Direct antiproliferative effects of melatonin on two metastatic cell sublines of mouse melanoma (B16BL6 and PG19)

The rationale for treating uveal melanoma with adjuvant melatonin: a review of the literature

Background

Uveal melanoma is a rare form of cancer with high mortality. The incidence of metastases is attributed to early seeding of micrometastases from the eye to distant organs, primarily the liver. Once these seeded clusters of dormant tumor cells grow into larger radiologically detectable macrometastases, median patient survival is about 1 year. Melatonin is an important hormone for synchronizing circadian rhythms. It is also involved in other aspects of human physiology and may offer therapeutic benefits for a variety of diseases including cancer.

Methods

Articles involving the physiological effects of melatonin, pharmacokinetics, and previous use in cancer studies were acquired using a comprehensive literature search in the Medline (PubMed) and Web of Science databases. In total, 147 publications were selected and included in the review.

Results

Melatonin has been observed to suppress the growth of cancer cells, inhibit metastatic spread, enhance immune system functions, and act as an anti-inflammatory in both in vitro and in vivo models. Melatonin may also enhance the efficacy of cancer treatments such as immuno- and chemotherapy. Numerous studies have shown promising results for oral melatonin supplementation in patients with other forms of cancer including cutaneous malignant melanoma. Cell line and animal studies support a hypothesis in which similar benefits may exist for uveal melanoma.

Conclusions

Given its low cost, good safety profile, and limited side effects, there may be potential for the use of melatonin as an adjuvant oncostatic treatment. Future avenues of research could include clinical trials to evaluate the effect of melatonin in prevention of macrometastases of uveal melanoma.

Melatonin: An important anticancer agent in colorectal cancer

Colorectal cancer is one of the most common cancers among the elderly, which is also seen in the forms of hereditary syndromes occurring in younger individuals. Numerous studies have been conducted to understand the molecular and cellular pathobiology underlying colorectal cancer. These studies have found that cellular signaling pathways are at the core of colorectal cancer pathology. Because of this, new agents have been proposed as possible candidates to accompany routine therapy regimens. One of these agents is melatonin, a neuro-hormone known best for its essential role in upholding the circadian rhythm and orchestrating the many physiologic changes it accompanies. Melatonin is shown to be able to modulate many signaling pathways involved in many essential cell functions, which if deregulated cause an accelerated pace towards cancer. More so, melatonin is involved in the regulation of immune function, tumor microenvironment, and acts as an antioxidant agent. Many studies have focused on the beneficial effects of melatonin in colorectal cancers, such as induction of apoptosis, increased sensitivity to chemotherapy agents and radiotherapy, limiting cellular proliferation, migration, and invasion. The present review aims to illustrate the known significance of melatonin in colorectal cancer and to address possible clinical use.

Participation of MT3 melatonin receptors in the synergistic effect of melatonin on cytotoxic and apoptotic actions evoked by chemotherapeutics

BACKGROUND

Melatonin has antitumor activity via several mechanisms including its antiproliferative and proapoptotic effects in addition to its potent antioxidant actions. Therefore, melatonin may be useful in the treatment of tumors in association with chemotherapy drugs.

PURPOSE AND METHODS

This study was performed to study the role of melatonin receptors on the cytotoxicity and apoptosis induced by the chemotherapeutic agents cisplatin and 5-fluorouracil in two tumor cell lines, such as human colorectal cancer HT-29 cells and cervical cancer HeLa cells.

RESULTS

We found that both melatonin and the two chemotherapeutic agents tested induced a decrease in HT-29 and HeLa cell viability. Furthermore, melatonin significantly increased the cytotoxic effect of chemotherapeutic agents, particularly, in 5-fluorouracil-challenged cells. Stimulation of cells with either of the two chemotherapeutic agents in the presence of melatonin further increased caspase-3 activation. Concomitant treatments with melatonin and chemotherapeutic agents augmented the population of apoptotic cells compared to the treatments with chemotherapeutics alone. Blockade of MT1 and/or MT2 receptors with luzindole or 4-P-PDOT was unable to reverse the enhancing effects of melatonin on both cytotoxicity, caspase-3 activation and the amount of apoptotic cells evoked by the chemotherapeutic agents, whereas when MT3 receptors were blocked with prazosin, the synergistic effect of melatonin with chemotherapy on cytotoxicity and apoptosis was reversed.

CONCLUSION

Our findings provided evidence that in vitro melatonin strongly enhances chemotherapeutic-induced cytotoxicity and apoptosis in two tumor cell lines, namely HT-29 and HeLa cells and, this potentiating effect of melatonin is mediated by MT3 receptor stimulation.

Melatonin increases the effect of 5-fluorouracil-based chemotherapy in human colorectal adenocarcinoma cells in vitro

Melatonin has antitumor activity via several mechanisms including its anti-proliferative and pro-apoptotic effects. Moreover, it has been proven that melatonin in combination with chemotherapeutic agents enhances chemotherapy-triggered apoptosis in several types of cancer. Therefore, this study was intended to evaluate whether melatonin is able to strengthen the anti-cancer potential of different chemotherapeutic drugs in human colorectal adenocarcinoma HT-29 cells. We found that treatment with 20 µM cisplatin (CIS) or 1 mM 5-fluorouracil (5-FU) for 72 h induced a decrease in HT-29 cell viability. Furthermore, 1 mM melatonin significantly (P < 0.05) increased the cytotoxic effects of 5-FU. Likewise, simultaneous stimulation with 1 mM melatonin and 1 mM 5-FU significantly (P < 0.05) enhanced the ratio of cells with an overproduction of intracellular reactive oxygen species and substantially augmented the population of apoptotic cells compared to the treatment with 5-FU alone. Nonetheless, melatonin only displayed moderate chemosensitizing effects in CIS-treated HT-29 cells, as suggested by a slight increment in the fraction of early apoptotic cells that was observed only after 48 h. Consistently, co-stimulation of HT-29 cells with 20 µM CIS or 1 mM 5-FU in the presence of 1 mM melatonin further increased caspase-3 activation. Apart from this, the cytostatic activity displayed by CIS due to S phase arrest was not affected by concomitant stimulation with melatonin. Overall, our results indicate that melatonin increases the sensitivity of HT-29 cells to 5-FU treatment and, consequently, the indolamine could be potentially applied to colorectal adenocarcinoma treatment as a potent chemosensitizing agent.

Melatonin decreases estrogen receptor binding to estrogen response elements sites on the OCT4 gene in human breast cancer stem cells

Cancer stem cells (CSCs) pose a challenge in cancer treatment, as these cells can drive tumor growth and are resistant to chemotherapy. Melatonin exerts its oncostatic effects through the estrogen receptor (ER) pathway in cancer cells, however its action in CSCs is unclear. Here, we evaluated the effect of melatonin on the regulation of the transcription factor OCT4 (Octamer Binding 4) by estrogen receptor alpha (ERα) in breast cancer stem cells (BCSCs). The cells were grown as a cell suspension or as anchorage independent growth, for the mammospheres growth, representing the CSCs population and treated with 10 nM estrogen (E2) or 10 μM of the environmental estrogen Bisphenol A (BPA) and 1 mM of melatonin. At the end, the cell growth as well as OCT4 and ERα expression and the binding activity of ERα to the OCT4 was assessed. The increase in number and size of mammospheres induced by E2 or BPA was reduced by melatonin treatment. Furthermore, binding of the ERα to OCT4 was reduced, accompanied by a reduction of OCT4 and ERα expression. Thus, melatonin treatment is effective against proliferation of BCSCs in vitro and impacts the ER pathway, demonstrating its potential therapeutic use in breast cancer.

Vitamin D and melatonin protect the cell's viability and ameliorate the CCl4 induced cytotoxicity in HepG2 and Hep3B hepatoma cell lines

Carbon tetrachloride (CCl4) is widely used to induce liver toxicity in in vitro/in vivo models. Lipid peroxidation (LPO) begins with toxicity and affects cell viability. Recently, the beneficial effects of melatonin and Vitamin D on cell proliferation in human normal and cancer cells were found. This study was planned to evaluate antioxidant and cytoprotective activity of melatonin and Vitamin D in CCl4 induced cytotoxicity in HepG2 and Hep3B hepatoma cell lines. Based on the cytotoxicity assay, melatonin and Vitamin D were evaluated for cytotoprotective potential against CCl4 induced toxicity in HepG2 and Hep3B liver cell lines by monitoring cell viability, LPO and glutathione (GSH) level. Different dosages of CCl4 (0.1, 0.2, 0.3 and 0.4 % v/v) were applied to HepG2 and Hep3B cells in order to determine the most toxic dosage of it in a time dependent manner. The same experiments were repeated with exogenously applied melatonin (MEL) and Vitamin D to groups treated with/without CCL4. Cell viability was determined with MTT measurements at the 2nd, 24th and 48th h. GSH content and Malondialdehyde levels were measured from the cell lysates. As a result, both melatonin and Vitamin D administration during CCl4 exposure protected liver cells from CCl4 induced cell damage. Increase in LPO and decrease in GSH were found in the CCl4 groups of both cells. Contrary to these results administration of MEL and Vitamin D on cells exhibited results similar to the control groups. Therefore, melatonin and Vitamin D might be a promising therapeutic agent in several toxic hepatic diseases.

Melatonin combined with endoplasmic reticulum stress induces cell death via the PI3K/Akt/mTOR pathway in B16F10 melanoma cells

This study investigated B16F10 melanoma cell death induced by melatonin combined with endoplasmic reticulum (ER) stress through the PI3K/Akt/mTOR pathway. Cell viability was significantly decreased after treatment with melatonin combined with ER stress from thapsigargin or tunicamycin compared to no treatment or treatment with melatonin only. Combined melatonin and ER stress also significantly reduced expression of p85β, p-Akt (Ser473, Thr308), and p-mTOR (Ser2448, Ser2481) compared to treatment with melatonin only. The ER stress protein p-PERK and p-eIF2α were significantly increased under combined melatonin and ER stress treatment compared to no treatment or treatment with melatonin only. Combined melatonin and ER stress significantly reduced Bcl-2 protein and augmented Bax protein compared to melatonin-only treatment. Also, the combined treatment significantly lowered expression of catalase, Cu/Zn-SOD, and Mn-SOD proteins compared to melatonin only. Expression of p85β was significantly more decreased under treatment with melatonin and thapsigargin or tunicamycin plus the PI3K inhibitors LY294002 or wortmannin than under treatment with only melatonin or a PI3K inhibitor. The PI3K downstream target p-Akt (Ser473, Thr308) showed significantly decreased expression under treatment with melatonin and thapsigargin or tunicamycin plus PI3K inhibitors than under treatment with melatonin or PI3K inhibitors only. These results indicate that survival of B16F10 melanoma cells after combined treatment with melatonin and ER stress inducers is suppressed through regulation of the PI3K/Akt/mTOR pathway. Melatonin combined with thapsigargin or tunicamycin appears to be a promising strategy for effective melanoma treatment.

Update on the role of melatonin in the prevention of cancer tumorigenesis and in the management of cancer correlates, such as sleep-wake and mood disturbances: review and remarks

The aim of this article was to perform a systematic review on the role of melatonin in the prevention of cancer tumorigenesis--in vivo and in vitro--as well as in the management of cancer correlates, such as sleep-wake and mood disturbances. The International Agency for Research on Cancer recently classified "shift-work that involves circadian disruption" as "probably carcinogenic to humans" (Group 2A) based on "limited evidence in humans for the carcinogenicity of shift-work that involves night-work", and "sufficient evidence in experimental animals for the carcinogenicity of light during the daily dark period (biological night)". The clinical implications and the potential uses of melatonin in terms of biologic clock influence (e.g. sleep and mood), immune function, cancer initiation and growth, as well as the correlation between melatonin levels and cancer risk, are hereinafter recorded and summarized. Additionally, this paper includes a description of the newly discovered effects that melatonin has on the management of sleep-wake and mood disturbances as well as with regard to cancer patients' life quality. In cancer patients depression and insomnia are frequent and serious comorbid conditions which definitely require a special attention. The data presented in this review encourage the performance of new clinical trials to investigate the possible use of melatonin in cancer patients suffering from sleep-wake and mood disturbances, also considering that melatonin registered a low toxicity in cancer patients.

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.

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.

Rotating night shifts and risk of skin cancer in the nurses' health study

Night shift work is associated with increased risk of several cancers, but the risk of skin cancer among night shift workers is unknown. We documented 10,799 incident skin cancers in 68,336 women in the Nurses' Health Study from June 1988 to June 2006 and examined the relationship between rotating night shifts and skin cancer. We used Cox proportional hazard models, adjusted for confounding variables (phenotypic and established risk factors of skin cancer), and performed stratified analysis to explore the modifying effect of hair color. Working 10 years or more on rotating night shifts was associated with a 14% decreased risk of skin cancer compared with never working night shifts (age-standardized incidence rate: 976 per 100,000 person-years (PY) vs 1070 per 100,000 PY, respectively; adjusted hazard ratios = 0.86, 95% confidence interval = 0.81 to 0.92, P(trend) < .001). This association was strongest for cutaneous melanoma; working 10 years or more of rotating night shifts was associated with 44% decreased risk of melanoma, after adjustment for melanoma risk factors (age-standardized incidence rate: 20 per 100,000 PY vs 35 per 100,000 PY, respectively; adjusted hazard ratios = 0.56, 95% confidence interval = 0.36 to 0.87, P(trend) = .005). Hair color, a surrogate for an individual's susceptibility to skin cancer, was a statistically significant effect modifier for the observed associations; darker-haired women had the lowest risk (P(interaction) = .02).

Melatonin induces mitochondrial-mediated apoptosis in human myeloid HL-60 cells

The role of melatonin in the mediation of apoptotic events has recently gained attention, especially after recent studies have reported that melatonin exerts antiapoptotic actions in normal cells but may activate proapoptotic pathways in some tumor cells. Here, we have evaluated the effect of melatonin on apoptosis in the human leukemia cell line HL-60. Melatonin treatment (1 mm) induced a significant increase in caspase-3 and -9 activities. The effect of melatonin on the activation of caspases was time dependent, reaching a maximum after 12 hr of stimulation, and then decreasing to a minimum after 72 hr. Treatment with melatonin also evoked mitochondrial membrane depolarization and permeability transition pore induction, which caused loss of mitochondrial staining by calcein, and increased cell death by apoptosis/necrosis as demonstrated by propidium iodide positive-staining of cells after 72 hr of stimulation. In addition, the exposure of cells to melatonin resulted in an activation and association of the proapoptotic proteins Bax and Bid, as well as promoting detectable increases in the expression of both proteins. We conclude that melatonin has proapoptotic and/or oncostatic effects in the human myeloid cell line HL-60.

ROCK-regulated cytoskeletal dynamics participate in the inhibitory effect of melatonin on cancer cell migration

Cell movement is generated by a driving force provided by dynamic cytoskeletal organization. Two main cytoskeletal-dependent features, essential for migration, are the highly cell polarized structure and focal adhesion complexes. Cell migration and substrate anchorage are finely regulated by external signaling exerted by growth factors and hormones. In particular, the serine threonine kinase activated by the small GTPase Rho, the Rho-associated protein kinase (ROCK), participate in both processes through regulation of actin rearrangements in lamellipodia, filopodia, ruffles, and stress fibers. Melatonin, the main product secreted by the pineal gland has oncostatic properties. In MCF-7 cells, 1 nm melatonin reduces migration and invasiveness through increased expression of two cell surface adhesion proteins, E-cadherin and beta(1)-integrin. In this work, we studied the microfilament and microtubule rearrangements elicited by melatonin in migrating leader MCF-7 cells by a wound-healing assay. Additionally, cell anchorage was estimated by quantification of focal adhesions in MCF-7 cells cultured with melatonin. ROCK participation in the indole effects on anchorage and migration was explored by inhibition of the kinase activity with the specific inhibitor of ROCK, the Y-27632 compound. The results indicate that ROCK participates in the melatonin inhibitory effects on cell migration by changing cytoskeletal organization of leader MCF-7 cells. Also, they indicated that indole increased the number of focal contacts through ROCK. These results support the notion that melatonin inhibits cancer cell invasion and metastasis formation via ROCK-regulated microfilament and microtubule organization that converge in a migration/anchorage switch.

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.

Melatonin and its synthesizing enzymes (arylalkylamine N-acetyltransferase-like and hydroxyindole-O-methyltransferase) in avian eggs and early embryos

The presence of melatonin and the enzymes (transcripts and activities) involved in its synthesis, i.e. arylalkylamine N-acetyltransferase (AA-NAT) and hydroxyindole-O-methyltransferase (HIOMT), was investigated in the eggs and early embryos of Japanese quail at Hamburger-Hamilton stages 1-10. Melatonin was present in the egg yolk (approximately 70 pg/g) and albumen (approximately 20 pg/g). The average content of melatonin was approximately 416 pg/egg. AA-NAT and HIOMT transcripts were present in the oocytes, blastoderms, and ovarian follicles. AA-NAT-like and HIOMT activities were detected in quail egg yolk. The activity of AA-NAT in yolk was comparable with that found in the pineal gland when calculated per milligram of yolk or pineal gland, but was significantly lower when re-calculated per milligram of protein in the yolk or pineal gland. AA-NAT-like activity was also identified in the ovarian follicles. Low HIOMT activity was detected in yolk, but not in the ovarian follicle. Both enzymes were essentially absent from early embryos although some residual activities, probably of yolk origin, were present in the stage 1 embryo. Melatonin and all the constituents needed for its synthesis (serotonin, AA-NAT and HIOMT activities) are contained within the avian yolk and could be used by the embryo from the very beginning of its development. The role of extrapineal melatonin in early avian development may be in protecting the embryo from the action of free radicals formed during intensive embryonic metabolism and/or it may participate (together with serotonin) in a 'diffuse neuroendocrine system' acting at early developmental stages, before differentiation of the nervous system.

Inhibition of proliferation and induction of apoptosis by melatonin in human myeloid HL-60 cells

Melatonin is an indoleamine that is synthesized in the pineal gland and has an extensive repertoire of biological activities. In the present study, we found that melatonin reduced the growth of the human myeloid leukemia cells HL-60, inhibiting progression from G(1) to S phase of the cell cycle and increasing apoptotic cell death. Furthermore, melatonin treatment elevated cytochrome c release from mitochondria and augmented caspase-3 and caspase-9 activities. Upregulation of Bax and downregulation of Bcl-2 was also observed upon melatonin treatment. The effects of melatonin were found not to be mediated by membrane receptors for the indoleamine. Together, our results suggest that melatonin reduces the viability of HL-60 cells via induction of apoptosis primarily through regulation of Bax/Bcl-2 expression.

Environmental discontinuity hypothesis: Buffer dysfunctions as a source of human disease

Adaptive physiologic buffers enable organisms to respond to environmental variation with appropriate plasticity. Modern humans have substantially remodeled their environment such that many interactions with the environment have become relatively discontinuous functions compared to the past. Examples include sunlight, temperature, and altitude. We propose that environmental discontinuity represents a Darwinian maladaptation and may promote disease by inducing buffer dysfunctions. Skin pigmentation is an adaptive, dynamic buffer that normalizes sunlight exposure to balance the potential harm of damaging rays with the importance of sunlight in driving systemic biologic functions such as melatonin and vitamin D. Due to lifestyle characteristics such as indoor-outdoor living, well-intended sun-avoidance campaigns, and inhomogeneous use of apparel and sunblock techniques, modern humans increasingly experience sunlight variation as a discontinuous function. The resulting skin pigmentation buffer dysfunction may promote diseases associated with over- or under-exposure to sunlight, the most striking example being melanoma. In addition to promoting discontinuity of sunlight exposure, sun-avoidance campaigns may undermine sun-dependent biologic pathways such as melatonin and vitamin D that appear to protect against cancer. These issues may partly explain the rise in melanoma rates despite the implementation of sun-avoidance campaigns. Also discussed is the potential role that discontinuous temperature variation associated with modern lifestyles plays in diseases such as viral infection, heart failure, and acute coronary syndromes. Acute discontinuous changes in pressure and oxygen levels related to air travel may contribute to autonomic dysfunction, venous thromboembolism, and viral infections. Therapeutic implications are discussed.

Melatonin induces apoptosis in human neuroblastoma cancer cells

Low concentrations (nanomolar) of melatonin had been previously shown to inhibit cell proliferation in several cancer cell lines as well as in experimental animal models. Additionally, cell growth inhibition and differentiation of prostate cancer cell lines by high concentrations (micromolar to millimolar) of melatonin have been recently reported. In the present paper, we show the induction of apoptosis by high doses of melatonin in the human neuroblastoma cell line SK-N-MC. We found accumulation of cells in the G2/M cell cycle phase and induction of cellular death, measured as lactate dehydrogenase (LDH) released into the culture medium, under millimolar concentration of melatonin. Apoptosis was evaluated using 4,6-diamidino-2-phenylindole staining, DNA gel electrophoresis, electron microscopy, and annexin V binding. Apoptosis progressed through the classical pathway, which involves caspase-3 activation. Cell death was dose and time-dependent; the lowest effective concentration of melatonin was 100 microm. Treatment with 1 mm melatonin for 6 days induced cell death in 75% of the cells. This novel finding shows that a nontoxic natural indoleamine may be potential therapy for some types of human neuroblastomas.

Serum melatonin levels following enucleation and transpupillary thermotherapy in patients with choroidal melanoma

PURPOSE

To study serum melatonin levels in patients with choroidal melanoma preoperatively and following enucleation and transpupillary thermotherapy.

METHODS

Forty patients with preoperative choroidal melanoma were included in the study. Of these, 15 patients underwent enucleation (group 1) and 25 patients received transpupillary thermotherapy (group 2). A further 20 patients without melanoma acted as age-matched controls. Serum melatonin levels were determined 1 day preoperatively, and at the first and sixth months postoperatively using ELISA.

RESULTS

Preoperative serum melatonin levels were highest in group 2 followed by group 1, but this was not statistically significant compared to controls. Postoperatively, a constant decrease of serum melatonin was observed in both groups after the first month, which reached statistical significance at the sixth month (P = 0.003). Also, a significant regression in tumour thickness was documented in group 2 (P = 0.003). Three patients in group 1 developed hepatic metastases.

CONCLUSIONS

Patients with choroidal melanomas had higher levels of serum melatonin compared to individuals without tumours. Smaller tumours were associated with more elevated melatonin levels compared to larger tumours. Serum melatonin levels fell considerably following enucleation and transpupillary thermotherapy.

Residential and occupational exposure to 50 Hz magnetic fields and malignant melanoma: a population based study

AIMS

To test the hypothesis that exposure to electromagnetic fields from high voltage power lines increases the incidence of cutaneous malignant melanoma in adults aged 16 and above.

METHODS

Nested case-control study. The study population comprised subjects aged 16 and above who had lived in a residence situated in a broad corridor around a high voltage power line in 1980, or one of the years from 1986 to 1996. The cases were incident cases that were diagnosed in 1980-96 and reported to the Cancer Registry of Norway. Two controls were matched to each case by year of birth, sex, municipality, and first year entering the cohort. Time weighted average exposure to residential magnetic fields generated by the power lines was calculated for the exposure follow up from 1 January 1967 until diagnosis by means of a computer program, in which distance from residency to the line, line configuration, and current load were taken into account. Exposure was analysed using cut off points at 0.05 and 0.2 microtesla ( microT). Exposure to magnetic fields at work was classified by an expert panel who assessed magnetic field exposure by combining branch and occupation into one of three levels: <4 hours, 4-24 hours, and >24 hours per week above background (0.1 micro T). The categories were cumulated over the occupationally active years for the exposure follow up from 1 January 1955 until diagnosis, and cut off points at 18 and 31 category-years were evaluated.

RESULTS

Analysis of the two upper residential magnetic field categories showed an odds ratio of 2.01 (95% CI 1.09 to 3.69) and 2.68 (95% CI 1.43 to 5.04) for women, and an odds ratio of 1.70 (95% CI 0.96 to 3.01) and 1.37 (95% CI 0.77 to 2.44) for men, respectively. Occupational exposure showed no significant association with cutaneous malignant melanoma, and analysis of both residential and occupational exposure simultaneously, showed no additional effect.

CONCLUSION

The present study provides some support for an association between exposure to calculated residential magnetic fields and cutaneous malignant melanoma, but because of the lack of a biological hypothesis and the known strong association between solar radiation and melanoma, no firm conclusions can be drawn and further studies would be of interest.

Potentiation of antiproliferative effects of tamoxifen and ethanol on mouse hepatoma cells by melatonin: possible involvement of mitogen-activated protein kinase and induction of apoptosis

Melatonin, the major secretory product of the pineal gland, is in focus of many research areas because of its ability to scavenge free oxygen radicals and thereby protect cells and tissues from radical damage. Some studies suggest melatonin may be a possible therapeutic agent with potential clinical applications against pathological states due to reactive oxygen species. Here, we investigated the effects of melatonin on the mouse hepatoma cell line HEPA 1-6, coincubated with ethanol, and tamoxifen, respectively. Cell proliferation rates were detected by the 3-[4,5 dimethylthiazol-2-y1]-2,5-diphenyltetrazolium bromide (MTT) proliferation assay. A dose-dependent inhibition of the proliferative activity by melatonin was observed from 640 microM to 3 mM, which was significantly higher (P < 0.01) than with the solvent (ethanol) alone. Concentrations of 320 microM and less had no effect on cell proliferation. This antiproliferative effect might be because of the prolonged activation of mitogen-activated protein kinase which was activated by phosphorylation 15 min after the induction with melatonin. Furthermore, apoptosis was found to be enhanced by melatonin (75% more than with the solvent alone, P < 0.001). Finally, we show that the inhibitory effect of tamoxifen (25 microM) is markedly enhanced by the coincubation with melatonin (1.3 mM) up to 75% (P < 0.001). These data show that the antiproliferative effects of tamoxifen and ethanol, respectively, on mouse hepatoma cell line HEPA 1-6 are enhanced by melatonin. Although at the conditions described here the antiproliferative effects of melatonin occur at supraphysiological concentrations, these data may help to support clinical studies where melatonin is given simultaneously with tamoxifen or other standard chemotherapeutica.