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Poly(D, L-lactide-co-glycolide) (PLGA) nanoparticles (NPs) are being considered as nanodelivery systems for photodynamic therapy. The physico-chemical and biological aspects of their use remain largely unknown. Herein we report the results of a study of PLGA NPs for the delivery of the model hydrophobic photosensitizer ZnTPP to HeLa cells. ZnTPP was encapsulated in PLGA with high efficiency and the NPs showed negative zeta potentials and diameters close to 110 nm. Poly(ethylene glycol) (PEG) coating, introduced to prevent opsonization and clearance by macrophages, decreased the size and zeta potential of the NPs by roughly a factor of two and improved their stability in the presence of serum proteins. Photophysical studies revealed two and three populations of ZnTPP and singlet oxygen in uncoated and PEGylated NPs, respectively. Singlet oxygen is confined within the NPs in bare PLGA while it is more easily released into the external medium after PEG coating, which contributes to a higher photocytotoxicity towards HeLa cells in vitro. PLGA NPs are internalized by endocytosis, deliver their cargo to lysosomes and induce cell death by apoptosis upon exposure to light. In conclusion, PLGA NPs coated with PEG show high potential as delivery systems for photodynamic applications. [ABSTRACT FROM AUTHOR]

Sequence analysis of eosinophil cationic protein (ECP), a ribonuclease of broad antimicrobial activity, allowed identification of residues 1–45 as the antimicrobial domain. We have further dissected ECP(1–45) with a view to defining the minimal requirements for antimicrobial activity. Structure-based downsizing has focused on both α-helices of ECP(1–45) and yielded analogues with substantial potency against Gram-negative and -positive strains. Analogues ECP(8–36) and ECP(6–17)-Ahx-(23–36) (Ahx, 6-aminohexanoic acid) involve 36% and 40% size reduction relative to (1–45), respectively, and display a remarkably ECP-like antimicrobial profile. Both retain segments required for self-aggregation and lipolysaccharide binding, as well as the bacterial agglutination ability of parent ECP. Analogue (6–17)-Ahx-(23–36), in particular, is shown by NMR to preserve the helical traits of the native 8–16 (α1) and 33–36 (α2) regions and can be proposed as the minimal structure capable of reproducing the activity of the entire protein. [ABSTRACT FROM AUTHOR]

ECP (eosinophil cationic protein) is an eosinophil secretion protein with antipathogen activities involved in the host immune defence system. The bactericidal capacity of ECP relies on its action on both the plasma membrane and the bacterial wall. In a search for the structural determinants of ECP antimicrobial activity, we have identified an N-terminal domain (residues 1–45) that retains most of ECP's membrane-destabilizing and antimicrobial activities. Two sections of this domain, ECP-(1–19) and ECP-(24–45), have also been evaluated. All three peptides bind and partially insert into lipid bilayers, inducing aggregation of lipid vesicles and leakage of their aqueous content. In such an environment, the peptides undergo conformational change, significantly increasing their α-helix content. The bactericidal activity of the three peptides against Escherichia coli and Staphylococcus aureus has been assessed at both the cytoplasmic membrane and the bacterial envelope levels. ECP-(1–45) and ECP-(24–45) partially retain the native proteins ability to bind LPS (lipopolysaccharides), and electron microscopy reveals cell damage by both peptides. Interestingly, in the E. coli cells agglutination activity of ECP is only retained by the longest segment ECP-(1–45). Comparative results suggest a task distribution, whereby residues 1–19 would contribute to membrane association and destabilization, while the 24–45 region would be essential for bactericidal action. Results also indicate that ECP cytotoxicity is not uniquely dependant on its membrane disruption capacity, and that specific interactions at the bacteria wall are also involved. [ABSTRACT FROM AUTHOR]