Knipholone, a selective inhibitor of leukotriene metabolism.
Inhibition of leukotriene formation is one of the approaches to the treatment of asthma and other inflammatory diseases. We have investigated knipholone, isolated from the roots of Kniphofia foliosa, Hochst (Asphodelaceae), for inhibition of leukotriene biosynthesis in an ex vivo bioassay using activated human neutrophile granulocytes. Moreover, activities on 12-lipoxygenase from human platelets and cycloxygenase (COX)-1 and -2 from sheep cotyledons and seminal vesicles, respectively, have been evaluated. Knipholone was found to be a selective inhibitor of leukotriene metabolism in a human blood assay with an IC(50) value of 4.2microM. However, at a concentration of 10microg/ml, the compound showed weak inhibition of 12(S)-HETE production in human platelets and at a concentration of 50microM it produced no inhibition of COX-1 and -2. In our attempt to explain the mechanism of inhibition, we examined the antioxidant activity of knipholone using various in vitro assay systems including free radical scavenging, non-enzymatic lipid peroxidation, and metal chelation. Knipholone was found to be a weak dose-independent free radical scavenger and lipid peroxidation inhibitor, but not a metal chelator. Therefore, the leukotriene biosynthesis inhibitory effect of knipholone was evident by its ability either to inhibit the 5-lipoxygenase activating protein (FLAP) or as a competitive (non-redox) inhibitor of the enzyme. Cytotoxicity results also provided evidence that knipholone exhibits less toxicity for a mammalian host cell.
Wube
A A
AA
Department of Pharmacognosy, Institute for Pharmaceutical Sciences, Karl-Franzens University Graz, Universitaetsplatz 4/1, A-8010 Graz, Austria.
Bucar
F
F
Asres
K
K
Gibbons
S
S
Adams
M
M
Streit
B
B
Bodensieck
A
A
Bauer
R
R
D000818:Animals; D000880:Anthraquinones / Q000494:pharmacology*; D001156:Artemia / Q000187:drug effects; D001713:Biphenyl Compounds; D016166:Free Radical Scavengers / Q000494:pharmacology; D006801:Humans; D015289:Leukotrienes / Q000096:biosynthesis*; D015227:Lipid Peroxidation / Q000187:drug effects; D019684:Magnoliopsida; D008297:Male; D008517:Phytotherapy; D010851:Picrates / Q000737:chemistry; D010920:Placenta / Q000187:drug effects; D010936:Plant Extracts / Q000494:pharmacology*; D018517:Plant Roots; D012669:Seminal Vesicles / Q000187:drug effects; D012756:Sheep
D000880:Anthraquinones; D001713:Biphenyl Compounds; D016166:Free Radical Scavengers; D015289:Leukotrienes; D010851:Picrates; D010936:Plant Extracts; C403586:knipholone; C004931:1,1-diphenyl-2-picrylhydrazyl