Ginkgo biloba extract suppresses endotoxin-mediated monocyte activation by inhibiting nitric oxide- and tristetraprolin-mediated toll-like receptor 4 expression.
Monocytes expressing toll-like receptor 4 (TLR4) play a major role in regulating the innate immune response and are involved in systemic inflammation. Previous studies have shown that Ginkgo biloba extract (GBE) may act as a therapeutic agent for some cardiovascular and neurological disorders. The objective of this study was to determine whether GBE could modulate immunity in human cells. The monocytic cell line THP-1 was used. Enzyme-linked immunosorbent assay results showed that lipopolysaccharide (LPS) induces the expression of monocyte chemotactic protein-1 (MIP-1), tumor necrosis factor-α, stromal cell-derived factor-1, and MIP-1α, and this induction may be repressed by GBE treatment due to TLR4 blockade. The Griess reagent assay and western blot analysis showed that GBE-mediated inhibition of TLR4 expression was associated with the activation of mitogen-activated protein kinase and production of nitric oxide (NO). Actinomycin D chase experiments demonstrated that GBE decreased the TLR4 mRNA stability in cells. Confocal microscopy and real-time polymerase chain reaction showed that GBE induced the expression of intracellular tristetraprolin (TTP). Transfection with TTP siRNA reversed the effects of GBE in naïve or TLR4-overexpressing cells. Treatment with SNAP (an NO donor) may increase intracellular TTP expression in cells. Immunoprecipitation analysis showed that GBE mediates TTP activation and increases the interaction of TTP with the 3' untranslated region (UTR) of TLR4 mRNA by regulating NO production. Our findings indicate that GBE could decrease the sensitivity of monocytes to LPS. Utilizing TTP to control TLR4 expression may be a promising approach for controlling systemic inflammation, and GBE may have potential applications in the clinical treatment of immune diseases.
Lee
Yuan-Wen
YW
Department of Anesthesiology, Taipei Medical University and Hospital, Taipei 110, Taiwan.
Lin
Jui-An
JA
Chang
Chuen-Chau
CC
Chen
Yung-Hsiang
YH
Liu
Po-Len
PL
Lee
Ai-Wei
AW
Tsai
Jui-Chi
JC
Li
Chi-Yuan
CY
Tsai
Chien-Sung
CS
Chen
Ta-Liang
TL
Lin
Feng-Yen
FY
D002460:Cell Line; D003609:Dactinomycin / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D020441:Ginkgo biloba / Q000737:chemistry*; D006801:Humans; D008070:Lipopolysaccharides; D009000:Monocytes / Q000187:drug effects* / Q000378:metabolism; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000494:pharmacology; D010936:Plant Extracts / Q000494:pharmacology*; D026423:S-Nitroso-N-Acetylpenicillamine / Q000494:pharmacology; D051197:Toll-Like Receptor 4 / Q000096:biosynthesis*; D051816:Tristetraprolin / Q000037:antagonists & inhibitors / Q000494:pharmacology
D008070:Lipopolysaccharides; D010936:Plant Extracts; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D051816:Tristetraprolin; D003609:Dactinomycin; D009569:Nitric Oxide; D026423:S-Nitroso-N-Acetylpenicillamine; D048049:Extracellular Signal-Regulated MAP Kinases