Ultra-high molecular weight polyethylene oxidation reduces metalloproteinase 2 secretion in human osteoblast-like cells in vitro: A mechanism of modulation of extracellular matrix

Ultra-high molecular weight polyethylene (UHMWPE) sterilization with gamma rays induced high oxidation levels both on the surface and in the bulk that alter its structure and mechanical properties. The oxidation process of gamma-radiated UHMWPE induces a reduction of molecular weight and, consequently, a less abrasive resistance that has been related, among others, to the failure of UHMWPE in vivo. To explain the role of cells in such events, human osteoblast-like cells were seeded onto UHMWPE and oxidized UHMWPE discs. Cellular viability and morphology were evaluated along with matrix metalloproteinases (MMPs) production and activity. Oxidized UHMWPE did not induce any significant cytotoxic effects as observed by lactate dehydrogenase activity compared to the nonoxidized form; no changes in the cell morphology after 4 and 8 days proliferation were observed. In growth medium metalloproteinase 2 (gelatinase-A, MMP-2) was produced and released by osteoblast-like cells. We observed that cells grown onto oxidized UHMWPE discs decreased the release and activity of MMP-2 after 4 and 8 days culture compared to cells grown on control and non-oxidized UHMWPE discs; metalloproteinase 9 (gelatinase-B, MMP-9) release was not significantly influenced. The absence of cytotoxic and morphological effects in the presence of a down-regulation of MMP-2 release and activity suggest that oxidized polyethylene surfaces may modulate matrix remodeling and, consequently, bone formation.