Highly Thiolated Poly (Beta-Amino Ester) Nanoparticles for Acute Redox Applications

Abstract

Disulfides are used extensively in reversible cross-linking because of the ease of reduction into click-reactive thiols. However, the free-radical scavenging properties upon reduction are often under-considered. The free thiols produced upon reduction of this disulfide material mimic the cellular reducing chemistry (glutathione) that serves as a buffer against acute oxidative stress. A nanoparticle formulation producing biologically relevant concentrations of thiols may not only provide ample chemical conjugation sites, but potentially be useful against severe acute oxidative stress exposure, such as in targeted radioprotection. In this work, we describe the synthesis and characterization of highly thiolated poly (β-amino ester) (PBAE) nanoparticles formed from the reduction of bulk disulfide cross-linked PBAE hydrogels. Degradation-tunable PBAE hydrogels were initially synthesized containing up to 26 wt % cystamine, which were reduced into soluble thiolated oligomers and formulated into nanoparticles upon single emulsion. These thiolated nanoparticles were size-stable in phosphate buffered saline consisting of up to 11.0 ± 1.1 mM (3.7 ± 0.3 mmol thiol/g, n = 3 M ± SD), which is an antioxidant concentration within the order of magnitude of cellular glutathione (1⁻10 mM).

Keywords: drug delivery; poly (β-amino ester) (PBAE); polymeric nanoparticle; redox; thiol.

Figure 1

Hydrogel-to-nanoparticle synthesis scheme. (A) disulfide poly (β-amino ester) (PBAE) hydrogel and conversion into (B) thiolated oligomers via a reducing agent (2-mercaptoethanol), and (C) single-emulsion into thiolated nanoparticles.

Figure 2

Disulfide hydrogel characteristics. (A) % CA loss of total CA added after washing in dimethylsulfoxide (DMSO), (B) % mass loss of hydrogel CA based on total mass before and after wash, and (C) conversion with FT-IR. (D) % mass remaining during sink condition degradation at 37 °C, (E) disulfide release, and (F) comparison of disulfide release to mass loss over time. n = 3, M ± SD.

Figure 3

Comparison of oligomer feed concentration. (A,C) Comparison of nanoparticle z-average diameter and (B,D) polydispersity index of HEDA/CA and DEGDA/CA based thiolated nanoparticles, respectively, in phosphate-buffered saline/polyvinyl alcohol/ethylenediaminetetraacetic acid (PBS/PVA/EDTA). n = 3, M ± SD. * Maximum concentration before particles became unstable.

Figure 4

Kinetics plots of HEDA/CA nanoparticles in PBS/EDTA/EDTA. (A) z-average diameter, (B) polydispersity index (PDI), (C) total thiol found, (D) total thiol found per mass of nanoparticles, (E) % intensity of dispersion over time, and (F) % of the theoretical maximum thiol concentration found after washing. n = 3, M ± SD.

Figure 5

Size and activity kinetics of DEGDA/CA nanoparticles in PBS/PVA/EDTA. (A) z-average diameter, (B) polydispersity index, (C) total thiol found, (D) total thiol found per mass of nanoparticles, (E) % intensity of dispersion over time, and (F) % of the theoretical maximum thiol concentration found after washing. n = 3, M ± SD. * Indicates p < 0.05 intensity change from original.