Calcitonin-derived carrier peptide plays a major role in the membrane localization of a peptide-cargo complex

Dermaseptins from Phyllomedusa oreades and Phyllomedusa distincta: Secondary structure, antimicrobial activity, and mammalian cell toxicity

The present study reports the structural characteristics, the biological activities, and preliminary clinical investigations of three synthetic members of the dermaseptin family of antimicrobial peptides. The three peptides showed similar tendencies to form alpha-helical structures in non-polar media. The antimicrobial activity towards bacteria and fungi was determined in the micromolar concentration and the peptides did not influenced peritoneal cells viability. One of the peptides was intravenously administered in mice at concentrations similar to those of antibiotics employed in bacterial/fungal infections and it did not cause any detectable changes in cells and tissues.

Calcitonin-derived peptide carriers: mechanisms and application

Among the family of the so-called cell-penetrating peptides (CPP) sequences derived from the native peptide hormone human calcitonin (hCT) have recently proven to translocate different bioactive molecules across cellular membranes. Herein, we give an extensive summary of the development of hCT-derived carrier peptides, beginning with the therapeutic nasal administration of full-length hCT. Hence, N-terminally truncated hCT fragments were investigated and subsequently optimised to extend their field of application. The latest generation of hCT-derived carrier peptides are highly effective, branched peptides. The current state of the art is reviewed concerning the structural requirements, mechanistic assumptions and metabolic features of these peptides as well as experiments proving their excellent carrier potential.

Acetyl-[Asn30,Tyr32]-calcitonin fragment 8-32 forms channels in phospholipid planar lipid membranes

The N-terminally truncated derivative of salmon calcitonin (sCt) (acetyl-[Asn(30),Tyr(32)]-calcitonin fragment 8-32) (AC 187) lacks hormonal activity and is a potent and selective antagonist of the hormone and amylin receptor. It was investigated for its capability to interact and form channels in palmitoleoylphosphatidylcholine:dioleoylphosphatidylglycerol planar lipid membranes. Interestingly, AC 187 exhibits channel activity, whose parameters, i.e., central conductance (Lambda (c)), occurrence (number of channels/min), voltage-dependence and lifetime, are similar to those found for sCt although, in the same experimental conditions, it takes longer to incorporate into the membrane than sCt. This channel activity can be modulated by changing either the holding potential or the pH of the medium, or by adding picomolar concentrations of SDS. One evident difference between the two peptides is that sCt is unselective (1.03) while AC 187 displays a cationic selectivity (P (K) (+)/P (Cl) (-) = 2.7) at pH 7, increasing to 3.87 when the pH drops to 3.8. The present findings indicate that the 1-7 disulfide bridge is sufficient but not necessary for membrane interaction, in accordance with the observation reported on the interaction with membrane receptors. Furthermore, the remarkable pH dependence of the cationic channel could be taken into consideration for full biotechnological study.

The Cell Penetrating Peptides pVEC and W2-pVEC Induce Transformation of Gel Phase Domains in Phospholipid Bilayers without Affecting Their Integrity

The cell penetrating peptide (CPP) pVEC has been shown to translocate efficiently the plasma membrane of different mammalian cell lines by a receptor-independent mechanism without exhibiting cellular toxicity. This ability renders CPPs of broad interest in cell biology, biotechnology, and drug delivery. To gain insight into the interaction of CPPs with biomembranes, we studied the interaction of pVEC and W2-pVEC, an Ile --> Trp modification of the former, with phase-separated supported phospholipid bilayers (SPB) by atomic force microscopy (AFM). W2-pVEC induced a transformation of dipalmitoyl phosphatidylcholine (DPPC) domains from a gel phase state via an intermediate state with branched structures into essentially flat bilayers. With pVEC the transformation followed a similar pathway but was slower. Employing fluorescence polarization, we revealed the capability of the investigated peptides to increase the fluidity of DPPC domains as the underlying mechanism of transformation. Due to their tighter packing, sphingomyelin (SM) domains were not transformed. By combination, AFM observations, dynamic light scattering studies, and liposome leakage experiments indicated that bilayer integrity was not compromised by the peptides. Transformation of gel phase domains in SPB by CPPs represents a novel aspect in the discussion on uptake mechanisms of CPPs.

Coexistence of a two-states organization for a cell-penetrating peptide in lipid bilayer

Primary amphipathic cell-penetrating peptides transport cargoes across cell membranes with high efficiency and low lytic activity. These primary amphipathic peptides were previously shown to form aggregates or supramolecular structures in mixed lipid-peptide monolayers, but their behavior in lipid bilayers remains to be characterized. Using atomic force microscopy, we have examined the interactions of P(alpha), a primary amphipathic cell-penetrating peptide which remains alpha-helical whatever the environment, with dipalmitoylphosphatidylcholine (DPPC) bilayers. Addition of P(alpha) at concentrations up to 5 mol % markedly modified the supported bilayers topography. Long and thin filaments lying flat at the membrane surface coexisted with deeply embedded peptides which induced a local thinning of the bilayer. On the other hand, addition of P(alpha) only exerted very limited effects on the corresponding liposome's bilayer physical state, as estimated from differential scanning calorimetry and diphenylhexatriene fluorescence anisotropy experiments. The use of a gel-fluid phase separated supported bilayers made of a dioleoylphosphatidylcholine/dipalmitoylphosphatidylcholine mixture confirmed both the existence of long filaments, which at low peptide concentration were preferentially localized in the fluid phase domains and the membrane disorganizing effects of 5 mol % P(alpha). The simultaneous two-states organization of P(alpha), at the membrane surface and deeply embedded in the bilayer, may be involved in the transmembrane carrier function of this primary amphipathic peptide.

Bilayer interaction and localization of cell penetrating peptides with model membranes: A comparative study of a human calcitonin (hCT)-derived peptide with pVEC and pAntp(43–58)

Cell-penetrating peptides (CPPs) are able to translocate problematic therapeutic cargoes across cellular membranes. The exact mechanisms of translocation are still under investigation. However, evidence for endocytic uptake is increasing. We investigated the interactions of CPPs with phospholipid bilayers as first step of translocation. To this purpose, we employed four independent techniques, comprising (i) liposome buffer equilibrium dialysis, (ii) Trp fluorescence quenching, (iii) fluorescence polarization, and (iv) determination of zeta-potentials. Using unilamellar vesicles (LUVs) of different phospholipid composition, we compared weakly cationic human calcitonin (hCT)-derived peptides with the oligocationic CPPs pVEC and penetratin (pAntp). Apparent partition coefficients of hCT-derived peptides in neutral POPC LUVs were dependent on amino acid composition and secondary structure; partitioning in negatively charged POPC/POPG (80:20) LUVs was increased and mainly governed by electrostatic interactions. For hCT(9-32) and its derivatives, D values raised from about 100-200 in POPC to about 1000 to 1500 when negatively charged lipids were present. Localization profiles of CPPs obtained by Trp fluorescence quenching were dependent on the charge density of LUVs. In POPC/POPG, hCT-derived CPPs were located on the bilayer surface, whereas pVEC and pAntp resided deeper in the membrane. In POPG LUVs, an increase of fluorescence polarization was observed for pVEC and pAntp but not for hCT-derived peptides. Generally, we found strong peptide-phospholipid interactions, especially when negatively charged lipids were present.