Corneal epithelium, multilayered

Reconstituted HCE (order no. RHC/S/5) is available from Skinethic, Nice, France. It consists of transformed human corneal epithelial cells immortalized by Roger Beuerman from the Louisiana State University-Eye Center, New Orleans, USA. This reconstituted human corneal epithelium forms a multilayered cell culture model that does not exhibit tight junctions and is therefore unsuitable for in vitro drug transport studies. Main focus of the model is eye irritation and toxicity testing and it is commonly used in this area with good prediction qualities. Major advantage of this model is the high reproducibility and uniform appearance. The commercial availability provides a ready-to-use model that is easy to handle. 

Located on the edge of the transparent cornea, it maintains the junction with the opaque sclera. On the level of the epithelium, it is the transition between a multilayer scale-like corneal epithelium and a cylindrical conjunctival epithelium with two cellular bases, with continuity of the basement membranes. At the epithelial level, the cells of the comeal epithelium are gradually replaced by a conjunctival epithelium made of two layers of cylindrical cells accompanied by calyciform cells. 

Human Corneal Epithelium cells, which develop into a multilayered tissue that morphologically... 

Microscopically, the cornea shows a rather simple and multilayered structure that can be divided into six layers the epithelium, basement membrane, Bowman s layer, stroma, Descemet s membrane, and endothelium. The corneal tissue consists of three different cell types epithelial cells, keratocytes (corneal fibroblasts), and endothelial cells. The outermost corneal surface is covered with the preocular tear film, which is functionally associated with the cornea. The epithelial surface must be kept moist and smooth, a role played by the tear film in conjunction with a spreading function of the eyelids during blinking motions. Furthermore, the tear film provides a protection against infectious agents that may gain access into the eye. 

Another 3-D cornea model, comprising rabbit primary cultures of epithelial and stromal cells as well as mouse immortalized endothelial cells, was described in 1994 by Zieske and coworkers [70], They showed the influence of endothelial cells on the formation of a tightly packed, multilayered epithelium as well as the expression of laminin, type VII collagen, a6 integrin, keratin K3, and a-enolase. Furthermore, their findings suggested that the formation of an in vivo-like epithelium requires the cultivation of the 3-D corneal construct under AIC conditions. By contrast, LCC methods of cultivating corneal equivalents in the absence of endothelial cells failed to promote the expression of differentiation markers and basement membrane components. 

In another approach, Parnigotto and coworkers reconstructed corneal structures in vitro by using corneal stroma containing keratocytes to which corneal epithelial cells from bovine primary cultures were overlaid [73], However, this particular corneal model did not contain an endothelial layer. This model was histochemically characterized and the toxicity of different surfactants was tested using MTT methods. This stroma-epithelium model has been reported to show a cornea-like morphology, where a multilayered epithelial barrier composed of basal cells (of a cuboidal shape) and superficial cells (of a flattened shape) is noted. Furthermore, the formation of a basement membrane equivalent and expression of the 64-kDa keratin were reported, indicating the presence of differentiated epithelial cells. The toxicity data for various surfactants obtained with this model correlate well with those seen by the Draize test [73], However, this corneal equivalent was not further validated or used as a model for permeation studies. 

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