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  • 1
    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.
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  • 2
    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
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  • 3
    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.
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  • 4
    ISSN: 1573-904X
    Keywords: controlled release ; lidocaine ; ventricular tachycardia ; arrhythmia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Epicardial antiarrhythmic drug administration was studied as a therapeutic approach for experimental ventricular tachycardia (VT) in an open-chest dog model. Lidocaine-polyurethane matrices (28%, w/w) were formulated as a model system. Matrices were placed on the left ventricular epicardium in each of 23 anesthetized open-chest dogs with ouabain-induced VT, to evaluate effectiveness in restoring sinus rhythm. Conversion occurred in all animals treated with matrices containing 300 mg or more of lidocaine after 1.5 to 7.0 min. The matrix lidocaine content correlated linearly with the time required for conversion to sinus rhythm (r = 0.75, P = 0.0002); irrespective of matrix size the myocardial/plasma lidocaine ratio was 20.1 ± 4.2 (mean ± SD) at the time of conversion. In a separate series of five dogs without ventricular tachycardia, systolic wall thickening measured with sonomicrometers after 5 min of controlled-release lidocaine administration (500- to 1000-mg matrix lidocaine content, 7.48 ± 3.49-mg/kg dose) was only minimally diminished (−14.1%) and this effect was observed only at the site of matrix placement on the anterior-apical epicardium. In contrast, intracoronary injection of 0.3 or 1.0 mg/kg of lidocaine-HCl resulted in complete elimination of wall thickening or replacement by systolic thinning. Thus epicardial administration of lidocaine from polyurethane matrices was an effective means of treating ouabain-induced ventricular tachycardia. Regional myocardial function in the vicinity of the matrices was modified to a very limited degree, supporting the view that the matrices can be used safely, without serious risk to ventricular contractile performance.
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  • 5
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Calcification of bioprosthetic heart valves fabricated from glutaraldehyde pretreated bovine pericardium or porcine aortic valves (PAV) is a frequent cause of the failure of these devices. Of all strategies considered thus far, only detergent preincubations using compounds such as sodium dodecyl sulfate (SDS) ingibited PAV bioprosthetic mineralization in circulatory sheep bioprosthetic valve replacements. The present study sought to characterize the mechanism of action of SDS preincubation. Results of transport and material characterization studies showed that SDS had a relatively high affinity for PAV, with a maximum uptake of 167.1 ± 6.8 μg SDS/mg tissue over 24 h at 37°C with a partition coefficient of 19.3. The PAV diffusion of SDS was 1.95 ± 0.35 10-6 cm2/sec. The principal effect of SDS on PAV was phospholipid extraction. The residual organic phospholipid extraction. The residual organic phosphate in the SDS pretreated tissue was 2.22 ± 0.72 nmol/mg tissue compared to the control untreated group with 18.52 ± 2.1 nmol/mg tissue. Incubations of PAV specimens in a 1% SDS solution for 24 h significantly inhibited calcification after 21 days in subdermal implants in 3-week-old male rats (PAV Ca2+ = 18.0 ± 11.8 μg/mg) compared to control (177.8 ± 6.0 μg/mg). In contrast, coimplants of 30% SDS silicone rubber polymers, for regional sustained SDS administration, did not impede PAV calcification in 21 day implants Ca2+ = 166.0 ± 14.0 μg/mg compared to the nondrug silicone matrix controls, (Ca2+ = 173.0 ± 6.6 μg/mg). Thus, we conclude that the mechanisms of SDS inhibition of PAV calcification is due to material effects which occur during preincubation, and is not facilitated by sustained SDS administration. © 1993 John Wiley & Sons, Inc.
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  • 6
    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.
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  • 7
    ISSN: 0021-9304
    Keywords: 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 failures of glutaraldehyde cross-linked porcine bioprosthetic heart valves (BPHV). It was demonstrated previously that 2-amino oleic acid (AOA) used as a bioprosthesis treatment was highly effective in mitigating aortic valve cusp but not aortic wall calcification. Our main objective was to study the efficacy of various AOA exposure conditions for inhibiting calcification of both cusps and aortic wall tissues using rat subdermal implants. BPHV tissues were treated with a saturated AOA solution for different time intervals before experimentation. Aortic wall AOA levels were consistently lower than that of the cusps after the same exposure times. The diffusion of calcium ion across both cusp and aortic wall tissues was evaluated, and the results demonstrated that there was an AOA exposure time-dependent retardation of calcium ion penetration for cusp but not aortic wall. An 8-month extraction study was performed to determine the stability of AOA binding. When Tween 80 was used as an extraction medium, cusp and aortic wall retained 12.9 and 48.7%, respectively, of their initial AOA levels. AOA inhibition of calcification in rat subdermal implants (60 days) was found to be exposure time-dependent with maximum treatment time (120 h), resulting in the lowest calcium levels (20.1 ± 10.3 and 71.4 ± 5.4 μg/mg of cusp and aortic wall, respectively) as compared with control (219.1 ± 6.8 and 104.9 ± 8.5 μg/mg of cusp and aortic wall respectively). The significance of AOA binding on BPHV tissue was determined by either blocking or reducing BPHV's (cusp and aortic wall) free aldehyde residues with lysine or NaBH4, respectively, before AOA treatment. For aortic cusps, the AOA contents after 72 h were 98.3 ± 2.7, 34.2 ± 3.6, and 54.1 ± 3.0 nM/mg of tissue for AOA (control), lysine-pretreated (plus AOA) and NaBH4-pretreated (plus AOA) tissues, respectively. However, their calcium levels after 60 days of rat subdermal implant were all comparable (i. e., 48.1 ± 6.2, 38.2 ± 9.1, and 47.0 ± 15.0 μg calcium per mg of tissue). Similar results were observed on BPHV aortic wall. It can thus be concluded that AOA inhibition of BPHV calcification is exposure time-dependent, but the efficacy of AOA for aortic wall is less than that noted for aortic cusps, perhaps because of lower AOA bindings and differences in calcium diffusion kinetics. © 1994 John Wiley & Sons, Inc.
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  • 8
    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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  • 9
    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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  • 10
    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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