Mitochondrial Oxidative Damage, Base-Excision Repair, and Antiretroviral Therapy

Abstract

Antiretroviral therapy (ART) has been enabling patients with HIV/AIDS to live longer and healthier, but do cause a number of side effects, including renal and hepatic toxicity, neural dysfunction, and metabolic disorders such as insulin resistance. Complications from ART can be attributed in large part to mitochondrial dysfunction, with decreased oxidative phosphorylation (OXPHOS) and increased oxidative stress, including mitochondrial DNA (mtDNA) oxidative damage. MtDNA damage can be repaired by several mechanisms including base-excision repair (BER), but whether BER is affected by or involved in HIV or ART-associated mitochondrial toxicity has not yet been evaluated. In this study, three BER enzymes (OGG1, MutYH, and FEN1) and their relationship to mitochondrial function and mtDNA oxidative damage during ART were investigated. First, BER enzyme mRNA levels were evaluated in peripheral blood mononuclear cells (PBMCs) from HIV-negative individuals and HIV-positive, ART-naïve patients at baseline and after receiving ART for 72 weeks (Chapter 2). Next, an in vitro model was developed to study ART-induced effects on BER during nephrotoxicity by treating primary human renal cells with protease inhibitor (PI)-based drug cocktails (Chapter 3). The hypothesis to be tested was that ART- induced mtDNA oxidative damage would lead to an increase in BER enzyme expression, and that higher levels of BER enzymes will be associated with decreased mitochondrial function. In the clinical study, mtDNA oxidative damage was higher in HIV-positive, ART-naïve patients than the HIV-negative participants, while mtDNA content, oxidative phosphorylation (OXPHOS) activity, and MutYH mRNA were lower in HIV patients at baseline. After 72 weeks of ART, these parameters improved. OGG1 and FEN1 mRNA correlated with mtDNA oxidative damage in HIV-negative individuals, but not in HIV-positive, ART-naïve patients. FEN1 mRNA decreased in HIV patients following ART initiation, and those with lower FEN1 levels at baseline showed a greater improvement in mtDNA oxidative damage than those with higher baseline FEN1. In the in vitro study, non-mitochondrial respiration and electron transport chain (ETC) proton leak were elevated in ART-treated cells, while both mtDNA oxidative damage and OGG1 mRNA increased during treatment. These results demonstrate that BER is affected by both HIV infection and ART, and the relationship between FEN1 expression and patient outcome could have implications for better personalized ART regimens in the future.