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Biomaterials

Biomaterials - Poster Session A

Poster C2 - Aromatic Peptide Amphiphiles for Emergency Overdose Treatment

Thursday, October 24, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  For non-opioid overdoses, activated charcoal (AC) remains the standard treatment. While numerous in vitro and in vivo studies have demonstrated the efficacy of AC for drug adsorption, its administration sometimes causes adverse effects, including pulmonary compromise, gastrointestinal obstruction, and even death. Despite these risks, AC remains the primary treatment for non-opioid overdoses due to its low cost and high capacity for drug adsorption.

However, a new class of aromatic peptide amphiphiles has been prepared as a promising alternative that may circumvent the issues associated with AC. The polymer is composed of a hydrophilic block and a hydrophobic block. The hydrophilic block mediates adhesion and adsorption via electrostatic interactions, while the hydrophobic block is responsible for adsorption via π-π interactions and aggregate formation. To encourage biocompatibility, polypeptides were chosen as the basis of the adsorbent material. Furthermore, the materials were designed with cost in mind, as amino acids are naturally occurring and are relatively inexpensive to purchase. If administered orally following a drug overdose, the material is designed to adsorb the target drugs and allow drug-entrapped aggregates to be cleared from the body before they are absorbed into the bloodstream.

Materials and

Methods:  Development of these materials involves synthesis, characterization, adsorption kinetics studies, adsorption capacity studies, and biocompatibility testing. Polypeptides were synthesized using ring-opening polymerization (ROP) of N-carboxyanhydride (NCA) monomers. The hydrophilic block is composed of glutamic acid residues to promote adsorption via electrostatic attraction with positively charged drug molecules. Tyrosine residues in the hydrophobic block encourage adsorption through π-π stacking interactions with aromatic drugs. Different initiators were used to create various polymer architectures, affecting the adsorption capacity. The insoluble nature of the material precludes characterization using a variety of techniques. However, certain physical and chemical characteristics can be determined through Brunauer-Emmett-Teller (BET) surface area analysis, dynamic light scattering (DLS), light microscopy, and scanning electron microscopy (SEM).

Studies were conducted in simulated biological fluids to determine the time to reach full adsorption (adsorption kinetics) and the maximum amount of drug that can be adsorbed to the polypeptide (adsorption capacity). Adsorption kinetics experiments used UV-Vis spectroscopy to measure drug concentration after incubation with the peptide adsorbent for various durations. The adsorption capacities for different drugs were determined using similar experimental conditions, but varying adsorbent-to-drug ratios. Fitting this data to different isotherm models reveals characteristics such as maximum adsorption capacity and binding affinity.

Mammalian cell studies were conducted to assess the toxicity of the peptide adsorbents at various concentrations. Both 3T3 fibroblast and macrophage cell types were monitored in the presence of the peptide adsorbent to determine percent viability. The data indicate that the peptide adsorbent formulations are cytocompatible regardless of the polymer architecture.

Results, Conclusions, and Discussions: Several peptide adsorbent formulations were developed to explore the structure-activity relationship of the material. The first, named “KEY,” includes lysine (K), glutamic acid (E), and tyrosine (Y). However, subsequent formulations excluded lysine (i.e., EYs) because most drugs are positively charged at physiological pH and do not interact attractively with lysine. At a 10:1 adsorbent-to-drug ratio in simulated intestinal fluid (SIF), EY200 (linear polymer, 200 tyrosine units) absorbed about 75% of amitriptyline, while KEY20 (linear polymer, 20 tyrosine units) absorbed only 20%. This trend was consistent across other drugs tested, demonstrating that formulations with greater mol % tyrosine were more effective at drug adsorption. Furthermore, adsorption may be enhanced by the absence of lysine residues, which can repel positively charged amines in many drugs.

To further investigate the effect of tyrosine incorporation on drug adsorption, EY peptides were synthesized at increasing mol percentages of tyrosine: EY20, EY75, EY100, EY125, and EY200. Studies demonstrated that drug adsorption increased with the degree of tyrosine polymerization, suggesting enhanced π-π stacking interactions with higher tyrosine content. Different polymer architectures, including EY200 star (tri-branched, planar) and EY200 TAT (tri-branched, 3D), were also explored. Hydrodynamic radius measurements showed a positive correlation between polymerization degree and size, with EY200 TAT being the largest due to its increased three-dimensionality. Microscopy and SEM imaging revealed greater cohesion and surface texture with larger Y-blocks and three-dimensional structures; EY200 TAT showed the most significant cohesion and texture (Figure 1). Although AC has a larger surface area than the peptide adsorbents, EY200 TAT has larger pore size and pore volume than AC, likely contributing to its enhanced adsorption properties.

Additional studies show that EY200 TAT has competitive adsorption properties compared to AC. In clinical settings, AC is typically administered at a 10:1 AC-to-drug ratio after overdose but sometimes fails to reach 100% drug adsorption. However, EY200 TAT at a 13:1 ratio in SIF adsorbed over 95% of amitriptyline and hydroxychloroquine within 30 minutes at physiological temperature. Although potentially more expensive to prepare, the high adsorption capacities and enhanced biocompatibility of these materials could make them attractive alternatives to AC for drug adsorption.

Acknowledgements (Optional):  I extend my sincere gratitude to Hunter Wood for his mentorship. I would also like to thank Joseph Dosch for his collaboration, and Dr. Stefanie Sydlik for providing me with the opportunity to contribute to the Sydlik lab. Additionally, I want to acknowledge and thank our collaborator Dr. James (Dazhe) Cao from UT Southwestern Medical Center, as well as the Medical Toxicology Foundation for funding this project.