Towards rational and evidence-based use of melatonin in prostate cancer prevention and treatment

Co-delivery of Siape1 and Melatonin by 125I-loaded PSMA-targeted Nanoparticles for the Treatment of Prostate Cancer

BACKGROUND

Both apurinic/apyrimidinic endodeoxyribonuclease 1 (APE1) inhibition and melatonin suppress prostate cancer (PCa) growth.

OBJECTIVE

This study evaluated the therapeutic efficiency of self-assembled and prostate-specific membrane antigen (PSMA)-targeted nanocarrier loading 125I radioactive particles and encapsulating siRNA targeting APE1 (siAPE1) and melatonin for PCa.

METHODS

The linear polyarginine R12 polypeptide was prepared using Fmoc-Arg-Pbf-OH. The PSMA-targeted polymer was synthesized by conjugating azide-modified R12 peptide to PSMA monoclonal antibody (mAb). Before experiments, the PSMA-R12 nanocarrier was installed with melatonin and siAPE1, which were subsequently labeled by 125I radioactive particles. In vitro biocompatibility and cytotoxicity of nanocomposites were examined in LNCaP cells and in vivo biodistribution and pharmacokinetics were determined using PCa tumor-bearing mice.

RESULTS

PSMA-R12 nanocarrier was ~120 nm in size and was increased to ~150 nm by melatonin encapsulation. PSMA-R12 nanoparticles had efficient loading capacities of siAPE1, melatonin, and 125I particles. The co-delivery of melatonin and siAPE1 by PSMA-R12-125I showed synergistic effects on suppressing LNCaP cell proliferation and Bcl-2 expression and promoting cell apoptosis and caspase-3 expression. Pharmacokinetics analysis showed that Mel@PSMA-R12-125I particles had high uptake activity in the liver, spleen, kidney, intestine, and tumor, and were accumulated in the tumor sites within the first 8 h p.i., but was rapidly cleared from all the tested organs at 24 h p.i. Administration of nanoparticles to PCa tumors in vivo showed that Mel@PSMA-R12- 125I/siAPE1 had high efficiency in suppressing PCa tumor growth.

CONCLUSION

The PSMA-targeted nanocarrier encapsulating siAPE1 and melatonin is a promising therapeutic strategy for PCa and can provide a theoretical basis for patent applications.

Exploring the Mechanical Perspective of a New Anti-Tumor Agent: Melatonin

Melatonin is a serotonin-derived pineal gland hormone with many biological functions like regulating the sleep-wake cycle, circadian rhythm, menstrual cycle, aging, immunity, and antioxidants. Melatonin synthesis and release are more pronounced during the night, whereas exposure to light decreases it. Evidence is mounting in favor of the therapeutic effects of melatonin in cancer prevention, treatment and delayed onset in various cancer subtypes. Melatonin exerts its anticancer effect through modification of its receptors such as melatonin 1 (MT1), melatonin 2 (MT2), and inhibition of cancer cell proliferation, epigenetic alterations (DNA methylation/demethylation, histone acetylation/deacetylation), metastasis, angiogenesis, altered cellular energetics, and immune evasion. Melatonin performs a significant function in immune modulation and enhances innate and cellular immunity. In addition, melatonin has a remarkable impact on epigenetic modulation of gene expression and alters the transcription of genes. As an adjuvant to cancer therapies, it acts by decreasing the side effects and boosting the therapeutic effects of chemotherapy. Since current treatments produce drug-induced unwanted toxicities and side effects, they require alternate therapies. A recent review article attempts to summarize the mechanistic perspective of melatonin in different cancer subtypes like skin cancer, breast cancer, hepatic cancer, renal cell cancer, non-small cell lung cancer (NSCLC), colon oral, neck, and head cancer. The various studies described in this review will give a firm basis for the future evolution of anticancer drugs.

Melatonin, an ubiquitous metabolic regulator: functions, mechanisms and effects on circadian disruption and degenerative diseases

The last four decades, we assist to an increasing scientific interest on melatonin, a circadian hormone, a metabolic regulator which influences not only plants' metabolism and their defense against pathogens but mostly the animals and humans' metabolic pathways, their response to circadian disruption, stress and burnout syndrome. In humans, as a hormonal regulator, produced in the pineal grand as well in mitochondria, melatonin is involved in different, complex intracellular signaling pathways, with antioxidant and immune stimulating effects, proving to act as a circadian synchronizer, as a preventive and therapeutic agent in many degenerative diseases, and especially in hormone-dependent cancers. Preclinical or clinical studies showed recently the mechanisms involved in regulating the cellular activity, its role in aging and circadian disturbances and impact on degenerative diseases. Melatonin proved to have an anti-inflammatory, antiapoptotic and powerful antioxidant effect by subtle mechanisms in mitochondrial metabolic pathways. This overview includes recent and relevant literature data related to the impact of endogenous and exogeneous melatonin on the prevention of cancer progression and treatment of various degenerative diseases. Metabolomics, an emerging new omics' technology, based on high performance liquid chromatography coupled with mass spectrometry is presented as an encouraging technique to fingerprint and realize a precise evaluation and monitoring of the turnover of melatonin and its metabolites in different pathological circumstances.

Insights on Melatonin as an Active Pharmacological Molecule in Cancer Prevention: What's New?

Along with playing an important role in circadian rhythm, melatonin is thought to play a significant role in preventing cells from damage, as well as in the inhibition of growth and in triggering apoptosis in malignant cells. Its relationship with circadian rhythms, energetic homeostasis, diet, and metabolism, is fundamental to achieve a better comprehension of how melatonin has been considered a chemopreventive molecule, though very few papers dealing with this issue. In this article, we tried to review the most recent evidence regarding the protective as well as the antitumoral mechanisms of melatonin, as related to diet and metabolic balance. From different studies, it was evident that an intracellular antioxidant defense mechanism is activated by upregulating an antioxidant gene battery in the presence of high-dose melatonin in malignant cells. Like other broad-spectrum antioxidant molecules, melatonin plays a vital role in killing tumor cells, preventing metastasis, and simultaneously keeping normal cells protected from oxidative stress and other types of tissue damage.

Ameliorative effects of melatonin against solid Ehrlich carcinoma progression in female mice

The current work estimated the antitumour efficacy of melatonin (MLT) on the growth of Ehrlich ascites carcinoma cells inoculated intramuscularly into the hind limbs of female BALB/c mice and to compare its effects with those of adriamycin (ADR). After solid tumours developed, the animals were divided into the three following groups: the tumour-bearing control, MLT-treated (20 mg/kg body weight) and ADR-treated (10 mg/kg body weight) groups. The results showed a significant reduction in the tumour masses of the treated animals in comparison with those of the control group. There were a significant decrease in the malondialdehyde level and a significant elevation of the glutathione concentration and the superoxide dismutase and catalase activities in the MLT and ADR groups. The current study indicated the increased expression levels of P53, caspase-3 and caspase-9 and the decreased expression levels of the rRNA and Bcl2. The MLT and ADR treatments resulted in histological changes, such as a marked degenerative area, the necrosis of neoplastic cells, the appearance of different forms of apoptotic cells and giant cells with condensed chromatin, and a deeply eosinophilic cytoplasm. The MLT and ADR treatments also significantly decreased the Ki-67 protein and vascular endothelial growth factor (VEGF) expression levels in the tumour masses. In conclusion, similar to ADR-treated tumour-bearing mice, MLT suppressed the growth and proliferation of tumour by inducing apoptosis and by inhibiting tumour vascularization. The current data recommend MLT as a safe natural chemotherapeutic adjuvant to overcome cancer progression after a clinical trial validates these results.

Melatonin and Docosahexaenoic Acid Decrease Proliferation of PNT1A Prostate Benign Cells via Modulation of Mitochondrial Bioenergetics and ROS Production

Prostate cancer development has been associated with changes in mitochondrial activity and reactive oxygen species (ROS) production. Melatonin (MLT) and docosahexaenoic acid (DHA) have properties to modulate both, but their protective role, mainly at early stages of prostate cancer, remains unclear. In this study, the effects of MLT and DHA, combined or not, on PNT1A cells with regard to mitochondria bioenergetics, ROS production, and proliferation-related pathways were examined. Based on dose response and lipid accumulation assays, DHA at 100 μM and MLT at 1 μM for 48 h were chosen. DHA doubled and MLT reduced (40%) superoxide anion production, but coincubation (DM) did not normalize to control. Hydrogen peroxide production decreased after MLT incubation only (p < 0.01). These alterations affected the area and perimeter of mitochondria, since DHA increased whereas MLT decreased, but such hormone has no effect on coincubation. DHA isolated did not change the oxidative phosphorylation rate (OXPHOS), but decreased (p < 0.001) the mitochondrial bioenergetic reserve capacity (MBRC) which is closely related to cell responsiveness to stress conditions. MLT, regardless of DHA, ameliorated OXPHOS and recovered MBRC after coincubation. All incubations decreased AKT phosphorylation; however, only MLT alone inhibited p-mTOR. MLT increased p-ERK1/2 and, when combined to DHA, increased GSTP1 expression (p < 0.01). DHA did not change the testosterone levels in the medium, whereas MLT alone or coincubated decreased by about 20%; however, any incubation affected AR expression. Moreover, incubation with luzindole revealed that MLT effects were MTR1/2-independent. In conclusion, DHA increased ROS production and impaired mitochondrial function which was probably related to AKT inactivation; MLT improved OXPHOS and decreased ROS which was related to AKT/mTOR dephosphorylation, and when coincubated, the antiproliferative action was related to mitochondrial bioenergetic modulation associated to AKT and ERK1/2 regulation. Together, these findings point to the potential application of DHA and MLT towards the prevention of proliferative prostate diseases.

Melatonin Can Strengthen the Effect of Retinoic Acid in HL-60 Cells

Melatonin is produced by the pineal gland. It can be regarded as an anticancer agent and used for combined therapy, owing to its oncostatic, antioxidant, and immunoregulatory activities. Retinoic acid is widely used for the treatment of acute promyelocytic leukemia; however, it has adverse effects on the human organism. We investigated the effect of melatonin and reduced concentrations of retinoic acid on the activation of proliferation in acute promyelocytic leukemiaon a cell model HL-60. The combined effect of these compounds leads to a reduction in the number of cells by 70% and the index of mitotic activity by 64%. Combined treatment with melatonin and retinoic acid decreased the expression of the Bcl-2. The mitochondrial isoform VDAC1 can be a target in the treatment of different tumors. The combined effect of and retinoic acid at a low concentration (10 nM) decreased VDAC1 expression. Melatonin in combination with retinoic acid produced a similar effect on the expression of the translocator protein. The coprecipitation of VDAC with 2′,3′-cyclonucleotide-3′-phosphodiesterase implies a possible role of its in cancer development. The combined effect of retinoic acid and melatonin decreased the activity of the electron transport chain complexes. The changes in the activation of proliferation in HL-60 cells, the mitotic index, and Bcl-2 expression under combined effect of retinoic acid (10 nM) with melatonin (1 mM) are similar to changes that are induced by 1 μM retinoic acid. Our results suggest that MEL is able to improve the action the other chemotherapeutic agent.

Melatonin Synergizes the Chemotherapeutic Effect of Cisplatin in Ovarian Cancer Cells Independently of MT1 Melatonin Receptors

BACKGROUND/AIM

Melatonin (MLT), through the interaction with membrane melatonin receptors MT1, can improve the effectiveness of cytostatic agents, including cisplatin (CP). The aim of this study was to examine the synergistic effect of MLT and CP in three cell lines: IOSE 364, SK-OV-3 and OVCAR-3, as well as to assess the role of MT1 receptors in this mechanism.

MATERIALS AND METHODS

Using the SRB assay we investigated the effect of different concentrations of CP and MLT on cell viability. Tests, using luzindole - MT1 inhibitor, allowed us to assess the potential involvement of MT1 in the mechanism of MLT action.

RESULTS

MLT at certain concentrations demonstrated a synergistic effect in combination with CP. The addition of luzindole did not affect the action of MLT in combination with CP.

CONCLUSION

In summary, the synergistic effect of MLT with CP seems to be independent of membrane MT1 receptors.

Melatonin and health: an umbrella review of health outcomes and biological mechanisms of action

BACKGROUND

Our aims were to evaluate critically the evidence from systematic reviews as well as narrative reviews of the effects of melatonin (MLT) on health and to identify the potential mechanisms of action involved.

METHODS

An umbrella review of the evidence across systematic reviews and narrative reviews of endogenous and exogenous (supplementation) MLT was undertaken. The Oxman checklist for assessing the methodological quality of the included systematic reviews was utilised. The following databases were searched: MEDLINE, EMBASE, Web of Science, CENTRAL, PsycINFO and CINAHL. In addition, reference lists were screened. We included reviews of the effects of MLT on any type of health-related outcome measure.

RESULTS

Altogether, 195 reviews met the inclusion criteria. Most were of low methodological quality (mean -4.5, standard deviation 6.7). Of those, 164 did not pool the data and were synthesised narratively (qualitatively) whereas the remaining 31 used meta-analytic techniques and were synthesised quantitatively. Seven meta-analyses were significant with P values less than 0.001 under the random-effects model. These pertained to sleep latency, pre-operative anxiety, prevention of agitation and risk of breast cancer.

CONCLUSIONS

There is an abundance of reviews evaluating the effects of exogenous and endogenous MLT on health. In general, MLT has been shown to be associated with a wide variety of health outcomes in clinically and methodologically heterogeneous populations. Many reviews stressed the need for more high-quality randomised clinical trials to reduce the existing uncertainties.

Melatonin and Hippo Pathway: Is There Existing Cross-Talk?

Melatonin is an indolic hormone that regulates a plethora of functions ranging from the regulation of circadian rhythms and antioxidant properties to the induction and maintenance of tumor suppressor pathways. It binds to specific receptors as well as to some cytosolic proteins, leading to several cellular signaling cascades. Recently, the involvement of melatonin in cancer insurgence and progression has clearly been demonstrated. In this review, we will first describe the structure and functions of melatonin and its receptors, and then discuss both molecular and epidemiological evidence on melatonin anticancer effects. Finally, we will shed light on potential cross-talk between melatonin signaling and the Hippo signaling pathway, along with the possible implications for cancer therapy.

Melatonin, a Full Service Anti-Cancer Agent: Inhibition of Initiation, Progression and Metastasis

There is highly credible evidence that melatonin mitigates cancer at the initiation, progression and metastasis phases. In many cases, the molecular mechanisms underpinning these inhibitory actions have been proposed. What is rather perplexing, however, is the large number of processes by which melatonin reportedly restrains cancer development and growth. These diverse actions suggest that what is being observed are merely epiphenomena of an underlying more fundamental action of melatonin that remains to be disclosed. Some of the arresting actions of melatonin on cancer are clearly membrane receptor-mediated while others are membrane receptor-independent and involve direct intracellular actions of this ubiquitously-distributed molecule. While the emphasis of melatonin/cancer research has been on the role of the indoleamine in restraining breast cancer, this is changing quickly with many cancer types having been shown to be susceptible to inhibition by melatonin. There are several facets of this research which could have immediate applications at the clinical level. Many studies have shown that melatonin's co-administration improves the sensitivity of cancers to inhibition by conventional drugs. Even more important are the findings that melatonin renders cancers previously totally resistant to treatment sensitive to these same therapies. Melatonin also inhibits molecular processes associated with metastasis by limiting the entrance of cancer cells into the vascular system and preventing them from establishing secondary growths at distant sites. This is of particular importance since cancer metastasis often significantly contributes to death of the patient. Another area that deserves additional consideration is related to the capacity of melatonin in reducing the toxic consequences of anti-cancer drugs while increasing their efficacy. Although this information has been available for more than a decade, it has not been adequately exploited at the clinical level. Even if the only beneficial actions of melatonin in cancer patients are its ability to attenuate acute and long-term drug toxicity, melatonin should be used to improve the physical wellbeing of the patients. The experimental findings, however, suggest that the advantages of using melatonin as a co-treatment with conventional cancer therapies would far exceed improvements in the wellbeing of the patients.

Melatonin in Edible and Non-Edible Plants

The concept of melatonin has become more important recently both in plants and in human who utilize plants for nutritional and health purposes. Melatonin, synthesized from L-tryptophan by enzyms, protects plants against difficult conditions. People have consumed these plants for their antioxidant, immunomodulator, antiinflammatory and anticancer effects. In parts of edible and non-edible plants, levels of melatonin are determined by cyclodextrin-modified micellar electrokinetic chromatography, enzyme-linked immuno sorbent assay, radioimmunoassay, high-performance liquid chromatography, liquid chromatography with electrochemical detection, liquid chromatography with fluorimetric detection, liquid chromatography-mass spectrometry, and liquid chromatography-ultraviolet spectrophotometry. In this review, biosynthesis of melatonin in both animal and plants, function of melatonin in plant kingdom, especially in medicinal/edible and nonedible plants, and detection of phytomelatonin content in those plants are presented.

Antitumour activity of melatonin in a mouse model of human prostate cancer: relationship with hypoxia signalling

Melatonin is known to exert antitumour activity in several types of human cancers, but the underlying mechanisms as well as the efficacy of different doses of melatonin are not well defined. Here, we test the hypothesis whether melatonin in the nanomolar range is effective in exerting antitumour activity in vivo and examine the correlation with the hypoxia signalling mechanism, which may be a major molecular mechanism by which melatonin antagonizes cancer. To test this hypothesis, LNCaP human prostate cancer cells were xenografted into seven-wk-old Foxn1nu/nu male mice that were treated with melatonin (18 i.p. injections of 1 mg/kg in 41 days). Saline-treated mice served as control. We found that the melatonin levels in plasma and xenografted tissue were 4× and 60× higher, respectively, than in control samples. Melatonin tended to restore the redox imbalance by increasing expression of Nrf2. As part of the phenotypic response to these perturbations, xenograft microvessel density was less in melatonin-treated animals, indicative of lower angiogenesis, and the xenograft growth rate was slower (P < 0.0001). These changes were accompanied by a reduced expression of Ki67, elevated expression of HIF-1α and increased phosphorylation of Akt in melatonin than saline-treated mice. We conclude that the beneficial effect of melatonin in reducing cancer growth in vivo was evident at melatonin plasma levels as low as 4 nm and was associated with decreased angiogenesis. Higher HIF-1α expression in xenograft tissue indicates that the antitumour effect cannot be due to a postulated antihypoxic effect, but may stem from lower angiogenesis potential.

Expression and putative functions of melatonin receptors in malignant cells and tissues

Melatonin, the popular hormone of the darkness, is primarily synthesized in the pineal gland, and acts classically through the G-protein coupled plasma membrane melatonin receptors MT1 and MT2, respectively. Although some of the receptor mediated functions of melatonin, especially those on the (central) circadian system, have been more or less clarified, the functional meaning of MT-receptors in various peripheral organs are still not sufficiently investigated yet. There is, however, accumulating evidence for oncostatic effects of melatonin with both, antioxidative and MT-receptor mediated mechanisms possibly playing a role. This review briefly summarizes the physiology of melatonin and MT-receptors, and discusses the expression and function of MT-receptors in human cancer cells and tissues.

Peripheral reproductive organ health and melatonin: ready for prime time

Melatonin has a wide variety of beneficial actions at the level of the gonads and their adnexa. Some actions are mediated via its classic membrane melatonin receptors while others seem to be receptor-independent. This review summarizes many of the published reports which confirm that melatonin, which is produced in the ovary, aids in advancing follicular maturation and preserving the integrity of the ovum prior to and at the time of ovulation. Likewise, when ova are collected for in vitro fertilization-embryo transfer, treating them with melatonin improves implantation and pregnancy rates. Melatonin synthesis as well as its receptors have also been identified in the placenta. In this organ, melatonin seems to be of particular importance for the maintenance of the optimal turnover of cells in the villous trophoblast via its ability to regulate apoptosis. For male gametes, melatonin has also proven useful in protecting them from oxidative damage and preserving their viability. Incubation of ejaculated animal sperm improves their motility and prolongs their viability. For human sperm as well, melatonin is also a valuable agent for protecting them from free radical damage. In general, the direct actions of melatonin on the gonads and adnexa of mammals indicate it is an important agent for maintaining optimal reproductive physiology.

Melatonin MT1 receptor-induced transcriptional up-regulation of p27(Kip1) in prostate cancer antiproliferation is mediated via inhibition of constitutively active nuclear factor kappa B (NF-κB): potential implications on prostate cancer chemoprevention and therapy

Our laboratory has recently demonstrated a melatonin MT1 receptor-mediated antiproliferative signaling mechanism in androgen receptor (AR)-positive prostate epithelial cells which involves up-regulation of p27(Kip1) through dual activation of Gα(s)/protein kinase A (PKA) and Gα(q)/protein kinase C (PKC) in parallel, and down-regulation of activated AR signaling via PKC stimulation. The aim of the present investigation was to identify the transcription factor that mediates melatonin's up-regulatory effect on p27(Kip1) in LNCaP and 22Rv1 prostate cancer cells. Deletion mapping and reporter assays of the p27(Kip1) promoter revealed that the putative melatonin-responsive transcription factor binds to a 116 base-pair region of the promoter sequence, which contains a potential nuclear factor kappa B (NF-κB) binding site. When the NF-κB binding site was abolished by site-directed mutagenesis, the stimulatory effect of melatonin on p27(Kip1) promoter activity was mitigated. Notably, melatonin inhibited the DNA binding of activated NF-κB via MT1 receptor-induced PKA and PKC stimulation. Furthermore, melatonin's up-regulatory effect on p27(Kip1) transcription and consequent cell antiproliferation were abrogated by NF-κB activator but mimicked by NF-κB inhibitor. The results indicate that inhibition of constitutively active NF-κB via melatonin MT1 receptor-induced dual activation of (Gα(s)) PKA and (Gα(q)) PKC can de-repress the p27(Kip1) promoter leading to transcriptional up-regulation of p27(Kip1). MT1 receptor-mediated inhibition of activated NF-κB signaling provides a novel mechanism supporting the use of melatonin in prostate cancer chemoprevention and therapy.

Melatonin prevents human pancreatic carcinoma cell PANC-1-induced human umbilical vein endothelial cell proliferation and migration by inhibiting vascular endothelial growth factor expression

Melatonin is an important natural oncostatic agent, and our previous studies have found its inhibitory action on tumor angiogenesis, but the mechanism remains unclear. It is well known that vascular endothelial growth factor (VEGF) plays key roles in tumor angiogenesis and has become an important target for antitumor therapy. Pancreatic cancer is a representative of the most highly vascularized and angiogenic solid tumors, which responds poorly to chemotherapy and radiation. Thus, seeking new treatment strategies targeting which have anti-angiogenic capability is urgent in clinical practice. In this study, a co-culture system between human umbilical vein endothelial cells (HUVECs) and pancreatic carcinoma cells (PANC-1) was used to investigate the direct effect of melatonin on the tumor angiogenesis and its possible action on VEGF expression. We found HUVECs exhibited an increased cell proliferation and cell migration when co-cultured with PANC-1 cells, but the process was prevented when melatonin added to the incubation medium. Melatonin at concentrations of 1 μm and 1 mm inhibited the cell proliferation and migration of HUVECs and also decreased both the VEGF protein secreted to the cultured medium and the protein produced by the PANC-1 cells. In addition, the VEGF mRNA expression was also down-regulated by melatonin. Taken together, our present study shows that melatonin at pharmacological concentrations inhibited the elevated cell proliferation and cell migration of HUVECs stimulated by co-culturing them with PANC-1 cells; this was associated with a suppression of VEGF expression in PANC-1 cells.

Functional interplay between melatonin receptor-mediated antiproliferative signaling and androgen receptor signaling in human prostate epithelial cells: potential implications for therapeutic strategies against prostate cancer

Recently, a novel melatonin MT(1) receptor-mediated antiproliferative signaling mechanism involving transcriptional up-regulation of p27(Kip1) due to paralleled stimulation of protein kinase A (PKA) and protein kinase C (PKC), as a result of respective dual activation of upstream Gα(s) and Gα(q) , has been reported in 22Rv1 and RWPE-1 human prostate epithelial cells. Here, we demonstrate that melatonin inhibits the proliferation of LNCaP and VCaP prostate cancer cells via activation of the same MT(1) receptor-mediated antiproliferative signaling pathway. Knockdown of the expression of wild-type androgen receptor (AR) and/or structural/functional AR variants in LNCaP, VCaP, 22Rv1, and RWPE-1 cells resulted in abrogation of melatonin receptor-mediated antiproliferation, indicating that the antiproliferative signaling pathway MT(1) /(Gα(s) ) PKA + (Gα(q) ) PKC/p27(Kip1) activated by melatonin in human prostate epithelial cells is AR dependent. Furthermore, melatonin was shown to decrease androgen/AR-mediated transactivation of the prostate-specific antigen promoter in the prostate epithelial cell lines. Together, our data indicate the presence of reciprocal functional interactions between MT(1) receptor and AR signaling in malignant and nontumorigenic prostate epithelial cells. Notably, the dual actions of the MT(1) receptor-mediated antiproliferative signaling, leading to down-regulation of activated AR signaling and up-regulation of p27(Kip1) , constitute the mechanistic basis for the potential use of melatonin in chemoprevention of prostate cancer, as well as in a novel therapeutic strategy, comprising a combination of melatonin repletion and androgen depletion, for the treatment of advanced or relapsed disease.

Signal transduction of receptor-mediated antiproliferative action of melatonin on human prostate epithelial cells involves dual activation of Gα(s) and Gα(q) proteins

Melatonin has been shown to inhibit the proliferation of malignant and transformed human prostate epithelial cells by transcriptional up-regulation of p27(Kip1) expression via MTNR1A receptor-mediated activation of protein kinase A (PKA) and protein kinase C (PKC) in parallel. Given that melatonin MTNR1A receptor is a G protein-coupled receptor, this study was conducted to identify the specific G proteins that mediate the antiproliferative action of melatonin on human prostate epithelial cells. In 22Rv1 and RWPE-1 cells, knockdown of either Gα(s) or Gα(q) , but not Gα(i2) expression by RNA interference, abrogated the effects of melatonin on p27(Kip1) and cell proliferation. Conversely, cellular overexpression of activated mutants of Gα(s) and Gα(q) in 22Rv1 and RWPE-1 cells mimicked the effects of melatonin on prostate epithelial cell antiproliferation by increasing p27(Kip1) expression through downstream activation of PKA and PKC in parallel. Moreover, melatonin or 2-iodomelatonin induced elevation of adenosine-3',5'-cyclic monophosphate (cAMP) in 22Rv1 and RWPE-1 cells. The effects of 2-iodomelatonin on cAMP were blocked by the nonselective MTNR1A/MTNR1B receptor antagonist luzindole but were not affected by the selective MTNR1B receptor antagonist 4-phenyl-2-propionamidotetraline (4-P-PDOT). Furthermore, knockdown of Gα(s) mitigated the stimulatory effects of 2-iodomelatonin on cAMP. Collectively, the data demonstrated, for the first time, functional coupling of MTNR1A receptor to Gα(s) in cancerous or transformed human cells expressing endogenous melatonin receptors. Our results also showed that dual activation of Gα(s) and Gα(q) proteins is involved in the signal transduction of MTNR1A receptor-mediated antiproliferative action of melatonin on human prostate epithelial cells.

New hypotheses for the health-protective mechanisms of whole-grain cereals: what is beyond fibre?

Epidemiological studies have clearly shown that whole-grain cereals can protect against obesity, diabetes, CVD and cancers. The specific effects of food structure (increased satiety, reduced transit time and glycaemic response), fibre (improved faecal bulking and satiety, viscosity and SCFA production, and/or reduced glycaemic response) and Mg (better glycaemic homeostasis through increased insulin secretion), together with the antioxidant and anti-carcinogenic properties of numerous bioactive compounds, especially those in the bran and germ (minerals, trace elements, vitamins, carotenoids, polyphenols and alkylresorcinols), are today well-recognised mechanisms in this protection. Recent findings, the exhaustive listing of bioactive compounds found in whole-grain wheat, their content in whole-grain, bran and germ fractions and their estimated bioavailability, have led to new hypotheses. The involvement of polyphenols in cell signalling and gene regulation, and of sulfur compounds, lignin and phytic acid should be considered in antioxidant protection. Whole-grain wheat is also a rich source of methyl donors and lipotropes (methionine, betaine, choline, inositol and folates) that may be involved in cardiovascular and/or hepatic protection, lipid metabolism and DNA methylation. Potential protective effects of bound phenolic acids within the colon, of the B-complex vitamins on the nervous system and mental health, of oligosaccharides as prebiotics, of compounds associated with skeleton health, and of other compounds such as alpha-linolenic acid, policosanol, melatonin, phytosterols and para-aminobenzoic acid also deserve to be studied in more depth. Finally, benefits of nutrigenomics to study complex physiological effects of the 'whole-grain package', and the most promising ways for improving the nutritional quality of cereal products are discussed.

Light-mediated perturbations of circadian timing and cancer risk: a mechanistic analysis

In industrialized countries, certain types of cancer, most notably, breast and prostate, are more frequent than in poorly developed nations. This high cancer frequency is not explained by any of the conventional causes. Within the past decade, numerous reports have appeared that link light at night with an elevated cancer risk. The three major consequences of light at night are sleep deprivation, chronodisruption, and melatonin suppression. Each of these individually or in combination may contribute to the reported rise in certain types of cancer. In this article, the potential mechanisms underlying the basis of the elevated cancer risk are briefly discussed. Finally, if cancer is a consequence of excessive nighttime light, it is likely that other diseases/conditions may also be exaggerated by the widespread use of light after darkness onset.

Melatonin: a multitasking molecule

Melatonin (N-acetyl-5-methoxytryptamine) has revealed itself as an ubiquitously distributed and functionally diverse molecule. The mechanisms that control its synthesis within the pineal gland have been well characterized and the retinal and biological clock processes that modulate the circadian production of melatonin in the pineal gland are rapidly being unravelled. A feature that characterizes melatonin is the variety of mechanisms it employs to modulate the physiology and molecular biology of cells. While many of these actions are mediated by well-characterized, G-protein coupled melatonin receptors in cellular membranes, other actions of the indole seem to involve its interaction with orphan nuclear receptors and with molecules, for example calmodulin, in the cytosol. Additionally, by virtue of its ability to detoxify free radicals and related oxygen derivatives, melatonin influences the molecular physiology of cells via receptor-independent means. These uncommonly complex processes often make it difficult to determine specifically how melatonin functions to exert its obvious actions. What is apparent, however, is that the actions of melatonin contribute to improved cellular and organismal physiology. In view of this and its virtual absence of toxicity, melatonin may well find applications in both human and veterinary medicine.

Malaria: therapeutic implications of melatonin

Malaria, which infects more than 300 million people annually, is a serious disease. Epidemiological surveys indicate that of those who are affected, malaria will claim the lives of more than one million individuals, mostly children. There is evidence that the synchronous maturation of Plasmodium falciparum, the parasite that causes a severe form of malaria in humans and Plasmodium chabaudi, responsible for rodent malaria, could be linked to circadian changes in melatonin concentration. In vitro melatonin stimulates the growth and development of P. falciparum through the activation of specific melatonin receptors coupled to phospholipase-C activation and the concomitant increase of intracellular Ca2+. The Ca2+ signaling pathway is important to stimulate parasite transition from the trophozoite to the schizont stage, the final stage of intraerythrocytic cycle, thus promoting the rise of parasitemia. Either pinealectomy or the administration of the melatonin receptor blocking agent luzindole desynchronizes the parasitic cell cycle. Therefore, the use of melatonin antagonists could be a novel therapeutic approach for controlling the disease. On the other hand, the complexity of melatonin's action in malaria is underscored by the demonstration that treatment with high doses of melatonin is actually beneficial for inhibiting apoptosis and liver damage resulting from the oxidative stress in malaria. The possibility that the coordinated administration of melatonin antagonists (to impair the melatonin signal that synchronizes P. falciparum) and of melatonin in doses high enough to decrease oxidative damage could be a novel approach in malaria treatment is discussed.

The changing biological roles of melatonin during evolution: from an antioxidant to signals of darkness, sexual selection and fitness

Melatonin is a molecule present in a multitude of taxa and may be ubiquitous in organisms. It has been found in bacteria, unicellular eukaryotes, macroalgae, fungi, plants and animals. A primary biological function of melatonin in primitive unicellular organisms is in antioxidant defence to protect against toxic free radical damage. During evolution, melatonin has been adopted by multicellular organisms to perform many other biological functions. These functions likely include the chemical expression of darkness in vertebrates, environmental tolerance in fungi and plants, sexual signaling in birds and fish, seasonal reproductive regulation in photoperiodic mammals, and immunomodulation and anti-inflammatory activity in all vertebrates tested. Moreover, its waning production during aging may indicate senescence in terms of a bio-clock in many organisms. Conversely, high melatonin levels can serve as a signal of vitality and health. The multiple biological functions of melatonin can partially be attributed to its unconventional metabolism which is comprised of multi-enzymatic, pseudo-enzymatic and non-enzymatic pathways. As a result, several bioactive metabolites of melatonin are formed during its metabolism and some of the presumed biological functions of melatonin reported to date may, in fact, be mediated by these metabolites. The changing biological roles of melatonin seem to have evolved from its primary function as an antioxidant.

Reducing oxidative/nitrosative stress: a newly-discovered genre for melatonin

The discovery of melatonin and its derivatives as antioxidants has stimulated a very large number of studies which have, virtually uniformly, documented the ability of these molecules to detoxify harmful reactants and reduce molecular damage. These observations have clear clinical implications given that numerous age-related diseases in humans have an important free radical component. Moreover, a major theory to explain the processes of aging invokes radicals and their derivatives as causative agents. These conditions, coupled with the loss of melatonin as organisms age, suggest that some diseases and some aspects of aging may be aggravated by the diminished melatonin levels in advanced age. Another corollary of this is that the administration of melatonin, which has an uncommonly low toxicity profile, could theoretically defer the progression of some diseases and possibly forestall signs of aging. Certainly, research in the next decade will help to define the role of melatonin in age-related diseases and in determining successful aging. While increasing life span will not necessarily be a goal of these investigative efforts, improving health and the quality of life in the aged should be an aim of this research.

Uptake of resveratrol and role of resveratrol-targeting protein, quinone reductase 2, in normally cultured human prostate cells

Resveratrol is a dietary polyphenol espoused to have chemopreventive activity against a variety of human cancer types. We first reported that resveratrol significantly decreases the proliferation of both androgen-dependent and hormone-refractory prostate cancer cells. However, the effects of resveratrol in normal prostate epithelial and stromal cells, particularly with regard to its uptake, subcellular distribution and intracellular targets, have not been investigated. To advance the knowledge on accessibility and cellular disposition of resveratrol in prostate cells, [(3)H] resveratrol, fractionation of cell extracts into subcellular compartments, Western blot analysis, resveratrol affinity column chromatography and flow cytometry were used to study the uptake and intracellular distribution of resveratrol in normally cultured prostate stromal (PrSCs) and epithelial cells (PrECs). Pretreatment of both PrSCs and PrECs for 2 days with resveratrol modulated its uptake and selectively increased its distribution to the membrane and organelle compartments. Resveratrol affinity column chromatography studies showed differential expression of a previously identified resveratrol-targeting protein, quinone reductase 2 (QR2), in PrSCs and PrECs. Flow cytometric analysis comparing resveratrol-treated and untreated PrSCs showed a large decrease in G(1)-phase and a concomitant increase in S and G(2)/M-phases of the cell cycle. These results suggest that resveratrol suppresses PrSC proliferation by affecting cell cycle phase distribution, which may involve the participation by QR2.

Posttranscriptional regulation of pineal melatonin synthesis in Octodon degus

Small laboratory animals have provided significant information about melatonin regulation, yet most of these organisms are nocturnal and regulate melatonin synthesis by mechanisms that diverge from those of humans. For example, in all rodents examined, melatonin secretion occurs with a time lag of several hours after the onset of darkness; in addition, arylalkylamine N-acetyltransferase (AANAT), the key enzyme in melatonin synthesis, displays dynamic transcriptional activation specifically at night in all rodents studied to date. In ungulates and primates including humans, on the other hand, melatonin secretion occurs immediately during the early night and is controlled by circadian posttranscriptional regulation of AANAT. We hypothesize that the diurnal Octodon degus (an Hystricognath rodent) could serve as an improved experimental model for studies of human melatonin regulation. To test this, we monitored melatonin production in degus using pineal microdialysis and characterized the regulation of melatonin synthesis by analyzing degu Aanat. Degu pineal melatonin rises with little latency at night, as in ungulates and primates. In addition, degu Aanat mRNA expression displays no detectable diurnal variation, suggesting that, like ungulates and primates, melatonin in this species is regulated by a posttranscriptional mechanism. Compared with AANAT from all rodents examined to date, the predicted amino acid sequence of degu AANAT is phylogenetically more closely related to ungulate and primate AANAT. These data suggest that Octodon degus may provide an ideal model system for laboratory investigation of mechanisms of melatonin synthesis and secretion in diurnal mammals.

Light Hygiene: Time to make preventive use of insights--old and new--into the nexus of the drug light, melatonin, clocks, chronodisruption and public health

Light is, clearly, a key to life on Earth and light, equally clearly, determines biological rhythmicity in organisms. Light does the latter by setting internal or endogenous clocks which allow a multitude of species, including man, to adjust their lives to changing external or environmental conditions. Critical changes over time occur from day to night and throughout the year. In this paper, we sum up how visible light provides electromagnetic information about environmental "time" via the ocular interface of newly discovered photoreceptive cells to a master clock in our brain, viz the suprachiasmatic nuclei [SCN], and how the SCN translate this input, with melatonin as a key biologic intermediary, into endogenous or biological time. We summarize experimental and epidemiological evidence suggesting how chronodisruption, a relevant disturbance of the temporal organization or order of physiology, endocrinology, metabolism and behaviour, is probably detrimental for human beings. On the basis of our synthesis, and in line with suggestions by other researchers voiced decades ago, light must, functionally, be considered as a drug equivalent. In this vein, the very timing, quality (wavelength), quantity (dose) and side effects, including chronodisruption, of light exposures can be critically important for health and disease in man. As a promising means to foster public health, we advocate an appropriate balance of exposures to the key Zeitgeber light in terms of "light hygiene", implying strong and appropriate rather than weak and confusing temporal information. This focus on "light hygiene", and thus on the key Zeitgeber light, does not mean to ignore that there are multiple entrainment pathways for our circadian clocks. Indeed, when dealing with light, chronodisruption and a multitude of adverse health effects, we ultimately need to consider Zeitgeber cues, and their possible interplay, beyond light alone. Confusions of the temporal programmes in humans can also stem from physical and social activities, stress and facets of food intake. And yet, since light possesses a rather unique and exclusive Zeitgeber role and in view of its ubiquitous nature, a specific, preventative focus on "light hygiene", as a contribution to a general "Zeitgeber hygiene", is warranted.

Melatonin down-regulates HIF-1 alpha expression through inhibition of protein translation in prostate cancer cells

Melatonin, the main secretory product of the pineal gland, has been shown to exert an oncostatic activity in cancer cells. Recently, several studies have shown that melatonin has antiangiogenic properties. However, the mechanism by which melatonin exerts antiangiogenenic effects is not understood. Hypoxia inducible factor (HIF)-1 is a transcription factor which mediates adaptive response to changes in tissue oxygenation. HIF-1 is a heterodimer formed by the association of a constitutively expressed HIF-1 beta subunit and a HIF-1 alpha subunit, the expression of which is highly regulated. In this study, pharmacologic concentrations of melatonin was found to inhibit expression of HIF-1 alpha protein under both normoxic and hypoxic conditions in DU145, PC-3, and LNCaP prostate cancer cells without affecting HIF-1 alpha mRNA levels. Consistent with the reduction in HIF-1 alpha protein levels, melatonin inhibited HIF-1 transcriptional activity and the release of vascular endothelial growth factor. We found that the suppression of HIF-1 alpha expression by melatonin correlated with dephosphorylation of p70S6K and its direct target RPS6, a pathway known to regulate HIF-1 alpha expression at the translational level. Metabolic labeling assays indicated that melatonin inhibits de novo synthesis of HIF-1 alpha protein. Taken together, these results suggest that the pharmacologic concentration of melatonin inhibits HIF-1 alpha expression through the suppression of protein translation in prostate cancer cells.

Melatonin enhances cartilage matrix synthesis by porcine articular chondrocytes

To develop a minimally invasive preventive measure for early osteoarthritis, the effect of melatonin on cartilage matrix synthesis of articular chondrocytes was evaluated in vitro in a pellet culture system. The chondrogenic markers were assessed using histology, TaqMan polymerase chain reaction, and western blot. Our results show that melatonin treatment yielded chondrocyte-pellets with a higher expression of chondrogenic markers consisting of collagen II, Sox 9, and aggrecan at both the mRNA and protein levels. A hypertrophic marker, collagen X, remained low. Moreover, up-regulation of internal transforming growth factor beta1 (TGF-beta1) expression was observed in the melatonin-treated cells. Our data indicate, for the first time, that the administration of melatonin enhances cartilage matrix synthesis of articular chondrocytes in a serum-containing pellet culture system, likely through the TGF-beta signal pathway. Melatonin may prove to be a highly valuable addition to current therapeutic models for degenerative cartilage repair.

Evidence for NQO2-mediated reduction of the carcinogenic estrogen ortho-quinones

The physiological function of NAD(P)H:quinone oxidoreductase (NQO1, DT-diaphorase) is to detoxify potentially reactive quinones by direct transfer of two electrons. A similar detoxification role has not been established for its homologue NRH:quinone oxidoreductase 2 (NQO2). Estrogen quinones, including estradiol(E(2))-3,4-Q, generated by estrogen metabolism, are thought to be responsible for estrogen-initiated carcinogenesis. In this investigation, we have shown for the first time that NQO2 catalyzes the reduction of electrophilic estrogen quinones and thereby may act as a detoxification enzyme. ESI and MALDI mass spectrometric binding studies involving E(2)-3,4-Q with NQO2 clearly support the formation of an enzyme-substrate physical complex. The problem of spontaneous reduction of substrate by cofactor, benzyldihydronicotinamide riboside (BNAH), was successfully overcome by taking advantage of the ping-pong mechanism of NQO2 catalysis. The involvement of the enzyme in the reduction of E(2)-3,4-Q was further supported by addition of the inhibitor quercetin to the assay mixture. NQO2 is a newly discovered binding site (MT3) of melatonin. However, addition of melatonin to the assay mixture did not affect the catalytic activity of NQO2. Preliminary kinetic studies show that NQO2 is faster in reducing estrogen quinones than its homologue NQO1. Both UV and liquid chromatography-tandem mass spectrometry assays unequivocally corroborate the reduction of estrogen ortho-quinones by NQO2, indicating that it could be a novel target for prevention of breast cancer initiation.

Melatonin protects from hepatic reperfusion injury through inhibition of IKK and JNK pathways and modification of cell proliferation

Reactive oxygen species (ROS) are involved in pathophysiology of ischemia/reperfusion injury. Melatonin is a potent scavenger of ROS. Thus, this study was designed to elucidate its effects in a combined hepatic warm ischemia and resection model. The right lateral and caudate lobes (32% of liver volume) of Sprague-Dawley rats underwent warm ischemia for 30 min followed by reperfusion and subsequent resection of the nonischemic liver tissue. Some rats were gavaged with 50 mg/kg melatonin 2 hr before the onset of experiments. Controls received the same volume of microcrystalline cellulose. Survival, transaminases, histology, flow cytometry, inducible nitric oxide synthase (iNOS) expression, and activation of signal transduction pathways [c-Jun N-terminal kinase (JNK), cJUN, IkappaB kinase alpha (IKKalpha), proliferating cell nuclear antigen (PCNA), and Ki67] were assessed for hepatic injury, oxidative stress, and cell proliferation. Melatonin significantly improved animal survival and decreased transaminase levels, the indices for necrosis, liver damage, leukocyte infiltration, and iNOS expression. In parallel, the expression of IKKalpha, JNK1, and cJUN decreased by 35-50% after melatonin (P < 0.05). At the same time, melatonin reduced the expression of both PCNA and Ki67 in liver (P < 0.05). Melatonin is hepatoprotective most likely via mechanisms including inhibition of IKK and JNK pathways and regulation of cell proliferation.

Melatonin induces cell cycle arrest and apoptosis in hepatocarcinoma HepG2 cell line

Melatonin reduces proliferation in many different cancer cell lines. However, studies on the oncostatic effects of melatonin in the treatment of hepatocarcinoma are limited. In this study, we examined the effect of melatonin administration on HepG2 human hepatocarcinoma cells, analyzing cell cycle arrest, apoptosis and mitogen-activated protein kinase (MAPK) signalling pathways. Melatonin was dissolved in the cell culture media in 0.2% dimethyl sulfoxide and administered at different concentrations for 2, 4, 6, 8 and 10 days. Melatonin at concentrations 1000-10,000 microM caused a dose- and time-dependent reduction in cell number. Furthermore, melatonin treatment induced apoptosis with increased caspase-3 activity and poly(ADP-ribose) polymerase proteolysis. Proapoptotic effects of melatonin were related to cytosolic cytochrome c release, upregulation of Bax and induction of caspase-9 activity. Melatonin treatment also resulted in increased caspase-8 activity, although no significant change was observed in Fas-L expression. In addition, JNK 1,-2 and -3 and p38, members of the MAPK family, were upregulated by melatonin treatment. Growth inhibition by melatonin altered the percentage or cells in G0-G1 and G2/M phases indicating cell cycle arrest in the G2/M phase. The reduced cell proliferation and alterations of cell cycle were coincident with a significant increase in the expression of p53 and p21 proteins. These novel findings show that melatonin, by inducing cell death and cell cycle arrest, might be useful as adjuvant in hepatocarcinoma therapy.

Melatonin as a negative mitogenic hormonal regulator of human prostate epithelial cell growth: potential mechanisms and clinical significance

Circannual variation in the human serum levels of prostate-specific antigen, a growth marker of the prostate gland, has been reported recently. The present study was conducted to investigate the role of the photoperiodic hormone melatonin (MLT) and its membrane receptors in the modulation of human prostate growth. Expression of MT(1) and MT(2) receptors was detected in benign human prostatic epithelial tissues and RWPE-1 cells. MLT and 2-iodomelatonin inhibited RWPE-1 cell proliferation and up-regulated p27(Kip1) gene and protein expression in the cells. The effects of MLT were blocked by the nonselective MT(1)/MT(2) receptor antagonist luzindole, but were not affected by the selective MT(2) receptor antagonist 4-phenyl-2-propionamidotetraline. Of note, the antiproliferative action of MLT on benign prostate epithelial RWPE-1 cells was effected via increased p27(Kip1) gene transcription through MT(1) receptor-mediated activation of protein kinase A (PKA) and protein kinase C (PKC) in parallel, a signaling process which has previously been demonstrated in 22Rv1 prostate cancer cells. Taken together, the demonstration of the MT(1)/PKA+PKC/p27(Kip1) antiproliferative pathway in benign and malignant prostate epithelial cell lines indicated the potential importance of this MLT receptor-mediated signaling mechanism in growth regulation of the human prostate gland in health and disease. Collectively, our data support the hypothesis that MLT may function as a negative mitogenic hormonal regulator of human prostate epithelial cell growth.

The antiproliferative activity of melatonin in B65 rat dopaminergic neuroblastoma cells is related to the downregulation of cell cycle-related genes

A potential application of melatonin is its ability to rescue many cell types from cell death, because of its antioxidant properties. Likewise, recent studies suggest that melatonin may also be used as an anti-tumor drug, due to its anti-proliferative properties in tumor cells when administered at physiologic or pharmacologic doses. In the present study, we investigated the mechanisms involved in the apoptosis induced by acute exposure to melatonin and roscovitine in the rat dopaminergic neuroblastoma B65 cell line. Cell growth studies revealed that, at 24 hr of treatment, roscovitine blocked cell growth and induced apoptosis whereas melatonin delayed cell growth and induced a slight increase in the number of apoptotic nuclei. Melatonin also increased the percentage of cells in the G1-phase of the cell cycle, whereas roscovitine blocked cells in the G2/M-phase. Both compounds significantly downregulated the transcriptional activity of cdk4, while melatonin also downregulated cdk2 and cyclin D1. Taken together, our data show that melatonin at millimolar concentrations inhibits dopaminergic B65 proliferation, induces cell apoptosis, and modulates cell cycle progression by inhibiting the transcriptional activity of cyclins and cdks related to the progression of the G1-phase.

Consumption of vegetables alters morning urinary 6-sulfatoxymelatonin concentration

Melatonin, which is contained in certain vegetables, may have an influence on circulatory melatonin concentrations. This study examined the effects of the consumption of vegetables on 6-sulfatoxymelatonin concentrations in morning urine. Ninety-four healthy women aged 24-55 were recruited through a city public health center in Japan. The women randomly allocated to the intervention group were requested to consume high amounts of six selected vegetables, with a target of 350 g/day for 65 days, while those in the control group were asked to avoid the same six vegetables during the same period. First-void morning urine was collected before and at the end of the intervention period, and creatinine-adjusted 6-sulfatoxymelatonin concentrations were measured. At the end of the intervention period, daily mean intake of melatonin from the six vegetables was 1288.0 ng in the intervention group and 5.3 ng in the control group. In the intervention group, the mean concentration of 6-sulfatoxymelatonin changed from 48.1 [95% confidence interval (CI): 40.4-57.2] ng/mg creatinine to 49.6 (95% CI: 42.8-57.3) ng/mg creatinine across the intervention period. In the control group, the mean concentration of 6-sulfatoxymelatonin changed from 55.5 (95% CI: 48.7-63.2) ng/mg creatinine to 50.8 (95% CI: 44.0-58.7) ng/mg creatinine across the intervention period. A comparison of the two groups with regard to the changes in the 6-sulfatoxymelatonin concentrations across the intervention period showed a significant difference (P = 0.03). The results indicate that increased consumption of vegetables raises circulatory melatonin concentrations.

Sleep duration and the risk of prostate cancer: the Ohsaki Cohort Study

In a prospective study of prostate cancer incidence (127 cases), among 22 320 Japanese men, sleep duration was associated with lower risk; the multivariate hazard ratio of men who slept ⩾9 h per day compared with those who slept less was 0.48 (95% confidence interval: 0.29–0.79, P for trend=0.02).

Effects of exogenous melatonin and circadian synchronization on tumor progression in melanoma-bearing C57BL6 mice

Circadian rhythmicity impairment reportedly becomes significant as a tumor progresses, while the incidence of cancer can be affected by disruption of the circadian system. Melatonin has oncostatic effects on several types of cancer (breast, prostate, and colorectal cancers), while it can be self-defeating in others, such as lymphoma. Melanoma is one of the most aggressive cancers in humans; however, it seems to respond positively to melatonin in vitro. The present work tested whether body temperature (BT) rhythms are impaired by tumor progression, and whether exogenous melatonin restricts tumor growth and restores circadian rhythmicity; therefore, enhancing survival. To this end, C57 mice were intraperitoneal implanted with a temperature data logger and subcutaneously inoculated with melanoma cells. Animals were then submitted to light-dark (LD) 12:12 cycles or continuous light (LL), with or without melatonin administration. Under LD light conditions, the BT rhythm exhibited a marked reduction in the first circadian harmonic amplitude, and increased phase instability (Rayleigh vector) as the tumor progressed. Melatonin administration (2 mg/kg BW/day), on the other hand, increased the BT rhythm amplitude and phase stability, reduced tumor weight and prevented intraperitoneal dissemination. Exposure to LL induced a free-running rhythm (1500 min), significantly increasing tumor malignity, and therefore reducing survival. Surprisingly, the highest tumor weights and morbidity by metastasis were seen in the LL group treated with melatonin probably because this indoleamine was being administered at different subjective hours to free-running animals. Circadian rhythmicity can thus be used as a marker rhythm for tumor progression, as rhythm impairment increases along with tumor malignancy. While melatonin administration improves rhythmicity and enhances survival under LD conditions, the results are self-defeating when they coexist with circadian disruption as it occurs under LL. This emphasizes the importance of taking into account endogenous rhythmicity and limiting melatonin administration to the subjective night in order to restrict melanoma progression.

Oxidative stress impairs oocyte quality and melatonin protects oocytes from free radical damage and improves fertilization rate

We investigated the relationship between oxidative stress and poor oocyte quality and whether the antioxidant melatonin improves oocyte quality. Follicular fluid was sampled at oocyte retrieval during in vitro fertilization and embryo transfer (IVF-ET). Intrafollicular concentrations of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in women with high rates of degenerate oocytes were significantly higher than those with low rates of degenerate oocytes. As there was a negative correlation between intrafollicular concentrations of 8-OHdG and melatonin, 18 patients undergoing IVF-ET were given melatonin (3 mg/day), vitamin E (600 mg/day) or both melatonin and vitamin E. Intrafollicular concentrations of 8-OHdG and hexanoyl-lysine adduct were significantly reduced by these antioxidant treatments. One hundred and fifteen patients who failed to become pregnant with a low fertilization rate (< or =50%) in the previous IVF-ET cycle were divided into two groups during the next IVF-ET procedure; 56 patients with melatonin treatment (3 mg/day) and 59 patients without melatonin treatment. The fertilization rate was improved by melatonin treatment compared to the previous IVF-ET cycle. However, the fertilization rate was not significantly changed without melatonin treatment. Oocytes recovered from preovulatory follicles in mice were incubated with H2O2 for 12 hr. The percentage of mature oocytes with a first polar body was significantly reduced by addition of H2O2 (300 microm). The inhibitory effect of H2O2 was significantly blocked by simultaneous addition of melatonin. In conclusion, oxidative stress causes toxic effects on oocyte maturation and melatonin protects oocytes from oxidative stress. Melatonin is likely to improve oocyte quality and fertilization rates.

Melatonin modulates the expression of VEGF and HIF-1 alpha induced by CoCl2 in cultured cancer cells

Melatonin is an important natural oncostatic agent. At present there are no data available as to its possible influence on tumor angiogenesis, which is a major biological mechanism responsible for tumor growth and dissemination. It is well known that vascular endothelial growth factor (VEGF) is crucial to a solid tumor's higher vascularization and development. To investigate the possible influence of melatonin on angiogenesis, we studied the effect of melatonin on endogenous VEGF expression in three human cancer cell lines (PANC-1, HeLa and A549 cells). In this study, we report that physiologic concentrations of melatonin have no obvious impact on the VEGF expression, whereas pharmacologic concentrations of melatonin suppress the VEGF mRNA and protein levels induced by hypoxia mimetic cobalt chloride (CoCl(2)). Melatonin also decreases hypoxia-inducible factor (HIF)-1alpha protein levels, suggesting a role for transcription factor HIF-1 in the suppression of VEGF expression. The effect of pharmacologic concentrations of melatonin on VEGF and HIF-1alpha under normoxia is uncertain, which indicates that the regulatory mechanisms of VEGF in the absence or presence of CoCl(2) are different and other or additional transcription factors may be involved. Taken together, our data show that melatonin in high concentrations markedly reduces the expression of endogenous VEGF and HIF-1alpha induced by CoCl(2) in cultured cancer cells.

Epigenetic regulation: a new research area for melatonin?

Epigenetic, modifications of DNA and histones, i.e. heritable alterations in gene expression that do not involve changes in DNA sequences, are known to be involved in disease. Two important epigenetic changes that contribute to disease are abnormal methylation patterns of DNA and modifications of histones in chromatin. Epimutations, such as the hypermethylation and epigenetic silencing of tumor suppressor genes, have revealed a new area for cancer treatment. Studies using DNA methyltransferase inhibitors such as procaine, hydralazine, and RG108 have had promising outcomes against cancer therapy. Melatonin, one of the most versatile molecules in nature, may hypothetically be involved in epigenetic regulation. In this review, the potential role of melatonin in inhibiting DNA methyltransferase and epigenetic regulation is discussed.

Melatonin in relation to the "strong" and "weak" versions of the free radical theory of aging

That free radicals and the damage they inflict are related to deteriorative cellular and organismal changes associated with aging and also with the development of a variety of age-related diseases is widely debated. There seems to be little doubt that free radical mutilation of essential molecules contributes to these conditions. Numerous investigators, on the basis of their experimental results, have drawn this conclusion. If the free radical theory of aging and disease development has validity, antioxidants could presumably be successfully used to delay the molecular destruction, cellular loss, and organismal death. In the current review we summarize the experimental data related to the utility of melatonin in protecting against reactive oxygen and reactive nitrogen species-induced cellular damage. While the data supporting a role for melatonin in forestalling aging and prolonging life span per se is not compelling, the findings related to melatonin's ability to reduce the severity of a variety of age-related diseases that have as their basis free radical damage is convincing. To date, the bulk of these investigations have been performed in experimental models of diseases in animals. It is now imperative that similar studies be conducted using humans whose quality of life may benefit from treatment with melatonin.