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Biomedical subjects

G B Köveker

Publications and source records attributed to G B Köveker.

10 recordsLinked to original sources
PubMed2000

Growth factors in clinical practice.

Wound repair consists of a complex interaction of cellular and biochemical events. Several growth factors have been identified as regulatory polypeptides co-ordinating the healing process. Although it is not known precisely why chronic wounds do not follow the normal pattern of healing, diminished growth factor content and accelerated growth factor degradation may contribute to poor healing. Topical application of different factors exert stimulatory effects on wounds in animal models. Human data are limited but the most investigated compound is recombinant human platelet-derived growth factor-BB (rhPDGF-BB). PDGF-BB enhances granulation tissue formation and facilitates epithelialisation. Clinical trials in patients with 'hard to heal' diabetic foot ulcers demonstrated significant improvement in the 'healing rate' and the 'time to healing' compared with controls. Refinement of therapeutic strategies with growth factors will take place in the future.

Chronic Disease↗
PubMed1999

Polyurethane vascular prostheses decreases neointimal formation compared with expanded polytetrafluoroethylene.

PURPOSE: Synthetic grafts have been increasingly used for complex vascular reconstructions in patients with limited autologous vein availability. Materials currently in use induce increased stenosis and graft thrombosis compared with autologous vein, especially in smaller vessels. We examined whether grafts constructed of a porous biodegradation-resistant polycarbonate polyurethane (PU) exert better biocompatibility in terms of faster endothelialization and decreased chronic proliferation of intimal cells compared with expanded polytetrafluoroethylene (ePTFE). METHODS: PU or ePTFE interposition grafts were implanted into the abdominal aortas of male Sprague-Dawley rats (PU, n = 37; ePTFE, n = 32). Grafts were removed at days 1, 7, 14, 28, and 56 and 6 months and were evaluated by immunohistochemical, electron microscopic, and morphometric techniques. Bromodeoxyuridine (BrdU) was injected at 1 and 24 hours before death to determine cellular proliferation. Endothelial cells and smooth muscle cells were identified with antibodies to von Willebrand factor and alpha-actin, respectively. RESULTS: The luminal surface of PU grafts took 4 weeks to completely endothelialize, whereas ePTFE grafts took 24 weeks (P <.05). Neointimal cell proliferation was lower in PU grafts compared with ePTFE at 56 days (1.4 +/- 0.1 versus 8.6 +/- 1.5, P <.001) and at 6 months (0.15 +/- 0.002 versus 3.4 +/- 0.5, p <.001). Neointimal thickness at 6 months after implantation was 3.2 +/- 0.8 micrometer for PU compared with 10.3 +/- 3.1 micrometer for ePTFE (P <.05). CONCLUSION: Polycarbonate polyurethane small vascular prostheses promoted faster luminal endothelialization, induced less chronic intimal proliferation, and produced a significantly thinner neointima than ePTFE grafts. These findings suggest that aliphatic-polycarbonate urethanes may offer advantages over standard materials such as ePTFE for vascular graft construction.

Animals↗
PubMed1994

Experimental improvement of microvascular allografts with the new material polyurethane and microvessel endothelial cell seeding.

The major aim of this experimental study was the improvement of hemo- and biocompatibility of microvascular allografts. Comparison of polyurethane and ePTFE (expanded polytetrafluoroethene) micrografts did not show a significant advantage of the new material polyurethane. When the endothelial cell seeding method was applied, endothelial cell harvesting from rat fat proved to be very difficult. Therefore, further research on microvessel endothelial cell seeding is planned.

Animals↗
PubMed1993

[Hereditary thrombophilia as a cause of recurrent transplant thromboses].

We report a case of hereditary protein S and protein C deficiency which are a rare defects of the anti-coagulation-system. Protein S is a vitamin K dependent glycoprotein that functions as a cofactor to activated Protein C in the inactivation of coagulation factors V and VIIIa. A deficiency of these proteins caused by a genetic defect increase the risk of recurrent thrombosis at a younger age. Acquired decreases in protein S and C concentration have been reported in connection with age, sex, pregnancy and with oral anticonception. The higher risk for thrombotic diseases of patients with thrombophilia requires a sufficient treatment and prophylaxis, e.g. with fresh frozen plasma or a protein C concentrate.

Adult↗
PubMed1991

Extracellular matrix preparation of expanded polytetrafluoroethylene grafts seeded with endothelial cells: influence on early platelet deposition, cellular growth, and luminal prostacyclin release.

The importance of blood and extracellular matrix precoating of expanded polytetrafluoroethylene (ePTFE) grafts on the effectiveness of endothelial cell (EC) seeding was assessed in a canine experimental model. Part I of the study documented ex vivo platelet deposition in 256 ePTFE grafts, 6 cm x 4 mm internal diameter, after implantation as femoral artery-femoral vein or carotid artery-jugular vein arteriovenous shunts. These conduits were precoated with blood, fibronectin, laminin, or collagen type IV with laminin, after which they were seeded with enzymatically derived and cultivated venous canine endothelium at a density of 30,000 to 40,000 EC/cm2 of graft surface. Luminal deposition of Indium 111-labeled platelets, expressed as 10(8) platelets/cm2, at 30 minutes (n = 176) and 24 hours (n = 80), respectively, was 2.29 and 0.30 for blood, 2.83 and 0.37 for fibronectin, 0.99 and 0.08 for laminin, and 0.98 and 0.11 for collagen type IV with laminin. Part II of the study documented in vivo luminal EC coverage at 14 days of 6 cm x 4 mm internal diameter ePTFE femoral or carotid arterial grafts (n = 8) prepared in the same manner as part I ex vivo shunt grafts. EC coverage with blood, fibronectin, laminin, and collagen type IV with laminin preparation was 42%, 49%, 44%, and 52%, respectively. The graft:carotid artery ratio of luminal 6-keto-PGF1 alpha release at 14 days with these same four preparations was 0.38, 0.31, 0.35, and 0.32, respectively. Precoatings of ePTFE prostheses with fibronectin, laminin, and collagen type IV are known to enhance the initial attachment of seeded EC. Fibronectin caused an insignificant increase in early platelet accumulation; laminin or laminin with collagen type IV preparations were associated with significantly less (p less than 0.005) deposition of platelets when compared to whole blood preparations. Most importantly, none of the four preparation techniques resulted in different in vivo rates of EC growth or luminal release of prostacyclin from conduits studied 14 days after implantation.

Animals↗
PubMed1989

[Incidence of recurrence following surgery of perforating and non-perforating complications in Crohn disease].

From 1980-1987 131 patients were operated for Crohn's disease. Among these 73 patients had perforated (PC) free perforation, abscess, fistula, and 47 had nonperforating complications (NC). Ileums, bleeding, stenosis reoperations (58 pts, 44%) were seen more often in the PC-group (57%) compared to 31% in the NC-group. Furthermore there was a high concordance in the indication for the initial and subsequent operations.

Adult↗
PubMed1988

Endothelial cell seeding of expanded polytetrafluoroethylene vena cava conduits: effects on luminal production of prostacyclin, platelet adherence, and fibrinogen accumulation.

The blood-surface interface of 12 mm ID x 5 cm ePTFE vena cava conduits, unseeded (n = 8) and seeded (n = 8) with enzymatically derived autologous endothelial cells, was studied in a canine model at 4 and 12 weeks after graft implantation. Acetylsalicylic acid (325 mg each day) and Coumadin (prothrombin time 1.4 to 1.7 times the control value) were administered preoperatively and continued 4 weeks postoperatively. Platelets labeled with 111In and 125I-labeled fibrinogen were administered 24 hours before graft removal. Luminal platelet adherence, expressed as 10(6) platelets/cm2 of graft surface, was 8.9 +/- 5.6 vs. 56.4 +/- 8.0 (p less than 0.008) and 4.0 +/- 0.9 vs. 12.4 +/- 2.3 (p less than 0.005) in seeded vs. unseeded grafts at 4 and 12 weeks, respectively. Luminal fibrinogen deposition, expressed in micrograms per square centimeter of graft surface, was 11.8 +/- 2.2 vs. 32.0 +/- 2.0 (p less than 0.06) and 6.1 +/- 2.4 vs. 12.4 +/- 6.3 (p less than 0.005) in seeded vs. unseeded grafts at 4 and 12 weeks, respectively. Cumulative 4- and 12-week luminal production of 6-keto-PGF1 alpha from seeded and unseeded grafts represented 11% and 5%, respectively, of that produced from the native iliac vein. Luminal endothelial cell coverage was 71% +/- 22% vs. 33% +/- 9% and 79% +/- 8% vs. 55% +/- 8% (p less than 0.05) in seeded and unseeded grafts at 4 and 12 weeks, respectively. Although endothelialization was not complete in seeded vena cava grafts, it is clear that seeded prostheses exhibited improved thromboresistance compared with unseeded conduits.

Animals↗
PubMed1986

Reduction of thrombogenicity in small-diameter vascular prostheses seeded with autologous endothelial cells.

In a canine model small-diameter vascular grafts of knitted Dacron were seeded with autologous endothelial cells. Four weeks after surgery the grafts were removed. Seeded grafts showed a pseudo-intima covered by a monolayer, whereas control grafts showed a cellular lining only at the anastomoses. Graft pretreatment with either fibrin glue or autologous blood in combination with endothelial cell seeding promoted the neointima formation.

Animals↗