Abstract
Diarctigenin was previously isolated as an inhibitor of nitric oxide (NO) production in macrophages from the seeds of Arctium lappa used as an alternative medicine for the treatment of inflammatory disorders. However, little is known about the molecular basis of these effects. Here, we demonstrated that diarctigenin inhibited the production of NO, prostaglandin E2, tumor necrosis factor-α, and interleukin (IL)-1β and IL-6 with IC50 values of 6 to 12 μM in zymosan- or lipopolysaccharide-(LPS) activated macrophages. Diarctigenin attenuated zymosan-induced mRNA synthesis of inducible NO synthase (iNOS) and also inhibited promoter activities of iNOS and cytokine genes in the cells. Because nuclear factor (NF)-κB plays a pivotal role in inflammatory gene transcription, we next investigated the effect of diarctigenin on NF-κB activation. Diarctigenin inhibited the transcriptional activity and DNA binding ability of NF-κB in zymosan-activated macrophages but did not affect the degradation and phosphorylation of inhibitory κB (IκB) proteins. Moreover, diarctigenin suppressed expression vector NF-κB p65-elicited NF-κB activation and also iNOS promoter activity, indicating that the compound could directly target an NF-κ-activating signal cascade downstream of IκB degradation and inhibit NF-κB-regulated iNOS expression. Diarctigenin also inhibited the in vitro DNA binding ability of NF-κB but did not affect the nuclear import of NF-κB p65 in the cells. Taken together, diarctigenin down-regulated zymosan- or LPS-induced inflammatory gene transcription in macrophages, which was due to direct inhibition of the DNA binding ability of NF-κB. Finally, this study provides a pharmacological potential of diarctigenin in the NF-κB-associated inflammatory disorders.
Footnotes
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This work was supported by Grant KRF-2005-005-J15001 from the Korean Government (MOEHRD, Basic Research Promotion Fund) and other research funds from Chungbuk BIT Research-Oriented University Consortium and from Research Center for Bioresource and Health.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.108.140145.
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ABBREVIATIONS: TNF, tumor necrosis factor; NO, nitric oxide; IL, interleukin; LPS, lipopolysaccharide; iNOS, inducible nitric-oxide synthase; NF, nuclear factor; IκB, inhibitory κB; TLR, toll-like receptor; IKK, IκB kinase; COX, cyclooxygenase; FBS, fetal bovine serum; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; SEAP, secretory alkaline phosphatase; NPT, neomycin phosphotransferase; PG, prostaglandin; ELISA, enzyme-linked immunosorbent assay; RT-PCR, reverse transcription-polymerase chain reaction; Luc, luciferase; bp, base pair; p, phosphor.
- Received April 16, 2008.
- Accepted August 8, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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