraction potentiated by Hcy plus Fe(2+). At a much lower concentration than mannitol, MLT (1 to 100 microM) significantly reduced the contractile effect of Hcy and Fe(2+) in a concentration-dependent manner. Hcy plus Fe(2+) significantly impaired calcium ionophore A 23187-induced relaxation (P < 0.0001), while MLT restored this relaxation in a concentration-dependent manner. These findings suggest that Hcy potentiates vascular tension in human umbilical artery, possibly by suppressing bioavailable NO. MLT protects against the vasoconstrictive effect of Hcy, most likely by scavenging (*)OH arising from Hcy autooxidation.

The effect of melatonin on in vitro fertilization and embryo development in mice

To examine the effect of melatonin on in vitro fertilization and embryonic development, mouse embryos after insemination in vitro were cultured in a physiological medium with or without melatonin. Melatonin increased the fertilization rate significantly at a concentration between 10(-6) and 10(-4) M (27.6 vs. 43.9 or 40.4%, P < 0.01). Furthermore, a significant increase in the rate of embryos reaching the four-cell stage (16.0 vs. 26.7%, P < 0.01), the eight-cell stage (12.1 vs. 25.8 or 23.5%, P < 0.01), and blastulation (8.9 vs. 23.5 or 17.5%, P < 0.01) was observed when the embryos were cultured in a medium containing 10(-8) or 10(-6) M melatonin. These results demonstrate that melatonin supports fertilization and early embryo development after in vitro fertilization.

Melatonin inhibits the vasorelaxant action of peroxynitrite in human umbilical artery

We evaluated the antioxidant property of melatonin as it relates to the vasorelaxant effect of peroxynitrite (ONOO ), a reaction product of superoxide anion radical (O2(-*)) and nitric oxide (NO), on the human umbilical artery. Helical sections of umbilical arteries were obtained from human placentas at elective cesarean delivery between weeks 37 and 39 of gestation. Changes in maximal tension induced by potassium chloride were measured in arterial sections with intact endothelium. Sections were treated with 3-morpholinosydomine (SIN-1), which releases O2(-*) and NO simultaneously, with or without pre-treatment either with hemoglobin (3 microM) or melatonin (0.1-10 microM). SIN-1 produced a significant dose-dependent relaxation of vascular tension. Pre-treatment with hemoglobin did not affect SIN-1-induced relaxation. Melatonin significantly reduced the vasorelaxant effect of SIN-1 in a concentration-dependent manner. These findings indicate that ONOO attenuates vascular tension in the human umbilical artery. Melatonin significantly suppressed the vasorelaxant effect of SIN-1, possibly due to its ability to scavenge ONOO-.

Melatonin protects against ischemia and reperfusion-induced oxidative lipid and DNA damage in fetal rat brain

To investigate whether melatonin reduces the susceptibility of the fetal rat brain to oxidative damage of lipids and DNA, we created a model of fetal ischemia/reperfusion using rats at day 19 of pregnancy. Fetal ischemia was induced by bilateral occlusion of the utero-ovarian artery for 20 min. Reperfusion was achieved by releasing the occlusion and restoring the circulation for 30 min. A sham operation was performed in control rats. Melatonin (10 mg/kg) or vehicle was injected intraperitoneally 60 min prior to the occlusion. We measured the concentration of thiobarbituric acid reactive substances (TBARS) in fetal brain homogenates, as well as levels of deoxyguanosine (dG) and 8-hydroxydeoxyguanosine (8-OHdG) in DNA extracted from those homogenates. Ischemia for 20 min did not significantly alter the levels of dG, 8-OHdG, and TBARS. Subsequent reperfusion, however, led to a significant reduction in the dG level (P < 0.05) and to significant increases in the levels of 8-OHdG (P < 0.05) and TBARS (P < 0.05), and in the 8-OHdG/dG ratio (P < 0.005). Melatonin administration prior to ischemia significantly reduced the ischemia/reperfusion-induced increases in the levels of 8-OHdG (14.33 +/- 6.52-5.15 +/- 3.28 pmol/mg of DNA, P < 0.001) and TBARS (11.61 +/- 3.85-4.73 +/- 3.80 nmol/mg of protein, P < 0.001) as well as in the 8-OHdG/dG ratio (7.19 +/- 2.49-1.61 +/- 0.98, P < 0.001). Furthermore, melatonin significantly increased the dG level (210.19 +/- 49.02-299.33 +/- 65.08 nmol/mg of DNA, P < 0.05). Results indicate that melatonin administration to the pregnant rat may prevent the ischemia/reperfusion-induced oxidative lipid and DNA damage in fetal rat brain.

Maternal-fetal transfer of melatonin in pregnant women near term

Our objective was to evaluate the maternal-fetal transfer of melatonin in pregnant women. Serum melatonin concentration was measured by high-performance liquid chromatography with electrochemical detection in a maternal vein and in the umbilical artery and umbilical vein at the time of birth. Blood samples were obtained from 12 women who had spontaneously delivered vaginally at night. A single oral dose of melatonin was administered to each of 33 patients who underwent a cesarean section, and, blood samples were taken at 1, 2, 3, or 4 hr after the administration of melatonin at delivery. Cesarean section was performed between 1300 and 1500 hr. The mean melatonin concentrations of melatonin in maternal peripheral venous blood and umbilical arterial and umbilical venous blood did not differ significantly, and positive correlations in the serum levels of melatonin were observed between the three sources of blood. The oral administration of 3 mg of melatonin to pregnant women led to marked increases in the serum levels of melatonin, with maximum levels observed 2 hr (21.84 +/- 2.09 ng/ml) after drug administration. Changes in serum levels of melatonin in the umbilical vein and artery resembled those found in the maternal vein. Serum melatonin concentrations did not differ significantly between the maternal vein and the umbilical veins. Serum levels of melatonin in the umbilical vein after the administration of melatonin were significantly and closely correlated with those in the maternal vein (r = 0.924, P < 0.001). These results suggest that, in humans, melatonin is transferred from the maternal to the fetal circulation both easily and rapidly. A potential for the therapeutic use of melatonin as an antioxidant exists in the patients with preeclampsia.