The metastability of glucosyl ceramide in aqueous phase: effect of hydration and phosphatidylcholines of various chain length

The thermotropic behavior of aqueous dispersions of glucosylceraroide and mixtures of (i) dimyristoylphosphatidylcholine-glucosylceramide; (ii) dipalmitoylphosphatidylcholineglucosylceramide; and (iii) egg phosphatidylcholine-glucosylceramide were investigated using differential scanning calorimetry. All these systems form a lamellar array in aqueous phase. Aqueous dispersions of glucocosylceramide exhibit complex thermotropic behavior due to the presence of metastable and stable gel allomorphs. This polymorphism results primarily from hydration-dehydration processes which involve head group-head group interactions. All three phosphatidylcholines disturb the complex thermotropic behavior of glucosylceramide. The data suggest that the interference with the intermolecular interactions among the glycosphingolipid molecules by phospholipid molecules is strongly dependent on the acyl chain of the phosphatidylcholine. This effect is directly related to phospholipid-glycosphingolipid molecular miscibility which is determined from the minimal mole % phosphatidylcholine required to abolish the complex thermotropic behavior of the cerebroside. Based on this criteria we found the following order of efficacy, dipalmitoylphosphatidylcholine > dimyristoylphosphatidylcholine >> egg-phosphatidylcholine (16.5 > 22.5 >> 60 mole %, phosphatidylcholine, respectively). Reducing the level of water below its saturation or replacing 50% of the water by ethylene glycol reduces this effect of the phosphatidylcholine. This supports the assumption that hydration and hydrogen bonding are involved. Phase separation occurs throughout all the phase diagrams of the egg phosphatidylcholine-glucosyl ceramide. This was not the case for the systems of the two disaturated phosphatidylcholines. The system of egg phosphatidylcholine-glucosyi ceramide may be of relevance to Gaucher's disease which is characterized by major accumulation of glucosyi ceramide in various organs.