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Biomedical subjects

A C Hunter

Publications and source records attributed to A C Hunter.

At least 19 recordsLinked to original sources
PubMed2003

Real-time evidence of surface modification at polystyrene lattices by poloxamine 908 in the presence of serum: in vivo conversion of macrophage-prone nanoparticles to stealth entities by poloxamine 908.

Intravenously injected polystyrene nanoparticles, which are prone to rapid sequestration by professional phagocytes, are converted to stealth entities by prior bolus intravenous injection of poloxamine 908. This behaviour is not due to alteration in macrophage phagocytic activity. Laser Doppler anemometry and surface plasmon resonance were used to unravel the mechanisms fundamental to generation of such stealth entities in vivo by poloxamine 908. Electrophoretic mobility of poloxamine pre-coated monodisperse polystyrene nanoparticles in serum, which behave as stealth entities in vivo, was similar to that of uncoated nanoparticles incubated in poloxamine pre-treated serum. This observation supported the notion that poloxamine in serum can modify the surface of nanoparticles with similar topography to that of stealth poloxamine pre-coated particles, i.e. with polyoxyethylene chains projected from the surface. Surface plasmon resonance optical phenomenon was used for real-time monitoring of protein-poloxamine interactions and adsorption at the polystyrene interface. It was found that poloxamine can not only adsorb to a serum-modified surface but in addition poloxamine in serum can form macromolecular complexes with high affinity for adsorption to a polystyrene lattice. A role for serum albumin in surface modification of nanoparticles by poloxamine 908 is also identified. Hence, our biophysical observations correlate precisely with the in vivo longevity of uncoated polystyrene nanoparticles in poloxamine pre-treated rats. This rational and sensitive biophysical approach has unravelled the probable mechanism fundamental to generation of stealth entities in vivo and therefore has application in the design and nano-engineering of stealth colloidal carriers for optimal biological performance.

Animals↗
PubMed2002

PEGylation of microspheres generates a heterogeneous population of particles with differential surface characteristics and biological performance.

Surface PEGylation of polystyrene microspheres with methoxy-poly(ethylene glycol)-5000 (mPEG-5000) generated a heterogeneous population of entities that differed in surface characteristics and in vitro biological performance (phagocytosis and complement activation). Surface heterogeneity was determined by hydrophobic interaction chromatography, measurements of particle electrophoretic mobility in a defined field and adlayer thickness of the projected mPEG chains. The particle population separation by hydrophobic interaction chromatography demonstrated a remarkable linear relationship between the particle zeta potential and phagocytosis by J774 A1 macrophage-like cells. Microsphere populations bearing a predominant surface of mPEG molecules as high-density mushroom-brush intermediate and/or brush configuration were most resistant to phagocytosis and activated the human complement system poorly. Conversely, those populations with predominant surface mPEGs in a mushroom regime were potent activators of the complement system and were prone to phagocytosis. Therefore, surface heterogeneity explains why a fraction of intravenously injected 'long-circulating' nanoparticles is cleared rapidly by macrophages of the reticuloendothelial system. Hydrophobic interaction chromatography can readily assess the extent of surface heterogeneity of PEGylated particulate drug delivery systems and pre-select particles with optimal retention times in the blood. These observations may also be relevant with respect to successful surface camouflaging of cells, drug depots and implantable devices.

Animals↗
PubMed2001

Recognition by macrophages and liver cells of opsonized phospholipid vesicles and phospholipid headgroups.

The interaction of liposomes with blood proteins is believed to play a critical role in the clearance pharmacokinetics and tissue distribution of intravenously injected liposomes. In this article we have focused our discussion on the interaction of liposomes with key blood proteins, which include immunoglobulins, complement proteins, apolipoproteins, fetuin, von Willebrand factor, and thrombospondin, and their role in liposome recognition by professional phagocytes and nonmacrophage hepatic cells. Alternatively, macrophages as well as hepatocytes and liver endothelial cells may phagocytose/endocytose liposomes via direct recognition of phospholipid headgroups. A number of plasma membrane receptors such as lectin receptors, CD14, various classes of scavenger receptors (e.g., classes A, B, and D), Fc-gammaRI and FcgammaRII-B2 may participate in phospholipid recognition. These concepts are also discussed.

Animals↗
PubMed2001

Volume--activated chloride currents in HeLa cells are blocked by tamoxifen but not by a membrane impermeant quaternary analogue.

BACKGROUND/AIMS: Tamoxifen has been shown to inhibit volume activated chloride currents in many cell types. Tamoxifen has also been reported to inhibit a number of cation channels as well as cytosolic proteins such as calmodulin. The mechanism of channel block by tamoxifen is not known but three hypotheses can be proposed: i) a direct effect following binding to the channel protein from the aqueous environment or ii) a direct effect on the channel protein after partitioning into the lipid membrane or iii) an indirect mechanism via binding to intracellular regulatory proteins after diffusion across the lipid membrane. The aim of these experiments was to distinguish between these hypotheses using membrane permeant and impermeant antioestrogens. METHODS: Volume activated chloride currents were recorded from single HeLa cells using whole cell patch clamp technique. The ability of tamoxifen and its membrane impermeant quaternary derivative ethyl bromide tamoxifen (EBT) to inhibit these currents was examined. RESULTS: Extracellular tamoxifen at 3 microM inhibited volume activated chloride currents in HeLa cells whereas EBT had no effect up to 10 microM when applied either to the extracellular bathing solution or the intracellular solution via the patch pipette. CONCLUSION: Eliminating the ability of tamoxifen to cross the plasma membrane abolishes its channel blocking activity against volume activated chloride channels in HeLa cells.

Chloride Channels↗
PubMed2001

Long-circulating and target-specific nanoparticles: theory to practice.

The rapid recognition of intravenously injected colloidal carriers, such as liposomes and polymeric nanospheres from the blood by Kupffer cells, has initiated a surge of development for "Kupffer cell-evading" or long-circulating particles. Such carriers have applications in vascular drug delivery and release, site-specific targeting (passive as well as active targeting), as well as transfusion medicine. In this article we have critically reviewed and assessed the rational approaches in the design as well as the biological performance of such constructs. For engineering and design of long-circulating carriers, we have taken a lead from nature. Here, we have explored the surface mechanisms, which affords red blood cells long-circulatory lives and the ability of specific microorganisms to evade macrophage recognition. Our analysis is then centered where such strategies have been translated and fabricated to design a wide range of particulate carriers (e.g., nanospheres, liposomes, micelles, oil-in-water emulsions) with prolonged circulation and/or target specificity. With regard to the targeting issues, attention is particularly focused on the importance of physiological barriers and disease states.

Animals↗
PubMed2001

Capture of stealth nanoparticles by the body's defences.

This article highlights and discusses our experience in the design, handling, and biological evaluation of long-circulating nanoparticles based on polyoxypropylene/polyoxyethylene copolymer nonionic surfactants. A frequently observed but ignored phenomenon following intravenous injection of such polymer-modified long-circulating colloidal systems is their eventual recognition and clearance by macrophages of the reticuloendothelial system. The pharmacokinetics as well as the tissue distribution of such so-called 'stealth" nanoparticles are also altered after repeated intravenous injection in a time-dependent manner. An understanding of immunological and pathological factors that control the pharmacokinetic and biological behavior of long-circulating particles after single or repeated administration is therefore crucial for the design of a system with an optimal diagnostic and/or therapeutic performance. Therefore, we have also examined and discussed the concept of macrophage recognition of a 'stealth-like nature" and factors that initiate this cascade. A critical discussion of the future of this interesting area of nano-biotechnology/engineering is also provided.

Animals↗
PubMed2000

Membrane impermeant antioestrogens discriminate between ligand- and voltage-gated cation channels in NG108-15 cells.

Native 5-HT(3) and AChR ligand-gated cation channels can be inhibited (blocked) by the non-steroidal antioestrogen tamoxifen. However, the exact site and mechanism of inhibition by tamoxifen on these channels remain unclear. We have investigated the action of the membrane impermeant quaternary derivative, ethylbromide tamoxifen (EBT), on native ligand-gated 5-HT(3) receptor channels and voltage-gated K(+) channels in NG108-15 cells using whole cell patch clamp. Extracellular EBT inhibited whole cell cationic currents of 5-HT(3) receptors with IC(50) of 0.22+/-0.4 microM (n(H)=1.05+/-0.2). The channel block was characterised by voltage independent and use independent behaviour (similar to that of tamoxifen). EBT was unable to inhibit voltage-gated K(+) currents in NG108-15 cells. This was in contrast to the inhibition by tamoxifen which, at similar concentrations, accelerated the apparent inactivation of these outward K(+) currents. The inhibition of 5-HT(3) receptors by a membrane impermeant derivative of tamoxifen supports the view that the binding site for antioestrogens is extracellular and the inhibition is not mediated through genomic/transcriptional activity.

Animals↗
PubMed2000

Poloxamers and poloxamines in nanoparticle engineering and experimental medicine.

Poloxamers and poloxamine nonionic surfactants have diverse applications in various biomedical fields ranging from drug delivery and medical imaging to management of vascular diseases and disorders. Although this is a progressive, rapidly advancing field in biotechnology, the future will depend on the recognition and rectification of a range of toxicity issues, which have to be addressed but have frequently been ignored until now.

Adjuvants, Immunologic↗
PubMed1989

Studies on mucus biosynthesis in the gastrointestinal tract.

Mucin biosynthesis in the rat gastrointestinal tract was measured by following the incorporation of radioactive precursors, [3H] glucosamine, [3H] galactose and [3H] serine. The radioactive mucin was isolated by a combination of equilibrium centrifugation in a CsCl density gradient and gel-filtration or, by papain digestion and removal of digested peptides by dialysis. Radioactive precursors were incorporated into mucin by stomach, duodenum and colon in vivo and by stomach in organ culture in vitro. In the latter, incorporation was approximately 20-fold greater than in vivo, over 6 h. In all cases lower molecular weight non-mucin glycoprotein, of the same buoyant density as mucin, became radioactively labelled (non-dialysable) and usually accounted for the majority of the incorporated radioactivity. Acetylcholine, dibutyryl cAMP and secretin stimulated radioactive incorporation into both gastric mucin and non-mucin components with acetylcholine and dcAMP stimulating specifically [3H] glucosamine into gastric mucin. Using these conditions no stimulation of incorporation into gastric mucin of all three radioactive precursors could be obtained with topical PGE2. In some biosynthesis studies by others, methods used to precipitate radioactive mucins do not distinguish between mucin and lower sized material. This study points to the need for a reappraisal of existing methods using radioactive isotopes to study mucin biosynthesis.

Animals↗
PubMed1984

Microflora and somatic cell content of goat milk.

The results of tests to determine the microflora and somatic cell content of 483 milk samples from 250 dairy goats in the North of Scotland are presented. Milk from uninfected udders had extremely low levels of bacterial contamination, 80 per cent of such samples having less than 100 bacteria/ml. One quarter of all samples were infected, the organisms isolated being coagulase negative staphylococci (83.5 per cent), coagulase positive staphylococci (12.4 per cent) streptococci (3.3 per cent) and Escherichia coli (0.8 per cent). Streptococcus agalactiae was not detected. Somatic cell count levels were higher than those usually found in cows' milk: 33 per cent more than 2,000,000/ml; 22 per cent between 1,000,000 and 2,000,000/ml; 25 per cent between 500,000 and 1,000,000/ml; 22 per cent less than 500,000/ml. The levels of cell counts were similar for uninfected halves and halves infected with coagulase negative staphylococci. Halves infected with coagulase positive staphylococci had much higher cell counts, eg, 73 per cent in excess of 2,000,000/ml. The interpretation of tests based on somatic cell content as indicators of mastitis in goats is discussed.

Animals↗
PubMed1983

Evaluation of the direct epifluorescent filter technique for assessing the hygienic condition of milking equipment.

The hygienic condition of 6 milking installations, 3 sanitized by circulation cleaning (CC) with chlorine-based chemicals and 3 by flushing with acidified boiling water (ABW), was tested using rinses of quarter strength Ringer's solution. The bacterial content of the rinses was determined using both colony counts and the direct epifluorescent filter technique (DEFT). A comparison of testing methods gave correlation coefficients between colony count and DEFT of 0.82 for plants using CC and 0.46 for plants using ABW. Five strains of bacteria belonging to different genera and commonly found on milking equipment were exposed to various degrees of heat and to various concentrations of chlorine. The effects of such treatments on the staining characteristics of the organisms were studied. It was observed that Staphylococcus aureus and Streptococcus lactis, although killed by heat treatment, stained a bright orange when treated with acridine orange dye. Pseudomonas fluorescens, Escherichia coli and vegetative cells of Bacillus cereus did not take up the orange stain after heat treatment, nor did any of the 5 strains stain orange after treatment with NaOCl. It is suggested that the DEFT is a useful and rapid means of counting bacteria in rinses of equipment where sterilization is due primarily to chlorination, but in the absence of a stain which can differentiate more accurately between dead and living organisms its use is limited where sterilization is carried out solely by heat.

Acridine Orange↗
PubMed1980

Ice treatment of injured ligaments: an experimental model.

Using the radiocarpal ligament of the domestic pig as an experimental model the effects of ice therapy were studied. The results indicate that application of ice causes: (1) Increased subcutaneous swelling to injured or uninjured soft tissue; (2) A diminution of histological evidence of inflammation in injured ligamentous tissue.

Animals↗
PubMed1975

Subclinical mastitis in suckler cows.

In a two-year study of the incidence of subclinical mastitis in two beef suckler herds over 2400 quarter milk samples from 180 cows were examined. Somatic cell counts and total bacterial counts were carried out and infecting organisms were isolated on sheep blood agar. Results of these tests indicated that: (a) in spite of extremely dirty udders, fewer contaminants were found in the suckler cow milk samples than in a group of over 1700 samples from typical dairy herds; (b) 18 per cent of all quarter milk samples were infected; (c) 67 per cent of all infections were due to staphylococci and 20 per cent to streptococci; (d) 56 per cent of staphylococcal infections were associated with cell counts less than 500,000 per ml compared with 39 per cent of other infections; (e) 70 per cent of samples had somatic cell counts less than 500,000 per ml. (f) 20 per cent of samples had somatic cell counts over 1 million per ml; (g) only 36 per cent of samples with cell counts over 1 million per ml were associated with udder infections; (h) high cell counts and udder infections were more frequent in early than in mid-lactation. Due to a shortage of animals in the late lactation little evidence was available to support the contention that cell counts rise and the numbers of infected quarters increase towards the end of lactation.

Animals↗