Development of novel phospholipid drug delivery systems for topical antimicrobial therapy

Učinkovita topikalna terapija infekcija kože te prevencija stvaranja biofilmova i razvoja rezistencije mikroorganizama od velikog su medicinskog značaja. Cilj ovog rada bio je razviti biorazgradljiv, djelotvoran i siguran terapijski sustav za topikalnu antimikrobnu terapiju, zasnovan na fosfolipidnim vezikulama (liposomima) uklopljenima u kitozansku podlogu. U tu svrhu pripravljeno je i evaluirano nekoliko tipova liposoma s uklopljenim azitromicinom (AZT) različitog naboja na površini i čvrstoće/elastičnosti fosfolipidnih dvoslojeva: konvencionalni liposomi (CL), deformabilni liposomi (DL), propilenglikol liposomi (PGL) i kationski liposomi (CATL). Čvrstoća/elastičnost fosfolipidnih dvoslojeva AZT-liposoma utjecala je na fizičku stabilnost, profil oslobađanja AZT-a i lokalizaciju antibiotika u koži. Najsporije oslobađanje AZT-a, te odlaganje na površini kože, postignuto je CATL-om, karakteriziranim čvrstim dvoslojevima. Elastični liposomi (DL i PGL) pokazali su brže oslobađanje te nakupljanje AZT-a u unutrašnjosti kože. Svi AZT-liposomi pokazali su antibakterijski učinak na MRSA kliničke izolate, pri čemu su minimalne biofilm inhibitorne koncentracije bile i do 32 puta manje od onih utvrđenih za AZT-otopinu. Najjači anti-MRSA učinak imali su CATL, potom slijede DL, PGL i CL. Svi AZT-liposomi bili su biokompatibilni s keratinocitima i fibroblastima, čak i pri značajno većim koncentracijama AZT-a od pripadajućih minimalnih inhibitornih koncentracija i minimalnih biofilm inhibitornih koncentracija. Uklapanjem AZT-liposoma u kitozansku podlogu produljeno je oslobađanje AZT-a i postignuta prikladna viskoznost za topikalnu primjenu na kožu. Anti-MRSA učinak svih formulacija liposomi-u-podlozi bio je znatno veći od onog postignutog s kontrolom. Teksturna analiza ispitivanih formulacija liposomi-u-podlozi pokazala je prikladnu čvrstoću, kohezivnost i adhezivnost formulacija, posebice PGL-u-podlozi, a koje su direktno povezane s njihovom primjenom i zadržavanjem na koži. Uzimajući u obzir rezultate svih provedenih ispitivanja, formulacija CATL-u-podlozi bila bi prikladna za liječenje MRSA-om uzrokovanih infekcija kod kojih je potrebna lokalizacija antibiotika u površinskim slojevima kože, dok bi formulacija PGL-u-podlozi omogućila bolju dostavu antibiotika u dublje slojeve kože. Međutim, potrebno je provesti in vivo animalna ispitivanja terapijske učinkovitosti kako bi se te pretpostavke i potvrdile.Effective topical therapy of complicated skin infections, prevention of biofilm formation and antimicrobial resistance is of great medical importance. The aim of this research was to develop a biodegradable, efficient and safe delivery system for topical antimicrobial therapy, based on the drug-loaded phospholipid vesicles (liposomes) incorporated into the chitosan-based vehicle. For that purpose several types of azithromycin-loaded (AZT) liposomes with different surface charges and rigidity/elasticity of (phospho)lipid bilayers have been prepared and evaluated: conventional liposomes (CLs), deformable liposomes (DLs), propylene glycol-embedding liposomes (PGLs) and cationic liposomes (CATLs). The rigidity/elasticity of AZT-loaded liposomes influenced their physical stability, AZT release profile and its localization inside the skin. The slowest release and deposition of AZT on the skin surface was achieved by CATLs, characterized with rigid bilayers, whereas elastic liposomes (DLs and PGLs) demostrated faster release and accumulation of the drug within the skin. All AZT-loaded liposomes showed antibacterial activity against MRSA clinical isolates, with minimal biofilm inhibitory concentrations up to 32-fold lower than those determined for the AZT-solution. The strongest anti-MRSA effect was demonstrated by CATLs, followed by DLs, PGLs and CLs. All AZT-loaded liposomes were biocompatible with keratinocytes and fibroblasts, even at AZT concentrations significantly higher than the corresponding minimal inhibitory concentrations and minimal biofilm inhibitory concentrations. Incorporation of AZT-loaded liposomes into the chitosan vehicle resulted in the prolonged AZT release and viscosity appropriate for skin application. AZT-liposomes incorporated into chitosan vehicle, especially CATL-in-vehicle, demonstrated significantly enhanced anti-MRSA effect, as compared to the chitosan vehicle embedding AZT-solution. Texture analysis of AZT-liposomes incoroporated into chitosan vehicle showed a suitable hardness, cohesiveness and adhesiveness, in particular PGL-in-vehicle, which are directly related to their skin application and retention. Considering the results of all the experiments performed, CATL-in-vehicle would be suitable for the treatment of MRSA-infections requiring localization of the antibiotic in the upper layers of the skin, while PGL-in-vehicle facilitates delivery of AZT into deeper skin layers. However, further in vivo animal studies are necessary to confirm those assumptions