Changes in the Serum and Tissue Levels of Free and Conjugated Sialic Acids, Neu5Ac, Neu5Gc, and KDN in Mice after the Oral Administration of Edible Bird’s Nests: An LC–MS/MS Quantitative Analysis

Abstract

Edible bird’s nests have a variety of biological activities, the main components of which are sialic acids. Sialic acids are a group of nine-carbon N-acetylated derivatives of neuraminic acid containing a keto group at position C2 and play important roles in many biological processes. To verify whether the oral administration of edible bird’s nests would change the content and distribution of sialic acid components in vivo, a liquid chromatography–mass spectrometry method for the quantitative analysis of sialic acid levels in serum and tissues was developed. In the negative ion mode, the mobile phases consist of 0.1% formic acid in water (A) and acetonitrile (v/v) (B). Isocratic elution was performed with 60% B for 0−15 min. The chromatographic separation was performed on a Morphling HILIC Amide column (2.1 mm × 150 mm, 5 μm) at a flow rate of 0.5 mL min−1. The results showed that the correlation coefficients of the typical calibration curves were all higher than 0.995, exhibiting good linearity. The levels of free and conjugated forms of N-glycolylneuraminic acid (Neu5Gc), N-acetylneuraminic acid (Neu5Ac), and 2-keto-3-deoxy-D-glycero-D-galactonononic acid (KDN) in the serum and different tissues were simultaneously detected after the oral administration of the edible bird’s nests at a daily dose of 300 and 700 mg Kg−1 for seven days in mice. Our study found that the oral administration of edible bird’s nests can significantly increase the concentration of total sialic acids (Neu5Gc + Neu5Ac + KDN) in serum and spleen and lungs tissues, which may be related to the anti-inflammatory and immune function of edible bird’s nest, but further studies are needed to verify this. Neu5Ac was the dominant sialic acid in brain tissue, and Neu5Gc was the dominant sialic acid in serum and other tissues, including heart, liver, spleen, lungs, and kidney. Moreover, we found that the forms of Neu5Ac and Neu5Gc were mainly conjugated in all groups except liver tissue. In conclusion, the method we established had good linearity and accuracy; it allowed the analytes to be effectively separated from the matrix and endogenous substances in serum or tissues, so it could effectively detect the distribution and concentration of free and conjugated forms of sialic acids in serum and tissues, which was beneficial to the research and exploitation of edible bird’s nests and sialic acids.