nitrite/ lens crystalline reaction: the mechanism of in-vitro protein damage

ABSTRACT

Recent work has explored the potential deleterious role that nitric oxides [NO] and their derivatives may have in human diseases. The many by-products of NO include nitrite ion, which accumulates in the anterior chamber of the eye during ocular inflammation or derived from cigarette smoking. These ions may cause lens damage and leads to cataract formation. The present study aims to examine the nitrite/ lens crystalline reaction and investigate the mechanism of lens proteins damage with nitrite ion. Rabbit lenses were incubated in different concentrations [0-200 mM] of sodium nitrite in a phosphate buffer at neural pH and body temperature, for 7 days. The following measurements were carried out on lens proteins total protein content, refractive index [RI], electrophoretic separation and amino acid separation. The results indicated a significant decrease of the total soluble lens proteins and an increase in the refractive index after incubation with nitrite. In addition, there is change in the molecular weight of lens proteins and amino acid pattern. These modifications are indicative of oxidative damage and are similar to changes seen in cataract formation. It was concluded that, nitrite accumulation within the lens environment could contribute to lens crystalline modification and cataract formation. Such changes may be due to lens protein oxidation. Nitrite has been shown to easily oxidized proteins, giving rise to disulphide bridge formation, and induces cross-linking, therefore enhancing protein aggregation and insolubolization