NAD is an essential metabolite that exists in NAD + or NADH form in all living cells. Despite its critical roles in regulating mitochondrial energy production through the NAD + /NADH redox state and modulating cellular signaling processes through the activity of the NAD + -dependent enzymes, the method for quantifying intracellular NAD contents and redox state is limited to a few in vitro or ex vivo assays, which are not suitable for studying a living brain or organ. Here, we present a magnetic resonance (MR) -based in vivo NAD assay that uses the high-field MR scanner and is capable of noninvasively assessing NAD + and NADH contents and the NAD + /NADH redox state in intact human brain. The results of this study provide the first insight, to our knowledge, into the cellular NAD concentrations and redox state in the brains of healthy volunteers. Furthermore, an age-dependent increase of intracellular NADH and age-dependent reductions in NAD + , total NAD contents, and NAD + /NADH redox potential of the healthy human brain were revealed in this study. The overall findings not only provide direct evidence of declined mitochondrial functions and altered NAD homeostasis that accompany the normal aging process but also, elucidate the merits and potentials of this new NAD assay for noninvasively studying the intracellular NAD metabolism and redox state in normal and diseased human brain or other organs in situ.redox state | NAD | in vivo 31 P MR spectroscopy | human brain | aging N AD, a multifunctional metabolite found in all living cells, has been the interest of many scientific investigations since its discovery in the early 20th century (1). NAD is known to convert between its oxidized NAD + and reduced NADH forms during the breakdown of nutrients; hence, the intracellular NAD + /NADH redox state reflects the metabolic balance of the cell in generating ATP energy through oxidative phosphorylation in mitochondria and/or glycolysis in cytosol (2). More recently, after several protein families associated with cell survival were found to use NAD + as their main substrate with activities also regulated by the availability of the NAD + , the full extent of the NAD's function as a metabolic regulator began to unfold (3-5). A growing number of studies have indicated that NAD + can modulate metabolic signaling pathways and mediate important cellular processes, including calcium homeostasis, gene expression, aging, degeneration, and cell death; therefore, the cellular NAD could serve as a therapeutic target for treating various metabolic or age-related diseases and promoting longevity (6-12).Despite the critical relevance of the intracellular NAD metabolism to human health and diseases, assessment of NAD contents and NAD + /NADH redox state is extremely challenging. Only a few invasive techniques based on biochemical assays or autofluorescence methods have been used to analyze tissue samples or cell extracts (13,14). However, during the preparation of such ex vivo sample, the NAD + and NADH contents are likely altered, beca...

Background Restless legs syndrome (RLS) is a neurological disorder characterized by a strong urge to move the legs and has been linked in many studies with abnormally low brain iron. Iron deficiency is associated with hypomyelination in brains of animals. Therefore we hypothesized that a myelin deficit should be present in the brains of patients with RLS. Methods We performed western blot analysis on myelin isolated from RLS (n=11) and control (n=11) brain tissue obtained at autopsy for the expression of the integral myelin proteins, myelin basic protein (MBP), and proteolipid protein (PLP) and the oligodendrocyte specific enzyme 3’5’-cyclic nucleotide phosphohydrolase (CNPase). To expand the postmortem findings to in vivo, we analyzed the brains of RLS patients (n=23) and controls (n=23) using Voxel-based morphometry (VBM). Results The expression of MBP, PLP and CNPase in the myelin from RLS was decreased by approximately 25% (p<0.05) compared to controls. The amounts of transferrin (Tf) and H-ferritin (H-Frt) in the myelin fraction were also significantly decreased in RLS compared to controls. The imaging analysis revealed significant small decreases in white matter volume in RLS patients compared to controls in the corpus callosum, anterior cingulum and precentral gyrus. Conclusion A decrease in myelin similar to that reported in animal models of iron deficiency was found in the brains of individuals with RLS. The evidence for less myelin and loss of myelin integrity in RLS brains, coupled with decreased ferritin and transferrin in the myelin fractions, is a compelling argument for brain iron insufficiency in RLS. These data also indicate the need to look beyond the sensorimotor symptoms that typically define the syndrome and its assumed relationship to the dopaminergic system. Understanding the full range of RLS pathology may help us better understand the complex, intermittent nature and diversity of the clinical features of RLS and expand our consideration of treatment options for RLS.

Cellular ATP energy metabolism and regulation are essential for brain function and health. Given the high ATP expenditure at resting-state, it is not yet clear how the human brain at working-state can effectively regulate ATP production to meet higher energy requirement. Through quantitative measurement of regional cerebral ATP production rates and associated neurophysiological parameters in human visual cortex at rest and during visual stimulation, we found significant stimulus-induced and highly correlated neuroenergetic changes, indicating distinctive and complementary roles of the ATP synthesis reactions in supporting evoked neuronal activity and maintaining ATP homeostasis. We also uncovered large individual variances in the neuroenergetic responses and significant reductions in intracellular [H] and free [Mg] during the stimulation. These results provide new insights into the mechanism underlying the brain ATP energy regulation and present a sensitive and much-needed neuroimaging tool for quantitatively assessing neuroenergetic state in healthy and diseased human brain.

Our results provide in vivo evidence of morphologic changes in the primary somatosensory system, which could be responsible for the sensory functional symptoms of RLS. These results provide a better understanding of the pathophysiology underlying the RLS sensory symptoms and could lead to a potential imaging marker for RLS.

In vivo31P MRS provides a unique and important imaging tool for studying high-energy phosphate metabolism and bioenergetics noninvasively. However, compared to 1H MRS, 31P MRS with a relatively low gyromagnetic ratio (γ) has a lower and limited sensitivity even at ultrahigh field. The proof of concept has been recently demonstrated that the use of high dielectric constant (HDC) materials between RF coil and object sample could increase MRI signal and reduce required RF transmission power for reaching the same RF pulse flip angle in the region of interest. For low-γ MRS applications operated at relatively lower frequency, however, it demands the dielectric materials with a much higher permittivity for achieving optimal performance. We conducted a 31P MRS imaging study using ultra-HDC (uHDC; with a relative permittivity of ~1200) material blocks incorporated with an RF volume coil at ultrahigh field of 7.0 T. The experimental results from phantom and human calf muscle demonstrate that the uHDC technique significantly enhanced RF magnetic transmit field ( B1+) and reception field ( B1-) and the gain could reach up to two folds in the tissue near the uHDC blocks. The overall results indicate that the incorporation of the uHDC materials having an appropriate permittivity value with a RF coil can significantly increase detection sensitivity and reduces RF transmission power for X-nuclei MRS applications at ultrahigh field. The uHDC technology could provide an efficient, cost-effective engineering solution for achieving high detection sensitivity and concurrently minimizing tissue heating concern for human MRS and MRI applications.

Characterization of the microstructural properties and topography of the human corpus callosum (CC) is key to understanding interhemispheric neural communication and brain function. In this work, we tested the hypothesis that high-resolution T 1 relaxometry at high field has adequate sensitivity and specificity for characterizing microstructural properties of the human CC, and elucidating the structural connectivity of the callosal fibers to the cortices of origin. The highresolution parametric T 1 images acquired from healthy subjects (N=16) at 7 Tesla clearly showed a consistent T 1 distribution among individuals with substantial variation along the human CC axis, which is highly similar with the spatial patterns of myelin density and myelinated axon size based on the histology study. Compared to the anterior part of the CC, the posterior mid-body and splenium had significantly higher T 1 values. In conjunction with T 1-based classification method, the splenial T 1 values were decoded more reliably compared to a conventional partitioning method, showing a much higher T 1 value in the inferior splenium than in the middle/superior splenium. Moreover, the T 1 profile of the callosal subdivision represented the topology of the fiber connectivity to the projected cortical regions: the fibers in the posterior midbody and inferior splenium with a higher T 1 (inferring a larger axon size) were mainly connected to motor-sensory and visual cortical areas, respectively; in contrast, the fibers in the anterior/posterior CC with a lower T 1 (inferring a smaller axon size) were primarily connected to the frontal/parietal-temporal areas. These findings indicate that high-resolution T 1 relaxometry imaging could provide a complementary and robust neuroimaging tool,useful for exploring the complex tissue properties and topographic organization of the human corpus callosum.

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