Long-Term Exposure of Mice to Nucleoside Analogues Disrupts Mitochondrial DNA Maintenance in Cortical Neurons

Yulin Zhang,Xi Chen,Wei Ding,Sufang Yang,Ronghua Jin,Dexi Chen,Luxin Qiao,Ziyun Gao,Fengli Song,Sherine Swee Lin Chan

doi:10.1371/journal.pone.0085637

Abstract

Nucleoside analogue reverse transcriptase inhibitor (NRTI), an integral component of highly active antiretroviral therapy (HAART), was widely used to inhibit HIV replication. Long-term exposure to NRTIs can result in mitochondrial toxicity which manifests as lipoatrophy, lactic acidosis, cardiomyopathy and myopathy, as well as polyneuropathy. But the cerebral neurotoxicity of NRTIs is still not well known partly due to the restriction of blood-brain barrier (BBB) and the complex microenvironment of the central nervous system (CNS). In this study, the Balb/c mice were administered 50 mg/kg stavudine (D4T), 100 mg/kg zidovudine (AZT), 50 mg/kg lamivudine (3TC) or 50 mg/kg didanosine (DDI) per day by intraperitoneal injection, five days per week for one or four months, and primary cortical neurons were cultured and exposed to 25 µM D4T, 50 µM AZT, 25 µM 3TC or 25 µM DDI for seven days. Then, single neuron was captured from mouse cerebral cortical tissues by laser capture microdissection. Mitochondrial DNA (mtDNA) levels of the primary cultured cortical neurons, and captured neurons or glial cells, and the tissues of brains and livers and muscles were analyzed by relative quantitative real-time PCR. The data showed that mtDNA did not lose in both NRTIs exposed cultured neurons and one month NRTIs treated mouse brains. In four months NRTIs treated mice, brain mtDNA levels remained unchanged even if the mtDNA levels of liver (except for 3TC) and muscle significantly decreased. However, mtDNA deletion was significantly higher in the captured neurons from mtDNA unchanged brains. These results suggest that long-term exposure to NRTIs can result in mtDNA deletion in mouse cortical neurons.

Highlights

With the advent of highly active antiretroviral therapy (HAART), the incidence of human immunodeficiency virus (HIV) associated dementia (HAD) has drastically fallen, while the cumulative prevalence of HIV associated neurocognitive disorders (HAND) has risen [1]
Long-term exposure to Nucleoside analogue reverse transcriptase inhibitor (NRTI) can result in side effects similar to manifestations of a series of genetic mitochondria diseases, including lactic acidosis, hepatic steatosis, myopathy, pancreatitis, lipodystrophy, and probably polyneuropathy [7]
It was showed that mitochondria DNA (mtDNA) loss was found in the D4T exposed mouse livers and the 3TC exposed mouse muscles, the mitochondrial toxicity of other nucleoside analogue did not seem to reach the threshold of mtDNA loss in the livers and the muscles (Fig. 1A)

Summary

Introduction

With the advent of highly active antiretroviral therapy (HAART), the incidence of HIV associated dementia (HAD) has drastically fallen, while the cumulative prevalence of HIV associated neurocognitive disorders (HAND) has risen [1]. Cognitive impairment remained stable in one group of HAND patients, but progressive in other group even with effective antiretroviral treatment [5,6] It is still not well known whether this disparity is caused by increased survival of the virus in the brain or by antiretroviral agent neurotoxicity. Long-term exposure to NRTIs can result in side effects similar to manifestations of a series of genetic mitochondria diseases, including lactic acidosis, hepatic steatosis, (cardio-) myopathy, pancreatitis, lipodystrophy, and probably polyneuropathy [7] The mechanisms of these toxicities have been found to involve inhibition of DNA polymerase gamma leading to inhibition of mitochondria DNA (mtDNA) synthesis, resulting in oxidative stress and eventual mitochondrial dysfunction [8,9,10]. The cerebral neurotoxicity of NRTIs which is restricted by blood-brain barrier (BBB) and microenvironment of the central nervous system (CNS) is still not clear

Methods

Results

Conclusion