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Biomedical subjects

K F Sewing

Publications and source records attributed to K F Sewing.

At least 19 recordsLinked to original sources
PubMed2000

Automated, fast and sensitive quantification of drugs in blood by liquid chromatography-mass spectrometry with on-line extraction: immunosuppressants.

We developed a universal LC-mass spectrometry assay with automated online extraction (LC/LC-MS) to quantify the immunosuppressants cyclosporine, tacrolimus, sirolimus and SDZ-RAD alone or in combination in whole blood. After protein precipitation, samples were loaded on a C18 extraction column, were washed and, after activation of the column-switching valve, were backflushed onto the C8 analytical column. [M+Na]+ ions were detected in the selected ion mode. For tacrolimus, sirolimus and SDZ-RAD, the assay was linear from 0.25 to 100 microg/l and for cyclosporine from 7.5 to 1250 microg/l (all r2>0.99). Analytical recovery was >85% and, in general, inter-day, intra-day variability for precision and accuracy were <10%.

Automation↗
PubMed2000

Helicobacter pylori reduces intracellular glutathione in gastric epithelial cells.

Helicobacter pylori infection has been associated with stimulation of gastric mucosal reactive oxygen species (ROS) production, and it was postulated that ROS production is due to neutrophil infiltration and activation. The aim of this study was to investigate the direct effect of H. pylori on ROS formation in gastric epithelial cells in vitro. The human gastric cancer cell line HM02 was incubated with H. pylori for 24 hr, and the effects on cell number and the intracellular radical scavenger reduced glutathione (GSH) were assessed. H. pylori caused a concentration-dependent reduction of cellular GSH concentrations over a broad bacteria-to-cell ratio (1.4-42) in the absence of cell necrosis. The radical scavengers MnTBAP (a cell permeable superoxide dismutase) and ebselen provided protection against H. pylori-induced decrease in cellular GSH concentrations. We conclude that H. pylori directly decreases cellular GSH concentrations in gastric epithelial cells. We suggest that this effect is caused by the release of ROS by H. pylori.

Azoles↗
PubMed2000

Pharmacokinetics of SDZ RAD and cyclosporin including their metabolites in seven kidney graft patients after the first dose of SDZ RAD.

AIMS: The aim of the study was to investigate the pharmacokinetics and metabolism of the new immunosuppressant SDZ RAD during concomitant therapy with cyclosporin in stable renal transplant patients. Furthermore, we studied the influence of SDZ RAD on the pharmacokinetics of cyclosporin at steady state levels. METHODS: SDZ RAD was administered orally in different doses (0.25-15 mg day-1) to seven patients, who were on standard cyclosporin-based immunosuppression. The blood concentrations of both drugs including their main groups of metabolites were measured simultaneously by LC/electrospray-mass spectrometry. RESULTS: The mean area under the blood concentration-time curve to 12 h (AUC(0,12 h)) was 4244 +/- 1311 microg l-1 h for cyclosporin before SDZ RAD treatment and 4683 +/- 1174 microg l-1 h (P = 0.106) on the day of SDZ RAD treatment (95% CI for difference -126, 1003). On both study days Cmax, and tmax of cyclosporin were not significantly different. The metabolite pattern of cyclosporin did not change. The pharmacokinetic data of SDZ RAD dose-normalized to 1 mg SDZ RAD were as follows: AUC(0,24 h): 35.4 +/- 13.1 microg l-1 h, Cmax: 7.9 +/- 2.7 microg l-1 and tmax: 1.5 +/- 0.9 h. The metabolites of SDZ RAD found in blood were hydroxy-SDZ RAD, dihydroxy-SDZ RAD, demethyl-SDZ RAD, and a ring-opened form of SDZ RAD. CONCLUSIONS: A single dose of SDZ RAD did not influence significantly the pharmacokinetics of cyclosporin. The most important metabolite of SDZ RAD was the hydroxy-SDZ RAD, its AUC(0,24 h) being nearly half that of the parent compound SDZ RAD.

Administration, Oral↗
PubMed2000

Role of vacA and cagA in Helicobacter pylori inhibition of mucin synthesis in gastric mucous cells.

The aim of this study was to investigate the effect of Helicobacter pylori on the function of gastric mucous cells. H. pylori (10(4) to 10(7) CFU/well) was incubated with the mucin-producing gastric cell line HM02 for 12 and 24 h. Mucin synthesis and secretion were determined by the incorporation of D-N-[acetyl-(14)C]glucosamine into intracellular and released high-molecular-weight glycoproteins. cagA-positive, cytotoxin-producing and non-cytotoxin-producing H. pylori strains impaired the incorporation of D-N-[acetyl-(14)C]glucosamine into intracellular glycoproteins. Significant inhibition of mucin synthesis was noted after 12 and 24 h of cocultivation with a bacterial load of >/=10(5) bacteria (bacterium/cell ratio = 0.25). The cagA-positive, cytotoxin-producing strains (HP64, HP57, and HP87) caused significantly stronger inhibition of intracellular mucin synthesis than the cagA-positive, non-cytotoxin-producing strains (HP05, HP83, and HP84). The cagA-negative, non-cytotoxin-producing strains (HP01, HP04, and HP85) did not affect intracellular mucin synthesis. The results indicate that H. pylori directly impairs mucin synthesis in gastric mucous cells and that cytotoxic cagA-positive strains cause more profound inhibition of mucin synthesis. We suggest that the increased inhibitory effect of cagA-positive, cytotoxin-producing strains on mucin synthesis can be considered one possible factor responsible for the increased risk of developing peptic ulceration with these H. pylori strains.

Acetylglucosamine↗
PubMed2000

Helicobacter pylori causes DNA damage in gastric epithelial cells.

Helicobacter pylori infection has been considered as a risk factor for gastric carcinoma. Strong evidence exists that reactive oxygen species (ROS) play an important role in carcinogenesis, and in vivo investigations have shown increased synthesis of ROS in the gastric mucosa of H.pylori-infected patients. In the present study the direct effects of H.pylori on ROS and DNA synthesis, induction of apoptosis and DNA repair were investigated in the gastric epithelial cell lines AGS and HM02. Incubation of gastric cells with H.pylori extract induced the synthesis of ROS, diminished the levels of reduced glutathione (GSH), induced DNA fragmentation and increased DNA synthesis in gastric cells. Poly(ADP-ribose) formation was increased in gastric cells exposed to H.pylori extract. FACS analysis of gastric cells exposed to H.pylori extract did not reveal any change in the percentage of cells in the G(2)/M phase of the cell cycle. The radical scavengers MnTBAP (a cell permeable superoxide dismutase mimic), ebselen (a GSH peroxidase mimic) and high doses of catalase completely blocked H.pylori extract-induced elevation in DNA synthesis. Our results indicate that H.pylori extract directly induces the synthesis of ROS in gastric epithelial cells and causes DNA damage.

Cell Cycle↗
PubMed2000

Lactonization is the critical first step in the disposition of the 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor atorvastatin.

In an in vitro study, we compared the cytochrome P450 (CYP)-dependent metabolism and drug interactions of the acid and lactone forms of the 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitor atorvastatin. Metabolism of atorvastatin acid and lactone by human liver microsomes resulted in para-hydroxy and ortho-hydroxy metabolites. Both substrates were metabolized mainly by CYP3A4 and CYP3A5. Atorvastatin lactone had a significantly higher affinity to CYP3A4 than the acid (K(m): para-hydroxy atorvastatin, 25.6 +/- 5.0 microM; para-hydroxy atorvastatin lactone, 1.4 +/- 0.2 microM; ortho-hydroxy atorvastatin, 29.7 +/- 9.4 microM; and ortho-hydroxy atorvastatin lactone, 3.9 +/- 0.2 microM). Compared with atorvastatin acid, CYP-dependent metabolism of atorvastatin lactone to its para-hydroxy metabolite was 83-fold higher [formation CL(int) (V(max)/K(m)): lactone 2949 +/- 3511 versus acid 35.5 +/- 48.1 microl. min(-1). mg(-1)] and to its ortho-hydroxy metabolite was 20-fold higher (CL(int): lactone 923 +/- 965 versus acid 45.8 +/- 59. 1 microl. min(-1). mg(-1)). Atorvastatin lactone inhibited the metabolism of atorvastatin acid by human liver microsomes with an inhibition constant (K(i)) of 0.9 microM while the K(i) for inhibition of atorvastatin by atorvastatin lactone was 90 microM. Binding free energy calculations of atorvastatin acid and atorvastatin lactone complexed with CYP3A4 revealed that the smaller desolvation energy of the neutral lactone compared with the anionic acid is the dominant contribution to the higher binding affinity of the lactone rather than an entropy advantage. Because atorvastatin lactone has a significantly higher metabolic clearance and the lactone is a strong inhibitor of atorvastatin acid metabolism, it can be expected that metabolism of the lactone is the relevant pathway for atorvastatin elimination and drug interactions. We hypothesize that most of the open acid metabolites present in human plasma are generated by interconversion of lactone metabolites.

Atorvastatin↗
PubMed1999

Simultaneous on-line extraction and analysis of sirolimus (rapamycin) and ciclosporin in blood by liquid chromatography-electrospray mass spectrometry.

We developed a sensitive and specific semi-automated liquid chromatography-electrospray mass spectrometric (HPLC-ESI-MS) assay for the simultaneous quantification of sirolimus and ciclosporin in blood. Following a simple protein precipitation step, the supernatants were injected into the HPLC system and extracted on-line. After column switching, the analytes were backflushed from the extraction column onto the analytical narrow-bore column and eluted into the ESI-MS system. The assay was linear from 0.4 to 100 microg/l sirolimus and from 2 to 1500 microg/l ciclosporin. The mean recoveries of sirolimus and ciclosporin were 98 and 96%, respectively. The mean interday precision/accuracy was 8.6%/-4.8% for sirolimus and 9.3%/-2.9% for ciclosporin.

Chromatography, High Pressure Liquid↗
PubMed1999

Growth characteristics and influence of antibiotics on rough/smooth phenotypic variants of Helicobacter pylori.

Helicobacter pylori shows a rather high variability of several biochemical markers including lipopolysaccharide structures. This study aimed to determine whether Helicobacter pylori has a potential for phenotypic variability and to describe its effects on bacterial pathogenesis. From colonies of three clinical strains of Helicobacter pylori with rough (R) colony morphology, spontaneous phenotypic variants with smooth (S) colony morphology were isolated that occurred with a frequency of 10(-2) to 10(-3), irrespective of growth conditions. R-variant bacteria produced exclusively low-molecular-mass lipopolysaccharide. They exhibited increased lysis in the presence of plain air. In contrast, the S variants produced low- and high-molecular-mass lipopolysaccharide and did not exhibit increased lysis in the presence of plain air. Cocultivation of bacterial cells with AGS stomach cancer cells revealed that R-variant bacteria but not S-variant bacteria effected an inhibition of high molecular-weight glycoprotein biosynthesis and secretion by the host cells. Skirrow supplement added as selective agent to liquid and/or solid media was tolerated to a similar extent among R- and S-variant bacteria, while all variants proved sensitive to metronidazole, amoxicillin and clarithromycin except for the R and S isolates of strain Hp57, which showed resistance to the latter compound. It was concluded that R- and S-variants of Helicobacter pylori may have distinct roles in pathogenesis; nevertheless, these bacteria may be isolated by traditional methods and eradicated by conventional anti-infective therapy.

Anti-Bacterial Agents↗
PubMed1999

LC/ESI-MS allows simultaneous and specific quantification of SDZ RAD and cyclosporine, including groups of their metabolites in human blood.

An analytic technique using liquid chromatography (LC) coupled with electrospray-mass spectrometry (ESI-MS) has been developed for the simultaneous determination of the new immunosuppressant SDZ RAD (40-O-[2-hydroxy)ethylrapamycin) and cyclosporine (Cs), including their metabolites in blood. With the time-sparing, automated on-line extraction technique, the recovery of SDZ RAD averaged 95% and that of Cs, 94%. The calibration lines were linear from 0.5 to 100 microg/L (r2 = 0.99) for SDZ RAD and from 10 to 1,000 microg/L (r2 = 0.99) for Cs. The method has been tested on blood samples from renal transplant recipients taken between 1 and 5 hours after oral SDZ RAD and Cs administration. In blood, we found the following metabolites: Hydroxy-SDZ RAD, dihydroxy-SDZ RAD, demethyl-SDZ RAD, and the ring-opened form of SDZ RAD. The main metabolite of SDZ RAD in blood was hydroxy-SDZ RAD. This novel LC/ESI-MS technique provided an excellent method for simultaneous quantitative monitoring of SDZ RAD and Cs, including their relevant groups of metabolites in patients treated simultaneously with these immunosuppressants.

Chromatography, High Pressure Liquid↗
PubMed1999

Small intestinal metabolism of the 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor lovastatin and comparison with pravastatin.

We compared the intestinal metabolism of the structurally related 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors lovastatin and pravastatin in vitro. Human small intestinal microsomes metabolized lovastatin to its major metabolites 6'beta-hydroxy (apparent K(m) = 11.2 +/- 3.3 microM) and 6'-exomethylene (apparent K(m) = 22.7 +/- 9.0 microM) lovastatin. The apparent K(m) values were similar for lovastatin metabolism by human liver microsomes. 6'beta-Hydroxylovastatin formation by pig small intestinal microsomes was inhibited with the following inhibition K(i) values: cyclosporine, 3.3 +/- 1.2 microM; ketoconazole, 0.4 +/- 0.1 microM; and troleandomycin, 0.8 +/- 0.9 microM. K(i) values for 6'-exomethylene lovastatin were similar. Incubation of pravastatin with human small intestinal microsomes resulted in the generation of 3'alpha,5'beta, 6'beta-trihydroxypravastatin (apparent K(m) = 4560 +/- 1410 microM) and hydroxypravastatin (apparent K(m) = 5290 +/- 1740 microM). In addition, as in the liver, pravastatin was metabolized in the small intestine by sulfation and subsequent degradation to its main metabolite 3'alpha-iso-pravastatin. It was concluded that lovastatin is metabolized by cytochrome P-450 3A enzymes in the small intestine. Compared with lovastatin, the cytochrome P-450-dependent intestinal intrinsic clearance of pravastatin was >5000-fold lower and cannot be expected to significantly affect its oral bioavailability or to be a significant site of drug interactions.

Animals↗
PubMed1999

Comparison of cytochrome P-450-dependent metabolism and drug interactions of the 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors lovastatin and pravastatin in the liver.

In an in vitro study, the cytochrome P-450 3A (CYP3A)-dependent metabolism and drug interactions of the 3-hydroxy-3-methylglutaryl-Co A reductase inhibitors lovastatin and pravastatin were compared. Lovastatin was metabolized by human liver microsomes to two major metabolites: 6'beta-hydroxy [Michaelis-Menten constant (Km): 7.8 +/- 2.7 microM] and 6'-exomethylene lovastatin (Km,10.3 +/- 2.6 microM). 6'beta-Hydroxylovastatin formation in the liver was inhibited by the specific CYP3A inhibitors cyclosporine (Ki, 7.6 +/- 2.3 microM), ketoconazole (Ki, 0.25 +/- 0.2 microM), and troleandomycin (Ki, 26.6 +/- 18.5 microM). Incubation of pravastatin with human liver microsomes resulted in the generation of 3'alpha,5'beta, 6'beta-trihydroxy pravastatin (Km, 4,887 +/- 2,185 microM) and hydroxy pravastatin (Km, 20,987 +/- 9,389 microM). The formation rates of 3'alpha,5'beta,6'beta-trihydroxy pravastatin by reconstituted CYP3A enzymes were (1,000 microM pravastatin) 1.9 +/- 0.6 pmol.min-1.pmol CYP3A4 and 0.06 +/- 0.04 pmol.min-1.pmol CYP3A5, and the formation rates of hydroxy pravastatin were 0.12 +/- 0.02 pmol.min-1.pmol CYP3A4 and 0.02 +/- 0.004 pmol.min-1.pmol CYP3A5. The specific CYP3A inhibitors cyclosporine, ketoconazole, and troleandomycin significantly inhibited hydroxy pravastatin formation by human liver microsomes, but only ketoconazole inhibited 3'alpha, 5'beta,6'beta-trihydroxy pravastatin formation, suggesting that other CYP enzymes are involved in its formation. It is concluded that, compared with lovastatin [CLint formation 6'beta-hydroxylovastatin (microl.min-1.mg-1): 199 +/- 248, 6'-exomethylene lovastatin: 138 +/- 104)], CYP3A-dependent metabolism of pravastatin [CLint formation 3'alpha,5'beta, 6'beta-trihydroxy pravastatin (microl.min-1.mg-1): 0.03 +/- 0.03 and hydroxy pravastatin: 0.02 +/- 0.02] is a minor elimination pathway. In contrast to lovastatin, drug interactions with pravastatin CYP3A-catalyzed metabolism cannot be expected to have a clinically significant effect on its pharmacokinetics.

Biotransformation↗
PubMed1998

Stimulation of pepsinogen release from chief cells by Helicobacter pylori: evidence for a role of calcium and calmodulin.

To define the mechanisms by which Helicobacter pylori stimulates pepsinogen secretion, the in vitro release of pepsinogen was studied using a preparation of pig chief cell monolayers. Helicobacter pylori induced a time- and concentration-dependent release of pepsinogen into the medium, with about a three-fold increase in pepsinogen secretion over controls found after 45 min of incubation. 3x10(7) H. pylori produced 50% of the maximal response found at a H. pylori count of 2x10(8). The action of H. pylori did not depend on the presence of the vacuolating toxin (vacA) and the cytotoxin-associated protein (cagA). Dibutyryl-cAMP and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate also markedly stimulated pepsinogen secretion and enhanced the stimulatory effect of H. pylori. Helicobacter pylori-stimulated pepsinogen release was inhibited by lanthanum and the calmodulin antagonist W-7, but not by the L-type Ca2+ channel blocker nifedipine, TMB-8, an agent that blocks the release of Ca2+ from intracellular stores, the protein kinase C inhibitor staurosporine and the protein kinase A inhibitor H-8. It is suggested that H. pylori directly stimulates pepsinogen release from gastric chief cells and that this effect is mediated via the calcium/calmodulin messenger branch.

Animals↗
PubMed1998

Effects of PGE2 and of different synthetic PGE derivatives on the glycosylation of pig gastric mucins.

The glycosylation of pig gastric mucins, discharged in response to prostaglandin (PG) E2 and to three synthetic PGE-derivatives (misoprostol, nocloprost, rioprostil) was compared. After a 20 h culture period in the absence or presence of 1 micromol/l of one of the PGs, mucins were isolated by gel chromatography and their glycosylation characterized by their linkage to a panel of lectins. For all tested PGs, a significantly increased lectin linkage to mucin glycoproteins of high molecular weight was detected; no significant effects were observed for low molecular weight glycoproteins. Within the stimulatory pattern, major effects were found for the linkage of peanut agglutinin and soybean agglutinin, suggesting predominant effects on the expression of galactose and N-acetyl-galactosamine. Only minor effects were found for sialic acid, mannose, N-acetyl-glucosamine and fucose expression, as evidenced by the linkage of Sambucus nigra agglutinin, Concanavalin A, Datura stramonium agglutinin and Ulex europaeus I agglutinin. All PGs exerted a similar stimulatory pattern. However, at the indicated concentration, misoprostol (281 +/- 36% of control) rendered a significantly higher overall effect than PGE2 (208 +/- 31%), whereas the increases induced by nocloprost (237 +/- 35%) and rioprostil (202 +/- 35%) were not significantly different from the PGE2 effects. These results, suggesting similar stimulatory effects of PGE2 and of the tested synthetic PGs on glycosylation of mucin oligosaccharides, discharged from mucous cells during an in vitro culture, may, at least in part, explain clinical findings that during an impairment of the endogenous PG synthesis, the tested synthetic PGs are effective exogenous substitutes for endogenous E-type prostaglandins and act as anti-ulcer drugs.

Acetylgalactosamine↗
PubMed1998

Helicobacter pylori fatty acid cis 9,10-methyleneoctadecanoic acid increases [Ca2+]i, activates protein kinase C and stimulates acid secretion in parietal cells.

The effect of the Helicobacter pylori (H. pylori) fatty acid cis 9,10-methyleneoctadecanoic acid (MOA) on gastric acid secretion was studied in isolated guinea-pig parietal cells. MOA (1 and 3 micromol/l) stimulated basal and enhanced histamine- and dibutyryl cyclic AMP-stimulated acid secretion in parietal cells. MOA increased intracellular free [Ca2+]i concentration in a concentration-dependent manner. The source of [Ca2+]i was extracellular as demonstrated by depletion of [Ca2+]i with EGTA. Furthermore, MOA caused activation of parietal cell protein kinase C (PKC). The effect of MOA upon PKC activation was [Ca2+]i-dependent but did not require phosphatidylserine as phospholipid co-factor. Similarly to the effect of diolein, MOA increased the stimulatory effect of phosphatidylserine at low [Ca2+]i concentrations. Treatment of parietal cells with MOA caused translocation of PKC from the cytosol to the membrane-associated cell fraction. We propose that MOA stimulates parietal cell acid secretion presumably by an increase of cytosolic free [Ca2+]i concentrations and PKC activation.

1-Methyl-3-isobutylxanthine↗
PubMed1998

Structural elucidation by electrospray mass spectrometry: an approach to the in vitro metabolism of the macrolide immunosuppressant SDZ RAD.

SDZ RAD [40-O-(2-hydroxyethyl)rapamycin] is a macrolide immunosuppressant that is currently under clinical investigation after organ transplantation. The elucidation of its metabolic pathway is essential to improve the understanding of its therapeutic potentials and safety. In this article we describe investigations on the structural identification of some major metabolites of the drug produced by human liver microsomes in vitro. The principles described may be generally applicable for the structural elucidation of complex compound mixtures in biological matrices. Under the conditions of electron impact ionization, SDZ RAD undergoes extensive fragmentation and no information sufficient for structural elucidation is obtained. Therefore, mass spectrometry based on soft electrospray ionization (ESI) in conjunction with collision-induced fragmentation was the method of choice. High-performance liquid chromatography coupled to an ESI mass spectrometer resulted in separation and identification of 16-O-demethyl-SDZ RAD, the ring-opened form of SDZ RAD, and its dehydrate. Additionally, we characterized several demethylated and hydroxylated metabolites.

Chromatography, High Pressure Liquid↗
PubMed1998

The Helicobacter pylori fatty acid cis-9,10-methyleneoctadecanoic acid stimulates protein kinase C and increases DNA synthesis of gastric HM02 cells.

Protein kinase C (PKC) has been implicated in the control of epithelial proliferative activity and in the process of malignant transformation. Helicobacter pylori (H.p.) infection is associated with increased gastric epithelial cell proliferation and has been linked with gastric carcinoma. In the present study, we report that the H.p. fatty acid cis-9,10-methyleneoctadecanoic acid (MOA) directly activates PKC (Ka 3.3 microM). The effect of MOA upon PKC activation was Ca2+ dependent but did not require phosphatidylserine as phospholipid cofactor. MOA increased the stimulatory effect of phosphatidylserine at low Ca2+ (1 microM) concentrations. These findings indicate that MOA interacts at the phospholipid- and the diacylglycerol-binding domain to elicit PKC activation. Treatment of gastric mucous cells HM02 caused translocation of PKC from the cytosol to the nuclear, mitochondrial and membrane fraction. Furthermore, MOA stimulated [3H]thymidine incorporation into the DNA of HM02 cells. Our results show that the H.p. fatty acid MOA activates PKC and increases DNA synthesis in gastric epithelial cells.

Animals↗