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Peptoids are peptidomimetic polymers that are resistant to proteolysis and less prone to immune responses; thus, they can provide a practical alternative to peptides. Among the various therapeutic applications that have been explored, cationic amphipathic peptoids have demonstrated broad-spectrum antibacterial activity, including activity towards drug-resistant bacterial strains. While their potency and activity spectrum can be manipulated by sequence variations, bacterial selectivity and systemic toxicity need to be improved for further clinical development. To this aim, we incorporated various hydrophobic or cationic residues to improve the selectivity of the previously developed antibacterial peptoid 1. The analogs with hydrophobic residues demonstrated non-specific cytotoxicity, while those with an additional cationic residue showed improved selectivity and comparable antibacterial activity. Specifically, compared to 1, peptoid 7 showed much lower hemolysis and cytotoxicity, while maintaining the antibacterial activity. Therefore, we believe that peptoid 7 has the potential to serve as a promising alternative to current antimicrobial therapies.

LL-37 is the sole cathelicidin-derived antimicrobial peptide found in humans. It becomes active upon C-terminal cleavage of its inactive precursor hCAP18. In addition to antimicrobial action, it also functions as an innate immune system stimulant in many tissues of the body. Here we report that hCAP18 and LL-37 are expressed in all organs of the human body that were studied with the highest basic levels being expressed in the GI tract and the brain. Its expression and functional role in the central nerve system (CNS) has not previously been reported. We found increased expression of LL-37 in IFNγ-stimulated human astrocytes and their surrogate U373 cells, as well as in LPS/IFNγ-stimulated human microglia and their surrogate monocyte-derived THP-1 cells. We found that treatment of microglia, astrocytes, THP-1 cells and U373 cells with LL-37 induced secretion of the inflammatory cytokines IL-1β and IL-6; the chemokines IL-8 and CCL-2, and other materials toxic to human neuroblastoma SH-SY5Y cells. The mechanism of LL-37 stimulation involves activation of intracellular proinflammatory pathways involving phospho-P38 MAP kinase and phospho-NFκB proteins. We blocked the inflammatory stimulant action of LL-37 by removing it with an anti-LL-37 antibody. The inflammatory effect was also prevented by treatment with inhibitors of PKC, PI3K and MEK-1/2 as well as with the intracellular Ca 2+ -chelator, BAPTA-AM. This indicates involvement of these intracellular pathways. Our data suggest that LL-37, in addition to its established roles, may play a role in the chronic neuroinflammation which is observed in neurodegenerative diseases such as Alzheimer's and Parkinson's disease.

One of the major challenges in regenerative medicine is the ability to recreate the stem cell niche, which is defined by its signaling molecules, the creation of cytokine gradients, and the modulation of matrix stiffness. A wide range of scaffolds has been developed in order to recapitulate the stem cell niche, among them hydrogels. This paper reports the development of a new silk–alginate based hydrogel with a focus on stem cell culture. This biocomposite allows to fine tune its elasticity during cell culture, addressing the importance of mechanotransduction during stem cell differentiation. The silk–alginate scaffold promotes adherence of mouse embryonic stem cells and cell survival upon transplantation. In addition, it has tunable stiffness as function of the silk–alginate ratio and the concentration of crosslinker – a characteristic that is very hard to accomplish in current hydrogels. The hydrogel and the presented results represents key steps on the way of creating artificial stem cell niche, opening up new paths in regenerative medicine.

Biomaterials that mimic the extracellular matrix in both modularity and crosslinking chemistry have the potential to recapitulate the instructive signals that ultimately control cell fate. Toward this goal, modular protein polymer-based hydrogels were created through genetic engineering and enzymatic crosslinking. Animal derived tissue transglutaminase (tTG) and recombinant human transglutaminase (hTG) enzymes were used for coupling two classes of protein polymers containing either lysine or glutamine, which have the recognition substrates for enzymatic crosslinking, evenly spaced along the protein backbone. Utilizing tTG under physiological conditions, crosslinking occurred within two minutes, as determined by particle tracking microrheology. Hydrogel composition impacted the elastic storage modulus of the gel over 4-fold and also influenced microstructure and degree of swelling, but did not appreciably effect degradation by plasmin. Mouse 3T3 and primary human fibroblasts were cultured in both 2- and 3-dimensions without a decrease in cell viability and displayed spreading in 2D. The properties of these gels, which are controlled through the specific nature of the protein polymer precursors, render these gels valuable for in situ therapies. Furthermore, the modular hydrogel composition allows tailoring of mechanical and physical properties for specific tissue engineering applications.

Hydrophobic lung surfactant proteins B and C (SP-B and SP-C) are critical for normal respiration in vertebrates, and each comprises specific structural attributes that enable the surface-tension-reducing ability of the lipid–protein mixture in lung surfactant. The difficulty in obtaining pure SP-B and SP-C on a large scale has hindered efforts to develop a non-animal-derived surfactant replacement therapy for respiratory distress. Although peptide-based SP-C mimics exhibit similar activity to the natural protein, helical peptide-based mimics of SP-B benefit from dimeric structures. To determine if in vitro surface activity improvements in a mixed lipid film could be garnered without creating a dimerized structural motif, a helical and cationic peptoid-based SP-B mimic was modified by SP-C-like N-terminus alkylation with octadecylamine. “Hybridized” mono- and dialkylated peptoids significantly decreased the maximum surface tension of the lipid film during cycling on the pulsating bubble surfactometer relative to the unalkylated variant. Peptoids were localized in the fluid phase of giant unilamellar vesicle lipid bilayers, as has been described for SP-B and SP-C. Using Langmuir–Wilhelmy surface balance epifluorescence imaging (FM) and atomic force microscopy (AFM), only lipid-alkylated peptoid films revealed micro- and nanostructures closely resembling films containing SP-B. AFM images of lipid-alkylated peptoid films showed gel condensed-phase domains surrounded by a distinct phase containing “nanosilo” structures believed to enhance re-spreading of submonolayer material. N-terminus alkylation may be a simple, effective method for increasing lipid affinity and surface activity of single-helix SP-B mimics.

Peptides can potentiate lipid-mediated gene delivery by modifying lipoplex physiochemical properties to overcome rate-limiting steps to gene transfer. The objectives of this study were to determine the regimes over which cationic peptides enhance lipofection and to investigate the mechanism of action, such as increased cellular association resulting from changes in lipoplex physical properties. Short, cationic peptides were incorporated into lipoplexes by mixing peptide, lipid and DNA. Lipoplexes were characterized using gel retardation, dynamic light scattering, and fluorescent microscopy, and the amount of surface-displayed amines was quantified by fluorescamine. Size, zeta potential, and surface amines for lipoplexes were dependent on peptide/DNA ratio. Inclusion of peptides in lipoplexes resulted in up to a 13-fold increase in percentage of cells transfected, and up to a 76-fold increase in protein expression. This transfection enhancement corresponded to a small particle diameter and positive zeta potential of lipoplexes, as well as increased amount of surface-displayed amines. Relative to lipid alone, these properties of the peptide-modified lipoplexes enhanced cellular association, which has been reported as a rate-limiting step for transfection with lipoplexes. The addition of peptides is a simple method of lipofection enhancement, as direct chemical modification of lipids is not necessary for increased transfection.

We present data showing a substantial narrowing of the polydispersity index (PDI) of high polymers occurring as a consequence of random chain scission events in a transient elongational flow field. In our experiments, semi-dilute aqueous solutions of high-molar mass, polydisperse polymers (PDI>1.4) were injected under pressure through an elongational flow field at the entrance of a capillary tube (i.d. 250 μm). Chain scission events occurring during multiple passes through the capillary entrance cause a marked decrease in PDI, to values as low as 1.12, along with the expected decrease of the average molar mass. The phenomenon appears to be entirely physical and independent of the chemical nature of the polymer, since similar results are obtained with polyacrylamide, polydimethylacrylamide, and poly(ethylene oxide). Statistical modeling of the evolution of the polymer molar mass distribution shows the results to be consistent with the random scission, near the mid-point, of those polymer chains that exceed a certain flow field-dependent critical chain length.

Among the families of peptidomimetic foldamers under development as novel biomaterials and therapeutics, poly-N-substituted glycines (peptoids) with α-chiral side chains are of particular interest for their ability to adopt stable, helical secondary structure in organic and aqueous solution. Here, we show that a peptoid 22-mer with a biomimetic sequence of side chains and an amphipathic, helical secondary structure acts as an excellent mimic of surfactant protein C (SP-C), a small protein that plays an important role in surfactant replacement therapy for the treatment of neonatal respiratory distress syndrome. When integrated into a lipid film, the helical peptoid SP mimic captures the essential surface-active behaviors of the natural protein. This work provides an example of how an abiological oligomer that closely mimics both the hydrophobic/polar sequence patterning and the fold of a natural protein can also mimic its biophysical function.

There is a medical need for robust, biocompatible hydrogels that can be rapidly crosslinked in situ through the use of gentle and non-toxic triggers, which could be used as a surgical adhesive, a bone-inductive material, or for drug and gene delivery. The complete gelation system described here includes calcium-loaded liposomes, hrFactor XIII. thrombin, and an enzymatic substrate based on a four-armed PEG in which each arm terminates with a 20mer peptide sequence derived from the gamma-chain of fibrin. Controlled release of calcium ions for efficient hrFXIII activation was accomplished by thermal triggering of a tailored liposome phase transition at 37 degrees C, which allowed the entire gelation system to be stored in aqueous solution at room temperature without premature gelation. When the system temperature was raised to 37 degrees C (body temperature), the released calcium activates the hrFactor XIII, and gelation was observed to occur within 9 min. Rheological studies performed to quantitatively determine the storage modulus (G') of the gel during oscillatory shear show that it behaves as a robust, elastic solid. Scanning electron microscopy studies revealed the hydrogel to have a very dense morphology overall, however spherical voids are observed in regions where calcium-loaded liposomes were entrapped during gelation.

We recently demonstrated that the molecular mass distribution of an uncharged polymer sample can be analyzed using free-solution capillary electrophoresis of DNA-polymer conjugates. In these conjugates, the DNA is providing the electromotive force while the uncharged polydisperse polymer chains of the sample retard the DNA engine with different amounts of hydrodynamic drag. Here we present a theoretical model of this new analytical method. We show that for the most favourable, diffusion-limited electrophoresis conditions, there is actually an optimal DNA size to achieve the separation of a given polymer sample. Moreover, we demonstrate that the effective friction coefficient of the polymer chains is related to the stiffness of the two polymers of the conjugate, thus offering a method to estimate the persistence length of the uncharged polymer through mobility measurements. Finally, we compare some of our predictions with available experimental results.