Monitoring intracellular melatonin levels in human prostate normal and cancer cells by HPLC

Evaluation of different internal standardization approaches for the quantification of melatonin in cell culture samples by multiple heart-cutting two dimensional liquid chromatography tandem mass spectrometry

We evaluate here different analytical strategies for the chromatographic separation and determination of N-acetyl-5-methoxytryptamine (MEL) and its oxidative metabolites N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK), N1-acetyl-5-methoxykynuramine (AMK) and cyclic 3-hydroxymelatonin (c3OHM) in cell culture samples. Two dimensional liquid chromatography (2D-LC) in the multiple heart-cutting mode was compared with regular 1D chromatographic separations of MEL and its oxidative metabolites. Our results showed that the use of trifluoroacetic acid (TFA) as mobile phase modifier was required to obtain a satisfactory resolution and peak shapes particularly for c3OHM. As TFA is not compatible with ESI ionization the application of the MHC mode was mandatory for a proper chromatographic separation. We evaluate also different internal standardization approaches based on the combined use of a surrogate standard (5-methoxytryptophol) and an internal standard (6-methoxytryptamine) for MEL quantification in cell culture samples obtaining unsatisfactory results both by 1D- and 2D-LC-ESI-MS/MS (from 9 ± 2 to 186 ± 38%). We demonstrate that only the application of isotope dilution Mass Spectrometry through the use of an in house synthesized ¹³C isotopically labelled analogue provided quantitative MEL recoveries both by using 1D- and 2D-LC-ESI-MS/MS (99±1 and 98±1. Respectively) in androgen-insensitive human prostate carcinoma PC3 cells.

Melatonin's Antineoplastic Potential Against Glioblastoma

Glioblastoma (GBM) is one of the most intransigent and aggressive brain tumors, and its treatment is extremely challenging and ineffective. To improve patients’ expectancy and quality of life, new therapeutic approaches were investigated. Melatonin is an endogenous indoleamine with an incredible variety of properties. Due to evidence demonstrating melatonin’s activity against several cancer hallmarks, there is growing interest in its use for preventing and treating cancer. In this review, we report on the potential effects of melatonin, alone or in combination with anticancer drugs, against GBM. We also summarize melatonin targets and/or the intracellular pathways involved. Moreover, we describe melatonin’s epigenetic activity responsible for its antineoplastic effects. To date, there are too few clinical studies (involving a small number of patients) investigating the antineoplastic effects of melatonin against GBM. Nevertheless, these studies described improvement of GBM patients’ quality of life and did not show significant adverse effects. In this review, we also report on studies regarding melatonin-like molecules with the tumor-suppressive properties of melatonin together with implemented pharmacokinetics. Melatonin effects and mechanisms of action against GBM require more research attention due to the unquestionably high potential of this multitasking indoleamine in clinical practice.

Melatonin reduces inflammatory response in human intestinal epithelial cells stimulated by interleukin-1β

Melatonin is the main secretory product of the pineal gland, and it is involved in the regulation of periodic events. A melatonin production independent of the photoperiod is typical of the gut. However, the local physiological role of melatonin at the intestinal tract is poorly characterized. In this study, we evaluated the anti-inflammatory activities of melatonin in an in vitro model of inflamed intestinal epithelium. To this purpose, we assessed different parameters usually associated with intestinal inflammation using IL-1β-stimulated Caco-2 cells. Differentiated monolayers of Caco-2 cells were preincubated with melatonin (1 nmol/L-50 μmol/L) and then exposed to IL-1β. After each treatment, different inflammatory mediators, DNA-breakage, and global DNA methylation status were assayed. To evaluate the involvement of melatonin membrane receptors, we also exposed differentiated monolayers to melatonin in the presence of luzindole, a MT1 and MT2 antagonist. Our results showed that melatonin, at concentrations similar to those obtained in the lumen gut after ingestion of dietary supplements for the treatment of sleep disorders, was able to attenuate the inflammatory response induced by IL-1β. Anti-inflammatory effects were expressed as both a decrease of the levels of inflammatory mediators, including IL-6, IL-8, COX-2, and NO, and a reduced increase in paracellular permeability. Moreover, the protection was associated with a reduced NF-κB activation and a prevention of DNA demethylation. Conversely, luzindole did not reverse the melatonin inhibition of stimulated-IL-6 release. In conclusion, our findings suggest that melatonin, through a local action, can modulate inflammatory processes at the intestinal level, offering new opportunities for a multimodal management of IBD.

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.

Influence of Melatonin on the Proliferative and Apoptotic Responses of the Prostate under Normal and Hyperglycemic Conditions

The antitumor properties of melatonin (MLT) are known for prostate cancer cells. This study investigated whether MLT affects prostate maturation and interferes with tissue injuries induced by diabetes. MLT was administered to Wistar rats from 5 weeks of age in the drinking water (10 μg/kg b.w.), and diabetes was induced at the 13th week by streptozotocin (4.5 mg/100g b.w., i.p.). The animals were euthanized in the 14th and 21st weeks. MLT reduced the immunostained cells for androgen receptor (AR) by 10% in younger rats. Diabetes decreased cell proliferation and increased apoptosis. MLT treatment impeded apoptosis (p = 0.02) and augmented proliferation (p = 0.0008) and PCNA content in prostate following long-term diabetes due to restoration of testosterone levels and expression of melatonin receptor type 1B. The effect of MLT (500 µM, 5 mM, and 10 mM) on androgen-dependent (22Rv1) and androgen-independent (PC3) cancer cells and human prostate epithelial cells (PNTA1) under normal and hyperglycemic conditions (HG, 450 mg/dL) was analyzed. Contrary to PNTA1 and 22Rv1 cells, MLT improved the proliferation of PC3 cells in hyperglycemic medium. The combined data indicated that MLT had proliferative and antiapoptotic effects in prostate cells subjected to HG levels and it seems to involve specific MLT pathways rather than AR.

Melatonin uptake through glucose transporters: a new target for melatonin inhibition of cancer

Melatonin is present in a multitude of taxa and it has a broad range of biological functions, from synchronizing circadian rhythms to detoxifying free radicals. Some functions of melatonin are mediated by its membrane receptors but others are receptor-independent. For the latter, melatonin must enter into the cell. Melatonin is a derivative of the amino acid tryptophan and reportedly easily crosses biological membranes due to its amphipathic nature. However, the mechanism by which melatonin enters into cells remains unknown. Changes in redox state, endocytosis pathways, multidrug resistance, glycoproteins or a variety of strategies have no effect on melatonin uptake. Herein, it is demonstrated that members of the SLC2/GLUT family glucose transporters have a central role in melatonin uptake. When studied by docking simulation, it is found that melatonin interacts at the same location in GLUT1 where glucose does. Furthermore, glucose concentration and the presence of competitive ligands of GLUT1 affect the concentration of melatonin into cells. As a regulatory mechanism, melatonin reduces the uptake of glucose and modifies the expression of GLUT1 transporter in prostate cancer cells. More importantly, glucose supplementation promotes prostate cancer progression in TRAMP mice, while melatonin attenuated glucose-induced tumor progression and prolonged the lifespan of tumor-bearing mice. This is the first time that a facilitated transport of melatonin is suggested. In fact, the important role of glucose transporters and glucose metabolism in cell fate might explain some of the diverse functions described for melatonin.

Melatonin enhances photo-oxidation of 2',7'-dichlorodihydrofluorescein by an antioxidant reaction that renders N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK)

The indolamine melatonin (MEL) is described as an antioxidant and a free radical scavenger. However occasionally, the indoleamine has been reported to increase free radicals with insufficient mechanistic explanation. In an attempt to find a reason for those controversial results, a potential mechanism that explains MEL prooxidant activity is investigated. The current controversy about redox detection methods has prompted us to search a possible interaction between MEL and dichlorodihydrofluorescein (DCFH₂), perhaps the most widely fluorescence probe employed for free radicals detection in cellular models. Here, it is demonstrated that melatonin potentiates the photooxidation of DCFH₂ in a cell-free system, increasing the production of its fluorescent metabolite. Indeed, MEL works as an antioxidant scavenging hydroxyl radicals in this system. Thus, this reaction between MEL and DCFH₂ produces N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK), a biogenic amine with antioxidant properties too. This reaction is O₂ and light dependent and it is prevented by antioxidants such as N-acetylcysteine or ascorbic acid. Furthermore, when DCFH₂ has been employed to evaluate antioxidant or prooxidant activities of MEL in cellular models it is confirmed that it works as an antioxidant but these results can be modulated by light misleading to a prooxidant conclusion. In conclusion, here is demonstrated that DCFH₂, light and melatonin interact and results obtained using these fluorescence probes in studies with melatonin have to be carefully interpreted.

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.

Selective and quantitative cell detection based both on aptamers and the conventional cell-staining methods

Aptamer-based biochips for selective cell detection and quantitation in combination of the recent biochip technology and the conventional cell staining methods are described. Using a model system comprising HER2- or PSMA-positive cells as the analytes and single-stranded RNA aptamers specific for HER2 or PSMA as immobilized ligands on chips, we could demonstrate that aptamers were equivalent or superior to antibodies in terms of specificity and sensitivity, respectively. In particular, our PSMA-specific sensor was found to have the characteristics of good stability, reproducibility and reusability, with detection limit as low as 10(3) LNCaP cells. In conclusion, we could show the suitability of nucleic acid aptamers as low molecular weight receptors on biochips for sensitive and specific cell detection and quantitation for future diagnostics development.

Phenotypic changes caused by melatonin increased sensitivity of prostate cancer cells to cytokine-induced apoptosis

Melatonin has antiproliferative properties in prostate cancer cells. Melatonin reduces proliferation without increasing apoptosis, and it promotes cell differentiation into a neuroendocrine phenotype. Because neuroendocrine cells displayed an androgen-independent growth and high resistance to radiotherapy and chemotherapy, the role of molecules that induce neuroendocrine differentiation was questioned in terms of their usefulness as oncostatic agents. By using human epithelial androgen-dependent and androgen-independent prostate cancer cells, the role of melatonin in drug-induced apoptosis was studied after acute treatments. In addition to cytokines such as hrTNF-alpha and TRAIL, chemotherapeutic compounds, including doxorubicin, docetaxel, or etoposide, were employed in combination with melatonin to promote cell death. Melatonin promotes cell toxicity caused by cytokines without influencing the actions of chemotherapeutic agents. In addition, antioxidant properties of melatonin were confirmed in prostate cancer cells. However, its ability to increase cell death caused by cytokines was independent of the redox changes. Finally, phenotypic changes caused by chronic treatment with the indole, that is, neuroendocrine differentiation, make cells significantly more sensitive to cytokines and slightly more sensitive to some chemotherapeutic compounds. Thus, melatonin is a good inhibitor of the proliferation of prostate cancer cells, promoting phenotypic changes that do not increase survival mechanisms and make cells more sensitive to cytokines such as TNF-alpha or TRAIL.

Antagonistic effects of a 50 Hz magnetic field and melatonin in the proliferation and differentiation of hepatocarcinoma cells

BACKGROUND/AIMS

Epidemiological and experimental evidence exists indicating that exposure to weak, extremely low frequency magnetic fields (ELF - MF) could affect cancer progression. It has been proposed that such hypothetical action could be mediated by MF-induced effects on the cellular response to melatonin (MEL), a potentially oncostatic neurohormone. The present study investigates the response of HepG2 cells to intermittent exposure to a 50 Hz, 10 µT MF, in the presence or absence of MEL at physiological (10 nM) or pharmacological doses (1 µM).

METHODS

The Trypan blue cell exclusion test, BrdU incorporation and PCNA expression assays were carried out to assess the cellular response in terms of viability and proliferation. In addition, albumin and alpha-fetoprotein, were analyzed as specific hepatocellular differentiation markers.

RESULTS

The results indicate that the MF exerts significant cytoproliferative and dedifferentiating effects that can be prevented by 10 nM MEL. Conversely, MEL exerts cytostatic and differentiating effects on HepG2 that are abolished by simultaneous exposure to MF.

CONCLUSION

As a whole, these results support the hypothesis that ELF - MF and MEL exert opposite, mutually counteracting effects on cell proliferation and differentiation.

Content of melatonin and other antioxidants in grape-related foodstuffs: measurement using a MEPS-HPLC-F method

The strong antioxidant activity of melatonin is well known and it is important to investigate its presence and levels in different foodstuffs, for the purpose of evaluating their nutraceutical properties. As a contribution towards this goal, an original analytical method has been developed for the simultaneous determination of melatonin and other indolic and phenolic antioxidants (including trans- and cis-resveratrol, ferulic acid, tryptophan, serotonin and 5-hydroxyindoleacetic acid) in grape-related foodstuffs and beverages: namely grape, grape juice, must, wine and grappa (Italian pomace brandy). These foodstuffs represent an important part of the diet, both traditionally and in recent times, especially in Mediterranean countries and could be (at least in part) responsible for the beneficial effects involved in the 'French paradox'. The analytical method is based on high-performance liquid chromatography coupled to fluorescence detection, exploiting the native fluorescence of the analytes. A C8 column was used as the stationary phase, while the mobile phase was composed of acidic phosphate buffer and acetonitrile; fluorescence intensity was monitored at λ=386nm while exciting at λ=298nm. The sample pretreatment was carried out by a fast and reliable microextraction by packed sorbent (MEPS) procedure. After validation, the method was applied to the analysis of melatonin and other antioxidants in food and beverages derived from grape, with very good results being obtained. Thus, this methodology may represent a promising tool for the evaluation of the antioxidant properties of nutraceuticals and functional foods.