Degree of heteroplasmy reflects oxidant damage in a large family with the mitochondrial DNA A8344G mutation

Milder Phenotype of Homoplasmic Versus Heteroplasmic m.8344A>G Variant in the Same Family: A Case Report

A myoclonic epilepsy with ragged-red fibers (MERRF) patient who carried the m.8344A>G variant in the homoplasmic form manifested a milder phenotype than his sister who carried the same variant in the heteroplasmic form, which has not yet been reported. The 27-year-old male, with an uneventful history, presented at age 19 with fatigue and persistent tremor in both hands. When he talked for a long time, his speech would slow down, and he would stutter. Although electroencephalography showed spike-wave complexes in both occipital projections with generalization, no anti-seizure drugs were given. At age 20, the patient suffered a fall due to muscle weakness. From age 21, generalized myocloni occurred. Because the sister had been diagnosed with MERRF-plus syndrome, the patient underwent genetic testing, which revealed the m.8344A>G variant in homoplasmy. L-carnitine was started. At age 27, the patient experienced a first "syncope" after a long walk, which subsequently recurred up to 2-3 times per day. EEG showed low-amplitude spikes, slow-spike waves at the posterior vertex, and generalized slow-spike waves. Clonazepam was recommended but declined by the patient. In conclusion, the m.8344A>G variant may manifest milder and with a later onset in the homoplasmic as compared to the heteroplasmic form. Further, the homoplasmy of the m.8344A>G variant appears to be more beneficial than harmful.

Blood biomarkers for assessment of mitochondrial dysfunction: An expert review

Although mitochondrial dysfunction is the known cause of primary mitochondrial disease, mitochondrial dysfunction is often difficult to measure and prove, especially when biopsies of affected tissue are not available. In order to identify blood biomarkers of mitochondrial dysfunction, we reviewed studies that measured blood biomarkers in genetically, clinically or biochemically confirmed primary mitochondrial disease patients. In this way, we were certain that there was an underlying mitochondrial dysfunction which could validate the biomarker. We found biomarkers of three classes: 1) functional markers measured in blood cells, 2) biochemical markers of serum/plasma and 3) DNA markers. While none of the reviewed single biomarkers may perfectly reveal all underlying mitochondrial dysfunction, combining biomarkers that cover different aspects of mitochondrial impairment probably is a good strategy. This biomarker panel may assist in the diagnosis of primary mitochondrial disease patients. As mitochondrial dysfunction may also play a significant role in the pathophysiology of multifactorial disorders such as Alzheimer's disease and glaucoma, the panel may serve to assess mitochondrial dysfunction in complex multifactorial diseases as well and enable selection of patients who could benefit from therapies targeting mitochondria.

Sepsis: Evidence-based pathogenesis and treatment

Sepsis can develop during the body’s response to a critical illness leading to multiple organ failure, irreversible shock, and death. Sepsis has been vexing health care providers for centuries due to its insidious onset, generalized metabolic dysfunction, and lack of specific therapy. A common factor underlying sepsis is the characteristic hypermetabolic response as the body ramps up every physiological system in its fight against the underlying critical illness. A hypermetabolic response requires supraphysiological amounts of energy, which is mostly supplied via oxidative phosphorylation generated ATP. A by-product of oxidative phosphorylation is hydrogen peroxide (H₂O₂), a toxic, membrane-permeable oxidizing agent that is produced in far greater amounts during a hypermetabolic state. Continued production of mitochondrial H₂O₂ can overwhelm cellular reductive (antioxidant) capacity leading to a build-up within cells and eventual diffusion into the bloodstream. H₂O₂ is a metabolic poison that can inhibit enzyme systems leading to organ failure, microangiopathic dysfunction, and irreversible septic shock. The toxic effects of H₂O₂ mirror the clinical and laboratory abnormalities observed in sepsis, and toxic levels of blood H₂O₂ have been reported in patients with septic shock. This review provides evidence to support a causal role for H₂O₂ in the pathogenesis of sepsis, and an evidence-based therapeutic intervention to reduce H₂O₂ levels in the body and restore redox homeostasis, which is necessary for normal organ function and vascular responsiveness.

Detecting Rare Variants and Heteroplasmy of Mitochondrial DNA from High-Throughput Sequencing in Patients with Coronary Artery Disease

Background

Although mutations and dysfunction of mitochondrial DNA (mtDNA) are related to a variety of diseases, few studies have focused on the relationship between mtDNA and coronary artery disease (CAD), especially the relationship between rare variants and CAD.

Material/Methods

Two-stage high-throughput sequencing was performed to detect mtDNA variants or heteroplasmy and the relationship between them and CAD phenotypes. In the discovery stage, mtDNA was analyzed by high-throughput sequencing of long-range PCR products generated from the peripheral blood of 85 CAD patients and 80 demographically matched controls. In the validation stage, high-throughput sequencing for mtDNA target regions captured by GenCap Kit was performed on 100 CAD samples and 100 controls. Finally, tRNA fine mapping was performed between our study and the reported Chinese CAD study.

Results

Among the tRNA genes, we confirmed a highly conserved rare variant, A5592G, previously reported in the Chinese CAD study, and 2 novel rare mutations that reached Bonferroni’s correction significance in the combined analysis were found (P=7.39×10⁻⁴ for T5628C in tRNA^Ala and P=1.01×10⁻⁵ for T681C in 12S rRNA) in the CAD study. Both of them were predicted to be pathological, with T5628C disrupting an extremely conservative base-pairing at the AC stem of tRNA^Ala. Furthermore, we confirmed the controversial issue that the number of non-synonymous heteroplasmic sites per sample was significantly higher in CAD patients.

Conclusions

In conclusion, our study confirmed the contribution of rare variants in CAD and showed that CAD patients had more non-synonymous heterogeneity mutations, which may be helpful in identifying the genetic and molecular basis of CAD.

Systemic Lupus Erythematosus: Pathogenesis at the Functional Limit of Redox Homeostasis

Systemic lupus erythematosus (SLE) is a disease characterized by the production of autoreactive antibodies and cytokines, which are thought to have a major role in disease activity and progression. Immune system exposure to excessive amounts of autoantigens that are not efficiently removed is reported to play a significant role in the generation of autoantibodies and the pathogenesis of SLE. While several mechanisms of cell death-based autoantigenic exposure and compromised autoantigen removal have been described in relation to disease onset, a significant association with the development of SLE can be attributed to increased apoptosis and impaired phagocytosis of apoptotic cells. Both apoptosis and impaired phagocytosis can be caused by hydrogen peroxide whose cellular production is enhanced by exposure to endogenous hormones or environmental chemicals, which have been implicated in the pathogenesis of SLE. Hydrogen peroxide can cause lymphocyte apoptosis and glutathione depletion, both of which are associated with the severity of SLE. The cellular accumulation of hydrogen peroxide is facilitated by the myriad of stimuli causing increased cellular bioenergetic activity that enhances metabolic production of this toxic oxidizing agent such as emotional stress and infection, which are recognized SLE exacerbating factors. When combined with impaired cellular hydrogen peroxide removal caused by xenobiotics and genetically compromised hydrogen peroxide elimination due to enzymatic polymorphic variation, a mechanism for cellular accumulation of hydrogen peroxide emerges, leading to hydrogen peroxide-induced apoptosis and impaired phagocytosis, enhanced autoantigen exposure, formation of autoantibodies, and development of SLE.

Primer effect in the detection of mitochondrial DNA point heteroplasmy by automated sequencing

The correct detection of mitochondrial DNA (mtDNA) heteroplasmy by automated sequencing presents methodological constraints. The main goals of this study are to investigate the effect of sense and distance of primers in heteroplasmy detection and to test if there are differences in the accurate determination of heteroplasmy involving transitions or transversions. A gradient of the heteroplasmy levels was generated for mtDNA positions 9477 (transition G/A) and 15,452 (transversion C/A). Amplification and subsequent sequencing with forward and reverse primers, situated at 550 and 150 bp from the heteroplasmic positions, were performed. Our data provide evidence that there is a significant difference between the use of forward and reverse primers. The forward primer is the primer that seems to give a better approximation to the real proportion of the variants. No significant differences were found concerning the distance at which the sequencing primers were placed neither between the analysis of transitions and transversions. The data collected in this study are a starting point that allows to glimpse the importance of the sequencing primers in the accurate detection of point heteroplasmy, providing additional insight into the overall automated sequencing strategy.

Selection against pathogenic mtDNA mutations in a stem cell population leads to the loss of the 3243A-->G mutation in blood

The mutation 3243A-->G is the most common heteroplasmic pathogenic mitochondrial DNA (mtDNA) mutation in humans, but it is not understood why the proportion of this mutation decreases in blood during life. Changing levels of mtDNA heteroplasmy are fundamentally related to the pathophysiology of the mitochondrial disease and correlate with clinical progression. To understand this process, we simulated the segregation of mtDNA in hematopoietic stem cells and leukocyte precursors. Our observations show that the percentage of mutant mtDNA in blood decreases exponentially over time. This is consistent with the existence of a selective process acting at the stem cell level and explains why the level of mutant mtDNA in blood is almost invariably lower than in nondividing (postmitotic) tissues such as skeletal muscle. By using this approach, we derived a formula from human data to correct for the change in heteroplasmy over time. A comparison of age-corrected blood heteroplasmy levels with skeletal muscle, an embryologically distinct postmitotic tissue, provides independent confirmation of the model. These findings indicate that selection against pathogenic mtDNA mutations occurs in a stem cell population.

Beneficial effects of creatine, CoQ10, and lipoic acid in mitochondrial disorders

Mitochondrial disorders share common cellular consequences: (1) decreased ATP production; (2) increased reliance on alternative anaerobic energy sources; and (3) increased production of reactive oxygen species. The purpose of the present study was to determine the effect of a combination therapy (creatine monohydrate, coenzyme Q(10), and lipoic acid to target the above-mentioned cellular consequences) on several outcome variables using a randomized, double-blind, placebo-controlled, crossover study design in patients with mitochondrial cytopathies. Three patients had mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), four had mitochondrial DNA deletions (three patients with chronic progressive external ophthalmoplegia and one with Kearns-Sayre syndrome), and nine had a variety of other mitochondrial diseases not falling into the two former groups. The combination therapy resulted in lower resting plasma lactate and urinary 8-isoprostanes, as well as attenuation of the decline in peak ankle dorsiflexion strength in all patient groups, whereas higher fat-free mass was observed only in the MELAS group. Together, these results suggest that combination therapies targeting multiple final common pathways of mitochondrial dysfunction favorably influence surrogate markers of cellular energy dysfunction. Future studies with larger sample sizes in relatively homogeneous groups will be required to determine whether such combination therapies influence function and quality of life.

The changes of oxidative stress and human 8-hydroxyguanine glycosylase1 gene expression in depressive patients with acute leukemia

The results of several recent studies indicated that free radicals are involved in the biochemical mechanisms that underlie neuropsychiatric disorders. In the present study, we evaluated changes in oxidative stress and human 8-hydroxyguanine glycosylase1 gene (hOGG1) expression in depressive patients with acute leukemia. Ninety two cases were assessed using the Zung self-rating depression scale (SDS) and multiple-item questionnaires. We measured total antioxidant capacity (T-AOC) and the concentrations of reactive oxygen species (ROS), superoxide dismutase (SOD), malondialdehyde (MDA) and nitric oxide (NO) during a pre-treatment period. The steady-state expression of hOGG1 mRNA transcripts was monitored. The incidence of depression was 47.83%. There was a significant decrease in serum T-AOC and SOD concentrations in depressive patients compared to the control subjects, whereas the opposite was the case for serum concentrations of ROS, NO and MDA. Real-time polymerase chain reaction (PCR) revealed that hOGG1 mRNA expression was greater in depressive patients than in the controls. Person correlation analysis revealed that depression was correlated positively with sex, the course of the disease and hOGG1 mRNA expression; depression was correlated negatively with T-AOC. Based on these results, we conclude that the antioxidant system is impaired in leukemic patients with affective disorders. Therefore, oxidative stress may play an important role in the pathophysiology of depression.

Oxidant Stress and Peripheral Neuropathy During Antiretroviral Therapy

BACKGROUND

Peripheral neuropathy that complicates HIV nucleoside reverse transcriptase inhibitor (NRTI) therapy is likely caused by mitochondrial injury. Mitochondria play a central role in regulating oxidant stress. We explored the relationships between oxidant stress and NRTI-induced peripheral neuropathy.

METHODS

The AIDS Clinical Trials Group (ACTG) studied the cases of 384 antiretroviral-naive individuals randomized to receive didanosine/stavudine or zidovudine/lamivudine, plus efavirenz, nelfinavir, or both. The participants were followed for up to 3 years. Peripheral neuropathy was ascertained by signs and symptoms. We performed a case-control study of ACTG 384 participants. Peripheral neuropathy cases and nonneuropathy control subjects were selected from didanosine/stavudine recipients. Alternate control subjects were selected from zidovudine/lamivudine recipients who developed peripheral neuropathy. Oxidant stress was assessed by quantifying F2-isoprostanes (F2-IsoPs) in cryopreserved plasma.

RESULTS

Seventy-five cases, 71 control subjects, and 18 alternate control subjects were identified. The median baseline F2-IsoP values were 53 (interquartile range [IQR], 40-85), 57 (IQR, 41-77), and 53 (IQR, 47-101) pg/mL, respectively, and did not differ between cases and control subjects (P = 0.78) or alternate control subjects (P = 0.60). Changes in F2-IsoPs from baseline to time of peripheral neuropathy did not differ significantly between cases (median, 10 [IQR, -17 to 26] pg/mL) and control subjects (median, 4 [IQR, -11 to 17] pg/mL; P = 0.48) or alternate control subjects (median, 1 [IQR, -48 to 10] pg/mL; P = 0.21).

CONCLUSIONS

Peripheral neuropathy that complicates antiretroviral therapy with NRTIs was not associated with increased systemic oxidant stress assessed by plasma F2-IsoPs.

Hemochromatosis (HFE) gene mutations and peripheral neuropathy during antiretroviral therapy

OBJECTIVE

Peripheral neuropathy (PN) often complicates nucleoside reverse transcriptase inhibitor (NRTI) therapy of HIV infection and may involve mitochondrial dysfunction. Since iron deficiency is associated with some types of PN, and iron is essential for mitochondrial function, we tested the hypothesis that hemochromatosis (HFE) gene mutations influence susceptibility to NRTI-induced PN.

DESIGN

Case-control study involving multicenter, AIDS Clinical Trials Group (ACTG) protocol 384 and ACTG Human DNA Repository specimens.

METHODS

Study participants were randomized to receive three- or four-drug antiretroviral therapy with didanosine (ddI) plus stavudine (d4T) or zidovudine plus lamivudine, given with efavirenz, nelfinavir, or both, with up to three years of follow-up. PN was ascertained based on signs and symptoms. HFE C282Y and H63D genotypes were determined, and associations with PN were assessed using logistic regression.

RESULTS

: Of 509 participants, 147 (29%) developed PN, 73% of whom had been randomized to receive ddI plus d4T. Among ddI/d4T-ever-treated individuals, HFE C282Y heterozygotes developed PN on ddI/d4T significantly less often than C282Y non-carriers, adjusting for age, CD4 lymphocyte count and viral load at baseline, and concomitant antiretroviral drugs [6% vs. 35%, respectively, in whites; adjusted odds ratio (OR), 0.17; 95% confidence interval (CI) 0.03-0.83; P = 0.021]. Regardless of race/ethnicity, ddI/d4T-associated PN was uncommon in C282Y heterozygotes [race-adjusted OR, 0.30; 95% CI 0.09-0.96); P = 0.042].

CONCLUSIONS

Iron-loading HFE mutations such as C282Y are associated with a decreased risk of PN during antiretroviral therapy. This finding has potential implications for the prediction and prevention of NRTI-associated PN, particularly in populations at risk of iron deficiency.