Controlled Hydrogen Sulfide Delivery to Enhance Cell Survival in Bone Tissue Engineering

The increased local concentration of calcium ions (Ca2+) and phosphate (Pi), a natural body process for bone healing and remodeling, as well as local delivery of these ions as signaling molecules by synthetic bone graft substitutes, may lead to cytotoxic ion levels that can result in Ca2+/ Pi mitochondria overload, oxidative stress, and cell death. In this research, the effect of H2S as a cytoprotective signaling molecule to increase the tolerance of mesenchymal stem cells (MSCs) in the presence of cytotoxic level of Ca2+/Pi was evaluated. Different concentrations of sodium hydrogen sulfide (NaSH), a fast-releasing H2S donor, were exposed to cells in order to evaluate the influence of H2S on MSC proliferation. The results suggested that a range of NaSH (i.e., 0.25 - 4 mM NaSH) was non-cytotoxic and could improve cell proliferation and differentiation in the presence of cytotoxic levels of Ca2+ (32 mM) and/or Pi (16 mM). To controllably deliver H2S over time, a novel donor molecule in thioglutamic acid (GluSH) was synthesized and evaluated for its H2S release profile. Excitingly, GluSH successfully maintained cytoprotective level of H2S over 7 days. Furthermore, MSCs exposed to cytotoxic Ca2+/Pi concentrations in the presence of GluSH were able to thrive and differentiate into osteoblasts. These findings suggest that the incorporation of a sustained H2S donor such as GluSH into CaP-based bone substitutes can facilitate considerable cytoprotection making it an attractive option for complex bone regenerative engineering applications.