PMMA particles may induce chondrocyte cell apoptosis

Inhibiting the expression of two enzymes may offer a potential approach for disrupting the progression of knee osteoarthritis.

CHICAGO — Particles of polymethylmethacrylate can induce the expression of two key enzymes, causing the production of nitric oxide and ultimately leading to chondrocyte cell death, according to a study presented here.

“PMMA (polymethylmethacrylate) particles induced apoptotic chondrocyte death associated with the induction and activation of Caspace 3, iNOS (inducible nitric oxide synthase) and nitric oxide production,” said Brett Cascio, MD. “This could offer an explanation for the progression of osteoarthritis in [patients who receive] partial knee replacement. And the suppression of the two enzyme systems may offer a potential approach for disrupting the progression of cell death.”

Cascio and colleagues at Johns Hopkins Medical Center, Baltimore, investigated the effects of PMMA particles on human chondrocytes. The researchers hypothesized that PMMA particles would induce apoptosis via the nitric oxide pathway.

“Nitrite is the main degradation product of nitric oxide, and the iNOS and Caspace 3 enzymes are critical to the apoptotic pathway,” said Cascio, who presented the results of the study here at the American Academy of Orthopaedic Surgeons 73rd Annual Meeting.

Isolating, incubating chondrocytes

For the study, researchers harvested articular cartilage from patients undergoing knee arthroplasty procedures and isolated chondrocytes from those cartilage samples. The chondrocytes were then incubated in three different culture media: a control medium, one containing 107 polystyrene particles, or one containing 107 PMMA particles.

Hoechst staining showed that both control cells and polystyrene-exposed cells maintained a normal morphology. However, the PMMA-exposed chondrocytes demonstrated a morphology indicative of apoptosis, including nuclear condensation, plasma membrane shrinkage and cell body shrinkage, Cascio said.

At 24 hours postexposure, 16% of PMMA-exposed cells appeared apoptotic, which increased to 37% at 48 hours postexposure.

Transmission electron microscopy provided further evidence of apoptosis among PMMA-exposed chondrocytes, including the presence of phagocytosed particles and extensive vacuolation. In contrast, control and polystyrene-exposed cells appeared to remain normal, Cascio said.

Further analysis also demonstrated that PMMA-exposed cells had elevated levels of iNOS and Caspace 3, “which is indicative of the nitric oxide pathway,” he added, noting that nitrite levels were found to be elevated in these cells.

For more information:
Cascio B, Al-Talib T, Polotsky AV, et al. Polymethylmethacrylate particles induce Caspace 3 iNOS expression and apoptotic chondrocyte death. #396. Presented at the American Academy of Orthopaedic Surgeons 73rd Annual Meeting. March 22-26, 2006. Chicago.