Abstract CN06-03: Green tea and pomegranate: The role of metabolites in chemoprevention
Authors: Henning Susanne M. , Wang Piwen , Wong Angela , Vicinanza Roberto , Aronson William J. , Heber David 
Published: January 2011

High consumption of fruit-, vegetable-, and plant-based beverages has been associated with a reduced incidence and mortality of various chronic diseases including cancer. A wide variety of phytochemicals contribute to these chemopreventive effects. The largest group of phytochemicals belongs to the family of flavonoids, which all share the common polyphenol structure. Considerable effort has been made to quantitate the dietary intake and main food sources of flavonoids. In the U.S., based on the USDA flavonoid database and NHANES 1999-2002 24-h dietary recall data, the average daily intake of flavonoids is 189.7 mg/d. The main daily mean food sources of flavonoids were tea (157 mg), citrus fruit juices (8 mg), wine (4 mg), and citrus fruit (3 mg) (1). In Spain, the mean flavonoid intake was 313 mg/d with the main sources being apples (23%), red wine (21%), unspecified fruit (12.8%), and oranges (9.3%) (2).

Tea polyphenols are consumed in such high quantity due to the popularity of tea worldwide and the high concentration of polyphenols per cup of tea (150 mg). Tea leaves from the plant Camellia sinensis are manufactured in nonfermented form as green tea or fermented form as black tea. Green tea contains the gallated polyphenols (-)-epigallocatechin-3-gallate (EGCG) and (-)-epicatechin-3-gallate (ECG) as well as non-gallated (-)-epigallocatechin (EGC) and (-)-epicatechin (EC). During fermentation to black tea these green tea polyphenols (GTP) undergo polymerization to theaflavin and thearubigin. Other examples of large polymeric polyphenols are ellagitannins from pomegranate and procyanidins from grape seed extract and cocoa. Daily pomegranate juice consumption has been shown to decrease the rate of rise of PSA in men treated for prostate cancer increasing the PSA doubling time from 15 to 54 weeks. We have conducted extensive studies of the bioavailability, metabolism by colonic microflora, and conjugation after absorption of polyphenols. For example, pomegranate ellagitannins are converted to gallagic acid (GA), ellagic acid (EA), urolithin A (UA) and B (UB), and tea polyphenols to phenolic acids, such as 3,4-dihydroxyphenyl acetic acid (3,4DHPAA) (3). These products can be found in the blood and urine and have biological activity. During the absorption process and in the tissues polyphenols and their metabolites are glucuronidated, sulfated and methylated. Interestingly, there are strong interindividual differences observed in the plasma and urine content of metabolites most likely due to differences in microbial composition, polymorphisms in metabolizing enzymes and transport proteins. Epidemiological studies show conflicting evidence of the chemopreventive effect of green tea. However, for prostate cancer, one randomized controlled trial (RCT) from Italy suggested that the consumption of GTP supplement inhibited the progression of premalignant lesions to prostate cancer and furthermore, that green tea catechins might positively influence quality-of-life issues in patients with high-grade prostate intraepithelial neoplasia. Another intervention study in the U.S. demonstrated a decrease in serum prostate-specific antigen, hepatocyte growth factor, and vascular endothelial growth factor after the consumption of 800 mg of EGCG for an average of 6 weeks. In an ongoing randomized pre-prostatectomy trial at UCLA we determined the concentration of GTPs and metabolites in prostate and urine of participants consuming 6 cups of green tea for 3-6 weeks. In the prostate only gallated tea polyphenols such as EGCG, 4″-O-MeEGCG and ECG were found with more than 50% in the nonconjugated free form. In urine the nongallated forms such as EGC, 4′-O-MeEGC and EC were found (3). The ratio of methylated EGCG to nonmethylated EGCG varies considerably among participants. Catechol-O-methyl transferase (COMT), the enzyme responsible for methylation of EGCG and other catechols, has three polymorphic sites. On codon 158 (exon 4) the G-&gt;A transition leading to Val-&gt;Met amino acid change is associated with a four time lower enzyme activity compare to wild type. An epidemiological cohort study by Wu et al. demonstrated that breast cancer risk reduction was only associated with green tea intake in women with at least one low-activity allele in COMT (4). However, in addition to the influence of the single nucleotide polymorphism on COMT activity, EGCG itself inhibits COMT activity. We demonstrated in PC3 prostate cancer cells that EGCG inhibited COMT enzyme activity significantly. The same effect was observed in vivo in severe combined immunodeficiency mice (SCID) implanted subcutaneously with LAPC4 prostate cancer cells. The administration of brewed green tea, instead of drinking water, lead to a decrease in tumor growth and COMT m-RNA expression.

Methylation and conjugation may also alter the biologic activities of the parent compound. For example, our cell culture experiments demonstrated differences in the antiproliferative activity, anti-inflammatory activity (NFkB stimulation), and stimulation of apoptosis of methylated EGCG compared to the parent compound in androgen dependent (LNCaP) and androgen independent (PC-3) prostate cancer cells. In the case of EGCG, methylation leads to a significant decrease of biological activity. However, in case of quercetin, there was no significant difference in the antiproliferative activity between methylated quercetin and the parent compound. Since quercetin is known as a strong natural methylation inhibitor we tested the effect of co-treatment of EGCG and quercetin on EGCG methylation and bioavailability. In cell culture experiments combining EGCG with quercetin decreased EGCG methylation and increased intracellular EGCG 10-fold. These results demonstrate that combination of polyphenols with differential effects on metabolism may be useful to enhance bioavailability and bioactivity. In summary, in vitro mechanistic investigations with translational potential, will need to be performed with the appropriate metabolites and concentrations found in vivo.

References:

1. Chun OK, Chung SJ, Song WO. Estimated dietary flavonoid intake and major food sources of U.S. adults. J Nutr. 2007, 137(5):1244-52.

2. Zamora-Ros R, Andres-Lacueva C, Lamuela-Raventós RM, Berenguer T, Jakszyn P, Barricarte A, Ardanaz E, Amiano P, Dorronsoro M, Larrañaga N, Martínez C, Sánchez MJ, Navarro C, Chirlaque MD, Tormo MJ, Quirós JR, González CA. Estimation of dietary sources and flavonoid intake in a Spanish adult population (EPIC-Spain). J Am Diet Assoc. 2010, 110(3):390-8.

3. Wang P,Aronson WJ, Huang M, Heber D, Henning SM. Methyl-Metabolites of Green Tea Polyphenols and Their Bioactivity in Prostate — Results of a Phase II Clinical Trial in Men with Prostate Cancer. Cancer Prev. Res. 2010, 3(8):985-93.

4. Wu AH, Tseng CC, Van Den Berg D, Yu MC. Tea intake, COMT genotype, and breast cancer in Asian-American women. Cancer Res. 2003, 63(21):7526-9.

Citation Information: Cancer Prev Res 2010;3(12 Suppl):CN06-03.