Sulforaphane, a cancer chemopreventive agent, induces pathways associated with membrane biosynthesis in response to tissue damage by aflatoxin B1
Introduction
Aflatoxin B1 (AFB1) is a known human carcinogen that significantly contributes to the burden of hepatocellular carcinoma (HCC) in many parts of the world, especially in areas with a warm and moist climate such as Asia and sub-Saharan Africa (Kensler et al., 2011). A critical mechanism responsible for the hepatotoxic and carcinogenic potential of AFB1 is based on the balance of its bioactivation and detoxification (Fig. 1). Several lines of evidence indicate that variation in the extent of glutathione (GSH) conjugation of the ultimate carcinogen, AFB1-8,9-epoxide, by glutathione S-transferases (GSTs) is an important detoxification pathway. Treatment of rats with oltipraz and 3H-1,2-dithiole-3-thione (D3T) leads to marked increases in the activity of liver GSTs, which resulted in reductions in both the extent of aflatoxin-DNA adduction and tumorigenesis (Kensler et al., 1987). The inducible A5 subunit of alpha-class GSTs in the rat has been identified as the GST isozyme that is primarily responsible for the enhanced detoxification of the AFB1-8,9-epoxide by chemopreventive agents (Hayes et al., 1991, Hayes et al., 1998). Modulation of GST activity is only one mechanism by which exogenous agents can influence aflatoxin carcinogenesis. This paper probes additional pathways.
Sulforaphane (SF), a potent isothiocyanate derivative found in broccoli and other cruciferous vegetables (Fahey et al., 1997), has received attention as a chemopreventive agent due to its ability to activate the transcription factor Nrf2 and induce phase II detoxification enzymes, including the GSTs (Fimognari and Hrelia, 2007, Myzak and Dashwood, 2006, Thimmulappa et al., 2002). Recent evidence illustrates protective effects of SF against AFB1-induced hepatotoxicity in rats attributable to increased GST expression. Treatment of rats with SF resulted in significant induction of hepatic total GST activity and a proportional reduction in the amounts of AFB1-N7-guanine (the principal DNA adduct of AFB1) formed in liver DNA (Fiala et al., 2011). Previous studies, however, have also identified additional chemopreventive mechanisms for SF that are independent of phase II enzyme induction. SF induces apoptosis in both in vitro (Fimognari et al., 2004, Karmakar et al., 2006) and in vivo models (Singh et al., 2004). SF-mediated cell cycle arrest has been reported in many previous studies, including induction of a dose-dependent growth arrest in prostate cancer cells by inhibiting the expression of cyclin D1 and DNA synthesis, along with a G1 cell cycle block (Chiao et al., 2002) and induction of G2/M accumulation and pre-metaphase arrest in bovine aortic endothelial (BAE) cells (Jackson et al., 2007). SF also exerts anti-inflammatory properties by inhibiting pro-inflammatory and pro-carcinogenic signaling factors such as IL-1β (Lin et al., 2008), COX-2 and TNF-α (Heiss et al., 2001). Understanding these phase II-independent pathways provides the rationale for the current project.
Cell regeneration and survival responses signal metabolic reprogramming that supports anabolic pathways required for tissue repair and growth (Ward and Thompson, 2012). The Keap1–Nrf2 complex, which is activated by SF, has been demonstrated to influence intermediary metabolism (Hayes and Dinkova-Kostova, 2014). This study aimed to assess the extent to which anabolic pathways modulated by SF provide protective mechanisms against AFB1 toxicity in vivo. The results revealed prominent reprogramming of gene sets involved in lipid synthesis in SF-pretreated rats, suggesting that SF facilitates regeneration of hepatic cells damaged by AFB1.
Section snippets
Chemicals
R,S-Sulforaphane (SF) was purchased from LKT Laboratories (St. Paul, MN). Aflatoxin B1 (AFB1) was purchased from Sigma Chemical (St. Louis, MO). RNAlater, RNeasy Mini Kit, and One-Step QuantiTech SYBR Green RT-PCR were obtained from QIAGEN (Valencia, CA). One-Cycle Target Labeling and Control Reagents complete kit (P/N 900493) and GeneChip® Rat Genome 230 2.0 arrays (Rat 230 2.0) were obtained from Affymetrix, Inc. (Santa Clara, CA). R-Phycoerythrinstreptavidin (SAPE) was purchased from
Gene expression analysis
The goal of this study was to compare the response of rat liver to aflatoxin alone, or aflatoxin in concert with SF. The transcriptional responses in the livers of AFB1-treated male rats induced by SF were investigated using a DNA microarray, an established tool to assess global gene expression changes. Groups of rats were pretreated with 0.7 mmol/kg SF by gavage at ages 30, 32, and 34 days, a dose previously shown to induce GSTs significantly and result in a substantial reduction of AFB1-N7
Discussion
AFB1 is one of the major risk factors for development of liver cancer, especially when it is present in concert with hepatitis B infection (Groopman and Kensler, 2005). Epidemiological investigations in human populations reveal an association of increased incidence of HCC with increasing dietary contamination by AFB1 (Wild and Gong, 2010). As the fungal species that produces AFB1 is ubiquitous, reduction of AFB1 exposure from ingestion may be problematic and impractical in certain areas of the
Conflict of interest
The authors declare no conflicts of interest in the support, conception, execution or publication of the work described herein.
Acknowledgments
This work was supported by National Institutes of Health grants ES016313, P30-ES002109, P01 ES006052, P30 ES003819, and P30 CA006973. The authors thank Drs. Stephen Slocum and Daam Settachan for critically reading the manuscript.
References (61)
- et al.
The citrate cleavage pathway and lipogenesis in rat adipose tissue: replenishment of oxaloacetate
J. Lipid Res.
(1967) - et al.
“Spot 14” protein functions at the pretranslational level in the regulation of hepatic metabolism by thyroid hormone and glucose
J. Biol. Chem.
(1997) - et al.
Sterol regulatory element-binding protein-1c mimics the negative effect of insulin on phosphoenolpyruvate carboxykinase (GTP) gene transcription
J. Biol. Chem.
(2001) - et al.
The biology of cancer: metabolic reprogramming fuels cell growth and proliferation
Cell Metab.
(2008) - et al.
Sulforaphane as a promising molecule for fighting cancer
Mutat. Res.
(2007) - et al.
Isothiocyanates as novel cytotoxic and cytostatic agents: molecular pathway on human transformed and non-transformed cells
Biochem. Pharmacol.
(2004) - et al.
Immunity, inflammation, and cancer
Cell
(2010) - et al.
Role of metabolism and viruses in aflatoxin-induced liver cancer
Toxicol. Appl. Pharmacol.
(2005) - et al.
Regulation of rat glutathione S-transferase A5 by cancer chemopreventive agents: mechanisms of inducible resistance to aflatoxin B1
Chem. Biol. Interact.
(1998) - et al.
The Nrf2 regulatory network provides an interface between redox and intermediary metabolism
Trends Biochem. Sci.
(2014)
Nuclear factor-{kappa}B is a molecular target for sulforaphane-mediated anti-inflammatory mechanisms
J. Biol. Chem.
Sulforaphane suppresses angiogenesis and disrupts endothelial mitotic progression and microtubule polymerization
Vasc. Pharmacol.
Revving the engine: signal transduction fuels T cell activation
Immunity
Activation of multiple molecular mechanisms for apoptosis in human malignant glioblastoma T98G and U87MG cells treated with sulforaphane
Neuroscience
Identification of rat S14 protein and comparison of its regulation with that of mRNA S14 employing synthetic peptide antisera
J. Biol. Chem.
Mouse Elovl-6 promoter is an SREBP target
Biochem. Biophys. Res. Commun.
Modulation of gene expression by cancer chemopreventive dithiolethiones through the Keap1-Nrf2 pathway. Identification of novel gene clusters for cell survival
J. Biol. Chem.
Sulforaphane suppressed LPS-induced inflammation in mouse peritoneal macrophages through Nrf2 dependent pathway
Biochem. Pharmacol.
S14 protein in breast cancer cells: direct evidence of regulation by SREBP-1c, super induction with progestin, and effects on cell growth
Exp. Cell Res.
Structure of the human gene encoding sterol regulatory element binding protein 2 (SREBF2)
Genomics
Chemoprotection by sulforaphane: keep one eye beyond Keap1
Cancer Lett.
SREBP-1 interacts with hepatocyte nuclear factor-4 alpha and interferes with PGC-1 recruitment to suppress hepatic gluconeogenic genes
J. Biol. Chem.
SREBP-1, a basic-helix-loop-helix-leucine zipper protein that controls transcription of the low density lipoprotein receptor gene
Cell
Insulin effects on sterol regulatory-element-binding protein-1c (SREBP-1c) transcriptional activity in rat hepatocytes
Biochem. J.
Relationship between inhibition of cell growth and of transferrin receptor expression by interferon (IFN) alpha: studies in IFN-sensitive and IFN-resistant Daudi cells
J. Gen. Virol.
Sulforaphane and its metabolite mediate growth arrest and apoptosis in human prostate cancer cells
Int. J. Oncol.
Integration of biological networks and gene expression data using Cytoscape
Nat. Protoc.
Beyond aerobic glycolysis: transformed cells can engage in glutamine metabolism that exceeds the requirement for protein and nucleotide synthesis
Proc. Natl. Acad. Sci. U. S. A.
The atypical PKCs in inflammation: NF-κB and beyond
Immunol. Rev.
Levels of aflatoxin–albumin biomarkers in rat plasma are modulated by both long-term and transient interventions with oltipraz
Carcinogenesis
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