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G Engel

Publications and source records attributed to G Engel.

At least 37 records · Page 2Linked to original sources
PubMed1996

Prediction of CYP2D6-mediated polymorphic drug metabolism (sparteine type) based on in vitro investigations.

Discovery of genetic polymorphism in drug metabolism has contributed a great deal to understanding the variability in dose-concentration relationships introduced by genetic factors, thereby elucidating the mechanisms responsible for unexpected drug reactions. This knowledge should find its way into clinical practice in order to make therapy more efficient and safe. Moreover, genetic factors in drug metabolism should be taken into account during drug development. Therefore, in vitro methods for identifying the metabolic pattern of new compounds during early stages of drug development should be improved. This review summarizes in vitro methods available to identify genetic polymorphism in drug oxidation, in particular the CYP2D6-related polymorphism.

Animals↗
PubMed1996

Antipyrine as a probe for human oxidative drug metabolism: identification of the cytochrome P450 enzymes catalyzing 4-hydroxyantipyrine, 3-hydroxymethylantipyrine, and norantipyrine formation.

BACKGROUND AND OBJECTIVE: Antipyrine has been widely used as a probe drug for human oxidative drug metabolism. To evaluate the role of antipyrine as a model drug, we have identified the cytochrome P450 enzymes involved in 4-hydroxyantipyrine, 3-hydroxymethylantipyrine, and norantipyrine formation. METHODS: We used the following methods for this study: (1) determination of enzyme kinetics for antipyrine metabolite formation in human liver microsomes, (2) inhibition studies with antibodies and inhibitors, and (3) formation of metabolites by stable expressed human P450 enzymes. RESULTS: Antipyrine biotransformation could be described by Michaelis-Menten kinetics: norantipyrine: maximum rate of metabolite formation (Vmax), 0.91 +/- 0.04 nmol . mg-1 . min-1; Michaelis-Menten constant (Km), 19.0 +/- 0.8 mmol/L; 4-hydroxyantipyrine: Vmax, 1.54 +/- 0.08 nmol . mg-1 . min-1;Km,39.6 +/- 2.5 mmol/L. Antibodies against CYP3A4 inhibited the formation of 4-hydroxyantipyrine by 25% to 65%. LKM-2 antibodies (anti-CYP2C) caused a 75% to 100% inhibition of norantipyrine and a 58% to 80% inhibition of 3-hydroxymethylantipyrine formation. Sulfaphenazole inhibited the formation of 3-hydroxymethylantipyrine and norantipyrine by about 50%. Furafylline and fluvoxamine inhibited norantipyrine, 4-hydroxyantipyrine, and 3-hydroxymethylantipyrine formation by about 30%, 30%, and 50%, respectively. Ketoconazole reduced formation of norantipyrine, 3-hydroxymethylantipyrine, and 4-hydroxyantipyrine by up to 80%. Formation in stable expressed enzymes indicated involvement of CYP1A2, CYP2B6, CYP2C, and CYP3A4 in metabolite formation. CONCLUSION: Antipyrine metabolites are formed by at least six hepatic cytochrome P450 enzymes (CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C18, and CYP3A4). 4-Hydroxylation is mainly catalyzed by CYP3A4 and, to a lesser extent, by CYP1A2. The CYP2C subfamily contains the predominant enzymes for norantipyrine formation, and CYP1A2 is also involved. Formation of 3-hydroxymethylantipyrine is mediated by CYP1A2 and CYP2C9. Because several cytochrome P450 enzymes are involved in the formation of each metabolite, antipyrine is not well suited as a probe for distinct human cytochrome P450 enzymes.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1995

Highly sensitive and specific gas chromatographic-tandem mass spectrometric method for the determination of trace amounts of antipyrine metabolites in biological material.

A highly sensitive and specific gas chromatographic-tandem mass spectrometric method was developed for the determination of the antipyrine (INN: phenazone) metabolites, norantipyrine, 4-hydroxyantipyrine and 3-hydroxy-methylantipyrine, in biological material. Deuterated analogues of the metabolites were used as internal standards. The method has a limit of quantitation of 5 ng per sample for the determination of norantipyrine, 4-hydroxy-antipyrine and 3-hyddroxymethylantipyrine with coefficients of variation of 19.4, 14.6 and 20.7%, respectively. Precision and accuracy are good over the whole range measured (5-500 ng/sample) with a coefficient of variation, respectively error of determination < or = 20%. Due to its high sensitivity the method can be used to study the formation of these metabolites in microsomal preparations containing only 100 micrograms of protein.

Animals↗
PubMed1994

Correlation between stromelysin-3 mRNA level and outcome of human breast cancer.

The expression level of stromelysin-3 (ST3) mRNA was analyzed by in situ hybridization of formalin-fixed, paraffin-embedded primary breast-tumor samples from 76 patients. Digital image analysis of the dark-field in situ hybridization signal was used to measure the maximal level of ST3 expression in each tumor. All 55 invasive ductal carcinomas and 9 of 10 invasive lobular carcinomas were positive for ST3. Invasive tumors had significantly higher levels of ST3 than in situ tumors. Furthermore, ST3 levels were higher in invasive ductal carcinomas than in invasive lobular carcinomas. The ST3 expression level was significantly correlated to fatal metastatic disease (mean follow-up 104 months). ST3 levels of < 2,500 units were associated with distant metastasis in 46% of patients, whereas levels of > 2,500 units were associated with metastasis in 79% of patients selected for study. ST3 mRNA levels did not correlate with tumor size, microvessel density, DNA ploidy or estrogen-receptor levels. Studies of ST3 expression may provide information valuable for the understanding of breast cancer biology and for prognosis.

Adult↗
PubMed1994

The somatostatin analogue octreotide protects against ethanol-induced microcirculatory stasis and elevated vascular permeability in rat gastric mucosa.

Somatostatin 14 and various derivatives protect rat gastric mucosa against ethanol-induced lesions. Their mechanism of action is unknown. We investigated the effect of two somatostatin derivatives, octreotide and 5-(L)-citrullin-octreotide, on ethanol-induced hemorrhagic lesions, microcirculatory stasis and elevated vascular permeability in the rat stomach, with the goal to elucitate the pharmacological and microcirculatory mechanisms behind the gastroprotective effect. Radioligand studies revealed a high affinity of octreotide for the somatostatin receptor (IC50 = 5 x 10(-10) mol/l), in contrast to 5-(L)-citrullin-octreotide (IC50 = 3 x 10(-6) mol/l). This was in good agreement with the inhibition of growth hormone release from rat anterior pituitary cells (octreotide: IC50 = 1.2 x 10(-10) mol/l; 5-(L)-citrullin-octreotide: IC50 = 3 x 10(-6) mol/l). Intragastric administration of ethanol to rats resulted in lesions of the gastric mucosa affecting 18.9 +/- 3.1% of the area of the glandular stomach. Octreotide reduced the area to 6.4 +/- 1.7% (P < 0.05). The dose-response curve was bell-shaped. 5-(L)-citrullin-octreotide was totally devoid of any protective activity (dose range: 0.1 ng/kg to 0.1 mg/kg). We further investigated the effect of the two peptides on ethanol-induced microcirculatory stasis and elevated vascular permeability. Ethanol in a concentration of 50% induced an increase in microvascular permeability, measured by the extravasation of the tracer fluorescein-isothiocyanate-dextran (molecular weight 150,000). Pretreatment with octreotide (0.1 ng/kg s.c.) prevented stasis and reduced capillary permeability significantly. 5-(L)-citrullin-octreotide had no effect on ethanol-induced microcirculatory stasis and elevated vascular permeability in rat gastric mucosa.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Isolation and characterization of the human interleukin-9 receptor gene.

To better understand the regulation of interleukin-9 (IL-9) receptor expression, we have isolated the genomic clone of the human IL-9 receptor based on its sequence homology with a human IL-9 receptor cDNA isolated from the human megakaryocyte cell line UT-7. The entire genomic structure has been determined. The human IL-9 receptor gene consists of 10 exons spread over approximately 13.7 kb of DNA. The nucleotide sequence of the coding region from the genomic DNA is identical to our cDNA clone. Several blocks of transcriptional control sequence have been identified at the 5' noncoding region of the IL-9 receptor gene that may play an important role in the regulation of the IL-9 receptor gene. A fusion gene containing 659 bp of human IL-9 receptor 5' noncoding region linked to the firefly luciferase gene directed expression of luciferase activity in human embryonic kidney 293 cell line, but not in the mouse fibroblast cell line NIH3T3 cells.

Amino Acid Sequence↗
PubMed1994

Oxyphilic Sertoli cell tumor of the ovary: a report of three cases, two in patients with the Peutz-Jeghers syndrome.

Three women, aged 19, 21, and 30 years, two with the Peutz-Jeghers syndrome (PJS), had unilateral ovarian tumors composed of Sertoli cells with abundant eosinophilic cytoplasm. Electron microscopical and immunohistochemical examinations in one case supported the diagnosis of a sex cord tumor. Two patients are well 3 and 20 months postoperatively; the third was well for 15 years when recurrent tumor involving multiple intraabdominal sites was discovered. The occurrence of two of these tumors in patients with PJS and the known increased frequency of sex cord tumors in patients with this syndrome indicate an association. Sertoli cell tumor should be included in the differential diagnosis of oxyphilic ovarian tumors, particularly if there is a tubular pattern.

Adult↗
PubMed1994

Tumorigenic and metastatic properties of two ras-oncogene transfected rat fibrosarcoma cell lines defective in c-jun.

We here report the spontaneous loss of both homologues of the c-jun gene in two cell lines, isolated after transfection of rat embryo fibroblasts with single ras-oncogenes. These cells lines (designated A14 and B25) grow rapidly in vitro, have transformed morphologies and are invasive through reconstituted basal membranes. Both c-jun defective cell lines were found to be tumorigenic and metastatic in athymic mice. Loss of c-jun was paralleled by a dramatic decrease in interstitial collagenase expression, whereas stromelysin mRNA expression in c-jun- A14 and B25 cells was similar to that observed in c-jun+ transformed cell lines. Transient transfection experiments using reporter plasmids showed that stromelysin promoter activity in A14 cells was severely impaired by a point mutation in the -71 to -65 AP-1 motif, and was inhibited by a Jun dominant negative mutant. Gel mobility shift studies demonstrated the presence of a factor in A14 nuclear extracts capable of binding the stromelysin TRE. This factor bound JunB, JunD and Fos antibodies. Our findings suggest that c-Jun is not required for the tumorigenic and metastatic potential of ras-transformed fibrosarcoma cells, and that AP-1 protein(s) lacking c-Jun are capable of activating the stromelysin gene promoter.

Animals↗
PubMed1993

Repression of stromelysin metalloprotease expression in rat fibrosarcoma cells by dimethylsulfoxide.

Metalloproteases are implicated in conferring invasive properties to tumor cells. We show here that treatment of ras-oncogene-transformed rat fibroblasts with dimethylsulfoxide (DMSO) results in a reversible decrease in stromelysin mRNA. Furthermore, stromelysin expression was found to be repressed by DMSO, but not by glucocorticoid hormone, in a fibrosarcoma cell line showing low AP-1 (fos/jun) transcription factor activity. In two fibrosarcoma cell lines which express high levels of stromelysin and low levels of 68 kDa type IV collagenase, the DMSO-induced decrease in stromelysin expression was paralleled by a decreased invasive propensity.

Animals↗
PubMed1993

Generation of pharmacokinetic data during routine therapeutic drug monitoring: Bayesian approach vs. pharmacokinetic studies.

In three groups (each n = 12) of unselected hospitalized patients treated either with digoxin, theophylline, or gentamicin routinely performed TDM measurement of trough steady-state plasma levels (+ peak levels in case of gentamicin) was combined with a pharmacokinetic study at steady state (multiple blood sampling during one dosing interval). Pharmacokinetic parameters (apparent volume of distribution Vd, total plasma clearance CL) needed for individualization of dosage were evaluated by the Bayesian approach and a model-(in)dependent pharmacokinetic program (TOPFIT). Comparison of both methods revealed some small differences in the pharmacokinetic parameters for all three drugs. Mean deviations of the Bayesian estimates from the pharmacokinetic calculations of the three drugs ranged between 20 and 38% for Vd and between 13 and 22% for CL, indicating that the Bayesian approach provided reliable pharmacokinetic estimates for individualizing drug dosage under routine conditions. Therefore, it is suggested that routine TDM combined with Bayesian-based analyses can be regarded as an alternative to pharmacokinetic studies in clinically relevant populations.

Adult↗
PubMed1993

Lymphocyte beta 2-adrenoceptors and adenosine 3':5'-cyclic monophosphate during and after normal pregnancy.

1. The beta 2-sympathomimetics, used to inhibit preterm labour, bind predominantly to beta 2-adrenoceptors, activating adenylate cyclase to form adenosine 3':5'-cyclic monophosphate (cyclic AMP), a messenger substance which inhibits the enzyme cascade triggering smooth muscle contraction. beta 2-Adrenoceptor density and cyclic AMP formation can be used as markers of beta 2-adrenergic effect. 2. The present study addresses the influence of pregnancy on the beta-adrenoceptor system. beta 2-Adrenoceptor density and cyclic AMP concentrations (basal and evoked by isoprenaline) in circulating lymphocytes were determined at three points in gestation (16, 29 and 37 weeks) and 9 weeks post partum in 22 normal pregnancies. (-)-[125Iodo]-cyanopindolol was used as the ligand to identify a homogeneous population of beta 2-adrenoceptors on lymphocytes. B- and T-cell fractions were estimated from the same samples. 3. beta 2-Adrenoceptor density decreased significantly during gestation until week 37 (P < 0.01), then increased post partum (P < 0.005). Cyclic AMP concentrations (basal and evoked by isoprenaline) were significantly lower after 16 weeks of gestation than post partum (P < 0.05). 4. The results, which cannot be explained in terms of a shift in the lymphocyte (B- and T-cell) ratio, indicate that beta-adrenoceptor density and function are reduced in normal pregnancy and only return to normal post partum. These findings may be of significance in devising future tocolytic therapy with beta 2-adrenoceptor agonists.

Cyclic AMP↗
PubMed1993

Lack of c-jun expression in a transformed cell line isolated by glucocorticoid promotion of ras-transfected rat embryo fibroblasts.

Rat embryo fibroblasts (REFs) are inefficiently transformed by the T24-ras oncogene. A contributing factor to cellular resistance to transformation is the limited tolerance to p21-ras oncoprotein expression. Here we present data suggesting that long-term glucocorticoid treatment of ras oncogene-transfected REFs results in increased tolerance to p21-ras oncoproteins, leading to expression of the transformed phenotype. Stably transformed cell lines that expressed high levels of H-ras and could be maintained in the absence of hormone were isolated. In three out of four lines studied, the AP-1-dependent collagenase gene was expressed at a low level. In one of these lines, low collagenase expression was paralleled by lack of c-jun mRNA. Immunochemical analysis revealed that progression to hormone independence was not paralleled by mutations in the p53 gene. We propose that a decreased expression of AP-1-driven genes may result in increased tolerance to p21-ras oncoprotein.

Animals↗
PubMed1992

Elevated stromelysin-1 and reduced collagenase-IV expression in invasive rat embryo fibroblasts expressing E1A deletion mutants + T24-H-ras.

We have studied the in vitro invasive properties of 3 cell lines derived from the co-transfection of rat embryo fibroblasts (REF) with EIA genes deficient in exon 2 and T24-ras. All 3 cell lines showed invasive properties at passage 10 after isolation. Invasive cells expressed elevated levels of stromelysin-1 and reduced levels of 68-kDa type-IV collagenase compared with untransfected REF. In 2 cell lines the invasive capacity increased during in vitro propagation. The expression of stromelysin-1 increased during this process, whereas 68-kDa type-IV collagenase was persistently expressed at reduced levels. In the third clone analyzed, the invasive capacity decreased during culture, in parallel with decreased expression of stromelysin-1. The low level of stromelysin-1 expression observed in this cell line did not result from loss of AP-1-transcription-factor activity, and was not reversed by phorbol-ester treatment.

Adenovirus Early Proteins↗
PubMed1991

Heat resistance of ascospores of Byssochlamys nivea in milk and cream.

Byssochlamys nivea strains of rather varying origin used for heat inactivation experiments were cultured for 28 days at 30 degrees C on malt extract agar, since under these conditions the highest degree of heat resistance of the ascospores was observed. Inactivation was performed in steel capillary tubes to obtain reproducible results under experimental conditions comparable to those prevailing in practice. An inactivation temperature of 92 degrees C proved to be most practical. Decimal reduction times for the individual strains at this temperature in Ringer's solution varied between 1.3 and 2.4 s. In the temperature range studied, inactivation of ascospores in UHT milk (1.5% w/w fat content) and cream (10% w/w fat content) has not been found to differ significantly from that in Ringer's solution. Homogenization of milk as applied in practice did not affect heat inactivation of ascospores. Assuming the most unfavorable conditions (50 ascospores/l and using the most heat-resistant strain) the following relations between the level of infected 500 g packages were calculated: 1 of 10(6) packs infected; 24 s at 92 degrees C; 1 of 10(3) packs infected; 16.5 s at 92 degrees C; 1 of 10(2) packs infected, 14 s at 92 degrees C.

Animals↗
PubMed1991

Conservative management of a combined endodontic-orthodontic lesion.

Pulp injury may occur during orthodontic tooth movement particularly in previously traumatized teeth. Therefore the management of such cases requires specific therapeutic considerations. An extensive periradicular lesion was detected in an orthodontically treated maxillary incisor with an uncertain history of a previous traumatic incident. Conservative endodontic therapy resolved the periradicular lesion thus enabling the orthodontic treatment to continue uneventfully. It is essential to closely monitor the patients undergoing orthodontic treatment and those who are in retention, particularly if a history of trauma is suspected.

Adolescent↗