Human neutrophil degranulation responses to nucleotides

Abstract

Background: Nucleotides have polymorphonuclear neutrophil (PMN)-stimulating actions resembling those of 5-hydroxyicosatetraenoate and its oxo analog, 5-oxoETE. Their effects on degranulation, however, are disputed even though this response may underlie their in vivo toxicity and is well-suited for comparing their mechanism of action with e.g., 5-oxoETE.

Experimental design: We measured the direct, synergistic, and cross-desensitizing actions of nine nucleotides and six other stimuli in degranulating unprimed and tumor necrosis factor (TNF)-alpha-primed human PMN.

Results: Nucleotides weakly degranulated unprimed PMN but caused far larger responses in TNF-alpha-primed cells. Their actions, while differing from those of N-formyl-MET-LEU-PHE, platelet-activating factor, leukotriene B4, ionomycin, or dioctanoylglycerol, resembled those of 5-oxoETE. Nucleotides also enhanced PMN degranulation responses to the latter stimuli, particularly 5-oxoETE. Nucleotide degranulating and enhancing potencies were: UTP > or = ATP > or = ATP gamma S > ITP > ADP > 2-MeSATP, nonphosphohydrolyzable analogs lacked activity, and adenosine and AMP blocked PMN degranulation. Finally, nucleotides desensitized degranulation responses to each other but not to 5-oxoETE or other agonists, and 5-oxoETE desensitized to itself but not to nucleotides.

Conclusions: Nucleotides have intrinsic and synergistic degranulating actions that under appropriate conditions (i.e., in concert with TNF-alpha or 5-oxoETE) are exceedingly prominent. Recognition systems mediating their effects differ from those for various stimuli including 5-oxoETE. These systems likely involve a common "nucleotide" receptor, but studies do not exclude possibilities that other purinergic receptors contribute to their actions.