TY - JOUR T1 - Nortriptyline Reverses Corticosteroid Insensitivity by Inhibition of Phosphoinositide-3-Kinase-δ JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 465 LP - 470 DO - 10.1124/jpet.110.175950 VL - 337 IS - 2 AU - Nicolas Mercado AU - Yasuo To AU - Kazuhiro Ito AU - Peter J. Barnes Y1 - 2011/05/01 UR - http://jpet.aspetjournals.org/content/337/2/465.abstract N2 - Corticosteroid insensitivity represents a major barrier to the treatment of chronic obstructive pulmonary disease (COPD) and severe asthma. It is caused by oxidative stress, leading to reduced histone deacetylase-2 (HDAC2) function through activation of phosphoinositide-3-kinase-δ (PI3Kδ). The tricyclic antidepressant nortriptyline has been identified in high-throughput screens as an agent that increases corticosteroid responsiveness. The aim of this study was to identify the molecular mechanism whereby nortriptyline increases corticosteroid sensitivity. Phosphorylation of Akt, a footprint of PI3K activation, and HDAC activity were evaluated by Western blotting and fluorescent activity assay in U937 monocytic cells. Corticosteroid sensitivity was evaluated by the inhibition of tumor necrosis factor α (TNFα)-induced interleukin 8 (IL-8) production by budesonide. Hydrogen peroxide (H2O2) or cigarette smoke extract (CSE) increased the level of phosphorylated Akt (pAkt) and reduced HDAC activity. Pretreatment with nortriptyline inhibited pAkt induced by CSE and H2O2 as well as restored HDAC activity that had been decreased by H2O2 and CSE. In addition, nortriptyline inhibited PI3Kδ activity, but had no effect on the PI3Kα and PI3Kγ isoforms. Although CSE reduced the effects of budesonide on TNFα-induced IL-8 production in U937 cells, nortriptyline reversed CSE-induced corticosteroid insensitivity. Nortriptyline restores corticosteroid sensitivity induced by oxidative stress via direct inhibition of PI3Kδ and is a potential treatment for corticosteroid-insensitive diseases such as COPD and severe asthma. ER -