Protective effects of N-acetylcysteine on triamcinolone acetonide-induced lens damage in rats

Protective Action of Hydrogen Sulfide-Releasing Compounds against Oxidative Stress-Induced Cataract Formation in Cultured Bovine Lenses

PURPOSE

The gaseous signalling molecule, hydrogen sulfide (H₂S) has antioxidant, anti-inflammatory and anti-apoptotic properties. Since oxidative stress has been implicated in the pathogenesis of cataracts and lenticular hydrogen peroxide (H₂O₂) is elevated in some cataract patients, the present study investigated the ability of H₂S-releasing compounds to prevent H₂O₂-induced cataract formation in cultured bovine lenses.

METHODS

Lenses were cultured in either Dulbecco's Modified Eagle Medium (DMEM; control); H₂O₂ (50 mM); ascorbic acid (AA; 3 mM) (positive control); and the H₂S-releasing compounds (diallyl trisulfide [DATS] or GYY4137) in the presence of H₂O₂ (50 mM). Lens opacity was determined using a plate reader to measure transmittance. Lens glutathione content (GSH), superoxide dismutase (SOD) activity and lactate dehydrogenase (LDH) cytotoxicity were assessed before and after treatment with the H₂S-releasing compounds.

RESULTS

Both DATS (10^-7M - 10^-4M) and GYY4137 (10^-7M - 10^-4M) significantly (p < .001) attenuated H₂O₂ (50 mM)-induced loss in transmittance, with DATS (10^-4M) and GYY4137 (10^-7M) achieving a maximal reversal of opacity by 56.86 ± 0.01% (n = 6) and 8.39 ± 0.11% (n = 6) after 120 hours, respectively. These observations were corroborated by photographic evaluation, where DATS (10^-5M - 10^-4M) and GYY4137 (10^-7M - 10^-5M)-treated lenses had relatively clear grids after 120 hours, compared to H₂O₂ (50 mM)-treated lenses. The H₂O₂ (50 mM)-induced decline in total GSH content and total SOD activity were significantly (p < .001; n = 5) reversed by DATS (10^-4M) and GYY4137 (10^-7M). After 24 hours, DATS (10^-4M) and GYY4137 (10^-7M) significantly (p < .001; n = 4) reduced cytotoxicity of primary bovine lens epithelial cells by 33.88 ± 4.59% and 36.19 ± 10.53%, respectively.

CONCLUSION

Both H₂S-releasing compounds protected cultured bovine lenses against oxidative stress-induced cataract formation. The slow-releasing H₂S compound, GYY4137 was more potent than DATS in restoring lenticular total GSH content and total SOD activity along with reducing H₂O₂ (50 mM)-induced cytotoxicity.

Current Trends in the Pharmacotherapy of Cataracts

Cataracts, one of the leading causes of preventable blindness worldwide, refers to lens degradation that is characterized by clouding, with consequent blurry vision. As life expectancies improve, the number of people affected with cataracts is predicted to increase worldwide, especially in low-income nations with limited access to surgery. Although cataract surgery is considered safe, it is associated with some complications such as retinal detachment, warranting a search for cheap, pharmacological alternatives to the management of this ocular disease. The lens is richly endowed with a complex system of non-enzymatic and enzymatic antioxidants which scavenge reactive oxygen species to preserve lens proteins. Depletion and/or failure in this primary antioxidant defense system contributes to the damage observed in lenticular molecules and their repair mechanisms, ultimately causing cataracts. Several attempts have been made to counteract experimentally induced cataract using in vitro, ex vivo, and in vivo techniques. The majority of the anti-cataract compounds tested, including plant extracts and naturally-occurring compounds, lies in their antioxidant and/or free radical scavenging and/or anti-inflammatory propensity. In addition to providing an overview of the pathophysiology of cataracts, this review focuses on the role of various categories of natural and synthetic compounds on experimentally-induced cataracts.

Standardization of a new method for assessing the development of cataract in cultured bovine lenses

PURPOSE

To standardize a new method for assessing cataractogenesis in isolated cultured bovine lenses using L-cysteine as the standard anti-cataract agent.

METHODS

Intact bovine lenses were cultured in DMEM with L-cysteine in presence or absence of hydrogen peroxide (H₂O₂). Lens opacity (transmittance) was determined using a plate reader. Lens homogenate glutathione (GSH) and superoxide dismutase (SOD) contents were measured using enzyme immunoassays kits.

RESULTS

DMEM-cultured lenses exhibited a time-dependent loss in transmittance (230-710 nm) up to 120 h, achieving the highest reduction of 38.6 ± 0.09% at 420 nm (p < .001;n = 12). Compared to untreated lenses (time in hours [t] = 0), L-cysteine (10^-6 M and 10^-5 M) significantly (p < .001;n = 6) increased time-dependent transmittance (420 nm) by 31.6 ± 0.17% and 28.0 ± 0.07%(t = 120), respectively. When compared to DMEM-cultured lenses (t = 0), H₂O₂ (10 mM, 50 mM and 100 mM) significantly (p < .001;n = 12) reduced transmittance by 57.8 ± 0.1, 57.4 ± 0.04 and 87.7 ± 0.6%(t = 120), respectively. Moreover, L-cysteine significantly (p < .001;n = 6) attenuated H₂O₂ (50 mM)-induced decrease in transmittance by 12.5 ± 0.05%(10^-6 M), 13.0 ± 0.09%(10^-5 M), 14.5 ± 0.08%(10^-4 M) and 8.6 ± 0.11%(10^-3 M)(t = 120), respectively. When compared to untreated lenses (t = 0), the time-dependent decrease (p < .001;n = 5) in lenticular total GSH content and total SOD activity of 46.1 ± 0.06% and 42.0 ± 1.65% (t = 120) was attenuated (p < .001;n = 5) by L-cysteine (10^-6 M) by 76.6 ± 0.06% and 7.4 ± 1.98%, respectively. Similarly, the H₂O₂(50 mM)-induced decline (p < .001; n = 5) in total GSH content and SOD activity of 82.6 ± 0.08% and 86.6 ± 0.66% (t = 120) was attenuated by L-cysteine (10^-4 M) by 74.7 ± 1.05% and 161.1 ± 4.9%, respectively.

CONCLUSION

Measurement of spectral transmission coupled with assessment of the activity of antioxidant enzymes in bovine cultured lens can provide a useful tool in studies of cataracts in an animal model of this disease.