Investigating the mechanisms of action of thyroid disruptors: A multimodal approach that integrates in vitro and metabolomic analysis.

The thyroid gland, a vital component of the endocrine system, plays a pivotal role in regulating metabolic processes, growth, and development. To better characterize thyroid system disrupting chemicals (TSDC), we followed the next-generation risk assessment approach, which further considers the mechanistic profile of xenobiotics. We combined targeted in vitro testing with untargeted metabolomics.

Scientific and Regulatory Policy Committee Points to Consider: Review of the United States Food and Drug Administration (FDA) Guidance on Pathology Peer Review in Nonclinical Toxicology Studies.

In December 2021, the United States Food and Drug Administration (FDA) issued the final guidance for industry titled . The stated purpose of the FDA guidance is to provide information to sponsors, applicants, and nonclinical laboratory personnel regarding the management and conduct of histopathology peer review as part of nonclinical toxicology studies conducted in compliance with good laboratory practice (GLP) regulations. On behalf of and in collaboration with global societies of toxicologic pathology and the Society of Quality Assurance, the Scientific and Regulatory Policy Committee (SRPC) of the Society of Toxicologic Pathology (STP) initiated a review of this FDA guidance.

Historical Control Data of Spontaneous Pathological Findings in C57BL/6J Mice Used in 18-Month Dietary Carcinogenicity Assays.

A retrospective analysis in C57BL6/J mice used in dietary carcinogenicity studies was performed to determine the survival rate, causes of death and incidences of spontaneous non-tumoral and tumoral findings. Data were collected from 1600 mice from control dose groups of sixteen 18-month carcinogenicity assays performed between 2003 and 2021 at the same test facility with similar environmental conditions and experimental procedures. The survival rate was high in both sexes (81%-85%) and the causes of humane euthanasia or death were mainly non-tumoral (chronic ulcerative dermatitis, atrial thrombosis).

Toxicologic Pathology Forum: Opinion on Not Euthanizing Control Animals in the Recovery Phase of Non-Rodent Toxicology Studies.

Nonclinical toxicology studies that are required to support human clinical trials of new drug candidates are generally conducted in a rodent and a non-rodent species. These studies typically contain a vehicle control group and low, intermediate, and high dose test article groups. In addition, a dosing-free recovery phase is sometimes included to determine reversibility of potential toxicities observed during the dosing phase and may include additional animals in the vehicle control and one or more dose groups.

Artificial Intelligence in Toxicological Pathology: Quantitative Evaluation of Compound-Induced Follicular Cell Hypertrophy in Rat Thyroid Gland Using Deep Learning Models.

Digital pathology has recently been more broadly deployed, fueling artificial intelligence (AI) application development and more systematic use of image analysis. Here, two different AI models were developed to evaluate follicular cell hypertrophy in hematoxylin and eosin-stained whole-slide-images of rat thyroid gland, using commercial AI-based-software. In the first, mean cytoplasmic area measuring approach (MCA approach), mean cytoplasmic area was calculated via several sequential deep learning (DL)-based algorithms including segmentation in microanatomical structures (separation of colloid and stroma from thyroid follicular epithelium), nuclear detection, and area measurements.

Opinion on Maintaining In-House GLP Status for Toxicologic Pathology in Pharmaceutical and (Agro)Chemical Development.

Many pharmaceutical companies have recently elected to stop maintaining good laboratory practices (GLP) status of their R&D sites. Similar discussions have also been engaged in the (agro)chemical industry. This opinion paper examines the pros and cons of maintaining facility GLP status for the purposes of performing the pathology interpretation or peer reviews of GLP studies internally.

Artificial Intelligence in Toxicologic Pathology: Quantitative Evaluation of Compound-Induced Hepatocellular Hypertrophy in Rats.

Digital pathology evolved rapidly, enabling more systematic usage of image analysis and development of artificial intelligence (AI) applications. Here, combined AI models were developed to evaluate hepatocellular hypertrophy in rat liver, using commercial AI-based software on hematoxylin and eosin-stained whole slide images. In a first approach, deep learning-based identification of critical tissue zones (centrilobular, midzonal, and periportal) enabled evaluation of region-specific cell size.

Towards a mechanism-based approach for the prediction of nongenotoxic carcinogenic potential of agrochemicals.

Chemical substances are subjected to assessment of genotoxic and carcinogenic effects before being marketed to protect man and the environment from health risks. For agrochemicals, the long-term rodent carcinogenicity study is currently required from a regulatory perspective. Although it is the current mainstay for the detection of nongenotoxic carcinogens, carcinogenicity studies are shown to have prominent weaknesses and are subject to ethical and scientific debate.

A comprehensive view on mechanistic approaches for cancer risk assessment of non-genotoxic agrochemicals.

Currently the only methods for non-genotoxic carcinogenic hazard assessment accepted by most regulatory authorities are lifetime carcinogenicity studies. However, these involve the use of large numbers of animals and the relevance of their predictive power and results has been scientifically challenged. With increased availability of innovative test methods and enhanced understanding of carcinogenic processes, it is believed that tumour formation can now be better predicted using mechanistic information.

Nonproliferative and Proliferative Lesions of the Rat and Mouse Endocrine System.

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) Project (www.toxpath.org/inhand.

Regulatory Forum opinion piece: image analysis-based cell proliferation studies using electronic images: the CEPA industry working group's proposal.

Electronic images of histopathological changes are commonly and increasingly used in toxicologic pathology for morphological evaluation, illustration, peer review, or reporting. Toxicity studies in which cell proliferation is an end point are also pivotal in determining the carcinogenic potential of new molecules. In this article, we describe the approach of the European Cell Proliferation and Apoptosis working group (CEPA) for performing cell proliferation studies and morphometry using electronic images.

Potential new targets involved in 1,3-dinitrobenzene induced testicular toxicity.

1,3-Dinitrobenzene (DNB) causes testicular injury, particularly to Sertoli cells, and induces apoptosis in the surrounding germinal cells in rodents; however, the mechanisms causing this toxicity are poorly understood. Our studies, using standard and molecular tools, were conducted to better understand the pathogenesis of the testicular effects. Four daily oral doses of 0.

Comparison of early morphological and molecular changes induced by 17-alpha-methyltestosterone and estradiol benzoate in the rat ovary.

Repeated exposure to 17-α-methyltestosterone (17MT) and estradiol benzoate (EB) for 28 or 90 days in rats induce similar ovarian atrophy. The objective of the present work was to identify and compare the early effects induced by 17MT and EB on the ovary using molecular and histopathological tools. Female rats were evaluated after 1, 3 or 7 days following an oral exposure by gavage at a daily dose of 600 mg/kg/day for 17MT and 5 mg/kg/day for EB.

Historical control data of neoplastic lesions in the Wistar Hannover Rat among eight 2-year carcinogenicity studies.

Incidences of neoplastic lesions were evaluated in untreated Hannover Wistar Rats RjHan: WI (470 males and 470 females) used as control animals in eight carcinogenicity studies. All these studies were performed in a similar environment either for the in vivo and the postmortem evaluation. The major neoplastic lesions were found in the endocrine, integumentary and reproductive systems.

A molecular and phenotypic integrative approach to identify a no-effect dose level for antiandrogen-induced testicular toxicity.

The safety assessment of chemicals for humans relies on identifying no-observed adverse effect levels (NOAELs) in animal toxicity studies using standard methods. With the advent of high information content technologies, especially microarrays, it is pertinent to determine the impact of molecular data on the NOAELs. Consequently, we conducted an integrative study to identify a no-transcriptomic effect dose using microarray analyses coupled with quantitative reverse transcriptase PCR (RT-qPCR) and determined how this correlated with the NOAEL.

Standard and molecular NOAELs for rat testicular toxicity induced by flutamide.

An important step in the safety assessment of chemicals for humans is to determine the no observed adverse effect level (NOAEL) in toxicity studies conducted in animal models. With the increasing use of molecular tools in toxicity studies, a question often posed is how a NOAEL derived from molecular data compares to a NOAEL established using standard methods. The objective of the present study was to address this question when considering testicular toxicity.

A mammary gland adenomyoepithelioma in a C57BL/6 mouse.

Mammary gland adenomyoepitheliomas are benign complex mammary gland tumors composed of neoplastic cells of epithelial and myoepithelial origins, described in many species (humans, dogs, cats, rats) and rarely in mice. We report here an adenomyoepithelioma in a C57BL/6 female mouse. Histologically, tubes and cords formed by neoplastic epithelial cells were separated by bundles of neoplastic myoepithelial cells in a clear and partially mucinous matrix.

An atypical case of histiocytic sarcoma in a Wistar rat (Rattus norvegicus).

Histiocytic sarcoma is the most frequent hematopoietic tumor in rats. We report here a histiocytic sarcoma infiltrating the liver, the spleen and the pancreas from a Wistar rat. In the liver, the tumor was associated with oval cell and bile duct hyperplasia.

ESTP comments on the draft updated OECD test guideline 407.

The revision of the OECD TG 407 test guideline (repeated dose 28-day oral toxicity study in rodents) focuses on endpoints to detect endocrine activities of chemicals. The new endpoints are likely to influence other previously established core endpoints of this study type. An expert group of pathologists and toxicologists within the European Society of Toxicologic Pathologists (ESTP) has contributed to the scientific discussion of the draft guideline.

Standardized assessment of cell proliferation: the approach of the RITA-CEPA working group.

Since 1985, quantitative data on cell proliferation increasingly form an integral part in the risk assessment of many pharmaceutical, chemical, and agrochemical compounds. Technical guides for the conduct of cell proliferation studies are not readily available. The detection of cell proliferation relies almost exclusively on immunohistochemistry, which is rarely standardized between laboratories.