首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
Carboxylic acids can undergo irreversible binding to proteins via their acyl glucuronide metabolites. Such binding occurs in humans and in vitro for bilirubin and the anti-inflammatory drugs zomepirac and tolmetin and may have toxicological significance. The mechanism of the binding is uncertain, but is thought to involve nucleophilic displacement of glucuronic acid by free cysteine thiols, tyrosine, or lysine residues of the protein. We now present evidence, using zomepirac glucuronide, for an alternative mechanism where irreversible binding occurs by isomerization of the glucuronide and formation of an imine linkage between the glucuronic acid moiety of the conjugate and a lysine or terminal amino group of the protein. Involvement of a protein thiol in the binding mechanism was ruled out by experiments with the thiol blocking agent, p-hydroxymercuribenzoate. Moreover, significant irreversible binding occurred when the cysteine free protein, alpha s1-casein, was incubated in solution with zomepirac glucuronide in vitro. When zomepirac glucuronide was added to solutions with albumin in the presence of the imine trapping reagent, sodium cyanide, or the reducing agent, sodium cyanoborohydride, irreversible binding of zomepirac increased 8.3- and 5.5-fold relative to controls, respectively, after 6 hr at 37 degrees C. The product formed after treatment of solutions of zomepirac glucuronide and albumin with sodium cyanoborohydride was stable in dilute acid, whereas similar acid treatment of zomepirac-albumin adduct from control incubations, obtained after sodium cyanide exposure, released 30% of the total adduct. Only isomeric conjugates of zomepirac glucuronide were released from zomepirac-albumin adduct by mild acid; no beta 1-isomer was detected.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

2.
Conjugation of carboxylate drugs with D-glucuronic acid is of considerable interest because of the inherent reactivity of the resulting β-1-O-acyl glucuronides. These conjugates can degrade by spontaneous hydrolysis and internal acyl migration. β-1-O-acyl glucuronides and their acyl migration products can also react covalently with macromolecules with potential toxicological consequences. The spontaneous degradation of the diastereoisomeric β-1-O-acyl glucuronide metabolites of the racemic drug ketoprofen, two of its ring-hydroxylated metabolites and of tolmetin β-1-O-acyl glucuronide was investigated by 1H-NMR spectroscopy in buffer solutions, at pH 7.4 and 37°C. A plot of the logarithm of the peak integrals against time revealed first-order kinetics. Degradation rates and half-lives were calculated for each glucuronide using first-order reaction equations. Tolmetin glucuronide had the fastest degradation rate, whilst all of the ketoprofen-related glucuronides had similar degradation rates. The degradation of the diastereoisomeric glucuronides was stereoselective, with the rate for the (S)-isomer always slower compared with the (R)-isomer by approximately a factor of 2.  相似文献   

3.
Fast and efficient tritium labelling of the nonsteroidal anti‐inflammatory drugs naproxen, tolmetin and zomepirac is reported. Naproxen along with its (R)‐enantiomer were labelled by catalytic tritium–halogen exchange of the corresponding 5‐bromo derivatives providing [3H]naproxen with a specific activity of 25.4 Ci/mmol. Tolmetin and zomepirac were labelled by the hydrogen isotope exchange reaction using Crabtree's catalyst. This provided [3H]tolmetin and [3H]zomepirac with specific activities of 80.8 and 64.3 Ci/mmol, respectively. All compounds were obtained in high radiochemical purity (>98%). Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

4.
To investigate further whether the effects of the dihydropyridine (DHP) drugs on calcium channels are related to those of these drugs on muscarinic receptors, the binding characteristics of the DHP calcium channel agonist, Bay K 8644, on muscarinic receptors and calcium channels were compared to those of the DHP calcium channel antagonists, nicardipine and nimodipine in the dog cardiac sarcolemma. Bay K 8644, nicardipine and nimodipine inhibited the specific [3H]QNB binding with K i values of 16.7μM, 3.5μM and 15.5μM respectively. Saturation data of [3H]QNB binding in the presence of these DHP drugs showed this inhibition to be competitive. Bay K 8644, like nicardipine and nimodipine, blocked the binding of [3H]nitrendipine to the high affinity DHP binding sites, but atropine did not, indicating that the muscarinic receptors and the DHP binding sites on calcium channels are distinct. The K i value of Bay K 8644 for the DHP binding sites was 4 nM. Nicardipine and nimodipine (K i :0.1–0.2 nM) were at least 20 times more potent than Bay K 8644 in inhibiting [3H]nitrendipine binding. Thus, the muscarinic receptors were about 4000 times less sensitive than these high affinity DHP binding sites to Bay K 8644. These results suggest that the DHP calcium agonist Bay K 8644 binds directly to the muscarinic receptors but its interaction with the muscarinic receptors is not related to its binding to the DHP binding sites on calcium channels.  相似文献   

5.
Osmotic shock, oxidative stress and Cl removal activate a non-selective Ca2+-permeable cation conductance in human erythrocytes. The entry of Ca2+ leads to activation of a scramblase with subsequent exposure of phosphatidylserine at the cell surface. Phosphatidylserine mediates binding to phosphatidylserine receptors on macrophages which engulf and degrade phosphatidylserine exposing cells. Moreover, phosphatidylserine exposure may lead to adherence of erythrocytes to the vascular wall. In the present study, we explored whether activation of the non-selective cation conductance and subsequent phosphatidylserine exposure might be influenced by catecholamines. Phosphatidylserine exposure has been determined by FITC-annexin V binding while cell volume was estimated from forward scatter in FACS analysis. Removal of Cl enhanced annexin binding and decreased forward scatter, an effect significantly blunted by the β agonist isoproterenol (IC50 approx. 1 μM). Fluo-3 fluorescence measurements revealed an increase of cytosolic Ca2+ activity following Cl removal, an effect again significantly blunted by isoproterenol exposure (10 μM). Whole-cell patch-clamp experiments performed in Cl free bath solution indeed disclosed a time-dependent inactivation of a non-selective cation conductance following isoproterenol exposure (10 μM). Phenylephrine (IC50<10 μM), dobutamine (IC50 approx. 1 μM) and dopamine (IC50 approx. 3 μM) similarly inhibited the effect of Cl removal on annexin binding and forward scatter. In conclusion, several catecholamines inhibit the Cl removal-activated Ca2+ entry into erythrocytes, thus preventing increase of cytosolic Ca2+ activity, subsequent cell shrinkage and activation of erythrocyte scramblase. The catecholamines thus counteract erythrocyte phosphatidylserine exposure and subsequent clearance of erythrocytes from circulating blood.  相似文献   

6.
Novel macrocyclic cobalt(II) complex C36H24N8O4S4CoCl2 with a butterfly topology was synthesized and characterized by spectroscopic (IR, 1H, 13C NMR, EPR, UV-Vis, ESI-MS) and analytical methods. The complex exhibits distorted octahedral geometry around Co(II) metal ion, which was confirmed by EPR measurements with ga, gb, and gc values (8.01, 2.20, and 1.66), respectively, and molar extinction coefficient ε = 58 M−1cm−1. The Interaction studies with human serum albumin (HSA) in phosphate buffer (0.1 M, pH 7.0) were studied by electronic absorption titration, fluorescence titration, circular dichroism, and cyclic voltammetry. Hyperchromism in fluorescence intensity indicates binding of complex with HSA near tryptophan residue in IIA subdomain leading to less polar microenvironment around tryptophan and more at tyrosine. The intrinsic binding constant K b obtained from absorption spectral titrations was found to be 9.3 × 104 M−1, suggesting medium binding affinity of HSA with complex. CD spectrum indicates α-helical structure up to β-pleated secondary structure. CV data confirmed medium reversible binding with HSA. The binding of complex with HSA shows typical reversible mode of binding, which enables the delivery of drug candidate to the tissue enzymes and receptors in an efficient manner, and thereby affects the uptake of the drug.  相似文献   

7.
Objective: Biotransformation of metoprolol to α-hydroxymetoprolol (HM) and O-demethylmetoprolol (ODM) is mediated by CYP2D6. The selective serotonin reuptake inhibitors (SSRIs) are known to inhibit CYP2D6. The aim was to study in vitro the potential inhibitory effect of SSRIs on metoprolol biotransformation. Methods: Using microsomes from two human livers, biotransformation of metoprolol to α-hydroxymetoprolol (HM) and O-demethylmetoprolol (ODM) as a function of the concentrations of the SSRIs and of some of their metabolites was studied. Results: The kinetics of the formation of both metabolites are best described by a biphasic enzyme model. The estimated values of Vmax and kM for the high affinity site are for the α-hydroxylation in human liver HL-1 32 pmol mg−1 min−1 and 75 μmol · l−1 respectively, and in human liver HL-9 39 pmol mg−1 · min−1 and 70 μmol · l−1 respectively; for the O-demethylation in HL-1 131 pmol mg−1 min−1 and 95 μmol · l−1 respectively, and in HL-9 145 pmol mg−1 min−1 and 94 μmol · l−1 respectively. Quinidine is for both pathways a potent inhibitor of the high-affinity site, with Ki values ranging from 0.03 to 0.18 μmol · l−1. Fluoxetine, norfluoxetine and paroxetine are likewise potent inhibitors, with Ki values ranging from 0.30 to 2.1 μmol · l−1 fluvoxamine, sertraline, desmethylsertraline, citalopram and desmethylcitalopram are less potent inhibitors, with Ki values above 10 μmol · l−1. Conclusion: The rank order of the SSRIs for inhibition of metoprolol metabolism is comparable to that reported in the literature for other CYP2D6 substrates, with fluoxetine, norfluoxetine and paroxetine being the most potent. These findings need further investigation to determine their clinical relevance. Received: 24 October 1997 / Accepted: 17 January 1998  相似文献   

8.
Conjugation of carboxylate drugs with D-glucuronic acid is of considerable interest because of the inherent reactivity of the resulting beta-1-O-acyl glucuronides. These conjugates can degrade by spontaneous hydrolysis and internal acyl migration. beta-1-O-acyl glucuronides and their acyl migration products can also react covalently with macromolecules with potential toxicological consequences. The spontaneous degradation of the diastereoisomeric beta-1-O-acyl glucuronide metabolites of the racemic drug ketoprofen, two of its ring-hydroxylated metabolites and of tolmetin beta-1-O-acyl glucuronide was investigated by (1)H-NMR spectroscopy in buffer solutions, at pH 7.4 and 37 degrees C. A plot of the logarithm of the peak integrals against time revealed first-order kinetics. Degradation rates and half-lives were calculated for each glucuronide using first-order reaction equations. Tolmetin glucuronide had the fastest degradation rate, whilst all of the ketoprofen-related glucuronides had similar degradation rates. The degradation of the diastereoisomeric glucuronides was stereoselective, with the rate for the (S)-isomer always slower compared with the (R)-isomer by approximately a factor of 2.  相似文献   

9.
10.
Objective: The affinity of (+)-, (−)- and (±)-fluvastatin, a new synthetic HMG-CoA reductase inhibitor developed as a racemate, for specific human P450 monooxygenases in liver microsomes was compared with that of the pharmacologically active acidic forms of lovastatin, pravastatin and simvastatin. Methods: Affinity was determined as the inhibitory potency for prototype reactions for 3 major drug metabolising enzymes: diclofenac 4′-hydroxylation (CYP2C9), dextromethorphan O-demethylation (CYP2D6), and midazolam 1′-hydroxylation (CYP3A4). Results: Lovastatin acid, pravastatin and simvastatin acid displayed moderate affinity for all three P450 isozymes (estimated Ki > 50 μmol⋅l−1). Racemic and (+)- and (−)-fluvastatin showed moderate affinity (estimated Ki > 50 μmol⋅l−1) for CYP2D6 and CYP3A4, whereas their affinity for CYP2C9 was high (estimated Ki < 1 μmol⋅l−1). Diclofenac 4′-hydroxylation was competitively and stereoselectively inhibited, with measured Ki’s of 0.06 and 0.28 μmol⋅l−1 for (+)- and (−)-fluvastatin, respectively. Conclusion: Fluvastatin selectively inhibits a major drug metabolising enzyme (CYP2C9), the (+)-isomer (pharmacologically more active) showing 4–5 fold higher affinity. As already reported for lovastatin and simvastatin, in vivo drug interactions by inhibition of liver oxidation of CYP2C9 substrates (e.g. hypoglyceamic sulphonylureas and oral anticoagulants) may be expected. Received: 9 June 1995/Accepted in revised form: 7 November 1995  相似文献   

11.
In order to assess the toxicity of heavy metals on the early development of Meretrix meretrix, the effects of mercury (Hg), cadmium (Cd) and lead (Pb) on embryogenesis, survival, growth and metamorphosis of larvae were investigated. The EC50 for embryogenesis was 5.4 μg l−1 for Hg, 1014 μg l−1 for Cd and 297 μg l−1 for Pb, respectively. The 96 h LC50 for D-shaped larvae was 14.0 μg l−1 for Hg, 68 μg l−1 for Cd and 353 μg l−1 for Pb, respectively. Growth was significantly retarded at 18.5 μg l−1 (0.1 μM) for Hg, 104 μg l−1 (1 μM) for Cd and 197 μg l−1 (1 μM) for Pb, respectively. The EC50 for metamorphosis, similar to 48 h LC50, was higher than 96 h LC50. Our results indicate that the early development of M. meretrix is highly sensitive to heavy metals and can be used as a test organism for ecotoxicology bioassays in temperate and subtropical regions.  相似文献   

12.
Objective: A series of studies was undertaken to determine the cytochrome P450 isoform(s) involved in naproxen demethylation and whether this included the same isoforms reported to be involved in the metabolism of other NSAIDs. Methods: (S)-Naproxen was incubated with human liver microsomes in the presence of a NADPH-generating system and the formation of desmethylnaproxen was measured by high-performance liquid chromatography (HPLC). To further clarify the specific isoforms involved, experiments were conducted with preparations expressing only a single P450 isoform (vaccinia virus-expressed cells and microsomes derived from a lymphoblastoid cell line, each transfected with specific P450 cDNAs) as well as inhibition studies using human liver microsomes and putative specific P450 inhibitors. Results: In human liver microsomes (n=7), desmethylnaproxen formation was observed with a mean kM of 92 (21) μmol · l−1, Vmax of 538 pmol · min−1 · mg−1 protein and Cint2 (reflective of a second binding site) of 0.36 μl · min−1 · mg−1 protein. This Cint2 term was added since Eadie-Scatchard analysis suggested the involvement of more than one enzyme. Studies using putative specific P450 inhibitors demonstrated inhibition of this␣reaction by sulfaphenazole, (apparent Ki= 1.6 μmol · l−1), warfarin (apparent Ki=27 μmol · l−1), piroxicam (apparent Ki=23 μmol · l−1) and tolbutamide (apparent Ki=128 μmol · l−1). No effect was observed when α-naphthoflavone and troleandomycin were employed as inhibitors, but reaction with furafylline produced, on average, a maximum inhibition of 23%. At a naproxen concentration of 150 μmol · l−1, formation of desmethylnaproxen was observed in cells expressing P450 1A2, 2C8, 2C9 and its allelic variant 2C9R144C. To further characterize these reactions, saturation kinetics experiments were conducted for the P450s 1A2, 2C8 and 2C9. The kM and Vmax for P450 1A2 were 189.5 μmol · l−1 and 7.3 pmol · min−1 · pmol−1 P450, respectively. Likewise, estimates of kM and Vmax for P450 2C9 were 340.5 μmol · l−1 and 41.4 pmol · min−1 · pmol−1 P450, respectively. Reliable estimates of kM and Vmax could not be made for P450 2C8 due to the nonsaturable nature of the process over the concentration range studied. Conclusion: Multiple cytochrome P450 isoforms (P450 1A2, 2C8 and 2C9) appear to be involved in naproxen demethylation, although 2C9 appears to be the predominant form. Received: 16 September 1996 / Accepted in revised form: 20 December 1996  相似文献   

13.
14.
We examined the effect of nicorandil on retinal blood vessels in rats in vivo. Male Wistar rats (8 to 10 weeks old) were anaesthetised with thiobutabarbital (120 mg/kg, intraperitoneal). Fundus images were captured with a digital camera that was equipped with a special objective lens. Diameters of retinal blood vessels were measured with a personal computer. Nicorandil (1–300 μg kg−1 min−1, intravenous [i.v.]) increased diameters of retinal blood vessels and decreased systemic blood pressure in a dose-dependent manner. Both responses to nicorandil were attenuated by glibenclamide (20 mg/kg, i.v.), an adenosine triphosphate (ATP)-dependent K+ (KATP) channel blocker. On the other hand, indomethacin (5 mg/kg, i.v.), a cyclooxygenase inhibitor, attenuated the vasodilation of retinal blood vessels, but not depressor response, to nicorandil and sodium nitroprusside. Pinacidil (1–300 μg kg−1 min−1, i.v.), a KATP channel opener, also dilated retinal blood vessels and decreased systemic blood pressure. The responses to pinacidil were prevented by glibenclamide, but not by indomethacin. The vasodilation of retinal arteriole, but not depressor response, to sodium nitroprusside (1–30 μg kg−1 min−1, i.v.), a nitric oxide donor, was attenuated by indomethacin. These results suggest that nicorandil dilates retinal blood vessels through opening of KATP channels and production of prostaglandins that are probably generated by nitric oxide.  相似文献   

15.
Acyl glucuronidation is the major metabolic conjugation reaction of most carboxylic acid drugs in mammals. The physiological consequences of this biotransformation have been investigated incompletely but include effects on drug metabolism, protein binding, distribution and clearance that impact upon pharmacological and toxicological outcomes. In marked contrast, the exceptional but widely disparate chemical reactivity of acyl glucuronides has attracted far greater attention. Specifically, the complex transacylation and glycation reactions with proteins have provoked much inconclusive debate over the safety of drugs metabolised to acyl glucuronides. It has been hypothesised that these covalent modifications could initiate idiosyncratic adverse drug reactions. However, despite a large body of in vitro data on the reactions of acyl glucuronides with protein, evidence for adduct formation from acyl glucuronides in vivo is limited and potentially ambiguous. The causal connection of protein adduction to adverse drug reactions remains uncertain. This review has assessed the intrinsic reactivity, metabolic stability and pharmacokinetic properties of acyl glucuronides in the context of physiological, pharmacological and toxicological perspectives. Although numerous experiments have characterised the reactions of acyl glucuronides with proteins, these might be attenuated substantially in vivo by rapid clearance of the conjugates. Consequently, to delineate a relationship between acyl glucuronide formation and toxicological phenomena, detailed pharmacokinetic analysis of systemic exposure to the acyl glucuronide should be undertaken adjacent to determining protein adduct concentrations in vivo. Further investigation is required to ascertain whether acyl glucuronide clearance is sufficient to prevent covalent modification of endogenous proteins and consequentially a potential immunological response. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

16.
Objective: Interindividual variations in immunoreactivity and function of three major human drug metabolising P450 monooxygenases has been investigated in liver microsomes from 42 Caucasians (kidney donors or liver biopsies). Methods: Diclofenac 4′-hydroxylation, dextromethorphan O-demethylation and midazolam 1′-hydroxylation, measured by HPLC in incubates, were used as probes to determine CYP2C9, CYP2D6 and CYP3A4 function kinetics, respectively. Immunoquantification of the three isoforms was achieved by Western blotting, using rabbit polyclonal antibodies raised against human CYP2C9 and human CYP3A4, and mouse monoclonal antibody raised against human CYP2D6. Results: Diclofenac 4′-hydroxylation exhibited Michaelis-Menten kinetics with kM= 3.4 μmol ⋅l−1 and Vmax = 45 nmole ⋅mg−1P ⋅h−1. Relative immunoreactivity of CYP2C9 was correlated with Vmax and CLint. Dextromethorphan O-demethylation in EM (extensive metabolisers) liver microsomes also showed Michaelis-Menten kinetics, with kM = 4.4 μmol ⋅l−1 and Vmax = 5.0 nmol ⋅mg−1P ⋅h−1. Relative immunoreactivity of CYP2D6 was correlated with Vmax and CLint. Midazolam 1′-hydroxylation also exhibited Michaelis-Menten kinetics with kM = 3.3 μmol ⋅l−1 and Vmax = 35 nmol ⋅mg−1P ⋅h−1. Relative immunoreactivity of CYP3A4 was correlated with Vmax and CLint. Immunoreactivity and function were correlated for each isozyme, but there was no cross correlation between isozymes. Conclusion: The velocity of metabolite formation (Vmax) by the three major human drug metabolising P450 monooxygenases is correlated with their immunoreactivity in liver microsomes. Interindividual variation was much larger for Vmax than kM. Interindividual variability was more pronounced for CYP2D6, probably due to the presence of several different functional alleles in the population of extensive metabolisers. Received: 27 December 1995/Accepted in revised form: 29 March 1996  相似文献   

17.
Receptor-mediated guanine nucleotide-binding regulatory protein (G protein) activation or functional coupling between receptors and G proteins has been investigated by means of agonist-induced [35S]guanosine-5′-O-(3-thio)triphosphate ([35S]GTPγS) binding, especially for the receptor subtypes negatively coupled to adenylyl cyclase through Gi type G proteins. In the present study, 5-HT-stimulated [35S]GTPγS binding to rat stritatal membranes was pharmacologically characterized in detail with the help of an extensive series of 5-HT receptor ligands. The optimum experimental conditions for the concentrations of GDP, MgCl2 and NaCl in the assay buffer were initially determined, and the standard assay was performed with 20 μM GDP, 5 mM MgCl2 and 100 mM NaCl. The specific [35S]GTPγS binding was stimulated by several compounds that had been shown to be agonists at 5-HT1B/1D receptors. The negative logarithmic values of the concentration eliciting half-maximal effect (pEC50) for these agonists were significantly correlated with their pK i’s reported in the previous study of 5-HT1B receptor binding in rat frontal cortical membranes. The increase in specific [35S]GTPγS binding in response to 1 μM 5-HT was potently inhibited by several 5-HT1B/1D receptor antagonists as well as β-adrenoceptor antagonists such as S(−)-cyanopindolol. On the other hand, 3-[4-(4-chlorophenyl)piperazin-1-yl]-1,1-diphenyl-2-propanol HCl (BRL15572), a selective antagonist against human 5-HT1D receptors, was inactive as an antagonist at least up to 1 μM. Additionally, the concentration-response curve for 2-[5-[3-(4-methylsulphonylamino)benzyl-1,2,4-oxadiazol-5-yl]-1H-indol-3-yl]ethanamine (L694247) was shifted rightward in parallel by the addition of S(−)-cyanopindolol at concentrations of 10 and 100 nM, indicative of the competitive inhibitory manner. The specific [35S]GTPγS binding was reduced by 1′-methyl-5-([2′-methyl-4′-(5-methyl-1,2,4-oxadiazol-3-yl)biphenyl-4-yl]carbonyl)-2,3,6,7-tetrahydrospirospiro(furo[2,3-f]indole-3,4′-piperidine) (SB224289) and methiothepin in a concentration-dependent manner. The inhibitory curve by either compound was shifted to the right by 10 and 100 nM S(−)-cyanopindolol, suggesting that these two drugs behaved as inverse agonists at 5-HT1B receptors in the present functional assay system. 5-HT-stimulated [35S]GTPγS binding to rat striatal membranes serves as a simple but useful method of investigating the functional interaction between the native 5-HT1B receptors and their coupled G proteins in this brain region.  相似文献   

18.
Purpose The present study examined the underlying mechanism by which 4-hydroxyacetophenone (4-HA), a bioactive compound found in several medicinal herbs, exerts its potent stimulatory effects on hepatic bile secretion.Methods Bile flow, and biliary excretion of 4-HA, its metabolites, and inorganic electrolytes was examined in both normal Wistar rats and in TR- Wistar rats that have a congenital defect in the multidrug resistance-associated protein-2, Mrp2/Abcc2. The effects of 4-HA were also examined in animals treated with buthionine sulfoximine to decrease hepatic glutathione (GSH) levels.Results In normal rats, 4-HA dramatically increased bile flow rate, whereas it failed to exert a choleretic effect in TR- rats. This choleresis was not explained by increased biliary output of Na+, K+, Cl or HCO3 , or by increased biliary GSH excretion. Depletion of hepatic GSH with buthionine sulfoximine had no effect on the 4-HA-induced choleresis. HPLC analysis revealed that a single major compound was present in bile, namely.4-hydroxyacetophenone-4-O-β-glucuronide, and that the parent compound was not detected in bile. Biliary excretion of the glucuronide was directly correlated with the increases in bile flow. In contrast to normal rats, this 4-HA metabolite was not present in bile of TR rats.Conclusions These results demonstrate that the major biliary metabolite of 4-HA in rats is the 4-O-β-glucuronide, a compound that is secreted into bile at high concentrations, and may thus account in large part for the choleretic effects of 4-HA. Transport of this metabolite across the canalicular membrane into bile requires expression of the Mrp2 transport protein.  相似文献   

19.
Binding of sulfaethidole to bovine serum albumin was studied by equilibrium dialysis, fluorescence probe technique, uv difference spectrophotometry and circular dichroism. Equilibrium dialysis method enabled us to estimate the total number of drug binding sites of albumin molecule. For sulfaethidole, albumin had 6 primary and 40 secondary binding sites. The primary and secondary binding constants were 0.9×105 M−1 and 0.2×106 M−1, respectively. 1-Anilino-8-naphthalenesulfonate (ANS) and 2-(4′-hydroxylbenzeneazo)-benzoic acid (HBAB) were used as the fluorescence probe and the uv spectrophotometric probe, respectively. In fluorescence probe technique, results indicated that the number of higher affinity drug binding site of albumin was 1 and the number of lower affinity drug binding sites of albumin was 3, and the primary and secondary drug binding constants for bovine serum albumin were 2.15×105 M−1 and 1.04×105 M−1, respectively. In uv difference spectrophotometry, binding sites were 3 and binding constant was 1.88×105 M−1. The above results suggest that several different methods should be used in ompensation for insufficient information about drug binding to albumin molecule given by only one method.  相似文献   

20.
Metabolism of carteolol by cDNA-expressed human cytochrome P450   总被引:2,自引:0,他引:2  
Objectives: To determine human cytochrome P450 isoform(s) (CYPs) involved in the metabolism of carteolol, the biotransformation of the compound was investigated in vitro using ten isoforms of human cytochrome P450 expressed in human AHH-1 TK ± cell lines. In addition, the inhibitory effects of carteolol on the activities of important CYP isoforms, namely, CYP1A2, 2C9, 2C19, 2E1, and 3A4, were examined. Results: Carteolol was metabolised to 8-hydroxycarteolol by CYP 2D6 with KM and Vmax values of 183 μmoles · l−1 and 26.09 pmol · min−1 · pmol−1 P450, respectively. CYP1A1, 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2E1 and 3A4 were not involved in the metabolism of the compound. CYP2D6-mediated carteolol 8-hydroxylase activity was inhibited by quinidine, propranolol, nortriptyline, dextromethorphan, sparteine, bufuralol, and biperiden. Biperiden competitively inhibited the catalytic reaction with a Ki value of 0.45 μmoles · l−1. Carteolol did not affect the following catalytic reactions:␣CYP1A2-mediated (R)-warfarin 6-hydroxylation, CYP2C9-mediated tolbutamide methylhydroxylation, CYP2C19-mediated (S)-mephenytoin 4-hydroxylation, CYP2E1-mediated chlorzoxazone 6-hydroxylation, and CYP3A4-mediated testosterone 6β-hydroxylation. Conclusion: 8-Hydroxylation is the only cytochrome P450-catalyzed metabolic reaction of carteolol by its expressed microsomes, and CYP2D6 is the principal isoform of the enzyme involved in the catalytic reaction. Carteolol has neither stimulative nor inhibitory effects on CYP1A2, 2C9, 2C19, 2E1, and 3A4 activities. Received: 17 December 1996 / Accepted in revised form: 11 March 1997  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号