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Biomedical subjects

G Geisslinger

Publications and source records attributed to G Geisslinger.

At least 91 records · Page 5Linked to original sources
PubMed1997

Lack of analgesic activity of morphine-6-glucuronide after short-term intravenous administration in healthy volunteers.

BACKGROUND: The analgesic activity of morphine-6-glucuronide (M-6-G) is well recognized for its contribution to the effects of morphine and its possible use as an opioid analgesic with a wider therapeutic range than morphine. The present study attempted to quantify the relative contribution of M-6-G to analgesia observed after systemic administration of morphine. METHODS: In a placebo-controlled, sixfold crossover study in 20 healthy men, the effects of M-6-G were assessed at steady-state plasma concentrations of M-6-G identical to and two and three times higher than those measured after administration of morphine. Morphine and M-6-G were administered as an intravenous bolus followed by infusion over 4 h. Dosage A was M-6-G-bolus of 0.015 mg/kg plus infusion of 0.0072 mg x kg(-1) x h(-1). Dosage B was M-6-G-bolus of 0.029 mg/kg plus infusion of 0.014 mg x kg(-1) x h(-1). Dosage C was M-6-G-bolus of 0.044 mg/kg plus infusion of 0.022 mg x kg(-1) x h(-1). Dosage D was a morphine bolus of 0.14 mg/kg plus infusion of 0.05 mg x kg(-1) x h(-1) for 4 h. Dosage E was M-6-G combined with morphine (doses A + D). Dosage F was a placebo. The analgesic effects of M-6-G and morphine were measured before administration of the bolus and after 3.5 h using an experimental pain model based on pain-related cortical potentials and pain ratings after specific stimulation of the nasal nociceptor with short pulses of gaseous carbon dioxide. RESULTS: Morphine significantly reduced subjective and objective pain correlates compared with placebo. In contrast, M-6-G produced no statistically significant effects. The addition of M-6-G to morphine did not increase the effects of morphine. Morphine produced significantly more side effects than M-6-G. CONCLUSION: After short-term intravenous administration at doses that produce plasma concentrations of M-6-G similar to those seen after administration of morphine, M-6-G had no analgesic effects in the present placebo-controlled study in healthy volunteers.

Adult↗
PubMed1997

Molecular cloning and expression of a 2-arylpropionyl-coenzyme A epimerase: a key enzyme in the inversion metabolism of ibuprofen.

The 2-arylpropionic acid derivatives, including ibuprofen, are the most widely used anti-inflammatory analgesic cyclooxygenase inhibitors. The (-)-R-enantiomer, which is inactive in terms of cyclooxygenase inhibition, is epimerized in vivo via the 2-arylpropionyl-coenzyme A (CoA) epimerase to the cyclooxygenase-inhibiting (+)-S-enantiomer. The molecular biology of the epimerization pathway is largely unknown. To clarify this mechanism, the sequence of the 2-arylpropionyl-CoA epimerase was identified, and the enzyme cloned and expressed. A cDNA clone encoding the 2-arylpropionyl-CoA epimerase was isolated from a rat liver cDNA library. The nucleotide and the deduced amino acid sequence of this enzyme was determined. Significant amino acid sequence similarity was found between the rat epimerase and carnitine dehydratases from Caenorhabditis elegans (41%) and Escherichia coli (27%). A bacterial expression system (E. coli strain M15[pREP4]) was used to express the epimerase protein, representing up to 20-30% of the total cellular E. coli protein. The expression of the epimerase was confirmed with Western blots using specific anti-epimerase antibodies and by measuring the rate of inversion of (R)-ibuprofenoyl-CoA. Northern blot analysis revealed a prominent 1.9-kb mRNA transcript in different rat tissues. In addition to its obvious importance in drug metabolism, the homology of the epimerase with carnitine dehydratases from several species suggests that this protein, which up to now has only been characterized as having a role in drug transformation, has a function in lipid metabolism.

Amino Acid Sequence↗
PubMed1997

Pharmacokinetics of imipenem-cilastatin in critically ill patients undergoing continuous venovenous hemofiltration.

The pharmacokinetics of imipenem-cilastatin were investigated in 12 critically ill patients with acute renal failure (ARF) managed by continuous veno-venous hemofiltration (CVVH) while receiving a fixed combination of 500 mg of imipenem-cilastatin intravenously three or four times daily. No adverse drug reactions were observed. Plasma and hemofiltrate samples were taken at specified times during one dosing interval, and the concentrations of imipenem and cilastatin were determined by high-performance liquid chromatography. Pharmacokinetic variables were calculated by a first-order, two-compartment pharmacokinetic model for both substances. Total clearances of imipenem and cilastatin (mean +/- standard deviations) were 122.2 +/- 28.6 and 29.2 +/- 13.7 ml/min, respectively, with hemofiltration clearances of 22.9 +/- 2.5 and 16.1 +/- 3.1 ml/min, respectively, and nonrenal, nonhemofiltration clearances of 90.8 +/- 26.3 and 13.2 +/- 13.9 ml/min, respectively. Mean imipenem dosage requirements were approximately 2,000 mg/24 h (2,111.8 +/- 493.4 mg/24 h). They were calculated in order to achieve an average steady-state concentration of 12 mg/liter to ensure that concentrations in plasma exceeded the MICs at which 90% of intermediately resistent bacteria are inhibited (8 mg/liter) during the majority of the dosing interval. By contrast, the recommended dosage for patients with end-stage renal failure (ESRF) and infections caused by intermediately resistant bacteria is 1,000 mg/24 h. This remarkable difference may be due (i) to differences in the nonrenal clearance of imipenem between patients with ARF and ESRF and (ii) to the additional clearance by the hemofilter. Since the total clearance of cilastatin was low, marked accumulation occurred, and this was particularly pronounced in patients with additional liver dysfunction. Thus, in patients with ARF managed by CVVH, rather high imipenem doses are required, and these inevitably result in a marked accumulation of cilastatin. The doses of imipenem recommended for patients with ESRF, however, will lead to underdosing and inadequate antibiotic therapy.

Acute Kidney Injury↗
PubMed1997

Pharmacokinetic-pharmacodynamic relationships for analgesics.

A major goal of current pain research is to develop scientifically-based guidelines to optimize selection of analgesic drug doses and control pain. Numerous clinical studies have shown that the drug dose required to effectively alleviate pain is often highly variable, both between patients and between pain episodes in individual patients. This high variability makes it difficult to predict appropriate dosing regimens that will adequately control pain in the individual patient. The result is a "trial and error" approach to analgesic therapy. Experimental tools that measure analgesic response and drug disposition after administration of analgesics can be used to better predict the therapeutic effects of analgesics in individual patients. The approach defines factors that contribute to variability in therapeutic response. Pharmacokinetic-pharmacodynamic (PK/PD) modeling involves analysis of drug disposition data and drug efficacy data. Modeling depends on sensitive and reliable methods to quantify both pain and plasma (or other body fluid) levels of analgesic agents. Two major approaches have been used to quantify pain. The first utilizes subjective reports from patients, while the second employs physiological correlates of pain, such as evoked potentials. Results from PK/PD analysis that successfully identify a relationship between drug dose, drug concentration, and effect can be used to predict the effects of drug dose on analgesic effect in individuals. The ultimate goal is to provide patients with better pain relief by understanding variables that affect the analgesic concentration/effect relationship. This review examines the available pharmacokinetic-pharmacodynamic (PK/PD) data for selected opioid and nonopioid analgesics. Even though most analgesics are used clinically in multiple doses, the majority of PK/PD studies conducted to date evaluate single dose effects. Further studies with multiple doses are required to evaluate the validity of PK/PD relationships defined from single dose studies.

Analgesics↗
PubMed1996

Isolation and characterization of rat liver microsomal R-ibuprofenoyl-CoA synthetase.

Microsomal long-chain acyl-CoA synthetase (EC 6.1.2.3.) has been suggested to be involved in the stereoselective formation of the CoA thioester of ibuprofen. In this study, we demonstrated that the microsomal enzyme from rat liver responsible for palmitoyl-CoA synthesis also catalyzes the formation of R-ibuprofenoyl-CoA in a Mg(2+)- and ATP-dependent process. Long-chain acyl-CoA synthetase from rat liver microsomes was purified to homogeneity as evidenced by SDS-gel electrophoresis. Simultaneous measurements of palmitoyl-CoA and R-ibuprofenoyl-CoA formation with HPLC in various fractions and purification steps during protein isolation revealed a high correlation between both activities. The purification procedure included solubilization of the microsomes obtained from rat livers with Triton X-100 and subsequent chromatography of the 100,000 x g supernatant on blue-sepharose, hydroxyapatite, and phosphocellulose. The purified enzyme exhibited an apparent molecular weight of 72 kDa as estimated by SDS gel electrophoresis, with specific activities of 71 nmol.min-1.mg-1 protein and 901 nmol.min-1.mg-1 protein for formation of R-ibuprofenoyl-CoA and palmitoyl-CoA, respectively. Palmitoyl-CoA formation catalyzed by the purified enzyme exhibited biphasic kinetics indicative of two isoforms, a high-affinity (KM 0.13 +/- 0.11 microM), low-capacity form and a low-affinity (KM 81 +/- 11.5 microM), high-capacity form. In contrast, measurement of R-ibuprofenoyl-CoA synthesis over a concentration range from 5 to 3000 microM showed the participation of a single CoA ligase with a KM of 184 +/- 19 microM, corresponding to the low-affinity isoform of palmitoyl-CoA synthesis with a marked enantioselectivity towards the R-form of ibuprofen. R-ibuprofenoyl-CoA formation of the enzyme preparation was inhibited by palmitic acid (KI 13.5 +/- 0.5 microM) and S-ibuprofen (KI 405 +/- 10 microM). In summary, these data give strong evidence for the identity of R-ibuprofenoyl-CoA and long-chain acyl-CoA synthetase.

Animals↗
PubMed1996

Up-regulation of cyclooxygenase-2 mRNA in the rat spinal cord following peripheral inflammation.

Prostaglandins (PG) have been described as mediators in spinal nociceptive processing after peripheral inflammation. Enzymes essential for PG biosynthesis, cyclooxygenase isozymes COX-1 and COX-2, have not yet been investigated in the spinal cord. In two studies on rats with adjuvant-induced peripheral inflammation levels of mRNA expression of both COX isoforms were analyzed in the lumbar section of the spinal cord using reverse transcription-polymerase chain reaction (RT-PCR) technique. We could show that mRNA of both COX isoforms is expressed constitutively in the spinal cord with COX-2 as the predominant isoform. Six hours after induction of peripheral inflammation, levels of COX-2 mRNA expression were raised significantly in respect to untreated control rats and returned to baseline within 3 days after induction of inflammation. COX-2 might therefore be regarded as the COX isozyme responsible for spinal PG release in nociceptive processing under a peripheral inflammatory stimulus.

Animals↗
PubMed1996

Stereospecific determination of tiaprofenic acid in plasma: problems with drug degradation.

A sensitive stereospecific high-performance liquid chromatographic assay for the quantification of tiaprofenic acid in human plasma was developed. The procedure involved extraction of tiaprofenic acid from acidified plasma into hexanediethyl ether (8:2, v/v). Stereospecific separation was achieved with a prepacked alpha1-acid glycoprotein column without derivatization. The mobile phase consisted of 2% 2-propanol in 0.01 M phosphate buffer, pH 6.5. Tiaprofenic acid was detected at 317 nm. The limit of quantification was found to be 25 ng/ml for each enantiomer using a 0.5 ml plasma sample. The assay was reproducible and accurate to be applied to the stereoselective pharmacokinetic analysis of tiaprofenic acid in plasma. Because of photoinstability of tiaprofenic acid plasma sampling and sample extraction should be performed under light protection.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1996

New insights into the site and mode of antinociceptive action of flurbiprofen enantiomers.

The S-enantiomer of flurbiprofen has been shown to have both antiinflammatory and antinociceptive effects, whereas R-flurbiprofen is antinociceptive but not antiinflammatory. Importantly, only S-flurbiprofen inhibited prostaglandin biosynthesis in vitro at therapeutic concentrations. R-flurbiprofen did not undergo significant chiral inversion to S-flurbiprofen in rats and humans. A study was conducted to gain new insight into the possible sites and modes of action of flurbiprofen enantiomers. In a modified Randall Selitto assay, both enantiomers were antinociceptive in a dose-dependent manner after systemic administration. After local administration into the inflamed paw, only S-flurbiprofen produced significant dose-related antinociception. In a physiologic study, we recorded extracellularly from nociceptive spinal cord neurons that were rendered hyperexcitable. Intravenous administration of R- and S-flurbiprofen reduced responses of neurons to pressure applied to the inflamed knee and the noninflamed ankle and paw in a dose-dependent manner. When injected directly into the knee joint, only S-flurbiprofen but not R-flurbiprofen reduced responses to pressure. These results suggest a central site of antinociceptive action for R- and S-flurbiprofen and an additional peripheral site for S-flurbiprofen. The findings may be of clinical relevance, as it was demonstrated that both enantiomers also were antinociceptive in humans. Because R-flurbiprofen caused less toxicity in rats than the S-enantiomer or the racemic compound, a reduction in the quantitatively most important side effects in the gastrointestinal tract might be achieved with the use of R-flurbiprofen for pain therapy.

Analgesics↗
PubMed1996

Pharmacokinetics of morphine and its glucuronides after intravenous infusion of morphine and morphine-6-glucuronide in healthy volunteers.

Steady-state pharmacokinetics of morphine and morphine-6-glucuronide (M-6-G) after intravenous administration of either morphine or M-6-G were determined in healthy volunteers. With a dosing regimen calculated on the basis of data obtained in a first series of experiments in four subjects (morphine: intravenous loading dose of 0.24 mg/kg for 5 minutes and an intravenous infusion of 0.069 mg.kg-1.hr-1 for 4 hours; M-6-G: loading dose of 0.011 mg/kg for 5 minutes and an infusion of 0.006 mg.kg-1.hr-1 for 4 hours), it was possible to yield plasma concentrations of morphine and M-6-G in another four subjects close to predefined targeted levels (35 and 45.5 ng/ml morphine and M-6-G, respectively). This dosing regimen may be used in further pharmacodynamic studies to compare the analgesic effects of morphine and M-6-G. In addition, metabolite kinetics of M-6-G were calculated as a function of time with use of a linear systems approach to the estimation of rate and fraction of morphine glucuronidation to M-6-G.

Adult↗
PubMed1996

A new reliable chemiluminescence immunoassay (CLIA) for prostaglandin E2 using enhanced luminol as substrate.

A sensitive and reliable chemiluminescence immunoassay suitable for the quantitative determination of prostaglandin E2 (PGE2) has been developed using 96 well microtiter plates (MTP). The assay is based on a competitive reaction between a highly specific monoclonal anti-PGE2 antibody (mouse), free antigen and solid phase bound antigen. The MTP was first coated with a bovine serum albumin (BSA)-PGE2 conjugate. Then, after preincubating, the anti-PGE2 antibody (Ab) and the analyte were added. The remaining amount of free antibody was captured by the solid phase bound BSA-PGE2 conjugate. The monoclonal antibody captured on the MTP was determined using biotinylated anti-mouse-Ab and a complex of avidin and biotin-labelled horseradish peroxidase (HRP). Substrate for HRP was the cyclic diacyl hydrazide compound luminol, enhanced by p-iodophenol. Photons emitted during the reaction were measured using a photomultiplier tube. The assay has been validated with assay buffer and human plasma over a concentration range of 10-50,000 pg/ml. The lower limit of quantification is 100 pg/ml (2 pg/well) and 150 pg/ml (3 pg/well) for buffer and plasma, respectively. The intra-day coefficients of variation (CV) for the range of 100-50,000 pg/ml are 3.2-8.9% (buffer) and 4.2-17.7% (plasma) and inter-day CV are 2.9-19.8% (buffer) and 3.6-21.2% (plasma). The method can be used for quantification of PGE2 in biological fluids like plasma and suction blister fluid.

Animals↗
PubMed1996

Pharmacokinetic-pharmacodynamic modeling of the new steroid hypnotic eltanolone in healthy volunteers.

BACKGROUND: In the last 4 y, several authors have reported largely satisfactory results using the new steroid intravenous anesthetic eltanolone (pregnanolone) to induce anesthesia. Until now, however, no investigations have addressed the infusion pharmacokinetics of eltanolone or used electroencephalographic effect data for full pharmacodynamic modeling. Thus the authors conducted a study to evaluate the pharmacokinetic and pharmacodynamic properties of eltanolone after infusion in healthy volunteers. METHODS: Eltanolone emulsion was administered to 12 healthy men using a computer-controlled infusion device. Linearly increasing serum concentrations were generated for two consecutive infusions with an anticipated slope of 0.075 microgram.ml-1.min-1 and a targeted concentration of 2-2.5 micrograms/ml. During and after the infusion, electroencephalographic data were recorded as a continuous pharmacodynamic parameter to measure the hypnotic effect. In addition, blood pressure, heart rate, pulse oximetry, clinical signs of anesthesia, and any undesirable effects were recorded. The appearance of burst suppression periods in the raw electroencephalographic wave form was used as an end point for the infusion. Arterial blood samples were drawn frequently until 720 min after the cessation of the last infusion cycle. Eltanolone serum concentrations were measured using a specific gas chromatography-mass spectrometry assay. Nonlinear regression analysis was used to relate a power spectral parameter of the electroencephalograph (median frequency) to the serum concentration using a sigmoid Emax model, including an effect compartment to minimize possible hysteresis. Population pharmacokinetics were analyzed using an open three-compartment model. RESULTS: The pharmacokinetic model parameters of eltanolone were characterized by a high total clearance (1.75 +/- 0.22 l/min), small volumes of distribution (Vc = 7.65 +/- 3.40 l; Vdss = 91.6 +/- 22 l), and relatively short half-lives (t1/2 alpha = 1.5 +/- 0.6 min; t1/2 beta = 27 +/- 5 min; t1/2 gamma = 184 +/- 32 min). With regard to the pharmacodynamic model parameters, eltanolone proved to be a potent hypnotic agent (Cp50 = 0.46 +/- 0.09 microgram/ml). The hypnotic effect coincided with a remarkable hysteresis between serum concentration and biophase, determined by an equilibration half-life of 8 min (ke0 = 0.087 +/- 0.013 min-1). All volunteers breathed spontaneously during the entire observation period and showed no clinically relevant hemodynamic changes. One volunteer experienced a convulsion while awakening. CONCLUSIONS: Eltanolone is a new potent steroid-type hypnotic agent with rapid elimination characteristics. Although it is short-acting, the remarkable hysteresis limits the control and might complicate administration of eltanolone if it is used as a component of a complete intravenous anesthesia regimen. Furthermore, it involves the potential disadvantage of drug accumulation and it prolongs recovery if larger-than-necessary doses are used to induce anesthesia rapidly.

Adult↗
PubMed1996

Transfer of different nonsteroidal antiinflammatory drugs via the lymphatic system in the rat.

The motility of lymphatic vessels is regulated by arachidonate metabolites and can, therefore, be altered by cyclooxygenase blockers such as nonsteroidal antiinflammatory drugs (NSAIDs). To investigate the transfer of different NSAIDs via the lymphatic system, pharmacokinetics in plasma and lymph after peroral administration of three model compounds (namely, racemic ibuprofen, tenoxicam, and nabumetone) were investigated in rats. Microsurgical cannulation of the thoracic duct allowed cumulative sampling of lymph fluid up to 48 hr (N = 16). Pharmacokinetic parameters in plasma were determined in a control group (N = 12). Concentrations of R-ibuprofen, S-ibuprofen, tenoxicam, nabumetone, and the metabolites OH-ibuprofen, COOH-ibuprofen and 6-methoxy-2-naphthylacetic acid (6MNA; a metabolite of nabumetone) were monitored in lymph and plasma by HPLC. The observed peak concentrations in lymph of the investigated drugs are likely to produce different biological effects with regard to cyclooxygenase-1 inhibition. To quantify the appearance in lymph fluid, a "lymphatic clearance" of the investigated compounds was defined by dividing the amount recovered in lymph by the corresponding area under the plasma concentration-time curve. The "lymphatic clearance" differed substantially between the investigated compounds (mean +/- SD: R-ibuprofen, 19.8 +/- 9.4; S-ibuprofen, 9.6 +/- 3.6; tenoxicam, 32.5 +/- 31.3; nabumetone, 133.6 +/- 75.2; 6MNA, 18.3 +/- 8.5 microliters/min/kg). Overall recovery of the investigated compounds in lymph did not exceed 5% of the doses given. The known fact that lymphatic drainage is regulated by arachidonate metabolites suggests that NSAIDs differing in their transfer via the lymphatic system could result in different responses of lymphatic vessels to an inflammatory fluid load.

Animals↗
PubMed1996

The effects on platelet aggregation and prostanoid biosynthesis of two parenteral analgesics: ketorolac tromethamine and dipyrone.

The pharmacokinetics and effects on platelet function of dipyrone (1.0 g; 2.5 g; i.v.) and ketorolac tromethamine (30 mg; i.m.) were studied in a three-way crossover study in twelve healthy subjects. The biosynthesis of thromboxane A2 in clotting whole blood ex vivo as well as collagen-induced platelet aggregation were determined before and up to 48 h after administration. Both prostanoid biosynthesis and platelet aggregation were inhibited by ketorolac tromethamine for a significantly longer period of time than by both doses of dipyrone. The changes in platelet functions correlated well with the serum concentrations of ketorolac or 4-methylaminoantipyrine and 4-aminoantipyrine. Using the sigmoidal Emax model the mean serum concentration (SD) of ketorolac, 4-methylaminoantipyrine and 4-aminoantipyrine inhibiting platelet TXB2 generation by 50% (EC50) in vitro was found to be 0.088 +/- 0.031, 1.2 +/- 0.3 and 10.2 +/- 3.4 micrograms ml-1, respectively. In conclusion the recovery of platelet function after dipyrone administration is faster as compared to ketorolac tromethamine. This is in line with clinical observations and may be an advantage when these drugs are given as postoperative analgesics at the doses tested.

Adult↗
PubMed1995

2-Arylpropionyl-CoA epimerase: partial peptide sequences and tissue localization.

The R-enantiomers of 2-arylpropionic acids (2-APAs) such as ibuprofen (IBU) exhibit the phenomenon of species- and substrate-dependent metabolic chiral inversion. Only R-enantiomers are activated to acyl-CoA-thioesters by an acyl-CoA-synthetase via an adenylate intermediate. The acyl-CoA-thioesters are substrates for an epimerase, which is responsible for chiral inversion. A 42 kDa epimerase from the cytosolic fraction of rat livers was isolated and purified to homogeneity. Polyclonal antibodies were raised against the epimerase in rabbits. The anti-epimerase antibodies were used for affinity column chromatography to separate homogeneous protein for amino acid sequence analysis. Sequence data analysis of 3 internal peptide sequences showed 50% and more homology with regions of enzymes involved in fatty acid metabolism. The polyclonal anti-epimerase antibodies were used to analyze the tissue distribution of the in guinea pigs and rats by Western blot analysis. Furthermore, the correlation of inversion enzyme activity in various tissues under comparable incubation conditions and cross-reactivity in Western blot analysis was investigated.

Amino Acid Sequence↗
PubMed1995

Inflammatory models of cutaneous hyperalgesia are sensitive to effects of ibuprofen in man.

A new experimental procedure was developed to quantify the analgesic actions of non-steroidal anti-inflammatory drugs (NSAIDs) in healthy human subjects. In order to mimic the clinical situation, the drug was 'therapeutically' administered 1 day after induction of inflammation by freezing a small skin area. The procedure was easily tolerated and led to a marked hyperalgesia without ongoing pain which was tested using mechanical impact stimulation and magnitude estimation. For comparison, we used a previously established model of repeated noxious pinching of an interdigital skin web which induces a hyperalgesia to pressure (rated via visual analogue scale), and topical application of capsaicin which leads to quantifiable flare and allodynia responses. The effects of a cumulative drug regime of ibuprofen in 2 different doses (3 x 400 mg and 3 x 800 mg at 2-h intervals) were tested versus placebo using a double-blind cross-over design with 24 volunteers of either gender. Ibuprofen caused a significant suppression of the hyperalgesia to repeated pinching and of the hyperalgesia to impact stimulation following freeze trauma. In contrast, there was no effect on the areas of flare and allodynia induced by capsaicin application and on the impact evoked sensations from untreated skin. The two dosages of ibuprofen, however, appeared to be equally effective in a way that suggests a plateauing of the antihyperalgesic effect. The two models in which hyperalgesia is affected by ibuprofen, i.e., repeated pinching and impact stimulation after freeze trauma, seem to provide comparable sensitivity. The freeze model may in the future have the advantage to allow for a better temporal resolution of the drug's action profile.

Adult↗