Anti-oxidative effects of theophylline on human neutrophils involve cyclic nucleotides and protein kinase A

Abstract

The effects were studied of the non-specific phosphodiesterase inhibitor, theophylline (37.5-300 microM), on intracellular levels of cyclic adenosine monophosphate (cAMP) and superoxide generation following exposure of human neutrophils to four different stimuli of neutrophil membrane-associated oxidative metabolism, each of which utilizes a different transductional mechanism to activate NADPH-oxidase, in vitro. Exposure of neutrophils to FMLP (1 microM), the calcium ionophore A23187 (1 microM), and opsonized zymosan (OZ, 0.5 mg/ml) was accompanied by activation of superoxide production and increased concentrations of intracellular cAMP. Inclusion of theophylline resulted in augmentation of cAMP and inhibition of superoxide production by these stimuli. These negative effects of theophylline on neutrophil superoxide generation were mimicked by dibutyryl cAMP and 8-bromo-cGMP, while the inhibitory activity of all 3 agents was antagonized by the protein kinase A inhibitor KT 5720, but not by the G-kinase inhibitor KT 5823. Unlike FMLP, OZ and A23187, intracellular cAMP levels did not increase in cells activated with phorbol-12-myristate-13-acetate (PMA, 25 ng/ml), while oxidant production activated by this stimulus was insensitive to the inhibitory effects of theophylline. These observations suggest that the beneficial, anti-inflammatory interactions of theophylline with human neutrophils are related to the phosphodiesterase inhibitory properties of this agent, and are selective for those pro-inflammatory stimuli which elevate cAMP, resulting in enhanced activity of protein kinase A and inhibition of the production of potentially harmful reactive oxidants by these cells.