Poly-(ADP-ribose) polymerases inhibition by olaparib attenuates activities of the NLRP3 inflammasome and of NF-κB in THP-1 monocytes.

Poly-(ADP-ribose) polymerases (PARPs) are a protein family that make ADP-ribose modifications on target genes and proteins. PARP family members contribute to the pathogenesis of chronic inflammatory diseases, including atherosclerosis, in which monocytes/macrophages play important roles. PARP inhibition is protective against atherosclerosis. However, the mechanisms by which PARP inhibition exerts this beneficial effect are not well understood. Here we show that in THP-1 monocytes, inhibition of PARP by olaparib attenuated oxidized low-density lipoprotein (oxLDL)-induced protein expressions of nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain-containing-3 (NLRP3) inflammasome components: NLRP3, apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC), and caspase-1. Consistent with this effect, olaparib decreased oxLDL-enhanced interleukin (IL)-1ß and IL-18 protein expression. Olaparib also decreased the oxLDL-mediated increase in mitochondrial reactive oxygen species. Similar to the effects of the NLRP3 inhibitor, MCC950, olaparib attenuated oxLDL-induced adhesion of monocytes to cultured human umbilical vein endothelial cells and reduced foam cell formation. Furthermore, olaparib attenuated the oxLDL-mediated activation of nuclear factor (NF)-κB through the oxLDL-mediated increase in IκBα phosphorylation and assembly of NF-κB subunits, demonstrated by co-immunoprecipitation of IκBα with RelA/p50 and RelB/p52 subunits. Moreover, PARP inhibition decreased oxLDL-mediated protein expression of a NF-κB target gene, VCAM1, encoding vascular cell adhesion molecule-1. This finding indicates an important role for NF-κB activity in PARP-mediated activation of the NLRP3 inflammasome. Thus, PARP inhibition by olaparib attenuates NF-κB and NLRP3 inflammasome activities, lessening monocyte cell adhesion and macrophage foam cell formation. These inhibitory effects of olaparib on NLRP3 activity potentially protect against atherosclerosis.

Angiotensin II receptor type 1 autoantibodies promote endothelial microparticles formation through activating p38 MAPK pathway.

BACKGROUND: Endothelial microparticles (EMPs) are small vesicular structures that serve as a marker of endothelial function. Angiotensin II receptor type 1 autoantibody (AT1-AA) can cause endothelial dysfunction. However, whether AT1-AA promotes EMPs formation and the mechanism remains obscure. METHODS: The titres of sera AT1-AA of 126 hypertensive patients and 30 normotensive individuals were evaluated by ELISA. EMPs in the sera and the supernatants of human umbilical vein endothelial cells (HUVECs) were measured by flow cytometry. The phosphorylation levels of mitogen-activated protein kinase (MAPK) pathways in HUVECs treated by AT1-AA were assessed and their correlation with microparticle formation was also analysed. Furthermore, the production of intracellular reactive oxygen species (ROS) and nitric oxide in HUVECs was examined after incubation with 'injured' endothelial microparticle (iEMPs) (EMPs derived from AT1-AA treated HUVECs). RESULTS: The positive rate of AT1-AA in 126 hypertensive patients was 21.4% (27/126), and higher than that in normotensive individuals [3.3% (1/30), P < 0.01]. Circulating EMP (CD31+/CD42b-) levels were corresponding to the AT1-AA titres in hypertensive group (r(2) = 0.3661, P < 0.01). AT1-AA promoted EMPs generation from HUVECs in a time and dose-dependent manner than the vehicle or nonspecific IgG. Meanwhile, AT1-AA significantly elevated phosphorylation level of P38 and ERK in HUVECs. Lorsartan and P38 inhibitor could suppress the AT1-AA's stimulation effect on EMPs generation. Moreover, the iEMP greatly increased ROS production and reduced nitric oxide synthesis in HUVECs. CONCLUSION: Our findings showed that circulating EMPs levels positively correlate to the serum AT1-AA titres in essential hypertension patients. The AT1-AA could promote EMPs generation in HUVECs through activation of P38 MAPK signalling pathway, and this effect could be effectively inhibited by losartan or p38 inhibitor. Angiotensin receptor blockers (ARBs) may be more suitable for AT1-AA(+) hypertensive patients on account of suppressing the AT1-AA's stimulation effect on EMPs generation.