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Background:  The reversibility of mitochondrial dysfunction in ART-associated lipoatrophy (LA) has not been investigated. We previously reported significant improvements in subcutaneous fat mitochondrial DNA (mtDNA) levels, adipocyte apoptosis scores and DEXA-measured fat content in 16 subjects who substituted abacavir (ABC) or zidovudine (ZDV) for stavudine (d4T). To assess the effect of this strategy on mitochondrial function, we measured activities of electron transport chain in skeletal muscle before and 48 weeks after the switch of d4T to ABC or ZDV.

Methods:  Skeletal muscle samples were obtained under heavy sedation with local anesthetic injected only above the fascia, so not to impair electron transport chain activities. Samples were immediately frozen at -70 C, until analyzed. Electron transport chain activities were measured using CLIA validated methods.

Results:  We enrolled 16 subjects:  14 replaced d4T with ABC and 2 with ZDV. Muscle from 49 HIV-uninfected donors in the same age range of the patients was used as control. At study entry, the mean values for electron transport chain assays, which measure the activity in complexes I through IV, ranged from 48% to 85% of the mean levels observed in the control samples. In particular, 7/16 patients had significant mitochondrial respiratory chain dysfunction, with marked deficiencies in at least 2 of the enzymes. The most consistent decreases in enzyme activities were associated with complexes I, III, and citrate synthase, the latter reflecting a quantitative loss of mitochondrial mass. At Week 48, there was significant improvement in activity of Complex I as expressed in nmol/min/mg protein (mean ± SD; 0.9±0.6 at week 48 vs 0.6±0.5 at study entry; p = 0.020) but surprisingly significant worsening in activity of Complex III as expressed in nmol/min/mg protein (mean ± SD; 6.0±3.9 at week 48 vs 12.3±5.5 at study entry; p = 0.027). Other enzyme activities remained unchanged.

Conclusions:  Despite improvement in fat content, mtDNA levels and fat apoptosis, only a partial improvement of mitochondrial function was seen 48 weeks after substitution of ABC or ZDV for d4T. This could be due to the fact that severe mitochondrial dysfunction may be partially irreversible or take longer than 48 weeks to reverse, or  mtDNA depletion may not be the sole mechanism involved in the NRTI-induced mitochondrial dysfunction.  Due to the small sample size these results should be confirmed.

Keywords: lipodystrophy; mitochondrial toxicity; lipoatrophy