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Biomedical subjects

J W Eaton

Publications and source records attributed to J W Eaton.

At least 127 records · Page 7Linked to original sources
PubMed1983

Increased adsorption of cytoplasmic proteins to the erythrocyte membrane in ATP-depleted normal and pyruvate kinase-deficient mature cells and reticulocytes.

How the metabolic defect of pyruvate kinase deficiency (PK(-)) accelerates red blood cell (RBC) destruction is not established, but may be related to RBC membrane abnormalities associated with altered cellular metabolism. Furthermore, it has been shown that PK(-) reticulocytes are especially sensitive to metabolic depletion. Therefore, we compared the membranes of reticulocyte-rich PK(-) RBC, both fresh and ATP depleted, with membranes of fresh and ATP depleted normal mature RBC and reticulocytes. There was no difference between the specific gravity (SG) of the membranes of normal mature RBC (SG 1.152 +/- 0.004) and membranes of reticulocyte-rich RBC from several anemias (SG 1.150 +/- 0.002). However, membranes from fresh, reticulocyte-rich PK(-) RBC were dense with SG of 1.165 +/- 0.004 which correlated with a corresponding increase of protein to lipid phosphorus ratio of 66 +/- 8 micrograms protein/micrograms lipid phosphorus (normal 52 +/- 6 micrograms/micrograms). The membrane density of PK(-) RBC was further increased when the PK(-) RBC ATP was depleted by anaerobic incubation (SG 1.188 +/- 0.004) or cyanide inhibition (SG 1.182 +/- 0.001). When ATP was depleted in normal RBC and in non-PK(-) reticulocytes, corresponding increases in membrane SG occurred. A distinctive 50,000 MW peptide is adsorbed from the cytoplasm to the membranes of reticulocytes (both normal and PK(-) when these cells were depleted of ATP. The increased membrane adsorption of cytoplasmic proteins by PK(-) RBC was not associated with increased RBC calcium uptake, sulfhydryl oxidation, or altered membrane protein phosphorylation. All the observed abnormalities of PK(-) RBC membranes could by reproduced by ATP depletion of reticulocyte-enriched non-PK(-) RBC.

Absorption↗
PubMed1983

A plasmodium protein kinase that is developmentally regulated, stimulated by spermine, and inhibited by quercetin.

Plasmodium berghei-infected murine red cells possess protein kinase activity that is associated with the isolated parasites. Schizonts contain significantly higher levels of this protein kinase than the more immature forms, suggesting a relationship between this enzyme activity and parasite development. Partially purified protein kinase has a Km for ATP of approximately 30 microMs, whereas the Km for GTP is approximately 300 microMs and the substrate preference is phosvitin greater than casein much greater than histone greater than protamine. The Mg2+ optimum is 10-20 mM, and the protein kinase activity is stimulated by the polyamines spermine and spermidine. The flavone, quercetin, inhibits the protein kinase activity in a competitive manner with respect to ATP (Ki approximately 3 microMs), and P chabaudi also has a very similarly regulated protein kinase. Protein kinases from both species are very similar to the type I casein kinase.

Animals↗
PubMed1983

Effect of arsenical drugs on glutathione metabolism of Litomosoides carinii.

Despite centuries of therapeutic use, the mechanism of action of arsenicals against various diseases remains unknown. Because of the known inhibition of sulfhydryl-containing enzymes by arsenicals, we investigated the possibility that the anti-filarial effects of arsenical drugs might be exerted specifically through impairment of parasite thiol metabolism. We find: (1) arsenicals readily inhibit glutathione reductase of Litomosoides carinii but have little effect upon mammalian enzyme. (2) Administration of Melarsen B to filaria-infected gerbils causes decreases in filarial - but not host - glutathione reductase and reduced glutathione. (3) Such in vivo treatment does not, however, acutely affect parasite energy (ATP) metabolism. These results support the proposition that arsenicals may act through preferential interference with parasite thiol metabolism. The much greater susceptibility of parasite glutathione reductase to inhibition by arsenicals suggests that this enzyme may be a useful point of attack for new drugs.

Adenosine Triphosphate↗
PubMed1983

Membrane-associated phosphoproteins in Plasmodium berghei-infected murine erythrocytes.

Normal and Plasmodium berghei (NYU-2 strain)-infected murine erythrocytes display substantially different patterns of plasma membrane phosphoproteins phosphorylation. Intact erythrocytes (normal and parasite infected) incubated with 32Pi and isolated washed erythrocyte plasma membranes incubated with gamma-32P-ATP were analyzed for phosphoproteins by SDS PAGE and autoradiography. Two new phosphoproteins of molecular weight 45,000 (pp45) and 68,000 (pp68), which are absent in normal erythrocyte membranes, are associated with the membranes of infected erythrocytes subjected to both intact-cell and isolated-membrane phosphorylation conditions. Two-dimensional gel electrophoresis indicates that pp45 and pp68 are of parasite origin. Partial or complete proteolytic digestion reveals that pp45 is phosphorylated at similar amino acid residues both in intact cells and in isolated membranes. The pp45 phosphoprotein can be detected at as low as 3% parasitemia and its phosphorylation is not affected by 10 microM cAMP, 1 mM Ca2+, or 5 mM EGTA. Extraction of isolated washed plasma membranes with 0.5% Triton X-100 or 0.1 M NaOH indicates that pp45 is detergent insoluble and only partially extractable with NaOH, suggesting that pp45 is closely associated with the host erythrocyte plasma membrane.

Animals↗
PubMed1983

Diamide inhibits pulmonary vasoconstriction induced by hypoxia or prostaglandin F2 alpha.

Diamide oxidizes glutathione and other cellular sulfhydryl groups. It decreases calcium ATPase activity and alters mitochondrial calcium flux, probably as a result of the sulfhydryl oxidation. We examined the effect of diamide (5 mg/kg, iv) on pulmonary vascular reactivity in 12 anesthetized dogs. Diamide reversed the pulmonary vasoconstriction caused by hypoxia in seven dogs (control delta PVR + 2.5 +/- 0.6 mm Hg/liter/min; postdiamide delta PVR - 0.1 +/- 0.4 mm Hg/liter/min; P less than 0.01). The pulmonary pressor response to prostaglandin F2 alpha (5 micrograms/kg/min, iv) was also reduced (control delta PVR + 3.8 +/- 0.5 mm Hg/liter/min; postdiamide delta PVR + 1.1 +/- 0.7 mm Hg/liter/min; P less than 0.01). However, in a further five dogs, diamide had only a small effect on the pulmonary vasoconstriction caused by angiotensin II, while the pressor response to hypoxia was again inhibited. The mechanism by which diamide reverses pulmonary vasoconstriction is not certain but the effect is rapid, consistent, and reversible. Because the intravenous infusion of diamide does not produce systemic hypotension, during its period of action on the pulmonary vasculature, unlike the drugs currently available for the clinical treatment of pulmonary hypertension, further studies of its mechanism of action are indicated.

Angiotensin II↗
PubMed1983

Antineoplastic effects of Bordetella pertussis adenylate cyclase.

Urea extracts of B. pertussis, but not B. bronchiseptica, cause large and sustained intracellular cAMP elevation in several neoplastic cell lines. These cAMP elevations are associated with growth inhibition (HL-60, Friend erythroleukemia) and a phenotypic change/differentiation (HL-60, L1210). B. pertussis extract injections prolong survival of L1210 tumor-bearing mice. Pretreatment of L1210 cells with B. pertussis extract both delays mortality and induces growth of solid tumors instead of ascites in subsequently inoculated mice. We conclude that B. pertussis adenylate cyclase is capable of invading a variety of neoplastic cells to catalyze the intracellular formation of large amounts of cAMP. These cAMP elevations are durable and promote growth arrest, differentiation, or phenotypic alterations reflected in altered biologic behavior. B. pertussis adenylate cyclase should prove to be a useful tool for manipulating cAMP levels in neoplastic cells to elucidate the role of cAMP in malignant transformation.

Adenylyl Cyclases↗
PubMed1982

Phagocyte impotence caused by an invasive bacterial adenylate cyclase.

For unknown reasons, humans infected with the bacterium Bordetella pertussis are exceptionally vulnerable to secondary infections. Bordetella species elaborate a soluble, heat-stable, and highly active adenylate cyclase. This enzyme is internalized by phagocytic cells and catalyzes the unregulated formation of adenosine 3',5'-monophosphate (cyclic AMP), thereby disrupting normal cellular function. This unusual phenomenon may explain Bordetella-induced aphylaxis and may prove to be useful for investigating a variety of cyclic AMP-governed processes.

Adenylyl Cyclases↗
PubMed1982

Haptoglobin: a natural bacteriostat.

The combination of bacteria and blood in a wound can have lethal consequences, probably because hemoglobin iron supports prolific bacterial growth. Rats inoculated intraperitoneally with pathogenic Escherichia coli and small amounts of hemoglobin die. Simultaneous administration of haptoglobin, a naturally occurring hemoglobin-binding protein, fully protects against lethality. Therefore, haptoglobin may not only accelerate the clearance of free hemoglobin, but also limit its utilization by adventitious bacteria. Haptoglobin may have therapeutic potential in the treatment of life-threatening, hemoglobin-driven bacterial infections.

Escherichia coli↗
PubMed1982

Spontaneous oxygen radical generation by sickle erythrocytes.

Since the various membrane abnormalities of sickle erythrocytes might result from excessive accumulation of oxidant damage, we have measured the generation of superoxide, peroxide, and hydroxyl radical by normal and sickle erythrocytes using assays involving reduction of cytochrome c, aminotriazole inhibition of catalase, and methane evolution from dimethyl sulfoxide, respectively. Compared with normal erythrocytes, sickle erythrocytes spontaneously generate approximately twice as much superoxide, peroxide, and hydroxyl radical. One possible source of hydroxyl radical generation was identified as hemichrome, excessive amounts of which are bound to sickle erythrocyte membranes. Hemichrome did not generate hydroxyl radical when exposed to superoxide alone or peroxide alone. However, in the presence of both superoxide and peroxide, hemichrome greatly facilitated hydroxyl radical generation. Supporting this, normal erythrocyte membranes induced to acquire sickle hemichrome concomitantly acquired an enhanced ability to mediate hydroxyl radical generation. Finally, sickle erythrocyte membranes greatly enhanced superoxide/peroxide-driven hydroxyl radical generation as compared with normal erythrocyte membranes. These data suggest that an excessive accumulation of oxidant damage in sickle erythrocyte membranes might contribute to the accelerated membrane senescence of these cells. They further indicate that accumulation of oxidant damage could be a determinant of normal erythrocyte membrane senescence.

Anemia, Sickle Cell↗
PubMed1982

Characterization of high- and low-metastatic clones derived from a methylcholanthrene-induced murine fibrosarcoma.

A methylcholanthrene-induced fibrosarcoma (3AM) and several of its clones were evaluated for pulmonary metastasis, growth rate, and chromosome composition. Heterogeneity was observed in the three parameters, and no correlation was found between growth rate and metastatic potential. Furthermore, three clones (10, 34, and 27) were identified with distinctive, high or low, metastatic potential and marker chromosomes. The marker chromosomes characteristic for each clone were identified in the early passages of the parental 3AM line, indicating the preexistence of the different cell types in the original neoplasm. The three clones were then characterized as to tendency to adhere to vascular endothelium, immunogenicity, and antigenic specificity. Clone 10, with two large metacentric markers (T2, 4 and T10, 15) and the highest metastatic potential (221 foci/lung), expressed the highest endothelial attachment and immunogenicity. Clone 27 was characterized with an extremely low rate of metastasis (nine foci/lung) and a T2, 7 large acrocentric marker, while clone 34 was characterized with a moderate rate of metastasis (107.5 foci/lung) and a T4, 16 acrocentric marker. Antigenically, clone 10 cross-reacted with clones 34 and 27 and 3AM, while clones 27 and 34 cross-reacted with clone 10 and 3AM but not with each other, suggesting that, within the original tumor, there were common tumor antigens shared by some cells but no universal antigen shared by all cells.

Animals↗
PubMed1982

Pathogen-host jujitsu: phagocyte impotence caused by internalized bacterial adenylate cyclase.

Humans and animals infected with Bordetella species show evidence of impaired host defenses. These pathogenic bacteria produce a unique adenylate cyclase which enters human phagocytes and catalyzes the unregulated formation of cAMP, a known cellular inhibitor. This unique pathogen-host interaction may explain the unusual features of human B. pertussis infection and represents a powerful new probe for the investigation of cAMP-governed processes.

Adenylyl Cyclases↗
PubMed1982

Assessment of red cell sodium transport in essential hypertension.

Abnormal erythrocyte Na+ transport has been reported in patients with essential hypertension and some first-degree relatives. The two major techniques now employed for estimating Na+ transport--Na+/Li+ countertransport and Na+/K+ cotransport--are rather intricate and time consuming. Furthermore, the precise nature of the transport processes being measured is not clear. We have developed a simpler, more direct technique based on measurement of 22Na+ accumulation by erythrocytes. 22Na+ uptake by red cells from patients with essential hypertension averages twice normal. Indeed, of 21 patients with essential hypertension, only 2 patients had values within the upper end of the normal range. In 12 patients with secondary hypertension and no family history of essential hypertension, erythrocyte 22Na+ accumulation was within normal limits. Control experiments indicate that our technique for estimating red cell 22Na+ uptake is highly reproducible and shows little day-to-day variation. This procedure for the assessment of erythrocyte Na+ transport should be useful in differential diagnosis and the presymptomatic identification of individuals genetically prone to essential hypertension.

Biological Transport↗
PubMed1982

Erythrocyte/endothelial interactions in the pathogenesis of sickle-cell disease: a "real logical" assessment.

Unconvinced that the pathophysiology of sickle-cell disease is fully explained by traditional rheologic considerations, we have searched for additional factors which might be implicated in the development of acute vasocclusive crises in this disease. Sickle RBC adhere abnormally to cultured human vascular endothelial cells, an abnormality requiring neither deoxygenation nor frank morphologic distortion of the RBC. This adherence appears to be caused by an aberrancy of RBC surface charge topography on sickle RBC. Propensity for RBC adherence individual. Among patients with sickle cell anemia, frequency of acute vasocclusive crises correlates significantly with RBC adherence to endothelium. Patients with the clinically less severe doubly heterozygous sickling disorders have a lesser RBC adherence to endothelium than do patients with sickle-cell anemia. RBC/endothelial interactions are modified by factors in the RBC's environment such as fibrinogen, providing a possible mechanism by which concurrent illness might predispose towards the development of vasocclusion. We hypothesize that sickle RBC adherence to endothelium is the factor which initiates acute vasocclusion in sickle-cell disease, either by primarily occluding small vessels or by slowing microvascular blood flow so that secondary, reversible RBC sickling can occur.

Anemia, Sickle Cell↗