RT Journal Article SR Electronic T1 Is proton magnetic resonance spectroscopy a valid method to quantify muscle carnosine in humans? JF bioRxiv FD Cold Spring Harbor Laboratory SP 568923 DO 10.1101/568923 A1 Vinicius da Eira Silva A1 Vitor de Salles Painelli A1 Samuel Katsuyuki Shinjo A1 Eduardo Maffud Cilli A1 Craig Sale A1 Bruno Gualano A1 Maria Concepción Otaduy A1 Guilherme Giannini Artioli YR 2019 UL http://biorxiv.org/content/early/2019/06/11/568923.abstract AB We aimed to examine the validity and reliability of Proton Magnetic Resonance Spectroscopy (1H-MRS) to quantify carnosine in human muscle. Phantoms containing different concentrations of pure carnosine, imidazole, histidine and protein (bovine serum albumin) were analyzed by 1H-MRS to verify signal linearity, and the influence of other sources of imidazole to carnosine signal. Carnosine was determined in the m. gastrocnemius by 1H-MRS and high-performance liquid chromatography (HPLC, reference method) in muscle biopsy samples. Signal quality was compared between in vivo and in vitro assessments. Test-retest reliability was determined with (n=10) and without (n=5) voxel repositioning and re-shimming. Convergent validity (n=16) was determined by comparing carnosine values obtained with 1H-MRS vs. HPLC. Discriminant validity (n=14) was determined by measuring carnosine before and after β-alanine supplementation. Carnosine signal showed excellent linearity within the physiological concentration range (2.5 to 50 mmol·L−1). A clear loss of quality was shown when carnosine was measured in vivo. Histidine and imidazole, but not protein, emitted quantifiable signals in the same chemical shift of carnosine. 1H-MRS coefficient of variation without repositioning voxel was 6.6% (ICC=0.924) and 16.9% (ICC=0.775) with voxel repositioning. 1H-MRS was able to detect a significant increase in muscle carnosine after β-alanine supplementation (p=0.04), but individual data analyses showed a substantial disagreement with HPLC. Comparison of 1H-MRS with HPLC showed poor convergent validity for 1H-MRS. In conclusion, 1H-MRS showed adequate discriminant validity, but limited reliability and poor agreement with a reference method. Low signal amplitude, low signal-to-noise ratio, and voxel repositioning are major sources of error.New & noteworthy Although most of the carnosine research relies on muscle carnosine determination by 1H-MRS, its validity remains unknown. We showed loss of signal quality and amplitude when carnosine is measured in vivo vs. pure carnosine, and poor test-retest reliability when voxel is repositioned. Although 1H-MRS was sensitive to detect mean group changes in muscle carnosine, poor agreement with a reference method was shown. 1H-MRS showed poor validity, suggesting that existing carnosine literature might need further re-examination.