Differences in DNA damage pathways induced by two ceramic nanoparticles

In our prophase studies, it has been proved that hydroxyapatite (HAP) and tricalcium phosphate (TCP) nanoparticles (NPs) had obvious cytotoxicity on rat macrophages. So, mechanisms of DNA damage induced by HAP and TCP NPs would be discussed in these studies.

Rat peritoneal macrophages were cultured and induced by NPs in vitro. Then, the expressions of P53, P21, growth arrest and DNA damage 45 (Gadd45), and heat shock protein 70 (HSP70) were examined by reverse transcription polymerase chain reaction.

The results showed that the expressions of P53, P21, and HSP70 increased with increasing concentrations of HAP NPs. The expressions of P53 and HSP70 were clearly higher than the negative control at 100 microg/mL HAP NPs ( p < 0.05), but the P21 expression decreased at 200 microg/mL HAP. HAP NPs had no effect on the Gadd45 expression ( p > 0.05). Furthermore, 20 microg/mL TCP NPs could markedly induce the expression of all four genes ( p < 0.05), although their expression decreased with increasing concentration of TCP NPs.

These studies confirm that only 20 microg/mL TCP NPs could induce DNA damage compared with 100 microg/mL HAP NPs. HAP NPs induced cell cycle arrest to allow enough time for DNA repair, while TCP NPs simultaneously promoted the removal of damaged nucleotides and cell cycle arrest to repair the damaged DNA. DNA damage was irreversible when the concentration of these NPs was greater than 200 mu g/mL. Therefore, HAP and TCP NPs induce DNA damage at the molecular level and induce different DNA damage responses.