Topobiological Targeting of the Blood Brain Barrier
Abstract
The endothelial glycocalyx is a membranous structure composed of glycoproteins and carbohydrate residues that sheaths the inner walls of our blood vessels, protects it from pathogen invasions and coordinates immune response. This highly hydrated vascular barrier can prevent access of bacteria, viruses, toxins to our cell membranes and can also determine the transport properties of targeted drugs and vaccines. Engineering a glycocalyx-mimetic interface on implantable biomaterials has several potential benefits. In the context of chemical and biological weapon defense, mechanistic questions underlying the interactions of pathogens with this glycocalyx are not well understood. For instance, some viruses are repelled by the glycocalyx, some are trapped within the glycocalyx, while others utilize specific and non-specific interactions with glycoproteins on the glycocalyx surface as a gateway to infect the cell. By developing a synthetic model of the glycocoalyx, we expect to identify the relevant physicochemical parameters that shape the interactions of viruses and virus-like species with this critical biological barrier. One key challenge in mimicking the glycocalyx is achieving a sufficiently high density of oligosaccharides in order to take advantage of multivalent interactions that drive carbohydrate–ligand recognition. Another challenge is designing receptor-mimicking affinity sites on the synthetic glycocalyx by exploiting the predominantly negative electrostatic charge of viruses and capturing them via non-specific electrostatic interactions. In our work, we have developed a tunable and modular model surface that recapitulates two crucial features of the sieve-like glycocalyx- the ability to resist non-specific protein adsorption as well as the capacity to specifically bind to target species through electrostatically mediated interactions. We accomplish this by designing a composite surface consisting of two elements. The first element, the base layer, is a copolymer formed by the chemical vapor deposition (CVD) copolymerization of two paracyclophane-based monomers, one co-monomer consisting of an atom transfer radical polymerization (ATRP) initiator and the other co-monomer containing an ionizable amine moiety. The protonated amine functions as a positively charged affinity site that binds to negatively charged species of interest such as viruses, bacteria, DNA etc. The second element, the top layer, consists of a glycomimetic polymer brush grafted from the ATRP initiation sites on the copolymer using surface-initiated ATRP (SI-ATRP), and serves as the non-fouling background. We have successfully synthesized polymer brushes bearing carbohydrate residues such as sorbitol, mannose, glucose and galactose using SI-ATRP, with precise control over polymer brush density and thickness. Using SI-ATRP we can control the spatial organization and density of carbohydrate residues on the polymer brush, thereby controlling multivalent biorecognition events. Our base copolymer composition is also tunable, as the ratio of the affinity sites to that of the ATRP initiation sites can be achieved by modifying the CVD copolymerization conditions. By varying the ratio of affinity sites to initiation sites, we were able to observe changes in adsorption profiles of model proteins and adenoviruses. An increase in affinity site surface density was found to promote adenovirus adhesion while the incorporation of a glycopolymer brush resulted in a significant reduction in viral adsorption. Our experimental results in conjunction with insights from our theoretical models demonstrate that pathogen and protein interactions with our model surface can be tailored by pH, electrolyte environment, affinity site density, brush thickness and brush composition. Our results can be used to guide the design of biosensors and of coating-based models for studying the onset of infectious diseases.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 26, 2016
- Source ID
- HDTRA11510045
Entities
People
- Joerg Lahann
Organizations
- Defense Threat Reduction Agency
- University of Michigan