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At least 973 records · Page 54Linked to original sources
PubMed2006

Considerations on the possibilities and limitations of comprehensive normal phase-reversed phase liquid chromatography (NPLC x RPLC).

A comprehensive normal phase system LC-reversed phase LC (NPLC x RPLC) was evaluated for the separation of a pharmaceutical mixture and citrus oil extracts. NPLC was performed on a 25 cm x 1 mm ID x 5 microm dp diol phase. In the second dimension, an RP 18 monolithic column (10 cm L x 4.6 mm ID x 2 microm macropore size) and an octadecyl silicagel-packed column (5 cm L x 4.6 mm ID x 3.5 microm dp) were applied for the analyses of the pharmaceutical sample and the citrus oil extracts, respectively. A two-position/ten-port switching valve was used as interface. Under optimised LC conditions, the high degree of orthogonality between NP and RP resulted in peak capacities of 300 for the pharmaceutical sample and of 450 for the citrus oil extract composed of lemon and orange oil. Despite the features of NPLC x RPLC, several shortcomings related with the solvent incompatibility between the two LC modes were identified and the practical consequences were discussed.

Chromatography, Liquid↗
PubMed2006

Study of the phase I and phase II metabolism of nephrotoxin aristolochic acid by liquid chromatography/tandem mass spectrometry.

Prolonged exposure to aristolochic acid (AA) was shown to pose rapid progressive renal fibrosis in Belgian women in a slimming regime in the early 1990s. AA was also demonstrated to be strong carcinogen in rats. The carcinogenicity of AA is generally believed to be related to the nitro-reduction of AA, in which the aristolactam-nitriumion ion with a delocalized positive charge is the ultimate carcinogen. In this study, the phase I and phase II metabolism of AA was investigated by using an in vitro system with rat liver S9 and an in vivo animal study with Sprague-Dawley rats. AA was found to have been undergone hydroxylation, lactam formation, and desnitro and desmethyl transformations. Three conjugated metabolites of AA, namely the N- and O-glucuronides of aristolactams, were detected directly in pre-concentrated urine sample, with no acid hydrolysis or enzymatic digestion. Structural elucidation of the metabolites was performed by using liquid chromatography/tandem mass spectrometry (LC/MS/MS). The results indicated that N-glucuronidation was the major phase II metabolic pathway for the aristolactams formed by AA after their nitro-reduction.

Aerobiosis↗
PubMedDate not supplied

Sample sizes for phase II and phase III clinical trials: an integrated approach.

In this paper the following problem of clinical research is explored. Several potential new treatments are available for use against a certain disease. These are evaluated in a series of pilot studies which will constitute phase II clinical trials. The most promising will then be compared with a standard treatment in a phase III trial. Of interest will be the number of patients needed for the complete research programme, the proportions of these that should be involved in each phase, and the number of treatments which should be tried. Optimal strategies are found which maximize the probability that the overall programme identifies a treatment which is significantly better than the standard.

Clinical Trials as Topic↗
PubMed1997

Monokine-producing cells predominate in the recruitment phase of NOD insulitis while cells producing Th1-type cytokines characterize the effector phase.

Cells infiltrating the Langerhans' islets of prediabetic NOD females were isolated from 6 weeks to 6 months of age. These cells were assayed at a single-cell level for production of eight different cytokines by intracellular immunofluorescent staining. Quiescent in vivo preactivated cells were detected by in vitro stimulation with PMA and ionomycin for 4 h. The cell recruitment phase, between 6 and 12 weeks of age, is predominated by production of the monokines IL-1alpha, IL-6, and TNF After stimulation IFN-gamma and occasional IL-10 and GM-CSF producing cells could also be observed. This cytokine pattern occurs simultaneously with increasing insulitis, and we suggest that these cytokines are important in attracting inflammatory cells to the islets and maintaining the inflammatory state. A high frequency of endocrine cells producing IL-6 during this period may denote a stress response caused by initial beta-cell destruction due to cytokines released by the inflammatory cells. During the effector phase, between 4 and 6 months, there is a characteristic Th1 cytokine profile with lymphocytes producing IL-2, IFN-gamma and TNF, supposedly TNF-beta. No IL-4 production could be detected and IL-10 was very rarely found, indicating the absence of a Th2 response. Our findings show that the effector phase in NOD insulitis is a Th1 rather than a Th2-mediated event. We also demonstrate that cytokines that may cause initial tissue destruction are produced during the recruitment of inflammatory cells.

Aging↗
PubMed1989

Can hydration forces induce lateral phase separations in lamellar phases?

Large repulsive forces measured between membranes of lamellar lipid phases at low hydration are attributed to hydration interactions which vary widely among lipid species. We include this interaction in a model of lamellar phases of two membrane components (two lipids or lipid and protein). The surface polarization of a mixture is taken as a linear combination of those of the components. The model predicts phase separation at low hydration. This may have important consequences for living cells which are dehydrated either by the osmotic effects of tissue freezing, or by desiccation in unsaturated atmospheres.

Lipid Bilayers↗
PubMed1985

Investigation by pyrolysis mass spectrometry, phage pattern and plasmid analysis of staphylococci that have reverted from 'L'-phase to bacterial phase.

No major differences have been found in series of Staphylococcus aureus strains which reverted from 'L'-phase, either by pyrolysis mass spectrometry or by phage-typing or sensitivity testing. In 'L'-phase they have been subcultured for a long time or transformed/reverted many times into/from 'L'-phase. Plasmids were lost during transformations/reversions, but there was some difference between the tetracycline-connected plasmids on the one hand and the erythromycin-connected ones on the other.

L Forms↗
PubMed1985

Generalized theory for two-phase ion-pair and complexometric titrations. I. Two-phase titrations without side reactions.

A systematic theoretical treatment of the two-phase titration based on ion-pair and metal-complex formation is presented. Equations for the titration curve, accuracy, equivalence point and choice of the indicator are derived. Much attention is paid to the parameters determining the 'titratability' viz. extraction constant, distribution constant, phase volume ratio and the concentration of the analyte. Special attention is given to the role of intermediate ion-pair and metal-complex formation in the aqueous phase. The ion-pair formation in aqueous solution is examined closer by means of the relationship between the association constant in water, the degree of dissociation of the ion pair (alpha) and the concentration of the counter ion. The merits of this theoretical treatment are illustrated with literature examples.

Chemical Phenomena↗
PubMed2001

Determination of alkylphenols and alkylphenol polyethoxylates by reversed-phase high-performance liquid chromatography and solid-phase extraction.

A simple, accurate and reproducible reversed-phase high-performance liquid chromatography (HPLC) method was developed for the separation and characterisation of alkylphenols (APs) and alkylphenol polyethoxylates (APEOs), using a C18 octadecyl silica (ODS) column. APs and each APEO oligomer were separated successfully within a reasonable time without gradient elution. An excellent resolution was obtained, even for mixtures of APs and low EO number APEOs, which are otherwise difficult to separate using conventional normal-phase HPLC methods. This method, combined with solid-phase extraction, was highly applicable for the simultaneous determination of alkylphenols and alkylphenol ethoxylates in real samples.

Journal Article↗
PubMed2000

New stationary phase based on beta-cyclodextrin for normal-phase HPLC group-separation of organic nitrates.

The synthesis of a beta-cyclodextrin-silica normal-phase (NP)-liquid chromatography (LC) stationary phase is reported. Silica gel was modified with (3-bromopropyl)trimethoxysilane to a 3-bromopropyl-silica that was reacted with beta-cyclodextrin, resulting in a beta-cyclodextrin-silica. To prove its usefulness in group-separation of organic nitrates among others, a mixture of three groups of organic nitrates was separated. The results are compared with those obtained on a nitrated polyol-silica that has recently been reported. The alkyl dinitrates exhibt higher retention relatively to alkyl mononitrates on the new phase. This allows to cut the LC fractions in a way that the alkyl mononitrates and phenylalkyl nitrates appear in one fraction and the dinitrates in a second one without any overlap of the two fractions.

Journal Article↗
PubMed2007

Posterior retroperitoneoscopic adrenalectomy: a comparison between the initial experience in the invention phase and introductory phase of the new surgical technique.

BACKGROUND: Today, the posterior retroperitoneoscopic technique has become a standard procedure in adrenal surgery. The procedure allows direct access to the adrenal glands, but it seems to be difficult because of the uncommon anatomic view. This study compares the learning period of the new procedure of "posterior retroperitoneoscopic adrenalectomy" in the primary invention phase and the secondary introductory phase in a different hospital 10 years later. MATERIALS AND METHODS: The analysis included 100 posterior retroperitoneoscopic adrenalectomies (PRA) and involved 50 procedures in each center. Group A consisted of 44 patients (14 males, 30 females; age: 48.7 +/- 14.5 years) undergoing surgery between 07/1994 and 8/1996 (24 right, 26 left; 8 Cushing adenomas, 14 Conn adenomas, 11 pheochromocytomas, 7 nonfunctioning adrenocortical adenomas, 10 ACTH-dependent adrenal hyperplasias). Group B consisted of 50 patients (12 males, 38 females; mean age 59.3 +/- 10.7 years) operated between 01/2004 and 01/2006 (28 right, 22 left tumors; 5 Cushing adenomas, 12 Conn adenomas, 4 pheochromocytomas, 29 nonfunctioning adrenocortical adenomas). All PRAs were performed with the patient in the prone position with 3-4 trocars placed caudally in the region of the 11th and 12th ribs. In group A, the surgical team developed the technique of PRA themselves. Before their first PRA, the surgical team of group B was introduced to the technique by the group A surgeons and afterwards were supervised continuously. RESULTS: No serious intraoperative or postoperative complication occurred in either group. Group A experienced 7 conversions to open surgery, whereas group B had one conversion and one early reoperation due to bleeding (P = 0.03; chi(2)-test). The mean operative time was 117 +/- 41 minutes versus 83 +/- 35 minutes (group A and B respectively; P < 0.001; t-test). Estimated blood loss was similar in the two groups (47.2 +/- 46.2 ml versus 54 +/- 16.3 ml, group A versus B, respectively; P = 0.36; t-test). CONCLUSIONS: The study demonstrates the feasibility, safety, and reproducibility of the new surgical method of PRA both when it is employed in the early phase of invention, as well as when performed by surgeon-learners. After comprehensive training, the operative time and conversion rate are dramatically reduced, allowing for a short learning period.

Adrenal Cortex Neoplasms↗
PubMed1978

The relationship of paroxysmal ventricular tachycardia complicating the acute phase and ventricular arrhythmia during the late hospital phase of myocardial infarction to long-term survival.

The long-term prognosis of paroxysmal ventricular tachycardia (PVT) complicating acute myocardial infarction remains unevaluated. Significant ventricular arrhythmia in the patient after infarction is said to carry a poor prognosis with regard to survival. To evaluate these two important aspects of myocardial infarction in man, 56 patients with documented myocardial infarction had Holter monitoring performed during the initial 24 hours and prior to hospital discharge. In 38 of the 45 survivors, Holter monitoring was repeated an average of 19 months after infarction. There were eight cardiac deaths during follow-up. Data analysis revealed that of 18 patients with PVT during the acute phase, one died during follow-up and 17 survived long-term. Even though the incidence of complex PVCs prior to hospital discharge and at long-term follow-up was higher in patients with PVT during the acute phase than in those without PVT, survival appeared unaffected. Thus, PVT during the acute phase of myocardial infarction and complex PVCs at the time of hospital discharge are not incompatible with long-term survival.

Acute Disease↗
PubMed1993

Differential regulation of early phase and late phase responses in human neutrophils by cAMP.

The elevation of intracellular levels of cyclic AMP by forskolin stimulation of adenylate cyclase regulates early and late phase neutrophil responses differentially. Early phase neutrophil responses as measured by shape change in response to chemotactic factors, transmigration across a polycarbonate membrane and priming were unaffected by forskolin-induced elevation of intracellular cAMP. Late phase neutrophil responses such as release of superoxide anions, activation of phospholipase A2 and platelet activating factor (PAF) synthesis were inhibited by increasing intracellular cAMP through the addition of 10 microM forskolin for 10 min prior to stimulation. N-Formyl-methionyl-leucyl-phenylalanine-stimulated arachidonic acid release fell from 9.3% (untreated cells) to 4.6% in forskolin-treated cells. PAF generation was also inhibited from 430 pg/10(6) cells in untreated cells to background levels in forskolin-treated cells (110 pg/10(6) cells). Also, the reduction of cytochrome c by superoxide anions fell from 4.2 nmol/10(6) cells in the absence of forskolin to 2.0 nmol/10(6) cells following forskolin treatment. These results indicate that in neutrophils the elevation of cAMP acts differentially on cellular responses, not affecting early activation events, but markedly inhibiting late events such as the release of inflammatory mediators.

Adenylyl Cyclases↗
PubMed1994

Phases and phase transitions of the glycoglycerolipids.

LIPIDAT is a computerized database providing access to the wealth of information scattered throughout the literature concerning synthetic and biologically derived polar lipid polymorphic and mesomorphic phase behavior. The database is considered comprehensive for glycerophospholipids, glycoglycerolipids, sphingolipids and natural membrane extracts. Here, a review of the LIPIDAT data subset referring to glycoglycerolipids is presented together with an analysis of these data. The glycoglycerolipids subset represents 4% of all LIPIDAT records. It includes data collected over a 20-year period and consists of 419 records obtained from 37 articles in 13 journals. An analysis of the data in the subset has allowed us to identify trends in hydrated glycoglycerolipids phase behavior reflecting differences in hydrocarbon chain length, chain branching, chain-glycerol linkage type (ether vs. ester), sugar headgroup-glycerol linkage type (alpha vs. beta) and sugar headgroup identity. Included is a summary of the data concerning the effect of pH and of stereochemical purity on glycoglycerolipid phase behavior. Information on the mesomorphism of biologically derived and dry glycoglycerolipids is also presented. This review includes 92 references.

Carbohydrate Sequence↗
PubMed1985

Early initiation of DNA synthesis in G1 phase HeLa cells following fusion with red cell ghosts loaded with S-phase cell extracts.

A modification of polyethylene glycol-mediated cell fusion procedure has been described and standardized for red blood cell mediated microinjection of proteins into cells in suspension. Using this procedure, proteins are routinely introduced into 50% of the target cells. We have applied this microinjection procedure to introduce cytoplasmic extracts obtained from S-phase HeLa cells into HeLa cells synchronized in G1. This experiment resulted in an accelerated entry of the G1 cells into S phase as measured by the incorporation of [3H]thymidine. This technique may provide a means to identify and characterize the S-phase factors responsible for the induction of DNA synthesis.

Cell Cycle↗
PubMed1993

Shape-selective separation of polycyclic aromatic hydrocarbons by reversed-phase liquid chromatography on tetraphenylporphyrin-based stationary phases.

The reversed-phase chromatographic behavior of planar and non-planar polycyclic aromatic hydrocarbons (PAHs) is investigated on tetraphenylporphyrin and two metallotetraphenylporphyrin [Sn(IV), In(III)] bonded stationary phases using methanol-water and acetonitrile-water as mixed solvent mobile phases. Large differences in the capacity factors of aromatic solute pairs having the same number of carbon atoms, but differing in three-dimensional shape (e.g., triphenylene/o-terphenyl and perylene/alpha, alpha'-binaphthyl), suggest that the three tetraphenylporphyrin-based supports possess shape selectivity toward small planar aromatic solutes. Capacity factors for planar PAH solutes on these supports are significantly greater than for non-planar polyaryls having the same number of carbon atoms.

Chromatography, High Pressure Liquid↗
PubMed1994

Effect of mobile phase composition on the separation of thyrotropin-releasing hormone and some metabolites by reversed-phase ion-pair chromatography.

Sodium dodecyl sulphate was used for the separation of thyrotropin-releasing hormone (TRH) and the related compounds deamido-TRH (TRHOH), histidylprolinediketopiperazine, proline and prolineamide by reversed-phase ion-pair chromatography. The effects of mobile phase composition on retention and selectivity were determined. The parameters studied included acetonitrile, pairing ion and salt concentrations, salt type and pH. The results show that the separation of TRH and its analogue TRHOH can be easily adjusted by small modifications of the pH in the vicinity of pH 2. A remarkable improvement of peak width and peak shape was observed for some analytes when a potassium salt was added to the mobile phase.

Acetonitriles↗
PubMed1983

Hepatic phase I and phase II biotransformations in quail and trout: comparison to other species commonly used in toxicity testing.

The ability of quail and trout to perform a number of representative phase I and phase II biotransformations was examined. To facilitate interspecies comparisons, metabolism of the same substrates was examined simultaneously under uniform conditions for rat, mouse, rabbit, guinea pig, cat, and dog. Both nonmammalian species can metabolize four representative substrates of phase I mixed-function oxidases and one substrate of epoxide hydrolase, though activity tended to be lower than that of the mammals. Important differences in the conjugative pathways were also noted. Among these differences were the quail's relative deficiency in glutathione conjugation and the trout's low ability to conjugate sulfate compounds. Trout liver UDP-glucuronosyltransferase activity was remarkably high toward testosterone and bilirubin, while quail liver formed glucuronides of naphthol, p-nitrophenol, and digitoxigenin-monodigitoxoside. Also noteworthy was the high N-acetyltransferase activity of both quail and trout toward isoniazid, beta-naphthylamine, and 2-aminofluorene. Differences in substrate specificity for a given enzymatic pathway may be an indication that multiple forms of drug metabolizing systems also occur in these nonmammalian species. Observation of several hundred- or even thousand-fold differences between species in their enzyme activities for certain substrates under uniform conditions re-emphasizes the need for caution in extrapolation of xenobiotic metabolism from one species to another.

Acetylation↗
PubMed1988

Comparison of a monoclonal anti-HIV 1 gag solid phase with a polyclonal anti-HIV solid phase for detecting anti-HIV 1 in a competition ELISA.

An anti-HIV 1 competitive ELISA was developed using a monoclonal anti-HIV 1 gag to capture viral antigen to the solid phase. This format of assay was compared with a competitive ELISA where a polyclonal human anti-HIV 1 was used, to capture the viral antigen. Several benefits were observed using the monoclonal-antibody form of the assay. Firstly, less viral antigen was needed on solid phase to give an equivalent test in terms of positive and negative optical density 450 nm values. Secondly, a slight increase in sensitivity was also gained without any loss of specificity and finally, as a result of the murine nature of the antibody on the solid phase, no cross-reaction with the labelled human antibody in the test conjugate was observed. Such cross-linking has been observed with the polyclonal form of the assay and can lead to false-negative reactions.

AIDS-Related Complex↗