METABOLISM OF GLYCYRRHETIC ACID BY RAT-LIVER MICROSOMES .2. 22 ALPHA-HYDROXYLATION AND 24-HYDROXYLATION
METABOLISM OF GLYCYRRHETIC ACID BY RAT-LIVER MICROSOMES .2. 22 ALPHA-HYDROXYLATION AND 24-HYDROXYLATION
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DOI：
10.1016/0006-2952(90)90690-m
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发表时间：
1990-07-15
影响因子：
5.8
通讯作者：
KOBASHI, K
中科院分区：
文献类型：
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作者：
AKAO, T;AOYAMA, M;KOBASHI, K
18.beta. -将甘草次酸（GA，甘草苷的糖苷配基）转化为3-氧代-18 β-在NADP+的存在下，大鼠肝匀浆中的甘草次酸（3-oxoGA），但在NADPH的存在下，GA转化为其他两种代谢产物，薄层色谱（TLC）显示较低的Rf值比GA和3-oxoGA的大鼠肝线粒体后上清液。在NADPH存在下的GA代谢活性定位在微粒体中，类似于GA氧化活性定位到3-oxoGA。GA代谢活性需要NADPH作为辅因子和O2才能完全发挥活性，并被CO抑制，表明GA通过细胞色素P450进行羟化反应。在制备型TLC上纯化两种代谢产物（I和II，分别为TLC上的较低和较高Rf值）。II和乙酰化I的甲酯的质谱（MS）分析表明形成了单羟基化代谢产物。基于3H-和13C-NMR归属，I和II被鉴定为22 α-和24-羟基-18 β甘草次酸。3-OxoGA和3-epi-28 β甘草次酸。3-氧代-GA和3-表-18 β-甘草次酸（3-epiGA）似乎也在C-22和C-24处羟基化。显示较低Rf值的3-oxoGA代谢物也被鉴定为22 α-羟基-3-氧代-18 β-通过MS以及3 H-NMR和13 C-NMR光谱分析确定甘草次酸。在22.alpha羟基化反应的最佳底物是3-oxoGA，其次是GA和3-epiGA。另一方面，对于24-羟基化，最佳底物依次为GA、3-oxoGA和3-epiGA。然而，18. alpha. -大黄酸（18 α- GA）对于22 α-β-葡糖苷酶和葡糖苷酶都是差的底物。和24-羟基化。
18.beta.-Glycyrrhetic acid (GA, an aglycone of glycyrrhizin) is converted to 3-oxo-18.beta.-glycyrrhetic acid (3-oxoGA) in the presence of NADP+ by rat liver homogenates, but GA was converted in the presence of NADPH to two other metabolites showing lower Rf values on thin-layer chromatography (TLC) than those of GA and 3-oxoGA by postmitochondrial supernatant of rat liver. The GA-metabolizing activity in the presence of NADPH was localized in microsomes, similar to localization of GA-oxidizing activity to 3-oxoGA. The GA-metabolizing activity required NADPH as a cofactor and O2 for full activity and was inhibited with CO, suggesting the hydroxylation reaction of GA by cytochrome P450. Two metabolites (I and II, lower and higher Rf values on TLC, respectively) were purified on preparative TLC. Mass spectral (MS) analyses of II and methyl ester of acetylated I indicated the formation of monohydroxylated metabolites. On the basis of 3H- and 13C-NMR assignments and I and II were identified to be 22.alpha.- and 24-hydroxy-18.beta.-glycyrrhetic acids, respectively. 3-OxoGA and 3-epi-28.beta.-glycyrrhetic acids, respectively. 3-oxo-GA and 3-epi-18.beta.-glycyrrhetic acid (3-epiGA) seem to be also hydroxylated at C-22 and C-24. A metabolite of 3-oxoGA showing a lower Rf value was also identified as 22.alpha.-hydroxy-3-oxo-18.beta.-glycyrrhetic acid by MS and 3H-and 13C-NMR spectral analyses. In 22.alpha.-hydroxylation the best substrate ws 3-oxoGA, followed by GA and 3-epiGA. On the other hand, for 24-hydroxylation the best substrate was GA, then 3-oxoGA, and 3-epiGA in order. However, 18.alpha.-glycyrrhetic acid (18.alpha.-GA) was a poor substrate for both 22.alpha.- and 24-hydroxylation.