Gaseous NO has been recognized as a potent antibiotic even against highly drug-resistant pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) in both animal and human studies. However, difficulties in the delivery of the toxic (and reactive) gas demands innovative techniques to deliver NO in a controlled manner to malignant sites throughout the body. Metal nitrosyls reported by our group have demonstrated rapid NO release under the complete control of visible and NIR light. Careful incorporation of these photoactive nitrosyls into polymer matrices has afforded a set of nitrosyl-polymer composites in order to localize the NO-donors at a targeted site, ensure reliable NO release kinetics in vivo, and prevent potentially cytotoxic interactions of the metal nitrosyl or its reaction-products with the treatment site. The work presented in this thesis was pursued to derive clinically relevant NO-delivery systems and demonstrate their utility for the treatment of infection.
In chapter 2, an NO-releasing polyurethane film (PUX-NO) is described with dispersed xerogel particles containing up to 3 mol% of [Mn(PaPy3)(NO)](ClO4) entrapped in a silica matrix and swelled with excess moisture. The polyurethane based xerogel-nitrosyl (PUX-NO) films demonstrated rapid NO photorelease upon illumination with low-power visible light which was sufficient to eradicate clinically relevant loads (105 CFU mL-1) of several gram-positive and gram-negative pathogenic bacteria, including a strain of methicillin-resistant of S. aureus. The results of this study suggest that PUX-NO films are suitable for use as a NO-releasing occlusive film for the treatment of skin and soft-tissue infections or chronic, non-healing wounds. Since the NO-release rate from the films can be modulated by simple adjustment of the intensity of the light source, the films could be used to first clear the microbial burden from the wound site using high fluxes of NO, and then, provide a moderate, sustained flux of NO in order to accelerate the wound healing process and mitigate the potential for recurrent infections.
Chapter 3 details the incorporation of a photoactive Mn nitrosyl in the mesopores of a MCM-41 type silicate to afford {Mn-NO}@MCM-41. To increase the interaction between the nitrosyl and the MCM-41 pore walls, an aluminosilicate-based material (Al-MCM-41) was used with 3 mol% AlIII substituted for tetrahedral SiIV sites, which introduced negative point charges capable of electrostatically binding the cationic nitrosyl. Homegenous loading of the Mn nitrosyl (up to 25 wt.%) throughout the hexagonally packed, uni-dimensional mesopores of the Al-MCM-41 particles was determined using various analytical techniques including ICP-MS, FAAS, PXRD, N2 sorption isometry, UV-vis DRS, FTIR, and SEM-EDX. Exposure of {Mn-NO}@Al-MCM-41 to visible light of similar intensity to sunlight on a bright day (100 mW cm-2) released high fluxes of NO that effectively eradicated a multi-drug resistant strain of Acinetobacter baumannii.
In another study, described in Chapter 4, the powdery material was used to demonstrate the effect of NO on the dimorphic fungal pathogen, Candida albicans. Since the virulence of C. albicans is dependent on the ability of the fungus to switch growth from an ovoid yeast form to an elongated hyphal form, careful studies of the dose-dependent effect of NO released from {Mn-NO}@Al-MCM-41 on morphologically pure cultures of C. albicans in the yeast and hyphal forms have revealed that the hyphal form is more susceptible to NO. Results of this work suggest that photo-activated NO-donating materials of this type could prevent commensal populations of C. albicans from invading vulnerable tissue by blocking the over-growth of the tissue penetrating hyphal form of the fungus.
