Abstract:
Chronic HIV treatment with antiretroviral drugs has been associated with adverse health
outcomes. Mitochondrial toxicity exhibited by nucleoside reverse transcriptase inhibitors
(NRTIs) is pinpointed as a molecular mechanism of toxicity. This study evaluated the effect
of NRTIs: Zidovudine (AZT, 7.1 μM), Stavudine (d4T, 4 μM) and Tenofovir (TFV, 1.2 μM),
on mitochondrial (mt) stress response, mtDNA integrity and oxidative stress response in
human hepatoma cells at 24 and 120 h. Markers for mt function, mt biogenesis, oxidative
stress parameters, and antioxidant response were evaluated by spectrophotometry,
luminometry, flow cytometry, qPCR and western blots. We found that AZT and d4T reduced
mtDNA integrity (120 h, AZT: 76.1%; d4T:36.1%, P < 0.05) and remained unchanged with
TFV. All three NRTIs, however, reduced ATP levels (AZT: 38%; d4T: 56.4%; TFV: 27.4%,
P = 0.01) and mt membrane potential at 120 h (P < 0.005). Oxidative damage and reactive
oxygen species (ROS) were increased by TFV and AZT at 24 h, and by d4T at 120 h (P
< 0.05). Antioxidant response molecules and mt biogenesis markers were elevated by all
NRTIs, with TFV causing the most significant increase (P < 0.05). Data from this study
suggest that AZT, d4T and TFV alter mt function. TFV, however, achieves this
independently of mtDNA depletion. Furthermore, AZT exerts toxicity soon after exposure as
noted from changes at 24 h and d4T exerts greater toxicity over prolonged exposure (120 h).
