Abstract
There are limited reports on the bioavailability and pharmacokinetics of isoflavones in elderly humans and aged animals. The present study was conducted to assess the effect of glycosidation of isoflavones on their bioavailability and pharmacokinetics in aged (20 month old) male Fischerโ344 (Fโ344) rats. The Fโ344 rat, developed by the National Institute on Aging, is an inbred rat model that is commonly used for aging studies and resembles many features of aging humans. Three sources of isoflavones; Novasoy^TM^ (a commercial supplement), a mixture of synthetic aglycons (daidzein, genistein and glycitein), and a mixture of synthetic glucosides (daidzin, genistin, and glycitin) were tested. Following administration, blood samples were collected at different times (0โ48 h postโoral gavage and 0โ8 h postโIV dosing). Plasma isoflavones and 7โhydroxyโ3โ(4โฒโhydroxyphenyl)โchroman (a metabolite of daidzein) were measured by LC/MS. The extent of absorption was determined by comparing the area under the curve (AUC) of the plasmaโconcentration time curve after intravenous (IV) administration with that following oral administration. The extent of bioavailability was then calculated as: %bioabailability = (AUC~or~/AUC~IV~)ร(Dose~IV~/Dose~or~)ร100. Bioavailabilities for genistein were significantly (p = 0.013) higher for the aglycon (35 ยฑ 9%) compared with the glucoside forms (11 ยฑ 3%). In contrast, the bioavailabilities for glycitein were significantly (p = 0.011) higher in Novasoy (27 ยฑ 13%) and the glucoside form (21 ยฑ 10%) compared with the aglycon (8 ยฑ 3%). No significant differences in the bioavailability of daidzein were observed in aged rats dosed with aglycon, glucoside or Novasoy. However, aged rats were able to produce equol as early as 8 h postโdosing. In summary, the source of isoflavones had significant effects on genistein and glycitein bioavailability in aged male rats.