Metabolism and Kinetics of Bisphenol A in Humans at Low Doses Following Oral Administration Wolfgang Vo ¨lkel, † Thomas Colnot, †,‡ Gyo ¨rgy A. Csana ´ dy, § Johannes G. Filser, § and Wolfgang Dekant* ,† Institut fu ¨ r Toxikologie, Universita ¨ t Wu ¨ rzburg, Versbacher Strasse 9, 97078 Wu ¨ rzburg, Germany, Institut fu ¨ r Toxikologie, GSF-Mu ¨ nchen, Ingolsta ¨ dter Landstrasse 1, 85764 Oberschleissheim, Germany, and Merck KGaA, Institut fu ¨ r Toxikologie, Frankfurter Strasse 250, 64293 Darmstadt, Germany Received April 24, 2002 Bisphenol A is a widely used industrial chemical with many potential sources of human exposure. Bisphenol A is a weak estrogen and has been implicated as an “endocrine disruptor”. This term is used for a variety of chemicals encountered in the environment which have estrogenic activity. It has been postulated that human exposure to these chemicals may elicit unwanted estrogenic effects in humans such as reduced fertility, altered development and cancer. Up to now the body burden of bisphenol A in humans is unknown. Therefore, we investigated the metabolism and toxicokinetics of bisphenol A in humans exposed to low doses since systemic bioavailability has a major influence on possible estrogenic effects in vivo. Human subjects (three males and three females, and four males for detailed description of blood kinetics) were administered d 16 -bisphenol A (5 mg). Blood and urine samples were taken in intervals (up to 96 h), metabolites formed were identified by GC/MS and LC-MS/MS and quantified by GC/MS-NCI and LC-MS/MS. d 16 -Bisphenol A glucuronide was the only metabolite of d 16 - bisphenol A detected in urine and blood samples, and concentrations of free d 16 -bisphenol A were below the limit of detection both in urine (6 nM) and blood samples (10 nM). d 16 -Bisphenol A glucuronide was cleared from human blood and excreted with urine with terminal half-lives of less than 6 h; the applied doses were completely recovered in urine as d 16 -bisphenol A glucuronide. Maximum blood levels of d 16 -bisphenol A glucuronide (∼800 nM) were measured 80 min after oral administration of d 16 -bisphenol A (5 mg). The obtained data indicate major species differences in the disposition of bisphenol A. Enterohepatic circulation of bisphenol A glucuronide in rats results in a slow rate of excretion, whereas bisphenol A is rapidly conjugated and excreted by humans due to the absence of enterohepatic circulation. The efficient glucuronidation of bisphenol A and the rapid excretion of the formed glucuronide result in a low body burden of the estrogenic bisphenol A in humans following oral absorption of low doses. Introduction Bisphenol A is a component of polycarbonate plastics and used for a variety of applications such as dental composite fillings and food-can linings. In rats, the weak estrogenicity of bisphenol A, as measured by special protocols, has been known for decades (1, 2). Recently, scientific and public attention has been focused on chemicals which may mimic endogenous hormone action and thus interfere with endocrine function (3-6). These chemicals, which include certain pesticides and plasticiz- ers, are designated as “endocrine disruptors” and human exposure to these chemicals from the environment is sometimes postulated to alter normal hormonal function in humans and wildlife (5, 7). Suspected effects of modified endocrine functions may be reduced fertility, altered development, and cancer in estrogen-sensitive tissues. The interest in endocrine disruptors has led to intensified studies on estrogenic effects of bisphenol A due to widespread potential human exposure. In vitro, bisphenol A exhibits weak estrogenic activity (compared to 17-estradiol) by binding and activating estrogen receptors (8, 9). In rats, high oral doses of bisphenol A (50-1 000 mg/kg) are required to induce estrogen de- pendent responses (1, 2, 10, 11). However, the estroge- nicity of bisphenol A in vivo is dependent on the route of administration. Subcutaneous administration of bisphe- nol A resulted in effects at substantially lower doses as compared to oral or intraperitoneal administration, sug- gesting that differences in bioavailability may be respon- sible for the different responses (12, 13). Indeed, signifi- cant differences in bioavailability and biotransformation of bisphenol A in rats, as shown by various studies, are dependent on the route of administration. Oral bioavail- ability of bisphenol A is low and intensive biotransfor- mation occurs in the liver resulting in the formation of bisphenol A glucuronide, which is devoid of estrogenicity (14-16). * To whom correspondence should be addressed. E-mail: dekant@ toxi.uni-wuerzburg.de. Phone: +49-931-20148-449. Fax: +49-931- 20148-865. † University of Wu ¨ rzburg. ‡ Present address: Merck KgaA Darmstadt. § GSF-Mu ¨ nchen. 1281 Chem. Res. Toxicol. 2002, 15, 1281-1287 10.1021/tx025548t CCC: $22.00 © 2002 American Chemical Society Published on Web 09/24/2002