Metabolic profiling of dietary polyphenols and methylxanthines in normal and malignant mammary tissues from breast cancer patients

Resumen

Background: Previous studies suggest a protective effect of dietary polyphenols against breast cancer. However, it is unknown whether polyphenols can reach human malignant breast tumors in molecular forms and/or at concentrations likely to act against cancer. Objective: We assessed the metabolic profiling of dietary polyphenols in normal (NT) and malignant (MT) glandular breast tissues from breast cancer patients, and explored the antiproliferative and estrogenic/antiestrogenic activities of the metabolites that could reach breast tissues. Methods: The clinical trial was a dietary intervention conducted between June and De- cember-2017. Patients were randomly allocated to consume (n=19) or not (control, n=8) three capsules daily containing resveratrol plus plant extracts (pomegranate, orange, le- mon, olive, cocoa and grape) from biopsy-confirmed diagnosis to surgery (6±2 days). Each patient consumed daily 37 different phenolics (473.7 mg) plus theobromine and caffeine (19.7 mg). NT and MT, blood and urine were collected during surgery and analyzed with ultra-high resolution liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry using a targeted metabolomics approach. Antiproliferative and estrogenic/ antiestrogenic activities were tested in MCF-7 breast cancer cells. Results: 101 metabolites were identified in urine, 69 in plasma, 39 in NT and 33 in MT. Phenolic-derived metabolites in MT and NT (85.5% and 86.6%, respectively) were mainly glucuronidated and/or sulfated. The most abundant phenolic metabolites (median and ran- ge, pmol/g) in MT were urolithin-A-3-O-glucuronide (26.2; 3.2−66.5), resveratrol-3-O-glucu- ronide (28.7; 20.0−41.1), 2,5-dihydroxybenzoic acid (40.2; 27.7−52.2), resveratrol-3-O-sulfate (86.4; 7.8−224.4), dihydroresveratrol-3-O-glucuronide (109.9; 10.3−229.4), and theobro- mine as the most abundant methylxanthine (715.0; 153.9−3,216). Metabolites detected in breast tissues did not exert in vitro antiproliferative or estrogenic/antiestrogenic activities. Conclusions: The metabolic profiling of phenolics and methylxanthines was similar in MT and NT. Conjugation of phenolic metabolites prevented in vitro activity against cancer cells. A long-term and/or indirect effect of transient-unconjugated metabolites cannot be excluded upon habitual intake of plant foods. Clinical trials are warranted to evaluate the polyphenols’ role in breast cancer prevention.