Green tea polyphenols and metabolites in prostatectomy tissue: implications for cancer prevention

Abstract

Epidemiologic, preclinical, and clinical trials suggest that green tea consumption may prevent prostate cancer through the action of green tea polyphenols including (-)-epigallocatechin-3-gallate (EGCG). To study the metabolism and bioactivity of green tea polyphenols in human prostate tissue, men with clinically localized prostate cancer consumed six cups of green tea (n = 8) daily or water (n = 9) for 3 to 6 weeks before undergoing radical prostatectomy. Using high-performance liquid chromatography, 4''-O-methyl EGCG (4''-MeEGCG) and EGCG were identified in comparable amounts, and (-)-epicatechin-3-gallate was identified in lower amounts in prostatectomy tissue from men consuming green tea (38.9 +/- 19.5, 42.1 +/- 32.4, and 17.8 +/- 10.1 pmol/g tissue, respectively). The majority of EGCG and other green tea polyphenols were not conjugated. Green tea polyphenols were not detected in prostate tissue or urine from men consuming water preoperatively. In the urine of men consuming green tea, 50% to 60% of both (-)-epigallocatechin and (-)-epicatechin were present in methylated form with 4'-O-MeEGC being the major methylated form of (-)-epigallocatechin. When incubated with EGCG, LNCaP prostate cancer cells were able to methylate EGCG to 4''-MeEGCG. The capacity of 4''-MeEGCG to inhibit proliferation and NF-kappaB activation and induce apoptosis in LNCaP cells was decreased significantly compared with EGCG. In summary, methylated and nonmethylated forms of EGCG are detectable in prostate tissue following a short-term green tea intervention, and the methylation status of EGCG may potentially modulate its preventive effect on prostate cancer, possibly based on genetic polymorphisms of catechol O-methyltransferase.

Figure 1

Chemical structure of green tea polyphenols.

Figure 2

Glucuronide- and sulfate-conjugation rate of EGCG, 4”-MeEGCG, and ECG in prostate tissue of men in the tea intervention group expressed as percent of total of each GTP (means of 8 participants).

Figure 3

Cellular uptake and metabolism of EGCG in LNCaP cells. EGCG concentration in medium after treatment of LNCaP cells with 40 or 80 μmol/L of EGCG (A). Intracellular concentration of EGCG and 4”-MeEGCG after treatment with 40 μmol/L of EGCG (B), 80 μmol/L of EGCG (C) or 80 μmol/L of 4”-MeEGCG (D).

Figure 3

Cellular uptake and metabolism of EGCG in LNCaP cells. EGCG concentration in medium after treatment of LNCaP cells with 40 or 80 μmol/L of EGCG (A). Intracellular concentration of EGCG and 4”-MeEGCG after treatment with 40 μmol/L of EGCG (B), 80 μmol/L of EGCG (C) or 80 μmol/L of 4”-MeEGCG (D).

Figure 4

Cell viability was inhibited by EGCG or 4”-MeEGCG. LNCaP cells were incubated with EGCG or 4”-MeEGCG (40 or 80 μmol/L) for different time points. Cell viability was detected by trypan blue exclusion assay. The superscript letters represent significant difference between groups (P<0.05): ^a compared to vehicle control; ^b compared to 40 μmol/L of 4”-MeEGCG treatment; ^c compared to 40 μmol/L EGCG treatment; ^d compared to 80 μmol/L 4”-MeEGCG treatment. Error bars represent standard deviation.

Figure 5

Inhibition of NF-κB activation by EGCG or 4”-MeEGCG. LNCaP cells were incubated with 40 or 80 μmol/L of EGCG or 4”-MeEGCG for 24h. NF-κB was stimulated by treatment with 10 ng/mL of TNF-α for 15 min. The IκB-α protein was determined by Western blotting. The superscript letters represent significant difference between groups (P<0.05): ^a compared to vehicle control; ^b compared to 40 μmol/L of 4”-MeEGCG treatment; ^c compared to 40 μmol/L of EGCG treatment; ^d compared to 80 μmol/L of 4”-MeEGCG treatment. Error bars represent standard deviation.

Figure 6

Induction of apoptosis by EGCG or 4”-MeEGCG. LNCaP cells were incubated with 40 and 80 μmol/L of EGCG or 4”-MeEGCG for different time points. The protein concentration of activated caspase 3 was determined by Western blotting. The superscript letters represent significant difference between groups (P<0.05): ^a compared to vehicle control; ^b compared to 4”-MeEGCG treatment at the same dose level; ^c compared to the previous time point. Error bars represent standard deviation.