Update on mitochondrial toxicity: where are we now?
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Long-term alterations to body metabolism have become apparent with the prolonged use of antiretroviral nucleoside analogue reverse transcriptase inhibitors (NRTIs). The NRTIs differ in the mechanisms, potency and probably also tissue specificity of mitochondrial toxicity. One group of NRTIs, the so-called "d-drugs" (zalcitabine> didanosine>stavudine) are relatively strong inhibitors of g-polymerase and thus cause a time- and dose-dependent decrease in the intracellular levels of mitochondrial DNA (mtDNA). The most important target organs of d-drugs are the liver, skeletal muscle, peripheral nerves and probably also the subcutaneous adipose tissue of lipoatrophic subjects. Hyperlactataemia may be observed. Zidovudine is an inhibitor of the mitochondrial adenine nucleotide translocator, binds to adenylate kinase and may also be converted into stavudine triphosphate in vivo. Persistent hyperlactataemia, mtDNA depletion and isolated cases of mitochondrial encephalomyopathies have been observed in babies under perinatal exposure with zidovudine. Nucleotide analogues such as tenofovir are avidly taken up into renal tubular epithelia. Isolated cases of renal failure and Fanconi syndrome require further investigation. Mitochondrial toxicity cannot yet be adequately monitored and predicted. Drugs with potential additive or synergistic toxicity, such as valproate, should be used with caution. Didanosine interacts with allopurinol, hydroxyurea and ribavirin. In established mitochondrial toxicity, cessation of the offending NRTI remains the most effective therapeutic intervention because vitamin cocktails and l-carnitine have, at best, only a marginal effect.Keywords:
Mitochondrial toxicity
Didanosine
Stavudine
Zalcitabine
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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.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.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.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.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.
Didanosine
Zalcitabine
Mitochondrial toxicity
Stavudine
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In this paper, an overview of the pharmacokinetics of currently available antiretroviral drugs is provided. Included in this article are the agents zidovudine, stavudine, zalcitabine, lamivudine, didanosine, abacavir, nevirapine, delavirdine, efavirenz, saquinavir, indinavir, ritonavir and nelfinavir. Key pharmacokinetic parameters, drug penetration in body compartments and drug interactions are discussed for each agent.
Indinavir
Didanosine
Saquinavir
Efavirenz
Nelfinavir
Nevirapine
Abacavir
Zalcitabine
Ritonavir
Stavudine
Etravirine
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Long-term alterations to body metabolism have become apparent with the prolonged use of antiretroviral nucleoside analogue reverse transcriptase inhibitors (NRTIs). The NRTIs differ in the mechanisms, potency and probably also tissue specificity of mitochondrial toxicity. One group of NRTIs, the so-called "d-drugs" (zalcitabine> didanosine>stavudine) are relatively strong inhibitors of g-polymerase and thus cause a time- and dose-dependent decrease in the intracellular levels of mitochondrial DNA (mtDNA). The most important target organs of d-drugs are the liver, skeletal muscle, peripheral nerves and probably also the subcutaneous adipose tissue of lipoatrophic subjects. Hyperlactataemia may be observed. Zidovudine is an inhibitor of the mitochondrial adenine nucleotide translocator, binds to adenylate kinase and may also be converted into stavudine triphosphate in vivo. Persistent hyperlactataemia, mtDNA depletion and isolated cases of mitochondrial encephalomyopathies have been observed in babies under perinatal exposure with zidovudine. Nucleotide analogues such as tenofovir are avidly taken up into renal tubular epithelia. Isolated cases of renal failure and Fanconi syndrome require further investigation. Mitochondrial toxicity cannot yet be adequately monitored and predicted. Drugs with potential additive or synergistic toxicity, such as valproate, should be used with caution. Didanosine interacts with allopurinol, hydroxyurea and ribavirin. In established mitochondrial toxicity, cessation of the offending NRTI remains the most effective therapeutic intervention because vitamin cocktails and l-carnitine have, at best, only a marginal effect.
Mitochondrial toxicity
Didanosine
Stavudine
Zalcitabine
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Citations (27)
The “D drug” HIV reverse-transcriptase inhibitors zalcitabine, didanosine, and stavudine are relatively strong inhibitors of polymerase-gamma compared with the “non-D drugs” zidovudine, lamivudine, and abacavir. D drugs deplete mitochondrial DNA (mtDNA) in cultured hepatocytes. This mtDNA depletion is associated with an increased in vitro production of lactate. To investigate the origin of hyperlactatemia in HIV-infected patients and the effects of antiretroviral therapy on liver mtDNA, we biopsied liver tissue from 94 individuals with chronic hepatitis C virus (HCV) infection. Eighty subjects were coinfected with HIV. Serum lactate was measured at the time of biopsy. Hepatic mtDNA and liver histology were centrally assessed. Liver mtDNA content of HIV-infected patients receiving D drugs at the time of biopsy (n = 34) was decreased by 47% ( P <.0001) compared with those without D drugs (n = 35). Aside from a possible association between HCV genotype I status and mtDNA depletion in multivariate analysis, there were no other virologic, immunologic, histologic, demographic or treatment-related variables that could explain the mtDNA depletion. Lactate was above the upper limit of normal in only three patients, all of whom were treated with D drugs. The mtDNA in each of them was lower than in any non-D drug patient and significantly ( P = .017) depleted compared with D drug patients with normal lactate. In conclusion, D drug treatment is associated with decreased hepatic mtDNA in HIV-infected patients with chronic HCV infection. Moderate mtDNA depletion in liver does not necessarily lead to hyperlactatemia, but more pronounced decreases in hepatic mtDNA may be an important contributor to lactate elevation. (Hepatology 2004;39:311-317.)
Didanosine
Stavudine
Zalcitabine
Mitochondrial toxicity
Hyperlactatemia
Abacavir
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Citations (160)
Studies on mitochondrial dysfunction in HIV-infected adults exposed to anti-retroviral therapy. A significant proportion of HIV-infected patients who require anti-retroviral therapy are or have been exposed to nucleoside analogue reverse transcriptase inhibitors (NRTIs). It has been consistently suggested that most of the NRTI-attributed adverse drug reactions (ADR) are due to mitochondrial dysfunction. In a sub-analysis of a large randomised clinical trial (Delta) the incidence of peripheral neuropathy (PN) was constant over time in all study arms, which does not support the hypothesis of cumulative toxicity previously proposed for NRTI-induced ADR. Patients taking zidovudine (AZT)/zalcitabine (ddC) combination were more likely to develop PN than patients on AZT monotherapy (RH= 2.30 95%CI= 1.62 - 3.28). The incidence of PN among patients exposed to zidovudine/didanosine (AZT/ddl) combination was not different from that observed in patients on AZT. In a multi-centre case-control study including 110 cases of lactic acidosis (LA) or severe hyperlactataemia (HL) patients with < 200 CD4 cell/pl were more likely to develop HL/LA than patients with higher levels of CD4 cells (OR=3.44 95%CI= 1.64 - 7.22). Female patients were found to be at higher risk for HULA than men (OR= 4.75 95%CI= 1.96 - 11.53). Patients exposed to either d4T, ddl or the combination of these two were four to six times more likely to develop HL/LA than patients taking other NRTIs based combinations. Interestingly, cases of HL/LA were exposed to d4T for shorter periods of time than controls. Almost 10 % of the cases included in the study were asymptomatic at the time of diagnosis. All these symptom-free cases had blood lactate ranging between 5 and 7 mmol/l. Therefore, case definitions for HL or LA based on clinical presentation may underestimate the magnitude of the problem.
Didanosine
Stavudine
Lactic acidosis
Zalcitabine
Reverse-transcriptase inhibitor
Nucleoside analogue
Mitochondrial toxicity
Combination therapy
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Liver related complications are currently the leading cause of morbidity and mortality among human immunodeficiency virus (HIV) infected individuals. In HIV monoinfected individuals on therapy, liver injury has been associated with the use of antiretroviral agents as most of them exhibit some degree of toxicity. In this study we proposed a mathematical model with the aim of investigating hepatotoxicity of combinational therapy of antiretroviral drugs. Therapy efficacy and toxicity were incorporated in the model as dose-response functions. With the parameter values used in the study, protease inhibitors-based regimens were found to be more toxic than nonnucleoside reverse transcriptase inhibitors-based regimens. In both regimens, the combination of stavudine and zidovudine was the most toxic baseline nucleoside reverse transcriptase inhibitors followed by didanosine with stavudine. However, the least toxic combinations were zidovudine and lamivudine followed by didanosine and lamivudine. The study proposed that, under the same second line regimens, the most toxic first line combination gives the highest viral load and vice versa.
Didanosine
Stavudine
Reverse-transcriptase inhibitor
Zalcitabine
Nucleoside analogue
Nevirapine
Mitochondrial toxicity
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Citations (3)
Drug-associated dysfunction of mitochondria is believed to play a role in the etiology of the various adverse symptoms that occur in human immunodeficiency virus (HIV)-infected patients treated with the nucleoside reverse transcriptase inhibitors (NRTIs). Tenofovir, a nucleotide analog recently approved for use in the treatment of HIV infection, was evaluated in vitro for its potential to cause mitochondrial toxicity and was compared to currently used NRTIs. Treatment with tenofovir (3 to 300 microM) for up to 3 weeks produced no significant changes in mitochondrial DNA (mtDNA) levels in human hepatoblastoma (HepG2) cells, skeletal muscle cells (SkMCs), or renal proximal tubule epithelial cells. The potencies of inhibition of mtDNA synthesis by the NRTIs tested were zalcitabine (ddC) > didanosine (ddI) > stavudine > zidovudine (ZDV) > lamivudine = abacavir = tenofovir, with comparable relative effects in the three cell types. Unlike ddC and ddI, tenofovir did not affect cellular expression of COX II and COX IV, two components of the mitochondrial cytochrome c oxidase complex. Lactate production was elevated by less than 20% in HepG2 cells or SkMCs following treatment with 300 microM tenofovir. In contrast, lactate synthesis increased by >200% in the presence of 300 microM ZDV. Thus, treatment of various human cell types with tenofovir at concentrations that greatly exceed those required for it both to have in vitro anti-HIV type 1 activity in peripheral blood mononuclear cells (50% effective concentration, 0.2 microM) and to achieve therapeutically relevant levels in plasma (maximum concentrations in plasma, 0.8 to 1.3 microM) is not associated with mitochondrial toxicity.
Mitochondrial toxicity
Tenofovir
Reverse-transcriptase inhibitor
Didanosine
Nucleoside analogue
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Didanosine
Zalcitabine
Mitochondrial toxicity
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Citations (187)
Background: Peripheral neuropathy is the dose-limiting toxicity of stavudine and didanosine (nucleoside analogs used in HIV treatment) and is attributed to mitochondrial toxicity from these drugs. Acetyl L-carnitine (ALC) and co-enzyme Q10 are proposed as neuropathy treatments, but evidence to support these is limited. Methods: We examined ALC and a water-soluble formulation of co-enzyme Q10 (HQO™) for the prevention of d4T and ddI neurotoxicity using cultured fetal rat DRG as an in vitro model. Results: DdI (33μM) and d4T (50μM) caused clear toxicity (impaired neurite growth) by day 8 of DRG culture. HQO™ at concentrations 1-100μM completely prevented the toxicity of 33μM ddI in vitro and ALC at concentrations 1-100 μM substantially (but incompletely) prevented ddI toxicity in this model. In contrast, ALC was ineffective at all concentrations tested for preventing the toxicity of 50μM d4T. HQO™ showed dose-dependent efficacy for preventing d4T toxicity. HQO™ (1μM) partially prevented d4T toxicity while 10 and 100μM HQO™ completely prevented d4T toxicity in this model. Conclusions: We find HQO™ is superior to ALC for preventing the neurotoxicity of d4T (the HIV treatment most associated with neuropathy) and ddI in vitro. Further study is needed to clarify any clinical role for co-enzyme Q10 coadministration with d4T and ddI and to assess whether this compound may have a role in treating established cases of neuropathy. Keywords: HIV, stavudine, neuropathy, coenzyme Q10, acetyl L-carnitine
Stavudine
Coenzyme Q10
Mitochondrial toxicity
Didanosine
Neurotoxicity
Nucleoside analogue
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The anti-human immunodeficiency virus (-HIV) nucleoside analogs azidothymidine (AZT), dideoxycytidine (ddC), dideoxyinosine (ddl), dideoxydidehydrothymidine (D4T), and dideoxydidehydrocytidine (D4C) and the anticancer drug cytosine arabinoside (AraC) were compared for their effects on the mitochondrial DNA (mtDNA) content in a human lymphoblastoid cell line, CEM. The potency of these compounds in reducing mtDNA content was in the order of ddC greater than D4C greater than D4T greater than AZT greater than ddl. AraC did not have a significant effect on mtDNA content. All of the compounds tested, except AraC, stimulated lactic acid production at concentrations that inhibited mtDNA synthesis. The action of ddC and ddl occurred at concentrations that did not affect cell growth significantly in 4 days but retarded cell growth by day 6. D4T and D4C decreased mtDNA content by 50% at doses lower than those that inhibited cell growth by 50% in 4 days (ID50). However, AZT required a dose higher than the ID50 to exert similar effects on mtDNA content. The decrease of mtDNA content caused by ddC also occurred in nerve growth factor-treated PC12 cells, which differentiate to neuron-like cells upon treatment with nerve growth factor. The preferential inhibition of mtDNA, compared with cell growth, by some of these anti-HIV nucleoside analogs correlates well with their ability to cause drug-limiting delayed toxicity, such as peripheral neuropathy, in patients. These data suggest that the selective mitochondrial toxicity could be responsible for the delayed toxicity caused by these anti-HIV analogs.
Mitochondrial toxicity
Nucleoside analogue
Didanosine
Cytosine
Growth inhibition
Zalcitabine
Mechanism of Action
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