Mitochondrial DNA replication, nucleoside reverse-transcriptase inhibitors, and AIDS cardiomyopathy

Mitochondrial dysfunctions in HIV infection and antiviral drug treatment

Introduction: With the introduction of highly active anti-retroviral therapy (HAART), treatment of HIV infection has improved radically, shifting the concept of HIV disease from a highly mortal epidemic to a chronic illness which needs systematic management. However, HAART does not target the integrated proviral DNA. Hence, prolonged use of antiviral drugs is needed for sustaining life. As a consequence, severe side effects emerge. Several parameters involve in causing these adverse effects. Mitochondrial dysfunctions were pointed as common factor among them. It is, therefore, necessary to critically examine mitochondrial dysfunction in order to understand the side effects.Areas covered: There are many events involved in causing drug-induced side-effects; in this review, we only highlight mitochondrial dysfunctions as one of the events. We present up-to-date findings on mitochondrial dysfunction caused by HIV infection and antiviral drug treatment. Both in vivo and in vitro studies on mitochondrial dysfunction like change in morphology, membrane depolarization, mitophagy, mitochondrial DNA depletion, and intrinsic apoptosis have been discussed.Expert opinion: Mitochondrial dysfunction is associated with severe complications that often lead to discontinuation or change in treatment regimen. Prior knowledge of side effects of antiviral drugs would help in better management and future research should focus to avoid mitochondrial targeting of antiviral drugs while maintaining their antiviral properties.

Intracellular metabolism and potential cardiotoxicity of a β-D-2'-C-methyl-2,6-diaminopurine ribonucleoside phosphoramidate that inhibits hepatitis C virus replication

β-D-2'-C-Methyl-2,6-diaminopurine ribonucleoside (2'-C-Me-DAPN) phosphoramidate prodrug (DAPN-PD) is a selective hepatitis C virus inhibitor that is metabolized intracellularly into two active metabolites: 2'-C-Methyl-DAPN triphosphate (2'-C-Me-DAPN-TP) and 2'-C-methyl-guanosine 5'-triphosphate (2'-C-Me-GTP). BMS-986094 and IDX-184 are also bioconverted to 2'-C-Me-GTP. A phase IIb clinical trial with BMS-986094 was abruptly halted due to adverse cardiac and renal effects. Herein, we developed an efficient large scale synthesis of DAPN-PD and determined intracellular pharmacology of DAPN-PD in comparison with BMS-986094 and IDX-184, versus Huh-7, HepG2 and interspecies primary hepatocytes and human cardiomyocytes. Imaging data of drug treated human cardiomyocytes was found to be most useful in determining toxicity potential as no obvious beating rate change was observed for IDX-184 up to 50 µM up at 48 h. However, with BMS-986094 and DAPN-PD at 10 µM changes to both beat rate and rhythm were noted.

A New Face of Cardiac Emergencies: Human Immunodeficiency Virus-Related Cardiac Disease

The human immunodeficiency virus epidemic is a major health challenge of the twenty-first century as the transition from infectious complications to noncommunicable disease becomes more evident. These patients may present to the emergency department with a variety of cardiovascular diseases, such as acute coronary syndromes, heart failure, pericardial disease, infective endocarditis, venothromboembolism, and other conditions. Increased awareness is needed among health care professionals to enhance adequate identification and promote prompt management of these patients.

HIV and Nonischemic Heart Disease

Human immunodeficiency virus (HIV)-associated heart disease encompasses a broad spectrum of diseases. HIV infection may involve the pericardium, myocardium, coronary arteries, pulmonary vasculature, and valves, as well as the systemic vasculature. Access to combination antiretroviral therapy, as well as health resources, has had a significant influence on the prevalence and severity of the effects on each cardiac structure. Investigations over the recent past have improved our understanding of the epidemiology and pathophysiology of HIV-associated cardiovascular disease. This review will focus on our current understanding of pathogenesis and risk factors associated with HIV infection and heart disease, and it will discuss relevant advances in diagnosis and management of these conditions.

An Organic Anion Transporter 1 (OAT1)-centered Metabolic Network

There has been a recent interest in the broader physiological importance of multispecific "drug" transporters of the SLC and ABC transporter families. Here, a novel multi-tiered systems biology approach was used to predict metabolites and signaling molecules potentially affected by the in vivo deletion of organic anion transporter 1 (Oat1, Slc22a6, originally NKT), a major kidney-expressed drug transporter. Validation of some predictions in wet-lab assays, together with re-evaluation of existing transport and knock-out metabolomics data, generated an experimentally validated, confidence ranked set of OAT1-interacting endogenous compounds enabling construction of an "OAT1-centered metabolic interaction network." Pathway and enrichment analysis indicated an important role for OAT1 in metabolism involving: the TCA cycle, tryptophan and other amino acids, fatty acids, prostaglandins, cyclic nucleotides, odorants, polyamines, and vitamins. The partly validated reconstructed network is also consistent with a major role for OAT1 in modulating metabolic and signaling pathways involving uric acid, gut microbiome products, and so-called uremic toxins accumulating in chronic kidney disease. Together, the findings are compatible with the hypothesized role of drug transporters in remote inter-organ and inter-organismal communication: The Remote Sensing and Signaling Hypothesis (Nigam, S. K. (2015) Nat. Rev. Drug Disc. 14, 29). The fact that OAT1 can affect many systemic biological pathways suggests that drug-metabolite interactions need to be considered beyond simple competition for the drug transporter itself and may explain aspects of drug-induced metabolic syndrome. Our approach should provide novel mechanistic insights into the role of OAT1 and other drug transporters implicated in metabolic diseases like gout, diabetes, and chronic kidney disease.

The physical and psychological effects of HIV infection and its treatment on perinatally HIV-infected children

INTRODUCTION

As highly active antiretroviral therapy (HAART) transforms human immunodeficiency virus (HIV) into a manageable chronic disease, new challenges are emerging in treating children born with HIV, including a number of risks to their physical and psychological health due to HIV infection and its lifelong treatment.

METHODS

We conducted a literature review to evaluate the evidence on the physical and psychological effects of perinatal HIV (PHIV+) infection and its treatment in the era of HAART, including major chronic comorbidities.

RESULTS AND DISCUSSION

Perinatally infected children face concerning levels of treatment failure and drug resistance, which may hamper their long-term treatment and result in more significant comorbidities. Physical complications from PHIV+ infection and treatment potentially affect all major organ systems. Although treatment with antiretroviral (ARV) therapy has reduced incidence of severe neurocognitive diseases like HIV encephalopathy, perinatally infected children may experience less severe neurocognitive complications related to HIV disease and ARV neurotoxicity. Major metabolic complications include dyslipidaemia and insulin resistance, complications that are associated with both HIV infection and several ARV agents and may significantly affect cardiovascular disease risk with age. Bone abnormalities, particularly amongst children treated with tenofovir, are a concern for perinatally infected children who may be at higher risk for bone fractures and osteoporosis. In many studies, rates of anaemia are significantly higher for HIV-infected children. Renal failure is a significant complication and cause of death amongst perinatally infected children, while new data on sexual and reproductive health suggest that sexually transmitted infections and birth complications may be additional concerns for perinatally infected children in adolescence. Finally, perinatally infected children may face psychological challenges, including higher rates of mental health and behavioural disorders. Existing studies have significant methodological limitations, including small sample sizes, inappropriate control groups and heterogeneous definitions, to name a few.

CONCLUSIONS

Success in treating perinatally HIV-infected children and better understanding of the physical and psychological implications of lifelong HIV infection require that we address a new set of challenges for children. A better understanding of these challenges will guide care providers, researchers and policymakers towards more effective HIV care management for perinatally infected children and their transition to adulthood.

Coronary Heart Disease Risk, Dyslipidemia, and Management in HIV-Infected Persons

Dyslipidemia and coronary heart disease (CHD) are of increasing concern in persons with human immunodeficiency virus (HIV) infection who are living longer because of the benefits of highly active antiretroviral therapy (HAART). All classes of drugs used in HAART have been associated with atherogenic changes in lipid profiles. The management of HIV-infected persons with dyslipidemia and/or CHD currently emphasizes the importance of monitoring and optimizing lipid levels through lifestyle changes, switching antiretrovirals (ARVs), and lipid-lowering treatments utilizing guidelines developed for persons without HIV infection. In HIV-infected persons, the use of lipid-lowering drugs may result in pharmacokinetic interactions with ARVs, complicating the management of patients. Recent advances in our understanding of the differential effects of specific ARVs on lipids is beginning to alter the clinical approach to management. In the absence of randomized clinical trials, clinicians should aggressively treat atherogenic dyslipidemia by primarily utilizing or switching to ARVs with the lowest potential to induce CHD or, when this is not possible or is ineffective, secondarily by the addition of lipid-lowering therapy. The current optimal management of HIV infection requires careful selection of ARVs with consideration given to the potential development of CHD and an understanding of how to manage dyslipidemia.

The impact of HAART on cardiomyopathy among children and adolescents perinatally infected with HIV-1

OBJECTIVE

Previous studies of cardiomyopathy among children perinatally infected with HIV were conducted before the routine use of HAART. Nucleoside analogs [nucleoside reverse transcriptase inhibitors (NRTIs)], the backbone of HAART, have been associated with mitochondrial toxicity, which can lead to cardiomyopathy. We evaluated the association of HAART and specific NRTIs associated with mitochondrial toxicity, on development of cardiomyopathy among perinatally HIV-infected children.

DESIGN

Three thousand and thirty-five perinatally HIV-infected children enrolled in a US-based multicenter prospective cohort study were followed for cardiomyopathy, defined as a clinical diagnosis or initiation of digoxin, from 1993 to 2007.

METHODS

Cox models were used to estimate the effects of HAART and NRTIs on cardiomyopathy, identify predictors of cardiomyopathy among HAART users, and estimate the association between development of cardiomyopathy and mortality.

RESULTS

Ninety-nine cases of cardiomyopathy were identified over follow-up (incidence rate: 5.6 cases per 1000 person-years) at a median age of 9.4 years. HAART was associated with a 50% lower incidence of cardiomyopathy compared with no HAART use (95% confidence interval: 20%, 70%). Zalcitabine (ddC) use, however, was associated with an 80% higher incidence of cardiomyopathy. Among HAART users, older age at HAART initiation, ddC use before HAART initiation, initiating a HAART regimen containing zidovudine (ZDV), and a nadir CD4 percentage less than 15% were independently associated with a higher rate of cardiomyopathy. Cardiomyopathy was associated with a six-fold higher mortality rate.

CONCLUSION

HAART has dramatically decreased the incidence of cardiomyopathy among perinatally HIV-infected children. However, they remain at increased risk for cardiomyopathy and ongoing ZDV exposure may increase this risk.

N-acetylcysteine reverses cardiac myocyte dysfunction in HIV-Tat proteinopathy

HIV cardiomyopathy remains highly prevalent among the estimated 33 million HIV-infected individuals worldwide. This is particularly true in developing countries. Potential mechanisms responsible for myocardial dysfunction following HIV infection include direct effects of HIV proteins. We have previously reported that cardiac myocyte-specific expression of HIV-Tat (Tat) results in a murine cardiomyopathy model. We now report that Tat exhibits decreased myocardial ATP [wild type (WT) vs. Tat transgenic (TG), P < 0.01] and myocyte GSH levels (WT vs. TG, P < 0.01), decreased GSH/GSSG ratio (WT vs. TG, P < 0.01), increased H(2)O(2) levels (WT vs. TG, P < 0.05), and increased catalase (TG vs. WT, P < 0.05) and GPX1 (glutathione peroxidase 1) activities (WT vs. TG, P < 0.05), blunted cardiac myocyte positive inotropy (% peak shortening, WT vs. TG, P < 0.01; +dl/dt, WT vs. TG, P < 0.01) and negative inotropy (-dl/dt, WT vs. TG, P < 0.01), and blunted inotropic responses to Ca(2+) (P < 0.01, for each) and shortened anatomical and functional survival in vitro (P < 0.01). The sulfhydryl donor, N-acetylcysteine (NAC; 10(-4) M), completely reversed both the positive and negative inotropic defects in Tat; increased GSH (P < 0.01) and GSH/GSSG (P < 0.01); reversed H(2)O(2) level (P < 0.05) and GPX1 activity (P < 0.05); and normalized the blunted inotropic response to Ca(2+) (P < 0.01). NAC (10(-7)) M normalized duration of contractile function from <40 min to >120 min (P < 0.01), with no effect on GSH and GSH/GSSG. NAC (10(-4) M) reverses cardiac myocyte dysfunction and markers of oxidative stress. NAC (10(-7) M) enhances myocyte function independent of changes in glutathione. Elucidating the molecular mechanisms involved in the GSH-dependent and GSH-independent salutary effects of NAC should identify novel therapeutic targets for myocardial proteinopathies recently appreciated in human cardiomyopathies.

Subcellular renal proximal tubular mitochondrial toxicity with tenofovir treatment

Nucleoside reverse transcriptase inhibitors (NRTIs) are drugs used in the treatment of HIV/AIDS. Despite the distinct benefits of NRTI-based therapies, tissue specific toxicity is a limiting factor. Although the mechanisms of these specific antiretroviral drug-related toxicities remain unclear, it has been hypothesized that as analogs to native nucleosides, NRTIs may potentially inhibit mammalian DNA polymerases, including mitochondrial DNA (mtDNA) polymerase γ. Tenofovir disoproxil fumarate (TDF) is a nucleotide analog of adenosine monophosphate and the only NRTI that is associated with renal disease. The inherent heterogeneity of kidney tissues could affect the outcome and interpretation of molecular studies to define the mechanism(s) of tenofovir tubular toxicity. Laser-capture microdissection (LCM) provided a specific, single-cell isolation of proximal tubules from fixed heterogeneous kidney tissues. LCM-captured renal proximal tubules from transgenic mice (TGs) showed decreased mtDNA abundance with tenofovir, demonstrating a subcellular specific mitochondrial toxicity of tenofovir in an AIDS model.

Assessment of mitochondrial toxicity by analysis of mitochondrial protein expression in mononuclear cells

BACKGROUND

Real-time PCR has quantified decreased mitochondrial DNA levels in association with nucleoside reverse transcriptase inhibitor (NRTI) therapy of HIV-infected populations. However, real-time PCR is best suited to distinguish log differences in an analyte. In an effort to monitor individuals in more detail, we developed a flow cytometric assay to gauge mitochondrial function.

METHODS

Flow cytometric quantification of a mitochondrial DNA-encoded mitochondrial protein (cytochrome c oxidase subunit I (COX-I)) and a nuclear DNA-encoded mitochondrial protein [ATP synthase subunit D (Sub-D)] was optimized and validated.

RESULTS

Intra-assay and interassay variability was low using peripheral blood mononuclear cells (PBMCs) (CV of 6.15% for COX-I and 7.11% Sub-D, and 9.38% and 9.83% for COX-I and Sub-D, respectively). Mitochondrial protein depletion was evident with in vitro treatment of cells with ethidium bromide (EtBr) and zalcitabine (ddC). Mitochondrial protein expression in 40 healthy adults clustered tightly. Depletion of mitochondrial protein, however, was neither detected in cryopreserved PBMC from NRTI-treated children (n = 9) nor in adults with a history of symptoms consistent with mitochondrial toxicity or ongoing treatment with didanosine (ddI) or stavudine (d4T) (n = 51).

CONCLUSIONS

A validated flow cytometric assay allows simultaneous detection of mitochondrial DNA and nuclear DNA encoded proteins at the single cell level, offering a method to monitor for mitochondrial function. Prospective studies are required to evaluate whether mitochondrial protein loss is observed in at-risk patients prior to the onset of symptoms from mitochondrial dysfunction.

Mitochondrial DNA base excision repair and mitochondrial DNA mutation in human hepatic HuH-7 cells exposed to stavudine

The mitochondrial toxicity of nucleoside reverse transcriptase inhibitors (NRTIs) is due to the inhibition of mitochondrial DNA (mtDNA) polymerase gamma (Pol gamma), resulting in a blockade of mtDNA replication and subsequent disruption of cellular energetics. Because mtDNA Pol gamma is not only involved in mtDNA replication but also responsible for mtDNA repair, we hypothesize that mitochondrial oxidative stress leads to changes in the balance between mtDNA repair and mutation following stavudine (d4T) treatment. However, the mechanisms underlying how changes in mtDNA base excision repair (mtBER) lead to mtDNA mutation remain unclear. To test this hypothesis, total mitochondrial repair capability, different steps of mtBER, mtDNA mutations in D-loop, and oxidative stress were all assessed in cultured HuH-7 human hepatoblast cells treated with d4T for 2 weeks. Assessment by denaturing Southern blotting and quantitative PCR revealed that d4T significantly reduced in vivo repair of H(2)O(2) damaged mtDNA in HuH-7 cells. d4T reduced total in vitro mtBER and DNA Pol gamma capability, but did not affect mtDNA oxoguanine glycosylase and apurinic/apyrimidinic endonuclease activity in HuH-7 cells. In addition, d4T treatment is associated with a significant increase in the frequency of mtDNA mutations in HuH-7 cells. In conclusion, d4T treatment reduces mtBER and contributes mechanistically to NRTI-induced mtDNA mutation. These events may potentially be associated with some diseases linked to mtDNA mutation.

Tenofovir renal toxicity targets mitochondria of renal proximal tubules

Tenofovir disoproxil fumarate (TDF) is an analog of adenosine monophosphate that inhibits HIV reverse transcriptase in HIV/AIDS. Despite its therapeutic success, renal tubular side effects are reported. The mechanisms and targets of tenofovir toxicity were determined using '2 x 2' factorial protocols, and HIV transgenic (TG) and wild-type (WT) littermate mice with or without TDF (5 weeks). A parallel study used didanosine (ddI) instead of TDF. At termination, heart, kidney, and liver samples were retrieved. Mitochondrial DNA (mtDNA) abundance, and histo- and ultrastructural pathology were analyzed. Laser-capture microdissection (LCM) was used to isolate renal proximal tubules for molecular analyses. Tenofovir increased mtDNA abundance in TG whole kidneys, but not in their hearts or livers. In contrast, ddI decreased mtDNA abundance in the livers of WTs and TGs, but had no effect on their hearts or kidneys. Histological analyses of kidneys showed no disruption of glomeruli or proximal tubules with TDF or ddI treatments. Ultrastructural changes in renal proximal tubules from TDF-treated TGs included an increased number and irregular shape of mitochondria with sparse fragmented cristae. LCM-captured renal proximal tubules from TGs showed decreased mtDNA abundance with tenofovir. The results indicate that tenofovir targets mitochondrial toxicity on the renal proximal tubule in an AIDS model.

Multi-level analysis of organic anion transporters 1, 3, and 6 reveals major differences in structural determinants of antiviral discrimination

Long-term exposure to antivirals is associated with serious cellular toxicity to the kidney and other tissues. Organic anion transporters (OATs) are believed to mediate the cellular uptake, and hence cytotoxicity, of many antivirals. However, a systematic in vitro and ex vivo analysis of interactions between these compounds with various OAT isoforms has been lacking. To characterize substrate interactions with mOat1, mOat3, and mOat6, a fluorescence-based competition assay in Xenopus oocytes as well as wild-type and knock-out whole embryonic kidney (WEK) organ culture systems was developed using 6-carboxyfluorescein, 5-carboxyfluorescein, and fluorescein. Of nine common antiviral drugs assessed in oocytes, many manifested higher affinity for SLC22a6 (mOat1), originally identified as NKT (e.g. adefovir and cidofovir), two (ddC and ddI) manifested significantly higher affinity for mOat3, while mOat6 had comparatively low but measurable affinity for certain antivirals. A live organ staining approach combined with fluorescent uptake in WEK cultures allowed the visualization of OAT-mediated uptake ex vivo into developing proximal tubule-like structures, as well as quantification of substrate interactions of individual OAT isoforms. In general, antiviral specificity of SLC22a6 (Oat1) (in Oat3(-/-) WEK culture) and SLC22a8 (Oat3) (in Oat1(-/-) WEK culture) was consistent with the Xenopus oocyte data. The combined observations suggest SLC22a8 (Oat3) is the major transporter interacting with ddC and ddI. Finally, quantitative structure-activity relationship analysis of the nine antivirals' physicochemical descriptors with their OAT affinity indicates that antiviral preferences of mOat1 are explained by high polar surface areas (e.g. phosphate groups), whereas mOat3 prefers hydrogen bond acceptors (e.g. amines, ketones) and low rotatable bond numbers. In contrast, hydrogen bond donors (e.g. amides, alcohols) diminish binding to mOat6. This suggests that, despite sharing close overall sequence homology, Oat1, Oat3, and Oat6 have signficantly different binding pockets. Taken together, the data provide a basis for understanding potential drug interactions in combination antiviral therapy, as well as suggesting structural mdifications for drug design, especially in the context of targeting toward or away from specific tissues.

Targeted transgenic overexpression of mitochondrial thymidine kinase (TK2) alters mitochondrial DNA (mtDNA) and mitochondrial polypeptide abundance: transgenic TK2, mtDNA, and antiretrovirals

Mitochondrial toxicity limits nucleoside reverse transcriptase inhibitors (NRTIs) for acquired immune deficiency syndrome. NRTI triphosphates, the active moieties, inhibit human immunodeficiency virus reverse transcriptase and eukaryotic mitochondrial DNA polymerase pol-gamma. NRTI phosphorylation seems to correlate with mitochondrial toxicity, but experimental evidence is lacking. Transgenic mice (TGs) with cardiac overexpression of thymidine kinase isoforms (mitochondrial TK2 and cytoplasmic TK1) were used to study NRTI mitochondrial toxicity. Echocardiography and nuclear magnetic resonance imaging defined cardiac performance and structure. TK gene copy and enzyme activity, mitochondrial (mt) DNA and polypeptide abundance, succinate dehydrogenase and cytochrome oxidase histochemistry, and electron microscopy correlated with transgenesis, mitochondrial structure, and biogenesis. Antiretroviral combinations simulated therapy. Untreated hTK1 or TK2 TGs exhibited normal left ventricle mass. In TK2 TGs, cardiac TK2 gene copy doubled, activity increased 300-fold, and mtDNA abundance doubled. Abundance of the 17-kd subunit of complex I, succinate dehydrogenase histochemical activity, and cristae density increased. NRTIs increased left ventricle mass 20% in TK2 TGs. TK activity increased 3 logs in hTK1 TGs, but no cardiac phenotype resulted. NRTIs abrogated functional effects of transgenically increased TK2 activity but had no effect on TK2 mtDNA abundance. Thus, NRTI mitochondrial phosphorylation by TK2 is integral to clinical NRTI mitochondrial toxicity.

Morphological and molecular course of mitochondrial pathology in cultured human cells exposed long-term to Zidovudine

Long-term use of antiretroviral nucleoside reverse transcriptase inhibitors (NRTIs) as therapy for human immunodeficiency virus-1 (HIV-1) infection is limited by mitochondrial toxicity. Here we document mitochondrial pathology during the long-term culture of human HeLa cells in the presence or absence of the NRTI Zidovudine(R) (AZT, 800 muM) for up to 77-passages (p), with samples taken at early (p5-p11), middle (p36 and p37), and late (p70-p77) passages. Samples were analyzed for changes in mitochondrial morphology, mitochondrial (mt)DNA quantity, nuclear and mitochondrial gene expression, and mitochondrial membrane potential. Mitochondria showed abnormal proliferation at p5 and abnormal morphology >/=p36. mtDNA quantity was increased at p5 and p11, and 65% depleted at p71. Hierarchical clustering of nuclear gene expression, examined at p37 by the NCI cDNA microarray in AZT-exposed cells, showed down-regulation of 13 out of 16 lipid-metabolizing genes, and up-regulation of most oxidative phosphorylation (OXPHOS) genes. OXPHOS genes encoded by mtDNA, examined at p5, p36, and p75 using the Mitochondrial Gene Mini Array, revealed up-regulation of genes coding for polypeptides of NADH dehydrogenase, ATP synthase, and cytochrome c oxidase. Mitochondrial membrane potential, monitored by JC1 staining, was elevated at p10 and p32, and essentially completely absent at p71. The data show that during chronic exposure of HeLa cells to AZT, a compensatory response was induced at the earlier passages (p5-p37), and by p71 there was widespread mitochondrial morphological damage, severe mtDNA depletion, and a substantial loss of mitochondrial membrane potential.

Tissue-specific mtDNA lesions and radical-associated mitochondrial dysfunction in human hearts exposed to doxorubicin

Doxorubicin causes a chronic cardiomyopathy. Although the exact pathogenesis is unknown, recent animal data suggest that somatically acquired alterations of mitochondrial DNA (mtDNA) and concomitant mitochondrial dysfunction play an important role in its onset. In this study, skeletal and myocardial muscles were examined from human autopsies. Compared to controls (n = 8), doxorubicin-exposed hearts (n = 6) showed low absolute enzyme activity of mtDNA-encoded nicotinamide adenine dinucleotide hydrogen dehydrogenase (NADH DH, 79% residual activity, p = 0.03) and cytochrome c oxidase (COX, 59% residual activity, p < 0.001), but not of succinate dehydrogenase (SDH), which is encoded exclusively by nuclear DNA. NADH DH/SDH and COX/SDH ratios were 37% (p < 0.001) and 27% (p < 0.001) of controls. Expression of the mtDNA-encoded subunit II of COX was reduced (82%, p = 0.04), compared to its unchanged nucleus-encoded subunit IV. MtDNA-content was diminished (56%, p = 0.02), but the 'common' mtDNA-deletion was increased (9.2-fold, p = 0.004). Doxorubicin-exposed hearts harboured numerous additional mtDNA rearrangements lacking direct repeats. They contained elevated levels of malondialdehyde (MDA) (p = 0.006, compared to controls), which correlated inversely with the COX/SDH ratio (r = -0.45, p = 0.02) and the mtDNA-content (r = -0.75, p = 0.002), and correlated positively with the levels of the 'common' deletion (r = 0.80, p < 0.001). Doxorubicin-exposed hearts also contained the highest levels of superoxide (p < 0.001, compared to controls), which correlated negatively with the mtDNA-encoded respiratory chain activities, such as the COX/SDH ratio (r = -0.57, p = 0.02) and the NADH/SDH ratio (r = -0.52, p = 0.04), as well as with the mtDNA content (r = -0.69, p = 0.003), and correlated positively with the frequency of the 'common' deletion (r = 0.76, p < 0.001) and the MDA levels (r = 0.86, p < 0.001). Doxorubicin-exposed hearts contained electron-dense deposits within mitochondria. Hearts exposed to other anthracyclines (n = 6) or skeletal muscle (all groups) had no mitochondrial dysfunction. Doxorubicin, unlike other anthracyclines, augments lipid peroxidation, induces mtDNA mutations and decreases mtDNA content in human hearts. These lesions have an impact on mitochondrial function and could be of importance in the pathogenesis of clinical cardiomyopathy.

Dyslipidaemia and cardiovascular risk in HIV infection

Cardiovascular disease is increasingly recognised as a consequence of human immunodeficiency virus (HIV) infection in the era of highly active antiretroviral therapy (HAART). Dyslipidaemia is also a feature of HIV infection itself and the antiretroviral drugs from the protease inhibitor classes. Increased rates of atherosclerotic disease and diabetes have been associated with lipodystrophy and now from one of the major causes of morbidity in HIV and acquired immunodeficiency syndrome (AIDS).This review, based on a multi-database keyword search, summarises the lipid changes observed in the course of HIV infection and its treatment, and puts them into the context of other risk factors for cardiac disease, and other causes of cardiovascular disease in HIV.

Rapid analysis of mitochondrial DNA depletion by fluorescence in situ hybridization and immunocytochemistry: potential strategies for HIV therapeutic monitoring

Nucleoside reverse transcriptase inhibitors (NRTIs) have been a mainstay in the treatment of human immunodeficiency virus since the introduction of azidothymidine (AZT) in 1987. However, none of the current therapies can completely eradicate the virus, necessitating long-term use of anti-retroviral drugs to prevent viral re-growth. One of the side effects associated with long-term use of NRTIs is mitochondrial toxicity stemming from inhibition of the mitochondrial DNA (mtDNA) polymerase gamma, which leads to mtDNA depletion and consequently to mitochondrial dysfunction. Here we report the use of fluorescence in situ hybridization (FISH) and immunocytochemistry (ICC) to monitor mtDNA depletion in cultured fibroblasts treated with the NRTI 2',3'-dideoxycytidine (ddC). These techniques are amenable to both microscopy and flow cytometry, allowing analysis of populations of cells on a single-cell basis. We show that, as mtDNA depletion progresses, a mosaic population develops, with some cells being depleted of and others retaining mtDNA. These techniques could be useful as potential therapeutic monitors to indicate when NRTI therapy should be interrupted to prevent mitochondrial toxicity and could aid in the development of less toxic NRTIs by providing an assay suitable for pharmacodynamic evaluation of candidate molecules.

Amperometric sensor for glutathione reductase activity determination in erythrocyte hemolysate

The development of an amperometric sensor for glutathione reductase (GR) activity in erythrocyte hemolysate to contribute to oxidative stress evaluation is presented. In this assay, the reduced form of glutathione, the product of the GR reaction, reacts with 5,5(')-dithiobis(2-nitrobenzoic acid), producing GSTNB, which is easily reduced in the electrode surface. The current was recorded during 180 s after the sample addition, applying a potential of -300 mV. The sensor presented a suitable sensitivity, a good operational range, and precision. The effects of pH variations and specific uncompetitive inhibitor (safranin-O) in the enzyme activity were also evaluated. The GR activity determination in human erythrocyte hemolysate using this method has provided results that are statistically equal to those obtained by the classical spectrophotometric method, with 95% of confidence. The advantages of this method are the saved time, reagents, and samples and the possibility of its use in the field.

Mitochondrial toxicity of NRTI antiviral drugs: an integrated cellular perspective

Highly active antiretroviral therapy (HAART) regimes based on nucleoside reverse transcriptase inhibitors (NRTIs) have revolutionized the treatment of AIDS in recent years. Although HAART can successfully suppress viral replication in the long term, it is not without significant toxicity, which can seriously compromise treatment effectiveness. A major toxicity that has been recognized for more than a decade is NRTI-related mitochondrial toxicity, which manifests as serious side effects such as hepatic failure and lactic acidosis. However, a lack of understanding of the mechanisms underlying mitochondrial toxicity has hampered efforts to develop novel drugs with better side-effect profiles. This review characterizes the pharmacological mechanisms and pathways that are involved in mitochondrial dysfunction caused by NRTIs, and suggests opportunities for future pharmacological research.

Mitochondrial dysfunction and nucleoside reverse transcriptase inhibitor therapy: experimental clarifications and persistent clinical questions

Nucleoside reverse transcriptase inhibitors (NRTIs) in combination with other antiretrovirals (HAART) are critical in current AIDS therapy, but mitochondrial side effects have come to light with the increased use of these compounds. Clinical experience, pharmacological, cell and molecular biological evidence links altered mitochondrial (mt-) DNA replication to the toxicity of NRTIs in many tissues, and conversely, mtDNA replication defects and mtDNA depletion in specific target tissues are observed. The shared features of mtDNA depletion and energy depletion became key observations and related the clinical and in vivo experimental findings to inhibition of mtDNA replication by NRTI triphosphates in vitro. Subsequent to those findings, other observations suggested that mitochondrial energy deprivation is concomitant with or the result of mitochondrial oxidative stress in AIDS (from HIV, for example) or from NRTI therapy itself. With increased use of NRTIs, mtDNA mutations may become increasingly important pathophysiologically. One important future goal is to prevent or attenuate the side effects so that improved efficacy is achieved.