Background:  Nucleoside reverse transcriptase inhibitors (NRTIs), such as zidovudine (AZT), are an integral component of HAART therapy.  We have previously reported that AZT treatment of mice results in abnormal endothelium dependent relaxation.  NRTI-mediated oxidative damage has been reported in both the heart and skeletal muscle.  Generation of reactive oxygen species may have significant effects on the availability of NO for endothelium-dependent relaxation and therefore result in impaired endothelium-dependent relaxation.  The present study tests the hypothesis that the effects of AZT on endothelium-dependent relaxation are related to increased superoxide generation.

Methods:  Free radical generation was examined in both ex vivo isolated aorta preparations and in vivo cellular preparations.  Ex vivo functional assays of contraction and relaxation were performed on isolated mouse aorta segments obtained from FVB/n wild-type mice exposed to AZT (100 mg/kg/day) or water for 35 days.  In vitro studies utilized electron spin resonance to examine superoxide dismutase-inhibitable production of superoxide in cells exposed to AZT (1 mM) or media  for 7 and 14 days.

Results:  AZT-treatment significantly reduced aortic sensitivity to the endothelium-dependent vasorelaxant acetylcholine (E.C.₅₀= 22.3 ± 1.7 vs 49.4 ± 4.5 nM in WT and WT+AZT respectively).  Addition of tiron (1 mM), a free radical scavenger, eliminated the difference in endothelium-dependent relaxation produced by AZT in WT mice (E.C.50=27.4 ± 5.5 nM).  Exposure of BAECs to AZT for 7 days did not affect superoxide production. However, exposure of BAECs to AZT for 14 days resulted in a significant increase in superoxide production.

Conclusions:  These results demonstrate that prolonged AZT exposure increases endothelial superoxide production.  The increase in superoxide production results in impaired endothelium-dependent relaxation.  These results indicate that AZT alters arterial function and suggest that NRTI therapy may contribute to cardiovascular complications in AIDS.