Molecular imaging for mitochondrial metabolism and oxidative stress in mitochondrial diseases and neurodegenerative disorders.

BACKGROUND: Increasing evidence from pathological and biochemical investigations suggests that mitochondrial metabolic impairment and oxidative stress play a crucial role in the pathogenesis of mitochondrial diseases, such as mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome, and various neurodegenerative disorders. Recent advances in molecular imaging technology with positron emission tomography (PET) and functional magnetic resonance imaging (MRI) have accomplished a direct and non-invasive evaluation of the pathophysiological changes in living patients. SCOPE OF REVIEW: In this review, we focus on the latest achievements of molecular imaging for mitochondrial metabolism and oxidative stress in mitochondrial diseases and neurodegenerative disorders. MAJOR CONCLUSIONS: Molecular imaging with PET and MRI exhibited mitochondrial metabolic changes, such as enhanced glucose utilization with lactic acid fermentation, suppressed fatty acid metabolism, decreased TCA-cycle metabolism, impaired respiratory chain activity, and increased oxidative stress, in patients with MELAS syndrome. In addition, PET imaging clearly demonstrated enhanced cerebral oxidative stress in patients with Parkinson's disease or amyotrophic lateral sclerosis. The magnitude of oxidative stress correlated well with clinical severity in patients, indicating that oxidative stress based on mitochondrial dysfunction is associated with the neurodegenerative changes in these diseases. GENERAL SIGNIFICANCE: Molecular imaging is a promising tool to improve our knowledge regarding the pathogenesis of diseases associated with mitochondrial dysfunction and oxidative stress, and this would facilitate the development of potential antioxidants and mitochondrial therapies.

Expanding the Phenotype: Neurodevelopmental Disorder, Mitochondrial, With Abnormal Movements and Lactic Acidosis, With or Without Seizures (NEMMLAS) due to WARS2 Biallelic Variants, Encoding Mitochondrial Tryptophanyl-tRNA Synthase.

BACKGROUND: WARS2 encodes a tryptophanyl tRNA synthetase, which is involved in mitochondrial protein synthesis. Biallelic mutations in WARS2 are rare and have been associated with a spectrum of clinical presentations, including neurodevelopmental disorder with abnormal movements, lactic acidosis with or without seizures (NEMMLAS). CASE PRESENTATION: Here we present the case of an 8-year-old girl with ataxia and parkinsonism with periventricular white matter abnormalities on magnetic resonance imaging (MRI) and global developmental delay. The initial investigations revealed an elevated lactate level. Extensive metabolic testing, including a muscle biopsy, was inconclusive. Cerebrospinal fluid (CSF) neurotransmitter levels were low; however, a trial of levodopa was unremarkable. The chromosomal microarray and initial ataxia gene panel was normal. Zinc supplementation for a heterozygous variant of unknown significance in the CP gene on the ataxia exome panel was not effective in treating her symptoms. Reanalysis of the ataxia exome panel highlighted biallelic mutations in WARS2, which lead to the diagnosis of neurodevelopmental disorder, mitochondrial, with abnormal movements and lactic acidosis, with or without seizures (NEMMLAS). This lead to parental genetic testing, redirected therapy, and helped to expand the symptomology of this rare condition. CONCLUSION: Here we emphasize the importance of imminent and repeat expanded genetic testing to ensure early diagnosis and treatment for rare pediatric disorders. The patient is being trialed on a mitochondrial cocktail in an attempt to compensate for defects in mitochondrial protein synthesis associated with this variant. Longitudinal monitoring of disease manifestation will help establish the currently unknown natural history of this condition.

Spectroscopic detection of brain propylene glycol in neonates: Effects of different pharmaceutical formulations of phenobarbital.

BACKGROUND: The first choice for treatment of neonatal convulsions is intravenous phenobarbital, which contains propylene glycol (PG) as a solvent. Although PG is generally considered safe, the dosage can exceed safety thresholds in neonates. High PG levels can cause lactic acidosis. PURPOSE/HYPOTHESIS: To investigate a relationship between brain PG concentration and medication administered to neonates, and to study if a correlation between spectroscopically detected PG and lactate was present. STUDY TYPE: Retrospective. POPULATION: Forty-one neonates who underwent MRI/MRS. FIELD STRENGTH/SEQUENCE: Short echo time single voxel MRS at 1.5T. ASSESSMENT: Spectra were quantified. Concentrations of PG were correlated with medication administered, because intravenously administered phenobarbital solutions contained 10, 25, or 50 mg phenobarbital per ml, all containing 350 mg PG per ml. The interval between medication and MRI/MRS was determined. STATISTICAL TESTS: Chi-square test, Student's t-test, Mann-Whitney U-test and Spearman correlation. RESULTS: Eighteen neonates had brain PG >1 mM (median 3.4 mM, maximum 9.5 mM). All 18 neonates with high brain PG and 14 neonates with low brain PG (<1 mM) received phenobarbital as the only source of PG. Nine neonates did not receive any phenobarbital/PG-containing medication. Neonates with high brain PG more often received 10 mg/ml phenobarbital, resulting in higher PG dose (high vs. low brain PG (median [interquartile range]: 1400 [595] vs. 350 [595] mg/kg, respectively, P < 0.01). In addition, the interval between the last phenobarbital dose and MRI was shorter in the high brain PG group (high vs. low brain PG: 16 [21] vs. 95 [83] hours, respectively, P < 0.001). Within neonates that received phenobarbital, there was no conclusive correlation between spectroscopically detected PG and lactate (Spearman's rho = 0.23, P = 0.10). DATA CONCLUSION: These MRS findings may increase awareness of potentially toxic PG concentrations in the neonatal brain due to intravenous phenobarbital administration and its dependence on the phenobarbital formulation used. LEVEL OF EVIDENCE: 4 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2019;49:1062-1068.

In vivo evaluation of tumour acidosis for assessing the early metabolic response and onset of resistance to dichloroacetate by using magnetic resonance pH imaging.

Dichloroacetate (DCA) can reverse the glycolytic phenotype that is responsible of increased lactate production and extracellular pH acidification in cancer cells. Magnetic resonance imaging-chemical exchange saturation transfer (MRI-CEST) pH mapping is a novel non-invasive imaging approach that can measure in vivo extracellular tumour pH. We examined whether MRI-CEST pH mapping can monitor in vivo changes in tumour acidosis for assessing treatment response to DCA. Cell viability and extracellular pH were assessed in TS/A breast cancer cells treated with 1-10 mM DCA for 24 h in normoxia or hypoxia (1% O2) conditions. Extracellular tumour pH values were measured in vivo by MRI-CEST pH mapping of TS/A tumour-bearing mice before, three days and fifteen days after DCA or saline treatment. Reduced extracellular acidification and vitality were observed in DCA-treated TS/A cells. Tumour-bearing mice showed a marked and significant increase of tumour extracellular pH at 3 days post-DCA treatment, reflecting DCA-induced glycolysis inhibition, as confirmed by reduced lactate production. After 15 days of DCA treatment, the onset of resistance to DCA was observed, with recover of tumour extracellular acidification and lactate levels that returned to baseline values. A significant correlation was observed between tumour extracellular pH values and lactate levels (r= -0.97, P<0.05). These results suggest that MRI-CEST pH imaging is a promising tool to monitor the early response and efficacy of cancer metabolic targeting drugs.

Lymphoma and Lactic Acidosis.

A 39-year-old man presented with new onset of sinus congestion, shortness of breath, and diaphoresis. His laboratory tests were notable for hypercalcemia and lactic acidosis. A CT scan of the head demonstrated mild paranasal disease. CT scan of the chest, abdomen, and pelvis demonstrated omental caking with lymphadenopathy and a thickened loop of bowel in the left upper quadrant suggestive of lymphoma. All abdominal lesions seen in the CT were intensely F-FDG avid with diffuse uptake in the bone marrow. There was markedly decreased F-FDG uptake in both the brain and liver. Histopathology was positive for Burkitt lymphoma.

EARS2 mutations cause fatal neonatal lactic acidosis, recurrent hypoglycemia and agenesis of corpus callosum.

Mitochondrial aminoacyl tRNA synthetases are essential for organelle protein synthesis. Genetic defects affecting the function of these enzymes may cause pediatric mitochondrial disease. Here, we report on a child with fatal neonatal lactic acidosis and recurrent hypoglycemia caused by mutations in EARS2, encoding mitochondrial glutamyl-tRNA synthetase 2. Brain ultrasound revealed agenesis of corpus callosum. Studies on patient-derived skin fibroblasts showed severely decreased EARS2 protein levels, elevated reactive oxygen species (ROS) production, and altered mitochondrial morphology. Our report further illustrates the clinical spectrum of the severe neonatal-onset form of EARS2 mutations. Moreover, in this case the live-cell parameters appeared to be more sensitive to mitochondrial dysfunction compared to standard diagnostics, which indicates the potential relevance of fibroblast studies in children with mitochondrial diseases.

Unexpected primary osseous lymphoma as the cause of lactic acidosis in a patient suffering from pancreatitis.

A 45-year-old man was admitted due to acute pancreatitis. A severe lactic acidosis was found. Following active therapy, the signs and symptoms from pancreatitis was improved, but acidosis was exacerbated. FDG PET/CT images were acquired to investigate the etiology of lactic acidosis and/or other unknown pathology. The images showed widespread abnormal FDG activity in the bone marrows throughout the body, suggestive of hematologic malignancy, which was confirmed as primary osseous non-Hodgkin lymphoma following a histopathological examination of the bone marrow. Chemotherapy against lymphoma was initiated and status of the lactic acidosis was rapidly corrected.

Neuroradiologic findings in Sengers syndrome.

Sengers syndrome is characterized by a constellation of congenital cataracts, hypertrophic cardiomyopathy, skeletal myopathy, and lactic acidosis. Two forms of the disease have been described: a fatal neonatal form, and a more benign form in which patients live into their second or third decades. With the exception of time to death, no findings have distinguished these two forms. We present 3 cases of neonatal Sengers syndrome with significant central nervous system involvement, a finding not previously described. We suggest that the fatal neonatal form of Sengers syndrome would be more accurately described as a mitochondrial encephalomyopathy. Cranial imaging may help distinguish the two types of this syndrome.

Cerebral blood flow and glucose metabolism in mitochondrial disorders.

OBJECTIVE: To investigate cerebral metabolism by 2-[18F]fluorodeoxy-d-glucose (FDG) uptake using PET and cerebrovascular reverse capacity by transcranial Doppler sonography (TCD) in different mitochondrial diseases (mitochondrial myopathy; mitochondrial encephalopathy, lactacidosis, and stroke-like episodes [MELAS]; and chronic external ophthalmoplegia). BACKGROUND: Previous studies on individual patients with mitochondriopathies revealed abnormal accumulations of mitochondria in endothelium, smooth muscle cells, and pericytes of blood vessels in different parts of the nervous system (cerebrum, cerebellum, sural nerve) and skeletal muscle. On this basis, some investigators suggested a pathogenic role of vascular involvement in the MELAS syndrome and other encephalopathies. smhd1 DESIGN/METHODS: The authors investigated neuronal metabolism and cerebrovascular involvement with PET in 5 cases and with TCD with acetazolamide stimulation in 15 cases. The patients were divided into three groups: 1) interictal MELAS (n = 4); 2) progressive external ophthalmoplegia (n = 6); and 3) pure mitochondrial myopathy and neuropathy (n = 5). The results were compared with those from matched normal control subjects. The diagnoses were based on clinical phenotype as well as histopathologic and molecular analysis. RESULTS: Cerebral glucose uptake was impaired in all patients, both with and without CNS symptoms, particularly in the occipital and temporal lobes. The vasoreactivity of the small arterioles to acetazolamide did not differ significantly between the patients and healthy control subjects or between the different groups of mitochondrial disorders. CONCLUSIONS: MELAS does not appear to be a functional disturbance of arterioles leading to an ischemic vascular event. The clinical symptoms in MELAS are not the result of a mitochondrial angiopathy but are the consequences of a mitochondrial cytopathy affecting neurons or glia. There is no correlation between the decreased glucose metabolism and the duration of the disease.

Lactic acidosis and hypoglycemia in a patient with high-grade non-Hodgkin's lymphoma and elevated circulating TNF-alpha.

A 71-year-old patient with high-grade non-Hodgkin's lymphoma stage IVB, severe lactic acidosis and tumor-associated hypoglycemia is described. Endocrine causes of hypoglycemic episodes were excluded because of low serum concentrations of insulin and "insulin-like growth factor 1", and normal concentrations of growth hormone and thyroid hormone. Clinical conditions associated with lactic acidosis such as diabetes mellitus, biguanide intoxication, septicemia, acute hypoxemia, or circulatory insufficiency were ruled out. Enhanced glucose metabolism within the tumor was visualized by positron emission tomography employing 2-fluro-2-deoxy-D-glucose (FDG) as a tracer. A markedly elevated tumor necrosis factor-alpha (TNF-alpha) level was found which decreased after cytoreductive therapy paralleling the normalization of serum lactate. In contrast to the majority of cases of lymphoma-associated lactic acidoses reviewed to date, in our case lactate elimination was not reduced.

Cerebral oxygen and glucose metabolism and blood flow in mitochondrial encephalomyopathy: a PET study.

Cerebral blood flow (CBF), oxygen metabolism (CMRO2), and glucose metabolism (CMRGlc) were measured using positron emission tomography in five patients diagnosed as having mitochondrial encephalomyopathy. The molar ratio between the oxygen and glucose consumptions was reduced diffusely, as CMRO2 was markedly decreased and CMRGlc was slightly reduced. The CBF showed less changes. The CBF increase on hypercapnia was smaller than normal, though this was not significant. CBF with hypocapnia demonstrated a significant reduction compared with the normal. These results suggest that oxidative metabolism is impaired and anaerobic glycolysis relatively stimulated, due to a primary defect of mitochondrial function, and that mild lactic acidosis occurs in brain tissue because of impaired utilisation of pyruvate in the TCA cycle. As these findings appear to indicate directly a characteristic of this disease, such measurements may be a useful tool for assessment of the pathophysiology and for diagnosis of mitochondrial encephalomyopathy.

Idiopathic lactic acidemia with developmental delay and type 1 muscle fiber atrophy: report of two patients.

Two infants with generalized muscle hypotonia with mild muscle weakness and markedly delayed developmental milestones, had high lactate levels in serum and cerebrospinal fluid from early infancy. Biochemical and morphologic studies of biopsied muscles disclosed no abnormality except for type 1 fiber atrophy, which was quite different from patients with central nervous involvement with type 2 fiber atrophy. In both patients, the disease was not progressive and lactate levels gradually decreased. Although no metabolic defect was found, these patients probably shared common pathogenetic mechanism.

N-isopropyl-p-[123I]iodoamphetamine SPECT in MELAS syndrome: comparison with CT and MR imaging.

Regional cerebral perfusion was studied in three patients with the mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome, using single photon emission computed tomography (SPECT) with N-isopropyl-p-[123I]iodoamphetamine (IMP). Accumulation of the tracer was relatively decreased in the parietooccipital regions and also in the frontotemporal regions after stroke-like episodes. However, quantitative regional cerebral blood flow (rCBF) measurement showed that rCBF was relatively well preserved even at these sites, and a hyperemic state was observed at the sites of normal accumulation. IMP SPECT may be useful in the diagnosis and assessment of the progress of the MELAS syndrome.

HMPAO-SPECT imaging resembling Alzheimer-type dementia in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS).

Single-photon emission computed tomography (SPECT) of the brain using hexamethyl propylene amine oxime (HMPAO) was performed in a 37-year-old patient suffering from mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS). Reduced blood flow was observed bilaterally in the parieto-occipital regions (resembling Alzheimer type dementia) and in the right parietal lobe.

Mitochondrial encephalomyopathy (MELAS) with mental disorder. CT, MRI and SPECT findings.

A case of mitochondrial encephalomyopathy (MELAS) with mental disorder is reported. The SPECT study using 123I-iodoamphetamine (IMP) and MRI study revealed abnormality in the left parieto-occipital areas without abnormality in the brain CT or brain scintigram. These findings suggest a localized dysfunction of the brain capillary endothelium in association with the cerebral involvement of mitochondrial encephalomyopathy.

[The MELAS syndrome. Computed tomographic documentation of its course and magnetic resonance tomography]. / MELAS-Syndrom. Computertomographische Verlaufsdokumentation und Magnetresonanztomographie.

This is a case report on a patient with MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes). This study documents, by CT scan, the progression of the disease for 7 years. The first CT scan was normal; all subsequent CT scans were pathological. In addition, one MRI study was done.

Computed tomography and angiography in MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes); report of 3 cases.

Among mitochondrial encephalomyopathies, MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes, Pavlakis et al. 1983) is recognized as a distinct syndrome characterized by generalized convulsions and recurrent stroke-like episodes. The neuroradiological findings of three patients with MELAS are reported here. Retrospective review shows that MELAS should be included in the differential diagnosis of infarct-like lesions of the cerebrum.