Fluorescence properties and staining behavior of monodansylpentane, a structural homologue of the lysosomotropic agent monodansylcadaverine

We have recently shown that monodansylcadaverine labels autophagic vacuoles . Analysis of the mechanism underlying the labeling revealed that monodansy lcadaverine acts as a lysosomotropic agent, being concentrated into acidic compartments by an ion-trapping mechanism, and as a solvent polarity probe, increasing its relative fluorescence intensity by interacting with membran e lipids that are highly concentrated in the autophagic vacuoles. In this s tudy, we synthesized three structurally related derivatives of monodansylca daverine, replacing the primary amino group of monodansylcadaverine with a neutral (dansylamylamine; MDH), a polar (dansylaminopentanol; MDOH), or an acidic group (danslaminovaleric acid; MDA), to replace the lysosomotropic c haracter of the marker. Whereas MDH showed a specific staining of autophagi c vacuoles, the polar and acidic derivatives did not show any staining. We further demonstrate that the MDH staining of autophagic vacuoles is indepen dent on the acidic pH and thus on an ion-trapping mechanism, but it still s hows the same preferences for autophagic membrane lipids as monodansylcadav erine. We propose that MDH can specifically interact with lamellar bod lyso somal marker ies of the autophagic type as a solvent polarity probe. Theref ore, dansylated aminopentane can be used as a specific marker for autophagi c vacuoles in vivo and in fixed cells.