Biomedical subjects

U Brinkmann

Publications and source records attributed to U Brinkmann.

At least 19 recordsLinked to original sources

PubMed2001

Pharmacogenetics of the human drug-transporter gene MDR1: impact of polymorphisms on pharmacotherapy.

The blood- and tissue-concentrations, and thus the activity, of many drugs are influenced by factors that are subject to inter-individual variation. Variables that influence blood levels are metabolizing enzymes and transporters. Transporters control drug uptake, distribution and elimination. Transport by efflux pumps such as MDR1-encoded P-glycoprotein can influence the bioavailability of drugs. Knowledge of the transporter 'status' might allow for compensation of differences in drug uptake, such as by dose adjustment, which is important for drugs with narrow therapeutic windows. So far, intestinal expression of MDR1 has been determined by cumbersome methods, such as biopsies, although recently a functional polymorphism has been identified, which discriminates individual high or low-expressor alleles. As a result, clinical trials and therapy can be adapted to the 'MDR1-status' of individual patients.

Journal Article↗

PubMed2001

Frequency of C3435T polymorphism of MDR1 gene in African people.

The variability of P-glycoprotein expression between individuals is linked to a C3435T polymorphism of the human MDR1 gene. Concentration of P-glycoprotein in intestinal epithelial cells and in a subset of lymphoid cells is substantially lower in people with the T/T genotype than those with the C/C genotype. We compared allele frequencies of the C3435T polymorphism in random samples of west African, African American, white, and Japanese people. We recorded a significantly higher frequency of the C/C genotype in West Africans and African Americans (142 of 172 [83%] and 25 of 41 [61%], respectively), than in white people (139 of 537 [26%]) (p<0.0001). These findings could affect use of drugs that are P-glycoprotein substrates (such as HIV-1 protease inhibitors and ciclosporin) in African populations.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2001

Conjugation of an antibody Fv fragment to a virus coat protein: cell-specific targeting of recombinant polyoma-virus-like particles.

The development of cell-type-specific delivery systems is highly desirable for gene-therapeutic applications. Current virus-based vector systems show broad cell specificity, which results in the need to restrict the natural tropism of these viral systems. Here we demonstrate that tumour-cell-specific virus-like particles can be functionally assembled in vitro from recombinant viral coat protein expressed in Escherichia coli. The insertion of a negatively charged peptide in the HI loop of polyoma VP1 interferes with the binding of VP1 to the natural recognition site on mammalian cells and also serves as an adapter for the coupling of antibody fragments that contain complementary charged fusion peptides. A recombinant antibody fragment of the tumour-specific anti-(Lewis Y) antibody B3 could be coupled to the mutant VP1 by engineered polyionic peptides and an additional disulphide bond. With this system an entirely recombinant cell-specific delivery system assembled in vitro could be generated that transfers genes preferentially to cells presenting the tumour-specific antigen on the cell surface.

Amino Acid Sequence↗

PubMed2001

Polymorphisms in the ABC drug transporter gene MDR1.

In addition to genetically variable metabolic enzymes such as Cyp p450 proteins, blood and tissue levels of many drugs are influenced by controlled transport across compartmental boundaries. Major determinants in these transport processes are ATP-dependent efflux pumps such as P-glycoprotein and related proteins (eg MRPs), which can influence the bioavailability and CNS concentrations, as well as disposition of drugs. In addition to its recognized role in the development of multiple chemotherapy resistances, experimental evidence for the relevant influence of the MDR1 gene encoded P-glycoprotein, on the pharmacology of many other drugs has been gathered by the analyses of knockout mice, as well as in clinical studies. Recently, functional genetic polymorphisms in the MDR1 gene have been identified which influence the distribution and bioavailability of PGP substrates.

Animals↗

PubMed2001

The predictive value of MDR1, CYP2C9, and CYP2C19 polymorphisms for phenytoin plasma levels.

Phenytoin, an anticonvulsant, exhibits nonlinear pharmacokinetics with large interindividual differences. Because of its small therapeutic range with the risk of therapeutic failure or adverse drug effects in susceptible persons, therapeutic drug monitoring is frequently applied. The interindividual differences in dose response can partially be explained by known genetic polymorphisms in the metabolic enzyme CYP2C9 but a large deal of individual variability remains still unexplained. Part of this variability might be accounted for by variable uptake of phenytoin, which is a substrate of p-glycoprotein, encoded by the human MDR1 gene. We evaluated, whether phenytoin plasma levels correlate with a polymorphism in the MDR1 gene, C3435T, which is associated with intestinal PGP activity. Genotyping and analyses of plasma levels of phenytoin and metabolites in 96 healthy Turkish volunteers showed that the MDR1C > T3435 polymorphism affects phenytoin plasma levels (P = 0.064) and the metabolic ratio of p-HPPH vs phenytoin (MDR1*TT genotype, P = 0.026). The MDR1*CC genotype is more common in volunteers with low phenytoin levels (P < or = 0.001, chi2 test). A combined analysis of variable alleles of CYP2C9, 2C19 and MDR1 revealed that the number of mutant CYP2C9 alleles is a major determinant, the number of MDR1*T alleles further contributes to the prediction of phenytoin plasma levels and CYP2C19*2 does not explain individual variability. The regression equation that fitted the data best included the number of mutant CYP2C9 and MDR*T alleles as predictory variables and explained 15.4% of the variability of phenytoin data (r2 = 0.154, P = 0.0002). Furthermore, analysis of CYP2C9 and MDR1 genotypes in 35 phenytoin-treated patients recruited from therapeutic drug monitoring showed that combined CYP2C9 and MDR1 analysis has some predictive value not only in the controlled settings of a clinical trial, but also in the daily clinical practice.

Adolescent↗

PubMed2001

Frequency of single nucleotide polymorphisms in the P-glycoprotein drug transporter MDR1 gene in white subjects.

BACKGROUND: P-glycoprotein, the gene product of MDR1, confers multidrug resistance against antineoplastic agents but also plays an important role in the bioavailability of common drugs in medical treatment. Various polymorphisms in the MDR1 gene were recently identified. A silent mutation in exon 26 (C3435T) was correlated with intestinal P-glycoprotein expression and oral bioavailability of digoxin. OBJECTIVE: We wanted to establish easy-to-use and cost-effective genotyping assays for the major known MDR1 single nucleotide polymorphisms and study the allelic frequency distribution of the single nucleotide polymorphisms in a large sample of volunteers. METHODS: In this study, the distribution of the major MDR1 alleles was determined in 461 white volunteers with the use of polymerase chain reaction and restriction fragment length polymorphism. RESULTS: Five amino acid exchanges were found with allelic frequencies of 11.2% for Asn21Asp and 5.5% for Ser400Asn. Strikingly, in exon 21 three variants were discovered at the same locus: 2677G (56.4%), 2677T (41.6%), and 2677A (1.9%), coding for 893Ala, Ser, or Thr. A novel missense Gln1107Pro mutation was found in two cases (0.2%). The highest frequencies were observed for intronic and silent polymorphisms; C3435T occurred in 53.9% of the subjects heterozygously, and 28.6% of individuals were homozygous carriers of 3435T/T with functionally restrained P-glycoprotein. CONCLUSION: This study provides the first analysis of MDR1 variant genotype distribution in a large sample of white subjects. It gives a basis for large-scale clinical investigations on the functional role of MDR1 allelic variants for bioavailability of a substantial number of drugs.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2001

Genomic organization of the human CYP3A locus: identification of a new, inducible CYP3A gene.

Proteins encoded by the human CYP3A genes metabolize every second drug currently in use. The activity of CYP3A gene products in the general population is highly variable and may affect the efficacy and safety of drugs metabolized by these enzymes. The mechanisms underlying this variability are poorly understood, but they include gene induction, protein inhibition and unknown genetic polymorphisms. To better understand the regulation of CYP3A expression and to provide a basis for a screen of genetic polymorphisms, we determined and analysed the sequence of the human CYP3A locus. The 231 kb locus sequence contains the three CYP3A genes described previously (CYP3A4, CYP3A5 and CYP3A7), three pseudogenes as well as a novel CYP3A gene termed CYP3A43. The gene encodes a putative protein with between 71.5% and 75.8% identity to the other CYP3A proteins. The highest expression level of CYP3A43 mRNA is observed in the prostate, an organ with extensive steroid metabolism. CYP3A43 is also expressed in several other tissues including liver, where it can be induced by rifampicin. CYP3A43 transcripts undergo extensive splicing. The identification of a new member of the CYP3A family and the characterization of the full CYP3A locus will aid efforts to identify the genetic variants underlying its variable expression. This, in turn, will lead to a better optimization of therapies involving the numerous substrates of CYP3A proteins.

Amino Acid Sequence↗

PubMed2001

Cse1l is essential for early embryonic growth and development.

The CSE1L gene, the human homologue of the yeast chromosome segregation gene CSE1, is a nuclear transport factor that plays a role in proliferation as well as in apoptosis. CSE1 and CSE1L are essential genes in Saccharomyces cerevisiae and mammalian cells, as shown by conditional yeast mutants and mammalian cell culture experiments with antisense-mediated depletion of CSE1L. To analyze whether CSE1L is also essential in vivo and whether its absence can be compensated for by other genes or mechanisms, we have cloned the murine CSE1L gene (Cse1l) and analyzed its tissue- and development-specific expression: Cse1l was detected at embryonic day 7.0 (E7.0), E11.0, E15.0, and E17.0, and in adults, high expression was observed in proliferating tissues. Subsequently, we inactivated the Cse1l gene in embryonic stem cells to generate heterozygous and homozygous knockout mice. Mice heterozygous for Cse1l appear normal and are fertile. However, no homozygous pups were born after interbreeding of heterozygous mice. In 30 heterozygote interbreeding experiments, 50 Cse1l wild-type mice and 100 heterozygotes were born but no animal with both Cse1l alleles deleted was born. Embryo analyses showed that homozygous mutant embryos were already disorganized and degenerated by E5.5. This implicates with high significance (P < 0.0001, Pearson chi-square test) an embryonically lethal phenotype of homozygous murine CSE1 deficiency and suggests that Cse1l plays a critical role in early embryonic development.

Active Transport, Cell Nucleus↗

PubMed2001

ABC drug transporters: hereditary polymorphisms and pharmacological impact in MDR1, MRP1 and MRP2.

Transport by ATP-dependent efflux pumps, such as P-glycoprotein (PGP) and multi-drug resistance related proteins (MRPs), influences bioavailability and disposition of drugs. These efflux pumps serve as defence mechanisms and determine bioavailability and CNS concentrations of many drugs. However, despite the fact that substantial data have been accumulated on the structure, function and pharmacological role of ABC transporters and even though modification of PGP function is an important mechanism of drug interactions and adverse effects in humans, there is a striking lack of data on variability of the underlying genes. This review focuses on the human drug transporter proteins PGP (MDR1) and the multi-drug resistance proteins MRP1 and MRP2. An overview is provided of pharmacologically relevant genetic, structural and functional data as well as on hereditary polymorphisms, their phenotypical consequences and pharmacological implications.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed2001

Cambridge Healthtech Institute's 2nd Annual Conference on Pharmacogenomics Europe: presaging profits.

Pharmacogenomics promises to offer distinct strategic advantages to pharmaceutical companies, physicians, providers and patients. Cambridge Healthtech Institute's 2nd Annual Conference on 'Pharmacogenomics Europe: Presaging Profits' covered all aspects of pharmacogenomics and gave scientists from both academia and from pharmaceutical and biotech companies a great opportunity to discuss the latest progress in pharmacogenomic research. The meeting considered technologies for single nucleotide polymorphism (SNP) screening and expression profiling, bioinformatic tools for data evaluation and gave an overview on the state of affairs and novel approaches to implement pharmacogenomics and pharmacogenetics into drug development and medical treatment. The major strength of the meeting was the merging of scientists from many different disciplines, such as clinicians, pharmacologists, molecular biologists, engineers and bioinformatics experts, into one meeting.

Gene Expression Profiling↗

PubMed2001

Recombinant immunotoxins for cancer therapy.

Recombinant immunotoxins consist of Fv regions of tumour-selective antibodies fused to toxins found in bacteria, plants or fungi. These toxins must be modified to remove normal-tissue binding sites but to retain all other functions of cytotoxicity. The recombinant antibody fragments target the modified toxin to cancer cells which are killed, either by direct inhibition of protein synthesis, or by concomitant induction of apoptosis. Cells that are not recognised by the antibody fragment because they do not carry the tumour antigen, are spared. Many factors influence the in vivo antitumour activity of recombinant immunotoxins. Among them are considerations of which types of cancer may be the best targets for immunotoxin therapy as well as tumour specificity of the antigen that is targeted by the recombinant antibody. Other relevant issues are the affinity of immunotoxins and their ability to enter and penetrate into tissues and tumours, which in turn is dependent on the size of the protein. A great deal of protein-engineering is required to stabilise the recombinant antibody moiety of immunotoxins, since stability of the molecules is crucial for good clinical efficacy. Excellent activity and specificity can be observed for many recombinant immunotoxins in in vitro assays using cultured cancer cells as well as in animal tumour models. Ongoing clinical trials provide examples where the promising preclinical data correlate with successful results in experimental cancer therapy.

Animals↗

PubMed2001

High expression of the proliferation and apoptosis associated CSE1L/CAS gene in hepatitis and liver neoplasms: correlation with tumor progression.

The CSE1L/CAS protein (CAS) is a Ran-binding protein with a function as nuclear transport (export) factor. Like recently observed for ran and other ran-binding proteins, CSE1L/CAS simultaneously plays a role in the mitotic spindle checkpoint, which assures genomic stability during cell division. This checkpoint is frequently disturbed in neoplasias of various origin, including hepatic tumors. We have evaluated by immunohistology the expression of CAS in adult and embryonic liver, hepatitis, and in liver hyperplasias. Normal hepatocytes revealed no CAS expression while embryonic liver showed strong expression in all parenchymal cells. Bile ducts stained positive with anti-CAS antibodies, and strong CAS expression was also detected at the interface between bile ducts and hepatocytes under conditions associated with regenerative proliferation. The localization of these CAS expressing cells correlated with the distribution of putative liver stem-cells. In active viral (but not in inactive) hepatitis, strong hepatocytal CAS expression correlates in site and intensity with degree of inflammation. Neoplastic liver demonstrated different degrees of CAS expression: no remarkable expression in adenomas, moderate expression in a narrow rim of hepatocytes and in periseptal cholangiolar proliferations in focal nodular hyperplasia, and strong CAS expression in hepatocellular carcinoma. Less differentiated tumors stain stronger than well differentiated. Cholangio-cellular carcinomas show even stronger CAS expression than hepatocellular carcinomas. Our observation of strong expression of CAS in liver cells that are committed for proliferation among them possibly liver stem cells, and in liver neoplasms, is consistant with the fact that CAS functions not solely as a nuclear transport factor but that it is also essential for cell proliferation, particularly for the mitotic spindle checkpoint. Interestingly, genomic instability is frequently observed in hepatic tumors which we have shown here to express large amounts of CAS. Since the degree of CAS-expression correlates with the grade of tumor dedifferentiation, we suggest that CAS should also be further investigated as prognostic marker for hepatic neoplasms.

Adult↗

PubMed2001

Natural protein variants of pregnane X receptor with altered transactivation activity toward CYP3A4.

Between 45 and 60% of all drugs currently used are metabolized by the CYP3A4 protein. CYP3A4 expression in liver varies up to 60-fold in the general population, which can lead to ineffective drug therapy (high CYP3A4) or, on the other hand, to harmful drug reactions (low CYP3A4). Most of this variability has been attributed to genetic factors, but to date their identity remains unknown. Recently, it was shown that CYP3A expression is largely controlled by the pregnane X receptor (PXR). We, therefore, hypothesized that polymorphisms in PXR may contribute to CYP3A4 variability. The presence of PXR variants was investigated in two ethnic groups, Caucasians and Africans. Six missense mutations leading to variant PXR proteins were identified, and their consequences on CYP3A4 expression were analyzed. Expressed in LS174T cells, three protein variants, V140M, D163G, and A370T, exhibited altered basal and/or induced transactivation of CYP3A promoter reporter genes. Thus, these natural PXR protein variants may play a role in the observed interindividual variability of CYP3A4 expression and may be involved in rare, atypical responses to drugs or altered sensitivities to carcinogens.

Black People↗

PubMed2001

Effect of grapefruit juice on digoxin pharmacokinetics in humans.

OBJECTIVES: Grapefruit juice is responsible for drug interactions mediated by intestinal cytochrome P4503A4 inhibition and possibly P-glycoprotein inhibition in enterocytes. Our main objective was to determine whether grapefruit juice alters the bioavailability of digoxin, a P-glycoprotein substrate. The secondary objective was to determine whether the magnitude of the pharmacokinetic interaction was influenced by P-glycoprotein genetic polymorphism. METHODS: Twelve healthy volunteers participated in this open randomized crossover study comparing the effect of grapefruit juice consumption (versus water) on the pharmacokinetics of a single oral dose of digoxin (0.5 mg). The P-glycoprotein genotype was determined according to MDR1 genetic polymorphism in exon 26 (C3435T). RESULTS: Grapefruit juice had no significant effect on the maximum plasma drug concentration (C(max)) of digoxin or the area under the plasma concentration-time curve (AUC) from time zero to 48 hours. However, there was a 9% increase in the digoxin AUC from time zero to 4 hours and from time zero to 24 hours (P =.01) during grapefruit juice administration. The digoxin renal clearance remained unchanged during both periods. No relationship between MDR1 C3435T genotype and early digoxin pharmacokinetic changes could be detected. CONCLUSION: The modest changes in digoxin pharmacokinetics observed during grapefruit juice ingestion do not support an important P-glycoprotein inhibition. Under our experimental conditions, grapefruit juice-mediated P-glycoprotein inhibition does not appear to play a relevant role in drug interactions, at least when assessed by use of digoxin disposition kinetics.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2000

Functional polymorphisms of the human multidrug-resistance gene: multiple sequence variations and correlation of one allele with P-glycoprotein expression and activity in vivo.

To evaluate whether alterations in the multidrug-resistance (MDR)-1 gene correlate with intestinal MDR-1 expression and uptake of orally administered P-glycoprotein (PGP) substrates, we analyzed the MDR-1 sequence in 21 volunteers whose PGP expression and function in the duodenum had been determined by Western blots and quantitative immunohistology (n = 21) or by plasma concentrations after orally administered digoxin (n = 8 + 14). We observed a significant correlation of a polymorphism in exon 26 (C3435T) of MDR-1 with expression levels and function of MDR-1. Individuals homozygous for this polymorphism had significantly lower duodenal MDR-1 expression and the highest digoxin plasma levels. Homozygosity for this variant was observed in 24% of our sample population (n = 188). This polymorphism is expected to affect the absorption and tissue concentrations of numerous other substrates of MDR-1.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2000

Attenuating the growth of tumors by intratumoral administration of DNA encoding Pseudomonas exotoxin via cationic liposomes.

A gene therapy approach was taken to inhibit tumor growth by transfecting tumor cells with a plasmid encoding a truncated but active form of Pseudomonas exotoxin A (PE), using cationic lipids as the transfection reagent. Cells transfected with this plasmid express PE intracellularly and undergo apoptosis. Transfection was optimized in vitro using two cationic lipids, DOGS and DOSPER. A ratio of between 1:4 and 1:10 (wt/wt) was found to be optimal for DOSPER, and the ratio 1:4 was used for the in vivo study when a smaller injection volume was desired. Estimating the activity of the PE-encoding plasmid was done both directly, by counting cells in vitro after transfection, and by using a cytotoxicity assay, and indirectly, by cotransfecting the plasmid with a plasmid carrying a reporter beta-galactosidase gene and observing a reduction in beta-galactosidase activity with increasing amounts of the PE-encoding plasmid. The cotransfection method was found to be very sensitive, and showed transfection of cells even with 1-2 ng of the PE-encoding plasmid per 10(5) cells. Complexes of the PE-encoding plasmid together with cationic lipid were injected into tumor xenografts in athymic nude mice. The tumor growth of transfected tumors was attenuated compared with control untreated tumors or tumors transfected with a nontoxin-expressing vector. These results indicate the potential of such a treatment for attenuating solid tumor growth in vivo.

ADP Ribose Transferases↗

PubMed2000

Characterization of the glutathione S-transferase GSTT1 deletion: discrimination of all genotypes by polymerase chain reaction indicates a trimodular genotype-phenotype correlation.

Glutathione S-transferase theta enzyme activity involved in the metabolism of toxic compounds is absent in approximately 20% of Caucasians due to a homozygous deletion of GSTT1 (*0/0). Because the exact manner of the GSTT1 deletion was unknown, current genotyping of GSTT1 was limited to detect the presence versus complete absence of the gene by a GSTT1-specific polymerase chain reaction (PCR). Thus, heterozygous (*A/0) and homozygous (*A/A) samples could not be discriminated. We have characterized the boundaries of the deletion of the human glutathione S-transferase theta (GSTT1) gene: PCR mapping and sequencing revealed a 54251 bp fragment including GSTT1 to be deleted from chromosome 22, most likely by a homologous recombination event between two highly homologous sequence stretches that flank GSTT1. Based on the knowledge of the GSTT1*0 region, a PCR assay was devised for unambiguous discrimination of homozygously deleted (*0/0), heterozygously (*A/0) and homozygously GSTT1 carrying (*A/A) individuals. Genotyping of 180 samples of a Caucasian population revealed that the deletion consists of one defined allele, whose distribution in the population fits the Hardy-Weinberg equilibrium with observed 20% *0/0, 46% *A/0 and 34% *A/A individuals. The number of GSTT1*A alleles detected by this procedure correlated highly significant with the enzyme activity in erythrocytes. Genotype-phenotype comparisons demonstrated a codominant type of inheritance by a gene-dose effect: samples with two active alleles expressed a statistically significant higher enzymatic activity compared to those with one null allele (P < 0.0001, ANOVA).

Base Sequence↗

PubMed2000

How to manage individualized drug therapy: application of pharmacogenetic knowledge of drug metabolism and transport.

Significant fractions of health budgets must be spent for treatment of drug side effects and for inefficient drug therapy. Hereditary variants in drug metabolizing enzymes, drug transporters, and drug targets are important determinants of drug response and toxicity and may therefore aid in selection and dosage of drugs. Today there is extensive knowledge of genetic polymorphisms of cytochrome P450 (CYP) enzymes 2A6, 2C9, 2C19, and 2D6; of phase-2 enzymes such as thiopurine S-methyltransferase; and more recently of drug transporters such as the MDR-1 gene-product P-glycoprotein, affecting a significant share of currently used drugs. However, application of pharmacogenetic knowledge to clinical routine is limited in current practice. To promote the application of pharmacogenetic knowledge in clinical routine, research on genotype-based dose adjustments is still necessary - as is the promotion of faster and cheaper genotype analyses. Furthermore, the benefits of CYP genotype-directed drug therapy should be evaluated in properly designed prospective studies. Once such steps have been successfully taken, drug therapy could well become more prevention-directed and patient-tailored than it is possible today, replacing the current "one drug in one dose for one disease" strategy by a more individualized approach.

Cytochrome P-450 Enzyme System↗