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Low Antioxidant Status Seen in Glaucoma

Oxidative Stress & Development of Glaucoma

Primary open-angle glaucoma (POAG) is a chronic, slowly-progressing optic neuropathy characterized by a distinctive pattern of visual field defects. Psuedoexfoliation syndrome (PEX) is distinguished by abnormal extracellular fibrillar material that accumulates in the anterior segment of the eye and in other organs. PEX is the most common identifiable cause of open-angle glaucoma worldwide.

Oxidative stress – the presence of increased levels of reactive oxygen species relative to antioxidant defenses – may contribute to the development of both POAG and psuedoexfoliation glaucoma (PEG). Greater oxidative damage to trabecular meshwork cells has been reported in POAG and PEG vs. non-glaucoma patients (1), for example, and oxidative stress has been implicated as an underlying mechanism of retinal ganglion cell death (2).

In the present study, researchers examined the antioxidant status and established the presence of oxidative stress in patients with POAG and PEG3 (3).

Study Design

The study enrolled 23 POAG patients, 24 PEG patients, and 19 healthy control subjects; all 3 groups included men and women within the same age range.

As indicators of antioxidant status, the total antioxidant capacity of serum and total activity of superoxide dismutase were determined by spectrophotometry. Total antioxidant status represents the cumulative action of all antioxidants present in serum.

Total oxidant status, nitric oxide, protein carbonyl levels, and maldonaldehyde were also measured from blood sample by spectrophotometry as indicators of oxidative stress. Maldonaldehyde and protein carbonyl reflect the level of lipid peroxidation and protein oxidation, respectively.

Results

Antioxidant Status Indicators: Mean total antioxidant capacity in the POAG and PEG groups was about half that of controls (p = 0.001).

Mean superoxide dismutase levels were significantly higher in both glaucoma groups compared to the control group (p = 0.001). Concentrations of superoxide dismutase are known to rise as a consequence of oxidative stress, and in accordance with the degree of stress conditions.

Oxidative Stress Indicators: Mean total oxidant status was significantly higher in both glaucoma groups compared to controls (p = 0.001), as was maldonaldehyde (p = 0.001). The POAG group showed higher serum nitric oxide levels than controls (p = 0.005), although the PEG group did not.

Those with PEG had higher serum protein carbonyl levels than both the POAG and control groups (p = 0.001), while protein oxidation in the POAG group was no different from controls.

Comments

These results add to the growing body of evidence supporting a role for oxidative stress in POAG and PEG. The finding of lower antioxidant defense systems in the glaucoma patients are also consistent with reports from other researcher groups (4,5).

The relatively small number of subjects assessed can be considered a study limitation. However, the breadth of biomarkers measured is certainly one of the study’s strengths, since no one biomarker of antioxidant or oxidant status gives a full picture of the oxidative state. The consistency of results observed between the various biomarkers that were measured lends credence to the findings overall.

References

1. Izzotti A, et al. Mitochondrial damage in the trabecular meshwork occurs only in primary open-angle glaucoma and in pseudoexfoliative glaucoma. PloS 6(1)e14567, Jan, 2011.
2. Baltmr A, et al. Neuroprotection in glaucoma—Is there a future role? Exp Eye Res 91:554-66, 2010.
3. Erdurmus M, et al. Antioxidant status and oxidative stress in primary open angle glaucoma and pseudoexfoliative glaucoma. Curr Eye Res 36:713-718, 2011.
4. Ghanem AA, et al. Oxidative stress markers in patients with primary open-angle glaucoma. Cur Eye Res 35:295-301, 2010.
5. Engin KN, et al. Variability of serum oxidative stress biomarkers relative to biochemical data and clinical parameters of glaucoma patients. Mol Vis 16:1260-71, 2010.