Original Contribution
Iron chelation in the biological activity of curcumin

https://doi.org/10.1016/j.freeradbiomed.2005.11.003Get rights and content

Abstract

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 GSTα in cultured liver cells. Unexpectedly, however, although levels of GSTα 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.

Introduction

Curcumin (diferuloylmethane, or (E, E)-1, 7-bis (4-hydroxy-3-methoxyphenyl)-1, 6-heptadiene-3, 5-dione) is a natural yellow colored product extracted from the Indian herb, turmeric. This low molecular weight polyphenol is the major curcuminoid in Curcuma longa, a rhizome used in India for centuries as a spice, for coloring, and as a medicinal agent (reviewed in [1], [2]). Recent studies have demonstrated that curcumin has a wide range of beneficial pharmacological effects, including anti-inflammatory [3], antioxidant [4], antiviral [5], antiangiogenic and antitumorigenic [1] effects.

Particular interest has focused on curcumin's antitumor effects and its potential utility as a cancer chemopreventive agent. Curcumin has been shown to inhibit tumor formation in the skin, forestomach, duodenum, and colon in mice [6], and the mammary glands, colon, tongue, and sebaceous glands of rats (reviewed in [7]). These and other results have led to clinical trials exploring the utility of curcumin as a cancer chemopreventive agent in humans. Recently completed Phase I clinical trials have demonstrated that curcumin is exceptionally well tolerated, and curcumin has been recommended for further evaluation in Phase II trials [8], [9].

The mechanism of curcumin's cancer chemopreventive activity has not been completely defined, and is likely multifactorial. Curcumin inhibits tumor growth and induces tumor cell apoptosis in animal and cell culture models [10]. Curcumin also inhibits activation of NFκB through blockade of IκB kinase, and inhibits activation of COX2 [11], [12], [13], [14]. Curcumin also alters AP1 complexes [15] and inhibits Akt [16]. Another contributor to curcumin's chemopreventive activity is the induction of cytoprotective phase II enzymes. These include proteins such as glutamate-cysteine ligase [15], isoforms of glutathione S-transferase (GSTs) [17], as well as heme oxygenase [18], and NAD(P)H:quinone oxidoreductase 1 (NQO1) [19]. In addition to these effects on transcription and cell signaling, curcumin possesses chemical features that may further modulate its chemopreventive activity. For example, curcumin is an antioxidant and free radical scavenger [20]. Curcumin has also been shown to conjugate directly to thioredoxin reductase and modulate its activity [21]. Direct chemical measurements using cyclic voltammetry have recently shown that curcumin has a high affinity for iron, particulary Fe(III), with a formation constant of 1022 M−1 [22]. However, the extent to which these chemical properties contribute to curcumin's activity in vivo is uncertain.

Ferritin is a key protein in the maintenance of intracellular iron homeostasis. Our previous results have shown that ferritin transcription is induced concomitantly with other Phase II enzymes in response to chemical inducers of the Phase II response [23]. The ferritin apoprotein is a 480 kDa multimer of 24 subunits. The subunits of mammalian ferritin are of two types, termed ferritin H and ferritin L. The ratio of these subunits within the ferritin protein varies in a tissue-specific fashion, and is further modulated by inflammatory and environmental stimuli (reviewed in [24]). In addition to its regulation by Phase II inducers, ferritin is regulated by iron. This occurs via a well-studied regulatory circuit mediated by iron regulatory proteins (IRPs). IRPs interact with the iron-responsive element (IRE) in the 5′ UTR (untranslated region) of ferritin H and L mRNAs, as well with IREs in the 3′ UTR of transferrin receptor 1 [25], [26], a protein with a critical role in iron transport [26], [27]. The activity of the IRP proteins is in turn modulated by intracellular levels of “free” or “labile” iron. Under conditions of iron deprivation, the IRP proteins are activated to repress ferritin and stabilize transferrin receptor 1 mRNA; conversely, when iron is abundant, ferritin translation is induced and transferrin receptor 1 mRNA is degraded (reviewed in [24]). Translational repression of ferritin, activation of IRP, and induction of transferrin receptor 1 thus all serve as indicators of reduced intracellular iron, and are observed in cells treated with iron chelators [28].

The ability of curcumin to induce some proteins of the Phase II response led us to query whether curcumin also induced ferritin. Unexpectedly, we found that although curcumin induced GSTα and ferritin mRNA, it reduced ferritin protein. Curcumin also induced transferrin receptor 1 and activated IRP. These properties suggest that curcumin may exhibit iron chelator activity, and imply that iron chelation may be a novel mechanism that contributes to the potent cancer chemopreventive activity of curcumin.

Section snippets

Animals and treatment

Mice were treated according to the guidelines established by our institutional animal care and use committee. All experimentation followed approved protocols. Female FVB mice, 5 weeks of age, weighing an average of 13.5 g were purchased from Charles River (Wilmington, MA). Mice were maintained in a room controlled at 25°C with a relative humidity of 60% and 12 h light/dark cycle. After arrival, mice were allowed to acclimate for 1 week using standard pellet rodent diet, followed by

Curcumin induces GST and ferritin mRNA in cultured liver cells

One mechanism of action of synthetic chemopreventive agents is the induction of cytoprotective proteins [31]. These include ferritin, a protein that functions as a cytoprotective protein by virtue of its ability to bind iron and reduce oxidative stress. We have previously observed that oltipraz [23] as well as novel synthetic chemopreventive agents [29] induce ferritin as well as GSTα and NQO1. To test whether a natural chemopreventive agent such as curcumin might also function to induce

Discussion

There is a growing interest in the use of dietary agents in the prevention of cancer. Curcumin represents a particularly promising candidate chemopreventive agent. Curcumin prevents tumor formation in a number of animal models, including models of skin, colon, liver, esophageal, stomach, and breast cancer [33], [34], [35], [36]. Curcumin has also demonstrated the ability to improve patient outcomes in Phase I clinical trials [8]. Equally important to its potential application as a

Acknowledgments

We thank Rong Ma and Fan Zhang for technical assistance. We are grateful to Ralph B. D'Agostino Jr. of the Comprehensive Cancer Center of Wake Forest University for statistical analyses.

References (48)

  • S.Y. Qian et al.

    Iron and dioxygen chemistry is an important route to initiation of biological free radical oxidations: an electron paramagnetic resonance spin trapping study

    Free Radic. Biol. Med.

    (1999)
  • J. Emerit et al.

    Iron metabolism, free radicals, and oxidative injury

    Biomed. Pharmacother.

    (2001)
  • B.B. Aggarwal et al.

    Anticancer potential of curcumin: preclinical and clinical studies

    Anticancer Res.

    (2003)
  • Y.J. Surh

    Cancer chemoprevention with dietary phytochemicals

    Nat. Rev. Cancer

    (2003)
  • R. Srivastava et al.

    Modification of certain inflammation-induced biochemical changes by curcumin

    Indian J. Med. Res.

    (1985)
  • C.J. Li et al.

    Three inhibitors of type 1 human immunodeficiency virus long terminal repeat-directed gene expression and virus replication

    Proc. Natl. Acad. Sci. USA

    (1993)
  • R.A. Sharma et al.

    Effects of dietary curcumin on glutathione S-transferase and malondialdehyde-DNA adducts in rat liver and colon mucosa: relationship with drug levels

    Clin. Cancer Res.

    (2001)
  • G.J. Kelloff et al.

    Strategy and planning for chemopreventive drug development: clinical development plans II

    J. Cell. Biochem. Suppl.

    (1996)
  • A.L. Cheng et al.

    Phase I clinical trial of curcumin, a chemopreventive agent, in patients with high-risk or pre-malignant lesions

    Anticancer Res.

    (2001)
  • R.A. Sharma et al.

    Phase I clinical trial of oral curcumin: biomarkers of systemic activity and compliance

    Clin. Cancer Res.

    (2004)
  • S.M. Plummer et al.

    Inhibition of cyclo-oxygenase 2 expression in colon cells by the chemopreventive agent curcumin involves inhibition of NF-kappaB activation via the NIK/IKK signalling complex

    Oncogene

    (1999)
  • C. Jobin et al.

    Curcumin blocks cytokine-mediated NF-kappa B activation and proinflammatory gene expression by inhibiting inhibitory factor I-kappa B kinase activity

    J. Immunol.

    (1999)
  • D. Deeb et al.

    Curcumin sensitizes prostate cancer cells to tumor necrosis factor-related apoptosis-inducing ligand/Apo2L by inhibiting nuclear factor-kappaB through suppression of IkappaBalpha phosphorylation

    Mol. Cancer Ther.

    (2004)
  • S. Aggarwal et al.

    Inhibition of growth and survival of human head and neck squamous cell carcinoma cells by curcumin via modulation of nuclear factor-kappaB signaling

    Int. J. Cancer

    (2004)
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    Supported in part by grants from the American Institute for Cancer Research and NIH grant RO3ES011516 (S.V.T.), NIH Grant R37 DK 42412 (F.M.T.), and KO1 DK065876 (J.W.).

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