Ceramide-1-phosphate, in contrast to ceramide, is not segregated into lateral lipid domains in phosphatidylcholine bilayers.

ABSTRACT

Sphingolipids are key lipid regulators of cell viability ceramide is one of the key molecules in inducing programmed cell death (apoptosis), whereas other sphingolipids, such as ceramide 1-phosphate, are mitogenic. The thermotropic and structural behavior of binary systems of N-hexadecanoyl-D-erythro-ceramide (C(16)-ceramide) or N-hexadecanoyl-D-erythro-ceramide-1-phosphate (C(16)-ceramide-1-phosphate; C(16)-C1P) with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) was studied with DSC and deuterium nuclear magnetic resonance ((2)H-NMR). Partial-phase diagrams (up to a mole fraction of sphingolipids X = 0.40) for both mixtures were constructed based on DSC and (2)H-NMR observations. For C(16)-ceramide-containing bilayers DSC heating scans showed already at X(cer) = 0.025 a complex structure of the main-phase transition peak suggestive of lateral-phase separation. The transition width increased significantly upon increasing X(cer), and the upper-phase boundary temperature of the mixture shifted to approximately 65 degrees C at X(cer) = 0.40. The temperature range over which (2)H-NMR spectra of C(16)-ceramide/DPPC-d(62) mixtures displayed coexistence of gel and liquid crystalline domains increased from approximately 10 degrees for X(cer) = 0.1 to approximately 21 degrees for X(cer) = 0.4. For C16-C1P/DPPC mixtures, DSC and (2)H-NMR observations indicated that two-phase coexistence was limited to significantly narrower temperature ranges for corresponding C1P concentrations. To complement these findings, C(16)-ceramide/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and C16-C1P/POPC mixtures were also studied by (2)H-NMR and fluorescence techniques. These observations indicate that DPPC and POPC bilayers are significantly less perturbed by C(16)-C1P than by C(16)-ceramide and that C(16)-C1P is miscible within DPPC bilayers at least up to X(C1P) = 0.30.