Inclusion of 5-[4-(1-dodecanoylpyridinium)]-10,15,20-triphenylporphine in supramolecular aggregates of cationic amphiphilic cyclodextrins: physicochemical characterization of the complexes and strengthening of the antimicrobial photosensitizing activity

Recent findings suggest that visible light-promoted photooxidative processes mediated by sensitizers of appropriate chemical structure could represent a useful tool for properly addressing the problem of the increasing occurrence of infectious diseases caused by multiantibiotic-resistant microbial pathogens. The monocationic meso-substituted porphyrin 5-[4-(1-dodecanoylpyridinium)]-10,15,20-triphenyl-porphine (TDPyP) complexed into supramolecular aggregates of cationic amphiphilic -cyclodextrin (SC6NH2) (mean diameter ) 20 nm) appeared to be endowed with favorable properties to act as a photosensitizing agent, including a very high quantum yield (?? ) 0.90) for the generation of the highly reactive oxygen species, singlet oxygen (1O2). Although the yield of 1O2 generation was comparable to that obtained after TDPyP incorporation into cationic unilamellar liposomes of N-[1-(2,3- dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTAP) SC6NH2-bound TDPyP was more active than DOTAP-bound TDPyP in photosensitizing the inactivation of the Gram-positive methicillin-resistant bacterium Staphylococcus aureus (MRSA). At variance with DOTAP-bound TDPyP, photoactivated SC6NH2-bound TDPyP was efficient also in photokilling Gram-negative bacterial pathogens, such as Escherichia coli. These observations are in agreement with the well-known photobactericidal effect of positively charged porphyrin derivatives, which can be markedly enhanced after incorporation into carriers with multiple positive charges. In addition, transmission electron microscopy studies revealed that potentiation of the TDPyP-mediated photobactericidal effect by incorporation into SC6NH2 is a consequence of the carrier's ability to promote an efficient crossing of the very tightly organized three-dimensional architecture of the bacterial outer wall by the embedded porphyrin so that a prompt interaction between the short-lived photogenerated 1O2 and the nearby targets, whose integrity is critical for cell survival, can take place.