The effects of co-administration of antiretroviral drugs and/or topiramate on the migration of neural crest cells and neurogenesis in avian brains
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.
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