Melatonin Induces Melanogenesis in Human SK-MEL-1 Melanoma Cells Involving Glycogen Synthase Kinase-3 and Reactive Oxygen Species.

Melatonin is present in all living organisms where it displays a diversity of physiological functions. Attenuation of melanogenesis by melatonin has been reported in some mammals and also in rodent melanoma cells. However, melatonin may also stimulate melanogenesis in human melanoma cells through mechanisms that have not yet been revealed. Using the human melanoma cells SK-MEL-1 as a model, an increase in both tyrosinase activity and melanin was already observed at 24 h after melatonin treatment with maximal levels of both being detected at 72 h. This effect was associated with the induction in the expression of the enzymes involved in the synthesis of melanin. In this scenario, glycogen synthase kinase-3ß seems to play a significant function since melatonin decreased its phosphorylation and preincubation with specific inhibitors of this protein kinase (lithium or BIO) reduced the expression and activity of tyrosinase. Blocking of PI3K/AKT pathway stimulated melanogenesis and the effect was suppressed by the inhibitors of glycogen synthase kinase-3ß. Although melatonin is a recognized antioxidant, we found that it stimulates reactive oxygen species generation in SK-MEL-1 cells. These chemical species seem to be an important signal in activating the melanogenic process since the antioxidants N-acetyl-l-cysteine and glutathione decreased both the level and activity of tyrosinase stimulated by melatonin. Our results support the view that regulation of melanogenesis involves a cross-talk between several signaling pathways.

Frailty in hemodialysis and prediction of poor short-term outcome: mortality, hospitalization and visits to hospital emergency services.

Background: Frailty is an aging-associated state of increased vulnerability, which raises the risk of adverse outcomes. Chronic kidney disease is associated with higher prevalence of frailty. Our aim was to estimate frailty prevalence in a hemodialysis population and its influence on short-term outcomes. Design: Observational prospective longitudinal study of 277 prevalent hemodialysis patients. Frailty was estimated through the Edmonton Frail Scale (EFS). Demographic and clinical data, comorbidity index, and laboratory parameters were recorded. A 29-month follow-up was conducted on mortality, including hospitalization, and visits to hospital emergency services in the first 12 months of this period. Results: According to the EFS, 82 patients (29.6%) were frail, 53 (19.1%) were vulnerable, and 142 (51.3%) were non-frail. During follow-up, 58.5% frail patients, 30.2% vulnerable, and 16.2% non-frail ones died (p < .005). In the analysis of survival using an adjusted Cox model, a higher hazard of mortality was observed in frail than in non-frail patients (HR 2.34; 95% CI 1.39-3.95; p = .001). During follow-up the hospitalization rate was 852 episodes/1000 patient-years for frail patients, 784 episodes/1000 patient-years for vulnerable patients, and 417 episodes/1000 patient-years for non-frail patients (p = .0005). The incidence ratio of visits to emergency services was 3216, 1735, and 1545 visits/1000 patient-years for each group (p < .001). Conclusions: Hemodialysis patients present high frailty prevalence. Frailty is associated with poor short-term outcomes and higher rates of mortality, visits to hospital emergency services, and hospitalization.

Melatonin enhances hyperthermia-induced apoptotic cell death in human leukemia cells.

Melatonin is an endogenous indoleamine with a wide range of biological functions. In addition to modulating circadian rhythms, it plays important roles in the health as an antioxidant. Melatonin has also the ability to induce apoptosis in cancer cells and to enhance the antitumoral activity of chemotherapeutic agents. In this study, the effect of melatonin on hyperthermia-induced apoptosis was explored using human leukemia cells. The results demonstrate that melatonin greatly improved the cytotoxicity of hyperthermia in U937 cells. The potentiation of cell death was achieved with 1 mmol/L concentrations of the indoleamine but not with concentrations close to physiological levels in blood (1 nmol/L). This effect was associated to an enhancement of the apoptotic response, revealed by an increase in cells with hypodiploid DNA content and activation of multiple caspases (caspase-2, caspase-3, caspase-8, and caspase-9). Melatonin also increased hyperthermia-induced Bid activation as well as translocation of Bax from the cytosol to mitochondria and cytochrome c release. Hyperthermia-provoked apoptosis and potentiation by melatonin were abrogated by a broad-spectrum caspase inhibitor (z-VAD-fmk) as well as by specific inhibitors against caspase-8 or caspase-3. In contrast, blocking of the mitochondrial pathway of apoptosis either with a caspase-9 inhibitor or overexpressing the anti-apoptotic protein Bcl-2 (U937/Bcl-2) reduced the number of apoptotic cells in response to hyperthermia but it was unable to suppress melatonin enhancement. Melatonin appears to modulate the apoptotic response triggered by hyperthermia in a cell type-specific manner as similar results were observed in HL-60 but not in K562 or MOLT-3 cells.

Study of the protective effect on intestinal mucosa of the hydrosoluble fiber Plantago ovata husk.

BACKGROUND: Several studies have indicated that dietary fiber may have a protective effect on gastrointestinal mucosa. The aim of this study was to evaluate the protective action of the soluble fiber Plantago ovata husk against intestinal damage. METHODS: To evaluate the anti-ulcerogenic effect on duodenal mucosa of the soluble fiber Plantago ovata husk, low-dose acetylsalicylic acid (10 mg/kg) was given orally to animals once daily for 14 or 28 days with and without Plantago ovata husk (100 mg/kg). 24 h after final dosing duodenal samples were removed for anatomopathological evaluation. Villi were examined by both light and scanning electron microscopy. RESULTS: Acetylsalicylic acid induced severe lesions in duodenal mucosa of rabbits, including erosions, epithelium disorganization, and cell vacuolization, increasing as well the amount of mononuclear and caliciform cells. Damage was much more severe in animals treated for 28 days. In groups receiving Plantago ovata husk, a significant attenuation of acetylsalicylic acid-induced lesions was already observed in group treated for 14 days, becoming more evident in those treated for 28 days, all of them with duodenal cytoarchitecture normal and similar to control animals. CONCLUSIONS: These findings suggest that Plantago ovata husk may protect intestinal mucosa probably by limiting acetylsalicylic acid penetration into epithelial cells, although further studies are needed to confirm the same effect in other experimental models of induced mucosal damage and to elucidate the mechanisms of fiber protection.

Gardenin B-induced cell death in human leukemia cells involves multiple caspases but is independent of the generation of reactive oxygen species.

Flavonoids have attracted great interest due to their possible anticancer activities. Here we investigated the antiproliferative activity of the flavonoids isolated from Baccharis scandens against human leukemia cell lines and found that the methoxyflavonoid gardenin B was the most cytotoxic compound against HL-60 and U-937 cells, showing IC50 values between 1.6 and 3.0 µM, but had no significant cytotoxic effects against quiescent or proliferating human peripheral blood mononuclear cells. These effects on viability were accompanied by the concentration- and time-dependent appearance of apoptosis as evidenced by DNA fragmentation, formation of apoptotic bodies and a sub-G1 ratio increase. Comparative studies with the best-studied bioflavonoid quercetin indicate that gardenin B is a more cytotoxic and more apoptotic inducer than quercetin. Cell death induced by gardenin B was associated with: (i) a significant induction of caspase-2, -3, -8 and -9 activities; (ii) cleavage of the initiator caspases (caspase-2, -8 and -9), of the executioner caspase-3, and of poly(ADP-ribose) polymerase; and (iii) a concentration-dependent reactive oxygen species generation. In conclusion, apoptosis induced by gardenin B is associated with activation of both the extrinsic and the intrinsic apoptotic pathways of cell death and occurs through a mechanism that is independent of the generation of reactive oxygen species.

Induction of G2-M phase arrest and apoptosis by alpha-methylene-gamma-butyrolactones in human leukemia cells.

In this study, we investigated the effect of three synthetic alpha-methylene-gamma-butyrolactones (MBL) on viability of 10 human tumor cell lines and found that these lactones were highly cytotoxic against leukemia cells. Studies performed on HL-60 cells indicate that MBL induce G(2)-M arrest and apoptosis through a caspase-dependent mechanism. Apoptosis was associated to cytochrome c release, cleavage of procaspases-9 and -3, and hydrolysis of PARP. Intracellular reactive oxygen species (ROS) seem to play a key role since high levels of ROS were produced early (<15 min) and apoptosis was completely abrogated by the free radical scavenger N-acetyl-L-cysteine (NAC).