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PubMed2003

Effects of fatty acids in isolated mitochondria: implications for ischemic injury and cardioprotection.

Fatty acids accumulate during myocardial ischemia and are implicated in ischemia-reperfusion injury and mitochondrial dysfunction. Because functional recovery after ischemia-reperfusion ultimately depends on the ability of the mitochondria to recover membrane potential (DeltaPsim), we studied the effects of fatty acids on DeltaPsim regulation, cytochrome c release, and Ca2+ handling in isolated mitochondria under conditions that mimicked aspects of ischemia-reperfusion. Long-chain but not short-chain free fatty acids caused a progressive and reversible (with BSA) increase in inner membrane leakiness (proton leak), which limited mitochondrial ability to support DeltaPsim. In comparison, long-chain activated fatty acids promoted 1). a slower depolarization that was not reversible with BSA, 2). cytochrome c loss that was unrelated to permeability transition pore opening, and 3). inhibition of the adenine nucleotide translocator. Together, these results impaired both mitochondrial ATP production and Ca2+ handling. Diazoxide, a selective opener of mitochondrial ATP-dependent potassium (KATP) channels, partially protected against these effects. These findings indicate that long-chain fatty acid accumulation during ischemia-reperfusion may predispose mitochondria to cytochrome c loss and irreversible injury and identify a novel cardioprotective action of diazoxide.

Adenosine Triphosphate↗

PubMed2000

The role of mitochondria in the pathogenesis of neurodegenerative diseases.

A growing body of evidence indicates that mitochondrial dysfunction may play an important role in the pathogenesis of many neurodegenerative disorders. Because mitochondrial metabolism is not only the principal source of high energy intermediates, but also of free radicals, it has been suggested that inherited or acquired mitochondrial defects could be the cause of neuronal degeneration as a consequence of energy defects and oxidative damage. Mitochondrial respiratory chain dysfunction has been reported in association with primary mitochondrial DNA abnormalities, and also as a consequence of mutations in nuclear genes directly involved in mitochondrial functions, such as SURF1, frataxin, and paraplegin. Defects of oxidative phosphorylation and increased free radical production have also been observed in diseases that are not due to primary mitochondrial abnormalities. In these cases, the mitochondrial dysfunction is likely to be an epiphenomenon, which, nevertheless, could be of importance in precipitating a cascade of events leading to cell death. In either case, understanding the role of mitochondria in the pathogenesis of neurodegenerative diseases could be important for the development of therapeutic strategies in these disorders.

DNA, Mitochondrial↗

PubMed1999

Altered cardiac histology following apical right ventricular pacing in patients with congenital atrioventricular block.

Previous studies have demonstrated that right ventricular apical pacing inherently alters ventricular contraction, regional blood flow, wall stress, and predisposes to diminished function. However, histological consequences of chronic apical pacing potentially contributing to the observed ventricular dysfunction remain conjectural. Previous canine studies have demonstrated histopathological cellular abnormalities with apically initiated ventricular pacing that may result in the observed diminished ventricular function. To determine if comparable adverse changes also occur in the clinical setting, 16 endomyocardial biopsies were obtained from 14 age-matched patients with congenital complete atrioventricular block (CCAVB) and otherwise normal anatomy, divided into two groups: eight biopsies (median patient age 15.5 years) from patients prior to pacemaker implant and another eight biopsies (median patient age 16 years) from patients following 3-12 years (median 5.5) of chronic ventricular pacing. In one patient, biopsy samples were obtained before and after pacing. Results demonstrated a significant (P<0.05) increase in histopathological alterations among the patient biopsy samples following pacing, consisting of myofiber size variation, fibrosis, fat deposition, sclerosis, and mitochondrial morphological changes. These findings indicate that chronic apical right heart ventricular pacing may adversely alter myocellular growth, especially among the young, on the cellular and subcellular level, potentially contributing to the diminished function observed clinically.

Adolescent↗

PubMed2005

The alpha-ketoglutarate-dehydrogenase complex: a mediator between mitochondria and oxidative stress in neurodegeneration.

Damage from oxidative stress and mitochondrial dysfunction occur together in many common neurodegenerative diseases. The enzymes that form the mitochondrial alpha-ketoglutarate- dehydrogenase complex (KGDHC), a key and arguably rate-limiting enzyme system of the tricarboxylic acid cycle, might mediate the interaction of these processes. KGDHC activity is reduced in numerous age-related neurodegenerative diseases and is diminished by oxidative stress. In Alzheimer's disease (AD), the reduction correlates highly to diminished mental performance. Thus, research has focused on the mechanisms by which select oxidants reduce KGDHC and the consequences of such a reduction. Diminished KGDHC in cells is associated with apoptosis without changes in the mitochondrial membrane potential. Studies of isolated mitochondria and of animal models suggest that a reduction in KGDHC can predispose to damage by other toxins that promote neurodegeneration. Diminished oxidative metabolism can be plausibly linked to pathological features of neurodegenerative diseases (e.g., reduced mental function, the plaques and tangles in AD). Thus, reductions in KGDHC might be central to the pathophysiology of these diseases. Studies of proteins, cells, animal models, and humans suggest that treatments to diminish, or bypass, the reduction in KGDHC might be beneficial in age-related neurodegenerative disorders.

Animals↗

PubMed1998

Disorders of the mitochondria.

Recent advances in our understanding of the structure and function of mitochondria have led to the recognition that inherited and acquired mitochondrial dysfunction may be responsible for diseases affecting the liver and other organ systems. Mitochondrial health may also determine hepatocyte survival in other hepatic disorders not directly related to the mitochondrion. Primary mitochondrial hepatopathies are conditions in which there are inherited defects in structure or function of the mitochondria, most of which involve the respiratory chain and oxidative phosphorylation, fatty acid oxidation, the urea cycle, and other pathways confined to mitochondria. Maternally inherited mutations or deletions of the mitochondrial genome, or putative nuclear gene mutations encoding electron transport proteins, cause defective electron transport, oxidative stress, impaired oxidative phosphorylation, and other metabolic derangements that lead to hepatic failure or chronic liver dysfunction in affected children. The mitochondrial DNA (mtDNA) depletion syndrome, which similarly leads to liver failure and neurologic abnormalities, is caused by a putative nuclear gene that controls mtDNA replication or stability. Other proven or suspected primary mitochondrial hepatopathies include Pearson's marrow-pancreas syndrome, Alpers disease, mitochondrial neurogastrointestinal encephalomyopathy syndrome, and Navajo neuropathy. Secondary mitochondrial hepatopathies are conditions in which the mitochondria are major targets during liver injury from another cause, such as metal overload, certain drugs and toxins, alcoholic liver injury, and conditions of oxidant stress. Diagnosis of mitochondrial dysfunction may be difficult with currently available tools, however, elevated blood lactate: pyruvate ratios or arterial ketone body ratios with characteristic liver histology are initial tests. Measuring respiratory chain enzyme activities, mtDNA levels, and searching for mtDNA mutations and deletions are more specific tests. Treatment of these disorders is currently empirical, involving agents that may improve the redox status of mitochondria, promote electron flow, or act as mitochondrial antioxidants. Liver transplantation has occasionally been successful in patients who lack other systemic involvement.

Child↗

PubMed2005

The retrograde response links metabolism with stress responses, chromatin-dependent gene activation, and genome stability in yeast aging.

Yeast can be used as a model to understand the impact mitochondria have on aging in higher organisms. Mitochondrial dysfunction increases with replicative age in yeast, and this is associated with the induction of the retrograde response. This intracellular signaling pathway from the mitochondrion to the nucleus results in changes in the expression of metabolic and stress genes, which adapt the yeast cell to the loss of tricarboxylic acid cycle activity by providing alternate anaplerotic sources of biosynthetic precursors. The induction of the retrograde response increases longevity. Paradoxically, it also leads to the production of extrachromosomal ribosomal DNA circles, which cause yeast demise. The deleterious effects of these circles are mitigated by the retrograde response, which increases longevity in part due to this effect and partly due to other activities. Rtg2p is the retrograde signal transducer proximal to the mitochondrion, and it interacts with several proteins in relaying the retrograde signal to the transcription factor Rtg1p-Rtg3p. Rtg2p also suppresses ribosomal DNA circle production. When it is engaged in retrograde signaling, it cannot fulfill the latter role. The SAGA-like SLIK complex is one of the protein complexes in which Rtg2p has been found. This histone acetyltransferase, transcriptional co-activator complex contains Gcn5p, and it potentiates the activation of retrograde responsive genes. SLIK complex integrity, and in particular Gcn5p, are needed for retrograde response extension of life span. Thus, the retrograde response through SLIK links metabolism, stress responses, chromatin-dependent gene regulation, and genome stability in yeast aging. Gene regulatory phenomena akin to the retrograde response also operate in human cells, which display both common and cell-type specific changes in gene expression on loss of mitochondrial function.

Basic Helix-Loop-Helix Leucine Zipper Transcriptio↗

PubMed2006

Overexpression of farnesyl diphosphate synthase in Arabidopsis mitochondria triggers light-dependent lesion formation and alters cytokinin homeostasis.

To investigate the role of mitochondrial farnesyl diphosphate synthase (FPS) in plant isoprenoid biosynthesis we characterized transgenic Arabidopsis thaliana plants overexpressing FPS1L isoform. This overexpressed protein was properly targeted to mitochondria yielding a mature and active form of the enzyme of 40 kDa. Leaves from transgenic plants grown under continuous light exhibited symptoms of chlorosis and cell death correlating to H(2)O(2) accumulation, and leaves detached from the same plants displayed accelerated senescence. Overexpression of FPS in mitochondria also led to altered leaf cytokinin profile, with a reduction in the contents of physiologically active trans-zeatin- and isopentenyladenine-type cytokinins and their corresponding riboside monophosphates as well as enhanced levels of cis-zeatin 7-glucoside and storage cytokinin O-glucosides. Overexpression of 3-hydroxy-3-methylglutaryl coenzyme A reductase did not prevent chlorosis in plants overexpressing FPS1L, but did rescue accelerated senescence of detached leaves and restored wild-type levels of cytokinins. We propose that the overexpression of FPS1L leads to an enhanced uptake and metabolism of mevalonic acid-derived isopentenyl diphosphate and/or dimethylallyl diphosphate by mitochondria, thereby altering cytokinin homeostasis and causing a mitochondrial dysfunction that renders plants more sensitive to the oxidative stress induced by continuous light.

Acyl Coenzyme A↗

PubMed1991

Effects of hydrogen peroxide and hypochlorite on membrane potential of mitochondria in situ in rat heart cells.

Hydrogen peroxide (H2O2) and hypochlorite (HOCl) cause a variety of cellular dysfunctions. In this study we examined the effects of these agents on the electrical potential gradient across the inner membrane of mitochondria in situ in isolated rat heart myocytes. Myocytes were prepared by collagenase digestion and incubated in the presence of H2O2 or HOCl. Transmembrane electrical gradients were measured by distribution of [3H]triphenylmethylphosphonium+, a lipophilic cation. The particulate fraction was separated from the cytosolic compartment first by permeabilization using digitonin, followed by rapid centrifugal sedimentation through a bromododecane layer. We found that the mitochondrial membrane potential (161 +/- 7 mV, negative inside) was relatively well maintained under oxidant stress, i.e., the potential was decreased only at high concentrations of HOCl and H2O2 and gradually with time. The membrane potential of isolated rat heart mitochondria was affected similarly by H2O2 and HOCl in a concentration- and time-dependent manner. High concentrations of oxidants also reduced the cellular ATP level but did not significantly change the matrix volume. When the extra-mitochondrial free calcium concentration was increased in permeabilized myocytes, the transmembrane potential was decreased proportionally, and this decrease was potentiated further by H2O2. These results support the view that heart mitochondria are equipped with well-developed defense mechanisms against oxidants, but the action of H2O2 on the transmembrane electrical gradient is exacerbated by an increase in cytosolic calcium.

Animals↗

PubMed2000

Phosphorus 31 nuclear magnetic resonance spectroscopy suggests a mitochondrial defect in claudicating skeletal muscle.

OBJECTIVE: Decreased oxygen supply is generally accepted as the primary cause of muscle dysfunction in patients with peripheral arterial occlusive disease (PAOD) and intermittent claudication, although reported morphologic changes in the mitochondria of claudicating muscle suggest that impaired energy utilization may also play a role. With the measurement of the phosphate-rich compounds of muscle energy metabolism (adenosinetriphosphate [ATP], adenosinediphosphate [ADP], and phosphocreatine [PCr]) and pH, phosphorus P 31 magnetic resonance spectroscopy ((31)P MRS) provides a unique, noninvasive method to investigate this hypothesis further. METHODS: Calf muscle bioenergetics were studied in 12 men with moderate claudication (ankle-brachial index >/=0.5 and </=0.8) and 14 normal control subjects with the use of (31)P MRS and standard treadmill testing. Phosphorus MRS evaluation of the superficial posterior calf muscles was carried out with a 90-second submaximal isometric plantar flexion exercise. This mild exercise was chosen to permit in-magnet testing and to allow study of intrinsic mitochondrial efficiency under conditions of unchallenged blood flow. Phosphocreatine and ADP recovery time constants (t.c.), two very sensitive measures of oxidative mitochondrial function, as well as intracellular pH and ATP production via anaerobic glycolysis were determined during three exercise sessions and the results averaged and compared to known values obtained from a control population. RESULTS: During the (31)P MRS protocol, the end exercise intracellular pH (7.11 +/- 0.01 vs 7.11 +/- 0.01) and ATP production by anaerobic glycolysis (0.13 +/- 0.05 vs 0.14 +/- 0.03 mmol/L per second) were no different in PAOD patients versus control subjects, confirming that the protocol exercise did not significantly reduce oxygen supply. Phosphocreatine and ADP recovery t.c. (137 +/- 41 vs 44 +/- 3 seconds and 60 +/- 10 vs 29 +/- 2 seconds, respectively) were significantly slower than normal (P <.05, t test). There was, however, no correlation between these measures of mitochondrial function and any treadmill parameter (P >.5, Pearson moment correlation). CONCLUSIONS: Phosphorus 31 MRS provides the first direct evidence of defective energy metabolism in the mitochondria of claudicating calf muscle. This defect appears to be independent of both arterial flow and the severity of occlusive disease in patients with mild to moderate claudication. Coupled with documented ultrastructural and DNA abnormalities in the mitochondria of claudicating skeletal muscle, these data provide evidence for a secondary cause of muscle dysfunction in intermittent claudication.

Adenosine Diphosphate↗

PubMed2002

Localization of activator protein-1 complex with DNA binding activity in mitochondria of murine brain after in vivo treatment with kainate.

To elucidate mechanisms underlying mitochondrial dysfunctions induced by glutamate, we have examined the effects of in vivo treatment with the ionotropic glutamate receptor agonist kainate on localization of the transcription factor activator protein-1 (AP-1) in mitochondria as well as nuclei of murine brain. A systemic administration of kainate dramatically enhanced AP-1 DNA binding in both mitochondrial and nuclear extracts of mouse cerebral cortex and hippocampus 1 hr to 3 d later. Unlabeled AP-1 probe selectively competed for AP-1 DNA binding in mitochondrial extracts of cortex and hippocampus obtained from mice injected with kainate. Supershift and immunoblotting analyses revealed participation of c-Fos, Fos-B, and Jun-B proteins in potentiation by kainate of mitochondrial AP-1 DNA binding in cortex and hippocampus. An immunohistochemical study demonstrated marked expression by kainate of c-Fos protein in the pyramidal and dentate granular layers, whereas an immunoelectron microscopic analysis showed localization of c-Fos protein within mitochondria, as well as nuclei, of the CA1 pyramidal and dentate granular cells in hippocampus obtained 2 hr after the administration of kainate. Mitochondrial AP-1 DNA binding was inhibited by particular unlabeled oligonucleotides containing sequences similar to the AP-1 site found in the noncoding region of mitochondrial DNA. Kainate markedly potentiated binding of radiolabeled oligonucleotide probes containing sequences effective in competing for AP-1 DNA binding in hippocampal mitochondrial extracts. These results suggest that kainate may facilitate expression of the AP-1 complex and subsequent translocation into mitochondria to participate in mechanisms associated with transcriptional regulation of mitochondrial DNA in murine hippocampus.

Animals↗

PubMed1998

Early-onset sensorineural hearing loss and late-onset neurologic complaints caused by a mitochondrial mutation at position 7472.

OBJECTIVES: To detect a mitochondrial mutation responsible for maternally transmitted hearing loss with late-onset neurologic features in a 3-generation Dutch family, and to describe the hearing loss, associated symptoms, and vestibular dysfunction. PATIENTS AND METHODS: All maternally related family members (n = 69) were investigated using standard audiometry. In a selected group, vestibulo-ocular examinations and additional neurologic and ophthalmologic examinations were performed. Twenty milliliters of venous blood was taken from all participants for genetic studies. SETTING: University medical center. RESULTS: All maternally related individuals carried an extra C at position 7472 of the mitochondrial genome. Hearing loss was the only symptom or presenting symptom in most family members and most pronounced at higher frequencies. Hearing loss at lower frequencies was demonstrated in individuals 10 years and older. Most patients had vestibular hyperreactivity and were susceptible to motion sickness, suggesting vestibulocerebellar dysfunction. Neurologic complaints were infrequent and presented by older individuals; however, numerous enlarged mitochondria were found in a muscle biopsy specimen of an individual with hearing impairment but without neurologic symptoms. CONCLUSIONS: Respiratory chain dysfunction should be considered as a possible cause of progressive sensorineural hearing loss. More research into the causes of high-frequency impairment should be considered, especially when sensorineural hearing loss, syndromal or nonsyndromal, is exclusively maternally transmitted. Maternal transmission of hearing impairment can also be valuable in the diagnosis of unclear neurologic syndromes.

Adolescent↗

PubMed2003

Mitochondrial dysfunction and apoptosis in myopathic mice with collagen VI deficiency.

Collagen VI is an extracellular matrix protein that forms a microfilamentous network in skeletal muscles and other organs. Inherited mutations in genes encoding collagen VI in humans cause two muscle diseases, Bethlem myopathy and Ullrich congenital muscular dystrophy. We previously generated collagen VI-deficient (Col6a1-/-) mice and showed that they have a muscle phenotype that strongly resembles Bethlem myopathy. The pathophysiological defects and mechanisms leading to the myopathic disorder were not known. Here we show that Col6a1-/- muscles have a loss of contractile strength associated with ultrastructural alterations of sarcoplasmic reticulum (SR) and mitochondria and spontaneous apoptosis. We found a latent mitochondrial dysfunction in myofibers of Col6a1-/- mice on incubation with the selective F1F(O)-ATPase inhibitor oligomycin, which caused mitochondrial depolarization, Ca2+ deregulation and increased apoptosis. These defects were reversible, as they could be normalized by plating Col6a1-/- myofibers on collagen VI or by addition of cyclosporin A (CsA), the inhibitor of mitochondrial permeability transition pore (PTP). Treatment of Col6a1-/- mice with CsA rescued the muscle ultrastructural defects and markedly decreased the number of apoptotic nuclei in vivo. These findings indicate that collagen VI myopathies have an unexpected mitochondrial pathogenesis that could be exploited for therapeutic intervention.

Animals↗

PubMed2006

Iron and Friedreich ataxia.

Friedreich ataxia is due to insufficient levels of frataxin, a mitochondrial iron chaperone that shields this metal from reactive oxygen species (ROS) and renders it bioavailable as Fe II. Frataxin participates in the synthesis of iron-sulfur clusters (ISCs), cofactors of several enzymes, including mitochondrial and cytosolic aconitase, complexes I, II and III of the respiratory chain, and ferrochelatase. It also plays a role in the maintenance of ISCs, in particular for mitochondrial aconitase. A role of frataxin in heme synthesis has been postulated, but is controversial. Insufficient frataxin leads to deficit of ISC enzymes and energy deficit. Iron levels increase in mitochondria. Oxidative stress may result from respiratory chain dysfunction and from direct reaction between iron and ROS. Stress pathways are activated that may lead to apoptosis or other forms of cell death. The basis for the selective vulnerability of specific neurons, like sensory neurons, is still unknown.

Animals↗

PubMed2003

Protection against post-ischemic mitochondrial injury in rat liver by silymarin or TUDC.

BACKGROUND: Hepatic ischemia/reperfusion (I/R) injury is characterized by features such as cholestasis. Mitochondria become susceptible to damage during ischemia and after reperfusion. The aim of this study was to determine if silymarin and tauroursodeoxycholic acid (TUDC), would prevent impairment of liver mitochondrial function following I/R injury. METHODS: Livers of male Wistar rats were subjected to 45 min of hepatic ischemia. During the 90 min of reperfusion, livers were perfused with either vehicle, silymarin, or TUDC. Changes in membrane potential, mitochondrial respiration as well as susceptibility to mitochondrial permeability transition (MPT) induction were evaluated and endogenous adenine nucleotides were measured. RESULTS: In rats subjected to I/R, compared with the control group, a severe impairment of mitochondrial bioenergetics was observed. State 3 respiration was decreased and state 4 enhanced, associated with lower membrane potential developed following succinate energization. An increased susceptibility to MPT induction by calcium/phosphate was also observed. The effects of I/R injury were ameliorated in the presence of silymarin but not TUDC. Similarly, ATP levels following I/R were lower, in comparison with the control group and the silymarin treatment but not TUDC. CONCLUSION: Thus, silymarin, but not TUDC, prevents the most significant changes that occur in mitochondria during I/R, and probably, the associated cell dysfunction, through their central role in cellular bioenergetics.

Journal Article↗

PubMed2003

Clinical and molecular findings in a patient with a novel mutation in the deafness-dystonia peptide (DDP1) gene.

The Mohr-Tranebjaerg syndrome (MTS) is a rare neurodegenerative disorder characterized by early-onset deafness, dystonia and further neurological abnormalities such as cortical blindness, spasticity, dementia and mental retardation. Causative mutations were identified within the deafness-dystonia peptide (DDP1/TIMM8a) gene on the X-chromosome. The DDP1 protein is located in the intermembrane space of human mitochondria. Here, it acts in a complex together with its partner protein Tim13 in a chaperone-like manner to facilitate the import of nuclear-encoded precursor proteins into the mitochondrial inner membrane. Thus, MTS is a novel type of mitochondrial disorder. To obtain more insight into the pathophysiology of this neurodegenerative disorder, we performed for the first time a comprehensive clinical and functional characterization of a patient suffering from MTS. This patient exhibited a typical combination of deafness, dystonia and visual loss. Sequence analysis of the patient's DDP1 gene revealed a G to C transversion at nucleotide position 38 of the first exon. The mutation affects the ATG start codon, thereby changing methionine to isoleucine (M1I), and leads to a complete absence of the DDP1 protein. In addition, the partner protein Tim13 was found to be significantly reduced, suggesting that Tim13 requires the presence of DDP1 for its stabilization. The assessment of mitochondrial functions showed the enzyme activities of the mitochondrial energy-generating systems to be normal in the muscle biopsy. Structural abnormalities or aggregations of mitochondria were absent. Electron microscopy revealed only a mild neurogenic atrophy. Neurophysiological investigations showed cochlear dysfunction and disturbance of visual pathways. PET and MRI studies revealed a multifocal pattern of neurodegeneration with hypometabolic areas predominantly located over the right striatum and parietal cortex and marked atrophy of the occipital lobes. Although the visual loss is caused predominantly by neurodegeneration of the visual cortex, degeneration of the retina and the optic nerve contributes to the visual impairment. The pathological changes in basal ganglia and sensory cortex demonstrate the disintegration of subcortico-cortical circuits and correlate well with the clinical presentation of multifocal dystonia. The data presented here showed that, in contrast to most of the known mitochondrial disorders, MTS appears not to be associated with a functional defect of the energy generation system of the mitochondria. Whereas the specific mitochondrial dysfunction leading to neuronal loss in MTS remains to be clarified, the electrophysiological and neuroimaging findings allowed the multifocal manifestation of neurodegenerative lesions in MTS to be characterized specifically.

Adult↗

PubMed2002

Technical approaches to correction of oocyte aneuploidy.

BACKGROUND: This study describes the technical approaches used in treatment of age-related oocyte aneuploidy, the efficiency of each step of nuclear transplantation into mouse and human oocytes, and the ability of germinal vesicle (GV) transplantation to restore artificially induced ooplasmic damage. Finally, it examines the possibility of constructing viable female gametes by transferring diploid somatic cell nuclei into enucleated oocytes. METHODS: GV stage mouse oocytes were collected from unstimulated ovaries, and human GV oocytes were donated from consenting patients undergoing ICSI. Stromal (somatic) cells were isolated from uterine biopsies of consenting patients. Mouse cumulus cells were obtained after ovarian stimulation. GV ooplasts prepared by removing nuclei were transplanted either with GV nuclei or with somatic cells by micromanipulation. Grafted oocytes were electrofused and cultured to allow maturation, following which they were inseminated or analysed cytogenetically. Ooplasmic dysfunction was induced by photosensitization with a mitochondria-specific fluorescent dye. RESULTS: GV transplantation had an overall efficiency of 87 and 73% in the mouse and humans respectively. Maturation rates of 95 (mouse) and 64% (human) following reconstitution were comparable with those in control oocytes, as was the incidence of aneuploidy for five chromosome-specific probes after aneuploidy among the reconstituted oocytes. Photosensitization of oocytes significantly reduced the maturation rate to 4.2%, whereas 61.9% of oocytes matured after transfer of photosensitized GV karyoplasts into healthy ooplasts, with 52% of these mature oocytes being successfully fertilized by ICSI. Enucleated immature oocytes receiving mouse cumulus or human endometrial cell nuclei extruded a polar body in >40% of cases. Five out of seven successfully transferred aged human nuclei exhibited the expected number of signals with five chromosome-specific probes suggesting an appropriate chromosome separation in young ooplasm. CONCLUSIONS: Nuclear transplantation itself does not appear to interfere with chromosome segregation and can possibly rescue oocytes with damaged mitochondria. Finally, immature mouse ooplasm supported separation of somatic chromosomes to expected numbers, implying that haploidization may be occurring. The roles of genetic imprinting and fidelity of chromosome segregation are unknown.

Aneuploidy↗

PubMed2003

In vivo effects of arsenite on meiosis, preimplantation development, and apoptosis in the mouse.

Inorganic arsenic, an environmental contaminant, produces a variety of stress responses in mammalian cells, including metabolic abnormalities accompanied by growth inhibition and carcinogenesis. Much of the toxicity of arsenic is known to stem from its uncoupling effects on mitochondria. Because previously we had shown that mitochondrial dysfunction can disrupt oocyte and embryo development, we investigated effects of arsenite on meiotic progression and early embryo development in mice. Six-week-old CD-1 mice were treated with 0 (solvent as control), 8 mg/kg (a dose previously established in mice as the maternal no-observed-adverse-effect level), and 16 mg/kg doses of sodium arsenite every 2 days for a total of seven i.p. injections ver a period of 14 days. The incidence of meiotic anomalies, characterized by spindle disruption and/or chromosomal misalignment, was significantly increased in arsenite-treated groups (25% after 8 mg/kg and 62.5% after 16 mg/kg), compared to normal metaphase II in control oocytes. Further, arsenite treatment significantly decreased cleavage rates of zygotes at 24 h, morula formation at 72 h, and development to blastocysts at 96 h in a dose-dependent manner. The total cell number in developed blastocysts did not differ significantly between the 8 mg/kg arsenite treatment and control groups, but was significantly reduced in the 16 mg/kg arsenite treatment group. Moreover, the percentage of apoptotic nuclei was significantly increased in blastocysts following 16 mg/kg arsenite treatment. These data suggest that arsenite causes meiotic aberrations, which may contribute to decreased cleavage and preimplantation development, as well as increased apoptosis.

Animals↗

PubMed2002

Mitochondria as a pharmacological target.

Mitochondria play a central role in energy metabolism within the cell. Mitochondrial dysfunctions lead to various neurodegenerative disorders and to the so-called "mitochondrial diseases". A vast amount of evidence points to the implication of mitochondria in such complex processes as apoptosis and cardioprotection. The purpose of this review is to present a recent state of our knowledge and understanding of the action of various therapeutically applied substances on mitochondria. These include antitumor, immunosuppressant, and antiviral drugs, potassium channel openers, sulfonylureas, and anesthetics. Some of these substances are specifically designed to affect mitochondrial functions. In other cases, drugs with primary targets in other cellular locations may modify mitochondrial functions as side effects. In any case, identification of mitochondria as primary or secondary targets of a drug may help us to better understand the drug's mechanism of action and open new perspectives for its application. As far as possible, the molecular mechanisms of the interference of particular drugs in the mitochondrial metabolism will be described. In some cases, metabolic routes in which the drugs interfere will also be briefly outlined.

Animals↗