Endomyocardial biopsies for early detection of mitochondrial disorders in hypertrophic cardiomyopathies

Mitochondrial protective effects caused by the administration of mefenamic acid in sepsis

The pathophysiology of sepsis may involve the activation of the NOD-type receptor containing the pyrin-3 domain (NLPR-3), mitochondrial and oxidative damages. One of the primary essential oxidation products is 8-oxoguanine (8-oxoG), and its accumulation in mitochondrial DNA (mtDNA) induces cell dysfunction and death, leading to the hypothesis that mtDNA integrity is crucial for maintaining neuronal function during sepsis. In sepsis, the modulation of NLRP-3 activation is critical, and mefenamic acid (MFA) is a potent drug that can reduce inflammasome activity, attenuating the acute cerebral inflammatory process. Thus, this study aimed to evaluate the administration of MFA and its implications for the reduction of inflammatory parameters and mitochondrial damage in animals submitted to polymicrobial sepsis. To test our hypothesis, adult male Wistar rats were submitted to the cecal ligation and perforation (CLP) model for sepsis induction and after receiving an injection of MFA (doses of 10, 30, and 50 mg/kg) or sterile saline (1 mL/kg). At 24 h after sepsis induction, the frontal cortex and hippocampus were dissected to analyze the levels of TNF-α, IL-1β, and IL-18; oxidative damage (thiobarbituric acid reactive substances (TBARS), carbonyl, and DCF-DA (oxidative parameters); protein expression (mitochondrial transcription factor A (TFAM), NLRP-3, 8-oxoG; Bax, Bcl-2 and (ionized calcium-binding adaptor molecule 1 (IBA-1)); and the activity of mitochondrial respiratory chain complexes. It was observed that the septic group in both structures studied showed an increase in proinflammatory cytokines mediated by increased activity in NLRP-3, with more significant oxidative damage and higher production of reactive oxygen species (ROS) by mitochondria. Damage to mtDNA it was also observed with an increase in 8-oxoG levels and lower levels of TFAM and NGF-1. In addition, this group had an increase in pro-apoptotic proteins and IBA-1 positive cells. However, MFA at doses of 30 and 50 mg/kg decreased inflammasome activity, reduced levels of cytokines and oxidative damage, increased bioenergetic efficacy and reduced production of ROS and 8-oxoG, and increased levels of TFAM, NGF-1, Bcl-2, reducing microglial activation. As a result, it is suggested that MFA induces protection in the central nervous system early after the onset of sepsis.

Increased oxidative stress in the mitochondria isolated from lymphocytes of bipolar disorder patients during depressive episodes

The present study aims to investigate the oxidative stress parameters in isolated mitochondria, as well as looking at mitochondrial complex activity in patients with Bipolar Disorder (BD) during depressive or euthymic episodes. This study evaluated the levels of mitochondrial complex (I, II, II-III and IV) activity in lymphocytes from BD patients. We evaluated the following oxidative stress parameters: superoxide, thiobarbituric acid reactive species (TBARS) and carbonyl levels in submitochondrial particles of lymphocytes from bipolar patients. 51 bipolar patients were recruited into this study: 34 in the euthymic phase, and 17 in the depressive phase. Our results indicated that the depressive phase could increase the levels of mitochondrial superoxide, carbonyl and TBARS, and superoxide dismutase, and could decrease the levels of mitochondrial complex II activity in the lymphocytes of bipolar patients. It was also observed that there was a negative correlation between the Hamilton Depression Rating Scale (HDRS) and complex II activity in the lymphocytes of depressive bipolar patients. In addition, there was a positive correlation between HDRS and superoxide, superoxide dismutase, TBARS and carbonyl. Additionally, there was a negative correlation between complex II activity and oxidative stress parameters. In conclusion, our results suggest that mitochondrial oxidative stress and mitochondrial complex II dysfunction play important roles in the depressive phase of BD.

Mitochondrial function of immune cells in septic shock: A prospective observational cohort study

Background

Reduced cellular ATP synthesis due to impaired mitochondrial function of immune cells may be a factor influencing the immune response in septic shock. We investigate changes in mitochondrial function and bioenergetics of human monocytes and lymphocyte subsets.

Methods

Thirty patients with septic shock were studied at ICU admission, after 24 and 48 hours, and after resolution of shock. Enzymatic activities of citrate synthase and mitochondrial complexes I, IV, and ATP synthase and ATP content of monocytes, T-cells and B-cells and pro-inflammatory (IL-1β and IL-6) and anti-inflammatory (IL-10) cytokine plasma concentrations were compared to samples from 20 healthy volunteers.

Results

Large variations in mitochondrial enzymatic activities of immune cells of septic patients were detected. In monocytes, maximum levels of citrate synthase activity in sepsis were significantly lower when compared to controls (p = 0.021). Maximum relative enzymatic activity (ratio relative to citrate synthase activity) of complex I (p<0.001), complex IV (p = 0.017) and ATP synthase (p<0.001) were significantly higher. In T-cells, maximum levels of citrate synthase (p = 0.583) and relative complex IV (p = 0.602) activity did not differ between patients and controls, whereas levels of relative complex I (p = 0.006) and ATP synthase (p = 0.032) were significantly higher in septic patients. In B-cells of patients, maximum levels of citrate synthase activity (p = 0.004) and relative complex I (p<0.001) were significantly higher, and mean levels of relative complex IV (p = 0.042) lower than the control values, whereas relative ATP synthase activity did not differ (p = 1.0). No significant difference in cellular ATP content was detected in any cell line (p = 0.142–0.519). No significant correlations between specific cytokines and parameters of mitochondrial enzymatic activities or ATP content were observed.

Conclusions

Significant changes of mitochondrial enzymatic activities occur in human peripheral blood immune cells in septic shock when compared to healthy controls. Assessed sub-types of immune cells showed differing patterns of regulation. Total ATP-content of human immune cells did not differ between patients in septic shock and healthy volunteers.

Decaffeinated green tea extract rich in epigallocatechin-3-gallate prevents fatty liver disease by increased activities of mitochondrial respiratory chain complexes in diet-induced obesity mice

Nonalcoholic fatty liver disease has been considered the hepatic manifestation of obesity. It is unclear whether supplementation with green tea extract rich in epigallocatechin-3-gallate (EGCG) influences the activity of mitochondrial respiratory chain complexes and insulin resistance in the liver. EGCG regulated hepatic mitochondrial respiratory chain complexes and was capable of improving lipid metabolism, attenuating insulin resistance in obese mice. Mice were divided into four groups: control diet+water (CW) or EGCG (CE) and hyperlipidic diet+water (HFW) or EGCG (HFE). All animals received water and diets ad libitum for 16 weeks. Placebo groups received water (0.1 ml/day) and EGCG groups (0.1 ml EGCG and 50 mg/kg/day) by gavage. Cytokines concentrations were obtained by ELISA, protein expression through Western blotting and mitochondrial complex enzymatic activity by colorimetric assay of substrate degradation. HFW increased body weight gain, adiposity index, retroperitoneal and mesenteric adipose tissue relative weight, serum glucose, insulin and Homeostasis Model Assessment of Basal Insulin Resistance (HOMA-IR); glucose intolerance was observed in oral glucose tolerance test (OGTT) as well as ectopic fat liver deposition. HFE group decreased body weight gain, retroperitoneal and mesenteric adipose tissue relative weight, HOMA-IR, insulin levels and liver fat accumulation; increased complexes II-III and IV and malate dehydrogenase activities and improvement in glucose uptake in OGTT and insulin sensitivity by increased protein expression of total AKT, IRα and IRS1. We did not find alterations in inflammatory parameters analyzed. EGCG was able to prevent obesity stimulating the mitochondrial complex chain, increasing energy expenditure, particularly from the oxidation of lipid substrates, thereby contributing to the prevention of hepatic steatosis and improved insulin sensitivity.

Mitochondrial DNA defects in cardiomyopathy

Abnormalities in mitochondrial DNA (mtDNA) including specific deletions and point mutations have been found in an increasing number of cases of both dilated and hypertrophic cardiomyopathy. The role that these mutations may play in contributing to the cardiomyopathic phenotype is discussed in this survey of the recent literature.

Sexual dimorphism in the expression of mitochondria-related genes in rat heart at different ages

Cardiovascular disease (CVD) is the leading cause of mortality worldwide. Moreover, sex and age are considered major risk factors in the development of CVDs. Mitochondria are vital for normal cardiac function, and regulation of mitochondrial structure and function may impact susceptibility to CVD. To identify potential role of mitochondria in sex-related differences in susceptibility to CVD, we analyzed the basal expression levels of mitochondria-related genes in the hearts of male and female rats. Whole genome expression profiling was performed in the hearts of young (8-week), adult (21-week), and old (78-week) male and female Fischer 344 rats and the expression of 670 unique genes related to various mitochondrial functions was analyzed. A significant (p<0.05) sexual dimorphism in expression levels of 46, 114, and 41 genes was observed in young, adult and old rats, respectively. Gene Ontology analysis revealed the influence of sex on various biological pathways related to cardiac energy metabolism at different ages. The expression of genes involved in fatty acid metabolism was significantly different between the sexes in young and adult rat hearts. Adult male rats also showed higher expression of genes associated with the pyruvate dehydrogenase complex compared to females. In young and adult hearts, sexual dimorphism was not noted in genes encoding oxidative phosphorylation. In old rats, however, a majority of genes involved in oxidative phosphorylation had higher expression in females compared to males. Such basal differences between the sexes in cardiac expression of genes associated with energy metabolism may indicate a likely involvement of mitochondria in susceptibility to CVDs. In addition, female rats showed lower expression levels of apoptotic genes in hearts compared to males at all ages, which may have implications for better preservation of cardiac mass in females than in males.

Delphinidin inhibits VEGF induced-mitochondrial biogenesis and Akt activation in endothelial cells

Delphinidin, an anthocyanin present in red wine, has been reported to exert vasculoprotective properties on endothelial cells, including vasorelaxing and anti-apoptotic effects. Moreover, delphinidin treatment in a rat model of post-ischemic neovascularization has been described to exert anti-angiogenic property. Angiogenesis is an energetic process and VEGF-induced angiogenesis is associated with mitochondrial biogenesis. However, whether delphinidin induces changes in mitochondrial biogenesis has never been addressed. Effects of delphinidin were investigated in human endothelial cells at a concentration described to be anti-angiogenic in vitro (10(-2)g/l). mRNA expression of mitochondrial biogenesis factors, mitochondrial respiration, DNA content and enzyme activities were assessed after 48 h of stimulation. Delphinidin increased mRNA expression of several mitochondrial biogenesis factors, including NRF1, ERRα, Tfam, Tfb2m and PolG but did not affect neither mitochondrial respiration, DNA content nor enzyme activities. In presence of delphinidin, VEGF failed to increase mitochondrial respiration, DNA content, complex IV activity and Akt activation in endothelial cells. These results suggest a possible association between inhibition of VEGF-induced mitochondrial biogenesis through Akt pathway by delphinidin and its anti-angiogenic effect, providing a novel mechanism sustaining the beneficial effect of delphinidin against pathologies associated with excessive angiogenesis such as cancers.

Acute and chronic administration of cannabidiol increases mitochondrial complex and creatine kinase activity in the rat brain

OBJECTIVE

To investigate the effects of cannabidiol (CBD) on mitochondrial complex and creatine kinase (CK) activity in the rat brain using spectrophotometry.

METHOD

Male adult Wistar rats were given intraperitoneal injections of vehicle or CBD (15, 30, or 60 mg/kg) in an acute (single dose) or chronic (once daily for 14 consecutive days) regimen. The activities of mitochondrial complexes and CK were measured in the hippocampus, striatum, and prefrontal cortex.

RESULTS

Both acute and chronic injection of CBD increased the activity of the mitochondrial complexes (I, II, II-III, and IV) and CK in the rat brain.

CONCLUSIONS

Considering that metabolism impairment is certainly involved in the pathophysiology of mood disorders, the modulation of energy metabolism (e.g., by increased mitochondrial complex and CK activity) by CBD could be an important mechanism implicated in the action of CBD.

Hypertrophic Cardiomyopathy due to Mitochondrial Disease: Prenatal Diagnosis, Management, and Outcome

A case of prenatally diagnosed fetal hypertrophic cardiomyopathy is reported. The mother was referred to our department at 37 weeks' gestation because of suspected congenital heart disease. Prenatal echocardiography showed biventricular hypertrophy and pericardial effusion, without additional abnormalities. Postnatal echocardiography confirmed prenatal diagnosis. Neonatal EKG showed biventricular hypertrophy and Wolff-Parkinson-White syndrome. Skeletal muscle biopsy was consistent with mitochondrial oxidative phosphorylation defect involving a combined defect of respiratory complexes I and IV. Echocardiographic followup during the first year of life showed progressive regression of hypertrophy and evolution to left ventricular myocardial noncompaction.

Neonatal cardiomyopathies and metabolic crises due to oxidative phosphorylation defects

Neonatal cardiomyopathies due to mitochondrial oxidative phosphorylation (OXPHOS) defects are extremely severe conditions which can be either isolated or included in a multi-organ disease, with or without metabolic crises, of which profound lactic acidosis is the prominent feature. Cardiomyopathy is more often hypertrophic than dilated. Antenatal manifestations such as fetal cardiomyopathy, arrhythmia and/or hydrops have been reported. Pathophysiological mechanisms are complex, going beyond ATP deficiency of the high-energy-consuming neonatal myocardium. Birth is a key metabolic period when the myocardium switches ATP production from anaerobic glycolysis to mitochondrial fatty acid oxidation and OXPHOS. Heart-specificity of the defect may be related to the specific localization of the defect, to the high myocardium dependency on OXPHOS, and/or to interaction between the primary genetic alteration and other factors such as modifier genes. Therapeutic options are limited but standardized diagnostic procedures are mandatory to confirm the OXPHOS defect and to identify its causal mutation, allowing genetic counseling and potential prenatal diagnosis.

Drug management in emergent liver transplantation of mitochondrial disorder carriers: review of the literature

BACKGROUND

Mitochondrial respiratory-chain disorders (MRCD) lead to progressive disabling of neurological and cellular conditions that involve muscles, brain, kidney, and liver dysfunction. Affected individuals may need surgery, including orthotopic liver transplantation (OLT). Surgery poses anesthesia challenges because of the prolonged use of anesthetic drugs and sedatives, which may inhibit oxidative phosphorylation, mimic mitochondrial cytopathic disorders, or unveil them ex novo.

MATERIALS AND METHODS

We conducted a multilingual PubMed search of surgical and non-surgical anesthesia reports between the years 1992 and 2008, where anesthetic drugs were used in MRCD patients, especially for those undergoing urgent OLTs.

RESULTS

There were 51 case reports of 210 anesthesia and critical care interventions in patients with MRCD, a large part of them were children. Data pertaining to the safe usage of anesthesia and perioperative drugs were limited and conflicting. We found no article that addressed the issue of perioperative handling of urgent OLT in MRCD patients. We therefore suggest our own - although limited - experience for such occasions.

CONCLUSION

There are no randomized, controlled, trial-based indications regarding safe anesthetic drugs to be used perioperatively in MRCD carriers. Consultation among geneticists, anesthesiologists, intensivists, and surgeons is essential in patients with known/suspected metabolic syndrome for planning appropriate perioperative care.

Estrogen-related receptor alpha and PGC-1-related coactivator constitute a novel complex mediating the biogenesis of functional mitochondria

Mitochondrial biogenesis, which depends on nuclear as well as mitochondrial genes, occurs in response to increased cellular ATP demand. The nuclear transcriptional factors, estrogen-related receptor alpha (ERRalpha) and nuclear respiratory factors 1 and 2, are associated with the coordination of the transcriptional machinery governing mitochondrial biogenesis, whereas coactivators of the peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) family serve as mediators between the environment and this machinery. In the context of proliferating cells, PGC-1-related coactivator (PRC) is a member of the PGC-1 family, which is known to act in partnership with nuclear respiratory factors, but no functional interference between PRC and ERRalpha has been described so far. We explored three thyroid cell lines, FTC-133, XTC.UC1 and RO 82 W-1, each characterized by a different mitochondrial content, and studied their behavior towards PRC and ERRalpha in terms of respiratory efficiency. Overexpression of PRC and ERRalpha led to increased respiratory chain capacity and mitochondrial mass. The inhibition of ERRalpha decreased cell growth and respiratory chain capacity in all three cell lines. However, the inhibition of PRC and ERRalpha produced a greater effect in the oxidative cell model, decreasing the mitochondrial mass and the phosphorylating respiration, whereas the nonphosphorylating respiration remained unchanged. We therefore hypothesize that the ERRalpha-PRC complex plays a role in arresting the cell cycle through the regulation of oxidative phosphorylation in oxidative cells, and through some other pathway in glycolytic cells.

The in-depth evaluation of suspected mitochondrial disease

Mitochondrial disease confirmation and establishment of a specific molecular diagnosis requires extensive clinical and laboratory evaluation. Dual genome origins of mitochondrial disease, multi-organ system manifestations, and an ever increasing spectrum of recognized phenotypes represent the main diagnostic challenges. To overcome these obstacles, compiling information from a variety of diagnostic laboratory modalities can often provide sufficient evidence to establish an etiology. These include blood and tissue histochemical and analyte measurements, neuroimaging, provocative testing, enzymatic assays of tissue samples and cultured cells, as well as DNA analysis. As interpretation of results from these multifaceted investigations can become quite complex, the Diagnostic Committee of the Mitochondrial Medicine Society developed this review to provide an overview of currently available and emerging methodologies for the diagnosis of primary mitochondrial disease, with a focus on disorders characterized by impairment of oxidative phosphorylation. The aim of this work is to facilitate the diagnosis of mitochondrial disease by geneticists, neurologists, and other metabolic specialists who face the challenge of evaluating patients of all ages with suspected mitochondrial disease.

A novel mitochondrial DNA tRNAIle (m.4322dupC) mutation associated with idiopathic dilated cardiomyopathy

We identified a novel heteroplasmic mitochondrial DNA (mtDNA) (m.4322dupC) mutation in tRNA gene associated with isolated dilated cardiomyopathy (DCM) as maternal trait. Mutation screening techniques and automated DNA sequencing were performed to identify mtDNA mutations and to assess heteroplasmy in family's proband and healthy control subjects. All family members tested had heteroplasmic mtDNA m.4322dupC mutation. We also screened 350 normal controls for this mutation and found no evidence of heteroplasmy. The m.4322dupC mutation was found in the skeletal tissue from the proband that exhibited slightly reduced deficiency of mitochondrial respiratory chain enzymes (complex III). The present study reports the novel m.4322dupC mutation in tRNA gene, which is possibly associated to the disease, to isolated DCM. It was localized in a hot-spot region for mutations and is possibly pathogenic because of a cosegregation with the matrilineal transmission of DCM.

Contiguous X-chromosome deletion syndrome encompassing the BTK, TIMM8A, TAF7L, and DRP2 genes

X-linked agammaglobulinemia (XLA) is characterized by low levels of B-lymphocytes with early-onset, recurrent, microbial infections occasionally causing neurological symptoms. We observed an atypical clinical course of XLA, complicated since early childhood with neurological impairment, progressive sensorineural deafness, and dystonia in six boys of four unrelated families. The neurologic symptoms suggested the diagnosis of Mohr-Tranebjaerg syndrome, caused by mutations in the TIMM8A gene, previously known as DDP1, and located centromerically of BTK. Deafness dystonia peptide (DDP1) participates in neurological development and is a part of the mitochondrial protein import pathway. Mutation analysis of the BTK gene revealed gross deletions of different lengths in all patients, in one case extending approximately 196 kb, including the genes TIMM8A, TAF7L, and DRP2. The most prominent clinical findings of this contiguous deletion syndrome are the combination of immunodeficiency and sensorineural deafness, which were present in all affected boys. The severity of symptoms, however, did not correlate with the extent of the deletion.

Factors associated with establishing a causal diagnosis for children with cardiomyopathy

OBJECTIVE

The goal was to identify the clinical variables associated with establishing a cause of cardiomyopathy in children.

METHODS

The Pediatric Cardiomyopathy Registry contains clinical and causal testing information for 916 children who were diagnosed as having cardiomyopathy in North America between 1990 and 1995. Children with a causal diagnosis were compared with those without with respect to several demographic, clinical, and causal testing variables.

RESULTS

Cardiomyopathy was 1 of 4 types, hypertrophic (34.2%), dilated (53.8%), restrictive (3.2%), or other or mixed (8.9%). Only one third of cases had a known cause. Children with a known cause for hypertrophic cardiomyopathy were more likely to be female, to be relatively smaller, to present with congestive heart failure, and to have increased left ventricular posterior wall thickness without outflow tract obstruction. For dilated cardiomyopathy, a known cause was associated with older age, lower heart rate, smaller left ventricular dimensions, and greater shortening fraction. Family history of cardiomyopathy predicted a significantly higher rate of causal diagnoses for all cardiomyopathy types, whereas family histories of genetic syndromes and sudden death were also predictive of a cause for hypertrophic and dilated cardiomyopathies. For hypertrophic cardiomyopathy, only blood and urine testing was associated with a causal diagnosis, whereas both viral serologic testing or culture and endomyocardial biopsy were independent predictors of a causal diagnosis in dilated cardiomyopathy.

CONCLUSIONS

Certain patient characteristics, family history, echocardiographic findings, laboratory testing, and biopsy were associated significantly with establishing a cause of pediatric cardiomyopathy. Early endomyocardial biopsy should be considered strongly for children with dilated cardiomyopathy, for definitive diagnosis of viral myocarditis. Although not widely used, skeletal muscle biopsy may yield a cause for some patients with hypertrophic cardiomyopathy and for patients suspected of having a mitochondrial disorder.

Clinical presentations of mitochondrial cardiomyopathies

To determine the clinical manifestations and interfamilial variability of patients diagnosed with a mitochondrial cardiomyopathy, we reviewed the charts of 14 patients with cardiomyopathy out of 59 patients with mitochondrial disorders who attended the mitochondrial disease clinic at Wolfson Medical Center from 1996 to 2001. All patients underwent a metabolic evaluation including blood lactate, pyruvate, carnitine, and amino acids and urine organic acids. Respiratory chain enzymes were assessed in 10 patients. The mitochondrial DNA (mtDNA) was assessed for mutations. The age at presentation ranged between 6 months and 24 years. Six of the patients died, 5 from heart failure. The cardiomyopathy was hypertrophic in 10 and dilated in 4. Conduction and rhythm abnormalities were present in 6. Eleven patients had family members with mitochondrial disorders. All the patients had additional involvement of one or more systems. Seven patients exhibited a deficiency of a respiratory chain enzyme in the muscle. The MELAS mtDNA point mutation (3243) was found in one patient. Blood lactic acid levels were increased in 5. Brain MRI abnormalities were observed in 4.

CONCLUSIONS

Mitochondrial dysfunction frequently affects the heart and may cause both hypertrophic and dilated cardiomyopathy. The cardiomyopathy is usually a part of a multisystem involvement and may rarely be isolated. The course may be stable for many years, but rapid deterioration may occur. Understanding the biochemical and genetic features of these diseases will enable us to comprehend the clinical heterogeneity of these disorders.

[The mitochondrial organelle and the heart]

The heart is highly dependent for its function on oxidative energy generated in mitochondria, primarily by fatty acid beta-oxidation, respiratory electron chain and oxidative phosphorylation. Defects in mitochondrial structure and function have been found in association with cardiovascular diseases such as dilated and hypertrophy cardiomyopathy, cardiac conduction defects and sudden death, ischemic and alcoholic cardiomyopathy, as well as myocarditis. While a subset of these mitochondrial abnormalities have a defined genetic basis (e.g. mitochondrial DNA changes leading to oxidative phosphorylation dysfunction,fatty acid beta-oxidation defects due to specific nuclear DNA mutations), other abnormalities appear to be due to a more sporadic or environmental cardiotoxic insult or have not yet been characterized.This review focuses on abnormalities in mitochondrial bioenergetic function and mitochondrial DNA defects associated with cardiovascular diseases, their significance in cardiac pathogenesis as well as on the available diagnostic and therapeutic options. A concise background concerning mitochondrial biogenesis and bioenergetic pathways during cardiac growth,development and aging will also be provided.

Understanding the impact of mitochondrial defects in cardiovascular disease: a review

OBJECTIVE

Defects in mitochondrial structure and function have been found in association with cardiovascular diseases such as dilated and hypertrophic cardiomyopathy, cardiac conduction defects and sudden death, ischemic and alcoholic cardiomyopathy, and myocarditis. A genetic basis has been established for some mitochondrial abnormalities (eg, mitochondrial DNA changes leading to oxidative phosphorylation dysfunction, fatty acid beta-oxidation (FAO) defects resulting from specific nuclear mutations) whereas other abnormalities appear to be due to a more sporadic or environmental cardiotoxic insult or have not yet been characterized.

METHODS

This article reviews mitochondrial abnormalities in structure or function reported in cardiac diseases highlighting information about their potential etiology, significance in cardiac pathogenesis, and diagnostic and therapeutic options available to the clinician. We also provide a brief background concerning mitochondrial biogenesis and bioenergetic pathways in cardiac growth, development, and aging.

CONCLUSIONS

Although aberrations in bioenergetic functioning of mitochondria appear to be most often related to cardiac dysfunction, the primary defect(s) causing bioenergetic dysfunction may reside in a nonbioenergetic pathway (eg, signaling between mitochondria and nucleus) or in overall mitochondrial biogenesis or degradation pathways.

Clinical spectrum and diagnosis of mitochondrial disorders

Respiratory chain deficiencies have long been regarded as neuromuscular diseases mostly originating from mutations in the mitochondrial DNA. Actually, oxidative phosphorylation, i.e., adenosine triphosphate (ATP) synthesis-coupled electron transfer from substrate to oxygen through the respiratory chain, does not only occur in the neuromuscular system. For this reason, a respiratory chain deficiency can theoretically give rise to any symptom, in any organ or tissue, at any age and with any mode of inheritance, owing to the dual genetic origin of respiratory chain enzymes (nuclear DNA and mitochondrial DNA). In recent years, it has become increasingly clear that genetic defects of oxidative phosphorylation account for a large variety of clinical symptoms in both childhood and adulthood. Diagnosis of a respiratory chain deficiency is difficult initially when only one symptom is present, and easier when additional, seemingly unrelated, symptoms are observed. The clinical heterogeneity is echoed by the genetic heterogeneity illustrated by the increasing number of nuclear genes that have been shown to be involved in these diseases. In the absence of clear-cut genotype-phenotype correlations and in front of the large number of possibly involved genes, biochemical analyses are still the cornerstone of the diagnosis of this condition.

Dramatic improvement in mitochondrial cardiomyopathy following treatment with idebenone

Idebenone, a synthetic analogue of coenzyme Q10, has been shown to improve cardiac function in patients with Friedreich ataxia and a deficiency of respiratory chain complexes I-III. We describe a woman with severe combined right and left heart failure due to a mitochondrial cardiomyopathy. The patient underwent an endomyocardial biopsy as part of an evaluation for cardiac transplantation. It showed severely decreased respiratory complex activities dependent on CoQ, pointing to CoQ depletion. Following idebenone treatment there was a dramatic improvement in her clinical status with resolution of the heart failure.

The emerging concept of mitochondrial cardiomyopathies

OBJECTIVE

Our purpose was to present an updated review on the spectrum of mitochondrial DNA-related syndromes relevant to cardiac disturbances.

BACKGROUND

The advent of molecular genetics has provided important insight into the mechanisms underlying a variety of inherited heart disorders, including cardiac arrhythmias and cardiomyopathies. These studies pointed to defects in ion channels, contractile proteins, structural proteins, and signaling molecules as key players in disease pathogenesis, and they have opened up new mechanism-based approaches to therapy.

RESULTS AND CONCLUSIONS

Mitochondrial DNA defects and faulty oxidative phosphorylation are infrequently considered as causes of cardiomyopathies. This is surprising given the heavy dependence of the heart on oxidative metabolism and the recent advances in understanding the molecular features of mitochondrial disorders. This remarkable progress and the implications it may have for more common forms of cardiovascular disease are reviewed.

Biochemical and molecular basis for mitochondrial cardiomyopathy in neonates and children

Defects in myocardial bioenergetics have been reported in patients with cardiomyopathy but their molecular basis and role in pathophysiology remain unclear. We sought to establish a molecular basis for cardiac mitochondrial respiratory enzyme abnormalities frequently present (75%) in a group of 16 children (including 2 neonates) with end-stage cardiomyopathy. Decreased specific activity levels were found in complexes I, III, IV and V but not in II, the only complex that is entirely nuclear encoded. Sequence analysis of cardiac mtDNA revealed 4 patients harbouring heteroplasmic mtDNA mutations in cytb, tRNAArg, and ND5 at highly conserved positions. These mutations were present neither in controls nor in patients without enzymatic defect. In addition, 4 patients exhibited marked reduction in cardiac mtDNA levels. The basis for respiratory enzyme abnormalities can be explained in a subset of our patients as a result of either pathogenic mtDNA mutation or depletion. Patients harbouring both DNA and enzymatic defects fulfil rigorous criteria defining mitochondrial cardiomyopathy.

Effect of partial oxygen supply on mitochondrial electron transport system during complete cardiac ischemia

During complete ischemia we assessed myocardial utilization of the small amount of oxygen available. We also determined whether blood cardioplegia has any advantage over crystalloid cardioplegia in this setting. Patients with preserved left ventricular myocardial function and without anterolateral wall infarct or aneurysm were included to the study. Intermittent cold blood and crystalloid cardioplegia were used in 10 patients (group BC) and 9 patients (group CC), respectively. From myocardial biopsies, obtained before and after ischemia, complete electron transport system (ETS) enzyme activities (NDH, SDH, NCCR, SCCR, and COX) and lactate content were analyzed. Biochemical and hemodynamic analyses also were done. Myocardial and blood temperatures were monitored. Ischemic time was longer in group CC (p < 0.05). There were no important differences in biochemical and hemodynamic variables between the two groups. In addition, there was no difference in NDH and SDH activities as well as COX/SCCR and COX/RS-NCCR ratios between the two groups before and after ischemia. After Ischemia, RS-NCCR in group CC and SCCR and COX activities in both groups were lower than the control. For all enzymes, activity change ratios were not different between groups. Myocardial lactate content was increased in both groups after ischemia. However, the increase in group BC was less (p < 0.01). Based on our findings, we believe that the superiority of blood cardioplegia over crystalloid cardioplegia does not depend on oxygen content, but on other factors such as buffering and free oxygen radical scavenger effects among others. However, with the warm and continuous blood cardioplegia technique, oxygen content might be more important.

Functional and ultrastructural evidence of myocardial stunning after acute carbon monoxide poisoning

OBJECTIVE

To study human myocardial ultrastructural changes after carbon monoxide (CO) poisoning inducing reversible cardiac failure.

DESIGN

CASE REPORT

clinical, functional and morphologic findings.

SETTINGS

Public university-affiliated hospital and electron microscopy laboratory.

PATIENT

A 25-yr-old woman with functional evidence of cardiac failure after acute CO poisoning.

INTERVENTIONS

Hyperbaric and intensive care treatment over 10 days. Scintigraphic and cardiac angiography with endomyocardial biopsy.

MEASUREMENTS AND MAIN RESULTS

Scintigraphy with 99mTc hexakis 2-methoxy-2-isobutyl isonitrile (sestaMIBI) showed an uptake defect in the left anterior descending artery territory. The cardiac angiography demonstrated a slight hypokinesis of the superior two thirds of the anterior wall and of the septal region with completely normal coronary angiograms. Electron microscopy of left ventricular biopsies showed slight ultrastructural changes in the myocytes. In addition, large glycogen deposits were mostly associated with swollen mitochondria. The patient was discharged in good clinical condition on day 10.

CONCLUSIONS

Presence of glycogen deposits associated with abnormal mitochondria may be signs of the incapability of myocardial cells in utilizing energy substrata. In the presence of normal myocardial perfusion, our findings are consistent with the presence of a stunned myocardium-like syndrome. Early recognition and treatment of this clinical syndrome allow the prevention of myocardial infarction.

Mitochondrial gene expression and respiratory enzyme activities in cardiac diseases

Respiratory enzyme activities and steady-state level of two mitochondrial-encoded transcripts were quantified in heart muscle biopsies from patients suffering various types of cardiomyopathies unrelated to mitochondrial primary disorders. We have found that although the mitochondrial DNA copy number and the concentration of COI and ND4 transcripts remain fairly constant, there is an important increase (up to 6-fold) in respiratory enzyme activities affecting to several oxidative phosphorylation complexes. Idiopathic dilated cardiomyopathy shows the greatest increase, followed by ischemic heart and ventricular hypertrophy due to aortic stenosis. The results suggest an energetic compensatory mechanism in the heart muscle, in the absence of mitochondrial proliferation or activation of mitochondrial gene expression.

Human mitochondrial function during cardiac growth and development

Little information is presently available concerning mitochondrial respiratory and oxidative phosphorylation function in the normal human heart during growth and development. We investigated the levels of specific mitochondrial enzyme activities and content during cardiac growth and development from the early neonatal period (10-20 days) to adulthood (67 years). Biochemical analysis of enzyme specific activities and content and mitochondrial DNA (mtDNA) copy number was performed with left ventricular tissues derived from 30 control individuals. The levels of cytochrome c oxidase (COX) and complex V specific activity, mtDNA copy number and COX subunit II content remained unchanged in contrast to increased citrate synthase (CS) activity and content. The developmental increase in CS activity paralleled increasing CS polypeptide content, but was neither related to overall increases in mitochondrial number nor coordinately regulated with mitochondrial respiratory enzyme activities. Our findings of unchanged levels of cardiac mitochondrial respiratory enzyme activity during the progression from early childhood to older adult contrasts with the age-specific regulation found with CS, a Krebs cycle mitochondrial enzyme.

Biochemical parameters for the diagnosis of mitochondrial respiratory chain deficiency in humans, and their lack of age-related changes

It is now widely acknowledged that a large number of human diseases originate from respiratory-chain dysfunctions. Because the molecular bases of these diseases are still poorly known, a biochemical approach has to be used in the screening procedures for the diagnoses of these conditions. Assessment of respiratory-chain function in human samples faces several problems: (i) the small size of available samples, (ii) the determination of discriminating parameters, and (iii) the interfering factors, such as age and physical activity. The present study focuses on isolated mitochondria prepared from a minute amount (100-200 mg) of skeletal-muscle biopsies from 201 patients between 0 and 65 years. Whereas 42 patients presented an isolated complex (C)I, CII, CIII or CIV deficiency, no respiratory-chain dysfunction or indirect evidence for a mitochondrial disorder could be attested in 159 of these patients. In this reference group, there was little correlation between enzyme activities and age, whatever the age class considered, 0-3 or 0-65 years of age. However, a confident handling of data points was largely hampered by the marked scattering of enzyme activities measured in the reference population. Activity ratios between the various respiratory-chain complexes presenting a much reduced scattering may be considered as diagnostic tools. As to the effect of age, no correlation with any of the enzyme-activity ratios could be shown. Use of age-matched controls for the diagnosis of respiratory-chain disorders may therefore be avoided, enzyme-activity ratios being highly discriminating and age-independent parameters.

[Cardiac involvement in neuromuscular diseases]

Many neuromuscular disorders involve the heart, occasionally with overt clinical disease. Muscular dystrophies (dystrophinopathies, limb girdle muscular dystrophy, Emery-Dreifuss muscular dystrophy, Steinert's myotonic dystrophy), congenital myopathies, inflammatory myopathies and metabolic diseases (glycogenosis, periodic paralysis, mitochondrial diseases) may produce dilated or hypertrophic cardiomyopathy and heart rhythm or conduction disturbances. Furthermore the heart is commonly involved in some hereditary and degenerative diseases (Friedreich's ataxia and Kugelberg-Welander syndrome) and acquired (Guillain-Barré syndrome) or inherited (Refsum's disease and Charcot-Marie-Tooth syndrome) polyneuropathies. A cardiologist's high clinical suspicion and a simple but systematic skeletal muscle and peripheral nerve investigation, including muscle enzymes quantification, neurophysiological study and muscle biopsy, are necessary for an accurate diagnosis. In selected patients, more sophisticated biochemical and genetic analysis will be necessary. In most cases, endomyocardial biopsy is not essential for the diagnosis.

Aconitase and mitochondrial iron-sulphur protein deficiency in Friedreich ataxia

Friedreich ataxia (FRDA) is a common autosomal recessive degenerative disease (1/50,000 live births) characterized by a progressive-gait and limb ataxia with lack of tendon reflexes in the legs, dysarthria and pyramidal weakness of the inferior limbs. Hypertrophic cardiomyopathy is observed in most FRDA patients. The gene associated with the disease has been mapped to chromosome 9q13 (ref. 3) and encodes a 210-amino-acid protein, frataxin. FRDA is caused primarily by a GAA repeat expansion within the first intron of the frataxin gene, which accounts for 98% of mutant alleles. The function of the protein is unknown, but an increased iron content has been reported in hearts of FRDA patients and in mitochondria of yeast strains carrying a deleted frataxin gene counterpart (YFH1), suggesting that frataxin plays a major role in regulating mitochondrial iron transport. Here, we report a deficient activity of the iron-sulphur (Fe-S) cluster-containing subunits of mitochondrial respiratory complexes I, II and III in the endomyocardial biopsy of two unrelated FRDA patients. Aconitase, an iron-sulphur protein involved in iron homeostasis, was found to be deficient as well. Moreover, disruption of the YFH1 gene resulted in multiple Fe-S-dependent enzyme deficiencies in yeast. The deficiency of Fe-S-dependent enzyme activities in both FRDA patients and yeast should be related to mitochondrial iron accumulation, especially as Fe-S proteins are remarkably sensitive to free radicals. Mutated frataxin triggers aconitase and mitochondrial Fe-S respiratory enzyme deficiency in FRDA, which should therefore be regarded as a mitochondrial disorder.

Cardiac mitochondrial dysfunction and DNA depletion in children with hypertrophic cardiomyopathy

Abnormalities in specific mitochondrial respiratory enzymes and DNA (mtDNA) have been reported in cardiomyopathy. In this study, we report 4 cases of severe hypertrophic cardiomyopathy (HCM) in which specific cardiac mitochondrial enzyme activity defects were found, including complex I (n = 2), complex III (n = 2), complex IV (n = 2) and complex V (n = 1). Other abnormalities were also noted including a marked depletion of mtDNA (n = 1) and decreased content of subunit 2 of cytochrome c oxidase (n = 1). None of the mtDNA point mutations and common deletions previously found in association with cardiomyopathy were detected in these patients. These data indicate that specific respiratory enzyme activity defects are frequently present in HCM. Also, our finding of a marked depletion of mtDNA in 1 patient suggests that cardiac mtDNA depletion, previously unreported in HCM, needs further examination in order to establish whether it plays a primary role in its pathogenesis.

Renal involvement in mitochondrial cytopathies

Mitochondrial cytopathies have long been regarded as neuromuscular diseases. However, an oxidative phosphorylation disorder may give rise to various symptoms in other organs or tissues which are dependent upon mitochondrial energy supply. A broad spectrum of clinical symptoms have been described in these patients, including renal symptoms. The most frequent is proximal tubular dysfunction with a more or less complete de Toni-Debré-Fanconi syndrome. A few patients have been reported with tubular acidosis, Bartter syndrome, chronic tubulointerstitial nephritis, or nephrotic syndrome. The diagnosis of a respiratory chain deficiency is difficult when only renal symptoms are present but should be easier when another seemingly unrelated symptom is observed. Metabolic screening for abnormal oxidoreduction status in plasma, including lactate/pyruvate and ketone body molar ratios, can help to identify patients for further investigations. These include the measurement of oxygen consumption by mitochondria, the assessment of mitochondrial respiratory enzyme activities by spectrophotometric studies, and, when possible, the molecular analysis of mitochondrial DNA. Any mode of inheritance can be observed: sporadic, autosomal dominant or recessive, or maternal inheritance. No satisfactory therapy is presently available for mitochondrial disorders.

Clinical presentations and laboratory investigations in respiratory chain deficiency

Respiratory chain deficiencies have long been regarded as neuromuscular diseases. In fact, oxidative phosphorylation, i.e., ATP synthesis by the respiratory chain not only occurs in the neuromuscular system, indeed, a number of non-neuromuscular organs and tissues are dependent upon mitochondrial energy supply. For this reason, a respiratory chain deficiency can theoretically give rise to any symptom, in any organ or tissue, at any age with any mode of inheritance, due to the twofold genetic origin of respiratory enzymes (nuclear DNA and mitochondrial DNA).

Clinical presentation of mitochondrial disorders in childhood

Respiratory-chain deficiencies have long been regarded as neuromuscular diseases. In fact, oxidative phosphorylation, i.e. adenosine triphosphate (ATP) synthesis by the respiratory chain, does not occur only in the neuromuscular system. Indeed, a number of non-neuromuscular organs and tissues are dependent upon mitochondrial energy supply. For this reason, a respiratory chain deficiency can theoretically give rise to any symptom, in any organ or tissue, at any age and with any mode of inheritance, owing to the twofold genetic origin of respiratory enzymes (nuclear DNA and mitochondrial DNA, mtDNA). In recent years, it has become increasingly clear that genetic defects of oxidative phosphorylation account for a large variety of clinical symptoms in childhood. Among 100 patients with respiratory-chain deficiencies identified in our centre, 56% presented with a non-neuromuscular symptom and 44% were referred for a neuromuscular problem. It appears that the diagnosis of a respiratory-chain deficiency is difficult initially when only one symptom is present. In contrast, this diagnosis is easier to consider when two seemingly unrelated symptoms are observed.

Impaired mitochondrial function in idiopathic dilated cardiomyopathy: biochemical and molecular analysis

Mitochondrial defects at the biochemical and molecular levels are increasingly recognized in diseases involving the heart. The objective of this study was to assess the frequency and extent of mitochondrial defects in idiopathic dilated cardiomyopathy. Left ventricular tissues of 27 patients with idiopathic dilated cardiomyopathy undergoing orthotopic cardiac transplantation because of severe cardiac failure were examined to assess the specific activity levels of mitochondrial respiratory enzymes and changes in mtDNA structure and copy number. Abnormal specific activities of several mitochondrial enzymes were found in 55% of the cardiomyopathic tissues examined (15 patients), with six patients displaying single enzyme defects, including five in complex III and one in complex I. Multiple mitochondrial enzyme defects were found in nine patients, with the most frequent combination of defects seen in complex III and complex IV (5 cases). These enzymatic changes were shown not to be accompanied by changes in mtDNA copy number. In seven cases, however, including three young adults, there was a marked decrease in the levels of polymerase chain reaction products derived from specific mtDNA regions, which may be an indication of specific mtDNA damage. Specific mitochondrial abnormalities are frequently found in idiopathic dilated cardiomyopathy, with a variety of mitochondrial loci affected. These findings are not age dependent.

Cardiomyopathy in respiratory chain disorders

Disorders of mitochondrial oxidative phosphorylation may disturb cardiac energy metabolism and cause cardiomyopathy. Twenty one cases from the literature and one further patient with cardiomyopathy due to biochemically defined respiratory chain defects were reviewed for clinical course, morphology, and pathophysiological mechanisms of the cardiomyopathy. All cases showed concentric hypertrophy of the myocardium without an outflow tract obstruction. In most patients the cardiomyopathy was diagnosed early in infancy and showed rapid deterioration with death before the age of 2 years. Hypertrophy of the myocardium appears to result from swelling of the cardiomyocytes caused by accumulation of mitochondria and by morphologically abnormal megamitochondria.

Reference charts for respiratory chain activities in human tissues

This paper presents a collection of quantitative values for respiratory chain activities in human tissues. These were measured in the most widely used tissues in screening procedures for respiratory chain deficiencies. Investigations were mainly carried out using the different standardized micro-methods previously detailed (Rustin et al., Clin Chim Acta, 1994). The potential effect of the age of the patients on both absolute and relative levels of respiratory chain activities in their skeletal muscle tissue was first considered. No evidence for any significant difference between the various age groups in the studied population (ranging from 0 to above 50 years of age) was observed. Moreover, a quite similar picture of the organization of the respiratory chain was suggested independent of the tissue or the cells investigated. In particular, it was found that roughly identical enzyme activity ratios could be measured in all tissues, which allowed study of the differential involvement of organs and tissues in patients potentially affected by a respiratory chain deficiency. Some tissue-specific features were, however, observed, including varying rates of glycerol-3-phosphate dehydrogenase activities and increased succinate dehydrogenase activity in liver. The technical limitations remaining in the investigations of respiratory chain disorders in man are discussed in the conclusion.