Neurochemistry of Hypomyelination Investigated with MR Spectroscopy

Chloride Voltage-Gated Channel 2 (CLCN2)-Related Leukoencephalopathy Exhibiting Reduced Choline Levels on Magnetic Resonance Spectroscopy

In this article, we report the third case of chloride voltage-gated channel 2 (CLCN2)-related leukoencephalopathy (CC2L) in Japan. The patient presented with headache, vertigo, and mild visual impairment. The CLCN2 variant of the patient, NM_004366.6:c.61dup, p.(Leu21Profs*27), was also found in two other Japanese patients as this variant is relatively common in the Japanese population. Magnetic resonance imaging (MRI) revealed T2 prolongation with reduced diffusion in the bilateral posterior limbs of the internal capsule, cerebral peduncles, and superior and middle cerebellar peduncles. Magnetic resonance spectroscopy (MRS) of normal-appearing white matter revealed decreased choline content. This represents the first evidence of decreased choline levels in CC2L, highlighting the superior sensitivity of MRS over MRI.

Folate receptor α deficiency - Myelin-sensitive MRI as a reliable biomarker to monitor the efficacy and long-term outcome of a new therapeutic approach

Cerebral folate transport deficiency, caused by a genetic defect in folate receptor α, is a devastating neurometabolic disorder that, if untreated, leads to epileptic encephalopathy, psychomotor decline and hypomyelination. Currently, there are limited data on effective dosage and duration of treatment, though early diagnosis and therapy with folinic acid appears critical. The aim of this long-term study was to identify new therapeutic approaches and novel biomarkers for assessing efficacy, focusing on myelin-sensitive MRI. Clinical, biochemical, structural and quantitative MRI parameters of seven patients with genetically confirmed folate receptor α deficiency were acquired over 13 years. Multimodal MRI approaches comprised MR-spectroscopy (MRS), magnetization transfer (MTI) and diffusion tensor imaging (DTI) sequences. Patients started oral treatment immediately following diagnosis or in an interval of up to 2.5 years. Escalation to intravenous and intrathecal administration was performed in the absence of effects. Five patients improved, one with a presymptomatic start of therapy remained symptom-free, and one with inconsistent treatment deteriorated. While CSF 5-methyltetrahydrofolate and MRS parameters normalized immediately after therapy initiation, myelin-sensitive MTI and DTI measures correlated with gradual clinical improvement and ongoing myelination under therapy. Early initiation of treatment at sufficient doses, considering early intrathecal applications, is critical for favorable outcome. The majority of patients showed clinical improvements that correlated best with MTI parameters, allowing individualized monitoring of myelination recovery. Presymptomatic therapy seems to ensure normal development and warrants newborn screening. Furthermore, the quantitative parameters of myelin-sensitive MRI for therapy assessments can now be used for hypomyelination disorders in general.

Creatine Chemical Exchange Saturation Transfer (Cr-CEST) Imaging Can Evaluate Cisplatin-induced Testicular Damage

PURPOSE

This study aimed to investigate the ability of creatine-chemical exchange saturation transfer (Cr-CEST) technique assessed through 7-T MRI to evaluate cisplatin-induced testicular damage.

METHODS

We used 8-10 weeks C57BL/6 mice (n = 10) that were divided into a control group (n = 5) and a cisplatin-treated group (n = 5). The cisplatin group received cisplatin at a dose of 15 mg/kg, via intraperitoneal injection, while the control group received saline. MR images of mouse testes were acquired under anesthesia 18 days after the injection using a horizontal 7-T scanner. The pulse sequence consisted of rapid acquisition with a relaxation enhancement (RARE) with magnetization transfer. The Z-spectra were collected using a 2000-ms saturation pulse at a B1 amplitude of 1.2 μT, with frequencies varying from -4.8 to +4.8 parts per million (ppm). Maps of magnetization transfer ratio with asymmetric analysis (MTRasym) were reconstructed at a Cr metabolite concentration of 1.8 ppm.

RESULTS

The Cr-CEST effect was significantly reduced in the cisplatin-treated group compared to the control group (MTRasym of control mice vs. cisplatin-treated mice: 6.9 [6-7.5] vs. 5.2 [4-5.5], P = 0.008). Correlation analysis revealed a strong correlation between the Cr-CEST effect and the pathological score (ρ = 0.93, P < 0.001).

CONCLUSION

Cr-CEST MRI can be useful for the evaluation of cisplatin-induced testicular damage in mice.

Magnetic Resonance Imaging and Spectroscopy Analysis in a Pelizaeus-Merzbacher Disease Rat Model

Pelizaeus−Merzbacher disease (PMD) is an X-linked recessive disorder of the central nervous system. We performed 7 Tesla magnetic resonance imaging of the brain in Tama rats, a rodent PMD model, and control rats, as well as evaluated the diagnostic values. In the white matter of the Tama rats, the T2 values were prolonged, which is similar to that observed in patients with PMD (60.7 ± 1.8 ms vs. 51.6 ± 1.3 ms, p < 0.0001). The apparent diffusion coefficient values in the white matter of the Tama rats were higher than those of the control rats (0.68 ± 0.03 × 10−3 mm2/s vs. 0.64 ± 0.03 × 10−3 mm2/s, p < 0.05). In proton magnetic resonance spectroscopy, the N-acetylaspartate (6.97 ± 0.12 mM vs. 5.98 ± 0.25 mM, p < 0.01) and N-acetylaspartate + N-acetylaspartylglutamate values of the Tama rats were higher (8.22 ± 0.17 mM vs. 7.14 ± 0.35 mM, p < 0.01) than those of the control rats. The glycerophosphocholine + phosphocholine values of the Tama rats were lower than those of the control rats (1.04 ± 0.09 mM vs. 1.45 ± 0.04 mM, p < 0.001). By using Luxol fast blue staining, we confirmed dysmyelination in the Tama rats. These results are similar to those of patients with PMD and other PMD animal models.

Quantitative Structural Brain Magnetic Resonance Imaging Analyses: Methodological Overview and Application to Rett Syndrome

Congenital genetic disorders often present with neurological manifestations such as neurodevelopmental disorders, motor developmental retardation, epilepsy, and involuntary movement. Through qualitative morphometric evaluation of neuroimaging studies, remarkable structural abnormalities, such as lissencephaly, polymicrogyria, white matter lesions, and cortical tubers, have been identified in these disorders, while no structural abnormalities were identified in clinical settings in a large population. Recent advances in data analysis programs have led to significant progress in the quantitative analysis of anatomical structural magnetic resonance imaging (MRI) and diffusion-weighted MRI tractography, and these approaches have been used to investigate psychological and congenital genetic disorders. Evaluation of morphometric brain characteristics may contribute to the identification of neuroimaging biomarkers for early diagnosis and response evaluation in patients with congenital genetic diseases. This mini-review focuses on the methodologies and attempts employed to study Rett syndrome using quantitative structural brain MRI analyses, including voxel- and surface-based morphometry and diffusion-weighted MRI tractography. The mini-review aims to deepen our understanding of how neuroimaging studies are used to examine congenital genetic disorders.

Impaired GABAergic and glutamatergic neurometabolic activity in aged mice brain as measured by 1 H-[13 C]-NMR spectroscopy

Healthy aging is associated with a decline in cognitive function, and is a major risk factor for many neurodegenerative diseases. Although, there are several evidence that brain mitochondrial function is altered with aging its significance at the cellular level is elusive. In this study, we have investigated mitochondrial TCA cycle and neurotransmitter cycle fluxes associated with glutamatergic, GABAergic neurons and astroglia in the cerebral cortex and hippocampus of young (6 months) and aged (24 months) C57BL6 mice by using ¹ H-[¹³ C]-NMR spectroscopy together with timed infusion of ¹³ C-labeled glucose and acetate. The ratio V_Cyc /V_TCA was determined from a steady-state [2-¹³ C]acetate experiment. Metabolic fluxes were obtained by fitting a three-compartment metabolic model to ¹³ C turnover of amino acids from glucose. Levels of glutamate, aspartate and taurine were reduced in the cerebral cortex, while glutamine and choline were elevated in the hippocampus of aged mice. Interestingly, the rate of acetate oxidation increased in the cerebral cortex, while the flux of mitochondrial TCA cycle of glutamatergic neurons decreased in the cerebral cortex (P < .0001) and hippocampus (P = .025) of aged mice. The glutamate-glutamine neurotransmitter cycle flux was reduced in the cerebral cortex (P < .0001). The GABAergic TCA cycle flux was reduced in the cerebral cortex (P = .0008), while GABA-glutamine neurotransmitter cycling flux was also reduced in the cerebral cortex (P = .011) and hippocampus (P = .042) of aged brain. In conclusion, the reduction in excitatory and inhibitory neurotransmitter activity of glutamatergic and GABAergic neurons in the cerebral cortex and hippocampus correlates qualitatively with declined cognitive function in aged mice.

Molecular Biomarkers in Multiple Sclerosis and Its Related Disorders: A Critical Review

Multiple sclerosis (MS) is a chronic autoimmune disease affecting the central nervous system (CNS) which can lead to severe disability. Several diseases can mimic the clinical manifestations of MS. This can often lead to a prolonged period that involves numerous tests and investigations before a definitive diagnosis is reached. As well as the possibility of misdiagnosis. Molecular biomarkers can play a unique role in this regard. Molecular biomarkers offer a unique view into the CNS disorders. They help us understand the pathophysiology of disease as well as guiding our diagnostic, therapeutic, and prognostic approaches in CNS disorders. This review highlights the most prominent molecular biomarkers found in the literature with respect to MS and its related disorders. Based on numerous recent clinical and experimental studies, we demonstrate that several molecular biomarkers could very well aid us in differentiating MS from its related disorders. The implications of this work will hopefully serve clinicians and researchers alike, who regularly deal with MS and its related disorders.