Self-aggregation characteristics of recombinantly expressed human elastin polypeptides.

Elastin is an extracellular matrix protein found in tissues requiring extensibility and elastic recoil. Monomeric elastin has the ability to aggregate into fibrillar structures in vitro, and has been suggested to participate in the organization of its own assembly into a polymeric matrix in vivo. Although hydrophobic sequences in elastin have been suggested to be involved in this process of self-organization, the contributions of specific hydrophobic and crosslinking domains to the propensity of elastin to self-assemble have received less attention. We have used a series of defined, recombinant human elastin polypeptides to investigate the factors contributing to elastin self-assembly. In general, coacervation temperature of these polypeptides, used as a measure of their propensity to self-assemble, was influenced both by salt concentration and polypeptide concentration. In addition, hydrophobic domains appeared to be essential for the ability of these polypeptides to self-assemble. However, neither overall molecular mass, number of hydrophobic domains nor general hydropathy of the polypeptides provided a complete explanation for differences in coacervation temperature, suggesting that the specific nature of the sequences of these hydrophobic domains are an important determinant of the ability of elastin polypeptides to self-assemble.

Bisphosphonate (pamidronate/APD) prevents arthritis-induced loss of fracture toughness in the rabbit femoral diaphysis.

Patients with rheumatoid and other inflammatory arthritis have an increased risk for fracture. This study was designed to determine the effect of experimental inflammatory arthritis on the material properties (fracture toughness and shear modulus) and structural properties (torque, angular deflection, and absorbed energy) of femoral diaphyseal bone tested in torsion to fracture, as well as the effect on these properties of APD (3-amino-1-hydroxypropylidene-1,1-bisphosphonate), a drug known to block osteoclast activity. Two dose levels were investigated. Experimental inflammatory arthritis was induced by intra-articular injection of carrageenan into the right tibiofemoral joint, given over 7 weeks, in three groups of animals. Simultaneously, daily subcutaneous injections of APD were given to three groups of rabbits. Five groups (12 animals each) were established: normal, arthritis, normal/high dose APD, arthritis/high dose APD, and arthritis/low dose APD. The diaphyses of each excised right femur were loaded to fracture in torsion at an angular deflection rate of 8 degrees/sec. In the arthritis group, the fracture toughness was 39% lower than in the normal group, and the structural properties all were reduced significantly. By contrast, the shear modulus was unaffected by arthritis. In this study, the higher dose level (0.3 mg/kg of body weight) of APD prevented loss of fracture toughness and maintained the structural properties in experimental inflammatory arthritis; the low dose was not effective.

Microstructural and tensile properties of elastin-based polypeptides crosslinked with genipin and pyrroloquinoline quinone.

Elastin is an elastomeric, self-assembling extracellular matrix protein with potential for use in biomaterials applications. Here, we compare the microstructural and tensile properties of the elastin-based recombinant polypeptide (EP) EP20-244 crosslinked with either genipin (GP) or pyrroloquinoline quinone (PQQ). Recombinant EP-based sheets were produced via coacervation and subsequent crosslinking. The micron-scale topography of the GP-crosslinked sheets examined with atomic force microscopy revealed the presence of extensive mottling compared with that of the PQQ-crosslinked sheets, which were comparatively smoother. Confocal microscopy showed that the subsurface porosity in the GP-crosslinked sheets was much more open. GP-crosslinked EP-based sheets exhibited significantly greater tensile strength (P < or = 0.05). Mechanistically, GP appears to yield a higher crosslink density than PQQ, likely due to its capacity to form short-range and long-range crosslinks. In conclusion, GP is able to strongly modulate the microstructural and mechanical properties of elastin-based polypeptide biomaterials forming membranes with mechanical properties similar to native insoluble elastin.