Mitochondrial dysfunction in bipolar disorder

Dopamine toxicity involves mitochondrial complex I inhibition: implications to dopamine-related neuropsychiatric disorders

Dopamine, which is suggested as a prominent etiological factor in several neuropsychiatric disorders such as Parkinson's disease and schizophrenia, demonstrates neurotoxic properties. In such dopamine-related diseases mitochondrial dysfunction has been reported. Dopamine oxidized metabolites were shown to inhibit the mitochondrial respiratory system both in vivo and in vitro. In the present study, we suggest an additional mechanism for dopamine toxicity, which involves mitochondrial complex I inhibition by dopamine. In human neuroblastoma SH-SY5Y cells dopamine induced a reduction in ATP concentrations, which was negatively correlated to intracellular dopamine levels (r = - 0.96, P = 0.012), and was already evident at non-toxic dopamine doses. In disrupted mitochondria dopamine inhibited complex I activity with IC50 = 11.87 +/- 1.45 microm or 8.12 +/- 0.75 microM in the presence of CoQ or ferricyanide, respectively, with no effect on complexes IV and V activities. The catechol moiety, but not the amine group, of dopamine is essential for complex I inhibition, as is indicated by comparing the inhibitory potential of functionally and structurally dopamine-related compounds. In line with the latter is the finding that chelatable FeCl2 prevented dopamine-induced inhibition of complex I. Monoamine oxidase A and B inhibitors, as well as the antioxidant butylated hydroxytoluene (BHT), did not prevent dopamine-induced inhibition, suggesting that dopamine oxidation was not involved in this process. The present study suggests that dopamine toxicity involves, or is initiated by, its interaction with the mitochondrial oxidative phosphorylation system. We further hypothesize that this interaction between dopamine and mitochondria is associated with mitochondrial dysfunction observed in dopamine-related neuropsychiatric disorders, such as schizophrenia and Parkinson's disease.

Mitochondrial complex I subunits expression is altered in schizophrenia: a postmortem study

BACKGROUND

Several independent lines of evidence indicate mitochondrial dysfunction in schizophrenia in the brain and periphery, including mitochondrial hypoplasia, dysfunction of the oxidative phosphorylation system, and altered mitochondrial-related gene expression.

METHODS

In this study, three subunits of mitochondrial complex I were analyzed at the level of mRNA and protein in postmortem brain specimens from the prefrontal and the ventral parietooccipital cortex of patients with schizophrenia, major depression, bipolar disorder, and normal control subjects.

RESULTS

Both mRNA and protein levels of the 24-kDa and 51-kDa subunits of complex I were significantly decreased in the prefrontal cortex, but increased in the ventral parietooccipital cortices of schizophrenia patients compared with normal control subjects. In the latter region, protein levels of both subunits were increased in bipolar patients as well, being in line with the significant overlap in clinical symptoms between schizophrenia and bipolar patients. No change was observed in the 75-kDa subunit expression in the prefrontal cortex.

CONCLUSIONS

The schizophrenia-specific reduction in complex I subunits in the prefrontal cortex is consistent with one of schizophrenia's most prominent deficits, namely, hypofrontality, thus further supporting the hypothesis of mitochondrial dysfunction in this disorder. The abnormal, bidirectional expression of complex I in various brain regions, rather than in a circumscribed area, supports the idea of impaired cerebral circuitry in schizophrenia.

Reduced intracellular pH in the basal ganglia and whole brain measured by 31P-MRS in bipolar disorder

The authors have previously reported that intracellular pH measured by phosphorus-31 magnetic resonance spectroscopy (31P-MRS) was decreased in the frontal lobes of patients with bipolar disorder. In the present study, phosphorus metabolism in the basal ganglia was examined in 13 patients with bipolar disorder and 10 matched controls by localized 31P-MRS. While no significant alteration of peak area ratios was found for all phosphorus metabolites, intracellular pH was significantly reduced in the basal ganglia in patients with bipolar disorder (7.014 +/- 0.045) compared with control subjects (7.066 +/- 0.047, P < 0.05). Unexpectedly, non-localized 31P-MR spectra also showed significantly lower levels of intracellular pH (6.970 +/- 0.025) than controls (6.986 +/- 0.024, P < 0.05). These results suggest that decreased intracellular pH in the brain of patients with bipolar disorder is not caused by dysfunction of the frontal lobes but reflect altered metabolism at the cellular level.

Ethanolamine and phosphoethanolamine inhibit mitochondrial function in vitro: implications for mitochondrial dysfunction hypothesis in depression and bipolar disorder

BACKGROUND

A growing body of experimental evidence suggests that mitochondrial dysfunction, including alterations in phospholipid metabolism, might be involved in the pathophysiology of affective illnesses, such as depression and bipolar disorder. The purpose of this study was to determine whether the phosphomonoester phosphoethanolamine (PE) and the lipid metabolite choline (Cho), which are known to be altered in depression and bipolar disorder, and/or their precursors/metabolites, might directly affect mitochondrial bioenergetic function in vitro.

METHODS

To this end, rates of oxygen consumption in freshly isolated, intact mitochondria were determined polarographically in the presence and absence of PE, Cho, ethanolamine (Etn), glycerophosphoethanolamine (GPE), and glycerophosphocholine (GPC).

RESULTS

The data demonstrate that PE and Etn inhibit mitochondrial respiratory activity in a dose-dependent manner, whereas Cho, GPC, and GPE have no measurable effect on bioenergetic function.

CONCLUSIONS

This reflects a specific inhibition by Etn and PE on mitochondrial function rather than a more generalized phenomenon induced by similarities in structure between the lipid metabolites. These results also suggest a possible relationship between mitochondrial dysfunction and altered phospholipid metabolism in the brains of patients with depression and bipolar disorder.

Systematic changes in gene expression in postmortem human brains associated with tissue pH and terminal medical conditions

Studies of gene expression abnormalities in psychiatric or neurological disorders often involve the use of postmortem brain tissue. Compared with single-cell organisms or clonal cell lines, the biological environment and medical history of human subjects cannot be controlled, and are often difficult to document fully. The chance of finding significant and replicable changes depends on the nature and magnitude of the observed variations among the studied subjects. During an analysis of gene expression changes in mood disorders, we observed a remarkable degree of natural variation among 120 samples, which represented three brain regions in 40 subjects. Most of such diversity can be accounted for by two distinct expression patterns, which in turn are strongly correlated with tissue pH. Individuals who suffered prolonged agonal states, such as with respiratory arrest, multi-organ failure or coma, tended to have lower pH in the brain; whereas those who experienced brief deaths, associated with accidents, cardiac events or asphyxia, generally had normal pH. The lower pH samples exhibited a systematic decrease in expression of genes involved in energy metabolism and proteolytic activities, and a consistent increase of genes encoding stress-response proteins and transcription factors. This functional specificity of changed genes suggests that the difference is not merely due to random RNA degradation in low pH samples; rather it reflects a broad and actively coordinated biological response in living cells. These findings shed light on critical molecular mechanisms that are engaged during different forms of terminal stress, and may suggest clinical targets of protection or restoration.

Valproate disrupts regulation of inositol responsive genes and alters regulation of phospholipid biosynthesis

Valproate (VPA) is one of the two drugs approved by the Food and Drug Administration (FDA) for the treatment of bipolar disorder. The therapeutic mechanism of VPA has not been established. We have shown previously that growth of the yeast Saccharomyces cerevisiae in the presence of VPA causes a decrease in intracellular inositol and inositol-1-P, and a dramatic increase in expression of INO1, which encodes the rate limiting enzyme for de novo inositol biosynthesis. To understand the underlying mechanism of action of VPA, INO1, CHO1 and INO2 expression, intracellular inositol and phospholipid biosynthesis were studied as a function of acute and chronic exposure of growing cells to the drug. A decrease in intracellular inositol was apparent immediately after addition of VPA. Surprisingly, expression of genes that are usually derepressed during inositol depletion, including INO1, CHO1 and INO2 (that contain inositol-responsive UASINO sequences) decreased several fold during the first hour, after which expression began to increase. Incorporation of 32Pi into total phospholipids was significantly decreased. Pulse labelling of CDP-DG and PG, shown previously to increase during inositol depletion, increased within 30 min. However, pulse labelling of PS, which normally increases during inositol depletion, was decreased within 30 min. PS synthase activity in cell extracts decreased with time, although VPA did not directly inhibit PS synthase enzyme activity. Thus, in contrast to the effect of chronic VPA treatment, short-term exposure to VPA abrogated the normal response to inositol depletion of inositol responsive genes and led to aberrant synthesis of phospholipids.

Affective disorders, antidepressant drugs and brain metabolism

There is increasing evidence that affective disorders are associated with dysfunction of neurotransmitter postsynaptic transduction pathways and that chronic treatment with clinically active drugs results in adaptive modification of these pathways. Despite the close dependence of signal transduction on adenosine triphosphate (ATP) availability, the changes in energy metabolism in affective disorders are largely unknown. This question has been indirectly dealt with through functional imaging studies (PET, SPECT, MRS). Despite some inconsistencies, PET and SPECT studies suggest low activity in cortical (especially frontal) regions in depressed patients, both unipolar and bipolar, and normal or increased activity in the manic pole. Preliminary MRS studies indicate some alterations in brain metabolism, with reduced creatine phosphate and ATP levels in the brain of patients with affective disorders. However, the involvement of the energy metabolism in affective disorders is still debated. We propose direct neurochemical investigations on mitochondrial functional parameters of energy transduction, such as the activities of (a) the enzymatic systems of oxidative metabolic cycle (Kreb's cycle); (b) the electron transfer chain; (c) oxidative phosphorylation, and (d) the enzyme activities of ATP-requiring ATPases. These processes should be studied in affective disorders and in animals treated with antidepressant drugs or lithium.

Oral choline decreases brain purine levels in lithium-treated subjects with rapid-cycling bipolar disorder: a double-blind trial using proton and lithium magnetic resonance spectroscopy

OBJECTIVES

Oral choline administration has been reported to increase brain phosphatidylcholine levels. As phospholipid synthesis for maintaining membrane integrity in mammalian brain cells consumes approximately 10-15% of the total adenosine triphosphate (ATP) pool, an increased availability of brain choline may lead to an increase in ATP consumption. Given reports of genetic studies, which suggest mitochondrial dysfunction, and phosphorus (31P) magnetic resonance spectroscopy (MRS) studies, which report dysfunction in high-energy phosphate metabolism in patients with bipolar disorder, the current study is designed to evaluate the role of oral choline supplementation in modifying high-energy phosphate metabolism in subjects with bipolar disorder.

METHODS

Eight lithium-treated patients with DSM-IV bipolar disorder, rapid cycling type were randomly assigned to 50 mg/kg/day of choline bitartrate or placebo for 12 weeks. Brain purine, choline and lithium levels were assessed using 1H- and 7Li-MRS. Patients received four to six MRS scans, at baseline and weeks 2, 3, 5, 8, 10 and 12 of treatment (n = 40 scans). Patients were assessed using the Clinical Global Impression Scale (CGIS), the Young Mania Rating Scale (YRMS) and the Hamilton Depression Rating Scale (HDRS) at each MRS scan.

RESULTS

There were no significant differences in change-from-baseline measures of CGIS, YMRS, and HDRS, brain choline/creatine ratios, and brain lithium levels over a 12-week assessment period between the choline and placebo groups or within each group. However, the choline treatment group showed a significant decrease in purine metabolite ratios from baseline (purine/n-acetyl aspartate: coef = -0.08, z = -2.17, df = 22, p = 0.030; purine/choline: coef = -0.12, z = -1.97, df = 22, p = 0.049) compared to the placebo group, controlling for brain lithium level changes. Brain lithium level change was not a significant predictor of purine ratios.

CONCLUSIONS

The current study reports that oral choline supplementation resulted in a significant decrease in brain purine levels over a 12-week treatment period in lithium-treated patients with DSM-IV bipolar disorder, rapid-cycling type, which may be related to the anti-manic effects of adjuvant choline. This result is consistent with mitochondrial dysfunction in bipolar disorder inadequately meeting the demand for increased ATP production as exogenous oral choline administration increases membrane phospholipid synthesis.

Glucose/mitochondria in neurological conditions

Impairments of glucose and mitochondrial function are important causes of brain dysfunction and therefore of brain disease. Abnormalities have been found in association with disease of the nervous system in most of the components of glucose/mitochondrial metabolism. In many, molecular genetic abnormalities have been defined. Brain glucose oxidation is abnormal in common diseases of the nervous system, including Alzheimer disease and other dementias, Parkinson disease, delirium, probably schizophrenia and other psychoses, and of course cerebrovascular disease. Defects in a single component and even a single mutation can be associated with different clinical phenotypes. The same clinical phenotype can result from different genotypes. The complex relationship between biological abnormality in brain glucose utilization and clinical disorder is similar to that in other disorders that have been intensively studied at the genetic level. Genes for components of the pathways of brain glucose oxidation are good candidate genes for disease of the brain. Preliminary data support the proposal that treatments to normalize abnormalities in brain glucose oxidation may benefit many patients with common brain diseases.

Chronic treatment with lithium, but not sodium valproate, increases cortical N-acetyl-aspartate concentrations in euthymic bipolar patients

Previous studies have found that treatment with lithium over a 4-week period may increase the concentration of N-acetyl-aspartate (NAA) in both bipolar patients and controls. In view of other findings indicating that NAA concentrations may be a good marker for neuronal viability and/or functioning, it has been further suggested that some of the long term benefits of lithium may therefore be due to actions to improve these neuronal properties. The aim of the present study was to utilize H magnetic resonance spectroscopy ( H MRS) to further examine the effects of both lithium and sodium valproate upon NAA concentrations in treated euthymic bipolar patients. In the first part of the study, healthy controls (n =18) were compared with euthymic bipolar patients (type I and type II) who were taking either lithium (n =14) or sodium valproate (n =11), and NAA : creatine ratios were determined. In the second part, we examined a separate group of euthymic bipolar disorder patients taking sodium valproate (n =9) and compared these to age- and sex-matched healthy controls (n =11), and we quantified the exact concentrations of NAA using an external solution. The results from the first part of the study showed that bipolar patients chronically treated with lithium had a significant increase in NAA concentrations but, in contrast, there were no significant increases in the sodium valproate-treated patients compared to controls. The second part of the study also found no effects of sodium valproate on NAA concentrations. These findings are the first to compare NAA concentrations in euthymic bipolar patients being treated with lithium or sodium valproate. The results support suggestions that longer-term administration of lithium to bipolar patients may increase NAA concentrations. However, the study suggests that chronic administration of sodium valproate to patients does not lead to similar changes in NAA concentrations. These findings suggest that sodium valproate and lithium may not share a common mechanism of action in bipolar disorder involving neurotrophic or neuroprotective effects.

Subtraction libraries for the molecular characterization of gene-environmental interactions in bipolar disorder

OBJECTIVES

We endeavoured to identify gene-environmental interactions related to bipolar disorder.

METHODS

We generated subtraction libraries from the frontal cortex of brains obtained postmortem from individuals with bipolar disorder and age- and sex-matched unaffected controls.

RESULTS

There are a number of RNA transcripts which are apparently up-regulated or down-regulated in the frontal cortex of individuals with bipolar disorder as compared with the controls. Many of these transcripts are involved in processes crucial to brain function. Several are also related to pathways involved in infections or the inflammatory response in environmental stimuli.

CONCLUSIONS

Bipolar disorder may involve a complex set of interactions between genes which affect brain function and infections which control the expression of these genes.

Autosomal dominant external ophthalmoplegia and bipolar affective disorder associated with a mutation in the ANT1 gene

The authors report on a family with dominantly inherited progressive external ophthalmoplegia and a diagnostic and statistical manual (fourth revised edition) diagnosis of bipolar psychiatric disorder in several members. Skeletal muscle biopsy from the proposita showed decreased cytochrome c oxidase staining, several ragged-red fibers, and multiple mtDNA deletions. The authors identified a missense mutation (leucine 98-->proline) in the adenine nucleotide translocator 1 gene. The presence of bipolar affective disorder expands the phenotype of adenine nucleotide translocator 1 allelic variants.

Chronic progressive external ophthalmoplegia

Chronic progressive external ophthalmoplegia (CPEO) is a descriptive term for a heterogenous group of disorders characterized by chronic, progressive, bilateral, and usually symmetric ocular motility deficit and ptosis. Significant pain, proptosis, or pupil involvement are not features of CPEO and should prompt evaluation for alternative etiologies. Mitochondrial DNA mutations are increasingly being recognized as the etiology for CPEO syndromes. Clinicians should recognize the specific syndromes associated with CPEO, characterized by variable systemic, neurologic, or other findings. Treatment is limited, but newer therapies are being investigated.

Mitochondrial calcium response in human transformed lymphoblastoid cells

Human lymphoblastoid cell line (LCL) transformed by Epstein-Barr Virus (EBV) is a unique cellular model for the study of human diseases. Although pathophysiological significance of mitochondrial calcium regulation is drawing attention, it is not known whether or not mitochondria in LCLs play a role in intracellular calcium signaling. In this study, role of mitochondria of the lymphoblastoid cell line in calcium signaling was examined. Intra-mitochondrial calcium concentration ([Ca2+]m) was successfully measured using dihydro-Rhod-2, revealed by the decrease of fluorescence after application of carbonyl cyanide m-chlorophenylhydrazone (CCCP) and intracellular localization patterns imaged by fluorescent microscope. Platelet activating factor (PAF) concentration-dependently increased cytosolic calcium concentration ([Ca2+]i), while no increase of [Ca2+]m was observed. In contrast, 10 microM thapsigargin increased [Ca2+]i as well as [Ca2+]m. LCLs may be used for the study of possible pathophysiological role of mitochondrial calcium regulation in human diseases.

Biexponential transverse relaxation (T(2)) of the proton MRS creatine resonance in human brain

Differences in proton MRS T(2) values for phosphocreatine (PCr) and creatine (Cr) methyl groups (3.0 ppm) were investigated in studies of phantoms and human brain. Results from phantom studies revealed that T(2) of PCr in solution is significantly shorter than T(2) of Cr. Curve-fitting results indicated that the amplitude-TE curves of the total Cr resonance at 3.0 ppm in human brain (N = 26) fit a biexponential decay model significantly better than a monoexponential decay model (P < 0.006), yielding mean T(2) values of 117 +/- 21 ms and 309 +/- 21 ms. Using a localized, long-TE (272 ms) point-resolved spectroscopy (PRESS) proton MRS during 2 min of photic stimulation (PS), an increase of 12.1% +/- 3.5% in the mean intensity of the total Cr resonance in primary visual cortex (VI) was observed at the end of stimulation (P < 0.021). This increase is consistent with the conversion of 26% of PCr in VI to Cr, which is concordant with (31)P MRS findings reported by other investigators. These results suggest a significantly shorter T(2) for PCr than for Cr in vivo. This difference possibly could be exploited to quantify regional activation in functional spectroscopy studies, and could also lead to inaccuracies in some circumstances when the Cr resonance is used as an internal standard for (1)H MRS studies in vivo.

Moclobemide: evolution, pharmacodynamic, and pharmacokinetic properties

The benzamide moclobemide is a reversible inhibitor of monoamine-oxidase-A (RIMA). It has been extensively evaluated in the treatment of a wide spectrum of depressive disorders and less extensively in anxiety disorders. While clinical aspects will be presented in a subsequent review, this article focuses primarily on moclobemide's evolution, pharmacodynamic and pharmacokinetic properties. In particular, the effects on neurotransmission and intracellular signal transduction, the neuroendocrine system, the tyramine pressure response and animal models of depression are surveyed. In addition, other CNS effects are reviewed with special respect to experimental serotonergic syndrome, anxiolytic and antinociceptive activity, sleep, cognition and driving performance, neuroprotection and seizures.

The other, forgotten genome: mitochondrial DNA and mental disorders

This paper summarizes recent research on mitochondrial DNA (mtDNA)--which might be described as the "other, forgotten genome". Recent studies suggest the possible pathophysiological significance of mtDNA in schizophrenia and neurodegenerative and mood disorders. Decreased activity of the mitochondrial electron transport chain has been implicated in both Parkinson's and Alzheimer's disease and while age-related accumulation of mtDNA deletions has been suggested as a possible cause, there is no concrete evidence that particular mtDNA polymorphisms are responsible. In schizophrenia, the activity and/or mRNA expression of complex IV are involved, but the direction of the alteration is not the same and there is no evidence linking schizophrenia with mtDNA. In bipolar disorder, there is some evidence of parent-of-origin effects and association with mtDNA polymorphisms but further investigation is needed to elucidate the role of mtDNA in mental disorders.

Molecular genetics of bipolar disorder

Alteration of monoaminergic neurotransmission is implicated in the pathophysiology of bipolar disorder (manic-depressive illness). Candidate genes participating in monoaminergic neurotransmission, especially serotonin transporter and monoamine oxidase A, may be associated with bipolar disorder. And the regulating regions of these genes and the molecules participating in intracellular signal transduction are now under investigation. To date, 13 whole genome positional cloning studies have been performed and many candidate loci identified. Using patients from a pedigree in which schizophrenia, depression or bipolar disorder have been linked with a balanced translocation at 1 and 11, candidate pathogenetic genes were cloned as DISC1 (disrupted in schizophrenia-1) and DISC2. Recently, pathogenetic mutations have been identified in two genetic diseases frequently co-morbid with mood disorder; WFS1 for Wolfram syndrome and ATP2A2 (SERCA2) for Darier's disease. Transmission of bipolar disorder may be characterized by anticipation and parent-of-origin effect, and extended CTG repeat at SEF2-1B gene was identified from a bipolar patient. However, its pathogenetic role was not supported by subsequent studies. Association of bipolar disorder with mitochondrial DNA has also been suggested. The role of genomic imprinting is also possible because linkage to 18p11 is limited to paternally transmitted pedigrees. These results warrant further study of molecular genetics of bipolar disorder.