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Biomedical subjects

S Niu

Publications and source records attributed to S Niu.

17 recordsLinked to original sources
PubMed1992

Endothelial cell senescence inhibits unidirectional endothelialization in vitro.

We investigated the effects of cellular senescence on unidirectional endothelialization in vitro, simulating the anastomotic endothelialization of vascular prosthesis. The experiments were carried out with three different cumulative population-doubling levels (CPDLs) of bovine aortic endothelial cells (ECs), which have finite life span. Young ECs with 22 CPDL, middle aged with 46, and senescent with 70 at the time of inoculation were used. The effect of aging on unidirectional endothelialization, as well as cellular morphology and proliferative and migratory potentials of isolated cells, were qualitatively and quantitatively analyzed. The unidirectional endothelialization rate was determined by our newly designed method to prepare the square monolayer sheet with linear margins between cell-adhesion and noncell-adhesion regions. The results showed that endothelial cell senescence retarded not only proliferation and migration but also unidirectional endothelialization. Time-lapsed videomicroscopic study of unidirectional endothelialization process revealed that ECs at several rows back from the leading edge represented much slower rate of migration than did the ECs at the leading edge. These findings suggest that high cellular mobility observed for the ECs at the leading edge may result in localized excessive cell replication. Thus, atherosclerotic vessels containing senescent or injured ECs may have limited capability of anastomotic endothelialization.

Animals↗
PubMed1992

Quantitative analysis of unidirectional 2-D tissue formation of endothelial cells.

We developed a reliable and quantitative method for measuring the dynamic process of unidirectional two-dimensional (2-D) tissue formation of endothelial cells (ECs) in vitro. The culturing of bovine ECs in an assembled culture chamber provided a square monolayered cell sheet with a linear margin when disassembled at the confluency. The cell sheet maintained in culture showed a unidirectional which was determined from the daily observation of tissue, allowed us to determine quantitatively the dynamic process of unidirectional endothelialization in vitro. The endothelialized distance and the endothelializing zone on a glass slide were found to be nearly 500 microns/day and 750 microns in width, respectively. Thus, the method developed here provided information of the 2-D tissue formation process. This model would be useful as an in vitro model which simulates the anastomotic endothelialization of an artificial vascular graft.

Animals↗
PubMed1992

[Development of a method to prevent degenerative changes of the vein graft for arterial reconstruction].

Autologous vein graft is frequently used for arterial reconstruction in vascular surgery. Its' long-term patency rate, however, is low because of the degenerative changes of the vein wall. Of the basis of our hypothesis that the degenerative changes are mainly caused by an over-distension of vein wall in arterial system, in this study, autologous vein grafts of rabbit (N = 56) were implanted in the carotid arteries. To prevent overdistension, some of the grafts were covered with prosthesis which was made of microporous, compliant biodegradable polyurethane and were compared with those without prosthesis. The integrity of the architecture of the vein wall covered with prosthesis was well preserved at 6 weeks after implantation, where the biodegradation of prosthesis induced an optimal arterialization of the vein grafts. The results indicate that this method may prevent the degenerative changes of vein wall such as fibrosis and intimal hyperplasia, which would cause poor long-term patency of vein graft used for arterial reconstruction.

Animals↗
PubMed1991

Overexpression of dimeric guanylyl cyclase cores of an atrial natriuretic peptide receptor.

Using a bacterial expression system, large amounts of the catalytic core of an atrial natriuretic peptide receptor guanylyl cyclase were produced and purified. After refolding the protein from a buffer containing urea, the enzyme had positively cooperative kinetics with a Hill coefficient, nH = 1.42 +/- 0.08. Size exclusion chromatography and denaturing polyacrylamide gel electrophoresis demonstrated that the enzyme is composed of homodimers with interacting catalytic sites.

Animals↗
PubMed1990

[A case of "chronic expanding hematoma", with an intrapulmonary fresh hemorrhage resected 25 years after thoracic injury].

A case of a 60-year-old man who had a chronic expanding hematoma with an intrapulmonary fresh hemorrhage in the right thorax is reported. He suffered blunt trauma of his right thorax in a traffic accident 25 years ago. He has no symptoms and signs after the accident. But he had hemoptysis twice and he was taken to our hospital. He underwent the resection of the chronic expanding hematoma and right lower lobe of the lung. The surgical specimen consisted of the hematoma measuring 17 x 13 x 6 cm. The chronic expanding hematoma contained aseptic brownish muddy substances. The patient recovered without complications and hemoptysis. Chronic expanding hematomas occur in many locations, often simulating neoplasms. Although the mechanism of chronic expanding hematoma is unclear, the self-perpetuating expanding nature of the lesion may appear to be due to the irritant effects of blood and its breakdown products, causing repeated exudation or bleeding from capillaries in the granulation tissue.

Chronic Disease↗
PubMed1989

Intracellular predominance of the pyridoxal 5'-phosphate form of aspartate aminotransferase in Escherichia coli B and reversible transformation of this form by extracellular substances.

The intracellular proportion of the pyridoxal 5'-phosphate form of aspartate aminotransferase to the total enzyme in E. coli B cells was determined by a newly devised method, dependent on selective inactivation of the intracellular pyridoxal 5'-phosphate form of the enzyme by extracellularly added sodium borohydride. A large portion (80-99%) of the intracellular aspartate aminotransferase was in pyridoxal 5'-phosphate form in both natural and synthetic medium-grown bacterial cells. The intracellular predominancy of pyridoxal 5'-phosphate did not vary during the growth of bacteria and during incubation of bacterial cells in various kinds of buffers with different pH values. In contrast, the saturation levels generally used to describe in vivo the proportions of the apo and holo vitamin B6-dependent enzymes did not reflect the intracellular amount of the pyridoxal 5'-phosphate (holo) form of aspartate aminotransferase probably because the intracellular pyridoxal 5'-phosphate form was changed to an apo form by the disruption of bacterial cells for preparing crude extract. Various extracellularly-added vitamin B6 antagonists decreased the intracellular amount of pyridoxal 5'-phosphate without decrease in the total intracellular activity of the enzyme. The modified forms were stable in E. coli B cells and reversed into pyridoxal 5'-phosphate form by incubation of the antagonist-treated cells in the buffer containing pyridoxal. The present results showed that the sodium borohydride reduction method can be used for further analysis of the in vivo interaction of pyridoxal 5'-phosphate and apoaspartate aminotransferase. The fact that about 50% of the intracellular pyridoxal 5'-phosphate form was changed to a modified form without impairment of cell growth in the presence of 4-deoxypyridoxine, and that about 50% of intracellular modified aspartate aminotransferase was reversed to pyridoxal 5'-phosphate by the removal of antagonist followed by incubation suggested that there exists characteristically 2 different fractions of pyridoxal 5'-phosphate forms of aspartate aminotransferase in E. coli cells.

Aspartate Aminotransferases↗
PubMed1989

[A case report of successful treatment using ECMO in severe status asthmaticus during open heart surgery].

A 6-year-old boy who had a history of asthma attack since 3 years old, but whose symptom was well controlled with medication received a radical operation for ASD. During the operation, he suffered from severe asthma attack. In blood gas analysis, PCO2 was increased to 302 mmHg with a decrease of pH to 6.740. Every conventional treatment for asthma attack was not effective, and then extracorporeal membrane oxygenation (ECMO was performed within 2 hours after operation. Blood gas data normalized and his hemodynamic condition was well maintained by ECMO. After 4 hours 20 minutes, he was weaned off from ECMO. Post operative course was uneventful except for pneumothorax.

Asthma↗
PubMed1989

[Postoperative thromboembolism of acquired mitral valve disease--comparison between valve replacement and commissurotomy].

Thromboembolism after mitral commissurotomy (MC) was compared with that after mitral valve replacement (MVR). In 216 surgical cases of acquired mitral valve diseases, including combined operative cases of other valves, thromboembolic complications after MC were observed in 9/137 cases (13 times, 0.94%/patient-year), and those after MVR in 8/70 cases (11 times, 2.55%/patient-year). No thromboembolism occurred in 9 cases of annuloplasty. Thromboembolism-free period after MVR (49 +/- 44 months) was significantly shorter than that after MC (102 +/- 43 months, p less than 0.05). Postoperative CTR of thromboembolic cases (69.5 +/- 8.2%) was significantly larger than that of non-thromboembolic cases (61.4 +/- 9.9%) in MVR group (p less than 0.005), but no significant difference existed between thromboembolic and non-thromboembolic cases in MC group. Thromboembolism after MVR occurred in severe cases, but that after MC often occurred in mild cases. Postoperative echocardiogram of MC group showed significantly lower DDR in thromboembolic cases (1.9 +/- 0.7 cm/sec) than in non-thromboembolic cases (3.2 +/- 1.2 cm/sec, p less than 0.025). Mitral valve area (MVA) of all re-stenotic cases in thromboembolic cases after MC was under 1.5 cm2, comparing that in non-thromboembolic cases there were only two cases that had MVA under 1.5 cm2. After MC, careful management including anticoagulant therapy and reoperation is necessary especially in patients with atrial fibrillation, DDR under 2 cm/sec, and MVA under 1.5 cm2, even though they don't have cardiomegaly.

Adult↗
PubMedDate not supplied

An autologous connective tissue tube with high healing ability as a small diameter vascular substitute with temporary antithrombogenicity.

Although autologous connective tissue grafts (ACTG) are an ideal vascular substitute, they have not yet been used as small diameter vascular grafts because of thrombogenicity. We reported on ACTGs in which mesh tubes were fabricated from ultra-fine polyester fibers (UFPF) and used as a framework. Antithrombogenicity was established using an original heparinization method, with a 50% patency 1 month postimplantation. Early failure of these grafts was caused mainly by loss of antithrombogenicity before development of endothelialization on the inner surface. In this study, higher concentrations of heparin were used for in situ heparinization of the grafts before implantation in combination with antiplatelet therapy (cilostazol, OPC-13013 for the first month after substitution for canine carotid arteries. As a result, more complete healing of the grafts was attained, with a patency rate of 63% at 1 month, when small doses of antiplatelet agents were used. More intensive antiplatelet therapy resulted in impairment of graft healing, causing hematomas around the grafts. Thus, optimal doses of antiplatelet agents remain uncertain.

Animals↗
PubMedDate not supplied

Development of ultrafine polyester fiber vascular grafts with high endothelialization capability. Angiogenesis by ultrafine polyester fibers.

The authors previously showed that a vascular prosthesis made of ultrafine polyester fibers (UFPF) had high healing ability even when of low porosity. In this study, new highly porous vascular grafts fabricated from UFPF (water porosity: 3,600 ml/min/cm2, 8 mm in inner diameter and 5 cm in length), were developed and implanted in the thoracic descending aorta of dogs to evaluate their endothelialization capability. Two weeks after implantation, many colonies of endothelial cells with openings of capillary blood vessels were noted, even in the middle portion of the grafts. Numerous fibroblasts and capillary blood vessels were also observed in the synthetic walls. These results suggest that UFPF vascular grafts provide a suitable microenvironment for infiltration and proliferation of fibroblasts, which are accompanied by the capillary formation as nutrient supply; these capillaries provide multiple sources of endothelial coverage on the luminal surface. It is expected that the new, highly porous vascular grafts may have rich endothelialization capability and stable healing properties in humans.

Animals↗
PubMedDate not supplied

Control of cellular orientation in two-dimensional tissue formation. Surface topologic effect of collagen fibers on endothelialization.

The authors studied the effect of polymorphous states of collagen on in vitro cellular orientation of bovine aortic endothelial cells (ECs). Little orientation of adherent ECs was observed on a nonoriented collagen coated surface, irrespective of culture period. Only ECs that adhered to fiber bundles 10 microns in diameter exhibited cellular elongation or alignment. The collagen membrane with highly oriented fine fibers provided no cellular alignment for ECs in sparse culture. Resultant confluent monolayers, however, were characterized by cellular orientation, suggesting that surface microtopology of collagen induces cellular orientation on incubation. Control of cellular orientation would be an elementary requirement for cell seeding technology leading to hybrid artificial organs.

Animals↗
PubMedDate not supplied

Experimental study on limitations of anastomotic endothelialization of vascular prostheses.

We studied the effect of endothelial cell (EC) senescence on proliferation, migration, and endothelialization in vitro using a culture model. Two generations of cultured bovine aortic ECs were used. The results showed that 1) the senescent ECs had much reduced rates of proliferation, migration, and endothelialization in vitro, and 2) that the young ECs at the leading edge gradually developed morphology similar to that of the senescent ECs as endothelialization proceeded. Computerized videomicroscopic observation revealed that the ECs at the leading edge had higher motile activity than the ECs at the back. This suggests that the ECs at the leading edge, and circumvented from contact inhibition, may proliferate much more frequently than the ECs at the back. Localized cellular aging may result in decelerated or incomplete endothelialization, as found clinically.

Anastomosis, Surgical↗
PubMedDate not supplied

Healing process of vascular prostheses seeded with venous tissue fragments.

Rapid neointima formation in fabric vascular prostheses seeded with autologous venous tissue fragments was examined. A piece of peripheral vein was minced into small fragments and stirred into 20 ml of saline. This tissue suspension was sieved through the wall of Dacron prostheses. The prostheses implanted in the descending aortae of dogs showed extremely rapid healing of the neointima. Endothelial cells lined the entire luminal surface within 14 days. There was no difference in the healing process between the area near anastomotic sites and the center.

Animals↗
PubMedDate not supplied

In vitro model of endothelialization at anastomotic sites.

Endothelial cell (EC) migration from native arteries to vascular prostheses is one of the most important healing processes of implanted artificial grafts, which results in endothelial cell coverage of the luminal surface of the graft. This article presents an in vitro model of endothelialization at the anastomotic site, which can provide cellular level information on morphologic reconstruction, and its substrate dependency. Test materials included polyethylene terephthalate (PET), segmented polyurethanes (SPUs), and glass with or without protein precoating (collagen, fibronectin, and albumin). In vitro endothelialization on these substrates was quantitatively determined by phase contrast microscopy. The results obtained show: 1) The fastest endothelialization rate was found on PET, followed by relatively hydrophobic SPU, and glass--the slowest was on hydrophilic SPU; and 2) Precoating with proteins drastically altered the cellular behaviors; collagen greatly enhanced endothelialization in vitro, followed by fibronectin. Precoating by albumin, however, greatly retarded endothelialization. The present study strongly suggests that unidirectional endothelialization at the anastomotic sites is controlled by the surface characteristics of graft materials.

Anastomosis, Surgical↗
PubMedDate not supplied

Endothelialization on various segmented polyurethanes: cellular behavior and its substrate dependency.

Endothelialization on artificial substrates is essential for providing vital function to artificial and hybrid vascular prostheses. The authors studied fundamental behaviors of endothelial cells (EC), including adhesion, spreading, migration, and growth, on various segmented polyurethanes (SPU) with a wide variety of wettability. Endothelialization has a synergistic action on these cellular behaviors that was quantitatively evaluated by phase contrast microscopy. Surface characteristics of SPU were analyzed by contact angle measurement and X-ray photoelectron spectroscopy. Adhesion, spreading, migration, growth, and endothelialization in vitro of bovine aortic EC on relatively hydrophobic SPU exceeded those on both a hydrophilic SPU, and a very hydrophobic siliconized one. Minimal interaction with EC was found for hydrophilic SPU. Adherent cells tended to be delaminated from siliconized SPU in a later culture period. The addition of a peptidyl antagonist of adhesive protein receptor inhibited adhesion of EC on SPU. These results suggest that surface characteristics, possibly regulating adsorption of adhesive proteins, are important factors in the development of vascular SPU prostheses.

Animals↗
PubMedDate not supplied

Development of an autologous connective tissue tube as a small caliber vascular substitute.

A small-caliber vascular graft with good healing properties was developed using an autologous connective tissue tube (ACTT) and in situ heparinization. ACTT is the best material for implantable grafts, but as a small-caliber vascular graft, both the high thrombogenicity and requirement for time to preparation in situ were serious problems. To overcome these difficulties, an ultrafine polyester fiber (UFPF) mesh was used for the framework of the graft. it has been shown that UFPF provides a good framework for fibroblast migration and proliferation both in vivo and in vitro. The granulomatous connective tissue tube could be constructed very rapidly and had numerous capillary blood vessels, which opened onto the luminal surface of the graft when it was implanted as a vascular substitute and provided colonies of endothelial cells. These colonies spread rapidly all over the luminal surface, and the graft developed permanent antithrombogenicity by endothelialization. The next problem was attainment of temporary antithrombogenicity of the graft before complete endothelialization. Since collagen fibrils are highly thrombogenic, the fact that ACTT collagen fibrils face the luminal surface requires greater antithrombogenicity. A new technique for binding heparin to collagen fibrils in situ was also developed. This was proved to be useful in maintaining the antithrombogenicity of the grafts (3 mm in inner diameter, 6 to 7 cm in length) in the animal studies. The graft showed rapid healing of the neonintima with endothelialization and long-term stability of the graft wall.

Angiography↗