Damage to bone tissue due to heat shock is one of the main causes of the fa
ilure of osseointegration at the bone-implant interface. To investigate the
effect of heal shock on regeneration of bone tissue, osteoblasts were expo
sed to heat shuck for 10 minutes at 42, 45, or 48 degrees C or kept at 37 d
egrees C as a control. After 10 minutes of heat shock, disruption of actin
filaments was seen in the cells and the degree of disruption increased with
the temperature. The cytoskeleton reassembled after a 12-hour incubation a
t 37 degrees C in the cells treated at 42 or 45 degrees C, but this reversi
ble recovery did not occur in the cells treated at 48 degrees C. Flow cytom
etric analysis showed that heat shock at 48 degrees C increased the number
of necrotic cells to 15-20% within minutes (p < 0.05 compared with 37 degre
es C). Apoptosis, evidenced by annexin V staining, DNA laddering, and caspa
se 3 activation, started after 6-8 hours of incubation, reached a peak at 1
2 hours, and gradually declined (p < 0.05). Pretreatment with the antioxida
nt N-acetyl-L-cysteine reduced the necrosis induced at 48 degrees C of heat
shock by one-half (p < 0.05) but had no significant effect on caspase 3 ac
tivation induced by heat shock, suggesting that reactive oxygen species wer
e critical in heat shock-induced necrosis but not in apoptosis. Heat shock
at 48 degrees C induced a sustained translocation of p53 into the nucleus a
nd a sustained activation of c-jun N-terminal kinase, whereas that at 42 an
d 45 degrees C induced only transient p53 translocation and c-jun N-termina
l kinase activation. These results suggest that the sustained activation of
p53 and c-jun N-terminal kinase pathways may contribute to heat shock-indu
ced apoptosis. On the other hand, heat shock protein 70 increased dramatica
lly in the cells treated at 45 or 48 degrees C, suggesting that the protect
ing mechanism in the cells was also activated. Such protection was able to
prevent apoptosis in cells treated at 45 degrees C but not in those treated
at 48 degrees C.