N-Acetylcysteine and Hydrogen Sulfide Releasing Biomaterials for Neuronal Protection and Differentiation in Peripheral Nerve Injury Regeneration

In the United States, twenty million Americans suffer from peripheral nerve injury (PNI) due to trauma and medical disorders. The majority of these injuries are a result of upper limb trauma and can result in considerable physical disability and long term decrease in quality of life. This is partly due to the several limitation surgical treatments (e.g. direct nerve grafts, nerve transfer, etc) for neural injuries that are often associated with sub-optimal functional recovery with fewer than half of the patients who receive nerve repair procedures post-injury regain complete mobility and sensitivity. This highlights the inadequacy of present-day treatment methods. The use of hollow nerve guidance conduits for nerve repair is clinically approved as an alternative treatment to the “gold standard” autologous neural grafts for PNIs.

Recent efforts in the field have shifted towards exploring alternative solutions such as neural scaffolds that incorporate biological cues. Simple signaling molecule Hydrogen Sulfide (H₂S) has been shown to possess neuroprotectant and neural differentiation capability that could assist in the healing of PNI via hollow nerve guidance conduits. Another promising neuroprotectant is N-acetylcysteine (NAC), a known antioxidant derived from L-cysteine and is medication used to treat paracetamol (acetaminophen) overdose, and that has demonstrated capabilities in suppressing mitochondrial reactive oxidative species (ROS) by increasing intracellular Glutathione (GSH) concentration.

This research looks therapeutic capability for H₂S and NAC through cell proliferation and preliminary efforts to synthesize monomers thioglutamylglutamic acid (GluGluSH) and N-acetylcysteineglutamic acid (GluNAC). This was accomplished through cellular studies using neuroblastoma (NE-4C) cells exposed to either NAC or NaSH and H₂O₂. DNA, ATP assays and fluorescent microscopy were used to determine therapeutic window and capability of both NAC and NasH. Synthetic work done includes thiolation reaction of Boc-Glutamic (OBzl) acid and sequential palladium on carbon reduction reaction. Products formed were detected using thin-layer chromatography (TLC), purified using column chromatography, and characterized for their structure confirmation by employing Fourier transform infrared spectroscopy (FTIR) and proton (¹H) as well as carbon (¹³C) nuclear magnetic resonance (NMR) spectroscopy techniques.

Future research will focus on continued synthesis of GluNAC and GluGluSH monomer to then leverage for various degradable polymers (e.g, polyanhydrides and polyester), for which cell studies can be guided by the already established therapeutic window. Ultimately, these neurogenerative and neuroprotective biomaterials have the potential to be integrated in hollow nerve guidance conduits for treatment of peripheral nerve injuries.