Stoichiometry and Structure of Poly(amidoamine) Dendrimer−Lipid Complexes

Abstract

The energetics, stoichiometry, and structure of poly(amidoamine) (PAMAM) dendrimer-phospholipid interactions were measured with isothermal titration calorimetry (ITC), transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS), and molecular dynamics (MD) simulations. Dendrimers of sixth-generation and smaller interacted with the lipids at an average stoichiometry and enthalpy proportional to the number of primary amines per dendrimers (4.5 ± 0.1 lipids/primary amine and 6.3 ± 0.3 kJ/mol of primary amines, respectively). Larger dendrimers, however, demonstrated a decreased number of bound lipids and heat release per primary amine, presumably due to the steric restriction of dendrimer deformation on the lipid bilayer. For example, eighth-generation PAMAM dendrimers bound to 44% fewer lipids per primary amine and released 63% less heat per primary amine as compared to the smaller dendrimers. These differences in binding stoichiometry support generation-dependent models for dendrimer-lipid complexation, which are consistent with previously observed generation-dependent differences in dendrimer-induced membrane disruption. Dendrimers of seventh-generation and larger bound to lipids with an average stoichiometry consistent with each dendrimer having been wrapped by a bilayer of lipids, where as smaller dendrimers did not.

Centrifugation-based assay for examining nanoparticle–lipid membrane binding and disruption

“…22 Superparamagnetic iron oxide (SPIO) and gold (Au) nanoparticles have been reported in the field of tumor disgnostics and cancer treatment. [9][10][16][17][18][19][20][21] Semiconducting nanocrystals, e.g. quantum dots, were used to improve biological imaging for medical diagnostics, 14 and these crystals were able to offer resolutions up to 1,000 times better than conventional dyes used in many biological tests.…”

“…[19][20][21][22] Inductively coupled plasma optical emission spectrometry (ICP-OES) or mass spectrometry (MS) has also been used, for example, to probe the interaction between functionalized Au nanoparticles and silica sphere-supported lipid membranes (SSLMs) by measuring the concentrations of Au nanoparticles both in the aqueous electrolytes (supernatant) and in/on the lipid bilayers. 23 The electrophysiological approach 24 coupled with the droplet-in-oil methodology has been employed to study the interaction between nanoparticles and cell membranes.…”

A mechanistic view of lipid membrane disrupting effect of PAMAM dendrimers

“…It seems that besides the weakly correlated, fragmented lamellae, small proportion of micelles or other highly curved vesicles are present. Since G5 PAMAM dendrimers do not have a radius high enough to support individually a surrounding vesicle [17], aggregated dendrimers should be in the core of these assemblies. The microscale inhomogeneities observed on the TEM pictures give an explanation for the complex main transition peak on the DSC curve (Fig.2.).…”

“…The interaction between cell membranes and nanocarriers, such as dendrimers, is very important, because in the most cases carriers have to get across the lipid bilayer without disrupting it. Previous studies based on atomic force microscopy (AFM) [12][13][14][15][16][17] isothermal titration calorimetry (ITC), fluorescence correlated spectroscopy (FCS) [17][18], in vitro experiments [13,[19][20] and molecular dynamics simulations (MD) [14,17,[21][22][23][24] showed that cationic dendrimers disrupt lipid bilayers by forming holes on the bilayer surface and may remove lipids from it. The degree of the disruption depends on the size and charge of the dendrimer.…”

Multiscale Modeling for Host-Guest Chemistry of Dendrimers in Solution

“…The binding strength between dendrimer-guest complexes has been determined by isothermal titration calorimetry(ITC) [26][27][28][29], high performance liquid chromatography (HPLC) [30] and fluorescence spectroscopy [31][32][33]. Detailed conformations of dendrimers interacting with guest molecules have been studied by nuclear magnetic resonance(NMR) [34][35][36] and the size of the dendrimer-guest complexes has been measured by dynamic light scattering (DLS) [22,31].…”