Mukhtar H, Bik D P, Ruzicka T, Merk H F, Bickers D R
Department of Dermatology, University Hospitals, Case Western Reserve University, Cleveland, Ohio.
J Invest Dermatol. 1989 Aug;93(2):231-5. doi: 10.1111/1523-1747.ep12277578.
Leukotriene B4 (LTB4,5-12-dihydroxy 6,8,10,14-eicosatetraenoic acid), an enzyme-catalyzed oxidation product of arachidonic acid, is a major inflammatory mediator. Human polymorphonuclear leukocytes and rodent hepatic microsomes catabolize LTB4 to 20-OH-LTB4 and 20-COOH-LTB4, which is mediated by a cytochrome P-450 catalyzed reaction termed the LTB4 omega-hydroxylase. In this study we investigated the catabolism of LTB4 in rat, guinea pig, and human epidermis. The incubation of 3H-LTB4 (9 microM) for 60 min in the presence of oxygen, NADPH, and epidermal microsomes prepared from neonatal fat (3.0 mg) or adult guinea pig (2.6 mg) resulted in the formation of 20-OH-LTB4 and 20-COOH-LTB4. Metabolite identification was based on co-chromatography on high pressure liquid chromatography with highly purified reference standards. The formation of 20-OH-LTB4 and 20-COOH-LTB4 was accompanied by the disappearance of LTB4. The rate of formation of 20-OH-LTB4 was 9-12-fold higher than that of 20-COOH-LTB4. Product formation was negligible with boiled microsomes, required NADPH and oxygen, was linear with respect to incubation time and protein, and was maximal at pH 7.4. LTB4-omega-hydroxylase activity was inhibited (greater than 90%) by carbon monoxide or 2-diethylaminoethyl-2,2-diphenylvalerate hydrochloride (SKF-525A) (1 mM), whereas alpha-naphthoflavone produced only moderate (13%) or no effects. Topical application of 3-methylcholanthrene and other conventional inducers of epidermal monooxygenase activities to neonatal rats (100 mg/kg, single treatment) did not result in an increase in epidermal LTB4-omega-hydroxylase activity. The addition of 3H-LTB4 (30 nmoles) to primary human keratinocytes followed by incubation at 37 degrees C resulted in time-dependent disappearance of LTB4 and appearance of 20-OH-LTB4 and 20-COOH-LTB4 in the medium. These results suggest that LTB4 is catabolized by the cytochrome P-450-dependent enzyme system in rodent and human skin and that this may participate in modulating the effects of this proinflammatory lipid in this tissue.
白三烯B4（LTB4，5-12-二羟基-6,8,10,14-二十碳四烯酸）是花生四烯酸的一种酶催化氧化产物，是一种主要的炎症介质。人多形核白细胞和啮齿动物肝微粒体将LTB4分解为20-羟基-LTB4和20-羧基-LTB4，这是由一种称为LTB4 ω-羟化酶的细胞色素P-450催化反应介导的。在本研究中，我们研究了大鼠、豚鼠和人表皮中LTB4的分解代谢。在氧气、NADPH和由新生脂肪（3.0毫克）或成年豚鼠（2.6毫克）制备的表皮微粒体存在的情况下，将3H-LTB4（9微摩尔）孵育60分钟，导致形成20-羟基-LTB4和20-羧基-LTB4。代谢物鉴定基于与高度纯化的参考标准品在高压液相色谱上的共色谱法。20-羟基-LTB4和20-羧基-LTB4的形成伴随着LTB4的消失。20-羟基-LTB4的形成速率比20-羧基-LTB4高9-12倍。用煮沸的微粒体时产物形成可忽略不计，需要NADPH和氧气，与孵育时间和蛋白质呈线性关系，在pH 7.4时最大。LTB4-ω-羟化酶活性被一氧化碳或盐酸2-二乙氨基乙基-2,2-二苯基戊酸酯（SKF-525A）（1毫摩尔）抑制（大于90%），而α-萘黄酮仅产生中等程度（13%）的影响或无影响。对新生大鼠（100毫克/千克，单次处理）局部应用3-甲基胆蒽和其他表皮单加氧酶活性的传统诱导剂并未导致表皮LTB4-ω-羟化酶活性增加。向原代人角质形成细胞中加入3H-LTB4（30纳摩尔），然后在37℃孵育，导致LTB4随时间消失，培养基中出现20-羟基-LTB4和20-羧基-LTB4。这些结果表明，LTB4在啮齿动物和人类皮肤中被细胞色素P-450依赖性酶系统分解代谢，这可能参与调节该促炎脂质在该组织中的作用。
