Hydroxyapatite electret accelerates reendothelialization and attenuates intimal hyperplasia occurring after endothelial removal of the rabbit carotid artery

The present experiments were designed to investigate whether electrically polarized hydroxyapatite (HA electret) modifies reendothelialization and intimal hyperplasia occurring after endothelial removal of the rabbit carotid artery. Both HA electret and non-polarized HA, which served as a control, had been powdered and mixed with agarose gel. One of the two was applied around the external surface of the carotid artery. Histological analyses revealed that HA electret but not control HA significantly inhibited intimal hyperplasia. The number of Ki67-positive cells detectable in the intimal layer was significantly fewer in the HA electret group. In the HA electret group, abundant TUNEL-positive cells were detected in the media. The number of CD31-positive cells detected on the luminal surface was significantly higher in the HA electret group. Endothelium- and nitric oxide (NO)-dependent relaxation in response to carbachol was significantly improved only in the HA electret group. In conclusion, this is the first report demonstrating that HA electret significantly improved intimal hyperplasia by accelerating the regeneration of functioning endothelial cells and enhancing the apoptosis of medial smooth muscle cells.