Hypoxia-Inducible Factor-1 Activation by (−)-Epicatechin Gallate:  Potential Adverse Effects of Cancer Chemoprevention with High-Dose Green Tea Extracts

Abstract

Hypoxia-inducible factor-1 (HIF-1) is a transcription factor that induces oxygen-regulated genes in response to reduced oxygen conditions (hypoxia). Expression of the oxygen regulated HIF-1α subunit correlates positively with advanced disease stages and poor prognosis in cancer patients. Green tea catechins are believed to be responsible for the cancer chemopreventive activities of green tea. We found that (−)-epicatechin-3-gallate (ECG, 1), one of the major green tea catechins, strongly activates HIF-1 in T47D human breast carcinoma cells. Among the green tea catechins tested, 1 demonstrated the strongest HIF-1 inducing activity while (−)-epigallocatechin-3-gallate (EGCG, 2), was significantly less active. However, 2 is relatively unstable in the in vitro system studied. Compound 1 also increases the expression of HIF-1 target genes including GLUT-1, VEGF, and CDKN1A. In T47D cells, 1 induces nuclear HIF-1α protein without affecting HIF-1α mRNA. Both the induction of HIF-1α protein and activation of HIF-1 by 1 can be blocked by iron and ascorbate, indicating that 1 may activate HIF-1 through the chelation of iron. These results suggest that intended cancer chemoprevention with high-dose green tea extracts may be compromised, by the ability of tea catechins to promote tumor cell survival pathways associated with HIF-1 activation.Rapid tumor growth often outstrips the ability of blood vessels to supply oxygen and nutrients, leaving many regions inside solid tumors low in oxygen (hypoxia). In cancer patients, the extent of tumor hypoxia correlates positively with advanced disease stages, poor prognosis, and treatment resistance. 1 Hypoxia-inducible factor-1 (HIF-1) is a transcription factor that plays a critical role in hypoxia activated gene expression. 2 In tumor cells, HIF-1 activates the transcription of genes involved in anaerobic metabolism, angiogenesis, survival, invasion/metastasis and treatment resistance, thus promoting cellular This study investigates the effects of green tea catechins and related compounds on HIF-1 activity in vitro. Among the compounds tested [1-4, (+)-catechin (5), and gallic acid (6)], only catechins that contain the 3-gallate moiety (1 and 2) activate HIF-1 in a T47D cellbased reporter assay. In addition, 1 inhibits HIF-1 activation under hypoxic conditions. Apart from one hydroxyl group, 1 and 2 are structurally identical. However, 2 is chemically less stable than 1. The focus of this study is the regulation of HIF-1 activity by ECG (1). The pathways and mechanisms involved in HIF-1 activation have been extensively studied. 1,2,9 In the presence of oxygen, the HIF-1α subunit is prolyl hydroxylated, recognized by an E3 ubiquitin ligase complex that contains the von Hippel-Lindau tumor suppressor protein (pVHL), polyubiquitylated, and degraded by the 26S proteosome. [15][16][17] The HIF-1α protein is also asparaginyl hydroxylated to prevent HIF-1 activation. 18 At reduced cellular oxygen levels, inhibition of HIF-1α protein prolyl hydroxylation and degradation leads to an ...

Saururus cernuus lignans—Potent small molecule inhibitors of hypoxia-inducible factor-1

“…To monitor HIF-1 activity, a dual luciferase assay employing the pHRE3-TK-Luc reporter and an internal control pRL-TK (Promega) was performed as described [19].…”

“…Total RNA samples were extracted immediately following treatments with the RNeasy Mini Prep kit (QIAGEN). Synthesis of the first strand cDNAs, gene-specific primer sequences, quantitative real-time PCR reactions, and data analysis were described previously [19].…”

“…The plating of T47D cells, compound treatments, ELISA assay for secreted human VEGF proteins, and determination of the number of viable cells were the same as previously described [19].…”

Epigallocatechin-3-gallate (EGCG): Chemical and biomedical perspectives

“…It is conceivable that many of the effects observed with micromolar concentrations of EGCG are relevant to the potential benefits, side effects, and/or toxicity of either high-dose or megadose GTE and EGCG therapy (Pisters et al, 2001, Zhou et al, 2004. Likewise, the tumor cellspecific cytotoxic effects produced by high micromolar concentrations of EGCG may not represent phenomena that are physiologically relevant to dietary green tea consumption, but may be indicative of effects that may be achieved with high-dose supplementation of EGCG and other catechins.…”

Role of tea catechins in prevention of aging and age-related disorders

“…Also, green tea has been shown to protect against ethanol induced oxidative stress and aging in the blood serum of mice (Luczaj et al, 2004). Another set of studies showing the concentrationdependent effect of tea catechins, demonstrate, at lower concentrations they reduce MDA formation, displaying antioxidant properties, while at higher concentrations they induce oxidative stress (Raza and John, 2007;Zhou, 2004). While GPx activity decreases with age in a significant correlation with the total antioxidant capacity of plasma , a study on a hepatocyte cell line in rats indicates an increase in GPx activity in Se (+) cells with the addition of catechins in media (Nagata et al, 1999).…”