Juvenile Toxicology Studies Research Articles

Considerations for and against dosing rodent pups before 7 days of age in juvenile toxicology studies

This review focuses on preweaning ontogenic and developmental processes that can influence the selection of the appropriate age at which to start dosing rodent pups in juvenile animal studies (JAS). The ICH S11 guideline on ‘Nonclinical Safety Testing in Support of Development of Paediatric Medicines’ highlights the need to adapt the age from which animals are dosed according to the stage of development in the target organs/tissues of concern in the youngest pediatric patients. Rodents (rat or mouse) are the most common species for JAS. Despite previous practices, based on comparative ontogeny, it is rarely necessary to dose rodents younger than one week of age since postnatal day (PND)7 is appropriate to address concern for the vast majority of organs. In exceptional cases, earlier dosing (e.g., PND4) can be appropriate to address specific concern in preterm neonates and when a tissue of concern has a particularly early developmental trajectory in the rodent compared to humans. The comparative development of the CNS is particularly complex. While exposure of rodents from PND10 covers most CNS development stages relevant to human neonates, a later dosing start (yet, not later than PND14) can sometimes be appropriate to reflect specific aspects (e.g., transformation of GABAergic transmission). An extended study design including subsets of several ages can be helpful to address multiple concerns within a preweaning JAS. Such design can allow for individual assessment of each concern, whilst minimizing (potentially irrelevant) signals from tissues exposed at a developmental stage that do not match the human situation.

Brief Synopsis: "Instruction Manual for Juvenile Clinical Pathology".

This symposium synopsis summarizes key points discussed related to clinical pathology data interpretation for reproduction and juvenile toxicology studies. In pregnant and growing animals, several changes in clinical pathology parameters linked to growth/maturation of organ and physiological functions can occur, and understanding these changes is important to enable accurate interpretation of clinical pathology data. A brief overview of the general approach to clinical pathology data analysis according to contemporary practices is provided, followed by a discussion focused specifically on reproductive and juvenile clinical pathology. In this context, the approach to recognize and differentiate changes that may be related to pregnancy and growth as opposed to those that may be related to test article effects is highlighted.

A Transient Developmental Background Finding in the Retina Observed in Neonatal Dogs in Juvenile Toxicology Studies.

In a juvenile toxicology program, an unexpected finding of vacuolation of inner nuclear, ganglion cell, and nerve fiber layers of the retina was observed microscopically in routine Davidson's fixed and hematoxylin and eosin-stained tissue sections of eyes in beagle dogs at approximately 5 weeks of age. There was no necrosis or degeneration of the affected cells and no associated inflammation. Fluorescein angiography revealed no vascular leakage. Optical coherence tomography (OCT) indicated swollen cells in the same layers of the retina as observed at light microscopic examination. Transmission electron microscopy revealed that the retinal vacuolation likely was consistent with intracellular swelling of amacrine, horizontal, and/or bipolar cells of the inner nuclear layer as affected cells had an expanded cytoplasm but contained normal nucleus and organelles. As assessed by animal behavior and full-field electroretinography, the retinal vacuolation appeared to have no impact on visual function. Retinal vacuolation was seen in approximately 40% of dogs at 5 weeks of age using OCT and/or light microscopic examination. Because the change was transient and age related, did not result in degenerative retinal changes, and was not present in dogs older than 5 weeks of age, it was considered a background developmental observation in beagle dogs.

Postnatal Developmental Changes of the Kidneys of the Albino Rat

Background: Being a highly immature organ at birth, the rat kidney is morphologically as fetal when compared with humans. Events that occur during fetal development might determine adult renal diseases. Aim of work: This study aimed to characterize the postnatal developmental changes of the kidneys in albino rats using light microscope from postnatal day (PND) 2 until PND 70. This may give references to pathologists when evaluating juvenile toxicology studies. Materials and Methods: Ten healthy pregnant albino rats were used in this study. Twenty-five of their offsprings were obtained and divided according to age into five groups of 5 pups each.Group A: studied at PND 2. Group B: studied at PND 10. Group C: studied at PND 20. Group D: studied at PND 30. Group E: studied at PND 70. Kidneys were removed, processed for light microscopic study and 5 mm thick paraffin sections were obtained and stained with hematoxylin and eosin stain. Results: Light microscopic examination of the renal cortex at PND 2 revealed subcapsular nephrogenic zone contained immature renal developmental stages, juxtamedullary zone contained formed glomeruli with medullary rays between the two zones. The renal cortex acquired maturation centrifugally with the superficial nephrons was the last to mature by PND 20. The papilla was the most mature region of the kidney and at PND2; it had the structural composition of the inner stripe of outer medulla. The papillary maturation involved a process of tubular elongation and increase in the interstitium until reaching adult structure by PND 20. At PND 2, the medulla was the most immature zone being formed of islets of tubular structures among abundant interstitium with high degree of undifferentiation. Its maturation involved tubular elongation and decrease of the interstitium with the outer medulla was the last to mature as late as PND 30. Consequently, the medulla remained immature for a relatively long postnatal period, in comparison to the other kidney regions. Conclusion: It was concluded that, rat kidney is immature at birth and kidney sub regions mature at different rates during postnatal development. The papilla was the first to mature (PND 20) followed by the cortex (PND 20) and finally the medulla (PND 30).

Points to Consider in Designing and Conducting Juvenile Toxicology Studies.

In support of a clinical trial in the pediatric population, available nonclinical and clinical data provide input on the study design and safety monitoring considerations. When the existing data are lacking to support the safety of the planned pediatric clinical trial, a juvenile animal toxicity study is likely required. Usually a single relevant species, preferably a rodent, is chosen as the species of choice, while a nonrodent species can be appropriate when scientifically justified. Juvenile toxicology studies, in general, are complicated both conceptually and logistically. Development in young animals is a continuous process with different organs maturing at different rates and time. Structural and functional maturational differences have been shown to affect drug safety. Key points to consider in conducting a juvenile toxicology study include a comparative development of the organ systems, differences in the pharmacokinetics/absorption, distribution, metabolism, excretion (PK/ADME) profiles of the drug between young animal and child, and logistical requirement in the juvenile study design. The purpose of this publication is to note pertinent points to consider when designing and conducting juvenile toxicology studies and to aid in future modifications and enhancements of these studies to enable a superior predictability of safety of medicines in the pediatric population.

Methods for Conducting Intravenous Juvenile Toxicology Studies in Rats

Methods for Conducting Intravenous Juvenile Toxicology Studies in Rats

Current Topics in Postnatal Behavioral Testing.

The study of developmental neurotoxicity (DNT) continues to be an important component of safety evaluation of candidate therapeutic agents and of industrial and environmental chemicals. Developmental neurotoxicity is considered to be an adverse change in the central and/or peripheral nervous system during development of an organism and has been primarily evaluated by studying functional outcomes, such as changes in behavior, neuropathology, neurochemistry, and/or neurophysiology. Neurobehavioral evaluations are a component of a wide range of toxicology studies in laboratory animal models, whereas neurochemistry and neurophysiology are less commonly employed. Although the primary focus of this article is on neurobehavioral evaluation in pre- and postnatal development and juvenile toxicology studies used in pharmaceutical development, concepts may also apply to adult nonclinical safety studies and Environmental Protection Agency/chemical assessments. This article summarizes the proceedings of a symposium held during the 2015 American College of Toxicology annual meeting and includes a discussion of the current status of DNT testing as well as potential issues and recommendations. Topics include the regulatory context for DNT testing; study design and interpretation; behavioral test selection, including a comparison of core learning and memory systems; age of testing; repeated testing of the same animals; use of alternative animal models; impact of findings; and extrapolation of animal results to humans. Integration of the regulatory experience and scientific concepts presented during this symposium, as well as from subsequent discussion and input, provides a synopsis of the current state of DNT testing in safety assessment, as well as a potential roadmap for future advancement.

Post natal cardiovascular assessments in nonclinical pediatric studies using the jacketed external telemetry in beagles for juvenile toxicology studies

Post natal cardiovascular assessments in nonclinical pediatric studies using the jacketed external telemetry in beagles for juvenile toxicology studies

Post natal cardiovascular assessments in non-clinical pediatric studies using the jacketed external telemetry in beagles for juvenile toxicology studies

The effects of monobutyl phthalate (MBuP) on reproductive function were determined in pregnant and pseudopregnant rats. Rats were given MBuP by gastric intubation at 250, 500, 750, or 1000 mg/kg on days 0 to 8 of pregnancy and pregnancy outcome was determined on day 20 of pregnancy. The effects of MBuP on the uterine function, as a cause of early embryonic loss, were also determined in pseudopregnant rats, with an induced decidual cell response. The same doses of MBuP were given to pseudopregnant rats on days 0 to 8 of pseudopregnancy and the uterine weight on day 9 served as an index of uterine decidualization. MBuP at 1000 mg/kg caused significant increases in the incidences of preimplantation loss in females successfully mated and of postimplantation loss in females having implantations. Uterine decidualization in pseudopregnant rats was significantly decreased at 1000 mg/kg. These findings suggest that early embryonic loss due to MBuP is mediated, at least in part, via suppression of uterine decidualization, an impairment of uterine function.

Use of minipigs in non-clinical juvenile toxicology studies

Use of minipigs in non-clinical juvenile toxicology studies

Essentials for starting a pediatric clinical study (4): Clinical pediatric safety planning based on preclinical toxicity studies and pediatric pharmacovigilance guidance

Juvenile toxicology studies in animals provide useful information to guide monitoring of potential adverse effects in children especially on growth and development. In order to continue to gain knowledge and build upon these preclinical studies, recent experience has suggested that additional approaches for monitoring of safety concerns in the pediatric population may be required. Recently, pediatric guidance has become available from the health authorities which provide pharmacovigilance concepts as they specifically relate to drugs being developed for pediatric indications. Clinical trials are typically not robust enough to detect rare or delayed safety effects as the pediatric trials are relatively short-term. Furthermore, such long term or rare effects may not be detected via standard voluntary postmarketing surveillance. Safety monitoring of children with Juvenile Inflammatory Arthritis (JIA) taking nonsteroid anti-inflammatory drug (NSAID)s will be used as an example to describe a post-marketing risk management and pharmacovigilance program that serves to better evaluate safety data from various sources. The intent of this program is to identify adverse events (AE), including events with longer latency, which may be associated with NSAID use in a pediatric population. In this presentation, the 4 major components of the program are to be addressed. Such a program may serve as a model to proactively generate and monitor safety data in order to identify AEs that may be associated with new therapeutics for a pediatric population.

Evaluations of organ system development in juvenile toxicology testing

Juvenile toxicology studies for pharmaceutical and biotechnology products are becoming more commonly conducted. Regulatory guidance indicates a case-by-case approach to program and study design. Routine toxicology assessments can be applied to these studies, in addition the functional development of a series of organ systems, including nervous (behavior/cognition), cardiovascular, gastro-intestinal, pulmonary, renal, immune, skeletal (growth) and reproductive, have been identified for potential evaluation. Typically these tests can be added to both rodent and non-rodent studies, however there are some limitations. Testing of reproductive and behavioral development is routine in rodents but for non-rodents can present some problems. Toxicokinetics are typically incorporated in these studies and metabolic assessments, such as enzyme induction, can also be added to provide information on hepatobiliary development. It is concluded that, whilst the development of various organ systems can be evaluated, care in the use of these evaluations in juvenile toxicology testing programs is needed to ensure appropriate studies.