Mitochondrial reactive oxygen species affect sensitivity to curcumin-induced apoptosis

Curcumin exhibits anticancer activity in vivo and triggers tumor cell apoptosis in vivo and in vitro. Several in vitro studies suggest that curcumin-induced apoptosis is associated with reactive oxygen species (ROS) production and/or oxidative stress in transformed cells. This study compared and contrasted the effects of curcumin on human skin cancer cells and their respiration-deficient (rho0) clones to characterize the prospective oxidative stress signaling responsible for initiating apoptosis. Curcumin promoted a dose-and time-dependent G2/M cell cycle arrest and/or apoptosis in COLO 16 cells. Apoptosis induction in COLO 16 cells was associated with DNA fragmentation, cell shrinkage, the externalization of cell membrane phosphatidylserine, and mitochondrial disruption, which were preceded by an increase in intracellular ROS production. Pharmacologically lowering the mitochondrial bioenergetic capacity, as well as the constitutive ROS levels, in COLO 16 cells suppressed the cytotoxic effects of curcumin. Correspondingly, the rho0 counterparts of COLO 16 cells were markedly resistant to ROS production, mitochondrial disruption, and DNA fragmentation following curcumin exposure. These observations implied that the diminution of mitochondrial ROS production protected cells against the cytotoxic effects of curcumin, and support the notion that mitochondrial respiration and redox tone are pivotal determinants in apoptosis signaling by curcumin in human skin cancer cells.     

Versatile role of curcumin and its derivatives in lung cancer therapy

Lung cancer is a main cause of death all over the world with a high incidence rate. Metastasis into neighboring and distant tissues as well as resistance of cancer cells to chemotherapy demand novel strategies in lung cancer therapy. Curcumin is a naturally occurring nutraceutical compound derived from Curcuma longa (turmeric) that has great pharmacological effects, such as anti-inflammatory, neuroprotective, and antidiabetic. The excellent antitumor activity of curcumin has led to its extensive application in the treatment of various cancers. In the present review, we describe the antitumor activity of curcumin against lung cancer. Curcumin affects different molecular pathways such as vascular endothelial growth factors, nuclear factor-κB (NF-κB), mammalian target of rapamycin, PI3/Akt, microRNAs, and long noncoding RNAs in treatment of lung cancer. Curcumin also can induce autophagy, apoptosis, and cell cycle arrest to reduce the viability and proliferation of lung cancer cells. Notably, curcumin supplementation sensitizes cancer cells to chemotherapy and enhances chemotherapy-mediated apoptosis. Curcumin can elevate the efficacy of radiotherapy in lung cancer therapy by targeting various signaling pathways, such as epidermal growth factor receptor and NF-κB. Curcumin-loaded nanocarriers enhance the bioavailability, cellular uptake, and antitumor activity of curcumin. The aforementioned effects are comprehensively discussed in the current review to further direct studies for applying curcumin in lung cancer therapy.     

Curcumin,its derivatives,and their nanoformulations: Revolutionizing cancer treatment

Curcumin is a natural compound derived from turmeric and can target malignant tumor molecules involved in cancer propagation. It has potent antioxidant activity, but its effectiveness is limited due to poor absorption and rapid elimination from the body. Various curcumin derivatives have also shown anticancer potential in in-vitro and in-vivo models. Curcumin can target multiple signaling pathways involved in cancer development/progression or induce cancer cell death through apoptosis. In addition, curcumin and its derivatives could also enhance the effectiveness of conventional chemotherapy, radiation therapy and reduce their associated side effects. Lately, nanoparticle-based delivery systems are being developed/explored to overcome the challenges associated with curcumin's delivery, increasing its overall efficacy. The use of an imaging system to track these formulations could also give beneficial information about the bioavailability and distribution of the nano-curcumin complex. In conclusion, curcumin holds significant promise in the fight against cancer, especially in its nanoform, and could provide precise delivery to cancer cells without affecting normal healthy cells.     

Curcumin mediated apoptosis in AK-5 tumor cells involves the production of reactive oxygen intermediates.

Curcumin, the active ingredient of the rhizome of Curcuma longa has anti-inflammatory, antioxidant and antiproliferative activities. Although its precise mode of action remains elusive, studies have shown that chemopreventive action of curcumin might be due to its ability to induce apoptosis in cancer cells. Curcumin was shown to be responsible for the inhibition of AK-5 tumor (a rat histiocytoma) growth by inducing apoptosis in AK-5 tumor cells via caspase activation. This study was designed to investigate the mechanism leading to the induction of apoptosis in AK-5 tumor cells. Curcumin treatment resulted in the hyperproduction of reactive oxygen species (ROS), loss of mitochondrial membrane potential (delta psi(m)) and cytochrome c release to the cytosol, with the concomitant exposure of phosphatidylserine (PS) residues on the cell surface. This study suggests redox signalling and caspase activation as the mechanisms responsible for the induction of curcumin mediated apoptosis in AK-5 tumor cells.     

Inhibitory effect of curcumin on oral carcinoma CAL-27 cells via suppression of Notch-1 and NF-κB signaling pathways

Curcumin has been reported to inhibit cell growth and induce apoptosis in oral cancer cells. Although many studies have been done to uncover the mechanisms by which curcumin exerts its antitumor activity, the precise molecular mechanisms remain to be unclear. In the present study, we assessed the effects of curcumin on cell viability and apoptosis in oral cancer. For mechanistic studies, we used multiple cellular and molecular approaches such as gene transfection, real-time RT-PCR, Western blotting, invasion assay, and ELISA. For the first time, we found a significant reduction in cell viability in curcumin-treated cells, which was consistent with induction of apoptosis and also associated with down-regulation of Notch-1 and nuclear factor-κB (NF-κB). Taken together, we conclude that the down-regulation of Notch-1 by curcumin could be an effective approach, which will cause down-regulation of NF-κB, resulting in the inhibition of cell growth and invasion. These results suggest that antitumor activity of curcumin is mediated through a novel mechanism involving inactivation of Notch-1 and NF-κB signaling pathways.     

Modulation of apoptosis-related cell signalling pathways by curcumin as a strategy to inhibit tumor progression

A hallmark of cancer is resistance to apoptosis, with both the loss of proapoptotic signals and the gain of anti-apoptotic mechanisms contributing to tumorigenesis. As inducing apoptosis in malignant cells is one of the most challenging tasks regarding cancer, researchers increasingly focus on natural products to regulate apoptotic signaling pathways. Curcumin, a polyphenolic derivative of turmeric, is a natural compound derived from Curcuma longa, has attracted great interest in the research of cancer during the last half century. Extensive studies revealed that curcumin has chemopreventive properties, which are mainly due to its ability to arrest cell cycle and to induce apoptosis in cancer cells either alone or in combination with chemotherapeutic agents or radiation. The underlying action mechanisms of curcumin are diverse and has not been elucidated so far. By regulating multiple important cellular signalling pathways including NF-κB, TRAIL, PI3 K/Akt, JAK/STAT, Notch-1, JNK, etc., curcumin are known to activate cell death signals and induce apoptosis in pre-cancerous or cancer cells without affecting normal cells, thereby inhibiting tumor progression. Several phase I and phase II clinical trials indicate that curcumin is quite safe and may exhibit therapeutic efficacy. This article reviews the main effects of curcumin on the different apoptotic signaling pathways involved in curcumin induced apoptosis in cancer cells via cellular transduction pathways and provides an in depth assessment of its pharmacological activity in the management of tumor progression.     

Curcumin enhances the apoptosis-inducing potential of TRAIL in prostate cancer cells: molecular mechanisms of apoptosis, migration and angiogenesis

Background

We have recently shown that curcumin (a diferuloylmethane) inhibits growth and induces apoptosis, and also demonstrated that TRAIL induces apoptosis by binding to specific cell surface death receptors in prostate cancer cells. The objectives of this paper were to investigate the molecular mechanisms by which curcumin enhanced the apoptosis-inducing potential of TRAIL in prostate cancer cells.

Results

Curcumin enhanced the apoptosis-inducing potential of TRAIL in androgen-unresponsive PC-3 cells and sensitized androgen-responsive TRAIL-resistant LNCaP cells. Curcumin inhibited the expressions of Bcl-2, Bcl-X_L, survivin and XIAP, and induced the expressions Bax, Bak, PUMA, Bim, and Noxa and death receptors (TRAIL-R1/DR4 and TRAIL-R2/DR5) in both cell lines. Overexpression of dominant negative FADD inhibited the interactive effects of curcumin and TRAIL on apoptosis. Treatment of these cells with curcumin resulted in activation of caspase-3, and caspase-9, and drop in mitochondrial membrane potential, and these events were further enhanced when combined with TRAIL. Curcumin inhibited capillary tube formation and migration of HUVEC cells and these effects were further enhanced in the presence of MEK1/2 inhibitor PD98059.

Conclusion

The ability of curcumin to inhibit capillary tube formation and cell migration, and enhance the therapeutic potential of TRAIL suggests that curcumin alone or in combination with TRAIL can be used for prostate cancer prevention and/or therapy.     

Curcumin induced apoptosis is mediated through oxidative stress in mutated p53 and wild type p53 colon adenocarcinoma cell lines

Curcumin has anti‐oxidant, anti‐cancer and anti‐carcinogen property. Our laboratory had previously reported that, curcumin treatment induces reactive oxygen species (ROS) generation in HT‐29 cell line, an effect contradictory to its anti‐oxidant property. This study evaluates the role of p53 in curcumin mediated ROS generation and cell death. Curcumin induced ROS was determined by 2’,7’‐dichlorofluorescein and apoptosis by Hoechst33342/PI staining in HT‐29 and HCT‐116 cell lines. ROS generation occurs within 1 hour of 40 µM curcumin treatment and a reduction was observed by third hour in HCT‐116 insinuating p53 involvement. N‐acetyl cysteine (NAC) pre‐treatment effectively quenched ROS and inhibited membrane potential loss in HT‐29, but less effective in HCT‐116. Mitochondrial membrane potential loss is evident with 10 and 40 µM curcumin in HCT‐116 and at 40 µM curcumin in HT‐29. Total p53 protein level increase was observed by 24 hours in HCT‐116 upon NAC pre‐treatment. Our results indicate that curcumin induces ROS mediated cell death in colon adenocarcinoma cell lines and may be mediated via p53.     

Curcumin induces the apoptotic intrinsic pathway via upregulation of reactive oxygen species and JNKs in H9c2 cardiac myoblasts

Curcumin derived from the rhizome of turmeric (Curcuma longa L.), is a well known coloring culinary agent, that has therapeutic properties against diverse pathologies such as cancer, atherosclerosis and heart failure. Given the salutary potential of curcumin, deciphering its mode of action particularly in cardiac cells, is of outstanding value. Accumulating evidence implicates curcumin in the regulation of multiple signaling pathways leading to cell survival or apoptosis. Therefore, the present study aimed at elucidating the molecular mechanisms triggered by curcumin in H9c2 cells. Curcumin was found to activate p38-mitogen-activated protein kinase (p38-MAPK) as well as c-jun NH₂ terminal kinases (JNKs), in a dose- and time-dependent manner. We also observed curcumin to impair cell survival by promoting apoptosis, evidenced by chromatin condensation, poly(ADP-ribose) polymerase (PARP) and caspase-3 cleavage, as well as Bax translocation and cytochrome c release into the cytosol. Curcumin-induced apoptosis was ascribed to JNKs, since hindering their activity abolished PARP fragmentation. Furthermore, we identified curcumin to exert a pro-oxidative activity, with 2′,7′-dichlorofluorescin diacetate (DCFH-DA) staining revealing up-regulation of reactive oxygen species (ROS) levels and anti-oxidants found to abrogate PARP cleavage. In conclusion, curcumin was found to stimulate the apoptotic cell death of H9c2 cells by upregulating ROS generation and triggering activation of JNKs. With reports underscoring the capacity of curcumin to perturb the cellular redox balance ensuring survival or enhancing apoptosis, determination of its mode of action appears to be critical. Future studies should assess the appropriate administration conditions of curcumin, so as to optimize its therapeutic potential against cardiovascular pathologies.     

Curcumin induces radiosensitivity of in vitro and in vivo cancer models by modulating pre-mRNA processing factor 4 (Prp4)

Radiation therapy plays a central role in adjuvant strategies for the treatment of both pre- and post-operative human cancers. However, radiation therapy has low efficacy against cancer cells displaying radio-resistant phenotypes. Ionizing radiation has been shown to enhance ROS generation, which mediates apoptotic cell death. Further, concomitant use of sensitizers with radiation improves the efficiency of radiotherapy against a variety of human cancers. Here, the radio-sensitizing effect of curcumin (a derivative of turmeric) was investigated against growth of HCT-15 cells and tumor induction in C57BL/6J mice. Ionizing radiation induced apoptosis through ROS generation and down-regulation of Prp4K, which was further potentiated by curcumin treatment. Flow cytometry revealed a dose-dependent response for radiation-induced cell death, which was remarkably reversed by transfection of cells with Prp4K clone. Over-expression of Prp4K resulted in a significant decrease in ROS production possibly through activation of an anti-oxidant enzyme system. To elucidate an integrated mechanism, Prp4K knockdown by siRNA ultimately restored radiation-induced ROS generation. Furthermore, B16F10 xenografts in C57BL/6J mice were established in order to investigate the radio-sensitizing effect of curcumin in vivo. Curcumin significantly enhanced the efficacy of radiation therapy and reduced tumor growth as compared to control or radiation alone. Collectively, these results suggest a novel mechanism for curcumin-mediated radio-sensitization of cancer based on ROS generation and down-regulation of Prp4K.     

Curcumin induces concentration-dependent alterations in mitochondrial function through ROS in C2C12 mouse myoblasts

Curcumin exhibits antioxidant properties in normal cells where the uptake is low, unlike in tumor cells where uptake is high and curcumin increases reactive oxygen species (ROS) production and cell death. Mitochondria are the main source and primary target of cellular ROS. We hypothesized that curcumin would regulate cellular redox status and mitochondrial function, depending on cell sensitivity and/or curcumin concentration in normal cells. We examined the differences between low and high concentrations of curcumin, with specific attention focused on ROS levels, mitochondrial function, and cell viability in mouse C2C12 myoblast under normal and simulated conditions of diabetes. Cells incubated with high concentrations of curcumin (10–50 μM) resulted in decreased cell viability and sustained robust increases in ROS levels. Mechanistic studies showed that increased ROS levels in cells incubated with 20 μM curcumin induced opening of mitochondrial permeability transition pores and subsequent release of cytochrome c, activation of caspases 9 and 3/7, and apoptotic cell death. Low concentrations of curcumin (1–5 μM) did not affect cell viability, but induced a mild increase in ROS levels, which peaked at 2 hr after the treatment. Incubation with 5 μM curcumin also induced ROS-dependent increases in mitochondrial mass and membrane potential. Finally, pretreatment with 5 μM curcumin prevented high glucose-induced oxidative cell injury. Our study suggests that mitochondria respond differentially depending on curcumin concentration-dependent induction of ROS. The end result is either cell protection or death. Curcumin may be an effective therapeutic target for diabetes and other mitochondrial diseases when used in low concentrations.     

B19, a Novel Monocarbonyl Analogue of Curcumin,Induces Human Ovarian Cancer Cell Apoptosis via Activation of Endoplasmic Reticulum Stress and the Autophagy Signaling Pathway

Background: The unfolded protein response, autophagy and endoplasmic reticulum (ER) stress-induced apoptosis regulate tumor cell fate and have become novel signaling targets for the development of cancer therapeutic drugs. Curcumin has been used to treat several different cancers, including ovarian cancer, in clinical trials and research; however, the role of ER stress and autophagy in the therapeutic effects of curcumin and new curcumin analogues remains unclear.Methods: Cell viability was determined using the MTT assay. Apoptosis was detected using flow cytometry with PI/Annexin V-FITC staining. The expression levels of ER stress- and autophagy-related proteins were analyzed by western blotting. The activation of autophagy was detected using immunofluorescence staining.Results: We demonstrated that B19 induced HO8910 cell apoptosis in a dose-responsive manner. We also determined and that this effect was associated with corresponding increases in a series of key components in the UPR and ER stress-mediated apoptosis pathways, followed by caspase 3 cleavage and activation. We also observed that B19 treatment induced autophagy in HO8910 cells. The inhibition of autophagy using 3-methyladenine (3-MA) increased levels of intracellular misfolded proteins, which enhanced ovarian cancer apoptosis.Conclusions: Our data indicate that ER stress and autophagy may play a role in the apoptosis that is induced by the curcumin analogue B19 in an epithelial ovarian cancer cell line and that autophagy inhibition can increase curcumin analogue-induced apoptosis by inducing severe ER stress.     

Curcumin as an anti-inflammatory agent: Implications to radiotherapy and chemotherapy

Cancer is the second cause of death worldwide. Chemotherapy and radiotherapy are the most common modalities for the treatment of cancer. Experimental studies have shown that inflammation plays a central role in tumor resistance and the incidence of several side effects following both chemotherapy and radiotherapy. Inflammation resulting from radiotherapy and chemotherapy is responsible for adverse events such as dermatitis, mucositis, pneumonitis, fibrosis, and bone marrow toxicity. Chronic inflammation may also lead to the development of second cancer during years after treatment. A number of anti-inflammatory drugs such as nonsteroidal anti-inflammatory agents have been proposed to alleviate chronic inflammatory reactions after radiotherapy or chemotherapy. Curcumin is a well-documented herbal anti-inflammatory agents. Studies have proposed that curcumin can help management of inflammation during and after radiotherapy and chemotherapy. Curcumin targets various inflammatory mediators such as cyclooxygenase-2, inducible nitric oxide synthase, and nuclear factor κB (NF-κB), thereby attenuating the release of proinflammatory and profibrotic cytokines, and suppressing chronic production of free radicals, which culminates in the amelioration of tissue toxicity. Through modulation of NF-κB and its downstream signaling cascade, curcumin can also reduce angiogenesis, tumor growth, and metastasis. Low toxicity of curcumin is linked to its cytoprotective effects in normal tissues. This protective action along with the capacity of this phytochemical to sensitize tumor cells to radiotherapy and chemotherapy makes it a potential candidate for use as an adjuvant in cancer therapy. There is also evidence from clinical trials suggesting the potential utility of curcumin for acute inflammatory reactions during radiotherapy such as dermatitis and mucositis.     

Curcumin induces small cell lung cancer NCI-H446 cell apoptosis via the reactive oxygen species-mediated mitochondrial pathway and not the cell death receptor pathway

Curcumin (diferuloylmethane), an active component of the spice turmeric, induces apoptosis in several types of malignancies. However, little is known about its anticancer activity in small cell lung cancer (SCLC). SCLC represents a highly malignant and particularly aggressive form of cancer, with early and widespread metastases and a poor prognosis. In this study, we found that curcumin does not activate caspase-8 cleavage or alter the expression of apoptotic receptors FAS and TRAIL in NCI-H446 cells, suggesting that curcumin-induced apoptosis is not associated with death receptor-mediated pathways in these cells. Instead, curcumin caused apoptosis by increasing Bax expression while decreasing the expression of Bcl-2 and Bcl-xL. Curcumin induced a rapid decrease in mitochondrial membrane potential and the release of cytochrome c into the cytosol, followed by activation of caspase-9 and caspase-3. In addition, curcumin-induced apoptosis was accompanied by an increase of intracellular reactive oxygen species (ROS) level. These results indicated that a ROS-mediated mitochondrial pathway played an important role in the process of curcumin-induced apoptosis of human SCLC NCI-H446 cells.     

Curcumin inhibits hypoxia-induced migration in K1 papillary thyroid cancer cells

Curcumin, traditionally used as food and medicinal purposes, has recently been reported to have protective efficacy against hypoxia. Hypoxia is one of the important reactive factors in tumor metastasis, which is a key problem in clinical thyroid cancer therapy. In present study, we investigate the anti-metastatic effect of curcumin on the K1 papillary thyroid cancer cells as well as its potential mechanisms. The results show that curcumin effectively inhibits hypoxia-induced reactive oxygen species (ROS) upregulation and significantly decreases the mRNA and protein expression levels of hypoxia-inducible factor-1α (HIF-1α) in K1 cells. Curcumin also decreases the DNA binding ability of HIF-1α to hypoxia response element (HRE). Furthermore, curcumin enhances E-cadherin expression, inhibits metalloproteinase-9 (MMP-9) enzyme activity, and weakens K1 cells migration under hypoxic conditions. In summary, these results indicate that curcumin possesses a potent anti-metastatic effect and might be an effective tumoristatic agent for the treatment of aggressive papillary thyroid cancers.     

Curcumin induces cell death in esophageal cancer cells through modulating Notch signaling

Background

Curcumin inhibits the growth of esophageal cancer cell lines; however, the mechanism of action is not well understood. It is becoming increasingly clear that aberrant activation of Notch signaling has been associated with the development of esophageal cancer. Here, we have determined that curcumin inhibits esophageal cancer growth via a mechanism mediated through the Notch signaling pathway.

Methodology/Principal Findings

In this study, we show that curcumin treatment resulted in a dose and time dependent inhibition of proliferation and colony formation in esophageal cancer cell lines. Furthermore, curcumin treatment induced apoptosis through caspase 3 activation, confirmed by an increase in the ratio of Bax to Bcl2. Cell cycle analysis demonstrated that curcumin treatment induced cell death and down regulated cyclin D1 levels. Curcumin treatment also resulted in reduced number and size of esophagospheres. Furthermore, curcumin treatment led to reduced Notch-1 activation, expression of Jagged-1 and its downstream target Hes-1. This reduction in Notch-1 activation was determined to be due to the down-regulation of critical components of the γ-secretase complex proteins such as Presenilin 1 and Nicastrin. The combination of a known γ-secretase inhibitor DAPT and curcumin further decreased proliferation and induced apoptosis in esophageal cancer cells. Finally, curcumin treatment down-regulate the expressions of Notch-1 specific microRNAs miR-21 and miR-34a, and upregulated tumor suppressor let-7a miRNA.

Conclusion/Significance

Curcumin is a potent inhibitor of esophageal cancer growth that targets the Notch-1 activating γ-secretase complex proteins. These data suggest that Notch signaling inhibition is a novel mechanism of action for curcumin during therapeutic intervention in esophageal cancers.     

Curcumin Protects Microglia and Primary Rat Cortical Neurons against HIV-1 gp120-Mediated Inflammation and Apoptosis

Curcumin is a molecule found in turmeric root that has anti-inflammatory, antioxidant, and anti-tumor properties and has been widely used as both an herbal drug and a food additive to treat or prevent neurodegenerative diseases. To explore whether curcumin is able to ameliorate HIV-1-associated neurotoxicity, we treated a murine microglial cell line (N9) and primary rat cortical neurons with curcumin in the presence or absence of neurotoxic HIV-1 gp120 (V3 loop) protein. We found that HIV-1 gp120 profoundly induced N9 cells to produce reactive oxygen species (ROS), tumor necrosis factor-α (TNF-α) and monocyte chemoattractant protein-1 (MCP-1). HIV-1 gp120 also induced apoptosis of primary rat cortical neurons. Curcumin exerted a powerful inhibitory effect against HIV-1 gp120-induced neuronal damage, reducing the production of ROS, TNF-α and MCP-1 by N9 cells and inhibiting apoptosis of primary rat cortical neurons. Curcumin may exert its biological activities through inhibition of the delayed rectification and transient outward potassium (K⁺) current, as curcumin effectively reduced HIV-1 gp120-mediated elevation of the delayed rectification and transient outward K⁺ channel current in neurons. We conclude that HIV-1 gp120 increases ROS, TNF-α and MCP-1 production in microglia, and induces cortical neuron apoptosis by affecting the delayed rectification and transient outward K⁺ channel current. Curcumin reduces production of ROS and inflammatory mediators in HIV-1-gp120-stimulated microglia, and protects cortical neurons against HIV-1-mediated apoptosis, most likely through inhibition of HIV-1 gp120-induced elevation of the delayed rectification and transient outward K⁺ current.