Depletion of Mitochondrial DNA in Dual vs. Single NRTI Treatment
Depletion of Mitochondrial DNA in Dual vs. Single NRTI Treatment
Background: Most toxicities associated with nucleoside analogue reverse transcriptase inhibitors (NRTIs) are thought to result from mitochondrial toxicity. These toxicities include peripheral neuropathy, pancreatitis, lactic acidosis, and peripheral lipoatrophy. Unfortunately, there are no validated laboratory markers for clinically assessing, let alone predicting, the onset of mitochondrial toxicity associated with NRTI therapy.
Objectives: To provide preliminary evidence of the potential clinical utility of an assay which has been developed for quantifying mitochondrial DNA (mtDNA) in clinical samples from HIV-infected patients.
Methods: A single-tube duplex real-time DNA-nucleic acid sequence-based amplification (NASBA) assay (Mitox™, Primagen, Amsterdam, the Netherlands) was used to quantify mtDNA in cryopreserved peripheral blood mononuclear cells (PBMC) obtained from HIV-1-infected patients during their prior participation in a randomized placebo-controlled trial comparing zidovudine (ZDV) monotherapy with combinations of ZDV plus either dideoxycytidine (ddC) or didanosine (ddI) (the Delta trial). Patients were antiretroviral naïve prior to entering the trial. Samples obtained during the initial 48 weeks of treatment were tested.
Results: A significant decline of mtDNA, both in an intent-to-treat and in an as-treated analysis, was observed in patients treated with ZDV+ddC and ZDV+ddI, but not with ZDV alone, consistent with the results expected from the degree of mtDNA depletion described for each of these drugs in vitro.
Conclusions: This single-tube duplex real-time DNA-NASBA assay was shown to measure mtDNA accurately in PBMC. Treatment with a combination of two NRTIs was associated with greater reductions in mtDNA than obtained for ZDV monotherapy. The relevance of these results in predicting treatment toxicity requires further evaluation.
Current combination therapy for HIV infection mostly includes the prescription of nucleoside analogue reverse transcriptase inhibitors (NRTIs). This class of drugs has been associated with different clinical toxicities including peripheral neuropathy (cardio-)myopathy, pancreatitis, hepatic steatosis together with lactic acidaemia/acidosis, and possibly peripheral lipoatrophy. It has been suggested that these toxicities are a consequence of organ-specific mitochondrial dysfunction resulting from the depletion of mitochondrial DNA (mtDNA) caused by NRTI-induced inhibition of DNA polymerase-γ, the key enzyme responsible for replication of mtDNA. In vitro, NRTIs have been shown to differ with respect to their propensity for depleting mtDNA in different cell lines, with dideoxycytidine (ddC) consistently demonstrated to be more toxic than other NRTIs such as stavudine, didanosine (ddI), zidovudine (ZDV), lamivudine or abacavir. Unfortunately, validated laboratory markers for measuring, let alone predicting the onset of, mitochondrial toxicity in patients receiving NRTI-containing treatment for HIV infection are not available.
With this aim in mind, we set out to develop an assay for the quantification of mtDNA in patient samples, including peripheral blood mononuclear cells (PBMC).
Background: Most toxicities associated with nucleoside analogue reverse transcriptase inhibitors (NRTIs) are thought to result from mitochondrial toxicity. These toxicities include peripheral neuropathy, pancreatitis, lactic acidosis, and peripheral lipoatrophy. Unfortunately, there are no validated laboratory markers for clinically assessing, let alone predicting, the onset of mitochondrial toxicity associated with NRTI therapy.
Objectives: To provide preliminary evidence of the potential clinical utility of an assay which has been developed for quantifying mitochondrial DNA (mtDNA) in clinical samples from HIV-infected patients.
Methods: A single-tube duplex real-time DNA-nucleic acid sequence-based amplification (NASBA) assay (Mitox™, Primagen, Amsterdam, the Netherlands) was used to quantify mtDNA in cryopreserved peripheral blood mononuclear cells (PBMC) obtained from HIV-1-infected patients during their prior participation in a randomized placebo-controlled trial comparing zidovudine (ZDV) monotherapy with combinations of ZDV plus either dideoxycytidine (ddC) or didanosine (ddI) (the Delta trial). Patients were antiretroviral naïve prior to entering the trial. Samples obtained during the initial 48 weeks of treatment were tested.
Results: A significant decline of mtDNA, both in an intent-to-treat and in an as-treated analysis, was observed in patients treated with ZDV+ddC and ZDV+ddI, but not with ZDV alone, consistent with the results expected from the degree of mtDNA depletion described for each of these drugs in vitro.
Conclusions: This single-tube duplex real-time DNA-NASBA assay was shown to measure mtDNA accurately in PBMC. Treatment with a combination of two NRTIs was associated with greater reductions in mtDNA than obtained for ZDV monotherapy. The relevance of these results in predicting treatment toxicity requires further evaluation.
Current combination therapy for HIV infection mostly includes the prescription of nucleoside analogue reverse transcriptase inhibitors (NRTIs). This class of drugs has been associated with different clinical toxicities including peripheral neuropathy (cardio-)myopathy, pancreatitis, hepatic steatosis together with lactic acidaemia/acidosis, and possibly peripheral lipoatrophy. It has been suggested that these toxicities are a consequence of organ-specific mitochondrial dysfunction resulting from the depletion of mitochondrial DNA (mtDNA) caused by NRTI-induced inhibition of DNA polymerase-γ, the key enzyme responsible for replication of mtDNA. In vitro, NRTIs have been shown to differ with respect to their propensity for depleting mtDNA in different cell lines, with dideoxycytidine (ddC) consistently demonstrated to be more toxic than other NRTIs such as stavudine, didanosine (ddI), zidovudine (ZDV), lamivudine or abacavir. Unfortunately, validated laboratory markers for measuring, let alone predicting the onset of, mitochondrial toxicity in patients receiving NRTI-containing treatment for HIV infection are not available.
With this aim in mind, we set out to develop an assay for the quantification of mtDNA in patient samples, including peripheral blood mononuclear cells (PBMC).
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