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Biomedical subjects

J Stafford

Publications and source records attributed to J Stafford.

At least 37 records · Page 2Linked to original sources
PubMed1988

Functional coupling of tight junctions and microfilaments in T84 monolayers.

The actin-binding agent cytochalasin D (CD) in intact intestinal epithelium appears to elicit segmentation and contraction of a perijunctional ring of actomyosin and, consequently, to diminish tight junction resistance. We determined if an intestinal epithelial model composed of T84 cells also displayed such a perijunctional cytoskeletal specialization and, if so, whether exposure to CD also affected the tight junction barrier. We find T84 cells display a prominent perijunctional microfilament ring that is actin rich. CD elicits large decreases in transepithelial resistance due specifically to perturbed tight junction permeability as determined with dual Na+-mannitol flux analysis. Transepithelial mannitol and insulin fluxes also increase after CD exposure, but these molecules remain differentially restricted in accordance with their sizes, indicating that gross disruption of the monolayer has not occurred. Structurally, CD elicits segmentation and condensation of the perijunctional ring into actin-rich plaques. These features have similarity to those seen in native intestinal epithelia. This system may represent a simple model for studies of cytoskeletal-tight junction relationships.

Actin Cytoskeleton↗
PubMed1988

The selective and superoxide-independent disruption of intestinal epithelial tight junctions during leukocyte transmigration.

Polymorphonuclear leukocyte (PMN) transmigration across cultured intestinal epithelial monolayers has been shown to be associated with a decrease in transepithelial resistance to the passive flow of ions. Using flux techniques, we show that this effect reflects selective, PMN induced alterations in paracellular, as opposed to transcellular, ion permeability. Enhancement of paracellular permeability due to PMN transmigration is not simply due to expansion of the paracellular space resulting from cell death as cytotoxicity does not occur during this process. Thus, permeability alterations accompanying PMN transmigration can be specifically attributed to altered permeability of the rate limiting barrier of the paracellular pathway, the intercellular tight junction. We have also explored the mechanism by which PMN induce transient tight junction dissolution during transmigration. Use of inhibitors of toxic oxygen metabolites or use of PMN from patients with chronic granulomatous disease show that oxygen metabolites are neither required for transmigration or for the permeability abnormality accompanying transmigration. Similarly, use of protease inhibitors suggest that release of proteases by PMN during transmigration is not the basis by which PMN are able to cross tight junctions. Structural studies show that transient intimate PMN-epithelial cell plasma membrane associations and cytoskeletal specializations preceed junctional impalement by PMN. We speculate that such putative adhesion sites serve as the foothold from which PMN may generate the mechanical force necessary to cross tight junctions during transmigration.

Biological Transport, Active↗
PubMed1987

Vinyl chloride: an assessment of the risk of occupational exposure.

There is little doubt that exposure to high levels of VCM as a consequence of occupation can result in an increased incidence of ASL. A review of 20 epidemiological studies involving about 45,000 workers occupationally exposed to VCM showed that neoplasms of the liver showed an increase in incidence in the majority of studies. For brain cancer the association between exposure to VCM and an increased incidence was less clear because of the lower relative risk. Neoplasms of the respiratory tract, digestive system, lymphatic and haemopoietic system, buccal cavity, and pharynx, cardiovascular system and colon/stomach were reported to show an increased incidence in one or more studies, but to show no increase, or in some cases a decrease, in incidence in other studies. In view of the increased incidence of breast neoplasms in rodents exposed to VCM, the studies of Chaizze et al. (1980), who did not confirm these findings in humans, are of importance. The register of ASL cases now contains records of 99 persons with confirmed ASL and occupational exposure to VCM. The average latent period between first exposure to VCM and death from ASL is 21.9 years. The majority of cases occurred in autoclave workers, who are recognized as having been exposed to extremely high levels. Although precise estimates of exposure are not available for the periods of most interest, the pattern of cases roughly suggests that extremely high exposures were necessary for the induction of ASL. For example, ASL cases tended to occur in larger numbers in some plants than in others, a finding that can be explained most easily by differences in exposure patterns. There is an extensive series of animal studies on the carcinogenicity of VCM. Some of these precede the epidemiological studies confirming the association between VCM exposure and ASL in man. ASL and neoplasms of a number of other organs have been induced in laboratory rodents by VCM. Estimation of the exposure levels likely to cause a lifetime risk of ASL of 10(-6) on the basis of these data give extremely low levels (down to 3.9 X 10(-7) ppb) which appear to be unrealistic estimates for man. Part of the reason for this is that laboratory studies have shown that VCM is metabolized in the liver (and elsewhere in the body) to the reactive metabolites chloroethylene oxide and chloroacetaldehyde. The rate of conversion is limited at high levels of exposure giving inaccurate estimates of the slope of the dose-response relationship.(ABSTRACT TRUNCATED AT 400 WORDS)

Air Pollutants, Occupational↗
PubMed1987

Structural analysis of a human intestinal epithelial cell line.

Confluent monolayers of epithelial cell lines of intestinal derivation may serve as useful models for studies of intestinal epithelial structure and function. Cells of the T84 line appear to be a useful model for studies of Cl- secretion. We now define the fine structure of this cell line, the structural events that occur during monolayer formation, and the influence of plastic versus collagen substrates and permeable versus impermeable substrates on the structural development of these monolayers. When plated on collagen-coated filters at confluency, T84 cells cover the filter surface and lay down basement membrane-like material within 18 h. Such "monolayers" multifocally display areas with many cell layers alternating with areas composed of a single layer of cells. During this stage of development cell polarization is minimal, ultrastructural discontinuities exist that impart low transepithelial resistance, and morphologic features reminiscent of stratified intestinal epithelium during fetal development are present. Within 5 days of plating on collagen-coated filters, true monolayers form. These monolayers have high transepithelial resistance and consist of highly polarized columnar cells with structural similarity to intestinal crypt cells. Cells plated on a plastic substrate are also capable of rapidly producing basement membrane-like material but, unlike those plated on collagen-coated filters, under these conditions the rapid initial spreading of cells over the substrate surface does not occur. As a result, at 5 days monolayers plated on plastic are less uniform than those plated on collagen-coated filters, exhibit areas in which unpolarized flattened cells abound, and multifocally leak macromolecules. Studies using collagen-coated filters made impermeant with glass backing suggest that the enhancing effect of this substrate on monolayer structural development is not simply due to the greater access that basolateral membranes have to nutrient media when grown on permeable supports. This study defines the structure and structural development of this useful model epithelium, and demonstrates the importance of substrate selection.

Carcinoma↗
PubMed1987

Effects of polymorphonuclear leukocyte transmigration on the barrier function of cultured intestinal epithelial monolayers.

We describe a model to study the effects of polymorphonuclear leukocyte (PMN) transmigration on the intestinal epithelial barrier. Human PMN were induced to transmigrate across high resistance monolayers of a cultured human intestinal epithelial cell line (T84 cells) by chemotactic gradients produced by formyl methionyl leucyl phenylalanine (FMLP). With maximal transmigration monolayer resistance decreased by 48 +/- 12.6% in 15 min and by 83 +/- 1.6% in 60 min. This response was dependent on the size of the FMLP gradient and the density of PMN transmigration. The decrease in resistance correlated with number of PMN migrating across monolayers, and was accompanied by increases in flux of paracellular tracers. Macromolecular tracer studies localized the leak sites to foci at which PMN impaled the epithelium. Removal of the chemotactic gradient led to restoration of baseline resistance within 18 h. PMN transmigration across intestinal epithelial monolayers occurs via intercellular occluding junctions and may be associated with a reversible increase in epithelial permeability.

Cell Line↗
PubMed1985

Exposure to vinyl chloride and angiosarcoma of the liver: a report of the register of cases.

The Association of Plastic Manufacturers in Europe maintains a register of all cases of angiosarcoma of the liver (ASL) resulting from exposure to vinyl chloride monomer (VCM). This register has recorded all known VCM related cases of the disease worldwide that have been histologically confirmed. Although likely to be incomplete, it is the most comprehensive tabulation of such cases available and, by the end of 1984, 118 men had been registered. The information from analysis of the cases currently on the register is used to make an approximate projection of the number of cases to be expected in the future. The conclusion from this projection is that the industry is reaching the halfway stage in the appearance of VCM related ASL.

Adult↗
PubMed1984

Fine mapping of an immunoglobulin gene activator.

It has recently been shown that the promoter of a kappa immunoglobulin gene is activated for transcription by a downstream sequence element. Here we mapped the activating element to a resolution of about 20 base pairs by constructing a series of deletions in the cloned kappa gene. After transfection of each deleted gene into myeloma cells, a transient expression assay was used to measure the level of transcription from the kappa promoter. We found that the activating element extends through about 200 base pairs and encompasses a region of sequence that is conserved between mouse and human genes. As successively deeper deletions were made into the conserved region from either the 5' or 3' side, the activating ability was lost gradually rather than abruptly. Although several short segments in this region are homologous to sequences in viral enhancers, they did not seem to play a dominant role in the activating effect. We also found that the activating element remained functional when reversed in orientation or when moved upstream of the kappa gene.

Animals↗
PubMed1978

The Christchurch Hospital diabetes education programme.

The Christchurch Hospital diabetes teaching programme is now well established and towards the end of 1977 the results of an evaluation programme should be available. Our aim is to give diabetics and their families the best possible education and to stress the importance of patient self-sufficiency. Patient feedback methods are used to encourage continuing education. The assessment of the value of the educational programme warrants considerable attention and suitable methods of evaluation are being attempted.

Diabetes Mellitus↗
PubMedDate not supplied

Symmetrical and asymmetrical changes in brain tissue with age as measured on CT scans.

Age-related changes in mean CT attenuation values of brain tissue were analyzed by an objective, automated technique. Study participants included 64 healthy men ranging in age from 31 to 87 years. Five CT slices from each individual were evaluated: the last ventricular slice and the next four supraventricular slices. Regression analyses indicated that specific regions in the brain change with age. A schematic reconstruction of these regions suggests that several brain regions are selectively altered with age. On the medial aspect of the cerebral hemisphere there was bilaterally symmetrical atrophy of the cingulate gyrus and sulcus, the adjacent interhemispheric frontal gyri, the parietooccipital sulcus, and the marginal branch of the cingulate sulcus. On the convexity of the cerebral hemispheres there was asymmetrical widening of the central and postcentral sulcus on the left, and the intraparietal sulcus on the right.

Adult↗