Background:  Long-term NRTI therapy often leads to lipoatrophy. Although NRTI may inhibit adipocyte DNA polymerase-g, affecting mitochondrial (mt) replication and oxidative phosphorylation, published data are contradictory and it is unclear whether mtDNA depletion is the primary defect in NRTI-induced toxicity.

Methods:  We completed a prospective, randomized trial in 20 HIV^- healthy adults receiving d4T/3TC or AZT/3TC for 6 weeks followed by 6-weeks’ washout. Primary endpoint was change in expression of metabolism genes in adipocytes. Assessments included clinical history, fasting biochemistry, lipids, oral glucose tolerance tests, whole body DEXA, and 3-slice abdominal computerized tomography. Adipose tissue (flank) biopsies were performed at weeks 0 and 2, RNA extracted and real-time RT-PCR performed using primers for mitochondrial genes COX1, COX3, and cytochrome-b, and nuclear genes SREBP1 and PPARg. Results are expressed as ratios of gene expression to b-actin expression. Non-parametric analyses were applied.

Results:  Median age was 41 years (IQR 14.5) and 90% of subjects were male. Both groups were well matched for baseline parameters with no change in limb fat, serum lipids, glucose, or lactate between weeks 0 and 6. Mitochondrial and PPARg gene expression decreased significantly by week 2 (table 1), more so in the d4T/3TC group, although between-group comparisons were not significant at week 2. Changes in PPARg expression correlated with changes in mitochondrial genes (COX1 Rho = 0.52, p = 0.02; COX3 Rho = 0.56 p = 0.02; cytochrome-b Rho = 0.85, p = 0.0002).  SREBP1 was unaffected. There were no correlations between baseline age, lactate, glucose, cholesterol, BMI, or body composition and change in gene expression.

Values Are Median (IQR) Percentage Change from Baseline

Conclusions:  Independent of HIV infection, dual NRTI therapy with AZT/3TC or d4T/3TC decreases mitochondrial gene expression after only 2 weeks, predating changes in fat mass or metabolic parameters. Links with PPARg may explain the synergistic effect of protease inhibitors and NRTIs in the pathogenesis of HIV-lipodystrophy, although the NRTI effect on PPARg may not be mediated through SREBP1.

Keywords: Mitochondrial toxicity; Lipodystrophy; Antiretroviral toxicity