Using MALDI-TOF MS coupled with a high-mass detector to directly analyze intact proteins in thyroid tissues

Protein analysis is vital for biological and clinical research, but the measurement of unseparated, intact and high-mass proteins is also a challenging task by mass spectrometry-based methods. Here, we present a protocol for rapid and high-throughput analysis of intact proteins in tissue samples using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) combined with a high-mass detector platform. The method involves tissue specimens that undergo a simple protein extraction before MALDI-MS analysis. Using this method, the high abundance proteins in human thyroid carcinoma and paracarcinoma tissues were successfully investigated, and the mass spectra of the tissues of the 30 illustrated thyroid cancers showed remarkable differences. The peak intensity revealed a significant increase in human albumin in thyroid carcinoma tissues ( p <0.05). To validate the feasibility and credibility of this method, label-free proteomics quantitative analysis and Western blotting were used to relatively quantify the proteins in these tissues. Those results demonstrated a nearly 3-fold difference in human albumin levels between thyroid carcinoma and para-carcinoma tissues, which were consistent with the results of our method. The advantages of our method are easy sample handling, remarkable reproducibility and the ability to analyze high-mass proteins without digestion, which make them have the potential to be used in biological research and in clinical practice.