Biomedical subjects

S F Hackett

Publications and source records attributed to S F Hackett.

28 records · Page 2Linked to original sources

PubMed1991

Inhibition of growth factor effects in retinal pigment epithelial cells.

Several agents were examined for their effect on growth factor-stimulated processes in retinal pigment epithelial (RPE) cells. DNA synthesis was assessed by 3H-thymidine incorporation in density-arrested cells using previously determined maximally effective concentrations of various growth factors with and without test substances. Cell migration was assessed in Boyden chamber assays. For each test substance, trypan blue exclusion was used to determine noncytotoxic concentrations, and the effect of several concentrations were assessed on selected growth factors. The most effective, nontoxic concentration was then used for comparisons. Two cationic proteins, protamine and histone type II B, caused inhibition of RPE chemotaxis and 3H-thymidine incorporation induced by several growth factors, but a cationic polypeptide, polylysine, did not. Protamine and histone, were particularly effective inhibitors of acidic and basic fibroblast growth factors (FGF) but not if they were exposed to cells and then removed before growth factor addition. They had no effect on serum-stimulated chemotaxis or 3H-thymidine incorporation even when used in the presence of serum. Three anionic substances, heparin, pentosan polysulfate, and suramin, also inhibited RPE chemotaxis and 3H-thymidine incorporation induced by several different growth factors. They were less effective inhibitors of the FGFs than protamine and histone but were better inhibitors of serum-induced effects. Also unlike protamine and histone, the anionic substances maintained their inhibitory effect even when removed before growth factor addition. Since migration and proliferation of RPE cells are important processes in the pathogenesis of proliferative vitreoretinopathy, these agents and their mechanism of action deserve further study for potential therapeutic applications.

Adult↗

PubMed1990

Ultrastructural and immunocytochemical changes in retinal pigment epithelium, retinal glia, and fibroblasts in vitreous culture.

Retinal pigment epithelial (RPE) cells, retinal glial, and fibroblasts, three cell types believed to play a role in the pathogenesis of epiretinal membrane formation, were maintained in vitreous culture to determine the influence of vitreous on their ultrastructure and expression of cytokeratin, glial fibrillary acidic protein (GFAP), vimentin, and glutamine synthetase (GS). Using a highly sensitive, preembedding technique for the immunolocalization of these antigens at the ultrastructural level, most RPE cells were found to lose cytokeratin and vimentin within 1 day after seeding on irradiated vitreous. The percentage of keratin-positive cells then increased with time in culture. If the vitreous was placed on RPE cells cultured in monolayer instead of placing the cells on the vitreous, keratin and vimentin were expressed these intermediate filament proteins diminished with time. Glutamine synthetase was found in RPE cells grown in monolayer with or without a vitreous overlay, but not in RPE cells grown on the surface of vitreous. Retinal glial grown on vitreous showed a time-dependent decrease in the number of cells expressing GFAP and a corresponding increase in cells expressing vimentin or GS. Some fibroblasts in vitreous culture expressed vimentin but not the other antigens evaluated. A substantial number of cells in each culture did not stain positively for cytokeratin, GFAP, vimentin, or GS. All three cell types showed phenotypic diversity at the ultrastructural level with each cell type being capable of assuming the same morphologic appearance under certain conditions. These results demonstrate the phenotypic plasticity of RPE cells, retinal glia, and fibroblasts when grown in contact with vitreous and provide further evidence that neither ultrastructure, intermediate filament protein expression, nor the presence of GS is sufficient to determine the cell type of origin of cells in epiretinal membranes.

Animals↗

PubMed1990

Growth factor responsiveness of human retinal pigment epithelial cells.

Growth factor effects on DNA synthesis in density-arrested human retinal pigment epithelial cells were assessed by [3H]-thymidine incorporation. Acidic and basic fibroblast growth factor and epidermal growth factor were potent stimulators, whereas platelet-derived growth factor, insulinlike growth factor-1, and insulin were weak or modest stimulators when used alone. When used in combination, each of the above growth factors caused a significant enhancement of [3H]-thymidine incorporation regardless of its effect when used alone. The combination of all four growth factors was significantly more effective than all other combinations, demonstrating synergism in their action. Similar results were found in cell proliferation assays. In contrast to this, transforming growth factor-beta inhibited the ability of each of the other growth factors and serum-containing media to stimulate [3H]-thymidine incorporation. These data suggest that DNA synthesis in human retinal pigment epithelial cells can be modulated by several growth factors, some in a stimulatory or synergistic manner and at least one in an inhibitory manner. A better understanding of these complex interactions may provide insights relevant to normal and abnormal ocular wound healing.

Cells, Cultured↗

PubMed1989

Human retinal pigment epithelial cells in culture possess A2-adenosine receptors.

Adenosine agonists cause a marked stimulation in cyclic AMP accumulation in whole human retinal pigment epithelial (RPE) cells in the presence of adenosine deaminase and papaverine, a phosphodiesterase inhibitor. N-Ethylcarboxamidoadenosine (NECA) stimulates cyclic AMP accumulation 16.1-fold above basal with an EC50 of 2.5 x 10(-7) M. It is also an effective (1.9-fold) stimulator of adenylate cyclase activity in RPE membrane preparations and a modest (1.22-fold) stimulator in the presence of forskolin in RPE cell membranes prepared from freshly isolated porcine RPE. N6-Cyclopentyladenosine (CPA) and N6-phenylisopropyladenosine (PIA) also increase cyclic AMP levels with EC50s of 4.9 x 10(6) M (8.9-fold above basal) and 3.5 x 10(-6) M (8.0-fold above basal) respectively. This potency order (NECA greater than PIA greater than CPA) is typical of A2-adenosine receptors. The relatively A1-selective agonists 10(-7) M indicating that RPE cells do not have A1-receptors which inhibit adenylate cyclase. Three adenosine receptor antagonists, BW-A1433U, 8-cyclopentyltheophylline and 8-sulfophenyltheophylline, blocked the NECA-induced stimulation of cyclic AMP accumulation with IC50s of 0.36 microM, 1.5 microM, and 75 microM respectively. Since alteration of cAMP levels has been demonstrated to affect several RPE functions, including cell migration, resorption of subretinal fluid, and phagocytosis, adenosine may play a significant regulatory role in RPE.

Adenosine↗

PubMed1989

Subretinal fluid stimulation of retinal pigment epithelial cell migration and proliferation is dependent on certain features of the detachment or its treatment.

Subretinal fluid was collected without contamination by blood by placing capillary tubes within drainage sclerotomies when retinal reattachment surgery was performed. All samples (N = 24) stimulated retinal pigment epithelial (RPE) cell migration and proliferation, but a wide range of activity existed (migration, 27.5% to 322.5% above baseline; proliferation, 7.5% to 318.3% above baseline). The correlation between migration- and proliferation-stimulating activity was not strong, suggesting the possibility that different agents are responsible for each. Several variables were examined for correlation with each activity, including age and sex of the patient; extent, duration, and height of the detachment; protein content of the fluid; and amount of cryopexy. It was found that proliferation-stimulating activity increased with the extent of detachment and duration of detachment, while migration-stimulating activity correlated best with amount of cryopexy given before drainage. These data suggest that retinal cryopexy enhances RPE cell migration activity in subretinal fluid, while RPE proliferation activity increases with the size and duration of detachment.

Adult↗

PubMed1988

Human retinal pigment epithelial cells possess muscarinic receptors coupled to calcium mobilization.

Human retinal pigment epithelial (RPE) cells in culture demonstrated saturable specific binding of [3H]quinuclidinyl benzilate (QNB). Specific binding represents about 75% of total binding. Scatchard analysis yields a Kd of 0.178 nM and Bmax of 42 fmol/mg protein. Atropine and carbachol show typical displacement curves, and a Hill plot has a slope of 0.96, suggesting a homogeneous population of receptors. Muscarinic agonists have no effect on intracellular cyclic adenosine monophosphate levels in RPE cells measured by radioimmunoassay, nor do they alter the isoproterenol-induced stimulation of adenylate cyclase. However, both acetylcholine and carbachol cause a rapid increase in intracellular calcium concentration measured by the fluorescent indicator quin 2. Atropine reverses the calcium rise when added after agonist and prevents the rise when added prior to agonist. These data suggest that human RPE cells possess muscarinic receptors coupled to calcium mobilization.

Atropine↗

PubMed1988

Implication of protein carboxymethylation in retinal pigment epithelial cell chemotaxis.

Two chemoattractants for retinal pigment epithelial (RPE) cells, fibronectin (FN) and platelet-derived growth factor (PDGF) were found to enhance protein carboxymethylation mediated by S-adenosyl-L-methionine in RPE cells measured by [3H]methanol hydrolyzed from TCA precipitable protein methyl esters labelled with [3H]methionine. The effect was rapid, peaking at 2 min when [3H]methanol production was enhanced 120% by FN and 150% by PDGF. Erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA; 10 microM), adenosine (100 microM), and L-homocysteine thiolactone (100 microM) inhibited FN-induced carboxymethylation by 60%, and PDGF-induced carboxymethylation by 59%. In modified Boyden chamber assays, the combination of EHNA (10 microM), adenosine (100 microM), and L-homocysteine thiolactone (100 microM) markedly inhibited FN-induced chemotaxis by 88% and PDGF-induced chemotaxis by 93%). Migration of RPE cells has been implicated in the pathogenesis of proliferative vitreoretinopathy (PVR). Inhibition of protein carboxymethylation may provide a new target in the development of pharmacologic therapy for PVR.

Adenine↗

PubMed1987

Cyclic 3',5'-adenosine monophosphate modulates vascular endothelial cell migration in vitro.

Using a modified Boyden chamber assay, we have examined the effect of cyclic nucleotides on bovine aortic endothelial cell migration in vitro. Dibutyrl cyclic 3',5'-adenosine monophosphate (5 mM) inhibited endothelial cell random migration by 67% and inhibited fibronectin-induced chemotaxis by 75%. Agents which significantly stimulated adenylate cyclase activity in endothelial cell membranes were also effective inhibitors of endothelial cell migration. Timolol blocked both the isoproterenol-induced stimulation of adenylate cyclase and the ability of isoproterenol to inhibit endothelial cell migration. Caffeine and isoproterenol together had a greater inhibitory effect on endothelial cell motility than either alone. These data suggest that cAMP may modulate vascular endothelial cell migration in an inhibitory fashion.

Adenylyl Cyclases↗

PubMed1987

Characterization of adenylate cyclase in human retinal pigment epithelial cells in vitro.

Human retinal pigment epithelial cells in culture demonstrate adenylate cyclase activity. It is membrane-bound and modulated by GTP regulatory proteins. It is effectively activated only by beta-adrenergic agonists (L-isoproterenol greater than or equal to L-epinephrine greater than L-norepinephrine) and some prostaglandins (PGE1 and PGE2, but not PGF1 alpha). The adrenergic response appears to be mediated by beta-2 receptors. No inhibitory ligands could be demonstrated. Its characteristics, which are similar to functional adenylate cyclase complexes in other mammalian cells, and its selective and sensitive agonist responsiveness, suggest a possible physiologic role in the regulation of human retinal pigment epithelial-cell function.

Adenylyl Cyclases↗

PubMed1984

A method for measuring polymorphonuclear leukocyte concentrations in nasal mucus.

A method is described for measuring polymorphonuclear leukocyte (PMN) concentrations in expelled nasal mucus. Nasal mucus specimens (0.05-0.15 ml) were diluted 1:60 in Hank's balanced salt solution. Diluted mucus was vigorously agitated to disperse contained cells, and cells were counted in a hemocytometer. The mean PMN counts in nasal mucus from healthy young adults was 7.1 X 10(6) PMNs/ml mucus, but large daily fluctuations were observed in PMN counts in the same individual. This method may be useful to investigate inflammatory conditions of the nasal cavity.

Adult↗