Melatonin: from basic research to cancer treatment clinics

Induction of cell cycle arrest and apoptosis by the ethyl acetate fraction of Kalopanax pictus leaves in human colon cancer cells

Kalopanax pictus is a deciduous tree used in traditional medicine; its leaves are also consumed as a vegetable. In this study, the ethyl acetate fraction of K. pictus leaves (EFK) was tested in vitro for anticancer activity against four cell lines: human colon cancer (HT-29) cells, human stomach cancer (NCI-N87) cells, human breast cancer (MDA-MB231) cells, and mouse melanoma (B16F1) cells. Results indicated that EFK showed the most potent tumor selective growth inhibitory activity against HT-29 cells with less cytotoxic effect on normal cell lines. Cytotoxicity of EFK on HT-29 cells was associated mainly with cell chromatin condensation, DNA fragmentation, and loss of membrane phospholipid asymmetry with appearance of G2/M phase arrest. Cell death induced by EFK displayed features characteristic of apoptosis, and was associated with generation of reactive oxygen species (ROS) and increase of Bax/Bcl-2 ratio. These findings suggest that K. pictus leaves have anticancer properties and may be valuable for application in pharmaceutical industry.

Urinary 6-Sulphatoxymelatonin levels and risk of breast cancer in premenopausal women: the ORDET cohort

BACKGROUND

Lower urinary melatonin levels are associated with a higher risk of breast cancer in postmenopausal women. Literature for premenopausal women is scant and inconsistent.

METHODS

In a prospective case-control study, we measured the concentration of 6-sulphatoxymelatonin (aMT6s) in the 12-hour overnight urine of 180 premenopausal women with incident breast cancer and 683 matched controls.

RESULTS

In logistic regression models, the multivariate odds ratio (OR) of invasive breast cancer for women in the highest quartile of total overnight aMT6s output compared with the lowest was 1.43 [95% confidence interval (CI), 0.83-2.45; P(trend) = 0.03]. Among current nonsmokers, no association was existent (OR, 1.00; 95% CI, 0.52-1.94; P(trend) = 0.29). We observed an OR of 0.68 between overnight urinary aMT6s level and breast cancer risk in women with invasive breast cancer diagnosed >2 years after urine collection and a significant inverse association in women with a breast cancer diagnosis >8 years after urine collection (OR, 0.17; 95% CI, 0.04-0.71; P(trend) = 0.01). There were no important variations in ORs by tumor stage or hormone receptor status of breast tumors.

CONCLUSION

Overall, we observed a positive association between aMT6s and risk of breast cancer. However, there was some evidence to suggest that this might be driven by the influence of subclinical disease on melatonin levels, with a possible inverse association among women diagnosed further from recruitment. Thus, the influence of lag time on the association between melatonin and breast cancer risk needs to be evaluated in further studies.

Melatonin suppresses tumor angiogenesis by inhibiting HIF-1alpha stabilization under hypoxia

Angiogenesis is an important mediator of tumor progression. As tumors expand, diffusion distances from the existing vascular supply increases, resulting in hypoxia in the cancer cells. Sustained expansion of a tumor mass requires new blood vessel formation to provide rapidly proliferating tumor cells with an adequate supply of oxygen and nutrients. The key regulator of hypoxia-induced angiogenesis is the transcription factor known as hypoxia-inducible factor (HIF)-1. HIF-1alpha is stabilized by hypoxia-induced reactive oxygen species (ROS) and enhances the expression of several types of hypoxic genes, including that of the angiogenic activator known as vascular endothelial cell growth factor (VEGF). In this study, we found that melatonin, a small lipophilic molecule secreted primarily by the pineal gland, destabilizes hypoxia-induced HIF-1alpha protein levels in the HCT116 human colon cancer cell line. This destabilization of HIF-1alpha resulted from the antioxidant activity of melatonin against ROS induced by hypoxia. Moreover, under hypoxia, melatonin suppressed HIF-1 transcriptional activity, leading to a decrease in VEGF expression. Melatonin also blocked in vitro tube formation and invasion and migration of human umbilical vein endothelial cells induced by hypoxia-stimulated conditioned media of HCT116 cells. These findings suggest that melatonin could play a pivotal role in tumor suppression via inhibition of HIF-1-mediated angiogenesis.

Melatonin Inhibits Benzene-Induced Lipid Peroxidation in Rat Liver

We studied the antioxidative role of melatonin against benzene toxicity in rat liver. The inhibition of mitochondrial and microsomal lipid peroxidation differed between 24-hour (single-dose), 15-day, and 30-day treatments. Inhibition of mitochondrial lipid peroxidation was the highest after the single dose of melatonin, whereas highest microsomal inhibition was recorded after 30 days of melatonin treatment. No significant difference was recorded between 15-day and 30-day treatments. Cytochrome P 4502E1 (CYP 4502E1) activity declined after the single-dose and 15-day melatonin treatment in the benzene-treated group, but it rose again, though not significantly after 30 days of treatment. Liver histopathology generally supported these findings. Phenol concentration in the urine samples declined in melatonin and benzene-treated rats. Our results show that melatonin affects CYP 4502E1, which is responsible for benzene metabolism. Inhibition of its metabolism correlated with lower lipid peroxidation. In conclusion, melatonin was found to be protective against lipid peroxidation induced by benzene.

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.

Protective effect of melatonin against mitomycin C-induced genotoxic damage in peripheral blood of rats

Mitomycin C (MMC) generates free radicals when metabolized. We investigated the effect of melatonin against MMC-induced genotoxicity in polychromatic erythrocytes and MMC-induced lipid peroxidation in brain and liver homogenates. Rats (N = 36) were classified into 4 groups: control, melatonin, MMC, and MMC + melatonin. Melatonin and MMC doses of 10 mg/kg and 2 mg/kg, respectively, were injected intraperitoneally. Peripheral blood samples were collected at 0, 24, 48, 72, and 96 hours posttreatment and homogenates were obtained at 96 hours posttreatment. The number of micronucleated polychromatic erythrocytes (MN-PCE) per 1000 PCE was used as a genotoxic marker. Malondialdehyde (MDA) plus 4-hydroxyalkenal (4-HDA) levels were used as an index of lipid peroxidation. The MMC group showed a significant increase in MN-PCE at 24, 48, 72, and 96 hours that was significantly reduced with melatonin begin coadministrated. No significant differences were found in lipid peroxidation. Our results indicate that MMC-induced genotoxicity can be reduced by melatonin.

Dietary correlates of urinary 6-sulfatoxymelatonin concentrations in the Nurses' Health Study cohorts

BACKGROUND

Age and certain lifestyle factors, including a higher body mass index and exposure to light at night, are related to lower circulating concentrations of melatonin-a hormone with probable cancer-protective properties. Although melatonin is a direct derivative of the essential amino acid tryptophan, little is known about the relation of diet with melatonin concentrations.

OBJECTIVE

The objective was to examine cross-sectional associations of various nutrients and dietary factors as well as food groups with creatinine-adjusted first morning urinary melatonin (6-sulfatoxymelatonin; aMT6s) concentrations.

DESIGN

Participants were 998 healthy women from 2 independent cohorts: the Nurses' Health Study (NHS; n = 585) and NHS II (n = 413). We computed least-squares mean hormone concentrations across categories of dietary variables, with adjustment for total energy intake, age, and other nondietary factors known to be associated with aMT6s concentrations.

RESULTS

In multivariate analyses, we found no significant associations between the intake of various nutrients, including tryptophan and urinary melatonin concentrations. A higher intake of meat, particularly red meat, was associated with lower concentrations of aMT6s (adjusted mean concentrations of aMT6s across increasing quartiles of red meat intake were 17.9, 17.0, 18.1, and 15.3 ng/mg creatinine; P for trend = 0.02). In contrast, neither poultry intake (including turkey) nor fish intake was associated with aMT6s concentrations.

CONCLUSION

Although no specific nutrients were associated with altered concentrations of melatonin, our findings raise the possibility that several specific foods, including red meat, could affect cancer risk through the lowering of melatonin concentrations.

Melatonin exerts differential actions on X-ray radiation-induced apoptosis in normal mice splenocytes and Jurkat leukemia cells

The ability of melatonin as a potent antioxidant was used as a rationale for testing its antiapoptotic ability in normal cells. Recently, melatonin was shown to possess proapoptotic action by increasing reactive oxygen species in certain cancer cells. The modification of radiation-induced apoptosis by melatonin and the expression of apoptosis-associated upstream regulators were studied in normal mice splenocytes and Jurkat T leukemia cells. C57BL/6 mice were exposed to a single whole body X-ray radiation dose of 2 Gy with or without 250 mg/kg melatonin pretreatment. The Jurkat cells were divided into four groups of control, 1 mm melatonin alone, 4 Gy irradiation-only and melatonin pretreatment before irradiation. The highest level of apoptosis in the normal splenic white pulp was detected by TUNEL assay at 8 hr after irradiation. At this time, the apoptotic index of irradiation-only and melatonin pretreatment groups were 35.6% and 20.7%, respectively. This reduced apoptosis by melatonin was associated with the increase of Bcl-2 expression and a reduction of Bax/Bcl-2 ratio through a relative decrease of p53 mRNA and protein. In the Jurkat cells treated with a combination of melatonin and radiation, both Annexin V-FITC(+)/PI(-) and Annexin V-FITC(+) cells were increased at 48 hr after irradiation when compared with irradiation-only or melatonin alone. The expressions of p53 between groups were well correlated with the results of Annexin V binding. The irradiation or melatonin did not influence the JNK1 expression in Jurkat cells. The present results suggest that melatonin enhances radiation-induced apoptosis in Jurkat leukemia cells, while reducing radiation-induced apoptosis in normal mice splenocytes. These differential effects on radiation-induced apoptosis by melatonin might involve the regulation of p53 expression.

Circulating melatonin and the risk of breast and endometrial cancer in women

Several decades of observational data have accumulated to implicate a potential role for melatonin in cancer prevention. Experimental studies suggest that the antineoplastic action of melatonin arises through many different mechanisms, including melatonin's antioxidant, antimitotic, and antiangiogenic activity, as well as its ability to modulate the immune system and alter fat metabolism. Melatonin interacts with membrane and nuclear receptors, and may be linked to the regulation of tumor growth. Of particular relevance to breast cancer risk, melatonin may also block the estrogen receptor ERalpha and impact the enzyme aromatase, which produces estradiol. A growing number of epidemiologic studies have evaluated the relationship between night shift work as well as how varying duration of sleep affects peak melatonin secretion at night. While the studies demonstrate lower nightly melatonin levels in night workers, the evidence for an association between sleep duration and melatonin production is less clear. Similarly, both case-control and prospective cohort studies have consistently linked night shift work with breast cancer risk and, more recently, endometrial cancer - another tumor highly sensitive to estrogens. While, to date, the evidence for an association between sleep duration and breast cancer risk is less convincing, overall, there is increasing support for a potentially important link between melatonin and breast cancer risk and perhaps the risk of other tumors. As evidence increases, modifiable factors that have been shown to affect melatonin production, such as night shift work, are likely to gain increasing recognition as potential public health hazards. Additional studies are needed to delineate further the potential of melatonin in cancer prevention.

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 delivery in solid lipid nanoparticles: prevention of cyclosporine A induced cardiac damage

Melatonin is a potent antioxidant molecule with a capacity to protect tissues from damage caused by oxidative stress. It reduces cyclosporine A (CsA)-induced cardiotoxicity; this improvement required melatonin's binding to its membrane receptors. This experimental study examined whether melatonin is a useful tool for counteracting CsA-induced apoptosis in the heart of rats. We investigated melatonin's antiapoptotic efficacy in protecting the heart and tested whether this effect was totally dependent on its binding to membrane receptors or also involved radical scavenging. In some animals, solid lipid nanoparticles (SLN) as a melatonin delivery system were used. In one group of rats, melatonin (1 mg/kg/day i.p.) was given concurrently with CsA (15 mg/kg/day s.c.; CsA-MT) for 21 days. In other animals, melatonin loaded in SLN was injected with CsA (CsA-MTSLN). Oxidative stress in heart tissue was estimated using the evaluation of lipid peroxidation and the expression of the isoform of inducible nitric oxide (iNOS). The antiapoptotic effect of melatonin was evaluated using TUNEL staining and Bcl-2 protein family expression. CsA administration produced morphological and biochemical changes in the heart of rats, while melatonin reversed the changes. In particular, since the antiapoptotic melatonin's efficacy is mainly observed when it is loaded in SLN, we suggest that MT1/MT2 pathway is not sufficient for apoptosis antagonism and the additional intracellular effects may be required. Finally, we show that, (i) melatonin significantly reduces CsA cardiotoxicity acting also on apoptotic processes, and (ii) the reduction in CsA-induced cardiotoxicity is mediated mainly by its antioxidant effect.

Melatonin and breast cancer: cellular mechanisms, clinical studies and future perspectives

Recent studies have suggested that the pineal hormone melatonin may protect against breast cancer, and the mechanisms underlying its actions are becoming clearer. Melatonin works through receptors and distinct second messenger pathways to reduce cellular proliferation and to induce cellular differentiation. In addition, independently of receptors melatonin can modulate oestrogen-dependent pathways and reduce free-radical formation, thus preventing mutation and cellular toxicity. The fact that melatonin works through a myriad of signalling cascades that are protective to cells makes this hormone a good candidate for use in the clinic for the prevention and/or treatment of cancer. This review summarises cellular mechanisms governing the action of melatonin and then considers the potential use of melatonin in breast cancer prevention and treatment, with an emphasis on improving clinical outcomes.

Urinary melatonin levels and postmenopausal breast cancer risk in the Nurses' Health Study cohort

BACKGROUND

Melatonin seems to play a role in breast cancer etiology, but data addressing the association between melatonin levels and breast cancer risk in postmenopausal women is sparse.

METHODS

We conducted a nested case-control study in the Nurses' Health Study cohort. First spot morning urine was collected from 18,643 cancer-free women from March 2000 through December 2002. The concentration of the major metabolite of melatonin, 6-sulfatoxymelatonin (aMT6s), was available for 357 postmenopausal women who developed incident breast cancer through May 31, 2006, along with 533 matched control subjects. We used multivariable conditional logistic regression models to investigate associations. All statistical tests were two sided.

RESULTS

An increased concentration of urinary aMT6s was statistically significantly associated with a lower risk of breast cancer (odds ratio for the highest versus lowest quartile of morning urinary aMT6s, 0.62; 95% confidence interval, 0.41-0.95; P(trend) = 0.004). There was no apparent modification of risk by hormone receptor status of breast tumors, age, body mass index, or smoking status.

CONCLUSION

Results from this prospective study add substantially to the growing literature that supports an inverse association between melatonin levels and breast cancer risk.

Melatonin and ulcerative colitis: evidence, biological mechanisms, and future research

Ulcerative colitis (UC) is an inflammatory bowel disease that afflicts up to 1 million people in the US. Current treatments for UC are mostly nonspecific, not always effective, and often accompanied by serious side effects. Therefore, there is considerable interest in finding alternative and more tolerable treatments for this disease. Physiologic data suggest that melatonin is an important regulator of both inflammation and motility in the gastrointestinal tract, and data from in vitro studies, animal experiments, and limited studies in humans suggest that supplemental melatonin may have an ameliorative effect on colitis. In this review we summarize the evidence regarding melatonin as a possible therapeutic agent in UC and discuss possible biological mechanisms and directions for future research.

Antioxidant therapy and neuroprotection in the newborn

Injury to the perinatal brain is a leading cause of childhood mortality and lifelong disability. Despite recent improvements in neonatal care, no effective treatment for perinatal brain lesions is available. The newborn, especially if preterm, is highly prone to oxidative stress (OS) and to the toxic effect of free radicals (FRs). At birth, the newborn is exposed to a relatively hyperoxic environment caused by an increased oxygen bioavailability with greatly enhanced generation of FRs. Additional sources (e.g., inflammation, hypoxia, ischemia, glutamate and free iron release) occur, magnifying OS. In the preterm baby, the perinatal transition is accompanied by the immaturity of the antioxidant systems and the reduced ability to induce efficient homeostatic mechanisms designed to control overproduction of cell-damaging FRs. Improved understanding of the pathophysiological mechanism involved in perinatal brain lesions helps to identify potential targets for neuroprotective interventions, and the knowledge of these mechanisms has enabled scientists to develop new therapeutic strategies that have confirmed their neuroprotective effects in animal studies. Considering the growing role of OS in preterm newborn morbidity in respect to the higher risk of FR damage in these babies, erythropoietin, allopurinol, melatonin and hypothermia demonstrate great promise as potential neuroprotectans. This article provides an overview of the pathogenesis of FR-mediated diseases of the newborn and the antioxidant strategies now tested in order to reduce OS and its damaging effects.

Metabolism of melatonin by cytochrome P450s in rat liver mitochondria and microsomes

In the present study we provide direct evidence for the involvement of rat microsomal cytochrome P450s in melatonin O-demethylation and hydroxylation at two different positions: 2 and 6, as well as generation of N(1)-acetyl-N(2)-formyl-5-methoxy-kynuramine (AFMK) and two unknown products. Moreover, we found that mitochondrial cytochrome P450s also converts melatonin into AFMK, N-acetylserotonin, 2-hydroxymelatonin, 6-hydroxymelatonin and the same two unknown products. Eadie-Hofstee plots for 6-hydroxylation and O-demethylation reactions were curvilinear for all tested fractions, suggestive of involvement of at least two components, one with a high affinity and low capacity, and another with a low affinity and high capacity. Mitochondrial cytochrome P450s exhibited higher affinity (suggesting lower K(m) value) and higher V(max) for melatonin 6-hydroxylation and O-demethylation for both high-affinity and low-affinity components as compared with microsomal enzymes. The intrinsic clearance for melatonin hydroxylation by high- and low-affinity components displayed the highest values in all tested fractions, indicating that both mitochondrial and microsomal cytochrome P450s metabolize melatonin principally by 6-hydroxylation, with O-demethylation representing a minor metabolic pathway.

Epigenetic targets for melatonin: induction of histone H3 hyperacetylation and gene expression in C17.2 neural stem cells

We have reported the induction of glial cell line-derived neurotrophic factor, a potent survival factor for dopaminergic neurons, in the C17.2 neural stem cell line following in vitro treatment with melatonin. Furthermore, we have detected the melatonin MT(1) receptor in these cells. Given these findings and recent evidence that melatonin may play a role in cellular differentiation, we examined whether this indoleamine induces morphological and transcriptional changes suggestive of a neuronal phenotype in C17.2 cells. Moreover, in order to extend preliminary evidence of a potential role for melatonin in epigenetic modulation, its effects on the mRNA expression of several histone deacetylase (HDAC) isoforms and on histone acetylation were examined. Physiological concentrations of melatonin (nanomolar range) increased neurite-like extensions and induced mRNA expression of the neural stem cell marker, nestin, the early neuronal marker beta-III-tubulin and the orphan nuclear receptor nurr1 in C17.2 cells. The indoleamine also significantly increased mRNA expression for various HDAC isoforms, including HDAC3, HDAC5, and HDAC7. Importantly, treatment with melatonin for 24 hr caused a significant increase in histone H3 acetylation, which is associated with chromatin remodeling and gene transcription. Since the melatonin MT(2) receptor was not detected in C17.2 cells, it is likely that the MT(1) receptor is involved in mediating these physiological effects of melatonin. These findings suggest novel roles for melatonin in stem cell differentiation and epigenetic modulation of gene transcription.

Therapeutic Actions of Melatonin in Cancer: Possible Mechanisms

Melatonin is a phylogenetically well-preserved molecule with diverse physiological functions. In addition to its well-known regulatory control of the sleep/wake cycle, as well as circadian rhythms generally, melatonin is involved in immunomodulation, hematopoiesis, and antioxidative processes. Recent human and animal studies have now shown that melatonin also has important oncostatic properties. Both at physiological and pharmacological doses melatonin exerts growth inhibitory effects on breast cancer cell lines. In hepatomas, through its activation of MT 1 and MT2 receptors, melatonin inhibits linoleic acid uptake, thereby preventing the formation of the mitogenic metabolite 1,3-hydroxyoctadecadienoic acid. In animal model studies, melatonin has been shown to have preventative action against nitrosodiethylamine (NDEA)-induced liver cancer. Melatonin also inhibits the growth of prostate tumors via activation of MT1 receptors thereby inducing translocation of the androgen receptor to the cytoplasm and inhibition of the effect of endogenous androgens. There is abundant evidence indicating that melatonin is involved in preventing tumor initiation, promotion, and progression. The anticarcinogenic effect of melatonin on neoplastic cells relies on its antioxidant, immunostimulating, and apoptotic properties. Melatonin's oncostatic actions include the direct augmentation of natural killer (NK) cell activity, which increases immunosurveillance, as well as the stimulation of cytokine production, for example, of interleukin (IL)-2, IL-6, IL-12, and interferon (IFN)-γ. In addition to its direct oncostatic action, melatonin protects hematopoietic precursors from the toxic effect of anticancer chemotherapeutic drugs. Melatonin secretion is impaired in patients suffering from breast cancer, endometrial cancer, or colorectal cancer. The increased incidence of breast cancer and colorectal cancer seen in nurses and other night shift workers suggests a possible link between diminished secretion of melatonin and increased exposure to light during nighttime. The physiological surge of melatonin at night is thus considered a “natural restraint” on tumor initiation, promotion, and progression.

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.

Frequent silencing of a putative tumor suppressor gene melatonin receptor 1 A (MTNR1A) in oral squamous-cell carcinoma

Array-based comparative genomic hybridization (array-CGH) has good potential for the high-throughput identification of genetic aberrations in cell genomes. In the course of a program to screen a panel of 21 oral squamous-cell carcinoma (OSCC) cell lines for genome-wide copy-number aberrations by array-CGH using our in-house bacterial artificial chromosome arrays, we identified a frequent homozygous deletion at 4q35 loci with approximately 1 Mb in extent. Among the seven genes located within this region, the expression of the melatonin receptor 1 A (MTNR1A) messenger RNA (mRNA) was not detected or decreased in 35 out of the 39 (89%) OSCC cell lines, but was detected in immortalized normal oral epithelial cell line, and was restored in gene-silenced OSCC cells without its homozygous loss after treatment with 5-aza-2'-deoxycytidine. The hypermethylation of the CpG (cytosine and guanine separated by phosphate) island in the promoter region of MTNR1A was inversely correlated with its expression in OSCC lines without a homozygous deletion. Methylation of this CpG island was also observed in primary OSCC tissues. In an immunohistochemical analysis of 50 primary OSCC tumors, the absence of immunoreactive MTNR1A was significantly associated with tumor size and a shorter overall survival in patients with OSCC tumors, and seems to be an independent prognosticator in a multivariate analysis. Exogenous restoration of MTNR1A expression inhibited the growth of OSCC cells lacking its expression. Together with the known tumor-suppressive function of melatonin and MTNR1A in various tumors, our results indicate MTNR1A to be the most likely target for epigenetic silencing at 4q35 and to play a pivotal role during oral carcinogenesis.

Urinary 6-sulfatoxymelatonin levels and risk of breast cancer in postmenopausal women

BACKGROUND

Low urinary melatonin levels have been associated with an increased risk of breast cancer in premenopausal women. However, the association between melatonin levels and breast cancer risk in postmenopausal women remains unclear.

METHODS

We investigated the association between melatonin levels and breast cancer risk in postmenopausal women in a prospective case-control study nested in the Hormones and Diet in the Etiology of Breast Cancer Risk cohort, which included 3966 eligible postmenopausal women. The concentration of melatonin's major metabolite, 6-sulfatoxymelatonin, was measured in a baseline 12-hour overnight urine sample from 178 women who later developed incident breast cancer and from 710 matched control subjects. We used multivariable-adjusted conditional logistic regression models to investigate associations. Relative risks are reported as odds ratios (ORs). All statistical tests were two-sided.

RESULTS

Increased melatonin levels were associated with a statistically significantly lower risk of invasive breast cancer in postmenopausal women (for women in the highest quartile of total overnight 6-sulfatoxymelatonin output vs the lowest quartile, multivariable OR also adjusted for testosterone = 0.56, 95% confidence interval [CI] = 0.33 to 0.97; P(trend) = .02). This association was strongest among never and past smokers (OR = 0.38, 95% CI = 0.20 to 0.74; P(trend) = .001) and after excluding women who were diagnosed with invasive breast cancer within 4 years after urine collection (OR = 0.34, 95% CI = 0.15 to 0.75; P(trend) = .002). We did not observe substantial variation in relative risks by hormone receptor status of breast tumors. Among the 3966 women in the cohort, 40 of the 992 women in the highest quartile of 6-sulfatoxymelatonin developed breast cancer during follow-up, compared with 56 of the 992 women in the lowest quartile of 6-sulfatoxymelatonin.

CONCLUSION

Results from this prospective study provide evidence for a statistically significant inverse association between melatonin levels, as measured in overnight morning urine, and invasive breast cancer risk in postmenopausal women.

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.

Colon Cancer and Physical Activity: A Content Analysis of Reciprocal Relationship

Background

Colon cancer is among the leading causes of cancer mortality and its incidence is increasing worldwide. This is true in spite of broad basic research into colon cancer while, concurrently, physical activity has been shown to offer significant preventive potential. This background led to the formulation of the following research questions: • Why is physical activity so effective in decreasing the incidence of colon cancer? • Is there a common denominator to colon cancer and physical activity, which has a reciprocal function? • Knowing the potential for public health impact of physical activity on colon cancer, has physical activity-colon cancer relationship been in the forefront of research efforts?

Methods

Content analysis of archival literature has been carried out on census of 32,822 message units, extracted from the National Library of Medicine and its PubMed database. The following search terms were used: colon cancer, physical activity, melatonin, age/genetics, diet (obesity, vitamin D, calcium), immunity/inflammation, and bioactive substances incorporating insulin-like growth factor 1, interleukins, and prostaglandins. The research timeframe for each category began with the first article published and ended with the last one printed in 2005.

Results/Conclusions

The effectiveness of physical activity in decreasing the incidence of colon cancer is likely the result of its biologic activity within not one or two but all of the major known colon cancer etiologies, demonstrating a powerful reciprocal relationship. Melatonin is identified as a plausible common denominator of colon cancer and physical activity. The greatest volume of publications deals with colon cancer and genetics. A significant societal health care impact could be achieved by adopting physical activity as a major cancer control strategy.

Night shift work and the risk of endometrial cancer

Melatonin has several oncostatic properties, including possible anti-estrogenic and anti-aromatase activity, and seems to be linked with fat metabolism. Night workers have lower levels of melatonin, which may predispose them to develop cancer. Endometrial cancer risk is influenced significantly by hormonal and metabolic factors; therefore, we hypothesize that night workers may have an increased risk of endometrial cancer. Of the 121,701 women enrolled in a prospective cohort study, 53,487 women provided data on rotating night shift work in 1988 and were followed through on June 1, 2004. A total of 515 women developed medical record-confirmed invasive endometrial cancer. We used Cox regression models to calculate multivariate relative risks (MVRRs), controlling for endometrial cancer risk factors. Women who worked 20+ years of rotating night shifts had a significantly increased risk of endometrial cancer [MVRR, 1.47; 95% confidence interval (95% CI), 1.03-1.14]. In stratified analyses, obese women working rotating night shifts doubled their baseline risk of endometrial cancer (MVRR, 2.09; 95% CI, 1.24-3.52) compared with obese women who did no night work, whereas a nonsignificant increase was seen among non-obese women (MVRR, 1.07; 95% CI, 0.60-1.92). Women working rotating night shifts for a long duration have a significantly increased risk of endometrial cancer, particularly if they are obese. We speculate that this increased risk is attributable to the effects of melatonin on hormonal and metabolic factors. Our results add to growing literature that suggests women who work at night may benefit from cancer prevention strategies.

Involvement of protein kinase C in melatonin's oncostatic effect in C6 glioma cells

Classical anticancer therapies often are ineffective in patients with malignant glioma who have a survival of <1 year. Our previous studies showed a potent inhibitory effect of melatonin on glioma cell proliferation. This effect seems to be mediated by the well-known antioxidant properties of this molecule and the negative regulation of some intracellular effectors, such as the kinase Akt or the transcription factor nuclear factor (NF)-kappaB. Finally, protein kinase C (PKC) also seems to be implicated in this effect although the intracellular pathways involved have not been elucidated. In this study, we analyzed the role of PKC in the regulation by melatonin of intracellular effectors leading to inhibition of cell proliferation. Activation of PKC by incubation with triphorbol ester acetate (TPA) blocks the inhibitory effect of melatonin on Akt and NF-kappaB activity. Moreover, incubation with melatonin induces a decrease in p21 expression in these cells that is partially blocked by co-incubation with TPA. Taken together, these results suggest that melatonin's oncostatic effect on glioma cells is mediated, at least in part, by the inhibition of PKC activity which, in turn, results in Akt and NF-kappaB activity inhibition and modulation of cell cycle-related gene expression.

Somatostatin, retinoids, melatonin, vitamin D, bromocriptine, and cyclophosphamide in chemotherapy-pretreated patients with advanced lung adenocarcinoma and low performance status

BACKGROUND

We previously reported on an improvement in survival and quality of life in chemotherapy-naïve patients with advanced non-small-cell lung cancer and low performance status (PS) treated with a combination of biotherapeutical agents and cyclophosphamide. In this study, we assessed the survival, clinical status, and toxicity of this multidrug regimen in chemotherapy-pretreated patients with advanced lung adenocarcinoma and low PS.

METHODS

Patients with stage IIIB or IV lung adenocarcinoma, who had progressed after prior standard chemotherapy, and with an Eastern Cooperative Oncology Group PS > or = 2, received a daily combination of somatostatin, retinoids, melatonin, vitamin D, bromocriptine, and cyclophosphamide.

RESULTS

Twenty-three (23) patients were enrolled. The median age was 59 years (range, 42-75). The PS was 2 and 3 in 73.9% and 26.1% of patients, respectively. The median overall survival (intent-to-treat analysis) was 95 days (range, 19-214). The side-effects were mild, mostly consisting of diarrhea, nausea and vomiting, and drowsiness of Grade 1-2. There was an improvement in both respiratory and general symptoms, which was more evident in patients surviving more than 95 days.

CONCLUSIONS

The combined regimen of somatostatin, retinoids, melatonin, vitamin D, bromocriptine, and cyclophosphamide is well tolerated and can improve disease-related symptoms in heavily pretreated patients with late-stage lung adenocarcinoma and poor PS.

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

Prostate cancer is a public health problem of the elderly men. It has been estimated that one in six men will develop prostate cancer in his lifetime in the USA. There is thus a huge clinical demand for effective therapies for the prevention and treatment of the disease. Here, the scientific evidence supporting the effectiveness of melatonin in inhibiting the development and progression of prostate cancer is reviewed. The rational use of melatonin in prostate cancer prevention, stabilization of clinically localized favourable-risk prostate cancer and palliative treatment of advanced or metastatic tumour is discussed within the context of the molecular pathogenesis of the disease.

A radiobiological review on melatonin: a novel radioprotector

In spite of the fact that radiotherapy is a common and effective tool for cancer treatment; the radio sensitivity of normal tissues adjacent to the tumor which are unavoidably exposed to radiation limits therapeutic gain. For the sake of improvement in radiation therapy, radiobiology- the study of the action of ionizing radiation on living things- plays a crucial role through explaining observed phenomena, and suggesting improvements to existing therapies. Due to the damaging effects of ionizing radiation, radiobiologists have long been interested in identifying novel, nontoxic, effective, and convenient compounds to protect humans against radiation induced normal tissue injuries. In hundreds of investigations, melatonin (N-acetyl-5-methoxytryptamine), the chief secretory product of the pineal gland in the brain, has been documented to ameliorate the oxidative injuries due to ionizing radiation. This article reviews different features that make melatonin a potentially useful radioprotector. Moreover, based on radiobiological models we can hypothesize that melatonin may postpone the saturation of repair enzymes which leads to repairing more induced damage by repair system and more importantly allows the use of higher doses of radiation during radiotherapy to get a better therapeutic ratio. The implications of the accumulated observations suggest by virtue of melatonin's radioprotective and anticancer effects; it is time to use it as a radioprotector both for radiation workers and patients suffering from cancer either alone for cancer inhibition or in combination with traditional radiotherapy for getting a favorable efficacy/toxicity ratio during the treatment. Although compelling evidence suggests that melatonin may be effective for a variety of disorders, the optimum dose of melatonin for human radioprotection is yet to be determined. We propose that, in the future, melatonin improve the therapeutic ratio in radiation oncology.

Melatonin, environmental light, and breast cancer

Although many factors have been suggested as causes for breast cancer, the increased incidence of the disease seen in women working in night shifts led to the hypothesis that the suppression of melatonin by light or melatonin deficiency plays a major role in cancer development. Studies on the 7,12-dimethylbenz[a]anthracene and N-methyl-N-nitrosourea experimental models of human breast cancer indicate that melatonin is effective in reducing cancer development. In vitro studies in MCF-7 human breast cancer cell line have shown that melatonin exerts its anticarcinogenic actions through a variety of mechanisms, and that it is most effective in estrogen receptor (ER) alpha-positive breast cancer cells. Melatonin suppresses ER gene, modulates several estrogen dependent regulatory proteins and pro-oncogenes, inhibits cell proliferation, and impairs the metastatic capacity of MCF-7 human breast cancer cells. The anticarcinogenic action on MCF-7 cells has been demonstrated at the physiological concentrations of melatonin attained at night, suggesting thereby that melatonin acts like an endogenous antiestrogen. Melatonin also decreases the formation of estrogens from androgens via aromatase inhibition. Circulating melatonin levels are abnormally low in ER-positive breast cancer patients thereby supporting the melatonin hypothesis for breast cancer in shift working women. It has been postulated that enhanced endogenous melatonin secretion is responsible for the beneficial effects of meditation as a form of psychosocial intervention that helps breast cancer patients.

Melatonin: therapeutic and clinical utilization

Melatonin, acting through melatonin receptors, is involved in numerous physiological processes including circadian entrainment, blood pressure regulation, oncogenesis, retinal physiology, seasonal reproduction, ovarian physiology, immune function and most recently in inducing osteoblast differentiation. Moreover, melatonin was proved to be a potent-free radical scavenger and a broad-spectrum antioxidant. More research is required into the effects of therapeutically modulating the melatoninergic system on circadian haemodynamics and rhythm under varying physiopathological conditions and the possible impact on morbidity and mortality in humans.

Nutritional and lifestyle correlates of the cancer-protective hormone melatonin

CONTEXT

Despite growing support for melatonin as a promising agent for cancer treatment and possibly cancer prevention, few studies have elucidated factors that influence endogenous melatonin. This overview summarizes dietary and lifestyle factors that have been shown to affect circulating melatonin levels.

BIOLOGICAL MECHANISMS

To date, many animal studies and in vitro experiments have illustrated that melatonin possesses oncostatic activity. Mechanisms that are currently being studied include melatonin's activity as an indirect antioxidant and free radical scavenger; its action on the immune system; suppression of fatty acid uptake and metabolism; and its ability to increase the degradation of calmoduline and to induce apoptosis. Studies further suggest that melatonin reduces local estrogen synthesis, through down-regulation of the hypothalamic-pituitary reproductive axis and direct actions of melatonin at the tumor cell level, thus behaving as a SERM.

THERAPEUTIC APPLICATIONS

Several small clinical trials have demonstrated that melatonin has some potential, either alone or in combination with standard cancer therapy, to yield favorable responses. Melatonin or its precursor tryptophan have been found in numerous edible plants, but more studies are needed to evaluate the influence of diets rich in tryptophan and melatonin on circulating melatonin levels in humans. Age, BMI, parity, and the use of certain drugs remain the factors that have been associated most consistently with aMT6s levels.

DISCUSSION

Further insights into the effects of dietary and lifestyle factors that modulate circulating melatonin levels may provide the basis for novel interventions to exploit melatonin for the prevention and treatment of human diseases.

Quantification of the water/lipid affinity of melatonin and a pinoline derivative in lipid models

This study assessed the location of melatonin (N-acetyl-5-methoxytryptamine) and of a pinoline derivative (GWC22) [6-ethyl-1-(3-methoxyphenyl)-2-propyl-1,2,3,4-tetrahydro-beta-carboline], when present in lipid assemblies such as linoleate micelles, phosphatidylcholine liposomes or low density lipoproteins (LDL). The efficiency of radical scavenging by these compounds is highly dependent on their partitioning between the lipidic and aqueous phases. We determined the proportion of melatonin or GWC22 in the aqueous and lipid phases of each system (concentrations of the antioxidants ranging between 3 x 10(-5) and 10(-4) m) by assaying melatonin or GWC22 by HPLC/UV detection, or by fluorescence for melatonin in micelles. Our results show that melatonin and GWC22 were preferentially located in the aqueous phase of micelles (68.4% and 59.0%, respectively), whereas only 30.5% of melatonin and 39.0% of GWC22 were found in the lipid phase. By contrast, in phosphatidylcholine liposomes, both compounds were essentially present in the lipid phase (73.5% for melatonin and 79.1% for GWC22, versus 25.9% and 19.5% in the aqueous phase, respectively). In the case of LDL, 99.9% of the melatonin added was found in the methanol/water extracting phase containing phospholipids, unesterified cholesterol and apolipoprotein B100. The partitioning of melatonin and GWC22 in linoleate micelles gave new insights on the marked protective effect of GWC22 towards radiation-induced lipid peroxidation and allowed us to determine more accurately the lower limit values of the reaction rate constants of the two molecules studied with lipid peroxyl radicals, i.e. k(LOO.+melatonin)) >or= 9.0 x 10(4)m(-1)s(-1) and k(LOO.+GWC22) >or= 3.5 x 10(5)m(-1)s(-1).

Therapeutic effect of melatonin in patients with functional dyspepsia

BACKGROUND AND GOAL

Melatonin may inhibit reactive oxygen species-related pathogenesis in the alimentary tract by neutralizing free radicals. In the present study we assessed the potential protective action of melatonin in ulcerlike dyspepsia.

STUDY

Sixty patients aged 19 to 39 years with the diagnosis of functional dyspepsia according to the Rome Criteria II and no Helicobacter pylori infection were involved in the study. Melatonin, at a dose of 5 mg (n=30), or placebo (n=30) were taken in the evening for a period of 12 weeks. At this time, patients were on an equivalent diet and were only to take an alkaline drug in case of the abdominal pain.

RESULTS

After 12 weeks, the dyspeptic symptoms completely subsided in 17 patients in the melatonin-treatment group (56.6%). In other 9 individuals (30.0%) a partial improvement in health was achieved, especially in the frequency and intensity of nocturnal pain. After placebo, the majority of patients (93.3%) did not experience any improvement in symptoms. Multivariate analysis indicated that melatonin (odds ratio 95.86, 95% confidence interval 3.72-2469.37, P<0.01) correlated independently with significantly improved patients health. H. pylori past infection decreased positive effect of melatonin in ulcerlike dyspepsia.

CONCLUSIONS

Melatonin can be considered as an auxiliary drug in the treatment of ulcerlike dyspepsia.

Melatonin in pathogenesis and therapy of cancer

Melatonin is a neuroendocrine hormone secreted by the pineal gland to transduce the body's circadian rhythms. An internal 24 hour time keeping system (biological clock) regulated by melatonin, controls the sleep-wake cycle. Melatonin production is a highly conserved evolutionary phenomenon. The indole hormone is synthesized in the pinealocytes derived from photoreceptors. Altered patterns and/or levels of melatonin secretion have been reported to coincide with sleep disorders, jetlag, depression, stress, reproductive activities, some forms of cancer and immunological disorders. Lately, the physiological and pathological role of melatonin has become a priority area of investigation, particularly in breast cancer, melanoma, colon cancer, lung cancer and leukemia. According to the 'melatonin hypothesis' of cancer, the exposure to light at night (LAN) and anthropogenic electric and magnetic fields (EMFs) is related to the increased incidence of breast cancer and childhood leukaemia via melatonin disruption. Melatonin's hypothermic, antioxidant and free radical scavenging properties, attribute it to an immunomodulator and an oncostatic agent as well. Many clinical studies have envisaged the potential therapeutic role of melatonin in various pathophysiological disorders, particularly cancer. A substantial reduction in risk of death and low adverse effects were reported from various randomized controlled trials of melatonin treatment in cancer patients. This review summarizes the physiological significance of melatonin and its potential role in cancer therapy. Furthermore, the article focuses on melatonin hypothesis to represent the cause-effect relationship of the three aspects: EMF, LAN and cancer.

A strategy for controlling potential interactions between natural health products and chemotherapy: a review in pediatric oncology

The high prevalence of complementary and alternative medicine use including natural health products (NHPs) in the pediatric oncology population is well established. The potential for concurrent use of NHPs with conventional chemotherapy necessitates physician awareness regarding the potential risks and benefits that might come from this coadministration. Knowledge of interactions between NHPs and chemotherapy is poorly characterized; however, an understanding of potential mechanisms of interaction by researchers and clinicians is important. Concerns regarding the use of antioxidants during chemotherapy are controversial and evidence exists to support both adherents and detractors in this debate. Our review addresses issues regarding potential interactions between NHPs and chemotherapies used in pediatric oncology from a pharmacokinetic and pharmacodynamic perspective. Examples of combinations of NHP and chemotherapies are briefly presented in addition to a strategy to avoid (or induce) a possible interaction between a NHP and chemotherapy. In conclusion, more clinical research is needed to substantiate or preclude the use of NHPs in the treatment of cancer and especially in combination with chemotherapy.

Primer on integrative oncology

At the present time, there is no obvious answer for many of these design difficulties. This problem will continue to constrain ability to determine the efficacy of integrative medical techniques for patients who have cancer. Patients, however, will continue to gravitate toward alternative treatments, especially when standard cancer treatments fail. Therefore oncologists must be aware of alternative medical agents and techniques, and be able to guide their patients, rather than simply being dismissive.

Melatonin in cancer management: progress and promise

Physiologic and pharmacologic concentrations of the pineal hormone melatonin have shown chemopreventive, oncostatic, and tumor inhibitory effects in a variety of in vitro and in vivo experimental models of neoplasia. Multiple mechanisms have been suggested for the biological effects of melatonin. Not only does melatonin seem to control development alone but also has the potential to increase the efficacy and decrease the side effects of chemotherapy when used in adjuvant settings. This review critically evaluates progress in the ability of melatonin to prevent or reverse cancer development and progression. We also discuss future prospects of the possible development of melatonin as a chemopreventive agent.

Effect and mechanism of melatonin's action on the proliferation of human umbilical vein endothelial cells

Melatonin is the major secretory product of the pineal gland and is considered an important natural oncostatic agent. The anticancer activity of melatonin is due to its immunomodulatory, anti-proliferative and antioxidative effects. At present there are no direct data available as to melatonin's possible influence on angiogenesis, which is a major biological mechanism responsible for tumor growth and dissemination. The current study investigated the influence of melatonin on angiogenesis. Human umbilical vein endothelial cells (HUVECs) were cultured, identified, and purified. Cell growth and viability, DNA fragmentation and cell cycle analyses were determined. To elucidate the mechanism of action of melatonin, Western blot analyses for P53, Bax and Bcl-2 expression were carried out. The results demonstrate the anti-proliferative and apoptosis-inducing effects of melatonin; these changes were associated with cell cycle arrest, upregulation of P53 and Bax and downregulation of Bcl-2. Taken together, our data showed that melatonin in high concentrations markedly reduces HUVECs proliferation, induces cellular apoptosis, and modulates cell cycle length. P53 and Bax/Bcl-2 expression changes may be involved in these actions of melatonin.

Effect of topical melatonin on ultraviolet radiation-induced suppression of Mantoux reactions in humans

BACKGROUND

Melatonin, the central neurohormone in circadian rhythm pathways, is recognized to have a variety of immune-enhancing effects. It has previously been shown to reduce ultraviolet (UV) radiation-induced erythema in mice and in humans, but there are as yet no published studies on the effects of melatonin on UV-induced immunosuppression in humans.

METHODS

We investigated the effects of topical melatonin on solar-simulated (ss) UV-induced suppression of Mantoux reactions in 16 healthy, Mantoux-positive volunteers. Melatonin (5%) and its vehicle were applied in a double-blinded manner to separate areas on the lower back, immediately after each of three consecutive daily ssUV exposures. Various sites on the back received either no irradiation or one of three-graded ssUV doses. Mantoux testing was performed at each site 24 h after the final irradiation, and assessed 72 h later using a reflectance erythema meter. In a separate group of 19 volunteers, the effect of melatonin on minimal erythema dose was assessed both visually and with an erythema meter.

RESULTS

We found dose-responsive UV-induced suppression of the Mantoux response in the presence of both vehicle and melatonin; melatonin did not prevent UV-induced immunosuppression in this model. Melatonin was also found to have no effect on the minimal erythema dose.

CONCLUSIONS

Melatonin conferred no protection against immune suppression or sunburn when applied topically to human skin immediately after irradiation.