Solid-State NMR Reveals the Hydrophobic-Core Location of Poly(amidoamine) Dendrimers in Biomembranes

Abstract

Poly(amidoamine) (PAMAM) dendrimer nanobiotechnology shows great promise in targeted drug delivery and gene therapy. Because of the involvement of cell membrane lipids with the pharmacological activity of dendrimer nanomedicines, the interactions between dendrimers and lipids are of particular relevance to the pharmaceutical applications of dendrimers. In this study, solid-state NMR was used to obtain a molecular image of the complex of generation 5 PAMAM dendrimer with the lipid bilayer. Using 1H radio frequency driven dipolar recoupling (RFDR) and 1H magic angle spinning (MAS) nuclear Overhauser effect spectroscopy (NOESY) techniques, we show that dendrimers are thermodynamically stable when inserted into zwitterionic lipid bilayers. 14N and 31P NMR experiments on static samples and measurements of the mobility of C–H bonds using a 2D proton detected local field protocol under MAS corroborate these results. The localization of dendrimers in the hydrophobic core of lipid bilayers restricts the motion of bilayer lipid tails, with the smaller G5 dendrimer having more of an effect than the larger G7 dendrimer. Fragmentation of the membrane does not occur at low dendrimer concentrations in zwitterionic membranes. Because these results show that the amphipathic dendrimer molecule can be stably incorporated in the interior of the bilayer (as opposed to electrostatic binding at the surface), they are expected to be useful in the design of dendrimer-based nanobiotechnologies.

PAMAM dendrimer - cell membrane interactions

“…Supported lipid bilayers (SLBs) are well suited for studying the dendrimer-membrane interactions, as they lend themselves readily to quantitative analysis using a range of surface sensitive techniques such as X-ray and neutron reflectivity (XRR and NR) [14,80,81], atomic force microscopy (AFM) [82][83][84], ellipsometry [14,85], quartz crystal microbalance with dissipation (QCM-D) [81,85,86], NMR [87], differential scanning calorimetry (DSC) and Raman spectroscopy [88].…”

“…Cell membranes modulate their lipid phase behaviour by varying their composition. This results in different crystalline lipid phases, important for membrane fusion [92][93][94] and the formation of lipid rafts (microdomains of one lipid type) [95], conjectured to regulate membrane signalling and cellular entry [87]. The molecular packing and thus the bilayer structure can be tuned by using different lipids to mimic different membranes [83].…”

“…In a solid-state NMR study, Smith et al [87] found cationic G5 and G7 PAMAM localised in the hydrophobic region of zwitterionic DMPC MLVs, which led to increased acyl chain ordering and decreased chain flexibility. The lipid tails intercalated into the G5 dendrimers, but the more closely packed surface groups of the G7 dendrimers suppressed the lipid penetration.…”

Different patterns of nuclear and mitochondrial penetration by the G3 PAMAM dendrimer and its biotin–pyridoxal bioconjugate BC-PAMAM in normal and cancer cells in vitro

“…21,59 Investigations of the interaction between cationic dendrimers and artificial and cellular lipid bilayers revealed electrochemical as well as hydrophobic interactions that promote membrane disruption and impair transport mechanisms. 70,71 The formation of pores in the outer mitochondrial membrane promotes apoptotic cell death. 72 In our experiments, the localization of native and bioconjugate dendrimers in the mitochondria correlated well with International Journal of Nanomedicine downloaded from https://www.dovepress.com/ by 54.191.190.102 on 13-May-2018 For personal use only.…”

A mechanistic view of lipid membrane disrupting effect of PAMAM dendrimers

“…Smith and coworkers investigated the effect of G5 and G7 PAMAM dendrimers on multilamellar vesicles by solid-state NMR techniques. They have found that dendrimers have higher impact on alkyl chain region than on headgroups; besides they used partially hydrated or highly concentrated, fully hydrated membranes [37].…”