Alterations in P-glycoprotein expression in mouse tissues by doxorubicin: implications for pharmacokinetics in multiple dosing regimens.

The purpose of the studies presented here is to determine if alterations in doxorubicin (DOX) pharmacokinetics that seem to occur following multiple-dosing are due to changes in DOX elimination via P-glycoprotein (PGP) mediated transport in the liver, kidney and gut. A pharmacokinetic study in female Balb/c mice was carried out with blood and tissue DOX levels measured in animals following a single DOX treatment (6 mg/kg), and in animals following a second DOX treatment after receiving a DOX treatment a week earlier. The pharmacokinetics of DOX in blood and tissues was altered by earlier exposure to DOX, as the animals that were treated once a week for 2 weeks showed an increased rate of DOX elimination from blood and tissues following the second treatment. Immunoblot analysis of PGP expression in liver and kidney from na?ve and DOX-treated mice showed an approximately 1.2-fold elevation of PGP protein in these tissues in response to DOX exposure. Immunohistochemical staining of liver and small intestine sections for PGP showed 1.6-fold and 1.9-fold increases, respectively, in the DOX-treated tissues. These results have implications both in multiple-dosing regimens, as well as multiple-drug regimens, where DOX is used in combination with other drugs that are substrates for PGP-mediated efflux. Increases in PGP expression in both hepatic and extrahepatic tissues can lead to changes in the pharmacokinetics of DOX, as well as other drugs that are transported by PGP.     

COMPARATIVE STUDIES ON RESPIRATION : IX. THE EFFECTS OF ANTAGONISTIC SALTS ON THE RESPIRATION OF ASPERGILLUS NIGER.

1. In the presence of 0.05 per cent dextrose the respiration of Aspergillus niger is increased by NaCl in concentrations of 0.25 to 0.5M, and by 0.5M CaCl₂. 2. Stronger concentrations, as 2M NaCl and 1.25M CaCl₂, decrease the respiration. The decrease in the higher concentrations is probably an osmotic effect of these salts. 3. A mixture of 19 cc. of NaCl and 1 cc. of CaCl₂ (both 0.5M) showed antagonism, in that the respiration was normal, although each salt alone caused an increase. 4. Spores of Aspergillus niger did not germinate on 0.5M NaCl (plus 0.05 per cent dextrose) while they did on 0.5M CaCl₂ (plus 0.05 per cent dextrose) and on various mixtures of the two. This shows that a substance may have different effects on respiration from those which it has upon growth.     

Thrombin,a stimulator of bone resorption

It is shown that thrombin (0.1–7 units/ml) stimulates calcium mobilization and bone matrix degradation, as indicated by release of [³H]proline, from cultured calvarial bones. The second finding in this paper, that indomethacin blocks the stimulating effect of thrombin on bone resorption, is consistent with the concept that prostaglandin synthesis may be involved in this process. It is suggested that thrombin is a potential mediator of bone resorption associated with inflammatory and malignant processes.     

Labelling of high molecular weight hyaluronan with125I-tyrosine: studiesin vitro andin vivo in the rat

Studies on the metabolism of the polysaccharide hyaluronan has previously been hampered by the lack of radioactive hyaluronan of high molecular weight (MW) and high specific activity. In the present study¹²⁵I-tyrosine (T)-labelled hyaluronan was produced after CNBr-activation of the polysaccharide. A specific activity of approximately 0.1 MBq µg^–1 was achieved using 100 µg of 0.5×10⁶ Da hyaluronan labelled for 2 h with 18 MBq¹²⁵I. The¹²⁵I-T-hyaluronan kept a high MW-profile upon gel filtration chromatography and was found to be cleared from the circulation with the kinetics and organ distribution reported for biosynthetically labelled hyaluronan of high MW. The¹²⁵I-labelled polysaccharide is also taken up by liver endothelial cells bothin vivo andin vitro, indicating that the labelling does not interfere with the binding to specific cell-surface receptors found on these cells. The intracellular degradation is slower than that earlier reported for biosynthetically labelled hyaluronan and seems to be halted at the level of low MW oligo- or mono-saccharides that eventually leave the organism via the urine. Scintigraphic images of rats after intravenous injection of¹²⁵I-T-hyaluronan showed rapid uptake in the liver and a redistribution of radioactivity from liver to urine with time. Our results indicate that the¹²⁵I-T-hyaluronan is suitable for studies of hyaluronan-metabolism in a number of ways. The gamma emitters¹²⁵I and¹³¹I are easy to monitor and can be used also forin vivo 3D-imaging using single photon emission computer tomography.Abbreviations CNBr cyanogen bromide - T-HA tyrosine-labelled hyaluronan     

Mechanism of activation of liver glycogen synthase by swelling.

The mechanism linking the stimulation of liver glycogen synthesis to swelling induced either by amino acids or hypotonicity was studied in hepatocytes, in gel-filtered liver extracts, and in purified preparations of particulate glycogen to which glycogen-metabolizing enzymes are bound. High concentrations of KCl, but not of potassium glutamate, were found to inhibit glycogen synthesis in permeabilized hepatocytes. Similarly, physiological concentrations (30-50 mM) of Cl- ions were also found to inhibit synthase phosphatase in vitro, whereas 10-20 mM Cl- ions, a concentration found in swollen hepatocytes, did not inhibit synthase phosphatase. Synthase phosphatase activity was more sensitive to inhibition by Cl- ions at low (0.1%) than at high (1%) concentrations of glycogen. By contrast, 10 mM glutamate and aspartate, a concentration observed in hepatocytes incubated with glutamine or proline, stimulated synthase phosphatase in vitro. Therefore, it is proposed that the fall in intracellular Cl- concentration as well as the increase in intracellular glutamate and aspartate concentrations, that are observed in swollen hepatocytes in the presence of amino acids, are responsible, at least in part, for the stimulation of synthase phosphatase and, hence, of glycogen synthesis.     

Regulation of Bacterial Cell Division: Genetic and Phenotypic Analysis of Temperature-Sensitive, Multinucleate, Filament-Forming Mutants of Escherichia coli

Three mutants of Escherichia coli K-12 which form filaments during 42 C incubation have been characterized. The mutant strains AX621, AX629, and AX655 continued to grow and to synthesize deoxyribonucleic acid at 42 C for 150 to 180 min, after which time growth ceased. When cultures of the mutants were transferred from 42 to 28 C, septation of the filaments began after a 25- to 30-min period and continued at a greater than normal rate until no filaments remained. Addition of chloramphenicol at the time of transfer from 42 to 28 C prevented cell division in strain AX655 and caused lysis of strains AX621 and AX629. The temperature sensitivity mutation in each strain mapped near leu. For strain AX621, the mutation was specifically located between leu and nadC by P1 transduction. Properties of these strains are compared with those of other cell division mutants.     

Fast atom bombardment mass spectrometry and tandem mass spectrometry in antibiotics: identification of nucleoside antitumor antibiotic toyocamycin in fermentation broth

The presence of the nucleoside antitumor antibiotic toyocamycin in the fermentation broth was determined by a combination of negative and positive ion fast atom bombardment (FAB) mass spectrometry, high resolution FAB mass spectrometry and mass-analysed ion kinetic energy spectrometry (MIKES). A reasonable limit of detection for toyocamycin in the whole broth was obtained by combining the specificity of mass spectrometry/mass spectrometry (also called tandem mass spectrometry) to FAB. The role played by the fermentation matrix upon the production and the observation of characteristic ions by FAB using xenon atoms was examined. High-performance liquid chromatography (HPLC) and FAB mass spectrometry were used to monitor toyocamycin at all stages of strain development, fermentation and recovery.     

A rationale for the prophylactic use of monophosphoryl lipid A in sepsis and septic shock.

Monophosphoryl lipid A (MLA), a substructure of bacterial lipopolysaccharide (LPS), is being developed as a prophylactic for sepsis and septic shock. In the present study it was shown that MLA induced a rapid accumulation of IFN-gamma in mice that correlated with an in vivo priming of macrophages. Primed macrophages could be induced in vitro to synthesize nitric oxide, a key mediator of macrophage cytotoxicity. Due to its rapid clearance, MLA was not present in circulation at the time when IFN-gamma accumulated, suggesting that MLA could not synergize with IFN-gamma to systemically activate macrophages in vivo. MLA treatment tolerized mice against the IFN-gamma response--ie., treatment of mice with MLA on day 1 blocked LPS from inducing IFN-gamma on days 2-4. The significance of these results in relation to MLA's ability to enhance non-specific resistance and block LPS lethality in animals is discussed.