Spontaneous testicular lesions in purpose-bred beagle dogs

INSL3 Variation in Dogs Following Suppression and Recovery of the HPG Axis

Insulin-like peptide 3 (INSL3) is a constitutive product of mature, adult-type Leydig cells of the testes and consequently in most mammals is an ideal biomarker with which to monitor pubertal development. A new heterologous time-resolved fluorescence immunoassay was developed and validated to measure circulating INSL3 in the blood of adult male dogs. Compared to other species, INSL3 concentration is low with marked variation between individuals, which appears to be independent of breed, age, or weight. A model system was then used in which a cohort of beagle dogs was subject to a GnRH-agonist implant to suppress the HPG axis and spermatogenesis, followed by implant removal and recovery. Unlike testosterone, INSL3 levels were not fully suppressed in all animals by the GnRH agonist, nor was the recovery of Leydig cell function following implant removal uniform or complete, even after several weeks. In dogs, and dissimilar from other species (including humans), Leydig-cell INSL3 appears to be quite variable between individual dogs and only weakly connected to the physiology of the HPG axis after its suppression by a GnRH-agonist implant and recovery. Consequently, INSL3 may be less useful in this species for the assessment of testis function.

Morphologic Features and Deep Learning-Based Analysis of Canine Spermatogenic Stages

In nonclinical toxicity studies, stage-aware evaluation is often expected to assess drug-induced testicular toxicity. Although stage-aware evaluation does not require identification of specific stages, it is important to understand microscopic features of spermatogenic staging. Staging of the spermatogenic cycle in dogs is a challenging and time-consuming process. In this study, we first defined morphologic features for the eight spermatogenic stages in standard histology sections (H&E slides) of dog testes. For image analysis, we defined the key morphologic features of five stages/pooled stage groups (I-II, III-IV, V, VI-VII, and VIII). These criteria were used to develop a deep learning (DL) algorithm for staging of the spermatogenic cycle of control dog testes using whole slide images. In addition, a DL-based nucleus segmentation model was trained to detect and quantify the number of different germ cells, including spermatogonia, spermatocytes, and spermatids. Identification of spermatogenic stages and quantification of germ cell populations were successfully automated by the DL models. Combining these two algorithms provided color-coding visual spermatogenic staging and quantitative information on germ cell populations at specific stages that would facilitate the stage-aware evaluation and detection of changes in germ cell populations in nonclinical toxicity studies.

Spontaneous Findings in the Reproductive System of Sexually Mature Male Cynomolgus Macaques

Sexually mature nonhuman primates are often used in nonclinical safety testing when evaluating biopharmaceuticals; however, there is limited information in historical control databases or in the published literature on the spontaneous findings in the male reproductive system. This review evaluated digital slides from the male reproductive tract (testes, epididymides, prostate, and seminal vesicles) in sexually mature cynomolgus macaques ( Macaca fascicularis; n = 255) from vehicle control groups in nonclinical toxicology studies and compared the observations with body weight, organ weight, and geographical origin. The most common microscopic findings were hypospermatogenesis and tubular dilatation in the testes; inflammatory cell infiltrate, cellular debris, and decreased sperm in the epididymides; inflammatory cell infiltrate and acinar dilatation in the prostate; and corpora amylacea and atrophy in the seminal vesicles. There were a few correlative observations in animals when grouped by weight or geographical origin: animals with lower terminal body weights (<5 kg) often displayed features of late puberty despite having sperm in the epididymis, while animals originating from Mauritius had a lower incidence of inflammatory cell infiltrates than those from Southeast Asia/China. This review provides incidence, descriptions, and photomicrographs of the common spontaneous microscopic findings in the reproductive system of mature male cynomolgus macaques.

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

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 lesions observed in most tissues and organs from the dog 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, lesions induced by exposure to test materials, and relevant infectious and parasitic lesions. 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.

Postnatal testicular development in Vietnamese pot-bellied pigs

The Vietnamese pot-bellied pig is a breed with high investigation potential. However, at the reproductive level, its testicular characteristics are still unknown, as well as the different stages of its development. Therefore, the objective of this work is to describe the postnatal testicular development of Vietnamese pot-bellied pigs. In this study, we used pigs grouped into the neonatal stage, animals at zero weeks; prepubertal stage, animals at three and eight weeks; pubertal stage, animals at twelve and sixteen weeks; and postpubertal stage animals at twenty, twenty-four, twenty-eight and thirty-two weeks of age. The neonatal stage is characterized by gonocytes at different migration phases. In the prepubertal stage, gonocytes were differentiated into spermatogonia at 3 weeks of age, and the first spermatocytes were observed at 7 weeks of age. Puberty was determined to start at 12 weeks because seminiferous tubules are found with complete spermatogenesis and the highest peaks in positive cell counting of androgen receptors (AR) and proliferating cell nuclear antigen (PCNA) factor that later decreased and further stabilized in the following weeks. In the postpubertal stage, an increase in seminiferous tubule areas was observed. The number of apoptotic cells ranged from low to null at all ages. Testosterone (T) and gonadotropin levels had two important peaks at 3 and 24 weeks. The seminiferous epithelium cycle was found to have 11 stages according to acrosome development. These characteristics of Vietnamese pot-bellied pig testes, which are different from rat testes and more similar to human testicles, make them a viable model to study human male reproductive biology. The postnatal testicular development of pot-bellied pigs is different from the postnatal testicular development of other breeds. Therefore, due to this difference in size and easy manipulation, the Vietnamese pig is an alternative for investigation compared to other pig breeds.

Oral repeated-dose toxicity studies of BIA 10-2474 in beagle dogs

BIA 10-2474 is a novel fatty acid amide hydrolase inhibitor developed for the treatment of medical conditions which would benefit from enhanced levels of endogenous anandamide (AEA) such as pain disorders. During a Phase I clinical trial one subject died after receiving BIA 10-2474 and others displayed neurological signs. We describe here the toxicology studies in beagle dogs that supported phase I testing of BIA 10-2474 in humans. A Maximum Tolerated Dose (MTD) study using once-a-day oral (capsule) application of BIA 10-2474 was first conducted to establish suitable dose levels for subsequent studies. Based on these results, 100 mg/kg/day was considered to be the MTD. The 4-week oral (capsule) toxicity study with a 3-week recovery period for BIA 10-2474 was therefore carried out at 20, 50 or 100 mg/kg/day. There were no changes recorded at 50 mg/kg/day and this was considered the oral No Observed Effect Level (NOEL) for four-week once-a-day capsule administration to Beagle dogs. At 100 mg/kg/day, the dose-limiting findings consisted of clinical symptoms including tremor, loss of balance, abnormal gait, decreased motor activity, weakness, vomits, salivation increase and miosis, increased severity of thymic atrophy/involution, and moderate acute, focal/multifocal bronchopneumonia in lungs of three animals. In a 13-week oral (capsule) toxicity study in the Beagle dog with a 6-week recovery period, using the same dose levels, clinical signs were recorded during treatment with BIA 10-274 at 50 and 100 mg/kg/day. The most frequent signs included difficulty breathing, respiratory sounds (with or without auscultation) and cough. Incoordination of the hind limbs with absence of correction reflex were also observed on some occasions. As a result, the 50 and 100 mg/kg/day doses were reduced to 35 and 50 mg/kg/day respectively on day 37. Because of the continued signs, the doses in both groups were further reduced to 20 mg/kg/day from day 77. Under the conditions of this study and given the severe signs recorded in groups treated at 100-50-20 and 50-35-20 mg/kg/day and only very occasional presence of signs in the group treated for the 13-week period at 20 mg/kg/day (abnormal respiratory sounds once in two animals), the dose of 20 mg/kg/day was considered the No Observed Adverse Effect Level (NOAEL).

Age-related changes in interstitial fibrosis and germ cell degeneration of the canine testis

Fifty-five healthy medium-sized dogs were divided into four groups; young (1-3 years old, n = 14), adult (>3 to 6 years old, n = 12), old (>6 to 9 years old, n = 14) and senile (>9 years old, n = 15). After routine orchiectomy, testes were collected, and the degree of white streak areas on cut surfaces was subjectively assessed. Later, testicular tissue sections were stained with haematoxylin and eosin and Masson's trichrome for evaluation of germ cell degeneration and the proportion of interstitial connective tissue, respectively. Semiquantitative severity scoring of germ cell degeneration and quantitative analysis of spermatogenic cells for spermatic index (SI) and Sertoli cell index (SEI) was performed. The score of white streak on cut surface area of the testes increased with age, being higher (p < 0.05) in senile dogs than other age groups; no difference was found between adult and old dogs. The proportion of testicular interstitial fibrosis was highest (p < 0.05) in senile dogs. Positive correlations between age and white streak area (rho = 0.77, p < 0.01) as well as age and interstitial fibrosis (rho = 0.63, p < 0.01) were observed. The severity of germ cell degeneration gradually increased with age and differed among age groups (p < 0.05). Age positively correlated with atrophy of seminiferous tubules (rho = 0.93, p < 0.01). The SI was lower (p < 0.05) in senile dogs compared to other age groups, and SI was not different among young, adult and old dogs. Conversely, SEI was significantly higher in senile dogs compared to young, adult and old dogs. A negative correlation between age and SI (rho = -0.69) and a positive correlation between age and SEI (rho = 0.68) were significant (p < 0.01). In conclusion, influence of age on testicular interstitial fibrosis and germ cell degeneration/depletion were pronounced in dogs over 9 years old.

Distinguishing between endocrine disruption and non-specific effects on endocrine systems

The endocrine system is responsible for growth, development, maintaining homeostasis and for the control of many physiological processes. Due to the integral nature of its signaling pathways, it can be difficult to distinguish endocrine-mediated adverse effects from transient fluctuations, adaptive/compensatory responses, or adverse effects on the endocrine system that are caused by mechanisms outside the endocrine system. This is particularly true in toxicological studies that require generation of effects through the use of Maximum Tolerated Doses (or Concentrations). Endocrine-mediated adverse effects are those that occur as a consequence of the interaction of a chemical with a specific molecular component of the endocrine system, for example, a hormone receptor. Non-endocrine-mediated adverse effects on the endocrine system are those that occur by other mechanisms. For example, systemic toxicity, which perturbs homeostasis and affects the general well-being of an organism, can affect endocrine signaling. Some organs/tissues can be affected by both endocrine and non-endocrine signals, which must be distinguished. This paper examines in vitro and in vivo endocrine endpoints that can be altered by non-endocrine processes. It recommends an evaluation of these issues in the assessment of effects for the determination of endocrine disrupting properties of chemicals. This underscores the importance of using a formal weight of evidence (WoE) process to evaluate potential endocrine activity.

Comparative Aspects of Pre- and Postnatal Development of the Male Reproductive System

This review describes pre- and postnatal development of the male reproductive system in humans and laboratory animals, and highlights species differences in the timing and control of hormonal and morphologic events. Major differences are that the fetal testis is dependent on gonadotropins in humans, but is independent of such in rats; humans have an extended postnatal quiescent period, whereas rats exhibit no quiescence; and events such as secretion by the prostate and seminal vesicles, testicular descent, and the appearance of spermatogonia are all prenatal events in humans, but are postnatal events in rats. Major differences in the timing of the developmental sequence between rats and humans include: gonocyte transformation period (rat: postnatal day 0-9; human: includes gestational week 22 to 9 months of age); masculinization programming window (rat: gestational day 15.5-17.5; human: gestational week 9-14); and mini-puberty (rat: 0-6 hr after birth; human: 3-6 months of age). Endocrine disruptors can cause unique lesions in the prenatal and early postnatal testis; therefore, it is important to consider the differences in the timing of the developmental sequence when designing preclinical studies as identification of windows of sensitivity for endocrine disruption or toxicants will aid in interpretation of results and provide clues to a mode of action. Birth Defects Research 110:190-227, 2018. © 2017 Wiley Periodicals, Inc.

Impact of Age on the Male Reproductive System from the Pathologist’s Perspective

Age, and in particular young age, can significantly impact the response to toxicants in animals and can greatly influence the interpretation of tissue changes by the toxicologic pathologist. Although this applies to multiple organ systems, the current review focuses on the male reproductive system. When performing microscopic evaluation of male reproductive organs, the toxicologic pathologist must be aware of the dynamic changes in histomorphology, predominantly driven by timed hormonal alterations, at various life stages. Specific challenges pathologists face are understanding the appearance of male reproductive tissues throughout the neonatal, infantile, and juvenile developmental periods, recognizing when normal looks abnormal during tissue development, defining sexual maturity, and working with high interanimal variability in maturation rate and histologic appearance in developing large laboratory animals, such as nonhuman primates, dogs, and pigs. This review describes postnatal development of the male reproductive system in the rat, demonstrates how assessing toxicity during a defined window of postnatal development in the rat may improve definition of toxicant timing and targets, and discusses challenges associated with the interpretation of toxicity in immature large animal species. The emphasis is on key age-related characteristics that influence the interpretation of tissue changes by the toxicologic pathologist.

The Toxicology of HMG—CoA Reductase Inhibitors: Prediction of Human Risk

The discovery that 3-hydroxy-3-methyglutaryl coenzyme A reductase was a rate-determining step in the biosynthesis of cholesterol led to the discovery of inhibitors of this enzyme. To support the development of these agents (statins) as potential hypocholesterolemic drugs, a variety of preclinical studies were conducted in several animal species. Not unexpectedly due to the central role played by mevalonic acid and its products including cholesterol in development and maintenance of cellular homeostasis, administration of high dosage levels of these agents led to the expression of a broad variety of adverse effects in many different tissues. Using the tools of toxicologic pathology and classical risk assessment, these varied toxicities were evaluated by many groups relative to the conditions of use in human therapy and a perspective was developed on potential human risk. These approaches of mechanism-based risk assessment predicted that most of the adverse effects observed in animals would not be seen under conditions of human use and supported the successful introduction of one of the most important classes of human medicines.

Histological Development of Male Reproductive Organs in Microminipigs

Microminipigs are becoming increasingly attractive alternatives for various experimental applications, such as general toxicology studies, owing to their manageable size. However, there are limited studies on the male reproductive organs of microminipigs, particularly on the histological aspects of sexual maturity. To clarify the development of male reproductive organs, 35 male microminipigs, aged 0 to 12 months, were used in this study. Histological and histomorphological evaluation was performed based on spermatogenic development, measurement of tubular structure in testes and epididymides, and histological progress of accessory glands. In addition, spontaneous testicular changes were quantitatively assessed. Histologically, male microminipigs sexually matured around 4.5 months of age, when spermatogenesis in testes and structural development in genital organs were completed. Spontaneous testicular changes occurred in all the animals investigated. Multinucleated giant cell was most commonly observed, followed by hypospermatogenesis and tubular atrophy/hypoplasia. However, the number of affected tubules was less than 1% in testes after 4.5 months of age, suggesting that the influence of these changes on evaluation of toxicity studies may be minimal. It is preferable to use sexually mature animals in toxicology studies; therefore, the information obtained by the present study will be helpful for future toxicity evaluations in microminipigs.

Scientific and Regulatory Policy Committee Points to Consider Review: Inclusion of Reproductive and Pathology End Points for Assessment of Reproductive and Developmental Toxicity in Pharmaceutical Drug Development

Standard components of nonclinical toxicity testing for novel pharmaceuticals include clinical and anatomic pathology, as well as separate evaluation of effects on reproduction and development to inform clinical development and labeling. General study designs in regulatory guidances do not specifically mandate use of pathology or reproductive end points across all study types; thus, inclusion and use of these end points are variable. The Scientific and Regulatory Policy Committee of the Society of Toxicologic Pathology (STP) formed a Working Group to assess the current guidelines and practices on the use of reproductive, anatomic pathology, and clinical pathology end points in general, reproductive, and developmental toxicology studies. The Working Group constructed a survey sent to pathologists and reproductive toxicologists, and responses from participating organizations were collected through the STP for evaluation by the Working Group. The regulatory context, relevant survey results, and collective experience of the Working Group are discussed and provide the basis of each assessment by study type. Overall, the current practice of including specific end points on a case-by-case basis is considered appropriate. Points to consider are summarized for inclusion of reproductive end points in general toxicity studies and for the informed use of pathology end points in reproductive and developmental toxicity studies.

Spontaneous Pathology and Routine Clinical Pathology Parameters in Aging Beagle Dogs

AstraZeneca ran a bespoke study to generate age-matched clinical pathology and histopathology data from a cohort of Beagle dogs aged between 25 and 37 months to support the use of these older animals in routine preclinical toxicology studies. As the upper age range of Beagle dogs routinely used in toxicology studies does not normally exceed 24 months, there is an absence of appropriate age-matched historical control data. The generation of such data was crucial to understand whether age-related differences in spontaneous findings might confound the interpretation of toxicology study data. While the majority of the histopathology findings in all the older dogs occurred at a similar prevalence as those expected in young adult dogs (<24 months), a number of differences were observed in the thymus (involution), bone marrow (increased adiposity), testes (degenerative changes), and lung (fibrosis, pigment and alveolar hyperplasia) that could be misinterpreted as a test article effect. Minor differences in some clinical pathology values (hemoglobin, alkaline phosphatase, absolute reticulocytes) were of a small magnitude and considered unlikely to affect the interpretation of study data.

A 90-day dietary study of a (2R,4R)-monatin salt in Beagle dogs

(2R,4R)-Monatin salt (Na/K) [sodium/potassium (2R,4R)-2-amino-4-carboxy-4-hydroxy-5-(3-indolyl) pentanoate, hereafter "R,R-monatin"] was administered in the diets of groups of Beagle dogs (4/sex/group) at concentrations of 0 (basal diet), 5000, 20,000, or 35,000 ppm for 13 weeks. There were no effects on survival, clinical observations, body weight and body weight gain, feed consumption and feed efficiency, functional observational battery, ophthalmic examination, and electrocardiographic evaluation. No adverse effects on hematology, serum chemistry, and urinalysis parameters were reported. A statistically significant decrease in testicular weights associated with germ cell hypocellularity and reduced luminal sperm in the epididymides was reported in all treated male groups. Based on these findings, the dietary no-observed-adverse-effect level (NOAEL) of R,R-monatin for 90 days was considered 35,000 ppm for female dogs (approximately 1101 mg/kg bw/day) and <5000 ppm for male dogs (approximately <151 mg/kg bw/day).

Spontaneous Testicular Tubular Hypoplasia/Atrophy in the Göttingen Minipig

The aim of this retrospective study was to assess the incidence and severity of tubular atrophy/hypoplasia in the testes of 104 control Göttingen minipigs aged 4.5 to 15 months. The finding was termed “tubular hypoplasia/atrophy” according to published descriptions for the dog. It included different microscopic changes that were considered part of a continuum, namely seminiferous epithelium vacuolation, presence of multinucleated germ cells in the tubular lumen, and decreased numbers (hypospermatogenesis) or absence of germ cells. This retrospective study demonstrates that tubular hypoplasia/atrophy is present in more than 70% of Göttingen minipigs and can occur at a marked severity in control animals. It correlated with a higher level of cell debris and a decrease in sperm content in the epididymides and with lower absolute and relative testes weights. There was no correlation with the weight of other sexual organs, total bodyweight, or age, which demonstrates that this change was not related to sexual immaturity. The distinction between this background finding and a compound-related effect could be challenging for the pathologist.

Histopathology of incidental findings in beagles used in toxicity studies

The purpose of our publication is to widely communicate the pictures of spontaneous findings occurring in beagles. Spontaneous arteritis occurs commonly in beagles. Frequent sites of arteritis are the heart, spleen, pancreas, epididymis and spinal cord. Morphological similarities between spontaneous and drug-induced arterial lesions may cause confusion when evaluating vascular toxicity of chemicals such as vasodilating agents. Focal and minimal inflammatory lesions are occasionally seen in the lung and may be associated with aspiration of food particles or of unknown causes. A cystic change with copious mucin production occurs occasionally in the mucosal epithelium of the gall bladder. Nesidioblastosis is seen rarely in the pancreas of beagles. C-cell complex and lymphocytic thyroiditis are common thyroid lesions. Spontaneous focal hypospermatogenesis and lobular Sertoli-cell-only seminiferous tubules occurring frequently in beagles must be distinguished from drug-induced damage of the seminiferous tubules in toxicity studies. The morphological differences of the female genital system in each cycle need to be understood; therefore, we present the normal features of the cyclic changes of the female genital organs. Further, we provide more information on spontaneous findings in beagles for exact diagnoses in toxicity studies.

Incidence and nature of testicular toxicity findings in pharmaceutical development

BACKGROUND

Testicular toxicity (TT) is a sporadic and challenging issue in pharmaceutical drug development. Efforts to develop TT screening assays or biomarkers have been overshadowed by consortium efforts to predict drug-induced toxicities such as hepatic injury, which are encountered more frequently.

METHODS

To gauge the current state of the field and to prioritize future TT activities, the International Life Sciences Institute-Health and Environmental Sciences Institute Developmental and Reproductive Toxicology (DART) Technical Committee sponsored a survey to better understand the incidence and nature of TT findings encountered during drug development.

RESULTS

Highlights from the 16 survey respondents include: (1) Although preclinical TT was encountered relatively infrequently, half of the participants observed repeated problems with TT during pharmaceutical development, (2) despite control measures such as use of sexually mature animals to diminish confounding effects of spurious lesions, interpretation of TT remains a challenge, (3) "traditional" evaluation tools such as hormonal monitoring and newer approaches such as -omics are utilized to investigate testicular changes, and (4) an understanding of the risk and relevance of TT findings is achieved through joint consideration of factors such as species specificity, potential mode of action, and safety margins.

CONCLUSIONS

TT remains a relatively uncommon but persistent challenge in pharmaceutical development. Although current preclinical TT approaches appear to be effective in limiting the occurrence of pharmaceutical candidate attrition in clinical trials, improved biomarker or screening platforms would allow companies to identify TT at an earlier stage, thus decreasing the time and resources expended on safety evaluation of pharmaceutical candidates.

Histopathology of the male reproductive system II: interpretation

Histopathology is acknowledged as the most sensitive endpoint for detecting testicular toxicity. However, identification and interpretation of chemically induced changes in the testis require fundamental knowledge of spermatogenesis, its dynamics and regulation. Changes in the rest of the reproductive tract are also frequently inter-related, being the result of or cause of disturbance in testicular spermatogenesis. This unit provides practical guidelines on how to evaluate testicular histopathology and how to utilize staging in a qualitative evaluation. It also provides an overview of the most common chemically induced lesions and their potential significance with respect to etiology and functional consequences.

Spontaneous and Age-Related Testicular Findings in Beagle Dogs

This study was conducted to characterize spontaneous testicular and epididymal microscopic findings in eighty control beagle dogs from toxicity studies. Hypospermatogenesis, characterized by randomly scattered missing spermatids and/or spermatocytes within seminiferous tubules, was observed in 75% of dogs six to seven months of age and declined to fewer than 10% in dogs over eleven months of age. Atrophy/hypoplasia of seminiferous tubules, characterized by subcapsular triangular clusters of tubules containing no germ cells, was observed in 25 to 40% of dogs under twelve months old, decreasing with age to 14 to 17% in dogs twelve to thirty-six months old. Retained spermatids, multinucleate giant cells, intracytoplasmic vacuoles (presumably in Sertoli cells), and swollen spermatocytes were common findings of minimal severity. Six- and seven-month-old dogs had lower testicular weights, less filling of the epididymal tails with sperm, and a two-fold higher incidence of abnormal epididymal content compared to dogs more than eight months of age. Most male beagles were histologically sexually mature by eight to nine months of age. This study confirms published reports that dogs at least ten months of age at necropsy usually are adequate for routine microscopic evaluation of the testes. If evaluation of spermatogenesis is critical, the incidental findings can be minimized by using males over twelve months of age.