Photic stimulation-induced alteration of brain energy metabolism measured by 31P-MR spectroscopy in patients with MELAS

Is visual activation associated with changes in cerebral high-energy phosphate levels?

Phosphorus magnetic resonance spectroscopy (³¹P MRS) has been employed before to assess phosphocreatine (PCr) and other high-energy phosphates in the visual cortex during visual stimulation with inconsistent results. We performed functional ³¹P MRS imaging in the visual cortex and control regions during a visual stimulation paradigm at an unprecedented sensitivity, exploiting a dedicated RF coil design at a 7 T MR system. Visual stimulation in a 3 min 24 s on–off paradigm in eight young healthy adults generated a clear BOLD effect with traditional ¹H functional MRI in the visual cortex (average z score 9.9 ± 0.2). However, no significant event-related changes in any of the ³¹P metabolite concentrations, linewidths (7.9 ± 1.8 vs 7.8 ± 1.9 Hz) or tissue pH (7.07 ± 0.13 vs 7.06 ± 0.07) were detectable. Overall, our study of ³¹P MRSI in 15 cm³ voxels had a detection threshold for changes in PCr, Pi and γ-ATP between stimulation and rest of 5, 17 and 10%, respectively. In individual subjects, the mean coefficients of variance for PCr and Pi levels of control voxels were 6 ± 3 and 19 ± 8% (three time point average of 3 min 24 s). Altogether this indicates that energy supply for neuronal activation at this temporal resolution does not drain global PCr resources.

Neurobiological basis of bipolar disorder: Mitochondrial dysfunction hypothesis and beyond

Bipolar disorder is one of two major psychotic disorders together with schizophrenia and causes severe psychosocial disturbance. Lack of adequate animal models hampers development of new mood stabilizers. We proposed a mitochondrial dysfunction hypothesis and have been studying the neurobiology of bipolar disorder based on this hypothesis. We showed that deletions of mitochondrial DNA (ΔmtDNA) play a pathophysiological role at least in some patients with bipolar disorder possibly by affecting intracellular calcium regulation. Mutant polymerase γ transgenic mice that accumulate ΔmtDNA in the brain showed recurrent spontaneous depression-like episodes which were prevented by a serotonin-selective reuptake inhibitor and worsened by lithium withdrawal. The animal model would be useful to develop new mood stabilizers.

(31)P-MRS using visual stimulation protocols with different durations in healthy young adult subjects

Phosphorus magnetic resonance spectroscopy ((31)P-MRS) combined with visual stimulation in functional experiments allows the non-invasive dynamic study of brain energy metabolism. (31)P-MRS has been applied to several diseases and to healthy subjects, but works have shown variable findings and non-reproducible results, possibly caused by low numbers of subjects combined with different stimulation paradigms. In the present work, we used (31)P-MRS at 3 T with two different visual stimulation protocols with different block duration ("short" and "long") to evaluate metabolic changes under different workloads in 38 healthy subjects. We found a 15 % (short protocol-blocks of 1.5 min stimulation) and 3 % (long protocol-blocks of 5 min stimulation) increase in the inorganic phosphate (Pi) to α-adenosine triphosphate (α-ATP) ratio, and a 5 % (short protocol) and 2 % (long protocol) decrease in the nicotinamide adenine nucleotide (NADH + NAD(+)) to α-ATP ratio. The NADH + NAD(+) results are, to the best of our knowledge, the first functional magnetic resonance spectroscopy in vivo assessment of these compounds, but their interpretation is difficult since they cannot be separately quantified at 3 T. Our results show that longer stimulations produce smaller concentration changes in Pi/α-ATP and (NADH + NAD(+))/α-ATP ratios, which suggests a possible adaptation effect during longer stimulations that leads metabolic concentrations towards the initial equilibrium.

31P-MRS demonstrates a reduction in high-energy phosphates in the occipital lobe of migraine without aura patients

BACKGROUND

Differences in brain energy metabolism have been found between migraine patients and controls in previous phosphorus magnetic resonance spectroscopy ((31)P-MRS) studies, most of them emphasizing migraine with aura (MwA). The aim of this study was to verify potential changes in resting-state brain energy metabolism in patients with migraine without aura (MwoA) compared to control subjects by (31)P-MRS at 3 tesla.

METHODS

Quantification was performed using the phantom replacement technique. MRS measurements were performed interictally and in the medial occipital lobe of 19 MwoA patients and 26 age-matched controls.

RESULTS

A significantly decreased phosphocreatine concentration ([PCr]) was found as in previous studies. While adenosine triphosphate concentration ([ATP]) was considered to be constant in previously published work, this study found a significant decrease in the measured [ATP] in MwoA patients. The inorganic phosphate ([P(i)]) and magnesium ([Mg(2+)]) concentrations were not significantly different between MwoA patients and controls.

CONCLUSIONS

The altered metabolic concentrations indicate that the energy metabolism in MwoA patients is impaired, certainly in a subgroup of patients. The actual decrease in [ATP] adds further strength to the theory of the presence of a mitochondrial component in the pathophysiology of migraine.

Chronic progressive external ophthalmoplegia: MR spectroscopy and MR diffusion studies in the brain

OBJECTIVE

The purpose of our study was to show how, despite pathognomonic signs of cerebral involvement in chronic progressive external ophthalmoplegia (CPEO), mitochondrial respiratory chain insufficiency is associated with increased lactate and reduced N-acetylaspartate. CPEO and mitochondrial myopathy are caused by mitochondrial DNA mutations leading to impaired oxidative phosphorylation. Cortical and subcortical metabolites, cerebral diffusivity, and structural MRI were assessed to characterize possible subclinical cerebral pathology in CPEO.

SUBJECTS AND METHODS

Ten patients with CPEO (n = 8), mitochondrial myopathy (n = 1), and Kearns-Sayre syndrome (n = 1) and 13 control group volunteers were studied by MRI, both long TE (144) proton MR spectroscopic imaging (1H MRSI), and diffusion-weighted imaging. Relative concentrations of N-acetylaspartate, choline, creatine, and lactate were estimated by Linear Combination of Model Spectra (LCModel) in healthy-appearing white matter, gray matter, and white matter hyperintensities.

RESULTS

Of five patients with cortical atrophy, it was moderate in three and severe in two. One patient had severe and four had moderate cerebellar atrophy. Six of 10 patients showed unspecific white matter lesions, whereas the remainder had hyperintensities in the pyramidal tract (n =2) and middle cerebellar peduncle (n = 1) despite clinical signs. No basal ganglia lesions were found. Physiologic metabolite ratios were normal and lactate was absent in supratentorial healthy-appearing cortex and subcortical white matter. Global diffusion histogram metrics revealed no abnormalities.

CONCLUSION

Normal spectroscopic imaging in radiologic unaffected brain and healthy global brain parenchymal diffusion findings do not support the hypothesis of a generalized cerebral energy loss in CPEO. Bilateral structural alteration of central motor pathways in two patients without clinical pyramidal signs may, however, reflect subclinical axonal injury in predilection sites in some patients.

Magnetic resonance spectroscopy in patients with MELAS

Localized magnetic resonance spectroscopy (MRS) yields sensitive metabolic markers to provide insight into the pathophysiology of mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) in vivo. Findings in full MELAS syndrome at 1H MRS of the brain typically include severely elevated lactate and reduced N-acetylaspartate, glutamate, myo-inositol, and total creatine concentrations in stroke-like lesions. Similar but less extreme alterations are also common in gray matter (GM) regions that appear normal at magnetic resonance imaging. Phosphorus spectroscopy of peripheral muscle permits investigation of the bioenergetic status. A decline of the phosphorylation potential indicates a low energy reserve at rest. Phosphocreatine resynthesis during post-exercise recovery is delayed pointing to reduced mitochondrial capacity. As MRS is inherently non-invasive, follow-up studies can be performed to assess treatment response quantitatively.

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.

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.

Brain activation in normal subjects and in patients affected by mitochondrial disease without clinical central nervous system involvement: a phosphorus magnetic resonance spectroscopy study

It remains unclear whether brain energetics is disturbed in patients with mitochondrial disease without clinical central nervous system involvement (MDW). The authors used the high temporal and spatial resolution phosphorus magnetic resonance spectroscopy (31P MRS) technique that they developed to study high energy phosphates (HEPs) and intracellular pH (pH) in the visual cortex of 9 normal subjects and 5 MDW patients with single mtDNA deletion at rest, during, and after visual activation. In normal subjects, HEPs remained unchanged during activation but rose significantly (by 17%) during recovery, and pH increased during visual activation with a slow return to rest values. In MDW patients, HEPs were within the normal range at rest and did not change during activation, but fell significantly (by 22%) in the recovery period; pH did not reveal a homogeneous pattern. In the brain of patients with MDW, energy balance remains normal until oxidative metabolism is intensively stressed, as during a postactivation phase. The heterogeneity of the physicochemical environment (that is, pH) suggests various degrees of subclinical brain involvement. The combined use of MRS and brain activation is fundamental for the study of brain energetics and may prove an important diagnostic tool in patients with MDW.

Mitochondrial dysfunction in bipolar disorder

Mitochondrial dysfunction is implicated in bipolar disorder based on the following lines of evidence: 1) Abnormal brain energy metabolism measured by 31P-magnetic resonance spectroscopy, that is, decreased intracellular pH, decreased phosphocreatine (PCr), and enhanced response of PCr to photic stimulation. 2) Possible role of maternal inheritance in the transmission of bipolar disorder. 3) Increased levels of the 4977-bp deletion in mitochondrial DNA (mtDNA) in autopsied brains. 4) Comorbidity of affective disorders in certain types of mitochondrial disorders, such as autosomal inherited chronic progressive external ophthalmoplegia and mitochondrial diabetes mellitus with the 3243 mutation. Based on these findings, we searched for mtDNA mutations/ polymorphisms associated with bipolar disorder and found that 5178C and 10398A polymorphisms in mtDNA were risk factors for bipolar disorder. The 5178C genotype was associated with lower brain intracellular pH. mtDNA variations may play a part in the pathophysiology of bipolar disorder through alteration of intracellular calcium signaling systems. The mitochondrial dysfunction hypothesis, which comprehensively accounts for the pathophysiology of bipolar disorder, is proposed.