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P. A. Simmons, J.-E. Chang-Lin, Q. Chung, J. G. Vehige, D. Welty; Effect of Compatible Solutes on Transepithelial Electrical Resistance and Uptake in Primary Rabbit Corneal Epithelial Cell Layers Model. Invest. Ophthalmol. Vis. Sci. 2007;48(13):428.
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Compatible solutes (CS) are small non-ionic compounds that are used by many tissues to protect cellular function from damage due to hyperosmolarity, as may occur on the ocular surface in dry eye. We examined the protective effect of CS on cellular function using trans-epithelial electrical resistance (TEER) in primary culture of rabbit corneal epithelial cell layers (RCrECL). In addition, the uptake mechanism was assessed.
Corneal epithelial cells harvested from New Zealand White rabbits were cultured on TranswellTM filters until development of a confluent multilayer (Day 4-5). Osmotic stress was induced by addition of hypertonic (350-600 mOsmols/kg) solution to the apical (tear) compartment of the RCrECL cultures for up to 24 hrs, with the basolateral side maintained in isotonic (300 mOsm/kg) solution. Cultures were exposed to hypertonic fluid with or without addition of single or combinations of CS. CS included the animo acids taurine, betaine, and L-carnitine, and the polyols glycerol, erythritol, xylitol, and myo-inositol. Cellular function and integrity was determined by TEER measurement over time. Uptake and inhibition studies were conducted using radiolabeled CS. Uptake samples were collected and analyzed by liquid scintillation counter.
Hyperosmolarity induced either by NaCl or sucrose indicated TEER was a sensitive dose-dependent barrier function endpoint. CS were evaluated under hypertonic conditions at 0.5-100 mM concentrations. In addition, glycerol was evaluated at 0.5% (54.4 mM) and 1% (109 mM). The results demonstrated that all CS have some osmoprotective ability, with an optimal concentration range of 2-20 mM for amino acids and 0.2-1% for polyols. For CS combinations, two or three CS at different concentrations were evaluated and the results indicated that several combinations tested showed synergistic osmoprotective activity. Cellular uptake and inhibition studies indicated that L-carnitine and the polyols such as glycerol, xylitol and erythritol may be taken up by amino acid transporter(s) and aquaglyceroporin channel(s) known to exist in the corneal epithelium, respectively.
Compatible solutes such as L-carnitine, erythritol and glycerol may modulate different cellular activities to protect corneal epithelium from barrier dysfunction due to osmotic stress. Combinations of compatible solutes in artificial tears may provide benefit to dry eye patients.
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