Resveratrol derivatives potently induce apoptosis in human promyelocytic leukemia cells

Resveratrol has been shown to possess antioxidant and anticancer activities, but little is known on the effect of resveratrol derivatives. Recently we have isolated resveratrol and its dimers and trimers from peony (Paeonia lactiflora) seeds, and reported their strong antioxidant and cytotoxic activity. In the present study, we have evaluated cellular effects of resveratrol derivatives; viniferin, gnetin H, and suffruticosol B on the proliferation and apoptosis in HL-60 cells in vitro. All resveratrol and its derivatives reduced viability of HL-60 cells in a dose-dependent manner with their IC(50) values of 20-90 microM. Ascending orders of IC(50) values were suffruticosol B, gnetin H, viniferin and resveratrol respectively. HL-60 cells treated with the four stilbenes exhibited the distinct morphological changes characteristics of cell apoptosis such as chromatin condensation, apoptotic bodies, and DNA fragmentations. A time-dependent histogram of the cellular DNA analyzed by flow cytometry revealed a rapid increase in subdiploid cells and a concomitant decrease in diploid cells exposed to 100 microM resveratrol for 0-24 h. Cells treated with 25 microM of resveratrol, viniferin, gnetin H, and suffruticosol B for 24 h resulted in increment of sub-G1 population by 51, 5, 11 and 59%, respectively. Treatment of cells with 0-20 microM resveratrol for 5 h produced a concentration-dependent decrease in cytochrome P450 (CYP) 1B1 mRNA levels. Suffruticosol B also suppressed CYP1B1 gene expression. These results demonstrated that resveratrol oligomers also strongly suppressed HL-60 cell proliferation, and induced DNA damage. In addition, CYP1B1 gene supression may suggest an involvement in the resveratrol-induced apoptosis in HL-60 cells.     

Inhibition of gamma ray-induced apoptosis by stimulatory heterotrimeric GTP binding protein involves Bcl-xL down-regulation in SH-SY5Y human neuroblastoma cells

Heterotrimeric GTP-binding proteins (G proteins) transduce extracellular signals into intracellular signals by activating effector molecules including adenylate cyclases that catalyze cAMP formation, and thus regulate various cellular responses such as metabolism, proliferation, and apoptosis. cAMP signaling pathways have been reported to protect cells from ionizing radiation-induced apoptosis, but however, the protective mechanism is not clear. Therefore, this study aimed to investigate the signaling molecules and the mechanism mediating the anti-apoptotic action of cAMP signaling system in radiation-induced apoptosis. Stable expression of a constitutively active mutant of Gas (GalphasQL) protected gamma ray-induced apoptosis which was assessed by analysis of the cleavages of PARP, caspase-9, and caspase-3 and cytochrome C release in SH-SY5Y human neuroblastoma cells. GasQL repressed the gamma ray-induced down-regulation of Bcl-xL protein, but transfection of Bcl-xL siRNA increased the gamma ray-induced apoptosis and abolished the anti-apoptotic effect of GasQL. GasQL decreased the degradation rate of Bcl-xL protein, and it also restrained the decrease in Bcl-xL mRNA by increasing the stability following ionizing irradiation. Furthermore, prostaglandin E2 that activates Gas was found to protect gamma ray-induced apoptosis, and the protective effect was abolished by treatment with prostanoid receptor antagonist specific to EP2/4R subtype. Moreover, specific agonists for adenosine A1 receptor that inhibits cAMP signaling pathway augmented gamma ray-induced apoptosis. From this study, it is concluded that Galphas-cAMP signaling system can protect SH-SY5Y cells from gamma ray-induced apoptosis partly by restraining down-regulation of Bcl-xL expression, suggesting that radiation-induced apoptosis can be modulated by GPCR ligands to improve the efficiency of radiation therapy.     

Luteolin induces mitochondria-dependent apoptosis in human lung adenocarcinoma cell

The effects of luteolin on the proliferation of A549 cells were evaluated by MTT and clone formation assays. DNA ploidy and apoptotic cell percentage were calculated by flow cytometry. The expression of Bax, Bcl-xl, Bcl-2, Mcl-1, caspase-9, caspase-3, and PARP was analyzed by Western blotting. The membrane potential of mitochondria was detected by JC-1 fluorescence microscopy assay. Our results demonstrated that luteolin could inhibit the proliferation of A549 cells via induction of apoptosis, with the evidence of characteristic morphological changes of apoptosis in the nucleus. Furthermore, DNA flow cytometric analysis indicated that luteolin induced a S phase arrest of the cell cycle. The membrane potential of mitochondria was decreased. The protein levels of Bax, Bcl-xl, Bcl-2, Mcl-1, caspase-9, caspase-3, and PARP were activated after treatment with luteolin. Luteolin can inhibit the proliferation of A549 cells and trigger mitochondria- dependent apoptosis in them.     

Chamaejasmine induces apoptosis in human lung adenocarcinoma A549 cells through a Ros-mediated mitochondrial pathway

In the present study, the anticancer activity of chamaejasmine towards A549 human lung adenocarcinoma cells was investigated. In order to explore the underlying mechanism of cell growth inhibition of chamaejasmine, cell cycle distribution, ROS generation, mitochondrial membrane potential (Δψ(m)) disruption, and expression of cytochrome c, Bax, Bcl-2, caspase-3, caspase-9 and PARP were measured in A549 cells. Chamaejasmine inhibited the growth of A549 cells in a time and dose-dependent manner. The IC?? value was 7.72 μM after 72 h treatment. Chamaejasmine arrested the cell cycle in the G2/M phase and induced apoptosis via a ROS-mediated mitochondria-dependent pathway. Western blot analysis showed that chamaejasmine inhibited Bcl-2 expression and induced Bax expression to desintegrate the outer mitochondrial membrane and causing cytochrome c release. Mitochondrial cytochrome c release was associated with the activation of caspase-9 and caspase-3 cascade, and active-caspase-3 was involved in PARP cleavage. All of these signal transduction pathways are involved in initiating apoptosis. To the best of our knowledge, this is the first report demonstrating the cytotoxic activity of chamaejasmine towards A549 in vitro.     

Design,synthesis, cytotoxic activity,and apoptosis inducing effects of 4- and N-substituted benzoyltaurinamide derivatives

In this study, a group of 4-substituted benzoyltaurinamide derivatives were designed, synthesized, and investigated for their anticancer activity against three cancer cell lines and one nontumorigenic cell line by MTT assay. Among the final compounds, methoxyphenyl derivatives 14, 15, 16 were found to be effective against all the tested cancerous cell lines with promising selectivity. The most active compounds were further evaluated to determine the molecular mechanism of their anticancer activity by using western blot assay and the Annexin V-FITC/PI test. Compound 14 (in SH-SY5Y and MDA-MB-231 cell lines) and 15 (in SH-SY5Y cell line) were found to induce intrinsic apoptotic pathway by upregulating BAX, caspase-3, and caspase-9, while downregulating Bcl-2 and Bcl-xL expression levels. According to mechanistic studies, compounds displayed their anticancer activity via three different mechanisms: a. caspase-dependent, b. caspase-independent, and c. caspase-dependent pathway that excluded caspase-9 activation. As a result, this study provides interesting data which can be used to design new taurine-based anticancer derivatives.     

Davidone C Induces the Death of Hepatocellular Carcinoma Cells by Promoting Apoptosis and Autophagy

Davidone C is a newly discovered flavonoid compound purified from the ethyl acetate-soluble fraction of Sophora davidii (Franch.) Skeels. This study explored the anti-tumor activity of davidone C on hepatocellular carcinoma HepG2 and Bel-7402 cells and its mechanism through MTT method, morphological observation, flow cytometry and Western blotting. The results showed that davidone C significantly inhibited the proliferation of HepG2 and Bel-7402 cells in a time- and dose-dependent manner. The morphological changes of apoptotic cells can be observed under an inverted microscope, such as cell floating, chromosome condensation, apoptotic bodies, and other phenomena. The expressions of Bax, cleaved caspase-9, cleaved caspase-3 and cleaved PARP increased with the increase of dosage while Bcl-2 decreased, suggesting that the apoptotic mechanism might be related to the mitochondrial apoptotic pathway. Moreover, davidone C administration can down-regulate the expression of Grp78, and simultaneously up-regulate the expression of caspase-7 and caspase-12, indicating that the apoptotic mechanism might be related to the ERS pathway. In addition, davidone C can down-regulate the expression of p62, and simultaneously up-regulate the expression of LC3-I and LC3-II with a quantitative dependence, suggesting that the mechanism of apoptosis may be related to the autophagy signal pathway. All these results showed davidone C has potential effects on hepatocellular carcinoma.     

Pre-treatment of HT-29 cells with 5-LOX inhibitor (MK-886) induces changes in cell cycle and increases apoptosis after photodynamic therapy with hypericin

It may be hypothesized that the lipoxygenase (LOX) metabolic pathway plays an important role in photodynamic therapy (PDT) of malignant tumours, and modification of this pathway may result in administration of lower doses of photodynamic active agents accompanied by reduced side effects. In this study, we examine in more detail the cytokinetic parameters of human colon adenocarcinoma HT-29 cells pre-treated for 48 or 24h with LOX inhibitor MK-886, followed by PDT induced by hypericin. Based on MTT assay the concentrations of both agents (MK-886 and hypericin) with relatively slight (non-significant) cytotoxic effects were selected. These concentrations were used for combined treatment, where MTT response, total cell number, floating cells quantification, viability, cell cycle progression and DNA synthesis were detected. Hoechst/PI staining, PARP fragmentation and mitochondrial membrane potential (MMP) were evaluated to determine the extent of apoptosis. While MK-886 alone caused mainly necrosis, 48h pre-treatment of cells with MK-886 followed by PDT with hypericin clearly shifted the type of cell death to apoptosis. PDT with hypericin alone caused apoptosis in 19% of the cell population. Some combined modalities significantly potentiated the apoptotic effect (31% of apoptotic cells; 2.5microM MK-886/0.1microM hypericin), i.e., by 60% more than after single treatment with hypericin. Increased apoptosis was confirmed by PARP (116kDa) cleavage to characteristic 89kDa fragments and changes in MMP. Increasing concentration of MK-886 was accompanied by massive changes in the cell cycle progression. Combined treatment with lower concentrations of MK-886 and hypericin increased accumulation of cells in the S phase, accompanied by inhibition of DNA synthesis. Increasing concentration of MK-886 in this combination caused the opposite effect, manifesting significant accumulation of cells in the G0/G1 phase. More pronounced effects were observed after the 48h pre-treatment schedule. This anti-proliferative effect was confirmed by BrdU incorporation. These results indicate that combined treatment involving PDT and LOX inhibitor MK-886 may improve the therapeutic effectiveness of PDT.     

The Proteins from Sika deer antler as potential modulators on cisplatin-induced cytotoxicity in human embryonic kidney 293 cells

Our study aimed to investigate the protective role of SDAPR on cisplatin-induced cytotoxicity and its’ possible mechanism in HEK293 cells. Cell viability was measured by MTT assay. Oxidative stress (SOD, GSH, LDH and MDA), inflammatory factors (TNF-α and IL-6) and apoptosis-related proteins (caspase-3, Bax, Bcl-2) expression were measured. The apoptotic cells were observed by TUNEL staining. Our study results indicated that non-cytotoxic levels of SDAPR significantly increased viability rate (LD₅₀ value of cisplatin is 20 μM), which improved antioxidant defence, attenuated apoptosis by decreasing expression levels of cleaved-caspase-3 and Bax, increasing Bcl-2 expression and inhibiting apoptotic positive cells in HEK 293 cells. In addition, SDAPR treatment markedly inhibited the levels of TNF-α and IL-6. In conclusion, Sika deer antler protein, a potential modulator, could alleviate cisplatin-induced cytotoxicity in HEK 293 cells.     

Prisconnatanones A,a cytotoxic naphthoquinone from Prismatomeris connata,suppresses the proliferation of human laryngocarcinoma HEp-2 cells in vitro

Prisconnatanones A (Priscon-A) is a rare tetrahydroanthraquinone isolated from herbal Prismatomeris connate. In this study, we examine its anti-tumour activity on human laryngocarcinoma HEp-2 cells in vitro. The CCK-8 assay was performed to evaluate its cytotoxicity. Cell cycle and apoptosis were analysed using flow cytometric analysis. Here, we showed Priscon-A inhibited the proliferation of HEp-2 cells in a dose-dependent manner, and at 5 μM it almost completely inhibited cell growth. Its cytotoxicity was associated with the cell cycle arrest at G2/M phase. The Annexin V-FITC/PI binding assay showed that the cell death induced by Priscon-A was associated with apoptosis. And, western blot analysis revealed that the levels of the apoptosis protein, cleaved caspase-3, PARP, p21 and Bax protein increased, while the level of anti-apoptosis protein Bcl-2 decreased.. These data demonstrated that Priscon-A significantly inhibited HEp-2 cell growth, induced the cell cycle arrest at the G2/M phase and efficiently induced cell apoptosis.     

Essential oil from Cryptomeria japonica induces apoptosis in human oral epidermoid carcinoma cells via mitochondrial stress and activation of caspases

Cryptomeria japonica D. Don (C. japonica) has been used in traditional medicines from Asia for a variety of indications, including liver ailments, and an antitussive, and for its antiulcer activities. We examined the cell viability and apoptosis of KB cells treated with C. japonica essential oil at several concentrations for 12 h by MTT assay, Hoechst-33258 dye staining, DNA fragmentation, flow cytometry (cell cycle), and Western blotting for mitochondria stress, activation of caspases, and poly (ADP-ribose) polymerase. The essential oil induced the apoptosis of KB cells in a dose-dependent manner, which was verified by DNA fragmentation, appearance of apoptotic bodies, and the sub-G1 ratio. The essential oil also induced rapid and transient caspase-3 activity and cleavage of PARP of the KB cells. Treating the cells with the oil also caused changes in the mitochondrial level of the Bcl-2 family proteins such as Bcl-2 and Bax, thereby inducing the release of cytochrome c into the cytosol. The essential oil of C. japonica may have potential as a cancer chemopreventive and therapeutic agent.     

Optimization of photodynamic therapy response by survivin gene knockdown in human metastatic breast cancer T47D cells

Photodynamic therapy (PDT) leads to the generation of cytotoxic oxygen species that appears to stimulate several different signaling pathways, some of which lead to cell death, whereas others mediate cell survival. In this context, we observed that PDT mediated by methyl-5-aminolevulinic acid as the photosensitizer resulted in over-expression of survivin, a member of the inhibitor of apoptosis (IAP) family that correlates inversely with patient prognosis. The role of survivin in resistance to anti-cancer therapies has become an area of intensive investigation. In this study, we demonstrate a specific role for survivin in modulating PDT-mediated apoptotic response. In our experimental system, we use a DNA vector-based siRNA, which targets exon-1 of the human survivin mRNA (pSil_1) to silence survivin expression. Metastatic T47D cells treated with both pSil_1 and PDT exhibited increased apoptotic indexes and cytotoxicity when compared to single-agent treated cells. The treatment resulted in increased PARP and caspase-3 cleavage, a decrease in the Bcl-2/Bak ratio and no participation of heat shock proteins. In contrast, the overexpression of survivin by a survivin-expressed vector increased cell viability and reduced cell death in breast cancer cells treated with PDT. Therefore, our data suggest that combining PDT with a survivin inhibitor may attribute to a more favorable clinical outcome than the use of single-modality PDT.     

Sialic acid surface decoration enhances cellular uptake and apoptosis-inducing activity of selenium nanoparticles

A simple method for fabrication of sialic acid surface-decorated selenium nanoparticles (SA-Se-NPs) with enhanced cancer-targeting and cell-penetrating abilities has been demonstrated in the present study. Monodisperse and homogeneous spherical SA-Se-NPs with striking stability were prepared under the optimized conditions. SA surface decoration significantly increased the cellular uptake and cytotoxicity of Se-NPs in HeLa human cervical carcinoma cells. Treatments of SA-Se-NPs induced dose-dependent apoptosis in HeLa cells, as evidenced by increase in sub-G1 cell populations, nuclear condensation and formation of apoptotic bodies. Further investigation on molecular mechanisms reveals that SA-Se-NPs triggered cancer cell apoptosis through activation of caspase-3 and subsequent cleavage of PARP.     

Resveratrol-induced cell inhibition of growth and apoptosis in MCF7 human breast cancer cells are associated with modulation of phosphorylated akt and caspase-9

Resveratrol (trans-3,4N,-5-trihydroxystilbene), a phytoalexin present in grapes and red wine, is emerging as a natural compound with potential anticancer properties. Here we show that resveratrol affects the growth of human breast cancer cell lines MCF7, MDA-MB-231, SK-BR-3, and Bcap-37 in a dose-dependent manner and that MCF7 is the most sensitive among the four cell lines. MCF7 cells treated with resveratrol showed typical characteristics of apoptosis including the poly (ADP-ribose) polymerase cleavage, TdT-mediated dUTP nick end labeling-positive staining, and morphologic changes. Phosphorylation of the oncogene product Akt was significantly reduced followed by decreased phosphorylation and increased processing of pro-caspase-9 on resveratrol treatment. These results indicate that resveratrol seems to exert its growth-inhibitory/apoptotic effect on the breast cancer cell line MCF7 via the Akt-caspase-9 pathway.     

Photoactivation of pheophorbide a induces a mitochondrial-mediated apoptosis in Jurkat leukaemia cells

The mechanism of cell death by pheophorbide a (Pba) which has been established to be a potential photosensitizer was examined in experimental photodynamic therapy (PDT) on Jurkat cells, a human lymphoid tumor cell line. In 30-60 min after irradiation, Pba treated cells exhibited apoptotic features including membrane blebbing and DNA fragmentation. Pba/PDT caused a rapid release of cytochrome c from mitochondria into the cytosol. Sequentially, activation of caspase-3 and the cleavage of poly ADP-ribose polymerase (PARP) were followed. Meanwhile, no evidence of activation of caspase-8 was indicated in the cells. In experiments with caspase inhibitors, it was found that caspase-3 alone was sufficient initiator for the Pba-induced apoptosis of the cells. Pba specific emission spectra were confirmed in the mitochondrial fraction and the light irradiation caused a rapid change in its membrane potential. Thus, mitochondria were entailed as the crucial targets for Pba as well as a responsible component for the cytochrome c release to initiate apoptotic pathways. Taken together, it was concluded that the mode of Jurkat cell death by Pba/PDT is an apoptosis, which is initiated by mitochondrial cytochrome c release and caspase-3-pathways.     

The Anti-Tumor Effect and Underlying Apoptotic Mechanism of Ginsenoside Rk1 and Rg5 in Human Liver Cancer Cells

Ginsenoside Rk1 and Rg5 are minor ginseng saponins that have received more attention recently because of their high oral bioavailability. Each of them can effectively inhibit the survival and proliferation of human liver cancer cells, but the underlying mechanism remains largely unknown. Network pharmacology and bioinformatics analysis demonstrated that G-Rk1 and G-Rg5 yielded 142 potential targets, and shared 44 putative targets associated with hepatocellular carcinoma. Enrichment analysis of the overlapped genes showed that G-Rk1 and G-Rg5 may induce apoptosis of liver cancer cells through inhibition of mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) signal pathways. Methyl thiazolyl tetrazolium (MTT) assay was used to confirm the inhibition of cell viability with G-Rk1 or G-Rg5 in highly metastatic human cancer MHCC-97H cells. We evaluated the apoptosis of MHCC-97H cells by using flow cytometry and 4′,6-diamidino-2-phenylindole (DAPI) staining. The translocation of Bax/Bak led to the depolarization of mitochondrial membrane potential and release of cytochrome c and Smac. A sequential activation of caspase-9 and caspase-3 and the cleavage of poly(ADP-ribose) polymerase (PARP) were observed after that. The levels of anti-apoptotic proteins were decreased after treatment of G-Rk1 or G-Rg5 in MHCC-97H cells. Taken together, G-Rk1 and G-Rg5 promoted the endogenous apoptotic pathway in MHCC-97H cells by targeting and regulating some critical liver cancer related genes that are involved in the signal pathways associated with cell survival and proliferation.     

Dioscorealide B from the traditional Thai medicine Hua-Khao-Yen induces apoptosis in MCF-7 human breast cancer cells via modulation of Bax, Bak and Bcl-2 protein expression

Dioscorealide B is a pharmacologically active compound from the rhizome of the Thai medicinal plant Dioscorea membranacea. Here, we demonstrated that in vitro treatment of dioscorealide B resulted in a cytotoxic effect on MCF-7 human breast cancer cells (IC50 = 2.82 microM). To determine whether this compound induces apoptosis in MCF-7, the Annexin V assay was performed. The data showed that the number of apoptotic cells were increased 7-12 folds over that of the control cells after treatment with various concentrations of dioscorealide B (3, 6 and 12 microM) for 24 hours. Dioscorealide B-induced apoptosis was associated with modulation of the multidomain Bcl-2 family members Bax, Bak and Bcl-2. After treatment with 3 microM dioscorealide B, acceleration of the level of proapoptotic proteins Bax and Bak were observed at 6 hours and 12 hours, respectively, while the decrease in the expression of antiapoptotic protein Bcl-2 was observed 3 hours after the treatment. These effects of dioscorealide B might result in the activation of caspase-8, -9 and -7, which lead to apoptosis in MCF-7 cells. Taken together, the results of this study provide evidence that dioscorealide B possesses an antitumor property against human breast cancer cells and thus provide the molecular basis for the further development of dioscorealide B as a novel chemotherapeutic agent for breast cancer treatment.     

Repeated electroconvulsive seizure induces c-Myc down-regulation and Bad inactivation in the rat frontal cortex

Repeated electroconvulsive seizure (ECS), a model for electroconvulsive therapy (ECT), exerts neuroprotective and proliferative effects in the brain. This trophic action of ECS requires inhibition of apoptotic activity, in addition to activation of survival signals. c-Myc plays an important role in apoptosis of neurons, in cooperation with the Bcl-2 family proteins, and its activity and stability are regulated by phosphorylation and ubiquitination. We examined c-Myc and related proteins responsible for apoptosis after repeated ECS. In the rat frontal cortex, repeated ECS for 10 days reduced the total amount of c-Myc, while increasing phosphorylation of c-Myc at Thr58, which reportedly induces degradation of c-Myc. As expected, ubiquitination of both phosphorylated and total c-Myc increased after 10 days ECS, suggesting that ECS may reduce c-Myc protein level via ubiquitination-proteasomal degradation. Bcl-2 family proteins, caspase, and poly(ADP-ribose) polymerase (PARP) were investigated to determine the consequence of down-regulating c-Myc. Protein levels of Bcl-2, Bcl-X(L), Bax, and Bad showed no change, and cleavage of caspase-3 and PARP were not induced. However, phosphorylation of Bad at Ser-155 and binding of Bad to 14-3-3 increased without binding to Bcl-X(L) after repeated ECS, implying that repeated ECS sequesters apoptotic Bad and frees pro-survival Bcl-XL. Taken together, c-Myc down-regulation via ubiquitination-proteasomal degradation and Bad inactivation by binding to 14-3-3 may be anti-apoptotic mechanisms elicited by repeated ECS in the rat frontal cortex. This finding further supports the trophic effect of ECS blocking apoptosis as a possible therapeutic effect of ECT.     

Design and Synthesis of Novel Betulin Derivatives Containing Thio-/Semicarbazone Moieties as Apoptotic Inducers through Mitochindria-Related Pathways

Two new series of betulin derivatives with semicarbazone (7a–g) or thiosemicarbazone (8a–g) groups at the C-28 position were synthesized. All compounds were evaluated for their in vitro cytotoxicities in human hepatocellular carcinoma cells (HepG2), human breast carcinoma cells (MCF-7), human lung carcinoma cells (A549), human colorectal cells (HCT-116) and normal human gastric epithelial cells (GES-1). Among these compounds, 8f displayed the most potent cytotoxicity with an IC₅₀ value of 5.86 ± 0.61 μM against MCF-7 cells. Furthermore, the preliminary mechanism studies in MCF-7 cells showed that compound 8f could trigger the intracellular mitochondrial-mediated apoptosis pathway by losing MMP level, which was related with the upregulation of Bax, P53 and cytochrome c expression; the downregulation of Bcl-2 expression; activation of the expression levels of caspase-3, caspase-9, cleaved caspase-3 and cleaved caspase-9; and an increase in the amounts of intracellular reactive oxygen species. These results indicated that compound 8f may be used as a valuable skeleton structure for developing novel antitumor agents.     

Neurotoxic Effect of Flavonol Myricetin in the Presence of Excess Copper

Oxidative stress (OS) induced by the disturbed homeostasis of metal ions is one of the pivotal factors contributing to neurodegeneration. The aim of the present study was to investigate the effects of flavonoid myricetin on copper-induced toxicity in neuroblastoma SH-SY5Y cells. As determined by the MTT method, trypan blue exclusion assay and measurement of ATP production, myricetin heightened the toxic effects of copper and exacerbated cell death. It also increased copper-induced generation of reactive oxygen species, indicating the prooxidative nature of its action. Furthermore, myricetin provoked chromatin condensation and loss of membrane integrity without caspase-3 activation, suggesting the activation of both caspase-independent programmed cell death and necrosis. At the protein level, myricetin-induced upregulation of PARP-1 and decreased expression of Bcl-2, whereas copper-induced changes in the expression of p53, p73, Bax and NME1 were not further affected by myricetin. Inhibitors of ERK1/2 and JNK kinases, protein kinase A and L-type calcium channels exacerbated the toxic effects of myricetin, indicating the involvement of intracellular signaling pathways in cell death. We also employed atomic force microscopy (AFM) to evaluate the morphological and mechanical properties of SH-SY5Y cells at the nanoscale. Consistent with the cellular and molecular methods, this biophysical approach also revealed a myricetin-induced increase in cell surface roughness and reduced elasticity. Taken together, we demonstrated the adverse effects of myricetin, pointing out that caution is required when considering powerful antioxidants for adjuvant therapy in copper-related neurodegeneration.