Multireaction monitoring of 12 peptides for lowered immunity screening.

A multireaction monitoring method using high-performance liquid chromatography-tandem mass spectrometry was developed for 12 target peptides for determination of endogenous peptide concentrations in human serum. Chromatographic separation conditions were optimized and recoveries for liquid-liquid extraction, solid-phase extraction (SPE), and ultrafiltration of endogenous peptides from human serum were compared, and the SPE method was selected for 12 targeted peptide extractions. The optimized SPE method gave recoveries higher than 60 % for all targeted peptides. The limit of detection was 10 ng/ml for most peptides, except for N-formyl-methionyl-leucyl-phenylalanine (NFMLP) and adrenocorticotropic hormone (ACTH) (18-39). The limit of detection for these two peptides was 1 ng/ml. The real serum samples of 25 elderly and 23 young people were analyzed using the optimized extraction and analysis method. Half of the 12 peptides were below the limit of quantification, and B-type natriuretic peptide, cholecystokinin, ACTH(7-38), substance P, NFMLP, and valyl-glutamyl-prolyl-isoleucyl-prolyl-tyrosine were quantified in the concentration range from 0.1 to 50 ng/ml. The concentration of ACTH(7-38) was significantly higher in elderly people and that of NFMLP was significantly lower in elderly people compared with young people (p < 0.0001). This result implies that there be a possible relationships between ACTH, NFMLP and lowered immunity.