Carnosine levels in the same individuals as measured by different modalities

Carnosine is an endogenous di-peptide (b-alanine -L- histidine) involved
in maintaining tissue homeostasis. It is most abundant in skeletal muscle
where its concentration has been determined in biopsy samples using tandem
mass spectrometry (MS-MS). Carnosine levels can also be assessed in intact
leg muscles by proton magnetic resonance spectroscopy (1H-MRS) or in blood
and urine samples using mass spectrometry. Nevertheless, it remains
uncertain how carnosine levels from these distinct compartments are
correlated with each other when measured in the same individual.
Furthermore, it is unclear which measurement modality might be most
suitable for large-scale clinical studies. Hence, in 31 healthy
volunteers, we assessed carnosine levels in skeletal muscle, via 1H-MRS,
and in erythrocytes and urine by MS-MS. While muscle carnosine levels were
higher in males, there was no sex-associated difference in urinary or
erythrocyte levels. In a linear regression model adjusted for age, sex,
race, and diet, there was a positive association between erythrocyte and
urinary carnosine. However, no association was observed between 1H-MRS and
erythrocytes or urinary measures. In the relationship between muscle
versus urinary and erythrocyte measures, females had a positive
association, while males did not show any association. We also found that
1H-MRS measures were highly sensitive to location of measurement. Thus, it
is uncertain whether 1H-MRS can accurately and reliably predict endogenous
carnosine levels. In contrast, urinary and erythrocyte carnosine measures
may be stable and in greater synchrony, and given financial and logistical
concerns, may be a feasible alternative for large-scale clinical studies.