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J Kuhlmann

Publications and source records attributed to J Kuhlmann.

At least 37 records · Page 2Linked to original sources
PubMed1999

Conformational states of the nuclear GTP-binding protein Ran and its complexes with the exchange factor RCC1 and the effector protein RanBP1.

It has been shown before by (31)P NMR that Ras bound to the nonhydrolyzable GTP analogue guanosine 5'-O-(beta, gamma-imidotriphosphate) (GppNHp) exists in two conformations which are rapidly interconverting with a rate constant of 3200 s-1 at 30 degrees C [Geyer, M., et al. (1996) Biochemistry 35, 10308-10320]. Here we show that Ran complexed with GTP also exists in two conformational states, 1 and 2, which can be directly inferred from the occurrence of two (31)P NMR resonance lines for the gamma-phosphate group of bound GTP. The exchange between the two states is slow on the NMR time scale with a value of <200 s-1 at 5 degrees C for the corresponding first-order rate constants. In wild-type Ran, the equilibrium constant K' between the two states is 0.7 at 278 K, is different for various mutants, and is strongly dependent on the temperature. The standard enthalpy DeltaH degrees and the standard entropy DeltaS degrees for the conformational transitions determined from the NMR spectra are as follows: DeltaH degrees = 37 kJ mol-1 and DeltaS degrees = 130 J mol-1 K-1 for wild-type Ran.GTP. In complex with the Ran-binding protein RanBP1, one of the Ran.GTP conformations (state 2) is stabilized. The interaction of Ran with the guanine nucleotide exchange factor protein RCC1 was also studied by (31)P NMR spectroscopy. In the presence of nucleotide, the ternary complex of Ran.nucleotide.RCC1, an intermediate in the guanine nucleotide exchange reaction, could be observed. A model for the conformational transition of Ran.GTP is proposed where the two states observed are caused by the structural flexibility of the effector loop of Ran; in solution, state 2 resembles the GTP-bound form found in the crystal structure of the Ran-RanBP complex.

Cell Cycle Proteins↗
PubMed1999

[Responsibilities of clinical pharmacology in the early phase of drug development].

The path of a new drug from the idea to the product may be divided into 2 phases, namely drug discovery and drug development. Due to the scientific progress new and simple methods could be developed to determine the biological efficacy of a large number of compounds. During the first part of drug development necessary requirements for the first use in man are met by performing preclinical pharmacological, toxicological and pharmacokinetic investigations in the animal and in in-vitro testing. After a first clinical-pharmacological profile of the new substance has been established during phase I on the basis of which a decision for the continuation of the clinical trial is made, the aim of phases II and III is now to answer the important questions of the therapeutic efficacy and tolerability in a large number of patients with the target indication. Due to the continuously increasing time and costs of drug development, drug development should be streamlined combining preclinical and early clinical phases as an exploratory stage and later clinical development as a confirmatory stage. The development and appropriate use of surrogates and models may be helpful to determine drug actions in human and to assist in dose selection as the main requirement for a successful large clinical trial in the confirmatory stage. Identifying the genes responsible for the huge variations in how different patients respond to a drug, in terms of both the product's effectiveness and its side effects, and genotyping patients before including in large clinical trials may prevent selecting the wrong patient population and avoid expensive repetition of these studies. Taking responsibility as the link between research and development gives clinical pharmacology a major opportunity to assume a pivotal role in drug development. To reach this goal, clinical pharmacology must be fully integrated in the whole process of drug development from the candidate selection until the approval.

Animals↗
PubMed1999

Structure of a Ran-binding domain complexed with Ran bound to a GTP analogue: implications for nuclear transport.

The protein Ran is a small GTP-binding protein that binds to two types of effector inside the cell: Ran-binding proteins, which have a role in terminating export processes from the nucleus to the cytoplasm, and importin-beta-like molecules that bind cargo proteins during nuclear transport. The Ran-binding domain is a conserved sequence motif found in several proteins that participate in these transport processes. The Ran-binding protein RanBP2 contains four of these domains and constitutes a large part of the cytoplasmic fibrils that extend from the nuclear-pore complex. The structure of Ran bound to a non-hydrolysable GTP analogue (Ran x GppNHp) in complex with the first Ran-binding domain (RanBD1) of human RanBP2 reveals not only that RanBD1 has a pleckstrin-homology domain fold, but also that the switch-I region of Ran x GppNHp resembles the canonical Ras GppNHp structure and that the carboxy terminus of Ran is wrapped around RanBD1, contacting a basic patch on RanBD1 through its acidic end. This molecular 'embrace' enables RanBDs to sequester the Ran carboxy terminus, triggering the dissociation of Ran x GTP from importin-beta-related transport factors and facilitating GTP hydrolysis by the GTPase-activating protein ranGAP. Such a mechanism represents a new type of switch mechanism and regulatory protein-protein interaction for a Ras-related protein.

Amino Acid Sequence↗
PubMed1999

Increase in cerivastatin systemic exposure after single and multiple dosing in cyclosporine-treated kidney transplant recipients.

OBJECTIVE: The mutual drug-drug interaction potential of the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor cerivastatin and cyclosporine (INN, ciclosporin) in kidney transplant recipients receiving individual immunosuppressive treatment was evaluated with respect to pharmacokinetic behavior of either drug and tolerability of concomitant use. METHODS: Plasma and urine concentrations of cerivastatin and its major metabolites were determined after administration of 0.2 mg single-dose cerivastatin to 12 kidney transplant recipients (9 men and 3 women) who were receiving stable individual cyclosporine treatment (mainly 200 mg twice a day). These results were compared with the single-dose pharmacokinetic results obtained from a healthy control group (n = 12, age-comparable men). Cerivastatin steady-state pharmacokinetics were evaluated in the same patients during continued immunosuppressive treatment 4 to 6 weeks later, after a 7-day treatment of 0.2 mg cerivastatin once a day. Cyclosporine steady-state concentration-time profiles were determined in blood with monoclonal (EMIT [enzyme multiplied immunoassay technique] assay, parent drug specific) and polyclonal antibodies (FPIA [fluorescence polarization immunoassay] assay, cyclosporine plus metabolites) during cerivastatin cotreatment and compared with predosing data. RESULTS: Coadministration of 0.2 mg cerivastatin once a day to the kidney transplant recipients treated with individual doses of cyclosporine and other immunosuppressive agents resulted in a 3- to 5-fold increase in cerivastatin and metabolites plasma concentrations. Cerivastatin and metabolites elimination half-lives were unaffected, and no accumulation occurred during multiple-dosing conditions. Cerivastatin had no influence on steady-state blood concentrations of cyclosporine or cyclosporine metabolites in these patients. The concomitant use of both drugs was well tolerated. CONCLUSIONS: Cerivastatin and metabolites plasma concentrations were significantly increased in kidney transplant recipients treated with cyclosporine and other immunosuppressive agents. Displacement from the main site for cerivastatin distribution-the liver-by cyclosporine-inhibited liver transport processes may explain the decrease in both metabolic clearance and volume of distribution for cerivastatin and metabolites.

Adult↗
PubMed1999

The influence of valerian treatment on "reaction time, alertness and concentration" in volunteers.

A randomised, controlled, double-blind trial was performed on 102 male and female volunteers to determine whether reaction time, alertness and concentration might be impaired by treatment with a native valerian root extract (VRE). The effect was first examined the morning after a single evening dose of VRE (600 mg LI 156) vs. flunitrazepam (FNZ) (1 mg) and placebo (PL) (trial section A), and then after two weeks of evening administration of VRE (600 mg LI 156) vs. PL (trial section B). 99 volunteers were analysed in section A and 91 in section B. The primary criterion was the median of reaction time (MRT) measured with the Vienna Determination Test. Secondary criteria were cognitrones (alertness test), tracking test (two-handed co-ordination), sleep quality (VIS-A, Vis-M), further VDT parameters, and safety criteria. The single administration of LI 156 did not impair the reaction abilities, concentration and co-ordination. After 14 days of treatment, the equivalence of VRE and PL was proven by confirmative analysis concerning the improvement of MRT (p = 0.4481). Evaluation of the secondary criteria were consistent with the results of the primary criterion. It is concluded that neither single nor repeated evening administrations of 600 mg of VRE have a relevant negative impact on reaction time, alertness and concentration the morning after intake.

Adult↗
PubMed1999

Pharmacokinetics of cerivastatin in renal impairment are predicted by low serum albumin concentration rather than by low creatinine clearance.

The influence of renal impairment on the clearance of the new HMG-CoA reductase inhibitor cerivastatin was evaluated. A single oral dose of 300 microg cerivastatin was given to 18 patients with different degrees of renal impairment and 6 healthy controls. Concentrations of total cerivastatin, its fraction unbound, and the total concentrations of the active metabolites M1 and M23 were measured in plasma. Serum concentrations of unbound cerivastatin were calculated for each individual from the concentration of total cerivastatin and cerivastatin's fraction unbound at t = 2.5 hours. In contradiction to what had been expected, renal impairment significantly influenced the pharmacokinetics of cerivastatin. The best correlation to the AUC and Cmax of unbound cerivastatin was found with serum albumin concentration. Also, serum albumin concentration was the only factor significantly correlated to t 1/2 of cerivastatin. Significant but slighter correlation with the AUC and Cmax of unbound cerivastatin was also observed for creatinine clearance and cerivastatin's fraction unbound, while no correlation was observed with total plasma protein. No significant correlation of creatinine clearance, serum albumin concentration, fu, or total plasma protein concentration with the AUC and Cmax of total cerivastatin or the AUC, Cmax or t 1/2 of M1 and M23 was observed. The authors conclude that low serum albumin concentration rather than low creatinine clearance predicts the pharmacokinetics of cerivastatin in renal impairment.

Adult↗
PubMed1999

Alternative strategies in drug development: clinical pharmacological aspects.

Due to the continuous increase in time and cost of drug development and the considerable amount of resources required by the traditional approach, companies can no longer afford to continue to late phase 3 with drugs which are unlikely to be therapeutically effective. The future challenge must be for the pharmaceutical industry to slash its research and development costs by achieving a significant cut in the attrition rate for drugs entering preclinical and clinical development, and to reduce the development time and to increase the probability of success in later clinical trials by streamlining the development processes. In the 100 years to 1995, the pharmaceutical industry worked on about 500 targets with a limited number of compounds, whereas now, using new technologies like genomics, high throughput screening and combinatorial chemistry, drug companies will see an explosion in the number of targets and leads it can explore. Therefore, a tough selection process for picking candidate compounds out of research and a quick kill process for the candidate, which does not measure up in advanced trials, is mandatory to avoid wasting time, energy and money. To improve the transition from research to development it is necessary to validate new targets, define success criteria for research, integrate bioinformation at every stage in drug discovery, define prerequisites for development, identify the "losers" and select the "winners" early and concentrate efforts on them, and to automate the research and development (R&D) process to optimize resource requirements versus time lines and to ensure effective flow of information from drug discovery to late phase of development. In drug development a deeper understanding of a drugs' action is necessary from animal models and phase I, IIa studies prior to taking the drug further in development. Instead of moving from discovery thorough development phases in sequential steps, drug development should be streamlined combining preclinical and early clinical development as an exploratory stage and phases IIb, III as a confirmatory stage. Preclinical and clinical-pharmacological studies in the exploratory stage of drug development should be designed for decision making in contrast to later clinical trials that require power for proof-of-safety and efficacy. Strategies to improve the quality of decisions in drug development are: the use and integration of new tools and technologies such as pharmacogenomics to improve our knowledge about the origin of the disease and to identify new therapeutic strategies; modelling and simulation of preclinical and clinical trials to bridge the gap between the early stages of the development of a new drug and its potential effects in humans; more sophisticated clinical pharmacokinetics to answer the question if the drug is present at the disease site for a sufficient time and to provide information on concentration-effect-relationships; selecting and evaluating surrogates/biomarkers for safety and efficacy; involvement of the target population as soon as possible; using information technologies to make better use of existing data. The more thorough and profound studies have been carried out during this exploratory stage of development, the earlier a decision can be made on the continuation or discontinuation of further development, thus saving development time and money and assessing and considerably reducing the risk for the patients and increasing the success-rate of the project in the later confirmatory effectiveness trial. Taking responsibility as the link between research and development gives clinical pharmacology a major opportunity to assume a pivotal role in research and development of new drugs. To reach this goal, clinical pharmacology must be fully integrated in the whole process from the candidate selection to its approval.

Chemistry, Pharmaceutical↗
PubMed1998

The Cdc42/Rac interactive binding region motif of the Wiskott Aldrich syndrome protein (WASP) is necessary but not sufficient for tight binding to Cdc42 and structure formation.

Wiskott Aldrich syndrome is a rare hereditary disease that affects cell morphology and signal transduction in hematopoietic cells. Different size fragments of the Wiskott Aldrich syndrome protein, W4, W7 and W13, were expressed in Escherichia coli or obtained from proteolysis. All contain the GTPase binding domain (GBD), also called Cdc42/Rac interactive binding region (CRIB), found in many putative downstream effectors of Rac and Cdc42. We have developed assays to measure the binding interaction between these fragments and Cdc42 employing fluorescent N-methylanthraniloyl-guanine nucleotide analogues. The fragments bind with submicromolar affinities in a GTP-dependent manner, with the largest fragment having the highest affinity, showing that the GBD/CRIB motif is necessary but not sufficient for tight binding. Rate constants for the interaction with W13 have been determined via surface plasmon resonance, and the equilibrium dissociation constant obtained from their ratio agrees with the value obtained by fluorescence measurements. Far UV circular dichroism spectra show significant secondary structure only for W13, supported by fluorescence studies using intrinsic protein fluorescence and quenching by acrylamide. Proton and 15N NMR measurements show that the GBD/CRIB motif has no apparent secondary structure and that the region C-terminal to the GBD/CRIB region is alpha-helical. The binding of Cdc42 induces a structural rearrangement of residues in the GBD/CRIB motif, or alternatively, the Wiskott Aldrich syndrome protein fragments have an ensemble of conformations, one of which is stabilized by Cdc42 binding. Thus, in contrast to Ras effectors, which have no conserved sequence elements but a defined domain structure with ubiquitin topology, Rac/Cdc42 effectors have a highly conserved binding region but no defined domain structure in the absence of the GTP-binding protein. Deviating from common belief GBD/CRIB is neither a structural domain nor sufficient for tight binding as regions outside this motif are necessary for structure formation and tight interaction with Rho/Rac proteins.

Amino Acid Sequence↗
PubMed1998

Kinetic analysis by fluorescence of the interaction between Ras and the catalytic domain of the guanine nucleotide exchange factor Cdc25Mm.

Guanine nucleotide exchange factors (GEFs) activate Ras proteins by stimulating the exchange of GTP for GDP in a multistep mechanism which involves binary and ternary complexes between Ras, guanine nucleotide, and GEF. We present fluorescence measurements to define the kinetic constants that characterize the interactions between Ras, GEF, and nucleotides, similar to the characterization of the action of RCC1 on Ran [Klebe et al. (1995) Biochemistry 34, 12543-12552]. The dissociation constant for the binary complex between nucleotide-free Ras and the catalytic domain of mouse Cdc25, Cdc25(Mm285), was 4.6 nM, i.e., a 500-fold lower affinity than the Ras.GDP interaction. The affinities defining the ternary complex Ras. nucleotide.Cdc25(Mm285) are several orders of magnitude lower. The maximum acceleration by Cdc25(Mm285) of the GDP dissociation from Ras was more than 10(5)-fold. Kinetic measurements of the association of nucleotide to nucleotide-free Ras and to the binary complex Ras. Cdc25(Mm285) show that these reactions are practically identical: a fast binding step is followed by a reaction of the first order which becomes rate limiting at high nucleotide concentrations. The second reaction is thought to be a conformational change from a low- to a high-affinity nucleotide binding conformation in Ras. Taking into consideration all experimental data, the reverse isomerization reaction from a high- to a low-affinity binding conformation in the ternary complex Ras. GDP.Cdc25(Mm285) is postulated to be the rate-limiting step of the GEF-catalyzed exchange. Furthermore, we demonstrate that the disruption of the Mg2+-binding site is not the only factor in the mechanism of GEF-catalyzed nucleotide exchange on Ras.

Animals↗
PubMed1998

A domain within the tumor suppressor protein APC shows very similar biochemical properties as the microtubule-associated protein tau.

The tumor-suppressor protein APC (adenomatous polyposis coli) binds to microtubules and promotes tubulin assembly. In vivo the endogenous APC protein is mainly localized at the end of microtubules that are involved in active cell migration. Since most tumor-specific APC gene mutations lead to the loss of the microtubule binding domain this interaction is assumed to play a crucial role in tumorigenesis. In this study we show that an APC protein fragment (amino acids 2219-2580) within the C-terminal part is enough to bind to non-assembled tubulin with high affinity. The binding of APC to tubulin does not lead to an alteration of the intrinsic GTPase activity of the non-assembled tubulin. The APC protein induces the tubulin assembly in a fast reaction and below the critical assembly concentration of tubulin. The APC protein induces the bundling of the assembled microtubules in a concentration-dependent manner. Regarding its biochemical properties the analysed APC protein fragment strikingly resembles the members of the microtubule-associated protein family tau. This analogy may help to understand the role of the APC protein in the suppression of tumorigenesis.

Adenomatous Polyposis Coli Protein↗
PubMed1998

When are bioavailability studies required? A German proposal.

The Bundesinstitut für Arzneimittel und Medizinprodukte (BfArM), the German drug regulation authority, issued guidelines for determining whether bioavailability/bioequivalence studies are required for certain drugs. This decision tree is based on pharmacodynamic, pharmacokinetic, and physicochemical criteria. Details of this decision tree were worked out by an expert panel, the Bioavailability Commission at the BfArM. The decision tree has been in use by German regulatory authorities for more than 10 years. In the meantime, its essentials were adopted by the European Committee for Proprietary Medicinal Products (CPMP) and by the World Health Organization (WHO) for their "Guidelines on interchangeability of multisource pharmaceutical products." This article reviews the original decision tree of the BfArM and provides examples of drugs that have been assessed according to its rules. The current procedure of the German regulatory authorities for judging the necessity of bioavailability trials, which reflects the status quo of regulatory practice in Germany, is also discussed.

Biological Availability↗
PubMed1998

Influence of erythromycin pre- and co-treatment on single-dose pharmacokinetics of the HMG-CoA reductase inhibitor cerivastatin.

OBJECTIVE: Cerivastatin is a novel, synthetic, highly potent 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor that effectively reduces serum cholesterol levels at very low doses. It is exclusively cleared from humans via cytochrome P450-mediated biotransformation (demethylation M1; hydroxylation M23) and subsequent biliary/renal excretion of the metabolites. The influence of concomitant administration of erythromycin, a potent CYP3A4 inhibitor, on cerivastatin bioavailability and pharmacokinetics was investigated. METHODS: Twelve healthy young male subjects received single oral doses of 300 microg cerivastatin alone or on the 4th day of a 4-day pre- and co-treatment with erythromycin 500 mg t.i.d. in a randomised, non-blind crossover study. Plasma and urine samples were analysed for cerivastatin and its major metabolites by validated specific high-performance liquid chromatography assays. RESULTS: Cerivastatin was safe and well tolerated. No clinically relevant treatment-emergent changes in laboratory parameters were observed. The pre- and co-treatment with erythromycin 500 mg t.i.d. had a modest influence on cerivastatin clearance, leading to a mean increase in the maximum plasma concentration (Cmax) of 13% and a slightly increased terminal half-life (approximately 10%), resulting in a mean elevation of the area under the curve (AUC) of 21%; time to peak (tmax) remained unchanged. While the mean AUC of the metabolite M1 following the combined dosing was decreased by 60% compared with mono-dosing, the mean AUC of M23 exhibited an increase of approximately 60%. The respective Cmax results paralleled these pronounced effects, whereas the influence on mean terminal half-lives was small (i.e. for M23, an approximate 20% increase) or not observable (i.e. for M1). CONCLUSIONS: Concomitant administration of erythromycin 500 mg t.i.d. affects, to a certain extent, the metabolism of cerivastatin, administered as a single oral dose of 300 microg, resulting in a slightly increased exposure of the parent drug and active metabolites which, however, does not need dose adjustment. In addition, the small increase in cerivastatin half-life does not predict an accumulation beyond steady state. The pharmacokinetic data for the major metabolites suggest that the M1 metabolic pathway is more sensitive to CYP3A4 inhibition than the parallel M23 pathway, supporting recent in vitro findings that further cytochrome P450 isozymes are differently involved in the metabolic pathways of cerivastatin.

Adult↗
PubMed1998

Monitoring of proteinuria in phase I studies in healthy male subjects.

OBJECTIVE: The quantitative measurement of urinary marker proteins may improve the sensitivity of monitoring renal function in healthy male subjects in phase I studies. Little is known about the variability of physiological proteinuria in young, healthy male subjects. Thus, the biological and analytical variability of three marker proteins, i.e. albumin, alpha(1)-microglobulin and N-acetyl-beta-D-glucosaminidase (NAG), were investigated in this population. METHODS: Seven young, healthy male subjects participated in a prospective two-way cross-over study, and 139 in a retrospective study. Albumin and alpha(1)-microglobulin were determined by immunological methods (radial immunodiffusion and/or kinetic nephelometry), and NAG by enzyme activity in a colorimetric assay. RESULTS: The inter-assay precision of NAG, albumin and alpha(1)-microglobulin is good (< 15%) if automated kinetic nephelometry is applied for albumin and alpha(1)-microglobulin determination, but less impressive (< 25%) with radial immunodiffusion. The highest frequency of detectable proteinuria and highest creatinine-adjusted protein levels are found in the second morning urine voided after a night's rest. The intra-individual biological variability of NAG excretion from day to day is low (CV: 15-25%), irrespective of outpatient or inpatient settings. By contrast, albumin and alpha(1)-microglobulin excretion can differ by a factor of 2-3 from day to day, and higher levels are predominantly found in outpatient settings. The reference ranges for young, healthy male subjects are generally lower than published in cross-sectional studies in the total healthy population. CONCLUSION: These findings and established reference ranges for young, healthy male subjects may assist in the evaluation of proteinuria in clinical pharmacological phase I trials.

Acetylglucosaminidase↗
PubMed1998

The IQGAP-related protein DGAP1 interacts with Rac and is involved in the modulation of the F-actin cytoskeleton and control of cell motility.

DGAP1 of Dictyostelium discoideum is a cell cortex associated 95 kDa protein that shows homology to both RasGTPase-activating proteins (RasGAPs) and RasGAP-related proteins. When tested for RasGAP activity, recombinant DGAP1 protein did not promote the GTPase activity of human H-Ras or of Dictyostelium RasG in vitro. Instead, DGAP1 bound to Dictyostelium Rac1A and human Rac1, but not to human Cdc42. DGAP1 preferentially interacted with the activated GTP-bound forms of Rac1 and Rac1A, but did not affect the GTPase activities. Since Rho-type GTPases are implicated in the formation of specific F-actin structures and in the control of cell morphology, the microfilament system of mutants that either lack or overexpress DGAP1 has been analysed. DGAP1-null mutants showed elevated levels of F-actin that was organised in large leading edges, membrane ruffles or numerous large filopods. Expression of actin fused to green fluorescent protein (GFP) was used to monitor the actin dynamics in these cells, and revealed that the F-actin cytoskeleton of DGAP1-null cells was rapidly re-arranged to form ruffles and filopods. Conversely, in DGAP1-overexpressing cells, the formation of cellular projections containing F-actin was largely suppressed. Measurement of cell migration demonstrated that DGAP1 expression is inversely correlated with the speed of cell motility.

Actin Cytoskeleton↗
PubMed1998

Grapefruit juice increases oral nimodipine bioavailability.

The bioavailability of dihydropyridine calcium channel blockers following oral administration was shown to be increased by concomitant intake of grapefruit juice for all drugs of this class tested up to now. Here we report a randomized crossover interaction study on the effects of grapefruit juice on the pharmacokinetics of nimodipine and its metabolites. Eight healthy young men (4 smokers/4 nonsmokers) were included. Nimodipine was given as a single 30 mg tablet (Nimotop) with either 250 ml of water or 250 ml of grapefruit juice (751 mg naringin/l). Drug concentrations in plasma withdrawn up to 24 hours postdose were measured by GC-ECD, and model-independent pharmacokinetic parameters were estimated. The study was handled as an equivalence problem. Point estimators and ANOVA based 90% confidence intervals (CI) were calculated for the test (= grapefruit juice period) to reference (= water period) ratios using dose-normalized concentrations. The absence of a relevant interaction was assumed if the CIs were within the 0.67-1.50 range. Cmax for nimodipine reached 124% of the reference period (90% CI 0.76-2.01), AUC was increased to 151% (90% CI 114%-200%), respectively. The null hypothesis "relevant interaction" thus could not be rejected for the primary pharmacokinetic parameters AUC and Cmax. The ratios of metabolite AUC to parent drug AUC were slightly reduced with grapefruit juice intake. Additionally, there was evidence for a more pronounced hemodynamic response in the grapefruit juice period. To avoid the interaction, nimodipine should not be taken with grapefruit juice.

Administration, Oral↗
PubMed1998

Lack of drug-drug interaction between cerivastatin and nifedipine.

Cerivastatin is a novel, potent HMG-CoA reductase inhibitor. It is primarily cleared via demethylation and hydroxylation with involvement of cytochrome P450 (CYP) 3A4 and subsequent biliary and renal excretion of the metabolites. Both cerivastatin and the dihydropyridine calcium antagonist nifedipine, which is primarily metabolized by CYP 3A4, are used concomitantly in the prevention and therapy of coronary heart disease. To study the drug-drug interaction potential, the mutual effects of cerivastatin and nifedipine were investigated in a controlled, randomized, non-blind 3-way crossover study in healthy male subjects. Single oral doses of 0.3 mg cerivastatin or of 60 mg nifedipine were administered either alone or concomitantly under fasting conditions. The mean AUC- and Cmax ratios (combination treatment versus monotherapy) including 90% confidence intervals were 1.04 (0.98 - 1.10) and 1.00 (0.93 - 1.07) for cerivastatin, and 0.98 (0.73 - 1.32) and 0.95 (0.80 - 1. 13) for nifedipine, respectively. Our results indicate that no mutual drug-drug interaction between cerivastatin and nifedipine occurs.

Administration, Oral↗
PubMed1997

Dynamic and equilibrium studies on the interaction of Ran with its effector, RanBP1.

Ran, a small nuclear GTP-binding protein, is one of the most abundant Ras-related proteins in eucaryotic cells. Ran is essential for nucleo-cytoplasmatic transport and is primarily localized in the nucleus and at the nuclear pore complex. Here, we characterize the kinetics and equilibrium of the interaction between Ran and RanBP1 by two independent biophysical approaches: fluorescence spectroscopy using analogues of guanine nucleotides and surface plasmon resonance in the BIAcore system. Both approaches result in kinetic and equilibrium data which are in good agreement with each other. Affinities of RanBP1 for Ran in the GTP-bound state were in the nanomolar range, while Ran.GDP bound RanBP1 with a dissociation constant around 10 microM. Interestingly, the difference in affinity of RanBP1 for Ran.GDP was mostly due to a dramatic increase of the dissociation rate constant. Mutant Ran protein lacking the last five amino acids of the C-terminus (RanDeltaC) is unable to facilitate nuclear import in vitro and does not bind to RanBP1. Here, we show that RanBP1 binds RanDeltaC.mGppNHp with KD values around 10 microM, as is the case for its association with full-length Ran.GDP. The loss of affinity of RanBP1 for the triphosphate form of RanDeltaC was a result of both a decrease of the association rate and a moderately increased dissociation of the RanDeltaC.RanBP1 complex. Circular dichroism spectra indicate significant changes in the secondary structure of either Ran.GppNHp, RanBP1, or both proteins upon forming a stable complex with each other.

Biological Transport↗