Cleavage and inactivation of poly(ADP-ribose) polymerase in peripheral blood mononuclear cells of patients with acute respiratory distress syndrome

Olaparib, the first clinically approved poly (ADP-ribose) polymerase (PARP) inhibitor, may be repurposed for non-oncological conditions such as acute respiratory distress syndrome (ARDS), where PARP-1 inhibition has shown benefits in preclinical models. We investigated the expression and functional status of PARP-1 and the effects of olaparib in peripheral blood mononuclear cells (PBMCs) from ARDS patients and healthy controls. PBMCs from healthy volunteers (N = 8) and ARDS patients (N = 8) were isolated via Ficoll gradient. PARP-1, cleaved PARP (cPARP), and PAR polymers were assessed by Western blotting. Cytokine production was measured in plasma and in PBMC supernatants after 1 h preincubation with olaparib (10 µM) or vehicle, followed by LPS (100 ng/ml) stimulation for 4 h. Cellular bioenergetics were analyzed using Seahorse XFe24 after H2O2 (100 µM, 2 h) with or without olaparib pretreatment. Control PBMCs showed a lymphocyte-predominant population with mostly full-length PARP-1. In ARDS Day 1 samples, PARylated proteins increased and PARP became downregulated. By Day 8, PARylation decreased and full-length PARP-1, as well as cleaved PARP-1 were detectable. Olaparib treatment of the cells did not alter the LPS-induced cytokine responses. Exposure of healthy PBMCs to oxidative stress suppressed cellular bioenergetics, and this effect was attenuated by olaparib. However, in ARDS PBMCs, which were already bioenergetically suppressed, oxidative stress had no further effect, and olaparib was without protective effect. Thus, in PBMCs isolated from ARDS, olaparib’s cytoprotective effect is no longer detectable, likely due to PARP-1 inactivation and degradation.