Effect of ibopamine and the active metabolite epinine on the catecholamine content of rat hypothalamus and brainstem in vitro

The effect of ibopamine (IBO) (SB 7505, SK&F 100168-A), a new drug for the treatment of congestive heart failure, and its active metabolite epinine (EPN) (N-methyldopamine), on the catecholamine content of hypothalamus and brainstem was studied in vitro after monoamine oxidase inhibition with pargyline. IBO and EPN increased levels of epinephrine (EPI) in a concentration- and time-dependent manner in both brain areas without significantly affecting the concentration of other catecholamines. Inhibition of either dopamine beta-hydroxylase, the neuronal EPI and norepinephrine uptake system, or esterase hydrolysis of IBO prevented the increase of EPI, whereas inhibition of phenylethanolamine N-methyltransferase, enzymatic dealkylation or the neuronal dopamine or serotonin uptake system had no influence on the increase of EPI levels. These results suggest that IBO after hydrolysis to EPN can be converted enzymatically to EPI by dopamine beta-hydroxylase in hypothalamus and brainstem. EPN seems to be accumulated into adrenergic and noradrenergic neurons by the high affinity uptake system. Changes in the EPI content of the central nervous system neurons might be responsible for some of the pharmacologic effects of IBO.     

Phenytoin–Lipid Conjugates: Chemical,Plasma Esterase-Mediated,and Pancreatic Lipase-Mediated Hydrolysis in Vitro

Phenytoin–lipid conjugates obtained by covalent binding of hydroxymethylphenytoin to diacylglycerides and to 3-acyloxy-2-acyl-oxymethylpropionic acids formed dispersions with a particle size of 10–200 µm when briefly sonicated in a sodium taurodeoxycholate-containing ethanol–water mixture. In contrast to the corresponding bis-deacyl derivatives, the lipids were not significantly hydrolyzed in aqueous buffers and in plasma. Incubation with pancreatic lipase yielded primarily the bis-deacyl compounds, which are comparable to monoglycerides, and subsequently liberated phenytoin. The glyceride-derived prodrugs were better substrates for the enzyme than the 3-acyloxy-2-acyloxymethyl-propionic acid derivatives. It is concluded that the phenytoin lipid conjugates are hydrolyzed by pancreatic lipase in a similar manner as natural triglycerides.     

Bestimmung der Bindung von Trijodthyronin an Serumproteine mittels Dextran-Gel-Filtration

Zusammenfassung 1. Es wird eine Methode zur gleichzeitigen Bestimmung des sog. freien und des proteingebundenen Anteils von in vitro zugesetztem L-Trijodthyronin-¹³¹Jod im Serum mittels Dextran-Gel-Filtration angegeben. In der beschriebenen Form ist diese Technik für die routinemäßige Anwendung in der Klinik zur Bestimmung der Bindungs- und Transportverhältnisse von Trijodthyronin geeignet.2. In sog. Verdrängungsversuchen wurde nichtmarkiertes Trijodthyronin dem Inkubationsgemisch von Serum und L-Trijodthyronin-¹³¹Jod zugesetzt. Die zugesetzten Trijodthyroninmengen erschöpfen die Gesamtbindungskapazität der Serumproteine in dem gewählten Konzentrationsbereich keineswegs. Im Gegensatz zum Verhalten der prozentualen Anteile des sog. freien und des proteingebundenen Trijodthyronins steigt die absolute Menge des proteingebundenen Trijodthyronins dabei steil an. Man findet eine Kurve, die nicht einer einfachen Sättigunskurve entspricht, sondern eine Resultante aus Sättigungskurven verschiedener Trijodthyronin-bindender Proteine und Verdrängungskurven kompetitiv gebundener Substanzen (z.B. Thyroxin) darstellt.3. Dextran-Gel wirkt nicht als einfaches Molekülsieb für Trijodthyronin. Es greift vielmehr durch Adsorptionsvorgänge kompetitiv in die Serumproteinbindungsverhältnisse des Trijodthyronins ein. Die physiologische Bedeutung des sog. freien Anteils an Trijodthyronin wird diskutiert.4. Die Methode zur Bestimmung des proteingebundenen Jods (PB¹²⁷I) mittels alkalischer offener Veraschung (Barker) wurde technisch vereinfacht und bezüglich ihrer Reproduzierbarkeit untersucht. Die¹³¹Jodausbeute aus zugesetztem L-Thyroxin-¹³¹Jod lag bei diesem Verfahren bei ca. 80%.

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Summary 1. A method allowing the simultaneous determination in serum of the socalled free and the protein bound part of 1-triiodothyronine-¹³¹I added in vitro, using dextran gel filtration, is presented. Assessment of serum protein binding and transport of triiodothyronine can be conveniently performed for clinical purposes by this procedure.2. In socalled discharge experiments non-labelled triiodothyronine is added to incubation mixtures of serum and l-triiodothyronine-¹³¹I. The amount of added triiodothyronine did not exhaust the total binding capacity of serum proteins for triiodothyronine. In contrast to the behaviour of the percentages of socalled free and protein bound triiodothyronine the absolute amount of protein bound triiodothyronine was rising linearly with rising concentrations of triiodothyronine added. The curve obtained was interpreted as resulting from saturation curves of different triiodothyronine binding proteins and discharge curves of competitively bound substances, e.g. thyroxine.3. Dextran gel is not acting merely as molecular sieve for triiodothyronine, but rather competing actively with serum proteins for triiodothyronine, adsorbing the latter. The physiological rôle of the socalled free triiodothyronine is discussed.4. With addition of l-thyroxine-¹³¹I 80% of¹³¹iodine was recovered, when the method ofBarker for determination of serum protein bound¹²⁷iodine (open alkaline ashing) was used.

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Mit Unterstützung der Deutschen Forschungsgemeinschaft.

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Herrn Prof. Dr. Dr. h. c.Carl Krauspe in Verehrung zum 70. Geburtstag gewidmet.     

The 39-kilodalton protein of Borrelia burgdorferi: a target for bactericidal human monoclonal antibodies.

Three human monoclonal immunoglobulin M antibodies against Borrelia burgdorferi, obtained from in vitro-stimulated peripheral blood lymphocytes, reacted in Western blots (immunoblots) with a prominent 39-kDa peptide and a faint band of approximately 66 kDa. Two of these antibodies showed bactericidal activity without addition of complement. All three antibodies were reactive in an enzyme immunoassay with cloned P39 (W.J. Simpson, M.E. Schrumpf, and T.G. Schwan, J. Clin. Microbiol. 28:1329-1337, 1990), suggesting that the target molecule of these antibodies is identical to the P39 protein. In addition, the majority of supernatants from human lymphocytes stimulated in vitro with crude B. burgdorferi antigen reacted in this assay, demonstrating that P39, although a minor component of B. burgdorferi, is an immunodominant antigen in these spirochetes. A fourth monoclonal antibody, reacting with OspA, also exhibited bactericidal activity.     

Erfolgreiche Behandlung einer thyreotoxischen Krise durch kontinuierliche Plasmapherese am Blutzellseparator

Zusammenfassung Bei einem 26jährigen Patienten im thyreotoxischen Koma erwies sich die kontinuierliche Plasmapherese am IBM-Blutzellseparator klinisch als akut wirksame Krisentherapie. Schon während der Plasmapherese mit Austausch von 51 Plasma in 3 1/2 h wurde der Patient aus einem tiefen Koma heraus ansprechbar. Mit den 51 Plasma wurden 633 µg Thyroxin (T₄) und 13,6 µg Trijodthyronin (T₃) entzogen. Dies führte erstaunlicherweise nicht zu einem Abfall der Gesamtspiegel von T₄ und T₃ im Serum, ein Befund, der als Hinweis auf einen raschen Rückstrom aus dem Gewebe in die Blutbahn zu interpretieren ist. Die freien Schilddrüsenhormonspiegel nahmen dagegen signifikant ab, erkennbar am Abfall der Werte des T₃-in vitro-Tests und der T₄- und T₃-Ausscheidung im Urin. Diese Befunde zeigen auf, daß neben dem Entzug von Schilddrüsenhormon vor allem die Zufuhr freier Bindungsstellen für Schilddrüsenhormon mit dem Spenderplasma bei der Behandlung der thyreotoxischen Krise von Bedeutung ist.Mit Unterstützung der Sonderforschungsbereiche SFB 51¹ und SFB 37²     

Pathogenesis of Herpes simplex virus infections in guinea pigs.

The pathogenesis of herpes simplex virus types 1 and 2 has been studied in guinea pigs after inoculation by various routes (subcutaneous and intradermal infection in footpads and vaginal infection). Clinical observations as well as virus isolation studies are reported. Herpes simplex virus type 2 infection by all three routes of inoculation led to acute primary and recurrent lesions. Virus persisted in the nervous system, particularly in sensory ganglia, and locally at the site of inoculation. Herpes simplex virus type 1 infection induced no or very mild primary symptoms. Recurrent lesions were only observed after intradermal inoculation. Invasion of the nervous system and consequent establishment of latent ganglionic infection was less efficient than after herpes simplex virus type 2 infection. Peripheral persistence was, however, equally common.     

Development and validation of a capillary electrophoresis method for the simultaneous determination of impurities of escitalopram including the R-enantiomer

A stereospecific capillary electrophoresis assay for the simultaneous determination of related substances and the enantiomeric purity of escitalopram was developed by a central composite face-centered factorial design and subsequently validated. Separations were carried out in a 50 μm, 47/40 cm fused-silica capillary. The optimized conditions included 20 mM phosphate buffer, pH 2.5, containing 0.5 mg/ml β-cyclodextrin and 22 mg/ml sulfated β-cyclodextrin as background electrolyte, an applied voltage of −20 kV and a temperature of 28 °C. Salicylic acid was used as internal standard. The assay was validated for the (R)-enantiomer of citalopram and the enantiomers of the impurity citadiol in the range of 2.5–150 μg/ml and 2.5–50 μg/ml, respectively. The limit of detection was 0.02% for all compounds, the limit of quantitation 0.05%, relative to a concentration of escitalopram of 5 mg/ml. Intraday precision of migration time and peak area ratio were in the range of 0.17–0.44% and 1.64% and 6.25%, respectively. Relative standard deviations of interday precision ranged between 0.84% and 1.85% in the case of migration times and between 5.20% and 9.28% for peak area ratio. The assay was applied to the determination of the purity of escitalopram in bulk drug and tablets. (R)-Citalopram and (S)-citadiol were detected as impurities.     

Metabolism of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) by bovine brain microvessel endothelial cells

Incubation of bovine brain microvessel endothelial cell monolayers with the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine led to the monoamine oxidase (MAO)-mediated formation of the oxidative metabolites 1-methyl-4-phenyl-2,3-dihydropyridine and 1-methyl-4-phenylpyridine (MPP+). The flux of low nanomolar concentrations of [3H]MPP+ across endothelial cell monolayers appeared to be restricted, probably due to the oxidation by MAO. [3H]MPP+ did not significantly cross endothelial cell monolayers.