Showing papers in "Xenobiotica in 2008"
TL;DR: Altered P-gp/MDR1 activity due to induction and/or inhibition can cause drug–drug interactions with altered drug pharmacokinetics and response, and is of great clinical importance in non-cancer-related drug therapy due to its wide-ranging effects on the absorption and excretion of a variety of drugs.
Abstract: 1. P-glycoprotein (P-gp/MDR1), one of the most clinically important transmembrane transporters in humans, is encoded by the ABCB1/MDR1 gene. Recent insights into the structural features of P-gp/MDR...
497 citations
TL;DR: This review summarizes the general features and the substrates of the eleven human OATPs, and reviews what is known about the mechanism of their multispecificity, their predicted structure, their role in drug–food interactions, and their roles in cancer.
Abstract: 1. The organic anion transporting polypeptides (humans OATP; other species Oatp) belong to the SLCO gene superfamily of transporters and are twelve transmembrane domain glycoproteins expressed in various epithelial cells. Some OATPs/Oatps are expressed in a single organ, while others are expressed ubiquitously. 2. The functionally characterized members mediate sodium-independent transport of a variety of structurally independent, mainly amphipathic organic compounds, including bile salts, hormones and their conjugates, toxins, and various drugs. 3. This review summarizes the general features and the substrates of the eleven human OATPs. Furthermore, it reviews what is known about the mechanism of their multispecificity, their predicted structure, their role in drug-food interactions, and their role in cancer. 4. Finally, some open questions are raised that need to be addressed to advance OATP research in the near future.
367 citations
TL;DR: The paper reviews the structural characteristics of the peptide transporters, the structural requirements for substrates, the distribution and regulation in the organism in healthy and pathological situations.
Abstract: 1. The peptide transporters belong to the peptide transporter (PTR) family and serve as integral membrane proteins for the cellular uptake of di- and tripeptides in the organism. By their ability also to transport peptidomimetics and other substrates with therapeutic activities or precursors of pharmacologically active agents, they are of considerable importance in pharmacology. 2. PEPT1 is the low-affinity, high-capacity transporter and is mainly expressed in the small intestine, whereas PEPT2 is the high-affinity, low-capacity transporter and has a broader distribution in the organism. 3. Targeted mouse models have revealed PEPT2 to be the dominant transporter for the reabsorption of di- and tripeptides and its pharmacological substrates in the organism, and for the removal of these substrates from the cerebrospinal fluid. Moreover, the peptide transporters undergo physiological and pharmacological regulation and, of great interest, are present in disease states where PEPT1 exhibits ectopic expression in colonic inflammation. 4. The paper reviews the structural characteristics of the peptide transporters, the structural requirements for substrates, the distribution of the peptide transporters in the organism, and finally their regulation in the organism in healthy and pathological situations.
219 citations
TL;DR: The best-characterized members of the human SLC29 family of integral membrane proteins, hENT1 and hent2, possess similar broad permeant selectivities for purine and pyrimidine nucleosides, but hENT2 also efficiently transports nucleobases, while hENT3 and hENT4 are pH sensitive, and optimally active under acidic conditions.
Abstract: 1. The human (h) SLC29 family of integral membrane proteins is represented by four members, designated equilibrative nucleoside transporters (ENTs) because of the properties of the first-characterized family member, hENT1. They belong to the widely distributed eukaryotic ENT family of equilibrative and concentrative nucleoside/nucleobase transporter proteins. 2. A predicted topology of eleven transmembrane helices has been experimentally confirmed for hENT1. The best-characterized members of the family, hENT1 and hENT2, possess similar broad permeant selectivities for purine and pyrimidine nucleosides, but hENT2 also efficiently transports nucleobases. hENT3 has a similar broad permeant selectivity for nucleosides and nucleobases and appears to function in intracellular membranes, including lysosomes. 3. hENT4 is uniquely selective for adenosine, and also transports a variety of organic cations. hENT3 and hENT4 are pH sensitive, and optimally active under acidic conditions. ENTs, including those in parasitic protozoa, function in nucleoside and nucleobase uptake for salvage pathways of nucleotide synthesis and, in humans, are also responsible for the cellular uptake of nucleoside analogues used in the treatment of cancers and viral diseases. 4. By regulating the concentration of adenosine available to cell surface receptors, mammalian ENTs additionally influence physiological processes ranging from cardiovascular activity to neurotransmission.
179 citations
TL;DR: A regulatory viewpoint on transporters and their potential role in drug–drug interactions is provided and criteria that may warrant conduct of in vivo P-gp-mediated drug interaction studies based on in vitro assessment are explained.
Abstract: 1. Pharmacokinetic drug interactions can lead to serious adverse events and the evaluation of a new molecular entity's (NME) drug-drug interaction potential is an integral part of drug development and regulatory review before its market approval. Clinically relevant interactions mediated by transporters are of increasing interest in clinical development and research in this emerging area and it has been revealed that drug transporters can play an important role in modulating drug absorption, distribution, metabolism and elimination. 2. Acting alone or in concert with drug-metabolizing enzymes transporters can affect the pharmacokinetics and/or pharmacodynamics of a drug. The newly released drug interaction guidance by the US Food and Drug Administration (USFDA) includes new information addressing drug transporter interactions with a primary focus on P-glycoprotein (P-gp, ABCB1). 3. This paper provides a regulatory viewpoint on transporters and their potential role in drug-drug interactions. It first outlines information that might be needed during drug development and ultimately included in new drug application (NDA) submissions to address potential transporter-mediated drug interactions. Next, it explains criteria that may warrant conduct of in vivo P-gp-mediated drug interaction studies based on in vitro assessment. In addition, it includes a review case that describes the evaluation of data suggesting a P-gp-based induction interaction.
173 citations
TL;DR: Bile acid transporters are now understood to play central roles in driving bile flow, as well as adaptation to various pathological conditions, with complex regulation of activity and function in the nucleus, cytoplasm, and membrane.
Abstract: In recent years the discovery of a number of major transporter proteins expressed in the liver and intestine specifically involved in bile acid transport has led to improved understanding of bile acid homeostasis and the enterohepatic circulation. Sodium (Na+)-dependent bile acid uptake from portal blood into the liver is mediated primarily by the Na+ taurocholate co-transporting polypeptide (NTCP), while secretion across the canalicular membrane into the bile is carried out by the bile salt export pump (BSEP). In the ileum, absorption of bile acids from the lumen into epithelial cells is mediated by the apical Na+ bile salt transporter (ASBT), whereas exit into portal blood across the basolateral membrane is mediated by the organic solute transporter α/β (OSTα/β) heterodimer. Regulation of transporter gene expression and function occurs at several different levels: in the nucleus, members of the nuclear receptor superfamily, regulated by bile acids and other ligands are primarily involved in controlling ...
134 citations
TL;DR: This review summarizes current knowledge of the properties and functional roles of the cloned OATs, the relationships between transporter structure and function, and those factors that determine the efficacy of transport, as well as investigating the nature and consequences of transporter regulation at genomic and intracellular sites.
Abstract: 1. The transport of negatively charged drugs, xenobiotics, and metabolites by epithelial tissues, particularly the kidney, plays critical roles in controlling their distribution, concentration, and retention in the body. Thus, organic anion transporters (OATs) impact both their therapeutic efficacy and potential toxicity. 2. This review summarizes current knowledge of the properties and functional roles of the cloned OATs, the relationships between transporter structure and function, and those factors that determine the efficacy of transport. Such factors include plasma protein binding of substrates, genetic polymorphisms among the transporters, and regulation of transporter expression. 3. Clearly, much progress has been made in the decade since the first OAT was cloned. However, unresolved questions remain. Several of these issues--drug-drug interactions, functional characterization of newly cloned OATs, tissue differences in expression and function, and details of the nature and consequences of transporter regulation at genomic and intracellular sites--are discussed in the concluding Perspectives section.
124 citations
TL;DR: These validated Caco-2 assays are robust, reproducible and suitable for routine in vitro evaluation of candidate drugs and have been successfully applied to development projects resulting in the identification of two candidate drugs as substrates and inhibitors of P-gp, whereas a third was neither a substrate nor an inhibitor of this transporter.
Abstract: 1. An understanding of the role that transporters, in particular P-glycoprotein (P-gp), can play in the absorption, distribution, metabolism and excretion (ADME) of candidate drugs, and an assessment of how these processes might impact on toxicity and the potential for drug-drug interactions in the clinic, is required to support drug development and registration. It is therefore necessary to validate preclinical assays for the in vitro evaluation of candidate drugs as substrates or inhibitors of human P-gp. 2. The present study has characterized a Caco-2 cell monolayer model by determining the bi-directional apparent permeabilities and efflux ratios of the known P-gp substrates ([(3)H]-digoxin, [(3)H]-ketoconazole, [(3)H]-verapamil, [(3)H]-quinidine, dipyridamole and loratidine; 1-100 microM) a non-substrate ([(3)H]-propranolol; 10 microM), or by determining the inhibitory potencies (IC(50)) of inhibitors (verapamil, ketoconazole, quinidine, dipyridamole and probenecid; 0.1-100 microM) on the basolateral-to-apical transport of [(3)H]-digoxin (5 microM), in order to validate methodologies for the identification of substrates or inhibitors of P-gp, respectively. 3. The reproducibility of the [(3)H]-digoxin or verapamil data determined from replicate monolayers across different cell passages indicates that the functional expression of P-gp is consistent across the range of passages (25-40) utilized for transport experiments and that the determination of bi-directional apparent permeability, or IC(50) for inhibition of P-gp, respectively, need only be performed on one occasion for a test compound. [(3)H]-digoxin and [(3)H]-propranolol or verapamil and probenecid were considered to be appropriate positive and negative controls of P-gp-mediated transport, or inhibition of P-gp, respectively, to ensure performance of the assays when assessing candidate drugs. Additionally, the low IC(50) values determined for ketoconazole and quinidine indicated that these inhibitors were suitable to use to confirm the role of P-gp in the efflux of a test compound. 4. These validated Caco-2 assays are robust, reproducible and suitable for routine in vitro evaluation of candidate drugs. They have been successfully applied to development projects resulting in the identification of two candidate drugs as substrates and inhibitors of P-gp, whereas a third was neither a substrate nor an inhibitor of this transporter.
118 citations
TL;DR: A substantial amount of research has to be undertaken to clarify further the OCT structure–function relationships specifically to define the role of oligomerization on their activity and regulation, to identify intracellular interaction partners of OCTs, and to characterize their pharmacogenetic aspects.
Abstract: 1. Organic cation transporters (OCTs) translocate endogenous (e.g. dopamine) and exogenous (e.g. drugs) substances of cationic nature and, therefore, play an important role in the detoxification of exogenous compounds. This review aims to furnish essential information on OCTs, with an emphasis on pharmacological aspects. 2. Analysis of the literature on OCTs makes clear that there is a species- and organ-specific distribution of the different isoforms, which can also be differentially regulated. OCTs are responsible for the excretion and/or distribution of many drugs and also for serious tissue-specific side-effects such as cisplatin-induced nephrotoxicity. The presence of single nucleotide polymorphisms in these transporters significantly influences the response of patients to medication, as demonstrated for the antidiabetic drug metformin. 3. A substantial amount of research has to be undertaken to clarify further the OCT structure-function relationships specifically to define the role of oligomerization on their activity and regulation, to identify intracellular interaction partners of OCTs, and to characterize their pharmacogenetic aspects.
117 citations
TL;DR: The historical background and discovery of the ATP-driven xenobiotic export pumps encoded by MRP genes, biological functions of ABC transporters belonging to the MRP class, and regulation of gene expression of MRPs by oxidative stress are addressed.
Abstract: 1. The adenosine triphosphate (ATP) binding cassette (ABC) transporters form one of the largest protein families encoded in the human genome, and more than 48 genes encoding human ABC transporters have been identified and sequenced. It has been reported that mutations of ABC protein genes are causative in several genetic disorders in humans. 2. Many human ABC transporters are involved in membrane transport of drugs, xenobiotics, endogenous substances or ions, thereby exhibiting a wide spectrum of biological functions. According to the new nomenclature of human ABC transporter genes, the 'ABCC' gene sub-family comprises three classes involving multidrug resistance-associated proteins (MRPs), sulfonylurea receptors (SURs), and a cystic fibrosis transmembrane conductance regulator (CFTR). 3. Molecular cloning studies have identified a total of ten members of the human MRP class including ABCC11, ABCC12, and ABCC13 (pseudo-gene) that have recently been characterized. 4. This review addresses the historical background and discovery of the ATP-driven xenobiotic export pumps (GS-X pumps) encoded by MRP genes, biological functions of ABC transporters belonging to the MRP class, and regulation of gene expression of MRPs by oxidative stress.
117 citations
TL;DR: Multidrug and toxic compound extrusion (MATE)-type transporters, which were first identified as a bacterial drug transporter family, are present in almost all prokaryotes and eukaryotes, and are thus one of the mostly conserved transporter families in nature.
Abstract: 1. Multidrug and toxic compound extrusion (MATE)-type transporters, which were first identified as a bacterial drug transporter family, are present in almost all prokaryotes and eukaryotes, and are thus one of the mostly conserved transporter families in nature. 2. Recently, a mammalian MATE transporter was shown to be a long hypothesized electroneutral H(+)/organic cation exporter that is responsible for the excretion of metabolic waste products and xenobiotics at renal brush border membranes and bile canaliculi. Plant MATE-type transporters are involved in the detoxification of metals and secondary metabolites such as phenols through their vesicular storage or extrusion at the plasma membrane. 3. Thus, MATE transporters are involved in one of the basic mechanisms that maintain homeostasis through the excretion of metabolic waste products and xenobiotics in nature.
TL;DR: Examination of two of the major influences on the extent of brain penetration across species, namely plasma protein binding and brain tissue binding, suggest that passive diffusion across the blood–brain barrier is an important process for many drugs in humans and highlights the possibility for improved prediction of brain Penetration across species.
Abstract: The penetration of drugs into the central nervous system is a composite of both the rate of drug uptake across the blood-brain barrier and the extent of distribution into brain tissue compartments. Clinically, positron emission tomography (PET) is the primary technique for deriving information on drug biodistribution as well as target receptor occupancy. In contrast, rodent models have formed the basis for much of the current understanding of brain penetration within pharmaceutical Drug Discovery. Linking these two areas more effectively would greatly improve the translation of candidate compounds into therapeutic agents. This paper examines two of the major influences on the extent of brain penetration across species, namely plasma protein binding and brain tissue binding. An excellent correlation was noted between unbound brain fractions across species (R(2) > 0.9 rat, pig, and human, n = 21), which is indicative of the high degree of conservation of the central nervous system environment. In vitro estimates of human brain-blood or brain-plasma ratios of marketed central nervous system drugs and PET tracers agree well with in vivo values derived from clinical PET and post-mortem studies. These results suggest that passive diffusion across the blood-brain barrier is an important process for many drugs in humans and highlights the possibility for improved prediction of brain penetration across species.
TL;DR: A potential role for progesterone is suggested in regulating labetalol elimination by modulating the expression of UGT1A1, leading to enhanced drug metabolism during pregnancy.
Abstract: The authors recently reported the increased oral clearance of labetalol in pregnant women To elucidate the mechanism of the elevated oral clearance, it was hypothesized that female hormones, at th
TL;DR: The results suggest that atorvastatin is preferentially metabolized by CYP3A4 rather than by CYp3A5, and thus the genetic CYP 3A5 polymorphism might not be an important factor in the inter-individual variation of atorVastatin disposition and pharmacodynamics in human.
Abstract: Atorvastatin is a 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor that is mainly metabolized by cytochrome P450 (CYP) 3A4. A recent study showed that the lipid-lowering effect of statins is affected by the CYP3A5 polymorphism. Therefore, it was investigated whether CYP3A5 contributes to the metabolism of atorvastatin. Two metabolites of atorvastatin, para- and ortho-hydroxyatorvastatin, were produced by human liver microsomes and human recombinant CYP3A enzymes, and the enzyme kinetic pattern exhibited substrate inhibition. The intrinsic clearance (CL(int)) rates of para- and ortho-hydroxyatorvastatin by CYP3A4 were 2.4- and 5.0-fold of the respective CL(int) rates of CYP3A5, indicating that CYP3A4 is the major P450 isoform responsible for atorvastatin metabolism. These results suggest that atorvastatin is preferentially metabolized by CYP3A4 rather than by CYP3A5, and thus the genetic CYP3A5 polymorphism might not be an important factor in the inter-individual variation of atorvastatin disposition and pharmacodynamics in human.
TL;DR: 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.
Abstract: 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.
TL;DR: With a broad complement of drug-metabolizing enzymes, hepatocytes catalysed measurable CLint values for a greater proportion of the reference compounds and were particularly proficient at defining metabolic rates for drugs with predominantly phase 2 metabolic routes.
Abstract: A total of 110 drugs, selected to cover a range of physicochemical and pharmacokinetic properties, were used to explore standard approaches to the prediction of in vivo metabolic clearance using drug-depletion profiles from human liver microsomes (HLMs) and cyropreserved hepatocytes. A total of 41 drugs (37% of the compounds tested) showed measurable depletion rates using HLMs (depletion by 20% or more over the time course). The most reliable correlations in terms of bias (average fold error (AFE) = 2.32) and precision (root mean square error (RMSE) = 3501) were observed by comparing in vivo intrinsic clearance (CL(int)), calculated using the parallel-tube model and incorporating the fraction unbound in blood, with in vitro CL(int) adjusted for microsomal binding. For these reference drugs, 29% of predictions were within two-fold of the observed values and 66% were within five-fold. Compared with HLMs, clearance predictions with cryopreserved hepatocytes (57 drugs) were of similar precision (RMSE = 3608) but showed more bias (AFE = 5.21) with 18% of predictions within two-fold of the observed values and 46% within five-fold. However, with a broad complement of drug-metabolizing enzymes, hepatocytes catalysed measurable CL(int) values for a greater proportion (52%) of the reference compounds and were particularly proficient at defining metabolic rates for drugs with predominantly phase 2 metabolic routes.
TL;DR: This review focuses on several crucial aspects of hCNT biology and pharmacology: protein structure–function, structural determinants for transportability, pharmacogenetics of sLC28A1, A2, and A3 genes, role ofhCNT proteins in nucleoside-based therapeutics, and finally hC NT physiology.
Abstract: The human concentrative nucleoside transporter (hCNT) protein family has three members, hCNT1, 2, and 3, encoded by SLC28A1, A2, and A3 genes, respectively. hCNT1 and hCNT2 translocate pyrimidine- and purine-nucleosides, respectively, by a sodium-dependent mechanism, whereas hCNT3 shows broad substrate selectivity and the unique ability of translocating nucleosides both in a sodium- and a proton-coupled manner. hCNT proteins are also responsible for the uptake of most nucleoside-derived antiviral and anticancer drugs. Thus, hCNTs are key pharmacological targets. This review focuses on several crucial aspects of hCNT biology and pharmacology: protein structure-function, structural determinants for transportability, pharmacogenetics of hCNT-encoding genes, role of hCNT proteins in nucleoside-based therapeutics, and finally hCNT physiology.
TL;DR: The results demonstrate that CYP3A4 and CYP2C19 could be involved in the metabolism of triptolide in human liver, and that CYC3A 4 was the primary isoform responsible for its hydroxylation.
Abstract: Triptolide, the primary active component of a traditional Chinese medicine Tripterygium wilfordii Hook F, has a wide range of pharmacological activities. In the present study, the metabolism of triptolide by cytochrome P450s was investigated in human and rat liver microsomes. Triptolide was converted to four metabolites (M-1, M-2, M-3, and M-4) in rat liver microsomes and three (M-2, M-3, and M-4) in human liver microsomes. All the products were identified as mono-hydroxylated triptolides by liquid chromatography-mass spectrometry (LC-MS). The studies with chemical selective inhibitors, complementary DNA-expressed human cytochrome P450s, correlation analysis, and enzyme kinetics were also conducted. The results demonstrate that CYP3A4 and CYP2C19 could be involved in the metabolism of triptolide in human liver, and that CYP3A4 was the primary isoform responsible for its hydroxylation.
TL;DR: This study demonstrates the utility of using in silico PBPK approaches to make predictions of human pharmacokinetics before dosing for the first time in humans.
Abstract: 1. UK-453,061 is a novel second-generation non-nucleoside reverse transcriptase inhibitor (NNRTI). Following intravenous bolus administration of UK-453,061 in male rat and infusion administration in dog, UK-453,061 had the following mean pharmacokinetic properties: elimination T1/2 of 1.6 and 2.4 h, CLp of 26 and 10 ml min−1 kg−1 and Vss of 1.6 and 2 l kg−1, respectively.2. The half-lives of UK-453,061 disappearance in recombinant human CYPs 2C8, 2C9, 2A6, 2E1, 1A2, 2C19, 2D6 and 3A4 were 71, 100, 56, 101, 61, 34, 60 and 8 min, respectively. The disappearance half-life of UK-453,061 in human liver microsomes in the presence of UDPGA was 90 min.3. Human clearance values were predicted using single-species scaling from in vivo data and from in vitro data using SimCYP. The human distribution of UK-453,061 was estimated using an in silico physiologically based pharmacokinetics (PBPK) methodology and absorption was predicted from measured physicochemical, permeability, and solubility data using GastroPlus and ...
TL;DR: Comparison of the pharmacokinetics of PHA-794428 with a 40 kD PEG results in a ten- to 20-fold increase in area under the curve and a similar increase in half-life when compared with somatropin in human (at equivalent subcutaneous doses).
Abstract: 1. PHA-794428 is a PEGylated version of somatropin (human growth hormone). The pharmacokinetics of PHA-794428 have been studied in humans following single subcutaneous administration (dose range 10-500 microg kg(-1)). In the same study the pharmacokinetics of somatropin were also determined following a 3.6 mg (51 microg kg(-1)) subcutaneous dose. Comparison of the pharmacokinetics of both molecules indicates that PEGylation of somatropin with a 40 kD PEG results in a ten- to 20-fold increase in area under the curve and a similar increase in half-life when compared with somatropin in human (at equivalent subcutaneous doses). 2. Literature data indicate that somotropin is cleared by two mechanisms. The first processes is clearance by glomerular filtration. This is a passive, non-capacity-limited process. A second, capacity-limited, process is mediated by interaction with growth hormone receptors present in a number of tissues including the liver. It is hypothesized that PHA-794428 shares the same clearance mechanisms. However, the addition of the PEG moiety has modulated the clearance by both of these processes. Pharmacokinetic modelling of human serum concentration data obtained for these molecules strongly supports this hypothesis. The renal clearance is reduced due to the increased size of the molecule (Cl/F reduced from 9.6 to 0.1 l h(-1) for somatropin and PHA-794428, respectively). In addition, the reduction in growth hormone receptor affinity has reduced the clearance mediated by interaction with this receptor (somatropin Km = 3.6 microg l(-1) and Vmax = 104 microg h(-1)/PHA-794428 Km = 53 microg l(-1) and Vmax = 84 microg h(-1)).
TL;DR: The objective of this review is to provide up-to-date knowledge on genomics, proteomics and function of these two transporter systems.
Abstract: 1. Whole-body sterol (cholesterol and xenosterol) balance is delicately regulated by the gastrointestinal tract and liver, which control sterol absorption and excretion, respectively, in addition to the contribution to the cholesterol pool by whole-body cholesterol synthesis. In the past ten years enormous strides have been made not only in establishing that specific transporters mediate the entry and exit of sterols and how these may regulate selective sterol access to the body pools, but also in how these pathways operate to integrate these physiological pathways. 2. The entry of sterols from the gastrointestinal and biliary canalicular lumen into the body is mediated by NPC1L1, which was discovered by a novel method, via a genomics-bioinformatics approach. 3. Identification of the genetic basis responsible for causing sitosterolaemia, characterized by plant sterol accumulation, led to the identification of two half-transporters (ABCG5 and ABCG8) that normally efflux plant sterols (and cholesterol) into the intestinal and biliary lumen for faecal excretion. 4. The objective of this review is to provide up-to-date knowledge on genomics, proteomics and function of these two transporter systems.
TL;DR: The data generated in this study indicate a consistency in scaling factors between rat and dog, and any sex differences were observed.
Abstract: 1. In vivo clearance predictions from in vitro assays require scaling factors to relate the concentrations of hepatocytes or microsomal protein to the intact liver. 2. The aims were to measure the variability in scaling factors for Wistar rat and beagle dog for which the literature is particularly scarce and determine any sex differences. 3. Scaling factors were determined by comparing the cytochrome P450 (P450) content in hepatocytes or microsomes against the P450 content of fresh liver homogenate. The use of fresh homogenate is recommended as freezing can increase contamination and affect the P450 assay. 4. Mean(geo) hepatic microsomal concentrations in Wistar rats were 61 mg g(-1) liver (95% confidence interval (CI); 47-75 mg g(-1) liver) and in beagle dogs 55 mg g(-1) liver (95% CI = 48-62 mg g(-1) liver). Mean(geo) hepatocellularity was 163 x 10(6) cells g(-1) liver for Wistar rats (95% CI = 127-199 x 10(6) cells g(-1) liver) and 169 x 10(6) cells g(-1) liver (95% CI = 131-207 x 10(6) cells g(-1) liver) for beagle dogs. The data generated in this study indicate a consistency in scaling factors between rat and dog. No sex differences were observed.
TL;DR: The enterohepatic recirculation of MPA in the patients seems to be more extensive in UGT1A9-118(dT)10 allele carriers, and the exposure of AcMPAG is higher in patients carrying ABCC2 G1249A genotype than those with wild-type genotype.
Abstract: The aim was to investigate the effect of UGT1A9, UGT1A8, UGT2B7 and ABCC2 polymorphism on the pharmacokinetics of mycophenolic acid (MPA) and its metabolites phenolic glucuronide (MPAG) and acyl glucuronide (AcMPAG) in Chinese renal transplant recipients. Single nucleotide polymorphisms (SNP) in UGT1A9-118(dT)(9)/(10), UGT1A9 T-440C/C-331T, UGT1A8*3, UGT2B7 G211T, UGT2B7 C802T, ABCC2 C-24T, and ABCC2 G1249A were detected. A total of 46 recipients were enrolled in the pharmacokinetics study at day 30 after kidney transplantation. Differences in the MPA pharmacokinetic profiles confirmed large inter-patient variation of MPA exposure. A statistical significant increase in the dose-adjusted AUC(6-12) level of MPA was found in patients bearing the -118(dT)(10) allele of the UGT1A9 gene (T(9) = 7.34 +/- 4.11 mg h ml(-1) g(-1); T(9)/T(10) = 11.54 +/- 7.62 mg h ml(-1) g(-1); and T(10) = 11.89 +/-8.76 mg h ml(-1) g(-1), p = 0.041). A similar trend was also observed for the dose-adjusted AUC(0-12) and AUC(6-12) of MPAG. Patients carrying the heterozygous mutant alleles of ABCC2 G1249A exhibited higher AUC(6-12)/D of AcMPAG than those with wild-type genotype (p = 0.016). The other SNPs that were genotyped did not cause any significant variation in MPA and MPAG pharmacokinetic parameters. In conclusion, the enterohepatic recirculation of MPA in the patients seems to be more extensive in UGT1A9-118(dT)(10) allele carriers, and the exposure of AcMPAG is higher in patients carrying ABCC2 G1249A genotype than those with wild-type genotype.
TL;DR: The genetic variants of OCT2 (OCT2-T199I, -T201M, and -A270S) decreased the transport activity of metformin and thus may contribute to the inter-individual variation in meetformin disposition as OCT2 plays a pivotal role in renal excretion, the major disposition route of met formin.
Abstract: 1. The authors sought to evaluate the contribution of organic cation transporters (OCTs) to the renal tubular transport of metformin using LLC-PK1 cells as an in vitro model for the renal proximal tubule, and to investigate the effects of three non-synonymous genetic variants of OCT2 on the transport activity of metformin in vitro using an oocyte over-expression system. 2. The basolateral-to-apical transport of metformin was significantly greater than the apical-to-basolateral transport and showed concentration dependency with the kinetic parameters: maximum transport rate (V(max)), 922 pmol min(-1) per 5 x 10(5) cells; Michaelis-Menten constant (K(m)), 393 microM; intrinsic clearance (CL(int)), 2.35 microl min(-1) per 5 x 10(5) cells; and diffusion constant (K(d)), 0.33 microl min(-1) per 5 x 10(5) cells. The basolateral-to-apical transport of metformin was inhibited by phenoxybenzamine, an inhibitor of OCTs, but not by cyclosporine A, MK571, or fumitremorgin C, which are inhibitors of P-glycoprotein, multidrug resistance proteins (MRPs), and breast cancer resistance protein (BCRP), respectively, suggesting that OCTs play a role in renal tubular secretion of metformin. 3. Metformin uptake was much greater in oocytes expressing OCT2-wild type (OCT2-WT) than OCT1-WT compared with uptake in water-injected oocytes. Uptake was significantly decreased in oocytes expressing OCT2-T199I, -T201M, and -A270S compared with that in OCT2-WT, suggesting that metformin is a better substrate for OCT2 than for OCT1 and that the amino acid-substituted variants of OCT2 cause a functional decrease in metformin uptake. 4. In conclusion, the genetic variants of OCT2 (OCT2-T199I, -T201M, and -A270S) decreased the transport activity of metformin and thus may contribute to the inter-individual variation in metformin disposition as OCT2 plays a pivotal role in renal excretion, the major disposition route of metformin.
TL;DR: The weight of evidence suggests that only a small number of transport proteins need to be routinely considered in the drug-discovery setting driven by the magnitude of their impact on tissue distribution, pharmacokinetic variability and drug–drug interactions.
Abstract: 1. This review will explore, from a pharmaceutical industry perspective, the evidence and consequences of transport protein involvement in pharmacokinetic variability and safety of drugs in humans. With the preclinical and clinical evidence available, the transport proteins that are considered to be the most important in respect of pharmacokinetic variability and safety in humans will be highlighted. 2. A large number of transport proteins have been identified, at both the genetic and the cellular level, which have been suggested to play some role in the absorption, distribution or elimination of endogenous, xenobiotic or drug substrates. 3. The weight of evidence suggests that only a small number of transport proteins need to be routinely considered in the drug-discovery setting driven by the magnitude of their impact on tissue distribution, pharmacokinetic variability and drug-drug interactions. 4. For the majority of candidate drugs, an assessment of the role of transporter proteins in their disposition and safety need only be assessed if in vivo properties suggest that active transport is likely to be a significant factor, if transport proteins are implicated in a particular therapeutic target area or if the disposition and safety of a likely co-medication are known to be significantly modulated by transport proteins.
TL;DR: Febuxostat is a novel anti-hyperuricaemia drug with low drug–drug interaction potential in clinical use and Examination of the inhibitory effect of febUXostat on CYP enzymes suggests that febuxost at minimally inhibits the activities of any CYP.
Abstract: 1. The potential for drug-drug interactions with febuxostat was examined in the following three in vitro systems: the characteristics of the binding of febuxostat to human plasma proteins; identification of the cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT) enzymes participating in the metabolism of febuxostat; and the potential inhibitory effects of febuxostat on typical CYP reactions. 2. The results have shown that the presence of ibuprofen or warfarin did not change the plasma protein binding of febuxostat, and that febuxostat did not influence the plasma protein binding of ibuprofen or warfarin. These results indicate that there is little possibility that febuxostat causes a drug-drug interaction by binding to albumin. 3. The UGT 1 and 2 families were involved in the glucuronidation, and several CYPs participated in the metabolism of febuxostat, suggesting that there is little possibility that the blood concentration of febuxostat varies widely even if febuxostat is concomitantly administered with drugs that inhibit CYP or UGT enzyme. Examination of the inhibitory effect of febuxostat on CYP enzymes suggests that febuxostat minimally inhibits the activities of any CYP. 4. The results demonstrate that febuxostat is a novel anti-hyperuricaemia drug with low drug-drug interaction potential in clinical use.
TL;DR: Findings indicate that multiple factors play important roles in determining the pharmacokinetics of TSIIA.
Abstract: Tanshinone IIA (TSIIA) is a major active triterpenoid isolated from Salvia miltiorrhiza. The purposes of this study were to investigate various preclinical factors that determined the pharmacokinetics of TSIIA. After oral dosing at 6.7, 20, and 60 mg kg−1, TSIIA was detected mainly as glucuronidated conjugate (TSIIAG) with only small amounts of the unchanged in the plasma. TSIIA was predominantly excreted into the bile and faeces as TSIIAG, and urine to a minor extent. The Cmax and AUC0−t of TSIIAG after i.p. administration were significantly lower than those after intragastric administration. The plasma concentration–time profiles of TSIIA following oral dosing of TSIIA showed multiple peaks. The Cmax and AUC0−t of TSIIA and its glucuronides in rats with intact bile duct were significantly lower than those of rats with bile duct cannulation. Studies from the linked-rat model and intraduodenal injection of bile containing TSIIA and its metabolites indicate that TSIIA glucuronides underwent hydrolysis and ...
TL;DR: The results indicate that bilobalide, and to a lesser extent ginkgolide A, B, quercetin, and kaempferol, play a key role in the effects of EGb 761 on CYP induction.
Abstract: 1. Ginkgo biloba is one of the most popular herbal medicines worldwide due to its memory-enhancing and cognition-improving effects. The current study was designed to investigate the effects of five major constituents (bilobalide, ginkgolide A, B, quercetin, and kaempferol) in the standardized G. biloba extract EGb 761 on various cytochrome P450s (CYPs) in rats. 2. The activity of CYP450 was measured by the quantification of six metabolites from multiple cytochrome P450 probe substrates using a validated liquid chromatography coupled with tandem mass spectrometry detection (LC-MS/MS) method. The levels of messenger RNA (mRNA) and protein of various CYPs were determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting analysis, respectively. 3. Bilobalide significantly induced the activity, protein, and mRNA expression of CYP3A1 and 1A2, and increased CYP2E1 activity and CYP2B1/2 protein expression in a dose-dependent manner. 4. Ginkgolide A, B, quercetin, and kaempferol did not affect CYP3A1, but induced CYP1A2 in a dose-dependent manner. EGb 761 and the five individual constituents had no effects on rat CYP2D2, 2C11 and 2C7. 5. The results indicate that bilobalide, and to a lesser extent ginkgolide A, B, quercetin, and kaempferol, play a key role in the effects of EGb 761 on CYP induction. Further study is needed to elucidate the mechanism of CYP3A induction by EGb 761 and bilobalide.
TL;DR: In vitro data indicate that usnic acid has significant potential to interact with other medications and individual characteristics such as CYP1A induction status, co-administration of CYP 1A2 inhibitors, UGT1A1 polymorphisms, and related hyperbilirubinaemias could work alone or in consort with other idiosyncrasy risk factors to increase the risk of adverse events and/or hepatotoxicity.
Abstract: Usnic acid is a component of nutritional supplements promoted for weight loss that have been associated with liver-related adverse events including mild hepatic toxicity, chemical hepatitis, and liver failure requiring transplant. To determine if metabolism factors might have had a role in defining individual susceptibility to hepatotoxicity, in vitro metabolism studies were undertaken using human plasma, hepatocytes, and liver subcellular fractions. Usnic acid was metabolized to form three monohydroxylated metabolites and two regio-isomeric glucuronide conjugates of the parent drug. Oxidative metabolism was mainly by cytochrome P450 (CYP) 1A2 and glucuronidation was carried out by uridine diphosphate-glucuronosyltransferase (UGT) 1A1 and UGT1A3. In human hepatocytes, usnic acid at 20 microM was not an inducer of CYP1A2, CYP2B6, or CYP3A4 relative to positive controls omeprazole, phenobarbital, and rifampicin, respectively. Usnic acid was a relatively weak inhibitor of CYP2D6 and a potent inhibitor of CYP2C19 (the concentration eliciting 50% inhibition (IC(50)) = 9 nM) and CYP2C9 (IC(50) = 94 nM), with less potent inhibition of CYP2C8 (IC(50) = 1.9 microM) and CYP2C18 (IC(50) = 6.3 microM). Pre-incubation of microsomes with usnic acid did not afford any evidence of time-dependent inhibition of CYP2C19, although evidence of slight time-dependent inhibition of CYP2C9 (K(I) = 2.79 microM and K(inact) = 0.022 min(-1)) was obtained. In vitro data were used with SimCYP(R)to model potential drug interactions. Based on usnic acid doses in case reports of 450 mg to >1 g day(-1), these in vitro data indicate that usnic acid has significant potential to interact with other medications. Individual characteristics such as CYP1A induction status, co-administration of CYP1A2 inhibitors, UGT1A1 polymorphisms, and related hyperbilirubinaemias, or co-administration of low therapeutic index CYP2C substrates could work alone or in consort with other idiosyncrasy risk factors to increase the risk of adverse events and/or hepatotoxicity. Thus, usnic acid in nutritional supplements might be involved as both victim and/or perpetrator in clinically significant drug-drug interactions.
TL;DR: This review paper will address the new aspects of ABCG2 in terms of post-translational modifications ofABCG2 protein, high-speed screening, and quantitative structure–activity relationship (QSAR) analysis to evaluate ABCG 2–drug interactions, and genetic polymorphisms potentially associated with photosensitivity.
Abstract: 1. The human ABC transporter ABCG2 is regarded as a member of the phase III system for xenobiotic metabolism, and it has been suggested that this efflux pump is responsible for protecting the body from toxic xenobiotics and for removing metabolites. 2. This review paper will address the new aspects of ABCG2 in terms of post-translational modifications (i.e., disulfide bond formation, ubiquitination, and endoplasmic reticulum-associated degradation) of ABCG2 protein, high-speed screening, and quantitative structure-activity relationship (QSAR) analysis to evaluate ABCG2-drug interactions, and genetic polymorphisms potentially associated with photosensitivity. 3. In addition, new aspects of human ABCG4 and mouse Abcg4 are presented with respect to their molecular properties and potential physiological roles. Considering a high sequence similarity between ABCG1 and ABCG4, both Abcg4 and ABCG4 may be involved in the transport of cholesterol from neurons and astrocytes. Furthermore, high expression of the mouse Abcg4 protein in the testis implicates its involvement in transport of certain sex hormones.