Ceramide effects in the bicelle structure

This work describes the effects of the inclusion of ceramides with different chain lengths in the structure of bicelles formed by dimyristoylphosphocholine (DMPC) and dihexanoylphosphocholine (DHPC). By using a number of physical techniques we observed that the bicellar structures were affected by both the concentration and the type of ceramide. The 31P nuclear magnetic resonance showed that inclusion of the short chain ceramide in the system slightly affects the phosphorus resonance whereas the inclusion of the long chain ceramide promotes the differentiation of the peaks. The decrease in the ceramide chain length is associated with a less miscibility in DMPC. The values of d-spacing obtained by small angle X-ray scattering suggest that ceramides are organized in domains along the DMPC bilayer. The bicellar system studied supported the inclusion of 10 mol% of the long chain ceramide. This inclusion increased the particle size but did not affect the integrity of the structures. Freeze-fracture electron microscopy and dynamic light scattering techniques showed small bicelles with diameters around 15-20 nm and a low polydispersity index for this system. The inclusion of 10 mol% of the short chain ceramide in the bicellar system resulted in the formation of aggregates with two different morphologies: small rounded structures 15-20 nm in diameter and elongated structures 40 nm in length. The inclusion of 20 mol% of either of these two ceramides resulted in the formation of bigger structures in the range of 60-100 nm together with small bicelles.