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.     

Melatonin reduces indomethacin‐induced gastric mucosal cell apoptosis by preventing mitochondrial oxidative stress and the activation of mitochondrial pathway of apoptosis

Abstract: Augmentation of gastric mucosal cell apoptosis due to development of oxidative stress is one of the main pathogenic events in the development of nonsteroidal anti‐inflammatory drug (NSAID)‐induced gastropathy. Identification of a nontoxic, anti‐apoptotic molecule is warranted for therapy against NSAID‐induced gastropathy. The objective of the present study was to define the mechanism of the anti‐apoptotic effect of melatonin, a nontoxic molecule which scavenges reactive oxygen species. Using an array of experimental approaches, we have shown that melatonin prevents the development of mitochondrial oxidative stress and activation of mitochondrial pathway of apoptosis induced by indomethacin (a NSAID) in the gastric mucosa. Melatonin inhibits the important steps of indomethacin‐induced activation of mitochondrial pathway of apoptosis such as upregulation of the expression of Bax and Bak, and the downregulation of Bcl‐2 and BclxL. Melatonin also prevents indomethacin‐induced mitochondrial translocation of Bax and prevents the collapse of mitochondrial membrane potential. Moreover, melatonin reduces indomethacin‐mediated activation of caspase‐9 and caspase‐3 by blocking the release of cytochrome c and finally rescues gastric mucosal cells from indomethacin‐induced apoptosis as measured by the TUNEL assay. Histologic studies of gastric mucosa further document that melatonin almost completely protects against gastric damage induced by indomethacin. Thus, melatonin has significant anti‐apoptotic effects to protect gastric mucosa from NSAID‐induced apoptosis and gastropathy, which makes its use as potential therapy against gastric damage during NSAID treatment.     

Melatonin promotes angiogenesis during protection and healing of indomethacin‐induced gastric ulcer: role of matrix metaloproteinase‐2

Abstract: Matrix metalloproteinase (MMP)‐2 is considered as a crucial regulator of angiogenesis, a process of new blood vessel formation. We reported previously that melatonin (N‐acetyl‐5‐methoxy tryptamine), an antioxidant and anti‐inflammatory agent, prevents indomethacin‐induced gastric ulcers. Herein, we investigated the effect of melatonin on MMP‐2‐mediated angiogenesis during gastroprotection. Angiogenic properties of melatonin were tested in both rat corneal micropocket assay and in mouse model of indomethacin‐induced gastric lesions. Melatonin augmented angiogenesis that was associated with amelioration of MMP‐2 expression and activity and, upregulation of vascular endothelial growth factor (VEGF) in rat cornea. Melatonin prevented gastric lesions by promoting angiogenesis via upregulation of VEGF followed by over‐expression of MMP‐2. Similarly, healing of gastric lesions was associated with early expression of VEGF followed by MMP‐2. In addition, upregulation of MMP‐2 was parallel to MMP‐14 and inverse to tissue inhibitor of metalloprotease (TIMP)‐2 expression during gastroprotection. Our data demonstrated that melatonin exerts angiogenesis through MMP‐2 and VEGF over‐expression during protection and healing of gastric ulcers. This study highlights for the first time a phase‐associated regulation of MMP‐2 activity in gastric mucosa and an angiogenic action of melatonin to rescue indomethacin‐induced gastropathy.     

Melatonin ameliorates myocardial ischemia reperfusion injury through SIRT3‐dependent regulation of oxidative stress and apoptosis

Sirtuins are a family of highly evolutionarily conserved nicotinamide adenine nucleotide‐dependent histone deacetylases. Sirtuin‐3 (SIRT3) is a member of the sirtuin family that is localized primarily to the mitochondria and protects against oxidative stress‐related diseases, including myocardial ischemia/reperfusion (MI/R) injury. Melatonin has a favorable effect in ameliorating MI/R injury. We hypothesized that melatonin protects against MI/R injury by activating the SIRT3 signaling pathway. In this study, mice were pretreated with or without a selective SIRT3 inhibitor and then subjected to MI/R operation. Melatonin was administered intraperitoneally (20 mg/kg) 10 minutes before reperfusion. Melatonin treatment improved postischemic cardiac contractile function, decreased infarct size, diminished lactate dehydrogenase release, reduced the apoptotic index, and ameliorated oxidative damage. Notably, MI/R induced a significant decrease in myocardial SIRT3 expression and activity, whereas the melatonin treatment upregulated SIRT3 expression and activity, and thus decreased the acetylation of superoxide dismutase 2 (SOD2). In addition, melatonin increased Bcl‐2 expression and decreased Bax, Caspase‐3, and cleaved Caspase‐3 levels in response to MI/R. However, the cardioprotective effects of melatonin were largely abolished by the selective SIRT3 inhibitor 3‐(1H‐1,2,3‐triazol‐4‐yl)pyridine (3‐TYP), suggesting that SIRT3 plays an essential role in mediating the cardioprotective effects of melatonin. In vitro studies confirmed that melatonin also protected H9c2 cells against simulated ischemia/reperfusion injury (SIR) by attenuating oxidative stress and apoptosis, while SIRT3‐targeted siRNA diminished these effects. Taken together, our results demonstrate for the first time that melatonin treatment ameliorates MI/R injury by reducing oxidative stress and apoptosis via activating the SIRT3 signaling pathway.     

Melatonin attenuated early brain injury induced by subarachnoid hemorrhage via regulating NLRP3 inflammasome and apoptosis signaling

Subarachnoid hemorrhage (SAH) is a devastating condition with high morbidity and mortality rates due to the lack of effective therapy. Nucleotide‐binding oligomerization domain‐like receptor family pyrin domain‐containing 3 (NLRP3) inflammasome activation associated with the upregulation of apoptotic signaling pathway has been implicated in various inflammatory diseases including hemorrhagic insults. Melatonin is reported to possess substantial anti‐inflammatory properties, which is beneficial for early brain injury (EBI) after SAH. However, the molecular mechanisms have not been clearly identified. This study was designed to investigate the protective effects of melatonin against EBI induced by SAH and to elucidate the potential mechanisms. The adult mice were subjected to SAH. Melatonin or vehicle was injected intraperitoneally 2 hr after SAH. Melatonin was neuroprotective, as shown by increased survival rate, as well as elevated neurological score, greater survival of neurons, preserved brain glutathione levels, and reduced brain edema, malondialdehyde concentrations, apoptotic ratio, and blood–brain barrier (BBB) disruption. Melatonin also attenuated the expressions of NLRP3, apoptosis‐associated speck‐like protein containing a caspase recruitment domain (ASC), cleaved caspase‐1, interleukin‐1β (IL‐1β), and interleukin‐6 (IL‐6); these changes were also associated with an increase in the anti‐apoptotic factor (Bcl2) and reduction in the pro‐apoptotic factor (Bim). In summary, our results demonstrate that melatonin treatment attenuates the EBI following SAH by inhibiting NLRP3 inflammasome‐associated apoptosis.     

Melatonin promotes sorafenib‐induced apoptosis through synergistic activation of JNK/c‐jun pathway in human hepatocellular carcinoma

Melatonin has been shown to exert anticancer activity on hepatocellular carcinoma (HCC) through its antiproliferative and pro‐apoptotic effect in both experimental and clinical studies, and sorafenib is the only approved drug for the systemic treatment of HCC. Thus, this study was designed to investigate the combined effect of melatonin and sorafenib on proliferation, apoptosis, and its possible mechanism in human HCC. Here, we found that both melatonin and sorafenib resulted in a dose‐dependent growth inhibition of HuH‐7 cells after 48 hours treatment, and the combination of them enhanced the growth inhibition in a synergistic manner. Colony formation assay indicated that co‐treatment of HuH‐7 cells with melatonin and sorafenib significantly decreased the clonogenicity compared to the treatment with single agent. Furthermore, FACS and TUNEL assay confirmed that melatonin synergistically augmented the sorafenib‐induced apoptosis after 48 hours incubation, which was in accordance with the activation of caspase‐3 and the JNK/c‐jun pathway. Inhibition of JNK/c‐jun pathway with its inhibitor SP600125 reversed the phosphorylation of c‐jun and the activation of caspase‐3 induced by co‐treatment of HuH‐7 cells with melatonin and sorafenib in a dose‐dependent manner. Furthermore, SP600125 exhibited protective effect against apoptosis induced by the combination of melatonin and sorafenib. This study demonstrates that melatonin in combination with sorafenib synergistically inhibits proliferation and induces apoptosis in human HCC cells; therefore, supplementation of sorafenib with melatonin may serve as a potential therapeutic choice for advanced HCC.     

Melatonin inhibits matrix metalloproteinase‐9 activity by binding to its active site

The zinc‐dependent matrix metalloproteinases (MMPs) are key enzymes associated with extracellular matrix (ECM) remodeling; they play critical roles under both physiological and pathological conditions. MMP‐9 activity is linked to many pathological processes, including rheumatoid arthritis, atherosclerosis, gastric ulcer, tumor growth, and cancer metastasis. Specific inhibition of MMP‐9 activity may be a promising target for therapy for diseases characterized by dysregulated ECM turnover. Potent MMP‐9 inhibitors including an indole scaffold were recently reported in an X‐ray crystallographic study. Herein, we addressed whether melatonin, a secretory product of pineal gland, has an inhibitory effect on MMP‐9 function. Gelatin zymographic analysis showed a significant reduction in pro‐ and active MMP‐9 activity in vitro in a dose‐ and time‐dependent manner. In addition, a human gastric adenocarcinoma cell line (AGS) exhibited a reduced (~50%) MMP‐9 expression when incubated with melatonin, supporting an inhibitory effect of melatonin on MMP‐9. Atomic‐level interaction between melatonin and MMP‐9 was probed with computational chemistry tools. Melatonin docked into the active site cleft of MMP‐9 and interacted with key catalytic site residues including the three histidines that form the coordination complex with the catalytic zinc as well as proline 421 and alanine 191. We hypothesize that under physiological conditions, tight binding of melatonin in the active site might be involved in reducing the catalytic activity of MMP‐9. This finding could provide a novel approach to physical docking of biomolecules to the catalytic site of MMPs, which inhibits this protease, to arrest MMP‐9‐mediated inflammatory signals.     

Melatonin potentiates the antiproliferative and pro‐apoptotic effects of ursolic acid in colon cancer cells by modulating multiple signaling pathways

Ursolic acid (UA), a natural pentacyclic triterpenoid carboxylic acid, is largely distributed in medical herbs and edible plants. Melatonin is an indoleamine compound produced in the pineal gland and also a plant‐derived product. Both UA and melatonin have been shown to inhibit cancer cell growth in numerous studies, but they have never been combined altogether as an anticolon cancer treatment. In this study, we investigated whether the association between UA and melatonin leads to an enhanced antiproliferative and pro‐apoptotic activities in colon cancer SW480 and LoVo cells. We found that combined treatment with UA and melatonin significantly enhanced inhibition of cell viability and migration, promoted changes in cell morphology and spreading, and increased induction of apoptosis, thereby potentiating the effects of UA alone in colon cancer cells. Moreover, we found that the enhanced effects of UA and melatonin combination are mediated through simultaneous modulation of cytochrome c/caspase, MMP9/COX‐2, and p300/NF‐κB signaling pathways. Combined treatment with UA and melatonin triggered the release of cytochrome c from the mitochondrial intermembrane space into the cytosol, induced cleavage of caspase and PARP proteins, enhanced inhibition of MMP9 and COX‐2 expression, promoted p300 and NF‐κB translocation from cell nuclei to cytoplasm, and abrogated NF‐κB binding and p300 recruitment to COX‐2 promoter in colon cancer cells. These results, therefore, demonstrated that melatonin potentiated the antiproliferative and pro‐apoptotic effects of UA in colon cancer cells by modulating multiple signaling pathways and suggest that such a combinational treatment might potentially become an effective way in colon cancer therapy.     

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

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

Melatonin inhibits cell proliferation and induces caspase activation and apoptosis in human malignant lymphoid cell lines

Abstract: Melatonin exerts strong anti‐tumour activity via several mechanisms, including anti‐proliferative and pro‐apoptotic effects in addition to its potent antioxidant activity. Several studies have investigated the effects of melatonin on haematological malignancies. However, the previous studies investigating lymphoid malignancies have been largely restricted to a single type of malignancy, Burkitt’s lymphoma (BL). Thus, we examined the actions of melatonin on the growth and apoptosis in a small panel of cell lines representing different human lymphoid malignancies including Ramos (Epstein–Barr virus–negative BL), SU‐DHL‐4 (diffuse large B cell lymphoma), DoHH2 (follicular B non‐Hodgkin lymphoma) and JURKAT (acute T cell leukaemia). We showed that melatonin promotes cell cycle arrest and apoptosis in all these cells, although there was marked variations in responses among different cell lines (sensitivity; Ramos/DoHH2 > SU‐DHL‐4 > JURKAT). Melatonin‐induced apoptosis was relatively rapid, with increased caspase 3 and PARP cleavage detected within 0.5–1 h following melatonin addition. Moreover, there was evidence for rapid processing of both caspase 9, as well as a breakdown of the mitochondrial inner transmembrane potential. On the contrary, caspase activation was detected only in SU‐DHL‐4 and Ramos cells following melatonin treatment suggesting that the extrinsic pathway does not make a consistent contribution to melatonin‐induced apoptosis in malignant lymphocytes. Although all cell lines expressed the high‐affinity melatonin receptors, MT1 and MT2, melatonin‐induced caspase activation appeared to be independent these receptors. Our findings confirm that melatonin could be a potential chemotherapeutic/preventive agent for malignant lymphocytes. However, it is necessary to take into account that different lymphoid malignancies may differ in their response to melatonin.     

Melatonin induces pro‐apoptotic signaling pathway in human pancreatic carcinoma cells (PANC‐1)

Abstract: Pancreatic cancer is a highly lethal disease with a poor prognosis for long‐term survival rate at all stages of invasiveness. It responds poorly to radio‐ and chemotherapy because the tumor cells are resistant to apoptosis. Melatonin has been reported to inhibit pancreatic cancer growth in experimental studies in animals but the effect of melatonin on cultured human pancreatic carcinoma cells has not been tested. Moreover, we have recently shown that melatonin stimulates production of two major anti‐apoptotic heat shock proteins, HSP27 and HSP 90, in pancreatic carcinoma cells. This study investigated the changes in intrinsic pathway of apoptosis at the mitochondrial level and cascade of caspases in human pancreatic carcinoma cells (PANC‐1) cells subjected to melatonin and/or luzindole. Melatonin (10^?8–10^?12 m ), the nonselective melatonin receptor antagonist, luzindole (10^?8–10^?12 m ) or a combination of both agents were added to PANC‐1 cell cultures. Cells were harvested, and the cytoplasmic proteins were isolated after 24 and 48 hr of incubation and analyzed employing co‐immunoprecipitation and western blot. Administration of melatonin to the PANC‐1 cells resulted in the stimulation of Bcl‐2/Bax and caspase‐9 proteins levels. The strongest signal of these pro‐apoptotic factors was observed at the low concentration (10^?12 m ) of melatonin. Pretreatment with luzindole alone and prior to the addition of melatonin reversed the stimulatory effect of this indoloamine on Bcl‐2/Bax and caspase‐9 proteins expression in PANC‐1 cells. This is the first study to demonstrate a pro‐apoptotic effect of low (physiological) concentration of melatonin on the pancreatic carcinoma cells. In conclusion, melatonin induced pro‐apoptotic pathways in human pancreatic carcinoma, probably by interaction with the Mel‐1 A/B receptors.     

The inhibition of TNF‐α‐induced leucocyte apoptosis by melatonin involves membrane receptor MT1/MT2 interaction

The pro‐apoptotic signalling cascades induced by tumour necrosis factor‐alpha (TNF‐α) have been intensively studied in multiple cellular systems. So far, it is known that TNF‐α can simultaneously activate survival and apoptotic cell death responses. The balance between these signals determines the ultimate response of the cell to TNF‐α. Moreover, emerging evidence suggests that melatonin may be involved in the protection of different cell types against apoptosis. Thus, the objective of this study was to evaluate the effect of melatonin on TNF‐α‐induced apoptosis in human leucocytes. Cells were treated with TNF‐α alone or in the presence of cycloheximide (CHX), which promotes caspase‐8 activation by eliminating the endogenous caspase‐8 inhibitor, c‐FLIP. Treatment with TNF‐α/CHX led to apoptotic cell death, as ascertained by annexin V/propidium iodide (PI) staining. Likewise, in the presence of CHX, TNF‐α stimulation produced cFLIP down‐regulation and subsequent caspase‐8 activation, thus directly triggering caspase‐3 activation and causing Bid truncation and subsequent caspase‐9 activation. Conversely, pre‐incubation of cells with melatonin inhibited TNF‐α‐/CHX‐evoked leucocyte apoptosis. Similarly, pretreatment of leucocytes with melatonin increased cFLIP protein levels, thereby preventing TNF‐α‐/CHX‐mediated caspase processing. Blockade of melatonin membrane receptor MT1/MT2 or extracellular signal‐regulated kinase (ERK) pathway with luzindole or PD98059, respectively, abolished the inhibitory effects of melatonin on leucocyte apoptosis evoked by TNF‐α/CHX. In conclusion, the model proposed by these findings is that the MT1/MT2 receptors, which are under the positive control of melatonin, trigger an ERK‐dependent signalling cascade that interferes with the anti‐apoptotic protein cFLIP modulating the cell life/death balance of human leucocytes.     

Role of melatonin in regulating matrix metalloproteinase-9 via tissue inhibitors of metalloproteinase-1 during protection against endometriosis

Abstract:  Endometriosis is a gynecological disease of women and plausibly regulated by matrix metalloproteinases (MMPs). However, mechanisms of alterations in MMPs during endometriosis remain unclear. Human endometriotic tissues possessing varying degrees of severity were examined for expression of MMPs and tissue inhibitors of metalloproteinase (TIMP)-1. In addition, endometriosis was generated in mice and endometriotic tissues were tested for MMP-9 activity. Results show significant upregulation of secreted and synthesized proMMP-9 activity with duration and severity of endometriosis. Along with upregulation of activity, the expression of proMMP-9 was found increased while TIMP-1 expression followed an inverse trend. The effect of melatonin, a major secretory product of the pineal gland, on endometriosis was examined in preventive and therapeutic models in mice. The results show that melatonin arrested lipid peroxidation and protein oxidation and downregulated proMMP-9 activity and expression in a time and dose-dependent manner while protecting and regressing peritoneal endometriosis. Moreover, the attenuated activity and expression of proMMP-9 were associated with subsequent elevation in the expression of TIMP-1. Our study reveals for the first time the role of melatonin in arresting peritoneal endometriosis in mice and a novel marker, expression ratio of proMMP-9 versus TIMP-1, was identified for assessing severity and progression of endometriosis.     

Melatonin‐enhanced autophagy protects against neural apoptosis via a mitochondrial pathway in early brain injury following a subarachnoid hemorrhage

Melatonin is a strong antioxidant that has beneficial effects against early brain injury (EBI) following a subarachnoid hemorrhage (SAH) in rats; protection includes reduced mortality and brain water content. The molecular mechanisms underlying these clinical effects in the SAH model, however, have not been clearly identified. This study was undertaken to determine the influence of melatonin on neural apoptosis and the potential mechanism of these effects in EBI following SAH using the filament perforation model of SAH in male Sprague Dawley rats. Melatonin (150 mg/kg) or vehicle was given via an intraperitoneal injection 2 hr after SAH induction. Brain samples were extracted 24 hr after SAH. The results show that melatonin treatment markedly reduced caspase‐3 activity and the number of TUNEL‐positive cells, while the treatment increased the LC3‐II/LC3‐I, an autophagy marker, which indicated that melatonin‐enhanced autophagy ameliorated apoptotic cell death in rats subjected to SAH. To further identify the mechanism of autophagy protection, we demonstrated that melatonin administration reduced Bax translocation to the mitochondria and the release of cytochrome c into the cytosol. Taken together, this report demonstrates that melatonin improved the neurological outcome in rats by protecting against neural apoptosis after the induction of filament perforation SAH; moreover, the mechanism of these antiapoptosis effects was related to the enhancement of autophagy, which ameliorated cell apoptosis via a mitochondrial pathway.     

Simultaneous modulation of COX-2, p300, Akt, and Apaf-1 signaling by melatonin to inhibit proliferation and induce apoptosis in breast cancer cells

Melatonin exhibits anti-inflammatory and anticancer effects and could be a chemopreventive and chemotherapeutic agent against cancers, but the precise mechanisms involved remain largely unresolved. In this study, we evaluated the mechanism of action of melatonin in human MDA-MB-361 breast cancer cells. Melatonin at pharmacological concentrations (10(-3) m) significantly suppressed cell proliferation and induced apoptosis in a dose-dependent manner. The observed suppression of proliferation was accompanied by the melatonin-mediated inhibition of COX-2, p300, and NF-κB signaling. Melatonin significantly inhibited COX-2 expression and prostaglandin E(2) (PGE2) production, abrogated p300 histone acetyltransferase activity and p300-mediated NF-κB acetylation, thereby blocking NF-κB binding and p300 recruitment to COX-2 promoter. Pretreatment with a COX-2- or p300-selective inhibitor abrogated the melatonin-induced inhibition of cell proliferation, whereas PGE2 treatment or COX-2 transfection reversed the inhibition by melatonin. Moreover, melatonin markedly inhibited phosphorylation of PI3K, Akt, PRAS40, and GSK-3 proteins, thereby inactivating the PI3K/Akt signaling pathway. Pretreatment with a PI3K- or an Akt-selective inhibitor or an Akt-specific siRNA blocked the melatonin-mediated inhibition of cell proliferation. Conversely, gene delivery of a constitutively active Akt effectively reversed the inhibition by melatonin. Furthermore, melatonin induced Apaf-1 expression, triggered cytochrome C release, and stimulated caspase-3 and caspase-9 activities and cleavage, leading to an activation of the Apaf-1-dependent apoptotic pathway. Pretreatment with an Apaf-1-specific siRNA effectively attenuated the melatonin-induced apoptosis. These results therefore indicate that melatonin inhibits cell proliferation and induces apoptosis in MDA-MB-361 breast cancer cells in vitro by simultaneously suppressing the COX-2/PGE2, p300/NF-κB, and PI3K/Akt/signaling and activating the Apaf-1/caspase-dependent apoptotic pathway.     

Prognostic significance of p53 and matrix metalloproteinase-9 expression in follicular lymphoma

Objectives: p53 mutations and high protein expression are associated with adverse prognosis in several lymphoma subtypes. Matrix metalloproteinase‐9 (MMP‐9) has also been found to correlate with poor survival in all lymphomas studied. The data concerning the clinical role of protein expression of p53 or gelatinases and their inhibitors in follicular lymphoma are rare. The purpose of this study was to evaluate the prognostic and clinical implications of the immunoreactive proteins p53, MMP‐2, MMP‐9, tissue inhibitor of matrix metalloproteinase‐1 (TIMP‐1) and TIMP‐2 in follicular lymphoma. Methods: The material consisted of 67 patients with primarily non‐transformed follicular lymphoma. Diagnostic lymph node tissue sections of patients were stained by immunohistochemical method using specific monoclonal antibodies. Results: p53 over‐expression was detected in 8 (12%) out of 67 cases. p53 over‐expression correlated with high grade (P = 0.011), bulky tumour (P = 0.031) and forthcoming transformation (P = 0.001). It also correlated with poor overall (P = 0.001) and cause‐specific survival (P = 0.010) in multivariate analysis and had a strong inverse correlation with time to transformation (P < 0.001). MMP‐2, MMP‐9 and TIMP‐2 expression correlated with high grade. MMP‐9 positivity in centroblasts correlated with good chemotherapy response (P = 0.019), but it was not prognostic for survival. MMP‐2, TIMP‐1 or TIMP‐2 did not associate with survival, either. Conclusions: In this study, p53 over‐expression predicted both transformation to diffuse large B‐cell lymphoma and poorer overall and cause‐specific survival of patients with follicular lymphoma. Expression of gelatinases or their inhibitors did not have any significant correlations with prognosis, although MMP‐9 predicted a good response to first‐line chemotherapy.     

JAK2/STAT3 activation by melatonin attenuates the mitochondrial oxidative damage induced by myocardial ischemia/reperfusion injury

Ischemia/reperfusion injury (IRI) is harmful to the cardiovascular system and causes mitochondrial oxidative stress. Numerous data indicate that the JAK2/STAT3 signaling pathway is specifically involved in preventing myocardial IRI. Melatonin has potent activity against IRI and may regulate JAK2/STAT3 signaling. This study investigated the protective effect of melatonin pretreatment on myocardial IRI and elucidated its potential mechanism. Perfused isolated rat hearts and cultured neonatal rat cardiomyocytes were exposed to melatonin in the absence or presence of the JAK2/STAT3 inhibitor AG490 or JAK2 siRNA and then subjected to IR. Melatonin conferred a cardio‐protective effect, as shown by improved postischemic cardiac function, decreased infarct size, reduced apoptotic index, diminished lactate dehydrogenase release, up‐regulation of the anti‐apoptotic protein Bcl2, and down‐regulation of the pro‐apoptotic protein Bax. AG490 or JAK2 siRNA blocked melatonin‐mediated cardio‐protection by inhibiting JAK2/STAT3 signaling. Melatonin exposure also resulted in a well‐preserved mitochondrial redox potential, significantly elevated mitochondrial superoxide dismutase (SOD) activity, and decreased formation of mitochondrial hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), which indicates that the IR‐induced mitochondrial oxidative damage was significantly attenuated. However, this melatonin‐induced effect on mitochondrial function was reversed by AG490 or JAK2 siRNA treatment. In summary, our results demonstrate that melatonin pretreatment can attenuate IRI by reducing IR‐induced mitochondrial oxidative damage via the activation of the JAK2/STAT3 signaling pathway.