Abstract. Chalcones are a type of flavonoids characterized by an α-β unsaturated structural element which may react with thiol groups to activate pathways such as the Nrf2-Keap-1 system. Naringenin chalcone is abundant in the diet but little is known about its bioavailability. In this work, the bioavailability of naringenin chalcone from tomatoes was investigated in a group of healthy men (n=10). After ingestion of 600 grams of tomatoes providing a single dose of 17.3 mg naringenin chalcone, 0.2 mg of naringenin, and 195 mg naringin plasma levels of free and conjugated naringenin and naringenin chalcone (glucuronide and sulfate) were analyzed by UHPLC-QTOF-MS at 0.5, 1, 3, and 6 h post-consumption. Plasma levels of conjugated naringenin increased to about 12 nmol/L with a maximum at about 3 h. Concentrations of free naringenin hardly elevated above baseline. Plasma levels of free and conjugated naringenin chalcone significantly increased. A maximum of the conjugated chalcone was reached at about 3 h after ingestion with an average concentration of about 0.5 nmol/L. No free chalcone was detectable at baseline but low amounts of the unconjugated compound could be detected with an average maximum of 0.8 nmol/L at about 1 h after ingestion. The data demonstrate that naringenin chalcone is bioavailable in humans from cherry tomatoes as a dietary source. However, availability is poor and intramolecular cyclisation as well as extended metabolism likely contribute to the inactivation of the reactive alpha-beta unsaturated reactive center as well as the excretion of the biologically active molecule, respectively.
