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Biomedical subjects

K A Robinson

Publications and source records attributed to K A Robinson.

At least 55 records · Page 3Linked to original sources
PubMed1999

Short- and long-term histopathologic evaluation of stenting using a self-expanding nitinol stent in pig carotid and iliac arteries.

Stenting is increasingly being used to treat carotid artery disease. However, complications including distal embolization, stent thrombosis, stent collapse from external compression, the need for high-pressure inflation with increased neointimal response, or balloon rupture during stent expansion and stent loss are all potential problems and of concern. To address each of these specific concerns, a new stent was designed, which is self-expandable, made of nitinol, with temperature-dependent superelastic properties, and with high vessel wall surface coverage. Since this device has a number of novel characteristics, we aimed to assess the short- and long-term histopathologic response in pig carotid and iliac arteries. Single stents were deployed in pig carotid and iliac arteries after overstretch balloon injury. Angiograms were performed pre- and poststenting and prior to sacrifice. Intravascular ultrasound was used before implantation to determine vessel size. Vessels were examined histologically at 1 month (n = 6) and 6 months (n = 6) for morphometric analysis, hemorrhage and thrombus, endothelialization, and inflammatory and fibrotic responses. There was a 100% angiographic success rate at implantation. In one case, it was determined histologically that a single stent was implanted in a dissection plane of a pig's left iliac artery and was occluded by organized thrombus, with the true lumen being patent. At 6-month follow-up, this was the only evidence of a single stent occlusion, with flow adjacent to the stent in the true lumen. In the other vessels, the stents showed good vessel wall-stent apposition and the lumens were patent with a concentric and thin neointima. Inflammatory cells were rare and there were no mural thrombi. Coverage of the vessel wall by endothelial-like cells was complete at 1 month. The novel nitinol EndoStent appears to have favorable biocompatibility with minimal thrombus deposition or inflammatory response, and its use is feasible for clinical application in carotid and iliac arteries.

Alloys↗
PubMed1999

Binding of GM-CSF to adherent neutrophils activates phospholipase D.

When the hematopoietic growth factor granulocyte-macrophage colony-stimulating factor was incubated with neutrophils adherent to plastic tissue culture plates or plates coated with extracellular matrix proteins, a rapid (3 min) but transient formation of phosphatidic acid was observed. This stimulation was dependent on the dose of GM-CSF, with an EC50 of 140 pM, and was further enhanced (up to 350%) with the PA phosphatase inhibitor propranolol in a dose-dependent manner. Conversely, GM-CSF was unable to trigger any PA formation in neutrophils maintained in suspension, even in the presence of soluble fibronectin. However, GM-CSF did prime the cells for enhanced PA formation in the presence of a secondary stimulus (fMet-Leu-Phe or PAF). GM-CSF also caused a time-dependent stimulation of diacylglycerol formation in adherent, but not suspended, cells and elicited a time-dependent stimulation of phosphatidylethanol formation, with a concomitant decrease in the formation of PA only at early (< 7 min) times. These observations were consistent with a rapid activation of the enzyme phospholipase D in adherent cells stimulated with GM-CSF. Additional data indicated that the source of DAG was PLD coexisting with PLC, especially at later times ( > 7 min) of stimulation with GM-CSF. Finally, the formation of PA and PEt, and to a minor extent, DAG, were inhibited by the protein tyrosine kinase inhibitor erbstatin in conditions in which tyrosine phosphorylation occurred. Taken together the data indicate that GM-CSF rapidly activates PLD in adherent cells, which is responsible for the generation of PA. Thus, PLD activation is an early event in neutrophil signal transduction following exposure of adherent cells to GM-CSF.

Adrenergic beta-Antagonists↗
PubMed1999

p38 kinase is activated in the Alzheimer's disease brain.

The p38 mitogen-activated protein kinase is a stress-activated enzyme responsible for transducing inflammatory signals and initiating apoptosis. In the Alzheimer's disease (AD) brain, increased levels of phosphorylated (active) p38 were detected relative to age-matched normal brain. Intense phospho-p38 immunoreactivity was associated with neuritic plaques, neuropil threads, and neurofibrillary tangle-bearing neurons. The antibody against phosphorylated p38 recognized many of the same structures as an antibody against aberrantly phosphorylated, paired helical filament (PHF) tau, although PHF-positive tau did not cross-react with the phospho-p38 antibody. These findings suggest a neuroinflammatory mechanism in the AD brain, in which aberrant protein phosphorylation affects signal transduction elements, including the p38 kinase cascade, as well as cytoskeletal components.

Aged↗
PubMed1999

Decreased hexosamine biosynthesis in GH-deficient dwarf rat muscle. reversal with GH, but not IGF-I, therapy.

Enhanced glucose flux via the hexosamine biosynthesis pathway (HNSP) has been implicated in insulin resistance. We measured L-glutamine:D-fructose-6-phosphate amidotransferase activity (GFAT, a rate-limiting enzyme) and concentrations of UDP-N-acetyl hexosamines (UDP-HexNAc, major products of HNSP) in muscle and liver of growth hormone (GH)-deficient male dwarf (dw) rats. All parameters measured, except body weight, were similar in 5-wk-old control and dw rats. Muscle GFAT activity declined progressively with age in controls and dw rats but was consistently 30-60% lower in 8- to 14-wk-old dw rats vs. age-matched controls; UDP-HexNAc concentrations in muscle were concomitantly 30% lower in dw rats vs. controls (P < 0.01). Concentrations of UDP-hexoses, GDP-mannose, and UDP in muscle were similar in control and dw rats. Muscle HNSP activity was similarly diminished in fed and fasted dw rats. In liver, only a small difference in GFAT activity was evident between controls and dw rats, and no differences in UDP-HexNAc concentrations were observed. Treatment with recombinant human GH (rhGH) for 5 days restored UDP-HexNAc to control levels in dw muscles (P < 0.01) and partially restored GFAT activity. Insulin-like growth factor I treatment was ineffective. We conclude that GH participates in HNSP regulation in muscle.

Animals↗
PubMed1999

Disparate effects of three types of extracellular acidosis on left ventricular function.

Effects of acidosis on muscle contractile function have been studied extensively. However, the relative effects of different types of extracellular acidosis on left ventricular (LV) contractile function, especially the temporal features of contraction, have not been investigated in a single model. We constituted perfusion buffers of identical ionic composition, including Ca2+ concentration ([Ca2+]), to mimic physiological control condition (pH 7.40) and three types of acidosis with pH of 7.03: inorganic (IA), respiratory (RA), and lactic (LA). Isolated rabbit hearts (n = 9) were perfused with acidotic buffers chosen at random, each preceded by the control buffer. Under steady-state conditions, instantaneous LV pressure (Pv) and volume (Vv) were recorded for a range of Vv. The results were as follows. 1) LV passive (end-diastolic) elastance increased with IA and RA. However, this increase may not be a direct effect of acidosis; it can be explained on the basis of myocardial turgor. 2) Although LV inotropic state (peak active Pv and elastance) was depressed by all three acidotic buffers, the magnitude of inotropic depression was significantly less for LA. 3) Temporal features of Pv were altered differently. Whereas IA and RA reduced time to peak Pv (tmax) and hastened isovolumic relaxation at a common level of LV wall stress, LA significantly increased tmax and retarded relaxation. These results and a model-based interpretation suggest that cooperative feedback (i.e., force-activation interaction) plays an important role in acidosis-induced changes in LV contractile function. Furthermore, it is proposed that LA-induced responses comprise two components, one due to intracellular acidosis and the other due to pH-independent effects of lactate ions.

Acidosis↗
PubMed1999

Efficacy of Haemophilus influenzae type b conjugate vaccines and persistence of disease in disadvantaged populations. The Haemophilus Influenzae Study Group.

OBJECTIVES: The purpose of this study was to evaluate the effectiveness of Haemophilus influenzae type b (Hib) conjugate vaccines among children aged 2 to 18 months and to determine risk factors for invasive Hib disease during a period of declining incidence (1991-1994). METHODS: A prospective population-based case-control study was conducted in a multistate US population of 15.5 million. A laboratory-based active surveillance system was used for case detection. RESULTS: In a multivariate analysis, having a single-parent mother (odds ratio [OR] = 4.3, 95% confidence interval [CI] = 1.2, 14.8) and household crowding (OR = 3.5, 95% CI = 1.03, 11.7) were risk factors for Hib disease independent of vaccination status. After adjustment for these risk factors, the protective efficacy of 2 or more Hib vaccine doses was 86% (95% CI = 16%, 98%). Among undervaccinated subjects, living with a smoker (P = .02) and several indicators of lower socioeconomic status were risk factors for Hib disease. CONCLUSIONS: Hib disease still occurs at low levels in the United States, predominantly in socioeconomically disadvantaged populations. Low immunization coverage may facilitate continuing transmission of Hib. Special efforts to achieve complete and timely immunization in disadvantaged populations are needed.

Case-Control Studies↗
PubMed1998

Interaction of alpha-phenyl-N-tert-butyl nitrone and alternative electron acceptors with complex I indicates a substrate reduction site upstream from the rotenone binding site.

Mitochondrial complexes I, II, and III were studied in isolated brain mitochondrial preparations with the goal of determining their relative abilities to reduce O2 to hydrogen peroxide (H2O2) or to reduce the alternative electron acceptors nitroblue tetrazolium (NBT) and diphenyliodonium (DPI). Complex I and II stimulation caused H2O2 formation and reduced NBT and DPI as indicated by dichlorodihydrofluorescein oxidation, nitroformazan precipitation, and DPI-mediated enzyme inactivation. The O2 consumption rate was more rapid under complex II (succinate) stimulation than under complex I (NADH) stimulation. In contrast, H2O2 generation and NBT and DPI reduction kinetics were favored by NADH addition but were virtually unobservable during succinate-linked respiration. NADH oxidation was strongly suppressed by rotenone, but NADH-coupled H2O2 flux was accelerated by rotenone. Alpha-phenyl-N-tert-butyl nitrone (PBN), a compound documented to inhibit oxidative stress in models of stroke, sepsis, and parkinsonism, partially inhibited complex I-stimulated H2O2 flux and NBT reduction and also protected complex I from DPI-mediated inactivation while trapping the phenyl radical product of DPI reduction. The results suggest that complex I may be the principal source of brain mitochondrial H2O2 synthesis, possessing an "electron leak" site upstream from the rotenone binding site (i.e., on the NADH side of the enzyme). The inhibition of H2O2 production by PBN suggests a novel explanation for the broad-spectrum antioxidant and antiinflammatory activity of this nitrone spin trap.

Animals↗
PubMed1998

Human recombinant alpha 2-HS glycoprotein is produced in insect cells as a full length inhibitor of the insulin receptor tyrosine kinase.

Human Alpha 2-HS glycoprotein (AHSG), a glycoprotein synthesized by hepatocytes, was expressed in insect cells using the recombinant baculovirus system. The protein was purified from the cell supernatant, and appeared as a single band at about 52 kDa. Western blot using a specific antibody to the B-chain of AHSG indicated that the connecting peptide was present in the protein. When incubated with solubilized insulin receptors, recombinant AHSG inhibited the tyrosine kinase activity of the receptors in a dose-dependent fashion at concentrations in the range of those of the circulating protein. AHSG did not interfere with the binding of insulin to its receptor. These results indicate that human AHSG represents a natural inhibitor of the insulin receptor tyrosine kinase, is active as a single-chain protein and possesses a biological role similar to that of its homologue in rats, pp63, described by Auberger et al. (1).

Baculoviridae↗
PubMed1998

Phosphorylcholine-coated metallic stents in rabbit iliac and porcine coronary arteries.

The arterial wall reaction to phosphorylcholine-coated metal stents was examined in rabbits and pigs. Compared to non-coated stents, no significant difference was found by angiography and histology. We conclude that although phosphorylcholine-coating does not provoke arterial neointima formation or decrease luminal diameter compared to stainless steel stents, the coating does not seem to reduce restenosis.

Angiography↗
PubMed1997

Effects of overexpression of glutamine:fructose-6-phosphate amidotransferase (GFAT) and glucosamine treatment on translocation of GLUT4 in rat adipose cells.

Insulin resistance is associated with diabetes. Hyperglycemia per se causes insulin resistance as well as increased flux of glucose through the hexosamine biosynthetic pathway. The rate-limiting enzyme for entry of glucose into this pathway is glutamine:fructose-6-phosphate amidotransferase (GFAT). To directly evaluate the role of GFAT in modulating insulin-stimulated glucose transport, we co-transfected primary cultures of rat adipose cells with expression vectors for human GFAT as well as an epitope-tagged GLUT4 and examined the effect of overexpressed GFAT on insulin-stimulated translocation of GLUT4. When we measured cell surface tagged GLUT4 in response to insulin, cells overexpressing GFAT and tagged GLUT4 had an insulin-dose response curve that was similar to that of control cells expressing only tagged GLUT4. As an alternative means of increasing flux through the hexosamine biosynthetic pathway, we incubated adipose cells with glucosamine (a substrate of the pathway downstream from GFAT) and insulin. Interestingly, for short incubation times (4 h) we observed a decrease in both basal and insulin-stimulated glucose transport without a detectable effect on insulin-stimulated translocation of GLUT4. However, for longer incubation times (16 h), we observed a significant decrease in the amount of GLUT4 in the plasma membrane. Our data suggest that products of the hexosamine biosynthetic pathway may cause insulin resistance, in part, by acutely decreasing intrinsic activity of GLUT4 as well as chronically altering the amount of GLUT4 at the cell surface.

Adipocytes↗
PubMed1997

Effect of intravascular irradiation on cell proliferation, apoptosis, and vascular remodeling after balloon overstretch injury of porcine coronary arteries.

BACKGROUND: Ionizing radiation has been shown to reduce vascular lesion formation after balloon overstretch injury of pig coronary arteries. The present series of experiments examines the mechanism by which this occurs. METHODS AND RESULTS: Balloon injury was performed on porcine coronary arteries, followed immediately by ionizing radiation using either a source train of 90Sr/Y or 192Ir seeds designed to deliver 14 or 28 Gy at a depth of 2 mm from the source. The animals were killed 3, 7, or 14 days after injury. Bromodeoxyuridine was administered 24 hours before euthanasia to label proliferating cells. Cell proliferation was significantly reduced on day 3 in the adventitia and media of the irradiated vessels compared with controls. Two weeks after injury, there were fewer alpha-actin-positive myofibroblasts in the adventitia of the irradiated vessels than in nonirradiated controls, and morphometric analysis indicated that the vessel perimeter of the irradiated vessels was significantly larger than in controls. Together, these results suggest a positive effect of intravascular irradiation on vascular remodeling. Apoptosis was estimated by terminal transferase dUTP-biotin nick-end labeling (TUNEL) 3 and 7 days after injury. TUNEL-labeled cells were found primarily in the adventitia at the medial tear, but no differences were detected between irradiated and control vessels. CONCLUSIONS: These studies suggest that intracoronary radiation primarily inhibits the first wave of cell proliferation in the vessel wall and demonstrates a favorable effect on late remodeling by preventing adventitial fibrosis at the injury site.

Actins↗
PubMed1997

Intracoronary radiation decreases the second phase of intimal hyperplasia in a repeat balloon angioplasty model of restenosis.

PURPOSE: Repeat balloon angioplasty is likely to induce intimal proliferation, which is associated with a higher restenosis rate. This study examined the effect of intracoronary ionizing radiation on restenotic lesions using repeat balloon injury in a normolipemic swine. METHODS AND MATERIALS: Eight domestic normolipemic pigs underwent overstretch balloon angioplasty with a 3.5 mm balloon in the LAD and LCX, followed by repeat balloon injury at the same sites 4 weeks after the initial injury. At that time a high activity 192Iridium source was introduced immediately after the angioplasty by random assignment to deliver 14 Gy at 2 mm in eight of the injured coronary arteries (LAD and LCX). One month later the animals were killed and the coronary arteries pressure perfusion fixed. Serial sections were stained with H&E and VVG, then evaluated by histopathologic and morphometric techniques. Maximal intimal thickness (MIT), intimal area (IA), and intimal area corrected for the extent of injury (IA/FL) were measured in the irradiated and control arteries and were compared to control arteries with single injuries from previous studies. RESULTS: Repeat balloon injury induced significant additional medial damage, which was associated with marked intimal hyperplasia in a concentric pattern. Intracoronary irradiation significantly decreased the total of neointima area formation (IA 93 + 0.35 mm2 compared to control 1.38 + 0.33 mm2 p < 0.01) and the MIT was also significantly reduced in the irradiated vessels (0.57 + 0.18 mm vs. 0.71 + 0.08 mm, p = 0.05). CONCLUSIONS: Intracoronary irradiation immediately after the second balloon dilatation inhibits the intimal hyperplasia due to that injury. However, there was no effect on the existing neointima from the initial injury.

Angioplasty, Balloon↗
PubMed1997

Mechanism of glibenclamide inhibition of cystic fibrosis transmembrane conductance regulator Cl- channels expressed in a murine cell line.

1. The sulphonylurea drug glibenclamide is a widely used inhibitor of the cystic fibrosis transmembrane conductance regulator (CFTR). To investigate how glibenclamide inhibits CFTR, we studied CFTR Cl- channels using excised inside-out membrane patches from cells expressing wild-type human CFTR. 2. Addition of glibenclamide (10-100 microM) to the intracellular solution caused a concentration-dependent decrease in the open time of CFTR Cl- channels, but closed times did not change. This suggests that glibenclamide is an open-channel blocker of CFTR. 3. Glibenclamide is a weak organic acid. Acidification of the intracellular solution relieved glibenclamide inhibition of CFTR, suggesting that the anionic form of glibenclamide inhibits CFTR. 4. To begin to identify the glibenclamide binding site in CFTR, we investigated whether glibenclamide competes with either MgATP or Cl- ions for a common binding site. Glibenclamide inhibition of CFTR was unaffected by nucleotide-dependent stimulation of CFTR, suggesting that glibenclamide and intracellular MgATP interact with CFTR at distinct sites. 5. Glibenclamide inhibition of CFTR was voltage dependent and enhanced when the external Cl- concentration was decreased. The data suggest that glibenclamide and Cl- ions may compete for a common binding site located within a large intracellular vestibule that is part of the CFTR pore.

Animals↗
PubMed1997

Selective degeneration fo Purkinje cells with Lewy body-like inclusions in aged NFHLACZ transgenic mice.

Transgenic (NFHLacZ) mice expressing a fusion protein composed of a truncated high-molecular-weight mouse neurofilament (NF) protein (NFH) fused to beta-galactosidase (LacZ) develop inclusions in neurons throughout the CNS. These inclusions persist from birth to advanced age and contain massive filamentous aggregates including all three endogenous NF proteins and the NFHLacZ fusion protein. Further, the levels of endogenous NF proteins are selectively reduced in NFHLacZ mice. Because these inclusions resemble NF-rich Lewy bodies (LBs) in Parkinson's disease and LB dementia, we asked whether these lesions compromised the viability of affected neurons during aging. We studied hippocampal CA1 neurons, nearly all of which harbored inclusions (type I) devoid of cellular organelles, and cerebellar Purkinje cells, nearly all of which accumulated inclusions (type II) containing numerous entrapped organelles. Purkinje cells with type II inclusions began to degenerate in the NFHLacZ mice at approximately 1 year of age, and most were eliminated by 18 months of age. In contrast, there was no significant loss of type I inclusion-bearing CA1 neurons with age. These data suggest that the sequestration of cellular organelles in type II inclusions may isolate and impair the function of these organelles, thereby rendering Purkinje cells selectively vulnerable to degeneration with age as in neurodegenerative diseases of the elderly characterized by accumulation of LBs.

Aging↗
PubMed1997

Endoluminal local delivery of PCNA/cdc2 antisense oligonucleotides by porous balloon catheter does not affect neointima formation or vessel size in the pig coronary artery model of postangioplasty restenosis.

Localized delivery of antisense oligonucleotides directed against cell cycle regulatory proteins has been proposed as a means to prevent restenosis after angioplasty. To test whether single endoluminal delivery of a combination of proliferating cell nuclear antigen (PCNA) and cell-division cycle 2 kinase (cdc2) antisense might affect restenosis, we delivered 2 ml of lipid-complexed PCNA/cdc2 antisense oligomers (1.35 mg) to the coronary arteries of pigs after balloon overstretch angioplasty (AS group) and performed planimetric histomorphometry on arterial sections of the tissue, harvested at 4 wk. Compared with controls receiving 3'-5' reversed sequence oligomers (REV group), there were no differences in absolute intimal area (AS 1.36 +/- 0.08 mm2, REV 1.23 +/- 0.10 mm2, P = NS), intimal area normalized to extent of injury (AS 0.67 +/- 0.03, REV 0.77 +/- 0.10, P = NS), or vessel perimeter (AS 7.72 +/- 0.19 mm, REV 7.36 +/- 0.22 mm, P = NS). We conclude that single endoluminal delivery of antisense against key cell cycle regulatory proteins does not affect neointima formation or vessel size in this model of restenosis.

Angioplasty, Balloon, Coronary↗
PubMed1997

Pharmacokinetics and tissue localization of antisense oligonucleotides in balloon-injured pig coronary arteries after local delivery with an iontophoretic balloon catheter.

When delivered locally to the arterial wall by passive fluid transfer systems such as perforated balloons, water-soluble compounds in aqueous solution are not readily taken up by tissue, show low levels of cellular localization, and are quickly lost by wash-out. One approach to improve delivery is addition of an "active" component to the catheter system to change the nature of the drug-to-tissue interaction. Using an iontophoretic balloon catheter to deliver antisense oligonucleotide (ODN) to pig coronary arteries after balloon angioplasty, we determined the quantity and localization of ODN in the tissue. By radiolabeling, 7.3 +/- 2.4 micrograms ODN was present at 30 min, 1.5 +/- 0.6 at 2 h, 0.52 +/- 0.35 at 24 h, and 0.26 +/- 0.11 at 7 d. By fluorescent labeling, circumferential medial uptake and adventitial delivery at the site of medial injury was observed, with primarily cellular localization. The iontophoretic catheter thus appears to be a useful device for ODN delivery to arterial tissue.

Angioplasty, Balloon, Coronary↗
PubMed1997

Effects of exercise and feeding on the hexosamine biosynthetic pathway in rat skeletal muscle.

Products of the hexosamine biosynthesis pathway (HSNP) have been implicated in glucose-induced insulin resistance. We measured the major products of HSNP, UDP-N-acetyl hexosamines (UDP-HexNAc), and the activity of L-glutamine: D-fructose-6-phosphate amidotransferase (GFAT, rate-limiting enzyme) in rat hindlimb muscles immediately after exercise and 1, 3, and 16 h postexercise (swimming) in fed and fasted rats and sedentary controls. Muscle glycogen decreased by 50-75% postexercise. In sedentary rats, muscle GFAT activity decreased by approximately 30% (P < 0.002) after an 18-h fast. GFAT activity was not affected by exercise under any condition. Muscle UDP-HexNAc increased approximately 30% postexercise (P < 0.01) in ad libitum-fed but not in fasted rats. UDP-HexNAc remained elevated (approximately 30%, P < 0.002) for 16 h if animals were fed postexercise. Concentrations of UDP-hexoses, GDP-mannose, and UDP were unchanged postexercise. Conclusions are that muscle GFAT activity is regulated by the nutritional state but not by acute exercise. Glucose flux via HNSP may be increased postexercise in muscles of ad libitum-fed rats. Increased HSNP products may serve as negative feedback regulators to limit excessive muscle glycogen deposition postexercise.

Animal Feed↗