Lipoteichoic acid-induced nitric oxide synthase expression in RAW 264.7 macrophages is mediated by cyclooxygenase-2, prostaglandin E2, protein kinase A, p38 MAPK, and nuclear factor-kappaB pathways

We recently reported that lipoteichoic acid (LTA), a cell wall component of the gram-positive bacterium Staphylococcus aureus, stimulated inducible nitric oxide synthase (iNOS) expression, nitric oxide (NO) release, and cyclooxygenase-2 (COX-2) expression in RAW 264.7 macrophages. This study was carried out to further investigate the roles of COX-2 and prostaglandin E2 (PGE2) in LTA-induced iNOS expression and NO release in RAW 264.7 macrophages. Treatment of RAW 264.7 macrophages with LTA caused a time-dependent increase in PGE2 release. LTA-induced iNOS expression and NO release were inhibited by a non-selective COX inhibitor (indomethacin), a selective COX-2 inhibitor (NS-398), an adenylyl cyclase (AC) inhibitor (dideoxyadenosine, DDA), and a protein kinase A (PKA) inhibitor (KT-5720). Furthermore, both PGE2 and the direct PKA activator, dibutyryl-cAMP, also induced iNOS expression in a concentration-dependent manner. Stimulation of RAW 264.7 macrophages with LTA, PGE2, and dibutyryl-cAMP all caused p38 MAPK activation in a time-dependent manner. LTA-mediated p38 MAPK activation was inhibited by indomethacin, NS-398, and SB 203580, but not by PD 98059. The PGE2-mediated p38 MAPK activation was inhibited by DDA, KT-5720, and SB 203580, but not by PD 98059. LTA caused time-dependent activation of the nuclear factor-kappaB (NF-kappaB)-specific DNA-protein complex formation. The LTA-induced increase in kappaB-luciferase activity was inhibited by indomethacin, NS-398, KT-5720, and a dominant negative mutant of p38 alphaMAPK (p38 alphaMAPK DN). These results suggest that LTA-induced iNOS expression and NO release involve COX-2-generated PGE2 production, and AC, PKA, p38 MAPK, and NF-kappaB activation in RAW 264.7 macrophages.     

Acetylbritannilatone suppresses NO and PGE2 synthesis in RAW 264.7 macrophages through the inhibition of iNOS and COX-2 gene expression

In order to elucidate the mechanism of anti-inflammatory effect of 1-o-acetylbritannilatone (ABL) isolated from Inula Britannica-F, we investigated ABL for its ability to inhibit the inflammatory factor production in RAW 264.7 macrophages. The studies showed that ABL not only inhibited LPS/IFN-gamma-mediated nitric oxide (NO) production and inducible nitric synthase (iNOS) expression, but also decreased LPS/IFN-gamma-induced prostaglandin E2 (PGE2) production and cyclo-oxygenase-2 (COX-2) expression in a concentration-dependent manner. EMSA demonstrated that ABL inhibited effectively the association of NF-kappaB, which is necessary for the expression of iNOS and COX-2, with its binding motif in the promoter of target genes. These data suggest that ABL suppress NO and PGE2 synthesis in RAW 264.7 macrophages through the inhibition of iNOS and COX-2 gene expression, respectively. The anti-inflammatory effect of ABL involves blocking the binding of NF-kappaB to the promoter in the target genes and inhibiting the expression of iNOS and COX-2.     

Inhibition of inducible nitric oxide synthase and cyclooxygenase II by Platycodon grandiflorum saponins via suppression of nuclear factor-kappaB activation in RAW 264.7 cells

Saponins are glycosidic compounds present in many edible and inedible plants. They exhibit potent biological activities in mammalian systems, including several beneficial effects such as anti-inflammation and immunomodulation. In this study, we investigated the effects of seven platycodin saponins on the activities of inducible nitric oxide synthase (iNOS) and cyclooxygenase II (COX-2) in lipopolysaccharide (LPS)-induced RAW 264.7 macrophages. We found that 2"-O-acetyl polygalacin D (S1), platycodin A (S2), platycodin D (S3), and polygalacin D (S6) inhibited LPS-induced NO production in a concentration-dependent manner. Furthermore, these compounds inhibited the expression of LPS-induced iNOS and COX-2 protein and mRNA without an appreciable cytotoxic effect on RAW 264.7 macrophages, and could suppress induction by LPS of pro-inflammatory cytokines such as prostaglandin E2 (PGE2). Treatment with these compounds of RAW 264.7 cells transfected with a reporter construct indicated a reduced level of LPS-induced nuclear factor-kappaB (NF-kappaB) activity and effectively lowered NF-kappaB binding as measured by electrophoretic mobility shift assay (EMSA). The suppression of NF-kappaB activation appears to occur through the prevention of inhibitor kappaB (IkappaB) degradation. In vivo, platycodin saponin mixture (PS) and S3 protected mice from the lethal effects of LPS. The 89% lethality induced by LPS/galactosamine was reduced to 60% and 50% when PS and S3, respectively, were administered simultaneously with LPS. These results suggest that the main inhibitory mechanism of the platycodin saponins may be the reduction of iNOS and COX-2 gene expression through blocking of NF-kappaB activation.     

Astaxanthin inhibits nitric oxide production and inflammatory gene expression by suppressing I(kappa)B kinase-dependent NF-kappaB activation

Astaxanthin, a carotenoid without vitamin A activity, has shown anti-oxidant and anti-inflammatory activities; however, its molecular action and mechanism have not been elucidated. We examined in vitro and in vivo regulatory function of astaxanthin on production of nitric oxide (NO) and prostaglandin E2 (PGE2) as well as expression of inducible NO synthase (iNOS), cyclooxygenase-2, tumor necrosis factor-alpha (TNF-alpha), and interleukin-1beta (IL-1beta). Astaxanthin inhibited the expression or formation production of these proinflammatory mediators and cytokines in both lipopolysaccharide (LPS)-stimulated RAW264.7 cells and primary macrophages. Astaxanthin also suppressed the serum levels of NO, PGE2, TNF-alpha, and IL-1beta in LPS-administrated mice, and inhibited NF-kappaB activation as well as iNOS promoter activity in RAW264.7 cells stimulated with LPS. This compound directly inhibited the intracellular accumulation of reactive oxygen species in LPS-stimulated RAW264.7 cells as well as H2O2-induced NF-kappaB activation and iNOS expression. Moreover, astaxanthin blocked nuclear translocation of NF-kappaB p65 subunit and I(kappa)B(alpha) degradation, which correlated with its inhibitory effect on I(kappa)B kinase (IKK) activity. These results suggest that astaxanthin, probably due to its antioxidant activity, inhibits the production of inflammatory mediators by blocking NF-kappaB activation and as a consequent suppression of IKK activity and I(kappa)B-alpha degradation.     

HO-1 and JAK-2/STAT-1 signals are involved in preferential inhibition of iNOS over COX-2 gene expression by newly synthesized tetrahydroisoquinoline alkaloid, CKD712, in cells activated with lipopolysacchride

We found that CKD712, an S enantiomer of YS49, strongly inhibited inducible nitric oxide synthase (iNOS) and NO induction but showed a weak inhibitory effect on cyclooxygenase-2 (COX-2) and PGE(2) induction in LPS-stimulated RAW 264.7 cells. We, therefore, investigated the molecular mechanism(s) responsible for this by using CKD712 in LPS-activated RAW264.7 cells. Treatment with either SP600125, a specific JNK inhibitor or TPCK, a NF-kappaB inhibitor, but neither ERK inhibitor PD98059 nor p38 inhibitor SB203580, significantly inhibited LPS-mediated iNOS and COX-2 induction. CKD712 inhibited NF-kappaB (p65) activity and translocation but failed to prevent JNK activation. However, AG490, a specific JAK-2/STAT-1 inhibitor, efficiently prevented LPS-mediated iNOS induction but not the induction of COX-2, and CKD712 completely blocked STAT-1 phosphorylation by LPS, suggesting that the NF-kappaB and JAK-2/STAT-1 pathways but not the JNK pathway are important for CKD712 action. Interestingly, CKD712 induced heme oxygenase 1 (HO-1) gene expression in LPS-treated cells. LPS-induced NF-kappaB and STAT-1 activation was partially prevented by HO-1 overexpression. Furthermore, HO-1 siRNA partly reversed not only the LPS-induced NF-kappaB activation and STAT-1 phosphorylation but also inhibition of these actions by CKD 712. Additionally, silencing HO-1 by siRNA prevented CKD712 from inhibiting iNOS expression but not COX-2. When examined plasma NO and PGE(2) levels and iNOS and COX-2 protein levels in lung tissues of mice injected with LPS (10 mg/kg), pretreatment with CKD712 greatly prevented NO and iNOS induction in a dose-dependent manner and slightly affected PGE(2) and COX-2 production as expected. Taken together, we conclude that inhibition of JAK-2/STAT-1 pathways by CKD 712 is critical for the differential inhibition of iNOS and COX-2 by LPS in vitro and in vivo where HO-1 induction also contributes to this by partially modulating JAK-2/STAT-1 pathways.     

Inhibitory effects of Irigenin from the rhizomes of Belamcanda chinensis on nitric oxide and prostaglandin E(2) production in murine macrophage RAW 264.7 cells

In the present study, we investigated antiinflammatory effects of six flavonoids isolated from the rhizomes of Belamcanda chinensis (Iridaceae) in RAW 264.7 macrophages. The results indicated that irigenin concentration dependently inhibited lipopolysaccharide (LPS)-induced nitric oxide (NO) and prostaglandin (PG) E(2) production. Furthermore, this compound inhibited the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 proteins and mRNAs without an appreciable cytotoxic effect. Treatment of the transfectant RAW 264.7 cells with irigenin reduced the level of nuclear factor-kappaB (NF-kappaB) activity, also effectively lowered NF-kappaB binding measured by electrophoretic mobility shift assay (EMSA), which was associated with decreased p65 protein levels in the nucleus. On the basis of the above data, we suggest that the effect of irigenin in decreasing LPS-induced NO and PGE(2) synthesis is due to diminish the mRNA and protein expression of iNOS and COX-2, respectively, also may be due to under the suppression of NF-kappaB activation. Therefore, irigenin isolated from the rhizomes of Belamcanda chinensis could be offered as a leading compound for anti-inflammation.     

Regulation of cyclooxygenase-2 expression by macrophages in response to double-stranded RNA and viral infection

In this study the regulation of macrophage expression of cyclooxygenase-2 (COX-2) in response to dsRNA and virus infection was examined. Treatment of RAW 264.7 macrophages with dsRNA results in COX-2 mRNA accumulation and protein expression and the production of PGE(2). Similar to dsRNA, encephalomyocarditis virus (EMCV) infection of RAW 264.7 cells stimulates COX-2 expression and PGE(2) accumulation. The dsRNA-dependent protein kinase (PKR), which has been shown to participate in the regulation of gene expression in response to dsRNA and virus infection, does not appear to participate in the regulation of COX-2 expression by macrophages. Expression of dominant negative mutants of PKR in RAW 264.7 cells fails to attenuate dsRNA- and EMCV-induced COX-2 expression or PGE(2) production. Furthermore, dsRNA and EMCV stimulate COX-2 expression and PGE(2) accumulation to similar levels in macrophages isolated from wild-type and PKR-deficient mice. Recently, a novel PKR-independent role for the calcium-independent phospholipase A(2) (iPLA(2)) in the regulation of inducible NO synthase expression by macrophages in response to virus infection has been identified. The selective iPLA(2) suicide substrate inhibitor bromoenol lactone prevents dsRNA- and EMCV-stimulated inducible NO synthase expression; however, bromoenol lactone does not attenuate dsRNA- or EMCV-induced COX-2 expression by macrophages. In contrast, inhibition of NF-kappaB activation prevents dsRNA-stimulated COX-2 expression and PGE(2) accumulation by macrophages. These findings indicate that virus infection and treatment with dsRNA stimulate COX-2 expression by a mechanism that requires the activation of NF-kappaB and that is independent of PKR or iPLA(2) activation.     

Methanol extracts of Stewartia koreana inhibit cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) gene expression by blocking NF-kappaB transactivation in LPS-activated RAW 264.7 cells

Cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) are involved in various pathophysiological processes such as inflammation and carcinogenesis. In a search for inhibitors of COX-2 and iNOS production we found that extracts of Stewartia koreana strongly inhibited NO and PGE2 production in LPS-treated macrophage RAW 264.7 cells. We have now shown that the mRNA and protein levels of iNOS and COX-2 are reduced by the Stewartia koreana extract (SKE). SKE inhibited expression of an NF-kappaB reporter gene in response to LPS, and gel mobility shift assays revealed that SKE reduced NF-kappaB DNA-binding activity. The extract also inhibited LPS-induced phosphorylation of IkappaB-alpha and nuclear translocation of p65. Administration of the extract reduced the symptoms of arthritis in a collagen-induced arthritic mouse model. These results indicate that Stewartia extracts contain potentially useful agents for preventing and treating inflammatory diseases.     

Inhibition of nitric oxide synthase inhibitors and lipopolysaccharide induced inducible NOS and cyclooxygenase-2 gene expressions by rutin, quercetin, and quercetin pentaacetate in RAW 264.7 macrophages

Several natural flavonoids have been demonstrated to perform some beneficial biological activities, however, higher-effective concentrations and poor-absorptive efficacy in body of flavonoids blocked their practical applications. In the present study, we provided evidences to demonstrate that flavonoids rutin, quercetin, and its acetylated product quercetin pentaacetate were able to be used with nitric oxide synthase (NOS) inhibitors (N-nitro-L-arginine (NLA) or N-nitro-L-arginine methyl ester (L-NAME)) in treatment of lipopolysaccharide (LPS) induced nitric oxide (NO) and prostaglandin E2 (PGE2) productions, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) gene expressions in a mouse macrophage cell line (RAW 264.7). The results showed that rutin, quercetin, and quercetin pentaacetate-inhibited LPS-induced NO production in a concentration-dependent manner without obvious cytotoxic effect on cells by MTT assay using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide as an indicator. Decrease of NO production by flavonoids was consistent with the inhibition on LPS-induced iNOS gene expression by western blotting. However, these compounds were unable to block iNOS enzyme activity by direct and indirect measurement on iNOS enzyme activity. Quercetin pentaacetate showed the obvious inhibition on LPS-induced PGE2 production and COX-2 gene expression and the inhibition was not result of suppression on COX-2 enzyme activity. Previous study demonstrated that decrease of NO production by L-arginine analogs effectively stimulated LPS-induced iNOS gene expression, and proposed that stimulatory effects on iNOS protein by NOS inhibitors might be harmful in treating sepsis. In this study, NLA or L-NAME treatment stimulated significantly on LPS-induced iNOS (but not COX-2) protein in RAW 264.7 cells which was inhibited by these three compounds. Quercetin pentaacetate, but not quercetin and rutin, showed the strong inhibitory activity on PGE2 production and COX-2 protein expression in NLA/LPS or L-NAME/LPS co-treated RAW 264.7 cells. These results indicated that combinatorial treatment of L-arginine analogs and flavonoid derivates, such as quercetin pentaacetate, effectively inhibited LPS-induced NO and PGE2 productions, at the same time, inhibited enhanced expressions of iNOS and COX-2 genes.     

Effect of bismuth subgallate on nitric oxide and prostaglandin E2 production by macrophages

Bismuth subgallate (BSG) is used widely in clinics, including Vincent's angina, syphilis, and adenotonsillectomy. This study examined the effects of BSG on nitric oxide (NO) and prostaglandin E2 (PGE2) production in activated RAW 264.7 cells. BSG suppressed production of NO and PGE2 in a dose-dependent manner. BSG could increase TGF-beta1 production, which in turn might promote degradation of iNOS mRNA, thus inhibiting NO production. Additionally, BSG inhibited mPGES protein expression and COX-2 activity in activated RAW 264.7 cells. Exogenous addition of SNP reversed the inhibition effect of PGE2 production by BSG. This behavior indicates that PGE2 inhibition by BSG exerts an indirect effect through NO inhibition.     

Anti-inflammatory effect of chitosan oligosaccharides in RAW 264.7 cells

We examined the effects of chitosan oligosaccharides (COSs) with different molecular weights (COS-A, 10 kDa < MW < 20 kDa; COS-C, 1 kDa < MW < 3 kDa) on the lipopolysaccharide (LPS)-induced production of prostaglandin E₂ and nitric oxide and on the expression of cyclooxygenase-2 and inducible nitric oxide synthase in RAW264.7 macrophages. COS-A (0.4%) and COS-C (0.2%) significantly inhibited PGE2 production in LPS-stimulated macrophages without cytotoxicity. The effect of COS-A and COS-C on COX-2 expression in activated macrophages was also investigated by immunoblotting. The inhibition of PGE₂ by COS-A and COS-C can be attributed to the blocking of COX-2 protein expression. COS-A (0.4%) and COS-C (0.2%) also markedly inhibited the LPS-induced NO production of RAW 264.7 cells by 50.2% and 44.1%, respectively. The inhibition of NO by COSs was consistent with decreases in inducible nitric oxide synthase (iNOS) protein expression. To test the inhibitory effects of COS-A and COS-C on other cytokines, we also performed ELISA assays for IL-1β in LPS-stimulated RAW 264.7 macrophage cells, but only a dose-dependent decrease in the IL-1β production exerted by COS-A was observed. In order to test for irritation and the potential sensitization of COS-A and COS-C for use as cosmetic materials, human skin primary irritation tests were performed on 32 volunteers; no adverse reactions of COSs usage were observed. Based on these results, we suggest that COS-A and COS-C be considered possible anti-inflammatory candidates for topical application.     

Dipyrithione inhibits lipopolysaccharide-induced iNOS and COX-2 up-regulation in macrophages and protects against endotoxic shock in mice

Dipyrithione (PTS2) possesses anti-bacterial and anti-fungal activity. In the present study, we found that PTS2 dose-dependently inhibited the LPS-induced up-regulation of nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) protein level in RAW264.7 cells. RT-PCR experiments showed that PTS2 suppressed LPS-induced iNOS but not COX-2 expression at the mRNA level. As expected, PTS2 prevented NO secretion in RAW264.7 cells. Furthermore, PTS2 administration significantly decreased LPS-induced mortality in mice. Mechanistically, PTS2 decreased expression and phosphorylation of STAT1, but did not interfere with the MAPK and NF-kappaB pathways. In conclusion, PTS2 protects mice against endotoxic shock and inhibits LPS-induced production of pro-inflammatory mediators, suggesting that PTS2 could play an anti-inflammatory role in response to LPS.