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

Abstract

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.

Keywords:

• human endothelial cells
• gold nanoparticles
• nanorods
• glycocalyx
• heparan sulfate

Acknowledgments

For technical support and sharing equipment, the authors would like to thank Northeastern University’s summer interns Anisa Amiji and Mike Dumersaint, Professor Heather Clark, Assistant Professor Adam Ekenseair, the Department of Physics, and the Electronic Materials Research Institute. For financial support, the authors thank The National Institutes of Health (NIH) for the Mentored Career Development Award (K01-HL125499, granted to E Ebong); the National Science Foundation (NSF) for the Nanomedicine Science and Technology Integrative Graduate Education and Research Traineeship (IGERT) program (DGE-0965843, granted to Northeastern University); and the Northeastern University Departments of Chemical Engineering and Biology for graduate student stipends.

Author contributions

MJC, RK, and EEE designed the experiments. MJC, PP, and NNB performed the experiments and analyzed the data. MJC, NNB, and EEE interpreted the results of the experiments. NNB, MJC, PP, and EEE drafted the figures and manuscript. NNB, TJW, SS, and EEE edited, revised, and approved the final manuscript. TJW, SS, and EEE supervised the project. All authors contributed to data analysis, drafting and revising the article, gave final approval of the version to be published, and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.