Effects of Environmental Endocrine Disruptors and Phytoestrogens on the Kisspeptin System - Kisspeptin Signaling in Reproductive Biology - page 449

Compound Structure Description

Endogenous
Estrogen

Estradiol

Component of
plastics/epoxy resins

BPA

GEN Isoflavone

Phytoestrogen

PCBs Coolant, plasticizer

( no longer used but persists
in the environment )

Fig. 21.1 -estradiol and three common EDCs. Generally, the presence of a phenolic

ring indicates the potential for estrogenic activity either by classical or rapid signaling pathways

Structure of 17 β

transformers, and capacitors, but also as plasticizers and stabilizers in paints and
cement, fi re retardants, hydraulic fl uid, adhesives, pesticide mixtures, and sealants.
Structurally, there are two classes of PCBs, a coplanar group which makes them
chemically similar to dioxins and a noncoplanar group which is less toxic. PCBs were
almost always sold as complex mixtures, each of which differed considerably in terms
of toxicity. Many are known to have estrogenic, antiestrogenic, or antiandrogenic
properties [ 51 ]. In general, the desirable physical properties of the PCBs which made
them so useful, including their exceptional physical and chemical stability, unfortu-
nately confer resistance to decomposition. In 1979, they were classifi ed as persistent
organic pollutants by the EPA and subsequently banned in the USA. Because of their
persistence, they remain prevalent in the environment, and tend to bioaccumulate up
the food chain and within lipid-rich tissues. Thus, body burdens remain high in some
populations [ 16 , 52 ], and human exposure is ubiquitous and ongoing.
GEN is an isofl avone phytoestrogen found in soy and other legumes, and has been
extensively studied for both its benefi cial and endocrine-disrupting properties [ 19 , 53 ].
Intake of GEN is increasing primarily because people are choosing to consume more
soy-rich foods (such as soy milk, tofu, and tempeh) to take advantage of their pur-
ported health benefi ts. Increased consumption has been associated with reduced risk
of hormone-dependent cancer (breast and prostate), cardiovascular disease, and osteo-
porosis [ 19 ]. Importantly, in Western populations that do not traditionally consume an
abundance of soy-rich foods, intake may be higher than perceived because soy is
increasingly being incorporated into a wide array (upwards of 60%) of processed food
products, such as cereals, crackers, processed meats, bread, and granola bars to
increase their nutritional value [ 54 ]. Dietary supplements containing high levels of
GEN and other isofl avonoid phytoestrogens are also widely available [ 55 ]. Exposure