Initial experiences with proton MR spectroscopy in treatment monitoring of mitochondrial encephalopathy

Usefulness of Magnetic Resonance Spectroscopy for the Initial Diagnosis of Mitochondrial DNA-Associated Leigh Syndrome

Purpose: Diagnosing Leigh syndrome (LS), a representative mitochondrial disease, remains challenging. Mitochondrial DNA (mtDNA)-associated LS, which is maternally inherited, has relatively well-known genetic variants. We evaluated the usefulness of brain magnetic resonance spectroscopy (MRS) for the initial diagnosis of mtDNA-associated LS using data from LS patients.Methods: The study involved LS patients who visited Gangnam Severance Hospital between 2006 and 2018. Based on patients’ clinical findings, genetic evaluations, brain magnetic resonance imaging, and brain MRS findings, 24 mtDNA-associated and 49 gene-negative LS patients were included in the current study. Lactate peaks and decreased N-acetyl aspartate (NAA) peaks in brain MRS were compared between both groups. Results: In total, 11 mtDNA mutation subtypes were detected. Our findings showed a higher proportion of brain MRS abnormalities in mtDNA-associated LS patients than in gene-negative LS patients, but no statistically significant differences were observed between the two groups (lactate peak, P=0.080; decreased NAA peak, P=0.115). Conclusion: Brain MRS is currently limited as an initial diagnostic test for mtDNA-associated LS. However, it may be a useful non-invasive test for the follow-up evaluation of mtDNA-associated LS treatment. Ultra-high-field MRS technology is expected in the future.

Correlation of Serum Biomarkers and Magnetic Resonance Spectroscopy in Monitoring Disease Progression in Patients With Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes Due to mtDNA A3243G Mutation

Background: Analysis of serum biomarkers and magnetic resonance spectroscopy (MRS) are useful for monitoring disease progression in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). We evaluated the correlation of serum biomarkers and MRS parameters during changes associated with stroke-like episodes. Methods: In 13 symptomatic MELAS patients carrying the A3243G mutation, we retrospectively obtained 207 voxels from 41 MRS studies, which were divided into three groups according to the temporal association with stroke-like episodes. The MRS NAA/Cr, Cho/Cr, NAA/Cho ratios, the presence of a lactate peak, serum biomarkers, serum lactate level and the pyruvate (Lac/Pyr) ratio were determined. Results: In regions with acute infarcts, the severity of serum Lac/Pyr and that of the MRS lactate peak (P = 0.0007) correlated; serum lactate (P = 0.02), severity of elevated serum lactate (P = 0.04), and serum Lac/Pyr (P = 0.02) correlated weakly. In previously infarcted regions, the severity of the MRS lactate peak and serum Lac/Pyr (P = 0.03), as well as the severity of serum Lac/Pyr (P = 0.02) were weakly correlated. In structurally normal regions, we found a weak to moderate negative correlation between serum lactate and MRS NAA/Cr (P = 0.008), and between the severity of elevated serum lactate and MRS NAA/Cr (P = 0.002) as well as MRS NAA/Cho (P = 0.02). Conclusions: MRS parameters correlate with specific serum biomarkers, and are useful for monitoring changes in brain metabolites, particularly as related to stroke-like episodes.

Neuroimaging in mitochondrial disorders

MRI and 1H magnetic resonance spectroscopy (1HMRS) are the main neuroimaging methods to study mitochondrial diseases. MRI can demonstrate seven ‘elementary’ central nervous system (CNS) abnormalities in these disorders, including diffuse cerebellar atrophy, cerebral atrophy, symmetric signal changes in subcortical structures (basal ganglia, brainstem, cerebellum), asymmetric signal changes in the cerebral cortex and subcortical white matter, leukoencephalopathy, and symmetric signal changes in the optic nerve and the spinal cord. These elementary MRI abnormalities can be variably combined in the single patient, often beyond what can be expected based on the classically known clinical-pathological patterns. However, a normal brain MRI is also possible. 1HMRS has a diagnostic role in patients with suspected mitochondrial encephalopathy, especially in the acute phase, as it can detect within the lesions, but also in normal appearing nervous tissue or in the ventricular cerebrospinal fluid (CSF), an abnormally prominent lactate peak, reflecting failure of the respiratory chain with a shift from the Krebs cycle to anaerobic glycolysis. So far, studies correlating MRI findings with genotype in mitochondrial disease have been possible only in small samples and would greatly benefit from data pooling. MRI and 1HMRS have provided important information on the pathophysiology of CNS damage in mitochondrial diseases by enabling in vivo non-invasive assessment of tissue abnormalities, the associated changes of blood perfusion and cellular metabolic derangement. MRI and 1HMRS are expected to serve as surrogate biomarkers in trials investigating therapeutic options in mitochondrial disease.

High predictive value of brain MRI imaging in primary mitochondrial respiratory chain deficiency

Background

Because the mitochondrial respiratory chain (RC) is ubiquitous, its deficiency can theoretically give rise to any symptom in any organ or tissue at any age with any mode of inheritance, owing to the twofold genetic origin of respiratory enzyme machinery, that is, nuclear and mitochondrial. Not all respiratory enzyme deficiencies are primary and secondary or artefactual deficiency is frequently observed, leading to a number of misleading conclusions and inappropriate investigations in clinical practice. This study is aimed at investigating the potential role of brain MRI in distinguishing primary RC deficiency from phenocopies and other aetiologies.

Methods

Starting from a large series of 189 patients (median age: 3.5 years (8 days–56 years), 58% males) showing signs of RC enzyme deficiency, for whom both brain MRIs and disease-causing mutations were available, we retrospectively studied the positive predictive value (PPV) and the positive likelihood ratio (LR+) of brain MRI imaging and its ability to discriminate between two groups: primary deficiency of the mitochondrial RC machinery and phenocopies.

Results

Detection of (1) brainstem hyperintensity with basal ganglia involvement (P≤0.001) and (2) lactate peak with either brainstem or basal ganglia hyperintensity was highly suggestive of primary RC deficiency (P≤0.01). Fourteen items had a PPV>95% and LR+ was greater than 9 for seven signs. Biallelic SLC19A3 mutations represented the main differential diagnosis. Non-significant differences between the two groups were found for cortical/subcortical atrophy, leucoencephalopathy and involvement of caudate nuclei, spinothalamic tract and corpus callosum.

Conclusion

Based on these results and owing to invasiveness of skeletal muscle biopsies and cost of high-throughput DNA sequencing, we suggest giving consideration to brain MRI imaging as a diagnostic marker and an informative investigation to be performed in patients showing signs of RC enzyme deficiency.

Monitoring clinical progression with mitochondrial disease biomarkers

Mitochondrial disorders are genetically determined metabolic diseases due to a biochemical deficiency of the respiratory chain. Given that multi-system involvement and disease progression are common features of mitochondrial disorders they carry substantial morbidity and mortality. Despite this, no disease-modifying treatments exist with clear clinical benefits, and the current best management of mitochondrial disease is supportive. Several therapeutic strategies for mitochondrial disorders are now at a mature preclinical stage. Some are making the transition into early-phase patient trials, but the lack of validated biomarkers of disease progression presents a challenge when developing new therapies for patients. This update discusses current biomarkers of mitochondrial disease progression including metabolomics, circulating serum markers, exercise physiology, and both structural and functional imaging. We discuss the advantages and disadvantages of each approach, and consider emerging techniques with a potential role in trials of new therapies.

Mitochondrial disorders in children: toward development of small-molecule treatment strategies

This review presents our current understanding of the pathophysiology and potential treatment strategies with respect to mitochondrial disease in children. We focus on pathologies due to mutations in nuclear DNA‐encoded structural and assembly factors of the mitochondrial oxidative phosphorylation (OXPHOS) system, with a particular emphasis on isolated mitochondrial complex I deficiency. Following a brief introduction into mitochondrial disease and OXPHOS function, an overview is provided of the diagnostic process in children with mitochondrial disorders. This includes the impact of whole‐exome sequencing and relevance of cellular complementation studies. Next, we briefly present how OXPHOS mutations can affect cellular parameters, primarily based on studies in patient‐derived fibroblasts, and how this information can be used for the rational design of small‐molecule treatment strategies. Finally, we discuss clinical trial design and provide an overview of small molecules that are currently being developed for treatment of mitochondrial disease.

In Vivo NMR Studies of the Brain with Hereditary or Acquired Metabolic Disorders

Metabolic disorders, whether hereditary or acquired, affect the brain, and abnormalities of the brain are related to cellular integrity; particularly in regard to neurons and astrocytes as well as interactions between them. Metabolic disturbances lead to alterations in cellular function as well as microscopic and macroscopic structural changes in the brain with diabetes, the most typical example of metabolic disorders, and a number of hereditary metabolic disorders. Alternatively, cellular dysfunction and degeneration of the brain lead to metabolic disturbances in hereditary neurological disorders with neurodegeneration. Nuclear magnetic resonance (NMR) techniques allow us to assess a range of pathophysiological changes of the brain in vivo. For example, magnetic resonance spectroscopy detects alterations in brain metabolism and energetics. Physiological magnetic resonance imaging (MRI) detects accompanying changes in cerebral blood flow related to neurovascular coupling. Diffusion and T1/T2-weighted MRI detect microscopic and macroscopic changes of the brain structure. This review summarizes current NMR findings of functional, physiological and biochemical alterations within a number of hereditary and acquired metabolic disorders in both animal models and humans. The global view of the impact of these metabolic disorders on the brain may be useful in identifying the unique and/or general patterns of abnormalities in the living brain related to the pathophysiology of the diseases, and identifying future fields of inquiry.

Serum GDF15 Levels Correlate to Mitochondrial Disease Severity and Myocardial Strain, but Not to Disease Progression in Adult m.3243A>G Carriers

In this observational cohort study, we examined the prognostic value of growth and differentiation factor 15 (GDF15) in indicating and monitoring general mitochondrial disease severity and progression in adult carriers of the m.3243A>G mutation.Ninety-seven adult carriers of the m.3243A>G mutation were included in this study. The Newcastle mitochondrial disease adult scale was used for rating mitochondrial disease severity. In parallel, blood was drawn for GDF15 analysis by ELISA. Forty-nine carriers were included in a follow-up study. In a small subset of subjects of whom an echocardiogram was available from general patient care, myocardial deformation was assessed using two-dimensional speckle-tracking strain analysis.A moderate positive correlation was found between the concentration of GDF15 and disease severity (r = 0.59; p < 0.001). The concentration of serum GDF15 was higher in m.3243A>G carriers with diabetes mellitus, cardiomyopathy, and renal abnormalities. After a 2-year follow-up, no significant correlation was found between the change in disease severity and the change in the concentration of GDF15 or between the GDF15 level at the first assessment and the change in disease severity. In the subcohort of patients of whom an echocardiogram was available, the concentration of GDF15 correlated moderately to longitudinal global strain (r = 0.55; p = 0.006; n = 23) but not to circumferential or radial strain.Our results indicate that serum GDF15 is not a strong surrogate marker for general mitochondrial disease severity. Its value in indicating myocardial deformation should be confirmed in a prospective longitudinal study.

Diffusion kurtosis imaging predicts neoadjuvant chemotherapy responses within 4 days in advanced nasopharyngeal carcinoma patients

PURPOSE

To explore the clinical value of diffusion kurtosis imaging (DKI) and monoexponential diffusion-weighted imaging (DWI) for predicting early response to neoadjuvant chemotherapy (NAC) in patients with nasopharyngeal carcinoma (NPC).

MATERIALS AND METHODS

Fifty-nine patients with stage III-IVb NPC underwent four 3.0T MR scans: prior to, and on the 4th, 21st, 42nd days after NAC initiation. The parameters of DKI (corrected diffusion coefficient, D; excess diffusion kurtosis coefficient, K) and monoexponential DWI (apparent diffusion coefficient, ADC) were obtained at the first three scans. Statistical methods included Student's t-test or Mann-Whitney U-test, receiver operating characteristic (ROC) curve analyses and paired X(2) test.

RESULTS

D(pre) in responders group (RG) was significantly lower than nonresponders group (NRG) (1.029 ± 0.033 vs. 1.184 ± 0.055, ×10(-3) mm(2) /s, P = 0.020). ADC(day4) and ΔD(day4) were the most useful parameters of the two diffusional models to distinguish RG from NRG, respectively (area under the curve, 0.761 vs. 0.895). ΔD(day4) was more sensitive than ADC(day4) to predict treatment response to NAC (P = 0.006).

CONCLUSION

Both DKI and monoexponential DWI showed potential to predict treatment response to NAC prior to morphological change. DKI may be superior to monoexponential DWI for predicting early response to NAC in patients with locally advanced NPC.

Zolpidem induces paradoxical metabolic and vascular changes in a patient with PVS

INTRODUCTION

Zolpidem is a non-benzodiazepine drug used for the therapy of insomnia, which has selectivity for stimulating the effect of GABA-A receptors. Recently, a paradoxical arousing effect of zolpidem in patients with severe brain damage has been repeatedly reported.

METHODS

A placebo-controlled magnetic resonance study was conducted to evaluate its effect on BOLD and metabolites spectral signals in a patient with severe brain injuries and an age-matched healthy volunteer. A multi-modal analysis was used to assess aspects in the pharmacologically-induced changes in the resting-state brain metabolism.

RESULTS

A significantly increased BOLD signal was transiently localized in the left frontal cortices, bilateral anterior cingulated areas, left thalamus and right head of the caudate nucleus. The healthy subject showed a deactivation of the frontal, parietal and temporal cortices. BOLD signal changes were found to significantly correlate with concentrations of extravascular metabolites in the left frontal cortex. It is discussed that, when zolpidem attaches to modified GABA receptors of neurodormant brain cells, brain activation is induced. This might explain the significant correlations of BOLD signal changes and proton-MRS metabolites in this patient after zolpidem.

CONCLUSION

It was concluded that proton-MRS and BOLD signal assessment could be used to study zolpidem-induced metabolic modulation in a resting state.

Towards the harmonization of outcome measures in children with mitochondrial disorders

AIM

A clinical trial is only as reliable as its outcomes, therefore the careful and systematic selection of outcome measures is extremely important. Currently, the selection of outcome measures for clinical trials designed to evaluate new drugs in patients with mitochondrial disorders is inefficient and has not been addressed systematically. Given that meaningful data can be obtained only from trials in which outcomes are assessed using valid instruments, one should first focus on the validation of a set of selected instruments in the target population. The aim of this review is to systematically select a 'toolbox' of robust outcome measures that are relevant to all patients.

METHOD

Using an extensive search of published literature, we systematically compiled a toolbox with outcome measures based on a primary search for possible instruments Subsequently, we reduced this toolbox using strict criteria that were adapted from the United States Food and Drug Administration.

RESULTS

A toolbox with clinically relevant and psychometrically robust instruments for performing clinical research in children with mitochondrial disorders was compiled.

INTERPRETATION

In coming years, more experience using these outcome measures in children with various mitochondrial disease phenotypes must be obtained before reliable conclusions regarding the validity of these instruments can be drawn.

Metabolite measurements in the caudate nucleus, anterior cingulate cortex and hippocampus among patients with mitochondrial disorders: a case-control study using proton magnetic resonance spectroscopy

BACKGROUND

Mitochondrial disorders are clinical syndromes associated with mutations in the mitochondrial or nuclear genome that result in impaired oxidative phosphorylation and deficient energy production. Metabolic abnormalities in brain areas associated with cognitive functions could give rise to neuropsychiatric symptomatology. The aim of this study was to use single-voxel proton magnetic resonance spectroscopy to identify metabolic abnormalities in regions implicated in neuropsychiatric symptoms in patients with mitochondrial disorders.

METHODS

N-acetyl-aspartate and creatine levels were measured in the caudate nucleus, anterior cingulate cortex and hippocampus in 15 patients with mitochondrial disorders compared with 15 healthy controls matched for age and sex.

RESULTS

N-acetyl-aspartate levels were significantly lower in the caudate nucleus among patients with mitochondrial disorders (mean 7.04 ± 1.19 standard deviation [SD] institutional units) compared with healthy controls (mean 8.19 ± 1.18 SD institutional units; p = 0.02). Creatine levels were lower in the caudate nucleus among patients compared with controls (patients: mean 6.84 ± 1.42 SD institutional units; controls: mean 7.52 ± 0.76 SD institutional units; p = 0.03), but the results were no longer significant after correction for multiple comparisons. There were no significant differences in metabolite measurements between patients and controls in the anterior cingulate cortex and the hippocampus.

INTERPRETATION

Metabolic abnormalities were identified exclusively in the caudate nucleus, with significantly lower N-acetyl-aspartate levels among patients compared with controls. These results suggest that the corpus striatum may be highly susceptible to mitochondrial oxidative phosphorylation defects and resultant cell loss. Given the role of the caudate nucleus in cognitive and executive functions, our findings raise the possibility that metabolic abnormalities in the caudate nucleus may contribute to cognitive impairment and neuropsychiatric symptoms in patients with mitochondrial disorders, which could be investigated in future studies.

Brain uptake of Tc99m-HMPAO correlates with clinical response to the novel redox modulating agent EPI-743 in patients with mitochondrial disease

While decreased ATP production and redox imbalance are central to mitochondrial disease pathogenesis, efforts to develop effective treatments have been hampered by the lack of imaging markers of oxidative stress. In this study we wished to determine if Tc99m-HMPAO, a SPECT imaging marker of cerebral blood flow and glutathione/protein thiol content, could be used to monitor the effect(s) of EPI-743, an oral redox modulating, para-benzoquinone based therapeutic for mitochondrial disease. We hypothesized that treatment changes in HMPAO uptake would be inversely proportional to changes in oxidative stress within the brain and directly correlate to clinical response to EPI-743 therapy. Twenty-two patients with mitochondrial disease were treated with EPI-743. Each underwent baseline and 3-month Tc99m-HMPAO SPECT scanning along with clinical/neurologic evaluations. Diseases treated were: Leigh syndrome (n=7), polymerase γ deficiency (n=5), MELAS (n=5), Friedreich ataxia (n=2), Kearns-Sayre syndrome, Pearson syndrome, and mtDNA depletion syndrome. Neuro-anatomic uptake analyses of HMPAO were performed with NeuroGam™ (Segami Corp.) statistical software and clinical response was assessed by the Newcastle Paediatric Mitochondrial Disease Scale or Newcastle Mitochondrial Disease Adult Scale depending on patient age. For all 22 patients there was a significant linear correlation between the change in cerebellar uptake of HMPAO and the improvement in Newcastle score (r=0.623, **p=0.00161). The MELAS subgroup showed a significant relationship of whole brain uptake (n=5, r=0.917, *p=0.028) to improvement in Newcastle score. We conclude that Tc99m-HMPAO SPECT scanning has promise as a general marker of the oxidative state of the brain and its response to redox modulating therapies. Further studies will be needed to confirm these findings in a more homogenous study population.