Mechanisms of the influence of magnolol on eicosanoid metabolism in neutrophils.
We have demonstrated that magnolol suppressed thromboxane B2 (TXB2) and leukotriene B4 (LTB4) formation in A23187-stimulated rat neutrophils. Maximum inhibition was obtained with about 10 microM magnolol. Magnolol was more effective in the inhibition of cyclooxygenase (COX) activity than in the inhibition of 5-lipoxygenase (5-LO) activity as assessed by means of enzyme activity determination in vitro and COX and 5-LO metabolic capacity analyses in vivo. Magnolol alone stimulated cytosolic phospholipase A2 (cPLA2) phosphorylation and the translocation of 5-LO and cPLA2 to the membrane, and evoked arachidonic acid (AA) release. Recruitment of both 5-LO and cPLA2 to the membranes was suppressed by EGTA. Arachidonyl trifluoromethyl ketone (AACOCF3), a PLA2 inhibitor, bromoenol lactone (BEL), a Ca2+-independent PLA2 (iPLA2) inhibitor, and EGTA suppressed the magnolol-induced AA release. However, none of the follows affected magnolol-induced AA-release: 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole (SB203580), a p38 mitogen-activated protein kinase (MAPK) inhibitor, 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene (U0126), a MAPK kinase (MEK) inhibitor, or 2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)-maleimide (GF109203X), a protein kinase C (PKC) inhibitor. In addition, magnolol at 30 microM did not stimulate the p38 MAPK and extracellular signal-regulated kinase 2 (ERK2) enzyme activities. These results indicated that magnolol inhibits the formation of prostaglandins and leukotrienes in A23187-stimulated rat neutrophils, probably through a direct blockade of COX and 5-LO activities. The stimulatory effects of magnolol at high concentration on the membrane association of 5-LO and cPLA2 are attributable to the elevation of [Ca2+]i, and on the AA release is likely via activation of cPLA2 and iPLA2.
Hsu
Mei-Feng
MF
Department of Biochemistry, China Medical University, Taichung, Taiwan, ROC.
Lu
Min-Chi
MC
Tsao
Lo-Ti
LT
Kuan
Yu-Hsing
YH
Chen
Chien-Chih
CC
Wang
Jih-Pyang
JP
D000818:Animals; D001094:Arachidonate 5-Lipoxygenase / Q000378:metabolism; D016718:Arachidonic Acid / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D001713:Biphenyl Compounds / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004533:Egtazic Acid / Q000378:metabolism; D015777:Eicosanoids / Q000378:metabolism; D004789:Enzyme Activation; D066298:In Vitro Techniques; D017705:Lignans; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009504:Neutrophils / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism; D051381:Rats
D001713:Biphenyl Compounds; D015777:Eicosanoids; D017705:Lignans; C005498:magnolol; D016718:Arachidonic Acid; D004533:Egtazic Acid; D001094:Arachidonate 5-Lipoxygenase; D011451:Prostaglandin-Endoperoxide Synthases; D020928:Mitogen-Activated Protein Kinases; D010741:Phospholipases A; D054467:Phospholipases A2