Antioxidant status of dog aqueous humor after extracapsular lens extraction

Abstract

We determined the antioxidant status of the aqueous humor after extracapsular lens extraction in 14 mongrel dogs weighing about 10 kg. The animals were examined by slit lamp biomicroscopy, applanation tonometry and indirect ophthalmoscopy. One eye was submitted to conventional extracapsular lens extraction and the other was used as control. Samples of aqueous humor were obtained by anterior chamber paracentesis before and at days 1, 2, 3, 7 and 15 after surgery. Total antioxidant status was determined as the capacity of aqueous humor to inhibit free radical generation by 2,2-azobis(2-amidopropane) chlorine. Ascorbic acid concentration was measured by HPLC with UV detection. Protein content was determined with the biuret reagent. Statistical analysis was performed by ANOVA followed by the Tukey-Kramer test. Protein concentration increased from 0.61 to 22 mg/ml 24 h after surgery. These levels were maintained and returned to normal at day 7. Total antioxidant capacity was reduced from 50 to about 30 min until day 3 and at day 7 it was equal to control. Ascorbic acid levels were reduced from 252 to about 110 µM and then returned to control values at day 15. Considering the importance of ascorbic acid concentration in aqueous humor for the maintenance of the antioxidant status of the anterior segment of the eye, the decrease of antioxidant defenses suggests that the surgical procedures promote an oxidative stress condition in the eye.

Antioxidants and the Integrity of Ocular Tissues

“…There is evidence that after lenticular surgery, the total antioxidant capacity of aqueous humor decreased up to 40%, mainly due to the decreased concentration of ascorbic acid [32, 48]. This fact was also observed in human patients with idiopathic acute anterior uveitis [50].…”

“…Also, ascorbate can act as a pro-oxidant in the presence of excessive concentrations of ions Fe +3 and Cu +2 [6, 7, 14]. Ascorbate was detected in cornea [31], aqueous humor [32, 33], lens [34], vitreous humor [35], and retina [29]. …”

“…The eye is a metabolically active organ, consuming large amount of ATP. In addition, the transparency of the cornea, aqueous humor, lens, vitreous and retina allows a constant photochemical ROS generation [17, 32]. All ocular tissues and fluids are susceptible to damage by oxidative stress; however, those described below affect severely the function of the eye due to the physical changes they undergo [18].…”

“…It has been determined that ascorbic acid plays a fundamental role as UV filters in mammals, having a greater concentration in the aqueous humor from diurnal animals than nocturnal animals [17]. Also, ascorbic acid concentration in aqueous humor is higher than blood plasma [32, 48, 49]. …”

“…Another source of formation of large amounts of ROS was observed after surgery, paracentesis, or uveitis due to an increase in the amount of proteins and cells in aqueous humor [32, 48]. There is evidence that after lenticular surgery, the total antioxidant capacity of aqueous humor decreased up to 40%, mainly due to the decreased concentration of ascorbic acid [32, 48].…”