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Biomedical subjects

K F Sewing

Publications and source records attributed to K F Sewing.

At least 109 records · Page 6Linked to original sources
PubMed1991

Ciclosporin metabolite pattern in blood and urine of kidney graft patients in relation to liver function.

Ciclosporin, an immunosuppressant, is metabolized by the liver cytochrome P450 system. Changes in the pattern of its metabolites in blood and urine in patients with disturbed liver function have been studied. Forty seven kidney graft patients receiving 2.9 mg/kg/d ciclosporin b.i.d., and no additional medication that would interfere with ciclosporin metabolism, were allocated to three groups according to liver function: I with normal liver function (n = 19), II with elevated liver enzyme activity or bilirubin concentration in serum (n = 20), and III with cholestasis (n = 8). Ciclosporin and 17 metabolites were determined in blood and 24 h-urine. In blood the trough concentrations of metabolites M19 and M1A were significantly higher in group III than in groups I and II. The total quantity of metabolites excreted in 24 h-urine was significantly different for H230, M4N69 and M1A (group III greater than I = II). Renal excretion of the daily dose of ciclosporin in patients in group I was 2.7%, group II 3% and group III 5.7%. In group III compared to group I the ciclosporin metabolite pattern was shifted to a relatively higher concentration of M19 in blood and of H 230, M19 and M1A in urine. Since high ciclosporin metabolite concentrations appear to be associated with nephrotoxicity, the metabolite pattern in patients with impaired liver function should be monitored.

Alanine Transaminase↗
PubMed1991

Contribution of cyclosporin metabolites to immunosuppression in liver-transplanted patients with severe graft dysfunction.

The aim of this study was to analyse the immunosuppressive contribution of cyclosporin metabolites in liver-grafted patients. Therefore the immunosuppressive potency of 17 metabolites, alone and in combination, was tested in human mixed lymphocyte cultures, and the results were correlated with metabolite blood levels in liver-grafted patients. Of the 17 metabolites tested only six highly lipophilic metabolites showed a detectable immunosuppressive activity of up to 10% of the activity of cyclosporin; the effect of combining metabolites was additive. For calculation of the in vivo activity, blood levels of seven major cyclosporin metabolites were determined in liver-grafted patients with normal liver function (group A, 43 episodes) and with severe hyperbilirubinaemia (group B, 66 episodes). Both patient groups had comparable levels of parent drug (122.9 +/- 17.4 vs. 111.1 +/- 23.5 ng/ml by HPLC) and similar blood levels of the highly lipophilic metabolites 17, 1 and 18. By contrast, blood levels of the less lipophilic metabolites 8, 9, 26 and 203-218 were substantially increased in group B (P less than 0.05). High overall metabolite blood levels in group B were also indicated by a non-specific monoclonal RIA (520 +/- 199 ng/ml for group A vs. 1318 +/- 407 ng/ml for group B). Despite the very high levels in group B, however, the overall contribution of the metabolites to immunosuppression was similar in both groups (12.6 +/- 5.0% for group A vs. 13.8 +/- 5.6% for group B). These findings indicate that, despite a marked accumulation of cyclosporin metabolites in patients with severe cholestatic liver dysfunction, their immunosuppressive contribution remains low.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclosporins↗
PubMed1991

Isolation of an immunosuppressive metabolite of FK506 generated by human microsome preparations.

Metabolism of FK506, a 23 member macrolide under clinical investigation as immunosuppressant after transplantation, was studied using human liver microsomes. Two fractions isolated by semi-preparative HPLC were identified by negative fast atom bombardment mass spectrometry as FK506 metabolites with mass peaks at m/z = 790 indicating demethylation of the mother compound. The immunosuppressive activity of one metabolite was evaluated in a ConA-stimulated peripheral rat lymphocyte assay. FK506 had an IC50 of 0.186 nmol/L and the metabolite tested of 1.89 nmol/L.

Animals↗
PubMed1991

Additive and synergistic effects of cyclosporine metabolites on glomerular mesangial cells.

Out of the 29 cyclosporin (Cs) metabolites defined so far, 10 representative ones were isolated from bile of liver grafted patients, purified by HPLC, and their structure specified by FAB-MS and 1H NMR. These were used to determine the growth inhibitory effects on Sprague Dawley rat glomerular mesangial cells (MC). Metabolite dilutions were added to cultured MC for 72 hours and [3H]-thymidine incorporation was measured. A 50% growth inhibition by single metabolites (M) on MC was achieved at the following concentrations (mg/liter): Cs: 1.25; M21: 6.0; M18: 9.0; M26: 10.5; M1: 10.8; M8: 10.8; M17: 12.5; M13: greater than 20.0; M25: greater than 25.0; M203-218: greater than 50.0; H355: greater than 50.0. The activity was correlated to the degree of metabolization as the group of six "active" compounds included four primary metabolites (hydroxylated or demethylated derivatives of Cs: M21, M18, M1, M17), whereas the four "inactive" compounds exclusively were secondary metabolites (demethylated, hydroxylated and/or oxidized primary metabolites: M13, M25, M203-218, H355). Combinations of active metabolites with or without Cs resulted in an additive antiproliferative effect. Although single metabolite activities are not relevant in vivo, already combinations of three (M1 + M17 + M18) or four metabolites (M17 + M18 + M21 + H355) resulted in a significant growth inhibition at concentrations of the participating metabolites measured in urine of liver transplanted patients. Moreover, significant synergistic activities were determined with combinations including secondary metabolites. A final set of experiments discharged unspecific cytotoxic effects. The inhibition of MC [3H]-thymidine incorporation was completely reversible and moreover, direct mesangiolysis was excluded for both single and combined metabolite actions. Thus, considering rat MC proliferation as an initial kidney cell model system for subsequent, more detailed studies measuring functional parameters, we have demonstrated that activities of single metabolites are related to their chemical structure. More importantly, mimicking to some extent the patients' situation, combinations of metabolites at concentrations occurring in vivo reduced MC proliferation in culture in an at least an additive fashion, suggesting that side effects of Cs treatment might be attributed to combined Cs metabolite actions.

Animals↗
PubMed1991

Efficacy of low-dose antacids in the treatment of peptic ulcers: pharmacological explanation?

Antacids have been used as remedies for benign gastroduodenal disorders for centuries. They were regarded to be effective in relieving gastric pain and symptoms of hyperacidity and in promoting ulcer healing. The effectiveness was based on empiric observations and was not derived from the controlled clinical trials data. Until the introduction of histamine H2-receptor antagonists into peptic ulcer therapy, they dominated that field together with carbenoxolone. The enthusiasm for and euphoric attitude of gastroenterologists all over the world to H2-receptor antagonists resulted in a life of shadow for antacids. This changed when Peterson et al. published the first controlled clinical trial on Maalox (N Engl J Med 1977;267:341-5). (The use of trade names for antacids is justified as most of the antacids in use are composed of at least two if not more constituents).

Aluminum Oxide↗
PubMed1991

Effects of histamine and activators of the cyclic AMP system on protein synthesis in and release of high molecular weight glycoproteins from isolated gastric non-parietal cells.

1. Glycoprotein and protein synthesis in and release from pig isolated, enriched gastric mucous cells were measured by the incorporation of N-acetyl-[14C]-D-glucosamine and [3H]-L-leucine, respectively, into cellular and released acid precipitable material. 2. Histamine and activators of the adenosine 3':5'-cyclic monophosphate (cyclic AMP) system maximally stimulated total protein and glycoprotein synthesis in and release from the cells at concentrations of histamine (10 microM), forskolin (10-100 microM), 3-isobutyl-1-methylxanthine (100 microM), and dibutyryl cyclic AMP (1-3 mM), respectively. In the presence of 3-isobutyl-1-methylxanthine (30 microM) histamine stimulation was enhanced. 3. As shown by gel chromatography, stimulation by histamine (100 microM), forskolin (10 microM), 3-isobutyl-1-methylxanthine (100 microM) and dibutyryl cyclic AMP (1 mM) resulted in a release of high molecular weight (approximately 2 x 10(6) daltons) glycoproteins from the cells. The histamine H2-receptor antagonist, ranitidine (100 microM), blocked the effect of histamine. 4. We conclude that cyclic AMP-dependent processes are involved in the regulation of protein and glycoprotein synthesis in and the release of high molecular weight (mucous) glycoproteins from pig gastric non-parietal cells and that histamine may be a physiological activator of this system.

1-Methyl-3-isobutylxanthine↗
PubMed1991

Investigations on the metabolic pathways of cyclosporine: I. Excretion of cyclosporine and its metabolites in human bile--isolation of 12 new cyclosporine metabolites.

1. Cyclosporine metabolites of known and unknown structures were isolated, by semi-preparative h.p.l.c., from human bile from the T-tube of liver-grafted patients, who received cyclosporine treatment. Their structures were elucidated by FAB mass spectrometry and 1H-n.m.r. spectroscopy. 2. Twelve of the cyclosporine metabolites, with known chemical structures, were isolated and identified using authentic standard material. 3. Four isolated fractions contained tri-hydroxylated metabolites; two fractions contained di-hydroxylated, demethylated metabolites; one fraction contained a tri-hydroxylated, demethylated metabolite; and one fraction a mono-hydroxylated, demethylated metabolite. The exact metabolism sites were partially defined. 4. Two carboxylated cyclosporine metabolites, of which one was hydroxylated in an unknown position, were isolated. 5. One new metabolite proved to be a glucuronylated phase II metabolite. Deglucuronylation of this metabolite by beta-glururonidase yielded metabolite AM1c. The proposed structure was AM1c-Glc; is a proposed extension of the Hawk's Cay nomenclature of the cyclosporine metabolites for glucuronylated metabolites. 6. One of the unknown metabolites was hydroxylated in two positions of amino acid 1. The proposed nomenclature was 'AM11d', where '1d' indicates hydroxylation at the delta C of amino acid 1. 7. A metabolite with an aldehyde functional group at amino acid 1, which had two isomeric forms, was isolated. I.r.-spectroscopy indicated that isomerism may be caused by conjugation of the aldehyde group with the double bond between C6 and C7 of amino acid 1.

Aldehydes↗
PubMed1991

Investigations on the metabolic pathways of cyclosporine: II. Elucidation of the metabolic pathways in vitro by human liver microsomes.

1. Cyclosporine and its metabolites, isolated from human bile and identified by FAB mass spectrometry and 1H-n.m.r. spectroscopy, were metabolized by human liver microsomes for the identification of new cyclosporine metabolites. From these data a metabolic pathway for cyclosporine, which includes these new cyclosporine metabolites, has been proposed. The new metabolites were isolated by semi-preparative h.p.l.c. and their chemical structures were elucidated by FAB mass spectrometry. These isolated metabolites were further metabolized and the products identified by FAB mass spectrometry. 2. Fourteen metabolites, whose structure has not yet been elucidated, were isolated after metabolism of structurally identified cyclosporine metabolites, and chemical structures for five of these metabolites were proposed. 3. The structures of the new cyclosporine metabolites were: (i) a N-demethylated, carboxylated derivative (AM1A4N), (ii) a di-hydroxylated, N-demethylated derivative (AM14N9), (iii) a hydroxylated and carboxylated derivative (AM1A9), (iv) a di-hydroxylated, cyclized and N-demethylated derivative (AM1c4N9) and (v) a cyclized and carboxylated (AM1cA) derivative. 4. A proposed cyclosporine metabolic pathway comprises a total of 29 metabolites. It consists of four main branches originating from metabolites AM1, AM1c, AM9 and AM4N.

Bile↗
PubMed1991

Signal transduction pathway in gastric mucous cells.

In isolated and enriched guinea-pig gastric mucous cells the effects of carbachol, prostaglandin E2 (PG E2), prostaglandin F2 alpha (PG F2 alpha) and histamine on adenylate cyclase (AC) and cytosolic free Ca2+ were investigated, in order to study the biochemical mechanisms involved in secretagogue-mediated mucus release. Histamine and both prostaglandins stimulated AC in partially purified membranes of mucous cells. Histamine was most efficacious, followed by PG E2 and PG F2 alpha. The histamine effect was blocked by the H2-receptor antagonist ranitidine, but not by the H1-receptor antagonist mepyramine. Carbachol raised the resting [Ca2+]i in mucous cells from 120 to 306 nM. This carbachol effect was blocked by atropine. Histamine and PG E2 stimulation of AC was inhibited in a concentration-dependent manner by Ca2+ (IC50:31 microM). In the presence of TPA and phosphatidylserine, conditions which activate protein kinase C, the inhibitory action of Ca2+ on AC was significantly increased. These data indicate that there exists a negative feedback control mechanism between protein kinase C and histamine/prostaglandin E2-induced AC activation. From the finding that TPA and phosphatidylserine increased the inhibitory action of Ca2+ on cholera toxin-, but not on forskolin-stimulated AC we assume that the point, where protein kinase C exerts its inhibitory effect at the AC, is the guanine nucleotide regulatory protein.

Adenylyl Cyclases↗
PubMed1990

Interaction of the anti-inflammatory seleno-organic compound ebselen with acid secretion in isolated parietal cells and gastric H+/K(+)-ATPase.

The effects of the anti-inflammatory seleno-organic compound ebselen on gastric H+/K(+)-ATPase, H+/K(+)-ATPase-mediated proton transport and on parietal cell HCl production was studied. Ebselen inhibited K(+)-stimulated ATPase activity in leaky gastric membranes (IC50:0.15 microM) and H+/K(+)-ATPase-mediated proton transport in intact gastric membrane vesicles (IC50:0.7 microM). Histamine- and dibutyryl-cAMP-stimulated HCl production in isolated and enriched guinea-pig parietal cells was inhibited with an IC50 value of 12 microM. The mercaptan dithioerythritol and the nucleotide ATP prevents the H+/K(+)-ATPase against inactivation and dithioerythritol was found to restore already inhibited enzyme activity and ATPase mediated H+ transport. Furthermore, dithioerythritol could prevent ebselen-induced inhibition of HCl production in the parietal cell preparation. It is concluded that ebselen inhibits acid secretion in the parietal cell by interference with SH groups of the gastric proton pump, the H+/K(+)-ATPase. Therefore ebselen can be regarded as an anti-inflammatory drug for which in vitro anti-secretory properties can be demonstrated.

Adenosine Triphosphatases↗
PubMed1990

Substituted thieno[3,4-d]imidazoles, a novel group of H+/K(+)-ATPase inhibitors. Differentiation of their inhibition characteristics from those of omeprazole.

The action of the H+/K(+)-ATPase inhibitors, Hoe 731 and S 4216, both thieno-imidazole derivatives, was compared with that of the benzimidazole derivative, omeprazole. In intact, gastric membrane vesicles under conditions shown to result in acidification of the vesicle interior. Hoe 731 and S 4216 inhibited H+/K(+)-ATPase activity with an IC50 value of about 1.0 microM. In the absence of a generated pH gradient the respective IC50 values were 5.5 and 2.1 microM. In contrast, omeprazole inhibited the enzyme only in the presence of proton accumulation (IC50: 0.7 microM). The inhibitory action of omeprazole on H+/K(+)-ATPase-mediated proton transport was prevented by the membrane permeable mercaptane, dithioerythritol, but not by the membrane impermeable, mercaptane glutathione, whereas both mercaptanes were able to prevent the effect of Hoe 731 and S 4216. These results indicate that the thienoimidazoles react with intravesicular (luminal) and extravesicular (cytosolic) SH groups of the H+/K(+)-ATPase, whereas omeprazole interacts uniquely with luminal SH groups of the enzyme. In isolated parietal cells all drugs caused a concentration-dependent inhibition of HCl production, as measured by [14C]aminopyrine uptake, during histamine and dibutyryl-cAMP stimulation. The IC50 value was 0.1 microM for Hoe 731 and omeprazole and 0.4 microM for S 4216 after 30-min incubation. The inhibitory action of Hoe 731 and S 4216 faded with increasing incubation time, whereas omeprazole caused an unchanged inhibition over the entire 120-min incubation period. We suggest that several factors, e.g. weaker chemical stability of the drugs or perturbation of cellular glutathione levels, may be responsible for the fading inhibitory action of thienoimidazoles in the parietal cell.

Adenosine Triphosphatases↗
PubMed1990

Effects of PGE2, carbenoxolone, cholecystokinin, and the thromboxane-mimetic U46619 on protein and glycoprotein production by isolated pig gastric mucosal cells.

We studied the effects of prostaglandin (PG) E2, carbenoxolone, cholecystokinin-octapeptide (CCK-OP), and the thromboxane-mimetic U46619, all known to stimulate gastric mucus secretion in vivo, on protein and glycoprotein synthesis in and release from isolated and enriched pig gastric mucous cells, as measured by the incorporation of [3H]L-leucine and N-acetyl-[14C]D-glucosamine respectively into cellular and released acid insoluble material. PGE2 stimulated glycoprotein and protein synthesis (EC50 7 and 30 nmol/L, respectively) and release (EC50 50 and 140 nmol/L, respectively) in a concentration-dependent manner, whereas carbenoxolone, CCK-OP and U46619 failed to enhance the incorporation of the tracers. We conclude that stimulation of mucus secretion by PGE2 is related to direct effects on protein and glycoprotein production of gastric non-parietal cells, whereas indirect effects may be involved in the stimulation by carbenoxolone, CCK-OP, and U46619.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1990

Stimulation of glycoprotein and protein synthesis in isolated pig gastric mucosal cells by prostaglandins.

The purpose of this study is to evaluate the effects of different prostaglandin derivatives on protein and glycoprotein synthesis and secretion in isolated and enriched pig gastric mucous cells, as measured by the incorporation of [3H]L-leucine and N-acetyl-[14C]D-glucosamine respectively into acid insoluble macromolecules (AIM). PGE2 and 16,16-dimethyl-PGE2 enhanced the incorporation of the amino sugar into cellular (EC50 8 and 75 nmol/l) and secreted (EC50 30 and 270 nmol/l) AIM in a concentration dependent manner during a 20 hours incubation. After incubation for eight hours or more they also stimulated the incorporation of [3H]L-leucine into cellular AIM. PGF2 alpha was considerably less potent (EC50 greater than 1 mumol/l) than the E-type prostaglandins. Iloprost, a stable prostacyclin analogue, was ineffective.

16,16-Dimethylprostaglandin E2↗
PubMed1990

Interaction of calcium channel antagonists with parietal cell acid production, adenylate cyclase, intracellular-free Ca2+ and H+/K+-ATPase.

The calcium channel antagonists verapamil, gallopamil and nifedipine were tested for their effects on acid secretion stimulated by histamine and dibutyryl-cyclic AMP in isolated and enriched guinea pig parietal cells, on adenylate cyclase activity mediated by histamine H2 receptors, on histamine-stimulated increase in cytosolic-free Ca2+ concentration [Ca2+], on gastric H+/K(+)-ATPase activity and on H+/K(+)-ATPase-mediated proton uptake in intact gastric membrane vesicles. Verapamil and gallopamil impaired all cellular and enzymatic test systems studied. Both drugs affected with highest potency the acid secretion in the parietal cell preparation (IC50: 1-2 mumol/l) and the H+/K(+)-ATPase-mediated H+ uptake in gastric membrane vesicles, whereas their inhibitory action was less pronounced on adenylate cyclase and on histamine-induced increase in cytosolic-free [Ca2+]. The type of interaction found in the gastric membrane vesicle preparation indicates that both drugs act as protonophores. Nifedipine was less effective as an inhibitor of acid secretion in the parietal cell preparation and in reducing proton concentration in isolated gastric membrane vesicles. The drug failed to block adenylate cyclase and H+/K+-ATPase activity. Since nifedipine is a more effective calcium channel blocking agent but a less lipophilic drug than verapamil and gallopamil, we conclude that the antisecretory activity of calcium channel antagonists in vitro is mediated by a nonspecific, i.e. a protonophoric, action. We suggest that verapamil exhibits its antisecretory activity in vivo partially by its protonophoric action at the secretory membrane of the parietal cell, whereas the decrease in acid secretion by nifedipine is not mediated by this mechanism.

Adenosine Triphosphatases↗
PubMed1990

Effects of histamine on protein and glycoprotein production of isolated pig gastric mucosal cells.

The production of glycoprotein and protein by isolated pig gastric non-parietal cells was measured by incorporation of N-acetyl-[14C]-D-glucosamine [( 14C]GlcNAc) and [3H]-L-leucine [( 3H]Leu), respectively, into acid insoluble material (AIM). Histamine enhanced incorporation of the tracers into cellular and released AIM in a concentration-dependent manner. The H2 receptor antagonist ranitidine completely blocked the effects of histamine (100 mumol/l) on [3H]Leu incorporation into cellular and released AIM (IC50 37 and 32 mumol/l, respectively) but had no inhibitory effect on the 16,16-dimethylprostaglandin-E2 - and forskolin-stimulated tracer incorporation. The H1 receptor antagonist mepyramine did not inhibit the histamine effect. We conclude that histamine is a stimulant of protein, via H2 receptors, and glycoprotein production of isolated pig gastric non-parietal cells.

16,16-Dimethylprostaglandin E2↗
PubMed1990

[Secondary messengers in the hormonal regulation of the functional activity of the main and mucoid cells in the stomach].

The messenger role of Ca+2, cyclic nucleotides and inositol triphosphates in the stimulation of pepsinogen and mucous secretion were studied using isolated pig [correction of nug] gastric chief cells and guinea pig mucous cells, resp. Pepsinogen secretion was stimulated by agents either working at the postreceptor adenylate cyclase (AC) level (db-cAMP, forskolin) or after 12-o-tetradecanoyl-phorbol-13-acetate (TPA) stimulation of protein kinase C (PK C). Similar secretory effects were observed with histamine (H), carbachol (C) and cholecystokinin (CCK). [Ca-2] in was elevated by C and by CCK, but not by H in both types of cells. Like TPA, both C and CCK, but not H, stimulated the Ca+2-sensitive particulate PK C. H increased the activity of cAMP-dependent PK A. PGE2, C and CCK were found to increase inositol-1,4,5-triphosphate content in mucous cells. The findings indicate that two pathways of the regulation of pepsinogen and mucous secretion (AC-cAMP-PK C and phosphoinositol breakdown cascade) can act synergistically.

Adenylyl Cyclases↗