Inhibition of cyclic AMP-dependent protein kinase by curcumin

Oxidative Stress, Reductive Stress and Antioxidants in Vascular Pathogenesis and Aging

This review is focused on the mechanisms that regulate health, disease and aging redox status, the signal pathways that counteract oxidative and reductive stress, the role of food components and additives with antioxidant properties (curcumin, polyphenols, vitamins, carotenoids, flavonoids, etc.), and the role of the hormones irisin and melatonin in the redox homeostasis of animal and human cells. The correlations between the deviation from optimal redox conditions and inflammation, allergic, aging and autoimmune responses are discussed. Special attention is given to the vascular system, kidney, liver and brain oxidative stress processes. The role of hydrogen peroxide as an intracellular and paracrine signal molecule is also reviewed. The cyanotoxins β-N-methylamino-l-alanine (BMAA), cylindrospermopsin, microcystins and nodularins are introduced as potentially dangerous food and environment pro-oxidants.

Interactions between curcumin and human salt-induced kinase 3 elucidated from computational tools and experimental methods

Natural products are widely used for treating mitochondrial dysfunction-related diseases and cancers. Curcumin, a well-known natural product, can be potentially used to treat cancer. Human salt-induced kinase 3 (SIK3) is one of the target proteins for curcumin. However, the interactions between curcumin and human SIK3 have not yet been investigated in detail. In this study, we studied the binding models for the interactions between curcumin and human SIK3 using computational tools such as homology modeling, molecular docking, molecular dynamics simulations, and binding free energy calculations. The open activity loop conformation of SIK3 with the ketoenol form of curcumin was the optimal binding model. The I72, V80, A93, Y144, A145, and L195 residues played a key role for curcumin binding with human SIK3. The interactions between curcumin and human SIK3 were also investigated using the kinase assay. Moreover, curcumin exhibited an IC₅₀ (half-maximal inhibitory concentration) value of 131 nM, and it showed significant antiproliferative activities of 9.62 ± 0.33 µM and 72.37 ± 0.37 µM against the MCF-7 and MDA-MB-23 cell lines, respectively. This study provides detailed information on the binding of curcumin with human SIK3 and may facilitate the design of novel salt-inducible kinases inhibitors.

A State of the Art of Antioxidant Properties of Curcuminoids in Neurodegenerative Diseases

Neurodegenerative diseases represent a set of pathologies characterized by an irreversible and progressive, and a loss of neuronal cells in specific areas of the brain. Oxidative phosphorylation is a source of energy production by which many cells, such as the neuronal cells, meet their energy needs. Dysregulations of oxidative phosphorylation induce oxidative stress, which plays a key role in the onset of neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). To date, for most neurodegenerative diseases, there are no resolute treatments, but only interventions capable of alleviating the symptoms or slowing the course of the disease. Therefore, effective neuroprotection strategies are needed. In recent years, natural products, such as curcuminoids, have been intensively explored and studied for their therapeutic potentials in several neurodegenerative diseases. Curcuminoids are, nutraceutical compouns, that owen several therapeutic properties such as anti-oxidant, anti-inflammatory and neuroprotective effects. In this context, the aim of this review was to provide an overview of preclinical and clinical evidence aimed to illustrate the antioxidant effects of curcuminoids in neurodegenerative diseases. Promising results from preclinical studies encourage the use of curcuminoids for neurodegeneration prevention and treatment.

Curcumin downregulates 8-br-cAMP-induced steroidogenesis in mouse Leydig cells by suppressing the expression of Cyp11a1 and StAR independently of the PKA-CREB pathway

Although curcumin was widely applied as a functional food for different diseases, it was found to reduce serum testosterone level and fertility in male animals by unknown molecular mechanisms. Here in our study, we investigated the possible mechanisms of curcumin-suppressed testosterone production in Leydig cells. Our enzyme immunoassay results showed that curcumin cell-autonomously suppressed ovine luteinizing hormone-stimulated testosterone production in primary Leydig cells and 8-bromo-cyclic adenosine monophosphate (8-br-cAMP)-induced progesterone production in MA-10 cells. Furthermore, our real-time PCR, Western blot, and 22R-OHC/pregnenolone supplementing experiment data demonstrated that curcumin suppressed 8-br-cAMP-induced steroidogenesis in Leydig cells by inhibiting the expression of StAR and Cyp11a1. Interestingly, our Western blot data showed that although curcumin suppressed PKA activity, it did not alter the 8-br-cAMP-induced phosphorylation of CREB. On the contrary, the real-time PCR results showed that curcumin suppressed 8-br-cAMP-induced expression of Nr5a1 and Fos, which are crucial for cAMP-stimulated StAR and Cyp11a1 expression in Leydig cells. Collectively, our data demonstrated that curcumin may suppress cAMP-induced steroidogenesis in mouse Leydig cells by down-regulating Nr5a1/Fos-controlled StAR and Cyp11a1 expression independently of the PKA-CREB signaling pathway.

Inhibition of EV71 by curcumin in intestinal epithelial cells

EV71 is a positive-sense single-stranded RNA virus that belongs to the Picornaviridae family. EV71 infection may cause various symptoms ranging from hand-foot-and-mouth disease to neurological pathological conditions such as aseptic meningitis, ataxia, and acute transverse myelitis. There is currently no effective treatment or vaccine available. Various compounds have been examined for their ability to restrict EV71 replication. However, most experiments have been performed in rhabdomyosarcoma or Vero cells. Since the gastrointestinal tract is the entry site for this pathogen, we anticipated that orally ingested agents may exert beneficial effects by decreasing virus replication in intestinal epithelial cells. In this study, curcumin (diferuloylmethane, C₂₁H₂₀O₆), an active ingredient of turmeric (Curcuma longa Linn) with anti-cancer properties, was investigated for its anti-enterovirus activity. We demonstrate that curcumin treatment inhibits viral translation and increases host cell viability. Curcumin does not exert its anti-EV71 effects by modulating virus attachment or virus internal ribosome entry site (IRES) activity. Furthermore, curcumin-mediated regulation of mitogen-activated protein kinase (MAPK) signaling pathways is not involved. We found that protein kinase C delta (PKCδ) plays a role in virus translation in EV71-infected intestinal epithelial cells and that curcumin treatment decreases the phosphorylation of this enzyme. In addition, we show evidence that curcumin also limits viral translation in differentiated human intestinal epithelial cells. In summary, our data demonstrate the anti-EV71 properties of curcumin, suggesting that ingestion of this phytochemical may protect against enteroviral infections.

Determining whether curcumin degradation/condensation is actually bioactivation (Review)

Curcumin has been shown to exert therapeutic or protective effects against a variety of diseases, such as cancer, pulmonary diseases, neurological, liver, metabolic, autoimmune, cardiovascular diseases and numerous other chronic ailments. Over 116 clinical studies on curcumin in humans were registered with the US National Institutes of Health in 2015. However, it is mystifying how curcumin can be so effective in the treatment of many diseases since it has very low water solubility and bioavailability. Furthermore, curcumin is not stable under various conditions; its degradation or condensation into different bioactive compounds may be responsible for its biological activities rather than curcumin itself. In this review, we provide evidence of curcumin degradation and condensation into different compounds which have or may have health benefits themselves. Literature reviews strongly suggest that these molecules contribute to the observed health benefits, rather than curcumin itself.

Molecular mechanisms of curcumin action: gene expression

Curcumin derived from the tropical plant Curcuma longa has a long history of use as a dietary agent, food preservative, and in traditional Asian medicine. It has been used for centuries to treat biliary disorders, anorexia, cough, diabetic wounds, hepatic disorders, rheumatism, and sinusitis. The preventive and therapeutic properties of curcumin are associated with its antioxidant, anti-inflammatory, and anticancer properties. Extensive research over several decades has attempted to identify the molecular mechanisms of curcumin action. Curcumin modulates numerous molecular targets by altering their gene expression, signaling pathways, or through direct interaction. Curcumin regulates the expression of inflammatory cytokines (e.g., TNF, IL-1), growth factors (e.g., VEGF, EGF, FGF), growth factor receptors (e.g., EGFR, HER-2, AR), enzymes (e.g., COX-2, LOX, MMP9, MAPK, mTOR, Akt), adhesion molecules (e.g., ELAM-1, ICAM-1, VCAM-1), apoptosis related proteins (e.g., Bcl-2, caspases, DR, Fas), and cell cycle proteins (e.g., cyclin D1). Curcumin modulates the activity of several transcription factors (e.g., NF-κB, AP-1, STAT) and their signaling pathways. Based on its ability to affect multiple targets, curcumin has the potential for the prevention and treatment of various diseases including cancers, arthritis, allergies, atherosclerosis, aging, neurodegenerative disease, hepatic disorders, obesity, diabetes, psoriasis, and autoimmune diseases. This review summarizes the molecular mechanisms of modulation of gene expression by curcumin.

Rottlerin and curcumin: a comparative analysis

Rottlerin and curcumin are natural plant polyphenols with a long tradition in folk medicine. Over the past two decades, curcumin has been extensively investigated, while rottlerin has received much less attention, in part, as a consequence of its reputation as a selective PKCδ inhibitor. A comparative analysis of genomic, proteomic, and cell signaling studies revealed that rottlerin and curcumin share a number of targets and have overlapping effects on many biological processes. Both molecules, indeed, modulate the activity and/or expression of several enzymes (PKCδ, heme oxygenase, DNA methyltransferase, cyclooxygenase, lipoxygenase) and transcription factors (NF-κB, STAT), and prevent aggregation of different amyloid precursors (α-synuclein, amyloid Aβ, prion proteins, lysozyme), thereby exhibiting convergent antioxidant, anti-inflammatory, and antiamyloid actions. Like curcumin, rottlerin could be a promising candidate in the fight against a variety of human diseases.

Synthetic curcumin analog EF31 inhibits the growth of head and neck squamous cell carcinoma xenografts

Objectives are to examine the efficacy, pharmacokinetics, and toxicology of a synthetic curcumin analog EF31 in head and neck squamous cell carcinoma. The synthesis of EF31 was described for the first time. Solubility of EF24 and EF31 was compared using nephelometric analysis. Human head and neck squamous cell carcinoma Tu212 xenograft tumors were established in athymic nude mice and treated with EF31 i.p. once daily five days a week for about 5-6 weeks. The long term effect of EF31 on the NF-κB signaling system in the tumors was examined by Western blot analysis. EF31 at 25 mg kg(-1), i.p. inhibited tumor growth almost completely. Solubilities of EF24 and EF31 are <10 and 13 μg mL(-1) or <32 and 47 μM, respectively. The serum chemistry profiles of treated mice were within the limits of normal, they revealed a linear increase of C(max). EF31 decreased the level of phosphorylation of NF-κB p65. In conclusion, the novel synthetic curcumin analog EF31 is efficacious in inhibiting the growth of Tu212 xenograft tumors and may be useful for treating head and neck squamous cell carcinoma. The long term EF31 treatment inhibited NF-κB p65 phosphorylation in xenografts, implicating downregulation of cancer promoting transcription factors such as angiogenesis and metastasis.

Binding of isoxazole and pyrazole derivatives of curcumin with the activator binding domain of novel protein kinase C

The protein kinase C (PKC) family of serine/threonine kinases is an attractive drug target because of its involvement in the regulation of various cellular functions, including cell growth, differentiation, metabolism, and apoptosis. The endogenous PKC activator diacylglycerol contains two long carbon chains, which are attached to the glycerol moiety via ester linkage. Natural product curcumin (1), the active constituent of Curcuma L., contains two carbonyl and two hydroxyl groups. It modulates PKC activity and binds to the activator binding site (Majhi et al., Bioorg. Med. Chem.2010, 18, 1591). To investigate the role of the carbonyl and hydroxyl groups of curcumin in PKC binding and to develop curcumin derivatives as effective PKC modulators, we synthesized several isoxazole and pyrazole derivatives of curcumin (2-6), characterized their absorption and fluorescence properties, and studied their interaction with the activator-binding second cysteine-rich C1B subdomain of PKCδ, PKCε and PKCθ. The EC(50)s of the curcumin derivatives for protein fluorescence quenching varied in the range of 3-25 μM. All the derivatives showed higher binding with the PKCθC1B compared with PKCδC1B and PKCεC1B. Fluorescence emission maxima of 2-5 were blue shifted in the presence of the C1B domains, confirming their binding to the protein. Molecular docking revealed that hydroxyl, carbonyl and pyrazole ring of curcumin (1), pyrazole (2), and isoxazole (4) derivatives form hydrogen bonds with the protein residues. The present result shows that isoxazole and pyrazole derivatives bind to the activator binding site of novel PKCs and both carbonyl and hydroxy groups of curcumin play roles in the binding process, depending on the nature of curcumin derivative and the PKC isotype used.

Curcumin modulates PKCα activity by a membrane-dependent effect

Curcumin modulates the activity of protein kinase Cα (PKCα) when assayed in the presence of vesicles including phosphatidylcholine, phosphatidylserine and diacylglycerol. Increasing concentrations of curcumin progressively increased PKCα activity at concentrations lower than 20μM, but at higher concentrations of curcumin the activity decreased although, at concentrations of curcumin of up to 100μM the activity was always higher than the basal one (in the absence of curcumin). The maximum activity was reached at 3μM curcumin, at 20 and 30mol% of phosphatidylserine, 10μM Ca(2+) and 2mol% diacylglycerol. The same type of modulation was observed when changing the concentration of phosphatidylserine, diacylglycerol and Ca(2+). No effect of curcumin was found when the activity was assayed in the presence of Triton X-100 mixed micelles which included phosphatidylserine and diacylglycerol, indicating that the effect of curcumin was membrane-dependent. The pattern of binding of PKCα to membrane vesicles as a function of curcumin concentration closely correlated with the pattern of activating effect. It was concluded that the effect of curcumin on PKCα activity was related to its effect on the membrane, which may modulate the binding of the enzyme to the membrane.

The targets of curcumin

Curcumin (diferuloylmethane), an orange-yellow component of turmeric or curry powder, is a polyphenol natural product isolated from the rhizome of the plant Curcuma longa. For centuries, curcumin has been used in some medicinal preparation or used as a food-coloring agent. In recent years, extensive in vitro and in vivo studies suggested curcumin has anticancer, antiviral, antiarthritic, anti-amyloid, antioxidant, and anti-inflammatory properties. The underlying mechanisms of these effects are diverse and appear to involve the regulation of various molecular targets, including transcription factors (such as nuclear factor-kB), growth factors (such as vascular endothelial cell growth factor), inflammatory cytokines (such as tumor necrosis factor, interleukin 1 and interleukin 6), protein kinases (such as mammalian target of rapamycin, mitogen-activated protein kinases, and Akt) and other enzymes (such as cyclooxygenase 2 and 5 lipoxygenase). Thus, due to its efficacy and regulation of multiple targets, as well as its safety for human use, curcumin has received considerable interest as a potential therapeutic agent for the prevention and/or treatment of various malignant diseases, arthritis, allergies, Alzheimer's disease, and other inflammatory illnesses. This review summarizes various in vitro and in vivo pharmacological aspects of curcumin as well as the underlying action mechanisms. The recently identified molecular targets and signaling pathways modulated by curcumin are also discussed here.

Curcumin prevents leptin raising glucose levels in hepatic stellate cells by blocking translocation of glucose transporter-4 and increasing glucokinase

BACKGROUND AND PURPOSE

Hyperleptinemia is commonly found in obese patients, associated with non-alcoholic steatohepatitis and hepatic fibrosis. Hepatic stellate cells (HSCs) are the most relevant effectors during hepatic fibrogenesis. We recently reported that leptin stimulated HSC activation, which was eliminated by curcumin, a phytochemical from turmeric. This study was designed to explore the underlying mechanisms, focusing on their effects on intracellular glucose in HSCs. We hypothesized that leptin stimulated HSC activation by elevating the level of intracellular glucose, which was eliminated by curcumin by inhibiting the membrane translocation of glucose transporter-4 (GLUT4) and inducing the conversion of glucose to glucose-6-phosphate (G-6-P).

EXPERIMENTAL APPROACH

Levels of intracellular glucose were measured in rat HSCs and immortalized human hepatocytes. Contents of GLUT4 in cell fractions were analysed by Western blotting analyses. Activation of signalling pathways was assessed by comparing phosphorylation levels of protein kinases.

KEY RESULTS

Leptin elevated the level of intracellular glucose in cultured HSCs, which was diminished by curcumin. Curcumin suppressed the leptin-induced membrane translocation of GLUT4 by interrupting the insulin receptor substrates/phosphatidyl inositol 3-kinase/AKT signalling pathway. Furthermore, curcumin stimulated glucokinase activity, increasing conversion of glucose to G-6-P.

CONCLUSIONS AND IMPLICATIONS

Curcumin prevented leptin from elevating levels of intracellular glucose in activated HSCs in vitro by inhibiting the membrane translocation of GLUT4 and stimulating glucose conversion, leading to the inhibition of HSC activation. Our results provide novel insights into mechanisms of curcumin in inhibiting leptin-induced HSC activation.

An aqueous extract of Curcuma longa (turmeric) rhizomes stimulates insulin release and mimics insulin action on tissues involved in glucose homeostasis in vitro

Curcuma longa (turmeric) has been used widely as a spice, particularly in Asian countries. It is also used in the Ayurvedic system of medicine as an antiinflammatory and antimicrobial agent and for numerous other curative properties. The aim of this study was to investigate the effects of an aqueous extract of Curcuma longa (AEC) on tissues involved in glucose homeostasis. The extract was prepared by soaking 100 g of ground turmeric in 1 L of water, which was filtered and stored at -20°C prior to use. Pancreas and muscle tissues of adult mice were cultured in DMEM with 5 or 12 mmol/L glucose and varying doses of extract. The AEC stimulated insulin secretion from mouse pancreatic tissues under both basal and hyperglycaemic conditions, although the maximum effect was only 68% of that of tolbutamide. The AEC induced stepwise stimulation of glucose uptake from abdominal muscle tissues in the presence and absence of insulin, and the combination of AEC and insulin significantly potentiated the glucose uptake into abdominal muscle tissue. However, this effect was attenuated by wortmannin, suggesting that AEC possibly acts via the insulin-mediated glucose uptake pathway. In summary, water soluble compounds of turmeric exhibit insulin releasing and mimicking actions within in vitro tissue culture conditions.

beta-Cyclodextrin-curcumin self-assembly enhances curcumin delivery in prostate cancer cells

Curcumin, a hydrophobic polyphenolic compound derived from the rhizome of the herb Curcuma longa, possesses a wide range of biological applications including cancer therapy. However, its prominent application in cancer treatment is limited due to sub-optimal pharmacokinetics and poor bioavailability at the tumor site. In order to improve its hydrophilic and drug delivery characteristics, we have developed a beta-cyclodextrin (CD) mediated curcumin drug delivery system via encapsulation technique. Curcumin encapsulation into the CD cavity was achieved by inclusion complex mechanism. Curcumin encapsulation efficiency was improved by increasing the ratio of curcumin to CD. The formations of CD-curcumin complexes were characterized by Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA), scanning electron microscope (SEM), and transmission electron microscope (TEM) analyses. An optimized CD-curcumin complex (CD30) was evaluated for intracellular uptake and anti-cancer activity. Cell proliferation and clonogenic assays demonstrated that beta-cyclodextrin-curcumin self-assembly enhanced curcumin delivery and improved its therapeutic efficacy in prostate cancer cells compared to free curcumin.

Binding of curcumin and its long chain derivatives to the activator binding domain of novel protein kinase C

Protein kinase C (PKC) is a family of serine/threonine kinases that play a central role in cellular signal transduction. The second messenger diacylglycerol having two long carbon chains acts as the endogenous ligand for the PKCs. Polyphenol curcumin, the active constituent of Curcuma longa is an anti-cancer agent and modulates PKC activity. To develop curcumin derivatives as effective PKC activators, we synthesized several long chain derivatives of curcumin, characterized their absorption and fluorescence properties and studied their interaction with the activator binding second cysteine-rich C1B subdomain of PKCdelta, PKCepsilon and PKCtheta. Curcumin (1) and its C16 long chain analog (4) quenched the intrinsic fluorescence of PKCdeltaC1B, PKCepsilonC1B and PKCthetaC1B in a manner similar to that of PKC activator 12-O-tetradecanoylphorbol 13-acetate (TPA). The EC(50)s of the curcumin derivatives for fluorescence quenching varied in the range of 4-11 microM, whereas, EC(50)s for TPA varied in the range of 3-6 microM. Fluorescence emission maxima of 1 and 4 were blue shifted and the fluorescence anisotropy values were increased in the presence of the C1B domains in a manner similar to that shown by the fluorescent analog of TPA, sapintoxin-D, confirming that they were bound to the proteins. Molecular docking of 1 and 4 with novel PKC C1B revealed that both the molecules form hydrogen bonds with the protein residues. The present result shows that curcumin and its long chain derivatives bind to the C1B subdomain of novel PKCs and can be further modified structurally to improve its binding and activity.

Curcumin inhibits ACTH- and angiotensin II-stimulated cortisol secretion and Ca(v)3.2 current

Adrenocorticotropic hormone and angiotensin II stimulate cortisol secretion from bovine adrenal zona fasciculata cells by the activation of adenylate cyclase and phospholipase C-coupled receptors. Curcumin (1- 20 muM), a compound found in the spice turmeric, inhibited cortisol secretion stimulated by ACTH, AngII, and 8CPT-cAMP. Curcumin also suppressed ACTH-stimulated increases in mRNAs coding for steroid acute regulatory protein and CYP11a1 steroid hydroxylase. In whole cell patch clamp recordings from AZF cells, curcumin at slightly higher concentrations also inhibited Ca(v)3.2 current. These results identify curcumin as an effective inhibitor of ACTH- and AngII-stimulated cortisol secretion. The inhibition of Ca(v)3.2 current by curcumin may contribute to its suppression of secretion.

Pharmacological basis for the role of curcumin in chronic diseases: an age-old spice with modern targets

Curcumin (diferuloylmethane), a yellow pigment in the spice turmeric (also called curry powder), has been used for centuries as a treatment for inflammatory diseases. Extensive research within the past two decades has shown that curcumin mediates its anti-inflammatory effects through the downregulation of inflammatory transcription factors (such as nuclear factor kappaB), enzymes (such as cyclooxygenase 2 and 5 lipoxygenase) and cytokines (such as tumor necrosis factor, interleukin 1 and interleukin 6). Because of the crucial role of inflammation in most chronic diseases, the potential of curcumin has been examined in neoplastic, neurological, cardiovascular, pulmonary and metabolic diseases. The pharmacodynamics and pharmacokinetics of curcumin have been examined in animals and in humans. Various pharmacological aspects of curcumin in vitro and in vivo are discussed in detail here.

Role of curcumin in health and disease

Curcumin (diferuloylmethane) is an orange-yellow component of turmeric (Curcuma longa), a spice often found in curry powder. In recent years, considerable interest has been focused on curcumin due to its use to treat a wide variety of disorders without any side effects. It is one of the major curcuminoids of turmeric, which impart its characteristic yellow colour. It was used in ancient times on the Indian subcontinent to treat various illnesses such as rheumatism, body ache, skin diseases, intestinal worms, diarrhoea, intermittent fevers, hepatic disorders, biliousness, urinary discharges, dyspepsia, inflammations, constipation, leukoderma, amenorrhea, and colic. Curcumin has the potential to treat a wide variety of inflammatory diseases including cancer, diabetes, cardiovascular diseases, arthritis, Alzheimer's disease, psoriasis, etc, through modulation of numerous molecular targets. This article reviews the use of curcumin for the chemoprevention and treatment of various diseases.

CELL GROWTH REGULATION

Curcumin, the active ingredient of turmeric (Curcuma longa) used in culinary and medical practices in Asia, has immense potential for being used in cancer chemotherapy because of its control over the cell growth regulatory mechanisms. The present chapter throws light on the role of curcumin in modulating the various phases of the cell cycle and its apoptosis-inducing effects. This is followed by a discussion on the implications of these effects of curcumin for its use as a chemotherapeutic agent in cancer. Curcumin affects various cell cycle proteins and checkpoints involving downregulation of some of the cyclins and cyclin-dependent kinases, upregulation of cdk inhibitors, and inhibition of DNA synthesis. In addition, curcumin also exerts indirect control over cell division such as inhibition of telomerase activity. Remarkably, some studies point toward a selective growth-inhibitory effect of curcumin on transformed cell lines compared to nontransformed cell lines. Curcumin has also been demonstrated to have proapoptotic effects in several in vitro studies, mostly through the mitochondria-mediated pathway of apoptosis. Curcumin-mediated regulation of apoptosis involves caspases, Bcl2 family members, inhibitors of apoptosis proteins, and heat shock proteins. The accumulating data on the in vitro and in vivo actions of curcumin together with the ongoing human clinical trials will provide a better understanding of curcumin-mediated cell growth regulation, ultimately catering to the needs of human welfare.

CURCUMIN: THE INDIAN SOLID GOLD

Turmeric, derived from the plant Curcuma longa, is a gold-colored spice commonly used in the Indian subcontinent, not only for health care but also for the preservation of food and as a yellow dye for textiles. Curcumin, which gives the yellow color to turmeric, was first isolated almost two centuries ago, and its structure as diferuloylmethane was determined in 1910. Since the time of Ayurveda (1900 Bc) numerous therapeutic activities have been assigned to turmeric for a wide variety of diseases and conditions, including those of the skin, pulmonary, and gastrointestinal systems, aches, pains, wounds, sprains, and liver disorders. Extensive research within the last half century has proven that most of these activities, once associated with turmeric, are due to curcumin. Curcumin has been shown to exhibit antioxidant, anti-inflammatory, antiviral, antibacterial, antifungal, and anticancer activities and thus has a potential against various malignant diseases, diabetes, allergies, arthritis, Alzheimer's disease, and other chronic illnesses. These effects are mediated through the regulation of various transcription factors, growth factors, inflammatory cytokines, protein kinases, and other enzymes. Curcumin exhibits activities similar to recently discovered tumor necrosis factor blockers (e.g., HUMIRA, REMICADE, and ENBREL), a vascular endothelial cell growth factor blocker (e.g., AVASTIN), human epidermal growth factor receptor blockers (e.g., ERBITUX, ERLOTINIB, and GEFTINIB), and a HER2 blocker (e.g., HERCEPTIN). Considering the recent scientific bandwagon that multitargeted therapy is better than monotargeted therapy for most diseases, curcumin can be considered an ideal "Spice for Life".

Modulation of protein kinase C by curcumin; inhibition and activation switched by calcium ions

BACKGROUND AND PURPOSE

Previous studies have identified the natural polyphenol curcumin as a protein kinase C (PKC) inhibitor. In contrast, we found significant stimulation of PKC activity following curcumin treatment. Thus, the mechanism of curcumin interaction with PKC was investigated.

EXPERIMENTAL APPROACH

We employed phosphorylation assays in the presence of soluble or membrane-bound PKC substrates, followed by SDS-PAGE, autoradiography and phosphorylation intensity measurements.

KEY RESULTS

Curcumin inhibited PKC in the absence of membranes whereas stimulation was observed in the presence of membranes. Further analysis indicated that curcumin decreased PKC activity by competition with Ca(2+) stimulation of the kinase, resulting in inhibition of activity at lower Ca(2+) concentrations and stimulation at higher Ca(2+) concentrations. The role of the membrane is likely to be facilitation of Ca(2+)-binding to the kinase, thus relieving the curcumin inhibition observed at limited Ca(2+) concentrations. Curcumin was found to mildly stimulate the catalytic subunit of PKC, which does not require Ca(2+) for activation. In addition, studies on Ca(2+)-independent PKC isoforms as well as another curcumin target (the sarcoplasmic reticulum Ca(2+)-ATPase) confirmed a correlation between Ca(2+) concentration and the curcumin effects.

CONCLUSIONS AND IMPLICATIONS

Curcumin competes with Ca(2+) for the regulatory domain of PKC, resulting in a Ca(2+)-dependent dual effect on the kinase. We propose that curcumin interacts with the Ca(2+)-binding domains in target proteins. To our knowledge, this is the first study that defines an interaction domain for curcumin, and provides a rationale for the broad specificity of this polyphenol as a chemopreventive drug.

Elucidation of anti-allergic activities of curcumin-related compounds with a special reference to their anti-oxidative activities

The anti-allergic and anti-oxidative activities of curcumin-related compounds (glycosides, reductants and bis-demethoxy analogs) were investigated to elucidate the underlying active mechanisms and structural features of curcumin in exerting these activities. The anti-allergic activities were assessed by measurement of histamine release from rat basophilic leukemia cells, RBL-2H3. Curcumin and tetrahydrocurcumin (THC) caused a marked decrease in histamine release. Glycosides of curcumin, bis-demethoxycurcumin and THC also inhibited the release of histamine, though less potently than curcumin did. The anti-oxidative activities were assessed by measurement of cell-free or cellular radical scavenging. All compounds but diglycosides or bis-demethoxycurcumin analogs distinctly exerted anti-oxidative effects. The relationship between both of these activities revealed that all compounds with potent radical scavenging activities caused a definite decrease in histamine release, but some compounds with non-potent radical scavenging activities also inhibited the histamine release. These results suggest that the hydroxy groups of curcumin play a significant role in exerting both the anti-oxidative and anti-allergic activities, and that most of the compounds develop the anti-allergic activities through mechanisms related to anti-oxidative activities, but some through mechanisms unrelated to anti-oxidation activity.

Thioredoxin reductase is irreversibly modified by curcumin: a novel molecular mechanism for its anticancer activity

The thioredoxin reductase (TrxR) isoenzymes, TrxR1 in cytosol or nucleus and TrxR2 in mitochondria, are essential mammalian selenocysteine (Sec)-containing flavoenzymes with a -Gly-Cys-Sec-Gly active site. TrxRs are the only enzymes catalyzing the NADPH-dependent reduction of the active site disulfide in thioredoxins (Trxs), which play essential roles in substrate reductions, defense against oxidative stress, and redox regulation by thiol redox control. TrxRs have been found to be overexpressed by a number of human tumors. Curcumin, which is consumed daily by millions of people, is a polyphenol derived from the plant Curcuma longa. This phytochemical has well known anticancer and antiangiogenic properties. In this study we report that rat TrxR1 activity in Trx-dependent disulfide reduction was inhibited by curcumin. The IC(50) value for the enzyme was 3.6 microM after incubation at room temperature for 2 h in vitro. The inhibition occurred with enzyme only in the presence of NADPH and persisted after removal of curcumin. By using mass spectrometry and blotting analysis, we proved that this irreversible inhibition by curcumin was caused by alkylation of both residues in the catalytically active site (Cys(496)/Sec(497)) of the enzyme. However, the curcumin-modified enzyme showed a strongly induced NADPH oxidase activity to produce reactive oxygen species. Inhibition of TrxR by curcumin added to cultured HeLa cells was also observed with an IC(50) of around 15 microM. Modification of TrxR by curcumin provides a possible mechanistic explanation for its cancer preventive activity, shifting the enzyme from an antioxidant to a prooxidant.

Curcumin inhibits ultraviolet light induced human immunodeficiency virus gene expression

Recently, we reported that the herbal drug St. John's Wort is a potent inhibitor of UV-induced HIV-LTR activation in stably transfected HIVcat/HeLa cells. Our previous studies have demonstrated that the activation of p38 MAP kinase (stress-activated protein kinase-2) and NF-kappaB are both required for a full UV-induced HIV gene expression response. In this study we have investigated the mechanism by which curcumin inhibits UV-activated HIV-LTR gene expression. We found that treatment of HIVcat/HeLa cells with micromolar concentrations of curcumin completely abolished UV activation of HIV gene expression. Curcumin treatment at similar doses as those used to inhibit HIV gene expression also effectively blocked UV activation of NF-kappaB, as demonstrated by electrophoretic mobility shift assay. In contrast, curcumin did not inhibit UV-induced phosphorylation of p38 MAP kinase. This observation was also supported by findings that curcumin did not inhibit UV-induced phosphorylation of CREB/ATF-1 and ATF-2. Although curcumin was ineffective in preventing UV-induced p44/42 MAP kinase phosphorylation, the JNK (1 and 2) and AP-1 activation were efficiently blocked by curcumin in HeLa cells. We conclude that the mechanism by which curcumin modulates UV activation of HIV-LTR gene expression mainly involves the inhibition of NF-kappaB activation.

Requirement for PIKfyve enzymatic activity in acute and long-term insulin cellular effects

PIKfyve is a phosphoinositide 5-kinase that can also act as a protein kinase. PIKfyve's role in acute insulin action has been suggested on the basis of its association with the insulin stimulatable phosphatidylinositol-3-kinase and the ability of acute insulin to recruit and phosphorylate PIKfyve on intracellular membranes of 3T3-L1 adipocytes. Here we have examined several classical insulin-regulated long- and short-term responses in insulin-sensitive cells expressing high levels of either active PIKfyve or kinase-dead mutants with a dominant-negative effect. Up-regulation of PIKfyve protein expression was documented in the early stages of differentiation of cultured 3T3-L1 fibroblasts into adipocytes and a kinase-dead mutant, PIKfyveDeltaK, introduced into the preadipocyte stage profoundly delayed the hormone-induced adipogenesis. Next, insulin-induced mitogenesis was markedly inhibited in HEK293 stable cell lines, inducibly expressing the dominant-negative kinase-dead PIKfyve(K1831E) mutant but not in cells expressing PIKfyve(WT). Similarly, expression of the dominant negative mutants PIKfyve(K1831E) or PIKfyveDeltaK strongly inhibited insulin-stimulated translocation of GLUT4 in 3T3-L1 adipocytes, or GLUT1-mediated glucose uptake in Chinese hamster ovary T cells expressing the human insulin receptor. Expression of PIKfyveDeltaK and PIKfyve(WT) in Chinese hamster ovary T cells decreased or increased, respectively, insulin-stimulated Akt phosphorylation at Ser473 but not at Thr308. Furthermore, a powerful inhibition of PIKfyve was documented at a very low concentration (ID(50) = 6 micro M) of the cell-permeable kinase inhibitor curcumin. When introduced into 3T3-L1 adipocytes, curcumin markedly inhibited insulin-induced GLUT4 translocation and glucose transport. Together these data indicate that PIKfyve enzymatic activity functions as a positive regulatory intermediate in insulin acute and long-term biological responses and identify Ser473 in Akt as one potential PIKfyve downstream target.

Drug-induced suppression of phosphorylase kinase activity correlates with resolution of psoriasis as assessed by clinical, histological and immunohistochemical parameters

BACKGROUND

Phosphorylase kinase (PhK), also known as adenosine triphosphate (ATP)-phosphorylase b phosphotransferase, integrates multiple calcium/calmodulin-dependent signalling pathways, including those involved in cell migration and cell proliferation, while coupling these pathways to glycogenolysis and ATP-dependent phosphorylation, thus ensuring continuing energy supply for these activities.

OBJECTIVES

Our laboratory recently reported correlation of elevated PhK activity with psoriatic activity. This study further evaluates the significance of drug-induced suppression of PhK activity on psoriatic activity.

PATIENTS AND METHODS

PhK activity was assayed in four groups, each with 10 patients: (i) active untreated psoriasis; (ii) resolving psoriasis treated by calcipotriol (Dovonex(R), Bristol Myers Squibb, Princeton, NJ, U.S.A. ), a vitamin D3 analogue and an indirect inhibitor of PhK; (iii) curcumin (diferuloylmethane), a selective PhK inhibitor; and (iv) 10 normal non-psoriatic subjects.

RESULTS

PhK activity in units mg-1 protein was highest in active untreated psoriasis (1204 +/- 804.3; mean +/- SD), lower in the calcipotriol-treated group (550.7 +/- 192. 9), lower in curcumin-treated group (207.2 +/- 97.6), and lowest in normal skin (105.4 +/- 44.6). One-way analysis of variance performed on log-transformed PhK activity measure showed significant differences among the four groups, F3,36 = 48.79, P < 0.0001. Decreased PhK activity in curcumin-and calcipotriol-treated psoriasis was associated with corresponding decreases in keratinocyte transferrin receptor (TRR) expression, severity of parakeratosis and density of epidermal CD8+ T cells.

CONCLUSIONS

Our results demonstrate that drug-induced suppression of PhK activity is associated with resolution of psoriatic activity as assessed by clinical, histological and immunohistochemical criteria, and support the hypothesis that effective antipsoriatic activity may be achieved through modulation of PhK activity.

Effect of curcumin on the production of nitric oxide by cultured rat mammary gland

We have hypothesized that one aspect of the antitumor activity of curcumin (diferuloylmethane) during the promotion stage of mammary gland tumorigenesis may be linked to reduction of free radicals (Inano et al., Carcinogenesis, 20: 1011-1018, 1999). Nitric oxide (NO) has been found to inflict damage on important biomolecules, and the overproduction of NO in diseases may be implicated in carcinogenesis and tumor progression. We have reported that the presence of three isoforms of nitric oxide synthases (NOS) and NO generation in the mammary gland correlate with the mammary gland development and mammary carcinogenesis. We, therefore, investigated the inhibitory activity of curcumin for the production of NO in rat mammary glands by using an organ culture system to validate the effectiveness and usefulness of curcumin in the pathophysiology of the mammary gland. A diced mammary gland (approximately 3 mm cubes) from the inguinal part of a female Wistar-MS rat treated with estradiol and progesterone was cultured with 2 ml of 5% FCS/DMEM in the presence or absence of LPS (0.5 microg/ml) for 2-3 days. Curcumin ( approximately 100 microM) was added at the same time to the LPS-treated cultures. In some experiments, curcumin was added to the culture after the LPS had been washed out. The NO production was significantly increased (by almost 20-fold compared to the control) by the addition of LPS to the culture system. This enhancement of NO production by LPS was reduced to 76 and to 56% by addition of 30 and 100 microM curcumin, respectively, to the culture. When LPS was eliminated from the culture after prestimulation for 1 day, the production of NO by the mammary gland dropped off, although some NO was still detectable. Curcumin did not further inhibit the production of NO by the prestimulated mammary gland after the elimination of LPS from the culture. The inducible nitric oxide synthase (iNOS, 122 kDa) and endothelial nitric oxide synthase (eNOS, 152 kDa) isoforms were detected in the mammary gland extracts at the end of the organ culture. The quantity of iNOS was apparently increased in the gland treated with LPS, while the eNOS expression was clearly diminished. Curcumin (100 microM) obviously suppressed the iNOS expression in the mammary glands cultured with LPS, and a recovery in the eNOS expression was observed. On the other hand, curcumin exhibited scavenging activity for the NO released from N-ethyl-2-(1-ethyl-2-hydroxy-2-nitrosohydrazino)-ethanamine (NOC 12), a NO donor compound, in the coincubation mixture. These results indicate that curcumin has the ability to inhibit iNOS induction by LPS in the mammary gland and to scavenge NO radicals, which might explain, at least partly, its therapeutic properties in inflammation of the mammary gland.

Inhibition of eukaryote protein kinases and of a cyclic nucleotide-binding phosphatase by prenylated xanthones

A series of prenylated xanthones are variously potent inhibitors of the catalytic subunit (cAK) of rat liver cyclic AMP-dependent protein kinase (PKA), rat brain Ca2+ and phospholipid-dependent protein kinase C (PKC), chicken gizzard myosin light chain kinase (MLCK), wheat embryo Ca2+-dependent protein kinase (CDPK) and potato tuber cyclic nucleotide-binding phosphatase (Pase). The prenylated xanthones examined are mostly derivatives of alpha-mangostin in which the 3-hydroxyl and 6-hydroxyl are variously substituted with groups R or R', respectively, or derivatives of 3-isomangostin (mangostanol) in which the 9-hydroxyl is substituted with groups R' or the prenyl side chain is modified. The most potent inhibitors of cAK have non-protonatable and relatively small R' and R groups. Conversely, the most potent inhibitors of PKC and MLCK have bulkier and basic R' groups. Some prenylated xanthones are also potent inhibitors of CDPK. PKC and cAK are competitively inhibited by particular prenylated xanthones whereas the compounds that are the most potent inhibitors of MLCK and CDPK are non-competitive inhibitors. Prenylated xanthones having relatively small and non-protonatable R' and R groups inhibit a high-affinity cyclic nucleotide binding Pase in a non-competitive fashion.

Curcumin (Diferuloylmethane) inhibition of tumor necrosis factor (TNF)-mediated adhesion of monocytes to endothelial cells by suppression of cell surface expression of adhesion molecules and of nuclear factor-kappaB activation

Recruitment of leukocytes by endothelial cells and their subsequent migration from the vasculature into the tissue play major roles in inflammation. In the present study, we investigated the effect of curcumin, an antiinflammatory agent, on the adhesion of monocytes to human umbilical vein endothelial cells (EC). Treatment of EC with tumor necrosis factor (TNF) for 6 hr augmented the adhesion of monocytes to EC, and this adhesion was due to increased expression of intracellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and endothelial leukocyte adhesion molecule-1 (ELAM-1). Pretreatment of EC for 1 hr with curcumin completely blocked their adhesion to monocytes, as well as the cell surface expression of ICAM-1, VCAM-1, and ELAM-1 in EC. Although curcumin inhibited adhesion even when administered 1 hr after TNF treatment, maximum inhibition occurred when added either 1 hr before or at the same time as TNF. As the induction of various adhesion molecules by TNF requires activation of the transcription factor NF-kappaB, the effect of curcumin on the activation of this factor in the EC was also investigated. A 30-min treatment with TNF activated NF-kappaB; the activation was inhibited in a concentration-dependent manner by pretreatment with curcumin, indicating that NF-kappaB inhibition may play a role in the suppression of expression of adhesion molecules in EC. Our results demonstrate that the antiinflammatory properties of curcumin may be attributable, in part, to inhibition of leukocyte recruitment.

Differential inhibition of eukaryote protein kinases by condensed tannins

Condensed tannins, isolated from a variety of plant sources, were characterized according to the constituent flavans, being based on procyanidin and/or prodelphinidin and having a cis or trans stereochemistry at positions 2 and 3. All the tannin preparations are potent inhibitors of rat liver cyclic AMP-dependent protein kinase catalytic subunit (cAK) with IC50 values (concentrations for 50% inhibition) ranging from 0.009 to 0.2 microM. The tannin preparations are very good inhibitors of rat brain Ca(2+)- and phospholipid-dependent protein kinase C (PKC) (IC50 values in the range 0.3-7 microM), wheat embryo Ca(2+)-dependent protein kinase (CDPK) (IC50 values in the range 0.8-7 microM) and of calmodulin (CaM)-dependent myosin light chain kinase (MLCK) (IC50 values in the range 7-24 microM). One of the most effective preparations, that from the leaves of Ribes nigrum, has IC50 values with respect to cAK, PKC, CDPK and MLCK of 0.009, 0.6, 2.0 and 16 microM, respectively. In general, the order with respect to sensitivity to inhibition by these condensed tannins is cAK > PKC > CDPK > MLCK. The Ribes nigrum preparation is a competitive inhibitor of cAK with respect to both ATP and synthetic peptide substrate. These condensed tannin preparations are the most potent plant-derived inhibitors of cAK yet found.