Best practices for use of historical control data of proliferative rodent lesions

Historical Control Background Incidence of Spontaneous Nonneoplastic Lesions of Sprague Dawley Rats in 104-Week Carcinogenicity Studies

Microscopic observation data collected from approximately 1800 male and female Sprague Dawley (SD) control rats used on 104-week carcinogenicity studies performed at North American Labcorp Early Development, Inc, Madison, WI, were retrospectively evaluated for spontaneous nonneoplastic findings. This study provides incidence of the most common spontaneous nonneoplastic microscopic findings in each organ system of SD rats encountered during 104-week carcinogenicity studies. Some of the most common spontaneous background findings were cardiomyopathy; chronic progressive nephropathy; uterine cystic endometrial hyperplasia; prostate inflammation; pulmonary alveolar macrophage infiltrates; hepatocyte vacuolation, bile duct hyperplasia, and basophilic foci in the liver; pancreatic fibrosis; splenic extramedullary hematopoiesis and pigment; decreased lymphocytes and epithelial hyperplasia in the thymus; ventral brain compression; cystic degeneration and hyperplasia of the adrenal cortex; and mammary gland hyperplasia. The most common nonneoplastic findings in male SD rats were chronic progressive nephropathy (80.9%) and rodent progressive cardiomyopathy (73.2%). The most common nonnenoplastic findings in female SD rats were cystic degeneration of the adrenal cortex (64.7%) and ventral compression of the brain due to pituitary neoplasms (62.7%).

Pathologists' perspective on the study design, analysis, and interpretation of proliferative lesions in a lifetime rodent carcinogenicity bioassay of sucralose

Sucralose, a sugar substitute first approved for use in 1991, is a non-caloric sweetener regulated globally as a food additive. Based on numerous experimental animal studies (dating to the 1980s) and human epidemiology studies, international health agencies have determined that sucralose is safe when consumed as intended. A single lifetime rodent carcinogenicity bioassay conducted by the Ramazzini Institute (RI) reported that mice fed diets containing sucralose develop hematopoietic neoplasia, but controversy continues regarding the validity and relevance of these data for predicting health effects in humans. The present paper addresses the controversy by providing the perspective of experienced pathologists on sucralose-related animal toxicity and carcinogenicity data generally, and the RI carcinogenicity bioassay findings specifically, using results from publicly available papers and international regulatory authority decisions. In the authors' view, flaws in the design, methodology, data evaluation, and reporting of the RI carcinogenicity bioassay for sucralose diminish the value of the data as evidence that this agent represents a carcinogenic hazard to humans. This limitation will remain until the RI bioassay is repeated under Good Laboratory Practices and the design, data, and accuracy of the pathology diagnoses and interpretations are reviewed by qualified pathologists with experience in evaluating potential chemically-induced carcinogenic hazards.

HESI workshop summary: Interpretation of developmental and reproductive toxicity endpoints and the impact on data interpretation of adverse events

The Health and Environmental Sciences Institute Developmental and Reproductive Toxicology (HESI-DART) group held a hybrid in-person and virtual workshop in Washington, DC, in 2022. The workshop was entitled, "Interpretation of DART in Regulatory Contexts and Frameworks." There were 154 participants (37 in person and 117 virtual) across 9 countries. The purpose of the workshop was to capture key consensus approaches used to assess DART risks associated with chemical product exposure when a nonclinical finding is identified. The decision-making process for determining whether a DART endpoint is considered adverse is critical because the outcome may have downstream implications (e.g., increased animal usage, modifications to reproductive classification and pregnancy labeling, impact on enrollment in clinical trials and value chains). The workshop included a series of webinar modules to train and engage in discussions with federal and international regulators, clinicians, academic investigators, nongovernmental organizations, contract research organization scientists, and private sector scientists on the best practices and principles of interpreting DART and new approach methodologies in the context of regulatory requirements and processes. Despite the differences in regulatory frameworks between the chemical and pharmaceutical sectors, the same foundational principles for data interpretation should be applied. The discussions led to the categorization of principles, which offer guidance for the systematic interpretation of data. Step 1 entails identifying any hazard by closely analyzing the data at the study endpoint level, while Step 2 involves assessing risk using weight of evidence. These guiding principles were derived from the collective outcomes of the workshop deliberations.

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). Benign tumors were more frequent than malignant tumors and females were more affected than males. Pituitary gland adenoma in females, lymphoma, bronchioloalveolar adenoma, and harderian gland adenoma in both sexes were the most common tumors. Systemic amyloidosis, the most frequent non-tumoral lesion, was observed variably across studies without sex predilection. The analysis by cohort (3 time periods of 6 years) showed a tendency toward higher incidences of lymphoma and pituitary gland adenoma and lower incidences of amyloidosis over time. The results presented here provide for the first time a robust set of control historical data in untreated C57BL/6J mice kept for 18 months contributing to build in depth knowledge of this animal model.

The calculation of historical control limits in toxicology: Do's, don'ts and open issues from a statistical perspective

For reporting toxicology studies, the presentation of historical control data and the validation of the concurrent control group with respect to historical control limits have become requirements. However, many regulatory guidelines fail to define how such limits should be calculated and what kind of target value(s) they should cover. Hence, this manuscript is aimed to give a brief review on the methods for the calculation of historical control limits that are in use as well as on their theoretical background. Furthermore, this manuscript is aimed to identify open issues for the use of historical control limits that need to be discussed by the community. It seems that, even after 40 years of discussion, more issues remain open than solved, both, with regard to the available methodology as well as its implementation in user-friendly software. Since several of these topics equally apply to several research fields, this manuscript is addressed to all relevant stakeholders who deal with historical control data obtained from toxicological studies, regardless of their background or field of research.

Oral chronic toxicity and carcinogenicity study of alpha-glycosyl isoquercitrin (AGIQ) in Sprague Dawley rats

alpha-Glycosyl isoquercitrin (AGIQ) is a flavonoid that possesses antioxidant and tumor suppressive capabilities and is marketed as a food additive in Japan. The aim of this study was to assess the potential for oral chronic toxicity and carcinogenicity of AGIQ in male and female Sprague Dawley rats following up to 5.0% dietary exposure. In the chronic toxicity study, rats were exposed to AGIQ or vehicle for one year with a 6-month interim termination point; for the carcinogenicity study, rats were treated for 24 months. No signs of AGIQ-related toxicity clinically or histologically were observed for up to one year except for yellow discoloration of bone. In the carcinogenicity study, a statistically significant increase in the incidence of malignant glioma of the brain or spinal cord was observed in female rats exposed to 5.0% AGIQ compared to those exposed to control feed. A Scientific Advisory Panel of experienced neuropathologists reviewed the gliomas (routine stains and glial cell markers) and concluded that the gliomas were a rare, spontaneous, rat-specific neoplasm: malignant microglial tumor. The lesions could not definitively be attributed to AGIQ exposure and have limited implications with respect to predicting human cancer risk.

Retrospective analysis of the potential use of virtual control groups in preclinical toxicity assessment using the eTOX database

Virtual Control Groups (VCGs) based on Historical Control Data (HCD) in preclinical toxicity testing have the potential to reduce animal usage. As a case study we retrospectively analyzed the impact of replacing Concurrent Control Groups (CCGs) with VCGs on the treatment-relatedness of 28 selected histopathological findings reported in either rat or dog in the eTOX database. We developed a novel methodology whereby statistical predictions of treatment-relatedness using either CCGs or VCGs of varying covariate similarity to CCGs were compared to designations from original toxicologist reports; and changes in agreement were used to quantify changes in study outcomes. Generally, the best agreement was achieved when CCGs were replaced with VCGs with the highest level of similarity; the same species, strain, sex, administration route, and vehicle. For example, balanced accuracies for rat findings were 0.704 (predictions based on CCGs) vs. 0.702 (predictions based on VCGs). Moreover, we identified covariates which resulted in poorer identification of treatment-relatedness. This was related to an increasing incidence rate divergence in HCD relative to CCGs. Future databases which collect data at the individual animal level including study details such as animal age and testing facility are required to build adequate VCGs to accurately identify treatment-related effects.

Statistical analysis of preclinical inter-species concordance of histopathological findings in the eTOX database

Preclinical inter-species concordance can increase the predictivity of observations to the clinic, potentially reducing drug attrition caused by unforeseen adverse events. We quantified inter-species concordance of histopathological findings and target organ toxicities across four preclinical species in the eTOX database using likelihood ratios (LRs). This was done whilst only comparing findings between studies with similar compound exposure (Δ|C_max| ≤ 1 log-unit), repeat-dosing duration, and animals of the same sex. We discovered 24 previously unreported significant inter-species associations between histopathological findings encoded by the HPATH ontology. More associations with strong positive concordance (33% LR+ > 10) relative to strong negative concordance (12.5% LR- < 0.1) were identified. Of the top 10 most positively concordant associations, 60% were computed between different histopathological findings indicating potential differences in inter-species pathogenesis. We also observed low inter-species target organ toxicity concordance. For example, liver toxicity concordance in short-term studies between female rats and dogs observed an average LR+ of 1.84, and an average LR- of 0.73. This was corroborated by similarly low concordance between rodents and non-rodents for 75 candidate drugs in AstraZeneca. This work provides new statistically significant associations between preclinical species, but finds that concordance is rare, particularly between the absence of findings.

Hurdles and signposts on the road to virtual control groups-A case study illustrating the influence of anesthesia protocols on electrolyte levels in rats

Introduction: Virtual Control Groups (VCGs) represent the concept of using historical control data from legacy animal studies to replace concurrent control group (CCG) animals. Based on the data curation and sharing activities of the Innovative Medicine Initiatives project eTRANSAFE (enhancing TRANSlational SAFEty Assessment through Integrative Knowledge Management) the ViCoG working group was established with the objectives of i) collecting suitable historical control data sets from preclinical toxicity studies, ii) evaluating statistical methodologies for building adequate and regulatory acceptable VCGs from historical control data, and iii) sharing those control-group data across multiple pharmaceutical companies. During the qualification process of VCGs a particular focus was put on the identification of hidden confounders in the data sets, which might impair the adequate matching of VCGs with the CCG. Methods: During our analyses we identified such a hidden confounder, namely, the choice of the anesthetic procedure used in animal experiments before blood withdrawal. Anesthesia using CO₂ may elevate the levels of some electrolytes such as calcium in blood, while the use of isoflurane is known to lower these values. Identification of such hidden confounders is particularly important if the underlying experimental information (e.g., on the anesthetic procedure) is not routinely recorded in the standard raw data files, such as SEND (Standard for Exchange of Non-clinical Data). We therefore analyzed how the replacement of CCGs with VCGs would affect the reproducibility of treatment-related findings regarding electrolyte values (potassium, calcium, sodium, and phosphate). The analyses were performed using a legacy rat systemic toxicity study consisting of a control and three treatment groups conducted according to pertinent OECD guidelines. In the report of this study treatment-related hypercalcemia was reported. The rats in this study were anesthetized with isoflurane. Results: Replacing the CCGs with VCGs derived from studies comprising both anesthetics resulted in a shift of control electrolyte parameters. Instead of the originally reported hypercalcemia the use of VCG led to fallacious conclusions of no observed effect or hypocalcemia. Discussion: Our study highlights the importance of a rigorous statistical analysis including the detection and elimination of hidden confounders prior to the implementation of the VCG concept.

Scientific and Regulatory Policy Committee Best Practices: Recommended ("Best") Practices for Informed (Non-blinded) Versus Masked (Blinded) Microscopic Evaluation in Animal Toxicity Studies

This article describes the Society of Toxicologic Pathology's (STP) five recommended ("best") practices for appropriate use of informed (non-blinded) versus masked (blinded) microscopic evaluation in animal toxicity studies intended for regulatory review. (1) Informed microscopic evaluation is the default approach for animal toxicity studies. (2) Masked microscopic evaluation has merit for confirming preliminary diagnoses for target organs and/or defining thresholds ("no observed adverse effect level" and similar values) identified during an initial informed evaluation, addressing focused hypotheses, or satisfying guidance or requests from regulatory agencies. (3) If used as the approach for an animal toxicity study to investigate a specific research question, masking of the initial microscopic evaluation should be limited to withholding only information about the group (control or test article-treated) and dose equivalents. (4) The decision regarding whether or not to perform a masked microscopic evaluation is best made by a toxicologic pathologist with relevant experience. (5) Pathology peer review, performed to verify the microscopic diagnoses and interpretations by the study pathologist, should use an informed evaluation approach. The STP maintains that implementing these five best practices has and will continue to consistently deliver robust microscopic data with high sensitivity for animal toxicity studies intended for regulatory review. Consequently, when conducting animal toxicity studies, the advantages of informed microscopic evaluation for maximizing sensitivity outweigh the perceived advantages of minimizing bias through masked microscopic examination.

Systematic Review Methodologies and Endocrine Disrupting Chemicals: Improving Evaluations of the Plastic Monomer Bisphenol A

BACKGROUND

Endocrine disrupting chemicals (EDCs) are found in plastics, personal care products, household items, and other consumer goods. Risk assessments are intended to characterize a chemical's hazards, identify the doses at which adverse outcomes are observed, quantify exposure levels, and then compare these doses to determine the likelihood of risk in a given population. There are many problems with risk assessments for EDCs, allowing people to be exposed to levels that are later associated with serious health outcomes in epidemiology studies.

OBJECTIVE

In this review, we examine issues that affect the evaluation of EDCs in risk assessments (e.g., use of insensitive rodent strains and absence of disease-oriented outcomes in hazard assessments; inadequate exposure assessments). We then review one well-studied chemical, Bisphenol A (BPA; CAS #80-05-7) an EDC found in plastics, food packaging, and other consumer products. More than one hundred epidemiology studies suggest associations between BPA exposures and adverse health outcomes in environmentally exposed human populations.

FINDINGS

We present support for the use of systematic review methodologies in the evaluation of BPA and other EDCs. Systematic reviews would allow studies to be evaluated for their reliability and risk of bias. They would also allow all data to be used in risk assessments, which is a requirement for some regulatory agencies.

CONCLUSION

Systematic review methodologies can be used to improve evaluations of BPA and other EDCs. Their use could help to restore faith in risk assessments and ensure that all data are utilized in decision-making. Regulatory agencies are urged to conduct transparent, well-documented and proper systematic reviews for BPA and other EDCs.

Toxicity testing and endocrine disrupting chemicals

Regulatory agencies around the world depend on standardized testing approaches to evaluate environmental chemicals for endocrine disrupting properties. The US Environmental Protection Agency (EPA) has developed a two-tiered testing approach within its Endocrine Disruptor Screening Program (EDSP). The eleven Tier 1 and three Tier 2 EDSP assays can be used to identify chemicals that act as agonists or antagonists of estrogen receptor, androgen receptor, or thyroid hormone receptor, or chemicals that interfere with steroidogenesis. Additional assays have been developed in the context of Tox21, and others have been validated by the OECD. In spite of the availability of validated toxicity tests, problems have been identified with the approaches and methods used to identify endocrine disrupting chemicals (EDCs). This chapter will provide an overview of several of these issues including: (1) The way an EDC is defined by an agency impacts whether a specific test can be used to determine if a chemical is an EDC. This is especially important when considering which assays examine outcomes that are considered "adverse effects." (2) Some assumptions about the validated studies used to identify EDCs may not be true (e.g., their reproducibility has been questioned). (3) Many of the validated assays are less sensitive than other methods that have not yet been validated. Ultimately, these and other problems contribute to the current landscape, where testing approaches have failed to protect the public from known EDCs. The chapter concludes with a review of approaches that have been taken to improve current guideline studies.

Using historical control data in bioassays for regulatory toxicology

Historical control data (HCD) consist of pooled control group responses from bioassays. These data must be collected and are often used or reported in regulatory toxicology studies for multiple purposes: as quality assurance for the test system, to help identify toxicological effects and their effect-size relevance and to address the statistical multiple comparison problem. The current manuscript reviews the various classical and potential new approaches for using HCD. Issues in current practice are identified and recommendations for improved use and discussion are provided. Furthermore, stakeholders are invited to discuss whether it is necessary to consider uncertainty when using HCD formally and statistically in toxicological discussions and whether binary inclusion/exclusion criteria for HCD should be revised to a tiered information contribution to assessments. Overall, the critical value of HCD in toxicological bioassays is highlighted when used in a weight-of-evidence assessment.

Background data of 2-year-old male and female F344 gpt delta rats

Although gpt delta rats, as reporter gene-transgenic rats, were originally developed for in vivo mutation assays, they have also been used to evaluate chemical carcinogenesis and comprehensive toxicity. Therefore, it is necessary to accumulate background data on carcinogenicity and general toxicity in gpt delta rats. Here, we investigated the background data of 110-week-old male and female F344 gpt delta rats and wild-type rats. There was no effect of reporter gene transfection on animal survival rates and body weights during the experiment. The relative weight of male gpt delta rat adrenals was significantly higher than that of wild-type rats, possibly due to the higher incidence of pheochromocytoma. There were no intergenotype differences in the incidence of nonneoplastic lesions in both sexes, including chronic progressive nephropathy and focus of cellular alteration in the liver, which had a higher incidence in both genotypes. Additionally, the significantly higher incidence of adrenal pheochromocytoma in male gpt delta rats than that in wild-type rats was likely incidental because of the lack of differences in the incidences of preneoplastic (male and female) and neoplastic (female) adrenal lesions in both genotypes. Other neoplastic lesions in both sexes showed no intergenotype differences in incidence rates, although large granular lymphocytic leukemia in the spleen and Leydig cell tumors in the testes of males showed higher incidence rates. Overall, there were no effects of reporter gene transfection on the spectrum of spontaneous lesions in F344 gpt delta rats, thus supporting their applicability in evaluating chemical toxicity and carcinogenicity.

Historical control data for hematology parameters obtained from toxicity studies performed on different Wistar rat strains: Acceptable value ranges, definition of severity degrees, and vehicle effects

The physiological and health status of control animals may vary. Due to this variation, it is important to define acceptable ranges of control hematology parameters to gain a better understanding of adverse and non-adverse effects of test substances. After generating historical control data for two Wistar rat strains (RccHan™:WIST and Crl:WI(Han)) from different breeders, the data sets were statistically analyzed using Minitab®. After noticing that single outliers can affect the study control data set, the respective outliers were verified relative to the available histopathology findings, for example, inflammatory pulmonary lesions following vehicle aspiration or spontaneous sperm granuloma affecting the health status and hematology data of the respective animals. Such data points were excluded from the control data set. Comparing both data sets, it was obvious that different blood sampling and anesthesia methods as well as strain differences may result in slightly different values. After excluding the outliers, a data set from animals with presumably good health status was generated to define acceptable ranges and severity degrees. To evaluate effects, possibly influencing hematology parameters and defined acceptable ranges, selected vehicles and different study types were observed.

The Use and Misuse of Historical Controls in Regulatory Toxicology: Lessons from the CLARITY-BPA Study

For many endocrine-disrupting chemicals (EDCs) including Bisphenol A (BPA), animal studies show that environmentally relevant exposures cause harm; human studies are consistent with these findings. Yet, regulatory agencies charged with protecting public health continue to conclude that human exposures to these EDCs pose no risk. One reason for the disconnect between the scientific consensus on EDCs in the endocrinology community and the failure to act in the regulatory community is the dependence of the latter on so-called "guideline studies" to evaluate hazards, and the inability to incorporate independent scientific studies in risk assessment. The Consortium Linking Academic and Regulatory Insights on Toxicity (CLARITY) study was intended to bridge this gap, combining a "guideline" study with independent hypothesis-driven studies designed to be more appropriate to evaluate EDCs. Here we examined an aspect of "guideline" studies, the use of so-called "historical controls," which are essentially control data borrowed from prior studies to aid in the interpretation of current findings. The US Food and Drug Administration authors used historical controls to question the plausibility of statistically significant BPA-related effects in the CLARITY study. We examined the use of historical controls on 5 outcomes in the CLARITY "guideline" study: mammary neoplasms, pituitary neoplasms, kidney nephropathy, prostate inflammation and adenomas, and body weight. Using US Food and Drug Administration-proposed historical control data, our evaluation revealed that endpoints used in "guideline" studies are not as reproducible as previously held. Combined with other data comparing the effects of ethinyl estradiol in 2 "guideline" studies including CLARITY-BPA, we conclude that near-exclusive reliance on "guideline" studies can result in scientifically invalid conclusions.

Historical control data for the interpretation of ecotoxicity data: are we missing a trick?

Wildlife can be exposed to chemicals in the environment from various anthropogenic sources. Ecotoxicity studies, undertaken to address the risks from potential exposure to chemicals, vary in their design e.g. duration of exposure, effect types and endpoints measured. Ecotoxicity studies measure biological responses to test item exposure. Responses can be highly variable, with limited opportunity for control of extrinsic sources of variability. It is critical to distinguish between treatment-related effects and background 'normal variability' when interpreting results. Historical control data (HCD) can be a valuable tool in contextualising results from single studies against previous studies performed under similar conditions. This paper discusses the case for better use of HCD in ecotoxicology assessments, illustrating with case studies the value and difficulties of using HCD in interpretation of results of standard and higher-tier study designs. HCD are routinely used in mammalian toxicology for human health assessments, but not directly in ecotoxicology. The possible reasons for this are discussed e.g., different data types, the potential to mask effects, and the lack of guidance. These concerns are real but not insurmountable and we would like to see organisations such as OECD, EFSA and USEPA develop guidance on the principles of HCD collection. Hopefully, this would lead to greater use of HCD and regulatory acceptance. We believe this is not only a scientifically valid approach but also an ethical issue that is in line with societally driven legal mandates to minimise the use of vertebrate testing in chemical regulatory decision making.

Out of Control? Managing Baseline Variability in Experimental Studies with Control Groups

Control groups are expected to show what happens in the absence of the intervention of interest (negative control) or the effect of an intervention expected to have an effect (positive control). Although they usually give results we can anticipate, they are an essential component of all experiments, both in vitro and in vivo, and fulfil a number of important roles in any experimental design. Perhaps most importantly they help you understand the influence of variables that you cannot fully eliminate from your experiment and thus include them in your analysis of treatment effects. Because of this it is essential that they are treated as any other experimental group in terms of subjects, randomisation, blinding, etc. It also means that in almost all cases, contemporaneous control groups are required. Historical and baseline control groups serve a slightly different role and cannot fully replace control groups run as an integral part of the experiment. When used correctly, a good control group not only validates your experiment; it provides the basis for evaluating the effect of your treatments.

Addendum to Iwai and Hoberman (2014)-Reassessment of Developmental Toxicity of PFHxA in Mice

This article presents a supplemental data analysis and evaluation of the findings from an oral (gavage) combined developmental and perinatal/postnatal reproduction toxicity study of the ammonium salt of perfluorohexanoic acid (CASRN: 21615-47-4) in Crl: CD-1(ICR) mice. The original study has been cited as supporting a lowest-observed-adverse-effects level of 175 mg/kg/d and no-observed-adverse-effects level of 35 mg/kg/d for developmental effects from perfluorohexanoic acid (PFHxA, CASRN: 307-24-4) in mice. The statistical analysis reported in 2014 was accurate in terms of quantifying statistical significance within phase 2 of the study. However, given the low incidence of findings, the purpose of this article is to extend the analysis and interpretation of findings by pooling the control group information from both phases of the same study, comparing the study findings to the incidence rates for stillbirths and postpartum viability for this species and strain of mouse observed for similar studies conducted by the same laboratory, and evaluating data on the incidence and range of spontaneous eye abnormalities reported in the literature. Based on this supplemental evaluation, the original study supports a NOAEL of 175 mg/kg/d for PFHxA in mice, which is a factor of 5-fold higher than previously reported. Furthermore, to the extent that this study may be considered in the selection of a point of departure for PFHxA in mice, it is noted that 175 mg/kg/d for maternal exposure is an unbounded NOAEL for developmental effects, meaning that the study did not establish a dose at which developmental effects may occur.

Prediction intervals for overdispersed binomial data with application to historical controls

Bioassays are highly standardized trials for assessing the impact of a chemical compound on a model organism. In that context, it is standard to compare several treatment groups with an untreated control. If the same type of bioassay is carried out several times, the amount of information about the historical controls rises with every new study. This information can be applied to predict the outcome of one future control using a prediction interval. Since the observations are counts of success out of a given sample size, like mortality or histopathological findings, the data can be assumed to be binomial but may exhibit overdispersion caused by the variability between historical studies. We describe two approaches that account for overdispersion: asymptotic prediction intervals using the quasi-binomial assumption and prediction intervals based on the quantiles of the beta-binomial distribution. Both interval types were α-calibrated using bootstrap methods. For an assessment of the intervals coverage probabilities, a simulation study based on various numbers of historical studies and sample sizes as well as different binomial proportions and varying levels of overdispersion was run. It could be shown that α-calibration can improve the coverage probabilities of both interval types. The coverage probability of the calibrated intervals, calculated based on at least 10 historical studies, was satisfactory close to the nominal 95%. In a last step, the intervals were computed based on a real data set from the NTP homepage, using historical controls from bioassays with the mice strain B6C3F1.

Data Standardization, Pharmaceutical Drug Development, and the 3Rs

Despite the efforts, cost, and extensive use of animals for nonclinical research, only a small number of studies have methodically compared findings from animal toxicology studies to those from human clinical trials. Impediments to understanding the translation of nonclinical safety have included the lack of easy access to data and the need for extensive data curation given the diverse terminologies, formats, and data platforms in use. SEND and SDTM study data standards, developed by CDISC and about to become mandated by FDA, can address this and other drug development issues by facilitating access to data in ways that are not currently feasible. A consistent data standard across clinical and nonclinical will discourage the development of data silos, which easily become obstacles to data sharing and maximizing the value of animal and human data. The confluence of rapid scientific advances, increasingly larger quantities of diverse data, technological advances in data mining, and the FDA's requirements for standardized study data create new opportunities for the advancement of drug development and for refinement in the way we use animals.

A Diagnostic Approach for Rodent Progressive Cardiomyopathy and Like Lesions in Toxicology Studies up to 28 Days in the Sprague Dawley Rat (Part 1 of 2)

Spontaneous rodent progressive cardiomyopathy (PCM) in the Sprague Dawley rat may confound identification and/or interpretation of potential test article (TA)-related cardiotoxicity. Pathologists apply diagnostic term(s) and thresholds for diagnosing and assigning severity grades for PCM and/or PCM-like (PCM/like) lesions consistently within a study, which is necessary to identify and interpret TA-related findings. Due to differences in training and/or experiences, diagnostic terms and thresholds may vary between pathologists. Harmonized terminology and thresholds across studies will generate better historical control data, will likely enhance interpretation of study data, and may further enhance our understanding of the spontaneous change. An assessment of the diagnostic approaches of a group of 37 pathologists identified an approach that is relatively easily applied; and if adopted, it could enhance diagnostic consistency across studies. This approach uses the single "slash" term "necrosis/inflammatory cell infiltrate (NICI)" as the diagnosis for the spectrum of lesions seen in younger rats, uses no threshold for diagnosis (e.g., diagnose all lesions clearly identifiable as PCM/like), and uses aggregate lesion size of approximately ≥45% of the field of view (FOV) using a 10×/22 eyepiece and the 40× objective or approximately ≥100% of the FOV using the 60× objective as the criterion separating minimal from mild severities.

Glyphosate toxicity and carcinogenicity: a review of the scientific basis of the European Union assessment and its differences with IARC

Glyphosate is the most widely used herbicide worldwide. It is a broad spectrum herbicide and its agricultural uses increased considerably after the development of glyphosate-resistant genetically modified (GM) varieties. Since glyphosate was introduced in 1974, all regulatory assessments have established that glyphosate has low hazard potential to mammals, however, the International Agency for Research on Cancer (IARC) concluded in March 2015 that it is probably carcinogenic. The IARC conclusion was not confirmed by the EU assessment or the recent joint WHO/FAO evaluation, both using additional evidence. Glyphosate is not the first topic of disagreement between IARC and regulatory evaluations, but has received greater attention. This review presents the scientific basis of the glyphosate health assessment conducted within the European Union (EU) renewal process, and explains the differences in the carcinogenicity assessment with IARC. Use of different data sets, particularly on long-term toxicity/carcinogenicity in rodents, could partially explain the divergent views; but methodological differences in the evaluation of the available evidence have been identified. The EU assessment did not identify a carcinogenicity hazard, revised the toxicological profile proposing new toxicological reference values, and conducted a risk assessment for some representatives uses. Two complementary exposure assessments, human-biomonitoring and food-residues-monitoring, suggests that actual exposure levels are below these reference values and do not represent a public concern.

The adipokine leptin modulates adventitial pericyte functions by autocrine and paracrine signalling

Transplantation of adventitial pericytes (APCs) improves recovery from tissue ischemia in preclinical animal models by still unknown mechanisms. This study investigates the role of the adipokine leptin (LEP) in the regulation of human APC biological functions. Transcriptomic analysis of APCs showed components of the LEP signalling pathway are modulated by hypoxia. Kinetic studies indicate cultured APCs release high amounts of immunoreactive LEP following exposure to hypoxia, continuing upon return to normoxia. Secreted LEP activates an autocrine/paracrine loop through binding to the LEP receptor (LEPR) and induction of STAT3 phosphorylation. Titration studies using recombinant LEP and siRNA knockdown of LEP or LEPR demonstrate the adipokine exerts important regulatory roles in APC growth, survival, migration and promotion of endothelial network formation. Heterogeneity in LEP expression and secretion may influence the reparative proficiency of APC therapy. Accordingly, the levels of LEP secretion predict the microvascular outcome of APCs transplantation in a mouse limb ischemia model. Moreover, we found that the expression of the Lepr gene is upregulated on resident vascular cells from murine ischemic muscles, thus providing a permissive milieu to transplanted LEP-expressing APCs. Results highlight a new mechanism responsible for APC adaptation to hypoxia and instrumental to vascular repair.

A Bayesian analysis of quantal bioassay experiments incorporating historical controls via Bayes factors

This paper addresses model-based Bayesian inference in the analysis of data arising from bioassay experiments. In such experiments, increasing doses of a chemical substance are given to treatment groups (usually rats or mice) for a fixed period of time (usually 2 years). The goal of such an experiment is to determine whether an increased dosage of the chemical is associated with increased probability of an adverse effect (usually presence of adenoma or carcinoma). The data consists of dosage, survival time, and the occurrence of the adverse event for each unit in the study. To determine whether such relationship exists, this paper proposes using Bayes factors to compare two probit models, the model that assumes increasing dose effects and the model that assumes no dose effect. These models account for the survival time of each unit through a Poly-k type correction. In order to increase statistical power, the proposed approach allows the incorporation of information from control groups from previous studies. The proposed method is able to handle data with very few occurrences of the adverse event. The proposed method is compared with a variation of the Peddada test via simulation and is shown to have higher power. We demonstrate the method by applying it to the two bioassay experiment datasets previously analyzed by other authors. Copyright © 2017 John Wiley & Sons, Ltd.

The mouse mammary gland as a sentinel organ: distinguishing 'control' populations with diverse environmental histories

BACKGROUND

There are numerous examples of laboratory animals that were inadvertently exposed to endocrine disrupting chemicals (EDCs) during the process of conducting experiments. Controlling contaminations in the laboratory is challenging, especially when their source is unknown. Unfortunately, EDC contaminations can interfere with the interpretation of data during toxicological evaluations. We propose that the male CD-1 mouse mammary gland is a sensitive bioassay to evaluate the inadvertent contamination of animal colonies.

METHODS

We evaluated mammary glands collected from two CD-1 mouse populations with distinct environmental histories. Population 1 was born and raised in a commercial laboratory with unknown EDC exposures; Population 2 was the second generation raised in an animal facility with limited exposures to xenoestrogens from caging, feed, etc. Mammary glands were collected from all animals and evaluated using morphometric techniques to quantify morphological characteristics of the mammary gland.

RESULTS

Population 1 (with suspected history of environmental chemical exposure) and Population 2 (with known limited history of xenoestrogen exposure) were morphologically distinguishable in adult males, prepubertal females, and pubertal females. Mammary glands from males raised in the commercial animal facility were significantly more developed, with larger ductal trees and more branching points. The appearance of these mammary glands was consistent with prior reports of male mice exposed to low doses of bisphenol A (BPA) during early development. In females, the two populations were morphologically distinct at both prepuberty and puberty, with the most striking differences observed in the number, size, and density of terminal end buds, e.g. highly proliferative structures found in the developing mammary gland.

CONCLUSIONS

Collectively, these results suggest that the mouse mammary gland has the potential to be used as a sentinel organ to evaluate and distinguish animal colonies raised in different environmental conditions including potential EDC exposures. Our findings could help researchers that wish to perform a posteriori evaluations to determine whether inadvertent contamination with xenoestrogens (and potentially other EDCs) has occurred in their animal colonies, especially after new materials (feed, caging, water bottles) have been introduced. Finally, our results challenge the relatively common practice of using historical controls in toxicological experiments.

Sucralose Non-Carcinogenicity: A Review of the Scientific and Regulatory Rationale

Regulatory authorities worldwide have found the nonnutritive sweetener, sucralose, to be noncarcinogenic, based on a range of studies. A review of these and other studies found through a comprehensive search of electronic databases, using appropriate key terms, was conducted and results of that review are reported here. An overview of the types of studies relied upon by regulatory agencies to assess carcinogenicity potential is also provided as context. Physiochemical and pharmacokinetic/toxicokinetic studies confirm stability under conditions of use and reveal no metabolites of carcinogenic potential. In vitro and in vivo assays reveal no confirmed genotoxic activity. Long-term carcinogenicity studies in animal models provide no evidence of carcinogenic potential for sucralose. In studies in healthy adults, sucralose was well-tolerated and without evidence of toxicity or other changes that might suggest a potential for carcinogenic effects. In summary, sucralose does not demonstrate carcinogenic activity even when exposure levels are several orders of magnitude greater than the range of anticipated daily ingestion levels.

Impact of the Genetics and Source of Preclinical Safety Animal Models on Study Design, Results, and Interpretation

It has been long established that not only the species but also the strain and supplier of rodents used in preclinical safety studies can have a significant impact on the outcome of studies due to variability in their genetic background and thus spontaneous pathologic findings. In addition, local husbandry, housing, and other environmental conditions may have effects on the development and expression of comorbidities, particularly in longer-term or chronic studies. More recently, similar effects related to the source, including genetic and environmental variability, have been recognized in cynomolgus macaques ( Macaca fascicularis). The increased use of cynomolgus macaques from various sources of captive-bred animals (including nonnative, U.S./European Union-based breeding facilities or colonies) can affect study design and study results and outcome. It is important to acknowledge and understand the impact of this variability on the results and interpretation of research studies. This review includes recent examples where variability of preclinical animal models (rats and monkeys) affected the postmortem observations highlighting its relevance to study design or interpretation in safety studies.

Findings in Historical Control Harlan RCCHan™

Vehicle control Harlan RCCHan™:WIST rats were examined to provide control data for subsequent studies. The rats (180 male and 180 female) were dosed daily via oral gavage with reverse osmosis water for up to 104 weeks. At necropsy, body weights and macroscopic findings were recorded and tissues were collected for histopathology. The mean body weight at terminal sacrifice was 687 g for males and 466 g for females. The overall survival rate was 62% for males and 59% for females. The most common cause of death for males and females found dead or examined following unscheduled euthanasia was pituitary neoplasia with an incidence of 13.9% for males and 18.9% for females. Macroscopic and neoplastic and nonneoplastic microscopic findings are presented by body system.

Characterizing “Adversity” of Pathology Findings in Nonclinical Toxicity Studies

The identification of adverse health effects has a central role in the development and risk/safety assessment of chemical entities and pharmaceuticals. There is currently a need for better alignment regarding how nonclinical adversity is determined and characterized. The European Society of Toxicologic Pathology (ESTP) therefore coordinated a workshop to review available definitions of adversity, weigh determining and qualifying factors of adversity based on case examples, and recommend a practical approach to define and characterize adversity in toxicology reports, to serve as a valuable prerequisite for future organ- or lesion-specific workshops planned by the ESTP.

Regulatory Forum Opinion Piece: Carcinogen Risk Assessment: The Move from Screens to Science

Throughout the last 50 years, the paradigm for carcinogenicity assessment has depended on lifetime bioassays in rodents. Since 1997, the International Conference on Harmonisation (ICH) S1B has permitted the use of a 2-year rodent bioassay (usually in the rat) and an alternative, genetically modified mouse model to support cancer risk assessment of pharmaceuticals. Since its introduction, it has become apparent that many of the stated advantages of the 6-month Tg mouse bioassay have, in actual fact, not been realized, and the concern exists that an albeit imperfect, 2-year mouse bioassay has been replaced by a similarly imperfect 6-month equivalent. This essay argues strongly that model systems, using cancer as the end point, should be discontinued, and that the recent initiatives, from the Organization for Economic Cooperation and Development and Institute of Peace and Conflict Studies, on "mode of action," "adverse outcome pathways," and "human relevance framework" should be embraced as being risk assessments based upon the available science. The recent suggested revisions to the ICH S1 guidelines, utilizing carcinogenicity assessment documents, go some way to developing a science-based risk assessment that does not depend almost entirely on a single, imperfect, cancer-based end point in nonrelevant animal species.

In utero arsenic exposure in mice and early life susceptibility to cancer

In its review of the U.S. Environmental Protection Agency's toxicological review of inorganic arsenic (iAs), the National Academy of Sciences identified carcinogenic endpoints among the highest priority health effects of concern and stated the need to consider evidence that early life exposures may increase the risk of adverse health effects. Recent studies in mice suggest that in utero exposure to arsenic increases susceptibility to cancer later in life. These data are striking in light of the general lack of evidence for carcinogenicity in rodents exposed to iAs. To evaluate the transplacental carcinogenic potential of iAs, a detailed analysis of the toxicology literature evaluating the role of in utero arsenic exposure in carcinogenesis was conducted. Bladder, lung, and skin tumors, which are the tumor types most consistently reported in humans exposed to high arsenic levels, were not consistently increased in mouse studies. There was also a lack of concordance across studies for other tumor types not typically reported in humans. Therefore, we considered methodological and other critical issues that may have contributed to variable results and we suggest additional studies to address these issues. It was concluded that the available data do not provide evidence of a causal link between in utero arsenic exposure and cancer or indicate early life-stage susceptibility to arsenic-induced cancer, particularly at environmentally relevant doses.

Scientific and Regulatory Policy Committee (SRPC) Points to Consider: Histopathology Evaluation of the Pubertal Development and Thyroid Function Assay (OPPTS 890.1450, OPPTS 890.1500) in Rats to Screen for Endocrine Disruptors

The U.S. Environmental Protection Agency Endocrine Disruptor Screening Program (EDSP) is a multitiered approach to determine the potential for environmental chemicals to alter the endocrine system. The Pubertal Development and Thyroid Function in Intact Juvenile/Peripubertal Female and Male Rats (OPPTS 890.1450, 890.1500) are 2 of the 9 EDSP tier 1 test Guidelines, which assess upstream mechanistic pathways along with downstream morphological end points including histological evaluation of the kidneys, thyroid, and select male/female reproductive tissues (ovaries, uterus, testes, and epididymides). These assays are part of a battery of in vivo and in vitro screens used for initial detection of test article endocrine activity. In this Points to Consider article, we describe tissue processing, evaluation, and nomenclature to aid in standardization of assay results across laboratories. Pubertal assay end points addressed include organ weights, estrous cyclicity, clinical pathology, hormonal assays, and histological evaluation. Potential treatment-related findings that may indicate endocrine disruption are reviewed. Additional tissues that may be useful in assessment of endocrine disruption (vagina, mammary glands, and liver) are discussed. This Points to Consider article is intended to provide information for evaluating peripubertal tissues within the context of individual assay end points, the overall pubertal assay, and tier I assays of the EDSP program.

Pathobiology of aging mice and GEM: background strains and experimental design

The use of induced and spontaneous mutant mice and genetically engineered mice (and combinations thereof) to study cancers and other aging phenotypes to advance improved functional human life spans will involve studies of aging mice. Genetic background contributes to pathology phenotypes and to causes of death as well as to longevity. Increased recognition of expected phenotypes, experimental variables that influence phenotypes and research outcomes, and experimental design options and rationales can maximize the utility of genetically engineered mice (GEM) models to translational research on aging. This review aims to provide resources to enhance the design and practice of chronic and longevity studies involving GEM. C57BL6, 129, and FVB/N strains are emphasized because of their widespread use in the generation of knockout, transgenic, and conditional mutant GEM. Resources are included also for pathology of other inbred strain families, including A, AKR, BALB/c, C3H, C57L, C58, CBA, DBA, GR, NOD.scid, SAMP, and SJL/J, and non-inbred mice, including 4WC, AB6F1, Ames dwarf, B6, 129, B6C3F1, BALB/c,129, Het3, nude, SENCAR, and several Swiss stocks. Experimental strategies for long-term cross-sectional and longitudinal studies to assess causes of or contributors to death, disease burden, spectrum of pathology phenotypes, longevity, and functional healthy life spans (health spans) are compared and discussed.

Review of approaches to the recording of background lesions in toxicologic pathology studies in rats

Pathological evaluation of lesions caused directly by xenobiotic treatment must always take into account the recognition of background (incidental) findings. Background lesions can be congenital or hereditary, histological variations, changes related to trauma or normal aging and physiologic or hormonal changes. This review focuses on the importance and correct approach to recording of background changes and includes discussion on sources of variability in background changes, the correct use of terminology, the concept of thresholds, historical control data, diagnostic drift, blind reading of slides, scoring and artifacts. The review is illustrated with background lesions in Sprague Dawley and Wistar rats.

Reassessing the two-year rodent carcinogenicity bioassay: a review of the applicability to human risk and current perspectives

The 2-year rodent carcinogenicity test has been the regulatory standard for the prediction of human outcomes for exposure to industrial and agro-chemicals, food additives, pharmaceuticals and environmental pollutants for over 50 years. The extensive experience and data accumulated over that time has spurred a vigorous debate and assessment, particularly over the last 10 years, of the usefulness of this test in terms of cost and time for the information obtained. With renewed interest in the United States and globally, plus new regulations in the European Union, to reduce, refine and replace sentinel animals, this review offers the recommendation that reliance on information obtained from detailed shorter-term, 6 months rodent studies, combined with genotoxicity and chemical mode of action can realize effective prediction of human carcinogenicity instead of the classical two year rodent bioassay. The aim of carcinogenicity studies should not be on the length of time, and by obligation, number of animals expended but on the combined systemic pathophysiologic influence of a suspected chemical in determining disease. This perspective is in coordination with progressive regulatory standards and goals globally to utilize effectively resources of animal usage, time and cost for the goal of human disease predictability.

The use of whole food animal studies in the safety assessment of genetically modified crops: limitations and recommendations

There is disagreement internationally across major regulatory jurisdictions on the relevance and utility of whole food (WF) toxicity studies on GM crops, with no harmonization of data or regulatory requirements. The scientific value, and therefore animal ethics, of WF studies on GM crops is a matter addressable from the wealth of data available on commercialized GM crops and WF studies on irradiated foods. We reviewed available GM crop WF studies and considered the extent to which they add to the information from agronomic and compositional analyses. No WF toxicity study was identified that convincingly demonstrated toxicological concern or that called into question the adequacy, sufficiency, and reliability of safety assessments based on crop molecular characterization, transgene source, agronomic characteristics, and/or compositional analysis of the GM crop and its near-isogenic line. Predictions of safety based on crop genetics and compositional analyses have provided complete concordance with the results of well-conducted animal testing. However, this concordance is primarily due to the improbability of de novo generation of toxic substances in crop plants using genetic engineering practices and due to the weakness of WF toxicity studies in general. Thus, based on the comparative robustness and reliability of compositional and agronomic considerations and on the absence of any scientific basis for a significant potential for de novo generation of toxicologically significant compositional alterations as a sole result of transgene insertion, the conclusion of this review is that WF animal toxicity studies are unnecessary and scientifically unjustifiable.

Occurrence of Spontaneous Tumors in the Central Nervous System (CNS) of F344 and SD Rats

In order to accurately assess the carcinogenicity of chemicals with regard to rare tumors such as rat CNS tumors, sufficient information about spontaneous tumors are very important. This paper presents the data on the type, incidence and detected age of CNS tumors in F344/DuCrlCrlj (a total of 1363 males and 1363 females) and Crl:CD(SD) rats (a total of 1650 males and 1705 females) collected from in-house background data-collection studies and control groups of carcinogenicity studies at our laboratory, together with those previously reported in F344 and SD rats. The present data on F344/DuCrlCrlj rats (F344 rats) and Crl:CD(SD) rats (SD rats) clarified the following. (1) The incidences of all CNS tumors observed in F344 rats were less than 1%. (2) The incidences of malignant astrocytoma and granular cell tumor were higher in male SD rats than in female SD rats. (3) The incidences of astrocytoma and granular cell tumor were higher in SD rats than in F344 rats. (4) Among astrocytoma, oligodendroglioma and granular cell tumor, oligodendroglioma was detected at the youngest age, followed by astrocytoma, and ultimately, granular cell tumor developed in both strains. The incidences observed in our study were almost consistent with those previously reported in F344 and SD rats.