Heparin is a vital biomolecule in widespread clinical use as an anti-coagulant. Heparin sensors have potential applications in the bedside detection of heparin levels in human blood during surgery, while high-affinity heparin binders may enable the development of effective heparin reversal agents for use in patients once surgery is complete. However, human blood is a challenging medium in which to achieve selective high-affinity molecular recognition, and as such, this system provides a fascinating challenge to supramolecular chemists. This has encouraged research using a variety of different systems and is stimulating new approaches to the application of molecular recognition. This review article provides an overview of research from both clinical and supramolecular communities towards heparin binding and sensing and considers how this area may develop in the future.
We report the simple synthesis and full investigation
of a novel
heparin binding dye, mallard blue, an arginine-functionalized thionine.
This dye binds heparin in highly competitive media, including water
with high levels of competitive electrolyte, buffered aqueous solution
and human serum. The dye reports on heparin levels by a significant
change in its UV–vis spectroscopic profile. Molecular dynamics
modeling provides detailed insight into the binding mode. Heparin
binding is shown to be selective over other glycosaminoglycans, such
as hyaluronic acid and chondroitin sulfate. Importantly, we
demonstrate that, in the most competitive conditions, mallard blue
outperforms standard dyes used for heparin sensing such as azure A.
This paper investigates small molecules that self-assemble to display multivalent ligand arrays for heparin binding. In water, the self-assembled multivalent (SAMul) heparin binder is highly competitive with the current clinical heparin reversal agent, protamine. On addition of salt, the dimensions of the self-assembled nanostructure increase. This unique feature is due to the dynamic, responsive nature of assembly, predicted using multiscale modelling and proven experimentally, enhancing heparin binding of SAMul systems relative to fixed covalent multivalent nanostructures. Conversely, the presence of serum adversely affects the heparin binding of SAMul systems relative to covalent nanostructures due to partial destabilisation of the assemblies. Nonetheless, clotting assays in human plasma demonstrate that the SAMul system acts as a functional heparin reversal agent. Compound degradation, inducing nanostructure disassembly and loss of SAMul binding, takes place over 24 hours due to ester hydrolysis – but when bound to heparin, stability is enhanced. Heparin reversal in plasma, and the therapeutically useful degradation profile, make this SAMul approach of potential therapeutic value in replacing protamine, which has a number of adverse effects when used in the clinic
This communication presents simple cationic self-assembling multivalent (SAMul) first generation dendrons based on L or D lysine, which form identical nanoscale assemblies in terms of dimensions and charge densities but toward which DNA and heparin exhibit different chiral binding preferences. However, higher generation dendrons with larger hydrophilic head groups are bound identically by these polyanions, irrespective of chirality. We propose that well-organized chiral ligands on the surface of self-assembled nanostructures can exhibit enantioselective polyanion binding. This demonstrates that small structural changes can be amplified by self-assembly and impact on nanoscale binding.
We report a competition assay using our recently reported dye Mallard Blue, which allows us to identify synthetic heparin binders in competitive media, including human serum - using this we gain insight into the ability of PAMAM dendrimers to bind heparin, with the interesting result that low-generation G2-PAMAM is the preferred heparin binder.
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