Tests for mitochondrial function and DNA: potentials and pitfalls

Mitochondrial DNA copy number in autism spectrum disorder and attention deficit hyperactivity disorder: a systematic review and meta-analysis

Background

Several reports suggest that altered mitochondrial DNA copy number (mtDNA-cn), a common biomarker for aberrant mitochondrial function, is implicated in autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD), but the results are still elusive.

Methods

A meta-analysis was performed to summarize the current indication and to provide a more precise assessment of the mtDNA-cn in ASD and ADHD. A search in the MEDLINE-PubMed, Scopus, and EMBASE databases was done to identify related studies up to the end of February 2023. The meta-analysis was conducted according to recommendations of the Cochrane Handbook of Systematic Reviews.

Results

Fourteen studies involving 666 cases with ASD and ADHD and 585 controls were collected and judged relevant for the systematic review and meta-analysis. The pooled results by a random effects meta-analysis was reported as a geometric mean of the estimated average response ratio and 95% confidence interval. Overall analysis of studies reported differences in mtDNA-cn in blood samples (k = 10) and non-blood samples (brain tissues and oral samples; k = 4) suggested significantly higher mtDNA-cn in patients compared to controls (p = 0.0275). Sub-analysis by stratifying studies based on tissue type, showed no significant increase in mtDNA-cn in blood samples among patients and controls (p = 0.284). Conversely, higher mtDNA-cn was observed in non-blood samples in patients than in controls (p = 0.0122). Further stratified analysis based on blood-cell compositions as potential confounds showed no significant difference in mtDNA-cn in peripheral blood samples of patients comparted to controls (p = 0.074). In addition, stratified analysis of aged-matched ASD and ADHD patients and controls revealed no significant difference in mtDNA-cn in blood samples between patients and controls (p = 0.214), whereas a significant increase in mtDNA-cn was observed in non-blood samples between patients and controls (p < 0.001). Finally, when the mtDNA-cn was analyzed in blood samples of aged-matched patients with ASD (peripheral blood, leukocytes, and PBMCs) or ADHD (peripheral blood), no significant difference in mtDNA-cn was observed between ASD patients and controls (p = 0.385), while a significant increase in mtDNA-cn was found between ADHD patients and controls (p = 0.033).

Conclusion

In this first meta-analysis of the evaluation of mtDNA-cn in ASD/ADHD, our results show elevated mtDNA-cn in ASD and ADHD, further emphasizing the implication of mitochondrial dysfunction in neurodevelopmental disorders. However, our results indicate that the mtDNA-cn in blood is not reflected in other tissues in ASD/ADHD, and the true relationship between blood-derived mtDNA-cn and ASD/ADHD remains to be defined in future studies. The importance of blood-cell compositions as confounders of blood-based mtDNA-cn measurement and the advantages of salivary mtDNA-cn should be considered in future studies. Moreover, the potential of mtDNA-cn as a biomarker for mitochondrial malfunction in neurodevelopmental disorders deserves further investigations.

A case for measuring both cellular and cell-free mitochondrial DNA as a disease biomarker in human blood

Circulating mitochondrial DNA (mtDNA), widely studied as a disease biomarker, comprises of mtDNA located within mitochondria, indicative of mitochondrial function, and cell-free (cf) mtDNA linked to inflammation. The purpose of this study was to determine the ranges of, and relationship between, cellular and cf mtDNA in human blood. Whole blood from 23 controls (HC) and 20 patients with diabetes was separated into peripheral blood mononuclear cells (PBMCs), plasma, and serum. Total DNA was isolated and mtDNA copy numbers were determined using absolute quantification. Cellular mtDNA content in PBMCs was higher than in peripheral blood and a surprisingly high level of cf mtDNA was present in serum and plasma of HC, with no direct relationship between cellular and cf mtDNA content within individuals. Diabetes patients had similar levels of cellular mtDNA compared to healthy participants but a significantly higher cf mtDNA content. Furthermore, only in patients with diabetes, we observed a correlation between whole blood and plasma mtDNA levels, indicating that the relationship between cellular and cf mtDNA content is affected by disease status. In conclusion, when evaluating mtDNA in human blood as a biomarker of mitochondrial dysfunction, it is important to measure both cellular and cf mtDNA.

Mitochondrial Toxicogenomics for Antiretroviral Management: HIV Post-exposure Prophylaxis in Uninfected Patients

Background: Mitochondrial genome has been used across multiple fields in research, diagnosis, and toxicogenomics. Several compounds damage mitochondrial DNA (mtDNA), including biological and therapeutic agents like the human immunodeficiency virus (HIV) but also its antiretroviral treatment, leading to adverse clinical manifestations. HIV-infected and treated patients may show impaired mitochondrial and metabolic profile, but specific contribution of viral or treatment toxicity remains elusive. The evaluation of HIV consequences without treatment interference has been performed in naïve (non-treated) patients, but assessment of treatment toxicity without viral interference is usually restricted to in vitro assays.

Objective: The objective of the present study is to determine whether antiretroviral treatment without HIV interference can lead to mtDNA disturbances. We studied clinical, mitochondrial, and metabolic toxicity in non-infected healthy patients who received HIV post-exposure prophylaxis (PEP) to prevent further infection. We assessed two different PEP regimens according to their composition to ascertain if they were the cause of tolerability issues and derived toxicity.

Methods: We analyzed reasons for PEP discontinuation and main secondary effects of treatment withdrawal, mtDNA content from peripheral blood mononuclear cells and metabolic profile, before and after 28 days of PEP, in 23 patients classified depending on PEP composition: one protease inhibitor (PI) plus Zidovudine/Lamivudine (PI plus AZT + 3TC; n = 9) or PI plus Tenofovir/Emtricitabine (PI plus TDF + FTC; n = 14).

Results: Zidovudine-containing-regimens showed an increased risk for drug discontinuation (RR = 9.33; 95% CI = 1.34–65.23) due to adverse effects of medication related to gastrointestinal complications. In the absence of metabolic disturbances, 4-week PEP containing PI plus AZT + 3TC led to higher mitochondrial toxicity (−17.9 ± 25.8 decrease in mtDNA/nDNA levels) than PI plus TDF + FTC (which increased by 43.2 ± 24.3 units mtDNA/nDNA; p < 0.05 between groups). MtDNA changes showed a significant and negative correlation with baseline alanine transaminase levels (p < 0.05), suggesting that a proper hepatic function may protect from antiretroviral toxicity.

Conclusions: In absence of HIV infection, preventive short antiretroviral treatment can cause secondary effects responsible for treatment discontinuation and subclinical mitochondrial damage, especially pyrimidine analogs such as AZT, which still rank as the alternative option and first choice in certain cohorts for PEP. Forthcoming efforts should be focused on launching new strategies with safer clinical and mitotoxic profile.

Extracellular Mitochondrial DNA and N-Formyl Peptides in Trauma and Critical Illness: A Systematic Review

OBJECTIVES

Extracellular mitochondrial DNA and N-formyl peptides released following tissue damage may contribute to systemic inflammation through stimulation of the innate immune system. In this review, we evaluate existing in vivo human data regarding a role for mitochondrial DNA and N-formyl peptides in producing systemic inflammation in trauma and critical illness, investigate the utility of these molecules in risk prediction and clinical decision support, and provide suggestions for standardization of future research.

DATA SOURCES

PubMed, Embase (1971-2017).

STUDY SELECTION

Studies measuring extracellular mitochondrial DNA and/or N-formyl peptides in acutely ill patients.

DATA EXTRACTION

Fifty-four studies were analyzed. Data extracted included article characteristics, methods, results, and performance in clinical prediction.

DATA SYNTHESIS

The most common patient types investigated were trauma (19 studies) and sepsis (eight). In studies comparing patient mitochondrial DNA or N-formyl peptide levels to healthy controls, 38 (90.5%) reported significantly elevated mitochondrial DNA levels in patients at first reported time point, as did the one study making this comparison for N-formyl peptides. Nine studies (81.8%) reported significantly elevated plasma/serum mitochondrial DNA levels in at least one time point in patients who developed inflammatory complications of their primary pathology compared with patients without inflammatory complications. For the ability of mitochondrial DNA to predict complications or outcomes, the area under the curve was 0.7 or greater in 84.6% of receiver operating characteristic curves, and 92.9% of odds, adjusted odds, risk, and hazard ratios were statistically significant.

CONCLUSIONS

Extracellular mitochondrial DNA levels are elevated early in patients' hospital courses in many acute illnesses and are higher in patients who develop inflammatory complications. Elevated mitochondrial DNA levels may be clinically useful in risk prediction and clinical decision support systems. Further research is needed to determine the role of extracellular N-formyl peptides in systemic inflammation and their possible clinical utility.

Cardiac and mitochondrial function in HIV-uninfected fetuses exposed to antiretroviral treatment

BACKGROUND

Mitochondrial toxicity related to maternal combined antiretroviral treatment (cART) may have an impact on the heart of HIV-exposed uninfected (HEU) fetuses. Our objective was to evaluate fetal cardiovascular and mitochondrial biomarkers in HIV pregnancies.

METHODS

Prospective cohort including 47 HIV-infected and 47 non HIV-infected pregnancies. Fetal echocardiography was performed at 26-32 weeks of pregnancy. Umbilical cord blood and placental tissue were collected to study mitochondrial DNA content (mtDNA) (ratio 12SrRNA/RNAseP) and mitochondrial function (cytochrome c oxidase, COX, enzymatic activity) normalized by mitochondrial content (citrate synthase, CS).

RESULTS

HEU fetuses showed hypertrophic hearts (left myocardial wall thickness: HIV mean 3.21 mm (SD 0.81) vs. non-HIV 2.72 (0.42), p = 0.012), with signs of systolic and diastolic dysfunction (isovolumic relaxation time: HIV 52.2 ms (8.85) vs. non-HIV 42.5 ms (7.30); p<0.001). Cord blood mitochondrial content was significantly increased in HIV-exposed fetuses (CS activity: HIV 82.9 nmol/min.mg of protein (SD 40.5) vs. non-HIV 56.7 nmol/min.mg of protein (28.4); p = 0.007), with no differences in mtDNA content and COX activity. Both myocardial and mitochondrial mass parameters were significantly associated with zidovudine exposure.

CONCLUSIONS

HEU fetuses showed signs of increased myocardial and mitochondrial mass associated with maternal zidovudine treatment, suggesting a fetal adaptive response to cART toxicity.

Peripheral blood mitochondrial DNA copy number as a novel potential biomarker for diabetic nephropathy in type 2 diabetes patients

The mitochondrial DNA copy number (mtDNA-CN) is a surrogate measure of mitochondrial function and altered mtDNA-CN reflects the oxidant-induced cell damage. A previous study by our group demonstrated that a reduction in the renal mtDNA-CN is implicated in the pathogenesis of diabetic nephropathy (DN), a leading cause of end-stage renal disease in diabetic patients. In the present study, it was investigated whether the mtDNA-CN in the peripheral blood may be utilized as a biomarker for DN in type 2 diabetes (T2D) patients. The study included 50 non-diabetic and 100 diabetic subjects. The diabetic subjects were sub-divided based on their albumin-to-creatinine ratio (ACR) into T2D patients with normoalbuminuria (n=50), DN patients with microalbuminuria (n=29) and DN patients with macroalbuminuria (n=21). The mtDNA-CN was measured in the peripheral blood by real-time polymerase chain reaction analysis. Patients with DN had a lower mtDNA-CN than patients with T2D and healthy controls (P<0.05). A sub-group analysis with stratification by the ACR indicated that a decreased mtDNA-CN was associated with the severity and the presence of DN, as it was lower in DN patients with macroalbuminuria than in DN patients with microalbuminuria and T2D patients with normoalbuminuria (P<0.01). The area under the receiver operating characteristic curve (AUC) for mtDNA-CN was 0.916 (sensitivity, 86% and specificity, 74%) and 0.961 (sensitivity, 96% and specificity, 88%) for differentiating DN patients from T2D patients without DN and from healthy controls, respectively. Furthermore, the AUC of mtDNA-CN for differentiating DN patients with microalbuminuria from those with macroalbuminuria was 0.895 (sensitivity, 83% and specificity, 85%). Multivariate analysis revealed that the mtDNA-CN was significantly associated with the occurrence and progression of DN, even after adjustment for age, mean blood pressure, glycated haemoglobin A1c and total cholesterol (P<0.05). In patients with DN, a decreased mtDNA-CN was negatively correlated with albuminuria and conventional risk factors for DN, and was positively correlated with the estimated glomerular filtration rate. The present results therefore suggest the utilization of circulating mtDNA-CN as a novel biomarker for the early diagnosis of DN and indicate the significance of decreased mtDNA-CN as another independent risk factor for DN.

Adjusting MtDNA Quantification in Whole Blood for Peripheral Blood Platelet and Leukocyte Counts

Alterations of mitochondrial DNA copy number (mtDNAcn) in the blood (mitochondrial to nuclear DNA ratio) appear associated with several systemic diseases, including primary mitochondrial disorders, carcinogenesis, and hematologic diseases. Measuring mtDNAcn in DNA extracted from whole blood (WB) instead of from peripheral blood mononuclear cells or buffy coat may yield different results due to mitochondrial DNA present in platelets. The aim of this work is to quantify the contribution of platelets to mtDNAcn in whole blood [mtDNAcn(WB)] and to propose a correction formula to estimate leukocytes' mtDNAcn [mtDNAcn(L)] from mtDNAcn(WB). Blood samples from 10 healthy adults were combined with platelet-enriched plasma and saline solution to produce artificial blood preparations. Aliquots of each sample were combined with five different platelet concentrations. In 46 of these blood preparations, mtDNAcn was measured by qPCR. MtDNAcn(WB) increased 1.07 (95%CI 0.86, 1.29; p<0.001) per 1000 platelets present in the preparation. We proved that leukocyte count should also be taken into account as mtDNAcn(WB) was inversely associated with leukocyte count; it increased 1.10 (95%CI 0.95, 1.25, p<0.001) per unit increase of the ratio between platelet and leukocyte counts. If hematological measurements are available, subtracting 1.10 the platelets/leukocyte ratio from mtDNAcn(WB) may serve as an estimation for mtDNAcn(L). Both platelet and leukocyte counts in the sample are important sources of variation if comparing mtDNAcn among groups of patients when mtDNAcn is measured in DNA extracted from whole blood. Not taking the platelet/leukocyte ratio into account in whole blood measurements, may lead to overestimation and misclassification if interpreted as leukocytes' mtDNAcn.

Antiretroviral nucleoside analogues suppress antibody synthesis in human B-lymphocytes

BACKGROUND

Some antiretroviral nucleoside reverse transcriptase inhibitors (NRTI) impair mitochondrial polymerase-γ and T-cell proliferation, possibly by pyrimidine depletion. We aimed to analyse NRTI effects on the content of mitochondrial DNA (mtDNA) and B-cells, and on their proliferation and antibody synthesis.

METHODS

Peripheral blood B-lymphocytes from six healthy individuals were stimulated in vitro with interleukin-4 and Staphylococcus aureus superantigen in the presence or absence of NRTI in concentrations equivalent to, or fivefold exceeding, human peak plasma levels. We also tested the effects of uridine, a pyrimidine precursor, which has antagonized NRTI toxicities in other models.

RESULTS

During 9 days of culture, B-lymphocyte proliferation and vitality were not affected by NRTI. Didanosine and stavudine, but not zidovudine, dose-dependently induced mtDNA depletion. All three NRTI significantly and dose-dependently impaired the synthesis of all immunoglobulin classes. The lymphocytotoxic effects of the thymidine analogues zidovudine and stavudine on B-lymphocytes were antagonized by the addition of uridine.

CONCLUSIONS

Didanosine, stavudine and zidovudine induce mitochondrial toxicity in human B-lymphocytes and impair the immunoglobulin synthesis in vitro, warranting further studies on their in vivo effects.

Cytometric assessment of mitochondria using fluorescent probes

Mitochondria are most important organelles in the survival of eukaryotic aerobic cells because they are the primary producers of ATP, regulators of ion homeostasis or redox state, and producers of free radicals. The key role of mitochondria in the generation of primordial ATP for the survival and proliferation of eukaryotic cells has been proven by extensive biochemical studies. In this context, it is crucial to understand the complexity of the mitochondrial compartment and its functionality and to develop experimental tools allowing the assessment of its nature and its function and metabolism. This review covers the role of the mitochondria in the cell, focusing on its structure, the mechanism of the mitochondrial respiratory chain, the maintenance of the transmembrane potential and the production of reactive oxygen species. The main probes used for mitochondrial compartment monitoring are described. In addition, various applications using mitochondrial-specific probes are detailed to illustrate the potential of flow and image cytometry in the study of the mitochondrial compartment. This review contains a panel of tools to explore mitochondria and to help researchers design experiments, determine the approach to be employed, and interpret their results.

Short communication: decrease in mitochondrial transmembrane potential in peripheral blood mononuclear cells of HIV-uninfected subjects undergoing HIV postexposure prophylaxis

To monitor the mitochondrial transmembrane potential (ΔΨm), peripheral blood mononuclear cells (PBMCs) from 18 HIV-uninfected individuals completing a 4-week course of HIV postexposure prophylaxis (PEP) with emtricitabine/tenofovir and lopinavir/ritonavir were analyzed. ΔΨm was assessed by FACS analysis after staining with JC-1 using a mixed effects regression analysis. Apoptosis was determined by Annexin-V-FITC and propidium iodide staining. ΔΨm decreased significantly during HIV-PEP (p=0.0015 for the linear term, p=0.0039 for the quadratic term of days on PEP) and normalized several weeks after stopping antiretrovirals. The apoptosis rates did not change significantly (p=0.42). Even newer drugs such as tenofovir and emtricitabine may cause side effects due to mitochondrial dysfunction.

Mitochondrial dysfunction in CD4+ lymphocytes from stavudine-treated HIV patients

HIV therapy with nucleoside analogue reverse transcriptase inhibitors (NRTI) such as stavudine remains in widespread use in resource-limited nations due to potent efficacy, convenience of formulation and lack of practical alternatives. However, it remains unclear whether adverse side effects with NRTI include reduced mitochondrial respiratory function, particularly in peripheral blood lymphocytes (PBLs). The aim of this study was to determine whether stavudine-based highly active antiretroviral therapy (HAART) is associated with impaired mitochondrial respiratory transport chain function in patient derived CD4+PBLs. CD4+PBLs were isolated from asymptomatic HIV-infected patients treated with stavudine-HAART for 3 months (n=10), HIV-infected patients not on treatment (n=9) and uninfected controls (n=18). The basal mitochondrial oxygen consumption of CD4+PBLs from stavudine-treated patients was reduced relative to that of untreated HIV-infected patients and controls (stavudine treated group, 4.22 (25% 2.16, 75% 8.84); control uninfected, 11.2 (25% 3.95, 75% 16.6); untreated 18.1 (25% 11.8, 75% 37.9)ng oxygen atoms/min/ml). Maximal oxygen consumption (stimulated with the proton ionophore FCCP) in cells from stavudine treated patients was also reduced relative to that of untreated patients and controls (stavudine treated, 24.4+/-10.5; control uninfected, 50.6+/-39.5; untreated, 68.8+/-41.1 ng oxygen atoms/min/ml). Citrate synthase activities, relative mitochondrial volume (by electron microscopy) and mtDNA copy numbers per cell were not different between groups. Therapy with stavudine results in impaired mitochondrial function in CD4+PBLs that does not appear to be due to reduced mitochondrial volume or DNA content and cannot be attributed to infection with HIV.

Upregulation of nuclear-encoded mitochondrial LON protease in HAART-treated HIV-positive patients with lipodystrophy: implications for the pathogenesis of the disease

BACKGROUND

HAART can provoke metabolic changes and body fat redistribution, resulting in lipodystrophy, a side effect significantly involving mitochondrial function. Mitochondrial DNA (mtDNA) depletion caused by nucleosidic reverse transcription inhibitors is supposed to be a crucial mechanism in the pathogenesis of mitochondrial damages.

METHODS

In adipose tissue from 22 HIV-positive patients with lipodystrophy and 20 healthy controls, we analyzed gene expression by microarray analysis and real-time PCR. The most upregulated gene was further studied in the human adipocytic cell line SW872 by real-time PCR, western blot, transient transfection assays and flow cytometry.

RESULTS

We identified 18 genes differently expressed between lipodystrophy patients and controls, and focused our attention on the nuclear-encoded mitochondrial protease LON, essential in mtDNA maintenance. In SW872 cells, treatment with stavudine (d4T) doubled LON levels, in parallel with mtDNA depletion. As d4T increased reactive oxygen species (ROS) intracellular content, we measured LON in presence of deoxyribose, which causes oxidative stress but not mtDNA depletion, and observed LON upregulation. Ethidium bromide, which markedly depletes mtDNA, did not alter LON levels. The antioxidant glutathione inhibited the increase of intracellular ROS and the increase in LON caused by d4T or deoxyribose.

CONCLUSION

LON upregulation was due to d4T-induced ROS production, rather than due to mtDNA depletion, and represents a response to an oxidative stress. Other mechanisms than mtDNA depletion thus exist that explain nucleosidic reverse transcription inhibitors toxicity. This observation provides a rationale for possible therapeutic interventions aimed at reducing intracellular ROS content in patients assuming HAART.

Mitochondrial membrane potential and apoptosis of blood mononuclear cells in untreated HIV-1 infected patients

OBJECTIVES

Infection with HIV leads to progressive CD4 T-cell loss, resulting in AIDS. Apoptosis is the main mechanism for the loss of infected and bystander cells, but the complex interacting factors inducing and inhibiting apoptosis are not fully understood. Mitochondrial dysfunction is a pivotal step of the apoptotic cascade and can result in reduced mitochondrial membrane potential.

METHODS

The mitochondrial membrane potential of peripheral blood mononuclear cells (PBMC) was measured by flow cytometry using the dye JC-1 (Molecular Probes Inc). Apoptotic cells were identified using the Annexin V assay (Becton Dickinson GmbH).

RESULTS

The mitochondrial membrane potential of PBMC was significantly decreased and apoptotic cell rate was increased in HIV-infected therapy-naïve patients compared with HIV-negative controls. There was a highly significant correlation between the mitochondrial membrane potential and the rate of apoptosis. CD4 cell count was correlated negatively to the apoptotic rate and positively to the mitochondrial membrane potential.

CONCLUSIONS

The JC-1 assay is a sensitive tool to detect changes of mitochondrial membrane potential associated with apoptosis in HIV-infected therapy-naïve patients. We could show in vivo that a reduction of mitochondrial membrane potential is correlated to apoptosis of PBMC, CD4 cell count and HIV viral load during HIV infection.

Quantification of mitochondrial DNA copy number: pre-analytical factors

Mitochondrial DNA (mtDNA) content is important for understanding many cellular processes. Several pre-analytical factors, from sample collection to DNA extraction can affect measurement of mtDNA copy number. In the present study, whole blood samples yielded a higher mtDNA copy number than buffy coat samples. mtDNA content is affected by the cell separation method used and the time between blood withdrawal and cell separation. Thus, reference values must be established with the same type of sample. As to the DNA isolation and purification method, the manual phenol method can give randomly false high values. The QIAamp DNA Mini Kit provided the most highly reproducible mtDNA/nDNA yield.

Platelet contamination causes large variation as well as overestimation of mitochondrial DNA content of peripheral blood mononuclear cells

BACKGROUND

Alterations in the copy number of mitochondrial DNA (mtDNA) play a role in the pathogenesis of mitochondrial diseases and other many common diseases. Recently, the copy number of leukocyte mtDNA has been considered to serve as a biomarker to monitor or chase such diseases. Therefore, reproducible mtDNA measurement is required.

METHODS

Peripheral blood mononuclear cells were prepared by a density-based method. The mtDNA/cell was measured by quantitative realtime polymerase chain reaction.

RESULTS

The degree of platelet contamination varied to a large extent among preparations. The mtDNA copy numbers per mononuclear cell were 269 +/- 51 and 146 +/- 14 in the samples before and after the platelet depletion, respectively.

CONCLUSION

A density-based mononuclear cell preparation causes heavy platelet contamination. The platelet depletion from a sample is particularly important for comparing the mtDNA contents between different dates or between different patients.

Increased mtDNA levels without change in mitochondrial enzymes in peripheral blood mononuclear cells of infants born to HIV-infected mothers on antiretroviral therapy

BACKGROUND

The effects of gestational nucleoside reverse transcriptase inhibitors (NRTIs) on mitochondrial DNA (mtDNA) are controversial. The effects of mtDNA depletion on mitochondrial function have not been assessed.

METHOD

In peripheral blood mononuclear cells (PBMCs) from infants born to HIV-infected women and infants born to HIV-1-uninfected women, mtDNA copy numbers were determined by quantitative PCR; nuclear (COXIV)- and mitochondrial (COXII)-encoded polypeptides of the oxidative phosphorylation enzyme cytochrome c-oxidase (COX or complex IV) were quantified by Western blot.

RESULTS

Overall, 86 infants born to HIV-infected women and 50 controls were studied. HIV-infected mothers had a median CD4 count of 506 cells/microL; 59% had HIV RNA 50 copies/mL. No infant had clinical evidence of mitochondrial disease. The birth weight was lower (p = .016) and the body length higher (p = .002) in the HIV-exposed newborns. Eighty-one HIV-infected women had received gestational NRTIs (median duration 162 days). Median mtDNA copies/PBMC in the HIV-exposed infants were 505 (range, 120-1365) vs. 213 (27-426) in controls (p < .001). COX II/IV ratios were similar in both groups. Although mtDNA levels correlated inversely with maternal lactate, mitochondrial indices did not correlate with maternal CD4+ count, HIV RNA, smoking, or alcohol consumption.

CONCLUSION

We found elevated mtDNA copy numbers in PBMC of infants born to HIV-infected women, the majority of whom received NRTI-based therapy, when compared to those born to healthy HIV-negative controls, but there was no difference in mtDNA-encoded respiratory chain protein. The clinical consequence of these findings is unknown and requires further investigations.

Impact of nucleoside reverse transcriptase inhibitors on mitochondria in human immunodeficiency virus type 1-infected children receiving highly active antiretroviral therapy

Mitochondrial toxicity induced by nucleoside reverse transcriptase inhibitors (NRTIs) has been reported to be responsible for various adverse effects. The relative impact of NRTIs on the mitochondria of human immunodeficiency virus (HIV) type 1 (HIV-1)-infected children receiving highly active antiretroviral therapy (HAART) is unknown. Mitochondrial DNA (mtDNA) levels were quantified longitudinally from peripheral blood mononuclear cells (PBMCs) in 31 HIV-1-infected children from Pediatric AIDS Clinical Trial Group Study 382 who were receiving HAART, including nelfinavir, efavirenz, and different NRTIs, and who had had undetectable plasma HIV-1 RNA levels for >2 years. The median mtDNA levels in PBMCs increased from 137 copies/cell at the baseline to 179 copies/cell at week 48 (P = 0.01) and 198 copies/cell at week 104 (P < 0.001). Before the initiation of HAART, children who received regimens containing didanosine had mtDNA levels persistently lower than those in children not receiving didanosine (106 versus 140 copies/cell; P = 0.008). During HAART, the median increase in the mtDNA level from the baseline to week 104 was the lowest in children who received regimens containing didanosine (+26 copies/cell) compared to those in children who received other regimens (+79 copies/cell) (P = 0.02). A multivariate analysis also demonstrated that didanosine, as part of HAART, was the only NRTI associated with the change in mtDNA levels (P = 0.007). Children receiving didanosine-containing antiretroviral regimens have the lowest mtDNA levels in PBMCs and may be at greater risk for long-term adverse effects due to mitochondrial toxicity. This may be of particular importance in resource-limited countries where didanosine is widely used for the treatment of HIV-infected children.

The Influence of HIV Infection and Antiretroviral Therapy on the Mitochondrial Membrane Potential of Peripheral Mononuclear Cells

Objectives

Clinical disorders occurring in HIV-infected patients on antiretroviral therapy (ART) have been linked to mitochondrial dysfunction, for example, lactic acidosis and lipodystrophy. Mitochondrial membrane potential (ΔΨm) is the most direct measure of the state of energization of the mitochondria. We analysed ΔΨm of peripheral blood mononuclear cells (PBMCs) in HIV-negative, healthy subjects ( n=8), HIV-infected, treatment-naive patients ( n=30), and HIV-infected patients on ART ( n=58). The influence of ART was analysed in six patients who started their first regimen.

Methods

The ΔΨm of PBMC was measured by flow cytometry using the dye JC-1.

Results

The ΔΨm was significantly lower in HIV-infected patients than in HIV-negative controls. This difference was detected in both treated ( P=0.0001) and untreated patients ( P=0.001). The ΔΨm of PBMCs was highly correlated with CD4+ T-cell count in therapy-naive patients ( P=0.002, r=0.546) and in treated patients ( P=0.028, r=0.288). The ΔΨm increased significantly in therapy-naive patients after starting ART ( P=0.001). Patients with lipoatrophy had significantly lower ΔΨm than patients without lipodystrophy or with lipohypertrophy ( P=0.023).

Conclusions

In HIV-infected persons ΔΨm is significantly reduced. Patients with lipoatrophy have significantly reduced ΔΨm. This is the first study showing that the ΔΨm of PBMCs is highly correlated with CD4+ T-cell count in HIV infection.

The Impact of Reducing Stavudine dose versus switching to tenofovir on plasma lipids, body composition and mitochondrial function in HIV-infected patients

Background

Stavudine (d4T)-containing regimens are associated with a potential for lipoatrophy and dyslipidaemia. We assessed the safety and efficacy of reducing the dose of stavudine compared with switching to tenofovir or maintaining the standard dose of d4T.

Methods

Clinically stable HIV-infected patients receiving antiretroviral therapy containing stavudine 40 mg twice daily with a plasma HIV RNA <200 copies/ml for at least 6 months were randomized to maintain stavudine 40 mg twice daily (d4T40 arm), to reduce to 30 mg twice daily (d4T30 arm), or to switch from d4T to tenofovir (TDF arm).

Results

Fifty-eight (93% male) patients were included: 22 in the d4T40 arm, 19 in the d4T30 arm and 17 in TDF arm. At baseline, median time on d4T was 6 years (interquartile range [IQR] 2.6–7.1), median age 43 years (IQR 36–51) and median CD4+ T-cell count was 587/mm3 (IQR 329–892). At week 24, median limb fat changes (g) were as follows: d4T40=-182 (95% CI: -469—5); d4T30=527 (95% CI: -343–694); and TDF=402 (95% CI: 130–835; d4T40 versus TDF, P=0.0003). Significant differences between median values of laboratory parameters were detected: triglycerides (mg/dl): d4T40=19; d4T30=-23 and TDF=-79 (d4T40 versus TDF, P=0.03); and total cholesterol (mg/dl): d4t40=22, d4T30=-4, and TDF=-28 (d4T40 versus TDF, P=0.04). No significant difference was observed in mitochondrial function assessed in peripheral blood mononuclear cells.

Conclusions

Although both strategies were associated with a trend toward a decrease in plasma lipids and an increase in body fat, the only significant changes were observed among those who switched to tenofovir.

Tissue-specific associations between mitochondrial DNA levels and current treatment status in HIV-infected individuals

BACKGROUND

Tissue mitochondrial DNA (mtDNA) levels have been proposed as a marker of nucleoside analouge reverse transcriptase inhibitor (NRTI) toxicity. However, clinical studies have yielded conflicting data regarding possible associations with mtDNA levels. This study examined mtDNA levels in matched samples of peripheral blood mononuclear cells (PBMCs) and subcutaneous fat from a large Australian cohort to examine treatment, clinical, and demographic associations with mtDNA depletion.

METHODS

mtDNA was quantified by real-time polymerase chain reaction. Results were compared across patient treatment and demographic details using linear mixed models.

RESULTS

One hundred sixty-three PBMCs and 161 fat samples were available from 61 individuals. Current NRTI exposure was the major determinant of mtDNA levels. Both ddI (didanosine) and d4T (stavudine) exposures were associated with mtDNA depletion in fat (P < or = 0.0001 vs. those not on NRTIs). DdI exposure (P = 0.003), but not d4T exposure (P = 0.5), was associated with mtDNA depletion in PBMCs. No association between patient demographics or time on current therapy and mtDNA was observed.

CONCLUSIONS

Current NRTI exposure is the major determinant of tissue mtDNA, but the precise determinants are tissue specific. Both ddI and d4T exposure are associated with fat mtDNA depletion, whereas ddI exposure was the only observed association with mtDNA depletion in PBMCs.

Anti-HIV drugs and the mitochondria

Several drugs are currently used that can significantly prolong the course of the infection with the human immunodeficiency virus (HIV), the cause of the acquired immunodeficiency syndrome (AIDS). Among these drugs, the nucleosidic inhibitors of viral reverse transcriptase can alter mitochondrial (mt) function by inhibiting the mitochondrial DNA polymerase gamma (the enzyme responsible for the replication of mtDNA). Decreased mtDNA content provokes a diminished synthesis of respiratory chain enzymes, leading to alterations in mt function. These are in turn responsible for a variety of side effects frequently observed in HIV+ patients, that range from hyperlactatemia and lactic acidosis to lipodystrophy, a pathology characterized by accumulation of visceral fat, breast adiposity, cervical fat-pads, hyperlipidemia, insulin resistance and fat wasting in face and limbs. In this paper, data concerning the effects of different compounds on mitochondria, their role in the pathogenesis of lipodystrophy, and problems related to studies on the mt toxicity of antiviral drugs are reviewed and thoroughly discussed.

Mitochondrial Toxicity of Nucleoside Analogues in Primary Human Lymphocytes

Objective

To evaluate if nucleoside analogue reverse transcriptase inhibitors (NRTIs) and polymerase-gamma inhibitors deplete mitochondrial DNA (mtDNA) in cultured primary lymphocytes and if such depletion might be associated with functional defects.

Methods

Primary peripheral blood CD4 and CD8 lymphocytes were purified from six healthy humans (three male and three female), stimulated mitotically (CD3/CD28) and cultured for 10 days in the presence or absence of NRTIs. Lymphocyte proliferation, mtDNA content, the expression of mtDNA-encoded cytochrome c-oxidase II (COXII) and lactate production were assessed.

Results

In CD4 lymphocytes, 10-day exposure to zalcitabine (1.77 μM), didanosine (118 μM) and stavudine (36 μM) induced a time-dependent decline of mtDNA. Compared with controls, residual mtDNA levels were 25%, 21% and 40%, respectively. COXII was reduced to 55%, 35% and 70% of control values. Lactic acid production was increased (by 214%, 294% and 175%, respectively). At day 10, lymphocyte counts were reduced (to 60%, 51%, and 41%, respectively). Zidovudine (71 μM) also reduced lymphocyte counts to 34% and increased lactic acid production by 170%, but did not induce mtDNA and COXII depletion. All these changes were highly significant. Lower NRTI concentrations (0.177 μM of zalcitabine, 11.8 μM of didanosine, 3.6 μM of stavudine and 7.1 μM of zidovudine) had effects at the border of significance. Similar observations were made in CD8 lymphocytes.

Conclusions

In human lymphocytes, zalcitabine, didanosine and stavudine induce dose- and time-dependent mtDNA depletion, which is associated with decreased cell proliferation and increased lactate production. Zidovudine impairs lymphocyte division without inducing mtDNA depletion.

Possible Ways Nucleoside Analogues Can Affect Mitochondrial Dna Content and Gene Expression during HIV Therapy

In recent years, research into nucleoside reverse transcriptase inhibitor (NRTI)-related mitochondrial (mt) toxicity in HIV therapy has led to conflicting results and many unanswered questions regarding the molecular mechanisms that lead to such toxicity. From the early hypothesis that inhibition of the human mt polymerase γ by NRTIs was responsible for the drugs’ mt toxicity, an increasingly complex picture is emerging that probably involves multiple mt pathways. Results have been presented suggesting that NRTIs affect not only mtDNA but also mtRNA, nucleotide phosphorylation and the mt respiratory chain. Based on the current level of knowledge, this overview addresses some of the potential mechanisms through which NRTIs could affect mitochondria and ultimately cause the toxicity symptoms observed in HIV patients receiving NRTI-containing antiretroviral therapy.

Uridine in the Prevention and Treatment of Nrti-Related Mitochondrial Toxicity

Long-term side effects of antiretroviral therapy are attributed to the mitochondrial (mt) toxicity of nucleoside analogue reverse transcriptase inhibitors (NRTIs) and their ability to deplete mtDNA. Studies in hepatocytes suggest that uridine is able to prevent and treat mtDNA depletion by pyrimidine NRTIs [zalcitabine (ddC) and stavudine (d4T)] and to fully abrogate hepatocyte death, elevated lactate production and intracellular steatosis. Uridine was also found to improve the liver and haematopoietic toxicities of zidovudine (AZT), which are unrelated to mtDNA depletion, and to prevent neuronal cell death induced by ddC. Most recently, uridine was found to prevent the onset of a lipoatrophic phenotype (reduced intracellular lipids, increased apoptosis, mtDNA depletion and mt depolarization) in adipocytes incubated long-term with d4T and AZT. Various steps of mt nucleoside utilization may be involved in the protective effect, but competition of uridine metabolites with NRTIs at polymerase y or other enzymes is a plausible explanation. Pharmacokinetic studies suggest that uridine serum levels can be safely increased in humans to achieve concentrations which are protective in vitro (50–200 μM). Uridine was not found to interfere with the antiretroviral activity of NRTIs. Mitocnol, a sugar cane extract which effectively increases uridine in human serum, was beneficial in individual HIV patients with mt toxicity and is now being tested in placebo-controlled randomized trials. Until these data become available, the risk-benefit calculation of using uridine should be individualized. The current safety data justify the closely monitored use of uridine in individuals who suffer from mt toxicity but who cannot be switched to less toxic NRTIs.

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.

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.

Increased Mitochondrial Dna Content in Peripheral Blood Lymphocytes from HIV-Infected Patients with Lipodystrophy

We have evaluated mitochondrial (mt) DNA content in CD4 and CD8 peripheral blood lymphocytes (PBLs) from HIV-infected patients taking highly active antiretroviral therapy (HAART) who display different types of adipose tissue alterations. A cross-sectional study was performed in a total of 23 patients with lipodystrophy (LD): nine patients with fat accumulation, six patients with fat loss, eight patients with combined form, who were compared to 11 individuals infected by HIV without LD (HIV-positive) and 10 seronegative controls (CTRL). PBLs were obtained by standard methods, that is, gradient density centrifugation on Ficoll, and CD4 or CD8 cells were positively isolated by magnetic sorting to eliminate the contamination of platelets. mtDNA content was then measured by an original assay based upon real-time PCR. mtDNA content was significantly increased in CD4 T cells from patients with LD, while no differences were present between CD4 and CD8 cells from HIV-positive and CTRL individuals. Nor were any differences found when comparing LD or HIV-positive patients treated with stavudine or zidovudine, or taking D-drugs or non D-drugs. Patients with fat accumulation had significantly higher mtDNA content compared to HIV-positive and CTRL, this phenomenon regarding both CD4 and CD8 PBLs. Considering all HIV-positive patients (including LD), mtDNA content showed a significant, positive correlation with cholesterolaemia but not with triglyceridaemia and glycaemia. Relatively high mtDNA content in LD patients, as well as the correlation between mtDNA content and cholesterol in all HIV-positive subjects, suggest the involvement of mitochondria in such a pathology. However, further studies are needed to confirm these initial observations and ascertain whether the quantification of mtDNA in PBL is a useful and reliable marker to investigate and monitor HAART-related changes in fat distribution.