In vivo longitudinal micro-CT study of bent long limb bones in rat offspring

Evaluation of rat and rabbit embryofetal development studies with pharmaceuticals: the added value of a second species

Embryofetal development (EFD) studies are performed to characterize risk of drugs in pregnant women and on embryofetal development. In line with the ICH S5(R3) guideline, these studies are generally conducted in one rodent and one non-rodent species, commonly rats and rabbits. However, the added value of conducting EFD studies in two species to risk assessment is debatable. In this study, rat and rabbit EFD studies were evaluated to analyze the added value of a second species. Information on rat and rabbit EFD studies conducted for human pharmaceuticals submitted for marketing authorization to the European Medicines Agency between 2004 and 2022 was collected from the database of the Dutch Medicines Evaluation Board, along with EFD studies conducted for known human teratogens. In total, 369 compounds were included in the database. For 55.6% of the compounds similar effects were observed in rat and rabbit EFD studies. Discordance was observed for 44.6% of compounds. Discordance could often be explained based on occurrence of maternal toxicity or the compound's mechanism of action. For other compounds, discordance was considered of limited clinical relevance due to high exposure margins or less concerning EFD toxicity. For 6.2%, discordance could not be explained and was considered clinically relevant. Furthermore, for specific therapeutic classes, concordance between rat and rabbit could vary. In conclusion, in many cases the added value of conducting EFD studies in two species is limited. These data could help identify scenarios in which (additional) EFD studies could be waived or create a weight-of-evidence model to determine the need for (additional) EFD studies.

The ethanolic extract of Salvia lachnostachys Benth is not maternotoxic, does not alter reproductive performance, but has teratogenic potential

Salvia lachnostachys Benth is native to Brazil and has anti-inflammatory, anti-arthritic, cytotoxic, antitumor, and antihyperalgesic activities. The population, including pregnant women, consume this plant to treat pain, inflammation, flu, spasms, insomnia, and depression, mainly. There are no safety reports on the use of this plant during pregnancy. The present study aimed to evaluate the effects of S. lachnostachys ethanolic extract (EESl) on reproductive performance, embryofetal development, and DNA integrity of pregnant female mice. Pregnant females were randomly divided into three experimental groups (n = 10): The Control group was treated with a vehicle, and treatment groups were administered with EESl at 100 and 1000 mg/kg, respectively. Treatment occurred by gavage throughout the gestational period until day 18. Afterward, reproductive performance, embryofetal development, and DNA integrity parameters were evaluated. The results indicated that EESl did not alter any reproductive performance parameters. However, it changed embryofetal outcome through reduced placental weight (EESl 100 mg/kg), decreased fetal weight (EESl 100 and 1000 mg/kg), and increased frequency of small for gestational age fetuses (EESl 1000 mg/kg). In addition, EES1 increased the frequency of external, visceral, and skeletal malformations. Because of the above, it is considered that EESl is not maternotoxic, does not alter reproductive performance, but does alter embryofetal development. Its use in the gestational period is not indicated due to its teratogenic potential.

The postnatal resolution of developmental toxicity induced by pharmacological diacylglycerol acyltransferase 2 (DGAT2) inhibition during gestation in rats

Ervogastat (PF-06865571) is a small molecule diacylglycerol acyltransferase 2 (DGAT2) inhibitor being developed for the oral treatment of non-alcoholic steatohepatitis (NASH) with liver fibrosis. DGAT2 is a key enzyme in triglyceride synthesis in tissues and in regulating energy metabolism. Fertility and developmental toxicity studies with ervogastat were conducted in female rats and rabbits. There were no effects on female rat fertility or rabbit embryo-fetal development. Administration of ervogastat to pregnant rats during organogenesis reduced fetal weight and caused higher incidences of bent bones in fetuses that were shown to resolve by postnatal day 28 and were therefore considered to be transient variations secondary to developmental delay. Extended dosing in rats through the end of gestation and lactation (pre- and post-natal development study) caused impaired skin development, reduced offspring viability and growth retardation. The spectrum of developmental effects in rats is consistent with the intended pharmacology (altered triglyceride metabolism) and the transient nature of the skeletal findings, along with the late gestational window of sensitivity for the effects on skin barrier development, reduce the concern for potential adverse developmental effects following unintended early gestational exposure to ervogastat in humans where treatment can be discontinued once pregnancy is determined.

Digitalization of the IOM: A comprehensive cadaveric study for obtaining three-dimensional models and morphological properties of the forearm's interosseous membrane

State-of-the-art of preoperative planning for forearm orthopaedic surgeries is currently limited to simple bone procedures. The increasing interest of clinicians for more comprehensive analysis of complex pathologies often requires dynamic models, able to include the soft tissue influence into the preoperative process. Previous studies have shown that the interosseous membrane (IOM) influences forearm motion and stability, but due to the lack of morphological and biomechanical data, existing simulation models of the IOM are either too simple or clinically unreliable. This work aims to address this problematic by generating 3D morphological and tensile properties of the individual IOM structures. First, micro- and standard-CT acquisitions were performed on five fresh-frozen annotated cadaveric forearms for the generation of 3D models of the radius, ulna and each of the individual ligaments of the IOM. Afterwards, novel 3D methods were developed for the measurement of common morphological features, which were validated against established optical ex-vivo measurements. Finally, we investigated the individual tensile properties of each IOM ligament. The generated 3D morphological features can provide the basis for the future development of functional planning simulation of the forearm.

Bone development in laboratory mammals used in developmental toxicity studies

Evaluation of the skeleton in laboratory animals is a standard component of developmental toxicology testing. Standard methods of performing the evaluation have been established, and modification of the evaluation using imaging technologies is under development. The embryology of the rodent, rabbit, and primate skeleton has been characterized in detail and summarized herein. The rich literature on variations and malformations in skeletal development that can occur in the offspring of normal animals and animals exposed to test articles in toxicology studies is reviewed. These perturbations of skeletal development include ossification delays, alterations in number, shape, and size of ossification centers, and alterations in numbers of ribs and vertebrae. Because the skeleton is undergoing developmental changes at the time fetuses are evaluated in most study designs, transient delays in development can produce apparent findings of abnormal skeletal structure. The determination of whether a finding represents a permanent change in embryo development with adverse consequences for the organism is important in study interpretation. Knowledge of embryological processes and schedules can assist in interpretation of skeletal findings.

Proper Positioning and Restraint of a Rat Hind Limb for Focused High Resolution Imaging of Bone Micro-architecture Using In Vivo Micro-computed Tomography

The use of in vivo micro-computed tomography (µCT) is a powerful tool which involves the non-destructive imaging of internal structures at high resolutions in live animal models. This allows for repeated imaging of the same rodent over time. This feature not only reduces the total number of rodents required in an experimental design and thereby reduces the inter-subject variation that can arise, but also allows researchers to assess longitudinal or life-long responses to an intervention. To acquire high quality images that can be processed and analyzed to more accurately quantify outcomes of bone micro-architecture, users of in vivo µCT scanners must properly anesthetize the rat, and position and restrain the hind limb. To do this, it is imperative that the rat be anesthetized to a level of complete relaxation, and that pedal reflexes are lost. These guidelines may be modified for each individual rat, as the rate of isoflurane metabolism can vary depending on strain and body size. Proper technique for in vivo µCT image acquisition enables accurate and consistent measurement of bone micro-architecture within and across studies.

An Independent Active Contours Segmentation framework for bone micro-CT images

Micro-CT is an imaging technique for small tissues and objects that is gaining increased popularity especially as a pre-clinical application. Nevertheless, there is no well-established micro-CT segmentation method, while typical procedures lack sophistication and frequently require a degree of manual intervention, leading to errors and subjective results. To address these issues, a novel segmentation framework, called Independent Active Contours Segmentation (IACS), is proposed in this paper. The proposed IACS is based on two autonomous modules, namely automatic ROI extraction and IAC Evolution, which segments the ROI image using multiple Active Contours that evolve simultaneously and independently of one another. The proposed method is applied on a Phantom dataset and on real datasets. It is tested against several established segmentation methods that include Adaptive Thresholding, Otsu Thresholding, Region Growing, Chan-Vese (CV) AC, Geodesic AC and Automatic Local Ratio-CV AC, both qualitatively and quantitatively. The results prove its superior performance in terms of object identification capability, accuracy and robustness, under normal circumstances and under four types of artificially introduced noise. These enhancements can lead to more reliable analysis, better diagnostic procedures and treatment evaluation of several bone-related pathologies, and to the facilitation and further advancement of bone research.

Postnatal fate of prenatal-induced fetal alterations in laboratory animals

Currently it is common practice to evaluate the developmental toxicity hazard of chemicals or pharmaceuticals by evaluation of fetuses after administration of the compound to pregnant animals. These studies are designed to provide possible compound-related fetal changes near term, which are usually classified into malformations or variations. Malformations, but not variations are expected to adversely affect the survival or health. Therefore, classification has striking different regulatory consequences. For categorization as variation reversibility is an important criterion, but it is usually not examined in a standard guideline study. Although this issue has already been recognized long time ago, data dealing with the postnatal reversibility of fetal alterations are still rare. In the current review, literature data, regulatory documents as well as in-house data were compiled. Beside skeletal alterations of skull, vertebral column, ribs, shoulder and pelvic girdle, and extremities, kidney and heart defects are discussed and assessed.

Developmental Toxicity Studies with Pregabalin in Rats: Significance of Alterations in Skull Bone Morphology

Pregabalin was administered to pregnant Wistar rats during organogenesis to evaluate potential developmental toxicity. In an embryo‐fetal development study, compared with controls, fetuses from pregabalin‐treated rats exhibited increased incidence of jugal fused to maxilla (pregabalin 1250 and 2500 mg/kg) and fusion of the nasal sutures (pregabalin 2500 mg/kg). The alterations in skull development occurred in the presence of maternal toxicity (reduced body weight gain) and developmental toxicity (reduced fetal body weight and increased skeletal variations), and were initially classified as malformations. Subsequent investigative studies in pregnant rats treated with pregabalin during organogenesis confirmed the advanced jugal fused to maxilla, and fusion of the nasal sutures at cesarean section (gestation day/postmating day [PMD] 21) in pregabalin‐treated groups. In a study designed to evaluate progression of skull development, advanced jugal fused to maxilla and fusion of the nasal sutures was observed on PMD 20–25 and PMD 21–23, respectively (birth occurs approximately on PMD 22). On postnatal day (PND) 21, complete jugal fused to maxilla was observed in the majority of control and 2500 mg/kg offspring. No treatment‐related differences in the incidence of skull bone fusions occurred on PND 21, indicating no permanent adverse outcome. Based on the results of the investigative studies, and a review of historical data and scientific literature, the advanced skull bone fusions were reclassified as anatomic variations. Pregabalin was not teratogenic in rats under the conditions of these studies

Micro-CT imaging: Developing criteria for examining fetal skeletons in regulatory developmental toxicology studies - A workshop report

During the past two decades the use and refinements of imaging modalities have markedly increased making it possible to image embryos and fetuses used in pivotal nonclinical studies submitted to regulatory agencies. Implementing these technologies into the Good Laboratory Practice environment requires rigorous testing, validation, and documentation to ensure the reproducibility of data. A workshop on current practices and regulatory requirements was held with the goal of defining minimal criteria for the proper implementation of these technologies and subsequent submission to regulatory agencies. Micro-computed tomography (micro-CT) is especially well suited for high-throughput evaluations, and is gaining popularity to evaluate fetal skeletons to assess the potential developmental toxicity of test agents. This workshop was convened to help scientists in the developmental toxicology field understand and apply micro-CT technology to nonclinical toxicology studies and facilitate the regulatory acceptance of imaging data. Presentations and workshop discussions covered: (1) principles of micro-CT fetal imaging; (2) concordance of findings with conventional skeletal evaluations; and (3) regulatory requirements for validating the system. Establishing these requirements for micro-CT examination can provide a path forward for laboratories considering implementing this technology and provide regulatory agencies with a basis to consider the acceptability of data generated via this technology.

Relationship between bent long bones, bent scapulae, and wavy ribs: malformations or variations?

BACKGROUND

Shortened and bent long bones and bent scapulae are sometimes reported in fetuses with wavy ribs (Carney and Kimmel, ). Wavy ribs are typically seen in the presence of maternal and developmental toxicity, are transient and reversible postnatally, and are considered to be variations rather than malformations.

METHODS

We further assessed the literature cited in Kimmel and Carney () as well as papers published since then to determine under what conditions bent long bones in the absence of gross limb defects and bent scapulae were reported and whether information was available on the transient or permanent nature of these effects.

RESULTS

Long bone and/or scapular changes almost always occurred at a lower incidence than wavy ribs. In every case, maternal and fetal toxicity occurred at the same dose levels. In a few studies, pups were followed sequentially after birth and bent long bones and scapulae were transient in nature and appeared normal by the time of weaning. Rabbits were much less likely to show wavy ribs or long bone and scapular changes at birth, even in the presence of severe maternal and fetal toxicity. This species difference may be due in part to the great increase in bone mass and remodeling that occurs during the first few postnatal weeks in rodents, but which takes place during the longer fetal period in rabbits.

CONCLUSION

Our conclusion from this review is that bent long bones and scapulae, like wavy ribs, appear to be secondary to maternal and developmental toxicity, are transient, and like wavy ribs should be considered variations rather than malformations.

Comparison of Faxitron™ versus MicroCT imaging of the skeleton of the suckling rat

Currently, in pre and postnatal development studies or in juvenile rat studies, bone growth is assessed "for cause" by simple measurements of long bone length in vivo and at termination. This manuscript compares two radiographic methods for in vivo assessment of long bones in suckling rats; 2D imaging using a Faxitron™ and 3D imaging using μCT. This paper illustrates that it is possible to image the unanaesthetised postnatal day 1 rat by Faxitron™ using a simple Micropore™ tape restraint method. With isoflurane anaesthesia, it was possible to obtain high quality μCT images of pups from day of birth. No pups were rejected by their mothers following either technique. The Faxitron™ was straightforward and fast, however the μCT 3D images were of greater overall utility. Either method could be used for longitudinal investigation of long bone observations made previously in embryofetal development studies, or for other mechanistic work.

Imaging and morphology in reproductive toxicology - progress to date and future directions

This review looks at the recent development and application of imaging techniques for the morphological examination of fetuses from preclinical regulatory reproductive toxicology studies. Full replacement of the examination methods currently used in routine studies (microdissection, Bouin's fluid fixation/sectioning and alizarin red S/alcian blue preparations) by imaging techniques has yet to be achieved. Progress, especially in the application of micro-CT for skeletal examination, has been made but challenges, particularly the financial investment required, remain. Despite this apparent lack of progress the application of imaging techniques to "non-routine" preclinical reproductive toxicology studies has been used to good effect. The ability to acquire multiple images over a time course i.e. longitudinally has enabled the fate, particularly of skeletal features, to be determined. The additional evidence gained from such studies can be used to better inform the prenatal developmental hazard assessment of test compounds.