Ph.D Thesis

Ph.D StudentSchaal Shlomit
SubjectCharacterization of Oxygen-Induced Cataract
DepartmentDepartment of Medicine
Supervisor PROF. Ahuva Dovrat


PURPOSE. To investigate the effects of oxygen on the eye lens.

METHODS. Bovine lenses were incubated in organ culture conditions for 7-14 days and exposed to different combinations of ambient pressure and oxygen concentration. During culture lens optical quality was assessed using a computerized scanning laser system. Lens structure was investigated by inverted microscopy, histology and histochemistry. Lens function was assessed by analysis of specific enzyme activities. Protein modifications were investigated using SDS polyacrylamide gel electrophoresis. Lipid oxidation was investigated by Western blotting and analysis with specific anti-4-hydroxy-2-nonenal (HNE) antibodies. Lenses were treated by desferrioxamine (DFO) or by Zn- desferrioxamine (Zn-DFO) in an attempt to reduce oxygen-induced lenticular damage.

RESULTS. Repeated exposure to 100% oxygen under normal or increased ambient pressures reduced lens transparency, altered specific enzyme activities and caused lens structural changes.  Light intensity measurements showed one pattern for control lenses and a different pattern for lenses exposed to hyperbaric oxygen (HBO). All measured parameters showed that Zn-DFO is more effective in preventing lens oxidative damage than DFO. Analysis of enzyme activities indicated enhancement of physiological anti-oxidant activity as a possible explanation for the effects of Zn-DFO. The glycolytic pathway in HBO-exposed lens epithelium was inhibited by a significant reduction in hexokinase and lactate dehydrogenase (LDH) activities. The hexose-monophosphate shunt was activated by an elevation of glucose-6-phosphate dehydrogenase (G6PD) activity in HBO-exposed lenses. The Krebs cycle was activated in hyperbaric oxygen conditions as seen by elevated succinate dehydrogenase (SDH) activities. High oxygen load caused reduced catalase and ATPase activities. HBO-exposed lenses showed protein aggregation, mainly beta-crystallins, significant lipid peroxidation and HNE formation.

CONCLUSIONS. High oxygen load has toxic effects on bovine lenses in organ culture. These effects depend on oxygen partial pressure and duration of exposure: the higher the oxygen partial pressure and the greater the number of exposures, the more severe the changes observed in the lenses. Changes marking toxicity parallel the route of oxygen diffusion into the lens, from the periphery to the center. Oxygen toxicity to bovine lenses in culture conditions was demonstrated by changes in light intensity measurements, focal length variability values and confirmed by microscopy, Treatment with Zn-DFO reduced the oxidative damage. The mechanisms of oxygen-induced cataract involve lipid peroxidation, HNE formation, damage to enzymes and structural proteins, which lead to cell dysfunction and finally to cell death. Cautious interpretation of the results may indicate a role of oxygen in human cataract formation.