The mitochondrial hypothesis of bipolar disorder

Psychiatric symptoms correlate with metabolic indices in the hippocampus and cingulate in patients with mitochondrial disorders

There is increasing recognition that mitochondrial dysfunction may have a critical role in the pathophysiology of major psychiatric illnesses. Patients with mitochondrial disorders offer a unique window through which we can begin to understand the association between psychiatric symptoms and mitochondrial dysfunction in vivo. Using proton magnetic resonance spectroscopy ((1)H-MRS), we investigated metabolic indices in mitochondrial patients in regions of the brain that have been implicated in psychiatric illness: the caudate, cingulate cortex and hippocampus. In all, 15 patients with mitochondrial disorders and 15 age- and sex-matched controls underwent a comprehensive psychiatric assessment, including the administration of standardized psychiatric rating scales, followed by single voxel (1)H-MRS of the caudate, cingulate cortex and hippocampus to measure N-acetyl aspartate (NAA), creatine (Cr), glycerophosphocholine (GPC), myoinositol and glutamate+glutamine (Glx). Pearson's correlation coefficients were used to determine correlations between metabolites and the psychiatric rating scales. Anxiety symptoms in these patients correlated with higher GPC, Glx, myoinositol and Cr in the hippocampus. Impaired level of function as a result of psychiatric symptoms correlated with higher Glx and GPC in the cingulate cortex. In summary, we found remarkably consistent, and statistically significant, correlations between anxiety and metabolic indices in the hippocampus in patients with mitochondrial disorders, while overall impairment of functioning due to psychiatric symptoms correlated with metabolic markers in the cingulate cortex. These findings lend support to the notion that mitochondrial dysfunction in specific brain regions can give rise to psychiatric symptoms. In particular, they suggest that metabolic processes in the hippocampus may have an important role in the neurobiology of anxiety.

Mitochondrial respiratory chain activity in an animal model of mania induced by ouabain

OBJECTIVES

Bipolar disorder (BD) is a mental illness associated with higher rates of suicide. The present study aims to investigate the brain mitochondrial respiratory chain activity in an animal model of mania induced by ouabain.

METHODS

Adult male Wistar rats received a single intracerebroventricular administration of ouabain (10-3 and 10-2 M) or vehicle. Locomotor activity was measured using the open field test. Mitochondrial respiratory chain activity was measured in the brain of rats 1 h and 7 days after ouabain administration.

RESULTS

Our results showed that spontaneous locomotion was increased 1 h and 7 days after ouabain administration. Complexes I, III and IV activities were increased in the prefrontal cortex, hippocampus and striatum immediately after the administration of ouabain, at the concentration of 10-3 and 10-2 M. Moreover, complex II activity was increased only in the prefrontal cortex at the concentration of 10-2 M. On the other hand, no significant alterations were observed in complex I activity 7 days after ouabain administration. However, an increase in complexes II, III and IV activities was observed only in the prefrontal cortex at the concentration of 10-2 M.

CONCLUSION

Our findings suggest an increase in the activities of mitochondrial respiratory chain in this model of mania. A possible explanation is that these findings occur as a rebound effect trying to compensate for a decrease of ATP deprivation in BD. The present findings suggest that this model may present good face validity and a limitation in construct validity.

Creatine kinase levels in patients with bipolar disorder: depressive, manic, and euthymic phases

OBJECTIVE: Bipolar disorder is a severe, recurrent, and often chronic psychiatric illness associated with significant functional impairment, morbidity, and mortality. Creatine kinase is an important enzyme, particularly for cells with high and fluctuating energy requirements, such as neurons, and is a potential marker of brain injury. The aim of the present study was to compare serum creatine kinase levels between bipolar disorder patients, in the various phases (depressive, manic, and euthymic), and healthy volunteers. METHOD: Forty-eight bipolar patients were recruited: 18 in the euthymic phase; 17 in the manic phase; and 13 in the depressive phase. The control group comprised 41 healthy volunteers. The phases of bipolar disorder were defined as follows: euthymic-not meeting the DSM-IV criteria for a mood episode and scoring < 8 on the Hamilton Depression Rating Scale (HDRS) and Young Mania Rating Scale (YMRS); manic-scoring < 7 on the HDRS and > 7 on the YMRS; depressive-scoring > 7 on the HDRS and < 7 on the YMRS. Patients in mixed phases were excluded. Blood samples were collected from all participants. RESULTS: Creatine kinase levels were higher in the manic patients than in the controls. However, we observed no significant difference between euthymic and depressive patients in terms of the creatine kinase level. CONCLUSION: Our results suggest that the clinical differences among the depressive, manic, and euthymic phases of bipolar disorder are paralleled by contrasting levels of creatine kinase. However, further studies are needed in order to understand the state-dependent differences observed in serum creatine kinase activity.

Evaluation of brain creatine kinase activity in an animal model of mania induced by ouabain

Bipolar disorder (BD) is a common and severe mood disorder associated with higher rates of suicide and disability. The development of new animal models, and the investigation employing those available have extensively contributed to understand the pathophysiological mechanisms of BD. Intracerebroventricular (i.c.v.) administration of ouabain, a specific Na+,K+-ATPase inhibitor, has been used as an animal model for BD. It has been demonstrated that Na+,K+-ATPase is altered in psychiatric disorders, especially BD. Creatine kinase (CK) is important for brain energy homeostasis by exerting several integrated functions. In the present study,we evaluated CK activity in the striatum, prefrontal cortex and hippocampus of rats subjected to i.c.v. administration of ouabain. Adult male Wistar rats received a single i.c.v. administration of ouabain (10(-2) and 10(-3) M) or vehicle (control group). Locomotor activity was measured using the open field test. CK activity was measured in the brain of rats immediately (1 h) and 7 days after ouabain administration. Our results showed that spontaneous locomotion was increased 1 h after ouabain administration and that hyperlocomotion was also observed 7 days after that.Moreover, CK activity was inhibited immediately after the administration of ouabain in the striatum, hippocampus and prefrontal cortex. Moreover, the enzyme was not affected in the striatum and hippocampus 7 days after ouabain administration. On the other hand, an inhibition in CK activity in the prefrontal cortex was observed. If inhibition of CK also occurs in BD patients, it will be tempting to speculate that the reduction of brain metabolism may be related probably to the pathophysiology of this disease.

Decrease in creatine kinase messenger RNA expression in the hippocampus and dorsolateral prefrontal cortex in bipolar disorder

OBJECTIVES

Bipolar disorder (BPD) affects more than 2 million adults in the USA and ranks among the top 10 causes of worldwide disabilities. Despite its prevalence, very little is known about the etiology of BPD. Recent evidence suggests that cellular energy metabolism is disturbed in BPD. Mitochondrial function is altered, and levels of high-energy phosphates, such as phosphocreatine (PCr), are reduced in the brain. This evidence has led to the hypothesis that deficiencies in energy metabolism could account for some of the pathophysiology observed in BPD. To further explore this hypothesis, we examined levels of creatine kinase (CK) mRNA, the enzyme involved in synthesis and metabolism of PCr, in the hippocampus (HIP) and dorsolateral prefrontal cortex (DLPFC) of control, BPD and schizophrenia subjects.

METHODS

Tissue was obtained from the Harvard Brain Tissue Resource Center. Real-time quantitative polymerase chain reaction (HIP, DLPFC) and gene expression microarrays (HIP) were employed to compare the brain and mitochondrial 1 isoforms of CK.

RESULTS

Both CK isoforms were downregulated in BPD. Furthermore, mRNA transcripts for oligodendrocyte-specific proteins were downregulated in the DLPFC, whereas the mRNA for the neuron-specific protein microtubule-associated protein 2 was downregulated in the HIP.

CONCLUSION

Although some of the downregulation of CK might be explained by cell loss, a more general mechanism seems to be responsible. The downregulation of CK transcripts, if translated into protein levels, could explain the reduction of high-energy phosphates previously observed in BPD.

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.

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.