Targeted Intravenous Nanoparticle Delivery: Role of Flow and Endothelial Glycocalyx Integrity.

Therapies for atherosclerotic cardiovascular disease should target early disease stages and specific vascular sites where disease occurs. Endothelial glycocalyx (GCX) degradation compromises endothelial barrier function and increases vascular permeability. This initiates pro-atherosclerotic lipids and inflammatory cells to penetrate vessel walls, and at the same time this can be leveraged for targeted drug delivery. In prior cell culture studies, GCX degradation significantly increased endothelial cell uptake of nanoparticle vehicles that are designed for drug delivery, compared to the effects of intact GCX. The present study assessed if the cell culture findings translate to selective nanoparticle uptake in animal vessels. In mice, the left carotid artery (LCA) was partially ligated to disturb blood flow, which induces GCX degradation, endothelial dysfunction, and atherosclerosis. After ligation, the LCA vessel wall exhibited a loss of continuity of the GCX layer on the intima. 10-nm gold nanospheres (GNS) coated with polyethylene glycol (PEG) were delivered intravenously. GCX degradation in the ligated LCA correlated to increased GNS infiltration of the ligated LCA wall. This suggests that GCX dysfunction, which coincides with atherosclerosis, can indeed be targeted for enhanced drug delivery, offering a new approach in cardiovascular disease therapy.

Selection of an Efficient AAV Vector for Robust CNS Transgene Expression.

Adeno-associated virus (AAV) capsid libraries have generated improved transgene delivery vectors. We designed an AAV library construct, iTransduce, that combines a peptide library on the AAV9 capsid with a Cre cassette to enable sensitive detection of transgene expression. After only two selection rounds of the library delivered intravenously in transgenic mice carrying a Cre-inducible fluorescent protein, we flow sorted fluorescent cells from brain, and DNA sequencing revealed two dominant capsids. One of the capsids, termed AAV-F, mediated transgene expression in the brain cortex more than 65-fold (astrocytes) and 171-fold (neurons) higher than the parental AAV9. High transduction efficiency was sex-independent and sustained in two mouse strains (C57BL/6 and BALB/c), making it a highly useful capsid for CNS transduction of mice. Future work in large animal models will test the translation potential of AAV-F.

Ultrasmall gold nanorods: synthesis and glycocalyx-related permeability in human endothelial cells.

BACKGROUND: Clinical data show shed endothelial glycocalyx (GCX) components in blood samples of atherosclerotic patients, linking atherosclerotic development to endothelial GCX integrity. Healthy GCX has pores no >7 nm, and shed GCX has even larger pores. Therefore, we suggest targeting and treating atherosclerosis-prone blood vessels by using nanoscale vehicles to deliver drugs via the nanoscale GCX as it becomes dysfunctional. MATERIALS AND METHODS: To test our idea, we investigated permeability of nanoparticles in endothelium, as related to a GCX expression. The present work involves nanorods, which are expected to interact with larger portions of endothelial cell (EC) membranes, due to surface area of the nanorod long axis. Conventional nanorod diameters are orders of magnitude larger than the GCX pore size, so we adapted conventional synthesis methods to fabricate ultrasmall gold nanorods (GNRs). Our ultrasmall GNRs have an aspect ratio of 3.4, with a length of 27.9±3.1 nm and a diameter of 8.2±1.4 nm. In addition, we produced GNRs that are biocompatible and fluorescently visible, by coating the surface with functionalized polyethylene glycol and Alexa Fluor 647. To study GNR-GCX interactions, we used human ECs, for species relevance. RESULTS: Under life-like flow conditions, the human ECs are densely covered with a 1.3 µm thick layer of GCX, which coincides with minimal GNR permeability. When the GCX is weakened from lack of flow (static culture) or the presence of GCX degradation enzyme in the flow stream, the GCX shows 40% and 60% decreased thickness, respectively. GCX weakness due to lack of flow only slightly increases cellular permeability to GNRs, while GCX weakness due to the presence of enzyme in the flow leads to substantial increase in GNR permeability. CONCLUSION: These results clarify that the GCX structure is an avenue through which drug-carrying nanoparticles can be delivered for targeting affected blood vessels to treat atherosclerosis.

Synthesis of Functionalized 10-nm Polymer-coated Gold Particles for Endothelium Targeting and Drug Delivery.

Gold nanoparticles (AuNPs) have been used extensively in medical research due to their size, biocompatibility, and modifiable surface. Specific targeting and drug delivery are some of the applications of these AuNPs, but endothelial extracellular matrices' defensive properties hamper particle uptake. To address this issue, we describe a synthesis method for ultrasmall gold nanoparticles to improve vascular delivery, with customizable functional groups and polymer lengths for further adjustments. The protocol yields 2.5 nm AuNPs that are capped with tetrakis(hydroxymethyl)phosphonium chloride (THPC). The replacement of THPC with hetero-functional polyethylene glycol (PEG) on the surface of the AuNP increases the hydrodynamic radius to 10.5 nm while providing various functional groups on the surface. The last part of the protocol includes an optional addition of a fluorophore to allow the AuNPs to be visualized under fluorescence to track nanoparticle uptake. Dialysis and lyophilization were used to purify and isolate the AuNPs. These fluorescent nanoparticles can be visualized in both in vitro and in vivo experiments due to the biocompatible PEG coating and fluorescent probes. Additionally, the size range of these nanoparticles render them an ideal candidate for probing the glycocalyx without disrupting normal vasculature function, which may lead to improved delivery and therapeutics.

Regeneration of glycocalyx by heparan sulfate and sphingosine 1-phosphate restores inter-endothelial communication.

Vasculoprotective endothelium glycocalyx (GCX) shedding plays a critical role in vascular disease. Previous work demonstrated that GCX degradation disrupts endothelial cell (EC) gap junction connexin (Cx) proteins, likely blocking interendothelial molecular transport that maintains EC and vascular tissue homeostasis to resist disease. Here, we focused on GCX regeneration and tested the hypothesis that vasculoprotective EC function can be stimulated via replacement of GCX when it is shed. We used EC with [i] intact heparan sulfate (HS), the most abundant GCX component; [ii] degraded HS; or [iii] HS that was restored after enzyme degradation, by cellular self-recovery or artificially. Artificial HS restoration was achieved via treatment with exogenous HS, with or without the GCX regenerator and protector sphingosine 1- phosphate (S1P). In these cells we immunocytochemically examined expression of Cx isotype 43 (Cx43) at EC borders and characterized Cx-containing gap junction activity by measuring interendothelial spread of gap junction permeable Lucifer Yellow dye. With intact HS, 60% of EC borders expressed Cx43 and dye spread to 2.88 ± 0.09 neighboring cells. HS degradation decreased Cx43 expression to 30% and reduced dye spread to 1.87± 0.06 cells. Cellular self-recovery of HS restored baseline levels of Cx43 and dye transfer. Artificial HS recovery with exogenous HS partially restored Cx43 expression to 46% and yielded dye spread to only 1.03 ± 0.07 cells. Treatment with both HS and S1P, recovered HS and restored Cx43 to 56% with significant dye transfer to 3.96 ± 0.23 cells. This is the first evidence of GCX regeneration in a manner that effectively restores vasculoprotective EC communication.

Endothelial glycocalyx conditions influence nanoparticle uptake for passive targeting.

Cardiovascular diseases are facilitated by endothelial cell (EC) dysfunction and coincide with EC glycocalyx coat shedding. These diseases may be prevented by delivering medications to affected vascular regions using circulating nanoparticle (NP) drug carriers. The objective of the present study was to observe how the delivery of 10 nm polyethylene glycol-coated gold NPs (PEG-AuNP) to ECs is impacted by glycocalyx structure on the EC surface. Rat fat pad endothelial cells were chosen for their robust glycocalyx, verified by fluorescent immunolabeling of adsorbed albumin and integrated heparan sulfate (HS) chains. Confocal fluorescent imaging revealed a ~3 µm thick glycocalyx layer, covering 75% of the ECs and containing abundant HS. This healthy glycocalyx hindered the uptake of PEG-AuNP as expected because glycocalyx pores are typically 7 nm wide. Additional glycocalyx models tested included: a collapsed glycocalyx obtained by culturing cells in reduced protein media, a degraded glycocalyx obtained by applying heparinase III enzyme to specifically cleave HS, and a recovered glycocalyx obtained by supplementing exogenous HS into the media after enzyme degradation. The collapsed glycocalyx was2 µm thick with unchanged EC coverage and sustained HS content. The degraded glycocalyx showed similar changes in EC thickness and coverage but its HS thickness was reduced to 0.7 µm and spanned only 10% of the original EC surface. Both dysfunctional models retained six- to sevenfold more PEG-AuNP compared to the healthy glycocalyx. The collapsed glycocalyx permitted NPs to cross the glycocalyx into intracellular spaces, whereas the degraded glycocalyx trapped the PEG-AuNP within the glycocalyx. The repaired glycocalyx model partially restored HS thickness to 1.2 µm and 44% coverage of the ECs, but it was able to reverse the NP uptake back to baseline levels. In summary, this study showed that the glycocalyx structure is critical for NP uptake by ECs and may serve as a passive pathway for delivering NPs to dysfunctional ECs.

Dual MMP7-proximity-activated and folate receptor-targeted nanoparticles for siRNA delivery.

A dual-targeted siRNA nanocarrier has been synthesized and validated that is selectively activated in environments where there is colocalization of two breast cancer hallmarks, elevated matrix metalloproteinase (MMP) activity and folate receptor overexpression. This siRNA nanocarrier is self-assembled from two polymers containing the same pH-responsive, endosomolytic core-forming block but varying hydrophilic, corona-forming blocks. The corona block of one polymer consists of a 2 kDa PEG attached to a terminal folic acid (FA); the second polymer contains a larger (Y-shaped, 20 kDa) PEG attached to the core block by a proximity-activated targeting (PAT), MMP7-cleavable peptide. In mixed micelle smart polymer nanoparticles (SPNs) formed from the FA- and PAT-based polymers, the proteolytically removable PEG on the PAT polymers shields nonspecific SPN interactions with cells or proteins. When the PAT element is cleaved within an MMP-rich environment, the PEG shielding is removed, exposing the underlying FA and making it accessible for folate receptor-mediated SPN uptake. Characterization of mixed micelles prepared from these two polymers revealed that uptake and siRNA knockdown bioactivity of a 50% FA/50% PAT formulation was dependent on both proteolytic activation and FA receptor engagement. MMP activation and delivery of this formulation to breast cancer cells expressing the FA receptor achieved greater than 50% protein-level knockdown of a model gene with undetectable cytotoxicity. This modular nanoparticle design represents a new paradigm in cell-selective siRNA delivery and allows for stoichiometric tuning of dual-targeting components to achieve superior targeting specificity.