Mitochondrial toxicity in hearts of CD-1 mice following perinatal exposure to AZT, 3TC, or AZT/3TC in combination

Emerging methods for and novel insights gained by absolute quantification of mitochondrial DNA copy number and its clinical applications

The past thirty years have seen a surge in interest in pathophysiological roles of mitochondria, and the accurate quantification of mitochondrial DNA copy number (mCN) in cells and tissue samples is a fundamental aspect of assessing changes in mitochondrial health and biogenesis. Quantification of mCN between studies is surprisingly variable due to a combination of physiological variability and diverse protocols being used to measure this endpoint. The advent of novel methods to quantify nucleic acids like digital polymerase chain reaction (dPCR) and high throughput sequencing offer the ability to measure absolute values of mCN. We conducted an in-depth survey of articles published between 1969 -- 2020 to create an overview of mCN values, to assess consensus values of tissue-specific mCN, and to evaluate consistency between methods of assessing mCN. We identify best practices for methods used to assess mCN, and we address the impact of using specific loci on the mitochondrial genome to determine mCN. Current data suggest that clinical measurement of mCN can provide diagnostic and prognostic value in a range of diseases and health conditions, with emphasis on cancer and cardiovascular disease, and the advent of means to measure absolute mCN should improve future clinical applications of mCN measurements.

In utero and peripartum antiretroviral exposure as predictor of cognition in 6- to 10-year-old HIV-exposed Ugandan children - a prospective cohort study

OBJECTIVES

To quantify association between in utero/peripartum antiretroviral (IPA) exposure and cognition, i.e. executive function (EF) and socioemotional adjustment (SEA), in school-aged Ugandan children who were perinatally HIV-infected (CPHIV, n = 100) and children who were HIV-exposed but uninfected (CHEU, n = 101).

METHODS

Children were enrolled at age 6-10 years and followed for 12 months from March 2017 to December 2018. Caregiver-reported child EF and SEA competencies were assessed using validated questionnaires at baseline, 6 and 12 months. IPA type - combination antiretroviral therapy (cART), intrapartum single-dose nevirapine ± zidovudine (sdNVP ± ZDV), nevirapine + zidovudine + lamivudine (sdNVP + ZDV + 3TC) - or no IPA (reference) was verified via medical records. IPA-related standardized mean differences (SMDs) with corresponding 95% confidence intervals (CIs) in cognitive competencies were estimated from regression models with adjustment for caregiver sociodemographic and contextual factors. Models were fitted separately for CPHIV and CHEU.

RESULTS

Among CPHIV children, cART (SMD = -0.82, 95% CI: -1.37 to -0.28) and sdNVP ± ZDV (SMD = -0.41, 95% CI: -0.81 to -0.00) vs. no IPA predicted lower executive dysfunction over 12 months. Intrapartum sdNVP + ZDV + 3TC vs. no IPA predicted executive dysfunction (SMD = 0.80, 95% CI: 0.30-1.31), SEA problems (SMD = 0.63-0.76, 95% CI: 0.00-1.24) and lower adaptive skills (SMD = -0.36, 95% CI: -0.75-0.02) over 12 months among CHEU. Further adjustment for contextual factors attenuated associations, although most remained of moderate clinical importance (|SMD| > 0.33).

CONCLUSIONS

Among CPHIV children, cART and sdNVP ± ZDV IPA exposure predicted, on average, lower executive dysfunction 6-10 years later. However, peripartum sdNVP + ZDV + 3TC predicted executive and SEA dysfunction among CHEU 6-10 years later. These data underscore the need for more research into long-term effects of in utero ART to inform development of appropriate interventions so as to mitigate cognitive sequelae.

Differential effects of antiretroviral drug toxicity in male versus female children who are HIV-exposed but uninfected

: In recent years, widespread use of antiretroviral therapy (ART) during pregnancy has been increasingly effective in reducing risk of vertical transmission of HIV, with over 80% of pregnant women living with HIV now accessing ART, and a 41% reduction in new infections in children between 2010 and 2018. Despite these strides, the developmental toxicity of widely administered antiretroviral drugs (ARVs) remains poorly described and existing literature often fails to account for fetal and infant sex as a variable. Recent reports have identified associations between in-utero exposure to commonly used antiretroviral regimens and alteration in neurodevelopment, growth, and metabolism amongst children who are HIV-exposed but uninfected, with findings of sex differences in the prevalence and severity of ARV toxicity. These differences are potentially explained by variable exposure to ARV drugs in utero or exacerbation of existing sex-linked risk factors. Fetal ARV exposure is mediated by placental and fetal drug transporters and metabolic enzymes, which may contribute to the manifestation of sex differences. Existing evidence of sex differences in ARV toxicity in fetal development is concerning, and demands further research to guide optimal treatment options for maternal health and prevention of vertical HIV transmission.

Comparative toxicity of three phenolic compounds on the embryo of fathead minnow, Pimephales promelas

Phenols are classified as polar narcotics, which are thought to cause toxicity by non-specific mechanisms, possibly by disrupting membrane structure and function. Here we test three phenolic chemicals, phenol, 2,4-dichlorphenol and pentachlorophenol on embryo development, heartbeat rate and mitochondrial respiration in fathead minnow (Pimephales promelas). While these chemicals have been used on isolated mitochondria, they have not yet been used to verify respiration in intact embryos. Mitochondrial respiration in intact embryos was measured after optimizing the Seahorse XFe24 Extracellular Flux Analyzer. Heartbeat rate and mitochondrial respiration patterns of fathead minnow embryos at different developmental stages were also characterized. Exposures of embryos at developmental stage 20 occurred for 24 h with five concentrations of each phenolic compound ranging from 0.85 to 255 μM for phenol, 0.49 to 147 μM for 2,4-dichlorophenol and 0.3 to 90 μM for pentachlorophenol. Exposure to phenol at the concentrations tested had no effects on development, heartbeat or mitochondrial respiration. However, both 2,4-dichlorophenol and pentachlorophenol showed dose-dependent effects on development, heartbeat rate, and mitochondrial respiration, with the effects occurring at lower concentrations of pentachlorophenol, compared to 2,4-dichlorophenol, highlighting the higher toxicity of the more chlorinated phenols. Both 2,4-dichlorophenol and pentachlorophenol decreased basal mitochondrial respiration of embryos and ATP production. These results indicate that higher chlorinated phenolic chemicals cause developmental toxicity in fathead minnow embryos by decreasing mitochondrial respiration and heartbeat rate.

Drug-induced cardiac abnormalities in premature infants and neonates

The Cardiac Safety Research Consortium (CSRC) is a transparent, public-private partnership that was established in 2005 as a Critical Path Program and formalized in 2006 under a Memorandum of Understanding between the United States Food and Drug Administration and Duke University. Our continuing goal is to advance paradigms for more efficient regulatory science related to the cardiovascular safety of new therapeutics, both in the United States and globally, particularly where such safety questions add burden to innovative research and development. This White Paper provides a summary of discussions by a cardiovascular committee cosponsored by the CSRC and the US Food and Drug Administration (FDA) that initially met in December 2014, and periodically convened at FDA's White Oak headquarters from March 2015 to September 2016. The committee focused on the lack of information concerning the cardiac effects of medications in the premature infant and neonate population compared with that of the older pediatric and adult populations. Key objectives of this paper are as follows: Provide an overview of human developmental cardiac electrophysiology, as well as the electrophysiology of premature infants and neonates; summarize all published juvenile animal models relevant to drug-induced cardiac toxicity; provide a consolidated source for all reported drug-induced cardiac toxicities by therapeutic area as a resource for neonatologists; present drugs that have a known cardiac effect in an adult population, but no reported toxicity in the premature infant and neonate populations; and summarize what is not currently known about drug-induced cardiac toxicity in premature infants and neonates, and what could be done to address this lack of knowledge. This paper presents the views of the authors and should not be construed to represent the views or policies of the FDA or Health Canada.

Mitochondrial fusion, fission, and mitochondrial toxicity

Mitochondrial dynamics are regulated by two sets of opposed processes: mitochondrial fusion and fission, and mitochondrial biogenesis and degradation (including mitophagy), as well as processes such as intracellular transport. These processes maintain mitochondrial homeostasis, regulate mitochondrial form, volume and function, and are increasingly understood to be critical components of the cellular stress response. Mitochondrial dynamics vary based on developmental stage and age, cell type, environmental factors, and genetic background. Indeed, many mitochondrial homeostasis genes are human disease genes. Emerging evidence indicates that deficiencies in these genes often sensitize to environmental exposures, yet can also be protective under certain circumstances. Inhibition of mitochondrial dynamics also affects elimination of irreparable mitochondrial DNA (mtDNA) damage and transmission of mtDNA mutations. We briefly review the basic biology of mitodynamic processes with a focus on mitochondrial fusion and fission, discuss what is known and unknown regarding how these processes respond to chemical and other stressors, and review the literature on interactions between mitochondrial toxicity and genetic variation in mitochondrial fusion and fission genes. Finally, we suggest areas for future research, including elucidating the full range of mitodynamic responses from low to high-level exposures, and from acute to chronic exposures; detailed examination of the physiological consequences of mitodynamic alterations in different cell types; mechanism-based testing of mitotoxicant interactions with interindividual variability in mitodynamics processes; and incorporating other environmental variables that affect mitochondria, such as diet and exercise.

Inherited mitochondrial genomic instability and chemical exposures

There are approximately 1500 proteins that are needed for mitochondrial structure and function, most of which are encoded in the nuclear genome (Calvo et al., 2006). Each mitochondrion has its own genome (mtDNA), which in humans encodes 13 polypeptides, 22 tRNAs and 2 rRNAs required for oxidative phosphorylation. The mitochondrial genome of humans and most vertebrates is approximately 16.5kbp, double-stranded, circular, with few non-coding bases. Thus, maintaining mtDNA stability, that is, the ability of the cell to maintain adequate levels of mtDNA template for oxidative phosphorylation is essential and can be impacted by the level of mtDNA mutation currently within the cell or mitochondrion, but also from errors made during normal mtDNA replication, defects in mitochondrial quality control mechanisms, and exacerbated by exposures to exogenous and/or endogenous genotoxic agents. In this review, we expand on the origins and consequences of mtDNA instability, the current state of research regarding the mechanisms by which mtDNA instability can be overcome by cellular and chemical interventions, and the future of research and treatments for mtDNA instability.

Quercetin, a natural product supplement, impairs mitochondrial bioenergetics and locomotor behavior in larval zebrafish (Danio rerio)

Quercetin is a natural product that is sold as a supplement in health food stores. While there are reported benefits for this flavonoid as a dietary supplement due to antioxidant properties, the full scope of its biological interactions has not been fully addressed. To learn more about the mechanisms of action related to quercetin, we exposed zebrafish (Danio rerio) embryos to 1 and 10μg/L quercetin for 96h starting at 3h post fertilization. Quercetin up to 10μg/L did not induce significant mortality in developing fish, but did increase prevalence of an upward-curved dorsal plane in hatched larvae. To determine whether this developmental defect was potentially related to mitochondrial bioenergetics during development, we measured oxygen consumption rate in whole embryos following a 24-hour exposure to quercetin. Basal mitochondrial and ATP-linked respiration were decreased at 1 and 10μg/L quercetin, and maximal respiration was decreased at 10μg/L quercetin, suggesting that quercetin impairs mitochondrial bioenergetics. This is proposed to be related to the deformities observed during development. Due to the fact that ATP production was affected by quercetin, larval behaviors related to locomotion were investigated, as well as transcriptional responses of six myogenesis transcripts. Quercetin at 10μg/L significantly reduced the swimming velocity of zebrafish larvae. The expression levels of both myostatin A (mstna) and myogenic differentiation (myoD) were also altered by quercetin. Mstna, an inhibitory factor for myogenesis, was significantly increased at 1μg/L quercetin exposure, while myoD, a stimulatory factor for myogenesis, was significantly increased at 10μg/L quercetin exposure. There were no changes in transcripts related to apoptosis (bcl2, bax, casp3, casp7), but we did observe a decrease in mRNA levels for catalase (cat) in fish exposed to each dose, supporting an oxidative stress response. Our data support the hypothesis that quercetin may affect locomotion and induce deformities in zebrafish larvae by diminishing ATP production and by altering the expression of transcripts related to muscle formation and activity.

Effects of Zidovudine Treatment on Heart mRNA Expression and Mitochondrial DNA Copy Number Associated with Alterations in Deoxynucleoside Triphosphate Composition in a Neonatal Rat Model

The prevention of mother-to-child transmission (MTCT) of HIV is a crucial component in HIV therapy. Nucleoside reverse transcriptase inhibitors (NRTIs), primarily 3'-azido-3'-thymidine (AZT [zidovudine]), have been used to treat both mothers and neonates. While AZT is being replaced with less toxic drugs in treating mothers in MTCT prevention, it is still commonly used to treat neonates. Problems related to mitochondrial toxicity and potential mutagenesis associated with AZT treatment have been reported in treated cohorts. Yet little is known concerning the metabolism and potential toxicity of AZT on embryonic and neonatal tissues, especially considering that the enzymes of nucleoside metabolism change dramatically as many tissues convert from hyperplastic to hypertrophic growth during this period. AZT is known to inhibit thymidine phosphorylation and potentially alter deoxynucleoside triphosphate (dNTP) pools in adults. This study examines the effects of AZT on dNTP pools, mRNA expression of deoxynucleoside/deoxynucleotide metabolic enzymes, and mitochondrial DNA levels in a neonatal rat model. Results show that AZT treatment dramatically altered dNTP pools in the first 7 days of life after birth, which normalized to age-matched controls in the second and third weeks. Additionally, AZT treatment dramatically increased the mRNA levels of many enzymes involved in deoxynucleotide synthesis and mitochondrial biogenesis during the first week of life, which normalized to age-matched controls by the third week. These results were correlated with depletion of mitochondrial DNA noted in the second week. Taken together, results demonstrated that AZT treatment has a powerful effect on the deoxynucleotide synthesis pathways that may be associated with toxicity and mutagenesis.

In utero exposure to zidovudine and heart anomalies in the ANRS French perinatal cohort and the nested PRIMEVA randomized trial

BACKGROUND

Antiretroviral (ARV) regimens during pregnancy are highly effective in preventing mother-to-child transmission of human immunodeficiency virus (HIV). Congenital heart defects (CHDs) and anomalies in cardiac function have been reported in zidovudine (ZDV)-exposed uninfected children. We explored these associations in a large observational cohort and a randomized clinical trial.

METHODS

Since 1986, the French Perinatal Cohort prospectively enrolled all HIV-infected women in 90 centers and collected follow-up on their children through 2 years of age. All CHDs were reviewed by a specialist blinded to exposures. Additionally, in a randomized trial (PRIMEVA ANRS 135) of 2 ARV regimens during pregnancy, 1 of which was without nucleoside reverse transcriptase inhibitors, infants had a specific follow-up including echocardiography at 1 month and 12 months.

RESULTS

Among 12 888 children included, ZDV exposure in the first trimester was significantly associated with CHD (1.5% vs 0.7%; adjusted odds ratio, 2.2 [95% confidence interval, 1.3-3.7]; P < .001). This association was significant for ventricular septal defects (1.1% vs 0.6%; P = .001) and other CHDs (0.31% vs 0.11%; P = .02). In the randomized trial, among 50 infants, girls (but not boys) exposed in utero to ZDV/lamivudine/ritonavir-boosted lopinavir (LPV/r) had a higher left ventricular shortening fraction at 1 month (40% vs 36%; P = .008), and an increased posterior wall thickness at 1 year (5.4 mm vs 4.4 mm; P = .01) than the LPV/r group.

CONCLUSIONS

This study confirms a specific association between in utero exposure to ZDV and CHDs, and a long-lasting postnatal myocardial remodeling in girls. A potential common mechanism, including the involvement of mitochondrial dysfunction, must be explored, and long-term consequences on cardiac function warrant specific attention.

CLINICAL TRIALS REGISTRATION

NCT00424814.

Mitochondrial DNA mutations in ageing and disease: implications for HIV?

Mitochondrial DNA (mtDNA) mutations cause neurological and multisystem disease. Somatic (acquired) mtDNA mutations are also associated with degenerative diseases and with normal human ageing. It is well established that certain nucleoside reverse transcriptase inhibitor (NRTI) antiretroviral drugs cause inhibition of the mtDNA polymerase, pol γ, leading to a reduction in mtDNA content (depletion). Given this effect of NRTI therapy on mtDNA replication, it is plausible that NRTI treatment may also lead to increased mtDNA mutations. Here we review recent evidence for an effect of HIV infection or NRTI therapy on mtDNA mutations, as well as discussing the methodological challenges in addressing this question. Finally, we discuss the possible implications for HIV-infected persons, with particular reference to ageing.

Cardiac status of children infected with human immunodeficiency virus who are receiving long-term combination antiretroviral therapy: results from the Adolescent Master Protocol of the Multicenter Pediatric HIV/AIDS Cohort Study

IMPORTANCE

Prior to contemporary antiretroviral therapies (ARTs), children infected with human immunodeficiency virus (HIV) were more likely to have heart failure. This study suggests that highly active ART (HAART) does not appear to impair heart function.

OBJECTIVE

To determine the cardiac effects of prolonged exposure to HAART on HIV-infected children.

DESIGN

In the National Institutes of Health-funded Pediatric HIV/AIDS Cohort Study's Adolescent Master Protocol (AMP), we used linear regression models to compare echocardiographic measures.

SETTING

A total of 14 US pediatric HIV clinics.

PARTICIPANTS

Perinatally HIV-infected children receiving HAART (n = 325), HIV-exposed but uninfected children (n = 189), and HIV-infected (mostly HAART-unexposed) historical pediatric controls from the National Institutes of Health-funded Pulmonary and Cardiovascular Complications of Vertically Transmitted HIV Infection (P2C2-HIV) Study (n = 70). EXPOSURE Long-term HAART.

MAIN OUTCOMES AND MEASURES

Echocardiographic measures of left ventricular (LV) function and structure.

RESULTS

The 325 AMP HIV-infected children had lower viral loads, higher CD4 counts, and longer durations of ART than did the 70 HIV-infected children from the P2C2-HIV Study (all P < .001). The z scores for LV fractional shortening (a measure of cardiac function) were significantly lower among HIV-infected children from the P2C2-HIV Study than among the AMP HIV-infected group or the 189 AMP HIV-exposed but uninfected controls (P < .05). For HIV-infected children, a lower nadir CD4 percentage and a higher current viral load were associated with significantly lower cardiac function (LV contractility and LV fractional shortening z scores; all P = .001) and an increased LV end-systolic dimension z score (all P < .03). In an interaction analysis by HIV-infected cohort, the HIV-infected children from the P2C2-HIV Study with a longer ART exposure or a lower nadir CD4 percentage had lower mean LV fractional shortening z scores, whereas the mean z scores were relatively constant among AMP HIV-infected children (P < .05 for all interactions).

CONCLUSIONS AND RELEVANCE

Long-term HAART appears to be cardioprotective for HIV-infected children and adolescents.

Transplacental exposure to AZT induces adverse neurochemical and behavioral effects in a mouse model: protection by L-acetylcarnitine

Maternal-fetal HIV-1 transmission can be prevented by administration of AZT, alone or in combination with other antiretroviral drugs to pregnant HIV-1-infected women and their newborns. In spite of the benefits deriving from this life-saving prophylactic therapy, there is still considerable uncertainty on the potential long-term adverse effects of antiretroviral drugs on exposed children. Clinical and experimental studies have consistently shown the occurrence of mitochondrial dysfunction and increased oxidative stress following prenatal treatment with antiretroviral drugs, and clinical evidence suggests that the developing brain is one of the targets of the toxic action of these compounds possibly resulting in behavioral problems. We intended to verify the effects on brain and behavior of mice exposed during gestation to AZT, the backbone of antiretroviral therapy during human pregnancy. We hypothesized that glutamate, a neurotransmitter involved in excitotoxicity and behavioral plasticity, could be one of the major actors in AZT-induced neurochemical and behavioral alterations. We also assessed the antioxidant and neuroprotective effect of L-acetylcarnitine, a compound that improves mitochondrial function and is successfully used to treat antiretroviral-induced polyneuropathy in HIV-1 patients. We found that transplacental exposure to AZT given per os to pregnant mice from day 10 of pregnancy to delivery impaired in the adult offspring spatial learning and memory, enhanced corticosterone release in response to acute stress, increased brain oxidative stress also at birth and markedly reduced expression of mGluR1 and mGluR5 subtypes and GluR1 subunit of AMPA receptors in the hippocampus. Notably, administration during the entire pregnancy of L-acetylcarnitine was effective in preventing/ameliorating the neurochemical, neuroendocrine and behavioral adverse effects induced by AZT in the offspring. The present preclinical findings provide a mechanistic hypothesis for the neurobehavioral effects of AZT and strongly suggest that preventive administration of L-acetylcarnitine might be effective in reducing the neurological side-effects of antiretroviral therapy in fetus/newborn.

Effects of in utero antiretroviral exposure on mitochondrial DNA levels, mitochondrial function and oxidative stress

OBJECTIVES

HIV and antiretroviral (ART) exposure in utero may have deleterious effects on the infant, but uncertainty still exists. The objective of this study was to evaluate aspects of mitochondrial DNA (mtDNA) content, mitochondrial function and oxidative stress simultaneously in placenta, umbilical cord blood and infant blood in HIV/ART-exposed infants compared with uninfected controls.

METHODS

HIV-1-infected pregnant women and HIV-1-uninfected healthy pregnant controls were enrolled in the study prospectively. Placenta and umbilical cord blood were obtained at delivery and infant blood was obtained within 48 h of delivery. mtDNA content was determined for each specimen. Nuclear [subunit IV of cytochrome c-oxidase (COX IV)]- and mitochondrial (COX II)-encoded polypeptides of the oxidative phosphorylation enzyme cytochrome c-oxidase were quantified in cord and infant blood. Placental mitochondria malondialdehyde (MDA) concentrations were measured as a marker of oxidative stress.

RESULTS

Twenty HIV-positive/HIV-exposed and 26 control mother-infant pairs were enrolled in the study. All HIV-infected women and their infants received ART. Placental MDA concentration and mtDNA content in placenta and cord blood were similar between groups. The cord blood COX II:IV ratio was lower in the HIV-positive group than in the controls, whereas the infant peripheral blood mtDNA content was higher in the HIV-exposed infants, but the infant peripheral blood COX II:IV ratio was similar. No infant had clinical evidence of mitochondrial disease or acquired HIV infection. In multivariable regression analyses, the significant findings in cord and infant blood were both most associated with HIV/ART exposure.

CONCLUSIONS

HIV-exposed infants showed reduced umbilical cord blood mitochondrial enzyme expression with increased infant peripheral blood mitochondrial DNA levels, the latter possibly reflecting a compensatory mechanism to overcome HIV/ART-associated mitochondrial toxicity.

Bioenergetic profiling of zebrafish embryonic development

Many debilitating conditions are linked to bioenergetic defects. Developing screens to probe the genetic and/or chemical basis for such links has proved intractable. Furthermore, there is a need for a physiologically relevant assay of bioenergetics in whole organisms, especially for early stages in life where perturbations could increase disease susceptibility with aging. Thus, we asked whether we could screen bioenergetics and mitochondrial function in the developing zebrafish embryo. We present a multiplexed method to assay bioenergetics in zebrafish embryos from the blastula period (3 hours post-fertilization, hpf) through to hatching (48 hpf). In proof of principle experiments, we measured respiration and acid extrusion of developing zebrafish embryos. We quantified respiratory coupling to various bioenergetic functions by using specific pharmacological inhibitors of bioenergetic pathways. We demonstrate that changes in the coupling to ATP turnover and proton leak are correlated with developmental stage. The multiwell format of this assay enables the user to screen for the effects of drugs and environmental agents on bioenergetics in the zebrafish embryo with high sensitivity and reproducibility.

Cardiac effects of antiretroviral therapy in HIV-negative infants born to HIV-positive mothers: NHLBI CHAART-1 (National Heart, Lung, and Blood Institute Cardiovascular Status of HAART Therapy in HIV-Exposed Infants and Children cohort study)

OBJECTIVES

The aim of this study was to investigate the possible effects of antiretroviral therapy (ART) in utero on cardiac development and function in human immunodeficiency virus (HIV)-negative children.

BACKGROUND

ART reduces vertical HIV transmission. Long-term cardiotoxicity after in utero exposure to ART is unknown in children but has occurred in young animals.

METHODS

Using a prospective multisite cohort study design, echocardiograms taken between birth and 24 months were compared in 2 groups of HIV-negative infants of HIV-positive mothers: 136 infants exposed to ART (ART+) and 216 unexposed infants (ART-).

RESULTS

Mean left ventricular (LV) mass z-scores were consistently lower in ART+ girls than in ART- girls: differences in mean z-scores were -0.46 at birth (p = 0.005), -1.02 at 6 months (p < 0.001), -0.74 at 12 months (p < 0.001), and -0.79 at 24 months (p < 0.001). Corresponding differences in z-scores for boys were smaller: 0.13 at 1 month (p = 0.42), -0.44 at 6 months (p = 0.01), -0.15 at 12 months (p = 0.37), and -0.21 at 24 months (p = 0.21). Septal wall thickness and LV dimension were smaller than expected in ART+ infants, but LV contractility was consistently about 1 SD higher at all ages (p < 0.001). In ART+ infants, LV fractional shortening was higher than in ART- infants; girls showed a greater difference.

CONCLUSIONS

Fetal exposure to ART is associated with reduced LV mass, LV dimension, and septal wall thickness z-scores and increased LV fractional shortening and contractility up to age 2 years. These effects are more pronounced in girls than in boys. Fetal ART exposure may impair myocardial growth while improving depressed LV function.

Comparative phenotypic assessment of cardiac pathology, physiology, and gene expression in C3H/HeJ, C57BL/6J, and B6C3F1/J mice

Human cardiomyopathies often lead to heart failure, a major cause of morbidity and mortality in industrialized nations. Described here is a phenotypic characterization of cardiac function and genome-wide expression from C3H/HeJ, C57BL/6J, and B6C3F1/J male mice. Histopathologic analysis identified a low-grade background cardiomyopathy (murine progressive cardiomyopathy) in eight of nine male C3H/HeJ mice (age nine to ten weeks), but not in male C57BL/6J and in only of ten male B6C3F1/J mice. The C3H/HeJ mouse had an increased heart rate and a shorter RR interval compared to the B6C3F1/J and C57BL/6J mice. Cardiac genomic studies indicated the B6C3F1/J mice exhibited an intermediate gene expression phenotype relative to the 2 parental strains. Disease-centric enrichment analysis indicated a number of cardiomyopathy-associated genes were induced in B6C3F1/J and C3H/HeJ mice, including Myh7, My14, and Lmna and also indicated differential expression of genes associated with metabolic (e.g., Pdk2) and hypoxic stress (e.g. Hif1a). A novel coexpression and integrated pathway network analysis indicated Prkaa2, Pdk2, Rhoj, and Sgcb are likely to play a central role in the pathophysiology of murine progressive cardiomyopathy in C3H/HeJ mice. Our studies indicate that genetically determined baseline differences in cardiac phenotype have the potential to influence the results of cardiotoxicity studies.

Evaluation of mitochondrial toxicity in Marmota himalayana treated with metacavir, a novel 2',3'-dideoxyguanosine prodrug for treatment of hepatitis B Virus

Metacavir (PNA) is a novel synthetic nucleoside analogue for the treatment of hepatitis B virus (HBV). Our recent studies showed that PNA, a prodrug of 2',3'-dideoxyguanosine (ddG), exhibited lower mitochondrial toxicity in long-term cultures of HepG2 cells. In the current study, we examined the long-term effects of PNA on mitochondrial toxicity in Marmota himalayana (Himalayan marmot). Himalayan marmots were treated daily with oral PNA (50 or 100 mg/kg), ziduvidine (AZT) (100 mg/kg), or water (control) for 90 days. PNA treatment did not alter the body weight or plasma lactate acid level. In livers from the animals treated with PNA at 100 mg/kg/day, histopathology showed mild steatosis or small focal liver cell necrosis. Electron microscopy also showed minor proliferation and partial mitochondrial swelling with crista reduction. Measurement of respiratory chain complex enzyme activity and mitochondrial DNA (mtDNA) content revealed no significant differences in skeletal muscle, liver, and kidney tissues between animals treated with PNA and controls. In contrast, in Himalayan marmots treated with AZT we observed delayed toxicity, including lactic acidosis, severe hepatic steatosis, obvious mitochondrial damage, and significant decreases in respiratory chain complex enzyme activity and mtDNA content. This is similar to the delayed toxicity syndrome observed previously in animals and humans. In summary, PNA treatment did not alter mitochondrial enzyme activity or mtDNA content. This suggests that PNA could pose a very low risk for adverse mitochondrion-related effects. However, long-term hepatotoxic effects of PNA were observed, and this indicates a need for continued monitoring of PNA-associated hepatotoxicity in clinical trials.

The QPCR assay for analysis of mitochondrial DNA damage, repair, and relative copy number

The quantitative polymerase chain reaction (QPCR) assay allows measurement of DNA damage in the mitochondrial and nuclear genomes without isolation of mitochondria. It also permits measurement of relative mitochondrial genome copy number. Finally, it can be used for measurement of DNA repair in vivo when employed appropriately. In this manuscript we briefly review the methodology of the QPCR assay, discuss its strengths and limitations, address considerations for measurement of mitochondrial DNA repair, and describe methodological changes implemented in recent years. We present QPCR assay primers and reaction conditions for five species not previously described in a methods article: Caenorhabditis elegans, Fundulus heteroclitus, Danio rerio, Drosophila melanogaster, and adenovirus. Finally, we illustrate the use of the assay by measuring repair of ultraviolet C radiation-induced DNA damage in the nuclear but not mitochondrial genomes of a zebrafish cell culture.

In utero exposure of female CD-1 mice to AZT and/or 3TC: II. Persistence of functional alterations in cardiac tissue

To delineate temporal changes in the integrity and function of mitochondria/cardiomyocytes in hearts from mice exposed in utero to commonly used nucleoside analogs (NRTIs), CD-1 mice were exposed in utero to 80 mg AZT/kg, 40 mg 3TC/kg, 80 mg AZT/kg plus 40 mg 3TC/kg, or vehicle alone during days 12-18 of gestation and hearts from female mouse offspring were examined at 13 and 26 weeks postpartum. Alterations in cardiac mitochondrial DNA (mtDNA) content, oxidative phosphorylation (OXPHOS) enzyme activities, mtDNA mutations, and echocardiography of NRTI-exposed mice were assessed and compared with findings in vehicle-exposed control mice. A hybrid capture-chemiluminescence assay showed significant twofold increases in mtDNA levels in hearts from AZT- and AZT/3TC-exposed mice at 13 and 26 weeks postpartum, consistent with near doubling in mitochondrial numbers over time compared with vehicle-exposed mice. Echocardiographic measurements at 13 and 26 weeks postpartum indicated progressive thinning of the left ventricular posterior wall in NRTI-exposed mice, relative to controls, with differences becoming statistically significant by 26 weeks. Overall, progressive functional changes occurred in mouse mitochondria and cardiac tissue several months after in utero NRTI exposures; AZT and 3TC acted in concert to cause additive cardiotoxic effects of AZT/3TC compared with either drug alone.

In utero exposure of female CD-1 Mice to AZT and/or 3TC: I. Persistence of microscopic lesions in cardiac tissue

The current study was designed to delineate temporal changes in cardiomyocytes and mitochondria at the light and electron microscopic levels in hearts of mice exposed transplacentally to commonly used nucleoside analogs (NRTIs). Pregnant CD-1 mice were given 80 mg AZT/kg, 40 mg 3TC/kg, 80 mg AZT/kg plus 40 mg 3TC/kg, or vehicle alone during the last 7 days of gestation, and hearts from female mouse pups were examined at 13 and 26 weeks postpartum for histopathological or ultrastructural changes in cross-sections of both the ventricles and the interventricular septum. Using light microscopy and special staining techniques, transplacental exposure to AZT, 3TC, or AZT/3TC was shown to induce significant histopathological changes in myofibrils; these changes were more widespread at 13 weeks than at 26 weeks postpartum. While most light microscopic lesions resolved, some became more severe between 13 and 26 weeks postpartum. Transplacental NRTI exposure also resulted in progressive drug-specific changes in the number and ultrastructural integrity of cardiac mitochondria. These light and electron microscopic findings show that a subset of changes in cardiac mitochondria and myofibrils persisted and progressed months after transplacental exposure of an animal model to NRTIs, with combined AZT/3TC exposure yielding additive effects compared with either drug alone.

Consequences of long-term oral administration of the mitochondria-targeted antioxidant MitoQ to wild-type mice

The mitochondria-targeted quinone MitoQ protects mitochondria in animal studies of pathologies in vivo and is being developed as a therapy for humans. However, it is unclear whether the protective action of MitoQ is entirely due to its antioxidant properties, because long-term MitoQ administration may alter whole-body metabolism and gene expression. To address this point, we administered high levels of MitoQ orally to wild-type C57BL/6 mice for up to 28 weeks and investigated the effects on whole-body physiology, metabolism, and gene expression, finding no measurable deleterious effects. In addition, because antioxidants can act as pro-oxidants under certain conditions in vitro, we examined the effects of MitoQ administration on markers of oxidative damage. There were no changes in the expression of mitochondrial or antioxidant genes as assessed by DNA microarray analysis. There were also no increases in oxidative damage to mitochondrial protein, DNA, or cardiolipin, and the activities of mitochondrial enzymes were unchanged. Therefore, MitoQ does not act as a pro-oxidant in vivo. These findings indicate that mitochondria-targeted antioxidants can be safely administered long-term to wild-type mice.

Mechanisms of antiretroviral therapy-induced mitochondrial dysfunction

PURPOSE OF REVIEW

To discuss novel developments related to the mechanisms of antiretroviral therapy-related mitochondrial toxicity, describe some apparent paradoxes in the current understanding of this field, and present questions that should be addressed by future research.

RECENT FINDINGS

The early polymerase gamma hypothesis states that nucleoside reverse transcriptase inhibitors can inhibit mitochondrial DNA replication and cause mitochondrial toxicity through mtDNA depletion. This mechanism is supported by a large body of evidence. Clinical manifestations of mitochondrial dysfunction are not always associated with mtDNA depletion. Increased mtDNA levels after nucleoside reverse transcriptase inhibitor exposure, as well as seemingly severe mtDNA depletion in individuals who show no clinical toxicity, have been reported. These and other observations suggest that additional mechanisms are involved in antiretroviral therapy toxicity, a notion supported by recent studies. Individuals given the same antiretroviral regimen can differ vastly with respect to the development of mitochondrial toxicity symptoms, reflecting interindividual variability. Some factors that may modulate this variability will be discussed.

SUMMARY

Mitochondrial toxicity induced by nucleoside reverse transcriptase inhibitors and their metabolic intermediates is probably mediated through many direct and indirect mechanisms. Depending on the mechanisms at play, the long-term health consequences of this toxicity may vary.

In vivo assessment of mitochondrial toxicity of metacavir in Rhesus monkeys after three months of intravenous administration

AIM

To explore the potential mitochondrial toxicities and their severities of intravenously administered metacavir, a nucleoside analog, in rhesus monkeys.

METHODS

Totally 21 rhesus monkeys were randomly divided into 4 groups: metacavir 120 mg/kg group, metacavir 40 mg/kg group, zidovudine(AZT) 50 mg/kg group, and blank control group. Animals were killed after the completion of dosing or further observed in a 4-week recovery phase. Changes of structure of mitochondria in liver, kidney, skeletal muscles, and cardiac muscles were observed under transmission electron microscope(TEM). Changes of the activities of mitochondrial respiratory chain complexes and mitochondrial DNA were also determined.

RESULTS

In metacavir 120 mg/kg group, some mitochondrial injuries were found in skeletal muscle, cardiac muscle, and liver, including that some cristae was broken and became sparse in density in the skeletal muscle, the morphology and size of mitochondria remained unchanged. Metacavir decreased the activities of respiratory chain complexes I and II and the mtDNA contents in three tissues in a dose-dependent manner; however, the extent of such decrease was lower than that in AZT 50 mg/kg group. The mitochondrial injuries in metacavir 40 mg/kg group were mild in each tissue and no obvious change in mitochondrial function was noted. On week 4 in the recovery phase, results showed that all these injuries were reversible after drug withdrawal.

CONCLUSION

These results suggest that metacavir has not a high risk for potential mitochondrial-related effects in rhesus monkeys.

The long amplicon quantitative PCR for DNA damage assay as a sensitive method of assessing DNA damage in the environmental model, Atlantic killifish (Fundulus heteroclitus)

DNA damage is an important mechanism of toxicity for a variety of pollutants, and therefore, is often used as an indicator of pollutant effects in ecotoxicological studies. Here, we adapted a PCR-based assay for nuclear and mitochondrial DNA damage for use in an important environmental model, the Atlantic killifish (Fundulus heteroclitus). We refer to this assay as the long amplicon quantitative PCR (LA-QPCR) assay. To validate this method in killifish, DNA damage was measured in liver, brain, and muscle of fish dosed with 10 mg/kg benzo[a]pyrene. This exposure caused 0.4-0.8 lesions/10 kb. We also measured DNA damage in liver and muscle tissues from killifish inhabiting a Superfund site, confirming the utility of this method for biomonitoring. In both cases, damage levels were comparable in nuclear DNA (nDNA) and mitochondrial DNA (mtDNA). Since extensive nDNA sequence data are not readily available for many environmentally relevant species, but mitochondrial genomes are frequently fully sequenced, this assay can be adapted to examine mtDNA damage in virtually any species with little development. Therefore, we argue that this assay will be a valuable tool in assessing DNA damage in ecotoxicological studies.

An analysis of enzyme kinetics data for mitochondrial DNA strand termination by nucleoside reverse transcription inhibitors

Nucleoside analogs used in antiretroviral treatment have been associated with mitochondrial toxicity. The polymerase-γ hypothesis states that this toxicity stems from the analogs' inhibition of the mitochondrial DNA polymerase (polymerase-γ) leading to mitochondrial DNA (mtDNA) depletion. We have constructed a computational model of the interaction of polymerase-γ with activated nucleoside and nucleotide analog drugs, based on experimentally measured reaction rates and base excision rates, together with the mtDNA genome size, the human mtDNA sequence, and mitochondrial dNTP concentrations. The model predicts an approximately 1000-fold difference in the activated drug concentration required for a 50% probability of mtDNA strand termination between the activated di-deoxy analogs d4T, ddC, and ddI (activated to ddA) and the activated forms of the analogs 3TC, TDF, AZT, FTC, and ABC. These predictions are supported by experimental and clinical data showing significantly greater mtDNA depletion in cell culture and patient samples caused by the di-deoxy analog drugs. For zidovudine (AZT) we calculated a very low mtDNA replication termination probability, in contrast to its reported mitochondrial toxicity in vitro and clinically. Therefore AZT mitochondrial toxicity is likely due to a mechanism that does not involve strand termination of mtDNA replication.

While HIV/AIDS therapy is very successful at controlling HIV infection, the therapy must continue for the remainder of the patient's life. Approximately one-fourth of these patients suffer from serious drug toxicity problems. It is generally believed that the toxicity of these drugs is caused by damage to mitochondria, the “power plants” of every cell. But we do not know exactly how this damage occurs. The most common explanation is that these drugs damage mitochondria in the same way that they control the virus, by interfering with DNA replication. We tested that idea by analyzing data for the interaction of several AIDS drugs with the mitochondrial DNA polymerase, the protein responsible for copying mitochondrial DNA. By using a detailed simulation of the mitochondrial DNA polymerase, we show that some of these drugs do interact well enough with the mitochondrial DNA polymerase to lead to toxic effects. However, many of these drugs, including the commonly used drug AZT, had very little toxic effect in this simulation although AZT often causes toxicity in patients. This indicates that the toxicity of AZT occurs through some other process and not through the direct interruption of mitochondrial DNA replication.

K-ras cancer gene mutations in lung tumors from female Swiss (CD-1) mice exposed transplacentally to 3'-azido-3'-deoxythymidine

A transplacental carcinogenicity study was conducted by exposing pregnant Swiss (CD-1) mice to 0, 50, 100, 200, or 300 mg 3'-azido-3'-deoxythymidine (AZT)/kg body weight (BW) daily for the duration of gestation (18-19 days) [National Toxicology Program,2006]. The incidence of alveolar/bronchiolar adenomas and carcinomas in the 200 and 300 mg/kg groups was significantly higher (P = 0.027 and 0.007, respectively) in male offspring, but not in females (P = 0.338 and 0.315, respectively). The purpose of the present study was to evaluate K-ras mutation status in lung tumors from the female offspring in AZT exposed groups and to determine whether at the molecular level there were signature K-ras mutations in lung tumors that were different from spontaneous tumors. K-ras mutation was detected by cycle sequencing of polymerase chain reaction (PCR)-amplified DNA, isolated from formalin-fixed, paraffin-embedded lung tumors. K-ras mutations were detected in 17 of 28 (61%) lung tumors from the female offspring in AZT exposed groups. No K-ras mutations were detected in the 8 tumors examined from the female control group. The predominant mutations were Codon 12 G-->T transversions in the 50, 100, and 300 mg/kg groups, and Codon 12 G-->C transversions in the 200 and 300 mg/kg groups. K-ras Codon 12 G-->T transversions (TGT mutations) may be induced by oxidative DNA damage and 8-oxoguanine (8-oxoG), while K-ras Codon 12 G-->C transversions (CGT mutations) may be due to further oxidative lesions of guanine and 8-oxoG.

DNA polymerase gamma and mitochondrial disease: understanding the consequence of POLG mutations

DNA polymerase gamma is the only known DNA polymerase in human mitochondria and is essential for mitochondrial DNA replication and repair. It is well established that defects in mtDNA replication lead to mitochondrial dysfunction and disease. Over 160 coding variations in the gene encoding the catalytic subunit of DNA polymerase gamma (POLG) have been identified. Our group and others have characterized a number of the more common and interesting mutations, as well as those disease mutations in the DNA polymerase gamma accessory subunit. We review the results of these studies, which provide clues to the mechanisms leading to the disease state.

Effect of short-term exposure to zidovudine (AZT) on the expression of mitochondria-related genes in skeletal muscle of neonatal mice

Zidovudine (3'-azido-3'-deoxythymidine; AZT) is the main anti-retroviral drug given to HIV-1-infected pregnant women during pregnancy and to their infants after birth to reduce mother-to-child transmission of the virus. In animal studies, however, a significant mitochondrial morphological damage has been reported in skeletal muscle as a consequence of transplacental or perinatal exposure to AZT. Because proper muscle function is highly dependent on efficient mitochondrial function and information on AZT-induced mitochondrial toxicity during neonatal exposure is limited, we investigated the effect of AZT on the expression of 542 mitochondria-related genes encoded by both nuclear and mitochondrial DNA in the skeletal muscle of infant male and female mice using microarray technology. Animals were treated orally by gavage with AZT at 0, 10, 50, 100, and 200mg/kg body weight/day from postnatal day (PND) 1 through 8 and were sacrificed at 1- and 2-h following the last dose on PND 8. These doses in mice correspond to 0, 1.1, 5.5, 11.0, and 22.0mg/kg AZT in human infants [Center for Drug Evaluation and Research (CDER) 2005. Pharmacology and Toxicology, Guidance for industry. Estimating the maximum safe dose in initial clinical trials for therapeutics in adult healthy volunteers, p. 7. http://www.fda.gov/cder/guidance/index.htm.]. Microarray data were analyzed for effects of time, sex, treatment, and their interactions using a fixed effect linear model. The results showed modest, but significant, dose-related responses in the expression level of genes associated with apoptosis, fatty acid metabolism, mitochondrial DNA maintenance, and various mitochondrial membrane transporters. The transcription levels were not significantly different at both time points and were not sex dependent. The results suggest that changes in expression of mitochondria-related genes in skeletal muscle may be an initial response to short-term AZT exposure in infant mice.

Mitochondrial DNA impairment in nucleoside reverse transcriptase inhibitor-associated cardiomyopathy

Acquired immune deficiency syndrome (AIDS) is a global epidemic that continues to escalate. Recent World Health Organization estimates include over 33 million people currently diagnosed with HIV/AIDS. Another 20 million HIV-infected individuals died over the past quarter century. Antiretrovirals are effective treatments that changed the outcome of HIV infection from a fatal disease to a chronic illness. Cardiomyopathy (CM) is a bona fide component of HIV/AIDS with occurrence that is higher in HIV positive individuals. CM may result from individual or combined effects of HIV, immune reactions, or toxicities of prolonged antiretrovirals. Nucleoside reverse transcriptase inhibitors (NRTIs) are the cornerstone of antiretroviral therapy. Despite pharmacological benefits of NRTIs, NRTI side effects include increased risk for CM. Clinical observations and in vitro and in vivo studies support various mechanisms of CM. This perspective highlights some of the hypotheses and focuses on mitochondrial-associated pathways of NRTI- related CM.

Nucleoside reverse transcriptase inhibitors (NRTIs)-induced expression profile of mitochondria-related genes in the mouse liver

Mitochondrial dysfunction has been implicated in the adverse effects of nucleoside reverse transcriptase inhibitors (NRTIs) used to treat HIV-1 infections. To gain insight into the mechanism by which NRTIs alter mitochondrial function, the expression level of 542 genes associated with mitochondrial structure and functions was determined in the livers of p53 haplodeficient (+/-) C3B6F1 female mouse pups using mouse mitochondria-specific oligonucleotide microarray. The pups were transplacentally exposed to zidovudine (AZT) at 240 mg/kg bw/day or a combination of AZT and lamivudine (3TC) at 160 and 100mg/kg bw/day, respectively, from gestation day 12 through 18, followed by continuous treatment by oral administration from postnatal day 1-28. In addition, AZT/3TC effect was investigated in wild-type (+/+) C3B6F1 female mice. The genotype did not significantly affect the gene expression profile induced by AZT/3TC treatment. However, the transcriptional level of several genes associated with oxidative phosphorylation, mitochondrial tRNAs, fatty acid oxidation, steroid biosynthesis, and a few transport proteins were significantly altered in pups treated with AZT and AZT/3TC compared to their vehicle counterparts. Interestingly, AZT/3TC altered the expression level of 153 genes with false discovery rate of less than 0.05, in contrast to only 20 genes by AZT alone. These results suggest that NRTI-related effect on expression level of genes associated with mitochondrial functions was much greater in response to AZT/3TC combination treatment than AZT alone.

Mitochondrial Toxicity of Tenofovir, Emtricitabine and Abacavir Alone and in Combination with Additional Nucleoside Reverse Transcriptase Inhibitors

Background

Some nucleoside/nucleotide reverse transcriptase inhibitor (NRTI) combinations cause additive or synergistic interactions in vitro and in vivo.

Methods

We evaluated the mitochondrial toxicity of tenofovir (TFV), emtricitabine (FTC) and abacavir as carbovir (CBV) alone, with each other, and in combination with additional NRTIs. HepG2 human hepatoma cells were incubated with TFV, FTC, CBV, didanosine (ddI), stavudine (d4T), lamivudine (3TC) and zidovudine (AZT) at concentrations equivalent to 1 and 10x clinical steady-state peak plasma levels (Cmax). NRTIs were also used in double and triple combinations. Cell growth, lactate production, intracellular lipids, mtDNA and the mtDNA-encoded respiratory chain subunit II of cytochrome c oxidase (COXII) were monitored for 25 days.

Results

TFV and 3TC had no or minimal toxicity. FTC moderately reduced hepatocyte proliferation independent of effects on mtDNA. ddI and d4T induced a time- and dose-dependent loss of mtDNA and COXII, decreased cell growth and increased levels of lactate and intracellular lipids. CBV and AZT strongly impaired hepatocyte proliferation and increased lactate and lipid production, but did not induce mtDNA depletion. The dual combination of TFV plus 3TC had only minimal toxicity; TFV plus FTC slightly reduced cell proliferation without affecting mitochondrial parameters. All other combinations exhibited more pronounced adverse effects on mitochondrial endpoints. Toxic effects on mitochondrial parameters were observed in all combinations with ddI, d4T, AZT or CBV. TFV and 3TC both attenuated ddI-related cytotoxicity, but worsened the effects of CBV and AZT.

Conclusions

The data demonstrate unpredicted interactions between NRTIs with respect to toxicological endpoints and provide an argument against the liberal use of NRTI cocktails without first obtaining data from clinical trials.