(−)-Epigallocatechin-3-gallate Blocks the Induction of Nitric Oxide Synthase by Down-Regulating Lipopolysaccharide-Induced Activity of Transcription Factor Nuclear Factor-κB
- Yu-Li Lin and
- Jen-Kun Lin
- Institute of Biochemistry, College of Medicine, National Taiwan University, Taipei, Taiwan, Republic of China
Abstract
Nitric oxide (NO) plays an important role in inflammation and multiple stages of carcinogenesis. We investigated the effect of various tea polyphenols and caffeine on the induction of NO synthase (NOS) in thioglycollate-elicited and lipopolysaccharide (LPS)-activated peritoneal macrophages. Gallic acid (GA), (−)-epigallocatechin (EGC), and (−)-epigallocatechin-3-gallate (EGCG), the major tea catechin, were found to inhibit inducible NOS (iNOS) protein in activated macrophages. EGCG, a potent antitumor agent with anti-inflammatory and antioxidant properties, inhibited NO generation, as measured by the amount of nitrite released into the culture medium. Inhibition of NO production was observed when cells were cotreated with EGCG and LPS. iNOS activity in soluble extracts of lipopolysaccharide-activated macrophages treated with EGCG (5 and 10 μm) for 6–24 hr was significantly lower than that in macrophages without EGCG treatment. Western blot, reverse transcription-polymerase chain reaction, and Northern blot analyses demonstrated that significantly reduced 130-kDa protein and 4.5-kb mRNA levels of iNOS were expressed in lipopolysaccharide-activated macrophages with EGCG compared with those without EGCG. Electrophoretic mobility shift assay indicated that EGCG blocked the activation of nuclear factor-κB, a transcription factor necessary for iNOS induction. EGCG also blocked disappearance of inhibitor κB from cytosolic fraction. These results suggest that EGCG decreases the activity and protein levels of iNOS by reducing the expression of iNOS mRNA and the reduction could occur through prevention of the binding of nuclear factor-κB to the iNOS promoter, thereby inhibiting the induction of iNOS transcription.
Footnotes
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Send reprint requests to: Dr. Jen-Kun Lin, Institute of Biochemistry, College of Medicine, National Taiwan University, No. 1, Section 1, Jen-Ai Road, Taipei, Taiwan 100, R.O.C.
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↵1 Y.-L. Lin and J.-K. Lin, unpublished observations.
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This study was supported by National Science Council Grant NSC 86–2314-B-002–042 and National Health Research Institute Grant DOH 86-HR-403.
- Abbreviations:
- NO
- nitric oxide
- iNOS
- inducible nitric oxide synthase
- LPS
- lipopolysaccharide
- GA
- gallic acid
- EGC
- (−)-epigallocatechin
- EGCG
- (−)-epigallocatechin-3-gallate
- NF-κB
- nuclear factor-κB
- EC
- (−)-epicatechin
- ECG
- (−)-epicatechin-3-gallate
- ROI
- reactive oxygen intermediate
- PEC
- peritoneal exudate cell
- HEPES
- 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- DTT
- dithiothreitol
- GAPDH
- glyceraldehyde-3-phosphate dehydrogenase
- PCR
- polymerase chain reaction
- RT
- reverse transcription
- IκB
- inhibitor κB
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- Received December 26, 1996.
- Accepted April 16, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
