The other human genome

Dorsal Anterior Cingulate Lactate and Glutathione Levels in Euthymic Bipolar I Disorder: 1H-MRS Study

OBJECTIVE

Oxidative stress and mitochondrial dysfunction are 2 closely integrated processes implicated in the physiopathology of bipolar disorder. Advanced proton magnetic resonance spectroscopy techniques enable the measurement of levels of lactate, the main marker of mitochondrial dysfunction, and glutathione, the predominant brain antioxidant. The objective of this study was to measure brain lactate and glutathione levels in bipolar disorder and healthy controls.

METHODS

Eighty-eight individuals (50 bipolar disorder and 38 healthy controls) underwent 3T proton magnetic resonance spectroscopy in the dorsal anterior cingulate cortex (2x2x4.5cm(3)) using a 2-D JPRESS sequence. Lactate and glutathione were quantified using the ProFit software program.

RESULTS

Bipolar disorder patients had higher dorsal anterior cingulate cortex lactate levels compared with controls. Glutathione levels did not differ between euthymic bipolar disorder and controls. There was a positive correlation between lactate and glutathione levels specific to bipolar disorder. No influence of medications on metabolites was observed.

CONCLUSION

This is the most extensive magnetic resonance spectroscopy study of lactate and glutathione in bipolar disorder to date, and results indicated that euthymic bipolar disorder patients had higher levels of lactate, which might be an indication of altered mitochondrial function. Moreover, lactate levels correlated with glutathione levels, indicating a compensatory mechanism regardless of bipolar disorder diagnosis.

Mitochondria DNA change and oxidative damage in clinically stable patients with major depressive disorder

BACKGROUND

To compare alterations of mitochondria DNA (mtDNA) copy number, single nucleotide polymorphisms (SNPs), and oxidative damage of mtDNA in clinically stable patients with major depressive disorder (MDD).

METHODS

Patients met DSM-IV diagnostic criteria for MDD were recruited from the psychiatric outpatient clinic at Changhua Christian Hospital, Taiwan. They were clinically stable and their medications had not changed for at least the preceding two months. Exclusion criteria were substance-induced psychotic disorder, eating disorder, anxiety disorder or illicit substance abuse. Comparison subjects did not have any major psychiatric disorder and they were medically healthy. Peripheral blood leukocytes were analyzed to compare copy number, SNPs and oxidative damage of mtDNA between the two groups.

RESULTS

40 MDD patients and 70 comparison subjects were collected. The median age of the subjects was 42 years and 38 years in MDD and comparison groups, respectively. Leukocyte mtDNA copy number of MDD patients was significantly lower than that of the comparison group (p = 0.037). MDD patients had significantly higher mitochondrial oxidative damage than the comparison group (6.44 vs. 3.90, p<0.001). After generalized linear model adjusted for age, sex, smoking, family history, and psychotropic use, mtDNA copy number was still significantly lower in the MDD group (p<0.001). MtDNA oxidative damage was positively correlated with age (p<0.001) and MDD (p<0.001). Antipsychotic use was negatively associated with mtDNA copy number (p = 0.036).

LIMITATIONS

The study is cross-sectional with no longitudinal follow up. The cohort is clinically stable and generalizability of our result to other cohort should be considered.

CONCLUSIONS

Our study suggests that oxidative stress and mitochondria may play a role in the pathophysiology of MDD. More large-scale studies are warranted to assess the interplay between oxidative stress, mitochondria dysfunction and MDD.

Mitochondrial DNA variation and increased oxidative damage in euthymic patients with bipolar disorder

AIM

The aim of this study was to compare alterations of mitochondrial DNA (mtDNA) copy number, single nucleotide polymorphisms, and oxidative damage of mtDNA in clinically stable patients with bipolar I disorder (BD).

METHODS

Patients meeting DSM-IV diagnostic criteria for BD were recruited from the psychiatric outpatient clinic at Changhua Christian Hospital, Taiwan. They were clinically stable and their medications had not changed for at least the preceding 2 months. Exclusion criteria were substance-induced psychotic disorder, eating disorder, anxiety disorder or illicit substance abuse. Comparison subjects did not have any history of major psychiatric disorders and they were non-smokers. By analyzing peripheral blood leukocytes, copy number, single nucleotide polymorphisms and oxidative damage of mtDNA were compared between the two groups.

RESULTS

The median age of the subjects was 38 years and 41.5 years in the comparison and BD groups, respectively. The leukocyte mtDNA copy number of the BD group was significantly lower than that of the comparison group (P < 0.001). BD patients had significantly higher mitochondrial oxidative damage than the comparison group (6.1 vs 3.9, P < 0.001). After generalized linear model adjusting with age, sex, smoking, family history, and psychotropic use, mtDNA copy number was still significantly lower in the BD group (P < 0.001). MtDNA oxidative damage was positively correlated with age (P = 0.034), although mtDNA oxidative damage was similar between these two groups.

CONCLUSION

Possible involvement of oxidative stress and mitochondria in the pathophysiology of BD needs more large-scale studies. It is important that psychiatrists retain a high level of suspicion for mitochondrial dysfunction in patients with bipolar disorder.

Spectrum of genetic changes in patients with non-syndromic hearing impairment and extremely high carrier frequency of 35delG GJB2 mutation in Belarus

The genetic nature of sensorineural hearing loss (SNHL) has so far been studied for many ethnic groups in various parts of the world. The single-nucleotide guanine deletion (35delG) of the GJB2 gene coding for connexin 26 was shown to be the main genetic cause of autosomal recessive deafness among Europeans. Here we present the results of the first study of GJB2 and three mitochondrial mutations among two groups of Belarusian inhabitants: native people with normal hearing (757 persons) and 391 young patients with non-syndromic SNHL. We have found an extremely high carrier frequency of 35delG GJB2 mutation in Belarus -5.7%. This point deletion has also been detected in 53% of the patients with SNHL. The 312del14 GJB2 was the second most common mutation in the Belarus patient cohort. Mitochondrial A1555G mt-RNR1 substitution was found in two SNHL patients (0.55%) but none were found in the population cohort. No individuals carried the A7445G mutation of mitochondrial mt-TS1. G7444A as well as T961G substitutions were detected in mitochondrial mt-RNR1 at a rate of about 1% both in the patient and population cohorts. A possible reason for Belarusians having the highest mutation carrier frequency in Europe 35delG is discussed.

Mitochondrial involvement in psychiatric disorders

Recent findings of mitochondrial abnormalities in brains from subjects with neurological disorders have led to a renewed search for mitochondrial abnormalities in psychiatric disorders. A growing body of evidence suggests that there is mitochondrial dysfunction in schizophrenia, bipolar disorder, and major depressive disorder, including evidence from electron microscopy, imaging, gene expression, genotyping, and sequencing studies. Specific evidence of dysfunction such as increased common deletion and decreased gene expression in mitochondria in psychiatric illnesses suggests that direct examination of mitochondrial DNA from postmortem brain cells may provide further details of mitochondrial alterations in psychiatric disorders.

Identification and characterization of mitochondrial abasic (AP)-endonuclease in mammalian cells

Abasic (AP)-endonuclease (APE) is responsible for repair of AP sites, and single-strand DNA breaks with 3′ blocking groups that are generated either spontaneously or during repair of damaged or abnormal bases via the DNA base excision repair (BER) pathway in both nucleus and mitochondria. Mammalian cells express only one nuclear APE, 36 kDa APE1, which is essential for survival. Mammalian mitochondrial (mt) BER enzymes other than mtAPE have been characterized. In order to identify and characterize mtAPE, we purified the APE activity from beef liver mitochondria to near homogeneity, and showed that the mtAPE which has 3-fold higher specific activity relative to APE1 is derived from the latter with deletion of 33 N-terminal residues which contain the nuclear localization signal. The mtAPE-sized product could be generated by incubating ³⁵S-labeled APE1 with crude mitochondrial extract, but not with cytosolic or nuclear extract, suggesting that cleavage of APE1 by a specific mitochondria-associated N-terminal peptidase is a prerequisite for mitochondrial import. The low abundance of mtAPE, particularly in cultured cells might be the reason for its earlier lack of detection by western analysis.

Review of the literature on major mental disorders in adult patients with mitochondrial diseases

Mitochondria are intracellular organelles crucial to the production cellular energy. Mitochondrial disease results from a malfunction in this biochemical cascade. These disorders can affect any organ system, producing diverse signs and symptoms, including psychiatric ones. Several authors argue that mitochondrial dysfunction is related to the pathophysiology of bipolar disorder and schizophrenia. Also, the authors retrieved 19 case reports that describe patients with mitochondrial diseases and psychiatric disorders. Most of these patients have psychiatric presentations that preceded the diagnosis of mitochondrial disease. The most common physical findings are fatigue, muscle weakness with or without atrophy, and hearing loss.

Biochemical evaluation of mitochondrial respiratory chain enzymes in canine skeletal muscle

OBJECTIVE

To perform respiratory chain enzymatic activity assays on canine skeletal muscle biopsy specimens and establish reference range values of skeletal muscle enzyme activities for dogs.

SAMPLE POPULATION

Biopsy specimens from the vastus lateralis muscle were obtained from 24 dogs (8 sexually intact males and 14 sexually intact females) ranging from 15 months to 6 years of age.

PROCEDURE

Mean values of citrate synthase, cytochrome-c oxidase, succinate dehydrogenase, succinate dehydrogenase-cytochrome-c reductase, nicotinamide adenine dinucleotide (NADH) dehydrogenase, and NADH dehydrogenase-cytochrome-c reductase activities were established by use of 6 standard spectrophotometric assays for respiratory chain enzyme analysis.

RESULTS

Compared with published data for skeletal muscle enzyme activities in humans, skeletal muscle enzyme activities in dogs were 2- to 4-fold higher. Additionally, citrate synthase activity, a marker for mitochondrial volume, was positively correlated with age in dogs, suggesting that mitochondrial volume increases with age, although no apparent change in respiratory chain enzymatic activity with an increase in age was found.

CONCLUSIONS AND CLINICAL RELEVANCE

Reference range values for skeletal muscle enzyme activities of dogs are needed to accurately interpret results of respiratory chain enzymatic activity assays. During investigation of metabolic myopathies, if skeletal muscle biopsy specimens are evaluated for respiratory chain enzyme kinetics, they should be performed and evaluated in concert with skeletal muscle biopsy specimens from clinically normal animals of the same species.

The search for genotypes that underlie human performance phenotypes

For a species spread throughout the world, humans are remarkably invariant; yet there has always been more interest in the slight differences between individuals than in the great commonality. This is especially true in athletic endeavours, where nearly immeasurable differences in performance can separate the winner from the rest of the competitors. There is little doubt that performance is influenced by environment, as the effects of diet and training on athletic ability have long been known, if not completely understood; however, the contribution of an individual's genetic make-up is less clear. The dominance of particular nationalities, ethnic groups, or families in various sporting events is often perceived as evidence that heritage (biological or cultural), plays a role in the development of athletic skills. Further complicating the issue are the interactions between genetic background and environment, as both of these fundamental arbiters of development rarely act independently. Despite the complexity of the problem, numerous researchers have attempted to elucidate the effects of genetic background on physical performance and, more recently, to identify the specific genetic variants that contribute to performance. This article reviews some of these studies with a focus on the methodologies employed.

Evidence and age-related distribution of mtDNA D-loop point mutations in skeletal muscle from healthy subjects and mitochondrial patients

The progressive accumulation of mitochondrial DNA (mtDNA) alterations, ranging from single mutations to large-scale deletions, in both the normal ageing process and pathological conditions is a relevant phenomenon in terms of frequency and heteroplasmic degree. Recently, two point mutations (A189G and T408A) within the Displacement loop (D-loop) region, the control region for mtDNA replication, were shown to occur in skeletal muscles from aged individuals. We evaluated the presence and the heteroplasmy levels of these two mutations in muscle biopsies from 91 unrelated individuals of different ages (21 healthy subjects and 70 patients affected by mitochondrial encephalomyopathies). Overall, both mutations significantly accumulate with age. However, a different relationship was discovered among the different subgroups of patients: a higher number of A189G positive subjects younger than 53 years was detected in the subgroup of multiple-deleted patients; furthermore, a trend towards an increased risk for the mutations was evidenced among patients carrying multiple deletions when compared to healthy controls. These findings support the idea that a common biological mechanism determines the accumulation of somatic point mutations in the D-loop region, both in healthy subjects and in mitochondrial myopathy patients. At the same time, it appears that disorders caused by mutations of nuclear genes controlling mtDNA replication (the "mtDNA multiple deletions" syndromes) present a temporal advantage to mutate in the D-loop region. This observation may be relevant to the definition of the molecular pathogenesis of these latter syndromes.

Mouse models for neurological disease

The mouse has many advantages over human beings for the study of genetics, including the unique property that genetic manipulation can be routinely carried out in the mouse genome. Most importantly, mice and human beings share the same mammalian genes, have many similar biochemical pathways, and have the same diseases. In the minority of cases where these features do not apply, we can still often gain new insights into mouse and human biology. In addition to existing mouse models, several major programmes have been set up to generate new mouse models of disease. Alongside these efforts are new initiatives for the clinical, behavioural, and physiological testing of mice. Molecular genetics has had a major influence on our understanding of the causes of neurological disorders in human beings, and much of this has come from work in mice.