Submitted to: Cancer Epidemiology Biomarkers and Prevention
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2000
Publication Date: 4/20/2000
Interpretive Summary: The study of the health effects of any food requires having a good understanding of the active components in that food. In the soybean, there are many compounds that are considered potential active ingredients, and two of those are called genistein and daidzein. We have fed soyfoods to adult people and measure the levels of these compounds in the urine. Although we are primarily interested in children, we studied adults because we needed to establish the best and safest way to study this in children and we used urine because it is safer and easier to obtain than blood in children. We wanted to determine if urine would be an acceptable substitute for blood and to determine which compounds would be the best indicators. We found that urine is a good medium to follow these soy compounds and actual measurement of the sulfated compounds is better than a measure determined by the calculated differences.
Technical Abstract: Consumption of soybean-rich diets is thought to provide to provide significant health benefits such as prevention of cancer, primarily because of the high contents of factors such as the isoflavones genistein and diadzein. Isoflavones circulate and are excreted into the urine mainly as glucuronide and sulfate conjugates. This study was conducted to determine the urinary pharmacokinetics of sulfate and glucuronide conjugates of genistein and daidzein. Twelve volunteers consumed a soy beverage providing 1 and 0.6 mg/kg body weight of genistein and daidzein equivalents, respectively. Urine was collected at various times during the 48 h after soy consumption and was digested with either glucuronidase or sulfatase, and the liberated aglycones were extracted and analyzed by liquid chromatography-mass spectrometry. Urinary isoflavone sulfate levels were determined by two methods: (a) assessment of aglycone after sulfatase hydrolysis (measured); or (b) calculated by subtracting the aglycone + glucuronide levels from the total urinary isoflavone levels. The apparent terminal half-life for daidzein sulfate (3.9 +/- 0.5 H) that was determined from sulfatase-treated urine was 32% shorter (P = 0.02) than that of the calculated daidzein sulfate (5.7 +/- 0.08 H). A similar trend was obtained for genistein sulfate (4.5 +/- 0.7 versus 6.8 +/- 0.1 H). The apparent terminal half-lives for genistein and daidzein glucuronides were 6.0 +/- 0.4 and 3.8 +/- 0.4 H, respectively. These data suggest that the measured urinary isoflavone sulfate values provide a better understanding of the pharmacokinetics than the calculated values. Additional studies are needed to determine whether the apparent terminal half-lives can be attributed to elimination or absorption processes.