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  • 1
    Electronic Resource
    Electronic Resource
    Abrogation of Graft-versus-Host Disease Following Allotransplantation of Cytotoxically Deficient Bone Marrow across Major Histocompatibility Barriers (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 770 (1995), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1995.tb31065.x
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  • 2
    Electronic Resource
    Electronic Resource
    The Mechanism of Uptake of Biodegradable Microparticles in Caco-2 Cells Is Size Dependent (1997)
    Springer
    Pharmaceutical research 14 (1997), S. 1568-1573 
    Details
    ISSN: 1573-904X
    Keywords: drug carrier ; oral drug delivery ; vaccine ; absorption ; bioavailability ; endocytosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To study the uptake of biodegradable microparticles in Caco-2 cells. Methods. Biodegradable microparticles of polylactic polyglycolic acid co-polymer (PLGA 50:50) of mean diameters 0.1 μm, 1 μm, and 10 μm containing bovine serum albumin as a model protein and 6-coumarin as a fluorescent marker were formulated by a multiple emulsion technique. The Caco-2 cell monolayers were incubated with each diameter microparticles (100 μg/ml) for two hours. The microparticle uptake in Caco-2 cells was studied by confocal microscopy and also by quantitating the 6-coumarin content of the microparticles taken up by the cells. The effects of microparticle concentration, and incubation time and temperature on microparticle cell uptake were also studied. Results. The study demonstrated that the Caco-2 cell microparticle uptake significantly depends upon the microparticle diameter. The 0.1 μm diameter microparticles had 2.5 fold greater uptake on the weight basis than the 1 μm and 6 fold greater than the 10 μm diameter microparticles. Similarly in terms of number the uptake of 0.1 μm diameter microparticles was 2.7 × 103 fold greater than the 1 μm and 6.7 × 106 greater than the 10 μm diameter microparticles. The efficiency of uptake of 0.1 μm diameter microparticles at 100 μg/ml concentration was 41% compared to 15% and 6% for the 1 μm and the 10 μm diameter microparticles, respectively. The Caco-2 cell microparticle (0.1 μm) uptake increased with concentration in the range of 100 μg/ml to 500 μg/ml which then reached a plateau at higher concentration. The uptake of microparticles increased with incubation time, reaching a steady state at two hours. The uptake was greater at an incubation temperature of 37°C compared to at 4°C. Conclusions. The Caco-2 cell microparticle uptake was microparticle diameter, concentration, and incubation time and temperature dependent. The small diameter microparticles (0.1 μm) had significantly greater uptake compared to larger diameter microparticles. The results thus suggest that the mechanism of uptake of microparticles in Caco-2 cell is particle diameter dependent. Caco-2 cells are used as an in vitro model for gastrointestinal uptake, and therefore the results obtained in these studies could be of significant importance in optimizing the microparticle-based oral drug delivery systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012126301290
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  • 3
    Electronic Resource
    Electronic Resource
    Gastrointestinal Uptake of Biodegradable Microparticles: Effect of Particle Size (1996)
    Springer
    Pharmaceutical research 13 (1996), S. 1838-1845 
    Details
    ISSN: 1573-904X
    Keywords: oral ; drug delivery ; nanoparticles ; Peyer's patches ; size exclusion ; vaccine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To investigate the effect of microparticle size on gastrointestinal tissue uptake. Methods. Biodegradable microparticles of various sizes using polylactic polyglycolic acid (50:50) co-polymer (100 nm, 500 nm, 1µm, and 10 µm) and bovine serum albumin as a model protein were formulated by water-in-oil-in-water emulsion solvent evaporation technique. The uptake of microparticles was studied in rat in situ intestinal loop model and quantitatively analyzed for efficiency of uptake. Results. In general, the efficiency of uptake of 100 nm size particles by the intestinal tissue was 15–250 fold higher compared to larger size microparticles. The efficiency of uptake was dependent on the type of tissue, such as Peyer's patch and non patch as well as on the location of the tissue collected i.e. duodenum or ileum. Depending on the size of microparticles, the Peyer's patch tissue had 2–200 fold higher uptake of particles than the non-patch tissue collected from the same region of the intestine. Histological evaluation of the tissue sections demonstrated that 100 nm particles were diffused throughout the submucosal layers while the larger size nano/microparticles were predominantly localized in the epithelial lining of the tissue. Conclusions. There is a microparticle size dependent exclusion phenomena in the gastrointestinal mucosal tissue with 100 nm size particles showing significantly greater tissue uptake. This has important implications in designing of nanoparticle-based oral drug delivery systems, such as an oral vaccine system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016085108889
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  • 4
    Electronic Resource
    Electronic Resource
    Model Features of a Cardiac lontophoretic Drug Delivery Implant (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 790-795 
    Details
    ISSN: 1573-904X
    Keywords: iontophoresis ; controlled release ; ion exchange ; cardiac arrhythmia ; percolation ; drug delivery implant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016288315617
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  • 5
    Electronic Resource
    Electronic Resource
    Calcification of polyurethanes implanted subdermally in rats is enhanced by calciphylaxis (1996)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 31 (1996), S. 201-207 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Calcification complicates the use of the polymer polyurethane in cardiovascular implants. To date only costly experimental circulatory animal models have been useful for investigating this disease process. In this paper we report that polyurethane calcification in rat subdermal implants is enhanced by overdosing with a vitamin-D analog. The calcification-prone state, known as calciphylaxis, was induced in 4-week old rats by oral administration of a vitamin-D analog, dihydrotachysterol. We studied two commercially available polyurethanes (Biomer® and Mitrathane®) and two proprietary polyurethanes (PEU-2000 and PEU-100). PEU-100 is unique because it is derivatized with ethanehydroxy-bisphosphonate (EHBP) for calcification resistance. Polyurethane calcium and phosphate levels and morphological changes due to calciphylaxis were compared with those of control rat subdermal explants in 60-day studies. Increased polyurethane mineralization was observed due to calciphylaxis with 60-day rat subdermal explants of Biomer®, Mitrathane®, and PEU-2000 (calcium levels, respectively, 4.13 ± 0.56, 18.61 ± 2.73, and 3.37 ± 0.22 μg/mg, mean ± standard error) as compared to control explants (calcium levels, respectively, 1.22 ± 0.1, 12.57 ± 0.86, and 0.20 ± 0.86 μg/mg). The study also demonstrated that with 60-day implants calciphylaxis had no side effects on somatic growth and serum calcium levels. Explant surface morphology of these polyurethane explants examined by scanning electron microscopy, back scattering electron imaging coupled with energy dispersive X-ray spectroscopy, and light microscopy demonstrated the presence of predominantly surface-oriented calcification. PEU-100, derivatized with 100 n.moles/mg of EHBP, resisted calcification with explant calcium levels 0.51 ± 0.01 (calciphylaxis) and 0.38 ± 0.01 (control) μg/mg. It is concluded that calciphylaxis enhances superficial polyurethane calcification in rat subdermal implants and that an EHBP-modified polyurethane resists calcification despite calciphylaxis. Rat subdermal implants using calciphylaxis may be generally useful for evaluating the calcification potential of various biomedical polymers. © 1996 John Wiley & Sons, Inc.
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  • 6
    Electronic Resource
    Electronic Resource
    Differential calcification of cusps and aortic wall of failed stented porcine bioprosthetic valves (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 34 (1997), S. 411-415 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: In this study, we examined separately calcification of cusps (C) and associated aortic wall (AW) of 38 (13 aortic and 25 mitral) porcine bioprosthetic heart valves explanted from 37 patients (ages 25-80 years, mean 59) for structural dysfunction, following 54-210 months (mean 125 months aortic, 119 months mitral). Valves were sectioned into C and corresponding AW components; calcification was assessed by atomic absorption spectroscopy for calcium and histologic examination. Overall, AW calcification was half that of C (33.3 ± 5.4 vs. 65.9 ± 6.3 μg/mg, mean ± standard error of the mean respectively, p = 0.002). Correlation of calcification in individual C/AW pairs was weak (r2 = 0.34). Calcification in C was nodular, largely in the valve fibrosa, but AW calcification predominated in the cells between elastic lamellae; large nodules were sparse. We conclude that since AW calcification in these failed porcine valves was neither prominent nor clinically significant, this process should rarely if ever be a limiting factor in the function of stented porcine valves, and that development of anticalcification therapies directed toward the AW of stented valves should be of low priority. However, in stent-free valves, the AW is not covered by prosthetic material, and the level of calcification could be greater and more likely to cause clinical problems through stiffening, embolism, and/or protrusion into the lumen of calcific masses. © 1997 John Wiley & Sons, Inc.
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  • 7
    Electronic Resource
    Electronic Resource
    Prevention of calcification of glutaraldehyde-crosslinked porcine aortic cusps by ethanol preincubation: Mechanistic studies of protein structure and water-biomaterial relationships (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 40 (1998), S. 577-585 
    Details
    ISSN: 0021-9304
    Keywords: bioprostheses ; type I collagen ; infrared spectroscopy ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Clinical usage of bioprosthetic heart valves (BPHVs) fabricated from glutaraldehyde-pretreated porcine aortic valves is restricted due to calcification-related failure. We previously reported a highly efficacious ethanol pretreatment of BPHVs for the prevention of cuspal calcification. The aim of the present study is to extend our understanding of the material changes brought about by ethanol and the relationship of these material effects to the ethanol pretreatment anticalcification mechanism. Glutaraldehyde-crosslinked porcine aortic valve cusps (control and ethanol-pretreated) were studied for the effects of ethanol on tissue water content and for spin-lattice relaxation times (T1) using solid state proton NMR. Cusp samples were studied for protein conformational changes due to ethanol by ATR-FTIR spectroscopy. The changes in cuspal tissue-cholesterol (in vitro) interactions also were studied. Cusp material stability was assessed in terms of residual glutaraldehyde content and collagenase degradation. Water content of the cusp samples was decreased significantly due to ethanol pretreatment. The cuspal collagen conformational changes (per infrared spectroscopy) brought about by ethanol pretreatment were persistent even after rat subdermal implantation of cusp samples for 7 days. In vitro cholesterol uptake by cusps was greatly reduced as a result of ethanol pretreatment. Ethanol pretreatment of cusps also resulted in increased resistance to collagenase digestion. Cuspal glutaraldehyde content was not changed by ethanol pretreatment. We conclude that ethanol pretreatment of bioprosthetic heart valve cusps causes multi-component effects on the tissue/material and macromolecular characteristics, which partly may explain the ethanol-pretreatment anticalcification mechanism. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 577-585, 1998.
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  • 8
    Electronic Resource
    Electronic Resource
    Inhibition of aortic wall calcification in bioprosthetic heart valves by ethanol pretreatment: Biochemical and biophysical mechanisms (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 42 (1998), S. 30-37 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The effectiveness of ethanol pretreatment on preventing calcification of glutaraldehyde-fixed porcine aortic bioprosthetic heart valve (BPHV) cusps was previously demonstrated, and the mechanism of action of ethanol was attributed in part to both lipid removal and a specific collagen conformational change. In the present work, the effect of ethanol pretreatment on BPHV aortic wall calcification was investigated using both rat subdermal and sheep circulatory implants. Ethanol pretreatment significantly inhibited calcification of BPHV aortic wall, but with less than complete inhibition. The maximum inhibition of calcification of BPHV aortic wall was achieved using an 80% ethanol pretreatment; calcium levels were 71.80 ± 8.45 μg/mg with 80% ethanol pretreatment compared to the control calcium level of 129.90 ± 7.24 μg/mg (p = 0.001). Increasing the duration of ethanol exposure did not significantly improve the inhibitory effect of ethanol on aortic wall calcification. In the sheep circulatory implants, ethanol pretreatment partly prevented BPHV aortic wall calcification with a calcium level of 28.02 ± 4.42 μg/mg compared to the control calcium level of 56.35 ± 6.14 μg/mg (p = 0.004). Infrared spectroscopy (ATR-FTIR) studies of ethanol-pretreated BPHV aortic wall (vs. control) demonstrated a significant change in protein structure due to ethanol pretreatment. The water content of the aortic wall tissue and the spin-lattice relaxation times (T1) as assessed by proton nuclear magnetic resonance spectroscopy did not change significantly owing to ethanol pretreatment. The optimum condition of 80% ethanol pretreatment almost completely extracted both phospholipids and cholesterol from the aortic wall; despite this, significant calcification occurred. In conclusion, these results clearly demonstrate that ethanol pretreatment is significantly but only partially effective for inhibition of calcification of BPHV aortic wall and this effect may be due in part to lipid extraction and protein structure changes caused by ethanol. It is hypothesized that ethanol pretreatment may be of benefit for preventing bioprosthetic aortic wall calcification only in synergistic combination with another agent. © 1998 John Wiley & Sons, Inc. J. Biomed Mater Res, 42, 30-37, 1998.
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  • 9
    Electronic Resource
    Electronic Resource
    Calcification of valved aortic allografts in rats: Effects of age, crosslinking, and inhibitors (1995)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 29 (1995), S. 217-226 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Experiments were carried out to investigate rat aortic allograft calcification using valved abdominal aortic allografts. Results indicated that this was a potentially useful model for investigating fresh allograft calcification, as well as mineralization of glutaraldehyde-crosslinked valved allografts. Valve cusp results, however, were not comparable to those noted in large animal or human studies, while aortic wall calcification was more comparable. Calcification inhibitor investigations demonstrated that nearly complete inhibition of the calcification of the aortic wall of glutaraldehyde-crosslinked allografts was achieved using a number of individual inhibitors, including controlled release diphosphonates, and pretreatment with either ferric chloride or aluminum chloride. However, aminopropanehydroxydiphosphonate pretreatment was not efficacious, and sodium dodecyl sulfate pretreatment was only partially effective for inhibiting the aortic wall calcification in the glutaraldehyde-crosslinked allografts. It is concluded that valved aortic allografts in rats provide a useful model for investigating aortic wall (but not valve cusp) calcification and its inhibition. © 1995 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820290212
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  • 10
    Electronic Resource
    Electronic Resource
    Synergistic inhibition of calcification of porcine aortic root with preincubation in FeCl3 and α-amino oleic acid in a rat subdermal model (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 38 (1997), S. 43-48 
    Details
    ISSN: 0021-9304
    Keywords: valvular disease ; cardiac valve prostheses ; aortic cusp ; aortic wall ; anticalcification ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Postimplant calcific degeneration is a frequent cause of clinical failure of glutaraldehyde crosslinked porcine aortic valve bioprostheses. We demonstrated previously in rat subdermal and circulatory implants that α-amino oleic acid used as a bioprosthesis pretreatment was highly effective in mitigating aortic valve cusp but not aortic wall calcification. In this study we investigated the feasibility of synergistically applying two proven anticalcification agents (α-amino oleic acid and FeCl3) as pretreatments for mitigating both bioprosthetic cusp and aortic wall calcification. α-Amino oleic acid is hypothesized to prevent calcification by disrupting calcium phosphate formation kinetics, whereas suppression of alkaline phosphatase activity and ferric-phosphate complexation at cellular membrane initiation sites may be important factors in ferric ion's inhibition of calcification. In vivo implant studies (21-day rat subdermal model) indicated that individually FeCl3 (0.01 or 0.1 M for 24 h) or α-amino oleic acid (saturated solution) treatments were equally effective in mitigating cuspal calcification (tissue calcium levels: 30.2 ± 10.2, 29.8 ± 2.7, and 31.6 ± 7.8 μg/mg tissue, respectively). However, sequential application of first α-amino oleic acid and then FeCl3 synergistically reduced aortic wall calcification more effectively than either of the agents alone. The benefit of a synergistic application of two anticalcification treatments, α-amino oleic acid and FeCl3, was demonstrated. However, the synergistic effect was observed on aortic wall only at a higher FeCl3 concentration (i.e., 0.1 M). © 1997 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 38: 43-48, 1997
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