6-shogaol treatment improves experimental knee OA exerting a pleiotropic
effect over immune innate signaling response in chondrocytes
Background:The pathogenesis of osteoarthritis (OA) implicates a
low-grade inflammation associated to the activation of the innate immune
system. Toll like receptor (TLR) stimulation triggers the release of
inflammatory mediators, which aggravate OA severity. The aim was to
study the preventive effect of 6-shogaol (6S), a potential TLR4
inhibitor, on the treatment of experimental knee OA.
Experimentalapproach:OA was induced in C57BL6 mice by surgical section
of the medial meniscotibial ligament, which received 6S for eight weeks.
Cartilage damage, inflammatory mediator presence, and disease markers
were assessed in the joint tissues by immunohistochemistry.
Computational modeling was used to predict binding modes of 6S into the
TLR4/MD2 receptor and its permeability across cellular membranes.
Employing LPS-stimulated chondrocytes and MAPK assay we clarified 6S
action mechanisms. Results:6S treatment was able to prevent articular
cartilage lesions, synovitis, and the presence of pro-inflammatory
mediators and disease markers in OA animals. Molecular modeling studies
predicted 6S interaction with the TLR4/MD-2 heterodimer in an antagonist
conformation through its binding into the MD-2 pocket. In cell culture,
we confirmed that 6S reduced LPS-induced TLR4 inflammatory signaling
pathways. Besides, MAPK assay demonstrated that 6S directly inhibits the
ERK1/2 phosphorylation activity. Conclusion:6S evoked a preventive
action on cartilage and synovial inflammation in OA mice. 6S effect may
take place not only by hindering the interaction between TLR4 ligands
and the TLR4/MD-2 complex in chondrocytes, but also through inhibition
of ERK phosphorylation, implying a pleiotropic effect on different
mediators activated during OA, which proposes it as an attractive drug
for OA treatment.