Lipophilic Fluorophore Research Articles

Paramagnetic fluorescence quenching in a model membrane: a consideration of lifetime and temperature

To expand our understanding of paramagnetic quenching in membranes, the relationship between fluorophore excited-state lifetime (τ), temperature, and the collisional quenching was studied. Specifically, the ability of tempo to quench the steady-state and time-resolved emission from five lipophilic fluorophores (diphenylhexatriene, perylene, phenanthrene, pyrene, and triphenylene) partitioned into egg phosphatidylcholine (EggPC) liposomes was examined. Also, the temperature dependence of spin-labeled androstane to quench the emission (steady-state and time-resolved) from perylene in EggPC liposomes was determined. Unexpectedly, in EggPC liposomes, the apparent quenching efficiency decreased with increasing τ until the effect leveled off above ∼20 ns. Moreover, in EggPC liposomes, dynamic quenching decreased with increasing temperature. The results suggest that in membranes, paramagnetic quenching is more complex than generally recognized.

Tricyclic antidepressant-induced lipidosis in human peripheral monocytes in vitro, as well as in a monocyte-derived cell line, as monitored by spectrofluorimetry and flow cytometry after staining with nile red

Human mono- and lymphocytes from peripheral blood and the monoblastoid cell line U-937 were used in this in vitro study of drug-induced lipidosis. Mono- and lymphocytes were exposed for 4 days to three different tricyclic antidepressants (TCAs), imipramine (25 μM), clomipramine (10 μM) and citalopram (80 μM). The lipophilic fluorophore Nile red, which stains intracellular lipid structures selectively, was used as a lipid probe. Fluorescence microscopy, Spectrofluorimetry and flow cytometry were used to detect cellular lipidosis, as verified by electron microscopy. Our results demonstrate that imipramine, clomipramine and citalopram induce lipidosis in monocytes and U-937 cells, but not in lymphocytes. An accurate quantitation of induced intracellular lipidosis can be achieved by spectrofluorimetric and flow cytometric analysis.

How deep do intact liposomes penetrate into human skin?

Attempts were made to visualise intact liposomes in the human skin by fluoromicrography. To this end the aqueous compartment of the liposomes as well as the lipid bilayer were followed by labelling with hydrophilic and lipophilic fluorophores, respectively. Micrographs at various times after external application suggested that intact liposomes do not penetrate deeper than the horny layer.

Monitoring differential changes of the mobility of cell membrane components following treatment with a tumor promoter by using pyrene and a novel fatty acid fluorophore.

The effects of an active tumor promoter, 12-O-tetradecanoyl phorbol-13-acetate (TPA), on cell membrane components have been examined using two lipophilic fluorophores, pyrene and 12-[6-(N-methylanilino)-2-naphthalenesulfonyloxy]-stearic acid (MANSOS), in Chang liver cells. MANSOS has a high fluorescence quantum yield in water and shows a blue shift (15nm from the value of 445nm in phosphate buffer) of the emission maximum on incorporation into the cell membrane.Pretreatment of cells with TPA for 2 h induced differential changes in the fluorescence parameters of pyrene and MANSOS incorporated into the cell membrane; it decreased the lifetime and harmonic mean of the rotational relaxation time and amplified the quanching by KI of pyrene fluorescence, whereas it increased the harmonic mean of the rotational relaxation time and slightly attenuated the quenching of MANSOS fluorescence.Taken together, the findings suggest different partition characteristics of the two fluorescent probes in the cell membrane components, and differential effects of TPA on the two species of components as judged from the opposite mobility changes of the two probes.