Laboratory-grown corneas come into sight.
The products of that desperation, corneas built from laboratory-grown human cells, are described in the Dec. 10 SCIENCE. Such artificial tissues may help in the study of eye-wound healing, replace animals in some drug and cosmetic toxicology tests, and one day even serve as replacement corneas for people, say Griffith, Mitchell A. Watsky of the University of Tennessee College of Medicine in Memphis, and their colleagues.
The cornea--the window into the eye--has three cell layers. The outer one, called the epithelium, keeps foreign material out of the eye and helps distribute nutrients. Below that layer lies the stroma, containing water, the fibrous protein collagen, and cells called keratocytes. The endothelium, the innermost layer, has cells that remove excess water from the stroma to maintain the cornea's transparency.
To duplicate this structure, Griffith and her colleagues engineered each type of corneal cell to grow endlessly in the laboratory. They then laid down a sheet of epithelial cells and topped them with keratocytes infused into a collagen-containing matrix. Finally, they covered the matrix with endothelial cells.
The investigators grew the layered cells for 2 weeks in a medium containing vitamin C, which stimulates collagen production, and protease inhibitors, which slow degradation of the original collagen matrix. The resulting cornea had a transparency and internal structure closely resembling normal human corneas.
Moreover, the artificial corneas responded to chemicals much as corneas of live rabbits or donor human corneas do. Procter & Gamble Co., which helped fund the research, has begun to evaluate whether artificial corneas can substitute for animals in any of its toxicology tests, says Griffith.
Don't expect the artificial corneas in the eye clinic soon. Their long-term viability remains one of many open questions. Griffith's group hasn't tested the artificial corneas' longevity beyond 3 weeks. "At this point, I don't think they would last the lifetime of a person," she says.
"To think that we're close to an implantable artificial cornea would be stretching things," agrees ophthalmologist David G. Hwang of the University of California, San Francisco.
Still, Griffith and her team are looking into ways of improving the artificial corneas, such as strengthening the matrix supporting the cells in the stromal layer.
As the elderly population continues to increase, the demand for transplantable corneas will rise, notes Griffith. The popularity of laser eye surgery, which can rule out use of a person's cornea for later transplantation, may further reduce the supply. "We're already starting to see a shortage," says Griffith.
As a result, patients may turn to artificial corneas, even if they don't last. "At least [people] would see until a donor becomes available," says Griffith.
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|Article Type:||Brief Article|
|Date:||Dec 11, 1999|
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