Martini R, Murray M
Department of Medicine, University of Sydney, Westmead Hospital, NSW, Australia.
Arch Biochem Biophys. 1993 May 15;303(1):57-66. doi: 10.1006/abbi.1993.1255.
Cytochrome P450-mediated 4-hydroxylation is an important pathway in the termination of the biological action of retinoids. Several purified mammalian hepatic P450s have been shown to catalyze the 4-hydroxylation of all-trans-retinoic acid (retinoic acid) in reconstituted enzyme systems, but the nature of the activity in untreated rat liver microsomes has not been defined. In the present study, microsomal retinoic acid 4-hydroxylation was characterized in untreated liver from rats of both sexes and after a series of induction treatments. Thus, dexamethasone and phenobarbital, but not beta-naphthoflavone or dimethyl sulfoxide, increased the activity in male and female rats. An immunoglobulin G (IgG) fraction raised against P450 3A1 decreased the rate of retinoic acid 4-hydroxylation in untreated rat hepatic microsomes, but IgG directed against the P450s 2C11, 2B1, and 2C6 were noninhibitory. In vivo administration of triacetyloleandomycin, which has been shown to form a metabolite intermediate complex with P450 3A, followed by potassium ferricyanide oxidation in vitro, reactivated retinoic acid 4-hydroxylation and androst-4-ene-3,17-dione 6 beta-hydroxylation similarly (to 154 and 152% of the respective activities in the absence of potassium ferricyanide). Finally, exogenous retinoic acid (60 mg/kg ip for three days) markedly increased the rate of retinoic acid 4-hydroxylation in hepatic microsomes from male and female rats (3.8- and 3.7-fold, respectively). This occurred without comparable increases in other P450 activities. Despite these findings, the age- and sex-related profiles of microsomal retinoic acid 4-hydroxylation were clearly different from those measured for other P450 activities. Thus, on the basis of xenobiotic pretreatment, developmental, and immunochemical studies, the enzyme(s) involved in constitutive retinoic acid 4-hydroxylation appears distinct from a number of well-described P450s in untreated and induced rat liver. The data are consistent with the partial involvement of P450(s) from the 3A subfamily in retinoic acid 4-hydroxylation, but it seems clear that P450s 3A1 and 3A2 do not participate in this activity.
细胞色素P450介导的4-羟基化是类视黄醇生物活性终止的重要途径。在重组酶系统中，几种纯化的哺乳动物肝脏P450已被证明可催化全反式维甲酸（视黄酸）的4-羟基化，但未处理的大鼠肝脏微粒体中该活性的性质尚未明确。在本研究中，对未处理的雌雄大鼠肝脏以及一系列诱导处理后的肝脏微粒体视黄酸4-羟基化进行了表征。因此，地塞米松和苯巴比妥可增加雄性和雌性大鼠的该活性，而β-萘黄酮或二甲基亚砜则无此作用。针对P450 3A1产生的免疫球蛋白G（IgG）组分可降低未处理的大鼠肝脏微粒体中视黄酸4-羟基化的速率，但针对P450 2C11、2B1和2C6的IgG则无抑制作用。体内给予已证明可与P450 3A形成代谢物中间体复合物的三乙酰夹竹桃霉素，随后在体外进行铁氰化钾氧化，可使视黄酸4-羟基化和雄甾-4-烯-3,17-二酮6β-羟基化同样重新激活（分别为无铁氰化钾时各自活性的154%和152%）。最后，外源性视黄酸（60 mg/kg腹腔注射，连续三天）可显著提高雄性和雌性大鼠肝脏微粒体中视黄酸4-羟基化的速率（分别为3.8倍和3.7倍）。此过程中其他P450活性无类似增加。尽管有这些发现，但微粒体视黄酸4-羟基化的年龄和性别相关谱与其他P450活性的测量结果明显不同。因此，基于异生素预处理、发育和免疫化学研究，参与组成型视黄酸4-羟基化的酶似乎与未处理和诱导的大鼠肝脏中一些已充分描述的P450不同。数据表明3A亚家族的P450部分参与视黄酸4-羟基化，但很明显P450 3A1和3A2不参与此活性。
