Adjuvant Delivery Method and Nanoparticle Charge Influence Peptide Amphiphile Micelle Vaccine Bioactivity.

Vaccines are an indispensable public health measure that have enabled the eradication, near elimination, and prevention of a variety of pathogens. As research continues and our understanding of immunization strategies develops, subunit vaccines have emerged as exciting alternatives to existing whole vaccine approaches. Unfortunately, subunit vaccines often possess weak antigenicity, requiring delivery devices and adjuvant supplementation to improve their utility. Peptide amphiphile micelles have recently been shown to function as both delivery devices and self-adjuvanting systems that can be readily associated with molecular adjuvants to further improve vaccine-mediated host immunity. While promising, many "design rules" associated with the plethora of underlying adjustable parameters in the generation of a peptide amphiphile micelle vaccine have yet to be uncovered. This work explores the impact micellar adjuvant complexation method and incorporated antigen type have on their ability to activate dendritic cells and induce antigen specific responses. Interestingly, electrostatic complexation of CpG to micelles resulted in improved in vitro dendritic cell activation over hydrophobic association and antigen|adjuvant co-localization influenced cell-mediated, but not antibody-mediated immune responses. These exciting results complement those previously published to build the framework of a micelle vaccine toolbox that can be leveraged for future disease-specific formulations.

Hydrogen Sulfide Delivery to Enhance Bone Tissue Engineering Cell Survival.

Though crucial for natural bone healing, local calcium ion (Ca2+) and phosphate ion (Pi) concentrations can exceed the cytotoxic limit leading to mitochondrial overload, oxidative stress, and cell death. For bone tissue engineering applications, H2S can be employed as a cytoprotective molecule to enhance mesenchymal stem cell (MSC) tolerance to cytotoxic Ca2+/Pi concentrations. Varied concentrations of sodium hydrogen sulfide (NaSH), a fast-releasing H2S donor, were applied to assess the influence of H2S on MSC proliferation. The results suggested a toxicity limit of 4 mM for NaSH and that 1 mM of NaSH 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 (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 graft substitutes can facilitate considerable cytoprotection, making it an attractive option for complex bone regenerative engineering applications.

Inductive co-crosslinking of cellulose nanocrystal/chitosan hydrogels for the treatment of vertebral compression fractures.

Vertebral compression fractures are a very common consequence of osteoporosis for which injection of a non-biodegradable, non-bioactive, mechanically-stiff polymer bone cement into the vertebral body is the most common treatment. Recently, there has been growing interest in using bioactive, degradable, and bone biomechanics-matching products as an alternative approach for treating these fractures. In this research, we focused on creating injectable, chitosan-based hydrogels that can convey mechanical strength similar to vertebral bone as well as possess inherent osteoinductivity. First, we investigated the effects of three different factors - 1) bioactive phosphate ionic crosslinking; 2) genipin covalent crosslinking; 3) mechanically reinforcing cellulose nanocrystal incorporation - on the material properties of chitosan-based hydrogels. Mesenchymal stem cells were then exposed to hydrogels with optimum mechanical properties and stability in order to assess the biological effects of the bioactive phosphate ionic crosslinker. Our results show that hydrogels with higher ionic and covalent crosslinking ratios supplemented with neutral cellulose nanocrystals possessed desirable compressive strength and stability. Also, the significant osteoinductivity of these composite hydrogels demonstrated their potential to function as an injectable system for the future treatment of vertebral compression fractures.