Induction of apoptosis in U937 human leukaemia cells by the hexane fraction of an extract of immature Citrus grandis Osbeck fruits

The antiproliferative effect of an immature Citrus grandis Osbeck fruit extract was investigated using U937 human leukaemia cells. Maximum cytotoxicity was observed using the hexane fraction (HF) of the extract. Cell death was dose-dependent (IC₅₀ = ca. 60 μg/ml) and was characterised by chromatin condensation, apoptotic body formation, and DNA fragmentation. The induction of apoptosis was confirmed by caspase-3 activity assays and by immunoblotting using antibodies against Bcl-2, Bax, poly(ADP-ribose) polymerase (PARP), caspase-9, and caspase-3. The molecular mechanism underlying HF-induced apoptosis in U937 cells may involve a mitochondria-mediated signalling pathway, as demonstrated by an increase in the Bax/Bcl-2 expression ratio. Analyses of the HF by gas chromatography (GC) and GC-mass spectrometry (MS) tentatively identified 19 compounds, including γ-sitosterol (17.5%), 7-methoxy-8-(2-oxo-3-methylbutyl) coumarin (6.8%), stigmasterol (3.8%), and campesterol (3.4%). Together, our results provide the first evidence that the HF of an immature C. grandis Osbeck fruit extract induces apoptosis in U937 cells.     

Induction of apoptosis in HeLa cells by ethanolic extract of Corallina pilulifera

Marine organisms are rich sources of new, biologically active compounds. Seaweeds have traditionally been used as food, but have also been used as folk medicine, particularly by coastal peoples. Recently, much attention has been paid to the anticancer activity of seaweed. Thus, we have screened organic extracts of seaweeds for their anticancer activity against human cell lines, and selected Corallina pilulifera as a candidate for use in treatment. The ethanolic extracts of Corallina pilulifera (EECP) showed cytotoxic activity against human cervical adenocarcinoma cell line, HeLa. The IC₅₀ of EECP against the HeLa cells was 250 μg/ml. Treatment of HeLa cells with various concentrations of EECP resulted in growth inhibition and induction of apoptosis in a dose-dependent manner. In Western blot analysis, apoptosis in the HeLa cells was associated with the release of cytochrome C from mitochondria into the cytosol, activation of caspase-3 and caspase-8, and proteolytic cleavage of PARP (poly (ADP-ribose) polymerase). These results strongly suggest that EECP may be a potential candidate in the field of anticancer drug discovery.     

Quercitrin protects against oxidative stress-induced injury in lung fibroblast cells via up-regulation of Bcl-xL

The cytoprotective effect of quercitrin (QR) against oxidative stress induced cell damage by hydrogen peroxide (H₂O₂) in Chinese hamster lung fibroblast (V79-4) cells was investigated. QR evidenced a scavenging effect of 1,1-diphenyl-2-picrylhydrazyl (DPPH), superoxide, hydroxyl radicals and on intracellular ROS, and thus prevented lipid peroxidation. As a result, QR reduced H₂O₂-induced cell death and apoptosis in V79-4 cells. Moreover, H₂O₂ induced the cleavage of caspase-3, -9, and poly-ADP-ribose polymerase (PARP) and a reduction in Bcl-xL levels, whereas pretreatment with QR significantly inhibited caspase-3, -9, and PARP cleavage and the reduction in Bcl-xL levels, and ultimately ameliorated H₂O₂-induced apoptosis. Taken together, these results indicate that the treatment of V79-4 cells with QR can block H₂O₂-induced apoptosis via the regulation of Bcl-xL. QR may be exploited as a biopreservative in food applications or as a health supplement to alleviate oxidative stress.     

Geraniin-mediated apoptosis by cleavage of focal adhesion kinase through up-regulation of Fas ligand expression in human melanoma cells

Geraniin, a form of tannin separated from geranium, causes cell death through induction of apoptosis; however, cell death characteristics for geraniin have not yet been elucidated. Here, we investigated the mechanism of geraniin-induced apoptosis in human melanoma cells and demonstrated that geraniin was able to induce cell apoptosis in a concentration- and time-dependent manner. We also examined the signaling pathway related to geraniin-induced apoptosis. To clarify the relationship between focal adhesion kinase (FAK) and geraniin-induced apoptosis, we treated human melanoma cells with geraniin and found that this resulted dose- and time-dependent degradation in FAK. However, FAK cleavage was significantly inhibited when cells were pretreated with a selective inhibitor of caspase-3 (Ac-Asp-Glu-Val-Asp-CHO). Here, we demonstrated for the first time that geraniin triggered cell death by caspase-3-mediated cleavage of FAK. There were two possible mechanisms for activating caspase-3, mitochondria-mediated and receptor-mediated apoptosis. To confirm the geraniin-relevant signaling pathway, using immunoblot analysis we found that geraniin-induced apoptosis was associated with the up-regulation of Fas ligand expression, the activation of caspase-8, the cleavage of Bid, and the induction of cytochrome c release from mitochondria to the cytosol. Treatment with geraniin caused induction of caspase-3 activity in a dose- and time-dependent manner followed by proteolytic cleavage of poly-(ADP-ribose) polymerase, and DNA fragmentation factor 45. The geraniin-induced apoptosis may provide a pivotal mechanism for its cancer-chemopreventive action.     

INDUCTION OF APOPTOSIS BY GINSENG SAPONIN METABOLITE IN U937 HUMAN MONOCYTIC LEUKEMIA CELLS

We report the cytotoxicity of the ginseng saponin metabolite, Compound K (20‐O‐D‐glucopyranosyl‐20(S)‐protopanaxadiol, IH901) on various human leukemia cell lines. Compound K had the most effect on U937, a human monocytic leukemia cell line among the tested cell lines. Compound K‐treated U937 cells showed characteristics of apoptosis: an exposure of phosphatidylserine from the inner cell membrane to the outer cell membrane, the formation of apoptotic bodies and DNA fragmentation. Compound K induced apoptosis by up‐regulating Bax, disrupting the mitochondrial membrane potential, and by activating caspase 9 and caspase 3. Therefore, we suggest that Compound K inhibits U937 cell growth by inducing apoptosis through the up‐regulation of Bax and caspase activation.     

Neuroprotective effects of N-acetylglucosamine against hydrogen peroxide-induced apoptosis in human neuronal SK-N-SH cells by inhibiting the activation of caspase-3, PARP, and p38

Neuroprotective effects of N-acetylglucosamine (GlcNAc), a monosaccharide derivative of glucose, against H₂O₂-induced neurotoxicity and its underlying mechanism in human SK-N-SH neuroblastoma cells were investigated. Pretreatment of GlcNAc prior to exposure of cells to H₂O₂ stress significantly reduced the H₂O₂-mediated neuronal cell death and apoptosis. The GlcNAc dose-dependently decreased the level of intracellular reactive oxygen species (ROS) in H₂O₂-treated cells and also effectively inhibited H₂O₂-induced apoptotic features such as DNA fragmentation, caspase-3, and poly ADP-ribose polymerase (PARP) cleavages, and p38 phosphorylation. These results suggested that GlcNAc might potentially serve as agents for prevention of neurodegenerative diseases caused by oxidative stresses and this effect may be associated with the suppression of caspase-3, PARP, and p38 activation.     

Cell death induced by serum deprivation in luteal cells involves the intrinsic pathway of apoptosis

The corpus luteum is a transient endocrine gland specializing in the production of progesterone. The regression of the corpus luteum involves an abrupt decline in its capacity for producing progesterone followed by its structural involution, which is associated with apoptosis of the luteal cells. An in vitro experimental approach is needed to study the molecular mechanisms underlying hormonal regulation of luteal cell death under defined experimental conditions. In this study, we investigated simian virus-40-transformed luteal cells to determine whether they can be driven to apoptosis and, if so, to define the intracellular pathway involved. Luteal cells were cultured in the presence or absence of fetal bovine serum for 24 or 48 h. Under serum starvation conditions, the luteal cells underwent growth arrest accompanied by cell death as evaluated by dye exclusion, and confirmed by two-color fluorescence cell viability/cytotoxicity assay. We next studied whether serum starvation-induced death of luteal cells occurred by apoptosis. Morphologic features of apoptosis were observed in cells stained with hematoxylin after being subjected to serum starvation for 48 h. The apoptotic nature was further confirmed by in situ 3'-end labeling and fragmentation of genomic DNA. Apoptosis of serum-deprived luteal cells was dependent upon caspase activation. Serum starvation induced cleavage of poly (ADP-ribose) polymerase (PARP), suggesting that caspase-3 had been activated under the stress of withdrawal of growth factors. This was confirmed by cleavage of full-length procaspase-3. Finally, the fact that serum starvation promoted the cleavage of full-length procaspase-9 and the decrease in the expression of endogenous Bid, a BH-3-only proapoptotic protein of the Bcl-2 family, indicates that the intrinsic (i.e., mitochondrial) pathway of apoptosis was activated. In summary, we have characterized an in vitro experimental model of luteal cell death that can be utilized to evaluate the role of hormones in apoptosis of luteal cells under defined culture conditions, and to study the mechanism of luteal regression.     

Induction of apoptosis by ethanolic extract of mango peel and comparative analysis of the chemical constitutes of mango peel and flesh

The underlying mechanisms of the anticancer activity of the ethanolic extract of mango peel (EEMP) and its constituents were investigated. EEMP induced death of human cervical carcinoma HeLa cells through apoptosis, as evidenced by the increased cell population in the sub-G1 phase and the appearance of fragmented nuclei. Treatment of the cells with EEMP also downregulated anti-apoptotic Bcl-2 expression, resulting in the proteolytic activation of caspase-3, 7, 8, and 9 and the degradation of poly (ADP-ribose) polymerase (PARP) protein. The major components of mango peel were identified by liquid chromatography–electrospray ionisation tandem mass spectrometry and gas chromatography–mass spectrometry. Our data suggest that EEMP is an excellent source of quercetin 3-O-galactoside, mangiferin gallate, isomangiferin gallate, quercetin-3-O-arabinopyranoside, and mangiferin along with unsaturated fatty acids oleic acid, linoleic acid, and ethyl linoleate, which may help to prevent cervical cancer and may be a useful agent for the treatment of some other malignancies.     

Mechanism of Hericium erinaceus (Yamabushitake) mushroom-induced apoptosis of U937 human monocytic leukemia cells

Phytochemicals in some foods are a potential source of bioactive safe compounds for cancer chemoprevention and suppression of tumor initiation, promotion, and metastasis. In the present study, we evaluated hot water (HWE), microwaved 50% ethanol (MWE), acidic (ACE), and alkaline (AKE) extracts of the fruitbody (sporocarp) of Hericium erinaceus (Yamabushitake, Lion's Mane) mushrooms for their ability to induce apoptosis (programmed cell death) in U937 human monocytic leukemia cells. Cell culture, cell viability, cytotoxicity, flow cytometry, chromosomal DNA integrity, mitochondrial membrane potential, expression of pro- and anti-apoptotic proteins, and activation and inhibition of caspase assays were carried out to help define the mechanism of observed apoptosis. The aqueous and aqueous/ethanolic extracts were active in all assays, whereas the acidic and alkaline extracts with the similar proximate compositions were both inactive. The results of the bioassays with the active extracts are consistent with an apoptosis mechanism governing suppression of the cell proliferation pathway that involves activation of mitochondria-mediated caspase-3 and caspase-9 but not caspase-8. Proximate analysis of the freeze-dried mushroom powder showed that it contains high amounts of proteins, carbohydrates, and minerals. The results indicate that H. erinaceus mushrooms may have therapeutic potential against human leukemia.     

Analysis of programmed cell death in mouse fetal oocytes

We report a short-term culture system that allows to define novel characteristic of programmed cell death (PCD) in fetal oocytes and to underscore new aspects of this process. Mouse fetal oocytes cultured in conditions allowing meiotic prophase I progression underwent apoptotic degeneration waves as revealed by TUNEL staining. TEM observations revealed recurrent atypical apoptotic morphologies characterized by the absence of chromatin margination and nuclear fragmentation; oocytes with autophagic and necrotic features were also observed. Further characterization of oocyte death evidenced DNA ladder, Annexin V binding, PARP cleavage, and usually caspase activation (namely caspase-2). In the aim to modulate the oocyte death process, we found that the addition to the culture medium of the pan-caspase inhibitors Z-VAD or caspase-2-specific inhibitor Z-VDVAD resulted in a partial and transient prevention of this process. Oocyte death was significantly reduced by the antioxidant agent NAC and partly prevented by KL and IGF-I growth factors. Finally, oocyte apoptosis was reduced by calpain inhibitor I and increased by rapamycin after prolonged culture. These results support the notion that fetal oocytes undergo degeneration mostly by apoptosis. This process is, however, often morphologically atypical and encompasses other forms of cell death including caspase-independent apoptosis and autophagia. The observation that oocyte death occurs mainly at certain stages of meiosis and can only be attenuated by typical anti-apoptotic treatments favors the notion that it is controlled at least in part by stage-specific oocyte-autonomous meiotic checkpoints and when activated is little amenable to inhibition being the oocyte able to switch back and forth among different death pathways.     

虾青素保护PC-3细胞免受H2O2氧化应激的作用机制

目的：研究虾青素对过氧化氢诱导PC-3细胞氧化应激的保护作用,探索其信号通路机制。方法：建立H2O2 氧化应激模型,采用不同浓度虾青素预处理PC-3细胞,检测细胞存活率、细胞凋亡、活性氧（reactive oxygen species, ROS）水平、B淋巴细胞瘤-2（B-cell lymphoma-2,Bcl-2）、Bcl-2相关X蛋白（Bcl-2-associated X protein,Bax）、 活化半胱天冬酶-3表达及丝裂原活化蛋白激酶-核因子E2相关基因2-血红素氧合酶1（mitogen-activated protein kinases nuclear factor erythroid-2-related factor 2-heme oxygenase 1,MAPK-Nrf2-HO-1）通路的变化。结果：20 μmol/L虾青 素预处理显著提高H2O2所降低的细胞存活率、降低ROS水平（P＜0.05）,同时通过抑制Bcl-2/Bax比率下降及半胱 天冬酶-3的激活,从而使细胞凋亡率从51.4%降低至14.8%,进一步研究发现虾青素能够促进Nrf2磷酸化,并促进 HO-1的表达,呈现浓度依赖性。通过细胞外调节蛋白激酶（extracellular regulated protein kinases,ERK）抑制剂 （U0126）和Akt抑制剂（LY294002）预处理,发现当ERK和磷脂酰肌醇激酶/蛋白激酶B（phosphoinositide 3-kinase/ protein kinase B,PI3K/Akt）通路被抑制后,Nrf2表达降低,表明HO-1上调受上游ERK和胞内PI3K/Akt通路的调 控。在对MAPK途径对细胞毒性影响的研究中,ERK通路被抑制后细胞存活率显著下降,而c-Jun氨基末端激酶 （c-Jun N-terminal kinase,JNK）和p38 MAPK通路被抑制后并不影响其保护作用,表明虾青素抑制细胞存活率下降 是通过MAPK途径中的ERK通路,而不是JNK和p38通路。结论：虾青素预处理PC-3细胞可以减轻H2O2诱导的氧化 应激,维持细胞生理活性。     

Quercetin‐induced apoptotic cascade in cancer cells: Antioxidant versus estrogen receptor α‐dependent mechanisms

The flavonol quercetin, especially abundant in apple, wine, and onions, is reported to have anti‐proliferative effects in many cancer cell lines. Antioxidant or pro‐oxidant activities and kinase inhibition have been proposed as molecular mechanisms for these effects. In addition, an estrogenic activity has been observed but, at the present, it is poorly understood whether this latter activity plays a role in the quercetin‐induced anti‐proliferative effects. Here, we studied the molecular mechanisms of quercetin committed to the generation of an apoptotic cascade in cancer cells devoid or containing transfected estrogen receptor α (ERα; i.e., human cervix epitheloid carcinoma HeLa cells). Although none of tested quercetin concentrations increase reactive oxygen species (ROS) generation in HeLa cells, quercetin stimulation prevents the H₂O₂‐induced ROS production both in the presence and in the absence of ERα. However, this flavonoid induces the activation of p38/MAPK, leading to the pro‐apoptotic caspase‐3 activation and to the poly(ADP‐ribose) polymerase cleavage only in the presence of ERα. Notably, no down‐regulation of survival kinases (i.e., AKT and ERK) was reported. Taken together, these findings suggest that quercetin results in HeLa cell death through an ERα‐dependent mechanism involving caspase‐ and p38 kinase activation. These findings indicate new potential chemopreventive actions of flavonoids on cancer growth.     

Neferine induces reactive oxygen species mediated intrinsic pathway of apoptosis in HepG2 cells

Evidence has accumulated concerning the medicinal application of Nelumbo nucifera in the treatment of various diseases. Neferine, an alkaloid from N. nucifera was found to exert cytotoxicity on liver cancer cells HepG2 in a dose-dependent manner. We evaluated its anticancer potential by studying its effect on mitochondrial membrane potential, intracellular calcium levels [Ca²⁺]_i, cell membrane integrity, apoptotic body formation and DNA fragmentation in cultured HepG2 cells. The reactive oxygen species level has been increased upon neferine treatment with concomitant decrease in reduced glutathione. Our data further indicate reduction of ΔψM and increased [Ca²⁺]_i during apoptosis induction by neferine with increased expression of apoptotic proteins such as Bax, Bad, cleaved forms of caspase 3, caspase 9 and PARP, with the downregulation of anti-apoptotic protein Bcl2 in HepG2 cells. Moreover, the expressions of tumour suppressor proteins p53 and PTEN were upregulated along with the downregulation of P-Akt. In addition, expression levels of TNF-α, p38 and ERK1/2 MAP kinases were increased upon neferine treatment. These results imply that mitochondrial-mediated ROS generation induced by neferine leads to caspase-dependent apoptosis in HepG2 cells.     

Isoangustone A present in hexane/ethanol extract of Glycyrrhiza uralensis induces apoptosis in DU145 human prostate cancer cells via the activation of DR4 and intrinsic apoptosis pathway

Glycyrrhiza uralensis (licorice) is one of the most frequently prescribed ingredients in Oriental medicine, and licorice extract has been shown to exert anti‐carcinogenic effects. However, its use as a cancer chemopreventive agent is rather limited, due to the fact that its principal component, glycyrrhizin, is known to induce hypertension. This study determined the effects of a hexane/ethanol extract of G. uralensis (HEGU), which contains undetectable amounts of glycyrrhizin, on the apoptosis of androgen‐insensitive DU145 cells. HEGU induced apoptosis and increased the levels of cleaved caspase‐9, caspase‐7, caspase‐3 and poly (ADP‐ribose) polymerase (PARP). HEGU also induced mitochondrial membrane depolarization and cytochrome c release to the cytosol. HEGU increased the levels of Fas, death receptor 4 (DR4), cleaved caspase‐8, Mcl‐1S, and truncated Bid proteins. A caspase‐8 inhibitor suppressed HEGU‐induced apoptosis. An active fraction of HEGU was separated via column chromatography and the structure of the active compound isoangustone A was identified via ¹H‐NMR and ¹³C‐NMR. Isoangustone A increased apoptotic cells, the cleavage of PARP and caspases, and the levels of DR4 and Mcl‐1S. Transfection with DR4 small interfering RNA attenuated HEGU‐ and isoangustone A‐induced apoptosis. These results demonstrate that the activation of DR4 contributes to HEGU‐ and isoangustone A‐induced apoptosis of DU145 cells.     

阿魏菇乙酸乙酯相三萜类化合物对食管癌Eca109细胞的增殖抑制及机制

目的：探讨阿魏菇乙酸乙酯相三萜类化合物（ethyl acetate fraction of Pleurotus ferulatus triterpenoid,PFTP-E）对食管癌Eca109细胞的生长抑制作用及可能机制。方法：采用3-(4,5-二甲基噻-2)-2,5-二苯基四氮唑溴盐法检测PFTP-E体外抑制Eca109细胞的增殖活性;Hoechst 33258染色观察细胞凋亡;流式细胞术检测PFTP-E对Eca109细胞的增殖、周期、凋亡、线粒体膜电位以及胞内活性氧水平变化的影响;免疫印迹法检测PFTP-E对细胞凋亡相关蛋白Bcl2、Bax、聚腺苷二磷酸-核糖聚合酶（poly ADP-ribose polymerase,PARP）、含半胱氨酸的天冬氨酸蛋白水解酶（cysteinyl aspartate specific proteinase,Caspase）3、Caspase9、细胞周期相关蛋白Cyclin B1、内质网应激相关蛋白真核起始因子2α（eukaryotic initiation factor 2α,eIF2α）、CHOP以及丝裂原活化蛋白激酶（mitogen-activated protein kinase,MAPK）信号通路相关蛋白表达的影响。结果：PFTP-E以时间和剂量依赖性抑制Eca109细胞的增殖,并将细胞周期阻滞在G2/M期,进而诱导Eca109细胞凋亡。PFTP-E可引起Eca109细胞线粒体膜电位崩溃并导致胞内活性氧水平升高。PFTP-E可上调细胞色素c、Bax、p-eIF2α、CHOP表达,下调Bcl2、Cyclin B1表达,显著增强剪切型PARP、Caspase3及Caspase9表达,同时诱导内质网应激,激活MAPK/JNK信号通路。结论：PFTP-E能有效诱导Eca109细胞凋亡,其抗肿瘤机制与线粒体损伤途径、周期阻滞、内质网应激等有关。     

Eupafolin,a flavonoid isolated from Artemisia princeps,induced apoptosis in human cervical adenocarcinoma HeLa cells

Although eupafolin, a flavone found in Artemisia princeps Pampanini, has been shown to inhibit the growth of several human cancer cells, its mode of action is poorly understood. In this study, we investigated the pro‐apoptotic activities of eupafolin in human cervical carcinoma HeLa cells. It was found that eupafolin induced apoptosis in a dose‐dependent manner, as evidenced by DNA fragmentation and the accumulation of positive cells for annexin V. In addition, eupafolin triggered the activations of caspases‐3, ‐6, ‐7, ‐8, and ‐9 and the cleavages of their substrates, such as, poly (ADP‐ribose) polymerase and lamin A/C. Furthermore, treatment with eupafolin resulted in a loss of mitochondrial membrane potential (ΔΨ_m), increased the release of cytochrome c to the cytosol, and altered the expression levels of B‐cell lymphoma 2 (Bcl‐2) family proteins. Interestingly, caspase‐8, an initiator caspase, was activated after the loss of ΔΨ_m and the activations of caspases‐3 and ‐9. Moreover, treatment with z‐DEVD‐fmk (a specific caspase‐3 inhibitor) and the overexpression of Bcl‐2 prevented eupafolin‐stimulated caspase‐8 activation. Altogether, these results suggest that the eupafolin‐induced apoptosis in HeLa cells is mediated by caspase‐dependent pathways, involving caspases‐3, ‐9, and ‐8, which are initiated by the Bcl‐2‐dependent loss of ΔΨ_m.     

Inhibition of β-amyloid peptide-induced neurotoxicity by kaempferol 3-O-(6″-acetyl)-β-glucopyranoside from butterbur (Petasites japonicus) leaves in B103 cells

One of predominant hallmarks in Alzheimer’s disease (AD) is extracellular senile plaques containing β-amyloid peptide (Aβ). Aβ is known to be directly responsible for the free radical production and lipid peroxidation, leading to apoptosis and cellular death. In this study, we investigated the possible protective effect of kaempferol 3-O-(6″-acetyl)-β-glucopyranoside (KAG) isolated from butterbur (Petasites japonicus) leaves against Aβ-induced neurotoxicity. Exposure of mouse neuroblastoma B103 cells to Aβ(25–35) at the concentration of 50 μM significantly reduced cellular viability and increased both oxidative stress and apoptotic rate. However, pretreatment of B103 cell with isolated KAG at 10 μM significantly inhibited Aβ-induced apoptotic cellular damage and reactive oxygen species (ROS) generation. Pretreatment of KAG also completely inhibited caspase-3 activity to the basal level at the concentration of 10 mM. This study therefore demonstrated that Aβ induced cellular death might be prevented by KAG from butterbur leaves by the suppression of ROS and the subsequent recovery of apoptotic cell death.     

Xanthohumol induces apoptosis in cultured 40-16 human colon cancer cells by activation of the death receptor- and mitochondrial pathway

Xanthohumol (XN) is one of the major prenylflavonoids found in hop cones (Humulus lupulus L.). In this study, we investigated the cell growth inhibitory potential of XN on cultured human colon cancer cells. Cell proliferation was measured by sulforhodamine B staining. Poly(ADP-ribose)polymerase (PARP) cleavage, activation of caspases-3, -7, -8, and -9, and Bcl-2 family protein expression were detected by Western blot analyses. XN significantly reduced proliferation of the HCT 116-derived colon cancer cell line 40--16. Half-maximal inhibitory concentrations decreased from 4.1 microM after 24 h treatment to 3.6 and 2.6 microM after 48 and 72 h incubation, respectively. Treatment with 15 microM XN for 48 h and with 5 microM for 72 h led to the detection of the cleaved 89 kDa fragment of 116 kDa PARP as an indication of apoptosis induction. Concomitantly, we observed activation and cleavage of the effector caspases-3 and -7, induced by activation of the initiator caspases -8 and -9. Expression of anti-apoptotic Bcl-2 was down regulated when the cells were treated with XN for 48--72 h. We conclude that induction of apoptosis by downregulation of Bcl-2 and activation of the caspase cascade may contribute to the chemopreventive or therapeutic potential of XN.     

The mechanism underlying proliferation-inhibitory and apoptosis-inducing effects of curcumin on papillary thyroid cancer cells

Recently, many studies on health benefits associated with curcumin have been reported. In this study, the effects of curcumin on apoptosis of papillary thyroid cancer cell line K1 and its potential mechanisms were investigated. Curcumin was found to significantly inhibit cell viability and promoted cell apoptosis in a dose-dependent manner. Moreover, curcumin-induced cell apoptosis was characterized with a rapid stimulation of reactive oxygen species (ROS) production. Furthermore, curcumin-induced ROS generation led to the loss of mitochondrial membrane potential (MMP) and the disturbance of intracellular Ca²⁺ concentration. A decrease in expression of Bcl-2 and the cleavage of poly ADP-ribose polymerase (PARP) were observed after exposure to curcumin. Results of this study may elucidate the curcumin-induced apoptosis effects on K1 cells. Thus, our results indicate a role of curcumin as health-promoting food ingredient, as well as a potential chemotherapeutic agent which is able to fight against papillary thyroid cancer.