Phosphodiesterase 5 inhibitors augment UT-15C-stimulated ATP release from erythrocytes of humans with pulmonary arterial hypertension

Abstract

Both prostacyclin analogs and phosphodiesterase 5 (PDE5) inhibitors are effective treatments for pulmonary arterial hypertension (PAH). In addition to direct effects on vascular smooth muscle, prostacyclin analogs increase cAMP levels and ATP release from healthy human erythrocytes. We hypothesized that UT-15C, an orally available form of the prostacyclin analog, treprostinil, would stimulate ATP release from erythrocytes of humans with PAH and that this release would be augmented by PDE5 inhibitors. Erythrocytes were isolated and the effect of UT-15C on cAMP levels and ATP release were measured in the presence and absence of the PDE5 inhibitors, zaprinast or tadalafil. In addition, the ability of a soluble guanylyl cyclase inhibitor to prevent the effects of tadalafil was determined. Erythrocytes of healthy humans and humans with PAH respond to UT-15C with increases in cAMP levels and ATP release. In both groups, UT-15C-induced ATP release was potentiated by zaprinast and tadalafil. The effect of tadalafil was prevented by pre-treatment with an inhibitor of soluble guanylyl cyclase in healthy human erythrocytes. Importantly, UT-15C-induced ATP release was greater in PAH erythrocytes than in healthy human erythrocytes in both the presence and the absence of PDE5 inhibitors. The finding that prostacyclin analogs and PDE5 inhibitors work synergistically to enhance release of the potent vasodilator ATP from PAH erythrocytes provides a new rationale for the co-administration of these drugs in this disease. Moreover, these results suggest that the erythrocyte is a novel target for future drug development for the treatment of PAH.

The Roles of Mitochondrial Damage-Associated Molecular Patterns in Diseases

“…Third, it is also challenging to elucidate which cell types are responsible for the release of mitochondrial DAMPs and contribute to the immune responses in vivo. While a number of reports suggest immune function of extracellular ATP in human lung diseases, it is also important to note that circulating ATP secreted from red blood cells may play a protective role in the pathogenesis of pulmonary hypertension (12,151,152). Mitochondrial DAMPs secreted from different types of cells may have different biological roles in vivo.…”

Purinergic Signaling in the Cardiovascular System

“…ATP release from erythrocytes may be a novel target for the treatment of pulmonary arterial hypertension. 174 Suppression of endothelial CD39 nucleotidase is associated with vascular remodeling in pulmonary hypertension and may be a novel target for therapy. 175 It has been suggested in a recent article that P2X1 receptor antagonists could serve as a treatment for pulmonary hypertension.…”

Liposomal-delivery of phosphodiesterase 5 inhibitors augments UT-15C-stimulated ATP release from human erythrocytes

“…Blood obtained from 23 healthy human volunteers (13 females, 11 males; average age 56 years; range 27–78 years) was collected into heparinized tubes at the Phelps County Regional Medical Center or Saint Louis University and transported to the Missouri University of Science and Technology where it was centrifuged at 500 g at 4 °C for 10 min. The plasma, buffy coat, and uppermost layer of erythrocytes were removed by aspiration [5] , [6] , [7] , [8] . Care was taken to remove the fewest erythrocytes possible.…”

“…In contrast, PAH erythrocytes do release ATP when exposed to prostacyclin (PGI 2 ) analogs via a well-characterized signaling pathway that requires increases in intracellular cyclic adenosine monophosphate (cAMP) ( Fig. 1 ) [6] , [8] , [9] . In this pathway, levels of cAMP are regulated by phosphodiesterase 3 (PDE3), a PDE that is inhibited by local increases in cyclic guanosine monophosphate (cGMP) [10] .…”

“…Erythrocytes make cGMP; its levels are the product of synthesis by soluble guanylyl cyclase (sGC) and hydrolysis by PDE5 [11] . Importantly, incubation of both healthy human and PAH erythrocytes with inhibitors of PDE5 in solution have been shown to augment PGI 2 analog-induced ATP release [8] , [9] . Although both PGI 2 analogs and PDE5 inhibitors are used in the treatment of PAH, the effectiveness of these drugs alone or in combination is sometimes limited by untoward systemic side effects including hypotension, flushing and headache [12] , [13] .…”