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Biomedical subjects

P Martin

Publications and source records attributed to P Martin.

At least 163 records · Page 9Linked to original sources
PubMed2001

[Intimal muscular fibrodysplasia responsible for an ischemic gastric ulcer in a patient with a von Recklinghausen's disease: a case report].

A 78 year-old woman, suffering from a von Recklinghausen's disease sought medical assistance for hematemesis with anemia. This patient had previously experienced an amputation of the right arm for gangrene. Gastric fibroscopy unveiled a deep chronic ulcus developed in the antrum, highly suspect of malignancy. Multiple biopsies of the ulcer showed mainly interstitial gastritis. The persistence of the hematemesis imposed a subtotal gastrectomy. Pathological examination of the operative specimen evidenced an ischemic ulcer caused by arterial intimal muscular fibrodysplasia with associated neurofibromatosis in the neighboring sub-mucosal layer. This case report highlights the frequent association of phacomatosis especially von Recklinghausen's disease, with vascular lesions whose clinical expression mainly depends on the involved vascular area.

Aged↗
PubMed2001

Improved pharmacokinetic properties of a polyethylene glycol-modified form of interferon-beta-1a with preserved in vitro bioactivity.

Interferon therapies suffer from a relatively short half-life of the products in circulation. To address this issue we investigated the effects of polyethylene glycol modification (PEGylation) on the pharmacokinetic properties of human interferon (IFN)-beta-1a. PEGylation with a linear 20-kDa PEG targeted at a single site on the N-terminal amine had no deleterious effect on its specific activity in an in vitro antiviral assay. In monkeys, PEG IFN-beta-1a treatment induced neopterin and beta2-microglobulin expression (pharmacodynamic markers of activity). Systemic clearance values in monkeys, rats, and mice decreased, respectively, from 232, 261, and 247 ml/h/kg for the unmodified IFN-beta-1a to 30.5, 19.2, and 18.7 ml/h/kg for the PEGylated form, while volume of distribution values decreased from 427, 280, and 328 ml/kg to 284, 173, and 150 ml/kg. The decreased clearance and volume of distribution resulted in higher serum antiviral activity in the PEG IFN-beta-1a-treated animals. In the rat, a more extensive set of dosing routes was investigated, including intraperitoneal, intratracheal, and oral administration. Bioavailability for the PEG IFN-beta-1a was similar to the unmodified protein for each of the extravascular routes examined. For the intraperitoneal route, bioavailability was almost 100%, whereas for the oral and intratracheal routes absorption was low (<5%). In rats, subcutaneous bioavailability was moderate (28%), whereas in monkeys it was approximately 100%. In all instances an improved pharmacokinetic profile for the PEGylated IFN-beta-1a was observed. These findings demonstrate that PEGylation greatly alters the pharmacokinetic properties of IFN-beta-1a, resulting in an increase in systemic exposure following diverse routes of administration.

Animals↗
PubMed2001

[The myc oncogene and transdifferentiation of the retinal pigment epithelium].

The retinal pigment epithelium (RPE) develops from the same sheet of neuroepithelium as the neuroretina. When infected with MC29, a v-myc expressing virus, the RPE cells can be induced to transdifferentiate and to take a neuroretinal epithelium fate. After a PCR-based differential screening from these cells we have identified three genes of interest. Qath5, a quail basic helix-loop-helix (bHLH) gene that is closely related to the Drosophila atonal, and whose expression is found in the developing neuroretina. A Chx10-related homeobox gene also expressed in the developing neuroretina and HuD, a RNA-binding protein not expressed in the RPE but expressed during neurogenesis. Beside these genes whose function is involved in regulating neuronal differentiation myc also induced a transient Mitf expression. Mitf is expressed in the entire optic cup, later restricted to the pigmented retina. Mitf is involved in the regulation of the pigmented differentiation. We conclude that v-myc can reverse the RPE to the bipotential retinal primordia.

Alpharetrovirus↗
PubMed2001

A cost-effectiveness analysis of biliary anastomosis with or without T-tube after orthotopic liver transplantation.

Biliary reconstruction continues to be a major source of morbidity following orthotopic liver transplantation. We wished to determine if choledochocholedochostomy without a T-tube was associated with fewer biliary complications and was less costly than choledochocholedochostomy with a T-tube. A retrospective cohort study of patients who underwent liver transplantation was performed. Patients were stratified into two groups: group I had bile duct reconstruction with T-tube and group II did not have a T-tube. The results were interpreted on an intention-to-treat analysis. We identified 147 adult patients who underwent initial liver transplantation. There were 76 patients in group I and 71 patients in group II. There were no statistical differences between the two groups regarding underlying cause of liver disease, patient age, gender or United Network for Organ Sharing status. As the decision to use a T-tube was made at the time of surgery, the two groups may not be strictly comparable. The mean hospital stay was longer in group I (31.1 +/- 27.9d) than in group II (18.8 +/- 15.5d) (p = 0.001). Biliary complications were statistically more frequent in patients from group I patients (25/76, 32.9%) than in patients from group II (11/71, 15.5%) (p = 0.01). There was a trend for the costs associated with diagnostic and therapeutic procedures for the management of biliary complications to be greater for group I than for group II, although this was not statistically significant (p = 0.235). Our study suggests choledochocholedochostomy without T-tube reconstruction is the preferred strategy for biliary reconstruction in orthotopic liver transplantation. It is not only associated with fewer biliary complications, but also less costly than using choledochocholedochostomy over a T-tube. Randomized prospective studies are needed to confirm our results.

Anastomosis, Surgical↗
PubMed2001

[The channels for important new knowledge to medical doctors. The case of Helicobacter pylori and stomach and duodenal ulcers.].

UNLABELLED: A retrospective survey of the flow of information to medical doctors as regards the relationship between Helicobacter pylori and stomach and duodenal ulcer and other gastrointestinal diseases. This is the Icelandic part of a joint study in five Nordic countries. OBJECTIVE: The objective of the research was to assess the effectiveness of different sources of information, to measure the length of time it takes for the information to spread and influence medical practice. MATERIAL AND METHODS: The information was collected with the help of questionnaires that were sent to 159 general practitioners (GP) and 110 physicians in three medical specialities. Among the questions asked were when and how the information had reached the respondents and when and how it had influenced their medical practices. RESULTS: The knowledge about Helicobacter pylori had generally reached medical doctors six to eight years after it first appeared in the medical journals and had three years later led to changes in the routine examinations and treatment. The specialists got the news one to three years earlier than the GPs and also started to prescribe antibiotics one to three years earlier. The most frequently cited source of information was international medical journals, then scientific conferences, colleagues and The Icelandic Medical Journal. The most important source was considered to be international medical journals, then scientific conferences and colleagues. A certain difference was found between GPs and the specialist doctors. More GPs said they had got information from the pharmaceutical industry or through The Icelandic Medical Journal and relied on clinical diagnosis. More specialist doctors considered the most important source of new knowledge to be the colleagues, they also said they used endoscopy and took tissue samples more often and more often considered it correct to do so. CONCLUSIONS: Only a decade after the first reports on Helicobacter pylori appeared in medical journals most Icelandic doctors had got the knowledge and were prescribing appropriate treatment, the specialist doctors in the lead. International medical journals spread the news most effectively but The Icelandic Medical Journal played only a minor role. The question is if the process could have been accelerated any further by some more hitting Icelandic news and by more definite initiative in framing guidelines.

English Abstract↗
PubMed2000

Dynamic actin-based epithelial adhesion and cell matching during Drosophila dorsal closure.

BACKGROUND: The adhesion of two epithelial sheets is a fundamental process that occurs throughout embryogenesis and during wound repair. Sealing of the dorsal epidermis along the midline of the Drosophila embryo provides a genetically tractable model to analyse the closure of such holes. Several studies indicate that the actin cytoskeleton plays a critical role in dorsal closure. Although many components of the signalling cascade directing this process have been identified, the precise cell-biological events upon which these signals act remain poorly described. RESULTS: By confocal imaging of living fly embryos expressing green fluorescent protein (GFP)-tagged actin, we found that dorsal closure relies on the activity of dynamic filopodia and lamellipodia that extend from front-row cells to actively zipper the epithelial sheets together. As these epithelial fronts approach one another, we observed long, thin filopodia, apparently 'sampling' cells on the opposing face. When the assembly of these actin-based protrusions was blocked (by interfering with the activities of Cdc42 and Jun N-terminal kinase signalling), the adhesion and fusion of opposing epithelial cells was prevented and their ability to 'sense' correct partners was also blocked, leading to segment misalignment along the midline seam. CONCLUSIONS: Dynamic, actin-based protrusions (filopodia and lamellae) are critical, both in the mechanics of epithelial adhesion during dorsal closure and in the correct 'matching' of opposing cells along the fusion seam.

Actins↗
PubMed2000

Negative hair-bundle stiffness betrays a mechanism for mechanical amplification by the hair cell.

Hearing and balance rely on the ability of hair cells in the inner ear to sense miniscule mechanical stimuli. In each cell, sound or acceleration deflects the mechanosensitive hair bundle, a tuft of rigid stereocilia protruding from the cell's apical surface. By altering the tension in gating springs linked to mechanically sensitive transduction channels, this deflection changes the channels' open probability and elicits an electrical response. To detect weak stimuli despite energy losses caused by viscous dissipation, a hair cell can use active hair-bundle movement to amplify its mechanical inputs. This amplificatory process also yields spontaneous bundle oscillations. Using a displacement-clamp system to measure the mechanical properties of individual hair bundles from the bullfrog's ear, we found that an oscillatory bundle displays negative slope stiffness at the heart of its region of mechanosensitivity. Offsetting the hair bundle's position activates an adaptation process that shifts the region of negative stiffness along the displacement axis. Modeling indicates that the interplay between negative bundle stiffness and the motor responsible for mechanical adaptation produces bundle oscillation similar to that observed. Just as the negative resistance of electrically excitable cells and of tunnel diodes can be embedded in a biasing circuit to amplify electrical signals, negative stiffness can be harnessed to amplify mechanical stimuli in the ear.

Animals↗
PubMed2000

Putting ion channels to work: mechanoelectrical transduction, adaptation, and amplification by hair cells.

As in other excitable cells, the ion channels of sensory receptors produce electrical signals that constitute the cellular response to stimulation. In photoreceptors, olfactory neurons, and some gustatory receptors, these channels essentially report the results of antecedent events in a cascade of chemical reactions. The mechanoelectrical transduction channels of hair cells, by contrast, are coupled directly to the stimulus. As a consequence, the mechanical properties of these channels shape our hearing process from the outset of transduction. Channel gating introduces nonlinearities prominent enough to be measured and even heard. Channels provide a feedback signal that controls the transducer's adaptation to large stimuli. Finally, transduction channels participate in an amplificatory process that sensitizes and sharpens hearing.

Adaptation, Physiological↗