Powell W S, Gravelle F
Endocrine Laboratory, Royal Victoria Hospital, Montreal, Quebec, Canada.
J Biol Chem. 1990 Jun 5;265(16):9131-9.
Previous studies have shown that leukotriene B4 is metabolized by polymorphonuclear leukocytes (PMNL) by a 20-hydroxylase, a 19-hydroxylase, and a reductase. We have now identified for the first time LTB4 metabolites formed by a combination of the reductase and omega-oxidation pathways. We have also discovered that rat PMNL metabolize LTB4 by a novel pathway to 18-hydroxy products. Dihydro metabolites of LTB4 have formerly been reported only after incubation of exogenous LTB4 with PMNL, but we have now shown that they are formed to the same extent from endogenous arachidonic acid after stimulation of PMNL with the ionophore, A23187. The following metabolites have been identified after incubation of either LTB4 or arachidonic acid with rat PMNL: 10,11-dihydro-LTB4, 10,11-dihydro-12-epi-LTB4, 10,11-dihydro-12-oxo-LTB4, 19-hydroxy-LTB4, 19-hydroxy-10,11-dihydro-LTB4, 19-oxo-10,11-dihydro-LTB4, 18-hydroxy-LTB4, 18-hydroxy-10,11-dihydro-LTB4, and 18-hydroxy-10,11-dihydro-12-oxo-LTB4. Negligible amounts of 20-hydroxylated products were formed. Incubation of PMNL with 10,11-dihydro-LTB4 resulted in the formation of all of the above dihydro metabolites. However, none of the omega-oxidized metabolites of LTB4 was further metabolized to a significant extent when incubated with PMNL, possibly at least partially because they were not substrates for a specific LTB4 uptake mechanism. We found that the biosynthesis and metabolism of LTB4 is considerably enhanced in PMNL from an inflammatory site (carrageenan-induced pleurisy) compared with peripheral PMNL. When arachidonic acid was the substrate, the greatest increase was observed for products formed by the reductase pathway, which were about eight times higher in pleural PMNL. The rates of formation of both LTA hydrolase and omega-hydroxylase products were about three times higher, whereas the total amounts of 5-lipoxygenase products were about twice as high in pleural PMNL. The amounts of products formed by the above enzymatic pathways reached maximal levels about 4-6 h after injection of carrageenan and then declined.
先前的研究表明，白三烯B4可被多形核白细胞（PMNL）通过20-羟化酶、19-羟化酶和还原酶进行代谢。我们现已首次鉴定出由还原酶和ω-氧化途径共同作用形成的白三烯B4代谢产物。我们还发现，大鼠的多形核白细胞通过一条新途径将白三烯B4代谢为18-羟基产物。白三烯B4的二氢代谢产物以前仅在将外源性白三烯B4与多形核白细胞一起孵育后才有报道，但我们现在已表明，在用离子载体A23187刺激多形核白细胞后，内源性花生四烯酸也能以相同程度形成这些产物。在用白三烯B4或花生四烯酸与大鼠多形核白细胞孵育后，已鉴定出以下代谢产物：10,11-二氢白三烯B4、10,11-二氢-12-表白三烯B4、10,11-二氢-12-氧代白三烯B4、19-羟基白三烯B4、19-羟基-10,11-二氢白三烯B4、19-氧代-10,11-二氢白三烯B4、18-羟基白三烯B4、18-羟基-10,11-二氢白三烯B4和18-羟基-10,11-二氢-12-氧代白三烯B4。形成的20-羟基化产物数量可忽略不计。将多形核白细胞与未10,11-二氢白三烯B4一起孵育会导致形成上述所有二氢代谢产物。然而，当与多形核白细胞一起孵育时，白三烯B4的ω-氧化代谢产物均未进一步大量代谢，这可能至少部分是因为它们不是特定白三烯B4摄取机制的底物。我们发现，与外周多形核白细胞相比，炎症部位（角叉菜胶诱导的胸膜炎）的多形核白细胞中白三烯B4的生物合成和代谢显著增强。当花生四烯酸作为底物时，还原酶途径形成的产物增加最为明显，在胸膜多形核白细胞中约高出八倍。LTA水解酶和ω-羟化酶产物的形成速率约高出三倍，而胸膜多形核白细胞中5-脂氧合酶产物的总量约高出两倍。注射角叉菜胶后约4-6小时，上述酶促途径形成的产物量达到最高水平，然后下降。
