AST-120, an Adsorbent of Uremic Toxins, Improves the Pathophysiology of Heart Failure in Conscious Dogs.

PURPOSE: Several lines of evidence suggest that renal dysfunction is associated with cardiovascular toxicity through the action of uremic toxins. The levels of those uremic toxins can be reportedly reduced by the spherical carbon adsorbent AST-120. Because heart failure (HF) causes renal dysfunction by low cardiac output and renal edema, the removal of uremic toxins could be cardioprotective. METHOD: To determine whether blood levels of the uremic toxin indoxyl sulfate (IS) increase in HF and whether AST-120 can reduce those levels and improve HF. We induced HF in 12 beagle dogs by 6 weeks of rapid right ventricular pacing at 230 beats per min. We treated six dogs with a 1-g/kg/day oral dosage of AST-120 for 14 days from week 4 after the start of rapid ventricular pacing. The other six dogs did not receive any treatment (control group). RESULTS: In the untreated dogs, IS levels increased as cardiac function deteriorated. In contrast, plasma IS levels in the treated dogs decreased to baseline levels, with both left ventricular fractional shortening and pulmonary capillary wedge pressure also improving when compared with untreated dogs. Finally, AST-120 treatment was shown to reduce both myocardial apoptosis and fibrosis along with decreases in extracellular signal-regulated kinase phosphorylation, the Bax/Bcl-2 ratio, and TGF-ß1 expression and increases in AKT phosphorylation. CONCLUSIONS: IS levels are increased in HF. AST-120 treatment reduces the levels of IS and improves the pathophysiology of HF in a canine model. AST-120 could be a novel candidate for the treatment of HF.

Construction of 3 animal experimental models in the development of honeycomb microporous covered stents for the treatment of large wide-necked cerebral aneurysms.

The treatment of large or wide-necked cerebral aneurysms is extremely difficult, and carries a high risk of rupture, even when surgical or endovascular methods are available. We are developing novel honeycomb microporous covered stents for treating such aneurysms. In this study, 3 experimental animal models were designed and evaluated quantitatively before preclinical study. The stents were prepared using specially designed balloon-expandable stents (diameter 3.5-5.0 mm, length 16-28 mm) by dip-coating to completely cover their struts with polyurethane film (thickness 20 µm) and microprocessing to form the honeycomb pattern after expansion. (1) In an internal carotid artery canine model (n = 4), all stents mounted on the delivery catheter passed smoothly through the tortuous vessel with minimal arterial damage. (2) In an the large, wide-necked, outer-sidewall aneurysm canine model, almost all parts of the aneurysms had embolized immediately after stenting (n = 4), and histological examination at 2 months revealed neointimal formation with complete endothelialization at all stented segments and entirely organized aneurysms. (3) In a perforating artery rabbit model, all lumbar arteries remained patent (n = 3), with minimal change in the vascular flow pattern for over 1 year, even after placement of a second, overlapping stent (n = 3). At 2 months after stenting, the luminal surface was covered with complete thin neointimal formation. Excellent embolization performance of the honeycomb microporous covered stents without disturbing branching flow was confirmed at the aneurysms in this proof-of-concept study.

Development of an in vivo tissue-engineered valved conduit (type S biovalve) using a slitted mold.

In autologous valved conduits (biovalves) using in-body tissue architecture, the limited area available for leaflet formation is a concern. In this study, we designed a novel biovalve mold with slits to enhance in vivo cell migration, regardless of size. As a control, the original mold without slits was used. When both types of molds were embedded into subcutaneous pouches in beagle dogs for 8 weeks, the outer surfaces of all molds were completely covered with connective tissue to form conduit tissue. In the molds without slits, the leaflet size was limited to half of the design. In contrast, in the mold with slits, the complete leaflet area was formed. Upon trimming excess peripheral tissues, removing the mold, and cutting the connective tissue formed at the slits, completely autologous connective tissue biovalves with the designed leaflet area were obtained as type S (diameter, 6-28 mm) biovalves. The slit structure customized to the mold was effective for allowing cells to enter, thereby facilitating cell migration and contributing to the successful preparation of reliable biovalves of various physiological sizes suitable for all clinical uses.

Successful implantation of autologous valved conduits with self-expanding stent (stent-biovalve) within the pulmonary artery in beagle dogs.

OBJECTIVES: To evaluate the functionality of an autologous heart valve with stent (Stent-biovalve or SBV) after implantation in the pulmonic valve position in beagle dogs. ANIMALS: Five beagle dogs. METHODS: A mold with an aperture of a tri-leaflet structure was constructed from a pair of concave and convex rods to which a nitinol (NiTi) stent was mounted. This mold was embedded in a dorsal subcutaneous pouch in beagle dogs for 4 weeks. At the time of the removal, the surfaces of the molds were completely covered with connective tissues, tri-leaflet valves were formed and the NiTi stent was tightly connected to the structure. RESULTS: The mean burst strength of the SBV leaflet was 2710 mmHg (range 2280-3116 mmHg), which was approximately equal to that of the native pulmonic valve leaflet. After implantation in the pulmonary position, the SBV showed good functionality as a pulmonic valve. At 84 days after implantation, the SBV was replaced with autologous fibroblasts and collagenous tissues, and showed organization similar to that of native heart valves. CONCLUSION: Stent-Biovalves achieved good valvular function with laminar flow in the pulmonic valve position of beagle dogs.

Development of self-expanding valved stents with autologous tubular leaflet tissues for transcatheter valve implantation.

In this study, self-expanding valved stents were prepared by in-body tissue architecture technology. As molds, plastic rods (outer diameter; 14 or 25 mm), mounted with specially designed self-expanding stents, whose strut was a combination of two wavy rings and three pillars, were embedded into the subcutaneous pouches of goats or beagles for 1 month. Upon harvesting, the molds were fully encapsulated with membranous connective tissues, in which the stent strut was completely embedded. The tubular tissues with the stents were obtained by removing the internal rods. About a half of the tubular tissues as a leaflet part was folded inside the remaining tubular tissues having ring strut as a conduit part. When the overlapped tubular tissues were fixed at the three pillars, two different-sized self-expanding valved stents (internal diameter; 14 or 25 mm) with autologous tubular leaflet tissues were obtained as Stent-Biovales. After shape formation of the leaflets at the closed form, regurgitation rate was approximately 5 and 22 % at pulmonary and aortic condition, respectively. The Stent-Biovalves developed here may be useful as a heart valve for patients undergoing transcatheter heart valve implantation.

In situ observation and enhancement of leaflet tissue formation in bioprosthetic "biovalve".

Biovalves, autologous tri-leaflet valved conduits, are formed in the subcutaneous spaces of animals. The valves are formed using molds encapsulated with autologous connective tissues. However, tissue migration into the small apertures in the molds for leaflet formation is generally slower than that for conduit formation around the molds. In this study, the formation of the leaflet tissues was directly and non-invasively observed using a wireless capsule endoscope. The molds were assembled from 6 parts, one of which was impregnated with the endoscope, and embedded into subcutaneous pouches in goats (n = 30). Tissue ingrowth into the apertures gradually occurred from the edges of the leaflet parts. Tissue formation was accompanied by capillary formation. At 63.1 ± 17.1 days after embedding, the apertures were completely replaced with autologous connective tissue, forming the leaflet tissues. Leaflet formation was enhanced by including fat tissue (46.7 ± 4.2 days) or blood (41.1 ± 6.9 days) in the apertures before embedding. The creation of slit openings, in conjunction with addition of blood to the apertures, further enhanced leaflet formation (37.0 ± 2.8 days). Since leaflet formation could be observed endoscopically, the appropriate embedding period for complete biovalve formation could be determined.

Plasma atrial natriuretic peptide is an early diagnosis and disease severity marker of myxomatous mitral valve disease in dogs.

The aim of this study was to retrospectively assess the clinical usefulness of plasma atrial natriuretic peptide (ANP) concentrations for determining the severity of myxomatous mitral valve disease (MMVD) in dogs. Plasma ANP levels were found to be significantly higher in dogs with MMVD compared to healthy dogs, and plasma ANP levels increased significantly in dogs with progressive heart failure. In dogs with MMVD, stepwise regression analysis revealed that the left atrium/aorta ratio and fractional shortening could be used to predict the plasma ANP concentration. These results indicated that plasma ANP rose with an increase in the volume overload of the left side of the heart. Plasma ANP discriminated cardiomegaly from non-cardiomegaly caused by asymptomatic MMVD. We conclude, therefore, that plasma ANP concentrations may be a clinically useful tool for early diagnosis of asymptomatic MMVD in dogs.