Evaluating Neurodevelopmental Consequences of Perinatal Exposure to Antiretroviral Drugs: Current Challenges and New Approaches

As antiretroviral therapy (ART) becomes increasingly affordable and accessible to women of childbearing age across the globe, the number of children who are exposed to Human Immunodeficiency Viruses (HIV) but remain uninfected is on the rise, almost all of whom were also exposed to ART perinatally. Although ART has successfully aided in the decline of mother-to-child-transmission of HIV, the long-term effects of in utero exposure to ART on fetal and postnatal neurodevelopment remain unclear. Evaluating the safety and efficacy of therapeutic drugs for pregnant women is a challenge due to the historic limitations on their inclusion in clinical trials and the dynamic physiological states during pregnancy that can alter the pharmacokinetics of drug metabolism and fetal drug exposure. Thus, much of our data on the potential consequences of ART drugs on the developing nervous system comes from preclinical animal models and clinical observational studies. In this review, we will discuss the current state of knowledge and existing approaches to investigate whether ART affects fetal brain development, and describe novel human stem cell-based strategies that may provide additional information to better predict the impact of specific drugs on the human central nervous system. Graphical Abstract Approaches to evaluate the impact of drugs on the developing brain. Dysregulation of the developing nervous system can lead to long-lasting changes. Integration of data from animal models, clinical observations, and cell culture studies is needed to predict the safety of therapeutic antiretroviral drugs during pregnancy. New approaches include human induced pluripotent stem cell (iPSC)-based 2D and 3D models of neuronal networks and brain regions, as well as single cell profiling in response to drug exposure.

Mutational analysis of the mitochondrial tRNA genes and flanking regions in umbilical cord tissue from uninfected infants receiving AZT-based therapies for prophylaxis of HIV-1

A sensitive vertical denaturing gradient gel electrophoresis (DGGE) method, using 13 unipolar psoralen-clamped PCR primer pairs, was developed for detecting sequence variants in the 22 tRNA genes and flanking regions (together spanning approximately 21%) of the human mitochondrial genome. A study was conducted to determine (i) if mitochondrial DNA (mtDNA) polymorphisms and/or mutations were detectable in healthy newborns and (ii) if prepartum 3'-azido-2',3'-dideoxythymidine (AZT) based HIV-1 prophylaxis was associated with significant increases in mtDNA mutations and changes in the degree of heteroplasmy of sequence variants in uninfected infants born to HIV-1-infected mothers. DGGE analysis of umbilical cord tissue (where vascular endothelium and smooth muscle cells are the major source of mtDNA) showed that mtDNA sequence variants were significantly elevated by threefold in AZT-treated infants compared with unexposed controls (P < 0.001), with 24 changes observed in 19/52 (37%) treated newborns (averaging 0.46 changes/subject) versus only eight changes found in 7/55 (13%) unexposed newborns (averaging 0.15 changes/subject). Six distinct sequence variants occurring in unexposed controls were predominately synonymous and homoplasmic, representing previously reported polymorphisms. Uninfected infants exposed to a combination of AZT and 2',3'-dideoxy-3'-thiacytidine and "maternal HIV-1" had a significant shift in the spectrum of mutations (P = 0.04) driven by increases in nonsynonymous heteroplasmic sequence variants at polymorphic sites (10 distinct variants) and novel sites (four distinct variants). While the weight of evidence suggests that prepartum AZT-based prophylaxis produces mtDNA mutations, additional research is needed to determine the degree to which fetal responses to maternal HIV-1 infection, in the absence of antiretroviral treatment, contribute to prenatal mtDNA mutagenesis.

Relationship of Mitochondrial DNA Depletion and Respiratory Chain Activity in Preadipocytes treated with Nucleoside Reverse Transcriptase Inhibitors

Objective

To study the impact of adipocyte differentiation on nucleoside reverse transcriptase inhibitor (NRTI)-mediated mitochondrial DNA (mtDNA) depletion and to correlate mtDNA depletion with the activity of the respiratory chain complexes.

Methods

We studied adipocyte phenotype, viability, differentiation (CCAAT/enhancer-binding protein [C/EBP]-α and peroxisome proliferator-activated receptor [PPAR]-γ expression), adiponectin production, mtDNA content, activity of respiratory chain complexes and citrate synthase activity in 3T3–L1 adipocytes. Cells were exposed to zidovudine (6 μM or 180 μM), stavudine (3 μM or 90 μM), and zalcitabine (0.1 μM or 3 μM) at different developmental stages for up to 2 months.

Results

Zidovudine and stavudine impaired adiponectin production in vitro at therapeutic Cmax concentrations, but none of the tested NRTIs had a negative impact on adipocyte differentiation or led to mtDNA depletion at these concentrations. Susceptibility of preadipocytes to mtDNA depletion was dependent on cell proliferation and differentiation, and mtDNA depletion occurred only after exposure to high drug concentrations. Under these conditions, stavudine led to up to 80% mtDNA depletion in both dividing and differentiating preadipocytes, whereas zidovudine affected mtDNA only in the differentiating cells. Despite mtDNA depletion by NRTIs, activity of the respiratory chain complexes was found to be unimpaired.

Conclusions

We found mtDNA depletion in adipocytes but proliferation and/or differentiation of the cells seems to be a prerequisite for this phenomenon. Depletion of mtDNA up to 80%, however, was not associated with impaired respiratory chain activity in 3T3-L1 preadipocytes.