Dosage effects of curcumin on cell death types in a human osteoblast cell line

Curcumin stimulates reactive oxygen species production and potentiates apoptosis induction by the antitumor drugs arsenic trioxide and lonidamine in human myeloid leukemia cell lines

Arsenic trioxide (ATO, Trisenox) is an important antileukemic drug, but its efficacy is frequently low when used as a single agent. Here, we demonstrate that the apoptotic action of ATO is greatly increased when combined with subcytotoxic curcumin concentrations in U937 and HL60 human acute myeloid leukemia cells, and with lower efficacy in K562 chronic myelogenous leukemia cells. Curcumin exerts similar cooperative effect with the mitochondria-targeting drug lonidamine, whereas the response is negligible in combination with the DNA-targeting drug cisplatin. Curcumin plus ATO or lonidamine stimulates typical events of the mitochondrial executioner pathway (Bax and Bid activation, cytochrome c release, X-linked inhibitor of apoptosis down-regulation, and caspase-9/-3 activation) and causes mitochondrial transmembrane potential dissipation, which nevertheless represents a late event in the apoptotic response. Curcumin increases anion superoxide production, and its proapoptotic action in combination with ATO and lonidamine is mimicked by pro-oxidant agents (2-methoxyestradiol and H(2)O(2)) and prevented by antioxidant agents [Mn(III)tetrakis(4-benzoic acid)porphyrin chloride and N-acetyl-l-cysteine]. Within the assayed time period (16-24 h), curcumin does not significantly modify p38-mitogen-activated protein kinase and c-Jun NH(2)-terminal kinase phosphorylation/activation or nuclear factor-κB activity, but it greatly stimulates extracellular signal-regulated kinase (ERK) phosphorylation, and decreases Akt phosphorylation. Experiments using mitogen-activated protein kinase kinase/ERK inhibitors [2'-amino-3'-methoxyflavone (PD98059) and 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene (U0126)] and phosphatidylinositol 3-kinase inhibitor 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002) indicate that ERK activation does not mediate and even restrains apoptosis potentiation, whereas Akt down-regulation facilitates apoptosis generation. In summary, cotreatment with curcumin may represent a useful manner of increasing the efficacy of ATO and lonidamine as antitumor drugs in myeloid leukemia cells.

Hazardous effects of curcumin on mouse embryonic development through a mitochondria-dependent apoptotic signaling pathway

In this study, we examined the cytotoxic effects of curcumin, the yellow pigment of Curcuma longa, on the blastocyst stage of mouse embryos, subsequent embryonic attachment, and outgrowth in vitro and in vivo implantation by embryo transfer. Mouse blastocysts were incubated in medium with or without curcumin (6, 12 or 24 μM) for 24 h. Cell proliferation and growth were investigated using dual differential staining, apoptosis was analyzed with terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL), and implantation and post-implantation development of embryos were measured by in vitro development analysis and in vivo embryo transfer, respectively. Blastocysts treated with 24 μM curcumin displayed significantly increased apoptosis and decreased total cell number. Interestingly, we observed no marked differences in the implantation success rates between curcumin-pretreated and control blastocysts during in vitro embryonic development through implantation with a fibronectin-coated culture dish. However, in vitro treatment with 24 μM curcumin was associated with decreased implantation rate and increased resorption of postimplantation embryos in mouse uterus, as well as decreased fetal weight in the embryo transfer assay. Our results collectively indicate that in vitro exposure to curcumin triggers apoptosis and retards early postimplantation development after transfer to host mice. In addition, curcumin induces apoptotic injury effects on mouse blastocysts through ROS generation, and further promotes mitochondria-dependent apoptotic signaling processes to impair sequent embryonic development.

Uncoupling of oxidative phosphorylation by curcumin: implication of its cellular mechanism of action

Curcumin is a phytochemical isolated from the rhizome of turmeric. Recent reports have shown curcumin to have antioxidant, anti-inflammatory and anti-tumor properties as well as affecting the 5'-AMP activated protein kinase (AMPK), mTOR and STAT-3 signaling pathways. We provide evidence that curcumin acts as an uncoupler. Well-established biochemical techniques were performed on isolated rat liver mitochondria in measuring oxygen consumption, F(0)F(1)-ATPase activity and ATP biosynthesis. Curcumin displays all the characteristics typical of classical uncouplers like fccP and 2,4-dinitrophenol. In addition, at concentrations higher than 50 microM, curcumin was found to inhibit mitochondrial respiration which is a characteristic feature of inhibitory uncouplers. As a protonophoric uncoupler and as an activator of F(0)F(1)-ATPase, curcumin causes a decrease in ATP biosynthesis in rat liver mitochondria. The resulting change in ATP:AMP could disrupt the phosphorylation status of the cell; this provides a possible mechanism for its activation of AMPK and its downstream mTOR and STAT-3 signaling.

Inhibition of citrinin-induced apoptotic biochemical signaling in human hepatoma G2 cells by resveratrol

The mycotoxin citrinin (CTN), a natural contaminant in foodstuffs and animal feeds, exerts cytotoxic and genotoxic effects on various mammalian cells. CTN causes cell injury, including apoptosis, but its precise regulatory mechanisms of action are currently unclear. Resveratrol, a member of the phytoalexin family found in grapes and other dietary plants, possesses antioxidant and anti-tumor properties. In the present study, we examined the effects of resveratrol on apoptotic biochemical events in Hep G2 cells induced by CTN. Resveratrol inhibited CTN-induced ROS generation, activation of JNK, loss of mitochondrial membrane potential (MMP), as well as activation of caspase-9, caspase-3 and PAK2. Moreover, resveratrol and the ROS scavengers, NAC and α-tocopherol, abolished CTN-stimulated intracellular oxidative stress and apoptosis. Active JNK was required for CTN-induced mitochondria-dependent apoptotic biochemical changes, including loss of MMP, and activation of caspases and PAK2. Activation of PAK2 was essential for apoptosis triggered by CTN. These results collectively demonstrate that CTN stimulates ROS generation and JNK activation for mitochondria-dependent apoptotic signaling in Hep G2 cells, and these apoptotic biochemical events are blocked by pretreatment with resveratrol, which exerts antioxidant effects.

Curcumin and cancer cells: how many ways can curry kill tumor cells selectively?

Cancer is a hyperproliferative disorder that is usually treated by chemotherapeutic agents that are toxic not only to tumor cells but also to normal cells, so these agents produce major side effects. In addition, these agents are highly expensive and thus not affordable for most. Moreover, such agents cannot be used for cancer prevention. Traditional medicines are generally free of the deleterious side effects and usually inexpensive. Curcumin, a component of turmeric (Curcuma longa), is one such agent that is safe, affordable, and efficacious. How curcumin kills tumor cells is the focus of this review. We show that curcumin modulates growth of tumor cells through regulation of multiple cell signaling pathways including cell proliferation pathway (cyclin D1, c-myc), cell survival pathway (Bcl-2, Bcl-xL, cFLIP, XIAP, c-IAP1), caspase activation pathway (caspase-8, 3, 9), tumor suppressor pathway (p53, p21) death receptor pathway (DR4, DR5), mitochondrial pathways, and protein kinase pathway (JNK, Akt, and AMPK). How curcumin selectively kills tumor cells, and not normal cells, is also described in detail.

Evaluation of the cytotoxicity and genotoxicity of curcumin in PC12 cells

Neurotoxicity induced by reactive oxygen species can appear as an adverse effect of chemotherapy treatment with platinum compounds, such as cisplatin. The use of this drug in clinical practice is limited due to its adverse effects, including nephrotoxicity, ototoxicity, neurotoxicity and genotoxicity. Functional foods or nutraceuticals have demonstrated potential neuroprotective activity in several experiments and models. This study aimed to investigate the possible cytotoxicity and genotoxicity/antigenotoxic effects of curcumin in PC12 cells exposed to cisplatin. Cell viability and genotoxicity/antigenotoxicity were evaluated by the MTT assay and micronucleus test, respectively. PC12 cells were treated with different concentrations of cisplatin and curcumin (0.5 -- 128 microg/mL). Analysis of the results showed that high concentrations of curcumin were cytotoxic and increased micronuclei frequency compared to the control group. In the associated treatments, at all three concentrations evaluated, curcumin significantly reduced the total frequency of micronuclei induced by cisplatin. Determining the cytotoxic and genotoxic/antigenotoxic effects of this frequently used antioxidant in a neuronal model is important to assess possible hazards when combined with other chemical agents, including chemotherapy drugs used in cancer therapy.

A novel curcumin assay with the metal ion Cu (II) as a simple probe by resonance light scattering technique

A fantastic resonance light scattering (RLS) enhancement phenomenon was found when the interaction between the metal ion Cu (II) and a natural antioxidant curcumin (C(21)H(20)O(6)) occurred in certain conditions. Based on this phenomenon, a novel and convenient assay of curcumin was developed and successfully applied on the determination of curcumin in human urine samples. This assay applied the RLS technique with a common metal ion Cu (II) as the spectral probe. In the pH range of 6.5-7.5, the interaction between Cu (II) and curcumin occurred and the weak RLS intensity of Cu (II) was greatly enhanced by curcumin. The maximum peak was located at 538.5 nm. Under the optimum conditions, the enhanced RLS intensity was proportional to the concentration of curcumin ranging from 0.4 to 60 microg ml(-1) with the detection limit of 0.07 microg ml(-1). The synthetic and human urine samples were determined satisfactorily. Good recoveries (98.8-102.5%) were obtained in the determination of urine samples, which proved that the assay proposed was reliable and applicable in the determination of curcumin in body fluid. In this work, the RLS and fluorescence spectral characteristics of the chemicals, the optimum conditions of the reaction and the influencing factors were investigated.

Impact of methylglyoxal and high glucose co-treatment on human mononuclear cells

Hyperglycemia and elevation of methylglyoxal (MG) are symptoms of diabetes mellitus (DM). In this report, we show that co-treatment of human mononuclear cells (HMNCs) with MG (5 μM) and high glucose (HG; 15 – 30 mM) induces apoptosis or necrosis. HG/MG co-treatment directly enhanced the reactive oxygen species (ROS) content in HMNCs, leading to decreased intracellular ATP levels, which control cell death via apoptosis or necrosis. Concentrations of 5 μM MG and 15 mM glucose significantly increased cytoplasmic free calcium and nitric oxide (NO) levels, loss of mitochondrial membrane potential (MMP), activation of caspases-9 and -3, and cell death. In contrast, no apoptotic biochemical changes were detected in HMNCs treated with 5 μM MG and 25 mM glucose, which appeared to undergo necrosis. Pretreatment with nitric oxide (NO) scavengers inhibited apoptotic biochemical changes induced by 5 μM MG/15 mM glucose, and increased the gene expression levels of p53 and p21 involved in apoptotic signaling. The results collectively suggest that the treatment dosage of MG and glucose determines the mode of cell death (apoptosis vs. necrosis) of HMNCs, and that both ROS and NO play important roles in MG/HG-induced apoptosis.

Anticancer and carcinogenic properties of curcumin: considerations for its clinical development as a cancer chemopreventive and chemotherapeutic agent

A growing body of research suggests that curcumin, the major active constituent of the dietary spice turmeric, has potential for the prevention and therapy of cancer. Preclinical data have shown that curcumin can both inhibit the formation of tumors in animal models of carcinogenesis and act on a variety of molecular targets involved in cancer development. In vitro studies have demonstrated that curcumin is an efficient inducer of apoptosis and some degree of selectivity for cancer cells has been observed. Clinical trials have revealed that curcumin is well tolerated and may produce antitumor effects in people with precancerous lesions or who are at a high risk for developing cancer. This seems to indicate that curcumin is a pharmacologically safe agent that may be used in cancer chemoprevention and therapy. Both in vitro and in vivo studies have shown, however, that curcumin may produce toxic and carcinogenic effects under specific conditions. Curcumin may also alter the effectiveness of radiotherapy and chemotherapy. This review article analyzes the in vitro and in vivo cancer-related activities of curcumin and discusses that they are linked to its known antioxidant and pro-oxidant properties. Several considerations that may help develop curcumin as an anticancer agent are also discussed.

Caffeine induces cell death via activation of apoptotic signal and inactivation of survival signal in human osteoblasts

Caffeine consumption is a risk factor for osteoporosis, but the precise regulatory mechanisms are currently unknown. Here, we show that cell viability decreases in osteoblasts treated with caffeine in a dose-dependent manner. This cell death is attributed primarily to apoptosis and to a smaller extent, necrosis. Moreover, caffeine directly stimulates intracellular oxidative stress. Our data support caffeine-induced apoptosis in osteoblasts via a mitochondria-dependent pathway. The apoptotic biochemical changes were effectively prevented upon pretreatment with ROS scavengers, indicating that ROS plays a critical role as an upstream controller in the caffeine-induced apoptotic cascade. Additionally, p21-activated protein kinase 2 (PAK2) and c-Jun N-terminal kinase (JNK) were activated in caffeine-treated osteoblasts. Experiments further found that PAK2 activity is required for caffeine-induced JNK activation and apoptosis. Importantly, our data also show that caffeine triggers cell death via inactivation of the survival signal, including the ERK- and Akt-mediated anti-apoptotic pathways. Finally, exposure of rats to dietary water containing 10~20 μM caffeine led to bone mineral density loss. These results demonstrate for the first time that caffeine triggers apoptosis in osteoblasts via activation of mitochondria-dependent cell death signaling and inactivation of the survival signal, and causes bone mineral density loss in vivo.

Curcumin-induced fibroblast apoptosis and in vitro wound contraction are regulated by antioxidants and heme oxygenase: implications for scar formation

Fibroblast apoptosis plays a crucial role in normal and pathological scar formation and therefore we studied whether the putative apoptosis-inducing factor curcumin affects fibroblast apoptosis and may function as a novel therapeutic. We show that 25-μM curcumin causes fibroblast apoptosis and that this could be inhibited by co-administration of antioxidants N-acetyl-l-cysteine (NAC), biliverdin or bilirubin, suggesting that reactive oxygen species (ROS) are involved. This is supported by our observation that 25-μM curcumin caused the generation of ROS, which could be completely blocked by addition of NAC or bilirubin. Since biliverdin and bilirubin are downstream products of heme degradation by heme oxygenase (HO), it has been suggested that HO-activity protects against curcumin-induced apoptosis. Interestingly, exposure to curcumin maximally induced HO-1 protein and HO-activity at 10–15 μM, whereas, at a concentration of >20-μM curcumin HO-1-expression and HO-activity was negligible. NAC-mediated inhibition of 25-μM curcumin-induced apoptosis was demonstrated to act in part via restored HO-1-induction, since the rescuing effect of NAC could be reduced by inhibiting HO-activity. Moreover pre-induction of HO-1 using 5-μM curcumin protected fibroblasts against 25-μM curcumin-induced apoptosis. On a functional level, fibroblast-mediated collagen gel contraction, an in vitro wound contraction model, was completely prevented by 25-μM curcumin, while this could be reversed by co-incubation with NAC, an effect that was also partially HO-mediated. In conclusion, curcumin treatment in high doses (>25 μM) may provide a novel way to modulate pathological scar formation through the induction of fibroblast apoptosis, while antioxidants, HO-activity and its effector molecules act as a possible fine-tuning regulator.

Methylglyoxal and high glucose co-treatment induces apoptosis or necrosis in human umbilical vein endothelial cells

Hyperglycemia and elevation of methylglyoxal (MG) are symptoms of diabetes mellitus (DM). We previously showed that high glucose (HG; 30 mM) or MG (50-400 microM) could induce apoptosis in mammalian cells, but these doses are higher than the physiological concentrations of glucose and MG in the plasma of DM patients. The physiological concentration of MG and glucose in the normal blood circulation is about 1 microM and 5 mM, respectively. Here, we show that co-treatment with concentrations of MG and glucose comparable to those seen in the blood circulation of DM patients (5 microM and 15-30 mM, respectively) could cause cell apoptosis or necrosis in human umbilical vein endothelial cells (HUVECs) in vitro. HG/MG co-treatment directly increased the reactive oxygen species (ROS) content in HUVECs, leading to increases in intracellular ATP levels, which can control cell death through apoptosis or necrosis. Co-treatment of HUVECs with 5 microM MG and 20 mM glucose significantly increased cytoplasmic free calcium levels, activation of nitric oxide synthase (NOS), caspase-3 and -9, cytochrome c release, and apoptotic cell death. In contrast, these apoptotic biochemical changes were not detected in HUVECs treated with 5 microM MG and 30 mM glucose, which appeared to undergo necrosis. Pretreatment with nitric oxide (NO) scavengers could inhibit 5 microM MG/20 mM glucose-induced cytochrome c release, decrease activation of caspase-9 and caspase-3, and increase the gene expression and protein levels of p53 and p21, which are known to be involved in apoptotic signaling. Inhibition of p53 protein expression using small interfering RNA (siRNA) blocked the activation of p21 and the cell apoptosis induced by 5 microM MG/20 mM glucose. In contrast, inhibition of p21 protein expression by siRNA prevented apoptosis in HUVECs but had no effect on p53 expression. These results collectively suggest that the treatment dosage of MG and glucose could determine the mode of cell death (apoptosis vs. necrosis) in HUVECs, and both ROS and NO played important roles in MG/HG-induced apoptosis of these cells.

Curcumin in cell death processes: a challenge for CAM of age-related pathologies

Curcumin, the yellow pigment from the rhizoma of Curcuma longa, is a widely studied phytochemical which has a variety of biological activities: anti-inflammatory and anti-oxidative. In this review we discuss the biological mechanisms and possible clinical effects of curcumin treatment on cancer therapy, and neurodegenerative diseases such as Alzheimer's Disease, with particular attention to the cell death processes induced by curcumin. Since oxidative stress and inflammation are major determinants of the aging process, we also argue that curcumin can have a more general effect that slows down the rate of aging. Finally, the effects of curcumin can be described as xenohormetic, since it activates a sort of stress response in mammalian cells.

Curcumin induced suicidal erythrocyte death

The natural nutrient component Curcumin with anti-inflammatory and antitumor activity has previously been shown to stimulate apoptosis of several nucleated cell types. The present study has been performed to explore whether Curcumin could similarly induce suicidal death of erythrocytes or eryptosis, which is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine exposure at the erythrocyte surface. Phosphatidylserine exposing cells are phagocytosed and thus rapidly cleared from circulating blood. Erythrocyte membrane scrambling may be triggered by increase of cytosolic Ca(2+) activity or formation of ceramide. To test for eryptosis, erythrocyte phosphatidylserine exposure has been estimated from annexin V binding, and erythrocyte volume from forward scatter in FACS analysis. Exposure of erythrocytes to Curcumin (= 1 microM) increased annexin V binding and decreased forward scatter, pointing to phosphatidylserine exposure at the cell surface and cell shrinkage. According to Fluo3 fluorescence Curcumin increased cytosolic Ca(2+) activity and according to immunofluorescence Curcumin increased ceramide formation. As shown previously, hypertonic shock (addition of 550mM sucrose), chloride removal and glucose depletion decreased the forward scatter and increased annexin V binding. The effects on annexin binding were enhanced in the presence of Curcumin. Exposure to Curcumin did, however, not significantly enhance the shrinking effect of hypertonic shock or Cl(-) removal and reversed the shrinking effect of glucose withdrawal. The present observations disclose a proeryptotic effect of Curcumin which may affect the life span of circulating erythrocytes.

Endothelin signaling in osteoblasts: global genome view and implication of the calcineurin/NFAT pathway

Patients with prostate cancer develop osteoblastic metastases when tumor cells arrive in the bone and stimulate osteoblasts by secreting growth-promoting factors. Endothelin 1 (ET-1) is believed to be a key factor in promoting osteoblastic metastasis. Selective blockade of the ET(A) receptor is an established strategy in the development of cancer therapeutics. However, the molecular mechanisms whereby prostate cancer promotes abnormal bone growth are not fully understood. In this study, we have applied genomic approaches to elucidate the molecular mechanism of stimulation of osteoblasts by ET-1. To examine the ET-1 axis, we generated genomic signatures for osteoblasts treated with ET-1, in the presence and absence of a selective ET(A) antagonist (ABT-627). The ET-1 signature was comprised of several motifs, such as osteoblastic differentiation, invasion, and suppression of apoptosis. The signature also pointed at possible activation of the calcineurin/NFAT pathway. We showed that ET-1 activates calcineurin and causes nuclear translocation of NFATc1, implicating the pathway in the ET-1-mediated stimulation of osteoblasts. We also showed that ET-1 inhibits apoptosis in osteoblasts, implying that the suppression of apoptosis may be an important factor in the promotion of osteoblastic growth by ET-1.