Carbon monoxide releasing molecule induces endothelial nitric oxide synthase activation through a calcium and phosphatidylinositol 3-kinase/Akt mechanism

The production of nitric oxide (NO) by endothelial NO synthase (eNOS) plays a major role in maintaining vascular homeostasis. This study elucidated the potential role of carbon monoxide (CO)-releasing molecules (CORMs) in NO production and explored the underlying mechanisms in endothelial cells. We observed that 25 μM CORM-2 could increase NO production and stimulate an increase in the intracellular Ca2 + level. Furthermore, ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetra acetic acid caused CORM-2-induced NO production, which was abolished by 1,2-bis(2-aminophenoxy) ethane-N,N,N′,N′-tetraacetic acid tetraacetoxy-methyl ester (BAPTA-AM), indicating that intracellular Ca2 + release plays a major role in eNOS activation. The inhibition of the IP3 receptor diminished the CORM-2-induced intracellular Ca2 + increase and NO production. Furthermore, CORM-2 induced eNOS Ser1179 phosphorylation and eNOS dimerization, but it did not alter eNOS expression. CORM-2 (25 μM) also prolonged Akt phosphorylation, lasting for at least 12 h. Pretreatment with phosphatidylinositol 3-kinase inhibitors (wortmannin or LY294002) inhibited the increases in NO production and phosphorylation but did not affect eNOS dimerization. CORM-2-induced eNOS Ser1179 phosphorylation was intracellularly calcium-dependent, because pretreatment with an intracellular Ca2 + chelator (BAPTA-AM) inhibited this process. Although CORM-2 increases intracellular reactive oxygen species (ROS), pretreatment with antioxidant enzyme catalase and N-acetyl-cysteine did not abolish the CORM-2-induced eNOS activity or phosphorylation, signifying that ROS is not involved in this activity. Hence, CORM-2 enhances eNOS activation through intracellular calcium release, Akt phosphorylation, and eNOS dimerization.

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