Differential Effects of Antiretroviral Nucleoside Analogs on Mitochondrial Function in HepG2 Cells

Abstract

Numerous studies have reported effects of antiviral nucleoside analogs on mitochondrial function, but they have not correlated well with the observed toxic side effects. By comparing the effects of the five Food and Drug Administration-approved anti-human immunodeficiency virus nucleoside analogs, zidovudine (3-azido-3-deoxythymidine) (AZT), 2,3-dideoxycytidine (ddC), 2,3-dideoxyinosine (ddI), 2,3-didehydro-2,3-deoxythymidine (d4T), and ␤-L-2,3-dideoxy-3-thiacytidine (3TC), as well as the metabolite of AZT, 3-amino-3-deoxythymidine (AMT), on mitochondrial function in a human hepatoma cell line, this issue has been reexamined. Evidence for a number of mitochondrial defects with AZT, ddC, and ddI was found, but only AZT induced a marked rise in lactic acid levels. Only in mitochondria isolated from AZT (50 M)-treated cells was significant inhibition of cytochrome c oxidase and citrate synthase found. Our investigations also demonstrated that AZT, d4T, and 3TC did not affect the synthesis of the 11 polypeptides encoded by mitochondrial DNA, while ddC caused 70% reduction of total polypeptide content and ddI reduced by 43% the total content of 8 polypeptides (including NADH dehydrogenase subunits 1, 2, 4, and 5, cytochrome c oxidase subunits I to III, and cytochrome b). We hypothesize that in hepatocytes the reserve capacity for mitochondrial respiration is such that inhibition of respiratory enzymes is unlikely to become critical. In contrast, the combined inhibition of the citric acid cycle and electron transport greatly enhances the dependence of the cell on glycolysis and may explain why apparent mitochondrial dysfunction is more prevalent with AZT treatment.

3′-Azido-3′-deoxythymidine (AZT) inhibits thymidine phosphorylation in isolated rat liver mitochondria: A possible mechanism of AZT hepatotoxicity

“…Subsequent work in HIV negative rat models treated with AZT confirmed the presence of the same type of toxicities in the rat [11,15]. Cytotoxicity of AZT has also been shown in a variety of transformed cells, including the HepG2 cell line [10,22,27]. In all cases, the toxicity of AZT was correlated with abnormal mitochondria and mitochondrial DNA depletion, when examined.…”

Human UMP-CMP Kinase 2, a Novel Nucleoside Monophosphate Kinase Localized in Mitochondria

“…Antiretroviral or anticancer deoxynucleoside analogs can cause mtDNA depletion and lead to mitochondria dysfunction after long term treatment (20,21). Mutations or deletion of either TK2 or dGK result in myopathic or hepatocerebral forms of mtDNA depletion syndromes (MDS) (22)(23)(24)(25)(26).…”

Antiviral β-L-nucleosides specific for hepatitis B virus infection

“…This nucleoside analogrelated cellular toxicity has been attributed to decreased mtDNA content and altered mitochondrial function, leading to increased lactic acid production (5, 9-12, 28, 35). Concomitant morphological changes in mitochondria (e.g., loss of cristae, matrix dissolution and swelling, and lipid droplet formation) can be observed with ultrastructural analysis using transmission electron microscopy (10,29,35). In HepG2 cells incubated with 10 M fialuridine (FIAU; 1,2Ј-deoxy-2Ј-fluoro-1-␤-D-arabinofuranosly-5-iodo-uracil), a substantial increase in lactic acid production was observed (data not shown).…”