Carcinogenesis Advance Access originally published online on February 28, 2007
Carcinogenesis 2007 28(7):1478-1484; doi:10.1093/carcin/bgm045
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Fractionation of high molecular weight tannins in grape seed extract and identification of procyanidin B2-3,3'-di-O-gallate as a major active constituent causing growth inhibition and apoptotic death of DU145 human prostate carcinoma cells
1 Department of Pharmaceutical Sciences, School of Pharmacy, University of Colorado Health Sciences Center, Denver, CO 80262, USA
2 University of Colorado Cancer Center, University of Colorado Health Sciences Center, Denver, CO 80262, USA
* To whom correspondence should be addressed. Tel: +303 315 1382; Fax: +303 315 6281; Email: chapla.agarwal{at}uchsc.edu
Several studies have documented the anticancer and chemopreventive efficacy of grape seed extract (GSE) against various malignancies including prostate cancer (PCA). GSE is a complex mixture of polyphenols including gallic acid (GA), catechin (Cat), epicatechin (Epi) and procyanidins–oligomers of Cat and Epi, some of which are esterified with GA. Initial studies to identify the GSE components cytotoxic to human prostate carcinoma (DU145) cells demonstrated that GA and several crude chromatographic fractions containing procyanidin dimers and trimers were biologically active. The focus of the present work was to purify 14 procyanidins from the fractions and to identify those with highest activity toward growth inhibition, cell death and apoptosis in DU145 cells. The most active procyanidin was identified by mass spectrometry and enzymatic hydrolysis as the 3,3'-di-O-gallate ester of procyanidin dimer B2 (Epi–Epi). B2-digallate exhibited dose-dependent effects on DU145 cells over the range 25–100 µM, whereas GA exhibited comparable activity at lower doses but was highly lethal at 100 µM. Structure–activity studies demonstrated that all three hydroxyl groups of GA are necessary for activity, but a free carboxylic acid group is not required even though esterification reduced the activity of GA. These data, and the fact that non-esterified B2 exhibited little or no activity, suggest that the galloyl groups of B2-digallate are primarily responsible for its effects on DU145 cells. Taken together, these data identify procyanidin B2-3,3'-di-O-gallate as a novel biologically active agent in GSE that should be studied in greater detail to determine its effects against PCA.
Abbreviations: B2-G2, procyanidin B2-3,3'-di-O-gallate; Cat, catechin; Epi, epicatechin; GA, gallic acid; GPC, gel permeation chromatography; GSE, grape seed extract; HPLC, high-performance liquid chromatography; LC, liquid chromatography; MS, mass spectrometry; MS2 (MS/MS) or MS3, tandem MS; PCA, prostate cancer
Received October 23, 2006; revised February 20, 2007; accepted February 22, 2007.
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