Effect of Heat Shock on Apoptosis and Necrosis in Osteoblasts

Damage to bone tissue due to heat shock can cause complications or even failure of the surgery and treatment itself. Studies have shown that heat generation during drilling process or bone cutting can cause failure in osseointegration at the bone-implant interface or may even cause thermonecrosis at the cortical bone area resulting in bone loss. Bone loss at the newly placed surgical screws and pins may cause loosening of the screws postoperatively.

Objectives: The purpose of this study is to investigate the effect of various temperatures and time points on apoptosis and necrosis in osteoblasts.

Methods: Osteoblastic cell line ; MG63 derived from osteogenic sarcoma were exposed to temperatures of 37^oC, 40^oC, 43^oC, 46^oC and 48^oC for 1,5 and 10 minutes, then incubated for 24 hours at 37^oC, 5% CO₂ and 95% air. The cell line was assayed for apoptosis using an ELISA kit ( Cell Death Detection ELISA Plus/ Roche version April 2006). Specimens were also examined with scanning electron microscopy (SEM).

Results: Preliminary results showed that, increase in temperature leads to decrease in apoptosis and increase in necrosis at 5 minutes and 10 minutes exposures. However, exposing the osteoblasts to graded temperatures for 1 minute resulted in increased apoptosis. In contrast, necrosis in the 1 minute incubation cultures was reduced dramatically compared to the 5 and 10 minutes incubation above 40^oC. When the cells were exposed to temperature of 46^oC and 48^oC for 1 minute, there was more cell death by apoptosis rather than necrosis. Inverted microscopy revealed that the osteoblasts only recover after 1 minute exposure at all temperatures.

Conclusion: Heat treatment of over 40^oC for longer than 5 minutes leads to osteoblast necrosis. Reducing the treatment time to 1 minute eliminates necrosis, but there is an increase in apoptosis.