Characterization of an in vitro mouse follicle bioassay to study the effects of endocrine disrupters on ovarian homeostasis and gametogenesis

A variety of structurally diverse natural and synthetic chemicals, classified as endocrine-disrupting chemicals (EDCs) or in short endocrine disrupters (EDs), have been reported to interfere with the endocrine system and ultimately disturb the normal function of tissues and organs, particularly those of the reproductive system. In considering the risk of environmental exposures on reproductive function and women's health, special attention should be paid to those chemicals with the potential to impair ovarian function, because the ovary is critical to normal reproduction. Given their physicochemical differences and distinct biological effects, it is not surprising that there are a variety of ways in which EDs can affect ovarian function, making studies on their biological effects daunting. Both interference with steroid biosynthesis (steroidogenesis) and steroid action (through classical nuclear steroid receptors) are considered important mechanisms underlying direct endocrine disruption of ovarian functions. The number of targets for endocrine disruption is quite large when all glands, target tissues, receptors, enzymes and hormones are included, and the extra variable of developmental stage of the organism and critical windows of effects adds yet another dimension, as does species, strain, gender, and route and duration of potential exposure. Because hormones control virtually all living processes, and because they work at very low concentrations (in the pg/l or ng/l range), we are faced with the new prospect of some pollutants having also potency at unexpectedly small doses (or concentrations). Traditional chemical testing and risk assessment regimes are simply not designed to cope with such an unexpected mode of action, and the controls which now exist on the use of EDs were only imposed after serious environmental damage had been sustained. This is because these substances do not adversely affect organisms in the traditional sense of directly damaging their cellular or physiological processes, but instead interfere with their endocrine systems, either by mimicking hormones, by blocking their effects, or by interfering with their synthesis or excretion. Thus, endocrine disruption should not be considered as an endpoint in itself, presenting a risk to the environment, but instead as a mechanism of action that potentially could lead to adverse outcomes, for example carcinogenic, reproductive, neurotoxic or immunological responses. The actual role of EDs as risk factors for human health is still a matter of debate. However, it is important to know a chemical's critical toxicity and whether or not this is mediated by an endocrine mechanism, because in a human exposure situation this could result in neurotoxicity long before endocrine function is affected and unlike functional endocrine changes, this may be irreversible and acutely life-threatening. The most appropriate procedure for assessing evidence of endocrine disruption should involve a tiered testing strategy composed of in vitro and in vivo tests, which incorporates a weight of evidence of approach of all available data. However, the testing battery needs to be refined with biologically-relevant bioassays in order to improve the ability to catch the actually-relevant endpoints. Many candidate systems are available but lack proper validation. This research mainly involved a characterization of a standardized follicle culture system and revealed that receptor expression of namely estrogen receptor? (ER) and androgen receptor (AR), closely mimics in vivo expression, with the exception that ER was also found in granulosa cells.