Ultraviolet B-Induced Corneal and Lens Damage in Guinea Pigs on Low-Ascorbic Acid Diet

Abstract

To evaluate ocular morphological response to ultraviolet B (UV-B) exposure in guinea pigs fed with normal and low-ascorbic acid (ASA) diets, 24 guinea pigs were randomly divided into UVR (normal diet + UV-B), LVC (low-ASA diet + UV-B) and CTL (normal diet, without UV-B) groups. The irradiated animals were exposed to 8.2 J/cm² of UV-B over 29 weeks. Changes in the cornea and lens were examined using a Scheimpflug camera, specular microscope and histological studies. ASA contents in the plasma, aqueous humor and lens sections were measured by high-performance liquid chromatography. The results showed low contents of ASA in the plasma, aqueous humor and lens sections in LVC. Both irradiated groups displayed corneal epithelial edema, neovascularization in stroma, increase in corneal thickness, decrease in endothelial density, and lens epithelial damage. No significant morphological differences in cornea and lens were found between guinea pigs fed with low-ASA or normal diet.

The cornea of Guinea pig: structural and functional studies

“…For histological evaluations three animals in each group were killed with an overdose of ketamine, 5 and the whole eyes or the corneas were excised. The specimens were differentially fixed and processed for conventional light microscopy (LM), immunohistochemistry (IHC), and transmission electron microscopy (TEM).…”

“…The entry mechanism of AA into the cornea and its biological function on this part of the eye has also been studied using Guinea pigs 5–8 …”

Protective Effect of Ascorbic Acid Against Corneal Damage by Ultraviolet B Irradiation

“…A study conducted by Wu et al 14 found no significant morphologic differences between the corneas of guinea pigs fed a low-ASA diet and those that were fed a normal diet. The authors of that study believed that the low-ASA diet they provided contained enough ASA to protect the cornea from UV irraditation 14 ; however, we speculated that the results of their study occurred because of the low level of ocular transport of ASA that occurred after oral administration. 19 Therefore, we conducted this study to determine whether augmentation of ASA through another administration route would be effective.…”

“…This element, which efficiently absorbs UV between 280 and 310 nm, 10 is maintained at concentrations 14 times greater in the cornea than in the anterior chamber by sodium-dependent ascorbic acid transporter 2 protein, 11 and several studies have suggested that ASA protects against cataract formation as a result of UV exposure both in vivo and in vitro. 12,13 Although a study conducted on the effects of UVB found no difference in the amount of UVBinduced corneal damage in guinea pigs that were provided with a low-ASA diet and those that were provided a normal diet, 14 there have been no reports describing the protective effects of ASA that was provided intravenously.…”

Effect of 5-S-GAD on UV-B-induced cataracts in rats

“…9 Such rat models were probably established by Wegener and Hockwin, 6 and Tuffs et al 8 In their models, it was shown that continuous exposure to UV-A and/or UV-B induced phanerosis of the Y-suture in the anterior capsule of lenses as early lenticular changes and also induced opacities in anterior subcapsular lenses. Higher doses and longer durations of UV-A exposure were required to induce cataractogenesis.…”