Minocycline ameliorates LPS-induced inflammation in human monocytes by novel mechanisms including LOX-1, Nur77 and LITAF inhibition

Abstract

Background Minocycline exhibits anti-inflammatory properties independent of its antibiotic activity, ameliorating inflammatory responses in monocytes and macrophages. However, the mechanisms of minocycline anti-inflammatory effects are only partially understood. Methods Human circulating monocytes were cultured in the presence of lipopolysaccharide (LPS), 50 ng/ml, and minocycline (10–40 µM). Gene expression was determined by RT-PCR, cytokine and prostaglandin E2 (PGE2) release by ELISA, protein expression, phosphorylation and nuclear translocation by Western blotting. Results Minocycline significantly reduced the inflammatory response in LPS-challenged monocytes, decreasing LPS-induced transcription of pro-inflammatory tumor-necrosis factor alpha (TNF-α), interleukin-1 beta, interleukin-6 (IL-6) and cyclooxygenase-2 (COX-2), and the LPS-stimulated TNF-α, IL-6 and PGE2 release. Minocycline inhibited LPS-induced activation of the lectin-like oxidized low density lipoprotein receptor-1 (LOX-1), NF-κB, LPS-induced TNF-α factor (LITAF) and the Nur77 nuclear receptor. Mechanisms involved in the anti-inflammatory effects of minocycline include a reduction of LPS-stimulated p38 mitogen-activated protein kinase (p38 MAPK) activation and stimulation of the phosphoinositide 3-kinase (PI3K)/Akt pathway. Conclusions We provide novel evidence demonstrating that the anti-inflammatory effects of minocycline in human monocytes include, in addition to decreased NF-κB activation, abrogation of the LPS-stimulated LOX-1, LITAF, Nur77 pathways, p38 MAPK inhibition and PI3K/Akt activation. Our results reveal that minocycline inhibits points of convergence of distinct and interacting signaling pathways mediating multiple inflammatory signals which may influence monocyte activation, traffic and recruitment into the brain. General significance Our results in primary human monocytes contribute to explain the profound anti-inflammatory and protective effects of minocycline in cardiovascular and neurological diseases and may have direct translational relevance.

Nur77 attenuates endothelin-1 expression via downregulation of NF-κB and p38 MAPK in A549 cells and in an ARDS rat model

“…However, our results are different from those where incubation of primary human monocytes with LPS increased Nur77 nuclear translocation (65). There are several reasons to explain the disparity observed in these studies: different cell types, different dosage of LPS treatment, and different evaluation methods were used.…”

“…In the present study, A549 cells were treated with LPS at a dose of 10 μg/ml, and Nur77 subcellular location is determined by laser scanning confocal microscopy. In a previous study, primary human monocytes were treated with LPS at a dose of 50 ng/ml, and Nur77 nuclear translocation was detected in nuclear extracts with Western blotting analysis (65). LPS has been shown to trigger the inflammatory response in a dose-dependent and cell-specific manner (11, 76), since LPS promotes cell proliferation (43) at low doses and has been shown to induce cell apoptosis at high doses (33).…”

Minocycline selectively inhibits M1 polarization of microglia

“…24 We found that the protein and mRNA expression of NF- κ B were affected by minocycline in microglia (Figure 7). The data were reproducible in LPS-induced microglia activation and in the ALS mouse model, suggesting that minocycline may inhibit not only the nuclear translocation but also transcription of NF- κ B. Interestingly, IL-4 treatment did not induce the upregulation of NF- κ B expression.…”

Local Minocycline Effect on Inflammation and Clinical Attachment During Periodontal Maintenance: Randomized Clinical Trial

“…This probably relates to the anti‐inflammatory properties of minocycline. Potential mechanisms include reduction of the LPS‐induced inflammatory response in inflammatory cells 4 and inhibition of matrix metalloproteinases and proinflammatory cytokines, 5 including IL‐1β. However, neither group reduced IL‐1β/IL‐1ra after 12 months, although SRP and MM were applied at baseline and 6 months.…”

“…As a member of the tetracycline family of drugs, minocycline has been shown to have potent anti‐inflammatory and bone‐sparing properties. For instance, minocycline has been shown to reduce the inflammatory response in lipopolysaccharide (LPS)‐challenged monocytes, 4 inhibit matrix metalloproteinase and proinflammatory cytokines, 5 and prevent bone resorption by directly acting on osteoclast precursors 6 . Many studies indicated that minocycline can reduce inflammatory markers and improve clinical outcomes during short‐term evaluations and after initial therapy 7–15 .…”