中草药  2016, Vol. 47 Issue (20): 3668-3672
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氢溴酸槟榔碱体内对大鼠肝脏CYP2B表达的影响及其机制研究
黄祥涛, 肖润梅, 吴银祥, 陈勇     
湖北大学 中药生物技术省重点实验室, 湖北大学生物资源绿色转化协同创新中心, 湖北 武汉 430062
摘要: 目的 研究氢溴酸槟榔碱对大鼠肝脏细胞色素P450 2B(CYP2B)表达的影响及其调控机制。 方法 Wistar雄性大鼠连续ig氢溴酸槟榔碱(4、20、100 mg/kg)7 d,LC-MS/MS法检测肝脏CYP2B活性,Western blotting法检测肝脏CYP2B1/2、组成型雄甾烷受体(CAR)及核内CAR蛋白表达量,定量荧光PCR检测肝脏CYP2B1 mRNA表达量。 结果 氢溴酸槟榔碱对大鼠肝脏CYP2B蛋白的表达没有明显影响,但对肝脏CYP2B1 mRNA表达的诱导作用随剂量增加而增强,对CYP2B活性的诱导作用随剂量增加而减弱。此外,给药后肝细胞核内CAR蛋白量增加,但肝细胞总CAR蛋白的量无明显变化。 结论 氢溴酸槟榔碱体内通过促进CAR向核内转移,诱导了大鼠肝脏CYP2B活性,且对CYP2B的调控主要发生在转录水平,也可能存在翻译后修饰。
关键词: 氢溴酸槟榔碱     肝脏     CYP2B     CAR蛋白     药物代谢酶    
In vivo effect of arecoline hydrobromide on rat hepatic CYP2B expression and its mechanism
HUANG Xiang-tao, XIAO Run-mei, WU Yin-xiang, CHEN Yong     
Hubei Province Key Laboratory of Biotechnology of Chinese Traditional Medicine, Hubei Collaborative Innovation Center for Green Transformation of Bio-resources, Hubei University, Wuhan 430062, China
Abstract: Objective To study the effect of arecoline hydrobromide (AH) on rat hepatic CYP2B expression/activity, as well as the underlying regulation mechanism in vivo. Methods After oral administration of AH (4, 20, and 100 mg/kg/d) to rats for 7 consecutive days, the hepatic CYP2B activity was detected by LC-MS/MS method, the protein levels of hepatic CYP2B, total CAR, and endonuclear CAR were detected by Western blotting, and the hepatic CYP2B1 mRNA level was detected by real-time PCR. Results AH treatment had no effect on rat hepatic CYP2B protein level, but the hepatic CYP2B1 mRNA level was dose-dependently increased. Additionally, although the hepatic CYP2B activity was induced by AH treatment, the induction was weakened with the dose increase of AH. Furthermore, the protein content of hepatic endonuclear CAR was increased while the total CAR protein remained unchanged following AH treatment. Conclusion AH induces rat hepatic CYP2B by promoting nuclear translocation of CAR. The regulation of AH on rat hepatic CYP2B largely involve transcriptional activation of the gene, partially involve the post-translational modification of CYP2B protein. Our results also suggest that the risk of metabolic interaction could be existed when the substrate drugs of CYP2B are administered in betel-quid used human.
Key words: arecoline hydrobromide     liver     CYP2B     CAR protein     drug metabolism enzyme    

槟榔是棕榈科(Palmae)植物槟榔Areca catechu Linn. 的干燥成熟种子,位居我国四大南药(槟榔、益智、砂仁、巴戟)之首,是54种棕榈科植物中唯一含生物碱的植物。槟榔嚼块是仅次于烟草、酒精和咖啡因的世界第4种被广泛使用的嗜好品。嚼食槟榔与口腔癌、肥胖、糖尿病、高血压、高脂血症、肝硬化和肝细胞癌等相关[1-2],这与槟榔所含的主要生物碱成分可诱导DNA分子单链断裂,姊妹染色单体交换频率与基因突变密切相关[3-4]。槟榔碱是槟榔所含的主要生物碱,占干质量的0.1%~0.5%[5]

近年来国内外众多学者对槟榔碱药理、毒理等方面进行了深入研究,发现槟榔碱对口腔黏膜[6]、神经系统[7]、内分泌系统[8-10]、生殖细胞[11]等均存在一定毒副作用。此外,槟榔碱还能导致广泛的肝脏代谢影响,诱导肝脏代谢酶活性升高[12-14]

CYP2B6是人体一个重要的药物代谢酶,参与了许多药物、毒物及内源性神经递质的代谢清除。大鼠与人CYP2B6基因高度同源的是CYP2B1/2[15]。研究表明,大鼠、小鼠肝脏中CYP2B活性的升高,与肝纤维化及肝肿瘤形成有密切关系[16-17]。前期研究表明,氢溴酸槟榔碱在大鼠体内代谢产生了4个I相代谢物和2个II相代谢物[18],且氢溴酸槟榔碱短期给药诱导了大鼠肝脏CYP2B1/2活性[14]。但氢溴酸槟榔碱体内对大鼠肝脏CYP2B1/2的调控机制目前尚不清楚。本实验研究氢溴酸槟榔碱ig给药对大鼠肝脏CYP2B1/2表达的影响及其机制,为阐明槟榔碱的毒性及药物相互作用提供参考。

1 材料 1.1 实验动物

SPF级6周龄Wistar雄性大鼠,体质量200~250 g,购自湖北省实验动物研究中心,许可证号SCXK(鄂)2015-0018。

1.2 药品与试剂

氢溴酸槟榔碱(Sigma,美国);安非他酮、羟基安非他酮(Cayman Chemical,美国);TRIzol试剂(Invitrogen,美国);PVDF膜(millipore,美国);蛋白酶抑制剂cocktail(Roche,瑞典);RIPA裂解液、超敏ECL化学发光试剂盒(碧云天生物技术公司,南京);BCA蛋白测定试剂盒(Thermo Scientific,美国);小鼠抗β-actin单克隆抗体、兔抗组成型雄甾烷受体(CAR)单克隆抗体(Santa Cruz,美国);小鼠抗CYP2B1/2单克隆抗体(Abcam,美国);兔抗Lamin B抗体(武汉博士德生物工程有限公司);山羊抗小鼠/兔辣根过氧化物酶标记二抗(KPL,美国);定量PCR引物(Sunny,上海);逆转录试剂盒及SYBR qPCR Mix(Toyobo,日本);NE-PER核蛋白提取试剂盒(Thermo Fisher,美国)。

1.3 主要仪器

8040型高效液相色谱质谱联用仪(岛津,日本);组织匀浆器(IKA,德国),核酸蛋白测定仪(eppendorf,德国);CFX ConnectTM实时荧光定量PCR仪(Bio-Rad,美国);DYY-6C型电泳仪、DYC-40A型垂直电泳槽及DYC-40A型电转仪(北京六一生物科技有限公司)。

2 方法 2.1 实验动物分组与给药

雄性Wistar大鼠随机分为氢溴酸槟榔碱(溶解于生理盐水中)低、中、高剂量[4、20、100 mg/(kg·d)]组和对照组(等体积生理盐水),每组6只。饲养温度保持在20~25 ℃,相对湿度在40%~70%,自由取食、进水,昼夜交替时间为12 h/12 h。给药前大鼠禁食12 h,每天于同一时间ig给药(给药体积小于2.0 mL),连续给药7 d。末次给药后1 h颈椎脱臼处死大鼠,取肝脏组织,用预冷生理盐水冲洗后擦干,液氮中保存备用。

2.2 荧光定量PCR检测肝脏组织CYP2B1 mRNA的表达

每只大鼠取肝组织约100 mg,按TRIzol试剂盒说明书分别提取总RNA,用0.7%的琼脂糖凝胶电泳检测总RNA的完整性,用分光光度法检测260 nm和280 nm处吸光度比值检测总RNA的纯度。取2 μg RNA按逆转录试剂盒说明书逆转录成cDNA,cNDA再经实时荧光定量PCR扩增检测CYP2B1 mRNA的表达量。定量PCR引物序列如下,大鼠GAPDH:正向5’-AGGGCTGCCTTCTCTTGTGAC-3’,反向5’-TGGGTAGAATCATACTGGA- ACATGTAG-3’;大鼠CYP2B1:正向5’-AAGCACAGGGCCACCTTA- GAC-3’,反向5’-AAGCACAGGGCCACCTTAG- AC-3’。定量PCR实验条件为94 ℃变性15 s,58.4 ℃退火30 s,72 ℃延伸30 s,38个循环,反应体系为20 μL。基因表达水平采用2−ΔΔCt法计算[19]

2.3 Western blotting检测肝脏组织CYP2B和细胞内总CAR蛋白的表达

取适量(约100 mg)肝组织加入800 μL裂解液中冰浴匀浆,离心取上清,用BCA试剂盒检测蛋白量。取60 μg蛋白样品经SDS-PAGE(10%分离胶与5%浓缩胶)后转移到PVDF膜上,经5%脱脂奶粉封闭1.5 h后与一抗(小鼠抗β-actin单克隆抗体,小鼠抗CYP2B1/2单克隆抗体,兔抗CAR单克隆抗体,用一抗稀释液按1∶1 000稀释)4 ℃孵育过夜。用TBST洗涤后加二抗(用脱脂牛奶按1∶5 000稀释)37 ℃温孵1 h,再用TBST洗涤,加超敏 ECL化学发光液,经显影、定影后,根据扫描条带的大小与强度分析各蛋白的表达情况。

2.4 Western blotting检测细胞核内CAR蛋白的表达

取20 mg大鼠肝组织,用PBS洗涤后,500×g离心5 min,弃上清,按照核蛋白提取试剂盒说明书进行如下操作:加入预冷的CER I 200 μL,匀浆,剧烈涡旋15 s,于冰上静置10 min,然后加入预冷的CER II 11 μL,涡旋5 s,冰上静置1 min,再涡旋5 s,16 000×g离心5 min,弃上清,沉淀用预冷的NER 100 μL溶解。剧烈涡旋15 s,冰上静置10 min,再涡旋15 s,静置10 min,如此40 min(4次)。16 000×g离心10 min取上清,即为核蛋白溶液。用BCA试剂盒检测蛋白的量,取60 μg蛋白样品经SDS-PAGE(10%分离胶与5%浓缩胶)后转移到PVDF膜上,用5%脱脂奶粉封闭1.5 h后与一抗(兔抗Lamin B抗体,用一抗稀释液按1∶400稀释;兔抗CAR多克隆抗体,用一抗稀释液按1∶1 000稀释)4 ℃ 孵育过夜。用TBST洗涤后加二抗(用脱脂牛奶按1∶5 000稀释)37 ℃温孵1 h,再用TBST洗涤,加超敏ECL化学发光液,经显影、定影后,根据扫描条带的大小与强度分析核内CAR的表达情况。

2.5 LC-MS/MS法检测CYP2B 1/2活性

采用CaCl2沉淀低速离心法分别制备每只大鼠的肝微粒体(RLM),并用BCA法测定RLM中蛋白量。以安非他酮的羟基化作用表示RLM中CYP2B1/2活性(即每毫克微粒体蛋白每分钟催化探针底物产生的代谢物量)[18]

2.6 统计学分析

采用ANOVA统计学软件,数据以x±s表示,组间差异采用t检验。

3 结果 3.1 对大鼠肝脏CYP2B表达与活性的影响

连续给大鼠ig 4、20、100 mg/kg氢溴酸槟榔碱7 d后,定量荧光PCR检测大鼠肝脏CYP2B1 mRNA的表达量,结果见图 1,Western blotting检测大鼠肝脏CYP2B1/2的蛋白表达量结果见图 2。结果表明,与对照组相比,给药后肝脏CYP2B1 mRNA的表达量有剂量依赖性上调趋势(P<0.05);对大鼠肝脏CYP2B1/2的表达量无明显影响(P>0.05);对大鼠肝脏CYP2B1/2活性的诱导作用随剂量增大而减弱,对照组及氢溴酸槟榔碱低、中、高剂量组CYP2B的相对活性分别为(100.0±25.7)%、(169.5±23.8)%(P<0.01)、(151.4±11.2)%(P<0.01)、(121.6±12.3)%(P>0.05)。

与对照组比较:P<0.05 P < 0.05 vs control group 图 1 氢溴酸槟榔碱对大鼠肝脏CYP2B1 mRNA表达的影响(x±s,n = 6) Fig.1 Effect of AH on CYP2B1 mRNA expression in liver tissue of rats (x±s,n = 6)

图 2 氢溴酸槟榔碱对大鼠肝脏CYP2B蛋白表达的影响(x±s,n = 6) Fig.2 Effect of AH on CYP2B protein expression in liver tissue of rats (x±s,n = 6)

3.2 对大鼠肝脏总CAR及核内CAR蛋白表达水平的影响

大鼠肝脏细胞内总CAR与核内CAR的蛋白表达量结果见图 3。结果表明,氢溴酸槟榔碱给药后,胞内总CAR蛋白表达量较对照组几乎无变化;核内CAR的蛋白表达量呈明显的上调趋势(P<0.05)。

图 3 氢溴酸槟榔碱对肝细胞总CAR (A) 及肝细胞核内CAR(B) 蛋白表达的影响(x±s,n = 6) Fig.3 Effect of AH on protein expression of hepatic total CAR (A) and hepatic cell intranucleus CAR (B) (x±s,n = 6)

4 讨论

CYP2B6是重要的外源性毒物代谢酶之一,参与代谢杀虫剂(如甲氧滴滴涕)、前致癌物(如黄曲霉毒素B1、烟草中的亚硝胺类物质),以及抗肿瘤药物(如环磷酰胺、异环磷酰胺)的活化[20],其活性可以被许多外源性物质诱导[21-26]。外源物对大鼠肝脏CYP2B1/2和小鼠肝脏CYP2B9/10的转录激活是通过CAR的核移位实现的[27-28],CAR受体由胞浆向核内转移被认为是诱导CYP2B转录的起始步骤[29],CAR在核内与维甲酸X受体RXR形成异二聚体CAR-RXR,然后异二聚体结合到CYP2B基因上游的苯巴比妥反应增强原件PBREM上,启动CYP2B基因的转录[30]。本研究表明,给大鼠连续ig氢溴酸槟榔碱(4、20、100 mg/kg)7 d后,肝脏中CYP2B1 mRNA表达水平与CYP2B1/2活性上调,肝细胞核内CAR蛋白量增加,且肝脏总CAR蛋白量不变,结果表明,氢溴酸槟榔碱对大鼠肝脏CYP2B的诱导作用类似于苯巴比妥及其类似物,也是通过CAR的核移位实现的。

本研究还发现,氢溴酸槟榔碱对大鼠肝脏CYP2B mRNA表达及酶活的诱导作用存在相反的剂量关系,即CYP2B1 mRNA的表达量随氢溴酸槟榔碱的给药剂量增加而增加,而酶活性虽被诱导,但却随给药剂量增加而减弱。另外,氢溴酸槟榔碱给药对肝脏CYP2B1/2蛋白表达量无明显影响,提示槟榔碱对肝脏CYP2B1/2的调控可能存在翻译后修饰和/或RNA转运和/或mRNA降解,具体是何种原因导致的,将在接下来的实验中做进一步探究。对于CYP2B酶活上调而蛋白的量无变化,可能是槟榔碱增加了底物与CYP2B的亲和力。

本研究表明,低剂量(4 mg/kg)氢溴酸槟榔碱是大鼠肝脏CYP2B活性的诱导剂,提示槟榔咀嚼嗜好者在接受CYP2B底物治疗时,存在一定的代谢相互作用风险。

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