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Biomedical subjects

D Horn

Publications and source records attributed to D Horn.

At least 127 records · Page 7Linked to original sources
PubMed1985

The role of surface charge on the accelerating action of heparin on the antithrombin III-inhibited activity of alpha-thrombin.

We have compared surface charge and the surface charge density on the polyanions heparin and potassium polyvinyl sulfate (KPVS), as well as on hydrolyzed heparin and KPVS, with their accelerating effect on the inhibitory action of antithrombin III on thrombin. Polyelectrolyte titration of thrombin with KPVS or heparin at pH 7.4 clearly indicates an electrostatic interaction. In contrast, at the same pH no electrostatic interaction is observed between polyanions and antithrombin III. KPVS accelerates the inhibitory action of antithrombin III to the same extent as heparin on the basis of charge equivalence. Heparin and KPVS with a mean distance between two charged centers of less than 0.75 and 0.95 nm, respectively, accelerate strongly whereas hydrolysates with lower charge densities are far less active. The following observations are indicated. Intramolecular neutralization of oppositely charged residues occurs within thrombin, antithrombin III, and partially hydrolyzed heparin. Heparin acts on the antithrombin III-thrombin reaction through cooperative electrostatic binding to thrombin and nonelectrostatic interaction with antithrombin III. This indicates a quasi-catalytic action of the polyelectrolyte. Hydrolysis of only a few N-sulfate residues within the heparin molecule decreases the linear surface charge density to such an extent that the accelerating action is drastically reduced. The loss of accelerating capacity agrees with the sudden loss of counterion condensation due to the decrease of the linear surface charge density beyond limits postulated by Manning in a theory of polyelectrolytes.

Antithrombin III↗
PubMed1985

The effect of alternatives to formocresol on antigenicity of proteins.

As part of an overall evaluation of possible substitutes for the pulpotomy agent formocresol, this study was initiated to compare the antigenicity of the reaction products of protein with formaldehyde, glutaraldehyde, or dimethylsuberimidate (DMS). Rabbits were injected with rabbit serum albumin (RSA) which had been treated with one of the following solutions: phosphate-buffered saline, 2% glutaraldehyde, 4% formaldehyde, or 2% DMS. The antisera from the rabbits were analyzed for elicited antibodies by the enzyme-linked immunosorbent assay (ELISA) and in a horseradish peroxidase (HRP) assay using a spot technique on nitrocellulose paper. These assays demonstrated that DMS-treated RSA was the most antigenic of the reaction products tested. The least provocative was the glutaraldehyde-treated RSA; the reaction product of formaldehyde was intermediate. Our findings suggest that if non-immunogenicity of a pulpotomy agent is a desirable property, then DMS does not meet the criteria of an alternative pulp fixative. In contrast, the relatively low antigenicity of glutaraldehyde reinforces other favorable findings which support its use clinically.

Aldehydes↗
PubMed1984

A comparison of the Cavitron Biotronics tonometer to the Goldmann tonometer.

The Cavitron Biotronics tonometer operates on a principle similar to the Mackay-Marg tonometer by applanating the cornea with a probe and a 1.5 mm plunger. Measurements made with the Mackay-Marg tonometer have been shown to correlate with measurements made by other tonometers, but there are no reports of the validity or reliability of the Cavitron Biotronics tonometer. In this study, comparisons were made between intraocular pressure measurements obtained with the Cavitron Biotronics tonometer and the Goldmann tonometer. In addition, the test-retest reliability of the Cavitron Biotronics tonometer was examined.

Adult↗
PubMed1983

The surface charge of apolipoproteins, phospholipid liposomes, and human very low density lipoproteins.

The surface charge of isolated apolipoprotein A-I, apo-A-II, apo-C-II, and apo-C-III2 as well as of liposomes from synthetic highly purified phospholipids and isolated very low density lipoprotein (VLDL) particles from different donors (n = 35) was determined by polyelectrolyte titration. The particle size of apolipoproteins was evaluated from their molecular weight and specific volume, while that of VLDL particles was determined by photon correlation spectroscopy. The surface charge density of apolipoproteins and of VLDL at pH 7 was calculated from the number of surface charges of the particle and the surface area. The experimental net charge versus pH curves for apo-A-I and apo-A-II are very similar to the theoretical data. The differences between experimental and calculated results for apo-C-II and apo-C-III2 are believed to result from "polyelectrolyte" effects of neighboring charged centers within the protein molecule causing a decrease of dissociation of carboxylic residues. Neutral phospholipid liposomes do not exhibit anionic or cationic properties between pH 3 and 9. Liposomes from anionic phospholipids behave similar to polymeric carboxylic acids, i.e. their degree of dissociation increases with pH. The number of surface charges of VLDL particles increases with the particle size, while their surface charge density is about 1.10 +/- 0.36 charges/nm2 of the surface area.

Amino Acids↗
PubMed1983

Sequence-specific responses of restriction endonucleases to bromodeoxyuridine substitution in mammalian DNA.

Substitution of BrdU for dT in mammalian DNA alters the rates of DNA cleavage by restriction endonucleases in a manner that can be related to the specificity of cleavage. A formula is proposed that describes inhibitory and stimulatory contributions arising from the substitution of a Br atom for the CH3 group on T. The larger Br atom is postulated to sterically hinder the nuclease from binding to adjacent groups in the DNA cleavage site, while allowing a tighter binding to itself. The inhibition caused by steric hindrance is predicted to vary inversely with distance from the point of cleavage, whereas the stimulation caused by tighter binding is predicted to be independent of distance. The resultant formula gives a good fit to the data obtained for thirteen different restriction nucleases of known specificity. The parameters in the formula appear to be simple functions of ionic strength. This formula can be used to predict the effect of BrdU substitution on any endonuclease whose specificity of cleavage is known.

Animals↗
PubMed1983

Charge determination of proteins with polyelectrolyte titration.

A recently developed photometric version of polyelectrolyte titration was applied for the determination of the number of charged residues on globular proteins. Based on the observation that oppositely charged polyelectrolytes form, in general, stoichiometric polyelectrolyte complexes, the protein solutions were incubated in excess with an oppositely charged polyelectrolyte, and the residual amount was back-titrated using o-toluidine blue for end point detection. It was found that within the range pH 2 to pH 9 the interaction of the polyelectrolytes, potassium polyvinylsulfate, polydiallylammonium chloride, and N-methylglycolchitosan iodide, with various proteins of known amino acid composition (ribonuclease A, trypsin, chymotrypsin A, pepsin, cytochrome c) occurs stoichiometrically through 1:1 ion pair interaction, irrespective of the spatial distribution of the interacting ionic sites. The close correspondence between the experimental data for the net charge and the calculated balance of ionized residues for the proteins at a given pH indicates that in the native structure of these proteins oppositely charged ionic functions are largely neutralized by the formation of intramolecular salt linkages. It is concluded that polyelectrolyte titration offers an easy access to the determination of the surface charge of proteins and other biopolymers. The data further support the notion of the importance of electrostatic cooperative interactions in biological systems.

Animals↗
PubMed1983

Steroid derivatives for electrophilic affinity labelling of glucocorticoid binding sites: interaction with the glucocorticoid receptor and biological activity.

To investigate the possible use of electrophilic affinity labelling for the characterization of glucocorticoid receptors, different chemically reactive derivatives of deoxycorticosterone (deoxycorticosterone 21-mesylate and deoxycorticosterone 21-(1-imidazole) carboxylate), dexamethasone (dexamethasone 21-mesylate, dexamethasone 21-iodoacetate and dexamethasone 21-bromoacetate) and progesterone (21-chloro progesterone) were tested for their ability to bind irreversibly to the glucocorticoid receptor from goat lactating mammary gland. Using partially purified receptor, only one of the steroids tested, dexamethasone 21-mesylate (DXM-M) was found more effective than dexamethasone (DXM) in preventing exchange of radioactive dexamethasone in the receptor binding site. The affinity of DXM-M for the glucocorticoid receptor, measured by competitive binding assay, was 1/15 that of DXM. Polyacrylamide gel electrophoresis in sodium dodecyl sulphate of the [3H]-DXM-M labeled glucocorticoid receptor revealed a specific covalently radiolabeled fraction corresponding to an apparent molecular weight of 75,000 to 80,000. The biological activity of DXM-M was studied in RPMI 3460-clone 6 Syrian hamster melanoma cells, a cell line which is sensitive to growth inhibition by glucocorticoids. Like DXM, DXM-M inhibits the growth of RPMI 3460-clone 6 cells and it acts as a slowly reversible glucocorticoid agonist at concentrations which correlate with the affinity of DXM-M for the glucocorticoid receptor in vitro.

Affinity Labels↗
PubMed1982

Chromatographic study of interactions between polyvinylpyrrolidone and drugs.

A chromatographic technique for the study of possible interactions of drugs with soluble or insoluble polymer additives is proposed. Crospovidone was used as a stationary phase. The method allowed the rapid determination of interaction constants in the range of greater than 1 M-1 as relevant for applications in practice. The interaction of 39 drugs and model compounds of diverse chemical structure with povidone and crospovidone was studied. The results closely agreed with data obtained from conventional equilibrium dialysis and sorption studies. The complexation reaction was found to be dominated by hydrogen binding. A close correspondence between the strength of interaction and the nature, number, and position of hydrogen-donating functional groups in the active ingredient was observed. The binding tendency was enhanced when the functional groups were connected with aromatic residues. The carboxyl group was more effective than the hydroxide or amino groups. The binding can be quantified by the binding constants, Kp and Ks, respectively, describing the interaction with polyvinylpyrrolidone via independent binding sites. At pH 1, with the exception of tannic acid, all investigated drugs exhibited Kp and/or Ks values well below an upper limit of 10 M-1. Hence, with additive-drug ratios commonly used in pharmaceutical preparations, the bound amount of drug after oral administration can hardly exceed 3%. In view of this already low degree of potential binding and considering its reversible character and its decreasing tendency with increasing pH during GI passage, the presence of polyvinylpyrrolidone in pharmaceutical preparations is not expected to interfere with GI drug absorption.

Adsorption↗
PubMed1982

Glucocorticoids and melanoma: receptor properties of dexamethasone sensitive and resistant tumors.

We have grown solid tumors using dexamethasone-sensitive (clone 6) and -resistant (clone 5) cells cloned from RPMI 3460 Syrian hamster melanoma. Clone 6 but not clone 5 tumor growth was retarded by dexamethasone, indicating that these tumors retain the growth sensitivity to the hormone characteristic of the cells from which they are derived. Both tumor types contain cytosolic glucocorticoid receptors (significantly higher levels in clone 5 tumors) with similar affinity and steroid specificity characteristics and these can exist as stable, activated (nuclear binding) complexes. Despite these similarities the receptor in the two tumor types differ by some physiochemical criteria. By sucrose gradient analysis, cytosols from both tumors contain 7S receptor complexes but clone 6 contains an additional 13S form. Activated receptors isolated by DEAE-cellulose chromatography from both clone 5 and 6 tumor cytosols sediment as a single peak at 4-5S. However, the DEAE-cellulose profiles indicate that clone 6 but not clone 5 activated complexes (Peak I) appear heterogeneous with respect to charge. Interestingly, DNA-cellulose chromatography indicates that activated receptors from clone 5 tumor cytosols may bind more tightly to DNA than those from clone 6. We are investigating these receptor differences in more detail to determine more precisely the role and pathways of action of glucocorticoid hormones in melanoma.

Animals↗
PubMed1982

A program for achieving generalization of grammatical rules to spontaneous discourse.

Four language-disordered children were presented with a 4-step program designed to achieve generalization of target grammatical rules to spontaneous discourse. A multiple baseline design was used to compare trained and untrained rule usage. During each step of the program, the clinician arranged for the child's own intentions to evoke the target rule. Progression through the program entailed systematically increasing the number of nontarget events the child needed to convey, and decreasing the frequency with which the clinician modelled the target. Trained target rules increased in frequency while untrained rules did not. When therapy was then initiated on the untrained rules, they also increased in frequency while the first rules continued to be produced at mastery level.

Child↗
PubMed1981

Sorption properties of cross-linked insoluble polyvinylpyrrolidone.

The interaction of 32 drugs of diverse chemical structure with cross-linked insoluble polyvinylpyrrolidone (crospovidone) was studied. By using a polymer to drug ratio of 10:1, the sorbed amount for 20 compounds was found to be less than 5%. After a 10-fold decrease of the polymer concentration, the sorbed amount of eight other compounds fell to or below the 5% level. Only tannic acid and hexylresorcinol exhibited a significantly stronger sorption tendency. The interaction appeared to be controlled by phenolic groups in the active ingredient. The binding can be quantified by an interaction constant Ks, whose definition is based on a bulk phase model of interaction via independent binding sites. The exceptionally strong binding of hexylresorcinol, however, apparently was caused by cooperative interacting of the hexyl groups in the bound state. Desorption studies revealed that the binding was fully reversible in all cases. Therefore, the presence of cross-linked polyvinylpyrrolidone as a disintegrant in pharmaceutical preparations is not expected to interfere with GI drug absorption.

Adsorption↗
PubMed1981

Reliability of fixation disparity curves.

Fixation disparity curves were recorded in three normal subjects once per week over a period of 10 weeks. Results indicate that measurements of fixation disparity are reliable within limited ranges of forced convergence and forced divergence. Increases in the demand to maintain fusion lead to increases in observed variability of fixation disparity. It is suggested that variability of fixation disparity might be related to the ease with which the two eyes are used as a team.

Adult↗
PubMed1981

Growth inhibition by glucocorticoids in RPMI 3460 melanoma cells.

We have shown previously that dexamethasone inhibits the growth of RPMI 3460 melanoma cells and that cytosols of these cells contain a dexamethasone-binding macromolecule which has properties expected for a glucocorticoid receptor. In this paper, we show that two other glucocorticoids, triamcinolone acetonide and hydrocortisone, also cause growth inhibition in RPMI 3460 cells and that progesterone can block this response. The biological effect of these steroids correlates well with their previously reported ability to bind receptor, a result consistent with the concept that the glucocorticoid-induced growth inhibition is a receptor-mediated event. We have also investigated the nature of the growth response and shown that glucocorticoids inhibit growth in these melanoma cells by increasing the population-doubling time rather than by cytolytic effects. Moreover, a limited exposure to dexamethasone fails to trigger the growth inhibition, suggesting that the continued presence of steroid is necessary for growth inhibition to occur. Since serum-free medium and medium conditioned by exposure to cells do not affect the glucocorticoid-induced growth inhibition, we have obtained no evidence that either the interaction of glucocorticoids with serum factors or cell-induced changes in medium components are involved in the response. In addition to the effect on growth, we have also described morphological alterations which occur in the presence of dexamethasone.

Animals↗