PubMed Health⌕ Search

Biomedical subjects

D Hicks

Publications and source records attributed to D Hicks.

At least 73 records · Page 4Linked to original sources
PubMed1996

Differential modulation of basic fibroblast and epidermal growth factor receptor activation by ganglioside GM3 in cultured retinal Müller glia.

Polypeptide growth factors and membrane-bound gangliosides are involved in cell signaling, including that observed in cells of neural origin. To analyze possible interactions between these two systems, we investigated the modulation of short- and long-term responses to basic fibroblast and epidermal growth factor (bFGF and EGF, respectively) in cultured retinal Müller glial cells following experimental modification of their ganglioside composition. These glial cells readily incorporated exogenously administered GM3 ganglioside, which was not substantially metabolized within 24 h. Such treatments significantly inhibited bFGF-induced DNA replication and cell migration, while having much less effect on analogous EGF-mediated behaviors. To explore GM3/growth factor interactions further, different aspects of glial metabolism in response to bFGF or EGF stimulation were examined: membrane fluidity, growth factor binding, global and individual changes in growth factor-induced phosphotyrosine levels, and growth factor-induced activation of mitogen-activated protein kinase. GM3 reduced the intensity of immunocytochemical labeling of phosphotyrosine-containing proteins within bFGF-stimulated cells and down-regulated FGF receptor activation and tyrosine phosphorylation of its cellular substrates, whereas similar parameters in EGF-stimulated cells were much less affected. Hence the data reveal a complex relationship in normal neural cells between polypeptide growth factors and membrane-bound gangliosides, which may participate in retinal cellular physiology in vivo.

Animals↗
PubMed1996

Ganglioside effects on basic fibroblast and epidermal growth factor receptors in retinal glial cells.

Gangliosides have long been implicated in cell growth regulation and play an important role as modulators in protein phosphorylation. In order to better understand how glycosphingolipids and growth factors interact, we examined the modulation of epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) effects on retinal Müller glial cells (RMG), following modification of their GG composition. Treatment of MG cells with GG (GM1, GT1b) and asialoGM1 resulted in modifications of several aspects of cellular responses to EGF- and FGF-receptor (R) activation: mitogenesis, cell migration, tyrosine phosphorylation of the EGF-R and FGF-R and even their cellular substrates were particularly influenced by GG. Indeed GG caused modifications of EGF-R and FGF-R autophosphorylation kinetics. GG long term effects (mitogenesis and migration) correlate with short term effects (tyrosine phosphorylation) and differences in receptor tyrosine kinase signalling could explain the specificity in growth factor responses.

Animals↗
PubMed1996

Pharmacokinetics of the aldose reductase inhibitor tolrestat: studies in healthy young and elderly male and female subjects and in subjects with diabetes.

Tolrestat is an aldose reductase inhibitor undergoing clinical trials in diabetic subjects that may reduce the severity of chronic tissue damage associated with hyperglycemia. These studies were conducted to evaluate the pharmacokinetics of tolrestat in healthy young and elderly male and female subjects and in young and elderly subjects with diabetes. The drug was administered in a multiple-dose regimen, and steady-state parameters were obtained. There were no important gender-related differences, but mean values for apparent oral clearance, renal clearance, and corresponding unbound parameters were significantly lower for the elderly healthy subjects than for the young healthy subjects. The drug is highly bound to plasma proteins, and the unbound fraction (0.75%) did not differ among the subjects. The results from young and elderly diabetic subjects suggest that diabetes per se has no influence on tolrestat disposition but that there is an age-related reduction in apparent oral clearance (30 versus 18 ml/hr/kg) and a corresponding increase in the minimum steady-state plasma concentration (1.2 versus 1.9 micrograms/ml). These data indicate a possible need to reduce the dose of tolrestat in elderly subjects, assuming the same concentration-response relationship.

Administration, Oral↗
PubMed1996

Characterization and possible roles of fibroblast growth factors in retinal photoreceptor cells.

There is increasing evidence that soluble polypeptide growth factors such as those belonging to the fibroblast growth factor (FGF) family play important roles in many aspects of photoreceptor cell biology, including differentiation, continued survival and pathology. At least two members of this family, acidic FGF and basic FGF, are synthesized by, bind to and have profound effects upon these highly specialized retinal first-order neurons. The present review presents an overview of the evidence accumulated to date and will try to suggest future directions for research.

Animals↗
PubMed1996

Simplified ganglioside composition of photoreceptors compared to other retinal neurons.

PURPOSE: The quantitative and qualitative ganglioside composition of retinal photoreceptor cells is unknown. The aim of this study was to analyze the lipid, especially ganglioside, make-up of photoreceptors compared to other retinal cells. METHODS: Retinas from adult normal rats were mechanically separated into outer (photoreceptors) and inner (other retinal neurons and glia) halves be planar vibratome sectioning. Total lipids were extracted, and each fraction (neural, phospholipids, and glycosphingolipids) was eluted sequentially by column chromatography and quantitated through high-performance thin layer chromatogram analysis. Similar analyses were performed on entire retinas from adult normal rats, adult dystrophic rats lacking photoreceptors (RCS-rdy-p+ strain), and isolated photoreceptor outer segments. RESULTS: Whereas phospholipids were distributed equally between the two halves, inner retina contained significantly more cholesterol (68% total) and gangliosides (74% total) than outer retina on a unit protein basis. The distribution on a percent molar basis of specific gangliosides also was significantly different between the two halves: Outer retina was dominated by GD3 (45% total ganglioside) and contained only trace amounts (<4%) of complex species (GT1b and GQ1b); inner retina was more typical of mature brain tissue exhibiting substantial amounts (approximately 25%) of more complex species. These data were supported by lipid compositional analyses of mutant photoreceptor-less retina. However, isolated outer segments resembled whole retina in containing higher levels of complex gangliosides. CONCLUSIONS: These data indicate that, compared to other central nervous system-derived neurons, photoreceptor cell body membranes exhibit a highly unusual simplified ganglioside composition. Such an unusual neuronal lipid composition may reflect structural adaptations to their specialized function.

Animals↗
PubMed1996

Monosialoganglioside GM1 reduces ischemia--reperfusion-induced injury in the rat retina.

PURPOSE: Gangliosides are normal components of cell membranes, contribute to structural rigidity and membrane function, and have been shown to protect against various insults to the brain. This study evaluates the effect of exogenously administered monosialoganglioside GM1 on retinal damage induced by transient retinal ischemia and reperfusion. METHODS: Retinal ischemia was induced unilaterally in Long Evans rats by increasing intraocular pressure to 160 mm Hg for 60 minutes. GM1 (30 mg/kg, intraperitoneally) or buffer controls were administered at 48 hours, and 15 minutes before ischemia, and survival time after ischemia was either 8 or 15 days. The degree of retinal damage was assessed by histopathologic study according to Hughes' quantification of ischemic damage. RESULTS: Retinal ischemia led to significant reductions in thickness and cell number, principally in the inner retinal layers (30% to 80%), and to a lesser extent in the outer retinal layers (18% to 42%). Pretreatment with intraperitoneally injected monosialoganglioside GM1 conferred significant protection against retinal ischemic damage either 8 or 15 days after ischemic survival time. After 8 days reperfusion, the ischemic-induced loss in overall retinal thickness was reduced by 70%, and those of the inner nuclear and plexiform layers were reduced by 77% and 44%, respectively. Ischemic-induced ganglion cell, inner nuclear, and outer nuclear layer cell density losses were reduced by 45%, 40%, and 57%, respectively. After 15 days of reperfusion, approximately the same statistically significant differences could be observed in comparison with the 15-day ischemic--reperfusion group. CONCLUSIONS: Monosialoganglioside GM1 protects the rat retina from pressure-induced ischemic injury when administered intraperitoneally 2 days before insult. This protection afforded by GM1 can be observed even after 8 days or 15 days of reperfusion.

Animals↗
PubMed1996

[Retinal grafts: biological problems and clinical stakes].

Retinal transplantation, formerly perceived as unrealistic, has become over the past decade a major clinical and biological undertaking in several laboratories and eye clinics. We describe the insights gained through the pioneering experimental works of Del Cerro et al, Turner et al, Gouras et al, Aramant et al, Lund et al e.g. the survival of transplants, the lack of immune response to photoreceptors, their integration and expression of neuronal markers, but also the dysplastic arrangement into rosettes and the lack of a definitive proof for functionality. Our laboratory has undertaken to establish the trophic and synaptic functions of sheets of photoreceptors transplanted, as described by Silverman et al, in the subretinal space of mutant rd mice carrying a retinal degeneration similar to human retinitis pigmentosa. Clinical applications to this condition as well as in cases of end-stage age related macular degeneration are discussed.

Animals↗
PubMed1996

Survival and regeneration of adult human and other mammalian photoreceptors in culture.

PURPOSE: Fully mature neurons of central nervous system origin generally are considered unable to survive for extended periods of time in simple culture conditions. The authors report that adult and aged human, porcine, and rodent retinal neurons, including rod and cone photoreceptors, constitute an exception to this idea. METHODS: Cells were dissociated from human postmortem retinas, adult mammalian retinas, and selected brain regions and were seeded into tissue culture plates and left to develop as monolayer cultures for up to 2 months. A battery of antibody markers was used to identify the nature and morphology of the cells in vitro. RESULTS: Photoreceptor cell survival of rods and cones was observed routinely when the delay between the time of death until culture preparation was 50 hours or less, compatible with current eye bank practice. Two-week-old cultures were formed of rod photoreceptors, representing approximately 50% of neuronal cell types; cone photoreceptors, representing 5% to 30% of neuronal cell types; other retinal neurons (especially amacrine cells approximately 20%); and retinal glial cells, present in variable numbers. Glial cells were essential for long-term photoreceptor survival and neurite outgrowth. Adult mammalian brain neurons isolated under the same conditions did not survive. CONCLUSIONS: Fully adult human and other mammalian retinal neurons, including photoreceptors, exhibit remarkable plasticity in vitro, and such monolayer models may have applications in physiological, pharmacologic, and toxicologic studies of human and other mammalian retina.

Aged↗
PubMed1995

Rapamycin: distribution, pharmacokinetics, and therapeutic range investigations.

Rapamycin (RAPA) is a potent immunosuppressive drug that is presently undergoing clinical trials. The most of the drug is sequestered in erythrocytes resulting in whole blood concentrations being considerably higher than plasma concentrations. The drug is metabolized by the same P450 3A enzyme that is involved in the metabolism of cyclosporine and tacrolimus. Structural elucidation of RAPA metabolites is required. The drug has a relatively long half-life in both humans and animals with 24-h trough concentrations being within the analytic range of high-performance liquid chromatography (HPLC) when immunosuppressive doses are administered. For RAPA, a proportionality is exhibited between trough concentrations and dose. In animal transplant models, trough concentrations of the drug appear to be related to immunosuppressive efficacy and drug-related side effects. The studies described here should provide the basis for establishment of therapeutic monitoring protocols for the drug.

Animals↗
PubMed1994

Survival and regeneration of adult human photoreceptors in vitro.

Adult human retina from enucleated ocular tissue was enzymatically dissociated and plated into plastic dishes for cell culture in serum-supplemented medium. Within a few days following seeding, islands of glial-like cells with rounded neurons growing on top of them were visible. Immunocytochemical labelling of these cultures revealed that virtually all the surviving neurons (> 98%) were rod photoreceptors, and that they extended long neurites across the glial cell surface. Hence, adult human photoreceptors retain a remarkable capacity for survival and regrowth, and such preparations may be of value for physiopathological and retinal grafting studies.

Antibodies↗
PubMed1994

Human retinal pigmented epithelial cells produce nitric oxide in response to cytokines.

The present study demonstrates that human retinal pigmented epithelial cells produce nitric oxide (NO) upon co-treatment with interferon gamma (IFN gamma) and interleukin-1 beta (IL-1 beta). The biosynthesis of NO, which was measured by the accumulation of the stable end-product nitrite, requires an induction period of approximately 12 hours and continues for at least three days. The synthesis was abolished by the stereoselective inhibitors of NO synthase (NOS), NG-monomethyl-L-arginine, N omega-nitro-L-arginine and N omega-nitro-L-arginine methyl ester and by cycloheximide. Transforming growth factor beta suppressed cytokine-induced NOS. The results indicate that cytokines such as IFN gamma and IL-1 beta are capable of inducing NOS, while TGF beta prevents this induction, in subcultured pigmented epithelial cells from the human retina.

Amino Acid Oxidoreductases↗
PubMed1994

Superoxide inhibits proliferation and phagocytic internalization of photoreceptor outer segments by bovine retinal pigment epithelium in vitro.

Experiments were performed to investigate the effect of free radical damage on two aspects of retinal pigmented epithelium (RPE) metabolism, namely, proliferation and phagocytosis. Bovine RPE cells were maintained in monolayer cultures, either as passaged (for proliferation and lysosomal activity assays) or primary cultures (for phagocytosis measurements). Free radicals (superoxide anions) were generated by a xanthine oxidase (XO)-hypoxanthine (HX) reaction. Total phagocytosis (binding plus ingestion of rod outer segments (ROS)) was quantitated by radioimmunoassay using a specific anti-opsin antibody and iodinated secondary antibody. In some cases, agents with known or possible protective influences against oxidative damage, i.e., superoxide dismutase (SOD), vitamin E, and basic fibroblast growth factor (bFGF), were tested for their activity in this model system. RPE cell proliferation was inhibited in a HX-XO dose-dependent manner, in the absence of cell toxicity. Modifications of cell morphology were also noticed. Either simultaneous exposure of RPE cells to ROS membranes and HX-XO or pretreatment of ROS membranes with HX-XO prior to their addition to RPE monolayers led to a statistically significant 20-30% decrease in phagocytosis relative to control values. This decrease was essentially observed in the binding phase of phagocytosis, indicating damage to ROS surface molecules as the primary event. Addition of SOD or vitamin E prevented this loss of phagocytic activity, whereas bFGF had no effect. Superoxide radicals did not, however, affect phagocytosis when RPE cells were exposed to them alone, prior to incubation with ROS; nor did they alter a later stage in the phagocytic process, acid phosphatase activity. This tissue culture model represents a convenient system for analyzing free radical damage in different aspects of RPE-photoreceptor behavior and may be useful in studying this phenomenon in several retinal disorders.

Acid Phosphatase↗
PubMed1994

Differential tumor necrosis factor expression by resident retinal cells from experimental uveitis-susceptible and -resistant rat strains.

Experimental autoimmune uveoretinitis (EAU) and endotoxin-induced uveitis (EIU), models for human ocular immunopathological syndromes, result in ocular inflammation in susceptible, but not in resistant rat strains. Moreover rapid photoreceptor degeneration occurs in susceptible rats developing EAU. In order to see whether differences in local ocular immune regulation may account for changes in resistance or susceptibility, we have examined the in vitro production of the cytotoxic cytokine tumor necrosis factor (TNF) by two resident ocular cell types, retinal Müller glia (RMG) and retinal pigmented epithelium (RPE). These cells were isolated and cultured in vitro from Lewis (Lew) (highly susceptible), Lew x Brown-Norway (BN) F1 hybrid (susceptible), BN and Long-Evans (LE) (resistant or poorly susceptible) rats. Constitutive production of the cytokine TNF, or its liberation in response to either interferon-gamma (IFN-gamma) or lipopolysaccharide (LPS) alone, was very low in RMG and RPE cells, irrespective of the strain. It was strongly induced by combined treatment with IFN-gamma and LPS in Lew RMG and RPE cells (mean values of 140 and 150 pg/10(5) cells, respectively) and in Lew x BN F1 RMG and RPE cells (mean values of 125 and 190 pg/10(5) cells, respectively), much less so from BN RMG and RPE cells (30 and 20 pg/10(5) cells, respectively) and remained undetectable in LE RMG and RPE cells. Hence susceptibility to EAU and EIU in vivo is correlated with the extent of TNF production by these two cell types under in vitro conditions, which may play a key role in initiating or perpetuating local immune responses.

Animals↗
PubMed1994

Induction and regulation of nitric oxide synthase in retinal Müller glial cells.

Müller glial cells from the rat retina were examined for their capacity to produce nitric oxide (NO). Treatment of retinal Müller glial (RMG) cells with lipopolysaccharide (LPS), interferon-gamma, and tumor necrosis factor-alpha induced NO synthesis as determined by nitrite release in media. Simultaneous addition of LPS, interferon-gamma, and tumor necrosis factor-alpha caused the largest increase in NO synthesis. NO biosynthesis was detected after 12 h and was dependent on the dose of LPS, interferon-gamma, and tumor necrosis factor-alpha. Stereoselective inhibitors of NO synthase (NOS), cycloheximide and transforming growth factor-beta, blocked cytokine-induced NO production. Cytosol from LPS/cytokine-treated RMG cultures, but not from unstimulated cultures, produced a calcium/calmodulin-independent conversion of L-arginine to L-citrulline that was completely blocked by NOS inhibitor. The expression of NOS in RMG cells was confirmed by northern blot analysis, in which stimulation of these cells led to an increase in NOS mRNA levels. We conclude that RMG cells can express an inducible form of NOS similar to the macrophage isoform. High NO release from activated RMG cells might represent a protection from infection but may also contribute to the development of retinal pathologies.

Amino Acid Oxidoreductases↗
PubMed1994

BCL-2 expression in human colorectal adenomas and carcinomas.

As BCL-2 oncoprotein has been implicated as a survival factor in a number of tissues, we examined colorectal tumour specimens and cell lines for BCL-2 expression. BCL-2 protein was expressed in 19/22 adenocarcinomas and 12/13 adenomas. 6/9 carcinoma cell lines and 7/8 adenoma cell lines were also BCL-2 positive. BCL-2 expression was retained in metastases to the regional lymph nodes (3/3 specimens) and in the cell line SW620, derived from a lymph node metastasis. These studies suggest a role for BCL-2 in promoting cell survival of benign and malignant colorectal tumours and that BCL-2 deregulation may be a relatively early event in colorectal carcinogenesis. The retention of BCL-2 expression in the carcinomas and lymph node metastases may explain the resistance of colorectal tumours to chemotherapeutic treatment.

3T3 Cells↗