Estimation of skeletal muscle concentrations of NAD+ and NR/NMN using 1-H MRS at 7T with measured T1 and T2 relaxation corrections

Motivation: NAD+, NR, and NMN are pivotal in cellular energy transformation processes critical for overall muscle health. Quantification in healthy muscle is crucial in order to be able to detect differences associated with metabolic disorders. Goal(s): To determine skeletal muscle metabolite concentrations with 1-H MRS. Approach: MRS was performed using a spectrally-selective, slice-localized spin-echo sequence optimized for sensitivity to low concentration, downfield resonances. Results: T1s and T2s are particularly short in skeletal muscle, with T1 about 50 ms for NAD+ and 100 ms for NR/NMN, and T2s around 10-15 ms for each. [NAD+] was found to be 0.9-1.0 mM, while [NR/NMN] was 400 μM. Impact: For the first time, concentrations of NAD+ and NR/NMN have been estimated in skeletal muscle in vivo noninvasively with 1-H MRS.