药物毒理学：第二章 药物的毒代动力学

1、第二章 药物的毒代动力学23毒代动力学（Toxicokinetics ）What is Toxicokinetics? how a substance gets into the body and what happens to it in the body 4The term of toxicokinetics was originated from pharmacokineticsThe science of toxicology has evolved to include environmental and occupational chemicals as well as drugs

2、 Toxicokinetics is thus the appropriate term for the study of the kinetics of all toxic substances 5毒代动力学运用药物代谢动力学的原理和方法，定量地研究在毒性剂量下药物在动物体内的吸收、分布、代谢、排泄的过程和特点，进而探讨药物毒性的发生和发展规律的一门科学。67Four processes are involved in toxicokinetics8910How toxicokinetics of a substance can influence its toxicity?Why a su

3、bstance of low toxicity may be more of a hazard than a highly-toxic substance?Why two substances with equal toxicity and absorption may differ in hazard?11一、吸收（absorption ） The most important factors that affect the absorption:route of exposure; eg. DDTconcentration of the substance at the site of c

4、ontactchemical and physical properties of the substance1 毒物的吸收、分布、生物转化与排泄 12the primary routes of exposure 13other routes of exposure 14Cd15毒物分子的跨膜转运Cell membrane structure16（一）经胃肠道吸收 (Gastrointestinal Tract )1718影响消化道对毒物吸收速度的因素：1.毒物的理化性质2.胃肠道存留食物的多少3.毒物在胃肠道各部位的停留时间4.胃肠道的吸收面积和吸收能力5.胃肠道局部的pH6.胃肠道的分泌能

5、力7.肠道的微生物菌丛（约有60种细菌对毒物有转化作用）19胃肠道血液（二）经呼吸系统吸收 （Respiratory Tract ） 鼻咽支气管肺泡毒物20气体、挥发性溶剂或颗粒可经由肺部吸收，如吸人给药(吸入麻醉)、喷雾给药 (喷雾剂)，因此药物可通过肺泡壁吸收产生毒性作用。呼吸道表面积30100M2，毛细血管网的总长度约2000km21（三）经皮肤吸收 （Dermal Route）成人的体表面积约1.8平方米毒物通过皮肤吸收的途径1.单纯扩散 （大部分亲脂性毒物）2.毛发区的毛囊吸收3.汗腺管吸收4.经破损皮肤部位吸收影响毒物通过皮肤吸收的因素1.毒物的性质和浓度2.皮肤的酸碱度、水分含量

6、、面积和 厚度。3.皮肤的解剖和生理特性（与年龄、 种族和种属有关）22some notable toxicants can gain entry into the body following skin contamination：organophosphate pesticides neurological warfare agent, Sarin industrial solvents carbon tetrachloride Hexane 23毒物从血液向组织、细胞间液或细胞内液转运的过程称为分布。 二、分布（distribution）Distribution is the proce

7、ss whereby an absorbed chemical moves away from the site of absorption to other areas of the body. 24 How do chemicals move through the body? Does distribution vary with the route of exposure? Is a chemical distributed evenly to all organs or tissues? How fast is a chemical distributed? Why do some

8、chemicals stay in the body for a long time whereas others are eliminated quickly?Questions:25Once a chemical is in the blood stream it may be: ExcretedStoredbiotransformed into different chemicals (metabolites)its metabolites may be excreted or storedthe chemical or its metabolites may interact or b

9、ind with cellular components26（一）分布容积 distribution volume体内毒物总量和血浆药物浓度之比，Vd非体内生理空间，因此也叫表观分布容积 (Apparent volume of distribution) A：体内药物总量 C：平衡时血药浓度药物（毒物）在人体内的分布情况区域 总量的% 70kg人的体液（L） 给1g化合物后血浆浓度（mg/L）血浆 4.5 3 333总细胞外液 20 14 71总体液 55 38 26组织结合 - - 025281. 药物与血浆蛋白结合（Protein binding）可逆影响转运、无药理活性 不同药物与血浆蛋

10、白结合率不同药物之间有竞争性（二）药物（毒物在组织中的储存）29unbound90mg10mg boundunbound90mg + 5mg10mg -5mg bound95mg bound5mg unbound95mg 5mg bound5mg + 5mg unboundsignificantnegligible30与血浆蛋白结合率比较高的药物 95% boundThyroxine 甲状腺素Warfarin 华法林Diazepam 地西泮Frusemide 呋塞米Heparin 肝素Imipramine 丙咪嗪 90% but 95% boundGlibenclamide 格列本脲Pheny

11、toin 苯妥英Propranolol 普萘洛尔Sodium Valproate 丙戊酸钠312. 药物在肝脏和肾脏的储存肝脏细胞内的蛋白谷胱甘肽S-转移酶药物、毒物有机酸肝脏、肾脏中的金属硫蛋白金属离子323. 药物在脂肪组织中的储存高脂溶性的有机化合物，如硫喷妥。4. 药物在骨骼组织的储存含有氟、铅等金属的化合物, 药物中有四环素、氟喹诺酮strontium (Sr) or lead (Pb) may be substituted for calcium (Ca), and fluoride (F-) may be substituted for hydroxyl (OH-) ions33

12、SummaryThe primary sites for toxicant storage are adipose tissue, bone, liver and kidneys. Lipid-soluble toxicants are often stored in adipose tissues. 34（三） 体内生物膜屏障（membrane barriers)血脑屏障 Blood Brain Barrier胎盘屏障 Placental barriers 外来活性物质进入体内后，机体通过肝脏或其他部分的酶化合物进行结构修饰，以减弱其药理或毒理活性，并增加其水溶性以便加速从体内排泄，该过程称

13、为生物转化三、生物转化 BiotransformationBiotransformation is the process whereby a substance is changed from one chemical to another (transformed) by a chemical reaction within the body. BiotransformationDetoxificationeg. lipophilic toxicants; bilirubin bioactivation eg. vinyl chloride 371. 药物代谢的部位 肝脏：主要代谢器官 肝

14、外部位：肠、肾、脑等392.药物在体内转化的两个步骤： I相反应 II相反应药物 代谢物 结合物 （氧化、水解、还原等） （结合）药物经生物转化后，其结局如下： 灭活、毒性降低极性增加 产生毒性代谢物40RELATIVE HEPATIC CONTENT OF CYP ENZYMES% DRUGS METABOLIZED BY CYP ENZYMESROLE OF CYP ENZYMES IN HEPATIC DRUG METABOLISM41Fe3+-O DP-450HOH P-450P-450P-450P-450P-450Fe2+-O2- HFe2+-O2 DDDDFe2+ Fe3+ Fe3

15、+ DHHHHO2 e e 2H+ H2O(1)(2)(3)(4) D（结合）（活化）（加氧）（药物氧化）42Additional Effects on Drug Metabolism Species Differences Major differences in different species have been recognized for many years (R.T. Williams). Phenylbutazone (保泰松）half-life is 3 h in rabbit, 6 h in rat, guinea pig, and dog and 3 days in h

16、umans. Induction Two major categories of CYP inducers Phenobarbital is prototype of one group - enhances metabolism of wide variety of substrates by causing proliferation of SER and CYP in liver cells.Polycylic aromatic hydrocarbons are second type of inducer (ex: benzoapyrene). Induction appears to

17、 be environmental adaptive response of organismOrphan Nuclear Receptors (PXR, CAR) are regulators of drug metabolizing gene expression43PXR and CAR Protect Against XenobioticsxenobioticsPXRRXRCARcytoplasmnucleusxenoprotectiontarget genesco-activatorPBP44Wilkinson G. N Engl J Med 2005;352:2211-2221Me

18、chanism of Induction of CYP3A4-Mediated Metabolism of Drug Substrates (Panel A) and the Resulting Reduced Plasma Drug Concentration (Panel B)45CYP3A Inducers Activate Human, Rabbit, and Rat PXRrifampicinPCNdexamethasoneRU486clotrimazoleReporter activity (fold)troglitazone135791113151719tamoxifenCell

19、-basedreporter assay46Pregnane X Receptor (PXR)human PXRLigandDNAmouse PXR77%96%rat PXR76%96%82%94%rabbit PXRPXR is one of Nuclear Receptor (NR) family of ligand-activated transcription factors.Named on basis of activation by natural and synthetic C21 steroids (pregnanes), including pregnenolone 16a

20、-carbonitrile (PCN)Cloned due to homology with other nuclear receptorsHighly active in liver and intestineBinds as heterodimer with retinoic acid receptor (RXR)47Constitutive Androstane Receptor (CAR)Highly expressed in liver and intestineSequestered in cytoplasm Co-factor complex required for activ

21、ation; anchored by PPAR-binding protein (PBP) Binds response elements as RXR heterodimerHigh basal transcriptional activity without ligandActivated by xenobioticsphenobarbital, TCPOBOP (1,4-bis2-(3,5-dichloropyridyloxy)benzene)CARPXRS.A. Kliewer48PXR and CAR Regulate Overlapping GenesPCN (PXR) Phase

22、 I enzymesCyp3a11Cyp2b10Aldh1a1Aldh1a7 Phase II enzymesUgt1a1Gst-a1 TransportersMrp2Mrp3Oatp2(3.5x)(12x)(2.1x)(1.6x)(2.8x)(16x)(3.0 x)(9.2x)TCPOBOP (CAR)(3.4x)(110 x)(1.9x)(1.9x)(15x)(2.0 x)(1.9x)Liver RNAS.A. Kliewer49Acetaminophen (Paracetamol)Acetanilide（乙酰苯胺） 1886 accidentally discovered antipyr

23、etic; excessively toxic (methemoglobinemia); para-aminophenol and derivatives were tested. Phenacetin （乙氧基乙酰苯胺）introduced in 1887, and extensively used in analgesic mixtures until implicated in analgesic abuse nephropathyAcetaminophen （对乙酰氨基酚）recognized as metabolite in 18991948-49 Brodie and Axelro

24、d recognized methemoglobinemia due to acetanilide and analgesia to acetaminophen1955 acetaminophen introduced in US50Acetaminophen and p-AminophenolsAcetanilide, 1886(accidental discovery ofantipyretic activity; high toxicity)Phenacetin or acetophenetidin, 1887 (nephrotoxic, methemoglobinemia)Acetam

25、inophen, 1893Metabolic pathway quantified;(Brodie &Axelrod, 1948)popular in US since 195570-90%75-80%51Acetaminophen overdose results in more calls to poison control centers in the United States than overdose with any other pharmacologic substance. The American Liver Foundation reports that 35% of c

26、ases of severe liver failure are caused by acetaminophen poisoning which may require organ transplantation. N-acetyl cysteine（乙酰基半胱氨酸）is an effective antidote, especially if administered within 10 h of ingestion NEJM 319:1557-1562, 1988Management of acetaminophen overdose Trends Pharm Sci 24:154-157

27、, 2003Acetaminophen Toxicity52Acetominophen Metabolism60%35%CYP2E1*CYP1A2CYP3A11NAPQIN-acetyl-p-benzoquinone imine*induced by ethanol, isoniazidProtein adducts,Oxidative stressToxicity53Acetaminophen Protein AdductsCYPsHS-ProteinH2N-ProteinS.D. Nelson, Drug Metab. Rev. 27: 147-177 (1995)K.D. Welch e

28、t al., Chem Res Toxicol 18:924-33 (2005)54Acetaminophen toxicity mechanismN-acetyl cysteine is an effective agent to block GSH depletion and rescue from liver damaging toxicity CAR and PXR modulate acetaminophen toxicity (2002, 2004)CAR-null mice are resistant to acetaminophen toxicityhepatic GSH lo

29、wered in wild type (but not in KO) after acetaminophenCAR-humanized mice demonstrate same toxicity responseActivation of PXR induces CYP3A11 and markedly enhances acetaminophen toxicity in wild type miceCAR transcription co-activator KO blocks toxicity (2005)55NAPQI toxicity linked to PXR activation

30、G. Guo et al. 2004, Toxicol Sci 82(2):374-80oxidative stressmechanism ?CAR PXR CYP2E1*CYP3A11toxicityXenobioticstoxicity5657N-acetylation may form nitrenium ion which is a potent carcinogenic agent 58常见的肝药酶诱导剂Phenytoin 苯妥英Phenobarbitone 苯巴比妥Carbamazepine 卡马西平Rifampicin 利福平Griseofulvin 灰黄霉素Chronic al

31、cohol intake 长期饮酒Smoking 吸烟59Chloramphenicol 氯霉素Sodium valproate 丙戊酸盐Sulphonamides 磺胺类药Phenylbutazone 保泰松Isoniazid 异烟肼Amiodarone 胺碘酮Omeprazole 奥美拉唑常见的肝药酶抑制剂 四、排泄 excretion药物和毒物以原形或代谢产物形式通过排泄或分泌器官排出体外的过程排泄途径尿液粪便肺脏汗腺乳汁61 1.经尿液排泄 绝大部分药物经肾脏排出体外只有非与血浆蛋白结合的药物（分子量小于6000的化合物）可被肾小球滤过肾小管分泌：主动分泌 如丙磺舒，同类药物之间有竞争

32、性肾小管的重吸收：脂溶性药物在排泄过程中可被肾小管再吸收（与药物本身的pKa、血和尿的pH有关）62 尿液pH值对药物排泄的影响：弱酸性药物在碱性尿液中解离多，重吸收少，排泄快，而在酸性尿液中解离少，重吸收多，排泄慢。弱碱性药物则相反。（巴比妥类中毒时用碳酸氢钠解救） 意义：改变尿液pH值可以改变药物的排泄速度，用于药物中毒的解毒或增强疗效。2. 经其它途径排泄胃肠道及胆汁排泄肝肠循环63肠肝循环（enterohepatic circulation)LiverDrug指自胆汁排进十二指肠的结合型药物在肠中经水解后被再吸收的过程。64经肺排泄挥发性高的有机溶剂如乙醇等经唾液、汗腺排泄铅、砷等重金

33、属和某些生物碱等经乳汁、头发排泄许多金属、毒品、有机氯农药等可从乳汁排泄而影响婴儿。某些重金属可排泄到头发中。65药物的体内过程与毒性效应1、药物固有的作用特征2、药物到达靶器官的量和滞留时间3、机体对药物的处置能力4、机体靶器官对药物的异感性662 毒代动力学 Toxicokinetics 在药物毒理学研究中根据产生毒性作用的剂量，定性和定量地研究实验动物体内药物的吸收、分布、代谢和排泄随时间的动态变化规律。 毒代动力学研究所用的剂量远远高于药效剂量和临床拟用剂量，并且为多次重复用药。67外 推68药代动力学 VS 毒代动力学69研究目的1、有助于毒理学研究的设计；2、通过对暴露、时间依赖性

34、的靶器官剂量与毒性作用关系研究，解释毒性作用机制；3、明确重复给药的动力学特征；4、探索毒性反应的种属间差异关系；5、分析动物毒性表现对临床安全性评价的价值，为药物的后续评价提供信息。70药物毒代动力学模型动力学模型经典毒代动力学模型Classical Toxicokinetics生理毒代动力学模型Physiological Toxicokinetics研究模型71房室概念和房室模型： 动力学的房室(compartment)概念是抽象的数学概念，其划分取决于毒物在体内的转运及/或转化速率。一房室模型 (one compartment model) 二房室模型 (two compartment

35、model) 中央室 (central compartment) 周边室 (peripheral compartment)（一）经典动力学模型 Classical Toxicokinetics72一房室模型（First-order compartment model）药物吸收消除73二房室模型药物中 央 室 周边室吸收消除74一房室模型：体内药物瞬时在各部位达到平衡，即给药后血液中浓度和全身各组织器官部位浓度迅即达到平衡。 二房室模型：药物在某些部位的药物浓度和血液中的浓度迅速达平衡，而在另一些部位中的转运有一速率过程，但彼此近似，前者被归并为中央室，后者则归并成为外周室。 三房室模型：转运到

36、外周室的速率过程有较明显快慢之分。 75毒代动力学常用参数：AUC：生物利用度Cmax：峰浓度Tmax：达峰时间Vd：表观分布容积t1/2：半衰期7676 一级消除动力学 (First order elimination kinetics ) n = 1 dC/dt = - kC零级消除动力学 (Zero order elimination kinetics) n = 0 dC/dt = - kdC/dt = - kCn消除速率常数 (Rate constant for elimination) 速率常数：77零级 一级 零级 对数浓度 一级浓度 78一级消除动力学特点：消除速率与血药浓度有关

37、，属恒比消除有固定半衰期如浓度用对数表示则时量曲线为直线79 零级消除动力学特点：消除速率与血药浓度无关，属定量消除无固定半衰期血药浓度用对数表示时量曲线呈直线80(二)生理毒代动力学模型（了解内容） 生理毒代动力学房室模型与经典毒代动力学房室模型的基本差别:在于描述药物(毒物)转运进出房室的速率常数不同，可用以表示组织中药物的浓度。 经典毒代动力学由数据定义速率常数，因此这些模型通常基于数据进行论述；而生理毒代动力学则能体现已知的或假设的生理过程，因此这些模型通常基于生理学进行论述。8182药物毒代动力学的研究内容(1)描述引起试验动物全身中毒的量效关系和时效关系；(2)了解药物毒性研究中出现中毒症状与结果之间的关系，为预