Nitric oxide provokes tumor necrosis factor-alpha expression in adult feline myocardium through a cGMP-dependent...

The mechanism(s) responsible for the persistent coexpression of tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) in the failing heart is unknown.

To determine whether NO was sufficient to provoke TNF-alpha biosynthesis, we examined the effects of an NO donor, S-nitroso-N-acetyl penicillamine (SNAP), in buffer-perfused Langendorff hearts. SNAP (1 micromol/L) treatment resulted in a time- and dose-dependent increase in myocardial TNF-alpha mRNA and protein biosynthesis in adult cat hearts. The effects of SNAP were completely abrogated by a NO quenching agent, 2-(4-carboxyphenyl)-4, 4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (C-PTIO), and mimicked by sodium nitroprusside. Electrophoretic mobility shift assays demonstrated that SNAP treatment led to the rapid induction of nuclear factor kappa-beta (NF-kappaB) but not AP-1. The importance of the cGMP pathway in terms of mediating NO-induced TNF-alpha biosynthesis was shown by studies that demonstrated that 8-bromo-cGMP mimicked the effects of SNAP and that the effects of SNAP could be completely abrogated using a cGMP antagonist, 1H-(1,2, 4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ), or protein kinase G antagonist (Rp-8-Br-cGMPS). SNAP and 8-Br-cGMP were both sufficient to lead to the site-specific phosphorylation (serine 32) and degradation of IkappaBalpha in isolated cardiac myocytes. Finally, protein kinase G was sufficient to directly phosphorylate IkappaBalpha on serine 32, a critical step in the activation of NF-kappaB.

These studies show that NO provokes TNF-alpha biosynthesis through a cGMP-dependent pathway, which suggests that the coincident expression of TNF-alpha and NO may foster self-sustaining positive autocrine/paracrine feedback inflammatory circuits within the failing heart.