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The aim of this study was to evaluate skin delivery of ketoprofen when covalently tethered to mildly cationic (2 or 4) peptide dendrimers prepared wholly by solid phase peptide synthesis. The amino acids glycine, arginine and lysine formed the dendrimer with ketoprofen tethered either to the lysine side-arm (N) or periphery of dendrimeric branches. Passive diffusion, sonophoresis- and iontophoresis-assisted permeation of each peptide dendrimer-drug conjugate (D1-D4) was studied across mouse skin, both in vitro and in vivo. In addition, skin toxicity of dendrimeric conjugates when trialed with iontophoresis or sonophoresis was also evaluated. All dendrimeric conjugates improved aqueous solubility at least 5-fold, compared to ketoprofen alone, while also exhibiting appreciable lipophilicity. In vitro passive diffusion studies revealed that ketoprofen in its native form was delivered to a greater extent, compared with a dendrimer-conjugated form at the end of 24h (Q (μg/cm): ketoprofen (68.06±3.62)>D2 (49.62±2.92)>D4 (19.20±0.89)>D1 (6.45±0.40)>D3 (2.21±0.19). However, sonophoresis substantially increased the skin permeation of ketoprofen-dendrimer conjugates in 30min (Q (μg/cm): D4 (122.19±7.14)>D2 (66.74±3.86)>D1 (52.10±3.22)>D3 (41.66±3.22)) although ketoprofen alone again proved superior (Q: 167.99±9.11μg/cm). Next, application of iontophoresis was trialed and shown to considerably increase permeation of dendrimeric ketoprofen in 6h (Q (μg/cm): D2 (711.49±39.14)>D4 (341.23±16.43)>D3 (89.50±4.99)>D1 (50.91±2.98), with a Q value of 96.60±5.12μg/cm for ketoprofen alone). In vivo studies indicated that therapeutically relevant concentrations of ketoprofen could be delivered transdermally when iontophoresis was paired with D2 (985.49±43.25ng/mL). Further, histopathological analysis showed that the dendrimeric approach was a safe mode as ketoprofen alone. The present study successfully demonstrates that peptide dendrimer conjugates of ketoprofen, when combined with non-invasive modalities, such as iontophoresis can enhance skin permeation with clinically relevant concentrations achieved transdermally.

The aim of the present study was to evaluate the ability of the peptide dendrimers to facilitate transdermal delivery of antioxidants, silibinin, and epigallocatechin-3-gallate (EGCG). Drug-peptide dendrimer complexes were prepared and evaluated for their ability to permeate across the skin. The data revealed the ready formation of complexes between drug and peptide dendrimer in a molar ratio of 1:1. In vitro permeation studies using excised rat skin and drug-peptide dendrimer complexes showed highest values for cumulative drug permeation at the end of 12 h (Q), with corresponding permeability coefficient (Kp) and enhancement ratio values also determined at this time point. With silibinin, 3.96-, 1.81-, and 1.06-fold increase in skin permeation was observed from silibinin-peptide dendrimer complex, simultaneous application of silibinin + peptide dendrimer, and pretreatment of skin with peptide dendrimer, respectively, in comparison with passive diffusion. With EGCG, 9.82-, 2.04-, and 1.72-fold increase in skin permeation was observed from EGCG-peptide dendrimer complex, simultaneous application of EGCG + peptide dendrimer, and pretreatment of skin with peptide dendrimer, respectively, in comparison with passive diffusion. The present study demonstrates the application of peptide dendrimers in effectively delivering antioxidants such as EGCG and silibinin into the skin, thus offering the potential to provide antioxidant effects when delivered via appropriately formulated topical preparations.

This paper investigates the shell elastic properties and the number-concentration stability of a new acoustofluidic delivery agent liposome in comparison to Definity ™ , a monolayer ultrasonic contrast agent microbubble. The frequency dependent attenuation of an acoustic beam passing through a microbubble suspension was measured to estimate the shell parameters. The excitation voltage was adjusted to ensure constant acoustic pressure at all frequencies. The pressure was kept at the lowest possible magnitude to ensure that effects from nonlinear bubble behaviour which are not considered in the analytical model were minimal. The acoustofluidic delivery agent shell stiffness and friction parameters were determined as ( = ./ , = . × − / o C) in comparison to the Definity™ monolayer ultrasound contrast agent which were ( = ./ , = . × − / o C). When the temperature was raised to physiological levels, the friction coefficient decreased by 28% for the monolayer microbubbles and by only 9% for the liposomes. The stiffness parameter Sp of the monolayer microbubble decreased by 23% while the stiffness parameter of the liposome increased by a similar margin (27%) when the temperature was raised to 37 °C. The size distribution of the bubbles was measured using Tenable Resistive Pulse Sensing (TRPS) for freshly prepared microbubbles and for bubble solutions at 6 hours and 24 hours after activation to investigate their number-concentration stability profile. The liposome maintained > 80% of their number-concentration for 24 hours at physiological temperature, while the monolayer microbubbles maintained only 27% of their number-concentration over the same period. These results are important input parameters for the design of effective acoustofluidic delivery systems using the new liposomes.

The mechanism by which cell-penetrating peptides and antimicrobial peptides cross plasma membranes is unknown, as is how cell-penetrating peptides facilitate drug delivery, mediating the transport of small molecules. Once non-disruptive and non-endocytotic pathways are excluded, pore formation is one of the proposed mechanisms, including toroidal, barrel-stave, or carpet models.Spontaneous pores have been observed in coarse-grained simulations and less often in molecular dynamics simulations. While pores are widely assumed and inferred, there is no unambiguous Antibiotic-resistant bacteria constitute a significant public health problem 1,2 . Antimicrobial peptides (AMPs) -a class of small (≤50 residues), cationic or amphiphilic compounds -are amongst the most promising solutions currently known 3 . Cell-penetrating peptides (CPPs) are a similar class of peptides, important for their binding -usually via covalent conjugation through a disulfide bridge or by means of non-covalent interactions 4 -and delivery of drugs into cells for therapeutic applications [5][6][7] . Both CPPs and AMPs interact strongly with the membrane surface, penetrating or altering its permeability via a mechanism which is not well understood 8,9 , even after a plethora of experimental and simulation studies.Atomistic molecular dynamics (MD) can be applied to investigate certain aspects of the uptake mechanisms. Despite its limitations in terms of accessible spatial and temporal scales, MD has the potential to provide unique insights. Several studies have converged, via observations or deductions, to infer the formation or existence of pores in the membrane 10-14 . Pores have been observed in coarse-grained simulations 15,16 , and in molecular dynamics 17,18 . A spontaneous translocation of a TAT peptide was observed in one MD study 19 and explained in terms of pore formation. However, subsequently this result was found to have originated from incorrect use of electrostatic interactions 14 . When a phosphatidylcholine (POPC) membrane is exposed to a CPP such as maculatin 1.1, dye leakage was observed after ∼10 minutes. This result led the authors of the study to infer a physical mechanism based on membrane disruption or pore formation 20 .Binding energies of pore formation with alamethicin and melittin showed preference for cylindrical 21 and toroidal 22 pores, in accord with molecular dynamics results 23 .In contrast to the above picture, some experiments do not support the presence of pores.Considering that cationic peptides should interact more strongly with negatively charged compounds, one would have expected pore formations with a CPP oligoarginine peptide interacting with negatively charged lipids. Interestingly, a leakage was observed, but not with an ion-conductive structure 24 , which would have been expected in presence of holes or channels.Trans-activating transcriptional (TAT) peptide penetration has been observed in the absence of endocytosis, with the additional discovery that added fluorophores were not taken together with the...