Scientists have discovered that even extremely small amounts of environmental estrogens - chemical compounds found in pesticides, plastics and detergents, as well as phytoestrogens from sunflower seeds, soybeans and alfalfa sprouts - can cause major changes in endocrine cells, possibly leading to disruption of vital chemical messenger systems in humans and animals.

Researchers have become increasingly concerned about environmental estrogens over the last ten years in the face of evidence linking the chemicals to everything from deformed sexual organs in alligators to damaged fish and human sperm to increased proliferation of breast cancer cells. But lab experiments that aimed to measure the danger posed by environmental estrogens seemed to show that unrealistically high concentrations of the compounds would be needed to produce the observed effects.

The new study, described in a paper published in the November Environmental Health Perspectives and authored by University of Texas Medical Branch at Galveston (UTMB) research scientist Nataliya Bulayeva and UTMB human biological chemistry and genetics professor Cheryl Watson, looked at a different mechanism than the one traditionally believed responsible for cellular reactions to external signals. Instead of measuring the responses of the relatively slow-acting genetic machinery in the cells' nuclei, they focused on the much faster chemical responses set in motion by receptors in the cell membranes, the border between the interior and exterior of the cells. (These ?membrane-initiated? reactions have only recently begun to receive substantial attention from scientists, although their involvement in cellular responses was first hypothesized in the 1970s.)

?When people were looking for these responses before, they were focused on these macromolecular synthetic events that take long periods of time, 24 to 48 hours, and for the most part they saw very large concentrations being needed,? said Watson. ?We were looking at seconds to minutes to hours, and seeing responses at concentrations as much as a thousand to a million times lower than that. These things are just as potent as physiological estrogens like estradiol if you look at this mechanism.?

Physiological estrogens are steroid hormones made by humans and animals to control their own endocrine systems and thus guide the growth and development of different systems in their bodies. Xenoestrogens-including both man-made environmental estrogens and phytoestrogens from plants-are chemicals from outside the body that can inappropriately activate or interfere with endocrine signaling.

Watson and Bulayeva measured the responses of signaling molecules known as extracellular signal-regulated protein kinases (ERKs) in rat pituitary cells to representatives of three major classes of environmental estrogens: those found in organochlorine pesticides (endosulfan, dieldrin, and the DDT breakdown product DDE), detergents used in making plastics (p-nonylphenol and bisphenol A) and a compound found in alfalfa sprouts, soybeans, and sunflower seeds (coumestrol).

ERK responses are known to be involved in cell proliferation as well as the release of hormones, which affect many tissues of the body and have a particularly powerful effect on those associated with reproduction. ?Most of these reproductive hormones coordinate the whole animal, coordinating behavior with all the different tissues that have to participate in reproduction,? Watson said. ?If you upset that cascade of signals, then you've got big problems, systemically. So you can imagine a lot of scenarios that result in bad news for the animal that's affected-or maybe the people that are affected.?

University of Texas Medical Branch at Galveston
301 University Blvd.
Galveston, TX 77555-0144
United States
Phone 409-772-2618
Fax 409-772-6216
http://www2.utmb.edu/utmb/news/htm