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H Spahn-Langguth

Publications and source records attributed to H Spahn-Langguth.

At least 37 records · Page 2Linked to original sources
PubMed1998

Radioligand-binding assay employing P-glycoprotein-overexpressing cells: testing drug affinities to the secretory intestinal multidrug transporter.

PURPOSE: To develop a rapid and reliable system for affinity determination of conventional as well as newly synthesized compounds to P-gp. METHODS: The principles of radioligand-binding assay were adapted to the human intestinal P-gp. Acceptor protein was obtained from the human carcinoma cell line Caco-2, where overexpression of P-gp was induced by growing cells in the presence of the cytostatic drug vinblastine. 3H-Verapamil was chosen as radioligand. RESULTS: The saturability and specificity of 3H-verapamil as the radioligand for the binding to P-gp was demonstrated. From concentration dependence of displacement of the radioligand by various non-labeled ligands for P-gp, affinity constants to P-gp binding sites were calculated. The binding results obtained were in agreement with those published earlier where influx and efflux experiments with cell monolayers had been conducted in order to functionally characterize the P-gp -drug interaction. CONCLUSIONS: A radioligand-binding assay on the basis of P-gp overexpressing Caco-2 cells has been developed. The method might be suitable for high-throughput screening of drug interaction with human P-gp. It will allow modeling of the interaction of drugs with the human multidrug transporter and has also the potential to serve as a high-throughput screening tool to detect compounds prone to P-gp mediated intestinal secretion and potential P-gp related drug/drug interactions in drug discovery and early development.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

P-glycoprotein transporters and the gastrointestinal tract: evaluation of the potential in vivo relevance of in vitro data employing talinolol as model compound.

Among the different application routes peroral administration remains the one most widely used. Hence, mechanisms affecting p.o. bioavailability are of particular interest, also in drug development. In recent years, intestinal drug secretion mediated by the multi-drug resistance gene product P-glycoprotein (Pgp) has been discovered as a possible mechanism of low and erratic bioavailability. Due to the saturability of this process, a dose-dependent apparent oral clearance may be observed which decreases upon increasing dose. However, in vivo intestinal secretion might be revealed only in the lower or subtherapeutic dose range. In permeability studies with Caco-2 cell monolayers, the MDR-reversing agent verapamil inhibits secretion of P-glycoprotein substrates and, hence, increases apical-to-basolateral permeability. The aim of the rat studies with talinolol presented here was to test the relevance of the intestinal secretion process as well as the extent of inhibition by verapamil in ex vivo, in situ, and in vivo talinolol/verapamil drug-drug interaction studies. Intestinal secretion of talinolol was detected indirectly in ex vivo studies via transport inhibition with verapamil and directly in in situ intestinal perfusions in rats following a talinolol i.v. bolus. Both i.v. and p.o. verapamil appear to affect the concentration-time profiles of talinolol. Relevant observations with respect to drug absorption are the decreased apparent oral clearance upon verapamil coadministration as well as the decreased tmax and mean absorption times at high verapamil doses. Talinolol may be regarded as a potential model compound for mechanistic studies on Pgp interactions, including permeability as well as binding studies and the involvement of transporters other than Pgp.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Elucidation of phase I and phase II metabolic pathways of rhein: species differences and their potential relevance.

Because of previously observed species differences in rhein tolerability, with rabbits being very susceptible to kidney disturbances, in vivo and in vitro biotransformation studies were performed to find out whether the differences in the undesired effects of rhein are associated with qualitative, species-dependent differences in its metabolism. First hints on species-dependent biotransformation profiles were obtained from in vivo experiments with 14C-labeled rhein in rat, rabbit, dog, and man. TLC-analysis of urine samples obtained after oral administration of 14C-rhein to rabbits revealed an additional, hydrophilic metabolite fraction in rabbit urine as compared with dog and human urine, all of which contain phenolic monoglucuronide and monosulfate as major metabolites. An investigation of urine samples (obtained from dogs, rabbits, rats, and human volunteers after oral application of unlabeled rhein) was conducted by means of mass spectrometric tandem techniques including on-line HPLC-MS/MS. In vitro experiments with subcellular liver fractions of rats and rabbits revealed the presence of three monohydroxylated metabolites of rhein, their quinoid oxidation products, and a bishydroxylated derivative of rhein. The hydroxylated phase I metabolites were detected as glucuronides in urine samples of all investigated species, whereas the quinoid product was present only in rabbit urine. Moreover, two regioisomeric phenolic glucuronides and sulfates or glucosides of rhein were found as major phase II metabolites in urine of all species. Furthermore, acyl glucuronides of rhein and monohydroxylated rhein and their respective isomeric acyl migration products were identified in human urine. In rabbit urine we discovered different bisglucuronides (bisphenolic glucuronide, mixed ether/ ester glucuronides), whereas in rats only the bisether/ether glucuronide was present. In addition, the investigations of dog and human urine showed the formation of two regioisomeric phenolic glucosides. With respect to a potential reactivity with endogenous macromolecules the quinoid metabolites as well as the bisester/ether glucuronides appear most relevant.

Animals↗
PubMed1996

4-(6-methoxy-2-naphthyl)-2-butyl chloroformate enantiomers: new reagents for the enantiospecific analysis of amino compounds in biogenic matrices.

(+)- and (-)-4-(6-methoxy-2-naphthyl)-2-butyl chloroformate (NAB-C) were prepared from the prochiral non-steroidal anti-inflammatory agent nabumetone with the aim of developing easily detectable chloroformate reagents for the enantiospecific HPLC analysis of amino compounds in biogenic matrices on achiral stationary phases. The new reagents were tested in the derivatization of beta-adrenoceptor antagonists and anti-arrhythmic agents and allowed derivatization in the presence of water. (+)- and (-)-NAB-C were compared with other reagents with a 6-methoxy-2-naphthyl moiety as a chromophore. The reagents were suitable for the analysis of nanogram amounts of, for example, metoprolol enantiomers in plasma, a prerequisite for application in pharmaco- or toxicokinetic studies.

Adrenergic beta-Antagonists↗
PubMed1996

Evidence for intestinal secretion as an additional clearance pathway of talinolol enantiomers: concentration- and dose-dependent absorption in vitro and in vivo.

PURPOSE: To evaluate carrier-mediated intestinal secretion of talinolol enantiomers in vivo and in vitro. METHODS: In clinical studies with i.v. and p.o. dosage of rac-talinolol (30 mg and 100 mg, resp.) performed in a small number of cholecystectomized patients total and partial clearances were determined on the basis of plasma, bile and urine concentrations. The dose-dependence of AUC was investigated in 12 healthy volunteers (25, 50, 100, and 400 mg rac-talinolol as single p.o. doses). Concentration-dependence of the permeability across Caco-2 cell monolayers included concentrations from 0.1 to 2.0 mM, inhibition by verapamil was tested at 0.5 mM. RESULTS: The total clearance as well as the apparent oral clearance (CL/F) were slightly higher for S-(-)- than for R-(+)-talinolol. Calculation of the partial clearances showed that also the residual clearance was higher for the S- than for the R-enantiomer. In the healthy volunteers, CL/F increased with increasing doses, while the S/R ratio decreased approaching unity for the highest dose. Also the results from Caco-2 cell permeation studies yielded a clear concentration-dependence with decreasing stereoselectivity for the higher concentration range. Permeability of both enantiomers was considerably higher for b-->a than a-->b transport, however, this difference disappeared when verapamil was added. CONCLUSIONS: Although not very expressed, the detected stereoselectivities indicate a preferential absorption of R-(+)-talinolol in a lower concentration and dose range, which is most probably due to a moderate stereoselectivity at the carrier system involved in intestinal secretion.

Administration, Oral↗
PubMed1996

Pharmacokinetics and drug input characteristics for a diclofenac-codeine phosphate combination following oral and rectal administration.

In a single dose cross-over study with 12 healthy male volunteers the plasma concentrations of diclofenac (CAS 15307-86-5) and codeine (CAS 76-57-3) were determined after oral and rectal application of formulations containing 50 mg of each drug. For kinetic analysis of the concentration-time profiles non-compartmental as well as compartmental procedures were used. The compartment model included two disposition compartments supplemented by a dissolution and drug absorption step. For both compounds, the AUC0-infinity values of the two treatments were similar with only a slightly higher AUC for the suppositories, which was not found to be significantly different under the employed conditions (p > 0.05). Referring to the pharmacokinetic parameters Cmax and tmax typical differences between oral and rectal formulations were observed. For the suppositories, diclofenac and codeine average peak plasma concentrations were only half as high as for the tablets, whereas the respective tmax values were doubled. The results obtained show a similar extent of diclofenac and codeine bioavailability for both administration routes, but the rate of drug input was lower for the suppositories. The total mean input time (MITtot) was found to be significantly longer for the suppositories. This seems to be caused by a slow release from the dosage form or dissolution of the drugs, which is confirmed by a longer MITtot compared to the MRTsys in most of the volunteers.

Administration, Oral↗
PubMed1996

The renin-angiotensin-aldosterone system: focus on its distinct role in arterial hypertension and its various inhibitors as a therapeutic strategy to effectively lower blood pressure.

Chronically elevated blood pressure results from pathological alterations in control systems. Current approaches to elucidate the underlying etiology strongly emphasize the (patho)physiological significance of the Renin-Angiotensin-Aldosterone System (RAAS) which interestingly interacts with the sympathetic, the cholinergic and purinergic systems. While the angiotensin-II-receptor subtype 1 (AT1), which mediates the blood-pressure-related effects of angiotensin II (All), has so far been extensively investigated, the physiological relevance of the other angiotensin-II-receptor subtypes-in particular of the AT2-receptor subtype-is about to be evolved by analysis of the various signal transduction mechanisms and by evaluation of transgenic animals, e.g. the knock-out mice, following disruption of the single A-II-receptor subtypes. Based on the clinical success of ACE inhibitors, the blockade of the Renin-Angiotensin-Aldosterone System in many different ways has been recognized as a successful strategy to effectively lower blood pressure.

Angiotensin Receptor Antagonists↗
PubMed1996

Covalent binding of acidic drugs via reactive intermediates: detection of benoxaprofen and flunoxaprofen protein adducts in biological material.

The purpose of the study was the direct detection of intact protein adducts-resulting from in-vitro incubations of flunoxaprofen- and benoxaprofen glucuronides in biological materials or originating from in vivo studies-by polyacrylamide gel electrophoresis (SDS-PAGE) followed by blotting and fluorescent scan, presumably yielding better specificity for the macromolecular binding partner and avoiding alkaline cleavage to release the aglycone. Glucuronides were isolated from urine samples or generated by incubation of aglycone with cofactors and rat liver microsomes. Following dialysis against BSA solution, SDS-PAGE and subsequent electrotransblotting were performed. Apparently, albumin represents the major binding protein for the covalent binding of these acyl glucuronides in plasma following incubation with blank plasma. In microsomal proteins two fluorescent peaks (appr. 39 and 62 KD) were identified for flunoxaprofen and benoxaprofen incubations. In vivo covalent binding was detected for both flunoxaprofen and benoxaprofen in plasma samples. For the racemically administered benoxaprofen a slight preponderance in adduct concentrations was found for the S-enantiomer. The pharmacokinetic analysis of in vivo data obtained for R/S-benoxaprofen (dose: 600 mg racemate) and S-flunoxaprofen (dose: 100 mg racemate), both of which have been withdrawn from the market, (employing a stereospecific HPLC method when analyzing volunteers' and patients' samples collected in the last 14 years, yet not stored longer than 3-4 years) demonstrated that significant amounts of glucuronides occur for both drugs (n = 2 for each compound; average Cmax values of the glucuronides: S-flunoxaprofen: 395 ng/ml; S-benoxaprofen: 775 ng/ml; R-benoxaprofen: 563 ng/ml). Presumably because of stereoinversion in humans, aglycone and glucuronide concentrations were higher for S- than for R-benoxaprofen. In vivo aglycone/glucuronide ratios were smaller for S- than for R-benoxaprofen, although in vitro incubation with human liver microsomes resulted in preferential glucuronidation of the R-enantiomer of benoxaprofen. Plasma concentration-time curves of the glucuronides paralleled those of the respective aglycones in their terminal phase. S-Benoxaprofen adduct concentrations were higher than R-benoxaprofen adduct concentrations (S: 28 ng/ml; R: 18 ng/ml covalently bound) and S-flunoxaprofen adduct concentrations with 29 ng/ml in the same range as S-beoxaprofen adducts, although for the latter the dose range as well as the respective glucuronide concentrations were higher. This indicates a higher reactivity of S-flunoxaprofen as opposed to S-benoxaprofen glucuronides.

Animals↗
PubMed1995

A new rapid and sensitive high-performance liquid chromatographic assay for diclofenac in human plasma.

A new rapid and sensitive reversed-phase HPLC method for the routine analysis of diclofenac in human plasma is described. The method shows high selectivity, sensitivity, and reproducibility employing 4'-methoxydiclofenac as internal standard (IS) with UV-detection at 282 nm. The correlation of peak area ratios (diclofenac/IS) versus diclofenac plasma concentrations are linear between 5.0-2000 ng/ml with a detection limit of 3 ng/ml. Intra- and interday precision studies yielded coefficients of variation < 6.2% for all concentrations (range 20.0-1600 ng/ml). The method was applied for the assay of diclofenac in plasma of healthy volunteers after p.o. and rectal dosage of 50 mg diclofenac sodium and was found to be highly suitable for routine analyses.

Chromatography, High Pressure Liquid↗
PubMed1995

Celiprolol double-peak occurrence and gastric motility: nonlinear mixed effects modeling of bioavailability data obtained in dogs.

Investigation of the underlying mechanism leading to inter- and intrasubject variations in the plasma concentration-time profiles of drugs (1) can considerably benefit rational drug therapy. The significant effect of gastric emptying on the rate and extent of celiprolol absorption and its role with respect to double-peak formation was demonstrated in the present study. In four dogs racemic celiprolol was dosed perorally in a crossover design during four different phases of the fasted-state gastric cycle and gastric motility was recorded simultaneously using a manometric measurement system. Intravenous doses were also given to obtain disposition and bioavailability parameters. The blood samples were assayed by a stereoselective HPLC method (2). The time to onset of the active phase of the gastric cycle showed an excellent correlation with the time to celiprolol peak concentration. Furthermore, bioavailability was increased when celiprolol was administered during the active phase. Double peaks were observed when the first active phase was relatively short, suggesting that a portion of the drug remained in the stomach until the next active phase. Population pharmacokinetic modeling of the data with a two-compartment open model with two lag times incorporating the motility data confirmed the effect of time to gastric emptying on the variability of the oral pharmacokinetics of celiprolol. The fasted-state motility phases determine the rate and extent of celiprolol absorption and influence the occurrence of double peaks. Peak plasma levels of celiprolol exhibit less variability if lag times, and therefore gastric emptying times, are taken into consideration.

Adrenergic beta-Antagonists↗
PubMed1995

New specific and sensitive HPLC-assays for ethacrynic acid and its main metabolite--the cysteine conjugate--in biological material.

A reversed-phase high-performance liquid chromatography (HPLC) method was developed and validated for the determination of the loop diuretic ethacrynic acid and its potentially active main metabolite, the ethacrynic acid-cysteine conjugate, in biological material. Simple and rapid sample preparation procedures were established using solid-phase extraction for the parent drug and direct injection after one washing step for the metabolite. HPLC separation was performed on a Spherisorb ODS II (3 microns) analytical column using isocratic elution with different mixtures of mobile phases (phosphoric acid-methanol-acetonitrile-tetrahydrofuran or triethylamine buffer-methanol, respectively). The analytes were detected by measuring the UV absorption of the eluate at 275 nm. Stability studies revealed that considerable amounts of ethacrynic acid may be released from the cysteine conjugate unless the urine samples are pH stabilized (pH 3-4). The assay provided high sensitivity with limits of quantification of 20 ng ml-1 for ethacrynic acid in plasma and urine, and 240 ng ml-1 for the cysteine conjugate in urine. All validation parameters were within the required limits. For the presented assays, the applicability to pharmacokinetic studies and routine analyses was proved.

Chromatography, High Pressure Liquid↗
PubMed1995

Dose-effect and kinetic-dynamic relationships of the beta-adrenoceptor blocking properties of various doses of talinolol in healthy humans.

Twelve healthy subjects were investigated on six separate occasions at least 1 week apart when they either received a single oral dose of 80 mg propranolol; 25, 50, 100, or 400 mg talinolol; or placebo (double-blinded, period-balanced six-way cross-over design). The subjects were investigated during supine rest and performed supine bicycle ergometry 0200, 0500, 0730, 1000, and 2400 h after dosing. Isoprenaline (ISO) and epinephrine (EPI) were infused intravenously (i.v.) at a constant infusion rate of 1 microgram/min for 10 min, at 0315 and 0400 h after dosing, respectively. At various timepoints, blood was drawn for the high-performance liquid chromatography (HPLC) determination of the plasma concentrations of talinolol's enantiomers and for the ex vivo in vitro determination of beta 1- and beta 2-adrenoceptor binding and related concentrations by radioreceptor assay (RRA). Talinolol was confirmed to bind to beta-adrenoceptors with moderate affinity but to act as a highly selective and efficient beta 1-adrenoceptor antagonist in terms of the relative degree and duration of its ergometric effects. At doses < or = 100 mg talinolol hardly altered the reduction of estimated vascular total peripheral resistance (TPR) in response to the intravenous infusion of ISO and EPI. Only at doses of 400 mg did talinolol more closely approximate the effects of propranolol, which lead to a loss of the vasodilatory actions of EPI ("EPI reversal"). On the average, there was a smoothly linear relationship between the ergometric treatment effects and log-transformed dose, the logtransformed concentrations of the S(-)-enantiomer measured by HPLC, and the RRA-derived estimated occupancies beta 1-adrenoceptors.

Adrenergic beta-Antagonists↗
PubMed1994

Simultaneous determination of (R)- and (S)-brefanolol in human plasma: high-performance liquid chromatographic assay on a chiral stationary phase.

A new method for the quantitative enantiospecific determination of rac-brefanolol, a vasodilating beta-adrenoceptor blocking agent, in human plasma is described. After an alkaline liquid-liquid extraction from biological material and a preseparation on a silica gel column with fractional collection of the eluate, the separation of the underivatized enantiomers is performed by high-performance liquid chromatography on cellulose tris-4-methylbenzoic acid polymer coated on silica gel. The UV-absorbance of the eluate was monitored at 254 nm. Determination limits are 10 ng enantiomer per ml plasma and allow the performance of pharmacokinetic studies after the aimed therapeutic dosages.

Chromatography, High Pressure Liquid↗
PubMed1994

Variable gastric emptying and discontinuities in drug absorption profiles: dependence of rates and extent of cimetidine absorption on motility phase and pH.

The influence of various fasting-state gastrointestinal parameters on variability in absorption of cimetidine was studied using simulation and cimetidine administration as a duodenal infusion and as an oral tablet in fistulated mongrel dogs. In the simulation studies, the frequency of double-peak occurrence in plasma profiles was estimated employing average gastric emptying rates as well as interdigestive-migrating-motor-complex (IMMC) phase lengths that were systematically altered. Emptying rates and phase lengths were modeled as periodic step functions. Simulations indicated that double peaks occur when gastric emptying of the drug begins in early phase I or late phase II/III, which represent the periods of very low, medium, and high gastrointestinal motility, respectively. The incidence is increased for longer phase-I duration and higher elimination rate constants. For a compound with a 2 h elimination or disposition half-life, two concentration maxima (double peaks) were found in 12% of the simulated concentration-time profiles. The double peak frequency in simulated curves was considerably higher for t1/2 < 30 min. When cimetidine was administered to dogs as a duodenal infusion in the active and quiescent motility phases, discontinuous profiles were observed, although the variability of the various parameters was reduced when compared. Pharmacokinetic models were set up that were characterized by multi-segmental input (one- to 3-lag-time models were used) for the profiles resulting from oral and duodenal administration. The lag time for the first process characterized the onset of absorption. A significant difference between phases was detected for infusions at pH 8, where the initial lag time was longer in the quiescent phase. The mean input time (MIT) was calculated as the integral input parameter. There was a tendency for the MIT to be higher for pH 6 infusions than for pH 4 and pH 8. Bioavailability analysis indicated that cimetidine was more rapidly and completely absorbed at pH 8 than at pH 6. Bioavailability was also slightly higher at pH 4 than at pH 6. We concluded that gastric emptying increased the variability of the cimetidine concentration-against-time profiles and that it plays a role with respect to double-peak occurrence, although it is only one of several causative factors.

Administration, Oral↗
PubMed1994

The effect of ciclotropium on human heart rate.

Ciclotropium is a recently developed parasympathicolytic agent. Plasma concentration and heart rate increase (the most prominent anticholinergic effects) were measured in 12 healthy subjects before, during and after a 15-min intravenous infusion of 10 mg ciclotropium. The effect was described by using either a linear or a nonlinear (Emax) effect model linked to a linear three-compartment kinetic model via an effect compartment. Maximum heart rate increase was 33 (10) beats.min-1, and half-value duration of effect was 41 (9) min. Total plasma clearance was 0.51 (0.13) l.min-1, and mean terminal elimination half-life was 12(4) h, whereas the equilibration half-lives of drug removal from the effect compartment ranged from 2 to 14 min.

Adult↗
PubMed1994

Reversible binding of tolmetin, zomepirac, and their glucuronide conjugates to human serum albumin and plasma.

Acyl glucuronides of drugs and bilirubin have been shown in the past decade to be reactive metabolites undergoing acyl migration and irreversible binding. The latter reaction has been hypothesized to be facilitated by or to proceed through the formation of a reversible complex. Furthermore, it has been suggested that the decreased binding seen in patients with compromised excretory function may be due to competition by elevated plasma concentrations of the glucuronides. In these reversible binding studies, we characterized the extent and the "site" of binding of tolmetin, zomepirac, their glucuronides and isomeric conjugates. We also examined the displacement between the parent drugs and their glucuronide conjugates using a rapid ultrafiltration method. Tolmetin exhibited three classes of binding sites with a primary association constant of 1.7 x 10(6) M-1 (Kd1 = 0.60 microM). The primary association constant of zomepirac (1.16 x 10(6) M-1, Kd1 = 0.86 microM) is similar to that of tolmetin. The beta 1 and alpha/beta 3 glucuronides of both compounds bind to a lesser extent than their parent aglycones. The isomeric glucuronide conjugates of both compounds showed much stronger binding than the beta/1 conjugates. Of the four glucuronides investigated, tolmetin glucuronide-alpha/beta 3 isomer was bound by fatty acid free human serum albumin with the highest affinity (4.6 x 10(5) M-1, Kd = 2.22 microM). Protein binding of the parent drugs and conjugates were decreased significantly at pH 5.0. In displacement studies, except for salicylate and acetylsalicylate, drugs known to bind to Sites I and II as well as the digitoxin and tamoxifen binding sites had little inhibitory effect on the binding of tolmetin, zomepirac, and their glucuronide conjugates.

Adult↗