CARD6通过调控ASK1表达抑制炎症反应和细胞凋亡保护心肌缺血再灌注损伤

目的:探讨胱天蛋白酶募集域蛋白6(CARD6)对心肌缺血再灌注损伤(MIRI)中炎症反应和细胞凋亡的影响,并分析其相关分子机制。方法:将60只SD大鼠随机分为假手术组(Sham组)、模型组(MIRI组)、MIRI+空载慢病毒(LV-NC)组、MIRI+CARD6过表达慢病毒组(MIRI+LV-CARD6组),每组15只。除Sham组外,其他各组大鼠采用手术结扎冠状动脉左前降支的方法构建MIRI模型。采用全自动生化分析仪检测心肌损伤指标含量,酶联免疫吸附法(ELISA)检测炎性细胞因子水平,苏木精-伊红(HE)染色观察大鼠心肌组织形态学变化,原位末端标记测定(TUNEL)染色法检测大鼠心肌细胞凋亡情况,蛋白免疫印迹法(Western Blot)检测大鼠心肌组织中凋亡相关蛋白表达,实时定量聚合酶链式反应(RT-qPCR)法和Western Blot法检测大鼠心肌组织中CARD6、细胞凋亡信号调节激酶1(ASK1)mRNA和蛋白表达。结果:与Sham组比较,MIRI组大鼠心肌细胞水肿变性,大量间质炎性细胞浸润,存在明显心肌组织病理损伤;大鼠血清中乳酸脱氢酶(LDH)、肌酸激酶(CK)、肌酸激...     

曲美他嗪后处理与缺血后处理对大鼠再灌注心肌保护作用的对比

目的 对比观察曲美他嗪(TMZ)后处理与缺血后处理(IPOC)对大鼠心肌缺血再灌注损伤(MIRI)的保护作用.方法40只Wistar 大鼠随机分为4组(n=10):假手术组、模型组、曲美他嗪组(TMZ组)、缺血后处理组(IPOC组).结扎左冠状动脉前降支,建立大鼠心肌缺血/再灌注损伤模型,记录各组心肌梗死面积,光镜HE染色观察心肌组织细胞形态,透射电镜观察心肌细胞微观结构,测定血清肌酸激酶(CK)、乳酸脱氢酶(LDH)、谷草转氨酶(AST)活性变化.结果 TMZ组、IPOC组与模型组比较:①心肌梗死面积减少(P＜0.05);②心肌细胞损伤程度相当,较模型组有明显改善;③心肌细胞超微结构损伤程度相当,较模型组有明显改善;④心肌酶CK、LDH、AST活性较模型组均有明显降低(P＜0.05).结论 TMZ后处理与IPOD对MIRI心肌均有明显的保护作用,二者作用差异不明显.     

抑制鞘氨醇激酶-2活性加重血管紧张素II诱导的心肌细胞肥大

目的 本实验旨在明确鞘氨醇激酶（sphingosine kinase,SphK）2在血管紧张素（angiotensin,Ang）II诱导的心肌细胞肥大中的作用。方法 分离并体外培养SD乳鼠心肌细胞。给予AngII（10 μmol/L）处理24h诱导心肌细胞肥大。AngII刺激时分别给予溶媒或SphK2特异性抑制剂ABC294640（1 μmol/L）共处理。采用蛋白免疫印迹法检测心肌细胞SphK2蛋白表达。采用酶联免疫吸附试验（enzyme-linked immunosorbant assay,ELISA）检测心肌细胞细胞核1-磷酸鞘氨醇（sphingosine 1-phosphate,S1P）水平。采用结晶紫染色观察AngII诱导的心肌细胞肥大程度。采用实时定量聚合酶链式反应（real time-polymerase chain reaction,RT-PCR）检测心肌细胞肥大标志基因心房钠尿肽（atrial natriuretic peptide,ANP）、脑钠尿肽（brain natriuretic peptide,BNP）和β-肌球蛋白重链（β-myosin heavy chain,β-MHC）mRNA表达水平。结果 与对照组比较,AngII处理上调心肌细胞SphK2蛋白表达和S1P浓度（均P<0.05）,并增加心肌细胞横截面积与ANP、BNP和β-MHC mRNA表达水平（均P<0.05）。与溶媒组比较,ABC294640处理显著降低了心肌细胞核S1P浓度,并进一步增加了AngII处理后的心肌细胞横截面积和肥大标志基因mRNA表达水平（均P<0.05）。结论 抑制SphK2活性加重AngII诱导的心肌细胞肥大。SphK2有可能成为治疗病理性心肌肥大的新靶点。     

龙血竭总黄酮对心肌缺血再灌注损伤大鼠心肌细胞的保护作用研究

目的探讨龙血竭总黄酮对心肌缺血再灌注损伤大鼠心肌细胞的保护作用。方法将40只SD大鼠随机分为5组,空白对照组(Control组)、假手术组(Sham组)、心肌缺血再灌注损伤组(MIRI组)、假手术+SDF组(SDF组)、MIRI+SDF组(MIRISDF组),每组8只。采用结扎左冠状动脉前降支30 min再灌注2 h的方法建立大鼠MIRI模型,于术前1周开始灌药。采用比色法测定血清肌酸激酶(CK)、肌酸激酶同工酶(CK-MB)和乳酸脱氢酶(LDH)水平,采用TTC染色评估心肌坏死面积,用TUNEL法检测心肌细胞凋亡率。结果与Control、Sham和SDF组比较,MIRI组、MIRISDF组的CK、LDH、CK-MB的水平均明显升高(P0.05)。与MIRI组比较,MIRISDF组的CK、LDH、CK-MB的水平明显下降(P0.05)。MIRISDF组心肌梗死面积和心肌细胞的凋亡率明显小于MIRI组(P0.05)。结论龙血竭总黄酮对MIRI大鼠心肌细胞具有较好的保护作用。     

抑制1-磷酸鞘氨醇裂解酶活性加重缺血性心力衰竭

目的:观察1-磷酸鞘氨醇(S1P)裂解酶(SPL)在小鼠缺血性心衰(HF)模型中的作用。方法:将60只成年雄性C57/BL6J小鼠随机分为以下4组:假手术(Sham)组、心肌梗死(MI)组、假手术+THI(Sham+THI)组[THI是SPL的抑制剂]及MI+THI组,每组15只(n=15),将25 mg/L THI溶于饮水中,于手术24 h后连续饲喂2周。MI4周后,采用ELISA试剂盒测定心肌中S1P的含量。根据心脏质量/体质量(HW/BW)评价心肌肥厚。用小动物心脏超声评估小鼠心脏结构和功能,经Masson三色染剂染色法观察心脏纤维化。用Western blot检测转化生长因子-β(TGF-β)蛋白的表达。实时PCR检测Ⅰ、Ⅲ型胶原、心房钠尿肽(ANP)、脑钠尿肽(BNP)和平滑肌肌动蛋白-α(α-SMA)mRNA的水平。结果:与MI组相比,MI+THI组小鼠心肌组织中S1P的含量增加(P0.01);左心室射血分数(LVEF)降低(P0.01),左心室收缩末期内径(LVESD)和舒张末期内径(LVEDD)均增加(均P0.05),HW/BW增加(P0.01),心脏纤维化加重;TGF-β蛋白的表达增加(P0.01);Ⅰ、Ⅲ型胶原、ANP、BNP和α-SMA mRNA的水平均显著增加(均P0.01)。与Sham组相比,Sham+THI组小鼠上述指标无显著差异。结论:抑制SPL的活性可能增加梗死后心肌病理性S1P信号的激活,加重MI后的心脏重构和HF。     

作者单位：030001山西省太原市 山西医科大学基础医学院生理学系,细胞生理学山西省重点实验室通讯作者：贺忠梅,E-mail：hezmei@126.com

目的 探讨低氧诱导因子-1α(HIF-1α)稳定表达对大鼠心肌缺血再灌注细胞凋亡的影响及可能机制。方法 采用结扎冠脉左前降支45min,再灌注3h的方法,构建大鼠心肌缺血再灌注损伤模型;实验分为假手术组(Sham)、心肌缺血/再灌注组(MI/R)、HIF-1α活化剂DMOG 心肌缺血/再灌注组(D MI/R)、HIF-1α抑制剂YC-1 心肌缺血/再灌注组(YC-1 MI/R);采用全自动生化分析仪测定血清心肌酶(CK-MB,LDH)活性;Western blot检测心脏组织HIF-1α蛋白表达;Evens blue/TTC染色测定心肌梗死面积;TUNEL染色及Caspase-3,8,9活性测定心肌细胞凋亡。结果 (1)与MI/R 组相比,D MI/R 组的HIF-1α蛋白表达量明显增加,心肌酶CK-MB、LDH的活性降低,心肌梗死面积明显减小,并且心肌组织的病理损伤减轻;(2)稳定HIF-1α表达可明显降低心肌细胞凋亡率,且部分逆转了缺血再灌注后心肌组织Caspase-9与Caspase-3的活性升高。结论 HIF-1α稳定表达可抑制线粒体途径介导的心肌细胞凋亡,从而发挥对缺血再灌注损伤的心脏保护效应。     

生黄合剂对大鼠心肌缺血再灌注损伤的保护作用

目的观察生黄合剂对大鼠心肌缺血再灌注损伤(MIRI)的保护作用。方法将48只SD大鼠随机分为6组,即空白对照组、模型组、阳性药物组及生黄合剂低、中、高剂量组,每组8只,分别给药7 d后,建立MIRI模型。检测大鼠血清乳酸脱氢酶(LDH)及心肌丙二醛(MDA)和超氧化物歧化酶(SOD)的含量,用TUNEL法检测心肌细胞凋亡情况,并观察心肌组织形态学改变。结果与模型组比较,生黄合剂能降低大鼠LDH及MDA的含量,增加SOD活性,降低心肌细胞凋亡指数,改善心肌组织病理损害。结论生黄合剂对大鼠MIRI具有保护作用,其机制可能为通过抗自由基作用来抑制MIRI诱导的细胞凋亡。     

模拟失重大鼠胸主动脉和腹主动脉S1P/S1PRs通路改变

目的 研究四周模拟失重对大鼠胸主动脉(TA)和腹主动脉（AA）1-磷酸鞘氨醇（S1P）及其受体（S1PRs）蛋白表达和分布的影响。 方法 SD大鼠28只，随机分为对照（CON）组和悬吊（HU）组，每组14只（n=14）。采用尾部悬吊建立大鼠模拟失重模型，时间为4周。苏木精-伊红（HE）染色观察动脉的结构变化，Western blot和免疫组织化学染色检测神经鞘氨醇激酶（SphK）1和（SphK）2、S1P裂解酶（SGPL）1、1-3型S1PRs（S1PR1、S1PR2、S1PR3）、增殖细胞核抗原（PCNA）和I型胶原蛋白（COL1）的蛋白表达和分布变化。 结果 悬吊4周后，与CON组相比，HU组TA的SphK1表达无明显改变，而SphK2和SGPL1表达降低（P<0.05），S1PRs表达和分布均无明显改变；同时，与CON组相比，HU组大鼠TA内-中膜厚度（IMT）和横截面积(CSA)增加，PCNA表达显著增加（P<0.05），但COL1表达无明显变化。与TA不同，与CON组比较，四周尾部悬吊后AA的SphK1、SphK2与SGPL1表达显著增加（P<0.05），S1PR1和S1PR3表达显著降低（P<0.05），IMT、CSA和PCNA表达无显著变化，但COL1表达显著减少（P<0.05）。此外，CON组AA的SphK1、SphK2、SGPL1、S1PR3、PCNA和COL1的蛋白表达均显著低于TA（P<0.05），S1PR1蛋白表达则高于TA（P<0.05），IMT与CSA均小于TA（P<0.05）。 结论 模拟失重大鼠TA与AA的S1P合成和降解过程发生部位特异性改变，可能与其平滑肌细胞增殖程度有关；S1P及其受体含量在TA和AA间存在部位差异。      

当归多糖改善大鼠心肌缺血再灌注损伤的体内外观察及其机制探讨

目的 建立大鼠心肌缺血再灌注损伤（MIRI）的体内、体外模型，观察当归多糖（ASP）对大鼠MIRI的改善作用并探讨其机制。方法 在体内研究，成年SD大鼠随机分为假手术组、MIRI组、ASP低剂量组、ASP高剂量组，除假手术组外，均采用冠状动脉左前降支结扎再灌注的方法建立MIRI模型，ASP低、高剂量组在建模后分别给予50、100 mg/kg的ASP灌胃，假手术组及MIRI组给予等量生理盐水灌胃，持续4周；采用ELISA法检测各组血清心肌损伤标志物肌酸激酶同工酶（CK-MB）、乳酸脱氢酶（LDH）及炎症因子肿瘤坏死因子α(TNF-α)、白细胞介素6(IL-6)、IL-1β;Western blotting法检测各组心肌组织凋亡蛋白B淋巴细胞瘤2(Bcl-2)、Bcl-2关联X蛋白（Bax）、裂解的半胱胺酸蛋白酶（cleaved Caspase-3）及toll样受体4(TLR4)/核因子κB(NF-κB)通路相关蛋白TLR4、磷酸化核蛋白（p-p65）、磷酸化NF-κB抑制蛋白α(p-IκBα)表达。在体外研究，将大鼠心肌细胞分为对照组、H/R组、H/R+ASP低剂量组、H/R+ASP高剂...     

水溶性壳聚糖对缺血再灌注损伤大鼠心肌的作用

目的探讨水溶性壳聚糖(WSC)对心肌缺血再灌注损伤(IRI)大鼠心肌的作用机制。方法将60只SD大鼠随机分为假手术组、IRI模型组、低剂量WSC组、中剂量WSC组、高剂量WSC组,每组12只。其中,IRI模型组和各剂量WSC组大鼠用结扎左冠脉前室间支法建立大鼠IRI模型,假手术组大鼠仅分离而不结扎左冠脉前室间支。假手术组和IRI模型组给予生理盐水10 ml/kg、低、中、高剂量WSC组分别给予120、180 mg/kg和240 mg/kg,灌胃1次/d,15 d后处死大鼠,心脏取血,分离血清,用酶联免疫吸附(ELSIA)法检测血清中起氧化物歧化酶(SOD)、丙二醛(MDA)、白细胞介素(IL)-6和肿瘤坏死因子(TNF)-α水平,用酶动力法检测肌酸激酶(CK)和低密度脂蛋白(LDH)水平。在靠近心尖部1/3处平行于房室沟横行切取心肌组织块,固定后石蜡包埋。用苏木素-伊红(HE)染色法观察心肌组织形态变化。结果光镜下观察,假手术组心肌纤维排列整齐,结构清楚,细胞核染色清晰,心肌间质未见炎性细胞浸润;IRI模型组大鼠心肌纤维紊乱,界限不清,胞质淡染,核有浓缩或溶解,大量炎性细胞浸润,充血淤血,心肌纤维横纹消失,心肌组织灶性坏死;WSC干预组肌纤维偶有断裂、融解现象,少量心肌细胞颗粒变性、水肿,偶见炎性细胞浸润。与假手术组相比,IRI模型组SOD水平明显下降,而CK、LDH、MDA、IL-6和TNF-α水平明显升高(P0.01);与IRI模型组比较,低剂量WSC组、中剂量WSC组和高剂量WSC组可显著提高SOD水平,降低CK、LDH、MDA、IL-6和TNF-α水平(P0.05,P0.01)。结论 WSC逆转心肌IRI,对IRI大鼠心肌具有保护作用。这种作用可能与对抗IRI时氧化应激和炎症反应有关。     

1-Naphthyl isocyanate and 1-naphthylamine as metabolites of 1-naphthylisothiocyanate

Abstract: The importance of the bioactivation of 1-naphthylisothiocyanate was studied. Forty minutes after 1-naphthylisothiocyanate administration to rats, bile was collected over a 2.5-h period; the liver was then excised and homogenized. 1-naphthylisothiocyanate and its metabolites in bile and liver of rats were identified and quantified using coupled gas chromatography-mass spectrometry. Three main compounds were found in all 1-naphthylisothiocyanate-treated animals. They were identified as 1-naphthyl isocyanate, 1-naphthylamine and the parent compound, 1-naphthylisothiocyanate. When rats were given cycloheximide, which attenuates 1-naphthylisothiocyanate toxicity, 30 min before 1-naphthylisothiocyanate (300 mg/kg), 1-naphthyl isocyanate concentration was significantly lower than in rats receiving only 1-naphthylisothiocyanate. The appearance of 1-naphthylamine was also inhibited by cycloheximide, although not to the same extent as 1-naphthyl isocyanate. On the other hand, phenobarbital, which potentiates 1-naphthylisothiocyanate hepatotoxicity, enhanced 1-naphthyl isocyanate and 1-naphthylamine formation. It is suggested that 1-naphthyl isocyanate, 1-naphthylamine and the highly reactive sulfur released from 1-naphthylisothiocyanate might be involved in the hepatotoxic effect of 1-naphthylisothiocyanate.     

Cytochrome 1A1 and 1B1 gene diversity in the Zanzibar islands

Amodiaquine (AQ) is a 4‐aminoquinoline widely used in the treatment of malaria as part of the artemisinin combination therapy (ACT). AQ is metabolised towards its main metabolite desethylamodiaquine mainly by cytochrome P450 2C8 (CYP2C8). CYP1A1 and CYP1B1 play a minor role in the metabolism but they seem to be significantly involved in the formation of the short‐lived quinine‐imine. To complete the genetic variation picture of the main genes involved in AQ metabolism in the Zanzibar population, previously characterised for CYP2C8, we analysed in this study CYP1A1 and CYP1B1 main genetic polymorphisms. The results obtained show a low frequency of the CYP1A1*2B/C allele (2.4%) and a high frequency of CYP1B1*6 (approximately 42%) followed by CYP1B1*2 (approximately 27%) in Zanzibar islands. Genotype data for CYP1A1 and CYP1B1 show a low incidence of fast metabolisers, revealing a relatively safe genetic background in Zanzibar’s population regarding the appearance of adverse effects.     

Genetic link with cholelithiasis among pediatric SCA Tunisian patients: Examples of UGT1A1, SLCO1A2 and SLCO1B1

Aims and background: Hyperbilirubinemia is often observed in chronic hemolysis and results in the formation of pigment cholelithiasis that could be increased by the presence of defected enzymes involved in the bilirubin metabolism. Indeed, this is the first report that interested in the study of polymorphisms in genes encoded for enzymes involved in the bilirubin metabolism: rs 4149056 of SLCO1B1 and rs4149000 of SLCO1A2 in combination with rs8175347 and rs887829 of UGT1A1 in order to find a correlation between the polymorphisms studied and the presence of gallstones in a population of sickle cell anemia (SCA) pediatric Tunisians.

Material and methods: Our study involved 102 unrelated Tunisian subjects. All SCA patients are children (less than 16 years old) and were characterized by hyperbilirubinemia and 52 of them have cholelithiasis. The polymorphisms of the candidate genes were analyzed for all subjects by PCR/sequencing. Genotype and allele frequencies between cases and controls were compared using Pearson's chi-square test with a significance threshold of P?<?0.05 (compare 2, version 1.02).

Results: The novelty of this report is that children carrying the combined genotype of the rs studied: (TA7TA7)/TT/TC/GA have a higher risk to develop gallstones (P?=?0.0027, RR?=?18.27 (20.0061–915.28)).

Conclusion: Altogether our data provide the implication of UGT1A1 and SLCO1A2 in sickle cell anemia-related cholelithiasis.     

Pandemic H1N1 influenza

The 2009 H1N1 influenza A virus that has targeted not only those with chronic medical illness, the very young and old, but also a large segment of the patient population that has previously been afforded relative protection - those who are young, generally healthy, and immune naive. The illness is mild in most, but results in hospitalization and severe ARDS in an important minority. Among those who become critically ill, 20-40% will die, predominantly of severe hypoxic respiratory failure. However, and potentially in part due to the young age of those affected, intensive care with aggressive oxygenation support will allow most people to recover. The volume of patients infected and with critical illness placed substantial strain on the capacity of the health care system and critical care most specifically. Despite this, the 2009 pandemic has engaged our specialty and highlighted its importance like no other. Thus far, the national and global critical care response has been brisk, collaborative and helpful - not only for this pandemic, but for subsequent challenges in years ahead.     

PD-1/PD-L1抑制途径与自身免疫性糖尿病

PD-1(CD279)是一种负性协同刺激分子,属于CD28超家族成员,呈诱导性表达于活化的T、B和自然杀伤细胞表面.PD-L1(B7-H1,CD274)和PD-L2(B7-DC,CD273)是PD-1的两个配体.PD-1和PD-L1相互作用可以使活化的自身反应性T细胞获得负性信号,抑制其对自身抗原持续的免疫应答.若PD...     

甲型H1N1与季节性H1N1流感病毒血凝素基因比较分析

目的分析泰安市2008～2009年度季节性流感与2009年度甲型H1N1流感病原学检测结果 ,比较季节性H1N1与甲型H1N1血凝素基因变异情况。方法选择国家级流感监测哨点医院以及暴发疫情的疫点,采集流感样病例的鼻咽拭子标本,通过RealtimePCR进行病毒检测,用MDCK细胞进行病毒分离,通过RT-PCR扩增血凝素HA1片段的基因并测序,利用生物信息学进行序列分析。结果 2008～2009年共检测鼻咽拭子标本283份,分离出流感病毒33株,分离阳性率为11.67%,其中季节性H1N1亚型31株。2009年5月1日～12月31日,检测鼻咽拭子标本996份,流感核酸检测阳性417份,阳性率为41.86%,其中甲型H1N1337份,季节性H1N1亚型1份。6株季节性H1N1病毒均在多个氨基酸位点上发生变异,与疫苗株A/Brisbane/59/2007(H1N1)比较,有11个位点发生了突变,其中5个位点位于抗原决定簇上;测序成功的6株甲型H1N1病毒在多个氨基酸位点发生变异,与疫苗株A/California/07/2009(H1N1)比较,有6个位点发生突变,其中1个位点位于抗原决定簇的B区。结论 2008～2009年度季节性H1N1为优势株,甲流暴发后,甲型H1N1成为绝对优势毒株。季节性H1N1分离株有多处氨基酸替换,抗原决定簇B区变异频繁;甲型H1N1病毒分离株的基因有变异,但关键位点第222位仍为D(天冬氨酸),与疫苗株相比抗原决定簇的关键位点变化不大。     

Role of CYP2D6, CYP1A1, CYP2E1, GSTT1, and GSTM1 genes in the susceptibility to acute leukemias

Acute leukemias (ALs) are heterogeneous diseases. Functional polymorphisms in the genes encoding detoxification enzymes cause inter-individual differences, which contribute to leukemia susceptibility. The CYP2D6, CYP1A1, CYP2E1, GSTT1, and GSTM1 polymorphisms in ALL (n = 156) and AML (n = 94) patients and 140 healthy controls were genotyped by PCR and/or PCR-RFLP using blood or bone marrow samples. No association was observed between the GSTT1 gene deletion and patients (OR = 0.8, 95% CI = 0.4-1.7 for AMLs and OR = 0.9, 95% CI = 0.5-1.6 for ALLs). Patients with ALL and AML had a higher prevalence of the GSTM1 deletions compared to controls but only the difference among adult AML patients (OR = 2.1, 95% CI = 1.0-4.2) was statistically significant. The CYP2D6*3 variant allele frequency was lower in the overall acute leukemia patients (0.6%) compared to controls (P = 0.03). CYP2D6*1/*3 genotype frequency also showed a protective association in AML patients (OR = 0.09, 95% CI = 0.01-1.7; P = 0.04). We also found a risk association for CYP2E1*5 in ALL and AML (OR = 3.6, 95% CI = 1.4-9.4 and OR = 3.9, 95% CI = 1.4-10.5, respectively). No association was found for the studied CYP2D6*4, CYP1A1*2A, and GSTT1"null" variants and the risk of acute leuke-mia (ALL or AML). This case-control study suggests a contribution of CYP2E1, CYP2D6, and GSTM1 "null" variants to the development of acute leukemias.     

Inhibition of procarcinogen-bioactivating human CYP1A1, CYP1A2 and CYP1B1 enzymes by melatonin

Abstract:  Administration of melatonin to rodents decreases the incidence of tumorigenesis initiated by benzo[ a ]pyrene or 7,12-dimethylbenz[ a ]anthracene, which requires bioactivation by cytochrome P450 enzymes, such as CYP1A1, CYP1A2 and CYP1B1, to produce carcinogenic metabolites. The present study tested the hypothesis that melatonin is a modulator of human CYP1 catalytic activity and gene expression. As a comparison, we also investigated the effect of melatonin on the catalytic activity of CYP2A6, which is also a procarcinogen-bioactivating enzyme. Melatonin (3–300 μ m ) decreased 7-ethoxyresorufin O -dealkylation catalyzed by human hepatic microsomes and recombinant CYP1A1, CYP1A2 and CYP1B1, whereas it did not affect coumarin 7-hydroxylation catalyzed by hepatic microsomes or recombinant CYP2A6. Melatonin inhibited CYP1 enzymes by mixed inhibition, with apparent K _i values (mean ± S.E.M.) of 59 ± 1 (CYP1A1), 12 ± 1 (CYP1A2), 14 ± 2 (CYP1B1) and 46 ± 8 μ m (hepatic microsomes). Additional experiments indicated that melatonin decreased benzo[ a ]pyrene hydroxylation catalyzed by hepatic microsomes and CYP1A2 but not by CYP1A1 or CYP1B1. Treatment of MCF-10A human mammary epithelial cells with melatonin (up to 300 μ m ) did not affect basal or benzo[ a ]pyrene-inducible CYP1A1 or CYP1B1 gene expression. Consistent with this finding, melatonin did not influence reporter activity in aryl hydrocarbon receptor-dependent pGudluc6.1-transfected MCF-10A cells treated with or without benzo[ a ]pyrene, as assessed in an in vitro cell-based luciferase reporter gene assay. Overall, melatonin is an in vitro inhibitor of human CYP1 catalytic activity, and it may be useful to develop potent analogues of melatonin as potential cancer chemopreventive agents that block CYP1-mediated chemical carcinogenesis.