NDLI: Phosphorylation of thymidine and AZT in heart mitochondria : Elucidation of a novel mechanism of AZT cardiotoxicity

Content Provider	Springer Nature Link
Author	McKee, Edward E. Bentley, Alice T. Hatch, Matthew Gingerich, Joel Susan Resiga, Delia
Copyright Year	2005
Abstract	Antiretroviral nucleoside analogs used in highly active antiretroviral therapy (HAART) are associated with cardiovascular and other tissue toxicity associated with mitochondrial DNA depletion, suggesting a block in mitochondrial (mt)-DNA replication. Because the triphosphate forms of these analogs variably inhibit mt-DNA polymerase this enzyme has been promoted as the major target of toxicity associated with HAART. We have used isolated mitochondria from rat heart to study the mitochondrial transport and phosphorylation of thymidine and AZT (azidothymidine, or zidovudine), a component used in HAART. We demonstrate that isolated mitochondria readity transport thymidine and phosphorylate it to thymidine 5′-triphosphate (TTP) within the matrix. Under identical conditions, AZT is phosphorylated only to AZT-5′-monophosphate (AZT-MP). The kinetics of thymidine and AZT agest negative cooperatively of substrate interaction with the enzyme, consistent with work by others on mitochondrial thymidine kinase 2. Results show that TMP and AZT-MP are not transported across the inner membrane, suggesting that AZT-MP may accumulate with time in the matrix. Given the lack of AZT-5′-triphosphate (AZT-TP), it seems unlikely that the toxicity of AZT in the heart is mediated by AZT-TP inhibition of DNA polymerase γ. Rather, our work shows that AZT is a potent inhibitor of thymidine phosphorylation in heart mitochondria, having an inhibitory concentration (IC)$_{50}$ of 7.0±0.9 μM. Thus, the toxicity of AZT in some tissues may be mediated by disrupting the substrate supply of TTP for mt-DNA replication.
Starting Page	155
Ending Page	167
Page Count	13
File Format	PDF
ISSN	15307905
Journal	Cardiovascular Toxicology
Volume Number	4
Issue Number	2
e-ISSN	15590259
Language	English
Publisher	Humana Press
Publisher Date	2005-01-01
Publisher Place	Totowa
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Heart mitochondria AZT cardiotoxicity thymidine kinase TMP kinase mitochondrial DNA depletion Pharmacology/Toxicology Cardiology
Content Type	Text
Resource Type	Article
Subject	Molecular Biology Toxicology Cardiology and Cardiovascular Medicine

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