药物外排泵和转运蛋白对口服药物吸收影响的研究进展

人体肠道的药物外排泵和转运蛋白对口服药物的吸收有较大影响,常见的药物外排泵有P-糖蛋白和多药耐药相关蛋白,会降低相关底物吸收;其它的一些转运蛋白如有机离子转运蛋白家族、H+/单羧酸共转运蛋白和肽转运蛋白可促进相关底物的吸收.作者对药物外排泵和转运蛋白近年来的相关研究进行了综述,并指出了药物外排泵和转运蛋白今后可能的研究方向.     

寡肽转运载体PepT1的转运机制及其介导的药物吸收

寡肽转运载体PepT1广泛分布于人和动物体内的多种器官和组织,其底物主要为蛋白水解后的二肽和三肽.本文综合文献,阐述PepT1的体内分布及其质子依赖型的转运机制,从空间结构的角度分析其对底物分子的选择性,介绍评价底物与PepT1二者间亲和活性的体内外模型及PepT1底物修饰策略在促进药物吸收方面的应用.     

肝脏、小肠、脑和肾脏中的转运子在药物消除和组织选择性分布中的作用

转运子在药物的体内处置过程中发挥着重要作用。多种转运子，如有机阴离子转运多聚肽、有机阴离子转运子及多药耐药相关蛋白以其广泛的底物特弄性和转运子基因产物的多样性参与到机体的解毒系统中。由于转运子的组织选择性表达和底物特异性，转运子将在小分子药物向靶组织的传输中发挥重要作用。此外，多药耐药相关蛋白通过把它们的底物转运到组织外，从而在小肠、血脑屏障和血脑脊液屏障中发挥屏障作用。本文叙述了转运子的组织选择性分布及其在药物消除过程中的作用研究进展。     

有机阴离子转运多肽1A2对药物转运的影响

有机阴离子转运多肽1A2（OATP1A2）是人体内重要的膜转运蛋白,在肝、肾、小肠、血脑屏障等组织部位进行表达,介导内、外源物质的跨细胞转运,对药物的吸收、分布和消除起着十分重要的作用。本文将对OATP1A2的组织分布和基本功能、基因多态性及其对药物转运的影响作一综述。     

药物传递靶蛋白寡肽转运蛋白1的研究进展

目的:为相关临床安全用药和新药研发提供依据。方法:根据文献,综述了寡肽转运蛋白1(PEPT1)的组织分布、分子结构与功能、转运机制、底物、与药物相互作用等方面的内容。结果:PEPT1主要在小肠表达,肝和肾中表达较少;其基因编码的蛋白上有多个N-糖基化和蛋白激酶的识别位点,它们可能参与肽转运的调控,且其上的His-57是最关键的组氨酸残基,可能是转运蛋白发挥吸收功能时最关键的结合位点;其对大多数的二肽和三肽有高亲和性,能转运某些特定四肽,但不能转运更长的肽段;其转运机制为主动转运;其底物为二肽、三肽化合物等,但不包括氨基酸和四肽以上的大分子;其主要介导口服给药的肽类及肽类似物相关药物的相互作用。结论:虽然现国内有关PEPT1的研究才刚起步,但由于PEPT1具有底物丰富,能够转运亲脂性的、带电荷的以及不同大小的药物分子的特点,使其将会成为设计前药很好的靶蛋白。     

肽转运载体与药物转运

转运寡肽的载体称为肽转运载体(peptide trans- porter,PEFF),分为2种类型,即PEPT1和PEPT2。PEPT能以二肽和三肽作为生理性底物,与其他营养物的转运载体相比,有更广泛的底物特异性。结构相似的外源性化合物如β内酰胺类抗生素也可被PEPT识别。PEPT既可转运营养物质又可转运药     

药物转运蛋白功能及应用

细胞膜转运蛋白是一些药物的吸收、分布和消除的决定因素，具有重要的药剂学意义。作为异生物质排出细胞的通道，ABC转运蛋白对大多数现在使用的药物的体内行为产生重要影响，包括治疗肿瘤、艾滋病和微生物感染用药。小肽转运蛋白具有广谱的底物特异性．能够转运大量的口服的结构类似于小肽的药物。由于新的小肽和多肽模拟物类药物的迅速增加，小肽转运蛋白因可能成为药物转运系统而倍受关注。在分子水平加深对药物转运蛋白的理解势必促进药物设计与生物药剂学的发展。     

血脑屏障的膜蛋白对药物转运及临床治疗的影响

P-糖蛋白,乳腺癌耐药蛋白,多药耐药相关蛋白,有机阴离子转运多肽,有机阴离子转运体,有机阳离子转运体,单羧酸转运体是血脑屏障上常见的膜蛋白,它们与药物的中枢转运密切相关。本文对上述蛋白的底物、转运特点及对临床治疗的影响做了系统的回顾,为药物的优化使用提供参考。     

药物与肠道肽转运蛋白PEPT1的相互作用及影响因素

H^＋协同转运载体PEPT1主要存在于小肠上皮细胞的刷状缘膜上，肠道PEPT1对于消化道中蛋白质的降解产物二肽、三肽具有转运吸收的功能，另外肽类似药物如β-内酰胺类抗生素、血管紧张素转化酶抑制剂、非肽药物伐昔洛韦等也经此载体转运吸收。肠道PEPT1对于维持机体的内环境稳定以及药物的胃肠道吸收发挥重要作用。随着对PEPT1基因序列、蛋白结构、功能活性等方面研究的逐渐深入，对于调控PEPT1在膜上表达、影响其功能活性以及与底物亲和力的因素及相关的作用机制有了一定的了解，加之PEPT1广泛的底物专属性，使其成为新药开发中重要的药物传递的靶蛋白。了解药物与肠道肽转运蛋白PEPT1的相互作用及其影响因素，对于了解药物一药物相互作用，提高药物口服吸收的生物利用度，研究抗肿瘤药物的靶向治疗以及个体化给药等方面具有十分重要的意义。     

Caco-2细胞对酸枣仁皂苷A的跨膜转运

目的研究酸枣仁皂苷A（Jujuboside A,JuA）在Caco-2细胞的跨膜转运特性。方法采用体外培养的Caco-2细胞单层模型,考察时间、介质pH值、药物浓度、抑制剂对JuA在Caco-2细胞上转运的影响。结果 Caco-2细胞转运JuA呈时间及浓度依赖性;在pH为5.0～8.0范围内,Caco-2细胞对JuA的转运不受pH值的影响;P-糖蛋白（P-glycoprotein,P-gp）抑制剂维拉帕米（Verapamil,Ver）对Caco-2细胞转运JuA无影响;线粒体呼吸链复合体Ⅳ抑制剂叠氮化钠（Sodium azide）对Caco-2细胞转运JuA有抑制作用;JuA的AP-BL侧的Papp与BL-AP侧的Papp的两组均数比较无统计学意义。结论 JuA不是P-gp的底物,其跨膜转运是被动转运与主动转运共同参与的过程。     

Transport of Nicotinate and Structurally Related Compounds by Human SMCT1 (SLC5A8) and Its Relevance to Drug Transport in the Mammalian Intestinal Tract

Purpose To examine the involvement of human SMCT1, a Na⁺-coupled transporter for short-chain fatty acids, in the transport of nicotinate/structural analogs and monocarboxylate drugs, and to analyze its expression in mouse intestinal tract. Materials and Methods We expressed human SMCT1 in X. laevis oocytes and monitored its function by [¹⁴C]nicotinate uptake and substrate-induced inward currents. SMCT1 expression in mouse intestinal tract was examined by immunofluorescence. Results [¹⁴C]Nicotinate uptake was several-fold higher in SMCT1-expressing oocytes than in water-injected oocytes. The uptake was inhibited by short-chain/medium-chain fatty acids and various structural analogs of nicotinate. Exposure of SMCT1-expressing oocytes to nicotinate induced Na⁺-dependent inward currents. Measurements of nicotinate flux and associated charge transfer into oocytes suggest a Na⁺:nicotinate stoichiometry of 2:1. Monocarboxylate drugs benzoate, salicylate, and 5-aminosalicylate are also transported by human SMCT1. The transporter is expressed in the small intestine as well as colon, and the expression is restricted to the lumen-facing apical membrane of intestinal and colonic epithelial cells. Conclusions Human SMCT1 transports not only nicotinate and its structural analogs but also various monocarboxylate drugs. The transporter is expressed on the luminal membrane of the epithelial cells lining the intestinal tract. SMCT1 may participate in the intestinal absorption of monocarboxylate drugs.     

Nicotinate uptake by two kinetically distinct Na⁺-dependent carrier-mediated transport systems in the rat small intestine

Recent studies have identified monocarboxylate transporter 1 (MCT1), sodium-coupled monocarboxylate transporter 1 (SMCT1) and SMCT2 as those that may be involved in the carrier-mediated intestinal absorption of nicotinate, but their roles have not been fully clarified yet. To address the issue, we examined the uptake of nicotinate in the rat small intestine by using everted tissue sacs. The uptake of nicotinate was Na?-dependent and saturable at pH 7.4 in both the jejunum and ileum. The saturable transport consisted of a single component with the Michaelis constant (K(m)) of 1.18 mM in the jejunum, while in the ileum it consisted of the high and the low affinity components with the K(m) values of 8.62 μM and 2.36 mM, respectively, and the latter was prevailing in transport capacity and similar to the jejunal transport component. Nicotinate uptake activity attributable to a H?-dependent transporter like MCT1 was, however, only minimal in the two intestinal sites. These results suggest that a low affinity type of SMCT2-like transporter would be in operation with high capacity throughout the small intestine, playing the role as the major intestinal nicotinate uptake transporter, and a high affinity type of SMCT1-like transporter would be additionally in operation in the ileum.     

Interaction of Ibuprofen and Other Structurally Related NSAIDs with the Sodium-Coupled Monocarboxylate Transporter SMCT1 (SLC5A8)

Purpose Sodium-coupled monocarboxylate transporter 1 (SMCT1) is a Na⁺-coupled transporter for monocarboxylates. Many nonsteroidal anti-inflammatory drugs (NSAIDs) are monocarboxylates. Therefore, we investigated the interaction of these drugs with human SMCT1 (hSMCT1). Methods We expressed hSMCT1 in a mammalian cell line and in Xenopus laevis oocytes and used the uptake of nicotinate and propionate-induced currents to monitor its transport function, respectively. We also used [¹⁴C]-nicotinate and [³H]-ibuprofen for direct measurements of uptake in oocytes. Results In mammalian cells, hSMCT1-mediated nicotinate uptake was inhibited by ibuprofen and other structurally related NSAIDs. The inhibition was Na⁺ dependent. With ibuprofen, the concentration necessary for 50% inhibition was 64 ± 16 μM. In oocytes, the transport function of hSMCT1 was associated with inward currents in the presence of propionate. Under identical conditions, ibuprofen and other structurally related NSAIDs failed to induce inward currents. However, these compounds blocked propionate-induced currents. With ibuprofen, the blockade was dose dependent, Na⁺ dependent, and competitive. However, there was no uptake of [³H]-ibuprofen into oocytes expressing hSMCT1, although the uptake of [¹⁴C]-nicotinate was demonstrable under identical conditions. Conclusions Ibuprofen and other structurally related NSAIDs interact with hSMCT1 as blockers of its transport function rather than as its transportable substrates.     

The SLC16 monocaboxylate transporter family

1.?The monocarboxylate transporter (MCT, SLC16) family comprises 14 members, of which to date only MCT1–4 have been shown to carry monocarboxylates, transporting important metabolic compounds such as lactate, pyruvate and ketone bodies in a proton-coupled manner. The transport of such compounds is fundamental for metabolism, and the tissue locations, properties and regulation of these isoforms is discussed.

2.?Of the other members of the MCT family, MCT8 (a thyroid hormone transporter) and TAT1 (an aromatic amino acid transporter) have been characterized more recently, and their physiological roles are reviewed herein. The endogenous substrates and functions of the remaining members of the MCT family await elucidation.

3.?The MCT proteins have the typical twelve transmembrane-spanning domain (TMD) topology of membrane transporter proteins, and their structure–function relationship is discussed, especially in relation to the future impact of the single nucleotide polymorphism (SNP) databases and, given their ability to transport pharmacologically relevant compounds, the potential impact for pharmacogenomics.     

Fluorescein uptake by a monocarboxylic acid transporter in human intestinal Caco-2 cells.

The fluorescein transport characteristics of the human intestinal epithelial Caco-2 cell line were examined in monolayer cultures. The initial uptake rate was concentration-dependent and saturable; the Michealis constant and the maximum velocity were 0.40 mM and 1.32 nmol/min/mg protein, respectively. A protonophore, carbonyl cyanide m-chlorophenyl-hydrazone, reduced uptake significantly. The replacement of extracellular sodium ions by lithium ions did not alter the initial uptake rate. These facts imply that the transport is driven by a proton gradient. The initial uptake rate was strongly dependent upon extracellular pH, and the uptake was optimal at approximately pH 5.5. Based on the protolytic constants, the main species of fluorescein in the pH range of 5.5 to 6.0 was calculated to be a monoanion, suggesting that fluorescein was taken up by Caco-2 cells as a monocarboxylate. The following findings support this conclusion: the uptake was inhibited significantly by monocarboxylate compounds such as salicylate and pravastatin, but not by di- or tricarboxylic acids or by acidic amino acids. Furthermore, salicylate-preloaded cells showed remarkably enhanced uptake of fluorescein, indicating that monocarboxylates and fluorescein share a common transport carrier. The transporter has a wide spectrum of substrate recognition and seems likely to be different from MCT1.     

Mitochondrial uncoupling proteins as potential targets for pharmacological agents

It is widely acknowledged that the function of the original uncoupling protein, UCP1, is uncoupling of substrate oxidation from ATP synthesis, and that its physiological purpose is thermogenesis. The mechanisms and physiological functions of the novel uncoupling proteins, identified within the past seven years, are as yet poorly understood. These novel uncoupling proteins are part of a large family comprising approximately 35 mitochondrial anion carrier proteins. UCP2 and UCP3 appear to function in reactive oxygen species handling and/or in fatty acid metabolism; uncoupling might occur secondarily. There is little information on UCP4 and UCP5 (BMCP1), and phylogenetic analyses indicate that they are further removed from UCP1 than mitochondrial anion carrier proteins, and have distinct functions.     

Molecular features,regulation, and function of monocarboxylate transporters: implications for drug delivery

The diffusion of monocarboxylates such as lactate and pyruvate across the plasma membrane of mammalian cells is facilitated by a family of integral membrane transport proteins, the monocarboxylate transporters (MCTs). Currently, at least eight unique members of the MCT family have been discovered and orthologs to each have been identified in a variety of species. Four MCTs (MCT1-MCT4) have been functionally characterized. Each isoform possesses unique biochemical properties such as kinetic constants and sensitivity to known MCT inhibitors. Several fold changes in the expression of MCTs may be evoked by altered physiological conditions, yet the molecular mechanisms underlying the regulation of MCTs are poorly understood. Post-translational regulation of MCT1 and MCT4 occurs, in part, by interaction with CD147, an accessory protein that is necessary for trafficking, localization, and functional expression of these transporters. Because of the physiological importance of monocarboxylates to the overall maintenance of metabolic homeostasis, the function of MCTs is significant to several pathologies that occur with disease, such as ischemic stroke and cancer. Finally, the expression of MCT1 in the epithelium of the small intestine and colon and in the blood-brain barrier may provide routes for the intestinal and blood to brain transfer of carboxylated pharmaceutical agents and other exogenous monocarboxylates.     

杏香兔耳风提取物的小肠吸收机制

目的研究杏香兔耳风提取物的小肠吸收机制,并初步考察小肠上皮细胞一元羧酸转运蛋白对提取物吸收的影响。方法采用外翻肠囊模型,以杏香兔耳风提取物中绿原酸和3,5-二咖啡酰基奎宁酸为主要成分考察总酚酸在不同肠段(空肠、回肠)中的膜通透性,同时通过吸收抑制(阿魏酸、苯甲酸、布洛芬)试验,考察了一元羧酸转运蛋白对绿原酸和3,5-二咖啡酰基奎宁酸吸收的影响。结果在空肠和回肠中,绿原酸比3,5-二咖啡酰基奎宁酸的小肠渗透率都要高。三种抑制剂(阿魏酸、苯甲酸、布洛芬)可使绿原酸和3,5-二咖啡酰基奎宁酸在回肠的渗透率降低;对绿原酸和3,5-二咖啡酰基奎宁酸在空肠的渗透率影响较小。结论绿原酸和3,5-二咖啡酰基奎宁酸在小肠的吸收属于一级动力学过程,吸收机制为被动扩散。但是同时还存在以一元羧酸转运蛋白介导的主动转运。     

Mechanism of L-lactic acid transport in L6 skeletal muscle cells

L-lactic acid transport plays an important role in the regulation of L-lactic acid circulation into and out of muscle. To clarify the transport mechanism of L-lactic acid in skeletal muscle, L-lactic acid uptake was investigated using a L6 cell line. mRNAs of monocarboxylate transporter (MCT) 1, 2 and 4 were found to be expressed in L6 cells. The [(14)C] L-lactic acid uptake by L6 cells increased up to pH of 6.0. The [(14)C] L-lactic acid uptake at pH 6.0 was concentration-dependent with a K(m) of 3.7 mM. This process was reduced by alpha-cyano-4-hydroxycinnamate, a typical MCT1, 2 and 4 inhibitor. These results suggest that an MCT participates in the uptake of L-lactic acid by L6 cells. [(14)C] L-lactic acid uptake was markedly inhibited by monocarboxylic acids and monocarboxylate drugs but not by dicarboxylic acids and amino acids. Moreover, benzoic acid, a substrate for MCT1, competitively inhibited this process with K(i) of 1.7 mM. [(14)C] L-lactic acid efflux in L6 cells was inhibited by alpha-cyano-4-hydroxycinnamate but not by benzoic acid. These results suggest that [(14)C] L-lactic acid efflux in L6 cells is mediated by MCT other than MCT1.     

Induction of CYP1A1 and CYP2E1 in rat liver by histamine: binding and kinetic studies

Histamine (HA) may bind to cytochrome P450 (CYP450) in rat liver microsomes. The CYP450-HA complex seems to regulate some cellular processes such as proliferation. In the present work, it is shown that HA increases the activity and protein level of CYP1A1 and CYP2E1, in vivo. CYP1A1 is associated with polycyclic aromatic hydrocarbon-mediated carcinogenesis and CYP2E1 with liver damage by oxidative stress. Studies of enzyme kinetics and binding with rat liver microsomes and supersomes were carried out to determine whether HA is a substrate of CYP1A1 and/or CYP2E1. The lack of NADPH oxidation in the presence of HA showed that it is not a substrate for CYP1A1. Activity measurements using the O-dealkylation of ethoxyresorufin indicated that HA is a mixed-type inhibitor of CYP1A1 in both microsomes and supersomes. On the other hand, HA induced a significant NADPH oxidation catalyzed by CYP2E1 supersomes, strongly suggesting that HA is a substrate for this isoform. Furthermore, HA is consumed in the presence of CYP2E1-induced microsomes and supersomes, as determined by o-phtalaldehyde complexes with HA by HPLC. The present findings may contribute to understand better the physiological function of CYP450 in relation with inflammation and other physiological processes in which HA may have a relevant role.