The effects of co-administration of antiretroviral drugs and/or topiramate on the migration of neural crest cells and neurogenesis in avian brains
Date
2021
Authors
Tshabalala, Thabiso
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Abstract
The administration of combination antiretroviral drugs (cART) during pregnancy has been shown
to cause a myriad of congenital malformations. Birth defects such as cleft lip and palate, ventricular
septal defect, neuronal migration disorders and hydrocephalus have been observed in children
born to women who are on antiretroviral therapy. However, the mechanism of teratogenicity is
unclear and therefore the focus of this study. Some HIV patients on antiretrovirals develop seizures
and are therefore placed on antiepileptic drugs such as topiramate, which is also teratogenic. The
interactive effects arising from this therapeutic combination may affect their teratogenic propensity.
Due to the involvement of cranial and cardiac neural crest cells in the formation of craniofacial and
cardiovascular structures, the current study investigated the effect of cART and topiramate on the
migration of these two populations of cells. The extent of migration as well as proliferation of neural
tube-derived neurons was determined in order to investigate the mechanisms of neuronal migration
disorders. In addition, the study investigated the effects of cART and topiramate on the expression
of aquaporin 4 during Gallus gallus brain development due to the major role played by this gene in
the transportation of water in the brain. Appropriately cultured neural crest cells from dissected
neural tubes of 32 (cardiac) and 36-hour old (cranial) quail embryos exposed to culture media
containing peak plasma levels of Atripla, Topiramate and the combination of both were studied.
The migration of neural crest cells was determined using the migration assay and the cells were
stained with rhodamine phalloidin to evaluate the cell actin. In addition, cardiac quail neural crest
cells were brought into suspension and micro-injected into chick hosts to determine the migration
of the cells to the interventricular septum. The differentiation of cranial neural crest cells into
melanocytes, osteoblasts and neurites was also evaluated. Neural tube-derived neurons were
stained with DCX, while the expression of Rac and Rho were determined using quantitative PCR.
The expression of AQP4 and Ribosomal protein S17 was investigated using quantitative PCR. The
administration of cART and topiramate inhibited the migration of both cardiac and cranial neural
crest cells while it downregulated the expression of DCX and the Rac genes in neural tube-derived
neurons and induced the aquaporin 4 expression in early developing brain. These findings indicate
that cART and Topiramate cause ventricular septal defects and craniofacial anomalies by inhibiting
the migration of neural crest cells while they cause neuronal migration disorders and hydrocephalus
by inhibiting the migration of neurons and by inducing the expression of aquaporin 4 respectively.
In addition, these findings show that cART and Topiramate inhibit the migration of both cardiac and
cranial neural crest cells when administered individually and in combination. The combination with
Topiramate showed that Topiramate does not inhibit the activity of cART in most instances. These
results suggest that the combination of cART and Topiramate may be ideal for patients who require
treatment with antiretrovirals and antiepileptic drugs.
Description
A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Health Sciences, School of Anatomical Sciences, University of the Witwatersrand, Johannesburg, 2021