TY - JOUR
T1 - 3′-Azido-3′-deoxythymidine (AZT) is a competitive inhibitor of thymidine phosphorylation in isolated rat heart and liver mitochondria
AU - Lynx, Matthew D.
AU - McKee, Edward E.
N1 - Funding Information:
This work is supported by a pre-doctoral fellowship from the American Heart Association Greater Midwest Affiliate to M.D.L. and by a grant from the National Institute of Health, HL 72710 to E.E.M.
PY - 2006/7/14
Y1 - 2006/7/14
N2 - Long-term use of 3′-azido-3′-deoxythymidine (AZT) is associated with various tissue toxicities, including hepatotoxicity and cardiomyopathy, and with mitochondrial DNA depletion. AZT-5′-triphosphate (AZTTP) is a known inhibitor of the mitochondrial DNA polymerase γ and has been targeted as the source of the mitochondrial DNA depletion. However, in previous work from this laboratory with isolated rat heart and liver mitochondria, AZT itself was shown to be a more potent inhibitor of thymidine phosphorylation (IC50 of 7.0 ± 1.0 μM AZT in heart mitochondria and of 14.4 ± 2.6 μM AZT in liver mitochondria) than AZTTP is of polymerase γ (IC50 of >100 μM AZTTP), suggesting that depletion of mitochondrial stores of TTP may limit replication and could be the cause of the mitochondrial DNA depletion observed in tissues affected by AZT toxicity. The purpose of this work is to characterize the nature of AZT inhibition of thymidine phosphorylation in isolated rat heart and rat liver mitochondria. In both of these tissues, AZT was found to be a competitive inhibitor of the phosphorylation of thymidine to TMP, catalyzed by thymidine kinase 2. The inhibition constant (Ki) for heart mitochondria is 10.6 ± 4.5 μM AZT, and for liver mitochondria Ki is 14.0 ± 2.5 μM AZT. Since AZT is functioning as a competitive inhibitor, increasing thymidine concentrations may be one mechanism to overcome the inhibition and decrease AZT-related toxicity in these tissues.
AB - Long-term use of 3′-azido-3′-deoxythymidine (AZT) is associated with various tissue toxicities, including hepatotoxicity and cardiomyopathy, and with mitochondrial DNA depletion. AZT-5′-triphosphate (AZTTP) is a known inhibitor of the mitochondrial DNA polymerase γ and has been targeted as the source of the mitochondrial DNA depletion. However, in previous work from this laboratory with isolated rat heart and liver mitochondria, AZT itself was shown to be a more potent inhibitor of thymidine phosphorylation (IC50 of 7.0 ± 1.0 μM AZT in heart mitochondria and of 14.4 ± 2.6 μM AZT in liver mitochondria) than AZTTP is of polymerase γ (IC50 of >100 μM AZTTP), suggesting that depletion of mitochondrial stores of TTP may limit replication and could be the cause of the mitochondrial DNA depletion observed in tissues affected by AZT toxicity. The purpose of this work is to characterize the nature of AZT inhibition of thymidine phosphorylation in isolated rat heart and rat liver mitochondria. In both of these tissues, AZT was found to be a competitive inhibitor of the phosphorylation of thymidine to TMP, catalyzed by thymidine kinase 2. The inhibition constant (Ki) for heart mitochondria is 10.6 ± 4.5 μM AZT, and for liver mitochondria Ki is 14.0 ± 2.5 μM AZT. Since AZT is functioning as a competitive inhibitor, increasing thymidine concentrations may be one mechanism to overcome the inhibition and decrease AZT-related toxicity in these tissues.
KW - AZT
KW - Competitive inhibition
KW - Mitochondrial toxicity
KW - Nucleoside reverse transcriptase inhibitors (NRTIs)
KW - Thymidine
KW - Thymidine kinase 2
UR - http://www.scopus.com/inward/record.url?scp=33744915313&partnerID=8YFLogxK
U2 - 10.1016/j.bcp.2006.04.004
DO - 10.1016/j.bcp.2006.04.004
M3 - Article
C2 - 16720018
AN - SCOPUS:33744915313
SN - 0006-2952
VL - 72
SP - 239
EP - 243
JO - Biochemical Pharmacology
JF - Biochemical Pharmacology
IS - 2
ER -