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Biomedical subjects

B Sibanda

Publications and source records attributed to B Sibanda.

8 recordsLinked to original sources
PubMed2001

Development and characterization of tissue-engineered aortic valves.

Tissue-engineered aortic valves, known as recellularized heart valves, were developed by seeding human neonatal fibroblasts onto decellularized, porcine aortic valves. Recellularized heart valves were cultured up to 8 weeks in a novel bioreactor that imposed dynamic pulsatile fluid flow to expose the dermal fibroblasts to mechanical forces. Our data showed that, under static or dynamic flow conditions, dermal fibroblasts attached to and migrated into the decellularized, porcine valve scaffolding. The human cells remained viable as indicated by MTT viability staining. Gradual colonization of the decellularized porcine scaffolding by the human dermal fibroblasts was shown histologically by hematoxylin & eosin staining, immunocytochemically using a monoclonal antibody directed against prolyl-4-hydroxylase (an intracellular enzyme expressed by human fibroblasts synthesizing collagen), and quantitative digital image analyses. Thymidine and proline radiolabeled analog studies at 1, 2 and 4 weeks of individual leaflets cultured statically demonstrated that the human fibroblasts were mitotic and synthesized human extracellular matrix proteins, thereby supplementing the existing porcine matrix. The overall approach results in a heart valve populated with viable human cells. In the development of valves that perform in a similar manner as natural biological structures, this approach may present some unique benefits over current medical therapies.

Animals↗
PubMed1992

Long-term expression of a retrovirally introduced beta-galactosidase gene in rodent cells implanted in vivo using biodegradable polymer meshes.

Grafts of various types of cells have been performed using bioresorbable polymer matrices. These synthetic fibers are degraded by hydrolysis into normal metabolic intermediates and induce a number of events that are conductive to healing and/or repair, the most important of which may be angiogenesis. The use of biodegradable meshes to deliver genetically altered cells was studied. A beta-galactosidase gene was inserted into Long-Evans rat bone marrow stromal (BMS) cells or fibroblasts derived from C57BL/6J mouse embryos using the retroviral vector LNL-SLX beta gal. Expression was monitored using X-gal staining. X-gal+ cells from monolayer cultures were seeded onto either polyglycolic acid (PGA) or polyglactin (PGL) biodegradable meshes and grown to confluence. Two types of grafts were performed: (1) embryonic C57BL/6J mouse fibroblasts (EMF) into either nude mice or adult C57BL/6J mice, and (2) Long-Evans rat BMS into Long-Evans rats. Beta-Galactosidase activity was found for up to 152 days for EMF in nude mice, 123 days for EMF in adult C57BL/6J mice, and 90 days for grafts of syngeneic BMS cells into Long-Evans rats. Noninfected cells grafted using the same methods did not stain with X-gal.

Animals↗
PubMed1992

Differential effects of drugs upon hematopoiesis can be assessed in long-term bone marrow cultures established on nylon screens.

Hematotoxicity is associated with exposure to chemotherapeutic drugs and numerous other agents. Most measurements of the hematopoietic effects of prospective therapeutic drugs and environmental agents have been made in animal models. We tested the influence of various drugs on hematopoiesis in long-term cultures of Long-Evans rat bone marrow cells. These cultures were established on nylon screen-bone marrow stromal cell templates that were suspended in liquid medium. Previous phenotypic analyses of adherent zone cells of suspended nylon screen bone marrow cultures (NSBMC) using monoclonal antibodies and flow cytometry indicated that they maintain a multilineage character for extended periods in culture and display continuous proliferation of hematopoietic progenitors (colony-forming unit culture [CFU-C]). NSBMC of various ages were incubated for 21 hr with several concentrations of beta-D-cytosine arabinofuranoside, 5-fluorouracil, cyclophosphamide, or methotrexate. Adherent zone cells were dissociated enzymatically, phenotyped by flow cytometry, and assayed for colony-forming unit culture content. beta-D-cytosine arabinofuranoside, 5-fluorouracil, and methotrexate treatment of bone marrow cultures resulted in a dose-related diminution in colony-forming unit culture numbers in the adherent zones of NSBMC. Phenotypic analyses revealed similar trends but certain of these drugs manifested lineage specificities. Toxicity was also related to cyclophosphamide dose, but the presence of bone marrow stroma was necessary to demonstrate this effect in vitro. A subpopulation of these cells was found to metabolize ethoxyfluorescein ethyl ester to fluorescein after induction with 2,3,7,8-tetrachlorodibenzo-p-dioxin, an effect which was quantified by flow cytometry. NSBMC may be used to ascertain lineage-specific toxicities and evaluate the effects of drugs on the proliferation of hematopoietic progenitor cells.

Animals↗
PubMed1991

Hematopoiesis on suspended nylon screen-stromal cell microenvironments.

A three-dimensional culture system for the growth of primate and rodent bone marrow was developed in our laboratory. This method involves the seeding of stromal cells onto a nylon screen and the inoculation of fresh or cryopreserved bone marrow hematopoietic cells after stromal cell processes had extended across 3 to 4 out of every 5 mesh openings. Stromal cells attach, grow, and secrete matrix proteins which contribute to an intricate microenvironment for the support of multilineage hematopoiesis, which was observed for greater than 270 days in the rat model and for greater than 12 weeks in the human system, as evidenced by flow cytometry analysis and in vitro clonogenic assays. The adherent zones of these suspended nylon screen cultures consisted primarily of immature cells. These cultures could also be used as substrates for cytotoxicity measurements; treatment of rat bone marrow cultures of various ages with cytosine beta-D arabinofuranoside, cyclophosphamide, 5-fluorouracil, or methotrexate resulted in a dose-dependent decrease in CFU-C numbers and altered the phenotypic distribution of hematologic cells in the adherent zone. The use of a modification of this method to generate large numbers of active cytolytic cells after greater than 75 days culture of rat bone marrow-derived natural killer cells is described also. Suspended nylon screen bone marrow culture also has potential uses in genetic insertion and graft vs. host disease studies, blood component therapy, the evaluation of ex vivo purging programs, and in marrow expansion for transplantation.

Animals↗
PubMed1990

A pilot study for an HIV prevention programme among commercial sex workers in Bulawayo, Zimbabwe.

In a health education pilot study for a programme to reduce HIV transmission among commercial sex workers (CSWs), 113 CSWs were interviewed and observed in Bulawayo, Zimbabwe during 1989. The educational level of the sample was low and less than a quarter had another job, either as a self-employed vendor/hawker or a domestic servant. Inability to earn income in other ways was the major reason cited for engaging in commercial sex. Nearly half the sample went for check-ups every 3 months or more often. All interviewees had heard about AIDS, but they were uniformed about several facets of AIDS. CSWs reported that they worked an average of 3.6 nights a week, averaged 1.3 clients a night and charged a mean of U.S. $2.8 a session and U.S. $6.5 a night. CSWs reportedly saw a total of 221 clients in the past 7 days and used condoms with 87 (39.3%) clients. Nearly all CSWs said they had done something to reduce the risk of getting AIDS, but when asked what they had done, only 40% said they were using condoms more frequently and many cited ineffective precautions. CSWs who had a job, charged higher fees, experienced little client violence and believed that they were susceptible to AIDS were more likely to use condoms. Clients were a cross-section of Bulawayo society, with widely varying education, incomes and occupations and shared little except an interest in commercial sex. Ethnographic approaches demonstrated a lack of cohesion among CSWs and a consequent need to foster organized, motivated groups for health education, the importance of incorporating clients in health education and the feasibility of using bar security and sales personnel as health educators. It is concluded that health education is urgently needed among CSWs, but that it is equally important to direct health interventions at clients, many of whom are resistant to condom use.

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

A stereotypic, transplantable liver tissue-culture system.

A method of coculturing adult rat hepatic parenchymal cells (PC) and stromal cells in a three-dimensional framework of nylon filtration screens or biodegradable polymer meshes was developed in our laboratory. Rat liver stroma, which includes vascular and bile duct endothelial cells, fat-storing cells, fibroblasts, and Kupffer cells, were isolated by gradient centrifugation after in situ liver perfusion and expanded in monolayer culture prior to seeding onto nylon screens or bioresorbable polyglycolic acid (PGA) polymers oriented into a felt-like construct. A second inoculum of freshly isolated PC was applied after the stromal cells became established. Histological analyses revealed that PC proliferation occurred until all available space for expansion within the template was exhausted. These cells retained their rounded morphology, and after 4-5 wk 7-9 "layers" of PC filled the 140-microns deep template. Dioxin-inducible cytochrome P450 activity was detected for up to 58 d in culture, and albumin, fibrinogen, transferrin, and soluble fibronectin were detected in the medium by enzyme-linked immunosorbent assay (ELISA) for 48 d in vitro. Immunohistochemical analysis of sections through the cultures confirmed the presence of these proteins as well as cytokeratin at the cellular level; the extracellular matrix stained for both collagen type III and laminin. Long-term PC proliferation and function were enhanced by the presence of stromal cells as well as by a meshwork template whose geometry allows the interaction of PC with stroma and matrix on several different planes. To permit transplantation, cocultures of hepatic PC and stromal cells were established on PGA felt constructs instead of nylon screens. After approximately 24 d in vitro, these constructs were grafted into sites in the mesentery, omentum, and subcutaneous tissues of adult Long-Evans rats. The growth of hepatocytes after 30 d in situ was evident by histological analysis; grafts of cocultures regenerated a liver-like architecture consisting of sinusoids and putative biliary structures. In addition, PC at these extrahepatic graft sites were positive for albumin, transferrin, and fibrinogen synthesis by immunohistochemistry. Graft survival was enhanced when recipients were subjected to approximately 40% hepatectomy. Hepatic PC:stromal cell cocultures may prove useful in the restoration of liver function either by direct transplantation using PGA or similar templates, or as extracorporeal devices, using nylon screens.

Albumins↗