A new technology is tested for enzyme encapsulation. The capsules are small multilamellar vesicles of surfactant called spherulites which are produced by shearing a lamellar phase under well-controlled conditions. Encapsulation of alkaline phosphatase into spherulites is studied here as an example. Once encapsulated, the enzyme is shown to be unable to develop any enzymatic activity on its substrate, the p-nitrophenylphosphate. This is due to the absence of contact between the enzyme and the substrate. Interestingly, the whole enzymatic activity is recovered after destruction of the vesicles. Encapsulation efficiency ranges between 70% and 95% depending upon the enzyme over phospholipids ratio. Beyond the example of alkaline phosphatase, many applications of spherulites in the medical or in the biotechnology fields seem now at hand.
Encapsulation of DNA in a new non-cationic multilamellar vector (Spherulites), composed of phosphatidylcholine, cholesterol and polyoxyethylene alcohol, is described here for the first time. Spherulites entrapping DNA were prepared by shearing a phospholipid lyotropic lamellar phase, using a recently discovered method. The average diameter of these vesicles ranges around 300 nm, and can be adjusted depending on the conditions of the process. The formulation did not result in cytotoxicity for the human cells and could be used as a DNA delivery system. More emphasis is brought to the role of condensing agents like histones on the encapsulation yield, which has been studied using radiolabelled DNA. It is shown that use of histones (histone to DNA ratio of 0.4) can increase significantly the encapsulation of DNA, thus improving the transfection efficiency. Transfection experiments were done with success using the beta-galactoside reporter gene on human primary cells (human skin fibroblasts and human bone marrow stromal cells). The results suggest that the spherulites have to be considered as a new and promising tool for gene transfection.
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