Hepatic microsomal metabolism of leukotriene B4 in rats: biochemical characterization, effect of inducers, and age- and sex-dependent differences.
1. The cytochrome P-450-dependent metabolism of leukotriene B4 (LTB4) by rat hepatic microsomes was characterized. Hepatic microsomes were found to metabolize LTB4 to 20-hydroxy-LTB4 and 20-carboxy:LTB4. The rate of formation of 20-hydroxy-LTB4 (14.6 pmol/min per mg protein) was 5.8-fold higher than that of 20-carboxy-LTB4 (2.5 pmol/min per mg protein). 2. LTB4 omega-hydroxylase activity required NADPH and oxygen indicating that the reaction is mediated by a mono-oxygenase system. The omega-hydroxylase activity was optimal at pH 7.4 and product formation was linear with respect to time of incubation and protein concentration. The reaction was significantly inhibited by carbon monoxide (89%), SKF 525-A (1 mM), and metyrapone (0.1 mM) whereas alpha-naphthoflavone had only marginal inhibitory effects. The apparent Km and Vmax of LTB4 omega-hydroxylase were 4 microM and 19.6 pmol/min per mg protein, respectively. 3. Ontogenic studies revealed that LTB4 omega-hydroxylase activity was low in 4-day-old rats and that there was a steady increase in enzyme activity as the animal matured. 4. Phenobarbital, 3-methylcholanthrene or Aroclor 1254 treatment of rats did not induce LTB4 omega-hydroxylase activity whereas clofibrate resulted in 61% induction in enzyme activity. No significant sex-dependent differences were observed. 5. It is concluded that hepatic metabolism of LTB4 may afford an effective mechanism for limiting many of the pro-inflammatory effects of circulating leukotrienes.
Mukhtar
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Department of Dermatology, University Hospital of Cleveland, Case Western Reserve University, Ohio.
Khan
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Bik
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Das
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Bickers
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D000375:Aging / Q000378:metabolism; D000818:Animals; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000494:pharmacology; D000072470:Cytochrome P450 Family 4; D004794:Enzyme Repression / Q000187:drug effects; D005260:Female; D006893:Hydroxyeicosatetraenoic Acids / Q000378:metabolism; D007700:Kinetics; D007975:Leukotriene B4 / Q000378:metabolism* / Q000031:analogs & derivatives; D008862:Microsomes, Liver / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000378:metabolism; D009249:NADP / Q000494:pharmacology; D011247:Pregnancy; D051381:Rats; D012737:Sex Factors; D014316:Tritium
D065607:Cytochrome P-450 Enzyme Inhibitors; D006893:Hydroxyeicosatetraenoic Acids; D014316:Tritium; D007975:Leukotriene B4; D009249:NADP; C031571:5,12,20-trihydroxy-6,8,10,14-eicosatetraenoic acid; C031911:20-carboxyleukotriene B4; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D000072470:Cytochrome P450 Family 4; C040780:leukotriene B4 20-hydroxylase