title: Direct-S: a directed mass spectrometry method for biomarker verification in native serum.
abstract: Serum has been the logical choice and most-used bio-specimen for monitoring biomarkers. However, direct analysis of low-abundance biomarkers in serum is still a problem. Here, we have established a directed mass spectrometry (inclusion list driven MS) method, Direct-S, for direct quantification of protein biomarkers in native serum samples without high-abundance protein depletion or pre-fractionation. In Direct-S, an (18)O-labeling technique was used to produce internal standards of the targeted peptides, and only targeted peptides were selected for tandem mass spectrometry (MS/MS) fragmentation to increase sensitivity and efficiency. The (16)O/(18)O ion pairs of target peptides and the elution time/fragmental pattern of the internal standards were used to facilitate the identification of the low-abundance peptides. Using Direct-S, three candidate biomarkers, α1-antitrypsin (A1AT), galectin-3 binding protein (LG3BP) and cathepsin D (CTSD), which represent different abundance levels, were quantified in serum samples of colorectal cancer (CRC) patients and healthy candidates. Direct-S exhibited good linearity of response from 20 fmol to 0.5 nmol (r > 0.9845). Reliable quantification across five orders of magnitude and as low as 71 pg μL(-1) was achieved in serum samples. In conclusion, Direct-S is a low cost, convenient and accurate method for verifying serum biomarkers.
authors: Shanghai Cancer Centre and Institutes of Biomedical Sciences, Fudan University, Shanghai 200032, P. R. China. luhaojie@fudan.edu.cn.
authors: Hong-Rui
authors: HR
authors: Yin
authors: Li-Qi
authors: LQ
authors: Xie
authors: Ye
authors: Y
authors: Xu
authors: San-Jun
authors: SJ
authors: Cai
authors: Jun
authors: J
authors: Yao
authors: Peng-Yuan
authors: PY
authors: Yang
authors: Hao-Jie
authors: HJ
authors: Lu
mesh_terms: D000595:Amino Acid Sequence; D014408:Biomarkers, Tumor / Q000097:blood* / Q000737:chemistry; D001774:Blood Chemical Analysis / Q000379:methods* / Q000592:standards; D015179:Colorectal Neoplasms / Q000097:blood; D006801:Humans; D013058:Mass Spectrometry / Q000379:methods* / Q000592:standards; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000097:blood / Q000737:chemistry; D012015:Reference Standards
chemical_list: D014408:Biomarkers, Tumor; D009363:Neoplasm Proteins