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| Author(s): |
Maria Bernadete Riemma Pierre
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 1999-12-15 |
| Examining board members: |
Maria Vitoria Lopes Badra Bentley;
Erika Rosa Maria Kedor;
Antonio Claudio Tedesco
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| Advisor: | Maria Vitoria Lopes Badra Bentley |
| Abstract | |
Photodynamic Therapy (PDT) is a new treatment modality for skin cancer. which uses photosensitizers, located in the tumoral tissue and can produce the tissue destructuion by absorbing ligth of an appropriate wavelength and dose. After topical application of the porphyrins or its derivatives and other photosensitizers, the incidence of light lead to the production of singlet oxygen that cause the tumour necrosis. 5-aminolevulinic acid (5-ALA) is a pro-drug, that is an endogenous porphyrins precursor, mainly protoporphyrin IX (PplX), that is sinthetized in situ in a highly fluorescent substance in the heme biosynthetic pathway. However, most of these substances cross biological barriers poorly such as stratum corneum (SC) of the skin. Liposomes has been proposed as a skin drug localizers, improving in this way the biodistribution and consequently the local concentration of the drug, optimizing the cutaneous tumours topical therapy. This work has proposed the achievement of liposomes of lipidic composition similar to the mammalian SC as well as its evalluation. The liposomes were obtained by reverse phase evaporation technique following by extrusions and the formed vesicles were characterized by size exclusion chromatography on gel filtration. The average size vesicles was obtained by Dynamic Light Scattering and revelead an average size distribution around 500 nm. and it was significantly altered by 5-ALA (400, 1 nm). The vesicle observation on polarized light microscope has confirmed the liposome formation by Maltese crosses presence, indicative of the birrefringence properties of lipidic bilayers. DSC analysis has shown that there were an effective interaction among the lipids of the system. and the Tc was very close to the main Tc of SC lipids. In vitro 5-ALA permeation in liposomes was much smaller compared to the drug aqueous solution, while the in vitro retention of 5-ALA in the liposomal system was much higher. The encapsulation grade studies have shown a low 5-ALA encapsulation percentage in this system. Nevertheless, the application profile has shown appropriate to the topical application and thus, these obtained system with similar lipids, to those in the SC, can be explored as drug delivery systems for PDT-5-ALA topical of skin cancer. (AU) | |