November 2008

 

OPHTHALMOLOGY NEWS

 

The implication of oxidative damage


by Matt Young EyeWorld Contributing Editor

 

 
Dense posterior subcapsular cataract in a severe diabetic with long-standing poor control of blood sugar Source: Warren Hill, M.D.

Could there be some synergy between diabetes and cataract that leads to greater oxidative stress in a person? A new study suggests that yes, there could be. “Findings together indicate a strong synergistic effect of diabetes and cataract in diabetic cataract for oxidative stress-related parameters and a worsening of the lipid profile,” reported Vaishali V. Agte, Ph.D., Agharkar Research Institute, Pune, Maharashtra, India, and colleagues. They reported their findings in the May 2008 issue of the journal Nutrition. The researchers looked at four groups: Indian patients with type 2 diabetes mellitus (D group, 76 patients), those without diabetes but with cataract (NDC group, 100 patients), those with diabetes and cataract (DC group, 53 patients), and age- and sex-matched normal controls (90 participants). “The uniqueness of the present study lies in the simultaneous examination of oxidative stress, micronutrient status, and lens degeneration-related parameters in all four health groups,” Dr. Agte noted.

A synergistic effect?

So what exactly did Dr. Agte find to be the connection between cataract and diabetes? Plasma TBARS and fasting glucose were significantly higher in the DC group than in the other groups. TBARS refers to thiobarbituric acid-reactive substances and represents oxidative stress. “DC patients exhibited high levels of plasma TBARS, with highest values for DC women and DC men, followed by D and NDC men and women, respectively,” Dr. Agte reported. “In particular, the regression coefficient for plasma TBARS was 70.6 times higher in the DC group than in the NDC group and 10.4 times higher in the in the D group.” So what does this extra oxidative stress mean clinically for patients? “Individuals sharing uncommon factors of cataract and diabetes may be at a higher threat of damage with respect to lens degenerative changes and a high degree of pancreatic pathologies,” Dr. Agte concluded. “Chronic hyperglycemia is considered a major determinant in the development of secondary complications of diabetes, including diabetic cataract.” Women with both cataract and diabetes appear to be particularly vulnerable to oxidative stress. “Diabetic women with cataract exhibited the highest levels of plasma TBARS, indicating the DC women to be the most vulnerable group,” Dr. Agte reported. This fact continues the ocular tradition of women having a greater risk of visual problems than men, according to Dr. Agte. “Our data for plasma TBARS and S:T protein ratio of lens proteins in DC women, although a small sample, support this fact,” Dr. Agte wrote. Also of note: There was more zinc in lenses of DC patients than in other groups. “The increased concentration of zinc in lenses of DC patients might be suggestive of more zinc being transported to cope with increasing oxidative stress in the senile diabetic cataract,” Dr. Agte reported.

Overall, this report also advances the notion that diabetes has some effect on the development of cataract. “Lens TBARS levels were lower in the NDC than in the DC group and DC men had the highest levels,” Dr. Agte reported. “Oxidative damage has been found to play a role in the pathogenesis of cataract in diabetes. Studies have indicated that hyperglycemia and the duration of diabetes increase the risk of development of cataract.” Urging diabetic patients to use antioxidants could help prevent further complications and maintain good ocular health, Dr. Agte concluded. Still, evidence from this study as well as others make tenuous connections between diabetes and cataract. Diabetes and cataract, Dr. Agte noted, also clearly have common and uncommon etiologies. “Given the imprecision about the alliance of diabetes and cataract, studies with large samples from other parts of the country would be needed to draw further meaningful conclusions,” Dr. Agte pointed out.

Another view

Mark Packer, M.D., clinical associate professor of ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, Ore., suggested that oxidation really is about rusting of the body. “The process of oxidation seems to be a major problem for biochemical systems,” Dr. Packer said. “Oxi-dation is behind the loss of function of a lot of different proteins and structures.”

So it makes sense that sicker people—those that have both diabetes and cataracts—have more oxidative stress, Dr. Packer said. People with more oxidative stress also are at more risk for heart disease and stroke, Dr. Packer said. “It does make sense,” Dr. Packer said. “Although there is not good evidence that antioxidants protect against cataract.” Vitamins E and C do appear to be protective against heart disease, though, he said. And studies have suggested antioxidants are protective against progression from dry to wet macular degeneration. So, an agent like BSS Plus (Alcon, Fort Worth, Texas) could be helpful in ophthalmic surgery as it contains antioxidants. “It prevents oxidation of proteins in the corneal endothelium,” Dr. Packer said.

Editors’ note: Dr. Agte has no financial interests related to this study. Dr. Packer has financial interests with Alcon (Fort Worth, Texas).

Contact Information:

Agte: vaishaliagte@hotmail.com

Packer: 541-687-2110, mpacker@finemd.com

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