Open Access

Anton Oertl, Emmanouil Antonopoulos, Seruni Udyaningsih-Freisleben, Hans-Joachim Freisleben

• Background: 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.
• Latar belakang: Membran arkea memiliki lipid fitanil eter yang berbeda dengan ester asam lemak-gliserol dari sel bakteri dan sel eukariotik. Spesies Sulfolobus dan spesies Thermoplasma memiliki tetraeter lipid (TEL) unik sepanjang membran yang membentuk liposom stabil. Spesies Thermoplasma dari Tangkuban Perahu sudah berhasil dikultur dan TEL diisolasi. Pada penelitian ini, kami mengamati secara in vitro transfer carboxyfluorescein (CF) dari liposom TEL yang stabil ke sel karsinoma kolon dalam kultur. Metode: TEL diekstraksi dari kultur sel Thermoplasma dengan kloroform-metanol (1:1), kemudian difraksinasi dan dimurnikan melalui kolom dietilaminometil-selulose-asetat dan arang diaktivasi untuk pembentukan liposom yang stabil. Untuk menguji pertukaran fluoresensi, TEL liposom diisi dengan CF yang dapat larut dalam air. Pewarnaan diuji dengan berbagai kultur sel dan untuk percobaan utama dipilih sel karsinoma usus T84. Stabilitas liposom diuji melalui ukurannya dengan menggunakan light scattering particle sizer dan mikroskop elektron, serta melalui pelepasan CF non-spesifik pada pH rendah (6,0–7,4) dan suhu sangat tinggi (4–50°C/70°C). Hasil: Liposom TEL mempunyai stabilitas tinggi dan permeabilitas proton yang sangat kecil pada pH rendah. Pewarnaan CF sel karsinoma usus T84 dengan liposom TEL terlihat lebih intensif daripada dengan liposom dipalmitoylphosphatidylcholine. Kesimpulan: Hasil percobaan in vitro tersebut memperlihatkan transfer CF ke sel karsinoma kolon dan liposom TEL mempunyai stabilitas tinggi pada pH rendah, sesuai dengan kondisi di jalur gastro-intestinal dan di dalam sistem uro-genital. Oleh karena itu, penelitian in vivo tentang fotosensitizer fluoresensi liposomal untuk aplikasi lokal pada terapi fotodinamik kanker dalam usus besar dan kandung kemih sangat perlu dilakukan.