Abstract
In cholesterol-fed rabbits, site-specific targeting of prednisolone nanoparticles results in significantly reduced neo-intimal inflammation with a decreased infiltration of monocytes/macrophages. To understand the molecular mechanisms underlying this, the current study investigated whether prednisolone affects the immune attributes of 27-hydroxycholesterol (27OHChol), the major oxidized cholesterol molecule in circulation and tissue, in human (THP-1) monocyte/macrophage cells. THP-1 cells were exposed to 27OHChol in the presence of prednisolone followed by evaluation of inflammatory molecules at mRNA and protein levels by quantitative PCR, western blotting, ELISA and flow cytometry. The results revealed that prednisolone suppressed the 27OHChol-mediated expression of various macrophage (M)1 markers, including chemokine ligand 2, C-X-C chemokine motif 10, tumor necrosis factor-α and CD80. Treatment also impaired the 27OHCHol-enhanced migration of monocytic cells, downregulated the 27OHChol-induced cell surface expression of CD14 and inhibited the release of soluble CD14 comparable with a weakened lipopolysaccharide response. Furthermore, prednisolone suppressed the 27OHChol-induced expression of matrix metalloproteinase 9 at the transcriptional and protein level, as well as the phosphorylation of the p65 subunit. Prednisolone increased the transcription of CD163 and CD206 genes, and augmented the 27OHChol-induced transcription of CD163 without upregulating the 27OHChol-induced surface protein level of the gene. The results indicated that prednisolone inhibited the polarization of monocytes/macrophages towards the M1 phenotype, which that the immunostimulatory effects of 27OHCHol were being regulated and the immune responses in conditions that were rich in oxygenated cholesterol molecules were being modulated.
Highlights
Prednisolone is a corticosteroid drug, predominantly comprising glucocorticoid, and is a widely used therapeutic for immune suppression [1]
Since CCL2 is the key M1 molecule regulating migration of monocytes/macrophages, we examined the effects of prednisolone, in parallel with dexamethasone, on CCL2 expression at the transcriptional and protein levels
Increases in M1 markers validate that 27OHChol is an active molecule with inflammatory functions, whereas the increased transcription of M2 markers [24] is in agreement with a previous study that reported polarization of human macrophages toward the M2 immunomodulatory phenotype after short‐term exposure to this oxysterol [27]
Summary
Prednisolone is a corticosteroid drug, predominantly comprising glucocorticoid, and is a widely used therapeutic for immune suppression [1]. The drug abrogates the expression of inflammatory genes by inhibiting the transcriptional promoting activity of the AP‐1 and NF‐κB transcription factors, and enhances the release of anti‐inflammatory proteins such as IL‐4, IL‐13 or IL‐10 [2,3], suggesting that prednisolone modulates tissue responses by regulating gene regulation at sites of inflammation [4]. Data of animal studies suggest that prednisolone, the active metabolite of prednisone, exerts its pharmacological effects in cholesterol‐rich environments. Prednisone, which is metabolized by the liver to prednisolone, inhibits development of inflammatory lesions in the aortas of cholesterol‐fed rabbits, without lowering serum cholesterol levels [5]. Site‐specific targeting of nanoparticles of prednisolone reduces inflammation and formation of neo‐intima in a high cholesterol diet rabbit model of established atheroma [6]. It is yet to be established how prednisolone affects tissue responses occurring in a milieu rich in cholesterol molecules
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