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S Aust

Publications and source records attributed to S Aust.

7 recordsLinked to original sources

Sulfation of resveratrol in human liver: evidence of a major role for the sulfotransferases SULT1A1 and SULT1E1.

Sulfation of resveratrol, a polyphenolic compound present in grapes and wine with anticancer and cardioprotective activities, was studied in human liver cytosol. In the presence of 3'-phosphoadenosine-5'-phosphosulfate, three metabolites (M1-3) whose structures were identified by mass spectrometry and NMR as trans-resveratrol-3-O-sulfate, trans-resveratrol-4'-O-sulfate, and trans-resveratrol-3-O-4'-O-disulfate, respectively. The kinetics of M1 formation in human liver cytosol exhibited an pattern of substrate inhibition with a K(i) of 21.3 +/- 8.73 microM and a V(max)/K(m) of 1.63 +/- 0.41 microLmin(-1)mg(-1) protein. Formation of M2 and M3 showed sigmoidal kinetics with about 56-fold higher V(max)/K(m) values for M3 than for M2 (2.23 +/- 0.14 and 0.04 +/- 0.01 microLmin(-1)mg(-1)). Incubation in the presence of human recombinant sulfotransferases (SULTs) demonstrated that M1 is almost exclusively catalysed by SULT1A1 and only to a minor extent by SULT 1A2, 1A3 and 1E1, whereas M2 is selectively formed by SULT1A2. M3 is mainly catalysed by SULT1A2 and 1A3. In conclusion, the results elucidate the enzymatic pathways of resveratrol in human liver, which must be considered in humans following oral uptake of dietary resveratrol.

Adolescent↗

Biliary excretion of flavopiridol and its glucuronides in the isolated perfused rat liver: role of multidrug resistance protein 2 (Mrp2).

Flavopiridol (FLAP) is a novel anticancer agent that is extensively glucuronidated in patients. Biliary excretion is the main elimination pathway of FLAP conjugates responsible for enterohepatic recirculation and for the main side effect diarrhea. To investigate the hepatic transport system for FLAP glucuronides, livers of Wistar and Mrp2-deficient TR- rats were perfused with FLAP (30 microM) in a single pass system. Biliary excretion and efflux into perfusate during a 60 min period greatly differ in TR- rats. While cumulative biliary excretion of M1 and M2 was significantly reduced to 4.3% and 5.4% efflux into perfusate was increased by 1.5 and 4.2-fold. This indicates that in control rats, M1 and M2 are almost exclusively eliminated into bile by Mrp2. Cumulative FLAP secretion into bile and perfusate, however, was non-significantly reduced by 36.7% and 43.2% in the mutant rat strain, suggesting that besides Mrp2, other transporters might also be involved in FLAP elimination. FLAP stimulates bile flow up to 24% in control rats, but secretion is nearly absent in TR- rats further supporting an efficient transport of FLAP glucuronides by Mrp2. FLAP (30 microM) also reversibly inhibited the Mrp2-mediated biliary elimination of bilirubin and bromsulphthalein in Wistar rats by 54% and 51%, respectively, indicating a competition with the elimination of Mrp2-specific substrates. In summary, we found that FLAP glucuronides are substrates of Mrp2 effectively inhibiting the biliary excretion of bilirubin. This may explain the increased serum bilirubin levels observed in cancer patients during FLAP therapy.

ATP-Binding Cassette Transporters↗