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R J Levy

Publications and source records attributed to R J Levy.

At least 37 records · Page 2Linked to original sources
PubMed1998

Prevention of calcification of glutaraldehyde-crosslinked porcine aortic cusps by ethanol preincubation: mechanistic studies of protein structure and water-biomaterial relationships.

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.

Animals↗
PubMed1998

Inhibition of aortic wall calcification in bioprosthetic heart valves by ethanol pretreatment: biochemical and biophysical mechanisms.

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 microg/mg with 80% ethanol pretreatment compared to the control calcium level of 129.90+/-7.24 microg/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 microg/mg compared to the control calcium level of 56.35+/-6.14 microg/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.

Animals↗
PubMed1998

Arterial uptake of biodegradable nanoparticles: effect of surface modifications.

Restenosis is the reobstruction of an artery following interventional procedures such as balloon angioplasty or stenting. Local pharmacotherapeutic approaches using controlled release systems are under investigation to inhibit the regional pathophysiologic process of restenosis. We have been investigating biodegradable nanoparticles (100 +/- 39 nm in diameter, mean +/- sd) for the local intra-arterial drug delivery. The purpose of this study was to investigate nanoparticle surface modifications (see Table 1) to enhance their arterial uptake. The PLGA (polylactic polyglycolic acid copolymer) nanoparticles were formulated by an oil-in-water emulsion solvent evaporation technique using a 2-aminochromone (U-86983, Upjohn and Pharmacia) (U-86) as a model antiproliferative agent. The various formulations of nanoparticles were evaluated for the arterial wall uptake by using an ex-vivo dog femoral artery model. The selected formulations were then tested in vivo in acute dog femoral artery and pig coronary artery models. The nanoparticles surface modified with a cationic compound, didodecyldimethylammonium bromide (DMAB), demonstrated 7-10-fold greater arterial U-86 levels compared to the unmodified nanoparticles in different ex-vivo and in-vivo studies. The mean U-86 levels were 10.7 +/- 1.7 microg/10 mg (dog) and 6.6 +/- 0.6 microg/10 mg (pig) in the artery segments ( approximately 2 cm) which were infused with the nanoparticles. The pig coronary studies further demonstrated that the infusion of nanoparticles with higher U-86 loading reduced the arterial U-86 levels, whereas increasing the nanoparticle concentration in the infusion solutions increased the arterial U-86 levels. The biodistribution studies in pigs following coronary arterial administration of nanoparticles demonstrated disposition of U-86 in the myocardium and distally in the liver and the lung. The mechanism of enhanced arterial uptake of the DMAB surface modified nanoparticles seems to be due to the alteration in the nanoparticle surface charge. The unmodified nanoparticles had a zeta potential of -27.8 +/- 0.5 mV (mean +/- sem, n = 5), whereas the DMAB modified nanoparticles demonstrated a zeta potential of +22.1 +/- 3.2 mV (mean +/- sem, n = 5). The adsorption of DMAB to the nanoparticle surface followed the Freundlich isotherm with binding capacity k = 28.1 microg/mg and affinity constant p = 2. 33. In conclusion, surface modified nanoparticles have potential applications for intra-arterial drug delivery to localize therapeutic agents in the arterial wall to inhibit restenosis.

Animals↗
PubMed1998

A DNA controlled-release coating for gene transfer: transfection in skeletal and cardiac muscle.

In this paper we report a novel technique of DNA-polymer coating for gene transfer. A proprietary DNA polymer solution was used for thin-layer coating on a chromic gut suture as a model study. The coated sutures were characterized for physical properties such as coating thickness, mass of the DNA deposited on the suture, surface characteristics as determined by scanning electron microscopy, and in vitro DNA release characteristics under simulated physiologic conditions. The in vivo gene transfection using DNA-coated sutures was demonstrated in rat skeletal muscle and in canine atrial myocardium. A heat-stable human placental alkaline phosphatase (AP) plasmid was used as a marker gene. Incisions of 1 to 1.5 cm were made in the rat skeletal muscles or the canine atrial myocardium. The sites were closed with either the DNA-coated sutures or control sutures. Two weeks after the surgery, the tissue samples adjacent to the suture lines were retrieved and analyzed for AP activity. The DNA-coated sutures demonstrated a sustained release of the DNA under in vitro conditions, with an approximately 84% cumulative DNA release occurring in 26 days. An agarose gel electrophoresis of the DNA samples released from the suture demonstrated two bands, with the lower band corresponding to the input DNA (supercoiled). It seems that there was a partial transformation of the DNA from a supercoiled to an open circular form due to the polymer coating. The tissue sites, which received the DNA-coated sutures, demonstrated a significantly higher AP activity compared with the tissue sites that received control sutures. In the rat studies, the mean AP activity (square root of cpm/microgram protein) was 43.6 +/- 3.3 vs 20.6 +/- 2.1 (p = 0.001) at the control sites. Similarly, in the canine studies, the AP activity was 73.6 +/- 7.4 Vs 21.6 +/- 1.4 (p = 0.0009) at the control sites. Thus, our studies demonstrated a successful gene transfer using our DNA-polymer coating technique. This technique could be useful for coating sutures used in vascular and general surgery, and also for coating medical devices, such as stents, catheters, or orthopedic devices, to achieve a site-specific gene delivery.

Animals↗
PubMed1998

Prevention of acute inducible atrial flutter in dogs by using an ibutilide-polymer-coated pacing electrode.

Atrial arrhythmias (atrial fibrillation or atrial flutter) after coronary artery bypass graft surgery are difficult to prevent or treat and often result in significant morbidity. Prior experimental studies by our group showed improved therapeutic efficacy for antiarrhythmic drugs delivered via controlled-release polymeric matrices implanted on the epicardial surface. These experiments were conducted to test the hypothesis that direct atrial epicardial administration of ibutilide from a controlled-release system (compared with intravenous administration) can reduce the inducibility of atrial flutter in the acute postoperative atrial myocardium. Polymeric sustained-release preparations were formulated by solvent casting of an ibutilide and polyurethane (Pellathane) solution in tetrahydrofurane. Multilayer solvent-casted coatings on pacing electrode wires were carried out to fabricate a sustained-release electrode system. In animal model studies, each dog underwent a thoracotomy, followed by a right atriotomy that was repaired. Induction of atrial flutter was attempted by burst pacing with the bipolar pacing catheter. Sinus rhythm was restored with overdrive pacing. After determining the induction rate (percentage) of atrial flutter in the baseline state, a stainless-steel wire coated with the drug-delivery system, 10% ibutilide/90% polyurethane (n = 7), or without drug (polyurethane coating without ibutilide, n = 5; control) was sewn onto the right atrium. Systemic intravenous administration of ibutilide (1.2 microg/kg/h) also was carried out in a separate group of animals after atriotomy (n = 5). For ibutilide (at an estimated dose of 1.2 microg/kg/h), the atrial-flutter results were 41.85 +/- 2.21% induction for baseline compared with 12.42 +/- 5.26% (p = 0.02) after the ibutilide wire implant. In the control dogs, atrial flutter was induced 29.4 +/- 4.7% at baseline and 25.2 +/- 5.1% after implantation of the control wire (p = 0.4). Ibutilide coronary venous serum concentrations at the end of the ibutilide-polyurethane electrode experiments were 2.25 +/- 0.2 ng/ml (mean +/- SEM) versus systemic levels that were below the limits of detection. Systemic intravenous ibutilide infusions had no effect on the inducibility of atrial flutter. In conclusion, an epicardial implantable electrode coating with an ibutilide controlled drug-release system significantly reduced the inducibility of atrial flutter in an experimental atriotomy model. These results suggest that atrial arrhythmias occurring after coronary bypass surgery may be prevented by local atrial administration of ibutilide from a controlled-release pacing electrode.

Animals↗
PubMed1998

Diabetes and transport: a potentially bittersweet combination.

These cases represent a portion of the spectrum of medical issues that may be seen in patients with a diagnosis of IDDM. As the first case suggests, knowledge of the disease process and an expanded differential diagnosis is imperative when acting as medical command for these patients. Interfacility transport does not only involve rapid and safe transport between institutions, but must also offer the highest level of expertise available for the referring physician and the patient. For this reason, we recommend the immediate availability of a senior level experienced pediatric physician for involvement in all but the most routine pediatric interfacility transports. Rapid recognition at the time of initial presentation or transport of the correct diagnosis in patient one may have altered potential outcome. Case 2 represents a potential untoward outcome which might be potentiated or exacerbated by the care given during transport. Although this patient's transport time was short, a similar patient may present who needs prolonged transport. The patient might also present to the transport service prior to neurologic deterioration. One must be prepared to intervene for all potential complications as they arise. Case 3 represents a patient whose physical examination suggested more intense therapy was needed than is offered by many DKA protocols. It is important to listen to what the patients are trying to tell us, rather than relying strictly on protocols or guidelines. While protocols or guidelines offer a menu of potential therapies, one must be prepared to vary from these guidelines if suggested by the patient's condition. Recognition of delayed capillary refill in patient 3 allowed for an increase in fluid administration and rapid patient improvement. While not evident with the presented short transports, the use of point of care testing in a transport vehicle can be useful for these types of patients. The opportunity to closely monitor blood chemistry evaluations and gasses can give insight about an ongoing process, suggest therapies, and help direct interventions that, in the past, often waited until the patient arrived at the receiving hospital. That additional information can be invaluable for the ill patient whose outcome may hinge on early recognition of subtle changes with subsequent appropriate interventions.

Brain Edema↗
PubMed1997

Differential calcification of cusps and aortic wall of failed stented porcine bioprosthetic valves.

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 microg/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.

Adult↗
PubMed1997

Capillary electrophoresis of supercoiled and linear DNA in dilute hydroxyethyl cellulose solution.

Capillary electrophoresis in dilute hydroxyethyl cellulose is shown to separate supercoiled DNA in the size range 2000-16,000 base pairs. The plasmids migrate more slowly than linear ds-DNA of the same sizes. Plasmid bandwidths are larger than observed for ds-DNA, allowing identification of the type of DNA by bandwidth. The differing dependence of mobility on chain length can be explained by assuming that a plasmid migrates as an elastic rod, while ds-DNA migrates as a wormlike chain.

Cellulose↗
PubMed1997

Prevention of bioprosthetic heart valve calcification by ethanol preincubation. Efficacy and mechanisms.

BACKGROUND: Calcification of the cusps of bioprosthetic heart valves fabricated from either glutaraldehyde cross-linked porcine aortic valves or bovine pericardium frequently causes the clinical failure of these devices. Our investigations studied ethanol pretreatment of glutaraldehyde cross-linked porcine aortic valves as a new approach to prevent cuspal calcification. The hypothesis governing this approach holds that ethanol pretreatment inhibits calcification resulting from protein structural alterations and lipid extraction. METHODS AND RESULTS: Results demonstrated complete inhibition of calcification of glutaraldehyde-pretreated porcine bioprosthetic aortic valve cusps by 80.0% ethanol in rat subdermal implants (60-day ethanol-pretreated calcium level, 1.87 +/- 0.29 micrograms/mg tissue compared with control calcium level, 236.00 +/- 6.10 micrograms/mg tissue) and in sheep mitral valve replacements (ethanol-pretreated calcium level, 5.22 +/- 2.94 micrograms/mg tissue; control calcium level, 32.50 +/- 11.50 micrograms/mg tissue). The mechanism of ethanol inhibition may be explained by several observations: ethanol pretreatment resulted in an irreversible alteration in the amide I band noted in the infrared spectra for both purified type I collagen and glutaraldehyde cross-linked porcine aortic leaflets. Ethanol pretreatment also resulted in nearly complete extraction of leaflet cholesterol and phospholipid. CONCLUSIONS: Ethanol pretreatment of glutaraldehyde cross-linked porcine aortic valve bioprostheses represents a highly efficacious and mechanistically based approach and may prevent calcific bioprosthetic heart valve failure.

Animals↗
PubMed1997

Synergistic inhibition of calcification of porcine aortic root with preincubation in FeCl3 and alpha-amino oleic acid in a rat subdermal model.

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 alpha-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 (alpha-amino oleic acid and FeCl3) as pretreatments for mitigating both bioprosthetic cusp and aortic wall calcification. alpha-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 a 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 alpha-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 micrograms/mg tissue, respectively). However, sequential application of first alpha-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, alpha-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).

Animals↗
PubMed1997

Influence of local delivery of the protein tyrosine kinase receptor inhibitor tyrphostin-47 on smooth-muscle cell proliferation in a rat carotid balloon-injury model.

Smooth-muscle cell proliferation in response to arterial injury represents an important etiologic factor in restenosis after angioplasty. Tyrphostin-47, a protein tyrosine kinase inhibitor, inhibits smooth-muscle cell proliferation in vitro. In this study tyrphostin-47 was incorporated into matrixes to determine whether prolonged local delivery would result in a reduction of neointimal proliferation after arterial injury in a rat carotid balloon-injury model. A polymer matrix (polylactic polyglycolic acid copolymer and pluronic gel F-127, mean matrix weight 7.83 +/- 0.39 mg) was loaded with tyrphostin-47 (25% w/w). Release studies demonstrated delivery of 11% of the incorporated drug over a 21-day release period. In cell culture, tyrphostin-47 released from the polymer matrix produced a reduction in smooth-muscle cell proliferation (p < 0.0007). Balloon denudation injury of the left common carotid artery of 34 animals was performed. In 12 animals, polymer matrixes containing tyrphostin-47 were wrapped around the injured arteries to provide prolonged drug delivery (estimated dosage 28 micrograms/kg/24 hr); in 10 animals a polymer matrix without tyrphostin-47 was implanted; and in 12 animals only balloon injury was performed. The mean neointimal cross-sectional areas, luminal areas, and intima/media ratios were not significantly different among animals receiving local treatment with tyrphostin-47, sham polymer after injury, or balloon injury without polymer implantation. We conclude that despite inhibition of smooth-muscle cell proliferation by tyrphostin-47 in vitro, sustained local delivery of this tyrosine kinase inhibitor does not result in a reduction of neointimal proliferation in the rat carotid injury model.

Animals↗
PubMed1997

Refinement of the alpha aminooleic acid bioprosthetic valve anticalcification technique.

BACKGROUND: Aminooleic acid treatment has been demonstrated to prevent porcine valve calcification and to protect valvular hemodynamic function. Initial enthusiasm was tempered by histologic studies of these AOA valves, which showed cuspal hematomas, structural loosening, and surface roughening. This prompted a systematic review of the AOA treatment process. Unsolubilized particles of alpha aminooleic acid present in the treatment solution were identified as the cause of mechanical abrasion of valve cusps during processing. These particles were eliminated with a revamped protocol, which included filtration of the AOA solution before valve preparation. METHODS: Porcine aortic valve cusps treated with this modified AOA protocol (AOA II) were studied in a rat subdermal implant model of mineralization. A juvenile sheep trial was then used to confirm the antimineralization effects of AOA II on glutaraldehyde-fixed porcine aortic roots in a circulatory model of accelerated calcification. RESULTS: Retrieved AOA II-treated cusps from the subdermal model were markedly less calcified than control cusps (AOA II, 1 +/- 0, 17 +/- 4, 23 +/- 6, and 17 +/- 10 versus control, 189 +/- 14, 251 +/- 16, 250 +/- 14, and 265 +/- 10 mg calcium/mg sample at 4, 8, 12, and 16 weeks, respectively; p < 0.0001). Morphologic examination of the AOA II cusps of the valves retrieved from the sheep demonstrated freedom from the structural loosening, surface roughening, and hematoma formation that had limited the utility of the original AOA preparation technique. Cusps from AOA II-treated porcine roots had significantly less calcium than control cusps (AOA II, 5.5 +/- 3.0 mg/g; control, 91.2 +/- 19.5 mg/g; p = 0.0004). The aortic walls had similar levels of calcification (AOA II, 156 +/- 73 mg/g; control, 159 +/- 10 mg/g; p = not significant). CONCLUSIONS: These data suggest that the modified AOA technique warrants further evaluation as an antimineralization treatment for glutaraldehyde-fixed porcine bioprostheses.

Animals↗
PubMed1997

The mechanism of uptake of biodegradable microparticles in Caco-2 cells is size dependent.

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 micron, 1 micron, and 10 microns 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 micrograms/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 micron diameter microparticles had 2.5 fold greater uptake on the weight basis than the 1 micron and 6 fold greater than the 10 microns diameter microparticles. Similarly in terms of number the uptake of 0.1 micron diameter microparticles was 2.7 x 10(3) fold greater than the 1 micron and 6.7 x 10(6) greater than the 10 microns diameter microparticles. The efficiency of uptake of 0.1 micron diameter microparticles at 100 micrograms/ml concentration was 41% compared to 15% and 6% for the 1 micron and the 10 microns diameter microparticles, respectively. The Caco-2 cell microparticle (0.1 micron) uptake increased with concentration in the range of 100 micrograms/ml to 500 micrograms/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 degrees C compared to at 4 degrees C. CONCLUSIONS: The Caco-2 cell microparticle uptake was microparticle diameter, concentration, and incubation time and temperature dependent. The small diameter microparticles (0.1 micron) 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.

Animals↗
PubMed1996

Calcification of polyurethanes implanted subdermally in rats is enhanced by calciphylaxis.

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 microgram/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 microgram/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) microgram/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.

Animals↗
PubMed1996

Sustained-release local hirulog therapy decreases early thrombosis but not neointimal thickening after arterial stenting.

Adventitial heparin delivery has been shown to inhibit thrombosis and neointimal thickening in a rat carotid injury model. To determine whether sustained, local delivery of hirulog, a potent antithrombin agent, inhibits thrombus formation and neointimal thickening after arterial stenting, silicone polymers containing hirulog were formulated at a concentration of 5.8% by weight and were tested in vitro to determine the rate of drug release. An oversized metallic stent was implanted in the carotid artery of 18 juvenile farm pigs. Hirulog-impregnated silicone polymers were placed around the adventitial surface of one stented segment of each animal and a control polymer was placed contralaterally. Intravenous hirulog (4 mg/kg/hr) was infused for the duration of the procedure to maintain the activated clotting time of > 300 sec. Ex vivo testing estimated the release of hirulog to be 1.54 micrograms/mg matrix/day with no loss of anticoagulant activity of the released peptide. In four pigs killed on days 3 through 5, macroscopic thrombus was very faintly visible on the stent struts of one arterial segment treated with sustained-release hirulog but was readily evident in all control arteries. However, electron microscopy showed platelet adhesion and microscopic thrombus formation on each stent of both treated and untreated sides. Fourteen pigs were killed 32 +/- 4 days after stenting. Histologic analysis showed no difference between hirulog-treated and control sides in the volume of neointima (540 +/- 129 units vs 357 +/- 95 units, p = 0.27) or in the average intima to media ratio (0.44 +/- 0.12 vs 0.34 +/- 0.24, p = 0.47) over the length of the stented segment. Late thrombotic occlusion occurred in two hirulog-treated and two control arteries. In this model, local adventitial hirulog delivery at the dose and delivery rate used may reduce, but does not prevent, thrombus formation and does not reduce the severity of neointimal thickening after carotid stent implantation.

Animals↗
PubMed1996

Gastrointestinal uptake of biodegradable microparticles: effect of particle size.

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, 1 micron, and 10 microns) 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.

Animals↗
PubMed1995

Iontophoresis for modulation of cardiac drug delivery in dogs.

Cardiac arrhythmias are a frequent cause of death and morbidity. Conventional antiarrhythmia therapy involving oral or intravenous medication is often ineffective and complicated by drug-associated side effects. Previous studies from our laboratory have demonstrated the advantages of cardiac drug-polymer implants for enhanced efficacy for cardiac arrhythmia therapy compared with conventional administration. However, these studies were based on systems that deliver drugs at a fixed release rate. Modulation of the drug delivery rate has the advantage of regulating the amount of the drug delivered depending upon the disease state of the patient. We hypothesized that iontophoresis could be used to modulate cardiac drug delivery. In this study, we report our investigations of a cardiac drug implant in dogs that is capable of iontophoretic modulation of the administration of the antiarrhythmic agent sotalol. We used a heterogeneous cation-exchange membrane (HCM) as an electrically sensitive and highly efficient rate-limiting barrier on the cardiac-contacting surface of the implant. Thus, electric current is passed only through the HCM and not the myocardium. The iontophoretic cardiac implant demonstrated in vitro drug release rates that were responsive to current modulation. In vivo results in dogs have confirmed that iontophoresis resulted in regional coronary enhancement of sotalol levels with current-responsive increases in drug concentrations. We also observed acute current-dependent changes in ventricular effective refractory periods reflecting sotalol-induced refractoriness due to regional drug administration. In 30-day dog experiments, iontophoretic cardiac implants demonstrated robust sustained function and reproducible modulation of drug delivery kinetics.

Animals↗