The role of cyclic AMP response element-binding protein in testosterone-induced differentiation of granular convoluted tubule cells in the rat submandibular gland.

The postnatal development of granular convoluted tubules (GCT) in the duct system of the rodent submandibular gland is known to be androgen-dependent, but the underlying molecular mechanism is unclear. To test the possible role of the transcription factor, cyclic AMP response element-binding protein (CREB), in the androgen-induced differentiation of GCT, the effect of testosterone on the expression and localization of epidermal growth factor (EGF), a marker of GCT cells, and of CREB was examined in the submandibular glands of immature 3-week-old rats. Northern blotting demonstrated increases in both EGF and CREB mRNA 1-4 days after testosterone administration. Immunoprecipitation also indicated that CREB protein was increased in amount with testosterone administration, and that induced CREB was phosphorylated at the serine residue as in the active form of CREB. In situ hybridization demonstrated that cells with CREB mRNA signal first appeared in the distal portions of striated ducts at 1 day and had increased in number by 4 days after giving testosterone, when cells with EGF mRNA signal became evident in the same duct portions. Immunohistochemistry also showed the occurrence of CREB protein in the nuclei of duct epithelial cells before their differentiation into EGF-positive GCT cells. Finally, pieces of submandibular gland from immature rats were cultured in vitro and their expression of EGF mRNA analysed by the reverse transcriptase-polymerase chain reaction. Testosterone in the medium caused a marked enhancement of EGF expression in the gland in 1-4 days, which was attenuated by simultaneous administration of the antisense oligonucleotide for CREB as well as that for the androgen receptor. These results suggest the CREB is upregulated by androgen and has a crucial role in androgen-induced differentiation of GCT in the duct system of the rat submandibular gland.

Inhibition by troglitazone of the antigen-induced production of leukotrienes in immunoglobulin E-sensitized RBL-2H3 cells.

1. The effect of troglitazone, an anti-diabetic drug with insulin-sensitizing action, on antigen-induced production of leukotriene (LT) B(4), C(4) and E(4) and prostaglandin D(2) (PGD(2)) was examined in dinitrophenol (DNP)-specific immunoglobulin E (IgE)-sensitized RBL-2H3 mast cells following stimulation by the antigen, DNP-conjugated human serum albumin. Levels of LTB(4), C(4) and E(4) and PGD(2) in the conditioned medium were enzyme-immunoassayed. 2. Troglitazone inhibited the antigen-induced production of LTB(4), C(4) and E(4) and the potency of the inhibition was comparable to that of zileuton, a specific inhibitor of 5-lipoxygenase (5-LOX) and a clinically used anti-asthmatic drug. Neither troglitazone nor zileuton affected antigen-induced production of PGD(2), arachidonic acid release from membrane phospholipids and degranulation. 3. Troglitazone inhibited LTB(4) production by the supernatant fraction of RBL-2H3 cell lysate with similar potency to zileuton, suggesting that troglitazone inhibits LT production by direct inhibition of 5-LOX activity. 4. Furthermore, it was shown that troglitazone as well as zileuton inhibited LTB(4) production in A23187-stimulated rat peritoneal neutrophils. 5. These findings suggest that troglitazone inhibits antigen-induced LT production in the IgE-sensitized RBL-2H3 cells and A23187-stimulated rat peritoneal neutrophils by direct inhibition of 5-LOX activity.

Metabolism of pravastatin sodium by 3 alpha-hydroxysteroid dehydrogenase.

When incubated with isolated rat hepatocytes, pravastatin sodium (PS) yielded a small amount of a metabolite in addition to two major metabolites that have already been reported. The previously uncharacterized metabolite was found to be formed by at first being enzymatically dehydrogenated to 6'-keto intermediate (R-104), followed by decomposition to give the aromatized metabolite (R-195), through spontaneous deesterification with accompanying aromatization. The PS-6'beta-hydroxydehydrogenase activity was localized in cytosolic fraction and required NADP, preferentially over NAD, as a cofactor. The formation of R-195 by rat liver cytosol was strongly inhibited by indomethacin, 3 alpha-hydroxysteroids (but not 3 beta-isomers) and 3-ketosteroids. The results and high substrate specificity of purified PS-6'beta-hydroxydehydrogenase toward 3 alpha-hydroxysteroids suggested that the enzyme is identical to 3 alpha-hydroxysteroid dehydrogenase.

Enzyme-linked immunosorbent assay of pravastatin, a HMG-CoA reductase inhibitor, in human plasma.

An enzyme-linked immunosorbent assay (ELISA) was developed for sensitive and specific determination of pravastatin (PS) sodium, a HMG-CoA reductase inhibitor. Preparation of immunogens to obtain antisera was carried out using chemically modified PS; beta-alanine derivative of PS (for ELISA-1) and 5-deoxy- PS (for ELISA-2) were linked to bovine serum albumin via its terminal carboxylic acid by the N-succinimidyl ester method, to avoid intramolecular lactonization of PS. Enzyme-labeled antigens were prepared similarly by coupling with horseradish peroxidase, and were used by homogeneous combination of antisera. The enzymic activity was determined using a microtiter plate coated with second antibody and tetramethylbenzidine as a chromogenic substrate. Both of the ELISA systems enabled the determination of PS in a range of 5 to 500 pg/well, with an IC50 of 36 to 130 pg/well. Cross-reactivties with main metabolites in plasma, which differed from PS in decaline moiety, were less than a few percent. When ELISA-1 was applied to the determination of PS in human plasma directly after dilution with the ELISA buffer, the detection limit and the intra-assay coefficient (5 ng/ml of PS) were 500 pg/ml and 4.5%, respectively. Further, ELISA-1 was validated by gas chromatography-mass spectrometry with the determination of PS in human plasma after oral administration at a dose of 10 mg/body.

Highly sensitive and specific determination of pravastatin sodium in plasma by high-performance liquid chromatography with laser-induced fluorescence detection after immobilized antibody extraction.

A method for the determination of pravastatin sodium (PS), a cholesterol-lowering agent, in plasma was developed by using an immobilized antibody column extraction followed by high-performance liquid chromatography (HPLC). The analyte was monitored by a laser-induced fluorescence detector after fluorogenic derivatization. The PS antibody was coupled to Sepharose 4B and used as an extraction phase for sample cleanup and extraction of the drug. A plasma sample was applied to the column and washed with water, and the drug was eluted with methanol. N-Dansylethylenediamine (DNS-ED) was coupled to the carboxyl moiety of the drug in the presence of diethyl phosphorocyanidate (DEPC) and triethylamine (TEA) in dioxane. Derivatization was completed in 5 min at room temperature. A column-switching technique was utilized to remove excess reagents and byproducts. A He-Cd laser-induced fluorescence detector was applied to achieve an ultrasensitive determination. The detection limit was 2 pg/injection of PS, which was 20 times more sensitive than the conventional fluorescence detection. The limit of quantitation was 100 pg/mL when 1 mL of plasma sample was available. An average coefficient of variations of the overall method were less than 8% at the concentration range of 1-100 ng/mL. A single oral dose of PS in rats (20 mg/kg) and dogs (5 mg/kg) resulted in average maximum concentrations of 142 and 310 ng/mL, respectively.

Biotransformation of pravastatin sodium (I). Mechanisms of enzymic transformation and epimerization of an allylic hydroxy group of pravastatin sodium.

One of the major metabolites, R-416(3'alpha-OH), of pravastatin sodium(PV, 6'beta-OH), and a minor metabolite, R-418 (6'alpha-OH), were produced in rat liver cytosol in the presence of adenosine 3'-phosphate 5'-phosphosulfate as a cofactor. The reactions were inhibited by the inhibitors for sulfotransferases, and 18OH was introduced to the 3'alpha- and 6'alpha-positions of R-416 and R-418, respectively, by incubation with H2 18O. These results strongly suggested that PV was metabolically activated by sulfation at the 6'beta-hydroxy group by sulfotransferases, followed by nucleophilic attack of hydroxy anions at the 3'alpha- or 6'alpha-position, to give R-416 or R-418, respectively.

Metabolism of pravastatin sodium in isolated rat hepatocytes. I. Glutathione conjugate formation reaction.

1. The metabolic fate of pravastatin sodium (sodium (+)-(3R,5R)-3,5-dihydroxy-7-((1'S,2'S,6'S,8'S,8'aR)-6'-hydroxy-2'methyl- 8'-[(S)-2"-methylbutyryloxy]-1',2',6',7',8', 8'a-hexahydro-1'-naphthyl) heptanoate) was studied in isolated rat hepatocytes. 2. Two polar metabolites were isolated and identified as a glutathione conjugate and a dihydrodiol. 3. Both metabolites were formed via an epoxide which has been identified as the 4'a beta,5' beta-epoxide on the decalin moiety. 4. Formation of the glutathione conjugate was enzymic, while the dihydrodiol was formed by non-enzymic hydrolysis of the epoxide accompanied by the intramolecular migration of the double bond.

Preparation of immunoaffinity mini-columns for the analysis of platelet activating factor (PAF) in biological samples.

Using an antibody to BN 52719, an analogue of platelet activating factor (PAF), immunoaffinity mini-columns for the separation of PAF from biological samples were prepared. Rabbits were immunized with BN 52719 and immunoglobulin G (IgG) from the antiserum was coupled with Sepharose 4B. The resulting suspension of the IgG-coated Sepharose 4B in 25 mM phosphate buffer (pH 6.9) was poured into a plastic mini-column (bed volume 2.0 x 0.8 cm). Stepwise elution of the column with methanol revealed that lyso-PAF is eluted with 20-30% methanol in water whereas PAF is eluted with 50-80% methanol. For the determination of PAF in biological samples, it is recommended that lipids are extracted from the samples and the extract, reconstituted in 20% methanol, is loaded on the column. The column is then washed with 50% methanol followed by elution of PAF with 80% methanol. A small amount of [3H]PAF is added to the samples for measurement of the recoveries of PAF during the procedures of extraction and elution. The PAF is then quantified by radioimmunoassay or bioassay. Employing the immunoaffinity mini-column and radioimmunoassay, the contents of PAF in macrophages and conditioned medium after stimulation with calcium ionophore A23187, or tumor promoters such as TPA and thapsigargin, were measured.

A sensitive nonisotopic method for the determination of intracellular azidothymidine 5'-mono-, 5'-di-, and 5'-triphosphate.

In order to analyze the efficacy of azidothymidine (AZT), it is important to know intracellular concentrations of AZT metabolites. However, it has been impossible to measure intracellular AZT 5'-monophosphate (AZT-MP), AZT 5'-diphosphate (AZT-DP), and AZT 5'-triphosphate (AZT-TP) without using isotopes. In the present study, we developed a new method to measure intracellular AZT metabolites without radiolabeled compounds. The method employed was a high-performance liquid chromatography (HPLC) system programmed for column switching technique, in which two columns were used: column 1 (TSK-G2000-SW, 300 x 7.5 mm) to preseparate AZT metabolites from major cell components, and column 2 (YMC-A-312-ODS, 150 x 6 mm) to determine the metabolites. The limit of detectability of this system was 3.3 pmol/injection. When MT-4 cells were incubated with various concentrations of AZT, intracellular concentrations of AZT-MP increased in parallel with extracellular AZT. Those of AZT-DP and AZT-TP, however, reached plateaus at 5 and 2 microM of AZT, respectively. In MT-4 and Molt-4 cells incubated with 5 microM AZT, concentrations of AZT-MP increased time dependently, while the AZT-DP/AZT-MP ratios decreased with time. These data suggest that high dose of AZT may not necessarily increase intracellular concentration of AZT-TP. The concentrations of AZT metabolites in peripheral blood mononuclear cells in a patient with AIDS and an asymptomatic carrier were measured; the concentrations were comparable to those in cultured cells. Quantitative analysis of intracellular AZT metabolites without the use of isotopes will increase safety and convenience of measurement, and take an effective step in studying pharmacokinetics of AZT in clinical materials.

Metabolism of pravastatin sodium in isolated rat hepatocytes. II. Structure elucidation of the metabolites by n.m.r. spectroscopy.

1. The structures, including stereochemistry, of the two major metabolites of pravastatin sodium in an isolated rat hepatocyte system, i.e. the 4'a alpha-glutathione conjugate (CM-1) and the 3',5'-dihydrodiol (CM-2), were determined by one- and two-dimensional n.m.r. spectroscopy. 2. The structures of two synthetic pravastatin epoxides, possible precursors of the metabolites, were also established. 3. One of the synthetic epoxides, 4'a beta, 5' beta-epoxide was converted to the pravastatin metabolite, 4'a alpha-glutathione conjugate (CM-1) by a rat liver cytosol system and is proposed as the common metabolic intermediate between pravastatin sodium and the metabolites, CM-1 and CM-2.

Simultaneous determination of gemfibrozil and its metabolites in plasma and urine by a fully automated high performance liquid chromatographic system.

Sensitive and specific methods for the simultaneous determination of gemfibrozil (Lopid), a lipid-lowering agent, and its metabolites in plasma and urine are described. The methods are based on a fully automated high performance liquid chromatographic (HPLC) system with fluorescence detection. Urine samples, diluted with acetonitrile, were directly analysed by HPLC using a flow and eluent programming method. In the case of plasma, gemfibrozil and its main metabolites were extracted from acidified samples and the resulting extracts injected into the chromatographic system. The sensitivity was approximately 100 ng/mL for gemfibrozil and its four metabolites using 0.5 mL plasma or urine. An acyl glucuronide of gemfibrozil excreted in human urine after oral administration of the drug was isolated and its structure and stability examined.

Development of a selective clean-up method using immobilized antibody and its application to HPLC and GC/MS determination of a carbacyclin derivative, CS-570, in plasma.

Methods for the determination of CS-570, a chemically stable prostacyclin analogue, in plasma were developed by using an immobilized antibody column followed by fluorescence HPLC and GC/MS. The CS-570 antibody, obtained from rabbit plasma by giving CS-570-BSA for a few months, was coupled to Sepharose 4B and used as extraction phase for sample clean-up and extraction of the drug. A plasma sample was applied to this column, washed with water and the drug was eluted with 90% acetonitrile. 0.02% (w/v) 9-anthryldiazomethane (ADAM) was added to the extract to form a fluorescent derivative. The CS-570-ADAM adduct exhibited high sensitivity when applied to HPLC with fluorescence detection and column switching. The detection limit was 1 ng/mL when 1 mL of plasma was available. Additionally, a pentafluorobenzyltrimethylsilyl derivative of CS-570 showed excellent sensitivity when determined by capillary GC interfaced to negative ion chemical ionization MS using a stable isotope labelled analogue as an internal standard.

Drug monitoring by a fully automated high-performance liquid chromatographic technique, involving direct injection of plasma.

A procedure involving direct injection of whole plasma for analyses of drugs by an automated high-performance liquid chromatograph was developed. This system comprised two columns, two pumps, one detector, two programmable switching valves, an automatic sample injector with a cooling device for sample tubes and a microprocessor. Effluents from the first column, containing a drug of interest, were selectively introduced into the second column for further separation. The columns used were an aqueous gel chromatography column (column 1) and an ODS column (column 2). The solvent for column 1 must be weaker than that for column 2, so that the solutes from the former will be enriched at the top of the latter. The validity and applicability of this procedure for the study of drug metabolism were demonstrated with the antibiotic cefmetazole, the anticoagulant warfarin, the antitumour agent carboquone and the anaesthetic ketamine.

Simultaneous purification and properties of dehydropeptidase-I and aminopeptidase-M from rat kidney.

Two peptidases, dehydropeptidase-I and aminopeptidase-M were solubilized from rat kidney microsomes by treatment with papain and separated by DE-52 ion exchange chromatography. Each enzyme was further purified by Sephacryl S-300 gel filtration and affinity chromatography on Con-A Sepharose. Purified dehydropeptidase-I and aminopeptidase-M were homogeneous by SDS-polyacrylamide gel electrophoresis, and their molecular weights were estimated by gel filtration to be 148,000 and 240,000, respectively; both being homodimer, with a 78,000 subunit for the former and a 120,000 subunit for the latter. Both dehydropeptidase-I and aminopeptidase-M were capable of hydrolyzing L-leucyl-L-leucine with a Km valve of 1.1 mM and 1.7 mM, respectively, although the hydrolyzing activity of aminopeptidase-M was much higher than that of dehydropeptidase-I. Aminopeptidase-M was inhibited by bestatin, and dehydropeptidase-I was significantly inhibited by cilastatin. Dehydropeptidase-I catalyzed the conversion of leukotriene D4 to E4 and the hydrolysis of L-cystinyl-bis-glycine, but aminopeptidase-M did not to any appreciable extent. The physiological significance of dehydropeptidase-I was pointed out and discussed.

Enhanced rectal absorption of cefmetazole and cefoxitin in the presence of epinephrine metabolites in rats and a high-performance liquid chromatographic assay for cephamycin antibiotics.

4-Hydroxy-3-methoxymandelic acid and 3,4-dihydroxymandelic acid were found to be potent adjuvants for the rectal absorption of water-soluble compounds in rats. Both adjuvants enhanced the absorption of two cephamycin antibiotics, cefmetazole and cefoxitin. Maximum plasma levels of the antibiotics were obtained within 30 min after rectal administration. The bioavailability of both antibiotics appeared to depend on the concentration of the adjuvant in the microenema, the dosage form used in these experiments. Instead of a microbial assay, a new chemical method involving high-performance liquid chromatography with an ion-pairing technique was developed for analyzing the cephamycin antibiotic plasma levels.