Thalidomide upper limb embryopathy - pathogenesis, past and present management and future considerations

Cereblon E3 ligase complex genes are expressed in tissues sensitive to thalidomide in chicken and zebrafish embryos but are unchanged following thalidomide exposure

Thalidomide is an infamous drug used initially as a sedative until it was tragically discovered it has highly teratogenic properties. Despite this it is now being used to successfully treat a range of clinical conditions including erythema nodosum leprosum (ENL) and multiple myeloma (MM). Cereblon (CRBN), a ubiquitin ligase, is a binding target of thalidomide for both its therapeutic and teratogenic activities and forms part of an CRL4-E3 ubiquitin ligase complex with the proteins Damaged DNA Binding protein 1 (DDB1) and Cullin-4A (CUL4A). This complex mediates degradation of the zinc-finger transcription factors Ikaros (IKZF1) and Aiolos (IKZF3), to mediate thalidomide's anti-myeloma response. To better understand the importance of CRBN and its binding partners for thalidomide teratogenesis here we analysed the expression patterns of CRBN and some of its known E3 complex binding partners in wildtype and thalidomide-treated chicken and zebrafish embryos. CRBN and DDB1 are expressed in many tissues throughout development including those that are thalidomide-sensitive while CUL4A and targets of the CRL4-CRBN E3 Ligase Complex IKZF1 and IKZF3 are expressed at different timepoints and in fewer tissues in the body than CRBN. Furthermore, IKZF3 is expressed in tissues of the eye that CRBN is not. However, although we observed rapid changes to the chicken yolk-sac membrane vasculature following thalidomide exposure, we did not detect CRL4-CRBN E3 Ligase Complex expression in the yolk-sac membrane vessels. Furthermore, we did not detect any changes in CRBN, DDB1, CUL4, IKZF1 and IKZF3 expression following thalidomide exposure in chicken and zebrafish embryos. These findings demonstrate that the anti-angiogenic activities of thalidomide may occur independent of CRBN and that thalidomide does not regulate CRL4-CRBN E3 Ligase Complex gene expression at the mRNA level.

Embryonic Vascular Dysgenesis: The Origin of Proximal Femoral Focal Deficiency

BACKGROUND

Proximal Femoral Focal Deficiency (PFFD) is the most proximal manifestation of a syndrome involving Congenitally Shortened lower Limbs (CSL), which also affects the fibula and midline metatarsals. This pattern of congenital human long bone deficiencies corresponds, in a time dependent manner, to the failed ingrowth pathways of new blood vessels of the growing embryonic limb. The distal femoral condyles are, in contrast, served by an alternative vascular supply from around the knee joint, and so remain resistant to the CSL deficiency.

AIM

We hypothesize that embryonic vascular dysgenesis causes PFFD, as well as the cardinal features of the Femoral, Fibular and midline Metatarsal deficiencies (FFM) syndrome.

RESULTS

Arteriography of CSL with PFFD reveals diminution or failed formation of the Femoral Artery (FA), which corresponds to downstream skeletal reductions. It may also reveal preservation of the primitive Axial Artery (AA) of the embryonic limb. The combination of missing and retained primitive vessels inform the time, place, and nature of the etiologic vascular events. This suggests that PFFD is the visible expression of a normally prefigured cartilaginous scaffold of the femur, which develops in conformity with the available pattern of blood vessels present. The teratogen thalidomide, known to affect the forming embryonic vasculature, also produces PFFD indistinguishable from the naturally occurring entity.

CONCLUSION

The entire spectrum of PFFD, including phocomelia, fibular, and metatarsal dystrophisms, should thus be regarded as downstream skeletal results of embryonic arterial dysgeneses.

Embryonic development grand challenge: crosslinking advances

Research on embryonic development is entering into a new era. As a traditionally descriptive discipline within anatomy, embryologists have formed international consortia and digitized important histological collections for preservation and open access. Embryonic development has recently received a wider attention in context with temporo-spatial transcriptomics at single cell level. These can be expected to fuel the realization of the transdisciplinary significance of efforts to decipher embryonic development. Addressing its complexities encompasses a wealth of challenges that intersect across the domains of science, society, and politics underlining its outstanding importance as well as its inherently interdisciplinary nature. The challenges of this field are by no means confined to understanding the intricate biological mechanisms but also have humanitarian implications. To fully appreciate the mechanisms underlying human development, principles of embryogenesis have predominantly been analyzed employing animal models which allow us to broaden our view on developmental processes. As a result of recent pioneering work and technical progress centered around stem cell-based 3D approaches, we are entering into a historical new phase of learning about mammalian embryonic development. In vertebrates, a growing concern now focuses the reduction of animal experimentation. This perspective article outlines the major challenges in this amazing field that offer an enormous potential for basic biomedical sciences as well as related translational approaches if they are tackled in a multidisciplinary discourse.

Perspectives on chick embryo models in developmental and reproductive toxicity screening

Teratology, the study of congenital anomalies and their causative factors intersects with developmental and reproductive toxicology, employing innovative methodologies. Evaluating the potential impacts of teratogens on fetal development and assessing human risk is an essential prerequisite in preclinical research. The chicken embryo model has emerged as a powerful tool for understanding human embryonic development due to its remarkable resemblance to humans. This model offers a unique platform for investigating the effects of substances on developing embryos, employing techniques such as ex ovo and in ovo assays, chorioallantoic membrane assays, and embryonic culture techniques. The advantages of chicken embryonic models include their accessibility, cost-effectiveness, and biological relevance to vertebrate development, enabling efficient screening of developmental toxicity. However, these models have limitations, such as the absence of a placenta and maternal metabolism, impacting the study of nutrient exchange and hormone regulation. Despite these limitations, understanding and mitigating the challenges posed by the absence of a placenta and maternal metabolism are critical for maximizing the utility of the chick embryo model in developmental toxicity testing. Indeed, the insights gained from utilizing these assays and their constraints can significantly contribute to our understanding of the developmental impacts of various agents. This review underscores the utilization of chicken embryonic models in developmental toxicity testing, highlighting their advantages and disadvantages by addressing the challenges posed by their physiological differences from mammalian systems.

Teratogenicity and Reactive Oxygen Species after transient embryonic hypoxia: Experimental and clinical evidence with focus on drugs causing failed abortion in humans

Teratogenicity and Reactive Oxygen Species after transient embryonic hypoxia: Experimental and clinical evidence with focus on drugs with human abortive potential. Reactive Oxygen Species (ROS) can be harmful to embryonic tissues. The adverse embryonic effects are dependent on the severity and duration of the hypoxic event and when during organongenesis hypoxia occurs. The vascular endothelium of recently formed arteries in the embryo is highly susceptible to ROS damage. Endothelial damage results in vascular disruption, hemorrhage and maldevelopment of organs, which normally should have been supplied by the artery. ROS can also induce irregular heart rhythm in the embryo resulting in alterations in blood flow and pressure from when the tubular heart starts beating. Such alterations in blood flow and pressure during cardiogenesis can result in a variety of cardiovascular defects, for example transpositions and ventricular septal defects. One aim of this article is to review and compare the pattern of malformations produced by transient embryonic hypoxia of various origins in animal studies with malformations associated with transient embryonic hypoxia in human pregnancy due to a failed abortion process. The results show that transient hypoxia and compounds with potential to cause failed abortion in humans, such as misoprostol and hormone pregnancy tests (HPTs) like Primodos, have been associated with a similar spectrum of teratogenicity. The spectrum includes limb reduction-, cardiovascular- and central nervous system defects. The hypoxia-ROS related teratogenicity of misoprostol and HPTs, is likely to be secondary to uterine contractions and compression of uterinoplacental/embryonic vessels during organogenesis.