(593ap) Elastin Based Nano Particles for Treatment of Chronic Wounds

Introduction: Chronic wounds affect 5.7 million patients and cost an estimated 20 billion dollars annually. Recently, we developed a growth factor delivery platform based on elastin like peptides (ELPs) for growth factor delivery to chronic wounds. Elastin like peptides are repeats of the pentapeptide (VPGXG, X=guest residue can be anything but Proline) derived from natural elastin. They are attractive delivery vehicles due to their unique phase transition properties and are genetically encodable and biocompatible. The unique phase transition property of ELPs is a direct function of the chain length and guest residue, which allows us to design biomaterial delivery systems with desirable physical properties. Interestingly, we also observed that ELPs were not only useful for delivery of growth factors but also enhanced granulation in the wound through modulation of fibroblast growth and function. In this study, we aim to elucidate the effect of chain length and guest residues on the ELP induced modulation of fibroblast function.

Materials and Methods: We created several ELPs with different chain lengths (number of VPGVG repeats) and having different cysteines in the guest residue position. These ELPs were recombinantly produced in bacteria using standard molecular biology and protein expression techniques. The protein was purified to high homogeneity using inverse temperature cycling which exploits the phase transitioning property of ELPs. The purity was tested using SDS-PAGE and the physical properties of ELPs were characterized using dynamic light scattering and transmission electron microscopy. Normal human dermal fibroblasts were treated with different ELPs and proliferation was evaluated using Hoechst assay. We used RT-PCR to assess the effect of ELPs on several genes associated with normal fibroblast functions such as collagen production, matrix metalloproteinase activity and fibrillin expression.

Results: We observed that ELPs self-assembled into nanoparticles with different hydrodynamic diameters depending on their chain length and proportion of cysteines. We further found that ELPs increased fibroblast proliferation significantly. Interestingly, this increase was dependent on the chain length and proportion of cysteines. This increase of proliferation was successfully blocked using lactose suggesting that ELPs bind to the elastin receptor to induce proliferation.

Conclusions: Our study suggests that ELPs induce fibroblast proliferation. This biological activity of ELPs is dependent on chain length as well as guest residues which also determine the physical phase transition properties of ELPs. Furthermore, our data suggest that ELPs induce their biological effect on fibroblasts through interaction with the elastin receptor complex present on the fibroblast surface. An understanding of the exact interaction of ELPs and identifying the determinants of this interaction (i.e. chain length, guest residue) will help us in the design of unique ELP based biomaterials having the desired physical and biological properties that are conducive to the healing of chronic wounds. Thus they will not only be useful as drug delivery vehicles but also may induce healing synergistically through their intrinsic biological activities.