Antiinflammatory properties of PAH drugs

In patients suffering from pulmonary arterial hypertension (PAH) elevated levels of monocyte-derived cytokines have been described in early stage of disease. Beside vasodilatory potential, specific anti-inflammatory activities of current PAH drugs might contribute to their therapeutic efficacy. We studied the anti-inflammatory properties of different classes of PAH drugs in human cultured monocytes.

CD14⁺ monocytes were isolated from blood taken from healthy donors with their informed consent. Peripheral mononuclear cells were isolated via density gradient centrifugation, following by magnetic cells sorting with an anti-CD-14⁺ specific antibody. Cultured cells were stimulated with different concentrations of macitentan, riociguat, prostacyclin I₂ analogues (iloprost, treprostinil) and the selective nonprostanoid prostacyclin receptor agonist selexipag w/o LPS [100 ng/ml] for 24h. For blocking experiments of the Toll-like receptor 4 pathway cells were pretreated with an inhibitor of NfκB or MAPK activation, followed by incubation with LPS and the medications. The IL-6, IL-10 and TNF-α concentration of cell supernatants were measured with a commercially available ELISA based assay system.

Only monocytes stimulated with iloprost or treprostinil showed a significant reduction of TNF-α, but no effect on the IL-6 and IL-10 release. The effect of treprostinil compared to iloprost was much stronger.

TNF-alpha suppression by prostacyclines has been described in various cell types and disease models. The detailed interaction between the cyclooxygenase system and the toll-like-receptor-4 pathway (TLR4) still has to be elucidated.

We show that PGI₂ analogues pronounced suppress TLR4-dependent TNF-α expression in human monocytes via the MAPK and NFκB pathway. This observation suggests a specific anti-TNF class effect of prostacyclin analogues in PAH therapy.