MALDI-TOF mass spectrometry of Aβ peptide variants in conditioned medium of human glioblastoma cells stably transfected with an APP cDNA harboring a triplet of FAD-linked missense mutations (“Swedish”_670/671 plus “Indiana”₇₁₇). In the top panel, the cells were treated with the dimethyl sulfoxide (0.1% vol/vol) vehicle alone. The medium was harvested, immune precipitated with the mAb 4G8, and subjected to MALDI-TOF analysis. In the middle panel, the cells were treated with 10 μM SIB-1405 in 0.1% DMSO for 16 hours. The medium was analyzed as described in the text. In the bottom panel, the cells were treated with 10 μM SIB-1281 in 0.1% DMSO for 16 hours, and medium was prepared as described in the text. The 12–28 Aβ peptide standard serves as a positive control that is added to medium before the immune precipitation step in order to assess quantitative recovery of peptides.