Serum protein profiling by miniaturized solid-phase extraction and matrix-assisted laser desorption/ionization mass spectrometry.
Serum profiling by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) holds promise as a clinical tool for early diagnosis of cancer and other human diseases. Sample preparation is key to achieving reproducible and well-resolved signals in MALDI-MS; a prerequisite for translation of MALDI-MS based diagnostic methods to clinical applications. We have investigated a number of MALDI matrices and several miniaturized solid-phase extraction (SPE) methods for serum protein concentration and desalting with the aim of generating reproducible, high-quality protein profiles by MALDI-MS. We developed a simple protocol for serum profiling that combines a matrix mixture of 2,5-dihydroxybenzoic acid and alpha-cyano-4-hydroxycinnamic acid with miniaturized SPE and MALDI-MS. Functionalized membrane discs with hydrophobic, ion-exchange or chelating properties allowed reproducible MALDI mass spectra (m/z 1000-12,000) to be obtained from serum. In a proof-of-principle application, SPE with chelating material and MALDI-MS identified protein peaks in serum that had been previously reported for distinguishing a person diagnosed with breast cancer from a control. These preliminary results indicate that this simple SPE/MALDI-MS method for serum profiling provides a versatile and scalable platform for clinical proteomics.