Collaborative work on evaluation of ovarian toxicity. 12) Effects of 2- or 4-week repeated dose studies and fertility study of indomethacin in female rats

Predictors of Phthalate Metabolites Exposure among Healthy Pregnant Women in the United States, 2010-2015

Phthalate use and the concentrations of their metabolites in humans vary by geographic region, race, ethnicity, sex, product use and other factors. Exposure during pregnancy may be associated with detrimental reproductive and developmental outcomes. No studies have evaluated the predictors of exposure to a wide range of phthalate metabolites in a large, diverse population. We examined the determinants of phthalate metabolites in a cohort of racially/ethnically diverse nulliparous pregnant women. We report on urinary metabolites of nine parent phthalates or replacement compounds-Butyl benzyl phthalate (BBzP), Diisobutyl phthalate (DiBP), Diethyl phthalate (DEP), Diisononyl phthalate (DiNP), D-n-octyl phthalate (DnOP), Di-2-ethylhexyl terephthalate (DEHTP), Di-n/i-butyl phthalate (DnBP), Di-isononyl phthalate (DiNP) and Di-(2-ethylhexyl) phthalate (DEHP) from urine collected up to three times from 953 women enrolled in the Nulliparous Mothers To Be Study. Phthalate metabolites were adjusted for specific gravity. Generalized estimating equations (GEEs) were used to identify the predictors of each metabolite. Overall predictors include age, race and ethnicity, education, BMI and clinical site of care. Women who were Non-Hispanic Black, Hispanic or Asian, obese or had lower levels of education had higher concentrations of selected metabolites. These findings indicate exposure patterns that require policies to reduce exposure in specific subgroups.

Luteal toxicity evaluation in rats

The corpora lutea (CL) are endocrine glands that form in the ovary after ovulation and secrete the steroid hormone, progesterone (P4). P4 plays a critical role in estrous and menstrual cycles, implantation, and pregnancy. The incomplete rodent estrous cycle stably lasts 4–5 days and its morphological features can be distinguished during each estrous cycle stage. In rat ovaries, there are two main types of CL: newly formed ones due to the current ovulation (new CL), and CL remaining from prior estrous cycles (old CL). In the luteal regression process, CL were almost fully regressed after four estrous cycles in Sprague-Dawley rats. P4 secretion from CL in rodents is regulated by the balance between synthesis and catabolism. In general, luteal toxicity should be evaluated by considering antemortem and postmortem data. Daily vaginal smear observations provided useful information on luteal toxicity. In histopathological examinations, not only the ovaries and CL but also other related tissues and organs including the uterus, vagina, mammary gland, and adrenal glands, must be carefully examined for exploring luteal changes. In this review, histological and functional characteristics of CL in rats are summarized, and representative luteal toxicity changes are presented for improved luteal toxicity evaluation in preclinical toxicity research.

Altered gene expression profile in ovarian follicle in rats treated with indomethacin and RU486

It is well-known that indomethacin (the cyclooxygenase 1 & 2 inhibitor) and RU486 (or mifepristone, the progesterone receptor antagonist) block follicular rupture in rats. To characterize genetic alterations in unruptured follicles, gene expression profiles in ovarian follicle were analyzed in indomethacin- and RU486-treated female Sprague-Dawley rats. Ovaries are collected at 22:00 on the proestrus day and 10:00 on the following estrus day after a single dose of indomethacin and RU486. Histopathologically, changes depicting responses to LH surge were observed in ovaries, uteri and vagina. Total RNA was extracted from pre-ovulatory follicles or unruptured follicles collected by laser microdissection and analyzed by Genechip(®). Among genes showing statistically significant changes compared to control groups, following changes were considered relevant to induction of unruptured follicles. In indomethacin-treated rats, Wnt4 was down-regulated, suggesting effect on tissue integrity and steroid genesis. In RU486-treated rats, Adamts1, Adamts9, Edn2, Ednra, Lyve1, Plat, and Pparg were down-regulated. These changes suggest effects on proteolysis for extra cellular matrix or surrounding tissue (Adamts1 & 9, and Plat), constriction of smooth muscle surrounding follicles (Edn2, Ednra, and Pparg), follicular fluid (Lyve1), and angiogenesis (Pparg). Down-regulation of angiogenesis related genes (Angpt2, Hmox1, and Vegfa) was observed in both treatment groups. Here, we clarify genetic alterations induced by the inhibition of cyclooxygenase or progesterone receptor.

Nonproliferative and proliferative lesions of the rat and mouse female reproductive system

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) Project (www.toxpath.org/inhand.asp) is a joint initiative of the Societies of Toxicological Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in the female reproductive tract of laboratory rats and mice, with color photomicrographs illustrating examples of some lesions. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous and aging lesions as well as lesions induced by exposure to test materials. There is also a section on normal cyclical changes observed in the ovary, uterus, cervix and vagina to compare normal physiological changes with pathological lesions. A widely accepted and utilized international harmonization of nomenclature for female reproductive tract lesions in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

Transitional gene expression profiling in ovarian follicle during ovulation in normal-cycle rats

Evaluation of ovarian toxicity requires an understanding of the physiological changes related to the estrous cycle in the ovary. The authors investigated the transitional gene expression profile of ovulatory follicles in rats that show normal estrous cyclicity. Ovaries were collected at 10:00 and 22:00 on the proestrus day and at 10:00 on the estrus day. Ovarian follicles or early corpora lutea were isolated using laser microdissection, and extracted total RNA was analyzed using microarray technology. Clustering analysis revealed four different expression patterns: transient up- or down-regulation only at 22:00 on the proestrus day (pattern 1), up- or down-regulation only at 10:00 on the estrus day (pattern 2), continuous increase at 22:00 on the proestrus day and at 10:00 on the estrus day (pattern 3), and up- or down-regulation at 22:00 on the proestrus day and level maintenance at 10:00 on the estrus day (pattern 4). In addition, these probe sets were functionally categorized in each pattern using the Ingenuity Pathways Analysis database. These data will aid in understanding the physiology of ovulation and may be useful in assessing ovarian toxicity and its mechanism, such as in investigations of chemical-induced ovulatory impairment.

Collaborative work on evaluation of ovarian toxicity by repeated-dose and fertility studies in female rats

The National Institute of Health Sciences (NIHS) and 18 pharmaceutical companies of the Japan Pharmaceutical Manufacturers Association (JPMA) have conducted a validation study intended to evaluate whether a 2-week repeated general toxicity period with histopathological examination is sufficient to detect ovarian toxicity or not. The current repeated dose general toxicity study is considered to be insufficient in terms of evaluating female reproductive function due to a lack of evidence indicating that it is adequate. Evaluation of ovarian toxicity by comprehensive histopathological examination of the female reproductive organs based on the underlying morphology of a normal cycle of the reproductive tract including the ovary and additional immunohistochemical staining with proliferative cell nuclear antigen (PCNA) to identify small follicles may be a good tool to assess female reproductive function. In the collaborative study, 2- or 4-week repeated dose toxicity studies with ovarian histopathological examinations were conducted. A female fertility study was also conducted to compare the results with those of the ovarian histopathological findings. A total of 17 test substances were evaluated and categorized into hormone analogues, primordial follicle damaging agents, metabolite imbalance inducers, and endocrine imbalance inducers. Based on the results, ovarian toxicity could be detected by a careful histopatholgical examination. A 2-week dosing period may be sufficient for the evaluation of ovarian toxicity, except for cytotoxic compounds such as alkylating agents. The pathological findings of ovarian toxicity (decreases in follicles, increases in atretic follicles, increases in currently formed corpora lutea, etc) reflected the female fertility parameters (irregular estrous cycle, pre-implantation loss).

Morphological characterization of the ovary under normal cycling in rats and its viewpoints of ovarian toxicity detection

Identification of ovarian toxicity is very important for safety assessment of drugs and other environmental chemicals. The detection of interference with ovarian function is very hard without a thorough understanding of the normal ovarian morphology based on reproductive physiology. The focus of the present study was therefore a practical analysis in each stage of the estrous cycles using ovaries obtained from 143 rats demonstrating normal cycling. Transversely dissected maximum areas in the ovaries were examined microscopically for the two major features, follicles and corpora lutea (CL). Classification of growing follicles was in reference to Pedersen and Peters (1968), and functionally divided into follicular stimulating hormone (FSH)-independent and dependent categories. The former, small and medium-sized follicles, respectively primordial/primary and preantral follicles, could be readily detected by immunohistochemical staining for proliferating cell nuclear antigen (PCNA). The large antral and Graafian follicles and large sized atretic follicles showed sequential changes depending on the estrous cycle stage. CL could be divided into currently and previously formed examples. Currently formed CL underwent remarkable changes in their appearance with the cycle, reflecting ovulation and progesterone production. Thus morphological analysis that is synchronized the large antral follicle changes with recently formed CL ones allows the ovary to be classified into the each estrous cycle stage. Morphological deviation from any synchronized combination provides a first pointer of ovarian toxicity. PCNA immunohistochemical staining is also useful to detect small follicles.