Effect of Hydrogen Peroxide on Lens Transparency, Intracellular PH, Gap Junction Coupling, Hydrostatic Pressure and Membrane Water Permeability

Clouding of the eye lens or cataract is an age-related anomaly that affects middle-aged humans. Exploration of the etiology points to a great extent to oxidative stress due to different forms of reactive oxygen species/metabolites such as Hydrogen peroxide (HO) that are generated due to intracellular metabolism and environmental factors like radiation. If accumulated and left unchecked, the imbalance between the production and degradation of HO in the lens could lead to cataracts. Our objective was to explore ex vivo the effects of HO on lens physiology. We investigated transparency, intracellular pH (pH), intercellular gap junction coupling (GJC), hydrostatic pressure (HP) and membrane water permeability after subjecting two-month-old C57 wild-type (WT) mouse lenses for 3 h or 8 h in lens saline containing 50 μM HO; the results were compared with control lenses incubated in the saline without HO. There was a significant decrease in lens transparency in HO-treated lenses. In control lenses, pH decreases from ∼7.34 in the surface fiber cells to 6.64 in the center. Experimental lenses exposed to HO for 8 h showed a significant decrease in surface pH (from 7.34 to 6.86) and central pH (from 6.64 to 6.56), compared to the controls. There was a significant increase in GJC resistance in the differentiating (12-fold) and mature (1.4-fold) fiber cells compared to the control. Experimental lenses also showed a significant increase in HP which was ∼2-fold higher at the junction between the differentiating and mature fiber cells and ∼1.5-fold higher at the center compared to these locations in control lenses; HP at the surface was 0 mm Hg in either type lens. Fiber cell membrane water permeability significantly increased in HO-exposed lenses compared to controls. Our data demonstrate that elevated levels of lens intracellular HO caused a decrease in intracellular pH and led to acidosis which most likely uncoupled GJs, and increased AQP0-dependent membrane water permeability causing a consequent rise in HP. We infer that an abnormal increase in intracellular HO could induce acidosis, cause oxidative stress, alter lens microcirculation, and lead to the development of accelerated lens opacity and age-related cataracts.