Summary
Objectives: The purposes of this study were to determine: 1) the efficacy of polycaprolac-tone-g-polyethylene
glycol (PCL-g-PEG) and polylactic-co-glycolic acid (PLGA-g-PEG) hydrogels and an absorbable
collagen sponge (ACS) as carriers for lysophosphatidic acid (LPA), 2) the effect of
LPA on bone healing in dogs, and 3) the ideal dose of LPA to maximally stimulate bone
healing.
Methods: Bilateral ulnar ostectomies were performed on purpose bred dogs. Control defects
were filled with a PCL-g-PEG or PLGA-g-PEG hydrogel, or a saline soaked ACS. Contralateral
defects were filled with a PCL-g-PEG or PLGA-g-PEG hydrogel, or an ACS with each carrying
differing concentrations of an LPA solution. Dual-energy X-ray absorptiometry (DXA)
was performed. Total bone area (TBA), mineral density (BMD), and mineral content (BMC)
were determined at each time point. Relationships between the effect of treatment
over time on TBA, BMC and BMD were determined.
Results: Phase 1 - There was no significant difference in DXA-based TBA (p = 0.09), BMC (p
= 0.33), or BMD (p = 0.74) over time between LPA treatments, or between the LPA treated
and control groups TBA (p = 0.95), BMC (p = 0.99), or BMD (p = 0.46). Phase 2 - There
was no significant difference over time between LPA treatments in DXA-based TBA (p
= 0.33), BMC (p = 0.45), or BMD (p = 0.43), or between the LPA treated and control
groups TBA (p = 0.94), BMC (p = 0.38), or BMD (p = 0.17). Phase 3 - There was no significant
difference over time between LPA treatments in DXA-based TBA (p = 0.78), BMC (p =
0.88), or BMD (p = 0.35), or between the LPA treated and control groups TBA (p = 0.07),
BMC (p = 0.85), or BMD (p = 0.06). There was a significant increase in TBA (p <0.0001)
and BMC (p = 0.0014), but a significant decrease in BMD (p <0.0001) was noted over
time when all groups were combined.
Clinical significance: Although LPA has shown promise as an osteoinductive agent in research, its performance
as a bone graft substitute, as utilized in this study, is unsupported. Further studies
are necessary to determine the incorporation and elution kinetics of LPA from the
PLGA-g-PEG hydrogel and from an ACS. Hydrogels may have clinical applications for
delaying or preventing bone formation.
Keywords
Lysophosphatidic acid - hydrogel - polycaprolactone - bone healing - osteogenesis