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Biomedical subjects

M Leonard

Publications and source records attributed to M Leonard.

At least 37 records · Page 2Linked to original sources
PubMed2000

Expression of specific markers and particle transport in a new human intestinal M-cell model.

The aim of this work was to establish a new, simplified in vitro model of the human M-cell. Cocultures of physically separated human intestinal epithelial Caco-2 cells and B-cell lymphoma Raji cells were established. The cocultures were characterized under the criteria of morphology, integrity, expression of M-cell markers and cell adhesion molecules (CAMs), and altered particle transport. Using this construct, the epithelial cells were transformed to cells with an M-cell-like morphology and had altered expression of potential human M-cell markers (alkaline phosphatase down-regulation and Sialyl Lewis A antigen up-regulation). The expression of intercellular adhesion molecule-1 and vascular cell adhesion molecule was altered and there was an increased binding of lectins wheat germ agglutinin and peanut agglutinin with a 40-fold increase in microparticle transport. The particle transport was size-dependent and could be inhibited at 4 degrees C or by replacing the Raji B-cells with Jurkat T-cells. This new coculture model will enable controlled studies of M-cell development and function in vitro.

Alkaline Phosphatase↗
PubMed2000

Surface modification of poly(lactic acid) nanospheres using hydrophobically modified dextrans as stabilizers in an o/w emulsion/evaporation technique.

Sterically stabilized biocompatible poly(lactic acid) (PLA) nanospheres were prepared by an o/w emulsion/evaporation technique, using hydrophobically modified dextrans (DexP) as the emulsion stabilizer. Photon correlation spectroscopy, zetametry, and differential scanning calorimetry studies corroborated that interfacial adhesion between immiscible dextran and PLA chains was achieved by compatibilization of polymer segments via hydrophobic groups grafted onto dextran and thus leading to the formation of entanglements between the hydrophobic dextran parts and the PLA matrix. The presence of dextran exposed at the particle surface was confirmed by X-ray photoelectron spectroscopy and by the fact that the suspensions showed an increased stability in concentrated NaCl solutions and a reduction of bovine serum albumin adsorption compared to uncoated PLA nanoparticles. A comparison of the characteristics of PLA nanospheres DexP-coated via the emulsion procedure (NS(em)) with those of PLA particles coated by DexP adsorption (NS(ad)) suggests that the conformation of the polymer in the superficial layers may be different. However, both DexP layers behave similarly in terms of stability and protein adsorption.

Adsorption↗
PubMed2000

Evaluation of the Caco-2 monolayer as a model epithelium for iontophoretic transport.

PURPOSE: To assess the Caco-2 monolayer as a model for iontophoresis of drugs across a model epithelium. METHODS: The apparent permeability co-efficient (Papp) of mannitol, thyrotrophin releasing hormone (TRH), dexamethasone and a range of sizes of fluorescein isothiocyanate (FITC) dextrans across Caco-2 monolayers was measured under passive and electrically stimulated conditions. Trans-epithelial electrical resistance (TEER) was determined throughout. Transmission electron micrographs (TEM) of the monolayers were taken. Confocal laser scanning microscopy (CLSM) was used to visualize the iontophoretic transport route of FITC-Dextran (MW = 20 kDa) across a Caco-2 monolayer. RESULTS: Application of 14.3 micro-Eq x cm(-2) across the monolayer evoked a transient drop in TEER. The drop in TEER was accompanied by statistically significant increases in fluxes of all the agents in the mucosal to serosal direction except for FD-70. TEM of test samples exhibited tight junction dilatation, in addition to intracellular vacuolisation. The iontophoresis of FD-20 was visualised with confocal laser scanning microscopy and was localised in paracellular spaces of the monolayer. CONCLUSIONS: The fluxes of mannitol, TRH, dexamethasone, FD-4, FD-10 and FD-20 across the Caco-2 monolayer were significantly enhanced when electric field was applied. The iontophoretic effect appeared to be directly upon tight junctions

Biological Transport↗
PubMed2000

Antioxidant levels in the cord blood of term fetus.

The aim of this study was to compare the differences in the total antioxidant levels in the cord blood after a normal vaginal delivery and after an elective caesarean section. This was a prospective study approved by the Wirral Hospital ethical research committee. The study was carried out in a district general hospital. We investigated 96 healthy pregnant women who had normal antenatal period with singleton pregnancies between 37 and 42 completed weeks of gestation. Sixty-five women had a spontaneous normal vaginal delivery and 31 underwent elective caesarean section. Umbilical cord blood was obtained immediately after delivery. Antioxidants such as glutathione peroxidase (GPX) and superoxide dismutase (SOD) were measured and compared between the normal vaginal delivery and elective ceasarean sections. The mean values for GPx in umbilical cord arterial blood (95; 86-103, n=74) was found to be significantly higher (P=0.0133) than that found in umbilical cord venous blood (84; 80-88, n=95). The arterial SOD values were found to be significantly higher (P=0.0337) in infants who had been delivered by caesarean section (1188; 1065-1311, n=22) than by vaginal delivery (1021;958-1083, n=39). The differences in the levels of GPX between the arterial and venous systems is not well documented but may be due to differences in the level of selenium, hydroperoxides or glutathione. In addition, why infants delivered by ceasarian section have a higher level of arterial SOD than those delivered by vaginal delivery remains unclear, but it may be a reflection of a relatively low level in infants subjected to the stress of labour.

Journal Article↗
PubMed2000

Surface modification of polystyrene nanoparticles using dextrans and dextran-POE copolymers: polymer adsorption and colloidal characterization.

Hydrophobically-modified dextran (dextran-phenoxy, DexP) and dextran-phenoxy-poly(oxyethylene) (DexP-POE) copolymers have been used to modify the surface properties and the stability of polystyrene nanoparticles. We examined the effect of phenoxy group and POE chain concentrations on their adsorption behaviour. The adsorbed amount was determined by the standard depletion method and the layer thickness of the adsorbed layer by photon correlation spectroscopy and electrokinetic measurements. The results show that the hydrophobic interaction is the driving force during the adsorption while the layer thickness correlates with the interfacial concentration of grafted POE chains. The effects of adsorbed layers on the properties of latex dispersions have been characterized in terms of the stability of the dispersions toward added electrolyte and temperature. The conformation of the adsorbed copolymers is discussed in relation to layer thickness and colloidal stability of suspensions.

Adsorption↗
PubMed1999

Comparative Pore Structure Analysis of Dextran-Coated Polystyrene Particles.

Porous poly(styrene-divinylbenzene) (PS-DVB) particles were modified by adsorption of hydrophobically-modified dextrans, to provide chromatographic matrices for biomolecule chromatography. The dextran distribution and the pore characteristics of various coated PS-DVB beads were examined using nitrogen adsorption-desorption, mercury intrusion, and size exclusion chromatography. It was found that the adsorption of dextran does not result in homogeneous layers but rather in inhomogeneous ones. At high dextran loading and high content of hydrophobic groups in the adsorbed polymer, most of the pores of the macroporous rigid material are filled with a soft and porous dextran network being stabilized by hydrophobic interactions. According to chromatographic experiments, most of the surface was nevertheless expected to be covered at least by a thin and dense protecting layer since proteins-even those that are small enough to penetrate the dextran network-cannot interact nonspecifically with the internal pore surface. At low content of hydrophobic groups, dextran deposits preferentially as a thicker and more diffuse layer. However, the thickness of the coating is expected to be irregular and probably contributes to an increase in the roughness of the polystyrene surface. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Role of MAP kinase pathways in mediating IL-6 production in human primary mesangial and proximal tubular cells.

BACKGROUND: Both interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) are pleiotropic cytokines that have been implicated in the development of glomerular and tubular injury in various forms of immune-mediated renal disease, including glomerulonephritis. Although TNF-alpha has been shown to stimulate IL-6 production in renal cells in culture, the signaling mechanisms that regulate IL-6 production are not fully understood. The aim of this study was to examine the role of the p38 and extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) pathways in regulating TNF-alpha-mediated IL-6 production from both primary human mesangial cells (HMCs) and human proximal tubular (HPT) cells. METHODS: Primary mesangial and proximal tubular cells were prepared from nephrectomized human kidney tissue. Cells were treated for 24 hours with TNF-alpha in the presence and absence of the specific p38 and ERK1,2 MAPK inhibitors SB203580 and PD98059, respectively, either alone or in combination. IL-6 levels in the cell culture media were measured by enzyme-linked immunosorbent assay. MAPK activation was demonstrated by immunoblot for the active kinase (tyrosine/threonine phosphorylated) in whole cell extracts using phospho-specific antibodies. p38 MAPK activity in HPT cells was measured using an in vitro immunokinase assay using ATF2 as the substrate. RESULTS: TNF-alpha (0.1 to 100 ng/ml) stimulated a dose-dependent increase in IL-6 production in both renal cell types. The activation of the p38 and the ERK1,2 MAPKs occurred following TNF-alpha stimulation. The role of these activations in IL-6 production was confirmed by the ability of both inhibitors SB203580 (1 to 30 microM) and PD98059 (0.01 to 10 microM) to inhibit basal and TNF-alpha-stimulated IL-6 production in both cell types. The addition of both inhibitors in combination caused greater decreases in IL-6 production compared with either inhibitor alone. Pretreatment with SB203580 (10 microM) had no effect on basal or TNF-alpha-stimulated phosphorylation of p38 MAPK but completely abolished TNF-alpha-stimulated p38 MAPK activity. PD98059 decreased both basal and TNF-alpha-stimulated phosphorylation of ERK1,2. CONCLUSIONS: This study provides evidence that both the p38 and ERK MAPK pathways are important for the regulation of the production of IL-6 from the proximal tubular and glomerular mesangial regions of the nephron. In response to TNF-alpha, the activation of both pathways leads to IL-6 production. These findings could aid in an understanding of the cellular mechanisms that regulate IL-6 production and could provide insights into possible pharmacological strategies in inflammatory renal disease.

Cells, Cultured↗
PubMed1999

Factors produced by activated leukocytes alter renal epithelial cell differentiation.

The development of tubulointerstitial fibrosis in inflammatory renal diseases has been linked to disease progression to end-stage renal failure. Understanding the interactions of the factors influencing inflammation and activating the fibrotic process, that is, the inflammatory infiltrate and the resident proximal tubular cells, may lead to a determination of the mechanisms that regulate tubulointerstitial fibrosis. We used an in vitro model of human proximal tubule cells that were stimulated with supernatant from activated peripheral blood mononuclear cells (leukocytes) to study the alterations in cellular phenotype, and examined the signaling pathways mediating epithelial-fibroblast like transdifferentiation. Our hypothesis of the proposed sequence of events leading to tubulointerstitial fibrosis is explained.

Cell Differentiation↗
PubMed1999

Treatment outcome and prognostic factors for infants with acute lymphoblastic leukemia treated on two consecutive trials of the Children's Cancer Group.

PURPOSE: Infants represent a very poor risk group for acute lymphoblastic leukemia (ALL). We report treatment outcome for such patients treated with intensive therapy on consecutive Children's Cancer Group (CCG) protocols. PATIENTS AND METHODS: Between 1984 and 1993, infants with newly diagnosed ALL were enrolled onto CCG-107 (n = 99) and CCG-1883 (n = 135) protocols. Postconsolidation therapy was more intensive on CCG-1883. On both studies, prophylactic treatment of the CNS included both high-dose systemic chemotherapy and intrathecal therapy, in contrast to whole-brain radiotherapy, which was used in earlier studies. RESULTS: Most patients (>95%) achieved remission with induction therapy. The most frequent event was a marrow relapse (46 patients on CCG-107 and 66 patients on CCG- 1883). Four-year event-free survival was 33% (SE = 4.7%) on CCG-107 and 39% (SE = 4.2%) on CCG- 1883. Both studies represent an improvement compared with a 22% (SE = 5.1%) event-free survival for historical controls. Four-year cumulative probabilities of any marrow relapse or an isolated CNS relapse were, respectively, 49% (SE = 5%) and 9% (SE = 3%) on CCG-107 and 50% (SE = 5%) and 3% (SE = 2%) on CCG-1883, compared with 63% (SE = 6%) and 5% (SE = 3%) for the historical controls. Independent adverse prognostic factors were age less than 3 months, WBC count of more than 50,000/microL, CD10 negativity, slow response to induction therapy, and presence of the translocation t(4;11). CONCLUSION: Outcome for infants on CCG-107 and CCG- 1883 improved, compared with historical controls. Marrow relapse remains the primary mode of failure. Isolated CNS relapse rates are low, indicating that intrathecal chemotherapy combined with very-high-dose systemic therapy provides adequate protection of the CNS. The overall unsatisfactory outcome observed for the infant ALL population warrants the future use of novel alternative therapies.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1999

Trismus: what is it, what causes it, and how to treat it.

Trismus is a common complication. In many ways, it is a pretty innocuous one, but for the patient, it could give rise to many constraints, including social injunctions that can cause anxiety and anger. In a few instances, there have been instigation of lawsuits. Therefore, it is important for clinicians to be aware of this significant condition, its primary causes, and its treatments.

Dental Care for Chronically Ill↗
PubMed1998

Coronary venous hypertension prevents the formation of the electrophysiological arrhythmogenic substrate of acute ischemia in the dog: salutary effects of preserved myocardial hydration.

Coronary venous hypertension induced by partial coronary sinus obstruction (CSO) in the dog, prevents or delays the predictable ventricular fibrillation (VF) of the early phase of acute ischemia. Also, CSO acting presumably through enhanced myocardial hydration, normalizes the inhomogenous extracellular potassium ([K+]o) accumulation, a major factor in producing the electrophysiological disparities, characteristic of arrhythmogenic substrate. To further clarify the mechanism of early ischemic VF prevention in dogs, radioactive microspheres were used to evaluate regional perfusion changes, resulting from CSO sufficient to raise the coronary sinus pressure to 40 mmHg, before and during ischemia induced by double coronary artery occlusion (CAO) (n=5). Also, global or regional unipolar electrogram mapping was used to assess changes of epicardial ventricular activation times (AT) and sequence and activation recovery intervals (ARI) during CSO, CAO and combined CSO and CAO, induced in random order (n=8). CSO did not affect regional perfusion nor improved collateral blood flow during ischemia. With CSO, AT shortened modestly over time (0.41+/-1.1 ms/min, r=0.85, P<0. 05) and ARI transiently decreased by up to 5.5%. With CAO, AT became variably delayed and isochrone map distortions were indicative of localized conduction delays or blocks, consistent with elevated [K+]o. In contrast, when CAO was preceded by CSO, AT delays were homogenous and normal activation sequence was preserved. Also, whereas with CAO, ARI shortened unequally over the ischemic region by as much as 43% at individual sites (average of 38.3+/-6.8 ms, P<0. 001), with combined CSO and CAO, ARI shortening was less pronounced and more homogenous (26.1+/-5.6 ms, P<0.05), not exceeding 29% at any site. Thus, in accordance with previous findings of enhanced [K+]o homogeneity, coronary venous hypertension reduces the disparities of activation and refractoriness of ischemia attributable, at least in part, to disparate [K+]o accumulation. Since no collateral blood flow improvement could be identified, the salutary electrophysiological effects of CSO may reflect a more homogenous extracellular environment, due to preservation of normal microvascular pressure (Pmv) and sustained filtration and lymph flow.

Acute Disease↗