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Ascorbic acid and the eye lens
1Department of Ophthalmology, School of Medicine, University of Maryland, Baltimore.
Abstract:
Exposure of mice to hyperbaric oxygen leads to an inhibition of the mitotic activity in the germinative epithelium of the lens. This is followed by an eventual development of cataracts. Cataracts have also been observed in human beings treated with hyperbaric oxygen for different afflictions. The lens damage and cataract formation appears to be due to in situ generation of active radicals and other active species of oxygen. These oxygen derivatives may also contribute to the multifactorial process of senile cataract formation in human beings. This hypothesis is based on in vitro experiments with rat lenses cultured in medium generating oxygen radicals, the generation of the radicals being accomplished either photochemically or enzymatically. The ability of the lens to transport rubidium and amino acids from such a medium is adversely affected. This is a recognized index of the damage to the tissue physiology. Scavengers of active oxygen species have been found to protect against this damage. Ascorbate, present in concentrations similar to that in the primate aqueous and lens, is also protective. The studies, therefore, point to an antioxidant and perhaps an anti-cataract effect of ascorbate. Pyruvate is another agent useful in this regard.
Insights
Hyperbaric oxygen exposure causes lens cataracts in mice by generating damaging oxygen radicals. Antioxidants like ascorbate may prevent this, suggesting a role in combating cataracts.
Area of Science:
- Ophthalmology
- Cell Biology
- Biochemistry
Background:
- Hyperbaric oxygen (HBO) exposure induces lens mitotic inhibition and cataracts in mice.
- Similar cataracts are observed in humans undergoing HBO therapy.
- Lens damage is hypothesized to result from in situ reactive oxygen species (ROS) generation.
Purpose of the Study:
- To investigate the role of ROS in HBO-induced lens damage and cataract formation.
- To evaluate the protective effects of antioxidants against ROS-induced lens injury.
- To explore the potential anti-cataract effects of ascorbate and pyruvate.
Main Methods:
- In vitro experiments using rat lenses cultured in a medium generating oxygen radicals (photochemically or enzymatically).
- Assessment of lens tissue physiology by measuring rubidium and amino acid transport.
- Evaluation of protective effects of ROS scavengers, ascorbate, and pyruvate.
Main Results:
- HBO exposure leads to inhibition of mitotic activity and cataract development in the mouse lens.
- In vitro experiments demonstrated adverse effects on lens transport functions due to ROS.
- ROS scavengers, ascorbate (at physiological concentrations), and pyruvate showed protective effects against lens damage.
Conclusions:
- In situ generation of ROS is a key factor in HBO-induced lens damage and cataract formation.
- Ascorbate and pyruvate exhibit antioxidant and potential anti-cataract properties.
- These findings suggest a link between oxidative stress and senile cataractogenesis, with potential therapeutic implications for antioxidants.