The need for juvenile animal studies – A critical review

Juvenile toxicity study of deer antler extract in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Deer (Cervus elaphus Linnaeus) antler extract has been traditionally used in many Asian countries to prevent and treat various diseases. Deer antler extract is generally considered to be safe because humans have been exposed to it for a long time and it has been used as a tonic medicine originating from naturally occurring product. However, the comprehensive toxicological potential of deer antler extract during the juvenile period has not been investigated and its safety for juveniles remains unclear.

AIM OF THE STUDY

The aim of the present study was to comprehensively investigate the potential toxicological effects of deer antler extract during the juvenile period.

MATERIALS AND METHODS

As part of a safety assessment of the juvenile period, two separate studies, a juvenile toxicity study and a uterotrophic bioassay, were conducted in accordance with Good Laboratory Practice regulations and test guidelines. In the juvenile toxicity study, deer antler extract was administered daily by oral gavage to Sprague-Dawley rats at doses of 0, 500, 1000, and 2000 mg/kg during the juvenile period to investigate potential toxicities on general systemic, developmental, and reproductive functions. For the uterotrophic bioassay, deer antler extract was administered daily by oral gavage to Sprague-Dawley rats at doses of 0, 1000, and 2000 mg/kg on postnatal days 19-21 to investigate the estrogen-mimicking effects.

RESULTS

The results showed that deer antler extract was non-toxic and no observable adverse effects on general systemic function, developmental and reproductive function, and estrogen-mimetic effects were observed with dosing up to 2000 mg/kg during the juvenile period.

CONCLUSION

The safety of deer antler extracts was demonstrated in these studies and the results of this study can be used to evaluate human risk or determine the maximum recommended starting dose of deer antler extract for further clinical trials.

Proof of Concept: First Pediatric [14 C]microtracer Study to Create Metabolite Profiles of Midazolam

Growth and development affect drug-metabolizing enzyme activity thus could alter the metabolic profile of a drug. Traditional studies to create metabolite profiles and study the routes of excretion are unethical in children due to the high radioactive burden. To overcome this challenge, we aimed to show the feasibility of an absorption, distribution, metabolism, and excretion (ADME) study using a [14 C]midazolam microtracer as proof of concept in children. Twelve stable, critically ill children received an oral [14 C]midazolam microtracer (20 ng/kg; 60 Bq/kg) while receiving intravenous therapeutic midazolam. Blood was sampled up to 24 hours after dosing. A time-averaged plasma pool per patient was prepared reflecting the mean area under the curve plasma level, and subsequently one pool for each age group (0-1 month, 1-6 months, 0.5-2 years, and 2-6 years). For each pool [14 C]levels were quantified by accelerator mass spectrometry, and metabolites identified by high resolution mass spectrometry. Urine and feces (n = 4) were collected up to 72 hours. The approach resulted in sufficient sensitivity to quantify individual metabolites in chromatograms. [14 C]1-OH-midazolam-glucuronide was most abundant in all but one age group, followed by unchanged [14 C]midazolam and [14 C]1-OH-midazolam. The small proportion of unspecified metabolites most probably includes [14 C]midazolam-glucuronide and [14 C]4-OH-midazolam. Excretion was mainly in urine; the total recovery in urine and feces was 77-94%. This first pediatric pilot study makes clear that using a [14 C]midazolam microtracer is feasible and safe to generate metabolite profiles and study recovery in children. This approach is promising for first-in-child studies to delineate age-related variation in drug metabolite profiles.

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.

Lack of value of juvenile animal toxicity studies for supporting the safety of pediatric oncology phase I trials

Toxicity studies in juvenile animals (JAS) are sometimes performed to support clinical trials in pediatric oncology patients, and there are differing conclusions on the value of JAS for pediatric drug development. This manuscript provides a review of the pediatric clinical data for 25 molecularly-targeted and 4 biologic anticancer therapeutics. Other publications that evaluated the value of JAS in pediatric drug development focus on differences in toxicity between juvenile animals and adult animals. The present paper examines pediatric-specific clinical findings to focus on dose setting in pediatric oncology patients and safety monitoring in terms of the potential value of JAS. Our assessment demonstrates that pediatric starting doses were safe for all 29 therapeutics examined in that no life-threatening toxicities occurred in the first cohort, and overall the ratio of the pediatric maximum tolerated dose (MTD) to the recommended adult dose was close to 1. In addition, the 4 serious adverse events (SAEs) that weren't detectable with standard monitoring plans for pediatric oncology trials would not have been detectable in a standard JAS. This review demonstrates that safe starting doses in pediatric oncology patients for these therapeutics could have been solely based on adult doses without any knowledge of findings in JAS.

Juvenile Animal Testing: Assessing Need and Use in the Drug Product Label

BACKGROUND

Juvenile animal testing has become an established part of drug development to support safe clinical use in the human pediatric population and for eventual drug product label use.

METHODS AND RESULTS

A review of European Paediatric Investigation Plan decisions showed that from 2007 to mid-2017, 229 drugs had juvenile animal work requested, almost exclusively incorporating general toxicology study designs, in rat (57.5%), dog (8%), mouse (4.5%), monkey (4%), pig (2%), sheep (1%), rabbit (1%), hamster (0.5%), and species not specified (21.5%). A range of therapeutic areas were found, but the most common areas were infectious diseases (15%), endocrinology (13.5%), oncology (13%), neurology (11%), and cardiovascular diseases (10%). Examination of major clinical indications within these therapeutic areas showed some level of consistency in the species of choice for testing and the pediatric age that required support. Examination of juvenile animal study findings presented in product labels raises questions around how useful the data are to allow prescribing the drug to a child.

CONCLUSION

It is hopeful that the new ICH S11 guideline "Nonclinical Safety Testing in Support of Development of Pediatric Medicines" currently in preparation will aid drug developers in clarifying the need for juvenile animal studies as well as in promoting a move away from toxicology studies with a conventional design. This would permit more focused testing to examine identified areas of toxicity or safety concerns and clarify the presentation/interpretation of juvenile animal study findings for proper risk assessment by a drug prescriber.

Neonatal and Juvenile Ocular Development in Sprague-Dawley Rats: A Histomorphological and Immunohistochemical Study

As in many altricial species, rats are born with fused eyelids and markedly underdeveloped eyes. While the normal histology of the eyes of mature rats is known, the histomorphological changes occurring during postnatal eye development in this species remain incompletely characterized. This study was conducted to describe the postnatal development of ocular structures in Sprague-Dawley (SD) rats during the first month of age using histology and immunohistochemistry (IHC). Both eyes were collected from 51 SD rats at 13 time points between postnatal day (PND)1 and PND30. Histologic examination of hematoxylin and eosin-stained sections was performed, as well as IHC for cleaved-caspase-3 and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) to evaluate apoptosis, and IHC for Ki-67 and phospho-histone-H3 to evaluate cell proliferation. Extensive ocular tissue remodeling occurred prior to the eyelid opening around PND14 and reflected the interplay between apoptosis and cell proliferation. Apoptosis was particularly remarkable in the maturing subcapsular anterior epithelium of the lens, the inner nuclear and ganglion cell layers of the developing retina, and the Harderian gland, and was involved in the regression of the hyaloid vasculature. Nuclear degradation in the newly formed secondary lens fibers was noteworthy after birth and was associated with TUNEL-positive nuclear remnants lining the lens organelle-free zone. Cell proliferation was marked in the developing retina, cornea, iris, ciliary body and Harderian gland. The rat eye reached histomorphological maturity at PND21 after a rapid phase of morphological changes characterized by the coexistence of cell death and proliferation.

An integrated approach to the safety assessment of food additives in early life

During the development of international standards by the Codex Alimentarius Commission, infant foods and their constituent ingredients are subject to rigorous risk analysis and are strictly regulated by many authorities. Various jurisdictions have approved only a limited number of additives specifically with regard to infant foods to fulfill specific technical requirements of quality. As part of the approval process, a rigorous safety assessment is essential to confirm that the use of additives does not pose any health risk for the consumer. An acceptable daily intake (ADI) may be derived from the toxicological databases. However, the ADI may not be applicable to infants because of the possible developmental sensitivities and potentially high exposure scenarios, leading to possible lower margins of safety than would often be determined for adult populations. There is interest in defining better food safety assessment approaches for pre-weaned infants aged less than 12–16 weeks. To confirm safe use in infants, we reviewed the suitability of the existing safety databases of six additives with historical uses in infant nutrition products. To determine further toxicity testing strategies, it is necessary to understand whether the chemical used in the additives is identical to endogenous physiological metabolites and/or whether immature organs of infants are targets of toxicity. Combined with an in-depth review of the existing relevant toxicological and nutritional studies, this integrated approach will facilitate decision-making. We propose a decision tree as a tool within this approach to help guide appropriate data requirements and identify data gaps. In cases of reasonable uncertainty, studies of targeted juvenile should be considered to investigate the safe use levels in food products.

Juvenile Toxicology: Relevance and Challenges for Toxicologists and Pathologists

The Society of Toxicologic Pathology (STP) Education Committee and the STP Reproductive Special Interest Group held a North Carolina regional meeting entitled, "Juvenile Toxicology: Relevance and Challenges for Toxicologists and Pathologists" on March 13, 2015, at the National Institute of Environmental Health Sciences/National Toxicology Program in Research Triangle Park, North Carolina. The purpose of this regional meeting was to familiarize attendees with the topic of juvenile toxicity testing and discuss its relevance to clinical pediatric medicine, regulatory perspectives, challenges of appropriate study design confronted by toxicologists, and challenges of histopathologic examination and interpretation of juvenile tissues faced by pathologists. The 1-day meeting was a success with over 60 attendees representing industry, government, research organizations, and academia.

Paediatric drug development: the impact of evolving regulations

Children deserve medicines that are adapted to their needs. The need to include children in drug development has been recognised increasingly over the past few decades. Legal and regulatory frameworks are well established in the EU and US. The amount of work done to study medicines for children is significantly greater than it was 10 years go. Proof-of-concept has been demonstrated for all segments of the paediatric drug development pipeline. It is now time to examine how the practice of developing medicines for children has evolved within those frameworks and to determine how that work should be generalised. This review describes the development of medicines for children and critically appraises the work that has been done within those frameworks. Significant effort is needed to realize the potential provided by the current regulatory framework. Using the work programme of the Global Research in Paediatrics (GRiP) Network of Excellence as a template we outline current work and future growing points.