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Br J Pharmacol. 2017 May;174(10):1090-1103. doi: 10.1111/bph.13746. Epub 2017 Mar 31.

Phenolic 1,3-diketones attenuate lipopolysaccharide-induced inflammatory response by an alternative magnesium-mediated mechanism.

Author information

1
Department of Pharmaceutical and Pharmacological Sciences, University of Padua, Padua, Italy.
2
Department of Pharmacy and Biotechnology, Alma Mater Studiorum-University of Bologna, Bologna, Italy.
3
Department of Molecular Medicine, University of Padua, Padua, Italy.
4
Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, QC, Canada.
5
Molecular Modeling Section, Department of Pharmaceutical and Pharmacological Sciences, University of Padua, Padua, Italy.

Abstract

BACKGROUND AND PURPOSE:

Toll-like receptor 4 (TLR4) plays a key role in the induction of inflammatory responses both in peripheral organs and the CNS. Curcumin exerts anti-inflammatory functions by interfering with LPS-induced dimerization of TLR4-myeloid differentiation protein-2 (MD-2) complex and suppressing pro-inflammatory mediator release. However, the inhibitory mechanism of curcumin remains to be defined.

EXPERIMENTAL APPROACH:

Binding of bis-demethoxycurcumin (GG6) and its cyclized pyrazole analogue (GG9), lacking the 1,3-dicarbonyl function, to TLR4-MD-2 was determined using molecular docking simulations. The effects of these compounds on cytokine release and NF-κB activation were examined by ELISA and fluorescence staining in LPS-stimulated primary microglia. Interference with TLR4 dimerization was assessed by immunoprecipitation in Ba/F3 cells.

KEY RESULTS:

Both curcumin analogues bound to the hydrophobic region of the MD-2 pocket. However, only curcumin and GG6, both possessing the 1,3-diketone moiety, inhibited LPS-induced TLR4 dimerization, activation of NF-κB and secretion of pro-inflammatory cytokines in primary microglia. Consistent with the ability of 1,3-diketones to coordinate divalent metal ions, LPS stimulation in a low magnesium environment decreased pro-inflammatory cytokine release and NF-κB p65 nuclear translocation in microglia and decreased TLR4-MD-2 dimerization in Ba/F3 cells. Curcumin and GG6 also significantly reduced cytokine output in contrast to the pyrazole analogue GG9.

CONCLUSIONS AND IMPLICATIONS:

These results indicate that phenolic 1,3-diketones, with a structural motif able to coordinate magnesium ions, can modulate LPS-mediated TLR4-MD-2 signalling. Taken together, these studies identify a previously uncharacterized mechanism involving magnesium, underlying the inflammatory responses to LPS.

PMID:
28198010
PMCID:
PMC5406298
DOI:
10.1111/bph.13746
[Indexed for MEDLINE]
Free PMC Article

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