Gerben A E van 't Klooster (original) (raw)

Papers by Gerben A E van 't Klooster

Research paper thumbnail of Improved high-performance liquid chromatographic method for the determination of ethylmorphine and its metabolites in microsomal incubations and cell culture media

Journal of Chromatography A

Ethylmorphine N-demethylation is used as a marker pathway in studies of rat cytochrome P450 3A an... more Ethylmorphine N-demethylation is used as a marker pathway in studies of rat cytochrome P450 3A and 2C11 biotransformations. At present, microsomal activities are generally measured by a colorimetric determination of the formed formaldehyde. In the present study, a high-performance liquid chromatographic method of separating and quantifying both the N-demethylated (norethylmorphine) and the O-de-ethylated (morphine) metabolites is described. Either samples are extracted with ethyl acetate or proteins are precipitated with zinc sulphate-barium hydroxide. Separation is achieved on a CN reversed-phase column, using a mobile phase of phosphate buffer (pH 4.5)-acetonitrile (90:10, v/v). At a flow-rate of 1.5 ml/min, the analysis time is 30 min. The limit of detection (ultraviolet, 210 nm) for ethylmorphine and its metabolites is 0.5 micrograms/ml.

Research paper thumbnail of Improved high-performance liquid chromatographic method for the determination of coenzyme Q10 in plasma

Journal of Chromatography A

Coenzyme (Co) Q10 was dissociated from lipoproteins in plasma by treatment with methanol and extr... more Coenzyme (Co) Q10 was dissociated from lipoproteins in plasma by treatment with methanol and extraction with n-hexane. Subsequent clean-up on silica gel and C18 solid-phase extraction cartridges with complete recovery (99 +/- 1.2%) produced a clean extract. High-performance liquid chromatographic (HPLC) separation was performed on a C18 reversed-phase column. Three simple, rapid procedures are presented: HPLC with final UV (275 nm) detection, a microanalysis utilizing a three-electrode electrochemical detector and a microanalysis with column-switching HPLC and electrochemical detection. The methods correlate very well with classical ethanol-n-hexane extraction with UV detection. The identity and purity of the Co Q10 peak were investigated and the resulting methods were concluded to be suitable for total plasma Co Q10 determination. The average level in healthy subjects was 0.80 +/- 0.20 mg/l; the minimum detectable Co Q10 plasma level was 0.05 and 0.005 mg/l for UV and electrochemic...

Research paper thumbnail of Correlations between Factors Determining the Pharmacokinetics and Antiviral Activity of HIV-1 Non-Nucleoside Reverse Transcriptase Inhibitors of the Diaryltriazine and Diarylpyrimidine Classes of Compounds

Drugs in R & D, 2004

To investigate the important factors that determine the bioavailability and the antiviral activit... more To investigate the important factors that determine the bioavailability and the antiviral activity of the diaryltriazine (DATA) and diarylpyrimidine (DAPY) non-nucleoside reverse transcriptase inhibitors (NNRTIs) of HIV-1 in animal species and humans using cell-based assays, physicochemical and computed parameters. This naturalistic study included 15 parameters ranging from molecular mechanics calculations to phase I clinical trials. The calculated parameters were solvent-accessible surface area (SASA), polar surface area and Gibbs free energy of solvation. Physicochemical parameters comprised lipophilicity (octanol/water partition coefficient [cLogP]), ionisation constant (pKa), solubility and aggregate radius. Cell-based assays included human colonic adenocarcinoma cell (Caco-2) permeability (transepithelial transport), drug metabolism and antiviral activity (negative logarithm of the molar effective concentration inhibiting viral replication by 50% [pEC50]). Exposure was tested in rats, dogs and human volunteers. Of the 15 parameters, eight correlated consistently among one another. Exposure (area under the plasma concentration-time curve [AUC]) in humans correlated positively with that in rats (r = 1.00), with transepithelial transport (r = 0.83), lipophilicity (r = 0.60), ionisability (r = 0.89), hydrodynamic radius of aggregates (r = 0.66) and with antiviral activity (r = 0.61). Exposure in humans was also seen to correlate negatively with SASA (r = -0.89). No consistent correlation was found between exposure in dogs and the eight parameters. Of the 14 DATA/DAPY molecules, 11 form aggregates with radii between 34 and 100 nm. We observed correlations between exposure in humans with exposure in rats, transepithelial transport (Caco-2 cells), ionisability, lipophilicity, aggregate radius and SASA in the class of DATA/DAPY NNRTI compounds. The lipophilic DATA/DAPY compounds form aggregates. It can be assumed that absorption in the intestinal tract and endocytosis in infected cells of these lipophilic compounds are governed by the common phenomenon of aggregate formation. As the lymphatic system offers a pathway for intestinal uptake of aggregates, this may offer a therapeutic advantage in the treatment of HIV-1 infection. Although it was not the objective of the study, we found that the rat was a better in vivo model than the dog for the prediction of systemic exposure in this particular set of compounds.

Research paper thumbnail of Efficacy, Safety, Pharmacokinetics, and Pharmacodynamics of Filgotinib, a Selective JAK-1 Inhibitor, After Short-Term Treatment of Rheumatoid Arthritis: Results of Two Randomized Phase IIa Trials

Research paper thumbnail of Hepatic cytochrome P450 induction in goatsEffects of model inducers on the metabolism of alkoxyresorufins, testosterone and ethylmorphine, and on apoprotein and mRNA levels

Biochemical Pharmacology, 1993

Male and female African dwarf goats were treated orally with phenobarbital (PB) or triacetylolean... more Male and female African dwarf goats were treated orally with phenobarbital (PB) or triacetyloleandomycin (TAO), or subcutaneously with beta-naphthoflavone (BNF). Hepatic microsomal cytochrome P450 content was increased by PB and TAO, but not by BNF. PB effects on P450 activities were non-selective: ethoxyresorufin deethylase (EROD) and pentoxyresorufin depentylase (PROD), hydroxylation of testosterone (TST) and demethylation of ethylmorphine (ETM) were all induced by a factor of 2-3. A similar non-selective induction was observed with TAO, except for EROD and PROD (no effects). After PB and TAO treatment, increased levels of a protein cross-reactive with anti-sheep P450 3A and 2B were found. Thus, in dwarf goats, both PB and TAO appeared to be P450 3A inducers. Selective PB effects related to a P450 2B form on PROD are lacking but 16 alpha-hydroxylation of TST was induced markedly. At the mRNA level, PB induced an mRNA that showed good sequence homology with a human P450 3A4 cDNA probe, rather than with a rat 3A1 probe. BNF selectively induced EROD, whereas TST hydroxylation and ETM dealkylation were inhibited. With BNF-treated animals, increased concentrations of a protein cross-reactive with anti-rat P450 1A1/1A2 and of an mRNA that showed homology with a human 1A1 cDNA probe, but not with a mouse 1A1/1A2 probe, were observed.

Research paper thumbnail of Improved high-performance liquid chromatographic method for the determination of ethylmorphine and its metabolites in microsomal incubations and cell culture media

Journal of Chromatography B: Biomedical Sciences and Applications, 1992

Research paper thumbnail of Hepatic cytochrome P450 induction in goats. Effects of model inducers on the metabolism of alkoxyresorufins, testosterone and ethylmorphine, and on apoprotein and mRNA levels

Biochemical Pharmacology

Male and female African dwarf goats were treated orally with phenobarbital (PB) or triacetylolean... more Male and female African dwarf goats were treated orally with phenobarbital (PB) or triacetyloleandomycin (TAO), or subcutaneously with beta-naphthoflavone (BNF). Hepatic microsomal cytochrome P450 content was increased by PB and TAO, but not by BNF. PB effects on P450 activities were non-selective: ethoxyresorufin deethylase (EROD) and pentoxyresorufin depentylase (PROD), hydroxylation of testosterone (TST) and demethylation of ethylmorphine (ETM) were all induced by a factor of 2-3. A similar non-selective induction was observed with TAO, except for EROD and PROD (no effects). After PB and TAO treatment, increased levels of a protein cross-reactive with anti-sheep P450 3A and 2B were found. Thus, in dwarf goats, both PB and TAO appeared to be P450 3A inducers. Selective PB effects related to a P450 2B form on PROD are lacking but 16 alpha-hydroxylation of TST was induced markedly. At the mRNA level, PB induced an mRNA that showed good sequence homology with a human P450 3A4 cDNA pr...

Research paper thumbnail of Primary bovine hepatocytes in the study of cytokine induced acute-phase protein secretion in vitro

Veterinary Immunology and Immunopathology, 1996

To investigate the utility of primary cultures of bovine hepatocytes for compartmentalized acute ... more To investigate the utility of primary cultures of bovine hepatocytes for compartmentalized acute phase protein studies the secretion of serum amyloid-A (SAA) and haptoglobin (Hp) was measured after stimulation by pro-inflammatory cytokines (recombinant human IL-6 (rhIL-6) and recombinant human tumour necrosis factor-alpha (rhTNF-alpha)). During the incubation period of the experiment, the SAA and Hp secretion into the culture medium increased (P < 0.05). SAA concentrations showed an additional increase following treatment with each of the cytokines (P < 0.01). Hp concentrations remained unchanged, whereas incubation with a combination of both resulted in a significant increase of the medium concentration of both SAA (P < 0.01) and Hp (P < 0.05). From these findings it is concluded that primary bovine hepatocytes can be used for in vitro studies on acute-phase protein secretion.

Research paper thumbnail of The influence of cisapride and clarithromycin on QT intervals in healthy volunteers

Clinical Pharmacology & Therapeutics, 1998

Research paper thumbnail of Determination of trimethoprim and its oxidative metabolites in cell culture media and microsomal incubation mixtures by high-performance liquid chromatography

Journal of chromatography, Jan 2, 1992

A high-performance liquid chromatographic method is presented for the determination of trimethopr... more A high-performance liquid chromatographic method is presented for the determination of trimethoprim (TMP), 3'-hydroxy-TMP, 4'-hydroxy-TMP, alpha-hydroxy-TMP and two TMP N-oxides. The last two metabolites appear to decompose on liquid extraction. TMP and its oxidative metabolites are separated using a C18 radial-compression column and quantified by UV detection at 230 nm. Calibration curves are linear from 0.5 to at least 50 microM. The limit of detection is 0.05-0.15 micrograms/ml. In in vitro rat liver metabolism studies. 3'- and 4'-hydroxylation of TMP appear to be important metabolic pathways whereas TMP N-oxides are minor metabolites.

Research paper thumbnail of Cytochrome P450 in the metabolism of xenobiotics and drug-drug interactions

Pharmacochemistry Library, 1997

... Ther. 48, 71-94 (1990). 2. Gonzalez, FJ, TIPS 13, 346-352 (1992). 3. Cholerton, S., Daly, AK ... more ... Ther. 48, 71-94 (1990). 2. Gonzalez, FJ, TIPS 13, 346-352 (1992). 3. Cholerton, S., Daly, AK and Idle, JR, TIPS 13, 434-439 (1992). ... Pharmacokinet. 8, 371-377 (1983). 10. Okey, AB, Roberts, EA, Harper, PA and Denison, MS, Clin. Biochem. 19, 132-141 (1986). 11. ...

Research paper thumbnail of AB0460 Glpg0634, A Selective JAK1 Inhibitor, Confirms Its Low Liability for Drug-Drug Interactions

Annals of the Rheumatic Diseases, 2014

In vitro, filgotinib and its metabolite do not inhibit key drug transporters. The lowest IC 50 va... more In vitro, filgotinib and its metabolite do not inhibit key drug transporters. The lowest IC 50 value (OCT2) is ≥ 3-fold the C max at 200 mg once daily.

Research paper thumbnail of THU0123 Dose Selection of GLPG0634, a Selective JAK1 Inhibitor, for Rheumatoid Arthritis Phase 2B Studies: PK/PD and Exposure-DAS28 Modeling Approach

Annals of the Rheumatic Diseases, 2014

Research paper thumbnail of Induction of hepatic drug metabolizing enzymes and interaction with carbon tetrachloride in rats after a single oral exposure to atrazine

Toxicology Letters, 1993

A single oral dose (430 mg/kg) of atraxine, a widely employed s-triazine herbicide, was administe... more A single oral dose (430 mg/kg) of atraxine, a widely employed s-triazine herbicide, was administered to young male rats. There was a si~ifi~t increase of the in vivo elimination of hexobarbital and a signiticant induction of the activity of 7-pentoxyresorutin-0-dealkylase, while cytochrome P-450 content and other mixed function oxidase activities remained unaltered. The administration of carbon tetrachloride (Ccl.,) to atrazine pretreated rats did not substantially augment the impairment of drug metabolizing enzymes brought about by Ccl4 alone. Results suggest that atrazine behaves like a relatively weak inducer of phenobarbital-inducible families of cytochrome P-450.

Research paper thumbnail of Applicability of cultured hepatocytes derived from goat, sheep and cattle in comparative drug metabolism studies

Xenobiotica, 1994

1. Using trimethoprim (TMP), scoparone (SCOP), ethylmorphine (EtM), 1-naphthol (1-N) and phenol r... more 1. Using trimethoprim (TMP), scoparone (SCOP), ethylmorphine (EtM), 1-naphthol (1-N) and phenol red (PhR) as test substrates, biotransformation activities were investigated in cultured hepatocytes from male and female rat, male and female goat, and female sheep and cattle. 2. As compared with rat hepatocytes, the total culture cytochrome P450 content was relatively well maintained in ruminant hepatocytes. In 72 h, it decreased to approximately half the initial content, whereas in rat hepatocytes only 30% was maintained. In ruminant hepatocytes, sulphation of 1-N remained fairly stable, glucuronidation of PhR decreased gradually, and glucuronidation of 1-N increased during the 72-h culture period. 3. Oxidative metabolism of TMP was rapid in goat and sheep hepatocytes, as compared with rat hepatocytes, reflecting species differences in TMP pharmacokinetics in vivo. In contrast with rat hepatocytes, 6-O-demethylation was by far the major pathway of scoparone metabolism in ruminant hepatocytes. The glucuronidation and sulphation activities were similar among the species. 4. In goat liver cells, sex differences in some oxidative biotransformations were observed, females being more active than males. In rat hepatocytes, a reverse sex difference was observed. 5. In conclusion, cultured hepatocytes from agricultural target species appear a useful in vitro model to study comparative metabolism of veterinary drugs and other xenobiotics. Comparing rat and ruminant, sex and species differences and similarities in drug metabolism can be observed that reflect the in vivo situation.

Research paper thumbnail of Effects of various medium formulations and attachment substrata on the performance of cultured ruminant hepatocytes in biotransformation studies

Xenobiotica, 1992

1. A procedure for the isolation and primary culture of hepatocytes from goat and cattle is descr... more 1. A procedure for the isolation and primary culture of hepatocytes from goat and cattle is described. Hepatocyte culture performance was monitored for 51 h by measuring viability, cytochrome P-450 maintenance, dealkylation of scoparone and ethylmorphine, and glucuronidation of phenol red. 2. Culture medium composition is discussed in relation to differences between splanchnic blood composition of ruminant and monogastric animal species. Main differences are in glucose and volatile fatty acid concentrations. Modified Williams' E culture medium did not yield higher culture performance than non-modified Williams' E. 3. Coating of culture dishes with either collagen or fibronectin did not improve culture performance. 4. Williams' E, although developed for rodent cells, proves to be a suitable basal medium for ruminant hepatocytes. In this medium, culture quality is high for at least several days. 5. In cultured goat hepatocytes, biotransformation rate for scoparone amounted to 20 nmol/mg protein per h, for ethylmorphine 96 nmol/mg protein per h and for phenol red 2 nmol/mg protein per h. Biotransformation activity in cow hepatocytes is approximately half that in goat hepatocytes.

Research paper thumbnail of Metabolism of antipyrine and sulphadimidine in dwarf goats: effects of the enzyme-inducing agents phenobarbital, troleandomycin and rifampicin

Xenobiotica, 1992

1. Antipyrine (AP) and sulphadimidine (SDD) plasma elimination and metabolite formation were stud... more 1. Antipyrine (AP) and sulphadimidine (SDD) plasma elimination and metabolite formation were studied in dwarf goats before and after treatment with phenobarbital (PB), triacetyloleandomycin (TAO), and rifampicin (RIF). 2. PB treatment significantly increased AP plasma clearance in both male and female goats. With SDD, only male goats were studied, which showed a significant increase of SDD plasma clearance following PB treatment. 3. After PB treatment, partial clearance values of four AP metabolites, 3-hydroxymethylantipyrine (HMA), norantipyrine (NORA), 4-hydroxyantipyrine (OHA) and 4,4'-dihydroxyantipyrine (DOHA), were significantly increased. This induction effect was different for the individual metabolites and also showed sex-dependency. 4. In PB-induced male goats the formation of the hydroxylated SDD metabolites, 6-hydroxymethyl-SDD and 5-hydroxy-SDD, was significantly increased. 5. After TAO treatment, female goats showed a slightly reduced AP plasma clearance and a decreased partial clearance of two AP metabolites, HMA and DOHA. There was no effect on SDD plasma elimination or metabolite excretion. 6. In male goats, RIF had no effect on plasma elimination of AP and SDD. With SDD, it decreased the urinary excretion of the unchanged drug and its N4-acetylated metabolite. 7. Induction/inhibition studies of drug metabolism in food-producing animal species are desirable to gain more insight into the regulation of enzymes involved in the metabolism of xenobiotics.

Research paper thumbnail of The use of cultured hepatocytes from goats and cattle to investigate xenobiotic oxidative metabolism

Veterinary Research Communications, 1996

Monte&a, C., Anfossi, P., Van? Klooster, G. and Mengelers, M., 1996. The use of cultured hepatocy... more Monte&a, C., Anfossi, P., Van? Klooster, G. and Mengelers, M., 1996. The use of cultured hepatocytes from goats and cattle to investigate xenobiotic oxidative metabolism. Veterinary Research Communications, 20 Q, 449460

Research paper thumbnail of The influence of nitrite, nitrate and nitric oxide on ammonia use and urea production in primary cultures of sheep hepatocytes

Toxicology in Vitro, 1995

ABSTRACT Inorganic nitrite introduced into the living organism is rapidly converted into nitrate ... more ABSTRACT Inorganic nitrite introduced into the living organism is rapidly converted into nitrate and nitric oxide (NO). It is known that nitrite decreases ammonia use and urea formation in vitro and it seems that nitrite also influences these processes in vivo. However, the mechanism underlying this effect is not known. Therefore, we decided to compare the influence of sodium nitrite (NaNO2), sodium nitrate (NaNO3) and NO on ammonia use and ureagenesis in monolayer cultures of sheep hepatocytes during 18 hr of cultivation. It was found that 0.5 and 2.5 mmNaNO2 significantly reduced ammonia use in a dose-dependent manner for the first 6 hr of incubation; at higher concentrations (2.5 mm), it also decreased urea formation. Also, the presence of nitrite did not affect the lactate dehydrogenase (LDH) activity in the medium which indicates that the nitrite effect did not result from its cytotoxic action. NaNO3 (0.5 and 2.5 mm) did not induce any changes in ammonia use and urea synthesis in hepatocytes. With sodium nitroprusside (SNP) (0.001, 0.01, 0.1, 0.5 and 1.0 mm) a decrease of ammonia use and urea production was observed corresponding to the nitrite effect, but contrary to nitrite exposure these changes in metabolism were persistent during the whole cultivation period. On the other hand, potassium cyanide (KCN) (0.1 and 0.5 mm) did not influence either urea formation or ammonia use. Thus, it can be concluded that in isolated hepatocytes nitrate and/or NO are not the mediators of nitrite effects on nitrogen metabolism. Furthermore, there is no evidence that nitrite effects are mediated by impaired mitochondrial respiration and energy production.

Research paper thumbnail of Sulfadimidine metabolism in vitro: II. comparative studies in cultured rat, goat, sheep and cattle hepatocytes

Journal of Veterinary Pharmacology and Therapeutics, 1993

metabolism in vitro: 11. comparative studies in cultured rat, goat, sheep and cattle hepatocytes.... more metabolism in vitro: 11. comparative studies in cultured rat, goat, sheep and cattle hepatocytes. J . vet. PAarmacol. Therap. 16, 454-46 1.

Research paper thumbnail of Improved high-performance liquid chromatographic method for the determination of ethylmorphine and its metabolites in microsomal incubations and cell culture media

Journal of Chromatography A

Ethylmorphine N-demethylation is used as a marker pathway in studies of rat cytochrome P450 3A an... more Ethylmorphine N-demethylation is used as a marker pathway in studies of rat cytochrome P450 3A and 2C11 biotransformations. At present, microsomal activities are generally measured by a colorimetric determination of the formed formaldehyde. In the present study, a high-performance liquid chromatographic method of separating and quantifying both the N-demethylated (norethylmorphine) and the O-de-ethylated (morphine) metabolites is described. Either samples are extracted with ethyl acetate or proteins are precipitated with zinc sulphate-barium hydroxide. Separation is achieved on a CN reversed-phase column, using a mobile phase of phosphate buffer (pH 4.5)-acetonitrile (90:10, v/v). At a flow-rate of 1.5 ml/min, the analysis time is 30 min. The limit of detection (ultraviolet, 210 nm) for ethylmorphine and its metabolites is 0.5 micrograms/ml.

Research paper thumbnail of Improved high-performance liquid chromatographic method for the determination of coenzyme Q10 in plasma

Journal of Chromatography A

Coenzyme (Co) Q10 was dissociated from lipoproteins in plasma by treatment with methanol and extr... more Coenzyme (Co) Q10 was dissociated from lipoproteins in plasma by treatment with methanol and extraction with n-hexane. Subsequent clean-up on silica gel and C18 solid-phase extraction cartridges with complete recovery (99 +/- 1.2%) produced a clean extract. High-performance liquid chromatographic (HPLC) separation was performed on a C18 reversed-phase column. Three simple, rapid procedures are presented: HPLC with final UV (275 nm) detection, a microanalysis utilizing a three-electrode electrochemical detector and a microanalysis with column-switching HPLC and electrochemical detection. The methods correlate very well with classical ethanol-n-hexane extraction with UV detection. The identity and purity of the Co Q10 peak were investigated and the resulting methods were concluded to be suitable for total plasma Co Q10 determination. The average level in healthy subjects was 0.80 +/- 0.20 mg/l; the minimum detectable Co Q10 plasma level was 0.05 and 0.005 mg/l for UV and electrochemic...

Research paper thumbnail of Correlations between Factors Determining the Pharmacokinetics and Antiviral Activity of HIV-1 Non-Nucleoside Reverse Transcriptase Inhibitors of the Diaryltriazine and Diarylpyrimidine Classes of Compounds

Drugs in R & D, 2004

To investigate the important factors that determine the bioavailability and the antiviral activit... more To investigate the important factors that determine the bioavailability and the antiviral activity of the diaryltriazine (DATA) and diarylpyrimidine (DAPY) non-nucleoside reverse transcriptase inhibitors (NNRTIs) of HIV-1 in animal species and humans using cell-based assays, physicochemical and computed parameters. This naturalistic study included 15 parameters ranging from molecular mechanics calculations to phase I clinical trials. The calculated parameters were solvent-accessible surface area (SASA), polar surface area and Gibbs free energy of solvation. Physicochemical parameters comprised lipophilicity (octanol/water partition coefficient [cLogP]), ionisation constant (pKa), solubility and aggregate radius. Cell-based assays included human colonic adenocarcinoma cell (Caco-2) permeability (transepithelial transport), drug metabolism and antiviral activity (negative logarithm of the molar effective concentration inhibiting viral replication by 50% [pEC50]). Exposure was tested in rats, dogs and human volunteers. Of the 15 parameters, eight correlated consistently among one another. Exposure (area under the plasma concentration-time curve [AUC]) in humans correlated positively with that in rats (r = 1.00), with transepithelial transport (r = 0.83), lipophilicity (r = 0.60), ionisability (r = 0.89), hydrodynamic radius of aggregates (r = 0.66) and with antiviral activity (r = 0.61). Exposure in humans was also seen to correlate negatively with SASA (r = -0.89). No consistent correlation was found between exposure in dogs and the eight parameters. Of the 14 DATA/DAPY molecules, 11 form aggregates with radii between 34 and 100 nm. We observed correlations between exposure in humans with exposure in rats, transepithelial transport (Caco-2 cells), ionisability, lipophilicity, aggregate radius and SASA in the class of DATA/DAPY NNRTI compounds. The lipophilic DATA/DAPY compounds form aggregates. It can be assumed that absorption in the intestinal tract and endocytosis in infected cells of these lipophilic compounds are governed by the common phenomenon of aggregate formation. As the lymphatic system offers a pathway for intestinal uptake of aggregates, this may offer a therapeutic advantage in the treatment of HIV-1 infection. Although it was not the objective of the study, we found that the rat was a better in vivo model than the dog for the prediction of systemic exposure in this particular set of compounds.

Research paper thumbnail of Efficacy, Safety, Pharmacokinetics, and Pharmacodynamics of Filgotinib, a Selective JAK-1 Inhibitor, After Short-Term Treatment of Rheumatoid Arthritis: Results of Two Randomized Phase IIa Trials

Research paper thumbnail of Hepatic cytochrome P450 induction in goatsEffects of model inducers on the metabolism of alkoxyresorufins, testosterone and ethylmorphine, and on apoprotein and mRNA levels

Biochemical Pharmacology, 1993

Male and female African dwarf goats were treated orally with phenobarbital (PB) or triacetylolean... more Male and female African dwarf goats were treated orally with phenobarbital (PB) or triacetyloleandomycin (TAO), or subcutaneously with beta-naphthoflavone (BNF). Hepatic microsomal cytochrome P450 content was increased by PB and TAO, but not by BNF. PB effects on P450 activities were non-selective: ethoxyresorufin deethylase (EROD) and pentoxyresorufin depentylase (PROD), hydroxylation of testosterone (TST) and demethylation of ethylmorphine (ETM) were all induced by a factor of 2-3. A similar non-selective induction was observed with TAO, except for EROD and PROD (no effects). After PB and TAO treatment, increased levels of a protein cross-reactive with anti-sheep P450 3A and 2B were found. Thus, in dwarf goats, both PB and TAO appeared to be P450 3A inducers. Selective PB effects related to a P450 2B form on PROD are lacking but 16 alpha-hydroxylation of TST was induced markedly. At the mRNA level, PB induced an mRNA that showed good sequence homology with a human P450 3A4 cDNA probe, rather than with a rat 3A1 probe. BNF selectively induced EROD, whereas TST hydroxylation and ETM dealkylation were inhibited. With BNF-treated animals, increased concentrations of a protein cross-reactive with anti-rat P450 1A1/1A2 and of an mRNA that showed homology with a human 1A1 cDNA probe, but not with a mouse 1A1/1A2 probe, were observed.

Research paper thumbnail of Improved high-performance liquid chromatographic method for the determination of ethylmorphine and its metabolites in microsomal incubations and cell culture media

Journal of Chromatography B: Biomedical Sciences and Applications, 1992

Research paper thumbnail of Hepatic cytochrome P450 induction in goats. Effects of model inducers on the metabolism of alkoxyresorufins, testosterone and ethylmorphine, and on apoprotein and mRNA levels

Biochemical Pharmacology

Male and female African dwarf goats were treated orally with phenobarbital (PB) or triacetylolean... more Male and female African dwarf goats were treated orally with phenobarbital (PB) or triacetyloleandomycin (TAO), or subcutaneously with beta-naphthoflavone (BNF). Hepatic microsomal cytochrome P450 content was increased by PB and TAO, but not by BNF. PB effects on P450 activities were non-selective: ethoxyresorufin deethylase (EROD) and pentoxyresorufin depentylase (PROD), hydroxylation of testosterone (TST) and demethylation of ethylmorphine (ETM) were all induced by a factor of 2-3. A similar non-selective induction was observed with TAO, except for EROD and PROD (no effects). After PB and TAO treatment, increased levels of a protein cross-reactive with anti-sheep P450 3A and 2B were found. Thus, in dwarf goats, both PB and TAO appeared to be P450 3A inducers. Selective PB effects related to a P450 2B form on PROD are lacking but 16 alpha-hydroxylation of TST was induced markedly. At the mRNA level, PB induced an mRNA that showed good sequence homology with a human P450 3A4 cDNA pr...

Research paper thumbnail of Primary bovine hepatocytes in the study of cytokine induced acute-phase protein secretion in vitro

Veterinary Immunology and Immunopathology, 1996

To investigate the utility of primary cultures of bovine hepatocytes for compartmentalized acute ... more To investigate the utility of primary cultures of bovine hepatocytes for compartmentalized acute phase protein studies the secretion of serum amyloid-A (SAA) and haptoglobin (Hp) was measured after stimulation by pro-inflammatory cytokines (recombinant human IL-6 (rhIL-6) and recombinant human tumour necrosis factor-alpha (rhTNF-alpha)). During the incubation period of the experiment, the SAA and Hp secretion into the culture medium increased (P < 0.05). SAA concentrations showed an additional increase following treatment with each of the cytokines (P < 0.01). Hp concentrations remained unchanged, whereas incubation with a combination of both resulted in a significant increase of the medium concentration of both SAA (P < 0.01) and Hp (P < 0.05). From these findings it is concluded that primary bovine hepatocytes can be used for in vitro studies on acute-phase protein secretion.

Research paper thumbnail of The influence of cisapride and clarithromycin on QT intervals in healthy volunteers

Clinical Pharmacology & Therapeutics, 1998

Research paper thumbnail of Determination of trimethoprim and its oxidative metabolites in cell culture media and microsomal incubation mixtures by high-performance liquid chromatography

Journal of chromatography, Jan 2, 1992

A high-performance liquid chromatographic method is presented for the determination of trimethopr... more A high-performance liquid chromatographic method is presented for the determination of trimethoprim (TMP), 3'-hydroxy-TMP, 4'-hydroxy-TMP, alpha-hydroxy-TMP and two TMP N-oxides. The last two metabolites appear to decompose on liquid extraction. TMP and its oxidative metabolites are separated using a C18 radial-compression column and quantified by UV detection at 230 nm. Calibration curves are linear from 0.5 to at least 50 microM. The limit of detection is 0.05-0.15 micrograms/ml. In in vitro rat liver metabolism studies. 3'- and 4'-hydroxylation of TMP appear to be important metabolic pathways whereas TMP N-oxides are minor metabolites.

Research paper thumbnail of Cytochrome P450 in the metabolism of xenobiotics and drug-drug interactions

Pharmacochemistry Library, 1997

... Ther. 48, 71-94 (1990). 2. Gonzalez, FJ, TIPS 13, 346-352 (1992). 3. Cholerton, S., Daly, AK ... more ... Ther. 48, 71-94 (1990). 2. Gonzalez, FJ, TIPS 13, 346-352 (1992). 3. Cholerton, S., Daly, AK and Idle, JR, TIPS 13, 434-439 (1992). ... Pharmacokinet. 8, 371-377 (1983). 10. Okey, AB, Roberts, EA, Harper, PA and Denison, MS, Clin. Biochem. 19, 132-141 (1986). 11. ...

Research paper thumbnail of AB0460 Glpg0634, A Selective JAK1 Inhibitor, Confirms Its Low Liability for Drug-Drug Interactions

Annals of the Rheumatic Diseases, 2014

In vitro, filgotinib and its metabolite do not inhibit key drug transporters. The lowest IC 50 va... more In vitro, filgotinib and its metabolite do not inhibit key drug transporters. The lowest IC 50 value (OCT2) is ≥ 3-fold the C max at 200 mg once daily.

Research paper thumbnail of THU0123 Dose Selection of GLPG0634, a Selective JAK1 Inhibitor, for Rheumatoid Arthritis Phase 2B Studies: PK/PD and Exposure-DAS28 Modeling Approach

Annals of the Rheumatic Diseases, 2014

Research paper thumbnail of Induction of hepatic drug metabolizing enzymes and interaction with carbon tetrachloride in rats after a single oral exposure to atrazine

Toxicology Letters, 1993

A single oral dose (430 mg/kg) of atraxine, a widely employed s-triazine herbicide, was administe... more A single oral dose (430 mg/kg) of atraxine, a widely employed s-triazine herbicide, was administered to young male rats. There was a si~ifi~t increase of the in vivo elimination of hexobarbital and a signiticant induction of the activity of 7-pentoxyresorutin-0-dealkylase, while cytochrome P-450 content and other mixed function oxidase activities remained unaltered. The administration of carbon tetrachloride (Ccl.,) to atrazine pretreated rats did not substantially augment the impairment of drug metabolizing enzymes brought about by Ccl4 alone. Results suggest that atrazine behaves like a relatively weak inducer of phenobarbital-inducible families of cytochrome P-450.

Research paper thumbnail of Applicability of cultured hepatocytes derived from goat, sheep and cattle in comparative drug metabolism studies

Xenobiotica, 1994

1. Using trimethoprim (TMP), scoparone (SCOP), ethylmorphine (EtM), 1-naphthol (1-N) and phenol r... more 1. Using trimethoprim (TMP), scoparone (SCOP), ethylmorphine (EtM), 1-naphthol (1-N) and phenol red (PhR) as test substrates, biotransformation activities were investigated in cultured hepatocytes from male and female rat, male and female goat, and female sheep and cattle. 2. As compared with rat hepatocytes, the total culture cytochrome P450 content was relatively well maintained in ruminant hepatocytes. In 72 h, it decreased to approximately half the initial content, whereas in rat hepatocytes only 30% was maintained. In ruminant hepatocytes, sulphation of 1-N remained fairly stable, glucuronidation of PhR decreased gradually, and glucuronidation of 1-N increased during the 72-h culture period. 3. Oxidative metabolism of TMP was rapid in goat and sheep hepatocytes, as compared with rat hepatocytes, reflecting species differences in TMP pharmacokinetics in vivo. In contrast with rat hepatocytes, 6-O-demethylation was by far the major pathway of scoparone metabolism in ruminant hepatocytes. The glucuronidation and sulphation activities were similar among the species. 4. In goat liver cells, sex differences in some oxidative biotransformations were observed, females being more active than males. In rat hepatocytes, a reverse sex difference was observed. 5. In conclusion, cultured hepatocytes from agricultural target species appear a useful in vitro model to study comparative metabolism of veterinary drugs and other xenobiotics. Comparing rat and ruminant, sex and species differences and similarities in drug metabolism can be observed that reflect the in vivo situation.

Research paper thumbnail of Effects of various medium formulations and attachment substrata on the performance of cultured ruminant hepatocytes in biotransformation studies

Xenobiotica, 1992

1. A procedure for the isolation and primary culture of hepatocytes from goat and cattle is descr... more 1. A procedure for the isolation and primary culture of hepatocytes from goat and cattle is described. Hepatocyte culture performance was monitored for 51 h by measuring viability, cytochrome P-450 maintenance, dealkylation of scoparone and ethylmorphine, and glucuronidation of phenol red. 2. Culture medium composition is discussed in relation to differences between splanchnic blood composition of ruminant and monogastric animal species. Main differences are in glucose and volatile fatty acid concentrations. Modified Williams' E culture medium did not yield higher culture performance than non-modified Williams' E. 3. Coating of culture dishes with either collagen or fibronectin did not improve culture performance. 4. Williams' E, although developed for rodent cells, proves to be a suitable basal medium for ruminant hepatocytes. In this medium, culture quality is high for at least several days. 5. In cultured goat hepatocytes, biotransformation rate for scoparone amounted to 20 nmol/mg protein per h, for ethylmorphine 96 nmol/mg protein per h and for phenol red 2 nmol/mg protein per h. Biotransformation activity in cow hepatocytes is approximately half that in goat hepatocytes.

Research paper thumbnail of Metabolism of antipyrine and sulphadimidine in dwarf goats: effects of the enzyme-inducing agents phenobarbital, troleandomycin and rifampicin

Xenobiotica, 1992

1. Antipyrine (AP) and sulphadimidine (SDD) plasma elimination and metabolite formation were stud... more 1. Antipyrine (AP) and sulphadimidine (SDD) plasma elimination and metabolite formation were studied in dwarf goats before and after treatment with phenobarbital (PB), triacetyloleandomycin (TAO), and rifampicin (RIF). 2. PB treatment significantly increased AP plasma clearance in both male and female goats. With SDD, only male goats were studied, which showed a significant increase of SDD plasma clearance following PB treatment. 3. After PB treatment, partial clearance values of four AP metabolites, 3-hydroxymethylantipyrine (HMA), norantipyrine (NORA), 4-hydroxyantipyrine (OHA) and 4,4'-dihydroxyantipyrine (DOHA), were significantly increased. This induction effect was different for the individual metabolites and also showed sex-dependency. 4. In PB-induced male goats the formation of the hydroxylated SDD metabolites, 6-hydroxymethyl-SDD and 5-hydroxy-SDD, was significantly increased. 5. After TAO treatment, female goats showed a slightly reduced AP plasma clearance and a decreased partial clearance of two AP metabolites, HMA and DOHA. There was no effect on SDD plasma elimination or metabolite excretion. 6. In male goats, RIF had no effect on plasma elimination of AP and SDD. With SDD, it decreased the urinary excretion of the unchanged drug and its N4-acetylated metabolite. 7. Induction/inhibition studies of drug metabolism in food-producing animal species are desirable to gain more insight into the regulation of enzymes involved in the metabolism of xenobiotics.

Research paper thumbnail of The use of cultured hepatocytes from goats and cattle to investigate xenobiotic oxidative metabolism

Veterinary Research Communications, 1996

Monte&a, C., Anfossi, P., Van? Klooster, G. and Mengelers, M., 1996. The use of cultured hepatocy... more Monte&a, C., Anfossi, P., Van? Klooster, G. and Mengelers, M., 1996. The use of cultured hepatocytes from goats and cattle to investigate xenobiotic oxidative metabolism. Veterinary Research Communications, 20 Q, 449460

Research paper thumbnail of The influence of nitrite, nitrate and nitric oxide on ammonia use and urea production in primary cultures of sheep hepatocytes

Toxicology in Vitro, 1995

ABSTRACT Inorganic nitrite introduced into the living organism is rapidly converted into nitrate ... more ABSTRACT Inorganic nitrite introduced into the living organism is rapidly converted into nitrate and nitric oxide (NO). It is known that nitrite decreases ammonia use and urea formation in vitro and it seems that nitrite also influences these processes in vivo. However, the mechanism underlying this effect is not known. Therefore, we decided to compare the influence of sodium nitrite (NaNO2), sodium nitrate (NaNO3) and NO on ammonia use and ureagenesis in monolayer cultures of sheep hepatocytes during 18 hr of cultivation. It was found that 0.5 and 2.5 mmNaNO2 significantly reduced ammonia use in a dose-dependent manner for the first 6 hr of incubation; at higher concentrations (2.5 mm), it also decreased urea formation. Also, the presence of nitrite did not affect the lactate dehydrogenase (LDH) activity in the medium which indicates that the nitrite effect did not result from its cytotoxic action. NaNO3 (0.5 and 2.5 mm) did not induce any changes in ammonia use and urea synthesis in hepatocytes. With sodium nitroprusside (SNP) (0.001, 0.01, 0.1, 0.5 and 1.0 mm) a decrease of ammonia use and urea production was observed corresponding to the nitrite effect, but contrary to nitrite exposure these changes in metabolism were persistent during the whole cultivation period. On the other hand, potassium cyanide (KCN) (0.1 and 0.5 mm) did not influence either urea formation or ammonia use. Thus, it can be concluded that in isolated hepatocytes nitrate and/or NO are not the mediators of nitrite effects on nitrogen metabolism. Furthermore, there is no evidence that nitrite effects are mediated by impaired mitochondrial respiration and energy production.

Research paper thumbnail of Sulfadimidine metabolism in vitro: II. comparative studies in cultured rat, goat, sheep and cattle hepatocytes

Journal of Veterinary Pharmacology and Therapeutics, 1993

metabolism in vitro: 11. comparative studies in cultured rat, goat, sheep and cattle hepatocytes.... more metabolism in vitro: 11. comparative studies in cultured rat, goat, sheep and cattle hepatocytes. J . vet. PAarmacol. Therap. 16, 454-46 1.