PubMed Health⌕ Search

Biomedical subjects

E Baker

Publications and source records attributed to E Baker.

At least 19 recordsLinked to original sources
PubMed1992

Intermediate steps in cellular iron uptake from transferrin. Detection of a cytoplasmic pool of iron, free of transferrin.

The uptake of transferrin-bound iron by receptor-mediated endocytosis has been the subject of extensive experimental investigation. However, the path followed by iron (Fe) after release from transferrin (Tf) remains obscure. Once Fe is released from Tf within the endosome, it must be transported across the endosomal membrane into the cell. The present investigation describes the presence of a cytoplasmic Tf-free Fe pool which is detectable only when cells are detached from their culture dishes at low temperature, after initial incorporation of diferric transferrin at 37 degrees C. This cellular iron pool was greatly reduced if incubation temperatures were maintained at 37 degrees C or if cells were treated with pronase. Human melanoma cells (SK-MEL-28) in culture were prelabeled by incubation with human 125I-59Fe-transferrin for 2 h, washed, and reincubated at 4 degrees C or 37 degrees C in balanced salt solution in the presence or absence of pronase. The cells were then mechanically detached from the plates and separated into "internalized" and supernatant fractions by centrifugation. Approximately 90% of cellular 59Fe and 20% of 125I-Tf remained internalized when this reincubation procedure was carried out in balanced salt solution at 37 degrees C. However, at 4 degrees C, cellular internalized iron was reduced to approximately 50% of the initial value. The release of this component of cellular 59Fe (approximately 40% of total cell 59Fe) at 4 degrees C was completely inhibited in the presence of pronase and other general proteinases at 4 degrees C and at 37 degrees C, without affecting internalized transferrin levels. Similar results were obtained in fibroblasts and hepatoma cells, indicating that this phenomenon is not unique to melanoma cells. The characterization of this Tf-free cellular Fe pool which is detectable at low temperature may yield valuable insights into the metabolic fate of iron following its transport across the membrane of the endocytotic vesicle.

Cytoplasm↗
PubMed1992

Clearance from plasma of lymph chylomicrons and chylomicron remnants labelled with 125I-tyramine-cellobiose.

The aims of the present study were to evaluate the metabolism of chylomicrons (CM) and of CM remnants after labelling with radioactive iodine and converting the iodinated CM into remnants in vitro. Lymph CM were radiolabelled with 125I or sham-labelled with 127I by either the ICl procedure or the tyramine-cellobiose (TC) procedure, then injected into rats. The clearance from plasma of the iodinated CM was compared with control non-iodinated lipid-labelled CM. After iodination with ICl, the plasma removal of endogenously labelled CM was significantly different from non-iodinated CM, with increased uptake of CM triacylglycerols by the liver. In contrast, the clearances from plasma and the uptake by organs of radiolabelled lipids of CM iodinated by the TC method (TC-CM) were similar to control CM. About 40% of the label from 125I-TC-CM was insoluble in 50% propan-2-ol, indicating association with CM apolipoprotein B48. Only about 8% of label was lipid soluble, mostly in phosphatidylethanolamine. Radioactivity from 125I-TC-CM injected intravenously in rats was cleared rapidly and by 30 min only 20% remained in plasma, whereas 48% was recovered in the liver. After fractionation of the plasma by density-gradient ultracentrifugation, most label remained associated with d (relative density) less than 1.006 lipoproteins. In intact rats label was also found associated with the low-density and high-density lipoprotein fractions of plasma. When the liver was excluded from circulation, the recovery of label in low-density- and high-density-lipoprotein fractions was greatly decreased. CM remnants were prepared in vivo by injecting 125I-TC-CM into functionally hepatectomized donors and compared with remnants prepared in vitro by incubation with purified bovine milk lipoprotein lipase. Although remnants prepared in vitro cleared from plasma slower than remnants prepared in vivo, the size, lipid composition and apolipoprotein profile on gradient PAGE of the remnants were similar. We conclude that labelling of CM by the TC method avoided the 'artefactual' changes in metabolism seen after labelling by the ICl procedure. CM remnants when prepared in vitro using lipoprotein lipase were found to be similar to those prepared in vivo after injection into functionally hepatectomized rats.

Animals↗
PubMed1992

Two mechanisms of iron uptake from transferrin by melanoma cells. The effect of desferrioxamine and ferric ammonium citrate.

The effects of ferric ammonium citrate (FAC) and desferrioxamine (DFO) on iron (Fe), and transferrin (Tf) uptake have been investigated using SK-MEL-28 human melanoma cells, which express the Tf homologue, melanotransferrin, in high concentrations. Previously we demonstrated two separate Fe uptake mechanisms from Tf, viz. a specific process mediated by the transferrin receptor (TfR) and a nonspecific process (Richardson, D. R., and Baker, E. (1990) Biochim. Biophys. Acta 1053, 1-12). Cells exposed to DFO demonstrated up-regulation of the TfR with a concurrent increase in the rate of Fe uptake. Desferrioxamine also stimulated the nonspecific process of Fe uptake, resulting in a further increase in accumulation of Fe over Tf after saturation of the specific TfR. Ferric ammonium citrate had two effects. First, it resulted in down-regulation of the TfR. Second, and paradoxically, it markedly stimulated the rate of Fe uptake from Tf by the nonspecific process without increasing the rate of nonspecific Tf uptake. These data conclusively demonstrate that two entirely different mechanisms of iron uptake from Tf exist in melanoma cells and that ferric ammonium citrate may be a useful experimental tool to further characterize the specific and nonspecific mechanisms of Fe uptake from Tf.

Biological Transport↗
PubMed1992

A low-spin iron complex in human melanoma and rat hepatoma cells and a high-spin iron(II) complex in rat hepatoma cells.

Human melanoma and rat hepatoma cells cultured in the presence of low concentrations (2.5 microM) of low-molecular-weight iron (Fe) chelates and Fe-transferrin complexes have been studied with 57Fe Mössbauer spectroscopy. The spectra show that holoferritin is only a minor fraction of the total iron present in the cells. The major form of Fe was in a low-spin state unlike the high-spin Fe(III) found in ferritin. Only about 10% of the Fe could be attributed to ferritin. In addition, the hepatoma cells had a high-spin Fe(II) spectral component which made up about 20% of the Fe present.

Animals↗
PubMed1992

The effect of desferrioxamine and ferric ammonium citrate on the uptake of iron by the membrane iron-binding component of human melanoma cells.

The effect of ferric ammonium citrate (FAC) and desferrioxamine (DFO) on membrane iron and transferrin uptake have been investigated using SK-MEL-28 human melanoma cells which express the membrane-bound transferrin homologue, melanotransferrin, at high concentrations. Exposure of melanoma cells to DFO increased membrane non-Tf-bound Fe uptake (putative melanotransferrin Fe-binding sites), suggesting upregulation of the membrane Fe-binding component. However, exposure to FAC did not result in down-regulation. Indeed, an increase in non-Tf-bound membrane Fe was apparent. Results suggested that non-Tf-bound membrane Fe uptake occurred by two processes corresponding to the specific and non-specific mechanisms of Fe uptake from Tf described previously (Richardson, D.R. and Baker, E. (1990) Biochim. Biophys. Acta 1053, 1-12).

Cell Membrane↗
PubMed1992

Evaluation of the iron chelation potential of hydrazones of pyridoxal, salicylaldehyde and 2-hydroxy-1-naphthylaldehyde using the hepatocyte in culture.

A range of new analogues of the promising iron chelator pyridoxal isonicotinoyl hydrazone was prepared and assessed for activity in reducing hepatocyte iron, mechanism of action and potential in iron-chelation therapy. A total of 45 compounds were synthesized by condensation of aromatic aldehydes (pyridoxal, salicylaldehyde and 2-hydroxy-1-naphthylaldehyde) with various acid hydrazides prepared by systematic substitutions on the benzene ring or by the replacement of the ring with an acetyl, pyridyl, furoyl or thiophene moiety. The effects of these compounds on 59Fe uptake and intracellular distribution in hepatocytes in culture and on 59Fe mobilization from prelabeled hepatocytes were assessed. Toxicity, lipophilicity and the ability to chelate plasma transferrin-bound 59Fe were also evaluated. Several compounds were much more active than pyridoxal isonicotinoyl hydrazone and may have clinical potential. These included pyridoxal benzoyl hydrazone, pyridoxal p-methoxybenzoyl hydrazone, pyridoxal m-fluorobenzoyl hydrazone and pyridoxal 2-pyridyl hydrazone. All were more effective at reducing iron uptake than mobilizing hepatocyte iron; they also may act primarily on the transit iron pool rather than on storage iron. Other compounds (e.g., salicylaldehyde p-t-butyl-benzoyl hydrazone) redistributed ferritin-59Fe to different intracellular sites but had little net effect on hepatocyte iron levels.

Animals↗
PubMed1992

The interleukin-7 receptor gene is at 5p13.

A DNA probe for the interleukin-7 receptor gene was used for in situ hybridisation and Southern blot analysis of a series of rodent-human hybrid cell lines. The IL-7 receptor gene maps to 5p13.

Animals↗
PubMed1992

Countercurrent aortography: an alternative to cardiac catheterization in infancy.

Countercurrent aortography via a peripheral artery was used to clarify the aortic arch anatomy in 25 infants in whom cross-sectional and Doppler evaluation was inconclusive. Ages ranged from 3 days to 11 months (median 9 days), and 80% were neonates. The suspected diagnosis was aortic coarctation in 21 infants, interrupted aortic arch in two, recoarctation in one, and vascular ring in one. A countercurrent aortogram provided adequate diagnostic information in 24 infants. A diagnosis of coarctation was confirmed in 15, interruption of the aortic arch in two, and vascular ring in one. In six infants countercurrent aortography excluded the presence of anomalies of the aortic arch. In only one infant, who had an anomalous origin of the right subclavian artery from the descending aorta, did this technique fail to provide adequate information. The only complication observed was transient ischemia of the arm in one patient. Countercurrent aortography is a minimally invasive procedure that can provide adequate angiographic information without the need for cardiac catheterization in patients with inconclusive echocardiographic evaluation. Injection into a right upper limb artery is preferred, because it gives better opacification of the ascending and transverse aortic arch than injection into a left one.

Aorta, Thoracic↗
PubMed1992

Correlates and predictors of smoking among black adolescents.

Little is known about the etiology of cigarette smoking among minority populations. This study examines the correlates and predictors of smoking among inner-city black seventh graders (N = 608). Enhanced self-reports of cigarette smoking were collected along with data concerning demographic, social, and psychological factors hypothesized to promote smoking initiation. Results indicate that social environmental factors, such as the smoking status of friends and siblings, and individual factors, such as refusal assertiveness, general assertiveness, and age are predictive of current smoking. Similarly, the smoking status of friends, attitudes concerning the harmful effects of smoking, and low self-esteem concerning schools are predictive of behavioral intention to smoke in the future. Overall, the factors that were the most salient predictors of smoking for the black adolescents in this study are generally congruent with the existing literature for other populations.

Adolescent↗
PubMed1992

Smoking prevention among urban minority youth: assessing effects on outcome and mediating variables.

We tested the effectiveness of a social resistance/competence enhancement approach to smoking prevention among predominantly Hispanic seventh graders (N = 3,153) from 47 New York City schools. After blocking on school type (public and parochial) and ethnic composition (percent Hispanic), schools were randomly assigned either to receive the 15-session prevention program or to serve as no-contact controls. Using the school as the unit of analysis, significant program effects were found for cigarette smoking, normative expectations concerning peer and adult smoking, smoking prevalence knowledge, social acceptability knowledge, and knowledge of smoking consequences. Using structural modeling techniques, a significant relation was found between the normative expectation and knowledge variables affected by the intervention and posttest smoking, suggesting that changes on these variables mediated the impact of the intervention on cigarette smoking. This study extends the results of previous prevention research and demonstrates the generalizability of this approach to predominantly Hispanic urban minority students.

Adolescent↗
PubMed1992

Financial strain, economic values, and somatic symptoms in later life.

The purpose of this study was to evaluate whether the impact of financial strain on psychological distress depends on the value that older adults place on economic success. Feelings of personal control were specified as an intervening variable in this process. The data came from a nationwide survey of 819 people in Canada who were 55 years of age and older. The findings reveal that financial problems are associated with diminished feelings of control and that these effects are stronger when elderly people value economic achievement highly. In addition, financial strain and diminished feelings of control are related to increased distress regardless of how highly economic success is valued.

Achievement↗
PubMed1992

Fragile X syndrome without CCG amplification has an FMR1 deletion.

We describe a patient with typical clinical features of the fragile X syndrome, but without cytogenetic expression of the fragile X or an amplified CCG trinucleotide repeat fragment. The patient has a previously uncharacterized submicroscopic deletion encompassing the CCG repeat, the entire FMR1 gene and about 2.5 megabases of flanking sequences. This finding confirms that the fragile X phenotype can exist, without amplification of the CCG repeat or cytogenetic expression of the fragile X, and that fragile X syndrome is a genetically homogeneous disorder involving FMR1. We also found random X-inactivation in the mother of the patient who was shown to be a carrier of this deletion.

Adult↗
PubMed1992

Neuropsychological and neuroanatomical dimensions of ideomotor apraxia.

Fifty-five right-handed men with left hemisphere stroke were systematically investigated for ideomotor apraxia of various body parts. Standardized aphasia and apraxia examinations in all cases, and appropriately timed CT in 28 cases, were used for analysis of psychological and anatomical properties of ideomotor apraxia. It is not possible to ignore the modality of eliciting the movement (command or imitation) and the body part being moved (buccofacial, limb or whole body) from any comprehensive theory about ideomotor apraxia. Different levels of performance are seen with different body parts to different modalities in different aphasic groups. Some subtypes of ideomotor apraxia (buccofacial) have highly specified anatomical basis. Some (limb) have apparently distributed anatomies, and others (whole body) have as yet unknown bases.

Adult↗
PubMed1992

Providing support to others and well-being in later life.

Although there is now a voluminous literature on supportive social relations in later life, most of this research has been concerned with assessing the beneficial effects of receiving support from others. The purpose of this study is to assess whether giving support to others within informal as well as formal settings might also benefit older help-providers. Findings from a recent nationwide survey of the elderly suggest that giving informal assistance to others (but not formal assistance) appears to bolster feelings of personal control in later life. The data further reveal that greater feelings of personal control are in turn related to lower levels of depressive symptomatology.

Activities of Daily Living↗