Background: Recent studies have shown that osteoblast-like
cells respond directly to ultra-high molecular weight polyethylene
particles in culture, suggesting that they may be involved in aseptic loosening
of endoprostheses. We tested the hypothesis that the state of cell
maturation plays a role in the response of osteogenic cells to ultra-high
molecular weight polyethylene particles.
Methods: MG63 cells (immature osteoblast-like cells),
OCT-1 cells (mature secretory osteoblast-like cells), and MLO-Y4
cells (osteocyte-like cells) were treated for twenty-four hours
with commercial ultra-high molecular weight polyethylene particles
with an average diameter of 1 mm. The effect of particle treatment
on cell proliferation was assessed by measuring the number of cells,
whereas the effects on differentiation and local factor production
were assessed by measuring the production of osteocalcin, prostaglandin
E2, and nitric oxide. The effect of particles on apoptosis was also
Results: The addition of ultra-high molecular weight
polyethylene particles increased the number of MG63 cells, did not
affect the number of OCT-1 cells, and led to a decrease in the number
of MLO-Y4 cells. The observed changes in cell number were not due
to programmed cell death, as no more than 3% of the cells
in cultures treated with the highest concentration of particles
were undergoing apoptosis. Osteocalcin production was not affected
by the addition of particles. Prostaglandin E2 production was increased
in all three types of cultures, but the effect was greatest in OCT-1
cell cultures, as was the absolute amount of prostaglandin E2 produced.
Nitric oxide production was unaffected in MG63 cell cultures, but
it was stimulated in OCT-1 and MLO-Y4 cell cultures.
Conclusions: The results of the present study support
the hypothesis that osteoblast cell maturation state plays an important
role in the response to ultra-high molecular weight polyethylene
particles and that the terminally differentiated osteocyte may be involved
in the bone response to wear debris in vivo.
Clinical Relevance: Because maturation state in
the osteoblast lineage is an important factor in the cellular response
to wear debris and the osteocyte is surprisingly sensitive to ultra-high
molecular weight polyethylene particles, and because these cells
have been shown to be in direct contact with the bone-implant interface
via canaliculi, their role in aseptic loosening needs to be considered.