The cardioprotective nucleoside adenosine has important effects on the regulation of coronary flow, heart rate, ischemic preconditioning, angiogenesis and platelet antiaggregation. Furthermore it inhibits expression of cytokines, chemokines and adhesions molecules thus reducing inflammatory responses. Additionally it plays a key role in the maintenance of endothelial barrier function. Typically adenosine is produced in intracellular and extracellular regions of the heart. Although the extracellular adenosine production rate is relatively small it might be very important, because adenosine acts via surface receptors located next to the extracellular site of production. Substrate for extracellular adenosine production is provided by a highly active nucleotide breakdown cascade (ATP - ADP - AMP), which is catalyzed by CD39, a 70–100 kDa transmembrane E-NTPDase1. The final step of hydrolysis (AMP - adenosine) is catalyzed by CD73, a 69 kDa GPI-anchored cell surface protein, and regarded to be rate limiting. It is therefore of particular interest for translational and posttranslational regulation. It is known that lipid mediators formed during inflammation and ischemia, namely lysophosphatidylcholine (LPC) and platelet activating factor (PAF) but not the phospholipid lysophosphatidylic acid (LPA) enhance extracellular production of adenosine significantly. Recently we showed that this effect is not mediated via calcium and protein kinase C. Further analysis revealed an inhibitory effect of safingol on extracellular AMP degradation probably aside form PKC inhibition. However, the mechanism of increased conversion of AMP to adenosine during lysophospholipid application remains unclear to date.

To further characterize the LPC and PAF mediated effect and the role of safingol we measured the extracellular dephosphorylation rate of ethenoAMP to ethenoAdenosine by HPLC in human umbilical vein endothelial cells (HUVEC).

We have found that the effect of LPC and PAF were concentration and time dependent. Furthermore we could show an additive effect after combined application of both LPC and PAF in HUVEC. Increased production of adenosine is recovered in the single supernatants of stimulated cells and in cell homogenates the LPC and PAF effect were small. Similar to safingol the natural sphingoid base D-erythro dihydrosphinganine shares the inhibitory potential. The increased effect by LPC and PAF is not confined to production of adenosine but also extends to production of AMP from ADP and ATP in presence AOPCP.

In conclusion, LPC and PAF increase the production of adenosine as well as AMP in HUVEC concentration and time dependently beside the PKC pathway. L-threo - and D-erythro dihydrosphinganine abolish this effect. We now critically evaluate the role of dihydrosphinganine regarding to the increase production of adenosine and AMP.