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Biomedical subjects

K R Bridges

Publications and source records attributed to K R Bridges.

31 records · Page 2Linked to original sources
PubMed1986

Drinking behavior of high risk college men: contradictory preliminary findings.

Seventeen high risk and seventeen low risk college-aged men were compared with respect to drinking behavior/problems and certain implicated personality characteristics. The low risk subjects were, surprisingly, found to drink and become intoxicated more frequently than high risk subjects. They also reported significantly higher sensation seeking scores. This latter variable accounted for the greatest amount of variance in both risk status and frequency of drinking. By contrast, high risk subjects reported somewhat more lifetime alcohol-related symptomatology and significantly more preadult antisocial symptoms. Preadult antisocial symptoms, alone, explained 39% and 29%, respectively, of the variance in alcohol-related symptoms and the amount consumed on a typical drinking day. The implications and limitations of the findings with respect to the development of alcoholism are discussed.

Adolescent↗
PubMed1986

The influence of both drinking and familial risk statuses on cognitive functioning of social drinkers.

Problem and nonproblem drinking, college student sons of alcoholics were compared to problem and nonproblem drinking college student sons of nonalcoholic fathers with respect to cognitive functioning. Problem drinkers performed more poorly on two of the four cognitive tasks, Group Embedded Figures and Symbol-Digit Paired Associates Learning Task, thus supporting earlier findings of cognitive deficits in problem drinking nonalcoholics. Additionally, sons of alcoholics tended to perform more poorly than sons of nonalcoholics on the Group Embedded Figures Test. Cognitive performance was not predicted by any of four measures of impulsive/antisocial personality and behavior-preadult antisocial behavior, childhood behavior problems, sensation seeking, and the MacAndrew Alcoholism Scale. The findings of the research pointed to the importance of considering both drinking and familial alcoholism risk statuses in studies of the cognitive performance of nonalcoholics. Further implications and limitations of the findings are discussed.

Adolescent↗
PubMed1985

Iron metabolism in K562 erythroleukemic cells.

Iron delivery to K562 cells is enhanced by desferrioxamine through induction of transferrin receptors. Experiments were performed to further characterize this event with respect to iron metabolism and heme synthesis. In control cells, up to 85% of the iron taken up from iron-transferrin was incorporated into ferritin, 7% into heme, and the remainder into compartments not yet identified. In cells grown with desferrioxamine, net accumulation of intracellular desferrioxamine (14-fold) was observed and iron incorporation into ferritin and heme was inhibited by 86% and 75%, respectively. In contrast, complete inhibition of heme synthesis in cells grown with succinylacetone had no effect on transferrin binding or iron uptake. Exogenous hemin (30 microM) inhibited transferrin binding and iron uptake by 70% and heme synthesis by 90%. These effects were already evident after 2 h. Thus, although heme production could be reduced by desferrioxamine, succinylacetone, and hemin, cell iron uptake was enhanced only by the intracellular iron chelator. The effects of exogenous heme are probably unphysiologic and the greater inhibition of iron flow into heme can be explained by effects on early steps of heme synthesis. We conclude that in this cell model a chelatable intracellular iron pool rather than heme synthesis mediates regulation of iron uptake.

Cell Line↗
PubMed1985

Discordance between transferrin receptor expression and susceptibility to lysis by natural killer cells.

Expression of the transferrin receptor on target cell lines has recently been implicated as a determinant of susceptibility to cytolysis by natural killer (NK) lymphocytes. We have examined this proposed relationship in several ways. First, K562 (a cell line highly vulnerable to NK lysis) cells were grown for 24 h in the iron chelator desferrioxamine. Under these conditions, the cells doubled their surface transferrin receptor expression as determined both by radioligand binding and surface binding of the OK-T9 monoclonal anti-transferrin receptor antibody. In contrast, cells grown for the same period of time in hemin halved their receptor expression. This fourfold change in transferrin receptor expression between the desferrioxamine-treated and hemin-treated cells produced no change in susceptibility to NK cytolysis. Second, HeLa (a cell line which in its native state is very resistant to NK cytolysis) cells were compared with K562 cells with respect to surface transferrin receptor expression. The difference in NK susceptibility of the two cell lines was not reflected in differences in transferrin receptor expression: the K562 cells expressed approximately 1.5 X 10(5) receptors per cell while HeLa cells expressed 2.0 X 10(5) receptors/cell. Third, infection of HeLa cells by measles virus greatly increased their susceptibility to NK lysis but produced no change in surface transferrin receptor expression. Furthermore, when measles-infected HeLa cells were grown for 6 d in medium supplemented with iron-saturated human transferrin they underwent a 50% reduction in receptor expression but no change in NK susceptibility. Finally, possible alterations in the surface expression of NK target antigens on modified cells were further assayed by their ability to serve as cold-target inhibitors of cytolysis of NK-sensitive target cells. We examined two groups of cells in which transferrin receptor expression was reduced. These were the transferrin-treated, measles-infected HeLa cells with the 50% receptor reduction, and K562 cells grown in medium containing hemin and iron salts where the reduction was five- to sixfold relative to control. In neither case was there a change in the apparent expression of NK target antigen(s). We conclude that there is a discordance between transferrin receptor expression and susceptibility to NK cytolysis in the model systems examined. Therefore, it is unlikely that the transferrin receptor per se is the target recognition structure for human NK cells, although a role in concert with other, as yet undefined molecules, cannot be excluded.

Binding, Competitive↗
PubMed1984

Effect of iron chelators on the transferrin receptor in K562 cells.

Delivery of iron to K562 cells by diferric transferrin involves a cycle of binding to surface receptors, internalization into an acidic compartment, transfer of iron to ferritin, and release of apotransferrin from the cell. To evaluate potential feedback effects of iron on this system, we exposed cells to iron chelators and monitored the activity of the transferrin receptor. In the present study, we found that chelation of extracellular iron by the hydrophilic chelators desferrioxamine B, diethylenetriaminepentaacetic acid, or apolactoferrin enhanced the release from the cells of previously internalized 125I-transferrin. Presaturation of these compounds with iron blocked this effect. These chelators did not affect the uptake of iron from transferrin. In contrast, the hydrophobic chelator 2,2-bipyridine, which partitions into cell membranes, completely blocked iron uptake by chelating the iron during its transfer across the membrane. The 2,2-bipyridine did not, however, enhance the release of 125I-transferrin from the cells, indicating that extracellular iron chelation is the key to this effect. Desferrioxamine, unlike the other hydrophilic chelators, can enter the cell and chelate an intracellular pool of iron. This produced a parallel increase in surface and intracellular transferrin receptors, reaching 2-fold at 24 h and 3-fold at 48 h. This increase in receptor number required ongoing protein synthesis and could be blocked by cycloheximide. Diethylenetriaminepentaacetic acid or desferrioxamine presaturated with iron did not induce new transferrin receptors. The new receptors were functionally active and produced an increase in 59Fe uptake from 59Fe-transferrin. We conclude that the transferrin receptor in the K562 cell is regulated in part by chelatable iron: chelation of extracellular iron enhances the release of apotransferrin from the cell, while chelation of an intracellular iron pool results in the biosynthesis of new receptors.

Apoproteins↗
PubMed1983

Receptor-mediated endocytosis of transferrin in K562 cells.

Human diferric transferrin binds to the surface of K562 cells, a human leukemic cell line. There are about 1.6 X 10(5) binding sites per cell surface, exhibiting a KD of about 10(-9) M. Upon warming cells to 37 degrees C there is a rapid increase in uptake to a steady state level of twice that obtained at 0 degree C. This is accounted for by internalization of the ligand as shown by the development of resistance to either acid wash or protease treatment of the ligand-cell association. After a minimum residency time of 4-5 min, undegraded transferrin is released from the cell. Internalization is rapid but is dependent upon cell surface occupancy; at occupancies of 20% or greater the rate coefficient is maximal at about 0.1-0.2 min-1. In the absence of externally added ligand only 50% of the internalized transferrin completes the cycle and is released to the medium with a rate coefficient of 0.05 min-1. The remaining transferrin can be released from the cell only by the addition of ligand, suggesting a tight coupling between cell surface binding, internalization, and release of internalized ligand. There is a loss of cell surface-binding capacity that accompanies transferrin internalization. At low (less than 50%) occupancy this loss is monotonic with the extent of internalization. Even at saturating levels of transferrin, the loss of surface receptors upon internalization never exceeds 60-70% of the initial binding capacity. This suggests that receptors enter the cell with ligand but are replaced so as to maintain a constant, albeit reduced, receptor number on the cell surface. In the absence of ligand, the cell surface receptor number returns at 37 degrees C. Neither sodium azide nor NH4Cl blocks internalization of ligand. However, they both prevent the release of transferrin from the cell thus halting the transferrin cycle. Excess ligand can overcome the block due to NH4Cl but not azide although the cycle is markedly slower. Iron is delivered to these cells by transferrin at 37 degrees C with a rate coefficient of 0.15 to 0.2 min-1. The iron is released from the transferrin and the majority is found in intracellular ferritin. There is a large internal receptor pool comprising 70 to 80% of the total cell receptors and this may be involved in maintaining the steady state iron uptake.

Ammonium Chloride↗
PubMed1983

Binding of apotransferrin to K562 cells: explanation of the transferrin cycle.

The binding of apotransferrin to the transferrin receptor on the surface of human leukemic K562 cells was found to be significantly less tight than that of the holoprotein, diferric transferrin. The finding that both ligands displayed linear Scatchard plots with similar receptor number (approximately equal to 150,000 per cell) and mutually inhibit each other's binding suggested that they bind to the same receptor. Both the dissociation and association rate of apotransferrin were markedly increased (28-fold and 15-fold, respectively) at pH 7.2 compared to pH 4.8. Using the values of these binding parameters, we propose a mechanism to account for the recycling of transferrin subsequent to internalization and residence within an acidic nonlysosomal organelle where iron is removed.

Apoproteins↗
PubMed1982

Receptor-mediated endocytosis of transferrin and the uptake of fe in K562 cells: identification of a nonlysosomal acidic compartment.

At physiological temperature, the Fe-carrier transferrin is taken up by K562 human erythroleukemia cells through receptor-mediated endocytosis. Both ligand (now minus Fe) and receptor recycle back to the cell surface where the receptor is rapidly reutilized. After endocytosis, transferrin becomes transiently lodged within an acidic compartment inside the cell, as judged by the changed spectral characteristics and quantum yield of fluorescein isothiocyanate-labeled transferrin that is cell-associated at 37 degrees C. Upon binding to transferrin, anti-fluorescein antibody strongly quenches the emission of the fluorescein-labeled residues on the protein and is used to assess whether the transferrin is at the cell surface (incubation at 0 degrees C) or mainly internalized into the cell (incubation at 37 degrees C). Using Percoll gradient fractionation of postnuclear supernatants, we show that the acidic compartment is not the lysosomal compartment.

Cell Compartmentation↗
PubMed1975

The acetylation of hemoglobin by aspirin. In vitro and in vivo.

The chemical modification of hemoglobin by aspirin (ASA) has been studied, both in intact human red cells and in purified hemoglobin solutions. After incubation of red cells with 20 mM [acetyl-1minus14C]ASA, incorporation of radioactivity into hemoglobin was observed in agreement with the results of Klotz and Tam (1973. Proc. Natl. Acad. Sci. U. S. A. 70: 1313-1315). In contrast, no labeling of hemoglobin was seen when [carbosyl-14-C]ASA was used. These results indicate that ASA acetylates hemoglobin. The acetylated hemoglobin was readily separated from unmodified hemoglobin by both gel electrofocusing and by column chromatography. Quantitation of the extent of acetylation by densitometric scanning of gels agreed very well with estimates obtained from radioactivity measurements. Hemolysates prepared from red cells incubated with ASA showed normal oxygen affinity and heme-heme interaction. Purified acetylated hemoglobin had a slightly increased oxygen affinity and decreased heme-heme interaction. There was no difference in the rate of acetylation of oxy- and deoxyhemoglobin. ASA acetylated column-purified hemoglobin A more readily than hemoglobin in crude hemolysate, but less rapidly than purified human serum albumin. The rate of acetylation of hemoglobulin increased with pH up to approximately pH 8,5. Structural studies were done on hemoglobin incubated with 2.0 mM and 20 mM [acetyl-1-14-C]ASA. Alpha- and beta-chains were acetylated almost equally. Tryptic digests of purified acetylated subunits were fingerprinted on cellulose thin layer plates and autoradiographed. Both alpha- and beta-chains showed a number of radioactive spots that were either ninhydrin negative or weakly ninhydrin positive. These results indicate that hemoglobin is acetylated at a number of sites, probably at the epislon-amino group of lysine residues. To determine whether ASA acetylates hemoglobin in vivo, hemolysates of 14 patients on long-term high-dose ASA therapy were analyzed by gel electrofocusing and compared to specimens of individuals not receiving ASA. The ASA-treated group had a twofold increase in a minor hemoglobin component having an isoelectric point lower than that of hemoglobin A, and indistinguishable from the minoe component which appears when hemoglobin is incubated with ASA in vitro.

Acetylation↗