Curcumin is a modulator of bilayer material properties

Curcumin (1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) is the major bioactive compound in turmeric (Curcuma longa) with antioxidant, antiinflammatory, anticarcinogenic, and antimutagenic effects. At low muM concentrations, curcumin modulates many structurally and functionally unrelated proteins, including membrane proteins. Because the cell membranes' lipid bilayer serves as a gate-keeper and regulator of many cell functions, we explored whether curcumin modifies general bilayer properties using channels formed by gramicidin A (gA). gA channels form when two monomers from opposing monolayers associate to form a conducting dimer with a hydrophobic length that is less than the bilayer hydrophobic thickness; gA channel formation thus causes a local bilayer thinning. The energetic cost of this bilayer deformation alters the gA monomer <--> dimer equilibrium, which makes the channels' appearance rate and lifetime sensitive to changes in bilayer material properties, and the gA channels become probes for changes in bilayer properties. Curcumin decreases bilayer stiffness, increasing both gA channel lifetimes and appearance rates, meaning that the energetic cost of the gA-induced bilayer deformation is reduced. These results show that curcumin may exert some of its effects on a diverse range of membrane proteins through a bilayer-mediated mechanism.     

Apoptosis-Independent Alterations in Membrane Dynamics Induced by Curcumin

Curcumin is a well-known natural compound with antiinflammatory properties. Its antiproliferative effect and ability to modulate apoptotic response are considered essential in cancer therapy. The physicochemical properties of curcumin suggest membranous localization, which prompted an investigation of the mechanisms of membrane disturbances evoked by curcumin. We chose the erythrocyte as a convenient model for studying membrane effects of curcumin and showed its nonspecific, apoptosis-independent way of action. Curcumin was found to expand the cell membrane, inducing echinocytosis. Changes in cell shape were accompanied by transient exposure of phosphatidylserine. Membrane asymmetry was recovered by the action of aminophospholipid translocase, which remained active in the presence of curcumin. Lipids rearrangements and drug partitioning caused changes of lipid fluidity. Such nonspecific effects of curcumin on cellular membranes would produce artifacts of apoptosis measurement, since several methods are based on membrane changes.     

Curcumin inhibits cell motility and alters microfilament organization and function in prostate cancer cells

Curcumin is a dietary phytochemical associated with anti-tumorigenic effects, but the mechanisms by which it inhibits cancer cell growth and metastasis are not completely understood. For example, little information is available regarding the effects of curcumin on cytoskeletal organization and function. In this study, time-lapse video and immunofluorescence labeling methods were used to demonstrate that curcumin significantly alters microfilament organization and cell motility in PC-3 and LNCaP human prostate cancer cells in vitro. Curcumin rapidly arrests cell movements and subsequently alters cell shape in the highly motile PC-3 cell line, but has a less noticeable effect on the relatively immobile LNCaP cell line. Stress fibers are augmented, and the overall quantity of f-actin appears to increase in both types of cells following curcumin treatment. Cytochalasin B (CB) disrupts microfilament organization in both cell lines, and causes vigorous membrane blebbing in PC-3 cells, but not LNCaP cells. Pre-treatment of cells with curcumin suppresses changes in microfilament organization caused by CB, and blocks PC-3 membrane blebbing. At least some of the effects of curcumin appear to be mediated by protein kinase C (PKC), as treatment with the PKC inhibitor bisindolylmaleimide inhibits the ability of curcumin to block CB-induced membrane blebbing. These findings demonstrate that curcumin exerts significant effects on the actin cytoskeleton in prostate cancer cells, including altering microfilament organization and function. This is a novel observation that may represent an important mechanism by which curcumin functions as a chemopreventative agent, and as an inhibitor of angiogenesis and metastasis.     

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.     

Cardiolipin mediates curcumin interactions with mitochondrial membranes

Curcumin, the main molecular ingredient of the turmeric spice, has been reported to exhibit therapeutic properties for varied diseases and pathological conditions. While curcumin appears to trigger multiple signaling pathways, the precise mechanisms accounting for its therapeutic activity have not been deciphered. Here we show that curcumin exhibits significant interactions with cardiolipin (CL), a lipid exclusively residing in the mitochondrial membrane. Specifically, we found that curcumin affected the structures and dynamics of CL-containing biomimetic and biological mitochondrial membranes. Application of several biophysical techniques reveals the CL-promoted association and internalization of curcumin into lipid bilayers. In parallel, curcumin association with CL containing bilayers increased their fluidity and reduced lipid ordering. These findings suggest that membrane modifications mediated by CL interactions may play a role in the therapeutic functions of curcumin, and that the inner mitochondrial membrane in general might constitute a potential drug target.     

Dietary antioxidant curcumin inhibits microtubule assembly through tubulin binding

Curcumin, a component of turmeric, has potent antitumor activity against several tumor types. However, its molecular target and mechanism of antiproliferative activity are not clear. Here, we identified curcumin as a novel antimicrotubule agent. We have examined the effects of curcumin on cellular microtubules and on reconstituted microtubules in vitro. Curcumin inhibited HeLa and MCF-7 cell proliferation in a concentration-dependent manner with IC(50) of 13.8 +/- 0.7 microm and 12 +/- 0.6 microm, respectively. At higher inhibitory concentrations (> 10 microm), curcumin induced significant depolymerization of interphase microtubules and mitotic spindle microtubules of HeLa and MCF-7 cells. However, at low inhibitory concentrations there were minimal effects on cellular microtubules. It disrupted microtubule assembly in vitro, reduced GTPase activity, and induced tubulin aggregation. Curcumin bound to tubulin at a single site with a dissociation constant of 2.4 +/- 0.4 microm and the binding of curcumin to tubulin induced conformational changes in tubulin. Colchicine and podophyllotoxin partly inhibited the binding of curcumin to tubulin, while vinblastine had no effect on the curcumin-tubulin interactions. The data together suggested that curcumin may inhibit cancer cells proliferation by perturbing microtubule assembly dynamics and may be used to develop efficacious curcumin analogues for cancer chemotherapy.     

Curcumin inhibits growth of Saccharomyces cerevisiae through iron chelation

Curcumin, a polyphenol derived from turmeric, is an ancient therapeutic used in India for centuries to treat a wide array of ailments. Interest in curcumin has increased recently, with ongoing clinical trials exploring curcumin as an anticancer therapy and as a protectant against neurodegenerative diseases. In vitro, curcumin chelates metal ions. However, although diverse physiological effects have been documented for this compound, curcumin's mechanism of action on mammalian cells remains unclear. This study uses yeast as a model eukaryotic system to dissect the biological activity of curcumin. We found that yeast mutants lacking genes required for iron and copper homeostasis are hypersensitive to curcumin and that iron supplementation rescues this sensitivity. Curcumin penetrates yeast cells, concentrates in the endoplasmic reticulum (ER) membranes, and reduces the intracellular iron pool. Curcumin-treated, iron-starved cultures are enriched in unbudded cells, suggesting that the G(1) phase of the cell cycle is lengthened. A delay in cell cycle progression could, in part, explain the antitumorigenic properties associated with curcumin. We also demonstrate that curcumin causes a growth lag in cultured human cells that is remediated by the addition of exogenous iron. These findings suggest that curcumin-induced iron starvation is conserved from yeast to humans and underlies curcumin's medicinal properties.     

Cholesterol modulates curcumin partitioning and membrane effects

Curcumin, a polyphenol molecule, presents a wide range of biological activities as antioxidant, anticancer, anti-inflammatory, antimicrobial and wound healing. Although some strengths attributed to curcumin derive from promiscuous biological activity, possibly because curcumin can interfere on many membrane located processes, knowledge of underlying interactions are lacking. Mammalian cell membranes characteristically contain 25 to 50% cholesterol/phospholipid ratio; however, most studies involving lipid bilayers and curcumin consider pure phosphatidylcholine and compare effects of curcumin on membranes with those of cholesterol. We investigated the interaction of curcumin with lipid bilayers containing cholesterol mimicking mammalian cells, and used spectroscopy techniques to determine partition coefficients, rigidity parameters and lytic activity. We found that curcumin partitions into different lipid bilayers (10⁴ order coefficients that vary by less than a factor of two), containing cholesterol or not, and in the presence of sphingomyelin or phosphatidylserine. Curcumin decreases rigidity in all tested compositions, except that containing 40% cholesterol in which it increases the lipid packing order. In addition, curcumin induces leakage from giant unilamellar vesicles on a cholesterol concentration dependent way. Our results are compatible with the hypothesis of curcumin interaction with membranes being modulated by the liquid disordered phase and by the coexistence of liquid-ordered/liquid disordered phases. In bilayers containing cholesterol, curcumin assumes a more superficial location, drastically stiffens the 40% cholesterol bilayer and decreases the lytic effect. Our study may help researchers in the analysis of the biological effects of curcumin and curcumin-derived formulations by calling the attention to the discriminating role of the cholesterol content.     

Iron chelation in the biological activity of curcumin

Curcumin is among the more successful chemopreventive compounds investigated in recent years, and is currently in human trials to prevent cancer. The mechanism of action of curcumin is complex and likely multifactorial. We have made the unexpected observation that curcumin strikingly modulates proteins of iron metabolism in cells and in tissues, suggesting that curcumin has properties of an iron chelator. Curcumin increased mRNA levels of ferritin and GSTalpha in cultured liver cells. Unexpectedly, however, although levels of GSTalpha protein increased in parallel with mRNA levels in response to curcumin, levels of ferritin protein declined. Since iron chelators repress ferritin translation, we considered that curcumin may act as an iron chelator. To test this hypothesis, we measured the effect of curcumin on transferrin receptor 1, a protein stabilized under conditions of iron limitation, as well as the ability of curcumin to activate iron regulatory proteins (IRPs). Both transferrin receptor 1 and activated IRP, indicators of iron depletion, increased in response to curcumin. Consistent with the hypothesis that curcumin acts as an iron chelator, mice that were fed diets supplemented with curcumin exhibited a decline in levels of ferritin protein in the liver. These results suggest that iron chelation may be an additional mode of action of curcumin.     

Curcumin stimulates proliferation of embryonic neural progenitor cells and neurogenesis in the adult hippocampus

Curcumin is a natural phenolic component of yellow curry spice, which is used in some cultures for the treatment of diseases associated with oxidative stress and inflammation. Curcumin has been reported to be capable of preventing the death of neurons in animal models of neurodegenerative disorders, but its possible effects on developmental and adult neuroplasticity are unknown. In the present study, we investigated the effects of curcumin on mouse multi-potent neural progenitor cells (NPC) and adult hippocampal neurogenesis. Curcumin exerted biphasic effects on cultured NPC; low concentrations stimulated cell proliferation, whereas high concentrations were cytotoxic. Curcumin activated extracellular signal-regulated kinases (ERKs) and p38 kinases, cellular signal transduction pathways known to be involved in the regulation of neuronal plasticity and stress responses. Inhibitors of ERKs and p38 kinases effectively blocked the mitogenic effect of curcumin in NPC. Administration of curcumin to adult mice resulted in a significant increase in the number of newly generated cells in the dentate gyrus of hippocampus, indicating that curcumin enhances adult hippocampal neurogenesis. Our findings suggest that curcumin can stimulate developmental and adult hippocampal neurogenesis, and a biological activity that may enhance neural plasticity and repair.     

Curcumin suppresses the TPA-induced invasion through inhibition of PKCα-dependent MMP-expression in MCF-7 human breast cancer cells

Curcumin (diferuloylmethane) is a polyphenol derived from the plant turmeric (Curcuma longa), which is commonly used as a spice. Although anti-carcinogenic, anti-oxidant, anti-inflammation, and anti-angiogenic properties have been reported, the effect of curcumin on breast cancer metastasis is unknown. Matrix metalloproteinase-9 (MMP-9) is a major component in cancer cell invasion. In this study, we investigated the inhibitory effect of curcumin on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced MMP-9 expression and cell invasion and the molecular mechanisms involved in MCF-7 cells. Our results showed that curcumin inhibits TPA-induced MMP-9 expression and cell invasion through suppressing NF-κB and AP-1 activation. Also, curcumin strongly repressed the TPA-induced phosphorylation of p38 and JNK and inhibited TPA-induced translocation of PKCα from the cytosol to the membrane, but did not affect the translocation of PKCδ. These results indicate that curcumin-mediated inhibition of TPA-induced MMP-9 expression and cell invasion involves the suppression of the PKCα, MAPK and NF-κB/AP-1 pathway in MCF-7 cells. Curcumin may have potential value in restricting breast cancer metastasis.     

Photokilling of bacteria by the natural dye curcumin

Curcumin is a yellow-orange compound derived from the root of Curcuma longa (Zingiberaceae family), that has been used as a medicine, spice and coloring agent. Curcumin has proved nontoxic in a number of cell culture and whole animal studies. Curcumin has, however, been reported to have bactericidal effects at very high concentrations. When illuminated, curcumin exerted potent phototoxic effects in micromolar amounts. Gram-negative bacteria displayed greater resistance to curcumin phototoxicity relative to Gram-positive bacteria. Oxygen was required for curcumin phototoxicity. Curcumin binding to cells was not required for photokilling; the reactive intermediate therefore must be relatively long-lived. The mechanism(s) of curcumin phototoxicity may involve hydrogen peroxide production. Singlet excited oxygen was not detected.Publication no 35 of the Center for Photochemical Sciences     

Can curcumin provide an ideal contraceptive?

The population explosion, unintended pregnancies, sexually transmitted diseases, and cancer (cervical and breast) continue to cause major public health issues worldwide. Curcumin, diferuloyl methane, the yellow pigment component of the curry spice turmeric (Curcuma longa), has immense biological effects and has recently drawn considerable attention. Curcumin has antibacterial, antiviral, antiinflammatory, and anticancer properties. It has shown a lack of toxicity in animals and human clinical trials. Yet, its effect on reproduction has not been examined. The present study was conducted to examine if curcumin affects sperm function in vitro and fertility in vivo. Sperm (human and murine) were collected and incubated with curcumin to examine the effect on motility, capacitation/acrosome reaction, and in vitro fertilization. The effect on in vivo fertility using the mouse model was also examined. Incubation of sperm with curcumin caused a concentration-dependent decrease in sperm forward motility, capacitation/acrosome reaction, and murine fertilization in vitro. At higher concentrations, there was a complete block of sperm motility and function within 5-15 min. Administration of curcumin, especially intravaginally, caused a significant (P<0.001) reduction in fertility. The antifertility effect of curcumin was reversible. This is the first study to report the inhibitory effect of curcumin on sperm function, fertilization, and fertility. The findings suggest that curcumin may constitute a double-edged sword to block conception, infection, and cancer, thus providing an ideal contraceptive.     

Effect of curcumin on glioblastoma cells

Curcumin is a polyphenolic compound derived from Curcumin longa L. There are growing bodies of evidence revealing the antitumor effect of curcumin in different tumors; although the molecular mechanism behind this inhibition in glioblastoma multiform (GBM) still remains unclear. Here we investigated the antitumor activity of nano micelles curcumin compared with erlotinib in U-373 cells in monolayer cell cultures and spheroids models. Furthermore, we characterized affecting cell cycle perturbation, as well as apoptosis induction in GBM cells. The antiproliferative activity of nano micelles curcumin and erlotinib were assessed in monolayer and spheroid models. The influence of the cell cycle and expression levels of nuclear factor κB (NF-κB) and Wnt/β-catenin pathway was checked. Nano micelles curcumin suppressed cell growth in U-373 cells via modulation of Wnt and NF-κB pathways. Moreover, cells developed an early G2/M cell cycle arrest followed by sub-G1 apoptosis and apoptotic bodies formation posttreatment with nano micelles curcumin and erlotinib. In the core signaling pathways of GBM, nano micelles curcumin either significantly influences the NF-κB pathway by decreasing p-65 expression or significantly inhibits the Wnt/β-catenin pathway by declining cyclin D1 expression. In conclusion, we have shown that nano micelles curcumin effectively prevent proliferation, and invasion of GBM cells through perturbation of Wnt/β-catenin and NF-κB pathways, suggesting further investigations on the therapeutic application of this novel anticancer drug in in vivo models.     

Curcumin as a promising anticandidal of clinical interest

Curcumin, an important Asian spice, is part of many Indian food preparations. This work evaluates the antifungal activity of curcumin against 14 strains of Candida (10 clinical and 4 standard). Curcumin displayed antifungal properties against all tested Candida strains, with minimum inhibitory concentrations (MICs) varying from 250 to 2000 μg·mL?1. The in vitro effect of curcumin on growth, sterol content, proteinase secretion, and H+ extrusion by plasma membrane ATPase was investigated for 2 standard strains Candida albicans ATCC 10261 and Candida glabrata ATCC 90030 and compared with the effect of fluconazole. At MIC, curcumin inhibited H+ extrusion in 2 species of Candida by 42% and 32% in the absence of glucose and by 28% and 18% in the presence of glucose. Respective inhibition of H+ extrusion caused by the MIC of fluconazole was 85% and 89% in the absence of glucose and 61% and 66% in its presence. Ergosterol content decreased by 70% and 53% for the 2 strains following exposure to curcumin at MIC; comparative values for fluconazole at MIC were 93% and 98%. Curcumin and fluconazole decreased proteinase secretion by 49% and 53%, respectively, in C. albicans and by 39% and 46%, respectively, in C. glabrata. In conclusion, curcumin is found to be active against all tested clinical and standard strains but is less effective than fluconazole. Antifungal activity of curcumin might be originating from alteration of membrane-associated properties of ATPase activity, ergosterol biosynthesis, and proteinase secretion.     

Curcumin enhances the polyglutamine-expanded truncated N-terminal huntingtin-induced cell death by promoting proteasomal malfunction

Formation of neuronal intranuclear inclusions of the disease proteins that are ubiquitinated and often associated with various proteasome components is the major hallmark of the polyglutamine diseases. Curcumin is a polyphenolic compound having anti-inflammatory, anti-tumor, and anti-oxidative properties. Recently, curcumin has been reported to suppress the amyloid-beta accumulation, oxidative damage, and inflammation in the transgenic mice model of Alzheimer's disease. Here, we found that the treatment of curcumin increases the polyglutamine-expanded truncated N-terminal huntingtin (mutant huntingtin) aggregation and mutant huntingtin-dependent cell death. Curcumin also causes rapid proteasomal malfunction in the mutant huntingtin expressing cells in comparison with normal glutamine repeat expressing cells. Finally, we show that N-acetyl cysteine (NAC), a potent antioxidant, reverted the curcumin-induced mutant huntingtin aggregation and proteasomal malfunction in the mutant huntingtin expressing cells. NAC also protects curcumin-induced cell death. Our result suggests that curcumin promotes mutant huntingtin-induced cell death by mimicking proteasomal dysfunction.     

Curcumin inhibits bTREK-1 K+ channels and stimulates cortisol secretion from adrenocortical cells

Bovine adrenal zona fasciculata (AZF) cells express bTREK-1 K⁺ channels that set the resting membrane potential. Inhibition of these channels by adrenocorticotropic hormone (ACTH) is coupled to membrane depolarization and cortisol secretion. Curcumin, a phytochemical with medicinal properties extracted from the spice turmeric, was found to modulate both bTREK-1 K⁺ currents and cortisol secretion from AZF cells. In whole-cell patch clamp experiments, curcumin inhibited bTREK-1 with an IC₅₀ of 0.93 μM by a mechanism that was voltage-independent. bTREK-1 inhibition by curcumin occurred through interaction with an external binding site and was independent of ATP hydrolysis. Curcumin produced a concentration-dependent increase in cortisol secretion that persisted for up to 24 h. At a maximally effective concentration of 50 μM, curcumin increased secretion as much as 10-fold. These results demonstrate that curcumin potently inhibits bTREK-1 K⁺ channels and stimulates cortisol secretion from bovine AZF cells. The inhibition of bTREK-1 by curcumin may be linked to cortisol secretion through membrane depolarization. Since TREK-1 is widely expressed in a variety of cells, it is likely that some of the biological actions of curcumin, including its therapeutic effects, may be mediated through inhibition of these K⁺ channels.     

Curcumin is an in vivo inhibitor of angiogenesis

BACKGROUND: Curcumin is a small-molecular-weight compound that is isolated from the commonly used spice turmeric. In animal models, curcumin and its derivatives have been shown to inhibit the progression of chemically induced colon and skin cancers. The genetic changes in carcinogenesis in these organs involve different genes, but curcumin is effective in preventing carcinogenesis in both organs. A possible explanation for this finding is that curcumin may inhibit angiogenesis. MATERIALS AND METHODS: Curcumin was tested for its ability to inhibit the proliferation of primary endothelial cells in the presence and absence of basic fibroblast growth factor (bFGF), as well as its ability to inhibit proliferation of an immortalized endothelial cell line. Curcumin and its derivatives were subsequently tested for their ability to inhibit bFGF-induced corneal neovascularization in the mouse cornea. Finally, curcumin was tested for its ability to inhibit phorbol ester-stimulated vascular endothelial growth factor (VEGF) mRNA production. RESULTS: Curcumin effectively inhibited endothelial cell proliferation in a dose-dependent manner. Curcumin and its derivatives demonstrated significant inhibition of bFGF-mediated corneal neovascularization in the mouse. Curcumin had no effect on phorbol ester-stimulated VEGF production. CONCLUSIONS: These results indicate that curcumin has direct antiangiogenic activity in vitro and in vivo. The activity of curcumin in inhibiting carcinogenesis in diverse organs such as the skin and colon may be mediated in part through angiogenesis inhibition.     

Retracted: Curcumin derivative L6H4 inhibits proliferation and invasion of gastric cancer cell line BGC-823

Curcumin and its chalcone derivatives have well-known, explicit biological antitumor properties, such as instance antiproliferative and apoptotic effects via multiple molecular targets. In this study, we investigated the anticancer activity of curcumin derivative L6H4 (curcumin L6H4) on gastric cancer cells. Inhibitory effects of curcumin L6H4 on gastric cancer cells (BGC-823) were studied by the diphenyltetrazolium (MTT) assay, and cell apoptosis was detected by Annexin-V/propidium iodide (PI) staining and then analyzed by flow cytometry. A mouse xenotransplant gastric tumor model was established to detect the role of curcumin L6H4 in vivo. The apoptosis-related proteins p53, p21, Bax, and Bcl-2 in BGC-823 cells and mouse xenotransplant models treated with curcumin L6H4 were determined by Western blot analysis. Curcumin L6H4 can significantly inhibit the proliferation and induce the apoptosis of BGC-823 cells, thus enhancing the expression levels of p53, p21, Bax, and Bcl-2 noticeably in vivo and in vitro. Meanwhile, curcumin L6H4 can remarkably suppress the growth of tumor cells in animal models. These results suggest that curcumin derivative L6H4 has potent of antitumor properties in vitro or in vivo.