The Effects of Hyaluronic Acid on Canine Posterior Lens Capsule Opacification In Vitro
Creators:Haeussler, David Jr.
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Series/Report no.:2010 Edward F. Hayes Graduate Research Forum. 24th
Purpose: Posterior capsular opacification (PCO) is the most common complication following cataract surgery. During PCO formation, residual lens epithelial cells undergo posterior migration and proliferation. During dynamic cellular events such as inflammation and wound repair, hyaluronic acid (HA) interacts with cell surface receptors and can induce cellular migration and proliferation. HA is one of the components found in the viscoelastic agents commonly used intraoperatively during cataract surgery. The introduction of exogenous HA in the form of viscoelastics during cataract surgery may promote lens epithelial cell migration and thus contribute to PCO formation. Based on these observations the purposes of this research were 1) to confirm that HA receptors are present in the canine lens and 2) to determine if the rate of lens epithelial cell migration and proliferation is altered following treatment with HA. Methods: Canine lens epithelial cells from normal (n=12) and cataractous (n=12) lenses were evaluated using immunohistochemistry and RT-PCR for expression of CD44 and CD168. Two in vitro models of PCO were used to determine if various HA concentrations altered lens epithelial cell migration and proliferation. In the first model, a one millimeter scratch was created in cultures of confluent canine lens epithelial cells. Cells were treated with 0, 0.2, or 1.0 mg/mL (n=6) of HA dissolved in unsupplemented DMEM. Migration of lens epithelial cells into the scratch was monitored over 24 hours and quantified using ImageJ (available from the National Institutes of Health). In the second model, mock cataract surgery was performed on canine cadaver eyes. Following removal of lens fibres, capsules were re-distended and remaining lens epithelial cells were incubated with one of the following treatments (n=6): no viscoelastic (DMEM only), 0% HA viscoelastic (contains hydroxypropyl methylcellulose), 1.2% HA viscoelastic, or 2.0% HA viscoelastic. Treatment remained in the capsule for 5 minutes before removal by irrigation and aspiration. Capsules were monitored daily and the rate of migration and proliferation onto the posterior capsule was evaluated by counting all LEC adhered to the capsule in sequential H&E histologic sections. RT-PCR for CD44 and CD168 was performed on samples from both in vitro models of PCO. Results: Both normal and cataractous lens epithelial cells were positive for CD44 and CD168 protein and mRNA. In the first model of PCO, there was a significant increase in the rate of migration and proliferation in lens epithelial cells treated with 0.2 and 1.0 mg/mL of HA compared to lens epithelial cells receiving 0 mg/mL of HA (p = 0.001). Following treatment with both 0.2 and 1.0 mg/mL HA, there was an increase in CD44 and CD168 mRNA expression. In the second model of PCO, lens epithelial cells treated with either 1.2% or 2.0% HA-containing viscoelastics reached confluence on the posterior capsule significantly faster than lens epithelial cells receiving no or 0% HA viscoelastic (p=0.003). Expression of CD44 and CD168 was higher in capsules receiving HA-containing viscoelastic compared to controls, as determined by RT-PCR. Implications: Cataract is the most common cause of vision impairment in both dogs and humans, and surgery is currently the only accepted method for eliminating cataracts and related vision loss. PCO occurs in up to 50% of adult humans; in canine patients and pediatric humans, the incidence of PCO approaches 100%. This research demonstrates that canine lens epithelial cells possess the appropriate receptors to respond to HA signaling. Treatment with various HA concentrations increased the rate of lens epithelial cell migration, proliferation, and expression of CD44 and CD168. In addition, acute exposure to viscoelastics containing HA significantly increased the rate of PCO in vitro. The introduction of exogenous HA in the form of viscoelastics during cataract surgery may promote lens epithelial cell migration and thus contribute to PCO formation in vivo. These results may help both human and veterinary ophthalmologists determine which viscoelastics should be used intraoperatively to decrease the prevalence of PCO.
Professional Biological Sciences: 1st Place (The Ohio State University Edward F. Hayes Graduate Research Forum)
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