Mechanisms of HIV and nucleoside reverse transcriptase inhibitor injury to mitochondria

Available evidence suggests that a number of important clinical events in individuals with HIV infection are related to mt dysfunction. Several factors may contribute to the development of these events and the tissue(s) in which the event occurs. Some individuals are likely to have important genetic predispositions for mt disease, which may be unmasked by the presence of HIV infection or the introduction of NRTI antiretrovirals. HIV infection per se is associated with reduction in mtDNA content and changes in mt morphology and function, which in some cases leads to clinical events such as myopathy or peripheral neuropathy. NRTI antiretrovirals may impact mtDNA content and function through a number of different mechanisms and have been demonstrated to be causative of a number of clinical toxicities. In in vitro and in clinical studies, newer nucleoside and nucleotides agents such as lamivudine, emtricitabine, abacavir and tenofovir appear to be much weaker inhibitors of mtDNA polymerase-gamma or other mt functions, and appear to be associated with a lower risk of events thought to be related to mt toxicity. Simple, non-invasive tests for mt function are not available at present in the clinical routine, and assays of mtDNA content in blood cells may miss key aspects of mt function, require careful sample handling and may not reflect events occurring in other tissues. There remains a need for the development of rapid, cheap and clinically applicable assays that would enable the prediction of increased likelihood of mt events.     

Long-term foscarnet therapy remodels thymidine analogue mutations and alters resistance to zidovudine and lamivudine in HIV-1

OBJECTIVE: To study the evolution of multi-drug-resistant HIV-1 in treatment-experienced patients receiving foscarnet (PFA) as part of salvage therapy and to investigate the virological consequences of emerging mutations. METHODS: Genotypic and phenotypic resistance tests were performed on plasma viruses from seven patients at baseline and during treatment with PFA. The phenotypic effects of mutations suspected to be associated with PFA resistance were evaluated by site-directed mutagenesis of wild-type or thymidine analogue mutations (TAM)-carrying pNL4-3. Reversion of single mutations was performed in a patient-derived recombinant clone. RESULTS: Baseline multi-drug-resistant isolates exhibited hypersusceptibility to PFA. In two patients who received > 12 months of PFA treatment, a novel mutation pattern including K70G, V75T, K219R and L228R emerged. These viruses had 3-6-fold resistance to PFA, a 2-20-fold decrease in resistance to zidovudine compared to baseline, and 14-39-fold resistance to lamivudine, in the absence of M184V. In wild-type clones mutations K70G and V75T induced moderate PFA resistance. In the case of TAMs, combinations of > or = 3 mutations (K70G+K219R+L228R+/-V75T) induced PFA resistance and decreased zidovudine resistance 3-13-fold. These mutants exhibited high-level lamivudine resistance (>20-fold) without mutation M184V. Reversion of K70G --> R and K219R --> E in a patient-derived clone confirmed the contribution of individual mutations and the negative association between PFA resistance and zidovudine resistance. CONCLUSIONS: In the context of multiple TAMs, hypersusceptibility to PFA was observed and a novel pattern of resistance, including alternative amino acid substitutions at TAM loci, emerged. This mutational pattern was associated with decreases in zidovudine resistance and surprisingly high-level lamivudine resistance.     

Emergence of the H208Y mutation in the reverse transcriptase (RT) of HIV-1 in association with nucleoside RT inhibitor therapy

OBJECTIVES: The aim of the study was to determine whether mutations at RT codon 208 are associated with nucleoside RT inhibitor (NRTI) exposure, NRTI resistance patterns and HIV-1 subtype. METHODS: Six thousand three hundred and fifty two genotypic resistance tests linked to a clinical database were analysed. RESULTS: The prevalence of mutations at codon 208 was 6/2347 (0.3%) in treatment-naive and 165/4005 (4.1%) in treatment-experienced persons. H208Y was the most common mutation in both groups (0.2% and 3.8%, respectively) and occurred in 4.5% of treatment-experienced persons with Subtype B, 1.7% of those with Subtype C and 0.7% of those with other non-B subtypes (P=0.001). The association with subtypes was independent of treatment experience. H208Y showed a strong association with NRTI experience, which persisted after adjusting for subtype [odds ratio (OR) 19.34; 95% confidence interval (CI) 7.87-47.54; P=0.0001]. The prevalence of H208Y was highest in genotypes harbouring M184V and the thymidine analogue mutations (TAMs) M41L, D67N, L210W and T215Y. The median number of TAMs was 4 and 0 in genotypes with and without H208Y, respectively (P=0.0001). The prevalence of H208Y declined over time, being highest in 1998 (9.9%) and lowest in 2003 (0.9%) (P=0.0001). CONCLUSIONS: There is a strong association between H208Y and NRTI experience, particularly in persons with Subtype B harbouring multiple NRTI resistance mutations. These findings indicate an accessory role for H208Y in NRTI resistance.