Interaction between the Polyelectrolytes Unfractionated Heparin and Universal Heparin Reversal Agents

Area of Science:

• Biomaterials Science
• Chemical Biology
• Polymer Chemistry

Background:

• Unfractionated heparin (UFH) is a widely used anticoagulant, but its effects can be difficult to reverse.
• A universal heparin reversal agent (UHRA-7) has been developed, featuring a polyglycerol core with charged Me-TREN groups and mPEG shielding.
• UHRA-7 has demonstrated biocompatibility and efficacy in neutralizing heparin.

Purpose of the Study:

• To investigate the interaction mechanism between unfractionated heparin (UFH) and universal heparin reversal agent 7 (UHRA-7).
• To determine the binding constant (Kb) and thermodynamic contributions (counterion/water release) to the UFH-UHRA-7 interaction.
• To propose a detailed model of the UFH-UHRA-7 binding based on experimental and simulation data.

Main Methods:

• Isothermal titration calorimetry (ITC) to measure binding constants at varying temperatures and salt concentrations.
• Analysis using theoretical models to dissect contributions of counterion and water release.
• Nuclear Magnetic Resonance (NMR) spectroscopy and molecular dynamics (MD) simulations to support interaction modeling.

Main Results:

• The binding constant (Kb) for UFH-UHRA-7 interaction was determined across a range of temperatures (278–323 K) and NaCl concentrations (0.06–0.20 M).
• Analysis revealed the significant roles of counterion and water release in driving the binding process.
• A model was proposed where binding is primarily mediated by electrostatic interactions between negatively charged UFH and positively charged Me-TREN/mPEG groups on UHRA-7.

Conclusions:

• UHRA-7 effectively binds to UFH, primarily through charge-charge interactions.
• The interaction is thermodynamically driven by counterion and water release, as elucidated by ITC and theoretical modeling.
• NMR and MD simulations provide structural insights, supporting the proposed binding model for UHRA-7 as a heparin antagonist.