Proapoptotic nitric oxide production in amyloid β protein-treated cerebral microvascular endothelial cells

Objective: The objective of this study was to investigate the effects of amyloid β protein (Aβ) on cerebral microvascular endothelium, and their possible involvement in Aβ-induced apoptosis in the neighboring cells. Methods: Cultured bovine brain microvascular endothelial cells (BBECs) were incubated with Aβ for 24 h. Production of nitric oxide (NO) was assessed by nitric oxide-sensitive fluorescent dye, DAF-2, and the expression of NO synthase (NOS) proteins was examined by Western blotting. Effects of Aβ-treated microvascular endothelium on the DNA damage of the neighboring cells were assessed by single-cell gel electrophoresis. Results: Aβ increased the expression of iNOS protein, but did not affect eNOS and nNOS expressions in BBECs. Aβ-treated BBECs showed spontaneous NO production in the presence of L-arginine. The neural cell line PC12 showed marked apoptosis after being co-cultured with Aβ-treated BBECs for 48 h, and the apoptosis was as potent as that induced by the inflammatory stimuli lipopolysaccharide and interferon-β. The DNA damage of PC12 cells evoked by co-culture with Aβ-treated BBECs was prevented by L-NG-nitroarginine methyl ester, an inhibitor of NOS. Conclusions: These results indicate that Aβ induces the expression of iNOS in BBECs, and that microvascular endothelium-derived NO may induce apoptosis in neighboring neural cells.