The bioavailability, dispostion kinetics and dosage of sulphadimethoxine in dogs.
The disposition kinetics of sulphadimethoxine were studied in six normal beagle dogs after intravenous injection of a single dose (55 mg/kg). The median (range) distribution and elimination half times of the drug were 2.36 (2.06-3.35) hours and 13.10 (9.71-16.50) hours, respectively. Total body clearance of the drug had a median value of 21.7 ml/kg/h and a mean value of 21.4 ml/kg/h. While the overall tissue to plasma level ratio (k12/k21) of the drug was 0.55 after distribution equilibrium had been attained, analogue computer simulated curves showed that at 24 hours the fractions (percentage) of the dose in the central and tissue compartments were 12 and 11%, respectively. The drug was shown, by equilibrium dialysis method, to be highly bound to plasma proteins (greater than 75%) within the usual therapeutic range (50 to 150 mug/ml) of plasma levels. The systemic availability of sulphadimethoxine from the oral suspension was 32.8% (22.5-80.0). Since the absorption half time, 1.87 (0.86-3.22) hours, was considerably shorter than the half-life, 13.10 (9.71-16.50) hours, of the drug, the rate of absorption would have little influence on the dosage regimen. Based on the experimental data obtained, a satisfactory dosage regimen might consist of a priming dose of 55 mg/kg by the intravenous route and maintenance doses of either 27.5 mg/kg of sulphadimethoxine injection given intravenously or 55 mg/kg of the oral suspension administered at 24 hour intervals. The adequacy and duration of therapy will depend upon the clinical response obtained. (+info)
UK-18892, a new aminoglycoside: an in vitro study.
UK-18892 is a new aminoglycoside antibiotic, a derivative of kanamycin A structurally related to amikacin. It was found to be active against a wide range of pathogenic bacteria, including many gentamicin-resistant strains. The spectrum and degree of activity of UK-18892 were similar to those of amikacin, and differences were relatively minor. UK-18892 was about twice as active as amikacin against gentamicin-susceptible strains of Pseudomonas aeruginosa. Both amikacin and UK-18892 were equally active against gentamicin-resistant strains of P. aeruginosa. There were no appreciable differences in the activity of UK-18892 and amikacin against Enterobacteriaceae and Staphylococcus aureus. Cross-resistance between these two antimicrobials was also apparent. (+info)
A cell-surface superoxide dismutase is a binding protein for peroxinectin, a cell-adhesive peroxidase in crayfish.
Peroxinectin, a cell-adhesive peroxidase (homologous to human myeloperoxidase), from the crayfish Pacifastacus leniusculus, was shown by immuno-fluorescence to bind to the surface of crayfish blood cells (haemocytes). In order to identify a cell surface receptor for peroxinectin, labelled peroxinectin was incubated with a blot of haemocyte membrane proteins. It was found to specifically bind two bands of 230 and 90 kDa; this binding was decreased in the presence of unlabelled peroxinectin. Purified 230/90 kDa complex also bound peroxinectin in the same assay. In addition, the 230 kDa band binds the crayfish beta-1,3-glucan-binding protein. The 230 kDa band could be reduced to 90 kDa, thus showing that the 230 kDa is a multimer of 90 kDa units. The peroxinectin-binding protein was cloned from a haemocyte cDNA library, using immuno-screening or polymerase chain reaction based on partial amino acid sequence of the purified protein. It has a signal sequence, a domain homologous to CuZn-containing superoxide dismutases, and a basic, proline-rich, C-terminal tail, but no membrane-spanning segment. In accordance, the 90 and 230 kDa bands had superoxide dismutase activity. Immuno-fluorescence of non-permeabilized haemocytes with affinity-purified antibodies confirmed that the crayfish CuZn-superoxide dismutase is localized at the cell surface; it could be released from the membrane with high salt. It was thus concluded that the peroxinectin-binding protein is an extracellular SOD (EC-SOD) and a peripheral membrane protein, presumably kept at the cell surface via ionic interaction with its C-terminal region. This interaction with a peroxidase seems to be a novel function for an SOD. The binding of the cell surface SOD to the cell-adhesive/opsonic peroxinectin may mediate, or regulate, cell adhesion and phagocytosis; it may also be important for efficient localized production of microbicidal substances. (+info)
Absorption, metabolism, and excretion of 14C-temozolomide following oral administration to patients with advanced cancer.
The purpose of this study is to characterize the absorption, metabolism, and excretion of carbon 14-labeled temozolomide (14C-TMZ) administered p.o. to adult patients with advanced solid malignancies. On day 1 of cycle 1, six patients received a single oral 200-mg dose of 14C-TMZ (70.2 microCi). Whole blood, plasma, urine, and feces were collected from days 1-8 and on day 14 of cycle 1. Total radioactivity was measured in all samples. TMZ, 5-(3-methyltriazen-1-yl)imidazole-4-carboxamide (MTIC), and 4-amino-5-imidazole-carboxamide (AIC) concentrations were determined in plasma, and urine and plasma samples were profiled for metabolite/degradation products. Maximum TMZ plasma concentrations were achieved between 0.33 to 2 h (mean, 1.2 h), and half-life, apparent volume of distribution, and oral clearance values averaged 1.9 h, 17 liters/m2, and 104 ml/min/m2, respectively. A first-order absorption, one-compartment linear model, which included first-order formation of MTIC from TMZ and elimination of MTIC via degradation to AIC, and a peripheral distribution compartment for AIC, adequately described the plasma TMZ, MTIC, and AIC concentrations. MTIC systemic clearance was estimated to be 5384 ml/min/m2, and the half-life was calculated to be 2.5 min. Metabolite profiles of plasma at 1 and 4 h after treatment showed that 14C-derived radioactivity was primarily associated with TMZ, and a smaller amount was attributed to AIC. Profiles of urine samples from 0-24 h revealed that 14C-TMZ-derived urinary radioactivity was primarily associated with unchanged drug (5.6%), AIC (12%), or 3-methyl-2,3-dihydro-4-oxoimidazo[5,1-d]tetrazine-8-carboxyl ic acid (2.3%). The recovered radioactive dose (39%) was principally eliminated in the urine (38%), and a small amount (0.8%) was excreted in the feces. TMZ exhibits rapid oral absorption and high systemic availability. The primary elimination pathway for TMZ is by pH-dependent degradation to MTIC and further degradation to AIC. Incomplete recovery of radioactivity may be explained by the incorporation of AIC into nucleic acids. (+info)
The crayfish plasma clotting protein: a vitellogenin-related protein responsible for clot formation in crustacean blood.
Coagulation in crayfish blood is based on the transglutaminase-mediated crosslinking of a specific plasma clotting protein. Here we report the cloning of the subunit of this clotting protein from a crayfish hepatopancreas cDNA library. The ORF encodes a protein of 1,721 amino acids, including a signal peptide of 15 amino acids. Sequence analysis reveals that the clotting protein is homologous to vitellogenins, which are proteins found in vitellogenic females of egg-laying animals. The clotting protein and vitellogenins are all lipoproteins and share a limited sequence similarity to certain other lipoproteins (e.g., mammalian apolipoprotein B and microsomal triglyceride transfer protein) and contain a stretch with similarity to the D domain of mammalian von Willebrand factor. The crayfish clotting protein is present in both sexes, unlike the female-specific vitellogenins. Electron microscopy was used to visualize individual clotting protein molecules and to study the transglutaminase-mediated clotting reaction. In the presence of an endogenous transglutaminase, the purified clotting protein molecules rapidly assemble into long, flexible chains that occasionally branch. (+info)
Cryptocyanin, a crustacean molting protein: evolutionary link with arthropod hemocyanins and insect hexamerins.
Cryptocyanin, a copper-free hexameric protein in crab (Cancer magister) hemolymph, has been characterized and the amino acid sequence has been deduced from its cDNA. It is markedly similar in sequence, size, and structure to hemocyanin, the copper-containing oxygen-transport protein found in many arthropods. Cryptocyanin does not bind oxygen, however, and lacks three of the six highly conserved copper-binding histidine residues of hemocyanin. Cryptocyanin has no phenoloxidase activity, although a phenoloxidase is present in the hemolymph. The concentration of cryptocyanin in the hemolymph is closely coordinated with the molt cycle and reaches levels higher than hemocyanin during premolt. Cryptocyanin resembles insect hexamerins in the lack of copper, molt cycle patterns of biosynthesis, and potential contributions to the new exoskeleton. Phylogenetic analysis of sequence similarities between cryptocyanin and other members of the hemocyanin gene family shows that cryptocyanin is closely associated with crustacean hemocyanins and suggests that cryptocyanin arose as a result of a hemocyanin gene duplication. The presence of both hemocyanin and cryptocyanin in one animal provides an example of how insect hexamerins might have evolved from hemocyanin. Our results suggest that multiple members of the hemocyanin gene family-hemocyanin, cryptocyanin, phenoloxidase, and hexamerins-may participate in two vital functions of molting animals, oxygen binding and molting. Cryptocyanin may provide important molecular data to further investigate evolutionary relationships among all molting animals. (+info)
Quantitative prediction of metabolic inhibition of midazolam by itraconazole and ketoconazole in rats: implication of concentrative uptake of inhibitors into liver.
To evaluate the extent of drug-drug interaction concerning metabolic inhibition in the liver quantitatively, we tried to predict the plasma concentration increasing ratio of midazolam (MDZ) by itraconazole (ITZ) or ketoconazole (KTZ) in rats. MDZ was administered at a dose of 10 mg/kg through the portal vein at 60 min after bolus administration of 20 mg/kg ITZ or during 0.33 mg/h/body of KTZ infusion. The ratio values in the area under the plasma concentration curve of MDZ in the presence of ITZ and KTZ was 2.14 and 1.67, respectively. The liver-unbound concentration to plasma-unbound concentration ratios of ITZ and KTZ were 11 approximately 14 and 1.3, respectively, suggesting a concentrative uptake of both drugs into the liver. ITZ and KTZ competitively inhibited the oxidative metabolism of MDZ in rat liver microsomes, and Ki values of ITZ and KTZ were 0.23 microM and 0.16 microM, respectively. We predicted the ratio values of MDZ in the presence of ITZ and KTZ, using Ki values and unbound concentrations of both drugs in the plasma or liver. The predicted ratio values in the presence of ITZ or KTZ calculated by using unbound concentration in the plasma were 1.03 approximately 1.05 and 1.39, whereas those calculated using unbound concentration in the liver were 1.73 approximately 1.97 and 1.51, respectively, which were very close to the observed ratio values. These findings indicated the necessity to consider the concentrative uptake of inhibitors into the liver for the quantitative prediction of the drug-drug interactions concerning metabolic inhibition in the liver. (+info)
Airway inflammatory response to ozone in subjects with different asthma severity.
The aim of this study was to evaluate whether ozone exposure induces a similar airway inflammatory response in subjects with different degrees of asthma severity. Two groups of asthmatic subjects were studied: seven with intermittent mild asthma not requiring regular treatment (group A); and seven with persistent mild asthma requiring regular treatment with inhaled corticosteroids and long-acting beta2-agonists (group B). All subjects were exposed, in a randomized cross-over design, to air or O3 (0.26 parts per million (ppm) for 2 h with intermittent exercise); subjects in group B withdrew from regular treatment 72 h before each exposure. Before the exposure, and 1 and 2 h after the beginning of the exposure they performed a pulmonary function test, and a questionnaire was completed to obtain a total symptom score (TSS). Six hours after the end of the exposure, hypertonic saline (HS) sputum induction was conducted. Sputum cell percentages, eosinophil cationic protein (ECP) and interleukin (IL)-8 concentrations in the sputum supernatant were measured. TSS significantly increased and forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) significantly decreased after O3 exposure in comparison with air exposure in group A, whereas no changes were observed in group B except for a significant decrement of FEV1 2 h after the beginning of O3 exposure. Sputum neutrophil percentage was significantly higher after O3 exposure than after air exposure in both groups (Group A: 70.2% (28-87) versus 26.6% (8.6-73.2); Group B: 62.1% (25-82.4) versus 27.9% (14.4-54)). IL-8 was higher in sputum supernatant collected 6 h after O3 exposure than after air, only in group A. No change due to O3 has been found in sputum eosinophil percentage and ECP concentration in both groups. In conclusion, the degree of airway response to a short-term exposure to ozone is different in subjects with asthma of different severity. The available data do not allow elucidation of whether this difference depends on the severity of the disease or on the regular anti-inflammatory treatment. (+info)