Derya Aytemiz

Development of Small-Diameter Vascular Grafts Based on Silk Fibroin Fibers from Bombyx mori for Vascular Regeneration

In the field of surgical revascularization, the need for functional small-diameter (1.5–4.0 mm in diameter) 1vascular grafts is increasing. Several synthetic biomaterials have been tested for this purpose, but in many cases they cause thrombosis. In this study, we report the development of small-diameter vascular grafts made from silk fibroin fibers from the domestic silkworm Bombyx mori or recombinant silk fibroin fibers from a transgenic silkworm. The vascular grafts were prepared by braiding, flattening and winding the silk fibers twice onto a cylindrical polymer tube followed by coating with an aqueous silk fibroin solution. The grafts, which are 1.5 mm in inner diameter and 10 mm in length, were implanted into rat abdominal aorta. An excellent patency (ca. 85%, n= 27) at 12 months after grafting with wild-type silk fibers was obtained. Endothelial cells and smooth muscle cells migrated into the silk fibroin graft early after implantation, and became organized into an endothelium and a media-like smooth muscle layer.

Small‐Diameter Silk Vascular Grafts (3 mm Diameter) with a Double‐Raschel Knitted Silk Tube Coated with Silk Fibroin Sponge

Small-diameter (less than 6 mm in diameter) vascular grafts are highly desirable due to the large demand for surgical revascularization; however, there are no available artificial grafts. Vascular grafts of 1.5 mm diameter prepared by our group with silk fibroin fiber have been proved to be excellent grafts with remarkably high patency and remodeling, based on rat implantation experiment (Enomoto et al., 2010). In this study, a silk fibroin vascular graft with 3 mm diameter which can be used for the coronary arteries or lower extremity arteries is prepared with a double-raschel knitted Bombyx mori silk fiber tube coated with B. mori silk fibroin sponge. Here the silk sponge is prepared from an aqueous solution of the silk fibroin and poly(ethylene) glycol diglycidyl ether as porogen. Sufficient strength, proper elasticity, and protection from loose ends in the implantation process are obtained for the silk fibroin graft; low water permeability and relatively large compliance are also attained. These excellent physical properties make silk fibroin grafts suitable to be implanted in a canine model.

The Effect of Pimobendan on Left Atrial Pressure in Dogs with Mitral Valve Regurgitation

BACKGROUND The effects of pimobendan on left atrial pressure (LAP) in dogs with mitral valve disease (MR) have not been documented in a quantitative manner. OBJECTIVE The objective was to document and study the short-term effects of pimobendan on LAP and echocardiographic parameters in MR dogs. ANIMALS Eight healthy Beagle dogs weighing 10.0-14.7 kg (3 males and 5 females; aged 2 years) were used. METHODS Experimental, cross-over, and interventional study. Dogs with surgically induced MR received pimobendan at either 0.25 mg/kg or 0.50 mg/kg p.o. q12h for 7 days and then, after a 7-day wash-out period, the other dosage. LAP was measured for 30 minutes at baseline and again on days 1, 2, 4, and 7 of pimobendan administration. RESULTS Mean LAP was significantly decreased after the administration of 0.25 mg/kg (15.81 ± 5.44 mmHg to 12.67 ± 5.71 mmHg, P < .001) and 0.50 mg/kg (15.76 ± 5.45 mmHg to 10.77 ± 5.23 mmHg, P < .001). Also, the 0.50 mg/kg group led to a significantly lower LAP (P < .01) compared with the 0.25 mg/kg group. Significant reduction was seen for the first time 4 days after the administration of 0.25 mg/kg and a day after the administration of 0.50 mg/kg. CONCLUSIONS AND CLINICAL IMPORTANCE Pimobendan decreased LAP in a dose-dependent manner in dogs with acute MR caused by experimental chordal rupture. This study did not evaluate adverse effects of high-dose pimobendan, and additional studies in clinical patients are warranted.

Characterization of silk sponge in the wet state using 13C solid state NMR for development of a porous silk vascular graft with small diameter

The 13C solid state NMR spectra of the sponge prepared from Bombyx mori silk fibroin with different 13C labeling sites, [3-13C]Ser, [3-13C]Tyr and [3-13C]Ala were observed in dry and wet states. Here the silk fibroin sponge was prepared using poly(ethylene) glycol diglycidyl ether (PGDE) as porogen. Two broad peaks assigned to β-sheet and random coil were observed for each 13C-labeled site in the dry state. Moreover, in the wet state, one additional sharp peak assigned to random coil with high mobility due to the presence of water was observed. When the silk fibroin aqueous solution and PGDE was mixed in the sponge preparation process, the slow structural change from random coil to β-sheet structure occurs together with decrease in the motion of the silk fibroin backbone chain. The silk fibroin graft with small diameter was prepared with a knitted silk fiber tube coated with this silk fibroin sponge. The high porosity and suture retention strength which are comparable to an ePTFE vascular graft were attained. The excellent results, high patency and high tissue ingrowth, were obtained with the porous silk fibroin graft with small diameter by a rat abdominal aorta implantation experiment.

The Effect of Furosemide on Left Atrial Pressure in Dogs with Mitral Valve Regurgitation: Left Atrial Pressure in Dogs

BACKGROUND The effects of furosemide on left atrial pressure (LAP) in dogs with mitral regurgitation (MR) have not been documented in a quantitative manner and between different routes of administration. OBJECTIVE To document LAP and echocardiographic parameters in MR dogs administered furosemide IV or PO, in order to document changes in LAP after furosemide treatment. ANIMALS Five healthy Beagle dogs (3 males and 2 females; aged 2 years) were used. METHODS Experimental, cross-over, and interventional study. LAP was measured before the administration of furosemide, and 30 minutes, 1, 1.5, 2, 3, 4, 5, 6, 8, 12, and 24 hours after administration. Furosemide 1, 2, or 4 mg/kg IV, PO or placebo was administered. RESULTS LAP was significantly decreased with all administrations of furosemide but not after placebo (P < .05, respectively). The max reduction was observed 1 hour (1 mg/kg IV, 15.04 ± 7.02 mmHg), 3 hours (2, 4 mg/kg IV, 13.28 ± 8.01, 9.23 ± 4.92 mmHg), 4 hours (1 mg/kg PO, 14.68 ± 11.51 mmHg), and 5 hours (2, 4 mg/kg PO, 13.19 ± 10.52, 10.70 ± 7.69 mmHg). E wave and E/Ea were significantly decreased corresponding to the reduction of LAP after administration of 2 and 4 mg/kg (P < .05, respectively). CONCLUSIONS AND CLINICAL IMPORTANCE LAP was decreased in proportion to the dosage of furosemide, which did not significantly differ between IV and PO of the same dosages. E wave and E/Ea might be useful for the treatment evaluation of furosemide.

Effect of fibroin sponge coating on in vivo performance of knitted silk small diameter vascular grafts

ABSTRACT Vascular grafts under 5 mm or less in diameter are not developed due to a problem caused by early thrombus formation, neointimal hyperplasia, etc. Bombyx mori silk fibroin (SF) which has biodegradability and tissue infiltration is focused as tube and coating material of vascular grafts. Coating is an important factor to maintain the strength of the anastomotic region of vascular grafts, and to prevent the blood leak from the vascular grafts after implantation. Therefore, in this research, we focused on the SF concentration of the coating solution, and tissue infiltration and remodeling were compared among each SF concentration. Silk poly (-ethylene) glycol diglycidyl ether (PGDE) coating with concentrations of 1.0%, 2.5%, 5.0%, and 7.5% SF were applied for the double-raschel knitted small-sized vessel with 1.5 mm diameter and 1cm in length. The grafts were implanted in the rat abdominal aorta and removed after 3 weeks or 3 months. Vascular grafts patency was monitored by ultrasound, and morphological evaluation was performed by histopathological examination. SF concentration had no significant effects on the patency rate. However, tissue infiltration was significantly higher in the sample of 2.5% SF in 3 weeks, and 1.0% and 2.5% SF in 3 months. Also, in comparison of length inside of the graft, stenosis were not found in 3 weeks, however, found with 5.0% and 7.5% in 3 months. From these results, it is clear that 2.5% SF coating is the most suitable concentration, based on the characteristics of less stenosis, early tissue infiltration, and less neointimal hyperplasia.

Application of Bombyx mori Silk Fibroin as a Biomaterial for Vascular Grafts

Although silk is known primarily as a textile material, silk fibroin from silkworm (Bombyx mori) has been used as a biomedical suture material for centuries. This review focuses on the application of B. mori silk fibroin to biomaterials, particularly vascular grafts with small diameter (<6 mm). The benefits of silk fibroin for use as a biomaterial are emphasized, especially with respect to the development of silk vascular grafts.

Transarterial Coil Embolization of an Abdominal Aortocaval Fistula in a Dog

A 3-year-old, 5 kg, male Toy Poodle with a mast cell tumor on the left pelvic limb was referred to Tokyo University of Agriculture and Technology Animal Hospital for an oncologic evaluation. On physical examination, a continuous bruit was auscultated over the left inguinal region with a palpable thrill. Cardiac auscultation identified a grade II/VI systolic and a grade I/VI diastolic murmur over the mitral and the aortic valves, respectively. No signs of peripheral cyanosis or congestion were noted. On thoracic radiographs, moderate, generalized enlargement of the cardiac silhouette was observed without evidence of pulmonary edema or pleural effusion. Color Doppler echocardiography identified mild pulmonic, mitral, and aortic valve regurgitation. Measurements of the left ventricle (LV) indicated an increased internal diameter with normal LV wall and septal thicknesses, normal fractional shortening and mild left atrial (LA) enlargement, with normal sinus rhythm. Normal mean arterial blood pressure was obtained on the thoracic limb using the oscillometric method. Laboratory test results (complete blood count, serum biochemistry profile, electrolytes, coagulation profile) were within the normal reference ranges. Ultrasonography of the caudal abdomen showed a caudal vena cava (CVC) with a diameter of 24.6 mm (dog <10 kg, reference values 0.65 0.12 mm) at the site of shunt. Color Doppler with simultaneous electrocardiogram showed turbulent flow in the CVC during the arterial phase. Continuous-wave Doppler interrogation showed continuous low-velocity flow with a pulsatile pattern and spectral broadening of Doppler waveform and peak flow velocity of 3 m/s across the aortocaval shunt (Fig 1). Contrast-enhanced computed tomography (CT) was performed under general anesthesia for anatomic evaluation of the arteriovenous shunt. The contrast timing bolus method was used to synchronize image acquisition. Iodinated contrast medium (2 mL/kg of iodine) was injected into the cephalic vein at flow rate of 1 mL/s. After a 20-second delay, the entire abdomen was scanned with a dual-slice spiral CT scanner. Reconstruction was carried out using contiguous images with a slice thickness of 1.0 mm (total of 149 slices). Post imaging processing showed an aortocaval connection by an anomalous vessel (shunt) located caudal to the renal arteries and a saccular dilatation of the CVC elongating in the caudal direction. The major dilatation was observed caudal to the fistula, 2.6-fold greater than the dilatation observed cranial to the fistula (Fig 2A,B). Endovascular repair was performed under general anesthesia that was maintained with isoflurane. The dog was positioned in right lateral recumbency for a cervical left lateral approach and a small incision in the skin was made to access the left common carotid artery. A 4-Fr multipurpose catheter was inserted through a puncture in the artery and advanced over a guide wire. The catheter tip was positioned in the abdominal aorta, cranial to the fistula to perform aortography. A 5-mL bolus injection of iodinated contrast medium showed the contrast medium being diverted from the aorta into the CVC (Fig 3A). Blood flow in the renal arteries was preserved as observed by contrast filling of the arteries and renal excretion. The tip of the catheter then was repositioned into the AVF over a guide wire to deliver the embolization coil, because contrast injection showed that adequate coil deployment could be achieved through the aorta. An embolization coil of 6.5 mm diameter, 5 loops, and 10 cm in length was deployed along the fistula lumen under fluoroscopic guidance. Aortography a few minutes after coil deployment identified residual flow through the fistula (Fig 3B). Residual flow was also observed on Doppler ultrasonography, but the shunt flow velocity had decreased to 1.5 m/s. Recovery from the anesthesia was uneventful. Postoperative mean arterial blood pressure ranged from From the Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Tokyo, Japan (Nakata, Tanaka, Hamabe, Yoshiyuki, Kim, Suzuki, Aytemiz, Huai-Che, Shimizu, Fukushima). Corresponding author: Ryou Tanaka, DVM, PhD, Department of Veterinary Surgery, Tokyo University of Agriculture and Technology, Saiwai-cho 3-5-8, Fuchu, Tokyo 183-8509, Japan; e-mail: ryo@vet.ne.jp. Submitted May 17, 2013; Revised November 19, 2013; Accepted December 16, 2013. Copyright

Evaluation of changes in left ventricular myocardial function observed in canine myocardial dysfunction model using a two-dimensional tissue tracking technique

This study was conducted to assess the ability of two-dimensional tissue tracking (2DTT) to evaluate changes in left ventricular (LV) myocardial function associated with sustained high electrical pacing. Pacemakers were implanted at the right ventricular (RV) apex of five female Beagles, and sustained high electrical pacing of 250 beats per minute (bpm) was performed for three consecutive weeks. Conventional echocardiography and 2DTT were performed at baseline, and at every week for three weeks with pacing. The baseline parameters were then compared to those of weeks 1, 2, and 3. Three weeks of pacing resulted in significant reduction of radial and circumferential global strains (p < 0.001). Regional analysis revealed reduction of segmental strains in both radial and circumferential directions, as well as increased dyssynchrony after three weeks of pacing in the radial direction (p = 0.0007). The results of this study revealed the ability of 2DTT to measure radial and circumferential strains in dogs with sustained high-electrical pacing, and allowed assessment of global and regional myocardial function and the degree of dyssynchrony.

Effects of a Sustained-Release Form of Isosorbide Dinitrate on Left Atrial Pressure in Dogs with Experimentally Induced Mitral Valve Regurgitation

BACKGROUND The effects of isosorbide dinitrate (ISDN) have not been sufficiently investigated in conscious dogs with mitral valve regurgitation (MR). OBJECTIVE The objective was to investigate the effects of a sustained-release form of ISDN (sr-ISDN) on hemodynamics and the autonomic nervous system in dogs with MR. ANIMALS Six healthy Beagles weighing 11.2 ± 2.2 kg (2 years of age; 2 males and 4 females) were used. METHODS Experimental, crossover, and interventional study. Dogs with experimentally induced MR were administered placebo, 2, 5, and 10 mg/kg sr-ISDN PO on separate days with a 7-day washout period between randomized dosings. Left atrial pressure (LAP) had been recorded continuously from 30 minutes before administration of sr-ISDN to 12 hours after administration. RESULTS LAP was significantly decreased after administration in the 5 and 10 mg/kg groups. Significant decrease was observed at 3 and 4 hours after administration in the 5 mg/kg group. In the 10 mg/kg group, significant decrease was observed at 2, 3, 4, 5, 6, 7, 10, and 11 hours after administration. The lowest value was observed at 4 hours after administration in the 5 and 10 mg/kg groups (20.9 ± 4.2 to 15.9 ± 3.9 mmHg, P < .01, and 21.3 ± 4.0 to 13.6 ± 4.2 mmHg, P < .001). CONCLUSIONS AND CLINICAL IMPORTANCE Sustained-release form of ISDN showed significant decrease of LAP in the 5 mg/kg and 10 mg/kg groups, and duration of effect was dose related.