Abstract
Ceramides are potent bioactive molecules in cells. However, they are very hydrophobic molecules, and difficult to deliver efficiently to cells. We have made fluid bilayers from a short-chain D-erythro-ceramide (C6-Cer) and cholesteryl phosphocholine (CholPC), and have used this as a formulation to deliver ceramide to cells. C6-Cer complexed with CholPC led to much larger biological effects in cultured cells (rat thyroid FRTL-5 and human HeLa cells in culture) compared to C6-Cer dissolved in dimethyl sulfoxide (DMSO). Inhibition of cell proliferation and induction of apoptosis was significantly more efficient by C6-Cer/CholPC compared to C6-Cer dissolved in DMSO. C6-Cer/CholPC also permeated cell membranes and caused mitochondrial Ca2+ influx more efficiently than C6-Cer in DMSO. Even though CholPC was taken up by cells to some extent (from C6-Cer/CholPC bilayers), and was partially hydrolyzed to free cholesterol (about 9%), none of the antiproliferative effects were due to CholPC or excess cholesterol. The ceramide effect was not limited to D-erythro-C6-Cer, since L-erythro-C6-Cer and D-erythro-C6-dihydroCer also inhibited cell priolifereation and affected Ca2+ homeostasis. We conclude that C6-Cer complexed to CholPC increased the bioavailability of the short-chain ceramide for cells, and potentiated its effects in comparison to solvent-dissolved C6-Cer. This new ceramide formulation appears to be superior to previous solvent delivery approaches, and may even be useful with longer-chain ceramides.
Highlights
Sphingolipids constitute an important group of lipids with specific structural and functional properties [1,2,3]
Formulations To measure the uptake and cellular association of [3H]chain D-erythro-ceramide (C6-Cer), FRTL-5 cells were exposed to 0.05 mM of [3H]C6-Cer (,0.011 mCi/mmol) complexed with cholesteryl phosphocholine (CholPC) or dissolved in dimethyl sulfoxide (DMSO)
Comparing the cellular uptake of [3H]C6-Cer from either [3H]C6-Cer/CholPC or [3H]C6-Cer/DMSO, it was observed that cell association of [3H]C6-Cer appeared to be more efficient from DMSO solvent compared to CholPC bilayers
Summary
Sphingolipids constitute an important group of lipids with specific structural and functional properties [1,2,3]. We have in this study compared the bioactivity of Nhexanoyl ceramide (C6-Cer) in two cell types (HeLa and rat thyroid FRTL cells) when presented to cells either as a complex with CholPC or dissolved in DMSO. Our results show that CholPC-complexed C6-Cer was much more potent in causing inhibition of proliferation, apoptosis, and disturbed Ca2+ homeostasis, as compared to solvent-delivered C6-Cer. We suggest that C6-Cer in a bilayer with CholPC provides a much better bioavailability, and can be successfully used to deliver ceramides to cells in culture.
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