Role for Lipids Secreted by Irradiated Peripheral Blood Mononuclear Cells in Inflammatory Resolution in Vitro

Abstract

<jats:p>Periodontal inflammation is associated with dying cells that potentially release metabolites helping to promote inflammatory resolution. We had shown earlier that the secretome of irradiated, dying peripheral blood mononuclear cells support in vitro angiogenesis. However, the ability of the secretome to promote inflammatory resolution remains unknown. Here, we determined the expression changes of inflammatory cytokines in murine bone marrow macrophages, RAW264.7 cells, and gingival fibroblasts exposed to the secretome obtained from γ-irradiated peripheral blood mononuclear cells in vitro by RT-PCR and immunoassays. Nuclear translocation of p65 was detected by immunofluorescence staining. Phosphorylation of p65 and degradation of IκB was determined by Western blot. The secretome of irradiated peripheral blood mononuclear cells significantly decreased the expression of IL1 and IL6 in primary macrophages and RAW264.7 cells when exposed to LPS or saliva, and of IL1, IL6, and IL8 in gingival fibroblasts when exposed to IL-1β and TNFα. These changes were associated with decreased phosphorylation and nuclear translocation of p65 but not degradation of IκB in macrophages. We also show that the lipid fraction of the secretome lowered the inflammatory response of macrophages exposed to the inflammatory cues. These results demonstrate that the secretome of irradiated peripheral blood mononuclear cells can lower an in vitro simulated inflammatory response, supporting the overall concept that the secretome of dying cells promotes inflammatory resolution.</jats:p>

Comparing the efficacy of γ- and electron-irradiation of PBMCs to promote secretion of paracrine, regenerative factors

“…Recently, potent anti-inflammatory actions were attributed to lipids present in the PBMCsec, 20 , 35 and γ-irradiation of PBMCs was necessary for inducing various oxidized phospholipid (PL) species 15 implicated in immunomodulation. 36 Therefore, we determined the presence of lipid species in PBMCsec and the secretome of electron-irradiated PBMCs by tandem mass spectrometry.…”

TGF-β in the Secretome of Irradiated Peripheral Blood Mononuclear Cells Supports In Vitro Osteoclastogenesis

“…The secretome of PBMCs previously showed to suppress the differentiation of hematopoietic cells towards the dendritic lineage [ 28 ] and to shift macrophages from M1-to-M2 [ 29 ], together suggesting a potent impact on the lineage decision of hematopoietic cells. Considering that osteoclasts also belong to the hematopoietic lineage, it might be feasible that the secretome of PBMCs affects osteoclastogenesis.…”

“…The secretome of irradiated PBMCs that underwent apoptosis and necroptotic cell death [ 18 ] can provide such a paracrine environment. This secretome has already proven to control the differentiation switch of hematopoietic progenitors to suppress dendritic cells formation [ 28 ] and to shift macrophages from an inflammatory M1 towards a resolving M2 phenotype [ 29 ]. In bone, it requires osteoclasts to remove damaged tissue before osteoblasts can rebuild the mineralized matrix [ 1 ].…”

“…In vitro, the secretome of irradiated PBMCs suppressed the development of dendritic cells [ 28 ] and the anti-inflammatory activity on macrophages, indicated by an M1-to-M2 shift [ 29 ]. It was particularly the lipid fraction of the secretome that was identified to mediate the indicated effects [ 28 , 29 ]. Dendritic cells and macrophages both originate from hematopoietic cells, similar to the osteoclasts [ 30 ].…”

Molecular Mechanisms of Periodontal Disease

“…Magrin et al revealed that, among the SCFAs, butylate might exacerbate the gingival epithelium inflammatory response in their in vitro study [ 4 ] and systematic review [ 5 ]. On the other hand, the lipids secreted from dying peripheral blood mononuclear cells activate macrophages’ inflammatory cytokine production [ 6 ].…”