Fish study proves “the pill” is NOT man’s best friend.
Brown, KH, IR Schultz, JG Cloud, and JJ Nagler. 2008. Aneuploid sperm formation in rainbow trout exposed to the environmental estrogen 17α –ethynylestradiol. Proceedings of the National Academies of Science doi:10.1073/pnas.0808333105.
|Sperm from rainbow trout exposed to the synthetic estrogen in birth control pills can have the wrong number of chormosomes.|
Aneuploidy is the scientific term for having an abnormal number of chromosomes in the nucleus of each cell. The disorder affects humans and other animals that reproduce sexually, including fish.
The chromosomal disorder occurs in nearly 5 percent of all human pregnancies and is the leading cause of miscarriage worldwide. Although most aneuploid pregnancies fail naturally, some babies are born and do survive. Anueploidy is the number one reason for congenital birth defects - such as Down's syndrom and Turner syndrome -- and mental retardation (Hassold 2007).
Normally, human cells contain two copies -- a pair -- of each of the 23 chromosomes found in people - for a total of 46. Each parent contributes one copy through either the egg or the sperm. When a sperm fertilizes an egg, the chromosomes from the egg pair with the like chromosomes in the sperm.
Aneuploidy, though, occurs when the egg or the sperm contribute either more than one or no chromosomes. Instead of a pair, the affected chromosome ends up having three copies -- called trisomy -- or just one copy -- called monosomy. The vast majority of people born with the condition are trisomy.
Although sperm with the wrong number of chromosomes can cause aneuploidy, most disorders in people can be traced back to the mother’s eggs, which form when she is in the womb. It is well established that the risk for miscarriage and aneuploidy increases with a woman’s age.
Presently, the causes of anueploidy are poorly understood, particularly because of the difficulty in studying how eggs and sperm form in both humans and experimental animal models.
Recent studies -- specifically those led by Dr. Patricia Hunt at Washington State University -- show that environmental contaminants may contribute to aneuploidy conditions. In their research, bisphenol A (BPA) causes a 10-fold increase in aneuploidy in the eggs of female mice that were exposed to the chemical while they were developing in the womb (Hassold 2007). BPA is an estrogenic chemical widely used in the manufacture of plastics, epoxy resins and carbon papers.
Average sperm counts worldwide appear to have declined by nearly 50 percent since 1940. Infertility and reproductive problems have risen during the same time period. While there may be many reasons, -- including aneuploidy caused by environmental factors -- exposure to environmental contaminants generally, and endocrine disruptors in particular, may be a major contributing factor.
Environmental estrogens (like BPA) are widespread in US rivers, lakes and other waterways (Kolpin 2002). Sources include flushed pharmaceuticals, runoff from agricultural fields and industry effluent.
Millions of women take oral contraceptives to prevent pregnancies. The estrogen hormone 17-beta-ethinylestradiol (EE2) is an active ingredient in birth control pills. The hormone can end up in the environment after passing through wastewater treatment plants.
Animal studies and observations of wildlife provide sufficient clues to warrant concern about health effects from environmental estrogens. Male reproduction seems expecially vulnerable. Exposure is linked to intersex (born with both male and female characteristics) conditions, lower sperm counts, genital tract malformations, increased sperm and egg death and embryonic mortality.
Prior fish studies found sperm problems lead to lower survival in trout offspring that were exposed to environmental estrogens, including EE2. Sperm chromosome damage was not investigated as a possible cause until now.
Scientists exposed juvenile rainbow trout to 10 nanograms/liter (10 ppb) of 17α-ethynylestradiol (EE2) for 50 days. The synthetic hormone is the active ingredient in most formulations of the birth control pill. Importantly, 10 ppb is a relevant dose, because it is nearly identical to reported levels in contaminated rivers or streams.
The fish were exposed when they were maturing into adults and beginning to make sperm.
After 50 days, sperm was collected. Some of it was used to fertilize eggs from females that were not exposed to EE2. The remainder of the sperm was analyzed, and the number of chromosomes was scored to determine the frequency of aneuploidy.
Aneuploidy was identified through fluorescence -- a technique using colored probes that “stick” to particular chromosomes. The probes can be seen with a special microscope. In this study, chromosome #20 appeared green, and the Y chromosome appeared red. The scientists then counted the number of red and green dots in each sperm cell.
Normal sperm cells have one red and one green dot. If a cell had more than one of each color or if a cell was lacking one of the two colors, then the cell was determined to be anueploid.
Reprinted from Brown et al. 2008.
Normal sperm cell (A) and aneuploid sperm cells (B,C,D).
Exposure to minute quantities of EE2 caused nearly a 25-fold increase in the frequency of aneuploid sperm in fish maturing to adults.
In a normal, unexposed fish, only about 1.2 percent of the total sperm are considered aneuploid. This is the exact frequency of aneuploid sperm found in most humans.
More than half -- 58 percent -- of the embryos derived from eggs fertilized with sperm from the exposed males contained an abnormal number of chromosomes.
Among the aneuploid embryos, 42% were hypodiploid, (containing fewer than the normal number of chromosomes), and 16% were hyperdiploid (more chromosomes than normal).
For the first time, scientists demonstrate that rainbow trout exposed to the active ingredient in the birth control pill have nearly a 25-fold increase in the frequency of sperm containing abnormal numbers of chromosomes. Such defective sperm can affect egg fertilization, embryo development and offspring survival.
Prior studies find that juvenile male fish exposed to EE2 during sexual maturation father embryos with lower survival rates. Up until this study, there was no explanation for these findings. Now, the reason for the reduced survival in those studies may be because EE2 causes aneuploidy in the developing sperm, the authors assert.
How EE2 causes aneuploidy is not known, but the environmental consequences are clear. First, minute quantities of environmental estrogens have adverse affects on reproduction in wildlife populations. Second, males appear to be acutely sensitive to these environmental estrogens, even at very minute quantities. Third, pharmaceuticals that humans often consider harmless, do end up on our public waterways and at levels which clearly affect wildlife.
The possible impacts on humans who use the same water -- whether for drinking, recreation, agricultural irrigation or other purpose -- remain to be determined.
Women taking oral contraceptives excrete EE2, and wastewater treatment facilities fail to effectively remove it from the effluent. Thus, increasing levels of the estrogenic contaminant is found in some public water supplies. Levels approaching 8 parts per billion (ppb), or nearly equal to the amount the fish were exposed to in the present study, have been measured in several North American waterways used for irrigation, recreation and drinking. Consequently, male fish are not the only ones exposed or possibly alarmed by the findings of this work.
Nevertheless, there are new developing green chemistry technologies that may be able to facilitate the removal of environmental estrogens from waste water treatment plants and public water supplies (Collins 2002). Scientists and policy makers need to come together to decide where and how investments should be made to mitigate this threat to wildlife and potentially to humans.
Kolpin, DW, et al. 2002. Pharmaceuticals, hormones, and other organic wastewater contaminants in U.S. streams, 1999-2000: a national reconnaissance. Environmental Science and Technology 36(6):1202-11.
Swan, SH, EP Elkin and L Fenster. 2000. The question of declining sperm density revisited: An analysis of 101 studies published 1934-1996. Environmental Health Perspectives 108:961-966.