Effects of Constituents from the Bark of Magnolia obovata on Nitric Oxide Production in Lipopolysaccharide-Activated Macrophages.

Abstract

Inducible nitric oxide synthase (iNOS) is involved in pathological processes related to overproduction of nitric oxide (NO), and is expressed in response to pro-inflammatory agents such as interleukin (IL)-1b, tumor necrosis factor (TNF)-a and lipopolysaccharide (LPS) in various cell types including macrophages, endothelial cells, and smooth muscle cells.1) Nuclear factor (NF)-kB is a major transcription factor involved in iNOS, TNF-a, IL-1b, and IL-8 genes expression. NF-kB activation involves dissociation of an inhibitory subunit, IkB, which keeps NF-kB in the cytoplasm, thereby preventing activation of the target gene in the nucleus. Cellular signals lead to phosphorylation of IkB following elimination of IkB from NF-kB by proteolytic degradation. Then, the activated-NF-kB is released and translocated into the nucleus to activate transcription of its target genes.2) Inhibition of iNOS enzyme activity or iNOS induction and inhibition of NF-kB activation may be of therapeutic benefit in various types of inflammation. 10) In the course of our studies on constituents with NO production inhibitory activity from natural medicines, 11) the methanolic extract from the dried bark of M. obovata was found to inhibit nitrite (NO 2 Ϫ , a product of NO) accumulation in LPS-activated mouse macrophages (IC 50 ϭ25 mg/ml).Previous reports demonstrated that two neolignans [magnolol (1), honokiol (2)] showed inhibitory effects on NO production from LPS-activated RAW 264.7 cells.12) However, effects of other constituents on NO production from LPS-activated mouse macrophages and their cytotoxicities for macrophages have not been examined. This report describes the effects of the constituents from the bark of M. obovata on NO production in LPS-stimulated macrophages. In addition, we describe the effects of principal active neolignan constituents [magnolol (1), honokiol (2), obovatol (3)] on iNOS enzyme activity, induction of iNOS, and activation of NF-kB to clarify their action mechanisms. Results and DiscussionIsolation of Chemical Constituents from the Dried Bark of M. obovata The bark of Japanese M. obovata was extracted with methanol under reflux. The methanolic extract was subjected to ordinary-and reversed-phase silica gel column chromatography and finally HPLC to furnish five neolignans, magnolol (1, 13) 2.1% from the natural medicine), honokiol (2, 14) 0.43%), obovatol (3, 15) 0.26%), 4-O-methylhonokiol (4, 16) 0.0031%), and 6Ј-O-methylhonokiol (5, 10,16) 0.0031%), seven sesquiterpene-neolignans, eudesmagnolol (6, 17) 0.096%), clovanemagnolol (7, 18) 0.0061%), caryolanemagnolol (8, 10) 0.0044%), eudeshonokiols A (9, 10) 0.0056%) and B (10, 10) 0.0054%), eudesobovatols A (11, 19) 0.043%) and B (12,19) 0.024%), a trineolignan, magnolianin (13,20) 0.27%), a phenylpropanoid glycoside, syringin (14, 21) 0.39%), two lignan glycosides, liriodendrin (15,22) 0.15%) and (ϩ)-syringaresinol 4Ј-O-b-D-glucopyranoside (16,23) 0.029%), and four sesquiterpenes, caryophyllene oxide (17, 24) 0.0049%), a-eudesmol (18, 11g,24) 0.096%), b...

Inhibitory effects of honokiol on LPS and PMA-induced cellular responses of macrophages and monocytes

“…In the present study, we reevaluated the modulatory effect of this compound on various NO productive conditions induced by different NO stimulatory ligands. As previously reported (12), honokiol suppressed LPS-induced NO production in a dose-dependent manner (Fig. 3B, left panel).…”

“…2A). It is well known that honokiol suppresses NO production in macrophages (12). In the present study, we reevaluated the modulatory effect of this compound on various NO productive conditions induced by different NO stimulatory ligands.…”

Honokiol Inhibits the Progression of Collagen-Induced Arthritis by Reducing Levels of Pro-inflammatory Cytokines and Matrix Metalloproteinases and Blocking Oxidative Tissue Damage

“…Honokiol evidences a variety of pharmacological activities, including antioxidative (20 -22), anti-inflammatory (23,24), and antitumor activities (25,26). In this study, we attempted to determine whether the oral administration of honokiol might prevent the progression of collagen-induced arthritis (CIA), which has been used as an animal model for studies of RA pathogenesis and to evaluate potential therapeutic agents (27).…”

Magnolol Inhibits LPS-induced NF-κB/Rel Activation by Blocking p38 Kinase in Murine Macrophages

“…It has been reported that magnolol, a compound purified from Magnolia officinalis, relaxes rat vascular smooth muscle [2], scavenges hydroxyl radicals [3], inhibits neutrophil aggregation and superoxide anion generation [4,5], suppresses the expression of vascular cell adhesion molecule-1 in endothelial cells [6], inhibits nitric oxide (NO) production in lipopolysaccharide (LPS)-activated macrophages [7]. Recently, it has been reported that the anti-inflammatory effects of magnolol are mediated through inhibition of the downstream pathway of MEKK-1 in NF-κB activation signaling [8].…”