The present invention relates to methods and compositions for modulating levels of amyloid-β peptide (Aβ) exhibited by non-neuronal (i.e., peripheral) cells, fluids, or tissues. The invention also relates to modulation of Aβ levels via selective modulation (e.g., inhibition) of γ-secretase activity. The invention also relates to methods of preventing, treating or ameliorating the symptoms of a disorder, including but not limited to an Aβ-related disorder, by administering a compound that result in the modulation of γ-secretase in a non-neuronal tissue, either directly or indirectly to prevent, treat or ameliorate the symptoms of a brain Aβ disorder, such as Alzheimer's disease.