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Biomedical subjects

J M Anderson

Publications and source records attributed to J M Anderson.

At least 127 records · Page 7Linked to original sources
PubMed1997

The differential effects of poly(2-hydroxyethyl methacrylate) and poly(2-hydroxyethyl methacrylate)/poly(caprolactone) polymers on cell proliferation and collagen synthesis by human lung fibroblasts.

Because of its chemical versatility and demonstrated biocompatibility, poly(2-hydroxyethyl methacrylate) (pHEMA) has been widely used as a polymer for biomedical applications. Since this hydrophilic material shows a poor interface with cells, blendings with other polymers were done to improve cytocompatibility. In our polymer, the presence of hydrophobic dominions on the material surface, due to the interpenetrating polymerization of pHEMA with poly(caprolactone) (PCL), seems to ameliorate the cytocompatibility in terms of cell adhesion and metabolism. For our experiments, we used IMR-90 human fibroblasts, as these cells strongly regulate DNA, RNA, and protein synthesis as anchorage-dependent variables. Cell attachment on a pHEMA/PCL interpenetrating polymer network was optimal, suggesting a strong adhesion between the cells and the polymer surface. Cell adhesion was weaker on pHEMA, as a significant fraction of the fibroblasts revealed a lack of spreading, with most cells remaining spherical. Moreover, only fibroblasts seeded on pHEMA significantly decreased mRNA synthesis; collagen production and cell shapes ranged from fully flat and proliferating, to minimally spread and nonproliferating. Finally, DNA synthesis, as a measure of cell proliferation, was markedly inhibited in cells cultured on pHEMA but not on pHEMA/PCL. In conclusion, our results suggest that control of cell growth and metabolism by biomedical polymers is based on physicochemical mechanism(s) in which the hydrophilicity/hydrophobicity ratio of the material surfaces may play an important role.

Base Sequence↗
PubMed1997

Recognition of unique carboxyl-terminal motifs by distinct PDZ domains.

The oriented peptide library technique was used to investigate the peptide-binding specificities of nine PDZ domains. Each PDZ domain selected peptides with hydrophobic residues at the carboxyl terminus. Individual PDZ domains selected unique optimal motifs defined primarily by the carboxyl terminal three to seven residues of the peptides. One family of PDZ domains, including those of the Discs Large protein, selected peptides with the consensus motif Glu-(Ser/Thr)-Xxx-(Val/Ile) (where Xxx represents any amino acid) at the carboxyl terminus. In contrast, another family of PDZ domains, including those of LIN-2, p55, and Tiam-1, selected peptides with hydrophobic or aromatic side chains at the carboxyl terminal three residues. On the basis of crystal structures of the PSD-95-3 PDZ domain, the specificities observed with the peptide library can be rationalized.

Amino Acid Sequence↗
PubMed1997

In vivo biocompatibility and biostability of modified polyurethanes.

Modified segmented polyurethanes were examined for biostability and biocompatibility using an in vivo cage implant system for time intervals of 1, 2, 3, 5, and 10 weeks. Two types of materials were used: polyether polyurethanes and polycarbonate polyurethanes. Two unmodified polyether polyurethanes (PEUU A' and SPU-PRM), one PDMS endcapped polyether polyurethane (SPU-S), and two polycarbonate polyurethanes (SPU-PCU and SPU-C) were investigated in this study. Techniques used to characterize untreated materials were dynamic water contact angle, stress-strain analysis, and gel permeation chromatography. Cellular response was measured by exudate analysis and by macrophage and foreign body giant cell (FBGC) densities. Material characterization, postimplantation, was done by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) in order to quantify biodegradation and scanning electron microscopy (SEM) to qualitatively describe the cellular response and biodegradation. The exudate analysis showed that the acute and chronic inflammatory responses for all materials were similar. Lower FBGC densities and cell coverage on SPU-S were attributed to the hydrophobic surface provided by the PDMS endgroups. The polycarbonate polyurethanes did not show any significant differences in cell coverage or FBGC densities even though the macrophage densities were slightly lower compared to polyether polyurethanes. By 10 weeks, biodegradation in the case of PEUU A' and SPU-PRM was extensive as compared to SPU-S because the PDMS endcaps of SPU-S provided a shield against the oxygen radicals secreted by macrophages and FBGCs and lowered the rate of biodegradation. In the case of polycarbonate polyurethanes, the oxidative stability of the carbonate linkage lowered the rate of biodegradation tremendously as compared to the polyether polyurethanes (including SPU-S). The minor amount of biodegradation seen in polycarbonate polyurethanes at 10 weeks was attributed to hydrolysis of the carbonate linkage.

Animals↗
PubMed1997

Leukotriene synthesis by isolated perinatal ovine intrapulmonary vessels correlates with age-related changes in 5-lipoxygenase protein.

Leukotrienes (LT) are potent vasoconstrictors in the pulmonary circulation. We have investigated the synthesis of LTC4 by intrapulmonary arteries and veins of perinatal lambs. Paired vessels of near-term fetal 146 +/- 2- and 2- to 7-day-old newborn lambs (each n = 7), were incubated for 10 min at 37 degrees C in baseline, with 1 mumol/L A32187 or 0.1 mmol/L arachidonic acid. Produced leukotriene C4 was assayed from media by ELISA. Baseline production of leukotriene (ng/mg tissue, means +/- SEM) by vessels for arteries was 0.006 +/- 0.001 and 0.059 +/- 0.009 for fetus and newborn, respectively. In veins, the values were 0.013 +/- 0.003 and 0.073 +/- 0.007 for fetus and newborn, respectively. On stimulation with the calcium ionophore A23187, production by arteries increased 25-fold in the fetus, but 4-fold in the newborn. The corresponding values for stimulated veins were 37-fold and 9-fold in fetus and newborn, respectively. Generally, production by veins was greater than production by the matching arteries. In all instances, the fetal vessels produced less leukotrienes than the newborn vessels. Western analysis of stimulated and unstimulated vessel membrane protein showed greater expression of 5-lipoxygenase in veins than in arteries (P < 0.05). Our data show that veins produce more LTC4 due to greater expression of 5-lipoxygenase in the vessels and thus suggest that veins of perinatal lamb lungs may be more susceptible to LT-induced vasoreactivity in the perinatal pulmonary circulation. We speculate that a higher production of LTC4 by fetal veins may be necessary to maintain a high venous tone in fetal lungs.

Age Factors↗
PubMed1997

Differential distribution of the tight-junction-associated protein ZO-1 isoforms alpha+ and alpha- in guinea pig Sertoli cells: a possible association with F-actin and G-actin.

To elucidate the significance of alpha- and alpha+ isoforms of the tight-junction-associated protein ZO-1 in Sertoli cell tight junction regulation, taking into consideration that different isoforms are expressed in cells with different junctional morphologies, we investigated whether alpha- and alpha+ are differentially associated with junctions forming the continuous occluding zonules responsible for the blood-testis barrier, and/or with junctions forming the focal discontinuous occluding zonules. In addition, since Sertoli cells contact Sertoli cells and germ cells, we investigated whether each isoform is differentially associated with distinct classes of germ cells. Our immunoblot analyses of isolated seminiferous tubules, using affinity-purified polyclonal antibodies recognizing rat and human alpha- and alpha+, showed that guinea pig testis contained the two ZO-1 isoforms initially described in rat and human kidneys, and that alpha+ and alpha- were predominantly expressed during puberty and adulthood, respectively, indicating that alpha+ was predominant during periods of increased junction assembly/disassembly. We used the same antibodies and immunoperoxidase labeling on fetal, neonatal, pubertal, and adult guinea pig testes sections. Both isoforms were expressed at the site of Sertoli cell-Sertoli cell and Sertoli cell-germ cell junctions in the seminiferous epithelium, before and after birth, and both were localized in continuous and in discontinuous tight junctions. However, the distribution of alpha- and alpha+ was not the same in different locations of the tight junctions. Only alpha- was incorporated into junctions joining the Sertoli cells to all classes of germ cells. The alpha+ involved junctions joining Sertoli cells to particular classes of germ cells, suggesting that Sertoli cell expression of ZO-1 isoforms could be regulated by unique germ cell-Sertoli cell contacts. Conversely, we found a correspondence between the distribution of F-actin and ZO-1alpha+, indicating that the spatial organization of the subsurface actin accompanying cell junctions may affect alpha+/alpha(-)-plasma membrane association.

Actins↗
PubMed1997

Weighted least-squares reconstruction methods for positron emission tomography.

We present unpenalized and penalized weighted least-squares (WLS) reconstruction methods for positron emission tomography (PET), where the weights are based on the covariance of a model error and depend on the unknown parameters. The penalty function for the latter method is chosen so that certain a priori information is incorporated. The algorithms used to minimize the WLS objective functions guarantee nonnegative estimates and, experimentally, they converged faster than the maximum likelihood expectation-maximization (ML-EM) algorithm and produced images that had significantly better resolution and contrast. Although simulations suggest that the proposed algorithms are globally convergent, a proof of convergence has not yet been found. Nevertheless, we are able to show that the unpenalized method produces estimates that decrease the objective function monotonically with increasing iterations.

Algorithms↗
PubMed1997

Rounded biphasic waveform reduces energy requirements for transvenous catheter cardioversion of atrial fibrillation and flutter.

We postulated that reducing peak leading edge shock voltage and its rate of rise (waveform rounding) would reduce energy requirements for cardioversion of AF and AFl, and may therefore reduce patient discomfort. Transvenous defibrillating catheters (In-Control Inc.) were placed in the RAA (active fixation) and the CS of six anesthetized sheep. AF or AFl was induced by electrical stimulation (100 Hz, 2 V; Grass stimulator). A standard trapezoidal biphasic (S) waveform (3-ms duration each phase) was compared with a similar waveform that had the first phase rounded (R). Cardioversion was attempted after 30 seconds of arrhythmia, using a Ventritex HVS-O2 defibrillator modified to allow waveform rounding. Each waveform was randomly tested several times at 100-, 150-, and 200-V leading edges, and percentage cardioversion success calculated. Shock energy was calculated from delivered current and voltage using Flukeview (Fluke, Inc.) software. At 100-V leading edge R (64% success) and S (59%), shocks were similarly efficacious (P = 0.37). However, R delivered less current, voltage, and energy than the comparable S shock (means 1.30 A, 65.0 V, 0.33 J R vs 1.92 A, 94.2 V, 0.47 J S; P = 0.0001). Both waveforms were equally successful at 150 V (88% vs 100%; P = NS) and 200 V (100% vs 100%), but again R delivered less current, voltage, and energy (2.05 A, 102.5 V, 0.82 J R vs 2.78 A, 142.3 V, 1.11 J S at 150 V; 2.76 A, 141.2 V, 1.58 J R vs 3.77 A, 189.4 V, 2.03 J S at 200 V; both P = 0.0001). No arrhythmic or other complications occurred in the 174 shocks delivered. Waveform rounding reduces delivered peak voltage, current, and energy without reducing defibrillation efficacy. To determine if these changes are associated with a reduction in discomfort, patients with AF are currently being cardioverted with these waveforms during electrophysiological studies.

Animals↗
PubMed1997

Cytoskeletal rearrangement mediates human microvascular endothelial tight junction modulation by cytokines.

The tight junction (TJ) is a specialized intercellular structure responsible for the regulation of ionic and macromolecular flux across cell monolayers. Because plasma leakage is believed to occur mainly across the microvasculature, we hypothesized that microvascular endothelial cells (MVEC) may form more intact, regulatable TJ than other endothelial cell (EC) types, allowing further insight into the control of EC permeability. Primary cultures of MVEC monolayers produced transmonolayer electrical resistances (TER) of 120-155 omega.cm2, approximately 10 times that of large-vessel EC. Treatment with tumor necrosis factor and interferon-gamma caused a 50% decrease in the TER and a striking fragmentation of the basal, continuous interendothelial cell zonula occludens-1 protein (ZO-1) distribution determined by immunofluorescence. Fragmentation was inhibited by cytochalasin D, and confocal microscopy demonstrated a colocalization between F actin and ZO-1. These findings suggest that the F actin cytoskeleton plays a central role in endothelial TJ barrier regulation and that dynamic cytoskeletal alterations may primarily control vascular permeability.

1-Methyl-3-isobutylxanthine↗
PubMed1997

Search patterns using the line bisection test for neglect.

BACKGROUND/OBJECTIVE: Neglect has been attributed to sensory-attentional, motor-intentional, and representational disorders. Although patients with neglect may have defective visual exploration, the nature of this exploration deficit has not been entirely elucidated. The purpose of this study is to learn how, compared with control subjects, a patient with neglect performs visual exploration. METHODS: The line bisection test is commonly used to detect and evaluate the performance of patients with unilateral or hemispatial spatial neglect. We tested an experimental subject with left premotor-intentional neglect using an infrared eye monitoring instrument. Thirteen right-handed healthy volunteers served as control subjects. From different starting ocular positions, we assessed the direction of eye movements when the subjects initially oriented to the line, scanned the line, and then attempted to look at the center of the line. RESULTS: Independent of starting ocular position, normal subjects most often initially orient to the left end of the line, scan rightward, then look leftward to the center. However, the eye movements in our experimental subject with neglect were directed to the right end of the line without any scanning or leftward eye movement back to the center of the line. CONCLUSION: Our subject with neglect had defective line exploration that may be attributed to a directional ocular motor intentional deficit.

Adult↗
PubMed1997

Tight junction assembly during mouse blastocyst formation is regulated by late expression of ZO-1 alpha+ isoform.

The mouse preimplantation embryo has been used to investigate the de novo synthesis of tight junctions during trophectoderm epithelial differentiation. We have shown previously that individual components of the tight junction assemble in a temporal sequence, with membrane assembly of the cytoplasmic plaque protein ZO-1 occurring 12 hours before that of cingulin. Subsequently, two alternatively spliced isoforms of ZO-1 (alpha+ and alpha-), differing in the presence or absence of an 80 residue alpha domain were reported. Here, the temporal and spatial expression of these ZO-1 isoforms has been investigated at different stages of preimplantation development. ZO-1alpha- mRNA was present in oocytes and all preimplantation stages, whilst ZO-1alpha+ transcripts were first detected in embryos at the morula stage, close to the time of blastocoele formation. mRNAs for both isoforms were detected in trophectoderm and ICM cells. Immunoprecipitation of 35S-labelled embryos also showed synthesis of ZO-1alpha- throughout cleavage, whereas synthesis of ZO-1alpha+ was only apparent from the blastocyst stage. In addition, 33P-labelling showed both isoforms to be phosphorylated at the early blastocyst stage. The pattern and timing of membrane assembly of the two isoforms was also distinct. ZO-1alpha- was initially seen as punctate sites at the cell-cell contacts of compact 8-cell embryos. These sites then coalesced laterally along the membrane until they completely surrounded each cell with a zonular belt by the late morula stage. ZO-1alpha+ however, was first seen as perinuclear foci in late morulae before assembling at the tight junction. Membrane assembly of ZO-1alpha+ first occurred during the 32-cell stage and was zonular just prior to the early blastocyst stage. Immunostaining indicative of both isoforms was restricted to the trophectoderm lineage. Membrane assembly of ZO-1alpha+ and blastocoele formation were sensitive to brefeldin A, an inhibitor of intracellular trafficking beyond the Golgi complex. In addition, the tight junction transmembrane protein occludin co-localised with ZO-1alpha+ at the perinuclear sites in late morulae and at the newly assembled cell junctions. These results provide direct evidence from a native epithelium that ZO-1 isoforms perform distinct roles in tight junction assembly. Moreover, the late expression of ZO-1alpha+ and its apparent intracellular interaction with occludin may act as a final rate-limiting step in the synthesis of the tight junction, thereby regulating the time of junction sealing and blastocoele formation in the early embryo.

Alternative Splicing↗
PubMed1997

Occludin confers adhesiveness when expressed in fibroblasts.

Occludin is an integral membrane protein specifically associated with tight junctions. Previous studies suggest it is likely to function in forming the intercellular seal. In the present study, we expressed occludin under an inducible promotor in occludin-null fibroblasts to determine whether this protein confers intercellular adhesion. When human occludin is stably expressed in NRK and Rat-1 fibroblasts, which lack endogenous occludin and tight junctions but do have well developed ZO-1-containing adherens-like junctions, occludin colocalizes with ZO-1 to points of cell-cell contact. In contrast, L-cell fibroblasts which lack cadherin-based adherens junctions, target neither ZO-1 nor occludin to sites of cell contact. Occludin-induced adhesion was next quantified using a suspended cell assay. In NRK and Rat-1 cells, occludin expression induces adhesion in the absence of calcium, thus independent of cadherin-cadherin contacts. In contrast, L-cells are nonadhesive in this assay and show no increase in adhesion after induction of occludin expression. Binding of an antibody to the first of the putative extracellular loops of occludin confirmed that this sequence was exposed on the cell surface, and synthetic peptides containing the amino acid sequence of this loop inhibit adhesion induced by occludin expression. These results suggest that the extracellular surface of occludin is directly involved in cell-cell adhesion and the ability to confer adhesiveness correlates with the ability to colocalize with its cytoplasmic binding protein, ZO-1.

Amino Acid Sequence↗
PubMed1997

Inhibition of migration of endothelial cells by type V collagen and high molecular weight kininogens.

The failure of synthetic vascular grafts in humans is complex and related not only to the type of material but also to the accumulation of cellular and noncellular components onto or within the material. Proteins that adsorb on biomaterials such as vascular grafts may be involved in modulating cell function. Of these components, type V collagen and high molecular weight kininogens (HMWKs) are known to localize on the surface of vascular grafts. We have investigated the effect of type V collagen and HMWKs in the prevention of endothelialization of vascular prostheses by inhibiting cell migration. Inhibition of endothelial cell migration may lead to incomplete endothelialization and thus, failure of these devices. Various concentrations of type V collagen and HMWK solutions were placed at the bottom of 24 well tissue culture plates with porous membrane inserts (8 microns pore size) placed on top. Suspended human umbilical vein endothelial cells (HUVECs) were placed on top of the insert and incubated at 37 degrees C for 2 hours. Following incubation, the inserts were fixed and the cells that migrated through the pores were counted by microscopy. Our results showed that migration of endothelial cells was significantly inhibited in a dose dependent manner by type V collagen and HMWKs.

Cell Movement↗
PubMed1997

Protein adsorption on chemically modified surfaces.

Following the implantation of a biomaterial, the first event to occur at the tissue-material interface is protein adsorption. Once proteins have adsorbed to the surface of a material, cells no longer see the material, but only the protein coated surface layer. This adsorbed protein layer can mediate the type of cells that adhere to the surface, which ultimately can determine the type of tissue that develops. In this experiment, glass and polystyrene surfaces were chemically modified forming ionic, non-ionic, hydrophobic, and hydrophilic surfaces. The modified surfaces were incubated in a RPMI diluted serum solution. After incubation, a radioimmunoassay was used to quantify the exposed proteins adsorbed onto the surface of the material. In general, albumin, complement C3 (C3), fibronectin (FN) and vitronectin (VN) competitively adsorbed to the modified surface in a similar fashion, whereas IgG adsorption was the opposite. The hydrophobic surfaces had higher adsorbance of the adhesion proteins (C3, FN and VN) compared to higher adsorption of albumin and IgG onto the hydrophilic surfaces. The surface mobility of the silane modified surfaces also affected the adhesion of proteins. The differences seen in protein adsorption did not directly correlate to monocyte adhesion and Foreign Body Giant Cell (FBGC) development on these surfaces.

Adsorption↗
PubMed1996

The SH3 domain of the tight junction protein ZO-1 binds to a serine protein kinase that phosphorylates a region C-terminal to this domain.

ZO-1 is a tight junction phosphoprotein partially homologous to a tumor suppressor in Drosophila. The homologous region contains an SH3 domain with an unidentified function. Using fusion proteins containing the SH3 domain and various N- and C-terminal sequences, we tested for association of a kinase with this protein domain in extracts of MDCK cells. We show that the SH3 domain of ZO-1 binds a serine protein kinase that phosphorylates a region immediately C-terminal to the SH3 domain. This kinase associates specifically with the SH3 domain of ZO-1 and appears to be also associated with junctional complexes extracted from MDCK cells.

Animals↗
PubMed1996

Protein-protein interactions: PDZ domain networks.

PDZ domains can dimerize or bind to the carboxyl termini of unrelated proteins. Crystallographic studies demonstrate the structural basis for these interactions, which contribute to the ability of PDZ domains to create networks associated with the plasma membrane.

Amino Acid Sequence↗
PubMed1996

Cell signalling: MAGUK magic.

Diverse extracellular signals are coupled at the plasma membrane to intracellular signal transduction pathways and the cytoskeleton. Members of a ubiquitous multidomain family of proteins, the MAGUK proteins, are emerging as common mediators of this coupling.

Actins↗
PubMed1996

Biological response to Bard Clamshell Septal Occluders in the canine heart.

BACKGROUND: The Clamshell Septal Occluder has been used to close various congenital heart defects. The purpose of this study was to evaluate the long-term biological response to this device after placement in the canine heart. Previous in vivo studies with device placement were limited to 60 days. METHODS AND RESULTS: An atrial septal defect was created in dogs by blade septostomy followed by balloon dilation. Both old and new (redesigned) devices were placed. Angiographic follow-up was performed at 1, 3, and 6 months and 1 and 2 years after device placement with groups of dogs euthanitized at the same intervals. Gross and microscopic assessment was done on the explanted devices. The implants were covered at least 50% by neointima at 1 month and covered completely by 3 months. There was no thrombus formation. Areas of focal hemorrhage were evident at 1 month and were not present at 3 months. The fibrous capsule that covered the device became more densely organized and neovascularized by 2 years. A focal foreign body reaction at the device-tissue interface persisted for 2 years. There were no arm fractures with either the old or new devices in these dogs. CONCLUSIONS: The Bard Clamshell Septal Occluder is well tolerated in the canine heart for at least 2 years and elicits a normal healing process.

Animals↗