Developing a marker of exposure to xenoestrogen mixtures in human serum

It has been hypothesized that environmental estrogens may play a role in the increasing incidence of breast cancer, testicular cancer, and other problems of the reproductive system. While a single causal agent can be identified in cases in which humans have had occupational exposures, wildlife showing signs of reproductive damage have usually been exposed to a combination of endocrine disruptors that may act cumulatively. The development of appropriate biomarkers of cumulative exposure, and their measurement at developmental points where exposure is critical, are required to test the environmental estrogen hypothesis. Measuring levels of each of the xenoestrogens in blood is a better approximation of real exposure at the target organ level than inferring cumulative exposure by estimating from mass balance of dietary levels. However, the cumulative estrogenicity of mixtures cannot be directly concluded from individual xenoestrogen plasma levels. Two approaches may be used to assess total load: a) the development of methods to study mixtures of these xenoestrogens, to quantify their cumulative effects, and to begin to understand their interactions (i.e., additivity, synergy, antagonism, or independent action), so that plasma concentrations may be translated into units of activity such as "estradiol equivalents"; and b) the development of methods to separate xenoestrogens from ovarian estrogens in blood and to directly measure the estrogenic activity of the xenoestrogen extract using a bioassay. The cumulative activity may be used as a marker of exposure to xenoestrogens. This article reports the development of a method to extract and separate xenoestrogens from ovarian estrogens using human serum as a source, followed by using a bioassay for determination of the cumulative xenoestrogen load as "estradiol equivalents."