Nonproliferative and Proliferative Lesions of the Ratand Mouse Special Sense Organs(Ocular [eye and glands], Olfactory and Otic)

Histology Atlas of the Developing Mouse Respiratory System From Prenatal Day 9.0 Through Postnatal Day 30

Respiratory diseases are one of the leading causes of death and disability around the world. Mice are commonly used as models of human respiratory disease. Phenotypic analysis of mice with spontaneous, congenital, inherited, or treatment-related respiratory tract abnormalities requires investigators to discriminate normal anatomic features of the respiratory system from those that have been altered by disease. Many publications describe individual aspects of normal respiratory tract development, primarily focusing on morphogenesis of the trachea and lung. However, a single reference providing detailed low- and high-magnification, high-resolution images of routine hematoxylin and eosin (H&E)-stained sections depicting all major structures of the entire developing murine respiratory system does not exist. The purpose of this atlas is to correct this deficiency by establishing one concise reference of high-resolution color photomicrographs from whole-slide scans of H&E-stained tissue sections. The atlas has detailed descriptions and well-annotated images of the developing mouse upper and lower respiratory tracts emphasizing embryonic days (E) 9.0 to 18.5 and major early postnatal events. The selected images illustrate the main structures and events at key developmental stages and thus should help investigators both confirm the chronological age of mouse embryos and distinguish normal morphology as well as structural (cellular and organ) abnormalities.

Guide for Combining Primary Tumors for Statistical Analysis in Rodent Carcinogenicity Studies

The Tumor Combination Guide was created at the request of the U. S. Food and Drug Administration (FDA) by a Working Group of biopharmaceutical experts from international societies of toxicologic pathology, the Food and Drug Administration (FDA), and members of the Standard for Exchange of Nonclinical Data (SEND) initiative, to assist pharmacology/toxicology reviewers and biostatisticians in statistical analysis of nonclinical tumor data. The guide will also be useful to study and peer review pathologists in interpreting the tumor data. This guide provides a higher-level hierarchy of tumor types or categories correlating the tumor names from the International Harmonization of Nomenclature and Diagnostic Criteria (INHAND) publications with those available in the NEOPLASM controlled terminology (CT) code list in SEND. The version of CT used in a study should be referenced in the nonclinical study data reviewer's guide (SDRG) (section 3.1) of electronic submissions to the FDA. The tumor combination guide instructions and examples are in a tabular format to make informed decisions for combining tumor data for statistical analysis. The strategy for combining tumor types for statistical analysis is based on scientific criteria gleaned from the current scientific literature; as SEND and INHAND terminology and information evolve, this guide will be updated.

European Society of Toxicologic Pathology (Pathology 2.0 Molecular Pathology Special Interest Group): Review of In Situ Hybridization Techniques for Drug Research and Development

In situ hybridization (ISH) is used for the localization of specific nucleic acid sequences in cells or tissues by complementary binding of a nucleotide probe to a specific target nucleic acid sequence. In the last years, the specificity and sensitivity of ISH assays were improved by innovative techniques like synthetic nucleic acids and tandem oligonucleotide probes combined with signal amplification methods like branched DNA, hybridization chain reaction and tyramide signal amplification. These improvements increased the application spectrum for ISH on formalin-fixed paraffin-embedded tissues. ISH is a powerful tool to investigate DNA, mRNA transcripts, regulatory noncoding RNA, and therapeutic oligonucleotides. ISH can be used to obtain spatial information of a cell type, subcellular localization, or expression levels of targets. Since immunohistochemistry and ISH share similar workflows, their combination can address simultaneous transcriptomics and proteomics questions. The goal of this review paper is to revisit the current state of the scientific approaches in ISH and its application in drug research and development.

Two cases of cartilaginous metaplasia in the sclera of Japanese White rabbits

Spontaneous cartilaginous metaplasia of the sclera has not been reported in rabbits. Herein, we report two cases of spontaneous cartilaginous metaplasia in the sclera of Japanese White (JW) rabbits. Case 1 was noted in a 14-week-old male Kbs:JW rabbit that received a single ocular instillation of 20% isoproterenol (IP) a day before necropsy, and showed no abnormalities in clinical signs, ophthalmological assessments, and necropsy. Case 2 was noted in a 38-week-old male Kbs:JW rabbit that was housed under light-emitting diode (LED) lighting for 26 weeks and showed no effects of LED on clinical signs, ophthalmological assessments, and necropsy. Histological sections of the eyes of both animals were prepared and stained with hematoxylin and eosin (H&E) and Alcian blue, and immunohistochemical staining for vimentin was performed. The H&E-stained specimens showed focal hyaline cartilage-like tissues distributed between the scleral fibers at the posterior pole in both cases. The surrounding scleral fibers were compressed and/or partially destroyed by the cartilage-like tissue. The cartilage-like matrix was stained blue by Alcian blue, and immunohistochemistry showed that chondrocyte-like cells were positive for vimentin. Based on these findings, we diagnosed cartilaginous metaplasia in the sclera of Kbs:JW rabbits. The lesion was farther from the IP administration site in Case 1 and was not accompanied by other ophthalmological or histopathological abnormalities in either of the cases. This implies that the lesions occurred spontaneously owing to the abnormal differentiation of neural crest-derived cells.

Bromelain protects against cisplatin-induced ocular toxicity through mitigating oxidative stress and inflammation

The aim of this study was to investigate the molecular, biochemical, and histopathological effects of bromelain, which has antioxidant and anti-inflammatory properties, against cisplatin-induced ocular toxicity. The groups were designed as (1) Control, (2) Cisplatin (7 mg/kg, intraperitoneally), (3) Cisplatin + Bromelain (50 mg/kg, orally for 14 consecutive days), (4) Cisplatin + Bromelain (100 mg/kg, orally for 14 consecutive days). The activity of total antioxidant capacity (TAC) and total oxidant status (TOS) and levels of reactive oxygen species (ROS), superoxide dismutase (SOD), malondialdehyde (MDA), interleukin-1β (IL-1β), IL-10, nuclear factor kappa B (NF-κB), tumor necrosis factor-alpha (TNF-α) and 8-OHdG were measured in ocular tissue. The mRNA expression of NF-κB and Caspase-3 was also evaluated. Also, ocular sections were evaluated histopathologically. Bromelain demonstrated a dose-dependent protective effect in cisplatin-induced toxicity by regulating oxidative stress, inflammation, and tissue damage. Our results suggested that bromelain may be a potential adjuvant that can protect the eye from cisplatin-induced toxicity.

New Evidences about the Carcinogenic Effects of Ochratoxin A and Possible Prevention by Target Feed Additives

A review of the carcinogenic effects of ochratoxin A (OTA) on various tissues and internal organs in laboratory and farm animals is made. Suggestions are made regarding how to recognize and differentiate the common spontaneous neoplastic changes characteristic for advanced age and the characteristic neoplasia in different tissues and organs in laboratory animals/poultry exposed to OTA. The synergistic effects of OTA together with its natural combination of penicillic acid are also investigated regarding possible carcinogenic effects. The malignancy and the target location of OTA-induced neoplasia is studied. The sex-differences of such neoplasia are investigated in the available literature. The time of appearance of the first neoplasia is investigated in long-term carcinogenic studies with OTA-treated animals. The possibility of target feed additives or herbs to counteract the toxic and carcinogenic effects of OTA is studied in the available literature. Some effective manners of prophylaxis and/or prevention against OTA contamination of feedstuffs/foods or animal production are suggested. The suitability of various laboratory animals to serve as experimental model for humans with regard to OTA-induced tumorigenesis is investigated.

Pigment Epithelia of the Eye: Cell-Type Conversion in Regeneration and Disease

Pigment epithelial cells (PECs) of the retina (RPE), ciliary body, and iris (IPE) are capable of altering their phenotype. The main pathway of phenotypic switching of eye PECs in vertebrates and humans in vivo and/or in vitro is neural/retinal. Besides, cells of amphibian IPE give rise to the lens and its derivatives, while mammalian and human RPE can be converted along the mesenchymal pathway. The PECs’ capability of conversion in vivo underlies the lens and retinal regeneration in lower vertebrates and retinal diseases such as proliferative vitreoretinopathy and fibrosis in mammals and humans. The present review considers these processes studied in vitro and in vivo in animal models and in humans. The molecular basis of conversion strategies in PECs is elucidated. Being predetermined onto- and phylogenetically, it includes a species-specific molecular context, differential expression of transcription factors, signaling pathways, and epigenomic changes. The accumulated knowledge regarding the mechanisms of PECs phenotypic switching allows the development of approaches to specified conversion for many purposes: obtaining cells for transplantation, creating conditions to stimulate natural regeneration of the retina and the lens, blocking undesirable conversions associated with eye pathology, and finding molecular markers of pathology to be targets of therapy.

Research-Relevant Conditions and Pathology of Laboratory Mice, Rats, Gerbils, Guinea Pigs, Hamsters, Naked Mole Rats, and Rabbits

Animals are valuable resources in biomedical research in investigations of biological processes, disease pathogenesis, therapeutic interventions, safety, toxicity, and carcinogenicity. Interpretation of data from animals requires knowledge not only of the processes or diseases (pathophysiology) under study but also recognition of spontaneous conditions and background lesions (pathology) that can influence or confound the study results. Species, strain/stock, sex, age, anatomy, physiology, spontaneous diseases (noninfectious and infectious), and neoplasia impact experimental results and interpretation as well as animal welfare. This review and the references selected aim to provide a pathology resource for researchers, pathologists, and veterinary personnel who strive to achieve research rigor and validity and must understand the spectrum of "normal" and expected conditions to accurately identify research-relevant experimental phenotypes as well as unusual illness, pathology, or other conditions that can compromise studies involving laboratory mice, rats, gerbils, guinea pigs, hamsters, naked mole rats, and rabbits.

Scientific and Regulatory Policy Committee Points to Consider: Fixation, Trimming, and Sectioning of Nonrodent Eyes and Ocular Tissues for Examination in Ocular and General Toxicity Studies

A Working Group of the Society of Toxicologic Pathology's Scientific and Regulatory Policy Committee conducted a technical and scientific review of current practices relating to the fixation, trimming, and sectioning of the nonrodent eye to identify key points and species-specific anatomical landmarks to consider when preparing and evaluating eyes of rabbits, dogs, minipigs, and nonhuman primates from ocular and general toxicity studies. The topics addressed in this Points to Consider article include determination of situations when more comprehensive evaluation of the globe and/or associated extraocular tissues should be implemented (expanded ocular sampling), and what constitutes expanded ocular sampling. In addition, this manuscript highlights the practical aspects of fixing, trimming, and sectioning the eye to ensure adequate histopathological evaluation of all major ocular structures, including the cone-dense areas (visual streak/macula/fovea) of the retina for rabbits, dogs, minipigs, and nonhuman primates, which is a current regulatory expectation for ocular toxicity studies.[Box: see text].

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Non-proliferative and Proliferative Lesions of the Non-human Primate (M. fascicularis)

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions Project (www.toxpath.org/inhand.asp) is a joint initiative of the Societies of Toxicologic 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 most tissues and organs from the nonhuman primate used in nonclinical safety studies. Some of the lesions are illustrated by color photomicrographs. 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 lesions as well as lesions induced by exposure to test materials. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

The Microvillar and Solitary Chemosensory Cells as the Novel Targets of Infection of SARS-CoV-2 in Syrian Golden Hamsters

Patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019, suffer from respiratory and non-respiratory symptoms. Among these symptoms, the loss of smell has attracted considerable attention. The objectives of this study were to determine which cells are infected, what happens in the olfactory system after viral infection, and how these pathologic changes contribute to olfactory loss. For this purpose, Syrian golden hamsters were used. First, we verified the olfactory structures in the nasal cavity of Syrian golden hamsters, namely the main olfactory epithelium, the vomeronasal organ, and their cellular components. Second, we found angiotensin-converting enzyme 2 expression, a receptor protein of SARS-CoV-2, in both structures and infections of supporting, microvillar, and solitary chemosensory cells. Third, we observed pathological changes in the infected epithelium, including reduced thickness of the mucus layer, detached epithelia, indistinct layers of epithelia, infiltration of inflammatory cells, and apoptotic cells in the overall layers. We concluded that a structurally and functionally altered microenvironment influences olfactory function. We observed the regeneration of the damaged epithelium, and found multilayers of basal cells, indicating that they were activated and proliferating to reconstitute the injured epithelium.

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Nonproliferative and Proliferative Lesions of the Minipig

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions) Project (www.toxpath.org/inhand.asp) is a joint initiative of the Societies of Toxicologic 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 most tissues and organs from the minipig used in nonclinical safety studies. Some of the lesions are illustrated by color photomicrographs. 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 lesions as well as lesions induced by exposure to test materials. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

Exacerbation of Background Nuclear Cataracts in Sprague-Dawley Rats in Embryo-Fetal Development Studies With JNJ-42165279, a Fatty Acid Amide Hydrolase Inhibitor

Fetal examinations in embryo-fetal developmental (EFD) studies are based on macroscopic and dissecting microscopic evaluations, and histopathology is rarely performed other than to confirm macroscopic findings. Fetal lens examination is therefore generally limited to the presence, size, shape, and color of any abnormality. In a Sprague-Dawley rat EFD study with the fatty acid amide hydrolase (FAAH) inhibitor JNJ-42165279, an unusually high incidence of macroscopic granular foci was noted within the lens of gestation day 21 fetuses across all groups including controls, with higher incidence in the high-dose group. On histological evaluation of the lenses from fetuses with/without gross findings, primary lens fiber hypertrophy (swelling) and degeneration were observed across vehicle- and JNJ-42165279-exposed fetuses. In a follow-up study to investigate the progression or resolution of the fetal lens changes, animals exposed to suprapharmacological doses of JNJ-42165279 in utero had higher incidence of nuclear cataracts as detected via slit-lamp ophthalmic examinations on postnatal days 18 to 21 and 35 to 41. No histologic correlates for these cataracts were identified. We conclude that fetal primary lens fiber hypertrophy and nuclear cataracts at ophthalmology, are common background changes in this rat strain that are exacerbated by in utero exposure to the FAAH inhibitor JNJ-42165279.

The Role of Mesenchymal Stem Cells in the Treatment of a Chronic Rhinosinusitis-An In Vivo Mouse Model

Objectives/Hypothesis: It is acknowledged that the treatment of chronic rhinosinusitis (CRS) represents an important challenge for rhinology and for social and economic life. At present, one of the most common treatments for CRS is represented by local corticosteroids followed by endoscopic sinus surgery (ESS). Starting from the example of the mesenchymal stem cell’s (MSC) capacity to migrate and to modulate a real response in the nasal mucosa of an allergic rhinitis mouse model, we try to obtain a response in a CRS mouse model, using MSC derived by adipose tissue. The aim of this study is to demonstrate that the MSC can be used in CRS treatment and could change its priorities. Methods: Seventy female mice (6 MSC donor mice) were randomized in two stages of study, 32 Aspergillus fumigatus (Af) exposure mice (20 for histological comparison to 1st control mice and 12 for MSC administration, to CRS/MCS model) and 32 control mice (20 for histological comparison to CRS model and 12 for MSC administration and histological control to MSC model); in the first stage, the Aspergillus fumigatus (Af) CRS mouse model was targeted, in this section were included 64 (n = 32) mice (treated and control group). In order to assess the inflammation level (histological analysis), the animals were euthanized; in the second stage MSCs (1 × 10⁶/animal) were administered intravenously to a total of 24 (n = 24) mice (12 mice from the exposed group and 12 mice from the second control group). Results: After 12 weeks of Af intranasal instillation, the inflammation parameters evaluated indicated a severe diffuse chronic inflammation, associated with diffuse severe hyperplasia and mature diffuse squamous metaplasia. The MSCs’ injection via the ophthalmic vein induced important histopathological changes in the CRS experimental group, starting with the presence of MSCs in all samples and continuing with the important degenerative character of inflammation. Conclusions: MSC administration demonstrated a real improvement of CRS evolution on the CRS mouse model.

Safety evaluation after acute and sub-chronic oral administration of high purity nicotinamide mononucleotide (NMN-C®) in Sprague-Dawley rats

β-nicotinamide mononucleotide (NMN) is a natural molecule intermediate in the biosynthesis of nicotinamide adenine dinucleotide (NAD⁺). Preclinical evidences point to the beneficial effect of NMN administration on several age-related conditions. The present work aimed at studying mutagenicity, and genotoxicity, acute oral toxicity and subchronic oral toxicity of a high purity synthetic form of NMN (NMN-C®) following the OECD guidelines. In the experimental conditions tested, NMN-C® was not mutagenic or genotoxic. Acute toxicity assay revealed that at an oral limit dose of 2666 mg/kg, NMN-C® did not lead to any mortality or treatment-related adverse signs. Over a 90-day sub-chronic period of repeated oral administration of NMN-C® at doses of 375, 750 and 1500 mg/kg/d followed by a 28-day treatment-free recovery period, NMN-C® appeared to be safe and did not promote toxic effects as seen from body weight change, food and water consumption, feed conversion efficiency, biochemical and blood parameters as well as organ toxicity and histological examinations of main organs. In conclusion, we provide the first data highlighting the safety of short to intermediate term (sub-chronic) oral administration of NMN and our experimental results allowed to determine a No-Observable Adverse Effect Level (NOAEL) for NMN-C® to be ≥ 1500 mg/kg/d.

Deep Learning in Toxicologic Pathology: A New Approach to Evaluate Rodent Retinal Atrophy

Quantification of retinal atrophy, caused by therapeutics and/or light, by manual measurement of retinal layers is labor intensive and time-consuming. In this study, we explored the role of deep learning (DL) in automating the assessment of retinal atrophy, particularly of the outer and inner nuclear layers, in rats. Herein, we report our experience creating and employing a hybrid approach, which combines conventional image processing and DL to quantify rodent retinal atrophy. Utilizing a DL approach based upon the VGG16 model architecture, models were trained, tested, and validated using 10,746 image patches scanned from whole slide images (WSIs) of hematoxylin-eosin stained rodent retina. The accuracy of this computational method was validated using pathologist annotated WSIs throughout and used to separately quantify the thickness of the outer and inner nuclear layers of the retina. Our results show that DL can facilitate the evaluation of therapeutic and/or light-induced atrophy, particularly of the outer retina, efficiently in rodents. In addition, this study provides a template which can be used to train, validate, and analyze the results of toxicologic pathology DL models across different animal species used in preclinical efficacy and safety studies.

Follow up long term preliminary studies on carcinogenic and toxic effects of ochratoxin A in rats and the putative protection of phenylalanine

Carcinogenic effects of ochratoxin A (OTA) on liver, kidneys, intestine, lung and eyes of Wistar rats exposed to 10 ppm or 5 ppm OTA in the diet and additionally supplemented or not with phenylalanine (PHE) were examined during 24-months experimental period. OTA was seen to provoke strong degenerative changes and slight pericapillary oedema in most internal organs, e.g. kidneys, liver, intestine, spleen and brain. Six of total nine neoplasms were identified as malignant and three as benign. Five of total six malignant neoplasms and two of total three benign neoplasms were seen in male rats. The pathological finding in rats after two weeks feeding with OTA-contaminated feed was dominated by degenerative changes in various internal organs, which were weaker in the group additionally supplemented with PHE. The protective effect of PHE was evident with respect to OTA-induced decrease of serum glucose and serum protein, but this protection was not singnificant with respect to serum enzymes activity. The number of neoplasms in PHE-supplemented group exposed to 10 ppm OTA was similar to that in the group exposed to twice lower feed levels of OTA alone, suggesting about a possible protective effect of PHE. The rats would not be able to serve as experimental model for humans with regard to OTA-induced tumorigenesis, because the target organ of OTA-toxicity in humans and pigs is mainly the kidney as opposed to the significant damages and carcinogenic effects seen in various organs in rats exposed to OTA.

Corneal Dystrophy in Dutch Belted Rabbits as a Possible Model of Thiel-Behnke Subtype of Epithelial-Stromal TGFβ-Induced Corneal Dystrophy

The International Committee for Classification of Corneal Dystrophies (IC3D) categorized corneal dystrophies in humans using anatomic, genotypic, and clinicopathologic phenotypic features. Relative to the IC3D classification, a review of the veterinary literature confirmed that corneal dystrophy is imprecisely applied to any corneal opacity and to multiple poorly characterized histologic abnormalities of the cornea in animals. True corneal dystrophy occurs in mice with targeted mutations and spontaneously in pet dogs and cats and in Dutch belted (DB) rabbits, but these instances lack complete phenotyping or genotyping. Corneal dystrophy in DB rabbits can be an important confounding finding in ocular toxicology studies but has only been described once. Therefore, the ophthalmology and pathology of corneal dystrophy in 13 DB rabbits were characterized to determine whether the findings were consistent with or a possible model of any corneal dystrophy subtypes in humans. Slit lamp and optical coherence tomography (OCT) imaging were used to characterize corneal dystrophy over 4 months in young DB rabbits. The hyperechoic OCT changes correlated with light microscopic findings in the anterior stroma, consisting of highly disordered collagen fibers and enlarged keratocytes. Histochemical stains did not reveal abnormal deposits. Small clusters of 8 to 16 nm diameter curly fibers identified by transmission electron microscopy were consistent with Thiel-Behnke (TBCD) subtype of epithelial-stromal transforming growth factor β-induced dystrophies. Sporadic corneal dystrophy in DB rabbits appears to be a potential animal model of TBCD, but genotypic characterization will be required to confirm this categorization.

Mucosa-Associated Lymphoid Tissue and Tertiary Lymphoid Structures of the Eye and Ear in Laboratory Animals

Mucosa-associated lymphoid tissue (MALT) of special senses is poorly described and can be confused with nonspecific mononuclear cell infiltrates and tertiary lymphoid structures (TLS). In the eye, MALT consists mostly of conjunctiva-associated lymphoid tissue (CALT) and lacrimal drainage-associated lymphoid tissue (LDALT). In humans, CALT and LDALT are important components of the normal eye-associated lymphoid tissue (EALT), but EALT is less frequently described in ocular tissues of animals. The EALT are acquired postnatally in preferential mucosal sites, expand with antigenic exposure, form well-developed lymphoid follicles, and are reported to senesce. Lymphoid follicles that are induced concurrently with chronic inflammation are more appropriately considered TLS but must be differentiated from inflammation in MALT. Less understood is the etiology for formation of lymphoid tissue aggregates in the ciliary body, limbus, or choroid of healthy eyes in animals and humans. In the healthy eustachian tube and middle ear of animals and humans, MALT may be present but is infrequently described. Concurrent with otitis media, lymphoid follicles in the eustachian tube are probably expanded MALT, but lymphoid follicles in the middle ear may be TLS. The purpose of this comparative review is to familiarize toxicologic pathologists with MALT in the special senses and to provide considerations for differentiating and reporting eye and ear MALT from immune or inflammatory cell infiltrates or inflammation in nonclinical studies, and the circumstances for reporting TLS in compartments of the eye and ear.

Neuroanatomy and Sampling of Central Projections for the Visual System in Mammals Used in Toxicity Testing

Visual system toxicity may manifest anywhere in the visual system, from the eye proper to the visual brain. Therefore, effective screening for visual system toxicity must evaluate not only ocular structures (ie, eye and optic nerve) but also multiple key brain regions involved in vision (eg, optic tract, subcortical relay nuclei, and primary and secondary visual cortices). Despite a generally comparable pattern across species, the neuroanatomic organization and function of the visual brain in rodents and rabbits exhibit appreciable differences relative to nonrodents. Currently recognized sampling practices for general toxicity studies in animals, which are based on easily discerned external neuroanatomic landmarks and guided by extant stereotaxic brain atlases, typically will permit histopathologic evaluation of many brain centers involved in visual sensation (eg, optic chiasm, optic tract, dorsal lateral geniculate nucleus, primary and secondary visual cortices) and often some subcortical brain nuclei involved in light-modulated nonvisual activities needed for visual attention and orientation (eg, rostral colliculus in quadrupeds, termed the superior colliculus in bipeds; several cranial nerve nuclei). Pathologic findings induced by toxicants in the visual brain centers are similar to those that are produced in other brain regions.

Spontaneous Background and Procedure-Related Microscopic Findings and Common Artifacts in Ocular Tissues of Laboratory Animals in Ocular Studies

Identification of test article-related microscopic findings in ocular toxicology studies requires a working knowledge of the artifacts and procedure-related or background findings commonly encountered in such studies. The objective of this article is to provide a mini-atlas of the artifacts and procedure-related or spontaneous background findings commonly observed in ocular tissues from animals in toxicology studies of ocular drug candidates. Artifacts in the eye are often related to collection or fixation procedures and include swelling and vacuolation of lens fibers, separation of the neuroretina from the retinal pigment epithelium (RPE), and vacuolation of the optic nerve. Common in-life procedure-related findings include intravitreal injection needle tracks in the sclera and ciliary body pars plana and foci of RPE hypertrophy and/or hyperpigmentation at subretinal injection sites. Common background findings include corneal mineralization, uveal mononuclear cell infiltrates, and peripheral displacement of photoreceptor nuclei in the retina. A few uncommon spontaneous background findings that may be confused with test article-related findings, such as bilateral optic atrophy in macaques, are also included.

Conditioning Regimens in Long-Term Pre-Clinical Studies to Support Development of Ex Vivo Gene Therapy: Review of Nonproliferative and Proliferative Changes

Hematopoietic stem cell gene therapy has become a successful therapeutic strategy for some inherited genetic disorders. Pre-clinical toxicity studies performed to support the human clinical trials using viral-mediated gene transfer and autologous hematopoietic stem and progenitor cell (HSPC) transplantation are complex and the use of mouse models of human diseases makes interpretation of the results challenging. In addition, they rely on the use of conditioning agents that must induce enough myeloablation to allow engraftment of transduced and transplanted HSPC. Busulfan and total body irradiation (TBI) are the most commonly used conditioning regimens in the mouse. Lenticular degeneration and atrophy of reproductive organs are expected histopathological changes. Proliferative and nonproliferative lesions can be observed with different incidence and distribution across strains and mouse models of diseases. The occurrence of these lesions can interfere with the interpretation of pre-clinical toxicity and tumorigenicity studies performed to support the human clinical studies. As such, it is important to be aware of the background incidence of lesions induced by different conditioning regimens. We review the histopathology results from seven long-term studies, five using TBI and two using busulfan.

Neonatal and Juvenile Ocular Development in Göttingen Minipigs and Domestic Pigs: A Histomorphological and Immunohistochemical Study

Pigs are considered one of the relevant animal models for ocular research as they share several histological and anatomical similarities with the human eye. With the increasing interest in juvenile animal models, this study aimed to describe the postnatal development of ocular structures in 16 Göttingen minipigs and 25 F2 domestic pigs, between birth and 6 months of age, using histopathology and immunohistochemistry against Ki-67, caspase-3, calbindin, glial fibrillary acidic protein, rhodopsin, and synaptophysin. All ocular structures in both pig breeds were incompletely developed at birth and for variable periods postnatally. Noteworthy histological features of immaturity included vascularization in the corneal stroma in neonatal Göttingen minipigs, increased cellularity in different substructures, remnants of the hyaloid vasculature, short and poorly ramified ciliary body processes, and a poorly developed cone inner segment. Increased cellular proliferation, highlighted by abundant Ki-67 immunolabeling, was observed in almost all developing structures of the pig eye for variable periods postnatally. Apoptosis, highlighted with caspase-3 immunolabeling, was observed in the retinal inner nuclear layer at birth and in the regressing hyaloid vasculature remnants. Immunohistochemistry against rhodopsin, synaptophysin, and calbindin demonstrated the short size of the developing photoreceptors and the immature cone inner segment morphology. Calbindin labeling revealed significant differences in the amount of positively labeled cone nuclei between the retinal area centralis and the non-area centralis regions. The elongation of Müller cell processes in the developing retina was shown with glial fibrillary acidic protein. In both pig breeds, the eyes reached histomorphological and immunohistochemical maturity at 6 months of age.

Human CD34+ Hematopoietic Stem Cell-Engrafted NSG Mice: Morphological and Immunophenotypic Features

Immunodeficient mice engrafted with human immune cells represent an innovative tool to improve translatability of animal models for the study of human diseases. Immunophenotyping in these mice focuses on engraftment rates and cellular differentiation in blood and secondary lymphoid organs, and is predominantly carried out by FACS (fluorescent activated cell sorting) analysis; information on the morphological aspects of engraftment and the prevalence of histologic lesions is limited. We histologically examined 3- to 6-month-old NSG mice, naïve or engrafted with CD34⁺ human hemopoietic stem cells (HSC), and employed a quantitative immunohistochemical approach to identify human and murine cell compartments, comparing the results with the FACS data. NSG mice mainly exhibited incidental findings in lungs, kidneys, testes, and adrenal glands. A 6-month-old NSG mouse had a mediastinal lymphoblastic lymphoma. The lymphoid organs of NSG mice lacked typical lymphoid tissue architecture but frequently exhibited small periarteriolar leukocyte clusters in the spleen. Mice engrafted with human HSC frequently showed nephropathy, ovarian atrophy, cataract, and abnormal retinal development, lesions considered secondary to irradiation. In addition, 20% exhibited multisystemic granulomatous inflammatory infiltrates, dominated by human macrophages and T cells, leading to the observed 7% mortality and morbidity. Immunophenotypic data revealed variable repopulation of lymphoid organs with hCD45⁺ human cells, which did not always parallel the engraftment levels measured via FACS. The study describes the most common pathological features in young NSG mice after human HSC engraftment. As some of these lesions contribute to morbidity, morphological assessment of the engraftment at tissue level might help improve immunophenotypic evaluations of this animal model.

Incidences and Range of Spontaneous Microscopic Lesions in the Eye of Sprague-Dawley Rats and Han Wistar Rats Used in Toxicity Studies

The incidence and range of spontaneous microscopic lesions were determined in the eyes of male and female control Sprague-Dawley and Han Wistar rats. Data were collected retrospectively from 1411, 817, 970, 658, and 3999 rats from control groups of 4-, 13-, 26-, 52-, and 104-week studies, respectively, carried out between 1997 and 2019. Microscopic lesions of the eye were rare in 4- and 13-week studies, uncommon in 26- and 52-week studies, and were of relatively higher incidence in 104-week studies. Neoplastic lesions were sporadic and were only observed in 104-week studies. In Sprague-Dawley rats, the most common lesions (>1% in 104-week studies) were retinal degeneration, retinal rosettes/folds, and lenticular degeneration. The Han Wistar rats presented a range of ocular lesions similar to the Sprague-Dawley rats. However, retinal degeneration occurred with an earlier onset and at higher incidences, ranging from >5% in 26-week studies up to 45.72% in 104-week studies. In both strains, females exhibited higher incidences and severities of retinal degeneration. It is hoped that reference to the incidences reported here will facilitate the differentiation of spontaneous lesions from test article-induced lesions in toxicology studies in these strains of rat.

Selected Aspects of Ocular Toxicity Studies With a Focus on High-Quality Pathology Reports: A Pathology/Toxicology Consultant's Perspective

Ocular toxicity studies are the bedrock of nonclinical ocular drug and drug-device development, and there has been an evolution in experience, technologies, and challenges to address that ensures safe clinical trials and marketing authorization. The expectations of a well-designed ocular toxicity study and the generation of a coherent, integrative ocular toxicology report and subreports are high, and this article provides a pathology/toxicology consultant's perspective on achieving that goal. The first objective is to cover selected aspects of study designs for ocular toxicity studies including considerations for contract research organization selection, minipig species selection, unilateral versus bilateral dosing, and in-life parameters based on fit-for-purpose study objectives. The main objective is a focus on a high-quality ocular pathology report that includes ocular histology procedures to meet regulatory expectations and a report narrative and tables that correlate microscopic findings with key ophthalmic findings and presents a clear interpretation of test article-, vehicle-, and procedure-related ocular and extraocular findings with identification of adversity and a pathology peer review. The last objective covers considerations for a high-quality ophthalmology report, which in concert with a high-quality pathology report, will pave the way for a best quality toxicology report for an ocular toxicity study.