Melatonin suppression of PC12 cell growth and death

Genetic Pathways Associated With Sleep Problems in Children With Autism Spectrum Disorder

AIMS

Children on the autism spectrum are more likely to have sleep problems than non-autistic children. Sleep disturbance may exacerbate emotional and behavioral problems of children on the autism spectrum. A better understanding of the biological mechanisms underlying sleep disturbance provide clues to better management for this co-morbid condition in autism. The goal of the current study is to identify genetic variants associated with sleep disturbance and melatonin levels in autistic children.

METHODS

A total of 969 children on the autism spectrum were genotyped using the Global Screening Array v1 or Global Screening Array v2. Sleep problems were assessed using the Children's Sleep Habits Questionnaire (CSHQ). Melatonin levels were measured using the urine samples of 219 probands. The relationship between the melatonin level and CSHQ score was examined using the general linear model. The genetic variants associated with the CSHQ score and melatonin level as two separate quantitative traits were determined using genomewide association studies.

RESULTS

The data indicates that urine melatonin levels were positively associated with CSHQ scores, suggesting that autistic children with a poorer sleep qualiy could has higher melatonin level. Furthermore, genetic assocication studies suggest that genetic pathways involved in pro-inflammatory responses might be involved in sleep disturbance, while genetic pathways involved in catecholamine-secreting PC12 cells and Schwann cells could be associated with melatonin levels.

CONCLUSIONS

Taken together, our findings indicate that sleep disturbance and melatonin metabolism could be attributable to distinct biological mechanisms in autistic children since they might not share genetic contributors.

Melatonin MT1 and MT2 receptor ERK signaling is differentially dependent on Gi/o and Gq/11 proteins

G protein-coupled receptors (GPCRs) transmit extracellular signals into cells by activating G protein- and β-arrestin-dependent pathways. Extracellular signal-regulated kinases (ERKs) play a central role in integrating these different linear inputs coming from a variety of GPCRs to regulate cellular functions. Here, we investigated human melatonin MT₁ and MT₂ receptors signaling through the ERK1/2 cascade by employing different biochemical techniques together with pharmacological inhibitors and siRNA molecules. We show that ERK1/2 activation by both receptors is exclusively G protein-dependent, without any participation of β-arrestin1/2 in HEK293 cells. ERK1/2 activation by MT₁ is only mediated though G_i/o proteins, while MT₂ is dependent on the cooperative activation of G_i/o and G_q/11 proteins. In the absence of G_q/11 proteins, however, MT₂ -induced ERK1/2 activation switches to a β-arrestin1/2-dependent mode. The signaling cascade downstream of G proteins is the same for both receptors and involves activation of the PI3K/PKCζ/c-Raf/MEK/ERK cascade. The differential G protein dependency of MT₁ - and MT₂ -mediated ERK activation was confirmed at the level of EGR1 and FOS gene expression, two ERK1/2 target genes. G_i/o /G_q/11 cooperativity was also observed in Neuroscreen-1 cells expressing endogenous MT₂ , whereas in the mouse retina, where MT₂ is engaged into MT₁ /MT₂ heterodimers, ERK1/2 signaling is exclusively G_i/o -dependent. Collectively, our data reveal differential signaling modes of MT₁ and MT₂ in terms of ERK1/2 activation, with an unexpected G_i/o /G_q/11 cooperativity exclusively for MT₂ . The plasticity of ERK activation by MT₂ is highlighted by the switch to a β-arrestin1/2-dependent mode in the absence of G_q/11 proteins and by the switch to a G_i/o mode when engaged into MT₁ /MT₂ heterodimers, revealing a new mechanism underlying tissue-specific responses to melatonin.

New insights into the role of melatonin in plants and animals

Melatonin is a hormone produced in animals by the pineal gland and in plants under stress. Melatonin research has expanded rapidly, affecting an impressive enhancement in the understanding of its functions in plants and animals. However, far less focus has been directed to clarifying the nature of melatonin dose-response relationships. Here, we provide substantial evidence of melatonin-induced biphasic dose-response relationships from a series of independent studies involving plant and animal models. The characteristics of these dose responses are similar to those of the broad toxicological and pharmacological hormesis literature. Our analysis suggests that melatonin, in coordination with the circadian rhythms, is involved in stress adaptive responses, and may act as a conditioning agent protecting organisms against subsequent health threats within an hormetic framework. Incorporation of melatonin-induced hormesis in research protocols has the potential to enhance the treatment of neuropsychiatric diseases, cancers, and other animal diseases, as well as protection against environmental stress and to increase plant productivity.

The protective effect of melatonin in lungs of newborn rats exposed to maternal nicotine

We investigated possible healing effects of melatonin (MEL) on biochemical and histological changes in the lungs of rat offspring caused by exposure to nicotine (NT) in utero. Pregnant rats were divided randomly into five groups. The SP group was treated with physiological saline. The EA group was treated with ethyl alcohol. The MEL group was treated with MEL. The NT group was treated with NT. The NT + MEL group was treated with NT and MEL. At the end of the study, the biochemistry and histopathology of lung tissue of the offspring were examined. Reduced alveolar development and increased numbers of alveolar macrophages and mast cells were observed in the NT group compared to the SP, EA and MEL groups. We also found increased malondialdehyde (MDA) levels and decreased total glutathione (GSH) levels in the NT group. Application of MEL ameliorated the histological and biochemical damage caused by NT. The number of alveoli was greater in the NT + MEL group than in the NT group. Also, the increased numbers of alveolar macrophages and mast cells resulting from exposure to NT were decreased following MEL treatment. We found that MEL caused a significant decrease in the level of MDA. Maternal exposure to NT caused significant structural and biochemical changes in the lungs of the offspring and administration of MEL ameliorated the changes.

Melatonin up-regulates the expression of the GATA-4 transcription factor and increases testosterone secretion from Leydig cells through RORα signaling in an in vitro goat spermatogonial stem cell differentiation culture system

Because androgen function is regulated by its receptors, androgen-androgen receptor signaling is crucial for regulating spermatogenesis. Androgen is mainly testosterone secreted by testis. Based on the results of early studies in goats, the administration of melatonin over an extended period of time increases steroid production, but the underlying mechanism remains unclear. Here, we report the expression of the melatonin membrane receptors MT1 and MT2 and the retinoic acid receptor-related orphan receptor-alpha (RORα) in the goat testis. An in vitro differentiation system using spermatogonial stem cells (SSCs) cultured in the presence of testicular somatic cells was able to support the formation of sperm-like cells with a single flagellum. The addition of 10^-7 M melatonin to the in vitro culture system increased RORα expression and considerably improved the efficiency of haploid cell differentiation, and the addition of the RORα agonist CGP52608 significantly increased the testosterone concentration and expression of GATA binding factor 4 (GATA-4). Furthermore, inhibitors of melatonin membrane receptors and a RORα antagonist (T0901317) also led to a considerable reduction in the efficiency of haploid spermatid formation, which was coupled with the suppression of GATA-4 expression. Based on these results, RORα may play a crucial role in enhancing melatonin-regulated GATA-4 transcription and steroid hormone synthesis in the goat spermatogonial stem cell differentiation culture system.

The acute exposure of tetrachloro-p-benzoquinone (a.k.a. chloranil) triggers inflammation and neurological dysfunction via Toll-like receptor 4 signaling: The protective role of melatonin preconditioning

This study is aimed to investigate the inflammation and neurological dysfunction induced by tetrachloro-p-benzoquinone (TCBQ) through Toll-like receptor 4 (TLR4) signaling. We also investigated the protective role of melatonin as an antioxidant and anti-inflammatory agent. In vitro model was established by rat pheochromocytoma PC12 cells, meanwhile, TLR4 wild-type (C57BL/6) and knockout mice (C57BL/10ScNJ TLR4^-/-) were used as in vivo model. In vitro study showed TCBQ exposure enhanced the expression of TLR4, myeloid differentiation factor 88 (MyD88) at both transcriptional and post-transcriptional levels. By contrast, melatonin decreased TLR4 and MyD88 expressions. Moreover, our result indicated that melatonin disrupted the formation of TLR4/MyD88/MD2/CD14 complex. In addition, melatonin terminated TCBQ-mediated phosphorylation of c-Jun N-terminal kinase (JNK), p38, and extracellular regulated protein kinase (ERK) signaling and hampered its downstream pro-inflammatory cytokine releases. In vivo result also indicated TLR4 deficiency partially protected against TCBQ-induced morphological and neuropathological changes in mice brain, suggested the role of TLR4. In conclusion, melatonin modulates TCBQ-mediated inflammatory genes through TLR4/MyD88-dependent signaling pathway. Our current study, to the best of our knowledge, is the first time show melatonin not only disrupt the binding of TLR4 and MyD88, but also restricted the formation of TLR4/MD2/CD14 complex, suggesting that melatonin supplementary may represent a valuable therapeutic strategy for inflammatory neurological dysfunction.

Melatonin promotes osteoblast differentiation and mineralization of MC3T3-E1 cells under hypoxic conditions through activation of PKD/p38 pathways

Osteoblastic differentiation and bone-forming capacity are known to be suppressed under hypoxic conditions. Melatonin has been shown to influence cell differentiation. A number of in vitro and in vivo studies have suggested that melatonin also has an anabolic effect on bone, by promoting osteoblastic differentiation. However, the precise mechanisms and the signaling pathways involved in this process, particularly under hypoxic conditions, are unknown. This study investigated whether melatonin could promote osteoblastic differentiation and mineralization of preosteoblastic MC3T3-E1 cells under hypoxic conditions. Additionally, we examined the molecular signaling pathways by which melatonin mediates this process. We found that melatonin is capable of promoting differentiation and mineralization of MC3T3-E1 cells cultured under hypoxic conditions. Melatonin upregulated ALP activity and mRNA levels of Alp, Osx, Col1, and Ocn in a time- and concentration-dependent manner. Alizarin red S staining showed that the mineralized matrix in hypoxic MC3T3-E1 cells formed in a manner that was dependent on melatonin concentration. Moreover, melatonin stimulated phosphorylation of p38 Mapk and Prkd1 in these MC3T3-E1 cells. We concluded that melatonin promotes osteoblastic differentiation of MC3T3-E1 cells under hypoxic conditions via the p38 Mapk and Prkd1 signaling pathways.

Melatonin regulates human bone sialoprotein gene transcription

Melatonin is produced by the pineal gland and regulates various physiological processes including osteoblast differentiation and bone formation. Bone sialoprotein (BSP) is a mineralized connective tissue-specific protein expressed in the early stage of cementum and bone mineralization. To elucidate the effects of melatonin on human BSP gene expression, we utilized human Saos2 osteoblast-like cells. Melatonin (100 nM) increased the level of BSP mRNA at 3 h, and the level became maximal at 12 and 24 h. We then investigated the melatonin-induced transcriptional activity of luciferase constructs (between -84LUC and -868LUC) including different lengths of the human BSP gene promoter transfected into Saos2 cells. The effects of melatonin abrogated in constructs included 2-bp mutations in the two cAMP response elements (CRE1 and CRE2). The effects of melatonin were suppressed by protein kinase A, tyrosine kinase, ERK1/2 and phosphatidylinositol 3-kinase inhibitors. Gel mobility shift assays showed that melatonin increased the binding of nuclear proteins to CRE1 and CRE2, and antibodies against CRE binding protein 1 (CREB1), phospho-CREB1, c-Fos, c-Jun, JunD and Fra2 disrupted CRE1 and CRE2 protein complex formation. These data indicate that melatonin induces BSP transcription via the CRE1 and CRE2 elements in the human BSP gene promoter. (J Oral Sci 56, 67-76, 2014).

Molecular mechanisms of melatonin's inhibitory actions on breast cancers

Melatonin is involved in many physiological functions and it plays an important role in many pathological processes as well. Melatonin has been shown to reduce the incidence of experimentally induced cancers and can significantly inhibit the growth of some human tumors, namely hormone-dependent cancers. The anticancer effects of melatonin have been observed in breast cancer, both in in vivo with models of chemically induced rat mammary tumors, and in vitro studies on human breast cancer cell lines. Melatonin acts at different physiological levels and its antitumoral properties are supported by a set of complex, different mechanisms of action, involving apoptosis activation, inhibition of proliferation, and cell differentiation.

A Comparison of B16 Melanoma Cells and 3T3 Fibroblasts Concerning Cell Viability and ROS Production in the Presence of Melatonin, Tested Over a Wide Range of Concentrations

Melatonin is a pleiotropic molecule with many cellular and systemic actions, including chronobiotic effects. Beneficial effects are widely documented concerning the treatment of neoplastic diseases in vivo as well as reductions in viability of cultured cells from melanoma, one of the most aggressive cancers in humans. However, studies of its effects on non-tumor cells in vitro have not focused on viability, except for experiments aiming to protect against oxidotoxicity or other toxicological insults. Furthermore, there is no agreement on the range of effective melatonin concentrations in vitro, and the mechanisms that reduce cell viability have remained unclear. Tumor cell-specific increases in the production of reactive oxygen and nitrogen species (ROS/RNS) may provide a possible explanation. Our aim was to analyze the potential inhibition of tumor (B16 melanoma 4A5) and non-tumor cell (3T3 Swiss albino) viability using a wide range of melatonin concentrations (10⁻¹¹–10⁻² M), and to determine whether intracellular ROS enhancement was involved in this process. In the absence of fetal bovine serum (FBS), low melatonin concentrations (10⁻⁹–10⁻⁵ M) reduced the proliferation of melanoma cells with no effect in fibroblasts, whereas, in the presence of FBS, they had no effect or even increased the proliferation of both fibroblast and melanoma cells. Melatonin concentrations in the upper millimolar range increased ROS levels and reduced the viability of both cell types, but more markedly so in non-tumor cells. Thus, low melatonin concentrations reduce proliferation in this specific melanoma cell line, whereas high concentrations affect the viability of both tumor (B16 4A5 melanoma) and non-tumor (3T3 fibroblasts) cells. Increased ROS levels in both lines indicate a role for ROS production in the reduction of cell viability at high—but not low—melatonin concentrations, although the mechanism of action still remains to be elucidated.

Effects of melatonin on the proliferation and differentiation of rat adipose-derived stem cells

Background:

Osteogenesis driven by adipose-derived stem cells (ADSCs) is regulated by physiological and pathological factors. Accumulating evidence from in vitro and in vivo experiments suggests that melatonin may have an influence on bone formation. However, little is known about the effects of melatonin on osteogenesis, which thus remains to be elucidated. This study was performed to determine whether melatonin at physiological concentrations (0.01-10 nM) could affect the in vitro proliferation and osteogenic differentiation of rat ADSCs.

Materials and Methods:

ADSCs were isolated from the fat of adult rats. After cell expansion in culture media and through three passages, osteogenesis was induced in a monolayer culture using osteogenic medium with or without melatonin at physiological concentrations (0.01-10 nM). After four weeks, the cultures were examined for mineralization by Alizarin Red S and von Kossa staining and for alkaline phosphatase (ALP) activity using an ALP kit. Cell viability and apoptosis were also assayed by 3-(4, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTT) assay and flow cytometry, respectively.

Results:

The results indicated that at physiological concentrations, melatonin suppressed proliferation and differentiation of ADSCs. These data indicate that ADSCs exposed to melatonin, had a lower ALP activity in contrast to the cells exposed to osteogenic medium alone. Similarly, mineral deposition (calcium level) also decreased in the presence of melatonin. Flow cytometry confirmed that cell growth had decreased and that the numbers of apoptotic cells had increased.

Conclusion:

These results suggest that the physiological concentration of melatonin has a negative effect on ADSC osteogenesis.

Melatonin influences the proliferative and differentiative activity of neural stem cells

Though melatonin has a wide variety of biological functions, its effects on the neural stem cells (NSCs) is still unknown. In this study, we examined the effects of melatonin at either physiological (0.01-10 nm) or pharmacological concentrations (1-100 microM) on the proliferation and neural and astroglial differentiation of NSCs derived from the mouse embryo striatum using an in vitro culture system. We found that melatonin at pharmacological concentrations, but not at physiological concentrations, suppressed epidermal growth factor (EGF)-stimulated NSC proliferation (increment of viable cells, DNA synthesis and neurosphere formation) in a concentration-dependent manner. Furthermore, treatment with melatonin at a pharmacological concentration during the proliferation period facilitated 1% FBS-induced neural differentiation of NSCs without affecting the astroglial differentiation. In contrast, the treatment with melatonin at pharmacological concentrations during the differentiation period decreased the neural differentiation of the NSCs. As with melatonin, MCI-186, an antioxidant, suppressed EGF-stimulated NSC proliferation and facilitated the subsequent neural differentiation of NSCs. These results suggest that melatonin exerts potent modulatory effects on NSC functions including the suppression of the proliferation and facilitation of neuronal differentiation, likely via its antioxidant activity. As neurogenesis is thought to play an important role in ameliorating the deficit in neurodegenerative diseases, melatonin might be beneficially used for the treatment diseases such as cerebral infarction.

Melatonin protection against lead-induced changes in human neuroblastoma cell cultures

The nervous system is the primary target for low-levels of lead (Pb) exposure and the developing brain appears to be especially vulnerable to Pb neurotoxicity. Chronic low-level Pb exposure causes growth retardation and intellectual impairment. In the present study the protective effect of melatonin during exposure to low-levels of Pb in human SH-SY5Y neuroblastoma cell cultures was assessed. The cells were exposed to Pb (0.01 to 10 microM) for 48 h. Pb inhibited the proliferation of neuroblastoma cells significantly in a concentration-dependent manner. A 50% inhibition (IC50) of cell proliferation was observed at about 5 microM Pb. Pb decreased (16% to 62%) the levels of total cellular glutathione (GSH) in a concentration (0.1 to 10 microM)-dependent manner. Exposure of cells to Pb (5 microM) for 48 h resulted in an eightfold increase in caspase-3 activity and prostaglandin E2 (PGE2) level. Pretreatment with melatonin (10 microM) blocked the effects of Pb on GSH content and caspase-3 activity, and showed significant improvement in reducing the level of PGE2. The results suggest that some of the neurotoxic effects of Pb may be partly mediated by apoptosis and pretreatment with melatonin can prevent these effects. The present study asserts the neuroprotective effect of melatonin in conditions of Pb-induced toxicity in neuroblastoma cell cultures.

Melatonin as antioxidant, geroprotector and anticarcinogen

The effect of the pineal indole hormone melatonin on the life span of mice, rats and fruit flies has been studied using various approaches. It has been observed that in female CBA, SHR, SAM and transgenic HER-2/neu mice long-term administration of melatonin was followed by an increase in the mean life span. In rats, melatonin treatment increased survival of male and female rats. In D. melanogaster, supplementation of melatonin to nutrient medium during developmental stages produced contradictory results, but and increase in the longevity of fruit flies has been observed when melatonin was added to food throughout the life span. In mice and rats, melatonin is a potent antioxidant both in vitro and in vivo. Melatonin alone turned out neither toxic nor mutagenic in the Ames test and revealed clastogenic activity at high concentration in the COMET assay. Melatonin has inhibited mutagenesis and clastogenic effect of a number of indirect chemical mutagens. Melatonin inhibits the development of spontaneous and 7-12-dimethlbenz(a)anthracene (DMBA)- or N-nitrosomethylurea-induced mammary carcinogenesis in rodents; colon carcinogenesis induced by 1,2-dimethylhydrazine in rats, N-diethylnitrosamine-induced hepatocarcinogenesis in rats, DMBA-induced carcinogenesis of the uterine cervix and vagina in mice; benzo(a)pyrene-induced soft tissue carcinogenesis and lung carcinogenesis induced by urethan in mice. To identify molecular events regulated by melatonin, gene expression profiles were studied in the heart and brain of melatonin-treated CBA mice using cDNA gene expression arrays (15,247 and 16,897 cDNA clone sets, respectively). It was shown that genes controlling the cell cycle, cell/organism defense, protein expression and transport are the primary effectors for melatonin. Melatonin also increased the expression of some mitochondrial genes (16S, cytochrome c oxidases 1 and 3 (COX1 and COX3), and NADH dehydrogenases 1 and 4 (ND1 and ND4)), which agrees with its ability to inhibit free radical processes. Of great interest is the effect of melatonin upon the expression of a large number of genes related to calcium exchange, such as Cul5, Dcamkl1 and Kcnn4; a significant effect of melatonin on the expression of some oncogenesis-related genes was also detected. Thus, we believe that melatonin may be used for the prevention of premature aging and carcinogenesis.

LNP 906, the first high-affinity photoaffinity ligand selective for I1 imidazoline receptors

1 The hypotensive effect of imidazoline-like drugs, such as clonidine, was attributed both to alpha2-adrenergic receptors and nonadrenergic imidazoline receptors, which are divided into I1, I2 and I3 subtypes. 2 We have recently synthesized a derivative of (2-(2-chloro-4-iodo-phenylamino)-5-methyl-pyrroline (LNP 911), the first high-affinity and selective ligand for I1 receptors (I1R), with a photoactivable function (LNP 906). 3 This work aims to test whether this derivative retained the binding properties of LNP 911 and bound irreversibly to I1R. 4 Binding studies showed that LNP 906 exhibited nanomolar affinity for I1R and was selective for I1R over I2 receptors and alpha2-adrenergic receptors (alpha2Ars). 5 Upon exposure to u.v. light, LNP 906 irreversibly blocked the binding of [125I]-paraiodoclonidine (PIC) to I1R, time- and dose-dependently, on PC12 cell membranes and interacted with I1R in a reversible and competitive manner in the absence of light. Pharmacological studies showed that this blockade was prevented by the concomitant presence of rilmenidine (a well-known I1 agonist), but not by rauwolscine (an alpha2 antagonist). 6 Finally, LNP 906 clearly antagonized the decrease in forskolin-stimulated cAMP level induced by rilmenidine, but not by melatonin. 7 These results indicate that LNP 906 is the first high-affinity and selective photoaffinity ligand for I1R and that it behaves as an I1R antagonist.

Melatonin inhibition of nicotine-stimulated dopamine release in PC12 cells

Melatonin, a pineal hormone, modifies numerous physiologic processes including circadian rhythms and sleep. In specific tissues, melatonin appears to have an inverse relationship with dopamine. To examine this relationship, a pheochromocytoma cell line (PC12) was used to determine the extent of melatonin's ability to inhibit nicotine-stimulated dopamine release. Multiple experiments were conducted that examined: (1). the dose response of acute melatonin (5 min); (2). the effects of chronic melatonin (16 h pre-exposure); (3). the effects of prior nicotine or melatonin exposure (5 min) on melatonin's ability to alter dopamine release from a second 5-min nicotine exposure; and (4). the role of melatonin receptors (by pertussis toxin inhibition) on nicotine-stimulated dopamine release. In the dose response studies, melatonin inhibited nicotine-stimulated dopamine release with an ED50 of 8.6 microM. Chronic exposure to melatonin had no effect on melatonin's acute inhibition of nicotine-stimulated dopamine release. Prior nicotine or melatonin exposure had little effect on subsequent melatonin or nicotine exposure, except that the cells exposed to nicotine were not responsive to a second exposure to nicotine. Blockade of melatonin receptor function by pre-exposure to pertussis toxin (16 h) did not prevent melatonin's inhibition of nicotine-stimulated dopamine release. However, the toxin-treated cells were less inhibited by melatonin when compared to control cells suggesting a partial role for melatonin receptors. These results indicate that melatonin can acutely inhibit nicotine-stimulated dopamine release in PC12 cells. This model system allows detailed examination of melatonin's cellular actions as well as supporting a role for melatonin on neuronal dopamine release.

Glutathione depletion-induced apoptosis of Ha-ras-transformed NIH3T3 cells can be prevented by melatonin

It is well known that intracellular antioxidant glutathione (GSH) plays major roles in the maintenance of redox status and defense of oxidative stress. Ras, a small GTP-binding protein, may send growth-stimulating message to the nucleus through downstream Rac oncoprotein and superoxide (O(2*-)). These findings led us to investigate the effects of GSH and melatonin, a free-radical scavenger, on Ras-Rac-O(2*-)-related growth signal transduction. Our results demonstrate that overexpression of the inducible Ha-ras oncogene by isopropyl-beta-D-thiogalactoside (IPTG) increases the levels of reactive oxygen species (ROS, including O(2*-) and hydrogen peroxide (H(2)O(2))) and GSH in an Ha-ras-transformed NIH/3T3 fibroblast cell line. On the contrary, melatonin significantly suppresses ras-triggered cell growth by inhibiting the increase of ROS and GSH. Moreover, severe apoptosis of this transformed cell line occurred when the cell redox balance between ROS and GSH was dramatically changed in the presence of IPTG and L-buthionine-[S,R]-sulfoximine (BSO, a specific inhibitor of GSH synthetase). That BSO-induced cell apoptosis needs Ras to increase the ROS level was demonstrated by the free-radical scavenger melatonin. It effectively blocked cell apoptosis, but cell growth was also slowed without affecting Ras expression. Based on our studies, two approaches can be applied to treating ras-related cancers. One is utilizing melatonin to suppress cancer cell proliferation, and the other is utilizing BSO to induce cancer-cell apoptosis. Cotreatment of ras-related cancer cells with melatonin and BSO stops cell growth as well as apoptosis. Whether these cancer cells will undergo further regression or become recurrent merits investigation.

Melatonin-induced suppression of PC12 cell growth is mediated by its Gi coupled transmembrane receptors

The effects of pertussis toxin, an uncoupler of Gi protein from adenylate cyclase, and luzindole, a competitive inhibitor of melatonin receptor binding, were examined for their ability to inhibit melatonin-induced suppression of PC12 cell growth. Both agents inhibited the melatonin response suggesting that melatonin may be acting through one of its Gi coupled cell surface receptors. This is confirmed by Western blots demonstrating the presence of MT1 receptors in PC12 cells. Coupling of the Gi protein to these receptors is demonstrated by failure of melatonin to suppress cell growth in PKA deficient A126-1B2-1 mutant PC12 cells. Similarly, melatonin failed to prevent cell proliferation when cells were incubated in the presence of the PKA inhibitor, Rp-cAMP. Retinoic acid and dexamethasone, agents known to effect PC12 cell growth and/or differentiation, displayed differential effects on the actions of melatonin. In the presence of melatonin and low concentrations of retinoic acid (100 nM), PC12 cell proliferation was stimulated compared to that seen with either agent alone, whereas no increase in cell proliferation was observed when higher concentrations of retinoic acid (100 microM) were used. The effects of dexamethasone on suppression of PC12 cell growth were additive with that of melatonin whereas, 1,25-dihydroxyvitamin D(3) (IC(50)=10 nM), which by itself had no effect on PC12 cell growth, was found to inhibit the melatonin response. This study demonstrates that inhibition of PC12 cell growth, at physiological concentrations of melatonin, is mediated by cAMP-dependent cell surface receptors and this response is altered by other growth factors known to effect PC12 cell proliferation and differentiation.

Apoptosis: biphasic dose responses

The features of apoptotic dose responses typically have been evaluated over a broad dose-response continuum to differentiate apoptotic and necrotic responses. The present article specifically addresses the dose-response relationship for apoptosis in detail. It was determined that a number of well-documented cases exist in which the dose-response relationship for apoptosis is biphasic. The underlying mechanisms and biomedical implications of this biphasic dose-response phenomenon are discussed.

Alteration of Bcl-2 expression in the nigrostriatal system after kainate injection with or without melatonin co-treatment

In order to understand further the role of the anti-apoptotic Bcl-2 proto-oncogene protein in excitotoxin-induced brain injury and possible interaction between Bcl-2 and the antioxidant melatonin, the expression of Bcl-2 in various brain parts was studied after intrastriatal injection of kainate (KA, 2.5 nmol) with or without co-treatment of melatonin (10 mg/kg, intraperitoneally (i.p.)). Three days after unilateral injection of KA to the striatum in the rat, a dramatic direct cytotoxic effect was observed, as indicated an expression of Bcl-2 immunoreactivity in TUNEL- and OX-42-positive cells in the KA-injected striatum and traumatized cortical region. A less severe detrimental effect was also observed in the ipsilateral substantia nigra and peritraumatic cortex, as reflected by an upregulation of Bcl-2-immunostained neurons. Surprisingly, a reduction in Bcl-2-immunoreactive neurons that was accompanied by a less severe loss of tyrosine hydroxylase-immunoreactive neurons in the nigrostriatal pathway was observed after co-treatment with melatonin. Western blot analysis confirmed that Bcl-2 expression is elevated in striatum and cortex on the lesioned side, and that its expression was attenuated substantially after systemic administration of melatonin. The results showing an upregulation of Bcl-2 in nigral neurons and reactive microglia after KA lesion are consistent with the view that Bcl-2 is protective in function in the central nervous system.

Can melatonin regulate the expression of prohormone convertase 1 and 2 genes via monomeric and dimeric forms of RZR/ROR nuclear receptor, and can melatonin influence the processes of embryogenesis or carcinogenesis by disturbing the proportion of cAMP and cGMP concentrations? Theoretic model of controlled apoptosis

The presented model of controlled apoptosis has been based on the assumption that correct information exchange between an organism as a whole, and each of its cells is conditioned by mutual proportions of cAMP and cGMP concentrations (CcAMP, CcGMP), according to the formula CcAMP x CcGMP = 'a' (constant). The regulation of balance of these 'second messengers' in a cell and an extracellular space would depend on the mutual proportions of concentrations of Melatonin and monomers of Melanin. These indoloderived compounds could be the activators of the transcription factors i.e. RZR and NFkappa-B, regulating the expression of Prohormone Convertase (PC) gen and Nitric Oxide Synthase (NOS) gen, respectively. Additionally, maternal Melatonin and Nitric Oxide (NO), being able to pass through trophoblast or placenta freely, would play decisive role in the synchronization of embryogenesis and intrauterine development of the fetus. In case of an embryo or a fetus, the result of CcAMP and CcGMP multiplication, different from the proper constant 'a'-value, would mean occurrence of disorders in the structure and functioning of the cellular tensegrity system and, in consequence, disturbances in the intercellular information exchange. It would lead to deviation in cellular metabolism, oriented cell movement, uncontrolled apoptosis, and as a consequence, would lead to the development of fetal defects. In case of a child or an adult, a sudden occurrence and prolongation of such disturbances in CcAMP-CcGMP proportions would induce a process of apoptosis of normal cells and an initiation of a cancerogenesis. On the other hand, the recovery of equilibrium in the information exchange system would initiate apoptosis of neoplastic cells, and simultaneously, proliferation of connective tissue cells. According to the presented hypothesis, a decrease in CcAMP and destabilization of the CcAMP-CcGMP balance in an embryo or a fetus would result from relatively excessive amounts of maternal Melatonin (monomers) in fetal circulation, while a decrease of CcAMP and destabilization of the CcAMP-CcGMP balance in a child or an adult would be a consequence of relatively insufficient amounts of Melatonin (dimers) in an organism. It seems possible, that determination of both CcAMP and CcGMP would enable an early detection of high risk of developmental defects occurrence in an embryo or a fetus and neoplastic processes in a child or an adult. This method might also be considerably useful in monitoring a safe substitutional hormonotherapy.

Growth-inhibitory activity of melatonin on human androgen-independent DU 145 prostate cancer cells

BACKGROUND

The pineal hormone melatonin has been shown to exert a direct oncostatic activity on neoplastic cells, particularly from breast cancer. In the present study, we evaluated the effects of melatonin on the proliferation and on the cell cycle distribution of human androgen-independent DU 145 prostate cancer cells. Experiments were also performed to gain insights into the possible mechanism of action of the hormone.

METHODS

The effects of melatonin on DU 145 cell proliferation was analyzed by counting the cells by hemocytometer at the end of treatment. The effects of the pineal hormone on cell cycle distribution were evaluated by FACS analysis. RT-PCR studies were performed to detect Mel(1a) and Mel(1b) expression in DU 145 cells. The cellular localization of (125)I-melatonin binding sites was investigated by radioreceptor assay. A commercially available binding-protein assay kit was utilized to evaluate intracellular cAMP levels.

RESULTS

Melatonin, in physiological doses, significantly inhibited DU 145 cell proliferation and induced cell cycle withdrawal by accumulating cells in G0/G1 phase. The mRNA for Mel(1a) receptors was found to be expressed in DU 145 cells; however, by radioreceptor assay, no binding sites for (125)I-melatonin could be detected in membrane preparations, suggesting that, in these cells, the level of translation of this mRNA is too low to possibly mediate the antiproliferative action of the hormone. In agreement with this hypothesis, melatonin did not affect forskolin-induced intracellular cAMP accumulation. Binding sites for (125)I-melatonin were found in nuclear extracts of DU 145 cells.

CONCLUSIONS

Melatonin exerts a direct oncostatic activity on human androgen-independent prostate cancer cells, by affecting cell cycle progression. This activity seems to be mediated by nuclear, but not by membrane, receptors.

The endogenous oxindoles 5-hydroxyoxindole and isatin are antiproliferative and proapoptotic

Oxindole-core synthetic molecules are currently being developed as anticancer drugs that target protein tyrosine kinases associated with growth factor receptors. Oxindole, 5-Hydroxyoxindole, and 2, 3-dioxindole [isatin] are natural molecules found in mammalian body fluids and tissues and we addressed the question of similar properties of endogenous oxindoles. 5-Hydroxyoxindole and isatin, but not oxindole, inhibited N1E-115, BALB/c3T3, BBC, PC12, and HL60 proliferation at submicromolar concentrations. Acute treatment with 5-hydroxyoxindole and isatin reduced the activity of extracellular signal regulated protein kinases (ERKs) by 35% at 100 microM and ERK1 activity was strongly inhibited by 5-Hydroxyoxindole at 10 microM. Survival of PMA-differentiated HL60 and FGF(2)-differentiated PC12 cells was not affected by 5-Hydroxyoxindole and isatin treatment, suggesting that endogenous oxindoles interact with growth factors signaling. The physiological implications of these data and the potential utility of 5-Hydroxyoxindole and isatin as antitumor agents are discussed.

Circadian rhythm of serotonin N -acetyltransferase activity in rat lens

Activity of serotonin N -acetyltransferase (NAT), a key regulatory enzyme in melatonin biosynthesis, was detected in the rat lens. NAT activity in the lens showed significant diurnal variation in vivo and in vitro, peaking during the period of darkness, when the lenses were maintained under 14 hr light/10 hr dark cycle. Cultured lenses exhibited a circadian rhythm of NAT activity when maintained under constant darkness. However, the rhythm in vitro was not entrained when the light/dark cycle was delayed 8 hr from the cycle in intact animals. These data strongly suggest that the rat lens contains a circadian clock that controls NAT activity, although the circadian clock appears to lack a photic entrainment mechanism.

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.

Cis-platinum-induced immunosuppression: relationship to melatonin in human peripheral blood mononuclear cells

OBJECTIVES

The purpose of this study was to investigate the immunomodulatory effect of melatonin (MLT) on human peripheral blood mononuclear cells (PBMC) and to address its effects on Cis-platinum (CDDP)-induced cytotoxicity.

METHODS AND RESULTS

The obtained data from this study revealed that treatment of cells with MLT (100 microg/ml) for 24 h enhanced cell viability. When cells were exposed to CDDP (5 microg/ml), cell proliferation in response to phytohaemagglutinin (PHA) stimulation was reduced by 49.63% compared to control cells as detected by 3[H]-thymidine uptake. Furthermore, Cis-platinum significantly depleted intracellular glutathione (GSH) levels by approximately 47% below that of untreated cells and led to apoptotic changes in the target cells as evidenced by DNA fragmentation (45% compared to 5% in control cells as measured by diphenylamine assay). DNA fragmentation was also confirmed by agarose gel electrophoresis. However, MLT enhanced cell proliferation by approximately 8.63% above the control values, and counteracted the antiproliferative effect of CDDP. The GSH levels were significantly increased in response to MLT (71% above control values) and it protected the cells against GSH depletion induced by CDDP. Moreover, DNA fragmentation and laddering produced by CDDP were significantly reduced or even disappeared when the cells were pretreated with MLT or the latter was simultaneously added with CDDP.

CONCLUSIONS

The findings from this study indicated that melatonin is a potent immunomodulatory hormone that protects PBMC against cis-platinum-induced immunosuppressive effects. These effects might improve the patients' response to cis-platinum therapy and, therefore, their survival rates.

Melatonin promotes osteoblast differentiation and bone formation

Prior studies have demonstrated that the pineal hormone, melatonin, can stimulate chloramphenicol acetyltransferase activity in Drosophila SL-3 cells transfected with a chloramphenicol acetyltransferase reporter construct containing the response element of rat bone sialoprotein (BSP). Based on these findings, studies were performed to determine whether melatonin could similarly modulate the expression of BSP in two cell lines, the MC3T3-E1(MC3T3) pre-osteoblast and rat osteoblast-like osteosarcoma 17/2.8 cell. Initial studies demonstrated that MC3T3 cells grown in the presence of 50 nM melatonin underwent cell differentiation and mineralization by day 12 instead of the 21-day period normally required for cells grown in untreated media. Melatonin increased gene expression of BSP and the other bone marker proteins, including alkaline phosphatase (ALP); osteopontin; secreted protein, acidic and rich in cysteine; and osteocalcin in MC3T3 cells in a concentration-dependent manner. Levels of melatonin as low as 10 nM were capable of stimulating transcription of these genes when cells were grown in the presence of beta-glycerophosphate and ascorbic acid. Under these conditions, melatonin induced gene expression of the bone marker proteins; however, this does not occur until the 5th day after seeding the culture dishes. Thereafter, MC3T3 cells responded to melatonin within 2 h of treatment. The fully differentiated rat osteoblast-like osteosarcoma 17/2.8 cells responded rapidly to melatonin and displayed an increase in the expression of BSP, ALP, and osteocalcin genes within 1 h of exposure to the hormone. To determine whether melatonin-induced osteoblast differentiation and bone formation are mediated via the transmembrane receptor, MC3T3 cells were treated in the presence and absence of melatonin with either luzindole, a competitive inhibitor of the binding of melatonin to the transmembrane receptors, or pertussis toxin, an uncoupler of G(i) from adenylate cyclase. Both luzindole and pertussis toxin were shown to reduce melatonin-induced expression of BSP and ALP. These results demonstrate, for the first time, that the pineal hormone, melatonin, is capable of promoting osteoblast differentiation and mineralization of matrix in culture and suggest that this hormone may play an essential role in regulating bone growth.