Development of water-in-oil microemulsions with the potential of prolonged release for oral delivery of L-glutathione.

Oral delivery of L-L-glutathione is quite a challenge due to the enzymatic and physical barriers in the gastrointestinal tract (GIT). Colloidal delivery systems such as microemulsions (ME) can be valuable for oral delivery of L-glutathione, because they may protect L-glutathione from enzymatic degradation and enhance its permeability across the intestinal epithelium. The aim of this study was to identify ME systems capable of accommodating maximum amounts of L-glutathione in internal aqueous phase intended for oral delivery. Pseudoternary phase diagrams for the systems based on a single or a blend of two oily components, one or two nonionic surfactants and an aqueous phase loaded with L-glutathione were constructed, identified and characterized in terms of morphological, rheological and in vitro release studies. Among the tested formulations, the coarse emulsions resulted in the highest release rate, while the ME and liquid crystal systems provided sustained release of L-glutathione in vitro. There was a linear relationship between the cumulative amount of L-glutathione released from the ME and the liquid crystals, and the square root of time indicting a diffusion controlled process. The release of L-glutathione from the ME and the liquid crystal was related to the concentration of L-glutathione remaining in the formulations. In conclusion, two novel delivery colloidal systems of L-glutathione loaded water-in-oil ME and liquid crystal systems were developed and characterized. In addition, a simple isocratic HPLC analytic method was developed and validated, and was used for the qualitative and quantitative analysis of L-glutathione released from the selected formulations.