Stable archaeal tetraether lipid liposomes for photodynamic application: transfer of carboxyfluorescein to cultured T84 tumor cells
Abstract: Archaeal membranes
have phytanyl ether lipids instead of common fatty acid-glycerol esters in
bacterial and eukaryotic cells. Sulfolobus and Thermoplasma species have unique
membrane-spanning tetraether lipids (TEL), which form stable liposomes.
Recently, we cultured Thermoplasma species from the Indonesian volcano
Tangkuban Perahu and isolated TEL. The purpose of this in vitro study is to
investigate the transfer of fluorescent dye from stable TEL liposomes to
cultured colon carcinoma cells.
Methods: TEL was extracted from cultured cells with chloroform-methanol
(1:1), then it was fractionated and purified via diethylaminoethyl-cellulose-acetate
columns and activated charcoal for the formation of stable liposomes. For the
fluorescence exchange assay, TEL liposomes were loaded with water-soluble
carboxyfluorescein (CF). Staining experiments were conducted with various cell
cultures, and T84 colon carcinoma cells were chosen for the main experiments.
Liposome stability was tested by light scattering and electron microscopic size
determinations as well as by unspecific CF release at low pH (6.0–7.4) and
increased temperature (4–50°C/70°C).
Results: TEL liposomes exhibit high stability and extremely low proton
permeability at low pH. CF staining of cultured T84 colon carcinoma cells
appeares more intensive from TEL liposomes than from
dipalmitoylphosphatidylcholine liposomes.
Conclusion: The results of this in vitro study demonstrate CF staining of
colon carcinoma cells and high stability of TEL liposomes at low pH, matching
the condition in the gastro-intestinal (GI) route and in the urogentital (UG)
tract. For this reason, in vivo studies on liposomal fluorescent
photosensitizers for topical application of photodynamic cancer therapy in the
GI and UG tracts should be carried out.
Keywords: archaea;
archaeosomes; carboxyfluorescein; liposomes; T84 colon carcinoma cells;
tetraether lipid; Thermoplasma
Author: Anton Oertl, Emmanouil
Antonopoulos, Seruni U. Freisleben, Hans-Joachim Freisleben
Journal Code: jpkedokterangg160315
