Abstract
Nicotinamide adenine dinucleotide (NAD) is an important cofactor of energy-producing pathways. The redox ratio (NAD+/NADH) reflects the cellular oxidoreductive state. Oxidative stress and redox dysregulation have been suggested to contribute to various neurological diseases. The assessment of NAD content has been recently demonstrated in large animals and human brains by 31P magnetic resonance spectroscopy. However, its measurement in small rodents has never been attempted. The purpose of this study was to investigate, in vivo, the NAD content during mouse brain neurodevelopment. 31P-MR-spectra were acquired in the mouse brain at postnatal days P20, P40, P90 and P250 at 14.1 T using a 3D-localization sequence. High spectral quality was achieved at 14.1 T. NAD+ and NADH were quantified with mean Cramér-Rao lower bound of 10% and 14%, respectively. An increase in NAD+/NADH was observed from P20 to P250 due to a decrease in [NADH]. The intracellular pH was significantly reduced with age, while the free [Mg2+] in the brain was significantly increased. This study demonstrates for the first time the feasibility of the measurement of NAD content in vivo in mouse brains during development, which opens the prospect of longitudinally studying energy metabolism and redox dysfunction in mouse models of brain pathology.
Highlights
Nicotinamide adenine dinucleotide (NAD) is an important cofactor of energy-producing pathways
At P250, the positive correlation between NADH and the [Mg2+] (R2 = 0.8276; P = 0.032) was again observed. This is the first in vivo study demonstrating the measurement of NAD content and redox state during mouse brain development
The high sensitivity and spectral resolution at 14.1 T allowed excellent spectral quality and permitted us to highlight the increase in the redox ratio (RR) during development from P20 to P250 together with reductions in PME/PDE and p Hint and an increase in [Mg2+]
Summary
Nicotinamide adenine dinucleotide (NAD) is an important cofactor of energy-producing pathways. The redox ratio ( NAD+/NADH) reflects the cellular oxidoreductive state. Two ex vivo approaches have generally been used for the assessment of NAD contents: one is based on autofluorescence of the intracellular NADH signal, and the other relies on biochemical analysis. Autofluorescence provides a weak endogenous signal in living cells that is derived mainly from mitochondrial compartments This approach suffers from low detection sensitivity and limited tissue penetration, with the major drawback. The biochemical analysis effectuated with HPLC, capillary electrophoresis or enzymatic cycling assays requires a tissue biopsy and some extraction prior to a nalysis[15,16,17] This process might lead to large quantification errors for the highly sensitive redox pairs that have been shown to be rapidly altered after death[18,19]
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