Mechanisms of anticarcinogenic properties of curcumin: the effect of curcumin on glutathione linked detoxification enzymes in rat liver

https://doi.org/10.1016/S1357-2725(98)00015-6Get rights and content

Abstract

Curcumin, an antioxidant isolated from turmeric (curcuma longa), has been shown to attenuate chemical carcinogenesis in rodents. Previous studies have shown that curcumin causes an increase in glutathione S-transferase (GST) activity in rodent liver which may contribute to its anti-cancer and anti-inflammatory activities. Since the effects of curcumin on specific GST isozymes and other glutathione (GSH)-linked enzymes are incompletely defined, we have examined in the present studies the effect of curcumin on hepatic non-protein sulfhydryls and GSH-linked enzymes in male Sprague-Dawley rats. When rats were fed curcumin at doses from 1 to 500 mg kg−1 body weight daily for 14 days, the induction of hepatic GST activity towards 1-chloro-2,4-dinitrobenzene (CDNB) was found to be biphasic, with maximal induction of about 1.5 fold at the 25 to 50 mg kg−1 body weight dosage. At higher doses, a decrease was observed in the activity and in the rats treated with 500 mg kg−1 curcumin this activity was below the levels observed in controls. In contrast, GST activity towards 4-hydroxynonenal (4-HNE) increased in a saturable, dose dependent manner. Western-blot analyses of liver cytosols revealed that curcumin caused a dose dependent induction of rGST 8-8, an isozyme which is known to display the highest activity towards 4-HNE, a highly toxic product of lipid peroxidation. Glutathione peroxidase (GPx) activity towards cumene hydroperoxide in liver homogenate was also found to be increased in a saturable manner with respect to curcumin dose. Our results suggest that induction of enzymes involved in the detoxification of the electrophilic products of lipid peroxidation may contribute to the anti-inflammatory and anti-cancer activities of curcumin.

Introduction

Chronic inflammatory response to damage caused by chemical or biologic toxins has been associated with increased ambient tissue oxidative stress which in turn has been linked with carcinogenesis[1]. This provides the basis for numerous studies in which anti-inflammatory agents and anti-oxidants have been considered as logical choices for their potential use as pharmacologic cancer preventatives2, 3, 4, 5, 6. In fact, a number of antioxidants have been shown to retard chemically induced neoplasia in animal models2, 4, 5, 6, 7, 8, 9, 10, 11. Curcumin (diferuoyl methane), a phenolic antioxidant originally isolated from turmeric (curcuma longa), a rhizome used in India for centuries as a spice and medicinal agent, has been shown to be an effective antioxidant as well as a powerful anti-inflammatory agent12, 13, 14. Recently, a number of animal studies have shown that curcumin is an effective deterrent to chemically induced neoplasia by several structurally unrelated carcinogens suggesting that it could be an effective dietary chemo-preventive agent in humans10, 12. The use of curcumin as a potential pharmacologic cancer-preventative agent in humans is, however, hampered by the lack of appropriate surrogate biomarkers which could be used to titrate its dosage for optimal cancer preventative effects. Use of such biomarkers during antioxidant therapy aimed at cancer prevention is critical because antioxidant cancer-preventatives can also function as carcinogens upon prolonged exposure at high doses[15].

Preferential induction of phase II biotransformation enzymes such as glutathione S-transferases (GSTs) and NAD(P)H:quinone reductase (as opposed to phase I biotransformation enzymes of the cytochrome P-450 system) has been suggested to be one possible mechanism for the cancer preventative effects of a number of antioxidants2, 7, 16, 17. Although orally administered curcumin has been shown to increase GST activity towards 1-chloro-2,4-dinitrobenzene (CDNB) in mouse liver, the magnitude of this effect is quite small (~1.4 fold) even at a high dose of curcumin (500 mg kg−1 day−1 for 14 days)[18]. Because GSTs consist of several catalytically distinct isozymes, each of whose expression is differentially regulated perhaps by the oxidant or pro-oxidant environment within the cell[19], this mild increase in total GST activity towards one substrate cannot necessarily be interpreted as a biomarker for curcumin's antioxidant, cancer-preventative effects[7]. Therefore, the present studies were designed to investigate the effects of oral curcumin exposure on GSH-linked antioxidant defenses including GSTs, glutathione peroxidase (GPx), and γ-glutamyl-cysteinyl synthetase (γ-GCS) activities, and non-protein sulfhydryl (NPSH) levels in rat liver. Since the level of expression of individual GST isozymes may be useful as a biomarker of curcumin dosage, we quantified the dose dependent effects of curcumin on individual GST isozymes separated by liquid column isoelectric focusing (IEF). We were particularly interested in examining the effects of curcumin on the α-class GST isozyme, rGST8-8, which we have shown to be selectively expressed in tissues of mesodermal origin, including granulocytes (monocyte/macrophage and neutrophils), vascular smooth muscle, and endothelium20, 21, 22. Because this isozyme and its human orthologs have relatively high activity towards the electrophilic products of lipid peroxidation, such as 4-hydroxynonenal (4-HNE), epoxides and hydroperoxides20, 23, 24, and is expressed in cells which are a significant source of tissue oxidative stress20, 21, 22, we reasoned that effects of curcumin on the level of expression of this isozyme may be a significant contributor to the antioxidant effects of curcumin.

Section snippets

Materials and methods

Curcumin (technical grade, Cat. # 23,838-4) was purchased from Aldrich Chemicals, Milwaukee Wisconsin. Because purified curcumin has not proven to be a better cancer-preventative, technical grade curcumin was chosen for these studies. The choice of technical grade of curcumin is supported by data showing that dietary administration of 2% turmeric inhibits 7,12-dimethylbenz[a]anthracene and benz[a]pyrene induced forestomach tumors[25]. The sources of reagents and chemicals for affinity

Effect of curcumin on rat liver NPSH levels and γ-GCS activity

Hepatic NPSH content, which corresponds roughly to tissue GSH content, was found to increase in a saturable manner with respect to curcumin dosage (Fig. 1). The basal NPSH levels in rat liver were found to be consistent with previously reported values[35]. A statistically significant increase in NPSH levels above control was observed at all doses above 1 mg kg−1 (p<0.001 by t-test) with a maximum increase of 1.3 fold over control. These results indicated that within the dose range of curcumin

Discussion

Results of our studies indicate that the antioxidant and anti-inflammatory properties of curcumin may be mediated through complex dose dependent effects on induction of enzymatic activities involved in the GSH-linked detoxification of the electrophilic products of lipid peroxidation. NPSH, a surrogate for GSH, was found to be increased with curcumin exposure in a dose dependent fashion. This increase appeared to be at least partially attributable to an increased activity of γ-GCS, which

Acknowledgements

Supported in part by USPHS grants CA27967 (YCA) and CA63660 (SA). JTP is supported by EPA STAR Fellowship U 915006-01-1. Support for JTP from NIEHS Toxicology Training Grant 2T32-ESO7254 is also acknowledged.

References (37)

  • Y.C. Awasthi et al.

    Purification and properties of human erythrocyte glutathione peroxidase

    J. Biol. Chem.

    (1975)
  • G.F. Seelig et al.

    Gamma-glutamylcysteine synthetase. Interactions of an essential sulfhydryl group

    J. Biol. Chem.

    (1984)
  • M.M. Bradford

    A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding

    Anal. Biochem.

    (1976)
  • S.S. Singhal et al.

    Purification and characterization of glutathione S-transferases of rat uterus

    Int. J. Biochem. Cell Biol.

    (1996)
  • M.F. Khan et al.

    Iron induced lipid peroxidation in rat liver is accompanied with preferential induction of glutathione S-transferase 8-8

    Toxicol. Appl. Pharmacol.

    (1995)
  • B.N. Ames et al.

    Oxidants, antioxidants and the degenerative diseases of aging

    Proc. Natl. Acad. Sci. USA

    (1993)
  • L.W. Wattenberg

    Chemoprevention of cancer

    Cancer Res.

    (1985)
  • M. Nagabushan et al.

    Curcumin as an inhibitor of cancer

    J. Am. Coll. Nutr.

    (1992)
  • Cited by (231)

    • Curcumin-loaded PLA-PEG copolymer nanoparticles for treatment of liver inflammation in streptozotocin-induced diabetic rats

      2019, Colloids and Surfaces B: Biointerfaces
      Citation Excerpt :

      On the other hand, CUR up-regulates the expression of nuclear factor erythroid-2-related factor-2 (Nrf2) that regulates the expression of antioxidant proteins responsible for protecting the cells from oxidative stress [42]. Additionally, CUR upregulates genes that contain antioxidant response element (AREs) in their promoters, involving catalase (CAT) [42], superoxide dismutase, glutathione peroxidase (GPx) [43] and glutathione reductase (GR). This improved the bioavailability of CUR and enhanced its solubility with longer circulation time of encapsulated-CUR-NPs which resulted in more efficient anti-oxidative than free CUR [17].

    • Potential role of curcumin and its derivatives against alzheimer disease

      2019, Curcumin for Neurological and Psychiatric Disorders: Neurochemical and Pharmacological Properties
    • A Review of the Biochemical and Pathophysiological Properties of Curcumin

      2024, Journal of Mazandaran University of Medical Sciences
    View all citing articles on Scopus
    1

    The first and second authors contributed equally to these studies.

    View full text