Insulin complexes with PEGylated basic oligopeptides.

Biodegradable oligolysine and oligoarginine-type homopeptides functionalized with PEG of two different molecular weights interact with insulin, at physiological pH, affording complexes studied by dynamic light scattering, ζ-potential, circular dichroism, FTIR spectroscopy, and isothermal titration calorimetry (ITC). High levels of insulin complexation efficiencies (>99.5%) were determined for all derivatives. FTIR spectra suggest that the positively charged homo-oligopeptide derivatives interact with B chain C-terminus of insulin leading to the formation of nanoparticles than can be traced even at low oligopeptide/insulin molar ratios. The ITC profiles are complex, displaying significant endothermic and exothermic contributions. Oligoarginine-type derivatives exhibit the strongest interactions, while PEGylation of either oligopeptide with the high molecular weight chains significantly affects the ITC profiles and leads to larger enthalpy changes. This may be attributed to PEG-induced aggregation of insulin due to the depletion attraction effect leading to the formation of stable nanocomplexes. Stabilization of complexed insulin against enzymatic degradation by trypsin and α-chymotrypsin is observed especially for the high molecular weight PEGylated arginine-based derivative. Insulin release rates in simulated intestinal fluid are controlled by the length of PEG chains and the presence of arginine end-groups. Released insulin retains its secondary structure as established by circular dichroism spectroscopy.

Arginine end-functionalized poly(L-lysine) dendrigrafts for the stabilization and controlled release of insulin.

Second generation biodegradable poly(l-lysine) dendrigrafts functionalized with 12-48 arginine end-groups interact, at physiological pH, with insulin affording dendrigraft/insulin complexes as established by dynamic light scattering, ζ-potential, circular dichroism and isothermal titration calorimetry. Binding occurs in two steps; at low dendrigraft/insulin molar ratios (< or = 0.07) interaction is accompanied with the endothermic dissociation of insulin dimers, while at higher molar ratios, complexation of insulin monomers with dendrigraft derivatives occurs exothermically. High levels of insulin complexation efficiencies (>99%) were determined for all derivatives. Stabilization of complexed insulin against enzymatic degradation by trypsin and α-chymotrypsin is observed especially for the highly arginine end-functionalized dendrigrafts. Insulin release rates in simulated intestinal fluid are being controlled by the number of arginine end-groups and released insulin retains its conformation.

Structural features of interacting complementary liposomes promoting formation of multicompartment structures.

The structural features of complementary liposomes and factors favoring formation of multicompartment systems are investigated. Specifically, liposomal formulations consisting of PEGylated unilamellar liposomes with guanidinium moieties located at the distal end of polyethylene glycol (PEG) chains interact with complementary multilamellar liposomes bearing phosphate moieties. Furthermore, the number of PEG chains attached to the unilamellar interface of the liposomes is enhanced by incorporating PEGylated cholesterol in their bilayer. While molecular recognition of the liposomes is the driving force for initiating multicompartmentalization, it is the enhanced PEGylation at the liposomal interface that synergistically promotes fusion resulting in large and well-formed multicompartment systems. A mechanism is proposed according to which initial adhesion of the liposomes, followed by reorganization of their membrane lipids, leads to giant bilayer aggregates incorporating large liposomes.