Optimization of conditions for the enzymatic hydrolysis of phytoestrogen conjugates in urine and plasma

Optimal pH, temperature, and concentration of enzyme conditions for the rate of hydrolysis of five isoflavone conjugates (daidzein, O-desmethylangolensin, equol, genistein, and glycitein) and two lignans (enterodiol and enterolactone) from two biological matrices (urine and plasma) were studied using β-glucuronidase from Helix pomatia. In addition, the use of mixtures of β-glucuronidase and sulfatase enzymes from different sources was investigated to find enzyme preparations that contained lower amounts of naturally present phytoestrogens. Quantification of aglycones spiked with 13C3-labeled internal standards was carried out by LC-MS/MS. In urine, all of the phytoestrogen conjugates hydrolyzed within 2 h under standard hydrolysis conditions (24 μl H. pomatia, pH 5, 37 °C). Hydrolysis rates were improved at 45 °C and by doubling the enzyme concentration and may be used to further reduce hydrolysis times down to 100 min. In plasma, a 16-h hydrolysis was required to ensure complete hydrolysis of all conjugates. As with urine, the use of increased temperature or increased enzyme concentration reduced hydrolysis times for most analytes. However, the rate of hydrolysis in plasma was significantly slower than that in urine for all analytes except enterodiol, for which the reverse was true. Neither increased temperature nor increased enzyme concentration increased the rate of hydrolysis of enterolactone. Hydrolysis at pH 6 proved to be detrimental to hydrolysis of phytoestrogen conjugates, especially those in plasma. Other enzyme preparations from different sources, such as β-glucuronidase from Escherichia coli, were found to contain lower amounts of contaminating phytoestrogens and showed increased enzyme activity for isoflavones, but lower activity for lignans, when used with other sulfatase enzymes. In addition, this involved complicating the analytical procedure through using mixtures of enzymes. Therefore, the use of β-glucuronidase from H. pomatia combined with an enzyme “blank” to correct for phytoestrogen contamination was shown to be a suitable method for hydrolysis of phytoestrogens.