Regulation of Ecto-5´-Nucleotidase by Docosahexaenoic Acid in Human Endothelial Cells

Abstract

Background/Aims: Modulation of extracellular adenine nucleotide and adenosine concentrations is one potential mechanism by which docosahexaenoic acid (DHA) may exert beneficial effects in critically ill patients. This study assessed DHA effects on extracellular adenine purines. Methods: Experiments used human pulmonary endothelial cells (HPMEC) and umbilical vein endothelial cells (HUVEC) treated with DHA (48 h). mRNA level (real-time PCR), expression (western blot, flow cytometry) and activities (hydrolysis of etheno(ε)-purines and fluorescence HPLC) of CD73 (ecto-5´-nucleotidase) and CD39 (ecto-NTPDase-1) were quantified. Results: DHA elevated total CD73 membrane protein expression concentration-dependently but CD73 mRNA level did not change. Increased expression was paralleled by increased enzyme activity. Effects observed on membrane level were reversed in intact cells, in which ε-AMP hydrolysis decreased after DHA. In intact endothelial cells ATP release was enhanced and CD39 activity blunted following DHA treatment. Hence, extracellular ATP and ADP concentrations increased and this inhibited ε-AMP hydrolysis. Conclusion: In human endothelial cells DHA caused 1) up-regulation of CD73 protein content and increased AMP hydrolysis at the cell membrane level, 2) increased cellular ATP release, and 3) decreased extracellular ATP/ADP hydrolysis. Thus, reorganization of the extracellular adenine-nucleotide-adenosine axis in response to DHA resulted in an increased extracellular ATP/adenosine ratio.