Environmental Endocrine Disruption
Human beings have been altering our environment since prehistoric times and these changes impact human health and development in many different ways. In modern times, the levels of chemical environmental contaminates that the average human is exposed to have been increasing at an incredible rate with significant impact on health. Regulation and public awareness have slowed the entry of industrial chemical waste into the environment, but not all environmental contamination is as obvious. A class of environmental contaminates currently being studied are endocrine disrupting chemicals including pharmaceutical products, pesticides, compounds such as Bisphenol A (BPA) used in the plastics industry and in consumer products, industrial by-products and pollutants and even some naturally produced botanical chemicals. Disruption of the endocrine system can directly interfere with development, behavior, fertility, and maintenance of homeostasis in significant ways. However, it is often overlooked that the endocrine system and hormone levels also modulate immune response and regulate the maturation, distribution, proliferation, and functionality several immune cell populations. If endocrine hormones impact the immune system, then chemical disruption of the endocrine system also affects immune function. Many on going studies concern the effects of environmental exposure to various kinds of endocrine disrupting chemicals, as well as means of exposure and levels of these compounds absorbed and retained in various body tissues as a result of typical daily life. Disturbingly some of these studies have shown the levels of exposure necessary to observe effects can be quite low compared to typical environmental contact, and in at least some cases, even brief exposures can show effects throughout life.
A recent study by Palacios-Arreola et al. demonstrated just a single neonatal exposure to BPA can cause changes in the immune system influencing tumor formation and breast cancer disease progression in adulthood. Female mice were exposed to a single dose of BPA (250 ug/kg body weight) 72 hours after birth. At 8 weeks old, treated, control, and vehicle mice were further divided into control and tumor induction groups. The tumor induction mice were implanted with 4T1 cells to induce mammary tumors after which tumor growth was monitored for 25 days. The mice treated with the single dose BPA did not demonstrate any of the reproductive effects such as early onset puberty, estrous cycle alteration, or basal levels of serum estradiol (Arbor Assays Estradiol Serum EIA Kit, KB30-H ) often associated with prolonged exposure to endocrine disrupting chemicals. However, somewhat remarkably, tumor growth was significantly promoted with the single neonatal exposure. Since none of the more direct reproductive system effects were observed with this single dose it is possible permanent alterations in the immune system may be responsible. Expression of ERalpha, the major estrogen receptor in immune cells was found to be higher in immune cells of exposed animals, a change potentially mimicing increased estrogen levels within immune cells without changes in the serum levels of the hormone itself.
Further studies are needed to understand the long term effects of exposure to endocrine disrupting chemicals such as BPA. However, the data available thus far does support the idea even very limited exposure could have quite long lasting effects, making it all the more important we pay attention to the chemicals we introduce into our environments, both as waste, and in products.