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ABSTRACT: This study was initiated to evaluate tissue acceptance and stability of a novel type VI collagen preparation (CxGelsix) as a biomaterial in the rabbit corneal stroma. We hypothesized that CxGelsix, embedded intrastromally, does not have any adverse affect on surrounding corneal tissues, and remains intact in the presence of an acute inflammatory reaction during corneal wound healing.
Type VI collagen was extracted and purified from rabbit corneal stroma under nondenaturing conditions. This preparation, Gelsix, was concentrated and cross-linked with polyethylene glycol to produce a transparent film (CxGelsix). Discs of CxGelsix, 4.0-mm diameter, 9- to 35-microm thick were implanted intrastromally and clinically examined periodically for 4 months. In another experiment, implantation of CxGelsix, 2.0-mm-diameter, was followed by corneal wounding adjacent to the implant and examined clinically for 30 weeks. At the end of these periods, the tissues from these experiments were processed for light and transmission electron microscopy.
An intralamellar 4.0-mm-diameter disc of CxGelsix does not alter the structure of corneal epithelium above the implant, suggesting normal transport of nutrients through CxGelsix. Moreover, no structural abnormalities were seen in the rest of the cornea, and the cornea remains transparent. Although the cornea accepts the presence of CxGelsix disc as judged by clinical criteria, gradual degradation of the implant is seen ultrastructurally. CxGelsix is remarkably stable despite its exposure to endogenous enzymes during inflammation and wound healing. Partial degradation of the implant occurs only after many months, and it is gradually replaced with bundles of fine collagen fibrils reminiscent of normal cornea.
The results of this study suggest that CxGelsix is potentially useful as a biomaterial.
Cornea 04/2000; 19(2):194-203. · 1.73 Impact Factor
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ABSTRACT: To identify a protein that copurifies with type VI collagen from rabbit cornea and to determine its cell source in rabbit corneal tissues by in situ hybridization.
Type VI collagen was extracted from cornea with urea and purified by ammonium sulfate precipitation and gel chromatography. The purity of the collagen was assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). On reduction with mercaptoethanol or dithiothreitol, the alpha chains of type VI collagen ran into the gel. In addition to the type VI collagen polypeptides, an extra 68-kDa protein band appeared, suggesting that this protein is present as a large molecular weight component before reduction. Amino acid sequencing indicated that protein was related to beta ig-h3 from humans. Western blot analysis was used to determine immunologic similarity to this human protein. A rabbit stromal cell cDNA library was screened with human beta ig-h3 cDNA probe. Positive clones were sequenced and analyzed for sequence homology. Oligonucleotide probes prepared from rabbit cDNA sequences were used for Northern blot analysis and in situ hybridization of corneal tissues.
Electroblotting of the SDS-PAGE and amino acid sequence analysis of the first 10 N-terminal amino acids of the 68-kDa band gave 100% homology with a known protein produced by human adenocarcinoma cells, beta ig-h3. This 68-kDa protein was identical immunologically to beta ig-h3 by Western blot analysis. Sequence analysis of a rabbit cDNA clone contained the whole coding region and had high identity with both human beta ig-h3 and mouse beta ig-m3. The deduced amino acid sequence had 92% identity with these species. An oligonucleotide probe from the rabbit cDNA sequence detected a single band of mRNA from cultures of stromal cells consistent in size with human beta ig-h3 mRNA. The authors refer to the rabbit form of beta ig-h3 as beta ig because the protein was obtained from normal rabbit cornea and the mRNA comes from primary cultures of rabbit stromal cells and not from a cloned cell line. In situ hybridization of rabbit corneal tissue indicated that the beta ig mRNA is located primarily in the epithelium of normal adult cornea, in fetal stromal cells, and both endothelium- and stroma-derived cells in healing corneal wounds. Normal adult endothelium and stroma did not show beta ig mRNA label.
The highly conserved amino acid sequence homology between the human, mouse, and rabbit proteins and the temporal expression of beta ig message during corneal healing and development suggest this protein plays an important role in the morphogenesis of corneal tissues.
Investigative Ophthalmology & Visual Science 05/1997; 38(5):893-900. · 3.60 Impact Factor
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ABSTRACT: To identify the cell types responsible for type XII collagen synthesis in normal and healing rabbit cornea, a partial cDNA sequence of rabbit type XII collagen, obtained from an adult rabbit cornea cDNA library, was used to develop highly specific oligonucleotide probes for Northern blot analysis and in situ hybridization. Approximately 2000 bases of a type XII collagen 2.2 kb cDNA clone were sequenced. Comparative sequence analysis of the bases showed a 74% identity with chick alpha 1 (XII) chain of type XII collagen. The deduced amino acid sequence indicated a 72% identity with chick type XII collagen. Northern blot analysis showed that cultures of cornea stromal and endothelial cells each contain two RNA species, greater than 10 kb, that hybridize to rabbit type XII collagen oligonucleotide probes. Although normal stromal cells failed to show type XII collagen mRNA, normal endothelial cells contain mRNA for this collagen. These results indicate that endothelium of normal rabbit cornea has a potential to synthesize type XII collagen. During corneal wound healing, both endothelium-derived and stroma-derived cells in the developing scar tissue contained type XII mRNA. In view of the known presence of type XII collagen in corneal stromas from chick and mouse, the distribution of mRNA in normal cornea is puzzling.
Experimental Eye Research 06/1995; 60(5):551-61. · 3.26 Impact Factor
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ABSTRACT: To develop molecular probes and to identify the cell types responsible for decorin synthesis in healing cornea.
Adult rabbit cornea and rabbit corneal stromal cell (keratocyte) culture cDNA libraries were constructed. The libraries were screened with commercially available human cDNA and oligonucleotide probes. Positive clones were sequenced to obtain a full length rabbit decorin cDNA. Synthetic oligonucleotides for rabbit decorin were chosen as probes for Northern blot analysis and in situ hybridization of healing rabbit corneas.
The cDNA sequences of the positive clones from the two libraries were identical in areas of overlap. The combined cDNA sequence indicated a 1.5-kb length with a complete open reading frame for decorin. The cDNA and deduced amino acid sequences are 90% and 88% identical, respectively, to previously reported human fibroblast and bovine bone decorin sequences. A hypervariable region near the N-terminal has little homology to decorins of other species or other rabbit protein. Northern blot analysis detected a 2.0-kb and a 2.3-kb band in mRNA from rabbit keratocyte cultures. Decorin mRNA was detected in keratocytes of normal and healing rabbit corneas by in situ hybridization. Label in the healing tissue was markedly increased above normal. Normal endothelium and epithelium in normal and healing cornea failed to show label.
Decorin mRNA from normal adult rabbit cornea is identical to decorin mRNA from keratocytes in culture and is highly homologous to decorin from other animal species. In situ hybridization indicated an upregulation of decorin message in cells adjacent to and within the healing tissue. Both stroma-derived and endothelium-derived cells in the wound synthesize message for decorin.
Investigative Ophthalmology & Visual Science 02/1995; 36(1):206-15. · 3.60 Impact Factor
