Quantification of N^τ -Methylhistidine and N^π-Methylhistidine in Chicken Plasma by Liquid Chromatography–Tandem Mass Spectrometry

The concentration of Nτ-methylhistidine in plasma provides an index of skeletal muscle protein breakdown. This study aimed to establish a quantitative method for measuring the concentrations of Nτ-methylhistidine and its isomer Nπ-methylhistidine in chicken plasma, using liquid chromatography–tandem mass spectrometry with stable isotope dilution analysis. The acceptable linear ranges of detection were 1.56–50.00 μmol/L for Nτ-methylhistidine and 0.78–25.00 μmol/L for Nπ-methylhistidine. The proposed method detected changes in the plasma levels of Nτ-methylhistidine and Nπ-methylhistidine in response to fasting and re-feeding. These results suggest that the method developed in this study can be used for the simultaneous measurement of Nτ-methylhistidine and Nπ-methylhistidine in chicken plasma.