Biomedical subjects

A C Nicholson

Publications and source records attributed to A C Nicholson.

32 records · Page 2Linked to original sources

PubMed1995

Altered cholesterol trafficking in herpesvirus-infected arterial cells. Evidence for viral protein kinase-mediated cholesterol accumulation.

Herpesvirus infection of arterial smooth muscle cells has been shown to cause cholesteryl ester (CE) accumulation. However, the effects of human herpes simplex virus type 1 (HSV-1) infection on cholesterol binding and internalization, intracellular metabolism, and efflux have not been evaluated. In addition, the effects of viral infection on signal transduction pathways that impact upon cholesterol metabolism have not been studied. We show in studies reported herein that HSV-1 infection of arterial smooth muscle cells enhances low density lipoprotein (LDL) binding and uptake which parallels an increase in LDL receptor steady state mRNA levels and transcription of the LDL receptor gene. HSV-2 also increases CE synthesis and 3-hydroxy- 3-methylglutaryl-CoA reductase activity but concomitantly reduces CE hydrolysis and cholesterol efflux. Interestingly, this viral infection was associated with a time-dependent decrease in protein kinase A activity and an increase in viral-induced protein kinase (VPK) activity commensurate with the accumulation of esterified cholesterol. The relationship between increased VPK activity and alterations in CE accumulation in virally infected cells was explored using an HSV-1 VPK- mutant in which the portion of the HSV-1 genome encoding VPK had been deleted. Cholesteryl ester accumulation was significantly increased (> 50-fold) in HSV-1-infected cells compared to uninfected cells. However, the HSV-1 VPK- mutant had no significant effect on CE accumulation. The relationship between VPK activity and these alterations in cholesterol metabolism was further supported by the observation that staurosporine and calphostin C (protein kinase inhibitors) reduced protein kinase activity in HSV-1-infected cells. These results suggest several potential mechanisms by which alterations in kinase activities in response to HSV-1 infection of vascular cells may alter cholesterol trafficking processes that eventually lead to CE accumulation.

Arteries↗

PubMed1995

Signal transduction in atherosclerosis: second messengers and regulation of cellular cholesterol trafficking.

The data summarized in this review demonstrate that the regulation of intracellular cholesterol trafficking is mediated not only by extracellular lipoprotein concentrations and transcriptional responses to alterations in intracellular free cholesterol content. Rather, the modulation of cholesterol trafficking is also regulated by the products synthesized following activation of signal transduction pathways originating at the cell surface. Furthermore, we have identified those cell-derived factors which utilize these signal transduction pathways to elicit alterations in cholesterol trafficking, and demonstrated the importance of the generation of second messengers, most notably eicosanoids, and cyclic AMP in promoting a modulatory influence on specific pro-atherogenic effects of mitogens.

Animals↗

PubMed1995

Inhibition of cholesterol esterification in macrophages and vascular smooth muscle foam cells: evaluation of E5324, an acyl-CoA cholesterol acyltransferase inhibitor.

Cholesteryl esters (CE) comprise the principal lipid class that accumulates within macrophages and smooth muscle cells of the atherosclerotic lesion. Acyl-CoA cholesterol acyl-transferase (ACAT) is the major enzyme responsible for esterification of intracellular cholesterol. We evaluated the ability of E5324 (n-butyl-N'-[-2-[3-(5-ethyl-4-phenyl-1H-imidazol-1-yl)propoxy]-6- methyl-phenyl]urea), a novel, orally absorbable ACAT inhibitor, to inhibit esterification of fatty acids to cholesterol and CE accumulation in macrophages and in smooth muscle cells. E5324 significantly inhibited cholesterol esterification in rat aortic smooth muscle cells and in macrophages. In addition, E5324 reduced the cellular mass of CE, the significant measure of the efficacy of drugs designed to modulate cholesterol metabolism. E5324 treatment of macrophages exposed to acetylated low-density lipoprotein reduced CE mass by 97%, and treatment of lipid-loaded smooth muscle cells reduced CE mass by 29%. Although free cholesterol increased approximately twofold, this free cholesterol would presumably be accessible to the membrane for efflux in vivo (reverse cholesterol transport). These results demonstrate that E5324 can inhibit cholesterol esterification and CE mass in atherosclerotic foam cells, derived from either macrophages or arterial smooth muscle cells.

Animals↗

PubMed1995

Oxidized LDL binds to CD36 on human monocyte-derived macrophages and transfected cell lines. Evidence implicating the lipid moiety of the lipoprotein as the binding site.

Accumulating evidence strongly implicates oxidized LDL (Ox-LDL) in the pathogenesis of atherosclerosis. Several receptors have been identified that bind and internalize Ox-LDL, but their relative importance in vivo is unclear. CD36 is an 88-kD transmembrane glycoprotein expressed on monocytes/macrophages, platelets, and microvascular endothelium that has been implicated as a putative receptor for Ox-LDL. We demonstrate that an anti-CD36 monoclonal antibody inhibited 50% of the specific binding and 26% of the specific degradation of Ox-LDL by human monocyte-derived macrophages. To characterize more completely this binding we evaluated interactions between CD36 and Ox-LDL in murine NIH-3T3 cells stably transfected with human CD36 cDNA. Ox-LDL bound to CD36-transfected 3T3 cells in a saturable manner. Specific binding, internalization, and degradation of Ox-LDL were increased fourfold in CD36-transfected cell lines compared with 3T3 cells transfected with vector alone. Binding of Ox-LDL to CD36-transfected 3T3 cells was inhibited by a panel of anti-CD36 antibodies and by soluble CD36 but not by thrombospondin. Specificity of binding was demonstrated by the equivalent binding of LDL and acetylated LDL to control and CD36-transfected 3T3 cells. The epitope or epitopes on Ox-LDL recognized by CD36 are undefined. Two observations suggest that CD36 recognizes a lipid moiety or that the lipid portion of the lipoprotein is essential for apoprotein recognition. The first is that the increased binding of Ox-LDL to CD36-transfected 3T3 cells is abrogated by delipidation of the lipoprotein, and the second is that oleic acid competes for the binding of Ox-LDL to CD36-transfected 3T3 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

3T3 Cells↗

PubMed1994

Basic fibroblast growth factor-induced low density lipoprotein receptor transcription and surface expression. Signal transduction pathways mediated by the bFGF receptor tyrosine kinase.

Basic fibroblast growth factor (bFGF) has been implicated in the regulation of cell proliferation and cholesterol metabolism. In studies reported herein, we show bFGF increases low density lipoprotein (LDL) binding, uptake, and degradation in arterial smooth muscle cells in a dose-dependent manner. This increase was paralleled by an increase in LDL receptor mRNA steady state levels. To determine if bFGF activated transcription of the LDL receptor gene, we transiently transfected smooth muscle cells with a gene construct consisting of the 5'-upstream promoter region of the DNA from the human LDL receptor gene ligated to a plasmid containing the luciferase gene. We found that bFGF and a protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate, significantly induced luciferase activity driven by the LDL receptor promoter, whereas 25-hydroxycholesterol reduced the luciferase activity in bFGF-stimulated cells. These findings show that bFGF and PKC are inducing LDL receptor gene transcription. We also evaluated potential signal transduction pathways induced by bFGF to establish the mechanism(s) leading to the activation of the LDL receptor gene. Activation of the activity of FGF receptor tyrosine kinase in smooth muscle cells by ligand binding resulted in tyrosine phosphorylation of one of the FGF receptors and a 90-kDa-protein as well as increased tyrosine phosphorylation of phospholipase C-gamma. Parallel observations were made in that increased PKC and protein kinase A activities occurred with bFGF as compared with control cells. Inhibitors of receptor tyrosine kinase and other protein kinases significantly reduced transcription and surface expression of LDL receptor. Finally, several key enzymes that are central to the regulation of LDL-cholesteryl ester metabolism were also studied in bFGF-stimulated cells. An increase in acyl-CoA:cholesterol acyltransferase activity and cholesterol esterification was observed with bFGF stimulation, but there was no effect on the lysosomal or cytoplasmic cholesteryl ester hydrolase activities. Our findings suggest potential signal transduction pathways activated by bFGF which play a role in regulating transcription and surface expression of the LDL receptor.

Animals↗

PubMed1994

Validation of cutaneous stimulation interventions for pain management.

The purpose of this study was to identify and validate specific activities considered important in the implementation of selected cutaneous stimulation pain management interventions including heat and cold application, massage and Transcutaneous Electrical Nerve Stimulation (TENS). A two-round Delphi survey was completed by nurses selected for their expertise in pain management. Data were analyzed using a modification of Fehring's diagnostic content validity method. Consistently high scores were obtained by the raters for each intervention and activity, with most activities perceived as critical to the intervention. From this process, a list of activities for each cutaneous stimulation intervention evolved that are applicable to education, clinical practice and clinical nursing research.

Cryotherapy↗

PubMed1993

Cytokine regulation of low density lipoprotein receptor gene transcription in HepG2 cells.

Elevated plasma levels of cytokines have been demonstrated in inflammatory, malignant, and infectious diseases. These disease states are often associated with abnormal lipid metabolism and reductions in plasma cholesterol levels. To determine if inflammatory cytokines could influence hepatic lipid metabolism, we evaluated low density lipoprotein (LDL) receptor function and gene expression in cytokine stimulated HepG2 cells, a hepatoblastoma-derived cell line which shares many functional similarities with normal hepatocytes. Tumor necrosis factor-alpha (TNF) and interleukin-1 beta (IL-1) increased LDL binding to HepG2 cells in a dose-responsive manner. Other cytokines including macrophage-colony stimulating factor, granulocyte macrophage-colony stimulating factor, and gamma-interferon had no significant effects on LDL binding. Increased binding in response to TNF or IL-1 was paralleled by increased steady-state levels of LDL receptor mRNA. Evaluation of LDL receptor mRNA half-life revealed no significant change in mRNA stability between control and TNF- or IL-1-stimulated cells. A fusion gene construct consisting of 1563 base pairs of the 5'-flanking DNA of the human LDL receptor gene was coupled to a luciferase reporter gene, transfected into HepG2 cells, and promoter activity was assayed after TNF and IL-1 challenge to the cells. TNF and IL-1 increased promoter activity 200-400%, while treatment with LDL inhibited promoter activity by 70-85%. TNF or IL-1 co-incubation with LDL could not override transcriptional inhibition by LDL. Pretreatment with cycloheximide prevented induction of LDL receptor mRNA by TNF, but not by IL-1, suggesting stimulation of LDL receptor transcription by TNF requires protein synthesis. We propose that TNF and IL-1, acting via distinct signal transduction pathways, increase surface LDL receptors by increasing gene transcription. Our findings suggest that cytokine-induced hypocholesterolemia may be related to TNF and/or IL-1 stimulation of hepatic LDL receptor gene expression and function.

Cycloheximide↗

PubMed1993

Macrophage and foam cell release of matrix-bound growth factors. Role of plasminogen activation.

We have determined whether macrophage derived-foam cells, a prominent component of the atherosclerotic lesion, express more urokinase-type plasminogen activator (uPA) and whether their ability to generate plasmin stimulates the release of matrix-bound growth factors. Steady state levels of uPA mRNA and both membrane and intracellular uPA activities were significantly increased in foam cells. When cultured on cell-derived matrices containing bound 125I-basic fibroblast growth factor (bFGF), both macrophage and foam cells released intact 125I-bFGF into their media. The release of 125I-bFGF by either cell was significantly enhanced in the presence of plasminogen. However, foam cells, which expressed more membrane uPA, released more 125I-bFGF than control cells. The release of matrix-bound bFGF was independent of heparanase activity, since neither macrophage nor foam cells degraded 35SO4-labeled heparan sulfate proteoglycans. In addition, media derived from foam cells cultured on cell-derived matrices in the presence of plasminogen had increased levels of transforming growth factor (TGF) beta activity as compared to cells grown in the absence of plasminogen. In contrast, plasminogen had no effect on TGF-beta activity recovered in the media of foam cells grown on plastic. Moreover, when macrophage were cultured on matrices containing bound 125I-TGF-beta, the release of labeled TGF-beta was increased in the presence of plasminogen. This is the first demonstration that foam cells can release two important growth regulators, bFGF and TGF-beta, from the extracellular matrix, and provides a mechanism by which macrophage and foam cells can stimulate atherosclerotic lesion development.

Animals↗

PubMed1993

Developmentally regulated herpesvirus plaque formation in arterial smooth muscle cells.

Previous studies of age-related susceptibility to viral infection have focused largely on the effects of aging on the immune response. Little attention has been given to age-related changes in the infectivity of target cells. We show here a fourfold greater plating efficiency of herpes simplex virus type 1 (HSV-1) for cultured vascular smooth muscle cells derived from adult rats compared with cells from genetically identical pup rats. The difference in plating efficiency appeared to be due to differences in initial attachment of the virion to the cell surface. There were no differences in the rate of viral entry or the efficiency of viral replication at high multiplicities of infection and no resistant "subpopulation" of pup cells. The pup cells did not release a soluble inhibitor of infection. Infection in both cell types was inhibited similarly by basic fibroblast growth factor (bFGF). Although adult cells exhibited a more vigorous mitogenic response to bFGF than did pup cells, binding studies did not demonstrate significant differences in the binding of bFGF to the cell surface, suggesting that differential expression of high-affinity FGF receptors could not be correlated with the difference in infectivity. We speculate that differences in the distribution of heparan sulfate in the cell surface, which serves as the initial attachment site for HSV-1, may explain the observed differences in plating efficiency. Since age is a risk factor for the development of atherosclerosis, these results have potential implications for susceptibility of the vasculature to herpesviral infections as a function of the development of the vessel wall.

Age Factors↗

PubMed1992

Transforming growth factor-beta up-regulates low density lipoprotein receptor-mediated cholesterol metabolism in vascular smooth muscle cells.

The effects of transforming growth factor-beta (TGF-beta) on low density lipoprotein (LDL) receptor-mediated cholesterol metabolism were evaluated in vascular smooth muscle cells. TGF-beta significantly increased the binding, uptake, and degradation of 125I-LDL. This increase was paralleled by an increase in LDL receptor mRNA steady state levels and an increase in cholesterol esterification. The increase in LDL cholesterol metabolism was independent of proliferation. LDL receptor expression in response to TGF-beta was not affected by coincubation with an antibody against platelet-derived growth factor or by cyclooxygenase inhibitors in arterial smooth muscle cells, suggesting that TGF-beta's effect was not mediated through platelet-derived growth factor or prostaglandins, as demonstrated in other cell systems. However, coincubation with pertussis toxin abrogated the effect of TGF-beta on LDL receptor expression, suggesting that a pertussis toxin-sensitive G-protein may be involved in the signal transduction pathway. These results are discussed in terms of their potential effects on cellular cholesterol trafficking.

Animals↗

PubMed1992

Dihydropyridine calcium antagonist modulates cholesterol metabolism and eicosanoid biosynthesis in vascular cells.

Recent clinical studies have shown that calcium channel blockers can retard and possibly reduce the angiographic progression of coronary artery disease. Calcium channel blockers also inhibit dietary-induced atherosclerosis in animal models of this disease. In this study, we delineate potential cellular and molecular mechanisms by which nicardipine, a dihydropyridine calcium antagonist, may alter lipoprotein and cholesterol trafficking, affect the regulatory signal transduction pathways involved in accelerating cholesteryl ester (CE) catabolism in vascular smooth muscle cells, and modulate cell-cell interactions of vascular and inflammatory cells. We demonstrate in arterial smooth muscle cells that nicardipine increases 1) LDL binding, uptake, and degradation, 2) RNA transcript levels for the LDL receptor, 3) CE catabolic activity, 4) PGI2 release, and 5) RNA transcript levels for cyclooxygenase. Furthermore, nicardipine blocked cytokine-induced monocyte adhesion to endothelial cells and smooth muscle cells. Taken together, these findings support the hypothesis that nicardipine may function as an anti-atherosclerotic agent by promoting CE catabolism and cholesterol clearance and by reducing monocyte adhesion to the activated endothelium.

Animals↗

PubMed1989

Decreased messenger RNA translation in herpesvirus-infected arterial cells: effects on cholesteryl ester hydrolase.

Herpes simplex viruses (HSVs) contain a function that can cause the degradation of host mRNA and mediate the shutoff of host protein synthesis. Previously, we observed that HSV infection causes a 40-fold increase in cholesteryl ester (CE) accretion in arterial smooth muscle cells due, in part, to a substantial decrease in CE hydrolysis. In studies reported herein, we found that HSV infection leads to reduced immunoprecipitable lysosomal (acid) CE hydrolase (ACEH) and beta-galactosidase, another lysosomal enzyme in vascular smooth muscle cells. The HSV-induced reduction was greater with respect to ACEH than beta-galactosidase. To determine whether degradation of host cellular mRNA or inhibition of cellular translation was responsible for decreased CE hydrolysis in HSV-infected smooth muscle cells, we utilized an in vitro translation system that permitted us to compensate for any mRNA degradation during viral infection. Reduced ACEH activity was observed in the total cellular RNA translation products of HSV-infected smooth muscle cells compared to uninfected cells owing to posttranscriptional modification. We conclude that the decrease in CE hydrolysis in HSV-infected smooth muscle cells is caused primarily by decreased ACEH synthesis and activity, which can contribute to CE accretion in these vascular cells.

Animals↗

PubMed1988

Aging and arteriosclerosis. The increased proliferation of arterial smooth muscle cells isolated from old rats is associated with increased platelet-derived growth factor-like activity.

In vivo studies have suggested that the aorta from an old animal responds to injury with an exaggerated proliferation of smooth muscle cells (SMCs) compared with the response of this aorta from a young animal. In this study we compared proliferation of SMCs derived from uninjured old (less than 19 mo) and young (3-4 mo) rat aortas. Old SMCs grew more rapidly than young SMCs in the presence of medium containing competence factors (10% FCS or platelet-derived growth factor [PDGF]) as well as in their absence (2% PDS or serum-free media) as determined both by a short-term thymidine incorporation assay and by cell counts. Lysates prepared from old SMCs that had been grown in the absence of serum or PDGF stimulated proliferation of target cells more than lysates prepared from young SMCs; the effect was inversely related to cell density of the SMCs. This stimulatory effect of lysates was completely blocked by antibody to PDGF. After the growth-promoting activity of lysates was eliminated by anti-PDGF, growth-inhibiting activity was revealed. Lysates prepared from old SMCs had significantly less capacity to inhibit target cell growth. In the presence of exogenous heparin both the serum- or PDGF-stimulated proliferation and serum-free proliferation of old SMCs were decreased to the level of proliferation of young SMCs. These results suggest that the balance between growth-promoting and growth-inhibiting factors is altered in SMCs from old rats. This may contribute to the increased proliferative capacity of these cells in culture and may facilitate the development of atherosclerosis with age.

Aging↗

PubMedDate not supplied

Effects of child visitation in adult critical care units: a pilot study.

OBJECTIVE: To examine the behavioral and emotional responses of the child and of the nonhospitalized adult family member (NHAFM) to facilitated child visitation in the critical care setting. DESIGN: Quasi-experimental, posttreatment design. SETTING: An adult surgical intensive care unit at a large Midwestern teaching hospital. PARTICIPANTS: Twenty families participated in the study, 10 families in a restricted and 10 families in a facilitated visitation group. Each family unit had a child, an NHAFM, and a critically ill family member. In the control group the NHAFMs visited the patient in the customary routine, but children were restricted from visiting. After a 2-week waiting period a facilitated child visitation intervention was implemented for the experimental group. OUTCOME MEASURES: The child completed measures on anxiety as measured by the Manifest Anxiety Scale and behavioral and emotional changes as measured by the Perceived Change Scale. The NHAFM completed measures on anxiety as measured by the State-Trait Anxiety Inventory and mood as measured by the Mood Adjective Check List. Family functioning, as measured by the Feetham Family Functioning Survey, and life event changes, as measured by the Life Event Scale, were examined as extraneous variables. INTERVENTION: The Child Visitation Intervention encompassed systematic facilitation and supervision of children visiting a critically ill adult family member in a surgical intensive care unit and provision of emotional support before, during, and after visitation (the intervention protocol may be obtained from the investigators on request). RESULTS: Children in the facilitated visitation group had a greater reduction (t = 4.0, df = 18, p = 0.0004) in negative behavioral and emotional changes as measured by the Child-Perceived Change Scale when compared with children in the restricted visitation group. CONCLUSION: Facilitated child visitation may help children deal with the critical illness of an adult family member and deserves further study.

Adolescent↗