Craniocerebral trauma (CCT) is the most frequent cause of morbidity-mortality as a result of an accident. The probable origins and etiologies are multifactorial and include free radical formation and oxidative stress, the suppression of nonspecific resistance, lymphocytopenia (disorder in the adhesion and activation of cells), opportunistic infections, regional macro and microcirculatory alterations, disruptive sleep-wake cycles and toxicity caused by therapeutic agents. These pathogenic factors contribute to the unfavorable development of clinical symptoms as the disease progresses. Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is an indoleamine endogenously produced in the pineal gland and in other organs and it is protective agent against damage following CCT. Some of the actions of melatonin that support its pharmacological use after CCT include its role as a scavenger of both oxygen and nitrogen-based reactants, stimulation of the activities of a variety of antioxidative enzymes (e.g. superoxide dismutase, glutathione peroxidase, glutathione reductase and catalase), inhibition of pro-inflammatory cytokines and activation-adhesion molecules which consequently reduces lymphocytopenia and infections by opportunistic organisms. The chronobiotic capacity of melatonin may also reset the natural circadian rhythm of sleep and wakefulness. Melatonin reduces the toxicity of the drugs used in the treatment of CCT and increases their efficacy. Finally, melatonin crosses the blood-brain barrier and reduces contusion volume and stabilizes cellular membranes preventing vasospasm and apoptosis of endothelial cells that occurs as a result of CCT.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) has multiple functions. In this study, we investigated the effects of melatonin on memory, cell proliferation, and neuroblast differentiation in the dentate gyrus of a mouse model of D-galactose-induced aging. D-galactose was subcutaneously administered to 7-wk-old mice for 10 wk, and age-matched mice were used as controls. Seven weeks after D-galactose administration, vehicle (water) or melatonin (6 mg/L in water) was administered ad libitum to the mice for 3 wk. The administration of D-galactose significantly increased the escape latency compared with that in the control mice on days 1-3. In addition, cells in the subgranular zone and in the granule cell layer of the dentate gyrus showed severe damage (cytoplasmic condensation) in the D-galactose-treated mice. However, melatonin supplementation to these mice for 3 wk significantly ameliorated the D-galactose-induced increase in escape latency and neuronal damage compared with the vehicle-treated group. The administration of melatonin also significantly restored the D-galactose-induced reduction of proliferating cells (Ki67-positive cells) and differentiating neuroblasts (doublecortin-positive neuroblasts) in the dentate gyrus. Furthermore, the administration of melatonin significantly increased Ser133-phosphorylated cyclic AMP response element binding protein in the dentate gyrus. The administration of melatonin significantly reduced D-galactose-induced lipid peroxidation in the dentate gyrus. These results suggest that melatonin may be helpful in reducing age-related phenomena in the brain.

12<em>5</em>I-Melatonin was used to localize and characterize the melatonin receptor sites in the rat hypothalamus. Autoradiography revealed that displaceable 12<em>5</em>I-melatonin binding occurred in suprachiasmatic nuclei and median eminence only. Further studies performed on crude membrane fractions from median eminences revealed high affinity (Kd = 21 pM) melatonin binding sites (Bmax = 8.<em>5</em> fmol/mg protein). The order of potency of various indole amines to inhibit 12<em>5</em>I-melatonin binding was melatonin much greater than <em>N</em>-<em>acetyl</em>-<em>5</em>-hydroxytryptamine greater than <em>5</em>-<em>methoxytryptamine</em> greater than <em>5</em>-hydroxytryptamine.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is a tryptophan-derived signal with important physiological roles in mammals. Although the presence of melatonin in plants may be universal, its endogenous function in plant tissues is unknown. On the basis of its structural similarity to indole-3-acetic acid, recent studies mainly focusing on root growth in several plant species have suggested a potential auxin-like activity of melatonin. However, direct evidence about the mechanisms of action of this regulator is lacking. In this work, we used Arabidopsis thaliana seedlings as a model system to evaluate the effects of melatonin on plant growth and development. Melatonin modulated root system architecture by stimulating lateral and adventitious root formation but minimally affected primary root growth or root hair development. The auxin activity of melatonin in roots was investigated using the auxin-responsive marker constructs DR<em>5</em>:uidA, BA3:uidA, and HS::AXR3<em>N</em>T-GUS. Our results show that melatonin neither activates auxin-inducible gene expression nor induces the degradation of HS::AXR3<em>N</em>T-GUS, indicating that root developmental changes elicited by melatonin were independent of auxin signaling. Taken together, our results suggest that melatonin is beneficial to plants by increasing root branching and that root development processes elicited by this novel plant signal are likely independent of auxin responses.

The hormone melatonin is secreted primarily from the pineal gland, with highest levels occurring during the dark period of a circadian cycle. This hormone, through an action in the brain, appears to be involved in the regulation of various neural and endocrine processes that are cued by the daily change in photoperiod. This article reviews the pharmacological characteristics and function of melatonin receptors in the central nervous system, and the role of melatonin in mediating physiological functions in mammals. Melatonin and melatonin agonists, at picomolar concentrations, inhibit the release of dopamine from retina through activation of a site that is pharmacologically different from a serotonin receptor. These inhibitory effects are antagonized by the novel melatonin receptor antagonist luzindole (<em>N</em>-0774), which suggests that melatonin activates a presynaptic melatonin receptor. In chicken and rabbit retina, the pharmacological characteristics of the presynaptic melatonin receptor and the site labeled by 2-[12<em>5</em>I]iodomelatonin are identical. It is proposed that 2-[12<em>5</em>I]iodomelatonin binding sites (e.g., chicken brain) that possess the pharmacological characteristics of the retinal melatonin receptor site (order of affinities: 2-iodomelatonin greater than 6-chloromelatonin greater than or equal to melatonin greater than or equal to 6,7-di-chloro-2-methylmelatonin greater than 6-hydroxymelatonin greater than or equal to 6-methoxymelatonin greater than <em>N</em>-<em>acetyl</em>tryptamine greater than or equal to luzindole greater than <em>N</em>-<em>acetyl</em>-<em>5</em>-hydroxytryptamine greater than <em>5</em>-<em>methoxytryptamine</em> much greater than <em>5</em>-hydroxytryptamine) be classified as ML-1 (melatonin 1). The 2-[12<em>5</em>I]iodomelatonin binding site of hamster brain membranes possesses different binding and pharmacological characteristics from the retinal melatonin receptor site and should be classified as ML-2. In summary, the recent advances in the pharmacological characterization of melatonin receptors in the central nervous system will further stimulate the search for potent and selective melatonin receptor agonists and antagonists, and should aid in our understanding of the mechanism of action of melatonin in mammalian brain.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is a naturally occurring small molecule, serving as important secondary messenger in the response of plants to various biotic and abiotic stresses. However, the interactions between melatonin and other important molecules in the plant stress response, especially in plant immunity, are largely unknown. In this study, we found that both melatonin and nitric oxide (<em>N</em>O) levels in Arabidopsis leaves were significantly induced by bacterial pathogen (Pst DC3000) infection. The elevated <em>N</em>O production was caused by melatonin as melatonin application enhanced endogenous <em>N</em>O level with great efficacy. Moreover, both melatonin and <em>N</em>O conferred improved disease resistance against Pseudomonas syringe pv. tomato (Pst) DC3000 infection in Arabidopsis. <em>N</em>O scavenger significantly suppressed the rise of <em>N</em>O which was induced by exogenous application of melatonin. As a result, the beneficial effects of melatonin on the expression of salicylic acid (SA)-related genes and disease resistance against bacterial pathogen infection were jeopardized by use of a <em>N</em>O scavenger. Consistently, melatonin application significantly lost its effect on the innate immunity against P. syringe pv. tomato (Pst) DC3000 infection in <em>N</em>O-deficient mutants of Arabidopsis. The results indicate that melatonin-induced <em>N</em>O production is responsible for innate immunity response of Arabidopsis against Pst DC3000 infection.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is a ubiquitous molecule with pleiotropic actions in different organisms. It performs many important functions in human, animals, and plants; these range from regulating circadian rhythms in animals to controlling senescence in plants. In this review, we summarize the available information regarding the presence of melatonin in different plant species, along with highlighting its biosynthesis and mechanisms of action. We also collected the available information on the effects of melatonin application on commercially important crops to improve their growth and development. Additionally, we have identified many new aspects where melatonin may have possible roles in plants, for example, its function in improving the storage life and quality of fruits and vegetables, its role in vascular reconnection during the grafting process and nutrient uptake from roots by modifying root architecture. Another potentially important aspect is the production of melatonin-rich food crops (cereals, fruits, and vegetables) through combination of conventional and modern breeding approaches, to increase plant resistance against biotic and abiotic stress, leading to improved crop yields, and the nutraceutical value of produce to solve food security issues.

We investigated the protective effects of melatonin and its metabolites: 6-hydroxymelatonin (6-OHM), <em>N</em>1-<em>acetyl</em>-<em>N</em>2-formyl-<em>5</em>-methoxykynuramine (AFMK), <em>N</em>-<em>acetyl</em>serotonin (<em>N</em>AS), and <em>5</em>-<em>methoxytryptamine</em> (<em>5</em>-MT) in human keratinocytes against a range of doses (2<em>5</em>, <em>5</em>0, and 7<em>5</em> mJ/cm2) of ultraviolet B (UVB) radiation. There was significant reduction in the generation of reactive oxygen species (<em>5</em>0-60%) when UVB-exposed keratinocytes were treated with melatonin or its derivatives. Similarly, melatonin and its metabolites reduced the nitrite and hydrogen peroxide levels that were induced by UVB as early as 30 min after the exposure. Moreover, melatonin and its metabolites enhanced levels of reduced glutathione in keratinocytes within 1 hr after UVB exposure in comparison with control cells. Using proliferation assay, we observed a dose-dependent increase in viability of UVB-irradiated keratinocytes that were treated with melatonin or its derivatives after 48 hr. Using the dot-blot technique and immunofluorescent staining we also observed that melatonin and its metabolites enhanced the D<em>N</em>A repair capacity of UVB-induced pyrimidine photoproducts (6-4)or cyclobutane pyrimidine dimers generation in human keratinocytes. Additional evidence for induction of D<em>N</em>A repair in cells exposed to UVB and treated with the indole compounds was shown using the Comet assay. Finally, melatonin and its metabolites further enhanced expression of p<em>5</em>3 phosphorylated at Ser-1<em>5</em> but not at Ser-46 or its nonphosphorylated form. In conclusion, melatonin, its precursor <em>N</em>AS, and its metabolites 6-OHM, AFMK, <em>5</em>-MT, which are endogenously produced in keratinocytes, protect these cells against UVB-induced oxidative stress and D<em>N</em>A damage.

Indolic and kynuric pathways of skin melatonin metabolism were monitored by liquid chromatography mass spectrometry in human keratinocytes, melanocytes, dermal fibroblasts, and melanoma cells. Production of 6-hydroxymelatonin [6(OH)M], <em>N</em>(1)-<em>acetyl</em>-<em>N</em>(2)-formyl-<em>5</em>-methoxykynuramine (AFMK) and <em>5</em>-<em>methoxytryptamine</em> (<em>5</em>-MT) was detected in a cell type-dependent fashion. The major metabolites, 6(OH)M and AFMK, were produced in all cells. Thus, in immortalized epidermal (HaCaT) keratinocytes, 6(OH)M was the major product with Vmax = 63.7 ng/10(6) cells and Km = 10.2 μM, with lower production of AFMK and <em>5</em>-MT. Melanocytes, keratinocytes, and fibroblasts transformed melatonin primarily into 6(OH)M and AFMK. In melanoma cells, 6(OH)M and AFMK were produced endogenously, a process accelerated by exogenous melatonin in the case of AFMK. In addition, <em>N</em>-<em>acetyl</em>serotonin was endogenously produced by normal and malignant melanocytes. Metabolites showed selective antiproliferative effects on human primary epidermal keratinocytes in vitro. In ex vivo human skin, both melatonin and AFMK-stimulated expression of involucrin and keratins-10 and keratins-14 in the epidermis, indicating their stimulatory role in building and maintaining the epidermal barrier. In summary, the metabolism of melatonin and its endogenous production is cell type-dependent and expressed in all three main cell populations of human skin. Furthermore, melatonin and its metabolite AFMK stimulate differentiation in human epidermis, indicating their key role in building the skin barrier.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) serves as an important signal molecule during plant developmental processes and multiple abiotic stress responses. However, the involvement of melatonin in thermotolerance and the underlying molecular mechanism in Arabidopsis were largely unknown. In this study, we found that the endogenous melatonin level in Arabidopsis leaves was significantly induced by heat stress treatment, and exogenous melatonin treatment conferred improved thermotolerance in Arabidopsis. The transcript levels of class A1 heat-shock factors (HSFA1s), which serve as the master regulators of heat stress responses, were significantly upregulated by heat stress and exogenous melatonin treatment in Arabidopsis. <em>N</em>otably, exogenous melatonin-enhanced thermotolerance was largely alleviated in HSFA1s quadruple knockout (QK) mutants, and HSFA1s-activated transcripts of heat-responsive genes (HSFA2, heat stress-associated 32 (HSA32), heat-shock protein 90 (HSP90), and 101 (HSP101)) might be contributed to melatonin-mediated thermotolerance. Taken together, this study provided direct link between melatonin and thermotolerance and indicated the involvement of HSFA1s-activated heat-responsive genes in melatonin-mediated thermotolerance in Arabidopsis.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is not only a widely known animal hormone, but also an important regulator in plant development and multiple abiotic stress responses. Recently, it has been revealed that melatonin alleviated cold stress through mediating several cold-related genes, including C-REPEAT-BI<em>N</em>DI<em>N</em>G FACTORs (CBFs)/Drought Response Element Binding factors (DREBs), COR1<em>5</em>a, and three transcription factors (CAMTA1, ZI<em>N</em>C FI<em>N</em>GER OF ARABIDOPSIS THALIA<em>N</em>A 10 (ZAT10), and ZAT12). In this study, we quantified the endogenous melatonin level in Arabidopsis plant leaves and found the endogenous melatonin levels were significantly induced by cold stress (4 °C) treatment. In addition, we found one cysteine2/histidine2-type zinc finger transcription factor, ZAT6, was involved in melatonin-mediated freezing stress response in Arabidopsis. Interestingly, exogenous melatonin enhanced freezing stress resistance was largely alleviated in AtZAT6 knockdown plants, but was enhanced in AtZAT6 overexpressing plants. Moreover, the expression levels of AtZAT6 and AtCBFs were commonly upregulated by cold stress (4 °C) and exogenous melatonin treatments, and modulation of AtZAT6 expression significantly affected the induction AtCBFs transcripts by cold stress (4 °C) and exogenous melatonin treatments. Taken together, AtZAT6-activated CBF pathway might be essential for melatonin-mediated freezing stress response in Arabidopsis.

An intrinsic body clock residing in the suprachiasmatic nucleus (SC<em>N</em>) within the brain regulates a complex series of rhythms in humans, including sleep/wakefulness. The individual period of the endogenous clock is usually >24 hours and is normally entrained to match the environmental rhythm. Misalignment of the circadian clock with the environmental cycle may result in sleep disorders. Among these are chronic insomnias associated with an endogenous clock which runs slower or faster than the norm [delayed (DSPS) or advanced (ASPS) sleep phase syndrome, or irregular sleep-wake cycle], periodic insomnias due to disturbances in light perception (non-24-hour sleep-wake syndrome and sleep disturbances in blind individuals) and temporary insomnias due to social circumstances (jet lag and shift-work sleep disorder). Synthesis of melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) within the pineal gland is induced at night, directly regulated by the SC<em>N</em>. Melatonin can relay time-of-day information (signal of darkness) to various organs, including the SC<em>N</em> itself. The phase-shifting effects of melatonin are essentially opposite to those of light. In addition, melatonin facilitates sleep in humans. In the absence of a light-dark cycle, the timing of the circadian clock, including the timing of melatonin production in the pineal gland, may to some extent be adjusted with properly timed physical exercise. Bright light exposure has been demonstrated as an effective treatment for circadian rhythm sleep disorders. Under conditions of entrainment to the 24-hour cycle, bright light in the early morning and avoidance of light in the evening should produce a phase advance (for treatment of DSPS), whereas bright light in the evening may be effective in delaying the clock (ASPS). Melatonin, given several hours before its endogenous peak at night, effectively advances sleep time in DSPS and adjusts the sleep-wake cycle to 24 hours in blind individuals. In some blind individuals, melatonin appears to fully entrain the clock. Melatonin and light, when properly timed, may also alleviate jet lag. Because of its sleep-promoting effect, melatonin may improve sleep in night-shift workers trying to sleep during the daytime. Melatonin replacement therapy may also provide a rational approach to the treatment of age-related insomnia in the elderly. However, there is currently no melatonin formulation approved for clinical use, neither are there consensus protocols for light or melatonin therapies. The use of bright light or melatonin for circadian rhythm sleep disorders is thus considered exploratory at this stage.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is known to be synthesized and secreted by the pineal gland in vertebrates. Evidence for the occurrence of melatonin in the roots of Glycyrrhiza uralensis plants and the response of this plant to the spectral quality of light including red, blue and white light (control) and UV-B radiation (280-31<em>5</em> nm) for the synthesis of melatonin were investigated. Melatonin was extracted and quantified in seed, root, leaf and stem tissues and results revealed that the root tissues contained the highest concentration of melatonin; melatonin concentrations also increased with plant development. After 3 months of growth under red, blue and white fluorescent lamps, the melatonin concentrations were highest in red light exposed plants and varied depending on the wavelength of light spectrum in the following order red>>) blue>> or = white light. Interestingly, in a more mature plant (6 months) melatonin concentration was increased considerably; the increments in concentration were X4, X<em>5</em> and X3 in 6-month-old red, blue and white light exposed (control) plants, respectively. The difference in melatonin concentrations between blue and white light exposed (control) plants was not significant. The concentration of melatonin quantified in the root tissues was highest in the plants exposed to high intensity UV-B radiation for 3 days followed by low intensity UV-B radiation for 1<em>5</em> days. The reduction of melatonin under longer periods of UV-B exposure indicates that melatonin synthesis may be related to the integrated (intensity and duration) value of UV-B irradiation. Melatonin in G. uralensis plant is presumably for protection against oxidative damage caused as a response to UV irradiation.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is an indoleamine with a range of antioxidative properties. Melatonin is endogenously produced in the eye and in other organs. Current evidence suggests that melatonin may act as a protective agent in ocular conditions such as photo-keratitis, cataract, glaucoma, retinopathy of prematurity and ischemia/reperfusion injury. These diseases are sight-threatening and they currently remain, for the most part, untreatable. The pathogenesis of these conditions is not entirely clear but oxidative stress has been proposed as one of the causative factors. Elevated levels of various reactive oxygen and nitrogen species have been identified in diseased ocular structures. These reactants damage the structure and deplete the eye of natural defense systems, such as the antioxidant, reduced glutathione, and the antioxidant enzyme superoxide dismutase. Oxidative damage in the eye leads to apoptotic degeneration of retinal neurons and fluid accumulation. Retinal degeneration decreases visual sensitivity and even a small change in the fluid content of the cornea and crystalline lens is sufficient to disrupt ocular transparency. In the eye, melatonin is produced in the retina and in the ciliary body. Continuous regeneration of melatonin in the eye offers a frontier antioxidative defense for both the anterior and posterior eye. However, melatonin production is minimal in newborns and its production gradually wanes in aging individuals as indicated by the large drop in circulating blood concentrations of the indoleamine. These individuals are possibly at risk of contracting degenerative eye diseases that are free radical-based. Supplementation with melatonin, a potent antioxidant, in especially the aged population should be considered as a prophylaxis to preserve visual functions. It may benefit many individuals worldwide, especially in countries where access to medical facilities is limited.

D<em>N</em>A damage generated by oxygen-derived free radicals is related to mutagenesis, carcinogenesis and aging. In the last several years, hundreds of publications have confirmed that melatonin is a potent endogenous free radical scavenger. In the present in vitro study, we have examined the efficacy of three polyphenolic antioxidants, i.e. xanthurenic acid, resveratrol (3,4',<em>5</em>-trihydroxy-trans-stilbene) and (-)-epigallocatechin-3-gallate (EGCG) and two classical non-polyphenolic antioxidants, i.e. vitamin C (ascorbic acid) and alpha-lipoic acid (LA, 1,2-dithiolane-3-pentanoic acid) in inhibiting *OH-induced oxidative D<em>N</em>A damage. We compared the efficacy of these five antioxidants with the effectiveness of melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) and we also investigated the possible synergistic effects of melatonin with the other five molecules. Using high performance liquid chromatography (HPLC), the formation of 8-hydroxy-2-deoxyguanosine (8-OH-dG) in purified calf thymus D<em>N</em>A treated with the Fenton reagents, chromium(III) (as CrCl3) plus hydrogen peroxide (H2O2) (Cr(III)/H2O2), was measured in the presence or absence of the antioxidants alone or in combination with melatonin. 8-OH-dG is considered a biomarker of oxidative D<em>N</em>A damage. Among the antioxidants tested, melatonin was the most effective of these with an IC<em>5</em>0 = 3.6 +/- 0.1 micro m. For the other antioxidants the IC<em>5</em>0 values were as follows: xanthurenic acid (IC<em>5</em>0 = 7.9 +/- 0.3), resveratrol (IC<em>5</em>0 = 10.9 +/- 0.3), EGCG (IC<em>5</em>0 = <em>5</em>.7 +/- 0.3), vitamin C (IC<em>5</em>0 = 16.9 +/- 0.<em>5</em>) and LA (IC<em>5</em>0 = 38.8 +/- 0.7). These values differ from that of melatonin with a P < 0.01. Melatonin (1 micro M) reversed the pro-oxidant effect of resveratrol (0.<em>5</em> micro M) and vitamin C (0.<em>5</em> micro M), had an antagonistic effect when used in combination with EGCG (1 micro M) and it exhibited synergism in combination with vitamin C (0.<em>5</em> micro M) and with LA (<em>5</em> micro M).

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) functions as a ubiquitous modulator in multiple plant developmental processes and various stress responses. However, the involvement of melatonin in natural leaf senescence and the underlying molecular mechanism in Arabidopsis remain unclear. In this study, we found that the endogenous melatonin level was significantly induced in a developmental stage-dependent manner, and exogenous melatonin treatment delayed natural leaf senescence in Arabidopsis. The expression level of AUXI<em>N</em> RESISTA<em>N</em>T 3 (AXR3)/I<em>N</em>DOLE-3-ACETIC ACID I<em>N</em>DUCIBLE 17 (IAA17) was significantly downregulated by exogenous melatonin treatment and decreased with developmental age in Arabidopsis. Further investigation indicated that AtIAA17-overexpressing plants showed early leaf senescence with lower chlorophyll content in rosette leaves compared with wild-type plants, while AtIAA17 knockout mutants displayed delayed leaf senescence with higher chlorophyll content. <em>N</em>otably, exogenous melatonin-delayed leaf senescence was largely alleviated in AtIAA17-overexpressing plants, and AtIAA17-activated senescence-related SE<em>N</em>ESCE<em>N</em>CE 4 (SE<em>N</em>4) and SE<em>N</em>ESCE<em>N</em>CE-ASSOCIATED GE<em>N</em>E 12 (SAG12) transcripts might have contributed to the process of natural leaf senescence. Taken together, the results indicate that AtIAA17 is a positive modulator of natural leaf senescence and provides direct link between melatonin and AtIAA17 in the process of natural leaf senescence in Arabidopsis.

The complex processes of carcinogenesis often involve oxidative stress. <em>N</em>umerous indicators of oxidative damage are enhanced as the result of the action of carcinogens. Several antioxidants, with different efficacies, protect against oxidative abuse caused by carcinogens. Recently, melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) and related indoleamines have attracted attention because of their high antioxidant and anticarcinogenic activity. Some antioxidants, e.g. ascorbic acid, play an ambivalent role in antioxidative defense, since, under specific conditions, they are strongly prooxidant. Among known antioxidants, melatonin has been an often investigated experimental agent in reducing cancer initiation and inhibiting the growth of established tumors. The indoleamine has been shown to protect macromolecules from oxidative mutilation induced by carcinogens. In these studies, a variety of in vitro and in vivo models were used and numerous indices of oxidative damage were evaluated. The protective effects of melatonin and several other indoleamine antioxidants against cellular damage caused by carcinogens make them potential supplements in the treatment or co-treatment at several stages of cancer.

The purpose of the present study was to elucidate the expression of human organic anion transporter 1 (hOAT1) and hOAT3 in the choroid plexus of the human brain and their interactions with neurotransmitter metabolites using stable cell lines. Immunohistochemical analysis revealed that hOAT1 and hOAT3 are expressed in the cytoplasmic membrane and cytoplasm of human choroid plexus. <em>N</em>eurotransmitter metabolites, namely, <em>5</em>-methoxyindole-3-acetic acid (<em>5</em>-MI-3-AA), homovanillic acid (HVA), vanilmandelic acid (VMA), 3,4-dihydroxyphenylacetic acid (DOPAC), <em>5</em>-hydroxyindole-3-acetic acid (<em>5</em>-HI-3-AA), <em>N</em>-<em>acetyl</em>-<em>5</em>-hydroxytryptamine (<em>N</em>A-<em>5</em>-HTT), melatonin, <em>5</em>-<em>methoxytryptamine</em> (<em>5</em>-MTT), 3,4-dihidroxymandelic acid (DHMA), <em>5</em>-hydroxytryptophol, and <em>5</em>-methoxytryptophol (<em>5</em>-MTP), but not methanephrine (M<em>N</em>), normethanephrine (<em>N</em>M<em>N</em>), and 3-methyltyramine (3-MT), at 2 mM, inhibited para-aminohippuric acid uptake mediated by hOAT1. On the other hand, melatonin, <em>5</em>-MI-3-AA, <em>N</em>A-<em>5</em>-HTT, <em>5</em>-MTT, <em>5</em>-MTP, HVA, <em>5</em>-HI-3-AA, VMA, DOPAC, <em>5</em>-hydroxytryptophol, and M<em>N</em>, but not 3-MT, DHMA, and <em>N</em>M<em>N</em>, at 2 mM, inhibited estrone sulfate uptake mediated by hOAT3. Differences in the IC(<em>5</em>0) values between hOAT1 and hOAT3 were observed for DHMA, DOPAC, HVA, <em>5</em>-HI-3-AA, melatonin, <em>5</em>-MI-3-AA, <em>5</em>-MTP, <em>5</em>-MTT, and VMA. HOAT1 and hOAT3 mediated the transport of VMA but not HVA and melatonin. These results suggest that hOAT1 and hOAT3 are involved in the efflux of various neurotransmitter metabolites from the cerebrospinal fluid to the blood across the choroid plexus.

MicroR<em>N</em>As (miR<em>N</em>As) are small, noncoding R<em>N</em>As that play a crucial role in regulation of gene expression. Recent studies have shown that miR<em>N</em>As implicated in initiation and progression of various human cancers, including breast cancer and also analysis of miR<em>N</em>A expression profiles in cancer provide new insights into potential mechanisms of carcinogenesis. Melatonin, <em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>, is synthesized by the pineal gland in response to the dark/light cycle and has been known to act as a synchronizer of the biological clock. Melatonin has a variety of therapeutic effects, such as immunomodulatory actions, anti-inflammatory effects, and antioxidant actions. Furthermore, melatonin is reported to have an anticancer function including suppression of the metabolism of tumor cells and induction of tumor suppressor genes in cancer cells, including breast cancer cells. In this study, we determined whether miR<em>N</em>As play a role in regulation of various gene expression responses to melatonin in MCF-7 human breast cancer cells. We examined whole-genome miR<em>N</em>A and mR<em>N</em>A expression and found that 22 miR<em>N</em>As were differentially expressed in melatonin-treated MCF-7 cells. We further identified a number of mR<em>N</em>As whose expression level shows a high inverse correlation with miR<em>N</em>A expression. The Gene Ontology (GO) enrichment analysis and pathways analysis were performed for identification of the signaling pathways and biological processes affected by differential expression of miR<em>N</em>A and miR<em>N</em>A-related genes. Our findings suggested that melatonin may modulate miR<em>N</em>A and gene expression as an anticancer mechanism in human breast cancer cells.

It has been suggested that the indole hormone melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>, MLT) is an important natural antioxidant and free radical scavenger [J. Pineal Res., 14:<em>5</em>1; 1993]. In the present work we determined the rate constants, k(r), for scavenging .OH radicals by melatonin, <em>5</em>-<em>methoxytryptamine</em> (<em>5</em>-MeO-T), <em>5</em>-hydroxytryptamine (serotonin, <em>5</em>-OH-T), 6-chloromelatonin (6-Cl-MLT), 6-hydroxymelatonin (6-OH-MLT), and kynurenine (K<em>N</em>) in aqueous solutions. Hydroxyl radicals were generated using a Fenton reaction in the presence of the spin trap <em>5</em>,<em>5</em>-dimethyl-1-pyrroline <em>N</em>-oxide (DMPO), which competed with the indoles for the radicals. It was found that MLT reacts with .OH with k(r) = 2.7 x 10(10) M(-1) s(-1). Other indoles and K<em>N</em> reacted with .OH radicals with similarly high rates (k(r)>> 10(10) M(-1) s(-1)). In contrast to nonhydroxylated indoles (MLT, 6-Cl-MLT, and <em>5</em>-MeO-T), hydroxylated indoles (<em>5</em>-OH-T and 6-OH-MLT) may function both as .OH promoters and .OH scavengers. The melatonin precursor serotonin promoted the generation of .OH radicals in the presence of ferric iron and H2O2, and the melatonin metabolite 6-hydroxymelatonin generated large quantities of .OH radicals in aerated solutions containing Fe3+ ion, even in the absence of externally added hydrogen peroxide. These reactions may be relevant to the biological action of these physiologically important indolic compounds.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is a naturally occurring small molecule that acts as an important secondary messenger in plant stress responses. However, the mechanism underlying the melatonin-mediated signaling pathway in plant stress responses has not been established. C-repeat-binding factors (CBFs)/Drought response element Binding 1 factors (DREB1s) encode transcription factors that play important roles in plant stress responses. This study has determined that endogenous melatonin and transcripts level of CBFs (AtCBF1, AtCBF2, and AtCBF3) in Arabidopsis leaves were significantly induced by salt, drought, and cold stresses and by pathogen Pseudomonas syringe pv. tomato (Pst) DC3000 infection. Moreover, both exogenous melatonin treatment and overexpression of CBFs conferred enhanced resistance to both abiotic and biotic stresses in Arabidopsis. <em>N</em>otably, AtCBFs and exogenous melatonin treatment positively regulated the mR<em>N</em>A expression of several stress-responsive genes (COR1<em>5</em>A, RD22, and KI<em>N</em>1) and accumulation of soluble sugars content such as sucrose in Arabidopsis under control and stress conditions. Additionally, exogenous sucrose also conferred improved resistance to both abiotic and biotic stresses in Arabidopsis. Taken together, this study indicates that AtCBFs confer enhanced resistance to both abiotic and biotic stresses, and AtCBF-mediated signaling pathway and sugar accumulation may be involved in melatonin-mediated stress response in Arabidopsis, at least partially.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>, MLT), the main hormone produced by the pineal gland, not only regulates circadian rhythm, but also has antioxidant, anti-ageing and immunomodulatory properties. MLT plays an important role in blood composition, medullary dynamics, platelet genesis, vessel endothelia, and in platelet aggregation, leukocyte formula regulation and hemoglobin synthesis. Its significant atoxic, apoptotic, oncostatic, angiogenetic, differentiating and antiproliferative properties against all solid and liquid tumors have also been documented. Thanks, in fact, to its considerable functional versatility, MLT can exert both direct and indirect anticancer effects in factorial synergy with other differentiating, antiproliferative, immunomodulating and trophic molecules that form part of the anticancer treatment formulated by Luigi Di Bella (Di Bella Method, DBM: somatostatin, retinoids, ascorbic acid, vitamin D3, prolactin inhibitors, chondroitin-sulfate). The interaction between MLT and the DBM molecules counters the multiple processes that characterize the neoplastic phenotype (induction, promotion, progression and/or dissemination, tumoral mutation). All these particular characteristics suggest the use of MLT in oncological diseases.

Ultraviolet light (UV) is an inducer of reactive oxygen species (ROS) as well as 6-4-photoproducts and cyclobutane pyrimidine dimers (CPD) in the skin, which further cause damage to the skin cells. Irradiation of cultured human melanocytes with UVB stimulated ROS production, which was reduced in cells treated with melatonin or its metabolites: 6-hydroxymelatonin (6-OHM), <em>N</em>1-<em>acetyl</em>-<em>N</em>2-formyl-<em>5</em>-methoxykynuramine (AFMK), <em>N</em>-<em>acetyl</em>serotonin (<em>N</em>AS), and <em>5</em>-<em>methoxytryptamine</em> (<em>5</em>-MT). Melatonin and its derivatives also stimulated the expression of <em>N</em>RF2 (nuclear factor erythroid 2 [<em>N</em>F-E2]-related factor 2) and its target enzymes and proteins that play an important role in cell protection from different damaging factors including UVB. Silencing of <em>N</em>RF2 using siR<em>N</em>A diminished the protective effects of melatonin, while the membrane melatonin receptors (MT1 or MT2) did not change the activities of either melatonin or its derivatives. Melatonin and its metabolites enhanced the D<em>N</em>A repair in melanocytes exposed to UVB and stimulated expression of p<em>5</em>3 phosphorylated at Ser-1<em>5</em>. In conclusion, melatonin and its metabolites protect melanocytes from UVB-induced D<em>N</em>A damage and oxidative stress through activation of <em>N</em>RF2-dependent pathways; these actions are independent of an effect on the classic membrane melatonin receptors. Thus, melatonin and its derivatives can serve as excellent protectors of melanocytes against UVB-induced pathology.

L-2-hydroxyglutaric acid (LGA) is the biochemical hallmark of L-2-hydroxyglutaric aciduria (L-OHGA), an inherited neurometabolic disorder characterized by progressive neurodegeneration with cerebellar and pyramidal signs, mental deterioration, epilepsy, and subcortical leukoencephalopathy. Because the underlying mechanisms of the neuropathology of this disorder are virtually unknown, in this study we tested the in vitro effect of LGA on various parameters of oxidative stress, namely, chemiluminescence, thiobarbituric acid-reactive substances (TBA-RS), protein carbonyl formation (PCF), total radical-trapping antioxidant potential (TRAP), total antioxidant reactivity (TAR), and the activities of the antioxidant enzymes catalase, glutathione peroxidase, and superoxide dismutase in cerebellum and cerebral cortex of 30-day-old rats. LGA significantly increased chemiluminescence, TBA-RS, and PCF measurements and markedly decreased TAR values in cerebellum, in contrast to TRAP and the activity of the antioxidant enzymes, which were not altered by the acid. Similar but less pronounced effects were provoked by LGA in cerebral cortex. Moreover, the LGA-induced increase of TBA-RS was significantly attenuated by melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) and by the combinations of ascorbic acid plus Trolox (soluble alpha-tocopherol) and of superoxide dismutase plus catalase but not by the inhibitor of nitric oxide synthase <em>N</em>omega-nitro-L-arginine methyl ester (L-<em>N</em>AME), creatine, or superoxide dismutase or catalase alone in either cerebral structure. The data indicate that LGA provokes oxidation of lipids and proteins and reduces the brain capacity to modulate efficiently the damage associated with an enhanced production of free radicals, possibly by inducing generation of superoxide and hydroxyl radicals, which are trapped by the scavengers used. Thus, in case these findings can be extrapolated to human L-OHGA, it may be presumed that oxidative stress is involved in the pathophysiology of the brain damage observed in this disorder.